1 方法概览

类	方法名	简介
Thread	sleep相关
	join	等待其他线程执行完毕
	yield相关	放弃已经获取到的CPU资源
	currentThread	获取当前执行线程的引用
	start/run相关	启动线程相关
	interrupt相关	中断线程
	~~stop~~/~~suspend~~/~~resume~~相关	已废弃
Object	wait/notify/notifyAll相关扫描二维码关注公众号，回复： 8894415 查看本文章	让线程暂时休息和唤醒

/**
 * 演示打印main, Thread-0, Thread-1
 */
public class CurrentThread implements Runnable {
    public static void main(String[] args) {
        CurrentThread tread = new CurrentThread();
        tread.run();
        new Thread(tread).start();
        new Thread(tread).start();
    }
    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName());
    }
}

2 wait/notify/notifyAll

作用/用法：阻塞阶段、唤醒阶段、遇到中断

/**
 * 展示wait和notify的基本用法
 *      1. 研究代码执行顺序
 *      2. 证明wait释放锁
 */
public class Wait {
    public static Object object = new Object();
    static class Thread1 extends Thread {
        @Override
        public void run() {
            synchronized (object) {
                System.out.println(Thread.currentThread().getName() + "开始执行了");
                try {
                    //释放monitor锁
                    object.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println("线程" + Thread.currentThread().getName() + "获取到了锁。");
            }
        }
    }
    static class Thread2 extends Thread {
        @Override
        public void run() {
            synchronized (object) {
                object.notify();
                System.out.println("线程" + Thread.currentThread().getName() + "调用了notify()");
            }
        }
    }
    public static void main(String[] args) throws InterruptedException {
        Thread1 thread1 = new Thread1();
        Thread2 thread2 = new Thread2();
        thread1.start();
        Thread.sleep(200);
        thread2.start();
    }
}

/**
 * 3个线程，线程1和线程2首先被阻塞，线程3唤醒它们。notify, notifyAll。 start先执行不代表线程先启动。
 */
public class WaitNotifyAll implements Runnable {
    private static final Object resourceA = new Object();
    @Override
    public void run() {
        synchronized (resourceA) {
            System.out.println(Thread.currentThread().getName()+" got resourceA lock.");
            try {
                System.out.println(Thread.currentThread().getName()+" waits to start.");
                resourceA.wait();
                System.out.println(Thread.currentThread().getName()+"'s waiting to end.");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
    public static void main(String[] args){
        Runnable r = new WaitNotifyAll();
        Thread threadA = new Thread(r);
        Thread threadB = new Thread(r);
        
        Thread threadC = new Thread(() -> {
            synchronized (resourceA) {
                resourceA.notifyAll();
                //resourceA.notify();
                System.out.println("ThreadC notified.");
            }
        });
        threadA.start();
        threadB.start();
        //Thread.sleep(200);
        threadC.start();
    }
}

/**
 * 证明wait只释放当前的那把锁(只释放当前monitor)
 */
public class WaitNotifyReleaseOwnMonitor {
    private static Object resourceA = new Object();
    private static Object resourceB = new Object();
    public static void main(String[] args) {
        Thread thread1 = new Thread(() -> {
            synchronized (resourceA) {
                System.out.println("ThreadA got resourceA lock.");
                synchronized (resourceB) {
                    System.out.println("ThreadA got resourceB lock.");
                    try {
                        System.out.println("ThreadA releases resourceA lock.");
                        //释放A
                        resourceA.wait();
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                }
            }
        });

        Thread thread2 = new Thread(() -> {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            synchronized (resourceA) {
                System.out.println("ThreadB got resourceA lock.");
                System.out.println("ThreadB tries to resourceB lock.");
                synchronized (resourceB) {
                    System.out.println("ThreadB got resourceB lock.");
                }
            }
        });
        thread1.start();
        thread2.start();
    }
}

手写生产者消费者设计模式

/**
 * 用wait/notify来实现生产者消费者模式
 */
public class ProducerConsumerModel {
    public static void main(String[] args) {
        EventStorage eventStorage = new EventStorage();

        Producer producer = new Producer(eventStorage);
        Consumer consumer = new Consumer(eventStorage);
        new Thread(producer).start();
        new Thread(consumer).start();
    }
}

class Producer implements Runnable {
    private EventStorage storage;
    public Producer(
            EventStorage storage) {
        this.storage = storage;
    }
    @Override
    public void run() {
        for (int i = 0; i < 100; i++) {
            storage.put();
        }
    }
}

class Consumer implements Runnable {
    private EventStorage storage;
    public Consumer(EventStorage storage) {
        this.storage = storage;
    }
    @Override
    public void run() {
        for (int i = 0; i < 100; i++) {
            storage.take();
        }
    }
}

//实现效果类似于阻塞队列
class EventStorage {
    private int maxSize;
    private LinkedList<Date> storage;
    public EventStorage() {
        maxSize = 10;
        storage = new LinkedList<>();
    }
    // 生产者 添加
    public synchronized void put() {
        while (storage.size() == maxSize) {
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        storage.add(new Date());
        System.out.println("仓库里有了" + storage.size() + "个产品。");
        this.notify();
    }
    // 消费者 消费
    public synchronized void take() {
        while (storage.size() == 0) {
            try {
                this.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        System.out.println("拿到了" + storage.poll() + "，现在仓库还剩下" + storage.size());
        this.notify();
    }
}

两个线程交替打印0~100的奇偶数

偶线程：0

奇线程：1

偶线程：2

/**
 * 两个线程交替打印0~100的奇偶数，用synchronized关键字实现
 */
public class WaitNotifyPrintOddEvenSyn {
    private static int count;
    private static final Object lock = new Object();
    //新建2个线程
    //1个只处理偶数，第二个只处理奇数（用位运算）
    //用synchronized来通信
    public static void main(String[] args) {

        new Thread(() -> {
            while (count < 100) {
                synchronized (lock) {
                    if ((count & 1) == 0) {
                        System.out.println(Thread.currentThread().getName() + ":" + count++);
                    }
                }
            }
        }, "偶数").start();

        new Thread(() -> {
            while (count < 100) {
                synchronized (lock) {
                    if ((count & 1) == 1) {
                        System.out.println(Thread.currentThread().getName() + ":" + count++);
                    }
                }
            }
        }, "奇数").start();
    }
}

第一种方法虽然能实现效果，但是有很多不必要的运算

/**
 * 两个线程交替打印0~100的奇偶数，用wait和notify
 */
public class WaitNotifyPrintOddEveWait {
    private static int count = 0;
    private static final Object lock = new Object();
    public static void main(String[] args) throws InterruptedException {
        new Thread(new TurningRunner(), "偶数").start();
        //Thread.sleep(100);
        new Thread(new TurningRunner(), "奇数").start();
    }
    //1. 拿到锁，我们就打印
    //2. 打印完，唤醒其他线程，自己就休眠
    static class TurningRunner implements Runnable {
        @Override
        public void run() {
            while (count <= 100) {
                synchronized (lock) {
                    //拿到锁就打印
                    System.out.println(Thread.currentThread().getName() + ":" + count++);
                    lock.notify();
                    if (count <= 100) {
                        try {
                            //如果任务还没结束，就让出当前的锁，并休眠
                            lock.wait();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                }
            }
        }
    }
}

3 sleep

作用：我只想让线程在预期的时间执行，其他时候不要占用CPU资源

不释放锁：包括synchronized和lock （和wait不同）

/**
 * 展示线程sleep的时候不释放synchronized的monitor，等sleep时间到了以后，正常结束后才释放锁
 */
public class SleepDontReleaseMonitor implements Runnable {
    public static void main(String[] args) {
        SleepDontReleaseMonitor sleepDontReleaseMonitor = new SleepDontReleaseMonitor();
        new Thread(sleepDontReleaseMonitor).start();
        new Thread(sleepDontReleaseMonitor).start();
    }
    @Override
    public void run() {
        syn();
    }
    private synchronized void syn() {
        System.out.println("线程" + Thread.currentThread().getName() + "获取到了monitor。");
        try {
            Thread.sleep(5000);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("线程" + Thread.currentThread().getName() + "退出了同步代码块");
    }
}

/**
 * 演示sleep不释放lock（lock需要手动释放）
 */
public class SleepDontReleaseLock implements Runnable {
    private static final Lock lock = new ReentrantLock();
    @Override
    public void run() {
        lock.lock();
        System.out.println("线程" + Thread.currentThread().getName() + "获取到了锁");
        try {
            Thread.sleep(5000);
            System.out.println("线程" + Thread.currentThread().getName() + "已经苏醒");
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            lock.unlock();
        }
    }
    public static void main(String[] args) {
        SleepDontReleaseLock sleepDontReleaseLock = new SleepDontReleaseLock();
        new Thread(sleepDontReleaseLock).start();
        new Thread(sleepDontReleaseLock).start();
    }
}

sleep方法响应中断

抛出InterruptedException

清除中断状态

/**
 * 每个1秒钟输出当前时间，被中断，观察。
 *      1.Thread.sleep()
 *      2.TimeUnit.SECONDS.sleep()
 */
public class SleepInterrupted implements Runnable{
    public static void main(String[] args) throws InterruptedException {
        Thread thread = new Thread(new SleepInterrupted());
        thread.start();
        Thread.sleep(6500);
        thread.interrupt();
    }
    @Override
    public void run() {
        for (int i = 0; i < 10; i++) {
            System.out.println(new Date());
            try {
                //sleep：3个小时25分钟1秒
                TimeUnit.HOURS.sleep(3);
                TimeUnit.MINUTES.sleep(25);
                TimeUnit.SECONDS.sleep(1);
            } catch (InterruptedException e) {
                System.out.println("我被中断了！");
                e.printStackTrace();
            }
        }
    }
}

TimeUnit：https://www.cnblogs.com/zhaoyanjun/p/5486726.html

一句话总结

sleep方法可以让线程进入Waiting状态，并且不占用CPU资源，但是不释放锁，直到规定时间后再执行，休眠期间如果被中断，会抛出异常并清除中断状态

public class Main {
    public static void main(String[] args) {
        Thread myThread = new Thread(() -> {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
                //false 清除中断状态
                System.out.println(Thread.currentThread().isInterrupted());
            }
        });
        myThread.start();
        //false
        System.out.println(myThread.isInterrupted());
        try {
            Thread.sleep(500);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        myThread.interrupt();
    }
}

sleep方法—常见面试问题

4 join

作用：因为新的线程加入了我们，所以我们要等他执行完再出发

用法：main等待thread1执行完毕

/**
 * 演示join，注意语句输出顺序，会变化。
 */
public class Join {
    public static void main(String[] args) throws InterruptedException {
        Thread thread = new Thread(() -> {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName() + "执行完毕");
        });

        Thread thread2 = new Thread(() -> {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName() + "执行完毕");
        });
        thread.start();
        thread2.start();
        System.out.println("开始等待子线程运行完毕");
        //主线程(main)等待着两个子线程执行完，在往下执行
        thread.join();
        thread2.join();
        System.out.println("所有子线程执行完毕");
    }
}

/**
 * 演示join期间被中断的效果
 */
public class JoinInterrupt {
    public static void main(String[] args) {
        Thread mainThread = Thread.currentThread();

        Thread thread1 = new Thread(() -> {
            try {
                mainThread.interrupt();
                Thread.sleep(5000);
                System.out.println("Thread1 finished.");
            } catch (InterruptedException e) {
                System.out.println("子线程中断");
            }
        });
        thread1.start();
        System.out.println("等待子线程运行完毕");

        try {
            thread1.join();
        } catch (InterruptedException e) {//!!!这里的异常是主线程抛出的
            System.out.println(Thread.currentThread().getName()+"主线程中断了");
            thread1.interrupt();
        }
        System.out.println("子线程已运行完毕");
    }
}

/**
 * 1.先join再mainThread.getState()
 * 2.通过debugger看线程join前后状态的对比
 */
public class JoinThreadState {
    public static void main(String[] args) throws InterruptedException {
        Thread mainThread = Thread.currentThread();
        Thread thread = new Thread(() -> {
            try {
                Thread.sleep(3000);
                System.out.println(mainThread.getState());
                System.out.println("Thread-0运行结束");
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        });
        thread.start();
        System.out.println("等待子线程运行完毕");
        thread.join();
        System.out.println("子线程运行完毕");
    }
}

!!! 每一个Thread类在run方运行结束后会自动执行notify类似的操作（Thread.wait() 不建议这样使用）

//java.lang.Thread#join(long)
public final synchronized void join(long millis) throws InterruptedException {
	long base = System.currentTimeMillis();
	long now = 0;
	if (millis < 0) {
		throw new IllegalArgumentException("timeout value is negative");
	}
	if (millis == 0) {
		while (isAlive()) {
			wait(0);
		}
	} else {
		while (isAlive()) {
			long delay = millis - now;
			if (delay <= 0) {
				break;
			}
			wait(delay);
			now = System.currentTimeMillis() - base;
		}
	}
}

等级代码书写

/**
 * 通过join原理，分析出join的代替写法
 */
public class JoinPrinciple {
    public static void main(String[] args) throws InterruptedException {
        Thread thread = new Thread(() -> {
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName() + "执行完毕");
            //自动执行notify类似的操作
        });

        thread.start();
        System.out.println("开始等待子线程运行完毕");
        //thread.join();
        synchronized (thread) {
            thread.wait();
        }
        System.out.println("所有子线程执行完毕");
    }
}

CountDownLatch或CyclicBarrier类

5 yield

作用：释放我的CPU时间片

定位：JVM不保证遵循

yield和sleep区别：是否随时可能再次被调度

底层_码农

发布了515 篇原创文章 · 获赞 97 · 访问量 108万+

他的留言板关注

Thread和Object类中的重要方法详解

1 方法概览

2 wait/notify/notifyAll

3 sleep

4 join

5 yield

猜你喜欢