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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 */