semget (2)

Leading comments

Copyright (c) 1995 David Hovemeyer <daveho@infocom.com>

All rights reserved.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
   notice, this list of conditions and the following disclaimer in the
   d...

(The comments found at the beginning of the groff file "man2/semget.2freebsd".)

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:

• IPC_PRIVATE may be specified, in which case a new IPC object will be created.
• An integer constant may be specified. If no IPC object corresponding to Fa key is specified and the IPC_CREAT bit is set in Fa flag , a new one will be created.
• The ftok(3) function may be used to generate a key from a pathname.

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)