[ViewVC] Diff of: cvs/AnyEvent-MP/MP.pm

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.37 by root, Fri Aug 7 16:47:23 2009 UTC vs.
Revision 1.97 by root, Fri Oct 2 13:29:49 2009 UTC

…		…
1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent::MP - multi-processing/message-passing framework	3	AnyEvent::MP - erlang-style multi-processing/message-passing framework
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::MP;	7	use AnyEvent::MP;
8		8
9	$NODE # contains this node's noderef	9	$NODE # contains this node's node ID
10	NODE # returns this node's noderef	10	NODE # returns this node's node ID
11	NODE $port # returns the noderef of the port
12		11
		12	$SELF # receiving/own port id in rcv callbacks
		13
		14	# initialise the node so it can send/receive messages
		15	configure;
		16
		17	# ports are message destinations
		18
		19	# sending messages
13	snd $port, type => data...;	20	snd $port, type => data...;
		21	snd $port, @msg;
		22	snd @msg_with_first_element_being_a_port;
14		23
15	$SELF # receiving/own port id in rcv callbacks	24	# creating/using ports, the simple way
		25	my $simple_port = port { my @msg = @_ };
16		26
17	rcv $port, smartmatch => $cb->($port, @msg);	27	# creating/using ports, tagged message matching
18		28	my $port = port;
19	# examples:
20	rcv $port2, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
21	rcv $port1, pong => sub { warn "pong received\n" };	30	rcv $port, pong => sub { warn "pong received\n" };
22	snd $port2, ping => $port1;
23		31
24	# more, smarter, matches (_any_ is exported by this module)	32	# create a port on another node
25	rcv $port, [child_died => $pid] => sub { ...	33	my $port = spawn $node, $initfunc, @initdata;
26	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3
27		34
28	# monitoring	35	# monitoring
29	mon $port, $cb->(@msg) # callback is invoked on death	36	mon $localport, $cb->(@msg) # callback is invoked on death
30	mon $port, $otherport # kill otherport on abnormal death	37	mon $localport, $otherport # kill otherport on abnormal death
31	mon $port, $otherport, @msg # send message on death	38	mon $localport, $otherport, @msg # send message on death
		39
		40	=head1 CURRENT STATUS
		41
		42	bin/aemp - stable.
		43	AnyEvent::MP - stable API, should work.
		44	AnyEvent::MP::Intro - explains most concepts.
		45	AnyEvent::MP::Kernel - mostly stable API.
		46	AnyEvent::MP::Global - stable API.
32		47
33	=head1 DESCRIPTION	48	=head1 DESCRIPTION
34		49
35	This module (-family) implements a simple message passing framework.	50	This module (-family) implements a simple message passing framework.
36		51
37	Despite its simplicity, you can securely message other processes running	52	Despite its simplicity, you can securely message other processes running
38	on the same or other hosts.	53	on the same or other hosts, and you can supervise entities remotely.
39		54
40	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	55	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
41	manual page.	56	manual page and the examples under F<eg/>.
42
43	At the moment, this module family is severly broken and underdocumented,
44	so do not use. This was uploaded mainly to reserve the CPAN namespace -
45	stay tuned! The basic API should be finished, however.
46		57
47	=head1 CONCEPTS	58	=head1 CONCEPTS
48		59
49	=over 4	60	=over 4
50		61
51	=item port	62	=item port
52		63
53	A port is something you can send messages to (with the C<snd> function).	64	Not to be confused with a TCP port, a "port" is something you can send
		65	messages to (with the C<snd> function).
54		66
55	Some ports allow you to register C<rcv> handlers that can match specific	67	Ports allow you to register C<rcv> handlers that can match all or just
56	messages. All C<rcv> handlers will receive messages they match, messages	68	some messages. Messages send to ports will not be queued, regardless of
57	will not be queued.	69	anything was listening for them or not.
58		70
59	=item port id - C<noderef#portname>	71	=item port ID - C<nodeid#portname>
60		72
61	A port id is normaly the concatenation of a noderef, a hash-mark (C<#>) as	73	A port ID is the concatenation of a node ID, a hash-mark (C<#>) as
62	separator, and a port name (a printable string of unspecified format). An	74	separator, and a port name (a printable string of unspecified format).
63	exception is the the node port, whose ID is identical to its node
64	reference.
65		75
66	=item node	76	=item node
67		77
68	A node is a single process containing at least one port - the node	78	A node is a single process containing at least one port - the node port,
69	port. You can send messages to node ports to find existing ports or to	79	which enables nodes to manage each other remotely, and to create new
70	create new ports, among other things.	80	ports.
71		81
72	Nodes are either private (single-process only), slaves (connected to a	82	Nodes are either public (have one or more listening ports) or private
73	master node only) or public nodes (connectable from unrelated nodes).	83	(no listening ports). Private nodes cannot talk to other private nodes
		84	currently.
74		85
75	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	86	=item node ID - C<[A-Z_][a-zA-Z0-9_\-.:]*>
76		87
77	A node reference is a string that either simply identifies the node (for	88	A node ID is a string that uniquely identifies the node within a
78	private and slave nodes), or contains a recipe on how to reach a given	89	network. Depending on the configuration used, node IDs can look like a
79	node (for public nodes).	90	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		91	doesn't interpret node IDs in any way.
80		92
81	This recipe is simply a comma-separated list of C<address:port> pairs (for	93	=item binds - C<ip:port>
82	TCP/IP, other protocols might look different).
83		94
84	Node references come in two flavours: resolved (containing only numerical	95	Nodes can only talk to each other by creating some kind of connection to
85	addresses) or unresolved (where hostnames are used instead of addresses).	96	each other. To do this, nodes should listen on one or more local transport
		97	endpoints - binds. Currently, only standard C<ip:port> specifications can
		98	be used, which specify TCP ports to listen on.
86		99
87	Before using an unresolved node reference in a message you first have to	100	=item seed nodes
88	resolve it.	101
		102	When a node starts, it knows nothing about the network. To teach the node
		103	about the network it first has to contact some other node within the
		104	network. This node is called a seed.
		105
		106	Apart from the fact that other nodes know them as seed nodes and they have
		107	to have fixed listening addresses, seed nodes are perfectly normal nodes -
		108	any node can function as a seed node for others.
		109
		110	In addition to discovering the network, seed nodes are also used to
		111	maintain the network and to connect nodes that otherwise would have
		112	trouble connecting. They form the backbone of an AnyEvent::MP network.
		113
		114	Seed nodes are expected to be long-running, and at least one seed node
		115	should always be available. They should also be relatively responsive - a
		116	seed node that blocks for long periods will slow down everybody else.
		117
		118	=item seeds - C<host:port>
		119
		120	Seeds are transport endpoint(s) (usually a hostname/IP address and a
		121	TCP port) of nodes that should be used as seed nodes.
		122
		123	The nodes listening on those endpoints are expected to be long-running,
		124	and at least one of those should always be available. When nodes run out
		125	of connections (e.g. due to a network error), they try to re-establish
		126	connections to some seednodes again to join the network.
89		127
90	=back	128	=back
91		129
92	=head1 VARIABLES/FUNCTIONS	130	=head1 VARIABLES/FUNCTIONS
93		131
95		133
96	=cut	134	=cut
97		135
98	package AnyEvent::MP;	136	package AnyEvent::MP;
99		137
100	use AnyEvent::MP::Base;	138	use AnyEvent::MP::Kernel;
101		139
102	use common::sense;	140	use common::sense;
103		141
104	use Carp ();	142	use Carp ();
105		143
106	use AE ();	144	use AE ();
107		145
108	use base "Exporter";	146	use base "Exporter";
109		147
110	our $VERSION = '0.1';	148	our $VERSION = 1.2;
		149
111	our @EXPORT = qw(	150	our @EXPORT = qw(
112	NODE $NODE *SELF node_of _any_	151	NODE $NODE *SELF node_of after
113	resolve_node initialise_node	152	configure
114	snd rcv mon kil reg psub	153	snd rcv mon mon_guard kil psub spawn cal
115	port	154	port
116	);	155	);
117		156
118	our $SELF;	157	our $SELF;
119		158
…		…
123	kil $SELF, die => $msg;	162	kil $SELF, die => $msg;
124	}	163	}
125		164
126	=item $thisnode = NODE / $NODE	165	=item $thisnode = NODE / $NODE
127		166
128	The C<NODE> function returns, and the C<$NODE> variable contains	167	The C<NODE> function returns, and the C<$NODE> variable contains, the node
129	the noderef of the local node. The value is initialised by a call	168	ID of the node running in the current process. This value is initialised by
130	to C<become_public> or C<become_slave>, after which all local port	169	a call to C<configure>.
131	identifiers become invalid.
132		170
133	=item $noderef = node_of $port	171	=item $nodeid = node_of $port
134		172
135	Extracts and returns the noderef from a portid or a noderef.	173	Extracts and returns the node ID from a port ID or a node ID.
136		174
137	=item initialise_node $noderef, $seednode, $seednode...	175	=item configure $profile, key => value...
138		176
139	=item initialise_node "slave/", $master, $master...	177	=item configure key => value...
140		178
141	Before a node can talk to other nodes on the network it has to initialise	179	Before a node can talk to other nodes on the network (i.e. enter
142	itself - the minimum a node needs to know is it's own name, and optionally	180	"distributed mode") it has to configure itself - the minimum a node needs
143	it should know the noderefs of some other nodes in the network.	181	to know is its own name, and optionally it should know the addresses of
		182	some other nodes in the network to discover other nodes.
144		183
145	This function initialises a node - it must be called exactly once (or	184	This function configures a node - it must be called exactly once (or
146	never) before calling other AnyEvent::MP functions.	185	never) before calling other AnyEvent::MP functions.
147		186
148	All arguments are noderefs, which can be either resolved or unresolved.
149
150	There are two types of networked nodes, public nodes and slave nodes:
151
152	=over 4	187	=over 4
153		188
154	=item public nodes	189	=item step 1, gathering configuration from profiles
155		190
156	For public nodes, C<$noderef> must either be a (possibly unresolved)	191	The function first looks up a profile in the aemp configuration (see the
157	noderef, in which case it will be resolved, or C<undef> (or missing), in	192	L<aemp> commandline utility). The profile name can be specified via the
158	which case the noderef will be guessed.	193	named C<profile> parameter or can simply be the first parameter). If it is
		194	missing, then the nodename (F<uname -n>) will be used as profile name.
159		195
160	Afterwards, the node will bind itself on all endpoints and try to connect	196	The profile data is then gathered as follows:
161	to all additional C<$seednodes> that are specified. Seednodes are optional
162	and can be used to quickly bootstrap the node into an existing network.
163		197
164	=item slave nodes	198	First, all remaining key => value pairs (all of which are conveniently
		199	undocumented at the moment) will be interpreted as configuration
		200	data. Then they will be overwritten by any values specified in the global
		201	default configuration (see the F<aemp> utility), then the chain of
		202	profiles chosen by the profile name (and any C<parent> attributes).
165		203
166	When the C<$noderef> is the special string C<slave/>, then the node will	204	That means that the values specified in the profile have highest priority
167	become a slave node. Slave nodes cannot be contacted from outside and will	205	and the values specified directly via C<configure> have lowest priority,
168	route most of their traffic to the master node that they attach to.	206	and can only be used to specify defaults.
169		207
170	At least one additional noderef is required: The node will try to connect	208	If the profile specifies a node ID, then this will become the node ID of
171	to all of them and will become a slave attached to the first node it can	209	this process. If not, then the profile name will be used as node ID. The
172	successfully connect to.	210	special node ID of C<anon/> will be replaced by a random node ID.
		211
		212	=item step 2, bind listener sockets
		213
		214	The next step is to look up the binds in the profile, followed by binding
		215	aemp protocol listeners on all binds specified (it is possible and valid
		216	to have no binds, meaning that the node cannot be contacted form the
		217	outside. This means the node cannot talk to other nodes that also have no
		218	binds, but it can still talk to all "normal" nodes).
		219
		220	If the profile does not specify a binds list, then a default of C<*> is
		221	used, meaning the node will bind on a dynamically-assigned port on every
		222	local IP address it finds.
		223
		224	=item step 3, connect to seed nodes
		225
		226	As the last step, the seeds list from the profile is passed to the
		227	L<AnyEvent::MP::Global> module, which will then use it to keep
		228	connectivity with at least one node at any point in time.
173		229
174	=back	230	=back
175		231
176	This function will block until all nodes have been resolved and, for slave	232	Example: become a distributed node using the local node name as profile.
177	nodes, until it has successfully established a connection to a master	233	This should be the most common form of invocation for "daemon"-type nodes.
178	server.
179		234
180	Example: become a public node listening on the default node.	235	configure
181		236
182	initialise_node;	237	Example: become an anonymous node. This form is often used for commandline
		238	clients.
183		239
184	Example: become a public node, and try to contact some well-known master	240	configure nodeid => "anon/";
185	servers to become part of the network.
186		241
187	initialise_node undef, "master1", "master2";	242	Example: configure a node using a profile called seed, which si suitable
		243	for a seed node as it binds on all local addresses on a fixed port (4040,
		244	customary for aemp).
188		245
189	Example: become a public node listening on port C<4041>.	246	# use the aemp commandline utility
		247	# aemp profile seed nodeid anon/ binds '*:4040'
190		248
191	initialise_node 4041;	249	# then use it
		250	configure profile => "seed";
192		251
193	Example: become a public node, only visible on localhost port 4044.	252	# or simply use aemp from the shell again:
		253	# aemp run profile seed
194		254
195	initialise_node "locahost:4044";	255	# or provide a nicer-to-remember nodeid
196		256	# aemp run profile seed nodeid "$(hostname)"
197	Example: become a slave node to any of the specified master servers.
198
199	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
200
201	=item $cv = resolve_node $noderef
202
203	Takes an unresolved node reference that may contain hostnames and
204	abbreviated IDs, resolves all of them and returns a resolved node
205	reference.
206
207	In addition to C<address:port> pairs allowed in resolved noderefs, the
208	following forms are supported:
209
210	=over 4
211
212	=item the empty string
213
214	An empty-string component gets resolved as if the default port (4040) was
215	specified.
216
217	=item naked port numbers (e.g. C<1234>)
218
219	These are resolved by prepending the local nodename and a colon, to be
220	further resolved.
221
222	=item hostnames (e.g. C<localhost:1234>, C<localhost>)
223
224	These are resolved by using AnyEvent::DNS to resolve them, optionally
225	looking up SRV records for the C<aemp=4040> port, if no port was
226	specified.
227
228	=back
229		257
230	=item $SELF	258	=item $SELF
231		259
232	Contains the current port id while executing C<rcv> callbacks or C<psub>	260	Contains the current port id while executing C<rcv> callbacks or C<psub>
233	blocks.	261	blocks.
234		262
235	=item SELF, %SELF, @SELF...	263	=item *SELF, SELF, %SELF, @SELF...
236		264
237	Due to some quirks in how perl exports variables, it is impossible to	265	Due to some quirks in how perl exports variables, it is impossible to
238	just export C<$SELF>, all the symbols called C<SELF> are exported by this	266	just export C<$SELF>, all the symbols named C<SELF> are exported by this
239	module, but only C<$SELF> is currently used.	267	module, but only C<$SELF> is currently used.
240		268
241	=item snd $port, type => @data	269	=item snd $port, type => @data
242		270
243	=item snd $port, @msg	271	=item snd $port, @msg
244		272
245	Send the given message to the given port ID, which can identify either	273	Send the given message to the given port, which can identify either a
246	a local or a remote port, and can be either a string or soemthignt hat	274	local or a remote port, and must be a port ID.
247	stringifies a sa port ID (such as a port object :).
248		275
249	While the message can be about anything, it is highly recommended to use a	276	While the message can be almost anything, it is highly recommended to
250	string as first element (a portid, or some word that indicates a request	277	use a string as first element (a port ID, or some word that indicates a
251	type etc.).	278	request type etc.) and to consist if only simple perl values (scalars,
		279	arrays, hashes) - if you think you need to pass an object, think again.
252		280
253	The message data effectively becomes read-only after a call to this	281	The message data logically becomes read-only after a call to this
254	function: modifying any argument is not allowed and can cause many	282	function: modifying any argument (or values referenced by them) is
255	problems.	283	forbidden, as there can be considerable time between the call to C<snd>
		284	and the time the message is actually being serialised - in fact, it might
		285	never be copied as within the same process it is simply handed to the
		286	receiving port.
256		287
257	The type of data you can transfer depends on the transport protocol: when	288	The type of data you can transfer depends on the transport protocol: when
258	JSON is used, then only strings, numbers and arrays and hashes consisting	289	JSON is used, then only strings, numbers and arrays and hashes consisting
259	of those are allowed (no objects). When Storable is used, then anything	290	of those are allowed (no objects). When Storable is used, then anything
260	that Storable can serialise and deserialise is allowed, and for the local	291	that Storable can serialise and deserialise is allowed, and for the local
261	node, anything can be passed.	292	node, anything can be passed. Best rely only on the common denominator of
		293	these.
262		294
263	=item $local_port = port	295	=item $local_port = port
264		296
265	Create a new local port object that can be used either as a pattern	297	Create a new local port object and returns its port ID. Initially it has
266	matching port ("full port") or a single-callback port ("miniport"),	298	no callbacks set and will throw an error when it receives messages.
267	depending on how C<rcv> callbacks are bound to the object.
268		299
269	=item $port = port { my @msg = @_; $finished }	300	=item $local_port = port { my @msg = @_ }
270		301
271	Creates a "miniport", that is, a very lightweight port without any pattern	302	Creates a new local port, and returns its ID. Semantically the same as
272	matching behind it, and returns its ID. Semantically the same as creating
273	a port and calling C<rcv $port, $callback> on it.	303	creating a port and calling C<rcv $port, $callback> on it.
274		304
275	The block will be called for every message received on the port. When the	305	The block will be called for every message received on the port, with the
276	callback returns a true value its job is considered "done" and the port	306	global variable C<$SELF> set to the port ID. Runtime errors will cause the
277	will be destroyed. Otherwise it will stay alive.	307	port to be C<kil>ed. The message will be passed as-is, no extra argument
		308	(i.e. no port ID) will be passed to the callback.
278		309
279	The message will be passed as-is, no extra argument (i.e. no port id) will	310	If you want to stop/destroy the port, simply C<kil> it:
280	be passed to the callback.
281		311
282	If you need the local port id in the callback, this works nicely:	312	my $port = port {
283		313	my @msg = @_;
284	my $port; $port = port {	314	...
285	snd $otherport, reply => $port;	315	kil $SELF;
286	};	316	};
287		317
288	=cut	318	=cut
289		319
290	sub rcv($@);	320	sub rcv($@);
		321
		322	sub _kilme {
		323	die "received message on port without callback";
		324	}
291		325
292	sub port(;&) {	326	sub port(;&) {
293	my $id = "$UNIQ." . $ID++;	327	my $id = "$UNIQ." . $ID++;
294	my $port = "$NODE#$id";	328	my $port = "$NODE#$id";
295		329
296	if (@_) {	330	rcv $port, shift \|\| \&_kilme;
297	rcv $port, shift;
298	} else {
299	$PORT{$id} = sub { }; # nop
300	}
301		331
302	$port	332	$port
303	}	333	}
304		334
305	=item reg $port, $name
306
307	=item reg $name
308
309	Registers the given port (or C<$SELF><<< if missing) under the name
310	C<$name>. If the name already exists it is replaced.
311
312	A port can only be registered under one well known name.
313
314	A port automatically becomes unregistered when it is killed.
315
316	=cut
317
318	sub reg(@) {
319	my $port = @_ > 1 ? shift : $SELF \|\| Carp::croak 'reg: called with one argument only, but $SELF not set,';
320
321	$REG{$_[0]} = $port;
322	}
323
324	=item rcv $port, $callback->(@msg)	335	=item rcv $local_port, $callback->(@msg)
325		336
326	Replaces the callback on the specified miniport (after converting it to	337	Replaces the default callback on the specified port. There is no way to
327	one if required).	338	remove the default callback: use C<sub { }> to disable it, or better
328		339	C<kil> the port when it is no longer needed.
329	=item rcv $port, tagstring => $callback->(@msg), ...
330
331	=item rcv $port, $smartmatch => $callback->(@msg), ...
332
333	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
334
335	Register callbacks to be called on matching messages on the given full
336	port (after converting it to one if required) and return the port.
337
338	The callback has to return a true value when its work is done, after
339	which is will be removed, or a false value in which case it will stay
340	registered.
341		340
342	The global C<$SELF> (exported by this module) contains C<$port> while	341	The global C<$SELF> (exported by this module) contains C<$port> while
343	executing the callback.	342	executing the callback. Runtime errors during callback execution will
		343	result in the port being C<kil>ed.
344		344
345	Runtime errors wdurign callback execution will result in the port being	345	The default callback received all messages not matched by a more specific
346	C<kil>ed.	346	C<tag> match.
347		347
348	If the match is an array reference, then it will be matched against the	348	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
349	first elements of the message, otherwise only the first element is being
350	matched.
351		349
352	Any element in the match that is specified as C<_any_> (a function	350	Register (or replace) callbacks to be called on messages starting with the
353	exported by this module) matches any single element of the message.	351	given tag on the given port (and return the port), or unregister it (when
		352	C<$callback> is C<$undef> or missing). There can only be one callback
		353	registered for each tag.
354		354
355	While not required, it is highly recommended that the first matching	355	The original message will be passed to the callback, after the first
356	element is a string identifying the message. The one-string-only match is	356	element (the tag) has been removed. The callback will use the same
357	also the most efficient match (by far).	357	environment as the default callback (see above).
358		358
359	Example: create a port and bind receivers on it in one go.	359	Example: create a port and bind receivers on it in one go.
360		360
361	my $port = rcv port,	361	my $port = rcv port,
362	msg1 => sub { ...; 0 },	362	msg1 => sub { ... },
363	msg2 => sub { ...; 0 },	363	msg2 => sub { ... },
364	;	364	;
365		365
366	Example: create a port, bind receivers and send it in a message elsewhere	366	Example: create a port, bind receivers and send it in a message elsewhere
367	in one go:	367	in one go:
368		368
369	snd $otherport, reply =>	369	snd $otherport, reply =>
370	rcv port,	370	rcv port,
371	msg1 => sub { ...; 0 },	371	msg1 => sub { ... },
372	...	372	...
373	;	373	;
374		374
		375	Example: temporarily register a rcv callback for a tag matching some port
		376	(e.g. for a rpc reply) and unregister it after a message was received.
		377
		378	rcv $port, $otherport => sub {
		379	my @reply = @_;
		380
		381	rcv $SELF, $otherport;
		382	};
		383
375	=cut	384	=cut
376		385
377	sub rcv($@) {	386	sub rcv($@) {
378	my $port = shift;	387	my $port = shift;
379	my ($noderef, $portid) = split /#/, $port, 2;	388	my ($nodeid, $portid) = split /#/, $port, 2;
380		389
381	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	390	$NODE{$nodeid} == $NODE{""}
382	or Carp::croak "$port: rcv can only be called on local ports, caught";	391	or Carp::croak "$port: rcv can only be called on local ports, caught";
383		392
384	if (@_ == 1) {	393	while (@_) {
		394	if (ref $_[0]) {
		395	if (my $self = $PORT_DATA{$portid}) {
		396	"AnyEvent::MP::Port" eq ref $self
		397	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		398
		399	$self->[2] = shift;
		400	} else {
385	my $cb = shift;	401	my $cb = shift;
386	delete $PORT_DATA{$portid};
387	$PORT{$portid} = sub {	402	$PORT{$portid} = sub {
388	local $SELF = $port;	403	local $SELF = $port;
389	eval {	404	eval { &$cb }; _self_die if $@;
390	&$cb	405	};
391	and kil $port;
392	};	406	}
393	_self_die if $@;	407	} elsif (defined $_[0]) {
394	};
395	} else {
396	my $self = $PORT_DATA{$portid} \|\|= do {	408	my $self = $PORT_DATA{$portid} \|\|= do {
397	my $self = bless {	409	my $self = bless [$PORT{$port} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
398	id => $port,
399	}, "AnyEvent::MP::Port";
400		410
401	$PORT{$portid} = sub {	411	$PORT{$portid} = sub {
402	local $SELF = $port;	412	local $SELF = $port;
403		413
404	eval {
405	for (@{ $self->{rc0}{$_[0]} }) {	414	if (my $cb = $self->[1]{$_[0]}) {
406	$_ && &{$_->[0]}	415	shift;
407	&& undef $_;	416	eval { &$cb }; _self_die if $@;
408	}	417	} else {
409
410	for (@{ $self->{rcv}{$_[0]} }) {
411	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
412	&& &{$_->[0]}	418	&{ $self->[0] };
413	&& undef $_;
414	}
415
416	for (@{ $self->{any} }) {
417	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
418	&& &{$_->[0]}
419	&& undef $_;
420	}	419	}
421	};	420	};
422	_self_die if $@;	421
		422	$self
423	};	423	};
424		424
425	$self
426	};
427
428	"AnyEvent::MP::Port" eq ref $self	425	"AnyEvent::MP::Port" eq ref $self
429	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	426	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
430		427
431	while (@_) {
432	my ($match, $cb) = splice @_, 0, 2;	428	my ($tag, $cb) = splice @_, 0, 2;
433		429
434	if (!ref $match) {	430	if (defined $cb) {
435	push @{ $self->{rc0}{$match} }, [$cb];	431	$self->[1]{$tag} = $cb;
436	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
437	my ($type, @match) = @$match;
438	@match
439	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
440	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
441	} else {	432	} else {
442	push @{ $self->{any} }, [$cb, $match];	433	delete $self->[1]{$tag};
443	}	434	}
444	}	435	}
445	}	436	}
446		437
447	$port	438	$port
…		…
483	$res	474	$res
484	}	475	}
485	}	476	}
486	}	477	}
487		478
488	=item $guard = mon $port, $cb->(@reason)	479	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
489		480
490	=item $guard = mon $port, $rcvport	481	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
491		482
492	=item $guard = mon $port	483	=item $guard = mon $port # kill $SELF when $port dies
493		484
494	=item $guard = mon $port, $rcvport, @msg	485	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
495		486
496	Monitor the given port and do something when the port is killed, and	487	Monitor the given port and do something when the port is killed or
497	optionally return a guard that can be used to stop monitoring again.	488	messages to it were lost, and optionally return a guard that can be used
		489	to stop monitoring again.
498		490
499	In the first form (callback), the callback is simply called with any	491	In the first form (callback), the callback is simply called with any
500	number of C<@reason> elements (no @reason means that the port was deleted	492	number of C<@reason> elements (no @reason means that the port was deleted
501	"normally"). Note also that I<< the callback B<must> never die >>, so use	493	"normally"). Note also that I<< the callback B<must> never die >>, so use
502	C<eval> if unsure.	494	C<eval> if unsure.
503		495
504	In the second form (another port given), the other port (C<$rcvport)	496	In the second form (another port given), the other port (C<$rcvport>)
505	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	497	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
506	"normal" kils nothing happens, while under all other conditions, the other	498	"normal" kils nothing happens, while under all other conditions, the other
507	port is killed with the same reason.	499	port is killed with the same reason.
508		500
509	The third form (kill self) is the same as the second form, except that	501	The third form (kill self) is the same as the second form, except that
510	C<$rvport> defaults to C<$SELF>.	502	C<$rvport> defaults to C<$SELF>.
511		503
512	In the last form (message), a message of the form C<@msg, @reason> will be	504	In the last form (message), a message of the form C<@msg, @reason> will be
513	C<snd>.	505	C<snd>.
		506
		507	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		508	alert was raised), they are removed and will not trigger again.
514		509
515	As a rule of thumb, monitoring requests should always monitor a port from	510	As a rule of thumb, monitoring requests should always monitor a port from
516	a local port (or callback). The reason is that kill messages might get	511	a local port (or callback). The reason is that kill messages might get
517	lost, just like any other message. Another less obvious reason is that	512	lost, just like any other message. Another less obvious reason is that
518	even monitoring requests can get lost (for exmaple, when the connection	513	even monitoring requests can get lost (for example, when the connection
519	to the other node goes down permanently). When monitoring a port locally	514	to the other node goes down permanently). When monitoring a port locally
520	these problems do not exist.	515	these problems do not exist.
521		516
		517	C<mon> effectively guarantees that, in the absence of hardware failures,
		518	after starting the monitor, either all messages sent to the port will
		519	arrive, or the monitoring action will be invoked after possible message
		520	loss has been detected. No messages will be lost "in between" (after
		521	the first lost message no further messages will be received by the
		522	port). After the monitoring action was invoked, further messages might get
		523	delivered again.
		524
		525	Inter-host-connection timeouts and monitoring depend on the transport
		526	used. The only transport currently implemented is TCP, and AnyEvent::MP
		527	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		528	non-idle connection, and usually around two hours for idle connections).
		529
		530	This means that monitoring is good for program errors and cleaning up
		531	stuff eventually, but they are no replacement for a timeout when you need
		532	to ensure some maximum latency.
		533
522	Example: call a given callback when C<$port> is killed.	534	Example: call a given callback when C<$port> is killed.
523		535
524	mon $port, sub { warn "port died because of <@_>\n" };	536	mon $port, sub { warn "port died because of <@_>\n" };
525		537
526	Example: kill ourselves when C<$port> is killed abnormally.	538	Example: kill ourselves when C<$port> is killed abnormally.
…		…
532	mon $port, $self => "restart";	544	mon $port, $self => "restart";
533		545
534	=cut	546	=cut
535		547
536	sub mon {	548	sub mon {
537	my ($noderef, $port) = split /#/, shift, 2;	549	my ($nodeid, $port) = split /#/, shift, 2;
538		550
539	my $node = $NODE{$noderef} \|\| add_node $noderef;	551	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
540		552
541	my $cb = @_ ? $_[0] : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';	553	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
542		554
543	unless (ref $cb) {	555	unless (ref $cb) {
544	if (@_) {	556	if (@_) {
545	# send a kill info message	557	# send a kill info message
546	my (@msg) = @_;	558	my (@msg) = ($cb, @_);
547	$cb = sub { snd @msg, @_ };	559	$cb = sub { snd @msg, @_ };
548	} else {	560	} else {
549	# simply kill other port	561	# simply kill other port
550	my $port = $cb;	562	my $port = $cb;
551	$cb = sub { kil $port, @_ if @_ };	563	$cb = sub { kil $port, @_ if @_ };
…		…
553	}	565	}
554		566
555	$node->monitor ($port, $cb);	567	$node->monitor ($port, $cb);
556		568
557	defined wantarray	569	defined wantarray
558	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	570	and ($cb += 0, AnyEvent::Util::guard { $node->unmonitor ($port, $cb) })
559	}	571	}
560		572
561	=item $guard = mon_guard $port, $ref, $ref...	573	=item $guard = mon_guard $port, $ref, $ref...
562		574
563	Monitors the given C<$port> and keeps the passed references. When the port	575	Monitors the given C<$port> and keeps the passed references. When the port
564	is killed, the references will be freed.	576	is killed, the references will be freed.
565		577
566	Optionally returns a guard that will stop the monitoring.	578	Optionally returns a guard that will stop the monitoring.
567		579
568	This function is useful when you create e.g. timers or other watchers and	580	This function is useful when you create e.g. timers or other watchers and
569	want to free them when the port gets killed:	581	want to free them when the port gets killed (note the use of C<psub>):
570		582
571	$port->rcv (start => sub {	583	$port->rcv (start => sub {
572	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	584	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
573	undef $timer if 0.9 < rand;	585	undef $timer if 0.9 < rand;
574	});	586	});
575	});	587	});
576		588
577	=cut	589	=cut
…		…
586		598
587	=item kil $port[, @reason]	599	=item kil $port[, @reason]
588		600
589	Kill the specified port with the given C<@reason>.	601	Kill the specified port with the given C<@reason>.
590		602
591	If no C<@reason> is specified, then the port is killed "normally" (linked	603	If no C<@reason> is specified, then the port is killed "normally" (ports
592	ports will not be kileld, or even notified).	604	monitoring other ports will not necessarily die because a port dies
		605	"normally").
593		606
594	Otherwise, linked ports get killed with the same reason (second form of	607	Otherwise, linked ports get killed with the same reason (second form of
595	C<mon>, see below).	608	C<mon>, see above).
596		609
597	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	610	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
598	will be reported as reason C<< die => $@ >>.	611	will be reported as reason C<< die => $@ >>.
599		612
600	Transport/communication errors are reported as C<< transport_error =>	613	Transport/communication errors are reported as C<< transport_error =>
601	$message >>.	614	$message >>.
602		615
603	=back
604
605	=head1 NODE MESSAGES
606
607	Nodes understand the following messages sent to them. Many of them take
608	arguments called C<@reply>, which will simply be used to compose a reply
609	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
610	the remaining arguments are simply the message data.
611
612	While other messages exist, they are not public and subject to change.
613
614	=over 4
615
616	=cut	616	=cut
617		617
618	=item lookup => $name, @reply	618	=item $port = spawn $node, $initfunc[, @initdata]
619		619
620	Replies with the port ID of the specified well-known port, or C<undef>.	620	Creates a port on the node C<$node> (which can also be a port ID, in which
		621	case it's the node where that port resides).
621		622
622	=item devnull => ...	623	The port ID of the newly created port is returned immediately, and it is
		624	possible to immediately start sending messages or to monitor the port.
623		625
624	Generic data sink/CPU heat conversion.	626	After the port has been created, the init function is called on the remote
		627	node, in the same context as a C<rcv> callback. This function must be a
		628	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		629	specify a function in the main program, use C<::name>.
625		630
626	=item relay => $port, @msg	631	If the function doesn't exist, then the node tries to C<require>
		632	the package, then the package above the package and so on (e.g.
		633	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		634	exists or it runs out of package names.
627		635
628	Simply forwards the message to the given port.	636	The init function is then called with the newly-created port as context
		637	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		638	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		639	the port might not get created.
629		640
630	=item eval => $string[ @reply]	641	A common idiom is to pass a local port, immediately monitor the spawned
		642	port, and in the remote init function, immediately monitor the passed
		643	local port. This two-way monitoring ensures that both ports get cleaned up
		644	when there is a problem.
631		645
632	Evaluates the given string. If C<@reply> is given, then a message of the	646	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
633	form C<@reply, $@, @evalres> is sent.	647	caller before C<spawn> returns (by delaying invocation when spawn is
		648	called for the local node).
634		649
635	Example: crash another node.	650	Example: spawn a chat server port on C<$othernode>.
636		651
637	snd $othernode, eval => "exit";	652	# this node, executed from within a port context:
		653	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		654	mon $server;
638		655
639	=item time => @reply	656	# init function on C<$othernode>
		657	sub connect {
		658	my ($srcport) = @_;
640		659
641	Replies the the current node time to C<@reply>.	660	mon $srcport;
642		661
643	Example: tell the current node to send the current time to C<$myport> in a	662	rcv $SELF, sub {
644	C<timereply> message.	663	...
		664	};
		665	}
645		666
646	snd $NODE, time => $myport, timereply => 1, 2;	667	=cut
647	# => snd $myport, timereply => 1, 2, <time>	668
		669	sub _spawn {
		670	my $port = shift;
		671	my $init = shift;
		672
		673	# rcv will create the actual port
		674	local $SELF = "$NODE#$port";
		675	eval {
		676	&{ load_func $init }
		677	};
		678	_self_die if $@;
		679	}
		680
		681	sub spawn(@) {
		682	my ($nodeid, undef) = split /#/, shift, 2;
		683
		684	my $id = "$RUNIQ." . $ID++;
		685
		686	$_[0] =~ /::/
		687	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		688
		689	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		690
		691	"$nodeid#$id"
		692	}
		693
		694	=item after $timeout, @msg
		695
		696	=item after $timeout, $callback
		697
		698	Either sends the given message, or call the given callback, after the
		699	specified number of seconds.
		700
		701	This is simply a utility function that comes in handy at times - the
		702	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		703	so it may go away in the future.
		704
		705	=cut
		706
		707	sub after($@) {
		708	my ($timeout, @action) = @_;
		709
		710	my $t; $t = AE::timer $timeout, 0, sub {
		711	undef $t;
		712	ref $action[0]
		713	? $action[0]()
		714	: snd @action;
		715	};
		716	}
		717
		718	=item cal $port, @msg, $callback[, $timeout]
		719
		720	A simple form of RPC - sends a message to the given C<$port> with the
		721	given contents (C<@msg>), but adds a reply port to the message.
		722
		723	The reply port is created temporarily just for the purpose of receiving
		724	the reply, and will be C<kil>ed when no longer needed.
		725
		726	A reply message sent to the port is passed to the C<$callback> as-is.
		727
		728	If an optional time-out (in seconds) is given and it is not C<undef>,
		729	then the callback will be called without any arguments after the time-out
		730	elapsed and the port is C<kil>ed.
		731
		732	If no time-out is given, then the local port will monitor the remote port
		733	instead, so it eventually gets cleaned-up.
		734
		735	Currently this function returns the temporary port, but this "feature"
		736	might go in future versions unless you can make a convincing case that
		737	this is indeed useful for something.
		738
		739	=cut
		740
		741	sub cal(@) {
		742	my $timeout = ref $_[-1] ? undef : pop;
		743	my $cb = pop;
		744
		745	my $port = port {
		746	undef $timeout;
		747	kil $SELF;
		748	&$cb;
		749	};
		750
		751	if (defined $timeout) {
		752	$timeout = AE::timer $timeout, 0, sub {
		753	undef $timeout;
		754	kil $port;
		755	$cb->();
		756	};
		757	} else {
		758	mon $_[0], sub {
		759	kil $port;
		760	$cb->();
		761	};
		762	}
		763
		764	push @_, $port;
		765	&snd;
		766
		767	$port
		768	}
648		769
649	=back	770	=back
650		771
651	=head1 AnyEvent::MP vs. Distributed Erlang	772	=head1 AnyEvent::MP vs. Distributed Erlang
652		773
653	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	774	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
654	== aemp node, Erlang process == aemp port), so many of the documents and	775	== aemp node, Erlang process == aemp port), so many of the documents and
655	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	776	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
656	sample:	777	sample:
657		778
658	http://www.Erlang.se/doc/programming_rules.shtml	779	http://www.erlang.se/doc/programming_rules.shtml
659	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	780	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
660	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	781	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
661	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	782	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
662		783
663	Despite the similarities, there are also some important differences:	784	Despite the similarities, there are also some important differences:
664		785
665	=over 4	786	=over 4
666		787
667	=item * Node references contain the recipe on how to contact them.	788	=item * Node IDs are arbitrary strings in AEMP.
668		789
669	Erlang relies on special naming and DNS to work everywhere in the	790	Erlang relies on special naming and DNS to work everywhere in the same
670	same way. AEMP relies on each node knowing it's own address(es), with	791	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
671	convenience functionality.	792	configuration or DNS), but will otherwise discover other odes itself.
672		793
673	This means that AEMP requires a less tightly controlled environment at the	794	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
674	cost of longer node references and a slightly higher management overhead.	795	uses "local ports are like remote ports".
		796
		797	The failure modes for local ports are quite different (runtime errors
		798	only) then for remote ports - when a local port dies, you I<know> it dies,
		799	when a connection to another node dies, you know nothing about the other
		800	port.
		801
		802	Erlang pretends remote ports are as reliable as local ports, even when
		803	they are not.
		804
		805	AEMP encourages a "treat remote ports differently" philosophy, with local
		806	ports being the special case/exception, where transport errors cannot
		807	occur.
675		808
676	=item * Erlang uses processes and a mailbox, AEMP does not queue.	809	=item * Erlang uses processes and a mailbox, AEMP does not queue.
677		810
678	Erlang uses processes that selctively receive messages, and therefore	811	Erlang uses processes that selectively receive messages, and therefore
679	needs a queue. AEMP is event based, queuing messages would serve no useful	812	needs a queue. AEMP is event based, queuing messages would serve no
680	purpose.	813	useful purpose. For the same reason the pattern-matching abilities of
		814	AnyEvent::MP are more limited, as there is little need to be able to
		815	filter messages without dequeuing them.
681		816
682	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	817	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).
683		818
684	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	819	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
685		820
686	Sending messages in Erlang is synchronous and blocks the process. AEMP	821	Sending messages in Erlang is synchronous and blocks the process (and
687	sends are immediate, connection establishment is handled in the	822	so does not need a queue that can overflow). AEMP sends are immediate,
688	background.	823	connection establishment is handled in the background.
689		824
690	=item * Erlang can silently lose messages, AEMP cannot.	825	=item * Erlang suffers from silent message loss, AEMP does not.
691		826
692	Erlang makes few guarantees on messages delivery - messages can get lost	827	Erlang makes few guarantees on messages delivery - messages can get lost
693	without any of the processes realising it (i.e. you send messages a, b,	828	without any of the processes realising it (i.e. you send messages a, b,
694	and c, and the other side only receives messages a and c).	829	and c, and the other side only receives messages a and c).
695		830
696	AEMP guarantees correct ordering, and the guarantee that there are no	831	AEMP guarantees correct ordering, and the guarantee that after one message
697	holes in the message sequence.	832	is lost, all following ones sent to the same port are lost as well, until
698		833	monitoring raises an error, so there are no silent "holes" in the message
699	=item * In Erlang, processes can be declared dead and later be found to be	834	sequence.
700	alive.
701
702	In Erlang it can happen that a monitored process is declared dead and
703	linked processes get killed, but later it turns out that the process is
704	still alive - and can receive messages.
705
706	In AEMP, when port monitoring detects a port as dead, then that port will
707	eventually be killed - it cannot happen that a node detects a port as dead
708	and then later sends messages to it, finding it is still alive.
709		835
710	=item * Erlang can send messages to the wrong port, AEMP does not.	836	=item * Erlang can send messages to the wrong port, AEMP does not.
711		837
712	In Erlang it is quite possible that a node that restarts reuses a process	838	In Erlang it is quite likely that a node that restarts reuses a process ID
713	ID known to other nodes for a completely different process, causing	839	known to other nodes for a completely different process, causing messages
714	messages destined for that process to end up in an unrelated process.	840	destined for that process to end up in an unrelated process.
715		841
716	AEMP never reuses port IDs, so old messages or old port IDs floating	842	AEMP never reuses port IDs, so old messages or old port IDs floating
717	around in the network will not be sent to an unrelated port.	843	around in the network will not be sent to an unrelated port.
718		844
719	=item * Erlang uses unprotected connections, AEMP uses secure	845	=item * Erlang uses unprotected connections, AEMP uses secure
720	authentication and can use TLS.	846	authentication and can use TLS.
721		847
722	AEMP can use a proven protocol - SSL/TLS - to protect connections and	848	AEMP can use a proven protocol - TLS - to protect connections and
723	securely authenticate nodes.	849	securely authenticate nodes.
724		850
725	=item * The AEMP protocol is optimised for both text-based and binary	851	=item * The AEMP protocol is optimised for both text-based and binary
726	communications.	852	communications.
727		853
728	The AEMP protocol, unlike the Erlang protocol, supports both	854	The AEMP protocol, unlike the Erlang protocol, supports both programming
729	language-independent text-only protocols (good for debugging) and binary,	855	language independent text-only protocols (good for debugging) and binary,
730	language-specific serialisers (e.g. Storable).	856	language-specific serialisers (e.g. Storable). By default, unless TLS is
		857	used, the protocol is actually completely text-based.
731		858
732	It has also been carefully designed to be implementable in other languages	859	It has also been carefully designed to be implementable in other languages
733	with a minimum of work while gracefully degrading fucntionality to make the	860	with a minimum of work while gracefully degrading functionality to make the
734	protocol simple.	861	protocol simple.
735		862
736	=item * AEMP has more flexible monitoring options than Erlang.	863	=item * AEMP has more flexible monitoring options than Erlang.
737		864
738	In Erlang, you can chose to receive I<all> exit signals as messages	865	In Erlang, you can chose to receive I<all> exit signals as messages
…		…
741	Erlang, as one can choose between automatic kill, exit message or callback	868	Erlang, as one can choose between automatic kill, exit message or callback
742	on a per-process basis.	869	on a per-process basis.
743		870
744	=item * Erlang tries to hide remote/local connections, AEMP does not.	871	=item * Erlang tries to hide remote/local connections, AEMP does not.
745		872
746	Monitoring in Erlang is not an indicator of process death/crashes,	873	Monitoring in Erlang is not an indicator of process death/crashes, in the
747	as linking is (except linking is unreliable in Erlang).	874	same way as linking is (except linking is unreliable in Erlang).
748		875
749	In AEMP, you don't "look up" registered port names or send to named ports	876	In AEMP, you don't "look up" registered port names or send to named ports
750	that might or might not be persistent. Instead, you normally spawn a port	877	that might or might not be persistent. Instead, you normally spawn a port
751	on the remote node. The init function monitors the you, and you monitor	878	on the remote node. The init function monitors you, and you monitor the
752	the remote port. Since both monitors are local to the node, they are much	879	remote port. Since both monitors are local to the node, they are much more
753	more reliable.	880	reliable (no need for C<spawn_link>).
754		881
755	This also saves round-trips and avoids sending messages to the wrong port	882	This also saves round-trips and avoids sending messages to the wrong port
756	(hard to do in Erlang).	883	(hard to do in Erlang).
757		884
758	=back	885	=back
759		886
		887	=head1 RATIONALE
		888
		889	=over 4
		890
		891	=item Why strings for port and node IDs, why not objects?
		892
		893	We considered "objects", but found that the actual number of methods
		894	that can be called are quite low. Since port and node IDs travel over
		895	the network frequently, the serialising/deserialising would add lots of
		896	overhead, as well as having to keep a proxy object everywhere.
		897
		898	Strings can easily be printed, easily serialised etc. and need no special
		899	procedures to be "valid".
		900
		901	And as a result, a miniport consists of a single closure stored in a
		902	global hash - it can't become much cheaper.
		903
		904	=item Why favour JSON, why not a real serialising format such as Storable?
		905
		906	In fact, any AnyEvent::MP node will happily accept Storable as framing
		907	format, but currently there is no way to make a node use Storable by
		908	default (although all nodes will accept it).
		909
		910	The default framing protocol is JSON because a) JSON::XS is many times
		911	faster for small messages and b) most importantly, after years of
		912	experience we found that object serialisation is causing more problems
		913	than it solves: Just like function calls, objects simply do not travel
		914	easily over the network, mostly because they will always be a copy, so you
		915	always have to re-think your design.
		916
		917	Keeping your messages simple, concentrating on data structures rather than
		918	objects, will keep your messages clean, tidy and efficient.
		919
		920	=back
		921
760	=head1 SEE ALSO	922	=head1 SEE ALSO
		923
		924	L<AnyEvent::MP::Intro> - a gentle introduction.
		925
		926	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		927
		928	L<AnyEvent::MP::Global> - network maintainance and port groups, to find
		929	your applications.
		930
		931	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		932	all nodes.
761		933
762	L<AnyEvent>.	934	L<AnyEvent>.
763		935
764	=head1 AUTHOR	936	=head1 AUTHOR
765		937

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Revision 1.97 by root, Fri Oct 2 13:29:49 2009 UTC