semget(2)
NAME
semget − get set of semaphores
SYNTAX
#include <sys/types.h>
#include <sys/ipc.h>
#include <sys/sem.h>
int semget(key, nsems, semflg)
key_t key;
int nsems, semflg;
DESCRIPTION
The semget system call returns the semaphore identifier associated with key.
A semaphore identifier and associated data structure and set containing nsems semaphores are created for key if one of the following are true:
•The key is equal to IPC_PRIVATE.
•The key does not already have a semaphore identifier associated with it, and ( semflg & IPC_CREAT ) is true.
For further information, see intro(2).
Upon creation, the data structure associated with the new semaphore identifier is initialized as follows:
•The sem_perm.cuid, sem_perm.uid, sem_perm.cgid, and sem_perm.gid are set equal to the effective user ID and effective group ID, respectively, of the calling process.
•The low-order 9 bits of sem_perm.mode are set equal to the low-order 9 bits of semflg.
•The value of sem_nsems is set equal to nsems.
•The value of sem_otime is set equal to 0, and the value of sem_ctime is set equal to the current time.
RETURN VALUE
If successful, returns a semaphore identifier. If unsuccessful, returns a −1, and the global variable errno indicates the error code.
DIAGNOSTICS
The call will fail if:
[EINVAL] The specified nsems either is less than or equal to zero or is greater than the system-imposed limit.
[EACCES] A semaphore identifier exists for key, but operation permission as specified by the low-order 9 bits of semflg would not be granted. For further information, see intro(2).
[EINVAL] 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.
[ENOENT] A semaphore identifier does not exist for key, and ( semflg & IPC_CREAT ) is false.
[ENOSPC] A semaphore identifier is to be created, but the system-imposed limit on the maximum number of allowed semaphores system wide would be exceeded.
[EEXIST] A semaphore identifier exists for key, but ( ( semflg & IPC_CREAT ) and ( semflg & IPC_EXCL ) ) are true.