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Revision 1.27 by root, Tue Aug 4 22:13:45 2009 UTC vs.
Revision 1.130 by root, Fri Mar 9 17:05:26 2012 UTC

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

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