/*
* Copyright (c) 1991-1994 by Xerox Corporation. All rights reserved.
* Copyright (c) 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.
*
* 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.
*
*/
/*
* This contains interfaces to the GC marker that are likely to be useful to
* clients that provide detailed heap layout information to the collector.
* This interface should not be used by normal C or C++ clients.
* It will be useful to runtimes for other languages.
*
* Note that this file is not "namespace-clean", i.e. it introduces names
* not prefixed with GC_, which may collide with the client's names. It
* should be included only in those few places that directly provide
* information to the collector.
*/
#ifndef GC_MARK_H
# define GC_MARK_H
# ifndef GC_H
# include "gc.h"
# endif
/* A client supplied mark procedure. Returns new mark stack pointer. */
/* Primary effect should be to push new entries on the mark stack. */
/* Mark stack pointer values are passed and returned explicitly. */
/* Global variables decribing mark stack are not necessarily valid. */
/* (This usually saves a few cycles by keeping things in registers.) */
/* Assumed to scan about GC_PROC_BYTES on average. If it needs to do */
/* much more work than that, it should do it in smaller pieces by */
/* pushing itself back on the mark stack. */
/* Note that it should always do some work (defined as marking some */
/* objects) before pushing more than one entry on the mark stack. */
/* This is required to ensure termination in the event of mark stack */
/* overflows. */
/* This procedure is always called with at least one empty entry on the */
/* mark stack. */
/* Currently we require that mark procedures look for pointers in a */
/* subset of the places the conservative marker would. It must be safe */
/* to invoke the normal mark procedure instead. */
/* WARNING: Such a mark procedure may be invoked on an unused object */
/* residing on a free list. Such objects are cleared, except for a */
/* free list link field in the first word. Thus mark procedures may */
/* not count on the presence of a type descriptor, and must handle this */
/* case correctly somehow. */
# define GC_PROC_BYTES 100
struct GC_ms_entry;
typedef struct GC_ms_entry * (*GC_mark_proc) GC_PROTO((
GC_word * addr, struct GC_ms_entry * mark_stack_ptr,
struct GC_ms_entry * mark_stack_limit, GC_word env));
# define GC_LOG_MAX_MARK_PROCS 6
# define GC_MAX_MARK_PROCS (1 << GC_LOG_MAX_MARK_PROCS)
/* In a few cases it's necessary to assign statically known indices to */
/* certain mark procs. Thus we reserve a few for well known clients. */
/* (This is necessary if mark descriptors are compiler generated.) */
#define GC_RESERVED_MARK_PROCS 8
# define GC_GCJ_RESERVED_MARK_PROC_INDEX 0
/* Object descriptors on mark stack or in objects. Low order two */
/* bits are tags distinguishing among the following 4 possibilities */
/* for the high order 30 bits. */
#define GC_DS_TAG_BITS 2
#define GC_DS_TAGS ((1 << GC_DS_TAG_BITS) - 1)
#define GC_DS_LENGTH 0 /* The entire word is a length in bytes that */
/* must be a multiple of 4. */
#define GC_DS_BITMAP 1 /* 30 (62) bits are a bitmap describing pointer */
/* fields. The msb is 1 iff the first word */
/* is a pointer. */
/* (This unconventional ordering sometimes */
/* makes the marker slightly faster.) */
/* Zeroes indicate definite nonpointers. Ones */
/* indicate possible pointers. */
/* Only usable if pointers are word aligned. */
#define GC_DS_PROC 2
/* The objects referenced by this object can be */
/* pushed on the mark stack by invoking */
/* PROC(descr). ENV(descr) is passed as the */
/* last argument. */
# define GC_MAKE_PROC(proc_index, env) \
(((((env) << GC_LOG_MAX_MARK_PROCS) \
| (proc_index)) << GC_DS_TAG_BITS) | GC_DS_PROC)
#define GC_DS_PER_OBJECT 3 /* The real descriptor is at the */
/* byte displacement from the beginning of the */
/* object given by descr & ~DS_TAGS */
/* If the descriptor is negative, the real */
/* descriptor is at (*<object_start>) - */
/* (descr & ~DS_TAGS) - GC_INDIR_PER_OBJ_BIAS */
/* The latter alternative can be used if each */
/* object contains a type descriptor in the */
/* first word. */
/* Note that in multithreaded environments */
/* per object descriptors maust be located in */
/* either the first two or last two words of */
/* the object, since only those are guaranteed */
/* to be cleared while the allocation lock is */
/* held. */
#define GC_INDIR_PER_OBJ_BIAS 0x10
extern GC_PTR GC_least_plausible_heap_addr;
extern GC_PTR GC_greatest_plausible_heap_addr;
/* Bounds on the heap. Guaranteed valid */
/* Likely to include future heap expansion. */
/* Handle nested references in a custom mark procedure. */
/* Check if obj is a valid object. If so, ensure that it is marked. */
/* If it was not previously marked, push its contents onto the mark */
/* stack for future scanning. The object will then be scanned using */
/* its mark descriptor. */
/* Returns the new mark stack pointer. */
/* Handles mark stack overflows correctly. */
/* Since this marks first, it makes progress even if there are mark */
/* stack overflows. */
/* Src is the address of the pointer to obj, which is used only */
/* for back pointer-based heap debugging. */
/* It is strongly recommended that most objects be handled without mark */
/* procedures, e.g. with bitmap descriptors, and that mark procedures */
/* be reserved for exceptional cases. That will ensure that */
/* performance of this call is not extremely performance critical. */
/* (Otherwise we would need to inline GC_mark_and_push completely, */
/* which would tie the client code to a fixed colllector version.) */
struct GC_ms_entry *GC_mark_and_push
GC_PROTO((GC_PTR obj,
struct GC_ms_entry * mark_stack_ptr,
struct GC_ms_entry * mark_stack_limit, GC_PTR *src));
#define GC_MARK_AND_PUSH(obj, msp, lim, src) \
(((GC_word)obj >= (GC_word)GC_least_plausible_heap_addr && \
(GC_word)obj <= (GC_word)GC_greatest_plausible_heap_addr)? \
GC_mark_and_push(obj, msp, lim, src) : \
msp)
#endif /* GC_MARK_H */
