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Revision 1.11 by root, Sun Aug 2 18:08:38 2009 UTC vs.
Revision 1.153 by root, Sat Nov 2 01:30:49 2019 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	configure
90	create_port create_port_on	213
91	create_miniport	214	NODE $NODE
92	become_slave become_public	215	*SELF
		216
		217	node_of port_is_local
		218
		219	snd kil
		220	port rcv mon mon_guard psub peval spawn cal
		221	db_set db_del db_reg
		222	db_mon db_family db_keys db_values
		223
		224	after
93	);	225	);
94		226
		227	our $SELF;
		228
		229	sub _self_die() {
		230	my $msg = $@;
		231	$msg =~ s/\n+$// unless ref $msg;
		232	kil $SELF, die => $msg;
		233	}
		234
95	=item NODE / $NODE	235	=item $thisnode = NODE / $NODE
96		236
97	The C<NODE ()> function and the C<$NODE> variable contain the noderef of	237	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	238	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.	239	a call to C<configure>.
100		240
		241	=item $nodeid = node_of $port
		242
		243	Extracts and returns the node ID from a port ID or a node ID.
		244
		245	=item $is_local = port_is_local $port
		246
		247	Returns true iff the port is a local port.
		248
		249	=item configure $profile, key => value...
		250
		251	=item configure key => value...
		252
		253	Before a node can talk to other nodes on the network (i.e. enter
		254	"distributed mode") it has to configure itself - the minimum a node needs
		255	to know is its own name, and optionally it should know the addresses of
		256	some other nodes in the network to discover other nodes.
		257
		258	This function configures a node - it must be called exactly once (or
		259	never) before calling other AnyEvent::MP functions.
		260
		261	The key/value pairs are basically the same ones as documented for the
		262	F<aemp> command line utility (sans the set/del prefix), with these additions:
		263
		264	=over 4
		265
		266	=item norc => $boolean (default false)
		267
		268	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
		269	be consulted - all configuration options must be specified in the
		270	C<configure> call.
		271
		272	=item force => $boolean (default false)
		273
		274	IF true, then the values specified in the C<configure> will take
		275	precedence over any values configured via the rc file. The default is for
		276	the rc file to override any options specified in the program.
		277
		278	=back
		279
		280	=over 4
		281
		282	=item step 1, gathering configuration from profiles
		283
		284	The function first looks up a profile in the aemp configuration (see the
		285	L<aemp> commandline utility). The profile name can be specified via the
		286	named C<profile> parameter or can simply be the first parameter). If it is
		287	missing, then the nodename (F<uname -n>) will be used as profile name.
		288
		289	The profile data is then gathered as follows:
		290
		291	First, all remaining key => value pairs (all of which are conveniently
		292	undocumented at the moment) will be interpreted as configuration
		293	data. Then they will be overwritten by any values specified in the global
		294	default configuration (see the F<aemp> utility), then the chain of
		295	profiles chosen by the profile name (and any C<parent> attributes).
		296
		297	That means that the values specified in the profile have highest priority
		298	and the values specified directly via C<configure> have lowest priority,
		299	and can only be used to specify defaults.
		300
		301	If the profile specifies a node ID, then this will become the node ID of
		302	this process. If not, then the profile name will be used as node ID, with
		303	a unique randoms tring (C</%u>) appended.
		304
		305	The node ID can contain some C<%> sequences that are expanded: C<%n>
		306	is expanded to the local nodename, C<%u> is replaced by a random
		307	strign to make the node unique. For example, the F<aemp> commandline
		308	utility uses C<aemp/%n/%u> as nodename, which might expand to
		309	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		310
		311	=item step 2, bind listener sockets
		312
		313	The next step is to look up the binds in the profile, followed by binding
		314	aemp protocol listeners on all binds specified (it is possible and valid
		315	to have no binds, meaning that the node cannot be contacted from the
		316	outside. This means the node cannot talk to other nodes that also have no
		317	binds, but it can still talk to all "normal" nodes).
		318
		319	If the profile does not specify a binds list, then a default of C<*> is
		320	used, meaning the node will bind on a dynamically-assigned port on every
		321	local IP address it finds.
		322
		323	=item step 3, connect to seed nodes
		324
		325	As the last step, the seed ID list from the profile is passed to the
		326	L<AnyEvent::MP::Global> module, which will then use it to keep
		327	connectivity with at least one node at any point in time.
		328
		329	=back
		330
		331	Example: become a distributed node using the local node name as profile.
		332	This should be the most common form of invocation for "daemon"-type nodes.
		333
		334	configure
		335
		336	Example: become a semi-anonymous node. This form is often used for
		337	commandline clients.
		338
		339	configure nodeid => "myscript/%n/%u";
		340
		341	Example: configure a node using a profile called seed, which is suitable
		342	for a seed node as it binds on all local addresses on a fixed port (4040,
		343	customary for aemp).
		344
		345	# use the aemp commandline utility
		346	# aemp profile seed binds '*:4040'
		347
		348	# then use it
		349	configure profile => "seed";
		350
		351	# or simply use aemp from the shell again:
		352	# aemp run profile seed
		353
		354	# or provide a nicer-to-remember nodeid
		355	# aemp run profile seed nodeid "$(hostname)"
		356
		357	=item $SELF
		358
		359	Contains the current port id while executing C<rcv> callbacks or C<psub>
		360	blocks.
		361
		362	=item *SELF, SELF, %SELF, @SELF...
		363
		364	Due to some quirks in how perl exports variables, it is impossible to
		365	just export C<$SELF>, all the symbols named C<SELF> are exported by this
		366	module, but only C<$SELF> is currently used.
		367
101	=item snd $portid, type => @data	368	=item snd $port, type => @data
102		369
103	=item snd $portid, @msg	370	=item snd $port, @msg
104		371
105	Send the given message to the given port ID, which can identify either	372	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	373	local or a remote port, and must be a port ID.
107	stringifies a sa port ID (such as a port object :).
108		374
109	While the message can be about anything, it is highly recommended to use a	375	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	376	use a string as first element (a port ID, or some word that indicates a
111	type etc.).	377	request type etc.) and to consist if only simple perl values (scalars,
		378	arrays, hashes) - if you think you need to pass an object, think again.
112		379
113	The message data effectively becomes read-only after a call to this	380	The message data logically becomes read-only after a call to this
114	function: modifying any argument is not allowed and can cause many	381	function: modifying any argument (or values referenced by them) is
115	problems.	382	forbidden, as there can be considerable time between the call to C<snd>
		383	and the time the message is actually being serialised - in fact, it might
		384	never be copied as within the same process it is simply handed to the
		385	receiving port.
116		386
117	The type of data you can transfer depends on the transport protocol: when	387	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	388	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	389	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	390	that Storable can serialise and deserialise is allowed, and for the local
121	node, anything can be passed.	391	node, anything can be passed. Best rely only on the common denominator of
		392	these.
122		393
123	=item $local_port = create_port	394	=item $local_port = port
124		395
125	Create a new local port object. See the next section for allowed methods.	396	Create a new local port object and returns its port ID. Initially it has
		397	no callbacks set and will throw an error when it receives messages.
		398
		399	=item $local_port = port { my @msg = @_ }
		400
		401	Creates a new local port, and returns its ID. Semantically the same as
		402	creating a port and calling C<rcv $port, $callback> on it.
		403
		404	The block will be called for every message received on the port, with the
		405	global variable C<$SELF> set to the port ID. Runtime errors will cause the
		406	port to be C<kil>ed. The message will be passed as-is, no extra argument
		407	(i.e. no port ID) will be passed to the callback.
		408
		409	If you want to stop/destroy the port, simply C<kil> it:
		410
		411	my $port = port {
		412	my @msg = @_;
		413	...
		414	kil $SELF;
		415	};
126		416
127	=cut	417	=cut
128		418
129	sub create_port {	419	sub rcv($@);
130	my $id = "$AnyEvent::MP::Base::UNIQ." . ++$AnyEvent::MP::Base::ID;
131		420
132	my $self = bless {	421	my $KILME = sub {
133	id => "$NODE#$id",	422	(my $tag = substr $_[0], 0, 30) =~ s/([^\x20-\x7e])/./g;
134	names => [$id],	423	kil $SELF, unhandled_message => "no callback found for message '$tag'";
135	}, "AnyEvent::MP::Port";	424	};
136		425
137	$AnyEvent::MP::Base::PORT{$id} = sub {	426	sub port(;&) {
138	unshift @_, $self;	427	my $id = $UNIQ . ++$ID;
		428	my $port = "$NODE#$id";
139		429
140	for (@{ $self->{rc0}{$_[1]} }) {	430	rcv $port, shift || $KILME;
141	$_ && &{$_->[0]}	431
142	&& undef $_;	432	$port
		433	}
		434
		435	=item rcv $local_port, $callback->(@msg)
		436
		437	Replaces the default callback on the specified port. There is no way to
		438	remove the default callback: use C<sub { }> to disable it, or better
		439	C<kil> the port when it is no longer needed.
		440
		441	The global C<$SELF> (exported by this module) contains C<$port> while
		442	executing the callback. Runtime errors during callback execution will
		443	result in the port being C<kil>ed.
		444
		445	The default callback receives all messages not matched by a more specific
		446	C<tag> match.
		447
		448	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
		449
		450	Register (or replace) callbacks to be called on messages starting with the
		451	given tag on the given port (and return the port), or unregister it (when
		452	C<$callback> is C<$undef> or missing). There can only be one callback
		453	registered for each tag.
		454
		455	The original message will be passed to the callback, after the first
		456	element (the tag) has been removed. The callback will use the same
		457	environment as the default callback (see above).
		458
		459	Example: create a port and bind receivers on it in one go.
		460
		461	my $port = rcv port,
		462	msg1 => sub { ... },
		463	msg2 => sub { ... },
		464	;
		465
		466	Example: create a port, bind receivers and send it in a message elsewhere
		467	in one go:
		468
		469	snd $otherport, reply =>
		470	rcv port,
		471	msg1 => sub { ... },
		472	...
		473	;
		474
		475	Example: temporarily register a rcv callback for a tag matching some port
		476	(e.g. for an rpc reply) and unregister it after a message was received.
		477
		478	rcv $port, $otherport => sub {
		479	my @reply = @_;
		480
		481	rcv $SELF, $otherport;
		482	};
		483
		484	=cut
		485
		486	sub rcv($@) {
		487	my $port = shift;
		488	my ($nodeid, $portid) = split /#/, $port, 2;
		489
		490	$nodeid eq $NODE
		491	or Carp::croak "$port: rcv can only be called on local ports, caught";
		492
		493	while (@_) {
		494	if (ref $_[0]) {
		495	if (my $self = $PORT_DATA{$portid}) {
		496	"AnyEvent::MP::Port" eq ref $self
		497	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		498
		499	$self->[0] = shift;
		500	} else {
		501	my $cb = shift;
		502	$PORT{$portid} = sub {
		503	local $SELF = $port;
		504	eval { &$cb }; _self_die if $@;
		505	};
		506	}
		507	} elsif (defined $_[0]) {
		508	my $self = $PORT_DATA{$portid} ||= do {
		509	my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port";
		510
		511	$PORT{$portid} = sub {
		512	local $SELF = $port;
		513
		514	if (my $cb = $self->[1]{$_[0]}) {
		515	shift;
		516	eval { &$cb }; _self_die if $@;
		517	} else {
		518	&{ $self->[0] };
		519	}
		520	};
		521
		522	$self
		523	};
		524
		525	"AnyEvent::MP::Port" eq ref $self
		526	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		527
		528	my ($tag, $cb) = splice @_, 0, 2;
		529
		530	if (defined $cb) {
		531	$self->[1]{$tag} = $cb;
		532	} else {
		533	delete $self->[1]{$tag};
		534	}
143	}	535	}
		536	}
144		537
145	for (@{ $self->{rcv}{$_[1]} }) {	538	$port
146	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]	539	}
147	&& &{$_->[0]}
148	&& undef $_;
149	}
150		540
151	for (@{ $self->{any} }) {	541	=item peval $port, $coderef[, @args]
152	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]	542
153	&& &{$_->[0]}	543	Evaluates the given C<$codref> within the context of C<$port>, that is,
154	&& undef $_;	544	when the code throws an exception the C<$port> will be killed.
155	}	545
		546	Any remaining args will be passed to the callback. Any return values will
		547	be returned to the caller.
		548
		549	This is useful when you temporarily want to execute code in the context of
		550	a port.
		551
		552	Example: create a port and run some initialisation code in it's context.
		553
		554	my $port = port { ... };
		555
		556	peval $port, sub {
		557	init
		558	or die "unable to init";
156	};	559	};
157		560
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	561	=cut
166		562
167	sub create_miniport(&) {	563	sub peval($$) {
		564	local $SELF = shift;
168	my $cb = shift;	565	my $cb = shift;
169	my $id = "$AnyEvent::MP::Base::UNIQ." . ++$AnyEvent::MP::Base::ID;
170		566
171	$AnyEvent::MP::Base::PORT{$id} = sub {	567	if (wantarray) {
172	&$cb	568	my @res = eval { &$cb };
173	and delete $AnyEvent::MP::Base::PORT{$id};	569	_self_die if $@;
174	};	570	@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 {	571	} else {
234	push @{ $self->{any} }, [$cb, $match];	572	my $res = eval { &$cb };
		573	_self_die if $@;
		574	$res
235	}	575	}
236	}	576	}
237		577
238	=item $port->register ($name)	578	=item $closure = psub { BLOCK }
239		579
240	Registers the given port under the well known name C<$name>. If the name	580	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
241	already exists it is replaced.	581	closure is executed, sets up the environment in the same way as in C<rcv>
		582	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
242		583
243	A port can only be registered under one well known name.	584	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		585	BLOCK }, @_ } >>.
		586
		587	This is useful when you register callbacks from C<rcv> callbacks:
		588
		589	rcv delayed_reply => sub {
		590	my ($delay, @reply) = @_;
		591	my $timer = AE::timer $delay, 0, psub {
		592	snd @reply, $SELF;
		593	};
		594	};
244		595
245	=cut	596	=cut
246		597
247	sub register {	598	sub psub(&) {
248	my ($self, $name) = @_;	599	my $cb = shift;
249		600
250	$self->{wkname} = $name;	601	my $port = $SELF
251	$AnyEvent::MP::Base::WKP{$name} = "$self";	602	or Carp::croak "psub can only be called from within rcv or psub callbacks, not";
		603
		604	sub {
		605	local $SELF = $port;
		606
		607	if (wantarray) {
		608	my @res = eval { &$cb };
		609	_self_die if $@;
		610	@res
		611	} else {
		612	my $res = eval { &$cb };
		613	_self_die if $@;
		614	$res
		615	}
		616	}
252	}	617	}
253		618
254	=item $port->destroy	619	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
255		620
256	Explicitly destroy/remove/nuke/vaporise the port.	621	=item $guard = mon $port # kill $SELF when $port dies
257		622
258	Ports are normally kept alive by there mere existance alone, and need to	623	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
259	be destroyed explicitly.	624
		625	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		626
		627	Monitor the given port and do something when the port is killed or
		628	messages to it were lost, and optionally return a guard that can be used
		629	to stop monitoring again.
		630
		631	The first two forms distinguish between "normal" and "abnormal" kil's:
		632
		633	In the first form (another port given), if the C<$port> is C<kil>'ed with
		634	a non-empty reason, the other port (C<$rcvport>) will be kil'ed with the
		635	same reason. That is, on "normal" kil's nothing happens, while under all
		636	other conditions, the other port is killed with the same reason.
		637
		638	The second form (kill self) is the same as the first form, except that
		639	C<$rvport> defaults to C<$SELF>.
		640
		641	The remaining forms don't distinguish between "normal" and "abnormal" kil's
		642	- it's up to the callback or receiver to check whether the C<@reason> is
		643	empty and act accordingly.
		644
		645	In the third form (callback), the callback is simply called with any
		646	number of C<@reason> elements (empty @reason means that the port was deleted
		647	"normally"). Note also that I<< the callback B<must> never die >>, so use
		648	C<eval> if unsure.
		649
		650	In the last form (message), a message of the form C<$rcvport, @msg,
		651	@reason> will be C<snd>.
		652
		653	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		654	alert was raised), they are removed and will not trigger again, even if it
		655	turns out that the port is still alive.
		656
		657	As a rule of thumb, monitoring requests should always monitor a remote
		658	port locally (using a local C<$rcvport> or a callback). The reason is that
		659	kill messages might get lost, just like any other message. Another less
		660	obvious reason is that even monitoring requests can get lost (for example,
		661	when the connection to the other node goes down permanently). When
		662	monitoring a port locally these problems do not exist.
		663
		664	C<mon> effectively guarantees that, in the absence of hardware failures,
		665	after starting the monitor, either all messages sent to the port will
		666	arrive, or the monitoring action will be invoked after possible message
		667	loss has been detected. No messages will be lost "in between" (after
		668	the first lost message no further messages will be received by the
		669	port). After the monitoring action was invoked, further messages might get
		670	delivered again.
		671
		672	Inter-host-connection timeouts and monitoring depend on the transport
		673	used. The only transport currently implemented is TCP, and AnyEvent::MP
		674	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		675	non-idle connection, and usually around two hours for idle connections).
		676
		677	This means that monitoring is good for program errors and cleaning up
		678	stuff eventually, but they are no replacement for a timeout when you need
		679	to ensure some maximum latency.
		680
		681	Example: call a given callback when C<$port> is killed.
		682
		683	mon $port, sub { warn "port died because of <@_>\n" };
		684
		685	Example: kill ourselves when C<$port> is killed abnormally.
		686
		687	mon $port;
		688
		689	Example: send us a restart message when another C<$port> is killed.
		690
		691	mon $port, $self => "restart";
260		692
261	=cut	693	=cut
262		694
263	sub destroy {	695	sub mon {
264	my ($self) = @_;	696	my ($nodeid, $port) = split /#/, shift, 2;
265		697
266	delete $AnyEvent::MP::Base::WKP{ $self->{wkname} };	698	my $node = $NODE{$nodeid} || add_node $nodeid;
267		699
268	delete $AnyEvent::MP::Base::PORT{$_}	700	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
269	for @{ $self->{names} };	701
		702	unless (ref $cb) {
		703	if (@_) {
		704	# send a kill info message
		705	my (@msg) = ($cb, @_);
		706	$cb = sub { snd @msg, @_ };
		707	} else {
		708	# simply kill other port
		709	my $port = $cb;
		710	$cb = sub { kil $port, @_ if @_ };
		711	}
		712	}
		713
		714	$node->monitor ($port, $cb);
		715
		716	defined wantarray
		717	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
270	}	718	}
271		719
		720	=item $guard = mon_guard $port, $ref, $ref...
		721
		722	Monitors the given C<$port> and keeps the passed references. When the port
		723	is killed, the references will be freed.
		724
		725	Optionally returns a guard that will stop the monitoring.
		726
		727	This function is useful when you create e.g. timers or other watchers and
		728	want to free them when the port gets killed (note the use of C<psub>):
		729
		730	$port->rcv (start => sub {
		731	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
		732	undef $timer if 0.9 < rand;
		733	});
		734	});
		735
		736	=cut
		737
		738	sub mon_guard {
		739	my ($port, @refs) = @_;
		740
		741	#TODO: mon-less form?
		742
		743	mon $port, sub { 0 && @refs }
		744	}
		745
		746	=item kil $port[, @reason]
		747
		748	Kill the specified port with the given C<@reason>.
		749
		750	If no C<@reason> is specified, then the port is killed "normally" -
		751	monitor callback will be invoked, but the kil will not cause linked ports
		752	(C<mon $mport, $lport> form) to get killed.
		753
		754	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
		755	form) get killed with the same reason.
		756
		757	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		758	will be reported as reason C<< die => $@ >>.
		759
		760	Transport/communication errors are reported as C<< transport_error =>
		761	$message >>.
		762
		763	Common idioms:
		764
		765	# silently remove yourself, do not kill linked ports
		766	kil $SELF;
		767
		768	# report a failure in some detail
		769	kil $SELF, failure_mode_1 => "it failed with too high temperature";
		770
		771	# do not waste much time with killing, just die when something goes wrong
		772	open my $fh, "<file"
		773	or die "file: $!";
		774
		775	=item $port = spawn $node, $initfunc[, @initdata]
		776
		777	Creates a port on the node C<$node> (which can also be a port ID, in which
		778	case it's the node where that port resides).
		779
		780	The port ID of the newly created port is returned immediately, and it is
		781	possible to immediately start sending messages or to monitor the port.
		782
		783	After the port has been created, the init function is called on the remote
		784	node, in the same context as a C<rcv> callback. This function must be a
		785	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		786	specify a function in the main program, use C<::name>.
		787
		788	If the function doesn't exist, then the node tries to C<require>
		789	the package, then the package above the package and so on (e.g.
		790	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		791	exists or it runs out of package names.
		792
		793	The init function is then called with the newly-created port as context
		794	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		795	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		796	the port might not get created.
		797
		798	A common idiom is to pass a local port, immediately monitor the spawned
		799	port, and in the remote init function, immediately monitor the passed
		800	local port. This two-way monitoring ensures that both ports get cleaned up
		801	when there is a problem.
		802
		803	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		804	caller before C<spawn> returns (by delaying invocation when spawn is
		805	called for the local node).
		806
		807	Example: spawn a chat server port on C<$othernode>.
		808
		809	# this node, executed from within a port context:
		810	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		811	mon $server;
		812
		813	# init function on C<$othernode>
		814	sub connect {
		815	my ($srcport) = @_;
		816
		817	mon $srcport;
		818
		819	rcv $SELF, sub {
		820	...
		821	};
		822	}
		823
		824	=cut
		825
		826	sub _spawn {
		827	my $port = shift;
		828	my $init = shift;
		829
		830	# rcv will create the actual port
		831	local $SELF = "$NODE#$port";
		832	eval {
		833	&{ load_func $init }
		834	};
		835	_self_die if $@;
		836	}
		837
		838	sub spawn(@) {
		839	my ($nodeid, undef) = split /#/, shift, 2;
		840
		841	my $id = $RUNIQ . ++$ID;
		842
		843	$_[0] =~ /::/
		844	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		845
		846	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		847
		848	"$nodeid#$id"
		849	}
		850
		851
		852	=item after $timeout, @msg
		853
		854	=item after $timeout, $callback
		855
		856	Either sends the given message, or call the given callback, after the
		857	specified number of seconds.
		858
		859	This is simply a utility function that comes in handy at times - the
		860	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		861	so it may go away in the future.
		862
		863	=cut
		864
		865	sub after($@) {
		866	my ($timeout, @action) = @_;
		867
		868	my $t; $t = AE::timer $timeout, 0, sub {
		869	undef $t;
		870	ref $action[0]
		871	? $action[0]()
		872	: snd @action;
		873	};
		874	}
		875
		876	#=item $cb2 = timeout $seconds, $cb[, @args]
		877
		878	=item cal $port, @msg, $callback[, $timeout]
		879
		880	A simple form of RPC - sends a message to the given C<$port> with the
		881	given contents (C<@msg>), but adds a reply port to the message.
		882
		883	The reply port is created temporarily just for the purpose of receiving
		884	the reply, and will be C<kil>ed when no longer needed.
		885
		886	A reply message sent to the port is passed to the C<$callback> as-is.
		887
		888	If an optional time-out (in seconds) is given and it is not C<undef>,
		889	then the callback will be called without any arguments after the time-out
		890	elapsed and the port is C<kil>ed.
		891
		892	If no time-out is given (or it is C<undef>), then the local port will
		893	monitor the remote port instead, so it eventually gets cleaned-up.
		894
		895	Currently this function returns the temporary port, but this "feature"
		896	might go in future versions unless you can make a convincing case that
		897	this is indeed useful for something.
		898
		899	=cut
		900
		901	sub cal(@) {
		902	my $timeout = ref $_[-1] ? undef : pop;
		903	my $cb = pop;
		904
		905	my $port = port {
		906	undef $timeout;
		907	kil $SELF;
		908	&$cb;
		909	};
		910
		911	if (defined $timeout) {
		912	$timeout = AE::timer $timeout, 0, sub {
		913	undef $timeout;
		914	kil $port;
		915	$cb->();
		916	};
		917	} else {
		918	mon $_[0], sub {
		919	kil $port;
		920	$cb->();
		921	};
		922	}
		923
		924	push @_, $port;
		925	&snd;
		926
		927	$port
		928	}
		929
272	=back	930	=back
273		931
274	=head1 FUNCTIONS FOR NODES	932	=head1 DISTRIBUTED DATABASE
		933
		934	AnyEvent::MP comes with a simple distributed database. The database will
		935	be mirrored asynchronously on all global nodes. Other nodes bind to one
		936	of the global nodes for their needs. Every node has a "local database"
		937	which contains all the values that are set locally. All local databases
		938	are merged together to form the global database, which can be queried.
		939
		940	The database structure is that of a two-level hash - the database hash
		941	contains hashes which contain values, similarly to a perl hash of hashes,
		942	i.e.:
		943
		944	$DATABASE{$family}{$subkey} = $value
		945
		946	The top level hash key is called "family", and the second-level hash key
		947	is called "subkey" or simply "key".
		948
		949	The family must be alphanumeric, i.e. start with a letter and consist
		950	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		951	pretty much like Perl module names.
		952
		953	As the family namespace is global, it is recommended to prefix family names
		954	with the name of the application or module using it.
		955
		956	The subkeys must be non-empty strings, with no further restrictions.
		957
		958	The values should preferably be strings, but other perl scalars should
		959	work as well (such as C<undef>, arrays and hashes).
		960
		961	Every database entry is owned by one node - adding the same family/subkey
		962	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		963	but the result might be nondeterministic, i.e. the key might have
		964	different values on different nodes.
		965
		966	Different subkeys in the same family can be owned by different nodes
		967	without problems, and in fact, this is the common method to create worker
		968	pools. For example, a worker port for image scaling might do this:
		969
		970	db_set my_image_scalers => $port;
		971
		972	And clients looking for an image scaler will want to get the
		973	C<my_image_scalers> keys from time to time:
		974
		975	db_keys my_image_scalers => sub {
		976	@ports = @{ $_[0] };
		977	};
		978
		979	Or better yet, they want to monitor the database family, so they always
		980	have a reasonable up-to-date copy:
		981
		982	db_mon my_image_scalers => sub {
		983	@ports = keys %{ $_[0] };
		984	};
		985
		986	In general, you can set or delete single subkeys, but query and monitor
		987	whole families only.
		988
		989	If you feel the need to monitor or query a single subkey, try giving it
		990	it's own family.
		991
		992	=over
		993
		994	=item $guard = db_set $family => $subkey [=> $value]
		995
		996	Sets (or replaces) a key to the database - if C<$value> is omitted,
		997	C<undef> is used instead.
		998
		999	When called in non-void context, C<db_set> returns a guard that
		1000	automatically calls C<db_del> when it is destroyed.
		1001
		1002	=item db_del $family => $subkey...
		1003
		1004	Deletes one or more subkeys from the database family.
		1005
		1006	=item $guard = db_reg $family => $port => $value
		1007
		1008	=item $guard = db_reg $family => $port
		1009
		1010	=item $guard = db_reg $family
		1011
		1012	Registers a port in the given family and optionally returns a guard to
		1013	remove it.
		1014
		1015	This function basically does the same as:
		1016
		1017	db_set $family => $port => $value
		1018
		1019	Except that the port is monitored and automatically removed from the
		1020	database family when it is kil'ed.
		1021
		1022	If C<$value> is missing, C<undef> is used. If C<$port> is missing, then
		1023	C<$SELF> is used.
		1024
		1025	This function is most useful to register a port in some port group (which
		1026	is just another name for a database family), and have it removed when the
		1027	port is gone. This works best when the port is a local port.
		1028
		1029	=cut
		1030
		1031	sub db_reg($$;$) {
		1032	my $family = shift;
		1033	my $port = @_ ? shift : $SELF;
		1034
		1035	my $clr = sub { db_del $family => $port };
		1036	mon $port, $clr;
		1037
		1038	db_set $family => $port => $_[0];
		1039
		1040	defined wantarray
		1041	and &Guard::guard ($clr)
		1042	}
		1043
		1044	=item db_family $family => $cb->(\%familyhash)
		1045
		1046	Queries the named database C<$family> and call the callback with the
		1047	family represented as a hash. You can keep and freely modify the hash.
		1048
		1049	=item db_keys $family => $cb->(\@keys)
		1050
		1051	Same as C<db_family>, except it only queries the family I<subkeys> and passes
		1052	them as array reference to the callback.
		1053
		1054	=item db_values $family => $cb->(\@values)
		1055
		1056	Same as C<db_family>, except it only queries the family I<values> and passes them
		1057	as array reference to the callback.
		1058
		1059	=item $guard = db_mon $family => $cb->(\%familyhash, \@added, \@changed, \@deleted)
		1060
		1061	Creates a monitor on the given database family. Each time a key is
		1062	set or is deleted the callback is called with a hash containing the
		1063	database family and three lists of added, changed and deleted subkeys,
		1064	respectively. If no keys have changed then the array reference might be
		1065	C<undef> or even missing.
		1066
		1067	If not called in void context, a guard object is returned that, when
		1068	destroyed, stops the monitor.
		1069
		1070	The family hash reference and the key arrays belong to AnyEvent::MP and
		1071	B<must not be modified or stored> by the callback. When in doubt, make a
		1072	copy.
		1073
		1074	As soon as possible after the monitoring starts, the callback will be
		1075	called with the intiial contents of the family, even if it is empty,
		1076	i.e. there will always be a timely call to the callback with the current
		1077	contents.
		1078
		1079	It is possible that the callback is called with a change event even though
		1080	the subkey is already present and the value has not changed.
		1081
		1082	The monitoring stops when the guard object is destroyed.
		1083
		1084	Example: on every change to the family "mygroup", print out all keys.
		1085
		1086	my $guard = db_mon mygroup => sub {
		1087	my ($family, $a, $c, $d) = @_;
		1088	print "mygroup members: ", (join " ", keys %$family), "\n";
		1089	};
		1090
		1091	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1092
		1093	my $guard; $guard = db_mon My::Module::workers => sub {
		1094	my ($family, $a, $c, $d) = @_;
		1095	return unless %$family;
		1096	undef $guard;
		1097	print "My::Module::workers now nonempty\n";
		1098	};
		1099
		1100	Example: print all changes to the family "AnyEvent::Fantasy::Module".
		1101
		1102	my $guard = db_mon AnyEvent::Fantasy::Module => sub {
		1103	my ($family, $a, $c, $d) = @_;
		1104
		1105	print "+$_=$family->{$_}\n" for @$a;
		1106	print "*$_=$family->{$_}\n" for @$c;
		1107	print "-$_=$family->{$_}\n" for @$d;
		1108	};
		1109
		1110	=cut
		1111
		1112	=back
		1113
		1114	=head1 AnyEvent::MP vs. Distributed Erlang
		1115
		1116	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
		1117	== aemp node, Erlang process == aemp port), so many of the documents and
		1118	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
		1119	sample:
		1120
		1121	http://www.erlang.se/doc/programming_rules.shtml
		1122	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
		1123	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
		1124	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
		1125
		1126	Despite the similarities, there are also some important differences:
275		1127
276	=over 4	1128	=over 4
277		1129
278	=item mon $noderef, $callback->($noderef, $status, $)	1130	=item * Node IDs are arbitrary strings in AEMP.
279		1131
280	Monitors the given noderef.	1132	Erlang relies on special naming and DNS to work everywhere in the same
		1133	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
		1134	configuration or DNS), and possibly the addresses of some seed nodes, but
		1135	will otherwise discover other nodes (and their IDs) itself.
281		1136
282	=item become_public endpoint...	1137	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
		1138	uses "local ports are like remote ports".
283		1139
284	Tells the node to become a public node, i.e. reachable from other nodes.	1140	The failure modes for local ports are quite different (runtime errors
		1141	only) then for remote ports - when a local port dies, you I<know> it dies,
		1142	when a connection to another node dies, you know nothing about the other
		1143	port.
285		1144
286	If no arguments are given, or the first argument is C<undef>, then	1145	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	1146	they are not.
288	local nodename resolves to.
289		1147
290	Otherwise the first argument must be an array-reference with transport	1148	AEMP encourages a "treat remote ports differently" philosophy, with local
291	endpoints ("ip:port", "hostname:port") or port numbers (in which case the	1149	ports being the special case/exception, where transport errors cannot
292	local nodename is used as hostname). The endpoints are all resolved and	1150	occur.
293	will become the node reference.
294		1151
295	=cut	1152	=item * Erlang uses processes and a mailbox, AEMP does not queue.
		1153
		1154	Erlang uses processes that selectively receive messages out of order, and
		1155	therefore needs a queue. AEMP is event based, queuing messages would serve
		1156	no useful purpose. For the same reason the pattern-matching abilities
		1157	of AnyEvent::MP are more limited, as there is little need to be able to
		1158	filter messages without dequeuing them.
		1159
		1160	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1161	being event-based, while Erlang is process-based.
		1162
		1163	You can have a look at L<Coro::MP> for a more Erlang-like process model on
		1164	top of AEMP and Coro threads.
		1165
		1166	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
		1167
		1168	Sending messages in Erlang is synchronous and blocks the process until
		1169	a connection has been established and the message sent (and so does not
		1170	need a queue that can overflow). AEMP sends return immediately, connection
		1171	establishment is handled in the background.
		1172
		1173	=item * Erlang suffers from silent message loss, AEMP does not.
		1174
		1175	Erlang implements few guarantees on messages delivery - messages can get
		1176	lost without any of the processes realising it (i.e. you send messages a,
		1177	b, and c, and the other side only receives messages a and c).
		1178
		1179	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1180	guarantee that after one message is lost, all following ones sent to the
		1181	same port are lost as well, until monitoring raises an error, so there are
		1182	no silent "holes" in the message sequence.
		1183
		1184	If you want your software to be very reliable, you have to cope with
		1185	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
		1186	simply tries to work better in common error cases, such as when a network
		1187	link goes down.
		1188
		1189	=item * Erlang can send messages to the wrong port, AEMP does not.
		1190
		1191	In Erlang it is quite likely that a node that restarts reuses an Erlang
		1192	process ID known to other nodes for a completely different process,
		1193	causing messages destined for that process to end up in an unrelated
		1194	process.
		1195
		1196	AEMP does not reuse port IDs, so old messages or old port IDs floating
		1197	around in the network will not be sent to an unrelated port.
		1198
		1199	=item * Erlang uses unprotected connections, AEMP uses secure
		1200	authentication and can use TLS.
		1201
		1202	AEMP can use a proven protocol - TLS - to protect connections and
		1203	securely authenticate nodes.
		1204
		1205	=item * The AEMP protocol is optimised for both text-based and binary
		1206	communications.
		1207
		1208	The AEMP protocol, unlike the Erlang protocol, supports both programming
		1209	language independent text-only protocols (good for debugging), and binary,
		1210	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1211	used, the protocol is actually completely text-based.
		1212
		1213	It has also been carefully designed to be implementable in other languages
		1214	with a minimum of work while gracefully degrading functionality to make the
		1215	protocol simple.
		1216
		1217	=item * AEMP has more flexible monitoring options than Erlang.
		1218
		1219	In Erlang, you can chose to receive I<all> exit signals as messages or
		1220	I<none>, there is no in-between, so monitoring single Erlang processes is
		1221	difficult to implement.
		1222
		1223	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1224	between automatic kill, exit message or callback on a per-port basis.
		1225
		1226	=item * Erlang tries to hide remote/local connections, AEMP does not.
		1227
		1228	Monitoring in Erlang is not an indicator of process death/crashes, in the
		1229	same way as linking is (except linking is unreliable in Erlang).
		1230
		1231	In AEMP, you don't "look up" registered port names or send to named ports
		1232	that might or might not be persistent. Instead, you normally spawn a port
		1233	on the remote node. The init function monitors you, and you monitor the
		1234	remote port. Since both monitors are local to the node, they are much more
		1235	reliable (no need for C<spawn_link>).
		1236
		1237	This also saves round-trips and avoids sending messages to the wrong port
		1238	(hard to do in Erlang).
296		1239
297	=back	1240	=back
298		1241
299	=head1 NODE MESSAGES	1242	=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		1243
306	=over 4	1244	=over 4
307		1245
308	=cut	1246	=item Why strings for port and node IDs, why not objects?
309		1247
310	=item wkp => $name, @reply	1248	We considered "objects", but found that the actual number of methods
		1249	that can be called are quite low. Since port and node IDs travel over
		1250	the network frequently, the serialising/deserialising would add lots of
		1251	overhead, as well as having to keep a proxy object everywhere.
311		1252
312	Replies with the port ID of the specified well-known port, or C<undef>.	1253	Strings can easily be printed, easily serialised etc. and need no special
		1254	procedures to be "valid".
313		1255
314	=item devnull => ...	1256	And as a result, a port with just a default receiver consists of a single
		1257	code reference stored in a global hash - it can't become much cheaper.
315		1258
316	Generic data sink/CPU heat conversion.	1259	=item Why favour JSON, why not a real serialising format such as Storable?
317		1260
318	=item relay => $port, @msg	1261	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1262	format, but currently there is no way to make a node use Storable by
		1263	default (although all nodes will accept it).
319		1264
320	Simply forwards the message to the given port.	1265	The default framing protocol is JSON because a) JSON::XS is many times
		1266	faster for small messages and b) most importantly, after years of
		1267	experience we found that object serialisation is causing more problems
		1268	than it solves: Just like function calls, objects simply do not travel
		1269	easily over the network, mostly because they will always be a copy, so you
		1270	always have to re-think your design.
321		1271
322	=item eval => $string[ @reply]	1272	Keeping your messages simple, concentrating on data structures rather than
323		1273	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		1274
341	=back	1275	=back
342		1276
		1277	=head1 PORTING FROM AnyEvent::MP VERSION 1.X
		1278
		1279	AEMP version 2 has a few major incompatible changes compared to version 1:
		1280
		1281	=over 4
		1282
		1283	=item AnyEvent::MP::Global no longer has group management functions.
		1284
		1285	At least not officially - the grp_* functions are still exported and might
		1286	work, but they will be removed in some later release.
		1287
		1288	AnyEvent::MP now comes with a distributed database that is more
		1289	powerful. Its database families map closely to port groups, but the API
		1290	has changed (the functions are also now exported by AnyEvent::MP). Here is
		1291	a rough porting guide:
		1292
		1293	grp_reg $group, $port # old
		1294	db_reg $group, $port # new
		1295
		1296	$list = grp_get $group # old
		1297	db_keys $group, sub { my $list = shift } # new
		1298
		1299	grp_mon $group, $cb->(\@ports, $add, $del) # old
		1300	db_mon $group, $cb->(\%ports, $add, $change, $del) # new
		1301
		1302	C<grp_reg> is a no-brainer (just replace by C<db_reg>), but C<grp_get> is
		1303	no longer instant, because the local node might not have a copy of the
		1304	group. You can either modify your code to allow for a callback, or use
		1305	C<db_mon> to keep an updated copy of the group:
		1306
		1307	my $local_group_copy;
		1308	db_mon $group => sub { $local_group_copy = $_[0] };
		1309
		1310	# now "keys %$local_group_copy" always returns the most up-to-date
		1311	# list of ports in the group.
		1312
		1313	C<grp_mon> can be replaced by C<db_mon> with minor changes - C<db_mon>
		1314	passes a hash as first argument, and an extra C<$chg> argument that can be
		1315	ignored:
		1316
		1317	db_mon $group => sub {
		1318	my ($ports, $add, $chg, $del) = @_;
		1319	$ports = [keys %$ports];
		1320
		1321	# now $ports, $add and $del are the same as
		1322	# were originally passed by grp_mon.
		1323	...
		1324	};
		1325
		1326	=item Nodes not longer connect to all other nodes.
		1327
		1328	In AEMP 1.x, every node automatically loads the L<AnyEvent::MP::Global>
		1329	module, which in turn would create connections to all other nodes in the
		1330	network (helped by the seed nodes).
		1331
		1332	In version 2.x, global nodes still connect to all other global nodes, but
		1333	other nodes don't - now every node either is a global node itself, or
		1334	attaches itself to another global node.
		1335
		1336	If a node isn't a global node itself, then it attaches itself to one
		1337	of its seed nodes. If that seed node isn't a global node yet, it will
		1338	automatically be upgraded to a global node.
		1339
		1340	So in many cases, nothing needs to be changed - one just has to make sure
		1341	that all seed nodes are meshed together with the other seed nodes (as with
		1342	AEMP 1.x), and other nodes specify them as seed nodes. This is most easily
		1343	achieved by specifying the same set of seed nodes for all nodes in the
		1344	network.
		1345
		1346	Not opening a connection to every other node is usually an advantage,
		1347	except when you need the lower latency of an already established
		1348	connection. To ensure a node establishes a connection to another node,
		1349	you can monitor the node port (C<mon $node, ...>), which will attempt to
		1350	create the connection (and notify you when the connection fails).
		1351
		1352	=item Listener-less nodes (nodes without binds) are gone.
		1353
		1354	And are not coming back, at least not in their old form. If no C<binds>
		1355	are specified for a node, AnyEvent::MP assumes a default of C<*:*>.
		1356
		1357	There are vague plans to implement some form of routing domains, which
		1358	might or might not bring back listener-less nodes, but don't count on it.
		1359
		1360	The fact that most connections are now optional somewhat mitigates this,
		1361	as a node can be effectively unreachable from the outside without any
		1362	problems, as long as it isn't a global node and only reaches out to other
		1363	nodes (as opposed to being contacted from other nodes).
		1364
		1365	=item $AnyEvent::MP::Kernel::WARN has gone.
		1366
		1367	AnyEvent has acquired a logging framework (L<AnyEvent::Log>), and AEMP now
		1368	uses this, and so should your programs.
		1369
		1370	Every module now documents what kinds of messages it generates, with
		1371	AnyEvent::MP acting as a catch all.
		1372
		1373	On the positive side, this means that instead of setting
		1374	C<PERL_ANYEVENT_MP_WARNLEVEL>, you can get away by setting C<AE_VERBOSE> -
		1375	much less to type.
		1376
		1377	=back
		1378
		1379	=head1 LOGGING
		1380
		1381	AnyEvent::MP does not normally log anything by itself, but since it is the
		1382	root of the context hierarchy for AnyEvent::MP modules, it will receive
		1383	all log messages by submodules.
		1384
343	=head1 SEE ALSO	1385	=head1 SEE ALSO
		1386
		1387	L<AnyEvent::MP::Intro> - a gentle introduction.
		1388
		1389	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1390
		1391	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1392	your applications.
		1393
		1394	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1395
		1396	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1397	all nodes.
344		1398
345	L<AnyEvent>.	1399	L<AnyEvent>.
346		1400
347	=head1 AUTHOR	1401	=head1 AUTHOR
348		1402

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