[fpc-pascal] Invalid standard handles in Windows service mode?

[MegaBrutal]

Hi all,

I have a Windows service application, and recently I noticed it doesn't
work if I compile it with FPC 2.6.2. It can be started in user mode too,
and in that case I didn't find any problem - at first I was really puzzled
what might be the reason. With some cumbersome debugging, I found the
application crashes when it tries to write to the standard output.

Right, writing to the standard output when the application has been started
by the service manager is kind of useless because the output won't be seen
anywhere. But still, it just worked until this point. When the program is
started from the console, the output is seen; and when it is started as a
service, who cares?

I wonder, however, why does the FP runtime library initializes the
application differently than it does when the app is started from console?
I have an {$APPTYPE CONSOLE} directive in my program, so Free Pascal should
believe it's a console application. Older FP runtimes didn't have this
problem. I actually wonder, how does the runtime ever gets to know whether
the program is started on console or as service? (This is an interesting
question for me, because even I can only determine whether the program is
running as a service when I try to call StartServiceCtrlDispatcher - if
that fails, my application believe's it's running on the console. I wonder
if there is a more effective way that FP runtime is using.)

To be clear: the very same source compiled with FPC 2.6.0 works on the very
same OS, while compiled with FPC 2.6.2 the application crashes. So I
suspect the problem is not that Windows wouldn't make stdout accessible in
service mode, or stuff like that.

If I need to check whether I can use stdout before using it, so be it, but
still I'd like to know the background of this issue. Along the way, maybe I
find a better way to check for service mode. Anyway, how can I check if I
have a valid stdout handle before actually trying to write to it?


MegaBrutal
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.freepascal.org/pipermail/fpc-pascal/attachments/20140221/9a835e89/attachment.html>