sigsem(2)                 SYSTEM CALLS                  sigsem(2)



NAME
     sigsem - signals a process waiting on a semaphore.

SYNOPSIS
     cc [flag ...] file ... -lx
     sigsem(int sem_num);

DESCRIPTION
     sigsem signals a process that is waiting  on  the  semaphore
     sem_num that it may proceed and use the resource governed by
     the semaphore.  sigsem is used in conjunction  with  waitsem
     to  allow  synchronization  of processes wishing to access a
     resource.  One or more processes may waitsem  on  the  given
     semaphore  and  will be put to sleep until the process which
     currently has access to the resource issues a  sigsem  call.
     If  there  are any waiting processes, sigsem causes the pro-
     cess which is next in line on the semaphore's  queue  to  be
     rescheduled  for execution.  The semaphore's queue is organ-
     ized in First In, First Out (FIFO) order.

DIAGNOSTICS
     sigsem returns the value (int) -1 if an  error  occurs.   If
     sem_num  does  not  refer to a semaphore type file, errno is
     set to ENOTNAM.  If sem_num has not been  previously  opened
     by opensem, errno is set to EBADF.  If the process issuing a
     sigsem call is not the current ``owner''  of  the  semaphore
     (i.e.,  if  the process has not issued a waitsem call before
     the sigsem), errno is set to ENAVAIL.

SEE ALSO
     creatsem(2), opensem(2), waitsem(2).
























             Last change: XENIX Compatiblity Package            1