Java Thread Performance Vs. Virtual Threads
During an interview, some interviewer asked me about the differences between Java Threads performance vs. Virtual Threads. I answered that because Virtual Threads are actually light weight threads handled by JVM, they must be faster, but I was curious about the exact performance difference between these two. So, I did a simple benchmark to see the performance improvements in Virtual Threads.
This is a very simple test, I create a very huge number of threads and virtual threads, each takes 5 seconds to finish. Then I calculate the duration of running app.
This is Java code I used for this benchmark:
package info.behzadian.thread;
import java.util.concurrent.CountDownLatch;
public class Main {
public static void main(String[] args) throws InterruptedException {
int numThreads = 100000;
CountDownLatch latch = new CountDownLatch(numThreads);
long start = System.currentTimeMillis();
for(int i =0; i < numThreads; i++) {
startThreads(latch);
}
latch.await(); // wait for all threads to finish
long end = System.currentTimeMillis();
System.out.println("Time taken with regular threads: " + (end - start) + "ms");
latch = new CountDownLatch(numThreads); // reset the latch
start = System.currentTimeMillis();
for(int i =0; i < numThreads; i++) {
startVirtualThreads(latch);
}
latch.await(); // wait for all virtual threads to finish
end = System.currentTimeMillis();
System.out.println("Time taken with virtual threads: " + (end - start) + "ms");
}
private static void startThreads(CountDownLatch latch) {
new Thread(new Runnable() {
@Override
public void run() {
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
latch.countDown(); // decrement the count of the latch
}
}
}).start();
}
private static void startVirtualThreads(CountDownLatch latch) {
Thread.startVirtualThread(new Runnable() {
@Override
public void run() {
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
} finally {
latch.countDown(); // decrement the count of the latch
}
}
});
}
}
In first run, I started with 100,000 threads vs. virtual threads and this is the result:
Time taken with regular threads: 54639ms
Time taken with virtual threads: 9477ms
As you can see, virtual threads are much faster. They take around 17% running time of threads.
Then, I tried with 200,000 threads benchmark and this is the result:
Time taken with regular threads: 98614ms
Time taken with virtual threads: 12260ms
As you can see, when we increase the number of threads, virtual threads work even better! They take around 12.4% running time of threads.
I was using Java version 21.0.2 on a laptop running windows 11 with 16GB of RAM.