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semaphore: fix a hangup problem under load on NetBSD hosts.

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Fix following bugs in "fallback implementation of counting semaphores
with mutex+condvar" added in c166cb72f1:
 - waiting threads are not restarted properly if more than one threads
   are waiting unblock signals in qemu_sem_timedwait()
 - possible missing pthread_cond_signal(3) calls when waiting threads
   are returned by ETIMEDOUT
 - fix an uninitialized variable
The problem is analyzed by and fix is provided by Noriyuki Soda.

Also put additional cleanup suggested by Laszlo Ersek:
 - make QemuSemaphore.count unsigned (it won't be negative)
 - check a return value of in pthread_cond_wait() in qemu_sem_wait()

Signed-off-by: Izumi Tsutsui <tsutsui@ceres.dti.ne.jp>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
Message-id: 1372841894-10634-1-git-send-email-tsutsui@ceres.dti.ne.jp
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
This commit is contained in:
Izumi Tsutsui 2013-07-03 17:58:14 +09:00 • committed by Anthony Liguori
parent e1d0fb378a
commit 79761c6681
2 changed files with 20 additions and 16 deletions
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2
include/qemu/thread-posix.h
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@ -15,7 +15,7 @@ struct QemuSemaphore {
#if defined(__APPLE__) || defined(__NetBSD__)
pthread_mutex_t lock;
pthread_cond_t cond;
int count;
unsigned int count;
#else
sem_t sem;
#endif