[fpc-pascal] When Pascal code is too fast

[Peter Vreman]

> On 11/1/07, Marc Santhoff <M.Santhoff at t-online.de> wrote:
>> Am Donnerstag, den 01.11.2007, 00:45 +0200 schrieb ik:
>> > Hi List,
>> >
>> > I have a weird problem. the "fpWrite" is too "slow" for FPC code. When
>> > I have the same exact code in C that writes a big amount of buffers of
>> > the same size with the same content. It seems that the fpWrite is way
>> > too fast, and the can't handle another call in the loop, and I need to
>> > slow down the loop using usleep.
>> > At the beginning I thought that it was a problem with fpWrite, so I
>> > created my own binding, but still the problem is the same.
>> >
>> > Except then the fact that it seems that FPC is much faster the GCC,
>> > any other ideas for such a behavior and what might be the reasons for
>> > it ?
>> >
>> > A POC for such code btw, can be as follows:
>> >
>> > Pascal:
>> > ...
>> > while not EOF(f) do
>> >   begin
>> >       readln(f,s);
>> >       fpwrite(f2, S[0], length(S));
>> >   end;
>> > ....
>> >
>> > C:
>> > ...
>> > while (! feof(f)) {
>> >   s_size = fread(f, s, MAX_BUFFER);
>> >   write(f2, s, s_size);
>> > }
>> > ...
>>
>> What error do you get? Lastly I had something similar with fpc writing
>> to fast to a non-blocking stderr channel. I haven't had time to do for
>> my code, but if you get "ressource temporartily unavailable"-like errors
>> switching the file to blocking mode might help.
>>
>> Something like
>>
>>         fcntl(fileno(stderr), F_GETFL) & O_NONBLOCK
>>
>> or the pascal equivalent should do.
>
> I'm getting -1 from fpWrite for a "long" period of time, like 6-7 loop
> returns before it can continue getting the my next content, only to
> have the same problem repeated...

This is not about Pascal or C. The code is only calling the linux kernel. You can use strace to
analyze this kind of issues.

Peter