Solved: Calling application.run for thttpapplicat doesn't return for
finally par
lazarus / 38-Networking and Web Programming

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vangli · 2023-08-24 09:57

Hi, I am running Ubuntu 22.04 with Lazarus version 3.0RC1 and FPC
3.2.2. I am playing around with creating a webserver application for
myself. I am doing this for fun and to keep my brain active as a
pensioner. The following code is an shortened extract of my code to
pinpoint my question. Its a command line application I start in a
terminal window. It runs perfectly, and I am able to terminate with
Ctrl-C from terminal. I am aware that Application.Run is a blocking
call, which in my case is perfect. What I do expect in my confused
thinking, is that after pressing Ctrl-C, the application should write
the text in the finally section after returning from the
Application.Run call. But No. Where am I wrong (I know, it could
probably be me??   )?
Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i program
aWebServer;  {$mode objfpc}{$H+} uses  {$ifdef UNIX}  cthreads, cmem, 
{$endif}  fphttpapp, httpdefs, httproute, sysutils;  begin  try   
Application.Port := 8081; // Service port for webserver.   
Application.Threaded := true;    Application.Initialize;   
Application.Run;  finally    writeln('Ending application!');  end;end.

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Чебурашка · 2023-08-24 11:11

Run must be terminated calling Application.Terminate method.

Since the thread where Run is called is blocked inside the Run call,
you need to have another thread, that you will use to do the Terminate
call. Probably it is enough to create callback for CTRL+C, and call
Terminate from it, without creating explicitely an extra thread for
that.

Something like this should work (I did not test).

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i program
aWebServer; {$mode objfpc}{$H+} uses  {$ifdef UNIX}  cthreads, cmem, 
{$endif}   BaseUnix,   fphttpapp, httpdefs, httproute,
sysutils; procedure HandleSigInt(aSignal: LongInt); cdecl;begin 
Writeln('Calling terminate after SIGINT'); 
Application.Terminate();end; begin  if FpSignal(SigInt, @HandleSigInt)
= signalhandler(SIG_ERR) then  begin    Writeln('Failed to install
signal error: ', fpGetErrno);    Halt(1);  end;   Writeln('Starting
application, press CTRL+C to terminate...');   try    Application.Port
:= 8081; // Service port for webserver.    Application.Threaded :=
true;    Application.Initialize;    Application.Run;  finally   
writeln('Ending application!');  end;end.

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vangli · 2023-08-24 11:35

Thks. I will test this. Your explanation looks logical. I will follow
up after testing.

Edit after testing: Still not work 100%. However, I certainly catch
the Ctrl+C keypress and enter the HandleSigInt procedure. Then it
hangs on Application.Terminate statement. Replacing with a Halt()
function do terminate, but the finally statement isn't reached then,
naturally. It looks like I have to move sigint functionality into the
THtppApplication class through a user defined inherited class.

Anyway, thks a lot for the help, Чебурашка. I will explore more, and
when I found a way update this thread.

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ojz0r · 2023-08-24 12:08

Another option is to include a simple button in the webpage that calls
terminate and launch the app as nohup (no hang up).
That way the app will run as a daemon and not block the shell.

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Чебурашка · 2023-08-24 12:29

Quote from: vangli on August 24, 2023, 01:35:54 pmThks. I will test
this. Your explanation looks logical. I will follow up after testing.

Edit after testing: Still not work 100%. However, I certainly catch
the Ctrl+C keypress and enter the HandleSigInt procedure. Then it
hangs on Application.Terminate statement. Replacing with a Halt()
function do terminate, but the finally statement isn't reached then,
naturally. It looks like I have to move sigint functionality into the
THtppApplication class through a user defined inherited class.

Anyway, thks a lot for the help, Чебурашка. I will explore more, and
when I found a way update this thread.

I checked where I use this class and for me the described approach
works, except that I have also

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
HandleSigInt(aSignal: LongInt); cdecl;begin  Writeln('Calling
terminate after SIGINT');  Application.Terminate();   while (not
Application.Terminated) do Sleep(1); // WAS MISSING, SORRY!!!end; 
but I also have to say that I have wrapped the http app into a thread
separated by the main thread. And I Terminate the http app like showed
before.

Maybe this is why it does not work for you.

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vangli · 2023-08-24 12:43

Yes Чебурашка. It look like I has to create a separate thread like you
describe. The while statement has no effect. Application.Terminate
doesn't work because Application.Run is blocking, I think, in my
oversimplified approach.

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vangli · 2023-08-24 19:23

Found a workable way. Basically moved the exit information to the
HandleSigInt procedure, and there calling Application.Terminate, which
set Application.Terminated to True. Wait for the flag to be set, and
then free the hole application Instance. And then write some exit
information before Halt, and I am back to command line. Wonder if this
method introduce some kind of Memory leakage.

Thks Чебурашка for your kind help.

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i program
aWebServer; {$mode objfpc}{$H+} uses  {$ifdef UNIX}  cthreads, cmem, 
{$endif}  fphttpapp, httpdefs, httproute, sysutils, BaseUnix; 
procedure HandleSigInt(aSignal: LongInt); cdecl;begin 
Writeln(LineEnding,'Calling terminate after SIGINT'); 
Application.Terminate;  while not Application.Terminated do
Sleep(10);  Application.FreeInstance;  writeln('Write some information
when application ends....');  Halt(0);end;          begin  if
FpSignal(SigInt, @HandleSigInt) = signalhandler(SIG_ERR) then  begin 
 Writeln('Failed to install signal error: ', fpGetErrno);    Halt(1); 
end;  Writeln('Starting application, press CTRL+C to terminate...'); 
try    Application.Port := 8081;    Application.Threaded := true;   
Application.Initialize;    Application.Run;  finally   
writeln('Error!');  end;end.

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zen010101 · 2024-07-17 18:32

It is a bug mentioned here:

https://gitlab.com/freepascal.org/fpc/source/-/issues/36741#original-
reporter-info-from-mantis-luca-olivlucareporter-name-luca-olivetti

There is an ugly workaround:

Code: Pascal  [Select][+][-]window.onload = function(){var x1 =
document.getElementById("main_content_section"); if (x1) { var x =
document.getElementsByClassName("geshi");for (var i = 0; i procedure
signalHandler(signum: cint); cdecl;begin    Raise
Exception.Create('EXIT THE APPLICATION');end; 
Everything is working fine, but you might see an exception message pop
up, no need to worry about any memory leaks.