Delphi中三種延時方法及其定時精度分析(轉(zhuǎn)載)
在Delphi中，通?？梢杂靡韵氯N方法來實現(xiàn)程序的延時，即TTtimer控件，Sleep函數(shù)，GetTickCount函數(shù)。但是其精度是各不相同的。
一、三種方法的簡單介紹
1）TTtimer控件
TTtimer控件的實質(zhì)是調(diào)用Windows API定時函數(shù)SetTimer和KillTimer來實現(xiàn)的，并簡化了對WM_TIMER 消息的處理過程。通過設(shè)置OnTimer事件和Interval屬性，我們可以很方便的產(chǎn)生一些簡單的定時事件。
2）Sleep函數(shù)
Sleep函數(shù)用來使程序的執(zhí)行延時給定的時間值。Sleep的調(diào)用形式為Sleep(milliseconds)，暫停當(dāng)前的進程milliseconds毫秒。Sleep的實現(xiàn)方法其實也是調(diào)用Windows API的Sleep函數(shù)。例如：
sleep(1000); //延遲1000毫秒
Sleep會引起程序停滯，如果你延遲的時間較長的話，你的程序?qū)⒉荒軌蝽憫?yīng)延時期間的發(fā)生的其他消息，所以程序看起來好像暫時死機。
3）GetTickCount函數(shù)
在主程序中延時，為了達到延時和響應(yīng)消息這兩個目的，GetTickCount()構(gòu)成的循環(huán)就是一種廣為流傳的方法。例如：
procedure Delay(MSecs: Longint);
//延時函數(shù)，MSecs單位為毫秒(千分之1秒)
var
FirstTickCount, Now: Longint;
begin
FirstTickCount := GetTickCount();
repeat
Application.ProcessMessages;
Now := GetTickCount();
until (Now - FirstTickCount >= MSecs) or (Now < FirstTickCount);
end;
二、高精度的微妙級性能計數(shù)器（high-resolution performance counter）介紹
為了比較以上方法的精度，首先需要找到一個參考的定時器。在這里，我提供了兩個參考的定時器。一是用單片機每隔1.024ms產(chǎn)生一個實時中斷RTI，作為計數(shù)器；二是選用了一個高精度的微妙級性能計數(shù)器（參見： http://msdn.microsoft.com/msdnmag/issues/04/03/HighResolutionTimer/default.aspx ，或者 http://community.csdn.net/Expert/FAQ/FAQ_Index.asp?id=200249
）
1）計數(shù)器的Delphi源代碼
{
A high-precision counter/timer. Retrieves time differences
downto microsec.
Quick Reference:
THPCounter inherits from TComponent.
Key-Methods:
Start: Starts the counter. Place this call just before the
code you want to measure.
Read: Reads the counter as a string. Place this call just
after the code you want to measure.
ReadInt: Reads the counter as an Int64. Place this call just
after the code you want to measure.
--------------------------------------------------------------------------------
}
unit HPCounter;
interface
uses
SysUtils, WinTypes, WinProcs, Messages, Classes, Graphics, Controls,
Forms, Dialogs, StdCtrls, ExtCtrls;
type
TInt64 = TLargeInteger;
THPCounter = class(TComponent)
private
Frequency: TLargeInteger;
lpPerformanceCount1: TLargeInteger;
lpPerformanceCount2: TLargeInteger;
fAbout: string;
procedure SetAbout(Value: string);
{ Private declarations }
public
constructor Create(AOwner: TComponent); override;
destructor Destroy; override;
procedure Start;
function Read: string;
function ReadInt: TLargeInteger;
{ Private declarations }
published
property About: string read fAbout write SetAbout;
{ Published declarations }
end;
procedure Register;
implementation
procedure Register;
begin
RegisterComponents(‘MAs Prod.‘, [THPCounter]);
end;
constructor THPCounter.Create(AOwner: TComponent);
begin
inherited Create(AOwner);
fAbout:= ‘Version 1.1, 2000® Mats Asplund, EMail: masprod@telia.com, Site: http:///masdp
end;
destructor THPCounter.Destroy;
begin
inherited Destroy;
end;
function THPCounter.Read: string;
begin
QueryPerformanceCounter(TInt64((@lpPerformanceCount2)^));
QueryPerformanceFrequency(TInt64((@Frequency)^));
Result:=IntToStr(Round(1000000 * (lpPerformanceCount2 -
lpPerformanceCount1) / Frequency));
end;
function THPCounter.ReadInt: TLargeInteger;
begin
QueryPerformanceCounter(TInt64((@lpPerformanceCount2)^));
QueryPerformanceFrequency(TInt64((@Frequency)^));
Result:=Round(1000000 * (lpPerformanceCount2 -
lpPerformanceCount1) / Frequency);
end;
procedure THPCounter.SetAbout(Value: string);
begin
Exit;
end;
procedure THPCounter.Start;
begin
QueryPerformanceCounter(TInt64((@lpPerformanceCount1)^));
end;
end.
2）使用方法：
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Classes, Graphics, Controls, Forms, Dialogs,
HPCounter, StdCtrls;
type
TForm1 = class(TForm)
Button1: TButton;
Edit1: TEdit;
Label1: TLabel;
Label2: TLabel;
procedure Button1Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.DFM}
procedure TForm1.Button1Click(Sender: TObject);
begin
Edit1.Text:= ‘‘;
Application.ProcessMessages;
with THPCounter.Create(Self) do
begin
Start;
// Place code to measure here
Sleep(1000);
// Place code to measure here
Edit1.Text:=Read;
Free;
end;
end;
end.
二、三種方法的精度比較
為了比較，采用以上3種方法，分別設(shè)置延時時間為1ms、2ms、5ms、10ms、20ms、50ms、100ms、200ms、500ms、1000ms，循環(huán)次數(shù)為5次，得到實際的延時時間。
1）TTtimer控件
實際延時時間（ms）
1ms： 8.012 21.551 6.875 21.647 9.809
2ms： 9.957 20.675 14.671 11.903 20.551
5ms： 9.952 20.605 9.924 20.705 12.682
10ms：14.852 9.96 21.547 9.82 20.634
20ms：27.512 34.291 26.427 31.244 30.398
50ms：61.196 61.307 64.027 62.048 63.059
100ms：102.495 108.408 112.318 110.322 102.531
200ms：193.955 202.135 207.016 205.082 202.194
500ms：496.659 500.534 503.398 495.551 500.394
1000ms：999.699 1003.576 993.698 1004.443 995.625
2）Sleep函數(shù)
1ms： 1.895 1.895 1.896 1.897 1.898
2ms： 2.868 2.874 2.852 2.872 2.869
5ms： 5.8 5.797 5.79 5.79 5.791
10ms：10.675 10.683 10.611 10.669 10.67
20ms：20.404 20.434 20.447 20.477 20.368
50ms：50.67 50.691 50.69 50.682 50.671
100ms：100.515 100.469 100.484 100.481 100.484
200ms：200.101 200.126 199.892 200.066 200.108
500ms：499.961 499.961 499.958 499.961 499.96
1000ms：1000.034 1000.04 1000.03 1000.018 1000.029
3）GetTickCount函數(shù)
1ms： 15.54 15.596 15.527 15.566 15.838
2ms： 15.561 15.563 15.603 15.477 15.571
5ms： 15.519 15.549 15.569 15.666 15.394
10ms：15.558 15.561 15.522 15.568 15.518
20ms：31.186 31.137 31.17 31.17 31.19
50ms：62.445 62.4 63.893 60.88 62.404
100ms：109.276 109.298 109.273 109.28 109.28
200ms：203.027 203.084 203.021 203.027 203.046
500ms：499.959 499.961 499.963 499.967 499.965
1000ms：1000.023 1000.022 1000.026 1000.029 1000.021
可見，相對而言，Sleep的精度最高，尤其是在10ms以內(nèi)的延時，只有sleep函數(shù)才能夠做到。TTimer控件的定時精度最差，而且穩(wěn)定性不好，波動很大。GetTickCount函數(shù)所能實現(xiàn)的最短延時為15ms左右，穩(wěn)定性相對TTimer要好一些。
