sem_wait(3)
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SEM_WAIT(3) NetBSD Library Functions Manual SEM_WAIT(3)
NAME
sem_wait, sem_trywait -- decrement (lock) a semaphore
LIBRARY
POSIX Real-time Library (librt, -lrt)
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
The sem_wait() function returns the value 0 if successful; otherwise the
value -1 is returned and the global variable errno is set to indicate the
error.
ERRORS
sem_wait() and sem_trywait() will fail if:
[EINVAL] sem points to an invalid semaphore.
Additionally, sem_trywait() will fail if:
[EAGAIN] The semaphore value was zero, and thus could not be
decremented.
SEE ALSO
sem_post(3)
STANDARDS
sem_wait() and sem_trywait() conform to ISO/IEC 9945-1:1996
(``POSIX.1'').
NetBSD 6.0.3 January 22, 2003 NetBSD 6.0.3
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