pinvoke.net: Edit: kernel32.QueryPerformanceCounter

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Summary: The QueryPerformanceCounter API

!!!!C# Signature:
 [DllImport("kernel32.dll", SetLastError=true)]
 static extern bool QueryPerformanceCounter(out long lpPerformanceCount);

!!!!VB.NET Signature:
 <DllImport("kernel32.dll", SetLastError:=True)> _
 Shared Function QueryPerformanceCounter(ByRef lpPerformanceCount As Long) As Boolean
 End Function

!!!!Manage C++ Signature:
 [DllImport("Kernel32.dll", SetLastError=true)]
 extern bool QueryPerformanceCounter(long *lpPerformanceCount);

!!!!User-Defined Types:
None.

!!!!Notes:
Arguably one of the most frequently used and most important PInvokes used, this is the only way in .NET to get a high performance counter for measurement, unique seeding of Random Variables (although you could perhaps transfer a GUID to a numeric equivalent), and in general what this global consultant would consider a 'must include' in almost any application where Instrumentation is a must.

!!!!Tips & Tricks:
For this particular method, execution time is often critical.  Security can be traded for additional speed by applying the SuppressUnmanagedCodeSecurity attribute to the method declaration.  This will prevent the runtime from doing a security stack walk at runtime.

[DllImport("kernel32.dll"),SuppressUnmanagedCodeSecurity]
 static extern bool QueryPerformanceCounter(out long lpPerformanceCount);

If you are interested in this API you are probably also looking for the QueryPerformanceFrequency API.

!!!!VB.NET Sample Code:
 Imports System.Runtime.InteropServices
 Imports System.Security

Friend Enum TimeState
    Started
    Stopped

End Enum

Public Class HighResTimer

<DllImport("kernel32.dll"), SuppressUnmanagedCodeSecurity()> _
    Private Shared Function QueryPerformanceCounter(ByRef lpPerformanceCount As Long) As Boolean
    End Function

<DllImport("kernel32.dll"), SuppressUnmanagedCodeSecurity()> _
    Private Shared Function QueryPerformanceFrequency(ByRef lpPerformanceFreq As Long) As Boolean
    End Function

Private Shared freq As Long
    Shared Sub New()
        If Not QueryPerformanceFrequency(freq) Then

Throw New System.ComponentModel.Win32Exception
        End If
    End Sub

Private startTime, endTime As Long
    Private _duration As Double
    Private state As TimeState = TimeState.Stopped

Public Sub Start()
        If state = TimeState.Started Then
            Throw New ApplicationException("Cant' start, already started")
        End If
        state = TimeState.Started
        QueryPerformanceCounter(startTime)
    End Sub

Public Function [Stop]() As Double
        QueryPerformanceCounter(endTime)
        If state = TimeState.Stopped Then
            Throw New ApplicationException("Cant' start, already started")
        End If
        state = TimeState.Stopped
        _duration = ((endTime - startTime) / freq)
        Return _duration
    End Function

Public ReadOnly Property Duration() As Double
        Get
            If state = TimeState.Started Then
                Throw New ApplicationException("Must call Stop() first")
            End If
            Return _duration
        End Get
    End Property

End Class

!!!!C# Sample Code:
    using System;
    using System.Runtime.InteropServices;

public class HighResTimer {
	[DllImport("kernel32.dll", SetLastError = false)]
	private static extern bool QueryPerformanceCounter(out long lpPerformanceCount);

[DllImport("kernel32.dll", SetLastError = false)]
	private static extern bool QueryPerformanceFrequency(out long lpPerformanceFreq);

private static long freq;

static HighResTimer() {
		if (!QueryPerformanceFrequency(out freq)) {
			throw new System.ComponentModel.Win32Exception();
		}
	}

private long startTime, endTime;
	private double duration;

private bool timerStarted;

public void Start() {
		if (timerStarted) {
			throw new ApplicationException("Cant' start, already started");
		}

timerStarted = true;
		QueryPerformanceCounter(out startTime);
	}

public void Stop() {
		QueryPerformanceCounter(out endTime);

if (!timerStarted) {
			throw new ApplicationException("Cant' start, already started");
		}

duration = (((endTime - startTime) / (double)freq));

timerStarted = false;
	}

public double Duration {
		get {
			if (timerStarted) {
				throw new ApplicationException("Must call Stop() first");
			}
			return duration;
		}
	    }
        }

static void Main(string[] args) {
             HighResTimer hrtimer = new HighResTimer();
             hrtimer.Start();
             //some code... For example:
             System.Threading.Thread.Sleep(1000);
             //End example
             hrtimer.Stop();
             double time = hrtimer.Duration * 1000;

Console.WriteLine("Time in miliseconds " + time.ToString());
        }

!!!!Alternative Managed API:
There is a class named StopWatch (namespace System.Diagnostics) who uses the Performance Counter and Frequency functions.  This class is within the 2.0 version of the .NET Framework.

Documentation: QueryPerformanceCounter@msdn on MSDN, SuppressUnmanagedCodeSecurityAttribute@msdn on MSDN