path: root/src/thread/sem_timedwait.c
diff options
authorRich Felker <>2014-08-25 20:24:07 -0400
committerRich Felker <>2014-08-25 20:24:07 -0400
commitf5fb20b0e934770c37093105524ea644dcaba5e2 (patch)
treedcf0555f52553e2ef67b6aef1d8de05b5c89bd8a /src/thread/sem_timedwait.c
parent97a7512b6819014d15c679c8998caa0006d13c29 (diff)
refrain from spinning on locks when there is already a waiter
if there is already a waiter for a lock, spinning on the lock is essentially an attempt to steal it from whichever waiter would obtain it via any priority rules in place, and is therefore undesirable. in the current implementation, there is always an inherent race window at unlock during which a newly-arriving thread may steal the lock from the existing waiters, but we should aim to keep this window minimal rather than enlarging it.
Diffstat (limited to 'src/thread/sem_timedwait.c')
1 files changed, 1 insertions, 1 deletions
diff --git a/src/thread/sem_timedwait.c b/src/thread/sem_timedwait.c
index df5f3a6c..b5a60add 100644
--- a/src/thread/sem_timedwait.c
+++ b/src/thread/sem_timedwait.c
@@ -11,7 +11,7 @@ int sem_timedwait(sem_t *restrict sem, const struct timespec *restrict at)
if (!sem_trywait(sem)) return 0;
int spins = 100;
- while (spins-- && sem->__val[0] <= 0) a_spin();
+ while (spins-- && sem->__val[0] <= 0 && !sem->__val[1]) a_spin();
while (sem_trywait(sem)) {
int r;