On Fri, 21 Feb 2014, MegaBrutal wrote:
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?
It does not. The FP runtime has no idea about service apps or not.
The same binary can run as regular or as service application.
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.)
Well, to my knowledge, the runtime does not try to check whether it is a
service or not.
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.
No, it may be that the stdout routines simply check better what they are doing,
and report errors correctly.
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?
You can check the handle of the StdOutputHandle variable.
if it is invalid (-1), you don't have output.
Michael.
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