Mega Code Archive
Tthreadfunc - defines the function to be called by beginthread
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type TThreadFunc : Function(Parameter : Pointer) : Integer;
Description
The TThreadFunc type defines a function rather than data. This function is normally used as a parameter to a BeginThread function call when starting a separate thread of operation. The defined function performs the thread activities.
The return code for the function is the exit code for the thread.
Related commands
BeginThread Begins a separate thread of code execution
EndThread Terminates a thread with an exit code
ThreadVar Defines variables that are given separate instances per thread
Example code : A simple example
// Full Unit code.
// -----------------------------------------------------------
// You must store this code in a unit called Unit1 with a form
// called Form1 that has an OnCreate event called FormCreate.
unit Unit1;
interface
uses
Forms, Dialogs, Windows, SysUtils;
type
TMsgRecord = record
thread : Integer;
msg : string[30];
end;
TForm1 = class(TForm)
procedure FormCreate(Sender: TObject);
end;
var
Form1: TForm1;
Implementation
{$R *.dfm} // Include form definitions
ThreadVar // We must allow each thread its own instances
// of the passed record variable
msgPtr : ^TMsgRecord;
// Private thread procedure to show a string
function ShowMsg(Parameter : Pointer) : Integer;
begin
// Set up a 0 return value
Result := 0;
// Map the pointer to the passed data
// Note that each thread has a separate copy of msgPtr
msgPtr := Parameter;
// Display this message
ShowMessagePos('Thread '+IntToStr(msgPtr.thread)+' '+msgPtr.msg,
200*msgPtr.thread, 100);
// End the thread
EndThread(0);
end;
procedure TForm1.FormCreate(Sender: TObject);
var
id1, id2 : LongWord;
thread1, thread2 : Integer;
msg1, msg2 : TMsgRecord;
showMsgFunc : TThreadFunc;
begin
// Set up the thread function
showMsgFunc := Addr(ShowMsg);
// Set up our display messages
msg1.thread := 1;
msg1.msg := 'Hello World';
msg2.thread := 2;
msg2.msg := 'Goodbye World';
// Start the first thread running asking for users first name
thread1 := BeginThread(nil,
0,
showMsgFunc,
Addr(msg1),
0,
id1);
// And also ask for the surname
thread2 := BeginThread(nil,
0,
showMsgFunc,
Addr(msg2),
0,
id2);
// Ensure that the threads are only closed when all done
ShowMessagePos('Press this when other dialogs finished.', 200, 300);
// Finally, tidy up by closing the threads
CloseHandle(thread1);
CloseHandle(thread2);
end;
end.
Three dialogs are displayed:
Thread 1 Hello World
Thread 2 Goodbye World
Press this when other dialogs finished.
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