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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.6 by root, Sat Aug 1 10:02:33 2009 UTC vs.
Revision 1.126 by root, Sat Mar 3 19:43:41 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 unique randoms tring (C</%u>) appended.
		277
		278	The node ID can contain some C<%> sequences that are expanded: C<%n>
		279	is expanded to the local nodename, C<%u> is replaced by a random
		280	strign to make the node unique. For example, the F<aemp> commandline
		281	utility uses C<aemp/%n/%u> as nodename, which might expand to
		282	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		283
		284	=item step 2, bind listener sockets
		285
		286	The next step is to look up the binds in the profile, followed by binding
		287	aemp protocol listeners on all binds specified (it is possible and valid
		288	to have no binds, meaning that the node cannot be contacted form the
		289	outside. This means the node cannot talk to other nodes that also have no
		290	binds, but it can still talk to all "normal" nodes).
		291
		292	If the profile does not specify a binds list, then a default of C<*> is
		293	used, meaning the node will bind on a dynamically-assigned port on every
		294	local IP address it finds.
		295
		296	=item step 3, connect to seed nodes
		297
		298	As the last step, the seed ID list from the profile is passed to the
		299	L<AnyEvent::MP::Global> module, which will then use it to keep
		300	connectivity with at least one node at any point in time.
		301
		302	=back
		303
		304	Example: become a distributed node using the local node name as profile.
		305	This should be the most common form of invocation for "daemon"-type nodes.
		306
		307	configure
		308
		309	Example: become a semi-anonymous node. This form is often used for
		310	commandline clients.
		311
		312	configure nodeid => "myscript/%n/%u";
		313
		314	Example: configure a node using a profile called seed, which is suitable
		315	for a seed node as it binds on all local addresses on a fixed port (4040,
		316	customary for aemp).
		317
		318	# use the aemp commandline utility
		319	# aemp profile seed binds '*:4040'
		320
		321	# then use it
		322	configure profile => "seed";
		323
		324	# or simply use aemp from the shell again:
		325	# aemp run profile seed
		326
		327	# or provide a nicer-to-remember nodeid
		328	# aemp run profile seed nodeid "$(hostname)"
		329
		330	=item $SELF
		331
		332	Contains the current port id while executing C<rcv> callbacks or C<psub>
		333	blocks.
		334
		335	=item *SELF, SELF, %SELF, @SELF...
		336
		337	Due to some quirks in how perl exports variables, it is impossible to
		338	just export C<$SELF>, all the symbols named C<SELF> are exported by this
		339	module, but only C<$SELF> is currently used.
		340
160	=item snd $portid, type => @data	341	=item snd $port, type => @data
161		342
162	=item snd $portid, @msg	343	=item snd $port, @msg
163		344
164	Send the given message to the given port ID, which can identify either a	345	Send the given message to the given port, which can identify either a
165	local or a remote port.	346	local or a remote port, and must be a port ID.
166		347
167	While the message can be about anything, it is highly recommended to use	348	While the message can be almost anything, it is highly recommended to
168	a constant string as first element.	349	use a string as first element (a port ID, or some word that indicates a
		350	request type etc.) and to consist if only simple perl values (scalars,
		351	arrays, hashes) - if you think you need to pass an object, think again.
169		352
170	The message data effectively becomes read-only after a call to this	353	The message data logically becomes read-only after a call to this
171	function: modifying any argument is not allowed and can cause many	354	function: modifying any argument (or values referenced by them) is
172	problems.	355	forbidden, as there can be considerable time between the call to C<snd>
		356	and the time the message is actually being serialised - in fact, it might
		357	never be copied as within the same process it is simply handed to the
		358	receiving port.
173		359
174	The type of data you can transfer depends on the transport protocol: when	360	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	361	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	362	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	363	that Storable can serialise and deserialise is allowed, and for the local
178	node, anything can be passed.	364	node, anything can be passed. Best rely only on the common denominator of
		365	these.
179		366
180	=cut	367	=item $local_port = port
181		368
182	sub snd(@) {	369	Create a new local port object and returns its port ID. Initially it has
183	my ($noderef, $port) = split /#/, shift, 2;	370	no callbacks set and will throw an error when it receives messages.
184		371
185	add_node $noderef	372	=item $local_port = port { my @msg = @_ }
186	unless exists $NODE{$noderef};
187		373
188	$NODE{$noderef}->send (["$port", [@_]]);	374	Creates a new local port, and returns its ID. Semantically the same as
		375	creating a port and calling C<rcv $port, $callback> on it.
		376
		377	The block will be called for every message received on the port, with the
		378	global variable C<$SELF> set to the port ID. Runtime errors will cause the
		379	port to be C<kil>ed. The message will be passed as-is, no extra argument
		380	(i.e. no port ID) will be passed to the callback.
		381
		382	If you want to stop/destroy the port, simply C<kil> it:
		383
		384	my $port = port {
		385	my @msg = @_;
		386	...
		387	kil $SELF;
		388	};
		389
		390	=cut
		391
		392	sub rcv($@);
		393
		394	sub _kilme {
		395	die "received message on port without callback";
189	}	396	}
190		397
		398	sub port(;&) {
		399	my $id = $UNIQ . ++$ID;
		400	my $port = "$NODE#$id";
		401
		402	rcv $port, shift \|\| \&_kilme;
		403
		404	$port
		405	}
		406
191	=item rcv $portid, type => $callback->(@msg)	407	=item rcv $local_port, $callback->(@msg)
192		408
193	=item rcv $portid, $smartmatch => $callback->(@msg)	409	Replaces the default callback on the specified port. There is no way to
		410	remove the default callback: use C<sub { }> to disable it, or better
		411	C<kil> the port when it is no longer needed.
194		412
195	=item rcv $portid, [$smartmatch...] => $callback->(@msg)	413	The global C<$SELF> (exported by this module) contains C<$port> while
		414	executing the callback. Runtime errors during callback execution will
		415	result in the port being C<kil>ed.
196		416
197	Register a callback on the port identified by C<$portid>, which I<must> be	417	The default callback received all messages not matched by a more specific
198	a local port.	418	C<tag> match.
199		419
200	The callback has to return a true value when its work is done, after	420	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
201	which is will be removed, or a false value in which case it will stay
202	registered.
203		421
204	If the match is an array reference, then it will be matched against the	422	Register (or replace) callbacks to be called on messages starting with the
205	first elements of the message, otherwise only the first element is being	423	given tag on the given port (and return the port), or unregister it (when
206	matched.	424	C<$callback> is C<$undef> or missing). There can only be one callback
		425	registered for each tag.
207		426
208	Any element in the match that is specified as C<_any_> (a function	427	The original message will be passed to the callback, after the first
209	exported by this module) matches any single element of the message.	428	element (the tag) has been removed. The callback will use the same
		429	environment as the default callback (see above).
210		430
211	While not required, it is highly recommended that the first matching	431	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	432
213	also the most efficient match (by far).	433	my $port = rcv port,
		434	msg1 => sub { ... },
		435	msg2 => sub { ... },
		436	;
		437
		438	Example: create a port, bind receivers and send it in a message elsewhere
		439	in one go:
		440
		441	snd $otherport, reply =>
		442	rcv port,
		443	msg1 => sub { ... },
		444	...
		445	;
		446
		447	Example: temporarily register a rcv callback for a tag matching some port
		448	(e.g. for an rpc reply) and unregister it after a message was received.
		449
		450	rcv $port, $otherport => sub {
		451	my @reply = @_;
		452
		453	rcv $SELF, $otherport;
		454	};
214		455
215	=cut	456	=cut
216		457
217	sub rcv($@) {	458	sub rcv($@) {
218	my ($port, $match, $cb) = @_;	459	my $port = shift;
219
220	my $port = $PORT{$port}
221	or do {
222	my ($noderef, $lport) = split /#/, $port;	460	my ($nodeid, $portid) = split /#/, $port, 2;
223	"AnyEvent::MP::Node::Self" eq ref $NODE{$noderef}	461
		462	$NODE{$nodeid} == $NODE{""}
224	or Carp::croak "$port: can only rcv on local ports";	463	or Carp::croak "$port: rcv can only be called on local ports, caught";
225		464
226	$PORT{$lport}	465	while (@_) {
227	or Carp::croak "$port: port does not exist";	466	if (ref $_[0]) {
228		467	if (my $self = $PORT_DATA{$portid}) {
229	$PORT{$port} = $PORT{$lport} # also return	468	"AnyEvent::MP::Port" eq ref $self
230	};	469	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
231		470
232	if (!ref $match) {	471	$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 {	472	} else {
240	push @{ $port->{any} }, [$cb, $match];	473	my $cb = shift;
241	}	474	$PORT{$portid} = sub {
242	}	475	local $SELF = $port;
243		476	eval { &$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	}	477	};
304	$cv->end;	478	}
		479	} elsif (defined $_[0]) {
		480	my $self = $PORT_DATA{$portid} \|\|= do {
		481	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
		482
		483	$PORT{$portid} = sub {
		484	local $SELF = $port;
		485
		486	if (my $cb = $self->[1]{$_[0]}) {
		487	shift;
		488	eval { &$cb }; _self_die if $@;
		489	} else {
		490	&{ $self->[0] };
		491	}
		492	};
		493
		494	$self
305	};	495	};
306		496
307	# my (undef, undef, undef, undef, @ipv4) = gethostbyname $nodename;	497	"AnyEvent::MP::Port" eq ref $self
308	#	498	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
309	# for (@ipv4) {	499
310	# push @res, [	500	my ($tag, $cb) = splice @_, 0, 2;
311	# $pri,	501
312	# AnyEvent::Socket::format_hostport AnyEvent::Socket::format_address $_, $t \|\| $DEFAULT_PORT,	502	if (defined $cb) {
313	# ];	503	$self->[1]{$tag} = $cb;
314	# }
315	} else {	504	} else {
316	my ($host, $port) = AnyEvent::Socket::parse_hostport $t, "aemp=$DEFAULT_PORT"	505	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	}	506	}
330	}	507	}
331	}	508	}
332		509
333	$cv->end;	510	$port
334
335	$cv
336	}	511	}
337		512
338	sub become_public {	513	=item peval $port, $coderef[, @args]
339	return if $PUBLIC;
340		514
341	my $noderef = join ",", ref $_[0] ? @{+shift} : shift;	515	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
342	my @args = @_;	516	when the code throews an exception the C<$port> will be killed.
343		517
344	$NODE = (normalise_noderef $noderef)->recv;	518	Any remaining args will be passed to the callback. Any return values will
		519	be returned to the caller.
345		520
346	for my $t (split /,/, $NODE) {	521	This is useful when you temporarily want to execute code in the context of
347	$NODE{$t} = $NODE{""};	522	a port.
348		523
349	my ($host, $port) = AnyEvent::Socket::parse_hostport $t;	524	Example: create a port and run some initialisation code in it's context.
350		525
351	$LISTENER{$t} = AnyEvent::MP::Transport::mp_server $host, $port,	526	my $port = port { ... };
352	@args,
353	on_error => sub {
354	die "on_error<@_>\n";#d#
355	},
356	on_connect => sub {
357	my ($tp) = @_;
358		527
359	$NODE{$tp->{remote_id}} = $_[0];	528	peval $port, sub {
360	},	529	init
361	sub {	530	or die "unable to init";
362	my ($tp) = @_;	531	};
363		532
364	$NODE{"$tp->{peerhost}:$tp->{peerport}"} = $tp;	533	=cut
365	},	534
366	;	535	sub peval($$) {
		536	local $SELF = shift;
		537	my $cb = shift;
		538
		539	if (wantarray) {
		540	my @res = eval { &$cb };
		541	_self_die if $@;
		542	@res
		543	} else {
		544	my $res = eval { &$cb };
		545	_self_die if $@;
		546	$res
367	}	547	}
368
369	$PUBLIC = 1;
370	}	548	}
371		549
372	=back	550	=item $closure = psub { BLOCK }
373		551
374	=head1 NODE MESSAGES	552	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
		553	closure is executed, sets up the environment in the same way as in C<rcv>
		554	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
375		555
376	Nodes understand the following messages sent to them. Many of them take	556	The effect is basically as if it returned C<< sub { peval $SELF, sub {
377	arguments called C<@reply>, which will simply be used to compose a reply	557	BLOCK }, @_ } >>.
378	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
379	the remaining arguments are simply the message data.
380		558
381	=over 4	559	This is useful when you register callbacks from C<rcv> callbacks:
382		560
383	=cut	561	rcv delayed_reply => sub {
		562	my ($delay, @reply) = @_;
		563	my $timer = AE::timer $delay, 0, psub {
		564	snd @reply, $SELF;
		565	};
		566	};
384		567
385	#############################################################################	568	=cut
386	# self node code
387		569
388	sub _new_port($) {	570	sub psub(&) {
389	my ($name) = @_;	571	my $cb = shift;
390		572
		573	my $port = $SELF
		574	or Carp::croak "psub can only be called from within rcv or psub callbacks, not";
		575
		576	sub {
		577	local $SELF = $port;
		578
		579	if (wantarray) {
		580	my @res = eval { &$cb };
		581	_self_die if $@;
		582	@res
		583	} else {
		584	my $res = eval { &$cb };
		585	_self_die if $@;
		586	$res
		587	}
		588	}
		589	}
		590
		591	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
		592
		593	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
		594
		595	=item $guard = mon $port # kill $SELF when $port dies
		596
		597	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		598
		599	Monitor the given port and do something when the port is killed or
		600	messages to it were lost, and optionally return a guard that can be used
		601	to stop monitoring again.
		602
		603	In the first form (callback), the callback is simply called with any
		604	number of C<@reason> elements (no @reason means that the port was deleted
		605	"normally"). Note also that I<< the callback B<must> never die >>, so use
		606	C<eval> if unsure.
		607
		608	In the second form (another port given), the other port (C<$rcvport>)
		609	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
		610	"normal" kils nothing happens, while under all other conditions, the other
		611	port is killed with the same reason.
		612
		613	The third form (kill self) is the same as the second form, except that
		614	C<$rvport> defaults to C<$SELF>.
		615
		616	In the last form (message), a message of the form C<@msg, @reason> will be
		617	C<snd>.
		618
		619	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		620	alert was raised), they are removed and will not trigger again.
		621
		622	As a rule of thumb, monitoring requests should always monitor a port from
		623	a local port (or callback). The reason is that kill messages might get
		624	lost, just like any other message. Another less obvious reason is that
		625	even monitoring requests can get lost (for example, when the connection
		626	to the other node goes down permanently). When monitoring a port locally
		627	these problems do not exist.
		628
		629	C<mon> effectively guarantees that, in the absence of hardware failures,
		630	after starting the monitor, either all messages sent to the port will
		631	arrive, or the monitoring action will be invoked after possible message
		632	loss has been detected. No messages will be lost "in between" (after
		633	the first lost message no further messages will be received by the
		634	port). After the monitoring action was invoked, further messages might get
		635	delivered again.
		636
		637	Inter-host-connection timeouts and monitoring depend on the transport
		638	used. The only transport currently implemented is TCP, and AnyEvent::MP
		639	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		640	non-idle connection, and usually around two hours for idle connections).
		641
		642	This means that monitoring is good for program errors and cleaning up
		643	stuff eventually, but they are no replacement for a timeout when you need
		644	to ensure some maximum latency.
		645
		646	Example: call a given callback when C<$port> is killed.
		647
		648	mon $port, sub { warn "port died because of <@_>\n" };
		649
		650	Example: kill ourselves when C<$port> is killed abnormally.
		651
		652	mon $port;
		653
		654	Example: send us a restart message when another C<$port> is killed.
		655
		656	mon $port, $self => "restart";
		657
		658	=cut
		659
		660	sub mon {
391	my ($noderef, $portname) = split /#/, $name;	661	my ($nodeid, $port) = split /#/, shift, 2;
392		662
393	$PORT{$name} =	663	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
394	$PORT{$portname} = {	664
395	names => [$name, $portname],	665	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
		666
		667	unless (ref $cb) {
		668	if (@_) {
		669	# send a kill info message
		670	my (@msg) = ($cb, @_);
		671	$cb = sub { snd @msg, @_ };
		672	} else {
		673	# simply kill other port
		674	my $port = $cb;
		675	$cb = sub { kil $port, @_ if @_ };
		676	}
		677	}
		678
		679	$node->monitor ($port, $cb);
		680
		681	defined wantarray
		682	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
		683	}
		684
		685	=item $guard = mon_guard $port, $ref, $ref...
		686
		687	Monitors the given C<$port> and keeps the passed references. When the port
		688	is killed, the references will be freed.
		689
		690	Optionally returns a guard that will stop the monitoring.
		691
		692	This function is useful when you create e.g. timers or other watchers and
		693	want to free them when the port gets killed (note the use of C<psub>):
		694
		695	$port->rcv (start => sub {
		696	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
		697	undef $timer if 0.9 < rand;
		698	});
		699	});
		700
		701	=cut
		702
		703	sub mon_guard {
		704	my ($port, @refs) = @_;
		705
		706	#TODO: mon-less form?
		707
		708	mon $port, sub { 0 && @refs }
		709	}
		710
		711	=item kil $port[, @reason]
		712
		713	Kill the specified port with the given C<@reason>.
		714
		715	If no C<@reason> is specified, then the port is killed "normally" -
		716	monitor callback will be invoked, but the kil will not cause linked ports
		717	(C<mon $mport, $lport> form) to get killed.
		718
		719	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
		720	form) get killed with the same reason.
		721
		722	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		723	will be reported as reason C<< die => $@ >>.
		724
		725	Transport/communication errors are reported as C<< transport_error =>
		726	$message >>.
		727
		728	=cut
		729
		730	=item $port = spawn $node, $initfunc[, @initdata]
		731
		732	Creates a port on the node C<$node> (which can also be a port ID, in which
		733	case it's the node where that port resides).
		734
		735	The port ID of the newly created port is returned immediately, and it is
		736	possible to immediately start sending messages or to monitor the port.
		737
		738	After the port has been created, the init function is called on the remote
		739	node, in the same context as a C<rcv> callback. This function must be a
		740	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		741	specify a function in the main program, use C<::name>.
		742
		743	If the function doesn't exist, then the node tries to C<require>
		744	the package, then the package above the package and so on (e.g.
		745	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		746	exists or it runs out of package names.
		747
		748	The init function is then called with the newly-created port as context
		749	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		750	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		751	the port might not get created.
		752
		753	A common idiom is to pass a local port, immediately monitor the spawned
		754	port, and in the remote init function, immediately monitor the passed
		755	local port. This two-way monitoring ensures that both ports get cleaned up
		756	when there is a problem.
		757
		758	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		759	caller before C<spawn> returns (by delaying invocation when spawn is
		760	called for the local node).
		761
		762	Example: spawn a chat server port on C<$othernode>.
		763
		764	# this node, executed from within a port context:
		765	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		766	mon $server;
		767
		768	# init function on C<$othernode>
		769	sub connect {
		770	my ($srcport) = @_;
		771
		772	mon $srcport;
		773
		774	rcv $SELF, sub {
		775	...
		776	};
		777	}
		778
		779	=cut
		780
		781	sub _spawn {
		782	my $port = shift;
		783	my $init = shift;
		784
		785	# rcv will create the actual port
		786	local $SELF = "$NODE#$port";
		787	eval {
		788	&{ load_func $init }
		789	};
		790	_self_die if $@;
		791	}
		792
		793	sub spawn(@) {
		794	my ($nodeid, undef) = split /#/, shift, 2;
		795
		796	my $id = $RUNIQ . ++$ID;
		797
		798	$_[0] =~ /::/
		799	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		800
		801	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		802
		803	"$nodeid#$id"
		804	}
		805
		806
		807	=item after $timeout, @msg
		808
		809	=item after $timeout, $callback
		810
		811	Either sends the given message, or call the given callback, after the
		812	specified number of seconds.
		813
		814	This is simply a utility function that comes in handy at times - the
		815	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		816	so it may go away in the future.
		817
		818	=cut
		819
		820	sub after($@) {
		821	my ($timeout, @action) = @_;
		822
		823	my $t; $t = AE::timer $timeout, 0, sub {
		824	undef $t;
		825	ref $action[0]
		826	? $action[0]()
		827	: snd @action;
396	};	828	};
397	}	829	}
398		830
399	$NODE{""} = new AnyEvent::MP::Node::Self noderef => $NODE;	831	=item cal $port, @msg, $callback[, $timeout]
400	_new_port "";
401		832
402	=item relay => $port, @msg	833	A simple form of RPC - sends a message to the given C<$port> with the
		834	given contents (C<@msg>), but adds a reply port to the message.
403		835
404	Simply forwards the message to the given port.	836	The reply port is created temporarily just for the purpose of receiving
		837	the reply, and will be C<kil>ed when no longer needed.
405		838
406	=cut	839	A reply message sent to the port is passed to the C<$callback> as-is.
407		840
408	rcv "", relay => \&snd;	841	If an optional time-out (in seconds) is given and it is not C<undef>,
		842	then the callback will be called without any arguments after the time-out
		843	elapsed and the port is C<kil>ed.
409		844
410	=item eval => $string[ @reply]	845	If no time-out is given (or it is C<undef>), then the local port will
		846	monitor the remote port instead, so it eventually gets cleaned-up.
411		847
412	Evaluates the given string. If C<@reply> is given, then a message of the	848	Currently this function returns the temporary port, but this "feature"
413	form C<@reply, $@, @evalres> is sent.	849	might go in future versions unless you can make a convincing case that
		850	this is indeed useful for something.
414		851
415	Example: crash another node.
416
417	snd $othernode, eval => "exit";
418
419	=cut	852	=cut
420		853
421	rcv "", eval => sub {	854	sub cal(@) {
422	my (undef, $string, @reply) = @_;	855	my $timeout = ref $_[-1] ? undef : pop;
423	my @res = eval $string;	856	my $cb = pop;
424	snd @reply, "$@", @res if @reply;
425	};
426		857
427	=item time => @reply	858	my $port = port {
		859	undef $timeout;
		860	kil $SELF;
		861	&$cb;
		862	};
428		863
429	Replies the the current node time to C<@reply>.	864	if (defined $timeout) {
		865	$timeout = AE::timer $timeout, 0, sub {
		866	undef $timeout;
		867	kil $port;
		868	$cb->();
		869	};
		870	} else {
		871	mon $_[0], sub {
		872	kil $port;
		873	$cb->();
		874	};
		875	}
430		876
431	Example: tell the current node to send the current time to C<$myport> in a	877	push @_, $port;
432	C<timereply> message.	878	&snd;
433		879
434	snd $NODE, time => $myport, timereply => 1, 2;	880	$port
435	# => snd $myport, timereply => 1, 2, <time>	881	}
436
437	=cut
438
439	rcv "", time => sub { shift; snd @_, AE::time };
440		882
441	=back	883	=back
442		884
		885	=head1 DISTRIBUTED DATABASE
		886
		887	AnyEvent::MP comes with a simple distributed database. The database will
		888	be mirrored asynchronously at all global nodes. Other nodes bind to one of
		889	the global nodes for their needs.
		890
		891	The database consists of a two-level hash - a hash contains a hash which
		892	contains values.
		893
		894	The top level hash key is called "family", and the second-level hash key
		895	is called "subkey" or simply "key".
		896
		897	The family must be alphanumeric, i.e. start with a letter and consist
		898	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		899	pretty much like Perl module names.
		900
		901	As the family namespace is global, it is recommended to prefix family names
		902	with the name of the application or module using it.
		903
		904	The subkeys must be non-empty strings, with no further restrictions.
		905
		906	The values should preferably be strings, but other perl scalars should
		907	work as well (such as undef, arrays and hashes).
		908
		909	Every database entry is owned by one node - adding the same family/subkey
		910	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		911	but the result might be nondeterministic, i.e. the key might have
		912	different values on different nodes.
		913
		914	Different subkeys in the same family can be owned by different nodes
		915	without problems, and in fact, this is the common method to create worker
		916	pools. For example, a worker port for image scaling might do this:
		917
		918	db_set my_image_scalers => $port;
		919
		920	And clients looking for an image scaler will want to get the
		921	C<my_image_scalers> keys:
		922
		923	db_keys "my_image_scalers" => 60 => sub {
		924	#d##TODO#
		925
		926	=over
		927
		928	=item db_set $family => $subkey [=> $value]
		929
		930	Sets (or replaces) a key to the database - if C<$value> is omitted,
		931	C<undef> is used instead.
		932
		933	=item db_del $family => $subkey
		934
		935	Deletes a key from the database.
		936
		937	=item $guard = db_reg $family => $subkey [=> $value]
		938
		939	Sets the key on the database and returns a guard. When the guard is
		940	destroyed, the key is deleted from the database. If C<$value> is missing,
		941	then C<undef> is used.
		942
		943	=cut
		944
		945	=back
		946
		947	=head1 AnyEvent::MP vs. Distributed Erlang
		948
		949	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
		950	== aemp node, Erlang process == aemp port), so many of the documents and
		951	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
		952	sample:
		953
		954	http://www.erlang.se/doc/programming_rules.shtml
		955	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
		956	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
		957	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
		958
		959	Despite the similarities, there are also some important differences:
		960
		961	=over 4
		962
		963	=item * Node IDs are arbitrary strings in AEMP.
		964
		965	Erlang relies on special naming and DNS to work everywhere in the same
		966	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
		967	configuration or DNS), and possibly the addresses of some seed nodes, but
		968	will otherwise discover other nodes (and their IDs) itself.
		969
		970	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
		971	uses "local ports are like remote ports".
		972
		973	The failure modes for local ports are quite different (runtime errors
		974	only) then for remote ports - when a local port dies, you I<know> it dies,
		975	when a connection to another node dies, you know nothing about the other
		976	port.
		977
		978	Erlang pretends remote ports are as reliable as local ports, even when
		979	they are not.
		980
		981	AEMP encourages a "treat remote ports differently" philosophy, with local
		982	ports being the special case/exception, where transport errors cannot
		983	occur.
		984
		985	=item * Erlang uses processes and a mailbox, AEMP does not queue.
		986
		987	Erlang uses processes that selectively receive messages out of order, and
		988	therefore needs a queue. AEMP is event based, queuing messages would serve
		989	no useful purpose. For the same reason the pattern-matching abilities
		990	of AnyEvent::MP are more limited, as there is little need to be able to
		991	filter messages without dequeuing them.
		992
		993	This is not a philosophical difference, but simply stems from AnyEvent::MP
		994	being event-based, while Erlang is process-based.
		995
		996	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		997	top of AEMP and Coro threads.
		998
		999	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
		1000
		1001	Sending messages in Erlang is synchronous and blocks the process until
		1002	a conenction has been established and the message sent (and so does not
		1003	need a queue that can overflow). AEMP sends return immediately, connection
		1004	establishment is handled in the background.
		1005
		1006	=item * Erlang suffers from silent message loss, AEMP does not.
		1007
		1008	Erlang implements few guarantees on messages delivery - messages can get
		1009	lost without any of the processes realising it (i.e. you send messages a,
		1010	b, and c, and the other side only receives messages a and c).
		1011
		1012	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1013	guarantee that after one message is lost, all following ones sent to the
		1014	same port are lost as well, until monitoring raises an error, so there are
		1015	no silent "holes" in the message sequence.
		1016
		1017	If you want your software to be very reliable, you have to cope with
		1018	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
		1019	simply tries to work better in common error cases, such as when a network
		1020	link goes down.
		1021
		1022	=item * Erlang can send messages to the wrong port, AEMP does not.
		1023
		1024	In Erlang it is quite likely that a node that restarts reuses an Erlang
		1025	process ID known to other nodes for a completely different process,
		1026	causing messages destined for that process to end up in an unrelated
		1027	process.
		1028
		1029	AEMP does not reuse port IDs, so old messages or old port IDs floating
		1030	around in the network will not be sent to an unrelated port.
		1031
		1032	=item * Erlang uses unprotected connections, AEMP uses secure
		1033	authentication and can use TLS.
		1034
		1035	AEMP can use a proven protocol - TLS - to protect connections and
		1036	securely authenticate nodes.
		1037
		1038	=item * The AEMP protocol is optimised for both text-based and binary
		1039	communications.
		1040
		1041	The AEMP protocol, unlike the Erlang protocol, supports both programming
		1042	language independent text-only protocols (good for debugging), and binary,
		1043	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1044	used, the protocol is actually completely text-based.
		1045
		1046	It has also been carefully designed to be implementable in other languages
		1047	with a minimum of work while gracefully degrading functionality to make the
		1048	protocol simple.
		1049
		1050	=item * AEMP has more flexible monitoring options than Erlang.
		1051
		1052	In Erlang, you can chose to receive I<all> exit signals as messages or
		1053	I<none>, there is no in-between, so monitoring single Erlang processes is
		1054	difficult to implement.
		1055
		1056	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1057	between automatic kill, exit message or callback on a per-port basis.
		1058
		1059	=item * Erlang tries to hide remote/local connections, AEMP does not.
		1060
		1061	Monitoring in Erlang is not an indicator of process death/crashes, in the
		1062	same way as linking is (except linking is unreliable in Erlang).
		1063
		1064	In AEMP, you don't "look up" registered port names or send to named ports
		1065	that might or might not be persistent. Instead, you normally spawn a port
		1066	on the remote node. The init function monitors you, and you monitor the
		1067	remote port. Since both monitors are local to the node, they are much more
		1068	reliable (no need for C<spawn_link>).
		1069
		1070	This also saves round-trips and avoids sending messages to the wrong port
		1071	(hard to do in Erlang).
		1072
		1073	=back
		1074
		1075	=head1 RATIONALE
		1076
		1077	=over 4
		1078
		1079	=item Why strings for port and node IDs, why not objects?
		1080
		1081	We considered "objects", but found that the actual number of methods
		1082	that can be called are quite low. Since port and node IDs travel over
		1083	the network frequently, the serialising/deserialising would add lots of
		1084	overhead, as well as having to keep a proxy object everywhere.
		1085
		1086	Strings can easily be printed, easily serialised etc. and need no special
		1087	procedures to be "valid".
		1088
		1089	And as a result, a port with just a default receiver consists of a single
		1090	code reference stored in a global hash - it can't become much cheaper.
		1091
		1092	=item Why favour JSON, why not a real serialising format such as Storable?
		1093
		1094	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1095	format, but currently there is no way to make a node use Storable by
		1096	default (although all nodes will accept it).
		1097
		1098	The default framing protocol is JSON because a) JSON::XS is many times
		1099	faster for small messages and b) most importantly, after years of
		1100	experience we found that object serialisation is causing more problems
		1101	than it solves: Just like function calls, objects simply do not travel
		1102	easily over the network, mostly because they will always be a copy, so you
		1103	always have to re-think your design.
		1104
		1105	Keeping your messages simple, concentrating on data structures rather than
		1106	objects, will keep your messages clean, tidy and efficient.
		1107
		1108	=back
		1109
443	=head1 SEE ALSO	1110	=head1 SEE ALSO
		1111
		1112	L<AnyEvent::MP::Intro> - a gentle introduction.
		1113
		1114	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1115
		1116	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1117	your applications.
		1118
		1119	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1120
		1121	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1122	all nodes.
444		1123
445	L<AnyEvent>.	1124	L<AnyEvent>.
446		1125
447	=head1 AUTHOR	1126	=head1 AUTHOR
448		1127

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Revision 1.126 by root, Sat Mar 3 19:43:41 2012 UTC