Java 如何避免在循环中使用 Thread.sleep()

Question

从我的主线程开始，我启动了两个线程，分别称为生产者和消费者。两者都包含 while(true) 循环。生产者循环是 UDP 服务器，因此它不需要睡眠。我的问题出在消费者循环中。消费者循环从链接队列中删除对象并将其传递给函数以进行进一步处理。根据研究，在循环中使用线程睡眠不是一个好习惯，因为有时 O/S 不会在设定时间结束时释放。如果我在应用程序理想时删除线程休眠，它会将 CPU 拖到 20 到 30%。

class Producer implements Runnable {
    private DatagramSocket dsocket;
    FError fer = new FError();

    int port =1548;
    ConcurrentLinkedQueue<String> queue;

    Producer(ConcurrentLinkedQueue<String> queue){
        this.queue = queue; 
    }

    @Override
    public void run() {

        try {

            // Create a socket to listen on the port.
            dsocket = new DatagramSocket(port);
            // Create a buffer to read datagrams into.
            byte[] buffer = new byte[30000];
            // Create a packet to receive data into the buffer
            DatagramPacket packet = new DatagramPacket(buffer,
            buffer.length);

            while (true) {
                try {

                   // Wait to receive a datagram
                    dsocket.receive(packet);
                    //Convert the contents to a string,
                    String msg = new String(buffer, 0, packet.getLength());

                    int ltr = msg.length();
                     // System.out.println("MSG =" + msg);

                    if(ltr>4)
                    {

                        SimpleDateFormat sdfDate = new SimpleDateFormat  ("yyyy-MM-dd HH:mm:ss");//dd/MM/yyyy

                        Date now = new Date();
                        String strDate = sdfDate.format(now);

                        //System.out.println(strDate);

                        queue.add(msg + "&" + strDate);

                     // System.out.println("MSG =" + msg);
                    }

                  // Reset the length of the packet before reusing it.
                   packet.setLength(buffer.length);

                } catch (IOException e) {
                    fer.felog("svr class", "producer", "producer thread",e.getClass().getName() + ": " + e.getMessage());
                    dsocket.close();
                    break; 
                }
            }

        } catch (SocketException e) {
          fer.felog("svr class", "producer","Another App using the udp port " + port, e.getClass().getName() + ": " + e.getMessage()); 

        }

    }

}

class Consumer implements Runnable {

    String str;  
    ConcurrentLinkedQueue<String> queue;

    Consumer(ConcurrentLinkedQueue<String> queue) {
        this.queue = queue;  
    }

    @Override
    public void run() {

        while (true) {
            try {

                while ((str = queue.poll()) != null) {

                    call(str);  // do further processing

                   }
            } catch (IOException e) {
                ferpt.felog("svr class", "consumer", "consumer thread", e.getClass().getName() + ": " + e.getMessage());
                break;
            }

            try {
                Thread.sleep(500);
            } catch (InterruptedException ex) {

                ferpt.felog("svr class", "consumer","sleep", ex.getClass().getName() + ": " + ex.getMessage());
            }

        }

    }

}

Answer 1

您可以更改代码以合并一个 ScheduledExecutorService，而不是让 Consumer extend Runnable 每半秒运行一次队列轮询，而不是让线程休眠。这方面的一个例子是

public void schedule() {
    ScheduledExecutorService executor = Executors.newSingleThreadScheduledExecutor();
    executor.scheduleAtFixedRate(() -> {
        String str;
        try {
            while ((str = queue.poll()) != null) {
                call(str);  // do further processing
            }
        } catch (IOException e) {
            ferpt.felog("svr class", "consumer", "consumer thread", e.getClass().getName() + ": " + e.getMessage());
        }
    }, 0, 500, TimeUnit.MILLISECONDS);
}

Answer 2

让消费者 wait() 都可以访问一个对象，并让生产者 notify() 在有新消息时监听这个对象。消费者应该删除所有消息，而不是像示例中那样只删除一条消息。

Answer 3

您的问题的正确解决方案是使用阻塞队列。它为您提供了几个优势：

不浪费cpu忙等
可以有有限的容量 - 想象你有一个快速的生产者，但一个慢速的消费者 -> 如果队列的大小没有限制，那么你的应用程序很容易达到 OutOfMemory 条件

这是一个小演示，您可以玩一下：

import java.util.concurrent.ArrayBlockingQueue;
import java.util.concurrent.BlockingQueue;

public class ProdConsTest {
    public static void main(String[] args) throws InterruptedException {
        final BlockingQueue<Integer> queue = new ArrayBlockingQueue<>(10);
        final Runnable producer = () -> {
            for (int i = 0; i < 1000; i++) {
                try {
                    System.out.println("Producing: " + i);
                    queue.put(i);

                    //Adjust production speed by modifying the sleep time
                    Thread.sleep(100);
                } catch (InterruptedException e) {
                    //someone signaled us to terminate
                    break;
                }
            }
        };

        final Runnable consumer = () -> {
            while (true) {
                final Integer integer;
                try {
                    //Uncomment to simulate slow consumer:
                    //Thread.sleep(1000);

                    integer = queue.take();
                } catch (InterruptedException e) {
                    //someone signaled us to terminate
                    break;
                }
                System.out.println("Consumed: " + integer);
            }
        };


        final Thread consumerThread = new Thread(consumer);
        consumerThread.start();

        final Thread producerThread = new Thread(producer);
        producerThread.start();

        producerThread.join();
        consumerThread.interrupt();
        consumerThread.join();
    }
}

现在取消注释消费者中的 sleep() 并观察应用程序发生了什么。如果您使用的是基于计时器的解决方案，例如提议的 ScheduledExecutorService 或者您正忙于等待，那么使用快速生产者时，队列将不受控制地增长并最终使您的应用程序崩溃

Java 如何避免在循环中使用 Thread.sleep()

Java how to avoid using Thread.sleep() in a loop

java

producer-consumer