test.php

<?php

final class Runnable
{
    private $callables;

    public function __construct(callable ...$callables)
    {
        $this->callables = $callables;
    }

    public function run()
    {
        do {

            $callable = array_shift($this->callables);
            $callable();

        } while (count($this->callables) > 0);
    }
}

$runnable = new Runnable(
    function () { echo 'Task 1.' . PHP_EOL; },
    function () { echo 'Task 2.' . PHP_EOL; },
    function () { echo 'Task 3.' . PHP_EOL; },
    function () { echo 'Task 4.' . PHP_EOL; },
    function () { echo 'Task 5.' . PHP_EOL; }
);

fhread_create(
    $runnable,
    $id,
    $handle
);
fhread_join(
    $handle,
    $error
);