[Gambas-user] Important change in revision #6691

[Jussi Lahtinen]

Watch seems to raise read event for empty file, is this correct behavior?
>From the documentation ( http://gambaswiki.org/wiki/lang/open ) I would say
it shouldn't.
See the attachment.


Jussi

On Mon, Dec 1, 2014 at 12:52 AM, Benoît Minisini <
gambas at ...1...> wrote:

> Hi,
>
> I'm trying to fix a problem in the Gambas process management that annoys
> a lot of people for a long time.
>
> Sometimes, the output of the process is not entirely read. Some data is
> lost.
>
> This is because I was using a way of detecting data availability that
> was not reliable. I thought it was, but I was wrong.
>
> Concretely, the select() system call tells you if there is data
> available to read, but, in some cases, it wakes up and there is actually
> no data to read.
>
> So I tried to use a end-of-stream check by using various system calls
> (it depends on the type of file descriptor: file, pipe, socket...). But
> this routine sometimes fails.
>
> To change that, I now read data ahead by chunk of 1KB before actually
> raising the Read event.
>
> Apparently, using select() + read() is the correct way of accurately
> detecting end of stream, especially on pipes.
>
> Consequently, if the read ahead fails, I decide there is nothing to read
> anymore and I close the stream.
>
> Hopefully, this was not a big job, as internally read ahead was already
> implemented for optimizing the INPUT and LINE INPUT instruction.
>
> But this is a big change that may have side effects, so I ask people who
> run Gambas projects that watch a lot of file descriptors, and read the
> output of a lot of external processes, to use that revision and report
> any problem.
>
> Regards,
>
> --
> Benoît Minisini
>
>
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