Java線程-按順序調用線程

Question

我希望線程按順序打印出它們的名稱。 輸出應如下所示：Thread-0
線程1
線程2
線程3
線程4
線程5
線程1
線程2
線程3

public class NameOutput extends Thread {
    static final int N = 5;
    static int activeThread = 0;

    public static void main(String[] args){

        for (int i = 1; i <= N; i++) {
            new NameOutput().start();
        }
    }

    @Override
    public void run(){
        while(true){
            this.printThreadName();
        }

    }
    private synchronized void printThreadName(){
        String threadName = "Thread-"+ activeThread;
        //Check if thread is in the right order
        if(!threadName.equals(this.getName())){
            try{
                wait();
            }catch (InterruptedException e){
                System.out.println(this.getName()+" was interrupted!");
            }
        }else{
            System.out.println(this.getName());
            activeThread = (activeThread + 1) % N;
            notifyAll();
        }
    }
}

不知何故，如果首先選擇了Thread-0，那么輸出就是Thread-0。 在第一個線程等待之后，程序停止。

Answer 1

問題是您創建了多個NameOutput ，並且它們使用了自己的監視程序鎖 ，這意味着它們之間將沒有“通信”（信號）。

相反，您需要共享監視器鎖定：

public class NameOutput extends Thread {
    static final int N = 5;
    static int activeThread = 0;
    static final Object lock = new Object(); // shared monitor lock

    public static void main(String[] args){

        for (int i = 1; i <= N; i++) {
            new NameOutput().start();
        }
    }

    @Override
    public void run(){
        while(true){
            this.printThreadName();
        }

    }
    private void printThreadName(){
        synchronized (lock) {
            String threadName = "Thread-"+ activeThread;
            //Check if thread is in the right order
            if(!threadName.equals(this.getName())){
                try{
                    lock.wait();
                }catch (InterruptedException e){
                    System.out.println(this.getName()+" was interrupted!");
                }
            }else{
                System.out.println(this.getName());
                activeThread = (activeThread + 1) % N;
                lock.notifyAll();
            }
        }
    }
}

---

另一個問題， wait 應該總是在while循環中使用，您可以做更多的事情：

private void printThreadName(){
    synchronized (lock) {
        while (!("Thread-"+ activeThread).equals(this.getName())) {
            try{
                lock.wait();
            }catch (InterruptedException e){
                System.out.println(this.getName()+" was interrupted!");
            }
        }
        System.out.println(this.getName());
        activeThread = (activeThread + 1) % N;
        lock.notifyAll();
    }
}

---

輸出：

Thread-0
Thread-1
Thread-2
Thread-3
Thread-4
Thread-0
Thread-1
Thread-2
Thread-3