Inter Process Communication (IPC)

To communicate between processes on a same system there is 2 approaches: sharing memory or passing messages through a socket.

The later is the safest of the two (but not exempt of problems) and you will find here the building blocks to communicate via a socket.

The adage share state through messages and not messages through state is a pillar of the actor model and initially of object oriented programming.

ServerClient

use Innmind\IO\Sockets\Unix\Address;
use Innmind\Url\Path;
use Innmind\TimeContinuum\Period;
use Innmind\Immutable\{
    Sequence,
    Str,
};

$server = $os
    ->sockets()
    ->open(Address::of(Path::of('/tmp/foo')))
    ->unwrap();
    ->timeoutAfter(Period::second(1));

while (true) {
    $_ = $server
        ->accept()
        ->match(
            static fn($client) => $client
                ->sink(Sequence::of(Str::of('Hello')))
                ->flatMap(static fn() => $client->close())
                ->match(
                    static fn() => null, // everyhting is ok
                    static fn(\Throwable $e) => throw $e,
                ),
            static fn() => null, // no new connection available
        ),
}

use Innmind\IO\{
    Sockets\Unix\Address,
    Frame,
};
use Innmind\Url\Path;

$client = $os
    ->sockets()
    ->connectTo(Address::of(Path::of('/tmp/foo')))
    ->unwrap();

echo $client
    ->watch()
    ->frames(Frame::chunk(5)->strict())
    ->one()
    ->match(
        static fn($data) => $data->toString(),
        static fn() => 'unable to read the stream',
    );

In the case the server is started first then the client would print Hello.

This is a very rough implementation of communication between processes. DO NOT use this simple implementation in your code, instead use a higher level API such as innmind/ipc.