java - 线程仍在等待

Question

public class Communicate {

    public static void main(String... args) {
        Producer prod = new Producer();
        Consumer cons = new Consumer(prod);

        Thread pThread = new Thread(prod, "ProducerThread");
        Thread cThread = new Thread(cons, "ConsumerThread");

        pThread.start();
        cThread.start();
    }
}
class Producer extends Thread {

    StringBuffer sb;
    Producer() {                        //constructor
        sb = new StringBuffer();        //allot memory 
    }

    @Override
    public void run() {
        synchronized (sb) {
            for (int i = 1; i <= 10; i++) {
                try {
                    sb.append("daksh    ");
                    Thread.sleep(100);
                    System.out.println("appending " + i);
                } catch (InterruptedException ex) {
                }
            }//end of loop

            //data production is over, so notify Consumer Thread
            System.out.println("Done production");
            sb.notifyAll();
        }
    }
}

class Consumer extends Thread {

    Producer prod;

    Consumer(Producer production) {           //constructor
        this.prod = production;
    }

    @Override
    public void run() {
        System.out.println("sup");
        synchronized (prod.sb) {
      //wait till the notification is received from the Producer thread.
            try {
                System.out.println("waiting");
                prod.sb.wait();
            } catch (InterruptedException ie) {
            }
            System.out.println("done");
        }
        System.out.println(prod.sb);
    }
}

我正在尝试让生产者和消费者线程与notify()进行通信

在pThread完成其通知工作后，cThread继续等待无限长的时间。知道为什么 prod.sb.wait(); 没有被 sb.notify();

noitified

Answer 1

在wait()之前调用notifyAll()，因此“信号”丢失。这就是为什么在使用 wait/notify 时需要条件变量。

boolean produced = false;
// In producer
produced = true;
asd.notifyAll();

// in consumer
while(!produced)
    wait();