---
name: "Linux::FD::Event"
section: "3pm"
platform: "linux"
package: "liblinux-fd-perl"
version: "0.017-1"
release: "Debian 13 (Trixie)"
platforms: ["linux"]
url: "https://new.carta.tech/Linux::FD::Event"
---

# Linux::FD::Event(3pm)

Event filehandles for Linux

## NAME

Linux::FD::Event - Event filehandles for Linux

## VERSION

version 0.017

## SYNOPSIS

```
 use Linux::FD::Event;

 my $foo = Linux::FD::Event->new(42);
 if (fork) {
     say $foo->get while sleep 1
 }
 else {
     $foo->add($_) while <>;
 }
```

## DESCRIPTION

This creates an eventfd object that can be used as an event wait/notify mechanism by userspace applications, and by the kernel to notify userspace applications of events. The object contains an unsigned 64-bit integer counter that is maintained by the kernel. It has two modes, default and semaphore, that differ only in `"get"` behavior as described below.

## METHODS

### new($initial\_value, @flags)

This creates a new eventfd filehandler. The counter is initialized with the value specified in the argument `$initial_value`. `@flags` is an optional list of flags, currently limited to `'non-blocking'` (requires Linux 2.6.27), and `'semaphore'` (requires Linux 2.6.30).

### get()

If the eventfd counter has a non-zero value, and `'semaphore'` is not set, then a `"get"` returns 64 bit unsigned integer containing that value, and the counter's value is reset to zero. If `'semaphore'` is set, it decrements the counter by one and returns one. In either case, if the counter is zero at the time of the `"get"`, then the call either blocks until the counter becomes non-zero, or fails with the error EAGAIN if the file handle has been made non-blocking.

### add($value)

A `"add"` call adds the 64 bit unsigned integer value `$value` to the counter. The maximum value that may be stored in the counter is the largest unsigned 64-bit value minus 1 (i.e., 0xfffffffffffffffe). If the addition would cause the counter's value to exceed the maximum, then the `"add"` either blocks until a `"get"` is performed on the file descriptor, or fails with the error EAGAIN if the file descriptor has been made non-blocking. A `"add"` will fail with the error EINVAL if an attempt is made to write the value 0xffffffffffffffff.

## AUTHOR

Leon Timmermans \<leont@cpan.org\>

## COPYRIGHT AND LICENSE

This software is copyright (c) 2010 by Leon Timmermans.

This is free software; you can redistribute it and/or modify it under the same terms as the Perl 5 programming language system itself.