How to stop thread returning before Join() is called

Question

This is purely a theoretical question as I'm not sure the conditions to cause this issue would be common.

Say for example you have a thread that you kick off with it's start method:

Thread c = new Thread();
c.start();

Then directly after, you call the Join() method on the thread to tell the method you are in to wait until the thread had been executed to continue.

c.join();

Isn't it a possibility that the thread could possibly be executed and finish before the join method is called, therefore leaving the method unaware that it had to wait for c to finish before it continued? I suppose you could try calling the join() method before you call the start() method, yet whenever I've tried this in test cases, there is an error.

Anyone know a possible fix for this, or does the JVM handle it? As I said I haven't been able to trigger this sort of situation, but theoretically it is possible...

Answer 1

According to the Thread#join(long millis) source code, the isAlive() method is used to check the thread state.

/**
 * Tests if this thread is alive. A thread is alive if it has
 * been started and has not yet died.
 *
 * @return  <code>true</code> if this thread is alive;
 *          <code>false</code> otherwise.
 */
public final native boolean isAlive();

This method obviously returns false if the thread has finished, so thread.join() will immediately exit.