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.