How to create a separate process per collection using ReactPHP

Let's assume i have following collections:

$collection1 = collect([1,2,3,4]);
$collection2 = collect([5,6,7,8]);
$collection3 = collect([9,10,11,12]);

How to use ReactPhp to process all collections concurrently like: 1,5,9,2,6,10,... instead of 1,2,3,4,5,6,7...