From b552b05251980f693c729e251f93f5225b400714 Mon Sep 17 00:00:00 2001
From: Paul Smith <psmith@gnu.org>
Date: Sat, 3 Jun 2017 16:20:51 -0400
Subject: [SV 51159] Use a non-blocking read with pselect to avoid hangs.
* posixos.c (set_blocking): Set blocking on a file descriptor.
(jobserver_setup): Set non-blocking on the jobserver read side.
(jobserver_parse_auth): Ditto.
(jobserver_acquire_all): Set blocking to avoid a busy-wait loop.
(jobserver_acquire): If the non-blocking read() returns without
taking a token then try again.
---
posixos.c | 97 ++++++++++++++++++++++++++++++++++++++++++++++-----------------
1 file changed, 71 insertions(+), 26 deletions(-)
diff --git a/posixos.c b/posixos.c
index e642d7f..dbafa51 100644
--- a/posixos.c
+++ b/posixos.c
@@ -62,6 +62,24 @@ make_job_rfd (void)
#endif
}
+static void
+set_blocking (int fd, int blocking)
+{
+ // If we're not using pselect() don't change the blocking
+#ifdef HAVE_PSELECT
+ int flags;
+ EINTRLOOP (flags, fcntl (fd, F_GETFL));
+ if (flags >= 0)
+ {
+ int r;
+ flags = blocking ? (flags & ~O_NONBLOCK) : (flags | O_NONBLOCK);
+ EINTRLOOP (r, fcntl (fd, F_SETFL, flags));
+ if (r < 0)
+ pfatal_with_name ("fcntl(O_NONBLOCK)");
+ }
+#endif
+}
+
unsigned int
jobserver_setup (int slots)
{
@@ -86,6 +104,9 @@ jobserver_setup (int slots)
pfatal_with_name (_("init jobserver pipe"));
}
+ /* When using pselect() we want the read to be non-blocking. */
+ set_blocking (job_fds[0], 0);
+
return 1;
}
@@ -121,6 +142,9 @@ jobserver_parse_auth (const char *auth)
return 0;
}
+ /* When using pselect() we want the read to be non-blocking. */
+ set_blocking (job_fds[0], 0);
+
return 1;
}
@@ -169,7 +193,10 @@ jobserver_acquire_all (void)
{
unsigned int tokens = 0;
- /* Close the write side, so the read() won't hang. */
+ /* Use blocking reads to wait for all outstanding jobs. */
+ set_blocking (job_fds[0], 1);
+
+ /* Close the write side, so the read() won't hang forever. */
close (job_fds[1]);
job_fds[1] = -1;
@@ -236,18 +263,12 @@ jobserver_pre_acquire (void)
unsigned int
jobserver_acquire (int timeout)
{
- sigset_t empty;
- fd_set readfds;
struct timespec spec;
struct timespec *specp = NULL;
- int r;
- char intake;
+ sigset_t empty;
sigemptyset (&empty);
- FD_ZERO (&readfds);
- FD_SET (job_fds[0], &readfds);
-
if (timeout)
{
/* Alarm after one second (is this too granular?) */
@@ -256,28 +277,52 @@ jobserver_acquire (int timeout)
specp = &spec;
}
- r = pselect (job_fds[0]+1, &readfds, NULL, NULL, specp, &empty);
-
- if (r == -1)
+ while (1)
{
- /* Better be SIGCHLD. */
- if (errno != EINTR)
- pfatal_with_name (_("pselect jobs pipe"));
- return 0;
- }
+ fd_set readfds;
+ int r;
+ char intake;
- if (r == 0)
- /* Timeout. */
- return 0;
+ FD_ZERO (&readfds);
+ FD_SET (job_fds[0], &readfds);
- /* The read FD is ready: read it! */
- EINTRLOOP (r, read (job_fds[0], &intake, 1));
- if (r < 0)
- pfatal_with_name (_("read jobs pipe"));
+ r = pselect (job_fds[0]+1, &readfds, NULL, NULL, specp, &empty);
+ if (r < 0)
+ switch (errno)
+ {
+ case EINTR:
+ /* SIGCHLD will show up as an EINTR. */
+ return 0;
+
+ case EBADF:
+ /* Someone closed the jobs pipe.
+ That shouldn't happen but if it does we're done. */
+ O (fatal, NILF, _("job server shut down"));
- /* What does it mean if read() returns 0? It shouldn't happen because only
- the master make can reap all the tokens and close the write side...?? */
- return r > 0;
+ default:
+ pfatal_with_name (_("pselect jobs pipe"));
+ }
+
+ if (r == 0)
+ /* Timeout. */
+ return 0;
+
+ /* The read FD is ready: read it! This is non-blocking. */
+ EINTRLOOP (r, read (job_fds[0], &intake, 1));
+
+ if (r < 0)
+ {
+ /* Someone sniped our token! Try again. */
+ if (errno == EAGAIN)
+ continue;
+
+ pfatal_with_name (_("read jobs pipe"));
+ }
+
+ /* read() should never return 0: only the master make can reap all the
+ tokens and close the write side...?? */
+ return r > 0;
+ }
}
#else
--
cgit v1.0-41-gc330
