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<$MAX_OUTSTANDING> will not automatically use the
extra request slots. To increase C<$MAX_OUTSTANDING> and make
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 = '1.0';

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

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

our $BUSY;
our $DONE; # finished all jobs
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 = AE::timer $pdu->timeout, 0, 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] = AE::io $transport->socket, 0, 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 =
         AE::timer $pdu->timeout, 0, 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;
   }

   $DONE and $DONE->() unless $BUSY;
}

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 = AE::timer $delay, 0, sub {
         undef $delay_w;
         push @QUEUE, $pdu;
         --$BUSY;
         kick_job;
      };
      return 1;
   }

   push @QUEUE, $pdu;
   kick_job;

   1
}

sub activate($) {
   while ($BUSY) {
      $DONE = AE::cv;
      $DONE->recv;
      undef $DONE;
   }
}

sub one_event($) {
   # should not ever be used
   AnyEvent->one_event; #d# todo
}

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:	1.9
Committed:	Wed Jan 6 10:43:20 2010 UTC (14 years, 5 months ago) by root
Branch:	MAIN
CVS Tags:	rel-1_0
Changes since 1.8:	+8 -6 lines
Log Message:	* empty log message *
#	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	extra request slots. To increase C<$MAX_OUTSTANDING> and make
81	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 = '1.0';
151
152	$Net::SNMP::DISPATCHER = instance Net::SNMP::Dispatcher;
153
154	our $MESSAGE_PROCESSING = $Net::SNMP::Dispatcher::MESSAGE_PROCESSING;
155
156	our $BUSY;
157	our $DONE; # finished all jobs
158	our @TRANSPORT; # fileno => [count, watcher]
159	our @QUEUE;
160	our $MAX_OUTSTANDING = 50;
161	our $MIN_RECVQUEUE = 8;
162	our $MAX_RECVQUEUE = 64;
163
164	sub kick_job;
165
166	sub _send_pdu {
167	my ($pdu, $retries) = @_;
168
169	# mostly copied from Net::SNMP::Dispatch
170
171	# Pass the PDU to Message Processing so that it can
172	# create the new outgoing message.
173	my $msg = $MESSAGE_PROCESSING->prepare_outgoing_msg ($pdu);
174
175	if (!defined $msg) {
176	--$BUSY;
177	kick_job;
178	# Inform the command generator about the Message Processing error.
179	$pdu->status_information ($MESSAGE_PROCESSING->error);
180	return;
181	}
182
183	# Actually send the message.
184	if (!defined $msg->send) {
185	$MESSAGE_PROCESSING->msg_handle_delete ($pdu->msg_id)
186	if $pdu->expect_response;
187
188	# A crude attempt to recover from temporary failures.
189	if ($retries-- > 0 && ($!{EAGAIN} \|\| $!{EWOULDBLOCK} \|\| $!{ENOSPC})) {
190	my $retry_w; $retry_w = AE::timer $pdu->timeout, 0, sub {
191	undef $retry_w;
192	_send_pdu ($pdu, $retries);
193	};
194	} else {
195	--$BUSY;
196	kick_job;
197	}
198
199	# Inform the command generator about the send() error.
200	$pdu->status_information ($msg->error);
201	return;
202	}
203
204	# Schedule the timeout handler if the message expects a response.
205	if ($pdu->expect_response) {
206	my $transport = $msg->transport;
207	my $fileno = $transport->fileno;
208
209	# register the transport
210	unless ($TRANSPORT[$fileno][0]++) {
211	$TRANSPORT[$fileno][1] = AE::io $transport->socket, 0, sub {
212	for my $count (1..$MAX_RECVQUEUE) { # handle up to this many requests in one go
213	# Create a new Message object to receive the response
214	my ($msg, $error) = Net::SNMP::Message->new (-transport => $transport);
215
216	if (!defined $msg) {
217	die sprintf 'Failed to create Message object [%s]', $error;
218	}
219
220	# Read the message from the Transport Layer
221	if (!defined $msg->recv) {
222	if ($transport->connectionless) {
223	# if we handled very few replies and we have queued work, try
224	# to increase the parallelity as we probably can handle more.
225	if ($count < $MIN_RECVQUEUE && @QUEUE) {
226	++$MAX_OUTSTANDING;
227	kick_job;
228	}
229	} else {
230	# for some reason, connected-oriented transports seem to need this
231	delete $TRANSPORT[$fileno]
232	unless --$TRANSPORT[$fileno][0];
233	}
234
235	$msg->error;
236	return;
237	}
238
239	# For connection-oriented Transport Domains, it is possible to
240	# "recv" an empty buffer if reassembly is required.
241	if (!$msg->length) {
242	return;
243	}
244
245	# Hand the message over to Message Processing.
246	if (!defined $MESSAGE_PROCESSING->prepare_data_elements ($msg)) {
247	$MESSAGE_PROCESSING->error;
248	return;
249	}
250
251	# Set the error if applicable.
252	$msg->error ($MESSAGE_PROCESSING->error) if $MESSAGE_PROCESSING->error;
253
254	# Notify the command generator to process the response.
255	$msg->process_response_pdu;
256
257	# Cancel the timeout.
258	my $rtimeout_w = $msg->timeout_id;
259	if ($$rtimeout_w) {
260	undef $$rtimeout_w;
261
262	--$BUSY;
263	kick_job;
264
265	unless (--$TRANSPORT[$fileno][0]) {
266	delete $TRANSPORT[$fileno];
267	return;
268	}
269	}
270	}
271
272	# when we end up here, we successfully handled $MAX_RECVQUEUE
273	# replies in one iteration, so assume we are overloaded
274	# and reduce the amount of parallelity.
275	$MAX_OUTSTANDING = (int $MAX_OUTSTANDING * 0.95) \|\| 1;
276	};
277	}
278
279	$msg->timeout_id (\(my $rtimeout_w =
280	AE::timer $pdu->timeout, 0, sub {
281	my $rtimeout_w = $msg->timeout_id;
282	if ($$rtimeout_w) {
283	undef $$rtimeout_w;
284	delete $TRANSPORT[$fileno]
285	unless --$TRANSPORT[$fileno][0];
286	}
287
288	if ($retries--) {
289	_send_pdu ($pdu, $retries);
290	} else {
291	$MESSAGE_PROCESSING->msg_handle_delete ($pdu->msg_id);
292	$pdu->status_information ("No response from remote host '%s'", $pdu->hostname);
293
294	--$BUSY;
295	kick_job;
296	}
297	})
298	);
299	} else {
300	--$BUSY;
301	kick_job;
302	}
303	}
304
305	sub kick_job {
306	while ($BUSY < $MAX_OUTSTANDING) {
307	my $pdu = shift @QUEUE
308	or last;
309
310	++$BUSY;
311	_send_pdu $pdu, $pdu->retries;
312	}
313
314	$DONE and $DONE->() unless $BUSY;
315	}
316
317	sub send_pdu($$$) {
318	my (undef, $pdu, $delay) = @_;
319
320	# $delay is not very sensibly implemented by AnyEvent::SNMP,
321	# but apparently it is not a very sensible feature.
322	if ($delay > 0) {
323	++$BUSY;
324	my $delay_w; $delay_w = AE::timer $delay, 0, sub {
325	undef $delay_w;
326	push @QUEUE, $pdu;
327	--$BUSY;
328	kick_job;
329	};
330	return 1;
331	}
332
333	push @QUEUE, $pdu;
334	kick_job;
335
336	1
337	}
338
339	sub activate($) {
340	while ($BUSY) {
341	$DONE = AE::cv;
342	$DONE->recv;
343	undef $DONE;
344	}
345	}
346
347	sub one_event($) {
348	# should not ever be used
349	AnyEvent->one_event; #d# todo
350	}
351
352	sub set_max_outstanding($) {
353	$MAX_OUTSTANDING = $_[0];
354	kick_job;
355	}
356
357	=head1 SEE ALSO
358
359	L<AnyEvent>, L<Net::SNMP>, L<Net::SNMP::XS>, L<Net::SNMP::EV>.
360
361	=head1 AUTHOR
362
363	Marc Lehmann <schmorp@schmorp.de>
364	http://home.schmorp.de/
365
366	=cut
367
368	1
369