Differences

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--- otm:ordering_of_messages:fifo [2011/01/05 20:12]
aspectscript
+++ otm:ordering_of_messages:fifo [2011/06/27 05:25]
aspectscript
@@ Line 1: / Line 1: @@
-Web applications typically update data from servers (//eg.// whether, time).  Developers has to overcome the issue of using obsolete data due to a late response of a server. For example, consider a website that shows the current time of a certain country using two Ajax requests. If the response second request arrives before than the response the first ajax request arrive, the showed time will be incorrect. Using a customized strategy, named **discardLate**, of ordering that discard the obsolete response, we can avoid aforementioned problem.
+====== The FIFO strategy ======
-<code javascript>
+A mashup application is created from the combination of information retrieved from different servers, //e.g.// Housing Maps. Programmers have to overcome the issue of creating an incorrect Web page due to an arbitrary (and unexpected) order of server responses. For instance, consider a Web page that is created with two Ajax requests. If the second server response is processed before the first server response, the Web page is created incorrectly. A **FIFO** strategy, which processes the server responses in the same order as the Ajax requests are sent, ensures that the Web page is always created correctly.
-var discardLate = function(jp) {
-  if(!this.isLate(jp)){     //is obsolete this join point?
+When the "activate order" button is clicked, the web page is created correctly. When the "deactivate order" button is clicked, the web page could create incorrectly. **NOTE:** Please first watch the application without clicking the "activate order" button to appreciate clearly the aforementioned issue.
-    jp.proceed();
-    this.updateCr(jp); //notifies that join point was executed.
-  }
-}
-</code>
-The implementation follows:
 <html>
-   <link href="/aspectscript/external/otm/paperExample-SPE/order/style.css" rel="stylesheet" type="text/css"/>
+   <link href="/aspectscript/external/otm/paperExample-SPE/style.css" rel="stylesheet" type="text/css"/>
-  <script type="text/javascript" language="javascript" src="/aspectscript/external/otm/paperExample-SPE/order/lib.js"> </script>
+     <script type="text/javascript" language="javascript" src="/aspectscript/external/otm/paperExample-SPE/lib.js"> </script>
    <iframe id="example" src="/aspectscript/external/otm/paperExample-SPE/order/fifo" width="810" height="470"></iframe>
     <iframe id="code" style="display:none" src="/aspectscript/external/otm/paperExample-SPE/order/fifo/script.js" width="810" height="470"></iframe>
    <a id="button" class="button" onclick="toggle('code','example')"> <span>Toggle between the code and example </span></a>
 </html>
+The FIFO strategy is implemented as a piece of advice, which is a JavaScript function, that is executed every time a server response is received:
+<code javascript>
+var FIFO = function(jp){
+  var request = jp . target ;
+  if (this.idServerRespExpected != request.idServerResp){
+    this.jpsQueue.push(jp) ;
+  }
+  else{
+    jp.proceed() ;
+    this.idServerRespExpected = request.idServerResp + 1;
+   // executing jp proceeds that can be executed now
+   this.idServerRespExpected =this.jpsQueue.execRecEarlyJPs( this . idServerRespExpected ) ;
+  }
+}
+</code>
+Go back the [[otm/ordering_of_messages|the parent Web page]].