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gh-117688: Fix deadlock in test_no_stale_references with GIL disabled (#117720)

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Check `my_object_collected.wait()` in a loop to give the main thread a
chance to merge the reference count fields. Additionally, call
`my_object_collected.set()` in a background thread to avoid deadlocking
when the destructor is called asynchronously via the eval breaker
within the body of of `my_object_collected.wait()`.
This commit is contained in:
Sam Gross 2024-04-15 12:54:56 -04:00 committed by GitHub
parent 106e9ddc43
commit 520cf2170e
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1 changed files with 21 additions and 11 deletions
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32
Lib/test/test_concurrent_futures/executor.py
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@ -83,24 +83,34 @@ class ExecutorTest:
# references.
my_object = MyObject()
my_object_collected = threading.Event()
my_object_callback = weakref.ref(
my_object, lambda obj: my_object_collected.set())
fut = self.executor.submit(my_object.my_method)
def set_event():
if Py_GIL_DISABLED:
# gh-117688 Avoid deadlock by setting the event in a
# background thread. The current thread may be in the middle
# of the my_object_collected.wait() call, which holds locks
# needed by my_object_collected.set().
threading.Thread(target=my_object_collected.set).start()
else:
my_object_collected.set()
my_object_callback = weakref.ref(my_object, lambda obj: set_event())
# Deliberately discarding the future.
self.executor.submit(my_object.my_method)
del my_object
if Py_GIL_DISABLED:
# Due to biased reference counting, my_object might only be
# deallocated while the thread that created it runs -- if the
# thread is paused waiting on an event, it may not merge the
# refcount of the queued object. For that reason, we wait for the
# task to finish (so that it's no longer referenced) and force a
# GC to ensure that it is collected.
fut.result() # Wait for the task to finish.
support.gc_collect()
# refcount of the queued object. For that reason, we alternate
# between running the GC and waiting for the event.
wait_time = 0
collected = False
while not collected and wait_time <= support.SHORT_TIMEOUT:
support.gc_collect()
collected = my_object_collected.wait(timeout=1.0)
wait_time += 1.0
else:
del fut # Deliberately discard the future.
collected = my_object_collected.wait(timeout=support.SHORT_TIMEOUT)
collected = my_object_collected.wait(timeout=support.SHORT_TIMEOUT)
self.assertTrue(collected,
"Stale reference not collected within timeout.")