how to run code in background

[rcmz]

hi,

How can I run code in background?

In Delphi I uses TBackgroundWorker

Any ideas?

TIA
rcmz

[cdbc]

Hi
I think, underneath "TBackgroundWorker" is a thread, sooo use a thread 
Regards Benny

[Zvoni]

TThread?

[AlanTheBeast]

TThread?

Without objections, I would do:

Code: Pascal  [Select][+][-]

1. Function Achunkofrealpascal (p:pointer):ptrint;
2. VAR
3.    z:somerecord;
4. BEGIN
5.    z := somerecord(p^);
6.    While not z.Shutdown do
7.       begin
8.          stuff;
9.          sleep(z.SleepPeriod);
10.       end;
11.    exit(0);
12. END;
13.  
14. //somewhere in main:
15.   With BlockOfData do
16.     begin
17.        Shutdown := false;
18.        SleepPeriod := 100;  //ms
19.        Otherstuff := ...
20.    end;
21.   TID := BeginThread(@Achunkofrealpascal, @Blockofdata);

Notes: use flags or data in the referenced record to send signals into/out of the background thread.

You can kill the thread using TID as a reference, or (in the case above) by setting Shutdown to true.

[Jiyahana]

You can use TThread specifically by creating a descendant of the TThread class. Implement the code that needs to run in the background within the execute method of the TThread descendant.

Example.

uses
  System.Classes;

type
  TMyBackgroundThread = class(TThread)
  protected
    procedure Execute; override;
  end;

procedure TMyBackgroundThread.Execute;
begin
  // Perform the background operations here
  // Ensure synchronization if accessing UI elements
end;

Instantiate and start the background thread where needed in your Delphi application.

var
  MyThread: TMyBackgroundThread;
begin
  MyThread := TMyBackgroundThread.Create(True); // Create suspended
  MyThread.FreeOnTerminate := True; // Auto-free thread when done
  MyThread.Start; // Start the background thread
end;

I hope example will help.

[Thaddy]

Not really.
Much easier are the options possible for TThread,ExecuteInThread()

[rcmz]

Thx,

I will try it.

[KodeZwerg]

If its something where you not need to take much care about ...

Code: Pascal  [Select][+][-]

1. procedure ThreadProc;
2. begin
3.   // all code that needs to run threaded belong in here
4.   Sleep(5000);
5.   Form1.Button1.Enabled := True;
6. end;
7.  
8. procedure TForm1.Button1Click(Sender: TObject);
9. var
10.   AProc: TProcedure;
11. begin
12.   Button1.Enabled := False;
13.   AProc := @ThreadProc;
14.   TThread.CreateAnonymousThread(AProc).Start;
15. end;

Have in mind, code will run to its endphase even if you closed your process somehow.

[Thaddy]

I would still also save the result of the not so anonymous thread, since it returns a valid TThread that can be used later when needed. Comes to mind TThread.CheckTerminated.

[Zvoni]

I would still also save the result of the not so anonymous thread, since it returns a valid TThread that can be used later when needed. Comes to mind TThread.CheckTerminated.

Nevermind WaitFor and OnTerminated

[CM630]

Code: Pascal  [Select][+][-]

1. procedure ThreadProc;
2. begin
3.   // all code that needs to run threaded belong in here
4.   Sleep(5000);
5.   Form1.Button1.Enabled := True;
6. end;
7.  
8. procedure TForm1.Button1Click(Sender: TObject);
9. var
10.   AProc: TProcedure;
11. begin
12.   Button1.Enabled := False;
13.   AProc := @ThreadProc;
14.   TThread.CreateAnonymousThread(AProc).Start;
15. end;

Have in mind, code will run to its endphase even if you closed your process somehow.

Can this code be modified in order to pass a parameter to ThreadProc? For example, procedure ThreadProc(Sender: TObject);

[cdbc]

Hi
Yes, in multiple ways 
But I think, the easiest way is to use one of its siblings, namely:

Code: Pascal  [Select][+][-]

1.     Class Function ExecuteInThread(AMethod : TThreadExecuteCallback; AData : Pointer = Nil; AOnTerminate: TNotifyCallBack = Nil) : TThread; overload;static;

This class method is /lifted/ from TThread in FPC 3.2.2...
With that you get:
· a proc to execute in the thread
· a 'pointer' param to said procedure - remember 'TObject' is just a pointer...
·· the pointer param, you just typecast to the proper type, first thing in proc.
· a callback-proc to execute, when the thread terminates...

What more could you ask for?!? 
Oh and btw. the 'AData' & 'AOnTerminate' can be nil, without hassle.
Try and give that a whirl...
Regards Benny

Ps.: It's all there in the source, have a good 'looksee' in there...

[CM630]

I did not find examples for ExecuteInThread (except some in delphimode), maybe I should try harder.

What I did is:

Code: Pascal  [Select][+][-]

1.   TUpdatePortsThread = class(TThread)
2.     private
3.  
4.     protected
5.       procedure Execute; override;
6.     public
7.       Owner: TCustomComboBox;
8.       Constructor Create(CreateSuspended : boolean);
9.   end;
10.  
11.  
12. ...
13. constructor TUpdatePortsThread.Create(CreateSuspended : boolean);
14. begin
15.   inherited Create(CreateSuspended);
16.   FreeOnTerminate := True;
17. end;
18.  
19. procedure TUpdatePortsThread.Execute;
20. begin
21.   try
22.     Application.QueueAsyncCall(@TSerialSelector(Owner).UpdatePorts,0);
23.   finally
24.     Terminate;
25.   end; //try
26. end;

The program crashes, I have a suspicion why it does, but anyway, when it does not crash it hangs until called function is complete 
I am wondering if is QueueAsyncCall that hangs my interface, despite using a thread.

[cdbc]

Hi
I have to run an errin, so if you can wait a little bit, I'll write you an example of use of the above 'ExecuteInThread', when I get back...
Otherwise I'll need more info, to be able to help you... Ok?

Ps.: Your use of 'QueueAsyncCall' in this situ, defeats the use of a thread, the code you want run, runs in the main thread!!! Not exactly your aim 

Regards Benny

[CM630]

...
I have to run an errin, so if you can wait a little bit, I'll write you an example of use of the above 'ExecuteInThread', when I get back...
...

Thanks, waiting a few days (weeks) is not an issue. But if Threads are not a cure, there is no point to write an example (though writing to wiki is usually a good thing).

If I do not run the routine with QueueAsyncCall the app crashes (https://forum.lazarus.freepascal.org/index.php/topic,24490.msg572378.html#msg572378) - sometimes executing one of the lines of the routine takes more than five seconds, when it happens faster, everything is fine.

So if threads do not help, what else could I do? Run the routine in a virtual form and somehow signal the main form when the data is ready?
Or maybe it I should seek a less impatient WMI query routine.

Edit: I made some changes to the WMI caller; it seems to work without asynccall now. I will retry with threads these days.