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jeremybenn |
/*
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* This is a simple API to implement pointer back tracing, i.e.
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* to answer questions such as "who is pointing to this" or
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* "why is this object being retained by the collector"
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*
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* This API assumes that we have an ANSI C compiler.
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*
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* Most of these calls yield useful information on only after
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* a garbage collection. Usually the client will first force
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* a full collection and then gather information, preferably
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* before much intervening allocation.
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*
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* The implementation of the interface is only about 99.9999%
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* correct. It is intended to be good enough for profiling,
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* but is not intended to be used with production code.
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*
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* Results are likely to be much more useful if all allocation is
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* accomplished through the debugging allocators.
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*
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* The implementation idea is due to A. Demers.
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*/
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#ifndef GC_BACKPTR_H
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#define GC_BACKPTR_H
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/* Store information about the object referencing dest in *base_p */
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/* and *offset_p. */
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/* If multiple objects or roots point to dest, the one reported */
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/* will be the last on used by the garbage collector to trace the */
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/* object. */
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/* source is root ==> *base_p = address, *offset_p = 0 */
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/* source is heap object ==> *base_p != 0, *offset_p = offset */
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/* Returns 1 on success, 0 if source couldn't be determined. */
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/* Dest can be any address within a heap object. */
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typedef enum { GC_UNREFERENCED, /* No reference info available. */
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GC_NO_SPACE, /* Dest not allocated with debug alloc */
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GC_REFD_FROM_ROOT, /* Referenced directly by root *base_p */
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GC_REFD_FROM_REG, /* Referenced from a register, i.e. */
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/* a root without an address. */
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GC_REFD_FROM_HEAP, /* Referenced from another heap obj. */
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GC_FINALIZER_REFD /* Finalizable and hence accessible. */
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} GC_ref_kind;
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GC_ref_kind GC_get_back_ptr_info(void *dest, void **base_p, size_t *offset_p);
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/* Generate a random heap address. */
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/* The resulting address is in the heap, but */
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/* not necessarily inside a valid object. */
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void * GC_generate_random_heap_address(void);
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/* Generate a random address inside a valid marked heap object. */
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void * GC_generate_random_valid_address(void);
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/* Force a garbage collection and generate a backtrace from a */
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/* random heap address. */
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/* This uses the GC logging mechanism (GC_printf) to produce */
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/* output. It can often be called from a debugger. The */
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/* source in dbg_mlc.c also serves as a sample client. */
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void GC_generate_random_backtrace(void);
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/* Print a backtrace from a specific address. Used by the */
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/* above. The client should call GC_gcollect() immediately */
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/* before invocation. */
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void GC_print_backtrace(void *);
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#endif /* GC_BACKPTR_H */
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