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Revision 1.52 by root, Fri Aug 14 15:13:20 2009 UTC vs.
Revision 1.142 by root, Fri Mar 23 13:44:01 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
42		43
43	=head1 CURRENT STATUS	44	# temporarily execute code in port context
		45	peval $port, sub { die "kill the port!" };
44		46
45	AnyEvent::MP - stable API, should work	47	# execute callbacks in $SELF port context
46	AnyEvent::MP::Intro - outdated	48	my $timer = AE::timer 1, 0, psub {
47	AnyEvent::MP::Kernel - WIP	49	die "kill the port, delayed";
48	AnyEvent::MP::Transport - mostly stable	50	};
49
50	stay tuned.
51		51
52	=head1 DESCRIPTION	52	=head1 DESCRIPTION
53		53
54	This module (-family) implements a simple message passing framework.	54	This module (-family) implements a simple message passing framework.
55		55
56	Despite its simplicity, you can securely message other processes running	56	Despite its simplicity, you can securely message other processes running
57	on the same or other hosts.	57	on the same or other hosts, and you can supervise entities remotely.
58		58
59	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	59	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
60	manual page.	60	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		61
66	=head1 CONCEPTS	62	=head1 CONCEPTS
67		63
68	=over 4	64	=over 4
69		65
70	=item port	66	=item port
71		67
72	A port is something you can send messages to (with the C<snd> function).	68	Not to be confused with a TCP port, a "port" is something you can send
		69	messages to (with the C<snd> function).
73		70
74	Some ports allow you to register C<rcv> handlers that can match specific	71	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	72	some messages. Messages send to ports will not be queued, regardless of
76	will not be queued.	73	anything was listening for them or not.
77		74
		75	Ports are represented by (printable) strings called "port IDs".
		76
78	=item port id - C<noderef#portname>	77	=item port ID - C<nodeid#portname>
79		78
80	A port id is normaly the concatenation of a noderef, a hash-mark (C<#>) as	79	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	80	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	81	format created by AnyEvent::MP).
83	reference.
84		82
85	=item node	83	=item node
86		84
87	A node is a single process containing at least one port - the node	85	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	86	which enables nodes to manage each other remotely, and to create new
89	create new ports, among other things.	87	ports.
90		88
91	Nodes are either private (single-process only), slaves (connected to a	89	Nodes are either public (have one or more listening ports) or private
92	master node only) or public nodes (connectable from unrelated nodes).	90	(no listening ports). Private nodes cannot talk to other private nodes
		91	currently, but all nodes can talk to public nodes.
93		92
94	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	93	Nodes is represented by (printable) strings called "node IDs".
95		94
96	A node reference is a string that either simply identifies the node (for	95	=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		96
100	This recipe is simply a comma-separated list of C<address:port> pairs (for	97	A node ID is a string that uniquely identifies the node within a
101	TCP/IP, other protocols might look different).	98	network. Depending on the configuration used, node IDs can look like a
		99	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		100	doesn't interpret node IDs in any way except to uniquely identify a node.
102		101
103	Node references come in two flavours: resolved (containing only numerical	102	=item binds - C<ip:port>
104	addresses) or unresolved (where hostnames are used instead of addresses).
105		103
106	Before using an unresolved node reference in a message you first have to	104	Nodes can only talk to each other by creating some kind of connection to
107	resolve it.	105	each other. To do this, nodes should listen on one or more local transport
		106	endpoints - binds.
		107
		108	Currently, only standard C<ip:port> specifications can be used, which
		109	specify TCP ports to listen on. So a bind is basically just a tcp socket
		110	in listening mode thta accepts conenctions form other nodes.
		111
		112	=item seed nodes
		113
		114	When a node starts, it knows nothing about the network it is in - it
		115	needs to connect to at least one other node that is already in the
		116	network. These other nodes are called "seed nodes".
		117
		118	Seed nodes themselves are not special - they are seed nodes only because
		119	some other node I<uses> them as such, but any node can be used as seed
		120	node for other nodes, and eahc node cna use a different set of seed nodes.
		121
		122	In addition to discovering the network, seed nodes are also used to
		123	maintain the network - all nodes using the same seed node form are part of
		124	the same network. If a network is split into multiple subnets because e.g.
		125	the network link between the parts goes down, then using the same seed
		126	nodes for all nodes ensures that eventually the subnets get merged again.
		127
		128	Seed nodes are expected to be long-running, and at least one seed node
		129	should always be available. They should also be relatively responsive - a
		130	seed node that blocks for long periods will slow down everybody else.
		131
		132	For small networks, it's best if every node uses the same set of seed
		133	nodes. For large networks, it can be useful to specify "regional" seed
		134	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		135	each other. What's important is that all seed nodes connections form a
		136	complete graph, so that the network cannot split into separate subnets
		137	forever.
		138
		139	Seed nodes are represented by seed IDs.
		140
		141	=item seed IDs - C<host:port>
		142
		143	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
		144	TCP port) of nodes that should be used as seed nodes.
		145
		146	=item global nodes
		147
		148	An AEMP network needs a discovery service - nodes need to know how to
		149	connect to other nodes they only know by name. In addition, AEMP offers a
		150	distributed "group database", which maps group names to a list of strings
		151	- for example, to register worker ports.
		152
		153	A network needs at least one global node to work, and allows every node to
		154	be a global node.
		155
		156	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		157	node and tries to keep connections to all other nodes. So while it can
		158	make sense to make every node "global" in small networks, it usually makes
		159	sense to only make seed nodes into global nodes in large networks (nodes
		160	keep connections to seed nodes and global nodes, so makign them the same
		161	reduces overhead).
108		162
109	=back	163	=back
110		164
111	=head1 VARIABLES/FUNCTIONS	165	=head1 VARIABLES/FUNCTIONS
112		166
…		…
114		168
115	=cut	169	=cut
116		170
117	package AnyEvent::MP;	171	package AnyEvent::MP;
118		172
		173	use AnyEvent::MP::Config ();
119	use AnyEvent::MP::Kernel;	174	use AnyEvent::MP::Kernel;
		175	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
120		176
121	use common::sense;	177	use common::sense;
122		178
123	use Carp ();	179	use Carp ();
124		180
125	use AE ();	181	use AnyEvent ();
		182	use Guard ();
126		183
127	use base "Exporter";	184	use base "Exporter";
128		185
129	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	186	our $VERSION = $AnyEvent::MP::Config::VERSION;
130		187
131	our @EXPORT = qw(	188	our @EXPORT = qw(
132	NODE $NODE *SELF node_of _any_	189	NODE $NODE *SELF node_of after
133	resolve_node initialise_node	190	configure
134	snd rcv mon kil reg psub spawn	191	snd rcv mon mon_guard kil psub peval spawn cal
135	port	192	port
		193	db_set db_del db_reg
		194	db_mon db_family db_keys db_values
136	);	195	);
137		196
138	our $SELF;	197	our $SELF;
139		198
140	sub _self_die() {	199	sub _self_die() {
…		…
143	kil $SELF, die => $msg;	202	kil $SELF, die => $msg;
144	}	203	}
145		204
146	=item $thisnode = NODE / $NODE	205	=item $thisnode = NODE / $NODE
147		206
148	The C<NODE> function returns, and the C<$NODE> variable contains the	207	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	208	ID of the node running in the current process. This value is initialised by
150	C<initialise_node>.	209	a call to C<configure>.
151		210
152	=item $noderef = node_of $port	211	=item $nodeid = node_of $port
153		212
154	Extracts and returns the noderef from a port ID or a noderef.	213	Extracts and returns the node ID from a port ID or a node ID.
155		214
156	=item initialise_node $noderef, $seednode, $seednode...	215	=item configure $profile, key => value...
157		216
158	=item initialise_node "slave/", $master, $master...	217	=item configure key => value...
159		218
160	Before a node can talk to other nodes on the network it has to initialise	219	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	220	"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.	221	to know is its own name, and optionally it should know the addresses of
		222	some other nodes in the network to discover other nodes.
163		223
164	This function initialises a node - it must be called exactly once (or	224	This function configures a node - it must be called exactly once (or
165	never) before calling other AnyEvent::MP functions.	225	never) before calling other AnyEvent::MP functions.
166		226
167	All arguments (optionally except for the first) are noderefs, which can be	227	The key/value pairs are basically the same ones as documented for the
168	either resolved or unresolved.	228	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		229
178	=over 4	230	=over 4
179		231
180	=item public nodes	232	=item norc => $boolean (default false)
181		233
182	For public nodes, C<$noderef> (supplied either directly to	234	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	235	be consulted - all configuraiton options must be specified in the
184	noderef (possibly unresolved, in which case it will be resolved).	236	C<configure> call.
185		237
186	After resolving, the node will bind itself on all endpoints and try to	238	=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		239
191	=item slave nodes	240	IF true, then the values specified in the C<configure> will take
192		241	precedence over any values configured via the rc file. The default is for
193	When the C<$noderef> (either as given or overriden by the config file)	242	the rc file to override any options specified in the program.
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
198	At least one additional noderef is required (either by specifying it
199	directly or because it is part of the configuration profile): The node
200	will try to connect to all of them and will become a slave attached to the
201	first node it can successfully connect to.
202		243
203	=back	244	=back
204		245
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	246	=over 4
248		247
249	=item the empty string	248	=item step 1, gathering configuration from profiles
250		249
251	An empty-string component gets resolved as if the default port (4040) was	250	The function first looks up a profile in the aemp configuration (see the
252	specified.	251	L<aemp> commandline utility). The profile name can be specified via the
		252	named C<profile> parameter or can simply be the first parameter). If it is
		253	missing, then the nodename (F<uname -n>) will be used as profile name.
253		254
254	=item naked port numbers (e.g. C<1234>)	255	The profile data is then gathered as follows:
255		256
256	These are resolved by prepending the local nodename and a colon, to be	257	First, all remaining key => value pairs (all of which are conveniently
257	further resolved.	258	undocumented at the moment) will be interpreted as configuration
		259	data. Then they will be overwritten by any values specified in the global
		260	default configuration (see the F<aemp> utility), then the chain of
		261	profiles chosen by the profile name (and any C<parent> attributes).
258		262
259	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	263	That means that the values specified in the profile have highest priority
		264	and the values specified directly via C<configure> have lowest priority,
		265	and can only be used to specify defaults.
260		266
261	These are resolved by using AnyEvent::DNS to resolve them, optionally	267	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	268	this process. If not, then the profile name will be used as node ID, with
263	specified.	269	a unique randoms tring (C</%u>) appended.
		270
		271	The node ID can contain some C<%> sequences that are expanded: C<%n>
		272	is expanded to the local nodename, C<%u> is replaced by a random
		273	strign to make the node unique. For example, the F<aemp> commandline
		274	utility uses C<aemp/%n/%u> as nodename, which might expand to
		275	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		276
		277	=item step 2, bind listener sockets
		278
		279	The next step is to look up the binds in the profile, followed by binding
		280	aemp protocol listeners on all binds specified (it is possible and valid
		281	to have no binds, meaning that the node cannot be contacted form the
		282	outside. This means the node cannot talk to other nodes that also have no
		283	binds, but it can still talk to all "normal" nodes).
		284
		285	If the profile does not specify a binds list, then a default of C<*> is
		286	used, meaning the node will bind on a dynamically-assigned port on every
		287	local IP address it finds.
		288
		289	=item step 3, connect to seed nodes
		290
		291	As the last step, the seed ID list from the profile is passed to the
		292	L<AnyEvent::MP::Global> module, which will then use it to keep
		293	connectivity with at least one node at any point in time.
264		294
265	=back	295	=back
		296
		297	Example: become a distributed node using the local node name as profile.
		298	This should be the most common form of invocation for "daemon"-type nodes.
		299
		300	configure
		301
		302	Example: become a semi-anonymous node. This form is often used for
		303	commandline clients.
		304
		305	configure nodeid => "myscript/%n/%u";
		306
		307	Example: configure a node using a profile called seed, which is suitable
		308	for a seed node as it binds on all local addresses on a fixed port (4040,
		309	customary for aemp).
		310
		311	# use the aemp commandline utility
		312	# aemp profile seed binds '*:4040'
		313
		314	# then use it
		315	configure profile => "seed";
		316
		317	# or simply use aemp from the shell again:
		318	# aemp run profile seed
		319
		320	# or provide a nicer-to-remember nodeid
		321	# aemp run profile seed nodeid "$(hostname)"
266		322
267	=item $SELF	323	=item $SELF
268		324
269	Contains the current port id while executing C<rcv> callbacks or C<psub>	325	Contains the current port id while executing C<rcv> callbacks or C<psub>
270	blocks.	326	blocks.
271		327
272	=item SELF, %SELF, @SELF...	328	=item *SELF, SELF, %SELF, @SELF...
273		329
274	Due to some quirks in how perl exports variables, it is impossible to	330	Due to some quirks in how perl exports variables, it is impossible to
275	just export C<$SELF>, all the symbols called C<SELF> are exported by this	331	just export C<$SELF>, all the symbols named C<SELF> are exported by this
276	module, but only C<$SELF> is currently used.	332	module, but only C<$SELF> is currently used.
277		333
278	=item snd $port, type => @data	334	=item snd $port, type => @data
279		335
280	=item snd $port, @msg	336	=item snd $port, @msg
281		337
282	Send the given message to the given port ID, which can identify either	338	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.	339	local or a remote port, and must be a port ID.
284		340
285	While the message can be about anything, it is highly recommended to use a	341	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	342	use a string as first element (a port ID, or some word that indicates a
287	type etc.).	343	request type etc.) and to consist if only simple perl values (scalars,
		344	arrays, hashes) - if you think you need to pass an object, think again.
288		345
289	The message data effectively becomes read-only after a call to this	346	The message data logically becomes read-only after a call to this
290	function: modifying any argument is not allowed and can cause many	347	function: modifying any argument (or values referenced by them) is
291	problems.	348	forbidden, as there can be considerable time between the call to C<snd>
		349	and the time the message is actually being serialised - in fact, it might
		350	never be copied as within the same process it is simply handed to the
		351	receiving port.
292		352
293	The type of data you can transfer depends on the transport protocol: when	353	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	354	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	355	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	356	that Storable can serialise and deserialise is allowed, and for the local
297	node, anything can be passed.	357	node, anything can be passed. Best rely only on the common denominator of
		358	these.
298		359
299	=item $local_port = port	360	=item $local_port = port
300		361
301	Create a new local port object and returns its port ID. Initially it has	362	Create a new local port object and returns its port ID. Initially it has
302	no callbacks set and will throw an error when it receives messages.	363	no callbacks set and will throw an error when it receives messages.
…		…
321		382
322	=cut	383	=cut
323		384
324	sub rcv($@);	385	sub rcv($@);
325		386
326	sub _kilme {	387	my $KILME = sub {
327	die "received message on port without callback";	388	(my $tag = substr $_[0], 0, 30) =~ s/([\x20-\x7e])/./g;
328	}	389	kil $SELF, unhandled_message => "no callback found for message '$tag'";
		390	};
329		391
330	sub port(;&) {	392	sub port(;&) {
331	my $id = "$UNIQ." . $ID++;	393	my $id = $UNIQ . ++$ID;
332	my $port = "$NODE#$id";	394	my $port = "$NODE#$id";
333		395
334	rcv $port, shift || \&_kilme;	396	rcv $port, shift || $KILME;
335		397
336	$port	398	$port
337	}	399	}
338		400
339	=item rcv $local_port, $callback->(@msg)	401	=item rcv $local_port, $callback->(@msg)
…		…
344		406
345	The global C<$SELF> (exported by this module) contains C<$port> while	407	The global C<$SELF> (exported by this module) contains C<$port> while
346	executing the callback. Runtime errors during callback execution will	408	executing the callback. Runtime errors during callback execution will
347	result in the port being C<kil>ed.	409	result in the port being C<kil>ed.
348		410
349	The default callback received all messages not matched by a more specific	411	The default callback receives all messages not matched by a more specific
350	C<tag> match.	412	C<tag> match.
351		413
352	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...	414	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
353		415
354	Register callbacks to be called on messages starting with the given tag on	416	Register (or replace) callbacks to be called on messages starting with the
355	the given port (and return the port), or unregister it (when C<$callback>	417	given tag on the given port (and return the port), or unregister it (when
356	is C<$undef>).	418	C<$callback> is C<$undef> or missing). There can only be one callback
		419	registered for each tag.
357		420
358	The original message will be passed to the callback, after the first	421	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	422	element (the tag) has been removed. The callback will use the same
360	environment as the default callback (see above).	423	environment as the default callback (see above).
361		424
…		…
373	rcv port,	436	rcv port,
374	msg1 => sub { ... },	437	msg1 => sub { ... },
375	...	438	...
376	;	439	;
377		440
		441	Example: temporarily register a rcv callback for a tag matching some port
		442	(e.g. for an rpc reply) and unregister it after a message was received.
		443
		444	rcv $port, $otherport => sub {
		445	my @reply = @_;
		446
		447	rcv $SELF, $otherport;
		448	};
		449
378	=cut	450	=cut
379		451
380	sub rcv($@) {	452	sub rcv($@) {
381	my $port = shift;	453	my $port = shift;
382	my ($noderef, $portid) = split /#/, $port, 2;	454	my ($nodeid, $portid) = split /#/, $port, 2;
383		455
384	($NODE{$noderef} || add_node $noderef) == $NODE{""}	456	$NODE{$nodeid} == $NODE{""}
385	or Carp::croak "$port: rcv can only be called on local ports, caught";	457	or Carp::croak "$port: rcv can only be called on local ports, caught";
386		458
387	while (@_) {	459	while (@_) {
388	if (ref $_[0]) {	460	if (ref $_[0]) {
389	if (my $self = $PORT_DATA{$portid}) {	461	if (my $self = $PORT_DATA{$portid}) {
390	"AnyEvent::MP::Port" eq ref $self	462	"AnyEvent::MP::Port" eq ref $self
391	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	463	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
392		464
393	$self->[2] = shift;	465	$self->[0] = shift;
394	} else {	466	} else {
395	my $cb = shift;	467	my $cb = shift;
396	$PORT{$portid} = sub {	468	$PORT{$portid} = sub {
397	local $SELF = $port;	469	local $SELF = $port;
398	eval { &$cb }; _self_die if $@;	470	eval { &$cb }; _self_die if $@;
399	};	471	};
400	}	472	}
401	} elsif (defined $_[0]) {	473	} elsif (defined $_[0]) {
402	my $self = $PORT_DATA{$portid} ||= do {	474	my $self = $PORT_DATA{$portid} ||= do {
403	my $self = bless [$PORT{$port} || sub { }, { }, $port], "AnyEvent::MP::Port";	475	my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port";
404		476
405	$PORT{$portid} = sub {	477	$PORT{$portid} = sub {
406	local $SELF = $port;	478	local $SELF = $port;
407		479
408	if (my $cb = $self->[1]{$_[0]}) {	480	if (my $cb = $self->[1]{$_[0]}) {
…		…
430	}	502	}
431		503
432	$port	504	$port
433	}	505	}
434		506
		507	=item peval $port, $coderef[, @args]
		508
		509	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		510	when the code throews an exception the C<$port> will be killed.
		511
		512	Any remaining args will be passed to the callback. Any return values will
		513	be returned to the caller.
		514
		515	This is useful when you temporarily want to execute code in the context of
		516	a port.
		517
		518	Example: create a port and run some initialisation code in it's context.
		519
		520	my $port = port { ... };
		521
		522	peval $port, sub {
		523	init
		524	or die "unable to init";
		525	};
		526
		527	=cut
		528
		529	sub peval($$) {
		530	local $SELF = shift;
		531	my $cb = shift;
		532
		533	if (wantarray) {
		534	my @res = eval { &$cb };
		535	_self_die if $@;
		536	@res
		537	} else {
		538	my $res = eval { &$cb };
		539	_self_die if $@;
		540	$res
		541	}
		542	}
		543
435	=item $closure = psub { BLOCK }	544	=item $closure = psub { BLOCK }
436		545
437	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	546	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>	547	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.	548	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		549
		550	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		551	BLOCK }, @_ } >>.
440		552
441	This is useful when you register callbacks from C<rcv> callbacks:	553	This is useful when you register callbacks from C<rcv> callbacks:
442		554
443	rcv delayed_reply => sub {	555	rcv delayed_reply => sub {
444	my ($delay, @reply) = @_;	556	my ($delay, @reply) = @_;
…		…
468	$res	580	$res
469	}	581	}
470	}	582	}
471	}	583	}
472		584
473	=item $guard = mon $port, $cb->(@reason)	585	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
474		586
475	=item $guard = mon $port, $rcvport	587	=item $guard = mon $port # kill $SELF when $port dies
476		588
477	=item $guard = mon $port	589	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
478		590
479	=item $guard = mon $port, $rcvport, @msg	591	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
480		592
481	Monitor the given port and do something when the port is killed or	593	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	594	messages to it were lost, and optionally return a guard that can be used
483	to stop monitoring again.	595	to stop monitoring again.
484		596
		597	The first two forms distinguish between "normal" and "abnormal" kil's:
		598
		599	In the first form (another port given), if the C<$port> is C<kil>'ed with
		600	a non-empty reason, the other port (C<$rcvport>) will be kil'ed with the
		601	same reason. That is, on "normal" kil's nothing happens, while under all
		602	other conditions, the other port is killed with the same reason.
		603
		604	The second form (kill self) is the same as the first form, except that
		605	C<$rvport> defaults to C<$SELF>.
		606
		607	The remaining forms don't distinguish between "normal" and "abnormal" kil's
		608	- it's up to the callback or receiver to check whether the C<@reason> is
		609	empty and act accordingly.
		610
		611	In the third form (callback), the callback is simply called with any
		612	number of C<@reason> elements (empty @reason means that the port was deleted
		613	"normally"). Note also that I<< the callback B<must> never die >>, so use
		614	C<eval> if unsure.
		615
		616	In the last form (message), a message of the form C<$rcvport, @msg,
		617	@reason> will be C<snd>.
		618
		619	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		620	alert was raised), they are removed and will not trigger again, even if it
		621	turns out that the port is still alive.
		622
		623	As a rule of thumb, monitoring requests should always monitor a remote
		624	port locally (using a local C<$rcvport> or a callback). The reason is that
		625	kill messages might get lost, just like any other message. Another less
		626	obvious reason is that even monitoring requests can get lost (for example,
		627	when the connection to the other node goes down permanently). When
		628	monitoring a port locally these problems do not exist.
		629
485	C<mon> effectively guarantees that, in the absence of hardware failures,	630	C<mon> effectively guarantees that, in the absence of hardware failures,
486	that after starting the monitor, either all messages sent to the port	631	after starting the monitor, either all messages sent to the port will
487	will arrive, or the monitoring action will be invoked after possible	632	arrive, or the monitoring action will be invoked after possible message
488	message loss has been detected. No messages will be lost "in between"	633	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	634	the first lost message no further messages will be received by the
490	port). After the monitoring action was invoked, further messages might get	635	port). After the monitoring action was invoked, further messages might get
491	delivered again.	636	delivered again.
492		637
493	In the first form (callback), the callback is simply called with any	638	Inter-host-connection timeouts and monitoring depend on the transport
494	number of C<@reason> elements (no @reason means that the port was deleted	639	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	640	relies on TCP to detect node-downs (this can take 10-15 minutes on a
496	C<eval> if unsure.	641	non-idle connection, and usually around two hours for idle connections).
497		642
498	In the second form (another port given), the other port (C<$rcvport>)	643	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	644	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	645	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		646
516	Example: call a given callback when C<$port> is killed.	647	Example: call a given callback when C<$port> is killed.
517		648
518	mon $port, sub { warn "port died because of <@_>\n" };	649	mon $port, sub { warn "port died because of <@_>\n" };
519		650
…		…
526	mon $port, $self => "restart";	657	mon $port, $self => "restart";
527		658
528	=cut	659	=cut
529		660
530	sub mon {	661	sub mon {
531	my ($noderef, $port) = split /#/, shift, 2;	662	my ($nodeid, $port) = split /#/, shift, 2;
532		663
533	my $node = $NODE{$noderef} || add_node $noderef;	664	my $node = $NODE{$nodeid} || add_node $nodeid;
534		665
535	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';	666	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
536		667
537	unless (ref $cb) {	668	unless (ref $cb) {
538	if (@_) {	669	if (@_) {
…		…
547	}	678	}
548		679
549	$node->monitor ($port, $cb);	680	$node->monitor ($port, $cb);
550		681
551	defined wantarray	682	defined wantarray
552	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	683	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
553	}	684	}
554		685
555	=item $guard = mon_guard $port, $ref, $ref...	686	=item $guard = mon_guard $port, $ref, $ref...
556		687
557	Monitors the given C<$port> and keeps the passed references. When the port	688	Monitors the given C<$port> and keeps the passed references. When the port
558	is killed, the references will be freed.	689	is killed, the references will be freed.
559		690
560	Optionally returns a guard that will stop the monitoring.	691	Optionally returns a guard that will stop the monitoring.
561		692
562	This function is useful when you create e.g. timers or other watchers and	693	This function is useful when you create e.g. timers or other watchers and
563	want to free them when the port gets killed:	694	want to free them when the port gets killed (note the use of C<psub>):
564		695
565	$port->rcv (start => sub {	696	$port->rcv (start => sub {
566	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	697	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
567	undef $timer if 0.9 < rand;	698	undef $timer if 0.9 < rand;
568	});	699	});
569	});	700	});
570		701
571	=cut	702	=cut
…		…
580		711
581	=item kil $port[, @reason]	712	=item kil $port[, @reason]
582		713
583	Kill the specified port with the given C<@reason>.	714	Kill the specified port with the given C<@reason>.
584		715
585	If no C<@reason> is specified, then the port is killed "normally" (linked	716	If no C<@reason> is specified, then the port is killed "normally" -
586	ports will not be kileld, or even notified).	717	monitor callback will be invoked, but the kil will not cause linked ports
		718	(C<mon $mport, $lport> form) to get killed.
587		719
588	Otherwise, linked ports get killed with the same reason (second form of	720	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
589	C<mon>, see below).	721	form) get killed with the same reason.
590		722
591	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	723	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
592	will be reported as reason C<< die => $@ >>.	724	will be reported as reason C<< die => $@ >>.
593		725
594	Transport/communication errors are reported as C<< transport_error =>	726	Transport/communication errors are reported as C<< transport_error =>
595	$message >>.	727	$message >>.
596		728
597	=cut	729	Common idioms:
		730
		731	# silently remove yourself, do not kill linked ports
		732	kil $SELF;
		733
		734	# report a failure in some detail
		735	kil $SELF, failure_mode_1 => "it failed with too high temperature";
		736
		737	# do not waste much time with killing, just die when something goes wrong
		738	open my $fh, "<file"
		739	or die "file: $!";
598		740
599	=item $port = spawn $node, $initfunc[, @initdata]	741	=item $port = spawn $node, $initfunc[, @initdata]
600		742
601	Creates a port on the node C<$node> (which can also be a port ID, in which	743	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).	744	case it's the node where that port resides).
603		745
604	The port ID of the newly created port is return immediately, and it is	746	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.	747	possible to immediately start sending messages or to monitor the port.
606		748
607	After the port has been created, the init function is	749	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	750	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	751	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
610	program, use C<::name>.	752	specify a function in the main program, use C<::name>.
611		753
612	If the function doesn't exist, then the node tries to C<require>	754	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.	755	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	756	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
615	exists or it runs out of package names.	757	exists or it runs out of package names.
616		758
617	The init function is then called with the newly-created port as context	759	The init function is then called with the newly-created port as context
618	object (C<$SELF>) and the C<@initdata> values as arguments.	760	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		761	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		762	the port might not get created.
619		763
620	A common idiom is to pass your own port, monitor the spawned port, and	764	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	765	port, and in the remote init function, immediately monitor the passed
622	ensures that both ports get cleaned up when there is a problem.	766	local port. This two-way monitoring ensures that both ports get cleaned up
		767	when there is a problem.
		768
		769	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		770	caller before C<spawn> returns (by delaying invocation when spawn is
		771	called for the local node).
623		772
624	Example: spawn a chat server port on C<$othernode>.	773	Example: spawn a chat server port on C<$othernode>.
625		774
626	# this node, executed from within a port context:	775	# this node, executed from within a port context:
627	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	776	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
642		791
643	sub _spawn {	792	sub _spawn {
644	my $port = shift;	793	my $port = shift;
645	my $init = shift;	794	my $init = shift;
646		795
		796	# rcv will create the actual port
647	local $SELF = "$NODE#$port";	797	local $SELF = "$NODE#$port";
648	eval {	798	eval {
649	&{ load_func $init }	799	&{ load_func $init }
650	};	800	};
651	_self_die if $@;	801	_self_die if $@;
652	}	802	}
653		803
654	sub spawn(@) {	804	sub spawn(@) {
655	my ($noderef, undef) = split /#/, shift, 2;	805	my ($nodeid, undef) = split /#/, shift, 2;
656		806
657	my $id = "$RUNIQ." . $ID++;	807	my $id = $RUNIQ . ++$ID;
658		808
659	$_[0] =~ /::/	809	$_[0] =~ /::/
660	or Carp::croak "spawn init function must be a fully-qualified name, caught";	810	or Carp::croak "spawn init function must be a fully-qualified name, caught";
661		811
662	($NODE{$noderef} || add_node $noderef)	812	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
663	->send (["", "AnyEvent::MP::_spawn" => $id, @_]);
664		813
665	"$noderef#$id"	814	"$nodeid#$id"
666	}	815	}
667		816
		817
		818	=item after $timeout, @msg
		819
		820	=item after $timeout, $callback
		821
		822	Either sends the given message, or call the given callback, after the
		823	specified number of seconds.
		824
		825	This is simply a utility function that comes in handy at times - the
		826	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		827	so it may go away in the future.
		828
		829	=cut
		830
		831	sub after($@) {
		832	my ($timeout, @action) = @_;
		833
		834	my $t; $t = AE::timer $timeout, 0, sub {
		835	undef $t;
		836	ref $action[0]
		837	? $action[0]()
		838	: snd @action;
		839	};
		840	}
		841
		842	#=item $cb2 = timeout $seconds, $cb[, @args]
		843
		844	=item cal $port, @msg, $callback[, $timeout]
		845
		846	A simple form of RPC - sends a message to the given C<$port> with the
		847	given contents (C<@msg>), but adds a reply port to the message.
		848
		849	The reply port is created temporarily just for the purpose of receiving
		850	the reply, and will be C<kil>ed when no longer needed.
		851
		852	A reply message sent to the port is passed to the C<$callback> as-is.
		853
		854	If an optional time-out (in seconds) is given and it is not C<undef>,
		855	then the callback will be called without any arguments after the time-out
		856	elapsed and the port is C<kil>ed.
		857
		858	If no time-out is given (or it is C<undef>), then the local port will
		859	monitor the remote port instead, so it eventually gets cleaned-up.
		860
		861	Currently this function returns the temporary port, but this "feature"
		862	might go in future versions unless you can make a convincing case that
		863	this is indeed useful for something.
		864
		865	=cut
		866
		867	sub cal(@) {
		868	my $timeout = ref $_[-1] ? undef : pop;
		869	my $cb = pop;
		870
		871	my $port = port {
		872	undef $timeout;
		873	kil $SELF;
		874	&$cb;
		875	};
		876
		877	if (defined $timeout) {
		878	$timeout = AE::timer $timeout, 0, sub {
		879	undef $timeout;
		880	kil $port;
		881	$cb->();
		882	};
		883	} else {
		884	mon $_[0], sub {
		885	kil $port;
		886	$cb->();
		887	};
		888	}
		889
		890	push @_, $port;
		891	&snd;
		892
		893	$port
		894	}
		895
668	=back	896	=back
669		897
670	=head1 NODE MESSAGES	898	=head1 DISTRIBUTED DATABASE
671		899
672	Nodes understand the following messages sent to them. Many of them take	900	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	901	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	902	of the global nodes for their needs. Every node has a "local database"
675	the remaining arguments are simply the message data.	903	which contains all the values that are set locally. All local databases
		904	are merged together to form the global database, which can be queried.
676		905
677	While other messages exist, they are not public and subject to change.	906	The database structure is that of a two-level hash - the database hash
		907	contains hashes which contain values, similarly to a perl hash of hashes,
		908	i.e.:
678		909
		910	$DATABASE{$family}{$subkey} = $value
		911
		912	The top level hash key is called "family", and the second-level hash key
		913	is called "subkey" or simply "key".
		914
		915	The family must be alphanumeric, i.e. start with a letter and consist
		916	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		917	pretty much like Perl module names.
		918
		919	As the family namespace is global, it is recommended to prefix family names
		920	with the name of the application or module using it.
		921
		922	The subkeys must be non-empty strings, with no further restrictions.
		923
		924	The values should preferably be strings, but other perl scalars should
		925	work as well (such as C<undef>, arrays and hashes).
		926
		927	Every database entry is owned by one node - adding the same family/subkey
		928	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		929	but the result might be nondeterministic, i.e. the key might have
		930	different values on different nodes.
		931
		932	Different subkeys in the same family can be owned by different nodes
		933	without problems, and in fact, this is the common method to create worker
		934	pools. For example, a worker port for image scaling might do this:
		935
		936	db_set my_image_scalers => $port;
		937
		938	And clients looking for an image scaler will want to get the
		939	C<my_image_scalers> keys from time to time:
		940
		941	db_keys my_image_scalers => sub {
		942	@ports = @{ $_[0] };
		943	};
		944
		945	Or better yet, they want to monitor the database family, so they always
		946	have a reasonable up-to-date copy:
		947
		948	db_mon my_image_scalers => sub {
		949	@ports = keys %{ $_[0] };
		950	};
		951
		952	In general, you can set or delete single subkeys, but query and monitor
		953	whole families only.
		954
		955	If you feel the need to monitor or query a single subkey, try giving it
		956	it's own family.
		957
679	=over 4	958	=over
		959
		960	=item $guard = db_set $family => $subkey [=> $value]
		961
		962	Sets (or replaces) a key to the database - if C<$value> is omitted,
		963	C<undef> is used instead.
		964
		965	When called in non-void context, C<db_set> returns a guard that
		966	automatically calls C<db_del> when it is destroyed.
		967
		968	=item db_del $family => $subkey...
		969
		970	Deletes one or more subkeys from the database family.
		971
		972	=item $guard = db_reg $family => $port => $value
		973
		974	=item $guard = db_reg $family => $port
		975
		976	=item $guard = db_reg $family
		977
		978	Registers a port in the given family and optionally returns a guard to
		979	remove it.
		980
		981	This function basically does the same as:
		982
		983	db_set $family => $port => $value
		984
		985	Except that the port is monitored and automatically removed from the
		986	database family when it is kil'ed.
		987
		988	If C<$value> is missing, C<undef> is used. If C<$port> is missing, then
		989	C<$SELF> is used.
		990
		991	This function is most useful to register a port in some port group (which
		992	is just another name for a database family), and have it removed when the
		993	port is gone. This works best when the port is a local port.
680		994
681	=cut	995	=cut
682		996
683	=item lookup => $name, @reply	997	sub db_reg($$;$) {
		998	my $family = shift;
		999	my $port = @_ ? shift : $SELF;
684		1000
685	Replies with the port ID of the specified well-known port, or C<undef>.	1001	my $clr = sub { db_del $family => $port };
		1002	mon $port, $clr;
686		1003
687	=item devnull => ...	1004	db_set $family => $port => $_[0];
688		1005
689	Generic data sink/CPU heat conversion.	1006	defined wantarray
		1007	and &Guard::guard ($clr)
		1008	}
690		1009
691	=item relay => $port, @msg	1010	=item db_family $family => $cb->(\%familyhash)
692		1011
693	Simply forwards the message to the given port.	1012	Queries the named database C<$family> and call the callback with the
		1013	family represented as a hash. You can keep and freely modify the hash.
694		1014
695	=item eval => $string[ @reply]	1015	=item db_keys $family => $cb->(\@keys)
696		1016
697	Evaluates the given string. If C<@reply> is given, then a message of the	1017	Same as C<db_family>, except it only queries the family I<subkeys> and passes
698	form C<@reply, $@, @evalres> is sent.	1018	them as array reference to the callback.
699		1019
700	Example: crash another node.	1020	=item db_values $family => $cb->(\@values)
701		1021
702	snd $othernode, eval => "exit";	1022	Same as C<db_family>, except it only queries the family I<values> and passes them
		1023	as array reference to the callback.
703		1024
704	=item time => @reply	1025	=item $guard = db_mon $family => $cb->($familyhash, \@added, \@changed, \@deleted)
705		1026
706	Replies the the current node time to C<@reply>.	1027	Creates a monitor on the given database family. Each time a key is set
		1028	or or is deleted the callback is called with a hash containing the
		1029	database family and three lists of added, changed and deleted subkeys,
		1030	respectively. If no keys have changed then the array reference might be
		1031	C<undef> or even missing.
707		1032
708	Example: tell the current node to send the current time to C<$myport> in a	1033	If not called in void context, a guard object is returned that, when
709	C<timereply> message.	1034	destroyed, stops the monitor.
710		1035
711	snd $NODE, time => $myport, timereply => 1, 2;	1036	The family hash reference and the key arrays belong to AnyEvent::MP and
712	# => snd $myport, timereply => 1, 2, <time>	1037	B<must not be modified or stored> by the callback. When in doubt, make a
		1038	copy.
		1039
		1040	As soon as possible after the monitoring starts, the callback will be
		1041	called with the intiial contents of the family, even if it is empty,
		1042	i.e. there will always be a timely call to the callback with the current
		1043	contents.
		1044
		1045	It is possible that the callback is called with a change event even though
		1046	the subkey is already present and the value has not changed.
		1047
		1048	The monitoring stops when the guard object is destroyed.
		1049
		1050	Example: on every change to the family "mygroup", print out all keys.
		1051
		1052	my $guard = db_mon mygroup => sub {
		1053	my ($family, $a, $c, $d) = @_;
		1054	print "mygroup members: ", (join " ", keys %$family), "\n";
		1055	};
		1056
		1057	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1058
		1059	my $guard; $guard = db_mon My::Module::workers => sub {
		1060	my ($family, $a, $c, $d) = @_;
		1061	return unless %$family;
		1062	undef $guard;
		1063	print "My::Module::workers now nonempty\n";
		1064	};
		1065
		1066	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		1067
		1068	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		1069	my ($family, $a, $c, $d) = @_;
		1070
		1071	print "+$_=$family->{$_}\n" for @$a;
		1072	print "*$_=$family->{$_}\n" for @$c;
		1073	print "-$_=$family->{$_}\n" for @$d;
		1074	};
		1075
		1076	=cut
713		1077
714	=back	1078	=back
715		1079
716	=head1 AnyEvent::MP vs. Distributed Erlang	1080	=head1 AnyEvent::MP vs. Distributed Erlang
717		1081
718	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	1082	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	1083	== 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	1084	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
721	sample:	1085	sample:
722		1086
723	http://www.Erlang.se/doc/programming_rules.shtml	1087	http://www.erlang.se/doc/programming_rules.shtml
724	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	1088	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	1089	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	1090	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
727		1091
728	Despite the similarities, there are also some important differences:	1092	Despite the similarities, there are also some important differences:
729		1093
730	=over 4	1094	=over 4
731		1095
732	=item * Node references contain the recipe on how to contact them.	1096	=item * Node IDs are arbitrary strings in AEMP.
733		1097
734	Erlang relies on special naming and DNS to work everywhere in the	1098	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	1099	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
736	convenience functionality.	1100	configuration or DNS), and possibly the addresses of some seed nodes, but
		1101	will otherwise discover other nodes (and their IDs) itself.
737		1102
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	1103	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
742	uses "local ports are like remote ports".	1104	uses "local ports are like remote ports".
743		1105
744	The failure modes for local ports are quite different (runtime errors	1106	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,	1107	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	1108	when a connection to another node dies, you know nothing about the other
…		…
753	ports being the special case/exception, where transport errors cannot	1115	ports being the special case/exception, where transport errors cannot
754	occur.	1116	occur.
755		1117
756	=item * Erlang uses processes and a mailbox, AEMP does not queue.	1118	=item * Erlang uses processes and a mailbox, AEMP does not queue.
757		1119
758	Erlang uses processes that selectively receive messages, and therefore	1120	Erlang uses processes that selectively receive messages out of order, and
759	needs a queue. AEMP is event based, queuing messages would serve no	1121	therefore needs a queue. AEMP is event based, queuing messages would serve
760	useful purpose. For the same reason the pattern-matching abilities of	1122	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	1123	of AnyEvent::MP are more limited, as there is little need to be able to
762	filter messages without dequeing them.	1124	filter messages without dequeuing them.
763		1125
764	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	1126	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1127	being event-based, while Erlang is process-based.
		1128
		1129	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1130	top of AEMP and Coro threads.
765		1131
766	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1132	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
767		1133
768	Sending messages in Erlang is synchronous and blocks the process (and	1134	Sending messages in Erlang is synchronous and blocks the process until
		1135	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,	1136	need a queue that can overflow). AEMP sends return immediately, connection
770	connection establishment is handled in the background.	1137	establishment is handled in the background.
771		1138
772	=item * Erlang suffers from silent message loss, AEMP does not.	1139	=item * Erlang suffers from silent message loss, AEMP does not.
773		1140
774	Erlang makes few guarantees on messages delivery - messages can get lost	1141	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,	1142	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).	1143	b, and c, and the other side only receives messages a and c).
777		1144
778	AEMP guarantees correct ordering, and the guarantee that there are no	1145	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1146	guarantee that after one message is lost, all following ones sent to the
		1147	same port are lost as well, until monitoring raises an error, so there are
779	holes in the message sequence.	1148	no silent "holes" in the message sequence.
780		1149
781	=item * In Erlang, processes can be declared dead and later be found to be	1150	If you want your software to be very reliable, you have to cope with
782	alive.	1151	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
783		1152	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	1153	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		1154
792	=item * Erlang can send messages to the wrong port, AEMP does not.	1155	=item * Erlang can send messages to the wrong port, AEMP does not.
793		1156
794	In Erlang it is quite likely that a node that restarts reuses a process ID	1157	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	1158	process ID known to other nodes for a completely different process,
796	destined for that process to end up in an unrelated process.	1159	causing messages destined for that process to end up in an unrelated
		1160	process.
797		1161
798	AEMP never reuses port IDs, so old messages or old port IDs floating	1162	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.	1163	around in the network will not be sent to an unrelated port.
800		1164
801	=item * Erlang uses unprotected connections, AEMP uses secure	1165	=item * Erlang uses unprotected connections, AEMP uses secure
802	authentication and can use TLS.	1166	authentication and can use TLS.
803		1167
804	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1168	AEMP can use a proven protocol - TLS - to protect connections and
805	securely authenticate nodes.	1169	securely authenticate nodes.
806		1170
807	=item * The AEMP protocol is optimised for both text-based and binary	1171	=item * The AEMP protocol is optimised for both text-based and binary
808	communications.	1172	communications.
809		1173
810	The AEMP protocol, unlike the Erlang protocol, supports both	1174	The AEMP protocol, unlike the Erlang protocol, supports both programming
811	language-independent text-only protocols (good for debugging) and binary,	1175	language independent text-only protocols (good for debugging), and binary,
812	language-specific serialisers (e.g. Storable).	1176	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1177	used, the protocol is actually completely text-based.
813		1178
814	It has also been carefully designed to be implementable in other languages	1179	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	1180	with a minimum of work while gracefully degrading functionality to make the
816	protocol simple.	1181	protocol simple.
817		1182
818	=item * AEMP has more flexible monitoring options than Erlang.	1183	=item * AEMP has more flexible monitoring options than Erlang.
819		1184
820	In Erlang, you can chose to receive I<all> exit signals as messages	1185	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	1186	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	1187	difficult to implement.
823	Erlang, as one can choose between automatic kill, exit message or callback	1188
824	on a per-process basis.	1189	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1190	between automatic kill, exit message or callback on a per-port basis.
825		1191
826	=item * Erlang tries to hide remote/local connections, AEMP does not.	1192	=item * Erlang tries to hide remote/local connections, AEMP does not.
827		1193
828	Monitoring in Erlang is not an indicator of process death/crashes,	1194	Monitoring in Erlang is not an indicator of process death/crashes, in the
829	as linking is (except linking is unreliable in Erlang).	1195	same way as linking is (except linking is unreliable in Erlang).
830		1196
831	In AEMP, you don't "look up" registered port names or send to named ports	1197	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	1198	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	1199	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	1200	remote port. Since both monitors are local to the node, they are much more
835	more reliable.	1201	reliable (no need for C<spawn_link>).
836		1202
837	This also saves round-trips and avoids sending messages to the wrong port	1203	This also saves round-trips and avoids sending messages to the wrong port
838	(hard to do in Erlang).	1204	(hard to do in Erlang).
839		1205
840	=back	1206	=back
841		1207
842	=head1 RATIONALE	1208	=head1 RATIONALE
843		1209
844	=over 4	1210	=over 4
845		1211
846	=item Why strings for ports and noderefs, why not objects?	1212	=item Why strings for port and node IDs, why not objects?
847		1213
848	We considered "objects", but found that the actual number of methods	1214	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	1215	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	1216	the network frequently, the serialising/deserialising would add lots of
851	overhead, as well as having to keep a proxy object.	1217	overhead, as well as having to keep a proxy object everywhere.
852		1218
853	Strings can easily be printed, easily serialised etc. and need no special	1219	Strings can easily be printed, easily serialised etc. and need no special
854	procedures to be "valid".	1220	procedures to be "valid".
855		1221
856	And a a miniport consists of a single closure stored in a global hash - it	1222	And as a result, a port with just a default receiver consists of a single
857	can't become much cheaper.	1223	code reference stored in a global hash - it can't become much cheaper.
858		1224
859	=item Why favour JSON, why not real serialising format such as Storable?	1225	=item Why favour JSON, why not a real serialising format such as Storable?
860		1226
861	In fact, any AnyEvent::MP node will happily accept Storable as framing	1227	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	1228	format, but currently there is no way to make a node use Storable by
863	default.	1229	default (although all nodes will accept it).
864		1230
865	The default framing protocol is JSON because a) JSON::XS is many times	1231	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	1232	faster for small messages and b) most importantly, after years of
867	experience we found that object serialisation is causing more problems	1233	experience we found that object serialisation is causing more problems
868	than it gains: Just like function calls, objects simply do not travel	1234	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	1235	easily over the network, mostly because they will always be a copy, so you
870	always have to re-think your design.	1236	always have to re-think your design.
871		1237
872	Keeping your messages simple, concentrating on data structures rather than	1238	Keeping your messages simple, concentrating on data structures rather than
873	objects, will keep your messages clean, tidy and efficient.	1239	objects, will keep your messages clean, tidy and efficient.
874		1240
875	=back	1241	=back
876		1242
		1243	=head1 PORTING FROM AnyEvent::MP VERSION 1.X
		1244
		1245	AEMP version 2 has a few major incompatible changes compared to version 1:
		1246
		1247	=over 4
		1248
		1249	=item AnyEvent::MP::Global no longer has group management functions.
		1250
		1251	At least not officially - the grp_* functions are still exported and might
		1252	work, but they will be removed in some later release.
		1253
		1254	AnyEvent::MP now comes with a distributed database that is more
		1255	powerful. Its database families map closely to port groups, but the API
		1256	has changed (the functions are also now exported by AnyEvent::MP). Here is
		1257	a rough porting guide:
		1258
		1259	grp_reg $group, $port # old
		1260	db_reg $group, $port # new
		1261
		1262	$list = grp_get $group # old
		1263	db_keys $group, sub { my $list = shift } # new
		1264
		1265	grp_mon $group, $cb->(\@ports, $add, $del) # old
		1266	db_mon $group, $cb->(\%ports, $add, $change, $del) # new
		1267
		1268	C<grp_reg> is a no-brainer (just replace by C<db_reg>), but C<grp_get> is
		1269	no longer instant, because the local node might not have a copy of the
		1270	group. You can either modify your code to allow for a callback, or use
		1271	C<db_mon> to keep an updated copy of the group:
		1272
		1273	my $local_group_copy;
		1274	db_mon $group => sub { $local_group_copy = $_[0] };
		1275
		1276	# now "keys %$local_group_copy" always returns the most up-to-date
		1277	# list of ports in the group.
		1278
		1279	C<grp_mon> can be replaced by C<db_mon> with minor changes - C<db_mon>
		1280	passes a hash as first argument, and an extra C<$chg> argument that can be
		1281	ignored:
		1282
		1283	db_mon $group => sub {
		1284	my ($ports, $add, $chg, $lde) = @_;
		1285	$ports = [keys %$ports];
		1286
		1287	# now $ports, $add and $del are the same as
		1288	# were originally passed by grp_mon.
		1289	...
		1290	};
		1291
		1292	=item Nodes not longer connect to all other nodes.
		1293
		1294	In AEMP 1.x, every node automatically loads the L<AnyEvent::MP::Global>
		1295	module, which in turn would create connections to all other nodes in the
		1296	network (helped by the seed nodes).
		1297
		1298	In version 2.x, global nodes still connect to all other global nodes, but
		1299	other nodes don't - now every node either is a global node itself, or
		1300	attaches itself to another global node.
		1301
		1302	If a node isn't a global node itself, then it attaches itself to one
		1303	of its seed nodes. If that seed node isn't a global node yet, it will
		1304	automatically be upgraded to a global node.
		1305
		1306	So in many cases, nothing needs to be changed - one just has to make sure
		1307	that all seed nodes are meshed together with the other seed nodes (as with
		1308	AEMP 1.x), and other nodes specify them as seed nodes. This is most easily
		1309	achieved by specifying the same set of seed nodes for all nodes in the
		1310	network.
		1311
		1312	Not opening a connection to every other node is usually an advantage,
		1313	except when you need the lower latency of an already established
		1314	connection. To ensure a node establishes a connection to another node,
		1315	you can monitor the node port (C<mon $node, ...>), which will attempt to
		1316	create the connection (and notify you when the connection fails).
		1317
		1318	=item Listener-less nodes (nodes without binds) are gone.
		1319
		1320	And are not coming back, at least not in their old form. If no C<binds>
		1321	are specified for a node, AnyEvent::MP assumes a default of C<*:*>.
		1322
		1323	There are vague plans to implement some form of routing domains, which
		1324	might or might not bring back listener-less nodes, but don't count on it.
		1325
		1326	The fact that most connections are now optional somewhat mitigates this,
		1327	as a node can be effectively unreachable from the outside without any
		1328	problems, as long as it isn't a global node and only reaches out to other
		1329	nodes (as opposed to being contacted from other nodes).
		1330
		1331	=item $AnyEvent::MP::Kernel::WARN has gone.
		1332
		1333	AnyEvent has acquired a logging framework (L<AnyEvent::Log>), and AEMP now
		1334	uses this, and so should your programs.
		1335
		1336	Every module now documents what kinds of messages it generates, with
		1337	AnyEvent::MP acting as a catch all.
		1338
		1339	On the positive side, this means that instead of setting
		1340	C<PERL_ANYEVENT_MP_WARNLEVEL>, you can get away by setting C<AE_VERBOSE> -
		1341	much less to type.
		1342
		1343	=back
		1344
		1345	=head1 LOGGING
		1346
		1347	AnyEvent::MP does not normally log anything by itself, but sinc eit is the
		1348	root of the contetx hierarchy for AnyEvent::MP modules, it will receive
		1349	all log messages by submodules.
		1350
877	=head1 SEE ALSO	1351	=head1 SEE ALSO
		1352
		1353	L<AnyEvent::MP::Intro> - a gentle introduction.
		1354
		1355	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1356
		1357	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1358	your applications.
		1359
		1360	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1361
		1362	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1363	all nodes.
878		1364
879	L<AnyEvent>.	1365	L<AnyEvent>.
880		1366
881	=head1 AUTHOR	1367	=head1 AUTHOR
882		1368

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