Initial revision

1 files changed, 884 insertions, 0 deletions

diff --git a/gc/alloc.c b/gc/alloc.c
new file mode 100644
index 0000000..1c57951
--- /dev/null
+++ b/gc/alloc.c
@@ -0,0 +1,884 @@
+/*
+ * Copyright 1988, 1989 Hans-J. Boehm, Alan J. Demers
+ * Copyright (c) 1991-1994 by Xerox Corporation.  All rights reserved.
+ * Copyright (c) 1998 by Silicon Graphics.  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 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 "gc_priv.h"
+
+# include <stdio.h>
+# ifndef MACOS
+#   include <signal.h>
+#   include <sys/types.h>
+# endif
+
+/*
+ * 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;
+
+#ifndef SMALL_CONFIG
+  int GC_incremental = 0;    /* By default, stop the world.	*/
+#endif
+
+int GC_full_freq = 4;	   /* Every 5th collection is a full	*/
+			   /* collection.			*/
+
+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. ",
+"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_mem_found;  /* Number of reclaimed longwords	*/
+				  /* 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 GC_PROTO((void)) { return(0); }
+
+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 TIME_LIMIT		*/
+
+#ifdef SMALL_CONFIG
+#   define GC_timeout_stop_func GC_never_stop_func
+#else
+  int GC_timeout_stop_func GC_PROTO((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 >= TIME_LIMIT) {
+#   	ifdef PRINTSTATS
+	    GC_printf0("Abandoning stopped marking after ");
+	    GC_printf1("%lu msecs", (unsigned long)time_diff);
+	    GC_printf1("(attempt %d)\n", (unsigned long) GC_n_attempts);
+#	endif
+    	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_words_allocd()
+{
+#   ifdef THREADS
+ 	/* We punt, for now. */
+ 	register signed_word stack_size = 10000;
+#   else
+        int dummy;
+        register 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 = BYTES_TO_WORDS(GC_heapsize - GC_large_free_bytes
+			       + (GC_large_free_bytes >> 2)
+				   /* use a bit more of large empty heap */
+			       + total_root_size);
+    if (GC_incremental) {
+        return scan_size / (2 * GC_free_space_divisor);
+    } else {
+        return scan_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_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.	*/
+    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 >> 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_words_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];
+    register int i;
+    
+    for (i = 0; i < NWORDS; i++) frames[i] = 0;
+}
+
+/* Have we allocated enough to amortize a collection? */
+GC_bool GC_should_collect()
+{
+    return(GC_adj_words_allocd() >= min_words_allocd());
+}
+
+void GC_notify_full_gc()
+{
+    if (GC_start_call_back != (void (*)())0) {
+	(*GC_start_call_back)();
+    }
+}
+
+/* 
+ * 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;
+    GC_bool is_full_gc = FALSE;
+
+    if (GC_should_collect()) {
+        if (!GC_incremental) {
+	    GC_notify_full_gc();
+            GC_gcollect_inner();
+            n_partial_gcs = 0;
+            return;
+        } else if (n_partial_gcs >= GC_full_freq) {
+#   	    ifdef PRINTSTATS
+	      GC_printf2(
+	        "***>Full mark for 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();
+	    (void)GC_reclaim_all((GC_stop_func)0, TRUE);
+	    GC_clear_marks();
+            n_partial_gcs = 0;
+	    GC_notify_full_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.			*/
+        GET_TIME(GC_start_time);
+        if (GC_stopped_mark(GC_timeout_stop_func)) {
+#           ifdef SAVE_CALL_CHAIN
+                GC_save_callers(GC_last_stack);
+#           endif
+            GC_finish_collection();
+        } else {
+	    if (!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.
+ */
+GC_bool GC_try_to_collect_inner(stop_func)
+GC_stop_func stop_func;
+{
+    if (GC_incremental && GC_collection_in_progress()) {
+#   ifdef PRINTSTATS
+	GC_printf0(
+	    "GC_try_to_collect_inner: finishing collection in progress\n");
+#    endif /* PRINTSTATS */
+      /* Just finish collection already in progress.	*/
+    	while(GC_collection_in_progress()) {
+    	    if (stop_func()) return(FALSE);
+    	    GC_collect_a_little_inner(1);
+    	}
+    }
+#   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();
+    /* 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.		*/
+	if (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.	*/
+    GC_clear_marks();
+#   ifdef SAVE_CALL_CHAIN
+        GC_save_callers(GC_last_stack);
+#   endif
+    if (!GC_stopped_mark(stop_func)) {
+      if (!GC_incremental) {
+    	/* We're partially done and have no way to complete or use 	*/
+    	/* current work.  Reestablish invariants as cheaply as		*/
+    	/* possible.							*/
+    	GC_invalidate_mark_state();
+	GC_unpromote_black_lists();
+      } /* else we claim the world is already still consistent.  We'll 	*/
+        /* finish incrementally.					*/
+      return(FALSE);
+    }
+    GC_finish_collection();
+    return(TRUE);
+}
+
+
+
+/*
+ * Perform n units of garbage collection work.  A unit is intended to touch
+ * roughly GC_RATE pages.  Every once in a while, we do more than that.
+ * This needa to be a fairly large number with our current incremental
+ * GC strategy, since otherwise we allocate too much during GC, and the
+ * cleanup gets expensive.
+ */
+# define GC_RATE 10 
+# define MAX_PRIOR_ATTEMPTS 1
+ 	/* Maximum number of prior attempts at world stop marking	*/
+ 	/* A value of 1 means that we finish the seconf time, no matter */
+ 	/* how long it takes.  Doesn't count the initial root scan	*/
+ 	/* for a full GC.						*/
+
+int GC_deficit = 0;	/* The number of extra calls to GC_mark_some	*/
+			/* that we have made.				*/
+
+void GC_collect_a_little_inner(n)
+int n;
+{
+    register int i;
+    
+    if (GC_incremental && GC_collection_in_progress()) {
+    	for (i = GC_deficit; i < GC_RATE*n; i++) {
+    	    if (GC_mark_some((ptr_t)0)) {
+    	        /* Need to finish a collection */
+#     		ifdef SAVE_CALL_CHAIN
+        	    GC_save_callers(GC_last_stack);
+#     		endif
+		if (GC_n_attempts < MAX_PRIOR_ATTEMPTS) {
+		  GET_TIME(GC_start_time);
+		  if (!GC_stopped_mark(GC_timeout_stop_func)) {
+		    GC_n_attempts++;
+		    break;
+		  }
+		} else {
+		  (void)GC_stopped_mark(GC_never_stop_func);
+		}
+    	        GC_finish_collection();
+    	        break;
+    	    }
+    	}
+    	if (GC_deficit > 0) GC_deficit -= GC_RATE*n;
+	if (GC_deficit < 0) GC_deficit = 0;
+    } else {
+        GC_maybe_gc();
+    }
+}
+
+int GC_collect_a_little GC_PROTO(())
+{
+    int result;
+    DCL_LOCK_STATE;
+
+    DISABLE_SIGNALS();
+    LOCK();
+    GC_collect_a_little_inner(1);
+    result = (int)GC_collection_in_progress();
+    UNLOCK();
+    ENABLE_SIGNALS();
+    return(result);
+}
+
+/*
+ * Assumes lock is held, signals are disabled.
+ * We stop the world.
+ * If stop_func() ever returns TRUE, we may fail and return FALSE.
+ * Increment GC_gc_no if we succeed.
+ */
+GC_bool GC_stopped_mark(stop_func)
+GC_stop_func stop_func;
+{
+    register int i;
+    int dummy;
+#   ifdef PRINTSTATS
+	CLOCK_TYPE start_time, current_time;
+#   endif
+	
+    STOP_WORLD();
+#   ifdef PRINTSTATS
+	GET_TIME(start_time);
+	GC_printf1("--> Marking for collection %lu ",
+	           (unsigned long) GC_gc_no + 1);
+	GC_printf2("after %lu allocd bytes + %lu wasted bytes\n",
+	   	   (unsigned long) WORDS_TO_BYTES(GC_words_allocd),
+	   	   (unsigned long) WORDS_TO_BYTES(GC_words_wasted));
+#   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_gc();
+	for(i = 0;;i++) {
+	    if ((*stop_func)()) {
+#   		    ifdef PRINTSTATS
+		    	GC_printf0("Abandoned stopped marking after ");
+			GC_printf1("%lu iterations\n",
+				   (unsigned long)i);
+#		    endif
+		    GC_deficit = i; /* Give the mutator a chance. */
+	            START_WORLD();
+	            return(FALSE);
+	    }
+	    if (GC_mark_some((ptr_t)(&dummy))) break;
+	}
+	
+    GC_gc_no++;
+#   ifdef PRINTSTATS
+      GC_printf2("Collection %lu reclaimed %ld bytes",
+		  (unsigned long) GC_gc_no - 1,
+	   	  (long)WORDS_TO_BYTES(GC_mem_found));
+      GC_printf1(" ---> heapsize = %lu bytes\n",
+      	        (unsigned long) GC_heapsize);
+      /* Printf arguments may be pushed in funny places.  Clear the	*/
+      /* space.								*/
+      GC_printf0("");
+#   endif      
+
+    /* Check all debugged objects for consistency */
+        if (GC_debugging_started) {
+            (*GC_check_heap)();
+        }
+    
+#   ifdef PRINTTIMES
+	GET_TIME(current_time);
+	GC_printf1("World-stopped marking took %lu msecs\n",
+	           MS_TIME_DIFF(current_time,start_time));
+#   endif
+    START_WORLD();
+    return(TRUE);
+}
+
+
+/* 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
+    if (GC_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);
+	      }
+	    }
+	  }
+	}
+	GC_start_reclaim(TRUE);
+	  /* The above just checks; it doesn't really reclaim anything. */
+    }
+
+    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        */
+    /* (or GC_find_leak is set and they were intentionally marked.)	 */
+    /* 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);
+
+#   ifdef PRINTSTATS
+	GC_printf2(
+		  "Immediately reclaimed %ld bytes in heap of size %lu bytes",
+	          (long)WORDS_TO_BYTES(GC_mem_found),
+	          (unsigned long)GC_heapsize);
+#	ifdef USE_MUNMAP
+	  GC_printf1("(%lu unmapped)", GC_unmapped_bytes);
+#	endif
+	GC_printf2(
+		"\n%lu (atomic) + %lu (composite) collectable bytes in use\n",
+	        (unsigned long)WORDS_TO_BYTES(GC_atomic_in_use),
+	        (unsigned long)WORDS_TO_BYTES(GC_composite_in_use));
+#   endif
+
+      GC_n_attempts = 0;
+    /* 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 USE_MUNMAP
+      GC_unmap_old();
+#   endif
+#   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 */
+# if defined(__STDC__) || defined(__cplusplus)
+    int GC_try_to_collect(GC_stop_func stop_func)
+# else
+    int GC_try_to_collect(stop_func)
+    GC_stop_func stop_func;
+# endif
+{
+    int result;
+    DCL_LOCK_STATE;
+    
+    GC_INVOKE_FINALIZERS();
+    DISABLE_SIGNALS();
+    LOCK();
+    ENTER_GC();
+    if (!GC_is_initialized) GC_init_inner();
+    /* Minimize junk left in my registers */
+      GC_noop(0,0,0,0,0,0);
+    result = (int)GC_try_to_collect_inner(stop_func);
+    EXIT_GC();
+    UNLOCK();
+    ENABLE_SIGNALS();
+    if(result) GC_INVOKE_FINALIZERS();
+    return(result);
+}
+
+void GC_gcollect GC_PROTO(())
+{
+    GC_notify_full_gc();
+    (void)GC_try_to_collect(GC_never_stop_func);
+}
+
+word GC_n_heap_sects = 0;	/* Number of sections currently in heap. */
+
+/*
+ * Use the chunk of memory starting at p of size 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;
+    hdr * phdr;
+    
+    if (GC_n_heap_sects >= 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);
+    phdr = HDR(p);
+    phdr -> hb_sz = words;
+    phdr -> hb_map = (char *)1;   /* A value != GC_invalid_map	*/
+    phdr -> hb_flags = 0;
+    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;
+    }
+}
+
+# if !defined(NO_DEBUGGING)
+void GC_print_heap_sects()
+{
+    register unsigned i;
+    
+    GC_printf1("Total heap size: %lu\n", (unsigned long) GC_heapsize);
+    for (i = 0; i < GC_n_heap_sects; i++) {
+        unsigned long start = (unsigned long) GC_heap_sects[i].hs_start;
+        unsigned long len = (unsigned long) GC_heap_sects[i].hs_bytes;
+        struct hblk *h;
+        unsigned nbl = 0;
+        
+    	GC_printf3("Section %ld from 0x%lx to 0x%lx ", (unsigned long)i,
+    		   start, (unsigned long)(start + len));
+    	for (h = (struct hblk *)start; h < (struct hblk *)(start + len); h++) {
+    	    if (GC_is_black_listed(h, HBLKSIZE)) nbl++;
+    	}
+    	GC_printf2("%lu/%lu blacklisted\n", (unsigned long)nbl,
+    		   (unsigned long)(len/HBLKSIZE));
+    }
+}
+# endif
+
+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);
+}
+
+# if defined(__STDC__) || defined(__cplusplus)
+    void GC_set_max_heap_size(GC_word n)
+# else
+    void GC_set_max_heap_size(n)
+    GC_word n;
+# endif
+{
+    GC_max_heapsize = n;
+}
+
+GC_word GC_max_retries = 0;
+
+/*
+ * 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.
+ */
+GC_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;
+    /* Make sure bytes is a multiple of GC_page_size */
+      {
+	word mask = GC_page_size - 1;
+	bytes += mask;
+	bytes &= ~mask;
+      }
+    
+    if (GC_max_heapsize != 0 && GC_heapsize + bytes > GC_max_heapsize) {
+        /* Exceeded self-imposed limit */
+        return(FALSE);
+    }
+    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));
+# 	ifdef UNDEFINED
+	  GC_printf1("Root size = %lu\n", GC_root_size);
+	  GC_print_block_list(); GC_print_hblkfreelist();
+	  GC_printf0("\n");
+#	endif
+#   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. */
+/* Arguments is in bytes.						*/
+# if defined(__STDC__) || defined(__cplusplus)
+  int GC_expand_hp(size_t bytes)
+# else
+  int GC_expand_hp(bytes)
+  size_t bytes;
+# endif
+{
+    int result;
+    DCL_LOCK_STATE;
+    
+    DISABLE_SIGNALS();
+    LOCK();
+    if (!GC_is_initialized) GC_init_inner();
+    result = (int)GC_expand_hp_inner(divHBLKSZ((word)bytes));
+    UNLOCK();
+    ENABLE_SIGNALS();
+    return(result);
+}
+
+unsigned GC_fail_count = 0;  
+			/* How many consecutive GC/expansion failures?	*/
+			/* Reset by GC_allochblk.			*/
+
+GC_bool GC_collect_or_expand(needed_blocks, ignore_off_page)
+word needed_blocks;
+GC_bool ignore_off_page;
+{
+    if (!GC_incremental && !GC_dont_gc && GC_should_collect()) {
+      GC_notify_full_gc();
+      GC_gcollect_inner();
+    } else {
+      word blocks_to_get = GC_heapsize/(HBLKSIZE*GC_free_space_divisor)
+      			   + needed_blocks;
+      
+      if (blocks_to_get > MAXHINCR) {
+          word slop;
+          
+          if (ignore_off_page) {
+              slop = 4;
+          } else {
+	      slop = 2*divHBLKSZ(BL_LIMIT);
+	      if (slop > needed_blocks) slop = needed_blocks;
+	  }
+          if (needed_blocks + slop > MAXHINCR) {
+              blocks_to_get = needed_blocks + slop;
+          } else {
+              blocks_to_get = MAXHINCR;
+          }
+      }
+      if (!GC_expand_hp_inner(blocks_to_get)
+        && !GC_expand_hp_inner(needed_blocks)) {
+      	if (GC_fail_count++ < GC_max_retries) {
+      	    WARN("Out of Memory!  Trying to continue ...\n", 0);
+	    GC_notify_full_gc();
+	    GC_gcollect_inner();
+	} else {
+	    WARN("Out of Memory!  Returning NIL!\n", 0);
+	    return(FALSE);
+	}
+      } else {
+#	  ifdef PRINTSTATS
+            if (GC_fail_count) {
+	      GC_printf0("Memory available again ...\n");
+	    }
+#	  endif
+      }
+    }
+    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) {
+      ENTER_GC();
+      /* Do our share of marking work */
+        if(GC_incremental && !GC_dont_gc) GC_collect_a_little_inner(1);
+      /* Sweep blocks for objects of this size */
+          GC_continue_reclaim(sz, kind);
+      EXIT_GC();
+      if (*flh == 0) {
+        GC_new_hblk(sz, kind);
+      }
+      if (*flh == 0) {
+        ENTER_GC();
+        if (!GC_collect_or_expand((word)1,FALSE)) {
+	    EXIT_GC();
+	    return(0);
+	}
+	EXIT_GC();
+      }
+    }
+    
+    return(*flh);
+}