Catching java.lang.OutOfMemoryError?

Question

Documentation for java.lang.Error says:

An Error is a subclass of Throwable that indicates serious problems that a reasonable application

Answer 1

I have an application that needs to recover from OutOfMemoryError failures, and in single-threaded programs it always works, but sometimes doesn't in multi-threaded programs. The application is an automated Java testing tool that executes generated test sequences to the maximum possible depth on test classes. Now, the UI must be stable, but the test engine can run out of memory while growing the tree of test cases. I handle this by the following kind of code idiom in the test engine:

boolean isOutOfMemory = false;  // flag used for reporting
try {
   SomeType largeVar;
   // Main loop that allocates more and more to largeVar
   // may terminate OK, or raise OutOfMemoryError
}
catch (OutOfMemoryError ex) {
   // largeVar is now out of scope, so is garbage
   System.gc();                // clean up largeVar data
   isOutOfMemory = true;       // flag available for use
}
// program tests flag to report recovery

This works every time in single-threaded applications. But I recently put my test engine into a separate worker-thread from the UI. Now, the out of memory may occur arbitrarily in either thread, and it is not clear to me how to catch it.

For example, I had the OOME occur while the frames of an animated GIF in my UI were being cycled by a proprietary thread that is created behind-the-scenes by a Swing class that is out of my control. I had thought that I had allocated all the resources needed in advance, but clearly the animator is allocating memory every time it fetches the next image. If anyone has an idea about how to handle OOMEs raised in any thread, I would love to hear.