bpo-44422: threading.Thread reuses the _delete() method

[vstinner]

The _bootstrap_inner() method of threading.Thread now reuses its
_delete() method rather than accessing _active() directly. It became
possible since _active_limbo_lock became reentrant. Moreover, it no
longer ignores any exception when deleting the thread from the
_active dictionary.

https://bugs.python.org/issue44422

[vstinner]

History:

• (B) commit 95cd5c0 replaces the _delete() call with inlined code (modify directly _active dictionary)

    - Fix Issue #1703448: A joined thread could show up in the
      threading.enumerate() list after the join() for a brief period until
      it actually exited.

• (A) commit f21b2aa added try: ... except: pass

    Thread.__bootstrap(): ignore exceptions in the self.__delete() call in
    the finally clause.  An exception here could happen when a daemon
    thread exits after the threading module has already been trashed by
    the import finalization, and there's not much of a point in trying to
    insist doing the cleanup in that stage.
    
    This should fix SF bug ##497111: active_limbo_lock error at program
    exit.
    
    2.1.2 and 2.2.1 Bugfix candidate!

[vstinner]

(B) commit 95cd5c0 replaces the _delete() call with inlined code (modify directly _active dictionary)

This is https://bugs.python.org/issue1703448

The fix adds test_enumerate_after_join() to Lib/test/test_threading.py which still exists. Running test_threading should be enough to check for non-regression.

(A) commit f21b2aa added try: ... except: pass

This is https://bugs.python.org/issue497111

[vstinner]

cc @iritkatriel

[iritkatriel]

How did you conclude that the try-except is no longer needed?

[vstinner]

How did you conclude that the try-except is no longer needed?

except: pass ignores any exception. At least, we should only catch KeyError.

I don't understand in which case an exception can occur. In case of doubt, I prefer to remove it. We can add the try/except KeyError again if someone hits the issue.

https://bugs.python.org/issue497111 was reported 20 years ago. The Python code base changed a lot in 20 years.

For example, I modified the Python finalization to clear daemon threads earlier: commit 9ad58ac.

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @vstinner for commit d32b7fc 🤖

If you want to schedule another build, you need to add the ":hammer: test-with-buildbots" label again.

[iritkatriel]

Makes sense.

[vstinner]

@iritkatriel: Thanks for the review. I merged my PR.