java - Java中子线程如何向主线程(方法)发送连续的消息？

Question

我有一个想要相互通信的人的 HashMap，如下所示:

{zidane=[rooney, rooney, rooney, scholes, rooney], rooney=[scholes, messi, scholes], scholes=[ronaldo], ronaldo=[rooney, messi, scholes], messi=[zidane]}

在这里， key 中的每个人都有自己的线程，他们将在其中向列表中的每个人发送消息并接收响应。

public class Master {
    public Map callsMap = new HashMap<String, List>();

    public static void main(String[] args) throws InterruptedException, ExecutionException {
        Master m = new Master();
        m.readFile();
        ExecutorService executorService = Executors.newFixedThreadPool(6);
        List<Future<String>> returnFutures = new ArrayList<>();
        Iterator<Map.Entry<String, List>> it = m.callsMap.entrySet().iterator();
        while (it.hasNext()) {
            Map.Entry<String, List> pair = it.next();
            String caller = pair.getKey();
            List receiverList = pair.getValue();
            returnFutures.add(executorService.submit(new SubTasks(caller, receiverList) ));
        }

        while(executorService.awaitTermination(1, TimeUnit.SECONDS));
        for(Future<String> returnFuture: returnFutures){
            System.out.println(returnFuture.get());
        }
        executorService.shutdown();
    }
}

Master 类将为 HashMap 中的每个键迭代创建一个线程。请注意，readFile 方法只会从文本文件中读取并生成我上面提到的输入(到callsMap 变量中)。它对于这个上下文来说并不是特别重要，所以我在这里省略了它。

我有 SubTasks 类，它实现了 Callable 接口(interface)并为每个交互创建消息。该类不会创建任何额外的线程，而只是对它收到的调用者和接收者列表进行操作，如下所示:

import java.util.List;
import java.util.concurrent.Callable;

public  class SubTasks implements Callable<String> {
    private String caller;
    private List receiverList;
    private volatile String returnMessage;
    private volatile String callerMessage;
    private volatile String str = "";

    SubTasks(String s, List l){
        caller = s;
        receiverList = l;
    }

    @Override
    public String call (){
        for (int i = 0; i < receiverList.size(); i++) {
            callerMessage = receiverList.get(i)+" received intro message from "+caller +" ["+System.currentTimeMillis()+"]";
            //System.out.println(callerMessage);
            returnMessage = caller+" received reply message from "+receiverList.get(i) +" ["+System.currentTimeMillis()+"]";
            //System.out.println(returnMessage);
            str = str + callerMessage +"\n"+ returnMessage +"\n";
        }
        return null;
    }
}

如果我直接在子线程中打印，我会得到所需的结果，因为消息以随机顺序打印:

rooney received intro message from zidane [1592165414388]
ronaldo received intro message from scholes [1592165414388]
scholes received intro message from rooney [1592165414388]
rooney received intro message from ronaldo [1592165414389]
zidane received intro message from messi [1592165414389]
scholes received reply message from ronaldo [1592165414434]
zidane received reply message from rooney [1592165414434]
...
...

但我希望这些消息在主方法而不是子线程中打印。我尝试通过连接 returnMessage 和 callerMessage 来返回消息，但由于我在每个线程末尾返回，因此它们似乎是按顺序打印的(每对的调用回复)如下:

rooney received intro message from zidane [1592165584566]
zidane received reply message from rooney [1592165584614]
rooney received intro message from zidane [1592165584632]
zidane received reply message from rooney [1592165584632]
rooney received intro message from zidane [1592165584632]
zidane received reply message from rooney [1592165584632]
...
...

所以，我的问题是如何在主方法中打印每个 callerMessage 和 returnMessage 而不是子线程创建后立即打印？

Answer 1

这看起来像是生产者-消费者问题的典型示例，其中您的 SubTasks 是生产者，而 Master 是单个消费者。它可以使用低级 java 并发结构以多种不同的方式解决，但最简单的一种可能是使用某种线程安全的中间队列。您可以首先查看 Producer/Consumer threads using a Queue .