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Revision 1.17 by root, Mon Aug 3 08:35:40 2009 UTC vs.
Revision 1.143 by root, Fri Mar 23 17:54:36 2012 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent::MP - multi-processing/message-passing framework	3	AnyEvent::MP - erlang-style multi-processing/message-passing framework
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::MP;	7	use AnyEvent::MP;
8		8
9	NODE # returns this node identifier
10	$NODE # contains this node identifier	9	$NODE # contains this node's node ID
		10	NODE # returns this node's node ID
11		11
		12	$SELF # receiving/own port id in rcv callbacks
		13
		14	# initialise the node so it can send/receive messages
		15	configure;
		16
		17	# ports are message destinations
		18
		19	# sending messages
12	snd $port, type => data...;	20	snd $port, type => data...;
		21	snd $port, @msg;
		22	snd @msg_with_first_element_being_a_port;
13		23
14	rcv $port, smartmatch => $cb->($port, @msg);	24	# creating/using ports, the simple way
		25	my $simple_port = port { my @msg = @_ };
15		26
16	# examples:	27	# creating/using ports, tagged message matching
		28	my $port = port;
17	rcv $port2, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
18	rcv $port1, pong => sub { warn "pong received\n" };	30	rcv $port, pong => sub { warn "pong received\n" };
19	snd $port2, ping => $port1;
20		31
21	# more, smarter, matches (_any_ is exported by this module)	32	# create a port on another node
22	rcv $port, [child_died => $pid] => sub { ...	33	my $port = spawn $node, $initfunc, @initdata;
23	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3	34
		35	# destroy a port again
		36	kil $port; # "normal" kill
		37	kil $port, my_error => "everything is broken"; # error kill
		38
		39	# monitoring
		40	mon $port, $cb->(@msg) # callback is invoked on death
		41	mon $port, $localport # kill localport on abnormal death
		42	mon $port, $localport, @msg # send message on death
		43
		44	# temporarily execute code in port context
		45	peval $port, sub { die "kill the port!" };
		46
		47	# execute callbacks in $SELF port context
		48	my $timer = AE::timer 1, 0, psub {
		49	die "kill the port, delayed";
		50	};
		51
		52	# 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 thta accepts conenctions form 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 cna 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 form are part of
		137	the same network. If a network is split into multiple subnets because e.g.
		138	the network link between the parts goes down, then using the same seed
		139	nodes 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 makign 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(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
78		189
79	use common::sense;	190	use common::sense;
80		191
81	use Carp ();	192	use Carp ();
82		193
83	use AE ();	194	use AnyEvent ();
		195	use Guard ();
84		196
85	use base "Exporter";	197	use base "Exporter";
86		198
87	our $VERSION = '0.02';	199	our $VERSION = $AnyEvent::MP::Config::VERSION;
		200
88	our @EXPORT = qw(	201	our @EXPORT = qw(
89	NODE $NODE $PORT snd rcv _any_	202	NODE $NODE *SELF node_of after
90	create_port create_port_on	203	configure
91	create_miniport	204	snd rcv mon mon_guard kil psub peval spawn cal
92	become_slave become_public	205	port
		206	db_set db_del db_reg
		207	db_mon db_family db_keys db_values
93	);	208	);
94		209
		210	our $SELF;
		211
		212	sub _self_die() {
		213	my $msg = $@;
		214	$msg =~ s/\n+$// unless ref $msg;
		215	kil $SELF, die => $msg;
		216	}
		217
95	=item NODE / $NODE	218	=item $thisnode = NODE / $NODE
96		219
97	The C<NODE ()> function and the C<$NODE> variable contain the noderef of	220	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	221	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.	222	a call to C<configure>.
100		223
		224	=item $nodeid = node_of $port
		225
		226	Extracts and returns the node ID from a port ID or a node ID.
		227
		228	=item configure $profile, key => value...
		229
		230	=item configure key => value...
		231
		232	Before a node can talk to other nodes on the network (i.e. enter
		233	"distributed mode") it has to configure itself - the minimum a node needs
		234	to know is its own name, and optionally it should know the addresses of
		235	some other nodes in the network to discover other nodes.
		236
		237	This function configures a node - it must be called exactly once (or
		238	never) before calling other AnyEvent::MP functions.
		239
		240	The key/value pairs are basically the same ones as documented for the
		241	F<aemp> command line utility (sans the set/del prefix), with these additions:
		242
		243	=over 4
		244
		245	=item norc => $boolean (default false)
		246
		247	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
		248	be consulted - all configuraiton options must be specified in the
		249	C<configure> call.
		250
		251	=item force => $boolean (default false)
		252
		253	IF true, then the values specified in the C<configure> will take
		254	precedence over any values configured via the rc file. The default is for
		255	the rc file to override any options specified in the program.
		256
		257	=back
		258
		259	=over 4
		260
		261	=item step 1, gathering configuration from profiles
		262
		263	The function first looks up a profile in the aemp configuration (see the
		264	L<aemp> commandline utility). The profile name can be specified via the
		265	named C<profile> parameter or can simply be the first parameter). If it is
		266	missing, then the nodename (F<uname -n>) will be used as profile name.
		267
		268	The profile data is then gathered as follows:
		269
		270	First, all remaining key => value pairs (all of which are conveniently
		271	undocumented at the moment) will be interpreted as configuration
		272	data. Then they will be overwritten by any values specified in the global
		273	default configuration (see the F<aemp> utility), then the chain of
		274	profiles chosen by the profile name (and any C<parent> attributes).
		275
		276	That means that the values specified in the profile have highest priority
		277	and the values specified directly via C<configure> have lowest priority,
		278	and can only be used to specify defaults.
		279
		280	If the profile specifies a node ID, then this will become the node ID of
		281	this process. If not, then the profile name will be used as node ID, with
		282	a unique randoms tring (C</%u>) appended.
		283
		284	The node ID can contain some C<%> sequences that are expanded: C<%n>
		285	is expanded to the local nodename, C<%u> is replaced by a random
		286	strign to make the node unique. For example, the F<aemp> commandline
		287	utility uses C<aemp/%n/%u> as nodename, which might expand to
		288	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		289
		290	=item step 2, bind listener sockets
		291
		292	The next step is to look up the binds in the profile, followed by binding
		293	aemp protocol listeners on all binds specified (it is possible and valid
		294	to have no binds, meaning that the node cannot be contacted form the
		295	outside. This means the node cannot talk to other nodes that also have no
		296	binds, but it can still talk to all "normal" nodes).
		297
		298	If the profile does not specify a binds list, then a default of C<*> is
		299	used, meaning the node will bind on a dynamically-assigned port on every
		300	local IP address it finds.
		301
		302	=item step 3, connect to seed nodes
		303
		304	As the last step, the seed ID list from the profile is passed to the
		305	L<AnyEvent::MP::Global> module, which will then use it to keep
		306	connectivity with at least one node at any point in time.
		307
		308	=back
		309
		310	Example: become a distributed node using the local node name as profile.
		311	This should be the most common form of invocation for "daemon"-type nodes.
		312
		313	configure
		314
		315	Example: become a semi-anonymous node. This form is often used for
		316	commandline clients.
		317
		318	configure nodeid => "myscript/%n/%u";
		319
		320	Example: configure a node using a profile called seed, which is suitable
		321	for a seed node as it binds on all local addresses on a fixed port (4040,
		322	customary for aemp).
		323
		324	# use the aemp commandline utility
		325	# aemp profile seed binds '*:4040'
		326
		327	# then use it
		328	configure profile => "seed";
		329
		330	# or simply use aemp from the shell again:
		331	# aemp run profile seed
		332
		333	# or provide a nicer-to-remember nodeid
		334	# aemp run profile seed nodeid "$(hostname)"
		335
		336	=item $SELF
		337
		338	Contains the current port id while executing C<rcv> callbacks or C<psub>
		339	blocks.
		340
		341	=item *SELF, SELF, %SELF, @SELF...
		342
		343	Due to some quirks in how perl exports variables, it is impossible to
		344	just export C<$SELF>, all the symbols named C<SELF> are exported by this
		345	module, but only C<$SELF> is currently used.
		346
101	=item snd $portid, type => @data	347	=item snd $port, type => @data
102		348
103	=item snd $portid, @msg	349	=item snd $port, @msg
104		350
105	Send the given message to the given port ID, which can identify either	351	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	352	local or a remote port, and must be a port ID.
107	stringifies a sa port ID (such as a port object :).
108		353
109	While the message can be about anything, it is highly recommended to use a	354	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	355	use a string as first element (a port ID, or some word that indicates a
111	type etc.).	356	request type etc.) and to consist if only simple perl values (scalars,
		357	arrays, hashes) - if you think you need to pass an object, think again.
112		358
113	The message data effectively becomes read-only after a call to this	359	The message data logically becomes read-only after a call to this
114	function: modifying any argument is not allowed and can cause many	360	function: modifying any argument (or values referenced by them) is
115	problems.	361	forbidden, as there can be considerable time between the call to C<snd>
		362	and the time the message is actually being serialised - in fact, it might
		363	never be copied as within the same process it is simply handed to the
		364	receiving port.
116		365
117	The type of data you can transfer depends on the transport protocol: when	366	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	367	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	368	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	369	that Storable can serialise and deserialise is allowed, and for the local
121	node, anything can be passed.	370	node, anything can be passed. Best rely only on the common denominator of
		371	these.
122		372
123	=item $local_port = create_port	373	=item $local_port = port
124		374
125	Create a new local port object. See the next section for allowed methods.	375	Create a new local port object and returns its port ID. Initially it has
		376	no callbacks set and will throw an error when it receives messages.
		377
		378	=item $local_port = port { my @msg = @_ }
		379
		380	Creates a new local port, and returns its ID. Semantically the same as
		381	creating a port and calling C<rcv $port, $callback> on it.
		382
		383	The block will be called for every message received on the port, with the
		384	global variable C<$SELF> set to the port ID. Runtime errors will cause the
		385	port to be C<kil>ed. The message will be passed as-is, no extra argument
		386	(i.e. no port ID) will be passed to the callback.
		387
		388	If you want to stop/destroy the port, simply C<kil> it:
		389
		390	my $port = port {
		391	my @msg = @_;
		392	...
		393	kil $SELF;
		394	};
126		395
127	=cut	396	=cut
128		397
129	sub create_port {	398	sub rcv($@);
130	my $id = "$AnyEvent::MP::Base::UNIQ." . $AnyEvent::MP::Base::ID++;
131		399
132	my $self = bless {	400	my $KILME = sub {
133	id => "$NODE#$id",	401	(my $tag = substr $_[0], 0, 30) =~ s/([\x20-\x7e])/./g;
134	names => [$id],	402	kil $SELF, unhandled_message => "no callback found for message '$tag'";
135	}, "AnyEvent::MP::Port";	403	};
136		404
137	$AnyEvent::MP::Base::PORT{$id} = sub {	405	sub port(;&) {
138	unshift @_, $self;	406	my $id = $UNIQ . ++$ID;
		407	my $port = "$NODE#$id";
139		408
140	for (@{ $self->{rc0}{$_[1]} }) {	409	rcv $port, shift || $KILME;
141	$_ && &{$_->[0]}	410
142	&& undef $_;	411	$port
		412	}
		413
		414	=item rcv $local_port, $callback->(@msg)
		415
		416	Replaces the default callback on the specified port. There is no way to
		417	remove the default callback: use C<sub { }> to disable it, or better
		418	C<kil> the port when it is no longer needed.
		419
		420	The global C<$SELF> (exported by this module) contains C<$port> while
		421	executing the callback. Runtime errors during callback execution will
		422	result in the port being C<kil>ed.
		423
		424	The default callback receives all messages not matched by a more specific
		425	C<tag> match.
		426
		427	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
		428
		429	Register (or replace) callbacks to be called on messages starting with the
		430	given tag on the given port (and return the port), or unregister it (when
		431	C<$callback> is C<$undef> or missing). There can only be one callback
		432	registered for each tag.
		433
		434	The original message will be passed to the callback, after the first
		435	element (the tag) has been removed. The callback will use the same
		436	environment as the default callback (see above).
		437
		438	Example: create a port and bind receivers on it in one go.
		439
		440	my $port = rcv port,
		441	msg1 => sub { ... },
		442	msg2 => sub { ... },
		443	;
		444
		445	Example: create a port, bind receivers and send it in a message elsewhere
		446	in one go:
		447
		448	snd $otherport, reply =>
		449	rcv port,
		450	msg1 => sub { ... },
		451	...
		452	;
		453
		454	Example: temporarily register a rcv callback for a tag matching some port
		455	(e.g. for an rpc reply) and unregister it after a message was received.
		456
		457	rcv $port, $otherport => sub {
		458	my @reply = @_;
		459
		460	rcv $SELF, $otherport;
		461	};
		462
		463	=cut
		464
		465	sub rcv($@) {
		466	my $port = shift;
		467	my ($nodeid, $portid) = split /#/, $port, 2;
		468
		469	$NODE{$nodeid} == $NODE{""}
		470	or Carp::croak "$port: rcv can only be called on local ports, caught";
		471
		472	while (@_) {
		473	if (ref $_[0]) {
		474	if (my $self = $PORT_DATA{$portid}) {
		475	"AnyEvent::MP::Port" eq ref $self
		476	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		477
		478	$self->[0] = shift;
		479	} else {
		480	my $cb = shift;
		481	$PORT{$portid} = sub {
		482	local $SELF = $port;
		483	eval { &$cb }; _self_die if $@;
		484	};
		485	}
		486	} elsif (defined $_[0]) {
		487	my $self = $PORT_DATA{$portid} ||= do {
		488	my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port";
		489
		490	$PORT{$portid} = sub {
		491	local $SELF = $port;
		492
		493	if (my $cb = $self->[1]{$_[0]}) {
		494	shift;
		495	eval { &$cb }; _self_die if $@;
		496	} else {
		497	&{ $self->[0] };
		498	}
		499	};
		500
		501	$self
		502	};
		503
		504	"AnyEvent::MP::Port" eq ref $self
		505	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		506
		507	my ($tag, $cb) = splice @_, 0, 2;
		508
		509	if (defined $cb) {
		510	$self->[1]{$tag} = $cb;
		511	} else {
		512	delete $self->[1]{$tag};
		513	}
143	}	514	}
		515	}
144		516
145	for (@{ $self->{rcv}{$_[1]} }) {	517	$port
146	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]	518	}
147	&& &{$_->[0]}
148	&& undef $_;
149	}
150		519
151	for (@{ $self->{any} }) {	520	=item peval $port, $coderef[, @args]
152	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]	521
153	&& &{$_->[0]}	522	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
154	&& undef $_;	523	when the code throews an exception the C<$port> will be killed.
155	}	524
		525	Any remaining args will be passed to the callback. Any return values will
		526	be returned to the caller.
		527
		528	This is useful when you temporarily want to execute code in the context of
		529	a port.
		530
		531	Example: create a port and run some initialisation code in it's context.
		532
		533	my $port = port { ... };
		534
		535	peval $port, sub {
		536	init
		537	or die "unable to init";
156	};	538	};
157		539
158	$self
159	}
160
161	=item $portid = miniport { my @msg = @_; $finished }
162
163	Creates a "mini port", that is, a very lightweight port without any
164	pattern matching behind it, and returns its ID.
165
166	The block will be called for every message received on the port. When the
167	callback returns a true value its job is considered "done" and the port
168	will be destroyed. Otherwise it will stay alive.
169
170	The message will be passed as-is, no extra argument (i.e. no port id) will
171	be passed to the callback.
172
173	If you need the local port id in the callback, this works nicely:
174
175	my $port; $port = miniport {
176	snd $otherport, reply => $port;
177	};
178
179	=cut	540	=cut
180		541
181	sub miniport(&) {	542	sub peval($$) {
		543	local $SELF = shift;
182	my $cb = shift;	544	my $cb = shift;
183	my $id = "$AnyEvent::MP::Base::UNIQ." . $AnyEvent::MP::Base::ID++;
184		545
185	$AnyEvent::MP::Base::PORT{$id} = sub {	546	if (wantarray) {
186	&$cb	547	my @res = eval { &$cb };
187	and delete $AnyEvent::MP::Base::PORT{$id};	548	_self_die if $@;
188	};	549	@res
189
190	"$NODE#$id"
191	}
192
193	package AnyEvent::MP::Port;
194
195	=back
196
197	=head1 METHODS FOR PORT OBJECTS
198
199	=over 4
200
201	=item "$port"
202
203	A port object stringifies to its port ID, so can be used directly for
204	C<snd> operations.
205
206	=cut
207
208	use overload
209	'""' => sub { $_[0]{id} },
210	fallback => 1;
211
212	=item $port->rcv (type => $callback->($port, @msg))
213
214	=item $port->rcv ($smartmatch => $callback->($port, @msg))
215
216	=item $port->rcv ([$smartmatch...] => $callback->($port, @msg))
217
218	Register a callback on the given port.
219
220	The callback has to return a true value when its work is done, after
221	which is will be removed, or a false value in which case it will stay
222	registered.
223
224	If the match is an array reference, then it will be matched against the
225	first elements of the message, otherwise only the first element is being
226	matched.
227
228	Any element in the match that is specified as C<_any_> (a function
229	exported by this module) matches any single element of the message.
230
231	While not required, it is highly recommended that the first matching
232	element is a string identifying the message. The one-string-only match is
233	also the most efficient match (by far).
234
235	=cut
236
237	sub rcv($@) {
238	my ($self, $match, $cb) = @_;
239
240	if (!ref $match) {
241	push @{ $self->{rc0}{$match} }, [$cb];
242	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
243	my ($type, @match) = @$match;
244	@match
245	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
246	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
247	} else {	550	} else {
248	push @{ $self->{any} }, [$cb, $match];	551	my $res = eval { &$cb };
		552	_self_die if $@;
		553	$res
249	}	554	}
250	}	555	}
251		556
252	=item $port->register ($name)	557	=item $closure = psub { BLOCK }
253		558
254	Registers the given port under the well known name C<$name>. If the name	559	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
255	already exists it is replaced.	560	closure is executed, sets up the environment in the same way as in C<rcv>
		561	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
256		562
257	A port can only be registered under one well known name.	563	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		564	BLOCK }, @_ } >>.
		565
		566	This is useful when you register callbacks from C<rcv> callbacks:
		567
		568	rcv delayed_reply => sub {
		569	my ($delay, @reply) = @_;
		570	my $timer = AE::timer $delay, 0, psub {
		571	snd @reply, $SELF;
		572	};
		573	};
258		574
259	=cut	575	=cut
260		576
261	sub register {	577	sub psub(&) {
262	my ($self, $name) = @_;	578	my $cb = shift;
263		579
264	$self->{wkname} = $name;	580	my $port = $SELF
265	$AnyEvent::MP::Base::WKP{$name} = "$self";	581	or Carp::croak "psub can only be called from within rcv or psub callbacks, not";
		582
		583	sub {
		584	local $SELF = $port;
		585
		586	if (wantarray) {
		587	my @res = eval { &$cb };
		588	_self_die if $@;
		589	@res
		590	} else {
		591	my $res = eval { &$cb };
		592	_self_die if $@;
		593	$res
		594	}
		595	}
266	}	596	}
267		597
268	=item $port->destroy	598	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
269		599
270	Explicitly destroy/remove/nuke/vaporise the port.	600	=item $guard = mon $port # kill $SELF when $port dies
271		601
272	Ports are normally kept alive by there mere existance alone, and need to	602	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
273	be destroyed explicitly.	603
		604	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		605
		606	Monitor the given port and do something when the port is killed or
		607	messages to it were lost, and optionally return a guard that can be used
		608	to stop monitoring again.
		609
		610	The first two forms distinguish between "normal" and "abnormal" kil's:
		611
		612	In the first form (another port given), if the C<$port> is C<kil>'ed with
		613	a non-empty reason, the other port (C<$rcvport>) will be kil'ed with the
		614	same reason. That is, on "normal" kil's nothing happens, while under all
		615	other conditions, the other port is killed with the same reason.
		616
		617	The second form (kill self) is the same as the first form, except that
		618	C<$rvport> defaults to C<$SELF>.
		619
		620	The remaining forms don't distinguish between "normal" and "abnormal" kil's
		621	- it's up to the callback or receiver to check whether the C<@reason> is
		622	empty and act accordingly.
		623
		624	In the third form (callback), the callback is simply called with any
		625	number of C<@reason> elements (empty @reason means that the port was deleted
		626	"normally"). Note also that I<< the callback B<must> never die >>, so use
		627	C<eval> if unsure.
		628
		629	In the last form (message), a message of the form C<$rcvport, @msg,
		630	@reason> will be C<snd>.
		631
		632	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		633	alert was raised), they are removed and will not trigger again, even if it
		634	turns out that the port is still alive.
		635
		636	As a rule of thumb, monitoring requests should always monitor a remote
		637	port locally (using a local C<$rcvport> or a callback). The reason is that
		638	kill messages might get lost, just like any other message. Another less
		639	obvious reason is that even monitoring requests can get lost (for example,
		640	when the connection to the other node goes down permanently). When
		641	monitoring a port locally these problems do not exist.
		642
		643	C<mon> effectively guarantees that, in the absence of hardware failures,
		644	after starting the monitor, either all messages sent to the port will
		645	arrive, or the monitoring action will be invoked after possible message
		646	loss has been detected. No messages will be lost "in between" (after
		647	the first lost message no further messages will be received by the
		648	port). After the monitoring action was invoked, further messages might get
		649	delivered again.
		650
		651	Inter-host-connection timeouts and monitoring depend on the transport
		652	used. The only transport currently implemented is TCP, and AnyEvent::MP
		653	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		654	non-idle connection, and usually around two hours for idle connections).
		655
		656	This means that monitoring is good for program errors and cleaning up
		657	stuff eventually, but they are no replacement for a timeout when you need
		658	to ensure some maximum latency.
		659
		660	Example: call a given callback when C<$port> is killed.
		661
		662	mon $port, sub { warn "port died because of <@_>\n" };
		663
		664	Example: kill ourselves when C<$port> is killed abnormally.
		665
		666	mon $port;
		667
		668	Example: send us a restart message when another C<$port> is killed.
		669
		670	mon $port, $self => "restart";
274		671
275	=cut	672	=cut
276		673
277	sub destroy {	674	sub mon {
278	my ($self) = @_;	675	my ($nodeid, $port) = split /#/, shift, 2;
279		676
280	delete $AnyEvent::MP::Base::WKP{ $self->{wkname} };	677	my $node = $NODE{$nodeid} || add_node $nodeid;
281		678
282	delete $AnyEvent::MP::Base::PORT{$_}	679	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
283	for @{ $self->{names} };	680
		681	unless (ref $cb) {
		682	if (@_) {
		683	# send a kill info message
		684	my (@msg) = ($cb, @_);
		685	$cb = sub { snd @msg, @_ };
		686	} else {
		687	# simply kill other port
		688	my $port = $cb;
		689	$cb = sub { kil $port, @_ if @_ };
		690	}
		691	}
		692
		693	$node->monitor ($port, $cb);
		694
		695	defined wantarray
		696	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
284	}	697	}
285		698
		699	=item $guard = mon_guard $port, $ref, $ref...
		700
		701	Monitors the given C<$port> and keeps the passed references. When the port
		702	is killed, the references will be freed.
		703
		704	Optionally returns a guard that will stop the monitoring.
		705
		706	This function is useful when you create e.g. timers or other watchers and
		707	want to free them when the port gets killed (note the use of C<psub>):
		708
		709	$port->rcv (start => sub {
		710	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
		711	undef $timer if 0.9 < rand;
		712	});
		713	});
		714
		715	=cut
		716
		717	sub mon_guard {
		718	my ($port, @refs) = @_;
		719
		720	#TODO: mon-less form?
		721
		722	mon $port, sub { 0 && @refs }
		723	}
		724
		725	=item kil $port[, @reason]
		726
		727	Kill the specified port with the given C<@reason>.
		728
		729	If no C<@reason> is specified, then the port is killed "normally" -
		730	monitor callback will be invoked, but the kil will not cause linked ports
		731	(C<mon $mport, $lport> form) to get killed.
		732
		733	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
		734	form) get killed with the same reason.
		735
		736	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		737	will be reported as reason C<< die => $@ >>.
		738
		739	Transport/communication errors are reported as C<< transport_error =>
		740	$message >>.
		741
		742	Common idioms:
		743
		744	# silently remove yourself, do not kill linked ports
		745	kil $SELF;
		746
		747	# report a failure in some detail
		748	kil $SELF, failure_mode_1 => "it failed with too high temperature";
		749
		750	# do not waste much time with killing, just die when something goes wrong
		751	open my $fh, "<file"
		752	or die "file: $!";
		753
		754	=item $port = spawn $node, $initfunc[, @initdata]
		755
		756	Creates a port on the node C<$node> (which can also be a port ID, in which
		757	case it's the node where that port resides).
		758
		759	The port ID of the newly created port is returned immediately, and it is
		760	possible to immediately start sending messages or to monitor the port.
		761
		762	After the port has been created, the init function is called on the remote
		763	node, in the same context as a C<rcv> callback. This function must be a
		764	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		765	specify a function in the main program, use C<::name>.
		766
		767	If the function doesn't exist, then the node tries to C<require>
		768	the package, then the package above the package and so on (e.g.
		769	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		770	exists or it runs out of package names.
		771
		772	The init function is then called with the newly-created port as context
		773	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		774	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		775	the port might not get created.
		776
		777	A common idiom is to pass a local port, immediately monitor the spawned
		778	port, and in the remote init function, immediately monitor the passed
		779	local port. This two-way monitoring ensures that both ports get cleaned up
		780	when there is a problem.
		781
		782	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		783	caller before C<spawn> returns (by delaying invocation when spawn is
		784	called for the local node).
		785
		786	Example: spawn a chat server port on C<$othernode>.
		787
		788	# this node, executed from within a port context:
		789	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		790	mon $server;
		791
		792	# init function on C<$othernode>
		793	sub connect {
		794	my ($srcport) = @_;
		795
		796	mon $srcport;
		797
		798	rcv $SELF, sub {
		799	...
		800	};
		801	}
		802
		803	=cut
		804
		805	sub _spawn {
		806	my $port = shift;
		807	my $init = shift;
		808
		809	# rcv will create the actual port
		810	local $SELF = "$NODE#$port";
		811	eval {
		812	&{ load_func $init }
		813	};
		814	_self_die if $@;
		815	}
		816
		817	sub spawn(@) {
		818	my ($nodeid, undef) = split /#/, shift, 2;
		819
		820	my $id = $RUNIQ . ++$ID;
		821
		822	$_[0] =~ /::/
		823	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		824
		825	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		826
		827	"$nodeid#$id"
		828	}
		829
		830
		831	=item after $timeout, @msg
		832
		833	=item after $timeout, $callback
		834
		835	Either sends the given message, or call the given callback, after the
		836	specified number of seconds.
		837
		838	This is simply a utility function that comes in handy at times - the
		839	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		840	so it may go away in the future.
		841
		842	=cut
		843
		844	sub after($@) {
		845	my ($timeout, @action) = @_;
		846
		847	my $t; $t = AE::timer $timeout, 0, sub {
		848	undef $t;
		849	ref $action[0]
		850	? $action[0]()
		851	: snd @action;
		852	};
		853	}
		854
		855	#=item $cb2 = timeout $seconds, $cb[, @args]
		856
		857	=item cal $port, @msg, $callback[, $timeout]
		858
		859	A simple form of RPC - sends a message to the given C<$port> with the
		860	given contents (C<@msg>), but adds a reply port to the message.
		861
		862	The reply port is created temporarily just for the purpose of receiving
		863	the reply, and will be C<kil>ed when no longer needed.
		864
		865	A reply message sent to the port is passed to the C<$callback> as-is.
		866
		867	If an optional time-out (in seconds) is given and it is not C<undef>,
		868	then the callback will be called without any arguments after the time-out
		869	elapsed and the port is C<kil>ed.
		870
		871	If no time-out is given (or it is C<undef>), then the local port will
		872	monitor the remote port instead, so it eventually gets cleaned-up.
		873
		874	Currently this function returns the temporary port, but this "feature"
		875	might go in future versions unless you can make a convincing case that
		876	this is indeed useful for something.
		877
		878	=cut
		879
		880	sub cal(@) {
		881	my $timeout = ref $_[-1] ? undef : pop;
		882	my $cb = pop;
		883
		884	my $port = port {
		885	undef $timeout;
		886	kil $SELF;
		887	&$cb;
		888	};
		889
		890	if (defined $timeout) {
		891	$timeout = AE::timer $timeout, 0, sub {
		892	undef $timeout;
		893	kil $port;
		894	$cb->();
		895	};
		896	} else {
		897	mon $_[0], sub {
		898	kil $port;
		899	$cb->();
		900	};
		901	}
		902
		903	push @_, $port;
		904	&snd;
		905
		906	$port
		907	}
		908
286	=back	909	=back
287		910
288	=head1 FUNCTIONS FOR NODES	911	=head1 DISTRIBUTED DATABASE
		912
		913	AnyEvent::MP comes with a simple distributed database. The database will
		914	be mirrored asynchronously on all global nodes. Other nodes bind to one
		915	of the global nodes for their needs. Every node has a "local database"
		916	which contains all the values that are set locally. All local databases
		917	are merged together to form the global database, which can be queried.
		918
		919	The database structure is that of a two-level hash - the database hash
		920	contains hashes which contain values, similarly to a perl hash of hashes,
		921	i.e.:
		922
		923	$DATABASE{$family}{$subkey} = $value
		924
		925	The top level hash key is called "family", and the second-level hash key
		926	is called "subkey" or simply "key".
		927
		928	The family must be alphanumeric, i.e. start with a letter and consist
		929	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		930	pretty much like Perl module names.
		931
		932	As the family namespace is global, it is recommended to prefix family names
		933	with the name of the application or module using it.
		934
		935	The subkeys must be non-empty strings, with no further restrictions.
		936
		937	The values should preferably be strings, but other perl scalars should
		938	work as well (such as C<undef>, arrays and hashes).
		939
		940	Every database entry is owned by one node - adding the same family/subkey
		941	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		942	but the result might be nondeterministic, i.e. the key might have
		943	different values on different nodes.
		944
		945	Different subkeys in the same family can be owned by different nodes
		946	without problems, and in fact, this is the common method to create worker
		947	pools. For example, a worker port for image scaling might do this:
		948
		949	db_set my_image_scalers => $port;
		950
		951	And clients looking for an image scaler will want to get the
		952	C<my_image_scalers> keys from time to time:
		953
		954	db_keys my_image_scalers => sub {
		955	@ports = @{ $_[0] };
		956	};
		957
		958	Or better yet, they want to monitor the database family, so they always
		959	have a reasonable up-to-date copy:
		960
		961	db_mon my_image_scalers => sub {
		962	@ports = keys %{ $_[0] };
		963	};
		964
		965	In general, you can set or delete single subkeys, but query and monitor
		966	whole families only.
		967
		968	If you feel the need to monitor or query a single subkey, try giving it
		969	it's own family.
		970
		971	=over
		972
		973	=item $guard = db_set $family => $subkey [=> $value]
		974
		975	Sets (or replaces) a key to the database - if C<$value> is omitted,
		976	C<undef> is used instead.
		977
		978	When called in non-void context, C<db_set> returns a guard that
		979	automatically calls C<db_del> when it is destroyed.
		980
		981	=item db_del $family => $subkey...
		982
		983	Deletes one or more subkeys from the database family.
		984
		985	=item $guard = db_reg $family => $port => $value
		986
		987	=item $guard = db_reg $family => $port
		988
		989	=item $guard = db_reg $family
		990
		991	Registers a port in the given family and optionally returns a guard to
		992	remove it.
		993
		994	This function basically does the same as:
		995
		996	db_set $family => $port => $value
		997
		998	Except that the port is monitored and automatically removed from the
		999	database family when it is kil'ed.
		1000
		1001	If C<$value> is missing, C<undef> is used. If C<$port> is missing, then
		1002	C<$SELF> is used.
		1003
		1004	This function is most useful to register a port in some port group (which
		1005	is just another name for a database family), and have it removed when the
		1006	port is gone. This works best when the port is a local port.
		1007
		1008	=cut
		1009
		1010	sub db_reg($$;$) {
		1011	my $family = shift;
		1012	my $port = @_ ? shift : $SELF;
		1013
		1014	my $clr = sub { db_del $family => $port };
		1015	mon $port, $clr;
		1016
		1017	db_set $family => $port => $_[0];
		1018
		1019	defined wantarray
		1020	and &Guard::guard ($clr)
		1021	}
		1022
		1023	=item db_family $family => $cb->(\%familyhash)
		1024
		1025	Queries the named database C<$family> and call the callback with the
		1026	family represented as a hash. You can keep and freely modify the hash.
		1027
		1028	=item db_keys $family => $cb->(\@keys)
		1029
		1030	Same as C<db_family>, except it only queries the family I<subkeys> and passes
		1031	them as array reference to the callback.
		1032
		1033	=item db_values $family => $cb->(\@values)
		1034
		1035	Same as C<db_family>, except it only queries the family I<values> and passes them
		1036	as array reference to the callback.
		1037
		1038	=item $guard = db_mon $family => $cb->(\%familyhash, \@added, \@changed, \@deleted)
		1039
		1040	Creates a monitor on the given database family. Each time a key is set
		1041	or or is deleted the callback is called with a hash containing the
		1042	database family and three lists of added, changed and deleted subkeys,
		1043	respectively. If no keys have changed then the array reference might be
		1044	C<undef> or even missing.
		1045
		1046	If not called in void context, a guard object is returned that, when
		1047	destroyed, stops the monitor.
		1048
		1049	The family hash reference and the key arrays belong to AnyEvent::MP and
		1050	B<must not be modified or stored> by the callback. When in doubt, make a
		1051	copy.
		1052
		1053	As soon as possible after the monitoring starts, the callback will be
		1054	called with the intiial contents of the family, even if it is empty,
		1055	i.e. there will always be a timely call to the callback with the current
		1056	contents.
		1057
		1058	It is possible that the callback is called with a change event even though
		1059	the subkey is already present and the value has not changed.
		1060
		1061	The monitoring stops when the guard object is destroyed.
		1062
		1063	Example: on every change to the family "mygroup", print out all keys.
		1064
		1065	my $guard = db_mon mygroup => sub {
		1066	my ($family, $a, $c, $d) = @_;
		1067	print "mygroup members: ", (join " ", keys %$family), "\n";
		1068	};
		1069
		1070	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1071
		1072	my $guard; $guard = db_mon My::Module::workers => sub {
		1073	my ($family, $a, $c, $d) = @_;
		1074	return unless %$family;
		1075	undef $guard;
		1076	print "My::Module::workers now nonempty\n";
		1077	};
		1078
		1079	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		1080
		1081	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		1082	my ($family, $a, $c, $d) = @_;
		1083
		1084	print "+$_=$family->{$_}\n" for @$a;
		1085	print "*$_=$family->{$_}\n" for @$c;
		1086	print "-$_=$family->{$_}\n" for @$d;
		1087	};
		1088
		1089	=cut
		1090
		1091	=back
		1092
		1093	=head1 AnyEvent::MP vs. Distributed Erlang
		1094
		1095	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
		1096	== aemp node, Erlang process == aemp port), so many of the documents and
		1097	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
		1098	sample:
		1099
		1100	http://www.erlang.se/doc/programming_rules.shtml
		1101	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
		1102	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
		1103	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
		1104
		1105	Despite the similarities, there are also some important differences:
289		1106
290	=over 4	1107	=over 4
291		1108
292	=item mon $noderef, $callback->($noderef, $status, $)	1109	=item * Node IDs are arbitrary strings in AEMP.
293		1110
294	Monitors the given noderef.	1111	Erlang relies on special naming and DNS to work everywhere in the same
		1112	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
		1113	configuration or DNS), and possibly the addresses of some seed nodes, but
		1114	will otherwise discover other nodes (and their IDs) itself.
295		1115
296	=item become_public endpoint...	1116	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
		1117	uses "local ports are like remote ports".
297		1118
298	Tells the node to become a public node, i.e. reachable from other nodes.	1119	The failure modes for local ports are quite different (runtime errors
		1120	only) then for remote ports - when a local port dies, you I<know> it dies,
		1121	when a connection to another node dies, you know nothing about the other
		1122	port.
299		1123
300	If no arguments are given, or the first argument is C<undef>, then	1124	Erlang pretends remote ports are as reliable as local ports, even when
301	AnyEvent::MP tries to bind on port C<4040> on all IP addresses that the	1125	they are not.
302	local nodename resolves to.
303		1126
304	Otherwise the first argument must be an array-reference with transport	1127	AEMP encourages a "treat remote ports differently" philosophy, with local
305	endpoints ("ip:port", "hostname:port") or port numbers (in which case the	1128	ports being the special case/exception, where transport errors cannot
306	local nodename is used as hostname). The endpoints are all resolved and	1129	occur.
307	will become the node reference.
308		1130
309	=cut	1131	=item * Erlang uses processes and a mailbox, AEMP does not queue.
		1132
		1133	Erlang uses processes that selectively receive messages out of order, and
		1134	therefore needs a queue. AEMP is event based, queuing messages would serve
		1135	no useful purpose. For the same reason the pattern-matching abilities
		1136	of AnyEvent::MP are more limited, as there is little need to be able to
		1137	filter messages without dequeuing them.
		1138
		1139	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1140	being event-based, while Erlang is process-based.
		1141
		1142	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1143	top of AEMP and Coro threads.
		1144
		1145	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
		1146
		1147	Sending messages in Erlang is synchronous and blocks the process until
		1148	a conenction has been established and the message sent (and so does not
		1149	need a queue that can overflow). AEMP sends return immediately, connection
		1150	establishment is handled in the background.
		1151
		1152	=item * Erlang suffers from silent message loss, AEMP does not.
		1153
		1154	Erlang implements few guarantees on messages delivery - messages can get
		1155	lost without any of the processes realising it (i.e. you send messages a,
		1156	b, and c, and the other side only receives messages a and c).
		1157
		1158	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1159	guarantee that after one message is lost, all following ones sent to the
		1160	same port are lost as well, until monitoring raises an error, so there are
		1161	no silent "holes" in the message sequence.
		1162
		1163	If you want your software to be very reliable, you have to cope with
		1164	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
		1165	simply tries to work better in common error cases, such as when a network
		1166	link goes down.
		1167
		1168	=item * Erlang can send messages to the wrong port, AEMP does not.
		1169
		1170	In Erlang it is quite likely that a node that restarts reuses an Erlang
		1171	process ID known to other nodes for a completely different process,
		1172	causing messages destined for that process to end up in an unrelated
		1173	process.
		1174
		1175	AEMP does not reuse port IDs, so old messages or old port IDs floating
		1176	around in the network will not be sent to an unrelated port.
		1177
		1178	=item * Erlang uses unprotected connections, AEMP uses secure
		1179	authentication and can use TLS.
		1180
		1181	AEMP can use a proven protocol - TLS - to protect connections and
		1182	securely authenticate nodes.
		1183
		1184	=item * The AEMP protocol is optimised for both text-based and binary
		1185	communications.
		1186
		1187	The AEMP protocol, unlike the Erlang protocol, supports both programming
		1188	language independent text-only protocols (good for debugging), and binary,
		1189	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1190	used, the protocol is actually completely text-based.
		1191
		1192	It has also been carefully designed to be implementable in other languages
		1193	with a minimum of work while gracefully degrading functionality to make the
		1194	protocol simple.
		1195
		1196	=item * AEMP has more flexible monitoring options than Erlang.
		1197
		1198	In Erlang, you can chose to receive I<all> exit signals as messages or
		1199	I<none>, there is no in-between, so monitoring single Erlang processes is
		1200	difficult to implement.
		1201
		1202	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1203	between automatic kill, exit message or callback on a per-port basis.
		1204
		1205	=item * Erlang tries to hide remote/local connections, AEMP does not.
		1206
		1207	Monitoring in Erlang is not an indicator of process death/crashes, in the
		1208	same way as linking is (except linking is unreliable in Erlang).
		1209
		1210	In AEMP, you don't "look up" registered port names or send to named ports
		1211	that might or might not be persistent. Instead, you normally spawn a port
		1212	on the remote node. The init function monitors you, and you monitor the
		1213	remote port. Since both monitors are local to the node, they are much more
		1214	reliable (no need for C<spawn_link>).
		1215
		1216	This also saves round-trips and avoids sending messages to the wrong port
		1217	(hard to do in Erlang).
310		1218
311	=back	1219	=back
312		1220
313	=head1 NODE MESSAGES	1221	=head1 RATIONALE
314
315	Nodes understand the following messages sent to them. Many of them take
316	arguments called C<@reply>, which will simply be used to compose a reply
317	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
318	the remaining arguments are simply the message data.
319		1222
320	=over 4	1223	=over 4
321		1224
322	=cut	1225	=item Why strings for port and node IDs, why not objects?
323		1226
324	=item wkp => $name, @reply	1227	We considered "objects", but found that the actual number of methods
		1228	that can be called are quite low. Since port and node IDs travel over
		1229	the network frequently, the serialising/deserialising would add lots of
		1230	overhead, as well as having to keep a proxy object everywhere.
325		1231
326	Replies with the port ID of the specified well-known port, or C<undef>.	1232	Strings can easily be printed, easily serialised etc. and need no special
		1233	procedures to be "valid".
327		1234
328	=item devnull => ...	1235	And as a result, a port with just a default receiver consists of a single
		1236	code reference stored in a global hash - it can't become much cheaper.
329		1237
330	Generic data sink/CPU heat conversion.	1238	=item Why favour JSON, why not a real serialising format such as Storable?
331		1239
332	=item relay => $port, @msg	1240	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1241	format, but currently there is no way to make a node use Storable by
		1242	default (although all nodes will accept it).
333		1243
334	Simply forwards the message to the given port.	1244	The default framing protocol is JSON because a) JSON::XS is many times
		1245	faster for small messages and b) most importantly, after years of
		1246	experience we found that object serialisation is causing more problems
		1247	than it solves: Just like function calls, objects simply do not travel
		1248	easily over the network, mostly because they will always be a copy, so you
		1249	always have to re-think your design.
335		1250
336	=item eval => $string[ @reply]	1251	Keeping your messages simple, concentrating on data structures rather than
337		1252	objects, will keep your messages clean, tidy and efficient.
338	Evaluates the given string. If C<@reply> is given, then a message of the
339	form C<@reply, $@, @evalres> is sent.
340
341	Example: crash another node.
342
343	snd $othernode, eval => "exit";
344
345	=item time => @reply
346
347	Replies the the current node time to C<@reply>.
348
349	Example: tell the current node to send the current time to C<$myport> in a
350	C<timereply> message.
351
352	snd $NODE, time => $myport, timereply => 1, 2;
353	# => snd $myport, timereply => 1, 2, <time>
354		1253
355	=back	1254	=back
356		1255
		1256	=head1 PORTING FROM AnyEvent::MP VERSION 1.X
		1257
		1258	AEMP version 2 has a few major incompatible changes compared to version 1:
		1259
		1260	=over 4
		1261
		1262	=item AnyEvent::MP::Global no longer has group management functions.
		1263
		1264	At least not officially - the grp_* functions are still exported and might
		1265	work, but they will be removed in some later release.
		1266
		1267	AnyEvent::MP now comes with a distributed database that is more
		1268	powerful. Its database families map closely to port groups, but the API
		1269	has changed (the functions are also now exported by AnyEvent::MP). Here is
		1270	a rough porting guide:
		1271
		1272	grp_reg $group, $port # old
		1273	db_reg $group, $port # new
		1274
		1275	$list = grp_get $group # old
		1276	db_keys $group, sub { my $list = shift } # new
		1277
		1278	grp_mon $group, $cb->(\@ports, $add, $del) # old
		1279	db_mon $group, $cb->(\%ports, $add, $change, $del) # new
		1280
		1281	C<grp_reg> is a no-brainer (just replace by C<db_reg>), but C<grp_get> is
		1282	no longer instant, because the local node might not have a copy of the
		1283	group. You can either modify your code to allow for a callback, or use
		1284	C<db_mon> to keep an updated copy of the group:
		1285
		1286	my $local_group_copy;
		1287	db_mon $group => sub { $local_group_copy = $_[0] };
		1288
		1289	# now "keys %$local_group_copy" always returns the most up-to-date
		1290	# list of ports in the group.
		1291
		1292	C<grp_mon> can be replaced by C<db_mon> with minor changes - C<db_mon>
		1293	passes a hash as first argument, and an extra C<$chg> argument that can be
		1294	ignored:
		1295
		1296	db_mon $group => sub {
		1297	my ($ports, $add, $chg, $lde) = @_;
		1298	$ports = [keys %$ports];
		1299
		1300	# now $ports, $add and $del are the same as
		1301	# were originally passed by grp_mon.
		1302	...
		1303	};
		1304
		1305	=item Nodes not longer connect to all other nodes.
		1306
		1307	In AEMP 1.x, every node automatically loads the L<AnyEvent::MP::Global>
		1308	module, which in turn would create connections to all other nodes in the
		1309	network (helped by the seed nodes).
		1310
		1311	In version 2.x, global nodes still connect to all other global nodes, but
		1312	other nodes don't - now every node either is a global node itself, or
		1313	attaches itself to another global node.
		1314
		1315	If a node isn't a global node itself, then it attaches itself to one
		1316	of its seed nodes. If that seed node isn't a global node yet, it will
		1317	automatically be upgraded to a global node.
		1318
		1319	So in many cases, nothing needs to be changed - one just has to make sure
		1320	that all seed nodes are meshed together with the other seed nodes (as with
		1321	AEMP 1.x), and other nodes specify them as seed nodes. This is most easily
		1322	achieved by specifying the same set of seed nodes for all nodes in the
		1323	network.
		1324
		1325	Not opening a connection to every other node is usually an advantage,
		1326	except when you need the lower latency of an already established
		1327	connection. To ensure a node establishes a connection to another node,
		1328	you can monitor the node port (C<mon $node, ...>), which will attempt to
		1329	create the connection (and notify you when the connection fails).
		1330
		1331	=item Listener-less nodes (nodes without binds) are gone.
		1332
		1333	And are not coming back, at least not in their old form. If no C<binds>
		1334	are specified for a node, AnyEvent::MP assumes a default of C<*:*>.
		1335
		1336	There are vague plans to implement some form of routing domains, which
		1337	might or might not bring back listener-less nodes, but don't count on it.
		1338
		1339	The fact that most connections are now optional somewhat mitigates this,
		1340	as a node can be effectively unreachable from the outside without any
		1341	problems, as long as it isn't a global node and only reaches out to other
		1342	nodes (as opposed to being contacted from other nodes).
		1343
		1344	=item $AnyEvent::MP::Kernel::WARN has gone.
		1345
		1346	AnyEvent has acquired a logging framework (L<AnyEvent::Log>), and AEMP now
		1347	uses this, and so should your programs.
		1348
		1349	Every module now documents what kinds of messages it generates, with
		1350	AnyEvent::MP acting as a catch all.
		1351
		1352	On the positive side, this means that instead of setting
		1353	C<PERL_ANYEVENT_MP_WARNLEVEL>, you can get away by setting C<AE_VERBOSE> -
		1354	much less to type.
		1355
		1356	=back
		1357
		1358	=head1 LOGGING
		1359
		1360	AnyEvent::MP does not normally log anything by itself, but sinc eit is the
		1361	root of the contetx hierarchy for AnyEvent::MP modules, it will receive
		1362	all log messages by submodules.
		1363
357	=head1 SEE ALSO	1364	=head1 SEE ALSO
		1365
		1366	L<AnyEvent::MP::Intro> - a gentle introduction.
		1367
		1368	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1369
		1370	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1371	your applications.
		1372
		1373	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1374
		1375	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1376	all nodes.
358		1377
359	L<AnyEvent>.	1378	L<AnyEvent>.
360		1379
361	=head1 AUTHOR	1380	=head1 AUTHOR
362		1381

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