-
Creating a new thread causes some performance overhead.
-
Too many threads can lead to reduced performance, as the
CPU
needs to switch between these threads.
- You cannot easily control the number of threads, therefore you may run into out of memory errors due to too many threads.
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
public class TestExecutor {
private static final int NTHREDS = 10;
/**
* @param args
*/
public static void main(String[] args) {
long l=System.currentTimeMillis();
ExecutorService executor = Executors.newFixedThreadPool(NTHREDS);
for (int i = 0; i < 10000; i++) {
Runnable worker = new Test(i);
executor.execute(worker);
}
// This will make the executor accept no new threads
// and finish all existing threads in the queue
executor.shutdown();
// Wait until all threads are finish
while (!executor.isTerminated()) {
}
System.out.println("Total time: "+ (System.currentTimeMillis()-l));
}public class Test implements Runnable {
private int id;
public Test(int id) {
this.id = id;
}
@Override
public void run() {
int sum=id;
for(int j=0; j<10000000;j++)
sum += j;
System.out.println("My sum = "+sum);
}
}
You may note that I have used a thread pool with ten threads, you can change the size of the pool according to your need.
You may wonder what actually applying concurrency does to your application's performance. Here's a comparison of CPU usage without and with using threads.
My application without using threads!
Application is running in the time gap
of 40 - 0 seconds in the CPU history
graph. You may note that CPU
utilization is 30% & 100%. i.e. not
effectively utilized.
My application using threads!
Application is running in the time gap
of 25 - 0 seconds in the CPU history
graph. You may note that CPU
utilization is 100% & 100%. Thus the
both CPUs are effectively utilized.
There is another way that you can get the advantage of Java Executor Framework, I will elaborate on that in my next post! :)
Happy Threading!! :D
