同時運行線程

Question

我有下一個代碼：

    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.");
    }
}

我得到下一個結果：

>     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，如果我在下一個代碼中使用塊同步：

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.");
    }
}

並得到下一個結果：

 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! 

但是我需要像第一個示例中那樣的結果。 並且不能使用CountDownLatch之類的某些功能-僅同步塊（這是實驗室實驗，這是必需項）

有誰知道如何做到這一點？

Answer 1

如果我正確理解了問題，那么問題就出在第二個示例中，您如何使用同步塊。

您已synchronized了整個邏輯，包括同步塊內的for循環。 正確的方法是保持

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

//for loop logic

---

為什么？

因為您只希望線程等待主線程開始工作，並且一旦它們收到通知，您就不希望邏輯以synchronized方式執行，因此釋放監視器 。 因為您在for循環時按住監視器，所以其他線程無法繼續進行直到持有該監視器的線程完成。

Answer 2

感謝Narendra Pathai。

我的代碼的結束變種如下：

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();
        }
    }
}

我添加了課程：

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();