source: trunk/gcc/boehm-gc/include/gc_mark.h

Last change on this file was 2, checked in by bird, 22 years ago

Initial revision
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File size: 6.6 KB
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1/*
2 * Copyright (c) 1991-1994 by Xerox Corporation. All rights reserved.
3 * Copyright (c) 2001 by Hewlett-Packard Company. All rights reserved.
4 *
5 * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
6 * OR IMPLIED. ANY USE IS AT YOUR OWN RISK.
7 *
8 * Permission is hereby granted to use or copy this program
9 * for any purpose, provided the above notices are retained on all copies.
10 * Permission to modify the code and to distribute modified code is granted,
11 * provided the above notices are retained, and a notice that the code was
12 * modified is included with the above copyright notice.
13 *
14 */
15
16/*
17 * This contains interfaces to the GC marker that are likely to be useful to
18 * clients that provide detailed heap layout information to the collector.
19 * This interface should not be used by normal C or C++ clients.
20 * It will be useful to runtimes for other languages.
21 *
22 * Note that this file is not "namespace-clean", i.e. it introduces names
23 * not prefixed with GC_, which may collide with the client's names. It
24 * should be included only in those few places that directly provide
25 * information to the collector.
26 */
27#ifndef GC_MARK_H
28# define GC_MARK_H
29
30# ifndef GC_H
31# include "gc.h"
32# endif
33
34/* A client supplied mark procedure. Returns new mark stack pointer. */
35/* Primary effect should be to push new entries on the mark stack. */
36/* Mark stack pointer values are passed and returned explicitly. */
37/* Global variables decribing mark stack are not necessarily valid. */
38/* (This usually saves a few cycles by keeping things in registers.) */
39/* Assumed to scan about GC_PROC_BYTES on average. If it needs to do */
40/* much more work than that, it should do it in smaller pieces by */
41/* pushing itself back on the mark stack. */
42/* Note that it should always do some work (defined as marking some */
43/* objects) before pushing more than one entry on the mark stack. */
44/* This is required to ensure termination in the event of mark stack */
45/* overflows. */
46/* This procedure is always called with at least one empty entry on the */
47/* mark stack. */
48/* Currently we require that mark procedures look for pointers in a */
49/* subset of the places the conservative marker would. It must be safe */
50/* to invoke the normal mark procedure instead. */
51/* WARNING: Such a mark procedure may be invoked on an unused object */
52/* residing on a free list. Such objects are cleared, except for a */
53/* free list link field in the first word. Thus mark procedures may */
54/* not count on the presence of a type descriptor, and must handle this */
55/* case correctly somehow. */
56# define GC_PROC_BYTES 100
57struct GC_ms_entry;
58typedef struct GC_ms_entry * (*GC_mark_proc) GC_PROTO((
59 GC_word * addr, struct GC_ms_entry * mark_stack_ptr,
60 struct GC_ms_entry * mark_stack_limit, GC_word env));
61
62# define GC_LOG_MAX_MARK_PROCS 6
63# define GC_MAX_MARK_PROCS (1 << GC_LOG_MAX_MARK_PROCS)
64
65/* In a few cases it's necessary to assign statically known indices to */
66/* certain mark procs. Thus we reserve a few for well known clients. */
67/* (This is necessary if mark descriptors are compiler generated.) */
68#define GC_RESERVED_MARK_PROCS 8
69# define GC_GCJ_RESERVED_MARK_PROC_INDEX 0
70
71/* Object descriptors on mark stack or in objects. Low order two */
72/* bits are tags distinguishing among the following 4 possibilities */
73/* for the high order 30 bits. */
74#define GC_DS_TAG_BITS 2
75#define GC_DS_TAGS ((1 << GC_DS_TAG_BITS) - 1)
76#define GC_DS_LENGTH 0 /* The entire word is a length in bytes that */
77 /* must be a multiple of 4. */
78#define GC_DS_BITMAP 1 /* 30 (62) bits are a bitmap describing pointer */
79 /* fields. The msb is 1 iff the first word */
80 /* is a pointer. */
81 /* (This unconventional ordering sometimes */
82 /* makes the marker slightly faster.) */
83 /* Zeroes indicate definite nonpointers. Ones */
84 /* indicate possible pointers. */
85 /* Only usable if pointers are word aligned. */
86#define GC_DS_PROC 2
87 /* The objects referenced by this object can be */
88 /* pushed on the mark stack by invoking */
89 /* PROC(descr). ENV(descr) is passed as the */
90 /* last argument. */
91# define GC_MAKE_PROC(proc_index, env) \
92 (((((env) << GC_LOG_MAX_MARK_PROCS) \
93 | (proc_index)) << GC_DS_TAG_BITS) | GC_DS_PROC)
94#define GC_DS_PER_OBJECT 3 /* The real descriptor is at the */
95 /* byte displacement from the beginning of the */
96 /* object given by descr & ~DS_TAGS */
97 /* If the descriptor is negative, the real */
98 /* descriptor is at (*<object_start>) - */
99 /* (descr & ~DS_TAGS) - GC_INDIR_PER_OBJ_BIAS */
100 /* The latter alternative can be used if each */
101 /* object contains a type descriptor in the */
102 /* first word. */
103 /* Note that in multithreaded environments */
104 /* per object descriptors maust be located in */
105 /* either the first two or last two words of */
106 /* the object, since only those are guaranteed */
107 /* to be cleared while the allocation lock is */
108 /* held. */
109#define GC_INDIR_PER_OBJ_BIAS 0x10
110
111extern GC_PTR GC_least_plausible_heap_addr;
112extern GC_PTR GC_greatest_plausible_heap_addr;
113 /* Bounds on the heap. Guaranteed valid */
114 /* Likely to include future heap expansion. */
115
116/* Handle nested references in a custom mark procedure. */
117/* Check if obj is a valid object. If so, ensure that it is marked. */
118/* If it was not previously marked, push its contents onto the mark */
119/* stack for future scanning. The object will then be scanned using */
120/* its mark descriptor. */
121/* Returns the new mark stack pointer. */
122/* Handles mark stack overflows correctly. */
123/* Since this marks first, it makes progress even if there are mark */
124/* stack overflows. */
125/* Src is the address of the pointer to obj, which is used only */
126/* for back pointer-based heap debugging. */
127/* It is strongly recommended that most objects be handled without mark */
128/* procedures, e.g. with bitmap descriptors, and that mark procedures */
129/* be reserved for exceptional cases. That will ensure that */
130/* performance of this call is not extremely performance critical. */
131/* (Otherwise we would need to inline GC_mark_and_push completely, */
132/* which would tie the client code to a fixed colllector version.) */
133struct GC_ms_entry *GC_mark_and_push
134 GC_PROTO((GC_PTR obj,
135 struct GC_ms_entry * mark_stack_ptr,
136 struct GC_ms_entry * mark_stack_limit, GC_PTR *src));
137
138#define GC_MARK_AND_PUSH(obj, msp, lim, src) \
139 (((GC_word)obj >= (GC_word)GC_least_plausible_heap_addr && \
140 (GC_word)obj <= (GC_word)GC_greatest_plausible_heap_addr)? \
141 GC_mark_and_push(obj, msp, lim, src) : \
142 msp)
143
144#endif /* GC_MARK_H */
145
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