SerialNumberManager.java
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上传日期:2018-01-08
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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.*;
- /** Manage name-to-serial-number maps for users and groups. */
- class SerialNumberManager {
- /** This is the only instance of {@link SerialNumberManager}.*/
- static final SerialNumberManager INSTANCE = new SerialNumberManager();
- private SerialNumberMap<String> usermap = new SerialNumberMap<String>();
- private SerialNumberMap<String> groupmap = new SerialNumberMap<String>();
- private SerialNumberManager() {}
- int getUserSerialNumber(String u) {return usermap.get(u);}
- int getGroupSerialNumber(String g) {return groupmap.get(g);}
- String getUser(int n) {return usermap.get(n);}
- String getGroup(int n) {return groupmap.get(n);}
- {
- getUserSerialNumber(null);
- getGroupSerialNumber(null);
- }
- private static class SerialNumberMap<T> {
- private int max = 0;
- private int nextSerialNumber() {return max++;}
- private Map<T, Integer> t2i = new HashMap<T, Integer>();
- private Map<Integer, T> i2t = new HashMap<Integer, T>();
- synchronized int get(T t) {
- Integer sn = t2i.get(t);
- if (sn == null) {
- sn = nextSerialNumber();
- t2i.put(t, sn);
- i2t.put(sn, t);
- }
- return sn;
- }
- synchronized T get(int i) {
- if (!i2t.containsKey(i)) {
- throw new IllegalStateException("!i2t.containsKey(" + i
- + "), this=" + this);
- }
- return i2t.get(i);
- }
- /** {@inheritDoc} */
- public String toString() {
- return "max=" + max + ",n t2i=" + t2i + ",n i2t=" + i2t;
- }
- }
- }