jack: client_thread_id should return the data thread

Add a function in data-loop to get the natvive thread and use that
in client_thread_id() so that it returns the pthread of the
data thread instead of the caller thread.

pipewire-jack/src/pipewire-jack.c

@@ -3239,7 +3239,15 @@ int jack_get_client_pid (const char *name)
 SPA_EXPORT
 jack_native_thread_t jack_client_thread_id (jack_client_t *client)
 {
-	return pthread_self();
+	struct client *c = (struct client *) client;
+	void *thr;
+
+	spa_return_val_if_fail(c != NULL, -EINVAL);
+
+	thr = pw_data_loop_get_thread(c->loop);
+	if (thr == NULL)
+		return pthread_self();
+	return *(pthread_t*)thr;
 }
 
 SPA_EXPORT

src/pipewire/data-loop.c

@@ -253,6 +253,18 @@ bool pw_data_loop_in_thread(struct pw_data_loop * loop)
 	return pthread_equal(loop->thread, pthread_self());
 }
 
+/** Get the thread object.
+ * \param loop the data loop to get the thread of
+ * \return the thread object or NULL when the thread is not running
+ *
+ * On posix based systems this returns a pthread_t *
+ */
+SPA_EXPORT
+void *pw_data_loop_get_thread(struct pw_data_loop * loop)
+{
+	return loop->running ? &loop->thread : NULL;
+}
+
 SPA_EXPORT
 int pw_data_loop_invoke(struct pw_data_loop *loop,
 		spa_invoke_func_t func, uint32_t seq, const void *data, size_t size,

src/pipewire/data-loop.h

@@ -87,6 +87,9 @@ int pw_data_loop_stop(struct pw_data_loop *loop);
 /** Check if the current thread is the processing thread */
 bool pw_data_loop_in_thread(struct pw_data_loop *loop);
 
+/** Get the thread object */
+void *pw_data_loop_get_thread(struct pw_data_loop *loop);
+
 /** invoke func in the context of the thread or in the caller thread when
  * the loop is not running. Since 0.3.3 */
 int pw_data_loop_invoke(struct pw_data_loop *loop,