Broken thread safety #88
Comments
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I had to repeat it a few times to trigger this behavior, but I see it. |
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Standalone reproducer for a different race condition: import threading
import time
import lazy_loader as lazy
def repeat_lazy():
time.sleep(0.5)
np = lazy.load('numpy')
for _ in range(50):
threading.Thread(target=repeat_lazy).start() |
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@eindenbom Can you give #90 a try? |
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I do not think #90 fixes the same race condition as reported in this issue. You are fixing a possible race (I am not sure that there is any) in lazy_loader.load(), while in librosa it is executed at librosa load time and therefore protected by module load lock. The race I have reported is in |
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The tests confirm that the other race condition exists, but you are right that #90 does not address this issue. |
Agreed, this is a CPython bug: import importlib
import threading
import sys
spec = importlib.util.find_spec('http')
module = importlib.util.module_from_spec(spec)
http = sys.modules['http'] = module
loader = importlib.util.LazyLoader(spec.loader)
loader.exec_module(module)
def check():
return http.HTTPStatus.ACCEPTED == 202
for _ in range(5):
threading.Thread(target=check).start()This looks painful to fix, since attempting to attach a lock to the |
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Thanks for investigating, @effigies! Adding |
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Can we simply lock up import importlib
import threading
import sys
import time
spec = importlib.util.find_spec('http')
module = importlib.util.module_from_spec(spec)
http = sys.modules['http'] = module
lock = threading.Lock()
def lock_func(f):
def locked(*args, **kwargs):
with lock:
return f(*args, **kwargs)
return locked
loader = importlib.util.LazyLoader(spec.loader)
loader.exec_module = lock_func(loader.exec_module)
loader.exec_module(module)
def check():
time.sleep(0.2)
return http.HTTPStatus.ACCEPTED == 202
for _ in range(5):
threading.Thread(target=check).start() |
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I don't think so, because |
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Yes, but look at the above example, which wraps exec_module in a lock. |
In [1]: import importlib
...: import threading
...: import sys
...: import time
...:
...: spec = importlib.util.find_spec('http')
...: module = importlib.util.module_from_spec(spec)
...: http = sys.modules['http'] = module
...:
...: lock = threading.Lock()
...:
...: def lock_func(f):
...: def locked(*args, **kwargs):
...: with lock:
...: return f(*args, **kwargs)
...: return locked
...:
...: loader = importlib.util.LazyLoader(spec.loader)
...: loader.exec_module = lock_func(loader.exec_module)
...: loader.exec_module(module)
...:
...:
...: def check():
...: time.sleep(0.2)
...: return http.HTTPStatus.ACCEPTED == 202
...:
...: for _ in range(5):
...: threading.Thread(target=check).start()
...:
Exception in thread Thread-2 (check):
Traceback (most recent call last):
File "/home/chris/mambaforge/envs/default/lib/python3.10/threading.py", line 1016, in _bootstrap_inner
self.run()
File "/home/chris/mambaforge/envs/default/lib/python3.10/threading.py", line 953, in run
self._target(*self._args, **self._kwargs)
File "<ipython-input-1-1b0c7fd1f576>", line 25, in check
Exception in thread Thread-5 (check):
Traceback (most recent call last):
File "/home/chris/mambaforge/envs/default/lib/python3.10/threading.py", line 1016, in _bootstrap_inner
self.run()
File "/home/chris/mambaforge/envs/default/lib/python3.10/threading.py", line 953, in run
self._target(*self._args, **self._kwargs)
File "<ipython-input-1-1b0c7fd1f576>", line 25, in check
AttributeError: module 'http' has no attribute 'HTTPStatus'
AttributeError: module 'http' has no attribute 'HTTPStatus' |
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Hrm, yes, looks like I have to use |
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The loader isn't where the race is. I might be wrong, but I don't think that will protect the actual critical operations. |
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Right, so we'll have to ensure "attribute access + lazy loading" becomes an atomic operation. |
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I went ahead and opened python/cpython#114763. I think I have a fix. |
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@eindenbom If you're prepared to build your whole dependency tree for 3.13-dev, you could test out python/cpython#114781. I suspect it can be rebased on the 3.12 branch as well, if you'd prefer. |
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Thanks to @effigies, this issue has been addressed by python/cpython#114781. @eindenbom This should soon be backported to the 3.11 and 3.12 source trees. |
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Should be out in 3.11.9 (python/cpython#115871 - ETA April 1) and 3.12.3 (python/cpython#115870 - ETA April 9). |
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No, my read is that these are two independent races. |
lazy_loader loaded modules are not thread-safe: when concurrently accessed from several threads all but the first thread get partially loaded module missing most of functionality.
For example
librosauses lazy_loader to loadresampyand gets the following error:To Reproduce
Run the following snippet:
Expected behavior
No errors reported.
Actual output
Software versions
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