146 lines
6.6 KiB
C
146 lines
6.6 KiB
C
/*
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* Copyright (c) 1991-1994 by Xerox Corporation. All rights reserved.
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* Copyright (c) 2001 by Hewlett-Packard Company. All rights reserved.
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*
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* THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
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* OR IMPLIED. ANY USE IS AT YOUR OWN RISK.
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*
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* Permission is hereby granted to use or copy this program
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* for any purpose, provided the above notices are retained on all copies.
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* Permission to modify the code and to distribute modified code is granted,
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* provided the above notices are retained, and a notice that the code was
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* modified is included with the above copyright notice.
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*
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*/
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/*
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* This contains interfaces to the GC marker that are likely to be useful to
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* clients that provide detailed heap layout information to the collector.
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* This interface should not be used by normal C or C++ clients.
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* It will be useful to runtimes for other languages.
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*
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* Note that this file is not "namespace-clean", i.e. it introduces names
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* not prefixed with GC_, which may collide with the client's names. It
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* should be included only in those few places that directly provide
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* information to the collector.
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*/
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#ifndef GC_MARK_H
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# define GC_MARK_H
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# ifndef GC_H
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# include "gc.h"
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# endif
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/* A client supplied mark procedure. Returns new mark stack pointer. */
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/* Primary effect should be to push new entries on the mark stack. */
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/* Mark stack pointer values are passed and returned explicitly. */
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/* Global variables decribing mark stack are not necessarily valid. */
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/* (This usually saves a few cycles by keeping things in registers.) */
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/* Assumed to scan about GC_PROC_BYTES on average. If it needs to do */
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/* much more work than that, it should do it in smaller pieces by */
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/* pushing itself back on the mark stack. */
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/* Note that it should always do some work (defined as marking some */
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/* objects) before pushing more than one entry on the mark stack. */
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/* This is required to ensure termination in the event of mark stack */
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/* overflows. */
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/* This procedure is always called with at least one empty entry on the */
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/* mark stack. */
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/* Currently we require that mark procedures look for pointers in a */
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/* subset of the places the conservative marker would. It must be safe */
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/* to invoke the normal mark procedure instead. */
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/* WARNING: Such a mark procedure may be invoked on an unused object */
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/* residing on a free list. Such objects are cleared, except for a */
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/* free list link field in the first word. Thus mark procedures may */
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/* not count on the presence of a type descriptor, and must handle this */
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/* case correctly somehow. */
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# define GC_PROC_BYTES 100
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struct GC_ms_entry;
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typedef struct GC_ms_entry * (*GC_mark_proc) GC_PROTO((
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GC_word * addr, struct GC_ms_entry * mark_stack_ptr,
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struct GC_ms_entry * mark_stack_limit, GC_word env));
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# define GC_LOG_MAX_MARK_PROCS 6
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# define GC_MAX_MARK_PROCS (1 << GC_LOG_MAX_MARK_PROCS)
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/* In a few cases it's necessary to assign statically known indices to */
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/* certain mark procs. Thus we reserve a few for well known clients. */
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/* (This is necessary if mark descriptors are compiler generated.) */
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#define GC_RESERVED_MARK_PROCS 8
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# define GC_GCJ_RESERVED_MARK_PROC_INDEX 0
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/* Object descriptors on mark stack or in objects. Low order two */
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/* bits are tags distinguishing among the following 4 possibilities */
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/* for the high order 30 bits. */
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#define GC_DS_TAG_BITS 2
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#define GC_DS_TAGS ((1 << GC_DS_TAG_BITS) - 1)
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#define GC_DS_LENGTH 0 /* The entire word is a length in bytes that */
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/* must be a multiple of 4. */
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#define GC_DS_BITMAP 1 /* 30 (62) bits are a bitmap describing pointer */
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/* fields. The msb is 1 iff the first word */
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/* is a pointer. */
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/* (This unconventional ordering sometimes */
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/* makes the marker slightly faster.) */
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/* Zeroes indicate definite nonpointers. Ones */
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/* indicate possible pointers. */
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/* Only usable if pointers are word aligned. */
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#define GC_DS_PROC 2
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/* The objects referenced by this object can be */
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/* pushed on the mark stack by invoking */
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/* PROC(descr). ENV(descr) is passed as the */
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/* last argument. */
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# define GC_MAKE_PROC(proc_index, env) \
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(((((env) << GC_LOG_MAX_MARK_PROCS) \
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| (proc_index)) << GC_DS_TAG_BITS) | GC_DS_PROC)
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#define GC_DS_PER_OBJECT 3 /* The real descriptor is at the */
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/* byte displacement from the beginning of the */
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/* object given by descr & ~DS_TAGS */
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/* If the descriptor is negative, the real */
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/* descriptor is at (*<object_start>) - */
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/* (descr & ~DS_TAGS) - GC_INDIR_PER_OBJ_BIAS */
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/* The latter alternative can be used if each */
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/* object contains a type descriptor in the */
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/* first word. */
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/* Note that in multithreaded environments */
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/* per object descriptors maust be located in */
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/* either the first two or last two words of */
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/* the object, since only those are guaranteed */
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/* to be cleared while the allocation lock is */
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/* held. */
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#define GC_INDIR_PER_OBJ_BIAS 0x10
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extern GC_PTR GC_least_plausible_heap_addr;
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extern GC_PTR GC_greatest_plausible_heap_addr;
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/* Bounds on the heap. Guaranteed valid */
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/* Likely to include future heap expansion. */
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/* Handle nested references in a custom mark procedure. */
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/* Check if obj is a valid object. If so, ensure that it is marked. */
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/* If it was not previously marked, push its contents onto the mark */
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/* stack for future scanning. The object will then be scanned using */
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/* its mark descriptor. */
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/* Returns the new mark stack pointer. */
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/* Handles mark stack overflows correctly. */
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/* Since this marks first, it makes progress even if there are mark */
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/* stack overflows. */
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/* Src is the address of the pointer to obj, which is used only */
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/* for back pointer-based heap debugging. */
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/* It is strongly recommended that most objects be handled without mark */
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/* procedures, e.g. with bitmap descriptors, and that mark procedures */
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/* be reserved for exceptional cases. That will ensure that */
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/* performance of this call is not extremely performance critical. */
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/* (Otherwise we would need to inline GC_mark_and_push completely, */
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/* which would tie the client code to a fixed colllector version.) */
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struct GC_ms_entry *GC_mark_and_push
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GC_PROTO((GC_PTR obj,
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struct GC_ms_entry * mark_stack_ptr,
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struct GC_ms_entry * mark_stack_limit, GC_PTR *src));
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#define GC_MARK_AND_PUSH(obj, msp, lim, src) \
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(((GC_word)obj >= (GC_word)GC_least_plausible_heap_addr && \
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(GC_word)obj <= (GC_word)GC_greatest_plausible_heap_addr)? \
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GC_mark_and_push(obj, msp, lim, src) : \
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msp)
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#endif /* GC_MARK_H */
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