fsmonitor: add timeout to daemon stop command

The "fsmonitor--daemon stop" command polls in a loop waiting for the
daemon to exit after sending a "quit" command over IPC.  If the daemon
fails to shut down (e.g. it is stuck or wedged), this loop spins
forever.

Add a 30-second timeout so the stop command returns an error instead
of blocking indefinitely.

Signed-off-by: Paul Tarjan <github@paulisageek.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: ptarjan

builtin/fsmonitor--daemon.c

@@ -86,6 +86,8 @@ static int do_as_client__send_stop(void)
 {
 	struct strbuf answer = STRBUF_INIT;
 	int ret;
+	int max_wait_ms = 30000;
+	int elapsed_ms = 0;
 
 	ret = fsmonitor_ipc__send_command("quit", &answer);
 
@@ -96,8 +98,16 @@ static int do_as_client__send_stop(void)
 		return ret;
 
 	trace2_region_enter("fsm_client", "polling-for-daemon-exit", NULL);
-	while (fsmonitor_ipc__get_state() == IPC_STATE__LISTENING)
+	while (fsmonitor_ipc__get_state() == IPC_STATE__LISTENING) {
+		if (elapsed_ms >= max_wait_ms) {
+			trace2_region_leave("fsm_client",
+					    "polling-for-daemon-exit", NULL);
+			return error(_("daemon did not stop within %d seconds"),
+				     max_wait_ms / 1000);
+		}
 		sleep_millisec(50);
+		elapsed_ms += 50;
+	}
 	trace2_region_leave("fsm_client", "polling-for-daemon-exit", NULL);
 
 	return 0;