semget.2freebsd

Langue: en

Version: 266133 (debian - 07/07/09)

Section: 2 (Appels système)

Sommaire


BSD mandoc

NAME

semget - obtain a semaphore id

LIBRARY

Lb libc

SYNOPSIS

In sys/types.h In sys/ipc.h In sys/sem.h Ft int Fn semget key_t key int nsems int flag

DESCRIPTION

Based on the values of Fa key and Fa flag , Fn semget returns the identifier of a newly created or previously existing set of semaphores. The key is analogous to a filename: it provides a handle that names an IPC object. There are three ways to specify a key:

The mode of a newly created IPC object is determined by OR 'ing the following constants into the Fa flag argument:

SEM_R
Read access for user.
SEM_A
Alter access for user.
( SEM_R>>3
Read access for group.
( SEM_A>>3
Alter access for group.
( SEM_R>>6
Read access for other.
( SEM_A>>6
Alter access for other.

If a new set of semaphores is being created, Fa nsems is used to indicate the number of semaphores the set should contain. Otherwise, Fa nsems may be specified as 0.

RETURN VALUES

The Fn semget system call returns the id of a semaphore set if successful; otherwise, -1 is returned and errno is set to indicate the error.

ERRORS

The Fn semget system call will fail if:
Bq Er EACCES
Access permission failure.
Bq Er EEXIST
IPC_CREAT and IPC_EXCL were specified, and a semaphore set corresponding to Fa key already exists.
Bq Er EINVAL
The number of semaphores requested exceeds the system imposed maximum per set.
Bq Er ENOSPC
Insufficiently many semaphores are available.
Bq Er ENOSPC
The kernel could not allocate a Fa struct semid_ds .
Bq Er ENOENT
No semaphore set was found corresponding to Fa key , and IPC_CREAT was not specified.

SEE ALSO

semctl(2), semop(2), ftok(3)