sem_post(3) [netbsd man page]

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

NAME

     sem_post -- increment (unlock) a semaphore

LIBRARY

     POSIX Real-time Library (librt, -lrt)

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().

     sem_post() 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

     sem_post() will fail if:

     [EINVAL]		sem points to an invalid semaphore.

SEE ALSO

     sem_trywait(3), sem_wait(3)

STANDARDS

     sem_post() conforms to ISO/IEC 9945-1:1996 (``POSIX.1'').

BSD
								 January 22, 2003							       BSD

sem_post(3)						     Library Functions Manual						       sem_post(3)

NAME

       sem_post - Unlocks a semaphore (P1003.1b)

LIBRARY

       Realtime Library (librt.so, librt.a)

SYNOPSIS

       #include <semaphore.h>

       int sem_post (
       sem_t *sem);

PARAMETERS

       sem	 Pointer to the semaphore to be unlocked.

DESCRIPTION

       The sem_post function unlocks the specified semaphore by performing the semaphore unlock operation on that semaphore. The appropriate func-
       tion (sem_open for named semaphores or sem_init for unnamed semaphores) must be called for a semaphore before you can call the locking  and
       unlocking functions, sem_wait, sem_trywait, and sem_post.

       If the semaphore value after a sem_post function is positive, no processes were blocked waiting for the semaphore to be unlocked; the sema-
       phore value is incremented.  If the semaphore value after a sem_post function is zero, one of the processes blocked waiting for	the  sema-
       phore is allowed to return successfully from its call to sem_wait.

       If  more  than one process is blocked while waiting for the semaphore, only one process is unblocked and the state of the semaphore remains
       unchanged when the sem_post function returns. The process to be unblocked is selected according to the scheduling policies  and	priorities
       of  all	blocked  processes. If the scheduling policy is SCHED_FIFO or SCHED_RR, the highest-priority waiting process is unblocked. If more
       than one process of that priority is blocked, then the process that has waited the longest is unblocked.

       The sem_post function can be called from a signal-catching function.

RETURN VALUES

       On successful completion, the sem_post function returns the value 0 (zero) and performs a semaphore unlock operation, unblocking a process.

       Otherwise, the function returns the value -1 and sets errno to indicate the error.  The state of the semaphore remains unchanged.

ERRORS

       The sem_post function fails under the following condition:

       [EINVAL]       The sem does not refer to a valid semaphore.

RELATED INFORMATION

       Functions: sem_trywait(3), sem_wait(3)

       Guide to Realtime Programming delim off

																       sem_post(3)