sys_sem.h(0P)		   POSIX Programmer's Manual		 sys_sem.h(0P)

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 symbolic constant for
       use as a semaphore operation flag:

       SEM_UNDO	   Set up adjust on exit entry.

       The <sys/sem.h> header shall define the following symbolic constants
       for use as commands for the semctl() function:

       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 <sys/sem.h> header shall define the semid_ds structure, which shall
       include 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 <sys/sem.h> header shall define the pid_t, size_t, and time_t types
       as described in <sys/types.h>.

       A semaphore shall be represented by an anonymous structure, which shall
       include 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 <sys/sem.h> header shall define the sembuf structure, which shall
       include 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, the <sys/sem.h> header shall include the <sys/ipc.h>
       header.

       The following sections are informative.

APPLICATION USAGE
       None.

RATIONALE
       None.

FUTURE DIRECTIONS
       None.

SEE ALSO
       <sys_ipc.h>, <sys_types.h>

       The System Interfaces volume of POSIX.1‐2017, semctl(), semget(),
       semop()

COPYRIGHT
       Portions of this text are reprinted and reproduced in electronic form
       from IEEE Std 1003.1-2017, Standard for Information Technology --
       Portable Operating System Interface (POSIX), The Open Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       Any typographical or formatting errors that appear in this page are
       most likely to have been introduced during the conversion of the source
       files to man page format. To report such errors, see
       https://www.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group		     2017			 sys_sem.h(0P)