AJAX "crashes" IE on close of Window.

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  • Sommer.pde@googlemail.com
    #1

    AJAX "crashes" IE on close of Window.

    It took me some time to find out when and why this happens.

    When the window of Internet Explorer is closed with an AJAX call still
    pending, something funny happens. Do it twice, and you will have to
    restart the browser.

    Here a little sample: http://truefriendz.de/iedos

    The script on this site will open 5 test-windows one at a time.

    The test-windows will issue an AJAX-Call. This call would only be
    answered after 10 seconds, but the windows will be closed before
    the answer arrives. (This is not a question of the window.close().
    The same would happen if the close is issued by a user closing the
    window)

    Using IE6/w2k and IE7/vista (and assumedly other versions of IE)
    the 3rd and following windows will appear without content. FireFox
    performs perfectly well.

    I found a workarround, which I regard as clumsy.

    <body .... onAbort="cleanu p();" onUnload="clean up();">
    function cleanup() { xmlHttp.abort() ;}

    Demonstration here: http://truefriendz.de/iedos2

    My findings so far: When a window with a pending AJAX-request
    ActiveXObject(" Microsoft.XMLHT TP") is closed, a TCP-socket remains
    eternally in state close_wait. Check with netstat.

    (It seems perfectly normal that sockets enter the state close_wait
    (although if I understand the documents correctly this state should
    only be entered by SERVERS),
    and it seems that sockets can (normally) be reused succesfully from
    this state. In "normal operation" such socktes do disappear after a
    certain time)

    My thoughts: Due to the fact that this Socket is still existing, IE
    does
    reuse it, but it does not work properly. These Sockets seem
    to be damaged somehow.

    Funny enough, I did not find any mention of this problem on the web.

    Anyone, who can suggest a better, more elegant way to handle this?

    Sorry for any mistakes, I did my very best, but I'm not a native
    speaker.

    Tags: None
    • -Lost
      #2
      Re: AJAX &quot;crashes&q uot; IE on close of Window.

      Sommer.pde@goog lemail.com wrote:
      It took me some time to find out when and why this happens.
      >
      When the window of Internet Explorer is closed with an AJAX call still
      pending, something funny happens. Do it twice, and you will have to
      restart the browser.
      >
      Here a little sample: http://truefriendz.de/iedos
      >
      The script on this site will open 5 test-windows one at a time.
      Really? In my Internet Explorer 6 it merely says it is opening and
      closing windows, but it does not open or close anything.

      I do however get:

      Line: 39
      Char: 2
      Error: Object doesn't support this property or method
      Code: 0
      URL: http://truefriendz.de/iedos/

      ....5 times.

      <snip>

      --
      -Lost
      Remove the extra words to reply by e-mail. Don't e-mail me. I am
      kidding. No I am not.

        Comment

        • Sommer.pde@googlemail.com
          #3
          Re: AJAX &quot;crashes&q uot; IE on close of Window.

          On May 8, 2:51 am, -Lost <maventheextraw o...@techie.com wrote:
          The script on this site will open 5 test-windows one at a time.
          Really? In my Internet Explorer 6 it merely says it is opening and
          closing windows, but it does not open or close anything.
          Well, it should, and it *does* on my computer. :)

          Thank for giving it a try. The site where this script is hosted is
          not mine, so I can do nothing about it *at this site*. But I
          made a modified copy here:

          http://sommerb.so.funpic.de/ajax/iedos.html


          Perhaps this one wil do the Trick. Sorry, this site is not cpmpletely
          ad-free, but this was the only PHP-enabled web space I could find
          in short time.

          I would be very grateful if anybody would have a look at this. I'm
          completely at loss, since I found out that even the version *with*
          calls to abort() of the AJAX does indeed throw a exception in
          FireFox.

          TIA

            Comment

            • Sommer.pde@googlemail.com
              #4
              Re: AJAX &quot;crashes&q uot; IE on close of Window.

              Just to give more informations:

              <head>
              var xmlHttp;

              function ajax_call(){

              //create AJAX.object
              xmlHttp = new ActiveXObject(v ersions[idx]);

              // Define onreadystatecha nge and issue call to very slow site
              xmlHttp.open('G ET', 'response-10s.php', true);
              xmlHttp.onready statechange = function () {
              if (xmlHttp.readyS tate == 4 && xmlHttp.status == 200) {
              alert(xmlHttp.r esponseText);
              }
              };
              xmlHttp.send(nu ll);
              }

              function cleanup() {
              if (xmlHttp) {xmlHttp.abort( )}
              }
              </head>

              <body onLoad="ajax_ca ll();" onAbort="cleanu p();" onUnload="clean up();"
              >
              ....

              Without cleanup() this will do damage to Internet-Explorer
              (sockets permanently in state close_wait) if the window
              is closed with the AJAX still waiting for the response.

              Obviously the Ajax doesn't "like" to go into non-existence
              without a pending call beeing aborted.

              I have very foggy ideas about an Ajax-object that enlists
              itself for cleanup...

              Somehow to add this cleanup into a chain of operations that are
              done automatically on close of the window. I examined some
              AJAX-Libraries, but found nothing like that in any of them.

                Comment

                • -Lost
                  #5
                  Re: AJAX &quot;crashes&q uot; IE on close of Window.

                  Sommer.pde@goog lemail.com wrote:
                  I would be very grateful if anybody would have a look at this. I'm
                  completely at loss, since I found out that even the version *with*
                  calls to abort() of the AJAX does indeed throw a exception in
                  FireFox.
                  I do not have the time to peruse your code again, but I can tell you two
                  things.

                  1) Depending on your use of your XHR object, abort() is not necessary.
                  For example, calling the open() method twice on a single XHR object
                  will reset the object, its connection (what was previously opened/sent),
                  and will disconnect any event handlers.

                  2) Firefox does not like the abort() method. Most notably in cases of
                  use in the onreadystatecha nge event.

                  NOTE: About the above, it is essential to use abort() in Firefox when
                  canceling an XHR request, just not in the above mentioned event.

                  --
                  -Lost
                  Remove the extra words to reply by e-mail. Don't e-mail me. I am
                  kidding. No I am not.

                    Comment

                    • Steve Kirkendall
                      #6
                      Re: AJAX &quot;crashes&q uot; IE on close of Window.

                      Sommer.pde@goog lemail.com wrote:
                      >
                      When the window of Internet Explorer is closed with an AJAX call still
                      pending, something funny happens. Do it twice, and you will have to
                      restart the browser.
                      This sounds like a manifestation of a garbage-collection bug in IE.
                      When a document references javascript, and the javascript references
                      back to the document (which is pretty much all the time with AJAX)
                      then closing the document won't cause the javascript to be terminated.

                      Furthermore, IE has a very small limit on the number of connections
                      that it will allow to be simultaneously open to a given site. This
                      means that when your XmlHttp connections don't terminate, you quickly
                      run out of connections. This leaves you stuck until the XmlHttp
                      connections time out, which can take several minutes.

                      It's a pain in the ass. IE has had this bug for years. I don't know
                      if the newest version of IE still has the bug, but you have to plan
                      for the worst -- assume IE always has the bug.

                      See http://www.litotes.demon.co.uk/examp...finalizer.html
                      for more on the problem, and one possible solution.

                      Another technique which I've read about BUT NEVER TRIED is to use
                      different names for the server, so you increase the number of possible
                      connections. For example, supposedly "google.com " and "www.google.com "
                      will have separate connection pools even if they reference the same
                      site. The reason I never tried this technique is that it seems like
                      it'd take a lot of intricate site-specific engineering to make it
                      work reliably.

                        Comment

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