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Revision 1.31 by root, Wed Aug 5 19:55:58 2009 UTC vs.
Revision 1.125 by root, Sat Mar 3 13:07:19 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).	76	Not to be confused with a TCP port, a "port" is something you can send
		77	messages to (with the C<snd> function).
49		78
50	Some ports allow you to register C<rcv> handlers that can match specific	79	Ports allow you to register C<rcv> handlers that can match all or just
51	messages. All C<rcv> handlers will receive messages they match, messages	80	some messages. Messages send to ports will not be queued, regardless of
52	will not be queued.	81	anything was listening for them or not.
53		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
54	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
55		86
56	A port id is normaly the concatenation of a noderef, a hash-mark (C<#>) as	87	A port ID is the concatenation of a node ID, a hash-mark (C<#>)
57	separator, and a port name (a printable string of unspecified format). An	88	as separator, and a port name (a printable string of unspecified
58	exception is the the node port, whose ID is identical to its node	89	format created by AnyEvent::MP).
59	reference.
60		90
61	=item node	91	=item node
62		92
63	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,
64	port. You can send messages to node ports to find existing ports or to	94	which enables nodes to manage each other remotely, and to create new
65	create new ports, among other things.	95	ports.
66		96
67	Nodes are either private (single-process only), slaves (connected to a	97	Nodes are either public (have one or more listening ports) or private
68	master node only) or public nodes (connectable from unrelated nodes).	98	(no listening ports). Private nodes cannot talk to other private nodes
		99	currently, but all nodes can talk to public nodes.
69		100
70	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	101	Nodes is represented by (printable) strings called "node IDs".
71		102
72	A node reference is a string that either simply identifies the node (for	103	=item node ID - C<[A-Za-z0-9_\-.:]*>
73	private and slave nodes), or contains a recipe on how to reach a given
74	node (for public nodes).
75		104
76	This recipe is simply a comma-separated list of C<address:port> pairs (for	105	A node ID is a string that uniquely identifies the node within a
77	TCP/IP, other protocols might look different).	106	network. Depending on the configuration used, node IDs can look like a
		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.
78		109
79	Node references come in two flavours: resolved (containing only numerical	110	=item binds - C<ip:port>
80	addresses) or unresolved (where hostnames are used instead of addresses).
81		111
82	Before using an unresolved node reference in a message you first have to	112	Nodes can only talk to each other by creating some kind of connection to
83	resolve it.	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).
84		170
85	=back	171	=back
86		172
87	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
88		174
…		…
90		176
91	=cut	177	=cut
92		178
93	package AnyEvent::MP;	179	package AnyEvent::MP;
94		180
		181	use AnyEvent::MP::Config ();
95	use AnyEvent::MP::Base;	182	use AnyEvent::MP::Kernel;
		183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
96		184
97	use common::sense;	185	use common::sense;
98		186
99	use Carp ();	187	use Carp ();
100		188
101	use AE ();	189	use AE ();
		190	use Guard ();
102		191
103	use base "Exporter";	192	use base "Exporter";
104		193
105	our $VERSION = '0.1';	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
		195
106	our @EXPORT = qw(	196	our @EXPORT = qw(
107	NODE $NODE *SELF node_of _any_	197	NODE $NODE *SELF node_of after
108	resolve_node initialise_node	198	configure
109	snd rcv mon kil reg psub	199	snd rcv mon mon_guard kil psub peval spawn cal
110	port	200	port
		201	db_set db_del db_reg
111	);	202	);
112		203
113	our $SELF;	204	our $SELF;
114		205
115	sub _self_die() {	206	sub _self_die() {
…		…
118	kil $SELF, die => $msg;	209	kil $SELF, die => $msg;
119	}	210	}
120		211
121	=item $thisnode = NODE / $NODE	212	=item $thisnode = NODE / $NODE
122		213
123	The C<NODE> function returns, and the C<$NODE> variable contains	214	The C<NODE> function returns, and the C<$NODE> variable contains, the node
124	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
125	to C<become_public> or C<become_slave>, after which all local port	216	a call to C<configure>.
126	identifiers become invalid.
127		217
128	=item $noderef = node_of $portid	218	=item $nodeid = node_of $port
129		219
130	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.
131		221
132	=item $cv = resolve_node $noderef	222	=item configure $profile, key => value...
133		223
134	Takes an unresolved node reference that may contain hostnames and	224	=item configure key => value...
135	abbreviated IDs, resolves all of them and returns a resolved node
136	reference.
137		225
138	In addition to C<address:port> pairs allowed in resolved noderefs, the	226	Before a node can talk to other nodes on the network (i.e. enter
139	following forms are supported:	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:
140		236
141	=over 4	237	=over 4
142		238
143	=item the empty string	239	=item norc => $boolean (default false)
144		240
145	An empty-string component gets resolved as if the default port (4040) was	241	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
146	specified.	242	be consulted - all configuraiton options must be specified in the
		243	C<configure> call.
147		244
148	=item naked port numbers (e.g. C<1234>)	245	=item force => $boolean (default false)
149		246
150	These are resolved by prepending the local nodename and a colon, to be	247	IF true, then the values specified in the C<configure> will take
151	further resolved.	248	precedence over any values configured via the rc file. The default is for
152		249	the rc file to override any options specified in the program.
153	=item hostnames (e.g. C<localhost:1234>, C<localhost>)
154
155	These are resolved by using AnyEvent::DNS to resolve them, optionally
156	looking up SRV records for the C<aemp=4040> port, if no port was
157	specified.
158		250
159	=back	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)"
160		326
161	=item $SELF	327	=item $SELF
162		328
163	Contains the current port id while executing C<rcv> callbacks or C<psub>	329	Contains the current port id while executing C<rcv> callbacks or C<psub>
164	blocks.	330	blocks.
165		331
166	=item SELF, %SELF, @SELF...	332	=item *SELF, SELF, %SELF, @SELF...
167		333
168	Due to some quirks in how perl exports variables, it is impossible to	334	Due to some quirks in how perl exports variables, it is impossible to
169	just export C<$SELF>, all the symbols called C<SELF> are exported by this	335	just export C<$SELF>, all the symbols named C<SELF> are exported by this
170	module, but only C<$SELF> is currently used.	336	module, but only C<$SELF> is currently used.
171		337
172	=item snd $portid, type => @data	338	=item snd $port, type => @data
173		339
174	=item snd $portid, @msg	340	=item snd $port, @msg
175		341
176	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
177	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.
178	stringifies a sa port ID (such as a port object :).
179		344
180	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
181	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
182	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.
183		349
184	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
185	function: modifying any argument is not allowed and can cause many	351	function: modifying any argument (or values referenced by them) is
186	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.
187		356
188	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
189	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
190	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
191	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
192	node, anything can be passed.	361	node, anything can be passed. Best rely only on the common denominator of
		362	these.
193		363
194	=item kil $portid[, @reason]	364	=item $local_port = port
195		365
196	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.
197		368
198	If no C<@reason> is specified, then the port is killed "normally" (linked	369	=item $local_port = port { my @msg = @_ }
199	ports will not be kileld, or even notified).
200		370
201	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
202	C<mon>, see below).	372	creating a port and calling C<rcv $port, $callback> on it.
203		373
204	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
205	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.
206		378
207	Transport/communication errors are reported as C<< transport_error =>	379	If you want to stop/destroy the port, simply C<kil> it:
208	$message >>.
209		380
210	=item $guard = mon $portid, $cb->(@reason)	381	my $port = port {
		382	my @msg = @_;
		383	...
		384	kil $SELF;
		385	};
211		386
212	=item $guard = mon $portid, $otherport	387	=cut
213		388
214	=item $guard = mon $portid, $otherport, @msg	389	sub rcv($@);
215		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;
		469	} else {
		470	my $cb = shift;
		471	$PORT{$portid} = sub {
		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	}
		504	}
		505	}
		506
		507	$port
		508	}
		509
		510	=item peval $port, $coderef[, @args]
		511
		512	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		513	when the code throews an exception the C<$port> will be killed.
		514
		515	Any remaining args will be passed to the callback. Any return values will
		516	be returned to the caller.
		517
		518	This is useful when you temporarily want to execute code in the context of
		519	a port.
		520
		521	Example: create a port and run some initialisation code in it's context.
		522
		523	my $port = port { ... };
		524
		525	peval $port, sub {
		526	init
		527	or die "unable to init";
		528	};
		529
		530	=cut
		531
		532	sub peval($$) {
		533	local $SELF = shift;
		534	my $cb = shift;
		535
		536	if (wantarray) {
		537	my @res = eval { &$cb };
		538	_self_die if $@;
		539	@res
		540	} else {
		541	my $res = eval { &$cb };
		542	_self_die if $@;
		543	$res
		544	}
		545	}
		546
		547	=item $closure = psub { BLOCK }
		548
		549	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
		550	closure is executed, sets up the environment in the same way as in C<rcv>
		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 $SELF, sub {
		554	BLOCK }, @_ } >>.
		555
		556	This is useful when you register callbacks from C<rcv> callbacks:
		557
		558	rcv delayed_reply => sub {
		559	my ($delay, @reply) = @_;
		560	my $timer = AE::timer $delay, 0, psub {
		561	snd @reply, $SELF;
		562	};
		563	};
		564
		565	=cut
		566
		567	sub psub(&) {
		568	my $cb = shift;
		569
		570	my $port = $SELF
		571	or Carp::croak "psub can only be called from within rcv or psub callbacks, not";
		572
		573	sub {
		574	local $SELF = $port;
		575
		576	if (wantarray) {
		577	my @res = eval { &$cb };
		578	_self_die if $@;
		579	@res
		580	} else {
		581	my $res = eval { &$cb };
		582	_self_die if $@;
		583	$res
		584	}
		585	}
		586	}
		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 $port dies
		595
216	Monitor the given port and do something when the port is killed.	596	Monitor the given port and do something when the port is killed or
		597	messages to it were lost, and optionally return a guard that can be used
		598	to stop monitoring again.
217		599
218	In the first form, the callback is simply called with any number	600	In the first form (callback), the callback is simply called with any
219	of C<@reason> elements (no @reason means that the port was deleted	601	number of C<@reason> elements (no @reason means that the port was deleted
220	"normally"). Note also that I<< the callback B<must> never die >>, so use	602	"normally"). Note also that I<< the callback B<must> never die >>, so use
221	C<eval> if unsure.	603	C<eval> if unsure.
222		604
223	In the second form, the other port will be C<kil>'ed with C<@reason>, iff	605	In the second form (another port given), the other port (C<$rcvport>)
224	a @reason was specified, i.e. on "normal" kils nothing happens, while	606	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
225	under all other conditions, the other port is killed with the same reason.	607	"normal" kils nothing happens, while under all other conditions, the other
		608	port is killed with the same reason.
226		609
		610	The third form (kill self) is the same as the second form, except that
		611	C<$rvport> defaults to C<$SELF>.
		612
227	In the last form, a message of the form C<@msg, @reason> will be C<snd>.	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.
228		642
229	Example: call a given callback when C<$port> is killed.	643	Example: call a given callback when C<$port> is killed.
230		644
231	mon $port, sub { warn "port died because of <@_>\n" };	645	mon $port, sub { warn "port died because of <@_>\n" };
232		646
233	Example: kill ourselves when C<$port> is killed abnormally.	647	Example: kill ourselves when C<$port> is killed abnormally.
234		648
235	mon $port, $self;	649	mon $port;
236		650
237	Example: send us a restart message another C<$port> is killed.	651	Example: send us a restart message when another C<$port> is killed.
238		652
239	mon $port, $self => "restart";	653	mon $port, $self => "restart";
240		654
241	=cut	655	=cut
242		656
243	sub mon {	657	sub mon {
244	my ($noderef, $port) = split /#/, shift, 2;	658	my ($nodeid, $port) = split /#/, shift, 2;
245		659
246	my $node = $NODE{$noderef} || add_node $noderef;	660	my $node = $NODE{$nodeid} || add_node $nodeid;
247		661
248	my $cb = shift;	662	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
249		663
250	unless (ref $cb) {	664	unless (ref $cb) {
251	if (@_) {	665	if (@_) {
252	# send a kill info message	666	# send a kill info message
253	my (@msg) = ($cb, @_);	667	my (@msg) = ($cb, @_);
…		…
260	}	674	}
261		675
262	$node->monitor ($port, $cb);	676	$node->monitor ($port, $cb);
263		677
264	defined wantarray	678	defined wantarray
265	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	679	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
266	}	680	}
267		681
268	=item $guard = mon_guard $port, $ref, $ref...	682	=item $guard = mon_guard $port, $ref, $ref...
269		683
270	Monitors the given C<$port> and keeps the passed references. When the port	684	Monitors the given C<$port> and keeps the passed references. When the port
271	is killed, the references will be freed.	685	is killed, the references will be freed.
272		686
273	Optionally returns a guard that will stop the monitoring.	687	Optionally returns a guard that will stop the monitoring.
274		688
275	This function is useful when you create e.g. timers or other watchers and	689	This function is useful when you create e.g. timers or other watchers and
276	want to free them when the port gets killed:	690	want to free them when the port gets killed (note the use of C<psub>):
277		691
278	$port->rcv (start => sub {	692	$port->rcv (start => sub {
279	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	693	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
280	undef $timer if 0.9 < rand;	694	undef $timer if 0.9 < rand;
281	});	695	});
282	});	696	});
283		697
284	=cut	698	=cut
285		699
286	sub mon_guard {	700	sub mon_guard {
287	my ($port, @refs) = @_;	701	my ($port, @refs) = @_;
288		702
		703	#TODO: mon-less form?
		704
289	mon $port, sub { 0 && @refs }	705	mon $port, sub { 0 && @refs }
290	}	706	}
291		707
292	=item lnk $port1, $port2	708	=item kil $port[, @reason]
293		709
294	Link two ports. This is simply a shorthand for:	710	Kill the specified port with the given C<@reason>.
295		711
296	mon $port1, $port2;	712	If no C<@reason> is specified, then the port is killed "normally" -
297	mon $port2, $port1;	713	monitor callback will be invoked, but the kil will not cause linked ports
		714	(C<mon $mport, $lport> form) to get killed.
298		715
299	It means that if either one is killed abnormally, the other one gets	716	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
300	killed as well.	717	form) get killed with the same reason.
301		718
302	=item $local_port = port	719	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		720	will be reported as reason C<< die => $@ >>.
303		721
304	Create a new local port object that can be used either as a pattern	722	Transport/communication errors are reported as C<< transport_error =>
305	matching port ("full port") or a single-callback port ("miniport"),	723	$message >>.
306	depending on how C<rcv> callbacks are bound to the object.
307		724
308	=item $portid = port { my @msg = @_; $finished }	725	=cut
309		726
310	Creates a "mini port", that is, a very lightweight port without any	727	=item $port = spawn $node, $initfunc[, @initdata]
311	pattern matching behind it, and returns its ID.
312		728
313	The block will be called for every message received on the port. When the	729	Creates a port on the node C<$node> (which can also be a port ID, in which
314	callback returns a true value its job is considered "done" and the port	730	case it's the node where that port resides).
315	will be destroyed. Otherwise it will stay alive.
316		731
317	The message will be passed as-is, no extra argument (i.e. no port id) will	732	The port ID of the newly created port is returned immediately, and it is
318	be passed to the callback.	733	possible to immediately start sending messages or to monitor the port.
319		734
320	If you need the local port id in the callback, this works nicely:	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>.
321		739
322	my $port; $port = port {	740	If the function doesn't exist, then the node tries to C<require>
323	snd $otherport, reply => $port;	741	the package, then the package above the package and so on (e.g.
		742	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		743	exists or it runs out of package names.
		744
		745	The init function is then called with the newly-created port as context
		746	object (C<$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 }
324	};	786	};
325
326	=cut
327
328	sub port(;&) {
329	my $id = "$UNIQ." . $ID++;
330	my $port = "$NODE#$id";
331
332	if (@_) {
333	my $cb = shift;
334	$PORT{$id} = sub {
335	local $SELF = $port;
336	eval {
337	&$cb
338	and kil $id;
339	};
340	_self_die if $@;	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->();
341	};	866	};
342	} else {	867	} else {
343	my $self = bless {	868	mon $_[0], sub {
344	id => "$NODE#$id",	869	kil $port;
345	}, "AnyEvent::MP::Port";	870	$cb->();
346
347	$PORT_DATA{$id} = $self;
348	$PORT{$id} = sub {
349	local $SELF = $port;
350
351	eval {
352	for (@{ $self->{rc0}{$_[0]} }) {
353	$_ && &{$_->[0]}
354	&& undef $_;
355	}
356
357	for (@{ $self->{rcv}{$_[0]} }) {
358	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
359	&& &{$_->[0]}
360	&& undef $_;
361	}
362
363	for (@{ $self->{any} }) {
364	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
365	&& &{$_->[0]}
366	&& undef $_;
367	}
368	};
369	_self_die if $@;
370	};	871	};
371	}	872	}
372		873
		874	push @_, $port;
		875	&snd;
		876
373	$port	877	$port
374	}	878	}
375		879
376	=item reg $portid, $name
377
378	Registers the given port under the name C<$name>. If the name already
379	exists it is replaced.
380
381	A port can only be registered under one well known name.
382
383	A port automatically becomes unregistered when it is killed.
384
385	=cut
386
387	sub reg(@) {
388	my ($portid, $name) = @_;
389
390	$REG{$name} = $portid;
391	}
392
393	=item rcv $portid, $callback->(@msg)
394
395	Replaces the callback on the specified miniport (or newly created port
396	object, see C<port>). Full ports are configured with the following calls:
397
398	=item rcv $portid, tagstring => $callback->(@msg), ...
399
400	=item rcv $portid, $smartmatch => $callback->(@msg), ...
401
402	=item rcv $portid, [$smartmatch...] => $callback->(@msg), ...
403
404	Register callbacks to be called on matching messages on the given port.
405
406	The callback has to return a true value when its work is done, after
407	which is will be removed, or a false value in which case it will stay
408	registered.
409
410	The global C<$SELF> (exported by this module) contains C<$portid> while
411	executing the callback.
412
413	Runtime errors wdurign callback execution will result in the port being
414	C<kil>ed.
415
416	If the match is an array reference, then it will be matched against the
417	first elements of the message, otherwise only the first element is being
418	matched.
419
420	Any element in the match that is specified as C<_any_> (a function
421	exported by this module) matches any single element of the message.
422
423	While not required, it is highly recommended that the first matching
424	element is a string identifying the message. The one-string-only match is
425	also the most efficient match (by far).
426
427	=cut
428
429	sub rcv($@) {
430	my $portid = shift;
431	my ($noderef, $port) = split /#/, $port, 2;
432
433	($NODE{$noderef} || add_node $noderef) == $NODE{""}
434	or Carp::croak "$noderef#$port: rcv can only be called on local ports, caught";
435
436	my $self = $PORT_DATA{$port}
437	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";
438
439	"AnyEvent::MP::Port" eq ref $self
440	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";
441
442	while (@_) {
443	my ($match, $cb) = splice @_, 0, 2;
444
445	if (!ref $match) {
446	push @{ $self->{rc0}{$match} }, [$cb];
447	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
448	my ($type, @match) = @$match;
449	@match
450	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
451	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
452	} else {
453	push @{ $self->{any} }, [$cb, $match];
454	}
455	}
456
457	$portid
458	}
459
460	=item $closure = psub { BLOCK }
461
462	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
463	closure is executed, sets up the environment in the same way as in C<rcv>
464	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
465
466	This is useful when you register callbacks from C<rcv> callbacks:
467
468	rcv delayed_reply => sub {
469	my ($delay, @reply) = @_;
470	my $timer = AE::timer $delay, 0, psub {
471	snd @reply, $SELF;
472	};
473	};
474
475	=cut
476
477	sub psub(&) {
478	my $cb = shift;
479
480	my $port = $SELF
481	or Carp::croak "psub can only be called from within rcv or psub callbacks, not";
482
483	sub {
484	local $SELF = $port;
485
486	if (wantarray) {
487	my @res = eval { &$cb };
488	_self_die if $@;
489	@res
490	} else {
491	my $res = eval { &$cb };
492	_self_die if $@;
493	$res
494	}
495	}
496	}
497
498	=back	880	=back
499		881
500	=head1 FUNCTIONS FOR NODES	882	=head1 DISTRIBUTED DATABASE
501		883
502	=over 4	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.
503		887
504	=item become_public $noderef	888	The database consists of a two-level hash - a hash contains a hash which
		889	contains values.
505		890
506	Tells the node to become a public node, i.e. reachable from other nodes.	891	The top level hash key is called "family", and the second-level hash key
		892	is simply called "key".
507		893
508	The first argument is the (unresolved) node reference of the local node	894	The family must be alphanumeric, i.e. start with a letter and consist
509	(if missing then the empty string is used).	895	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		896	pretty much like Perl module names.
510		897
511	It is quite common to not specify anything, in which case the local node	898	As the family namespace is global, it is recommended to prefix family names
512	tries to listen on the default port, or to only specify a port number, in	899	with the name of the application or module using it.
513	which case AnyEvent::MP tries to guess the local addresses.	900
		901	The keys must be strings, with no other limitations.
		902
		903	The values should preferably be strings, but other perl scalars should
		904	work as well (such as undef, arrays and hashes).
		905
		906	Every database entry is owned by one node - adding the same family/key
		907	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		908	but the result might be nondeterministic, i.e. the key might have
		909	different values on different nodes.
		910
		911	=item db_set $family => $key => $value
		912
		913	Sets (or replaces) a key to the database.
		914
		915	=item db_del $family => $key
		916
		917	Deletes a key from the database.
		918
		919	=item $guard = db_reg $family => $key [=> $value]
		920
		921	Sets the key on the database and returns a guard. When the guard is
		922	destroyed, the key is deleted from the database. If C<$value> is missing,
		923	then C<undef> is used.
514		924
515	=cut	925	=cut
516		926
517	=back	927	=back
518		928
519	=head1 NODE MESSAGES
520
521	Nodes understand the following messages sent to them. Many of them take
522	arguments called C<@reply>, which will simply be used to compose a reply
523	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
524	the remaining arguments are simply the message data.
525
526	While other messages exist, they are not public and subject to change.
527
528	=over 4
529
530	=cut
531
532	=item lookup => $name, @reply
533
534	Replies with the port ID of the specified well-known port, or C<undef>.
535
536	=item devnull => ...
537
538	Generic data sink/CPU heat conversion.
539
540	=item relay => $port, @msg
541
542	Simply forwards the message to the given port.
543
544	=item eval => $string[ @reply]
545
546	Evaluates the given string. If C<@reply> is given, then a message of the
547	form C<@reply, $@, @evalres> is sent.
548
549	Example: crash another node.
550
551	snd $othernode, eval => "exit";
552
553	=item time => @reply
554
555	Replies the the current node time to C<@reply>.
556
557	Example: tell the current node to send the current time to C<$myport> in a
558	C<timereply> message.
559
560	snd $NODE, time => $myport, timereply => 1, 2;
561	# => snd $myport, timereply => 1, 2, <time>
562
563	=back
564
565	=head1 AnyEvent::MP vs. Distributed Erlang	929	=head1 AnyEvent::MP vs. Distributed Erlang
566		930
567	AnyEvent::MP got lots of its ideas from distributed erlang (erlang node	931	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
568	== aemp node, erlang process == aemp port), so many of the documents and	932	== aemp node, Erlang process == aemp port), so many of the documents and
569	programming techniques employed by erlang apply to AnyEvent::MP. Here is a	933	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
570	sample:	934	sample:
571		935
572	http://www.erlang.se/doc/programming_rules.shtml	936	http://www.erlang.se/doc/programming_rules.shtml
573	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	937	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
574	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6	938	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
…		…
576		940
577	Despite the similarities, there are also some important differences:	941	Despite the similarities, there are also some important differences:
578		942
579	=over 4	943	=over 4
580		944
581	=item * Node references contain the recipe on how to contact them.	945	=item * Node IDs are arbitrary strings in AEMP.
582		946
583	Erlang relies on special naming and DNS to work everywhere in the	947	Erlang relies on special naming and DNS to work everywhere in the same
584	same way. AEMP relies on each node knowing it's own address(es), with	948	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
585	convenience functionality.	949	configuration or DNS), and possibly the addresses of some seed nodes, but
		950	will otherwise discover other nodes (and their IDs) itself.
586		951
587	This means that AEMP requires a less tightly controlled environment at the	952	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
588	cost of longer node references and a slightly higher management overhead.	953	uses "local ports are like remote ports".
		954
		955	The failure modes for local ports are quite different (runtime errors
		956	only) then for remote ports - when a local port dies, you I<know> it dies,
		957	when a connection to another node dies, you know nothing about the other
		958	port.
		959
		960	Erlang pretends remote ports are as reliable as local ports, even when
		961	they are not.
		962
		963	AEMP encourages a "treat remote ports differently" philosophy, with local
		964	ports being the special case/exception, where transport errors cannot
		965	occur.
589		966
590	=item * Erlang uses processes and a mailbox, AEMP does not queue.	967	=item * Erlang uses processes and a mailbox, AEMP does not queue.
591		968
592	Erlang uses processes that selctively receive messages, and therefore	969	Erlang uses processes that selectively receive messages out of order, and
593	needs a queue. AEMP is event based, queuing messages would serve no useful	970	therefore needs a queue. AEMP is event based, queuing messages would serve
594	purpose.	971	no useful purpose. For the same reason the pattern-matching abilities
		972	of AnyEvent::MP are more limited, as there is little need to be able to
		973	filter messages without dequeuing them.
595		974
596	(But see L<Coro::MP> for a more erlang-like process model on top of AEMP).	975	This is not a philosophical difference, but simply stems from AnyEvent::MP
		976	being event-based, while Erlang is process-based.
		977
		978	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		979	top of AEMP and Coro threads.
597		980
598	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	981	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
599		982
600	Sending messages in erlang is synchronous and blocks the process. AEMP	983	Sending messages in Erlang is synchronous and blocks the process until
601	sends are immediate, connection establishment is handled in the	984	a conenction has been established and the message sent (and so does not
602	background.	985	need a queue that can overflow). AEMP sends return immediately, connection
		986	establishment is handled in the background.
603		987
604	=item * Erlang can silently lose messages, AEMP cannot.	988	=item * Erlang suffers from silent message loss, AEMP does not.
605		989
606	Erlang makes few guarantees on messages delivery - messages can get lost	990	Erlang implements few guarantees on messages delivery - messages can get
607	without any of the processes realising it (i.e. you send messages a, b,	991	lost without any of the processes realising it (i.e. you send messages a,
608	and c, and the other side only receives messages a and c).	992	b, and c, and the other side only receives messages a and c).
609		993
610	AEMP guarantees correct ordering, and the guarantee that there are no	994	AEMP guarantees (modulo hardware errors) correct ordering, and the
		995	guarantee that after one message is lost, all following ones sent to the
		996	same port are lost as well, until monitoring raises an error, so there are
611	holes in the message sequence.	997	no silent "holes" in the message sequence.
612		998
613	=item * In erlang, processes can be declared dead and later be found to be	999	If you want your software to be very reliable, you have to cope with
614	alive.	1000	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
615		1001	simply tries to work better in common error cases, such as when a network
616	In erlang it can happen that a monitored process is declared dead and	1002	link goes down.
617	linked processes get killed, but later it turns out that the process is
618	still alive - and can receive messages.
619
620	In AEMP, when port monitoring detects a port as dead, then that port will
621	eventually be killed - it cannot happen that a node detects a port as dead
622	and then later sends messages to it, finding it is still alive.
623		1003
624	=item * Erlang can send messages to the wrong port, AEMP does not.	1004	=item * Erlang can send messages to the wrong port, AEMP does not.
625		1005
626	In erlang it is quite possible that a node that restarts reuses a process	1006	In Erlang it is quite likely that a node that restarts reuses an Erlang
627	ID known to other nodes for a completely different process, causing	1007	process ID known to other nodes for a completely different process,
628	messages destined for that process to end up in an unrelated process.	1008	causing messages destined for that process to end up in an unrelated
		1009	process.
629		1010
630	AEMP never reuses port IDs, so old messages or old port IDs floating	1011	AEMP does not reuse port IDs, so old messages or old port IDs floating
631	around in the network will not be sent to an unrelated port.	1012	around in the network will not be sent to an unrelated port.
632		1013
633	=item * Erlang uses unprotected connections, AEMP uses secure	1014	=item * Erlang uses unprotected connections, AEMP uses secure
634	authentication and can use TLS.	1015	authentication and can use TLS.
635		1016
636	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1017	AEMP can use a proven protocol - TLS - to protect connections and
637	securely authenticate nodes.	1018	securely authenticate nodes.
638		1019
639	=item * The AEMP protocol is optimised for both text-based and binary	1020	=item * The AEMP protocol is optimised for both text-based and binary
640	communications.	1021	communications.
641		1022
642	The AEMP protocol, unlike the erlang protocol, supports both	1023	The AEMP protocol, unlike the Erlang protocol, supports both programming
643	language-independent text-only protocols (good for debugging) and binary,	1024	language independent text-only protocols (good for debugging), and binary,
644	language-specific serialisers (e.g. Storable).	1025	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1026	used, the protocol is actually completely text-based.
645		1027
646	It has also been carefully designed to be implementable in other languages	1028	It has also been carefully designed to be implementable in other languages
647	with a minimum of work while gracefully degrading fucntionality to make the	1029	with a minimum of work while gracefully degrading functionality to make the
648	protocol simple.	1030	protocol simple.
649		1031
		1032	=item * AEMP has more flexible monitoring options than Erlang.
		1033
		1034	In Erlang, you can chose to receive I<all> exit signals as messages or
		1035	I<none>, there is no in-between, so monitoring single Erlang processes is
		1036	difficult to implement.
		1037
		1038	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1039	between automatic kill, exit message or callback on a per-port basis.
		1040
		1041	=item * Erlang tries to hide remote/local connections, AEMP does not.
		1042
		1043	Monitoring in Erlang is not an indicator of process death/crashes, in the
		1044	same way as linking is (except linking is unreliable in Erlang).
		1045
		1046	In AEMP, you don't "look up" registered port names or send to named ports
		1047	that might or might not be persistent. Instead, you normally spawn a port
		1048	on the remote node. The init function monitors you, and you monitor the
		1049	remote port. Since both monitors are local to the node, they are much more
		1050	reliable (no need for C<spawn_link>).
		1051
		1052	This also saves round-trips and avoids sending messages to the wrong port
		1053	(hard to do in Erlang).
		1054
650	=back	1055	=back
651		1056
		1057	=head1 RATIONALE
		1058
		1059	=over 4
		1060
		1061	=item Why strings for port and node IDs, why not objects?
		1062
		1063	We considered "objects", but found that the actual number of methods
		1064	that can be called are quite low. Since port and node IDs travel over
		1065	the network frequently, the serialising/deserialising would add lots of
		1066	overhead, as well as having to keep a proxy object everywhere.
		1067
		1068	Strings can easily be printed, easily serialised etc. and need no special
		1069	procedures to be "valid".
		1070
		1071	And as a result, a port with just a default receiver consists of a single
		1072	code reference stored in a global hash - it can't become much cheaper.
		1073
		1074	=item Why favour JSON, why not a real serialising format such as Storable?
		1075
		1076	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1077	format, but currently there is no way to make a node use Storable by
		1078	default (although all nodes will accept it).
		1079
		1080	The default framing protocol is JSON because a) JSON::XS is many times
		1081	faster for small messages and b) most importantly, after years of
		1082	experience we found that object serialisation is causing more problems
		1083	than it solves: Just like function calls, objects simply do not travel
		1084	easily over the network, mostly because they will always be a copy, so you
		1085	always have to re-think your design.
		1086
		1087	Keeping your messages simple, concentrating on data structures rather than
		1088	objects, will keep your messages clean, tidy and efficient.
		1089
		1090	=back
		1091
652	=head1 SEE ALSO	1092	=head1 SEE ALSO
		1093
		1094	L<AnyEvent::MP::Intro> - a gentle introduction.
		1095
		1096	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1097
		1098	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1099	your applications.
		1100
		1101	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1102
		1103	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1104	all nodes.
653		1105
654	L<AnyEvent>.	1106	L<AnyEvent>.
655		1107
656	=head1 AUTHOR	1108	=head1 AUTHOR
657		1109

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