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| author | Raymond Hettinger <python@rcn.com> | 2013-03-04 08:34:09 (GMT) |
|---|---|---|
| committer | Raymond Hettinger <python@rcn.com> | 2013-03-04 08:34:09 (GMT) |
| commit | f2c17a9276e5793b4a0e9e84a338a1c874ddd01c (patch) | |
| tree | a7aabb999cf23a0818133489f12e47256ae1b187 /Lib | |
| parent | 03923426733dcc9f6c998057114212c168c3b1cd (diff) | |
| download | cpython-f2c17a9276e5793b4a0e9e84a338a1c874ddd01c.zip cpython-f2c17a9276e5793b4a0e9e84a338a1c874ddd01c.tar.gz cpython-f2c17a9276e5793b4a0e9e84a338a1c874ddd01c.tar.bz2 | |
Fix other re-entrancy nits for the lru_cache.
Keep references for oldkey and oldvalue so they can't
trigger a __del__ method to reenter our thread.
Move the cache[key]=link step to the end, after the link
data is in a consistent state.
Under exotic circumstances, the cache[key]=link step could
trigger reentrancy (i.e. the key would have to have a hash
exactly equal to that for another key in the cache and the
key would need a __eq__ method that makes a reentrant call
our cached function).
Diffstat (limited to 'Lib')
| -rw-r--r-- | Lib/functools.py | 18 |
1 files changed, 11 insertions, 7 deletions
diff --git a/Lib/functools.py b/Lib/functools.py index 36466f9..87c1b69 100644 --- a/Lib/functools.py +++ b/Lib/functools.py @@ -267,19 +267,23 @@ def lru_cache(maxsize=128, typed=False): # computed result and update the count of misses. pass elif full: - # use root to store the new key and result - root[KEY] = key - root[RESULT] = result - cache[key] = root + # use the old root to store the new key and result + oldroot = root + oldroot[KEY] = key + oldroot[RESULT] = result # empty the oldest link and make it the new root - root = root[NEXT] - del cache[root[KEY]] + root = oldroot[NEXT] + oldkey = root[KEY] + oldvalue = root[RESULT] root[KEY] = root[RESULT] = None + # now update the cache dictionary for the new links + del cache[oldkey] + cache[key] = oldroot else: # put result in a new link at the front of the queue last = root[PREV] link = [last, root, key, result] - cache[key] = last[NEXT] = root[PREV] = link + last[NEXT] = root[PREV] = cache[key] = link currsize += 1 full = (currsize == maxsize) misses += 1 |