[Lazarus] TProcess.Input hangs

["Leonardo M. Ramé"]

On 17/10/14 20:54, Andrew Haines wrote:
> On 10/17/14 11:46, "Leonardo M. Ramé" wrote:
>> Hi, I'm using this code to convert WAV files to MP3 on the fly, using
>> lame. It was working great until today.
>>
>> It looks like this code has problems with large files sent to stdin.
>>
>> lProcess := TProcess.Create(nil);
>> lProcess.Executable := '/usr/bin/lame';
>> lProcess.Parameters.Add('-');  // stdin
>> lProcess.Parameters.Add('-');  // stdout
>> lProcess.Options := [poUsePipes];
>> lProcess.Execute;
>> lWav.LoadFromFile('/home/leonardo/16310.wav');
>> lWav.Position:= 0;
>> lWav.SaveToStream(lProcess.Input); // <--  here hangs
>> lProcess.CloseInput;
>>
>>
>> I also tried using this:
>>
>>    repeat
>>      lReadCount := lProcess.Input.Write(lWav.Memory^, 500);
>>      if lReadCount < 500 then
>>        lReadCount := 0;
>>    until lReadCount = 0;
>>
>> But also hangs before lReadCount < 500.
>>
>> Any hint?
>
>
> You are writing to stdin while the process is generating data to stdout.
> If you don't empty stdout and stderr the process will hang.
>
> There's lots of info here:
> http://wiki.freepascal.org/Executing_External_Programs
>
> You need something like
>
> while lProcess.Running or (lProcess.StdOut.NumBytesAvailable > 0) do
> begin
>    while lProcess.StdOut.NumBytesAvailable > 0 do
>    begin
>      lReadCount := lProcess.StdOut.Read(Buffer, SizeOf(Buffer);
>      if lReadCount > 0 then
>        // do something with encoded data
>    end;
>
>    // also you need to keep lProcess.StdErr empty or it can hang if it
> gets full.
>    while lProcess.StdErr.NumBytesAvailable > 0 do
>    begin
>      lReadCount := lProcess.StdErr.Read(Buffer, SizeOf(Buffer);
>      if lReadCount > 0 then
>        // do something with Stderr data
>    end;
>
>     // now write data to be encoded.
>     lReadCount := lWav.Read(Buffer, SizeOf(Buffer));
>     lProcess.Input.Write(Buffer, lReadCount);
> end;
>
> Regards,
>
> Andrew Haines

Thanks Andrew!, that fixed the issue.


-- 
Leonardo M. Ramé
http://leonardorame.blogspot.com