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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.31 by root, Wed Aug 5 19:55:58 2009 UTC vs.
Revision 1.104 by root, Fri Nov 6 17:47:20 2009 UTC

…		…
1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent::MP - multi-processing/message-passing framework	3	AnyEvent::MP - erlang-style multi-processing/message-passing framework
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::MP;	7	use AnyEvent::MP;
8		8
9	$NODE # contains this node's noderef	9	$NODE # contains this node's node ID
10	NODE # returns this node's noderef	10	NODE # returns this node's node ID
11	NODE $port # returns the noderef of the port
12		11
		12	$SELF # receiving/own port id in rcv callbacks
		13
		14	# initialise the node so it can send/receive messages
		15	configure;
		16
		17	# ports are message destinations
		18
		19	# sending messages
13	snd $port, type => data...;	20	snd $port, type => data...;
		21	snd $port, @msg;
		22	snd @msg_with_first_element_being_a_port;
14		23
15	$SELF # receiving/own port id in rcv callbacks	24	# creating/using ports, the simple way
		25	my $simple_port = port { my @msg = @_ };
16		26
17	rcv $port, smartmatch => $cb->($port, @msg);	27	# creating/using ports, tagged message matching
18		28	my $port = port;
19	# examples:
20	rcv $port2, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
21	rcv $port1, pong => sub { warn "pong received\n" };	30	rcv $port, pong => sub { warn "pong received\n" };
22	snd $port2, ping => $port1;
23		31
24	# more, smarter, matches (_any_ is exported by this module)	32	# create a port on another node
25	rcv $port, [child_died => $pid] => sub { ...	33	my $port = spawn $node, $initfunc, @initdata;
26	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3	34
		35	# destroy a prot 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 its 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-Z_][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 = 1.23;
		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 initialise_node	164	configure
109	snd rcv mon kil reg psub	165	snd rcv mon mon_guard kil psub peval spawn cal
110	port	166	port
111	);	167	);
112		168
113	our $SELF;	169	our $SELF;
114		170
…		…
118	kil $SELF, die => $msg;	174	kil $SELF, die => $msg;
119	}	175	}
120		176
121	=item $thisnode = NODE / $NODE	177	=item $thisnode = NODE / $NODE
122		178
123	The C<NODE> function returns, and the C<$NODE> variable contains	179	The C<NODE> function returns, and the C<$NODE> variable contains, the node
124	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
125	to C<become_public> or C<become_slave>, after which all local port	181	a call to C<configure>.
126	identifiers become invalid.
127		182
128	=item $noderef = node_of $portid	183	=item $nodeid = node_of $port
129		184
130	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.
131		186
132	=item $cv = resolve_node $noderef	187	=item configure $profile, key => value...
133		188
134	Takes an unresolved node reference that may contain hostnames and	189	=item configure key => value...
135	abbreviated IDs, resolves all of them and returns a resolved node
136	reference.
137		190
138	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
139	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	This function configures a node - it must be called exactly once (or
		197	never) before calling other AnyEvent::MP functions.
140		198
141	=over 4	199	=over 4
142		200
143	=item the empty string	201	=item step 1, gathering configuration from profiles
144		202
145	An empty-string component gets resolved as if the default port (4040) was	203	The function first looks up a profile in the aemp configuration (see the
146	specified.	204	L<aemp> commandline utility). The profile name can be specified via the
		205	named C<profile> parameter or can simply be the first parameter). If it is
		206	missing, then the nodename (F<uname -n>) will be used as profile name.
147		207
148	=item naked port numbers (e.g. C<1234>)	208	The profile data is then gathered as follows:
149		209
150	These are resolved by prepending the local nodename and a colon, to be	210	First, all remaining key => value pairs (all of which are conveniently
151	further resolved.	211	undocumented at the moment) will be interpreted as configuration
		212	data. Then they will be overwritten by any values specified in the global
		213	default configuration (see the F<aemp> utility), then the chain of
		214	profiles chosen by the profile name (and any C<parent> attributes).
152		215
153	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	216	That means that the values specified in the profile have highest priority
		217	and the values specified directly via C<configure> have lowest priority,
		218	and can only be used to specify defaults.
154		219
155	These are resolved by using AnyEvent::DNS to resolve them, optionally	220	If the profile specifies a node ID, then this will become the node ID of
156	looking up SRV records for the C<aemp=4040> port, if no port was	221	this process. If not, then the profile name will be used as node ID. The
157	specified.	222	special node ID of C<anon/> will be replaced by a random node ID.
		223
		224	=item step 2, bind listener sockets
		225
		226	The next step is to look up the binds in the profile, followed by binding
		227	aemp protocol listeners on all binds specified (it is possible and valid
		228	to have no binds, meaning that the node cannot be contacted form the
		229	outside. This means the node cannot talk to other nodes that also have no
		230	binds, but it can still talk to all "normal" nodes).
		231
		232	If the profile does not specify a binds list, then a default of C<*> is
		233	used, meaning the node will bind on a dynamically-assigned port on every
		234	local IP address it finds.
		235
		236	=item step 3, connect to seed nodes
		237
		238	As the last step, the seeds list from the profile is passed to the
		239	L<AnyEvent::MP::Global> module, which will then use it to keep
		240	connectivity with at least one node at any point in time.
158		241
159	=back	242	=back
		243
		244	Example: become a distributed node using the local node name as profile.
		245	This should be the most common form of invocation for "daemon"-type nodes.
		246
		247	configure
		248
		249	Example: become an anonymous node. This form is often used for commandline
		250	clients.
		251
		252	configure nodeid => "anon/";
		253
		254	Example: configure a node using a profile called seed, which si suitable
		255	for a seed node as it binds on all local addresses on a fixed port (4040,
		256	customary for aemp).
		257
		258	# use the aemp commandline utility
		259	# aemp profile seed nodeid anon/ binds '*:4040'
		260
		261	# then use it
		262	configure profile => "seed";
		263
		264	# or simply use aemp from the shell again:
		265	# aemp run profile seed
		266
		267	# or provide a nicer-to-remember nodeid
		268	# aemp run profile seed nodeid "$(hostname)"
160		269
161	=item $SELF	270	=item $SELF
162		271
163	Contains the current port id while executing C<rcv> callbacks or C<psub>	272	Contains the current port id while executing C<rcv> callbacks or C<psub>
164	blocks.	273	blocks.
165		274
166	=item SELF, %SELF, @SELF...	275	=item *SELF, SELF, %SELF, @SELF...
167		276
168	Due to some quirks in how perl exports variables, it is impossible to	277	Due to some quirks in how perl exports variables, it is impossible to
169	just export C<$SELF>, all the symbols called C<SELF> are exported by this	278	just export C<$SELF>, all the symbols named C<SELF> are exported by this
170	module, but only C<$SELF> is currently used.	279	module, but only C<$SELF> is currently used.
171		280
172	=item snd $portid, type => @data	281	=item snd $port, type => @data
173		282
174	=item snd $portid, @msg	283	=item snd $port, @msg
175		284
176	Send the given message to the given port ID, which can identify either	285	Send the given message to the given port, which can identify either a
177	a local or a remote port, and can be either a string or soemthignt hat	286	local or a remote port, and must be a port ID.
178	stringifies a sa port ID (such as a port object :).
179		287
180	While the message can be about anything, it is highly recommended to use a	288	While the message can be almost anything, it is highly recommended to
181	string as first element (a portid, or some word that indicates a request	289	use a string as first element (a port ID, or some word that indicates a
182	type etc.).	290	request type etc.) and to consist if only simple perl values (scalars,
		291	arrays, hashes) - if you think you need to pass an object, think again.
183		292
184	The message data effectively becomes read-only after a call to this	293	The message data logically becomes read-only after a call to this
185	function: modifying any argument is not allowed and can cause many	294	function: modifying any argument (or values referenced by them) is
186	problems.	295	forbidden, as there can be considerable time between the call to C<snd>
		296	and the time the message is actually being serialised - in fact, it might
		297	never be copied as within the same process it is simply handed to the
		298	receiving port.
187		299
188	The type of data you can transfer depends on the transport protocol: when	300	The type of data you can transfer depends on the transport protocol: when
189	JSON is used, then only strings, numbers and arrays and hashes consisting	301	JSON is used, then only strings, numbers and arrays and hashes consisting
190	of those are allowed (no objects). When Storable is used, then anything	302	of those are allowed (no objects). When Storable is used, then anything
191	that Storable can serialise and deserialise is allowed, and for the local	303	that Storable can serialise and deserialise is allowed, and for the local
192	node, anything can be passed.	304	node, anything can be passed. Best rely only on the common denominator of
		305	these.
193		306
194	=item kil $portid[, @reason]	307	=item $local_port = port
195		308
196	Kill the specified port with the given C<@reason>.	309	Create a new local port object and returns its port ID. Initially it has
		310	no callbacks set and will throw an error when it receives messages.
197		311
198	If no C<@reason> is specified, then the port is killed "normally" (linked	312	=item $local_port = port { my @msg = @_ }
199	ports will not be kileld, or even notified).
200		313
201	Otherwise, linked ports get killed with the same reason (second form of	314	Creates a new local port, and returns its ID. Semantically the same as
202	C<mon>, see below).	315	creating a port and calling C<rcv $port, $callback> on it.
203		316
204	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	317	The block will be called for every message received on the port, with the
205	will be reported as reason C<< die => $@ >>.	318	global variable C<$SELF> set to the port ID. Runtime errors will cause the
		319	port to be C<kil>ed. The message will be passed as-is, no extra argument
		320	(i.e. no port ID) will be passed to the callback.
206		321
207	Transport/communication errors are reported as C<< transport_error =>	322	If you want to stop/destroy the port, simply C<kil> it:
208	$message >>.
209		323
210	=item $guard = mon $portid, $cb->(@reason)	324	my $port = port {
		325	my @msg = @_;
		326	...
		327	kil $SELF;
		328	};
211		329
212	=item $guard = mon $portid, $otherport	330	=cut
213		331
214	=item $guard = mon $portid, $otherport, @msg	332	sub rcv($@);
215		333
		334	sub _kilme {
		335	die "received message on port without callback";
		336	}
		337
		338	sub port(;&) {
		339	my $id = "$UNIQ." . $ID++;
		340	my $port = "$NODE#$id";
		341
		342	rcv $port, shift \|\| \&_kilme;
		343
		344	$port
		345	}
		346
		347	=item rcv $local_port, $callback->(@msg)
		348
		349	Replaces the default callback on the specified port. There is no way to
		350	remove the default callback: use C<sub { }> to disable it, or better
		351	C<kil> the port when it is no longer needed.
		352
		353	The global C<$SELF> (exported by this module) contains C<$port> while
		354	executing the callback. Runtime errors during callback execution will
		355	result in the port being C<kil>ed.
		356
		357	The default callback received all messages not matched by a more specific
		358	C<tag> match.
		359
		360	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
		361
		362	Register (or replace) callbacks to be called on messages starting with the
		363	given tag on the given port (and return the port), or unregister it (when
		364	C<$callback> is C<$undef> or missing). There can only be one callback
		365	registered for each tag.
		366
		367	The original message will be passed to the callback, after the first
		368	element (the tag) has been removed. The callback will use the same
		369	environment as the default callback (see above).
		370
		371	Example: create a port and bind receivers on it in one go.
		372
		373	my $port = rcv port,
		374	msg1 => sub { ... },
		375	msg2 => sub { ... },
		376	;
		377
		378	Example: create a port, bind receivers and send it in a message elsewhere
		379	in one go:
		380
		381	snd $otherport, reply =>
		382	rcv port,
		383	msg1 => sub { ... },
		384	...
		385	;
		386
		387	Example: temporarily register a rcv callback for a tag matching some port
		388	(e.g. for an rpc reply) and unregister it after a message was received.
		389
		390	rcv $port, $otherport => sub {
		391	my @reply = @_;
		392
		393	rcv $SELF, $otherport;
		394	};
		395
		396	=cut
		397
		398	sub rcv($@) {
		399	my $port = shift;
		400	my ($nodeid, $portid) = split /#/, $port, 2;
		401
		402	$NODE{$nodeid} == $NODE{""}
		403	or Carp::croak "$port: rcv can only be called on local ports, caught";
		404
		405	while (@_) {
		406	if (ref $_[0]) {
		407	if (my $self = $PORT_DATA{$portid}) {
		408	"AnyEvent::MP::Port" eq ref $self
		409	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		410
		411	$self->[0] = shift;
		412	} else {
		413	my $cb = shift;
		414	$PORT{$portid} = sub {
		415	local $SELF = $port;
		416	eval { &$cb }; _self_die if $@;
		417	};
		418	}
		419	} elsif (defined $_[0]) {
		420	my $self = $PORT_DATA{$portid} \|\|= do {
		421	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
		422
		423	$PORT{$portid} = sub {
		424	local $SELF = $port;
		425
		426	if (my $cb = $self->[1]{$_[0]}) {
		427	shift;
		428	eval { &$cb }; _self_die if $@;
		429	} else {
		430	&{ $self->[0] };
		431	}
		432	};
		433
		434	$self
		435	};
		436
		437	"AnyEvent::MP::Port" eq ref $self
		438	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		439
		440	my ($tag, $cb) = splice @_, 0, 2;
		441
		442	if (defined $cb) {
		443	$self->[1]{$tag} = $cb;
		444	} else {
		445	delete $self->[1]{$tag};
		446	}
		447	}
		448	}
		449
		450	$port
		451	}
		452
		453	=item peval $port, $coderef[, @args]
		454
		455	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		456	when the code throews an exception the C<$port> will be killed.
		457
		458	Any remaining args will be passed to the callback. Any return values will
		459	be returned to the caller.
		460
		461	This is useful when you temporarily want to execute code in the context of
		462	a port.
		463
		464	Example: create a port and run some initialisation code in it's context.
		465
		466	my $port = port { ... };
		467
		468	peval $port, sub {
		469	init
		470	or die "unable to init";
		471	};
		472
		473	=cut
		474
		475	sub peval($$) {
		476	local $SELF = shift;
		477	my $cb = shift;
		478
		479	if (wantarray) {
		480	my @res = eval { &$cb };
		481	_self_die if $@;
		482	@res
		483	} else {
		484	my $res = eval { &$cb };
		485	_self_die if $@;
		486	$res
		487	}
		488	}
		489
		490	=item $closure = psub { BLOCK }
		491
		492	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
		493	closure is executed, sets up the environment in the same way as in C<rcv>
		494	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		495
		496	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		497	BLOCK } } >>.
		498
		499	This is useful when you register callbacks from C<rcv> callbacks:
		500
		501	rcv delayed_reply => sub {
		502	my ($delay, @reply) = @_;
		503	my $timer = AE::timer $delay, 0, psub {
		504	snd @reply, $SELF;
		505	};
		506	};
		507
		508	=cut
		509
		510	sub psub(&) {
		511	my $cb = shift;
		512
		513	my $port = $SELF
		514	or Carp::croak "psub can only be called from within rcv or psub callbacks, not";
		515
		516	sub {
		517	local $SELF = $port;
		518
		519	if (wantarray) {
		520	my @res = eval { &$cb };
		521	_self_die if $@;
		522	@res
		523	} else {
		524	my $res = eval { &$cb };
		525	_self_die if $@;
		526	$res
		527	}
		528	}
		529	}
		530
		531	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
		532
		533	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
		534
		535	=item $guard = mon $port # kill $SELF when $port dies
		536
		537	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		538
216	Monitor the given port and do something when the port is killed.	539	Monitor the given port and do something when the port is killed or
		540	messages to it were lost, and optionally return a guard that can be used
		541	to stop monitoring again.
217		542
218	In the first form, the callback is simply called with any number	543	In the first form (callback), the callback is simply called with any
219	of C<@reason> elements (no @reason means that the port was deleted	544	number of C<@reason> elements (no @reason means that the port was deleted
220	"normally"). Note also that I<< the callback B<must> never die >>, so use	545	"normally"). Note also that I<< the callback B<must> never die >>, so use
221	C<eval> if unsure.	546	C<eval> if unsure.
222		547
223	In the second form, the other port will be C<kil>'ed with C<@reason>, iff	548	In the second form (another port given), the other port (C<$rcvport>)
224	a @reason was specified, i.e. on "normal" kils nothing happens, while	549	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
225	under all other conditions, the other port is killed with the same reason.	550	"normal" kils nothing happens, while under all other conditions, the other
		551	port is killed with the same reason.
226		552
		553	The third form (kill self) is the same as the second form, except that
		554	C<$rvport> defaults to C<$SELF>.
		555
227	In the last form, a message of the form C<@msg, @reason> will be C<snd>.	556	In the last form (message), a message of the form C<@msg, @reason> will be
		557	C<snd>.
		558
		559	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		560	alert was raised), they are removed and will not trigger again.
		561
		562	As a rule of thumb, monitoring requests should always monitor a port from
		563	a local port (or callback). The reason is that kill messages might get
		564	lost, just like any other message. Another less obvious reason is that
		565	even monitoring requests can get lost (for example, when the connection
		566	to the other node goes down permanently). When monitoring a port locally
		567	these problems do not exist.
		568
		569	C<mon> effectively guarantees that, in the absence of hardware failures,
		570	after starting the monitor, either all messages sent to the port will
		571	arrive, or the monitoring action will be invoked after possible message
		572	loss has been detected. No messages will be lost "in between" (after
		573	the first lost message no further messages will be received by the
		574	port). After the monitoring action was invoked, further messages might get
		575	delivered again.
		576
		577	Inter-host-connection timeouts and monitoring depend on the transport
		578	used. The only transport currently implemented is TCP, and AnyEvent::MP
		579	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		580	non-idle connection, and usually around two hours for idle connections).
		581
		582	This means that monitoring is good for program errors and cleaning up
		583	stuff eventually, but they are no replacement for a timeout when you need
		584	to ensure some maximum latency.
228		585
229	Example: call a given callback when C<$port> is killed.	586	Example: call a given callback when C<$port> is killed.
230		587
231	mon $port, sub { warn "port died because of <@_>\n" };	588	mon $port, sub { warn "port died because of <@_>\n" };
232		589
233	Example: kill ourselves when C<$port> is killed abnormally.	590	Example: kill ourselves when C<$port> is killed abnormally.
234		591
235	mon $port, $self;	592	mon $port;
236		593
237	Example: send us a restart message another C<$port> is killed.	594	Example: send us a restart message when another C<$port> is killed.
238		595
239	mon $port, $self => "restart";	596	mon $port, $self => "restart";
240		597
241	=cut	598	=cut
242		599
243	sub mon {	600	sub mon {
244	my ($noderef, $port) = split /#/, shift, 2;	601	my ($nodeid, $port) = split /#/, shift, 2;
245		602
246	my $node = $NODE{$noderef} \|\| add_node $noderef;	603	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
247		604
248	my $cb = shift;	605	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
249		606
250	unless (ref $cb) {	607	unless (ref $cb) {
251	if (@_) {	608	if (@_) {
252	# send a kill info message	609	# send a kill info message
253	my (@msg) = ($cb, @_);	610	my (@msg) = ($cb, @_);
…		…
260	}	617	}
261		618
262	$node->monitor ($port, $cb);	619	$node->monitor ($port, $cb);
263		620
264	defined wantarray	621	defined wantarray
265	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	622	and ($cb += 0, AnyEvent::Util::guard { $node->unmonitor ($port, $cb) })
266	}	623	}
267		624
268	=item $guard = mon_guard $port, $ref, $ref...	625	=item $guard = mon_guard $port, $ref, $ref...
269		626
270	Monitors the given C<$port> and keeps the passed references. When the port	627	Monitors the given C<$port> and keeps the passed references. When the port
271	is killed, the references will be freed.	628	is killed, the references will be freed.
272		629
273	Optionally returns a guard that will stop the monitoring.	630	Optionally returns a guard that will stop the monitoring.
274		631
275	This function is useful when you create e.g. timers or other watchers and	632	This function is useful when you create e.g. timers or other watchers and
276	want to free them when the port gets killed:	633	want to free them when the port gets killed (note the use of C<psub>):
277		634
278	$port->rcv (start => sub {	635	$port->rcv (start => sub {
279	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	636	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
280	undef $timer if 0.9 < rand;	637	undef $timer if 0.9 < rand;
281	});	638	});
282	});	639	});
283		640
284	=cut	641	=cut
285		642
286	sub mon_guard {	643	sub mon_guard {
287	my ($port, @refs) = @_;	644	my ($port, @refs) = @_;
288		645
		646	#TODO: mon-less form?
		647
289	mon $port, sub { 0 && @refs }	648	mon $port, sub { 0 && @refs }
290	}	649	}
291		650
292	=item lnk $port1, $port2	651	=item kil $port[, @reason]
293		652
294	Link two ports. This is simply a shorthand for:	653	Kill the specified port with the given C<@reason>.
295		654
296	mon $port1, $port2;	655	If no C<@reason> is specified, then the port is killed "normally" (ports
297	mon $port2, $port1;	656	monitoring other ports will not necessarily die because a port dies
		657	"normally").
298		658
299	It means that if either one is killed abnormally, the other one gets	659	Otherwise, linked ports get killed with the same reason (second form of
300	killed as well.	660	C<mon>, see above).
301		661
302	=item $local_port = port	662	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		663	will be reported as reason C<< die => $@ >>.
303		664
304	Create a new local port object that can be used either as a pattern	665	Transport/communication errors are reported as C<< transport_error =>
305	matching port ("full port") or a single-callback port ("miniport"),	666	$message >>.
306	depending on how C<rcv> callbacks are bound to the object.
307		667
308	=item $portid = port { my @msg = @_; $finished }	668	=cut
309		669
310	Creates a "mini port", that is, a very lightweight port without any	670	=item $port = spawn $node, $initfunc[, @initdata]
311	pattern matching behind it, and returns its ID.
312		671
313	The block will be called for every message received on the port. When the	672	Creates a port on the node C<$node> (which can also be a port ID, in which
314	callback returns a true value its job is considered "done" and the port	673	case it's the node where that port resides).
315	will be destroyed. Otherwise it will stay alive.
316		674
317	The message will be passed as-is, no extra argument (i.e. no port id) will	675	The port ID of the newly created port is returned immediately, and it is
318	be passed to the callback.	676	possible to immediately start sending messages or to monitor the port.
319		677
320	If you need the local port id in the callback, this works nicely:	678	After the port has been created, the init function is called on the remote
		679	node, in the same context as a C<rcv> callback. This function must be a
		680	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		681	specify a function in the main program, use C<::name>.
321		682
322	my $port; $port = port {	683	If the function doesn't exist, then the node tries to C<require>
323	snd $otherport, reply => $port;	684	the package, then the package above the package and so on (e.g.
		685	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		686	exists or it runs out of package names.
		687
		688	The init function is then called with the newly-created port as context
		689	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		690	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		691	the port might not get created.
		692
		693	A common idiom is to pass a local port, immediately monitor the spawned
		694	port, and in the remote init function, immediately monitor the passed
		695	local port. This two-way monitoring ensures that both ports get cleaned up
		696	when there is a problem.
		697
		698	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		699	caller before C<spawn> returns (by delaying invocation when spawn is
		700	called for the local node).
		701
		702	Example: spawn a chat server port on C<$othernode>.
		703
		704	# this node, executed from within a port context:
		705	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		706	mon $server;
		707
		708	# init function on C<$othernode>
		709	sub connect {
		710	my ($srcport) = @_;
		711
		712	mon $srcport;
		713
		714	rcv $SELF, sub {
		715	...
		716	};
		717	}
		718
		719	=cut
		720
		721	sub _spawn {
		722	my $port = shift;
		723	my $init = shift;
		724
		725	# rcv will create the actual port
		726	local $SELF = "$NODE#$port";
		727	eval {
		728	&{ load_func $init }
324	};	729	};
		730	_self_die if $@;
		731	}
325		732
326	=cut	733	sub spawn(@) {
		734	my ($nodeid, undef) = split /#/, shift, 2;
327		735
328	sub port(;&) {
329	my $id = "$UNIQ." . $ID++;	736	my $id = "$RUNIQ." . $ID++;
330	my $port = "$NODE#$id";
331		737
332	if (@_) {	738	$_[0] =~ /::/
333	my $cb = shift;	739	or Carp::croak "spawn init function must be a fully-qualified name, caught";
334	$PORT{$id} = sub {	740
335	local $SELF = $port;	741	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
336	eval {	742
337	&$cb	743	"$nodeid#$id"
338	and kil $id;	744	}
339	};	745
340	_self_die if $@;	746	=item after $timeout, @msg
		747
		748	=item after $timeout, $callback
		749
		750	Either sends the given message, or call the given callback, after the
		751	specified number of seconds.
		752
		753	This is simply a utility function that comes in handy at times - the
		754	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		755	so it may go away in the future.
		756
		757	=cut
		758
		759	sub after($@) {
		760	my ($timeout, @action) = @_;
		761
		762	my $t; $t = AE::timer $timeout, 0, sub {
		763	undef $t;
		764	ref $action[0]
		765	? $action[0]()
		766	: snd @action;
		767	};
		768	}
		769
		770	=item cal $port, @msg, $callback[, $timeout]
		771
		772	A simple form of RPC - sends a message to the given C<$port> with the
		773	given contents (C<@msg>), but adds a reply port to the message.
		774
		775	The reply port is created temporarily just for the purpose of receiving
		776	the reply, and will be C<kil>ed when no longer needed.
		777
		778	A reply message sent to the port is passed to the C<$callback> as-is.
		779
		780	If an optional time-out (in seconds) is given and it is not C<undef>,
		781	then the callback will be called without any arguments after the time-out
		782	elapsed and the port is C<kil>ed.
		783
		784	If no time-out is given (or it is C<undef>), then the local port will
		785	monitor the remote port instead, so it eventually gets cleaned-up.
		786
		787	Currently this function returns the temporary port, but this "feature"
		788	might go in future versions unless you can make a convincing case that
		789	this is indeed useful for something.
		790
		791	=cut
		792
		793	sub cal(@) {
		794	my $timeout = ref $_[-1] ? undef : pop;
		795	my $cb = pop;
		796
		797	my $port = port {
		798	undef $timeout;
		799	kil $SELF;
		800	&$cb;
		801	};
		802
		803	if (defined $timeout) {
		804	$timeout = AE::timer $timeout, 0, sub {
		805	undef $timeout;
		806	kil $port;
		807	$cb->();
341	};	808	};
342	} else {	809	} else {
343	my $self = bless {	810	mon $_[0], sub {
344	id => "$NODE#$id",	811	kil $port;
345	}, "AnyEvent::MP::Port";	812	$cb->();
346
347	$PORT_DATA{$id} = $self;
348	$PORT{$id} = sub {
349	local $SELF = $port;
350
351	eval {
352	for (@{ $self->{rc0}{$_[0]} }) {
353	$_ && &{$_->[0]}
354	&& undef $_;
355	}
356
357	for (@{ $self->{rcv}{$_[0]} }) {
358	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
359	&& &{$_->[0]}
360	&& undef $_;
361	}
362
363	for (@{ $self->{any} }) {
364	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
365	&& &{$_->[0]}
366	&& undef $_;
367	}
368	};
369	_self_die if $@;
370	};	813	};
371	}	814	}
372		815
		816	push @_, $port;
		817	&snd;
		818
373	$port	819	$port
374	}	820	}
375		821
376	=item reg $portid, $name
377
378	Registers the given port under the name C<$name>. If the name already
379	exists it is replaced.
380
381	A port can only be registered under one well known name.
382
383	A port automatically becomes unregistered when it is killed.
384
385	=cut
386
387	sub reg(@) {
388	my ($portid, $name) = @_;
389
390	$REG{$name} = $portid;
391	}
392
393	=item rcv $portid, $callback->(@msg)
394
395	Replaces the callback on the specified miniport (or newly created port
396	object, see C<port>). Full ports are configured with the following calls:
397
398	=item rcv $portid, tagstring => $callback->(@msg), ...
399
400	=item rcv $portid, $smartmatch => $callback->(@msg), ...
401
402	=item rcv $portid, [$smartmatch...] => $callback->(@msg), ...
403
404	Register callbacks to be called on matching messages on the given port.
405
406	The callback has to return a true value when its work is done, after
407	which is will be removed, or a false value in which case it will stay
408	registered.
409
410	The global C<$SELF> (exported by this module) contains C<$portid> while
411	executing the callback.
412
413	Runtime errors wdurign callback execution will result in the port being
414	C<kil>ed.
415
416	If the match is an array reference, then it will be matched against the
417	first elements of the message, otherwise only the first element is being
418	matched.
419
420	Any element in the match that is specified as C<_any_> (a function
421	exported by this module) matches any single element of the message.
422
423	While not required, it is highly recommended that the first matching
424	element is a string identifying the message. The one-string-only match is
425	also the most efficient match (by far).
426
427	=cut
428
429	sub rcv($@) {
430	my $portid = shift;
431	my ($noderef, $port) = split /#/, $port, 2;
432
433	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}
434	or Carp::croak "$noderef#$port: rcv can only be called on local ports, caught";
435
436	my $self = $PORT_DATA{$port}
437	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";
438
439	"AnyEvent::MP::Port" eq ref $self
440	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";
441
442	while (@_) {
443	my ($match, $cb) = splice @_, 0, 2;
444
445	if (!ref $match) {
446	push @{ $self->{rc0}{$match} }, [$cb];
447	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
448	my ($type, @match) = @$match;
449	@match
450	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
451	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
452	} else {
453	push @{ $self->{any} }, [$cb, $match];
454	}
455	}
456
457	$portid
458	}
459
460	=item $closure = psub { BLOCK }
461
462	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
463	closure is executed, sets up the environment in the same way as in C<rcv>
464	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
465
466	This is useful when you register callbacks from C<rcv> callbacks:
467
468	rcv delayed_reply => sub {
469	my ($delay, @reply) = @_;
470	my $timer = AE::timer $delay, 0, psub {
471	snd @reply, $SELF;
472	};
473	};
474
475	=cut
476
477	sub psub(&) {
478	my $cb = shift;
479
480	my $port = $SELF
481	or Carp::croak "psub can only be called from within rcv or psub callbacks, not";
482
483	sub {
484	local $SELF = $port;
485
486	if (wantarray) {
487	my @res = eval { &$cb };
488	_self_die if $@;
489	@res
490	} else {
491	my $res = eval { &$cb };
492	_self_die if $@;
493	$res
494	}
495	}
496	}
497
498	=back	822	=back
499		823
500	=head1 FUNCTIONS FOR NODES
501
502	=over 4
503
504	=item become_public $noderef
505
506	Tells the node to become a public node, i.e. reachable from other nodes.
507
508	The first argument is the (unresolved) node reference of the local node
509	(if missing then the empty string is used).
510
511	It is quite common to not specify anything, in which case the local node
512	tries to listen on the default port, or to only specify a port number, in
513	which case AnyEvent::MP tries to guess the local addresses.
514
515	=cut
516
517	=back
518
519	=head1 NODE MESSAGES
520
521	Nodes understand the following messages sent to them. Many of them take
522	arguments called C<@reply>, which will simply be used to compose a reply
523	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
524	the remaining arguments are simply the message data.
525
526	While other messages exist, they are not public and subject to change.
527
528	=over 4
529
530	=cut
531
532	=item lookup => $name, @reply
533
534	Replies with the port ID of the specified well-known port, or C<undef>.
535
536	=item devnull => ...
537
538	Generic data sink/CPU heat conversion.
539
540	=item relay => $port, @msg
541
542	Simply forwards the message to the given port.
543
544	=item eval => $string[ @reply]
545
546	Evaluates the given string. If C<@reply> is given, then a message of the
547	form C<@reply, $@, @evalres> is sent.
548
549	Example: crash another node.
550
551	snd $othernode, eval => "exit";
552
553	=item time => @reply
554
555	Replies the the current node time to C<@reply>.
556
557	Example: tell the current node to send the current time to C<$myport> in a
558	C<timereply> message.
559
560	snd $NODE, time => $myport, timereply => 1, 2;
561	# => snd $myport, timereply => 1, 2, <time>
562
563	=back
564
565	=head1 AnyEvent::MP vs. Distributed Erlang	824	=head1 AnyEvent::MP vs. Distributed Erlang
566		825
567	AnyEvent::MP got lots of its ideas from distributed erlang (erlang node	826	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
568	== aemp node, erlang process == aemp port), so many of the documents and	827	== aemp node, Erlang process == aemp port), so many of the documents and
569	programming techniques employed by erlang apply to AnyEvent::MP. Here is a	828	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
570	sample:	829	sample:
571		830
572	http://www.erlang.se/doc/programming_rules.shtml	831	http://www.erlang.se/doc/programming_rules.shtml
573	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	832	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
574	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6	833	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
…		…
576		835
577	Despite the similarities, there are also some important differences:	836	Despite the similarities, there are also some important differences:
578		837
579	=over 4	838	=over 4
580		839
581	=item * Node references contain the recipe on how to contact them.	840	=item * Node IDs are arbitrary strings in AEMP.
582		841
583	Erlang relies on special naming and DNS to work everywhere in the	842	Erlang relies on special naming and DNS to work everywhere in the same
584	same way. AEMP relies on each node knowing it's own address(es), with	843	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
585	convenience functionality.	844	configuration or DNS), and possibly the addresses of some seed nodes, but
		845	will otherwise discover other nodes (and their IDs) itself.
586		846
587	This means that AEMP requires a less tightly controlled environment at the	847	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
588	cost of longer node references and a slightly higher management overhead.	848	uses "local ports are like remote ports".
		849
		850	The failure modes for local ports are quite different (runtime errors
		851	only) then for remote ports - when a local port dies, you I<know> it dies,
		852	when a connection to another node dies, you know nothing about the other
		853	port.
		854
		855	Erlang pretends remote ports are as reliable as local ports, even when
		856	they are not.
		857
		858	AEMP encourages a "treat remote ports differently" philosophy, with local
		859	ports being the special case/exception, where transport errors cannot
		860	occur.
589		861
590	=item * Erlang uses processes and a mailbox, AEMP does not queue.	862	=item * Erlang uses processes and a mailbox, AEMP does not queue.
591		863
592	Erlang uses processes that selctively receive messages, and therefore	864	Erlang uses processes that selectively receive messages, and therefore
593	needs a queue. AEMP is event based, queuing messages would serve no useful	865	needs a queue. AEMP is event based, queuing messages would serve no
594	purpose.	866	useful purpose. For the same reason the pattern-matching abilities of
		867	AnyEvent::MP are more limited, as there is little need to be able to
		868	filter messages without dequeuing them.
595		869
596	(But see L<Coro::MP> for a more erlang-like process model on top of AEMP).	870	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).
597		871
598	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	872	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
599		873
600	Sending messages in erlang is synchronous and blocks the process. AEMP	874	Sending messages in Erlang is synchronous and blocks the process (and
601	sends are immediate, connection establishment is handled in the	875	so does not need a queue that can overflow). AEMP sends are immediate,
602	background.	876	connection establishment is handled in the background.
603		877
604	=item * Erlang can silently lose messages, AEMP cannot.	878	=item * Erlang suffers from silent message loss, AEMP does not.
605		879
606	Erlang makes few guarantees on messages delivery - messages can get lost	880	Erlang implements few guarantees on messages delivery - messages can get
607	without any of the processes realising it (i.e. you send messages a, b,	881	lost without any of the processes realising it (i.e. you send messages a,
608	and c, and the other side only receives messages a and c).	882	b, and c, and the other side only receives messages a and c).
609		883
610	AEMP guarantees correct ordering, and the guarantee that there are no	884	AEMP guarantees correct ordering, and the guarantee that after one message
611	holes in the message sequence.	885	is lost, all following ones sent to the same port are lost as well, until
612		886	monitoring raises an error, so there are no silent "holes" in the message
613	=item * In erlang, processes can be declared dead and later be found to be	887	sequence.
614	alive.
615
616	In erlang it can happen that a monitored process is declared dead and
617	linked processes get killed, but later it turns out that the process is
618	still alive - and can receive messages.
619
620	In AEMP, when port monitoring detects a port as dead, then that port will
621	eventually be killed - it cannot happen that a node detects a port as dead
622	and then later sends messages to it, finding it is still alive.
623		888
624	=item * Erlang can send messages to the wrong port, AEMP does not.	889	=item * Erlang can send messages to the wrong port, AEMP does not.
625		890
626	In erlang it is quite possible that a node that restarts reuses a process	891	In Erlang it is quite likely that a node that restarts reuses a process ID
627	ID known to other nodes for a completely different process, causing	892	known to other nodes for a completely different process, causing messages
628	messages destined for that process to end up in an unrelated process.	893	destined for that process to end up in an unrelated process.
629		894
630	AEMP never reuses port IDs, so old messages or old port IDs floating	895	AEMP never reuses port IDs, so old messages or old port IDs floating
631	around in the network will not be sent to an unrelated port.	896	around in the network will not be sent to an unrelated port.
632		897
633	=item * Erlang uses unprotected connections, AEMP uses secure	898	=item * Erlang uses unprotected connections, AEMP uses secure
634	authentication and can use TLS.	899	authentication and can use TLS.
635		900
636	AEMP can use a proven protocol - SSL/TLS - to protect connections and	901	AEMP can use a proven protocol - TLS - to protect connections and
637	securely authenticate nodes.	902	securely authenticate nodes.
638		903
639	=item * The AEMP protocol is optimised for both text-based and binary	904	=item * The AEMP protocol is optimised for both text-based and binary
640	communications.	905	communications.
641		906
642	The AEMP protocol, unlike the erlang protocol, supports both	907	The AEMP protocol, unlike the Erlang protocol, supports both programming
643	language-independent text-only protocols (good for debugging) and binary,	908	language independent text-only protocols (good for debugging) and binary,
644	language-specific serialisers (e.g. Storable).	909	language-specific serialisers (e.g. Storable). By default, unless TLS is
		910	used, the protocol is actually completely text-based.
645		911
646	It has also been carefully designed to be implementable in other languages	912	It has also been carefully designed to be implementable in other languages
647	with a minimum of work while gracefully degrading fucntionality to make the	913	with a minimum of work while gracefully degrading functionality to make the
648	protocol simple.	914	protocol simple.
649		915
		916	=item * AEMP has more flexible monitoring options than Erlang.
		917
		918	In Erlang, you can chose to receive I<all> exit signals as messages
		919	or I<none>, there is no in-between, so monitoring single processes is
		920	difficult to implement. Monitoring in AEMP is more flexible than in
		921	Erlang, as one can choose between automatic kill, exit message or callback
		922	on a per-process basis.
		923
		924	=item * Erlang tries to hide remote/local connections, AEMP does not.
		925
		926	Monitoring in Erlang is not an indicator of process death/crashes, in the
		927	same way as linking is (except linking is unreliable in Erlang).
		928
		929	In AEMP, you don't "look up" registered port names or send to named ports
		930	that might or might not be persistent. Instead, you normally spawn a port
		931	on the remote node. The init function monitors you, and you monitor the
		932	remote port. Since both monitors are local to the node, they are much more
		933	reliable (no need for C<spawn_link>).
		934
		935	This also saves round-trips and avoids sending messages to the wrong port
		936	(hard to do in Erlang).
		937
650	=back	938	=back
651		939
		940	=head1 RATIONALE
		941
		942	=over 4
		943
		944	=item Why strings for port and node IDs, why not objects?
		945
		946	We considered "objects", but found that the actual number of methods
		947	that can be called are quite low. Since port and node IDs travel over
		948	the network frequently, the serialising/deserialising would add lots of
		949	overhead, as well as having to keep a proxy object everywhere.
		950
		951	Strings can easily be printed, easily serialised etc. and need no special
		952	procedures to be "valid".
		953
		954	And as a result, a miniport consists of a single closure stored in a
		955	global hash - it can't become much cheaper.
		956
		957	=item Why favour JSON, why not a real serialising format such as Storable?
		958
		959	In fact, any AnyEvent::MP node will happily accept Storable as framing
		960	format, but currently there is no way to make a node use Storable by
		961	default (although all nodes will accept it).
		962
		963	The default framing protocol is JSON because a) JSON::XS is many times
		964	faster for small messages and b) most importantly, after years of
		965	experience we found that object serialisation is causing more problems
		966	than it solves: Just like function calls, objects simply do not travel
		967	easily over the network, mostly because they will always be a copy, so you
		968	always have to re-think your design.
		969
		970	Keeping your messages simple, concentrating on data structures rather than
		971	objects, will keep your messages clean, tidy and efficient.
		972
		973	=back
		974
652	=head1 SEE ALSO	975	=head1 SEE ALSO
		976
		977	L<AnyEvent::MP::Intro> - a gentle introduction.
		978
		979	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		980
		981	L<AnyEvent::MP::Global> - network maintainance and port groups, to find
		982	your applications.
		983
		984	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		985	all nodes.
653		986
654	L<AnyEvent>.	987	L<AnyEvent>.
655		988
656	=head1 AUTHOR	989	=head1 AUTHOR
657		990

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Revision 1.104 by root, Fri Nov 6 17:47:20 2009 UTC