Multithreaded Programming (4)--from CreateThread (the third parameter to the bottom)

Reprinted from: In Case of blog

function CreateThread (    lpthreadattributes:pointer;    Dwstacksize:dword;    Lpstartaddress:tfnthreadstartroutine;    Lpparameter:pointer;    {Parameters of the entry function}    Dwcreationflags:dword;    var Lpthreadid; DWORD;): Thandle; stdcall;

　　　　

　　the argument to the thread entry function is an untyped pointer (Pointer), which allows you to specify any data (which is one of the powerful pointers); This example is the entry function that passes the coordinates of the mouse click on the form to the thread, and creates a thread each time a click on the form, running the following

The code is as follows

Unit unit1;interfaceuses Windows, Messages, sysutils, variants, Classes, Graphics, Controls, Forms, Dialogs;type TF Orm1=class (Tform) procedure formmouseup (sender:tobject;            Button:tmousebutton; Shift:tshiftstate;    X, Y:integer);    End;var form1:tform1;implementation{$R *.dfm}var pt:tpoint; This coordinate point is passed to the thread as a pointer, and it should be the global function Mythreadfun (p:pointer): Integer;    Stdcall;var I:integer;        Pt2:tpoint;    Since the points given by the pointer parameters are changing at any time, the local variables of the thread need to be stored up begin pt2:= PPoint (p) ^;            Convert for i:=0 to 1000000 does begin with Form1.canvas do begin Lock; TextOut (pt2. X, Pt2.            Y, IntToStr (i));        UnLock;    End    End result:= 0;end;procedure tform1.formmouseup (sender:tobject;    Button:tmousebutton; Shift:tshiftstate;    x, Y:integer); var id:dword;begin pt:= Point (x, Y);    CreateThread (nil, 0, @MyThreadFun, @pt, 0, ID); The following wording is better understood, in fact, because PPoint will automatically convert to Pointer's//createthread (nil, 0, @MyThreadFun, Pointer (@pT), 0, ID); End;end. 

　　　　

Form files

Object Form1:tform1 Left  = 0  Top = 0  Caption = ' Form1 '  clientheight =  clientwidth = 229  Color = Clbtnface  font.charset = default_charset  font.color = clwindowtext  font.height = -11  font.name = ' Tahoma '  font.style = []  oldcreateorder = False  OnMouseUp = formmouseup  pixelsperinch =  TextHeight = 13end

　　　　

This example is not rigorous: when a thread lock form is canvas, the other threads are waiting, and the threads are waiting, and the technology is increasing. This is to say: Now does not deal with thread synchronization, synchronization is the most important topic in multi-threading, it is almost

Another tip: The thread function parameter is a 32-bit (4-byte) pointer, and for this example, it can carry X and y respectively for its "high 16-bit" and "low 16-bit", so that the global PT variable is not needed.

In fact, in Windows message that is the way to pass the coordinates, in the Windows message generally high-byte is Y, low byte is x; let's do this so we can use some handy functions for message preparation.

Override This example code (of course the run effect is the same as the form file):

Unit Unit1;interface Windows, Messages, sysutils, variants, Classes, Graphics, Controls, Forms, Dialogs;type tform1= Class (Tform) procedure formmouseup (sender:tobject; Button:tmousebutton; Shift:tshiftstate;    X, Y:integer); End;var form1:tform1;implementation{$R *.dfm}function mythreadfun (p:pointer): Integer;            Stdcall;var I:integer;            Integer is 32bit,4 bytes x, Y:word;    Word is a 16bit,2 byte begin x:= LoWord (Integer (p));    Converts p to integer and obtains its low-byte y:= hiword (Integer (p));    Similar to the above {if you do not use the LoWord, HiWord function, you can do the following:}//x:= Integer (p);        y:= Integer (p) shr 16;            For i:= 0 to 1000000 does begin with Form1.canvas do begin Lock;            TextOut (x, Y, IntToStr (i));        UnLock;    End    End result:= 0;end;procedure tform1.formmouseup (sender:tobject;    Button:tmousebutton; Shift:tshiftstate;    X, Y:integer); var Id:dword;    Num:integer;begin num:= Makelong (X, Y); {If you do not use Makelong, MAKEWPAFunctions such as RAM, Makelparam, Makeresult, etc. can be as follows:}//num:= Y SHL +x;    CreateThread (nil, 0, @MuThreadFun, Ptr (num), 0, ID); {Above Ptr is a function that converts a number to a pointer, and of course it can}//createthread (nil, 0, @MyThreadFun, Pointer (num), 0, ID); End;end.

　　　

Multithreaded Programming (4)--from CreateThread (the third parameter to the bottom)