Rich Felker
1fa0521010
due to moving waiters from the cond var to the mutex in bcast, these waiters upon wakeup would steal slots in the count from newer waiters that had not yet been signaled, preventing the signal function from taking any action. to solve the problem, we simply use two separate waiter counts, and so that the original "total" waiters count is undisturbed by broadcast and still available for signal.
68 lines
1.4 KiB
C
68 lines
1.4 KiB
C
#include "pthread_impl.h"
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struct cm {
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pthread_cond_t *c;
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pthread_mutex_t *m;
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};
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static void unwait(pthread_cond_t *c, pthread_mutex_t *m)
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{
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int w;
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/* Removing a waiter is non-trivial if we could be using requeue
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* based broadcast signals, due to mutex access issues, etc. */
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if (c->_c_mutex == (void *)-1) {
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a_dec(&c->_c_waiters);
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return;
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}
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while (a_swap(&c->_c_lock, 1))
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__wait(&c->_c_lock, &c->_c_lockwait, 1, 1);
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/* Atomically decrement waiters2 if positive, else mutex waiters. */
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do w = c->_c_waiters2;
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while (w && a_cas(&c->_c_waiters2, w, w-1)!=w);
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if (!w) a_dec(&m->_m_waiters);
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a_store(&c->_c_lock, 0);
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if (c->_c_lockwait) __wake(&c->_c_lock, 1, 1);
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}
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static void cleanup(void *p)
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{
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struct cm *cm = p;
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unwait(cm->c, cm->m);
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pthread_mutex_lock(cm->m);
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}
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int pthread_cond_timedwait(pthread_cond_t *c, pthread_mutex_t *m, const struct timespec *ts)
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{
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struct cm cm = { .c=c, .m=m };
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int r, e=0, seq;
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if (ts && ts->tv_nsec >= 1000000000UL)
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return EINVAL;
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pthread_testcancel();
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if (c->_c_mutex != (void *)-1) c->_c_mutex = m;
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a_inc(&c->_c_waiters);
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a_inc(&c->_c_waiters2);
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seq = c->_c_seq;
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if ((r=pthread_mutex_unlock(m))) return r;
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do e = __timedwait(&c->_c_seq, seq, c->_c_clock, ts, cleanup, &cm, 0);
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while (c->_c_seq == seq && (!e || e==EINTR));
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if (e == EINTR) e = 0;
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unwait(c, m);
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if ((r=pthread_mutex_lock(m))) return r;
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return e;
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}
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