creating tag sfa-0.9-11

[sfa.git] / sfa / util / cache.py

diff --git a/sfa/util/cache.py b/sfa/util/cache.py
new file mode 100644 (file)
index 0000000..45961fe
--- /dev/null
+++ b/sfa/util/cache.py
@@ -0,0 +1,62 @@
+#
+# This module implements general purpose caching system
+#
+from __future__ import with_statement
+import time
+import threading
+from datetime import datetime
+
+# maximum lifetime of cached data (in seconds) 
+MAX_CACHE_TTL = 60 * 60
+
+class CacheData:
+
+    data = None
+    created = None
+    expires = None
+    lock = None
+
+    def __init__(self, data, ttl = MAX_CACHE_TTL):
+        self.lock = threading.RLock()
+        self.data = data
+        self.renew(ttl)
+
+    def is_expired(self):
+        return time.time() > self.expires
+
+    def get_created_date(self):
+        return str(datetime.fromtimestamp(self.created))
+
+    def get_expires_date(self):
+        return str(datetime.fromtimestamp(self.expires))
+
+    def renew(self, ttl = MAX_CACHE_TTL):
+        self.created = time.time()
+        self.expires = self.created + ttl   
+       
+    def set_data(self, data, renew=True, ttl = MAX_CACHE_TTL):
+        with self.lock: 
+            self.data = data
+            if renew:
+                self.renew(ttl)
+    
+    def get_data(self):
+        return self.data
+
+class Cache:
+
+    cache  = {}
+    lock = threading.RLock()
+   
+    def add(self, key, value, ttl = MAX_CACHE_TTL):
+        with self.lock:
+            if self.cache.has_key(key):
+                self.cache[key].set_data(value, ttl=ttl)
+            else:
+                self.cache[key] = CacheData(value, ttl)
+           
+    def get(self, key):
+        data = self.cache.get(key)
+        if not data or data.is_expired():
+            return None 
+        return data.get_data()