MAPREDUCE-4229. Intern counter names in the JT (bobby via daryn)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/trunk@1401473 13f79535-47bb-0310-9956-ffa450edef68

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/StringInterner.java

@@ -0,0 +1,78 @@
+/**
+ * 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.
+ */
+
+package org.apache.hadoop.util;
+
+import org.apache.hadoop.classification.InterfaceAudience;
+import org.apache.hadoop.classification.InterfaceStability;
+
+import com.google.common.collect.Interner;
+import com.google.common.collect.Interners;
+
+/**
+ * Provides equivalent behavior to String.intern() to optimize performance, 
+ * whereby does not consume memory in the permanent generation.
+ */
+@InterfaceAudience.Public
+@InterfaceStability.Stable
+public class StringInterner {
+  
+  /**
+   * Retains a strong reference to each string instance it has interned.
+   */
+  private final static Interner<String> strongInterner;
+  
+  /**
+   * Retains a weak reference to each string instance it has interned. 
+   */
+  private final static Interner<String> weakInterner;
+  
+  
+  
+  static {
+    strongInterner = Interners.newStrongInterner();
+    weakInterner = Interners.newWeakInterner();
+  }
+  
+  /**
+   * Interns and returns a reference to the representative instance 
+   * for any of a collection of string instances that are equal to each other.
+   * Retains strong reference to the instance, 
+   * thus preventing it from being garbage-collected. 
+   * 
+   * @param sample string instance to be interned
+   * @return strong reference to interned string instance
+   */
+  public static String strongIntern(String sample) {
+    return strongInterner.intern(sample);
+  }
+  
+  /**
+   * Interns and returns a reference to the representative instance 
+   * for any of a collection of string instances that are equal to each other.
+   * Retains weak reference to the instance, 
+   * and so does not prevent it from being garbage-collected.
+   * 
+   * @param sample string instance to be interned
+   * @return weak reference to interned string instance
+   */
+  public static String weakIntern(String sample) {
+    return weakInterner.intern(sample);
+  }
+
+}

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/util/TestStringInterner.java

@@ -0,0 +1,76 @@
+/**
+ * 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.
+ */
+
+package org.apache.hadoop.util;
+
+import static org.junit.Assert.*;
+import static org.apache.hadoop.util.StringInterner.*;
+
+import org.junit.Test;
+
+/**
+ * 
+ * Tests string interning {@link StringInterner}
+ */
+public class TestStringInterner {
+
+  /**
+   * Test different references are returned for any of string 
+   * instances that are equal to each other but not interned.
+   */
+  @Test
+  public void testNoIntern() {
+    String literalABC = "ABC";
+    String substringABC = "ABCDE".substring(0,3);
+    String heapABC = new String("ABC");
+    assertNotSame(literalABC, substringABC);
+    assertNotSame(literalABC, heapABC);
+    assertNotSame(substringABC, heapABC);
+  }
+  
+  
+  /**
+   * Test the same strong reference is returned for any 
+   * of string instances that are equal to each other.
+   */
+  @Test
+  public void testStrongIntern() {
+    String strongInternLiteralABC = strongIntern("ABC");
+    String strongInternSubstringABC = strongIntern("ABCDE".substring(0,3));
+    String strongInternHeapABC = strongIntern(new String("ABC"));
+    assertSame(strongInternLiteralABC, strongInternSubstringABC);
+    assertSame(strongInternLiteralABC, strongInternHeapABC);
+    assertSame(strongInternSubstringABC, strongInternHeapABC);
+  }
+  
+  
+  /**
+   * Test the same weak reference is returned for any 
+   * of string instances that are equal to each other.
+   */
+  @Test
+  public void testWeakIntern() {
+    String weakInternLiteralABC = weakIntern("ABC");
+    String weakInternSubstringABC = weakIntern("ABCDE".substring(0,3));
+    String weakInternHeapABC = weakIntern(new String("ABC"));
+    assertSame(weakInternLiteralABC, weakInternSubstringABC);
+    assertSame(weakInternLiteralABC, weakInternHeapABC);
+    assertSame(weakInternSubstringABC, weakInternHeapABC);
+  }
+
+}