[Python-checkins] cpython (2.7): Issue #7105: weak dict iterators are fragile because of unpredictable GC runs
kristjan.jonsson
python-checkins at python.org
Thu Dec 5 11:05:12 CET 2013
http://hg.python.org/cpython/rev/03fcc12282fc
changeset: 87778:03fcc12282fc
branch: 2.7
parent: 87754:ae9fb85ab4e0
user: Kristján Valur Jónsson <sweskman at gmail.com>
date: Thu Dec 05 10:03:45 2013 +0000
summary:
Issue #7105: weak dict iterators are fragile because of unpredictable GC runs
Backport the fix from pyton 3.x for this issue.
files:
Doc/library/weakref.rst | 4 +-
Lib/test/test_weakref.py | 97 ++++++++++++++++++++-
Lib/test/test_weakset.py | 49 +++++++++++
Lib/weakref.py | 120 ++++++++++++++++++++------
4 files changed, 235 insertions(+), 35 deletions(-)
diff --git a/Doc/library/weakref.rst b/Doc/library/weakref.rst
--- a/Doc/library/weakref.rst
+++ b/Doc/library/weakref.rst
@@ -163,7 +163,7 @@
.. method:: WeakKeyDictionary.iterkeyrefs()
- Return an :term:`iterator` that yields the weak references to the keys.
+ Return an iterable of the weak references to the keys.
.. versionadded:: 2.5
@@ -195,7 +195,7 @@
.. method:: WeakValueDictionary.itervaluerefs()
- Return an :term:`iterator` that yields the weak references to the values.
+ Return an iterable of the weak references to the values.
.. versionadded:: 2.5
diff --git a/Lib/test/test_weakref.py b/Lib/test/test_weakref.py
--- a/Lib/test/test_weakref.py
+++ b/Lib/test/test_weakref.py
@@ -4,6 +4,8 @@
import UserList
import weakref
import operator
+import contextlib
+import copy
from test import test_support
@@ -903,7 +905,7 @@
def check_len_cycles(self, dict_type, cons):
N = 20
items = [RefCycle() for i in range(N)]
- dct = dict_type(cons(o) for o in items)
+ dct = dict_type(cons(i, o) for i, o in enumerate(items))
# Keep an iterator alive
it = dct.iteritems()
try:
@@ -913,18 +915,23 @@
del items
gc.collect()
n1 = len(dct)
+ list(it)
del it
gc.collect()
n2 = len(dct)
- # one item may be kept alive inside the iterator
- self.assertIn(n1, (0, 1))
+ # iteration should prevent garbage collection here
+ # Note that this is a test on an implementation detail. The requirement
+ # is only to provide stable iteration, not that the size of the container
+ # stay fixed.
+ self.assertEqual(n1, 20)
+ #self.assertIn(n1, (0, 1))
self.assertEqual(n2, 0)
def test_weak_keyed_len_cycles(self):
- self.check_len_cycles(weakref.WeakKeyDictionary, lambda k: (k, 1))
+ self.check_len_cycles(weakref.WeakKeyDictionary, lambda n, k: (k, n))
def test_weak_valued_len_cycles(self):
- self.check_len_cycles(weakref.WeakValueDictionary, lambda k: (1, k))
+ self.check_len_cycles(weakref.WeakValueDictionary, lambda n, k: (n, k))
def check_len_race(self, dict_type, cons):
# Extended sanity checks for len() in the face of cyclic collection
@@ -1090,6 +1097,86 @@
self.assertEqual(len(values), 0,
"itervalues() did not touch all values")
+ def check_weak_destroy_while_iterating(self, dict, objects, iter_name):
+ n = len(dict)
+ it = iter(getattr(dict, iter_name)())
+ next(it) # Trigger internal iteration
+ # Destroy an object
+ del objects[-1]
+ gc.collect() # just in case
+ # We have removed either the first consumed object, or another one
+ self.assertIn(len(list(it)), [len(objects), len(objects) - 1])
+ del it
+ # The removal has been committed
+ self.assertEqual(len(dict), n - 1)
+
+ def check_weak_destroy_and_mutate_while_iterating(self, dict, testcontext):
+ # Check that we can explicitly mutate the weak dict without
+ # interfering with delayed removal.
+ # `testcontext` should create an iterator, destroy one of the
+ # weakref'ed objects and then return a new key/value pair corresponding
+ # to the destroyed object.
+ with testcontext() as (k, v):
+ self.assertFalse(k in dict)
+ with testcontext() as (k, v):
+ self.assertRaises(KeyError, dict.__delitem__, k)
+ self.assertFalse(k in dict)
+ with testcontext() as (k, v):
+ self.assertRaises(KeyError, dict.pop, k)
+ self.assertFalse(k in dict)
+ with testcontext() as (k, v):
+ dict[k] = v
+ self.assertEqual(dict[k], v)
+ ddict = copy.copy(dict)
+ with testcontext() as (k, v):
+ dict.update(ddict)
+ self.assertEqual(dict, ddict)
+ with testcontext() as (k, v):
+ dict.clear()
+ self.assertEqual(len(dict), 0)
+
+ def test_weak_keys_destroy_while_iterating(self):
+ # Issue #7105: iterators shouldn't crash when a key is implicitly removed
+ dict, objects = self.make_weak_keyed_dict()
+ self.check_weak_destroy_while_iterating(dict, objects, 'iterkeys')
+ self.check_weak_destroy_while_iterating(dict, objects, 'iteritems')
+ self.check_weak_destroy_while_iterating(dict, objects, 'itervalues')
+ self.check_weak_destroy_while_iterating(dict, objects, 'iterkeyrefs')
+ dict, objects = self.make_weak_keyed_dict()
+ @contextlib.contextmanager
+ def testcontext():
+ try:
+ it = iter(dict.iteritems())
+ next(it)
+ # Schedule a key/value for removal and recreate it
+ v = objects.pop().arg
+ gc.collect() # just in case
+ yield Object(v), v
+ finally:
+ it = None # should commit all removals
+ self.check_weak_destroy_and_mutate_while_iterating(dict, testcontext)
+
+ def test_weak_values_destroy_while_iterating(self):
+ # Issue #7105: iterators shouldn't crash when a key is implicitly removed
+ dict, objects = self.make_weak_valued_dict()
+ self.check_weak_destroy_while_iterating(dict, objects, 'iterkeys')
+ self.check_weak_destroy_while_iterating(dict, objects, 'iteritems')
+ self.check_weak_destroy_while_iterating(dict, objects, 'itervalues')
+ self.check_weak_destroy_while_iterating(dict, objects, 'itervaluerefs')
+ dict, objects = self.make_weak_valued_dict()
+ @contextlib.contextmanager
+ def testcontext():
+ try:
+ it = iter(dict.iteritems())
+ next(it)
+ # Schedule a key/value for removal and recreate it
+ k = objects.pop().arg
+ gc.collect() # just in case
+ yield k, Object(k)
+ finally:
+ it = None # should commit all removals
+ self.check_weak_destroy_and_mutate_while_iterating(dict, testcontext)
+
def test_make_weak_keyed_dict_from_dict(self):
o = Object(3)
dict = weakref.WeakKeyDictionary({o:364})
diff --git a/Lib/test/test_weakset.py b/Lib/test/test_weakset.py
--- a/Lib/test/test_weakset.py
+++ b/Lib/test/test_weakset.py
@@ -11,6 +11,7 @@
import collections
import gc
import contextlib
+from UserString import UserString as ustr
class Foo:
@@ -448,6 +449,54 @@
self.assertGreaterEqual(n2, 0)
self.assertLessEqual(n2, n1)
+ def test_weak_destroy_while_iterating(self):
+ # Issue #7105: iterators shouldn't crash when a key is implicitly removed
+ # Create new items to be sure no-one else holds a reference
+ items = [ustr(c) for c in ('a', 'b', 'c')]
+ s = WeakSet(items)
+ it = iter(s)
+ next(it) # Trigger internal iteration
+ # Destroy an item
+ del items[-1]
+ gc.collect() # just in case
+ # We have removed either the first consumed items, or another one
+ self.assertIn(len(list(it)), [len(items), len(items) - 1])
+ del it
+ # The removal has been committed
+ self.assertEqual(len(s), len(items))
+
+ def test_weak_destroy_and_mutate_while_iterating(self):
+ # Issue #7105: iterators shouldn't crash when a key is implicitly removed
+ items = [ustr(c) for c in string.ascii_letters]
+ s = WeakSet(items)
+ @contextlib.contextmanager
+ def testcontext():
+ try:
+ it = iter(s)
+ next(it)
+ # Schedule an item for removal and recreate it
+ u = ustr(str(items.pop()))
+ gc.collect() # just in case
+ yield u
+ finally:
+ it = None # should commit all removals
+
+ with testcontext() as u:
+ self.assertFalse(u in s)
+ with testcontext() as u:
+ self.assertRaises(KeyError, s.remove, u)
+ self.assertFalse(u in s)
+ with testcontext() as u:
+ s.add(u)
+ self.assertTrue(u in s)
+ t = s.copy()
+ with testcontext() as u:
+ s.update(t)
+ self.assertEqual(len(s), len(t))
+ with testcontext() as u:
+ s.clear()
+ self.assertEqual(len(s), 0)
+
def test_main(verbose=None):
test_support.run_unittest(TestWeakSet)
diff --git a/Lib/weakref.py b/Lib/weakref.py
--- a/Lib/weakref.py
+++ b/Lib/weakref.py
@@ -20,7 +20,7 @@
ProxyType,
ReferenceType)
-from _weakrefset import WeakSet
+from _weakrefset import WeakSet, _IterationGuard
from exceptions import ReferenceError
@@ -48,10 +48,24 @@
def remove(wr, selfref=ref(self)):
self = selfref()
if self is not None:
- del self.data[wr.key]
+ if self._iterating:
+ self._pending_removals.append(wr.key)
+ else:
+ del self.data[wr.key]
self._remove = remove
+ # A list of keys to be removed
+ self._pending_removals = []
+ self._iterating = set()
UserDict.UserDict.__init__(self, *args, **kw)
+ def _commit_removals(self):
+ l = self._pending_removals
+ d = self.data
+ # We shouldn't encounter any KeyError, because this method should
+ # always be called *before* mutating the dict.
+ while l:
+ del d[l.pop()]
+
def __getitem__(self, key):
o = self.data[key]()
if o is None:
@@ -59,6 +73,11 @@
else:
return o
+ def __delitem__(self, key):
+ if self._pending_removals:
+ self._commit_removals()
+ del self.data[key]
+
def __contains__(self, key):
try:
o = self.data[key]()
@@ -77,8 +96,15 @@
return "<WeakValueDictionary at %s>" % id(self)
def __setitem__(self, key, value):
+ if self._pending_removals:
+ self._commit_removals()
self.data[key] = KeyedRef(value, self._remove, key)
+ def clear(self):
+ if self._pending_removals:
+ self._commit_removals()
+ self.data.clear()
+
def copy(self):
new = WeakValueDictionary()
for key, wr in self.data.items():
@@ -120,16 +146,18 @@
return L
def iteritems(self):
- for wr in self.data.itervalues():
- value = wr()
- if value is not None:
- yield wr.key, value
+ with _IterationGuard(self):
+ for wr in self.data.itervalues():
+ value = wr()
+ if value is not None:
+ yield wr.key, value
def iterkeys(self):
- return self.data.iterkeys()
+ with _IterationGuard(self):
+ for k in self.data.iterkeys():
+ yield k
- def __iter__(self):
- return self.data.iterkeys()
+ __iter__ = iterkeys
def itervaluerefs(self):
"""Return an iterator that yields the weak references to the values.
@@ -141,15 +169,20 @@
keep the values around longer than needed.
"""
- return self.data.itervalues()
+ with _IterationGuard(self):
+ for wr in self.data.itervalues():
+ yield wr
def itervalues(self):
- for wr in self.data.itervalues():
- obj = wr()
- if obj is not None:
- yield obj
+ with _IterationGuard(self):
+ for wr in self.data.itervalues():
+ obj = wr()
+ if obj is not None:
+ yield obj
def popitem(self):
+ if self._pending_removals:
+ self._commit_removals()
while 1:
key, wr = self.data.popitem()
o = wr()
@@ -157,6 +190,8 @@
return key, o
def pop(self, key, *args):
+ if self._pending_removals:
+ self._commit_removals()
try:
o = self.data.pop(key)()
except KeyError:
@@ -172,12 +207,16 @@
try:
wr = self.data[key]
except KeyError:
+ if self._pending_removals:
+ self._commit_removals()
self.data[key] = KeyedRef(default, self._remove, key)
return default
else:
return wr()
def update(self, dict=None, **kwargs):
+ if self._pending_removals:
+ self._commit_removals()
d = self.data
if dict is not None:
if not hasattr(dict, "items"):
@@ -245,9 +284,29 @@
def remove(k, selfref=ref(self)):
self = selfref()
if self is not None:
- del self.data[k]
+ if self._iterating:
+ self._pending_removals.append(k)
+ else:
+ del self.data[k]
self._remove = remove
- if dict is not None: self.update(dict)
+ # A list of dead weakrefs (keys to be removed)
+ self._pending_removals = []
+ self._iterating = set()
+ if dict is not None:
+ self.update(dict)
+
+ def _commit_removals(self):
+ # NOTE: We don't need to call this method before mutating the dict,
+ # because a dead weakref never compares equal to a live weakref,
+ # even if they happened to refer to equal objects.
+ # However, it means keys may already have been removed.
+ l = self._pending_removals
+ d = self.data
+ while l:
+ try:
+ del d[l.pop()]
+ except KeyError:
+ pass
def __delitem__(self, key):
del self.data[ref(key)]
@@ -306,10 +365,11 @@
return L
def iteritems(self):
- for wr, value in self.data.iteritems():
- key = wr()
- if key is not None:
- yield key, value
+ with _IterationGuard(self):
+ for wr, value in self.data.iteritems():
+ key = wr()
+ if key is not None:
+ yield key, value
def iterkeyrefs(self):
"""Return an iterator that yields the weak references to the keys.
@@ -321,19 +381,23 @@
keep the keys around longer than needed.
"""
- return self.data.iterkeys()
+ with _IterationGuard(self):
+ for wr in self.data.iterkeys():
+ yield wr
def iterkeys(self):
- for wr in self.data.iterkeys():
- obj = wr()
- if obj is not None:
- yield obj
+ with _IterationGuard(self):
+ for wr in self.data.iterkeys():
+ obj = wr()
+ if obj is not None:
+ yield obj
- def __iter__(self):
- return self.iterkeys()
+ __iter__ = iterkeys
def itervalues(self):
- return self.data.itervalues()
+ with _IterationGuard(self):
+ for value in self.data.itervalues():
+ yield value
def keyrefs(self):
"""Return a list of weak references to the keys.
--
Repository URL: http://hg.python.org/cpython
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