Java Language Concurrent Programming (Threads) Get status of all threads started by your program excluding system threads


Example

Code snippet:

import java.util.Set;

public class ThreadStatus {
    public static void main(String args[]) throws Exception {
        for (int i = 0; i < 5; i++){
            Thread t = new Thread(new MyThread());
            t.setName("MyThread:" + i);
            t.start();
        }
        int threadCount = 0;
        Set<Thread> threadSet = Thread.getAllStackTraces().keySet();
        for (Thread t : threadSet) {
            if (t.getThreadGroup() == Thread.currentThread().getThreadGroup()) {
                System.out.println("Thread :" + t + ":" + "state:" + t.getState());
                ++threadCount;
            }
        }
        System.out.println("Thread count started by Main thread:" + threadCount);
    }
}

class MyThread implements Runnable {
    public void run() {
        try {
            Thread.sleep(2000);
        } catch(Exception err) {
            err.printStackTrace();
        }
    }
}

Output:

Thread :Thread[MyThread:1,5,main]:state:TIMED_WAITING
Thread :Thread[MyThread:3,5,main]:state:TIMED_WAITING
Thread :Thread[main,5,main]:state:RUNNABLE
Thread :Thread[MyThread:4,5,main]:state:TIMED_WAITING
Thread :Thread[MyThread:0,5,main]:state:TIMED_WAITING
Thread :Thread[MyThread:2,5,main]:state:TIMED_WAITING
Thread count started by Main thread:6

Explanation:

Thread.getAllStackTraces().keySet() returns all Threads including application threads and system threads. If you are interested only in status of Threads, started by your application, iterate the Thread set by checking Thread Group of a particular thread against your main program thread.

In absence of above ThreadGroup condition, the program returns status of below System Threads:

Reference Handler
Signal Dispatcher
Attach Listener
Finalizer