* ext/thread: Import the "fastthread" implementation by MenTaLguY

  in the original form.  This module is not hooked into the build
  yet since it needs some style fixes and adjustments.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_1_8@11677 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

2 files changed, 1304 insertions, 0 deletions

diff --git a/ext/thread/extconf.rb b/ext/thread/extconf.rb
new file mode 100644
index 0000000000..f83dacae39
--- /dev/null
+++ b/ext/thread/extconf.rb
@@ -0,0 +1,2 @@
+require 'mkmf'
+create_makefile("thread")
diff --git a/ext/thread/thread.c b/ext/thread/thread.c
new file mode 100644
index 0000000000..23dca6aa74
--- /dev/null
+++ b/ext/thread/thread.c
@@ -0,0 +1,1302 @@
+/*
+ * Optimized Ruby Mutex implementation, loosely based on thread.rb by
+ * Yukihiro Matsumoto <matz@ruby-lang.org>
+ *
+ *  Copyright 2006-2007  MenTaLguY <mental@rydia.net>
+ *
+ * RDoc taken from original.
+ *
+ * This file is made available under the same terms as Ruby.
+ */
+
+#include <ruby.h>
+#include <intern.h>
+#include <rubysig.h>
+
+#define USE_MEM_POOLS 1
+
+static VALUE rb_cMutex;
+static VALUE rb_cConditionVariable;
+static VALUE rb_cQueue;
+static VALUE rb_cSizedQueue;
+
+static VALUE
+return_value(value)
+  VALUE value;
+{
+  return value;
+}
+
+typedef struct _Entry {
+  VALUE value;
+  struct _Entry *next;
+} Entry;
+
+typedef struct _List {
+  Entry *entries;
+  Entry *last_entry;
+  Entry *entry_pool;
+  unsigned long size;
+} List;
+
+static void
+init_list(List *list)
+{
+  list->entries = NULL;
+  list->last_entry = NULL;
+  list->entry_pool = NULL;
+  list->size = 0;
+}
+
+static void
+mark_list(List *list)
+{
+  Entry *entry;
+  for ( entry = list->entries ; entry ; entry = entry->next ) {
+    rb_gc_mark(entry->value);
+  }
+}
+
+static void
+free_entries(Entry *first)
+{
+  Entry *next;
+  while (first) {
+    next = first->next;
+    free(first);
+    first = next;
+  }
+}
+
+static void
+finalize_list(List *list)
+{
+  free_entries(list->entries);
+  free_entries(list->entry_pool);
+}
+
+static void
+push_list(List *list, VALUE value)
+{
+  Entry *entry;
+
+  if (list->entry_pool) {
+    entry = list->entry_pool;
+    list->entry_pool = entry->next;
+  } else {
+    entry = (Entry *)malloc(sizeof(Entry));
+  }
+
+  entry->value = value;
+  entry->next = NULL;
+
+  if (list->last_entry) {
+    list->last_entry->next = entry;
+  } else {
+    list->entries = entry;
+  }
+  list->last_entry = entry;
+
+  ++list->size;
+}
+
+static void push_multiple_list _((List *, VALUE *, unsigned));
+
+static void
+push_multiple_list(list, values, count)
+  List *list;
+  VALUE *values;
+  unsigned count;
+{
+  unsigned i;
+  for ( i = 0 ; i < count ; i++ ) {
+    push_list(list, values[i]);
+  }
+}
+
+static VALUE shift_list _((List *));
+
+static VALUE
+shift_list(list)
+  List *list;
+{
+  Entry *entry;
+  VALUE value;
+
+  entry = list->entries;
+  if (!entry) return Qundef;
+
+  list->entries = entry->next;
+  if ( entry == list->last_entry ) {
+    list->last_entry = NULL;
+  }
+
+  --list->size;
+
+  value = entry->value;
+  if (USE_MEM_POOLS) {
+    entry->next = list->entry_pool;
+    list->entry_pool = entry;
+  } else {
+    free(entry);
+  }
+
+  return value;
+}
+
+static void clear_list _((List *));
+
+static void
+clear_list(list)
+  List *list;
+{
+  if (list->last_entry) {
+    if (USE_MEM_POOLS) {
+      list->last_entry->next = list->entry_pool;
+      list->entry_pool = list->entries;
+    } else {
+      free_entries(list->entries);
+    }
+    list->entries = NULL;
+    list->last_entry = NULL;
+    list->size = 0;
+  }
+}
+
+static VALUE array_from_list _((List const *));
+
+static VALUE
+array_from_list(list)
+  List const *list;
+{
+  VALUE ary;
+  Entry *entry;
+  ary = rb_ary_new();
+  for ( entry = list->entries ; entry ; entry = entry->next ) {
+    rb_ary_push(ary, entry->value);
+  }
+  return ary;
+}
+
+static VALUE wake_thread _((VALUE));
+
+static VALUE
+wake_thread(thread)
+  VALUE thread;
+{
+  return rb_rescue2(rb_thread_wakeup, thread,
+                    return_value, Qnil, rb_eThreadError, 0);
+}
+
+static VALUE run_thread _((VALUE));
+
+static VALUE
+run_thread(thread)
+  VALUE thread;
+{
+  return rb_rescue2(rb_thread_run, thread,
+                    return_value, Qnil, rb_eThreadError, 0);
+}
+
+static VALUE wake_one _((List *));
+
+static VALUE
+wake_one(list)
+  List *list;
+{
+  VALUE waking;
+
+  waking = Qnil;
+  while ( list->entries && !RTEST(waking) ) {
+    waking = wake_thread(shift_list(list));
+  }
+
+  return waking;
+}
+
+static VALUE wake_all _((List *));
+
+static VALUE
+wake_all(list)
+  List *list;
+{
+  while (list->entries) {
+    wake_one(list);
+  }
+  return Qnil;
+}
+
+static void assert_no_survivors _((List *, const char *, void *));
+
+static void
+assert_no_survivors(waiting, label, addr)
+  List *waiting;
+  const char *label;
+  void *addr;
+{
+  Entry *entry;
+  for ( entry = waiting->entries ; entry ; entry = entry->next ) {
+    if (RTEST(wake_thread(entry->value))) {
+      rb_bug("%s %p freed with live thread(s) waiting", label, addr);
+    }
+  }
+}
+
+/*
+ * Document-class: Mutex
+ *
+ * Mutex implements a simple semaphore that can be used to coordinate access to
+ * shared data from multiple concurrent threads.
+ *
+ * Example:
+ *
+ *   require 'thread'
+ *   semaphore = Mutex.new
+ *
+ *   a = Thread.new {
+ *     semaphore.synchronize {
+ *       # access shared resource
+ *     }
+ *   }
+ *
+ *   b = Thread.new {
+ *     semaphore.synchronize {
+ *       # access shared resource
+ *     }
+ *   }
+ *
+ */
+
+typedef struct _Mutex {
+  VALUE owner;
+  List waiting;
+} Mutex;
+
+static void mark_mutex _((Mutex *));
+
+static void
+mark_mutex(mutex)
+  Mutex *mutex;
+{
+  rb_gc_mark(mutex->owner);
+  mark_list(&mutex->waiting);
+}
+
+static void finalize_mutex _((Mutex *));
+
+static void
+finalize_mutex(mutex)
+  Mutex *mutex;
+{
+  finalize_list(&mutex->waiting);
+}
+
+static void free_mutex _((Mutex *));
+
+static void
+free_mutex(mutex)
+  Mutex *mutex;
+{
+  assert_no_survivors(&mutex->waiting, "mutex", mutex);
+  finalize_mutex(mutex);
+  free(mutex);
+}
+
+static void init_mutex _((Mutex *));
+
+static void
+init_mutex(mutex)
+  Mutex *mutex;
+{
+  mutex->owner = Qnil;
+  init_list(&mutex->waiting);
+}
+
+/*
+ * Document-method: new
+ * call-seq: Mutex.new
+ * 
+ * Creates a new Mutex
+ *
+ */
+
+static VALUE rb_mutex_alloc _((VALUE));
+
+static VALUE 
+rb_mutex_alloc(klass)
+  VALUE klass;
+{
+  Mutex *mutex;
+  mutex = (Mutex *)malloc(sizeof(Mutex));
+  init_mutex(mutex);
+  return Data_Wrap_Struct(klass, mark_mutex, free_mutex, mutex);
+}
+
+/*
+ * Document-method: locked?
+ * call-seq: locked?
+ *
+ * Returns +true+ if this lock is currently held by some thread.
+ *
+ */
+
+static VALUE rb_mutex_locked_p _((VALUE));
+
+static VALUE
+rb_mutex_locked_p(self)
+  VALUE self;
+{
+  Mutex *mutex;
+  Data_Get_Struct(self, Mutex, mutex);
+  return ( RTEST(mutex->owner) ? Qtrue : Qfalse );
+}
+
+/*
+ * Document-method: try_lock
+ * call-seq: try_lock
+ *
+ * Attempts to obtain the lock and returns immediately. Returns +true+ if the
+ * lock was granted.
+ *
+ */
+
+static VALUE rb_mutex_try_lock _((VALUE));
+
+static VALUE
+rb_mutex_try_lock(self)
+  VALUE self;
+{
+  Mutex *mutex;
+  VALUE result;
+
+  Data_Get_Struct(self, Mutex, mutex);
+
+  result = Qfalse;
+
+  rb_thread_critical = 1;
+  if (!RTEST(mutex->owner)) {
+    mutex->owner = rb_thread_current();
+    result = Qtrue;
+  }
+  rb_thread_critical = 0;
+
+  return result;
+}
+
+/*
+ * Document-method: lock
+ * call-seq: lock
+ *
+ * Attempts to grab the lock and waits if it isn't available.
+ *
+ */
+
+static void lock_mutex _((Mutex *));
+
+static void
+lock_mutex(mutex)
+  Mutex *mutex;
+{
+  VALUE current;
+  current = rb_thread_current();
+
+  rb_thread_critical = 1;
+
+  while (RTEST(mutex->owner)) {
+    push_list(&mutex->waiting, current);
+    rb_thread_stop();
+
+    rb_thread_critical = 1;
+  }
+  mutex->owner = current; 
+
+  rb_thread_critical = 0;
+}
+
+static VALUE rb_mutex_lock _((VALUE));
+
+static VALUE
+rb_mutex_lock(self)
+  VALUE self;
+{
+  Mutex *mutex;
+  Data_Get_Struct(self, Mutex, mutex);
+  lock_mutex(mutex);
+  return self;
+}
+
+/*
+ * Document-method: unlock
+ *
+ * Releases the lock. Returns +nil+ if ref wasn't locked.
+ *
+ */
+
+static VALUE unlock_mutex_inner _((Mutex *));
+
+static VALUE
+unlock_mutex_inner(mutex)
+  Mutex *mutex;
+{
+  VALUE waking;
+
+  if (!RTEST(mutex->owner)) {
+    return Qundef;
+  }
+  mutex->owner = Qnil;
+  waking = wake_one(&mutex->waiting);
+
+  return waking;
+}
+
+static VALUE set_critical _((VALUE));
+
+static VALUE
+set_critical(value)
+  VALUE value;
+{
+  rb_thread_critical = (int)value;
+  return Qnil;
+}
+
+static VALUE unlock_mutex _((Mutex *));
+
+static VALUE
+unlock_mutex(mutex)
+  Mutex *mutex;
+{
+  VALUE waking;
+
+  rb_thread_critical = 1;
+  waking = rb_ensure(unlock_mutex_inner, (VALUE)mutex, set_critical, 0);
+
+  if ( waking == Qundef ) {
+    return Qfalse;
+  }
+
+  if (RTEST(waking)) {
+    run_thread(waking);
+  }
+
+  return Qtrue;
+}
+
+static VALUE rb_mutex_unlock _((VALUE));
+
+static VALUE
+rb_mutex_unlock(self)
+  VALUE self;
+{
+  Mutex *mutex;
+  Data_Get_Struct(self, Mutex, mutex);
+
+  if (RTEST(unlock_mutex(mutex))) {
+    return self;
+  } else {
+    return Qnil;
+  }
+}
+
+/*
+ * Document-method: exclusive_unlock
+ * call-seq: exclusive_unlock { ... }
+ *
+ * If the mutex is locked, unlocks the mutex, wakes one waiting thread, and
+ * yields in a critical section.
+ *
+ */
+
+static VALUE rb_mutex_exclusive_unlock_inner _((Mutex *));
+
+static VALUE
+rb_mutex_exclusive_unlock_inner(mutex)
+  Mutex *mutex;
+{
+  VALUE waking;
+  waking = unlock_mutex_inner(mutex);
+  rb_yield(Qundef);
+  return waking;
+}
+
+static VALUE rb_mutex_exclusive_unlock _((VALUE));
+
+static VALUE
+rb_mutex_exclusive_unlock(self)
+  VALUE self;
+{
+  Mutex *mutex;
+  VALUE waking;
+  Data_Get_Struct(self, Mutex, mutex);
+
+  rb_thread_critical = 1;
+  waking = rb_ensure(rb_mutex_exclusive_unlock_inner, (VALUE)mutex, set_critical, 0);
+
+  if ( waking == Qundef ) {
+    return Qnil;
+  }
+
+  if (RTEST(waking)) {
+    run_thread(waking);
+  }
+
+  return self;
+}
+
+/*
+ * Document-method: synchronize
+ * call-seq: synchronize { ... }
+ *
+ * Obtains a lock, runs the block, and releases the lock when the block
+ * completes.  See the example under Mutex.
+ *
+ */
+
+static VALUE rb_mutex_synchronize _((VALUE));
+
+static VALUE
+rb_mutex_synchronize(self)
+  VALUE self;
+{
+  rb_mutex_lock(self);
+  return rb_ensure(rb_yield, Qundef, rb_mutex_unlock, self);
+}
+
+/*
+ * Document-class: ConditionVariable
+ *
+ * ConditionVariable objects augment class Mutex. Using condition variables,
+ * it is possible to suspend while in the middle of a critical section until a
+ * resource becomes available.
+ *
+ * Example:
+ *
+ *   require 'thread'
+ *
+ *   mutex = Mutex.new
+ *   resource = ConditionVariable.new
+ *
+ *   a = Thread.new {
+ *     mutex.synchronize {
+ *       # Thread 'a' now needs the resource
+ *       resource.wait(mutex)
+ *       # 'a' can now have the resource
+ *     }
+ *   }
+ *
+ *   b = Thread.new {
+ *     mutex.synchronize {
+ *       # Thread 'b' has finished using the resource
+ *       resource.signal
+ *     }
+ *   }
+ *
+ */
+
+typedef struct _ConditionVariable {
+  List waiting;
+} ConditionVariable;
+
+static void mark_condvar _((ConditionVariable *));
+
+static void
+mark_condvar(condvar)
+  ConditionVariable *condvar;
+{
+  mark_list(&condvar->waiting);
+}
+
+static void finalize_condvar _((ConditionVariable *));
+
+static void
+finalize_condvar(condvar)
+  ConditionVariable *condvar;
+{
+  finalize_list(&condvar->waiting);
+}
+
+static void free_condvar _((ConditionVariable *));
+
+static void
+free_condvar(condvar)
+  ConditionVariable *condvar;
+{
+  assert_no_survivors(&condvar->waiting, "condition variable", condvar);
+  finalize_condvar(condvar);
+  free(condvar);
+}
+
+static void init_condvar _((ConditionVariable *));
+
+static void
+init_condvar(condvar)
+  ConditionVariable *condvar;
+{
+  init_list(&condvar->waiting);
+}
+
+/*
+ * Document-method: new
+ * call-seq: ConditionVariable.new
+ *
+ * Creates a new ConditionVariable
+ *
+ */
+
+static VALUE rb_condvar_alloc _((VALUE));
+
+static VALUE
+rb_condvar_alloc(klass)
+  VALUE klass;
+{
+  ConditionVariable *condvar;
+
+  condvar = (ConditionVariable *)malloc(sizeof(ConditionVariable));
+  init_condvar(condvar);
+
+  return Data_Wrap_Struct(klass, mark_condvar, free_condvar, condvar);
+}
+
+/*
+ * Document-method: wait
+ * call-seq: wait
+ *
+ * Releases the lock held in +mutex+ and waits; reacquires the lock on wakeup.
+ *
+ */
+
+static void wait_condvar _((ConditionVariable *, Mutex *));
+
+static void
+wait_condvar(condvar, mutex)
+  ConditionVariable *condvar;
+  Mutex *mutex;
+{
+  rb_thread_critical = 1;
+  if (!RTEST(mutex->owner)) {
+    rb_thread_critical = Qfalse;
+    return;
+  }
+  if ( mutex->owner != rb_thread_current() ) {
+    rb_thread_critical = Qfalse;
+    rb_raise(rb_eThreadError, "Not owner");
+  }
+  mutex->owner = Qnil;
+  push_list(&condvar->waiting, rb_thread_current());
+  rb_thread_stop();
+
+  lock_mutex(mutex);
+}
+
+static VALUE legacy_exclusive_unlock _((VALUE));
+
+static VALUE
+legacy_exclusive_unlock(mutex)
+  VALUE mutex;
+{
+  return rb_funcall(mutex, rb_intern("exclusive_unlock"), 0);
+}
+
+typedef struct {
+  ConditionVariable *condvar;
+  VALUE mutex;
+} legacy_wait_args;
+
+static VALUE legacy_wait _((VALUE, legacy_wait_args *));
+
+static VALUE
+legacy_wait(unused, args)
+  VALUE unused;
+  legacy_wait_args *args;
+{
+  push_list(&args->condvar->waiting, rb_thread_current());
+  rb_thread_stop();
+  rb_funcall(args->mutex, rb_intern("lock"), 0);
+  return Qnil;
+}
+
+static VALUE rb_condvar_wait _((VALUE, VALUE));
+
+static VALUE
+rb_condvar_wait(self, mutex_v)
+  VALUE self;
+  VALUE mutex_v;
+{
+  ConditionVariable *condvar;
+  Data_Get_Struct(self, ConditionVariable, condvar);
+
+  if ( CLASS_OF(mutex_v) != rb_cMutex ) {
+    /* interoperate with legacy mutex */
+    legacy_wait_args args;
+    args.condvar = condvar;
+    args.mutex = mutex_v;
+    rb_iterate(legacy_exclusive_unlock, mutex_v, legacy_wait, (VALUE)&args);
+  } else {
+    Mutex *mutex;
+    Data_Get_Struct(mutex_v, Mutex, mutex);
+    wait_condvar(condvar, mutex);
+  }
+
+  return self;
+}
+
+/*
+ * Document-method: broadcast
+ * call-seq: broadcast
+ *
+ * Wakes up all threads waiting for this condition.
+ *
+ */
+
+static VALUE rb_condvar_broadcast _((VALUE));
+
+static VALUE
+rb_condvar_broadcast(self)
+  VALUE self;
+{
+  ConditionVariable *condvar;
+
+  Data_Get_Struct(self, ConditionVariable, condvar);
+  
+  rb_thread_critical = 1;
+  rb_ensure(wake_all, (VALUE)&condvar->waiting, set_critical, 0);
+  rb_thread_schedule();
+
+  return self;
+}
+
+/*
+ * Document-method: signal
+ * call-seq: signal
+ *
+ * Wakes up the first thread in line waiting for this condition.
+ *
+ */
+
+static void signal_condvar _((ConditionVariable *condvar));
+
+static void
+signal_condvar(condvar)
+  ConditionVariable *condvar;
+{
+  VALUE waking;
+  rb_thread_critical = 1;
+  waking = rb_ensure(wake_one, (VALUE)&condvar->waiting, set_critical, 0);
+  if (RTEST(waking)) {
+    run_thread(waking);
+  }
+}
+
+static VALUE rb_condvar_signal _((VALUE));
+
+static VALUE
+rb_condvar_signal(self)
+  VALUE self;
+{
+  ConditionVariable *condvar;
+  Data_Get_Struct(self, ConditionVariable, condvar);
+  signal_condvar(condvar);
+  return self;
+}
+
+/*
+ * Document-class: Queue
+ *
+ * This class provides a way to synchronize communication between threads.
+ *
+ * Example:
+ *
+ *   require 'thread'
+ *
+ *   queue = Queue.new
+ *
+ *   producer = Thread.new do
+ *     5.times do |i|
+ *       sleep rand(i) # simulate expense
+ *       queue << i
+ *       puts "#{i} produced"
+ *     end
+ *   end
+ *
+ *   consumer = Thread.new do
+ *     5.times do |i|
+ *       value = queue.pop
+ *       sleep rand(i/2) # simulate expense
+ *       puts "consumed #{value}"
+ *     end
+ *   end
+ *
+ *   consumer.join
+ *
+ */
+
+typedef struct _Queue {
+  Mutex mutex;
+  ConditionVariable value_available;
+  ConditionVariable space_available;
+  List values;
+  unsigned long capacity;
+} Queue;
+
+static void mark_queue _((Queue *));
+
+static void
+mark_queue(queue)
+  Queue *queue;
+{
+  mark_mutex(&queue->mutex);
+  mark_condvar(&queue->value_available);
+  mark_condvar(&queue->space_available);
+  mark_list(&queue->values);
+}
+
+static void finalize_queue _((Queue *));
+
+static void
+finalize_queue(queue)
+  Queue *queue;
+{
+  finalize_mutex(&queue->mutex);
+  finalize_condvar(&queue->value_available);
+  finalize_condvar(&queue->space_available);
+  finalize_list(&queue->values);
+}
+
+static void free_queue _((Queue *));
+
+static void
+free_queue(queue)
+  Queue *queue;
+{
+  assert_no_survivors(&queue->mutex.waiting, "queue", queue);
+  assert_no_survivors(&queue->space_available.waiting, "queue", queue);
+  assert_no_survivors(&queue->value_available.waiting, "queue", queue);
+  finalize_queue(queue);
+  free(queue);
+}
+
+static void init_queue _((Queue *));
+
+static void
+init_queue(queue)
+  Queue *queue;
+{
+  init_mutex(&queue->mutex);
+  init_condvar(&queue->value_available);
+  init_condvar(&queue->space_available);
+  init_list(&queue->values);
+  queue->capacity = 0;
+}
+
+/*
+ * Document-method: new
+ * call-seq: new
+ *
+ * Creates a new queue.
+ *
+ */
+
+static VALUE rb_queue_alloc _((VALUE));
+
+static VALUE
+rb_queue_alloc(klass)
+  VALUE klass;
+{
+  Queue *queue;
+  queue = (Queue *)malloc(sizeof(Queue));
+  init_queue(queue);
+  return Data_Wrap_Struct(klass, mark_queue, free_queue, queue);
+}
+
+static VALUE rb_queue_marshal_load _((VALUE, VALUE));
+
+static VALUE
+rb_queue_marshal_load(self, data)
+  VALUE self;
+  VALUE data;
+{
+  Queue *queue;
+  VALUE array;
+  Data_Get_Struct(self, Queue, queue);
+
+  array = rb_marshal_load(data);
+  if ( TYPE(array) != T_ARRAY ) {
+    rb_raise(rb_eRuntimeError, "expected Array of queue data");
+  }
+  if ( RARRAY(array)->len < 1 ) {
+    rb_raise(rb_eRuntimeError, "missing capacity value");
+  }
+  queue->capacity = NUM2ULONG(rb_ary_shift(array));
+  push_multiple_list(&queue->values, RARRAY(array)->ptr, (unsigned)RARRAY(array)->len);
+
+  return self;
+}
+
+static VALUE rb_queue_marshal_dump _((VALUE));
+
+static VALUE
+rb_queue_marshal_dump(self)
+  VALUE self;
+{
+  Queue *queue;
+  VALUE array;
+  Data_Get_Struct(self, Queue, queue);
+
+  array = array_from_list(&queue->values);
+  rb_ary_unshift(array, ULONG2NUM(queue->capacity));
+  return rb_marshal_dump(array, Qnil);
+}
+
+/*
+ * Document-method: clear
+ * call-seq: clear
+ *
+ * Removes all objects from the queue.
+ *
+ */
+
+static VALUE rb_queue_clear _((VALUE));
+
+static VALUE
+rb_queue_clear(self)
+  VALUE self;
+{
+  Queue *queue;
+  Data_Get_Struct(self, Queue, queue);
+
+  lock_mutex(&queue->mutex);
+  clear_list(&queue->values);
+  signal_condvar(&queue->space_available);
+  unlock_mutex(&queue->mutex);
+
+  return self;
+}
+
+/*
+ * Document-method: empty?
+ * call-seq: empty?
+ *
+ * Returns +true+ if the queue is empty.
+ *
+ */
+
+static VALUE rb_queue_empty_p _((VALUE));
+
+static VALUE
+rb_queue_empty_p(self)
+  VALUE self;
+{
+  Queue *queue;
+  VALUE result;
+  Data_Get_Struct(self, Queue, queue);
+
+  lock_mutex(&queue->mutex);
+  result = ( ( queue->values.size == 0 ) ? Qtrue : Qfalse );
+  unlock_mutex(&queue->mutex);
+
+  return result;
+}
+
+/*
+ * Document-method: length
+ * call-seq: length
+ *
+ * Returns the length of the queue.
+ *
+ */
+
+static VALUE rb_queue_length _((VALUE));
+
+static VALUE
+rb_queue_length(self)
+  VALUE self;
+{
+  Queue *queue;
+  VALUE result;
+  Data_Get_Struct(self, Queue, queue);
+
+  lock_mutex(&queue->mutex);
+  result = ULONG2NUM(queue->values.size);
+  unlock_mutex(&queue->mutex);
+
+  return result;
+}
+
+/*
+ * Document-method: num_waiting
+ * call-seq: num_waiting
+ *
+ * Returns the number of threads waiting on the queue.
+ *
+ */
+
+static VALUE rb_queue_num_waiting _((VALUE));
+
+static VALUE
+rb_queue_num_waiting(self)
+  VALUE self;
+{
+  Queue *queue;
+  VALUE result;
+  Data_Get_Struct(self, Queue, queue);
+
+  lock_mutex(&queue->mutex);
+  result = ULONG2NUM(queue->value_available.waiting.size +
+                     queue->space_available.waiting.size);
+  unlock_mutex(&queue->mutex);
+
+  return result;
+}
+
+/*
+ * Document-method: pop
+ * call_seq: pop(non_block=false)
+ *
+ * Retrieves data from the queue.  If the queue is empty, the calling thread is
+ * suspended until data is pushed onto the queue.  If +non_block+ is true, the
+ * thread isn't suspended, and an exception is raised.
+ *
+ */
+
+static VALUE rb_queue_pop _((int, VALUE *, VALUE));
+
+static VALUE
+rb_queue_pop(argc, argv, self)
+  int argc;
+  VALUE *argv;
+  VALUE self;
+{
+  Queue *queue;
+  int should_block;
+  VALUE result;
+  Data_Get_Struct(self, Queue, queue);
+
+  if ( argc == 0 ) {
+    should_block = 1;
+  } else if ( argc == 1 ) {
+    should_block = !RTEST(argv[0]);
+  } else {
+    rb_raise(rb_eArgError, "wrong number of arguments (%d for 1)", argc);
+  }
+
+  lock_mutex(&queue->mutex);
+  if ( !queue->values.entries && !should_block ) {
+    unlock_mutex(&queue->mutex);
+    rb_raise(rb_eThreadError, "queue empty");
+  }
+
+  while (!queue->values.entries) {
+    wait_condvar(&queue->value_available, &queue->mutex);
+  }
+
+  result = shift_list(&queue->values);
+  if ( queue->capacity && queue->values.size < queue->capacity ) {
+    signal_condvar(&queue->space_available);
+  }
+  unlock_mutex(&queue->mutex);
+
+  return result;
+}
+
+/*
+ * Document-method: push
+ * call-seq: push(obj)
+ *
+ * Pushes +obj+ to the queue.
+ *
+ */
+
+static VALUE rb_queue_push _((VALUE, VALUE));
+
+static VALUE
+rb_queue_push(self, value)
+  VALUE self;
+  VALUE value;
+{
+  Queue *queue;
+  Data_Get_Struct(self, Queue, queue);
+
+  lock_mutex(&queue->mutex);
+  while ( queue->capacity && queue->values.size >= queue->capacity ) {
+    wait_condvar(&queue->space_available, &queue->mutex);
+  }
+  push_list(&queue->values, value);
+  signal_condvar(&queue->value_available);
+  unlock_mutex(&queue->mutex);
+
+  return self;
+}
+
+/*
+ * Document-class: SizedQueue
+ *
+ * This class represents queues of specified size capacity.  The push operation
+ * may be blocked if the capacity is full.
+ *
+ * See Queue for an example of how a SizedQueue works.
+ *
+ */
+
+/*
+ * Document-method: new
+ * call-seq: new
+ *
+ * Creates a fixed-length queue with a maximum size of +max+.
+ *
+ */
+
+/*
+ * Document-method: max
+ * call-seq: max
+ *
+ * Returns the maximum size of the queue.
+ *
+ */
+
+static VALUE rb_sized_queue_max _((VALUE));
+
+static VALUE
+rb_sized_queue_max(self)
+  VALUE self;
+{
+  Queue *queue;
+  VALUE result;
+  Data_Get_Struct(self, Queue, queue);
+
+  lock_mutex(&queue->mutex);
+  result = ULONG2NUM(queue->capacity);
+  unlock_mutex(&queue->mutex);
+
+  return result;
+}
+
+/*
+ * Document-method: max=
+ * call-seq: max=(size)
+ *
+ * Sets the maximum size of the queue.
+ *
+ */
+
+static VALUE rb_sized_queue_max_set _((VALUE, VALUE));
+
+static VALUE
+rb_sized_queue_max_set(self, value)
+  VALUE self;
+  VALUE value;
+{
+  Queue *queue;
+  unsigned long new_capacity;
+  unsigned long difference;
+  Data_Get_Struct(self, Queue, queue);
+
+  new_capacity = NUM2ULONG(value);
+
+  if ( new_capacity < 1 ) {
+    rb_raise(rb_eArgError, "value must be positive");
+  }
+
+  lock_mutex(&queue->mutex);
+  if ( queue->capacity && new_capacity > queue->capacity ) {
+    difference = new_capacity - queue->capacity;
+  } else {
+    difference = 0;
+  }
+  queue->capacity = new_capacity;
+  for ( ; difference > 0 ; --difference ) {
+    signal_condvar(&queue->space_available);
+  }
+  unlock_mutex(&queue->mutex);
+
+  return self;
+}
+
+/*
+ * Document-method: push
+ * call-seq: push(obj)
+ *
+ * Pushes +obj+ to the queue.  If there is no space left in the queue, waits
+ * until space becomes available.
+ *
+ */
+
+/*
+ * Document-method: pop
+ * call-seq: pop(non_block=false)
+ *
+ * Retrieves data from the queue and runs a waiting thread, if any.
+ *
+ */
+
+/* for marshalling mutexes and condvars */
+
+static VALUE dummy_load _((VALUE, VALUE)); 
+
+static VALUE
+dummy_load(self, string)
+  VALUE self;
+  VALUE string;
+{
+  return Qnil;
+}
+
+static VALUE dummy_dump _((VALUE));
+
+static VALUE
+dummy_dump(self)
+  VALUE self;
+{
+  return rb_str_new2("");
+}
+
+void
+Init_thread()
+{
+  rb_cMutex = rb_define_class("Mutex", rb_cObject);
+  rb_define_alloc_func(rb_cMutex, rb_mutex_alloc);
+  rb_define_method(rb_cMutex, "marshal_load", dummy_load, 1);
+  rb_define_method(rb_cMutex, "marshal_dump", dummy_dump, 0);
+  rb_define_method(rb_cMutex, "initialize", return_value, 0);
+  rb_define_method(rb_cMutex, "locked?", rb_mutex_locked_p, 0);
+  rb_define_method(rb_cMutex, "try_lock", rb_mutex_try_lock, 0);
+  rb_define_method(rb_cMutex, "lock", rb_mutex_lock, 0);
+  rb_define_method(rb_cMutex, "unlock", rb_mutex_unlock, 0);
+  rb_define_method(rb_cMutex, "exclusive_unlock", rb_mutex_exclusive_unlock, 0);
+  rb_define_method(rb_cMutex, "synchronize", rb_mutex_synchronize, 0);
+
+  rb_cConditionVariable = rb_define_class("ConditionVariable", rb_cObject);
+  rb_define_alloc_func(rb_cConditionVariable, rb_condvar_alloc);
+  rb_define_method(rb_cConditionVariable, "marshal_load", dummy_load, 1);
+  rb_define_method(rb_cConditionVariable, "marshal_dump", dummy_dump, 0);
+  rb_define_method(rb_cConditionVariable, "initialize", return_value, 0);
+  rb_define_method(rb_cConditionVariable, "wait", rb_condvar_wait, 1);
+  rb_define_method(rb_cConditionVariable, "broadcast", rb_condvar_broadcast, 0);
+  rb_define_method(rb_cConditionVariable, "signal", rb_condvar_signal, 0);
+
+  rb_cQueue = rb_define_class("Queue", rb_cObject);
+  rb_define_alloc_func(rb_cQueue, rb_queue_alloc);
+  rb_define_method(rb_cQueue, "marshal_load", rb_queue_marshal_load, 1);
+  rb_define_method(rb_cQueue, "marshal_dump", rb_queue_marshal_dump, 0);
+  rb_define_method(rb_cQueue, "initialize", return_value, 0);
+  rb_define_method(rb_cQueue, "clear", rb_queue_clear, 0);
+  rb_define_method(rb_cQueue, "empty?", rb_queue_empty_p, 0);
+  rb_define_method(rb_cQueue, "length", rb_queue_length, 0);
+  rb_define_method(rb_cQueue, "num_waiting", rb_queue_num_waiting, 0);
+  rb_define_method(rb_cQueue, "pop", rb_queue_pop, -1);
+  rb_define_method(rb_cQueue, "push", rb_queue_push, 1);
+  rb_alias(rb_cQueue, rb_intern("<<"), rb_intern("push"));
+  rb_alias(rb_cQueue, rb_intern("deq"), rb_intern("pop"));
+  rb_alias(rb_cQueue, rb_intern("shift"), rb_intern("pop"));
+  rb_alias(rb_cQueue, rb_intern("size"), rb_intern("length"));
+
+  rb_cSizedQueue = rb_define_class("SizedQueue", rb_cQueue);
+  rb_define_method(rb_cSizedQueue, "initialize", rb_sized_queue_max_set, 1);
+  rb_define_method(rb_cSizedQueue, "num_waiting", rb_queue_num_waiting, 0);
+  rb_define_method(rb_cSizedQueue, "pop", rb_queue_pop, -1);
+  rb_define_method(rb_cSizedQueue, "push", rb_queue_push, 1);
+  rb_define_method(rb_cSizedQueue, "max", rb_sized_queue_max, 0);
+  rb_define_method(rb_cSizedQueue, "max=", rb_sized_queue_max_set, 1);
+  rb_alias(rb_cSizedQueue, rb_intern("<<"), rb_intern("push"));
+  rb_alias(rb_cSizedQueue, rb_intern("deq"), rb_intern("pop"));
+  rb_alias(rb_cSizedQueue, rb_intern("shift"), rb_intern("pop"));
+}
+