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sem.h, sem - semaphore facility

#include <sys/sem.h>

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

Semaphore operation flags: SEM_UNDO

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

GETPID GETVAL GETALL GETZCNT SETVAL SETALL

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).

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

ATTRIBUTE TYPE ATTRIBUTE VALUE

Interface Stability Standard

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