sem_trywait(3p) — Linux manual page

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.1‐2017, Section 3.291, 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.1‐2017, Section 3.291,
       Priority Inversion, Section 4.12, Memory Synchronization,
       semaphore.h(0p)

COPYRIGHT         top

       Portions of this text are reprinted and reproduced in electronic
       form from IEEE Std 1003.1-2017, Standard for Information
       Technology -- Portable Operating System Interface (POSIX), The
       Open Group Base Specifications Issue 7, 2018 Edition, Copyright
       (C) 2018 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 original Standard can be
       obtained online at http://www.opengroup.org/unix/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               2017                   SEM_TRYWAIT(3P)

Pages that refer to this page: semaphore.h(0p)semctl(3p)semget(3p)sem_getvalue(3p)sem_init(3p)semop(3p)sem_open(3p)sem_post(3p)sem_timedwait(3p)sem_wait(3p)