- semaphore facility
The <sys/sem.h> header defines the following constants and structures.
Semaphore operation flags:
Set up adjust on exit entry.
Command definitions for the semctl() function are provided as listed below. See semctl(2).
Get all cases of semval.
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).
See attributes(5) for descriptions of the following attributes: