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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.29 by root, Tue Aug 4 23:16:57 2009 UTC vs.
Revision 1.118 by root, Thu Jun 30 09:31:58 2011 UTC

…		…
1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent::MP - multi-processing/message-passing framework	3	AnyEvent::MP - erlang-style multi-processing/message-passing framework
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::MP;	7	use AnyEvent::MP;
8		8
9	$NODE # contains this node's noderef	9	$NODE # contains this node's node ID
10	NODE # returns this node's noderef	10	NODE # returns this node's node ID
11	NODE $port # returns the noderef of the port
12		11
		12	$SELF # receiving/own port id in rcv callbacks
		13
		14	# initialise the node so it can send/receive messages
		15	configure;
		16
		17	# ports are message destinations
		18
		19	# sending messages
13	snd $port, type => data...;	20	snd $port, type => data...;
		21	snd $port, @msg;
		22	snd @msg_with_first_element_being_a_port;
14		23
15	$SELF # receiving/own port id in rcv callbacks	24	# creating/using ports, the simple way
		25	my $simple_port = port { my @msg = @_ };
16		26
17	rcv $port, smartmatch => $cb->($port, @msg);	27	# creating/using ports, tagged message matching
18		28	my $port = port;
19	# examples:
20	rcv $port2, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
21	rcv $port1, pong => sub { warn "pong received\n" };	30	rcv $port, pong => sub { warn "pong received\n" };
22	snd $port2, ping => $port1;
23		31
24	# more, smarter, matches (_any_ is exported by this module)	32	# create a port on another node
25	rcv $port, [child_died => $pid] => sub { ...	33	my $port = spawn $node, $initfunc, @initdata;
26	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3	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.
27		59
28	=head1 DESCRIPTION	60	=head1 DESCRIPTION
29		61
30	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
31		63
32	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
33	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
34		66
35	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	67	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
36	manual page.	68	manual page and the examples under F<eg/>.
37
38	At the moment, this module family is severly broken and underdocumented,
39	so do not use. This was uploaded mainly to reserve the CPAN namespace -
40	stay tuned! The basic API should be finished, however.
41		69
42	=head1 CONCEPTS	70	=head1 CONCEPTS
43		71
44	=over 4	72	=over 4
45		73
46	=item port	74	=item port
47		75
48	A port is something you can send messages to (with the C<snd> function).	76	Not to be confused with a TCP port, a "port" is something you can send
		77	messages to (with the C<snd> function).
49		78
50	Some ports allow you to register C<rcv> handlers that can match specific	79	Ports allow you to register C<rcv> handlers that can match all or just
51	messages. All C<rcv> handlers will receive messages they match, messages	80	some messages. Messages send to ports will not be queued, regardless of
52	will not be queued.	81	anything was listening for them or not.
53		82
54	=item port id - C<noderef#portname>	83	=item port ID - C<nodeid#portname>
55		84
56	A port id is normaly the concatenation of a noderef, a hash-mark (C<#>) as	85	A port ID is the concatenation of a node ID, a hash-mark (C<#>) as
57	separator, and a port name (a printable string of unspecified format). An	86	separator, and a port name (a printable string of unspecified format).
58	exception is the the node port, whose ID is identical to it's node
59	reference.
60		87
61	=item node	88	=item node
62		89
63	A node is a single process containing at least one port - the node	90	A node is a single process containing at least one port - the node port,
64	port. You can send messages to node ports to find existing ports or to	91	which enables nodes to manage each other remotely, and to create new
65	create new ports, among other things.	92	ports.
66		93
67	Nodes are either private (single-process only), slaves (connected to a	94	Nodes are either public (have one or more listening ports) or private
68	master node only) or public nodes (connectable from unrelated nodes).	95	(no listening ports). Private nodes cannot talk to other private nodes
		96	currently.
69		97
70	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	98	=item node ID - C<[A-Za-z0-9_\-.:]*>
71		99
72	A node reference is a string that either simply identifies the node (for	100	A node ID is a string that uniquely identifies the node within a
73	private and slave nodes), or contains a recipe on how to reach a given	101	network. Depending on the configuration used, node IDs can look like a
74	node (for public nodes).	102	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		103	doesn't interpret node IDs in any way.
75		104
76	This recipe is simply a comma-separated list of C<address:port> pairs (for	105	=item binds - C<ip:port>
77	TCP/IP, other protocols might look different).
78		106
79	Node references come in two flavours: resolved (containing only numerical	107	Nodes can only talk to each other by creating some kind of connection to
80	addresses) or unresolved (where hostnames are used instead of addresses).	108	each other. To do this, nodes should listen on one or more local transport
		109	endpoints - binds. Currently, only standard C<ip:port> specifications can
		110	be used, which specify TCP ports to listen on.
81		111
82	Before using an unresolved node reference in a message you first have to	112	=item seed nodes
83	resolve it.	113
		114	When a node starts, it knows nothing about the network. To teach the node
		115	about the network it first has to contact some other node within the
		116	network. This node is called a seed.
		117
		118	Apart from the fact that other nodes know them as seed nodes and they have
		119	to have fixed listening addresses, seed nodes are perfectly normal nodes -
		120	any node can function as a seed node for others.
		121
		122	In addition to discovering the network, seed nodes are also used to
		123	maintain the network and to connect nodes that otherwise would have
		124	trouble connecting. They form the backbone of an AnyEvent::MP network.
		125
		126	Seed nodes are expected to be long-running, and at least one seed node
		127	should always be available. They should also be relatively responsive - a
		128	seed node that blocks for long periods will slow down everybody else.
		129
		130	=item seeds - C<host:port>
		131
		132	Seeds are transport endpoint(s) (usually a hostname/IP address and a
		133	TCP port) of nodes that should be used as seed nodes.
		134
		135	The nodes listening on those endpoints are expected to be long-running,
		136	and at least one of those should always be available. When nodes run out
		137	of connections (e.g. due to a network error), they try to re-establish
		138	connections to some seednodes again to join the network.
84		139
85	=back	140	=back
86		141
87	=head1 VARIABLES/FUNCTIONS	142	=head1 VARIABLES/FUNCTIONS
88		143
90		145
91	=cut	146	=cut
92		147
93	package AnyEvent::MP;	148	package AnyEvent::MP;
94		149
95	use AnyEvent::MP::Base;	150	use AnyEvent::MP::Kernel;
96		151
97	use common::sense;	152	use common::sense;
98		153
99	use Carp ();	154	use Carp ();
100		155
101	use AE ();	156	use AE ();
102		157
103	use base "Exporter";	158	use base "Exporter";
104		159
105	our $VERSION = '0.1';	160	our $VERSION = '1.30';
		161
106	our @EXPORT = qw(	162	our @EXPORT = qw(
107	NODE $NODE *SELF node_of _any_	163	NODE $NODE *SELF node_of after
108	resolve_node	164	configure
109	become_slave become_public	165	snd rcv mon mon_guard kil psub peval spawn cal
110	snd rcv mon kil reg psub
111	port	166	port
112	);	167	);
113		168
114	our $SELF;	169	our $SELF;
115		170
…		…
119	kil $SELF, die => $msg;	174	kil $SELF, die => $msg;
120	}	175	}
121		176
122	=item $thisnode = NODE / $NODE	177	=item $thisnode = NODE / $NODE
123		178
124	The C<NODE> function returns, and the C<$NODE> variable contains	179	The C<NODE> function returns, and the C<$NODE> variable contains, the node
125	the noderef of the local node. The value is initialised by a call	180	ID of the node running in the current process. This value is initialised by
126	to C<become_public> or C<become_slave>, after which all local port	181	a call to C<configure>.
127	identifiers become invalid.
128		182
129	=item $noderef = node_of $portid	183	=item $nodeid = node_of $port
130		184
131	Extracts and returns the noderef from a portid or a noderef.	185	Extracts and returns the node ID from a port ID or a node ID.
132		186
133	=item $cv = resolve_node $noderef	187	=item configure $profile, key => value...
134		188
135	Takes an unresolved node reference that may contain hostnames and	189	=item configure key => value...
136	abbreviated IDs, resolves all of them and returns a resolved node
137	reference.
138		190
139	In addition to C<address:port> pairs allowed in resolved noderefs, the	191	Before a node can talk to other nodes on the network (i.e. enter
140	following forms are supported:	192	"distributed mode") it has to configure itself - the minimum a node needs
		193	to know is its own name, and optionally it should know the addresses of
		194	some other nodes in the network to discover other nodes.
		195
		196	The key/value pairs are basically the same ones as documented for the
		197	F<aemp> command line utility (sans the set/del prefix).
		198
		199	This function configures a node - it must be called exactly once (or
		200	never) before calling other AnyEvent::MP functions.
141		201
142	=over 4	202	=over 4
143		203
144	=item the empty string	204	=item step 1, gathering configuration from profiles
145		205
146	An empty-string component gets resolved as if the default port (4040) was	206	The function first looks up a profile in the aemp configuration (see the
147	specified.	207	L<aemp> commandline utility). The profile name can be specified via the
		208	named C<profile> parameter or can simply be the first parameter). If it is
		209	missing, then the nodename (F<uname -n>) will be used as profile name.
148		210
149	=item naked port numbers (e.g. C<1234>)	211	The profile data is then gathered as follows:
150		212
151	These are resolved by prepending the local nodename and a colon, to be	213	First, all remaining key => value pairs (all of which are conveniently
152	further resolved.	214	undocumented at the moment) will be interpreted as configuration
		215	data. Then they will be overwritten by any values specified in the global
		216	default configuration (see the F<aemp> utility), then the chain of
		217	profiles chosen by the profile name (and any C<parent> attributes).
153		218
154	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	219	That means that the values specified in the profile have highest priority
		220	and the values specified directly via C<configure> have lowest priority,
		221	and can only be used to specify defaults.
155		222
156	These are resolved by using AnyEvent::DNS to resolve them, optionally	223	If the profile specifies a node ID, then this will become the node ID of
157	looking up SRV records for the C<aemp=4040> port, if no port was	224	this process. If not, then the profile name will be used as node ID. The
158	specified.	225	special node ID of C<anon/> will be replaced by a random node ID.
		226
		227	=item step 2, bind listener sockets
		228
		229	The next step is to look up the binds in the profile, followed by binding
		230	aemp protocol listeners on all binds specified (it is possible and valid
		231	to have no binds, meaning that the node cannot be contacted form the
		232	outside. This means the node cannot talk to other nodes that also have no
		233	binds, but it can still talk to all "normal" nodes).
		234
		235	If the profile does not specify a binds list, then a default of C<*> is
		236	used, meaning the node will bind on a dynamically-assigned port on every
		237	local IP address it finds.
		238
		239	=item step 3, connect to seed nodes
		240
		241	As the last step, the seeds list from the profile is passed to the
		242	L<AnyEvent::MP::Global> module, which will then use it to keep
		243	connectivity with at least one node at any point in time.
159		244
160	=back	245	=back
		246
		247	Example: become a distributed node using the local node name as profile.
		248	This should be the most common form of invocation for "daemon"-type nodes.
		249
		250	configure
		251
		252	Example: become an anonymous node. This form is often used for commandline
		253	clients.
		254
		255	configure nodeid => "anon/";
		256
		257	Example: configure a node using a profile called seed, which si suitable
		258	for a seed node as it binds on all local addresses on a fixed port (4040,
		259	customary for aemp).
		260
		261	# use the aemp commandline utility
		262	# aemp profile seed nodeid anon/ binds '*:4040'
		263
		264	# then use it
		265	configure profile => "seed";
		266
		267	# or simply use aemp from the shell again:
		268	# aemp run profile seed
		269
		270	# or provide a nicer-to-remember nodeid
		271	# aemp run profile seed nodeid "$(hostname)"
161		272
162	=item $SELF	273	=item $SELF
163		274
164	Contains the current port id while executing C<rcv> callbacks or C<psub>	275	Contains the current port id while executing C<rcv> callbacks or C<psub>
165	blocks.	276	blocks.
166		277
167	=item SELF, %SELF, @SELF...	278	=item *SELF, SELF, %SELF, @SELF...
168		279
169	Due to some quirks in how perl exports variables, it is impossible to	280	Due to some quirks in how perl exports variables, it is impossible to
170	just export C<$SELF>, all the symbols called C<SELF> are exported by this	281	just export C<$SELF>, all the symbols named C<SELF> are exported by this
171	module, but only C<$SELF> is currently used.	282	module, but only C<$SELF> is currently used.
172		283
173	=item snd $portid, type => @data	284	=item snd $port, type => @data
174		285
175	=item snd $portid, @msg	286	=item snd $port, @msg
176		287
177	Send the given message to the given port ID, which can identify either	288	Send the given message to the given port, which can identify either a
178	a local or a remote port, and can be either a string or soemthignt hat	289	local or a remote port, and must be a port ID.
179	stringifies a sa port ID (such as a port object :).
180		290
181	While the message can be about anything, it is highly recommended to use a	291	While the message can be almost anything, it is highly recommended to
182	string as first element (a portid, or some word that indicates a request	292	use a string as first element (a port ID, or some word that indicates a
183	type etc.).	293	request type etc.) and to consist if only simple perl values (scalars,
		294	arrays, hashes) - if you think you need to pass an object, think again.
184		295
185	The message data effectively becomes read-only after a call to this	296	The message data logically becomes read-only after a call to this
186	function: modifying any argument is not allowed and can cause many	297	function: modifying any argument (or values referenced by them) is
187	problems.	298	forbidden, as there can be considerable time between the call to C<snd>
		299	and the time the message is actually being serialised - in fact, it might
		300	never be copied as within the same process it is simply handed to the
		301	receiving port.
188		302
189	The type of data you can transfer depends on the transport protocol: when	303	The type of data you can transfer depends on the transport protocol: when
190	JSON is used, then only strings, numbers and arrays and hashes consisting	304	JSON is used, then only strings, numbers and arrays and hashes consisting
191	of those are allowed (no objects). When Storable is used, then anything	305	of those are allowed (no objects). When Storable is used, then anything
192	that Storable can serialise and deserialise is allowed, and for the local	306	that Storable can serialise and deserialise is allowed, and for the local
193	node, anything can be passed.	307	node, anything can be passed. Best rely only on the common denominator of
		308	these.
194		309
195	=item kil $portid[, @reason]	310	=item $local_port = port
196		311
197	Kill the specified port with the given C<@reason>.	312	Create a new local port object and returns its port ID. Initially it has
		313	no callbacks set and will throw an error when it receives messages.
198		314
199	If no C<@reason> is specified, then the port is killed "normally" (linked	315	=item $local_port = port { my @msg = @_ }
200	ports will not be kileld, or even notified).
201		316
202	Otherwise, linked ports get killed with the same reason (second form of	317	Creates a new local port, and returns its ID. Semantically the same as
203	C<mon>, see below).	318	creating a port and calling C<rcv $port, $callback> on it.
204		319
205	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	320	The block will be called for every message received on the port, with the
206	will be reported as reason C<< die => $@ >>.	321	global variable C<$SELF> set to the port ID. Runtime errors will cause the
		322	port to be C<kil>ed. The message will be passed as-is, no extra argument
		323	(i.e. no port ID) will be passed to the callback.
207		324
208	Transport/communication errors are reported as C<< transport_error =>	325	If you want to stop/destroy the port, simply C<kil> it:
209	$message >>.
210		326
211	=item $guard = mon $portid, $cb->(@reason)	327	my $port = port {
		328	my @msg = @_;
		329	...
		330	kil $SELF;
		331	};
212		332
213	=item $guard = mon $portid, $otherport	333	=cut
214		334
215	=item $guard = mon $portid, $otherport, @msg	335	sub rcv($@);
216		336
		337	sub _kilme {
		338	die "received message on port without callback";
		339	}
		340
		341	sub port(;&) {
		342	my $id = "$UNIQ." . $ID++;
		343	my $port = "$NODE#$id";
		344
		345	rcv $port, shift \|\| \&_kilme;
		346
		347	$port
		348	}
		349
		350	=item rcv $local_port, $callback->(@msg)
		351
		352	Replaces the default callback on the specified port. There is no way to
		353	remove the default callback: use C<sub { }> to disable it, or better
		354	C<kil> the port when it is no longer needed.
		355
		356	The global C<$SELF> (exported by this module) contains C<$port> while
		357	executing the callback. Runtime errors during callback execution will
		358	result in the port being C<kil>ed.
		359
		360	The default callback received all messages not matched by a more specific
		361	C<tag> match.
		362
		363	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
		364
		365	Register (or replace) callbacks to be called on messages starting with the
		366	given tag on the given port (and return the port), or unregister it (when
		367	C<$callback> is C<$undef> or missing). There can only be one callback
		368	registered for each tag.
		369
		370	The original message will be passed to the callback, after the first
		371	element (the tag) has been removed. The callback will use the same
		372	environment as the default callback (see above).
		373
		374	Example: create a port and bind receivers on it in one go.
		375
		376	my $port = rcv port,
		377	msg1 => sub { ... },
		378	msg2 => sub { ... },
		379	;
		380
		381	Example: create a port, bind receivers and send it in a message elsewhere
		382	in one go:
		383
		384	snd $otherport, reply =>
		385	rcv port,
		386	msg1 => sub { ... },
		387	...
		388	;
		389
		390	Example: temporarily register a rcv callback for a tag matching some port
		391	(e.g. for an rpc reply) and unregister it after a message was received.
		392
		393	rcv $port, $otherport => sub {
		394	my @reply = @_;
		395
		396	rcv $SELF, $otherport;
		397	};
		398
		399	=cut
		400
		401	sub rcv($@) {
		402	my $port = shift;
		403	my ($nodeid, $portid) = split /#/, $port, 2;
		404
		405	$NODE{$nodeid} == $NODE{""}
		406	or Carp::croak "$port: rcv can only be called on local ports, caught";
		407
		408	while (@_) {
		409	if (ref $_[0]) {
		410	if (my $self = $PORT_DATA{$portid}) {
		411	"AnyEvent::MP::Port" eq ref $self
		412	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		413
		414	$self->[0] = shift;
		415	} else {
		416	my $cb = shift;
		417	$PORT{$portid} = sub {
		418	local $SELF = $port;
		419	eval { &$cb }; _self_die if $@;
		420	};
		421	}
		422	} elsif (defined $_[0]) {
		423	my $self = $PORT_DATA{$portid} \|\|= do {
		424	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
		425
		426	$PORT{$portid} = sub {
		427	local $SELF = $port;
		428
		429	if (my $cb = $self->[1]{$_[0]}) {
		430	shift;
		431	eval { &$cb }; _self_die if $@;
		432	} else {
		433	&{ $self->[0] };
		434	}
		435	};
		436
		437	$self
		438	};
		439
		440	"AnyEvent::MP::Port" eq ref $self
		441	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		442
		443	my ($tag, $cb) = splice @_, 0, 2;
		444
		445	if (defined $cb) {
		446	$self->[1]{$tag} = $cb;
		447	} else {
		448	delete $self->[1]{$tag};
		449	}
		450	}
		451	}
		452
		453	$port
		454	}
		455
		456	=item peval $port, $coderef[, @args]
		457
		458	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		459	when the code throews an exception the C<$port> will be killed.
		460
		461	Any remaining args will be passed to the callback. Any return values will
		462	be returned to the caller.
		463
		464	This is useful when you temporarily want to execute code in the context of
		465	a port.
		466
		467	Example: create a port and run some initialisation code in it's context.
		468
		469	my $port = port { ... };
		470
		471	peval $port, sub {
		472	init
		473	or die "unable to init";
		474	};
		475
		476	=cut
		477
		478	sub peval($$) {
		479	local $SELF = shift;
		480	my $cb = shift;
		481
		482	if (wantarray) {
		483	my @res = eval { &$cb };
		484	_self_die if $@;
		485	@res
		486	} else {
		487	my $res = eval { &$cb };
		488	_self_die if $@;
		489	$res
		490	}
		491	}
		492
		493	=item $closure = psub { BLOCK }
		494
		495	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
		496	closure is executed, sets up the environment in the same way as in C<rcv>
		497	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		498
		499	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		500	BLOCK }, @_ } >>.
		501
		502	This is useful when you register callbacks from C<rcv> callbacks:
		503
		504	rcv delayed_reply => sub {
		505	my ($delay, @reply) = @_;
		506	my $timer = AE::timer $delay, 0, psub {
		507	snd @reply, $SELF;
		508	};
		509	};
		510
		511	=cut
		512
		513	sub psub(&) {
		514	my $cb = shift;
		515
		516	my $port = $SELF
		517	or Carp::croak "psub can only be called from within rcv or psub callbacks, not";
		518
		519	sub {
		520	local $SELF = $port;
		521
		522	if (wantarray) {
		523	my @res = eval { &$cb };
		524	_self_die if $@;
		525	@res
		526	} else {
		527	my $res = eval { &$cb };
		528	_self_die if $@;
		529	$res
		530	}
		531	}
		532	}
		533
		534	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
		535
		536	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
		537
		538	=item $guard = mon $port # kill $SELF when $port dies
		539
		540	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		541
217	Monitor the given port and do something when the port is killed.	542	Monitor the given port and do something when the port is killed or
		543	messages to it were lost, and optionally return a guard that can be used
		544	to stop monitoring again.
218		545
219	In the first form, the callback is simply called with any number	546	In the first form (callback), the callback is simply called with any
220	of C<@reason> elements (no @reason means that the port was deleted	547	number of C<@reason> elements (no @reason means that the port was deleted
221	"normally"). Note also that I<< the callback B<must> never die >>, so use	548	"normally"). Note also that I<< the callback B<must> never die >>, so use
222	C<eval> if unsure.	549	C<eval> if unsure.
223		550
224	In the second form, the other port will be C<kil>'ed with C<@reason>, iff	551	In the second form (another port given), the other port (C<$rcvport>)
225	a @reason was specified, i.e. on "normal" kils nothing happens, while	552	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
226	under all other conditions, the other port is killed with the same reason.	553	"normal" kils nothing happens, while under all other conditions, the other
		554	port is killed with the same reason.
227		555
		556	The third form (kill self) is the same as the second form, except that
		557	C<$rvport> defaults to C<$SELF>.
		558
228	In the last form, a message of the form C<@msg, @reason> will be C<snd>.	559	In the last form (message), a message of the form C<@msg, @reason> will be
		560	C<snd>.
		561
		562	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		563	alert was raised), they are removed and will not trigger again.
		564
		565	As a rule of thumb, monitoring requests should always monitor a port from
		566	a local port (or callback). The reason is that kill messages might get
		567	lost, just like any other message. Another less obvious reason is that
		568	even monitoring requests can get lost (for example, when the connection
		569	to the other node goes down permanently). When monitoring a port locally
		570	these problems do not exist.
		571
		572	C<mon> effectively guarantees that, in the absence of hardware failures,
		573	after starting the monitor, either all messages sent to the port will
		574	arrive, or the monitoring action will be invoked after possible message
		575	loss has been detected. No messages will be lost "in between" (after
		576	the first lost message no further messages will be received by the
		577	port). After the monitoring action was invoked, further messages might get
		578	delivered again.
		579
		580	Inter-host-connection timeouts and monitoring depend on the transport
		581	used. The only transport currently implemented is TCP, and AnyEvent::MP
		582	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		583	non-idle connection, and usually around two hours for idle connections).
		584
		585	This means that monitoring is good for program errors and cleaning up
		586	stuff eventually, but they are no replacement for a timeout when you need
		587	to ensure some maximum latency.
229		588
230	Example: call a given callback when C<$port> is killed.	589	Example: call a given callback when C<$port> is killed.
231		590
232	mon $port, sub { warn "port died because of <@_>\n" };	591	mon $port, sub { warn "port died because of <@_>\n" };
233		592
234	Example: kill ourselves when C<$port> is killed abnormally.	593	Example: kill ourselves when C<$port> is killed abnormally.
235		594
236	mon $port, $self;	595	mon $port;
237		596
238	Example: send us a restart message another C<$port> is killed.	597	Example: send us a restart message when another C<$port> is killed.
239		598
240	mon $port, $self => "restart";	599	mon $port, $self => "restart";
241		600
242	=cut	601	=cut
243		602
244	sub mon {	603	sub mon {
245	my ($noderef, $port, $cb) = ((split /#/, shift, 2), shift);	604	my ($nodeid, $port) = split /#/, shift, 2;
246		605
247	my $node = $NODE{$noderef} \|\| add_node $noderef;	606	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
248		607
249	#TODO: ports must not be references	608	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
250	if (!ref $cb or "AnyEvent::MP::Port" eq ref $cb) {	609
		610	unless (ref $cb) {
251	if (@_) {	611	if (@_) {
252	# send a kill info message	612	# send a kill info message
253	my (@msg) = ($cb, @_);	613	my (@msg) = ($cb, @_);
254	$cb = sub { snd @msg, @_ };	614	$cb = sub { snd @msg, @_ };
255	} else {	615	} else {
…		…
260	}	620	}
261		621
262	$node->monitor ($port, $cb);	622	$node->monitor ($port, $cb);
263		623
264	defined wantarray	624	defined wantarray
265	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	625	and ($cb += 0, AnyEvent::Util::guard { $node->unmonitor ($port, $cb) })
266	}	626	}
267		627
268	=item $guard = mon_guard $port, $ref, $ref...	628	=item $guard = mon_guard $port, $ref, $ref...
269		629
270	Monitors the given C<$port> and keeps the passed references. When the port	630	Monitors the given C<$port> and keeps the passed references. When the port
271	is killed, the references will be freed.	631	is killed, the references will be freed.
272		632
273	Optionally returns a guard that will stop the monitoring.	633	Optionally returns a guard that will stop the monitoring.
274		634
275	This function is useful when you create e.g. timers or other watchers and	635	This function is useful when you create e.g. timers or other watchers and
276	want to free them when the port gets killed:	636	want to free them when the port gets killed (note the use of C<psub>):
277		637
278	$port->rcv (start => sub {	638	$port->rcv (start => sub {
279	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	639	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
280	undef $timer if 0.9 < rand;	640	undef $timer if 0.9 < rand;
281	});	641	});
282	});	642	});
283		643
284	=cut	644	=cut
285		645
286	sub mon_guard {	646	sub mon_guard {
287	my ($port, @refs) = @_;	647	my ($port, @refs) = @_;
288		648
		649	#TODO: mon-less form?
		650
289	mon $port, sub { 0 && @refs }	651	mon $port, sub { 0 && @refs }
290	}	652	}
291		653
292	=item lnk $port1, $port2	654	=item kil $port[, @reason]
293		655
294	Link two ports. This is simply a shorthand for:	656	Kill the specified port with the given C<@reason>.
295		657
296	mon $port1, $port2;	658	If no C<@reason> is specified, then the port is killed "normally" -
297	mon $port2, $port1;	659	monitor callback will be invoked, but the kil will not cause linked ports
		660	(C<mon $mport, $lport> form) to get killed.
298		661
299	It means that if either one is killed abnormally, the other one gets	662	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
300	killed as well.	663	form) get killed with the same reason.
301		664
302	=item $local_port = port	665	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		666	will be reported as reason C<< die => $@ >>.
303		667
304	Create a new local port object that supports message matching.	668	Transport/communication errors are reported as C<< transport_error =>
		669	$message >>.
305		670
306	=item $portid = port { my @msg = @_; $finished }	671	=cut
307		672
308	Creates a "mini port", that is, a very lightweight port without any	673	=item $port = spawn $node, $initfunc[, @initdata]
309	pattern matching behind it, and returns its ID.
310		674
311	The block will be called for every message received on the port. When the	675	Creates a port on the node C<$node> (which can also be a port ID, in which
312	callback returns a true value its job is considered "done" and the port	676	case it's the node where that port resides).
313	will be destroyed. Otherwise it will stay alive.
314		677
315	The message will be passed as-is, no extra argument (i.e. no port id) will	678	The port ID of the newly created port is returned immediately, and it is
316	be passed to the callback.	679	possible to immediately start sending messages or to monitor the port.
317		680
318	If you need the local port id in the callback, this works nicely:	681	After the port has been created, the init function is called on the remote
		682	node, in the same context as a C<rcv> callback. This function must be a
		683	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		684	specify a function in the main program, use C<::name>.
319		685
320	my $port; $port = miniport {	686	If the function doesn't exist, then the node tries to C<require>
321	snd $otherport, reply => $port;	687	the package, then the package above the package and so on (e.g.
		688	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		689	exists or it runs out of package names.
		690
		691	The init function is then called with the newly-created port as context
		692	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		693	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		694	the port might not get created.
		695
		696	A common idiom is to pass a local port, immediately monitor the spawned
		697	port, and in the remote init function, immediately monitor the passed
		698	local port. This two-way monitoring ensures that both ports get cleaned up
		699	when there is a problem.
		700
		701	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		702	caller before C<spawn> returns (by delaying invocation when spawn is
		703	called for the local node).
		704
		705	Example: spawn a chat server port on C<$othernode>.
		706
		707	# this node, executed from within a port context:
		708	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		709	mon $server;
		710
		711	# init function on C<$othernode>
		712	sub connect {
		713	my ($srcport) = @_;
		714
		715	mon $srcport;
		716
		717	rcv $SELF, sub {
		718	...
		719	};
		720	}
		721
		722	=cut
		723
		724	sub _spawn {
		725	my $port = shift;
		726	my $init = shift;
		727
		728	# rcv will create the actual port
		729	local $SELF = "$NODE#$port";
		730	eval {
		731	&{ load_func $init }
322	};	732	};
		733	_self_die if $@;
		734	}
323		735
324	=cut	736	sub spawn(@) {
		737	my ($nodeid, undef) = split /#/, shift, 2;
325		738
326	sub port(;&) {
327	my $id = "$UNIQ." . $ID++;	739	my $id = "$RUNIQ." . $ID++;
328	my $port = "$NODE#$id";
329		740
330	if (@_) {	741	$_[0] =~ /::/
331	my $cb = shift;	742	or Carp::croak "spawn init function must be a fully-qualified name, caught";
332	$PORT{$id} = sub {	743
333	local $SELF = $port;	744	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
334	eval {	745
335	&$cb	746	"$nodeid#$id"
336	and kil $id;	747	}
337	};	748
338	_self_die if $@;	749	=item after $timeout, @msg
		750
		751	=item after $timeout, $callback
		752
		753	Either sends the given message, or call the given callback, after the
		754	specified number of seconds.
		755
		756	This is simply a utility function that comes in handy at times - the
		757	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		758	so it may go away in the future.
		759
		760	=cut
		761
		762	sub after($@) {
		763	my ($timeout, @action) = @_;
		764
		765	my $t; $t = AE::timer $timeout, 0, sub {
		766	undef $t;
		767	ref $action[0]
		768	? $action[0]()
		769	: snd @action;
		770	};
		771	}
		772
		773	=item cal $port, @msg, $callback[, $timeout]
		774
		775	A simple form of RPC - sends a message to the given C<$port> with the
		776	given contents (C<@msg>), but adds a reply port to the message.
		777
		778	The reply port is created temporarily just for the purpose of receiving
		779	the reply, and will be C<kil>ed when no longer needed.
		780
		781	A reply message sent to the port is passed to the C<$callback> as-is.
		782
		783	If an optional time-out (in seconds) is given and it is not C<undef>,
		784	then the callback will be called without any arguments after the time-out
		785	elapsed and the port is C<kil>ed.
		786
		787	If no time-out is given (or it is C<undef>), then the local port will
		788	monitor the remote port instead, so it eventually gets cleaned-up.
		789
		790	Currently this function returns the temporary port, but this "feature"
		791	might go in future versions unless you can make a convincing case that
		792	this is indeed useful for something.
		793
		794	=cut
		795
		796	sub cal(@) {
		797	my $timeout = ref $_[-1] ? undef : pop;
		798	my $cb = pop;
		799
		800	my $port = port {
		801	undef $timeout;
		802	kil $SELF;
		803	&$cb;
		804	};
		805
		806	if (defined $timeout) {
		807	$timeout = AE::timer $timeout, 0, sub {
		808	undef $timeout;
		809	kil $port;
		810	$cb->();
339	};	811	};
340	} else {	812	} else {
341	my $self = bless {	813	mon $_[0], sub {
342	id => "$NODE#$id",	814	kil $port;
343	}, "AnyEvent::MP::Port";	815	$cb->();
344
345	$PORT_DATA{$id} = $self;
346	$PORT{$id} = sub {
347	local $SELF = $port;
348
349	eval {
350	for (@{ $self->{rc0}{$_[0]} }) {
351	$_ && &{$_->[0]}
352	&& undef $_;
353	}
354
355	for (@{ $self->{rcv}{$_[0]} }) {
356	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
357	&& &{$_->[0]}
358	&& undef $_;
359	}
360
361	for (@{ $self->{any} }) {
362	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
363	&& &{$_->[0]}
364	&& undef $_;
365	}
366	};
367	_self_die if $@;
368	};	816	};
369	}	817	}
370		818
		819	push @_, $port;
		820	&snd;
		821
371	$port	822	$port
372	}	823	}
373		824
374	=item reg $portid, $name
375
376	Registers the given port under the name C<$name>. If the name already
377	exists it is replaced.
378
379	A port can only be registered under one well known name.
380
381	A port automatically becomes unregistered when it is killed.
382
383	=cut
384
385	sub reg(@) {
386	my ($portid, $name) = @_;
387
388	$REG{$name} = $portid;
389	}
390
391	=item rcv $portid, tagstring => $callback->(@msg), ...
392
393	=item rcv $portid, $smartmatch => $callback->(@msg), ...
394
395	=item rcv $portid, [$smartmatch...] => $callback->(@msg), ...
396
397	Register callbacks to be called on matching messages on the given port.
398
399	The callback has to return a true value when its work is done, after
400	which is will be removed, or a false value in which case it will stay
401	registered.
402
403	The global C<$SELF> (exported by this module) contains C<$portid> while
404	executing the callback.
405
406	Runtime errors wdurign callback execution will result in the port being
407	C<kil>ed.
408
409	If the match is an array reference, then it will be matched against the
410	first elements of the message, otherwise only the first element is being
411	matched.
412
413	Any element in the match that is specified as C<_any_> (a function
414	exported by this module) matches any single element of the message.
415
416	While not required, it is highly recommended that the first matching
417	element is a string identifying the message. The one-string-only match is
418	also the most efficient match (by far).
419
420	=cut
421
422	sub rcv($@) {
423	my ($noderef, $port) = split /#/, shift, 2;
424
425	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}
426	or Carp::croak "$noderef#$port: rcv can only be called on local ports, caught";
427
428	my $self = $PORT_DATA{$port}
429	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";
430
431	"AnyEvent::MP::Port" eq ref $self
432	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";
433
434	while (@_) {
435	my ($match, $cb) = splice @_, 0, 2;
436
437	if (!ref $match) {
438	push @{ $self->{rc0}{$match} }, [$cb];
439	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
440	my ($type, @match) = @$match;
441	@match
442	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
443	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
444	} else {
445	push @{ $self->{any} }, [$cb, $match];
446	}
447	}
448	}
449
450	=item $closure = psub { BLOCK }
451
452	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
453	closure is executed, sets up the environment in the same way as in C<rcv>
454	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
455
456	This is useful when you register callbacks from C<rcv> callbacks:
457
458	rcv delayed_reply => sub {
459	my ($delay, @reply) = @_;
460	my $timer = AE::timer $delay, 0, psub {
461	snd @reply, $SELF;
462	};
463	};
464
465	=cut
466
467	sub psub(&) {
468	my $cb = shift;
469
470	my $port = $SELF
471	or Carp::croak "psub can only be called from within rcv or psub callbacks, not";
472
473	sub {
474	local $SELF = $port;
475
476	if (wantarray) {
477	my @res = eval { &$cb };
478	_self_die if $@;
479	@res
480	} else {
481	my $res = eval { &$cb };
482	_self_die if $@;
483	$res
484	}
485	}
486	}
487
488	=back	825	=back
489		826
490	=head1 FUNCTIONS FOR NODES
491
492	=over 4
493
494	=item become_public $noderef
495
496	Tells the node to become a public node, i.e. reachable from other nodes.
497
498	The first argument is the (unresolved) node reference of the local node
499	(if missing then the empty string is used).
500
501	It is quite common to not specify anything, in which case the local node
502	tries to listen on the default port, or to only specify a port number, in
503	which case AnyEvent::MP tries to guess the local addresses.
504
505	=cut
506
507	=back
508
509	=head1 NODE MESSAGES
510
511	Nodes understand the following messages sent to them. Many of them take
512	arguments called C<@reply>, which will simply be used to compose a reply
513	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
514	the remaining arguments are simply the message data.
515
516	While other messages exist, they are not public and subject to change.
517
518	=over 4
519
520	=cut
521
522	=item lookup => $name, @reply
523
524	Replies with the port ID of the specified well-known port, or C<undef>.
525
526	=item devnull => ...
527
528	Generic data sink/CPU heat conversion.
529
530	=item relay => $port, @msg
531
532	Simply forwards the message to the given port.
533
534	=item eval => $string[ @reply]
535
536	Evaluates the given string. If C<@reply> is given, then a message of the
537	form C<@reply, $@, @evalres> is sent.
538
539	Example: crash another node.
540
541	snd $othernode, eval => "exit";
542
543	=item time => @reply
544
545	Replies the the current node time to C<@reply>.
546
547	Example: tell the current node to send the current time to C<$myport> in a
548	C<timereply> message.
549
550	snd $NODE, time => $myport, timereply => 1, 2;
551	# => snd $myport, timereply => 1, 2, <time>
552
553	=back
554
555	=head1 AnyEvent::MP vs. Distributed Erlang	827	=head1 AnyEvent::MP vs. Distributed Erlang
556		828
557	AnyEvent::MP got lots of its ideas from distributed erlang (erlang node	829	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
558	== aemp node, erlang process == aemp port), so many of the documents and	830	== aemp node, Erlang process == aemp port), so many of the documents and
559	programming techniques employed by erlang apply to AnyEvent::MP. Here is a	831	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
560	sample:	832	sample:
561		833
562	http://www.erlang.se/doc/programming_rules.shtml	834	http://www.erlang.se/doc/programming_rules.shtml
563	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	835	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
564	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6	836	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
…		…
566		838
567	Despite the similarities, there are also some important differences:	839	Despite the similarities, there are also some important differences:
568		840
569	=over 4	841	=over 4
570		842
571	=item * Node references contain the recipe on how to contact them.	843	=item * Node IDs are arbitrary strings in AEMP.
572		844
573	Erlang relies on special naming and DNS to work everywhere in the	845	Erlang relies on special naming and DNS to work everywhere in the same
574	same way. AEMP relies on each node knowing it's own address(es), with	846	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
575	convenience functionality.	847	configuration or DNS), and possibly the addresses of some seed nodes, but
		848	will otherwise discover other nodes (and their IDs) itself.
576		849
577	This means that AEMP requires a less tightly controlled environment at the	850	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
578	cost of longer node references and a slightly higher management overhead.	851	uses "local ports are like remote ports".
		852
		853	The failure modes for local ports are quite different (runtime errors
		854	only) then for remote ports - when a local port dies, you I<know> it dies,
		855	when a connection to another node dies, you know nothing about the other
		856	port.
		857
		858	Erlang pretends remote ports are as reliable as local ports, even when
		859	they are not.
		860
		861	AEMP encourages a "treat remote ports differently" philosophy, with local
		862	ports being the special case/exception, where transport errors cannot
		863	occur.
579		864
580	=item * Erlang uses processes and a mailbox, AEMP does not queue.	865	=item * Erlang uses processes and a mailbox, AEMP does not queue.
581		866
582	Erlang uses processes that selctively receive messages, and therefore	867	Erlang uses processes that selectively receive messages, and therefore
583	needs a queue. AEMP is event based, queuing messages would serve no useful	868	needs a queue. AEMP is event based, queuing messages would serve no
584	purpose.	869	useful purpose. For the same reason the pattern-matching abilities of
		870	AnyEvent::MP are more limited, as there is little need to be able to
		871	filter messages without dequeuing them.
585		872
586	(But see L<Coro::MP> for a more erlang-like process model on top of AEMP).	873	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).
587		874
588	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	875	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
589		876
590	Sending messages in erlang is synchronous and blocks the process. AEMP	877	Sending messages in Erlang is synchronous and blocks the process (and
591	sends are immediate, connection establishment is handled in the	878	so does not need a queue that can overflow). AEMP sends are immediate,
592	background.	879	connection establishment is handled in the background.
593		880
594	=item * Erlang can silently lose messages, AEMP cannot.	881	=item * Erlang suffers from silent message loss, AEMP does not.
595		882
596	Erlang makes few guarantees on messages delivery - messages can get lost	883	Erlang implements few guarantees on messages delivery - messages can get
597	without any of the processes realising it (i.e. you send messages a, b,	884	lost without any of the processes realising it (i.e. you send messages a,
598	and c, and the other side only receives messages a and c).	885	b, and c, and the other side only receives messages a and c).
599		886
600	AEMP guarantees correct ordering, and the guarantee that there are no	887	AEMP guarantees (modulo hardware errors) correct ordering, and the
		888	guarantee that after one message is lost, all following ones sent to the
		889	same port are lost as well, until monitoring raises an error, so there are
601	holes in the message sequence.	890	no silent "holes" in the message sequence.
602
603	=item * In erlang, processes can be declared dead and later be found to be
604	alive.
605
606	In erlang it can happen that a monitored process is declared dead and
607	linked processes get killed, but later it turns out that the process is
608	still alive - and can receive messages.
609
610	In AEMP, when port monitoring detects a port as dead, then that port will
611	eventually be killed - it cannot happen that a node detects a port as dead
612	and then later sends messages to it, finding it is still alive.
613		891
614	=item * Erlang can send messages to the wrong port, AEMP does not.	892	=item * Erlang can send messages to the wrong port, AEMP does not.
615		893
616	In erlang it is quite possible that a node that restarts reuses a process	894	In Erlang it is quite likely that a node that restarts reuses a process ID
617	ID known to other nodes for a completely different process, causing	895	known to other nodes for a completely different process, causing messages
618	messages destined for that process to end up in an unrelated process.	896	destined for that process to end up in an unrelated process.
619		897
620	AEMP never reuses port IDs, so old messages or old port IDs floating	898	AEMP never reuses port IDs, so old messages or old port IDs floating
621	around in the network will not be sent to an unrelated port.	899	around in the network will not be sent to an unrelated port.
622		900
623	=item * Erlang uses unprotected connections, AEMP uses secure	901	=item * Erlang uses unprotected connections, AEMP uses secure
624	authentication and can use TLS.	902	authentication and can use TLS.
625		903
626	AEMP can use a proven protocol - SSL/TLS - to protect connections and	904	AEMP can use a proven protocol - TLS - to protect connections and
627	securely authenticate nodes.	905	securely authenticate nodes.
628		906
629	=item * The AEMP protocol is optimised for both text-based and binary	907	=item * The AEMP protocol is optimised for both text-based and binary
630	communications.	908	communications.
631		909
632	The AEMP protocol, unlike the erlang protocol, supports both	910	The AEMP protocol, unlike the Erlang protocol, supports both programming
633	language-independent text-only protocols (good for debugging) and binary,	911	language independent text-only protocols (good for debugging) and binary,
634	language-specific serialisers (e.g. Storable).	912	language-specific serialisers (e.g. Storable). By default, unless TLS is
		913	used, the protocol is actually completely text-based.
635		914
636	It has also been carefully designed to be implementable in other languages	915	It has also been carefully designed to be implementable in other languages
637	with a minimum of work while gracefully degrading fucntionality to make the	916	with a minimum of work while gracefully degrading functionality to make the
638	protocol simple.	917	protocol simple.
639		918
		919	=item * AEMP has more flexible monitoring options than Erlang.
		920
		921	In Erlang, you can chose to receive I<all> exit signals as messages
		922	or I<none>, there is no in-between, so monitoring single processes is
		923	difficult to implement. Monitoring in AEMP is more flexible than in
		924	Erlang, as one can choose between automatic kill, exit message or callback
		925	on a per-process basis.
		926
		927	=item * Erlang tries to hide remote/local connections, AEMP does not.
		928
		929	Monitoring in Erlang is not an indicator of process death/crashes, in the
		930	same way as linking is (except linking is unreliable in Erlang).
		931
		932	In AEMP, you don't "look up" registered port names or send to named ports
		933	that might or might not be persistent. Instead, you normally spawn a port
		934	on the remote node. The init function monitors you, and you monitor the
		935	remote port. Since both monitors are local to the node, they are much more
		936	reliable (no need for C<spawn_link>).
		937
		938	This also saves round-trips and avoids sending messages to the wrong port
		939	(hard to do in Erlang).
		940
640	=back	941	=back
641		942
		943	=head1 RATIONALE
		944
		945	=over 4
		946
		947	=item Why strings for port and node IDs, why not objects?
		948
		949	We considered "objects", but found that the actual number of methods
		950	that can be called are quite low. Since port and node IDs travel over
		951	the network frequently, the serialising/deserialising would add lots of
		952	overhead, as well as having to keep a proxy object everywhere.
		953
		954	Strings can easily be printed, easily serialised etc. and need no special
		955	procedures to be "valid".
		956
		957	And as a result, a port with just a default receiver consists of a single
		958	code reference stored in a global hash - it can't become much cheaper.
		959
		960	=item Why favour JSON, why not a real serialising format such as Storable?
		961
		962	In fact, any AnyEvent::MP node will happily accept Storable as framing
		963	format, but currently there is no way to make a node use Storable by
		964	default (although all nodes will accept it).
		965
		966	The default framing protocol is JSON because a) JSON::XS is many times
		967	faster for small messages and b) most importantly, after years of
		968	experience we found that object serialisation is causing more problems
		969	than it solves: Just like function calls, objects simply do not travel
		970	easily over the network, mostly because they will always be a copy, so you
		971	always have to re-think your design.
		972
		973	Keeping your messages simple, concentrating on data structures rather than
		974	objects, will keep your messages clean, tidy and efficient.
		975
		976	=back
		977
642	=head1 SEE ALSO	978	=head1 SEE ALSO
		979
		980	L<AnyEvent::MP::Intro> - a gentle introduction.
		981
		982	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		983
		984	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		985	your applications.
		986
		987	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		988
		989	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		990	all nodes.
643		991
644	L<AnyEvent>.	992	L<AnyEvent>.
645		993
646	=head1 AUTHOR	994	=head1 AUTHOR
647		995

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Revision 1.118 by root, Thu Jun 30 09:31:58 2011 UTC