| /** |
| * 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. */ |
| protected SequentialNumber(final long initialValue) { |
| currentValue = new AtomicLong(initialValue); |
| } |
| |
| /** @return the current value. */ |
| public long getCurrentValue() { |
| return currentValue.get(); |
| } |
| |
| /** Set current 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. */ |
| 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); |
| } |
| } |