# EventLoop Component

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](https://github.com/m4rw3r/php-libev)). 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

## Usage

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

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

    $server = stream_socket_server('tcp://127.0.0.1:8080');
    stream_set_blocking($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($data)) {
                fclose($conn);
                $loop->removeStream($conn);
            } 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";
    });

    $loop->run();

**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.
