zircon/third_party/ulib/musl/pthread/pthread_rwlock_unlock.c

#include "futex_impl.h"
#include "threads_impl.h"

int pthread_rwlock_unlock(pthread_rwlock_t* rw) {
  int val, cnt, waiters, new;

  do {
    val = atomic_load(&rw->_rw_lock);
    cnt = val & PTHREAD_MUTEX_RWLOCK_COUNT_MASK;
    waiters = atomic_load(&rw->_rw_waiters);
    new = (cnt == PTHREAD_MUTEX_RWLOCK_LOCKED_FOR_WR || cnt == 1) ? PTHREAD_MUTEX_RWLOCK_UNLOCKED
                                                                  : val - 1;
  } while (a_cas_shim(&rw->_rw_lock, val, new) != val);

  if (!new && (waiters || (val & PTHREAD_MUTEX_RWLOCK_CONTESTED_BIT)))
    _zx_futex_wake(&rw->_rw_lock, cnt);

  return 0;
}