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Merge branch '1517-bus-ownership-race' into 'master'

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gdbusnameowning: Subscribe to NameLost before calling RequestName

Closes #1517

See merge request GNOME/glib!1367
This commit is contained in:
Sebastian Dröge 2020-02-17 19:07:23 +00:00
commit 8e0bd39b51
2 changed files with 56 additions and 39 deletions
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94
gio/gdbusnameowning.c
View File

@ -310,7 +310,7 @@ request_name_cb (GObject *source_object,
Client *client = user_data;
GVariant *result;
guint32 request_name_reply;
gboolean subscribe;
gboolean unsubscribe;
request_name_reply = 0;
result = NULL;
@ -325,22 +325,18 @@ request_name_cb (GObject *source_object,
g_variant_unref (result);
}
subscribe = FALSE;
unsubscribe = FALSE;
switch (request_name_reply)
{
case 1: /* DBUS_REQUEST_NAME_REPLY_PRIMARY_OWNER */
/* We got the name - now listen for NameLost and NameAcquired */
call_acquired_handler (client);
subscribe = TRUE;
client->needs_release = TRUE;
break;
case 2: /* DBUS_REQUEST_NAME_REPLY_IN_QUEUE */
/* Waiting in line - listen for NameLost and NameAcquired */
call_lost_handler (client);
subscribe = TRUE;
client->needs_release = TRUE;
break;
default:
@ -349,53 +345,34 @@ request_name_cb (GObject *source_object,
case 4: /* DBUS_REQUEST_NAME_REPLY_ALREADY_OWNER */
/* Some other part of the process is already owning the name */
call_lost_handler (client);
unsubscribe = TRUE;
client->needs_release = FALSE;
break;
}
if (subscribe)
/* If we’re not the owner and not in the queue, there’s no point in continuing
* to listen to NameAcquired or NameLost. */
if (unsubscribe)
{
GDBusConnection *connection = NULL;
/* if cancelled, there is no point in subscribing to signals - if not, make sure
* we use a known good Connection object since it may be set to NULL at any point
* after being cancelled
/* make sure we use a known good Connection object since it may be set to
* NULL at any point after being cancelled
*/
G_LOCK (lock);
if (!client->cancelled)
connection = g_object_ref (client->connection);
G_UNLOCK (lock);
/* Start listening to NameLost and NameAcquired messages. We hold
* references to the Client in the signal closures, since it’s possible
* for a signal to be in-flight after unsubscribing the signal handler.
* This creates a reference count cycle, but that’s explicitly broken by
* disconnecting the signal handlers before calling client_unref() in
* g_bus_unown_name(). */
if (connection != NULL)
{
client->name_lost_subscription_id =
g_dbus_connection_signal_subscribe (connection,
"org.freedesktop.DBus",
"org.freedesktop.DBus",
"NameLost",
"/org/freedesktop/DBus",
client->name,
G_DBUS_SIGNAL_FLAGS_NONE,
on_name_lost_or_acquired,
client_ref (client),
(GDestroyNotify) client_unref);
client->name_acquired_subscription_id =
g_dbus_connection_signal_subscribe (connection,
"org.freedesktop.DBus",
"org.freedesktop.DBus",
"NameAcquired",
"/org/freedesktop/DBus",
client->name,
G_DBUS_SIGNAL_FLAGS_NONE,
on_name_lost_or_acquired,
client_ref (client),
(GDestroyNotify) client_unref);
if (client->name_acquired_subscription_id > 0)
g_dbus_connection_signal_unsubscribe (client->connection, client->name_acquired_subscription_id);
if (client->name_lost_subscription_id > 0)
g_dbus_connection_signal_unsubscribe (client->connection, client->name_lost_subscription_id);
client->name_acquired_subscription_id = 0;
client->name_lost_subscription_id = 0;
g_object_unref (connection);
}
}
@ -439,7 +416,42 @@ has_connection (Client *client)
G_CALLBACK (on_connection_disconnected),
client);
/* Start listening to NameLost and NameAcquired messages. We hold
* references to the Client in the signal closures, since it’s possible
* for a signal to be in-flight after unsubscribing the signal handler.
* This creates a reference count cycle, but that’s explicitly broken by
* disconnecting the signal handlers before calling client_unref() in
* g_bus_unown_name().
*
* Subscribe to NameLost and NameAcquired before calling RequestName() to
* avoid the potential race of losing the name between receiving a reply to
* RequestName() and subscribing to NameLost. The #PreviousCall state will
* ensure that the user callbacks get called an appropriate number of times. */
client->name_lost_subscription_id =
g_dbus_connection_signal_subscribe (client->connection,
"org.freedesktop.DBus",
"org.freedesktop.DBus",
"NameLost",
"/org/freedesktop/DBus",
client->name,
G_DBUS_SIGNAL_FLAGS_NONE,
on_name_lost_or_acquired,
client_ref (client),
(GDestroyNotify) client_unref);
client->name_acquired_subscription_id =
g_dbus_connection_signal_subscribe (client->connection,
"org.freedesktop.DBus",
"org.freedesktop.DBus",
"NameAcquired",
"/org/freedesktop/DBus",
client->name,
G_DBUS_SIGNAL_FLAGS_NONE,
on_name_lost_or_acquired,
client_ref (client),
(GDestroyNotify) client_unref);
/* attempt to acquire the name */
client->needs_release = TRUE;
g_dbus_connection_call (client->connection,
"org.freedesktop.DBus", /* bus name */
"/org/freedesktop/DBus", /* object path */
@ -944,6 +956,10 @@ g_bus_unown_name (guint owner_id)
{
g_warning ("Unexpected reply %d when releasing name %s", release_name_reply, client->name);
}
else
{
client->needs_release = FALSE;
}
g_variant_unref (result);
}
}

1
gio/tests/gdbus-names.c
View File

@ -297,6 +297,7 @@ test_bus_own_name (void)
g_assert_cmpint (data2.num_acquired, ==, 0);
g_assert_cmpint (data2.num_lost, ==, 1);
g_bus_unown_name (id2);
g_main_loop_run (loop);
g_assert_cmpint (data2.num_bus_acquired, ==, 1);
g_assert_cmpint (data2.num_acquired, ==, 0);
g_assert_cmpint (data2.num_lost, ==, 1);