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Lock around strong cache updates #973

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merged 1 commit into from Nov 3, 2019
Merged

Lock around strong cache updates #973

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1 change: 1 addition & 0 deletions changelog.d/973.bugfix.rst
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@@ -0,0 +1 @@
Fixed a race condition in the ``tzoffset`` and ``tzstr`` "strong" caches on Python 2.7. Reported by @kainjow (gh issue #901).
29 changes: 18 additions & 11 deletions dateutil/tz/_factories.py
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Expand Up @@ -2,6 +2,8 @@
import weakref
from collections import OrderedDict

from six.moves import _thread


class _TzSingleton(type):
def __init__(cls, *args, **kwargs):
Expand All @@ -26,6 +28,8 @@ def __init__(cls, *args, **kwargs):
cls.__strong_cache = OrderedDict()
cls.__strong_cache_size = 8

cls._cache_lock = _thread.allocate_lock()

def __call__(cls, name, offset):
if isinstance(offset, timedelta):
key = (name, offset.total_seconds())
Expand All @@ -37,12 +41,13 @@ def __call__(cls, name, offset):
instance = cls.__instances.setdefault(key,
cls.instance(name, offset))

cls.__strong_cache[key] = cls.__strong_cache.pop(key, instance)
# This lock may not be necessary in Python 3. See GH issue #901
with cls._cache_lock:
cls.__strong_cache[key] = cls.__strong_cache.pop(key, instance)

# Remove an item if the strong cache is overpopulated
# TODO: Maybe this should be under a lock?
if len(cls.__strong_cache) > cls.__strong_cache_size:
cls.__strong_cache.popitem(last=False)
# Remove an item if the strong cache is overpopulated
if len(cls.__strong_cache) > cls.__strong_cache_size:
cls.__strong_cache.popitem(last=False)

return instance

Expand All @@ -53,6 +58,8 @@ def __init__(cls, *args, **kwargs):
cls.__strong_cache = OrderedDict()
cls.__strong_cache_size = 8

cls.__cache_lock = _thread.allocate_lock()

def __call__(cls, s, posix_offset=False):
key = (s, posix_offset)
instance = cls.__instances.get(key, None)
Expand All @@ -61,13 +68,13 @@ def __call__(cls, s, posix_offset=False):
instance = cls.__instances.setdefault(key,
cls.instance(s, posix_offset))

cls.__strong_cache[key] = cls.__strong_cache.pop(key, instance)

# This lock may not be necessary in Python 3. See GH issue #901
with cls.__cache_lock:
cls.__strong_cache[key] = cls.__strong_cache.pop(key, instance)

# Remove an item if the strong cache is overpopulated
# TODO: Maybe this should be under a lock?
if len(cls.__strong_cache) > cls.__strong_cache_size:
cls.__strong_cache.popitem(last=False)
# Remove an item if the strong cache is overpopulated
if len(cls.__strong_cache) > cls.__strong_cache_size:
cls.__strong_cache.popitem(last=False)

return instance