[qarshd] Fix timeout when child exits

We ran into an issue where qarsh would wait for 3 seconds
after a command ran.  This was traced back to the select()
in handle_qarsh() being restarted when SIGCHLD was received.
I moved the waitpid() to just before the select() and turned off
the signal restart.  This closes those timing windows and allows
qarshd to quickly finish after the child exits.

1 files changed, 8 insertions, 2 deletions

diff --git a/qarshd.c b/qarshd.c
index 49e763d..5c041c3 100644
--- a/qarshd.c
+++ b/qarshd.c
@@ -246,8 +246,12 @@ handle_qarsh()
 	int z_in = 0;		/* Number of bytes in stdin buffer */
 	int eof_in = 0;		/* Have we seen EOF on stdin yet? */
 	int nbytes;
+	struct sigaction chldact;
 
 	signal(SIGPIPE, SIG_IGN);
+	chldact.sa_handler = sig_handler;
+	chldact.sa_flags = 0; /* Make sure SA_RESTART is NOT set so select doesn't timeout on SIGCHLD */
+	sigaction(SIGCHLD, &chldact, NULL);
 
 	qp = make_qp_data_allow(0, QARSHD_BUFSIZE);
 	send_packet(qoutfd, qp);
@@ -273,14 +277,16 @@ handle_qarsh()
 			maxfd = childfds[2] > maxfd ? childfds[2] : maxfd;
 		}
 
-		nfd = select(maxfd+1, &rfds, &wfds, NULL, &timeout);
-
+		/* Check the child just before we do the select so there's no time
+		 * for the child to exit before the select, causing the select to hang */
 		if (child_pid && waitpid(child_pid, &child_status, WNOHANG) == child_pid) {
 			rp = make_qp_cmdexit(child_pid, child_status);
 			send_packet(qoutfd, rp);
 			qpfree(rp);
 			child_pid = 0;
 		}
+
+		nfd = select(maxfd+1, &rfds, &wfds, NULL, &timeout);
 		if (nfd < 0) {
 			if (errno == EINTR) {
 				/* signals handled above here */