是否可以在hashmap中存儲線程對象？

Question

我有一個場景，我調用了大約10個Thread ，並且每個Thread都必須等到Notifier類通知我要通知特定的Thread ，我正在做的事情是我正在使用HashMap並將Thread id作為key並將Thread實例作為值。 稍后在Notifier我試圖通過遍歷提供Thread實例的映射map.get(threadId)來通知它，並且嘗試在其上調用notify，但是它拋出IllegalmonitorException 。 我不確定在Waiter和Notifier類中要同步HashMap還是Thread 。

package com.cgi.sample.jms.requestor;

import java.util.HashMap;
import java.util.Map;
import java.util.UUID;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class RequestorApplication {
    private final Object lock = new Object();
    public static String correlationId;

    public static String getCorrelationId() {
        correlationId = UUID.randomUUID().toString();
        return correlationId;
    }

    public static void main(String args[]) throws Exception {

        Map<Long, Thread> map = new HashMap<Long, Thread>();

        ExecutorService executor = Executors.newFixedThreadPool(5);
        for (int i = 0; i < 2; i++) {

            Waiter waiter = new Waiter(map);

            executor.execute(waiter);

            Notifier notifier = new Notifier(map);
            executor.execute(notifier);
        }

        System.out.println("All the threads are started");
    }
}

class Waiter implements Runnable {

    Map<Long, Thread> map;
    ExecutorService executor = Executors.newFixedThreadPool(5);

    public Waiter(Map<Long, Thread> map) {
        this.map = map;
    }

    public void run() {

        ExecutorService executor = Executors.newFixedThreadPool(5);

        for (int i = 0; i < 2; i++) {

            Runner instance = new Runner();

            System.out.println("Executing thread " + " with " + Thread.currentThread().getName());

            long threadId = Thread.currentThread().getId();

            String threadname = Thread.currentThread().getName();

            executor.execute(instance);

            synchronized (map) {

                map.put(threadId, Thread.currentThread());

                try {
                    instance.wait();
                    System.out.println(threadname + "  Thread entered into waiting state!!!");
                    // Thread.currentThread().wait();
                    System.out.println(threadname + "  Thread woke up from wait!!!!!");

                } catch (InterruptedException e) {

                    e.printStackTrace();
                }
            }
        }

    }

}

class Notifier implements Runnable {

    Map<Long, Thread> map;

    public Notifier(Map<Long, Thread> map)

    {
        this.map = map;
    }

    public synchronized void run() {

        synchronized (map) {

            for (Map.Entry<Long, Thread> entry : map.entrySet()) {

                System.out.println("stored threads in map are--->" + map.get(entry.getKey()));

                map.get(entry.getKey()).notify();

            }

        }
    }
}

class Runner implements Runnable {

    public void run() {
        System.out.println("runner invoked");

    }
}

Answer 1

您的問題的答案是： 是 。 因為線程是對象，所以可以將其存儲到HashMap中。

否則，@ TJCrowder告訴您，您使用通知的方式是錯誤的。 這是因為您正在通過沒有線程鎖的對象 （ map.get(entry.getKey()).notify(); ）調用通知 。 而不是您應該調用對象Runner （ instance.notify() ）的notify ，該對象具有線程鎖定，如您的代碼所示： instance.wait();

首先！ 您必須與對象instance同步阻塞對象，該對象instance將使用wait方法阻塞線程，例如：

synchronized(instance){ 
  try{
    instance.wait() 
  }catch(...)
  {
     //Do Something else
  }
}

然后，調用對象Runner notify方法停止等待並繼續執行線程並離開syncrhonized塊，如下所示：

map.get(entry.getKey()).getRunnerInstance().notify();

但是，考慮一下，當前的代碼很難實現此技巧，因為您必須重寫幾個部分，例如： 您正在使用對象的代碼，該對象位於for循環的上下文中以阻塞線程 。

for (int i = 0; i < 2; i++) {

  Runner instance = new Runner();
  //...
  synchronized (map) {

            map.put(threadId, Thread.currentThread());

            try {
                instance.wait(); //You are blocking over a instance declared into the For Loop.
            }catch(..){
               //..
            };
  }

}