Unique IP access checker with concurrency control

IpCheck.php

<?php

/**
 * Check if a IP exists in a storage with concurrency control for several HTTP requests
 *
 * Based in divengine\nodes::waitAndDo() queue algorithm 
 *
 * @author rafageist
 */
function IpCheck($ip)
{
    $exclusiveFolder = "./ips";
    $mark = 'used';
    $max_execution_time = 60;
    $ipFolder = "$exclusiveFolder/".str_replace(".", "/", $ip);

    $threadId = uniqid('', true);

    @mkdir($ipFolder, 0777, true);

    file_put_contents("$ipFolder/$threadId", $max_execution_time); // max execution time in seconds for this thread

    $i = 0;
    $last = null;
    $file = null;
    do {

        // current thread
        $dir = opendir($ipFolder);
        $file = readdir($dir);
        while ($file == '.' || $file == '..' || $file == $mark) {
            $file = @readdir($dir);
        }
        closedir($dir);

        if ($file == false) {
            throw new Exception("No access to the queue");
        }

        // If at the same time another process already deleted the current item, then ignore and continue
        $max = intval(@file_get_contents("$ipFolder/$file")); // Get the maximum time of the current thread

        if ($file === $threadId) {
            // it's my turn, I stop the loopUnique IP access checker with concurrency control
            break;
        }

        if ($last !== $file) {
            // if another thread deletes the item, renew the max count
            $i = 0;
        }

        $last = $file;

        usleep(1000); //sleep 1/1000 seconds

        $i++;

        if ($i > $max * 100) {
            // ignore if file does not exist
            // release the item and continue
            @unlink("$ipFolder/$file");
            $i = 0;
        }

    } while ($file !== false && $file !== $threadId);

    // Turn for me...Do something...

    $result = false;
    if (!file_exists("$ipFolder/used")) {
        $result = true;
        file_put_contents("$ipFolder/$mark", date("Y-m-d h:i:s"));
    }

    // Done!

    // Destroy thread in the queue
    @unlink("$ipFolder/$threadId");

    return $result;
}


// test
var_dump(IpCheck("10.1.1.2"));