Condition可以代替Object监视器方法( wait , notify和notifyAll ),必须和Lock配合使用, Lock替换synchronized方法和语句的使用, Condition取代了对象监视器方法的使用。可以使某个线程挂起,直到其他线程唤醒,就像Object.wait()方法,一个Condition实例本质上绑定到一个锁。 要获得特定Condition实例,请使用lLock的newCondition()方法。
可以看出它是一个接口,所以其逻辑必须由实现类代替
获取Condition
private ReentrantLock lock = new ReentrantLock();
private Condition condition = lock.newCondition();
关于ReentrantLock请移步并发编程之ReentrantLock解析
* @return the Condition object
*/
public Condition newCondition() {
return sync.newCondition();
}
//真正的实现类
final ConditionObject newCondition() {
return new ConditionObject();
}
重要方法
/**
* 阻塞该线程,直到其他线程signal()方法或者signalAll()方法,亦或者被其他线程打断,会清楚中断状态
*
**/
void await() throws InterruptedException;
/**
* 在await()方法上设置了超时时间而已
*
**/
boolean await(long time, TimeUnit unit) throws InterruptedException;
/**
* 唤醒阻塞的线程如果有多个线程阻塞,随机唤醒一个
*
**/
void signal();
/**
* 唤醒所有阻塞的线程
*
**/
void signalAll();
案例分析
Condition在阻塞队列应用的比较多如ArrayBlockingQueue的put方法
/**
* 将指定的元素加入队列,如果队列满了发生阻塞
*
* @throws InterruptedException {@inheritDoc}
* @throws NullPointerException {@inheritDoc}
*/
public void put(E e) throws InterruptedException {
Objects.requireNonNull(e);
final ReentrantLock lock = this.lock;
//加锁
lock.lockInterruptibly();
try {
while (count == items.length)
//当队列满了就阻塞
notFull.await();
//有可用空间就插入元素
enqueue(e);
} finally {
//释放锁
lock.unlock();
}
}
关于ArrayBlockingQueue请移步ArrayBlockingQueue详解
/**
* 描述: 演示Condition的基本用法
*/
public class ConditionDemo1 {
private ReentrantLock lock = new ReentrantLock();
private Condition condition = lock.newCondition();
void method1() throws InterruptedException {
lock.lock();
try{
System.out.println("条件不满足,开始await");
condition.await();
System.out.println("条件满足了,开始执行后续的任务");
}finally {
lock.unlock();
}
}
void method2() {
lock.lock();
try{
System.out.println("准备工作完成,唤醒其他的线程");
condition.signal();
}finally {
lock.unlock();
}
}
public static void main(String[] args) throws InterruptedException {
ConditionDemo1 conditionDemo1 = new ConditionDemo1();
new Thread(new Runnable() {
@Override
public void run() {
try {
Thread.sleep(1000);
conditionDemo1.method2();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}).start();
conditionDemo1.method1();
}
}
/**
* 描述: 演示用Condition实现生产者消费者模式
*/
public class ConditionDemo2 {
private int queueSize = 10;
private PriorityQueue<Integer> queue = new PriorityQueue<Integer>(queueSize);
private Lock lock = new ReentrantLock();
private Condition notFull = lock.newCondition();
private Condition notEmpty = lock.newCondition();
public static void main(String[] args) {
ConditionDemo2 conditionDemo2 = new ConditionDemo2();
Producer producer = conditionDemo2.new Producer();
Consumer consumer = conditionDemo2.new Consumer();
producer.start();
consumer.start();
}
class Consumer extends Thread {
@Override
public void run() {
consume();
}
private void consume() {
while (true) {
lock.lock();
try {
while (queue.size() == 0) {
System.out.println("队列空,等待数据");
try {
notEmpty.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
queue.poll();
notFull.signalAll();
System.out.println("从队列里取走了一个数据,队列剩余" + queue.size() + "个元素");
} finally {
lock.unlock();
}
}
}
}
class Producer extends Thread {
@Override
public void run() {
produce();
}
private void produce() {
while (true) {
lock.lock();
try {
while (queue.size() == queueSize) {
System.out.println("队列满,等待有空余");
try {
notFull.await();
} catch (InterruptedException e) {
e.printStackTrace();
}
}
queue.offer(1);
notEmpty.signalAll();
System.out.println("向队列插入了一个元素,队列剩余空间" + (queueSize - queue.size()));
} finally {
lock.unlock();
}
}
}
}
}
转载:https://blog.csdn.net/qq_34800986/article/details/106145257
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