SwingWorker: don't stop that train!

lunes agosto 15, 2005 | SwingWorker | Permalink | Comentarios [4]

So imagine you're comfortably sleeping at home. Suddenly you wake up and you find out you're sitting in your car, driving at 65 MPH in the highway. That's a dangerous situation, right? Now imagine you're a JDBC driver and you're comfortably performing a query against a server. You're talking, say, OCI to an Oracle server. Suddenly someone "Thread.interrupt()"s you and then asks you to "close()" the JDBC connection. You may be able to successfully close the connection. Or you may not. Maybe you can close the connection, but the server is left in a weird state, thinking you're still asking for the query. What I mean is that Thread.interrupt() (or SwingWorker.cancel()) certain operations may not be a very good idea. By interrupting threads you may be interrupting network protocols, for instance, and that may be asking for trouble with some JDBC drivers. You can build a SQL application and interrupt and close the connections perfectly well with a given driver, and completely fail with another driver. What I really mean is that if you want to suddenly cancel a running process (whatever that is) you should try to do that in the safest, cleanest way. An idea is to use a "boolean wantsToRun=true" flag somewhere in your SwingWorker constructors and keep the things rolling in the "doInBackground()" method as long as "wantsToRun" is true. So there comes our SwingWorker suggestion number II: SwingWorker suggestion II: try to cancel() as cleanly as possible Use a flag in your "doInBackground()" loops to check if your SwingWorker is still expected to be run. Since you cannot override "cancel(boolean)" in your SwingWorker (it's final :-( ) then write a method to gracefully ask for cancellation. If you use SwingWorker.cancel(true) to stop your running process doublecheck that everything is correctly cancelled by thoroughly testing your application. Note that this suggestion applies to SwingWorkers and to any Thread you build. So, to summarize, think it twice before suddenly stopping trains Threads. Results might be quite different from what you expect. Happy Swinging, Antonio