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man pages section 3: Library Interfaces and Headers

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Updated: Thursday, June 13, 2019
 
 

sem(3HEAD)

Name

sem.h, sem - semaphore facility

Synopsis

#include <sys/sem.h>

Description

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

Semaphore operation flags:

SEM_UNDO

Set up adjust on exit entry.

Command definitions for the semctl() function are provided as listed below. See semctl(2).

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 contains 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 are defined as described in <sys/types.h>. See types.h(3HEAD).

A semaphore is 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 contains the following members:


unsigned short sem_num     /* semaphore number */
short          sem_op      /* semaphore operation */
short          sem_flg     /* operation flags */

All of the symbols from <sys/ipc.h> are defined when this header is included. See ipc.h(3HEAD).

Attributes

See attributes(7) for descriptions of the following attributes:

ATTRIBUTE TYPE
ATTRIBUTE VALUE
Interface Stability
Committed
Standard

See Also

semctl(2), semget(2), semop(2), ipc.h(3HEAD), types.h(3HEAD), attributes(7), standards(7)