Accurately Measure Elapsed Time Using Delphi Performance Counter

For routine desktop database applications, adding a single second to a task's execution time rarely makes a difference to end users — but when you need to process millions of tree leaves or generate billions of unique random numbers, speed-of-execution becomes more important.

Timing Out Your Code

In some applications, very accurate, high-precision time measurement methods are important and luckily Delphi provides a high-performance counter to qualify these times.

Using RTL's Now Function

One option uses the Now function. Now, defined in the SysUtils unit, returns the current system date and time.

A few lines of code measure elapsed time between the "start" and "stop" of some process:

The Now function returns the current system date and time that is accurate up to 10 milliseconds (Windows NT and later) or 55 milliseconds (Windows 98).

For very small intervals the precision of "Now" is sometimes not enough.

Using Windows API GetTickCount

For even more precise data, use the GetTickCount Windows API function. GetTickCount retrieves the number of milliseconds that have elapsed since the system was started, but the function only has the precision of 1 ms and may not always be accurate if the computer remains powered-up for long periods of time.

The elapsed time is stored as a DWORD (32-bit) value. Therefore, the time will wrap around to zero if Windows is run continuously for 49.7 days.

GetTickCount is also limited to the accuracy of the system timer (10 / 55 ms).

High Precision Timing Out Your Code

If your PC supports a high-resolution performance counter, use the QueryPerformanceFrequency Windows API function to express the frequency, in counts per second. The value of the count is processor dependent.

The QueryPerformanceCounter function retrieves the current value of the high-resolution performance counter. By calling this function at the beginning and end of a section of code, an application uses the counter as a high-resolution timer.

The accuracy of high-resolution timers is around a few hundred nanoseconds. A nanosecond is a unit of time representing 0.000000001 seconds -- or 1 billionth of a second.

TStopWatch: Delphi Implementation of a High-Resolution Counter

With a nod to .Net naming conventions, a counter like TStopWatch offers a high-resolution Delphi solution for precise time measurements.

TStopWatch measures elapsed time by counting timer ticks in the underlying timer mechanism.

• The IsHighResolution property indicates whether the timer is based on a high-resolution performance counter.
• The Start method starts measuring elapsed time.
• The Stop method stops measuring elapsed time.
• The ElapsedMilliseconds property gets the total elapsed time in milliseconds.
• The Elapsed property gets the total elapsed time in timer ticks.

Here's an example of usage: