source: trunk/gc6.8/include/gc_mark.h

Last change on this file was 132, checked in by cinc, 19 years ago

Boehm-Demers-Weiser garbage collector. Single-threaded for OS/2.
File size: 9.1 KB
Line 
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 * This is an experts-only interface! There are many ways to break the
23 * collector in subtle ways by using this functionality.
24 */
25#ifndef GC_MARK_H
26# define GC_MARK_H
27
28# ifndef GC_H
29# include "gc.h"
30# endif
31
32/* A client supplied mark procedure. Returns new mark stack pointer. */
33/* Primary effect should be to push new entries on the mark stack. */
34/* Mark stack pointer values are passed and returned explicitly. */
35/* Global variables decribing mark stack are not necessarily valid. */
36/* (This usually saves a few cycles by keeping things in registers.) */
37/* Assumed to scan about GC_PROC_BYTES on average. If it needs to do */
38/* much more work than that, it should do it in smaller pieces by */
39/* pushing itself back on the mark stack. */
40/* Note that it should always do some work (defined as marking some */
41/* objects) before pushing more than one entry on the mark stack. */
42/* This is required to ensure termination in the event of mark stack */
43/* overflows. */
44/* This procedure is always called with at least one empty entry on the */
45/* mark stack. */
46/* Currently we require that mark procedures look for pointers in a */
47/* subset of the places the conservative marker would. It must be safe */
48/* to invoke the normal mark procedure instead. */
49/* WARNING: Such a mark procedure may be invoked on an unused object */
50/* residing on a free list. Such objects are cleared, except for a */
51/* free list link field in the first word. Thus mark procedures may */
52/* not count on the presence of a type descriptor, and must handle this */
53/* case correctly somehow. */
54# define GC_PROC_BYTES 100
55struct GC_ms_entry;
56typedef struct GC_ms_entry * (*GC_mark_proc) GC_PROTO((
57 GC_word * addr, struct GC_ms_entry * mark_stack_ptr,
58 struct GC_ms_entry * mark_stack_limit, GC_word env));
59
60# define GC_LOG_MAX_MARK_PROCS 6
61# define GC_MAX_MARK_PROCS (1 << GC_LOG_MAX_MARK_PROCS)
62
63/* In a few cases it's necessary to assign statically known indices to */
64/* certain mark procs. Thus we reserve a few for well known clients. */
65/* (This is necessary if mark descriptors are compiler generated.) */
66#define GC_RESERVED_MARK_PROCS 8
67# define GC_GCJ_RESERVED_MARK_PROC_INDEX 0
68
69/* Object descriptors on mark stack or in objects. Low order two */
70/* bits are tags distinguishing among the following 4 possibilities */
71/* for the high order 30 bits. */
72#define GC_DS_TAG_BITS 2
73#define GC_DS_TAGS ((1 << GC_DS_TAG_BITS) - 1)
74#define GC_DS_LENGTH 0 /* The entire word is a length in bytes that */
75 /* must be a multiple of 4. */
76#define GC_DS_BITMAP 1 /* 30 (62) bits are a bitmap describing pointer */
77 /* fields. The msb is 1 iff the first word */
78 /* is a pointer. */
79 /* (This unconventional ordering sometimes */
80 /* makes the marker slightly faster.) */
81 /* Zeroes indicate definite nonpointers. Ones */
82 /* indicate possible pointers. */
83 /* Only usable if pointers are word aligned. */
84#define GC_DS_PROC 2
85 /* The objects referenced by this object can be */
86 /* pushed on the mark stack by invoking */
87 /* PROC(descr). ENV(descr) is passed as the */
88 /* last argument. */
89# define GC_MAKE_PROC(proc_index, env) \
90 (((((env) << GC_LOG_MAX_MARK_PROCS) \
91 | (proc_index)) << GC_DS_TAG_BITS) | GC_DS_PROC)
92#define GC_DS_PER_OBJECT 3 /* The real descriptor is at the */
93 /* byte displacement from the beginning of the */
94 /* object given by descr & ~DS_TAGS */
95 /* If the descriptor is negative, the real */
96 /* descriptor is at (*<object_start>) - */
97 /* (descr & ~DS_TAGS) - GC_INDIR_PER_OBJ_BIAS */
98 /* The latter alternative can be used if each */
99 /* object contains a type descriptor in the */
100 /* first word. */
101 /* Note that in multithreaded environments */
102 /* per object descriptors maust be located in */
103 /* either the first two or last two words of */
104 /* the object, since only those are guaranteed */
105 /* to be cleared while the allocation lock is */
106 /* held. */
107#define GC_INDIR_PER_OBJ_BIAS 0x10
108
109extern GC_PTR GC_least_plausible_heap_addr;
110extern GC_PTR GC_greatest_plausible_heap_addr;
111 /* Bounds on the heap. Guaranteed valid */
112 /* Likely to include future heap expansion. */
113
114/* Handle nested references in a custom mark procedure. */
115/* Check if obj is a valid object. If so, ensure that it is marked. */
116/* If it was not previously marked, push its contents onto the mark */
117/* stack for future scanning. The object will then be scanned using */
118/* its mark descriptor. */
119/* Returns the new mark stack pointer. */
120/* Handles mark stack overflows correctly. */
121/* Since this marks first, it makes progress even if there are mark */
122/* stack overflows. */
123/* Src is the address of the pointer to obj, which is used only */
124/* for back pointer-based heap debugging. */
125/* It is strongly recommended that most objects be handled without mark */
126/* procedures, e.g. with bitmap descriptors, and that mark procedures */
127/* be reserved for exceptional cases. That will ensure that */
128/* performance of this call is not extremely performance critical. */
129/* (Otherwise we would need to inline GC_mark_and_push completely, */
130/* which would tie the client code to a fixed collector version.) */
131/* Note that mark procedures should explicitly call FIXUP_POINTER() */
132/* if required. */
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
144extern size_t GC_debug_header_size;
145 /* The size of the header added to objects allocated through */
146 /* the GC_debug routines. */
147 /* Defined as a variable so that client mark procedures don't */
148 /* need to be recompiled for collector version changes. */
149#define GC_USR_PTR_FROM_BASE(p) ((GC_PTR)((char *)(p) + GC_debug_header_size))
150
151/* And some routines to support creation of new "kinds", e.g. with */
152/* custom mark procedures, by language runtimes. */
153/* The _inner versions assume the caller holds the allocation lock. */
154
155/* Return a new free list array. */
156void ** GC_new_free_list GC_PROTO((void));
157void ** GC_new_free_list_inner GC_PROTO((void));
158
159/* Return a new kind, as specified. */
160int GC_new_kind GC_PROTO((void **free_list, GC_word mark_descriptor_template,
161 int add_size_to_descriptor, int clear_new_objects));
162 /* The last two parameters must be zero or one. */
163int GC_new_kind_inner GC_PROTO((void **free_list,
164 GC_word mark_descriptor_template,
165 int add_size_to_descriptor,
166 int clear_new_objects));
167
168/* Return a new mark procedure identifier, suitable for use as */
169/* the first argument in GC_MAKE_PROC. */
170int GC_new_proc GC_PROTO((GC_mark_proc));
171int GC_new_proc_inner GC_PROTO((GC_mark_proc));
172
173/* Allocate an object of a given kind. Note that in multithreaded */
174/* contexts, this is usually unsafe for kinds that have the descriptor */
175/* in the object itself, since there is otherwise a window in which */
176/* the descriptor is not correct. Even in the single-threaded case, */
177/* we need to be sure that cleared objects on a free list don't */
178/* cause a GC crash if they are accidentally traced. */
179/* ptr_t */char * GC_generic_malloc GC_PROTO((GC_word lb, int k));
180
181/* FIXME - Should return void *, but that requires other changes. */
182
183typedef void (*GC_describe_type_fn) GC_PROTO((void *p, char *out_buf));
184 /* A procedure which */
185 /* produces a human-readable */
186 /* description of the "type" of object */
187 /* p into the buffer out_buf of length */
188 /* GC_TYPE_DESCR_LEN. This is used by */
189 /* the debug support when printing */
190 /* objects. */
191 /* These functions should be as robust */
192 /* as possible, though we do avoid */
193 /* invoking them on objects on the */
194 /* global free list. */
195# define GC_TYPE_DESCR_LEN 40
196
197void GC_register_describe_type_fn GC_PROTO((int kind, GC_describe_type_fn knd));
198 /* Register a describe_type function */
199 /* to be used when printing objects */
200 /* of a particular kind. */
201
202#endif /* GC_MARK_H */
203
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