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Reading and Publishing Performance Counters in .NET


May 20, 2004

Windows uses performance counters to collect and present performance data from running processes. Windows itself provides hundreds of performance counters, each monitoring a specific aspect of your system, from CPU utilization to network traffic. In addition, other applications such as SQL Server or Exchange publish their own custom performance counters that integrate into the Windows performance monitoring system.

Performance counters are grouped into categories such as Memory, Processor and PhysicalDisk. Each category contains one or more performance counters. For example, the Memory category includes such categories as Available Bytes, Cache Bytes, and Committed Bytes. Some categories also support an intermediate level of organization called an instance. For example, the Network Interface category has one instance for each network interface in your computer. You can thus decide which network card to monitor with this instance.

Windows provides the System Monitor application (shown in Figure 1) to let you see performance counters in action. But if you're working in .NET, you can go much deeper than this by using the System.Diagnostics.PerformanceCounter class. In this article, I'll show you how to monitor existing performance counters and how to create your own performance counters.

Windows System Monitor in action

Reading Performance Data

Visual Studio .NET makes it supremely easy to read existing performance counters in your application, thanks to Server Explorer. If you haven't discovered Server Explorer yet, it's normally docked as a slide-out window on the left hand side of the VS .NET workspace. When you slide it out, you'll find a treeview that lets you drill into all sorts of resources, as shown in Figure 2. As you can see, Performance Counters are one of the categories of resource that you can find here.

Performance counters in Server Explorer

In this screenshot, Skyrocket is the name of my local computer, .NET CLR Security is a performance counter category, Total Runtime Checks is a performance counter, and _Global_ is a performance counter instance. You can drag and drop a performance counter instance from Server Explorer to a .NET Windows form. When you do this, Visual Studio .NET creates a performance counter component on the form. This is a visual wrapper for an instance of the PerformanceCounter class.

For a quick demonstration, I dragged a performance counter and a timer control to a form, added some buttons and a listbox, and wrote a tiny bit of code:


Private Sub btnShowCPU_Click(ByVal sender As System.Object, _
 ByVal e As System.EventArgs) Handles btnShowCPU.Click
    ' Toggle the state of the CPU performance
    ' counter display in the list box
    If btnShowCPU.Text = "Show CPU usage" Then
        btnShowCPU.Text = "Stop"
        Timer1.Enabled = True
    Else
        btnShowCPU.Text = "Show CPU usage"
        Timer1.Enabled = False
    End If
End Sub

Private Sub Timer1_Tick(ByVal sender As Object, _
 ByVal e As System.EventArgs) Handles Timer1.Tick
    ' Display a new performance counter value
    ' in the list box
    lbPerfData.Items.Add("CPU usage: " & pcCpuTime.NextValue() & "%")
End Sub

Figure 3 shows this form in action, collecting samples of CPU usage. As you can see in the code, the samples are generated by calling the NextValue() method of a PerformanceCounter object named pcCpuTime.

Collecting performance data in .NET

Looking into the code that the Windows Forms Designer generated shows how easy it is to set up a PerformanceCounter for an existing performance counter:


Friend WithEvents pcCpuTime As System.Diagnostics.PerformanceCounter

Me.pcCpuTime.CategoryName = "Processor"
Me.pcCpuTime.CounterName = "% Processor Time"
Me.pcCpuTime.InstanceName = "_Total"
Me.pcCpuTime.MachineName = "skyrocket"

After you set the CategoryName, CounterName, InstanceName, and MachineName properties, you can read a sample of the performance counter any time that you like. The NextValue method will return the system's calculated value for the performance counter. There's also a NextSample method which returns a point-in-time sample; this may differ from the calculated value for counters which require multiple samples (for example, those that return a bytes per second rate).

Creating Your Own Performance Counter

Creating your own performance counters uses several classes, all in the System.Diagnostics namespace. Here's an example that creates two performance counters:


Private Sub btnRegisterCustom_Click(ByVal sender As System.Object, _
 ByVal e As System.EventArgs) Handles btnRegisterCustom.Click
    ' Create a custom performance counter
    If Not PerformanceCounterCategory.Exists("Developer.com") Then
        Dim ccd1 As New CounterCreationData
        ccd1.CounterName = "RandomCounter"
        ccd1.CounterType = PerformanceCounterType.NumberOfItems32

        Dim ccd2 As New CounterCreationData
        ccd2.CounterName = "IncreasingCounter"
        ccd2.CounterType = PerformanceCounterType.NumberOfItems32

        Dim ccds As New CounterCreationDataCollection
        ccds.Add(ccd1)
        ccds.Add(ccd2)

        PerformanceCounterCategory.Create("Developer.com", _
         "Developer.com counters", ccds)

        btnShowCustom.Enabled = True
    End If
End Sub

The CounterCreationData class contains the information necessary to create a single counter: its name and its type. Instances of this calss can be collected into an instance of the CounterCreationDataCollection class. That collection, in turn, can be passed to the PerformanceCounterCategory.Create method to create both the category and the counters. Note that .NET doesn't let you add new performance counters to an existing category.

After running this code, you'll find the new category and the new counters exposed in the Server Explorer tree. You can drag them to the form and work with them just like any other performance counter. However, as things stand, the counters won't have any value. They're waiting for you to create one.

Supplying Values for Performance Counters

There isn't any great trick to supplying your own values for performance counters that you create (note that you can't supply a value for any of the system counters). Here's a bit of code to both modify and display the custom performance counters that I just created:


Private Sub btnShowCustom_Click(ByVal sender As System.Object, _
 ByVal e As System.EventArgs) Handles btnShowCustom.Click
    ' Turn on the custom counter display
    Timer2.Enabled = True
End Sub

Private Sub Timer2_Tick(ByVal sender As System.Object, _
 ByVal e As System.EventArgs) Handles Timer2.Tick
    ' Update and display the custom counters

    ' First, get the counters
    Dim pcRandomCounter As PerformanceCounter = _
     New PerformanceCounter("Developer.com", "RandomCounter", False)
    Dim pcIncreasingCounter As PerformanceCounter = _
     New PerformanceCounter("Developer.com", "IncreasingCounter", False)

    ' Now adjust their values
    pcRandomCounter.RawValue = Int(Rnd(1) * 50000)
    pcIncreasingCounter.Increment()

    ' Display in the list box
    lbPerfData.Items.Add("Random Counter: " & _
     pcRandomCounter.NextValue())
    lbPerfData.Items.Add("Increasing Counter: " & _
     pcIncreasingCounter.NextValue())

End Sub

The trick here is in the constructor for the PerformanceCounter class. The three arguments to this particular form of the constructor are the category name, the counter name, and a boolean that indicates whether the counter should be opened read-only. Supplying False for this boolean indicates that I want a read-write counter. After that, the code can just set the RawValue property of the counter, or it can call the Increment or Decrement methods to adjust the value by 1 unit at a time. Figure 4 shows this code in action.

Setting and reading custom counters

Another Bit of Fit and Finish

I hope you'll agree that working with performance counters in .NET is pretty simple. The next step is to integrate counters into your own applications. While most applications won't need to display the system counters, it can be very helpful to your users to create your own custom counters. For example, suppose you're working on an application to process incoming Web requests for a particular set of files. Would it be helpful to administrators to have counters howing how many requests were successful and how many failed? You bet! And it will only take you a few lines of code to build them.

Mike Gunderloy is the author of over 20 books and numerous articles on development topics, and the lead developer for Larkware. Check out his latest book, Coder to Developer from Sybex. When he's not writing code, Mike putters in the garden on his farm in eastern Washington state.

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