Re: [Dclib-devel] non blocking patch

[Davis K. <dav...@us...>]

Indeed, that's what dlib::timeout does.

How about I just add the timeout directly to the read() function?  It sounds
like that is all you need.   And maybe in the future we can setup some kind
of nonblocking_connection object with full support for using select on
multiple connections and all that good stuff.

Cheers,
Davis

On Sat, May 23, 2009 at 2:06 PM, Miguel Grinberg <mig...@ve...>wrote:

> Well, the problem is not that the call to read blocks, it is that it blocks
> forever. The readable() method I added has a timeout, so with that I can
> control for how long I want to block while waiting for data. It is a much
> cleaner way than using dlib::timeout, which if I understand it correctly
> would close the connection when the timeout expires.
>
> Miguel
>
> Davis King wrote:
>
>> Yeah, I think you are right about the non-blocking reading.
>> Right now the only way to implement a timeout on a read operation is to
>> use the dlib::timeout class which is sort of a heavyweight solution.  So
>> having non-blocking reading seems like it would be a nice alternative.
>> What do you usually do when you aren't blocking on a call to read?  You
>> have to be blocking on a call to something else right? sleep() maybe?
>>  Either that or you are spinning in a loop and killing CPU time.
>>
>> Cheers,
>> Davis
>>
>> On Sat, May 23, 2009 at 2:21 AM, Miguel Grinberg <mig...@ve...<mailto:
>> mig...@ve...>> wrote:
>>
>>    Hi Davis,
>>
>>    I guess for the write side this change is more of a
>>    "ready_to_send" function. A non-blocking operation cannot be
>>    guaranteed, the only thing you can ensure is that at least part of
>>    your data buffer will get through right away.
>>
>>    I'm only using the non-blocking read function right now, that one
>>    doesn't seem to have any side effects, it seems to me that for
>>    read with the use of select you can achieve true non-blocking
>>    behavior.
>>
>>    In my experience non-blocking writing isn't all that common
>>    anyway, I normally use non-blocking I/O to prevent my application
>>    from blocking while waiting for the other end to send data, but
>>    when I'm the one sending I don't mind blocking.
>>
>>    Thanks for your email.
>>
>>    Miguel
>>
>>    Davis King wrote:
>>
>>        I have been testing out this patch for a while (on windows and
>>        linux) and trying to think if there are any funny corner
>>        cases.  I also spent a lot of time a few years ago trying to
>>        work something like this into the connection object and ended
>>        up giving up but I forgot why until just now.
>>        Anyway, I found a problem related to sending data via send().
>>         The problem is that send() will block, even if select() says
>>        it won't, if you give it a buffer larger than a certain value
>>        (the value depends on your platform and isn't at all
>>        portable).  Linux allows you to set the MSG_DONTWAIT flag
>>        which fixes the issue but MSG_DONTWAIT isn't a POSIX thing and
>>        so isn't portable to other platforms.          See
>>        http://www.opengroup.org/onlinepubs/009695399/functions/send.html
>>        for example.
>>
>>        I think the only safe way to get this to work is to create the
>>        socket in non-blocking mode to begin with.  Then we don't have
>>        to worry about functions blocking when hidden buffer size
>>        limits are hit.  So I think that would mean making a new
>>        object that explicitly represented a non-blocking socket.
>>        I'm not in any dire need for non-blocking sockets so I
>>        probably won't be implementing this any time soon.
>>        You might also want to check out the asio library
>>        (http://think-async.com/Asio/).  It has a whole lot of support
>>        for varous kinds of networking modes.  It is also, in all
>>        probability, the networking library that will eventually make
>>        it into C++ standard library.  So it might be worth learning
>>        just for that reason :)
>>
>>        Cheers,
>>        Davis
>>
>>        On Fri, Apr 17, 2009 at 7:35 PM, miguelg50
>>        <mig...@ve... <mailto:mig...@ve...>
>>        <mailto:mig...@ve... <mailto:mig...@ve...>>>
>>        wrote:
>>
>>           Davis,
>>
>>           Attached is the patch for the non-blocking socket changes I've
>>           made. I hope
>>           it is useful.
>>
>>           Miguel
>>
>>
>>
>>
>>
>>
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