Implementing ListeningExecutorService in Java 5

Question

In Java 5, the ExecutorService interface declares the method:

<T> List<Future<T>> invokeAll(Collection<Callable<T>> tasks)
    throws InterruptedException;

whereas Guava 11.0.2, written in Java 6 but supposedly compatible with Java 5, overrides it in ListeningExecutorService as:

 <T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)
     throws InterruptedException;

If I want to implement my own ListeningExecutorService, I would need to implement both of these methods, but I am also not able to have two methods the same erasure, so it's a bit of a Catch 22.

Is there any way around this problem? More specifically, is there any way to implement a ListeningExecutorService in Java 5?

As a side note to any Guava folks--is it actually necessary for Guava to re-declare this method since it's already inherited from ExecutorService?

Answer 1

The original method signature has been reported as a bug and fixed for JDK 6: https://bugs.java.com/bugdatabase/view_bug?bug_id=6267833

To quote the resolution message:

• is binary compatible.

• is source compatible for users of an ExecutorService
• requires minor source code changes for the small set of developers who have implemented ExecutorService without inheriting the default implementations in AbstractExecutorService. The set of affected developers are developers creating sophisticated thread pool applications, putting them into the "concurrency rocket scientist" category. They will generally appreciate this change. The possible compiler error is trivial to fix in the source code.