Difference between multithreading with and without Executor

Question

I am trying to find out about the performance difference between normal multithreading and multithreading using executor (to maintain a thread pool).

The below are code

Answer 1

To see how something scales, I would try to keep the cost of monitoring to a minimum and I would compare a small number to a large number.

public class Executor_Demo {
    public static void main(String... arg) throws ExecutionException, InterruptedException {
        int nThreads = 5100;
        ExecutorService executor = Executors.newFixedThreadPool(nThreads, new DaemonThreadFactory());

        List> futures = new ArrayList>();
        for (int i = 0; i < nThreads; i++) {
            futures.add(executor.submit(new BackgroundCallable()));
        }
        Results result = new Results();
        for (Future future : futures) {
            result.merge(future.get());
        }
        executor.shutdown();

        result.print(System.out);

    }

    static class Results {
        private long cpuTime;
        private long userTime;

        Results() {
            final ThreadMXBean tb = ManagementFactory.getThreadMXBean();
            cpuTime = tb.getCurrentThreadCpuTime();
            userTime = tb.getCurrentThreadUserTime();
        }


        public void merge(Results results) {
            cpuTime += results.cpuTime;
            userTime += results.userTime;
        }

        public void print(PrintStream out) {
            ThreadMXBean tb = ManagementFactory.getThreadMXBean();

            List pools = ManagementFactory.getMemoryPoolMXBeans();
            for (int i = 0, poolsSize = pools.size(); i < poolsSize; i++) {
                MemoryPoolMXBean pool = pools.get(i);
                MemoryUsage peak = pool.getPeakUsage();
                out.format("Peak %s memory used:\t%,d%n", pool.getName(), peak.getUsed());
                out.format("Peak %s memory reserved:\t%,d%n", pool.getName(), peak.getCommitted());
            }

            out.println("Total thread CPU time\t" + cpuTime);
            out.println("Total thread user time\t" + userTime);
            out.println("Total started thread count\t" + tb.getTotalStartedThreadCount());
            out.println("Current Thread Count\t" + tb.getThreadCount());
            out.println("Peak Thread Count\t" + tb.getPeakThreadCount());
            out.println("Daemon Thread Count\t" + tb.getDaemonThreadCount());
        }
    }

    static class DaemonThreadFactory implements ThreadFactory {
        @Override
        public Thread newThread(Runnable r) {
            Thread t = new Thread(r);
            t.setDaemon(true);
            return t;
        }
    }

    static class BackgroundCallable implements Callable {
        @Override
        public Results call() throws Exception {
            Thread.sleep(100);
            return new Results();
        }
    }
}

when tested with -XX:MaxNewSize=64m (this limits the size temporary memory spaces will increase)

100 threads
Peak Code Cache memory used:    386,880
Peak Code Cache memory reserved:    2,555,904
Peak PS Eden Space memory used: 41,280,984
Peak PS Eden Space memory reserved: 50,331,648
Peak PS Survivor Space memory used: 0
Peak PS Survivor Space memory reserved: 8,388,608
Peak PS Old Gen memory used:    0
Peak PS Old Gen memory reserved:    192,675,840
Peak PS Perm Gen memory used:   3,719,616
Peak PS Perm Gen memory reserved:   21,757,952
Total thread CPU time   20000000
Total thread user time  20000000
Total started thread count  105
Current Thread Count    93
Peak Thread Count   105
Daemon Thread Count 92

5100 threads
Peak Code Cache memory used:    425,728
Peak Code Cache memory reserved:    2,555,904
Peak PS Eden Space memory used: 59,244,544
Peak PS Eden Space memory reserved: 59,244,544
Peak PS Survivor Space memory used: 2,949,152
Peak PS Survivor Space memory reserved: 8,388,608
Peak PS Old Gen memory used:    3,076,400
Peak PS Old Gen memory reserved:    192,675,840
Peak PS Perm Gen memory used:   3,787,096
Peak PS Perm Gen memory reserved:   21,757,952
Total thread CPU time   810000000
Total thread user time  150000000
Total started thread count  5105
Current Thread Count    5105
Peak Thread Count   5105
Daemon Thread Count 5104

The main increase is the increase in old gen used ~ 3 MB or about 6 KB per thread. and the CPU used by 956 ms or about 0.2 ms per thread.

---

In your first example, you are creating one thread, in the second you are creating 1000.

The output you are performing appears to be most of the work and you have much more output in the second case than the first.

You need to be sure your testing and monitoring is far more light weight than want you are trying to monitor/measure.