ipc: Reset waitframe semaphore when client disconnects

The semaphore was usually kept at a value of 1 after a client disconnected,
meaning the next client to connect was never blocked on it.

src/xrt/ipc/ipc_server.h

@@ -212,6 +212,15 @@ void
 ipc_server_wait_add_frame(struct ipc_wait *iw,
                           volatile struct ipc_client_state *cs);
 
+/*!
+ * Reset the wait state for wait frame, after the client disconnected
+ *
+ * @ingroup ipc_server
+ * @public @memberof ipc_wait
+ */
+void
+ipc_server_wait_reset_client(struct ipc_wait *iw,
+                             volatile struct ipc_client_state *cs);
 
 #ifdef __cplusplus
 }

src/xrt/ipc/ipc_server_client.c

@@ -454,6 +454,8 @@ client_loop(volatile struct ipc_client_state *cs)
 	if (cs->server->exit_on_disconnect) {
 		cs->server->running = false;
 	}
+
+	ipc_server_wait_reset_client(cs->server->iw, cs);
 }
 
 

src/xrt/ipc/ipc_server_wait.c

@@ -114,6 +114,28 @@ ipc_server_wait_add_frame(struct ipc_wait *iw,
 	os_thread_helper_unlock(&iw->oth);
 }
 
+void
+ipc_server_wait_reset_client(struct ipc_wait *iw,
+                             volatile struct ipc_client_state *cs)
+{
+	os_thread_helper_lock(&iw->oth);
+
+	/* ipc_server_wait_add_frame would overwrite dangling references,
+	 * but clean them up anyway to be less confusing. */
+	for (int i = 0; i < IPC_MAX_CLIENTS; i++) {
+		if (iw->cs[i] == cs) {
+			iw->cs[i] = NULL;
+		}
+	}
+
+	volatile struct ipc_shared_memory *ism = iw->s->ism;
+	sem_init((sem_t *)&ism->wait_frame.sem, true, 0);
+	ism->wait_frame.predicted_display_period = 0;
+	ism->wait_frame.predicted_display_time = 0;
+
+	os_thread_helper_unlock(&iw->oth);
+}
+
 void
 ipc_server_wait_free(struct ipc_wait **out_iw)
 {