From: Joseph McDonald <joe@...>
Date: 2002-06-30T08:04:38+09:00
Subject: select loop question


Hi,

I've got a question on using a select loop.  Here is the basic way I
am using select:

if (answer = select(readfds, writefds, nil, 10))
  answer[0].each do |r|
     # handle reads
  end
  answer[1].each do |w|
     # handle writes
  end
else
  # timeout
end

The question is:  How do I know which file descriptors were returned
in the answer arrays?  That is:  after I get an answer and I finish
reading from the socket, I want to remove that socket from the readsfs
array, but I'm not sure how to do that.  Do I need to do something
like:
  answer[0].each do |r|
    readfds.each_with_index do |orig,i|
       if r == orig
         # nuke this one
         readfds.slice!(i)
        end
    end
  end

  That seems like an awful lot of overhead (cartesian product?) which
  I why I think I'm doing it wrong...

Does anyone have some example code using a select loop?  I would like
to use it to multiplex connections to web servers.  That is, I have
10000 url's that I would like to retrieve the contents from, and would
like to do it using 50 parallel connections using select loop.  I know
you can use threads for such an operation, but I would prefer to use
the select loop method.

thanks,
-joe