获取Java中活动线程的数量

Question

I have a class (extends Thread ) of which I am running multiple threads.

Here is the class:

public class Abc extends Thread{
    private String key;
    public void run(){}
}

Now, I want to know how many active threads are there of this class based on value of key .

eg. I set the value of key as "X" in 10 threads and "Y" in 15. I want to create a map:

map<String, int> :: {"X"=10, "Y"=15}

How can I do that?

EDIT:

This Map<> will be stored in the Execute class, which is creating the threads. It has nothing to do with Abc .

Answer 1

You can increment a counter when the task starts and decrement it when it finishes.

Something like

public void run() {
     AtomicInteger counter = counterMap.computeIfAbsent(key, k -> new AtomicInteger());
     counter.incrementAndGet();
     try {
         doRun();
     } finally {
         counter.getAndDecrement();
     }
 }

Answer 2

将您的key静态，以便它将其值保留在线程之间。

Answer 3

You can do something like this:

static HashMap<String, Integer> threadsCount = new HashMap<String, Integer>();
String key;

public Abc(String key) {
    this.key = key;
    synchronized (threadsCount) {
        if (threadsCount.containsKey(key)) {
            threadsCount.put(key, threadsCount.get(key) + 1);
        } else {
            threadsCount.put(key, 1);
        }
    }
}

and decrement the count when a thread finishes:

@Override
public void run() {
    ....
    synchronized (threadsCount) {
        if (threadsCount.containsKey(this.key)) {
            threadsCount.put(key, threadsCount.get(this.key) - 1);
        }
    }
}

@vish4071, based on your comment, I think that a better solution for your use case will be this:

public class Abc extends Thread {
    String key;

    public Abc(String key) {
        this.key = key;
    }

    public String getKey(){
        return key;
    }
    ....
}

And to get the count:

HashMap<String, Integer> threadsCount = new HashMap<String, Integer>();

for (Thread t : Thread.getAllStackTraces().keySet()) {
    if (t instanceof Abc) {
        if (t.getState() != Thread.State.TERMINATED) {
            String key = ((Abc)t).getKey();
            if (threadsCount.containsKey(key)) {
                threadsCount.put(key, threadsCount.get(key) + 1);
            } else {
                threadsCount.put(key, 1);
            }
        }
    }
}

Answer 4

    public class Abc extends Thread{
        private static Map<String, Integer> map = new ConcurrentHashMap<>();
        private String key;
        public void run(){
            synchronized (key) {
                Integer current = map.get(key);
                if(null == current) {
                    map.put(key, 1);
                } else {
                    map.put(key, current +1);
                }
            }

            //Run execution code here.
            synchronized (key) {
                Integer current = map.get(key);
                map.put(key, current -1);
            }
        }
    }