1 /**
2 * Licensed to the Apache Software Foundation (ASF) under one
3 * or more contributor license agreements. See the NOTICE file
4 * distributed with this work for additional information
5 * regarding copyright ownership. The ASF licenses this file
6 * to you under the Apache License, Version 2.0 (the
7 * "License"); you may not use this file except in compliance
8 * with the License. You may obtain a copy of the License at
9 *
10 * http://www.apache.org/licenses/LICENSE-2.0
11 *
12 * Unless required by applicable law or agreed to in writing, software
13 * distributed under the License is distributed on an "AS IS" BASIS,
14 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15 * See the License for the specific language governing permissions and
16 * limitations under the License.
17 */
18 package org.apache.hadoop.hbase.util;
19
20 import java.net.URL;
21 import java.net.URLClassLoader;
22 import java.util.concurrent.ConcurrentHashMap;
23
24 import org.apache.hadoop.hbase.classification.InterfaceAudience;
25
26 import com.google.common.base.Preconditions;
27
28 /**
29 * Base class loader that defines couple shared constants used
30 * by sub-classes. It also defined method getClassLoadingLock for parallel
31 * class loading and JDK 1.6 support. This method (getClassLoadingLock)
32 * is similar to the same method in the base class Java ClassLoader
33 * introduced in JDK 1.7, but not in JDK 1.6.
34 */
35 @InterfaceAudience.Private
36 public class ClassLoaderBase extends URLClassLoader {
37
38 // Maps class name to the corresponding lock object
39 private final ConcurrentHashMap<String, Object> parallelLockMap
40 = new ConcurrentHashMap<String, Object>();
41
42 protected static final String DEFAULT_LOCAL_DIR = "/tmp/hbase-local-dir";
43 protected static final String LOCAL_DIR_KEY = "hbase.local.dir";
44
45 /**
46 * Parent class loader.
47 */
48 protected final ClassLoader parent;
49
50 /**
51 * Creates a DynamicClassLoader that can load classes dynamically
52 * from jar files under a specific folder.
53 *
54 * @param parent the parent ClassLoader to set.
55 */
56 public ClassLoaderBase(final ClassLoader parent) {
57 super(new URL[]{}, parent);
58 Preconditions.checkNotNull(parent, "No parent classloader!");
59 this.parent = parent;
60 }
61
62 /**
63 * Returns the lock object for class loading operations.
64 */
65 protected Object getClassLoadingLock(String className) {
66 Object lock = parallelLockMap.get(className);
67 if (lock != null) {
68 return lock;
69 }
70
71 Object newLock = new Object();
72 lock = parallelLockMap.putIfAbsent(className, newLock);
73 if (lock == null) {
74 lock = newLock;
75 }
76 return lock;
77 }
78 }