From 54226846fe8fcb23d780a04a4ba203441f033196 Mon Sep 17 00:00:00 2001
From: Stefan Nordhausen <nordhausen@linux-z4v3.site>
Date: Fri, 13 Jan 2012 13:57:20 +0100
Subject: __init__.py: - put() now checks if we already have the given key in
 cache. This   prevents overwriting other existing items when put() on same
 item is   called repeatedly. - Remove the "end" variable. It never terminated
 the loop, anyway,   because the item at this position always had res==True.

tests.py:
- Adapt test case to accept the slightly changed eviction strategy.
- Make the test runnable from the command line.
- Add newlines for structuring, remove unneeded whitespace.
---
 repoze/lru/__init__.py | 18 ++++++++++++++----
 repoze/lru/tests.py    | 38 +++++++++++++++++++++++++++-----------
 2 files changed, 41 insertions(+), 15 deletions(-)
 mode change 100644 => 100755 repoze/lru/tests.py

diff --git a/repoze/lru/__init__.py b/repoze/lru/__init__.py
index 64bd7ba..0711c7c 100644
--- a/repoze/lru/__init__.py
+++ b/repoze/lru/__init__.py
@@ -47,9 +47,19 @@ class LRUCache(object):
         data = self.data
         lock = self.lock
 
-        end = hand - 1
-        if end < 0:
-            end = maxpos
+        entry = self.data.get(key)
+        if entry is not None:
+            lock.acquire()
+            try:
+                # We already have key. Only make sure data is up to date and to
+                # remember that it was used.
+                pos, old_val = entry
+                if old_val is not val:
+                    data[key] = (pos, val)
+                self.clock[pos]['ref'] = True
+                return
+            finally:
+                lock.release()
 
         while 1:
             current = clock[hand]
@@ -59,7 +69,7 @@ class LRUCache(object):
                 hand = hand + 1
                 if hand > maxpos:
                     hand = 0
-            elif ref is False or hand == end:
+            else:
                 lock.acquire()
                 try:
                     oldkey = current['key']
diff --git a/repoze/lru/tests.py b/repoze/lru/tests.py
old mode 100644
new mode 100755
index 41a509a..5994f35
--- a/repoze/lru/tests.py
+++ b/repoze/lru/tests.py
@@ -1,3 +1,4 @@
+#!/usr/bin/python -tt
 import unittest
 
 class LRUCacheTests(unittest.TestCase):
@@ -14,6 +15,7 @@ class LRUCacheTests(unittest.TestCase):
     def test_it(self):
         cache = self._makeOne(3)
         self.assertEqual(cache.get('a'), None)
+
         cache.put('a', '1')
         pos, value = cache.data.get('a')
         self.assertEqual(cache.clock[pos]['ref'], True)
@@ -21,35 +23,46 @@ class LRUCacheTests(unittest.TestCase):
         self.assertEqual(value, '1')
         self.assertEqual(cache.get('a'), '1')
         self.assertEqual(cache.hand, pos+1)
+
         pos, value = cache.data.get('a')
         self.assertEqual(cache.clock[pos]['ref'], True)
         self.assertEqual(cache.hand, pos+1)
         self.assertEqual(len(cache.data), 1)
+
         cache.put('b', '2')
         pos, value = cache.data.get('b')
         self.assertEqual(cache.clock[pos]['ref'], True)
         self.assertEqual(cache.clock[pos]['key'], 'b')
         self.assertEqual(len(cache.data), 2)
+
         cache.put('c', '3')
         pos, value = cache.data.get('c')
         self.assertEqual(cache.clock[pos]['ref'], True)
         self.assertEqual(cache.clock[pos]['key'], 'c')
         self.assertEqual(len(cache.data), 3)
+
         pos, value = cache.data.get('a')
         self.assertEqual(cache.clock[pos]['ref'], True)
+
         cache.get('a')
+        # All items have ref==True. cache.hand points to "a". Putting
+        # "d" will set ref=False on all items and then replace "a",
+        # because "a" is the first item with ref==False that is found.
         cache.put('d', '4')
         self.assertEqual(len(cache.data), 3)
-        self.assertEqual(cache.data.get('b'), None)
+        self.assertEqual(cache.data.get('a'), None)
+
+        # Only item "d" has ref==True. cache.hand points at "b", so "b"
+        # will be evicted when "e" is inserted. "c" will be left alone.
         cache.put('e', '5')
         self.assertEqual(len(cache.data), 3)
-        self.assertEqual(cache.data.get('c'), None)
+        self.assertEqual(cache.data.get('b'), None)
         self.assertEqual(cache.get('d'), '4')
         self.assertEqual(cache.get('e'), '5')
-        self.assertEqual(cache.get('a'), '1')
+        self.assertEqual(cache.get('a'), None)
         self.assertEqual(cache.get('b'), None)
-        self.assertEqual(cache.get('c'), None)
-                         
+        self.assertEqual(cache.get('c'), '3')
+
 class DecoratorTests(unittest.TestCase):
     def _getTargetClass(self):
         from repoze.lru import lru_cache
@@ -73,11 +86,11 @@ class DecoratorTests(unittest.TestCase):
         self.assertEqual(result, 1)
         self.assertEqual(len(cache), 1)
         result = decorated(2)
-        self.assertEqual(cache[(2,)], 2) 
+        self.assertEqual(cache[(2,)], 2)
         self.assertEqual(result, 2)
         self.assertEqual(len(cache), 2)
         result = decorated(2)
-        self.assertEqual(cache[(2,)], 2) 
+        self.assertEqual(cache[(2,)], 2)
         self.assertEqual(result, 2)
         self.assertEqual(len(cache), 2)
 
@@ -88,12 +101,15 @@ class DecoratorTests(unittest.TestCase):
             return args
         decorated = decorator(moreargs)
         result = decorated(3, 4, 5)
-        self.assertEqual(cache[(3,4,5)], (3,4,5)) 
+        self.assertEqual(cache[(3,4,5)], (3,4,5))
         self.assertEqual(result, (3,4,5))
         self.assertEqual(len(cache), 1)
-            
-   
+
+
 class DummyLRUCache(dict):
     def put(self, k, v):
         return self.__setitem__(k, v)
-    
+
+if __name__ == "__main__":
+    unittest.main()
+
-- 
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