hadoop EmptyIOStatisticsContextImpl 源码
haddop EmptyIOStatisticsContextImpl 代码
文件路径：/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/fs/statistics/impl/EmptyIOStatisticsContextImpl.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.fs.statistics.impl;
import org.apache.hadoop.fs.statistics.IOStatistics;
import org.apache.hadoop.fs.statistics.IOStatisticsAggregator;
import org.apache.hadoop.fs.statistics.IOStatisticsContext;
import org.apache.hadoop.fs.statistics.IOStatisticsSnapshot;
/**
* Empty IOStatistics context which serves no-op for all the operations and
* returns an empty Snapshot if asked.
*
*/
final class EmptyIOStatisticsContextImpl implements IOStatisticsContext {
private static final IOStatisticsContext EMPTY_CONTEXT = new EmptyIOStatisticsContextImpl();
private EmptyIOStatisticsContextImpl() {
}
/**
* Create a new empty snapshot.
* A new one is always created for isolation.
*
* @return a statistics snapshot
*/
@Override
public IOStatisticsSnapshot snapshot() {
return new IOStatisticsSnapshot();
}
@Override
public IOStatisticsAggregator getAggregator() {
return EmptyIOStatisticsStore.getInstance();
}
@Override
public IOStatistics getIOStatistics() {
return EmptyIOStatistics.getInstance();
}
@Override
public void reset() {}
/**
* The ID is always 0.
* As the real context implementation counter starts at 1,
* we are guaranteed to have unique IDs even between them and
* the empty context.
* @return 0
*/
@Override
public long getID() {
return 0;
}
/**
* Get the single instance.
* @return an instance.
*/
static IOStatisticsContext getInstance() {
return EMPTY_CONTEXT;
}
}
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