[Antoine]
> Oh, I also get the following sporadic failure
> which is triggered by slight change in semantics
> with Thread.join(timeout) :-)
> ======================================================================
> FAIL: test_various_ops (test.test_threading.ThreadTests)
> ----------------------------------------------------------------------
> Traceback (most recent call last):
>  File "/home/antoine/cpython/default/Lib/test/test_threading.py", line 113, in test_various_ops
>    self.assertTrue(not t.is_alive())
> AssertionError: False is not true

Really!  In context, the test does:

            t.join()
            self.assertTrue(not t.is_alive())

(BTW, that would be clearer as self.assertFalse(t.is_alive()) ;-) )

It was the intent that this continue to work - the only intended change in Python-visible semantics had to do with join'ing with a timeout.

Without a timeout, I confess I don't see how this can fail.  join() is join(timeout=None), which does:

        self._stopped.wait(timeout)
        if self._stopped.is_set():
            self._wait_for_tstate_lock(timeout is None)

which is

        self._stopped.wait(None)
        if self._stopped.is_set():
            self._wait_for_tstate_lock(True)

which should be the same as

        self._stopped.wait()
        self._wait_for_tstate_lock(True)

after which _stopped should be set and _tstate_lock should be None.  The subsequent is_alive() should then return False, via its

        return self._tstate_lock is not None

What's going wrong?