alloc.c

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/*
 * Copyright 1988, 1989 Hans-J. Boehm, Alan J. Demers
 * Copyright (c) 1991-1996 by Xerox Corporation.  All rights reserved.
 * Copyright (c) 1998 by Silicon Graphics.  All rights reserved.
 * Copyright (c) 1999-2004 Hewlett-Packard Development Company, L.P.
 *
 * 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 use or copy this program
 * for any purpose,  provided the above notices are retained on all copies.
 * Permission to modify the code and to distribute modified code is granted,
 * provided the above notices are retained, and a notice that the code was
 * modified is included with the above copyright notice.
 *
 */


# include "private/gc_priv.h"

# include <stdio.h>
# if !defined(MACOS) && !defined(MSWINCE)
#   include <signal.h>
#   include <sys/types.h>
# endif

/*
 * Separate free lists are maintained for different sized objects
 * up to MAXOBJBYTES.
 * 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;

#ifndef SMALL_CONFIG
  int GC_incremental = 0;  /* By default, stop the world.	*/
#endif

int GC_parallel = FALSE;   /* By default, parallel GC is off.	*/

int GC_full_freq = 19;	   /* Every 20th collection is a full	*/
			   /* collection, whether we need it 	*/
			   /* or not.			        */

GC_bool GC_need_full_gc = FALSE;
			   /* Need full GC do to heap growth.	*/

#ifdef THREADS
  GC_bool GC_world_stopped = FALSE;
# define IF_THREADS(x) x
#else
# define IF_THREADS(x)
#endif

word GC_used_heap_size_after_full = 0;

char * GC_copyright[] =
{"Copyright 1988,1989 Hans-J. Boehm and Alan J. Demers ",
"Copyright (c) 1991-1995 by Xerox Corporation.  All rights reserved. ",
"Copyright (c) 1996-1998 by Silicon Graphics.  All rights reserved. ",
"Copyright (c) 1999-2001 by Hewlett-Packard Company.  All rights reserved. ",
"THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY",
" EXPRESSED OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.",
"See source code for details." };

# include "version.h"

/* some more variables */

extern signed_word GC_bytes_found; /* Number of reclaimed bytes		*/
				  /* after garbage collection      	*/

GC_bool GC_dont_expand = 0;

word GC_free_space_divisor = 3;

extern GC_bool GC_collection_in_progress();
		/* Collection is in progress, or was abandoned.	*/

int GC_never_stop_func (void) { return(0); }

unsigned long GC_time_limit = TIME_LIMIT;

CLOCK_TYPE GC_start_time;  	/* Time at which we stopped world.	*/
				/* used only in GC_timeout_stop_func.	*/

int GC_n_attempts = 0;		/* Number of attempts at finishing	*/
				/* collection within GC_time_limit.	*/

#if defined(SMALL_CONFIG) || defined(NO_CLOCK)
#   define GC_timeout_stop_func GC_never_stop_func
#else
  int GC_timeout_stop_func (void)
  {
    CLOCK_TYPE current_time;
    static unsigned count = 0;
    unsigned long time_diff;
    
    if ((count++ & 3) != 0) return(0);
    GET_TIME(current_time);
    time_diff = MS_TIME_DIFF(current_time,GC_start_time);
    if (time_diff >= GC_time_limit) {
	if (GC_print_stats) {
	    GC_log_printf("Abandoning stopped marking after ");
	    GC_log_printf("%lu msecs", time_diff);
	    GC_log_printf("(attempt %d)\n", GC_n_attempts);
	}
    	return(1);
    }
    return(0);
  }
#endif /* !SMALL_CONFIG */

/* Return the minimum number of words that must be allocated between	*/
/* collections to amortize the collection cost.				*/
static word min_bytes_allocd()
{
#   ifdef THREADS
 	/* We punt, for now. */
 	signed_word stack_size = 10000;
#   else
        int dummy;
        signed_word stack_size = (ptr_t)(&dummy) - GC_stackbottom;
#   endif
    word total_root_size;  	    /* includes double stack size,	*/
    				    /* since the stack is expensive	*/
    				    /* to scan.				*/
    word scan_size;		/* Estimate of memory to be scanned 	*/
				/* during normal GC.			*/
    
    if (stack_size < 0) stack_size = -stack_size;
    total_root_size = 2 * stack_size + GC_root_size;
    scan_size = 2 * GC_composite_in_use + GC_atomic_in_use
		+ total_root_size;
    if (TRUE_INCREMENTAL) {
        return scan_size / (2 * GC_free_space_divisor);
    } else {
        return scan_size / GC_free_space_divisor;
    }
}

/* Return the number of bytes allocated, adjusted for explicit storage	*/
/* management, etc..  This number is used in deciding when to trigger	*/
/* collections.								*/
word GC_adj_bytes_allocd(void)
{
    signed_word result;
    signed_word expl_managed =
    		(signed_word)GC_non_gc_bytes
		- (signed_word)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_bytes_allocd
    	     - (signed_word)GC_bytes_freed 
	     + (signed_word)GC_finalizer_bytes_freed
	     - expl_managed;
    if (result > (signed_word)GC_bytes_allocd) {
        result = GC_bytes_allocd;
    	/* probably client bug or unfortunate scheduling */
    }
    result += GC_bytes_finalized;
    	/* We count objects enqueued for finalization as though they	*/
    	/* had been reallocated this round. Finalization is user	*/
    	/* visible progress.  And if we don't count this, we have	*/
    	/* stability problems for programs that finalize all objects.	*/
    if (result < (signed_word)(GC_bytes_allocd >> 3)) {
    	/* 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_bytes_allocd >> 3);
    } else {
        return(result);
    }
}


/* Clear up a few frames worth of 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];
    int i;
    
    for (i = 0; i < NWORDS; i++) frames[i] = 0;
}

/* Heap size at which we need a collection to avoid expanding past	*/
/* limits used by blacklisting.						*/
static word GC_collect_at_heapsize = (word)(-1);

/* Have we allocated enough to amortize a collection? */
GC_bool GC_should_collect(void)
{
    return(GC_adj_bytes_allocd() >= min_bytes_allocd()
	   || GC_heapsize >= GC_collect_at_heapsize);
}


void GC_notify_full_gc(void)
{
    if (GC_start_call_back != (void (*) (void))0) {
	(*GC_start_call_back)();
    }
}

GC_bool GC_is_full_gc = FALSE;

/* 
 * Initiate a garbage collection if appropriate.
 * Choose judiciously
 * between partial, full, and stop-world collections.
 * Assumes lock held, signals disabled.
 */
void GC_maybe_gc(void)
{
    static int n_partial_gcs = 0;

    if (GC_should_collect()) {
        if (!GC_incremental) {
            GC_gcollect_inner();
            n_partial_gcs = 0;
            return;
        } else {
#   	  ifdef PARALLEL_MARK
	    GC_wait_for_reclaim();
#   	  endif
	  if (GC_need_full_gc || n_partial_gcs >= GC_full_freq) {
	    if (GC_print_stats) {
	        GC_log_printf(
	          "***>Full mark for collection %lu after %ld allocd bytes\n",
     		  (unsigned long)GC_gc_no+1,
		  (long)GC_bytes_allocd);
	    }
	    GC_promote_black_lists();
	    (void)GC_reclaim_all((GC_stop_func)0, TRUE);
	    GC_clear_marks();
            n_partial_gcs = 0;
	    GC_notify_full_gc();
 	    GC_is_full_gc = TRUE;
          } else {
            n_partial_gcs++;
          }
	}
        /* We try to mark with the world stopped.	*/
        /* If we run out of time, this turns into	*/
        /* incremental marking.			*/
#	ifndef NO_CLOCK
          if (GC_time_limit != GC_TIME_UNLIMITED) { GET_TIME(GC_start_time); }
#	endif
        if (GC_stopped_mark(GC_time_limit == GC_TIME_UNLIMITED? 
			    GC_never_stop_func : GC_timeout_stop_func)) {
#           ifdef SAVE_CALL_CHAIN
                GC_save_callers(GC_last_stack);
#           endif
            GC_finish_collection();
        } else {
	    if (!GC_is_full_gc) {
		/* Count this as the first attempt */
	        GC_n_attempts++;
	    }
	}
    }
}


/*
 * Stop the world garbage collection.  Assumes lock held, signals disabled.
 * If stop_func is not GC_never_stop_func, then abort if stop_func returns TRUE.
 * Return TRUE if we successfully completed the collection.
 */
GC_bool GC_try_to_collect_inner(GC_stop_func stop_func)
{
    CLOCK_TYPE start_time, current_time;
    if (GC_dont_gc) return FALSE;
    if (GC_incremental && GC_collection_in_progress()) {
      if (GC_print_stats) {
	GC_log_printf(
	    "GC_try_to_collect_inner: finishing collection in progress\n");
      }
      /* Just finish collection already in progress.	*/
    	while(GC_collection_in_progress()) {
    	    if (stop_func()) return(FALSE);
    	    GC_collect_a_little_inner(1);
    	}
    }
    if (stop_func == GC_never_stop_func) GC_notify_full_gc();
    if (GC_print_stats) {
        GET_TIME(start_time);
	GC_log_printf(
	   "Initiating full world-stop collection %lu after %ld allocd bytes\n",
	   (unsigned long)GC_gc_no+1, (long)GC_bytes_allocd);
    }
    GC_promote_black_lists();
    /* Make sure all blocks have been reclaimed, so sweep routines	*/
    /* don't see cleared mark bits.					*/
    /* If we're guaranteed to finish, then this is unnecessary.		*/
    /* In the find_leak case, we have to finish to guarantee that 	*/
    /* previously unmarked objects are not reported as leaks.		*/
#       ifdef PARALLEL_MARK
	    GC_wait_for_reclaim();
#       endif
 	if ((GC_find_leak || stop_func != GC_never_stop_func)
	    && !GC_reclaim_all(stop_func, FALSE)) {
	    /* Aborted.  So far everything is still consistent.	*/
	    return(FALSE);
	}
    GC_invalidate_mark_state();  /* Flush mark stack.	*/