/*
* Copyright 2012-2015 org.opencloudb.
*
* Licensed 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.opencloudb.queue;
import java.util.concurrent.locks.ReentrantLock;
/**
* 固定容量的阻塞队列
*
* @author mycat
*/
public final class FixedQueue<E> {
private final E[] items;
private int putIndex;
private int takeIndex;
private int count;
private final ReentrantLock lock;
@SuppressWarnings("unchecked")
public FixedQueue(int capacity) {
if (capacity <= 0) {
throw new IllegalArgumentException();
}
this.items = (E[]) new Object[capacity];
this.lock = new ReentrantLock();
}
public int size() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
return count;
} finally {
lock.unlock();
}
}
public boolean offer(E e) {
if (e == null) {
throw new NullPointerException();
}
final ReentrantLock lock = this.lock;
lock.lock();
try {
if (count >= items.length) {
return false;
} else {
insert(e);
return true;
}
} finally {
lock.unlock();
}
}
public E poll() {
final ReentrantLock lock = this.lock;
lock.lock();
try {
if (count == 0) {
return null;
}
return extract();
} finally {
lock.unlock();
}
}
public void clear() {
final E[] items = this.items;
final ReentrantLock lock = this.lock;
lock.lock();
try {
int i = takeIndex;
int j = count;
while (j-- > 0) {
items[i] = null;
i = inc(i);
}
count = 0;
putIndex = 0;
takeIndex = 0;
} finally {
lock.unlock();
}
}
private void insert(E x) {
items[putIndex] = x;
putIndex = inc(putIndex);
++count;
}
private E extract() {
E[] items = this.items;
int i = takeIndex;
E x = items[i];
items[i] = null;
takeIndex = inc(i);
--count;
return x;
}
private int inc(int i) {
return (++i == items.length) ? 0 : i;
}
}