Stopwatch - a High-Resolution code timer class

• Download source - 1.03 Kb

Introduction

Creating an application requires precisely measuring how long specific operations take to complete. You may be searching for performance bottlenecks prior to shipping, measuring to ensure that changes do not unexpectedly degrade performance, or (in my case), testing alternative architectural approaches. You can use a real stopwatch and measure your application's response time, but fumbling and other miscues will render about a 1/4 second (0.25) resolution, at best. The Tick count available in VB is more accurate and fumble-proof, and it has a resolution of about 10ms (0.01).

The Windows Kernel includes a much finer-grained tick counter, which it exposes in an API call named QueryPerformanceCounter. This timer boasts near microsecond (0.000001) resolution and is easily callable from VB. The Stopwatch class wraps this call, masking all the sordid details.

Background

Stopwatch merely implements the code described in Microsoft Knowledge Base article 306978 (10/02) in a easily used class. I can't claim any originality - the technical details are by Microsoft, and the "stopwatch" class idea is from an old C++ article I read in 1993 or so (and implemented back then using mmsystem.dll in Windows 3.1; yikes!).

Using the code

There are two ways to use Stopwatch: create a Stopwatch instance and tell it to ReportToConsole when the code being measured is done; or reuse a single Stopwatch instance again and again, saving off elapsed time values each time.

Here's a very simple way to display how long a process takes on the console:

Dim swatch as New Stopwatch("My process")
'Perform my process (presumably a loop or one or more method calls)
swatch.ReportToConsole()

'Output: "My process (0.332131039000767 seconds)"

You can use the same Stopwatch instance repeatedly:

Dim firstResult, secondResult as Double
Dim swatch as New Stopwatch()
'...perform process...
firstResult = swatch.ElapsedTime() ' Note: ElapsedTime does 
                                   ' not stop the clock
'...more process work...
swatch.Done()
secondResult = swatch.ElapsedTime()
Console.WriteLine(
    "First took {0} seconds; First and Second took {1} seconds.", _
    firstResult, secondResult)
swatch.Start()
'...a third bunch of work...
swatch.Done()
MsgBox("The third thing took " & CStr(swatch.ElapsedTime()) & " seconds.")

'Output: "First took 0.0131530683368976 seconds; 
'First and Second took 8.8372527793337 seconds."

Points of Interest

This code also manages to demonstrate how to call the Windows API and how to define a custom exception class. Microsoft Knowledge Base article 172338 describes how to use QueryPerformanceCounter in VB 6 and other environments, and it contributed the idea of calculating the API call overhead so that it could be subtracted from the result.