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sem_post(3p) — Linux manual page

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

SEM_POST(3P)            POSIX Programmer's ManualSEM_POST(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_post — unlock a semaphore

SYNOPSIS top

       #include <semaphore.h>       int sem_post(sem_t *sem);

DESCRIPTION top

       Thesem_post() function shall unlock the semaphore referenced bysem 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 tosem_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.       Thesem_post() function shall be async-signal-safe and may be       invoked from a signal-catching function.

RETURN VALUE top

       If successful, thesem_post() function shall return zero;       otherwise, the function shall return -1 and seterrno to indicate       the error.

ERRORS top

       Thesem_post() function may fail if:EINVALThesem argument does not refer to a valid semaphore.The following sections are informative.

EXAMPLES top

       Seesem_timedwait(3p).

APPLICATION USAGE top

       None.

RATIONALE top

       None.

FUTURE DIRECTIONS top

       None.

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 athttp://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, seehttps://www.kernel.org/doc/man-pages/reporting_bugs.html .IEEE/The Open Group                2017SEM_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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