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No need to create and destroy links when updating a fixed-sized circular queue.

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This commit is contained in:
Raymond Hettinger 2012-03-30 19:15:18 -07:00
parent 3288e948f3
commit 41eb79a016
1 changed files with 16 additions and 11 deletions
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27
Lib/functools.py
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@ -219,7 +219,7 @@ def wrapper(*args, **kwds):
def wrapper(*args, **kwds):
# size limited caching that tracks accesses by recency
nonlocal hits, misses
nonlocal root, hits, misses
key = make_key(args, kwds, typed) if kwds or typed else args
with lock:
link = cache_get(key)
@ -236,16 +236,21 @@ def wrapper(*args, **kwds):
return result
result = user_function(*args, **kwds)
with lock:
# put result in a new link at the front of the list
last = root[PREV]
link = [last, root, key, result]
cache[key] = last[NEXT] = root[PREV] = link
if _len(cache) > maxsize:
# purge the least recently used cache entry
old_prev, old_next, old_key, old_result = root[NEXT]
root[NEXT] = old_next
old_next[PREV] = root
del cache[old_key]
if _len(cache) < maxsize:
# put result in a new link at the front of the list
last = root[PREV]
link = [last, root, key, result]
cache[key] = last[NEXT] = root[PREV] = link
else:
# use root to store the new key and result
root[KEY] = key
root[RESULT] = result
cache[key] = root
# empty the oldest link and make it the new root
root = root[NEXT]
del cache[root[KEY]]
root[KEY] = None
root[RESULT] = None
misses += 1
return result