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Hi! The lock cannot be reacquired, otherwise it can deadlock (if the PTHREAD_BARRIER_SERIAL_THREAD thread returns without unlocking and the other try to reacquire the lock). i486+ and x86_64 assembly is already doing this, which is why it works. 2004-02-20 Jakub Jelinek <jakub@redhat.com> * sysdeps/pthread/pthread_barrier_wait.c (pthread_barrier_wait): Release lock before the loop, don't reacquire it. * DESIGN-barrier.txt: Likewise. --- libc/nptl/sysdeps/pthread/pthread_barrier_wait.c.jj 2004-02-20 16:36:30.000000000 +0100 +++ libc/nptl/sysdeps/pthread/pthread_barrier_wait.c 2004-02-20 19:12:29.731215880 +0100 @@ -55,17 +55,13 @@ pthread_barrier_wait (barrier) /* The number of the event we are waiting for. The barrier's event number must be bumped before we continue. */ unsigned int event = ibarrier->curr_event; - do - { - /* Before suspending, make the barrier available to others. */ - lll_unlock (ibarrier->lock); - /* Wait for the event counter of the barrier to change. */ - lll_futex_wait (&ibarrier->curr_event, event); + /* Before suspending, make the barrier available to others. */ + lll_unlock (ibarrier->lock); - /* We are going to access shared data. */ - lll_lock (ibarrier->lock); - } + /* Wait for the event counter of the barrier to change. */ + do + lll_futex_wait (&ibarrier->curr_event, event); while (event == ibarrier->curr_event); } --- nptl/DESIGN-barrier.txt.jj 2004-02-19 17:50:39.000000000 +0100 +++ nptl/DESIGN-barrier.txt 2004-02-20 19:06:05.957558344 +0100 @@ -31,12 +31,9 @@ pthread_barrier_wait(barrier_t *barrier) result = BARRIER_SERIAL_THREAD; } else { event = barrier->curr_event; + lll_unlock(barrier->lock); do { - lll_unlock(barrier->lock); - futex_wait(&barrier->curr_event, event) - - lll_lock(barrier->lock); } while (event == barrier->curr_event); } Jakub
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