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(.).
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 sem_nsems is set equal to the value of nsems.
The sem_otime is set equal to 0 and sem_ctime is set equal to the current time.
RETURN VALUE
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 will fail if one or more of the following are 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 9 bits of semflg would not be granted. For further information, see errno(.).
[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 system wide would be exceeded.
[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 ) & (semflg & IPC_EXCL )) is "true".