IPC::Semaphore

Section: User Contributed Perl Documentation (3)
Updated: 2021-01-27
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NAME

IPC::Semaphore - SysV Semaphore IPC object class

SYNOPSIS

    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) for more details. For example

    $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.

    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.

    uid
    gid
    cuid
    cgid
    mode
    ctime
    otime
    nsems

AUTHORS

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

COPYRIGHT

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