Delphi : thread safely suspend in excute module - delphi

Question

I am a beginner of DELPHI.
I have to develop a application based on thread.
How can I suspend thread in thread execute function, not in UI thread....
Please give me sample

Answer 1

Suspend a thread simply by pausing. For instance you can sleep for a specified amount of time. Or you can wait on a synchronisation object. For instance, you might wait on an event. When another thread signals that event, the paused thread will resume.

Answer 2

Assuming you are working on Windows platform...
There are many ways to suspend a thread. Which one to use depends largely on when/why it should resume, and whether or not the thread has a message queue.
The point about the message queue is especially important if you need to suspend a thread for a long time. Any thread not processing Windows message can hang many operations, DDE communications, message broadcast, etc. The contract being "If your thread has a message queue, it NEEDS to treat them.", and it needs to do so in a timely fashion. In this case, I would suggest calling MsgWaitForMultipleObjects from the thread. The function works even if you are not waiting on any objects, which allows you to both wait on messages and have a timeout. WaitMessage could work too, but it doesn't timeout which has, amongst other implication, that you would need to send a message to the thread after terminating it, otherwise, it might never terminate.
If the thread does not have a message queue, then there are plenty of options. Sleep is a valid one if you want to wait for a specific amount of time. If you want to wait for a specific event to resume the thread, the TEvent class might be what you are looking for.
Hard to give a definitive answer without more details.

Answer 3

This example runs OK. By working with threads, by very careful. This is a very difficult section.
unit Unit1;
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls;
type
TMyThread=class(tthread)
FEvent:THandle;
private
procedure SetText;
protected
procedure Execute;override;
public
constructor Create(CreateSuspended:Boolean=false);
destructor Destroy; override;
procedure Start;
procedure Stop;
procedure StopAndTerminate;
end;
type
TForm1 = class(TForm)
OutMem: TMemo;
BtnStart: TButton;
BtnStop: TButton;
procedure FormCreate(Sender: TObject);
procedure FormDestroy(Sender: TObject);
procedure BtnStartClick(Sender: TObject);
procedure BtnStopClick(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form1: TForm1;
mythread:tmythread;
implementation
{$R *.dfm}
procedure TForm1.FormCreate(Sender: TObject);
begin
mythread:=tmythread.Create();
end;
{ TMyThread }
constructor TMyThread.Create(CreateSuspended: Boolean);
begin
Inherited Create(CreateSuspended);
FEvent:=CreateEvent(nil,true,false,pchar(inttostr(handle)));
end;
destructor TMyThread.Destroy;
begin
CloseHandle(FEVENT);
inherited;
end;
procedure TMyThread.Execute;
begin
while not terminated do
begin
WaitForSingleObject(FEvent,INFINITE);
if terminated then exit;
Synchronize(SetText);
{ Methods and properties of objects in visual components (forms, buttons, memo and other)
can only be used in a method called using Synchronize}
end;
end;
procedure TMyThread.SetText;
begin
form1.OutMem.Lines.Append(inttostr(gettickcount));
application.ProcessMessages;
// Application.ProcessMessages method must be call ONLY in MainThread.
// by using Synchronize, SetText procedure will be run in MainThread.
end;
procedure TMyThread.Start;
begin
SetEvent(FEVENT);
end;
procedure TMyThread.Stop;
begin
ResetEvent(FEVENT);
end;
procedure TMyThread.StopAndTerminate;
begin
Terminate;
PulseEvent(FEVENT);
end;
procedure TForm1.FormDestroy(Sender: TObject);
begin
mythread.StopAndTerminate;
mythread.WaitFor;
mythread.Free;
end;
procedure TForm1.BtnStartClick(Sender: TObject);
begin
mythread.Start;
end;
procedure TForm1.BtnStopClick(Sender: TObject);
begin
mythread.Stop;
end;
end.