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Revision 1.16 by root, Sun Aug 2 19:29:41 2009 UTC vs.
Revision 1.137 by root, Wed Mar 21 23:48:39 2012 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent::MP - multi-processing/message-passing framework	3	AnyEvent::MP - erlang-style multi-processing/message-passing framework
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::MP;	7	use AnyEvent::MP;
8		8
9	NODE # returns this node identifier
10	$NODE # contains this node identifier	9	$NODE # contains this node's node ID
		10	NODE # returns this node's node ID
11		11
		12	$SELF # receiving/own port id in rcv callbacks
		13
		14	# initialise the node so it can send/receive messages
		15	configure;
		16
		17	# ports are message destinations
		18
		19	# sending messages
12	snd $port, type => data...;	20	snd $port, type => data...;
		21	snd $port, @msg;
		22	snd @msg_with_first_element_being_a_port;
13		23
14	rcv $port, smartmatch => $cb->($port, @msg);	24	# creating/using ports, the simple way
		25	my $simple_port = port { my @msg = @_ };
15		26
16	# examples:	27	# creating/using ports, tagged message matching
		28	my $port = port;
17	rcv $port2, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
18	rcv $port1, pong => sub { warn "pong received\n" };	30	rcv $port, pong => sub { warn "pong received\n" };
19	snd $port2, ping => $port1;
20		31
21	# more, smarter, matches (_any_ is exported by this module)	32	# create a port on another node
22	rcv $port, [child_died => $pid] => sub { ...	33	my $port = spawn $node, $initfunc, @initdata;
23	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3	34
		35	# destroy a port again
		36	kil $port; # "normal" kill
		37	kil $port, my_error => "everything is broken"; # error kill
		38
		39	# monitoring
		40	mon $port, $cb->(@msg) # callback is invoked on death
		41	mon $port, $localport # kill localport on abnormal death
		42	mon $port, $localport, @msg # send message on death
		43
		44	# temporarily execute code in port context
		45	peval $port, sub { die "kill the port!" };
		46
		47	# execute callbacks in $SELF port context
		48	my $timer = AE::timer 1, 0, psub {
		49	die "kill the port, delayed";
		50	};
		51
		52	=head1 CURRENT STATUS
		53
		54	bin/aemp - stable.
		55	AnyEvent::MP - stable API, should work.
		56	AnyEvent::MP::Intro - explains most concepts.
		57	AnyEvent::MP::Kernel - mostly stable API.
		58	AnyEvent::MP::Global - stable API.
24		59
25	=head1 DESCRIPTION	60	=head1 DESCRIPTION
26		61
27	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
28		63
29	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
30	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
31		66
32	At the moment, this module family is severly brokena nd underdocumented,	67	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
33	so do not use. This was uploaded mainly to resreve the CPAN namespace -	68	manual page and the examples under F<eg/>.
34	stay tuned!
35		69
36	=head1 CONCEPTS	70	=head1 CONCEPTS
37		71
38	=over 4	72	=over 4
39		73
40	=item port	74	=item port
41		75
42	A port is something you can send messages to with the C<snd> function, and	76	Not to be confused with a TCP port, a "port" is something you can send
43	you can register C<rcv> handlers with. All C<rcv> handlers will receive	77	messages to (with the C<snd> function).
44	messages they match, messages will not be queued.
45		78
		79	Ports allow you to register C<rcv> handlers that can match all or just
		80	some messages. Messages send to ports will not be queued, regardless of
		81	anything was listening for them or not.
		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
46	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
47		86
48	A port id is always the noderef, a hash-mark (C<#>) as separator, followed	87	A port ID is the concatenation of a node ID, a hash-mark (C<#>)
49	by a port name (a printable string of unspecified format).	88	as separator, and a port name (a printable string of unspecified
		89	format created by AnyEvent::MP).
50		90
51	=item node	91	=item node
52		92
53	A node is a single process containing at least one port - the node	93	A node is a single process containing at least one port - the node port,
54	port. You can send messages to node ports to let them create new ports,	94	which enables nodes to manage each other remotely, and to create new
55	among other things.	95	ports.
56		96
57	Initially, nodes are either private (single-process only) or hidden	97	Nodes are either public (have one or more listening ports) or private
58	(connected to a master node only). Only when they epxlicitly "become	98	(no listening ports). Private nodes cannot talk to other private nodes
59	public" can you send them messages from unrelated other nodes.	99	currently, but all nodes can talk to public nodes.
60		100
61	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	101	Nodes is represented by (printable) strings called "node IDs".
62		102
		103	=item node ID - C<[A-Za-z0-9_\-.:]*>
		104
63	A noderef is a string that either uniquely identifies a given node (for	105	A node ID is a string that uniquely identifies the node within a
64	private and hidden nodes), or contains a recipe on how to reach a given	106	network. Depending on the configuration used, node IDs can look like a
65	node (for public nodes).	107	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		108	doesn't interpret node IDs in any way except to uniquely identify a node.
		109
		110	=item binds - C<ip:port>
		111
		112	Nodes can only talk to each other by creating some kind of connection to
		113	each other. To do this, nodes should listen on one or more local transport
		114	endpoints - binds.
		115
		116	Currently, only standard C<ip:port> specifications can be used, which
		117	specify TCP ports to listen on. So a bind is basically just a tcp socket
		118	in listening mode thta accepts conenctions form other nodes.
		119
		120	=item seed nodes
		121
		122	When a node starts, it knows nothing about the network it is in - it
		123	needs to connect to at least one other node that is already in the
		124	network. These other nodes are called "seed nodes".
		125
		126	Seed nodes themselves are not special - they are seed nodes only because
		127	some other node I<uses> them as such, but any node can be used as seed
		128	node for other nodes, and eahc node cna use a different set of seed nodes.
		129
		130	In addition to discovering the network, seed nodes are also used to
		131	maintain the network - all nodes using the same seed node form are part of
		132	the same network. If a network is split into multiple subnets because e.g.
		133	the network link between the parts goes down, then using the same seed
		134	nodes for all nodes ensures that eventually the subnets get merged again.
		135
		136	Seed nodes are expected to be long-running, and at least one seed node
		137	should always be available. They should also be relatively responsive - a
		138	seed node that blocks for long periods will slow down everybody else.
		139
		140	For small networks, it's best if every node uses the same set of seed
		141	nodes. For large networks, it can be useful to specify "regional" seed
		142	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		143	each other. What's important is that all seed nodes connections form a
		144	complete graph, so that the network cannot split into separate subnets
		145	forever.
		146
		147	Seed nodes are represented by seed IDs.
		148
		149	=item seed IDs - C<host:port>
		150
		151	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
		152	TCP port) of nodes that should be used as seed nodes.
		153
		154	=item global nodes
		155
		156	An AEMP network needs a discovery service - nodes need to know how to
		157	connect to other nodes they only know by name. In addition, AEMP offers a
		158	distributed "group database", which maps group names to a list of strings
		159	- for example, to register worker ports.
		160
		161	A network needs at least one global node to work, and allows every node to
		162	be a global node.
		163
		164	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		165	node and tries to keep connections to all other nodes. So while it can
		166	make sense to make every node "global" in small networks, it usually makes
		167	sense to only make seed nodes into global nodes in large networks (nodes
		168	keep connections to seed nodes and global nodes, so makign them the same
		169	reduces overhead).
66		170
67	=back	171	=back
68		172
69	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
70		174
…		…
72		176
73	=cut	177	=cut
74		178
75	package AnyEvent::MP;	179	package AnyEvent::MP;
76		180
		181	use AnyEvent::MP::Config ();
77	use AnyEvent::MP::Base;	182	use AnyEvent::MP::Kernel;
		183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
78		184
79	use common::sense;	185	use common::sense;
80		186
81	use Carp ();	187	use Carp ();
82		188
83	use AE ();	189	use AE ();
		190	use Guard ();
84		191
85	use base "Exporter";	192	use base "Exporter";
86		193
87	our $VERSION = '0.02';	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
		195
88	our @EXPORT = qw(	196	our @EXPORT = qw(
89	NODE $NODE $PORT snd rcv _any_	197	NODE $NODE *SELF node_of after
90	create_port create_port_on	198	configure
91	create_miniport	199	snd rcv mon mon_guard kil psub peval spawn cal
92	become_slave become_public	200	port
		201	db_set db_del db_reg
		202	db_mon db_family db_keys db_values
93	);	203	);
94		204
		205	our $SELF;
		206
		207	sub _self_die() {
		208	my $msg = $@;
		209	$msg =~ s/\n+$// unless ref $msg;
		210	kil $SELF, die => $msg;
		211	}
		212
95	=item NODE / $NODE	213	=item $thisnode = NODE / $NODE
96		214
97	The C<NODE ()> function and the C<$NODE> variable contain the noderef of	215	The C<NODE> function returns, and the C<$NODE> variable contains, the node
98	the local node. The value is initialised by a call to C<become_public> or	216	ID of the node running in the current process. This value is initialised by
99	C<become_slave>, after which all local port identifiers become invalid.	217	a call to C<configure>.
100		218
		219	=item $nodeid = node_of $port
		220
		221	Extracts and returns the node ID from a port ID or a node ID.
		222
		223	=item configure $profile, key => value...
		224
		225	=item configure key => value...
		226
		227	Before a node can talk to other nodes on the network (i.e. enter
		228	"distributed mode") it has to configure itself - the minimum a node needs
		229	to know is its own name, and optionally it should know the addresses of
		230	some other nodes in the network to discover other nodes.
		231
		232	This function configures a node - it must be called exactly once (or
		233	never) before calling other AnyEvent::MP functions.
		234
		235	The key/value pairs are basically the same ones as documented for the
		236	F<aemp> command line utility (sans the set/del prefix), with these additions:
		237
		238	=over 4
		239
		240	=item norc => $boolean (default false)
		241
		242	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
		243	be consulted - all configuraiton options must be specified in the
		244	C<configure> call.
		245
		246	=item force => $boolean (default false)
		247
		248	IF true, then the values specified in the C<configure> will take
		249	precedence over any values configured via the rc file. The default is for
		250	the rc file to override any options specified in the program.
		251
		252	=item secure => $pass->(@msg)
		253
		254	In addition to specifying a boolean, you can specify a code reference that
		255	is called for every code execution attempt - the execution request is
		256	granted iff the callback returns a true value.
		257
		258	Most of the time the callback should look only at
		259	C<$AnyEvent::MP::Kernel::SRCNODE> to make a decision, and not at the
		260	actual message (which can be about anything, and is mostly provided for
		261	diagnostic purposes).
		262
		263	See F<semp setsecure> for more info.
		264
		265	=back
		266
		267	=over 4
		268
		269	=item step 1, gathering configuration from profiles
		270
		271	The function first looks up a profile in the aemp configuration (see the
		272	L<aemp> commandline utility). The profile name can be specified via the
		273	named C<profile> parameter or can simply be the first parameter). If it is
		274	missing, then the nodename (F<uname -n>) will be used as profile name.
		275
		276	The profile data is then gathered as follows:
		277
		278	First, all remaining key => value pairs (all of which are conveniently
		279	undocumented at the moment) will be interpreted as configuration
		280	data. Then they will be overwritten by any values specified in the global
		281	default configuration (see the F<aemp> utility), then the chain of
		282	profiles chosen by the profile name (and any C<parent> attributes).
		283
		284	That means that the values specified in the profile have highest priority
		285	and the values specified directly via C<configure> have lowest priority,
		286	and can only be used to specify defaults.
		287
		288	If the profile specifies a node ID, then this will become the node ID of
		289	this process. If not, then the profile name will be used as node ID, with
		290	a unique randoms tring (C</%u>) appended.
		291
		292	The node ID can contain some C<%> sequences that are expanded: C<%n>
		293	is expanded to the local nodename, C<%u> is replaced by a random
		294	strign to make the node unique. For example, the F<aemp> commandline
		295	utility uses C<aemp/%n/%u> as nodename, which might expand to
		296	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		297
		298	=item step 2, bind listener sockets
		299
		300	The next step is to look up the binds in the profile, followed by binding
		301	aemp protocol listeners on all binds specified (it is possible and valid
		302	to have no binds, meaning that the node cannot be contacted form the
		303	outside. This means the node cannot talk to other nodes that also have no
		304	binds, but it can still talk to all "normal" nodes).
		305
		306	If the profile does not specify a binds list, then a default of C<*> is
		307	used, meaning the node will bind on a dynamically-assigned port on every
		308	local IP address it finds.
		309
		310	=item step 3, connect to seed nodes
		311
		312	As the last step, the seed ID list from the profile is passed to the
		313	L<AnyEvent::MP::Global> module, which will then use it to keep
		314	connectivity with at least one node at any point in time.
		315
		316	=back
		317
		318	Example: become a distributed node using the local node name as profile.
		319	This should be the most common form of invocation for "daemon"-type nodes.
		320
		321	configure
		322
		323	Example: become a semi-anonymous node. This form is often used for
		324	commandline clients.
		325
		326	configure nodeid => "myscript/%n/%u";
		327
		328	Example: configure a node using a profile called seed, which is suitable
		329	for a seed node as it binds on all local addresses on a fixed port (4040,
		330	customary for aemp).
		331
		332	# use the aemp commandline utility
		333	# aemp profile seed binds '*:4040'
		334
		335	# then use it
		336	configure profile => "seed";
		337
		338	# or simply use aemp from the shell again:
		339	# aemp run profile seed
		340
		341	# or provide a nicer-to-remember nodeid
		342	# aemp run profile seed nodeid "$(hostname)"
		343
		344	=item $SELF
		345
		346	Contains the current port id while executing C<rcv> callbacks or C<psub>
		347	blocks.
		348
		349	=item *SELF, SELF, %SELF, @SELF...
		350
		351	Due to some quirks in how perl exports variables, it is impossible to
		352	just export C<$SELF>, all the symbols named C<SELF> are exported by this
		353	module, but only C<$SELF> is currently used.
		354
101	=item snd $portid, type => @data	355	=item snd $port, type => @data
102		356
103	=item snd $portid, @msg	357	=item snd $port, @msg
104		358
105	Send the given message to the given port ID, which can identify either	359	Send the given message to the given port, which can identify either a
106	a local or a remote port, and can be either a string or soemthignt hat	360	local or a remote port, and must be a port ID.
107	stringifies a sa port ID (such as a port object :).
108		361
109	While the message can be about anything, it is highly recommended to use a	362	While the message can be almost anything, it is highly recommended to
110	string as first element (a portid, or some word that indicates a request	363	use a string as first element (a port ID, or some word that indicates a
111	type etc.).	364	request type etc.) and to consist if only simple perl values (scalars,
		365	arrays, hashes) - if you think you need to pass an object, think again.
112		366
113	The message data effectively becomes read-only after a call to this	367	The message data logically becomes read-only after a call to this
114	function: modifying any argument is not allowed and can cause many	368	function: modifying any argument (or values referenced by them) is
115	problems.	369	forbidden, as there can be considerable time between the call to C<snd>
		370	and the time the message is actually being serialised - in fact, it might
		371	never be copied as within the same process it is simply handed to the
		372	receiving port.
116		373
117	The type of data you can transfer depends on the transport protocol: when	374	The type of data you can transfer depends on the transport protocol: when
118	JSON is used, then only strings, numbers and arrays and hashes consisting	375	JSON is used, then only strings, numbers and arrays and hashes consisting
119	of those are allowed (no objects). When Storable is used, then anything	376	of those are allowed (no objects). When Storable is used, then anything
120	that Storable can serialise and deserialise is allowed, and for the local	377	that Storable can serialise and deserialise is allowed, and for the local
121	node, anything can be passed.	378	node, anything can be passed. Best rely only on the common denominator of
		379	these.
122		380
123	=item $local_port = create_port	381	=item $local_port = port
124		382
125	Create a new local port object. See the next section for allowed methods.	383	Create a new local port object and returns its port ID. Initially it has
		384	no callbacks set and will throw an error when it receives messages.
		385
		386	=item $local_port = port { my @msg = @_ }
		387
		388	Creates a new local port, and returns its ID. Semantically the same as
		389	creating a port and calling C<rcv $port, $callback> on it.
		390
		391	The block will be called for every message received on the port, with the
		392	global variable C<$SELF> set to the port ID. Runtime errors will cause the
		393	port to be C<kil>ed. The message will be passed as-is, no extra argument
		394	(i.e. no port ID) will be passed to the callback.
		395
		396	If you want to stop/destroy the port, simply C<kil> it:
		397
		398	my $port = port {
		399	my @msg = @_;
		400	...
		401	kil $SELF;
		402	};
126		403
127	=cut	404	=cut
128		405
129	sub create_port {	406	sub rcv($@);
130	my $id = "$AnyEvent::MP::Base::UNIQ." . $AnyEvent::MP::Base::ID++;
131		407
132	my $self = bless {	408	my $KILME = sub {
133	id => "$NODE#$id",	409	(my $tag = substr $_[0], 0, 30) =~ s/([\x20-\x7e])/./g;
134	names => [$id],	410	kil $SELF, unhandled_message => "no callback found for message '$tag'";
135	}, "AnyEvent::MP::Port";	411	};
136		412
137	$AnyEvent::MP::Base::PORT{$id} = sub {	413	sub port(;&) {
138	unshift @_, $self;	414	my $id = $UNIQ . ++$ID;
		415	my $port = "$NODE#$id";
139		416
140	for (@{ $self->{rc0}{$_[1]} }) {	417	rcv $port, shift || $KILME;
141	$_ && &{$_->[0]}	418
142	&& undef $_;	419	$port
		420	}
		421
		422	=item rcv $local_port, $callback->(@msg)
		423
		424	Replaces the default callback on the specified port. There is no way to
		425	remove the default callback: use C<sub { }> to disable it, or better
		426	C<kil> the port when it is no longer needed.
		427
		428	The global C<$SELF> (exported by this module) contains C<$port> while
		429	executing the callback. Runtime errors during callback execution will
		430	result in the port being C<kil>ed.
		431
		432	The default callback receives all messages not matched by a more specific
		433	C<tag> match.
		434
		435	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
		436
		437	Register (or replace) callbacks to be called on messages starting with the
		438	given tag on the given port (and return the port), or unregister it (when
		439	C<$callback> is C<$undef> or missing). There can only be one callback
		440	registered for each tag.
		441
		442	The original message will be passed to the callback, after the first
		443	element (the tag) has been removed. The callback will use the same
		444	environment as the default callback (see above).
		445
		446	Example: create a port and bind receivers on it in one go.
		447
		448	my $port = rcv port,
		449	msg1 => sub { ... },
		450	msg2 => sub { ... },
		451	;
		452
		453	Example: create a port, bind receivers and send it in a message elsewhere
		454	in one go:
		455
		456	snd $otherport, reply =>
		457	rcv port,
		458	msg1 => sub { ... },
		459	...
		460	;
		461
		462	Example: temporarily register a rcv callback for a tag matching some port
		463	(e.g. for an rpc reply) and unregister it after a message was received.
		464
		465	rcv $port, $otherport => sub {
		466	my @reply = @_;
		467
		468	rcv $SELF, $otherport;
		469	};
		470
		471	=cut
		472
		473	sub rcv($@) {
		474	my $port = shift;
		475	my ($nodeid, $portid) = split /#/, $port, 2;
		476
		477	$NODE{$nodeid} == $NODE{""}
		478	or Carp::croak "$port: rcv can only be called on local ports, caught";
		479
		480	while (@_) {
		481	if (ref $_[0]) {
		482	if (my $self = $PORT_DATA{$portid}) {
		483	"AnyEvent::MP::Port" eq ref $self
		484	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		485
		486	$self->[0] = shift;
		487	} else {
		488	my $cb = shift;
		489	$PORT{$portid} = sub {
		490	local $SELF = $port;
		491	eval { &$cb }; _self_die if $@;
		492	};
		493	}
		494	} elsif (defined $_[0]) {
		495	my $self = $PORT_DATA{$portid} ||= do {
		496	my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port";
		497
		498	$PORT{$portid} = sub {
		499	local $SELF = $port;
		500
		501	if (my $cb = $self->[1]{$_[0]}) {
		502	shift;
		503	eval { &$cb }; _self_die if $@;
		504	} else {
		505	&{ $self->[0] };
		506	}
		507	};
		508
		509	$self
		510	};
		511
		512	"AnyEvent::MP::Port" eq ref $self
		513	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		514
		515	my ($tag, $cb) = splice @_, 0, 2;
		516
		517	if (defined $cb) {
		518	$self->[1]{$tag} = $cb;
		519	} else {
		520	delete $self->[1]{$tag};
		521	}
143	}	522	}
		523	}
144		524
145	for (@{ $self->{rcv}{$_[1]} }) {	525	$port
146	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]	526	}
147	&& &{$_->[0]}
148	&& undef $_;
149	}
150		527
151	for (@{ $self->{any} }) {	528	=item peval $port, $coderef[, @args]
152	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]	529
153	&& &{$_->[0]}	530	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
154	&& undef $_;	531	when the code throews an exception the C<$port> will be killed.
155	}	532
		533	Any remaining args will be passed to the callback. Any return values will
		534	be returned to the caller.
		535
		536	This is useful when you temporarily want to execute code in the context of
		537	a port.
		538
		539	Example: create a port and run some initialisation code in it's context.
		540
		541	my $port = port { ... };
		542
		543	peval $port, sub {
		544	init
		545	or die "unable to init";
156	};	546	};
157		547
158	$self
159	}
160
161	=item $portid = miniport { my @msg = @_; $finished }
162
163	Creates a "mini port", that is, a very lightweight port without any
164	pattern matching behind it, and returns its ID.
165
166	The block will be called for every message received on the port. When the
167	callback returns a true value its job is considered "done" and the port
168	will be destroyed. Otherwise it will stay alive.
169
170	The message will be passed as-is, no extra argument (ie.. no port id) will
171	be passed to the callback.
172
173	If you need the local port id in the callback, this works nicely:
174
175	my $port; $port = miniport {
176	snd $otherport, reply => $port;
177	};
178
179	=cut	548	=cut
180		549
181	sub miniport(&) {	550	sub peval($$) {
		551	local $SELF = shift;
182	my $cb = shift;	552	my $cb = shift;
183	my $id = "$AnyEvent::MP::Base::UNIQ." . $AnyEvent::MP::Base::ID++;
184		553
185	$AnyEvent::MP::Base::PORT{$id} = sub {	554	if (wantarray) {
186	&$cb	555	my @res = eval { &$cb };
187	and delete $AnyEvent::MP::Base::PORT{$id};	556	_self_die if $@;
188	};	557	@res
189
190	"$NODE#$id"
191	}
192
193	package AnyEvent::MP::Port;
194
195	=back
196
197	=head1 METHODS FOR PORT OBJECTS
198
199	=over 4
200
201	=item "$port"
202
203	A port object stringifies to its port ID, so can be used directly for
204	C<snd> operations.
205
206	=cut
207
208	use overload
209	'""' => sub { $_[0]{id} },
210	fallback => 1;
211
212	=item $port->rcv (type => $callback->($port, @msg))
213
214	=item $port->rcv ($smartmatch => $callback->($port, @msg))
215
216	=item $port->rcv ([$smartmatch...] => $callback->($port, @msg))
217
218	Register a callback on the given port.
219
220	The callback has to return a true value when its work is done, after
221	which is will be removed, or a false value in which case it will stay
222	registered.
223
224	If the match is an array reference, then it will be matched against the
225	first elements of the message, otherwise only the first element is being
226	matched.
227
228	Any element in the match that is specified as C<_any_> (a function
229	exported by this module) matches any single element of the message.
230
231	While not required, it is highly recommended that the first matching
232	element is a string identifying the message. The one-string-only match is
233	also the most efficient match (by far).
234
235	=cut
236
237	sub rcv($@) {
238	my ($self, $match, $cb) = @_;
239
240	if (!ref $match) {
241	push @{ $self->{rc0}{$match} }, [$cb];
242	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
243	my ($type, @match) = @$match;
244	@match
245	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
246	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
247	} else {	558	} else {
248	push @{ $self->{any} }, [$cb, $match];	559	my $res = eval { &$cb };
		560	_self_die if $@;
		561	$res
249	}	562	}
250	}	563	}
251		564
252	=item $port->register ($name)	565	=item $closure = psub { BLOCK }
253		566
254	Registers the given port under the well known name C<$name>. If the name	567	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
255	already exists it is replaced.	568	closure is executed, sets up the environment in the same way as in C<rcv>
		569	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
256		570
257	A port can only be registered under one well known name.	571	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		572	BLOCK }, @_ } >>.
		573
		574	This is useful when you register callbacks from C<rcv> callbacks:
		575
		576	rcv delayed_reply => sub {
		577	my ($delay, @reply) = @_;
		578	my $timer = AE::timer $delay, 0, psub {
		579	snd @reply, $SELF;
		580	};
		581	};
258		582
259	=cut	583	=cut
260		584
261	sub register {	585	sub psub(&) {
262	my ($self, $name) = @_;	586	my $cb = shift;
263		587
264	$self->{wkname} = $name;	588	my $port = $SELF
265	$AnyEvent::MP::Base::WKP{$name} = "$self";	589	or Carp::croak "psub can only be called from within rcv or psub callbacks, not";
		590
		591	sub {
		592	local $SELF = $port;
		593
		594	if (wantarray) {
		595	my @res = eval { &$cb };
		596	_self_die if $@;
		597	@res
		598	} else {
		599	my $res = eval { &$cb };
		600	_self_die if $@;
		601	$res
		602	}
		603	}
266	}	604	}
267		605
268	=item $port->destroy	606	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
269		607
270	Explicitly destroy/remove/nuke/vaporise the port.	608	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
271		609
272	Ports are normally kept alive by there mere existance alone, and need to	610	=item $guard = mon $port # kill $SELF when $port dies
273	be destroyed explicitly.	611
		612	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		613
		614	Monitor the given port and do something when the port is killed or
		615	messages to it were lost, and optionally return a guard that can be used
		616	to stop monitoring again.
		617
		618	In the first form (callback), the callback is simply called with any
		619	number of C<@reason> elements (no @reason means that the port was deleted
		620	"normally"). Note also that I<< the callback B<must> never die >>, so use
		621	C<eval> if unsure.
		622
		623	In the second form (another port given), the other port (C<$rcvport>)
		624	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
		625	"normal" kils nothing happens, while under all other conditions, the other
		626	port is killed with the same reason.
		627
		628	The third form (kill self) is the same as the second form, except that
		629	C<$rvport> defaults to C<$SELF>.
		630
		631	In the last form (message), a message of the form C<@msg, @reason> will be
		632	C<snd>.
		633
		634	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		635	alert was raised), they are removed and will not trigger again.
		636
		637	As a rule of thumb, monitoring requests should always monitor a port from
		638	a local port (or callback). The reason is that kill messages might get
		639	lost, just like any other message. Another less obvious reason is that
		640	even monitoring requests can get lost (for example, when the connection
		641	to the other node goes down permanently). When monitoring a port locally
		642	these problems do not exist.
		643
		644	C<mon> effectively guarantees that, in the absence of hardware failures,
		645	after starting the monitor, either all messages sent to the port will
		646	arrive, or the monitoring action will be invoked after possible message
		647	loss has been detected. No messages will be lost "in between" (after
		648	the first lost message no further messages will be received by the
		649	port). After the monitoring action was invoked, further messages might get
		650	delivered again.
		651
		652	Inter-host-connection timeouts and monitoring depend on the transport
		653	used. The only transport currently implemented is TCP, and AnyEvent::MP
		654	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		655	non-idle connection, and usually around two hours for idle connections).
		656
		657	This means that monitoring is good for program errors and cleaning up
		658	stuff eventually, but they are no replacement for a timeout when you need
		659	to ensure some maximum latency.
		660
		661	Example: call a given callback when C<$port> is killed.
		662
		663	mon $port, sub { warn "port died because of <@_>\n" };
		664
		665	Example: kill ourselves when C<$port> is killed abnormally.
		666
		667	mon $port;
		668
		669	Example: send us a restart message when another C<$port> is killed.
		670
		671	mon $port, $self => "restart";
274		672
275	=cut	673	=cut
276		674
277	sub destroy {	675	sub mon {
278	my ($self) = @_;	676	my ($nodeid, $port) = split /#/, shift, 2;
279		677
280	delete $AnyEvent::MP::Base::WKP{ $self->{wkname} };	678	my $node = $NODE{$nodeid} || add_node $nodeid;
281		679
282	delete $AnyEvent::MP::Base::PORT{$_}	680	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
283	for @{ $self->{names} };	681
		682	unless (ref $cb) {
		683	if (@_) {
		684	# send a kill info message
		685	my (@msg) = ($cb, @_);
		686	$cb = sub { snd @msg, @_ };
		687	} else {
		688	# simply kill other port
		689	my $port = $cb;
		690	$cb = sub { kil $port, @_ if @_ };
		691	}
		692	}
		693
		694	$node->monitor ($port, $cb);
		695
		696	defined wantarray
		697	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
284	}	698	}
285		699
		700	=item $guard = mon_guard $port, $ref, $ref...
		701
		702	Monitors the given C<$port> and keeps the passed references. When the port
		703	is killed, the references will be freed.
		704
		705	Optionally returns a guard that will stop the monitoring.
		706
		707	This function is useful when you create e.g. timers or other watchers and
		708	want to free them when the port gets killed (note the use of C<psub>):
		709
		710	$port->rcv (start => sub {
		711	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
		712	undef $timer if 0.9 < rand;
		713	});
		714	});
		715
		716	=cut
		717
		718	sub mon_guard {
		719	my ($port, @refs) = @_;
		720
		721	#TODO: mon-less form?
		722
		723	mon $port, sub { 0 && @refs }
		724	}
		725
		726	=item kil $port[, @reason]
		727
		728	Kill the specified port with the given C<@reason>.
		729
		730	If no C<@reason> is specified, then the port is killed "normally" -
		731	monitor callback will be invoked, but the kil will not cause linked ports
		732	(C<mon $mport, $lport> form) to get killed.
		733
		734	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
		735	form) get killed with the same reason.
		736
		737	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		738	will be reported as reason C<< die => $@ >>.
		739
		740	Transport/communication errors are reported as C<< transport_error =>
		741	$message >>.
		742
		743	Common idioms:
		744
		745	# silently remove yourself, do not kill linked ports
		746	kil $SELF;
		747
		748	# report a failure in some detail
		749	kil $SELF, failure_mode_1 => "it failed with too high temperature";
		750
		751	# do not waste much time with killing, just die when something goes wrong
		752	open my $fh, "<file"
		753	or die "file: $!";
		754
		755	=item $port = spawn $node, $initfunc[, @initdata]
		756
		757	Creates a port on the node C<$node> (which can also be a port ID, in which
		758	case it's the node where that port resides).
		759
		760	The port ID of the newly created port is returned immediately, and it is
		761	possible to immediately start sending messages or to monitor the port.
		762
		763	After the port has been created, the init function is called on the remote
		764	node, in the same context as a C<rcv> callback. This function must be a
		765	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		766	specify a function in the main program, use C<::name>.
		767
		768	If the function doesn't exist, then the node tries to C<require>
		769	the package, then the package above the package and so on (e.g.
		770	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		771	exists or it runs out of package names.
		772
		773	The init function is then called with the newly-created port as context
		774	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		775	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		776	the port might not get created.
		777
		778	A common idiom is to pass a local port, immediately monitor the spawned
		779	port, and in the remote init function, immediately monitor the passed
		780	local port. This two-way monitoring ensures that both ports get cleaned up
		781	when there is a problem.
		782
		783	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		784	caller before C<spawn> returns (by delaying invocation when spawn is
		785	called for the local node).
		786
		787	Example: spawn a chat server port on C<$othernode>.
		788
		789	# this node, executed from within a port context:
		790	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		791	mon $server;
		792
		793	# init function on C<$othernode>
		794	sub connect {
		795	my ($srcport) = @_;
		796
		797	mon $srcport;
		798
		799	rcv $SELF, sub {
		800	...
		801	};
		802	}
		803
		804	=cut
		805
		806	sub _spawn {
		807	my $port = shift;
		808	my $init = shift;
		809
		810	# rcv will create the actual port
		811	local $SELF = "$NODE#$port";
		812	eval {
		813	&{ load_func $init }
		814	};
		815	_self_die if $@;
		816	}
		817
		818	sub spawn(@) {
		819	my ($nodeid, undef) = split /#/, shift, 2;
		820
		821	my $id = $RUNIQ . ++$ID;
		822
		823	$_[0] =~ /::/
		824	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		825
		826	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		827
		828	"$nodeid#$id"
		829	}
		830
		831
		832	=item after $timeout, @msg
		833
		834	=item after $timeout, $callback
		835
		836	Either sends the given message, or call the given callback, after the
		837	specified number of seconds.
		838
		839	This is simply a utility function that comes in handy at times - the
		840	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		841	so it may go away in the future.
		842
		843	=cut
		844
		845	sub after($@) {
		846	my ($timeout, @action) = @_;
		847
		848	my $t; $t = AE::timer $timeout, 0, sub {
		849	undef $t;
		850	ref $action[0]
		851	? $action[0]()
		852	: snd @action;
		853	};
		854	}
		855
		856	#=item $cb2 = timeout $seconds, $cb[, @args]
		857
		858	=item cal $port, @msg, $callback[, $timeout]
		859
		860	A simple form of RPC - sends a message to the given C<$port> with the
		861	given contents (C<@msg>), but adds a reply port to the message.
		862
		863	The reply port is created temporarily just for the purpose of receiving
		864	the reply, and will be C<kil>ed when no longer needed.
		865
		866	A reply message sent to the port is passed to the C<$callback> as-is.
		867
		868	If an optional time-out (in seconds) is given and it is not C<undef>,
		869	then the callback will be called without any arguments after the time-out
		870	elapsed and the port is C<kil>ed.
		871
		872	If no time-out is given (or it is C<undef>), then the local port will
		873	monitor the remote port instead, so it eventually gets cleaned-up.
		874
		875	Currently this function returns the temporary port, but this "feature"
		876	might go in future versions unless you can make a convincing case that
		877	this is indeed useful for something.
		878
		879	=cut
		880
		881	sub cal(@) {
		882	my $timeout = ref $_[-1] ? undef : pop;
		883	my $cb = pop;
		884
		885	my $port = port {
		886	undef $timeout;
		887	kil $SELF;
		888	&$cb;
		889	};
		890
		891	if (defined $timeout) {
		892	$timeout = AE::timer $timeout, 0, sub {
		893	undef $timeout;
		894	kil $port;
		895	$cb->();
		896	};
		897	} else {
		898	mon $_[0], sub {
		899	kil $port;
		900	$cb->();
		901	};
		902	}
		903
		904	push @_, $port;
		905	&snd;
		906
		907	$port
		908	}
		909
286	=back	910	=back
287		911
288	=head1 FUNCTIONS FOR NODES	912	=head1 DISTRIBUTED DATABASE
		913
		914	AnyEvent::MP comes with a simple distributed database. The database will
		915	be mirrored asynchronously on all global nodes. Other nodes bind to one
		916	of the global nodes for their needs. Every node has a "local database"
		917	which contains all the values that are set locally. All local databases
		918	are merged together to form the global database, which can be queried.
		919
		920	The database structure is that of a two-level hash - the database hash
		921	contains hashes which contain values, similarly to a perl hash of hashes,
		922	i.e.:
		923
		924	$DATABASE{$family}{$subkey} = $value
		925
		926	The top level hash key is called "family", and the second-level hash key
		927	is called "subkey" or simply "key".
		928
		929	The family must be alphanumeric, i.e. start with a letter and consist
		930	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		931	pretty much like Perl module names.
		932
		933	As the family namespace is global, it is recommended to prefix family names
		934	with the name of the application or module using it.
		935
		936	The subkeys must be non-empty strings, with no further restrictions.
		937
		938	The values should preferably be strings, but other perl scalars should
		939	work as well (such as C<undef>, arrays and hashes).
		940
		941	Every database entry is owned by one node - adding the same family/subkey
		942	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		943	but the result might be nondeterministic, i.e. the key might have
		944	different values on different nodes.
		945
		946	Different subkeys in the same family can be owned by different nodes
		947	without problems, and in fact, this is the common method to create worker
		948	pools. For example, a worker port for image scaling might do this:
		949
		950	db_set my_image_scalers => $port;
		951
		952	And clients looking for an image scaler will want to get the
		953	C<my_image_scalers> keys from time to time:
		954
		955	db_keys my_image_scalers => sub {
		956	@ports = @{ $_[0] };
		957	};
		958
		959	Or better yet, they want to monitor the database family, so they always
		960	have a reasonable up-to-date copy:
		961
		962	db_mon my_image_scalers => sub {
		963	@ports = keys %{ $_[0] };
		964	};
		965
		966	In general, you can set or delete single subkeys, but query and monitor
		967	whole families only.
		968
		969	If you feel the need to monitor or query a single subkey, try giving it
		970	it's own family.
		971
		972	=over
		973
		974	=item $guard = db_set $family => $subkey [=> $value]
		975
		976	Sets (or replaces) a key to the database - if C<$value> is omitted,
		977	C<undef> is used instead.
		978
		979	When called in non-void context, C<db_set> returns a guard that
		980	automatically calls C<db_del> when it is destroyed.
		981
		982	=item db_del $family => $subkey...
		983
		984	Deletes one or more subkeys from the database family.
		985
		986	=item $guard = db_reg $family => $port => $value
		987
		988	=item $guard = db_reg $family => $port
		989
		990	=item $guard = db_reg $family
		991
		992	Registers a port in the given family and optionally returns a guard to
		993	remove it.
		994
		995	This function basically does the same as:
		996
		997	db_set $family => $port => $value
		998
		999	Except that the port is monitored and automatically removed from the
		1000	database family when it is kil'ed.
		1001
		1002	If C<$value> is missing, C<undef> is used. If C<$port> is missing, then
		1003	C<$SELF> is used.
		1004
		1005	This function is most useful to register a port in some port group (which
		1006	is just another name for a database family), and have it removed when the
		1007	port is gone. This works best when the port is a local port.
		1008
		1009	=cut
		1010
		1011	sub db_reg($$;$) {
		1012	my $family = shift;
		1013	my $port = @_ ? shift : $SELF;
		1014
		1015	my $clr = sub { db_del $family => $port };
		1016	mon $port, $clr;
		1017
		1018	db_set $family => $port => $_[0];
		1019
		1020	defined wantarray
		1021	and &Guard::guard ($clr)
		1022	}
		1023
		1024	=item db_family $family => $cb->(\%familyhash)
		1025
		1026	Queries the named database C<$family> and call the callback with the
		1027	family represented as a hash. You can keep and freely modify the hash.
		1028
		1029	=item db_keys $family => $cb->(\@keys)
		1030
		1031	Same as C<db_family>, except it only queries the family I<subkeys> and passes
		1032	them as array reference to the callback.
		1033
		1034	=item db_values $family => $cb->(\@values)
		1035
		1036	Same as C<db_family>, except it only queries the family I<values> and passes them
		1037	as array reference to the callback.
		1038
		1039	=item $guard = db_mon $family => $cb->($familyhash, \@added, \@changed, \@deleted)
		1040
		1041	Creates a monitor on the given database family. Each time a key is set
		1042	or or is deleted the callback is called with a hash containing the
		1043	database family and three lists of added, changed and deleted subkeys,
		1044	respectively. If no keys have changed then the array reference might be
		1045	C<undef> or even missing.
		1046
		1047	If not called in void context, a guard object is returned that, when
		1048	destroyed, stops the monitor.
		1049
		1050	The family hash reference and the key arrays belong to AnyEvent::MP and
		1051	B<must not be modified or stored> by the callback. When in doubt, make a
		1052	copy.
		1053
		1054	As soon as possible after the monitoring starts, the callback will be
		1055	called with the intiial contents of the family, even if it is empty,
		1056	i.e. there will always be a timely call to the callback with the current
		1057	contents.
		1058
		1059	It is possible that the callback is called with a change event even though
		1060	the subkey is already present and the value has not changed.
		1061
		1062	The monitoring stops when the guard object is destroyed.
		1063
		1064	Example: on every change to the family "mygroup", print out all keys.
		1065
		1066	my $guard = db_mon mygroup => sub {
		1067	my ($family, $a, $c, $d) = @_;
		1068	print "mygroup members: ", (join " ", keys %$family), "\n";
		1069	};
		1070
		1071	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1072
		1073	my $guard; $guard = db_mon My::Module::workers => sub {
		1074	my ($family, $a, $c, $d) = @_;
		1075	return unless %$family;
		1076	undef $guard;
		1077	print "My::Module::workers now nonempty\n";
		1078	};
		1079
		1080	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		1081
		1082	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		1083	my ($family, $a, $c, $d) = @_;
		1084
		1085	print "+$_=$family->{$_}\n" for @$a;
		1086	print "*$_=$family->{$_}\n" for @$c;
		1087	print "-$_=$family->{$_}\n" for @$d;
		1088	};
		1089
		1090	=cut
		1091
		1092	=back
		1093
		1094	=head1 AnyEvent::MP vs. Distributed Erlang
		1095
		1096	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
		1097	== aemp node, Erlang process == aemp port), so many of the documents and
		1098	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
		1099	sample:
		1100
		1101	http://www.erlang.se/doc/programming_rules.shtml
		1102	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
		1103	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
		1104	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
		1105
		1106	Despite the similarities, there are also some important differences:
289		1107
290	=over 4	1108	=over 4
291		1109
292	=item mon $noderef, $callback->($noderef, $status, $)	1110	=item * Node IDs are arbitrary strings in AEMP.
293		1111
294	Monitors the given noderef.	1112	Erlang relies on special naming and DNS to work everywhere in the same
		1113	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
		1114	configuration or DNS), and possibly the addresses of some seed nodes, but
		1115	will otherwise discover other nodes (and their IDs) itself.
295		1116
296	=item become_public endpoint...	1117	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
		1118	uses "local ports are like remote ports".
297		1119
298	Tells the node to become a public node, i.e. reachable from other nodes.	1120	The failure modes for local ports are quite different (runtime errors
		1121	only) then for remote ports - when a local port dies, you I<know> it dies,
		1122	when a connection to another node dies, you know nothing about the other
		1123	port.
299		1124
300	If no arguments are given, or the first argument is C<undef>, then	1125	Erlang pretends remote ports are as reliable as local ports, even when
301	AnyEvent::MP tries to bind on port C<4040> on all IP addresses that the	1126	they are not.
302	local nodename resolves to.
303		1127
304	Otherwise the first argument must be an array-reference with transport	1128	AEMP encourages a "treat remote ports differently" philosophy, with local
305	endpoints ("ip:port", "hostname:port") or port numbers (in which case the	1129	ports being the special case/exception, where transport errors cannot
306	local nodename is used as hostname). The endpoints are all resolved and	1130	occur.
307	will become the node reference.
308		1131
309	=cut	1132	=item * Erlang uses processes and a mailbox, AEMP does not queue.
		1133
		1134	Erlang uses processes that selectively receive messages out of order, and
		1135	therefore needs a queue. AEMP is event based, queuing messages would serve
		1136	no useful purpose. For the same reason the pattern-matching abilities
		1137	of AnyEvent::MP are more limited, as there is little need to be able to
		1138	filter messages without dequeuing them.
		1139
		1140	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1141	being event-based, while Erlang is process-based.
		1142
		1143	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1144	top of AEMP and Coro threads.
		1145
		1146	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
		1147
		1148	Sending messages in Erlang is synchronous and blocks the process until
		1149	a conenction has been established and the message sent (and so does not
		1150	need a queue that can overflow). AEMP sends return immediately, connection
		1151	establishment is handled in the background.
		1152
		1153	=item * Erlang suffers from silent message loss, AEMP does not.
		1154
		1155	Erlang implements few guarantees on messages delivery - messages can get
		1156	lost without any of the processes realising it (i.e. you send messages a,
		1157	b, and c, and the other side only receives messages a and c).
		1158
		1159	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1160	guarantee that after one message is lost, all following ones sent to the
		1161	same port are lost as well, until monitoring raises an error, so there are
		1162	no silent "holes" in the message sequence.
		1163
		1164	If you want your software to be very reliable, you have to cope with
		1165	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
		1166	simply tries to work better in common error cases, such as when a network
		1167	link goes down.
		1168
		1169	=item * Erlang can send messages to the wrong port, AEMP does not.
		1170
		1171	In Erlang it is quite likely that a node that restarts reuses an Erlang
		1172	process ID known to other nodes for a completely different process,
		1173	causing messages destined for that process to end up in an unrelated
		1174	process.
		1175
		1176	AEMP does not reuse port IDs, so old messages or old port IDs floating
		1177	around in the network will not be sent to an unrelated port.
		1178
		1179	=item * Erlang uses unprotected connections, AEMP uses secure
		1180	authentication and can use TLS.
		1181
		1182	AEMP can use a proven protocol - TLS - to protect connections and
		1183	securely authenticate nodes.
		1184
		1185	=item * The AEMP protocol is optimised for both text-based and binary
		1186	communications.
		1187
		1188	The AEMP protocol, unlike the Erlang protocol, supports both programming
		1189	language independent text-only protocols (good for debugging), and binary,
		1190	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1191	used, the protocol is actually completely text-based.
		1192
		1193	It has also been carefully designed to be implementable in other languages
		1194	with a minimum of work while gracefully degrading functionality to make the
		1195	protocol simple.
		1196
		1197	=item * AEMP has more flexible monitoring options than Erlang.
		1198
		1199	In Erlang, you can chose to receive I<all> exit signals as messages or
		1200	I<none>, there is no in-between, so monitoring single Erlang processes is
		1201	difficult to implement.
		1202
		1203	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1204	between automatic kill, exit message or callback on a per-port basis.
		1205
		1206	=item * Erlang tries to hide remote/local connections, AEMP does not.
		1207
		1208	Monitoring in Erlang is not an indicator of process death/crashes, in the
		1209	same way as linking is (except linking is unreliable in Erlang).
		1210
		1211	In AEMP, you don't "look up" registered port names or send to named ports
		1212	that might or might not be persistent. Instead, you normally spawn a port
		1213	on the remote node. The init function monitors you, and you monitor the
		1214	remote port. Since both monitors are local to the node, they are much more
		1215	reliable (no need for C<spawn_link>).
		1216
		1217	This also saves round-trips and avoids sending messages to the wrong port
		1218	(hard to do in Erlang).
310		1219
311	=back	1220	=back
312		1221
313	=head1 NODE MESSAGES	1222	=head1 RATIONALE
314
315	Nodes understand the following messages sent to them. Many of them take
316	arguments called C<@reply>, which will simply be used to compose a reply
317	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
318	the remaining arguments are simply the message data.
319		1223
320	=over 4	1224	=over 4
321		1225
322	=cut	1226	=item Why strings for port and node IDs, why not objects?
323		1227
324	=item wkp => $name, @reply	1228	We considered "objects", but found that the actual number of methods
		1229	that can be called are quite low. Since port and node IDs travel over
		1230	the network frequently, the serialising/deserialising would add lots of
		1231	overhead, as well as having to keep a proxy object everywhere.
325		1232
326	Replies with the port ID of the specified well-known port, or C<undef>.	1233	Strings can easily be printed, easily serialised etc. and need no special
		1234	procedures to be "valid".
327		1235
328	=item devnull => ...	1236	And as a result, a port with just a default receiver consists of a single
		1237	code reference stored in a global hash - it can't become much cheaper.
329		1238
330	Generic data sink/CPU heat conversion.	1239	=item Why favour JSON, why not a real serialising format such as Storable?
331		1240
332	=item relay => $port, @msg	1241	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1242	format, but currently there is no way to make a node use Storable by
		1243	default (although all nodes will accept it).
333		1244
334	Simply forwards the message to the given port.	1245	The default framing protocol is JSON because a) JSON::XS is many times
		1246	faster for small messages and b) most importantly, after years of
		1247	experience we found that object serialisation is causing more problems
		1248	than it solves: Just like function calls, objects simply do not travel
		1249	easily over the network, mostly because they will always be a copy, so you
		1250	always have to re-think your design.
335		1251
336	=item eval => $string[ @reply]	1252	Keeping your messages simple, concentrating on data structures rather than
337		1253	objects, will keep your messages clean, tidy and efficient.
338	Evaluates the given string. If C<@reply> is given, then a message of the
339	form C<@reply, $@, @evalres> is sent.
340
341	Example: crash another node.
342
343	snd $othernode, eval => "exit";
344
345	=item time => @reply
346
347	Replies the the current node time to C<@reply>.
348
349	Example: tell the current node to send the current time to C<$myport> in a
350	C<timereply> message.
351
352	snd $NODE, time => $myport, timereply => 1, 2;
353	# => snd $myport, timereply => 1, 2, <time>
354		1254
355	=back	1255	=back
356		1256
		1257	=head1 PORTING FROM AnyEvent::MP VERSION 1.X
		1258
		1259	AEMP version 2 has three major incompatible changes compared to version 1:
		1260
		1261	=over 4
		1262
		1263	=item AnyEvent::MP::Global no longer has group management functions.
		1264
		1265	AnyEvent::MP now comes with a distributed database that is more
		1266	powerful. It's database families map closely to ports, but the API has
		1267	minor differences:
		1268
		1269	grp_reg $group, $port # old
		1270	db_reg $group, $port # new
		1271
		1272	$list = grp_get $group # old
		1273	db_keys $group, sub { my $list = shift } # new
		1274
		1275	grp_mon $group, $cb->(\@ports, $add, $del) # old
		1276	db_mon $group, $cb->(\%ports, $add, $change, $del) # new
		1277
		1278	C<grp_reg> is a no-brainer (just replace by C<db_reg>), but C<grp_get>
		1279	is no longer instant, because the local node might not have a copy of
		1280	the group. This can be partially remedied by using C<db_mon> to keep an
		1281	updated copy of the group:
		1282
		1283	my $local_group_copy;
		1284	db_mon $group => sub { $local_group_copy = shift };
		1285
		1286	# no keys %$local_group_copy always returns the most up-to-date
		1287	# list of ports in the group.
		1288
		1289	C<grp_mon> can almost be replaced by C<db_mon>:
		1290
		1291	db_mon $group => sub {
		1292	my ($ports, $add, $chg, $lde) = @_;
		1293	$ports = [keys %$ports];
		1294
		1295	# now $ports, $add and $del are the same as
		1296	# were originally passed by grp_mon.
		1297	...
		1298	};
		1299
		1300	=item Nodes not longer connect to all other nodes.
		1301
		1302	In AEMP 1.x, every node automatically loads the L<AnyEvent::MP::Global>
		1303	module, which in turn would create connections to all other nodes in the
		1304	network (helped by the seed nodes).
		1305
		1306	In version 2.x, global nodes still connect to all other global nodes, but
		1307	other nodes don't - now every node either is a global node itself, or
		1308	attaches itself to another global node.
		1309
		1310	If a node isn't a global node itself, then it attaches itself to one
		1311	of its seed nodes. If that seed node isn't a global node yet, it will
		1312	automatically be upgraded to a global node.
		1313
		1314	So in many cases, nothing needs to be changed - one just has to make sure
		1315	that all seed nodes are meshed together with the other seed nodes (as with
		1316	AEMP 1.x), and other nodes specify them as seed nodes.
		1317
		1318	Not opening a connection to every other node is usually an advantage,
		1319	except when you need the lower latency of an already established
		1320	connection. To ensure a node establishes a connection to another node,
		1321	you can monitor the node port (C<mon $node, ...>), which will attempt to
		1322	create the connection (And notify you when the connection fails).
		1323
		1324	=item Listener-less nodes are gone.
		1325
		1326	And are not coming back, at least not in their old form.
		1327
		1328	There are vague plans to implement some form of routing domains, which
		1329	might or might not bring back listener-less nodes, but don't count on it.
		1330
		1331	The fact that most connections are now optional somewhat mitigates this,
		1332	as a node can be effectively unreachable from the outside without any
		1333	problems, as long as it isn't a global node and only reaches out to other
		1334	nodes (as opposed to being contacted from other nodes).
		1335
		1336	=back
		1337
357	=head1 SEE ALSO	1338	=head1 SEE ALSO
		1339
		1340	L<AnyEvent::MP::Intro> - a gentle introduction.
		1341
		1342	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1343
		1344	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1345	your applications.
		1346
		1347	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1348
		1349	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1350	all nodes.
358		1351
359	L<AnyEvent>.	1352	L<AnyEvent>.
360		1353
361	=head1 AUTHOR	1354	=head1 AUTHOR
362		1355

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