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```{index} single: IPC::Semaphore
```

# IPC::Semaphore

SysV Semaphore IPC object class

## SYNOPSIS

```perl
use IPC::SysV qw(IPC_PRIVATE S_IRUSR S_IWUSR IPC_CREAT);
use IPC::Semaphore;

$sem = IPC::Semaphore->new(IPC_PRIVATE, 10, S_IRUSR | S_IWUSR | IPC_CREAT);

$sem->setall( (0) x 10);

@sem = $sem->getall;

$ncnt = $sem->getncnt;

$zcnt = $sem->getzcnt;

$ds = $sem->stat;

$sem->remove;
```

## DESCRIPTION

A class providing an object based interface to SysV IPC semaphores.

## METHODS

- new ( KEY , NSEMS , FLAGS )

    Create a new semaphore set associated with `KEY`. `NSEMS` is the number
    of semaphores in the set. A new set is created if

    - `KEY` is equal to `IPC_PRIVATE`
    - `KEY` does not already have a semaphore identifier
    associated with it, and `_FLAGS_ & IPC_CREAT` is true.

    On creation of a new semaphore set `FLAGS` is used to set the
    permissions.  Be careful not to set any flags that the Sys V
    IPC implementation does not allow: in some systems setting
    execute bits makes the operations fail.

- getall

    Returns the values of the semaphore set as an array.

- getncnt ( SEM )

    Returns the number of processes waiting for the semaphore `SEM` to
    become greater than its current value

- getpid ( SEM )

    Returns the process id of the last process that performed an operation
    on the semaphore `SEM`.

- getval ( SEM )

    Returns the current value of the semaphore `SEM`.

- getzcnt ( SEM )

    Returns the number of processes waiting for the semaphore `SEM` to
    become zero.

- id

    Returns the system identifier for the semaphore set.

- op ( OPLIST )

    `OPLIST` is a list of operations to pass to `semop`. `OPLIST` is
    a concatenation of smaller lists, each which has three values. The
    first is the semaphore number, the second is the operation and the last
    is a flags value. See [semop(2)](http://man.he.net/man2/semop) for more details. For example

    ```perl
    $sem->op(
        0, -1, IPC_NOWAIT,
        1,  1, IPC_NOWAIT
    );
    ```

- remove

    Remove and destroy the semaphore set from the system.

- set ( STAT )
- set ( NAME => VALUE \[, NAME => VALUE ...\] )

    `set` will set the following values of the `stat` structure associated
    with the semaphore set.

    ```text
    uid
    gid
    mode (only the permission bits)
    ```

    `set` accepts either a stat object, as returned by the `stat` method,
    or a list of _name_-_value_ pairs.

- setall ( VALUES )

    Sets all values in the semaphore set to those given on the `VALUES` list.
    `VALUES` must contain the correct number of values.

- setval ( N , VALUE )

    Set the `N`th value in the semaphore set to `VALUE`

- stat

    Returns an object of type `IPC::Semaphore::stat` which is a sub-class of
    `Class::Struct`. It provides the following fields. For a description
    of these fields see your system documentation.

    ```text
    uid
    gid
    cuid
    cgid
    mode
    ctime
    otime
    nsems
    ```

## SEE ALSO

[IPC::SysV](SysV.md), [Class::Struct](../Class/Struct.md), [semget(2)](http://man.he.net/man2/semget), [semctl(2)](http://man.he.net/man2/semctl), [semop(2)](http://man.he.net/man2/semop)

## AUTHORS

Graham Barr <gbarr@pobox.com>,
Marcus Holland-Moritz <mhx@cpan.org>

## COPYRIGHT

Version 2.x, Copyright (C) 2007-2013, Marcus Holland-Moritz.

Version 1.x, Copyright (c) 1997, Graham Barr.

This program is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.