From cfe581b6bc795e3f00ac30791314ec0f9be4b4ad Mon Sep 17 00:00:00 2001
From: Rich Felker <dalias@aerifal.cx>
Date: Thu, 10 Mar 2011 21:52:18 -0500
Subject: fix some semaphore wait semantics (race condition deadlock and error
 checking)

---
 src/thread/sem_trywait.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

(limited to 'src/thread/sem_trywait.c')

diff --git a/src/thread/sem_trywait.c b/src/thread/sem_trywait.c
index d0e928ef..c5370c70 100644
--- a/src/thread/sem_trywait.c
+++ b/src/thread/sem_trywait.c
@@ -5,7 +5,8 @@ int sem_trywait(sem_t *sem)
 {
 	int val = a_fetch_add(sem->__val, -1);
 	if (val > 0) return 0;
-	a_inc(sem->__val);
+	if (!a_fetch_add(sem->__val, 1))
+		__wake(sem->__val, 1, 0);
 	errno = EAGAIN;
 	return -1;
 }
-- 
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