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NetBSD 6.1.5 - man page for sem_wait (netbsd section 3)

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SEM_WAIT(3)			   BSD 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'').

BSD					 January 22, 2003				      BSD
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