You should NOT jam UI code into your workers!
/**
* TWO CHOICES:
* - Monitor your threads and report errors,
* - setup a callback to do something.
*/
public class ThreadExceptions {
/** Demo of {@link RunnableCatch} */
public static void main(String[] argv) throws InterruptedException {
final Runnable bad = new NaughtyThread();
// safe1 doesnt have a callback
final RunnableCatch safe1 = new RunnableCatch(bad);
// safe2 DOES have a callback
final RunnableCatch safe2 = new RunnableCatch(bad, new RunnableCallback() {
public void handleException(Runnable runnable, Exception exception) {
System.out.println("Callback handled: " + exception.getMessage());
exception.printStackTrace();
}
});
final Thread t1 = new Thread(safe1, "myThread");
final Thread t2 = new Thread(safe2, "myThread");
t1.start();
t2.start();
t1.join();
t2.join();
if (safe1.getException() != null) {
System.out.println("thread finished with exceptions");
safe1.getException().printStackTrace();
}
System.out.println("done");
}
}
/** Throws an exception 50% of the time */
class NaughtyThread implements Runnable {
public void run() {
try {
if (Math.random() > .5) {
throw new RuntimeException("badness");
}
} finally {
System.out.println("ran");
}
}
}
/** Called when an exception occurs */
interface RunnableCallback {
void handleException(Runnable runnable, Exception exception);
}
/**
* Catches exceptions thrown by a Runnable,
* so you can check/view them later and/or
* deal with them from some callback.
*/
class RunnableCatch implements Runnable {
/** Proxy we will run */
private final Runnable _proxy;
/** Callback, if any */
private final RunnableCallback _callback;
/** @guarded-by(this) */
private Exception _exception;
public RunnableCatch(final Runnable proxy) {
this(proxy, null);
}
public RunnableCatch(final Runnable proxy, RunnableCallback target) {
_proxy = proxy;
_callback = target;
}
public void run() {
try {
_proxy.run();
} catch (Exception e) {
synchronized (this) {
_exception = e;
}
if (_callback != null) {
_callback.handleException(_proxy, e);
}
}
}
/** @return any exception that occured, or NULL */
public synchronized Exception getException() {
return _exception;
}
}