move KeyLockedLazyCache to its own file

1 files changed, 47 insertions, 0 deletions

diff --git a/stage1/KeyLockedLazyCache.scala b/stage1/KeyLockedLazyCache.scala
new file mode 100644
index 0000000..50c6f9e
--- /dev/null
+++ b/stage1/KeyLockedLazyCache.scala
@@ -0,0 +1,47 @@
+package cbt
+
+import java.util.concurrent.ConcurrentHashMap
+
+private[cbt] class LockableKey
+/**
+A cache that lazily computes values if needed during lookup.
+Locking occurs on the key, so separate keys can be looked up
+simultaneously without a deadlock.
+*/
+final private[cbt] class KeyLockedLazyCache[Key <: AnyRef,Value <: AnyRef](
+  val keys: ConcurrentHashMap[Key,AnyRef],
+  val values: ConcurrentHashMap[AnyRef,Value],
+  logger: Option[Logger]
+){
+  def get( key: Key, value: => Value ): Value = {
+    val lockableKey = keys.synchronized{
+      if( ! (keys containsKey key) ){
+        val lockableKey = new LockableKey
+        //logger.foreach(_.resolver("CACHE MISS: " ++ key.toString))
+        keys.put( key, lockableKey )
+        lockableKey
+      } else {
+        val lockableKey = keys get key
+        //logger.foreach(_.resolver("CACHE HIT: " ++ lockableKey.toString ++ " -> " ++ key.toString))
+        lockableKey
+      }
+    }
+    import collection.JavaConversions._
+    //logger.resolver("CACHE: \n" ++ keys.mkString("\n"))
+    // synchronizing on key only, so asking for a particular key does
+    // not block the whole cache, but just that cache entry
+    key.synchronized{
+      if( ! (values containsKey lockableKey) ){
+        values.put( lockableKey, value )
+      }
+      values get lockableKey      
+    }
+  }
+  def remove( key: Key ) = keys.synchronized{    
+    assert(keys containsKey key)
+    val lockableKey = keys get key
+    keys.remove( key )
+    assert(values containsKey lockableKey)
+    values.remove( lockableKey )
+  }
+}