semget(2) System Calls Manual 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 system call returns the semaphore identifier associated with key. A semaphore identifier and associated data structure and set con-
taining nsems semaphores are created for key, if one of the following is true:
o The key is equal to IPC_PRIVATE
o The key does not already have a semaphore identifier associated with it, and (semflg & IPC_CREAT ) is true.
For further information, see
Upon creation, the data structure associated with the new semaphore identifier is initialized as follows:
o 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, respec-
tively, of the calling process.
o The low-order nine bits of sem_perm.mode are set equal to the low-order nine bits of semflg.
o The sem_nsems is set equal to the value of nsems.
o The sem_otime is set equal to zero (0) and sem_ctime is set equal to the current time.
Return Values
Upon successful completion, a nonnegative integer, namely a semaphore identifier, is returned. Otherwise, a value of -1 is returned and
errno is set to indicate the error.
Diagnostics
The semget system call fails if any of the following is true:
[EINVAL] The nsems is either less than or equal to zero or greater than the system-imposed limit
[EACCES] A semaphore identifier exists for key, but operation permission, as specified by the low-order nine bits of semflg would not
be granted. For further information, see
[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 semaphore identifiers
in the system would be exceeded.
[EEXIST] A semaphore identifier exists for key but ((semflg & IPC_CREAT ) & (semflg & IPC_EXCL )) is true.
See Also
semctl(2), semop(2), ftok(3)
semget(2)
