The .Net frog

I did load testing last week on the component I am developing and found out that the performances were just miserable... It was barely capable of handling 60 messages per seconds which was: 1) bad and 2) surprising! (Basically it's doing some kind of real-time caching/transformation/redirection of messages).

I then spent 5mins in dotrace trying to get a picture of what was going on. I found that in the thread that is monitoring the queue and sending messages, I had used an instance of ManualResetEvent instead of AutoResetEvent.

If you never used them, these 2 classes allow you to send signals between 2 threads. That way, the "monitor" thread is not wasting any resources until it's notified by the other thread that there is something in the queue. For instance, Thread 1 will wait for a queue to be filled with something like that:

 
private AutoResetEvent _mySignal = new AutoResetEvent(false);
 
private void MonitorQueue()
{
	while(!monitorQueue)
	{
		_mySignal.WaitOne();
		GetItemsInTheQueueAndDoStuff();
	}
}

And thread 2 will inject data in the queue:

 
public void EnqueueItem(Item myItem)
{
	InsertInQueue(myItem);
	_mySignal.Set();
}
 

As I said, my problem is that I used a ManualResetEvent instead of an AutoResetEvent. These 2 classes are almost the same except that when you use ManualResetEvent, you need to reset the signal manually with mySignal.Reset();. In my case, instead of blocking on mySignal.WaitOne(); the code was constantly looping and using a lot of CPU!

I fixed it and reran the load testing: now I'm at 5000 messages per seconds at 40% CPU. Much better!