NAME

       sys/sem.h - XSI semaphore facility

SYNOPSIS

       #include <sys/sem.h>

DESCRIPTION

       The <sys/sem.h> header shall define the following constants and structures.

       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 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 .