dbusServices: Allow to inhibit auto-shutdown

While we only shut down after a method call completed or (if the
interface has signals) the sender disconnects from the bus, services
may need to inhibit auto-shutdown for more specific reasons themselves,
for example when a method call kicks off an operation that should
complete before shutting down.

Add hold() and release() methods like Gio.Application for those cases.

https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1115

js/dbusServices/dbusService.js

@@ -18,6 +18,7 @@ var ServiceImplementation = class {
         this._injectTracking('return_value_with_unix_fd_list');
 
         this._senders = new Map();
+        this._holdCount = 0;
 
         this._hasSignals = this._dbusImpl.get_info().signals.length > 0;
         this._shutdownTimeoutId = 0;
@@ -38,6 +39,22 @@ var ServiceImplementation = class {
         this._dbusImpl.unexport();
     }
 
+    hold() {
+        this._holdCount++;
+    }
+
+    release() {
+        if (this._holdCount === 0) {
+            logError(new Error('Unmatched call to release()'));
+            return;
+        }
+
+        this._holdCount--;
+
+        if (this._holdCount === 0)
+            this._queueShutdownCheck();
+    }
+
     /**
      * _handleError:
      * @param {Gio.DBusMethodInvocation}
@@ -69,7 +86,7 @@ var ServiceImplementation = class {
         if (!this._autoShutdown)
             return;
 
-        if (this._senders.size > 0)
+        if (this._holdCount > 0)
             return;
 
         this.emit('shutdown');
@@ -93,6 +110,7 @@ var ServiceImplementation = class {
         if (this._senders.has(sender))
             return;
 
+        this.hold();
         this._senders.set(sender,
             this._dbusImpl.get_connection().watch_name(
                 sender,
@@ -108,7 +126,7 @@ var ServiceImplementation = class {
             this._dbusImpl.get_connection().unwatch_name(id);
 
         if (this._senders.delete(sender))
-            this._queueShutdownCheck();
+            this.release();
     }
 
     _injectTracking(methodName) {