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sem_post(3) [freebsd man page]

SEM_POST(3)						   BSD Library Functions Manual 					       SEM_POST(3)

sem_post -- increment (unlock) a semaphore LIBRARY
Standard C Library (libc, -lc) SYNOPSIS
#include <semaphore.h> int sem_post(sem_t *sem); DESCRIPTION
The sem_post() function increments (unlocks) the semaphore pointed to by sem. If there are threads blocked on the semaphore when sem_post() is called, then the highest priority thread that has been blocked the longest on the semaphore will be allowed to return from sem_wait(). The sem_post() function is signal-reentrant and may be called within signal handlers. RETURN VALUES
The sem_post() function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indi- cate the error. ERRORS
The sem_post() function will fail if: [EINVAL] The sem argument points to an invalid semaphore. [EOVERFLOW] The semaphore value would exceed SEM_VALUE_MAX. SEE ALSO
sem_getvalue(3), sem_trywait(3), sem_wait(3) STANDARDS
The sem_post() function conforms to ISO/IEC 9945-1:1996 (``POSIX.1''). BSD
January 28, 2015 BSD

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SEM_POST(3)						     Linux Programmer's Manual						       SEM_POST(3)

sem_post - unlock a semaphore SYNOPSIS
#include <semaphore.h> int sem_post(sem_t *sem); Link with -lrt or -pthread. DESCRIPTION
sem_post() increments (unlocks) the semaphore pointed to by sem. If the semaphore's value consequently becomes greater than zero, then another process or thread blocked in a sem_wait(3) call will be woken up and proceed to lock the semaphore. RETURN VALUE
sem_post() returns 0 on success; on error, the value of the semaphore is left unchanged, -1 is returned, and errno is set to indicate the error. ERRORS
EINVAL sem is not a valid semaphore. EOVERFLOW The maximum allowable value for a semaphore would be exceeded. CONFORMING TO
sem_post() is async-signal-safe: it may be safely called within a signal handler. EXAMPLE
See sem_wait(3). SEE ALSO
sem_getvalue(3), sem_wait(3), sem_overview(7) COLOPHON
This page is part of release 3.27 of the Linux man-pages project. A description of the project, and information about reporting bugs, can be found at Linux 2009-03-30 SEM_POST(3)
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