From: Eric Hodel <drbrain@...7.net>
Date: 2007-10-14T16:58:55+09:00
Subject: Re: write_nonblock is blocking?

On Oct 14, 2007, at 24:13 , Christoffer Lernö wrote:
> On 14 Oct 2007, at 01:23, Eric Hodel wrote:
>> On Oct 13, 2007, at 14:55 , Christoffer Lernö wrote:
>>> Anyone know what's up with TCPSocket#write_noblock actually  
>>> blocking when sending a packet that exceeds the buffer size of  
>>> the socket in 1.8.6 on Mac.
>>>
>>> The behaviour seems slightly counter-productive.
>>
>> How long does it block?  I see ruby occasionally being delayed  
>> 10ms when using write_nonblock, but not repeatably for the same  
>> packet sizes.  Probably my benchmark script is wrong.
>>
>> Could you supply a benchmark script that illustrates your problem?
>>
>> #write_nonblock first does rb_io_check_closed() which might call  
>> down to fseek(3) then write(2) before calling rb_io_set_nonblock 
>> ().  I'm not even close to being a sockets expert though, I just  
>> read the man pages.
>
> Thanks. Know it "should work" made me try to analyze the situation.  
> Here is an example code:
>
> [...]
>
> It looks like write_nonblock together with accept_nonblock causes  
> some issues.
>
> Now I could be using these wrong as both are new (in 1.8.6?)

I couldn't reproduce with your this test using:

$ ruby -v
ruby 1.8.6 (2007-09-23 patchlevel 5000) [powerpc-darwin8.10.0]

I'll to try again tomorrow though, since I'm tired.

I experimented a bit with your benchmark, and found that writing a  
large string would only write as much as the socket buffer would  
accept (81660 bytes, in my case).

Maybe you need to set the TCP_NODELAY socket option?

   socket.setsockopt Socket::IPPROTO_TCP, Socket::TCP_NODELAY, 1

I once made write_nonblock raise Errno::EAGAIN, but I accidentally  
deleted that change.  I'll play some more tomorrow when I'm not so  
tired.

--
Poor workers blame their tools. Good workers build better tools. The
best workers get their tools to do the work for them. -- Syndicate Wars