hadoop SinkQueue 源码
haddop SinkQueue 代码
文件路径:/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/metrics2/impl/SinkQueue.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.metrics2.impl;
import java.util.ConcurrentModificationException;
/**
* A half-blocking (nonblocking for producers, blocking for consumers) queue
* for metrics sinks.
*
* New elements are dropped when the queue is full to preserve "interesting"
* elements at the onset of queue filling events
*/
class SinkQueue<T> {
interface Consumer<T> {
void consume(T object) throws InterruptedException;
}
// A fixed size circular buffer to minimize garbage
private final T[] data;
private int head; // head position
private int tail; // tail position
private int size; // number of elements
private Thread currentConsumer = null;
@SuppressWarnings("unchecked")
SinkQueue(int capacity) {
this.data = (T[]) new Object[Math.max(1, capacity)];
head = tail = size = 0;
}
synchronized boolean enqueue(T e) {
if (data.length == size) {
return false;
}
++size;
tail = (tail + 1) % data.length;
data[tail] = e;
notify();
return true;
}
/**
* Consume one element, will block if queue is empty
* Only one consumer at a time is allowed
* @param consumer the consumer callback object
*/
void consume(Consumer<T> consumer) throws InterruptedException {
T e = waitForData();
try {
consumer.consume(e); // can take forever
_dequeue();
}
finally {
clearConsumerLock();
}
}
/**
* Consume all the elements, will block if queue is empty
* @param consumer the consumer callback object
* @throws InterruptedException
*/
void consumeAll(Consumer<T> consumer) throws InterruptedException {
waitForData();
try {
for (int i = size(); i-- > 0; ) {
consumer.consume(front()); // can take forever
_dequeue();
}
}
finally {
clearConsumerLock();
}
}
/**
* Dequeue one element from head of the queue, will block if queue is empty
* @return the first element
* @throws InterruptedException
*/
synchronized T dequeue() throws InterruptedException {
checkConsumer();
while (0 == size) {
wait();
}
return _dequeue();
}
private synchronized T waitForData() throws InterruptedException {
checkConsumer();
while (0 == size) {
wait();
}
setConsumerLock();
return front();
}
private synchronized void checkConsumer() {
if (currentConsumer != null) {
throw new ConcurrentModificationException("The "+
currentConsumer.getName() +" thread is consuming the queue.");
}
}
private synchronized void setConsumerLock() {
currentConsumer = Thread.currentThread();
}
private synchronized void clearConsumerLock() {
currentConsumer = null;
}
private synchronized T _dequeue() {
if (0 == size) {
throw new IllegalStateException("Size must > 0 here.");
}
--size;
head = (head + 1) % data.length;
T ret = data[head];
data[head] = null; // hint to gc
return ret;
}
synchronized T front() {
return data[(head + 1) % data.length];
}
synchronized T back() {
return data[tail];
}
synchronized void clear() {
checkConsumer();
for (int i = data.length; i-- > 0; ) {
data[i] = null;
}
size = 0;
}
synchronized int size() {
return size;
}
int capacity() {
return data.length;
}
}
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