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SEM_WAIT(3) FreeBSD Library Functions Manual SEM_WAIT(3)
NAME
sem_wait, sem_trywait - decrement (lock) a semaphore
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS
#include <semaphore.h>
int
sem_wait(sem_t *sem);
int
sem_trywait(sem_t *sem);
DESCRIPTION
The sem_wait() function decrements (locks) the semaphore pointed to by
sem, but blocks if the value of sem is zero, until the value is non-zero
and the value can be decremented.
The sem_trywait() function decrements (locks) the semaphore pointed to by
sem only if the value is non-zero. Otherwise, the semaphore is not
decremented and an error is returned.
RETURN VALUES
Upon successful completion, the value 0 is returned; otherwise the
value -1 is returned and the global variable errno is set to indicate the
error.
ERRORS
The sem_wait() and sem_trywait() functions will fail if:
[EINVAL] The sem argument points to an invalid semaphore.
Additionally, sem_wait() will fail if:
[EINTR] A signal interrupted this function.
Additionally, sem_trywait() will fail if:
[EAGAIN] The semaphore value was zero, and thus could not be
decremented.
SEE ALSO
sem_getvalue(3), sem_post(3), sem_timedwait(3)
STANDARDS
The sem_wait() and sem_trywait() functions conform to ISO/IEC 9945-1:1996
("POSIX.1").
FreeBSD 14.0-RELEASE-p6 April 16, 2013 FreeBSD 14.0-RELEASE-p6