[Solved] Thread problems on Linux Ubuntu 12.04 Lazarus 1.0
lazarus / 32-Linux

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Max JRB · 2012-10-04 18:22

Hi, i'm new on Lazarus, and this is my fisrt question on the forum.

I'm having problems when I run an application using threads, on
windows works fine, but when I run it on Linux Ubuntu 12.04 my app
crashes.

It's a very small app just to understand threads.

this is the code:

for type:

Code: [Select]unit Unit1;

{$mode objfpc}{$H+}

interface

uses
  Classes, SysUtils, FileUtil, Forms, Controls, Graphics, Dialogs,
StdCtrls,
  ComCtrls;

type

  { TMyThread }

  TMyThread = class(TThread)
  private
    fStatusText: string;
    procedure CambiaLabel();
  protected
    procedure Execute; override;
  public
    constructor Create(CreateSuspended: boolean);
  end;

implementation

{$R *.lfm}

{ TMyThread }
procedure TMyThread.CambiaLabel();
begin
    Form1.Label1.Caption:=fStatusText;

        Form1.ProgressBar1.StepIt;

    if Form1.ProgressBar1.Position = Form1.ProgressBar1.Max then begin
       Form1.miHilo.Terminate;
       Form1.ProgressBar1.Position := 0;
    end;
end;

procedure TMyThread.Execute;
var
  newStatus : string;
begin
  fStatusText := 'TMyThread comenzando...';
  fStatusText := 'TMyThread Corriendo ...';
  while (not Terminated) and (true {any condition required}) do begin

    //here goes the code of the main thread loop

     Synchronize(@CambiaLabel);

  end;
end;

constructor TMyThread.Create(CreateSuspended: boolean);
begin
  FreeOnTerminate := True;
  inherited Create(CreateSuspended);
end;


and the form:

Code: [Select]{ TForm1 }

procedure TForm1.Button1Click(Sender: TObject);

begin

    if miHilo <> nil then begin
   ShowMessage('Ya se esta ejecutando');
   end
   else begin
   miHilo := TMyThread.Create(false);
   end;

end;

procedure TForm1.Button2Click(Sender: TObject);
begin
   if miHilo <> nil then begin
   miHilo.Terminate;
   ShowMessage('Hilo terminado');
   miHilo:=nil;
   end;
end;



procedure TForm1.FormCreate(Sender: TObject);
begin

end;





end.
I attached images with the error messages that shows when crashing

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Blaazen · 2012-10-04 19:23

And your *.lpr file ?

You have to add there line {$define UseCThreads}:
Code: [Select]program myproject;
{$mode objfpc}{$H+}
{$define UseCThreads}

uses   
{$IFDEF UNIX}{$IFDEF UseCThreads}
  cthreads,
  {$ENDIF}{$ENDIF}
....

Do you have it there ?

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tomek · 2012-10-04 21:14

X11 isn't thread safe. Only main thread for the GUI.

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Max JRB · 2012-10-05 03:16

Thanks for the answers, checking the .lpr files comparing it with the
one from the multithread example I found that had one difference.

the one from my project had this:

Code: [Select]{$mode objfpc}{$H+}

uses
  {$IFDEF UNIX}{$IFDEF UseCThreads}
  cthreads,
  {$ENDIF}{$ENDIF}
and the one from multithreadingexample:

Code: [Select]  {$IFDEF UNIX}
  cthreads,
  {$ENDIF}

doesn't have this validation {$IFDEF UseCThreads} I deleted it and now
works thanks

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Max JRB · 2012-10-05 03:25

Quote from: Blaazen on October 04, 2012, 09:23:07 pmAnd your *.lpr
file ?

You have to add there line {$define UseCThreads}:
Code: [Select]program myproject;
{$mode objfpc}{$H+}
{$define UseCThreads}

uses   
{$IFDEF UNIX}{$IFDEF UseCThreads}
  cthreads,
  {$ENDIF}{$ENDIF}
....

Do you have it there ?

Oh! thanks! I just see your answer
That was the problem, thanks again, I'm happy to see such a quick
answers on this forum