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Revision 1.22 by root, Tue Aug 4 18:33:30 2009 UTC vs.
Revision 1.129 by root, Thu Mar 8 21:37:51 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 # contains this node's noderef	9	$NODE # contains this node's node ID
10	NODE # returns this node's noderef	10	NODE # returns this node's node ID
11	NODE $port # returns the noderef of the port
12		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
13	snd $port, type => data...;	20	snd $port, type => data...;
		21	snd $port, @msg;
		22	snd @msg_with_first_element_being_a_port;
14		23
15	$SELF # receiving/own port id in rcv callbacks	24	# creating/using ports, the simple way
		25	my $simple_port = port { my @msg = @_ };
16		26
17	rcv $port, smartmatch => $cb->($port, @msg);	27	# creating/using ports, tagged message matching
18		28	my $port = port;
19	# examples:
20	rcv $port2, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
21	rcv $port1, pong => sub { warn "pong received\n" };	30	rcv $port, pong => sub { warn "pong received\n" };
22	snd $port2, ping => $port1;
23		31
24	# more, smarter, matches (_any_ is exported by this module)	32	# create a port on another node
25	rcv $port, [child_died => $pid] => sub { ...	33	my $port = spawn $node, $initfunc, @initdata;
26	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.
27		59
28	=head1 DESCRIPTION	60	=head1 DESCRIPTION
29		61
30	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
31		63
32	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
33	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
34		66
35	At the moment, this module family is severly brokena nd underdocumented,	67	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
36	so do not use. This was uploaded mainly to reserve the CPAN namespace -	68	manual page and the examples under F<eg/>.
37	stay tuned!
38		69
39	=head1 CONCEPTS	70	=head1 CONCEPTS
40		71
41	=over 4	72	=over 4
42		73
43	=item port	74	=item port
44		75
45	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
46	you can register C<rcv> handlers with. All C<rcv> handlers will receive	77	messages to (with the C<snd> function).
47	messages they match, messages will not be queued.
48		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
49	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
50		86
51	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<#>)
52	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).
53		90
54	=item node	91	=item node
55		92
56	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,
57	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
58	among other things.	95	ports.
59		96
60	Initially, nodes are either private (single-process only) or hidden	97	Nodes are either public (have one or more listening ports) or private
61	(connected to a master node only). Only when they epxlicitly "become	98	(no listening ports). Private nodes cannot talk to other private nodes
62	public" can you send them messages from unrelated other nodes.	99	currently, but all nodes can talk to public nodes.
63		100
64	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	101	Nodes is represented by (printable) strings called "node IDs".
65		102
		103	=item node ID - C<[A-Za-z0-9_\-.:]*>
		104
66	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
67	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
68	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).
69		170
70	=back	171	=back
71		172
72	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
73		174
…		…
75		176
76	=cut	177	=cut
77		178
78	package AnyEvent::MP;	179	package AnyEvent::MP;
79		180
		181	use AnyEvent::MP::Config ();
80	use AnyEvent::MP::Base;	182	use AnyEvent::MP::Kernel;
		183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
81		184
82	use common::sense;	185	use common::sense;
83		186
84	use Carp ();	187	use Carp ();
85		188
86	use AE ();	189	use AE ();
		190	use Guard ();
87		191
88	use base "Exporter";	192	use base "Exporter";
89		193
90	our $VERSION = '0.02';	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
		195
91	our @EXPORT = qw(	196	our @EXPORT = qw(
92	NODE $NODE *SELF node_of _any_	197	NODE $NODE *SELF node_of after
93	become_slave become_public	198	configure
94	snd rcv mon kil reg psub	199	snd rcv mon mon_guard kil psub peval spawn cal
95	port	200	port
		201	db_set db_del db_reg
		202	db_mon db_family db_keys db_values
96	);	203	);
97		204
98	our $SELF;	205	our $SELF;
99		206
100	sub _self_die() {	207	sub _self_die() {
…		…
103	kil $SELF, die => $msg;	210	kil $SELF, die => $msg;
104	}	211	}
105		212
106	=item $thisnode = NODE / $NODE	213	=item $thisnode = NODE / $NODE
107		214
108	The C<NODE> function returns, and the C<$NODE> variable contains	215	The C<NODE> function returns, and the C<$NODE> variable contains, the node
109	the noderef of the local node. The value is initialised by a call	216	ID of the node running in the current process. This value is initialised by
110	to C<become_public> or C<become_slave>, after which all local port	217	a call to C<configure>.
111	identifiers become invalid.
112		218
113	=item $noderef = node_of $portid	219	=item $nodeid = node_of $port
114		220
115	Extracts and returns the noderef from a portid or a noderef.	221	Extracts and returns the node ID from a port ID or a node ID.
		222
		223	=item configure $profile, key => value...
		224
		225	=item configure key => value...
		226
		227	Before a node can talk to other nodes on the network (i.e. enter
		228	"distributed mode") it has to configure itself - the minimum a node needs
		229	to know is its own name, and optionally it should know the addresses of
		230	some other nodes in the network to discover other nodes.
		231
		232	This function configures a node - it must be called exactly once (or
		233	never) before calling other AnyEvent::MP functions.
		234
		235	The key/value pairs are basically the same ones as documented for the
		236	F<aemp> command line utility (sans the set/del prefix), with these additions:
		237
		238	=over 4
		239
		240	=item norc => $boolean (default false)
		241
		242	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
		243	be consulted - all configuraiton options must be specified in the
		244	C<configure> call.
		245
		246	=item force => $boolean (default false)
		247
		248	IF true, then the values specified in the C<configure> will take
		249	precedence over any values configured via the rc file. The default is for
		250	the rc file to override any options specified in the program.
		251
		252	=item secure => $pass->($nodeid)
		253
		254	In addition to specifying a boolean, you can specify a code reference that
		255	is called for every remote execution attempt - the execution request is
		256	granted iff the callback returns a true value.
		257
		258	See F<semp setsecure> for more info.
		259
		260	=back
		261
		262	=over 4
		263
		264	=item step 1, gathering configuration from profiles
		265
		266	The function first looks up a profile in the aemp configuration (see the
		267	L<aemp> commandline utility). The profile name can be specified via the
		268	named C<profile> parameter or can simply be the first parameter). If it is
		269	missing, then the nodename (F<uname -n>) will be used as profile name.
		270
		271	The profile data is then gathered as follows:
		272
		273	First, all remaining key => value pairs (all of which are conveniently
		274	undocumented at the moment) will be interpreted as configuration
		275	data. Then they will be overwritten by any values specified in the global
		276	default configuration (see the F<aemp> utility), then the chain of
		277	profiles chosen by the profile name (and any C<parent> attributes).
		278
		279	That means that the values specified in the profile have highest priority
		280	and the values specified directly via C<configure> have lowest priority,
		281	and can only be used to specify defaults.
		282
		283	If the profile specifies a node ID, then this will become the node ID of
		284	this process. If not, then the profile name will be used as node ID, with
		285	a unique randoms tring (C</%u>) appended.
		286
		287	The node ID can contain some C<%> sequences that are expanded: C<%n>
		288	is expanded to the local nodename, C<%u> is replaced by a random
		289	strign to make the node unique. For example, the F<aemp> commandline
		290	utility uses C<aemp/%n/%u> as nodename, which might expand to
		291	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		292
		293	=item step 2, bind listener sockets
		294
		295	The next step is to look up the binds in the profile, followed by binding
		296	aemp protocol listeners on all binds specified (it is possible and valid
		297	to have no binds, meaning that the node cannot be contacted form the
		298	outside. This means the node cannot talk to other nodes that also have no
		299	binds, but it can still talk to all "normal" nodes).
		300
		301	If the profile does not specify a binds list, then a default of C<*> is
		302	used, meaning the node will bind on a dynamically-assigned port on every
		303	local IP address it finds.
		304
		305	=item step 3, connect to seed nodes
		306
		307	As the last step, the seed ID list from the profile is passed to the
		308	L<AnyEvent::MP::Global> module, which will then use it to keep
		309	connectivity with at least one node at any point in time.
		310
		311	=back
		312
		313	Example: become a distributed node using the local node name as profile.
		314	This should be the most common form of invocation for "daemon"-type nodes.
		315
		316	configure
		317
		318	Example: become a semi-anonymous node. This form is often used for
		319	commandline clients.
		320
		321	configure nodeid => "myscript/%n/%u";
		322
		323	Example: configure a node using a profile called seed, which is suitable
		324	for a seed node as it binds on all local addresses on a fixed port (4040,
		325	customary for aemp).
		326
		327	# use the aemp commandline utility
		328	# aemp profile seed binds '*:4040'
		329
		330	# then use it
		331	configure profile => "seed";
		332
		333	# or simply use aemp from the shell again:
		334	# aemp run profile seed
		335
		336	# or provide a nicer-to-remember nodeid
		337	# aemp run profile seed nodeid "$(hostname)"
116		338
117	=item $SELF	339	=item $SELF
118		340
119	Contains the current port id while executing C<rcv> callbacks or C<psub>	341	Contains the current port id while executing C<rcv> callbacks or C<psub>
120	blocks.	342	blocks.
121		343
122	=item SELF, %SELF, @SELF...	344	=item *SELF, SELF, %SELF, @SELF...
123		345
124	Due to some quirks in how perl exports variables, it is impossible to	346	Due to some quirks in how perl exports variables, it is impossible to
125	just export C<$SELF>, all the symbols called C<SELF> are exported by this	347	just export C<$SELF>, all the symbols named C<SELF> are exported by this
126	module, but only C<$SELF> is currently used.	348	module, but only C<$SELF> is currently used.
127		349
128	=item snd $portid, type => @data	350	=item snd $port, type => @data
129		351
130	=item snd $portid, @msg	352	=item snd $port, @msg
131		353
132	Send the given message to the given port ID, which can identify either	354	Send the given message to the given port, which can identify either a
133	a local or a remote port, and can be either a string or soemthignt hat	355	local or a remote port, and must be a port ID.
134	stringifies a sa port ID (such as a port object :).
135		356
136	While the message can be about anything, it is highly recommended to use a	357	While the message can be almost anything, it is highly recommended to
137	string as first element (a portid, or some word that indicates a request	358	use a string as first element (a port ID, or some word that indicates a
138	type etc.).	359	request type etc.) and to consist if only simple perl values (scalars,
		360	arrays, hashes) - if you think you need to pass an object, think again.
139		361
140	The message data effectively becomes read-only after a call to this	362	The message data logically becomes read-only after a call to this
141	function: modifying any argument is not allowed and can cause many	363	function: modifying any argument (or values referenced by them) is
142	problems.	364	forbidden, as there can be considerable time between the call to C<snd>
		365	and the time the message is actually being serialised - in fact, it might
		366	never be copied as within the same process it is simply handed to the
		367	receiving port.
143		368
144	The type of data you can transfer depends on the transport protocol: when	369	The type of data you can transfer depends on the transport protocol: when
145	JSON is used, then only strings, numbers and arrays and hashes consisting	370	JSON is used, then only strings, numbers and arrays and hashes consisting
146	of those are allowed (no objects). When Storable is used, then anything	371	of those are allowed (no objects). When Storable is used, then anything
147	that Storable can serialise and deserialise is allowed, and for the local	372	that Storable can serialise and deserialise is allowed, and for the local
148	node, anything can be passed.	373	node, anything can be passed. Best rely only on the common denominator of
		374	these.
149		375
150	=item kil $portid[, @reason]	376	=item $local_port = port
151		377
152	Kill the specified port with the given C<@reason>.	378	Create a new local port object and returns its port ID. Initially it has
		379	no callbacks set and will throw an error when it receives messages.
153		380
154	If no C<@reason> is specified, then the port is killed "normally" (linked	381	=item $local_port = port { my @msg = @_ }
155	ports will not be kileld, or even notified).
156		382
157	Otherwise, linked ports get killed with the same reason (second form of	383	Creates a new local port, and returns its ID. Semantically the same as
158	C<mon>, see below).	384	creating a port and calling C<rcv $port, $callback> on it.
159		385
160	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	386	The block will be called for every message received on the port, with the
161	will be reported as reason C<< die => $@ >>.	387	global variable C<$SELF> set to the port ID. Runtime errors will cause the
		388	port to be C<kil>ed. The message will be passed as-is, no extra argument
		389	(i.e. no port ID) will be passed to the callback.
162		390
163	Transport/communication errors are reported as C<< transport_error =>	391	If you want to stop/destroy the port, simply C<kil> it:
164	$message >>.
165		392
166	=item $guard = mon $portid, $cb->(@reason)	393	my $port = port {
167		394	my @msg = @_;
168	=item $guard = mon $portid, $otherport	395	...
169		396	kil $SELF;
170	=item $guard = mon $portid, $otherport, @msg	397	};
171
172	Monitor the given port and do something when the port is killed.
173
174	In the first form, the callback is simply called with any number
175	of C<@reason> elements (no @reason means that the port was deleted
176	"normally"). Note also that I<< the callback B<must> never die >>, so use
177	C<eval> if unsure.
178
179	In the second form, the other port will be C<kil>'ed with C<@reason>, iff
180	a @reason was specified, i.e. on "normal" kils nothing happens, while
181	under all other conditions, the other port is killed with the same reason.
182
183	In the last form, a message of the form C<@msg, @reason> will be C<snd>.
184
185	Example: call a given callback when C<$port> is killed.
186
187	mon $port, sub { warn "port died because of <@_>\n" };
188
189	Example: kill ourselves when C<$port> is killed abnormally.
190
191	mon $port, $self;
192
193	Example: send us a restart message another C<$port> is killed.
194
195	mon $port, $self => "restart";
196		398
197	=cut	399	=cut
198		400
199	sub mon {	401	sub rcv($@);
200	my ($noderef, $port, $cb) = ((split /#/, shift, 2), shift);
201		402
202	my $node = $NODE{$noderef} || add_node $noderef;	403	sub _kilme {
		404	die "received message on port without callback";
		405	}
203		406
204	#TODO: ports must not be references	407	sub port(;&) {
205	if (!ref $cb or "AnyEvent::MP::Port" eq ref $cb) {	408	my $id = $UNIQ . ++$ID;
		409	my $port = "$NODE#$id";
		410
		411	rcv $port, shift || \&_kilme;
		412
		413	$port
		414	}
		415
		416	=item rcv $local_port, $callback->(@msg)
		417
		418	Replaces the default callback on the specified port. There is no way to
		419	remove the default callback: use C<sub { }> to disable it, or better
		420	C<kil> the port when it is no longer needed.
		421
		422	The global C<$SELF> (exported by this module) contains C<$port> while
		423	executing the callback. Runtime errors during callback execution will
		424	result in the port being C<kil>ed.
		425
		426	The default callback received all messages not matched by a more specific
		427	C<tag> match.
		428
		429	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
		430
		431	Register (or replace) callbacks to be called on messages starting with the
		432	given tag on the given port (and return the port), or unregister it (when
		433	C<$callback> is C<$undef> or missing). There can only be one callback
		434	registered for each tag.
		435
		436	The original message will be passed to the callback, after the first
		437	element (the tag) has been removed. The callback will use the same
		438	environment as the default callback (see above).
		439
		440	Example: create a port and bind receivers on it in one go.
		441
		442	my $port = rcv port,
		443	msg1 => sub { ... },
		444	msg2 => sub { ... },
		445	;
		446
		447	Example: create a port, bind receivers and send it in a message elsewhere
		448	in one go:
		449
		450	snd $otherport, reply =>
		451	rcv port,
		452	msg1 => sub { ... },
		453	...
		454	;
		455
		456	Example: temporarily register a rcv callback for a tag matching some port
		457	(e.g. for an rpc reply) and unregister it after a message was received.
		458
		459	rcv $port, $otherport => sub {
		460	my @reply = @_;
		461
		462	rcv $SELF, $otherport;
		463	};
		464
		465	=cut
		466
		467	sub rcv($@) {
		468	my $port = shift;
		469	my ($nodeid, $portid) = split /#/, $port, 2;
		470
		471	$NODE{$nodeid} == $NODE{""}
		472	or Carp::croak "$port: rcv can only be called on local ports, caught";
		473
		474	while (@_) {
206	if (@_) {	475	if (ref $_[0]) {
207	# send a kill info message	476	if (my $self = $PORT_DATA{$portid}) {
208	my (@msg) = ($cb, @_);	477	"AnyEvent::MP::Port" eq ref $self
209	$cb = sub { snd @msg, @_ };	478	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		479
		480	$self->[0] = shift;
210	} else {	481	} else {
211	# simply kill other port	482	my $cb = shift;
212	my $port = $cb;	483	$PORT{$portid} = sub {
213	$cb = sub { kil $port, @_ if @_ };	484	local $SELF = $port;
		485	eval { &$cb }; _self_die if $@;
		486	};
		487	}
		488	} elsif (defined $_[0]) {
		489	my $self = $PORT_DATA{$portid} ||= do {
		490	my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port";
		491
		492	$PORT{$portid} = sub {
		493	local $SELF = $port;
		494
		495	if (my $cb = $self->[1]{$_[0]}) {
		496	shift;
		497	eval { &$cb }; _self_die if $@;
		498	} else {
		499	&{ $self->[0] };
		500	}
		501	};
		502
		503	$self
		504	};
		505
		506	"AnyEvent::MP::Port" eq ref $self
		507	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		508
		509	my ($tag, $cb) = splice @_, 0, 2;
		510
		511	if (defined $cb) {
		512	$self->[1]{$tag} = $cb;
		513	} else {
		514	delete $self->[1]{$tag};
		515	}
214	}	516	}
215	}	517	}
216		518
217	$node->monitor ($port, $cb);
218
219	defined wantarray
220	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }
221	}
222
223	=item $guard = mon_guard $port, $ref, $ref...
224
225	Monitors the given C<$port> and keeps the passed references. When the port
226	is killed, the references will be freed.
227
228	Optionally returns a guard that will stop the monitoring.
229
230	This function is useful when you create e.g. timers or other watchers and
231	want to free them when the port gets killed:
232
233	$port->rcv (start => sub {
234	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {
235	undef $timer if 0.9 < rand;
236	});
237	});
238
239	=cut
240
241	sub mon_guard {
242	my ($port, @refs) = @_;
243
244	mon $port, sub { 0 && @refs }
245	}
246
247	=item $local_port = port
248
249	Create a new local port object that supports message matching.
250
251	=item $portid = port { my @msg = @_; $finished }
252
253	Creates a "mini port", that is, a very lightweight port without any
254	pattern matching behind it, and returns its ID.
255
256	The block will be called for every message received on the port. When the
257	callback returns a true value its job is considered "done" and the port
258	will be destroyed. Otherwise it will stay alive.
259
260	The message will be passed as-is, no extra argument (i.e. no port id) will
261	be passed to the callback.
262
263	If you need the local port id in the callback, this works nicely:
264
265	my $port; $port = miniport {
266	snd $otherport, reply => $port;
267	};
268
269	=cut
270
271	sub port(;&) {
272	my $id = "$UNIQ." . $ID++;
273	my $port = "$NODE#$id";
274
275	if (@_) {
276	my $cb = shift;
277	$PORT{$id} = sub {
278	local $SELF = $port;
279	eval {
280	&$cb
281	and kil $id;
282	};
283	_self_die if $@;
284	};
285	} else {
286	my $self = bless {
287	id => "$NODE#$id",
288	}, "AnyEvent::MP::Port";
289
290	$PORT_DATA{$id} = $self;
291	$PORT{$id} = sub {
292	local $SELF = $port;
293
294	eval {
295	for (@{ $self->{rc0}{$_[0]} }) {
296	$_ && &{$_->[0]}
297	&& undef $_;
298	}
299
300	for (@{ $self->{rcv}{$_[0]} }) {
301	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
302	&& &{$_->[0]}
303	&& undef $_;
304	}
305
306	for (@{ $self->{any} }) {
307	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
308	&& &{$_->[0]}
309	&& undef $_;
310	}
311	};
312	_self_die if $@;
313	};
314	}
315
316	$port	519	$port
317	}	520	}
318		521
319	=item reg $portid, $name	522	=item peval $port, $coderef[, @args]
320		523
321	Registers the given port under the name C<$name>. If the name already	524	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
322	exists it is replaced.	525	when the code throews an exception the C<$port> will be killed.
323		526
324	A port can only be registered under one well known name.	527	Any remaining args will be passed to the callback. Any return values will
		528	be returned to the caller.
325		529
326	A port automatically becomes unregistered when it is killed.	530	This is useful when you temporarily want to execute code in the context of
		531	a port.
		532
		533	Example: create a port and run some initialisation code in it's context.
		534
		535	my $port = port { ... };
		536
		537	peval $port, sub {
		538	init
		539	or die "unable to init";
		540	};
327		541
328	=cut	542	=cut
329		543
330	sub reg(@) {	544	sub peval($$) {
331	my ($portid, $name) = @_;	545	local $SELF = shift;
		546	my $cb = shift;
332		547
333	$REG{$name} = $portid;	548	if (wantarray) {
334	}	549	my @res = eval { &$cb };
335		550	_self_die if $@;
336	=item rcv $portid, tagstring => $callback->(@msg), ...	551	@res
337
338	=item rcv $portid, $smartmatch => $callback->(@msg), ...
339
340	=item rcv $portid, [$smartmatch...] => $callback->(@msg), ...
341
342	Register callbacks to be called on matching messages on the given port.
343
344	The callback has to return a true value when its work is done, after
345	which is will be removed, or a false value in which case it will stay
346	registered.
347
348	The global C<$SELF> (exported by this module) contains C<$portid> while
349	executing the callback.
350
351	Runtime errors wdurign callback execution will result in the port being
352	C<kil>ed.
353
354	If the match is an array reference, then it will be matched against the
355	first elements of the message, otherwise only the first element is being
356	matched.
357
358	Any element in the match that is specified as C<_any_> (a function
359	exported by this module) matches any single element of the message.
360
361	While not required, it is highly recommended that the first matching
362	element is a string identifying the message. The one-string-only match is
363	also the most efficient match (by far).
364
365	=cut
366
367	sub rcv($@) {
368	my ($noderef, $port) = split /#/, shift, 2;
369
370	($NODE{$noderef} || add_node $noderef) == $NODE{""}
371	or Carp::croak "$noderef#$port: rcv can only be called on local ports, caught";
372
373	my $self = $PORT_DATA{$port}
374	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";
375
376	"AnyEvent::MP::Port" eq ref $self
377	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";
378
379	while (@_) {
380	my ($match, $cb) = splice @_, 0, 2;
381
382	if (!ref $match) {
383	push @{ $self->{rc0}{$match} }, [$cb];
384	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
385	my ($type, @match) = @$match;
386	@match
387	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
388	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
389	} else {	552	} else {
390	push @{ $self->{any} }, [$cb, $match];	553	my $res = eval { &$cb };
391	}	554	_self_die if $@;
		555	$res
392	}	556	}
393	}	557	}
394		558
395	=item $closure = psub { BLOCK }	559	=item $closure = psub { BLOCK }
396		560
397	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	561	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
398	closure is executed, sets up the environment in the same way as in C<rcv>	562	closure is executed, sets up the environment in the same way as in C<rcv>
399	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.	563	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		564
		565	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		566	BLOCK }, @_ } >>.
400		567
401	This is useful when you register callbacks from C<rcv> callbacks:	568	This is useful when you register callbacks from C<rcv> callbacks:
402		569
403	rcv delayed_reply => sub {	570	rcv delayed_reply => sub {
404	my ($delay, @reply) = @_;	571	my ($delay, @reply) = @_;
…		…
428	$res	595	$res
429	}	596	}
430	}	597	}
431	}	598	}
432		599
		600	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
		601
		602	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
		603
		604	=item $guard = mon $port # kill $SELF when $port dies
		605
		606	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		607
		608	Monitor the given port and do something when the port is killed or
		609	messages to it were lost, and optionally return a guard that can be used
		610	to stop monitoring again.
		611
		612	In the first form (callback), the callback is simply called with any
		613	number of C<@reason> elements (no @reason means that the port was deleted
		614	"normally"). Note also that I<< the callback B<must> never die >>, so use
		615	C<eval> if unsure.
		616
		617	In the second form (another port given), the other port (C<$rcvport>)
		618	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
		619	"normal" kils nothing happens, while under all other conditions, the other
		620	port is killed with the same reason.
		621
		622	The third form (kill self) is the same as the second form, except that
		623	C<$rvport> defaults to C<$SELF>.
		624
		625	In the last form (message), a message of the form C<@msg, @reason> will be
		626	C<snd>.
		627
		628	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		629	alert was raised), they are removed and will not trigger again.
		630
		631	As a rule of thumb, monitoring requests should always monitor a port from
		632	a local port (or callback). The reason is that kill messages might get
		633	lost, just like any other message. Another less obvious reason is that
		634	even monitoring requests can get lost (for example, when the connection
		635	to the other node goes down permanently). When monitoring a port locally
		636	these problems do not exist.
		637
		638	C<mon> effectively guarantees that, in the absence of hardware failures,
		639	after starting the monitor, either all messages sent to the port will
		640	arrive, or the monitoring action will be invoked after possible message
		641	loss has been detected. No messages will be lost "in between" (after
		642	the first lost message no further messages will be received by the
		643	port). After the monitoring action was invoked, further messages might get
		644	delivered again.
		645
		646	Inter-host-connection timeouts and monitoring depend on the transport
		647	used. The only transport currently implemented is TCP, and AnyEvent::MP
		648	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		649	non-idle connection, and usually around two hours for idle connections).
		650
		651	This means that monitoring is good for program errors and cleaning up
		652	stuff eventually, but they are no replacement for a timeout when you need
		653	to ensure some maximum latency.
		654
		655	Example: call a given callback when C<$port> is killed.
		656
		657	mon $port, sub { warn "port died because of <@_>\n" };
		658
		659	Example: kill ourselves when C<$port> is killed abnormally.
		660
		661	mon $port;
		662
		663	Example: send us a restart message when another C<$port> is killed.
		664
		665	mon $port, $self => "restart";
		666
		667	=cut
		668
		669	sub mon {
		670	my ($nodeid, $port) = split /#/, shift, 2;
		671
		672	my $node = $NODE{$nodeid} || add_node $nodeid;
		673
		674	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
		675
		676	unless (ref $cb) {
		677	if (@_) {
		678	# send a kill info message
		679	my (@msg) = ($cb, @_);
		680	$cb = sub { snd @msg, @_ };
		681	} else {
		682	# simply kill other port
		683	my $port = $cb;
		684	$cb = sub { kil $port, @_ if @_ };
		685	}
		686	}
		687
		688	$node->monitor ($port, $cb);
		689
		690	defined wantarray
		691	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
		692	}
		693
		694	=item $guard = mon_guard $port, $ref, $ref...
		695
		696	Monitors the given C<$port> and keeps the passed references. When the port
		697	is killed, the references will be freed.
		698
		699	Optionally returns a guard that will stop the monitoring.
		700
		701	This function is useful when you create e.g. timers or other watchers and
		702	want to free them when the port gets killed (note the use of C<psub>):
		703
		704	$port->rcv (start => sub {
		705	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
		706	undef $timer if 0.9 < rand;
		707	});
		708	});
		709
		710	=cut
		711
		712	sub mon_guard {
		713	my ($port, @refs) = @_;
		714
		715	#TODO: mon-less form?
		716
		717	mon $port, sub { 0 && @refs }
		718	}
		719
		720	=item kil $port[, @reason]
		721
		722	Kill the specified port with the given C<@reason>.
		723
		724	If no C<@reason> is specified, then the port is killed "normally" -
		725	monitor callback will be invoked, but the kil will not cause linked ports
		726	(C<mon $mport, $lport> form) to get killed.
		727
		728	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
		729	form) get killed with the same reason.
		730
		731	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		732	will be reported as reason C<< die => $@ >>.
		733
		734	Transport/communication errors are reported as C<< transport_error =>
		735	$message >>.
		736
		737	=cut
		738
		739	=item $port = spawn $node, $initfunc[, @initdata]
		740
		741	Creates a port on the node C<$node> (which can also be a port ID, in which
		742	case it's the node where that port resides).
		743
		744	The port ID of the newly created port is returned immediately, and it is
		745	possible to immediately start sending messages or to monitor the port.
		746
		747	After the port has been created, the init function is called on the remote
		748	node, in the same context as a C<rcv> callback. This function must be a
		749	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		750	specify a function in the main program, use C<::name>.
		751
		752	If the function doesn't exist, then the node tries to C<require>
		753	the package, then the package above the package and so on (e.g.
		754	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		755	exists or it runs out of package names.
		756
		757	The init function is then called with the newly-created port as context
		758	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		759	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		760	the port might not get created.
		761
		762	A common idiom is to pass a local port, immediately monitor the spawned
		763	port, and in the remote init function, immediately monitor the passed
		764	local port. This two-way monitoring ensures that both ports get cleaned up
		765	when there is a problem.
		766
		767	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		768	caller before C<spawn> returns (by delaying invocation when spawn is
		769	called for the local node).
		770
		771	Example: spawn a chat server port on C<$othernode>.
		772
		773	# this node, executed from within a port context:
		774	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		775	mon $server;
		776
		777	# init function on C<$othernode>
		778	sub connect {
		779	my ($srcport) = @_;
		780
		781	mon $srcport;
		782
		783	rcv $SELF, sub {
		784	...
		785	};
		786	}
		787
		788	=cut
		789
		790	sub _spawn {
		791	my $port = shift;
		792	my $init = shift;
		793
		794	# rcv will create the actual port
		795	local $SELF = "$NODE#$port";
		796	eval {
		797	&{ load_func $init }
		798	};
		799	_self_die if $@;
		800	}
		801
		802	sub spawn(@) {
		803	my ($nodeid, undef) = split /#/, shift, 2;
		804
		805	my $id = $RUNIQ . ++$ID;
		806
		807	$_[0] =~ /::/
		808	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		809
		810	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		811
		812	"$nodeid#$id"
		813	}
		814
		815
		816	=item after $timeout, @msg
		817
		818	=item after $timeout, $callback
		819
		820	Either sends the given message, or call the given callback, after the
		821	specified number of seconds.
		822
		823	This is simply a utility function that comes in handy at times - the
		824	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		825	so it may go away in the future.
		826
		827	=cut
		828
		829	sub after($@) {
		830	my ($timeout, @action) = @_;
		831
		832	my $t; $t = AE::timer $timeout, 0, sub {
		833	undef $t;
		834	ref $action[0]
		835	? $action[0]()
		836	: snd @action;
		837	};
		838	}
		839
		840	#=item $cb2 = timeout $seconds, $cb[, @args]
		841
		842	=item cal $port, @msg, $callback[, $timeout]
		843
		844	A simple form of RPC - sends a message to the given C<$port> with the
		845	given contents (C<@msg>), but adds a reply port to the message.
		846
		847	The reply port is created temporarily just for the purpose of receiving
		848	the reply, and will be C<kil>ed when no longer needed.
		849
		850	A reply message sent to the port is passed to the C<$callback> as-is.
		851
		852	If an optional time-out (in seconds) is given and it is not C<undef>,
		853	then the callback will be called without any arguments after the time-out
		854	elapsed and the port is C<kil>ed.
		855
		856	If no time-out is given (or it is C<undef>), then the local port will
		857	monitor the remote port instead, so it eventually gets cleaned-up.
		858
		859	Currently this function returns the temporary port, but this "feature"
		860	might go in future versions unless you can make a convincing case that
		861	this is indeed useful for something.
		862
		863	=cut
		864
		865	sub cal(@) {
		866	my $timeout = ref $_[-1] ? undef : pop;
		867	my $cb = pop;
		868
		869	my $port = port {
		870	undef $timeout;
		871	kil $SELF;
		872	&$cb;
		873	};
		874
		875	if (defined $timeout) {
		876	$timeout = AE::timer $timeout, 0, sub {
		877	undef $timeout;
		878	kil $port;
		879	$cb->();
		880	};
		881	} else {
		882	mon $_[0], sub {
		883	kil $port;
		884	$cb->();
		885	};
		886	}
		887
		888	push @_, $port;
		889	&snd;
		890
		891	$port
		892	}
		893
433	=back	894	=back
434		895
435	=head1 FUNCTIONS FOR NODES	896	=head1 DISTRIBUTED DATABASE
		897
		898	AnyEvent::MP comes with a simple distributed database. The database will
		899	be mirrored asynchronously at all global nodes. Other nodes bind to one of
		900	the global nodes for their needs.
		901
		902	The database consists of a two-level hash - a hash contains a hash which
		903	contains values.
		904
		905	The top level hash key is called "family", and the second-level hash key
		906	is called "subkey" or simply "key".
		907
		908	The family must be alphanumeric, i.e. start with a letter and consist
		909	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		910	pretty much like Perl module names.
		911
		912	As the family namespace is global, it is recommended to prefix family names
		913	with the name of the application or module using it.
		914
		915	The subkeys must be non-empty strings, with no further restrictions.
		916
		917	The values should preferably be strings, but other perl scalars should
		918	work as well (such as undef, arrays and hashes).
		919
		920	Every database entry is owned by one node - adding the same family/subkey
		921	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		922	but the result might be nondeterministic, i.e. the key might have
		923	different values on different nodes.
		924
		925	Different subkeys in the same family can be owned by different nodes
		926	without problems, and in fact, this is the common method to create worker
		927	pools. For example, a worker port for image scaling might do this:
		928
		929	db_set my_image_scalers => $port;
		930
		931	And clients looking for an image scaler will want to get the
		932	C<my_image_scalers> keys from time to time:
		933
		934	db_keys my_image_scalers => sub {
		935	@ports = @{ $_[0] };
		936	};
		937
		938	Or better yet, they want to monitor the database family, so they always
		939	have a reasonable up-to-date copy:
		940
		941	db_mon my_image_scalers => sub {
		942	@ports = keys %{ $_[0] };
		943	};
		944
		945	In general, you can set or delete single subkeys, but query and monitor
		946	whole families only.
		947
		948	If you feel the need to monitor or query a single subkey, try giving it
		949	it's own family.
		950
		951	=over
		952
		953	=item db_set $family => $subkey [=> $value]
		954
		955	Sets (or replaces) a key to the database - if C<$value> is omitted,
		956	C<undef> is used instead.
		957
		958	=item db_del $family => $subkey
		959
		960	Deletes a key from the database.
		961
		962	=item $guard = db_reg $family => $subkey [=> $value]
		963
		964	Sets the key on the database and returns a guard. When the guard is
		965	destroyed, the key is deleted from the database. If C<$value> is missing,
		966	then C<undef> is used.
		967
		968	=item db_family $family => $cb->(\%familyhash)
		969
		970	Queries the named database C<$family> and call the callback with the
		971	family represented as a hash. You can keep and freely modify the hash.
		972
		973	=item db_keys $family => $cb->(\@keys)
		974
		975	Same as C<db_family>, except it only queries the family I<subkeys> and passes
		976	them as array reference to the callback.
		977
		978	=item db_values $family => $cb->(\@values)
		979
		980	Same as C<db_family>, except it only queries the family I<values> and passes them
		981	as array reference to the callback.
		982
		983	=item $guard = db_mon $family => $cb->($familyhash, \@subkeys...)
		984
		985	Creates a monitor on the given database family. Each time a key is set or
		986	or is deleted the callback is called with a hash containing the database
		987	family and an arrayref with subkeys that have changed.
		988
		989	Specifically, if one of the passed subkeys exists in the $familyhash, then
		990	it is currently set to the value in the $familyhash. Otherwise, it has
		991	been deleted.
		992
		993	The family hash reference belongs to AnyEvent::MP and B<must not be
		994	modified or stored> by the callback. When in doubt, make a copy.
		995
		996	The first call will be with the current contents of the family and all
		997	keys, as if they were just added.
		998
		999	It is possible that the callback is called with a change event even though
		1000	the subkey is already present and the value has not changed.
		1001
		1002	The monitoring stops when the guard object is destroyed.
		1003
		1004	Example: on every change to the family "mygroup", print out all keys.
		1005
		1006	my $guard = db_mon mygroup => sub {
		1007	my ($family, $keys) = @_;
		1008	print "mygroup members: ", (join " ", keys %$family), "\n";
		1009	};
		1010
		1011	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1012
		1013	my $guard; $guard = db_mon My::Module::workers => sub {
		1014	my ($family, $keys) = @_;
		1015	return unless %$family;
		1016	undef $guard;
		1017	print "My::Module::workers now nonempty\n";
		1018	};
		1019
		1020	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		1021
		1022	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		1023	my ($family, $keys) = @_;
		1024
		1025	for (@$keys) {
		1026	print "$_: ",
		1027	(exists $family->{$_}
		1028	? $family->{$_}
		1029	: "(deleted)"),
		1030	"\n";
		1031	}
		1032	};
		1033
		1034	=cut
		1035
		1036	=back
		1037
		1038	=head1 AnyEvent::MP vs. Distributed Erlang
		1039
		1040	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
		1041	== aemp node, Erlang process == aemp port), so many of the documents and
		1042	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
		1043	sample:
		1044
		1045	http://www.erlang.se/doc/programming_rules.shtml
		1046	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
		1047	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
		1048	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
		1049
		1050	Despite the similarities, there are also some important differences:
436		1051
437	=over 4	1052	=over 4
438		1053
439	=item become_public endpoint...	1054	=item * Node IDs are arbitrary strings in AEMP.
440		1055
441	Tells the node to become a public node, i.e. reachable from other nodes.	1056	Erlang relies on special naming and DNS to work everywhere in the same
		1057	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
		1058	configuration or DNS), and possibly the addresses of some seed nodes, but
		1059	will otherwise discover other nodes (and their IDs) itself.
442		1060
443	If no arguments are given, or the first argument is C<undef>, then	1061	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
444	AnyEvent::MP tries to bind on port C<4040> on all IP addresses that the	1062	uses "local ports are like remote ports".
445	local nodename resolves to.
446		1063
447	Otherwise the first argument must be an array-reference with transport	1064	The failure modes for local ports are quite different (runtime errors
448	endpoints ("ip:port", "hostname:port") or port numbers (in which case the	1065	only) then for remote ports - when a local port dies, you I<know> it dies,
449	local nodename is used as hostname). The endpoints are all resolved and	1066	when a connection to another node dies, you know nothing about the other
450	will become the node reference.	1067	port.
451		1068
452	=cut	1069	Erlang pretends remote ports are as reliable as local ports, even when
		1070	they are not.
		1071
		1072	AEMP encourages a "treat remote ports differently" philosophy, with local
		1073	ports being the special case/exception, where transport errors cannot
		1074	occur.
		1075
		1076	=item * Erlang uses processes and a mailbox, AEMP does not queue.
		1077
		1078	Erlang uses processes that selectively receive messages out of order, and
		1079	therefore needs a queue. AEMP is event based, queuing messages would serve
		1080	no useful purpose. For the same reason the pattern-matching abilities
		1081	of AnyEvent::MP are more limited, as there is little need to be able to
		1082	filter messages without dequeuing them.
		1083
		1084	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1085	being event-based, while Erlang is process-based.
		1086
		1087	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1088	top of AEMP and Coro threads.
		1089
		1090	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
		1091
		1092	Sending messages in Erlang is synchronous and blocks the process until
		1093	a conenction has been established and the message sent (and so does not
		1094	need a queue that can overflow). AEMP sends return immediately, connection
		1095	establishment is handled in the background.
		1096
		1097	=item * Erlang suffers from silent message loss, AEMP does not.
		1098
		1099	Erlang implements few guarantees on messages delivery - messages can get
		1100	lost without any of the processes realising it (i.e. you send messages a,
		1101	b, and c, and the other side only receives messages a and c).
		1102
		1103	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1104	guarantee that after one message is lost, all following ones sent to the
		1105	same port are lost as well, until monitoring raises an error, so there are
		1106	no silent "holes" in the message sequence.
		1107
		1108	If you want your software to be very reliable, you have to cope with
		1109	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
		1110	simply tries to work better in common error cases, such as when a network
		1111	link goes down.
		1112
		1113	=item * Erlang can send messages to the wrong port, AEMP does not.
		1114
		1115	In Erlang it is quite likely that a node that restarts reuses an Erlang
		1116	process ID known to other nodes for a completely different process,
		1117	causing messages destined for that process to end up in an unrelated
		1118	process.
		1119
		1120	AEMP does not reuse port IDs, so old messages or old port IDs floating
		1121	around in the network will not be sent to an unrelated port.
		1122
		1123	=item * Erlang uses unprotected connections, AEMP uses secure
		1124	authentication and can use TLS.
		1125
		1126	AEMP can use a proven protocol - TLS - to protect connections and
		1127	securely authenticate nodes.
		1128
		1129	=item * The AEMP protocol is optimised for both text-based and binary
		1130	communications.
		1131
		1132	The AEMP protocol, unlike the Erlang protocol, supports both programming
		1133	language independent text-only protocols (good for debugging), and binary,
		1134	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1135	used, the protocol is actually completely text-based.
		1136
		1137	It has also been carefully designed to be implementable in other languages
		1138	with a minimum of work while gracefully degrading functionality to make the
		1139	protocol simple.
		1140
		1141	=item * AEMP has more flexible monitoring options than Erlang.
		1142
		1143	In Erlang, you can chose to receive I<all> exit signals as messages or
		1144	I<none>, there is no in-between, so monitoring single Erlang processes is
		1145	difficult to implement.
		1146
		1147	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1148	between automatic kill, exit message or callback on a per-port basis.
		1149
		1150	=item * Erlang tries to hide remote/local connections, AEMP does not.
		1151
		1152	Monitoring in Erlang is not an indicator of process death/crashes, in the
		1153	same way as linking is (except linking is unreliable in Erlang).
		1154
		1155	In AEMP, you don't "look up" registered port names or send to named ports
		1156	that might or might not be persistent. Instead, you normally spawn a port
		1157	on the remote node. The init function monitors you, and you monitor the
		1158	remote port. Since both monitors are local to the node, they are much more
		1159	reliable (no need for C<spawn_link>).
		1160
		1161	This also saves round-trips and avoids sending messages to the wrong port
		1162	(hard to do in Erlang).
453		1163
454	=back	1164	=back
455		1165
456	=head1 NODE MESSAGES	1166	=head1 RATIONALE
457
458	Nodes understand the following messages sent to them. Many of them take
459	arguments called C<@reply>, which will simply be used to compose a reply
460	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
461	the remaining arguments are simply the message data.
462		1167
463	=over 4	1168	=over 4
464		1169
465	=cut	1170	=item Why strings for port and node IDs, why not objects?
466		1171
467	=item lookup => $name, @reply	1172	We considered "objects", but found that the actual number of methods
		1173	that can be called are quite low. Since port and node IDs travel over
		1174	the network frequently, the serialising/deserialising would add lots of
		1175	overhead, as well as having to keep a proxy object everywhere.
468		1176
469	Replies with the port ID of the specified well-known port, or C<undef>.	1177	Strings can easily be printed, easily serialised etc. and need no special
		1178	procedures to be "valid".
470		1179
471	=item devnull => ...	1180	And as a result, a port with just a default receiver consists of a single
		1181	code reference stored in a global hash - it can't become much cheaper.
472		1182
473	Generic data sink/CPU heat conversion.	1183	=item Why favour JSON, why not a real serialising format such as Storable?
474		1184
475	=item relay => $port, @msg	1185	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1186	format, but currently there is no way to make a node use Storable by
		1187	default (although all nodes will accept it).
476		1188
477	Simply forwards the message to the given port.	1189	The default framing protocol is JSON because a) JSON::XS is many times
		1190	faster for small messages and b) most importantly, after years of
		1191	experience we found that object serialisation is causing more problems
		1192	than it solves: Just like function calls, objects simply do not travel
		1193	easily over the network, mostly because they will always be a copy, so you
		1194	always have to re-think your design.
478		1195
479	=item eval => $string[ @reply]	1196	Keeping your messages simple, concentrating on data structures rather than
480		1197	objects, will keep your messages clean, tidy and efficient.
481	Evaluates the given string. If C<@reply> is given, then a message of the
482	form C<@reply, $@, @evalres> is sent.
483
484	Example: crash another node.
485
486	snd $othernode, eval => "exit";
487
488	=item time => @reply
489
490	Replies the the current node time to C<@reply>.
491
492	Example: tell the current node to send the current time to C<$myport> in a
493	C<timereply> message.
494
495	snd $NODE, time => $myport, timereply => 1, 2;
496	# => snd $myport, timereply => 1, 2, <time>
497		1198
498	=back	1199	=back
499		1200
500	=head1 SEE ALSO	1201	=head1 SEE ALSO
		1202
		1203	L<AnyEvent::MP::Intro> - a gentle introduction.
		1204
		1205	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1206
		1207	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1208	your applications.
		1209
		1210	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1211
		1212	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1213	all nodes.
501		1214
502	L<AnyEvent>.	1215	L<AnyEvent>.
503		1216
504	=head1 AUTHOR	1217	=head1 AUTHOR
505		1218

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