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#include <semaphore.h> #include "pthread_impl.h" int sem_trywait(sem_t *sem) { int val = a_fetch_add(sem->__val, -1); if (val > 0) return 0; if (!a_fetch_add(sem->__val, 1)) __wake(sem->__val, 1, 0); errno = EAGAIN; return -1; }