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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.7 by root, Sat Aug 1 15:04:30 2009 UTC vs.
Revision 1.125 by root, Sat Mar 3 13:07:19 2012 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 # returns this node identifier
10	$NODE # contains this node identifier	9	$NODE # contains this node's node ID
		10	NODE # returns this node's node ID
11		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
12	snd $port, type => data...;	20	snd $port, type => data...;
		21	snd $port, @msg;
		22	snd @msg_with_first_element_being_a_port;
13		23
14	rcv $port, smartmatch => $cb->($port, @msg);	24	# creating/using ports, the simple way
		25	my $simple_port = port { my @msg = @_ };
15		26
16	# examples:	27	# creating/using ports, tagged message matching
		28	my $port = port;
17	rcv $port2, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
18	rcv $port1, pong => sub { warn "pong received\n" };	30	rcv $port, pong => sub { warn "pong received\n" };
19	snd $port2, ping => $port1;
20		31
21	# more, smarter, matches (_any_ is exported by this module)	32	# create a port on another node
22	rcv $port, [child_died => $pid] => sub { ...	33	my $port = spawn $node, $initfunc, @initdata;
23	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3	34
		35	# destroy a port again
		36	kil $port; # "normal" kill
		37	kil $port, my_error => "everything is broken"; # error kill
		38
		39	# monitoring
		40	mon $localport, $cb->(@msg) # callback is invoked on death
		41	mon $localport, $otherport # kill otherport on abnormal death
		42	mon $localport, $otherport, @msg # send message on death
		43
		44	# temporarily execute code in port context
		45	peval $port, sub { die "kill the port!" };
		46
		47	# execute callbacks in $SELF port context
		48	my $timer = AE::timer 1, 0, psub {
		49	die "kill the port, delayed";
		50	};
		51
		52	=head1 CURRENT STATUS
		53
		54	bin/aemp - stable.
		55	AnyEvent::MP - stable API, should work.
		56	AnyEvent::MP::Intro - explains most concepts.
		57	AnyEvent::MP::Kernel - mostly stable API.
		58	AnyEvent::MP::Global - stable API.
24		59
25	=head1 DESCRIPTION	60	=head1 DESCRIPTION
26		61
27	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
28		63
29	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
30	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
31		66
32	At the moment, this module family is severly brokena nd underdocumented,	67	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
33	so do not use. This was uploaded mainly to resreve the CPAN namespace -	68	manual page and the examples under F<eg/>.
34	stay tuned!
35		69
36	=head1 CONCEPTS	70	=head1 CONCEPTS
37		71
38	=over 4	72	=over 4
39		73
40	=item port	74	=item port
41		75
42	A port is something you can send messages to with the C<snd> function, and	76	Not to be confused with a TCP port, a "port" is something you can send
43	you can register C<rcv> handlers with. All C<rcv> handlers will receive	77	messages to (with the C<snd> function).
44	messages they match, messages will not be queued.
45		78
		79	Ports allow you to register C<rcv> handlers that can match all or just
		80	some messages. Messages send to ports will not be queued, regardless of
		81	anything was listening for them or not.
		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
46	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
47		86
48	A port id is always the noderef, a hash-mark (C<#>) as separator, followed	87	A port ID is the concatenation of a node ID, a hash-mark (C<#>)
49	by a port name (a printable string of unspecified format).	88	as separator, and a port name (a printable string of unspecified
		89	format created by AnyEvent::MP).
50		90
51	=item node	91	=item node
52		92
53	A node is a single process containing at least one port - the node	93	A node is a single process containing at least one port - the node port,
54	port. You can send messages to node ports to let them create new ports,	94	which enables nodes to manage each other remotely, and to create new
55	among other things.	95	ports.
56		96
57	Initially, nodes are either private (single-process only) or hidden	97	Nodes are either public (have one or more listening ports) or private
58	(connected to a master node only). Only when they epxlicitly "become	98	(no listening ports). Private nodes cannot talk to other private nodes
59	public" can you send them messages from unrelated other nodes.	99	currently, but all nodes can talk to public nodes.
60		100
61	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	101	Nodes is represented by (printable) strings called "node IDs".
62		102
		103	=item node ID - C<[A-Za-z0-9_\-.:]*>
		104
63	A noderef is a string that either uniquely identifies a given node (for	105	A node ID is a string that uniquely identifies the node within a
64	private and hidden nodes), or contains a recipe on how to reach a given	106	network. Depending on the configuration used, node IDs can look like a
65	node (for public nodes).	107	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		108	doesn't interpret node IDs in any way except to uniquely identify a node.
		109
		110	=item binds - C<ip:port>
		111
		112	Nodes can only talk to each other by creating some kind of connection to
		113	each other. To do this, nodes should listen on one or more local transport
		114	endpoints - binds.
		115
		116	Currently, only standard C<ip:port> specifications can be used, which
		117	specify TCP ports to listen on. So a bind is basically just a tcp socket
		118	in listening mode thta accepts conenctions form other nodes.
		119
		120	=item seed nodes
		121
		122	When a node starts, it knows nothing about the network it is in - it
		123	needs to connect to at least one other node that is already in the
		124	network. These other nodes are called "seed nodes".
		125
		126	Seed nodes themselves are not special - they are seed nodes only because
		127	some other node I<uses> them as such, but any node can be used as seed
		128	node for other nodes, and eahc node cna use a different set of seed nodes.
		129
		130	In addition to discovering the network, seed nodes are also used to
		131	maintain the network - all nodes using the same seed node form are part of
		132	the same network. If a network is split into multiple subnets because e.g.
		133	the network link between the parts goes down, then using the same seed
		134	nodes for all nodes ensures that eventually the subnets get merged again.
		135
		136	Seed nodes are expected to be long-running, and at least one seed node
		137	should always be available. They should also be relatively responsive - a
		138	seed node that blocks for long periods will slow down everybody else.
		139
		140	For small networks, it's best if every node uses the same set of seed
		141	nodes. For large networks, it can be useful to specify "regional" seed
		142	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		143	each other. What's important is that all seed nodes connections form a
		144	complete graph, so that the network cannot split into separate subnets
		145	forever.
		146
		147	Seed nodes are represented by seed IDs.
		148
		149	=item seed IDs - C<host:port>
		150
		151	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
		152	TCP port) of nodes that should be used as seed nodes.
		153
		154	=item global nodes
		155
		156	An AEMP network needs a discovery service - nodes need to know how to
		157	connect to other nodes they only know by name. In addition, AEMP offers a
		158	distributed "group database", which maps group names to a list of strings
		159	- for example, to register worker ports.
		160
		161	A network needs at least one global node to work, and allows every node to
		162	be a global node.
		163
		164	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		165	node and tries to keep connections to all other nodes. So while it can
		166	make sense to make every node "global" in small networks, it usually makes
		167	sense to only make seed nodes into global nodes in large networks (nodes
		168	keep connections to seed nodes and global nodes, so makign them the same
		169	reduces overhead).
66		170
67	=back	171	=back
68		172
69	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
70		174
72		176
73	=cut	177	=cut
74		178
75	package AnyEvent::MP;	179	package AnyEvent::MP;
76		180
77	use AnyEvent::MP::Util ();	181	use AnyEvent::MP::Config ();
78	use AnyEvent::MP::Node;	182	use AnyEvent::MP::Kernel;
79	use AnyEvent::MP::Transport;	183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
80		184
81	use utf8;
82	use common::sense;	185	use common::sense;
83		186
84	use Carp ();	187	use Carp ();
85		188
86	use AE ();	189	use AE ();
		190	use Guard ();
87		191
88	use base "Exporter";	192	use base "Exporter";
89		193
90	our $VERSION = '0.01';	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
91	our @EXPORT = qw(NODE $NODE $PORT snd rcv _any_);
92		195
93	our $DEFAULT_SECRET;	196	our @EXPORT = qw(
94	our $DEFAULT_PORT = "4040";	197	NODE $NODE *SELF node_of after
		198	configure
		199	snd rcv mon mon_guard kil psub peval spawn cal
		200	port
		201	db_set db_del db_reg
		202	);
95		203
96	our $CONNECT_INTERVAL = 5; # new connect every 5s, at least	204	our $SELF;
97	our $CONNECT_TIMEOUT = 30; # includes handshake
98		205
99	sub default_secret {	206	sub _self_die() {
100	unless (defined $DEFAULT_SECRET) {	207	my $msg = $@;
101	if (open my $fh, "<$ENV{HOME}/.aemp-secret") {	208	$msg =~ s/\n+$// unless ref $msg;
102	sysread $fh, $DEFAULT_SECRET, -s $fh;	209	kil $SELF, die => $msg;
103	} else {
104	$DEFAULT_SECRET = AnyEvent::MP::Util::nonce 32;
105	}
106	}
107
108	$DEFAULT_SECRET
109	}	210	}
110		211
111	=item NODE / $NODE	212	=item $thisnode = NODE / $NODE
112		213
113	The C<NODE ()> function and the C<$NODE> variable contain the noderef of	214	The C<NODE> function returns, and the C<$NODE> variable contains, the node
114	the local node. The value is initialised by a call to C<become_public> or	215	ID of the node running in the current process. This value is initialised by
115	C<become_slave>, after which all local port identifiers become invalid.	216	a call to C<configure>.
116		217
117	=cut	218	=item $nodeid = node_of $port
118		219
119	our $UNIQ = sprintf "%x.%x", $$, time; # per-process/node unique cookie	220	Extracts and returns the node ID from a port ID or a node ID.
120	our $ID = "a0";
121	our $PUBLIC = 0;
122	our $NODE;
123	our $PORT;
124		221
125	our %NODE; # node id to transport mapping, or "undef", for local node	222	=item configure $profile, key => value...
126	our %PORT; # local ports
127	our %LISTENER; # local transports
128		223
129	sub NODE() { $NODE }	224	=item configure key => value...
130		225
131	{	226	Before a node can talk to other nodes on the network (i.e. enter
132	use POSIX ();	227	"distributed mode") it has to configure itself - the minimum a node needs
133	my $nodename = (POSIX::uname)[1];	228	to know is its own name, and optionally it should know the addresses of
134	$NODE = "$$\@$nodename";	229	some other nodes in the network to discover other nodes.
135	}
136		230
137	sub _ANY_() { 1 }	231	This function configures a node - it must be called exactly once (or
138	sub _any_() { \&_ANY_ }	232	never) before calling other AnyEvent::MP functions.
139		233
140	sub add_node {	234	The key/value pairs are basically the same ones as documented for the
141	my ($noderef) = @_;	235	F<aemp> command line utility (sans the set/del prefix), with two additions:
142		236
143	return $NODE{$noderef}	237	=over 4
144	if exists $NODE{$noderef};
145		238
146	for (split /,/, $noderef) {	239	=item norc => $boolean (default false)
147	return $NODE{$noderef} = $NODE{$_}
148	if exists $NODE{$_};
149	}
150		240
151	# for indirect sends, use a different class	241	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
152	my $node = new AnyEvent::MP::Node::Direct $noderef;	242	be consulted - all configuraiton options must be specified in the
		243	C<configure> call.
153		244
154	$NODE{$_} = $node	245	=item force => $boolean (default false)
155	for $noderef, split /,/, $noderef;
156		246
157	$node	247	IF true, then the values specified in the C<configure> will take
158	}	248	precedence over any values configured via the rc file. The default is for
		249	the rc file to override any options specified in the program.
159		250
		251	=back
		252
		253	=over 4
		254
		255	=item step 1, gathering configuration from profiles
		256
		257	The function first looks up a profile in the aemp configuration (see the
		258	L<aemp> commandline utility). The profile name can be specified via the
		259	named C<profile> parameter or can simply be the first parameter). If it is
		260	missing, then the nodename (F<uname -n>) will be used as profile name.
		261
		262	The profile data is then gathered as follows:
		263
		264	First, all remaining key => value pairs (all of which are conveniently
		265	undocumented at the moment) will be interpreted as configuration
		266	data. Then they will be overwritten by any values specified in the global
		267	default configuration (see the F<aemp> utility), then the chain of
		268	profiles chosen by the profile name (and any C<parent> attributes).
		269
		270	That means that the values specified in the profile have highest priority
		271	and the values specified directly via C<configure> have lowest priority,
		272	and can only be used to specify defaults.
		273
		274	If the profile specifies a node ID, then this will become the node ID of
		275	this process. If not, then the profile name will be used as node ID, with
		276	a slash (C</>) attached.
		277
		278	If the node ID (or profile name) ends with a slash (C</>), then a random
		279	string is appended to make it unique.
		280
		281	=item step 2, bind listener sockets
		282
		283	The next step is to look up the binds in the profile, followed by binding
		284	aemp protocol listeners on all binds specified (it is possible and valid
		285	to have no binds, meaning that the node cannot be contacted form the
		286	outside. This means the node cannot talk to other nodes that also have no
		287	binds, but it can still talk to all "normal" nodes).
		288
		289	If the profile does not specify a binds list, then a default of C<*> is
		290	used, meaning the node will bind on a dynamically-assigned port on every
		291	local IP address it finds.
		292
		293	=item step 3, connect to seed nodes
		294
		295	As the last step, the seed ID list from the profile is passed to the
		296	L<AnyEvent::MP::Global> module, which will then use it to keep
		297	connectivity with at least one node at any point in time.
		298
		299	=back
		300
		301	Example: become a distributed node using the local node name as profile.
		302	This should be the most common form of invocation for "daemon"-type nodes.
		303
		304	configure
		305
		306	Example: become an anonymous node. This form is often used for commandline
		307	clients.
		308
		309	configure nodeid => "anon/";
		310
		311	Example: configure a node using a profile called seed, which is suitable
		312	for a seed node as it binds on all local addresses on a fixed port (4040,
		313	customary for aemp).
		314
		315	# use the aemp commandline utility
		316	# aemp profile seed binds '*:4040'
		317
		318	# then use it
		319	configure profile => "seed";
		320
		321	# or simply use aemp from the shell again:
		322	# aemp run profile seed
		323
		324	# or provide a nicer-to-remember nodeid
		325	# aemp run profile seed nodeid "$(hostname)"
		326
		327	=item $SELF
		328
		329	Contains the current port id while executing C<rcv> callbacks or C<psub>
		330	blocks.
		331
		332	=item *SELF, SELF, %SELF, @SELF...
		333
		334	Due to some quirks in how perl exports variables, it is impossible to
		335	just export C<$SELF>, all the symbols named C<SELF> are exported by this
		336	module, but only C<$SELF> is currently used.
		337
160	=item snd $portid, type => @data	338	=item snd $port, type => @data
161		339
162	=item snd $portid, @msg	340	=item snd $port, @msg
163		341
164	Send the given message to the given port ID, which can identify either a	342	Send the given message to the given port, which can identify either a
165	local or a remote port.	343	local or a remote port, and must be a port ID.
166		344
167	While the message can be about anything, it is highly recommended to use	345	While the message can be almost anything, it is highly recommended to
168	a constant string as first element.	346	use a string as first element (a port ID, or some word that indicates a
		347	request type etc.) and to consist if only simple perl values (scalars,
		348	arrays, hashes) - if you think you need to pass an object, think again.
169		349
170	The message data effectively becomes read-only after a call to this	350	The message data logically becomes read-only after a call to this
171	function: modifying any argument is not allowed and can cause many	351	function: modifying any argument (or values referenced by them) is
172	problems.	352	forbidden, as there can be considerable time between the call to C<snd>
		353	and the time the message is actually being serialised - in fact, it might
		354	never be copied as within the same process it is simply handed to the
		355	receiving port.
173		356
174	The type of data you can transfer depends on the transport protocol: when	357	The type of data you can transfer depends on the transport protocol: when
175	JSON is used, then only strings, numbers and arrays and hashes consisting	358	JSON is used, then only strings, numbers and arrays and hashes consisting
176	of those are allowed (no objects). When Storable is used, then anything	359	of those are allowed (no objects). When Storable is used, then anything
177	that Storable can serialise and deserialise is allowed, and for the local	360	that Storable can serialise and deserialise is allowed, and for the local
178	node, anything can be passed.	361	node, anything can be passed. Best rely only on the common denominator of
		362	these.
179		363
180	=cut	364	=item $local_port = port
181		365
182	sub snd(@) {	366	Create a new local port object and returns its port ID. Initially it has
183	my ($noderef, $port) = split /#/, shift, 2;	367	no callbacks set and will throw an error when it receives messages.
184		368
185	add_node $noderef	369	=item $local_port = port { my @msg = @_ }
186	unless exists $NODE{$noderef};
187		370
188	$NODE{$noderef}->send (["$port", [@_]]);	371	Creates a new local port, and returns its ID. Semantically the same as
		372	creating a port and calling C<rcv $port, $callback> on it.
		373
		374	The block will be called for every message received on the port, with the
		375	global variable C<$SELF> set to the port ID. Runtime errors will cause the
		376	port to be C<kil>ed. The message will be passed as-is, no extra argument
		377	(i.e. no port ID) will be passed to the callback.
		378
		379	If you want to stop/destroy the port, simply C<kil> it:
		380
		381	my $port = port {
		382	my @msg = @_;
		383	...
		384	kil $SELF;
		385	};
		386
		387	=cut
		388
		389	sub rcv($@);
		390
		391	sub _kilme {
		392	die "received message on port without callback";
189	}	393	}
190		394
		395	sub port(;&) {
		396	my $id = $UNIQ . ++$ID;
		397	my $port = "$NODE#$id";
		398
		399	rcv $port, shift \|\| \&_kilme;
		400
		401	$port
		402	}
		403
191	=item rcv $portid, type => $callback->(@msg)	404	=item rcv $local_port, $callback->(@msg)
192		405
193	=item rcv $portid, $smartmatch => $callback->(@msg)	406	Replaces the default callback on the specified port. There is no way to
		407	remove the default callback: use C<sub { }> to disable it, or better
		408	C<kil> the port when it is no longer needed.
194		409
195	=item rcv $portid, [$smartmatch...] => $callback->(@msg)	410	The global C<$SELF> (exported by this module) contains C<$port> while
		411	executing the callback. Runtime errors during callback execution will
		412	result in the port being C<kil>ed.
196		413
197	Register a callback on the port identified by C<$portid>, which I<must> be	414	The default callback received all messages not matched by a more specific
198	a local port.	415	C<tag> match.
199		416
200	The callback has to return a true value when its work is done, after	417	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
201	which is will be removed, or a false value in which case it will stay
202	registered.
203		418
204	If the match is an array reference, then it will be matched against the	419	Register (or replace) callbacks to be called on messages starting with the
205	first elements of the message, otherwise only the first element is being	420	given tag on the given port (and return the port), or unregister it (when
206	matched.	421	C<$callback> is C<$undef> or missing). There can only be one callback
		422	registered for each tag.
207		423
208	Any element in the match that is specified as C<_any_> (a function	424	The original message will be passed to the callback, after the first
209	exported by this module) matches any single element of the message.	425	element (the tag) has been removed. The callback will use the same
		426	environment as the default callback (see above).
210		427
211	While not required, it is highly recommended that the first matching	428	Example: create a port and bind receivers on it in one go.
212	element is a string identifying the message. The one-string-only match is	429
213	also the most efficient match (by far).	430	my $port = rcv port,
		431	msg1 => sub { ... },
		432	msg2 => sub { ... },
		433	;
		434
		435	Example: create a port, bind receivers and send it in a message elsewhere
		436	in one go:
		437
		438	snd $otherport, reply =>
		439	rcv port,
		440	msg1 => sub { ... },
		441	...
		442	;
		443
		444	Example: temporarily register a rcv callback for a tag matching some port
		445	(e.g. for an rpc reply) and unregister it after a message was received.
		446
		447	rcv $port, $otherport => sub {
		448	my @reply = @_;
		449
		450	rcv $SELF, $otherport;
		451	};
214		452
215	=cut	453	=cut
216		454
217	sub rcv($@) {	455	sub rcv($@) {
218	my ($port, $match, $cb) = @_;	456	my $port = shift;
219
220	my $port = $PORT{$port}
221	or do {
222	my ($noderef, $lport) = split /#/, $port;	457	my ($nodeid, $portid) = split /#/, $port, 2;
223	"AnyEvent::MP::Node::Self" eq ref $NODE{$noderef}	458
		459	$NODE{$nodeid} == $NODE{""}
224	or Carp::croak "$port: can only rcv on local ports";	460	or Carp::croak "$port: rcv can only be called on local ports, caught";
225		461
226	$PORT{$lport}	462	while (@_) {
227	or Carp::croak "$port: port does not exist";	463	if (ref $_[0]) {
228		464	if (my $self = $PORT_DATA{$portid}) {
229	$PORT{$port} = $PORT{$lport} # also return	465	"AnyEvent::MP::Port" eq ref $self
230	};	466	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
231		467
232	if (!ref $match) {	468	$self->[0] = shift;
233	push @{ $port->{rc0}{$match} }, [$cb];
234	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
235	my ($type, @match) = @$match;
236	@match
237	? push @{ $port->{rcv}{$match->[0]} }, [$cb, \@match]
238	: push @{ $port->{rc0}{$match->[0]} }, [$cb];
239	} else {	469	} else {
240	push @{ $port->{any} }, [$cb, $match];	470	my $cb = shift;
241	}	471	$PORT{$portid} = sub {
242	}	472	local $SELF = $port;
243		473	eval { &$cb }; _self_die if $@;
244	sub _inject {
245	my ($port, $msg) = @{+shift};
246
247	$port = $PORT{$port}
248	or return;
249
250	@_ = @$msg;
251
252	for (@{ $port->{rc0}{$msg->[0]} }) {
253	$_ && &{$_->[0]}
254	&& undef $_;
255	}
256
257	for (@{ $port->{rcv}{$msg->[0]} }) {
258	$_ && [@_[1..$#{$_->[1]}]] ~~ $_->[1]
259	&& &{$_->[0]}
260	&& undef $_;
261	}
262
263	for (@{ $port->{any} }) {
264	$_ && [@_[0..$#{$_->[1]}]] ~~ $_->[1]
265	&& &{$_->[0]}
266	&& undef $_;
267	}
268	}
269
270	sub normalise_noderef($) {
271	my ($noderef) = @_;
272
273	my $cv = AE::cv;
274	my @res;
275
276	$cv->begin (sub {
277	my %seen;
278	my @refs;
279	for (sort { $a->[0] <=> $b->[0] } @res) {
280	push @refs, $_->[1] unless $seen{$_->[1]}++
281	}
282	shift->send (join ",", @refs);
283	});
284
285	$noderef = $DEFAULT_PORT unless length $noderef;
286
287	my $idx;
288	for my $t (split /,/, $noderef) {
289	my $pri = ++$idx;
290
291	#TODO: this should be outside normalise_noderef and in become_public
292	if ($t =~ /^\d*$/) {
293	my $nodename = (POSIX::uname)[1];
294
295	$cv->begin;
296	AnyEvent::Socket::resolve_sockaddr $nodename, $t \|\| "aemp=$DEFAULT_PORT", "tcp", 0, undef, sub {
297	for (@_) {
298	my ($service, $host) = AnyEvent::Socket::unpack_sockaddr $_->[3];
299	push @res, [
300	$pri += 1e-5,
301	AnyEvent::Socket::format_hostport AnyEvent::Socket::format_address $host, $service
302	];
303	}	474	};
304	$cv->end;	475	}
		476	} elsif (defined $_[0]) {
		477	my $self = $PORT_DATA{$portid} \|\|= do {
		478	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
		479
		480	$PORT{$portid} = sub {
		481	local $SELF = $port;
		482
		483	if (my $cb = $self->[1]{$_[0]}) {
		484	shift;
		485	eval { &$cb }; _self_die if $@;
		486	} else {
		487	&{ $self->[0] };
		488	}
		489	};
		490
		491	$self
305	};	492	};
306		493
307	# my (undef, undef, undef, undef, @ipv4) = gethostbyname $nodename;	494	"AnyEvent::MP::Port" eq ref $self
308	#	495	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
309	# for (@ipv4) {	496
310	# push @res, [	497	my ($tag, $cb) = splice @_, 0, 2;
311	# $pri,	498
312	# AnyEvent::Socket::format_hostport AnyEvent::Socket::format_address $_, $t \|\| $DEFAULT_PORT,	499	if (defined $cb) {
313	# ];	500	$self->[1]{$tag} = $cb;
314	# }
315	} else {	501	} else {
316	my ($host, $port) = AnyEvent::Socket::parse_hostport $t, "aemp=$DEFAULT_PORT"	502	delete $self->[1]{$tag};
317	or Carp::croak "$t: unparsable transport descriptor";
318
319	$cv->begin;
320	AnyEvent::Socket::resolve_sockaddr $host, $port, "tcp", 0, undef, sub {
321	for (@_) {
322	my ($service, $host) = AnyEvent::Socket::unpack_sockaddr $_->[3];
323	push @res, [
324	$pri += 1e-5,
325	AnyEvent::Socket::format_hostport AnyEvent::Socket::format_address $host, $service
326	];
327	}
328	$cv->end;
329	}	503	}
330	}	504	}
331	}	505	}
332		506
333	$cv->end;	507	$port
334
335	$cv
336	}	508	}
337		509
338	sub become_public {	510	=item peval $port, $coderef[, @args]
339	return if $PUBLIC;
340		511
341	my $noderef = join ",", ref $_[0] ? @{+shift} : shift;	512	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
342	my @args = @_;	513	when the code throews an exception the C<$port> will be killed.
343		514
344	$NODE = (normalise_noderef $noderef)->recv;	515	Any remaining args will be passed to the callback. Any return values will
		516	be returned to the caller.
345		517
346	for my $t (split /,/, $NODE) {	518	This is useful when you temporarily want to execute code in the context of
347	$NODE{$t} = $NODE{""};	519	a port.
348		520
349	my ($host, $port) = AnyEvent::Socket::parse_hostport $t;	521	Example: create a port and run some initialisation code in it's context.
350		522
351	$LISTENER{$t} = AnyEvent::MP::Transport::mp_server $host, $port,	523	my $port = port { ... };
352	@args,
353	on_error => sub {
354	die "on_error<@_>\n";#d#
355	},
356	on_connect => sub {
357	my ($tp) = @_;
358		524
359	$NODE{$tp->{remote_id}} = $_[0];	525	peval $port, sub {
360	},	526	init
361	sub {	527	or die "unable to init";
362	my ($tp) = @_;	528	};
363		529
364	$NODE{"$tp->{peerhost}:$tp->{peerport}"} = $tp;	530	=cut
365	},	531
366	;	532	sub peval($$) {
		533	local $SELF = shift;
		534	my $cb = shift;
		535
		536	if (wantarray) {
		537	my @res = eval { &$cb };
		538	_self_die if $@;
		539	@res
		540	} else {
		541	my $res = eval { &$cb };
		542	_self_die if $@;
		543	$res
367	}	544	}
368
369	$PUBLIC = 1;
370	}	545	}
371		546
372	=back	547	=item $closure = psub { BLOCK }
373		548
374	=head1 NODE MESSAGES	549	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
		550	closure is executed, sets up the environment in the same way as in C<rcv>
		551	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
375		552
376	Nodes understand the following messages sent to them. Many of them take	553	The effect is basically as if it returned C<< sub { peval $SELF, sub {
377	arguments called C<@reply>, which will simply be used to compose a reply	554	BLOCK }, @_ } >>.
378	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
379	the remaining arguments are simply the message data.
380		555
381	=over 4	556	This is useful when you register callbacks from C<rcv> callbacks:
382		557
383	=cut	558	rcv delayed_reply => sub {
		559	my ($delay, @reply) = @_;
		560	my $timer = AE::timer $delay, 0, psub {
		561	snd @reply, $SELF;
		562	};
		563	};
384		564
385	#############################################################################	565	=cut
386	# self node code
387		566
388	sub _new_port($) {	567	sub psub(&) {
389	my ($name) = @_;	568	my $cb = shift;
390		569
		570	my $port = $SELF
		571	or Carp::croak "psub can only be called from within rcv or psub callbacks, not";
		572
		573	sub {
		574	local $SELF = $port;
		575
		576	if (wantarray) {
		577	my @res = eval { &$cb };
		578	_self_die if $@;
		579	@res
		580	} else {
		581	my $res = eval { &$cb };
		582	_self_die if $@;
		583	$res
		584	}
		585	}
		586	}
		587
		588	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
		589
		590	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
		591
		592	=item $guard = mon $port # kill $SELF when $port dies
		593
		594	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		595
		596	Monitor the given port and do something when the port is killed or
		597	messages to it were lost, and optionally return a guard that can be used
		598	to stop monitoring again.
		599
		600	In the first form (callback), the callback is simply called with any
		601	number of C<@reason> elements (no @reason means that the port was deleted
		602	"normally"). Note also that I<< the callback B<must> never die >>, so use
		603	C<eval> if unsure.
		604
		605	In the second form (another port given), the other port (C<$rcvport>)
		606	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
		607	"normal" kils nothing happens, while under all other conditions, the other
		608	port is killed with the same reason.
		609
		610	The third form (kill self) is the same as the second form, except that
		611	C<$rvport> defaults to C<$SELF>.
		612
		613	In the last form (message), a message of the form C<@msg, @reason> will be
		614	C<snd>.
		615
		616	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		617	alert was raised), they are removed and will not trigger again.
		618
		619	As a rule of thumb, monitoring requests should always monitor a port from
		620	a local port (or callback). The reason is that kill messages might get
		621	lost, just like any other message. Another less obvious reason is that
		622	even monitoring requests can get lost (for example, when the connection
		623	to the other node goes down permanently). When monitoring a port locally
		624	these problems do not exist.
		625
		626	C<mon> effectively guarantees that, in the absence of hardware failures,
		627	after starting the monitor, either all messages sent to the port will
		628	arrive, or the monitoring action will be invoked after possible message
		629	loss has been detected. No messages will be lost "in between" (after
		630	the first lost message no further messages will be received by the
		631	port). After the monitoring action was invoked, further messages might get
		632	delivered again.
		633
		634	Inter-host-connection timeouts and monitoring depend on the transport
		635	used. The only transport currently implemented is TCP, and AnyEvent::MP
		636	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		637	non-idle connection, and usually around two hours for idle connections).
		638
		639	This means that monitoring is good for program errors and cleaning up
		640	stuff eventually, but they are no replacement for a timeout when you need
		641	to ensure some maximum latency.
		642
		643	Example: call a given callback when C<$port> is killed.
		644
		645	mon $port, sub { warn "port died because of <@_>\n" };
		646
		647	Example: kill ourselves when C<$port> is killed abnormally.
		648
		649	mon $port;
		650
		651	Example: send us a restart message when another C<$port> is killed.
		652
		653	mon $port, $self => "restart";
		654
		655	=cut
		656
		657	sub mon {
391	my ($noderef, $portname) = split /#/, $name;	658	my ($nodeid, $port) = split /#/, shift, 2;
392		659
393	$PORT{$name} =	660	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
394	$PORT{$portname} = {	661
395	names => [$name, $portname],	662	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
		663
		664	unless (ref $cb) {
		665	if (@_) {
		666	# send a kill info message
		667	my (@msg) = ($cb, @_);
		668	$cb = sub { snd @msg, @_ };
		669	} else {
		670	# simply kill other port
		671	my $port = $cb;
		672	$cb = sub { kil $port, @_ if @_ };
		673	}
		674	}
		675
		676	$node->monitor ($port, $cb);
		677
		678	defined wantarray
		679	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
		680	}
		681
		682	=item $guard = mon_guard $port, $ref, $ref...
		683
		684	Monitors the given C<$port> and keeps the passed references. When the port
		685	is killed, the references will be freed.
		686
		687	Optionally returns a guard that will stop the monitoring.
		688
		689	This function is useful when you create e.g. timers or other watchers and
		690	want to free them when the port gets killed (note the use of C<psub>):
		691
		692	$port->rcv (start => sub {
		693	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
		694	undef $timer if 0.9 < rand;
		695	});
		696	});
		697
		698	=cut
		699
		700	sub mon_guard {
		701	my ($port, @refs) = @_;
		702
		703	#TODO: mon-less form?
		704
		705	mon $port, sub { 0 && @refs }
		706	}
		707
		708	=item kil $port[, @reason]
		709
		710	Kill the specified port with the given C<@reason>.
		711
		712	If no C<@reason> is specified, then the port is killed "normally" -
		713	monitor callback will be invoked, but the kil will not cause linked ports
		714	(C<mon $mport, $lport> form) to get killed.
		715
		716	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
		717	form) get killed with the same reason.
		718
		719	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		720	will be reported as reason C<< die => $@ >>.
		721
		722	Transport/communication errors are reported as C<< transport_error =>
		723	$message >>.
		724
		725	=cut
		726
		727	=item $port = spawn $node, $initfunc[, @initdata]
		728
		729	Creates a port on the node C<$node> (which can also be a port ID, in which
		730	case it's the node where that port resides).
		731
		732	The port ID of the newly created port is returned immediately, and it is
		733	possible to immediately start sending messages or to monitor the port.
		734
		735	After the port has been created, the init function is called on the remote
		736	node, in the same context as a C<rcv> callback. This function must be a
		737	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		738	specify a function in the main program, use C<::name>.
		739
		740	If the function doesn't exist, then the node tries to C<require>
		741	the package, then the package above the package and so on (e.g.
		742	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		743	exists or it runs out of package names.
		744
		745	The init function is then called with the newly-created port as context
		746	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		747	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		748	the port might not get created.
		749
		750	A common idiom is to pass a local port, immediately monitor the spawned
		751	port, and in the remote init function, immediately monitor the passed
		752	local port. This two-way monitoring ensures that both ports get cleaned up
		753	when there is a problem.
		754
		755	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		756	caller before C<spawn> returns (by delaying invocation when spawn is
		757	called for the local node).
		758
		759	Example: spawn a chat server port on C<$othernode>.
		760
		761	# this node, executed from within a port context:
		762	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		763	mon $server;
		764
		765	# init function on C<$othernode>
		766	sub connect {
		767	my ($srcport) = @_;
		768
		769	mon $srcport;
		770
		771	rcv $SELF, sub {
		772	...
		773	};
		774	}
		775
		776	=cut
		777
		778	sub _spawn {
		779	my $port = shift;
		780	my $init = shift;
		781
		782	# rcv will create the actual port
		783	local $SELF = "$NODE#$port";
		784	eval {
		785	&{ load_func $init }
		786	};
		787	_self_die if $@;
		788	}
		789
		790	sub spawn(@) {
		791	my ($nodeid, undef) = split /#/, shift, 2;
		792
		793	my $id = $RUNIQ . ++$ID;
		794
		795	$_[0] =~ /::/
		796	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		797
		798	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		799
		800	"$nodeid#$id"
		801	}
		802
		803
		804	=item after $timeout, @msg
		805
		806	=item after $timeout, $callback
		807
		808	Either sends the given message, or call the given callback, after the
		809	specified number of seconds.
		810
		811	This is simply a utility function that comes in handy at times - the
		812	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		813	so it may go away in the future.
		814
		815	=cut
		816
		817	sub after($@) {
		818	my ($timeout, @action) = @_;
		819
		820	my $t; $t = AE::timer $timeout, 0, sub {
		821	undef $t;
		822	ref $action[0]
		823	? $action[0]()
		824	: snd @action;
396	};	825	};
397	}	826	}
398		827
399	$NODE{""} = new AnyEvent::MP::Node::Self noderef => $NODE;	828	=item cal $port, @msg, $callback[, $timeout]
400	_new_port "";
401		829
402	=item devnull => ...	830	A simple form of RPC - sends a message to the given C<$port> with the
		831	given contents (C<@msg>), but adds a reply port to the message.
403		832
404	Generic data sink/CPU heat conversion.	833	The reply port is created temporarily just for the purpose of receiving
		834	the reply, and will be C<kil>ed when no longer needed.
405		835
406	=cut	836	A reply message sent to the port is passed to the C<$callback> as-is.
407		837
408	rcv "", devnull => sub { () };	838	If an optional time-out (in seconds) is given and it is not C<undef>,
		839	then the callback will be called without any arguments after the time-out
		840	elapsed and the port is C<kil>ed.
409		841
410	=item relay => $port, @msg	842	If no time-out is given (or it is C<undef>), then the local port will
		843	monitor the remote port instead, so it eventually gets cleaned-up.
411		844
412	Simply forwards the message to the given port.	845	Currently this function returns the temporary port, but this "feature"
		846	might go in future versions unless you can make a convincing case that
		847	this is indeed useful for something.
413		848
414	=cut	849	=cut
415		850
416	rcv "", relay => sub { \&snd; () };	851	sub cal(@) {
		852	my $timeout = ref $_[-1] ? undef : pop;
		853	my $cb = pop;
417		854
418	=item eval => $string[ @reply]	855	my $port = port {
		856	undef $timeout;
		857	kil $SELF;
		858	&$cb;
		859	};
419		860
420	Evaluates the given string. If C<@reply> is given, then a message of the	861	if (defined $timeout) {
421	form C<@reply, $@, @evalres> is sent.	862	$timeout = AE::timer $timeout, 0, sub {
		863	undef $timeout;
		864	kil $port;
		865	$cb->();
		866	};
		867	} else {
		868	mon $_[0], sub {
		869	kil $port;
		870	$cb->();
		871	};
		872	}
422		873
423	Example: crash another node.	874	push @_, $port;
		875	&snd;
424		876
425	snd $othernode, eval => "exit";	877	$port
426		878	}
427	=cut
428
429	rcv "", eval => sub {
430	my (undef, $string, @reply) = @_;
431	my @res = eval $string;
432	snd @reply, "$@", @res if @reply;
433	()
434	};
435
436	=item time => @reply
437
438	Replies the the current node time to C<@reply>.
439
440	Example: tell the current node to send the current time to C<$myport> in a
441	C<timereply> message.
442
443	snd $NODE, time => $myport, timereply => 1, 2;
444	# => snd $myport, timereply => 1, 2, <time>
445
446	=cut
447
448	rcv "", time => sub { shift; snd @_, AE::time; () };
449		879
450	=back	880	=back
451		881
		882	=head1 DISTRIBUTED DATABASE
		883
		884	AnyEvent::MP comes with a simple distributed database. The database will
		885	be mirrored asynchronously at all global nodes. Other nodes bind to one of
		886	the global nodes for their needs.
		887
		888	The database consists of a two-level hash - a hash contains a hash which
		889	contains values.
		890
		891	The top level hash key is called "family", and the second-level hash key
		892	is simply called "key".
		893
		894	The family must be alphanumeric, i.e. start with a letter and consist
		895	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		896	pretty much like Perl module names.
		897
		898	As the family namespace is global, it is recommended to prefix family names
		899	with the name of the application or module using it.
		900
		901	The keys must be strings, with no other limitations.
		902
		903	The values should preferably be strings, but other perl scalars should
		904	work as well (such as undef, arrays and hashes).
		905
		906	Every database entry is owned by one node - adding the same family/key
		907	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		908	but the result might be nondeterministic, i.e. the key might have
		909	different values on different nodes.
		910
		911	=item db_set $family => $key => $value
		912
		913	Sets (or replaces) a key to the database.
		914
		915	=item db_del $family => $key
		916
		917	Deletes a key from the database.
		918
		919	=item $guard = db_reg $family => $key [=> $value]
		920
		921	Sets the key on the database and returns a guard. When the guard is
		922	destroyed, the key is deleted from the database. If C<$value> is missing,
		923	then C<undef> is used.
		924
		925	=cut
		926
		927	=back
		928
		929	=head1 AnyEvent::MP vs. Distributed Erlang
		930
		931	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
		932	== aemp node, Erlang process == aemp port), so many of the documents and
		933	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
		934	sample:
		935
		936	http://www.erlang.se/doc/programming_rules.shtml
		937	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
		938	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
		939	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
		940
		941	Despite the similarities, there are also some important differences:
		942
		943	=over 4
		944
		945	=item * Node IDs are arbitrary strings in AEMP.
		946
		947	Erlang relies on special naming and DNS to work everywhere in the same
		948	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
		949	configuration or DNS), and possibly the addresses of some seed nodes, but
		950	will otherwise discover other nodes (and their IDs) itself.
		951
		952	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
		953	uses "local ports are like remote ports".
		954
		955	The failure modes for local ports are quite different (runtime errors
		956	only) then for remote ports - when a local port dies, you I<know> it dies,
		957	when a connection to another node dies, you know nothing about the other
		958	port.
		959
		960	Erlang pretends remote ports are as reliable as local ports, even when
		961	they are not.
		962
		963	AEMP encourages a "treat remote ports differently" philosophy, with local
		964	ports being the special case/exception, where transport errors cannot
		965	occur.
		966
		967	=item * Erlang uses processes and a mailbox, AEMP does not queue.
		968
		969	Erlang uses processes that selectively receive messages out of order, and
		970	therefore needs a queue. AEMP is event based, queuing messages would serve
		971	no useful purpose. For the same reason the pattern-matching abilities
		972	of AnyEvent::MP are more limited, as there is little need to be able to
		973	filter messages without dequeuing them.
		974
		975	This is not a philosophical difference, but simply stems from AnyEvent::MP
		976	being event-based, while Erlang is process-based.
		977
		978	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		979	top of AEMP and Coro threads.
		980
		981	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
		982
		983	Sending messages in Erlang is synchronous and blocks the process until
		984	a conenction has been established and the message sent (and so does not
		985	need a queue that can overflow). AEMP sends return immediately, connection
		986	establishment is handled in the background.
		987
		988	=item * Erlang suffers from silent message loss, AEMP does not.
		989
		990	Erlang implements few guarantees on messages delivery - messages can get
		991	lost without any of the processes realising it (i.e. you send messages a,
		992	b, and c, and the other side only receives messages a and c).
		993
		994	AEMP guarantees (modulo hardware errors) correct ordering, and the
		995	guarantee that after one message is lost, all following ones sent to the
		996	same port are lost as well, until monitoring raises an error, so there are
		997	no silent "holes" in the message sequence.
		998
		999	If you want your software to be very reliable, you have to cope with
		1000	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
		1001	simply tries to work better in common error cases, such as when a network
		1002	link goes down.
		1003
		1004	=item * Erlang can send messages to the wrong port, AEMP does not.
		1005
		1006	In Erlang it is quite likely that a node that restarts reuses an Erlang
		1007	process ID known to other nodes for a completely different process,
		1008	causing messages destined for that process to end up in an unrelated
		1009	process.
		1010
		1011	AEMP does not reuse port IDs, so old messages or old port IDs floating
		1012	around in the network will not be sent to an unrelated port.
		1013
		1014	=item * Erlang uses unprotected connections, AEMP uses secure
		1015	authentication and can use TLS.
		1016
		1017	AEMP can use a proven protocol - TLS - to protect connections and
		1018	securely authenticate nodes.
		1019
		1020	=item * The AEMP protocol is optimised for both text-based and binary
		1021	communications.
		1022
		1023	The AEMP protocol, unlike the Erlang protocol, supports both programming
		1024	language independent text-only protocols (good for debugging), and binary,
		1025	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1026	used, the protocol is actually completely text-based.
		1027
		1028	It has also been carefully designed to be implementable in other languages
		1029	with a minimum of work while gracefully degrading functionality to make the
		1030	protocol simple.
		1031
		1032	=item * AEMP has more flexible monitoring options than Erlang.
		1033
		1034	In Erlang, you can chose to receive I<all> exit signals as messages or
		1035	I<none>, there is no in-between, so monitoring single Erlang processes is
		1036	difficult to implement.
		1037
		1038	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1039	between automatic kill, exit message or callback on a per-port basis.
		1040
		1041	=item * Erlang tries to hide remote/local connections, AEMP does not.
		1042
		1043	Monitoring in Erlang is not an indicator of process death/crashes, in the
		1044	same way as linking is (except linking is unreliable in Erlang).
		1045
		1046	In AEMP, you don't "look up" registered port names or send to named ports
		1047	that might or might not be persistent. Instead, you normally spawn a port
		1048	on the remote node. The init function monitors you, and you monitor the
		1049	remote port. Since both monitors are local to the node, they are much more
		1050	reliable (no need for C<spawn_link>).
		1051
		1052	This also saves round-trips and avoids sending messages to the wrong port
		1053	(hard to do in Erlang).
		1054
		1055	=back
		1056
		1057	=head1 RATIONALE
		1058
		1059	=over 4
		1060
		1061	=item Why strings for port and node IDs, why not objects?
		1062
		1063	We considered "objects", but found that the actual number of methods
		1064	that can be called are quite low. Since port and node IDs travel over
		1065	the network frequently, the serialising/deserialising would add lots of
		1066	overhead, as well as having to keep a proxy object everywhere.
		1067
		1068	Strings can easily be printed, easily serialised etc. and need no special
		1069	procedures to be "valid".
		1070
		1071	And as a result, a port with just a default receiver consists of a single
		1072	code reference stored in a global hash - it can't become much cheaper.
		1073
		1074	=item Why favour JSON, why not a real serialising format such as Storable?
		1075
		1076	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1077	format, but currently there is no way to make a node use Storable by
		1078	default (although all nodes will accept it).
		1079
		1080	The default framing protocol is JSON because a) JSON::XS is many times
		1081	faster for small messages and b) most importantly, after years of
		1082	experience we found that object serialisation is causing more problems
		1083	than it solves: Just like function calls, objects simply do not travel
		1084	easily over the network, mostly because they will always be a copy, so you
		1085	always have to re-think your design.
		1086
		1087	Keeping your messages simple, concentrating on data structures rather than
		1088	objects, will keep your messages clean, tidy and efficient.
		1089
		1090	=back
		1091
452	=head1 SEE ALSO	1092	=head1 SEE ALSO
		1093
		1094	L<AnyEvent::MP::Intro> - a gentle introduction.
		1095
		1096	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1097
		1098	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1099	your applications.
		1100
		1101	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1102
		1103	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1104	all nodes.
453		1105
454	L<AnyEvent>.	1106	L<AnyEvent>.
455		1107
456	=head1 AUTHOR	1108	=head1 AUTHOR
457		1109

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Revision 1.125 by root, Sat Mar 3 13:07:19 2012 UTC