[Python-checkins] cpython: Improve the memory utilization (and speed) of functools.lru_cache().
raymond.hettinger
python-checkins at python.org
Fri Mar 16 09:19:07 CET 2012
http://hg.python.org/cpython/rev/3b2856d8614b
changeset: 75729:3b2856d8614b
parent: 75725:d2460ff173ff
user: Raymond Hettinger <python at rcn.com>
date: Fri Mar 16 01:16:31 2012 -0700
summary:
Improve the memory utilization (and speed) of functools.lru_cache().
files:
Lib/functools.py | 53 +++++++++++++++++++++--------------
Misc/NEWS | 2 +
2 files changed, 34 insertions(+), 21 deletions(-)
diff --git a/Lib/functools.py b/Lib/functools.py
--- a/Lib/functools.py
+++ b/Lib/functools.py
@@ -12,7 +12,7 @@
'total_ordering', 'cmp_to_key', 'lru_cache', 'reduce', 'partial']
from _functools import partial, reduce
-from collections import OrderedDict, namedtuple
+from collections import namedtuple
try:
from _thread import allocate_lock as Lock
except:
@@ -147,17 +147,20 @@
# to allow the implementation to change (including a possible C version).
def decorating_function(user_function,
- *, tuple=tuple, sorted=sorted, map=map, len=len, type=type, KeyError=KeyError):
+ *, tuple=tuple, sorted=sorted, map=map, len=len, type=type):
+ cache = dict()
hits = misses = 0
+ cache_get = cache.get # bound method for fast lookup
kwd_mark = (object(),) # separates positional and keyword args
- lock = Lock() # needed because OrderedDict isn't threadsafe
+ lock = Lock() # needed because linkedlist isn't threadsafe
+ root = [] # root of circular doubly linked list
+ root[:] = [root, root, None, None] # initialize by pointing to self
if maxsize is None:
- cache = dict() # simple cache without ordering or size limit
-
@wraps(user_function)
def wrapper(*args, **kwds):
+ # simple caching without ordering or size limit
nonlocal hits, misses
key = args
if kwds:
@@ -167,23 +170,18 @@
key += tuple(map(type, args))
if kwds:
key += tuple(type(v) for k, v in sorted_items)
- try:
- result = cache[key]
+ result = cache_get(key)
+ if result is not None:
hits += 1
return result
- except KeyError:
- pass
result = user_function(*args, **kwds)
cache[key] = result
misses += 1
return result
else:
- cache = OrderedDict() # ordered least recent to most recent
- cache_popitem = cache.popitem
- cache_renew = cache.move_to_end
-
@wraps(user_function)
def wrapper(*args, **kwds):
+ # size limited caching that tracks accesses by recency
nonlocal hits, misses
key = args
if kwds:
@@ -193,20 +191,33 @@
key += tuple(map(type, args))
if kwds:
key += tuple(type(v) for k, v in sorted_items)
+ PREV, NEXT = 0, 1 # names of link fields
with lock:
- try:
- result = cache[key]
- cache_renew(key) # record recent use of this key
+ link = cache_get(key)
+ if link is not None:
+ link = cache[key]
+ # record recent use of the key by moving it to the front of the list
+ link_prev, link_next, key, result = link
+ link_prev[NEXT] = link_next
+ link_next[PREV] = link_prev
+ last = root[PREV]
+ last[NEXT] = root[PREV] = link
+ link[PREV] = last
+ link[NEXT] = root
hits += 1
return result
- except KeyError:
- pass
result = user_function(*args, **kwds)
with lock:
- cache[key] = result # record recent use of this key
+ last = root[PREV]
+ link = [last, root, key, result]
+ cache[key] = last[NEXT] = root[PREV] = link
+ if len(cache) > maxsize:
+ # purge 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]
misses += 1
- if len(cache) > maxsize:
- cache_popitem(0) # purge least recently used cache entry
return result
def cache_info():
diff --git a/Misc/NEWS b/Misc/NEWS
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -26,6 +26,8 @@
- Issue #11199: Fix the with urllib which hangs on particular ftp urls.
+- Improve the memory utilization and speed of functools.lru_cache.
+
- Issue #14222: Use the new time.steady() function instead of time.time() for
timeout in queue and threading modules to not be affected of system time
update.
--
Repository URL: http://hg.python.org/cpython
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