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Revision 1.35 by root, Thu Aug 6 10:21:48 2009 UTC vs.
Revision 1.136 by root, Wed Mar 21 15:22:16 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
27		34
28	# linking two ports, so they both crash together	35	# destroy a port again
29	lnk $port1, $port2;	36	kil $port; # "normal" kill
		37	kil $port, my_error => "everything is broken"; # error kill
30		38
31	# monitoring	39	# monitoring
32	mon $port, $cb->(@msg) # callback is invoked on death	40	mon $port, $cb->(@msg) # callback is invoked on death
33	mon $port, $otherport # kill otherport on abnormal death	41	mon $port, $localport # kill localport on abnormal death
34	mon $port, $otherport, @msg # send message on 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.
35		59
36	=head1 DESCRIPTION	60	=head1 DESCRIPTION
37		61
38	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
39		63
40	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
41	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
42		66
43	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>
44	manual page.	68	manual page and the examples under F<eg/>.
45
46	At the moment, this module family is severly broken and underdocumented,
47	so do not use. This was uploaded mainly to reserve the CPAN namespace -
48	stay tuned! The basic API should be finished, however.
49		69
50	=head1 CONCEPTS	70	=head1 CONCEPTS
51		71
52	=over 4	72	=over 4
53		73
54	=item port	74	=item port
55		75
56	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).
57		78
58	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
59	messages. All C<rcv> handlers will receive messages they match, messages	80	some messages. Messages send to ports will not be queued, regardless of
60	will not be queued.	81	anything was listening for them or not.
61		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
62	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
63		86
64	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<#>)
65	separator, and a port name (a printable string of unspecified format). An	88	as separator, and a port name (a printable string of unspecified
66	exception is the the node port, whose ID is identical to its node	89	format created by AnyEvent::MP).
67	reference.
68		90
69	=item node	91	=item node
70		92
71	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,
72	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
73	create new ports, among other things.	95	ports.
74		96
75	Nodes are either private (single-process only), slaves (connected to a	97	Nodes are either public (have one or more listening ports) or private
76	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.
77		100
78	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	101	Nodes is represented by (printable) strings called "node IDs".
79		102
80	A node reference is a string that either simply identifies the node (for	103	=item node ID - C<[A-Za-z0-9_\-.:]*>
81	private and slave nodes), or contains a recipe on how to reach a given
82	node (for public nodes).
83		104
84	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
85	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.
86		109
87	Node references come in two flavours: resolved (containing only numerical	110	=item binds - C<ip:port>
88	addresses) or unresolved (where hostnames are used instead of addresses).
89		111
90	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
91	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).
92		170
93	=back	171	=back
94		172
95	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
96		174
…		…
98		176
99	=cut	177	=cut
100		178
101	package AnyEvent::MP;	179	package AnyEvent::MP;
102		180
		181	use AnyEvent::MP::Config ();
103	use AnyEvent::MP::Base;	182	use AnyEvent::MP::Kernel;
		183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
104		184
105	use common::sense;	185	use common::sense;
106		186
107	use Carp ();	187	use Carp ();
108		188
109	use AE ();	189	use AE ();
		190	use Guard ();
110		191
111	use base "Exporter";	192	use base "Exporter";
112		193
113	our $VERSION = '0.1';	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
		195
114	our @EXPORT = qw(	196	our @EXPORT = qw(
115	NODE $NODE *SELF node_of _any_	197	NODE $NODE *SELF node_of after
116	resolve_node initialise_node	198	configure
117	snd rcv mon kil reg psub	199	snd rcv mon mon_guard kil psub peval spawn cal
118	port	200	port
		201	db_set db_del db_reg
		202	db_mon db_family db_keys db_values
119	);	203	);
120		204
121	our $SELF;	205	our $SELF;
122		206
123	sub _self_die() {	207	sub _self_die() {
…		…
126	kil $SELF, die => $msg;	210	kil $SELF, die => $msg;
127	}	211	}
128		212
129	=item $thisnode = NODE / $NODE	213	=item $thisnode = NODE / $NODE
130		214
131	The C<NODE> function returns, and the C<$NODE> variable contains	215	The C<NODE> function returns, and the C<$NODE> variable contains, the node
132	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
133	to C<become_public> or C<become_slave>, after which all local port	217	a call to C<configure>.
134	identifiers become invalid.
135		218
136	=item $noderef = node_of $port	219	=item $nodeid = node_of $port
137		220
138	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.
139		222
140	=item initialise_node $noderef, $seednode, $seednode...	223	=item configure $profile, key => value...
141		224
142	=item initialise_node "slave/", $master, $master...	225	=item configure key => value...
143		226
144	Before a node can talk to other nodes on the network it has to initialise	227	Before a node can talk to other nodes on the network (i.e. enter
145	itself - the minimum a node needs to know is it's own name, and optionally	228	"distributed mode") it has to configure itself - the minimum a node needs
146	it should know the noderefs of some other nodes in the network.	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.
147		231
148	This function initialises a node - it must be called exactly once (or	232	This function configures a node - it must be called exactly once (or
149	never) before calling other AnyEvent::MP functions.	233	never) before calling other AnyEvent::MP functions.
150		234
151	All arguments are noderefs, which can be either resolved or unresolved.	235	The key/value pairs are basically the same ones as documented for the
152		236	F<aemp> command line utility (sans the set/del prefix), with these additions:
153	There are two types of networked nodes, public nodes and slave nodes:
154		237
155	=over 4	238	=over 4
156		239
157	=item public nodes	240	=item norc => $boolean (default false)
158		241
159	For public nodes, C<$noderef> must either be a (possibly unresolved)	242	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
160	noderef, in which case it will be resolved, or C<undef> (or missing), in	243	be consulted - all configuraiton options must be specified in the
161	which case the noderef will be guessed.	244	C<configure> call.
162		245
163	Afterwards, the node will bind itself on all endpoints and try to connect	246	=item force => $boolean (default false)
164	to all additional C<$seednodes> that are specified. Seednodes are optional
165	and can be used to quickly bootstrap the node into an existing network.
166		247
167	=item slave nodes	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.
168		251
169	When the C<$noderef> is the special string C<slave/>, then the node will	252	=item secure => $pass->(@msg)
170	become a slave node. Slave nodes cannot be contacted from outside and will
171	route most of their traffic to the master node that they attach to.
172		253
173	At least one additional noderef is required: The node will try to connect	254	In addition to specifying a boolean, you can specify a code reference that
174	to all of them and will become a slave attached to the first node it can	255	is called for every code execution attempt - the execution request is
175	successfully connect to.	256	granted iff the callback returns a true value.
		257
		258	Most of the time the callback should look only at
		259	C<$AnyEvent::MP::Kernel::SRCNODE> to make a decision, and not at the
		260	actual message (which can be about anything, and is mostly provided for
		261	diagnostic purposes).
		262
		263	See F<semp setsecure> for more info.
176		264
177	=back	265	=back
178		266
179	This function will block until all nodes have been resolved and, for slave
180	nodes, until it has successfully established a connection to a master
181	server.
182
183	Example: become a public node listening on the default node.
184
185	initialise_node;
186
187	Example: become a public node, and try to contact some well-known master
188	servers to become part of the network.
189
190	initialise_node undef, "master1", "master2";
191
192	Example: become a public node listening on port C<4041>.
193
194	initialise_node 4041;
195
196	Example: become a public node, only visible on localhost port 4044.
197
198	initialise_node "locahost:4044";
199
200	Example: become a slave node to any of the specified master servers.
201
202	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
203
204	=item $cv = resolve_node $noderef
205
206	Takes an unresolved node reference that may contain hostnames and
207	abbreviated IDs, resolves all of them and returns a resolved node
208	reference.
209
210	In addition to C<address:port> pairs allowed in resolved noderefs, the
211	following forms are supported:
212
213	=over 4	267	=over 4
214		268
215	=item the empty string	269	=item step 1, gathering configuration from profiles
216		270
217	An empty-string component gets resolved as if the default port (4040) was	271	The function first looks up a profile in the aemp configuration (see the
218	specified.	272	L<aemp> commandline utility). The profile name can be specified via the
		273	named C<profile> parameter or can simply be the first parameter). If it is
		274	missing, then the nodename (F<uname -n>) will be used as profile name.
219		275
220	=item naked port numbers (e.g. C<1234>)	276	The profile data is then gathered as follows:
221		277
222	These are resolved by prepending the local nodename and a colon, to be	278	First, all remaining key => value pairs (all of which are conveniently
223	further resolved.	279	undocumented at the moment) will be interpreted as configuration
		280	data. Then they will be overwritten by any values specified in the global
		281	default configuration (see the F<aemp> utility), then the chain of
		282	profiles chosen by the profile name (and any C<parent> attributes).
224		283
225	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	284	That means that the values specified in the profile have highest priority
		285	and the values specified directly via C<configure> have lowest priority,
		286	and can only be used to specify defaults.
226		287
227	These are resolved by using AnyEvent::DNS to resolve them, optionally	288	If the profile specifies a node ID, then this will become the node ID of
228	looking up SRV records for the C<aemp=4040> port, if no port was	289	this process. If not, then the profile name will be used as node ID, with
229	specified.	290	a unique randoms tring (C</%u>) appended.
		291
		292	The node ID can contain some C<%> sequences that are expanded: C<%n>
		293	is expanded to the local nodename, C<%u> is replaced by a random
		294	strign to make the node unique. For example, the F<aemp> commandline
		295	utility uses C<aemp/%n/%u> as nodename, which might expand to
		296	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		297
		298	=item step 2, bind listener sockets
		299
		300	The next step is to look up the binds in the profile, followed by binding
		301	aemp protocol listeners on all binds specified (it is possible and valid
		302	to have no binds, meaning that the node cannot be contacted form the
		303	outside. This means the node cannot talk to other nodes that also have no
		304	binds, but it can still talk to all "normal" nodes).
		305
		306	If the profile does not specify a binds list, then a default of C<*> is
		307	used, meaning the node will bind on a dynamically-assigned port on every
		308	local IP address it finds.
		309
		310	=item step 3, connect to seed nodes
		311
		312	As the last step, the seed ID list from the profile is passed to the
		313	L<AnyEvent::MP::Global> module, which will then use it to keep
		314	connectivity with at least one node at any point in time.
230		315
231	=back	316	=back
		317
		318	Example: become a distributed node using the local node name as profile.
		319	This should be the most common form of invocation for "daemon"-type nodes.
		320
		321	configure
		322
		323	Example: become a semi-anonymous node. This form is often used for
		324	commandline clients.
		325
		326	configure nodeid => "myscript/%n/%u";
		327
		328	Example: configure a node using a profile called seed, which is suitable
		329	for a seed node as it binds on all local addresses on a fixed port (4040,
		330	customary for aemp).
		331
		332	# use the aemp commandline utility
		333	# aemp profile seed binds '*:4040'
		334
		335	# then use it
		336	configure profile => "seed";
		337
		338	# or simply use aemp from the shell again:
		339	# aemp run profile seed
		340
		341	# or provide a nicer-to-remember nodeid
		342	# aemp run profile seed nodeid "$(hostname)"
232		343
233	=item $SELF	344	=item $SELF
234		345
235	Contains the current port id while executing C<rcv> callbacks or C<psub>	346	Contains the current port id while executing C<rcv> callbacks or C<psub>
236	blocks.	347	blocks.
237		348
238	=item SELF, %SELF, @SELF...	349	=item *SELF, SELF, %SELF, @SELF...
239		350
240	Due to some quirks in how perl exports variables, it is impossible to	351	Due to some quirks in how perl exports variables, it is impossible to
241	just export C<$SELF>, all the symbols called C<SELF> are exported by this	352	just export C<$SELF>, all the symbols named C<SELF> are exported by this
242	module, but only C<$SELF> is currently used.	353	module, but only C<$SELF> is currently used.
243		354
244	=item snd $port, type => @data	355	=item snd $port, type => @data
245		356
246	=item snd $port, @msg	357	=item snd $port, @msg
247		358
248	Send the given message to the given port ID, which can identify either	359	Send the given message to the given port, which can identify either a
249	a local or a remote port, and can be either a string or soemthignt hat	360	local or a remote port, and must be a port ID.
250	stringifies a sa port ID (such as a port object :).
251		361
252	While the message can be about anything, it is highly recommended to use a	362	While the message can be almost anything, it is highly recommended to
253	string as first element (a portid, or some word that indicates a request	363	use a string as first element (a port ID, or some word that indicates a
254	type etc.).	364	request type etc.) and to consist if only simple perl values (scalars,
		365	arrays, hashes) - if you think you need to pass an object, think again.
255		366
256	The message data effectively becomes read-only after a call to this	367	The message data logically becomes read-only after a call to this
257	function: modifying any argument is not allowed and can cause many	368	function: modifying any argument (or values referenced by them) is
258	problems.	369	forbidden, as there can be considerable time between the call to C<snd>
		370	and the time the message is actually being serialised - in fact, it might
		371	never be copied as within the same process it is simply handed to the
		372	receiving port.
259		373
260	The type of data you can transfer depends on the transport protocol: when	374	The type of data you can transfer depends on the transport protocol: when
261	JSON is used, then only strings, numbers and arrays and hashes consisting	375	JSON is used, then only strings, numbers and arrays and hashes consisting
262	of those are allowed (no objects). When Storable is used, then anything	376	of those are allowed (no objects). When Storable is used, then anything
263	that Storable can serialise and deserialise is allowed, and for the local	377	that Storable can serialise and deserialise is allowed, and for the local
264	node, anything can be passed.	378	node, anything can be passed. Best rely only on the common denominator of
		379	these.
265		380
266	=item $local_port = port	381	=item $local_port = port
267		382
268	Create a new local port object that can be used either as a pattern	383	Create a new local port object and returns its port ID. Initially it has
269	matching port ("full port") or a single-callback port ("miniport"),	384	no callbacks set and will throw an error when it receives messages.
270	depending on how C<rcv> callbacks are bound to the object.
271		385
272	=item $port = port { my @msg = @_; $finished }	386	=item $local_port = port { my @msg = @_ }
273		387
274	Creates a "miniport", that is, a very lightweight port without any pattern	388	Creates a new local port, and returns its ID. Semantically the same as
275	matching behind it, and returns its ID. Semantically the same as creating
276	a port and calling C<rcv $port, $callback> on it.	389	creating a port and calling C<rcv $port, $callback> on it.
277		390
278	The block will be called for every message received on the port. When the	391	The block will be called for every message received on the port, with the
279	callback returns a true value its job is considered "done" and the port	392	global variable C<$SELF> set to the port ID. Runtime errors will cause the
280	will be destroyed. Otherwise it will stay alive.	393	port to be C<kil>ed. The message will be passed as-is, no extra argument
		394	(i.e. no port ID) will be passed to the callback.
281		395
282	The message will be passed as-is, no extra argument (i.e. no port id) will	396	If you want to stop/destroy the port, simply C<kil> it:
283	be passed to the callback.
284		397
285	If you need the local port id in the callback, this works nicely:	398	my $port = port {
286		399	my @msg = @_;
287	my $port; $port = port {	400	...
288	snd $otherport, reply => $port;	401	kil $SELF;
289	};	402	};
290		403
291	=cut	404	=cut
292		405
293	sub rcv($@);	406	sub rcv($@);
294		407
		408	my $KILME = sub {
		409	(my $tag = substr $_[0], 0, 30) =~ s/([\x20-\x7e])/./g;
		410	kil $SELF, unhandled_message => "no callback found for message '$tag'";
		411	};
		412
295	sub port(;&) {	413	sub port(;&) {
296	my $id = "$UNIQ." . $ID++;	414	my $id = $UNIQ . ++$ID;
297	my $port = "$NODE#$id";	415	my $port = "$NODE#$id";
298		416
299	if (@_) {
300	rcv $port, shift;	417	rcv $port, shift || $KILME;
301	} else {
302	$PORT{$id} = sub { }; # nop
303	}
304		418
305	$port	419	$port
306	}	420	}
307		421
308	=item reg $port, $name
309
310	Registers the given port under the name C<$name>. If the name already
311	exists it is replaced.
312
313	A port can only be registered under one well known name.
314
315	A port automatically becomes unregistered when it is killed.
316
317	=cut
318
319	sub reg(@) {
320	my ($port, $name) = @_;
321
322	$REG{$name} = $port;
323	}
324
325	=item rcv $port, $callback->(@msg)	422	=item rcv $local_port, $callback->(@msg)
326		423
327	Replaces the callback on the specified miniport (after converting it to	424	Replaces the default callback on the specified port. There is no way to
328	one if required).	425	remove the default callback: use C<sub { }> to disable it, or better
329		426	C<kil> the port when it is no longer needed.
330	=item rcv $port, tagstring => $callback->(@msg), ...
331
332	=item rcv $port, $smartmatch => $callback->(@msg), ...
333
334	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
335
336	Register callbacks to be called on matching messages on the given full
337	port (after converting it to one if required).
338
339	The callback has to return a true value when its work is done, after
340	which is will be removed, or a false value in which case it will stay
341	registered.
342		427
343	The global C<$SELF> (exported by this module) contains C<$port> while	428	The global C<$SELF> (exported by this module) contains C<$port> while
344	executing the callback.	429	executing the callback. Runtime errors during callback execution will
		430	result in the port being C<kil>ed.
345		431
346	Runtime errors wdurign callback execution will result in the port being	432	The default callback receives all messages not matched by a more specific
347	C<kil>ed.	433	C<tag> match.
348		434
349	If the match is an array reference, then it will be matched against the	435	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
350	first elements of the message, otherwise only the first element is being
351	matched.
352		436
353	Any element in the match that is specified as C<_any_> (a function	437	Register (or replace) callbacks to be called on messages starting with the
354	exported by this module) matches any single element of the message.	438	given tag on the given port (and return the port), or unregister it (when
		439	C<$callback> is C<$undef> or missing). There can only be one callback
		440	registered for each tag.
355		441
356	While not required, it is highly recommended that the first matching	442	The original message will be passed to the callback, after the first
357	element is a string identifying the message. The one-string-only match is	443	element (the tag) has been removed. The callback will use the same
358	also the most efficient match (by far).	444	environment as the default callback (see above).
		445
		446	Example: create a port and bind receivers on it in one go.
		447
		448	my $port = rcv port,
		449	msg1 => sub { ... },
		450	msg2 => sub { ... },
		451	;
		452
		453	Example: create a port, bind receivers and send it in a message elsewhere
		454	in one go:
		455
		456	snd $otherport, reply =>
		457	rcv port,
		458	msg1 => sub { ... },
		459	...
		460	;
		461
		462	Example: temporarily register a rcv callback for a tag matching some port
		463	(e.g. for an rpc reply) and unregister it after a message was received.
		464
		465	rcv $port, $otherport => sub {
		466	my @reply = @_;
		467
		468	rcv $SELF, $otherport;
		469	};
359		470
360	=cut	471	=cut
361		472
362	sub rcv($@) {	473	sub rcv($@) {
363	my $port = shift;	474	my $port = shift;
364	my ($noderef, $portid) = split /#/, $port, 2;	475	my ($nodeid, $portid) = split /#/, $port, 2;
365		476
366	($NODE{$noderef} || add_node $noderef) == $NODE{""}	477	$NODE{$nodeid} == $NODE{""}
367	or Carp::croak "$port: rcv can only be called on local ports, caught";	478	or Carp::croak "$port: rcv can only be called on local ports, caught";
368		479
369	if (@_ == 1) {	480	while (@_) {
		481	if (ref $_[0]) {
		482	if (my $self = $PORT_DATA{$portid}) {
		483	"AnyEvent::MP::Port" eq ref $self
		484	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		485
		486	$self->[0] = shift;
		487	} else {
370	my $cb = shift;	488	my $cb = shift;
371	delete $PORT_DATA{$portid};
372	$PORT{$portid} = sub {	489	$PORT{$portid} = sub {
373	local $SELF = $port;	490	local $SELF = $port;
374	eval {	491	eval { &$cb }; _self_die if $@;
375	&$cb	492	};
376	and kil $port;
377	};	493	}
378	_self_die if $@;	494	} elsif (defined $_[0]) {
379	};
380	} else {
381	my $self = $PORT_DATA{$portid} ||= do {	495	my $self = $PORT_DATA{$portid} ||= do {
382	my $self = bless {	496	my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port";
383	id => $port,
384	}, "AnyEvent::MP::Port";
385		497
386	$PORT{$portid} = sub {	498	$PORT{$portid} = sub {
387	local $SELF = $port;	499	local $SELF = $port;
388		500
389	eval {
390	for (@{ $self->{rc0}{$_[0]} }) {	501	if (my $cb = $self->[1]{$_[0]}) {
391	$_ && &{$_->[0]}	502	shift;
392	&& undef $_;	503	eval { &$cb }; _self_die if $@;
393	}	504	} else {
394
395	for (@{ $self->{rcv}{$_[0]} }) {
396	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
397	&& &{$_->[0]}	505	&{ $self->[0] };
398	&& undef $_;
399	}
400
401	for (@{ $self->{any} }) {
402	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
403	&& &{$_->[0]}
404	&& undef $_;
405	}	506	}
406	};	507	};
407	_self_die if $@;	508
		509	$self
408	};	510	};
409		511
410	$self
411	};
412
413	"AnyEvent::MP::Port" eq ref $self	512	"AnyEvent::MP::Port" eq ref $self
414	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	513	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
415		514
416	while (@_) {
417	my ($match, $cb) = splice @_, 0, 2;	515	my ($tag, $cb) = splice @_, 0, 2;
418		516
419	if (!ref $match) {	517	if (defined $cb) {
420	push @{ $self->{rc0}{$match} }, [$cb];	518	$self->[1]{$tag} = $cb;
421	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
422	my ($type, @match) = @$match;
423	@match
424	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
425	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
426	} else {	519	} else {
427	push @{ $self->{any} }, [$cb, $match];	520	delete $self->[1]{$tag};
428	}	521	}
429	}	522	}
430	}	523	}
431		524
432	$port	525	$port
433	}	526	}
434		527
		528	=item peval $port, $coderef[, @args]
		529
		530	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		531	when the code throews an exception the C<$port> will be killed.
		532
		533	Any remaining args will be passed to the callback. Any return values will
		534	be returned to the caller.
		535
		536	This is useful when you temporarily want to execute code in the context of
		537	a port.
		538
		539	Example: create a port and run some initialisation code in it's context.
		540
		541	my $port = port { ... };
		542
		543	peval $port, sub {
		544	init
		545	or die "unable to init";
		546	};
		547
		548	=cut
		549
		550	sub peval($$) {
		551	local $SELF = shift;
		552	my $cb = shift;
		553
		554	if (wantarray) {
		555	my @res = eval { &$cb };
		556	_self_die if $@;
		557	@res
		558	} else {
		559	my $res = eval { &$cb };
		560	_self_die if $@;
		561	$res
		562	}
		563	}
		564
435	=item $closure = psub { BLOCK }	565	=item $closure = psub { BLOCK }
436		566
437	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	567	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
438	closure is executed, sets up the environment in the same way as in C<rcv>	568	closure is executed, sets up the environment in the same way as in C<rcv>
439	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.	569	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		570
		571	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		572	BLOCK }, @_ } >>.
440		573
441	This is useful when you register callbacks from C<rcv> callbacks:	574	This is useful when you register callbacks from C<rcv> callbacks:
442		575
443	rcv delayed_reply => sub {	576	rcv delayed_reply => sub {
444	my ($delay, @reply) = @_;	577	my ($delay, @reply) = @_;
…		…
468	$res	601	$res
469	}	602	}
470	}	603	}
471	}	604	}
472		605
473	=item $guard = mon $port, $cb->(@reason)	606	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
474		607
475	=item $guard = mon $port, $otherport	608	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
476		609
477	=item $guard = mon $port, $otherport, @msg	610	=item $guard = mon $port # kill $SELF when $port dies
478		611
		612	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		613
479	Monitor the given port and do something when the port is killed.	614	Monitor the given port and do something when the port is killed or
		615	messages to it were lost, and optionally return a guard that can be used
		616	to stop monitoring again.
480		617
481	In the first form, the callback is simply called with any number	618	In the first form (callback), the callback is simply called with any
482	of C<@reason> elements (no @reason means that the port was deleted	619	number of C<@reason> elements (no @reason means that the port was deleted
483	"normally"). Note also that I<< the callback B<must> never die >>, so use	620	"normally"). Note also that I<< the callback B<must> never die >>, so use
484	C<eval> if unsure.	621	C<eval> if unsure.
485		622
486	In the second form, the other port will be C<kil>'ed with C<@reason>, iff	623	In the second form (another port given), the other port (C<$rcvport>)
487	a @reason was specified, i.e. on "normal" kils nothing happens, while	624	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
488	under all other conditions, the other port is killed with the same reason.	625	"normal" kils nothing happens, while under all other conditions, the other
		626	port is killed with the same reason.
489		627
		628	The third form (kill self) is the same as the second form, except that
		629	C<$rvport> defaults to C<$SELF>.
		630
490	In the last form, a message of the form C<@msg, @reason> will be C<snd>.	631	In the last form (message), a message of the form C<@msg, @reason> will be
		632	C<snd>.
		633
		634	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		635	alert was raised), they are removed and will not trigger again.
		636
		637	As a rule of thumb, monitoring requests should always monitor a port from
		638	a local port (or callback). The reason is that kill messages might get
		639	lost, just like any other message. Another less obvious reason is that
		640	even monitoring requests can get lost (for example, when the connection
		641	to the other node goes down permanently). When monitoring a port locally
		642	these problems do not exist.
		643
		644	C<mon> effectively guarantees that, in the absence of hardware failures,
		645	after starting the monitor, either all messages sent to the port will
		646	arrive, or the monitoring action will be invoked after possible message
		647	loss has been detected. No messages will be lost "in between" (after
		648	the first lost message no further messages will be received by the
		649	port). After the monitoring action was invoked, further messages might get
		650	delivered again.
		651
		652	Inter-host-connection timeouts and monitoring depend on the transport
		653	used. The only transport currently implemented is TCP, and AnyEvent::MP
		654	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		655	non-idle connection, and usually around two hours for idle connections).
		656
		657	This means that monitoring is good for program errors and cleaning up
		658	stuff eventually, but they are no replacement for a timeout when you need
		659	to ensure some maximum latency.
491		660
492	Example: call a given callback when C<$port> is killed.	661	Example: call a given callback when C<$port> is killed.
493		662
494	mon $port, sub { warn "port died because of <@_>\n" };	663	mon $port, sub { warn "port died because of <@_>\n" };
495		664
496	Example: kill ourselves when C<$port> is killed abnormally.	665	Example: kill ourselves when C<$port> is killed abnormally.
497		666
498	mon $port, $self;	667	mon $port;
499		668
500	Example: send us a restart message another C<$port> is killed.	669	Example: send us a restart message when another C<$port> is killed.
501		670
502	mon $port, $self => "restart";	671	mon $port, $self => "restart";
503		672
504	=cut	673	=cut
505		674
506	sub mon {	675	sub mon {
507	my ($noderef, $port) = split /#/, shift, 2;	676	my ($nodeid, $port) = split /#/, shift, 2;
508		677
509	my $node = $NODE{$noderef} || add_node $noderef;	678	my $node = $NODE{$nodeid} || add_node $nodeid;
510		679
511	my $cb = shift;	680	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
512		681
513	unless (ref $cb) {	682	unless (ref $cb) {
514	if (@_) {	683	if (@_) {
515	# send a kill info message	684	# send a kill info message
516	my (@msg) = ($cb, @_);	685	my (@msg) = ($cb, @_);
…		…
523	}	692	}
524		693
525	$node->monitor ($port, $cb);	694	$node->monitor ($port, $cb);
526		695
527	defined wantarray	696	defined wantarray
528	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	697	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
529	}	698	}
530		699
531	=item $guard = mon_guard $port, $ref, $ref...	700	=item $guard = mon_guard $port, $ref, $ref...
532		701
533	Monitors the given C<$port> and keeps the passed references. When the port	702	Monitors the given C<$port> and keeps the passed references. When the port
534	is killed, the references will be freed.	703	is killed, the references will be freed.
535		704
536	Optionally returns a guard that will stop the monitoring.	705	Optionally returns a guard that will stop the monitoring.
537		706
538	This function is useful when you create e.g. timers or other watchers and	707	This function is useful when you create e.g. timers or other watchers and
539	want to free them when the port gets killed:	708	want to free them when the port gets killed (note the use of C<psub>):
540		709
541	$port->rcv (start => sub {	710	$port->rcv (start => sub {
542	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	711	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
543	undef $timer if 0.9 < rand;	712	undef $timer if 0.9 < rand;
544	});	713	});
545	});	714	});
546		715
547	=cut	716	=cut
548		717
549	sub mon_guard {	718	sub mon_guard {
550	my ($port, @refs) = @_;	719	my ($port, @refs) = @_;
551		720
		721	#TODO: mon-less form?
		722
552	mon $port, sub { 0 && @refs }	723	mon $port, sub { 0 && @refs }
553	}	724	}
554		725
555	=item lnk $port1, $port2
556
557	Link two ports. This is simply a shorthand for:
558
559	mon $port1, $port2;
560	mon $port2, $port1;
561
562	It means that if either one is killed abnormally, the other one gets
563	killed as well.
564
565	=item kil $port[, @reason]	726	=item kil $port[, @reason]
566		727
567	Kill the specified port with the given C<@reason>.	728	Kill the specified port with the given C<@reason>.
568		729
569	If no C<@reason> is specified, then the port is killed "normally" (linked	730	If no C<@reason> is specified, then the port is killed "normally" -
570	ports will not be kileld, or even notified).	731	monitor callback will be invoked, but the kil will not cause linked ports
		732	(C<mon $mport, $lport> form) to get killed.
571		733
572	Otherwise, linked ports get killed with the same reason (second form of	734	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
573	C<mon>, see below).	735	form) get killed with the same reason.
574		736
575	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	737	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
576	will be reported as reason C<< die => $@ >>.	738	will be reported as reason C<< die => $@ >>.
577		739
578	Transport/communication errors are reported as C<< transport_error =>	740	Transport/communication errors are reported as C<< transport_error =>
579	$message >>.	741	$message >>.
580		742
		743	Common idioms:
		744
		745	# silently remove yourself, do not kill linked ports
		746	kil $SELF;
		747
		748	# report a failure in some detail
		749	kil $SELF, failure_mode_1 => "it failed with too high temperature";
		750
		751	# do not waste much time with killing, just die when something goes wrong
		752	open my $fh, "<file"
		753	or die "file: $!";
		754
		755	=item $port = spawn $node, $initfunc[, @initdata]
		756
		757	Creates a port on the node C<$node> (which can also be a port ID, in which
		758	case it's the node where that port resides).
		759
		760	The port ID of the newly created port is returned immediately, and it is
		761	possible to immediately start sending messages or to monitor the port.
		762
		763	After the port has been created, the init function is called on the remote
		764	node, in the same context as a C<rcv> callback. This function must be a
		765	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		766	specify a function in the main program, use C<::name>.
		767
		768	If the function doesn't exist, then the node tries to C<require>
		769	the package, then the package above the package and so on (e.g.
		770	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		771	exists or it runs out of package names.
		772
		773	The init function is then called with the newly-created port as context
		774	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		775	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		776	the port might not get created.
		777
		778	A common idiom is to pass a local port, immediately monitor the spawned
		779	port, and in the remote init function, immediately monitor the passed
		780	local port. This two-way monitoring ensures that both ports get cleaned up
		781	when there is a problem.
		782
		783	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		784	caller before C<spawn> returns (by delaying invocation when spawn is
		785	called for the local node).
		786
		787	Example: spawn a chat server port on C<$othernode>.
		788
		789	# this node, executed from within a port context:
		790	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		791	mon $server;
		792
		793	# init function on C<$othernode>
		794	sub connect {
		795	my ($srcport) = @_;
		796
		797	mon $srcport;
		798
		799	rcv $SELF, sub {
		800	...
		801	};
		802	}
		803
		804	=cut
		805
		806	sub _spawn {
		807	my $port = shift;
		808	my $init = shift;
		809
		810	# rcv will create the actual port
		811	local $SELF = "$NODE#$port";
		812	eval {
		813	&{ load_func $init }
		814	};
		815	_self_die if $@;
		816	}
		817
		818	sub spawn(@) {
		819	my ($nodeid, undef) = split /#/, shift, 2;
		820
		821	my $id = $RUNIQ . ++$ID;
		822
		823	$_[0] =~ /::/
		824	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		825
		826	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		827
		828	"$nodeid#$id"
		829	}
		830
		831
		832	=item after $timeout, @msg
		833
		834	=item after $timeout, $callback
		835
		836	Either sends the given message, or call the given callback, after the
		837	specified number of seconds.
		838
		839	This is simply a utility function that comes in handy at times - the
		840	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		841	so it may go away in the future.
		842
		843	=cut
		844
		845	sub after($@) {
		846	my ($timeout, @action) = @_;
		847
		848	my $t; $t = AE::timer $timeout, 0, sub {
		849	undef $t;
		850	ref $action[0]
		851	? $action[0]()
		852	: snd @action;
		853	};
		854	}
		855
		856	#=item $cb2 = timeout $seconds, $cb[, @args]
		857
		858	=item cal $port, @msg, $callback[, $timeout]
		859
		860	A simple form of RPC - sends a message to the given C<$port> with the
		861	given contents (C<@msg>), but adds a reply port to the message.
		862
		863	The reply port is created temporarily just for the purpose of receiving
		864	the reply, and will be C<kil>ed when no longer needed.
		865
		866	A reply message sent to the port is passed to the C<$callback> as-is.
		867
		868	If an optional time-out (in seconds) is given and it is not C<undef>,
		869	then the callback will be called without any arguments after the time-out
		870	elapsed and the port is C<kil>ed.
		871
		872	If no time-out is given (or it is C<undef>), then the local port will
		873	monitor the remote port instead, so it eventually gets cleaned-up.
		874
		875	Currently this function returns the temporary port, but this "feature"
		876	might go in future versions unless you can make a convincing case that
		877	this is indeed useful for something.
		878
		879	=cut
		880
		881	sub cal(@) {
		882	my $timeout = ref $_[-1] ? undef : pop;
		883	my $cb = pop;
		884
		885	my $port = port {
		886	undef $timeout;
		887	kil $SELF;
		888	&$cb;
		889	};
		890
		891	if (defined $timeout) {
		892	$timeout = AE::timer $timeout, 0, sub {
		893	undef $timeout;
		894	kil $port;
		895	$cb->();
		896	};
		897	} else {
		898	mon $_[0], sub {
		899	kil $port;
		900	$cb->();
		901	};
		902	}
		903
		904	push @_, $port;
		905	&snd;
		906
		907	$port
		908	}
		909
581	=back	910	=back
582		911
583	=head1 NODE MESSAGES	912	=head1 DISTRIBUTED DATABASE
584		913
585	Nodes understand the following messages sent to them. Many of them take	914	AnyEvent::MP comes with a simple distributed database. The database will
586	arguments called C<@reply>, which will simply be used to compose a reply	915	be mirrored asynchronously on all global nodes. Other nodes bind to one
587	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and	916	of the global nodes for their needs. Every node has a "local database"
588	the remaining arguments are simply the message data.	917	which contains all the values that are set locally. All local databases
		918	are merged together to form the global database, which can be queried.
589		919
590	While other messages exist, they are not public and subject to change.	920	The database structure is that of a two-level hash - the database hash
		921	contains hashes which contain values, similarly to a perl hash of hashes,
		922	i.e.:
591		923
		924	$DATABASE{$family}{$subkey} = $value
		925
		926	The top level hash key is called "family", and the second-level hash key
		927	is called "subkey" or simply "key".
		928
		929	The family must be alphanumeric, i.e. start with a letter and consist
		930	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		931	pretty much like Perl module names.
		932
		933	As the family namespace is global, it is recommended to prefix family names
		934	with the name of the application or module using it.
		935
		936	The subkeys must be non-empty strings, with no further restrictions.
		937
		938	The values should preferably be strings, but other perl scalars should
		939	work as well (such as C<undef>, arrays and hashes).
		940
		941	Every database entry is owned by one node - adding the same family/subkey
		942	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		943	but the result might be nondeterministic, i.e. the key might have
		944	different values on different nodes.
		945
		946	Different subkeys in the same family can be owned by different nodes
		947	without problems, and in fact, this is the common method to create worker
		948	pools. For example, a worker port for image scaling might do this:
		949
		950	db_set my_image_scalers => $port;
		951
		952	And clients looking for an image scaler will want to get the
		953	C<my_image_scalers> keys from time to time:
		954
		955	db_keys my_image_scalers => sub {
		956	@ports = @{ $_[0] };
		957	};
		958
		959	Or better yet, they want to monitor the database family, so they always
		960	have a reasonable up-to-date copy:
		961
		962	db_mon my_image_scalers => sub {
		963	@ports = keys %{ $_[0] };
		964	};
		965
		966	In general, you can set or delete single subkeys, but query and monitor
		967	whole families only.
		968
		969	If you feel the need to monitor or query a single subkey, try giving it
		970	it's own family.
		971
592	=over 4	972	=over
		973
		974	=item db_set $family => $subkey [=> $value]
		975
		976	Sets (or replaces) a key to the database - if C<$value> is omitted,
		977	C<undef> is used instead.
		978
		979	=item db_del $family => $subkey...
		980
		981	Deletes one or more subkeys from the database family.
		982
		983	=item $guard = db_reg $family => $subkey [=> $value]
		984
		985	Sets the key on the database and returns a guard. When the guard is
		986	destroyed, the key is deleted from the database. If C<$value> is missing,
		987	then C<undef> is used.
		988
		989	=item db_family $family => $cb->(\%familyhash)
		990
		991	Queries the named database C<$family> and call the callback with the
		992	family represented as a hash. You can keep and freely modify the hash.
		993
		994	=item db_keys $family => $cb->(\@keys)
		995
		996	Same as C<db_family>, except it only queries the family I<subkeys> and passes
		997	them as array reference to the callback.
		998
		999	=item db_values $family => $cb->(\@values)
		1000
		1001	Same as C<db_family>, except it only queries the family I<values> and passes them
		1002	as array reference to the callback.
		1003
		1004	=item $guard = db_mon $family => $cb->($familyhash, \@added, \@changed, \@deleted)
		1005
		1006	Creates a monitor on the given database family. Each time a key is set
		1007	or or is deleted the callback is called with a hash containing the
		1008	database family and three lists of added, changed and deleted subkeys,
		1009	respectively. If no keys have changed then the array reference might be
		1010	C<undef> or even missing.
		1011
		1012	If not called in void context, a guard object is returned that, when
		1013	destroyed, stops the monitor.
		1014
		1015	The family hash reference and the key arrays belong to AnyEvent::MP and
		1016	B<must not be modified or stored> by the callback. When in doubt, make a
		1017	copy.
		1018
		1019	As soon as possible after the monitoring starts, the callback will be
		1020	called with the intiial contents of the family, even if it is empty,
		1021	i.e. there will always be a timely call to the callback with the current
		1022	contents.
		1023
		1024	It is possible that the callback is called with a change event even though
		1025	the subkey is already present and the value has not changed.
		1026
		1027	The monitoring stops when the guard object is destroyed.
		1028
		1029	Example: on every change to the family "mygroup", print out all keys.
		1030
		1031	my $guard = db_mon mygroup => sub {
		1032	my ($family, $a, $c, $d) = @_;
		1033	print "mygroup members: ", (join " ", keys %$family), "\n";
		1034	};
		1035
		1036	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1037
		1038	my $guard; $guard = db_mon My::Module::workers => sub {
		1039	my ($family, $a, $c, $d) = @_;
		1040	return unless %$family;
		1041	undef $guard;
		1042	print "My::Module::workers now nonempty\n";
		1043	};
		1044
		1045	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		1046
		1047	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		1048	my ($family, $a, $c, $d) = @_;
		1049
		1050	print "+$_=$family->{$_}\n" for @$a;
		1051	print "*$_=$family->{$_}\n" for @$c;
		1052	print "-$_=$family->{$_}\n" for @$d;
		1053	};
593		1054
594	=cut	1055	=cut
595
596	=item lookup => $name, @reply
597
598	Replies with the port ID of the specified well-known port, or C<undef>.
599
600	=item devnull => ...
601
602	Generic data sink/CPU heat conversion.
603
604	=item relay => $port, @msg
605
606	Simply forwards the message to the given port.
607
608	=item eval => $string[ @reply]
609
610	Evaluates the given string. If C<@reply> is given, then a message of the
611	form C<@reply, $@, @evalres> is sent.
612
613	Example: crash another node.
614
615	snd $othernode, eval => "exit";
616
617	=item time => @reply
618
619	Replies the the current node time to C<@reply>.
620
621	Example: tell the current node to send the current time to C<$myport> in a
622	C<timereply> message.
623
624	snd $NODE, time => $myport, timereply => 1, 2;
625	# => snd $myport, timereply => 1, 2, <time>
626		1056
627	=back	1057	=back
628		1058
629	=head1 AnyEvent::MP vs. Distributed Erlang	1059	=head1 AnyEvent::MP vs. Distributed Erlang
630		1060
631	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	1061	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
632	== aemp node, Erlang process == aemp port), so many of the documents and	1062	== aemp node, Erlang process == aemp port), so many of the documents and
633	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	1063	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
634	sample:	1064	sample:
635		1065
636	http://www.Erlang.se/doc/programming_rules.shtml	1066	http://www.erlang.se/doc/programming_rules.shtml
637	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	1067	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
638	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	1068	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
639	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	1069	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
640		1070
641	Despite the similarities, there are also some important differences:	1071	Despite the similarities, there are also some important differences:
642		1072
643	=over 4	1073	=over 4
644		1074
645	=item * Node references contain the recipe on how to contact them.	1075	=item * Node IDs are arbitrary strings in AEMP.
646		1076
647	Erlang relies on special naming and DNS to work everywhere in the	1077	Erlang relies on special naming and DNS to work everywhere in the same
648	same way. AEMP relies on each node knowing it's own address(es), with	1078	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
649	convenience functionality.	1079	configuration or DNS), and possibly the addresses of some seed nodes, but
		1080	will otherwise discover other nodes (and their IDs) itself.
650		1081
651	This means that AEMP requires a less tightly controlled environment at the	1082	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
652	cost of longer node references and a slightly higher management overhead.	1083	uses "local ports are like remote ports".
		1084
		1085	The failure modes for local ports are quite different (runtime errors
		1086	only) then for remote ports - when a local port dies, you I<know> it dies,
		1087	when a connection to another node dies, you know nothing about the other
		1088	port.
		1089
		1090	Erlang pretends remote ports are as reliable as local ports, even when
		1091	they are not.
		1092
		1093	AEMP encourages a "treat remote ports differently" philosophy, with local
		1094	ports being the special case/exception, where transport errors cannot
		1095	occur.
653		1096
654	=item * Erlang uses processes and a mailbox, AEMP does not queue.	1097	=item * Erlang uses processes and a mailbox, AEMP does not queue.
655		1098
656	Erlang uses processes that selctively receive messages, and therefore	1099	Erlang uses processes that selectively receive messages out of order, and
657	needs a queue. AEMP is event based, queuing messages would serve no useful	1100	therefore needs a queue. AEMP is event based, queuing messages would serve
658	purpose.	1101	no useful purpose. For the same reason the pattern-matching abilities
		1102	of AnyEvent::MP are more limited, as there is little need to be able to
		1103	filter messages without dequeuing them.
659		1104
660	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	1105	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1106	being event-based, while Erlang is process-based.
		1107
		1108	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1109	top of AEMP and Coro threads.
661		1110
662	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1111	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
663		1112
664	Sending messages in Erlang is synchronous and blocks the process. AEMP	1113	Sending messages in Erlang is synchronous and blocks the process until
665	sends are immediate, connection establishment is handled in the	1114	a conenction has been established and the message sent (and so does not
666	background.	1115	need a queue that can overflow). AEMP sends return immediately, connection
		1116	establishment is handled in the background.
667		1117
668	=item * Erlang can silently lose messages, AEMP cannot.	1118	=item * Erlang suffers from silent message loss, AEMP does not.
669		1119
670	Erlang makes few guarantees on messages delivery - messages can get lost	1120	Erlang implements few guarantees on messages delivery - messages can get
671	without any of the processes realising it (i.e. you send messages a, b,	1121	lost without any of the processes realising it (i.e. you send messages a,
672	and c, and the other side only receives messages a and c).	1122	b, and c, and the other side only receives messages a and c).
673		1123
674	AEMP guarantees correct ordering, and the guarantee that there are no	1124	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1125	guarantee that after one message is lost, all following ones sent to the
		1126	same port are lost as well, until monitoring raises an error, so there are
675	holes in the message sequence.	1127	no silent "holes" in the message sequence.
676		1128
677	=item * In Erlang, processes can be declared dead and later be found to be	1129	If you want your software to be very reliable, you have to cope with
678	alive.	1130	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
679		1131	simply tries to work better in common error cases, such as when a network
680	In Erlang it can happen that a monitored process is declared dead and	1132	link goes down.
681	linked processes get killed, but later it turns out that the process is
682	still alive - and can receive messages.
683
684	In AEMP, when port monitoring detects a port as dead, then that port will
685	eventually be killed - it cannot happen that a node detects a port as dead
686	and then later sends messages to it, finding it is still alive.
687		1133
688	=item * Erlang can send messages to the wrong port, AEMP does not.	1134	=item * Erlang can send messages to the wrong port, AEMP does not.
689		1135
690	In Erlang it is quite possible that a node that restarts reuses a process	1136	In Erlang it is quite likely that a node that restarts reuses an Erlang
691	ID known to other nodes for a completely different process, causing	1137	process ID known to other nodes for a completely different process,
692	messages destined for that process to end up in an unrelated process.	1138	causing messages destined for that process to end up in an unrelated
		1139	process.
693		1140
694	AEMP never reuses port IDs, so old messages or old port IDs floating	1141	AEMP does not reuse port IDs, so old messages or old port IDs floating
695	around in the network will not be sent to an unrelated port.	1142	around in the network will not be sent to an unrelated port.
696		1143
697	=item * Erlang uses unprotected connections, AEMP uses secure	1144	=item * Erlang uses unprotected connections, AEMP uses secure
698	authentication and can use TLS.	1145	authentication and can use TLS.
699		1146
700	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1147	AEMP can use a proven protocol - TLS - to protect connections and
701	securely authenticate nodes.	1148	securely authenticate nodes.
702		1149
703	=item * The AEMP protocol is optimised for both text-based and binary	1150	=item * The AEMP protocol is optimised for both text-based and binary
704	communications.	1151	communications.
705		1152
706	The AEMP protocol, unlike the Erlang protocol, supports both	1153	The AEMP protocol, unlike the Erlang protocol, supports both programming
707	language-independent text-only protocols (good for debugging) and binary,	1154	language independent text-only protocols (good for debugging), and binary,
708	language-specific serialisers (e.g. Storable).	1155	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1156	used, the protocol is actually completely text-based.
709		1157
710	It has also been carefully designed to be implementable in other languages	1158	It has also been carefully designed to be implementable in other languages
711	with a minimum of work while gracefully degrading fucntionality to make the	1159	with a minimum of work while gracefully degrading functionality to make the
712	protocol simple.	1160	protocol simple.
713		1161
714	=item * AEMP has more flexible monitoring options than Erlang.	1162	=item * AEMP has more flexible monitoring options than Erlang.
715		1163
716	In Erlang, you can chose to receive I<all> exit signals as messages	1164	In Erlang, you can chose to receive I<all> exit signals as messages or
717	or I<none>, there is no in-between, so monitoring single processes is	1165	I<none>, there is no in-between, so monitoring single Erlang processes is
718	difficult to implement. Monitoring in AEMP is more flexible than in	1166	difficult to implement.
719	Erlang, as one can choose between automatic kill, exit message or callback
720	on a per-process basis.
721		1167
722	=item * Erlang has different semantics for monitoring and linking, AEMP has the same.	1168	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1169	between automatic kill, exit message or callback on a per-port basis.
723		1170
		1171	=item * Erlang tries to hide remote/local connections, AEMP does not.
		1172
724	Monitoring in Erlang is not an indicator of process death/crashes,	1173	Monitoring in Erlang is not an indicator of process death/crashes, in the
725	as linking is (except linking is unreliable in Erlang). In AEMP, the	1174	same way as linking is (except linking is unreliable in Erlang).
726	semantics of monitoring and linking are identical, linking is simply	1175
727	two-way monitoring with automatic kill.	1176	In AEMP, you don't "look up" registered port names or send to named ports
		1177	that might or might not be persistent. Instead, you normally spawn a port
		1178	on the remote node. The init function monitors you, and you monitor the
		1179	remote port. Since both monitors are local to the node, they are much more
		1180	reliable (no need for C<spawn_link>).
		1181
		1182	This also saves round-trips and avoids sending messages to the wrong port
		1183	(hard to do in Erlang).
728		1184
729	=back	1185	=back
730		1186
		1187	=head1 RATIONALE
		1188
		1189	=over 4
		1190
		1191	=item Why strings for port and node IDs, why not objects?
		1192
		1193	We considered "objects", but found that the actual number of methods
		1194	that can be called are quite low. Since port and node IDs travel over
		1195	the network frequently, the serialising/deserialising would add lots of
		1196	overhead, as well as having to keep a proxy object everywhere.
		1197
		1198	Strings can easily be printed, easily serialised etc. and need no special
		1199	procedures to be "valid".
		1200
		1201	And as a result, a port with just a default receiver consists of a single
		1202	code reference stored in a global hash - it can't become much cheaper.
		1203
		1204	=item Why favour JSON, why not a real serialising format such as Storable?
		1205
		1206	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1207	format, but currently there is no way to make a node use Storable by
		1208	default (although all nodes will accept it).
		1209
		1210	The default framing protocol is JSON because a) JSON::XS is many times
		1211	faster for small messages and b) most importantly, after years of
		1212	experience we found that object serialisation is causing more problems
		1213	than it solves: Just like function calls, objects simply do not travel
		1214	easily over the network, mostly because they will always be a copy, so you
		1215	always have to re-think your design.
		1216
		1217	Keeping your messages simple, concentrating on data structures rather than
		1218	objects, will keep your messages clean, tidy and efficient.
		1219
		1220	=back
		1221
731	=head1 SEE ALSO	1222	=head1 SEE ALSO
		1223
		1224	L<AnyEvent::MP::Intro> - a gentle introduction.
		1225
		1226	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1227
		1228	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1229	your applications.
		1230
		1231	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1232
		1233	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1234	all nodes.
732		1235
733	L<AnyEvent>.	1236	L<AnyEvent>.
734		1237
735	=head1 AUTHOR	1238	=head1 AUTHOR
736		1239

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