sem_post(3RT)						    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 semaphore.

       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  semaphore  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 semaphore, then the highest priority thread that has been waiting 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 system.

       EOVERFLOW       The semaphore value exceeds SEM_VALUE_MAX.

USAGE

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

EXAMPLES

       See sem_wait(3RT).

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+
       |MT-Level		     |Async-Signal-Safe 	   |
       +-----------------------------+-----------------------------+

SEE ALSO

       sched_setscheduler(3RT), sem_wait(3RT), semaphore(3C), attributes(5), standards(5)

SunOS 5.10							    12 Feb 2003 						     sem_post(3RT)