sem_trywait man page on OSF1

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sem_wait(3)							   sem_wait(3)

NAME
       sem_wait,  sem_trywait  -  Performs (or conditionally performs) a sema‐
       phore lock (P1003.1b)

SYNOPSIS
       #include <semaphore.h>

       int sem_wait ( sem_t *sem);

       int sem_trywait ( sem_t *sem)

LIBRARY
       Realtime Library (librt.so, librt.a)

PARAMETERS
       Specifies a pointer to the semaphore to be locked.

DESCRIPTION
       The sem_wait function locks the semaphore referenced by sem by perform‐
       ing  a  semaphore lock operation on it. If the semaphore value is zero,
       the sem_wait function blocks until it either locks the semaphore or  is
       interrupted by a signal.

       The  sem_trywait	 function  locks  a semaphore only if the semaphore is
       currently not locked. If the semaphore value is zero,  the  sem_trywait
       function returns without locking the semaphore.

       These functions help ensure that the resource associated with the sema‐
       phore cannot be accessed by  other  processes.  The  semaphore  remains
       locked  until  the process unlocks it with a call to the sem_post func‐
       tion.

       Use the sem_wait function instead of the sem_trywait  function  if  the
       process should wait for access to the semaphore.

RETURN VALUES
       If  the	sem_wait or sem_trywait function returns successfully, a value
       of 0 (zero) is returned and the function executes  the  semaphore  lock
       operation.

       On  an unsuccessful call, a value of -1 is returned and errno is set to
       indicate that an error occurred. The state  of  the  semaphore  remains
       unchanged.

ERRORS
       The  sem_wait and sem_trywait functions fail under the following condi‐
       tions: The semaphore was already locked and cannot  be  locked  by  the
       sem_trywait  operation	(sem_trywait only).  A signal interrupted this
       function.  The sem argument does not refer to a valid semaphore.

SEE ALSO
       Functions: sem_post(3)

       Guide to Realtime Programming

								   sem_wait(3)
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