From: Robert Klemme <bob.news@...>
Date: 2004-01-20T18:24:59+09:00
Subject: Re: threads, mutex, regexp and trouble


"Mark Probert" <probertm@nospam-acm.org> schrieb im Newsbeitrag
news:Xns9475D4B7958E5probertmnospamacmorg@207.35.177.135...
> Hello, rubyists.
>
> I have a bit of a problem suing threads.  The program reads in a list of
> commands, then fires them off, via a telnet session, to another device,
> collecting data as it goes.
>
> On a one-by-one basis, everything is fine.  the commands works,
> everything is peachy.  The problem is I have to do 250+ sessions in a
> fairly limited time.  Ok, use threads.
>
> The problem is that I appear to be occassional tromping a variable, and
> mutexing doesn't seem to work.  Sometimes its ok, often it not.
>
> The code in question looks like:
>
>       @threads << Thread.new(node) { |idx|
> nn, ip, usr, pwd = idx.split(/:/)
>
> begin
>   bsn = BSN.new(ip, @timeout)
>
>   # login and run each command
>   if bsn.login then
>
>     @cmds.each do |cmd|
>       mutex.synchronize do
>   puts "~~>> cmd=#{cmd}"
>   bsn.cmd(cmd)
>       end
>     end
>     bsn.logout
>   else
>     puts " !! Unable to reach node= #{nn}"
>   end
>       }
>     @threads.each { |thr| thr.join }
>
> The problem is that the "cmd" variable seems to get mashed by a regexp
> match within bsn.cmd().  A good run looks like:
>
>   .. Running 2 commands on 2 nodes.
>   .. threading now ...
> ~~>> cmd=show subs isp=*_eeua
> ~~>> cmd=show subs isp=*_eeua
>
> A bad run looks like:
>
>   .. Running 2 commands on 2 nodes.
>   .. threading now ...
> ~~>> cmd=show subs isp=*_eeua
> ~~>> cmd=show subs isp=ebg1_eeua
>
> These commands come from a text file and the line is "show subs
> isp=*_eeua".
>
> The regexp does a match on data returned from the node.  The first match
> for the first node is "ebg1_eeua".  So, it seems that the regexp is
> confusing the thread.
>
> Any thoughts?

Is it guaranteed that all threads use the same instance via 'mutex', i.e.
does synchronization work properly?  Or maybe you use gsub! instead of
gsub (which you should since apparently all threads share @cmds).

Additionally I'd add a rescue clause at the end of the thread's main block
to catch and display any exceptions.  Plus I'd put the bsn.logout into an
ensure clause:

@threads << Thread.new(node) { |idx|
  nn, ip, usr, pwd = idx.split(/:/)

  begin
    bsn = BSN.new(ip, @timeout)

    # login and run each command
    if bsn.login then
      begin
        @cmds.each do |cmd|
          mutex.synchronize do
            puts "~~>> cmd=#{cmd}"
            bsn.cmd(cmd)
          end
        end
      ensure
        bsn.logout
      end
    else
      $stderr.puts " !! Unable to reach node= #{nn}"
    end
  rescue Exception => e
    $stderr.puts e
  end
}

@threads.each { |thr| thr.join }

Btw: Your indentation was garbled.  Better use spaces.

Kind regards

    robert