From 365263addd08cf302dee0477c019a6193a617d00 Mon Sep 17 00:00:00 2001
From: Jay Hutchinson <jlhutch@gmail.com>
Date: Wed, 25 Aug 2010 03:31:21 -0500
Subject: Finished adding optional cache write-back semantics.

---
 lru.py  | 44 ++++++++++++++++++++++++--------------------
 test.py | 30 ++++++++++++++++++++++++++++++
 2 files changed, 54 insertions(+), 20 deletions(-)

diff --git a/lru.py b/lru.py
index f14ebf7..09225d2 100644
--- a/lru.py
+++ b/lru.py
@@ -67,12 +67,8 @@ class lrucache(object):
     def __len__(self):
         return len(self.table)
     
+    # Does not call callback to write any changes!
     def clear(self):
-        if self.callback:
-            for key in self.table:
-                node = self.table[key]
-                self.callback(node.key, node.obj)
-                
         self.table.clear()
 	
         node = self.head
@@ -80,11 +76,16 @@ class lrucache(object):
             node.key = None
             node.obj = None
             node = node.next
+            
     
     def __contains__(self, key):
         return key in self.table
         # XXX Should this move the object to front of list? XXX
     
+    def peek(self, key):
+        # Look up the node
+        node = self.table[key]
+        return node.obj
     
     def __getitem__(self, key):
     
@@ -258,30 +259,32 @@ class lrucache(object):
 
 
 
-# Wrapper using write-through semantics
 class lruwrap(object):
     def __init__(self, store, size, writethrough=True):
+        self.store = store
         self.writethrough = writethrough
 
         if self.writethrough:
             self.cache = lrucache(size)
         else:
-            self.cache = lrucache(size, self.ejectCallBack)
             self.dirty = set()
-        
-        self.store = store
-        
-        
+            def callback(key, value):
+                if key in self.dirty:
+                    self.store[key] = value
+                    self.dirty.remove(key)
+            self.cache = lrucache(size, callback)
         
     def __len__(self):
-        # XXX We could cache the size
         return len(self.store)
         
+    def size(self, size=None):
+        self.cache.size(size)
+        
     def clear(self):
         self.cache.clear()
-        if self.writethrough:    # XXX Remove this test XXX
-            assert len(self.dirty) == 0
         self.store.clear()
+        if not self.writethrough:
+            self.dirty.clear()
         
     def __contains__(self, key):
         # XXX Should this bring the key/value into the cache?
@@ -317,15 +320,16 @@ class lruwrap(object):
             pass
         del self.store[key]
         
-    def ejectCallback(self, key, value):
-        if key in self.dirty:
-            self.store[key] = value
-            self.dirty.remove(key)
+        
+    def sync(self):
+        if not self.writethrough:
+            for key in self.dirty:
+                value = self.cache.peek(key)  # Doesn't change the cache's order
+                self.store[key] = value
+            self.dirty.clear()
             
     def __del__(self):
-        # Flush the dirty objects
         self.sync()
-        
 
 
 class lrudecorator(object):
diff --git a/test.py b/test.py
index 1c0a94d..6b9b1b2 100644
--- a/test.py
+++ b/test.py
@@ -123,6 +123,35 @@ def wraptest():
 
         assert tmp1 == tmp2
         
+def wraptest2():
+    import random
+
+    q = dict()
+    x = lruwrap(q, 32, False)
+    for i in range(256):
+        a = random.randint(0, 256)
+        b = random.randint(0, 256)
+    
+        x[a] = b
+        
+    x.sync()
+    for i in range(512):
+        a = random.randint(0, 256)
+        tmp1 = None
+        tmp2 = None
+        try:
+            tmp1 = x[a]
+        except KeyError:
+            tmp1 = None
+           
+        try:
+            tmp2 = q[a]
+        except KeyError:
+            tmp2 = None
+
+        assert tmp1 == tmp2
+        
+        
 @lrudecorator(14)
 def cube(x):
     return x*x*x
@@ -131,6 +160,7 @@ if __name__ == '__main__':
     import random
     
     wraptest()
+    wraptest2()
     
     for i in range(300):
         x = random.randint(0, 25)
-- 
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