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Server functionality for HBase
/*
* 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.hbase.util;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.ReentrantLock;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.Collection;
import java.util.Comparator;
import java.util.Iterator;
import java.util.AbstractQueue;
import org.apache.hadoop.hbase.classification.InterfaceAudience;
import org.apache.hadoop.hbase.classification.InterfaceStability;
/**
* A generic bounded blocking Priority-Queue.
*
* The elements of the priority queue are ordered according to the Comparator
* provided at queue construction time.
*
* If multiple elements have the same priority this queue orders them in
* FIFO (first-in-first-out) manner.
* The head of this queue is the least element with respect to the specified
* ordering. If multiple elements are tied for least value, the head is the
* first one inserted.
* The queue retrieval operations poll, remove, peek, and element access the
* element at the head of the queue.
*/
@InterfaceAudience.Private
@InterfaceStability.Stable
public class BoundedPriorityBlockingQueue extends AbstractQueue implements BlockingQueue {
private static class PriorityQueue {
private final Comparator comparator;
private final E[] objects;
private int head = 0;
private int tail = 0;
@SuppressWarnings("unchecked")
public PriorityQueue(int capacity, Comparator comparator) {
this.objects = (E[])new Object[capacity];
this.comparator = comparator;
}
public void add(E elem) {
if (tail == objects.length) {
// shift down |-----AAAAAAA|
tail -= head;
System.arraycopy(objects, head, objects, 0, tail);
head = 0;
}
if (tail == head || comparator.compare(objects[tail - 1], elem) <= 0) {
// Append
objects[tail++] = elem;
} else if (head > 0 && comparator.compare(objects[head], elem) > 0) {
// Prepend
objects[--head] = elem;
} else {
// Insert in the middle
int index = upperBound(head, tail - 1, elem);
System.arraycopy(objects, index, objects, index + 1, tail - index);
objects[index] = elem;
tail++;
}
}
public E peek() {
return (head != tail) ? objects[head] : null;
}
public E poll() {
E elem = objects[head];
objects[head] = null;
head = (head + 1) % objects.length;
if (head == 0) tail = 0;
return elem;
}
public int size() {
return tail - head;
}
public Comparator comparator() {
return this.comparator;
}
public boolean contains(Object o) {
for (int i = head; i < tail; ++i) {
if (objects[i] == o) {
return true;
}
}
return false;
}
public int remainingCapacity() {
return this.objects.length - (tail - head);
}
private int upperBound(int start, int end, E key) {
while (start < end) {
int mid = (start + end) >>> 1;
E mitem = objects[mid];
int cmp = comparator.compare(mitem, key);
if (cmp > 0) {
end = mid;
} else {
start = mid + 1;
}
}
return start;
}
}
// Lock used for all operations
private final ReentrantLock lock = new ReentrantLock();
// Condition for blocking when empty
private final Condition notEmpty = lock.newCondition();
// Wait queue for waiting puts
private final Condition notFull = lock.newCondition();
private final PriorityQueue queue;
/**
* Creates a PriorityQueue with the specified capacity that orders its
* elements according to the specified comparator.
* @param capacity the capacity of this queue
* @param comparator the comparator that will be used to order this priority queue
*/
public BoundedPriorityBlockingQueue(int capacity,
Comparator comparator) {
this.queue = new PriorityQueue(capacity, comparator);
}
public boolean offer(E e) {
if (e == null) throw new NullPointerException();
lock.lock();
try {
if (queue.remainingCapacity() > 0) {
this.queue.add(e);
notEmpty.signal();
return true;
}
} finally {
lock.unlock();
}
return false;
}
public void put(E e) throws InterruptedException {
if (e == null) throw new NullPointerException();
lock.lock();
try {
while (queue.remainingCapacity() == 0) {
notFull.await();
}
this.queue.add(e);
notEmpty.signal();
} finally {
lock.unlock();
}
}
public boolean offer(E e, long timeout, TimeUnit unit)
throws InterruptedException {
if (e == null) throw new NullPointerException();
long nanos = unit.toNanos(timeout);
lock.lockInterruptibly();
try {
while (queue.remainingCapacity() == 0) {
if (nanos <= 0)
return false;
nanos = notFull.awaitNanos(nanos);
}
this.queue.add(e);
notEmpty.signal();
} finally {
lock.unlock();
}
return true;
}
public E take() throws InterruptedException {
E result = null;
lock.lockInterruptibly();
try {
while (queue.size() == 0) {
notEmpty.await();
}
result = queue.poll();
notFull.signal();
} finally {
lock.unlock();
}
return result;
}
public E poll() {
E result = null;
lock.lock();
try {
if (queue.size() > 0) {
result = queue.poll();
notFull.signal();
}
} finally {
lock.unlock();
}
return result;
}
public E poll(long timeout, TimeUnit unit)
throws InterruptedException {
long nanos = unit.toNanos(timeout);
lock.lockInterruptibly();
E result = null;
try {
while (queue.size() == 0 && nanos > 0) {
nanos = notEmpty.awaitNanos(nanos);
}
if (queue.size() > 0) {
result = queue.poll();
}
notFull.signal();
} finally {
lock.unlock();
}
return result;
}
public E peek() {
lock.lock();
try {
return queue.peek();
} finally {
lock.unlock();
}
}
public int size() {
lock.lock();
try {
return queue.size();
} finally {
lock.unlock();
}
}
public Iterator iterator() {
throw new UnsupportedOperationException();
}
public Comparator comparator() {
return queue.comparator();
}
public int remainingCapacity() {
lock.lock();
try {
return queue.remainingCapacity();
} finally {
lock.unlock();
}
}
public boolean remove(Object o) {
throw new UnsupportedOperationException();
}
public boolean contains(Object o) {
lock.lock();
try {
return queue.contains(o);
} finally {
lock.unlock();
}
}
public int drainTo(Collection c) {
return drainTo(c, Integer.MAX_VALUE);
}
public int drainTo(Collection c, int maxElements) {
if (c == null)
throw new NullPointerException();
if (c == this)
throw new IllegalArgumentException();
if (maxElements <= 0)
return 0;
lock.lock();
try {
int n = Math.min(queue.size(), maxElements);
for (int i = 0; i < n; ++i) {
c.add(queue.poll());
}
return n;
} finally {
lock.unlock();
}
}
}