Pablo Galindo Salgado <[email protected]> added the comment:
This is not a regression: the code only worked on 3.7 because there is a sleep
in the pool maintainance loop that makes the pool more likely being more
consistent, but is the same problem as there is a race condition. For example,
reducing the sleep in the loop (notice 3.8 does not use a sleep but instead
uses a more resilient system of sentinels) for the 3.7 version reproduces the
problem:
diff --git a/Lib/multiprocessing/pool.py b/Lib/multiprocessing/pool.py
index 3e9a0d6b48..f8d438d87c 100644
--- a/Lib/multiprocessing/pool.py
+++ b/Lib/multiprocessing/pool.py
@@ -410,7 +410,7 @@ class Pool(object):
# is terminated.
while thread._state == RUN or (pool._cache and thread._state !=
TERMINATE):
pool._maintain_pool()
- time.sleep(0.1)
+ time.sleep(0.00000001)
# send sentinel to stop workers
pool._taskqueue.put(None)
util.debug('worker handler exiting')
With that patch, 3.7 hangs as well. The problem here is that something
regarding the locks inside the SimpleQueue of inbound tasks is not in a
consistent state when Python finalization calls __del__.
----------
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Python tracker <[email protected]>
<https://bugs.python.org/issue39360>
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