diff --git a/jack/engine.h b/jack/engine.h
index 6151d7d..6a5118e 100644
--- a/jack/engine.h
+++ b/jack/engine.h
@@ -76,7 +76,7 @@ struct _jack_engine {
 
     /* engine serialization -- use precedence for deadlock avoidance */
     pthread_mutex_t request_lock;	/* precedes client_lock */
-    pthread_mutex_t client_lock;
+    pthread_rwlock_t client_lock;
     pthread_mutex_t port_lock;
     int		    process_errors;
     int		    period_msecs;
@@ -184,21 +184,26 @@ extern jack_timer_type_t clock_source;
 extern jack_client_internal_t *
 jack_client_internal_by_id (jack_engine_t *engine, jack_client_id_t id);
 
+static inline void jack_rdlock_graph (jack_engine_t* engine) {
+	DEBUG ("acquiring graph read lock");
+	pthread_rwlock_rdlock (&engine->client_lock);
+}
+
 static inline void jack_lock_graph (jack_engine_t* engine) {
 	DEBUG ("acquiring graph lock");
-	pthread_mutex_lock (&engine->client_lock);
+	pthread_rwlock_wrlock (&engine->client_lock);
 }
 
-static inline int jack_try_lock_graph (jack_engine_t *engine)
+static inline int jack_try_rdlock_graph (jack_engine_t *engine)
 {
-	DEBUG ("TRYING to acquiring graph lock");
-	return pthread_mutex_trylock (&engine->client_lock);
+	DEBUG ("TRYING to acquiring graph read lock");
+	return pthread_rwlock_tryrdlock (&engine->client_lock);
 }
 
 static inline void jack_unlock_graph (jack_engine_t* engine) 
 {
 	DEBUG ("releasing graph lock");
-	pthread_mutex_unlock (&engine->client_lock);
+	pthread_rwlock_unlock (&engine->client_lock);
 }
 
 static inline unsigned int jack_power_of_two (unsigned int n)
diff --git a/jackd/clientengine.c b/jackd/clientengine.c
index 7381a61..c52bc32 100644
--- a/jackd/clientengine.c
+++ b/jackd/clientengine.c
@@ -292,7 +292,7 @@ jack_client_by_name (jack_engine_t *engine, const char *name)
 	jack_client_internal_t *client = NULL;
 	JSList *node;
 
-	jack_lock_graph (engine);
+	jack_rdlock_graph (engine);
 
 	for (node = engine->clients; node; node = jack_slist_next (node)) {
 		if (strcmp ((const char *) ((jack_client_internal_t *)
@@ -313,7 +313,7 @@ jack_client_id_by_name (jack_engine_t *engine, const char *name)
 	jack_client_id_t id = 0;	/* NULL client ID */
 	JSList *node;
 
-	jack_lock_graph (engine);
+	jack_rdlock_graph (engine);
 
 	for (node = engine->clients; node; node = jack_slist_next (node)) {
 		if (strcmp ((const char *) ((jack_client_internal_t *)
@@ -948,7 +948,7 @@ jack_intclient_name_request (jack_engine_t *engine, jack_request_t *req)
 {
 	jack_client_internal_t *client;
 
-	jack_lock_graph (engine);
+	jack_rdlock_graph (engine);
 	if ((client = jack_client_internal_by_id (engine,
 						  req->x.intclient.id))) {
 		strncpy ((char *) req->x.intclient.name,
diff --git a/jackd/engine.c b/jackd/engine.c
index 8d64667..2214698 100644
--- a/jackd/engine.c
+++ b/jackd/engine.c
@@ -1392,7 +1392,7 @@ handle_external_client_request (jack_engine_t *engine, int fd)
 
 	DEBUG ("HIT: before lock");
 	
-	jack_lock_graph (engine);
+	jack_rdlock_graph (engine);
 
 	DEBUG ("HIT: before for");
 	
@@ -1694,7 +1694,7 @@ jack_engine_new (int realtime, int rtpriority, int do_mlock, int do_unlock,
 	jack_engine_reset_rolling_usecs (engine);
 	engine->max_usecs = 0.0f;
 
-	pthread_mutex_init (&engine->client_lock, 0);
+	pthread_rwlock_init (&engine->client_lock, 0);
 	pthread_mutex_init (&engine->port_lock, 0);
 	pthread_mutex_init (&engine->request_lock, 0);
 
@@ -2051,7 +2051,7 @@ jack_run_one_cycle (jack_engine_t *engine, jack_nframes_t nframes,
 		consecutive_excessive_delays = 0;
 	}
 
-	if (jack_try_lock_graph (engine)) {
+	if (jack_try_rdlock_graph (engine)) {
 		/* engine can't run. just throw away an entire cycle */
 		driver->null_cycle (driver, nframes);
 		return 0;
@@ -3514,10 +3514,11 @@ jack_use_driver (jack_engine_t *engine, jack_driver_t *driver)
 		engine->driver = 0;
 	}
 
-	engine->driver = driver;
-
 	if (driver) {
+		engine->driver = driver;
+
 		if (driver->attach (driver, engine)) {
+			engine->driver = 0;
 			return -1;
 		}
 
@@ -3773,7 +3774,7 @@ jack_do_get_port_connections (jack_engine_t *engine, jack_request_t *req,
 	int ret = -1;
 	int internal = FALSE;
 
-	jack_lock_graph (engine);
+	jack_rdlock_graph (engine);
 
 	port = &engine->internal_ports[req->x.port_info.port_id];