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<sys/sem.h>(P)		   POSIX Programmer's Manual		<sys/sem.h>(P)

PROLOG
       This  manual  page is part of the POSIX Programmer's Manual.  The Linux
       implementation of this interface may differ (consult the	 corresponding
       Linux  manual page for details of Linux behavior), or the interface may
       not be implemented on Linux.

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 fol‐
       lows:

       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 Technology
       -- 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 .

IEEE/The Open Group		     2003			<sys/sem.h>(P)
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