| /* |
| * 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.pig.impl.plan; |
| |
| import java.util.HashMap; |
| import java.util.Map; |
| import java.util.concurrent.atomic.AtomicLong; |
| |
| import com.google.common.annotations.VisibleForTesting; |
| |
| /** |
| * Generates IDs as long values in a thread safe manner. Each thread has its own generated IDs. |
| */ |
| public class NodeIdGenerator { |
| |
| /** |
| * Holds a map of generated scoped-IDs per thread. Each map holds generated IDs per scope. |
| */ |
| private ThreadLocal<Map<String, AtomicLong>> scopeToIdMap |
| = new ThreadLocal<Map<String, AtomicLong>>() { |
| protected Map<String, AtomicLong> initialValue() { |
| return new HashMap<String,AtomicLong>(); |
| } |
| }; |
| |
| /** |
| * Singleton instance. |
| */ |
| private static final NodeIdGenerator theGenerator = new NodeIdGenerator(); |
| |
| /** |
| * Private default constructor to force singleton use-case of this class. |
| */ |
| private NodeIdGenerator() {} |
| |
| /** |
| * Returns the NodeIdGenerator singleton. |
| * @return |
| */ |
| public static NodeIdGenerator getGenerator() { |
| return theGenerator; |
| } |
| |
| /** |
| * Returns the next ID to be used for the current Thread. |
| * |
| * @param scope |
| * @return |
| */ |
| public long getNextNodeId(final String scope) { |
| // ThreadLocal usage protects us from having the same HashMap instance |
| // being used by several threads, so we can use it without synchronized |
| // blocks and still be thread-safe. |
| Map<String, AtomicLong> map = scopeToIdMap.get(); |
| |
| // the concurrent properties of the AtomicLong are useless here but |
| // since it cost less to use such an object rather than created a |
| // Long object instance each time we increment a counter ... |
| AtomicLong l = map.get(scope); |
| if ( l == null ) |
| map.put( scope, l = new AtomicLong() ); |
| return l.getAndIncrement(); |
| } |
| |
| /** |
| * Reset the given scope IDs to 0 for the current Thread. |
| * @param scope |
| */ |
| @VisibleForTesting |
| public static void reset(final String scope) { |
| theGenerator.scopeToIdMap.get().remove(scope); |
| } |
| |
| /** |
| * Reset all scope IDs to 0 for the current Thread. |
| */ |
| @VisibleForTesting |
| public static void reset() { |
| theGenerator.scopeToIdMap.remove(); |
| } |
| } |