SEM_POSTSection: Linux Programmer's Manual (3)
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NAMEsem_post - unlock a semaphore
#include <semaphore.h> int sem_post(sem_t *sem);
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.
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.
- sem is not a valid semaphore.
- The maximum allowable value for a semaphore would be exceeded.
ATTRIBUTESFor an explanation of the terms used in this section, see attributes(7).
NOTESsem_post() is async-signal-safe: it may be safely called within a signal handler.
EXAMPLESSee sem_wait(3) and shm_open(3).
SEE ALSOsem_getvalue(3), sem_wait(3), sem_overview(7), signal-safety(7)
COLOPHONThis page is part of release 5.10 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.
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