Keeping your Swing Applications Responsive using FoxTrotand Friends

Rob Ratcliff

Swing’s Thread Model

Mostly not Thread Safe by design - very few thread safe operations

All events added to AWT Queue and processed sequentially

Events “popped” off queue by dispatcher running in AWT Thread and delivered to registered listeners

Long running listener code results in a non-responsive application

Sequence Diagram of Event Processing

Consequences of direct Swing calls in an alternate thread

Deadlock Quirky Painting Sluggish application

Alternatives – Worker Thread and InvokeLater()

// some swing codenew Thread(new Runnable() {public void run() {

// long running taskrunSwingCode();

} protected void runSwingCode() {

SwingUtilities.invokeLater(new Runnable(){public void run() {

// run more swing code}

}}

).start();

Alternatives – SwingWorker

// some swing code

new SwingWorker() {

public Object construct() {

// long running code

}

public void finished() {

// more swing code

}

}.start();

JDialog’s Approach

Modal dialog blocks AWT Event Thread Creates another thread to dispatch the

events to keep the GUI painting FoxTrot leverages this concept

FoxTrot Approach

Similar to JDialog Blocking call, but takes over event queue processing Natural Usage:

// some swing codetry {Object value = Worker.post(new Task() {public Object run() throws Exception {

// long running task}});

} catch (Exception e) {// do something}// more swing code

Dynamic Proxy Client

Wrap long running calls a Dynamic Proxy that wraps calls with Foxtrot

Avoid sprinkling Foxtrot calls everywhere

Assists developers in not having to worry about this stuff

Keep this stuff deep down in your framework

Demo Example

Comments on Dynamic Proxy for CallBacks

Example Problem – RMI Callback Callback calls Swing methods on RMI

dispatch thread to update GUI Inevitable that invokeLater() will be

forgotten by some developer on team resulting in an embarassing deadlock!

Embed InvokeLater into a proxy around the callback interface (See ChatListenerNotifierFactory.)

References

Foxtrot - http://foxtrot.sourceforge.net/ Simone Bordet - simone.bordet@hp.com

SwingWorker -http://java.sun.com/products/jfc/tsc/articles/threads/update.html

Threads and Swing - http://java.sun.com/products/jfc/tsc/articles/threads/threads1.html

Dyanamic Proxy -