sem_post(3)

1sem_post(3)                Library Functions Manual                sem_post(3)
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NAME

6       sem_post - unlock a semaphore
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LIBRARY

9       POSIX threads library (libpthread, -lpthread)
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SYNOPSIS

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

17       sem_post()  increments  (unlocks)  the semaphore pointed to by sem.  If
18       the semaphore's value consequently becomes greater than zero, then  an‐
19       other  process or thread blocked in a sem_wait(3) call will be woken up
20       and proceed to lock the semaphore.
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RETURN VALUE

23       sem_post() returns 0 on success; on error, the value of  the  semaphore
24       is left unchanged, -1 is returned, and errno is set to indicate the er‐
25       ror.
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ERRORS

28       EINVAL sem is not a valid semaphore.
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30       EOVERFLOW
31              The maximum allowable value for a semaphore would be exceeded.
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ATTRIBUTES

34       For an  explanation  of  the  terms  used  in  this  section,  see  at‐
35       tributes(7).
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37       ┌────────────────────────────────────────────┬───────────────┬─────────┐
38       │Interface                                   │ Attribute     │ Value   │
39       ├────────────────────────────────────────────┼───────────────┼─────────┤
40       │sem_post()                                  │ Thread safety │ MT-Safe │
41       └────────────────────────────────────────────┴───────────────┴─────────┘
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STANDARDS

44       POSIX.1-2008.
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HISTORY

47       POSIX.1-2001.
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NOTES

50       sem_post()  is async-signal-safe: it may be safely called within a sig‐
51       nal handler.
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EXAMPLES

54       See sem_wait(3) and shm_open(3).
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