Thread issue, App closes immediately

[dimonershov]

Hi all! I need help.

I use laz4android. This is my first app with a Thread. My application closes immediately!

Source code:

Code: Pascal  [Select][+][-]

1. {hint: Pascal files location: ...\Potok\jni }
2. unit unit1;
3.  
4. {$mode delphi}
5.  
6. interface
7.  
8. uses
9.   {$IFDEF UNIX}{$IFDEF UseCThreads}
10.   cthreads,
11.   {$ENDIF}{$ENDIF}
12.   Classes, SysUtils, AndroidWidget, Laz_And_Controls;
13.  
14. type
15.  
16.   { TAndroidModule1 }
17.  
18.   TAndroidModule1 = class(jForm)
19.     Button1: jButton;
20.     TextView1: jTextView;
21.     procedure Button1Click(Sender: TObject);
22.   private
23.     {private declarations}
24.   public
25.     {public declarations}
26.   end;
27.  
28.  
29. type
30.  
31.   { ShdkThread }
32.  
33.  ShdkThread=class(TThread)
34.   private
35.    stroka: string;
36.    procedure Show;
37.   protected
38.    procedure Execute; override;
39.  
40. end;
41.  
42. var
43.   AndroidModule1: TAndroidModule1;
44.   potok: ShdkThread;
45.  
46. implementation
47.  
48. {$R *.lfm}
49.  
50. { ShdkThread }
51.  
52. procedure ShdkThread.Show;
53. begin
54.  stroka:='Rabotaet';
55.  AndroidModule1.TextView1.Text:=stroka;
56. end;
57.  
58. procedure ShdkThread.Execute;
59. begin
60.  Synchronize(Show);
61. end;
62.  
63. { TAndroidModule1 }
64.  
65. procedure TAndroidModule1.Button1Click(Sender: TObject);
66. begin
67.   potok:=ShdkThread.Create(true);
68.   potok.FreeOnTerminate:=true;
69.   potok.stroka:='123';
70.   potok.Priority:=tpLower;
71.   potok.Resume;
72. end;
73. end.
74.  

Why does the app close when the button is clicked?

         

[KodeZwerg]

Welcome to forum!
Please use the [ # ] button and put your code within the [ code ] my code [ / code ] tag. Thank you.

[tetrastes]

Did you define UseCThreads somewhere?

Usually it looks like

Code: Pascal  [Select][+][-]

1. {$define UseCThreads}
2.  
3. uses
4.   {$IFDEF UNIX}{$IFDEF UseCThreads}
5.   cthreads,
6.   {$ENDIF}{$ENDIF}
7. ...

or simply

Code: Pascal  [Select][+][-]

1. uses
2.   {$IFDEF UNIX}
3.   cthreads,
4.   {$ENDIF}
5. ...

But AFAIK this must be in .lpr, at least for "normal" unixes.

[Peter H]

An uneducated guess:

Should it not read: Synchronize(@Show);

[Thaddy]

That is a good guess, but there is more because this:

Code: Pascal  [Select][+][-]

1. procedure ShdkThread.Execute;
2. begin
3.  Synchronize(Show);
4. end;

means he is misusing a thread and actually executes something what looks like a thread without using the benefits of a thread: It simply executes in consecutve order. (a.k.a. a Threat!  )
Bad code.
The output/result of a thread can be synchronized if needed, but plz not the whole thread....That is completely missing the point.

I know thread programming is difficult, but that is because it is, well, difficult.

[dimonershov]

Thank you!

In control.lpr it worked! Application doesn't crash

Code: Pascal  [Select][+][-]

1. ...
2. uses
3.   {$IFDEF UNIX}
4.   cthreads,
5.   {$ENDIF}
6. ...
7.  

But  my thread doesn't work! Help me? I press the button, nothing happens. The main form has only text and a button.

Code: Pascal  [Select][+][-]

1. {hint: Pascal files location: ...\Potok\jni }
2. unit unit1;
3.  
4. {$mode delphi}
5.  
6. interface
7.  
8. uses
9.  Classes, SysUtils, AndroidWidget, Laz_And_Controls;
10.  
11. type
12.  
13.   { ShdkThread }
14.  
15.  ShdkThread=class(TThread)
16.   private
17.    stroka: string;
18.    stop: boolean;
19.    ii: integer;
20.    procedure Show;
21.   protected
22.    procedure Execute; override;
23.   public
24.     constructor Create(CreateSuspended: boolean);
25. end;
26.  
27.  
28. type
29.  
30.   { TAndroidModule1 }
31.  
32.   TAndroidModule1 = class(jForm)
33.     Button1: jButton;
34.     TextView1: jTextView;
35.     procedure Button1Click(Sender: TObject);
36.   private
37.     {private declarations}
38.   public
39.     {public declarations}
40.   end;
41.  
42.  
43. var
44.   AndroidModule1: TAndroidModule1;
45.   potok: ShdkThread;
46.  
47. implementation
48.  
49. {$R *.lfm}
50.  
51. { TAndroidModule1 }
52.  
53. procedure TAndroidModule1.Button1Click(Sender: TObject);
54. begin
55.  potok:=ShdkThread.Create(true);
56.  potok.FreeOnTerminate:=true;
57.  potok.Priority:=tpNormal;
58.  potok.Resume;
59.  //potok.Start;
60. end;
61.  
62.  
63. { ShdkThread }
64.  
65. procedure ShdkThread.Show;
66. begin
67.  AndroidModule1.TextView1.Text:=stroka;
68. end;
69.  
70. procedure ShdkThread.Execute;
71. var
72.   newStatus : string;
73. begin
74.  stroka:='TMyThread Starting ...';
75.  Synchronize(Show);
76.  stroka:='TMyThread Running ...';
77.  while (not Terminated) and (true {any condition required}) do begin
78.  
79.     //here goes the code of the main thread loop
80.     newStatus:='TMyThread Time: '+FormatDateTime('YYYY-MM-DD HH:NN:SS',Now);
81.  
82.     if NewStatus <> stroka then begin
83.       stroka:=newStatus;
84.       Synchronize(Show);
85.     end;
86.     sleep(50); // alternatively the thread may wait for an event. E.g., external I/O
87.   end;
88.  
89. end;
90.  
91. constructor ShdkThread.Create(CreateSuspended: boolean);
92. begin
93.   FreeOnTerminate:=True;
94.   inherited Create(CreateSuspended);
95. end;
96. end.
97.  

[tetrastes]

An uneducated guess:

Should it not read: Synchronize(@Show);

Not in {$mode delphi}

[tetrastes]

But  my thread doesn't work! Help me? I press the button, nothing happens. The main form has only text and a button.

I cannot say why it doesn't work at android. At windows it works. But change your code

Code: Pascal  [Select][+][-]

1. procedure TAndroidModule1.Button1Click(Sender: TObject);
2. begin
3.  if not Assigned(potok) then
4.  begin
5.    potok:=ShdkThread.Create(true);
6.    potok.FreeOnTerminate:=true;
7.    potok.Priority:=tpNormal;
8.    potok.Resume;
9.    //potok.Start;
10.  end;
11. end;

and add smth like this

Code: Pascal  [Select][+][-]

1. procedure TAndroidModule1.FormClose(Sender: TObject; var CloseAction: TCloseAction);
2. begin
3.  if Assigned(potok) then
4.  begin
5.     potok.Terminate;
6.     potok.WaitFor;
7.  end;
8. end;

to avoid access violations.

[WayneSherman]

But  my thread doesn't work! Help me? I press the button, nothing happens. The main form has only text and a button.

Code: Pascal  [Select][+][-]

1. ...
2. Synchronize(Show);
3. ...

The last time I tried (in 2018), TThread.Synchronize did not work correctly using LAMW.  To work around the issue I used a timer to periodically check the status of thread operations.  Reference these discussions:

https://forum.lazarus.freepascal.org/index.php/topic,41523
https://forum.lazarus.freepascal.org/index.php/topic,57311

[dimonershov]

Thanks everyone! I'll upload the source code tomorrow.

[dimonershov]

Worked app is attached. For my small task i used jtimer and CheckSynchronize() function. Very nice! I will write more.