mirrors/cpython
1
0
Fork 0
mirror of https://github.com/python/cpython.git synced 2025-08-01 15:43:13 +00:00
Code Issues Projects Releases Packages Wiki Activity Actions 8

Issue #28969: Fixed race condition in C implementation of functools.lru_cache.

Browse source 
KeyError could be raised when cached function with full cache was
simultaneously called from differen threads with the same uncached arguments.
This commit is contained in:
Serhiy Storchaka 2017-01-12 19:12:21 +02:00
commit 42e1ea9a10
5 changed files with 78 additions and 29 deletions
Download patch file Download diff file Expand all files Collapse all files

56
Modules/_functoolsmodule.c
View file

@ -863,42 +863,56 @@ bounded_lru_cache_wrapper(lru_cache_object *self, PyObject *args, PyObject *kwds
}
if (self->full && self->root.next != &self->root) {
/* Use the oldest item to store the new key and result. */
PyObject *oldkey, *oldresult;
PyObject *oldkey, *oldresult, *popresult;
/* Extricate the oldest item. */
link = self->root.next;
lru_cache_extricate_link(link);
/* Remove it from the cache.
The cache dict holds one reference to the link,
and the linked list holds yet one reference to it. */
if (_PyDict_DelItem_KnownHash(self->cache, link->key,
link->hash) < 0) {
popresult = _PyDict_Pop_KnownHash(self->cache,
link->key, link->hash,
Py_None);
if (popresult == Py_None) {
/* Getting here means that this same key was added to the
cache while the lock was released. Since the link
update is already done, we need only return the
computed result and update the count of misses. */
Py_DECREF(popresult);
Py_DECREF(link);
Py_DECREF(key);
}
else if (popresult == NULL) {
lru_cache_append_link(self, link);
Py_DECREF(key);
Py_DECREF(result);
return NULL;
}
/* Keep a reference to the old key and old result to
prevent their ref counts from going to zero during the
update. That will prevent potentially arbitrary object
clean-up code (i.e. __del__) from running while we're
still adjusting the links. */
oldkey = link->key;
oldresult = link->result;
else {
Py_DECREF(popresult);
/* Keep a reference to the old key and old result to
prevent their ref counts from going to zero during the
update. That will prevent potentially arbitrary object
clean-up code (i.e. __del__) from running while we're
still adjusting the links. */
oldkey = link->key;
oldresult = link->result;
link->hash = hash;
link->key = key;
link->result = result;
if (_PyDict_SetItem_KnownHash(self->cache, key, (PyObject *)link,
hash) < 0) {
Py_DECREF(link);
link->hash = hash;
link->key = key;
link->result = result;
if (_PyDict_SetItem_KnownHash(self->cache, key, (PyObject *)link,
hash) < 0) {
Py_DECREF(link);
Py_DECREF(oldkey);
Py_DECREF(oldresult);
return NULL;
}
lru_cache_append_link(self, link);
Py_INCREF(result); /* for return */
Py_DECREF(oldkey);
Py_DECREF(oldresult);
return NULL;
}
lru_cache_append_link(self, link);
Py_INCREF(result); /* for return */
Py_DECREF(oldkey);
Py_DECREF(oldresult);
} else {
/* Put result in a new link at the front of the queue. */
link = (lru_list_elem *)PyObject_GC_New(lru_list_elem,