From: Florian Obser <florian@narrans.de>
Subject: watch(1): wait for child asynchronously
To: tech <tech@openbsd.org>
Date: Wed, 21 May 2025 11:46:00 +0200

OK?

diff --git watch.c watch.c
index da4f6c0eacf..3b7c917aa36 100644
--- watch.c
+++ watch.c
@@ -73,6 +73,7 @@ int start_line = 0, start_column = 0;	/* display offset coordinates */
 int pause_status = 0;		/* pause status */
 time_t lastupdate;		/* last updated time */
 int xflag = 0;
+pid_t pipe_pid;
 
 #define	addwch(_x)	addnwstr(&(_x), 1);
 #define	WCWIDTH(_x)	((wcwidth((_x)) > 0)? wcwidth((_x)) : 1)
@@ -122,6 +123,7 @@ int
 main(int argc, char *argv[])
 {
 	struct event ev_sigint, ev_sighup, ev_sigterm, ev_sigwinch, ev_stdin;
+	struct event ev_sigchld;
 	size_t len, rem;
 	int i, ch;
 	char *p;
@@ -209,10 +211,12 @@ main(int argc, char *argv[])
 	/*
 	 * Initialize signal
 	 */
+	signal_set(&ev_sigchld, SIGCHLD, on_signal, NULL);
 	signal_set(&ev_sigint, SIGINT, on_signal, NULL);
 	signal_set(&ev_sighup, SIGHUP, on_signal, NULL);
 	signal_set(&ev_sigterm, SIGTERM, on_signal, NULL);
 	signal_set(&ev_sigwinch, SIGWINCH, on_signal, NULL);
+	signal_add(&ev_sigchld, NULL);
 	signal_add(&ev_sigint, NULL);
 	signal_add(&ev_sighup, NULL);
 	signal_add(&ev_sigterm, NULL);
@@ -374,8 +378,7 @@ void
 read_result(BUFFER *buf)
 {
 	FILE	*fp;
-	int	 i, st, fds[2];
-	pid_t	 pipe_pid, pid;
+	int	 i, fds[2];
 
 	/* Clear buffer */
 	memset(buf, 0, sizeof(*buf));
@@ -411,12 +414,7 @@ read_result(BUFFER *buf)
 	    i++)
 		untabify((*buf)[i], sizeof((*buf)[i]));
 	fclose(fp);
-	do {
-		pid = waitpid(pipe_pid, &st, 0);
-	} while (pid == -1 && errno == EINTR);
 
-	/* Remember update time */
-	time(&lastupdate);
 }
 
 kbd_result_t
@@ -644,6 +642,8 @@ void
 on_signal(int sig, short event, void *arg)
 {
 	struct winsize ws;
+	int status;
+	pid_t pid;
 
 	switch(sig) {
 	case SIGWINCH:
@@ -652,6 +652,13 @@ on_signal(int sig, short event, void *arg)
 		doupdate();
 		display(cur_buf, prev_buf, highlight_mode);
 		break;
+	case SIGCHLD:
+		pid = waitpid(pipe_pid, &status, WNOHANG);
+		if (pid == pipe_pid) {
+			/* Remember update time */
+			time(&lastupdate);
+		}
+		break;
 	default:
 		quit();
 	}

-- 
In my defence, I have been left unsupervised.