React's core reactor event-loop
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Latest commit 164799f Mar 8, 2016 @cboden cboden Changelog update

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.

In addition to the interface there are some 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


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, 0, $written);

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


Note: The factory is just for convenience. It tries to pick the best available implementation. Libraries SHOULD allow the user to inject an instance of the loop. They MAY use the factory when the user did not supply a loop.