java - 如何告诉主线程部分线程工作已完成

Question

notify 真的只有在线程结束后才起作用吗？在下面的代码中，在我发表评论(true)之前我无法收到通知。如何告诉主线程部分线程工作已完成？

public class ThreadMain {
    public Thread reader;
    private class SerialReader implements Runnable {
        public void run() {
            while (true) {
                try {
                    Thread.sleep(3000);                
                    synchronized(this) {
                        System.out.println("notifying");
                        notify();
                        System.out.println("notifying done");
                    }                
                } catch (Exception e) {
                    System.out.println(e);
                }                
            }
        }
    }

    ThreadMain() {
        reader = new Thread(new SerialReader());
    }

    public static void main(String [] args) {
        ThreadMain d= new ThreadMain();    
        d.reader.start();
        synchronized(d.reader) {
            try {    
                d.reader.wait();
                System.out.println("got notify");
            } catch (Exception e) { 
                System.out.println(e);
            }    
        }        
    }
}

Answer 1

您应该尽量避免在较新版本的 Java 中使用 wait 和 notify，因为它们很难正确执行。尝试使用类似 BlockingQueue 的东西来代替

public class ThreadMain {
    public final BlockingQueue<Boolean> queue = new LinkedBlockingQueue<>();
    private class SerialReader implements Runnable {
        public void run() {
            while (true) {
                try {
                    Thread.sleep(3000);                
                    System.out.println("notifying");
                    queue.offer(Boolean.TRUE);
                    System.out.println("notifying done");            
                } catch (Exception e) {
                    System.out.println(e);
                }                
            }
        }
    }

    ThreadMain() {
        reader = new Thread(new SerialReader());
    }

    public static void main(String [] args) {
        ThreadMain d= new ThreadMain();    
        d.reader.start();
        try {    
            d.queue.take(); // block until something is put in the queue
            System.out.println("got notify");
        } catch (Exception e) { 
            System.out.println(e);
        }          
    }
}