sys_sem.h - Man Page

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.

#include <sys/sem.h>

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.

None.

None.

None.

<sys_ipc.h>, <sys_types.h>

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

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 .

semctl(3p), semget(3p), semop(3p).