sys/sem.h - 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 function semctl():
- Get semncnt.
- Get sempid.
- Get semval.
- Get all cases of semval.
- Get semzcnt.
- Set semval.
- Set all cases of semval.
The structure semid_ds contains the following members:
struct ipc_perm sem_perm operation permission structure unsigned short int 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>.
A semaphore is represented by an anonymous structure containing the following members:
unsigned short int semval semaphore value pid_t sempid process ID of last operation unsigned short int semncnt number of processes waiting for semval to become greater than current value unsigned short int semzcnt number of processes waiting for semval to become 0
The structure sembuf contains the following members:
unsigned short int sem_num semaphore number short int sem_op semaphore operation short int sem_flg operation flags
The following are declared as functions and may also be defined as macros. Function prototypes must be provided for use with an ISO C compiler.
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> will be defined when this header is included.
semctl(), semget(), semop(), <sys/types.h>.