[Lazarus] What to replace Application.Processmessages with?

Bo Berglund bo.berglund at gmail.com
Tue Oct 13 10:15:46 CEST 2020

I have been working some time to convert a rather big Delphi2007
Windows service application to a regular Linux program possible to run
as a Linux systemd service.
In Linux I was told that the application needs to be a regular program
to run in a non-logged on setting on a Linux server (without desktop).

So I have come a long way now and it feels like i am in the final
All of the TCP/IP socket communications to a client config app and
handling of serial ports and digital I/O has been solved.
The program runs OK at its core as a non-gui app and I can use the
existing client application on Windows to talk to it and configure the
system etc.

But now when I approach the actual core of the service, the ability to
run a longish task on external hardware while still being able to
handle incoming client requests etc I have found a possible problem...

The original server on Windows was built as a TService application and
had the GUI support maybe via a Delphi data module or otherwise so the
Application object is available.
I had to change this to a simple program instead and so I lost the
Application object.

In a lot of places in the task execution code there are
Application.Processmessages in wait loops and these I had to switch
off via a conditional named GUI_MODE and instead I have a sleep(T)
call there. Example:

while FContactResTestRunning and not FCancelOp do

Here the booleans FContactResTestRunning and FCancelOp are supposed to
be set in the main application on reception of certain events.

The class file where all of this is coded is also used in a GUI
application on Windows where the user communicates with the
instrumentation manually from the app. In that setting Application is
available and all works well.

The service application itself (from 2004) is based on timers to
perform things like execution of the measurement task itself in order
to isolate that from the main application. That is why there is
Application.Processmessages inside the wait loops so that things like
reception of RS232 messages from the equipment can be handled and
analyzed and flags be set which are waited for in the timer...

The TTimer objects have been replaced by TFpTimer objects in the
ported code and this seems to work fine, whereas TTimer does not.

I know that the system should have been designed using threads
instead, but that is not there and it is probably a too difficult
project to try and replace the current structure with threads.

Now I wonder if I could put something else into the loops so that the
main object of Application.Processmessages will be handled, namely to
let event functions run as needed.
Can I for example use CheckSynchronize in these loops?

I.e. Application.Processmessages ==> CheckSynchronize?

Or is there any other way?

Bo Berglund
Developer in Sweden

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