[gvfs/wip/oholy/gdbus-deadlock] gdbus: Add workaround for deadlocks when cancelling jobs

[Ondrej Holy <oholy src gnome org>]

commit 6d873fdc4b4c962711d8f2c5c73f30ea14d64e7f
Author: Ondrej Holy <oholy redhat com>
Date:   Thu Oct 10 09:34:02 2019 +0200

    gdbus: Add workaround for deadlocks when cancelling jobs
    
    GVfs calls gvfs_dbus_daemon_proxy_new() in cancelled signal handler which
    internally needs CONNECTION_LOCK(connection). The lock can be unfortunately
    held by gdbus worker thread which can call g_cancellable_disconnect(). This
    obviously leads to deadlocks. I don't see any reason why we have to block
    g_cancellable_disconnect() because of gvfs_dbus_daemon_proxy_new() resp.
    gvfs_dbus_daemon_call_cancel(). Let's call it over idle source to not block
    the cancelled signal handler in order to prevent the deadlocks.
    
    It would be better to fix this issue directly in gdbus codes, however, it
    is not fully clear to me, what is a proper way to fix this.
    
    https://gitlab.gnome.org/GNOME/glib/issues/1023

 client/gvfsdaemondbus.c | 29 +++++++++++++++++++++++++----
 1 file changed, 25 insertions(+), 4 deletions(-)
---
diff --git a/client/gvfsdaemondbus.c b/client/gvfsdaemondbus.c
index e12d2936..f8deb097 100644
--- a/client/gvfsdaemondbus.c
+++ b/client/gvfsdaemondbus.c
@@ -365,10 +365,8 @@ cancelled_got_proxy (GObject *source_object,
   g_object_unref (proxy);
 }
 
-/* Might be called on another thread */
-static void
-async_call_cancelled_cb (GCancellable *cancellable,
-                         gpointer _data)
+static gboolean
+async_call_cancelled_cb_on_idle (gpointer _data)
 {
   AsyncCallCancelData *data = _data;
 
@@ -380,6 +378,29 @@ async_call_cancelled_cb (GCancellable *cancellable,
                               NULL,
                               cancelled_got_proxy,
                               GUINT_TO_POINTER (data->serial));  /* not passing "data" in as long it may not 
exist anymore between async calls */
+
+  return FALSE;
+}
+
+/* Might be called on another thread */
+static void
+async_call_cancelled_cb (GCancellable *cancellable,
+                         gpointer _data)
+{
+  AsyncCallCancelData *data = _data;
+  AsyncCallCancelData *idle_data;
+
+  idle_data = g_new0 (AsyncCallCancelData, 1);
+  idle_data->connection = g_object_ref (data->connection);
+  idle_data->serial = data->serial;
+
+  /* Call on idle to not block g_cancellable_disconnect() as it causes deadlocks
+   * in gdbus codes, see: https://gitlab.gnome.org/GNOME/glib/issues/1023.
+   */
+  g_idle_add_full (G_PRIORITY_DEFAULT_IDLE,
+                   async_call_cancelled_cb_on_idle,
+                   idle_data,
+                   async_call_cancel_data_free);
 }
 
 gulong