How to wait for a thread that spawns it's own thread?

Question

I\'m trying to test a method that does it\'s work in a separate thread, simplified it\'s like this:

public void methodToTest()
{
    Thread thread = new Thre         


        

Answer 1

Without a reference to the thread created in methodToTest, you cannot, quite simply. Java provides no mechanism for finding "threads that were spawned during this particular time period" (and even if it did, it would arguably be an ugly mechanism to use).

As I see it, you have two choices:

• Make methodToTest wait for the thread it spawns. Of course, if you explicitly want this to be an asynchronous action, then you can't very well do that.
• Return the newly created thread from methodToTest, so that any callers can choose to wait for it if they so wish.

It may be noted that the second choice can be formulated in a few different ways. You could, for instance, return some abstract Future-like object rather than a thread, if you want to extend the liberty of methodToTest to use various ways of doing asynchronous work. You could perhaps also define some global task-pool that you enforce all your asynchronous tasks to run inside, and then wait for all tasks in the pool to finish before checking the assertion. Such a task pool could take the form of an ExecutorService, or a ThreadGroup, or any number of other forms. They all do the same thing in the end, but may be more or less suited to your environment -- the main point being that you have to explicitly give the caller access to the newly created thread, is some manner or another.