AnyEvent-SNMP/SNMP.pm

=head1 NAME

AnyEvent::SNMP - adaptor to integrate Net::SNMP into Anyevent.

=head1 SYNOPSIS

 use AnyEvent::SNMP;
 use Net::SNMP;

 # just use Net::SNMP and AnyEvent as you like:

 # use a condvar to transfer results, this is
 # just an example, you can use a naked callback as well.
 my $cv = AnyEvent->condvar;

 # ... start non-blocking snmp request(s)...
 Net::SNMP->session (-hostname => "127.0.0.1",
                     -community => "public",
                     -nonblocking => 1)
          ->get_request (-callback => sub { $cv->send (@_) });

 # ... do something else until the result is required
 my @result = $cv->wait;

=head1 DESCRIPTION

This module implements an alternative "event dispatcher" for Net::SNMP,
using AnyEvent as a backend.

This integrates Net::SNMP into AnyEvent: You can make non-blocking
Net::SNMP calls and as long as other parts of your program also use
AnyEvent (or some event loop supported by AnyEvent), they will run in
parallel.

Also, the Net::SNMP scheduler is very inefficient with respect to both CPU
and memory usage. Most AnyEvent backends (including the pure-perl backend)
fare much better than the Net::SNMP dispatcher.

A potential disadvantage is that replacing the dispatcher is not at all
a documented thing to do, so future changes in Net::SNP might break this
module (or the many similar ones).

This module does not export anything and does not require you to do
anything special apart from loading it I<before doing any non-blocking
requests with Net::SNMP>. It is recommended but not required to load this
module before C<Net::SNMP>.

=head1 GLOBAL VARIABLES

=over 4

=item $AnyEvent::SNMP::MAX_OUTSTANDING (default: C<50>, dynamic)

=item AnyEvent::SNMP::set_max_outstanding $new_value

Use this package variable to restrict the number of outstanding SNMP
requests at any point in time.

Net::SNMP is very fast at creating and sending SNMP requests, but much
slower at parsing (big, bulk) responses. This makes it easy to request a
lot of data that can take many seconds to parse.

In the best case, this can lead to unnecessary delays (and even time-outs,
as the data has been received but not yet processed) and in the worst
case, this can lead to packet loss, when the receive queue overflows and
the kernel can no longer accept new packets.

To avoid this, you can (and should) limit the number of outstanding
requests to a number low enough so that parsing time doesn't introduce
noticable delays.

Unfortunately, this number depends not only on processing speed and load
of the machine running Net::SNMP, but also on the network latency and the
speed of your SNMP agents.

AnyEvent::SNMP tries to dynamically adjust this number dynamically upwards
and downwards.

Increasing C<$MAX_OUTSTANDING> will not automatically use the
C<extra request slots. To increase $MAX_OUTSTANDING> and make
C<C<AnyEvent::SNMP> make use of the extra paralellity, call
C<AnyEvent::SNMP::set_max_outstanding> with the new value, e.g.:

   AnyEvent::SNMP::set_max_outstanding 500;

Although due to the dynamic adjustment, this might have little lasting
effect.

Note that you can use L<Net::SNMP::XS> to speed up parsing of responses
considerably.

=item $AnyEvent::SNMP::MIN_RECVQUEUE (default: C<8>)

=item $AnyEvent::SNMP::MAX_RECVQUEUE (default: C<64>)

These values specify the minimum and maximum receive queue length (in
units of one response packet).

When AnyEvent::SNMP handles $MAX_RECVQUEUE or more packets per iteration
it will reduce $MAX_OUTSTANDING. If it handles less than $MIN_RECVQUEUE,
it increases $MAX_OUTSTANDING.

This has the result of adjusting the number of outstanding requests so that
the recv queue is between the minimum and maximu, usually.

This algorithm works reasonably well as long as the responses, response
latencies and processing times are the same size per packet on average.

=back

=head1 COMPATIBILITY

This module may be used as a drop in replacement for the
Net::SNMP::Dispatcher in existing programs. You can still call
C<snmp_dispatcher> to start the event-loop, but then you loose the benefit
of mixing Net::SNMP events with other events.

   use AnyEvent::SNMP;
   use Net::SNMP;

   # just use Net::SNMP as before

   # ... start non-blocking snmp request(s)...
   Net::SNMP->session (
         -hostname    => "127.0.0.1",
         -community   => "public",
         -nonblocking => 1,
      )->get_request (-callback => sub { ... });

   snmp_dispatcher;

=cut

package AnyEvent::SNMP;

no warnings;
use strict qw(subs vars);

# it is possible to do this without loading
# Net::SNMP::Dispatcher, but much more awkward.
use Net::SNMP::Dispatcher;

sub Net::SNMP::Dispatcher::instance {
   AnyEvent::SNMP::
}

use Net::SNMP ();
use AnyEvent ();

our $VERSION = '0.2';

$Net::SNMP::DISPATCHER = instance Net::SNMP::Dispatcher;

our $MESSAGE_PROCESSING = $Net::SNMP::Dispatcher::MESSAGE_PROCESSING;

# avoid the method call
my $timer = sub { shift->timer (@_) };
AnyEvent::post_detect { $timer = AnyEvent->can ("timer") };

our $BUSY;
our @TRANSPORT; # fileno => [count, watcher]
our @QUEUE;
our $MAX_OUTSTANDING = 50;
our $MIN_RECVQUEUE   =  8;
our $MAX_RECVQUEUE   = 64;

sub kick_job;

sub _send_pdu {
   my ($pdu, $retries) = @_;

   # mostly copied from Net::SNMP::Dispatch

   # Pass the PDU to Message Processing so that it can
   # create the new outgoing message.
   my $msg = $MESSAGE_PROCESSING->prepare_outgoing_msg ($pdu);

   if (!defined $msg) {
      --$BUSY;
      kick_job;
      # Inform the command generator about the Message Processing error.
      $pdu->status_information ($MESSAGE_PROCESSING->error);
      return; 
   }

   # Actually send the message.
   if (!defined $msg->send) {
      $MESSAGE_PROCESSING->msg_handle_delete ($pdu->msg_id)
         if $pdu->expect_response;

      # A crude attempt to recover from temporary failures.
      if ($retries-- > 0 && ($!{EAGAIN} || $!{EWOULDBLOCK} || $!{ENOSPC})) {
         my $retry_w; $retry_w = AnyEvent->$timer (after => $pdu->timeout, cb => sub {
            undef $retry_w;
            _send_pdu ($pdu, $retries);
         });
      } else {
         --$BUSY;
         kick_job;
      }

      # Inform the command generator about the send() error.
      $pdu->status_information ($msg->error);
      return;
   }

   # Schedule the timeout handler if the message expects a response.
   if ($pdu->expect_response) {
      my $transport = $msg->transport;
      my $fileno    = $transport->fileno;

      # register the transport
      unless ($TRANSPORT[$fileno][0]++) {
         $TRANSPORT[$fileno][1] = AnyEvent->io (fh => $transport->socket, poll => 'r', cb => sub {
            for my $count (1..$MAX_RECVQUEUE) { # handle up to this many requests in one go
               # Create a new Message object to receive the response
               my ($msg, $error) = Net::SNMP::Message->new (-transport => $transport);

               if (!defined $msg) {
                  die sprintf 'Failed to create Message object [%s]', $error;
               }

               # Read the message from the Transport Layer
               if (!defined $msg->recv) {
                  if ($transport->connectionless) {
                     # if we handled very few replies and we have queued work, try
                     # to increase the parallelity as we probably can handle more.
                     if ($count < $MIN_RECVQUEUE && @QUEUE) {
                        ++$MAX_OUTSTANDING;
                        kick_job;
                     }
                  } else {
                     # for some reason, connected-oriented transports seem to need this
                     delete $TRANSPORT[$fileno]
                        unless --$TRANSPORT[$fileno][0];
                  }

                  $msg->error;
                  return;
               }

               # For connection-oriented Transport Domains, it is possible to
               # "recv" an empty buffer if reassembly is required.
               if (!$msg->length) {
                  return;
               }

               # Hand the message over to Message Processing.
               if (!defined $MESSAGE_PROCESSING->prepare_data_elements ($msg)) {
                  $MESSAGE_PROCESSING->error;
                  return;
               }

               # Set the error if applicable.
               $msg->error ($MESSAGE_PROCESSING->error) if $MESSAGE_PROCESSING->error;

               # Notify the command generator to process the response.
               $msg->process_response_pdu; 

               # Cancel the timeout.
               my $rtimeout_w = $msg->timeout_id;
               if ($$rtimeout_w) {
                  undef $$rtimeout_w;

                  --$BUSY;
                  kick_job;

                  unless (--$TRANSPORT[$fileno][0]) {
                     delete $TRANSPORT[$fileno];
                     return;
                  }
               }
            }

            # when we end up here, we successfully handled $MAX_RECVQUEUE
            # replies in one iteration, so assume we are overloaded
            # and reduce the amount of parallelity.
            $MAX_OUTSTANDING = (int $MAX_OUTSTANDING * 0.95) || 1;
         });
      }

      $msg->timeout_id (\(my $rtimeout_w =
         AnyEvent->$timer (after => $pdu->timeout, cb => sub {
            my $rtimeout_w = $msg->timeout_id;
            if ($$rtimeout_w) {
               undef $$rtimeout_w;
               delete $TRANSPORT[$fileno]
                  unless --$TRANSPORT[$fileno][0];
            }

            if ($retries--) {
               _send_pdu ($pdu, $retries);
            } else {
               $MESSAGE_PROCESSING->msg_handle_delete ($pdu->msg_id);
               $pdu->status_information ("No response from remote host '%s'", $pdu->hostname);

               --$BUSY;
               kick_job;
            }
         })
      )); 
   } else {
     --$BUSY;
     kick_job;
   }
}

sub kick_job {
   while ($BUSY < $MAX_OUTSTANDING) {
      my $pdu = shift @QUEUE
         or last;

      ++$BUSY;

      _send_pdu $pdu, $pdu->retries;
   }
}

sub send_pdu($$$) {
   my (undef, $pdu, $delay) = @_;

   # $delay is not very sensibly implemented by AnyEvent::SNMP,
   # but apparently it is not a very sensible feature.
   if ($delay > 0) {
      ++$BUSY;
      my $delay_w; $delay_w = AnyEvent->$timer (after => $delay, cb => sub {
         undef $delay_w;
         --$BUSY;
         push @QUEUE, $pdu;
         kick_job;
      });
      return 1;
   }

   push @QUEUE, $pdu;
   kick_job;

   1
}

sub activate($) {
   AnyEvent->one_event while $BUSY;
}

sub one_event($) {
   AnyEvent->one_event;
}

sub set_max_outstanding($) {
   $MAX_OUTSTANDING = $_[0];
   kick_job;
}

=head1 SEE ALSO

L<AnyEvent>, L<Net::SNMP>, L<Net::SNMP::XS>, L<Net::SNMP::EV>.

=head1 AUTHOR

 Marc Lehmann <schmorp@schmorp.de>
 http://home.schmorp.de/

=cut

1

Revision:	1.6
Committed:	Sat Apr 25 12:20:50 2009 UTC (15 years, 1 month ago) by root
Branch:	MAIN
CVS Tags:	rel-0_2
Changes since 1.5:	+21 -2 lines
Log Message:	0.2
#	User	Rev	Content
1	root	1.1	=head1 NAME
2
3			AnyEvent::SNMP - adaptor to integrate Net::SNMP into Anyevent.
4
5			=head1 SYNOPSIS
6
7			use AnyEvent::SNMP;
8			use Net::SNMP;
9
10			# just use Net::SNMP and AnyEvent as you like:
11
12			# use a condvar to transfer results, this is
13			# just an example, you can use a naked callback as well.
14			my $cv = AnyEvent->condvar;
15
16			# ... start non-blocking snmp request(s)...
17			Net::SNMP->session (-hostname => "127.0.0.1",
18			-community => "public",
19			-nonblocking => 1)
20			->get_request (-callback => sub { $cv->send (@_) });
21
22			# ... do something else until the result is required
23			my @result = $cv->wait;
24
25			=head1 DESCRIPTION
26
27			This module implements an alternative "event dispatcher" for Net::SNMP,
28			using AnyEvent as a backend.
29
30			This integrates Net::SNMP into AnyEvent: You can make non-blocking
31			Net::SNMP calls and as long as other parts of your program also use
32			AnyEvent (or some event loop supported by AnyEvent), they will run in
33			parallel.
34
35			Also, the Net::SNMP scheduler is very inefficient with respect to both CPU
36			and memory usage. Most AnyEvent backends (including the pure-perl backend)
37			fare much better than the Net::SNMP dispatcher.
38
39			A potential disadvantage is that replacing the dispatcher is not at all
40			a documented thing to do, so future changes in Net::SNP might break this
41			module (or the many similar ones).
42
43			This module does not export anything and does not require you to do
44			anything special apart from loading it I<before doing any non-blocking
45			requests with Net::SNMP>. It is recommended but not required to load this
46			module before C<Net::SNMP>.
47
48	root	1.3	=head1 GLOBAL VARIABLES
49
50			=over 4
51
52			=item $AnyEvent::SNMP::MAX_OUTSTANDING (default: C<50>, dynamic)
53
54	root	1.6	=item AnyEvent::SNMP::set_max_outstanding $new_value
55
56	root	1.3	Use this package variable to restrict the number of outstanding SNMP
57			requests at any point in time.
58
59			Net::SNMP is very fast at creating and sending SNMP requests, but much
60			slower at parsing (big, bulk) responses. This makes it easy to request a
61			lot of data that can take many seconds to parse.
62
63			In the best case, this can lead to unnecessary delays (and even time-outs,
64			as the data has been received but not yet processed) and in the worst
65			case, this can lead to packet loss, when the receive queue overflows and
66			the kernel can no longer accept new packets.
67
68	root	1.6	To avoid this, you can (and should) limit the number of outstanding
69			requests to a number low enough so that parsing time doesn't introduce
70			noticable delays.
71	root	1.3
72			Unfortunately, this number depends not only on processing speed and load
73			of the machine running Net::SNMP, but also on the network latency and the
74			speed of your SNMP agents.
75
76			AnyEvent::SNMP tries to dynamically adjust this number dynamically upwards
77			and downwards.
78
79	root	1.6	Increasing C<$MAX_OUTSTANDING> will not automatically use the
80			C<extra request slots. To increase $MAX_OUTSTANDING> and make
81			C<C<AnyEvent::SNMP> make use of the extra paralellity, call
82			C<AnyEvent::SNMP::set_max_outstanding> with the new value, e.g.:
83
84			AnyEvent::SNMP::set_max_outstanding 500;
85
86			Although due to the dynamic adjustment, this might have little lasting
87			effect.
88
89	root	1.3	Note that you can use L<Net::SNMP::XS> to speed up parsing of responses
90			considerably.
91
92	root	1.5	=item $AnyEvent::SNMP::MIN_RECVQUEUE (default: C<8>)
93	root	1.3
94			=item $AnyEvent::SNMP::MAX_RECVQUEUE (default: C<64>)
95
96			These values specify the minimum and maximum receive queue length (in
97			units of one response packet).
98
99			When AnyEvent::SNMP handles $MAX_RECVQUEUE or more packets per iteration
100			it will reduce $MAX_OUTSTANDING. If it handles less than $MIN_RECVQUEUE,
101			it increases $MAX_OUTSTANDING.
102
103			This has the result of adjusting the number of outstanding requests so that
104			the recv queue is between the minimum and maximu, usually.
105
106			This algorithm works reasonably well as long as the responses, response
107			latencies and processing times are the same size per packet on average.
108
109			=back
110
111			=head1 COMPATIBILITY
112
113			This module may be used as a drop in replacement for the
114			Net::SNMP::Dispatcher in existing programs. You can still call
115			C<snmp_dispatcher> to start the event-loop, but then you loose the benefit
116			of mixing Net::SNMP events with other events.
117
118			use AnyEvent::SNMP;
119			use Net::SNMP;
120
121			# just use Net::SNMP as before
122
123			# ... start non-blocking snmp request(s)...
124			Net::SNMP->session (
125			-hostname => "127.0.0.1",
126			-community => "public",
127			-nonblocking => 1,
128			)->get_request (-callback => sub { ... });
129
130			snmp_dispatcher;
131
132	root	1.1	=cut
133
134			package AnyEvent::SNMP;
135
136			no warnings;
137			use strict qw(subs vars);
138
139			# it is possible to do this without loading
140			# Net::SNMP::Dispatcher, but much more awkward.
141			use Net::SNMP::Dispatcher;
142
143			sub Net::SNMP::Dispatcher::instance {
144			AnyEvent::SNMP::
145			}
146
147			use Net::SNMP ();
148			use AnyEvent ();
149
150	root	1.3	our $VERSION = '0.2';
151	root	1.1
152			$Net::SNMP::DISPATCHER = instance Net::SNMP::Dispatcher;
153
154			our $MESSAGE_PROCESSING = $Net::SNMP::Dispatcher::MESSAGE_PROCESSING;
155
156			# avoid the method call
157			my $timer = sub { shift->timer (@_) };
158			AnyEvent::post_detect { $timer = AnyEvent->can ("timer") };
159
160			our $BUSY;
161	root	1.5	our @TRANSPORT; # fileno => [count, watcher]
162	root	1.3	our @QUEUE;
163			our $MAX_OUTSTANDING = 50;
164	root	1.5	our $MIN_RECVQUEUE = 8;
165	root	1.3	our $MAX_RECVQUEUE = 64;
166
167			sub kick_job;
168	root	1.1
169			sub _send_pdu {
170			my ($pdu, $retries) = @_;
171
172			# mostly copied from Net::SNMP::Dispatch
173
174			# Pass the PDU to Message Processing so that it can
175			# create the new outgoing message.
176			my $msg = $MESSAGE_PROCESSING->prepare_outgoing_msg ($pdu);
177
178			if (!defined $msg) {
179			--$BUSY;
180	root	1.3	kick_job;
181	root	1.1	# Inform the command generator about the Message Processing error.
182			$pdu->status_information ($MESSAGE_PROCESSING->error);
183			return;
184			}
185
186			# Actually send the message.
187			if (!defined $msg->send) {
188			$MESSAGE_PROCESSING->msg_handle_delete ($pdu->msg_id)
189			if $pdu->expect_response;
190
191			# A crude attempt to recover from temporary failures.
192			if ($retries-- > 0 && ($!{EAGAIN} \|\| $!{EWOULDBLOCK} \|\| $!{ENOSPC})) {
193			my $retry_w; $retry_w = AnyEvent->$timer (after => $pdu->timeout, cb => sub {
194			undef $retry_w;
195			_send_pdu ($pdu, $retries);
196			});
197			} else {
198			--$BUSY;
199	root	1.3	kick_job;
200	root	1.1	}
201
202			# Inform the command generator about the send() error.
203			$pdu->status_information ($msg->error);
204			return;
205			}
206
207			# Schedule the timeout handler if the message expects a response.
208			if ($pdu->expect_response) {
209			my $transport = $msg->transport;
210	root	1.5	my $fileno = $transport->fileno;
211	root	1.1
212			# register the transport
213	root	1.5	unless ($TRANSPORT[$fileno][0]++) {
214			$TRANSPORT[$fileno][1] = AnyEvent->io (fh => $transport->socket, poll => 'r', cb => sub {
215	root	1.3	for my $count (1..$MAX_RECVQUEUE) { # handle up to this many requests in one go
216			# Create a new Message object to receive the response
217			my ($msg, $error) = Net::SNMP::Message->new (-transport => $transport);
218
219			if (!defined $msg) {
220			die sprintf 'Failed to create Message object [%s]', $error;
221			}
222	root	1.1
223	root	1.3	# Read the message from the Transport Layer
224			if (!defined $msg->recv) {
225			if ($transport->connectionless) {
226	root	1.4	# if we handled very few replies and we have queued work, try
227			# to increase the parallelity as we probably can handle more.
228	root	1.3	if ($count < $MIN_RECVQUEUE && @QUEUE) {
229			++$MAX_OUTSTANDING;
230			kick_job;
231			}
232			} else {
233			# for some reason, connected-oriented transports seem to need this
234	root	1.5	delete $TRANSPORT[$fileno]
235			unless --$TRANSPORT[$fileno][0];
236	root	1.3	}
237	root	1.1
238	root	1.3	$msg->error;
239			return;
240	root	1.1	}
241
242	root	1.3	# For connection-oriented Transport Domains, it is possible to
243			# "recv" an empty buffer if reassembly is required.
244			if (!$msg->length) {
245			return;
246			}
247	root	1.1
248	root	1.3	# Hand the message over to Message Processing.
249			if (!defined $MESSAGE_PROCESSING->prepare_data_elements ($msg)) {
250			$MESSAGE_PROCESSING->error;
251			return;
252			}
253	root	1.1
254	root	1.3	# Set the error if applicable.
255			$msg->error ($MESSAGE_PROCESSING->error) if $MESSAGE_PROCESSING->error;
256	root	1.1
257	root	1.3	# Notify the command generator to process the response.
258			$msg->process_response_pdu;
259	root	1.1
260	root	1.3	# Cancel the timeout.
261			my $rtimeout_w = $msg->timeout_id;
262			if ($$rtimeout_w) {
263			undef $$rtimeout_w;
264
265			--$BUSY;
266			kick_job;
267
268	root	1.5	unless (--$TRANSPORT[$fileno][0]) {
269			delete $TRANSPORT[$fileno];
270	root	1.3	return;
271			}
272			}
273	root	1.1	}
274
275	root	1.4	# when we end up here, we successfully handled $MAX_RECVQUEUE
276			# replies in one iteration, so assume we are overloaded
277			# and reduce the amount of parallelity.
278	root	1.5	$MAX_OUTSTANDING = (int $MAX_OUTSTANDING * 0.95) \|\| 1;
279	root	1.1	});
280			}
281
282			$msg->timeout_id (\(my $rtimeout_w =
283			AnyEvent->$timer (after => $pdu->timeout, cb => sub {
284			my $rtimeout_w = $msg->timeout_id;
285			if ($$rtimeout_w) {
286			undef $$rtimeout_w;
287	root	1.5	delete $TRANSPORT[$fileno]
288			unless --$TRANSPORT[$fileno][0];
289	root	1.1	}
290
291			if ($retries--) {
292			_send_pdu ($pdu, $retries);
293			} else {
294			$MESSAGE_PROCESSING->msg_handle_delete ($pdu->msg_id);
295			$pdu->status_information ("No response from remote host '%s'", $pdu->hostname);
296	root	1.3
297			--$BUSY;
298			kick_job;
299	root	1.1	}
300			})
301			));
302			} else {
303			--$BUSY;
304	root	1.3	kick_job;
305	root	1.1	}
306			}
307
308	root	1.3	sub kick_job {
309			while ($BUSY < $MAX_OUTSTANDING) {
310			my $pdu = shift @QUEUE
311			or last;
312
313			++$BUSY;
314
315			_send_pdu $pdu, $pdu->retries;
316			}
317			}
318	root	1.6
319	root	1.1	sub send_pdu($$$) {
320			my (undef, $pdu, $delay) = @_;
321
322	root	1.3	# $delay is not very sensibly implemented by AnyEvent::SNMP,
323			# but apparently it is not a very sensible feature.
324	root	1.1	if ($delay > 0) {
325	root	1.3	++$BUSY;
326	root	1.1	my $delay_w; $delay_w = AnyEvent->$timer (after => $delay, cb => sub {
327			undef $delay_w;
328	root	1.3	--$BUSY;
329			push @QUEUE, $pdu;
330			kick_job;
331	root	1.1	});
332			return 1;
333			}
334
335	root	1.3	push @QUEUE, $pdu;
336			kick_job;
337
338	root	1.1	1
339			}
340
341			sub activate($) {
342			AnyEvent->one_event while $BUSY;
343			}
344
345			sub one_event($) {
346	root	1.3	AnyEvent->one_event;
347	root	1.1	}
348
349	root	1.6	sub set_max_outstanding($) {
350			$MAX_OUTSTANDING = $_[0];
351			kick_job;
352			}
353
354	root	1.1	=head1 SEE ALSO
355
356	root	1.3	L<AnyEvent>, L<Net::SNMP>, L<Net::SNMP::XS>, L<Net::SNMP::EV>.
357	root	1.1
358			=head1 AUTHOR
359
360			Marc Lehmann <schmorp@schmorp.de>
361			http://home.schmorp.de/
362
363			=cut
364
365			1
366