sem_post - Online Linux Manual PageSection : 3
Updated : 2022-12-15
Source : Linux man-pages 6.03

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NAMEsem_post − unlock a semaphore

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LIBRARYPOSIX threads library (libpthread, −lpthread)

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

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DESCRIPTIONsem_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.

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RETURN VALUEsem_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.

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ERRORSEINVAL  sem is not a valid semaphore. EOVERFLOW   The maximum allowable value for a semaphore would be exceeded.

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ATTRIBUTESFor an explanation of the terms used in this section, see attributes(7). InterfaceAttributeValue sem_post() Thread safetyMT-Safe

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STANDARDSPOSIX.1-2001.

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NOTESsem_post() is async-signal-safe: it may be safely called within a signal handler.

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EXAMPLESSee sem_wait(3) and shm_open(3).

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SEE ALSOsem_getvalue(3), sem_wait(3), sem_overview(7), signal−safety(7) 0

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