Add a method to trace call paths

Useful to debug reference count leaks where a lot objects are still
held just because a single object was not released elsewhere...

Totally not optimized and slows down a lot, but it gets the job done.

Author: Lekensteyn

Makefile

@@ -1,4 +1,5 @@
 HAVE_LIBUNWIND=1
+WITH_ORIGINS_TRACE=1
 
 ifeq ($(HAVE_LIBUNWIND), 1)
 	optional_libs=libunwind
@@ -13,6 +14,11 @@ LIBS=`pkg-config --libs gobject-2.0 $(optional_libs)`
 
 OBJS = gobject-list.o
 
+ifeq ($(WITH_ORIGINS_TRACE), 1)
+	BUILD_OPTIONS+=-DWITH_ORIGINS_TRACE
+	OBJS += bt-tree.o
+endif
+
 all: libgobject-list.so
 .PHONY: all clean
 clean:

README

@@ -39,6 +39,7 @@ GOBJECT_LIST_DISPLAY:
 	 • ‘refs’: Print information about every reference increment and
 	           decrement on objects.
 	 • ‘backtrace’: Include backtraces with every printed message.
+	 • ‘tracerefs’: At exit, for each object still alive, print a call tree.
 	 • ‘all’: All of the above.
 
 GOBJECT_LIST_FILTER:

bt-tree.c

@@ -0,0 +1,141 @@
+/**
+ * Stores a call trace ("backtrace") for later inspection.
+ *
+ * Copyright (C) 2014  Peter Wu <peter@lekensteyn.nl>
+ *
+ * This library is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU Lesser General Public
+ * License as published by the Free Software Foundation; either
+ * version 2.1 of the License, or (at your option) any later version.
+ *
+ * This library is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+ * Lesser General Public License for more details.
+ *
+ * You should have received a copy of the GNU Lesser General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301
+ * USA
+ */
+
+/* TODO
+ * - faster lookups. The path lookup can surely be optimized (cached?)
+ * - This code allocates memory which may or may not be a problem depending on
+ *   context.
+ */
+
+#include <glib.h>
+#include "bt-tree.h"
+
+enum {
+    COUNT_REF = 0,
+    COUNT_UNREF,
+
+    COUNT_LAST
+};
+
+typedef struct BtTrie {
+    GHashTable *children;
+    char *label;
+    unsigned count[COUNT_LAST];
+} BtTrie;
+
+BtTrie *
+bt_create (char *label)
+{
+    BtTrie *bt_trie = g_malloc0 (sizeof(BtTrie));
+    bt_trie->label = label;
+    bt_trie->children = g_hash_table_new_full (g_str_hash, g_str_equal,
+                                               NULL, (GDestroyNotify) bt_free);
+    return bt_trie;
+}
+
+void
+bt_free (BtTrie *bt_trie)
+{
+    g_free (bt_trie->label);
+    g_hash_table_unref (bt_trie->children);
+    g_free (bt_trie);
+}
+
+/* returns the child of bt_trie with the item at position i inserted. The memory
+ * is freed if such a child already exists. */
+static inline BtTrie *
+find_child (BtTrie *bt_trie, const GPtrArray *items, guint i)
+{
+    BtTrie *child = NULL;
+    char *label = g_ptr_array_index (items, i);
+    g_hash_table_lookup_extended (bt_trie->children, label,
+                                  NULL, (gpointer *)&child);
+    if (child == NULL) {
+        child = bt_create (label);
+        g_hash_table_insert (bt_trie->children, child->label, child);
+    } else {
+        /* unused label */
+        g_free (label);
+    }
+    return child;
+}
+
+/**
+ * Inserts a trace described by items into a trie. Memory can be allocated if a
+ * node is missing.
+ * @bt_trie: root of the tree.
+ * @items: the items to insert (in reverse order: the first element is the leaf,
+ * the last element is the root). Must not be empty. The control of the contents
+ * is transferred from the caller.
+ */
+void
+bt_insert (BtTrie *bt_trie, const GPtrArray *items, gboolean is_ref)
+{
+    guint i = items->len;
+    ++bt_trie->count[is_ref ? COUNT_REF : COUNT_UNREF]; /* mark root */
+    while (i-- > 0) {
+        bt_trie = find_child (bt_trie, items, i);
+        ++bt_trie->count[is_ref ? COUNT_REF : COUNT_UNREF];
+    }
+}
+
+static void
+_bt_print_tree (gpointer key, gpointer value, gpointer user_data)
+{
+    const char *label = key;
+    BtTrie *tree = value;
+    guint indent = GPOINTER_TO_INT (user_data), i;
+    gint diff = tree->count[COUNT_REF] - tree->count[COUNT_UNREF];
+    const char
+        *color_default  = "\e[1;34m", /* blue */
+        *color_unref    = "\e[0;31m", /* red */
+        *color_ref      = "\e[0;33m", /* yellow */
+        *color_diff;
+
+    if (diff == 0)      /* not important */
+        color_default = color_unref = color_ref = color_diff =
+            "\e[1;30m"; /* gray */
+    else if (diff < 0)  /* more unrefs than refs */
+        color_diff = "\e[1;31m"; /* red */
+    else /* diff > 0,      more refs than unrefs */
+        color_diff = "\e[1;33m"; /* yellow */
+
+    for (i = 0; i < indent; i++)
+        g_print("| ");
+    g_print ("%s# %s ", color_default, label); /* name */
+    g_print ("("
+             "%s+%u%s"      /* refs */
+             "/"
+             "%s-%u%s"      /* unrefs */
+             " = %s%d%s",   /* diff */
+             color_ref, tree->count[COUNT_REF], color_default,
+             color_unref, tree->count[COUNT_UNREF], color_default,
+             color_diff, diff, color_default);
+    g_print (")\e[m\n");
+    g_hash_table_foreach (tree->children, _bt_print_tree,
+                          GINT_TO_POINTER (indent + 1));
+}
+
+void
+bt_print_tree (BtTrie *root, guint indent)
+{
+    _bt_print_tree (root->label, root, GINT_TO_POINTER (indent));
+}

bt-tree.h

@@ -0,0 +1,7 @@
+
+typedef struct BtTrie BtTrie;
+
+BtTrie  *bt_create (char *label);
+void     bt_free (BtTrie *bt_trie);
+void     bt_insert (BtTrie *root, const GPtrArray *items, gboolean is_ref);
+void     bt_print_tree (BtTrie *root, guint indent);

gobject-list.c

@@ -34,14 +34,20 @@
 #include <libunwind.h>
 #endif
 
+#ifdef WITH_ORIGINS_TRACE
+#include "bt-tree.h"
+#endif
+
 typedef enum
 {
   DISPLAY_FLAG_NONE = 0,
   DISPLAY_FLAG_CREATE = 1,
   DISPLAY_FLAG_REFS = 1 << 2,
   DISPLAY_FLAG_BACKTRACE = 1 << 3,
+  DISPLAY_FLAG_TRACEREFS = 1 << 4,
   DISPLAY_FLAG_ALL =
-      DISPLAY_FLAG_CREATE | DISPLAY_FLAG_REFS | DISPLAY_FLAG_BACKTRACE,
+      DISPLAY_FLAG_CREATE | DISPLAY_FLAG_REFS | DISPLAY_FLAG_BACKTRACE |
+      DISPLAY_FLAG_TRACEREFS,
   DISPLAY_FLAG_DEFAULT = DISPLAY_FLAG_CREATE,
 } DisplayFlags;
 
@@ -57,6 +63,7 @@ DisplayFlagsMapItem display_flags_map[] =
   { "create", DISPLAY_FLAG_CREATE },
   { "refs", DISPLAY_FLAG_REFS },
   { "backtrace", DISPLAY_FLAG_BACKTRACE },
+  { "tracerefs", DISPLAY_FLAG_TRACEREFS },
   { "all", DISPLAY_FLAG_ALL },
 };
 
@@ -71,6 +78,11 @@ typedef struct {
    * We keep the string representing the type of the object as we won't be able
    * to get it when displaying later as the object would have been destroyed. */
   GHashTable *removed;  /* owned */
+
+#ifdef WITH_ORIGINS_TRACE
+  /* GObject -> BtTrie */
+  GHashTable *origins; /* owned */
+#endif
 } ObjectData;
 
 /* Global static state, which must be accessed with the @gobject_list mutex
@@ -128,6 +140,10 @@ display_filter (DisplayFlags flags)
       if (display_flags & DISPLAY_FLAG_BACKTRACE)
         g_print ("Warning: backtrace is not available, it needs libunwind\n");
 #endif
+#ifndef WITH_ORIGINS_TRACE
+      if (display_flags & DISPLAY_FLAG_TRACEREFS)
+        g_print ("Warning: tracerefs is not available, it needs libunwind\n");
+#endif
 
       parsed = TRUE;
     }
@@ -146,6 +162,49 @@ object_filter (const char *obj_name)
     return (strncmp (filter, obj_name, strlen (filter)) == 0);
 }
 
+static void
+save_trace (const char *key, gboolean is_ref)
+{
+#if defined(HAVE_LIBUNWIND) && defined(WITH_ORIGINS_TRACE)
+  unw_context_t uc;
+  unw_cursor_t cursor;
+  GPtrArray *trace;
+  BtTrie *root = NULL;
+  gboolean found;
+
+  if (!display_filter (DISPLAY_FLAG_TRACEREFS))
+    return;
+
+  trace = g_ptr_array_sized_new (10);
+
+  unw_getcontext (&uc);
+  unw_init_local (&cursor, &uc);
+
+  while (unw_step (&cursor) > 0)
+    {
+      gchar name[129];
+      unw_word_t off;
+      int result;
+
+      result = unw_get_proc_name (&cursor, name, sizeof (name), &off);
+      if (result < 0 && result != -UNW_ENOMEM)
+        break;
+
+      g_ptr_array_insert (trace, -1, g_strdup (name));
+    }
+
+  found = g_hash_table_lookup_extended (gobject_list_state.origins,
+                                        (gpointer) key,
+                                        NULL, (gpointer *)&root);
+  if (!found) {
+    root = bt_create (g_strdup (key));
+    g_hash_table_insert (gobject_list_state.origins, (gpointer) key, root);
+  }
+  bt_insert (root, trace, is_ref);
+  g_ptr_array_unref (trace);
+#endif
+}
+
 static void
 print_trace (void)
 {
@@ -234,13 +293,31 @@ _sig_usr2_handler (G_GNUC_UNUSED int signal)
   G_UNLOCK (gobject_list);
 }
 
+#ifdef WITH_ORIGINS_TRACE
+static void
+print_refs (G_GNUC_UNUSED gpointer key, gpointer value, gpointer user_data)
+{
+  gint *no = (gpointer) user_data;
+  BtTrie *bt_trie = value;
+  g_print ("#%d\n", ++*no);
+  bt_print_tree (bt_trie, 0);
+}
+#endif
+
 static void
 print_still_alive (void)
 {
   g_print ("\nStill Alive:\n");
 
   G_LOCK (gobject_list);
   _dump_object_list (gobject_list_state.objects);
+#ifdef WITH_ORIGINS_TRACE
+  if (display_filter (DISPLAY_FLAG_TRACEREFS)) {
+    guint no = 0;
+    g_print ("\nReferences:\n");
+    g_hash_table_foreach (gobject_list_state.origins, print_refs, (gpointer) &no);
+  }
+#endif
   G_UNLOCK (gobject_list);
 }
 
@@ -291,6 +368,10 @@ get_func (const char *func_name)
       gobject_list_state.objects = g_hash_table_new (NULL, NULL);
       gobject_list_state.added = g_hash_table_new (NULL, NULL);
       gobject_list_state.removed = g_hash_table_new_full (NULL, NULL, NULL, g_free);
+#ifdef WITH_ORIGINS_TRACE
+      gobject_list_state.origins =
+            g_hash_table_new_full (NULL, NULL, NULL, (GDestroyNotify) bt_free);
+#endif
 
       /* Set up exit handler */
       atexit (_exiting);
@@ -338,6 +419,9 @@ _object_finalized (G_GNUC_UNUSED gpointer data,
 
   g_hash_table_remove (gobject_list_state.objects, obj);
   g_hash_table_remove (gobject_list_state.added, obj);
+#ifdef WITH_ORIGINS_TRACE
+  g_hash_table_remove (gobject_list_state.origins, G_OBJECT_TYPE_NAME (obj));
+#endif
 
   G_UNLOCK (gobject_list);
 }
@@ -371,6 +455,7 @@ g_object_new (GType type,
 
           g_print (" ++ Created object %p, %s\n", obj, obj_name);
           print_trace();
+          save_trace (obj_name, TRUE);
 
           g_mutex_unlock(&output_mutex);
         }
@@ -424,6 +509,7 @@ g_object_ref (gpointer object)
       g_print (" +  Reffed object %p, %s; ref_count: %d -> %d\n",
           obj, obj_name, ref_count, obj->ref_count);
       print_trace();
+      save_trace (obj_name, TRUE);
 
       g_mutex_unlock(&output_mutex);
     }
@@ -449,6 +535,7 @@ g_object_unref (gpointer object)
       g_print (" -  Unreffed object %p, %s; ref_count: %d -> %d\n",
           obj, obj_name, obj->ref_count, obj->ref_count - 1);
       print_trace();
+      save_trace (obj_name, FALSE);
 
       g_mutex_unlock(&output_mutex);
     }