PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT

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

PROLOG         top

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

NAME         top

       sem_trywait, sem_wait — lock a semaphore

SYNOPSIS         top

       #include <semaphore.h>

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

DESCRIPTION         top

       The sem_trywait() function shall lock the semaphore referenced by sem
       only if the semaphore is currently not locked; that is, if the
       semaphore 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
       semaphore 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         top

       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         top

       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         top

       None.

APPLICATION USAGE         top

       Applications using these functions may be subject to priority
       inversion, as discussed in the Base Definitions volume of
       POSIX.1‐2008, Section 3.287, Priority Inversion.

RATIONALE         top

       None.

FUTURE DIRECTIONS         top

       None.

SEE ALSO         top

       semctl(3p), semget(3p), semop(3p), sem_post(3p), sem_timedwait(3p)

       The Base Definitions volume of POSIX.1‐2008, Section 3.287, Priority
       Inversion, Section 4.11, Memory Synchronization, semaphore.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2013 Edition, Standard for Information
       Technology -- 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 Standard 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)