sem_wait(3) - NetBSD Manual Pages

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 5.1.2 January 22, 2003 NetBSD 5.1.2

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