TDaemon and Thread Synchronization
lazarus / 34-Windows

----------------------------------------------------------------------
halmariane · 2013-06-12 11:45

Hello:

Yes, i know that there are more "forum threads" about this topic, but
...

I explain me:

There is an issue which i posted 15 days ago.
http://bugs.freepascal.org/view.php?id=24511

When i want to use Components that requires Thread Synchronization,
seems that in Windows does not work at all. The same code can be
executed in Linux and works, but not in Windows. The same code can be
executed in Delphi and works also, so:

There is some real problem with TDaemon for Windows?

Regards

----------------------------------------------------------------------
BigChimp · 2013-06-12 12:12

Please *attach* (as a zip file, i.e. do not write down the program
test) a *compilable*, *complete* example program in that bug report,
including an indication where it goes wrong.

This will help developers quickly check the code and bug, as well as
be useful for future regression tests. It is probably also the reason
why this bug report has not been looked at for a while (remember: the
devs are volunteers).

----------------------------------------------------------------------
halmariane · 2013-06-12 14:09

Quote from: BigChimp on June 12, 2013, 02:12:01 pmPlease *attach* (as
a zip file, i.e. do not write down the program test) a *compilable*,
*complete* example program in that bug report, including an indication
where it goes wrong.

This will help developers quickly check the code and bug, as well as
be useful for future regression tests. It is probably also the reason
why this bug report has not been looked at for a while (remember: the
devs are volunteers).

Yes BigChimp, you are right. It's for my age.

Ok, i have uploaded one simple project there
(http://bugs.freepascal.org/view.php?id=24511), and here also.

Such as i wrote http://bugs.freepascal.org/view.php?id=24511

Code: [Select]// Sample Code
// ***********
// In this sample code, the method "IntervalEvent" is never called
with Lazarus for Windows
//
// JUST HERE
procedure TSimpleThread.Execute;
begin
  while not Terminated do
    begin
      Sleep(3000);
      Inc(FCounter);
      if Assigned(FOnInterval) then
       Synchronize(@CallOnInterval);
    end;

end;

QuoteSynchronize(@CallOnInterval) ...... is never synchronized
The problem can be hard. There are components that requires thread
synchronization with the main application that does not work in
Windows with this issue (TDaemon).

May be i'm wrong, it will be for my age (and my brain).    

Regards

QuoteDon't forget to start the service from Windows Service Manager.
In linux just execute with -r param

----------------------------------------------------------------------
ChrisF · 2013-06-12 19:20

I don't know really how Synchronize is internally implemented in FPC.
It seems to send a WM_NULL message, which is processed to call the
CheckSynchronize proc in the main windows message loop.

If I'm trying your synchronize call directly inside a simple program
using a TThread and a TCustomDaemon, it's only working if I'm removing
the WaitMessage call inside the concerned loop (which is definitively
not a good idea), and if I implicitly call the CheckSynchronize proc
myself.

Modification for Unit ("fcl-extra" package must be recompiled and
replaced):
($lazdir)\fpc\2.6.2\source\packages\fcl-extra\src\win\daemonapp.inc
Code: [Select]      Repeat
// Note: Working only if WaitMessage not used
  CheckSynchronize;
        if PeekMessage(Msg, 0, 0, 0, PM_REMOVE) then
          begin
          if (Msg.Message<>WM_QUIT) and (Msg.Message<>WM_ENDSESSION)
then
            begin
// Note: Not working (No message sent)
//            if (Msg.Message=WM_NULL) then
//              CheckSynchronize
//            else
              begin
              TranslateMessage(Msg);
              DispatchMessage(Msg);
              end;
            end
          else
            Terminate;
          end;
// Note: removing the following instructions is a very BAD idea
//        if not Terminated then
//          WaitMessage;

My conclusion is that currently, no windows message is sent in this
case (if I've correctly guessed about the Synchronize implementation).
And that CheckSynchronize is not called (anyway, even if present it
won't be called if no message is sent, as the loop is stopped at
WaitMessage).

Once again, I'm not sure about this explanation, as it seems there are
some other part of the code that may not need any windows message.

For instance, in tthread.inc, function TThread.WaitFor:
Code: [Select]...
  if GetCurrentThreadID = MainThreadID then
    begin
      WaitHandles[0]:=FHandle;
      WaitHandles[1]:=THandle(SynchronizeTimeoutEvent);
      while true do
        begin
          case MsgWaitForMultipleObjects(2, WaitHandles, False,
INFINITE, QS_SENDMESSAGE) of
            WAIT_OBJECT_0:
              break;
            WAIT_OBJECT_0+1:
              CheckSynchronize;
            WAIT_OBJECT_0+2:
              PeekMessage(Msg, 0, 0, 0, PM_NOREMOVE)
          end;
        end;
    end
...

I guess the main coders of all these parts may probably have a more
accurate answer.


***EDIT***: My test modification for "daemonapp.inc" is not working
when using a daemon application: only if you are using 'directly' the
TCustomDaemon class (see this topic :
http://www.lazarus.freepascal.org/index.php/topic,20652 ). I guess
another windows message loop is used within a daemon application
(don't know which one).

----------------------------------------------------------------------
halmariane · 2013-06-12 21:05

Hi CrisF:

I don't know at this moment what's wrong. Seems that there is some
stuff unimplemented in TDaemonApplication. I knew this problem long
time ago.

Regards

----------------------------------------------------------------------
ttomas · 2015-07-09 11:29

Any workaround about this bug?
I finish my project as application where several threads are create
and use Synchronize to set something to main thread. Everything works
OK.
Now I convert my application to Windows service (TDaemon) and hit this
problem.
Synchronize is not executed and code after is not executed.
Code: [Select]TSomeThread.Someproc;
begin
    ...
    Synchronize(@SetDBEvents);   // SetDBEvents is not executed
    Log.Log('ReceiveRetReplication After Synchronize OK',5);   // This
code is never executed
    ...
end;
Any workaround how to signal mainthread (TDaemon) to execute some code
in mainthread from TSomeThread?

This bug is still open http://bugs.freepascal.org/view.php?id=24511

FPC 3.1.1 SVN Revision 48878/Win32/64

----------------------------------------------------------------------
ttomas · 2015-07-09 11:46

Can I use SendMessage/PostMessage to TDaemon?
Where is TDaemon.Handle?

----------------------------------------------------------------------
eny · 2015-07-09 13:03

Quote from: ttomas on July 09, 2015, 01:29:39 pm