如何：使用高分辨率计时器
更新：2007 年 11 月
一些设备支持高分辨率计时器。此计时器（如果存在）提供的测量结果比使用 TickCount 属性获得的测量结果（分辨率为 1 毫秒）更加精确。在看重准确的时间测量的应用程序中，高分辨率计时器可提供最佳结果。例如，当动画基于高分辨率计时器时，一些 Direct3D 应用程序能够更加平滑地显示。也可以在应用程序中使用此计时器来确定执行某个方法或代码部分所需的时间。
示例
此代码示例提供一个类，使您能够在 Windows CE 上的托管代码中轻松使用高分辨率计时器。此示例具有以下特性：
Windows CE 中本机方法的平台调用声明。
用于获取高分辨率计数器的频率的属性。
用于获取高分辨率计数器的值的属性。
支持 TickCount 属性的实现以作为在 QueryPerformanceCounter 函数不受支持或被模拟时的后备方式。
有关如何使用高分辨率计数器对操作进行计时的示例。
Public Class HiResTimer
Private isPerfCounterSupported As Boolean = False
Private timerFrequency As Int64 = 0
' Windows CE native library with QueryPerformanceCounter().
Private Const [lib] As String = "coredll.dll"
Public Declare Function QueryPerformanceCounter Lib "Coredll.dll" _
(ByRef count As Int64) As Integer
Public Declare Function QueryPerformanceFrequency Lib "Coredll.dll" _
(ByRef timerFrequency As Int64) As Integer
Public Sub New()
' Query the high-resolution timer only if it is supported.
' A returned frequency of 1000 typically indicates that it is not
' supported and is emulated by the OS using the same value that is
' returned by Environment.TickCount.
' A return value of 0 indicates that the performance counter is
' not supported.
Dim returnVal As Integer = QueryPerformanceFrequency(timerFrequency)
If returnVal <> 0 AndAlso timerFrequency <> 1000 Then
' The performance counter is supported.
isPerfCounterSupported = True
Else
' The performance counter is not supported. Use
' Environment.TickCount instead.
timerFrequency = 1000
End If
End Sub
Public ReadOnly Property Frequency() As Int64
Get
Return timerFrequency
End Get
End Property
Public ReadOnly Property Value() As Int64
Get
Dim tickCount As Int64 = 0
If isPerfCounterSupported Then
' Get the value here if the counter is supported.
QueryPerformanceCounter(tickCount)
Return tickCount
Else
' Otherwise, use Environment.TickCount
Return CType(Environment.TickCount, Int64)
End If
End Get
End Property
Shared Sub Main()
Dim timer As New HiResTimer()
' This example shows how to use the high-resolution counter to
' time an operation.
' Get counter value before the operation starts.
Dim counterAtStart As Int64 = timer.Value
' Perform an operation that takes a measureable amount of time.
Dim count As Integer
For count = 0 To 9999
count += 1
count -= 1
Next count
' Get counter value after the operation ends.
Dim counterAtEnd As Int64 = timer.Value
' Get time elapsed in tenths of milliseconds
Dim timeElapsedInTicks As Int64 = counterAtEnd - counterAtStart
Dim timeElapseInTenthsOfMilliseconds As Int64 = timeElapsedInTicks * 10000 / timer.Frequency
MessageBox.Show("Time Spent in operation (tenths of ms) " + timeElapseInTenthsOfMilliseconds.ToString + vbLf + "Counter Value At Start: " + counterAtStart.ToString + vbLf + "Counter Value At End : " + counterAtEnd.ToString + vbLf + "Counter Frequency : " + timer.Frequency.ToString)
End Sub
End Class
public class HiResTimer
{
private bool isPerfCounterSupported = false;
private Int64 frequency = 0;
// Windows CE native library with QueryPerformanceCounter().
private const string lib = "coredll.dll";
[DllImport(lib)]
private static extern int QueryPerformanceCounter(ref Int64 count);
[DllImport(lib)]
private static extern int QueryPerformanceFrequency(ref Int64 frequency);
public HiResTimer()
{
// Query the high-resolution timer only if it is supported.
// A returned frequency of 1000 typically indicates that it is not
// supported and is emulated by the OS using the same value that is
// returned by Environment.TickCount.
// A return value of 0 indicates that the performance counter is
// not supported.
int returnVal = QueryPerformanceFrequency(ref frequency);
if (returnVal != 0 && frequency != 1000)
{
// The performance counter is supported.
isPerfCounterSupported = true;
}
else
{
// The performance counter is not supported. Use
// Environment.TickCount instead.
frequency = 1000;
}
}
public Int64 Frequency
{
get
{
return frequency;
}
}
public Int64 Value
{
get
{
Int64 tickCount = 0;
if (isPerfCounterSupported)
{
// Get the value here if the counter is supported.
QueryPerformanceCounter(ref tickCount);
return tickCount;
}
else
{
// Otherwise, use Environment.TickCount.
return (Int64)Environment.TickCount;
}
}
}
static void Main()
{
HiResTimer timer = new HiResTimer();
// This example shows how to use the high-resolution counter to
// time an operation.
// Get counter value before the operation starts.
Int64 counterAtStart = timer.Value;
// Perform an operation that takes a measureable amount of time.
for (int count = 0; count < 10000; count++)
{
count++;
count--;
}
// Get counter value when the operation ends.
Int64 counterAtEnd = timer.Value;
// Get time elapsed in tenths of a millisecond.
Int64 timeElapsedInTicks = counterAtEnd - counterAtStart;
Int64 timeElapseInTenthsOfMilliseconds =
(timeElapsedInTicks * 10000) / timer.Frequency;
MessageBox.Show("Time Spent in operation (tenths of ms) "
+ timeElapseInTenthsOfMilliseconds +
"\nCounter Value At Start: " + counterAtStart +
"\nCounter Value At End : " + counterAtEnd +
"\nCounter Frequency : " + timer.Frequency);
}
}
编译代码
此示例需要引用下面的命名空间：