QPS Control example

Main.java

import java.util.concurrent.Callable;
import java.util.concurrent.Executors;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.ArrayList;
import java.util.Timer;
import java.util.TimerTask;
import java.util.Random;

class Main {
    static final int n = 20;
    static final int m = 3;

    static int arg = 0;

    static LinkedBlockingQueue<Task> tasks = new LinkedBlockingQueue<Task>();

    static ExecutorService exe = Executors.newFixedThreadPool(n);

    static Random random = new Random();
    public static void sendRequest(int arg) {
        if (random.nextDouble() < 0.5) {
            throw new RuntimeException();
        }
        System.out.println(arg);
    }

    public static void main(String[] args) {
        Timer timer = new Timer();
        Runner runner = new Runner();
        timer.scheduleAtFixedRate(runner, 0L, 1000L);
    }

    static class Runner extends TimerTask {
        public void run() {
            System.out.println("----------------------------------------");
            while (tasks.size() < n) {
                tasks.offer(new Task(arg++, m));
            }
            ArrayList<Task> toInvoke = new ArrayList<Task>();
            for (int i = 0; i < n; ++i) {
                toInvoke.add(tasks.poll());
            }
            try {
                exe.invokeAll(toInvoke);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    }

    static class Task implements Callable<Void> {
        private int arg;
        private int nRetry;
        public Task(int arg, int nRetry) {
            this.arg = arg;
            this.nRetry = nRetry;
        }
        public Void call() {
            try {
                sendRequest(arg);
            } catch (Exception e) {
                if (nRetry > 0) {
                    System.out.println("arg = " + arg + " failed. retrying...");
                    nRetry--;
                    tasks.offer(this);
                } else {
                    System.out.println("arg = " + arg + " tried " + m + " times, but failed.");
                }
            }
            return null;
        }
    }
}