TaskSet::joinNext

(PHP 8.6+, True Async 1.0)

public TaskSet::joinNext(): Async\Future

Returns a Future that resolves with the result of the first completed task — whether successful or failed. If the task finished with an error, the Future rejects with that exception.

After delivering the result, the entry is automatically removed from the set, and count() decreases by 1.

Remaining tasks continue running.

If a completed task already exists, the Future resolves immediately.

The returned Future supports a cancellation token via await(?Completable $cancellation).

Return Value

Async\Future — a future result of the first completed task. Call ->await() to get the value.

Errors

Throws Async\AsyncException if the set is empty.
The Future rejects with the task’s exception if the first completed task failed with an error.

Examples

Example #1 Sequential result processing

<?php

use Async\TaskSet;

spawn(function() {
    $set = new TaskSet();

    $set->spawn(fn() => fetchUser(1));
    $set->spawn(fn() => fetchUser(2));
    $set->spawn(fn() => fetchUser(3));

    echo "before: count=" . $set->count() . "\n"; // 3

    $first = $set->joinNext()->await();
    echo "after first: count=" . $set->count() . "\n"; // 2

    $second = $set->joinNext()->await();
    echo "after second: count=" . $set->count() . "\n"; // 1
});

Example #2 Processing loop

<?php

use Async\TaskSet;

spawn(function() {
    $set = new TaskSet(concurrency: 5);

    foreach ($urls as $url) {
        $set->spawn(fn() => httpClient()->get($url)->getBody());
    }
    $set->seal();

    while ($set->count() > 0) {
        try {
            $body = $set->joinNext()->await();
            processResponse($body);
        } catch (\Throwable $e) {
            log("Error: {$e->getMessage()}");
        }
    }
});

Example #3 With timeout

<?php

use Async\TaskSet;

spawn(function() {
    $set = new TaskSet();

    $set->spawn(fn() => slowApi()->fetchReport());
    $set->spawn(fn() => anotherApi()->fetchStats());

    try {
        $result = $set->joinNext()->await(Async\timeout(5.0));
    } catch (Async\TimeoutException) {
        echo "No task completed within 5 seconds\n";
    }
});

Documentation