Await ​

Imagine a classic distributed backend system. There's a dozen services tied together via JWT authorization. A user logs in through UserDirectory and lands in ProfileService to change some business data in their profile, for example their home address or a delivery address. The API's job is to update that data:

function profileExists(int $userId): bool {
    $result = $db->query('SELECT 1 FROM profiles WHERE user_id = ?', [$userId]);
    return $result->rowCount() > 0;
}

if (profileExists($userId)) {
    updateProfile($userId, $changes);
}

If the operation is deemed risky, it might be necessary to additionally validate the JWT token through UserDirectory:

function validateToken(string $token): bool 
{
    $response = file_get_contents("https://userdirectory.example.com/api/validate?token=$token");
    return json_decode($response)->valid;
}

if (profileExists($userId) && validateToken($token)) {
    updateProfile($userId, $changes);
}

The validateToken and profileExists functions perform I/O and take time, especially validateToken. It would make sense to run validateToken in a coroutine to reduce the total wait time:

$isValid = spawn(validateToken(...), $token);

if (profileExists($userId) && $isValid) {
    updateProfile($userId, $changes);
}

However, this code won't work, since spawn can't return a result immediately. We need some way to wait for the coroutine. That's what the await function is for.

use function Async\await;

$validation = spawn(validateToken(...), $token);

if (profileExists($userId) && await($validation)) {
    updateProfile($userId, $changes);
}

The await function pauses the flow of execution until the coroutine finishes, which lets you synchronize different coroutines with one another.