pylucene 3.5.0-3

[pylucene.git] / lucene-java-3.4.0 / lucene / src / java / org / apache / lucene / util / DoubleBarrelLRUCache.java

diff --git a/lucene-java-3.4.0/lucene/src/java/org/apache/lucene/util/DoubleBarrelLRUCache.java b/lucene-java-3.4.0/lucene/src/java/org/apache/lucene/util/DoubleBarrelLRUCache.java
deleted file mode 100644 (file)
index a476bd2..0000000
--- a/lucene-java-3.4.0/lucene/src/java/org/apache/lucene/util/DoubleBarrelLRUCache.java
+++ /dev/null
@@ -1,121 +0,0 @@
-package org.apache.lucene.util;
-
-/**
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements.  See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * The ASF licenses this file to You under the Apache License, Version 2.0
- * (the "License"); you may not use this file except in compliance with
- * the License.  You may obtain a copy of the License at
- *
- *     http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
-
-import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.atomic.AtomicInteger;
-import java.util.Map;
-
-/**
- * Simple concurrent LRU cache, using a "double barrel"
- * approach where two ConcurrentHashMaps record entries.
- *
- * <p>At any given time, one hash is primary and the other
- * is secondary.  {@link #get} first checks primary, and if
- * that's a miss, checks secondary.  If secondary has the
- * entry, it's promoted to primary (<b>NOTE</b>: the key is
- * cloned at this point).  Once primary is full, the
- * secondary is cleared and the two are swapped.</p>
- *
- * <p>This is not as space efficient as other possible
- * concurrent approaches (see LUCENE-2075): to achieve
- * perfect LRU(N) it requires 2*N storage.  But, this
- * approach is relatively simple and seems in practice to
- * not grow unbounded in size when under hideously high
- * load.</p>
- *
- * @lucene.internal
- */
-
-final public class DoubleBarrelLRUCache<K extends DoubleBarrelLRUCache.CloneableKey,V> {
-
-  public static abstract class CloneableKey {
-    @Override
-    abstract public Object clone();
-  }
-
-  private final Map<K,V> cache1;
-  private final Map<K,V> cache2;
-  private final AtomicInteger countdown;
-  private volatile boolean swapped;
-  private final int maxSize;
-
-  public DoubleBarrelLRUCache(int maxSize) {
-    this.maxSize = maxSize;
-    countdown = new AtomicInteger(maxSize);
-    cache1 = new ConcurrentHashMap<K,V>();
-    cache2 = new ConcurrentHashMap<K,V>();
-  }
-
-  @SuppressWarnings("unchecked") 
-  public V get(K key) {
-    final Map<K,V> primary;
-    final Map<K,V> secondary;
-    if (swapped) {
-      primary = cache2;
-      secondary = cache1;
-    } else {
-      primary = cache1;
-      secondary = cache2;
-    }
-
-    // Try primary first
-    V result = primary.get(key);
-    if (result == null) {
-      // Not found -- try secondary
-      result = secondary.get(key);
-      if (result != null) {
-        // Promote to primary
-        put((K) key.clone(), result);
-      }
-    }
-    return result;
-  }
-
-  public void put(K key, V value) {
-    final Map<K,V> primary;
-    final Map<K,V> secondary;
-    if (swapped) {
-      primary = cache2;
-      secondary = cache1;
-    } else {
-      primary = cache1;
-      secondary = cache2;
-    }
-    primary.put(key, value);
-
-    if (countdown.decrementAndGet() == 0) {
-      // Time to swap
-
-      // NOTE: there is saturation risk here, that the
-      // thread that's doing the clear() takes too long to
-      // do so, while other threads continue to add to
-      // primary, but in practice this seems not to be an
-      // issue (see LUCENE-2075 for benchmark & details)
-
-      // First, clear secondary
-      secondary.clear();
-
-      // Second, swap
-      swapped = !swapped;
-
-      // Third, reset countdown
-      countdown.set(maxSize);
-    }
-  }
-}