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/**
 * 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.hdfs.server.namenode;

import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ConcurrentMap;
import java.util.concurrent.atomic.AtomicInteger;

import org.apache.hadoop.classification.InterfaceAudience;

/**
 * Map object to serial number.
 * 
 * 

It allows to get the serial number of an object, if the object doesn't * exist in the map, a new serial number increased by 1 is generated to * map to the object. The mapped object can also be got through the serial * number. * *

The map is thread-safe. */ @InterfaceAudience.Private public class SerialNumberMap { private final AtomicInteger max = new AtomicInteger(1); private final ConcurrentMap t2i = new ConcurrentHashMap(); private final ConcurrentMap i2t = new ConcurrentHashMap(); public int get(T t) { if (t == null) { return 0; } Integer sn = t2i.get(t); if (sn == null) { sn = max.getAndIncrement(); if (sn < 0) { throw new IllegalStateException("Too many elements!"); } Integer old = t2i.putIfAbsent(t, sn); if (old != null) { return old; } i2t.put(sn, t); } return sn; } public T get(int i) { if (i == 0) { return null; } T t = i2t.get(i); if (t == null) { throw new IllegalStateException("!i2t.containsKey(" + i + "), this=" + this); } return t; } @Override public String toString() { return "max=" + max + ",\n t2i=" + t2i + ",\n i2t=" + i2t; } }





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