hadoop DirectoryDiffListFactory 源码
haddop DirectoryDiffListFactory 代码
文件路径：/hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/snapshot/DirectoryDiffListFactory.java
/**
* 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.snapshot;
import org.apache.hadoop.hdfs.server.namenode.snapshot.DirectoryWithSnapshotFeature.DirectoryDiff;
import org.slf4j.Logger;
import java.util.Random;
import java.util.concurrent.ThreadLocalRandom;
import java.util.function.IntFunction;
/** For creating {@link DiffList} for {@link DirectoryDiff}. */
public abstract class DirectoryDiffListFactory {
public static DiffList<DirectoryDiff> createDiffList(int capacity) {
return constructor.apply(capacity);
}
public static void init(int interval, int maxSkipLevels, Logger log) {
DirectoryDiffListFactory.skipInterval = interval;
DirectoryDiffListFactory.maxLevels = maxSkipLevels;
if (maxLevels > 0) {
constructor = c -> new DiffListBySkipList(c);
log.info("SkipList is enabled with skipInterval=" + skipInterval
+ ", maxLevels=" + maxLevels);
} else {
constructor = c -> new DiffListByArrayList<>(c);
log.info("SkipList is disabled");
}
}
private static volatile IntFunction<DiffList<DirectoryDiff>> constructor
= c -> new DiffListByArrayList<>(c);
private static volatile int skipInterval;
private static volatile int maxLevels;
/**
* Returns the level of a skip list node.
* @return A value in the range 0 to maxLevels.
*/
public static int randomLevel() {
final Random r = ThreadLocalRandom.current();
for (int level = 0; level < maxLevels; level++) {
// skip to the next level with probability 1/skipInterval
if (r.nextInt(skipInterval) > 0) {
return level;
}
}
return maxLevels;
}
private DirectoryDiffListFactory() {}
}
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