同时运行线程

Question

我有下一个代码：

    public class App 
{
    public static void main( String[] args )
    {
        NewSmartThread n = new NewSmartThread("ST");
        try{
            n.join();
        }catch(InterruptedException e){
            System.out.println( "Умный поток был прерван" );
        }
        System.out.println( "Hello World!" );
    }
}

class NewSimpleThread extends Thread {

    public NewSimpleThread(String name){
        super(name);
    }

    public void run(){
            try {
                for(int i =1; i<6; i++)
                {
                    System.out.println("Thread " + this.getName() + " : " + i);
                    Thread.sleep(500);
                }
            } catch (InterruptedException e) {
                System.out.println("Thread " + this.getName() + "был прерван.");
            }
        System.out.println("Thread " + this.getName() + " closed.");
}
}

class NewSmartThread extends Thread {
    //final CountDownLatch start = new CountDownLatch(1);
    //final CountDownLatch finish = new CountDownLatch(2);

    public NewSmartThread(String name) {
        super(name);
        start();
    }

    public void run(){
        //s1.split("(?<=\\G..)")

        NewSimpleThread n1 = new NewSimpleThread("1");
        NewSimpleThread n2 = new NewSimpleThread("2");
        NewSimpleThread n3 = new NewSimpleThread("3");

        n1.start();
        n2.start();
        n3.start();
        try{

            Thread.sleep(3000);


            n1.join();
            n2.join();
            n3.join();
        }catch(InterruptedException e){
            System.out.println("Thread " + "broke.");
        }
        System.out.println("Smart thread " + this.getName() + " closed.");
    }
}

我得到下一个结果：

>     Thread 2 : 1
>     Thread 3 : 1
>     Thread 1 : 1
>     Thread 3 : 2
>     Thread 1 : 2
>     Thread 2 : 2
>     Thread 2 : 3
>     Thread 1 : 3
>     Thread 3 : 3
>     Thread 2 : 4
>     Thread 1 : 4
>     Thread 3 : 4
>     Thread 1 : 5
>     Thread 2 : 5
>     Thread 3 : 5
>     Thread 1 closed.
>     Thread 2 closed.
>     Thread 3 closed.
>     Smart thread ST closed.
>     Hello World!

但是，如果我在下一个代码中使用块同步：

public class App 
{
    public static void main( String[] args )
    {
        NewSmartThread n = new NewSmartThread("ST");
        try{
            n.join();
        }catch(InterruptedException e){
            System.out.println( "Умный поток был прерван" );
        }
        System.out.println( "Hello World!" );
    }
}

class NewSimpleThread extends Thread {
    private static final Object monitor = new Object();
    public NewSimpleThread(String name){
        super(name);
    }

    public void run(){
        synchronized (monitor) {
            try {
                monitor.wait();
                for(int i =1; i<6; i++)
                {
                    System.out.println("Thread " + this.getName() + " : " + i);
                    Thread.sleep(500);
                }
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        System.out.println("Thread " + this.getName() + " closed.");
        }
    }

    public static void doNotifyAll(){
        synchronized (monitor) {
            monitor.notifyAll();
        }
    }
}
class NewSmartThread extends Thread {

    public NewSmartThread(String name) {
        super(name);
        start();
    }

    public void run(){
        NewSimpleThread n1 = new NewSimpleThread("1");
        NewSimpleThread n2 = new NewSimpleThread("2");
        NewSimpleThread n3 = new NewSimpleThread("3");

        n1.start();
        n2.start();
        n3.start();
        try{

            Thread.sleep(3000);
            NewSimpleThread.doNotifyAll();

            n1.join();
            n2.join();
            n3.join();
        }catch(InterruptedException e){
            System.out.println("Thread " + "broke.");
        }
        System.out.println("Smart thread " + this.getName() + " closed.");
    }
}

并得到下一个结果：

 Thread 3 : 1 Thread 3 : 2 Thread 3 : 3 Thread 3 : 4 Thread 3 : 5 Thread 3 closed. Thread 2 : 1 Thread 2 : 2 Thread 2 : 3 Thread 2 : 4 Thread 2 : 5 Thread 2 closed. Thread 1 : 1 Thread 1 : 2 Thread 1 : 3 Thread 1 : 4 Thread 1 : 5 Thread 1 closed. Smart thread ST closed. Hello World! 

但是我需要像第一个示例中那样的结果。 并且不能使用CountDownLatch之类的某些功能-仅同步块（这是实验室实验，这是必需项）

有谁知道如何做到这一点？

Answer 1

如果我正确理解了问题，那么问题就出在第二个示例中，您如何使用同步块。

您已synchronized了整个逻辑，包括同步块内的for循环。 正确的方法是保持

synchronized(monitor){
    monitor.wait(); //excluding exception handling
}

//for loop logic

---

为什么？

因为您只希望线程等待主线程开始工作，并且一旦它们收到通知，您就不希望逻辑以synchronized方式执行，因此释放监视器 。 因为您在for循环时按住监视器，所以其他线程无法继续进行直到持有该监视器的线程完成。

Answer 2

感谢Narendra Pathai。

我的代码的结束变种如下：

public class App 
{
    public static void main( String[] args )
    {
        NewSmartThread n = new NewSmartThread("ST");
        try{
            n.join();
        }catch(InterruptedException e){
            System.out.println( "Умный поток был прерван" );
        }
        System.out.println( "Hello World!" );
    }
}

class NewSimpleThread extends Thread {
    private static final Object monitor = new Object();
    public NewSimpleThread(String name){
        super(name);
    }

    public void run(){
        try {
            Latch.awaitZero();
            for(int i =1; i<6; i++)
            {
                System.out.println("Thread " + this.getName() + " : " + i);
                Thread.sleep(500);
            }
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println("Thread " + this.getName() + " closed.");
    }

    public static void doNotifyAll(){
        synchronized (monitor) {
            monitor.notifyAll();
        }
    }
}
class NewSmartThread extends Thread {

    public NewSmartThread(String name) {
        super(name);
        start();
    }

    public void run(){
        NewSimpleThread n1 = new NewSimpleThread("1");
        NewSimpleThread n2 = new NewSimpleThread("2");
        NewSimpleThread n3 = new NewSimpleThread("3");

        n1.start();
        n2.start();
        n3.start();
        try{

            Thread.sleep(3000);
            Latch.doNotifyAll();

            n1.join();
            n2.join();
            n3.join();
        }catch(InterruptedException e){
            System.out.println("Thread " + "broke.");
        }
        System.out.println("Smart thread " + this.getName() + " closed.");
    }
}

class Latch {
    private static final Object synchObj = new Object();

    public static void awaitZero() throws InterruptedException {
        synchronized (synchObj) {
                synchObj.wait();
        }
    }
    public static void doNotifyAll() {
        synchronized (synchObj) {
                synchObj.notifyAll();
        }
    }
}

我添加了课程：

class Latch {
    private static final Object synchObj = new Object();

    public static void awaitZero() throws InterruptedException {
        synchronized (synchObj) {
                synchObj.wait();
        }
    }
    public static void doNotifyAll() {
        synchronized (synchObj) {
                synchObj.notifyAll();
        }
    }
}

代替

class NewSimpleThread extends Thread {
    private static final Object monitor = new Object();