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fix race condition in main_notify.c

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The function wait_main_task() is racy: if the function
wakeup_via_cond() sees the mutex is locked just before
wait_main_task() executes pthread_cond_wait(), the main thread blocks
forever.

Work around this issue by adding a "pending" flag just like in my
notify.c code.  A standards-compliant solution should be implemented
later.

git-svn-id: https://svn.musicpd.org/mpd/trunk@7365 09075e82-0dd4-0310-85a5-a0d7c8717e4f
This commit is contained in:
Max Kellermann 2008-04-17 03:05:23 +00:00 committed by Eric Wong
parent 7c952c4f4b
commit 3c3620b301
1 changed files with 6 additions and 1 deletions
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7
src/main_notify.c
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@ -30,6 +30,7 @@ static int main_pipe[2];
static pthread_t main_task;
static pthread_cond_t main_wakeup = PTHREAD_COND_INITIALIZER;
static pthread_mutex_t main_wakeup_mutex = PTHREAD_MUTEX_INITIALIZER;
static volatile int pending;
static pthread_mutex_t select_mutex = PTHREAD_MUTEX_INITIALIZER;
static int ioops_fdset(fd_set * rfds,
@ -94,6 +95,8 @@ void wakeup_main_task(void)
{
assert(!pthread_equal(main_task, pthread_self()));
pending = 1;
if (!wakeup_via_pipe())
pthread_cond_signal(&main_wakeup);
}
@ -115,7 +118,9 @@ void wait_main_task(void)
assert(pthread_equal(main_task, pthread_self()));
pthread_mutex_lock(&main_wakeup_mutex);
pthread_cond_wait(&main_wakeup, &main_wakeup_mutex);
if (!pending)
pthread_cond_wait(&main_wakeup, &main_wakeup_mutex);
pending = 0;
pthread_mutex_unlock(&main_wakeup_mutex);
}