dbusService: Exempt org.gnome.Shell from sender tracking

If an interface has any signals, we don't want to auto-shutdown
while a caller is still connected to a signal.

Unfortunately we can't tell whether there are any signal connections,
so we track all callers instead, and keep the service alive while
any of them is still on the bus.

For services that we call from gnome-shell itself - like screencasts
or extensions - this has the unintended side effect of effectively
disabling auto-shutdown.

Address this by exempting the org.gnome.Shell name from sender
tracking.

Services that we expect to keep running for the lifetime of the
shell already disable auto-shutdown, so the only downside is a
small startup delay to resolve the well-known shell name.

https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/7250

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3052>

js/dbusServices/dbusService.js

@@ -21,6 +21,8 @@ export class ServiceImplementation {
         this._senders = new Map();
         this._holdCount = 0;
 
+        this._shellName = this._getUniqueShellName();
+
         this._hasSignals = this._dbusImpl.get_info().signals.length > 0;
         this._shutdownTimeoutId = 0;
 
@@ -115,6 +117,9 @@ export class ServiceImplementation {
         if (this._senders.has(sender))
             return;
 
+        if (sender === this._shellName)
+            return; // don't track the shell
+
         this.hold();
         this._senders.set(sender,
             this._dbusImpl.get_connection().watch_name(
@@ -148,6 +153,26 @@ export class ServiceImplementation {
             that._queueShutdownCheck();
         };
     }
+
+    _getUniqueShellName() {
+        try {
+            const res = Gio.DBus.session.call_sync(
+                'org.freedesktop.DBus',
+                '/org/freedesktop/DBus',
+                'org.freedesktop.DBus',
+                'GetNameOwner',
+                new GLib.Variant('(s)', ['org.gnome.Shell']),
+                null,
+                Gio.DBusCallFlags.NONE,
+                -1,
+                null);
+            const [name] = res.deepUnpack();
+            return name;
+        } catch (e) {
+            console.warn(`Failed to resolve shell name: ${e.message}`);
+            return '';
+        }
+    }
 }
 Signals.addSignalMethods(ServiceImplementation.prototype);