Realtime Library Functions                          sem_post(3RT)

NAME
     sem_post - increment the count of a semaphore

SYNOPSIS
     cc [ flag... ] file... -lrt [ library... ]
     #include <semaphore.h>

     int sem_post(sem_t *sem);

DESCRIPTION
     The sem_post() function unlocks the semaphore referenced  by
     sem by performing a semaphore unlock operation on that sema-
     phore.

     If the semaphore value  resulting  from  this  operation  is
     positive,  then  no  threads   were  blocked waiting for the
     semaphore to become unlocked; the semaphore value is  simply
     incremented.

     If the value of the semaphore resulting from this  operation
     is 0, then one of the threads  blocked waiting for the sema-
     phore will be allowed to return successfully from  its  call
     to  sem_wait(3RT).  If the symbol _POSIX_PRIORITY_SCHEDULING
     is defined, the thread  to be unblocked will be chosen in  a
     manner appropriate to the scheduling policies and parameters
     in effect for the  blocked  threads.  In  the  case  of  the
     schedulers  SCHED_FIFO  and  SCHED_RR,  the highest priority
     waiting thread  will be unblocked, and if there is more than
     one  highest  priority thread  blocked waiting for the sema-
     phore, then the highest priority thread that has been  wait-
     ing   the   longest   will   be  unblocked.  If  the  symbol
     _POSIX_PRIORITY_SCHEDULING is not defined, the choice  of  a
     thread  to unblock is unspecified.

RETURN VALUES
     If successful, sem_post() returns 0; otherwise it returns -1
     and sets errno to indicate the error.

ERRORS
     The sem_post() function will fail if:

     EINVAL
           The sem argument does not refer to a valid semaphore.

     ENOSYS
           The sem_post() function is not supported by  the  sys-
           tem.

     EOVERFLOW
           The semaphore value exceeds SEM_VALUE_MAX.

SunOS 5.9           Last change: 27 Mar 2000                    1

Realtime Library Functions                          sem_post(3RT)

USAGE
     The sem_post() function is reentrant with respect to signals
     and  may  be  invoked  from  a signal-catching function. The
     semaphore functionality described on this manual page is for
     the POSIX (see standards(5)) threads implementation. For the
     documentation  of  the  Solaris   threads   interface,   see
     semaphore(3THR)).

EXAMPLES
     Example 1: See sem_wait(3RT).

ATTRIBUTES
     See attributes(5) for descriptions of the  following  attri-
     butes:

     ____________________________________________________________
    |       ATTRIBUTE TYPE        |       ATTRIBUTE VALUE       |
    | MT-Level                    | Async-Signal-Safe           |
    |_____________________________|_____________________________|

SEE ALSO
     sched_setscheduler(3RT),   sem_wait(3RT),   semaphore(3THR),
     attributes(5), standards(5)