How to direct DumpExceptionBackTrace output to a file?
lazarus / 8-Other

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jl · 2009-07-13 04:45

I've been exploring with DumpExceptionBackTrace to help my debugging,
and trying to direct the output from DumpExceptionBackTrace output to
a file?

I'm able to direct DumpExceptionBackTrace output to a console in Linux
from my daemon, but not able to do so to a file on both windows and
linux.  Googled and looked at all articles, tried the following, but
it doesn't work.

Code: [Select] procedure TDaemon1.writelog(logtype, message: string);
var
  f: TextFile;
  sLogFile :string;
begin
try
  sLogFile:=sAppPath+'daemon.log';
  AssignFile(f, sLogFile);
  if FileExists(sLogFile) then Append(f) else ReWrite(f);
  WriteLn(f, formatdatetime('yyyy_mm_dd_hh_nn_ss',now)+#9+message);
  DumpExceptionBackTrace;
   CloseFile(f);
 except
    on E: Exception do
    begin
     WriteLn(formatdatetime('yyyy_mm_dd_hh_nn_ss',now)+#9+message);
     DumpExceptionBackTrace;
    end;
  end;
end;    
I also found the procedure for DumpExceptionBackTrace within
\lazarus\fpc\2.2.5\source\rtl\inc\system.inc

Code: [Select]{$ifdef FPC_HAS_FEATURE_EXCEPTIONS}
procedure DumpExceptionBackTrace(var f:text);
var
  FrameNumber,
  FrameCount   : longint;
  Frames       : PPointer;
begin
  if RaiseList=nil then
    exit;
  WriteLn(f,BackTraceStrFunc(RaiseList^.Addr));
  FrameCount:=RaiseList^.Framecount;
  Frames:=RaiseList^.Frames;
  for FrameNumber := 0 to FrameCount-1 do
    WriteLn(f,BackTraceStrFunc(Frames[FrameNumber]));
end;
{$endif FPC_HAS_FEATURE_EXCEPTIONS}
Here's more information:
http://www.freepascal.org/docs-
html/rtl/system/dumpexceptionbacktrace.html

Grateful for any pointers.

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Vincent Snijders · 2009-07-13 08:30

Are you sure you have an open console on windows? Otherwise Code:
[Select]WriteLn(formatdatetime('yyyy_mm_dd_hh_nn_ss',now)+#9+message);
will cause an exception in the exception handler.

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jl · 2009-07-13 13:35

Quote from: Vincent Snijders on July 13, 2009, 10:30:33 amAre you sure
you have an open console on windows? Otherwise Code:
[Select]WriteLn(formatdatetime('yyyy_mm_dd_hh_nn_ss',now)+#9+message);
will cause an exception in the exception handler.

no, as it's a service, but i don't see any exception.  however, i
tried debugln also, and the service hangs when i use that.  thks.

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Vincent Snijders · 2009-07-13 13:41

I am sorry, your response is not clear. Does writeln work or not in a
service?

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jl · 2009-07-13 15:30

The following works, i'm able to write the content of message to
sLogfile (pls refer to the whole procedure i posted previously).  It's
not possible for a Win32 service to WriteLn to a console, but it
possible to write to a file:

Code: [Select]  WriteLn(f,
formatdatetime('yyyy_mm_dd_hh_nn_ss',now)+#9+message);
  DumpExceptionBackTrace;  
What i'm not able to do is to write the output from
DumpExceptionBackTrace to a file.

As for the WriteLn within the exception - take note, there's no 'f'
parameter for this WriteLn - it has no 'visible' effect in a Win32
service.  I only use it for Linux daemon - the same code is used for
both binaries.

Code: [Select] except
    on E: Exception do
    begin
     WriteLn(formatdatetime('yyyy_mm_dd_hh_nn_ss',now)+#9+message);
     DumpExceptionBackTrace;
    end;
  end;

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Vincent Snijders · 2009-07-13 16:21

Well, on win32 gui applications, a writeln causes an exception, I just
wanted to be sure.

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jl · 2009-07-14 09:58

Quote from: Vincent Snijders on July 13, 2009, 06:21:49 pmWell, on
win32 gui applications, a writeln causes an exception, I just wanted
to be sure.

Yes, writeln does not generate an exception in a win32 service.

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Vincent Snijders · 2009-07-14 11:31

Did you read: http://wiki.lazarus.freepascal.org/Lazarus_Faq#How_can_I
_see_debug_output.3F

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jl · 2009-07-14 16:24

Quote from: Vincent Snijders on July 14, 2009, 01:31:21 pmDid you
read: http://wiki.lazarus.freepascal.org/Lazarus_Faq#How_can_I_see_deb
ug_output.3F


Yes, i also tried DebugLn, it outputs to console.

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Vincent Snijders · 2009-07-14 18:45

Oh, then you have an usual system configuration that ignores command
line parameters and environment variables. I am sorry, then your only
options is to change the lclproc code and hardcode the file name,
instead of reading it from the command line parameters or the
environment.

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jl · 2009-07-14 18:51

Thanks for replying, I can write text string to file using WriteLn on
both Linux and Win32, i.e. WriteLn ( var FileHandle  : TextFile; text:
String) ;

The problem which I'm facing is that I can't direct the output of
DumpExceptionBackTrace to the FileHandle.

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Paul Ishenin · 2009-07-15 23:07

I wrote previously:

Code: [Select]DumpExceptionBackTrace(var f:text)
It has f: file argument. Have you tried DumpExceptionBackTrace(f);?

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jl · 2009-07-16 05:26

Quote from: Paul Ishenin on July 16, 2009, 01:07:14 amI wrote
previously:

Code: [Select]DumpExceptionBackTrace(var f:text)
It has f: file argument. Have you tried DumpExceptionBackTrace(f);?


I tried that, it generates an exception:

Code: [Select]daemonunit1.pas(51,25) Error: Wrong number of parameters
specified for call to "DumpExceptionBackTrace"

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Vincent Snijders · 2009-07-16 06:50

Check if you use DumpExceptionBackTrace from the correct unit.

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jl · 2009-07-17 13:22

Quote from: Vincent Snijders on July 16, 2009, 08:50:43 amCheck if you
use DumpExceptionBackTrace from the correct unit.

Thanks Vincent, i removed LCLProc and it worked. 

I put that in them after reading some article, I guess it's the wrong
DumpExceptionBackTrace.