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Revision 1.139 by root, Thu Mar 22 20:07:31 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
13	$SELF # receiving/own port id in rcv callbacks	12	$SELF # receiving/own port id in rcv callbacks
14		13
15	# initialise the node so it can send/receive messages	14	# initialise the node so it can send/receive messages
16	initialise_node; # -OR-	15	configure;
17	initialise_node "localhost:4040"; # -OR-
18	initialise_node "slave/", "localhost:4040"
19		16
20	# ports are message endpoints	17	# ports are message destinations
21		18
22	# sending messages	19	# sending messages
23	snd $port, type => data...;	20	snd $port, type => data...;
24	snd $port, @msg;	21	snd $port, @msg;
25	snd @msg_with_first_element_being_a_port;	22	snd @msg_with_first_element_being_a_port;
26		23
27	# creating/using ports, the simple way	24	# creating/using ports, the simple way
28	my $somple_port = port { my @msg = @_; 0 };	25	my $simple_port = port { my @msg = @_ };
29		26
30	# creating/using ports, tagged message matching	27	# creating/using ports, tagged message matching
31	my $port = port;	28	my $port = port;
32	rcv $port, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
33	rcv $port, pong => sub { warn "pong received\n"; 0 };	30	rcv $port, pong => sub { warn "pong received\n" };
34		31
35	# create a port on another node	32	# create a port on another node
36	my $port = spawn $node, $initfunc, @initdata;	33	my $port = spawn $node, $initfunc, @initdata;
37		34
		35	# destroy a port again
		36	kil $port; # "normal" kill
		37	kil $port, my_error => "everything is broken"; # error kill
		38
38	# monitoring	39	# monitoring
39	mon $port, $cb->(@msg) # callback is invoked on death	40	mon $port, $cb->(@msg) # callback is invoked on death
40	mon $port, $otherport # kill otherport on abnormal death	41	mon $port, $localport # kill localport on abnormal death
41	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	};
42		51
43	=head1 CURRENT STATUS	52	=head1 CURRENT STATUS
44		53
		54	bin/aemp - stable.
45	AnyEvent::MP - stable API, should work	55	AnyEvent::MP - stable API, should work.
46	AnyEvent::MP::Intro - outdated	56	AnyEvent::MP::Intro - explains most concepts.
47	AnyEvent::MP::Kernel - WIP
48	AnyEvent::MP::Transport - mostly stable	57	AnyEvent::MP::Kernel - mostly stable API.
49		58	AnyEvent::MP::Global - stable API.
50	stay tuned.
51		59
52	=head1 DESCRIPTION	60	=head1 DESCRIPTION
53		61
54	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
55		63
56	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
57	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
58		66
59	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>
60	manual page.	68	manual page and the examples under F<eg/>.
61
62	At the moment, this module family is severly broken and underdocumented,
63	so do not use. This was uploaded mainly to reserve the CPAN namespace -
64	stay tuned!
65		69
66	=head1 CONCEPTS	70	=head1 CONCEPTS
67		71
68	=over 4	72	=over 4
69		73
70	=item port	74	=item port
71		75
72	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).
73		78
74	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
75	messages. All C<rcv> handlers will receive messages they match, messages	80	some messages. Messages send to ports will not be queued, regardless of
76	will not be queued.	81	anything was listening for them or not.
77		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
78	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
79		86
80	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<#>)
81	separator, and a port name (a printable string of unspecified format). An	88	as separator, and a port name (a printable string of unspecified
82	exception is the the node port, whose ID is identical to its node	89	format created by AnyEvent::MP).
83	reference.
84		90
85	=item node	91	=item node
86		92
87	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,
88	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
89	create new ports, among other things.	95	ports.
90		96
91	Nodes are either private (single-process only), slaves (connected to a	97	Nodes are either public (have one or more listening ports) or private
92	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.
93		100
94	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	101	Nodes is represented by (printable) strings called "node IDs".
95		102
96	A node reference is a string that either simply identifies the node (for	103	=item node ID - C<[A-Za-z0-9_\-.:]*>
97	private and slave nodes), or contains a recipe on how to reach a given
98	node (for public nodes).
99		104
100	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
101	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.
102		109
103	Node references come in two flavours: resolved (containing only numerical	110	=item binds - C<ip:port>
104	addresses) or unresolved (where hostnames are used instead of addresses).
105		111
106	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
107	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).
108		170
109	=back	171	=back
110		172
111	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
112		174
…		…
114		176
115	=cut	177	=cut
116		178
117	package AnyEvent::MP;	179	package AnyEvent::MP;
118		180
		181	use AnyEvent::MP::Config ();
119	use AnyEvent::MP::Kernel;	182	use AnyEvent::MP::Kernel;
		183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
120		184
121	use common::sense;	185	use common::sense;
122		186
123	use Carp ();	187	use Carp ();
124		188
125	use AE ();	189	use AE ();
		190	use Guard ();
126		191
127	use base "Exporter";	192	use base "Exporter";
128		193
129	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
130		195
131	our @EXPORT = qw(	196	our @EXPORT = qw(
132	NODE $NODE *SELF node_of _any_	197	NODE $NODE *SELF node_of after
133	resolve_node initialise_node	198	configure
134	snd rcv mon kil reg psub spawn	199	snd rcv mon mon_guard kil psub peval spawn cal
135	port	200	port
		201	db_set db_del db_reg
		202	db_mon db_family db_keys db_values
136	);	203	);
137		204
138	our $SELF;	205	our $SELF;
139		206
140	sub _self_die() {	207	sub _self_die() {
…		…
143	kil $SELF, die => $msg;	210	kil $SELF, die => $msg;
144	}	211	}
145		212
146	=item $thisnode = NODE / $NODE	213	=item $thisnode = NODE / $NODE
147		214
148	The C<NODE> function returns, and the C<$NODE> variable contains the	215	The C<NODE> function returns, and the C<$NODE> variable contains, the node
149	noderef of the local node. The value is initialised by a call to	216	ID of the node running in the current process. This value is initialised by
150	C<initialise_node>.	217	a call to C<configure>.
151		218
152	=item $noderef = node_of $port	219	=item $nodeid = node_of $port
153		220
154	Extracts and returns the noderef from a port ID or a noderef.	221	Extracts and returns the node ID from a port ID or a node ID.
155		222
156	=item initialise_node $noderef, $seednode, $seednode...	223	=item configure $profile, key => value...
157		224
158	=item initialise_node "slave/", $master, $master...	225	=item configure key => value...
159		226
160	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
161	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
162	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.
163		231
164	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
165	never) before calling other AnyEvent::MP functions.	233	never) before calling other AnyEvent::MP functions.
166		234
167	All arguments (optionally except for the first) are noderefs, which can be	235	The key/value pairs are basically the same ones as documented for the
168	either resolved or unresolved.	236	F<aemp> command line utility (sans the set/del prefix), with these additions:
169
170	The first argument will be looked up in the configuration database first
171	(if it is C<undef> then the current nodename will be used instead) to find
172	the relevant configuration profile (see L<aemp>). If none is found then
173	the default configuration is used. The configuration supplies additional
174	seed/master nodes and can override the actual noderef.
175
176	There are two types of networked nodes, public nodes and slave nodes:
177		237
178	=over 4	238	=over 4
179		239
180	=item public nodes	240	=item norc => $boolean (default false)
181		241
182	For public nodes, C<$noderef> (supplied either directly to	242	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
183	C<initialise_node> or indirectly via a profile or the nodename) must be a	243	be consulted - all configuraiton options must be specified in the
184	noderef (possibly unresolved, in which case it will be resolved).	244	C<configure> call.
185		245
186	After resolving, the node will bind itself on all endpoints and try to	246	=item force => $boolean (default false)
187	connect to all additional C<$seednodes> that are specified. Seednodes are
188	optional and can be used to quickly bootstrap the node into an existing
189	network.
190		247
191	=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.
192		251
193	When the C<$noderef> (either as given or overriden by the config file)	252	=item secure => $pass->(@msg)
194	is the special string C<slave/>, then the node will become a slave
195	node. Slave nodes cannot be contacted from outside and will route most of
196	their traffic to the master node that they attach to.
197		253
198	At least one additional noderef is required (either by specifying it	254	In addition to specifying a boolean, you can specify a code reference that
199	directly or because it is part of the configuration profile): The node	255	is called for every code execution attempt - the execution request is
200	will try to connect to all of them and will become a slave attached to the	256	granted iff the callback returns a true value.
201	first node it can successfully connect to.	257
		258	Most of the time the callback should look only at
		259	C<$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.
202		264
203	=back	265	=back
204		266
205	This function will block until all nodes have been resolved and, for slave
206	nodes, until it has successfully established a connection to a master
207	server.
208
209	Example: become a public node listening on the guessed noderef, or the one
210	specified via C<aemp> for the current node. This should be the most common
211	form of invocation for "daemon"-type nodes.
212
213	initialise_node;
214
215	Example: become a slave node to any of the the seednodes specified via
216	C<aemp>. This form is often used for commandline clients.
217
218	initialise_node "slave/";
219
220	Example: become a slave node to any of the specified master servers. This
221	form is also often used for commandline clients.
222
223	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
224
225	Example: become a public node, and try to contact some well-known master
226	servers to become part of the network.
227
228	initialise_node undef, "master1", "master2";
229
230	Example: become a public node listening on port C<4041>.
231
232	initialise_node 4041;
233
234	Example: become a public node, only visible on localhost port 4044.
235
236	initialise_node "localhost:4044";
237
238	=item $cv = resolve_node $noderef
239
240	Takes an unresolved node reference that may contain hostnames and
241	abbreviated IDs, resolves all of them and returns a resolved node
242	reference.
243
244	In addition to C<address:port> pairs allowed in resolved noderefs, the
245	following forms are supported:
246
247	=over 4	267	=over 4
248		268
249	=item the empty string	269	=item step 1, gathering configuration from profiles
250		270
251	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
252	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.
253		275
254	=item naked port numbers (e.g. C<1234>)	276	The profile data is then gathered as follows:
255		277
256	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
257	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).
258		283
259	=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.
260		287
261	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
262	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
263	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.
264		315
265	=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)"
266		343
267	=item $SELF	344	=item $SELF
268		345
269	Contains the current port id while executing C<rcv> callbacks or C<psub>	346	Contains the current port id while executing C<rcv> callbacks or C<psub>
270	blocks.	347	blocks.
271		348
272	=item SELF, %SELF, @SELF...	349	=item *SELF, SELF, %SELF, @SELF...
273		350
274	Due to some quirks in how perl exports variables, it is impossible to	351	Due to some quirks in how perl exports variables, it is impossible to
275	just export C<$SELF>, all the symbols called C<SELF> are exported by this	352	just export C<$SELF>, all the symbols named C<SELF> are exported by this
276	module, but only C<$SELF> is currently used.	353	module, but only C<$SELF> is currently used.
277		354
278	=item snd $port, type => @data	355	=item snd $port, type => @data
279		356
280	=item snd $port, @msg	357	=item snd $port, @msg
281		358
282	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
283	a local or a remote port, and must be a port ID.	360	local or a remote port, and must be a port ID.
284		361
285	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
286	string as first element (a port ID, or some word that indicates a request	363	use a string as first element (a port ID, or some word that indicates a
287	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.
288		366
289	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
290	function: modifying any argument is not allowed and can cause many	368	function: modifying any argument (or values referenced by them) is
291	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.
292		373
293	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
294	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
295	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
296	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
297	node, anything can be passed.	378	node, anything can be passed. Best rely only on the common denominator of
		379	these.
298		380
299	=item $local_port = port	381	=item $local_port = port
300		382
301	Create a new local port object and returns its port ID. Initially it has	383	Create a new local port object and returns its port ID. Initially it has
302	no callbacks set and will throw an error when it receives messages.	384	no callbacks set and will throw an error when it receives messages.
…		…
321		403
322	=cut	404	=cut
323		405
324	sub rcv($@);	406	sub rcv($@);
325		407
326	sub _kilme {	408	my $KILME = sub {
327	die "received message on port without callback";	409	(my $tag = substr $_[0], 0, 30) =~ s/([\x20-\x7e])/./g;
328	}	410	kil $SELF, unhandled_message => "no callback found for message '$tag'";
		411	};
329		412
330	sub port(;&) {	413	sub port(;&) {
331	my $id = "$UNIQ." . $ID++;	414	my $id = $UNIQ . ++$ID;
332	my $port = "$NODE#$id";	415	my $port = "$NODE#$id";
333		416
334	rcv $port, shift || \&_kilme;	417	rcv $port, shift || $KILME;
335		418
336	$port	419	$port
337	}	420	}
338		421
339	=item rcv $local_port, $callback->(@msg)	422	=item rcv $local_port, $callback->(@msg)
…		…
344		427
345	The global C<$SELF> (exported by this module) contains C<$port> while	428	The global C<$SELF> (exported by this module) contains C<$port> while
346	executing the callback. Runtime errors during callback execution will	429	executing the callback. Runtime errors during callback execution will
347	result in the port being C<kil>ed.	430	result in the port being C<kil>ed.
348		431
349	The default callback received all messages not matched by a more specific	432	The default callback receives all messages not matched by a more specific
350	C<tag> match.	433	C<tag> match.
351		434
352	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...	435	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
353		436
354	Register callbacks to be called on messages starting with the given tag on	437	Register (or replace) callbacks to be called on messages starting with the
355	the given port (and return the port), or unregister it (when C<$callback>	438	given tag on the given port (and return the port), or unregister it (when
356	is C<$undef>).	439	C<$callback> is C<$undef> or missing). There can only be one callback
		440	registered for each tag.
357		441
358	The original message will be passed to the callback, after the first	442	The original message will be passed to the callback, after the first
359	element (the tag) has been removed. The callback will use the same	443	element (the tag) has been removed. The callback will use the same
360	environment as the default callback (see above).	444	environment as the default callback (see above).
361		445
…		…
373	rcv port,	457	rcv port,
374	msg1 => sub { ... },	458	msg1 => sub { ... },
375	...	459	...
376	;	460	;
377		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, $otherport;
		469	};
		470
378	=cut	471	=cut
379		472
380	sub rcv($@) {	473	sub rcv($@) {
381	my $port = shift;	474	my $port = shift;
382	my ($noderef, $portid) = split /#/, $port, 2;	475	my ($nodeid, $portid) = split /#/, $port, 2;
383		476
384	($NODE{$noderef} || add_node $noderef) == $NODE{""}	477	$NODE{$nodeid} == $NODE{""}
385	or Carp::croak "$port: rcv can only be called on local ports, caught";	478	or Carp::croak "$port: rcv can only be called on local ports, caught";
386		479
387	while (@_) {	480	while (@_) {
388	if (ref $_[0]) {	481	if (ref $_[0]) {
389	if (my $self = $PORT_DATA{$portid}) {	482	if (my $self = $PORT_DATA{$portid}) {
390	"AnyEvent::MP::Port" eq ref $self	483	"AnyEvent::MP::Port" eq ref $self
391	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	484	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
392		485
393	$self->[2] = shift;	486	$self->[0] = shift;
394	} else {	487	} else {
395	my $cb = shift;	488	my $cb = shift;
396	$PORT{$portid} = sub {	489	$PORT{$portid} = sub {
397	local $SELF = $port;	490	local $SELF = $port;
398	eval { &$cb }; _self_die if $@;	491	eval { &$cb }; _self_die if $@;
399	};	492	};
400	}	493	}
401	} elsif (defined $_[0]) {	494	} elsif (defined $_[0]) {
402	my $self = $PORT_DATA{$portid} ||= do {	495	my $self = $PORT_DATA{$portid} ||= do {
403	my $self = bless [$PORT{$port} || sub { }, { }, $port], "AnyEvent::MP::Port";	496	my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port";
404		497
405	$PORT{$portid} = sub {	498	$PORT{$portid} = sub {
406	local $SELF = $port;	499	local $SELF = $port;
407		500
408	if (my $cb = $self->[1]{$_[0]}) {	501	if (my $cb = $self->[1]{$_[0]}) {
…		…
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, $rcvport # kill $rcvport when $port dies
474		607
475	=item $guard = mon $port, $rcvport	608	=item $guard = mon $port # kill $SELF when $port dies
476		609
477	=item $guard = mon $port	610	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
478		611
479	=item $guard = mon $port, $rcvport, @msg	612	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
480		613
481	Monitor the given port and do something when the port is killed or	614	Monitor the given port and do something when the port is killed or
482	messages to it were lost, and optionally return a guard that can be used	615	messages to it were lost, and optionally return a guard that can be used
483	to stop monitoring again.	616	to stop monitoring again.
484		617
		618	The first two forms distinguish between "normal" and "abnormal" kil's:
		619
		620	In the first form (another port given), if the C<$port> is C<kil>'ed with
		621	a non-empty reason, the other port (C<$rcvport>) will be kil'ed with the
		622	same reason. That is, on "normal" kil's nothing happens, while under all
		623	other conditions, the other port is killed with the same reason.
		624
		625	The second form (kill self) is the same as the first form, except that
		626	C<$rvport> defaults to C<$SELF>.
		627
		628	The remaining forms don't distinguish between "normal" and "abnormal" kil's
		629	- it's up to the callback or receiver to check whether the C<@reason> is
		630	empty and act accordingly.
		631
		632	In the third form (callback), the callback is simply called with any
		633	number of C<@reason> elements (empty @reason means that the port was deleted
		634	"normally"). Note also that I<< the callback B<must> never die >>, so use
		635	C<eval> if unsure.
		636
		637	In the last form (message), a message of the form C<$rcvport, @msg,
		638	@reason> will be C<snd>.
		639
		640	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		641	alert was raised), they are removed and will not trigger again, even if it
		642	turns out that the port is still alive.
		643
		644	As a rule of thumb, monitoring requests should always monitor a remote
		645	port locally (using a local C<$rcvport> or a callback). The reason is that
		646	kill messages might get lost, just like any other message. Another less
		647	obvious reason is that even monitoring requests can get lost (for example,
		648	when the connection to the other node goes down permanently). When
		649	monitoring a port locally these problems do not exist.
		650
485	C<mon> effectively guarantees that, in the absence of hardware failures,	651	C<mon> effectively guarantees that, in the absence of hardware failures,
486	that after starting the monitor, either all messages sent to the port	652	after starting the monitor, either all messages sent to the port will
487	will arrive, or the monitoring action will be invoked after possible	653	arrive, or the monitoring action will be invoked after possible message
488	message loss has been detected. No messages will be lost "in between"	654	loss has been detected. No messages will be lost "in between" (after
489	(after the first lost message no further messages will be received by the	655	the first lost message no further messages will be received by the
490	port). After the monitoring action was invoked, further messages might get	656	port). After the monitoring action was invoked, further messages might get
491	delivered again.	657	delivered again.
492		658
493	In the first form (callback), the callback is simply called with any	659	Inter-host-connection timeouts and monitoring depend on the transport
494	number of C<@reason> elements (no @reason means that the port was deleted	660	used. The only transport currently implemented is TCP, and AnyEvent::MP
495	"normally"). Note also that I<< the callback B<must> never die >>, so use	661	relies on TCP to detect node-downs (this can take 10-15 minutes on a
496	C<eval> if unsure.	662	non-idle connection, and usually around two hours for idle connections).
497		663
498	In the second form (another port given), the other port (C<$rcvport>)	664	This means that monitoring is good for program errors and cleaning up
499	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	665	stuff eventually, but they are no replacement for a timeout when you need
500	"normal" kils nothing happens, while under all other conditions, the other	666	to ensure some maximum latency.
501	port is killed with the same reason.
502
503	The third form (kill self) is the same as the second form, except that
504	C<$rvport> defaults to C<$SELF>.
505
506	In the last form (message), a message of the form C<@msg, @reason> will be
507	C<snd>.
508
509	As a rule of thumb, monitoring requests should always monitor a port from
510	a local port (or callback). The reason is that kill messages might get
511	lost, just like any other message. Another less obvious reason is that
512	even monitoring requests can get lost (for exmaple, when the connection
513	to the other node goes down permanently). When monitoring a port locally
514	these problems do not exist.
515		667
516	Example: call a given callback when C<$port> is killed.	668	Example: call a given callback when C<$port> is killed.
517		669
518	mon $port, sub { warn "port died because of <@_>\n" };	670	mon $port, sub { warn "port died because of <@_>\n" };
519		671
…		…
526	mon $port, $self => "restart";	678	mon $port, $self => "restart";
527		679
528	=cut	680	=cut
529		681
530	sub mon {	682	sub mon {
531	my ($noderef, $port) = split /#/, shift, 2;	683	my ($nodeid, $port) = split /#/, shift, 2;
532		684
533	my $node = $NODE{$noderef} || add_node $noderef;	685	my $node = $NODE{$nodeid} || add_node $nodeid;
534		686
535	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';	687	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
536		688
537	unless (ref $cb) {	689	unless (ref $cb) {
538	if (@_) {	690	if (@_) {
…		…
547	}	699	}
548		700
549	$node->monitor ($port, $cb);	701	$node->monitor ($port, $cb);
550		702
551	defined wantarray	703	defined wantarray
552	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	704	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
553	}	705	}
554		706
555	=item $guard = mon_guard $port, $ref, $ref...	707	=item $guard = mon_guard $port, $ref, $ref...
556		708
557	Monitors the given C<$port> and keeps the passed references. When the port	709	Monitors the given C<$port> and keeps the passed references. When the port
558	is killed, the references will be freed.	710	is killed, the references will be freed.
559		711
560	Optionally returns a guard that will stop the monitoring.	712	Optionally returns a guard that will stop the monitoring.
561		713
562	This function is useful when you create e.g. timers or other watchers and	714	This function is useful when you create e.g. timers or other watchers and
563	want to free them when the port gets killed:	715	want to free them when the port gets killed (note the use of C<psub>):
564		716
565	$port->rcv (start => sub {	717	$port->rcv (start => sub {
566	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	718	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
567	undef $timer if 0.9 < rand;	719	undef $timer if 0.9 < rand;
568	});	720	});
569	});	721	});
570		722
571	=cut	723	=cut
…		…
580		732
581	=item kil $port[, @reason]	733	=item kil $port[, @reason]
582		734
583	Kill the specified port with the given C<@reason>.	735	Kill the specified port with the given C<@reason>.
584		736
585	If no C<@reason> is specified, then the port is killed "normally" (linked	737	If no C<@reason> is specified, then the port is killed "normally" -
586	ports will not be kileld, or even notified).	738	monitor callback will be invoked, but the kil will not cause linked ports
		739	(C<mon $mport, $lport> form) to get killed.
587		740
588	Otherwise, linked ports get killed with the same reason (second form of	741	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
589	C<mon>, see below).	742	form) get killed with the same reason.
590		743
591	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	744	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
592	will be reported as reason C<< die => $@ >>.	745	will be reported as reason C<< die => $@ >>.
593		746
594	Transport/communication errors are reported as C<< transport_error =>	747	Transport/communication errors are reported as C<< transport_error =>
595	$message >>.	748	$message >>.
596		749
597	=cut	750	Common idioms:
		751
		752	# silently remove yourself, do not kill linked ports
		753	kil $SELF;
		754
		755	# report a failure in some detail
		756	kil $SELF, failure_mode_1 => "it failed with too high temperature";
		757
		758	# do not waste much time with killing, just die when something goes wrong
		759	open my $fh, "<file"
		760	or die "file: $!";
598		761
599	=item $port = spawn $node, $initfunc[, @initdata]	762	=item $port = spawn $node, $initfunc[, @initdata]
600		763
601	Creates a port on the node C<$node> (which can also be a port ID, in which	764	Creates a port on the node C<$node> (which can also be a port ID, in which
602	case it's the node where that port resides).	765	case it's the node where that port resides).
603		766
604	The port ID of the newly created port is return immediately, and it is	767	The port ID of the newly created port is returned immediately, and it is
605	permissible to immediately start sending messages or monitor the port.	768	possible to immediately start sending messages or to monitor the port.
606		769
607	After the port has been created, the init function is	770	After the port has been created, the init function is called on the remote
608	called. This function must be a fully-qualified function name	771	node, in the same context as a C<rcv> callback. This function must be a
609	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	772	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
610	program, use C<::name>.	773	specify a function in the main program, use C<::name>.
611		774
612	If the function doesn't exist, then the node tries to C<require>	775	If the function doesn't exist, then the node tries to C<require>
613	the package, then the package above the package and so on (e.g.	776	the package, then the package above the package and so on (e.g.
614	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	777	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
615	exists or it runs out of package names.	778	exists or it runs out of package names.
616		779
617	The init function is then called with the newly-created port as context	780	The init function is then called with the newly-created port as context
618	object (C<$SELF>) and the C<@initdata> values as arguments.	781	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		782	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		783	the port might not get created.
619		784
620	A common idiom is to pass your own port, monitor the spawned port, and	785	A common idiom is to pass a local port, immediately monitor the spawned
621	in the init function, monitor the original port. This two-way monitoring	786	port, and in the remote init function, immediately monitor the passed
622	ensures that both ports get cleaned up when there is a problem.	787	local port. This two-way monitoring ensures that both ports get cleaned up
		788	when there is a problem.
		789
		790	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		791	caller before C<spawn> returns (by delaying invocation when spawn is
		792	called for the local node).
623		793
624	Example: spawn a chat server port on C<$othernode>.	794	Example: spawn a chat server port on C<$othernode>.
625		795
626	# this node, executed from within a port context:	796	# this node, executed from within a port context:
627	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	797	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
642		812
643	sub _spawn {	813	sub _spawn {
644	my $port = shift;	814	my $port = shift;
645	my $init = shift;	815	my $init = shift;
646		816
		817	# rcv will create the actual port
647	local $SELF = "$NODE#$port";	818	local $SELF = "$NODE#$port";
648	eval {	819	eval {
649	&{ load_func $init }	820	&{ load_func $init }
650	};	821	};
651	_self_die if $@;	822	_self_die if $@;
652	}	823	}
653		824
654	sub spawn(@) {	825	sub spawn(@) {
655	my ($noderef, undef) = split /#/, shift, 2;	826	my ($nodeid, undef) = split /#/, shift, 2;
656		827
657	my $id = "$RUNIQ." . $ID++;	828	my $id = $RUNIQ . ++$ID;
658		829
659	$_[0] =~ /::/	830	$_[0] =~ /::/
660	or Carp::croak "spawn init function must be a fully-qualified name, caught";	831	or Carp::croak "spawn init function must be a fully-qualified name, caught";
661		832
662	($NODE{$noderef} || add_node $noderef)	833	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
663	->send (["", "AnyEvent::MP::_spawn" => $id, @_]);
664		834
665	"$noderef#$id"	835	"$nodeid#$id"
666	}	836	}
667		837
		838
		839	=item after $timeout, @msg
		840
		841	=item after $timeout, $callback
		842
		843	Either sends the given message, or call the given callback, after the
		844	specified number of seconds.
		845
		846	This is simply a utility function that comes in handy at times - the
		847	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		848	so it may go away in the future.
		849
		850	=cut
		851
		852	sub after($@) {
		853	my ($timeout, @action) = @_;
		854
		855	my $t; $t = AE::timer $timeout, 0, sub {
		856	undef $t;
		857	ref $action[0]
		858	? $action[0]()
		859	: snd @action;
		860	};
		861	}
		862
		863	#=item $cb2 = timeout $seconds, $cb[, @args]
		864
		865	=item cal $port, @msg, $callback[, $timeout]
		866
		867	A simple form of RPC - sends a message to the given C<$port> with the
		868	given contents (C<@msg>), but adds a reply port to the message.
		869
		870	The reply port is created temporarily just for the purpose of receiving
		871	the reply, and will be C<kil>ed when no longer needed.
		872
		873	A reply message sent to the port is passed to the C<$callback> as-is.
		874
		875	If an optional time-out (in seconds) is given and it is not C<undef>,
		876	then the callback will be called without any arguments after the time-out
		877	elapsed and the port is C<kil>ed.
		878
		879	If no time-out is given (or it is C<undef>), then the local port will
		880	monitor the remote port instead, so it eventually gets cleaned-up.
		881
		882	Currently this function returns the temporary port, but this "feature"
		883	might go in future versions unless you can make a convincing case that
		884	this is indeed useful for something.
		885
		886	=cut
		887
		888	sub cal(@) {
		889	my $timeout = ref $_[-1] ? undef : pop;
		890	my $cb = pop;
		891
		892	my $port = port {
		893	undef $timeout;
		894	kil $SELF;
		895	&$cb;
		896	};
		897
		898	if (defined $timeout) {
		899	$timeout = AE::timer $timeout, 0, sub {
		900	undef $timeout;
		901	kil $port;
		902	$cb->();
		903	};
		904	} else {
		905	mon $_[0], sub {
		906	kil $port;
		907	$cb->();
		908	};
		909	}
		910
		911	push @_, $port;
		912	&snd;
		913
		914	$port
		915	}
		916
668	=back	917	=back
669		918
670	=head1 NODE MESSAGES	919	=head1 DISTRIBUTED DATABASE
671		920
672	Nodes understand the following messages sent to them. Many of them take	921	AnyEvent::MP comes with a simple distributed database. The database will
673	arguments called C<@reply>, which will simply be used to compose a reply	922	be mirrored asynchronously on all global nodes. Other nodes bind to one
674	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and	923	of the global nodes for their needs. Every node has a "local database"
675	the remaining arguments are simply the message data.	924	which contains all the values that are set locally. All local databases
		925	are merged together to form the global database, which can be queried.
676		926
677	While other messages exist, they are not public and subject to change.	927	The database structure is that of a two-level hash - the database hash
		928	contains hashes which contain values, similarly to a perl hash of hashes,
		929	i.e.:
678		930
		931	$DATABASE{$family}{$subkey} = $value
		932
		933	The top level hash key is called "family", and the second-level hash key
		934	is called "subkey" or simply "key".
		935
		936	The family must be alphanumeric, i.e. start with a letter and consist
		937	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		938	pretty much like Perl module names.
		939
		940	As the family namespace is global, it is recommended to prefix family names
		941	with the name of the application or module using it.
		942
		943	The subkeys must be non-empty strings, with no further restrictions.
		944
		945	The values should preferably be strings, but other perl scalars should
		946	work as well (such as C<undef>, arrays and hashes).
		947
		948	Every database entry is owned by one node - adding the same family/subkey
		949	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		950	but the result might be nondeterministic, i.e. the key might have
		951	different values on different nodes.
		952
		953	Different subkeys in the same family can be owned by different nodes
		954	without problems, and in fact, this is the common method to create worker
		955	pools. For example, a worker port for image scaling might do this:
		956
		957	db_set my_image_scalers => $port;
		958
		959	And clients looking for an image scaler will want to get the
		960	C<my_image_scalers> keys from time to time:
		961
		962	db_keys my_image_scalers => sub {
		963	@ports = @{ $_[0] };
		964	};
		965
		966	Or better yet, they want to monitor the database family, so they always
		967	have a reasonable up-to-date copy:
		968
		969	db_mon my_image_scalers => sub {
		970	@ports = keys %{ $_[0] };
		971	};
		972
		973	In general, you can set or delete single subkeys, but query and monitor
		974	whole families only.
		975
		976	If you feel the need to monitor or query a single subkey, try giving it
		977	it's own family.
		978
679	=over 4	979	=over
		980
		981	=item $guard = db_set $family => $subkey [=> $value]
		982
		983	Sets (or replaces) a key to the database - if C<$value> is omitted,
		984	C<undef> is used instead.
		985
		986	When called in non-void context, C<db_set> returns a guard that
		987	automatically calls C<db_del> when it is destroyed.
		988
		989	=item db_del $family => $subkey...
		990
		991	Deletes one or more subkeys from the database family.
		992
		993	=item $guard = db_reg $family => $port => $value
		994
		995	=item $guard = db_reg $family => $port
		996
		997	=item $guard = db_reg $family
		998
		999	Registers a port in the given family and optionally returns a guard to
		1000	remove it.
		1001
		1002	This function basically does the same as:
		1003
		1004	db_set $family => $port => $value
		1005
		1006	Except that the port is monitored and automatically removed from the
		1007	database family when it is kil'ed.
		1008
		1009	If C<$value> is missing, C<undef> is used. If C<$port> is missing, then
		1010	C<$SELF> is used.
		1011
		1012	This function is most useful to register a port in some port group (which
		1013	is just another name for a database family), and have it removed when the
		1014	port is gone. This works best when the port is a local port.
680		1015
681	=cut	1016	=cut
682		1017
683	=item lookup => $name, @reply	1018	sub db_reg($$;$) {
		1019	my $family = shift;
		1020	my $port = @_ ? shift : $SELF;
684		1021
685	Replies with the port ID of the specified well-known port, or C<undef>.	1022	my $clr = sub { db_del $family => $port };
		1023	mon $port, $clr;
686		1024
687	=item devnull => ...	1025	db_set $family => $port => $_[0];
688		1026
689	Generic data sink/CPU heat conversion.	1027	defined wantarray
		1028	and &Guard::guard ($clr)
		1029	}
690		1030
691	=item relay => $port, @msg	1031	=item db_family $family => $cb->(\%familyhash)
692		1032
693	Simply forwards the message to the given port.	1033	Queries the named database C<$family> and call the callback with the
		1034	family represented as a hash. You can keep and freely modify the hash.
694		1035
695	=item eval => $string[ @reply]	1036	=item db_keys $family => $cb->(\@keys)
696		1037
697	Evaluates the given string. If C<@reply> is given, then a message of the	1038	Same as C<db_family>, except it only queries the family I<subkeys> and passes
698	form C<@reply, $@, @evalres> is sent.	1039	them as array reference to the callback.
699		1040
700	Example: crash another node.	1041	=item db_values $family => $cb->(\@values)
701		1042
702	snd $othernode, eval => "exit";	1043	Same as C<db_family>, except it only queries the family I<values> and passes them
		1044	as array reference to the callback.
703		1045
704	=item time => @reply	1046	=item $guard = db_mon $family => $cb->($familyhash, \@added, \@changed, \@deleted)
705		1047
706	Replies the the current node time to C<@reply>.	1048	Creates a monitor on the given database family. Each time a key is set
		1049	or or is deleted the callback is called with a hash containing the
		1050	database family and three lists of added, changed and deleted subkeys,
		1051	respectively. If no keys have changed then the array reference might be
		1052	C<undef> or even missing.
707		1053
708	Example: tell the current node to send the current time to C<$myport> in a	1054	If not called in void context, a guard object is returned that, when
709	C<timereply> message.	1055	destroyed, stops the monitor.
710		1056
711	snd $NODE, time => $myport, timereply => 1, 2;	1057	The family hash reference and the key arrays belong to AnyEvent::MP and
712	# => snd $myport, timereply => 1, 2, <time>	1058	B<must not be modified or stored> by the callback. When in doubt, make a
		1059	copy.
		1060
		1061	As soon as possible after the monitoring starts, the callback will be
		1062	called with the intiial contents of the family, even if it is empty,
		1063	i.e. there will always be a timely call to the callback with the current
		1064	contents.
		1065
		1066	It is possible that the callback is called with a change event even though
		1067	the subkey is already present and the value has not changed.
		1068
		1069	The monitoring stops when the guard object is destroyed.
		1070
		1071	Example: on every change to the family "mygroup", print out all keys.
		1072
		1073	my $guard = db_mon mygroup => sub {
		1074	my ($family, $a, $c, $d) = @_;
		1075	print "mygroup members: ", (join " ", keys %$family), "\n";
		1076	};
		1077
		1078	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1079
		1080	my $guard; $guard = db_mon My::Module::workers => sub {
		1081	my ($family, $a, $c, $d) = @_;
		1082	return unless %$family;
		1083	undef $guard;
		1084	print "My::Module::workers now nonempty\n";
		1085	};
		1086
		1087	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		1088
		1089	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		1090	my ($family, $a, $c, $d) = @_;
		1091
		1092	print "+$_=$family->{$_}\n" for @$a;
		1093	print "*$_=$family->{$_}\n" for @$c;
		1094	print "-$_=$family->{$_}\n" for @$d;
		1095	};
		1096
		1097	=cut
713		1098
714	=back	1099	=back
715		1100
716	=head1 AnyEvent::MP vs. Distributed Erlang	1101	=head1 AnyEvent::MP vs. Distributed Erlang
717		1102
718	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	1103	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
719	== aemp node, Erlang process == aemp port), so many of the documents and	1104	== aemp node, Erlang process == aemp port), so many of the documents and
720	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	1105	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
721	sample:	1106	sample:
722		1107
723	http://www.Erlang.se/doc/programming_rules.shtml	1108	http://www.erlang.se/doc/programming_rules.shtml
724	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	1109	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
725	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	1110	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
726	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	1111	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
727		1112
728	Despite the similarities, there are also some important differences:	1113	Despite the similarities, there are also some important differences:
729		1114
730	=over 4	1115	=over 4
731		1116
732	=item * Node references contain the recipe on how to contact them.	1117	=item * Node IDs are arbitrary strings in AEMP.
733		1118
734	Erlang relies on special naming and DNS to work everywhere in the	1119	Erlang relies on special naming and DNS to work everywhere in the same
735	same way. AEMP relies on each node knowing it's own address(es), with	1120	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
736	convenience functionality.	1121	configuration or DNS), and possibly the addresses of some seed nodes, but
		1122	will otherwise discover other nodes (and their IDs) itself.
737		1123
738	This means that AEMP requires a less tightly controlled environment at the
739	cost of longer node references and a slightly higher management overhead.
740
741	=item Erlang has a "remote ports are like local ports" philosophy, AEMP	1124	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
742	uses "local ports are like remote ports".	1125	uses "local ports are like remote ports".
743		1126
744	The failure modes for local ports are quite different (runtime errors	1127	The failure modes for local ports are quite different (runtime errors
745	only) then for remote ports - when a local port dies, you I<know> it dies,	1128	only) then for remote ports - when a local port dies, you I<know> it dies,
746	when a connection to another node dies, you know nothing about the other	1129	when a connection to another node dies, you know nothing about the other
…		…
753	ports being the special case/exception, where transport errors cannot	1136	ports being the special case/exception, where transport errors cannot
754	occur.	1137	occur.
755		1138
756	=item * Erlang uses processes and a mailbox, AEMP does not queue.	1139	=item * Erlang uses processes and a mailbox, AEMP does not queue.
757		1140
758	Erlang uses processes that selectively receive messages, and therefore	1141	Erlang uses processes that selectively receive messages out of order, and
759	needs a queue. AEMP is event based, queuing messages would serve no	1142	therefore needs a queue. AEMP is event based, queuing messages would serve
760	useful purpose. For the same reason the pattern-matching abilities of	1143	no useful purpose. For the same reason the pattern-matching abilities
761	AnyEvent::MP are more limited, as there is little need to be able to	1144	of AnyEvent::MP are more limited, as there is little need to be able to
762	filter messages without dequeing them.	1145	filter messages without dequeuing them.
763		1146
764	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	1147	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1148	being event-based, while Erlang is process-based.
		1149
		1150	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1151	top of AEMP and Coro threads.
765		1152
766	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1153	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
767		1154
768	Sending messages in Erlang is synchronous and blocks the process (and	1155	Sending messages in Erlang is synchronous and blocks the process until
		1156	a conenction has been established and the message sent (and so does not
769	so does not need a queue that can overflow). AEMP sends are immediate,	1157	need a queue that can overflow). AEMP sends return immediately, connection
770	connection establishment is handled in the background.	1158	establishment is handled in the background.
771		1159
772	=item * Erlang suffers from silent message loss, AEMP does not.	1160	=item * Erlang suffers from silent message loss, AEMP does not.
773		1161
774	Erlang makes few guarantees on messages delivery - messages can get lost	1162	Erlang implements few guarantees on messages delivery - messages can get
775	without any of the processes realising it (i.e. you send messages a, b,	1163	lost without any of the processes realising it (i.e. you send messages a,
776	and c, and the other side only receives messages a and c).	1164	b, and c, and the other side only receives messages a and c).
777		1165
778	AEMP guarantees correct ordering, and the guarantee that there are no	1166	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1167	guarantee that after one message is lost, all following ones sent to the
		1168	same port are lost as well, until monitoring raises an error, so there are
779	holes in the message sequence.	1169	no silent "holes" in the message sequence.
780		1170
781	=item * In Erlang, processes can be declared dead and later be found to be	1171	If you want your software to be very reliable, you have to cope with
782	alive.	1172	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
783		1173	simply tries to work better in common error cases, such as when a network
784	In Erlang it can happen that a monitored process is declared dead and	1174	link goes down.
785	linked processes get killed, but later it turns out that the process is
786	still alive - and can receive messages.
787
788	In AEMP, when port monitoring detects a port as dead, then that port will
789	eventually be killed - it cannot happen that a node detects a port as dead
790	and then later sends messages to it, finding it is still alive.
791		1175
792	=item * Erlang can send messages to the wrong port, AEMP does not.	1176	=item * Erlang can send messages to the wrong port, AEMP does not.
793		1177
794	In Erlang it is quite likely that a node that restarts reuses a process ID	1178	In Erlang it is quite likely that a node that restarts reuses an Erlang
795	known to other nodes for a completely different process, causing messages	1179	process ID known to other nodes for a completely different process,
796	destined for that process to end up in an unrelated process.	1180	causing messages destined for that process to end up in an unrelated
		1181	process.
797		1182
798	AEMP never reuses port IDs, so old messages or old port IDs floating	1183	AEMP does not reuse port IDs, so old messages or old port IDs floating
799	around in the network will not be sent to an unrelated port.	1184	around in the network will not be sent to an unrelated port.
800		1185
801	=item * Erlang uses unprotected connections, AEMP uses secure	1186	=item * Erlang uses unprotected connections, AEMP uses secure
802	authentication and can use TLS.	1187	authentication and can use TLS.
803		1188
804	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1189	AEMP can use a proven protocol - TLS - to protect connections and
805	securely authenticate nodes.	1190	securely authenticate nodes.
806		1191
807	=item * The AEMP protocol is optimised for both text-based and binary	1192	=item * The AEMP protocol is optimised for both text-based and binary
808	communications.	1193	communications.
809		1194
810	The AEMP protocol, unlike the Erlang protocol, supports both	1195	The AEMP protocol, unlike the Erlang protocol, supports both programming
811	language-independent text-only protocols (good for debugging) and binary,	1196	language independent text-only protocols (good for debugging), and binary,
812	language-specific serialisers (e.g. Storable).	1197	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1198	used, the protocol is actually completely text-based.
813		1199
814	It has also been carefully designed to be implementable in other languages	1200	It has also been carefully designed to be implementable in other languages
815	with a minimum of work while gracefully degrading fucntionality to make the	1201	with a minimum of work while gracefully degrading functionality to make the
816	protocol simple.	1202	protocol simple.
817		1203
818	=item * AEMP has more flexible monitoring options than Erlang.	1204	=item * AEMP has more flexible monitoring options than Erlang.
819		1205
820	In Erlang, you can chose to receive I<all> exit signals as messages	1206	In Erlang, you can chose to receive I<all> exit signals as messages or
821	or I<none>, there is no in-between, so monitoring single processes is	1207	I<none>, there is no in-between, so monitoring single Erlang processes is
822	difficult to implement. Monitoring in AEMP is more flexible than in	1208	difficult to implement.
823	Erlang, as one can choose between automatic kill, exit message or callback	1209
824	on a per-process basis.	1210	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1211	between automatic kill, exit message or callback on a per-port basis.
825		1212
826	=item * Erlang tries to hide remote/local connections, AEMP does not.	1213	=item * Erlang tries to hide remote/local connections, AEMP does not.
827		1214
828	Monitoring in Erlang is not an indicator of process death/crashes,	1215	Monitoring in Erlang is not an indicator of process death/crashes, in the
829	as linking is (except linking is unreliable in Erlang).	1216	same way as linking is (except linking is unreliable in Erlang).
830		1217
831	In AEMP, you don't "look up" registered port names or send to named ports	1218	In AEMP, you don't "look up" registered port names or send to named ports
832	that might or might not be persistent. Instead, you normally spawn a port	1219	that might or might not be persistent. Instead, you normally spawn a port
833	on the remote node. The init function monitors the you, and you monitor	1220	on the remote node. The init function monitors you, and you monitor the
834	the remote port. Since both monitors are local to the node, they are much	1221	remote port. Since both monitors are local to the node, they are much more
835	more reliable.	1222	reliable (no need for C<spawn_link>).
836		1223
837	This also saves round-trips and avoids sending messages to the wrong port	1224	This also saves round-trips and avoids sending messages to the wrong port
838	(hard to do in Erlang).	1225	(hard to do in Erlang).
839		1226
840	=back	1227	=back
841		1228
842	=head1 RATIONALE	1229	=head1 RATIONALE
843		1230
844	=over 4	1231	=over 4
845		1232
846	=item Why strings for ports and noderefs, why not objects?	1233	=item Why strings for port and node IDs, why not objects?
847		1234
848	We considered "objects", but found that the actual number of methods	1235	We considered "objects", but found that the actual number of methods
849	thatc an be called are very low. Since port IDs and noderefs travel over	1236	that can be called are quite low. Since port and node IDs travel over
850	the network frequently, the serialising/deserialising would add lots of	1237	the network frequently, the serialising/deserialising would add lots of
851	overhead, as well as having to keep a proxy object.	1238	overhead, as well as having to keep a proxy object everywhere.
852		1239
853	Strings can easily be printed, easily serialised etc. and need no special	1240	Strings can easily be printed, easily serialised etc. and need no special
854	procedures to be "valid".	1241	procedures to be "valid".
855		1242
856	And a a miniport consists of a single closure stored in a global hash - it	1243	And as a result, a port with just a default receiver consists of a single
857	can't become much cheaper.	1244	code reference stored in a global hash - it can't become much cheaper.
858		1245
859	=item Why favour JSON, why not real serialising format such as Storable?	1246	=item Why favour JSON, why not a real serialising format such as Storable?
860		1247
861	In fact, any AnyEvent::MP node will happily accept Storable as framing	1248	In fact, any AnyEvent::MP node will happily accept Storable as framing
862	format, but currently there is no way to make a node use Storable by	1249	format, but currently there is no way to make a node use Storable by
863	default.	1250	default (although all nodes will accept it).
864		1251
865	The default framing protocol is JSON because a) JSON::XS is many times	1252	The default framing protocol is JSON because a) JSON::XS is many times
866	faster for small messages and b) most importantly, after years of	1253	faster for small messages and b) most importantly, after years of
867	experience we found that object serialisation is causing more problems	1254	experience we found that object serialisation is causing more problems
868	than it gains: Just like function calls, objects simply do not travel	1255	than it solves: Just like function calls, objects simply do not travel
869	easily over the network, mostly because they will always be a copy, so you	1256	easily over the network, mostly because they will always be a copy, so you
870	always have to re-think your design.	1257	always have to re-think your design.
871		1258
872	Keeping your messages simple, concentrating on data structures rather than	1259	Keeping your messages simple, concentrating on data structures rather than
873	objects, will keep your messages clean, tidy and efficient.	1260	objects, will keep your messages clean, tidy and efficient.
874		1261
875	=back	1262	=back
876		1263
		1264	=head1 PORTING FROM AnyEvent::MP VERSION 1.X
		1265
		1266	AEMP version 2 has a few major incompatible changes compared to version 1:
		1267
		1268	=over 4
		1269
		1270	=item AnyEvent::MP::Global no longer has group management functions.
		1271
		1272	AnyEvent::MP now comes with a distributed database that is more
		1273	powerful. Its database families map closely to port groups, but the API
		1274	has changed (the functions are also now exported by AnyEvent::MP). Here is
		1275	a rough porting guide:
		1276
		1277	grp_reg $group, $port # old
		1278	db_reg $group, $port # new
		1279
		1280	$list = grp_get $group # old
		1281	db_keys $group, sub { my $list = shift } # new
		1282
		1283	grp_mon $group, $cb->(\@ports, $add, $del) # old
		1284	db_mon $group, $cb->(\%ports, $add, $change, $del) # new
		1285
		1286	C<grp_reg> is a no-brainer (just replace by C<db_reg>), but C<grp_get> is
		1287	no longer instant, because the local node might not have a copy of the
		1288	group. You can either modify your code to allow for a callback, or use
		1289	C<db_mon> to keep an updated copy of the group:
		1290
		1291	my $local_group_copy;
		1292	db_mon $group => sub { $local_group_copy = $_[0] };
		1293
		1294	# now "keys %$local_group_copy" always returns the most up-to-date
		1295	# list of ports in the group.
		1296
		1297	C<grp_mon> can be replaced by C<db_mon> with minor changes - C<db_mon>
		1298	passes a hash as first argument, and an extra C<$chg> argument that can be
		1299	ignored:
		1300
		1301	db_mon $group => sub {
		1302	my ($ports, $add, $chg, $lde) = @_;
		1303	$ports = [keys %$ports];
		1304
		1305	# now $ports, $add and $del are the same as
		1306	# were originally passed by grp_mon.
		1307	...
		1308	};
		1309
		1310	=item Nodes not longer connect to all other nodes.
		1311
		1312	In AEMP 1.x, every node automatically loads the L<AnyEvent::MP::Global>
		1313	module, which in turn would create connections to all other nodes in the
		1314	network (helped by the seed nodes).
		1315
		1316	In version 2.x, global nodes still connect to all other global nodes, but
		1317	other nodes don't - now every node either is a global node itself, or
		1318	attaches itself to another global node.
		1319
		1320	If a node isn't a global node itself, then it attaches itself to one
		1321	of its seed nodes. If that seed node isn't a global node yet, it will
		1322	automatically be upgraded to a global node.
		1323
		1324	So in many cases, nothing needs to be changed - one just has to make sure
		1325	that all seed nodes are meshed together with the other seed nodes (as with
		1326	AEMP 1.x), and other nodes specify them as seed nodes. This is most easily
		1327	achieved by specifying the same set of seed nodes for all nodes in the
		1328	network.
		1329
		1330	Not opening a connection to every other node is usually an advantage,
		1331	except when you need the lower latency of an already established
		1332	connection. To ensure a node establishes a connection to another node,
		1333	you can monitor the node port (C<mon $node, ...>), which will attempt to
		1334	create the connection (and notify you when the connection fails).
		1335
		1336	=item Listener-less nodes (nodes without binds) are gone.
		1337
		1338	And are not coming back, at least not in their old form. If no C<binds>
		1339	are specified for a node, AnyEvent::MP assumes a default of C<*:*>.
		1340
		1341	There are vague plans to implement some form of routing domains, which
		1342	might or might not bring back listener-less nodes, but don't count on it.
		1343
		1344	The fact that most connections are now optional somewhat mitigates this,
		1345	as a node can be effectively unreachable from the outside without any
		1346	problems, as long as it isn't a global node and only reaches out to other
		1347	nodes (as opposed to being contacted from other nodes).
		1348
		1349	=item $AnyEvent::MP::Kernel::WARN has gone.
		1350
		1351	AnyEvent has acquired a logging framework (L<AnyEvent::Log>), and AEMP now
		1352	uses this, and so should your programs.
		1353
		1354	Every module now documents what kinds of messages it generates, with
		1355	AnyEvent::MP acting as a catch all.
		1356
		1357	On the positive side, this means that instead of setting
		1358	C<PERL_ANYEVENT_MP_WARNLEVEL>, you can get away by setting C<AE_VERBOSE> -
		1359	much less to type.
		1360
		1361	=back
		1362
		1363	=head1 LOGGING
		1364
		1365	AnyEvent::MP does not normally log anything by itself, but sinc eit is the
		1366	root of the contetx hierarchy for AnyEvent::MP modules, it will receive
		1367	all log messages by submodules.
		1368
877	=head1 SEE ALSO	1369	=head1 SEE ALSO
		1370
		1371	L<AnyEvent::MP::Intro> - a gentle introduction.
		1372
		1373	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1374
		1375	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1376	your applications.
		1377
		1378	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1379
		1380	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1381	all nodes.
878		1382
879	L<AnyEvent>.	1383	L<AnyEvent>.
880		1384
881	=head1 AUTHOR	1385	=head1 AUTHOR
882		1386

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