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Revision 1.35 by root, Thu Aug 6 10:21:48 2009 UTC vs.
Revision 1.130 by root, Fri Mar 9 17:05:26 2012 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent::MP - multi-processing/message-passing framework	3	AnyEvent::MP - erlang-style multi-processing/message-passing framework
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::MP;	7	use AnyEvent::MP;
8		8
9	$NODE # contains this node's noderef	9	$NODE # contains this node's node ID
10	NODE # returns this node's noderef	10	NODE # returns this node's node ID
11	NODE $port # returns the noderef of the port
12		11
		12	$SELF # receiving/own port id in rcv callbacks
		13
		14	# initialise the node so it can send/receive messages
		15	configure;
		16
		17	# ports are message destinations
		18
		19	# sending messages
13	snd $port, type => data...;	20	snd $port, type => data...;
		21	snd $port, @msg;
		22	snd @msg_with_first_element_being_a_port;
14		23
15	$SELF # receiving/own port id in rcv callbacks	24	# creating/using ports, the simple way
		25	my $simple_port = port { my @msg = @_ };
16		26
17	rcv $port, smartmatch => $cb->($port, @msg);	27	# creating/using ports, tagged message matching
18		28	my $port = port;
19	# examples:
20	rcv $port2, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
21	rcv $port1, pong => sub { warn "pong received\n" };	30	rcv $port, pong => sub { warn "pong received\n" };
22	snd $port2, ping => $port1;
23		31
24	# more, smarter, matches (_any_ is exported by this module)	32	# create a port on another node
25	rcv $port, [child_died => $pid] => sub { ...	33	my $port = spawn $node, $initfunc, @initdata;
26	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3
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 => $pass->($nodeid)
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 remote execution attempt - the execution request is
175	successfully connect to.	256	granted iff the callback returns a true value.
		257
		258	See F<semp setsecure> for more info.
176		259
177	=back	260	=back
178		261
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	262	=over 4
214		263
215	=item the empty string	264	=item step 1, gathering configuration from profiles
216		265
217	An empty-string component gets resolved as if the default port (4040) was	266	The function first looks up a profile in the aemp configuration (see the
218	specified.	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.
219		270
220	=item naked port numbers (e.g. C<1234>)	271	The profile data is then gathered as follows:
221		272
222	These are resolved by prepending the local nodename and a colon, to be	273	First, all remaining key => value pairs (all of which are conveniently
223	further resolved.	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).
224		278
225	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	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.
226		282
227	These are resolved by using AnyEvent::DNS to resolve them, optionally	283	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	284	this process. If not, then the profile name will be used as node ID, with
229	specified.	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.
230		310
231	=back	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)"
232		338
233	=item $SELF	339	=item $SELF
234		340
235	Contains the current port id while executing C<rcv> callbacks or C<psub>	341	Contains the current port id while executing C<rcv> callbacks or C<psub>
236	blocks.	342	blocks.
237		343
238	=item SELF, %SELF, @SELF...	344	=item *SELF, SELF, %SELF, @SELF...
239		345
240	Due to some quirks in how perl exports variables, it is impossible to	346	Due to some quirks in how perl exports variables, it is impossible to
241	just export C<$SELF>, all the symbols called C<SELF> are exported by this	347	just export C<$SELF>, all the symbols named C<SELF> are exported by this
242	module, but only C<$SELF> is currently used.	348	module, but only C<$SELF> is currently used.
243		349
244	=item snd $port, type => @data	350	=item snd $port, type => @data
245		351
246	=item snd $port, @msg	352	=item snd $port, @msg
247		353
248	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
249	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.
250	stringifies a sa port ID (such as a port object :).
251		356
252	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
253	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
254	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.
255		361
256	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
257	function: modifying any argument is not allowed and can cause many	363	function: modifying any argument (or values referenced by them) is
258	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.
259		368
260	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
261	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
262	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
263	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
264	node, anything can be passed.	373	node, anything can be passed. Best rely only on the common denominator of
		374	these.
265		375
266	=item $local_port = port	376	=item $local_port = port
267		377
268	Create a new local port object that can be used either as a pattern	378	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"),	379	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		380
272	=item $port = port { my @msg = @_; $finished }	381	=item $local_port = port { my @msg = @_ }
273		382
274	Creates a "miniport", that is, a very lightweight port without any pattern	383	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.	384	creating a port and calling C<rcv $port, $callback> on it.
277		385
278	The block will be called for every message received on the port. When the	386	The block will be called for every message received on the port, with the
279	callback returns a true value its job is considered "done" and the port	387	global variable C<$SELF> set to the port ID. Runtime errors will cause the
280	will be destroyed. Otherwise it will stay alive.	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.
281		390
282	The message will be passed as-is, no extra argument (i.e. no port id) will	391	If you want to stop/destroy the port, simply C<kil> it:
283	be passed to the callback.
284		392
285	If you need the local port id in the callback, this works nicely:	393	my $port = port {
286		394	my @msg = @_;
287	my $port; $port = port {	395	...
288	snd $otherport, reply => $port;	396	kil $SELF;
289	};	397	};
290		398
291	=cut	399	=cut
292		400
293	sub rcv($@);	401	sub rcv($@);
294		402
		403	sub _kilme {
		404	die "received message on port without callback";
		405	}
		406
295	sub port(;&) {	407	sub port(;&) {
296	my $id = "$UNIQ." . $ID++;	408	my $id = $UNIQ . ++$ID;
297	my $port = "$NODE#$id";	409	my $port = "$NODE#$id";
298		410
299	if (@_) {	411	rcv $port, shift || \&_kilme;
300	rcv $port, shift;
301	} else {
302	$PORT{$id} = sub { }; # nop
303	}
304		412
305	$port	413	$port
306	}	414	}
307		415
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)	416	=item rcv $local_port, $callback->(@msg)
326		417
327	Replaces the callback on the specified miniport (after converting it to	418	Replaces the default callback on the specified port. There is no way to
328	one if required).	419	remove the default callback: use C<sub { }> to disable it, or better
329		420	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...] => $callback->(@msg), ...
335
336	Register callbacks to be called on matching messages on the given full
337	port (after converting it to one if required).
338
339	The callback has to return a true value when its work is done, after
340	which is will be removed, or a false value in which case it will stay
341	registered.
342		421
343	The global C<$SELF> (exported by this module) contains C<$port> while	422	The global C<$SELF> (exported by this module) contains C<$port> while
344	executing the callback.	423	executing the callback. Runtime errors during callback execution will
		424	result in the port being C<kil>ed.
345		425
346	Runtime errors wdurign callback execution will result in the port being	426	The default callback received all messages not matched by a more specific
347	C<kil>ed.	427	C<tag> match.
348		428
349	If the match is an array reference, then it will be matched against the	429	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
350	first elements of the message, otherwise only the first element is being
351	matched.
352		430
353	Any element in the match that is specified as C<_any_> (a function	431	Register (or replace) callbacks to be called on messages starting with the
354	exported by this module) matches any single element of the message.	432	given tag on the given port (and return the port), or unregister it (when
		433	C<$callback> is C<$undef> or missing). There can only be one callback
		434	registered for each tag.
355		435
356	While not required, it is highly recommended that the first matching	436	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	437	element (the tag) has been removed. The callback will use the same
358	also the most efficient match (by far).	438	environment as the default callback (see above).
		439
		440	Example: create a port and bind receivers on it in one go.
		441
		442	my $port = rcv port,
		443	msg1 => sub { ... },
		444	msg2 => sub { ... },
		445	;
		446
		447	Example: create a port, bind receivers and send it in a message elsewhere
		448	in one go:
		449
		450	snd $otherport, reply =>
		451	rcv port,
		452	msg1 => sub { ... },
		453	...
		454	;
		455
		456	Example: temporarily register a rcv callback for a tag matching some port
		457	(e.g. for an rpc reply) and unregister it after a message was received.
		458
		459	rcv $port, $otherport => sub {
		460	my @reply = @_;
		461
		462	rcv $SELF, $otherport;
		463	};
359		464
360	=cut	465	=cut
361		466
362	sub rcv($@) {	467	sub rcv($@) {
363	my $port = shift;	468	my $port = shift;
364	my ($noderef, $portid) = split /#/, $port, 2;	469	my ($nodeid, $portid) = split /#/, $port, 2;
365		470
366	($NODE{$noderef} || add_node $noderef) == $NODE{""}	471	$NODE{$nodeid} == $NODE{""}
367	or Carp::croak "$port: rcv can only be called on local ports, caught";	472	or Carp::croak "$port: rcv can only be called on local ports, caught";
368		473
369	if (@_ == 1) {	474	while (@_) {
		475	if (ref $_[0]) {
		476	if (my $self = $PORT_DATA{$portid}) {
		477	"AnyEvent::MP::Port" eq ref $self
		478	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		479
		480	$self->[0] = shift;
		481	} else {
370	my $cb = shift;	482	my $cb = shift;
371	delete $PORT_DATA{$portid};
372	$PORT{$portid} = sub {	483	$PORT{$portid} = sub {
373	local $SELF = $port;	484	local $SELF = $port;
374	eval {	485	eval { &$cb }; _self_die if $@;
375	&$cb	486	};
376	and kil $port;
377	};	487	}
378	_self_die if $@;	488	} elsif (defined $_[0]) {
379	};
380	} else {
381	my $self = $PORT_DATA{$portid} ||= do {	489	my $self = $PORT_DATA{$portid} ||= do {
382	my $self = bless {	490	my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port";
383	id => $port,
384	}, "AnyEvent::MP::Port";
385		491
386	$PORT{$portid} = sub {	492	$PORT{$portid} = sub {
387	local $SELF = $port;	493	local $SELF = $port;
388		494
389	eval {
390	for (@{ $self->{rc0}{$_[0]} }) {	495	if (my $cb = $self->[1]{$_[0]}) {
391	$_ && &{$_->[0]}	496	shift;
392	&& undef $_;	497	eval { &$cb }; _self_die if $@;
393	}	498	} else {
394
395	for (@{ $self->{rcv}{$_[0]} }) {
396	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
397	&& &{$_->[0]}	499	&{ $self->[0] };
398	&& undef $_;
399	}
400
401	for (@{ $self->{any} }) {
402	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
403	&& &{$_->[0]}
404	&& undef $_;
405	}	500	}
406	};	501	};
407	_self_die if $@;	502
		503	$self
408	};	504	};
409		505
410	$self
411	};
412
413	"AnyEvent::MP::Port" eq ref $self	506	"AnyEvent::MP::Port" eq ref $self
414	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	507	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
415		508
416	while (@_) {
417	my ($match, $cb) = splice @_, 0, 2;	509	my ($tag, $cb) = splice @_, 0, 2;
418		510
419	if (!ref $match) {	511	if (defined $cb) {
420	push @{ $self->{rc0}{$match} }, [$cb];	512	$self->[1]{$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 {	513	} else {
427	push @{ $self->{any} }, [$cb, $match];	514	delete $self->[1]{$tag};
428	}	515	}
429	}	516	}
430	}	517	}
431		518
432	$port	519	$port
433	}	520	}
434		521
		522	=item peval $port, $coderef[, @args]
		523
		524	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		525	when the code throews an exception the C<$port> will be killed.
		526
		527	Any remaining args will be passed to the callback. Any return values will
		528	be returned to the caller.
		529
		530	This is useful when you temporarily want to execute code in the context of
		531	a port.
		532
		533	Example: create a port and run some initialisation code in it's context.
		534
		535	my $port = port { ... };
		536
		537	peval $port, sub {
		538	init
		539	or die "unable to init";
		540	};
		541
		542	=cut
		543
		544	sub peval($$) {
		545	local $SELF = shift;
		546	my $cb = shift;
		547
		548	if (wantarray) {
		549	my @res = eval { &$cb };
		550	_self_die if $@;
		551	@res
		552	} else {
		553	my $res = eval { &$cb };
		554	_self_die if $@;
		555	$res
		556	}
		557	}
		558
435	=item $closure = psub { BLOCK }	559	=item $closure = psub { BLOCK }
436		560
437	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	561	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
438	closure is executed, sets up the environment in the same way as in C<rcv>	562	closure is executed, sets up the environment in the same way as in C<rcv>
439	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.	563	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		564
		565	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		566	BLOCK }, @_ } >>.
440		567
441	This is useful when you register callbacks from C<rcv> callbacks:	568	This is useful when you register callbacks from C<rcv> callbacks:
442		569
443	rcv delayed_reply => sub {	570	rcv delayed_reply => sub {
444	my ($delay, @reply) = @_;	571	my ($delay, @reply) = @_;
…		…
468	$res	595	$res
469	}	596	}
470	}	597	}
471	}	598	}
472		599
473	=item $guard = mon $port, $cb->(@reason)	600	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
474		601
475	=item $guard = mon $port, $otherport	602	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
476		603
477	=item $guard = mon $port, $otherport, @msg	604	=item $guard = mon $port # kill $SELF when $port dies
478		605
		606	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		607
479	Monitor the given port and do something when the port is killed.	608	Monitor the given port and do something when the port is killed or
		609	messages to it were lost, and optionally return a guard that can be used
		610	to stop monitoring again.
480		611
481	In the first form, the callback is simply called with any number	612	In the first form (callback), the callback is simply called with any
482	of C<@reason> elements (no @reason means that the port was deleted	613	number of C<@reason> elements (no @reason means that the port was deleted
483	"normally"). Note also that I<< the callback B<must> never die >>, so use	614	"normally"). Note also that I<< the callback B<must> never die >>, so use
484	C<eval> if unsure.	615	C<eval> if unsure.
485		616
486	In the second form, the other port will be C<kil>'ed with C<@reason>, iff	617	In the second form (another port given), the other port (C<$rcvport>)
487	a @reason was specified, i.e. on "normal" kils nothing happens, while	618	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.	619	"normal" kils nothing happens, while under all other conditions, the other
		620	port is killed with the same reason.
489		621
		622	The third form (kill self) is the same as the second form, except that
		623	C<$rvport> defaults to C<$SELF>.
		624
490	In the last form, a message of the form C<@msg, @reason> will be C<snd>.	625	In the last form (message), a message of the form C<@msg, @reason> will be
		626	C<snd>.
		627
		628	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		629	alert was raised), they are removed and will not trigger again.
		630
		631	As a rule of thumb, monitoring requests should always monitor a port from
		632	a local port (or callback). The reason is that kill messages might get
		633	lost, just like any other message. Another less obvious reason is that
		634	even monitoring requests can get lost (for example, when the connection
		635	to the other node goes down permanently). When monitoring a port locally
		636	these problems do not exist.
		637
		638	C<mon> effectively guarantees that, in the absence of hardware failures,
		639	after starting the monitor, either all messages sent to the port will
		640	arrive, or the monitoring action will be invoked after possible message
		641	loss has been detected. No messages will be lost "in between" (after
		642	the first lost message no further messages will be received by the
		643	port). After the monitoring action was invoked, further messages might get
		644	delivered again.
		645
		646	Inter-host-connection timeouts and monitoring depend on the transport
		647	used. The only transport currently implemented is TCP, and AnyEvent::MP
		648	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		649	non-idle connection, and usually around two hours for idle connections).
		650
		651	This means that monitoring is good for program errors and cleaning up
		652	stuff eventually, but they are no replacement for a timeout when you need
		653	to ensure some maximum latency.
491		654
492	Example: call a given callback when C<$port> is killed.	655	Example: call a given callback when C<$port> is killed.
493		656
494	mon $port, sub { warn "port died because of <@_>\n" };	657	mon $port, sub { warn "port died because of <@_>\n" };
495		658
496	Example: kill ourselves when C<$port> is killed abnormally.	659	Example: kill ourselves when C<$port> is killed abnormally.
497		660
498	mon $port, $self;	661	mon $port;
499		662
500	Example: send us a restart message another C<$port> is killed.	663	Example: send us a restart message when another C<$port> is killed.
501		664
502	mon $port, $self => "restart";	665	mon $port, $self => "restart";
503		666
504	=cut	667	=cut
505		668
506	sub mon {	669	sub mon {
507	my ($noderef, $port) = split /#/, shift, 2;	670	my ($nodeid, $port) = split /#/, shift, 2;
508		671
509	my $node = $NODE{$noderef} || add_node $noderef;	672	my $node = $NODE{$nodeid} || add_node $nodeid;
510		673
511	my $cb = shift;	674	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
512		675
513	unless (ref $cb) {	676	unless (ref $cb) {
514	if (@_) {	677	if (@_) {
515	# send a kill info message	678	# send a kill info message
516	my (@msg) = ($cb, @_);	679	my (@msg) = ($cb, @_);
…		…
523	}	686	}
524		687
525	$node->monitor ($port, $cb);	688	$node->monitor ($port, $cb);
526		689
527	defined wantarray	690	defined wantarray
528	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	691	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
529	}	692	}
530		693
531	=item $guard = mon_guard $port, $ref, $ref...	694	=item $guard = mon_guard $port, $ref, $ref...
532		695
533	Monitors the given C<$port> and keeps the passed references. When the port	696	Monitors the given C<$port> and keeps the passed references. When the port
534	is killed, the references will be freed.	697	is killed, the references will be freed.
535		698
536	Optionally returns a guard that will stop the monitoring.	699	Optionally returns a guard that will stop the monitoring.
537		700
538	This function is useful when you create e.g. timers or other watchers and	701	This function is useful when you create e.g. timers or other watchers and
539	want to free them when the port gets killed:	702	want to free them when the port gets killed (note the use of C<psub>):
540		703
541	$port->rcv (start => sub {	704	$port->rcv (start => sub {
542	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	705	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
543	undef $timer if 0.9 < rand;	706	undef $timer if 0.9 < rand;
544	});	707	});
545	});	708	});
546		709
547	=cut	710	=cut
548		711
549	sub mon_guard {	712	sub mon_guard {
550	my ($port, @refs) = @_;	713	my ($port, @refs) = @_;
551		714
		715	#TODO: mon-less form?
		716
552	mon $port, sub { 0 && @refs }	717	mon $port, sub { 0 && @refs }
553	}	718	}
554		719
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]	720	=item kil $port[, @reason]
566		721
567	Kill the specified port with the given C<@reason>.	722	Kill the specified port with the given C<@reason>.
568		723
569	If no C<@reason> is specified, then the port is killed "normally" (linked	724	If no C<@reason> is specified, then the port is killed "normally" -
570	ports will not be kileld, or even notified).	725	monitor callback will be invoked, but the kil will not cause linked ports
		726	(C<mon $mport, $lport> form) to get killed.
571		727
572	Otherwise, linked ports get killed with the same reason (second form of	728	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
573	C<mon>, see below).	729	form) get killed with the same reason.
574		730
575	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	731	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
576	will be reported as reason C<< die => $@ >>.	732	will be reported as reason C<< die => $@ >>.
577		733
578	Transport/communication errors are reported as C<< transport_error =>	734	Transport/communication errors are reported as C<< transport_error =>
579	$message >>.	735	$message >>.
580		736
		737	=cut
		738
		739	=item $port = spawn $node, $initfunc[, @initdata]
		740
		741	Creates a port on the node C<$node> (which can also be a port ID, in which
		742	case it's the node where that port resides).
		743
		744	The port ID of the newly created port is returned immediately, and it is
		745	possible to immediately start sending messages or to monitor the port.
		746
		747	After the port has been created, the init function is called on the remote
		748	node, in the same context as a C<rcv> callback. This function must be a
		749	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		750	specify a function in the main program, use C<::name>.
		751
		752	If the function doesn't exist, then the node tries to C<require>
		753	the package, then the package above the package and so on (e.g.
		754	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		755	exists or it runs out of package names.
		756
		757	The init function is then called with the newly-created port as context
		758	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		759	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		760	the port might not get created.
		761
		762	A common idiom is to pass a local port, immediately monitor the spawned
		763	port, and in the remote init function, immediately monitor the passed
		764	local port. This two-way monitoring ensures that both ports get cleaned up
		765	when there is a problem.
		766
		767	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		768	caller before C<spawn> returns (by delaying invocation when spawn is
		769	called for the local node).
		770
		771	Example: spawn a chat server port on C<$othernode>.
		772
		773	# this node, executed from within a port context:
		774	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		775	mon $server;
		776
		777	# init function on C<$othernode>
		778	sub connect {
		779	my ($srcport) = @_;
		780
		781	mon $srcport;
		782
		783	rcv $SELF, sub {
		784	...
		785	};
		786	}
		787
		788	=cut
		789
		790	sub _spawn {
		791	my $port = shift;
		792	my $init = shift;
		793
		794	# rcv will create the actual port
		795	local $SELF = "$NODE#$port";
		796	eval {
		797	&{ load_func $init }
		798	};
		799	_self_die if $@;
		800	}
		801
		802	sub spawn(@) {
		803	my ($nodeid, undef) = split /#/, shift, 2;
		804
		805	my $id = $RUNIQ . ++$ID;
		806
		807	$_[0] =~ /::/
		808	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		809
		810	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		811
		812	"$nodeid#$id"
		813	}
		814
		815
		816	=item after $timeout, @msg
		817
		818	=item after $timeout, $callback
		819
		820	Either sends the given message, or call the given callback, after the
		821	specified number of seconds.
		822
		823	This is simply a utility function that comes in handy at times - the
		824	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		825	so it may go away in the future.
		826
		827	=cut
		828
		829	sub after($@) {
		830	my ($timeout, @action) = @_;
		831
		832	my $t; $t = AE::timer $timeout, 0, sub {
		833	undef $t;
		834	ref $action[0]
		835	? $action[0]()
		836	: snd @action;
		837	};
		838	}
		839
		840	#=item $cb2 = timeout $seconds, $cb[, @args]
		841
		842	=item cal $port, @msg, $callback[, $timeout]
		843
		844	A simple form of RPC - sends a message to the given C<$port> with the
		845	given contents (C<@msg>), but adds a reply port to the message.
		846
		847	The reply port is created temporarily just for the purpose of receiving
		848	the reply, and will be C<kil>ed when no longer needed.
		849
		850	A reply message sent to the port is passed to the C<$callback> as-is.
		851
		852	If an optional time-out (in seconds) is given and it is not C<undef>,
		853	then the callback will be called without any arguments after the time-out
		854	elapsed and the port is C<kil>ed.
		855
		856	If no time-out is given (or it is C<undef>), then the local port will
		857	monitor the remote port instead, so it eventually gets cleaned-up.
		858
		859	Currently this function returns the temporary port, but this "feature"
		860	might go in future versions unless you can make a convincing case that
		861	this is indeed useful for something.
		862
		863	=cut
		864
		865	sub cal(@) {
		866	my $timeout = ref $_[-1] ? undef : pop;
		867	my $cb = pop;
		868
		869	my $port = port {
		870	undef $timeout;
		871	kil $SELF;
		872	&$cb;
		873	};
		874
		875	if (defined $timeout) {
		876	$timeout = AE::timer $timeout, 0, sub {
		877	undef $timeout;
		878	kil $port;
		879	$cb->();
		880	};
		881	} else {
		882	mon $_[0], sub {
		883	kil $port;
		884	$cb->();
		885	};
		886	}
		887
		888	push @_, $port;
		889	&snd;
		890
		891	$port
		892	}
		893
581	=back	894	=back
582		895
583	=head1 NODE MESSAGES	896	=head1 DISTRIBUTED DATABASE
584		897
585	Nodes understand the following messages sent to them. Many of them take	898	AnyEvent::MP comes with a simple distributed database. The database will
586	arguments called C<@reply>, which will simply be used to compose a reply	899	be mirrored asynchronously at all global nodes. Other nodes bind to one of
587	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and	900	the global nodes for their needs.
588	the remaining arguments are simply the message data.
589		901
590	While other messages exist, they are not public and subject to change.	902	The database consists of a two-level hash - a hash contains a hash which
		903	contains values.
591		904
		905	The top level hash key is called "family", and the second-level hash key
		906	is called "subkey" or simply "key".
		907
		908	The family must be alphanumeric, i.e. start with a letter and consist
		909	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		910	pretty much like Perl module names.
		911
		912	As the family namespace is global, it is recommended to prefix family names
		913	with the name of the application or module using it.
		914
		915	The subkeys must be non-empty strings, with no further restrictions.
		916
		917	The values should preferably be strings, but other perl scalars should
		918	work as well (such as undef, arrays and hashes).
		919
		920	Every database entry is owned by one node - adding the same family/subkey
		921	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		922	but the result might be nondeterministic, i.e. the key might have
		923	different values on different nodes.
		924
		925	Different subkeys in the same family can be owned by different nodes
		926	without problems, and in fact, this is the common method to create worker
		927	pools. For example, a worker port for image scaling might do this:
		928
		929	db_set my_image_scalers => $port;
		930
		931	And clients looking for an image scaler will want to get the
		932	C<my_image_scalers> keys from time to time:
		933
		934	db_keys my_image_scalers => sub {
		935	@ports = @{ $_[0] };
		936	};
		937
		938	Or better yet, they want to monitor the database family, so they always
		939	have a reasonable up-to-date copy:
		940
		941	db_mon my_image_scalers => sub {
		942	@ports = keys %{ $_[0] };
		943	};
		944
		945	In general, you can set or delete single subkeys, but query and monitor
		946	whole families only.
		947
		948	If you feel the need to monitor or query a single subkey, try giving it
		949	it's own family.
		950
592	=over 4	951	=over
		952
		953	=item db_set $family => $subkey [=> $value]
		954
		955	Sets (or replaces) a key to the database - if C<$value> is omitted,
		956	C<undef> is used instead.
		957
		958	=item db_del $family => $subkey...
		959
		960	Deletes one or more subkeys from the database family.
		961
		962	=item $guard = db_reg $family => $subkey [=> $value]
		963
		964	Sets the key on the database and returns a guard. When the guard is
		965	destroyed, the key is deleted from the database. If C<$value> is missing,
		966	then C<undef> is used.
		967
		968	=item db_family $family => $cb->(\%familyhash)
		969
		970	Queries the named database C<$family> and call the callback with the
		971	family represented as a hash. You can keep and freely modify the hash.
		972
		973	=item db_keys $family => $cb->(\@keys)
		974
		975	Same as C<db_family>, except it only queries the family I<subkeys> and passes
		976	them as array reference to the callback.
		977
		978	=item db_values $family => $cb->(\@values)
		979
		980	Same as C<db_family>, except it only queries the family I<values> and passes them
		981	as array reference to the callback.
		982
		983	=item $guard = db_mon $family => $cb->($familyhash, \@added, \@changed, \@deleted)
		984
		985	Creates a monitor on the given database family. Each time a key is set
		986	or or is deleted the callback is called with a hash containing the
		987	database family and three lists of added, changed and deleted subkeys,
		988	respectively. If no keys have changed then the array reference might be
		989	C<undef> or even missing.
		990
		991	The family hash reference and the key arrays belong to AnyEvent::MP and
		992	B<must not be modified or stored> by the callback. When in doubt, make a
		993	copy.
		994
		995	As soon as possible after the monitoring starts, the callback will be
		996	called with the intiial contents of the family, even if it is empty,
		997	i.e. there will always be a timely call to the callback with the current
		998	contents.
		999
		1000	It is possible that the callback is called with a change event even though
		1001	the subkey is already present and the value has not changed.
		1002
		1003	The monitoring stops when the guard object is destroyed.
		1004
		1005	Example: on every change to the family "mygroup", print out all keys.
		1006
		1007	my $guard = db_mon mygroup => sub {
		1008	my ($family, $a, $c, $d) = @_;
		1009	print "mygroup members: ", (join " ", keys %$family), "\n";
		1010	};
		1011
		1012	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1013
		1014	my $guard; $guard = db_mon My::Module::workers => sub {
		1015	my ($family, $a, $c, $d) = @_;
		1016	return unless %$family;
		1017	undef $guard;
		1018	print "My::Module::workers now nonempty\n";
		1019	};
		1020
		1021	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		1022
		1023	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		1024	my ($family, $a, $c, $d) = @_;
		1025
		1026	print "+$_=$family->{$_}\n" for @$a;
		1027	print "*$_=$family->{$_}\n" for @$c;
		1028	print "-$_=$family->{$_}\n" for @$d;
		1029	};
593		1030
594	=cut	1031	=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		1032
627	=back	1033	=back
628		1034
629	=head1 AnyEvent::MP vs. Distributed Erlang	1035	=head1 AnyEvent::MP vs. Distributed Erlang
630		1036
631	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	1037	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
632	== aemp node, Erlang process == aemp port), so many of the documents and	1038	== aemp node, Erlang process == aemp port), so many of the documents and
633	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	1039	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
634	sample:	1040	sample:
635		1041
636	http://www.Erlang.se/doc/programming_rules.shtml	1042	http://www.erlang.se/doc/programming_rules.shtml
637	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	1043	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
638	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	1044	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
639	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	1045	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
640		1046
641	Despite the similarities, there are also some important differences:	1047	Despite the similarities, there are also some important differences:
642		1048
643	=over 4	1049	=over 4
644		1050
645	=item * Node references contain the recipe on how to contact them.	1051	=item * Node IDs are arbitrary strings in AEMP.
646		1052
647	Erlang relies on special naming and DNS to work everywhere in the	1053	Erlang relies on special naming and DNS to work everywhere in the same
648	same way. AEMP relies on each node knowing it's own address(es), with	1054	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
649	convenience functionality.	1055	configuration or DNS), and possibly the addresses of some seed nodes, but
		1056	will otherwise discover other nodes (and their IDs) itself.
650		1057
651	This means that AEMP requires a less tightly controlled environment at the	1058	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
652	cost of longer node references and a slightly higher management overhead.	1059	uses "local ports are like remote ports".
		1060
		1061	The failure modes for local ports are quite different (runtime errors
		1062	only) then for remote ports - when a local port dies, you I<know> it dies,
		1063	when a connection to another node dies, you know nothing about the other
		1064	port.
		1065
		1066	Erlang pretends remote ports are as reliable as local ports, even when
		1067	they are not.
		1068
		1069	AEMP encourages a "treat remote ports differently" philosophy, with local
		1070	ports being the special case/exception, where transport errors cannot
		1071	occur.
653		1072
654	=item * Erlang uses processes and a mailbox, AEMP does not queue.	1073	=item * Erlang uses processes and a mailbox, AEMP does not queue.
655		1074
656	Erlang uses processes that selctively receive messages, and therefore	1075	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	1076	therefore needs a queue. AEMP is event based, queuing messages would serve
658	purpose.	1077	no useful purpose. For the same reason the pattern-matching abilities
		1078	of AnyEvent::MP are more limited, as there is little need to be able to
		1079	filter messages without dequeuing them.
659		1080
660	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	1081	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1082	being event-based, while Erlang is process-based.
		1083
		1084	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1085	top of AEMP and Coro threads.
661		1086
662	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1087	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
663		1088
664	Sending messages in Erlang is synchronous and blocks the process. AEMP	1089	Sending messages in Erlang is synchronous and blocks the process until
665	sends are immediate, connection establishment is handled in the	1090	a conenction has been established and the message sent (and so does not
666	background.	1091	need a queue that can overflow). AEMP sends return immediately, connection
		1092	establishment is handled in the background.
667		1093
668	=item * Erlang can silently lose messages, AEMP cannot.	1094	=item * Erlang suffers from silent message loss, AEMP does not.
669		1095
670	Erlang makes few guarantees on messages delivery - messages can get lost	1096	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,	1097	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).	1098	b, and c, and the other side only receives messages a and c).
673		1099
674	AEMP guarantees correct ordering, and the guarantee that there are no	1100	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1101	guarantee that after one message is lost, all following ones sent to the
		1102	same port are lost as well, until monitoring raises an error, so there are
675	holes in the message sequence.	1103	no silent "holes" in the message sequence.
676		1104
677	=item * In Erlang, processes can be declared dead and later be found to be	1105	If you want your software to be very reliable, you have to cope with
678	alive.	1106	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
679		1107	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	1108	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		1109
688	=item * Erlang can send messages to the wrong port, AEMP does not.	1110	=item * Erlang can send messages to the wrong port, AEMP does not.
689		1111
690	In Erlang it is quite possible that a node that restarts reuses a process	1112	In Erlang it is quite likely that a node that restarts reuses an Erlang
691	ID known to other nodes for a completely different process, causing	1113	process ID known to other nodes for a completely different process,
692	messages destined for that process to end up in an unrelated process.	1114	causing messages destined for that process to end up in an unrelated
		1115	process.
693		1116
694	AEMP never reuses port IDs, so old messages or old port IDs floating	1117	AEMP does not reuse port IDs, so old messages or old port IDs floating
695	around in the network will not be sent to an unrelated port.	1118	around in the network will not be sent to an unrelated port.
696		1119
697	=item * Erlang uses unprotected connections, AEMP uses secure	1120	=item * Erlang uses unprotected connections, AEMP uses secure
698	authentication and can use TLS.	1121	authentication and can use TLS.
699		1122
700	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1123	AEMP can use a proven protocol - TLS - to protect connections and
701	securely authenticate nodes.	1124	securely authenticate nodes.
702		1125
703	=item * The AEMP protocol is optimised for both text-based and binary	1126	=item * The AEMP protocol is optimised for both text-based and binary
704	communications.	1127	communications.
705		1128
706	The AEMP protocol, unlike the Erlang protocol, supports both	1129	The AEMP protocol, unlike the Erlang protocol, supports both programming
707	language-independent text-only protocols (good for debugging) and binary,	1130	language independent text-only protocols (good for debugging), and binary,
708	language-specific serialisers (e.g. Storable).	1131	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1132	used, the protocol is actually completely text-based.
709		1133
710	It has also been carefully designed to be implementable in other languages	1134	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	1135	with a minimum of work while gracefully degrading functionality to make the
712	protocol simple.	1136	protocol simple.
713		1137
714	=item * AEMP has more flexible monitoring options than Erlang.	1138	=item * AEMP has more flexible monitoring options than Erlang.
715		1139
716	In Erlang, you can chose to receive I<all> exit signals as messages	1140	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	1141	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	1142	difficult to implement.
719	Erlang, as one can choose between automatic kill, exit message or callback
720	on a per-process basis.
721		1143
722	=item * Erlang has different semantics for monitoring and linking, AEMP has the same.	1144	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1145	between automatic kill, exit message or callback on a per-port basis.
723		1146
		1147	=item * Erlang tries to hide remote/local connections, AEMP does not.
		1148
724	Monitoring in Erlang is not an indicator of process death/crashes,	1149	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	1150	same way as linking is (except linking is unreliable in Erlang).
726	semantics of monitoring and linking are identical, linking is simply	1151
727	two-way monitoring with automatic kill.	1152	In AEMP, you don't "look up" registered port names or send to named ports
		1153	that might or might not be persistent. Instead, you normally spawn a port
		1154	on the remote node. The init function monitors you, and you monitor the
		1155	remote port. Since both monitors are local to the node, they are much more
		1156	reliable (no need for C<spawn_link>).
		1157
		1158	This also saves round-trips and avoids sending messages to the wrong port
		1159	(hard to do in Erlang).
728		1160
729	=back	1161	=back
730		1162
		1163	=head1 RATIONALE
		1164
		1165	=over 4
		1166
		1167	=item Why strings for port and node IDs, why not objects?
		1168
		1169	We considered "objects", but found that the actual number of methods
		1170	that can be called are quite low. Since port and node IDs travel over
		1171	the network frequently, the serialising/deserialising would add lots of
		1172	overhead, as well as having to keep a proxy object everywhere.
		1173
		1174	Strings can easily be printed, easily serialised etc. and need no special
		1175	procedures to be "valid".
		1176
		1177	And as a result, a port with just a default receiver consists of a single
		1178	code reference stored in a global hash - it can't become much cheaper.
		1179
		1180	=item Why favour JSON, why not a real serialising format such as Storable?
		1181
		1182	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1183	format, but currently there is no way to make a node use Storable by
		1184	default (although all nodes will accept it).
		1185
		1186	The default framing protocol is JSON because a) JSON::XS is many times
		1187	faster for small messages and b) most importantly, after years of
		1188	experience we found that object serialisation is causing more problems
		1189	than it solves: Just like function calls, objects simply do not travel
		1190	easily over the network, mostly because they will always be a copy, so you
		1191	always have to re-think your design.
		1192
		1193	Keeping your messages simple, concentrating on data structures rather than
		1194	objects, will keep your messages clean, tidy and efficient.
		1195
		1196	=back
		1197
731	=head1 SEE ALSO	1198	=head1 SEE ALSO
		1199
		1200	L<AnyEvent::MP::Intro> - a gentle introduction.
		1201
		1202	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1203
		1204	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1205	your applications.
		1206
		1207	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1208
		1209	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1210	all nodes.
732		1211
733	L<AnyEvent>.	1212	L<AnyEvent>.
734		1213
735	=head1 AUTHOR	1214	=head1 AUTHOR
736		1215

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