Fix a crash when a generator is created in a C thread that is destroyed while
the generator is still used. The issue was that a generator contains a frame,
and the frame kept a reference to the Python state of the destroyed C thread.
The crash occurs when a trace function is setup.
crash when a generator is created in a C thread that is destroyed while the
generator is still used. The issue was that a generator contains a frame, and
the frame kept a reference to the Python state of the destroyed C thread. The
crash occurs when a trace function is setup.
Due to recent changes, a Thread doesn't know that it's over before
someone calls .join() or .is_alive(). That meant repr(Thread)
continued to include "started" (and not "stopped") before one of
those methods was called, even if hours passed since the thread
ended.
Repaired that.
The fix for issue 18808 left us checking two things to be sure a Thread
was done: an Event (._stopped) and a mutex (._tstate_lock). Clumsy &
brittle. This patch removes the Event, leaving just a happy lock :-)
The bulk of the patch removes two excruciating tests, which were
verifying sanity of the internals of the ._stopped Event after a fork.
Thanks to Antoine Pitrou for verifying that's the only real value
these tests had.
One consequence of moving from an Event to a mutex: waiters (threads
calling Thread.join()) used to block each on their own unique mutex
(internal to the ._stopped event), but now all contend on the same
mutex (._tstate_lock). These approaches have different performance
characteristics on different platforms. I don't think it matters in
this context.
Note that this is a potentially disruptive change since it may
release some system resources which would otherwise remain
perpetually alive (e.g. database connections kept in thread-local
storage).
