[3.12] gh-109047: concurrent.futures catches RuntimeError (#109810) (#110126)

gh-109047: concurrent.futures catches PythonFinalizationError (#109810)

concurrent.futures: The *executor manager thread* now catches
exceptions when adding an item to the *call queue*. During Python
finalization, creating a new thread can now raise RuntimeError. Catch
the exception and call terminate_broken() in this case.

Add test_python_finalization_error() to test_concurrent_futures.

concurrent.futures._ExecutorManagerThread changes:

* terminate_broken() no longer calls shutdown_workers() since the
  call queue is no longer working anymore (read and write ends of
  the queue pipe are closed).
* terminate_broken() now terminates child processes, not only
  wait until they complete.
* _ExecutorManagerThread.terminate_broken() now holds shutdown_lock
  to prevent race conditons with ProcessPoolExecutor.submit().

multiprocessing.Queue changes:

* Add _terminate_broken() method.
* _start_thread() sets _thread to None on exception to prevent
  leaking "dangling threads" even if the thread was not started
  yet.

(cherry picked from commit 6351842121)

Lib/multiprocessing/queues.py

@@ -158,6 +158,15 @@ class Queue(object):
         except AttributeError:
             pass
 
+    def _terminate_broken(self):
+        # Close a Queue on error.
+
+        # gh-94777: Prevent queue writing to a pipe which is no longer read.
+        self._reader.close()
+
+        self.close()
+        self.join_thread()
+
     def _start_thread(self):
         debug('Queue._start_thread()')
 
@@ -169,13 +178,19 @@ class Queue(object):
                   self._wlock, self._reader.close, self._writer.close,
                   self._ignore_epipe, self._on_queue_feeder_error,
                   self._sem),
-            name='QueueFeederThread'
+            name='QueueFeederThread',
+            daemon=True,
         )
-        self._thread.daemon = True
 
-        debug('doing self._thread.start()')
-        self._thread.start()
-        debug('... done self._thread.start()')
+        try:
+            debug('doing self._thread.start()')
+            self._thread.start()
+            debug('... done self._thread.start()')
+        except:
+            # gh-109047: During Python finalization, creating a thread
+            # can fail with RuntimeError.
+            self._thread = None
+            raise
 
         if not self._joincancelled:
             self._jointhread = Finalize(