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Revision 1.4 by root, Sat Aug 1 07:36:30 2009 UTC vs.
Revision 1.138 by root, Thu Mar 22 00:48:29 2012 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent::MP - multi-processing/message-passing framework	3	AnyEvent::MP - erlang-style multi-processing/message-passing framework
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::MP;	7	use AnyEvent::MP;
8		8
9	NODE # returns this node identifier
10	$NODE # contains this node identifier	9	$NODE # contains this node's node ID
		10	NODE # returns this node's node ID
11		11
		12	$SELF # receiving/own port id in rcv callbacks
		13
		14	# initialise the node so it can send/receive messages
		15	configure;
		16
		17	# ports are message destinations
		18
		19	# sending messages
12	snd $port, type => data...;	20	snd $port, type => data...;
		21	snd $port, @msg;
		22	snd @msg_with_first_element_being_a_port;
13		23
14	rcv $port, smartmatch => $cb->($port, @msg);	24	# creating/using ports, the simple way
		25	my $simple_port = port { my @msg = @_ };
15		26
16	# examples:	27	# creating/using ports, tagged message matching
		28	my $port = port;
17	rcv $port2, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
18	rcv $port1, pong => sub { warn "pong received\n" };	30	rcv $port, pong => sub { warn "pong received\n" };
19	snd $port2, ping => $port1;
20		31
21	# more, smarter, matches (_any_ is exported by this module)	32	# create a port on another node
22	rcv $port, [child_died => $pid] => sub { ...	33	my $port = spawn $node, $initfunc, @initdata;
23	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3	34
		35	# destroy a port again
		36	kil $port; # "normal" kill
		37	kil $port, my_error => "everything is broken"; # error kill
		38
		39	# monitoring
		40	mon $port, $cb->(@msg) # callback is invoked on death
		41	mon $port, $localport # kill localport on abnormal death
		42	mon $port, $localport, @msg # send message on death
		43
		44	# temporarily execute code in port context
		45	peval $port, sub { die "kill the port!" };
		46
		47	# execute callbacks in $SELF port context
		48	my $timer = AE::timer 1, 0, psub {
		49	die "kill the port, delayed";
		50	};
		51
		52	=head1 CURRENT STATUS
		53
		54	bin/aemp - stable.
		55	AnyEvent::MP - stable API, should work.
		56	AnyEvent::MP::Intro - explains most concepts.
		57	AnyEvent::MP::Kernel - mostly stable API.
		58	AnyEvent::MP::Global - stable API.
24		59
25	=head1 DESCRIPTION	60	=head1 DESCRIPTION
26		61
27	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
28		63
29	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
30	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
		66
		67	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
		68	manual page and the examples under F<eg/>.
31		69
32	=head1 CONCEPTS	70	=head1 CONCEPTS
33		71
34	=over 4	72	=over 4
35		73
36	=item port	74	=item port
37		75
38	A port is something you can send messages to with the C<snd> function, and	76	Not to be confused with a TCP port, a "port" is something you can send
39	you can register C<rcv> handlers with. All C<rcv> handlers will receive	77	messages to (with the C<snd> function).
40	messages they match, messages will not be queued.
41		78
		79	Ports allow you to register C<rcv> handlers that can match all or just
		80	some messages. Messages send to ports will not be queued, regardless of
		81	anything was listening for them or not.
		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
42	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
43		86
44	A port id is always the noderef, a hash-mark (C<#>) as separator, followed	87	A port ID is the concatenation of a node ID, a hash-mark (C<#>)
45	by a port name (a printable string of unspecified format).	88	as separator, and a port name (a printable string of unspecified
		89	format created by AnyEvent::MP).
46		90
47	=item node	91	=item node
48		92
49	A node is a single process containing at least one port - the node	93	A node is a single process containing at least one port - the node port,
50	port. You can send messages to node ports to let them create new ports,	94	which enables nodes to manage each other remotely, and to create new
51	among other things.	95	ports.
52		96
53	Initially, nodes are either private (single-process only) or hidden	97	Nodes are either public (have one or more listening ports) or private
54	(connected to a master node only). Only when they epxlicitly "become	98	(no listening ports). Private nodes cannot talk to other private nodes
55	public" can you send them messages from unrelated other nodes.	99	currently, but all nodes can talk to public nodes.
56		100
57	=item noderef - C<host:port,host:port...>, C<id@noderef, C<id>	101	Nodes is represented by (printable) strings called "node IDs".
58		102
		103	=item node ID - C<[A-Za-z0-9_\-.:]*>
		104
59	A noderef is a string that either uniquely identifies a given node (for	105	A node ID is a string that uniquely identifies the node within a
60	private and hidden nodes), or contains a recipe on how to reach a given	106	network. Depending on the configuration used, node IDs can look like a
61	node (for public nodes).	107	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		108	doesn't interpret node IDs in any way except to uniquely identify a node.
		109
		110	=item binds - C<ip:port>
		111
		112	Nodes can only talk to each other by creating some kind of connection to
		113	each other. To do this, nodes should listen on one or more local transport
		114	endpoints - binds.
		115
		116	Currently, only standard C<ip:port> specifications can be used, which
		117	specify TCP ports to listen on. So a bind is basically just a tcp socket
		118	in listening mode thta accepts conenctions form other nodes.
		119
		120	=item seed nodes
		121
		122	When a node starts, it knows nothing about the network it is in - it
		123	needs to connect to at least one other node that is already in the
		124	network. These other nodes are called "seed nodes".
		125
		126	Seed nodes themselves are not special - they are seed nodes only because
		127	some other node I<uses> them as such, but any node can be used as seed
		128	node for other nodes, and eahc node cna use a different set of seed nodes.
		129
		130	In addition to discovering the network, seed nodes are also used to
		131	maintain the network - all nodes using the same seed node form are part of
		132	the same network. If a network is split into multiple subnets because e.g.
		133	the network link between the parts goes down, then using the same seed
		134	nodes for all nodes ensures that eventually the subnets get merged again.
		135
		136	Seed nodes are expected to be long-running, and at least one seed node
		137	should always be available. They should also be relatively responsive - a
		138	seed node that blocks for long periods will slow down everybody else.
		139
		140	For small networks, it's best if every node uses the same set of seed
		141	nodes. For large networks, it can be useful to specify "regional" seed
		142	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		143	each other. What's important is that all seed nodes connections form a
		144	complete graph, so that the network cannot split into separate subnets
		145	forever.
		146
		147	Seed nodes are represented by seed IDs.
		148
		149	=item seed IDs - C<host:port>
		150
		151	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
		152	TCP port) of nodes that should be used as seed nodes.
		153
		154	=item global nodes
		155
		156	An AEMP network needs a discovery service - nodes need to know how to
		157	connect to other nodes they only know by name. In addition, AEMP offers a
		158	distributed "group database", which maps group names to a list of strings
		159	- for example, to register worker ports.
		160
		161	A network needs at least one global node to work, and allows every node to
		162	be a global node.
		163
		164	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		165	node and tries to keep connections to all other nodes. So while it can
		166	make sense to make every node "global" in small networks, it usually makes
		167	sense to only make seed nodes into global nodes in large networks (nodes
		168	keep connections to seed nodes and global nodes, so makign them the same
		169	reduces overhead).
62		170
63	=back	171	=back
64		172
65	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
66		174
…		…
68		176
69	=cut	177	=cut
70		178
71	package AnyEvent::MP;	179	package AnyEvent::MP;
72		180
73	use AnyEvent::MP::Util ();	181	use AnyEvent::MP::Config ();
74	use AnyEvent::MP::Node;	182	use AnyEvent::MP::Kernel;
75	use AnyEvent::MP::Transport;	183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
76		184
77	use utf8;
78	use common::sense;	185	use common::sense;
79		186
80	use Carp ();	187	use Carp ();
81		188
82	use AE ();	189	use AE ();
		190	use Guard ();
83		191
84	use base "Exporter";	192	use base "Exporter";
85		193
86	our $VERSION = '0.0';	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
87	our @EXPORT = qw(NODE $NODE $PORT snd rcv _any_);
88		195
89	our $DEFAULT_SECRET;	196	our @EXPORT = qw(
90	our $DEFAULT_PORT = "4040";	197	NODE $NODE *SELF node_of after
		198	configure
		199	snd rcv mon mon_guard kil psub peval spawn cal
		200	port
		201	db_set db_del db_reg
		202	db_mon db_family db_keys db_values
		203	);
91		204
92	our $CONNECT_INTERVAL = 5; # new connect every 5s, at least	205	our $SELF;
93	our $CONNECT_TIMEOUT = 30; # includes handshake
94		206
95	sub default_secret {	207	sub _self_die() {
96	unless (defined $DEFAULT_SECRET) {	208	my $msg = $@;
97	if (open my $fh, "<$ENV{HOME}/.aemp-secret") {	209	$msg =~ s/\n+$// unless ref $msg;
98	sysread $fh, $DEFAULT_SECRET, -s $fh;	210	kil $SELF, die => $msg;
99	} else {
100	$DEFAULT_SECRET = AnyEvent::MP::Util::nonce 32;
101	}
102	}
103
104	$DEFAULT_SECRET
105	}	211	}
106		212
107	=item NODE / $NODE	213	=item $thisnode = NODE / $NODE
108		214
109	The C<NODE ()> function and the C<$NODE> variable contain the noderef of	215	The C<NODE> function returns, and the C<$NODE> variable contains, the node
110	the local node. The value is initialised by a call to C<become_public> or	216	ID of the node running in the current process. This value is initialised by
111	C<become_slave>, after which all local port identifiers become invalid.	217	a call to C<configure>.
112		218
113	=cut	219	=item $nodeid = node_of $port
114		220
115	our $UNIQ = sprintf "%x.%x", $$, time; # per-process/node unique cookie	221	Extracts and returns the node ID from a port ID or a node ID.
116	our $PUBLIC = 0;
117	our $NODE;
118	our $PORT;
119		222
120	our %NODE; # node id to transport mapping, or "undef", for local node	223	=item configure $profile, key => value...
121	our %PORT; # local ports
122	our %LISTENER; # local transports
123		224
124	sub NODE() { $NODE }	225	=item configure key => value...
125		226
126	{	227	Before a node can talk to other nodes on the network (i.e. enter
127	use POSIX ();	228	"distributed mode") it has to configure itself - the minimum a node needs
128	my $nodename = (POSIX::uname)[1];	229	to know is its own name, and optionally it should know the addresses of
129	$NODE = "$$\@$nodename";	230	some other nodes in the network to discover other nodes.
130	}
131		231
132	sub _ANY_() { 1 }	232	This function configures a node - it must be called exactly once (or
133	sub _any_() { \&_ANY_ }	233	never) before calling other AnyEvent::MP functions.
134		234
135	sub add_node {	235	The key/value pairs are basically the same ones as documented for the
136	my ($noderef) = @_;	236	F<aemp> command line utility (sans the set/del prefix), with these additions:
137		237
138	return $NODE{$noderef}	238	=over 4
139	if exists $NODE{$noderef};
140		239
141	for (split /,/, $noderef) {	240	=item norc => $boolean (default false)
142	return $NODE{$noderef} = $NODE{$_}
143	if exists $NODE{$_};
144	}
145		241
146	# for indirect sends, use a different class	242	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
147	my $node = new AnyEvent::MP::Node::Direct $noderef;	243	be consulted - all configuraiton options must be specified in the
		244	C<configure> call.
148		245
149	$NODE{$_} = $node	246	=item force => $boolean (default false)
150	for $noderef, split /,/, $noderef;
151		247
152	$node	248	IF true, then the values specified in the C<configure> will take
153	}	249	precedence over any values configured via the rc file. The default is for
		250	the rc file to override any options specified in the program.
154		251
		252	=item secure => $pass->(@msg)
		253
		254	In addition to specifying a boolean, you can specify a code reference that
		255	is called for every code execution attempt - the execution request is
		256	granted iff the callback returns a true value.
		257
		258	Most of the time the callback should look only at
		259	C<$AnyEvent::MP::Kernel::SRCNODE> to make a decision, and not at the
		260	actual message (which can be about anything, and is mostly provided for
		261	diagnostic purposes).
		262
		263	See F<semp setsecure> for more info.
		264
		265	=back
		266
		267	=over 4
		268
		269	=item step 1, gathering configuration from profiles
		270
		271	The function first looks up a profile in the aemp configuration (see the
		272	L<aemp> commandline utility). The profile name can be specified via the
		273	named C<profile> parameter or can simply be the first parameter). If it is
		274	missing, then the nodename (F<uname -n>) will be used as profile name.
		275
		276	The profile data is then gathered as follows:
		277
		278	First, all remaining key => value pairs (all of which are conveniently
		279	undocumented at the moment) will be interpreted as configuration
		280	data. Then they will be overwritten by any values specified in the global
		281	default configuration (see the F<aemp> utility), then the chain of
		282	profiles chosen by the profile name (and any C<parent> attributes).
		283
		284	That means that the values specified in the profile have highest priority
		285	and the values specified directly via C<configure> have lowest priority,
		286	and can only be used to specify defaults.
		287
		288	If the profile specifies a node ID, then this will become the node ID of
		289	this process. If not, then the profile name will be used as node ID, with
		290	a unique randoms tring (C</%u>) appended.
		291
		292	The node ID can contain some C<%> sequences that are expanded: C<%n>
		293	is expanded to the local nodename, C<%u> is replaced by a random
		294	strign to make the node unique. For example, the F<aemp> commandline
		295	utility uses C<aemp/%n/%u> as nodename, which might expand to
		296	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		297
		298	=item step 2, bind listener sockets
		299
		300	The next step is to look up the binds in the profile, followed by binding
		301	aemp protocol listeners on all binds specified (it is possible and valid
		302	to have no binds, meaning that the node cannot be contacted form the
		303	outside. This means the node cannot talk to other nodes that also have no
		304	binds, but it can still talk to all "normal" nodes).
		305
		306	If the profile does not specify a binds list, then a default of C<*> is
		307	used, meaning the node will bind on a dynamically-assigned port on every
		308	local IP address it finds.
		309
		310	=item step 3, connect to seed nodes
		311
		312	As the last step, the seed ID list from the profile is passed to the
		313	L<AnyEvent::MP::Global> module, which will then use it to keep
		314	connectivity with at least one node at any point in time.
		315
		316	=back
		317
		318	Example: become a distributed node using the local node name as profile.
		319	This should be the most common form of invocation for "daemon"-type nodes.
		320
		321	configure
		322
		323	Example: become a semi-anonymous node. This form is often used for
		324	commandline clients.
		325
		326	configure nodeid => "myscript/%n/%u";
		327
		328	Example: configure a node using a profile called seed, which is suitable
		329	for a seed node as it binds on all local addresses on a fixed port (4040,
		330	customary for aemp).
		331
		332	# use the aemp commandline utility
		333	# aemp profile seed binds '*:4040'
		334
		335	# then use it
		336	configure profile => "seed";
		337
		338	# or simply use aemp from the shell again:
		339	# aemp run profile seed
		340
		341	# or provide a nicer-to-remember nodeid
		342	# aemp run profile seed nodeid "$(hostname)"
		343
		344	=item $SELF
		345
		346	Contains the current port id while executing C<rcv> callbacks or C<psub>
		347	blocks.
		348
		349	=item *SELF, SELF, %SELF, @SELF...
		350
		351	Due to some quirks in how perl exports variables, it is impossible to
		352	just export C<$SELF>, all the symbols named C<SELF> are exported by this
		353	module, but only C<$SELF> is currently used.
		354
155	=item snd $portid, type => @data	355	=item snd $port, type => @data
156		356
157	=item snd $portid, @msg	357	=item snd $port, @msg
158		358
159	Send the given message to the given port ID, which can identify either a	359	Send the given message to the given port, which can identify either a
160	local or a remote port.	360	local or a remote port, and must be a port ID.
161		361
162	While the message can be about anything, it is highly recommended to use	362	While the message can be almost anything, it is highly recommended to
163	a constant string as first element.	363	use a string as first element (a port ID, or some word that indicates a
		364	request type etc.) and to consist if only simple perl values (scalars,
		365	arrays, hashes) - if you think you need to pass an object, think again.
164		366
165	The message data effectively becomes read-only after a call to this	367	The message data logically becomes read-only after a call to this
166	function: modifying any argument is not allowed and can cause many	368	function: modifying any argument (or values referenced by them) is
167	problems.	369	forbidden, as there can be considerable time between the call to C<snd>
		370	and the time the message is actually being serialised - in fact, it might
		371	never be copied as within the same process it is simply handed to the
		372	receiving port.
168		373
169	The type of data you can transfer depends on the transport protocol: when	374	The type of data you can transfer depends on the transport protocol: when
170	JSON is used, then only strings, numbers and arrays and hashes consisting	375	JSON is used, then only strings, numbers and arrays and hashes consisting
171	of those are allowed (no objects). When Storable is used, then anything	376	of those are allowed (no objects). When Storable is used, then anything
172	that Storable can serialise and deserialise is allowed, and for the local	377	that Storable can serialise and deserialise is allowed, and for the local
173	node, anything can be passed.	378	node, anything can be passed. Best rely only on the common denominator of
		379	these.
		380
		381	=item $local_port = port
		382
		383	Create a new local port object and returns its port ID. Initially it has
		384	no callbacks set and will throw an error when it receives messages.
		385
		386	=item $local_port = port { my @msg = @_ }
		387
		388	Creates a new local port, and returns its ID. Semantically the same as
		389	creating a port and calling C<rcv $port, $callback> on it.
		390
		391	The block will be called for every message received on the port, with the
		392	global variable C<$SELF> set to the port ID. Runtime errors will cause the
		393	port to be C<kil>ed. The message will be passed as-is, no extra argument
		394	(i.e. no port ID) will be passed to the callback.
		395
		396	If you want to stop/destroy the port, simply C<kil> it:
		397
		398	my $port = port {
		399	my @msg = @_;
		400	...
		401	kil $SELF;
		402	};
174		403
175	=cut	404	=cut
176		405
177	sub snd(@) {	406	sub rcv($@);
178	my ($noderef, $port) = split /#/, shift, 2;
179		407
180	add_node $noderef	408	my $KILME = sub {
181	unless exists $NODE{$noderef};	409	(my $tag = substr $_[0], 0, 30) =~ s/([\x20-\x7e])/./g;
		410	kil $SELF, unhandled_message => "no callback found for message '$tag'";
		411	};
182		412
183	$NODE{$noderef}->send (["$port", [@_]]);	413	sub port(;&) {
		414	my $id = $UNIQ . ++$ID;
		415	my $port = "$NODE#$id";
		416
		417	rcv $port, shift || $KILME;
		418
		419	$port
184	}	420	}
185		421
186	=item rcv $portid, type => $callback->(@msg)	422	=item rcv $local_port, $callback->(@msg)
187		423
188	=item rcv $portid, $smartmatch => $callback->(@msg)	424	Replaces the default callback on the specified port. There is no way to
		425	remove the default callback: use C<sub { }> to disable it, or better
		426	C<kil> the port when it is no longer needed.
189		427
190	=item rcv $portid, [$smartmatch...] => $callback->(@msg)	428	The global C<$SELF> (exported by this module) contains C<$port> while
		429	executing the callback. Runtime errors during callback execution will
		430	result in the port being C<kil>ed.
191		431
192	Register a callback on the port identified by C<$portid>, which I<must> be	432	The default callback receives all messages not matched by a more specific
193	a local port.	433	C<tag> match.
194		434
195	The callback has to return a true value when its work is done, after	435	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
196	which is will be removed, or a false value in which case it will stay
197	registered.
198		436
199	If the match is an array reference, then it will be matched against the	437	Register (or replace) callbacks to be called on messages starting with the
200	first elements of the message, otherwise only the first element is being	438	given tag on the given port (and return the port), or unregister it (when
201	matched.	439	C<$callback> is C<$undef> or missing). There can only be one callback
		440	registered for each tag.
202		441
203	Any element in the match that is specified as C<_any_> (a function	442	The original message will be passed to the callback, after the first
204	exported by this module) matches any single element of the message.	443	element (the tag) has been removed. The callback will use the same
		444	environment as the default callback (see above).
205		445
206	While not required, it is highly recommended that the first matching	446	Example: create a port and bind receivers on it in one go.
207	element is a string identifying the message. The one-string-only match is	447
208	also the most efficient match (by far).	448	my $port = rcv port,
		449	msg1 => sub { ... },
		450	msg2 => sub { ... },
		451	;
		452
		453	Example: create a port, bind receivers and send it in a message elsewhere
		454	in one go:
		455
		456	snd $otherport, reply =>
		457	rcv port,
		458	msg1 => sub { ... },
		459	...
		460	;
		461
		462	Example: temporarily register a rcv callback for a tag matching some port
		463	(e.g. for an rpc reply) and unregister it after a message was received.
		464
		465	rcv $port, $otherport => sub {
		466	my @reply = @_;
		467
		468	rcv $SELF, $otherport;
		469	};
209		470
210	=cut	471	=cut
211		472
212	sub rcv($@) {	473	sub rcv($@) {
213	my ($port, $match, $cb) = @_;	474	my $port = shift;
214
215	my $port = $PORT{$port}
216	or do {
217	my ($noderef, $lport) = split /#/, $port;	475	my ($nodeid, $portid) = split /#/, $port, 2;
218	"AnyEvent::MP::Node::Self" eq ref $NODE{$noderef}	476
		477	$NODE{$nodeid} == $NODE{""}
219	or Carp::croak "$port: can only rcv on local ports";	478	or Carp::croak "$port: rcv can only be called on local ports, caught";
220		479
221	$PORT{$lport}	480	while (@_) {
222	or Carp::croak "$port: port does not exist";	481	if (ref $_[0]) {
223		482	if (my $self = $PORT_DATA{$portid}) {
224	$PORT{$port} = $PORT{$lport} # also return	483	"AnyEvent::MP::Port" eq ref $self
225	};	484	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
226		485
227	if (!ref $match) {	486	$self->[0] = shift;
228	push @{ $port->{rc0}{$match} }, [$cb];
229	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
230	my ($type, @match) = @$match;
231	@match
232	? push @{ $port->{rcv}{$match->[0]} }, [$cb, \@match]
233	: push @{ $port->{rc0}{$match->[0]} }, [$cb];
234	} else {	487	} else {
235	push @{ $port->{any} }, [$cb, $match];	488	my $cb = shift;
236	}	489	$PORT{$portid} = sub {
237	}	490	local $SELF = $port;
238		491	eval { &$cb }; _self_die if $@;
239	sub _inject {
240	my ($port, $msg) = @{+shift};
241
242	$port = $PORT{$port}
243	or return;
244
245	@_ = @$msg;
246
247	for (@{ $port->{rc0}{$msg->[0]} }) {
248	$_ && &{$_->[0]}
249	&& undef $_;
250	}
251
252	for (@{ $port->{rcv}{$msg->[0]} }) {
253	$_ && [@_[1..$#{$_->[1]}]] ~~ $_->[1]
254	&& &{$_->[0]}
255	&& undef $_;
256	}
257
258	for (@{ $port->{any} }) {
259	$_ && [@_[0..$#{$_->[1]}]] ~~ $_->[1]
260	&& &{$_->[0]}
261	&& undef $_;
262	}
263	}
264
265	sub normalise_noderef($) {
266	my ($noderef) = @_;
267
268	my $cv = AE::cv;
269	my @res;
270
271	$cv->begin (sub {
272	my %seen;
273	my @refs;
274	for (sort { $a->[0] <=> $b->[0] } @res) {
275	push @refs, $_->[1] unless $seen{$_->[1]}++
276	}
277	shift->send (join ",", @refs);
278	});
279
280	$noderef = $DEFAULT_PORT unless length $noderef;
281
282	my $idx;
283	for my $t (split /,/, $noderef) {
284	my $pri = ++$idx;
285
286	#TODO: this should be outside normalise_noderef and in become_public
287	if ($t =~ /^\d*$/) {
288	my $nodename = (POSIX::uname)[1];
289
290	$cv->begin;
291	AnyEvent::Socket::resolve_sockaddr $nodename, $t || "aemp=$DEFAULT_PORT", "tcp", 0, undef, sub {
292	for (@_) {
293	my ($service, $host) = AnyEvent::Socket::unpack_sockaddr $_->[3];
294	push @res, [
295	$pri += 1e-5,
296	AnyEvent::Socket::format_hostport AnyEvent::Socket::format_address $host, $service
297	];
298	}	492	};
299	$cv->end;	493	}
		494	} elsif (defined $_[0]) {
		495	my $self = $PORT_DATA{$portid} ||= do {
		496	my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port";
		497
		498	$PORT{$portid} = sub {
		499	local $SELF = $port;
		500
		501	if (my $cb = $self->[1]{$_[0]}) {
		502	shift;
		503	eval { &$cb }; _self_die if $@;
		504	} else {
		505	&{ $self->[0] };
		506	}
		507	};
		508
		509	$self
300	};	510	};
301		511
302	# my (undef, undef, undef, undef, @ipv4) = gethostbyname $nodename;	512	"AnyEvent::MP::Port" eq ref $self
303	#	513	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
304	# for (@ipv4) {	514
305	# push @res, [	515	my ($tag, $cb) = splice @_, 0, 2;
306	# $pri,	516
307	# AnyEvent::Socket::format_hostport AnyEvent::Socket::format_address $_, $t || $DEFAULT_PORT,	517	if (defined $cb) {
308	# ];	518	$self->[1]{$tag} = $cb;
309	# }
310	} else {	519	} else {
311	my ($host, $port) = AnyEvent::Socket::parse_hostport $t, "aemp=$DEFAULT_PORT"	520	delete $self->[1]{$tag};
312	or Carp::croak "$t: unparsable transport descriptor";
313
314	$cv->begin;
315	AnyEvent::Socket::resolve_sockaddr $host, $port, "tcp", 0, undef, sub {
316	for (@_) {
317	my ($service, $host) = AnyEvent::Socket::unpack_sockaddr $_->[3];
318	push @res, [
319	$pri += 1e-5,
320	AnyEvent::Socket::format_hostport AnyEvent::Socket::format_address $host, $service
321	];
322	}
323	$cv->end;
324	}	521	}
325	}	522	}
326	}	523	}
327		524
328	$cv->end;	525	$port
329
330	$cv
331	}	526	}
332		527
333	sub become_public {	528	=item peval $port, $coderef[, @args]
334	return if $PUBLIC;
335		529
336	my $noderef = join ",", ref $_[0] ? @{+shift} : shift;	530	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
337	my @args = @_;	531	when the code throews an exception the C<$port> will be killed.
338		532
339	$NODE = (normalise_noderef $noderef)->recv;	533	Any remaining args will be passed to the callback. Any return values will
		534	be returned to the caller.
340		535
341	for my $t (split /,/, $NODE) {	536	This is useful when you temporarily want to execute code in the context of
342	$NODE{$t} = $NODE{""};	537	a port.
343		538
344	my ($host, $port) = AnyEvent::Socket::parse_hostport $t;	539	Example: create a port and run some initialisation code in it's context.
345		540
346	$LISTENER{$t} = AnyEvent::MP::Transport::mp_server $host, $port,	541	my $port = port { ... };
347	@args,
348	on_error => sub {
349	die "on_error<@_>\n";#d#
350	},
351	on_connect => sub {
352	my ($tp) = @_;
353		542
354	$NODE{$tp->{remote_id}} = $_[0];	543	peval $port, sub {
355	},	544	init
356	sub {	545	or die "unable to init";
357	my ($tp) = @_;	546	};
358		547
359	$NODE{"$tp->{peerhost}:$tp->{peerport}"} = $tp;	548	=cut
360	},	549
361	;	550	sub peval($$) {
		551	local $SELF = shift;
		552	my $cb = shift;
		553
		554	if (wantarray) {
		555	my @res = eval { &$cb };
		556	_self_die if $@;
		557	@res
		558	} else {
		559	my $res = eval { &$cb };
		560	_self_die if $@;
		561	$res
362	}	562	}
363
364	$PUBLIC = 1;
365	}	563	}
366		564
367	=back	565	=item $closure = psub { BLOCK }
368		566
369	=head1 NODE MESSAGES	567	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
		568	closure is executed, sets up the environment in the same way as in C<rcv>
		569	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
370		570
371	Nodes understand the following messages sent to them:	571	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		572	BLOCK }, @_ } >>.
372		573
373	=over 4	574	This is useful when you register callbacks from C<rcv> callbacks:
		575
		576	rcv delayed_reply => sub {
		577	my ($delay, @reply) = @_;
		578	my $timer = AE::timer $delay, 0, psub {
		579	snd @reply, $SELF;
		580	};
		581	};
374		582
375	=cut	583	=cut
376		584
377	#############################################################################	585	sub psub(&) {
378	# self node code	586	my $cb = shift;
379		587
380	sub _new_port($) {	588	my $port = $SELF
381	my ($name) = @_;	589	or Carp::croak "psub can only be called from within rcv or psub callbacks, not";
382		590
		591	sub {
		592	local $SELF = $port;
		593
		594	if (wantarray) {
		595	my @res = eval { &$cb };
		596	_self_die if $@;
		597	@res
		598	} else {
		599	my $res = eval { &$cb };
		600	_self_die if $@;
		601	$res
		602	}
		603	}
		604	}
		605
		606	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
		607
		608	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
		609
		610	=item $guard = mon $port # kill $SELF when $port dies
		611
		612	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		613
		614	Monitor the given port and do something when the port is killed or
		615	messages to it were lost, and optionally return a guard that can be used
		616	to stop monitoring again.
		617
		618	In the first form (callback), the callback is simply called with any
		619	number of C<@reason> elements (no @reason means that the port was deleted
		620	"normally"). Note also that I<< the callback B<must> never die >>, so use
		621	C<eval> if unsure.
		622
		623	In the second form (another port given), the other port (C<$rcvport>)
		624	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
		625	"normal" kils nothing happens, while under all other conditions, the other
		626	port is killed with the same reason.
		627
		628	The third form (kill self) is the same as the second form, except that
		629	C<$rvport> defaults to C<$SELF>.
		630
		631	In the last form (message), a message of the form C<@msg, @reason> will be
		632	C<snd>.
		633
		634	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		635	alert was raised), they are removed and will not trigger again.
		636
		637	As a rule of thumb, monitoring requests should always monitor a port from
		638	a local port (or callback). The reason is that kill messages might get
		639	lost, just like any other message. Another less obvious reason is that
		640	even monitoring requests can get lost (for example, when the connection
		641	to the other node goes down permanently). When monitoring a port locally
		642	these problems do not exist.
		643
		644	C<mon> effectively guarantees that, in the absence of hardware failures,
		645	after starting the monitor, either all messages sent to the port will
		646	arrive, or the monitoring action will be invoked after possible message
		647	loss has been detected. No messages will be lost "in between" (after
		648	the first lost message no further messages will be received by the
		649	port). After the monitoring action was invoked, further messages might get
		650	delivered again.
		651
		652	Inter-host-connection timeouts and monitoring depend on the transport
		653	used. The only transport currently implemented is TCP, and AnyEvent::MP
		654	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		655	non-idle connection, and usually around two hours for idle connections).
		656
		657	This means that monitoring is good for program errors and cleaning up
		658	stuff eventually, but they are no replacement for a timeout when you need
		659	to ensure some maximum latency.
		660
		661	Example: call a given callback when C<$port> is killed.
		662
		663	mon $port, sub { warn "port died because of <@_>\n" };
		664
		665	Example: kill ourselves when C<$port> is killed abnormally.
		666
		667	mon $port;
		668
		669	Example: send us a restart message when another C<$port> is killed.
		670
		671	mon $port, $self => "restart";
		672
		673	=cut
		674
		675	sub mon {
383	my ($noderef, $portname) = split /#/, $name;	676	my ($nodeid, $port) = split /#/, shift, 2;
384		677
385	$PORT{$name} =	678	my $node = $NODE{$nodeid} || add_node $nodeid;
386	$PORT{$portname} = {	679
387	names => [$name, $portname],	680	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
		681
		682	unless (ref $cb) {
		683	if (@_) {
		684	# send a kill info message
		685	my (@msg) = ($cb, @_);
		686	$cb = sub { snd @msg, @_ };
		687	} else {
		688	# simply kill other port
		689	my $port = $cb;
		690	$cb = sub { kil $port, @_ if @_ };
		691	}
		692	}
		693
		694	$node->monitor ($port, $cb);
		695
		696	defined wantarray
		697	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
		698	}
		699
		700	=item $guard = mon_guard $port, $ref, $ref...
		701
		702	Monitors the given C<$port> and keeps the passed references. When the port
		703	is killed, the references will be freed.
		704
		705	Optionally returns a guard that will stop the monitoring.
		706
		707	This function is useful when you create e.g. timers or other watchers and
		708	want to free them when the port gets killed (note the use of C<psub>):
		709
		710	$port->rcv (start => sub {
		711	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
		712	undef $timer if 0.9 < rand;
		713	});
		714	});
		715
		716	=cut
		717
		718	sub mon_guard {
		719	my ($port, @refs) = @_;
		720
		721	#TODO: mon-less form?
		722
		723	mon $port, sub { 0 && @refs }
		724	}
		725
		726	=item kil $port[, @reason]
		727
		728	Kill the specified port with the given C<@reason>.
		729
		730	If no C<@reason> is specified, then the port is killed "normally" -
		731	monitor callback will be invoked, but the kil will not cause linked ports
		732	(C<mon $mport, $lport> form) to get killed.
		733
		734	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
		735	form) get killed with the same reason.
		736
		737	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		738	will be reported as reason C<< die => $@ >>.
		739
		740	Transport/communication errors are reported as C<< transport_error =>
		741	$message >>.
		742
		743	Common idioms:
		744
		745	# silently remove yourself, do not kill linked ports
		746	kil $SELF;
		747
		748	# report a failure in some detail
		749	kil $SELF, failure_mode_1 => "it failed with too high temperature";
		750
		751	# do not waste much time with killing, just die when something goes wrong
		752	open my $fh, "<file"
		753	or die "file: $!";
		754
		755	=item $port = spawn $node, $initfunc[, @initdata]
		756
		757	Creates a port on the node C<$node> (which can also be a port ID, in which
		758	case it's the node where that port resides).
		759
		760	The port ID of the newly created port is returned immediately, and it is
		761	possible to immediately start sending messages or to monitor the port.
		762
		763	After the port has been created, the init function is called on the remote
		764	node, in the same context as a C<rcv> callback. This function must be a
		765	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		766	specify a function in the main program, use C<::name>.
		767
		768	If the function doesn't exist, then the node tries to C<require>
		769	the package, then the package above the package and so on (e.g.
		770	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		771	exists or it runs out of package names.
		772
		773	The init function is then called with the newly-created port as context
		774	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		775	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		776	the port might not get created.
		777
		778	A common idiom is to pass a local port, immediately monitor the spawned
		779	port, and in the remote init function, immediately monitor the passed
		780	local port. This two-way monitoring ensures that both ports get cleaned up
		781	when there is a problem.
		782
		783	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		784	caller before C<spawn> returns (by delaying invocation when spawn is
		785	called for the local node).
		786
		787	Example: spawn a chat server port on C<$othernode>.
		788
		789	# this node, executed from within a port context:
		790	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		791	mon $server;
		792
		793	# init function on C<$othernode>
		794	sub connect {
		795	my ($srcport) = @_;
		796
		797	mon $srcport;
		798
		799	rcv $SELF, sub {
		800	...
		801	};
		802	}
		803
		804	=cut
		805
		806	sub _spawn {
		807	my $port = shift;
		808	my $init = shift;
		809
		810	# rcv will create the actual port
		811	local $SELF = "$NODE#$port";
		812	eval {
		813	&{ load_func $init }
		814	};
		815	_self_die if $@;
		816	}
		817
		818	sub spawn(@) {
		819	my ($nodeid, undef) = split /#/, shift, 2;
		820
		821	my $id = $RUNIQ . ++$ID;
		822
		823	$_[0] =~ /::/
		824	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		825
		826	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		827
		828	"$nodeid#$id"
		829	}
		830
		831
		832	=item after $timeout, @msg
		833
		834	=item after $timeout, $callback
		835
		836	Either sends the given message, or call the given callback, after the
		837	specified number of seconds.
		838
		839	This is simply a utility function that comes in handy at times - the
		840	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		841	so it may go away in the future.
		842
		843	=cut
		844
		845	sub after($@) {
		846	my ($timeout, @action) = @_;
		847
		848	my $t; $t = AE::timer $timeout, 0, sub {
		849	undef $t;
		850	ref $action[0]
		851	? $action[0]()
		852	: snd @action;
388	};	853	};
389	}	854	}
390		855
391	$NODE{""} = new AnyEvent::MP::Node::Self noderef => $NODE;	856	#=item $cb2 = timeout $seconds, $cb[, @args]
392	_new_port "";
393		857
394	=item relay => $port, @msg	858	=item cal $port, @msg, $callback[, $timeout]
395		859
396	Simply forwards the message to the given port.	860	A simple form of RPC - sends a message to the given C<$port> with the
		861	given contents (C<@msg>), but adds a reply port to the message.
		862
		863	The reply port is created temporarily just for the purpose of receiving
		864	the reply, and will be C<kil>ed when no longer needed.
		865
		866	A reply message sent to the port is passed to the C<$callback> as-is.
		867
		868	If an optional time-out (in seconds) is given and it is not C<undef>,
		869	then the callback will be called without any arguments after the time-out
		870	elapsed and the port is C<kil>ed.
		871
		872	If no time-out is given (or it is C<undef>), then the local port will
		873	monitor the remote port instead, so it eventually gets cleaned-up.
		874
		875	Currently this function returns the temporary port, but this "feature"
		876	might go in future versions unless you can make a convincing case that
		877	this is indeed useful for something.
397		878
398	=cut	879	=cut
399		880
400	rcv "", relay => \&snd;	881	sub cal(@) {
		882	my $timeout = ref $_[-1] ? undef : pop;
		883	my $cb = pop;
401		884
402	=item eval => $string[ @reply]	885	my $port = port {
		886	undef $timeout;
		887	kil $SELF;
		888	&$cb;
		889	};
403		890
404	Evaluates the given string. If C<@reply> is given, then a message of the	891	if (defined $timeout) {
405	form C<@reply, $@, @evalres> is sent (C<$reply[0]> is the port to reply to).	892	$timeout = AE::timer $timeout, 0, sub {
		893	undef $timeout;
		894	kil $port;
		895	$cb->();
		896	};
		897	} else {
		898	mon $_[0], sub {
		899	kil $port;
		900	$cb->();
		901	};
		902	}
		903
		904	push @_, $port;
		905	&snd;
		906
		907	$port
		908	}
		909
		910	=back
		911
		912	=head1 DISTRIBUTED DATABASE
		913
		914	AnyEvent::MP comes with a simple distributed database. The database will
		915	be mirrored asynchronously on all global nodes. Other nodes bind to one
		916	of the global nodes for their needs. Every node has a "local database"
		917	which contains all the values that are set locally. All local databases
		918	are merged together to form the global database, which can be queried.
		919
		920	The database structure is that of a two-level hash - the database hash
		921	contains hashes which contain values, similarly to a perl hash of hashes,
		922	i.e.:
		923
		924	$DATABASE{$family}{$subkey} = $value
		925
		926	The top level hash key is called "family", and the second-level hash key
		927	is called "subkey" or simply "key".
		928
		929	The family must be alphanumeric, i.e. start with a letter and consist
		930	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		931	pretty much like Perl module names.
		932
		933	As the family namespace is global, it is recommended to prefix family names
		934	with the name of the application or module using it.
		935
		936	The subkeys must be non-empty strings, with no further restrictions.
		937
		938	The values should preferably be strings, but other perl scalars should
		939	work as well (such as C<undef>, arrays and hashes).
		940
		941	Every database entry is owned by one node - adding the same family/subkey
		942	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		943	but the result might be nondeterministic, i.e. the key might have
		944	different values on different nodes.
		945
		946	Different subkeys in the same family can be owned by different nodes
		947	without problems, and in fact, this is the common method to create worker
		948	pools. For example, a worker port for image scaling might do this:
		949
		950	db_set my_image_scalers => $port;
		951
		952	And clients looking for an image scaler will want to get the
		953	C<my_image_scalers> keys from time to time:
		954
		955	db_keys my_image_scalers => sub {
		956	@ports = @{ $_[0] };
		957	};
		958
		959	Or better yet, they want to monitor the database family, so they always
		960	have a reasonable up-to-date copy:
		961
		962	db_mon my_image_scalers => sub {
		963	@ports = keys %{ $_[0] };
		964	};
		965
		966	In general, you can set or delete single subkeys, but query and monitor
		967	whole families only.
		968
		969	If you feel the need to monitor or query a single subkey, try giving it
		970	it's own family.
		971
		972	=over
		973
		974	=item $guard = db_set $family => $subkey [=> $value]
		975
		976	Sets (or replaces) a key to the database - if C<$value> is omitted,
		977	C<undef> is used instead.
		978
		979	When called in non-void context, C<db_set> returns a guard that
		980	automatically calls C<db_del> when it is destroyed.
		981
		982	=item db_del $family => $subkey...
		983
		984	Deletes one or more subkeys from the database family.
		985
		986	=item $guard = db_reg $family => $port => $value
		987
		988	=item $guard = db_reg $family => $port
		989
		990	=item $guard = db_reg $family
		991
		992	Registers a port in the given family and optionally returns a guard to
		993	remove it.
		994
		995	This function basically does the same as:
		996
		997	db_set $family => $port => $value
		998
		999	Except that the port is monitored and automatically removed from the
		1000	database family when it is kil'ed.
		1001
		1002	If C<$value> is missing, C<undef> is used. If C<$port> is missing, then
		1003	C<$SELF> is used.
		1004
		1005	This function is most useful to register a port in some port group (which
		1006	is just another name for a database family), and have it removed when the
		1007	port is gone. This works best when the port is a local port.
406		1008
407	=cut	1009	=cut
408		1010
409	rcv "", eval => sub {	1011	sub db_reg($$;$) {
410	my (undef, $string, @reply) = @_;	1012	my $family = shift;
411	my @res = eval $string;	1013	my $port = @_ ? shift : $SELF;
412	snd @reply, "$@", @res if @reply;
413	};
414		1014
415	=item time => @reply	1015	my $clr = sub { db_del $family => $port };
		1016	mon $port, $clr;
416		1017
417	Replies the the current node time to C<@reply>.	1018	db_set $family => $port => $_[0];
		1019
		1020	defined wantarray
		1021	and &Guard::guard ($clr)
		1022	}
		1023
		1024	=item db_family $family => $cb->(\%familyhash)
		1025
		1026	Queries the named database C<$family> and call the callback with the
		1027	family represented as a hash. You can keep and freely modify the hash.
		1028
		1029	=item db_keys $family => $cb->(\@keys)
		1030
		1031	Same as C<db_family>, except it only queries the family I<subkeys> and passes
		1032	them as array reference to the callback.
		1033
		1034	=item db_values $family => $cb->(\@values)
		1035
		1036	Same as C<db_family>, except it only queries the family I<values> and passes them
		1037	as array reference to the callback.
		1038
		1039	=item $guard = db_mon $family => $cb->($familyhash, \@added, \@changed, \@deleted)
		1040
		1041	Creates a monitor on the given database family. Each time a key is set
		1042	or or is deleted the callback is called with a hash containing the
		1043	database family and three lists of added, changed and deleted subkeys,
		1044	respectively. If no keys have changed then the array reference might be
		1045	C<undef> or even missing.
		1046
		1047	If not called in void context, a guard object is returned that, when
		1048	destroyed, stops the monitor.
		1049
		1050	The family hash reference and the key arrays belong to AnyEvent::MP and
		1051	B<must not be modified or stored> by the callback. When in doubt, make a
		1052	copy.
		1053
		1054	As soon as possible after the monitoring starts, the callback will be
		1055	called with the intiial contents of the family, even if it is empty,
		1056	i.e. there will always be a timely call to the callback with the current
		1057	contents.
		1058
		1059	It is possible that the callback is called with a change event even though
		1060	the subkey is already present and the value has not changed.
		1061
		1062	The monitoring stops when the guard object is destroyed.
		1063
		1064	Example: on every change to the family "mygroup", print out all keys.
		1065
		1066	my $guard = db_mon mygroup => sub {
		1067	my ($family, $a, $c, $d) = @_;
		1068	print "mygroup members: ", (join " ", keys %$family), "\n";
		1069	};
		1070
		1071	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1072
		1073	my $guard; $guard = db_mon My::Module::workers => sub {
		1074	my ($family, $a, $c, $d) = @_;
		1075	return unless %$family;
		1076	undef $guard;
		1077	print "My::Module::workers now nonempty\n";
		1078	};
		1079
		1080	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		1081
		1082	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		1083	my ($family, $a, $c, $d) = @_;
		1084
		1085	print "+$_=$family->{$_}\n" for @$a;
		1086	print "*$_=$family->{$_}\n" for @$c;
		1087	print "-$_=$family->{$_}\n" for @$d;
		1088	};
418		1089
419	=cut	1090	=cut
420		1091
421	rcv "", time => sub { shift; snd @_, AE::time };
422
423	=back	1092	=back
424		1093
		1094	=head1 AnyEvent::MP vs. Distributed Erlang
		1095
		1096	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
		1097	== aemp node, Erlang process == aemp port), so many of the documents and
		1098	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
		1099	sample:
		1100
		1101	http://www.erlang.se/doc/programming_rules.shtml
		1102	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
		1103	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
		1104	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
		1105
		1106	Despite the similarities, there are also some important differences:
		1107
		1108	=over 4
		1109
		1110	=item * Node IDs are arbitrary strings in AEMP.
		1111
		1112	Erlang relies on special naming and DNS to work everywhere in the same
		1113	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
		1114	configuration or DNS), and possibly the addresses of some seed nodes, but
		1115	will otherwise discover other nodes (and their IDs) itself.
		1116
		1117	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
		1118	uses "local ports are like remote ports".
		1119
		1120	The failure modes for local ports are quite different (runtime errors
		1121	only) then for remote ports - when a local port dies, you I<know> it dies,
		1122	when a connection to another node dies, you know nothing about the other
		1123	port.
		1124
		1125	Erlang pretends remote ports are as reliable as local ports, even when
		1126	they are not.
		1127
		1128	AEMP encourages a "treat remote ports differently" philosophy, with local
		1129	ports being the special case/exception, where transport errors cannot
		1130	occur.
		1131
		1132	=item * Erlang uses processes and a mailbox, AEMP does not queue.
		1133
		1134	Erlang uses processes that selectively receive messages out of order, and
		1135	therefore needs a queue. AEMP is event based, queuing messages would serve
		1136	no useful purpose. For the same reason the pattern-matching abilities
		1137	of AnyEvent::MP are more limited, as there is little need to be able to
		1138	filter messages without dequeuing them.
		1139
		1140	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1141	being event-based, while Erlang is process-based.
		1142
		1143	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1144	top of AEMP and Coro threads.
		1145
		1146	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
		1147
		1148	Sending messages in Erlang is synchronous and blocks the process until
		1149	a conenction has been established and the message sent (and so does not
		1150	need a queue that can overflow). AEMP sends return immediately, connection
		1151	establishment is handled in the background.
		1152
		1153	=item * Erlang suffers from silent message loss, AEMP does not.
		1154
		1155	Erlang implements few guarantees on messages delivery - messages can get
		1156	lost without any of the processes realising it (i.e. you send messages a,
		1157	b, and c, and the other side only receives messages a and c).
		1158
		1159	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1160	guarantee that after one message is lost, all following ones sent to the
		1161	same port are lost as well, until monitoring raises an error, so there are
		1162	no silent "holes" in the message sequence.
		1163
		1164	If you want your software to be very reliable, you have to cope with
		1165	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
		1166	simply tries to work better in common error cases, such as when a network
		1167	link goes down.
		1168
		1169	=item * Erlang can send messages to the wrong port, AEMP does not.
		1170
		1171	In Erlang it is quite likely that a node that restarts reuses an Erlang
		1172	process ID known to other nodes for a completely different process,
		1173	causing messages destined for that process to end up in an unrelated
		1174	process.
		1175
		1176	AEMP does not reuse port IDs, so old messages or old port IDs floating
		1177	around in the network will not be sent to an unrelated port.
		1178
		1179	=item * Erlang uses unprotected connections, AEMP uses secure
		1180	authentication and can use TLS.
		1181
		1182	AEMP can use a proven protocol - TLS - to protect connections and
		1183	securely authenticate nodes.
		1184
		1185	=item * The AEMP protocol is optimised for both text-based and binary
		1186	communications.
		1187
		1188	The AEMP protocol, unlike the Erlang protocol, supports both programming
		1189	language independent text-only protocols (good for debugging), and binary,
		1190	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1191	used, the protocol is actually completely text-based.
		1192
		1193	It has also been carefully designed to be implementable in other languages
		1194	with a minimum of work while gracefully degrading functionality to make the
		1195	protocol simple.
		1196
		1197	=item * AEMP has more flexible monitoring options than Erlang.
		1198
		1199	In Erlang, you can chose to receive I<all> exit signals as messages or
		1200	I<none>, there is no in-between, so monitoring single Erlang processes is
		1201	difficult to implement.
		1202
		1203	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1204	between automatic kill, exit message or callback on a per-port basis.
		1205
		1206	=item * Erlang tries to hide remote/local connections, AEMP does not.
		1207
		1208	Monitoring in Erlang is not an indicator of process death/crashes, in the
		1209	same way as linking is (except linking is unreliable in Erlang).
		1210
		1211	In AEMP, you don't "look up" registered port names or send to named ports
		1212	that might or might not be persistent. Instead, you normally spawn a port
		1213	on the remote node. The init function monitors you, and you monitor the
		1214	remote port. Since both monitors are local to the node, they are much more
		1215	reliable (no need for C<spawn_link>).
		1216
		1217	This also saves round-trips and avoids sending messages to the wrong port
		1218	(hard to do in Erlang).
		1219
		1220	=back
		1221
		1222	=head1 RATIONALE
		1223
		1224	=over 4
		1225
		1226	=item Why strings for port and node IDs, why not objects?
		1227
		1228	We considered "objects", but found that the actual number of methods
		1229	that can be called are quite low. Since port and node IDs travel over
		1230	the network frequently, the serialising/deserialising would add lots of
		1231	overhead, as well as having to keep a proxy object everywhere.
		1232
		1233	Strings can easily be printed, easily serialised etc. and need no special
		1234	procedures to be "valid".
		1235
		1236	And as a result, a port with just a default receiver consists of a single
		1237	code reference stored in a global hash - it can't become much cheaper.
		1238
		1239	=item Why favour JSON, why not a real serialising format such as Storable?
		1240
		1241	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1242	format, but currently there is no way to make a node use Storable by
		1243	default (although all nodes will accept it).
		1244
		1245	The default framing protocol is JSON because a) JSON::XS is many times
		1246	faster for small messages and b) most importantly, after years of
		1247	experience we found that object serialisation is causing more problems
		1248	than it solves: Just like function calls, objects simply do not travel
		1249	easily over the network, mostly because they will always be a copy, so you
		1250	always have to re-think your design.
		1251
		1252	Keeping your messages simple, concentrating on data structures rather than
		1253	objects, will keep your messages clean, tidy and efficient.
		1254
		1255	=back
		1256
		1257	=head1 PORTING FROM AnyEvent::MP VERSION 1.X
		1258
		1259	AEMP version 2 has three major incompatible changes compared to version 1:
		1260
		1261	=over 4
		1262
		1263	=item AnyEvent::MP::Global no longer has group management functions.
		1264
		1265	AnyEvent::MP now comes with a distributed database that is more
		1266	powerful. It's database families map closely to ports, but the API has
		1267	minor differences:
		1268
		1269	grp_reg $group, $port # old
		1270	db_reg $group, $port # new
		1271
		1272	$list = grp_get $group # old
		1273	db_keys $group, sub { my $list = shift } # new
		1274
		1275	grp_mon $group, $cb->(\@ports, $add, $del) # old
		1276	db_mon $group, $cb->(\%ports, $add, $change, $del) # new
		1277
		1278	C<grp_reg> is a no-brainer (just replace by C<db_reg>), but C<grp_get>
		1279	is no longer instant, because the local node might not have a copy of
		1280	the group. This can be partially remedied by using C<db_mon> to keep an
		1281	updated copy of the group:
		1282
		1283	my $local_group_copy;
		1284	db_mon $group => sub { $local_group_copy = shift };
		1285
		1286	# no keys %$local_group_copy always returns the most up-to-date
		1287	# list of ports in the group.
		1288
		1289	C<grp_mon> can almost be replaced by C<db_mon>:
		1290
		1291	db_mon $group => sub {
		1292	my ($ports, $add, $chg, $lde) = @_;
		1293	$ports = [keys %$ports];
		1294
		1295	# now $ports, $add and $del are the same as
		1296	# were originally passed by grp_mon.
		1297	...
		1298	};
		1299
		1300	=item Nodes not longer connect to all other nodes.
		1301
		1302	In AEMP 1.x, every node automatically loads the L<AnyEvent::MP::Global>
		1303	module, which in turn would create connections to all other nodes in the
		1304	network (helped by the seed nodes).
		1305
		1306	In version 2.x, global nodes still connect to all other global nodes, but
		1307	other nodes don't - now every node either is a global node itself, or
		1308	attaches itself to another global node.
		1309
		1310	If a node isn't a global node itself, then it attaches itself to one
		1311	of its seed nodes. If that seed node isn't a global node yet, it will
		1312	automatically be upgraded to a global node.
		1313
		1314	So in many cases, nothing needs to be changed - one just has to make sure
		1315	that all seed nodes are meshed together with the other seed nodes (as with
		1316	AEMP 1.x), and other nodes specify them as seed nodes.
		1317
		1318	Not opening a connection to every other node is usually an advantage,
		1319	except when you need the lower latency of an already established
		1320	connection. To ensure a node establishes a connection to another node,
		1321	you can monitor the node port (C<mon $node, ...>), which will attempt to
		1322	create the connection (and notify you when the connection fails).
		1323
		1324	=item Listener-less nodes (nodes without binds) are gone.
		1325
		1326	And are not coming back, at least not in their old form. If no C<binds>
		1327	are specified for a node, AnyEvent::MP now assumes a default of C<*:*>.
		1328
		1329	There are vague plans to implement some form of routing domains, which
		1330	might or might not bring back listener-less nodes, but don't count on it.
		1331
		1332	The fact that most connections are now optional somewhat mitigates this,
		1333	as a node can be effectively unreachable from the outside without any
		1334	problems, as long as it isn't a global node and only reaches out to other
		1335	nodes (as opposed to being contacted from other nodes).
		1336
		1337	=item $AnyEvent::MP::Kernel::WARN has gone.
		1338
		1339	AnyEvent has acquired a logging framework (L<AnyEvent::Log>), and AEMP now
		1340	uses this, and so should your programs.
		1341
		1342	Every module now documents what kinds of messages it generates, with
		1343	AnyEvent::MP acting as a catch all.
		1344
		1345	On the positive side, this means that instead of setting
		1346	C<PERL_ANYEVENT_MP_WARNLEVEL>, you can get away by setting C<AE_VERBOSE>,
		1347	much less to type.
		1348
		1349	=back
		1350
425	=head1 SEE ALSO	1351	=head1 SEE ALSO
		1352
		1353	L<AnyEvent::MP::Intro> - a gentle introduction.
		1354
		1355	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1356
		1357	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1358	your applications.
		1359
		1360	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1361
		1362	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1363	all nodes.
426		1364
427	L<AnyEvent>.	1365	L<AnyEvent>.
428		1366
429	=head1 AUTHOR	1367	=head1 AUTHOR
430		1368

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