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Revision 1.27 by root, Tue Aug 4 22:13:45 2009 UTC vs.
Revision 1.127 by root, Sat Mar 3 20:35:10 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 these 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	=item secure => $pass->($nodeid)
		252
		253	In addition to specifying a boolean, you can specify a code reference that
		254	is called for every remote execution attempt - the execution request is
		255	granted iff the callback returns a true value.
		256
		257	See F<semp setsecure> for more info.
		258
		259	=back
		260
		261	=over 4
		262
		263	=item step 1, gathering configuration from profiles
		264
		265	The function first looks up a profile in the aemp configuration (see the
		266	L<aemp> commandline utility). The profile name can be specified via the
		267	named C<profile> parameter or can simply be the first parameter). If it is
		268	missing, then the nodename (F<uname -n>) will be used as profile name.
		269
		270	The profile data is then gathered as follows:
		271
		272	First, all remaining key => value pairs (all of which are conveniently
		273	undocumented at the moment) will be interpreted as configuration
		274	data. Then they will be overwritten by any values specified in the global
		275	default configuration (see the F<aemp> utility), then the chain of
		276	profiles chosen by the profile name (and any C<parent> attributes).
		277
		278	That means that the values specified in the profile have highest priority
		279	and the values specified directly via C<configure> have lowest priority,
		280	and can only be used to specify defaults.
		281
		282	If the profile specifies a node ID, then this will become the node ID of
		283	this process. If not, then the profile name will be used as node ID, with
		284	a unique randoms tring (C</%u>) appended.
		285
		286	The node ID can contain some C<%> sequences that are expanded: C<%n>
		287	is expanded to the local nodename, C<%u> is replaced by a random
		288	strign to make the node unique. For example, the F<aemp> commandline
		289	utility uses C<aemp/%n/%u> as nodename, which might expand to
		290	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		291
		292	=item step 2, bind listener sockets
		293
		294	The next step is to look up the binds in the profile, followed by binding
		295	aemp protocol listeners on all binds specified (it is possible and valid
		296	to have no binds, meaning that the node cannot be contacted form the
		297	outside. This means the node cannot talk to other nodes that also have no
		298	binds, but it can still talk to all "normal" nodes).
		299
		300	If the profile does not specify a binds list, then a default of C<*> is
		301	used, meaning the node will bind on a dynamically-assigned port on every
		302	local IP address it finds.
		303
		304	=item step 3, connect to seed nodes
		305
		306	As the last step, the seed ID list from the profile is passed to the
		307	L<AnyEvent::MP::Global> module, which will then use it to keep
		308	connectivity with at least one node at any point in time.
		309
		310	=back
		311
		312	Example: become a distributed node using the local node name as profile.
		313	This should be the most common form of invocation for "daemon"-type nodes.
		314
		315	configure
		316
		317	Example: become a semi-anonymous node. This form is often used for
		318	commandline clients.
		319
		320	configure nodeid => "myscript/%n/%u";
		321
		322	Example: configure a node using a profile called seed, which is suitable
		323	for a seed node as it binds on all local addresses on a fixed port (4040,
		324	customary for aemp).
		325
		326	# use the aemp commandline utility
		327	# aemp profile seed binds '*:4040'
		328
		329	# then use it
		330	configure profile => "seed";
		331
		332	# or simply use aemp from the shell again:
		333	# aemp run profile seed
		334
		335	# or provide a nicer-to-remember nodeid
		336	# aemp run profile seed nodeid "$(hostname)"
119		337
120	=item $SELF	338	=item $SELF
121		339
122	Contains the current port id while executing C<rcv> callbacks or C<psub>	340	Contains the current port id while executing C<rcv> callbacks or C<psub>
123	blocks.	341	blocks.
124		342
125	=item SELF, %SELF, @SELF...	343	=item *SELF, SELF, %SELF, @SELF...
126		344
127	Due to some quirks in how perl exports variables, it is impossible to	345	Due to some quirks in how perl exports variables, it is impossible to
128	just export C<$SELF>, all the symbols called C<SELF> are exported by this	346	just export C<$SELF>, all the symbols named C<SELF> are exported by this
129	module, but only C<$SELF> is currently used.	347	module, but only C<$SELF> is currently used.
130		348
131	=item snd $portid, type => @data	349	=item snd $port, type => @data
132		350
133	=item snd $portid, @msg	351	=item snd $port, @msg
134		352
135	Send the given message to the given port ID, which can identify either	353	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	354	local or a remote port, and must be a port ID.
137	stringifies a sa port ID (such as a port object :).
138		355
139	While the message can be about anything, it is highly recommended to use a	356	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	357	use a string as first element (a port ID, or some word that indicates a
141	type etc.).	358	request type etc.) and to consist if only simple perl values (scalars,
		359	arrays, hashes) - if you think you need to pass an object, think again.
142		360
143	The message data effectively becomes read-only after a call to this	361	The message data logically becomes read-only after a call to this
144	function: modifying any argument is not allowed and can cause many	362	function: modifying any argument (or values referenced by them) is
145	problems.	363	forbidden, as there can be considerable time between the call to C<snd>
		364	and the time the message is actually being serialised - in fact, it might
		365	never be copied as within the same process it is simply handed to the
		366	receiving port.
146		367
147	The type of data you can transfer depends on the transport protocol: when	368	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	369	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	370	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	371	that Storable can serialise and deserialise is allowed, and for the local
151	node, anything can be passed.	372	node, anything can be passed. Best rely only on the common denominator of
		373	these.
152		374
153	=item kil $portid[, @reason]	375	=item $local_port = port
154		376
155	Kill the specified port with the given C<@reason>.	377	Create a new local port object and returns its port ID. Initially it has
		378	no callbacks set and will throw an error when it receives messages.
156		379
157	If no C<@reason> is specified, then the port is killed "normally" (linked	380	=item $local_port = port { my @msg = @_ }
158	ports will not be kileld, or even notified).
159		381
160	Otherwise, linked ports get killed with the same reason (second form of	382	Creates a new local port, and returns its ID. Semantically the same as
161	C<mon>, see below).	383	creating a port and calling C<rcv $port, $callback> on it.
162		384
163	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	385	The block will be called for every message received on the port, with the
164	will be reported as reason C<< die => $@ >>.	386	global variable C<$SELF> set to the port ID. Runtime errors will cause the
		387	port to be C<kil>ed. The message will be passed as-is, no extra argument
		388	(i.e. no port ID) will be passed to the callback.
165		389
166	Transport/communication errors are reported as C<< transport_error =>	390	If you want to stop/destroy the port, simply C<kil> it:
167	$message >>.
168		391
169	=item $guard = mon $portid, $cb->(@reason)	392	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, @_);	393	my @msg = @_;
212	$cb = sub { snd @msg, @_ };	394	...
		395	kil $SELF;
		396	};
		397
		398	=cut
		399
		400	sub rcv($@);
		401
		402	sub _kilme {
		403	die "received message on port without callback";
		404	}
		405
		406	sub port(;&) {
		407	my $id = $UNIQ . ++$ID;
		408	my $port = "$NODE#$id";
		409
		410	rcv $port, shift || \&_kilme;
		411
		412	$port
		413	}
		414
		415	=item rcv $local_port, $callback->(@msg)
		416
		417	Replaces the default callback on the specified port. There is no way to
		418	remove the default callback: use C<sub { }> to disable it, or better
		419	C<kil> the port when it is no longer needed.
		420
		421	The global C<$SELF> (exported by this module) contains C<$port> while
		422	executing the callback. Runtime errors during callback execution will
		423	result in the port being C<kil>ed.
		424
		425	The default callback received all messages not matched by a more specific
		426	C<tag> match.
		427
		428	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
		429
		430	Register (or replace) callbacks to be called on messages starting with the
		431	given tag on the given port (and return the port), or unregister it (when
		432	C<$callback> is C<$undef> or missing). There can only be one callback
		433	registered for each tag.
		434
		435	The original message will be passed to the callback, after the first
		436	element (the tag) has been removed. The callback will use the same
		437	environment as the default callback (see above).
		438
		439	Example: create a port and bind receivers on it in one go.
		440
		441	my $port = rcv port,
		442	msg1 => sub { ... },
		443	msg2 => sub { ... },
		444	;
		445
		446	Example: create a port, bind receivers and send it in a message elsewhere
		447	in one go:
		448
		449	snd $otherport, reply =>
		450	rcv port,
		451	msg1 => sub { ... },
		452	...
		453	;
		454
		455	Example: temporarily register a rcv callback for a tag matching some port
		456	(e.g. for an rpc reply) and unregister it after a message was received.
		457
		458	rcv $port, $otherport => sub {
		459	my @reply = @_;
		460
		461	rcv $SELF, $otherport;
		462	};
		463
		464	=cut
		465
		466	sub rcv($@) {
		467	my $port = shift;
		468	my ($nodeid, $portid) = split /#/, $port, 2;
		469
		470	$NODE{$nodeid} == $NODE{""}
		471	or Carp::croak "$port: rcv can only be called on local ports, caught";
		472
		473	while (@_) {
		474	if (ref $_[0]) {
		475	if (my $self = $PORT_DATA{$portid}) {
		476	"AnyEvent::MP::Port" eq ref $self
		477	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		478
		479	$self->[0] = shift;
213	} else {	480	} else {
214	# simply kill other port	481	my $cb = shift;
215	my $port = $cb;	482	$PORT{$portid} = sub {
216	$cb = sub { kil $port, @_ if @_ };	483	local $SELF = $port;
		484	eval { &$cb }; _self_die if $@;
		485	};
		486	}
		487	} elsif (defined $_[0]) {
		488	my $self = $PORT_DATA{$portid} ||= do {
		489	my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port";
		490
		491	$PORT{$portid} = sub {
		492	local $SELF = $port;
		493
		494	if (my $cb = $self->[1]{$_[0]}) {
		495	shift;
		496	eval { &$cb }; _self_die if $@;
		497	} else {
		498	&{ $self->[0] };
		499	}
		500	};
		501
		502	$self
		503	};
		504
		505	"AnyEvent::MP::Port" eq ref $self
		506	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		507
		508	my ($tag, $cb) = splice @_, 0, 2;
		509
		510	if (defined $cb) {
		511	$self->[1]{$tag} = $cb;
		512	} else {
		513	delete $self->[1]{$tag};
		514	}
217	}	515	}
218	}	516	}
219		517
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	518	$port
330	}	519	}
331		520
332	=item reg $portid, $name	521	=item peval $port, $coderef[, @args]
333		522
334	Registers the given port under the name C<$name>. If the name already	523	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
335	exists it is replaced.	524	when the code throews an exception the C<$port> will be killed.
336		525
337	A port can only be registered under one well known name.	526	Any remaining args will be passed to the callback. Any return values will
		527	be returned to the caller.
338		528
339	A port automatically becomes unregistered when it is killed.	529	This is useful when you temporarily want to execute code in the context of
		530	a port.
340		531
341	=cut	532	Example: create a port and run some initialisation code in it's context.
342		533
343	sub reg(@) {	534	my $port = port { ... };
344	my ($portid, $name) = @_;
345		535
346	$REG{$name} = $portid;	536	peval $port, sub {
347	}	537	init
		538	or die "unable to init";
		539	};
348		540
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<$portid> while
362	executing the callback.
363
364	Runtime errors wdurign callback execution will result in the port being
365	C<kil>ed.
366
367	If the match is an array reference, then it will be matched against the
368	first elements of the message, otherwise only the first element is being
369	matched.
370
371	Any element in the match that is specified as C<_any_> (a function
372	exported by this module) matches any single element of the message.
373
374	While not required, it is highly recommended that the first matching
375	element is a string identifying the message. The one-string-only match is
376	also the most efficient match (by far).
377
378	=cut	541	=cut
379		542
380	sub rcv($@) {	543	sub peval($$) {
381	my ($noderef, $port) = split /#/, shift, 2;	544	local $SELF = shift;
		545	my $cb = shift;
382		546
383	($NODE{$noderef} || add_node $noderef) == $NODE{""}	547	if (wantarray) {
384	or Carp::croak "$noderef#$port: rcv can only be called on local ports, caught";	548	my @res = eval { &$cb };
385		549	_self_die if $@;
386	my $self = $PORT_DATA{$port}	550	@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 {	551	} else {
403	push @{ $self->{any} }, [$cb, $match];	552	my $res = eval { &$cb };
404	}	553	_self_die if $@;
		554	$res
405	}	555	}
406	}	556	}
407		557
408	=item $closure = psub { BLOCK }	558	=item $closure = psub { BLOCK }
409		559
410	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	560	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>	561	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.	562	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		563
		564	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		565	BLOCK }, @_ } >>.
413		566
414	This is useful when you register callbacks from C<rcv> callbacks:	567	This is useful when you register callbacks from C<rcv> callbacks:
415		568
416	rcv delayed_reply => sub {	569	rcv delayed_reply => sub {
417	my ($delay, @reply) = @_;	570	my ($delay, @reply) = @_;
…		…
441	$res	594	$res
442	}	595	}
443	}	596	}
444	}	597	}
445		598
		599	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
		600
		601	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
		602
		603	=item $guard = mon $port # kill $SELF when $port dies
		604
		605	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		606
		607	Monitor the given port and do something when the port is killed or
		608	messages to it were lost, and optionally return a guard that can be used
		609	to stop monitoring again.
		610
		611	In the first form (callback), the callback is simply called with any
		612	number of C<@reason> elements (no @reason means that the port was deleted
		613	"normally"). Note also that I<< the callback B<must> never die >>, so use
		614	C<eval> if unsure.
		615
		616	In the second form (another port given), the other port (C<$rcvport>)
		617	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
		618	"normal" kils nothing happens, while under all other conditions, the other
		619	port is killed with the same reason.
		620
		621	The third form (kill self) is the same as the second form, except that
		622	C<$rvport> defaults to C<$SELF>.
		623
		624	In the last form (message), a message of the form C<@msg, @reason> will be
		625	C<snd>.
		626
		627	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		628	alert was raised), they are removed and will not trigger again.
		629
		630	As a rule of thumb, monitoring requests should always monitor a port from
		631	a local port (or callback). The reason is that kill messages might get
		632	lost, just like any other message. Another less obvious reason is that
		633	even monitoring requests can get lost (for example, when the connection
		634	to the other node goes down permanently). When monitoring a port locally
		635	these problems do not exist.
		636
		637	C<mon> effectively guarantees that, in the absence of hardware failures,
		638	after starting the monitor, either all messages sent to the port will
		639	arrive, or the monitoring action will be invoked after possible message
		640	loss has been detected. No messages will be lost "in between" (after
		641	the first lost message no further messages will be received by the
		642	port). After the monitoring action was invoked, further messages might get
		643	delivered again.
		644
		645	Inter-host-connection timeouts and monitoring depend on the transport
		646	used. The only transport currently implemented is TCP, and AnyEvent::MP
		647	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		648	non-idle connection, and usually around two hours for idle connections).
		649
		650	This means that monitoring is good for program errors and cleaning up
		651	stuff eventually, but they are no replacement for a timeout when you need
		652	to ensure some maximum latency.
		653
		654	Example: call a given callback when C<$port> is killed.
		655
		656	mon $port, sub { warn "port died because of <@_>\n" };
		657
		658	Example: kill ourselves when C<$port> is killed abnormally.
		659
		660	mon $port;
		661
		662	Example: send us a restart message when another C<$port> is killed.
		663
		664	mon $port, $self => "restart";
		665
		666	=cut
		667
		668	sub mon {
		669	my ($nodeid, $port) = split /#/, shift, 2;
		670
		671	my $node = $NODE{$nodeid} || add_node $nodeid;
		672
		673	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
		674
		675	unless (ref $cb) {
		676	if (@_) {
		677	# send a kill info message
		678	my (@msg) = ($cb, @_);
		679	$cb = sub { snd @msg, @_ };
		680	} else {
		681	# simply kill other port
		682	my $port = $cb;
		683	$cb = sub { kil $port, @_ if @_ };
		684	}
		685	}
		686
		687	$node->monitor ($port, $cb);
		688
		689	defined wantarray
		690	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
		691	}
		692
		693	=item $guard = mon_guard $port, $ref, $ref...
		694
		695	Monitors the given C<$port> and keeps the passed references. When the port
		696	is killed, the references will be freed.
		697
		698	Optionally returns a guard that will stop the monitoring.
		699
		700	This function is useful when you create e.g. timers or other watchers and
		701	want to free them when the port gets killed (note the use of C<psub>):
		702
		703	$port->rcv (start => sub {
		704	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
		705	undef $timer if 0.9 < rand;
		706	});
		707	});
		708
		709	=cut
		710
		711	sub mon_guard {
		712	my ($port, @refs) = @_;
		713
		714	#TODO: mon-less form?
		715
		716	mon $port, sub { 0 && @refs }
		717	}
		718
		719	=item kil $port[, @reason]
		720
		721	Kill the specified port with the given C<@reason>.
		722
		723	If no C<@reason> is specified, then the port is killed "normally" -
		724	monitor callback will be invoked, but the kil will not cause linked ports
		725	(C<mon $mport, $lport> form) to get killed.
		726
		727	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
		728	form) get killed with the same reason.
		729
		730	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		731	will be reported as reason C<< die => $@ >>.
		732
		733	Transport/communication errors are reported as C<< transport_error =>
		734	$message >>.
		735
		736	=cut
		737
		738	=item $port = spawn $node, $initfunc[, @initdata]
		739
		740	Creates a port on the node C<$node> (which can also be a port ID, in which
		741	case it's the node where that port resides).
		742
		743	The port ID of the newly created port is returned immediately, and it is
		744	possible to immediately start sending messages or to monitor the port.
		745
		746	After the port has been created, the init function is called on the remote
		747	node, in the same context as a C<rcv> callback. This function must be a
		748	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		749	specify a function in the main program, use C<::name>.
		750
		751	If the function doesn't exist, then the node tries to C<require>
		752	the package, then the package above the package and so on (e.g.
		753	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		754	exists or it runs out of package names.
		755
		756	The init function is then called with the newly-created port as context
		757	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		758	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		759	the port might not get created.
		760
		761	A common idiom is to pass a local port, immediately monitor the spawned
		762	port, and in the remote init function, immediately monitor the passed
		763	local port. This two-way monitoring ensures that both ports get cleaned up
		764	when there is a problem.
		765
		766	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		767	caller before C<spawn> returns (by delaying invocation when spawn is
		768	called for the local node).
		769
		770	Example: spawn a chat server port on C<$othernode>.
		771
		772	# this node, executed from within a port context:
		773	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		774	mon $server;
		775
		776	# init function on C<$othernode>
		777	sub connect {
		778	my ($srcport) = @_;
		779
		780	mon $srcport;
		781
		782	rcv $SELF, sub {
		783	...
		784	};
		785	}
		786
		787	=cut
		788
		789	sub _spawn {
		790	my $port = shift;
		791	my $init = shift;
		792
		793	# rcv will create the actual port
		794	local $SELF = "$NODE#$port";
		795	eval {
		796	&{ load_func $init }
		797	};
		798	_self_die if $@;
		799	}
		800
		801	sub spawn(@) {
		802	my ($nodeid, undef) = split /#/, shift, 2;
		803
		804	my $id = $RUNIQ . ++$ID;
		805
		806	$_[0] =~ /::/
		807	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		808
		809	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		810
		811	"$nodeid#$id"
		812	}
		813
		814
		815	=item after $timeout, @msg
		816
		817	=item after $timeout, $callback
		818
		819	Either sends the given message, or call the given callback, after the
		820	specified number of seconds.
		821
		822	This is simply a utility function that comes in handy at times - the
		823	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		824	so it may go away in the future.
		825
		826	=cut
		827
		828	sub after($@) {
		829	my ($timeout, @action) = @_;
		830
		831	my $t; $t = AE::timer $timeout, 0, sub {
		832	undef $t;
		833	ref $action[0]
		834	? $action[0]()
		835	: snd @action;
		836	};
		837	}
		838
		839	=item cal $port, @msg, $callback[, $timeout]
		840
		841	A simple form of RPC - sends a message to the given C<$port> with the
		842	given contents (C<@msg>), but adds a reply port to the message.
		843
		844	The reply port is created temporarily just for the purpose of receiving
		845	the reply, and will be C<kil>ed when no longer needed.
		846
		847	A reply message sent to the port is passed to the C<$callback> as-is.
		848
		849	If an optional time-out (in seconds) is given and it is not C<undef>,
		850	then the callback will be called without any arguments after the time-out
		851	elapsed and the port is C<kil>ed.
		852
		853	If no time-out is given (or it is C<undef>), then the local port will
		854	monitor the remote port instead, so it eventually gets cleaned-up.
		855
		856	Currently this function returns the temporary port, but this "feature"
		857	might go in future versions unless you can make a convincing case that
		858	this is indeed useful for something.
		859
		860	=cut
		861
		862	sub cal(@) {
		863	my $timeout = ref $_[-1] ? undef : pop;
		864	my $cb = pop;
		865
		866	my $port = port {
		867	undef $timeout;
		868	kil $SELF;
		869	&$cb;
		870	};
		871
		872	if (defined $timeout) {
		873	$timeout = AE::timer $timeout, 0, sub {
		874	undef $timeout;
		875	kil $port;
		876	$cb->();
		877	};
		878	} else {
		879	mon $_[0], sub {
		880	kil $port;
		881	$cb->();
		882	};
		883	}
		884
		885	push @_, $port;
		886	&snd;
		887
		888	$port
		889	}
		890
446	=back	891	=back
447		892
448	=head1 FUNCTIONS FOR NODES	893	=head1 DISTRIBUTED DATABASE
449		894
		895	AnyEvent::MP comes with a simple distributed database. The database will
		896	be mirrored asynchronously at all global nodes. Other nodes bind to one of
		897	the global nodes for their needs.
		898
		899	The database consists of a two-level hash - a hash contains a hash which
		900	contains values.
		901
		902	The top level hash key is called "family", and the second-level hash key
		903	is called "subkey" or simply "key".
		904
		905	The family must be alphanumeric, i.e. start with a letter and consist
		906	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		907	pretty much like Perl module names.
		908
		909	As the family namespace is global, it is recommended to prefix family names
		910	with the name of the application or module using it.
		911
		912	The subkeys must be non-empty strings, with no further restrictions.
		913
		914	The values should preferably be strings, but other perl scalars should
		915	work as well (such as undef, arrays and hashes).
		916
		917	Every database entry is owned by one node - adding the same family/subkey
		918	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		919	but the result might be nondeterministic, i.e. the key might have
		920	different values on different nodes.
		921
		922	Different subkeys in the same family can be owned by different nodes
		923	without problems, and in fact, this is the common method to create worker
		924	pools. For example, a worker port for image scaling might do this:
		925
		926	db_set my_image_scalers => $port;
		927
		928	And clients looking for an image scaler will want to get the
		929	C<my_image_scalers> keys:
		930
		931	db_keys "my_image_scalers" => 60 => sub {
		932	#d##TODO#
		933
450	=over 4	934	=over
451		935
452	=item become_public endpoint...	936	=item db_set $family => $subkey [=> $value]
453		937
454	Tells the node to become a public node, i.e. reachable from other nodes.	938	Sets (or replaces) a key to the database - if C<$value> is omitted,
		939	C<undef> is used instead.
455		940
456	If no arguments are given, or the first argument is C<undef>, then	941	=item db_del $family => $subkey
457	AnyEvent::MP tries to bind on port C<4040> on all IP addresses that the
458	local nodename resolves to.
459		942
460	Otherwise the first argument must be an array-reference with transport	943	Deletes a key from the database.
461	endpoints ("ip:port", "hostname:port") or port numbers (in which case the	944
462	local nodename is used as hostname). The endpoints are all resolved and	945	=item $guard = db_reg $family => $subkey [=> $value]
463	will become the node reference.	946
		947	Sets the key on the database and returns a guard. When the guard is
		948	destroyed, the key is deleted from the database. If C<$value> is missing,
		949	then C<undef> is used.
464		950
465	=cut	951	=cut
466		952
467	=back	953	=back
468		954
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	955	=head1 AnyEvent::MP vs. Distributed Erlang
514		956
515	AnyEvent::MP got lots of its ideas from distributed erlang (erlang node	957	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
516	== aemp node, erlang process == aemp port), so many of the documents and	958	== aemp node, Erlang process == aemp port), so many of the documents and
517	programming techniques employed by erlang apply to AnyEvent::MP. Here is a	959	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
518	sample:	960	sample:
519		961
520	http://www.erlang.se/doc/programming_rules.shtml	962	http://www.erlang.se/doc/programming_rules.shtml
521	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	963	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
522	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6	964	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
…		…
524		966
525	Despite the similarities, there are also some important differences:	967	Despite the similarities, there are also some important differences:
526		968
527	=over 4	969	=over 4
528		970
529	=item * Node references contain the recipe on how to contact them.	971	=item * Node IDs are arbitrary strings in AEMP.
530		972
531	Erlang relies on special naming and DNS to work everywhere in the	973	Erlang relies on special naming and DNS to work everywhere in the same
532	same way. AEMP relies on each node knowing it's own address(es), with	974	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
533	convenience functionality.	975	configuration or DNS), and possibly the addresses of some seed nodes, but
		976	will otherwise discover other nodes (and their IDs) itself.
534		977
535	This means that AEMP requires a less tightly controlled environment at the	978	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
536	cost of longer node references and a slightly higher management overhead.	979	uses "local ports are like remote ports".
		980
		981	The failure modes for local ports are quite different (runtime errors
		982	only) then for remote ports - when a local port dies, you I<know> it dies,
		983	when a connection to another node dies, you know nothing about the other
		984	port.
		985
		986	Erlang pretends remote ports are as reliable as local ports, even when
		987	they are not.
		988
		989	AEMP encourages a "treat remote ports differently" philosophy, with local
		990	ports being the special case/exception, where transport errors cannot
		991	occur.
537		992
538	=item * Erlang uses processes and a mailbox, AEMP does not queue.	993	=item * Erlang uses processes and a mailbox, AEMP does not queue.
539		994
540	Erlang uses processes that selctively receive messages, and therefore	995	Erlang uses processes that selectively receive messages out of order, and
541	needs a queue. AEMP is event based, queuing messages would serve no useful	996	therefore needs a queue. AEMP is event based, queuing messages would serve
542	purpose.	997	no useful purpose. For the same reason the pattern-matching abilities
		998	of AnyEvent::MP are more limited, as there is little need to be able to
		999	filter messages without dequeuing them.
543		1000
544	(But see L<Coro::MP> for a more erlang-like process model on top of AEMP).	1001	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1002	being event-based, while Erlang is process-based.
		1003
		1004	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1005	top of AEMP and Coro threads.
545		1006
546	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1007	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
547		1008
548	Sending messages in erlang is synchronous and blocks the process. AEMP	1009	Sending messages in Erlang is synchronous and blocks the process until
549	sends are immediate, connection establishment is handled in the	1010	a conenction has been established and the message sent (and so does not
550	background.	1011	need a queue that can overflow). AEMP sends return immediately, connection
		1012	establishment is handled in the background.
551		1013
552	=item * Erlang can silently lose messages, AEMP cannot.	1014	=item * Erlang suffers from silent message loss, AEMP does not.
553		1015
554	Erlang makes few guarantees on messages delivery - messages can get lost	1016	Erlang implements few guarantees on messages delivery - messages can get
555	without any of the processes realising it (i.e. you send messages a, b,	1017	lost without any of the processes realising it (i.e. you send messages a,
556	and c, and the other side only receives messages a and c).	1018	b, and c, and the other side only receives messages a and c).
557		1019
558	AEMP guarantees correct ordering, and the guarantee that there are no	1020	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1021	guarantee that after one message is lost, all following ones sent to the
		1022	same port are lost as well, until monitoring raises an error, so there are
559	holes in the message sequence.	1023	no silent "holes" in the message sequence.
560		1024
561	=item * In erlang, processes can be declared dead and later be found to be	1025	If you want your software to be very reliable, you have to cope with
562	alive.	1026	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
563		1027	simply tries to work better in common error cases, such as when a network
564	In erlang it can happen that a monitored process is declared dead and	1028	link goes down.
565	linked processes get killed, but later it turns out that the process is
566	still alive - and can receive messages.
567
568	In AEMP, when port monitoring detects a port as dead, then that port will
569	eventually be killed - it cannot happen that a node detects a port as dead
570	and then later sends messages to it, finding it is still alive.
571		1029
572	=item * Erlang can send messages to the wrong port, AEMP does not.	1030	=item * Erlang can send messages to the wrong port, AEMP does not.
573		1031
574	In erlang it is quite possible that a node that restarts reuses a process	1032	In Erlang it is quite likely that a node that restarts reuses an Erlang
575	ID known to other nodes for a completely different process, causing	1033	process ID known to other nodes for a completely different process,
576	messages destined for that process to end up in an unrelated process.	1034	causing messages destined for that process to end up in an unrelated
		1035	process.
577		1036
578	AEMP never reuses port IDs, so old messages or old port IDs floating	1037	AEMP does not reuse port IDs, so old messages or old port IDs floating
579	around in the network will not be sent to an unrelated port.	1038	around in the network will not be sent to an unrelated port.
580		1039
581	=item * Erlang uses unprotected connections, AEMP uses secure	1040	=item * Erlang uses unprotected connections, AEMP uses secure
582	authentication and can use TLS.	1041	authentication and can use TLS.
583		1042
584	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1043	AEMP can use a proven protocol - TLS - to protect connections and
585	securely authenticate nodes.	1044	securely authenticate nodes.
586		1045
		1046	=item * The AEMP protocol is optimised for both text-based and binary
		1047	communications.
		1048
		1049	The AEMP protocol, unlike the Erlang protocol, supports both programming
		1050	language independent text-only protocols (good for debugging), and binary,
		1051	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1052	used, the protocol is actually completely text-based.
		1053
		1054	It has also been carefully designed to be implementable in other languages
		1055	with a minimum of work while gracefully degrading functionality to make the
		1056	protocol simple.
		1057
		1058	=item * AEMP has more flexible monitoring options than Erlang.
		1059
		1060	In Erlang, you can chose to receive I<all> exit signals as messages or
		1061	I<none>, there is no in-between, so monitoring single Erlang processes is
		1062	difficult to implement.
		1063
		1064	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1065	between automatic kill, exit message or callback on a per-port basis.
		1066
		1067	=item * Erlang tries to hide remote/local connections, AEMP does not.
		1068
		1069	Monitoring in Erlang is not an indicator of process death/crashes, in the
		1070	same way as linking is (except linking is unreliable in Erlang).
		1071
		1072	In AEMP, you don't "look up" registered port names or send to named ports
		1073	that might or might not be persistent. Instead, you normally spawn a port
		1074	on the remote node. The init function monitors you, and you monitor the
		1075	remote port. Since both monitors are local to the node, they are much more
		1076	reliable (no need for C<spawn_link>).
		1077
		1078	This also saves round-trips and avoids sending messages to the wrong port
		1079	(hard to do in Erlang).
		1080
587	=back	1081	=back
588		1082
		1083	=head1 RATIONALE
		1084
		1085	=over 4
		1086
		1087	=item Why strings for port and node IDs, why not objects?
		1088
		1089	We considered "objects", but found that the actual number of methods
		1090	that can be called are quite low. Since port and node IDs travel over
		1091	the network frequently, the serialising/deserialising would add lots of
		1092	overhead, as well as having to keep a proxy object everywhere.
		1093
		1094	Strings can easily be printed, easily serialised etc. and need no special
		1095	procedures to be "valid".
		1096
		1097	And as a result, a port with just a default receiver consists of a single
		1098	code reference stored in a global hash - it can't become much cheaper.
		1099
		1100	=item Why favour JSON, why not a real serialising format such as Storable?
		1101
		1102	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1103	format, but currently there is no way to make a node use Storable by
		1104	default (although all nodes will accept it).
		1105
		1106	The default framing protocol is JSON because a) JSON::XS is many times
		1107	faster for small messages and b) most importantly, after years of
		1108	experience we found that object serialisation is causing more problems
		1109	than it solves: Just like function calls, objects simply do not travel
		1110	easily over the network, mostly because they will always be a copy, so you
		1111	always have to re-think your design.
		1112
		1113	Keeping your messages simple, concentrating on data structures rather than
		1114	objects, will keep your messages clean, tidy and efficient.
		1115
		1116	=back
		1117
589	=head1 SEE ALSO	1118	=head1 SEE ALSO
		1119
		1120	L<AnyEvent::MP::Intro> - a gentle introduction.
		1121
		1122	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1123
		1124	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1125	your applications.
		1126
		1127	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1128
		1129	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1130	all nodes.
590		1131
591	L<AnyEvent>.	1132	L<AnyEvent>.
592		1133
593	=head1 AUTHOR	1134	=head1 AUTHOR
594		1135

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