secret-backend: Add a way to uncache singleton instance

This is ugly, but necessary to handle instance uncaching in
SecretBackend when the backend instance is gone.

libsecret/secret-backend.c

@@ -122,6 +122,20 @@ backend_get_instance (void)
 	return instance;
 }
 
+void
+_secret_backend_uncache_instance (void)
+{
+	SecretBackend *instance = NULL;
+
+	G_LOCK (backend_instance);
+	instance = backend_instance;
+	backend_instance = NULL;
+	G_UNLOCK (backend_instance);
+
+	if (instance != NULL)
+		g_object_unref (instance);
+}
+
 static GType
 backend_get_impl_type (void)
 {

libsecret/secret-backend.h

@@ -97,6 +97,8 @@ struct _SecretBackendInterface
 
 void           _secret_backend_ensure_extension_point
                                          (void);
+void           _secret_backend_uncache_instance
+                                         (void);
 
 void           secret_backend_get        (SecretBackendFlags flags,
                                           GCancellable *cancellable,

libsecret/secret-service.c

@@ -191,6 +191,8 @@ service_uncache_instance (SecretService *which)
 	if (watch != 0)
 		g_bus_unwatch_name (watch);
 
+	_secret_backend_uncache_instance ();
+
 	return matched;
 }