posix man page for sem_trywait

SEM_TRYWAIT(3P) 					     POSIX Programmer's Manual						   SEM_TRYWAIT(3P)

PROLOG
       This  manual page is part of the POSIX Programmer's Manual.  The Linux implementation of this interface may differ (consult the correspond-
       ing Linux manual page for details of Linux behavior), or the interface may not be implemented on Linux.

NAME
       sem_trywait, sem_wait -- lock a semaphore

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 semaphore is currently not locked; that is, if the  sema-
       phore value is currently positive. Otherwise, it shall not lock the semaphore.

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

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

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

       EDEADLK
	      A deadlock condition was detected.

       EINTR  A signal interrupted this function.

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

       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 POSIX.1-2008,  Sec-
       tion 3.287, Priority Inversion.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       semctl(), semget(), semop(), sem_post(), sem_timedwait()

       The Base Definitions volume of POSIX.1-2008, Section 3.287, Priority Inversion, Section 4.11, Memory Synchronization, <semaphore.h>

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2013 Edition, Standard for Information Technol-
       ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 7, Copyright (C)  2013  by	the  Institute	of
       Electrical and Electronics Engineers, Inc and The Open Group.  (This is POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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 Stan-
       dard is the referee document. The original Standard can be obtained online at http://www.unix.org/online.html .

       Any typographical or formatting errors that appear in this page are most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE
/The Open Group						       2013							   SEM_TRYWAIT(3P)