[Lazarus] send complex command to linux

[Andrew Haines]

On 12/22/10 04:58, Lukasz Sokol wrote:
> Very Nice, can I ask, just:
> 
> 
> [1]
> 
>>   while Flac.Running or (Flac.Output.NumBytesAvailable > 0) do
>>     PipeOutput;
>>
> 
> Can this conditon happen to hit
> 
> Flac.Running=False 
> ..NumBytesAvailable > 0 (it'll probably be some garbage, but still)

No. Flac.Output is not initialized until Flac.Execute has succeded.
As soon as Flac.Execute is called Flac.Running = true unless an error
occurred.

I did while loop like that in case Flac stopped running but we hadn't
finished reading all it's data.

> 
> and would it be dangerous if so it happened ?
> 
> Maybe another 
>     while not Flac.Running do
>       begin
> 	Sleep(1);
> 	Application.ProcessMessages; // or even without this one
>       end;
> 
> be put at [1] ?
> 

This *could* cause an inescapable loop if for instance flac exited
before this was reached because we gave it some wrong options.

A safer example would be:

begin
  Flac := TProcess.Create(nil);

  Flac.Commandline := 'flac <some options>';
  Flac.Options = [poUsePipes];

  try
    Flac.Execute; // this will raise an exception if it
                  // cannot find or execute the command
  except
    ShowMessage('Error running Flac! Command Not Found');
  end;
  if not Flac.Running then
  begin
    // this will happen if flac ran but encountered
    // problems
    if Flax.ExitStatus <> 0 then
      ShowMessage('Flac exited with an error: ' +
IntToStr(Flac.ExitStatus));
  end
  else // Flac ran and has already finished with some data or is still
running
  begin
    While Flac.Running or (Flac.Output.NumBytesAvailable > 0) do
      PipeOutput;
  end;
  Flac.Free;
end;


Hope this clears things up :)

Regards,

Andrew

PS I didn't compile that so ther may be an error or three :)