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
#	Content
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	=head1 GLOBAL VARIABLES
49
50	=over 4
51
52	=item $AnyEvent::SNMP::MAX_OUTSTANDING (default: C<50>, dynamic)
53
54	=item AnyEvent::SNMP::set_max_outstanding $new_value
55
56	Use this package variable to restrict the number of outstanding SNMP
57	requests at any point in time.
58
59	Net::SNMP is very fast at creating and sending SNMP requests, but much
60	slower at parsing (big, bulk) responses. This makes it easy to request a
61	lot of data that can take many seconds to parse.
62
63	In the best case, this can lead to unnecessary delays (and even time-outs,
64	as the data has been received but not yet processed) and in the worst
65	case, this can lead to packet loss, when the receive queue overflows and
66	the kernel can no longer accept new packets.
67
68	To avoid this, you can (and should) limit the number of outstanding
69	requests to a number low enough so that parsing time doesn't introduce
70	noticable delays.
71
72	Unfortunately, this number depends not only on processing speed and load
73	of the machine running Net::SNMP, but also on the network latency and the
74	speed of your SNMP agents.
75
76	AnyEvent::SNMP tries to dynamically adjust this number dynamically upwards
77	and downwards.
78
79	Increasing C<$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	Note that you can use L<Net::SNMP::XS> to speed up parsing of responses
90	considerably.
91
92	=item $AnyEvent::SNMP::MIN_RECVQUEUE (default: C<8>)
93
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	=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	our $VERSION = '0.2';
151
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	our @TRANSPORT; # fileno => [count, watcher]
162	our @QUEUE;
163	our $MAX_OUTSTANDING = 50;
164	our $MIN_RECVQUEUE = 8;
165	our $MAX_RECVQUEUE = 64;
166
167	sub kick_job;
168
169	sub _send_pdu {
170	my ($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	kick_job;
181	# 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	kick_job;
200	}
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	my $fileno = $transport->fileno;
211
212	# register the transport
213	unless ($TRANSPORT[$fileno][0]++) {
214	$TRANSPORT[$fileno][1] = AnyEvent->io (fh => $transport->socket, poll => 'r', cb => sub {
215	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
223	# Read the message from the Transport Layer
224	if (!defined $msg->recv) {
225	if ($transport->connectionless) {
226	# if we handled very few replies and we have queued work, try
227	# to increase the parallelity as we probably can handle more.
228	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	delete $TRANSPORT[$fileno]
235	unless --$TRANSPORT[$fileno][0];
236	}
237
238	$msg->error;
239	return;
240	}
241
242	# For connection-oriented Transport Domains, it is possible to
243	# "recv" an empty buffer if reassembly is required.
244	if (!$msg->length) {
245	return;
246	}
247
248	# Hand the message over to Message Processing.
249	if (!defined $MESSAGE_PROCESSING->prepare_data_elements ($msg)) {
250	$MESSAGE_PROCESSING->error;
251	return;
252	}
253
254	# Set the error if applicable.
255	$msg->error ($MESSAGE_PROCESSING->error) if $MESSAGE_PROCESSING->error;
256
257	# Notify the command generator to process the response.
258	$msg->process_response_pdu;
259
260	# Cancel the timeout.
261	my $rtimeout_w = $msg->timeout_id;
262	if ($$rtimeout_w) {
263	undef $$rtimeout_w;
264
265	--$BUSY;
266	kick_job;
267
268	unless (--$TRANSPORT[$fileno][0]) {
269	delete $TRANSPORT[$fileno];
270	return;
271	}
272	}
273	}
274
275	# 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	$MAX_OUTSTANDING = (int $MAX_OUTSTANDING * 0.95) \|\| 1;
279	});
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	delete $TRANSPORT[$fileno]
288	unless --$TRANSPORT[$fileno][0];
289	}
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'", $pdu->hostname);
296
297	--$BUSY;
298	kick_job;
299	}
300	})
301	));
302	} else {
303	--$BUSY;
304	kick_job;
305	}
306	}
307
308	sub kick_job {
309	while ($BUSY < $MAX_OUTSTANDING) {
310	my $pdu = shift @QUEUE
311	or last;
312
313	++$BUSY;
314
315	_send_pdu $pdu, $pdu->retries;
316	}
317	}
318
319	sub send_pdu($$$) {
320	my (undef, $pdu, $delay) = @_;
321
322	# $delay is not very sensibly implemented by AnyEvent::SNMP,
323	# but apparently it is not a very sensible feature.
324	if ($delay > 0) {
325	++$BUSY;
326	my $delay_w; $delay_w = AnyEvent->$timer (after => $delay, cb => sub {
327	undef $delay_w;
328	--$BUSY;
329	push @QUEUE, $pdu;
330	kick_job;
331	});
332	return 1;
333	}
334
335	push @QUEUE, $pdu;
336	kick_job;
337
338	1
339	}
340
341	sub activate($) {
342	AnyEvent->one_event while $BUSY;
343	}
344
345	sub one_event($) {
346	AnyEvent->one_event;
347	}
348
349	sub set_max_outstanding($) {
350	$MAX_OUTSTANDING = $_[0];
351	kick_job;
352	}
353
354	=head1 SEE ALSO
355
356	L<AnyEvent>, L<Net::SNMP>, L<Net::SNMP::XS>, L<Net::SNMP::EV>.
357
358	=head1 AUTHOR
359
360	Marc Lehmann <schmorp@schmorp.de>
361	http://home.schmorp.de/
362
363	=cut
364
365	1
366