sem.h

<sys/sem.h>(P)						       <sys/sem.h>(P)



NAME
       sys/sem.h - XSI semaphore facility

SYNOPSIS
       #include <sys/sem.h>

DESCRIPTION
       The <sys/sem.h> header shall define the following constants and struc-
       tures.

       Semaphore operation flags:

       SEM_UNDO
	      Set up adjust on exit entry.


       Command definitions for the semctl() function  shall  be	 provided  as
       follows:

       GETNCNT
	      Get semncnt.

       GETPID Get sempid.

       GETVAL Get semval.

       GETALL Get all cases of semval.

       GETZCNT
	      Get semzcnt.

       SETVAL Set semval.

       SETALL Set all cases of semval.


       The semid_ds structure shall contain the following members:


	      struct ipc_perm  sem_perm	 Operation permission structure.
	      unsigned short   sem_nsems Number of semaphores in set.
	      time_t	       sem_otime Last semop
	       () time.
	      time_t	       sem_ctime Last time changed by semctl
	       ().

       The  pid_t,  time_t,  key_t,  and  size_t  types	 shall	be defined as
       described in <sys/types.h> .

       A semaphore shall be represented by an anonymous structure  containing
       the following members:


	      unsigned short  semval   Semaphore value.
	      pid_t	      sempid   Process ID of last operation.
	      unsigned short  semncnt  Number of processes waiting for semval
				       to become greater than current value.
	      unsigned short  semzcnt  Number of processes waiting for semval
				       to become 0.

       The sembuf structure shall contain the following members:


	      unsigned short  sem_num	Semaphore number.
	      short	      sem_op	Semaphore operation.
	      short	      sem_flg	Operation flags.

       The  following  shall be declared as functions and may also be defined
       as macros. Function prototypes shall be provided.


	      int   semctl(int, int, int, ...);
	      int   semget(key_t, int, int);
	      int   semop(int, struct sembuf *, size_t);

       In addition, all of the symbols from <sys/ipc.h> shall be defined when
       this header is included.

       The following sections are informative.

APPLICATION USAGE
       None.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       <sys/ipc.h> , <sys/types.h> , semctl(), semget(), semop()

COPYRIGHT
       Portions	 of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1, 2003 Edition, Standard for Information  Technol-
       ogy  --	Portable  Operating  System Interface (POSIX), The Open Group
       Base Specifications Issue 6, Copyright (C) 2001-2003 by the  Institute
       of  Electrical  and  Electronics Engineers, Inc and The Open Group. In
       the event of any discrepancy between this  version  and	the  original
       IEEE and The Open Group Standard, the original IEEE and The Open Group
       Standard is  the	 referee  document.  The  original  Standard  can  be
       obtained online at http://www.opengroup.org/unix/online.html .



POSIX				     2003		       <sys/sem.h>(P)