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Linux 2.6 - man page for sem_wait (linux section 3posix)

SEM_TRYWAIT(P)			    POSIX Programmer's Manual			   SEM_TRYWAIT(P)

NAME
       sem_trywait, sem_wait - lock a semaphore (REALTIME)

SYNOPSIS
       #include <semaphore.h>

       int sem_trywait(sem_t *sem);
       int sem_wait(sem_t *sem);

DESCRIPTION
       The  sem_trywait()  function  shall lock the semaphore referenced by sem only if the sema-
       phore is currently not locked; that is, if the semaphore value is currently positive. Oth-
       erwise, it shall not lock the semaphore.

       The  sem_wait()	function shall lock the semaphore referenced by sem by performing a sema-
       phore lock operation on that semaphore. If the semaphore value is currently zero, then the
       calling thread shall not return from the call to sem_wait() until it either locks the sem-
       aphore or the call is interrupted by a signal.

       Upon successful return, the state of the semaphore shall be locked and shall remain locked
       until the sem_post() function is executed and returns successfully.

       The sem_wait() function is interruptible by the delivery of a signal.

RETURN VALUE
       The  sem_trywait()  and sem_wait() functions shall return zero if the calling process suc-
       cessfully performed the semaphore lock operation on the semaphore designated by	sem.   If
       the call was unsuccessful, the state of the semaphore shall be unchanged, and the function
       shall return a value of -1 and set errno to indicate the error.

ERRORS
       The sem_trywait() and sem_wait() functions shall fail if:

       EAGAIN The semaphore was already locked,  so  it  cannot  be  immediately  locked  by  the
	      sem_trywait() operation ( sem_trywait() only).

       EINVAL The sem argument does not refer to a valid semaphore.

       The sem_trywait() and sem_wait() functions may fail if:

       EDEADLK
	      A deadlock condition was detected.

       EINTR  A signal interrupted this function.

       The following sections are informative.

EXAMPLES
       None.

APPLICATION USAGE
       Applications  using  these functions may be subject to priority inversion, as discussed in
       the Base Definitions volume of IEEE Std 1003.1-2001, Section 3.285, Priority Inversion.

       The sem_trywait() and sem_wait() functions are part of the Semaphores option and need  not
       be provided on all implementations.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       semctl() , semget() , semop() , sem_post() , sem_timedwait() , the Base Definitions volume
       of IEEE Std 1003.1-2001, <semaphore.h>

COPYRIGHT
       Portions of this text are reprinted and	reproduced  in	electronic  form  from	IEEE  Std
       1003.1,	2003  Edition,	Standard  for Information Technology -- Portable Operating System
       Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003  by
       the  Institute  of  Electrical  and  Electronics Engineers, Inc and The Open Group. In the
       event of any discrepancy between this version and the original IEEE  and  The  Open  Group
       Standard, the original IEEE and The Open Group Standard is the referee document. The orig-
       inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .

IEEE/The Open Group			       2003				   SEM_TRYWAIT(P)


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