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Revision 1.26 by root, Tue Aug 4 22:05:43 2009 UTC vs.
Revision 1.124 by root, Sat Mar 3 11:38:43 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 $localport, $cb->(@msg) # callback is invoked on death
		41	mon $localport, $otherport # kill otherport on abnormal death
		42	mon $localport, $otherport, @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	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	67	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
36	manual page.	68	manual page and the examples under F<eg/>.
37
38	At the moment, this module family is severly broken and underdocumented,
39	so do not use. This was uploaded mainly to reserve the CPAN namespace -
40	stay tuned! The basic API should be finished, however.
41		69
42	=head1 CONCEPTS	70	=head1 CONCEPTS
43		71
44	=over 4	72	=over 4
45		73
46	=item port	74	=item port
47		75
48	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
49	you can register C<rcv> handlers with. All C<rcv> handlers will receive	77	messages to (with the C<snd> function).
50	messages they match, messages will not be queued.
51		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
52	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
53		86
54	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<#>)
55	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).
56		90
57	=item node	91	=item node
58		92
59	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,
60	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
61	among other things.	95	ports.
62		96
63	Initially, nodes are either private (single-process only) or hidden	97	Nodes are either public (have one or more listening ports) or private
64	(connected to a master node only). Only when they epxlicitly "become	98	(no listening ports). Private nodes cannot talk to other private nodes
65	public" can you send them messages from unrelated other nodes.	99	currently, but all nodes can talk to public nodes.
66		100
67	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	101	Nodes is represented by (printable) strings called "node IDs".
68		102
		103	=item node ID - C<[A-Za-z0-9_\-.:]*>
		104
69	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
70	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
71	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).
72		170
73	=back	171	=back
74		172
75	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
76		174
…		…
78		176
79	=cut	177	=cut
80		178
81	package AnyEvent::MP;	179	package AnyEvent::MP;
82		180
		181	use AnyEvent::MP::Config ();
83	use AnyEvent::MP::Base;	182	use AnyEvent::MP::Kernel;
		183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
84		184
85	use common::sense;	185	use common::sense;
86		186
87	use Carp ();	187	use Carp ();
88		188
89	use AE ();	189	use AE ();
		190	use Guard ();
90		191
91	use base "Exporter";	192	use base "Exporter";
92		193
93	our $VERSION = '0.1';	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
		195
94	our @EXPORT = qw(	196	our @EXPORT = qw(
95	NODE $NODE *SELF node_of _any_	197	NODE $NODE *SELF node_of after
96	become_slave become_public	198	configure
97	snd rcv mon kil reg psub	199	snd rcv mon mon_guard kil psub peval spawn cal
98	port	200	port
		201	db_set db_del db_reg
99	);	202	);
100		203
101	our $SELF;	204	our $SELF;
102		205
103	sub _self_die() {	206	sub _self_die() {
…		…
106	kil $SELF, die => $msg;	209	kil $SELF, die => $msg;
107	}	210	}
108		211
109	=item $thisnode = NODE / $NODE	212	=item $thisnode = NODE / $NODE
110		213
111	The C<NODE> function returns, and the C<$NODE> variable contains	214	The C<NODE> function returns, and the C<$NODE> variable contains, the node
112	the noderef of the local node. The value is initialised by a call	215	ID of the node running in the current process. This value is initialised by
113	to C<become_public> or C<become_slave>, after which all local port	216	a call to C<configure>.
114	identifiers become invalid.
115		217
116	=item $noderef = node_of $portid	218	=item $nodeid = node_of $port
117		219
118	Extracts and returns the noderef from a portid or a noderef.	220	Extracts and returns the node ID from a port ID or a node ID.
		221
		222	=item configure $profile, key => value...
		223
		224	=item configure key => value...
		225
		226	Before a node can talk to other nodes on the network (i.e. enter
		227	"distributed mode") it has to configure itself - the minimum a node needs
		228	to know is its own name, and optionally it should know the addresses of
		229	some other nodes in the network to discover other nodes.
		230
		231	This function configures a node - it must be called exactly once (or
		232	never) before calling other AnyEvent::MP functions.
		233
		234	The key/value pairs are basically the same ones as documented for the
		235	F<aemp> command line utility (sans the set/del prefix), with two additions:
		236
		237	=over 4
		238
		239	=item norc => $boolean (default false)
		240
		241	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
		242	be consulted - all configuraiton options must be specified in the
		243	C<configure> call.
		244
		245	=item force => $boolean (default false)
		246
		247	IF true, then the values specified in the C<configure> will take
		248	precedence over any values configured via the rc file. The default is for
		249	the rc file to override any options specified in the program.
		250
		251	=back
		252
		253	=over 4
		254
		255	=item step 1, gathering configuration from profiles
		256
		257	The function first looks up a profile in the aemp configuration (see the
		258	L<aemp> commandline utility). The profile name can be specified via the
		259	named C<profile> parameter or can simply be the first parameter). If it is
		260	missing, then the nodename (F<uname -n>) will be used as profile name.
		261
		262	The profile data is then gathered as follows:
		263
		264	First, all remaining key => value pairs (all of which are conveniently
		265	undocumented at the moment) will be interpreted as configuration
		266	data. Then they will be overwritten by any values specified in the global
		267	default configuration (see the F<aemp> utility), then the chain of
		268	profiles chosen by the profile name (and any C<parent> attributes).
		269
		270	That means that the values specified in the profile have highest priority
		271	and the values specified directly via C<configure> have lowest priority,
		272	and can only be used to specify defaults.
		273
		274	If the profile specifies a node ID, then this will become the node ID of
		275	this process. If not, then the profile name will be used as node ID, with
		276	a slash (C</>) attached.
		277
		278	If the node ID (or profile name) ends with a slash (C</>), then a random
		279	string is appended to make it unique.
		280
		281	=item step 2, bind listener sockets
		282
		283	The next step is to look up the binds in the profile, followed by binding
		284	aemp protocol listeners on all binds specified (it is possible and valid
		285	to have no binds, meaning that the node cannot be contacted form the
		286	outside. This means the node cannot talk to other nodes that also have no
		287	binds, but it can still talk to all "normal" nodes).
		288
		289	If the profile does not specify a binds list, then a default of C<*> is
		290	used, meaning the node will bind on a dynamically-assigned port on every
		291	local IP address it finds.
		292
		293	=item step 3, connect to seed nodes
		294
		295	As the last step, the seed ID list from the profile is passed to the
		296	L<AnyEvent::MP::Global> module, which will then use it to keep
		297	connectivity with at least one node at any point in time.
		298
		299	=back
		300
		301	Example: become a distributed node using the local node name as profile.
		302	This should be the most common form of invocation for "daemon"-type nodes.
		303
		304	configure
		305
		306	Example: become an anonymous node. This form is often used for commandline
		307	clients.
		308
		309	configure nodeid => "anon/";
		310
		311	Example: configure a node using a profile called seed, which is suitable
		312	for a seed node as it binds on all local addresses on a fixed port (4040,
		313	customary for aemp).
		314
		315	# use the aemp commandline utility
		316	# aemp profile seed binds '*:4040'
		317
		318	# then use it
		319	configure profile => "seed";
		320
		321	# or simply use aemp from the shell again:
		322	# aemp run profile seed
		323
		324	# or provide a nicer-to-remember nodeid
		325	# aemp run profile seed nodeid "$(hostname)"
119		326
120	=item $SELF	327	=item $SELF
121		328
122	Contains the current port id while executing C<rcv> callbacks or C<psub>	329	Contains the current port id while executing C<rcv> callbacks or C<psub>
123	blocks.	330	blocks.
124		331
125	=item SELF, %SELF, @SELF...	332	=item *SELF, SELF, %SELF, @SELF...
126		333
127	Due to some quirks in how perl exports variables, it is impossible to	334	Due to some quirks in how perl exports variables, it is impossible to
128	just export C<$SELF>, all the symbols called C<SELF> are exported by this	335	just export C<$SELF>, all the symbols named C<SELF> are exported by this
129	module, but only C<$SELF> is currently used.	336	module, but only C<$SELF> is currently used.
130		337
131	=item snd $portid, type => @data	338	=item snd $port, type => @data
132		339
133	=item snd $portid, @msg	340	=item snd $port, @msg
134		341
135	Send the given message to the given port ID, which can identify either	342	Send the given message to the given port, which can identify either a
136	a local or a remote port, and can be either a string or soemthignt hat	343	local or a remote port, and must be a port ID.
137	stringifies a sa port ID (such as a port object :).
138		344
139	While the message can be about anything, it is highly recommended to use a	345	While the message can be almost anything, it is highly recommended to
140	string as first element (a portid, or some word that indicates a request	346	use a string as first element (a port ID, or some word that indicates a
141	type etc.).	347	request type etc.) and to consist if only simple perl values (scalars,
		348	arrays, hashes) - if you think you need to pass an object, think again.
142		349
143	The message data effectively becomes read-only after a call to this	350	The message data logically becomes read-only after a call to this
144	function: modifying any argument is not allowed and can cause many	351	function: modifying any argument (or values referenced by them) is
145	problems.	352	forbidden, as there can be considerable time between the call to C<snd>
		353	and the time the message is actually being serialised - in fact, it might
		354	never be copied as within the same process it is simply handed to the
		355	receiving port.
146		356
147	The type of data you can transfer depends on the transport protocol: when	357	The type of data you can transfer depends on the transport protocol: when
148	JSON is used, then only strings, numbers and arrays and hashes consisting	358	JSON is used, then only strings, numbers and arrays and hashes consisting
149	of those are allowed (no objects). When Storable is used, then anything	359	of those are allowed (no objects). When Storable is used, then anything
150	that Storable can serialise and deserialise is allowed, and for the local	360	that Storable can serialise and deserialise is allowed, and for the local
151	node, anything can be passed.	361	node, anything can be passed. Best rely only on the common denominator of
		362	these.
152		363
153	=item kil $portid[, @reason]	364	=item $local_port = port
154		365
155	Kill the specified port with the given C<@reason>.	366	Create a new local port object and returns its port ID. Initially it has
		367	no callbacks set and will throw an error when it receives messages.
156		368
157	If no C<@reason> is specified, then the port is killed "normally" (linked	369	=item $local_port = port { my @msg = @_ }
158	ports will not be kileld, or even notified).
159		370
160	Otherwise, linked ports get killed with the same reason (second form of	371	Creates a new local port, and returns its ID. Semantically the same as
161	C<mon>, see below).	372	creating a port and calling C<rcv $port, $callback> on it.
162		373
163	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	374	The block will be called for every message received on the port, with the
164	will be reported as reason C<< die => $@ >>.	375	global variable C<$SELF> set to the port ID. Runtime errors will cause the
		376	port to be C<kil>ed. The message will be passed as-is, no extra argument
		377	(i.e. no port ID) will be passed to the callback.
165		378
166	Transport/communication errors are reported as C<< transport_error =>	379	If you want to stop/destroy the port, simply C<kil> it:
167	$message >>.
168		380
169	=item $guard = mon $portid, $cb->(@reason)	381	my $port = port {
170
171	=item $guard = mon $portid, $otherport
172
173	=item $guard = mon $portid, $otherport, @msg
174
175	Monitor the given port and do something when the port is killed.
176
177	In the first form, the callback is simply called with any number
178	of C<@reason> elements (no @reason means that the port was deleted
179	"normally"). Note also that I<< the callback B<must> never die >>, so use
180	C<eval> if unsure.
181
182	In the second form, the other port will be C<kil>'ed with C<@reason>, iff
183	a @reason was specified, i.e. on "normal" kils nothing happens, while
184	under all other conditions, the other port is killed with the same reason.
185
186	In the last form, a message of the form C<@msg, @reason> will be C<snd>.
187
188	Example: call a given callback when C<$port> is killed.
189
190	mon $port, sub { warn "port died because of <@_>\n" };
191
192	Example: kill ourselves when C<$port> is killed abnormally.
193
194	mon $port, $self;
195
196	Example: send us a restart message another C<$port> is killed.
197
198	mon $port, $self => "restart";
199
200	=cut
201
202	sub mon {
203	my ($noderef, $port, $cb) = ((split /#/, shift, 2), shift);
204
205	my $node = $NODE{$noderef} || add_node $noderef;
206
207	#TODO: ports must not be references
208	if (!ref $cb or "AnyEvent::MP::Port" eq ref $cb) {
209	if (@_) {
210	# send a kill info message
211	my (@msg) = ($cb, @_);	382	my @msg = @_;
212	$cb = sub { snd @msg, @_ };	383	...
		384	kil $SELF;
		385	};
		386
		387	=cut
		388
		389	sub rcv($@);
		390
		391	sub _kilme {
		392	die "received message on port without callback";
		393	}
		394
		395	sub port(;&) {
		396	my $id = $UNIQ . ++$ID;
		397	my $port = "$NODE#$id";
		398
		399	rcv $port, shift || \&_kilme;
		400
		401	$port
		402	}
		403
		404	=item rcv $local_port, $callback->(@msg)
		405
		406	Replaces the default callback on the specified port. There is no way to
		407	remove the default callback: use C<sub { }> to disable it, or better
		408	C<kil> the port when it is no longer needed.
		409
		410	The global C<$SELF> (exported by this module) contains C<$port> while
		411	executing the callback. Runtime errors during callback execution will
		412	result in the port being C<kil>ed.
		413
		414	The default callback received all messages not matched by a more specific
		415	C<tag> match.
		416
		417	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
		418
		419	Register (or replace) callbacks to be called on messages starting with the
		420	given tag on the given port (and return the port), or unregister it (when
		421	C<$callback> is C<$undef> or missing). There can only be one callback
		422	registered for each tag.
		423
		424	The original message will be passed to the callback, after the first
		425	element (the tag) has been removed. The callback will use the same
		426	environment as the default callback (see above).
		427
		428	Example: create a port and bind receivers on it in one go.
		429
		430	my $port = rcv port,
		431	msg1 => sub { ... },
		432	msg2 => sub { ... },
		433	;
		434
		435	Example: create a port, bind receivers and send it in a message elsewhere
		436	in one go:
		437
		438	snd $otherport, reply =>
		439	rcv port,
		440	msg1 => sub { ... },
		441	...
		442	;
		443
		444	Example: temporarily register a rcv callback for a tag matching some port
		445	(e.g. for an rpc reply) and unregister it after a message was received.
		446
		447	rcv $port, $otherport => sub {
		448	my @reply = @_;
		449
		450	rcv $SELF, $otherport;
		451	};
		452
		453	=cut
		454
		455	sub rcv($@) {
		456	my $port = shift;
		457	my ($nodeid, $portid) = split /#/, $port, 2;
		458
		459	$NODE{$nodeid} == $NODE{""}
		460	or Carp::croak "$port: rcv can only be called on local ports, caught";
		461
		462	while (@_) {
		463	if (ref $_[0]) {
		464	if (my $self = $PORT_DATA{$portid}) {
		465	"AnyEvent::MP::Port" eq ref $self
		466	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		467
		468	$self->[0] = shift;
213	} else {	469	} else {
214	# simply kill other port	470	my $cb = shift;
215	my $port = $cb;	471	$PORT{$portid} = sub {
216	$cb = sub { kil $port, @_ if @_ };	472	local $SELF = $port;
		473	eval { &$cb }; _self_die if $@;
		474	};
		475	}
		476	} elsif (defined $_[0]) {
		477	my $self = $PORT_DATA{$portid} ||= do {
		478	my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port";
		479
		480	$PORT{$portid} = sub {
		481	local $SELF = $port;
		482
		483	if (my $cb = $self->[1]{$_[0]}) {
		484	shift;
		485	eval { &$cb }; _self_die if $@;
		486	} else {
		487	&{ $self->[0] };
		488	}
		489	};
		490
		491	$self
		492	};
		493
		494	"AnyEvent::MP::Port" eq ref $self
		495	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		496
		497	my ($tag, $cb) = splice @_, 0, 2;
		498
		499	if (defined $cb) {
		500	$self->[1]{$tag} = $cb;
		501	} else {
		502	delete $self->[1]{$tag};
		503	}
217	}	504	}
218	}	505	}
219		506
220	$node->monitor ($port, $cb);
221
222	defined wantarray
223	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }
224	}
225
226	=item $guard = mon_guard $port, $ref, $ref...
227
228	Monitors the given C<$port> and keeps the passed references. When the port
229	is killed, the references will be freed.
230
231	Optionally returns a guard that will stop the monitoring.
232
233	This function is useful when you create e.g. timers or other watchers and
234	want to free them when the port gets killed:
235
236	$port->rcv (start => sub {
237	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {
238	undef $timer if 0.9 < rand;
239	});
240	});
241
242	=cut
243
244	sub mon_guard {
245	my ($port, @refs) = @_;
246
247	mon $port, sub { 0 && @refs }
248	}
249
250	=item lnk $port1, $port2
251
252	Link two ports. This is simply a shorthand for:
253
254	mon $port1, $port2;
255	mon $port2, $port1;
256
257	It means that if either one is killed abnormally, the other one gets
258	killed as well.
259
260	=item $local_port = port
261
262	Create a new local port object that supports message matching.
263
264	=item $portid = port { my @msg = @_; $finished }
265
266	Creates a "mini port", that is, a very lightweight port without any
267	pattern matching behind it, and returns its ID.
268
269	The block will be called for every message received on the port. When the
270	callback returns a true value its job is considered "done" and the port
271	will be destroyed. Otherwise it will stay alive.
272
273	The message will be passed as-is, no extra argument (i.e. no port id) will
274	be passed to the callback.
275
276	If you need the local port id in the callback, this works nicely:
277
278	my $port; $port = miniport {
279	snd $otherport, reply => $port;
280	};
281
282	=cut
283
284	sub port(;&) {
285	my $id = "$UNIQ." . $ID++;
286	my $port = "$NODE#$id";
287
288	if (@_) {
289	my $cb = shift;
290	$PORT{$id} = sub {
291	local $SELF = $port;
292	eval {
293	&$cb
294	and kil $id;
295	};
296	_self_die if $@;
297	};
298	} else {
299	my $self = bless {
300	id => "$NODE#$id",
301	}, "AnyEvent::MP::Port";
302
303	$PORT_DATA{$id} = $self;
304	$PORT{$id} = sub {
305	local $SELF = $port;
306
307	eval {
308	for (@{ $self->{rc0}{$_[0]} }) {
309	$_ && &{$_->[0]}
310	&& undef $_;
311	}
312
313	for (@{ $self->{rcv}{$_[0]} }) {
314	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
315	&& &{$_->[0]}
316	&& undef $_;
317	}
318
319	for (@{ $self->{any} }) {
320	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
321	&& &{$_->[0]}
322	&& undef $_;
323	}
324	};
325	_self_die if $@;
326	};
327	}
328
329	$port	507	$port
330	}	508	}
331		509
332	=item reg $portid, $name	510	=item peval $port, $coderef[, @args]
333		511
334	Registers the given port under the name C<$name>. If the name already	512	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
335	exists it is replaced.	513	when the code throews an exception the C<$port> will be killed.
336		514
337	A port can only be registered under one well known name.	515	Any remaining args will be passed to the callback. Any return values will
		516	be returned to the caller.
338		517
339	A port automatically becomes unregistered when it is killed.	518	This is useful when you temporarily want to execute code in the context of
		519	a port.
340		520
341	=cut	521	Example: create a port and run some initialisation code in it's context.
342		522
343	sub reg(@) {	523	my $port = port { ... };
344	my ($portid, $name) = @_;
345		524
346	$REG{$name} = $portid;	525	peval $port, sub {
347	}	526	init
		527	or die "unable to init";
		528	};
348		529
349	=item rcv $portid, tagstring => $callback->(@msg), ...
350
351	=item rcv $portid, $smartmatch => $callback->(@msg), ...
352
353	=item rcv $portid, [$smartmatch...] => $callback->(@msg), ...
354
355	Register callbacks to be called on matching messages on the given port.
356
357	The callback has to return a true value when its work is done, after
358	which is will be removed, or a false value in which case it will stay
359	registered.
360
361	The global C<$SELF> (exported by this module) contains C<$portid> while
362	executing the callback.
363
364	Runtime errors wdurign callback execution will result in the port being
365	C<kil>ed.
366
367	If the match is an array reference, then it will be matched against the
368	first elements of the message, otherwise only the first element is being
369	matched.
370
371	Any element in the match that is specified as C<_any_> (a function
372	exported by this module) matches any single element of the message.
373
374	While not required, it is highly recommended that the first matching
375	element is a string identifying the message. The one-string-only match is
376	also the most efficient match (by far).
377
378	=cut	530	=cut
379		531
380	sub rcv($@) {	532	sub peval($$) {
381	my ($noderef, $port) = split /#/, shift, 2;	533	local $SELF = shift;
		534	my $cb = shift;
382		535
383	($NODE{$noderef} || add_node $noderef) == $NODE{""}	536	if (wantarray) {
384	or Carp::croak "$noderef#$port: rcv can only be called on local ports, caught";	537	my @res = eval { &$cb };
385		538	_self_die if $@;
386	my $self = $PORT_DATA{$port}	539	@res
387	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";
388
389	"AnyEvent::MP::Port" eq ref $self
390	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";
391
392	while (@_) {
393	my ($match, $cb) = splice @_, 0, 2;
394
395	if (!ref $match) {
396	push @{ $self->{rc0}{$match} }, [$cb];
397	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
398	my ($type, @match) = @$match;
399	@match
400	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
401	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
402	} else {	540	} else {
403	push @{ $self->{any} }, [$cb, $match];	541	my $res = eval { &$cb };
404	}	542	_self_die if $@;
		543	$res
405	}	544	}
406	}	545	}
407		546
408	=item $closure = psub { BLOCK }	547	=item $closure = psub { BLOCK }
409		548
410	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	549	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
411	closure is executed, sets up the environment in the same way as in C<rcv>	550	closure is executed, sets up the environment in the same way as in C<rcv>
412	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.	551	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		552
		553	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		554	BLOCK }, @_ } >>.
413		555
414	This is useful when you register callbacks from C<rcv> callbacks:	556	This is useful when you register callbacks from C<rcv> callbacks:
415		557
416	rcv delayed_reply => sub {	558	rcv delayed_reply => sub {
417	my ($delay, @reply) = @_;	559	my ($delay, @reply) = @_;
…		…
441	$res	583	$res
442	}	584	}
443	}	585	}
444	}	586	}
445		587
		588	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
		589
		590	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
		591
		592	=item $guard = mon $port # kill $SELF when $port dies
		593
		594	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		595
		596	Monitor the given port and do something when the port is killed or
		597	messages to it were lost, and optionally return a guard that can be used
		598	to stop monitoring again.
		599
		600	In the first form (callback), the callback is simply called with any
		601	number of C<@reason> elements (no @reason means that the port was deleted
		602	"normally"). Note also that I<< the callback B<must> never die >>, so use
		603	C<eval> if unsure.
		604
		605	In the second form (another port given), the other port (C<$rcvport>)
		606	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
		607	"normal" kils nothing happens, while under all other conditions, the other
		608	port is killed with the same reason.
		609
		610	The third form (kill self) is the same as the second form, except that
		611	C<$rvport> defaults to C<$SELF>.
		612
		613	In the last form (message), a message of the form C<@msg, @reason> will be
		614	C<snd>.
		615
		616	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		617	alert was raised), they are removed and will not trigger again.
		618
		619	As a rule of thumb, monitoring requests should always monitor a port from
		620	a local port (or callback). The reason is that kill messages might get
		621	lost, just like any other message. Another less obvious reason is that
		622	even monitoring requests can get lost (for example, when the connection
		623	to the other node goes down permanently). When monitoring a port locally
		624	these problems do not exist.
		625
		626	C<mon> effectively guarantees that, in the absence of hardware failures,
		627	after starting the monitor, either all messages sent to the port will
		628	arrive, or the monitoring action will be invoked after possible message
		629	loss has been detected. No messages will be lost "in between" (after
		630	the first lost message no further messages will be received by the
		631	port). After the monitoring action was invoked, further messages might get
		632	delivered again.
		633
		634	Inter-host-connection timeouts and monitoring depend on the transport
		635	used. The only transport currently implemented is TCP, and AnyEvent::MP
		636	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		637	non-idle connection, and usually around two hours for idle connections).
		638
		639	This means that monitoring is good for program errors and cleaning up
		640	stuff eventually, but they are no replacement for a timeout when you need
		641	to ensure some maximum latency.
		642
		643	Example: call a given callback when C<$port> is killed.
		644
		645	mon $port, sub { warn "port died because of <@_>\n" };
		646
		647	Example: kill ourselves when C<$port> is killed abnormally.
		648
		649	mon $port;
		650
		651	Example: send us a restart message when another C<$port> is killed.
		652
		653	mon $port, $self => "restart";
		654
		655	=cut
		656
		657	sub mon {
		658	my ($nodeid, $port) = split /#/, shift, 2;
		659
		660	my $node = $NODE{$nodeid} || add_node $nodeid;
		661
		662	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
		663
		664	unless (ref $cb) {
		665	if (@_) {
		666	# send a kill info message
		667	my (@msg) = ($cb, @_);
		668	$cb = sub { snd @msg, @_ };
		669	} else {
		670	# simply kill other port
		671	my $port = $cb;
		672	$cb = sub { kil $port, @_ if @_ };
		673	}
		674	}
		675
		676	$node->monitor ($port, $cb);
		677
		678	defined wantarray
		679	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
		680	}
		681
		682	=item $guard = mon_guard $port, $ref, $ref...
		683
		684	Monitors the given C<$port> and keeps the passed references. When the port
		685	is killed, the references will be freed.
		686
		687	Optionally returns a guard that will stop the monitoring.
		688
		689	This function is useful when you create e.g. timers or other watchers and
		690	want to free them when the port gets killed (note the use of C<psub>):
		691
		692	$port->rcv (start => sub {
		693	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
		694	undef $timer if 0.9 < rand;
		695	});
		696	});
		697
		698	=cut
		699
		700	sub mon_guard {
		701	my ($port, @refs) = @_;
		702
		703	#TODO: mon-less form?
		704
		705	mon $port, sub { 0 && @refs }
		706	}
		707
		708	=item kil $port[, @reason]
		709
		710	Kill the specified port with the given C<@reason>.
		711
		712	If no C<@reason> is specified, then the port is killed "normally" -
		713	monitor callback will be invoked, but the kil will not cause linked ports
		714	(C<mon $mport, $lport> form) to get killed.
		715
		716	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
		717	form) get killed with the same reason.
		718
		719	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		720	will be reported as reason C<< die => $@ >>.
		721
		722	Transport/communication errors are reported as C<< transport_error =>
		723	$message >>.
		724
		725	=cut
		726
		727	=item $port = spawn $node, $initfunc[, @initdata]
		728
		729	Creates a port on the node C<$node> (which can also be a port ID, in which
		730	case it's the node where that port resides).
		731
		732	The port ID of the newly created port is returned immediately, and it is
		733	possible to immediately start sending messages or to monitor the port.
		734
		735	After the port has been created, the init function is called on the remote
		736	node, in the same context as a C<rcv> callback. This function must be a
		737	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		738	specify a function in the main program, use C<::name>.
		739
		740	If the function doesn't exist, then the node tries to C<require>
		741	the package, then the package above the package and so on (e.g.
		742	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		743	exists or it runs out of package names.
		744
		745	The init function is then called with the newly-created port as context
		746	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		747	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		748	the port might not get created.
		749
		750	A common idiom is to pass a local port, immediately monitor the spawned
		751	port, and in the remote init function, immediately monitor the passed
		752	local port. This two-way monitoring ensures that both ports get cleaned up
		753	when there is a problem.
		754
		755	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		756	caller before C<spawn> returns (by delaying invocation when spawn is
		757	called for the local node).
		758
		759	Example: spawn a chat server port on C<$othernode>.
		760
		761	# this node, executed from within a port context:
		762	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		763	mon $server;
		764
		765	# init function on C<$othernode>
		766	sub connect {
		767	my ($srcport) = @_;
		768
		769	mon $srcport;
		770
		771	rcv $SELF, sub {
		772	...
		773	};
		774	}
		775
		776	=cut
		777
		778	sub _spawn {
		779	my $port = shift;
		780	my $init = shift;
		781
		782	# rcv will create the actual port
		783	local $SELF = "$NODE#$port";
		784	eval {
		785	&{ load_func $init }
		786	};
		787	_self_die if $@;
		788	}
		789
		790	sub spawn(@) {
		791	my ($nodeid, undef) = split /#/, shift, 2;
		792
		793	my $id = $RUNIQ . ++$ID;
		794
		795	$_[0] =~ /::/
		796	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		797
		798	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		799
		800	"$nodeid#$id"
		801	}
		802
		803
		804	=item after $timeout, @msg
		805
		806	=item after $timeout, $callback
		807
		808	Either sends the given message, or call the given callback, after the
		809	specified number of seconds.
		810
		811	This is simply a utility function that comes in handy at times - the
		812	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		813	so it may go away in the future.
		814
		815	=cut
		816
		817	sub after($@) {
		818	my ($timeout, @action) = @_;
		819
		820	my $t; $t = AE::timer $timeout, 0, sub {
		821	undef $t;
		822	ref $action[0]
		823	? $action[0]()
		824	: snd @action;
		825	};
		826	}
		827
		828	=item cal $port, @msg, $callback[, $timeout]
		829
		830	A simple form of RPC - sends a message to the given C<$port> with the
		831	given contents (C<@msg>), but adds a reply port to the message.
		832
		833	The reply port is created temporarily just for the purpose of receiving
		834	the reply, and will be C<kil>ed when no longer needed.
		835
		836	A reply message sent to the port is passed to the C<$callback> as-is.
		837
		838	If an optional time-out (in seconds) is given and it is not C<undef>,
		839	then the callback will be called without any arguments after the time-out
		840	elapsed and the port is C<kil>ed.
		841
		842	If no time-out is given (or it is C<undef>), then the local port will
		843	monitor the remote port instead, so it eventually gets cleaned-up.
		844
		845	Currently this function returns the temporary port, but this "feature"
		846	might go in future versions unless you can make a convincing case that
		847	this is indeed useful for something.
		848
		849	=cut
		850
		851	sub cal(@) {
		852	my $timeout = ref $_[-1] ? undef : pop;
		853	my $cb = pop;
		854
		855	my $port = port {
		856	undef $timeout;
		857	kil $SELF;
		858	&$cb;
		859	};
		860
		861	if (defined $timeout) {
		862	$timeout = AE::timer $timeout, 0, sub {
		863	undef $timeout;
		864	kil $port;
		865	$cb->();
		866	};
		867	} else {
		868	mon $_[0], sub {
		869	kil $port;
		870	$cb->();
		871	};
		872	}
		873
		874	push @_, $port;
		875	&snd;
		876
		877	$port
		878	}
		879
446	=back	880	=back
447		881
448	=head1 FUNCTIONS FOR NODES	882	=head1 DISTRIBUTED DATABASE
		883
		884	AnyEvent::MP comes with a simple distributed database. The database will
		885	be mirrored asynchronously at all global nodes. Other nodes bind to one of
		886	the global nodes for their needs.
		887
		888	The database consists of a two-level hash - a hash contains a hash which
		889	contains values.
		890
		891	The top level hash key is called "family", and the second-level hash key
		892	is simply called "key".
		893
		894	The family and key must be alphanumeric ASCII strings, i.e. start
		895	with a letter and consist of letters, digits, underscores and colons
		896	(C<[A-Za-z][A-Za-z0-9_:]*>, pretty much like Perl module names.
		897
		898	As the family namespaceis global, it is recommended to prefix family names
		899	with the name of the application or module using it.
		900
		901	The values should preferably be strings, but other perl scalars should
		902	work as well (such as arrays and hashes).
		903
		904	Every database entry is owned by one node - adding the same family/key
		905	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		906	but the result might be nondeterministic, i.e. the key might have
		907	different values on different nodes.
		908
		909	=item db_set $family => $key => $value
		910
		911	Sets (or replaces) a key to the database.
		912
		913	=item db_del $family => $key
		914
		915	Deletes a key from the database.
		916
		917	=item $guard = db_reg $family => $key [=> $value]
		918
		919	Sets the key on the database and returns a guard. When the guard is
		920	destroyed, the key is deleted from the database. If C<$value> is missing,
		921	then C<undef> is used.
		922
		923	=cut
		924
		925	=back
		926
		927	=head1 AnyEvent::MP vs. Distributed Erlang
		928
		929	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
		930	== aemp node, Erlang process == aemp port), so many of the documents and
		931	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
		932	sample:
		933
		934	http://www.erlang.se/doc/programming_rules.shtml
		935	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
		936	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
		937	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
		938
		939	Despite the similarities, there are also some important differences:
449		940
450	=over 4	941	=over 4
451		942
452	=item become_public endpoint...	943	=item * Node IDs are arbitrary strings in AEMP.
453		944
454	Tells the node to become a public node, i.e. reachable from other nodes.
455
456	If no arguments are given, or the first argument is C<undef>, then
457	AnyEvent::MP tries to bind on port C<4040> on all IP addresses that the
458	local nodename resolves to.
459
460	Otherwise the first argument must be an array-reference with transport
461	endpoints ("ip:port", "hostname:port") or port numbers (in which case the
462	local nodename is used as hostname). The endpoints are all resolved and
463	will become the node reference.
464
465	=cut
466
467	=back
468
469	=head1 NODE MESSAGES
470
471	Nodes understand the following messages sent to them. Many of them take
472	arguments called C<@reply>, which will simply be used to compose a reply
473	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
474	the remaining arguments are simply the message data.
475
476	=over 4
477
478	=cut
479
480	=item lookup => $name, @reply
481
482	Replies with the port ID of the specified well-known port, or C<undef>.
483
484	=item devnull => ...
485
486	Generic data sink/CPU heat conversion.
487
488	=item relay => $port, @msg
489
490	Simply forwards the message to the given port.
491
492	=item eval => $string[ @reply]
493
494	Evaluates the given string. If C<@reply> is given, then a message of the
495	form C<@reply, $@, @evalres> is sent.
496
497	Example: crash another node.
498
499	snd $othernode, eval => "exit";
500
501	=item time => @reply
502
503	Replies the the current node time to C<@reply>.
504
505	Example: tell the current node to send the current time to C<$myport> in a
506	C<timereply> message.
507
508	snd $NODE, time => $myport, timereply => 1, 2;
509	# => snd $myport, timereply => 1, 2, <time>
510
511	=back
512
513	=head1 AnyEvent::MP vs. Distributed Erlang
514
515	AnyEvent::MP got lots of its ideas from distributed erlang. Despite the
516	similarities (erlang node == aemp node, erlang process == aemp port and so
517	on), there are also some important differences:
518
519	=over 4
520
521	=item * Node references contain the recipe on how to contact them.
522
523	Erlang relies on special naming and DNS to work everywhere in the	945	Erlang relies on special naming and DNS to work everywhere in the same
524	same way. AEMP relies on each node knowing it's own address(es), with	946	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
525	convenience functionality.	947	configuration or DNS), and possibly the addresses of some seed nodes, but
		948	will otherwise discover other nodes (and their IDs) itself.
		949
		950	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
		951	uses "local ports are like remote ports".
		952
		953	The failure modes for local ports are quite different (runtime errors
		954	only) then for remote ports - when a local port dies, you I<know> it dies,
		955	when a connection to another node dies, you know nothing about the other
		956	port.
		957
		958	Erlang pretends remote ports are as reliable as local ports, even when
		959	they are not.
		960
		961	AEMP encourages a "treat remote ports differently" philosophy, with local
		962	ports being the special case/exception, where transport errors cannot
		963	occur.
526		964
527	=item * Erlang uses processes and a mailbox, AEMP does not queue.	965	=item * Erlang uses processes and a mailbox, AEMP does not queue.
528		966
529	Erlang uses processes that selctively receive messages, and therefore	967	Erlang uses processes that selectively receive messages out of order, and
530	needs a queue. AEMP is event based, queuing messages would serve no useful	968	therefore needs a queue. AEMP is event based, queuing messages would serve
531	purpose.	969	no useful purpose. For the same reason the pattern-matching abilities
		970	of AnyEvent::MP are more limited, as there is little need to be able to
		971	filter messages without dequeuing them.
532		972
533	(But see L<Coro::MP> for a more erlang-like process model on top of AEMP).	973	This is not a philosophical difference, but simply stems from AnyEvent::MP
		974	being event-based, while Erlang is process-based.
		975
		976	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		977	top of AEMP and Coro threads.
534		978
535	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	979	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
536		980
537	Sending messages in erlang is synchronous and blocks the process. AEMP	981	Sending messages in Erlang is synchronous and blocks the process until
538	sends are immediate, connection establishment is handled in the	982	a conenction has been established and the message sent (and so does not
539	background.	983	need a queue that can overflow). AEMP sends return immediately, connection
		984	establishment is handled in the background.
540		985
541	=item * Erlang can silently lose messages, AEMP cannot.	986	=item * Erlang suffers from silent message loss, AEMP does not.
542		987
543	Erlang makes few guarantees on messages delivery - messages can get lost	988	Erlang implements few guarantees on messages delivery - messages can get
544	without any of the processes realising it (i.e. you send messages a, b,	989	lost without any of the processes realising it (i.e. you send messages a,
545	and c, and the other side only receives messages a and c).	990	b, and c, and the other side only receives messages a and c).
546		991
547	AEMP guarantees correct ordering, and the guarantee that there are no	992	AEMP guarantees (modulo hardware errors) correct ordering, and the
		993	guarantee that after one message is lost, all following ones sent to the
		994	same port are lost as well, until monitoring raises an error, so there are
548	holes in the message sequence.	995	no silent "holes" in the message sequence.
549		996
550	=item * In erlang, processes can be declared dead and later be found to be	997	If you want your software to be very reliable, you have to cope with
551	alive.	998	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
552		999	simply tries to work better in common error cases, such as when a network
553	In erlang it can happen that a monitored process is declared dead and	1000	link goes down.
554	linked processes get killed, but later it turns out that the process is
555	still alive - and can receive messages.
556
557	In AEMP, when port monitoring detects a port as dead, then that port will
558	eventually be killed - it cannot happen that a node detects a port as dead
559	and then later sends messages to it, finding it is still alive.
560		1001
561	=item * Erlang can send messages to the wrong port, AEMP does not.	1002	=item * Erlang can send messages to the wrong port, AEMP does not.
562		1003
563	In erlang it is quite possible that a node that restarts reuses a process	1004	In Erlang it is quite likely that a node that restarts reuses an Erlang
564	ID known to other nodes for a completely different process, causing	1005	process ID known to other nodes for a completely different process,
565	messages destined for that process to end up in an unrelated process.	1006	causing messages destined for that process to end up in an unrelated
		1007	process.
566		1008
567	AEMP never reuses port IDs, so old messages or old port IDs floating	1009	AEMP does not reuse port IDs, so old messages or old port IDs floating
568	around in the network will not be sent to an unrelated port.	1010	around in the network will not be sent to an unrelated port.
569		1011
570	=item * Erlang uses unprotected connections, AEMP uses secure	1012	=item * Erlang uses unprotected connections, AEMP uses secure
571	authentication and can use TLS.	1013	authentication and can use TLS.
572		1014
573	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1015	AEMP can use a proven protocol - TLS - to protect connections and
574	securely authenticate nodes.	1016	securely authenticate nodes.
575		1017
		1018	=item * The AEMP protocol is optimised for both text-based and binary
		1019	communications.
		1020
		1021	The AEMP protocol, unlike the Erlang protocol, supports both programming
		1022	language independent text-only protocols (good for debugging), and binary,
		1023	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1024	used, the protocol is actually completely text-based.
		1025
		1026	It has also been carefully designed to be implementable in other languages
		1027	with a minimum of work while gracefully degrading functionality to make the
		1028	protocol simple.
		1029
		1030	=item * AEMP has more flexible monitoring options than Erlang.
		1031
		1032	In Erlang, you can chose to receive I<all> exit signals as messages or
		1033	I<none>, there is no in-between, so monitoring single Erlang processes is
		1034	difficult to implement.
		1035
		1036	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1037	between automatic kill, exit message or callback on a per-port basis.
		1038
		1039	=item * Erlang tries to hide remote/local connections, AEMP does not.
		1040
		1041	Monitoring in Erlang is not an indicator of process death/crashes, in the
		1042	same way as linking is (except linking is unreliable in Erlang).
		1043
		1044	In AEMP, you don't "look up" registered port names or send to named ports
		1045	that might or might not be persistent. Instead, you normally spawn a port
		1046	on the remote node. The init function monitors you, and you monitor the
		1047	remote port. Since both monitors are local to the node, they are much more
		1048	reliable (no need for C<spawn_link>).
		1049
		1050	This also saves round-trips and avoids sending messages to the wrong port
		1051	(hard to do in Erlang).
		1052
576	=back	1053	=back
577		1054
		1055	=head1 RATIONALE
		1056
		1057	=over 4
		1058
		1059	=item Why strings for port and node IDs, why not objects?
		1060
		1061	We considered "objects", but found that the actual number of methods
		1062	that can be called are quite low. Since port and node IDs travel over
		1063	the network frequently, the serialising/deserialising would add lots of
		1064	overhead, as well as having to keep a proxy object everywhere.
		1065
		1066	Strings can easily be printed, easily serialised etc. and need no special
		1067	procedures to be "valid".
		1068
		1069	And as a result, a port with just a default receiver consists of a single
		1070	code reference stored in a global hash - it can't become much cheaper.
		1071
		1072	=item Why favour JSON, why not a real serialising format such as Storable?
		1073
		1074	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1075	format, but currently there is no way to make a node use Storable by
		1076	default (although all nodes will accept it).
		1077
		1078	The default framing protocol is JSON because a) JSON::XS is many times
		1079	faster for small messages and b) most importantly, after years of
		1080	experience we found that object serialisation is causing more problems
		1081	than it solves: Just like function calls, objects simply do not travel
		1082	easily over the network, mostly because they will always be a copy, so you
		1083	always have to re-think your design.
		1084
		1085	Keeping your messages simple, concentrating on data structures rather than
		1086	objects, will keep your messages clean, tidy and efficient.
		1087
		1088	=back
		1089
578	=head1 SEE ALSO	1090	=head1 SEE ALSO
		1091
		1092	L<AnyEvent::MP::Intro> - a gentle introduction.
		1093
		1094	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1095
		1096	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1097	your applications.
		1098
		1099	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1100
		1101	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1102	all nodes.
579		1103
580	L<AnyEvent>.	1104	L<AnyEvent>.
581		1105
582	=head1 AUTHOR	1106	=head1 AUTHOR
583		1107

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