EventLoop Component

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Event loop abstraction layer that libraries can use for evented I/O.

In order for async based libraries to be interoperable, they need to use the same event loop. This component provides a common LoopInterface that any library can target. This allows them to be used in the same loop, with one single run() call that is controlled by the user.

Table of Contents

Quickstart example

Here is an async HTTP server built with just the event loop.

$loop = React\EventLoop\Factory::create();

$server = stream_socket_server('tcp://');
stream_set_blocking($server, 0);

$loop->addReadStream($server, function ($server) use ($loop) {
    $conn = stream_socket_accept($server);
    $data = "HTTP/1.1 200 OK\r\nContent-Length: 3\r\n\r\nHi\n";
    $loop->addWriteStream($conn, function ($conn) use (&$data, $loop) {
        $written = fwrite($conn, $data);
        if ($written === strlen($data)) {
        } else {
            $data = substr($data, $written);

$loop->addPeriodicTimer(5, function () {
    $memory = memory_get_usage() / 1024;
    $formatted = number_format($memory, 3).'K';
    echo "Current memory usage: {$formatted}\n";



Typical applications use a single event loop which is created at the beginning and run at the end of the program.

// [1]
$loop = React\EventLoop\Factory::create();

// [2]
$loop->addPeriodicTimer(1, function () {
    echo "Tick\n";

$stream = new React\Stream\ReadableResourceStream(
    fopen('file.txt', 'r'),

// [3]
  1. The loop instance is created at the beginning of the program. A convenience factory React\EventLoop\Factory::create() is provided by this library which picks the best available loop implementation.
  2. The loop instance is used directly or passed to library and application code. In this example, a periodic timer is registered with the event loop which simply outputs Tick every second and a readable stream is created by using ReactPHP's stream component for demonstration purposes.
  3. The loop is run with a single $loop->run() call at the end of the program.

Loop implementations

In addition to the interface there are the following implementations provided:

  • StreamSelectLoop: This is the only implementation which works out of the box with PHP. It does a simple select system call. It's not the most performant of loops, but still does the job quite well.

  • LibEventLoop: This uses the libevent pecl extension. libevent itself supports a number of system-specific backends (epoll, kqueue).

  • LibEvLoop: This uses the libev pecl extension (github). It supports the same backends as libevent.

  • ExtEventLoop: This uses the event pecl extension. It supports the same backends as libevent.

All of the loops support these features:

  • File descriptor polling
  • One-off timers
  • Periodic timers
  • Deferred execution of callbacks


The recommended way to install this library is through Composer. New to Composer?

This will install the latest supported version:

$ composer require react/event-loop


To run the test suite, you first need to clone this repo and then install all dependencies through Composer:

$ composer install

To run the test suite, go to the project root and run:

$ php vendor/bin/phpunit


MIT, see LICENSE file.