From: Raul Parolari <raulparolari@...>
Date: 2010-04-28T03:01:20+09:00
Subject: Re: Networking: select() blocks for seconds (> timeout)

Bill Kelly wrote:
>>... blocked for 5 seconds without signaling the 50 msec timeout.
> 
> Hi,
> Here was an original discussion of the issue:  (something like, select 
> may
> have already succeeded, before a bad UDP checksum is detected by the 
> kernel)
> 
> http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/148443
> 
>.. 
> Bill

Thanks, Bill, I will look in more detail what happens between the 
"select()" return, and the socket.recvfrom.

I must tell you that from other tests I did, simpler, not talking to 
firmware, just 2 ruby programs sending a packet continuously to each 
other inside a regular Mac (not on ubuntu, which is quite faster) I 
noticed this:
a) in average the round trip of a packet was 2.6 msec (good, taking in 
account that the sw prints something per packet, computes the min, avg 
and max round trip, etc).
b) but the maximum roundtrip time was 70 msec (the minimum was an 
astonishing 0.148msec, i.e. 148 microseconds).
c) when I increased the number of exchanges (from 1 million to 10 
millions) the average time was just a bit higher (from 2.6 msec to 2.89 
msec), but the maximum roundtrip time jumped to 93 msec. So the 
distribution is still close to the the average, but the "queue of the 
bell" (I am not sure how to say this exactly in English, but I think you 
understand) expands significantly, although very low.

So, Ruby is above our hopes ("in average") for high speed comm, but it 
is not predictable (the maximum delay in the above example being 25 
times the average, which would force us to set the timeouts absurdly 
high). Something happens inside Ruby once in a while which freezes it; 
from here, my suspicion of the garbage collector.

In any case, I will look carefully at what you mentioned and I will 
repeat my tests more rigorously (I should not do them on my dear Mac, 
because who knows what the os may do from time to time).

I appreciated your input very much

Raul



-- 
Posted via http://www.ruby-forum.com/.