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 thread
throw 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 thread
throw 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 thread
throw 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();
}
}