实现Runnable而不是扩展Thread时的不同行为

Question

Calculator calc = new Calculator();
new ReadCalculation(calc).start();
new ReadCalculation(calc).start();
calc.start();

public class NotifyAllAndWait {

public static void main(String[] args) {

        Calculator calc = new Calculator();
        Thread th01 = new Thread(new ReadCalculation(calc));
        th01.start();
        Thread th02 = new Thread(new ReadCalculation(calc));
        th02.start();

        Thread calcThread = new Thread(calc);
        calcThread.start();
    }
}

class ReadCalculation implements Runnable {

    private Calculator calc = null;
    ReadCalculation(Calculator calc) {
        this.calc = calc;
    }

    @Override
    public void run() {
        synchronized (calc) {
            try {
                System.out.println(Thread.currentThread().getName() + " Waiting for calculation...");
                calc.wait();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName() + " Total: " + calc.getTotal());
        }
    }
}

class Calculator implements Runnable {
    private int total = 0;
    @Override
    public void run() {
        synchronized(this) {
            System.out.println(Thread.currentThread().getName() + " RUNNING CALCULATION!");
            for(int i = 0; i < 100; i = i + 2){
                total = total + i;
            }
            notifyAll();
        }
    }
    public int getTotal() {
        return total;
    }
}

Answer 1

当执行wait()时，这需要在执行notify()块的状态更改之后进行循环。例如。

// when notify
changed = true;
x.notifyAll();

// when waiting
while(!changed)
    x.wait();

如果不这样做，您将遇到诸如wait（）错误醒来或notify（）丢失等问题。

注意：一个线程可以很容易地在其他线程开始之前完成100次迭代。预创建Thread对象可能会对性能产生足够的影响，从而改变您的情况下的结果。