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