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

#include <semaphore.h>

#include "atomic.h"
#include "threads_impl.h"

int sem_trywait(sem_t* sem) {
  int val;
  while ((val = atomic_load(&sem->_s_value)) > 0) {
    int new = val - 1 - (val == 1 && atomic_load(&sem->_s_waiters));
    if (a_cas_shim(&sem->_s_value, val, new) == val)
      return 0;
  }
  errno = EAGAIN;
  return -1;
}