Install a SIGCHLD handler so select(2) will be interrupted when a child

terminates.  Without this patch, 'make -j1 buildworld' takes about 30%
longer than 'make -B buildworld' on my 2.4 GHz P4; the difference is
probably even larger on faster systems.  With this patch, there is no
perceptible difference in wall time between the two.

Submitted by:	bde
MFC after:	3 days

1 files changed, 20 insertions, 0 deletions

diff --git a/usr.bin/make/main.c b/usr.bin/make/main.c
index 9fccf96..497eb77 100644
--- a/usr.bin/make/main.c
+++ b/usr.bin/make/main.c
@@ -410,6 +410,10 @@ chdir_verify_path(char *path, char *obpath)
 	return 0;
 }
 
+void
+catch_child(int sig)
+{
+}
 
 /*-
  * main --
@@ -452,6 +456,22 @@ main(int argc, char **argv)
 					/* avoid faults on read-only strings */
 	static char syspath[] = _PATH_DEFSYSPATH;
 
+	{
+	/*
+	 * Catch SIGCHLD so that we get kicked out of select() when we
+	 * need to look at a child.  This is only known to matter for the
+	 * -j case (perhaps without -P).
+	 *
+	 * XXX this is intentionally misplaced.
+	 */
+	struct sigaction sa;
+
+	sigemptyset(&sa.sa_mask);
+	sa.sa_flags = SA_RESTART | SA_NOCLDSTOP;
+	sa.sa_handler = catch_child;
+	sigaction(SIGCHLD, &sa, NULL);
+	}
+
 #ifdef WANT_ENV_MKLVL
 	if ((iMkLvl = szMkLvl ? atoi(szMkLvl) : 0) < 0) {
 	  iMkLvl = 0;