/*
 * Copyright (c) 1994 by Xerox Corporation.  All rights reserved.
 * Copyright (c) 1996 by Silicon Graphics.  All rights reserved.
 * Copyright (c) 1998 by Fergus Henderson.  All rights reserved.
 * Copyright (c) 2000-2009 by Hewlett-Packard Development Company.
 * All rights reserved.
 *
 * THIS MATERIAL IS PROVIDED AS IS, WITH ABSOLUTELY NO WARRANTY EXPRESSED
 * OR IMPLIED.  ANY USE IS AT YOUR OWN RISK.
 *
 * Permission is hereby granted to use or copy this program
 * for any purpose,  provided the above notices are retained on all copies.
 * Permission to modify the code and to distribute modified code is granted,
 * provided the above notices are retained, and a notice that the code was
 * modified is included with the above copyright notice.
 */

/*
 * 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

#ifndef GC_H
# include "gc.h"
#endif

#ifdef __cplusplus
  extern "C" {
#endif

/* 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_API GC_ref_kind GC_CALL 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.     */
GC_API void * GC_CALL GC_generate_random_heap_address(void);

/* Generate a random address inside a valid marked heap object. */
GC_API void * GC_CALL 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.          */
GC_API void GC_CALL 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.                                           */
GC_API void GC_CALL GC_print_backtrace(void *);

#ifdef __cplusplus
  } /* end of extern "C" */
#endif

#endif /* GC_BACKPTR_H */
