Reading TProcess.Output
lazarus / 8-Other

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PaulAtreides62 · 2009-04-05 20:38

Hi al all.
I have problems with the reading from Tprocess.Output (
TinputPipeStream type) effected in my Lazarus application.

Particularly the reading of TProcess.Output happens inside a Thread
where an external console program is performed, "prova1.exe", through
the use of a TProcess object.
The external program writes in the standard channel of output some
text.

I bring part of the code of my application

Code: [Select]  ...
  type
  TTestThread = class(TThread)
  private
    Processo1:Tprocess;
    s:string;
  protected  

  ...

  procedure Execute; override;
  end;

implementation

  ...  

procedure TTestThread.Execute;

var
   n: LongInt;
   ProntinLettura, i:Longint;
   buf:char;
   stringaoutput:string;

begin

   FreeOnTerminate := True;
   ...
   Processo1:=Tprocess.Create(nil) ;

   Processo1.CommandLine :='prova1.exe';
   Processo1.Options := [poUsePipes];
   Processo1.ShowWindow := swoHIDE;

   Processo1.Priority :=ppNormal;

   stringaoutput:='';

   try
     Processo1.Execute;
   except
     ....
   end;
   while Processo1.Running do
   begin

   Prontinlettura:=0;
   repeat
     if Fine then Terminate;
     if Terminated then
           begin
           ...
           end;
     Prontinlettura := Processo1.Output.NumBytesAvailable  ;
   until ProntinLettura > 0;
****************************************************************
   for i:=1 to ProntinLettura do
      begin
      n := Processo1.Output.Read(Buf, 1);

      if (buf<>#10) and (buf<>#13) then
         stringaoutput:=stringaoutput+buf
      else
         begin
         s:=stringaoutput;
         stringaoutput:='';
         if s<>'' then
            synchronize(@Appendi);
         end;
      end;
****************************************************************
   end; // qui il programma esterno è terminato...
   ...


The underlined code should allow the reading of the text produced by
the program prova1.exe also when this is in execution, instead, in
reality, the capture of the output happens later only, when prova1.exe
has finished its execution.
How come?
Is there a way to make up for?
Thanks to everybody

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Leledumbo · 2009-04-06 05:08

Not really sure, perhaps because you call Execute around try-except.

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PaulAtreides62 · 2009-04-06 07:17

Hi Leledumbo;
I have removed the block try-except, but the problem has remained.
Does someone have other ideas?

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Vincent Snijders · 2009-04-06 07:22

Does the called process flush its output? Or will it remain in its
buffer until it closes?

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PaulAtreides62 · 2009-04-06 13:28

Hi Vincent.
The process, if I have well understands what you ask me, flushs his
output while it's still running, and not only at the end of the
"running".

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Vincent Snijders · 2009-04-06 13:34

It depends on the amount of data the proces writes. If it is less
small (and a fpc program), it remains in the buffer of rtl (128 bytes,
IIRC), the OS may buffer 2,4 or even 64 kB, I don't know the details.

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PaulAtreides62 · 2009-04-06 20:21

The process writes no more then 10 Kbytes, i think, and the time of
execution depends on numeric data read by a text file specified by a
command line string. Some times almost instantly finishes, other times
the execution is much longer but, while running, the program keeps on
writing text on standard output channel ( I verified launching it in a
dos shell ). I know that an application, similar to mine but written
with visual c++, doesn't have this problem executing this external
program.
The external program is compiled by borland c++ ( last version).
The buffer depends on the compiler, the OS, or both?

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Vincent Snijders · 2009-04-06 20:25

Both.

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PaulAtreides62 · 2009-04-07 07:38

I can change the compiler of the external program, or is there
something of anything else other than can I do?

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Vincent Snijders · 2009-04-07 10:49

If it is a freepascal program, you can call Flush.

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PaulAtreides62 · 2009-04-08 07:18

Hi, Vincent.
I will make some other test, eventually modifying the code of the
external program, and i will see what it happens.
thanks