Multithreading with swing

Question

I have a question about the use of threads in a gui application. Say (as a simplistic example) i have a swing application with a series of images. I have two threads i want to run that fetch an image of a parent respectively. (So for a given number of students, get a mother image and a father image from each server endpoint). The returned image of the father and the mother is then appended on to the image on screen so i have a series of images with a mother, father, mother, father for multiple students.

How can i schedule this in a multithreaded environment? Each call to get a mother or father image has to be in parallel and not block the displaying of the images on screen. Does the image displayed on the screen refresh after each thread returns an image? How will this be structured?

Answer 1

Start with Concurrency in Swing.

The absolute simplest approach might be to use a SwingWorker that has a list of items it needs to look up and allow it to process the list.

The problem with this is it will only run each request one at the other, making it a little slower then other options. The benefit of this is that it provides easy functionality to re-sync with the Event Dispatching Thread so that you can notify the UI or make changes to it safely.

Another option might be to use Executors, in particular a Thread Pool implementation.

This allows you to submit a number of tasks that should be executed at some time in the future, but allows you to control the number of threads that the process can use at any one time.

The drawback is that you become responsible for syncing the changes back to the UI yourself when you want to update the UI, using SwingUtilities.invokeLater

Now. You "could" use both.

Basically you would need to setup some kind of "request" class that would allow you to pass the relevant information to, for example, the "mother" and "father" servers, the original image and possibly some kind of callback interface that would tell you when the final image had being rendered.

The requester would build some kind of Runnable or Callable which would wrap a SwingWorker.

When executed, this "request task" would start the SwingWorker, allowing it to fetch the images, merge them and publish the results, which would notify the callback interface. The "request task" would then simply wait until SwingWorker#get returns before exiting.

As an idea...