Threading in GWT (Client)

Question

From what I understand, the entire client side of a GWT application is converted to Javascript when you build, therefore I suppose this question is related to both Javascript and the possibilities that GWT offers.

I have a couple of dozen processes that will need to be initiated in my GWT application, each process will then continuously make calls to a server. Does GWT support threading? Does the GWT client side support threading?

EDIT:

This link states:

No JavaScript knowledge required If you’re just a user of the framework, 
which I am for the matter of discussion, you do not need to know JavaScript 
in order to write dynamic content, be it client-side such as rolling frames, 
docking panels or scheduled “multi-threading” tasks, or server-side calls 
using XMLHttpRequests (aka AJAX). 

or scheduled “multi-threading” tasks, what does this mean?

Answer 1

JavaScript doesn't support multithreading, so whatever GWT does, multithreading has to be done solely on the server side, because GWT can only use features that are already available on the client side.

Answer 2

There is work on Web Workers as part of HTML5 that is implemented in a number of browsers, but not on all (most notably internet explorer). You could use these features where available, but what you should do is look at the javascript programming model.

Javascript generally works asynchronously. Requests are fired off and at some point their answers are received as an event. You can have a large number of pending requests at the same time. This will require a bit of a redesign of your system though.

Answer 3

JavaScript doesn't support multithreading. However, GWT has a class to get something, which is not real multithreading, but in most cases does what you need: com.google.gwt.user.client.DeferredCommand. The technique is based on the timer class, which executes a method after the given time elapses.

For example, when placing the following code in you own code, the addCommand, will return directly and you code continues after the command, while the execute() method is executed using a the timer "trick":

DeferredCommand.addCommand(new Command() {
   public void execute() {
      .. code here is executed using the timer technique.
   }
});

You can also use the IncrementalCommand instead of Command, which can be used to run the command more than once, that is until the execute method returns false. You can use this to split tasks into sub tasks to get better threading behavior. See the JavaDoc of the classes mentioned here for more details.