Provide a hook to allow refcounting to be traced

This is designed to be used from a wrapper function, partly to supply
the same arguments every time for a particular class of object, and partly
to provide a more specific gdb breakpoint. It has several purposes:

* when under gdb, provide a function which can be used in breakpoints
* when not under valgrind and DBUS_MESSAGE_TRACE=1 is set, emit a
  _dbus_verbose when a message's refcount changes
* when under valgrind and DBUS_MESSAGE_TRACE=1 is set, emit a
  VALGRIND_PRINTF_BACKTRACE when a message's refcount changes,
  which lets you see the complete history of each message to track down
  reference leaks

Compile-time support is currently conditional on DBUS_ENABLE_VERBOSE_MODE,
but could be separated out if desired.

Bug: https://bugs.freedesktop.org/show_bug.cgi?id=37286
Signed-off-by: Simon McVittie <simon.mcvittie@collabora.co.uk>
Reviewed-by: Lennart Poettering <lennart@poettering.net>

diff --git a/dbus/dbus-internals.c b/dbus/dbus-internals.c
index 0c8510c..472e49c 100644 (file)
--- a/dbus/dbus-internals.c
+++ b/dbus/dbus-internals.c
@@ -26,6 +26,7 @@
 #include "dbus-protocol.h"
 #include "dbus-marshal-basic.h"
 #include "dbus-test.h"
+#include "dbus-valgrind-internal.h"
 #include <stdio.h>
 #include <stdarg.h>
 #include <string.h>
@@ -465,6 +466,72 @@ _dbus_verbose_reset_real (void)
   verbose_initted = FALSE;
 }
 
+void
+_dbus_trace_ref (const char *obj_name,
+                 void       *obj,
+                 int         old_refcount,
+                 int         new_refcount,
+                 const char *why,
+                 const char *env_var,
+                 int        *enabled)
+{
+  _dbus_assert (obj_name != NULL);
+  _dbus_assert (obj != NULL);
+  _dbus_assert (old_refcount >= -1);
+  _dbus_assert (new_refcount >= -1);
+
+  if (old_refcount == -1)
+    {
+      _dbus_assert (new_refcount == -1);
+    }
+  else
+    {
+      _dbus_assert (new_refcount >= 0);
+      _dbus_assert (old_refcount >= 0);
+      _dbus_assert (old_refcount > 0 || new_refcount > 0);
+    }
+
+  _dbus_assert (why != NULL);
+  _dbus_assert (env_var != NULL);
+  _dbus_assert (enabled != NULL);
+
+  if (*enabled < 0)
+    {
+      const char *s = _dbus_getenv (env_var);
+
+      *enabled = FALSE;
+
+      if (s && *s)
+        {
+          if (*s == '0')
+            *enabled = FALSE;
+          else if (*s == '1')
+            *enabled = TRUE;
+          else
+            _dbus_warn ("%s should be 0 or 1 if set, not '%s'", env_var, s);
+        }
+    }
+
+  if (*enabled)
+    {
+      if (old_refcount == -1)
+        {
+          VALGRIND_PRINTF_BACKTRACE ("%s %p ref stolen (%s)",
+                                     obj_name, obj, why);
+          _dbus_verbose ("%s %p ref stolen (%s)",
+                         obj_name, obj, why);
+        }
+      else
+        {
+          VALGRIND_PRINTF_BACKTRACE ("%s %p %d -> %d refs (%s)",
+                                     obj_name, obj,
+                                     old_refcount, new_refcount, why);
+          _dbus_verbose ("%s %p %d -> %d refs (%s)",
+                         obj_name, obj, old_refcount, new_refcount, why);
+        }
+    }
+}
+
 #endif /* DBUS_ENABLE_VERBOSE_MODE */
 
 /**

diff --git a/dbus/dbus-internals.h b/dbus/dbus-internals.h
index 2493d41..162a222 100644 (file)
--- a/dbus/dbus-internals.h
+++ b/dbus/dbus-internals.h
@@ -118,6 +118,14 @@ static void _dbus_verbose(const char * x,...) {;}
 #  define _dbus_is_verbose() FALSE 
 #endif /* !DBUS_ENABLE_VERBOSE_MODE */
 
+void _dbus_trace_ref (const char *obj_name,
+                      void       *obj,
+                      int         old_refcount,
+                      int         new_refcount,
+                      const char *why,
+                      const char *env_var,
+                      int        *enabled);
+
 const char* _dbus_strerror (int error_number);
 
 #ifdef DBUS_DISABLE_ASSERT