Eventmachine talk - Nov 2007 - Events on I/O other than sockets

Hi Francis,

Does EventMachine handle I/O events other than on sockets?  I''d love to
be
able to use it for other forms of async I/O, especially originating from
IO.popen style command pipes.  I see some hints in the Rdoc that it might be
there, but nothing concrete.

Best regards,

--Michael
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From: Michael S. Fischer
>
> Does EventMachine handle I/O events other than on sockets?
> I''d love to be able to use it for other forms of async I/O,
> especially originating from IO.popen style command pipes.
EM does support IO.popen on Unix.  (I believe the Windows
implementation is still pending... as there are blocking
I/O issues with the stdlib popen on Windows.)


Regards,

Bill

On Nov 20, 2007 8:20 PM, Bill Kelly <billk at cts.com> wrote:
>
> From: Michael S. Fischer
> >
> > Does EventMachine handle I/O events other than on sockets?
> > I''d love to be able to use it for other forms of async I/O,
> > especially originating from IO.popen style command pipes.
>
> EM does support IO.popen on Unix.  (I believe the Windows
> implementation is still pending... as there are blocking
> I/O issues with the stdlib popen on Windows.)

Great!  Any example code?

--Michael
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On Nov 20, 2007 11:02 PM, Michael S. Fischer <michael at dynamine.net>
wrote:
> Hi Francis,
>
> Does EventMachine handle I/O events other than on sockets?  I''d
love to be
> able to use it for other forms of async I/O, especially originating from
> IO.popen style command pipes.  I see some hints in the Rdoc that it might
be
> there, but nothing concrete.
>

As Bill says, we support process descriptors (#popen) and keyboard
events on *nix. There was some thought given to console events (in
order to support GUI programs), but looking at what happened to
Twisted when they tried to do that makes me hesitant to attempt it.

The next major feature is user-defined events, which can be used to
implement inter-process messaging.

What other kinds of events should we support?

On Nov 21, 2007, at 4:01 AM, Francis Cianfrocca wrote:
> On Nov 20, 2007 11:02 PM, Michael S. Fischer <michael at
dynamine.net>
> wrote:
>> Hi Francis,
>>
>> Does EventMachine handle I/O events other than on sockets? 
I''d
>> love to be
>> able to use it for other forms of async I/O, especially
>> originating from
>> IO.popen style command pipes.  I see some hints in the Rdoc that
>> it might be
>> there, but nothing concrete.
>>
>
>
> As Bill says, we support process descriptors (#popen) and keyboard
> events on *nix. There was some thought given to console events (in
> order to support GUI programs), but looking at what happened to
> Twisted when they tried to do that makes me hesitant to attempt it.
>
> The next major feature is user-defined events, which can be used to
> implement inter-process messaging.
>
> What other kinds of events should we support?
Is there a facility within EM for receiving events on any file
descriptor? This would be useful for a project or two where I am
essentially "tailing" a file and processing it whenever it changes.

On Nov 21, 2007 9:21 AM, Chuck Remes <cremes.devlist at mac.com> wrote:
 >
> Is there a facility within EM for receiving events on any file
> descriptor? This would be useful for a project or two where I am
> essentially "tailing" a file and processing it whenever it
changes.
>
I started writing that and never finished. It just felt like
processing disk i/o in an event-driven way would have a small payoff,
partly because disk controllers now do so much caching and partly
because there''s only so much I/O bandwidth in an Intel-based server in
the first place.

I could be convinced otherwise.

From: Michael S. Fischer
>
> On Nov 20, 2007 8:20 PM, Bill Kelly <billk at cts.com> wrote:
>
> > EM does support IO.popen on Unix.  (I believe the Windows
> > implementation is still pending... as there are blocking
> > I/O issues with the stdlib popen on Windows.)
>
> Great!  Any example code?
Here''s an example that popen''s a bunch of `tail -f` processes
on
a bunch of logfiles.

In this example, once we''ve received 10 lines from a given logfile
we close the connection.

(Note that EventMachine''s popen uses socketpair behind the scenes,
so it''s a full-duplex connection between the parent and the child.)


require ''eventmachine''

load ''../dorkbuster/server-info.cfg''


class WallflyLogtailHandler < EventMachine::Protocols::LineAndTextProtocol

  def owner_init(sv_nick)
    @sv_nick = sv_nick
    @lines_rcvd = 0
  end

  def receive_line(line)
    line.chomp!
    @lines_rcvd += 1
    printf("%12s: %s\n", @sv_nick, line)
    if @lines_rcvd == 10
      puts "********** #@sv_nick closing connection **********"
      close_connection
    end
  end

end

def open_all_logtails
  $server_list.each do |sv|
    logpath = "../dorkbuster/sv/#{sv.nick}/wallfly.log"
    EventMachine::popen("tail -n1 -f #{logpath}",
WallflyLogtailHandler) do |handler|
      handler.owner_init(sv.nick)
    end
  end
end

EventMachine.run {
  open_all_logtails
}



Hope this helps,

Bill

From: "Chuck Remes" <cremes.devlist at
mac.com>
>
> Is there a facility within EM for receiving events on any file
> descriptor? This would be useful for a project or two where I am
> essentially "tailing" a file and processing it whenever it
changes.
I''m doing this with:

  EventMachine::popen("tail -n1 -f #{logpath}", MyHandler) do ......

Obviously there''s some extra overhead here which may be
inappropriate if one is looking for a maximally efficient
solution...

But it''s working great with me for 50 logfiles or so.


Regards,

Bill

On Nov 21, 2007 2:01 AM, Francis Cianfrocca <garbagecat10 at gmail.com>
wrote:
>
> As Bill says, we support process descriptors (#popen) and keyboard
> events on *nix.

Would it be possible to get the return value from the process opened?  From
my reading of the code, it looks like pclose(3) is never called at EOF.  It
would be great if the exit status could be passed as a parameter to
EventMachine::Connection#unbind.

--Michael
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