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gh-90622: Prevent max_tasks_per_child use with a fork mp_context. (#91587)

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Prevent `max_tasks_per_child` use with a "fork" mp_context to avoid deadlocks.

Also defaults to "spawn" when no mp_context is supplied for safe convenience.
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Gregory P. Smith 2022-05-06 00:04:53 -07:00 • committed by GitHub
parent 2b563f1ad3
commit fa4f0a134e
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4 changed files with 43 additions and 11 deletions
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18
Lib/test/test_concurrent_futures.py
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@ -1039,10 +1039,15 @@ class ProcessPoolExecutorTest(ExecutorTest):
executor.shutdown()
def test_max_tasks_per_child(self):
context = self.get_context()
if context.get_start_method(allow_none=False) == "fork":
with self.assertRaises(ValueError):
self.executor_type(1, mp_context=context, max_tasks_per_child=3)
return
# not using self.executor as we need to control construction.
# arguably this could go in another class w/o that mixin.
executor = self.executor_type(
1, mp_context=self.get_context(), max_tasks_per_child=3)
1, mp_context=context, max_tasks_per_child=3)
f1 = executor.submit(os.getpid)
original_pid = f1.result()
# The worker pid remains the same as the worker could be reused
@ -1061,11 +1066,20 @@ class ProcessPoolExecutorTest(ExecutorTest):
executor.shutdown()
def test_max_tasks_per_child_defaults_to_spawn_context(self):
# not using self.executor as we need to control construction.
# arguably this could go in another class w/o that mixin.
executor = self.executor_type(1, max_tasks_per_child=3)
self.assertEqual(executor._mp_context.get_start_method(), "spawn")
def test_max_tasks_early_shutdown(self):
context = self.get_context()
if context.get_start_method(allow_none=False) == "fork":
raise unittest.SkipTest("Incompatible with the fork start method.")
# not using self.executor as we need to control construction.
# arguably this could go in another class w/o that mixin.
executor = self.executor_type(
3, mp_context=self.get_context(), max_tasks_per_child=1)
3, mp_context=context, max_tasks_per_child=1)
futures = []
for i in range(6):
futures.append(executor.submit(mul, i, i))