Memory leaks in IE JS while XMLHTTP requests_问答_开发者

Each ProcessingPayments() used memory increase. CollectGarbage() not helps. Use Drip to view memory usage, but don't view any DOM leaks.

I use only IE8 and tested on older versions. Other browsers not interested.

How can I decrease growing memory usage while execute this script?

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
    <html xmlns="http://www.w3.org/1999/xhtml">
     <head>
      <title>JS IE XMLHTTP - Memory leaks</title>
     </head>

    <body onload="ProcessingPayments();locCollectGarbage();">

    <script language="JScript">
    var toProcessingPayments;
    var ProcessingPaymentsPeriod = 1*60*1000;
    var SessionCount = 1;
    var CollectGarbageCount = 1;


    function ProcessPayment(arrParams) {
     var e;
     var strURL = "http://www.facebook.com/";
     var strURLParam = "";
     try {开发者_开发知识库 var locHTTPRequest = new ActiveXObject("MSXML2.XMLHTTP.6.0"); }
     catch (e) { var locHTTPRequest = new ActiveXObject("MSXML2.XMLHTTP"); }

     function ProcessPaymentHTTPRequest() {
      if (locHTTPRequest.readyState != 4) {
       return;
      }

      if (locHTTPRequest.status != 200) {
       document.getElementById("CurrentSession").innerHTML = document.getElementById("CurrentSession").innerHTML
        +arrParams.i+" = error code "+locHTTPRequest.status+"<br />";

       return false;
      }

      if (locHTTPRequest.getResponseHeader("Content-Type").indexOf("text/html") < 0) {
       document.getElementById("CurrentSession").innerHTML = document.getElementById("CurrentSession").innerHTML
        +arrParams.i+" = wrong content type "+locHTTPRequest.getResponseHeader("Content-Type").indexOf("text/html")+"<br />";

       return false;
      }

      try {
        document.getElementById("CurrentSession").innerHTML = document.getElementById("CurrentSession").innerHTML
         +arrParams.i+" = processed<br />";

        return true;

      }
      catch(e) {
       if (locHTTPRequest.responseXML.parseError != 0) {
        return false;
       }
       else {
        return false;
       }
      }

      locHTTPRequest.abort();
      delete locHTTPRequest["onreadystatechange"];
      locHTTPRequest = null;
     } // function ProcessPaymentHTTPRequest()

     strURLParam = "?"+arrParams.i;

     locHTTPRequest.open("get", strURL+strURLParam);

     document.getElementById("CurrentSession").innerHTML = document.getElementById("CurrentSession").innerHTML
       +arrParams.i+" = request<br />";

     locHTTPRequest.onreadystatechange = ProcessPaymentHTTPRequest;

     locHTTPRequest.send(null);
    }


    function ProcessingPayments(arrPayment) {
     var e;

     toProcessingPayments = null;

     document.getElementById("CurrentSession").innerHTML = "";

     for (var i = 0; i < 10; i++) {
      ProcessPayment({
       i:   i
      });
     }

     SessionCount++;

     document.getElementById("Session").innerText = SessionCount;

     toProcessingPayments = setTimeout(ProcessingPayments, ProcessingPaymentsPeriod);
    }


    function locCollectGarbage() {
     CollectGarbage();

     document.getElementById("CollectGarbage").innerText = CollectGarbageCount;

     CollectGarbageCount++;

     setTimeout(locCollectGarbage, 5*60*1000);
    }
    </script>
    </body>

    <p>Sessions: <span id="Session">0</span></p>
    <p>CollectGarbage(): <span id="CollectGarbage">0</span></p>
    <hr />
    <br />

    <p>Current session:</p>

    <p id="CurrentSession"></p>

    </html>

locHTTPRequest.onreadystatechange = ProcessPaymentHTTPRequest;

Creates a reference loop between a native-JScript object (the ProcessPaymentHTTPRequest function, which has the request object in scope) and a non-JScript object (the XMLHttpRequest ActiveX object). It is this kind of reference loop that makes IE fail to GC.

delete locHTTPRequest["onreadystatechange"];

Whilst that would be OK for a native JavaScript object, in reality delete doesn't actually work to remove an event handler from a DOM object. So the handler and reference loop remains in place. What is typically done instead is to overwrite the locHTTPRequest.onreadystatechange handler with a dud value, such as a predefined function that immediately returns, or '', or null. Or alternatively, use addEventListener/attachEvent and their corresponding remove-handler methods.

CollectGarbage();

What does that do? There's not really much you can do to influence GC from JS.

Aside:

<script language="JScript">

type="text/javascript" instead of language. I know you don't care about non-IE, but there seems little point in being gratuitous incompatible as well as non-standard.

 try { var locHTTPRequest = new ActiveXObject("MSXML2.XMLHTTP.6.0"); }
 catch (e) { var locHTTPRequest = new ActiveXObject("MSXML2.XMLHTTP"); }

There is no need to do this. You aren't using any features of the newer MSXML version, so just plump for unversioned XMLHttp. Also, go for native-JS XMLHttpRequest first. Not just because it exists on other browsers, but also because it's more efficient and, being native JS, doesn't cause memory leaks.

Best: add fallback for IE6:

if (!window.XMLHttpRequest && 'ActiveXObject' in window) {
    window.XMLHttpRequest= function() {
        return new ActiveXObject('MSXML2.XMLHttp');
    }
}

and then just use standard new XMLHttpRequest() everywhere.