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Revision 1.11 by root, Sun Aug 2 18:08:38 2009 UTC vs.
Revision 1.152 by root, Sun Jul 29 02:23:34 2018 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	# distributed database - modification
		53	db_set $family => $subkey [=> $value] # add a subkey
		54	db_del $family => $subkey... # delete one or more subkeys
		55	db_reg $family => $port [=> $value] # register a port
		56
		57	# distributed database - queries
		58	db_family $family => $cb->(\%familyhash)
		59	db_keys $family => $cb->(\@keys)
		60	db_values $family => $cb->(\@values)
		61
		62	# distributed database - monitoring a family
		63	db_mon $family => $cb->(\%familyhash, \@added, \@changed, \@deleted)
24		64
25	=head1 DESCRIPTION	65	=head1 DESCRIPTION
26		66
27	This module (-family) implements a simple message passing framework.	67	This module (-family) implements a simple message passing framework.
28		68
29	Despite its simplicity, you can securely message other processes running	69	Despite its simplicity, you can securely message other processes running
30	on the same or other hosts.	70	on the same or other hosts, and you can supervise entities remotely.
31		71
32	At the moment, this module family is severly brokena nd underdocumented,	72	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 -	73	manual page and the examples under F<eg/>.
34	stay tuned!
35		74
36	=head1 CONCEPTS	75	=head1 CONCEPTS
37		76
38	=over 4	77	=over 4
39		78
40	=item port	79	=item port
41		80
42	A port is something you can send messages to with the C<snd> function, and	81	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	82	messages to (with the C<snd> function).
44	messages they match, messages will not be queued.
45		83
		84	Ports allow you to register C<rcv> handlers that can match all or just
		85	some messages. Messages send to ports will not be queued, regardless of
		86	anything was listening for them or not.
		87
		88	Ports are represented by (printable) strings called "port IDs".
		89
46	=item port id - C<noderef#portname>	90	=item port ID - C<nodeid#portname>
47		91
48	A port id is always the noderef, a hash-mark (C<#>) as separator, followed	92	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).	93	as separator, and a port name (a printable string of unspecified
		94	format created by AnyEvent::MP).
50		95
51	=item node	96	=item node
52		97
53	A node is a single process containing at least one port - the node	98	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,	99	which enables nodes to manage each other remotely, and to create new
55	among other things.	100	ports.
56		101
57	Initially, nodes are either private (single-process only) or hidden	102	Nodes are either public (have one or more listening ports) or private
58	(connected to a master node only). Only when they epxlicitly "become	103	(no listening ports). Private nodes cannot talk to other private nodes
59	public" can you send them messages from unrelated other nodes.	104	currently, but all nodes can talk to public nodes.
60		105
61	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	106	Nodes is represented by (printable) strings called "node IDs".
62		107
		108	=item node ID - C<[A-Za-z0-9_\-.:]*>
		109
63	A noderef is a string that either uniquely identifies a given node (for	110	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	111	network. Depending on the configuration used, node IDs can look like a
65	node (for public nodes).	112	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		113	doesn't interpret node IDs in any way except to uniquely identify a node.
		114
		115	=item binds - C<ip:port>
		116
		117	Nodes can only talk to each other by creating some kind of connection to
		118	each other. To do this, nodes should listen on one or more local transport
		119	endpoints - binds.
		120
		121	Currently, only standard C<ip:port> specifications can be used, which
		122	specify TCP ports to listen on. So a bind is basically just a tcp socket
		123	in listening mode that accepts connections from other nodes.
		124
		125	=item seed nodes
		126
		127	When a node starts, it knows nothing about the network it is in - it
		128	needs to connect to at least one other node that is already in the
		129	network. These other nodes are called "seed nodes".
		130
		131	Seed nodes themselves are not special - they are seed nodes only because
		132	some other node I<uses> them as such, but any node can be used as seed
		133	node for other nodes, and eahc node can use a different set of seed nodes.
		134
		135	In addition to discovering the network, seed nodes are also used to
		136	maintain the network - all nodes using the same seed node are part of the
		137	same network. If a network is split into multiple subnets because e.g. the
		138	network link between the parts goes down, then using the same seed nodes
		139	for all nodes ensures that eventually the subnets get merged again.
		140
		141	Seed nodes are expected to be long-running, and at least one seed node
		142	should always be available. They should also be relatively responsive - a
		143	seed node that blocks for long periods will slow down everybody else.
		144
		145	For small networks, it's best if every node uses the same set of seed
		146	nodes. For large networks, it can be useful to specify "regional" seed
		147	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		148	each other. What's important is that all seed nodes connections form a
		149	complete graph, so that the network cannot split into separate subnets
		150	forever.
		151
		152	Seed nodes are represented by seed IDs.
		153
		154	=item seed IDs - C<host:port>
		155
		156	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
		157	TCP port) of nodes that should be used as seed nodes.
		158
		159	=item global nodes
		160
		161	An AEMP network needs a discovery service - nodes need to know how to
		162	connect to other nodes they only know by name. In addition, AEMP offers a
		163	distributed "group database", which maps group names to a list of strings
		164	- for example, to register worker ports.
		165
		166	A network needs at least one global node to work, and allows every node to
		167	be a global node.
		168
		169	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		170	node and tries to keep connections to all other nodes. So while it can
		171	make sense to make every node "global" in small networks, it usually makes
		172	sense to only make seed nodes into global nodes in large networks (nodes
		173	keep connections to seed nodes and global nodes, so making them the same
		174	reduces overhead).
66		175
67	=back	176	=back
68		177
69	=head1 VARIABLES/FUNCTIONS	178	=head1 VARIABLES/FUNCTIONS
70		179
…		…
72		181
73	=cut	182	=cut
74		183
75	package AnyEvent::MP;	184	package AnyEvent::MP;
76		185
		186	use AnyEvent::MP::Config ();
77	use AnyEvent::MP::Base;	187	use AnyEvent::MP::Kernel;
		188	use AnyEvent::MP::Kernel qw(
		189	%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID
		190	add_node load_func
		191
		192	NODE $NODE
		193	configure
		194	node_of port_is_local
		195	snd kil
		196	db_set db_del
		197	db_mon db_family db_keys db_values
		198	);
78		199
79	use common::sense;	200	use common::sense;
80		201
81	use Carp ();	202	use Carp ();
82		203
83	use AE ();	204	use AnyEvent ();
		205	use Guard ();
84		206
85	use base "Exporter";	207	use base "Exporter";
86		208
87	our $VERSION = '0.02';	209	our $VERSION = '2.02'; # also in MP/Config.pm
		210
88	our @EXPORT = qw(	211	our @EXPORT = qw(
89	NODE $NODE $PORT snd rcv _any_	212	NODE $NODE
90	create_port create_port_on	213	configure
91	create_miniport	214	node_of port_is_local
92	become_slave become_public	215	snd kil
		216	db_set db_del
		217	db_mon db_family db_keys db_values
		218
		219	*SELF
		220
		221	port rcv mon mon_guard psub peval spawn cal
		222	db_set db_del db_reg
		223	db_mon db_family db_keys db_values
		224
		225	after
93	);	226	);
94		227
		228	our $SELF;
		229
		230	sub _self_die() {
		231	my $msg = $@;
		232	$msg =~ s/\n+$// unless ref $msg;
		233	kil $SELF, die => $msg;
		234	}
		235
95	=item NODE / $NODE	236	=item $thisnode = NODE / $NODE
96		237
97	The C<NODE ()> function and the C<$NODE> variable contain the noderef of	238	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	239	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.	240	a call to C<configure>.
100		241
		242	=item $nodeid = node_of $port
		243
		244	Extracts and returns the node ID from a port ID or a node ID.
		245
		246	=item $is_local = port_is_local $port
		247
		248	Returns true iff the port is a local port.
		249
		250	=item configure $profile, key => value...
		251
		252	=item configure key => value...
		253
		254	Before a node can talk to other nodes on the network (i.e. enter
		255	"distributed mode") it has to configure itself - the minimum a node needs
		256	to know is its own name, and optionally it should know the addresses of
		257	some other nodes in the network to discover other nodes.
		258
		259	This function configures a node - it must be called exactly once (or
		260	never) before calling other AnyEvent::MP functions.
		261
		262	The key/value pairs are basically the same ones as documented for the
		263	F<aemp> command line utility (sans the set/del prefix), with these additions:
		264
		265	=over 4
		266
		267	=item norc => $boolean (default false)
		268
		269	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
		270	be consulted - all configuration options must be specified in the
		271	C<configure> call.
		272
		273	=item force => $boolean (default false)
		274
		275	IF true, then the values specified in the C<configure> will take
		276	precedence over any values configured via the rc file. The default is for
		277	the rc file to override any options specified in the program.
		278
		279	=back
		280
		281	=over 4
		282
		283	=item step 1, gathering configuration from profiles
		284
		285	The function first looks up a profile in the aemp configuration (see the
		286	L<aemp> commandline utility). The profile name can be specified via the
		287	named C<profile> parameter or can simply be the first parameter). If it is
		288	missing, then the nodename (F<uname -n>) will be used as profile name.
		289
		290	The profile data is then gathered as follows:
		291
		292	First, all remaining key => value pairs (all of which are conveniently
		293	undocumented at the moment) will be interpreted as configuration
		294	data. Then they will be overwritten by any values specified in the global
		295	default configuration (see the F<aemp> utility), then the chain of
		296	profiles chosen by the profile name (and any C<parent> attributes).
		297
		298	That means that the values specified in the profile have highest priority
		299	and the values specified directly via C<configure> have lowest priority,
		300	and can only be used to specify defaults.
		301
		302	If the profile specifies a node ID, then this will become the node ID of
		303	this process. If not, then the profile name will be used as node ID, with
		304	a unique randoms tring (C</%u>) appended.
		305
		306	The node ID can contain some C<%> sequences that are expanded: C<%n>
		307	is expanded to the local nodename, C<%u> is replaced by a random
		308	strign to make the node unique. For example, the F<aemp> commandline
		309	utility uses C<aemp/%n/%u> as nodename, which might expand to
		310	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		311
		312	=item step 2, bind listener sockets
		313
		314	The next step is to look up the binds in the profile, followed by binding
		315	aemp protocol listeners on all binds specified (it is possible and valid
		316	to have no binds, meaning that the node cannot be contacted from the
		317	outside. This means the node cannot talk to other nodes that also have no
		318	binds, but it can still talk to all "normal" nodes).
		319
		320	If the profile does not specify a binds list, then a default of C<*> is
		321	used, meaning the node will bind on a dynamically-assigned port on every
		322	local IP address it finds.
		323
		324	=item step 3, connect to seed nodes
		325
		326	As the last step, the seed ID list from the profile is passed to the
		327	L<AnyEvent::MP::Global> module, which will then use it to keep
		328	connectivity with at least one node at any point in time.
		329
		330	=back
		331
		332	Example: become a distributed node using the local node name as profile.
		333	This should be the most common form of invocation for "daemon"-type nodes.
		334
		335	configure
		336
		337	Example: become a semi-anonymous node. This form is often used for
		338	commandline clients.
		339
		340	configure nodeid => "myscript/%n/%u";
		341
		342	Example: configure a node using a profile called seed, which is suitable
		343	for a seed node as it binds on all local addresses on a fixed port (4040,
		344	customary for aemp).
		345
		346	# use the aemp commandline utility
		347	# aemp profile seed binds '*:4040'
		348
		349	# then use it
		350	configure profile => "seed";
		351
		352	# or simply use aemp from the shell again:
		353	# aemp run profile seed
		354
		355	# or provide a nicer-to-remember nodeid
		356	# aemp run profile seed nodeid "$(hostname)"
		357
		358	=item $SELF
		359
		360	Contains the current port id while executing C<rcv> callbacks or C<psub>
		361	blocks.
		362
		363	=item *SELF, SELF, %SELF, @SELF...
		364
		365	Due to some quirks in how perl exports variables, it is impossible to
		366	just export C<$SELF>, all the symbols named C<SELF> are exported by this
		367	module, but only C<$SELF> is currently used.
		368
101	=item snd $portid, type => @data	369	=item snd $port, type => @data
102		370
103	=item snd $portid, @msg	371	=item snd $port, @msg
104		372
105	Send the given message to the given port ID, which can identify either	373	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	374	local or a remote port, and must be a port ID.
107	stringifies a sa port ID (such as a port object :).
108		375
109	While the message can be about anything, it is highly recommended to use a	376	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	377	use a string as first element (a port ID, or some word that indicates a
111	type etc.).	378	request type etc.) and to consist if only simple perl values (scalars,
		379	arrays, hashes) - if you think you need to pass an object, think again.
112		380
113	The message data effectively becomes read-only after a call to this	381	The message data logically becomes read-only after a call to this
114	function: modifying any argument is not allowed and can cause many	382	function: modifying any argument (or values referenced by them) is
115	problems.	383	forbidden, as there can be considerable time between the call to C<snd>
		384	and the time the message is actually being serialised - in fact, it might
		385	never be copied as within the same process it is simply handed to the
		386	receiving port.
116		387
117	The type of data you can transfer depends on the transport protocol: when	388	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	389	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	390	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	391	that Storable can serialise and deserialise is allowed, and for the local
121	node, anything can be passed.	392	node, anything can be passed. Best rely only on the common denominator of
		393	these.
122		394
123	=item $local_port = create_port	395	=item $local_port = port
124		396
125	Create a new local port object. See the next section for allowed methods.	397	Create a new local port object and returns its port ID. Initially it has
		398	no callbacks set and will throw an error when it receives messages.
		399
		400	=item $local_port = port { my @msg = @_ }
		401
		402	Creates a new local port, and returns its ID. Semantically the same as
		403	creating a port and calling C<rcv $port, $callback> on it.
		404
		405	The block will be called for every message received on the port, with the
		406	global variable C<$SELF> set to the port ID. Runtime errors will cause the
		407	port to be C<kil>ed. The message will be passed as-is, no extra argument
		408	(i.e. no port ID) will be passed to the callback.
		409
		410	If you want to stop/destroy the port, simply C<kil> it:
		411
		412	my $port = port {
		413	my @msg = @_;
		414	...
		415	kil $SELF;
		416	};
126		417
127	=cut	418	=cut
128		419
129	sub create_port {	420	sub rcv($@);
130	my $id = "$AnyEvent::MP::Base::UNIQ." . ++$AnyEvent::MP::Base::ID;
131		421
132	my $self = bless {	422	my $KILME = sub {
133	id => "$NODE#$id",	423	(my $tag = substr $_[0], 0, 30) =~ s/([^\x20-\x7e])/./g;
134	names => [$id],	424	kil $SELF, unhandled_message => "no callback found for message '$tag'";
135	}, "AnyEvent::MP::Port";	425	};
136		426
137	$AnyEvent::MP::Base::PORT{$id} = sub {	427	sub port(;&) {
138	unshift @_, $self;	428	my $id = $UNIQ . ++$ID;
		429	my $port = "$NODE#$id";
139		430
140	for (@{ $self->{rc0}{$_[1]} }) {	431	rcv $port, shift || $KILME;
141	$_ && &{$_->[0]}	432
142	&& undef $_;	433	$port
		434	}
		435
		436	=item rcv $local_port, $callback->(@msg)
		437
		438	Replaces the default callback on the specified port. There is no way to
		439	remove the default callback: use C<sub { }> to disable it, or better
		440	C<kil> the port when it is no longer needed.
		441
		442	The global C<$SELF> (exported by this module) contains C<$port> while
		443	executing the callback. Runtime errors during callback execution will
		444	result in the port being C<kil>ed.
		445
		446	The default callback receives all messages not matched by a more specific
		447	C<tag> match.
		448
		449	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
		450
		451	Register (or replace) callbacks to be called on messages starting with the
		452	given tag on the given port (and return the port), or unregister it (when
		453	C<$callback> is C<$undef> or missing). There can only be one callback
		454	registered for each tag.
		455
		456	The original message will be passed to the callback, after the first
		457	element (the tag) has been removed. The callback will use the same
		458	environment as the default callback (see above).
		459
		460	Example: create a port and bind receivers on it in one go.
		461
		462	my $port = rcv port,
		463	msg1 => sub { ... },
		464	msg2 => sub { ... },
		465	;
		466
		467	Example: create a port, bind receivers and send it in a message elsewhere
		468	in one go:
		469
		470	snd $otherport, reply =>
		471	rcv port,
		472	msg1 => sub { ... },
		473	...
		474	;
		475
		476	Example: temporarily register a rcv callback for a tag matching some port
		477	(e.g. for an rpc reply) and unregister it after a message was received.
		478
		479	rcv $port, $otherport => sub {
		480	my @reply = @_;
		481
		482	rcv $SELF, $otherport;
		483	};
		484
		485	=cut
		486
		487	sub rcv($@) {
		488	my $port = shift;
		489	my ($nodeid, $portid) = split /#/, $port, 2;
		490
		491	$nodeid eq $NODE
		492	or Carp::croak "$port: rcv can only be called on local ports, caught";
		493
		494	while (@_) {
		495	if (ref $_[0]) {
		496	if (my $self = $PORT_DATA{$portid}) {
		497	"AnyEvent::MP::Port" eq ref $self
		498	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		499
		500	$self->[0] = shift;
		501	} else {
		502	my $cb = shift;
		503	$PORT{$portid} = sub {
		504	local $SELF = $port;
		505	eval { &$cb }; _self_die if $@;
		506	};
		507	}
		508	} elsif (defined $_[0]) {
		509	my $self = $PORT_DATA{$portid} ||= do {
		510	my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port";
		511
		512	$PORT{$portid} = sub {
		513	local $SELF = $port;
		514
		515	if (my $cb = $self->[1]{$_[0]}) {
		516	shift;
		517	eval { &$cb }; _self_die if $@;
		518	} else {
		519	&{ $self->[0] };
		520	}
		521	};
		522
		523	$self
		524	};
		525
		526	"AnyEvent::MP::Port" eq ref $self
		527	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		528
		529	my ($tag, $cb) = splice @_, 0, 2;
		530
		531	if (defined $cb) {
		532	$self->[1]{$tag} = $cb;
		533	} else {
		534	delete $self->[1]{$tag};
		535	}
143	}	536	}
		537	}
144		538
145	for (@{ $self->{rcv}{$_[1]} }) {	539	$port
146	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]	540	}
147	&& &{$_->[0]}
148	&& undef $_;
149	}
150		541
151	for (@{ $self->{any} }) {	542	=item peval $port, $coderef[, @args]
152	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]	543
153	&& &{$_->[0]}	544	Evaluates the given C<$codref> within the context of C<$port>, that is,
154	&& undef $_;	545	when the code throws an exception the C<$port> will be killed.
155	}	546
		547	Any remaining args will be passed to the callback. Any return values will
		548	be returned to the caller.
		549
		550	This is useful when you temporarily want to execute code in the context of
		551	a port.
		552
		553	Example: create a port and run some initialisation code in it's context.
		554
		555	my $port = port { ... };
		556
		557	peval $port, sub {
		558	init
		559	or die "unable to init";
156	};	560	};
157		561
158	$self
159	}
160
161	=item $portid = create_miniport { }
162
163	Creates a "mini port", that is, a port without much #TODO
164
165	=cut	562	=cut
166		563
167	sub create_miniport(&) {	564	sub peval($$) {
		565	local $SELF = shift;
168	my $cb = shift;	566	my $cb = shift;
169	my $id = "$AnyEvent::MP::Base::UNIQ." . ++$AnyEvent::MP::Base::ID;
170		567
171	$AnyEvent::MP::Base::PORT{$id} = sub {	568	if (wantarray) {
172	&$cb	569	my @res = eval { &$cb };
173	and delete $AnyEvent::MP::Base::PORT{$id};	570	_self_die if $@;
174	};	571	@res
175
176	"$NODE#$id"
177	}
178
179	package AnyEvent::MP::Port;
180
181	=back
182
183	=head1 METHODS FOR PORT OBJECTS
184
185	=over 4
186
187	=item "$port"
188
189	A port object stringifies to its port ID, so can be used directly for
190	C<snd> operations.
191
192	=cut
193
194	use overload
195	'""' => sub { $_[0]{id} },
196	fallback => 1;
197
198	=item $port->rcv (type => $callback->($port, @msg))
199
200	=item $port->rcv ($smartmatch => $callback->($port, @msg))
201
202	=item $port->rcv ([$smartmatch...] => $callback->($port, @msg))
203
204	Register a callback on the given port.
205
206	The callback has to return a true value when its work is done, after
207	which is will be removed, or a false value in which case it will stay
208	registered.
209
210	If the match is an array reference, then it will be matched against the
211	first elements of the message, otherwise only the first element is being
212	matched.
213
214	Any element in the match that is specified as C<_any_> (a function
215	exported by this module) matches any single element of the message.
216
217	While not required, it is highly recommended that the first matching
218	element is a string identifying the message. The one-string-only match is
219	also the most efficient match (by far).
220
221	=cut
222
223	sub rcv($@) {
224	my ($self, $match, $cb) = @_;
225
226	if (!ref $match) {
227	push @{ $self->{rc0}{$match} }, [$cb];
228	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
229	my ($type, @match) = @$match;
230	@match
231	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
232	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
233	} else {	572	} else {
234	push @{ $self->{any} }, [$cb, $match];	573	my $res = eval { &$cb };
		574	_self_die if $@;
		575	$res
235	}	576	}
236	}	577	}
237		578
238	=item $port->register ($name)	579	=item $closure = psub { BLOCK }
239		580
240	Registers the given port under the well known name C<$name>. If the name	581	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
241	already exists it is replaced.	582	closure is executed, sets up the environment in the same way as in C<rcv>
		583	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
242		584
243	A port can only be registered under one well known name.	585	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		586	BLOCK }, @_ } >>.
		587
		588	This is useful when you register callbacks from C<rcv> callbacks:
		589
		590	rcv delayed_reply => sub {
		591	my ($delay, @reply) = @_;
		592	my $timer = AE::timer $delay, 0, psub {
		593	snd @reply, $SELF;
		594	};
		595	};
244		596
245	=cut	597	=cut
246		598
247	sub register {	599	sub psub(&) {
248	my ($self, $name) = @_;	600	my $cb = shift;
249		601
250	$self->{wkname} = $name;	602	my $port = $SELF
251	$AnyEvent::MP::Base::WKP{$name} = "$self";	603	or Carp::croak "psub can only be called from within rcv or psub callbacks, not";
		604
		605	sub {
		606	local $SELF = $port;
		607
		608	if (wantarray) {
		609	my @res = eval { &$cb };
		610	_self_die if $@;
		611	@res
		612	} else {
		613	my $res = eval { &$cb };
		614	_self_die if $@;
		615	$res
		616	}
		617	}
252	}	618	}
253		619
254	=item $port->destroy	620	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
255		621
256	Explicitly destroy/remove/nuke/vaporise the port.	622	=item $guard = mon $port # kill $SELF when $port dies
257		623
258	Ports are normally kept alive by there mere existance alone, and need to	624	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
259	be destroyed explicitly.	625
		626	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		627
		628	Monitor the given port and do something when the port is killed or
		629	messages to it were lost, and optionally return a guard that can be used
		630	to stop monitoring again.
		631
		632	The first two forms distinguish between "normal" and "abnormal" kil's:
		633
		634	In the first form (another port given), if the C<$port> is C<kil>'ed with
		635	a non-empty reason, the other port (C<$rcvport>) will be kil'ed with the
		636	same reason. That is, on "normal" kil's nothing happens, while under all
		637	other conditions, the other port is killed with the same reason.
		638
		639	The second form (kill self) is the same as the first form, except that
		640	C<$rvport> defaults to C<$SELF>.
		641
		642	The remaining forms don't distinguish between "normal" and "abnormal" kil's
		643	- it's up to the callback or receiver to check whether the C<@reason> is
		644	empty and act accordingly.
		645
		646	In the third form (callback), the callback is simply called with any
		647	number of C<@reason> elements (empty @reason means that the port was deleted
		648	"normally"). Note also that I<< the callback B<must> never die >>, so use
		649	C<eval> if unsure.
		650
		651	In the last form (message), a message of the form C<$rcvport, @msg,
		652	@reason> will be C<snd>.
		653
		654	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		655	alert was raised), they are removed and will not trigger again, even if it
		656	turns out that the port is still alive.
		657
		658	As a rule of thumb, monitoring requests should always monitor a remote
		659	port locally (using a local C<$rcvport> or a callback). The reason is that
		660	kill messages might get lost, just like any other message. Another less
		661	obvious reason is that even monitoring requests can get lost (for example,
		662	when the connection to the other node goes down permanently). When
		663	monitoring a port locally these problems do not exist.
		664
		665	C<mon> effectively guarantees that, in the absence of hardware failures,
		666	after starting the monitor, either all messages sent to the port will
		667	arrive, or the monitoring action will be invoked after possible message
		668	loss has been detected. No messages will be lost "in between" (after
		669	the first lost message no further messages will be received by the
		670	port). After the monitoring action was invoked, further messages might get
		671	delivered again.
		672
		673	Inter-host-connection timeouts and monitoring depend on the transport
		674	used. The only transport currently implemented is TCP, and AnyEvent::MP
		675	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		676	non-idle connection, and usually around two hours for idle connections).
		677
		678	This means that monitoring is good for program errors and cleaning up
		679	stuff eventually, but they are no replacement for a timeout when you need
		680	to ensure some maximum latency.
		681
		682	Example: call a given callback when C<$port> is killed.
		683
		684	mon $port, sub { warn "port died because of <@_>\n" };
		685
		686	Example: kill ourselves when C<$port> is killed abnormally.
		687
		688	mon $port;
		689
		690	Example: send us a restart message when another C<$port> is killed.
		691
		692	mon $port, $self => "restart";
260		693
261	=cut	694	=cut
262		695
263	sub destroy {	696	sub mon {
264	my ($self) = @_;	697	my ($nodeid, $port) = split /#/, shift, 2;
265		698
266	delete $AnyEvent::MP::Base::WKP{ $self->{wkname} };	699	my $node = $NODE{$nodeid} || add_node $nodeid;
267		700
268	delete $AnyEvent::MP::Base::PORT{$_}	701	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
269	for @{ $self->{names} };	702
		703	unless (ref $cb) {
		704	if (@_) {
		705	# send a kill info message
		706	my (@msg) = ($cb, @_);
		707	$cb = sub { snd @msg, @_ };
		708	} else {
		709	# simply kill other port
		710	my $port = $cb;
		711	$cb = sub { kil $port, @_ if @_ };
		712	}
		713	}
		714
		715	$node->monitor ($port, $cb);
		716
		717	defined wantarray
		718	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
270	}	719	}
271		720
		721	=item $guard = mon_guard $port, $ref, $ref...
		722
		723	Monitors the given C<$port> and keeps the passed references. When the port
		724	is killed, the references will be freed.
		725
		726	Optionally returns a guard that will stop the monitoring.
		727
		728	This function is useful when you create e.g. timers or other watchers and
		729	want to free them when the port gets killed (note the use of C<psub>):
		730
		731	$port->rcv (start => sub {
		732	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
		733	undef $timer if 0.9 < rand;
		734	});
		735	});
		736
		737	=cut
		738
		739	sub mon_guard {
		740	my ($port, @refs) = @_;
		741
		742	#TODO: mon-less form?
		743
		744	mon $port, sub { 0 && @refs }
		745	}
		746
		747	=item kil $port[, @reason]
		748
		749	Kill the specified port with the given C<@reason>.
		750
		751	If no C<@reason> is specified, then the port is killed "normally" -
		752	monitor callback will be invoked, but the kil will not cause linked ports
		753	(C<mon $mport, $lport> form) to get killed.
		754
		755	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
		756	form) get killed with the same reason.
		757
		758	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		759	will be reported as reason C<< die => $@ >>.
		760
		761	Transport/communication errors are reported as C<< transport_error =>
		762	$message >>.
		763
		764	Common idioms:
		765
		766	# silently remove yourself, do not kill linked ports
		767	kil $SELF;
		768
		769	# report a failure in some detail
		770	kil $SELF, failure_mode_1 => "it failed with too high temperature";
		771
		772	# do not waste much time with killing, just die when something goes wrong
		773	open my $fh, "<file"
		774	or die "file: $!";
		775
		776	=item $port = spawn $node, $initfunc[, @initdata]
		777
		778	Creates a port on the node C<$node> (which can also be a port ID, in which
		779	case it's the node where that port resides).
		780
		781	The port ID of the newly created port is returned immediately, and it is
		782	possible to immediately start sending messages or to monitor the port.
		783
		784	After the port has been created, the init function is called on the remote
		785	node, in the same context as a C<rcv> callback. This function must be a
		786	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		787	specify a function in the main program, use C<::name>.
		788
		789	If the function doesn't exist, then the node tries to C<require>
		790	the package, then the package above the package and so on (e.g.
		791	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		792	exists or it runs out of package names.
		793
		794	The init function is then called with the newly-created port as context
		795	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		796	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		797	the port might not get created.
		798
		799	A common idiom is to pass a local port, immediately monitor the spawned
		800	port, and in the remote init function, immediately monitor the passed
		801	local port. This two-way monitoring ensures that both ports get cleaned up
		802	when there is a problem.
		803
		804	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		805	caller before C<spawn> returns (by delaying invocation when spawn is
		806	called for the local node).
		807
		808	Example: spawn a chat server port on C<$othernode>.
		809
		810	# this node, executed from within a port context:
		811	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		812	mon $server;
		813
		814	# init function on C<$othernode>
		815	sub connect {
		816	my ($srcport) = @_;
		817
		818	mon $srcport;
		819
		820	rcv $SELF, sub {
		821	...
		822	};
		823	}
		824
		825	=cut
		826
		827	sub _spawn {
		828	my $port = shift;
		829	my $init = shift;
		830
		831	# rcv will create the actual port
		832	local $SELF = "$NODE#$port";
		833	eval {
		834	&{ load_func $init }
		835	};
		836	_self_die if $@;
		837	}
		838
		839	sub spawn(@) {
		840	my ($nodeid, undef) = split /#/, shift, 2;
		841
		842	my $id = $RUNIQ . ++$ID;
		843
		844	$_[0] =~ /::/
		845	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		846
		847	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		848
		849	"$nodeid#$id"
		850	}
		851
		852
		853	=item after $timeout, @msg
		854
		855	=item after $timeout, $callback
		856
		857	Either sends the given message, or call the given callback, after the
		858	specified number of seconds.
		859
		860	This is simply a utility function that comes in handy at times - the
		861	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		862	so it may go away in the future.
		863
		864	=cut
		865
		866	sub after($@) {
		867	my ($timeout, @action) = @_;
		868
		869	my $t; $t = AE::timer $timeout, 0, sub {
		870	undef $t;
		871	ref $action[0]
		872	? $action[0]()
		873	: snd @action;
		874	};
		875	}
		876
		877	#=item $cb2 = timeout $seconds, $cb[, @args]
		878
		879	=item cal $port, @msg, $callback[, $timeout]
		880
		881	A simple form of RPC - sends a message to the given C<$port> with the
		882	given contents (C<@msg>), but adds a reply port to the message.
		883
		884	The reply port is created temporarily just for the purpose of receiving
		885	the reply, and will be C<kil>ed when no longer needed.
		886
		887	A reply message sent to the port is passed to the C<$callback> as-is.
		888
		889	If an optional time-out (in seconds) is given and it is not C<undef>,
		890	then the callback will be called without any arguments after the time-out
		891	elapsed and the port is C<kil>ed.
		892
		893	If no time-out is given (or it is C<undef>), then the local port will
		894	monitor the remote port instead, so it eventually gets cleaned-up.
		895
		896	Currently this function returns the temporary port, but this "feature"
		897	might go in future versions unless you can make a convincing case that
		898	this is indeed useful for something.
		899
		900	=cut
		901
		902	sub cal(@) {
		903	my $timeout = ref $_[-1] ? undef : pop;
		904	my $cb = pop;
		905
		906	my $port = port {
		907	undef $timeout;
		908	kil $SELF;
		909	&$cb;
		910	};
		911
		912	if (defined $timeout) {
		913	$timeout = AE::timer $timeout, 0, sub {
		914	undef $timeout;
		915	kil $port;
		916	$cb->();
		917	};
		918	} else {
		919	mon $_[0], sub {
		920	kil $port;
		921	$cb->();
		922	};
		923	}
		924
		925	push @_, $port;
		926	&snd;
		927
		928	$port
		929	}
		930
272	=back	931	=back
273		932
274	=head1 FUNCTIONS FOR NODES	933	=head1 DISTRIBUTED DATABASE
		934
		935	AnyEvent::MP comes with a simple distributed database. The database will
		936	be mirrored asynchronously on all global nodes. Other nodes bind to one
		937	of the global nodes for their needs. Every node has a "local database"
		938	which contains all the values that are set locally. All local databases
		939	are merged together to form the global database, which can be queried.
		940
		941	The database structure is that of a two-level hash - the database hash
		942	contains hashes which contain values, similarly to a perl hash of hashes,
		943	i.e.:
		944
		945	$DATABASE{$family}{$subkey} = $value
		946
		947	The top level hash key is called "family", and the second-level hash key
		948	is called "subkey" or simply "key".
		949
		950	The family must be alphanumeric, i.e. start with a letter and consist
		951	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		952	pretty much like Perl module names.
		953
		954	As the family namespace is global, it is recommended to prefix family names
		955	with the name of the application or module using it.
		956
		957	The subkeys must be non-empty strings, with no further restrictions.
		958
		959	The values should preferably be strings, but other perl scalars should
		960	work as well (such as C<undef>, arrays and hashes).
		961
		962	Every database entry is owned by one node - adding the same family/subkey
		963	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		964	but the result might be nondeterministic, i.e. the key might have
		965	different values on different nodes.
		966
		967	Different subkeys in the same family can be owned by different nodes
		968	without problems, and in fact, this is the common method to create worker
		969	pools. For example, a worker port for image scaling might do this:
		970
		971	db_set my_image_scalers => $port;
		972
		973	And clients looking for an image scaler will want to get the
		974	C<my_image_scalers> keys from time to time:
		975
		976	db_keys my_image_scalers => sub {
		977	@ports = @{ $_[0] };
		978	};
		979
		980	Or better yet, they want to monitor the database family, so they always
		981	have a reasonable up-to-date copy:
		982
		983	db_mon my_image_scalers => sub {
		984	@ports = keys %{ $_[0] };
		985	};
		986
		987	In general, you can set or delete single subkeys, but query and monitor
		988	whole families only.
		989
		990	If you feel the need to monitor or query a single subkey, try giving it
		991	it's own family.
		992
		993	=over
		994
		995	=item $guard = db_set $family => $subkey [=> $value]
		996
		997	Sets (or replaces) a key to the database - if C<$value> is omitted,
		998	C<undef> is used instead.
		999
		1000	When called in non-void context, C<db_set> returns a guard that
		1001	automatically calls C<db_del> when it is destroyed.
		1002
		1003	=item db_del $family => $subkey...
		1004
		1005	Deletes one or more subkeys from the database family.
		1006
		1007	=item $guard = db_reg $family => $port => $value
		1008
		1009	=item $guard = db_reg $family => $port
		1010
		1011	=item $guard = db_reg $family
		1012
		1013	Registers a port in the given family and optionally returns a guard to
		1014	remove it.
		1015
		1016	This function basically does the same as:
		1017
		1018	db_set $family => $port => $value
		1019
		1020	Except that the port is monitored and automatically removed from the
		1021	database family when it is kil'ed.
		1022
		1023	If C<$value> is missing, C<undef> is used. If C<$port> is missing, then
		1024	C<$SELF> is used.
		1025
		1026	This function is most useful to register a port in some port group (which
		1027	is just another name for a database family), and have it removed when the
		1028	port is gone. This works best when the port is a local port.
		1029
		1030	=cut
		1031
		1032	sub db_reg($$;$) {
		1033	my $family = shift;
		1034	my $port = @_ ? shift : $SELF;
		1035
		1036	my $clr = sub { db_del $family => $port };
		1037	mon $port, $clr;
		1038
		1039	db_set $family => $port => $_[0];
		1040
		1041	defined wantarray
		1042	and &Guard::guard ($clr)
		1043	}
		1044
		1045	=item db_family $family => $cb->(\%familyhash)
		1046
		1047	Queries the named database C<$family> and call the callback with the
		1048	family represented as a hash. You can keep and freely modify the hash.
		1049
		1050	=item db_keys $family => $cb->(\@keys)
		1051
		1052	Same as C<db_family>, except it only queries the family I<subkeys> and passes
		1053	them as array reference to the callback.
		1054
		1055	=item db_values $family => $cb->(\@values)
		1056
		1057	Same as C<db_family>, except it only queries the family I<values> and passes them
		1058	as array reference to the callback.
		1059
		1060	=item $guard = db_mon $family => $cb->(\%familyhash, \@added, \@changed, \@deleted)
		1061
		1062	Creates a monitor on the given database family. Each time a key is
		1063	set or is deleted the callback is called with a hash containing the
		1064	database family and three lists of added, changed and deleted subkeys,
		1065	respectively. If no keys have changed then the array reference might be
		1066	C<undef> or even missing.
		1067
		1068	If not called in void context, a guard object is returned that, when
		1069	destroyed, stops the monitor.
		1070
		1071	The family hash reference and the key arrays belong to AnyEvent::MP and
		1072	B<must not be modified or stored> by the callback. When in doubt, make a
		1073	copy.
		1074
		1075	As soon as possible after the monitoring starts, the callback will be
		1076	called with the intiial contents of the family, even if it is empty,
		1077	i.e. there will always be a timely call to the callback with the current
		1078	contents.
		1079
		1080	It is possible that the callback is called with a change event even though
		1081	the subkey is already present and the value has not changed.
		1082
		1083	The monitoring stops when the guard object is destroyed.
		1084
		1085	Example: on every change to the family "mygroup", print out all keys.
		1086
		1087	my $guard = db_mon mygroup => sub {
		1088	my ($family, $a, $c, $d) = @_;
		1089	print "mygroup members: ", (join " ", keys %$family), "\n";
		1090	};
		1091
		1092	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1093
		1094	my $guard; $guard = db_mon My::Module::workers => sub {
		1095	my ($family, $a, $c, $d) = @_;
		1096	return unless %$family;
		1097	undef $guard;
		1098	print "My::Module::workers now nonempty\n";
		1099	};
		1100
		1101	Example: print all changes to the family "AnyEvent::Fantasy::Module".
		1102
		1103	my $guard = db_mon AnyEvent::Fantasy::Module => sub {
		1104	my ($family, $a, $c, $d) = @_;
		1105
		1106	print "+$_=$family->{$_}\n" for @$a;
		1107	print "*$_=$family->{$_}\n" for @$c;
		1108	print "-$_=$family->{$_}\n" for @$d;
		1109	};
		1110
		1111	=cut
		1112
		1113	=back
		1114
		1115	=head1 AnyEvent::MP vs. Distributed Erlang
		1116
		1117	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
		1118	== aemp node, Erlang process == aemp port), so many of the documents and
		1119	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
		1120	sample:
		1121
		1122	http://www.erlang.se/doc/programming_rules.shtml
		1123	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
		1124	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
		1125	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
		1126
		1127	Despite the similarities, there are also some important differences:
275		1128
276	=over 4	1129	=over 4
277		1130
278	=item mon $noderef, $callback->($noderef, $status, $)	1131	=item * Node IDs are arbitrary strings in AEMP.
279		1132
280	Monitors the given noderef.	1133	Erlang relies on special naming and DNS to work everywhere in the same
		1134	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
		1135	configuration or DNS), and possibly the addresses of some seed nodes, but
		1136	will otherwise discover other nodes (and their IDs) itself.
281		1137
282	=item become_public endpoint...	1138	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
		1139	uses "local ports are like remote ports".
283		1140
284	Tells the node to become a public node, i.e. reachable from other nodes.	1141	The failure modes for local ports are quite different (runtime errors
		1142	only) then for remote ports - when a local port dies, you I<know> it dies,
		1143	when a connection to another node dies, you know nothing about the other
		1144	port.
285		1145
286	If no arguments are given, or the first argument is C<undef>, then	1146	Erlang pretends remote ports are as reliable as local ports, even when
287	AnyEvent::MP tries to bind on port C<4040> on all IP addresses that the	1147	they are not.
288	local nodename resolves to.
289		1148
290	Otherwise the first argument must be an array-reference with transport	1149	AEMP encourages a "treat remote ports differently" philosophy, with local
291	endpoints ("ip:port", "hostname:port") or port numbers (in which case the	1150	ports being the special case/exception, where transport errors cannot
292	local nodename is used as hostname). The endpoints are all resolved and	1151	occur.
293	will become the node reference.
294		1152
295	=cut	1153	=item * Erlang uses processes and a mailbox, AEMP does not queue.
		1154
		1155	Erlang uses processes that selectively receive messages out of order, and
		1156	therefore needs a queue. AEMP is event based, queuing messages would serve
		1157	no useful purpose. For the same reason the pattern-matching abilities
		1158	of AnyEvent::MP are more limited, as there is little need to be able to
		1159	filter messages without dequeuing them.
		1160
		1161	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1162	being event-based, while Erlang is process-based.
		1163
		1164	You can have a look at L<Coro::MP> for a more Erlang-like process model on
		1165	top of AEMP and Coro threads.
		1166
		1167	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
		1168
		1169	Sending messages in Erlang is synchronous and blocks the process until
		1170	a connection has been established and the message sent (and so does not
		1171	need a queue that can overflow). AEMP sends return immediately, connection
		1172	establishment is handled in the background.
		1173
		1174	=item * Erlang suffers from silent message loss, AEMP does not.
		1175
		1176	Erlang implements few guarantees on messages delivery - messages can get
		1177	lost without any of the processes realising it (i.e. you send messages a,
		1178	b, and c, and the other side only receives messages a and c).
		1179
		1180	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1181	guarantee that after one message is lost, all following ones sent to the
		1182	same port are lost as well, until monitoring raises an error, so there are
		1183	no silent "holes" in the message sequence.
		1184
		1185	If you want your software to be very reliable, you have to cope with
		1186	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
		1187	simply tries to work better in common error cases, such as when a network
		1188	link goes down.
		1189
		1190	=item * Erlang can send messages to the wrong port, AEMP does not.
		1191
		1192	In Erlang it is quite likely that a node that restarts reuses an Erlang
		1193	process ID known to other nodes for a completely different process,
		1194	causing messages destined for that process to end up in an unrelated
		1195	process.
		1196
		1197	AEMP does not reuse port IDs, so old messages or old port IDs floating
		1198	around in the network will not be sent to an unrelated port.
		1199
		1200	=item * Erlang uses unprotected connections, AEMP uses secure
		1201	authentication and can use TLS.
		1202
		1203	AEMP can use a proven protocol - TLS - to protect connections and
		1204	securely authenticate nodes.
		1205
		1206	=item * The AEMP protocol is optimised for both text-based and binary
		1207	communications.
		1208
		1209	The AEMP protocol, unlike the Erlang protocol, supports both programming
		1210	language independent text-only protocols (good for debugging), and binary,
		1211	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1212	used, the protocol is actually completely text-based.
		1213
		1214	It has also been carefully designed to be implementable in other languages
		1215	with a minimum of work while gracefully degrading functionality to make the
		1216	protocol simple.
		1217
		1218	=item * AEMP has more flexible monitoring options than Erlang.
		1219
		1220	In Erlang, you can chose to receive I<all> exit signals as messages or
		1221	I<none>, there is no in-between, so monitoring single Erlang processes is
		1222	difficult to implement.
		1223
		1224	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1225	between automatic kill, exit message or callback on a per-port basis.
		1226
		1227	=item * Erlang tries to hide remote/local connections, AEMP does not.
		1228
		1229	Monitoring in Erlang is not an indicator of process death/crashes, in the
		1230	same way as linking is (except linking is unreliable in Erlang).
		1231
		1232	In AEMP, you don't "look up" registered port names or send to named ports
		1233	that might or might not be persistent. Instead, you normally spawn a port
		1234	on the remote node. The init function monitors you, and you monitor the
		1235	remote port. Since both monitors are local to the node, they are much more
		1236	reliable (no need for C<spawn_link>).
		1237
		1238	This also saves round-trips and avoids sending messages to the wrong port
		1239	(hard to do in Erlang).
296		1240
297	=back	1241	=back
298		1242
299	=head1 NODE MESSAGES	1243	=head1 RATIONALE
300
301	Nodes understand the following messages sent to them. Many of them take
302	arguments called C<@reply>, which will simply be used to compose a reply
303	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
304	the remaining arguments are simply the message data.
305		1244
306	=over 4	1245	=over 4
307		1246
308	=cut	1247	=item Why strings for port and node IDs, why not objects?
309		1248
310	=item wkp => $name, @reply	1249	We considered "objects", but found that the actual number of methods
		1250	that can be called are quite low. Since port and node IDs travel over
		1251	the network frequently, the serialising/deserialising would add lots of
		1252	overhead, as well as having to keep a proxy object everywhere.
311		1253
312	Replies with the port ID of the specified well-known port, or C<undef>.	1254	Strings can easily be printed, easily serialised etc. and need no special
		1255	procedures to be "valid".
313		1256
314	=item devnull => ...	1257	And as a result, a port with just a default receiver consists of a single
		1258	code reference stored in a global hash - it can't become much cheaper.
315		1259
316	Generic data sink/CPU heat conversion.	1260	=item Why favour JSON, why not a real serialising format such as Storable?
317		1261
318	=item relay => $port, @msg	1262	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1263	format, but currently there is no way to make a node use Storable by
		1264	default (although all nodes will accept it).
319		1265
320	Simply forwards the message to the given port.	1266	The default framing protocol is JSON because a) JSON::XS is many times
		1267	faster for small messages and b) most importantly, after years of
		1268	experience we found that object serialisation is causing more problems
		1269	than it solves: Just like function calls, objects simply do not travel
		1270	easily over the network, mostly because they will always be a copy, so you
		1271	always have to re-think your design.
321		1272
322	=item eval => $string[ @reply]	1273	Keeping your messages simple, concentrating on data structures rather than
323		1274	objects, will keep your messages clean, tidy and efficient.
324	Evaluates the given string. If C<@reply> is given, then a message of the
325	form C<@reply, $@, @evalres> is sent.
326
327	Example: crash another node.
328
329	snd $othernode, eval => "exit";
330
331	=item time => @reply
332
333	Replies the the current node time to C<@reply>.
334
335	Example: tell the current node to send the current time to C<$myport> in a
336	C<timereply> message.
337
338	snd $NODE, time => $myport, timereply => 1, 2;
339	# => snd $myport, timereply => 1, 2, <time>
340		1275
341	=back	1276	=back
342		1277
		1278	=head1 PORTING FROM AnyEvent::MP VERSION 1.X
		1279
		1280	AEMP version 2 has a few major incompatible changes compared to version 1:
		1281
		1282	=over 4
		1283
		1284	=item AnyEvent::MP::Global no longer has group management functions.
		1285
		1286	At least not officially - the grp_* functions are still exported and might
		1287	work, but they will be removed in some later release.
		1288
		1289	AnyEvent::MP now comes with a distributed database that is more
		1290	powerful. Its database families map closely to port groups, but the API
		1291	has changed (the functions are also now exported by AnyEvent::MP). Here is
		1292	a rough porting guide:
		1293
		1294	grp_reg $group, $port # old
		1295	db_reg $group, $port # new
		1296
		1297	$list = grp_get $group # old
		1298	db_keys $group, sub { my $list = shift } # new
		1299
		1300	grp_mon $group, $cb->(\@ports, $add, $del) # old
		1301	db_mon $group, $cb->(\%ports, $add, $change, $del) # new
		1302
		1303	C<grp_reg> is a no-brainer (just replace by C<db_reg>), but C<grp_get> is
		1304	no longer instant, because the local node might not have a copy of the
		1305	group. You can either modify your code to allow for a callback, or use
		1306	C<db_mon> to keep an updated copy of the group:
		1307
		1308	my $local_group_copy;
		1309	db_mon $group => sub { $local_group_copy = $_[0] };
		1310
		1311	# now "keys %$local_group_copy" always returns the most up-to-date
		1312	# list of ports in the group.
		1313
		1314	C<grp_mon> can be replaced by C<db_mon> with minor changes - C<db_mon>
		1315	passes a hash as first argument, and an extra C<$chg> argument that can be
		1316	ignored:
		1317
		1318	db_mon $group => sub {
		1319	my ($ports, $add, $chg, $del) = @_;
		1320	$ports = [keys %$ports];
		1321
		1322	# now $ports, $add and $del are the same as
		1323	# were originally passed by grp_mon.
		1324	...
		1325	};
		1326
		1327	=item Nodes not longer connect to all other nodes.
		1328
		1329	In AEMP 1.x, every node automatically loads the L<AnyEvent::MP::Global>
		1330	module, which in turn would create connections to all other nodes in the
		1331	network (helped by the seed nodes).
		1332
		1333	In version 2.x, global nodes still connect to all other global nodes, but
		1334	other nodes don't - now every node either is a global node itself, or
		1335	attaches itself to another global node.
		1336
		1337	If a node isn't a global node itself, then it attaches itself to one
		1338	of its seed nodes. If that seed node isn't a global node yet, it will
		1339	automatically be upgraded to a global node.
		1340
		1341	So in many cases, nothing needs to be changed - one just has to make sure
		1342	that all seed nodes are meshed together with the other seed nodes (as with
		1343	AEMP 1.x), and other nodes specify them as seed nodes. This is most easily
		1344	achieved by specifying the same set of seed nodes for all nodes in the
		1345	network.
		1346
		1347	Not opening a connection to every other node is usually an advantage,
		1348	except when you need the lower latency of an already established
		1349	connection. To ensure a node establishes a connection to another node,
		1350	you can monitor the node port (C<mon $node, ...>), which will attempt to
		1351	create the connection (and notify you when the connection fails).
		1352
		1353	=item Listener-less nodes (nodes without binds) are gone.
		1354
		1355	And are not coming back, at least not in their old form. If no C<binds>
		1356	are specified for a node, AnyEvent::MP assumes a default of C<*:*>.
		1357
		1358	There are vague plans to implement some form of routing domains, which
		1359	might or might not bring back listener-less nodes, but don't count on it.
		1360
		1361	The fact that most connections are now optional somewhat mitigates this,
		1362	as a node can be effectively unreachable from the outside without any
		1363	problems, as long as it isn't a global node and only reaches out to other
		1364	nodes (as opposed to being contacted from other nodes).
		1365
		1366	=item $AnyEvent::MP::Kernel::WARN has gone.
		1367
		1368	AnyEvent has acquired a logging framework (L<AnyEvent::Log>), and AEMP now
		1369	uses this, and so should your programs.
		1370
		1371	Every module now documents what kinds of messages it generates, with
		1372	AnyEvent::MP acting as a catch all.
		1373
		1374	On the positive side, this means that instead of setting
		1375	C<PERL_ANYEVENT_MP_WARNLEVEL>, you can get away by setting C<AE_VERBOSE> -
		1376	much less to type.
		1377
		1378	=back
		1379
		1380	=head1 LOGGING
		1381
		1382	AnyEvent::MP does not normally log anything by itself, but since it is the
		1383	root of the context hierarchy for AnyEvent::MP modules, it will receive
		1384	all log messages by submodules.
		1385
343	=head1 SEE ALSO	1386	=head1 SEE ALSO
		1387
		1388	L<AnyEvent::MP::Intro> - a gentle introduction.
		1389
		1390	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1391
		1392	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1393	your applications.
		1394
		1395	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1396
		1397	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1398	all nodes.
344		1399
345	L<AnyEvent>.	1400	L<AnyEvent>.
346		1401
347	=head1 AUTHOR	1402	=head1 AUTHOR
348		1403

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