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PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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SEM_POST(3P) POSIX Programmer's Manual SEM_POST(3P)
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.
sem_post — unlock a semaphore
#include <semaphore.h>
int sem_post(sem_t *sem);
The sem_post() function shall unlock the semaphore referenced by
sem by performing a semaphore unlock operation on that semaphore.
If the semaphore value resulting from this operation is positive,
then no threads were blocked waiting for the semaphore to become
unlocked; the semaphore value is simply incremented.
If the value of the semaphore resulting from this operation is
zero, then one of the threads blocked waiting for the semaphore
shall be allowed to return successfully from its call to
sem_wait(). If the Process Scheduling option is supported, the
thread to be unblocked shall be chosen in a manner appropriate to
the scheduling policies and parameters in effect for the blocked
threads. In the case of the schedulers SCHED_FIFO and SCHED_RR,
the highest priority waiting thread shall be unblocked, and if
there is more than one highest priority thread blocked waiting
for the semaphore, then the highest priority thread that has been
waiting the longest shall be unblocked. If the Process Scheduling
option is not defined, the choice of a thread to unblock is
unspecified.
If the Process Sporadic Server option is supported, and the
scheduling policy is SCHED_SPORADIC, the semantics are as per
SCHED_FIFO above.
The sem_post() function shall be async-signal-safe and may be
invoked from a signal-catching function.
If successful, the sem_post() function shall return zero;
otherwise, the function shall return -1 and set errno to indicate
the error.
The sem_post() function may fail if:
EINVAL The sem argument does not refer to a valid semaphore.
The following sections are informative.
See sem_timedwait(3p).
None.
None.
None.
semctl(3p), semget(3p), semop(3p), sem_timedwait(3p),
sem_trywait(3p)
The Base Definitions volume of POSIX.1‐2017, Section 4.12, Memory
Synchronization, semaphore.h(0p)
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_POST(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_timedwait(3p), sem_trywait(3p)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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