IPC::Semaphore(3perl)

💖 NAME 💖

okay so bestie, welcome to IPC::Semaphore — it's the SysV Semaphore IPC object class. that's the whole vibe. it's the cute object-y interface to SysV IPC semaphores. (and hey, the header up top says IPC::Semaphore(3perl) from the Perl Programmers Reference Guide, so like, you're in the right place 🫶)

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✨ SYNOPSIS ✨

here's the whole thing in action, copy-paste energy, no notes:

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;

like… the range? the range is ranging. 💅

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🌸 DESCRIPTION 🌸

so basically, this is a class that gives you an object based interface to SysV IPC semaphores. that's it, that's the whole main character moment. it wraps the raw syscall nonsense in a nice little object so you don't have to rawdog the C API. iconic behavior, honestly.

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👑 METHODS 👑

🎀 new ( KEY , NSEMS , FLAGS )

creates a new semaphore set associated with KEY. NSEMS is the number of semaphores in the set. a new set gets 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.

when a new semaphore set is created, FLAGS is what sets the permissions. and listen — be careful not to set any flags that the Sys V IPC implementation does not allow: on some systems, setting execute bits makes the operations fail. like it just says no and everything breaks. so don't do that 🙈

lowkey the execute-bits thing is a trap. it's giving "why is nothing working" and the answer is the execute bits. beware.

🔥 getall

returns the values of the semaphore set as an array. that's it. all of them. every single one. slay.

💜 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. it's giving receipts. it remembers who touched it last 👀

⭐ 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
);

three values, three values, go off. math is mathing 📐✨

🧚 remove

remove and destroy the semaphore set from the system. it's gone. deleted. archived. no take-backs. 💀

🎀 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. your choice, bestie, both are valid 🫶

✨ setall ( VALUES )

sets all values in the semaphore set to those given on the VALUES list. VALUES must contain the correct number of values. (miss one? that's a you problem, no cap.)

🌸 setval ( N , VALUE )

set the Nth 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

and fr fr, see your system documentation for what those actually mean — the man page is not gonna guess for you 💖

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🦋 SEE ALSO 🦋

• IPC::SysV
• Class::Struct
• semget(2)
• semctl(2)
• semop(2)

like the whole friend group. they come as a set. iykyk 💜

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💜 AUTHORS 💜

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

two absolute legends. legends only. periodt. 👑

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💖 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.

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that's the whole page bestie. go make some semaphores, be careful with your flags, and don't set execute bits unless you wanna have a bad time 😭

and that's a wrap on this perl v5.44.0 era of the docs, dated 2026-10-17 — IPC::Semaphore(3perl), signing off 🎀✨💅