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gobject-list.c
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gobject-list.c
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/*
* gobject-list: a LD_PRELOAD library for tracking the lifetime of GObjects
*
* Copyright (C) 2011, 2014 Collabora Ltd.
*
* 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
*
* Authors:
* Danielle Madeley <danielle.madeley@collabora.co.uk>
* Philip Withnall <philip.withnall@collabora.co.uk>
*/
#include <glib-object.h>
/**
* In later versions of GLib, g_object_ref is defined as a macro to make the
* return value match the type of the ref'ed object, which conflicts with our
* declaration below.
*/
#undef g_object_ref
#include <dlfcn.h>
#include <signal.h>
#include <string.h>
#include <stdlib.h>
#ifdef HAVE_LIBUNWIND
#define UNW_LOCAL_ONLY
#include <libunwind.h>
#endif
typedef enum
{
DISPLAY_FLAG_NONE = 0,
DISPLAY_FLAG_CREATE = 1,
DISPLAY_FLAG_REFS = 1 << 2,
DISPLAY_FLAG_BACKTRACE = 1 << 3,
DISPLAY_FLAG_ALL =
DISPLAY_FLAG_CREATE | DISPLAY_FLAG_REFS | DISPLAY_FLAG_BACKTRACE,
DISPLAY_FLAG_DEFAULT = DISPLAY_FLAG_CREATE,
} DisplayFlags;
typedef struct
{
const gchar *name;
DisplayFlags flag;
} DisplayFlagsMapItem;
DisplayFlagsMapItem display_flags_map[] =
{
{ "none", DISPLAY_FLAG_NONE },
{ "create", DISPLAY_FLAG_CREATE },
{ "refs", DISPLAY_FLAG_REFS },
{ "backtrace", DISPLAY_FLAG_BACKTRACE },
{ "all", DISPLAY_FLAG_ALL },
};
typedef struct {
GHashTable *objects; /* owned */
/* Those 2 hash tables contains the objects which have been added/removed
* since the last time we catched the USR2 signal (check point). */
GHashTable *added; /* owned */
/* GObject -> (gchar *) type
*
* 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 */
} ObjectData;
/* Global static state, which must be accessed with the @gobject_list mutex
* held. */
static volatile ObjectData gobject_list_state = { NULL, };
/* Global lock protecting access to @gobject_list_state, since GObject methods
* may be called from multiple threads concurrently. */
G_LOCK_DEFINE_STATIC (gobject_list);
/* Global output mutex. We don't want multiple threads outputting their
* backtraces at the same time, otherwise the output becomes impossible to
* read */
static GMutex output_mutex;
static gboolean
display_filter (DisplayFlags flags)
{
static DisplayFlags display_flags = DISPLAY_FLAG_DEFAULT;
static gboolean parsed = FALSE;
if (!parsed)
{
const gchar *display = g_getenv ("GOBJECT_LIST_DISPLAY");
if (display != NULL)
{
gchar **tokens = g_strsplit (display, ",", 0);
guint len = g_strv_length (tokens);
guint i = 0;
/* If there really are items to parse, clear the default flags */
if (len > 0)
display_flags = 0;
for (; i < len; ++i)
{
gchar *token = tokens[i];
guint j = 0;
for (; j < G_N_ELEMENTS (display_flags_map); ++j)
{
if (!g_ascii_strcasecmp (token, display_flags_map[j].name))
{
display_flags |= display_flags_map[j].flag;
break;
}
}
}
g_strfreev (tokens);
}
#ifndef HAVE_LIBUNWIND
if (display_flags & DISPLAY_FLAG_BACKTRACE)
g_print ("Warning: backtrace is not available, it needs libunwind\n");
#endif
parsed = TRUE;
}
return (display_flags & flags) ? TRUE : FALSE;
}
static gboolean
object_filter (const char *obj_name)
{
const char *filter = g_getenv ("GOBJECT_LIST_FILTER");
if (filter == NULL)
return TRUE;
else
return (strncmp (filter, obj_name, strlen (filter)) == 0);
}
static void
print_trace (void)
{
#ifdef HAVE_LIBUNWIND
unw_context_t uc;
unw_cursor_t cursor;
guint stack_num = 0;
if (!display_filter (DISPLAY_FLAG_BACKTRACE))
return;
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)
{
g_print ("Error getting frame: %s (%d)\n",
unw_strerror (result), -result);
break;
}
g_print ("#%d %s + [0x%08x]\n", stack_num++, name, (unsigned int)off);
}
#endif
}
static void
_dump_object_list (GHashTable *hash)
{
GHashTableIter iter;
GObject *obj;
g_hash_table_iter_init (&iter, hash);
while (g_hash_table_iter_next (&iter, (gpointer) &obj, NULL))
{
/* FIXME: Not really sure how we get to this state. */
if (obj == NULL || obj->ref_count == 0)
continue;
g_print (" - %p, %s: %u refs\n",
obj, G_OBJECT_TYPE_NAME (obj), obj->ref_count);
}
g_print ("%u objects\n", g_hash_table_size (hash));
}
static void
_sig_usr1_handler (G_GNUC_UNUSED int signal)
{
g_print ("Living Objects:\n");
G_LOCK (gobject_list);
_dump_object_list (gobject_list_state.objects);
G_UNLOCK (gobject_list);
}
static void
_sig_usr2_handler (G_GNUC_UNUSED int signal)
{
GHashTableIter iter;
gpointer obj, type;
G_LOCK (gobject_list);
g_print ("Added Objects:\n");
_dump_object_list (gobject_list_state.added);
g_print ("\nRemoved Objects:\n");
g_hash_table_iter_init (&iter, gobject_list_state.removed);
while (g_hash_table_iter_next (&iter, &obj, &type))
{
g_print (" - %p, %s\n", obj, (gchar *) type);
}
g_print ("%u objects\n", g_hash_table_size (gobject_list_state.removed));
g_hash_table_remove_all (gobject_list_state.added);
g_hash_table_remove_all (gobject_list_state.removed);
g_print ("\nSaved new check point\n");
G_UNLOCK (gobject_list);
}
static void
print_still_alive (void)
{
g_print ("\nStill Alive:\n");
G_LOCK (gobject_list);
_dump_object_list (gobject_list_state.objects);
G_UNLOCK (gobject_list);
}
static void
_exiting (void)
{
print_still_alive ();
}
/* Handle signals which terminate the process. We’re technically not allowed to
* call printf() from this signal handler, but we do anyway as it’s only a
* best-effort debugging tool. */
static void
_sig_bad_handler (int sig_num)
{
signal (sig_num, SIG_DFL);
print_still_alive ();
raise (sig_num);
}
static void *
get_func (const char *func_name)
{
static void *handle = NULL;
void *func;
char *error;
G_LOCK (gobject_list);
if (G_UNLIKELY (g_once_init_enter (&handle)))
{
void *_handle;
_handle = dlopen("libgobject-2.0.so.0", RTLD_LAZY);
if (_handle == NULL)
g_error ("Failed to open libgobject-2.0.so.0: %s", dlerror ());
/* set up signal handlers */
signal (SIGUSR1, _sig_usr1_handler);
signal (SIGUSR2, _sig_usr2_handler);
signal (SIGINT, _sig_bad_handler);
signal (SIGTERM, _sig_bad_handler);
signal (SIGABRT, _sig_bad_handler);
signal (SIGSEGV, _sig_bad_handler);
/* set up objects map */
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);
/* Set up exit handler */
atexit (_exiting);
/* Prevent propagation to child processes. */
if (g_getenv ("GOBJECT_PROPAGATE_LD_PRELOAD") == NULL)
{
g_unsetenv ("LD_PRELOAD");
}
g_once_init_leave (&handle, _handle);
}
func = dlsym (handle, func_name);
if ((error = dlerror ()) != NULL)
g_error ("Failed to find symbol: %s", error);
G_UNLOCK (gobject_list);
return func;
}
static void
_object_finalized (G_GNUC_UNUSED gpointer data,
GObject *obj)
{
G_LOCK (gobject_list);
if (display_filter (DISPLAY_FLAG_CREATE))
{
g_mutex_lock(&output_mutex);
g_print (" -- Finalized object %p, %s\n", obj, G_OBJECT_TYPE_NAME (obj));
print_trace();
g_mutex_unlock(&output_mutex);
/* Only care about the object which were already existing during last
* check point. */
if (g_hash_table_lookup (gobject_list_state.added, obj) == NULL)
g_hash_table_insert (gobject_list_state.removed, obj,
g_strdup (G_OBJECT_TYPE_NAME (obj)));
}
g_hash_table_remove (gobject_list_state.objects, obj);
g_hash_table_remove (gobject_list_state.added, obj);
G_UNLOCK (gobject_list);
}
gpointer
g_object_new (GType type,
const char *first,
...)
{
gpointer (* real_g_object_new_valist) (GType, const char *, va_list);
va_list var_args;
GObject *obj;
const char *obj_name;
real_g_object_new_valist = get_func ("g_object_new_valist");
va_start (var_args, first);
obj = real_g_object_new_valist (type, first, var_args);
va_end (var_args);
obj_name = G_OBJECT_TYPE_NAME (obj);
G_LOCK (gobject_list);
if (g_hash_table_lookup (gobject_list_state.objects, obj) == NULL &&
object_filter (obj_name))
{
if (display_filter (DISPLAY_FLAG_CREATE))
{
g_mutex_lock(&output_mutex);
g_print (" ++ Created object %p, %s\n", obj, obj_name);
print_trace();
g_mutex_unlock(&output_mutex);
}
/* FIXME: For thread safety, GWeakRef should be used here, except it
* won’t give us notify callbacks. Perhaps an opportunistic combination
* of GWeakRef and g_object_weak_ref() — the former for safety, the latter
* for notifications (with the knowledge that due to races, some
* notifications may get omitted)?
*
* Alternatively, we could abuse GToggleRef. Inadvisable because other
* code could be using it.
*
* Alternatively, we could switch to a garbage-collection style of
* working, where gobject-list runs in its own thread and uses GWeakRefs
* to keep track of objects. Periodically, it would check the hash table
* and notify of which references have been nullified. */
g_object_weak_ref (obj, _object_finalized, NULL);
g_hash_table_insert (gobject_list_state.objects, obj,
GUINT_TO_POINTER (TRUE));
g_hash_table_insert (gobject_list_state.added, obj,
GUINT_TO_POINTER (TRUE));
}
G_UNLOCK (gobject_list);
return obj;
}
gpointer
g_object_ref (gpointer object)
{
gpointer (* real_g_object_ref) (gpointer);
GObject *obj = G_OBJECT (object);
const char *obj_name;
guint ref_count;
GObject *ret;
real_g_object_ref = get_func ("g_object_ref");
obj_name = G_OBJECT_TYPE_NAME (obj);
ref_count = obj->ref_count;
ret = real_g_object_ref (object);
if (object_filter (obj_name) && display_filter (DISPLAY_FLAG_REFS))
{
g_mutex_lock(&output_mutex);
g_print (" + Reffed object %p, %s; ref_count: %d -> %d\n",
obj, obj_name, ref_count, obj->ref_count);
print_trace();
g_mutex_unlock(&output_mutex);
}
return ret;
}
void
g_object_unref (gpointer object)
{
void (* real_g_object_unref) (gpointer);
GObject *obj = G_OBJECT (object);
const char *obj_name;
real_g_object_unref = get_func ("g_object_unref");
obj_name = G_OBJECT_TYPE_NAME (obj);
if (object_filter (obj_name) && display_filter (DISPLAY_FLAG_REFS))
{
g_mutex_lock(&output_mutex);
g_print (" - Unreffed object %p, %s; ref_count: %d -> %d\n",
obj, obj_name, obj->ref_count, obj->ref_count - 1);
print_trace();
g_mutex_unlock(&output_mutex);
}
real_g_object_unref (object);
}