path: root/alloc.c

/*
 * Copyright 1988, 1989 Hans-J. Boehm, Alan J. Demers
 * Copyright (c) 1991-1993 by Xerox Corporation.  All rights reserved.
 *
 * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
 * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
 *
 * Permission is hereby granted to copy this garbage collector for any purpose,
 * provided the above notices are retained on all copies.
 *
 */


# include <stdio.h>
# include <signal.h>
# include <sys/types.h>
# include "gc_private.h"

/*
 * Separate free lists are maintained for different sized objects
 * up to MAXOBJSZ.
 * The call GC_allocobj(i,k) ensures that the freelist for
 * kind k objects of size i points to a non-empty
 * free list. It returns a pointer to the first entry on the free list.
 * In a single-threaded world, GC_allocobj may be called to allocate
 * an object of (small) size i as follows:
 *
 *            opp = &(GC_objfreelist[i]);
 *            if (*opp == 0) GC_allocobj(i, NORMAL);
 *            ptr = *opp;
 *            *opp = obj_link(ptr);
 *
 * Note that this is very fast if the free list is non-empty; it should
 * only involve the execution of 4 or 5 simple instructions.
 * All composite objects on freelists are cleared, except for
 * their first word.
 */

/*
 *  The allocator uses GC_allochblk to allocate large chunks of objects.
 * These chunks all start on addresses which are multiples of
 * HBLKSZ.   Each allocated chunk has an associated header,
 * which can be located quickly based on the address of the chunk.
 * (See headers.c for details.) 
 * This makes it possible to check quickly whether an
 * arbitrary address corresponds to an object administered by the
 * allocator.
 */

word GC_non_gc_bytes = 0;  /* Number of bytes not intended to be collected */

word GC_gc_no = 0;

int GC_incremental = 0;    /* By default, stop the world.	*/

int GC_full_freq = 3;	   /* Every 4th collection is a full	*/
			   /* collection.			*/

char * GC_copyright[] =
{"Copyright 1988,1989 Hans-J. Boehm and Alan J. Demers",
"Copyright (c) 1991-1993 by Xerox Corporation.  All rights reserved.",
"THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY",
" EXPRESSED OR IMPLIED.  ANY USE IS AT YOUR OWN RISK."};


/* some more variables */

extern signed_word GC_mem_found;  /* Number of reclaimed longwords	*/
				  /* after garbage collection      	*/

bool GC_dont_expand = 0;

word GC_free_space_divisor = 4;

/* Return the minimum number of words that must be allocated between	*/
/* collections to amortize the collection cost.				*/
static word min_words_allocd()
{
    int dummy;
#   ifdef THREADS
 	/* We punt, for now. */
 	register signed_word stack_size = 10000;
#   else
        register signed_word stack_size = (ptr_t)(&dummy) - GC_stackbottom;
#   endif
    register word total_root_size;  /* includes double stack size,	*/
    				    /* since the stack is expensive	*/
    				    /* to scan.				*/
    
    if (stack_size < 0) stack_size = -stack_size;
    total_root_size = 2 * stack_size + GC_root_size;
    if (GC_incremental) {
        return(BYTES_TO_WORDS(GC_heapsize + total_root_size)
               / (2 * GC_free_space_divisor));
    } else {
        return(BYTES_TO_WORDS(GC_heapsize + total_root_size)
               / GC_free_space_divisor);
    }
}

/* Return the number of words allocated, adjusted for explicit storage	*/
/* management, etc..  This number is used in deciding when to trigger	*/
/* collections.								*/
word GC_adj_words_allocd()
{
    register signed_word result;
    register signed_word expl_managed =
    		BYTES_TO_WORDS((long)GC_non_gc_bytes
    				- (long)GC_non_gc_bytes_at_gc);
    
    /* Don't count what was explicitly freed, or newly allocated for	*/
    /* explicit management.  Note that deallocating an explicitly	*/
    /* managed object should not alter result, assuming the client	*/
    /* is playing by the rules.						*/
    result = (signed_word)GC_words_allocd
    	     - (signed_word)GC_mem_freed - expl_managed;
    if (result > (signed_word)GC_words_allocd) result = GC_words_allocd;
    	/* probably client bug or unfortunate scheduling */
    result += GC_words_wasted;
     	/* This doesn't reflect useful work.  But if there is lots of	*/
     	/* new fragmentation, the same is probably true of the heap,	*/
     	/* and the collection will be correspondingly cheaper.		*/
    if (result < (signed_word)(GC_words_allocd >> 2)) {
    	/* Always count at least 1/8 of the allocations.  We don't want	*/
    	/* to collect too infrequently, since that would inhibit	*/
    	/* coalescing of free storage blocks.				*/
    	/* This also makes us partially robust against client bugs.	*/
        return(GC_words_allocd >> 3);
    } else {
        return(result);
    }
}


/* Clear up a few frames worth og garbage left at the top of the stack.	*/
/* This is used to prevent us from accidentally treating garbade left	*/
/* on the stack by other parts of the collector as roots.  This 	*/
/* differs from the code in misc.c, which actually tries to keep the	*/
/* stack clear of long-lived, client-generated garbage.			*/
void GC_clear_a_few_frames()
{
#   define NWORDS 64
    word frames[NWORDS];
    register int i;
    
    for (i = 0; i < NWORDS; i++) frames[i] = 0;
}

/* Have we allocated enough to amortize a collection? */
bool GC_should_collect()
{
    return(GC_adj_words_allocd() >= min_words_allocd());
}

/* 
 * Initiate a garbage collection if appropriate.
 * Choose judiciously
 * between partial, full, and stop-world collections.
 * Assumes lock held, signals disabled.
 */
void GC_maybe_gc()
{
    static int n_partial_gcs = 0;
    if (GC_should_collect()) {
        if (!GC_incremental) {
            GC_gcollect_inner();
            n_partial_gcs = 0;
        } else if (n_partial_gcs >= GC_full_freq) {
            GC_initiate_full();
            n_partial_gcs = 0;
        } else {
            GC_initiate_partial(GC_gc_no+1);
            n_partial_gcs++;
        }
    }
}

/*
 * Stop the world garbage collection.  Assumes lock held, signals disabled.
 */
void GC_gcollect_inner()
{
#   ifdef PRINTSTATS
	GC_printf2(
	   "Initiating full world-stop collection %lu after %ld allocd bytes\n",
	   (unsigned long) GC_gc_no+1,
	   (long)WORDS_TO_BYTES(GC_words_allocd));
#   endif
    GC_promote_black_lists();
    /* GC_reclaim_or_delete_all();  -- not needed: no intervening allocation */
    GC_clear_marks();
    STOP_WORLD();
    GC_stopped_mark();
    START_WORLD();
    GC_finish_collection();
}

/*
 * Perform n units of garbage collection work.  A unit is intended to touch
 * roughly a GC_RATE pages.  Every once in a while, we do more than that.
 */
# define GC_RATE 8
void GC_collect_a_little(n)
int n;
{
    register int i;
    
    if (GC_collection_in_progress()) {
    	for (i = 0; i < GC_RATE*n; i++) {
    	    if (GC_mark_some()) {
    	        /* Need to finish a collection */
    	        STOP_WORLD();
    	        GC_stopped_mark();
    	        START_WORLD();
    	        GC_finish_collection();
    	        break;
    	    }
    	}
    } else {
        GC_maybe_gc();
    }
}

/*
 * World-stopped mark phase.  Assumes lock is held, signals are disabled,
 * and the world is stopped.
 */
void GC_stopped_mark()
{
#   ifdef PRINTTIMES
	CLOCK_TYPE start_time;
	CLOCK_TYPE done_time;
	
	GET_TIME(start_time);
#   endif
#   ifdef PRINTSTATS
	GC_printf2("Collection %lu reclaimed %ld bytes\n",
		  (unsigned long) GC_gc_no,
	   	  (long)WORDS_TO_BYTES(GC_mem_found));
#   endif
    GC_gc_no++;
#   ifdef PRINTSTATS
      GC_printf3(
       	"--> Collection number %lu after %lu allocated + %lu wasted bytes\n",
      	(unsigned long) GC_gc_no,
      	(unsigned long) WORDS_TO_BYTES(GC_words_allocd),
      	(unsigned long) WORDS_TO_BYTES(GC_words_wasted));
      GC_printf1("---> heapsize = %lu bytes\n",
      	        (unsigned long) GC_heapsize);
      /* Printf arguments may be pushed in funny places.  Clear the	*/
      /* space.								*/
      GC_printf0("");
#   endif      	        

    /* Mark from all roots.  */
        /* Minimize junk left in my registers and on the stack */
            GC_clear_a_few_frames();
            GC_noop(0,0,0,0,0,0);
	GC_initiate_partial(GC_gc_no);
	while(!GC_mark_some());

    /* Check all debugged objects for consistency */
        if (GC_debugging_started) {
            (*GC_check_heap)();
        }
    
#   ifdef PRINTTIMES
	GET_TIME(done_time);
	GC_printf1("World-stopped marking took %lu msecs\n",
	           MS_TIME_DIFF(done_time,start_time));
#   endif

}


/* Finish up a collection.  Assumes lock is held, signals are disabled,	*/
/* but the world is otherwise running.					*/
void GC_finish_collection()
{
#   ifdef PRINTTIMES
	CLOCK_TYPE start_time;
	CLOCK_TYPE finalize_time;
	CLOCK_TYPE done_time;
	
	GET_TIME(start_time);
	finalize_time = start_time;
#   endif

#   ifdef GATHERSTATS
        GC_mem_found = 0;
#   endif
#   ifdef FIND_LEAK
      /* Mark all objects on the free list.  All objects should be */
      /* marked when we're done.				   */
	{
	  register word size;		/* current object size		*/
	  register ptr_t p;	/* pointer to current object	*/
	  register struct hblk * h;	/* pointer to block containing *p */
	  register hdr * hhdr;
	  register int word_no;           /* "index" of *p in *q          */
	  int kind;

	  for (kind = 0; kind < GC_n_kinds; kind++) {
	    for (size = 1; size <= MAXOBJSZ; size++) {
	      for (p= GC_obj_kinds[kind].ok_freelist[size];
	           p != 0; p=obj_link(p)){
		h = HBLKPTR(p);
		hhdr = HDR(h);
		word_no = (((word *)p) - ((word *)h));
		set_mark_bit_from_hdr(hhdr, word_no);
	      }
	    }
	  }
	}
      /* Check that everything is marked */
	GC_start_reclaim(TRUE);
#   else

      GC_finalize();
#     ifdef STUBBORN_ALLOC
        GC_clean_changing_list();
#     endif

#     ifdef PRINTTIMES
	GET_TIME(finalize_time);
#     endif

      /* Clear free list mark bits, in case they got accidentally marked   */
      /* Note: HBLKPTR(p) == pointer to head of block containing *p        */
      /* Also subtract memory remaining from GC_mem_found count.           */
      /* Note that composite objects on free list are cleared.             */
      /* Thus accidentally marking a free list is not a problem;  only     */
      /* objects on the list itself will be marked, and that's fixed here. */
      {
	register word size;		/* current object size		*/
	register ptr_t p;	/* pointer to current object	*/
	register struct hblk * h;	/* pointer to block containing *p */
	register hdr * hhdr;
	register int word_no;           /* "index" of *p in *q          */
	int kind;

	for (kind = 0; kind < GC_n_kinds; kind++) {
	  for (size = 1; size <= MAXOBJSZ; size++) {
	    for (p= GC_obj_kinds[kind].ok_freelist[size];
	         p != 0; p=obj_link(p)){
		h = HBLKPTR(p);
		hhdr = HDR(h);
		word_no = (((word *)p) - ((word *)h));
		clear_mark_bit_from_hdr(hhdr, word_no);
#		ifdef GATHERSTATS
		    GC_mem_found -= size;
#		endif
	    }
	  }
	}
      }


#     ifdef PRINTSTATS
	GC_printf1("Bytes recovered before sweep - f.l. count = %ld\n",
	          (long)WORDS_TO_BYTES(GC_mem_found));
#     endif

    /* Reconstruct free lists to contain everything not marked */
      GC_start_reclaim(FALSE);
    
#   endif /* !FIND_LEAK */

#   ifdef PRINTSTATS
	GC_printf2(
		  "Immediately reclaimed %ld bytes in heap of size %lu bytes\n",
	          (long)WORDS_TO_BYTES(GC_mem_found),
	          (unsigned long)GC_heapsize);
	GC_printf2("%lu (atomic) + %lu (composite) bytes in use\n",
	           (unsigned long)WORDS_TO_BYTES(GC_atomic_in_use),
	           (unsigned long)WORDS_TO_BYTES(GC_composite_in_use));
#   endif

    /* Reset or increment counters for next cycle */
      GC_words_allocd_before_gc += GC_words_allocd;
      GC_non_gc_bytes_at_gc = GC_non_gc_bytes;
      GC_words_allocd = 0;
      GC_words_wasted = 0;
      GC_mem_freed = 0;
      
#   ifdef PRINTTIMES
	GET_TIME(done_time);
	GC_printf2("Finalize + initiate sweep took %lu + %lu msecs\n",
	           MS_TIME_DIFF(finalize_time,start_time),
	           MS_TIME_DIFF(done_time,finalize_time));
#   endif
}

/* Externally callable routine to invoke full, stop-world collection */
void GC_gcollect()
{
    DCL_LOCK_STATE;
    
    DISABLE_SIGNALS();
    LOCK();
    if (!GC_is_initialized) GC_init_inner();
    /* Minimize junk left in my registers */
      GC_noop(0,0,0,0,0,0);
    GC_gcollect_inner();
    UNLOCK();
    ENABLE_SIGNALS();
}

word GC_n_heap_sects = 0;	/* Number of sections currently in heap. */

/*
 * Use the chunk of memory starting at p of syze bytes as part of the heap.
 * Assumes p is HBLKSIZE aligned, and bytes is a multiple of HBLKSIZE.
 */
void GC_add_to_heap(p, bytes)
struct hblk *p;
word bytes;
{
    word words;
    
    if (GC_n_heap_sects >= MAX_HEAP_SECTS) {
        GC_err_printf0(
            "Too many heap sections: Increase MAXHINCR or MAX_HEAP_SECTS");
    	ABORT("Too many heap sections: Increase MAXHINCR or MAX_HEAP_SECTS");
    }
    if (!GC_install_header(p)) {
    	/* This is extremely unlikely. Can't add it.  This will		*/
    	/* almost certainly result in a	0 return from the allocator,	*/
    	/* which is entirely appropriate.				*/
    	return;
    }
    GC_heap_sects[GC_n_heap_sects].hs_start = (ptr_t)p;
    GC_heap_sects[GC_n_heap_sects].hs_bytes = bytes;
    GC_n_heap_sects++;
    words = BYTES_TO_WORDS(bytes - HDR_BYTES);
    HDR(p) -> hb_sz = words;
    GC_freehblk(p);
    GC_heapsize += bytes;
    if ((ptr_t)p <= GC_least_plausible_heap_addr
        || GC_least_plausible_heap_addr == 0) {
        GC_least_plausible_heap_addr = (ptr_t)p - sizeof(word);
        	/* Making it a little smaller than necessary prevents	*/
        	/* us from getting a false hit from the variable	*/
        	/* itself.  There's some unintentional reflection	*/
        	/* here.						*/
    }
    if ((ptr_t)p + bytes >= GC_greatest_plausible_heap_addr) {
        GC_greatest_plausible_heap_addr = (ptr_t)p + bytes;
    }
}

ptr_t GC_least_plausible_heap_addr = (ptr_t)ONES;
ptr_t GC_greatest_plausible_heap_addr = 0;

ptr_t GC_max(x,y)
ptr_t x, y;
{
    return(x > y? x : y);
}

ptr_t GC_min(x,y)
ptr_t x, y;
{
    return(x < y? x : y);
}

/*
 * this explicitly increases the size of the heap.  It is used
 * internally, but may also be invoked from GC_expand_hp by the user.
 * The argument is in units of HBLKSIZE.
 * Tiny values of n are rounded up.
 * Returns FALSE on failure.
 */
bool GC_expand_hp_inner(n)
word n;
{
    word bytes;
    struct hblk * space;
    word expansion_slop;	/* Number of bytes by which we expect the */
    				/* heap to expand soon.			  */

    if (n < MINHINCR) n = MINHINCR;
    bytes = n * HBLKSIZE;
    space = GET_MEM(bytes);
    if( space == 0 ) {
	return(FALSE);
    }
#   ifdef PRINTSTATS
	GC_printf2("Increasing heap size by %lu after %lu allocated bytes\n",
	           (unsigned long)bytes,
	           (unsigned long)WORDS_TO_BYTES(GC_words_allocd));
#   endif
    expansion_slop = 8 * WORDS_TO_BYTES(min_words_allocd());
    if (5 * HBLKSIZE * MAXHINCR > expansion_slop) {
        expansion_slop = 5 * HBLKSIZE * MAXHINCR;
    }
    if (GC_last_heap_addr == 0 && !((word)space & SIGNB)
        || GC_last_heap_addr != 0 && GC_last_heap_addr < (ptr_t)space) {
        /* Assume the heap is growing up */
        GC_greatest_plausible_heap_addr =
            GC_max(GC_greatest_plausible_heap_addr,
                   (ptr_t)space + bytes + expansion_slop);
    } else {
        /* Heap is growing down */
        GC_least_plausible_heap_addr =
            GC_min(GC_least_plausible_heap_addr,
                   (ptr_t)space - expansion_slop);
    }
    GC_prev_heap_addr = GC_last_heap_addr;
    GC_last_heap_addr = (ptr_t)space;
    GC_add_to_heap(space, bytes);
    return(TRUE);
}

/* Really returns a bool, but it's externally visible, so that's clumsy. */
int GC_expand_hp(n)
int n;
{
    int result;
    DCL_LOCK_STATE;
    
    DISABLE_SIGNALS();
    LOCK();
    if (!GC_is_initialized) GC_init_inner();
    result = (int)GC_expand_hp_inner((word)n);
    UNLOCK();
    ENABLE_SIGNALS();
    return(result);
}

bool GC_collect_or_expand(needed_blocks)
word needed_blocks;
{
    static int count = 0;  /* How many failures? */
    
    if (!GC_incremental && !GC_dont_gc && GC_should_collect()) {
      GC_gcollect_inner();
    } else {
      word blocks_to_get = GC_heapsize/(HBLKSIZE*GC_free_space_divisor)
      			   + needed_blocks;
      
      if (blocks_to_get > MAXHINCR) {
          if (needed_blocks > MAXHINCR) {
              blocks_to_get = needed_blocks;
          } else {
              blocks_to_get = MAXHINCR;
          }
      }
      if (!GC_expand_hp_inner(blocks_to_get)
        && !GC_expand_hp_inner(needed_blocks)) {
      	if (count++ < 20) {
      	    WARN("Out of Memory!  Trying to continue ...\n");
	    GC_gcollect_inner();
	} else {
	    WARN("Out of Memory!  Returning NIL!\n");
	    return(FALSE);
	}
      }
    }
    return(TRUE);
}

/*
 * Make sure the object free list for sz is not empty.
 * Return a pointer to the first object on the free list.
 * The object MUST BE REMOVED FROM THE FREE LIST BY THE CALLER.
 * Assumes we hold the allocator lock and signals are disabled.
 *
 */
ptr_t GC_allocobj(sz, kind)
word sz;
int kind;
{
    register ptr_t * flh = &(GC_obj_kinds[kind].ok_freelist[sz]);
    
    if (sz == 0) return(0);

    while (*flh == 0) {
      /* Do our share of marking work */
        if(GC_incremental && !GC_dont_gc) GC_collect_a_little(1);
      /* Sweep blocks for objects of this size */
          GC_continue_reclaim(sz, kind);
      if (*flh == 0) {
        GC_new_hblk(sz, kind);
      }
      if (*flh == 0) {
        if (!GC_collect_or_expand((word)1)) return(0);
      }
    }
    
    return(*flh);
}