#include <sys/types.h> #include <sys/ipc.h> #include <sys/sem.h>
int semget(key, nsems, semflg) key_t key; int nsems, semflg;
A semaphore identifier and associated data structure and set containing nsems semaphores (see intro.2 are created for key if one of the following are true:
Upon creation, the data structure associated with the new semaphore identifier is initialized as follows:
A semaphore identifier (semid) is a unique positive integer created by a semget.2 system call. Each semid has a set of semaphores and a data structure associated with it. The data structure is referred to as semid_ds and contains the following members:
struct ipc_perm sem_perm; /* operation permission struct */ ushort sem_nsems; /* number of sems in set */ time_t sem_otime; /* last operation time */ time_t sem_ctime; /* last change time */ /* Times measured in secs since */ /* 00:00:00 GMT, Jan. 1, 1970 */
sem_perm is an ipc_perm structure that specifies the semaphore operation permission (see below). This structure includes the following members:
ushort cuid; /* creator user id */ ushort cgid; /* creator group id */ ushort uid; /* user id */ ushort gid; /* group id */ ushort mode; /* r/a permission */
The value of
sem_nsems
is equal to the number of semaphores in the set.
Each semaphore in the set is referenced by a positive integer
referred to as a
sem_num.
sem_num
values run sequentially from 0 to the value of
sem_nsems
minus 1.
sem_otime
is the time of the last
semop.2
operation, and
sem_ctime
is the time of the last
semctl.2
operation that changed a member of the above structure.
A semaphore is a data structure that contains the following members:
ushort semval; /* semaphore value */ short sempid; /* pid of last operation */ ushort semncnt; /* # awaiting semval > cval */ ushort semzcnt; /* # awaiting semval = 0 */
semval is a non-negative integer. sempid is equal to the process ID of the last process that performed a semaphore operation on this semaphore. semncnt is a count of the number of processes that are currently suspended awaiting this semaphore's semval to become greater than its current value. semzcnt is a count of the number of processes that are currently suspended awaiting this semaphore's semval to become zero.
A semaphore identifier exists for key, but the number of semaphores in the set associated with it is less than nsems and nsems is not equal to zero.
A semaphore identifier is to be created but the system-imposed limit on the maximum number of allowed semaphores system wide would be exceeded.
Created by unroff & hp-tools. © somebody (See intro for details). All Rights Reserved. Last modified 11/5/97