text: Q:
  
  Cancel gwt rpc call
  
  In this example there is a pretty description of how to make a timeout logic using a Timer#schedule. But there is a pitfall there. We have 2 rpc requests: first makes a lot of computation on server(or maybe retrieving a large amount of data from database) and second a tiny request that returns results immediately. If we make first request, we will not recieve results immediately, instead we will have a timeout and after timeout we make the second tiny request and then abortFlag from example will be true, so we can retrieve the results of second request, but also we can retrieve the results of first request that was  timed out before(because the AsyncCallback object of first call was not destroyed).
  So we need some kind of cancelling the first rpc call after timeout occurs. how can I do this?
  
  A:
  
  Let me give you an analogy.
  You, the boss, made a call to a supplier, to get some product info. Supplier say they need to call you back because the info would take some time to be gathered. So, you gave them the contact of your foreman.
  Your foreman waits for the call. Then you told your foreman to cancel the info request if it takes more than 30 minutes.
  Your foreman thinks you are bonkers because he cannot cancel the request, because he does not have an account that gives him privilege to access the supplier's ordering system.
  So, your foreman simply ignores any response from the supplier after 30 minutes. Your ingenious foreman  sets up a timer in his phone that ignores the call from the supplier after 30 minutes. Even if you killed your foreman, cut off all communication links, the vendor would still be busy servicing your request.
  There is nothing on the GWT client-side to cancel. The callback is merely a javascript object waiting to be invoked. 
  To cancel the call, you need to tell the server-side to stop wasting cpu resources (if that is your concern). Your server-side must be programmed to provide a service API which when invoked would cancel the job and return immediately to trigger your GWT callback.
  You can refresh the page, and that would discard the page request and close the socket, but the server side would still be running. And when the server side completes its tasks and tries to perform a http response, it would fail, saying in the server logs that it had lost the client socket.
  It is a very straight forward piece of reasoning.
  Therefore, it falls into the design of your servlet/service, how a previous request can be identified by a subsequent request.
  Cascaded Callbacks
  If request 2 is dependent on the status of request 1, you should perform a cascaded callback. If request 2 is to be run on success then, you should place request 2 into the onFailure block of the callback. Rather than submitting the two requests one after another.
  Otherwise, your timer should trigger request 2, and request 2 would have two responsibilities:
  
  tell the server to cancel the previous request
  get the small piece of info
  
  