@Override
    public void run() {
        System.out.println("Start of index " + index);
        try {
            Thread.sleep(3000);
        } catch (InterruptedException e) {
            System.out.println("Exception " + index + " " + e);
        }
        System.out.println("End of index " + index);
    }
Facebook interview question
Implement a non block run which takes as many runnables as given but only
runs a specified number of threads.
You can also update maxSize in between which will change number of threads executing
http://tutorials.jenkov.com/java-concurrency/thread-pools.html
src/com/interview/multithreaded/ThreadPoolImpl.java