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sem_post(3p) [centos man page]

SEM_POST(3P)						     POSIX Programmer's Manual						      SEM_POST(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_post - unlock a semaphore (REALTIME) SYNOPSIS
#include <semaphore.h> int sem_post(sem_t *sem); DESCRIPTION
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 reentrant with respect to signals and may be invoked from a signal-catching function. RETURN VALUE
If successful, the sem_post() function shall return zero; otherwise, the function shall return -1 and set errno to indicate the error. ERRORS
The sem_post() function shall fail if: EINVAL The sem argument does not refer to a valid semaphore. The following sections are informative. EXAMPLES
None. APPLICATION USAGE
The sem_post() function is part of the Semaphores option and need not be available on all implementations. RATIONALE
None. FUTURE DIRECTIONS
None. SEE ALSO
semctl(), semget(), semop(), sem_timedwait(), sem_trywait(), sem_wait(), the Base Definitions volume of IEEE Std 1003.1-2001, <semaphore.h> COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol- ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 . IEEE
/The Open Group 2003 SEM_POST(3P)

Check Out this Related Man Page

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 (REALTIME) 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() and sem_wait() functions shall fail if: EAGAIN The semaphore was already locked, so it cannot be immediately locked by the sem_trywait() operation ( sem_trywait() only). EINVAL The sem argument does not refer to a valid semaphore. The sem_trywait() and sem_wait() functions may fail if: EDEADLK A deadlock condition was detected. EINTR A signal interrupted this function. 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 IEEE Std 1003.1-2001, Section 3.285, Priority Inversion. The sem_trywait() and sem_wait() functions are part of the Semaphores option and need not be provided on all implementations. RATIONALE
None. FUTURE DIRECTIONS
None. SEE ALSO
semctl(), semget(), semop(), sem_post(), sem_timedwait(), the Base Definitions volume of IEEE Std 1003.1-2001, <semaphore.h> COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol- ogy -- Portable Operating System Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 . IEEE
/The Open Group 2003 SEM_TRYWAIT(3P)
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