[Solved] Handle SIGTERM in Lazarus app

[AlexTP]

If I run "killall -SIGTERM cudatext", my text editor shuts down badly. TForm.OnClose is not called, it seems. So app cannot properly finalize and save history.

Why OnClose is not called on SIGTERM?
Can I call it on SIGTERM?
What other signal should I send?

[Zvoni]

hmmmm.... --> https://www.freepascal.org/docs-html/rtl/baseunix/fpsigaction.html

[MarkMLl]

hmmmm.... --> https://www.freepascal.org/docs-html/rtl/baseunix/fpsigaction.html

I agree. Them as don't ask, don't get.

However: /why/ are you using SIGTERM? SIGINT (by default raised by ^C) is far more common for this sort of thing.

See https://www.computerhope.com/unix/signals.htm, in particular the section "Sending signals from the keyboard", where ^C handling depends on terminal setup.

Also see the example handler I posted at https://forum.lazarus.freepascal.org/index.php/topic,67426.msg518817.html#msg518817

MarkMLl

[AlexTP]

Thanks.
I also asked this from AI and got this example:

[DELETED because code was wrong]

[Fred vS]

Hello Alex.

If you are asking to kill a app in a Wayland session, afaik Wayland does not allow it, one killed app = all the Wayland session killed.

[Zvoni]

Thanks.
I also asked this from AI and got this example:

Code: Pascal  [Select][+][-]

1. program GracefulShutdownExample;
2.  
3. uses
4.   SysUtils, Classes, Signal;
5.  
6. procedure HandleSignal(Sender: TObject);
7. begin
8.   Writeln('Received termination signal. Shutting down gracefully...');
9.   // Perform cleanup tasks here
10.   // For example, save data, close files, release resources, etc.
11.  
12.   // Exit the application
13.   Halt;
14. end;
15.  
16. var
17.   SignalHandler: TSignalHandler;
18.  
19. begin
20.   // Create a signal handler for SIGTERM and SIGINT
21.   SignalHandler := TSignalHandler.Create(nil);
22.   try
23.     SignalHandler.Signals := [sigTERM, sigINT];
24.     SignalHandler.OnSignal := HandleSignal;
25.  
26.     Writeln('Application is running. Press Ctrl+C to terminate.');
27.     // Simulate application running
28.     while True do
29.     begin
30.       Sleep(1000);
31.     end;
32.   finally
33.     SignalHandler.Free;
34.   end;
35. end.
36.  

Now I don't know where is the unit Signal?
I got reply:

The Signal unit in Free Pascal/Lazarus is part of the Free Pascal RTL (Run-Time Library) and is designed to provide signal handling capabilities. The unit is located in the rtl/win32 directory for Windows, and it aims to offer similar signal handling functionalities across different platforms[..]

Maybe because the unit-name is in fact "signals"...

On my machine at:
C:\lazarus\fpc\3.2.2\source\rtl\win32

Code: Pascal  [Select][+][-]

1. {
2.     This file is part of the Free Pascal run time library.
3.     This unit implements unix like signal handling for win32
4.     Copyright (c) 1999-2006 by the Free Pascal development team.
5.  
6.     See the file COPYING.FPC, included in this distribution,
7.     for details about the copyright.
8.  
9.     This program is distributed in the hope that it will be useful,
10.     but WITHOUT ANY WARRANTY; without even the implied warranty of
11.     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
12.  
13.  **********************************************************************}
14.  
15. unit signals;
16.  
17. interface
18.  
19. {$PACKRECORDS C}
20.  
21.   { Signals }
22.   const
23.     SIGABRT   = 288;
24.     SIGFPE    = 289;
25.     SIGILL    = 290;
26.     SIGSEGV   = 291;
27.     SIGTERM   = 292;
28.     SIGALRM   = 293;
29.     SIGHUP    = 294;
30.     SIGINT    = 295;
31.     SIGKILL   = 296;
32.     SIGPIPE   = 297;
33.     SIGQUIT   = 298;
34.     SIGUSR1   = 299;
35.     SIGUSR2   = 300;
36.     SIGNOFP   = 301;
37.     SIGTRAP   = 302;
38.     SIGTIMR   = 303;    { Internal for setitimer (SIGALRM, SIGPROF) }
39.     SIGPROF   = 304;
40.     SIGMAX    = 320;
41.  
42.     SIG_BLOCK   = 1;
43.     SIG_SETMASK = 2;
44.     SIG_UNBLOCK = 3;
45.  
46.   function SIG_DFL( x: longint) : longint; cdecl;
47.  
48.   function SIG_ERR( x: longint) : longint; cdecl;
49.  
50.   function SIG_IGN( x: longint) : longint; cdecl;
51.  
52.   type
53.  
54.     SignalHandler  = function (v : longint) : longint;cdecl;
55.  
56.     PSignalHandler = ^SignalHandler; { to be compatible with linux.pp }
57.  
58.   function signal(sig : longint;func : SignalHandler) : SignalHandler;
59.  
60.   const
61.  
62.      EXCEPTION_MAXIMUM_PARAMETERS = 15;
63.  
64.   type
65. //and so on....

[AlexTP]

I guess the French AI gave false info.

1. Unit it not 'Signal' but 'SignalS'.
2. In the unit, I don't see TSignalHandler type which is shown in AI example.

[Fred vS]

I guess the French AI gave false info.

1. Unit it not 'Signal' but 'SignalS'.
2. In the unit, I don't see TSignalHandler type which is shown in AI example.

Could be a nice game to test the different AI, what did you ask to the AI?

[Zvoni]

I guess the French AI gave false info.

2. In the unit, I don't see TSignalHandler type which is shown in AI example.

Ignore what AI said, und use the types as shown in the Unit?

Why are we discussing such things?!?!?

[Fred vS]

Why are we discussing such things?!?!?

Perhaps to show that AI still needs the Lazarus forum to be usable? 

[TRon]

Why are we discussing such things?!?!?

Because some people (still) do not realize that all AI wants from a user is engagement, and one that lasts as long and intensive as possible (for reasons that are well-known)

[MarkMLl]

I must say though that if somebody prefers to use an "AI" to find a half-correct answer to his question, I'm left wondering why I bother to try answering it and pointing to code that I know works.

MarkMLl

[AlexTP]

AI was mentioned just to show ppl, that Mistral AI is bad for Lazarus.
I took forum's answer, about using fpSigaction.
Mistral AI was helpful even WITH FORUM, it gave (in 2nd answer) ok example with fpSigaction.

Solved.

Also see the example handler I posted at https://forum.lazarus.freepascal.org/index.php/topic,67426.msg518817.html#msg518817

Mark, that example was less useful for me. AI's example (2nd one) was better and shorter 3x times.

[AlexTP]

I must post my final solved code:

Code: Pascal  [Select][+][-]

1. //1. main form's unit
2. uses BaseUnix;
3.  
4. {$ifndef windows}
5. procedure DoShutdown(Sig: Longint; Info: PSigInfo; Context: PSigContext); cdecl;
6. begin
7.   Writeln('CudaText got signal: '+IntToStr(Sig));
8.   if Assigned(fmMain) then
9.     fmMain.Close;
10. end;
11.  
12. procedure RegisterSignalHandler;
13. var
14.   New, Old: SigactionRec;
15. begin
16.   New.sa_handler:= @DoShutdown;
17.   FPSigaction(SIGTERM, @New, @Old);
18.   FPSigaction(SIGINT, @New, @Old);
19. end;
20. {$endif}
21.  
22.  
23. //2. LPR file
24.  
25.   {$IFDEF WINDOWS}
26.   //..
27.   {$ELSE}
28.   RegisterSignalHandler;
29.   {$IFEND}
30.  

[PascalDragon]

If you are asking to kill a app in a Wayland session, afaik Wayland does not allow it, one killed app = all the Wayland session killed.

This is wrong. One can KILL or TERM a Wayland application without issues for the remainder of the system. Would be insane if this wouldn't work, because especially SIGKILL can't be intercepted.

However: /why/ are you using SIGTERM? SIGINT (by default raised by ^C) is far more common for this sort of thing.

Because SIGTERM is the default signal of kill or killall maybe? And users might use that to terminate AlexTP's application if need be.