As a follow-up to the lengthy conversation we had about java.util.Random
and whether it is best to reuse a single one and synchronize on it or
just create a new one each time, I wrote a program to compare the
performance of the two. Here are the results (CentOS 4.4, JDK 6):
Testing with 1 threads for 5 seconds
Generated 1,191,083 random ints using seed-many method
Generated 24,562,853 random ints using seed-once method
====================
Testing with 5 threads for 5 seconds
Generated 1,736,231 random ints using seed-many method
Generated 11,417,596 random ints using seed-once method
====================
Testing with 10 threads for 5 seconds
Generated 1,749,759 random ints using seed-many method
Generated 10,706,179 random ints using seed-once method
====================
Testing with 25 threads for 5 seconds
Generated 1,727,634 random ints using seed-many method
Generated 10,922,547 random ints using seed-once method
====================
Testing with 50 threads for 5 seconds
Generated 1,732,329 random ints using seed-many method
Generated 10,734,163 random ints using seed-once method
====================
The difference was less pronounced under Windows XP (JDK 6), but
seed-once still won:
Testing with 1 threads for 5 seconds
Generated 2,335,585 random ints using seed-many method
Generated 45,853,345 random ints using seed-once method
====================
Testing with 5 threads for 5 seconds
Generated 3,290,170 random ints using seed-many method
Generated 6,214,038 random ints using seed-once method
====================
Testing with 10 threads for 5 seconds
Generated 3,283,141 random ints using seed-many method
Generated 6,706,248 random ints using seed-once method
====================
Testing with 25 threads for 5 seconds
Generated 3,258,902 random ints using seed-many method
Generated 6,597,599 random ints using seed-once method
====================
Testing with 50 threads for 5 seconds
Generated 3,244,338 random ints using seed-many method
Generated 6,650,498 random ints using seed-once method
====================
The source code is attached. If I messed up anywhere, please let me know.
-Ben
package test;
import java.text.DecimalFormat;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
public class RandomTest {
static class SeedMultiple implements Runnable {
static int activeThreads = 0;
static boolean stop = true;
static int count = 0;
public void run() {
++activeThreads;
while (stop)
Thread.yield();
while (!stop) {
new Random().nextInt();
++count;
}
--activeThreads;
}
public static void reset() {
stop = true;
count = 0;
}
}
static class SeedOnce implements Runnable {
static int activeThreads = 0;
static Random random = new Random();
static boolean stop = true;
static int count = 0;
public void run() {
++activeThreads;
while (stop)
Thread.yield();
while (!stop) {
synchronized (random) {
random.nextInt();
}
++count;
}
--activeThreads;
}
public static void reset() {
stop = true;
count = 0;
}
}
public static void runTest(int threadCount, long sleepSeconds)
throws InterruptedException {
DecimalFormat format = new DecimalFormat(",###");
// info
System.out.println("Testing with " + threadCount + " threads for "
+ sleepSeconds + " seconds");
// test the seed-many method
SeedMultiple.reset();
List<Thread> threads = new ArrayList<Thread>();
for (int i = 0; i < threadCount; i++) {
Thread thread = new Thread(new SeedMultiple());
thread.start();
threads.add(thread);
}
SeedMultiple.stop = false;
Thread.sleep(sleepSeconds * 1000);
SeedMultiple.stop = true;
while (SeedMultiple.activeThreads > 0)
Thread.yield();
System.out.println("Generated " + format.format(SeedMultiple.count)
+ " random ints using seed-many method");
// test the seed-once method
SeedOnce.reset();
threads.clear();
for (int i = 0; i < threadCount; i++) {
Thread thread = new Thread(new SeedOnce());
thread.start();
threads.add(thread);
}
SeedOnce.stop = false;
Thread.sleep(sleepSeconds * 1000);
SeedOnce.stop = true;
while (SeedOnce.activeThreads > 0)
Thread.yield();
System.out.println("Generated " + format.format(SeedOnce.count)
+ " random ints using seed-once method");
}
public static void main(String[] args) throws InterruptedException {
int[] threadCounts = new int[] { 1, 5, 10, 25, 50 };
long sleepSeconds = 5;
for (int count : threadCounts) {
runTest(count, sleepSeconds);
System.out.println("====================");
}
}
}
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