在Java中，子线程如何向主线程(方法)发送连续的消息？
在Java中，子线程如何向主线程(方法)发送连续的消息？
提问于 2020-06-15 04:18:11
我有一个想要彼此交流的人的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，密钥中的每个人都有自己的线程，在这些线程中，他们将向列表中的每个人发送一条消息并接收响应。
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类将迭代地为HashMap中的每个键创建一个线程。请注意，readFile方法将从文本文件中读取并生成我前面提到的输入(到callsMap变量中)。它对于这个上下文并不是特别重要，所以我在这里省略了它。
我有一个实现Callable接口并为每个交互创建消息的SubTasks类。这个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，我会得到想要的结果，因为消息是按随机顺序打印的：
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main方法中打印，而不是在子线程中打印。我试图通过连接returnMessage和callerMessage来返回消息，但由于我是在每个线程的末尾返回的，所以它们似乎是按如下顺序打印的(每对调用-回复)：
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main方法中打印每个callerMessage和returnMessage，而不是在创建后立即打印它们的子线程？
Stack Overflow用户
发布于 2020-06-15 04:57:09
这看起来像是生产者-消费者问题的经典例子，其中你的SubTasks是生产者，而Master是单一消费者。可以使用低级java并发构造以多种不同的方式解决此问题，但最简单的方法可能是使用某种线程安全的中间队列。您可以从查看Producer/Consumer threads using a Queue开始。
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/62377733
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