Nginx + PHP：在取消请求时停止进程

I have Nginx 1.4.4 and PHP 5.5.6. I'm making long-polling requests. Problem is, that if I cancel the HTTP request sent via Ajax, requests are still processing (they don't stop). I tested it with the PHP mail() function at end of file, and mail is still coming the file didn't stop).I have Nginx 1.4.4 and PHP 5.5.6. I'm making lo