Java集合源码学习(16)_BlockingQueue接口的实现ArrayBlockingQueue

ArrayBlockingQueue继承了AbstractQueue，实现了BlockingQueue接口；

1：内部使用数组来存储队列元素

2：元素的排序是按照FIFO的顺序，队列的第一个元素是入队列时间最久的那个元素；

3：是有界队列，初始化时设置队列大小，之后不可再次设置；

4：不允许null值

5：在初始化时可设置等待该队列的被阻塞的线程唤醒的策略，fairness设置为true，按照请求该队列的顺序唤醒；默认是false也就是随机的唤醒

1：成员变量

/** The queued items */private final E[] items;//队列元素的存放数组/** items index for next take, poll or remove */private int takeIndex;//出队列的元素index/** items index for next put, offer, or add. */private int putIndex;//如队列的元素index/** Number of items in the queue */private int count;/** Main lock guarding all access */private final ReentrantLock lock;//操作都要首先获取锁/** Condition for waiting takes */private final Condition notEmpty;/** Condition for waiting puts */private final Condition notFull;

2：重要方法

1:offer()方法

入队列，满了返回false，不阻塞

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();}}

private void insert(E x) {//实际插入元素的方法，使用该方法前应该获得锁items[putIndex] = x;putIndex = inc(putIndex);++count;notEmpty.signal();}

final int inc(int i) {//循环增加index的值return (++i == items.length) ? 0 : i;}

2:put()方法

一直阻塞

public void put(E e) throws InterruptedException {if (e == null)throw new NullPointerException();final E[] items = this.items;final ReentrantLock lock = this.lock;lock.lockInterruptibly();try {try {while (count == items.length)notFull.await();} catch (InterruptedException ie) {notFull.signal(); //因为在await之后，放弃了锁，被中断之后需要重新获取锁，要抛出异常了，需要唤醒其他在等待notFull的线程throw ie;}insert(e);} finally {lock.unlock();}}

3:offer(time)方法

阻塞固定时间

public boolean offer(E e, long timeout, TimeUnit unit) throws InterruptedException {if (e == null)throw new NullPointerException();long nanos = unit.toNanos(timeout);final ReentrantLock lock = this.lock;lock.lockInterruptibly();try {for (;;) {if (count != items.length) {insert(e);return true;}if (nanos <= 0)return false;try {nanos = notFull.awaitNanos(nanos);//返回还需要等待的时间} catch (InterruptedException ie) {notFull.signal(); // propagate to non-interrupted threadthrow ie;}}} finally {lock.unlock();}}

4:poll()方法

不阻塞，出队列

public E poll() {final ReentrantLock lock = this.lock;lock.lock();try {if (count == 0)return null;E x = extract();return x;} finally {lock.unlock();}}

private E extract() {final E[] items = this.items;E x = items[takeIndex];items[takeIndex] = null;takeIndex = inc(takeIndex);--count;notFull.signal();return x;}

5:take()方法

阻塞式获取方法

public E take() throws InterruptedException {final ReentrantLock lock = this.lock;lock.lockInterruptibly();try {try {while (count == 0)notEmpty.await();} catch (InterruptedException ie) {notEmpty.signal(); // propagate to non-interrupted threadthrow ie;}E x = extract();return x;} finally {lock.unlock();}}

6:poll(time)方法

阻塞指定时间段

public E poll(long timeout, TimeUnit unit) throws InterruptedException {long nanos = unit.toNanos(timeout);final ReentrantLock lock = this.lock;lock.lockInterruptibly();try {for (;;) {if (count != 0) {E x = extract();return x;}if (nanos <= 0)return null;try {nanos = notEmpty.awaitNanos(nanos);} catch (InterruptedException ie) {notEmpty.signal(); // propagate to non-interrupted threadthrow ie;}}} finally {lock.unlock();}}

7:peek()方法

public E peek() {final ReentrantLock lock = this.lock;lock.lock();try {return (count == 0) ? null : items[takeIndex];} finally {lock.unlock();}}