[fpc-pascal] Unbuffering I/O

[Marc Santhoff]

On Wed, 2018-08-29 at 15:01 +0000, Mark Morgan Lloyd wrote:

> I've got two programs intended to be functionally identical, one in Perl 
> and the other in FPC. They read a unix-domain datagram, decode the 
> message, and emit output; if this goes to a file then it's reasonable to 
> monitor it using  tail -f
> 
> Perl has a variable that you can set to force output to be unbuffered, 
> with the result that as soon as a message is output it's in the file in 
> its entirety.
> 
> Is there an equivalent for Pascal, or should I be using something like 
> fpSync(stdout) at opportune times?

I don't know if it really helps, but since I fiddled with a similar topic:

FreeBSD has stdio channel non blocking by default. I had some problems with
that and did this:


procedure SwitchFdBlocking(var channel: Text);
var
  res: cint;
begin
  res := fpfcntl(TextRec(channel).Handle, F_GETFL);
  if ((O_NONBLOCK AND res)>0) then
  begin
    res := res AND (NOT O_NONBLOCK);
    res := fpfcntl(TextRec(channel).Handle, F_SETFL, res);
    if (res=-1) then writeln(stderr, 'ERROR on SETFL');
  end;
end;

According to the man page of fcntl using the flag "O_DIRECT" instead of
"O_NONBLOCK" for switching of caching as far as possible. At least on FreeBSD
it is like this, check on Linux yourself...

-- 
Marc Santhoff <M.Santhoff at t-online.de>