ArrayBlockingQueue说明
一个由数组结构组成的有界阻塞队列。 队列的元素是FIFO（first in first out）。新进入的元素插入队列的尾，从队列的头返回元素。队列大小一旦创建后，就不能改变。如果队列满了，put元素会阻塞，如果take空队列会堵塞等待。
加入数据和取数据 公用一个锁，这个操作无法并行，吞吐量有些影响,插入或删除元素时不会产生或销毁任何额外的对象实例，性能会比队列的好些；
ArrayBlockingQueue源码分析
public class ArrayBlockingQueue<E> extends AbstractQueue<E> implements BlockingQueue<E>, java.io.Serializable{
final Object[] items;
//take poll peek remove
int takeIndex；
//put offer add
int putIndex;
//队列里元素的数量
int count;
//保护访问的锁
final ReentrantLock lock;
//Condition for waiting takes
private final Condition notEmpty;
//Condition for waiting puts
private final Condition notFull;
//构造方法
public ArrayBlockingQueue(int capacity){
this(capacity,false);
}
public ArrayBlockingQueue(int capacity,boolean fair){
if(capacity <= 0){
throw new IllegalArgumentException();
}
this.items = new Object[capacity];
lock = new ReentrantLock(fair);
notEmpty = new lock.newCondition();
notFull = new lock.newCondition();
}
public ArrayBlockingQueue(int capacity,boolean fair, Collection<? extends E> c){
this(capacity,fair);
final ReentrantLock = this.lock;
lock.lock()//加锁仅仅是为了可见 而不是互斥。 主要是在不同线程对数据操作都要写在主内存 而不是缓存中
try{
int i = 0;
try{
for(E e : c)
items[i++] = Objects.requireNotNull(e);
}catch(ArrayIndexOutOfBoundsException ex){
throw new IllegalArgumentException();
}
count = i;
putIndex = (i == capacity)?0:1;
}finally{
lock.unlock()
}
}
// 不阻塞 队列已经满了会排出异常，IllegalStateException
public boolean add(E e) {
//调用到offer
return super.add(e);
}
// 不阻塞 队列已经满了 返回false
public boolean offer(E e){
Objects.requireNotNull(e);
final ReentrantLock lock = this.lock;
lock.lock();
try{
if(count == items.length)
return fale
else{
enqueue(e);
return true;
}
}finally{
lock.unlock();
}
}
//如果队列满了 会等待，直到变成可用
public void put(E e) throw InterruptedException{
Objects.requireNotNull(e);
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try{
while(count == items.length)
//等待
notFull.await();
enqueue(e);
}finally{
lock.unlock();
}
}
public void offer(E e, long timeout, TimeUnit unit) throws InterruptedException{
Objects.requireNotNull(e);
// 毫微秒 十亿分之一秒
long nanos = unit.toNanos(timeout)
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try{
while(count == items.length){
if(nanos <= 0L)
return false;
//返回值表示剩余时间
nanos = notFull.awaitNanos(nanos);
}
enqueue(e);
return true;
}finally{
lock.unlock();
}
}
//不阻塞 队列为空 直接返回null
public E poll(){
final ReentrantLock lock = this.lock;
lock.lock();
try{
return (count == 0) ? null :dequeue();
}finally{
lock.unlock();
}
}
//队列为空 则一直等待， 直到被唤醒
public E take() throws InterruptedException{
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try{
while(count == 0)
notEmpty.await();
return dequeue();
}finally{
lock.unlock();
}
}
//如果队列空，等待，如果超时则返回null
public E poll(long timeout, TimeUnit unit){
long nanos = unit.toNanos(timeout);
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try{
while(count == 0){
if(nanos <= 0){
return null;
}
nanos = notEmpty.awaitNanos(nanos);
}
return dequeue();
}finally{
lock.unlock();
}
}
//如果队列为空 则返回null
public E peek(){
final ReentrantLock lock = this.lock;
lock.lock();
try{
return itemAt(takeIndex);
}finally{
lock.unlock();
}
}
//数组的末尾加入元素
private void enqueue(E x){
final Object[] items = this.items;
items[putIndex] = x;
if(putIndex == items.length)
putIndex = 0;
count++;
notEmpty.signal();
}
private E dequeue(){
final Object[] items = this.items;
E x = (E)items[takeIndex];
items[takeIndex] = null;
if(++takeIndex == items.length)
takeIndex = 0;
count--;
if (itrs != null)
itrs.elementDequeued();
notFull.signal();
return x;
}
}
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