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07e62953c7
this seems counter-intuitive since sem_trywait is supposed to just try once, not wait for the semaphore. however, the retry loop is not a wait. instead, it's to handle the case where the value changes due to a simultaneous post or wait from another thread while the semaphore value remains positive. in such a case, it's absolutely wrong for sem_trywait to fail with EAGAIN because the semaphore is not busy.
14 lines
254 B
C
14 lines
254 B
C
#include <semaphore.h>
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#include "pthread_impl.h"
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int sem_trywait(sem_t *sem)
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{
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int val;
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while ((val=sem->__val[0]) > 0) {
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int new = val-1-(val==1 && sem->__val[1]);
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if (a_cas(sem->__val, val, new)==val) return 0;
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}
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errno = EAGAIN;
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return -1;
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}
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