pylucene 3.5.0-3

[pylucene.git] / lucene-java-3.5.0 / lucene / src / java / org / apache / lucene / util / SimpleStringInterner.java

diff --git a/lucene-java-3.5.0/lucene/src/java/org/apache/lucene/util/SimpleStringInterner.java b/lucene-java-3.5.0/lucene/src/java/org/apache/lucene/util/SimpleStringInterner.java
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+++ b/lucene-java-3.5.0/lucene/src/java/org/apache/lucene/util/SimpleStringInterner.java
@@ -0,0 +1,85 @@
+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.
+ */
+
+
+/**
+ * Simple lockless and memory barrier free String intern cache that is guaranteed
+ * to return the same String instance as String.intern()
+ * does.
+ *
+ * @lucene.internal
+ */
+public class SimpleStringInterner extends StringInterner {
+
+  private static class Entry {
+    final private String str;
+    final private int hash;
+    private Entry next;
+    private Entry(String str, int hash, Entry next) {
+      this.str = str;
+      this.hash = hash;
+      this.next = next;
+    }
+  }
+
+  private final Entry[] cache;
+  private final int maxChainLength;
+
+  /**
+   * @param tableSize  Size of the hash table, should be a power of two.
+   * @param maxChainLength  Maximum length of each bucket, after which the oldest item inserted is dropped.
+   */
+  public SimpleStringInterner(int tableSize, int maxChainLength) {
+    cache = new Entry[Math.max(1,BitUtil.nextHighestPowerOfTwo(tableSize))];
+    this.maxChainLength = Math.max(2,maxChainLength);
+  }
+
+  @Override
+  public String intern(String s) {
+    int h = s.hashCode();
+    // In the future, it may be worth augmenting the string hash
+    // if the lower bits need better distribution.
+    int slot = h & (cache.length-1);
+
+    Entry first = this.cache[slot];
+    Entry nextToLast = null;
+
+    int chainLength = 0;
+
+    for(Entry e=first; e!=null; e=e.next) {
+      if (e.hash == h && (e.str == s || e.str.compareTo(s)==0)) {
+      // if (e.str == s || (e.hash == h && e.str.compareTo(s)==0)) {
+        return e.str;
+      }
+
+      chainLength++;
+      if (e.next != null) {
+        nextToLast = e;
+      }
+    }
+
+    // insertion-order cache: add new entry at head
+    s = s.intern();
+    this.cache[slot] = new Entry(s, h, first);
+    if (chainLength >= maxChainLength) {
+      // prune last entry
+      nextToLast.next = null;
+    }
+    return s;
+  }
+}
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