I’ve recently been playing with Event Counters in .Net. These are basically a way to record a set of metrics against a given program. In this post, I’ll cover how you can set these up and run them locally. In a later post, I’ll cover how you can do this in App Insights for a deployed app.

Initial Set-up

To run these locally, you’ll need to start by installing the dotnet tool for the counters:

dotnet tool install --global dotnet-counters --version 7.0.430602

Once you’ve installed this, you can have a look at the counters that are already running (you probably will have some):

dotnet counters ps

Write Some Code

Now that you’ve installed and seen dotnet counters, let’s create some code and watch our own code run. The first step is to just create a completely blank console app, then add a loop; for example:

for (int i = 1; i <= 1000; i++)
{
    await Task.Delay(500);
}

Running Locally

If you now run:

dotnet counters ps

You should be able to connect to this process:

dotnet counters monitor -p 24596

And you’ll see something like this:

These are just a list of stats that you can get out of the box. They will show for any .Net application - you don’t have to do anything, they’re just there already.

Let’s add our own.

Custom Counters

In the project, we’ll need a new class:

[EventSource(Name = "Aardvark")]
internal class EventSourceTest : EventSource
{
    EventCounter _eventCounter;

    public EventSourceTest()
    {
        _eventCounter = new EventCounter("test", this);
    }

    public void WriteSomeEvent()
    {
        string trace = $"test {Guid.NewGuid()}";            
        _eventCounter?.WriteMetric(Random.Shared.Next(100));
        Console.WriteLine(trace);
    }
} 

Whilst this class may not be doing anything actually useful, we can see that it writes a random number out - that’s our metric. The other thing to note is the name on the EventSource decorator.

In the main code, we can use this:

var eventSourceTest = new EventSourceTest();

for (int i = 1; i <= 1000; i++)
{
    await Task.Delay(500);
    eventSourceTest.WriteSomeEvent();       
}

Okay, now, if you run that, you won’t really notice any difference, nor will you notice any difference if you connect (as described above); however, if you connect to the event source specifically, you should start to see that new metric tracked:

dotnet counters monitor -p 13696 Aardvark

The name relates to the event source name above; and this should start to record the custom metric:

References

Event Counters