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Revision 1.29 by root, Tue Aug 4 23:16:57 2009 UTC vs.
Revision 1.134 by root, Mon Mar 12 14:47:23 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).	76	Not to be confused with a TCP port, a "port" is something you can send
		77	messages to (with the C<snd> function).
49		78
50	Some ports allow you to register C<rcv> handlers that can match specific	79	Ports allow you to register C<rcv> handlers that can match all or just
51	messages. All C<rcv> handlers will receive messages they match, messages	80	some messages. Messages send to ports will not be queued, regardless of
52	will not be queued.	81	anything was listening for them or not.
53		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
54	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
55		86
56	A port id is normaly the concatenation of a noderef, a hash-mark (C<#>) as	87	A port ID is the concatenation of a node ID, a hash-mark (C<#>)
57	separator, and a port name (a printable string of unspecified format). An	88	as separator, and a port name (a printable string of unspecified
58	exception is the the node port, whose ID is identical to it's node	89	format created by AnyEvent::MP).
59	reference.
60		90
61	=item node	91	=item node
62		92
63	A node is a single process containing at least one port - the node	93	A node is a single process containing at least one port - the node port,
64	port. You can send messages to node ports to find existing ports or to	94	which enables nodes to manage each other remotely, and to create new
65	create new ports, among other things.	95	ports.
66		96
67	Nodes are either private (single-process only), slaves (connected to a	97	Nodes are either public (have one or more listening ports) or private
68	master node only) or public nodes (connectable from unrelated nodes).	98	(no listening ports). Private nodes cannot talk to other private nodes
		99	currently, but all nodes can talk to public nodes.
69		100
70	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	101	Nodes is represented by (printable) strings called "node IDs".
71		102
72	A node reference is a string that either simply identifies the node (for	103	=item node ID - C<[A-Za-z0-9_\-.:]*>
73	private and slave nodes), or contains a recipe on how to reach a given
74	node (for public nodes).
75		104
76	This recipe is simply a comma-separated list of C<address:port> pairs (for	105	A node ID is a string that uniquely identifies the node within a
77	TCP/IP, other protocols might look different).	106	network. Depending on the configuration used, node IDs can look like a
		107	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		108	doesn't interpret node IDs in any way except to uniquely identify a node.
78		109
79	Node references come in two flavours: resolved (containing only numerical	110	=item binds - C<ip:port>
80	addresses) or unresolved (where hostnames are used instead of addresses).
81		111
82	Before using an unresolved node reference in a message you first have to	112	Nodes can only talk to each other by creating some kind of connection to
83	resolve it.	113	each other. To do this, nodes should listen on one or more local transport
		114	endpoints - binds.
		115
		116	Currently, only standard C<ip:port> specifications can be used, which
		117	specify TCP ports to listen on. So a bind is basically just a tcp socket
		118	in listening mode thta accepts conenctions form other nodes.
		119
		120	=item seed nodes
		121
		122	When a node starts, it knows nothing about the network it is in - it
		123	needs to connect to at least one other node that is already in the
		124	network. These other nodes are called "seed nodes".
		125
		126	Seed nodes themselves are not special - they are seed nodes only because
		127	some other node I<uses> them as such, but any node can be used as seed
		128	node for other nodes, and eahc node cna use a different set of seed nodes.
		129
		130	In addition to discovering the network, seed nodes are also used to
		131	maintain the network - all nodes using the same seed node form are part of
		132	the same network. If a network is split into multiple subnets because e.g.
		133	the network link between the parts goes down, then using the same seed
		134	nodes for all nodes ensures that eventually the subnets get merged again.
		135
		136	Seed nodes are expected to be long-running, and at least one seed node
		137	should always be available. They should also be relatively responsive - a
		138	seed node that blocks for long periods will slow down everybody else.
		139
		140	For small networks, it's best if every node uses the same set of seed
		141	nodes. For large networks, it can be useful to specify "regional" seed
		142	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		143	each other. What's important is that all seed nodes connections form a
		144	complete graph, so that the network cannot split into separate subnets
		145	forever.
		146
		147	Seed nodes are represented by seed IDs.
		148
		149	=item seed IDs - C<host:port>
		150
		151	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
		152	TCP port) of nodes that should be used as seed nodes.
		153
		154	=item global nodes
		155
		156	An AEMP network needs a discovery service - nodes need to know how to
		157	connect to other nodes they only know by name. In addition, AEMP offers a
		158	distributed "group database", which maps group names to a list of strings
		159	- for example, to register worker ports.
		160
		161	A network needs at least one global node to work, and allows every node to
		162	be a global node.
		163
		164	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		165	node and tries to keep connections to all other nodes. So while it can
		166	make sense to make every node "global" in small networks, it usually makes
		167	sense to only make seed nodes into global nodes in large networks (nodes
		168	keep connections to seed nodes and global nodes, so makign them the same
		169	reduces overhead).
84		170
85	=back	171	=back
86		172
87	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
88		174
…		…
90		176
91	=cut	177	=cut
92		178
93	package AnyEvent::MP;	179	package AnyEvent::MP;
94		180
		181	use AnyEvent::MP::Config ();
95	use AnyEvent::MP::Base;	182	use AnyEvent::MP::Kernel;
		183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
96		184
97	use common::sense;	185	use common::sense;
98		186
99	use Carp ();	187	use Carp ();
100		188
101	use AE ();	189	use AE ();
		190	use Guard ();
102		191
103	use base "Exporter";	192	use base "Exporter";
104		193
105	our $VERSION = '0.1';	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
		195
106	our @EXPORT = qw(	196	our @EXPORT = qw(
107	NODE $NODE *SELF node_of _any_	197	NODE $NODE *SELF node_of after
108	resolve_node	198	configure
109	become_slave become_public	199	snd rcv mon mon_guard kil psub peval spawn cal
110	snd rcv mon kil reg psub
111	port	200	port
		201	db_set db_del db_reg
		202	db_mon db_family db_keys db_values
112	);	203	);
113		204
114	our $SELF;	205	our $SELF;
115		206
116	sub _self_die() {	207	sub _self_die() {
…		…
119	kil $SELF, die => $msg;	210	kil $SELF, die => $msg;
120	}	211	}
121		212
122	=item $thisnode = NODE / $NODE	213	=item $thisnode = NODE / $NODE
123		214
124	The C<NODE> function returns, and the C<$NODE> variable contains	215	The C<NODE> function returns, and the C<$NODE> variable contains, the node
125	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
126	to C<become_public> or C<become_slave>, after which all local port	217	a call to C<configure>.
127	identifiers become invalid.
128		218
129	=item $noderef = node_of $portid	219	=item $nodeid = node_of $port
130		220
131	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.
132		222
133	=item $cv = resolve_node $noderef	223	=item configure $profile, key => value...
134		224
135	Takes an unresolved node reference that may contain hostnames and	225	=item configure key => value...
136	abbreviated IDs, resolves all of them and returns a resolved node
137	reference.
138		226
139	In addition to C<address:port> pairs allowed in resolved noderefs, the	227	Before a node can talk to other nodes on the network (i.e. enter
140	following forms are supported:	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:
141		237
142	=over 4	238	=over 4
143		239
144	=item the empty string	240	=item norc => $boolean (default false)
145		241
146	An empty-string component gets resolved as if the default port (4040) was	242	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
147	specified.	243	be consulted - all configuraiton options must be specified in the
		244	C<configure> call.
148		245
149	=item naked port numbers (e.g. C<1234>)	246	=item force => $boolean (default false)
150		247
151	These are resolved by prepending the local nodename and a colon, to be	248	IF true, then the values specified in the C<configure> will take
152	further resolved.	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.
153		251
154	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	252	=item secure => $pass->($nodeid)
155		253
156	These are resolved by using AnyEvent::DNS to resolve them, optionally	254	In addition to specifying a boolean, you can specify a code reference that
157	looking up SRV records for the C<aemp=4040> port, if no port was	255	is called for every remote execution attempt - the execution request is
158	specified.	256	granted iff the callback returns a true value.
		257
		258	See F<semp setsecure> for more info.
159		259
160	=back	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)"
161		338
162	=item $SELF	339	=item $SELF
163		340
164	Contains the current port id while executing C<rcv> callbacks or C<psub>	341	Contains the current port id while executing C<rcv> callbacks or C<psub>
165	blocks.	342	blocks.
166		343
167	=item SELF, %SELF, @SELF...	344	=item *SELF, SELF, %SELF, @SELF...
168		345
169	Due to some quirks in how perl exports variables, it is impossible to	346	Due to some quirks in how perl exports variables, it is impossible to
170	just export C<$SELF>, all the symbols called C<SELF> are exported by this	347	just export C<$SELF>, all the symbols named C<SELF> are exported by this
171	module, but only C<$SELF> is currently used.	348	module, but only C<$SELF> is currently used.
172		349
173	=item snd $portid, type => @data	350	=item snd $port, type => @data
174		351
175	=item snd $portid, @msg	352	=item snd $port, @msg
176		353
177	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
178	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.
179	stringifies a sa port ID (such as a port object :).
180		356
181	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
182	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
183	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.
184		361
185	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
186	function: modifying any argument is not allowed and can cause many	363	function: modifying any argument (or values referenced by them) is
187	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.
188		368
189	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
190	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
191	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
192	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
193	node, anything can be passed.	373	node, anything can be passed. Best rely only on the common denominator of
		374	these.
194		375
195	=item kil $portid[, @reason]	376	=item $local_port = port
196		377
197	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.
198		380
199	If no C<@reason> is specified, then the port is killed "normally" (linked	381	=item $local_port = port { my @msg = @_ }
200	ports will not be kileld, or even notified).
201		382
202	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
203	C<mon>, see below).	384	creating a port and calling C<rcv $port, $callback> on it.
204		385
205	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
206	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.
207		390
208	Transport/communication errors are reported as C<< transport_error =>	391	If you want to stop/destroy the port, simply C<kil> it:
209	$message >>.
210		392
211	=item $guard = mon $portid, $cb->(@reason)	393	my $port = port {
212		394	my @msg = @_;
213	=item $guard = mon $portid, $otherport	395	...
214		396	kil $SELF;
215	=item $guard = mon $portid, $otherport, @msg	397	};
216
217	Monitor the given port and do something when the port is killed.
218
219	In the first form, the callback is simply called with any number
220	of C<@reason> elements (no @reason means that the port was deleted
221	"normally"). Note also that I<< the callback B<must> never die >>, so use
222	C<eval> if unsure.
223
224	In the second form, the other port will be C<kil>'ed with C<@reason>, iff
225	a @reason was specified, i.e. on "normal" kils nothing happens, while
226	under all other conditions, the other port is killed with the same reason.
227
228	In the last form, a message of the form C<@msg, @reason> will be C<snd>.
229
230	Example: call a given callback when C<$port> is killed.
231
232	mon $port, sub { warn "port died because of <@_>\n" };
233
234	Example: kill ourselves when C<$port> is killed abnormally.
235
236	mon $port, $self;
237
238	Example: send us a restart message another C<$port> is killed.
239
240	mon $port, $self => "restart";
241		398
242	=cut	399	=cut
243		400
244	sub mon {	401	sub rcv($@);
245	my ($noderef, $port, $cb) = ((split /#/, shift, 2), shift);
246		402
247	my $node = $NODE{$noderef} || add_node $noderef;	403	my $KILME = sub {
		404	(my $tag = substr $_[0], 0, 30) =~ s/([\x20-\x7e])/./g;
		405	kil $SELF, unhandled_message => "missing (tag or fallback) callback for message '$tag'";
		406	};
248		407
249	#TODO: ports must not be references	408	sub port(;&) {
250	if (!ref $cb or "AnyEvent::MP::Port" eq ref $cb) {	409	my $id = $UNIQ . ++$ID;
		410	my $port = "$NODE#$id";
		411
		412	rcv $port, shift || $KILME;
		413
		414	$port
		415	}
		416
		417	=item rcv $local_port, $callback->(@msg)
		418
		419	Replaces the default callback on the specified port. There is no way to
		420	remove the default callback: use C<sub { }> to disable it, or better
		421	C<kil> the port when it is no longer needed.
		422
		423	The global C<$SELF> (exported by this module) contains C<$port> while
		424	executing the callback. Runtime errors during callback execution will
		425	result in the port being C<kil>ed.
		426
		427	The default callback receives all messages not matched by a more specific
		428	C<tag> match.
		429
		430	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
		431
		432	Register (or replace) callbacks to be called on messages starting with the
		433	given tag on the given port (and return the port), or unregister it (when
		434	C<$callback> is C<$undef> or missing). There can only be one callback
		435	registered for each tag.
		436
		437	The original message will be passed to the callback, after the first
		438	element (the tag) has been removed. The callback will use the same
		439	environment as the default callback (see above).
		440
		441	Example: create a port and bind receivers on it in one go.
		442
		443	my $port = rcv port,
		444	msg1 => sub { ... },
		445	msg2 => sub { ... },
		446	;
		447
		448	Example: create a port, bind receivers and send it in a message elsewhere
		449	in one go:
		450
		451	snd $otherport, reply =>
		452	rcv port,
		453	msg1 => sub { ... },
		454	...
		455	;
		456
		457	Example: temporarily register a rcv callback for a tag matching some port
		458	(e.g. for an rpc reply) and unregister it after a message was received.
		459
		460	rcv $port, $otherport => sub {
		461	my @reply = @_;
		462
		463	rcv $SELF, $otherport;
		464	};
		465
		466	=cut
		467
		468	sub rcv($@) {
		469	my $port = shift;
		470	my ($nodeid, $portid) = split /#/, $port, 2;
		471
		472	$NODE{$nodeid} == $NODE{""}
		473	or Carp::croak "$port: rcv can only be called on local ports, caught";
		474
		475	while (@_) {
251	if (@_) {	476	if (ref $_[0]) {
252	# send a kill info message	477	if (my $self = $PORT_DATA{$portid}) {
253	my (@msg) = ($cb, @_);	478	"AnyEvent::MP::Port" eq ref $self
254	$cb = sub { snd @msg, @_ };	479	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		480
		481	$self->[0] = shift;
255	} else {	482	} else {
256	# simply kill other port	483	my $cb = shift;
257	my $port = $cb;	484	$PORT{$portid} = sub {
258	$cb = sub { kil $port, @_ if @_ };	485	local $SELF = $port;
		486	eval { &$cb }; _self_die if $@;
		487	};
		488	}
		489	} elsif (defined $_[0]) {
		490	my $self = $PORT_DATA{$portid} ||= do {
		491	my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port";
		492
		493	$PORT{$portid} = sub {
		494	local $SELF = $port;
		495
		496	if (my $cb = $self->[1]{$_[0]}) {
		497	shift;
		498	eval { &$cb }; _self_die if $@;
		499	} else {
		500	&{ $self->[0] };
		501	}
		502	};
		503
		504	$self
		505	};
		506
		507	"AnyEvent::MP::Port" eq ref $self
		508	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		509
		510	my ($tag, $cb) = splice @_, 0, 2;
		511
		512	if (defined $cb) {
		513	$self->[1]{$tag} = $cb;
		514	} else {
		515	delete $self->[1]{$tag};
		516	}
259	}	517	}
260	}	518	}
261		519
262	$node->monitor ($port, $cb);
263
264	defined wantarray
265	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }
266	}
267
268	=item $guard = mon_guard $port, $ref, $ref...
269
270	Monitors the given C<$port> and keeps the passed references. When the port
271	is killed, the references will be freed.
272
273	Optionally returns a guard that will stop the monitoring.
274
275	This function is useful when you create e.g. timers or other watchers and
276	want to free them when the port gets killed:
277
278	$port->rcv (start => sub {
279	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {
280	undef $timer if 0.9 < rand;
281	});
282	});
283
284	=cut
285
286	sub mon_guard {
287	my ($port, @refs) = @_;
288
289	mon $port, sub { 0 && @refs }
290	}
291
292	=item lnk $port1, $port2
293
294	Link two ports. This is simply a shorthand for:
295
296	mon $port1, $port2;
297	mon $port2, $port1;
298
299	It means that if either one is killed abnormally, the other one gets
300	killed as well.
301
302	=item $local_port = port
303
304	Create a new local port object that supports message matching.
305
306	=item $portid = port { my @msg = @_; $finished }
307
308	Creates a "mini port", that is, a very lightweight port without any
309	pattern matching behind it, and returns its ID.
310
311	The block will be called for every message received on the port. When the
312	callback returns a true value its job is considered "done" and the port
313	will be destroyed. Otherwise it will stay alive.
314
315	The message will be passed as-is, no extra argument (i.e. no port id) will
316	be passed to the callback.
317
318	If you need the local port id in the callback, this works nicely:
319
320	my $port; $port = miniport {
321	snd $otherport, reply => $port;
322	};
323
324	=cut
325
326	sub port(;&) {
327	my $id = "$UNIQ." . $ID++;
328	my $port = "$NODE#$id";
329
330	if (@_) {
331	my $cb = shift;
332	$PORT{$id} = sub {
333	local $SELF = $port;
334	eval {
335	&$cb
336	and kil $id;
337	};
338	_self_die if $@;
339	};
340	} else {
341	my $self = bless {
342	id => "$NODE#$id",
343	}, "AnyEvent::MP::Port";
344
345	$PORT_DATA{$id} = $self;
346	$PORT{$id} = sub {
347	local $SELF = $port;
348
349	eval {
350	for (@{ $self->{rc0}{$_[0]} }) {
351	$_ && &{$_->[0]}
352	&& undef $_;
353	}
354
355	for (@{ $self->{rcv}{$_[0]} }) {
356	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
357	&& &{$_->[0]}
358	&& undef $_;
359	}
360
361	for (@{ $self->{any} }) {
362	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
363	&& &{$_->[0]}
364	&& undef $_;
365	}
366	};
367	_self_die if $@;
368	};
369	}
370
371	$port	520	$port
372	}	521	}
373		522
374	=item reg $portid, $name	523	=item peval $port, $coderef[, @args]
375		524
376	Registers the given port under the name C<$name>. If the name already	525	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
377	exists it is replaced.	526	when the code throews an exception the C<$port> will be killed.
378		527
379	A port can only be registered under one well known name.	528	Any remaining args will be passed to the callback. Any return values will
		529	be returned to the caller.
380		530
381	A port automatically becomes unregistered when it is killed.	531	This is useful when you temporarily want to execute code in the context of
		532	a port.
		533
		534	Example: create a port and run some initialisation code in it's context.
		535
		536	my $port = port { ... };
		537
		538	peval $port, sub {
		539	init
		540	or die "unable to init";
		541	};
382		542
383	=cut	543	=cut
384		544
385	sub reg(@) {	545	sub peval($$) {
386	my ($portid, $name) = @_;	546	local $SELF = shift;
		547	my $cb = shift;
387		548
388	$REG{$name} = $portid;	549	if (wantarray) {
389	}	550	my @res = eval { &$cb };
390		551	_self_die if $@;
391	=item rcv $portid, tagstring => $callback->(@msg), ...	552	@res
392
393	=item rcv $portid, $smartmatch => $callback->(@msg), ...
394
395	=item rcv $portid, [$smartmatch...] => $callback->(@msg), ...
396
397	Register callbacks to be called on matching messages on the given port.
398
399	The callback has to return a true value when its work is done, after
400	which is will be removed, or a false value in which case it will stay
401	registered.
402
403	The global C<$SELF> (exported by this module) contains C<$portid> while
404	executing the callback.
405
406	Runtime errors wdurign callback execution will result in the port being
407	C<kil>ed.
408
409	If the match is an array reference, then it will be matched against the
410	first elements of the message, otherwise only the first element is being
411	matched.
412
413	Any element in the match that is specified as C<_any_> (a function
414	exported by this module) matches any single element of the message.
415
416	While not required, it is highly recommended that the first matching
417	element is a string identifying the message. The one-string-only match is
418	also the most efficient match (by far).
419
420	=cut
421
422	sub rcv($@) {
423	my ($noderef, $port) = split /#/, shift, 2;
424
425	($NODE{$noderef} || add_node $noderef) == $NODE{""}
426	or Carp::croak "$noderef#$port: rcv can only be called on local ports, caught";
427
428	my $self = $PORT_DATA{$port}
429	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";
430
431	"AnyEvent::MP::Port" eq ref $self
432	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";
433
434	while (@_) {
435	my ($match, $cb) = splice @_, 0, 2;
436
437	if (!ref $match) {
438	push @{ $self->{rc0}{$match} }, [$cb];
439	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
440	my ($type, @match) = @$match;
441	@match
442	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
443	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
444	} else {	553	} else {
445	push @{ $self->{any} }, [$cb, $match];	554	my $res = eval { &$cb };
446	}	555	_self_die if $@;
		556	$res
447	}	557	}
448	}	558	}
449		559
450	=item $closure = psub { BLOCK }	560	=item $closure = psub { BLOCK }
451		561
452	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	562	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
453	closure is executed, sets up the environment in the same way as in C<rcv>	563	closure is executed, sets up the environment in the same way as in C<rcv>
454	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.	564	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		565
		566	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		567	BLOCK }, @_ } >>.
455		568
456	This is useful when you register callbacks from C<rcv> callbacks:	569	This is useful when you register callbacks from C<rcv> callbacks:
457		570
458	rcv delayed_reply => sub {	571	rcv delayed_reply => sub {
459	my ($delay, @reply) = @_;	572	my ($delay, @reply) = @_;
…		…
483	$res	596	$res
484	}	597	}
485	}	598	}
486	}	599	}
487		600
		601	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
		602
		603	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
		604
		605	=item $guard = mon $port # kill $SELF when $port dies
		606
		607	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		608
		609	Monitor the given port and do something when the port is killed or
		610	messages to it were lost, and optionally return a guard that can be used
		611	to stop monitoring again.
		612
		613	In the first form (callback), the callback is simply called with any
		614	number of C<@reason> elements (no @reason means that the port was deleted
		615	"normally"). Note also that I<< the callback B<must> never die >>, so use
		616	C<eval> if unsure.
		617
		618	In the second form (another port given), the other port (C<$rcvport>)
		619	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
		620	"normal" kils nothing happens, while under all other conditions, the other
		621	port is killed with the same reason.
		622
		623	The third form (kill self) is the same as the second form, except that
		624	C<$rvport> defaults to C<$SELF>.
		625
		626	In the last form (message), a message of the form C<@msg, @reason> will be
		627	C<snd>.
		628
		629	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		630	alert was raised), they are removed and will not trigger again.
		631
		632	As a rule of thumb, monitoring requests should always monitor a port from
		633	a local port (or callback). The reason is that kill messages might get
		634	lost, just like any other message. Another less obvious reason is that
		635	even monitoring requests can get lost (for example, when the connection
		636	to the other node goes down permanently). When monitoring a port locally
		637	these problems do not exist.
		638
		639	C<mon> effectively guarantees that, in the absence of hardware failures,
		640	after starting the monitor, either all messages sent to the port will
		641	arrive, or the monitoring action will be invoked after possible message
		642	loss has been detected. No messages will be lost "in between" (after
		643	the first lost message no further messages will be received by the
		644	port). After the monitoring action was invoked, further messages might get
		645	delivered again.
		646
		647	Inter-host-connection timeouts and monitoring depend on the transport
		648	used. The only transport currently implemented is TCP, and AnyEvent::MP
		649	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		650	non-idle connection, and usually around two hours for idle connections).
		651
		652	This means that monitoring is good for program errors and cleaning up
		653	stuff eventually, but they are no replacement for a timeout when you need
		654	to ensure some maximum latency.
		655
		656	Example: call a given callback when C<$port> is killed.
		657
		658	mon $port, sub { warn "port died because of <@_>\n" };
		659
		660	Example: kill ourselves when C<$port> is killed abnormally.
		661
		662	mon $port;
		663
		664	Example: send us a restart message when another C<$port> is killed.
		665
		666	mon $port, $self => "restart";
		667
		668	=cut
		669
		670	sub mon {
		671	my ($nodeid, $port) = split /#/, shift, 2;
		672
		673	my $node = $NODE{$nodeid} || add_node $nodeid;
		674
		675	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
		676
		677	unless (ref $cb) {
		678	if (@_) {
		679	# send a kill info message
		680	my (@msg) = ($cb, @_);
		681	$cb = sub { snd @msg, @_ };
		682	} else {
		683	# simply kill other port
		684	my $port = $cb;
		685	$cb = sub { kil $port, @_ if @_ };
		686	}
		687	}
		688
		689	$node->monitor ($port, $cb);
		690
		691	defined wantarray
		692	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
		693	}
		694
		695	=item $guard = mon_guard $port, $ref, $ref...
		696
		697	Monitors the given C<$port> and keeps the passed references. When the port
		698	is killed, the references will be freed.
		699
		700	Optionally returns a guard that will stop the monitoring.
		701
		702	This function is useful when you create e.g. timers or other watchers and
		703	want to free them when the port gets killed (note the use of C<psub>):
		704
		705	$port->rcv (start => sub {
		706	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
		707	undef $timer if 0.9 < rand;
		708	});
		709	});
		710
		711	=cut
		712
		713	sub mon_guard {
		714	my ($port, @refs) = @_;
		715
		716	#TODO: mon-less form?
		717
		718	mon $port, sub { 0 && @refs }
		719	}
		720
		721	=item kil $port[, @reason]
		722
		723	Kill the specified port with the given C<@reason>.
		724
		725	If no C<@reason> is specified, then the port is killed "normally" -
		726	monitor callback will be invoked, but the kil will not cause linked ports
		727	(C<mon $mport, $lport> form) to get killed.
		728
		729	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
		730	form) get killed with the same reason.
		731
		732	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		733	will be reported as reason C<< die => $@ >>.
		734
		735	Transport/communication errors are reported as C<< transport_error =>
		736	$message >>.
		737
		738	Common idioms:
		739
		740	# silently remove yourself, do not kill linked ports
		741	kil $SELF;
		742
		743	# report a failure in some detail
		744	kil $SELF, failure_mode_1 => "it failed with too high temperature";
		745
		746	# do not waste much time with killing, just die when something goes wrong
		747	open my $fh, "<file"
		748	or die "file: $!";
		749
		750	=item $port = spawn $node, $initfunc[, @initdata]
		751
		752	Creates a port on the node C<$node> (which can also be a port ID, in which
		753	case it's the node where that port resides).
		754
		755	The port ID of the newly created port is returned immediately, and it is
		756	possible to immediately start sending messages or to monitor the port.
		757
		758	After the port has been created, the init function is called on the remote
		759	node, in the same context as a C<rcv> callback. This function must be a
		760	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		761	specify a function in the main program, use C<::name>.
		762
		763	If the function doesn't exist, then the node tries to C<require>
		764	the package, then the package above the package and so on (e.g.
		765	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		766	exists or it runs out of package names.
		767
		768	The init function is then called with the newly-created port as context
		769	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		770	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		771	the port might not get created.
		772
		773	A common idiom is to pass a local port, immediately monitor the spawned
		774	port, and in the remote init function, immediately monitor the passed
		775	local port. This two-way monitoring ensures that both ports get cleaned up
		776	when there is a problem.
		777
		778	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		779	caller before C<spawn> returns (by delaying invocation when spawn is
		780	called for the local node).
		781
		782	Example: spawn a chat server port on C<$othernode>.
		783
		784	# this node, executed from within a port context:
		785	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		786	mon $server;
		787
		788	# init function on C<$othernode>
		789	sub connect {
		790	my ($srcport) = @_;
		791
		792	mon $srcport;
		793
		794	rcv $SELF, sub {
		795	...
		796	};
		797	}
		798
		799	=cut
		800
		801	sub _spawn {
		802	my $port = shift;
		803	my $init = shift;
		804
		805	# rcv will create the actual port
		806	local $SELF = "$NODE#$port";
		807	eval {
		808	&{ load_func $init }
		809	};
		810	_self_die if $@;
		811	}
		812
		813	sub spawn(@) {
		814	my ($nodeid, undef) = split /#/, shift, 2;
		815
		816	my $id = $RUNIQ . ++$ID;
		817
		818	$_[0] =~ /::/
		819	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		820
		821	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		822
		823	"$nodeid#$id"
		824	}
		825
		826
		827	=item after $timeout, @msg
		828
		829	=item after $timeout, $callback
		830
		831	Either sends the given message, or call the given callback, after the
		832	specified number of seconds.
		833
		834	This is simply a utility function that comes in handy at times - the
		835	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		836	so it may go away in the future.
		837
		838	=cut
		839
		840	sub after($@) {
		841	my ($timeout, @action) = @_;
		842
		843	my $t; $t = AE::timer $timeout, 0, sub {
		844	undef $t;
		845	ref $action[0]
		846	? $action[0]()
		847	: snd @action;
		848	};
		849	}
		850
		851	#=item $cb2 = timeout $seconds, $cb[, @args]
		852
		853	=item cal $port, @msg, $callback[, $timeout]
		854
		855	A simple form of RPC - sends a message to the given C<$port> with the
		856	given contents (C<@msg>), but adds a reply port to the message.
		857
		858	The reply port is created temporarily just for the purpose of receiving
		859	the reply, and will be C<kil>ed when no longer needed.
		860
		861	A reply message sent to the port is passed to the C<$callback> as-is.
		862
		863	If an optional time-out (in seconds) is given and it is not C<undef>,
		864	then the callback will be called without any arguments after the time-out
		865	elapsed and the port is C<kil>ed.
		866
		867	If no time-out is given (or it is C<undef>), then the local port will
		868	monitor the remote port instead, so it eventually gets cleaned-up.
		869
		870	Currently this function returns the temporary port, but this "feature"
		871	might go in future versions unless you can make a convincing case that
		872	this is indeed useful for something.
		873
		874	=cut
		875
		876	sub cal(@) {
		877	my $timeout = ref $_[-1] ? undef : pop;
		878	my $cb = pop;
		879
		880	my $port = port {
		881	undef $timeout;
		882	kil $SELF;
		883	&$cb;
		884	};
		885
		886	if (defined $timeout) {
		887	$timeout = AE::timer $timeout, 0, sub {
		888	undef $timeout;
		889	kil $port;
		890	$cb->();
		891	};
		892	} else {
		893	mon $_[0], sub {
		894	kil $port;
		895	$cb->();
		896	};
		897	}
		898
		899	push @_, $port;
		900	&snd;
		901
		902	$port
		903	}
		904
488	=back	905	=back
489		906
490	=head1 FUNCTIONS FOR NODES	907	=head1 DISTRIBUTED DATABASE
491		908
		909	AnyEvent::MP comes with a simple distributed database. The database will
		910	be mirrored asynchronously on all global nodes. Other nodes bind to one
		911	of the global nodes for their needs. Every node has a "local database"
		912	which contains all the values that are set locally. All local databases
		913	are merged together to form the global database, which can be queried.
		914
		915	The database structure is that of a two-level hash - the database hash
		916	contains hashes which contain values, similarly to a perl hash of hashes,
		917	i.e.:
		918
		919	$DATABASE{$family}{$subkey} = $value
		920
		921	The top level hash key is called "family", and the second-level hash key
		922	is called "subkey" or simply "key".
		923
		924	The family must be alphanumeric, i.e. start with a letter and consist
		925	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		926	pretty much like Perl module names.
		927
		928	As the family namespace is global, it is recommended to prefix family names
		929	with the name of the application or module using it.
		930
		931	The subkeys must be non-empty strings, with no further restrictions.
		932
		933	The values should preferably be strings, but other perl scalars should
		934	work as well (such as C<undef>, arrays and hashes).
		935
		936	Every database entry is owned by one node - adding the same family/subkey
		937	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		938	but the result might be nondeterministic, i.e. the key might have
		939	different values on different nodes.
		940
		941	Different subkeys in the same family can be owned by different nodes
		942	without problems, and in fact, this is the common method to create worker
		943	pools. For example, a worker port for image scaling might do this:
		944
		945	db_set my_image_scalers => $port;
		946
		947	And clients looking for an image scaler will want to get the
		948	C<my_image_scalers> keys from time to time:
		949
		950	db_keys my_image_scalers => sub {
		951	@ports = @{ $_[0] };
		952	};
		953
		954	Or better yet, they want to monitor the database family, so they always
		955	have a reasonable up-to-date copy:
		956
		957	db_mon my_image_scalers => sub {
		958	@ports = keys %{ $_[0] };
		959	};
		960
		961	In general, you can set or delete single subkeys, but query and monitor
		962	whole families only.
		963
		964	If you feel the need to monitor or query a single subkey, try giving it
		965	it's own family.
		966
492	=over 4	967	=over
493		968
494	=item become_public $noderef	969	=item db_set $family => $subkey [=> $value]
495		970
496	Tells the node to become a public node, i.e. reachable from other nodes.	971	Sets (or replaces) a key to the database - if C<$value> is omitted,
		972	C<undef> is used instead.
497		973
498	The first argument is the (unresolved) node reference of the local node	974	=item db_del $family => $subkey...
499	(if missing then the empty string is used).
500		975
501	It is quite common to not specify anything, in which case the local node	976	Deletes one or more subkeys from the database family.
502	tries to listen on the default port, or to only specify a port number, in	977
503	which case AnyEvent::MP tries to guess the local addresses.	978	=item $guard = db_reg $family => $subkey [=> $value]
		979
		980	Sets the key on the database and returns a guard. When the guard is
		981	destroyed, the key is deleted from the database. If C<$value> is missing,
		982	then C<undef> is used.
		983
		984	=item db_family $family => $cb->(\%familyhash)
		985
		986	Queries the named database C<$family> and call the callback with the
		987	family represented as a hash. You can keep and freely modify the hash.
		988
		989	=item db_keys $family => $cb->(\@keys)
		990
		991	Same as C<db_family>, except it only queries the family I<subkeys> and passes
		992	them as array reference to the callback.
		993
		994	=item db_values $family => $cb->(\@values)
		995
		996	Same as C<db_family>, except it only queries the family I<values> and passes them
		997	as array reference to the callback.
		998
		999	=item $guard = db_mon $family => $cb->($familyhash, \@added, \@changed, \@deleted)
		1000
		1001	Creates a monitor on the given database family. Each time a key is set
		1002	or or is deleted the callback is called with a hash containing the
		1003	database family and three lists of added, changed and deleted subkeys,
		1004	respectively. If no keys have changed then the array reference might be
		1005	C<undef> or even missing.
		1006
		1007	If not called in void context, a guard object is returned that, when
		1008	destroyed, stops the monitor.
		1009
		1010	The family hash reference and the key arrays belong to AnyEvent::MP and
		1011	B<must not be modified or stored> by the callback. When in doubt, make a
		1012	copy.
		1013
		1014	As soon as possible after the monitoring starts, the callback will be
		1015	called with the intiial contents of the family, even if it is empty,
		1016	i.e. there will always be a timely call to the callback with the current
		1017	contents.
		1018
		1019	It is possible that the callback is called with a change event even though
		1020	the subkey is already present and the value has not changed.
		1021
		1022	The monitoring stops when the guard object is destroyed.
		1023
		1024	Example: on every change to the family "mygroup", print out all keys.
		1025
		1026	my $guard = db_mon mygroup => sub {
		1027	my ($family, $a, $c, $d) = @_;
		1028	print "mygroup members: ", (join " ", keys %$family), "\n";
		1029	};
		1030
		1031	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1032
		1033	my $guard; $guard = db_mon My::Module::workers => sub {
		1034	my ($family, $a, $c, $d) = @_;
		1035	return unless %$family;
		1036	undef $guard;
		1037	print "My::Module::workers now nonempty\n";
		1038	};
		1039
		1040	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		1041
		1042	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		1043	my ($family, $a, $c, $d) = @_;
		1044
		1045	print "+$_=$family->{$_}\n" for @$a;
		1046	print "*$_=$family->{$_}\n" for @$c;
		1047	print "-$_=$family->{$_}\n" for @$d;
		1048	};
504		1049
505	=cut	1050	=cut
506		1051
507	=back	1052	=back
508		1053
509	=head1 NODE MESSAGES
510
511	Nodes understand the following messages sent to them. Many of them take
512	arguments called C<@reply>, which will simply be used to compose a reply
513	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
514	the remaining arguments are simply the message data.
515
516	While other messages exist, they are not public and subject to change.
517
518	=over 4
519
520	=cut
521
522	=item lookup => $name, @reply
523
524	Replies with the port ID of the specified well-known port, or C<undef>.
525
526	=item devnull => ...
527
528	Generic data sink/CPU heat conversion.
529
530	=item relay => $port, @msg
531
532	Simply forwards the message to the given port.
533
534	=item eval => $string[ @reply]
535
536	Evaluates the given string. If C<@reply> is given, then a message of the
537	form C<@reply, $@, @evalres> is sent.
538
539	Example: crash another node.
540
541	snd $othernode, eval => "exit";
542
543	=item time => @reply
544
545	Replies the the current node time to C<@reply>.
546
547	Example: tell the current node to send the current time to C<$myport> in a
548	C<timereply> message.
549
550	snd $NODE, time => $myport, timereply => 1, 2;
551	# => snd $myport, timereply => 1, 2, <time>
552
553	=back
554
555	=head1 AnyEvent::MP vs. Distributed Erlang	1054	=head1 AnyEvent::MP vs. Distributed Erlang
556		1055
557	AnyEvent::MP got lots of its ideas from distributed erlang (erlang node	1056	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
558	== aemp node, erlang process == aemp port), so many of the documents and	1057	== aemp node, Erlang process == aemp port), so many of the documents and
559	programming techniques employed by erlang apply to AnyEvent::MP. Here is a	1058	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
560	sample:	1059	sample:
561		1060
562	http://www.erlang.se/doc/programming_rules.shtml	1061	http://www.erlang.se/doc/programming_rules.shtml
563	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	1062	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
564	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6	1063	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
…		…
566		1065
567	Despite the similarities, there are also some important differences:	1066	Despite the similarities, there are also some important differences:
568		1067
569	=over 4	1068	=over 4
570		1069
571	=item * Node references contain the recipe on how to contact them.	1070	=item * Node IDs are arbitrary strings in AEMP.
572		1071
573	Erlang relies on special naming and DNS to work everywhere in the	1072	Erlang relies on special naming and DNS to work everywhere in the same
574	same way. AEMP relies on each node knowing it's own address(es), with	1073	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
575	convenience functionality.	1074	configuration or DNS), and possibly the addresses of some seed nodes, but
		1075	will otherwise discover other nodes (and their IDs) itself.
576		1076
577	This means that AEMP requires a less tightly controlled environment at the	1077	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
578	cost of longer node references and a slightly higher management overhead.	1078	uses "local ports are like remote ports".
		1079
		1080	The failure modes for local ports are quite different (runtime errors
		1081	only) then for remote ports - when a local port dies, you I<know> it dies,
		1082	when a connection to another node dies, you know nothing about the other
		1083	port.
		1084
		1085	Erlang pretends remote ports are as reliable as local ports, even when
		1086	they are not.
		1087
		1088	AEMP encourages a "treat remote ports differently" philosophy, with local
		1089	ports being the special case/exception, where transport errors cannot
		1090	occur.
579		1091
580	=item * Erlang uses processes and a mailbox, AEMP does not queue.	1092	=item * Erlang uses processes and a mailbox, AEMP does not queue.
581		1093
582	Erlang uses processes that selctively receive messages, and therefore	1094	Erlang uses processes that selectively receive messages out of order, and
583	needs a queue. AEMP is event based, queuing messages would serve no useful	1095	therefore needs a queue. AEMP is event based, queuing messages would serve
584	purpose.	1096	no useful purpose. For the same reason the pattern-matching abilities
		1097	of AnyEvent::MP are more limited, as there is little need to be able to
		1098	filter messages without dequeuing them.
585		1099
586	(But see L<Coro::MP> for a more erlang-like process model on top of AEMP).	1100	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1101	being event-based, while Erlang is process-based.
		1102
		1103	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1104	top of AEMP and Coro threads.
587		1105
588	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1106	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
589		1107
590	Sending messages in erlang is synchronous and blocks the process. AEMP	1108	Sending messages in Erlang is synchronous and blocks the process until
591	sends are immediate, connection establishment is handled in the	1109	a conenction has been established and the message sent (and so does not
592	background.	1110	need a queue that can overflow). AEMP sends return immediately, connection
		1111	establishment is handled in the background.
593		1112
594	=item * Erlang can silently lose messages, AEMP cannot.	1113	=item * Erlang suffers from silent message loss, AEMP does not.
595		1114
596	Erlang makes few guarantees on messages delivery - messages can get lost	1115	Erlang implements few guarantees on messages delivery - messages can get
597	without any of the processes realising it (i.e. you send messages a, b,	1116	lost without any of the processes realising it (i.e. you send messages a,
598	and c, and the other side only receives messages a and c).	1117	b, and c, and the other side only receives messages a and c).
599		1118
600	AEMP guarantees correct ordering, and the guarantee that there are no	1119	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1120	guarantee that after one message is lost, all following ones sent to the
		1121	same port are lost as well, until monitoring raises an error, so there are
601	holes in the message sequence.	1122	no silent "holes" in the message sequence.
602		1123
603	=item * In erlang, processes can be declared dead and later be found to be	1124	If you want your software to be very reliable, you have to cope with
604	alive.	1125	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
605		1126	simply tries to work better in common error cases, such as when a network
606	In erlang it can happen that a monitored process is declared dead and	1127	link goes down.
607	linked processes get killed, but later it turns out that the process is
608	still alive - and can receive messages.
609
610	In AEMP, when port monitoring detects a port as dead, then that port will
611	eventually be killed - it cannot happen that a node detects a port as dead
612	and then later sends messages to it, finding it is still alive.
613		1128
614	=item * Erlang can send messages to the wrong port, AEMP does not.	1129	=item * Erlang can send messages to the wrong port, AEMP does not.
615		1130
616	In erlang it is quite possible that a node that restarts reuses a process	1131	In Erlang it is quite likely that a node that restarts reuses an Erlang
617	ID known to other nodes for a completely different process, causing	1132	process ID known to other nodes for a completely different process,
618	messages destined for that process to end up in an unrelated process.	1133	causing messages destined for that process to end up in an unrelated
		1134	process.
619		1135
620	AEMP never reuses port IDs, so old messages or old port IDs floating	1136	AEMP does not reuse port IDs, so old messages or old port IDs floating
621	around in the network will not be sent to an unrelated port.	1137	around in the network will not be sent to an unrelated port.
622		1138
623	=item * Erlang uses unprotected connections, AEMP uses secure	1139	=item * Erlang uses unprotected connections, AEMP uses secure
624	authentication and can use TLS.	1140	authentication and can use TLS.
625		1141
626	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1142	AEMP can use a proven protocol - TLS - to protect connections and
627	securely authenticate nodes.	1143	securely authenticate nodes.
628		1144
629	=item * The AEMP protocol is optimised for both text-based and binary	1145	=item * The AEMP protocol is optimised for both text-based and binary
630	communications.	1146	communications.
631		1147
632	The AEMP protocol, unlike the erlang protocol, supports both	1148	The AEMP protocol, unlike the Erlang protocol, supports both programming
633	language-independent text-only protocols (good for debugging) and binary,	1149	language independent text-only protocols (good for debugging), and binary,
634	language-specific serialisers (e.g. Storable).	1150	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1151	used, the protocol is actually completely text-based.
635		1152
636	It has also been carefully designed to be implementable in other languages	1153	It has also been carefully designed to be implementable in other languages
637	with a minimum of work while gracefully degrading fucntionality to make the	1154	with a minimum of work while gracefully degrading functionality to make the
638	protocol simple.	1155	protocol simple.
639		1156
		1157	=item * AEMP has more flexible monitoring options than Erlang.
		1158
		1159	In Erlang, you can chose to receive I<all> exit signals as messages or
		1160	I<none>, there is no in-between, so monitoring single Erlang processes is
		1161	difficult to implement.
		1162
		1163	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1164	between automatic kill, exit message or callback on a per-port basis.
		1165
		1166	=item * Erlang tries to hide remote/local connections, AEMP does not.
		1167
		1168	Monitoring in Erlang is not an indicator of process death/crashes, in the
		1169	same way as linking is (except linking is unreliable in Erlang).
		1170
		1171	In AEMP, you don't "look up" registered port names or send to named ports
		1172	that might or might not be persistent. Instead, you normally spawn a port
		1173	on the remote node. The init function monitors you, and you monitor the
		1174	remote port. Since both monitors are local to the node, they are much more
		1175	reliable (no need for C<spawn_link>).
		1176
		1177	This also saves round-trips and avoids sending messages to the wrong port
		1178	(hard to do in Erlang).
		1179
640	=back	1180	=back
641		1181
		1182	=head1 RATIONALE
		1183
		1184	=over 4
		1185
		1186	=item Why strings for port and node IDs, why not objects?
		1187
		1188	We considered "objects", but found that the actual number of methods
		1189	that can be called are quite low. Since port and node IDs travel over
		1190	the network frequently, the serialising/deserialising would add lots of
		1191	overhead, as well as having to keep a proxy object everywhere.
		1192
		1193	Strings can easily be printed, easily serialised etc. and need no special
		1194	procedures to be "valid".
		1195
		1196	And as a result, a port with just a default receiver consists of a single
		1197	code reference stored in a global hash - it can't become much cheaper.
		1198
		1199	=item Why favour JSON, why not a real serialising format such as Storable?
		1200
		1201	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1202	format, but currently there is no way to make a node use Storable by
		1203	default (although all nodes will accept it).
		1204
		1205	The default framing protocol is JSON because a) JSON::XS is many times
		1206	faster for small messages and b) most importantly, after years of
		1207	experience we found that object serialisation is causing more problems
		1208	than it solves: Just like function calls, objects simply do not travel
		1209	easily over the network, mostly because they will always be a copy, so you
		1210	always have to re-think your design.
		1211
		1212	Keeping your messages simple, concentrating on data structures rather than
		1213	objects, will keep your messages clean, tidy and efficient.
		1214
		1215	=back
		1216
642	=head1 SEE ALSO	1217	=head1 SEE ALSO
		1218
		1219	L<AnyEvent::MP::Intro> - a gentle introduction.
		1220
		1221	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1222
		1223	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1224	your applications.
		1225
		1226	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1227
		1228	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1229	all nodes.
643		1230
644	L<AnyEvent>.	1231	L<AnyEvent>.
645		1232
646	=head1 AUTHOR	1233	=head1 AUTHOR
647		1234

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