thrpool: sleep instead of yield when poking thread

This unfortunate loop burned too much CPU on FreeBSD and caused
shutdown to take too long when using sched_yield.  nanosleep for
10ms instead, hopefully allowing the system to accomplish some
disk I/O and other tasks before we poke it again.

Reported-by: Mikolaj Golub

1 files changed, 12 insertions, 3 deletions

diff --git a/thrpool.c b/thrpool.c
index 8ed5963..80bf1ff 100644
--- a/thrpool.c
+++ b/thrpool.c
@@ -86,9 +86,18 @@ static void poke(pthread_t thr, int sig)
          * This is an uncommon code path and only triggered when
          * we lower thread counts or shut down
          */
-        while ((err = pthread_kill(thr, sig)) == 0)
-                mog_yield();
-
+        while ((err = pthread_kill(thr, sig)) == 0) {
+                /*
+                 * sleep for 10 ms, sched_yield still burns too much CPU
+                 * on FreeBSD (and likely other OSes) if a thread is waiting
+                 * on disk I/O.
+                 */
+                struct timespec ts = { .tv_sec = 0, .tv_nsec = 10e6 };
+                int rc = nanosleep(&ts, NULL);
+
+                if (rc != 0)
+                        assert(errno != EINVAL && "bug in using nanosleep");
+        }
         assert(err == ESRCH && "pthread_kill() usage bug");
 }