boehm-gc/include/gc_backptr.h

   1 /*
   2  * Copyright (c) 1994 by Xerox Corporation.  All rights reserved.
   3  * Copyright (c) 1996 by Silicon Graphics.  All rights reserved.
   4  * Copyright (c) 1998 by Fergus Henderson.  All rights reserved.
   5  * Copyright (c) 2000-2009 by Hewlett-Packard Development Company.
   6  * All rights reserved.
   7  *
   8  * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
   9  * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
  10  *
  11  * Permission is hereby granted to use or copy this program
  12  * for any purpose,  provided the above notices are retained on all copies.
  13  * Permission to modify the code and to distribute modified code is granted,
  14  * provided the above notices are retained, and a notice that the code was
  15  * modified is included with the above copyright notice.
  16  */
  17
  18 /*
  19  * This is a simple API to implement pointer back tracing, i.e.
  20  * to answer questions such as "who is pointing to this" or
  21  * "why is this object being retained by the collector"
  22  *
  23  * This API assumes that we have an ANSI C compiler.
  24  *
  25  * Most of these calls yield useful information on only after
  26  * a garbage collection.  Usually the client will first force
  27  * a full collection and then gather information, preferably
  28  * before much intervening allocation.
  29  *
  30  * The implementation of the interface is only about 99.9999%
  31  * correct.  It is intended to be good enough for profiling,
  32  * but is not intended to be used with production code.
  33  *
  34  * Results are likely to be much more useful if all allocation is
  35  * accomplished through the debugging allocators.
  36  *
  37  * The implementation idea is due to A. Demers.
  38  */
  39
  40 #ifndef GC_BACKPTR_H
  41 #define GC_BACKPTR_H
  42
  43 #ifndef GC_H
  44 # include "gc.h"
  45 #endif
  46
  47 #ifdef __cplusplus
  48   extern "C" {
  49 #endif
  50
  51 /* Store information about the object referencing dest in *base_p     */
  52 /* and *offset_p.                                                     */
  53 /* If multiple objects or roots point to dest, the one reported       */
  54 /* will be the last on used by the garbage collector to trace the     */
  55 /* object.                                                            */
  56 /*   source is root ==> *base_p = address, *offset_p = 0              */
  57 /*   source is heap object ==> *base_p != 0, *offset_p = offset       */
  58 /*   Returns 1 on success, 0 if source couldn't be determined.        */
  59 /* Dest can be any address within a heap object.                      */
  60 typedef enum {
  61     GC_UNREFERENCED,    /* No reference info available.         */
  62     GC_NO_SPACE,        /* Dest not allocated with debug alloc. */
  63     GC_REFD_FROM_ROOT,  /* Referenced directly by root *base_p. */
  64     GC_REFD_FROM_REG,   /* Referenced from a register, i.e.     */
  65                         /* a root without an address.           */
  66     GC_REFD_FROM_HEAP,  /* Referenced from another heap obj.    */
  67     GC_FINALIZER_REFD   /* Finalizable and hence accessible.    */
  68 } GC_ref_kind;
  69
  70 GC_API GC_ref_kind GC_CALL GC_get_back_ptr_info(void * /* dest */,
  71                                 void ** /* base_p */, size_t * /* offset_p */)
  72                                 GC_ATTR_NONNULL(1);
  73
  74 /* Generate a random heap address.            */
  75 /* The resulting address is in the heap, but  */
  76 /* not necessarily inside a valid object.     */
  77 GC_API void * GC_CALL GC_generate_random_heap_address(void);
  78
  79 /* Generate a random address inside a valid marked heap object. */
  80 GC_API void * GC_CALL GC_generate_random_valid_address(void);
  81
  82 /* Force a garbage collection and generate a backtrace from a   */
  83 /* random heap address.                                         */
  84 /* This uses the GC logging mechanism (GC_printf) to produce    */
  85 /* output.  It can often be called from a debugger.  The        */
  86 /* source in dbg_mlc.c also serves as a sample client.          */
  87 GC_API void GC_CALL GC_generate_random_backtrace(void);
  88
  89 /* Print a backtrace from a specific address.  Used by the      */
  90 /* above.  The client should call GC_gcollect() immediately     */
  91 /* before invocation.                                           */
  92 GC_API void GC_CALL GC_print_backtrace(void *) GC_ATTR_NONNULL(1);
  93
  94 #ifdef __cplusplus
  95   } /* end of extern "C" */
  96 #endif
  97
  98 #endif /* GC_BACKPTR_H */