hadoop SequentialNumber 源码
haddop SequentialNumber 代码
文件路径：/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/util/SequentialNumber.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.util;
import java.util.concurrent.atomic.AtomicLong;
import org.apache.hadoop.classification.InterfaceAudience;
/**
* Sequential number generator.
*
* This class is thread safe.
*/
@InterfaceAudience.Private
public abstract class SequentialNumber implements IdGenerator {
private final AtomicLong currentValue;
/**
* Create a new instance with the given initial value.
* @param initialValue initialValue.
*/
protected SequentialNumber(final long initialValue) {
currentValue = new AtomicLong(initialValue);
}
/** @return the current value. */
public long getCurrentValue() {
return currentValue.get();
}
/**
* Set current value.
* @param value value.
*/
public void setCurrentValue(long value) {
currentValue.set(value);
}
public boolean setIfGreater(long value) {
while(true) {
long local = currentValue.get();
if(value <= local) {
return false; // swap failed
}
if(currentValue.compareAndSet(local, value)) {
return true; // swap successful
}
// keep trying
}
}
/** Increment and then return the next value. */
public long nextValue() {
return currentValue.incrementAndGet();
}
/**
* Skip to the new value.
* @param newValue newValue.
* @throws IllegalStateException
* Cannot skip to less than the current value.
*/
public void skipTo(long newValue) throws IllegalStateException {
for(;;) {
final long c = getCurrentValue();
if (newValue < c) {
throw new IllegalStateException(
"Cannot skip to less than the current value (="
+ c + "), where newValue=" + newValue);
}
if (currentValue.compareAndSet(c, newValue)) {
return;
}
}
}
@Override
public boolean equals(final Object that) {
if (that == null || this.getClass() != that.getClass()) {
return false;
}
final AtomicLong thatValue = ((SequentialNumber)that).currentValue;
return currentValue.equals(thatValue);
}
@Override
public int hashCode() {
final long v = currentValue.get();
return (int)v ^ (int)(v >>> 32);
}
}
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