On Mon, Jan 23, 2017 at 11:21 PM, Luke Hutchison <luke.hu...@gmail.com> wrote:
> That looks like a variation of the classic class initialization deadlock >> problem. Your main thread is blocked in es.submit(callable).get(); while >> still within the static initializer of the LambdaBug class. If the executor >> thread also needs to ensure LambdaBug is initialized (which it will in the >> lambda case) then it will wait for the main thread to complete the >> initialization. Hence deadlock. >> > > Thanks for the explanation -- although I don't understand why a lambda > expression requires its defining class to be initialized, whereas an > anonymous inner class does not. > Also, I'm trying to determine if it is possible to detect cases like this at runtime without triggering the deadlock, since I have already had one bug report from a user of FastClasspathScanner running into this problem: https://github.com/lukehutch/fast-classpath-scanner/issues/103 This user could not understand why FastClasspathScanner appeared to deadlock when he passed in a lambda, but not when he passed in an anonymous inner class. Is it possible to examine an object to determine (1) if it was defined as a lambda, and (2) if the enclosing class (i.e. the class that defined the lambda) is initialized? (I can't see foolproof ways to do either of these things, based on a cursory search.) If so, at least I will be able to throw an exception in my code, which will be better than hitting a deadlock situation.
