path: root/ghc/rts/Schedule.c

/* ---------------------------------------------------------------------------
 * $Id: Schedule.c,v 1.108 2001/11/26 16:54:22 simonmar Exp $
 *
 * (c) The GHC Team, 1998-2000
 *
 * Scheduler
 *
 * Different GHC ways use this scheduler quite differently (see comments below)
 * Here is the global picture:
 *
 * WAY  Name     CPP flag  What's it for
 * --------------------------------------
 * mp   GUM      PAR       Parallel execution on a distributed memory machine
 * s    SMP      SMP       Parallel execution on a shared memory machine
 * mg   GranSim  GRAN      Simulation of parallel execution
 * md   GUM/GdH  DIST      Distributed execution (based on GUM)
 * --------------------------------------------------------------------------*/

//@node Main scheduling code, , ,
//@section Main scheduling code

/* 
 * Version with scheduler monitor support for SMPs (WAY=s):

   This design provides a high-level API to create and schedule threads etc.
   as documented in the SMP design document.

   It uses a monitor design controlled by a single mutex to exercise control
   over accesses to shared data structures, and builds on the Posix threads
   library.

   The majority of state is shared.  In order to keep essential per-task state,
   there is a Capability structure, which contains all the information
   needed to run a thread: its STG registers, a pointer to its TSO, a
   nursery etc.  During STG execution, a pointer to the capability is
   kept in a register (BaseReg).

   In a non-SMP build, there is one global capability, namely MainRegTable.

   SDM & KH, 10/99

 * Version with support for distributed memory parallelism aka GUM (WAY=mp):

   The main scheduling loop in GUM iterates until a finish message is received.
   In that case a global flag @receivedFinish@ is set and this instance of
   the RTS shuts down. See ghc/rts/parallel/HLComms.c:processMessages()
   for the handling of incoming messages, such as PP_FINISH.
   Note that in the parallel case we have a system manager that coordinates
   different PEs, each of which are running one instance of the RTS.
   See ghc/rts/parallel/SysMan.c for the main routine of the parallel program.
   From this routine processes executing ghc/rts/Main.c are spawned. -- HWL

 * Version with support for simulating parallel execution aka GranSim (WAY=mg):

   The main scheduling code in GranSim is quite different from that in std
   (concurrent) Haskell: while concurrent Haskell just iterates over the
   threads in the runnable queue, GranSim is event driven, i.e. it iterates
   over the events in the global event queue.  -- HWL
*/

//@menu
//* Includes::			
//* Variables and Data structures::  
//* Main scheduling loop::	
//* Suspend and Resume::	
//* Run queue code::		
//* Garbage Collextion Routines::  
//* Blocking Queue Routines::	
//* Exception Handling Routines::  
//* Debugging Routines::	
//* Index::			
//@end menu

//@node Includes, Variables and Data structures, Main scheduling code, Main scheduling code
//@subsection Includes

#include "PosixSource.h"
#include "Rts.h"
#include "SchedAPI.h"
#include "RtsUtils.h"
#include "RtsFlags.h"
#include "Storage.h"
#include "StgRun.h"
#include "StgStartup.h"
#include "Hooks.h"
#include "Schedule.h"
#include "StgMiscClosures.h"
#include "Storage.h"
#include "Interpreter.h"
#include "Exception.h"
#include "Printer.h"
#include "Main.h"
#include "Signals.h"
#include "Sanity.h"
#include "Stats.h"
#include "Itimer.h"
#include "Prelude.h"
#ifdef PROFILING
#include "Proftimer.h"
#include "ProfHeap.h"
#include "RetainerProfile.h"
#endif
#if defined(GRAN) || defined(PAR)
# include "GranSimRts.h"
# include "GranSim.h"
# include "ParallelRts.h"
# include "Parallel.h"
# include "ParallelDebug.h"
# include "FetchMe.h"
# include "HLC.h"
#endif
#include "Sparks.h"

#include <stdarg.h>

//@node Variables and Data structures, Prototypes, Includes, Main scheduling code
//@subsection Variables and Data structures

/* Main threads:
 *
 * These are the threads which clients have requested that we run.  
 *
 * In an SMP build, we might have several concurrent clients all
 * waiting for results, and each one will wait on a condition variable
 * until the result is available.
 *
 * In non-SMP, clients are strictly nested: the first client calls
 * into the RTS, which might call out again to C with a _ccall_GC, and
 * eventually re-enter the RTS.
 *
 * Main threads information is kept in a linked list:
 */
//@cindex StgMainThread
typedef struct StgMainThread_ {
  StgTSO *         tso;
  SchedulerStatus  stat;
  StgClosure **    ret;
#ifdef SMP
  pthread_cond_t wakeup;
#endif
  struct StgMainThread_ *link;
} StgMainThread;

/* Main thread queue.
 * Locks required: sched_mutex.
 */
static StgMainThread *main_threads;

/* Thread queues.
 * Locks required: sched_mutex.
 */
#if defined(GRAN)

StgTSO* ActiveTSO = NULL; /* for assigning system costs; GranSim-Light only */
/* rtsTime TimeOfNextEvent, EndOfTimeSlice;            now in GranSim.c */

/* 
   In GranSim we have a runable and a blocked queue for each processor.
   In order to minimise code changes new arrays run_queue_hds/tls
   are created. run_queue_hd is then a short cut (macro) for
   run_queue_hds[CurrentProc] (see GranSim.h).
   -- HWL
*/
StgTSO *run_queue_hds[MAX_PROC], *run_queue_tls[MAX_PROC];
StgTSO *blocked_queue_hds[MAX_PROC], *blocked_queue_tls[MAX_PROC];
StgTSO *ccalling_threadss[MAX_PROC];
/* We use the same global list of threads (all_threads) in GranSim as in
   the std RTS (i.e. we are cheating). However, we don't use this list in
   the GranSim specific code at the moment (so we are only potentially
   cheating).  */

#else /* !GRAN */

StgTSO *run_queue_hd, *run_queue_tl;
StgTSO *blocked_queue_hd, *blocked_queue_tl;
StgTSO *sleeping_queue;		/* perhaps replace with a hash table? */

#endif

/* Linked list of all threads.
 * Used for detecting garbage collected threads.
 */
StgTSO *all_threads;

/* Threads suspended in _ccall_GC.
 */
static StgTSO *suspended_ccalling_threads;

static StgTSO *threadStackOverflow(StgTSO *tso);

/* KH: The following two flags are shared memory locations.  There is no need
       to lock them, since they are only unset at the end of a scheduler
       operation.
*/

/* flag set by signal handler to precipitate a context switch */
//@cindex context_switch
nat context_switch;

/* if this flag is set as well, give up execution */
//@cindex interrupted
rtsBool interrupted;

/* Next thread ID to allocate.
 * Locks required: sched_mutex
 */
//@cindex next_thread_id
StgThreadID next_thread_id = 1;

/*
 * Pointers to the state of the current thread.
 * Rule of thumb: if CurrentTSO != NULL, then we're running a Haskell
 * thread.  If CurrentTSO == NULL, then we're at the scheduler level.
 */
 
/* The smallest stack size that makes any sense is:
 *    RESERVED_STACK_WORDS    (so we can get back from the stack overflow)
 *  + sizeofW(StgStopFrame)   (the stg_stop_thread_info frame)
 *  + 1                       (the realworld token for an IO thread)
 *  + 1                       (the closure to enter)
 *
 * A thread with this stack will bomb immediately with a stack
 * overflow, which will increase its stack size.  
 */

#define MIN_STACK_WORDS (RESERVED_STACK_WORDS + sizeofW(StgStopFrame) + 2)

/* Free capability list.
 * Locks required: sched_mutex.
 */
#ifdef SMP
Capability *free_capabilities; /* Available capabilities for running threads */
nat n_free_capabilities;       /* total number of available capabilities */
#else
Capability MainCapability;     /* for non-SMP, we have one global capability */
#endif

#if defined(GRAN)
StgTSO *CurrentTSO;
#endif

/*  This is used in `TSO.h' and gcc 2.96 insists that this variable actually 
 *  exists - earlier gccs apparently didn't.
 *  -= chak
 */
StgTSO dummy_tso;

rtsBool ready_to_gc;

/* All our current task ids, saved in case we need to kill them later.
 */
#ifdef SMP
//@cindex task_ids
task_info *task_ids;
#endif

void            addToBlockedQueue ( StgTSO *tso );

static void     schedule          ( void );
       void     interruptStgRts   ( void );
#if defined(GRAN)
static StgTSO * createThread_     ( nat size, rtsBool have_lock, StgInt pri );
#else
static StgTSO * createThread_     ( nat size, rtsBool have_lock );
#endif

static void     detectBlackHoles  ( void );

#ifdef DEBUG
static void sched_belch(char *s, ...);
#endif

#ifdef SMP
//@cindex sched_mutex
//@cindex term_mutex
//@cindex thread_ready_cond
//@cindex gc_pending_cond
pthread_mutex_t sched_mutex       = PTHREAD_MUTEX_INITIALIZER;
pthread_mutex_t term_mutex        = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t  thread_ready_cond = PTHREAD_COND_INITIALIZER;
pthread_cond_t  gc_pending_cond   = PTHREAD_COND_INITIALIZER;

nat await_death;
#endif

#if defined(PAR)
StgTSO *LastTSO;
rtsTime TimeOfLastYield;
rtsBool emitSchedule = rtsTrue;
#endif

#if DEBUG
char *whatNext_strs[] = {
  "ThreadEnterGHC",
  "ThreadRunGHC",
  "ThreadEnterInterp",
  "ThreadKilled",
  "ThreadComplete"
};

char *threadReturnCode_strs[] = {
  "HeapOverflow",			/* might also be StackOverflow */
  "StackOverflow",
  "ThreadYielding",
  "ThreadBlocked",
  "ThreadFinished"
};
#endif

#ifdef PAR
StgTSO * createSparkThread(rtsSpark spark);
StgTSO * activateSpark (rtsSpark spark);  
#endif

/*
 * The thread state for the main thread.
// ToDo: check whether not needed any more
StgTSO   *MainTSO;
 */

//@node Main scheduling loop, Suspend and Resume, Prototypes, Main scheduling code
//@subsection Main scheduling loop

/* ---------------------------------------------------------------------------
   Main scheduling loop.

   We use round-robin scheduling, each thread returning to the
   scheduler loop when one of these conditions is detected:

      * out of heap space
      * timer expires (thread yields)
      * thread blocks
      * thread ends
      * stack overflow

   Locking notes:  we acquire the scheduler lock once at the beginning
   of the scheduler loop, and release it when
    
      * running a thread, or
      * waiting for work, or
      * waiting for a GC to complete.

   GRAN version:
     In a GranSim setup this loop iterates over the global event queue.
     This revolves around the global event queue, which determines what 
     to do next. Therefore, it's more complicated than either the 
     concurrent or the parallel (GUM) setup.

   GUM version:
     GUM iterates over incoming messages.
     It starts with nothing to do (thus CurrentTSO == END_TSO_QUEUE),
     and sends out a fish whenever it has nothing to do; in-between
     doing the actual reductions (shared code below) it processes the
     incoming messages and deals with delayed operations 
     (see PendingFetches).
     This is not the ugliest code you could imagine, but it's bloody close.

   ------------------------------------------------------------------------ */
//@cindex schedule
static void
schedule( void )
{
  StgTSO *t;
  Capability *cap;
  StgThreadReturnCode ret;
#if defined(GRAN)
  rtsEvent *event;
#elif defined(PAR)
  StgSparkPool *pool;
  rtsSpark spark;
  StgTSO *tso;
  GlobalTaskId pe;
  rtsBool receivedFinish = rtsFalse;
# if defined(DEBUG)
  nat tp_size, sp_size; // stats only
# endif
#endif
  rtsBool was_interrupted = rtsFalse;
  
  ACQUIRE_LOCK(&sched_mutex);

#if defined(GRAN)

  /* set up first event to get things going */
  /* ToDo: assign costs for system setup and init MainTSO ! */
  new_event(CurrentProc, CurrentProc, CurrentTime[CurrentProc],
	    ContinueThread, 
	    CurrentTSO, (StgClosure*)NULL, (rtsSpark*)NULL);

  IF_DEBUG(gran,
	   fprintf(stderr, "GRAN: Init CurrentTSO (in schedule) = %p\n", CurrentTSO);
	   G_TSO(CurrentTSO, 5));

  if (RtsFlags.GranFlags.Light) {
    /* Save current time; GranSim Light only */
    CurrentTSO->gran.clock = CurrentTime[CurrentProc];
  }      

  event = get_next_event();

  while (event!=(rtsEvent*)NULL) {
    /* Choose the processor with the next event */
    CurrentProc = event->proc;
    CurrentTSO = event->tso;

#elif defined(PAR)

  while (!receivedFinish) {    /* set by processMessages */
                               /* when receiving PP_FINISH message         */ 
#else

  while (1) {

#endif

    IF_DEBUG(scheduler, printAllThreads());

    /* If we're interrupted (the user pressed ^C, or some other
     * termination condition occurred), kill all the currently running
     * threads.
     */
    if (interrupted) {
      IF_DEBUG(scheduler, sched_belch("interrupted"));
      deleteAllThreads();
      interrupted = rtsFalse;
      was_interrupted = rtsTrue;
    }

    /* Go through the list of main threads and wake up any
     * clients whose computations have finished.  ToDo: this
     * should be done more efficiently without a linear scan
     * of the main threads list, somehow...
     */
#ifdef SMP
    { 
      StgMainThread *m, **prev;
      prev = &main_threads;
      for (m = main_threads; m != NULL; m = m->link) {
	switch (m->tso->what_next) {
	case ThreadComplete:
	  if (m->ret) {
	    *(m->ret) = (StgClosure *)m->tso->sp[0];
	  }
	  *prev = m->link;
	  m->stat = Success;
	  pthread_cond_broadcast(&m->wakeup);
	  break;
	case ThreadKilled:
	  if (m->ret) *(m->ret) = NULL;
	  *prev = m->link;
	  if (was_interrupted) {
	    m->stat = Interrupted;
	  } else {
	    m->stat = Killed;
	  }
	  pthread_cond_broadcast(&m->wakeup);
	  break;
	default:
	  break;
	}
      }
    }

#else // not SMP

# if defined(PAR)
    /* in GUM do this only on the Main PE */
    if (IAmMainThread)
# endif
    /* If our main thread has finished or been killed, return.
     */
    {
      StgMainThread *m = main_threads;
      if (m->tso->what_next == ThreadComplete
	  || m->tso->what_next == ThreadKilled) {
	main_threads = main_threads->link;
	if (m->tso->what_next == ThreadComplete) {
	  /* we finished successfully, fill in the return value */
	  if (m->ret) { *(m->ret) = (StgClosure *)m->tso->sp[0]; };
	  m->stat = Success;
	  return;
	} else {
	  if (m->ret) { *(m->ret) = NULL; };
	  if (was_interrupted) {
	    m->stat = Interrupted;
	  } else {
	    m->stat = Killed;
	  }
	  return;
	}
      }
    }
#endif

    /* Top up the run queue from our spark pool.  We try to make the
     * number of threads in the run queue equal to the number of
     * free capabilities.
     */
#if defined(SMP)
    {
      nat n = n_free_capabilities;
      StgTSO *tso = run_queue_hd;

      /* Count the run queue */
      while (n > 0 && tso != END_TSO_QUEUE) {
	tso = tso->link;
	n--;
      }

      for (; n > 0; n--) {
	StgClosure *spark;
	spark = findSpark(rtsFalse);
	if (spark == NULL) {
	  break; /* no more sparks in the pool */
	} else {
	  /* I'd prefer this to be done in activateSpark -- HWL */
	  /* tricky - it needs to hold the scheduler lock and
	   * not try to re-acquire it -- SDM */
	  createSparkThread(spark);	  
	  IF_DEBUG(scheduler,
		   sched_belch("==^^ turning spark of closure %p into a thread",
			       (StgClosure *)spark));
	}
      }
      /* We need to wake up the other tasks if we just created some
       * work for them.
       */
      if (n_free_capabilities - n > 1) {
	  pthread_cond_signal(&thread_ready_cond);
      }
    }
#endif // SMP

    /* check for signals each time around the scheduler */
#ifndef mingw32_TARGET_OS
    if (signals_pending()) {
      startSignalHandlers();
    }
#endif

    /* Check whether any waiting threads need to be woken up.  If the
     * run queue is empty, and there are no other tasks running, we
     * can wait indefinitely for something to happen.
     * ToDo: what if another client comes along & requests another
     * main thread?
     */
    if (blocked_queue_hd != END_TSO_QUEUE || sleeping_queue != END_TSO_QUEUE) {
      awaitEvent(
	   (run_queue_hd == END_TSO_QUEUE)
#ifdef SMP
	&& (n_free_capabilities == RtsFlags.ParFlags.nNodes)
#endif
	);
    }
    /* we can be interrupted while waiting for I/O... */
    if (interrupted) continue;

    /* 
     * Detect deadlock: when we have no threads to run, there are no
     * threads waiting on I/O or sleeping, and all the other tasks are
     * waiting for work, we must have a deadlock of some description.
     *
     * We first try to find threads blocked on themselves (ie. black
     * holes), and generate NonTermination exceptions where necessary.
     *
     * If no threads are black holed, we have a deadlock situation, so
     * inform all the main threads.
     */
#ifndef PAR
    if (blocked_queue_hd == END_TSO_QUEUE
	&& run_queue_hd == END_TSO_QUEUE
	&& sleeping_queue == END_TSO_QUEUE
#ifdef SMP
	&& (n_free_capabilities == RtsFlags.ParFlags.nNodes)
#endif
	)
    {
	IF_DEBUG(scheduler, sched_belch("deadlocked, forcing major GC..."));
	GarbageCollect(GetRoots,rtsTrue);
	if (blocked_queue_hd == END_TSO_QUEUE
	    && run_queue_hd == END_TSO_QUEUE
	    && sleeping_queue == END_TSO_QUEUE) {
	    IF_DEBUG(scheduler, sched_belch("still deadlocked, checking for black holes..."));
	    detectBlackHoles();
	    if (run_queue_hd == END_TSO_QUEUE) {
		StgMainThread *m = main_threads;
#ifdef SMP
		for (; m != NULL; m = m->link) {
		    deleteThread(m->tso);
		    m->ret = NULL;
		    m->stat = Deadlock;
		    pthread_cond_broadcast(&m->wakeup);
		}
		main_threads = NULL;
#else
		deleteThread(m->tso);
		m->ret = NULL;
		m->stat = Deadlock;
		main_threads = m->link;
		return;
#endif
	    }
	}
    }
#elif defined(PAR)
    /* ToDo: add deadlock detection in GUM (similar to SMP) -- HWL */
#endif

#ifdef SMP
    /* If there's a GC pending, don't do anything until it has
     * completed.
     */
    if (ready_to_gc) {
      IF_DEBUG(scheduler,sched_belch("waiting for GC"));
      pthread_cond_wait(&gc_pending_cond, &sched_mutex);
    }
    
    /* block until we've got a thread on the run queue and a free
     * capability.
     */
    while (run_queue_hd == END_TSO_QUEUE || free_capabilities == NULL) {
      IF_DEBUG(scheduler, sched_belch("waiting for work"));
      pthread_cond_wait(&thread_ready_cond, &sched_mutex);
      IF_DEBUG(scheduler, sched_belch("work now available"));
    }
#endif

#if defined(GRAN)

    if (RtsFlags.GranFlags.Light)
      GranSimLight_enter_system(event, &ActiveTSO); // adjust ActiveTSO etc

    /* adjust time based on time-stamp */
    if (event->time > CurrentTime[CurrentProc] &&
        event->evttype != ContinueThread)
      CurrentTime[CurrentProc] = event->time;
    
    /* Deal with the idle PEs (may issue FindWork or MoveSpark events) */
    if (!RtsFlags.GranFlags.Light)
      handleIdlePEs();

    IF_DEBUG(gran, fprintf(stderr, "GRAN: switch by event-type\n"));

    /* main event dispatcher in GranSim */
    switch (event->evttype) {
      /* Should just be continuing execution */
    case ContinueThread:
      IF_DEBUG(gran, fprintf(stderr, "GRAN: doing ContinueThread\n"));
      /* ToDo: check assertion
      ASSERT(run_queue_hd != (StgTSO*)NULL &&
	     run_queue_hd != END_TSO_QUEUE);
      */
      /* Ignore ContinueThreads for fetching threads (if synchr comm) */
      if (!RtsFlags.GranFlags.DoAsyncFetch &&
	  procStatus[CurrentProc]==Fetching) {
	belch("ghuH: Spurious ContinueThread while Fetching ignored; TSO %d (%p) [PE %d]",
	      CurrentTSO->id, CurrentTSO, CurrentProc);
	goto next_thread;
      }	
      /* Ignore ContinueThreads for completed threads */
      if (CurrentTSO->what_next == ThreadComplete) {
	belch("ghuH: found a ContinueThread event for completed thread %d (%p) [PE %d] (ignoring ContinueThread)", 
	      CurrentTSO->id, CurrentTSO, CurrentProc);
	goto next_thread;
      }	
      /* Ignore ContinueThreads for threads that are being migrated */
      if (PROCS(CurrentTSO)==Nowhere) { 
	belch("ghuH: trying to run the migrating TSO %d (%p) [PE %d] (ignoring ContinueThread)",
	      CurrentTSO->id, CurrentTSO, CurrentProc);
	goto next_thread;
      }
      /* The thread should be at the beginning of the run queue */
      if (CurrentTSO!=run_queue_hds[CurrentProc]) { 
	belch("ghuH: TSO %d (%p) [PE %d] is not at the start of the run_queue when doing a ContinueThread",
	      CurrentTSO->id, CurrentTSO, CurrentProc);
	break; // run the thread anyway
      }
      /*
      new_event(proc, proc, CurrentTime[proc],
		FindWork,
		(StgTSO*)NULL, (StgClosure*)NULL, (rtsSpark*)NULL);
      goto next_thread; 
      */ /* Catches superfluous CONTINUEs -- should be unnecessary */
      break; // now actually run the thread; DaH Qu'vam yImuHbej 

    case FetchNode:
      do_the_fetchnode(event);
      goto next_thread;             /* handle next event in event queue  */
      
    case GlobalBlock:
      do_the_globalblock(event);
      goto next_thread;             /* handle next event in event queue  */
      
    case FetchReply:
      do_the_fetchreply(event);
      goto next_thread;             /* handle next event in event queue  */
      
    case UnblockThread:   /* Move from the blocked queue to the tail of */
      do_the_unblock(event);
      goto next_thread;             /* handle next event in event queue  */
      
    case ResumeThread:  /* Move from the blocked queue to the tail of */
      /* the runnable queue ( i.e. Qu' SImqa'lu') */ 
      event->tso->gran.blocktime += 
	CurrentTime[CurrentProc] - event->tso->gran.blockedat;
      do_the_startthread(event);
      goto next_thread;             /* handle next event in event queue  */
      
    case StartThread:
      do_the_startthread(event);
      goto next_thread;             /* handle next event in event queue  */
      
    case MoveThread:
      do_the_movethread(event);
      goto next_thread;             /* handle next event in event queue  */
      
    case MoveSpark:
      do_the_movespark(event);
      goto next_thread;             /* handle next event in event queue  */
      
    case FindWork:
      do_the_findwork(event);
      goto next_thread;             /* handle next event in event queue  */
      
    default:
      barf("Illegal event type %u\n", event->evttype);
    }  /* switch */
    
    /* This point was scheduler_loop in the old RTS */

    IF_DEBUG(gran, belch("GRAN: after main switch"));

    TimeOfLastEvent = CurrentTime[CurrentProc];
    TimeOfNextEvent = get_time_of_next_event();
    IgnoreEvents=(TimeOfNextEvent==0); // HWL HACK
    // CurrentTSO = ThreadQueueHd;

    IF_DEBUG(gran, belch("GRAN: time of next event is: %ld", 
			 TimeOfNextEvent));

    if (RtsFlags.GranFlags.Light) 
      GranSimLight_leave_system(event, &ActiveTSO); 

    EndOfTimeSlice = CurrentTime[CurrentProc]+RtsFlags.GranFlags.time_slice;

    IF_DEBUG(gran, 
	     belch("GRAN: end of time-slice is %#lx", EndOfTimeSlice));

    /* in a GranSim setup the TSO stays on the run queue */
    t = CurrentTSO;
    /* Take a thread from the run queue. */
    t = POP_RUN_QUEUE(); // take_off_run_queue(t);

    IF_DEBUG(gran, 
	     fprintf(stderr, "GRAN: About to run current thread, which is\n");
	     G_TSO(t,5));

    context_switch = 0; // turned on via GranYield, checking events and time slice

    IF_DEBUG(gran, 
	     DumpGranEvent(GR_SCHEDULE, t));

    procStatus[CurrentProc] = Busy;

#elif defined(PAR)
    if (PendingFetches != END_BF_QUEUE) {
        processFetches();
    }

    /* ToDo: phps merge with spark activation above */
    /* check whether we have local work and send requests if we have none */
    if (EMPTY_RUN_QUEUE()) {  /* no runnable threads */
      /* :-[  no local threads => look out for local sparks */
      /* the spark pool for the current PE */
      pool = &(MainRegTable.rSparks); // generalise to cap = &MainRegTable
      if (advisory_thread_count < RtsFlags.ParFlags.maxThreads &&
	  pool->hd < pool->tl) {
	/* 
	 * ToDo: add GC code check that we really have enough heap afterwards!!
	 * Old comment:
	 * If we're here (no runnable threads) and we have pending
	 * sparks, we must have a space problem.  Get enough space
	 * to turn one of those pending sparks into a
	 * thread... 
	 */

	spark = findSpark(rtsFalse);                /* get a spark */
	if (spark != (rtsSpark) NULL) {
	  tso = activateSpark(spark);       /* turn the spark into a thread */
	  IF_PAR_DEBUG(schedule,
		       belch("==== schedule: Created TSO %d (%p); %d threads active",
			     tso->id, tso, advisory_thread_count));

	  if (tso==END_TSO_QUEUE) { /* failed to activate spark->back to loop */
	    belch("==^^ failed to activate spark");
	    goto next_thread;
	  }               /* otherwise fall through & pick-up new tso */
	} else {
	  IF_PAR_DEBUG(verbose,
		       belch("==^^ no local sparks (spark pool contains only NFs: %d)", 
			     spark_queue_len(pool)));
	  goto next_thread;
	}
      }

      /* If we still have no work we need to send a FISH to get a spark
	 from another PE 
      */
      if (EMPTY_RUN_QUEUE()) {
      /* =8-[  no local sparks => look for work on other PEs */
	/*
	 * We really have absolutely no work.  Send out a fish
	 * (there may be some out there already), and wait for
	 * something to arrive.  We clearly can't run any threads
	 * until a SCHEDULE or RESUME arrives, and so that's what
	 * we're hoping to see.  (Of course, we still have to
	 * respond to other types of messages.)
	 */
	TIME now = msTime() /*CURRENT_TIME*/;
	IF_PAR_DEBUG(verbose, 
		     belch("--  now=%ld", now));
	IF_PAR_DEBUG(verbose,
		     if (outstandingFishes < RtsFlags.ParFlags.maxFishes &&
			 (last_fish_arrived_at!=0 &&
			  last_fish_arrived_at+RtsFlags.ParFlags.fishDelay > now)) {
		       belch("--$$ delaying FISH until %ld (last fish %ld, delay %ld, now %ld)",
			     last_fish_arrived_at+RtsFlags.ParFlags.fishDelay,
			     last_fish_arrived_at,
			     RtsFlags.ParFlags.fishDelay, now);
		     });
	
	if (outstandingFishes < RtsFlags.ParFlags.maxFishes &&
	    (last_fish_arrived_at==0 ||
	     (last_fish_arrived_at+RtsFlags.ParFlags.fishDelay <= now))) {
	  /* outstandingFishes is set in sendFish, processFish;
	     avoid flooding system with fishes via delay */
	  pe = choosePE();
	  sendFish(pe, mytid, NEW_FISH_AGE, NEW_FISH_HISTORY, 
		   NEW_FISH_HUNGER);

	  // Global statistics: count no. of fishes
	  if (RtsFlags.ParFlags.ParStats.Global &&
	      RtsFlags.GcFlags.giveStats > NO_GC_STATS) {
	    globalParStats.tot_fish_mess++;
	  }
	}
      
	receivedFinish = processMessages();
	goto next_thread;
      }
    } else if (PacketsWaiting()) {  /* Look for incoming messages */
      receivedFinish = processMessages();
    }

    /* Now we are sure that we have some work available */
    ASSERT(run_queue_hd != END_TSO_QUEUE);

    /* Take a thread from the run queue, if we have work */
    t = POP_RUN_QUEUE();  // take_off_run_queue(END_TSO_QUEUE);
    IF_DEBUG(sanity,checkTSO(t));

    /* ToDo: write something to the log-file
    if (RTSflags.ParFlags.granSimStats && !sameThread)
        DumpGranEvent(GR_SCHEDULE, RunnableThreadsHd);

    CurrentTSO = t;
    */
    /* the spark pool for the current PE */
    pool = &(MainRegTable.rSparks); // generalise to cap = &MainRegTable

    IF_DEBUG(scheduler, 
	     belch("--=^ %d threads, %d sparks on [%#x]", 
		   run_queue_len(), spark_queue_len(pool), CURRENT_PROC));

#if 1
    if (0 && RtsFlags.ParFlags.ParStats.Full && 
	t && LastTSO && t->id != LastTSO->id && 
	LastTSO->why_blocked == NotBlocked && 
	LastTSO->what_next != ThreadComplete) {
      // if previously scheduled TSO not blocked we have to record the context switch
      DumpVeryRawGranEvent(TimeOfLastYield, CURRENT_PROC, CURRENT_PROC,
			   GR_DESCHEDULE, LastTSO, (StgClosure *)NULL, 0, 0);
    }

    if (RtsFlags.ParFlags.ParStats.Full && 
	(emitSchedule /* forced emit */ ||
        (t && LastTSO && t->id != LastTSO->id))) {
      /* 
	 we are running a different TSO, so write a schedule event to log file
	 NB: If we use fair scheduling we also have to write  a deschedule 
	     event for LastTSO; with unfair scheduling we know that the
	     previous tso has blocked whenever we switch to another tso, so
	     we don't need it in GUM for now
      */
      DumpRawGranEvent(CURRENT_PROC, CURRENT_PROC,
		       GR_SCHEDULE, t, (StgClosure *)NULL, 0, 0);
      emitSchedule = rtsFalse;
    }
     
#endif
#else /* !GRAN && !PAR */
  
    /* grab a thread from the run queue
     */
    ASSERT(run_queue_hd != END_TSO_QUEUE);
    t = POP_RUN_QUEUE();

    // Sanity check the thread we're about to run.  This can be
    // expensive if there is lots of thread switching going on...
    IF_DEBUG(sanity,checkTSO(t));

#endif
    
    /* grab a capability
     */
#ifdef SMP
    cap = free_capabilities;
    free_capabilities = cap->link;
    n_free_capabilities--;
#else
    cap = &MainCapability;
#endif

    cap->r.rCurrentTSO = t;
    
    /* context switches are now initiated by the timer signal, unless
     * the user specified "context switch as often as possible", with
     * +RTS -C0
     */
    if (
#ifdef PROFILING
	RtsFlags.ProfFlags.profileInterval == 0 ||
#endif
	(RtsFlags.ConcFlags.ctxtSwitchTicks == 0
	 && (run_queue_hd != END_TSO_QUEUE
	     || blocked_queue_hd != END_TSO_QUEUE
	     || sleeping_queue != END_TSO_QUEUE)))
	context_switch = 1;
    else
	context_switch = 0;

    RELEASE_LOCK(&sched_mutex);

    IF_DEBUG(scheduler, sched_belch("-->> Running TSO %ld (%p) %s ...", 
			      t->id, t, whatNext_strs[t->what_next]));

#ifdef PROFILING
    startHeapProfTimer();
#endif

    /* +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ */
    /* Run the current thread 
     */
    switch (cap->r.rCurrentTSO->what_next) {
    case ThreadKilled:
    case ThreadComplete:
	/* Thread already finished, return to scheduler. */
	ret = ThreadFinished;
	break;
    case ThreadEnterGHC:
	ret = StgRun((StgFunPtr) stg_enterStackTop, &cap->r);
	break;
    case ThreadRunGHC:
	ret = StgRun((StgFunPtr) stg_returnToStackTop, &cap->r);
	break;
    case ThreadEnterInterp:
	ret = interpretBCO(cap);
	break;
    default:
      barf("schedule: invalid what_next field");
    }
    /* +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ */
    
    /* Costs for the scheduler are assigned to CCS_SYSTEM */
#ifdef PROFILING
    stopHeapProfTimer();
    CCCS = CCS_SYSTEM;
#endif
    
    ACQUIRE_LOCK(&sched_mutex);

#ifdef SMP
    IF_DEBUG(scheduler,fprintf(stderr,"scheduler (task %ld): ", pthread_self()););
#elif !defined(GRAN) && !defined(PAR)
    IF_DEBUG(scheduler,fprintf(stderr,"scheduler: "););
#endif
    t = cap->r.rCurrentTSO;
    
#if defined(PAR)
    /* HACK 675: if the last thread didn't yield, make sure to print a 
       SCHEDULE event to the log file when StgRunning the next thread, even
       if it is the same one as before */
    LastTSO = t; 
    TimeOfLastYield = CURRENT_TIME;
#endif

    switch (ret) {
    case HeapOverflow:
#if defined(GRAN)
      IF_DEBUG(gran, DumpGranEvent(GR_DESCHEDULE, t));
      globalGranStats.tot_heapover++;
#elif defined(PAR)
      globalParStats.tot_heapover++;
#endif

      // did the task ask for a large block?
      if (cap->r.rHpAlloc > BLOCK_SIZE_W) {
	  // if so, get one and push it on the front of the nursery.
	  bdescr *bd;
	  nat blocks;
	  
	  blocks = (nat)BLOCK_ROUND_UP(cap->r.rHpAlloc * sizeof(W_)) / BLOCK_SIZE;

	  IF_DEBUG(scheduler,belch("--<< thread %ld (%p; %s) stopped: requesting a large block (size %d)", 
				   t->id, t,
				   whatNext_strs[t->what_next], blocks));

	  // don't do this if it would push us over the
	  // alloc_blocks_lim limit; we'll GC first.
	  if (alloc_blocks + blocks < alloc_blocks_lim) {

	      alloc_blocks += blocks;
	      bd = allocGroup( blocks );

	      // link the new group into the list
	      bd->link = cap->r.rCurrentNursery;
	      bd->u.back = cap->r.rCurrentNursery->u.back;
	      if (cap->r.rCurrentNursery->u.back != NULL) {
		  cap->r.rCurrentNursery->u.back->link = bd;
	      } else {
		  ASSERT(g0s0->blocks == cap->r.rCurrentNursery &&
			 g0s0->blocks == cap->r.rNursery);
		  cap->r.rNursery = g0s0->blocks = bd;
	      }		  
	      cap->r.rCurrentNursery->u.back = bd;

	      // initialise it as a nursery block
	      bd->step = g0s0;
	      bd->gen_no = 0;
	      bd->flags = 0;
	      bd->free = bd->start;

	      // don't forget to update the block count in g0s0.
	      g0s0->n_blocks += blocks;
	      ASSERT(countBlocks(g0s0->blocks) == g0s0->n_blocks);

	      // now update the nursery to point to the new block
	      cap->r.rCurrentNursery = bd;

	      // we might be unlucky and have another thread get on the
	      // run queue before us and steal the large block, but in that
	      // case the thread will just end up requesting another large
	      // block.
	      PUSH_ON_RUN_QUEUE(t);
	      break;
	  }
      }

      /* make all the running tasks block on a condition variable,
       * maybe set context_switch and wait till they all pile in,
       * then have them wait on a GC condition variable.
       */
      IF_DEBUG(scheduler,belch("--<< thread %ld (%p; %s) stopped: HeapOverflow", 
			       t->id, t, whatNext_strs[t->what_next]));
      threadPaused(t);
#if defined(GRAN)
      ASSERT(!is_on_queue(t,CurrentProc));
#elif defined(PAR)
      /* Currently we emit a DESCHEDULE event before GC in GUM.
         ToDo: either add separate event to distinguish SYSTEM time from rest
	       or just nuke this DESCHEDULE (and the following SCHEDULE) */
      if (0 && RtsFlags.ParFlags.ParStats.Full) {
	DumpRawGranEvent(CURRENT_PROC, CURRENT_PROC,
			 GR_DESCHEDULE, t, (StgClosure *)NULL, 0, 0);
	emitSchedule = rtsTrue;
      }
#endif
      
      ready_to_gc = rtsTrue;
      context_switch = 1;		/* stop other threads ASAP */
      PUSH_ON_RUN_QUEUE(t);
      /* actual GC is done at the end of the while loop */
      break;
      
    case StackOverflow:
#if defined(GRAN)
      IF_DEBUG(gran, 
	       DumpGranEvent(GR_DESCHEDULE, t));
      globalGranStats.tot_stackover++;
#elif defined(PAR)
      // IF_DEBUG(par, 
      // DumpGranEvent(GR_DESCHEDULE, t);
      globalParStats.tot_stackover++;
#endif
      IF_DEBUG(scheduler,belch("--<< thread %ld (%p; %s) stopped, StackOverflow", 
			       t->id, t, whatNext_strs[t->what_next]));
      /* just adjust the stack for this thread, then pop it back
       * on the run queue.
       */
      threadPaused(t);
      { 
	StgMainThread *m;
	/* enlarge the stack */
	StgTSO *new_t = threadStackOverflow(t);
	
	/* This TSO has moved, so update any pointers to it from the
	 * main thread stack.  It better not be on any other queues...
	 * (it shouldn't be).
	 */
	for (m = main_threads; m != NULL; m = m->link) {
	  if (m->tso == t) {
	    m->tso = new_t;
	  }
	}
	threadPaused(new_t);
	PUSH_ON_RUN_QUEUE(new_t);
      }
      break;

    case ThreadYielding:
#if defined(GRAN)
      IF_DEBUG(gran, 
	       DumpGranEvent(GR_DESCHEDULE, t));
      globalGranStats.tot_yields++;
#elif defined(PAR)
      // IF_DEBUG(par, 
      // DumpGranEvent(GR_DESCHEDULE, t);
      globalParStats.tot_yields++;
#endif
      /* put the thread back on the run queue.  Then, if we're ready to
       * GC, check whether this is the last task to stop.  If so, wake
       * up the GC thread.  getThread will block during a GC until the
       * GC is finished.
       */
      IF_DEBUG(scheduler,
               if (t->what_next == ThreadEnterInterp) {
		   /* ToDo: or maybe a timer expired when we were in Hugs?
		    * or maybe someone hit ctrl-C
                    */
                   belch("--<< thread %ld (%p; %s) stopped to switch to Hugs", 
			 t->id, t, whatNext_strs[t->what_next]);
               } else {
                   belch("--<< thread %ld (%p; %s) stopped, yielding", 
			 t->id, t, whatNext_strs[t->what_next]);
               }
               );

      threadPaused(t);

      IF_DEBUG(sanity,
	       //belch("&& Doing sanity check on yielding TSO %ld.", t->id);
	       checkTSO(t));
      ASSERT(t->link == END_TSO_QUEUE);
#if defined(GRAN)
      ASSERT(!is_on_queue(t,CurrentProc));

      IF_DEBUG(sanity,
	       //belch("&& Doing sanity check on all ThreadQueues (and their TSOs).");
	       checkThreadQsSanity(rtsTrue));
#endif
#if defined(PAR)
      if (RtsFlags.ParFlags.doFairScheduling) { 
	/* this does round-robin scheduling; good for concurrency */
	APPEND_TO_RUN_QUEUE(t);
      } else {
	/* this does unfair scheduling; good for parallelism */
	PUSH_ON_RUN_QUEUE(t);
      }
#else
      /* this does round-robin scheduling; good for concurrency */
      APPEND_TO_RUN_QUEUE(t);
#endif
#if defined(GRAN)
      /* add a ContinueThread event to actually process the thread */
      new_event(CurrentProc, CurrentProc, CurrentTime[CurrentProc],
		ContinueThread,
		t, (StgClosure*)NULL, (rtsSpark*)NULL);
      IF_GRAN_DEBUG(bq, 
	       belch("GRAN: eventq and runnableq after adding yielded thread to queue again:");
	       G_EVENTQ(0);
	       G_CURR_THREADQ(0));
#endif /* GRAN */
      break;
      
    case ThreadBlocked:
#if defined(GRAN)
      IF_DEBUG(scheduler,
	       belch("--<< thread %ld (%p; %s) stopped, blocking on node %p [PE %d] with BQ: ", 
			       t->id, t, whatNext_strs[t->what_next], t->block_info.closure, (t->block_info.closure==(StgClosure*)NULL ? 99 : where_is(t->block_info.closure)));
	       if (t->block_info.closure!=(StgClosure*)NULL) print_bq(t->block_info.closure));

      // ??? needed; should emit block before
      IF_DEBUG(gran, 
	       DumpGranEvent(GR_DESCHEDULE, t)); 
      prune_eventq(t, (StgClosure *)NULL); // prune ContinueThreads for t
      /*
	ngoq Dogh!
      ASSERT(procStatus[CurrentProc]==Busy || 
	      ((procStatus[CurrentProc]==Fetching) && 
	      (t->block_info.closure!=(StgClosure*)NULL)));
      if (run_queue_hds[CurrentProc] == END_TSO_QUEUE &&
	  !(!RtsFlags.GranFlags.DoAsyncFetch &&
	    procStatus[CurrentProc]==Fetching)) 
	procStatus[CurrentProc] = Idle;
      */
#elif defined(PAR)
      IF_DEBUG(scheduler,
	       belch("--<< thread %ld (%p; %s) stopped, blocking on node %p with BQ: ", 
		     t->id, t, whatNext_strs[t->what_next], t->block_info.closure));
      IF_PAR_DEBUG(bq,

		   if (t->block_info.closure!=(StgClosure*)NULL) 
		     print_bq(t->block_info.closure));

      /* Send a fetch (if BlockedOnGA) and dump event to log file */
      blockThread(t);

      /* whatever we schedule next, we must log that schedule */
      emitSchedule = rtsTrue;

#else /* !GRAN */
      /* don't need to do anything.  Either the thread is blocked on
       * I/O, in which case we'll have called addToBlockedQueue
       * previously, or it's blocked on an MVar or Blackhole, in which
       * case it'll be on the relevant queue already.
       */
      IF_DEBUG(scheduler,
	       fprintf(stderr, "--<< thread %d (%p) stopped: ", t->id, t);
	       printThreadBlockage(t);
	       fprintf(stderr, "\n"));

      /* Only for dumping event to log file 
	 ToDo: do I need this in GranSim, too?
      blockThread(t);
      */
#endif
      threadPaused(t);
      break;
      
    case ThreadFinished:
      /* Need to check whether this was a main thread, and if so, signal
       * the task that started it with the return value.  If we have no
       * more main threads, we probably need to stop all the tasks until
       * we get a new one.
       */
      /* We also end up here if the thread kills itself with an
       * uncaught exception, see Exception.hc.
       */
      IF_DEBUG(scheduler,belch("--++ thread %d (%p) finished", t->id, t));
#if defined(GRAN)
      endThread(t, CurrentProc); // clean-up the thread
#elif defined(PAR)
      /* For now all are advisory -- HWL */
      //if(t->priority==AdvisoryPriority) ??
      advisory_thread_count--;
      
# ifdef DIST
      if(t->dist.priority==RevalPriority)
	FinishReval(t);
# endif
      
      if (RtsFlags.ParFlags.ParStats.Full &&
	  !RtsFlags.ParFlags.ParStats.Suppressed) 
	DumpEndEvent(CURRENT_PROC, t, rtsFalse /* not mandatory */);
#endif
      break;
      
    default:
      barf("schedule: invalid thread return code %d", (int)ret);
    }
    
#ifdef SMP
    cap->link = free_capabilities;
    free_capabilities = cap;
    n_free_capabilities++;
#endif

#ifdef PROFILING
    if (RtsFlags.ProfFlags.profileInterval==0 || performHeapProfile) {
	GarbageCollect(GetRoots, rtsTrue);
	heapCensus();
	performHeapProfile = rtsFalse;
	ready_to_gc = rtsFalse;	// we already GC'd
    }
#endif

#ifdef SMP
    if (ready_to_gc && n_free_capabilities == RtsFlags.ParFlags.nNodes) 
#else
    if (ready_to_gc) 
#endif
      {
      /* everybody back, start the GC.
       * Could do it in this thread, or signal a condition var
       * to do it in another thread.  Either way, we need to
       * broadcast on gc_pending_cond afterward.
       */
#ifdef SMP
      IF_DEBUG(scheduler,sched_belch("doing GC"));
#endif
      GarbageCollect(GetRoots,rtsFalse);
      ready_to_gc = rtsFalse;
#ifdef SMP
      pthread_cond_broadcast(&gc_pending_cond);
#endif
#if defined(GRAN)
      /* add a ContinueThread event to continue execution of current thread */
      new_event(CurrentProc, CurrentProc, CurrentTime[CurrentProc],
		ContinueThread,
		t, (StgClosure*)NULL, (rtsSpark*)NULL);
      IF_GRAN_DEBUG(bq, 
	       fprintf(stderr, "GRAN: eventq and runnableq after Garbage collection:\n");
	       G_EVENTQ(0);
	       G_CURR_THREADQ(0));
#endif /* GRAN */
    }

#if defined(GRAN)
  next_thread:
    IF_GRAN_DEBUG(unused,
		  print_eventq(EventHd));

    event = get_next_event();
#elif defined(PAR)
  next_thread:
    /* ToDo: wait for next message to arrive rather than busy wait */
#endif /* GRAN */

  } /* end of while(1) */

  IF_PAR_DEBUG(verbose,
	       belch("== Leaving schedule() after having received Finish"));
}

/* ---------------------------------------------------------------------------
 * deleteAllThreads():  kill all the live threads.
 *
 * This is used when we catch a user interrupt (^C), before performing
 * any necessary cleanups and running finalizers.
 * ------------------------------------------------------------------------- */
   
void deleteAllThreads ( void )
{
  StgTSO* t;
  IF_DEBUG(scheduler,sched_belch("deleting all threads"));
  for (t = run_queue_hd; t != END_TSO_QUEUE; t = t->link) {
      deleteThread(t);
  }
  for (t = blocked_queue_hd; t != END_TSO_QUEUE; t = t->link) {
      deleteThread(t);
  }
  for (t = sleeping_queue; t != END_TSO_QUEUE; t = t->link) {
      deleteThread(t);
  }
  run_queue_hd = run_queue_tl = END_TSO_QUEUE;
  blocked_queue_hd = blocked_queue_tl = END_TSO_QUEUE;
  sleeping_queue = END_TSO_QUEUE;
}

/* startThread and  insertThread are now in GranSim.c -- HWL */

//@node Suspend and Resume, Run queue code, Main scheduling loop, Main scheduling code
//@subsection Suspend and Resume

/* ---------------------------------------------------------------------------
 * Suspending & resuming Haskell threads.
 * 
 * When making a "safe" call to C (aka _ccall_GC), the task gives back
 * its capability before calling the C function.  This allows another
 * task to pick up the capability and carry on running Haskell
 * threads.  It also means that if the C call blocks, it won't lock
 * the whole system.
 *
 * The Haskell thread making the C call is put to sleep for the
 * duration of the call, on the susepended_ccalling_threads queue.  We
 * give out a token to the task, which it can use to resume the thread
 * on return from the C function.
 * ------------------------------------------------------------------------- */
   
StgInt
suspendThread( StgRegTable *reg )
{
  nat tok;
  Capability *cap;

  // assume that *reg is a pointer to the StgRegTable part of a Capability
  cap = (Capability *)((void *)reg - sizeof(StgFunTable));

  ACQUIRE_LOCK(&sched_mutex);

  IF_DEBUG(scheduler,
	   sched_belch("thread %d did a _ccall_gc", cap->r.rCurrentTSO->id));

  threadPaused(cap->r.rCurrentTSO);
  cap->r.rCurrentTSO->link = suspended_ccalling_threads;
  suspended_ccalling_threads = cap->r.rCurrentTSO;

  /* Use the thread ID as the token; it should be unique */
  tok = cap->r.rCurrentTSO->id;

#ifdef SMP
  cap->link = free_capabilities;
  free_capabilities = cap;
  n_free_capabilities++;
#endif

  RELEASE_LOCK(&sched_mutex);
  return tok; 
}

StgRegTable *
resumeThread( StgInt tok )
{
  StgTSO *tso, **prev;
  Capability *cap;

  ACQUIRE_LOCK(&sched_mutex);

  prev = &suspended_ccalling_threads;
  for (tso = suspended_ccalling_threads; 
       tso != END_TSO_QUEUE; 
       prev = &tso->link, tso = tso->link) {
    if (tso->id == (StgThreadID)tok) {
      *prev = tso->link;
      break;
    }
  }
  if (tso == END_TSO_QUEUE) {
    barf("resumeThread: thread not found");
  }
  tso->link = END_TSO_QUEUE;

#ifdef SMP
  while (free_capabilities == NULL) {
    IF_DEBUG(scheduler, sched_belch("waiting to resume"));
    pthread_cond_wait(&thread_ready_cond, &sched_mutex);
    IF_DEBUG(scheduler, sched_belch("resuming thread %d", tso->id));
  }
  cap = free_capabilities;
  free_capabilities = cap->link;
  n_free_capabilities--;
#else  
  cap = &MainCapability;
#endif

  cap->r.rCurrentTSO = tso;

  RELEASE_LOCK(&sched_mutex);
  return &cap->r;
}


/* ---------------------------------------------------------------------------
 * Static functions
 * ------------------------------------------------------------------------ */
static void unblockThread(StgTSO *tso);

/* ---------------------------------------------------------------------------
 * Comparing Thread ids.
 *
 * This is used from STG land in the implementation of the
 * instances of Eq/Ord for ThreadIds.
 * ------------------------------------------------------------------------ */

int cmp_thread(const StgTSO *tso1, const StgTSO *tso2) 
{ 
  StgThreadID id1 = tso1->id; 
  StgThreadID id2 = tso2->id;
 
  if (id1 < id2) return (-1);
  if (id1 > id2) return 1;
  return 0;
}

/* ---------------------------------------------------------------------------
 * Fetching the ThreadID from an StgTSO.
 *
 * This is used in the implementation of Show for ThreadIds.
 * ------------------------------------------------------------------------ */
int rts_getThreadId(const StgTSO *tso) 
{
  return tso->id;
}

/* ---------------------------------------------------------------------------
   Create a new thread.

   The new thread starts with the given stack size.  Before the
   scheduler can run, however, this thread needs to have a closure
   (and possibly some arguments) pushed on its stack.  See
   pushClosure() in Schedule.h.

   createGenThread() and createIOThread() (in SchedAPI.h) are
   convenient packaged versions of this function.

   currently pri (priority) is only used in a GRAN setup -- HWL
   ------------------------------------------------------------------------ */
//@cindex createThread
#if defined(GRAN)
/*   currently pri (priority) is only used in a GRAN setup -- HWL */
StgTSO *
createThread(nat stack_size, StgInt pri)
{
  return createThread_(stack_size, rtsFalse, pri);
}

static StgTSO *
createThread_(nat size, rtsBool have_lock, StgInt pri)
{
#else
StgTSO *
createThread(nat stack_size)
{
  return createThread_(stack_size, rtsFalse);
}

static StgTSO *
createThread_(nat size, rtsBool have_lock)
{
#endif

    StgTSO *tso;
    nat stack_size;

    /* First check whether we should create a thread at all */
#if defined(PAR)
  /* check that no more than RtsFlags.ParFlags.maxThreads threads are created */
  if (advisory_thread_count >= RtsFlags.ParFlags.maxThreads) {
    threadsIgnored++;
    belch("{createThread}Daq ghuH: refusing to create another thread; no more than %d threads allowed (currently %d)",
	  RtsFlags.ParFlags.maxThreads, advisory_thread_count);
    return END_TSO_QUEUE;
  }
  threadsCreated++;
#endif

#if defined(GRAN)
  ASSERT(!RtsFlags.GranFlags.Light || CurrentProc==0);
#endif

  // ToDo: check whether size = stack_size - TSO_STRUCT_SIZEW

  /* catch ridiculously small stack sizes */
  if (size < MIN_STACK_WORDS + TSO_STRUCT_SIZEW) {
    size = MIN_STACK_WORDS + TSO_STRUCT_SIZEW;
  }

  stack_size = size - TSO_STRUCT_SIZEW;

  tso = (StgTSO *)allocate(size);
  TICK_ALLOC_TSO(size-TSO_STRUCT_SIZEW, 0);

  SET_HDR(tso, &stg_TSO_info, CCS_SYSTEM);
#if defined(GRAN)
  SET_GRAN_HDR(tso, ThisPE);
#endif
  tso->what_next     = ThreadEnterGHC;

  /* tso->id needs to be unique.  For now we use a heavyweight mutex to
   * protect the increment operation on next_thread_id.
   * In future, we could use an atomic increment instead.
   */
  if (!have_lock) { ACQUIRE_LOCK(&sched_mutex); }
  tso->id = next_thread_id++; 
  if (!have_lock) { RELEASE_LOCK(&sched_mutex); }

  tso->why_blocked  = NotBlocked;
  tso->blocked_exceptions = NULL;

  tso->stack_size   = stack_size;
  tso->max_stack_size = round_to_mblocks(RtsFlags.GcFlags.maxStkSize) 
                              - TSO_STRUCT_SIZEW;
  tso->sp           = (P_)&(tso->stack) + stack_size;

#ifdef PROFILING
  tso->prof.CCCS = CCS_MAIN;
#endif

  /* put a stop frame on the stack */
  tso->sp -= sizeofW(StgStopFrame);
  SET_HDR((StgClosure*)tso->sp,(StgInfoTable *)&stg_stop_thread_info,CCS_SYSTEM);
  tso->su = (StgUpdateFrame*)tso->sp;

  // ToDo: check this
#if defined(GRAN)
  tso->link = END_TSO_QUEUE;
  /* uses more flexible routine in GranSim */
  insertThread(tso, CurrentProc);
#else
  /* In a non-GranSim setup the pushing of a TSO onto the runq is separated
   * from its creation
   */
#endif

#if defined(GRAN) 
  if (RtsFlags.GranFlags.GranSimStats.Full) 
    DumpGranEvent(GR_START,tso);
#elif defined(PAR)
  if (RtsFlags.ParFlags.ParStats.Full) 
    DumpGranEvent(GR_STARTQ,tso);
  /* HACk to avoid SCHEDULE 
     LastTSO = tso; */
#endif

  /* Link the new thread on the global thread list.
   */
  tso->global_link = all_threads;
  all_threads = tso;

#if defined(DIST)
  tso->dist.priority = MandatoryPriority; //by default that is...
#endif

#if defined(GRAN)
  tso->gran.pri = pri;
# if defined(DEBUG)
  tso->gran.magic = TSO_MAGIC; // debugging only
# endif
  tso->gran.sparkname   = 0;
  tso->gran.startedat   = CURRENT_TIME; 
  tso->gran.exported    = 0;
  tso->gran.basicblocks = 0;
  tso->gran.allocs      = 0;
  tso->gran.exectime    = 0;
  tso->gran.fetchtime   = 0;
  tso->gran.fetchcount  = 0;
  tso->gran.blocktime   = 0;
  tso->gran.blockcount  = 0;
  tso->gran.blockedat   = 0;
  tso->gran.globalsparks = 0;
  tso->gran.localsparks  = 0;
  if (RtsFlags.GranFlags.Light)
    tso->gran.clock  = Now; /* local clock */
  else
    tso->gran.clock  = 0;

  IF_DEBUG(gran,printTSO(tso));
#elif defined(PAR)
# if defined(DEBUG)
  tso->par.magic = TSO_MAGIC; // debugging only
# endif
  tso->par.sparkname   = 0;
  tso->par.startedat   = CURRENT_TIME; 
  tso->par.exported    = 0;
  tso->par.basicblocks = 0;
  tso->par.allocs      = 0;
  tso->par.exectime    = 0;
  tso->par.fetchtime   = 0;
  tso->par.fetchcount  = 0;
  tso->par.blocktime   = 0;
  tso->par.blockcount  = 0;
  tso->par.blockedat   = 0;
  tso->par.globalsparks = 0;
  tso->par.localsparks  = 0;
#endif

#if defined(GRAN)
  globalGranStats.tot_threads_created++;
  globalGranStats.threads_created_on_PE[CurrentProc]++;
  globalGranStats.tot_sq_len += spark_queue_len(CurrentProc);
  globalGranStats.tot_sq_probes++;
#elif defined(PAR)
  // collect parallel global statistics (currently done together with GC stats)
  if (RtsFlags.ParFlags.ParStats.Global &&
      RtsFlags.GcFlags.giveStats > NO_GC_STATS) {
    //fprintf(stderr, "Creating thread %d @ %11.2f\n", tso->id, usertime()); 
    globalParStats.tot_threads_created++;
  }
#endif 

#if defined(GRAN)
  IF_GRAN_DEBUG(pri,
		belch("==__ schedule: Created TSO %d (%p);",
		      CurrentProc, tso, tso->id));
#elif defined(PAR)
    IF_PAR_DEBUG(verbose,
		 belch("==__ schedule: Created TSO %d (%p); %d threads active",
		       tso->id, tso, advisory_thread_count));
#else
  IF_DEBUG(scheduler,sched_belch("created thread %ld, stack size = %lx words", 
				 tso->id, tso->stack_size));
#endif    
  return tso;
}

#if defined(PAR)
/* RFP:
   all parallel thread creation calls should fall through the following routine.
*/
StgTSO *
createSparkThread(rtsSpark spark) 
{ StgTSO *tso;
  ASSERT(spark != (rtsSpark)NULL);
  if (advisory_thread_count >= RtsFlags.ParFlags.maxThreads) 
  { threadsIgnored++;
    barf("{createSparkThread}Daq ghuH: refusing to create another thread; no more than %d threads allowed (currently %d)",
	  RtsFlags.ParFlags.maxThreads, advisory_thread_count);    
    return END_TSO_QUEUE;
  }
  else
  { threadsCreated++;
    tso = createThread_(RtsFlags.GcFlags.initialStkSize, rtsTrue);
    if (tso==END_TSO_QUEUE)	
      barf("createSparkThread: Cannot create TSO");
#if defined(DIST)
    tso->priority = AdvisoryPriority;
#endif
    pushClosure(tso,spark);
    PUSH_ON_RUN_QUEUE(tso);
    advisory_thread_count++;    
  }
  return tso;
}
#endif

/*
  Turn a spark into a thread.
  ToDo: fix for SMP (needs to acquire SCHED_MUTEX!)
*/
#if defined(PAR)
//@cindex activateSpark
StgTSO *
activateSpark (rtsSpark spark) 
{
  StgTSO *tso;

  tso = createSparkThread(spark);
  if (RtsFlags.ParFlags.ParStats.Full) {   
    //ASSERT(run_queue_hd == END_TSO_QUEUE); // I think ...
    IF_PAR_DEBUG(verbose,
		 belch("==^^ activateSpark: turning spark of closure %p (%s) into a thread",
		       (StgClosure *)spark, info_type((StgClosure *)spark)));
  }
  // ToDo: fwd info on local/global spark to thread -- HWL
  // tso->gran.exported =  spark->exported;
  // tso->gran.locked =   !spark->global;
  // tso->gran.sparkname = spark->name;

  return tso;
}
#endif

/* ---------------------------------------------------------------------------
 * scheduleThread()
 *
 * scheduleThread puts a thread on the head of the runnable queue.
 * This will usually be done immediately after a thread is created.
 * The caller of scheduleThread must create the thread using e.g.
 * createThread and push an appropriate closure
 * on this thread's stack before the scheduler is invoked.
 * ------------------------------------------------------------------------ */

void
scheduleThread(StgTSO *tso)
{
  if (tso==END_TSO_QUEUE){    
    schedule();
    return;
  }

  ACQUIRE_LOCK(&sched_mutex);

  /* Put the new thread on the head of the runnable queue.  The caller
   * better push an appropriate closure on this thread's stack
   * beforehand.  In the SMP case, the thread may start running as
   * soon as we release the scheduler lock below.
   */
  PUSH_ON_RUN_QUEUE(tso);
  THREAD_RUNNABLE();

#if 0
  IF_DEBUG(scheduler,printTSO(tso));
#endif
  RELEASE_LOCK(&sched_mutex);
}

/* ---------------------------------------------------------------------------
 * startTasks()
 *
 * Start up Posix threads to run each of the scheduler tasks.
 * I believe the task ids are not needed in the system as defined.
 *  KH @ 25/10/99
 * ------------------------------------------------------------------------ */

#if defined(PAR) || defined(SMP)
void
taskStart(void) /*  ( void *arg STG_UNUSED)  */
{
  scheduleThread(END_TSO_QUEUE);
}
#endif

/* ---------------------------------------------------------------------------
 * initScheduler()
 *
 * Initialise the scheduler.  This resets all the queues - if the
 * queues contained any threads, they'll be garbage collected at the
 * next pass.
 *
 * This now calls startTasks(), so should only be called once!  KH @ 25/10/99
 * ------------------------------------------------------------------------ */

#ifdef SMP
static void
term_handler(int sig STG_UNUSED)
{
  stat_workerStop();
  ACQUIRE_LOCK(&term_mutex);
  await_death--;
  RELEASE_LOCK(&term_mutex);
  pthread_exit(NULL);
}
#endif

static void
initCapability( Capability *cap )
{
    cap->f.stgChk0         = (F_)__stg_chk_0;
    cap->f.stgChk1         = (F_)__stg_chk_1;
    cap->f.stgGCEnter1     = (F_)__stg_gc_enter_1;
    cap->f.stgUpdatePAP    = (F_)__stg_update_PAP;
}

void 
initScheduler(void)
{
#if defined(GRAN)
  nat i;

  for (i=0; i<=MAX_PROC; i++) {
    run_queue_hds[i]      = END_TSO_QUEUE;
    run_queue_tls[i]      = END_TSO_QUEUE;
    blocked_queue_hds[i]  = END_TSO_QUEUE;
    blocked_queue_tls[i]  = END_TSO_QUEUE;
    ccalling_threadss[i]  = END_TSO_QUEUE;
    sleeping_queue        = END_TSO_QUEUE;
  }
#else
  run_queue_hd      = END_TSO_QUEUE;
  run_queue_tl      = END_TSO_QUEUE;
  blocked_queue_hd  = END_TSO_QUEUE;
  blocked_queue_tl  = END_TSO_QUEUE;
  sleeping_queue    = END_TSO_QUEUE;
#endif 

  suspended_ccalling_threads  = END_TSO_QUEUE;

  main_threads = NULL;
  all_threads  = END_TSO_QUEUE;

  context_switch = 0;
  interrupted    = 0;

  RtsFlags.ConcFlags.ctxtSwitchTicks =
      RtsFlags.ConcFlags.ctxtSwitchTime / TICK_MILLISECS;

  /* Install the SIGHUP handler */
#ifdef SMP
  {
    struct sigaction action,oact;

    action.sa_handler = term_handler;
    sigemptyset(&action.sa_mask);
    action.sa_flags = 0;
    if (sigaction(SIGTERM, &action, &oact) != 0) {
      barf("can't install TERM handler");
    }
  }
#endif

#ifdef SMP
  /* Allocate N Capabilities */
  {
    nat i;
    Capability *cap, *prev;
    cap  = NULL;
    prev = NULL;
    for (i = 0; i < RtsFlags.ParFlags.nNodes; i++) {
      cap = stgMallocBytes(sizeof(Capability), "initScheduler:capabilities");
      initCapability(cap);
      cap->link = prev;
      prev = cap;
    }
    free_capabilities = cap;
    n_free_capabilities = RtsFlags.ParFlags.nNodes;
  }
  IF_DEBUG(scheduler,fprintf(stderr,"scheduler: Allocated %d capabilities\n",
			     n_free_capabilities););
#else
  initCapability(&MainCapability);
#endif

#if defined(SMP) || defined(PAR)
  initSparkPools();
#endif
}

#ifdef SMP
void
startTasks( void )
{
  nat i;
  int r;
  pthread_t tid;
  
  /* make some space for saving all the thread ids */
  task_ids = stgMallocBytes(RtsFlags.ParFlags.nNodes * sizeof(task_info),
			    "initScheduler:task_ids");
  
  /* and create all the threads */
  for (i = 0; i < RtsFlags.ParFlags.nNodes; i++) {
    r = pthread_create(&tid,NULL,taskStart,NULL);
    if (r != 0) {
      barf("startTasks: Can't create new Posix thread");
    }
    task_ids[i].id = tid;
    task_ids[i].mut_time = 0.0;
    task_ids[i].mut_etime = 0.0;
    task_ids[i].gc_time = 0.0;
    task_ids[i].gc_etime = 0.0;
    task_ids[i].elapsedtimestart = elapsedtime();
    IF_DEBUG(scheduler,fprintf(stderr,"scheduler: Started task: %ld\n",tid););
  }
}
#endif

void
exitScheduler( void )
{
#ifdef SMP
  nat i;

  /* Don't want to use pthread_cancel, since we'd have to install
   * these silly exception handlers (pthread_cleanup_{push,pop}) around
   * all our locks.
   */
#if 0
  /* Cancel all our tasks */
  for (i = 0; i < RtsFlags.ParFlags.nNodes; i++) {
    pthread_cancel(task_ids[i].id);
  }
  
  /* Wait for all the tasks to terminate */
  for (i = 0; i < RtsFlags.ParFlags.nNodes; i++) {
    IF_DEBUG(scheduler,fprintf(stderr,"scheduler: waiting for task %ld\n", 
			       task_ids[i].id));
    pthread_join(task_ids[i].id, NULL);
  }
#endif

  /* Send 'em all a SIGHUP.  That should shut 'em up.
   */
  await_death = RtsFlags.ParFlags.nNodes;
  for (i = 0; i < RtsFlags.ParFlags.nNodes; i++) {
    pthread_kill(task_ids[i].id,SIGTERM);
  }
  while (await_death > 0) {
    sched_yield();
  }
#endif
}

/* -----------------------------------------------------------------------------
   Managing the per-task allocation areas.
   
   Each capability comes with an allocation area.  These are
   fixed-length block lists into which allocation can be done.

   ToDo: no support for two-space collection at the moment???
   -------------------------------------------------------------------------- */

/* -----------------------------------------------------------------------------
 * waitThread is the external interface for running a new computation
 * and waiting for the result.
 *
 * In the non-SMP case, we create a new main thread, push it on the 
 * main-thread stack, and invoke the scheduler to run it.  The
 * scheduler will return when the top main thread on the stack has
 * completed or died, and fill in the necessary fields of the
 * main_thread structure.
 *
 * In the SMP case, we create a main thread as before, but we then
 * create a new condition variable and sleep on it.  When our new
 * main thread has completed, we'll be woken up and the status/result
 * will be in the main_thread struct.
 * -------------------------------------------------------------------------- */

int 
howManyThreadsAvail ( void )
{
   int i = 0;
   StgTSO* q;
   for (q = run_queue_hd; q != END_TSO_QUEUE; q = q->link)
      i++;
   for (q = blocked_queue_hd; q != END_TSO_QUEUE; q = q->link)
      i++;
   for (q = sleeping_queue; q != END_TSO_QUEUE; q = q->link)
      i++;
   return i;
}

void
finishAllThreads ( void )
{
   do {
      while (run_queue_hd != END_TSO_QUEUE) {
         waitThread ( run_queue_hd, NULL );
      }
      while (blocked_queue_hd != END_TSO_QUEUE) {
         waitThread ( blocked_queue_hd, NULL );
      }
      while (sleeping_queue != END_TSO_QUEUE) {
         waitThread ( blocked_queue_hd, NULL );
      }
   } while 
      (blocked_queue_hd != END_TSO_QUEUE || 
       run_queue_hd     != END_TSO_QUEUE ||
       sleeping_queue   != END_TSO_QUEUE);
}

SchedulerStatus
waitThread(StgTSO *tso, /*out*/StgClosure **ret)
{
  StgMainThread *m;
  SchedulerStatus stat;

  ACQUIRE_LOCK(&sched_mutex);
  
  m = stgMallocBytes(sizeof(StgMainThread), "waitThread");

  m->tso = tso;
  m->ret = ret;
  m->stat = NoStatus;
#ifdef SMP
  pthread_cond_init(&m->wakeup, NULL);
#endif

  m->link = main_threads;
  main_threads = m;

  IF_DEBUG(scheduler, fprintf(stderr, "== scheduler: new main thread (%d)\n", 
			      m->tso->id));

#ifdef SMP
  do {
    pthread_cond_wait(&m->wakeup, &sched_mutex);
  } while (m->stat == NoStatus);
#elif defined(GRAN)
  /* GranSim specific init */
  CurrentTSO = m->tso;                // the TSO to run
  procStatus[MainProc] = Busy;        // status of main PE
  CurrentProc = MainProc;             // PE to run it on

  schedule();
#else
  schedule();
  ASSERT(m->stat != NoStatus);
#endif

  stat = m->stat;

#ifdef SMP
  pthread_cond_destroy(&m->wakeup);
#endif

  IF_DEBUG(scheduler, fprintf(stderr, "== scheduler: main thread (%d) finished\n", 
			      m->tso->id));
  free(m);

  RELEASE_LOCK(&sched_mutex);

  return stat;
}

//@node Run queue code, Garbage Collextion Routines, Suspend and Resume, Main scheduling code
//@subsection Run queue code 

#if 0
/* 
   NB: In GranSim we have many run queues; run_queue_hd is actually a macro
       unfolding to run_queue_hds[CurrentProc], thus CurrentProc is an
       implicit global variable that has to be correct when calling these
       fcts -- HWL 
*/

/* Put the new thread on the head of the runnable queue.
 * The caller of createThread better push an appropriate closure
 * on this thread's stack before the scheduler is invoked.
 */
static /* inline */ void
add_to_run_queue(tso)
StgTSO* tso; 
{
  ASSERT(tso!=run_queue_hd && tso!=run_queue_tl);
  tso->link = run_queue_hd;
  run_queue_hd = tso;
  if (run_queue_tl == END_TSO_QUEUE) {
    run_queue_tl = tso;
  }
}

/* Put the new thread at the end of the runnable queue. */
static /* inline */ void
push_on_run_queue(tso)
StgTSO* tso; 
{
  ASSERT(get_itbl((StgClosure *)tso)->type == TSO);
  ASSERT(run_queue_hd!=NULL && run_queue_tl!=NULL);
  ASSERT(tso!=run_queue_hd && tso!=run_queue_tl);
  if (run_queue_hd == END_TSO_QUEUE) {
    run_queue_hd = tso;
  } else {
    run_queue_tl->link = tso;
  }
  run_queue_tl = tso;
}

/* 
   Should be inlined because it's used very often in schedule.  The tso
   argument is actually only needed in GranSim, where we want to have the
   possibility to schedule *any* TSO on the run queue, irrespective of the
   actual ordering. Therefore, if tso is not the nil TSO then we traverse
   the run queue and dequeue the tso, adjusting the links in the queue. 
*/
//@cindex take_off_run_queue
static /* inline */ StgTSO*
take_off_run_queue(StgTSO *tso) {
  StgTSO *t, *prev;

  /* 
     qetlaHbogh Qu' ngaSbogh ghomDaQ {tso} yIteq!

     if tso is specified, unlink that tso from the run_queue (doesn't have
     to be at the beginning of the queue); GranSim only 
  */
  if (tso!=END_TSO_QUEUE) {
    /* find tso in queue */
    for (t=run_queue_hd, prev=END_TSO_QUEUE; 
	 t!=END_TSO_QUEUE && t!=tso;
	 prev=t, t=t->link) 
      /* nothing */ ;
    ASSERT(t==tso);
    /* now actually dequeue the tso */
    if (prev!=END_TSO_QUEUE) {
      ASSERT(run_queue_hd!=t);
      prev->link = t->link;
    } else {
      /* t is at beginning of thread queue */
      ASSERT(run_queue_hd==t);
      run_queue_hd = t->link;
    }
    /* t is at end of thread queue */
    if (t->link==END_TSO_QUEUE) {
      ASSERT(t==run_queue_tl);
      run_queue_tl = prev;
    } else {
      ASSERT(run_queue_tl!=t);
    }
    t->link = END_TSO_QUEUE;
  } else {
    /* take tso from the beginning of the queue; std concurrent code */
    t = run_queue_hd;
    if (t != END_TSO_QUEUE) {
      run_queue_hd = t->link;
      t->link = END_TSO_QUEUE;
      if (run_queue_hd == END_TSO_QUEUE) {
	run_queue_tl = END_TSO_QUEUE;
      }
    }
  }
  return t;
}

#endif /* 0 */

//@node Garbage Collextion Routines, Blocking Queue Routines, Run queue code, Main scheduling code
//@subsection Garbage Collextion Routines

/* ---------------------------------------------------------------------------
   Where are the roots that we know about?

        - all the threads on the runnable queue
        - all the threads on the blocked queue
        - all the threads on the sleeping queue
	- all the thread currently executing a _ccall_GC
        - all the "main threads"
     
   ------------------------------------------------------------------------ */

/* This has to be protected either by the scheduler monitor, or by the
	garbage collection monitor (probably the latter).
	KH @ 25/10/99
*/

void
GetRoots(evac_fn evac)
{
  StgMainThread *m;

#if defined(GRAN)
  {
    nat i;
    for (i=0; i<=RtsFlags.GranFlags.proc; i++) {
      if ((run_queue_hds[i] != END_TSO_QUEUE) && ((run_queue_hds[i] != NULL)))
	  evac((StgClosure **)&run_queue_hds[i]);
      if ((run_queue_tls[i] != END_TSO_QUEUE) && ((run_queue_tls[i] != NULL)))
	  evac((StgClosure **)&run_queue_tls[i]);
      
      if ((blocked_queue_hds[i] != END_TSO_QUEUE) && ((blocked_queue_hds[i] != NULL)))
	  evac((StgClosure **)&blocked_queue_hds[i]);
      if ((blocked_queue_tls[i] != END_TSO_QUEUE) && ((blocked_queue_tls[i] != NULL)))
	  evac((StgClosure **)&blocked_queue_tls[i]);
      if ((ccalling_threadss[i] != END_TSO_QUEUE) && ((ccalling_threadss[i] != NULL)))
	  evac((StgClosure **)&ccalling_threads[i]);
    }
  }

  markEventQueue();

#else /* !GRAN */
  if (run_queue_hd != END_TSO_QUEUE) {
      ASSERT(run_queue_tl != END_TSO_QUEUE);
      evac((StgClosure **)&run_queue_hd);
      evac((StgClosure **)&run_queue_tl);
  }
  
  if (blocked_queue_hd != END_TSO_QUEUE) {
      ASSERT(blocked_queue_tl != END_TSO_QUEUE);
      evac((StgClosure **)&blocked_queue_hd);
      evac((StgClosure **)&blocked_queue_tl);
  }
  
  if (sleeping_queue != END_TSO_QUEUE) {
      evac((StgClosure **)&sleeping_queue);
  }
#endif 

  for (m = main_threads; m != NULL; m = m->link) {
      evac((StgClosure **)&m->tso);
  }
  if (suspended_ccalling_threads != END_TSO_QUEUE) {
      evac((StgClosure **)&suspended_ccalling_threads);
  }

#if defined(SMP) || defined(PAR) || defined(GRAN)
  markSparkQueue(evac);
#endif
}

/* -----------------------------------------------------------------------------
   performGC

   This is the interface to the garbage collector from Haskell land.
   We provide this so that external C code can allocate and garbage
   collect when called from Haskell via _ccall_GC.

   It might be useful to provide an interface whereby the programmer
   can specify more roots (ToDo).
   
   This needs to be protected by the GC condition variable above.  KH.
   -------------------------------------------------------------------------- */

void (*extra_roots)(evac_fn);

void
performGC(void)
{
  GarbageCollect(GetRoots,rtsFalse);
}

void
performMajorGC(void)
{
  GarbageCollect(GetRoots,rtsTrue);
}

static void
AllRoots(evac_fn evac)
{
    GetRoots(evac);		// the scheduler's roots
    extra_roots(evac);		// the user's roots
}

void
performGCWithRoots(void (*get_roots)(evac_fn))
{
  extra_roots = get_roots;
  GarbageCollect(AllRoots,rtsFalse);
}

/* -----------------------------------------------------------------------------
   Stack overflow

   If the thread has reached its maximum stack size, then raise the
   StackOverflow exception in the offending thread.  Otherwise
   relocate the TSO into a larger chunk of memory and adjust its stack
   size appropriately.
   -------------------------------------------------------------------------- */

static StgTSO *
threadStackOverflow(StgTSO *tso)
{
  nat new_stack_size, new_tso_size, diff, stack_words;
  StgPtr new_sp;
  StgTSO *dest;

  IF_DEBUG(sanity,checkTSO(tso));
  if (tso->stack_size >= tso->max_stack_size) {

    IF_DEBUG(gc,
	     belch("@@ threadStackOverflow of TSO %d (%p): stack too large (now %ld; max is %ld",
		   tso->id, tso, tso->stack_size, tso->max_stack_size);
	     /* If we're debugging, just print out the top of the stack */
	     printStackChunk(tso->sp, stg_min(tso->stack+tso->stack_size, 
					      tso->sp+64)));

    /* Send this thread the StackOverflow exception */
    raiseAsync(tso, (StgClosure *)stackOverflow_closure);
    return tso;
  }

  /* Try to double the current stack size.  If that takes us over the
   * maximum stack size for this thread, then use the maximum instead.
   * Finally round up so the TSO ends up as a whole number of blocks.
   */
  new_stack_size = stg_min(tso->stack_size * 2, tso->max_stack_size);
  new_tso_size   = (nat)BLOCK_ROUND_UP(new_stack_size * sizeof(W_) + 
				       TSO_STRUCT_SIZE)/sizeof(W_);
  new_tso_size = round_to_mblocks(new_tso_size);  /* Be MBLOCK-friendly */
  new_stack_size = new_tso_size - TSO_STRUCT_SIZEW;

  IF_DEBUG(scheduler, fprintf(stderr,"== scheduler: increasing stack size from %d words to %d.\n", tso->stack_size, new_stack_size));

  dest = (StgTSO *)allocate(new_tso_size);
  TICK_ALLOC_TSO(new_tso_size-sizeofW(StgTSO),0);

  /* copy the TSO block and the old stack into the new area */
  memcpy(dest,tso,TSO_STRUCT_SIZE);
  stack_words = tso->stack + tso->stack_size - tso->sp;
  new_sp = (P_)dest + new_tso_size - stack_words;
  memcpy(new_sp, tso->sp, stack_words * sizeof(W_));

  /* relocate the stack pointers... */
  diff = (P_)new_sp - (P_)tso->sp; /* In *words* */
  dest->su    = (StgUpdateFrame *) ((P_)dest->su + diff);
  dest->sp    = new_sp;
  dest->stack_size = new_stack_size;
	
  /* and relocate the update frame list */
  relocate_stack(dest, diff);

  /* Mark the old TSO as relocated.  We have to check for relocated
   * TSOs in the garbage collector and any primops that deal with TSOs.
   *
   * It's important to set the sp and su values to just beyond the end
   * of the stack, so we don't attempt to scavenge any part of the
   * dead TSO's stack.
   */
  tso->what_next = ThreadRelocated;
  tso->link = dest;
  tso->sp = (P_)&(tso->stack[tso->stack_size]);
  tso->su = (StgUpdateFrame *)tso->sp;
  tso->why_blocked = NotBlocked;
  dest->mut_link = NULL;

  IF_PAR_DEBUG(verbose,
	       belch("@@ threadStackOverflow of TSO %d (now at %p): stack size increased to %ld",
		     tso->id, tso, tso->stack_size);
	       /* If we're debugging, just print out the top of the stack */
	       printStackChunk(tso->sp, stg_min(tso->stack+tso->stack_size, 
						tso->sp+64)));
  
  IF_DEBUG(sanity,checkTSO(tso));
#if 0
  IF_DEBUG(scheduler,printTSO(dest));
#endif

  return dest;
}

//@node Blocking Queue Routines, Exception Handling Routines, Garbage Collextion Routines, Main scheduling code
//@subsection Blocking Queue Routines

/* ---------------------------------------------------------------------------
   Wake up a queue that was blocked on some resource.
   ------------------------------------------------------------------------ */

#if defined(GRAN)
static inline void
unblockCount ( StgBlockingQueueElement *bqe, StgClosure *node )
{
}
#elif defined(PAR)
static inline void
unblockCount ( StgBlockingQueueElement *bqe, StgClosure *node )
{
  /* write RESUME events to log file and
     update blocked and fetch time (depending on type of the orig closure) */
  if (RtsFlags.ParFlags.ParStats.Full) {
    DumpRawGranEvent(CURRENT_PROC, CURRENT_PROC, 
		     GR_RESUMEQ, ((StgTSO *)bqe), ((StgTSO *)bqe)->block_info.closure,
		     0, 0 /* spark_queue_len(ADVISORY_POOL) */);
    if (EMPTY_RUN_QUEUE())
      emitSchedule = rtsTrue;

    switch (get_itbl(node)->type) {
	case FETCH_ME_BQ:
	  ((StgTSO *)bqe)->par.fetchtime += CURRENT_TIME-((StgTSO *)bqe)->par.blockedat;
	  break;
	case RBH:
	case FETCH_ME:
	case BLACKHOLE_BQ:
	  ((StgTSO *)bqe)->par.blocktime += CURRENT_TIME-((StgTSO *)bqe)->par.blockedat;
	  break;
#ifdef DIST
        case MVAR:
          break;
#endif	  
	default:
	  barf("{unblockOneLocked}Daq Qagh: unexpected closure in blocking queue");
	}
      }
}
#endif

#if defined(GRAN)
static StgBlockingQueueElement *
unblockOneLocked(StgBlockingQueueElement *bqe, StgClosure *node)
{
    StgTSO *tso;
    PEs node_loc, tso_loc;

    node_loc = where_is(node); // should be lifted out of loop
    tso = (StgTSO *)bqe;  // wastes an assignment to get the type right
    tso_loc = where_is((StgClosure *)tso);
    if (IS_LOCAL_TO(PROCS(node),tso_loc)) { // TSO is local
      /* !fake_fetch => TSO is on CurrentProc is same as IS_LOCAL_TO */
      ASSERT(CurrentProc!=node_loc || tso_loc==CurrentProc);
      CurrentTime[CurrentProc] += RtsFlags.GranFlags.Costs.lunblocktime;
      // insertThread(tso, node_loc);
      new_event(tso_loc, tso_loc, CurrentTime[CurrentProc],
		ResumeThread,
		tso, node, (rtsSpark*)NULL);
      tso->link = END_TSO_QUEUE; // overwrite link just to be sure 
      // len_local++;
      // len++;
    } else { // TSO is remote (actually should be FMBQ)
      CurrentTime[CurrentProc] += RtsFlags.GranFlags.Costs.mpacktime +
                                  RtsFlags.GranFlags.Costs.gunblocktime +
	                          RtsFlags.GranFlags.Costs.latency;
      new_event(tso_loc, CurrentProc, CurrentTime[CurrentProc],
		UnblockThread,
		tso, node, (rtsSpark*)NULL);
      tso->link = END_TSO_QUEUE; // overwrite link just to be sure 
      // len++;
    }
    /* the thread-queue-overhead is accounted for in either Resume or UnblockThread */
    IF_GRAN_DEBUG(bq,
		  fprintf(stderr," %s TSO %d (%p) [PE %d] (block_info.closure=%p) (next=%p) ,",
			  (node_loc==tso_loc ? "Local" : "Global"), 
			  tso->id, tso, CurrentProc, tso->block_info.closure, tso->link));
    tso->block_info.closure = NULL;
    IF_DEBUG(scheduler,belch("-- Waking up thread %ld (%p)", 
			     tso->id, tso));
}
#elif defined(PAR)
static StgBlockingQueueElement *
unblockOneLocked(StgBlockingQueueElement *bqe, StgClosure *node)
{
    StgBlockingQueueElement *next;

    switch (get_itbl(bqe)->type) {
    case TSO:
      ASSERT(((StgTSO *)bqe)->why_blocked != NotBlocked);
      /* if it's a TSO just push it onto the run_queue */
      next = bqe->link;
      // ((StgTSO *)bqe)->link = END_TSO_QUEUE; // debugging?
      PUSH_ON_RUN_QUEUE((StgTSO *)bqe); 
      THREAD_RUNNABLE();
      unblockCount(bqe, node);
      /* reset blocking status after dumping event */
      ((StgTSO *)bqe)->why_blocked = NotBlocked;
      break;

    case BLOCKED_FETCH:
      /* if it's a BLOCKED_FETCH put it on the PendingFetches list */
      next = bqe->link;
      bqe->link = (StgBlockingQueueElement *)PendingFetches;
      PendingFetches = (StgBlockedFetch *)bqe;
      break;

# if defined(DEBUG)
      /* can ignore this case in a non-debugging setup; 
	 see comments on RBHSave closures above */
    case CONSTR:
      /* check that the closure is an RBHSave closure */
      ASSERT(get_itbl((StgClosure *)bqe) == &stg_RBH_Save_0_info ||
	     get_itbl((StgClosure *)bqe) == &stg_RBH_Save_1_info ||
	     get_itbl((StgClosure *)bqe) == &stg_RBH_Save_2_info);
      break;

    default:
      barf("{unblockOneLocked}Daq Qagh: Unexpected IP (%#lx; %s) in blocking queue at %#lx\n",
	   get_itbl((StgClosure *)bqe), info_type((StgClosure *)bqe), 
	   (StgClosure *)bqe);
# endif
    }
  IF_PAR_DEBUG(bq, fprintf(stderr, ", %p (%s)", bqe, info_type((StgClosure*)bqe)));
  return next;
}

#else /* !GRAN && !PAR */
static StgTSO *
unblockOneLocked(StgTSO *tso)
{
  StgTSO *next;

  ASSERT(get_itbl(tso)->type == TSO);
  ASSERT(tso->why_blocked != NotBlocked);
  tso->why_blocked = NotBlocked;
  next = tso->link;
  PUSH_ON_RUN_QUEUE(tso);
  THREAD_RUNNABLE();
  IF_DEBUG(scheduler,sched_belch("waking up thread %ld", tso->id));
  return next;
}
#endif

#if defined(GRAN) || defined(PAR)
inline StgBlockingQueueElement *
unblockOne(StgBlockingQueueElement *bqe, StgClosure *node)
{
  ACQUIRE_LOCK(&sched_mutex);
  bqe = unblockOneLocked(bqe, node);
  RELEASE_LOCK(&sched_mutex);
  return bqe;
}
#else
inline StgTSO *
unblockOne(StgTSO *tso)
{
  ACQUIRE_LOCK(&sched_mutex);
  tso = unblockOneLocked(tso);
  RELEASE_LOCK(&sched_mutex);
  return tso;
}
#endif

#if defined(GRAN)
void 
awakenBlockedQueue(StgBlockingQueueElement *q, StgClosure *node)
{
  StgBlockingQueueElement *bqe;
  PEs node_loc;
  nat len = 0; 

  IF_GRAN_DEBUG(bq, 
		belch("##-_ AwBQ for node %p on PE %d @ %ld by TSO %d (%p): ", \
		      node, CurrentProc, CurrentTime[CurrentProc], 
		      CurrentTSO->id, CurrentTSO));

  node_loc = where_is(node);

  ASSERT(q == END_BQ_QUEUE ||
	 get_itbl(q)->type == TSO ||   // q is either a TSO or an RBHSave
	 get_itbl(q)->type == CONSTR); // closure (type constructor)
  ASSERT(is_unique(node));

  /* FAKE FETCH: magically copy the node to the tso's proc;
     no Fetch necessary because in reality the node should not have been 
     moved to the other PE in the first place
  */
  if (CurrentProc!=node_loc) {
    IF_GRAN_DEBUG(bq, 
		  belch("## node %p is on PE %d but CurrentProc is %d (TSO %d); assuming fake fetch and adjusting bitmask (old: %#x)",
			node, node_loc, CurrentProc, CurrentTSO->id, 
			// CurrentTSO, where_is(CurrentTSO),
			node->header.gran.procs));
    node->header.gran.procs = (node->header.gran.procs) | PE_NUMBER(CurrentProc);
    IF_GRAN_DEBUG(bq, 
		  belch("## new bitmask of node %p is %#x",
			node, node->header.gran.procs));
    if (RtsFlags.GranFlags.GranSimStats.Global) {
      globalGranStats.tot_fake_fetches++;
    }
  }

  bqe = q;
  // ToDo: check: ASSERT(CurrentProc==node_loc);
  while (get_itbl(bqe)->type==TSO) { // q != END_TSO_QUEUE) {
    //next = bqe->link;
    /* 
       bqe points to the current element in the queue
       next points to the next element in the queue
    */
    //tso = (StgTSO *)bqe;  // wastes an assignment to get the type right
    //tso_loc = where_is(tso);
    len++;
    bqe = unblockOneLocked(bqe, node);
  }

  /* if this is the BQ of an RBH, we have to put back the info ripped out of
     the closure to make room for the anchor of the BQ */
  if (bqe!=END_BQ_QUEUE) {
    ASSERT(get_itbl(node)->type == RBH && get_itbl(bqe)->type == CONSTR);
    /*
    ASSERT((info_ptr==&RBH_Save_0_info) ||
	   (info_ptr==&RBH_Save_1_info) ||
	   (info_ptr==&RBH_Save_2_info));
    */
    /* cf. convertToRBH in RBH.c for writing the RBHSave closure */
    ((StgRBH *)node)->blocking_queue = (StgBlockingQueueElement *)((StgRBHSave *)bqe)->payload[0];
    ((StgRBH *)node)->mut_link       = (StgMutClosure *)((StgRBHSave *)bqe)->payload[1];

    IF_GRAN_DEBUG(bq,
		  belch("## Filled in RBH_Save for %p (%s) at end of AwBQ",
			node, info_type(node)));
  }

  /* statistics gathering */
  if (RtsFlags.GranFlags.GranSimStats.Global) {
    // globalGranStats.tot_bq_processing_time += bq_processing_time;
    globalGranStats.tot_bq_len += len;      // total length of all bqs awakened
    // globalGranStats.tot_bq_len_local += len_local;  // same for local TSOs only
    globalGranStats.tot_awbq++;             // total no. of bqs awakened
  }
  IF_GRAN_DEBUG(bq,
		fprintf(stderr,"## BQ Stats of %p: [%d entries] %s\n",
			node, len, (bqe!=END_BQ_QUEUE) ? "RBH" : ""));
}
#elif defined(PAR)
void 
awakenBlockedQueue(StgBlockingQueueElement *q, StgClosure *node)
{
  StgBlockingQueueElement *bqe;

  ACQUIRE_LOCK(&sched_mutex);

  IF_PAR_DEBUG(verbose, 
	       belch("##-_ AwBQ for node %p on [%x]: ",
		     node, mytid));
#ifdef DIST  
  //RFP
  if(get_itbl(q)->type == CONSTR || q==END_BQ_QUEUE) {
    IF_PAR_DEBUG(verbose, belch("## ... nothing to unblock so lets just return. RFP (BUG?)"));
    return;
  }
#endif
  
  ASSERT(q == END_BQ_QUEUE ||
	 get_itbl(q)->type == TSO ||           
  	 get_itbl(q)->type == BLOCKED_FETCH || 
  	 get_itbl(q)->type == CONSTR); 

  bqe = q;
  while (get_itbl(bqe)->type==TSO || 
	 get_itbl(bqe)->type==BLOCKED_FETCH) {
    bqe = unblockOneLocked(bqe, node);
  }
  RELEASE_LOCK(&sched_mutex);
}

#else   /* !GRAN && !PAR */
void
awakenBlockedQueue(StgTSO *tso)
{
  ACQUIRE_LOCK(&sched_mutex);
  while (tso != END_TSO_QUEUE) {
    tso = unblockOneLocked(tso);
  }
  RELEASE_LOCK(&sched_mutex);
}
#endif

//@node Exception Handling Routines, Debugging Routines, Blocking Queue Routines, Main scheduling code
//@subsection Exception Handling Routines

/* ---------------------------------------------------------------------------
   Interrupt execution
   - usually called inside a signal handler so it mustn't do anything fancy.   
   ------------------------------------------------------------------------ */

void
interruptStgRts(void)
{
    interrupted    = 1;
    context_switch = 1;
}

/* -----------------------------------------------------------------------------
   Unblock a thread

   This is for use when we raise an exception in another thread, which
   may be blocked.
   This has nothing to do with the UnblockThread event in GranSim. -- HWL
   -------------------------------------------------------------------------- */

#if defined(GRAN) || defined(PAR)
/*
  NB: only the type of the blocking queue is different in GranSim and GUM
      the operations on the queue-elements are the same
      long live polymorphism!
*/
static void
unblockThread(StgTSO *tso)
{
  StgBlockingQueueElement *t, **last;

  ACQUIRE_LOCK(&sched_mutex);
  switch (tso->why_blocked) {

  case NotBlocked:
    return;  /* not blocked */

  case BlockedOnMVar:
    ASSERT(get_itbl(tso->block_info.closure)->type == MVAR);
    {
      StgBlockingQueueElement *last_tso = END_BQ_QUEUE;
      StgMVar *mvar = (StgMVar *)(tso->block_info.closure);

      last = (StgBlockingQueueElement **)&mvar->head;
      for (t = (StgBlockingQueueElement *)mvar->head; 
	   t != END_BQ_QUEUE; 
	   last = &t->link, last_tso = t, t = t->link) {
	if (t == (StgBlockingQueueElement *)tso) {
	  *last = (StgBlockingQueueElement *)tso->link;
	  if (mvar->tail == tso) {
	    mvar->tail = (StgTSO *)last_tso;
	  }
	  goto done;
	}
      }
      barf("unblockThread (MVAR): TSO not found");
    }

  case BlockedOnBlackHole:
    ASSERT(get_itbl(tso->block_info.closure)->type == BLACKHOLE_BQ);
    {
      StgBlockingQueue *bq = (StgBlockingQueue *)(tso->block_info.closure);

      last = &bq->blocking_queue;
      for (t = bq->blocking_queue; 
	   t != END_BQ_QUEUE; 
	   last = &t->link, t = t->link) {
	if (t == (StgBlockingQueueElement *)tso) {
	  *last = (StgBlockingQueueElement *)tso->link;
	  goto done;
	}
      }
      barf("unblockThread (BLACKHOLE): TSO not found");
    }

  case BlockedOnException:
    {
      StgTSO *target  = tso->block_info.tso;

      ASSERT(get_itbl(target)->type == TSO);

      if (target->what_next == ThreadRelocated) {
	  target = target->link;
	  ASSERT(get_itbl(target)->type == TSO);
      }

      ASSERT(target->blocked_exceptions != NULL);

      last = (StgBlockingQueueElement **)&target->blocked_exceptions;
      for (t = (StgBlockingQueueElement *)target->blocked_exceptions; 
	   t != END_BQ_QUEUE; 
	   last = &t->link, t = t->link) {
	ASSERT(get_itbl(t)->type == TSO);
	if (t == (StgBlockingQueueElement *)tso) {
	  *last = (StgBlockingQueueElement *)tso->link;
	  goto done;
	}
      }
      barf("unblockThread (Exception): TSO not found");
    }

  case BlockedOnRead:
  case BlockedOnWrite:
    {
      /* take TSO off blocked_queue */
      StgBlockingQueueElement *prev = NULL;
      for (t = (StgBlockingQueueElement *)blocked_queue_hd; t != END_BQ_QUEUE; 
	   prev = t, t = t->link) {
	if (t == (StgBlockingQueueElement *)tso) {
	  if (prev == NULL) {
	    blocked_queue_hd = (StgTSO *)t->link;
	    if ((StgBlockingQueueElement *)blocked_queue_tl == t) {
	      blocked_queue_tl = END_TSO_QUEUE;
	    }
	  } else {
	    prev->link = t->link;
	    if ((StgBlockingQueueElement *)blocked_queue_tl == t) {
	      blocked_queue_tl = (StgTSO *)prev;
	    }
	  }
	  goto done;
	}
      }
      barf("unblockThread (I/O): TSO not found");
    }

  case BlockedOnDelay:
    {
      /* take TSO off sleeping_queue */
      StgBlockingQueueElement *prev = NULL;
      for (t = (StgBlockingQueueElement *)sleeping_queue; t != END_BQ_QUEUE; 
	   prev = t, t = t->link) {
	if (t == (StgBlockingQueueElement *)tso) {
	  if (prev == NULL) {
	    sleeping_queue = (StgTSO *)t->link;
	  } else {
	    prev->link = t->link;
	  }
	  goto done;
	}
      }
      barf("unblockThread (I/O): TSO not found");
    }

  default:
    barf("unblockThread");
  }

 done:
  tso->link = END_TSO_QUEUE;
  tso->why_blocked = NotBlocked;
  tso->block_info.closure = NULL;
  PUSH_ON_RUN_QUEUE(tso);
  RELEASE_LOCK(&sched_mutex);
}
#else
static void
unblockThread(StgTSO *tso)
{
  StgTSO *t, **last;

  ACQUIRE_LOCK(&sched_mutex);
  switch (tso->why_blocked) {

  case NotBlocked:
    return;  /* not blocked */

  case BlockedOnMVar:
    ASSERT(get_itbl(tso->block_info.closure)->type == MVAR);
    {
      StgTSO *last_tso = END_TSO_QUEUE;
      StgMVar *mvar = (StgMVar *)(tso->block_info.closure);

      last = &mvar->head;
      for (t = mvar->head; t != END_TSO_QUEUE; 
	   last = &t->link, last_tso = t, t = t->link) {
	if (t == tso) {
	  *last = tso->link;
	  if (mvar->tail == tso) {
	    mvar->tail = last_tso;
	  }
	  goto done;
	}
      }
      barf("unblockThread (MVAR): TSO not found");
    }

  case BlockedOnBlackHole:
    ASSERT(get_itbl(tso->block_info.closure)->type == BLACKHOLE_BQ);
    {
      StgBlockingQueue *bq = (StgBlockingQueue *)(tso->block_info.closure);

      last = &bq->blocking_queue;
      for (t = bq->blocking_queue; t != END_TSO_QUEUE; 
	   last = &t->link, t = t->link) {
	if (t == tso) {
	  *last = tso->link;
	  goto done;
	}
      }
      barf("unblockThread (BLACKHOLE): TSO not found");
    }

  case BlockedOnException:
    {
      StgTSO *target  = tso->block_info.tso;

      ASSERT(get_itbl(target)->type == TSO);

      while (target->what_next == ThreadRelocated) {
	  target = target->link;
	  ASSERT(get_itbl(target)->type == TSO);
      }
      
      ASSERT(target->blocked_exceptions != NULL);

      last = &target->blocked_exceptions;
      for (t = target->blocked_exceptions; t != END_TSO_QUEUE; 
	   last = &t->link, t = t->link) {
	ASSERT(get_itbl(t)->type == TSO);
	if (t == tso) {
	  *last = tso->link;
	  goto done;
	}
      }
      barf("unblockThread (Exception): TSO not found");
    }

  case BlockedOnRead:
  case BlockedOnWrite:
    {
      StgTSO *prev = NULL;
      for (t = blocked_queue_hd; t != END_TSO_QUEUE; 
	   prev = t, t = t->link) {
	if (t == tso) {
	  if (prev == NULL) {
	    blocked_queue_hd = t->link;
	    if (blocked_queue_tl == t) {
	      blocked_queue_tl = END_TSO_QUEUE;
	    }
	  } else {
	    prev->link = t->link;
	    if (blocked_queue_tl == t) {
	      blocked_queue_tl = prev;
	    }
	  }
	  goto done;
	}
      }
      barf("unblockThread (I/O): TSO not found");
    }

  case BlockedOnDelay:
    {
      StgTSO *prev = NULL;
      for (t = sleeping_queue; t != END_TSO_QUEUE; 
	   prev = t, t = t->link) {
	if (t == tso) {
	  if (prev == NULL) {
	    sleeping_queue = t->link;
	  } else {
	    prev->link = t->link;
	  }
	  goto done;
	}
      }
      barf("unblockThread (I/O): TSO not found");
    }

  default:
    barf("unblockThread");
  }

 done:
  tso->link = END_TSO_QUEUE;
  tso->why_blocked = NotBlocked;
  tso->block_info.closure = NULL;
  PUSH_ON_RUN_QUEUE(tso);
  RELEASE_LOCK(&sched_mutex);
}
#endif

/* -----------------------------------------------------------------------------
 * raiseAsync()
 *
 * The following function implements the magic for raising an
 * asynchronous exception in an existing thread.
 *
 * We first remove the thread from any queue on which it might be
 * blocked.  The possible blockages are MVARs and BLACKHOLE_BQs.
 *
 * We strip the stack down to the innermost CATCH_FRAME, building
 * thunks in the heap for all the active computations, so they can 
 * be restarted if necessary.  When we reach a CATCH_FRAME, we build
 * an application of the handler to the exception, and push it on
 * the top of the stack.
 * 
 * How exactly do we save all the active computations?  We create an
 * AP_UPD for every UpdateFrame on the stack.  Entering one of these
 * AP_UPDs pushes everything from the corresponding update frame
 * upwards onto the stack.  (Actually, it pushes everything up to the
 * next update frame plus a pointer to the next AP_UPD object.
 * Entering the next AP_UPD object pushes more onto the stack until we
 * reach the last AP_UPD object - at which point the stack should look
 * exactly as it did when we killed the TSO and we can continue
 * execution by entering the closure on top of the stack.
 *
 * We can also kill a thread entirely - this happens if either (a) the 
 * exception passed to raiseAsync is NULL, or (b) there's no
 * CATCH_FRAME on the stack.  In either case, we strip the entire
 * stack and replace the thread with a zombie.
 *
 * -------------------------------------------------------------------------- */
 
void 
deleteThread(StgTSO *tso)
{
  raiseAsync(tso,NULL);
}

void
raiseAsync(StgTSO *tso, StgClosure *exception)
{
  StgUpdateFrame* su = tso->su;
  StgPtr          sp = tso->sp;
  
  /* Thread already dead? */
  if (tso->what_next == ThreadComplete || tso->what_next == ThreadKilled) {
    return;
  }

  IF_DEBUG(scheduler, sched_belch("raising exception in thread %ld.", tso->id));

  /* Remove it from any blocking queues */
  unblockThread(tso);

  /* The stack freezing code assumes there's a closure pointer on
   * the top of the stack.  This isn't always the case with compiled
   * code, so we have to push a dummy closure on the top which just
   * returns to the next return address on the stack.
   */
  if ( LOOKS_LIKE_GHC_INFO((void*)*sp) ) {
    *(--sp) = (W_)&stg_dummy_ret_closure;
  }

  while (1) {
    nat words = ((P_)su - (P_)sp) - 1;
    nat i;
    StgAP_UPD * ap;

    /* If we find a CATCH_FRAME, and we've got an exception to raise,
     * then build PAP(handler,exception,realworld#), and leave it on
     * top of the stack ready to enter.
     */
    if (get_itbl(su)->type == CATCH_FRAME && exception != NULL) {
      StgCatchFrame *cf = (StgCatchFrame *)su;
      /* we've got an exception to raise, so let's pass it to the
       * handler in this frame.
       */
      ap = (StgAP_UPD *)allocate(sizeofW(StgPAP) + 2);
      TICK_ALLOC_UPD_PAP(3,0);
      SET_HDR(ap,&stg_PAP_info,cf->header.prof.ccs);
	      
      ap->n_args = 2;
      ap->fun = cf->handler;	/* :: Exception -> IO a */
      ap->payload[0] = exception;
      ap->payload[1] = ARG_TAG(0); /* realworld token */

      /* throw away the stack from Sp up to and including the
       * CATCH_FRAME.
       */
      sp = (P_)su + sizeofW(StgCatchFrame) - 1; 
      tso->su = cf->link;

      /* Restore the blocked/unblocked state for asynchronous exceptions
       * at the CATCH_FRAME.  
       *
       * If exceptions were unblocked at the catch, arrange that they
       * are unblocked again after executing the handler by pushing an
       * unblockAsyncExceptions_ret stack frame.
       */
      if (!cf->exceptions_blocked) {
	*(sp--) = (W_)&stg_unblockAsyncExceptionszh_ret_info;
      }
      
      /* Ensure that async exceptions are blocked when running the handler.
       */
      if (tso->blocked_exceptions == NULL) {
	tso->blocked_exceptions = END_TSO_QUEUE;
      }
      
      /* Put the newly-built PAP on top of the stack, ready to execute
       * when the thread restarts.
       */
      sp[0] = (W_)ap;
      tso->sp = sp;
      tso->what_next = ThreadEnterGHC;
      IF_DEBUG(sanity, checkTSO(tso));
      return;
    }

    /* First build an AP_UPD consisting of the stack chunk above the
     * current update frame, with the top word on the stack as the
     * fun field.
     */
    ap = (StgAP_UPD *)allocate(AP_sizeW(words));
    
    ASSERT(words >= 0);
    
    ap->n_args = words;
    ap->fun    = (StgClosure *)sp[0];
    sp++;
    for(i=0; i < (nat)words; ++i) {
      ap->payload[i] = (StgClosure *)*sp++;
    }
    
    switch (get_itbl(su)->type) {
      
    case UPDATE_FRAME:
      {
	SET_HDR(ap,&stg_AP_UPD_info,su->header.prof.ccs /* ToDo */); 
	TICK_ALLOC_UP_THK(words+1,0);
	
	IF_DEBUG(scheduler,
		 fprintf(stderr,  "scheduler: Updating ");
		 printPtr((P_)su->updatee); 
		 fprintf(stderr,  " with ");
		 printObj((StgClosure *)ap);
		 );
	
	/* Replace the updatee with an indirection - happily
	 * this will also wake up any threads currently
	 * waiting on the result.
	 *
	 * Warning: if we're in a loop, more than one update frame on
	 * the stack may point to the same object.  Be careful not to
	 * overwrite an IND_OLDGEN in this case, because we'll screw
	 * up the mutable lists.  To be on the safe side, don't
	 * overwrite any kind of indirection at all.  See also
	 * threadSqueezeStack in GC.c, where we have to make a similar
	 * check.
	 */
	if (!closure_IND(su->updatee)) {
	    UPD_IND_NOLOCK(su->updatee,ap);  /* revert the black hole */
	}
	su = su->link;
	sp += sizeofW(StgUpdateFrame) -1;
	sp[0] = (W_)ap; /* push onto stack */
	break;
      }

    case CATCH_FRAME:
      {
	StgCatchFrame *cf = (StgCatchFrame *)su;
	StgClosure* o;
	
	/* We want a PAP, not an AP_UPD.  Fortunately, the
	 * layout's the same.
	 */
	SET_HDR(ap,&stg_PAP_info,su->header.prof.ccs /* ToDo */);
	TICK_ALLOC_UPD_PAP(words+1,0);
	
	/* now build o = FUN(catch,ap,handler) */
	o = (StgClosure *)allocate(sizeofW(StgClosure)+2);
	TICK_ALLOC_FUN(2,0);
	SET_HDR(o,&stg_catch_info,su->header.prof.ccs /* ToDo */);
	o->payload[0] = (StgClosure *)ap;
	o->payload[1] = cf->handler;
	
	IF_DEBUG(scheduler,
		 fprintf(stderr,  "scheduler: Built ");
		 printObj((StgClosure *)o);
		 );
	
	/* pop the old handler and put o on the stack */
	su = cf->link;
	sp += sizeofW(StgCatchFrame) - 1;
	sp[0] = (W_)o;
	break;
      }
      
    case SEQ_FRAME:
      {
	StgSeqFrame *sf = (StgSeqFrame *)su;
	StgClosure* o;
	
	SET_HDR(ap,&stg_PAP_info,su->header.prof.ccs /* ToDo */);
	TICK_ALLOC_UPD_PAP(words+1,0);
	
	/* now build o = FUN(seq,ap) */
	o = (StgClosure *)allocate(sizeofW(StgClosure)+1);
	TICK_ALLOC_SE_THK(1,0);
	SET_HDR(o,&stg_seq_info,su->header.prof.ccs /* ToDo */);
	o->payload[0] = (StgClosure *)ap;
	
	IF_DEBUG(scheduler,
		 fprintf(stderr,  "scheduler: Built ");
		 printObj((StgClosure *)o);
		 );
	
	/* pop the old handler and put o on the stack */
	su = sf->link;
	sp += sizeofW(StgSeqFrame) - 1;
	sp[0] = (W_)o;
	break;
      }
      
    case STOP_FRAME:
      /* We've stripped the entire stack, the thread is now dead. */
      sp += sizeofW(StgStopFrame) - 1;
      sp[0] = (W_)exception;	/* save the exception */
      tso->what_next = ThreadKilled;
      tso->su = (StgUpdateFrame *)(sp+1);
      tso->sp = sp;
      return;

    default:
      barf("raiseAsync");
    }
  }
  barf("raiseAsync");
}

/* -----------------------------------------------------------------------------
   resurrectThreads is called after garbage collection on the list of
   threads found to be garbage.  Each of these threads will be woken
   up and sent a signal: BlockedOnDeadMVar if the thread was blocked
   on an MVar, or NonTermination if the thread was blocked on a Black
   Hole.
   -------------------------------------------------------------------------- */

void
resurrectThreads( StgTSO *threads )
{
  StgTSO *tso, *next;

  for (tso = threads; tso != END_TSO_QUEUE; tso = next) {
    next = tso->global_link;
    tso->global_link = all_threads;
    all_threads = tso;
    IF_DEBUG(scheduler, sched_belch("resurrecting thread %d", tso->id));

    switch (tso->why_blocked) {
    case BlockedOnMVar:
    case BlockedOnException:
      raiseAsync(tso,(StgClosure *)BlockedOnDeadMVar_closure);
      break;
    case BlockedOnBlackHole:
      raiseAsync(tso,(StgClosure *)NonTermination_closure);
      break;
    case NotBlocked:
      /* This might happen if the thread was blocked on a black hole
       * belonging to a thread that we've just woken up (raiseAsync
       * can wake up threads, remember...).
       */
      continue;
    default:
      barf("resurrectThreads: thread blocked in a strange way");
    }
  }
}

/* -----------------------------------------------------------------------------
 * Blackhole detection: if we reach a deadlock, test whether any
 * threads are blocked on themselves.  Any threads which are found to
 * be self-blocked get sent a NonTermination exception.
 *
 * This is only done in a deadlock situation in order to avoid
 * performance overhead in the normal case.
 * -------------------------------------------------------------------------- */

static void
detectBlackHoles( void )
{
    StgTSO *t = all_threads;
    StgUpdateFrame *frame;
    StgClosure *blocked_on;

    for (t = all_threads; t != END_TSO_QUEUE; t = t->global_link) {

	while (t->what_next == ThreadRelocated) {
	    t = t->link;
	    ASSERT(get_itbl(t)->type == TSO);
	}
      
	if (t->why_blocked != BlockedOnBlackHole) {
	    continue;
	}

	blocked_on = t->block_info.closure;

	for (frame = t->su; ; frame = frame->link) {
	    switch (get_itbl(frame)->type) {

	    case UPDATE_FRAME:
		if (frame->updatee == blocked_on) {
		    /* We are blocking on one of our own computations, so
		     * send this thread the NonTermination exception.  
		     */
		    IF_DEBUG(scheduler, 
			     sched_belch("thread %d is blocked on itself", t->id));
		    raiseAsync(t, (StgClosure *)NonTermination_closure);
		    goto done;
		}
		else {
		    continue;
		}

	    case CATCH_FRAME:
	    case SEQ_FRAME:
		continue;
		
	    case STOP_FRAME:
		break;
	    }
	    break;
	}

    done: ;
    }   
}

//@node Debugging Routines, Index, Exception Handling Routines, Main scheduling code
//@subsection Debugging Routines

/* -----------------------------------------------------------------------------
   Debugging: why is a thread blocked
   -------------------------------------------------------------------------- */

#ifdef DEBUG

void
printThreadBlockage(StgTSO *tso)
{
  switch (tso->why_blocked) {
  case BlockedOnRead:
    fprintf(stderr,"is blocked on read from fd %d", tso->block_info.fd);
    break;
  case BlockedOnWrite:
    fprintf(stderr,"is blocked on write to fd %d", tso->block_info.fd);
    break;
  case BlockedOnDelay:
    fprintf(stderr,"is blocked until %d", tso->block_info.target);
    break;
  case BlockedOnMVar:
    fprintf(stderr,"is blocked on an MVar");
    break;
  case BlockedOnException:
    fprintf(stderr,"is blocked on delivering an exception to thread %d",
	    tso->block_info.tso->id);
    break;
  case BlockedOnBlackHole:
    fprintf(stderr,"is blocked on a black hole");
    break;
  case NotBlocked:
    fprintf(stderr,"is not blocked");
    break;
#if defined(PAR)
  case BlockedOnGA:
    fprintf(stderr,"is blocked on global address; local FM_BQ is %p (%s)",
	    tso->block_info.closure, info_type(tso->block_info.closure));
    break;
  case BlockedOnGA_NoSend:
    fprintf(stderr,"is blocked on global address (no send); local FM_BQ is %p (%s)",
	    tso->block_info.closure, info_type(tso->block_info.closure));
    break;
#endif
  default:
    barf("printThreadBlockage: strange tso->why_blocked: %d for TSO %d (%d)",
	 tso->why_blocked, tso->id, tso);
  }
}

void
printThreadStatus(StgTSO *tso)
{
  switch (tso->what_next) {
  case ThreadKilled:
    fprintf(stderr,"has been killed");
    break;
  case ThreadComplete:
    fprintf(stderr,"has completed");
    break;
  default:
    printThreadBlockage(tso);
  }
}

void
printAllThreads(void)
{
  StgTSO *t;

# if defined(GRAN)
  char time_string[TIME_STR_LEN], node_str[NODE_STR_LEN];
  ullong_format_string(TIME_ON_PROC(CurrentProc), 
		       time_string, rtsFalse/*no commas!*/);

  sched_belch("all threads at [%s]:", time_string);
# elif defined(PAR)
  char time_string[TIME_STR_LEN], node_str[NODE_STR_LEN];
  ullong_format_string(CURRENT_TIME,
		       time_string, rtsFalse/*no commas!*/);

  sched_belch("all threads at [%s]:", time_string);
# else
  sched_belch("all threads:");
# endif

  for (t = all_threads; t != END_TSO_QUEUE; t = t->global_link) {
    fprintf(stderr, "\tthread %d ", t->id);
    printThreadStatus(t);
    fprintf(stderr,"\n");
  }
}
    
/* 
   Print a whole blocking queue attached to node (debugging only).
*/
//@cindex print_bq
# if defined(PAR)
void 
print_bq (StgClosure *node)
{
  StgBlockingQueueElement *bqe;
  StgTSO *tso;
  rtsBool end;

  fprintf(stderr,"## BQ of closure %p (%s): ",
	  node, info_type(node));

  /* should cover all closures that may have a blocking queue */
  ASSERT(get_itbl(node)->type == BLACKHOLE_BQ ||
	 get_itbl(node)->type == FETCH_ME_BQ ||
	 get_itbl(node)->type == RBH ||
	 get_itbl(node)->type == MVAR);
    
  ASSERT(node!=(StgClosure*)NULL);         // sanity check

  print_bqe(((StgBlockingQueue*)node)->blocking_queue);
}

/* 
   Print a whole blocking queue starting with the element bqe.
*/
void 
print_bqe (StgBlockingQueueElement *bqe)
{
  rtsBool end;

  /* 
     NB: In a parallel setup a BQ of an RBH must end with an RBH_Save closure;
  */
  for (end = (bqe==END_BQ_QUEUE);
       !end; // iterate until bqe points to a CONSTR
       end = (get_itbl(bqe)->type == CONSTR) || (bqe->link==END_BQ_QUEUE), 
       bqe = end ? END_BQ_QUEUE : bqe->link) {
    ASSERT(bqe != END_BQ_QUEUE);                               // sanity check
    ASSERT(bqe != (StgBlockingQueueElement *)NULL);            // sanity check
    /* types of closures that may appear in a blocking queue */
    ASSERT(get_itbl(bqe)->type == TSO ||           
	   get_itbl(bqe)->type == BLOCKED_FETCH || 
	   get_itbl(bqe)->type == CONSTR); 
    /* only BQs of an RBH end with an RBH_Save closure */
    //ASSERT(get_itbl(bqe)->type != CONSTR || get_itbl(node)->type == RBH);

    switch (get_itbl(bqe)->type) {
    case TSO:
      fprintf(stderr," TSO %u (%x),",
	      ((StgTSO *)bqe)->id, ((StgTSO *)bqe));
      break;
    case BLOCKED_FETCH:
      fprintf(stderr," BF (node=%p, ga=((%x, %d, %x)),",
	      ((StgBlockedFetch *)bqe)->node, 
	      ((StgBlockedFetch *)bqe)->ga.payload.gc.gtid,
	      ((StgBlockedFetch *)bqe)->ga.payload.gc.slot,
	      ((StgBlockedFetch *)bqe)->ga.weight);
      break;
    case CONSTR:
      fprintf(stderr," %s (IP %p),",
	      (get_itbl(bqe) == &stg_RBH_Save_0_info ? "RBH_Save_0" :
	       get_itbl(bqe) == &stg_RBH_Save_1_info ? "RBH_Save_1" :
	       get_itbl(bqe) == &stg_RBH_Save_2_info ? "RBH_Save_2" :
	       "RBH_Save_?"), get_itbl(bqe));
      break;
    default:
      barf("Unexpected closure type %s in blocking queue", // of %p (%s)",
	   info_type((StgClosure *)bqe)); // , node, info_type(node));
      break;
    }
  } /* for */
  fputc('\n', stderr);
}
# elif defined(GRAN)
void 
print_bq (StgClosure *node)
{
  StgBlockingQueueElement *bqe;
  PEs node_loc, tso_loc;
  rtsBool end;

  /* should cover all closures that may have a blocking queue */
  ASSERT(get_itbl(node)->type == BLACKHOLE_BQ ||
	 get_itbl(node)->type == FETCH_ME_BQ ||
	 get_itbl(node)->type == RBH);
    
  ASSERT(node!=(StgClosure*)NULL);         // sanity check
  node_loc = where_is(node);

  fprintf(stderr,"## BQ of closure %p (%s) on [PE %d]: ",
	  node, info_type(node), node_loc);

  /* 
     NB: In a parallel setup a BQ of an RBH must end with an RBH_Save closure;
  */
  for (bqe = ((StgBlockingQueue*)node)->blocking_queue, end = (bqe==END_BQ_QUEUE);
       !end; // iterate until bqe points to a CONSTR
       end = (get_itbl(bqe)->type == CONSTR) || (bqe->link==END_BQ_QUEUE), bqe = end ? END_BQ_QUEUE : bqe->link) {
    ASSERT(bqe != END_BQ_QUEUE);             // sanity check
    ASSERT(bqe != (StgBlockingQueueElement *)NULL);  // sanity check
    /* types of closures that may appear in a blocking queue */
    ASSERT(get_itbl(bqe)->type == TSO ||           
	   get_itbl(bqe)->type == CONSTR); 
    /* only BQs of an RBH end with an RBH_Save closure */
    ASSERT(get_itbl(bqe)->type != CONSTR || get_itbl(node)->type == RBH);

    tso_loc = where_is((StgClosure *)bqe);
    switch (get_itbl(bqe)->type) {
    case TSO:
      fprintf(stderr," TSO %d (%p) on [PE %d],",
	      ((StgTSO *)bqe)->id, (StgTSO *)bqe, tso_loc);
      break;
    case CONSTR:
      fprintf(stderr," %s (IP %p),",
	      (get_itbl(bqe) == &stg_RBH_Save_0_info ? "RBH_Save_0" :
	       get_itbl(bqe) == &stg_RBH_Save_1_info ? "RBH_Save_1" :
	       get_itbl(bqe) == &stg_RBH_Save_2_info ? "RBH_Save_2" :
	       "RBH_Save_?"), get_itbl(bqe));
      break;
    default:
      barf("Unexpected closure type %s in blocking queue of %p (%s)",
	   info_type((StgClosure *)bqe), node, info_type(node));
      break;
    }
  } /* for */
  fputc('\n', stderr);
}
#else
/* 
   Nice and easy: only TSOs on the blocking queue
*/
void 
print_bq (StgClosure *node)
{
  StgTSO *tso;

  ASSERT(node!=(StgClosure*)NULL);         // sanity check
  for (tso = ((StgBlockingQueue*)node)->blocking_queue;
       tso != END_TSO_QUEUE; 
       tso=tso->link) {
    ASSERT(tso!=NULL && tso!=END_TSO_QUEUE);   // sanity check
    ASSERT(get_itbl(tso)->type == TSO);  // guess what, sanity check
    fprintf(stderr," TSO %d (%p),", tso->id, tso);
  }
  fputc('\n', stderr);
}
# endif

#if defined(PAR)
static nat
run_queue_len(void)
{
  nat i;
  StgTSO *tso;

  for (i=0, tso=run_queue_hd; 
       tso != END_TSO_QUEUE;
       i++, tso=tso->link)
    /* nothing */

  return i;
}
#endif

static void
sched_belch(char *s, ...)
{
  va_list ap;
  va_start(ap,s);
#ifdef SMP
  fprintf(stderr, "scheduler (task %ld): ", pthread_self());
#elif defined(PAR)
  fprintf(stderr, "== ");
#else
  fprintf(stderr, "scheduler: ");
#endif
  vfprintf(stderr, s, ap);
  fprintf(stderr, "\n");
}

#endif /* DEBUG */


//@node Index,  , Debugging Routines, Main scheduling code
//@subsection Index

//@index
//* MainRegTable::  @cindex\s-+MainRegTable
//* StgMainThread::  @cindex\s-+StgMainThread
//* awaken_blocked_queue::  @cindex\s-+awaken_blocked_queue
//* blocked_queue_hd::  @cindex\s-+blocked_queue_hd
//* blocked_queue_tl::  @cindex\s-+blocked_queue_tl
//* context_switch::  @cindex\s-+context_switch
//* createThread::  @cindex\s-+createThread
//* free_capabilities::  @cindex\s-+free_capabilities
//* gc_pending_cond::  @cindex\s-+gc_pending_cond
//* initScheduler::  @cindex\s-+initScheduler
//* interrupted::  @cindex\s-+interrupted
//* n_free_capabilities::  @cindex\s-+n_free_capabilities
//* next_thread_id::  @cindex\s-+next_thread_id
//* print_bq::  @cindex\s-+print_bq
//* run_queue_hd::  @cindex\s-+run_queue_hd
//* run_queue_tl::  @cindex\s-+run_queue_tl
//* sched_mutex::  @cindex\s-+sched_mutex
//* schedule::  @cindex\s-+schedule
//* take_off_run_queue::  @cindex\s-+take_off_run_queue
//* task_ids::  @cindex\s-+task_ids
//* term_mutex::  @cindex\s-+term_mutex
//* thread_ready_cond::  @cindex\s-+thread_ready_cond
//@end index