major semaphore improvements (performance and correctness)

1. make sem_[timed]wait interruptible by signals, per POSIX
2. keep a waiter count in order to avoid unnecessary futex wake syscalls

1 files changed, 30 insertions, 15 deletions

diff --git a/src/thread/sem_timedwait.c b/src/thread/sem_timedwait.c
index 11a01700..4f45c172 100644
--- a/src/thread/sem_timedwait.c
+++ b/src/thread/sem_timedwait.c
@@ -1,26 +1,41 @@
 #include <semaphore.h>
 #include "pthread_impl.h"
 
+static void cleanup(void *p)
+{
+	a_dec(p);
+}
+
 int sem_timedwait(sem_t *sem, const struct timespec *at)
 {
-	int val;
+	int r;
+
+	if (a_fetch_add(sem->__val, -1) > 0) return 0;
+	a_inc(sem->__val);
+
+	if (at && at->tv_nsec >= 1000000000UL) {
+		errno = EINVAL;
+		return -1;
+	}
+
+	a_inc(sem->__val+1);
+	pthread_cleanup_push(cleanup, sem->__val+1)
 
+	CANCELPT_BEGIN;
 	for (;;) {
-		if (a_fetch_add(sem->__val, -1) > 0) return 0;
-		val = a_fetch_add(sem->__val, 1)+1;
-		if (val==1) __wake(sem->__val, 1, 0);
-		if (at && at->tv_nsec >= 1000000000UL) {
-			errno = EINVAL;
-			return -1;
-		}
-		CANCELPT_BEGIN;
-		if (val <= 0 && __timedwait(sem->__val, val, CLOCK_REALTIME, at, 0) == ETIMEDOUT) {
-			errno = ETIMEDOUT;
-			CANCELPT_TRY;
-			CANCELPT_END;
-			return -1;
+		r = 0;
+		if (!sem_trywait(sem)) break;
+		r = __timedwait(sem->__val, 0, CLOCK_REALTIME, at, 0);
+		if (r) {
+			errno = r;
+			r = -1;
+			break;
 		}
 		CANCELPT_TRY;
-		CANCELPT_END;
 	}
+	CANCELPT_END;
+
+	pthread_cleanup_pop(1);
+
+	return r;
 }