<?php

class FileHelper
{
    public static function openAndLock($filename)
    {
        $fh = fopen($filename, 'r+');
        if (!$fh || !flock($fh, LOCK_EX)) {
            return false;
        }
        return $fh;
    }

    public static function readAll($fh)
    {
        if ($fh) {
            fseek($fh, 0);
            return stream_get_contents($fh);
        }
    }

    public static function overwrite($fh, $content)
    {   
        if ($fh) {
            fseek($fh, 0);
            ftruncate($fh, 0);
            fwrite($fh, $content);
        }
    }

    public static function closeAndUnlock($fh)
    {
        if ($fh) {
            flock($fh, LOCK_UN);
            fclose($fh);
        }
    }
}

class HttpHelper
{
    public static function callNoWait($url)
    {
        $parts = parse_url($url);
        $fp = fsockopen(
            $parts['host'],
            isset($parts['port']) ? $parts['port'] : (
                isset($parts['scheme']) && $parts['scheme'] == 'https' 
                ? '443'
                : '80'
            ),
            $errno,
            $errstr,
            30
        );
        $uri = $parts['path'];
        if (isset($parts['query'])) {
            $uri .= '?'.$parts['query'];
        }
        $out = "GET {$uri} HTTP/1.1\r\n"
             . "Host: {$parts['host']}\r\n"
             . "Connection: Close\r\n\r\n";
        fwrite($fp, $out);
        // did not read anything
        fclose($fp);        
    }

    public static function getUri($path = null)
    {
        if (!isset($path)) {
            $path = $_SERVER['REQUEST_URI'];
        }
        $scheme = !empty($_SERVER['HTTPS']) && 'off' !== strtolower($_SERVER['HTTPS'])
            ? 'https'
            : 'http';
        $port = $_SERVER['SERVER_PORT'];
        $host = ('http' === $scheme && $port === '80') || 
                ('https' === $scheme && $port === '443')
            ? $_SERVER['HTTP_HOST']
            : $_SERVER['HTTP_HOST'].':'.$port;
        return $scheme.'://'.$host.$path;
    }
}

$countFilename = __DIR__.'/loop.lock';
$action = isset($_GET['action']) ? $_GET['action'] : '';

switch ($action) {
    case 'stop':
        for ($i = 100; $i > 0; --$i) {
            if (!file_exists($countFilename) || @unlink($countFilename)) {
                exit('Stopped');
            }
            usleep(2);
        }
        exit('Cannot stop');
    case 'start':
        touch($countFilename);
    default:
        if (!file_exists($countFilename)) {
            exit('Run prohibited');
        }
        if (($fh = FileHelper::openAndLock($countFilename)) === false) {
            exit('Busy');
        }
        $count = intval(FileHelper::readAll($fh)) + 1;
}

register_shutdown_function(
    function($fh, $count) {
        // write counter and unlock
        FileHelper::overwrite($fh, (string)$count);
        FileHelper::closeAndUnlock($fh);
        // call itself without get-parameters
        $path = $_SERVER['REQUEST_URI'];
        if (($p = strpos($path, '?')) !== false) {
            $path = substr($path, 0, $p);
        }
        $uri = HttpHelper::getUri($path);
        HttpHelper::callNoWait($uri);
    },
    $fh,
    $count
);

// ... do something ...
echo 'Count: '.$count;
usleep(100);