sem (0p) - Linux Manuals

sem: XSI semaphore facility

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.

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 .