# HG changeset patch
# Parent bd0f73a9538e05f526feaf05821e68bdcff498fa
Limit the number of results cached by filecmp.cmp().

diff --git a/Lib/filecmp.py b/Lib/filecmp.py
--- a/Lib/filecmp.py
+++ b/Lib/filecmp.py
@@ -11,11 +11,18 @@
 
 import os
 import stat
+from collections import OrderedDict
 from itertools import ifilter, ifilterfalse, imap, izip
+try:
+    from thread import allocate_lock as Lock
+except:
+    from dummy_thread import allocate_lock as Lock
 
 __all__ = ["cmp","dircmp","cmpfiles"]
 
-_cache = {}
+_cache = OrderedDict()
+_cache_lock = Lock()
+_MAXCACHE = 500
 BUFSIZE=8*1024
 
 def cmp(f1, f2, shallow=1):
@@ -48,10 +55,18 @@
     if s1[1] != s2[1]:
         return False
 
-    result = _cache.get((f1, f2))
-    if result and (s1, s2) == result[:2]:
-        return result[2]
+    with _cache_lock:
+        result = _cache.get((f1, f2))
+        if result:
+            _cache.move_to_end((f1, f2))  # Record recent use of key (f1, f2).
+            if (s1, s2) == result[:2]:
+                return result[2]          # Cache entry is not stale. Use it.
+
     outcome = _do_cmp(f1, f2)
+    with _cache_lock:
+        _cache[f1, f2] = s1, s2, outcome
+        if len(_cache) > _MAXCACHE:
+            _cache.popitem(0)  # Cache is full. Drop least recently used entry.
     _cache[f1, f2] = s1, s2, outcome
     return outcome