path: root/gc.h

/* 
 * Copyright 1988, 1989 Hans-J. Boehm, Alan J. Demers
 * Copyright (c) 1991-1995 by Xerox Corporation.  All rights reserved.
 * Copyright 1996 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.
 */

/*
 * Note that this defines a large number of tuning hooks, which can
 * safely be ignored in nearly all cases.  For normal use it suffices
 * to call only GC_MALLOC and perhaps GC_REALLOC.
 * For better performance, also look at GC_MALLOC_ATOMIC, and
 * GC_enable_incremental.  If you need an action to be performed
 * immediately before an object is collected, look at GC_register_finalizer.
 * If you are using Solaris threads, look at the end of this file.
 * Everything else is best ignored unless you encounter performance
 * problems.
 */
 
#ifndef _GC_H

# define _GC_H
# define __GC
# include <stddef.h>

#if defined(__CYGWIN32__) && defined(GC_USE_DLL)
#include "libgc_globals.h"
#endif

#if defined(_MSC_VER) && defined(_DLL)
#ifdef GC_BUILD
#define GC_API __declspec(dllexport)
#else
#define GC_API __declspec(dllimport)
#endif
#endif

#ifndef GC_API
#define GC_API extern
#endif

# if defined(__STDC__) || defined(__cplusplus)
#   define GC_PROTO(args) args
    typedef void * GC_PTR;
# else
#   define GC_PROTO(args) ()
    typedef char * GC_PTR;
#  endif

# ifdef __cplusplus
    extern "C" {
# endif


/* Define word and signed_word to be unsigned and signed types of the 	*/
/* size as char * or void *.  There seems to be no way to do this	*/
/* even semi-portably.  The following is probably no better/worse 	*/
/* than almost anything else.						*/
/* The ANSI standard suggests that size_t and ptr_diff_t might be 	*/
/* better choices.  But those appear to have incorrect definitions	*/
/* on may systems.  Notably "typedef int size_t" seems to be both	*/
/* frequent and WRONG.							*/
typedef unsigned long GC_word;
typedef long GC_signed_word;

/* Public read-only variables */

GC_API GC_word GC_gc_no;/* Counter incremented per collection.  	*/
			/* Includes empty GCs at startup.		*/
			

/* Public R/W variables */

GC_API GC_PTR (*GC_oom_fn) GC_PROTO((size_t bytes_requested));
			/* When there is insufficient memory to satisfy */
			/* an allocation request, we return		*/
			/* (*GC_oom_fn)().  By default this just	*/
			/* returns 0.					*/
			/* If it returns, it must return 0 or a valid	*/
			/* pointer to a previously allocated heap 	*/
			/* object.					*/

GC_API int GC_quiet;	/* Disable statistics output.  Only matters if	*/
			/* collector has been compiled with statistics	*/
			/* enabled.  This involves a performance cost,	*/
			/* and is thus not the default.			*/

GC_API int GC_dont_gc;	/* Dont collect unless explicitly requested, e.g. */
			/* because it's not safe.			  */

GC_API int GC_dont_expand;
			/* Dont expand heap unless explicitly requested */
			/* or forced to.				*/

GC_API int GC_full_freq;    /* Number of partial collections between	*/
			    /* full collections.  Matters only if	*/
			    /* GC_incremental is set.			*/
			
GC_API GC_word GC_non_gc_bytes;
			/* Bytes not considered candidates for collection. */
			/* Used only to control scheduling of collections. */

GC_API GC_word GC_free_space_divisor;
			/* We try to make sure that we allocate at 	*/
			/* least N/GC_free_space_divisor bytes between	*/
			/* collections, where N is the heap size plus	*/
			/* a rough estimate of the root set size.	*/
			/* Initially, GC_free_space_divisor = 4.	*/
			/* Increasing its value will use less space	*/
			/* but more collection time.  Decreasing it	*/
			/* will appreciably decrease collection time	*/
			/* at the expense of space.			*/
			/* GC_free_space_divisor = 1 will effectively	*/
			/* disable collections.				*/

GC_API GC_word GC_max_retries;
			/* The maximum number of GCs attempted before	*/
			/* reporting out of memory after heap		*/
			/* expansion fails.  Initially 0.		*/
			
			
/* Public procedures */
/*
 * general purpose allocation routines, with roughly malloc calling conv.
 * The atomic versions promise that no relevant pointers are contained
 * in the object.  The nonatomic versions guarantee that the new object
 * is cleared.  GC_malloc_stubborn promises that no changes to the object
 * will occur after GC_end_stubborn_change has been called on the
 * result of GC_malloc_stubborn. GC_malloc_uncollectable allocates an object
 * that is scanned for pointers to collectable objects, but is not itself
 * collectable.  GC_malloc_uncollectable and GC_free called on the resulting
 * object implicitly update GC_non_gc_bytes appropriately.
 */
GC_API GC_PTR GC_malloc GC_PROTO((size_t size_in_bytes));
GC_API GC_PTR GC_malloc_atomic GC_PROTO((size_t size_in_bytes));
GC_API GC_PTR GC_malloc_uncollectable GC_PROTO((size_t size_in_bytes));
GC_API GC_PTR GC_malloc_stubborn GC_PROTO((size_t size_in_bytes));

/* The following is only defined if the library has been suitably	*/
/* compiled:								*/
GC_API GC_PTR GC_malloc_atomic_uncollectable GC_PROTO((size_t size_in_bytes));

/* Explicitly deallocate an object.  Dangerous if used incorrectly.     */
/* Requires a pointer to the base of an object.				*/
/* If the argument is stubborn, it should not be changeable when freed. */
/* An object should not be enable for finalization when it is 		*/
/* explicitly deallocated.						*/
/* GC_free(0) is a no-op, as required by ANSI C for free.		*/
GC_API void GC_free GC_PROTO((GC_PTR object_addr));

/*
 * Stubborn objects may be changed only if the collector is explicitly informed.
 * The collector is implicitly informed of coming change when such
 * an object is first allocated.  The following routines inform the
 * collector that an object will no longer be changed, or that it will
 * once again be changed.  Only nonNIL pointer stores into the object
 * are considered to be changes.  The argument to GC_end_stubborn_change
 * must be exacly the value returned by GC_malloc_stubborn or passed to
 * GC_change_stubborn.  (In the second case it may be an interior pointer
 * within 512 bytes of the beginning of the objects.)
 * There is a performance penalty for allowing more than
 * one stubborn object to be changed at once, but it is acceptable to
 * do so.  The same applies to dropping stubborn objects that are still
 * changeable.
 */
GC_API void GC_change_stubborn GC_PROTO((GC_PTR));
GC_API void GC_end_stubborn_change GC_PROTO((GC_PTR));

/* Return a pointer to the base (lowest address) of an object given	*/
/* a pointer to a location within the object.				*/
/* Return 0 if displaced_pointer doesn't point to within a valid	*/
/* object.								*/
GC_API GC_PTR GC_base GC_PROTO((GC_PTR displaced_pointer));

/* Given a pointer to the base of an object, return its size in bytes.	*/
/* The returned size may be slightly larger than what was originally	*/
/* requested.								*/
GC_API size_t GC_size GC_PROTO((GC_PTR object_addr));

/* For compatibility with C library.  This is occasionally faster than	*/
/* a malloc followed by a bcopy.  But if you rely on that, either here	*/
/* or with the standard C library, your code is broken.  In my		*/
/* opinion, it shouldn't have been invented, but now we're stuck. -HB	*/
/* The resulting object has the same kind as the original.		*/
/* If the argument is stubborn, the result will have changes enabled.	*/
/* It is an error to have changes enabled for the original object.	*/
/* Follows ANSI comventions for NULL old_object.			*/
GC_API GC_PTR GC_realloc GC_PROTO((GC_PTR old_object,
				   size_t new_size_in_bytes));
				   
/* Explicitly increase the heap size.	*/
/* Returns 0 on failure, 1 on success.  */
GC_API int GC_expand_hp GC_PROTO((size_t number_of_bytes));

/* Limit the heap size to n bytes.  Useful when you're debugging, 	*/
/* especially on systems that don't handle running out of memory well.	*/
/* n == 0 ==> unbounded.  This is the default.				*/
GC_API void GC_set_max_heap_size GC_PROTO((GC_word n));

/* Inform the collector that a certain section of statically allocated	*/
/* memory contains no pointers to garbage collected memory.  Thus it 	*/
/* need not be scanned.  This is sometimes important if the application */
/* maps large read/write files into the address space, which could be	*/
/* mistaken for dynamic library data segments on some systems.		*/
GC_API void GC_exclude_static_roots GC_PROTO((GC_PTR start, GC_PTR finish));

/* Clear the set of root segments.  Wizards only. */
GC_API void GC_clear_roots GC_PROTO((void));

/* Add a root segment.  Wizards only. */
GC_API void GC_add_roots GC_PROTO((char * low_address,
				   char * high_address_plus_1));

/* Add a displacement to the set of those considered valid by the	*/
/* collector.  GC_register_displacement(n) means that if p was returned */
/* by GC_malloc, then (char *)p + n will be considered to be a valid	*/
/* pointer to n.  N must be small and less than the size of p.		*/
/* (All pointers to the interior of objects from the stack are		*/
/* considered valid in any case.  This applies to heap objects and	*/
/* static data.)							*/
/* Preferably, this should be called before any other GC procedures.	*/
/* Calling it later adds to the probability of excess memory		*/
/* retention.								*/
/* This is a no-op if the collector was compiled with recognition of	*/
/* arbitrary interior pointers enabled, which is now the default.	*/
GC_API void GC_register_displacement GC_PROTO((GC_word n));

/* The following version should be used if any debugging allocation is	*/
/* being done.								*/
GC_API void GC_debug_register_displacement GC_PROTO((GC_word n));

/* Explicitly trigger a full, world-stop collection. 	*/
GC_API void GC_gcollect GC_PROTO((void));

/* Trigger a full world-stopped collection.  Abort the collection if 	*/
/* and when stop_func returns a nonzero value.  Stop_func will be 	*/
/* called frequently, and should be reasonably fast.  This works even	*/
/* if virtual dirty bits, and hence incremental collection is not 	*/
/* available for this architecture.  Collections can be aborted faster	*/
/* than normal pause times for incremental collection.  However,	*/
/* aborted collections do no useful work; the next collection needs	*/
/* to start from the beginning.						*/
typedef int (* GC_stop_func) GC_PROTO((void));
GC_API int GC_try_to_collect GC_PROTO((GC_stop_func stop_func));

/* Return the number of bytes in the heap.  Excludes collector private	*/
/* data structures.  Includes empty blocks and fragmentation loss.	*/
/* Includes some pages that were allocated but never written.		*/
GC_API size_t GC_get_heap_size GC_PROTO((void));

/* Return the number of bytes allocated since the last collection.	*/
GC_API size_t GC_get_bytes_since_gc GC_PROTO((void));

/* Enable incremental/generational collection.	*/
/* Not advisable unless dirty bits are 		*/
/* available or most heap objects are		*/
/* pointerfree(atomic) or immutable.		*/
/* Don't use in leak finding mode.		*/
/* Ignored if GC_dont_gc is true.		*/
GC_API void GC_enable_incremental GC_PROTO((void));

/* Perform some garbage collection work, if appropriate.	*/
/* Return 0 if there is no more work to be done.		*/
/* Typically performs an amount of work corresponding roughly	*/
/* to marking from one page.  May do more work if further	*/
/* progress requires it, e.g. if incremental collection is	*/
/* disabled.  It is reasonable to call this in a wait loop	*/
/* until it returns 0.						*/
GC_API int GC_collect_a_little GC_PROTO((void));

/* Allocate an object of size lb bytes.  The client guarantees that	*/
/* as long as the object is live, it will be referenced by a pointer	*/
/* that points to somewhere within the first 256 bytes of the object.	*/
/* (This should normally be declared volatile to prevent the compiler	*/
/* from invalidating this assertion.)  This routine is only useful	*/
/* if a large array is being allocated.  It reduces the chance of 	*/
/* accidentally retaining such an array as a result of scanning an	*/
/* integer that happens to be an address inside the array.  (Actually,	*/
/* it reduces the chance of the allocator not finding space for such	*/
/* an array, since it will try hard to avoid introducing such a false	*/
/* reference.)  On a SunOS 4.X or MS Windows system this is recommended */
/* for arrays likely to be larger than 100K or so.  For other systems,	*/
/* or if the collector is not configured to recognize all interior	*/
/* pointers, the threshold is normally much higher.			*/
GC_API GC_PTR GC_malloc_ignore_off_page GC_PROTO((size_t lb));
GC_API GC_PTR GC_malloc_atomic_ignore_off_page GC_PROTO((size_t lb));

/* Debugging (annotated) allocation.  GC_gcollect will check 		*/
/* objects allocated in this way for overwrites, etc.			*/
GC_API GC_PTR GC_debug_malloc
	GC_PROTO((size_t size_in_bytes, char * descr_string, int descr_int));
GC_API GC_PTR GC_debug_malloc_atomic
	GC_PROTO((size_t size_in_bytes, char * descr_string, int descr_int));
GC_API GC_PTR GC_debug_malloc_uncollectable
	GC_PROTO((size_t size_in_bytes, char * descr_string, int descr_int));
GC_API GC_PTR GC_debug_malloc_stubborn
	GC_PROTO((size_t size_in_bytes, char * descr_string, int descr_int));
GC_API void GC_debug_free GC_PROTO((GC_PTR object_addr));
GC_API GC_PTR GC_debug_realloc
	GC_PROTO((GC_PTR old_object, size_t new_size_in_bytes,
  		  char * descr_string, int descr_int));
  			 	 
GC_API void GC_debug_change_stubborn GC_PROTO((GC_PTR));
GC_API void GC_debug_end_stubborn_change GC_PROTO((GC_PTR));
# ifdef GC_DEBUG
#   define GC_MALLOC(sz) GC_debug_malloc(sz, __FILE__, __LINE__)
#   define GC_MALLOC_ATOMIC(sz) GC_debug_malloc_atomic(sz, __FILE__, __LINE__)
#   define GC_MALLOC_UNCOLLECTABLE(sz) GC_debug_malloc_uncollectable(sz, \
							__FILE__, __LINE__)
#   define GC_REALLOC(old, sz) GC_debug_realloc(old, sz, __FILE__, \
							       __LINE__)
#   define GC_FREE(p) GC_debug_free(p)
#   define GC_REGISTER_FINALIZER(p, f, d, of, od) \
	GC_debug_register_finalizer(p, f, d, of, od)
#   define GC_REGISTER_FINALIZER_IGNORE_SELF(p, f, d, of, od) \
	GC_debug_register_finalizer_ignore_self(p, f, d, of, od)
#   define GC_MALLOC_STUBBORN(sz) GC_debug_malloc_stubborn(sz, __FILE__, \
							       __LINE__)
#   define GC_CHANGE_STUBBORN(p) GC_debug_change_stubborn(p)
#   define GC_END_STUBBORN_CHANGE(p) GC_debug_end_stubborn_change(p)
#   define GC_GENERAL_REGISTER_DISAPPEARING_LINK(link, obj) \
	GC_general_register_disappearing_link(link, GC_base(obj))
#   define GC_REGISTER_DISPLACEMENT(n) GC_debug_register_displacement(n)
# else
#   define GC_MALLOC(sz) GC_malloc(sz)
#   define GC_MALLOC_ATOMIC(sz) GC_malloc_atomic(sz)
#   define GC_MALLOC_UNCOLLECTABLE(sz) GC_malloc_uncollectable(sz)
#   define GC_REALLOC(old, sz) GC_realloc(old, sz)
#   define GC_FREE(p) GC_free(p)
#   define GC_REGISTER_FINALIZER(p, f, d, of, od) \
	GC_register_finalizer(p, f, d, of, od)
#   define GC_REGISTER_FINALIZER_IGNORE_SELF(p, f, d, of, od) \
	GC_register_finalizer_ignore_self(p, f, d, of, od)
#   define GC_MALLOC_STUBBORN(sz) GC_malloc_stubborn(sz)
#   define GC_CHANGE_STUBBORN(p) GC_change_stubborn(p)
#   define GC_END_STUBBORN_CHANGE(p) GC_end_stubborn_change(p)
#   define GC_GENERAL_REGISTER_DISAPPEARING_LINK(link, obj) \
	GC_general_register_disappearing_link(link, obj)
#   define GC_REGISTER_DISPLACEMENT(n) GC_register_displacement(n)
# endif
/* The following are included because they are often convenient, and	*/
/* reduce the chance for a misspecifed size argument.  But calls may	*/
/* expand to something syntactically incorrect if t is a complicated	*/
/* type expression.  							*/
# define GC_NEW(t) (t *)GC_MALLOC(sizeof (t))
# define GC_NEW_ATOMIC(t) (t *)GC_MALLOC_ATOMIC(sizeof (t))
# define GC_NEW_STUBBORN(t) (t *)GC_MALLOC_STUBBORN(sizeof (t))
# define GC_NEW_UNCOLLECTABLE(t) (t *)GC_MALLOC_UNCOLLECTABLE(sizeof (t))

/* Finalization.  Some of these primitives are grossly unsafe.		*/
/* The idea is to make them both cheap, and sufficient to build		*/
/* a safer layer, closer to PCedar finalization.			*/
/* The interface represents my conclusions from a long discussion	*/
/* with Alan Demers, Dan Greene, Carl Hauser, Barry Hayes, 		*/
/* Christian Jacobi, and Russ Atkinson.  It's not perfect, and		*/
/* probably nobody else agrees with it.	    Hans-J. Boehm  3/13/92	*/
typedef void (*GC_finalization_proc)
  	GC_PROTO((GC_PTR obj, GC_PTR client_data));

GC_API void GC_register_finalizer
    	GC_PROTO((GC_PTR obj, GC_finalization_proc fn, GC_PTR cd,
		  GC_finalization_proc *ofn, GC_PTR *ocd));
GC_API void GC_debug_register_finalizer
    	GC_PROTO((GC_PTR obj, GC_finalization_proc fn, GC_PTR cd,
		  GC_finalization_proc *ofn, GC_PTR *ocd));
	/* When obj is no longer accessible, invoke		*/
	/* (*fn)(obj, cd).  If a and b are inaccessible, and	*/
	/* a points to b (after disappearing links have been	*/
	/* made to disappear), then only a will be		*/
	/* finalized.  (If this does not create any new		*/
	/* pointers to b, then b will be finalized after the	*/
	/* next collection.)  Any finalizable object that	*/
	/* is reachable from itself by following one or more	*/
	/* pointers will not be finalized (or collected).	*/
	/* Thus cycles involving finalizable objects should	*/
	/* be avoided, or broken by disappearing links.		*/
	/* All but the last finalizer registered for an object  */
	/* is ignored.						*/
	/* Finalization may be removed by passing 0 as fn.	*/
	/* Finalizers are implicitly unregistered just before   */
	/* they are invoked.					*/
	/* The old finalizer and client data are stored in	*/
	/* *ofn and *ocd.					*/ 
	/* Fn is never invoked on an accessible object,		*/
	/* provided hidden pointers are converted to real 	*/
	/* pointers only if the allocation lock is held, and	*/
	/* such conversions are not performed by finalization	*/
	/* routines.						*/
	/* If GC_register_finalizer is aborted as a result of	*/
	/* a signal, the object may be left with no		*/
	/* finalization, even if neither the old nor new	*/
	/* finalizer were NULL.					*/
	/* Obj should be the nonNULL starting address of an 	*/
	/* object allocated by GC_malloc or friends.		*/
	/* Note that any garbage collectable object referenced	*/
	/* by cd will be considered accessible until the	*/
	/* finalizer is invoked.				*/

/* Another versions of the above follow.  It ignores		*/
/* self-cycles, i.e. pointers from a finalizable object to	*/
/* itself.  There is a stylistic argument that this is wrong,	*/
/* but it's unavoidable for C++, since the compiler may		*/
/* silently introduce these.  It's also benign in that specific	*/
/* case.							*/
GC_API void GC_register_finalizer_ignore_self
	GC_PROTO((GC_PTR obj, GC_finalization_proc fn, GC_PTR cd,
		  GC_finalization_proc *ofn, GC_PTR *ocd));
GC_API void GC_debug_register_finalizer_ignore_self
	GC_PROTO((GC_PTR obj, GC_finalization_proc fn, GC_PTR cd,
		  GC_finalization_proc *ofn, GC_PTR *ocd));

/* The following routine may be used to break cycles between	*/
/* finalizable objects, thus causing cyclic finalizable		*/
/* objects to be finalized in the correct order.  Standard	*/
/* use involves calling GC_register_disappearing_link(&p),	*/
/* where p is a pointer that is not followed by finalization	*/
/* code, and should not be considered in determining 		*/
/* finalization order.						*/
GC_API int GC_register_disappearing_link GC_PROTO((GC_PTR * /* link */));
	/* Link should point to a field of a heap allocated 	*/
	/* object obj.  *link will be cleared when obj is	*/
	/* found to be inaccessible.  This happens BEFORE any	*/
	/* finalization code is invoked, and BEFORE any		*/
	/* decisions about finalization order are made.		*/
	/* This is useful in telling the finalizer that 	*/
	/* some pointers are not essential for proper		*/
	/* finalization.  This may avoid finalization cycles.	*/
	/* Note that obj may be resurrected by another		*/
	/* finalizer, and thus the clearing of *link may	*/
	/* be visible to non-finalization code.  		*/
	/* There's an argument that an arbitrary action should  */
	/* be allowed here, instead of just clearing a pointer. */
	/* But this causes problems if that action alters, or 	*/
	/* examines connectivity.				*/
	/* Returns 1 if link was already registered, 0		*/
	/* otherwise.						*/
	/* Only exists for backward compatibility.  See below:	*/
	
GC_API int GC_general_register_disappearing_link
	GC_PROTO((GC_PTR * /* link */, GC_PTR obj));
	/* A slight generalization of the above. *link is	*/
	/* cleared when obj first becomes inaccessible.  This	*/
	/* can be used to implement weak pointers easily and	*/
	/* safely. Typically link will point to a location	*/
	/* holding a disguised pointer to obj.  (A pointer 	*/
	/* inside an "atomic" object is effectively  		*/
	/* disguised.)   In this way soft			*/
	/* pointers are broken before any object		*/
	/* reachable from them are finalized.  Each link	*/
	/* May be registered only once, i.e. with one obj	*/
	/* value.  This was added after a long email discussion */
	/* with John Ellis.					*/
	/* Obj must be a pointer to the first word of an object */
	/* we allocated.  It is unsafe to explicitly deallocate */
	/* the object containing link.  Explicitly deallocating */
	/* obj may or may not cause link to eventually be	*/
	/* cleared.						*/
GC_API int GC_unregister_disappearing_link GC_PROTO((GC_PTR * /* link */));
	/* Returns 0 if link was not actually registered.	*/
	/* Undoes a registration by either of the above two	*/
	/* routines.						*/

/* Auxiliary fns to make finalization work correctly with displaced	*/
/* pointers introduced by the debugging allocators.			*/
GC_API GC_PTR GC_make_closure GC_PROTO((GC_finalization_proc fn, GC_PTR data));
GC_API void GC_debug_invoke_finalizer GC_PROTO((GC_PTR obj, GC_PTR data));

/* GC_set_warn_proc can be used to redirect or filter warning messages.	*/
/* p may not be a NULL pointer.						*/
typedef void (*GC_warn_proc) GC_PROTO((char *msg, GC_word arg));
GC_API GC_warn_proc GC_set_warn_proc GC_PROTO((GC_warn_proc p));
    /* Returns old warning procedure.	*/
	
/* The following is intended to be used by a higher level	*/
/* (e.g. cedar-like) finalization facility.  It is expected	*/
/* that finalization code will arrange for hidden pointers to	*/
/* disappear.  Otherwise objects can be accessed after they	*/
/* have been collected.						*/
/* Note that putting pointers in atomic objects or in 		*/
/* nonpointer slots of "typed" objects is equivalent to 	*/
/* disguising them in this way, and may have other advantages.	*/
# if defined(I_HIDE_POINTERS) || defined(GC_I_HIDE_POINTERS)
    typedef GC_word GC_hidden_pointer;
#   define HIDE_POINTER(p) (~(GC_hidden_pointer)(p))
#   define REVEAL_POINTER(p) ((GC_PTR)(HIDE_POINTER(p)))
    /* Converting a hidden pointer to a real pointer requires verifying	*/
    /* that the object still exists.  This involves acquiring the  	*/
    /* allocator lock to avoid a race with the collector.		*/
# endif /* I_HIDE_POINTERS */

typedef GC_PTR (*GC_fn_type) GC_PROTO((GC_PTR client_data));
GC_API GC_PTR GC_call_with_alloc_lock
        	GC_PROTO((GC_fn_type fn, GC_PTR client_data));

/* Check that p and q point to the same object.  		*/
/* Fail conspicuously if they don't.				*/
/* Returns the first argument.  				*/
/* Succeeds if neither p nor q points to the heap.		*/
/* May succeed if both p and q point to between heap objects.	*/
GC_API GC_PTR GC_same_obj GC_PROTO((GC_PTR p, GC_PTR q));

/* Checked pointer pre- and post- increment operations.  Note that	*/
/* the second argument is in units of bytes, not multiples of the	*/
/* object size.  This should either be invoked from a macro, or the	*/
/* call should be automatically generated.				*/
GC_API GC_PTR GC_pre_incr GC_PROTO((GC_PTR *p, size_t how_much));
GC_API GC_PTR GC_post_incr GC_PROTO((GC_PTR *p, size_t how_much));

/* Check that p is visible						*/
/* to the collector as a possibly pointer containing location.		*/
/* If it isn't fail conspicuously.					*/
/* Returns the argument in all cases.  May erroneously succeed		*/
/* in hard cases.  (This is intended for debugging use with		*/
/* untyped allocations.  The idea is that it should be possible, though	*/
/* slow, to add such a call to all indirect pointer stores.)		*/
/* Currently useless for multithreaded worlds.				*/
GC_API GC_PTR GC_is_visible GC_PROTO((GC_PTR p));

/* Check that if p is a pointer to a heap page, then it points to	*/
/* a valid displacement within a heap object.				*/
/* Fail conspicuously if this property does not hold.			*/
/* Uninteresting with ALL_INTERIOR_POINTERS.				*/
/* Always returns its argument.						*/
GC_API GC_PTR GC_is_valid_displacement GC_PROTO((GC_PTR	p));

/* Safer, but slow, pointer addition.  Probably useful mainly with 	*/
/* a preprocessor.  Useful only for heap pointers.			*/
#ifdef GC_DEBUG
#   define GC_PTR_ADD3(x, n, type_of_result) \
	((type_of_result)GC_same_obj((x)+(n), (x)))
#   define GC_PRE_INCR3(x, n, type_of_result) \
	((type_of_result)GC_pre_incr(&(x), (n)*sizeof(*x))
#   define GC_POST_INCR2(x, type_of_result) \
	((type_of_result)GC_post_incr(&(x), sizeof(*x))
#   ifdef __GNUC__
#       define GC_PTR_ADD(x, n) \
	    GC_PTR_ADD3(x, n, typeof(x))
#   define GC_PRE_INCR(x, n) \
	    GC_PRE_INCR3(x, n, typeof(x))
#   define GC_POST_INCR(x, n) \
	    GC_POST_INCR3(x, typeof(x))
#   else
	/* We can't do this right without typeof, which ANSI	*/
	/* decided was not sufficiently useful.  Repeatedly	*/
	/* mentioning the arguments seems too dangerous to be	*/
	/* useful.  So does not casting the result.		*/
#   	define GC_PTR_ADD(x, n) ((x)+(n))
#   endif
#else	/* !GC_DEBUG */
#   define GC_PTR_ADD3(x, n, type_of_result) ((x)+(n))
#   define GC_PTR_ADD(x, n) ((x)+(n))
#   define GC_PRE_INCR3(x, n, type_of_result) ((x) += (n))
#   define GC_PRE_INCR(x, n) ((x) += (n))
#   define GC_POST_INCR2(x, n, type_of_result) ((x)++)
#   define GC_POST_INCR(x, n) ((x)++)
#endif

/* Safer assignment of a pointer to a nonstack location.	*/
#ifdef GC_DEBUG
# ifdef __STDC__
#   define GC_PTR_STORE(p, q) \
	(*(void **)GC_is_visible(p) = GC_is_valid_displacement(q))
# else
#   define GC_PTR_STORE(p, q) \
	(*(char **)GC_is_visible(p) = GC_is_valid_displacement(q))
# endif
#else /* !GC_DEBUG */
#   define GC_PTR_STORE(p, q) *((p) = (q))
#endif

/* Fynctions called to report pointer checking errors */
GC_API void (*GC_same_obj_print_proc) GC_PROTO((GC_PTR p, GC_PTR q));

GC_API void (*GC_is_valid_displacement_print_proc)
	GC_PROTO((GC_PTR p));

GC_API void (*GC_is_visible_print_proc)
	GC_PROTO((GC_PTR p));

#ifdef SOLARIS_THREADS
/* We need to intercept calls to many of the threads primitives, so 	*/
/* that we can locate thread stacks and stop the world.			*/
/* Note also that the collector cannot see thread specific data.	*/
/* Thread specific data should generally consist of pointers to		*/
/* uncollectable objects, which are deallocated using the destructor	*/
/* facility in thr_keycreate.						*/
# include <thread.h>
# include <signal.h>
  int GC_thr_create(void *stack_base, size_t stack_size,
                    void *(*start_routine)(void *), void *arg, long flags,
                    thread_t *new_thread);
  int GC_thr_join(thread_t wait_for, thread_t *departed, void **status);
  int GC_thr_suspend(thread_t target_thread);
  int GC_thr_continue(thread_t target_thread);
  void * GC_dlopen(const char *path, int mode);

# ifdef _SOLARIS_PTHREADS
#   include <pthread.h>
    extern int GC_pthread_create(pthread_t *new_thread,
    			         const pthread_attr_t *attr,
          			 void * (*thread_execp)(void *), void *arg);
    extern int GC_pthread_join(pthread_t wait_for, void **status);

#   undef thread_t

#   define pthread_join GC_pthread_join
#   define pthread_create GC_pthread_create
#endif

# define thr_create GC_thr_create
# define thr_join GC_thr_join
# define thr_suspend GC_thr_suspend
# define thr_continue GC_thr_continue
# define dlopen GC_dlopen

# endif /* SOLARIS_THREADS */


#ifdef IRIX_THREADS
/* We treat these similarly. */
# include <pthread.h>
# include <signal.h>

  int GC_pthread_create(pthread_t *new_thread,
                        const pthread_attr_t *attr,
		        void *(*start_routine)(void *), void *arg);
  int GC_pthread_sigmask(int how, const sigset_t *set, sigset_t *oset);
  int GC_pthread_join(pthread_t thread, void **retval);

# define pthread_create GC_pthread_create
# define pthread_sigmask GC_pthread_sigmask
# define pthread_join GC_pthread_join

#endif /* IRIX_THREADS */

#if defined(SOLARIS_THREADS) || defined(IRIX_THREADS)
/* This returns a list of objects, linked through their first		*/
/* word.  Its use can greatly reduce lock contention problems, since	*/
/* the allocation lock can be acquired and released many fewer times.	*/
GC_PTR GC_malloc_many(size_t lb);
#define GC_NEXT(p) (*(GC_PTR *)(p)) 	/* Retrieve the next element	*/
					/* in returned list.		*/
extern void GC_thr_init();	/* Needed for Solaris/X86	*/

#endif /* SOLARIS_THREADS */

/*
 * If you are planning on putting
 * the collector in a SunOS 5 dynamic library, you need to call GC_INIT()
 * from the statically loaded program section.
 * This circumvents a Solaris 2.X (X<=4) linker bug.
 */
#if defined(sparc) || defined(__sparc)
#   define GC_INIT() { extern end, etext; \
		       GC_noop(&end, &etext); }
#else
# if defined(__CYGWIN32__) && defined(GC_USE_DLL)
    /*
     * Similarly gnu-win32 DLLs need explicit initialization
     */
#   define GC_INIT() { GC_add_roots(DATASTART, DATAEND); }
# else
#   define GC_INIT()
# endif
#endif

#ifdef __WATCOMC__
  /* Ivan Demakov: Programs compiled by Watcom C with -5r option
   * crash without this declaration
   * HB: Could this go into gc_priv.h?
   */
  void GC_noop(void*, ...);
#endif

#ifdef __cplusplus
    }  /* end of extern "C" */
#endif

#endif /* _GC_H */