Standard C Library Functions                         sempost(3C)



NAME
     sempost - increment the count of a semaphore

SYNOPSIS
     #include 

     int sempost(semt *sem);


DESCRIPTION
     The sempost() 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 semwait(3C). If the symbol POSIXPRIORITYSCHEDULING 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  SCHEDFIFO  and  SCHEDR,  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
     POSIXPRIORITYSCHEDULING is not defined, the choice  of  a
     thread  to unblock is unspecified.

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

ERORS
     The sempost() function will fail if:

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


     ENOSYS        The sempost() function is  not  supported  by
                   the system.






SunOS 5.11           Last change: 5 Feb 2008                    1






Standard C Library Functions                         sempost(3C)



     EOVERFLOW     The semaphore value exceeds SEMVALUEMAX.


USAGE
     The sempost() 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(3C)).

EXAMPLES
     See semwait(3C).

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



     
           ATRIBUTE TYPE               ATRIBUTE VALUE       
    
     Interface Stability          Committed                   
    
     MT-Level                     Async-Signal-Safe           
    
     Standard                     See standards(5).           
    


SEE ALSO
     schedsetscheduler(3C), semwait(3C), semaphore(3C),  attri-
     butes(5), standards(5)





















SunOS 5.11           Last change: 5 Feb 2008                    2