<?php
class Task {
    function Task($id, $start, $end) {
        $this->id    = $id;
        $this->start = $start;
        $this->end   = $end;
        $this->pos   = $this->start;
    }

    function execute() {
        if ($this->pos < $this->end) {
            return $this->pos++;
        } else return false;
    }
}

$range     = range(1, 100);
$ranges    = array_chunk($range, 10);
$tasks     = array();

while (count($ranges)) {
    $range = array_shift($ranges);

    $tasks[] = new Task(
        count($tasks) + 1,
        array_shift($range), 
        array_pop($range));
}

while (count($tasks)) {
    foreach ($tasks as $id => $task) {
        if ($task->execute() === false) {
            printf("task %d complete\n", $task->id);
            unset($tasks[$id]);
        } else printf("task %d position %d\n", $task->id, $task->pos);
    }
}
?>