Exponential backoff callback for https://github.com/igorw/retry

ExponentialBackoff.php

<?php

class ExponentialBackoff
{
    private $invoked = 0;
    private $slotTimeUsec;

    public function __construct($slotTimeUsec)
    {
        $this->slotTimeUsec = (int) $slotTimeUsec;
    }

    public function __invoke()
    {
        usleep(rand(0, (2 << (++$this->invoked - 1)) - 1) * $this->slotTimeUsec);
    }
}

function.php

<?php

function eb($slotTimeUsec) {
    $invoked = 0;

    return function() use (&$invoked, $slotTimeUsec) {
        usleep(rand(0, (2 << (++$invoked - 1)) - 1) * $slotTimeUsec);
    };
}