/* * 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; } }