Latest version: pecl install openswoole-22.1.2 | composer require openswoole/core:22.1.5


<?php OpenSwoole\Event::add(mixed $sock, callable $read_callback, callable $write_callback = null, int $flags = null)\:\ bool



fd, stream, sockets, stream_socket_client, fsockopen, object


Readable event callback function


Writeable event callback function


Flags: OpenSwoole\Constant::EVENT_READ OpenSwoole\Constant::EVENT_WRITE OpenSwoole\Constant::EVENT_READ|OpenSwoole\Constant::EVENT_WRITE



If success, it returns TRUE, meaning the event listener was successfully added

Otherwise it returns FALSE, meaning there was an issue registering the event


Registers the read, write callback functions and flags of a socket on the Event Loop, creating a new event listener.

Socket Types

  • int: File descriptors, including OpenSwoole\Client->$sock, OpenSwoole\Process->$pipe or any other fd
  • Stream Resource: A stream_socket_client/ fsockopen created PHP resource
  • Socket Resource: A socket_create resource, but you must enable socket support at compile time
  • Object: A OpenSwoole\Process Or OpenSwoole\Client, these are automatically converted to a UnixSocket for a process and a client uses socket(OpenSwoole\Client)



$fp = stream_socket_client("tcp://", $errno, $errstr, 30);
fwrite($fp,"GET / HTTP/1.1\r\nHost:\r\n\r\n");

OpenSwoole\Event::add($fp, function($fp) {

    $resp = fread($fp, 8192);

    // Remove the socket from event loop


// Will not block the process, this line of code will be executed sequentially
echo "Finish\n";

Above, the readable event callback is using fread to read from the socket (you can also must recv), you must always use the proper read functions otherwise the event will continue to be triggered, you can then remove the event by using OpenSwoole\Event::del as shown in the example.

When using the Writeable event callback, you must write to the socket after the call to OpenSwoole\Event::del because the event needs to be removed before doing any other operations.

If you execute fread, socekt_recv, socket_read, OpenSwoole\Client::recv and they return false, with the error code EAGAIN. It means the current socket bugger does not have any data to read and you must wait for the event loop to read again.

And if you execute fwrite, socket_write, socket_send, OpenSwoole\Client::send and they return false, with the error code EAGAIN. It means the socket transmission buffer is full, you are then temporarily unable to send data and need to wait for a read event to take place on the event loop.

Manage fds with the EventLoop, for example monitoring file changes with inotify:


$fd = inotify_init();

OpenSwoole\Event::add($fd, function () use ($fd) {

    $var = inotify_read($fd);

Last updated on September 20, 2022