Behavior of a Java process in case of OutOfMemoryError

Question

What would be the behavior of a Java program on getting OutOfMemoryError. Is there any defined behavior? Will the process crash or would it go into wait/sleep state?

Answer 1

OutOfMemoryError should be considered unrecoverable and the behavior of the JVM after such an error has been raised is undefined, so there is no point in expending effort to handle it. Any operations done after this exception is thrown by the JVM will have undefined behavior. They may execute, but more likely they will just cause another error to be thrown.

Answer 2

You can't determine the state of program when OutOfMemoryError occurs. If you are not catching Throwable then your program will terminate with the stacktrace. Even if you are catching Throwable, you should call System.exit since there is no point in recovering from it. "Error" is generally thrown by JVM, as oppose to Exception, which is application/programmer specific.

Answer 3

And OutOfMemoryError is handled like any other exception:

• If it is caught, then nothing more happens.
• If it is not caught, then either the threads or the threads groups uncaught exception handler handles it. This pretty much always leads to the thread being stopped.

However there are two factors that are not really there in other exceptions:

• OutOfMemoryError is an Error and not an Exception. This means that it's very unlikely to be caught anywhere: You should not try to catch an Error generally (with very few exceptions) and it's not usually done, so the chances of it being handled are rather low.
• When an OutOfMemoryError happens and no object become eligible for GC because of that, then you'll still have little memory left and chances are that you'll run into the exact same problem again later on.

And if the thread this happens to is the only non-daemon thread (often, but not necessarily, that's the main thread, that executes the main method), then that thread getting killed results in the whole JVM shutting down (which is often perceived as "a crash").

So the tl;dr is: It will probably kill the thread, and if the memory-issue is not solved, then this can happen to more and more threads.