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SEM_POST(3) Linux Programmer's Manual SEM_POST(3) NAME sem_post - unlock a semaphore SYNOPSIS #include <semaphore.h> int sem_post(sem_t *sem); Link with -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. ATTRIBUTES For an explanation of the terms used in this section, see attributes(7). ββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ¬ββββββββββββββββ¬ββββββββββ βInterface β Attribute β Value β ββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββΌββββββββββββββββΌββββββββββ€ βsem_post() β Thread safety β MT-Safe β ββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββββ΄ββββββββββββββββ΄ββββββββββ CONFORMING TO POSIX.1-2001. NOTES sem_post() is async-signal-safe: it may be safely called within a signal handler. EXAMPLES See sem_wait(3) and shm_open(3). SEE ALSO sem_getvalue(3), sem_wait(3), sem_overview(7), signal-safety(7) Linux 2021-03-22 SEM_POST(3)