bpo-38091: Import deadlock detection causes deadlock (GH-17518)

Automerge-Triggered-By: @brettcannon
This commit is contained in:
Armin Rigo 2020-03-03 02:37:25 +01:00 committed by GitHub
parent ce3a498408
commit 6daa37fd42
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4 changed files with 1694 additions and 1673 deletions

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@ -67,6 +67,7 @@ class _ModuleLock:
# Deadlock avoidance for concurrent circular imports.
me = _thread.get_ident()
tid = self.owner
seen = set()
while True:
lock = _blocking_on.get(tid)
if lock is None:
@ -74,6 +75,14 @@ class _ModuleLock:
tid = lock.owner
if tid == me:
return True
if tid in seen:
# bpo 38091: the chain of tid's we encounter here
# eventually leads to a fixpoint or a cycle, but
# does not reach 'me'. This means we would not
# actually deadlock. This can happen if other
# threads are at the beginning of acquire() below.
return False
seen.add(tid)
def acquire(self):
"""

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@ -436,16 +436,24 @@ class ImportTests(unittest.TestCase):
os.does_not_exist
def test_concurrency(self):
# bpo 38091: this is a hack to slow down the code that calls
# has_deadlock(); the logic was itself sometimes deadlocking.
def delay_has_deadlock(frame, event, arg):
if event == 'call' and frame.f_code.co_name == 'has_deadlock':
time.sleep(0.1)
sys.path.insert(0, os.path.join(os.path.dirname(__file__), 'data'))
try:
exc = None
def run():
sys.settrace(delay_has_deadlock)
event.wait()
try:
import package
except BaseException as e:
nonlocal exc
exc = e
sys.settrace(None)
for i in range(10):
event = threading.Event()

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@ -0,0 +1 @@
Tweak import deadlock detection code to not deadlock itself.

3349
Python/importlib.h generated

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