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author | Rich Felker <dalias@aerifal.cx> | 2014-08-25 16:38:25 -0400 |
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committer | Rich Felker <dalias@aerifal.cx> | 2014-08-25 16:38:25 -0400 |
commit | 2ff714c6138da8abb50fd532503fd8d68a18811a (patch) | |
tree | d962f59e257148b70dbfd60284738e004d5b0d02 | |
parent | 8b3d7d0d35f97051bc994800c928a7db53316dd2 (diff) | |
download | musl-2ff714c6138da8abb50fd532503fd8d68a18811a.zip musl-2ff714c6138da8abb50fd532503fd8d68a18811a.tar.gz musl-2ff714c6138da8abb50fd532503fd8d68a18811a.tar.bz2 |
spin in sem_[timed]wait before performing futex wait
empirically, this increases the maximum rate of wait/post operations
between two threads by 20-150 times on machines I tested, including
x86 and arm. conceptually, it makes sense to do some spinning because
semaphores are intended to be usable as a notification mechanism
between threads, not just as locks, and low-latency notification is a
valuable property to have.
-rw-r--r-- | src/thread/sem_timedwait.c | 5 |
1 files changed, 5 insertions, 0 deletions
diff --git a/src/thread/sem_timedwait.c b/src/thread/sem_timedwait.c index bfcb6dc..df5f3a6 100644 --- a/src/thread/sem_timedwait.c +++ b/src/thread/sem_timedwait.c @@ -8,6 +8,11 @@ static void cleanup(void *p) 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 (sem_trywait(sem)) { int r; a_inc(sem->__val+1); |