Async & Coroutines

The problem

Your app needs to call two APIs before rendering a page. Sequentially: 500ms + 300ms = 800ms. But the two calls don't depend on each other. What if you could run them at the same time and wait only for the slower one?

The mental model

Coroutines are like juggling. You throw ball 1 (API call 1) and while it's in the air, you throw ball 2 (API call 2). You catch them as they come down. You never waited idle — while one ball was airborne, your hands were busy throwing the next.

go() is throwing a ball. $ch->pop() is catching it.

The pattern: go() + Channel

use OpenSwoole\Coroutine\Channel;

$app->route('/dashboard', function() {
    $ch = new Channel(2);

    go(function() use ($ch) {
        co::sleep(0.5);                // simulate 500ms API call
        $ch->push(['users' => 42]);
    });

    go(function() use ($ch) {
        co::sleep(0.3);                // simulate 300ms DB query
        $ch->push(['posts' => 128]);
    });

    $results = [];
    for ($i = 0; $i < 2; $i++) {
        $results[] = $ch->pop();       // blocks THIS coroutine, not the worker
    }
    return $results;
    // Total: ~500ms (max), not 800ms (sum)
});

go() spawns a new coroutine on the same worker. $ch->pop() suspends the parent coroutine until a value arrives — but the worker thread is free to handle other requests while it waits.

Live demo: sequential vs parallel

The endpoint below runs three 100ms sleeps. Sequential: ~300ms. Parallel via go() + Channel: ~100ms.

co::sleep() vs usleep()

co::sleep(0.5);  // yields — other coroutines run while this one sleeps
usleep(500000);  // blocks — the worker thread is stuck for 500ms

Always use co::sleep() inside coroutine contexts. The one exception: inside a Generator returned from a route handler, co::sleep() is a no-op — use usleep() for artificial delays there.