[fpc-pascal] TProcess usage and reading program output

[Benito van der Zander]

Hi,

  how would you handle large output and large stderr?


When you read from one and it writes to the other, the read blocks. Then 
it keeps writing to the other buffer, till that is full, and then its 
write is blocked, and it is deadlocked.

Probably check NumBytesAvailable before reading?

Bye,
Benito



On 02/28/2017 05:28 PM, Michael Van Canneyt wrote:
>
>
> On Tue, 28 Feb 2017, Graeme Geldenhuys wrote:
>
>> Hi,
>>
>> Can anybody see if there is something wrong with the code shown below.
>> The code is copied from one of my earlier projects where I call the FPC
>> compiler and it worked just fine in that project.
>>
>> In the work I'm doing now, I'm calling the Delphi Command Line Compiler,
>> and made a few minor tweaks to the code, but this method never seems to
>> return when Delphi command line compiler is called, and I don't see any
>> output. If I call other utilities (eg: Git etc) then I do see output and
>> it works as expected. It's just the Delphi Command Line Compiler that
>> now seems to be giving troubles.
>>
>> I would really appreciate it is anybody could spare a moment. Many 
>> thanks.
>>
>> I marked two areas with "// ???" where I am unsure if I'm doing the
>> right thing.
>
> poWaitOnExit should not be needed, as this will cause Execute to wait 
> for process exit...
>
> It seems likely that this will interfere with reading from output: 
> when the
> output buffer is full, the executed process will block.
>
> The rest seems fine.
>
> Also:
> It may be that Delphi somehow writes directly to the console buffer, 
> in that
> case you will not catch any output. But then you should see the output on
> the screen (just not caught by your process)
>
> Michael.
>
>
>
>
>
>>
>>
>> ==================================
>> function TBuildDelphiProject.RunTProcess(const Binary: string; args:
>> TStrings): boolean;
>> const
>>  BufSize = 1024;
>> var
>>  p: TProcess;
>>  Buf: string;
>>  Count: integer;
>>  i: integer;
>>  LineStart: integer;
>>  OutputLine: string;
>> begin
>>  p := TProcess.Create(nil);
>>  try
>>    p.Executable := Binary;
>>    // ??? Is poWaitOnExit needed here, it is called later down the code
>>    p.Options := [poUsePipes, poStdErrToOutPut, poWaitOnExit];
>> //    p.CurrentDirectory := ExtractFilePath(p.Executable);
>>    p.ShowWindow := swoShowNormal;  // ??? Is this needed?
>>
>>    p.Parameters.Assign(args);
>>    DoLog(etInfo,'Running command "%s" with arguments
>> "%s"',[p.Executable, p.Parameters.Text]);
>>    p.Execute;
>>
>>    { Now process the output }
>>    OutputLine:='';
>>    SetLength(Buf,BufSize);
>>    repeat
>>      if (p.Output<>nil) then
>>      begin
>>        Count:=p.Output.Read(Buf[1],Length(Buf));
>>      end
>>      else
>>        Count:=0;
>>      LineStart:=1;
>>      i:=1;
>>      while i<=Count do
>>      begin
>>        if Buf[i] in [#10,#13] then
>>        begin
>>          OutputLine:=OutputLine+Copy(Buf,LineStart,i-LineStart);
>>          writeln(OutputLine);
>>          OutputLine:='';
>>          if (i<Count) and (Buf[i+1] in [#10,#13]) and
>> (Buf[i]<>Buf[i+1]) then
>>            inc(i);
>>          LineStart:=i+1;
>>        end;
>>        inc(i);
>>      end;
>>      OutputLine:=Copy(Buf,LineStart,Count-LineStart+1);
>>    until Count=0;
>>    if OutputLine <> '' then
>>      writeln(OutputLine);
>>    p.WaitOnExit;
>>    Result := p.ExitStatus = 0;
>>    if Not Result then
>>      Writeln('Command ', p.Executable ,' failed with exit code: ',
>> p.ExitStatus);
>>  finally
>>    FreeAndNil(p);
>>  end;
>> end;
>> ==================================
>>
>>
>> Regards,
>>  Graeme
>>
>> -- 
>> fpGUI Toolkit - a cross-platform GUI toolkit using Free Pascal
>> http://fpgui.sourceforge.net/
>>
>> My public PGP key:  http://tinyurl.com/graeme-pgp
>> _______________________________________________
>> fpc-pascal maillist  -  fpc-pascal at lists.freepascal.org
>> http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal
>>
> _______________________________________________
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