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Revision 1.36 by root, Thu Aug 6 10:46:48 2009 UTC vs.
Revision 1.135 by root, Mon Mar 12 14:55:55 2012 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent::MP - multi-processing/message-passing framework	3	AnyEvent::MP - erlang-style multi-processing/message-passing framework
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::MP;	7	use AnyEvent::MP;
8		8
9	$NODE # contains this node's noderef	9	$NODE # contains this node's node ID
10	NODE # returns this node's noderef	10	NODE # returns this node's node ID
11	NODE $port # returns the noderef of the port
12		11
		12	$SELF # receiving/own port id in rcv callbacks
		13
		14	# initialise the node so it can send/receive messages
		15	configure;
		16
		17	# ports are message destinations
		18
		19	# sending messages
13	snd $port, type => data...;	20	snd $port, type => data...;
		21	snd $port, @msg;
		22	snd @msg_with_first_element_being_a_port;
14		23
15	$SELF # receiving/own port id in rcv callbacks	24	# creating/using ports, the simple way
		25	my $simple_port = port { my @msg = @_ };
16		26
17	rcv $port, smartmatch => $cb->($port, @msg);	27	# creating/using ports, tagged message matching
18		28	my $port = port;
19	# examples:
20	rcv $port2, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
21	rcv $port1, pong => sub { warn "pong received\n" };	30	rcv $port, pong => sub { warn "pong received\n" };
22	snd $port2, ping => $port1;
23		31
24	# more, smarter, matches (_any_ is exported by this module)	32	# create a port on another node
25	rcv $port, [child_died => $pid] => sub { ...	33	my $port = spawn $node, $initfunc, @initdata;
26	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3
27		34
28	# linking two ports, so they both crash together	35	# destroy a port again
29	lnk $port1, $port2;	36	kil $port; # "normal" kill
		37	kil $port, my_error => "everything is broken"; # error kill
30		38
31	# monitoring	39	# monitoring
32	mon $port, $cb->(@msg) # callback is invoked on death	40	mon $port, $cb->(@msg) # callback is invoked on death
33	mon $port, $otherport # kill otherport on abnormal death	41	mon $port, $localport # kill localport on abnormal death
34	mon $port, $otherport, @msg # send message on death	42	mon $port, $localport, @msg # send message on death
		43
		44	# temporarily execute code in port context
		45	peval $port, sub { die "kill the port!" };
		46
		47	# execute callbacks in $SELF port context
		48	my $timer = AE::timer 1, 0, psub {
		49	die "kill the port, delayed";
		50	};
		51
		52	=head1 CURRENT STATUS
		53
		54	bin/aemp - stable.
		55	AnyEvent::MP - stable API, should work.
		56	AnyEvent::MP::Intro - explains most concepts.
		57	AnyEvent::MP::Kernel - mostly stable API.
		58	AnyEvent::MP::Global - stable API.
35		59
36	=head1 DESCRIPTION	60	=head1 DESCRIPTION
37		61
38	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
39		63
40	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
41	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
42		66
43	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	67	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
44	manual page.	68	manual page and the examples under F<eg/>.
45
46	At the moment, this module family is severly broken and underdocumented,
47	so do not use. This was uploaded mainly to reserve the CPAN namespace -
48	stay tuned! The basic API should be finished, however.
49		69
50	=head1 CONCEPTS	70	=head1 CONCEPTS
51		71
52	=over 4	72	=over 4
53		73
54	=item port	74	=item port
55		75
56	A port is something you can send messages to (with the C<snd> function).	76	Not to be confused with a TCP port, a "port" is something you can send
		77	messages to (with the C<snd> function).
57		78
58	Some ports allow you to register C<rcv> handlers that can match specific	79	Ports allow you to register C<rcv> handlers that can match all or just
59	messages. All C<rcv> handlers will receive messages they match, messages	80	some messages. Messages send to ports will not be queued, regardless of
60	will not be queued.	81	anything was listening for them or not.
61		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
62	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
63		86
64	A port id is normaly the concatenation of a noderef, a hash-mark (C<#>) as	87	A port ID is the concatenation of a node ID, a hash-mark (C<#>)
65	separator, and a port name (a printable string of unspecified format). An	88	as separator, and a port name (a printable string of unspecified
66	exception is the the node port, whose ID is identical to its node	89	format created by AnyEvent::MP).
67	reference.
68		90
69	=item node	91	=item node
70		92
71	A node is a single process containing at least one port - the node	93	A node is a single process containing at least one port - the node port,
72	port. You can send messages to node ports to find existing ports or to	94	which enables nodes to manage each other remotely, and to create new
73	create new ports, among other things.	95	ports.
74		96
75	Nodes are either private (single-process only), slaves (connected to a	97	Nodes are either public (have one or more listening ports) or private
76	master node only) or public nodes (connectable from unrelated nodes).	98	(no listening ports). Private nodes cannot talk to other private nodes
		99	currently, but all nodes can talk to public nodes.
77		100
78	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	101	Nodes is represented by (printable) strings called "node IDs".
79		102
80	A node reference is a string that either simply identifies the node (for	103	=item node ID - C<[A-Za-z0-9_\-.:]*>
81	private and slave nodes), or contains a recipe on how to reach a given
82	node (for public nodes).
83		104
84	This recipe is simply a comma-separated list of C<address:port> pairs (for	105	A node ID is a string that uniquely identifies the node within a
85	TCP/IP, other protocols might look different).	106	network. Depending on the configuration used, node IDs can look like a
		107	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		108	doesn't interpret node IDs in any way except to uniquely identify a node.
86		109
87	Node references come in two flavours: resolved (containing only numerical	110	=item binds - C<ip:port>
88	addresses) or unresolved (where hostnames are used instead of addresses).
89		111
90	Before using an unresolved node reference in a message you first have to	112	Nodes can only talk to each other by creating some kind of connection to
91	resolve it.	113	each other. To do this, nodes should listen on one or more local transport
		114	endpoints - binds.
		115
		116	Currently, only standard C<ip:port> specifications can be used, which
		117	specify TCP ports to listen on. So a bind is basically just a tcp socket
		118	in listening mode thta accepts conenctions form other nodes.
		119
		120	=item seed nodes
		121
		122	When a node starts, it knows nothing about the network it is in - it
		123	needs to connect to at least one other node that is already in the
		124	network. These other nodes are called "seed nodes".
		125
		126	Seed nodes themselves are not special - they are seed nodes only because
		127	some other node I<uses> them as such, but any node can be used as seed
		128	node for other nodes, and eahc node cna use a different set of seed nodes.
		129
		130	In addition to discovering the network, seed nodes are also used to
		131	maintain the network - all nodes using the same seed node form are part of
		132	the same network. If a network is split into multiple subnets because e.g.
		133	the network link between the parts goes down, then using the same seed
		134	nodes for all nodes ensures that eventually the subnets get merged again.
		135
		136	Seed nodes are expected to be long-running, and at least one seed node
		137	should always be available. They should also be relatively responsive - a
		138	seed node that blocks for long periods will slow down everybody else.
		139
		140	For small networks, it's best if every node uses the same set of seed
		141	nodes. For large networks, it can be useful to specify "regional" seed
		142	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		143	each other. What's important is that all seed nodes connections form a
		144	complete graph, so that the network cannot split into separate subnets
		145	forever.
		146
		147	Seed nodes are represented by seed IDs.
		148
		149	=item seed IDs - C<host:port>
		150
		151	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
		152	TCP port) of nodes that should be used as seed nodes.
		153
		154	=item global nodes
		155
		156	An AEMP network needs a discovery service - nodes need to know how to
		157	connect to other nodes they only know by name. In addition, AEMP offers a
		158	distributed "group database", which maps group names to a list of strings
		159	- for example, to register worker ports.
		160
		161	A network needs at least one global node to work, and allows every node to
		162	be a global node.
		163
		164	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		165	node and tries to keep connections to all other nodes. So while it can
		166	make sense to make every node "global" in small networks, it usually makes
		167	sense to only make seed nodes into global nodes in large networks (nodes
		168	keep connections to seed nodes and global nodes, so makign them the same
		169	reduces overhead).
92		170
93	=back	171	=back
94		172
95	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
96		174
…		…
98		176
99	=cut	177	=cut
100		178
101	package AnyEvent::MP;	179	package AnyEvent::MP;
102		180
		181	use AnyEvent::MP::Config ();
103	use AnyEvent::MP::Base;	182	use AnyEvent::MP::Kernel;
		183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
104		184
105	use common::sense;	185	use common::sense;
106		186
107	use Carp ();	187	use Carp ();
108		188
109	use AE ();	189	use AE ();
		190	use Guard ();
110		191
111	use base "Exporter";	192	use base "Exporter";
112		193
113	our $VERSION = '0.1';	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
		195
114	our @EXPORT = qw(	196	our @EXPORT = qw(
115	NODE $NODE *SELF node_of _any_	197	NODE $NODE *SELF node_of after
116	resolve_node initialise_node	198	configure
117	snd rcv mon kil reg psub	199	snd rcv mon mon_guard kil psub peval spawn cal
118	port	200	port
		201	db_set db_del db_reg
		202	db_mon db_family db_keys db_values
119	);	203	);
120		204
121	our $SELF;	205	our $SELF;
122		206
123	sub _self_die() {	207	sub _self_die() {
…		…
126	kil $SELF, die => $msg;	210	kil $SELF, die => $msg;
127	}	211	}
128		212
129	=item $thisnode = NODE / $NODE	213	=item $thisnode = NODE / $NODE
130		214
131	The C<NODE> function returns, and the C<$NODE> variable contains	215	The C<NODE> function returns, and the C<$NODE> variable contains, the node
132	the noderef of the local node. The value is initialised by a call	216	ID of the node running in the current process. This value is initialised by
133	to C<become_public> or C<become_slave>, after which all local port	217	a call to C<configure>.
134	identifiers become invalid.
135		218
136	=item $noderef = node_of $port	219	=item $nodeid = node_of $port
137		220
138	Extracts and returns the noderef from a portid or a noderef.	221	Extracts and returns the node ID from a port ID or a node ID.
139		222
140	=item initialise_node $noderef, $seednode, $seednode...	223	=item configure $profile, key => value...
141		224
142	=item initialise_node "slave/", $master, $master...	225	=item configure key => value...
143		226
144	Before a node can talk to other nodes on the network it has to initialise	227	Before a node can talk to other nodes on the network (i.e. enter
145	itself - the minimum a node needs to know is it's own name, and optionally	228	"distributed mode") it has to configure itself - the minimum a node needs
146	it should know the noderefs of some other nodes in the network.	229	to know is its own name, and optionally it should know the addresses of
		230	some other nodes in the network to discover other nodes.
147		231
148	This function initialises a node - it must be called exactly once (or	232	This function configures a node - it must be called exactly once (or
149	never) before calling other AnyEvent::MP functions.	233	never) before calling other AnyEvent::MP functions.
150		234
151	All arguments are noderefs, which can be either resolved or unresolved.	235	The key/value pairs are basically the same ones as documented for the
152		236	F<aemp> command line utility (sans the set/del prefix), with these additions:
153	There are two types of networked nodes, public nodes and slave nodes:
154		237
155	=over 4	238	=over 4
156		239
157	=item public nodes	240	=item norc => $boolean (default false)
158		241
159	For public nodes, C<$noderef> must either be a (possibly unresolved)	242	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
160	noderef, in which case it will be resolved, or C<undef> (or missing), in	243	be consulted - all configuraiton options must be specified in the
161	which case the noderef will be guessed.	244	C<configure> call.
162		245
163	Afterwards, the node will bind itself on all endpoints and try to connect	246	=item force => $boolean (default false)
164	to all additional C<$seednodes> that are specified. Seednodes are optional
165	and can be used to quickly bootstrap the node into an existing network.
166		247
167	=item slave nodes	248	IF true, then the values specified in the C<configure> will take
		249	precedence over any values configured via the rc file. The default is for
		250	the rc file to override any options specified in the program.
168		251
169	When the C<$noderef> is the special string C<slave/>, then the node will	252	=item secure => $pass->($nodeid)
170	become a slave node. Slave nodes cannot be contacted from outside and will
171	route most of their traffic to the master node that they attach to.
172		253
173	At least one additional noderef is required: The node will try to connect	254	In addition to specifying a boolean, you can specify a code reference that
174	to all of them and will become a slave attached to the first node it can	255	is called for every remote execution attempt - the execution request is
175	successfully connect to.	256	granted iff the callback returns a true value.
		257
		258	See F<semp setsecure> for more info.
176		259
177	=back	260	=back
178		261
179	This function will block until all nodes have been resolved and, for slave
180	nodes, until it has successfully established a connection to a master
181	server.
182
183	Example: become a public node listening on the default node.
184
185	initialise_node;
186
187	Example: become a public node, and try to contact some well-known master
188	servers to become part of the network.
189
190	initialise_node undef, "master1", "master2";
191
192	Example: become a public node listening on port C<4041>.
193
194	initialise_node 4041;
195
196	Example: become a public node, only visible on localhost port 4044.
197
198	initialise_node "locahost:4044";
199
200	Example: become a slave node to any of the specified master servers.
201
202	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
203
204	=item $cv = resolve_node $noderef
205
206	Takes an unresolved node reference that may contain hostnames and
207	abbreviated IDs, resolves all of them and returns a resolved node
208	reference.
209
210	In addition to C<address:port> pairs allowed in resolved noderefs, the
211	following forms are supported:
212
213	=over 4	262	=over 4
214		263
215	=item the empty string	264	=item step 1, gathering configuration from profiles
216		265
217	An empty-string component gets resolved as if the default port (4040) was	266	The function first looks up a profile in the aemp configuration (see the
218	specified.	267	L<aemp> commandline utility). The profile name can be specified via the
		268	named C<profile> parameter or can simply be the first parameter). If it is
		269	missing, then the nodename (F<uname -n>) will be used as profile name.
219		270
220	=item naked port numbers (e.g. C<1234>)	271	The profile data is then gathered as follows:
221		272
222	These are resolved by prepending the local nodename and a colon, to be	273	First, all remaining key => value pairs (all of which are conveniently
223	further resolved.	274	undocumented at the moment) will be interpreted as configuration
		275	data. Then they will be overwritten by any values specified in the global
		276	default configuration (see the F<aemp> utility), then the chain of
		277	profiles chosen by the profile name (and any C<parent> attributes).
224		278
225	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	279	That means that the values specified in the profile have highest priority
		280	and the values specified directly via C<configure> have lowest priority,
		281	and can only be used to specify defaults.
226		282
227	These are resolved by using AnyEvent::DNS to resolve them, optionally	283	If the profile specifies a node ID, then this will become the node ID of
228	looking up SRV records for the C<aemp=4040> port, if no port was	284	this process. If not, then the profile name will be used as node ID, with
229	specified.	285	a unique randoms tring (C</%u>) appended.
		286
		287	The node ID can contain some C<%> sequences that are expanded: C<%n>
		288	is expanded to the local nodename, C<%u> is replaced by a random
		289	strign to make the node unique. For example, the F<aemp> commandline
		290	utility uses C<aemp/%n/%u> as nodename, which might expand to
		291	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		292
		293	=item step 2, bind listener sockets
		294
		295	The next step is to look up the binds in the profile, followed by binding
		296	aemp protocol listeners on all binds specified (it is possible and valid
		297	to have no binds, meaning that the node cannot be contacted form the
		298	outside. This means the node cannot talk to other nodes that also have no
		299	binds, but it can still talk to all "normal" nodes).
		300
		301	If the profile does not specify a binds list, then a default of C<*> is
		302	used, meaning the node will bind on a dynamically-assigned port on every
		303	local IP address it finds.
		304
		305	=item step 3, connect to seed nodes
		306
		307	As the last step, the seed ID list from the profile is passed to the
		308	L<AnyEvent::MP::Global> module, which will then use it to keep
		309	connectivity with at least one node at any point in time.
230		310
231	=back	311	=back
		312
		313	Example: become a distributed node using the local node name as profile.
		314	This should be the most common form of invocation for "daemon"-type nodes.
		315
		316	configure
		317
		318	Example: become a semi-anonymous node. This form is often used for
		319	commandline clients.
		320
		321	configure nodeid => "myscript/%n/%u";
		322
		323	Example: configure a node using a profile called seed, which is suitable
		324	for a seed node as it binds on all local addresses on a fixed port (4040,
		325	customary for aemp).
		326
		327	# use the aemp commandline utility
		328	# aemp profile seed binds '*:4040'
		329
		330	# then use it
		331	configure profile => "seed";
		332
		333	# or simply use aemp from the shell again:
		334	# aemp run profile seed
		335
		336	# or provide a nicer-to-remember nodeid
		337	# aemp run profile seed nodeid "$(hostname)"
232		338
233	=item $SELF	339	=item $SELF
234		340
235	Contains the current port id while executing C<rcv> callbacks or C<psub>	341	Contains the current port id while executing C<rcv> callbacks or C<psub>
236	blocks.	342	blocks.
237		343
238	=item SELF, %SELF, @SELF...	344	=item *SELF, SELF, %SELF, @SELF...
239		345
240	Due to some quirks in how perl exports variables, it is impossible to	346	Due to some quirks in how perl exports variables, it is impossible to
241	just export C<$SELF>, all the symbols called C<SELF> are exported by this	347	just export C<$SELF>, all the symbols named C<SELF> are exported by this
242	module, but only C<$SELF> is currently used.	348	module, but only C<$SELF> is currently used.
243		349
244	=item snd $port, type => @data	350	=item snd $port, type => @data
245		351
246	=item snd $port, @msg	352	=item snd $port, @msg
247		353
248	Send the given message to the given port ID, which can identify either	354	Send the given message to the given port, which can identify either a
249	a local or a remote port, and can be either a string or soemthignt hat	355	local or a remote port, and must be a port ID.
250	stringifies a sa port ID (such as a port object :).
251		356
252	While the message can be about anything, it is highly recommended to use a	357	While the message can be almost anything, it is highly recommended to
253	string as first element (a portid, or some word that indicates a request	358	use a string as first element (a port ID, or some word that indicates a
254	type etc.).	359	request type etc.) and to consist if only simple perl values (scalars,
		360	arrays, hashes) - if you think you need to pass an object, think again.
255		361
256	The message data effectively becomes read-only after a call to this	362	The message data logically becomes read-only after a call to this
257	function: modifying any argument is not allowed and can cause many	363	function: modifying any argument (or values referenced by them) is
258	problems.	364	forbidden, as there can be considerable time between the call to C<snd>
		365	and the time the message is actually being serialised - in fact, it might
		366	never be copied as within the same process it is simply handed to the
		367	receiving port.
259		368
260	The type of data you can transfer depends on the transport protocol: when	369	The type of data you can transfer depends on the transport protocol: when
261	JSON is used, then only strings, numbers and arrays and hashes consisting	370	JSON is used, then only strings, numbers and arrays and hashes consisting
262	of those are allowed (no objects). When Storable is used, then anything	371	of those are allowed (no objects). When Storable is used, then anything
263	that Storable can serialise and deserialise is allowed, and for the local	372	that Storable can serialise and deserialise is allowed, and for the local
264	node, anything can be passed.	373	node, anything can be passed. Best rely only on the common denominator of
		374	these.
265		375
266	=item $local_port = port	376	=item $local_port = port
267		377
268	Create a new local port object that can be used either as a pattern	378	Create a new local port object and returns its port ID. Initially it has
269	matching port ("full port") or a single-callback port ("miniport"),	379	no callbacks set and will throw an error when it receives messages.
270	depending on how C<rcv> callbacks are bound to the object.
271		380
272	=item $port = port { my @msg = @_; $finished }	381	=item $local_port = port { my @msg = @_ }
273		382
274	Creates a "miniport", that is, a very lightweight port without any pattern	383	Creates a new local port, and returns its ID. Semantically the same as
275	matching behind it, and returns its ID. Semantically the same as creating
276	a port and calling C<rcv $port, $callback> on it.	384	creating a port and calling C<rcv $port, $callback> on it.
277		385
278	The block will be called for every message received on the port. When the	386	The block will be called for every message received on the port, with the
279	callback returns a true value its job is considered "done" and the port	387	global variable C<$SELF> set to the port ID. Runtime errors will cause the
280	will be destroyed. Otherwise it will stay alive.	388	port to be C<kil>ed. The message will be passed as-is, no extra argument
		389	(i.e. no port ID) will be passed to the callback.
281		390
282	The message will be passed as-is, no extra argument (i.e. no port id) will	391	If you want to stop/destroy the port, simply C<kil> it:
283	be passed to the callback.
284		392
285	If you need the local port id in the callback, this works nicely:	393	my $port = port {
286		394	my @msg = @_;
287	my $port; $port = port {	395	...
288	snd $otherport, reply => $port;	396	kil $SELF;
289	};	397	};
290		398
291	=cut	399	=cut
292		400
293	sub rcv($@);	401	sub rcv($@);
294		402
		403	my $KILME = sub {
		404	(my $tag = substr $_[0], 0, 30) =~ s/([\x20-\x7e])/./g;
		405	kil $SELF, unhandled_message => "no callback found for message '$tag'";
		406	};
		407
295	sub port(;&) {	408	sub port(;&) {
296	my $id = "$UNIQ." . $ID++;	409	my $id = $UNIQ . ++$ID;
297	my $port = "$NODE#$id";	410	my $port = "$NODE#$id";
298		411
299	if (@_) {
300	rcv $port, shift;	412	rcv $port, shift || $KILME;
301	} else {
302	$PORT{$id} = sub { }; # nop
303	}
304		413
305	$port	414	$port
306	}	415	}
307		416
308	=item reg $port, $name
309
310	=item reg $name
311
312	Registers the given port (or C<$SELF><<< if missing) under the name
313	C<$name>. If the name already exists it is replaced.
314
315	A port can only be registered under one well known name.
316
317	A port automatically becomes unregistered when it is killed.
318
319	=cut
320
321	sub reg(@) {
322	my $port = @_ > 1 ? shift : $SELF || Carp::croak 'reg: called with one argument only, but $SELF not set,';
323
324	$REG{$_[0]} = $port;
325	}
326
327	=item rcv $port, $callback->(@msg)	417	=item rcv $local_port, $callback->(@msg)
328		418
329	Replaces the callback on the specified miniport (after converting it to	419	Replaces the default callback on the specified port. There is no way to
330	one if required).	420	remove the default callback: use C<sub { }> to disable it, or better
331		421	C<kil> the port when it is no longer needed.
332	=item rcv $port, tagstring => $callback->(@msg), ...
333
334	=item rcv $port, $smartmatch => $callback->(@msg), ...
335
336	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
337
338	Register callbacks to be called on matching messages on the given full
339	port (after converting it to one if required) and return the port.
340
341	The callback has to return a true value when its work is done, after
342	which is will be removed, or a false value in which case it will stay
343	registered.
344		422
345	The global C<$SELF> (exported by this module) contains C<$port> while	423	The global C<$SELF> (exported by this module) contains C<$port> while
346	executing the callback.	424	executing the callback. Runtime errors during callback execution will
		425	result in the port being C<kil>ed.
347		426
348	Runtime errors wdurign callback execution will result in the port being	427	The default callback receives all messages not matched by a more specific
349	C<kil>ed.	428	C<tag> match.
350		429
351	If the match is an array reference, then it will be matched against the	430	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
352	first elements of the message, otherwise only the first element is being
353	matched.
354		431
355	Any element in the match that is specified as C<_any_> (a function	432	Register (or replace) callbacks to be called on messages starting with the
356	exported by this module) matches any single element of the message.	433	given tag on the given port (and return the port), or unregister it (when
		434	C<$callback> is C<$undef> or missing). There can only be one callback
		435	registered for each tag.
357		436
358	While not required, it is highly recommended that the first matching	437	The original message will be passed to the callback, after the first
359	element is a string identifying the message. The one-string-only match is	438	element (the tag) has been removed. The callback will use the same
360	also the most efficient match (by far).	439	environment as the default callback (see above).
361		440
362	Example: create a port and bind receivers on it in one go.	441	Example: create a port and bind receivers on it in one go.
363		442
364	my $port = rcv port,	443	my $port = rcv port,
365	msg1 => sub { ...; 0 },	444	msg1 => sub { ... },
366	msg2 => sub { ...; 0 },	445	msg2 => sub { ... },
367	;	446	;
368		447
369	Example: create a port, bind receivers and send it in a message elsewhere	448	Example: create a port, bind receivers and send it in a message elsewhere
370	in one go:	449	in one go:
371		450
372	snd $otherport, reply =>	451	snd $otherport, reply =>
373	rcv port,	452	rcv port,
374	msg1 => sub { ...; 0 },	453	msg1 => sub { ... },
375	...	454	...
376	;	455	;
377		456
		457	Example: temporarily register a rcv callback for a tag matching some port
		458	(e.g. for an rpc reply) and unregister it after a message was received.
		459
		460	rcv $port, $otherport => sub {
		461	my @reply = @_;
		462
		463	rcv $SELF, $otherport;
		464	};
		465
378	=cut	466	=cut
379		467
380	sub rcv($@) {	468	sub rcv($@) {
381	my $port = shift;	469	my $port = shift;
382	my ($noderef, $portid) = split /#/, $port, 2;	470	my ($nodeid, $portid) = split /#/, $port, 2;
383		471
384	($NODE{$noderef} || add_node $noderef) == $NODE{""}	472	$NODE{$nodeid} == $NODE{""}
385	or Carp::croak "$port: rcv can only be called on local ports, caught";	473	or Carp::croak "$port: rcv can only be called on local ports, caught";
386		474
387	if (@_ == 1) {	475	while (@_) {
		476	if (ref $_[0]) {
		477	if (my $self = $PORT_DATA{$portid}) {
		478	"AnyEvent::MP::Port" eq ref $self
		479	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		480
		481	$self->[0] = shift;
		482	} else {
388	my $cb = shift;	483	my $cb = shift;
389	delete $PORT_DATA{$portid};
390	$PORT{$portid} = sub {	484	$PORT{$portid} = sub {
391	local $SELF = $port;	485	local $SELF = $port;
392	eval {	486	eval { &$cb }; _self_die if $@;
393	&$cb	487	};
394	and kil $port;
395	};	488	}
396	_self_die if $@;	489	} elsif (defined $_[0]) {
397	};
398	} else {
399	my $self = $PORT_DATA{$portid} ||= do {	490	my $self = $PORT_DATA{$portid} ||= do {
400	my $self = bless {	491	my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port";
401	id => $port,
402	}, "AnyEvent::MP::Port";
403		492
404	$PORT{$portid} = sub {	493	$PORT{$portid} = sub {
405	local $SELF = $port;	494	local $SELF = $port;
406		495
407	eval {
408	for (@{ $self->{rc0}{$_[0]} }) {	496	if (my $cb = $self->[1]{$_[0]}) {
409	$_ && &{$_->[0]}	497	shift;
410	&& undef $_;	498	eval { &$cb }; _self_die if $@;
411	}	499	} else {
412
413	for (@{ $self->{rcv}{$_[0]} }) {
414	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
415	&& &{$_->[0]}	500	&{ $self->[0] };
416	&& undef $_;
417	}
418
419	for (@{ $self->{any} }) {
420	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
421	&& &{$_->[0]}
422	&& undef $_;
423	}	501	}
424	};	502	};
425	_self_die if $@;	503
		504	$self
426	};	505	};
427		506
428	$self
429	};
430
431	"AnyEvent::MP::Port" eq ref $self	507	"AnyEvent::MP::Port" eq ref $self
432	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	508	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
433		509
434	while (@_) {
435	my ($match, $cb) = splice @_, 0, 2;	510	my ($tag, $cb) = splice @_, 0, 2;
436		511
437	if (!ref $match) {	512	if (defined $cb) {
438	push @{ $self->{rc0}{$match} }, [$cb];	513	$self->[1]{$tag} = $cb;
439	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
440	my ($type, @match) = @$match;
441	@match
442	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
443	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
444	} else {	514	} else {
445	push @{ $self->{any} }, [$cb, $match];	515	delete $self->[1]{$tag};
446	}	516	}
447	}	517	}
448	}	518	}
449		519
450	$port	520	$port
451	}	521	}
452		522
		523	=item peval $port, $coderef[, @args]
		524
		525	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		526	when the code throews an exception the C<$port> will be killed.
		527
		528	Any remaining args will be passed to the callback. Any return values will
		529	be returned to the caller.
		530
		531	This is useful when you temporarily want to execute code in the context of
		532	a port.
		533
		534	Example: create a port and run some initialisation code in it's context.
		535
		536	my $port = port { ... };
		537
		538	peval $port, sub {
		539	init
		540	or die "unable to init";
		541	};
		542
		543	=cut
		544
		545	sub peval($$) {
		546	local $SELF = shift;
		547	my $cb = shift;
		548
		549	if (wantarray) {
		550	my @res = eval { &$cb };
		551	_self_die if $@;
		552	@res
		553	} else {
		554	my $res = eval { &$cb };
		555	_self_die if $@;
		556	$res
		557	}
		558	}
		559
453	=item $closure = psub { BLOCK }	560	=item $closure = psub { BLOCK }
454		561
455	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	562	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
456	closure is executed, sets up the environment in the same way as in C<rcv>	563	closure is executed, sets up the environment in the same way as in C<rcv>
457	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.	564	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		565
		566	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		567	BLOCK }, @_ } >>.
458		568
459	This is useful when you register callbacks from C<rcv> callbacks:	569	This is useful when you register callbacks from C<rcv> callbacks:
460		570
461	rcv delayed_reply => sub {	571	rcv delayed_reply => sub {
462	my ($delay, @reply) = @_;	572	my ($delay, @reply) = @_;
…		…
486	$res	596	$res
487	}	597	}
488	}	598	}
489	}	599	}
490		600
491	=item $guard = mon $port, $cb->(@reason)	601	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
492		602
493	=item $guard = mon $port, $rcvport	603	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
494		604
495	=item $guard = mon $port	605	=item $guard = mon $port # kill $SELF when $port dies
496		606
497	=item $guard = mon $port, $rcvport, @msg	607	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
498		608
499	Monitor the given port and do something when the port is killed, and	609	Monitor the given port and do something when the port is killed or
500	optionally return a guard that can be used to stop monitoring again.	610	messages to it were lost, and optionally return a guard that can be used
		611	to stop monitoring again.
501		612
502	In the first form (callback), the callback is simply called with any	613	In the first form (callback), the callback is simply called with any
503	number of C<@reason> elements (no @reason means that the port was deleted	614	number of C<@reason> elements (no @reason means that the port was deleted
504	"normally"). Note also that I<< the callback B<must> never die >>, so use	615	"normally"). Note also that I<< the callback B<must> never die >>, so use
505	C<eval> if unsure.	616	C<eval> if unsure.
506		617
507	In the second form (another port given), the other port (C<$rcvport)	618	In the second form (another port given), the other port (C<$rcvport>)
508	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	619	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
509	"normal" kils nothing happens, while under all other conditions, the other	620	"normal" kils nothing happens, while under all other conditions, the other
510	port is killed with the same reason.	621	port is killed with the same reason.
511		622
512	The third form (kill self) is the same as the second form, except that	623	The third form (kill self) is the same as the second form, except that
513	C<$rvport> defaults to C<$SELF>.	624	C<$rvport> defaults to C<$SELF>.
514		625
515	In the last form (message), a message of the form C<@msg, @reason> will be	626	In the last form (message), a message of the form C<@msg, @reason> will be
516	C<snd>.	627	C<snd>.
517		628
		629	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		630	alert was raised), they are removed and will not trigger again.
		631
		632	As a rule of thumb, monitoring requests should always monitor a port from
		633	a local port (or callback). The reason is that kill messages might get
		634	lost, just like any other message. Another less obvious reason is that
		635	even monitoring requests can get lost (for example, when the connection
		636	to the other node goes down permanently). When monitoring a port locally
		637	these problems do not exist.
		638
		639	C<mon> effectively guarantees that, in the absence of hardware failures,
		640	after starting the monitor, either all messages sent to the port will
		641	arrive, or the monitoring action will be invoked after possible message
		642	loss has been detected. No messages will be lost "in between" (after
		643	the first lost message no further messages will be received by the
		644	port). After the monitoring action was invoked, further messages might get
		645	delivered again.
		646
		647	Inter-host-connection timeouts and monitoring depend on the transport
		648	used. The only transport currently implemented is TCP, and AnyEvent::MP
		649	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		650	non-idle connection, and usually around two hours for idle connections).
		651
		652	This means that monitoring is good for program errors and cleaning up
		653	stuff eventually, but they are no replacement for a timeout when you need
		654	to ensure some maximum latency.
		655
518	Example: call a given callback when C<$port> is killed.	656	Example: call a given callback when C<$port> is killed.
519		657
520	mon $port, sub { warn "port died because of <@_>\n" };	658	mon $port, sub { warn "port died because of <@_>\n" };
521		659
522	Example: kill ourselves when C<$port> is killed abnormally.	660	Example: kill ourselves when C<$port> is killed abnormally.
…		…
528	mon $port, $self => "restart";	666	mon $port, $self => "restart";
529		667
530	=cut	668	=cut
531		669
532	sub mon {	670	sub mon {
533	my ($noderef, $port) = split /#/, shift, 2;	671	my ($nodeid, $port) = split /#/, shift, 2;
534		672
535	my $node = $NODE{$noderef} || add_node $noderef;	673	my $node = $NODE{$nodeid} || add_node $nodeid;
536		674
537	my $cb = @_ ? $_[0] : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';	675	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
538		676
539	unless (ref $cb) {	677	unless (ref $cb) {
540	if (@_) {	678	if (@_) {
541	# send a kill info message	679	# send a kill info message
542	my (@msg) = @_;	680	my (@msg) = ($cb, @_);
543	$cb = sub { snd @msg, @_ };	681	$cb = sub { snd @msg, @_ };
544	} else {	682	} else {
545	# simply kill other port	683	# simply kill other port
546	my $port = $cb;	684	my $port = $cb;
547	$cb = sub { kil $port, @_ if @_ };	685	$cb = sub { kil $port, @_ if @_ };
…		…
549	}	687	}
550		688
551	$node->monitor ($port, $cb);	689	$node->monitor ($port, $cb);
552		690
553	defined wantarray	691	defined wantarray
554	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	692	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
555	}	693	}
556		694
557	=item $guard = mon_guard $port, $ref, $ref...	695	=item $guard = mon_guard $port, $ref, $ref...
558		696
559	Monitors the given C<$port> and keeps the passed references. When the port	697	Monitors the given C<$port> and keeps the passed references. When the port
560	is killed, the references will be freed.	698	is killed, the references will be freed.
561		699
562	Optionally returns a guard that will stop the monitoring.	700	Optionally returns a guard that will stop the monitoring.
563		701
564	This function is useful when you create e.g. timers or other watchers and	702	This function is useful when you create e.g. timers or other watchers and
565	want to free them when the port gets killed:	703	want to free them when the port gets killed (note the use of C<psub>):
566		704
567	$port->rcv (start => sub {	705	$port->rcv (start => sub {
568	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	706	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
569	undef $timer if 0.9 < rand;	707	undef $timer if 0.9 < rand;
570	});	708	});
571	});	709	});
572		710
573	=cut	711	=cut
…		…
578	#TODO: mon-less form?	716	#TODO: mon-less form?
579		717
580	mon $port, sub { 0 && @refs }	718	mon $port, sub { 0 && @refs }
581	}	719	}
582		720
583	=item lnk $port1, $port2
584
585	=item lnk $otherport
586
587	Link two ports. This is simply a shorthand for:
588
589	mon $port1, $port2;
590	mon $port2, $port1;
591
592	It means that if either one is killed abnormally, the other one gets
593	killed as well.
594
595	The one-argument form assumes that one port is C<$SELF>.
596
597	=cut
598
599	sub lnk {
600	my $port1 = shift;
601	my $port2 = @_ ? shift : $SELF || Carp::croak 'lnk: called with one argument only, but $SELF not set,';
602
603	mon $port1, $port2;
604	mon $port2, $port1;
605	}
606
607	=item kil $port[, @reason]	721	=item kil $port[, @reason]
608		722
609	Kill the specified port with the given C<@reason>.	723	Kill the specified port with the given C<@reason>.
610		724
611	If no C<@reason> is specified, then the port is killed "normally" (linked	725	If no C<@reason> is specified, then the port is killed "normally" -
612	ports will not be kileld, or even notified).	726	monitor callback will be invoked, but the kil will not cause linked ports
		727	(C<mon $mport, $lport> form) to get killed.
613		728
614	Otherwise, linked ports get killed with the same reason (second form of	729	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
615	C<mon>, see below).	730	form) get killed with the same reason.
616		731
617	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	732	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
618	will be reported as reason C<< die => $@ >>.	733	will be reported as reason C<< die => $@ >>.
619		734
620	Transport/communication errors are reported as C<< transport_error =>	735	Transport/communication errors are reported as C<< transport_error =>
621	$message >>.	736	$message >>.
622		737
		738	Common idioms:
		739
		740	# silently remove yourself, do not kill linked ports
		741	kil $SELF;
		742
		743	# report a failure in some detail
		744	kil $SELF, failure_mode_1 => "it failed with too high temperature";
		745
		746	# do not waste much time with killing, just die when something goes wrong
		747	open my $fh, "<file"
		748	or die "file: $!";
		749
		750	=item $port = spawn $node, $initfunc[, @initdata]
		751
		752	Creates a port on the node C<$node> (which can also be a port ID, in which
		753	case it's the node where that port resides).
		754
		755	The port ID of the newly created port is returned immediately, and it is
		756	possible to immediately start sending messages or to monitor the port.
		757
		758	After the port has been created, the init function is called on the remote
		759	node, in the same context as a C<rcv> callback. This function must be a
		760	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		761	specify a function in the main program, use C<::name>.
		762
		763	If the function doesn't exist, then the node tries to C<require>
		764	the package, then the package above the package and so on (e.g.
		765	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		766	exists or it runs out of package names.
		767
		768	The init function is then called with the newly-created port as context
		769	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		770	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		771	the port might not get created.
		772
		773	A common idiom is to pass a local port, immediately monitor the spawned
		774	port, and in the remote init function, immediately monitor the passed
		775	local port. This two-way monitoring ensures that both ports get cleaned up
		776	when there is a problem.
		777
		778	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		779	caller before C<spawn> returns (by delaying invocation when spawn is
		780	called for the local node).
		781
		782	Example: spawn a chat server port on C<$othernode>.
		783
		784	# this node, executed from within a port context:
		785	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		786	mon $server;
		787
		788	# init function on C<$othernode>
		789	sub connect {
		790	my ($srcport) = @_;
		791
		792	mon $srcport;
		793
		794	rcv $SELF, sub {
		795	...
		796	};
		797	}
		798
		799	=cut
		800
		801	sub _spawn {
		802	my $port = shift;
		803	my $init = shift;
		804
		805	# rcv will create the actual port
		806	local $SELF = "$NODE#$port";
		807	eval {
		808	&{ load_func $init }
		809	};
		810	_self_die if $@;
		811	}
		812
		813	sub spawn(@) {
		814	my ($nodeid, undef) = split /#/, shift, 2;
		815
		816	my $id = $RUNIQ . ++$ID;
		817
		818	$_[0] =~ /::/
		819	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		820
		821	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		822
		823	"$nodeid#$id"
		824	}
		825
		826
		827	=item after $timeout, @msg
		828
		829	=item after $timeout, $callback
		830
		831	Either sends the given message, or call the given callback, after the
		832	specified number of seconds.
		833
		834	This is simply a utility function that comes in handy at times - the
		835	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		836	so it may go away in the future.
		837
		838	=cut
		839
		840	sub after($@) {
		841	my ($timeout, @action) = @_;
		842
		843	my $t; $t = AE::timer $timeout, 0, sub {
		844	undef $t;
		845	ref $action[0]
		846	? $action[0]()
		847	: snd @action;
		848	};
		849	}
		850
		851	#=item $cb2 = timeout $seconds, $cb[, @args]
		852
		853	=item cal $port, @msg, $callback[, $timeout]
		854
		855	A simple form of RPC - sends a message to the given C<$port> with the
		856	given contents (C<@msg>), but adds a reply port to the message.
		857
		858	The reply port is created temporarily just for the purpose of receiving
		859	the reply, and will be C<kil>ed when no longer needed.
		860
		861	A reply message sent to the port is passed to the C<$callback> as-is.
		862
		863	If an optional time-out (in seconds) is given and it is not C<undef>,
		864	then the callback will be called without any arguments after the time-out
		865	elapsed and the port is C<kil>ed.
		866
		867	If no time-out is given (or it is C<undef>), then the local port will
		868	monitor the remote port instead, so it eventually gets cleaned-up.
		869
		870	Currently this function returns the temporary port, but this "feature"
		871	might go in future versions unless you can make a convincing case that
		872	this is indeed useful for something.
		873
		874	=cut
		875
		876	sub cal(@) {
		877	my $timeout = ref $_[-1] ? undef : pop;
		878	my $cb = pop;
		879
		880	my $port = port {
		881	undef $timeout;
		882	kil $SELF;
		883	&$cb;
		884	};
		885
		886	if (defined $timeout) {
		887	$timeout = AE::timer $timeout, 0, sub {
		888	undef $timeout;
		889	kil $port;
		890	$cb->();
		891	};
		892	} else {
		893	mon $_[0], sub {
		894	kil $port;
		895	$cb->();
		896	};
		897	}
		898
		899	push @_, $port;
		900	&snd;
		901
		902	$port
		903	}
		904
623	=back	905	=back
624		906
625	=head1 NODE MESSAGES	907	=head1 DISTRIBUTED DATABASE
626		908
627	Nodes understand the following messages sent to them. Many of them take	909	AnyEvent::MP comes with a simple distributed database. The database will
628	arguments called C<@reply>, which will simply be used to compose a reply	910	be mirrored asynchronously on all global nodes. Other nodes bind to one
629	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and	911	of the global nodes for their needs. Every node has a "local database"
630	the remaining arguments are simply the message data.	912	which contains all the values that are set locally. All local databases
		913	are merged together to form the global database, which can be queried.
631		914
632	While other messages exist, they are not public and subject to change.	915	The database structure is that of a two-level hash - the database hash
		916	contains hashes which contain values, similarly to a perl hash of hashes,
		917	i.e.:
633		918
		919	$DATABASE{$family}{$subkey} = $value
		920
		921	The top level hash key is called "family", and the second-level hash key
		922	is called "subkey" or simply "key".
		923
		924	The family must be alphanumeric, i.e. start with a letter and consist
		925	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		926	pretty much like Perl module names.
		927
		928	As the family namespace is global, it is recommended to prefix family names
		929	with the name of the application or module using it.
		930
		931	The subkeys must be non-empty strings, with no further restrictions.
		932
		933	The values should preferably be strings, but other perl scalars should
		934	work as well (such as C<undef>, arrays and hashes).
		935
		936	Every database entry is owned by one node - adding the same family/subkey
		937	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		938	but the result might be nondeterministic, i.e. the key might have
		939	different values on different nodes.
		940
		941	Different subkeys in the same family can be owned by different nodes
		942	without problems, and in fact, this is the common method to create worker
		943	pools. For example, a worker port for image scaling might do this:
		944
		945	db_set my_image_scalers => $port;
		946
		947	And clients looking for an image scaler will want to get the
		948	C<my_image_scalers> keys from time to time:
		949
		950	db_keys my_image_scalers => sub {
		951	@ports = @{ $_[0] };
		952	};
		953
		954	Or better yet, they want to monitor the database family, so they always
		955	have a reasonable up-to-date copy:
		956
		957	db_mon my_image_scalers => sub {
		958	@ports = keys %{ $_[0] };
		959	};
		960
		961	In general, you can set or delete single subkeys, but query and monitor
		962	whole families only.
		963
		964	If you feel the need to monitor or query a single subkey, try giving it
		965	it's own family.
		966
634	=over 4	967	=over
		968
		969	=item db_set $family => $subkey [=> $value]
		970
		971	Sets (or replaces) a key to the database - if C<$value> is omitted,
		972	C<undef> is used instead.
		973
		974	=item db_del $family => $subkey...
		975
		976	Deletes one or more subkeys from the database family.
		977
		978	=item $guard = db_reg $family => $subkey [=> $value]
		979
		980	Sets the key on the database and returns a guard. When the guard is
		981	destroyed, the key is deleted from the database. If C<$value> is missing,
		982	then C<undef> is used.
		983
		984	=item db_family $family => $cb->(\%familyhash)
		985
		986	Queries the named database C<$family> and call the callback with the
		987	family represented as a hash. You can keep and freely modify the hash.
		988
		989	=item db_keys $family => $cb->(\@keys)
		990
		991	Same as C<db_family>, except it only queries the family I<subkeys> and passes
		992	them as array reference to the callback.
		993
		994	=item db_values $family => $cb->(\@values)
		995
		996	Same as C<db_family>, except it only queries the family I<values> and passes them
		997	as array reference to the callback.
		998
		999	=item $guard = db_mon $family => $cb->($familyhash, \@added, \@changed, \@deleted)
		1000
		1001	Creates a monitor on the given database family. Each time a key is set
		1002	or or is deleted the callback is called with a hash containing the
		1003	database family and three lists of added, changed and deleted subkeys,
		1004	respectively. If no keys have changed then the array reference might be
		1005	C<undef> or even missing.
		1006
		1007	If not called in void context, a guard object is returned that, when
		1008	destroyed, stops the monitor.
		1009
		1010	The family hash reference and the key arrays belong to AnyEvent::MP and
		1011	B<must not be modified or stored> by the callback. When in doubt, make a
		1012	copy.
		1013
		1014	As soon as possible after the monitoring starts, the callback will be
		1015	called with the intiial contents of the family, even if it is empty,
		1016	i.e. there will always be a timely call to the callback with the current
		1017	contents.
		1018
		1019	It is possible that the callback is called with a change event even though
		1020	the subkey is already present and the value has not changed.
		1021
		1022	The monitoring stops when the guard object is destroyed.
		1023
		1024	Example: on every change to the family "mygroup", print out all keys.
		1025
		1026	my $guard = db_mon mygroup => sub {
		1027	my ($family, $a, $c, $d) = @_;
		1028	print "mygroup members: ", (join " ", keys %$family), "\n";
		1029	};
		1030
		1031	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1032
		1033	my $guard; $guard = db_mon My::Module::workers => sub {
		1034	my ($family, $a, $c, $d) = @_;
		1035	return unless %$family;
		1036	undef $guard;
		1037	print "My::Module::workers now nonempty\n";
		1038	};
		1039
		1040	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		1041
		1042	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		1043	my ($family, $a, $c, $d) = @_;
		1044
		1045	print "+$_=$family->{$_}\n" for @$a;
		1046	print "*$_=$family->{$_}\n" for @$c;
		1047	print "-$_=$family->{$_}\n" for @$d;
		1048	};
635		1049
636	=cut	1050	=cut
637
638	=item lookup => $name, @reply
639
640	Replies with the port ID of the specified well-known port, or C<undef>.
641
642	=item devnull => ...
643
644	Generic data sink/CPU heat conversion.
645
646	=item relay => $port, @msg
647
648	Simply forwards the message to the given port.
649
650	=item eval => $string[ @reply]
651
652	Evaluates the given string. If C<@reply> is given, then a message of the
653	form C<@reply, $@, @evalres> is sent.
654
655	Example: crash another node.
656
657	snd $othernode, eval => "exit";
658
659	=item time => @reply
660
661	Replies the the current node time to C<@reply>.
662
663	Example: tell the current node to send the current time to C<$myport> in a
664	C<timereply> message.
665
666	snd $NODE, time => $myport, timereply => 1, 2;
667	# => snd $myport, timereply => 1, 2, <time>
668		1051
669	=back	1052	=back
670		1053
671	=head1 AnyEvent::MP vs. Distributed Erlang	1054	=head1 AnyEvent::MP vs. Distributed Erlang
672		1055
673	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	1056	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
674	== aemp node, Erlang process == aemp port), so many of the documents and	1057	== aemp node, Erlang process == aemp port), so many of the documents and
675	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	1058	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
676	sample:	1059	sample:
677		1060
678	http://www.Erlang.se/doc/programming_rules.shtml	1061	http://www.erlang.se/doc/programming_rules.shtml
679	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	1062	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
680	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	1063	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
681	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	1064	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
682		1065
683	Despite the similarities, there are also some important differences:	1066	Despite the similarities, there are also some important differences:
684		1067
685	=over 4	1068	=over 4
686		1069
687	=item * Node references contain the recipe on how to contact them.	1070	=item * Node IDs are arbitrary strings in AEMP.
688		1071
689	Erlang relies on special naming and DNS to work everywhere in the	1072	Erlang relies on special naming and DNS to work everywhere in the same
690	same way. AEMP relies on each node knowing it's own address(es), with	1073	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
691	convenience functionality.	1074	configuration or DNS), and possibly the addresses of some seed nodes, but
		1075	will otherwise discover other nodes (and their IDs) itself.
692		1076
693	This means that AEMP requires a less tightly controlled environment at the	1077	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
694	cost of longer node references and a slightly higher management overhead.	1078	uses "local ports are like remote ports".
		1079
		1080	The failure modes for local ports are quite different (runtime errors
		1081	only) then for remote ports - when a local port dies, you I<know> it dies,
		1082	when a connection to another node dies, you know nothing about the other
		1083	port.
		1084
		1085	Erlang pretends remote ports are as reliable as local ports, even when
		1086	they are not.
		1087
		1088	AEMP encourages a "treat remote ports differently" philosophy, with local
		1089	ports being the special case/exception, where transport errors cannot
		1090	occur.
695		1091
696	=item * Erlang uses processes and a mailbox, AEMP does not queue.	1092	=item * Erlang uses processes and a mailbox, AEMP does not queue.
697		1093
698	Erlang uses processes that selctively receive messages, and therefore	1094	Erlang uses processes that selectively receive messages out of order, and
699	needs a queue. AEMP is event based, queuing messages would serve no useful	1095	therefore needs a queue. AEMP is event based, queuing messages would serve
700	purpose.	1096	no useful purpose. For the same reason the pattern-matching abilities
		1097	of AnyEvent::MP are more limited, as there is little need to be able to
		1098	filter messages without dequeuing them.
701		1099
702	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	1100	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1101	being event-based, while Erlang is process-based.
		1102
		1103	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1104	top of AEMP and Coro threads.
703		1105
704	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1106	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
705		1107
706	Sending messages in Erlang is synchronous and blocks the process. AEMP	1108	Sending messages in Erlang is synchronous and blocks the process until
707	sends are immediate, connection establishment is handled in the	1109	a conenction has been established and the message sent (and so does not
708	background.	1110	need a queue that can overflow). AEMP sends return immediately, connection
		1111	establishment is handled in the background.
709		1112
710	=item * Erlang can silently lose messages, AEMP cannot.	1113	=item * Erlang suffers from silent message loss, AEMP does not.
711		1114
712	Erlang makes few guarantees on messages delivery - messages can get lost	1115	Erlang implements few guarantees on messages delivery - messages can get
713	without any of the processes realising it (i.e. you send messages a, b,	1116	lost without any of the processes realising it (i.e. you send messages a,
714	and c, and the other side only receives messages a and c).	1117	b, and c, and the other side only receives messages a and c).
715		1118
716	AEMP guarantees correct ordering, and the guarantee that there are no	1119	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1120	guarantee that after one message is lost, all following ones sent to the
		1121	same port are lost as well, until monitoring raises an error, so there are
717	holes in the message sequence.	1122	no silent "holes" in the message sequence.
718		1123
719	=item * In Erlang, processes can be declared dead and later be found to be	1124	If you want your software to be very reliable, you have to cope with
720	alive.	1125	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
721		1126	simply tries to work better in common error cases, such as when a network
722	In Erlang it can happen that a monitored process is declared dead and	1127	link goes down.
723	linked processes get killed, but later it turns out that the process is
724	still alive - and can receive messages.
725
726	In AEMP, when port monitoring detects a port as dead, then that port will
727	eventually be killed - it cannot happen that a node detects a port as dead
728	and then later sends messages to it, finding it is still alive.
729		1128
730	=item * Erlang can send messages to the wrong port, AEMP does not.	1129	=item * Erlang can send messages to the wrong port, AEMP does not.
731		1130
732	In Erlang it is quite possible that a node that restarts reuses a process	1131	In Erlang it is quite likely that a node that restarts reuses an Erlang
733	ID known to other nodes for a completely different process, causing	1132	process ID known to other nodes for a completely different process,
734	messages destined for that process to end up in an unrelated process.	1133	causing messages destined for that process to end up in an unrelated
		1134	process.
735		1135
736	AEMP never reuses port IDs, so old messages or old port IDs floating	1136	AEMP does not reuse port IDs, so old messages or old port IDs floating
737	around in the network will not be sent to an unrelated port.	1137	around in the network will not be sent to an unrelated port.
738		1138
739	=item * Erlang uses unprotected connections, AEMP uses secure	1139	=item * Erlang uses unprotected connections, AEMP uses secure
740	authentication and can use TLS.	1140	authentication and can use TLS.
741		1141
742	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1142	AEMP can use a proven protocol - TLS - to protect connections and
743	securely authenticate nodes.	1143	securely authenticate nodes.
744		1144
745	=item * The AEMP protocol is optimised for both text-based and binary	1145	=item * The AEMP protocol is optimised for both text-based and binary
746	communications.	1146	communications.
747		1147
748	The AEMP protocol, unlike the Erlang protocol, supports both	1148	The AEMP protocol, unlike the Erlang protocol, supports both programming
749	language-independent text-only protocols (good for debugging) and binary,	1149	language independent text-only protocols (good for debugging), and binary,
750	language-specific serialisers (e.g. Storable).	1150	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1151	used, the protocol is actually completely text-based.
751		1152
752	It has also been carefully designed to be implementable in other languages	1153	It has also been carefully designed to be implementable in other languages
753	with a minimum of work while gracefully degrading fucntionality to make the	1154	with a minimum of work while gracefully degrading functionality to make the
754	protocol simple.	1155	protocol simple.
755		1156
756	=item * AEMP has more flexible monitoring options than Erlang.	1157	=item * AEMP has more flexible monitoring options than Erlang.
757		1158
758	In Erlang, you can chose to receive I<all> exit signals as messages	1159	In Erlang, you can chose to receive I<all> exit signals as messages or
759	or I<none>, there is no in-between, so monitoring single processes is	1160	I<none>, there is no in-between, so monitoring single Erlang processes is
760	difficult to implement. Monitoring in AEMP is more flexible than in	1161	difficult to implement.
761	Erlang, as one can choose between automatic kill, exit message or callback
762	on a per-process basis.
763		1162
764	=item * Erlang has different semantics for monitoring and linking, AEMP has the same.	1163	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1164	between automatic kill, exit message or callback on a per-port basis.
765		1165
		1166	=item * Erlang tries to hide remote/local connections, AEMP does not.
		1167
766	Monitoring in Erlang is not an indicator of process death/crashes,	1168	Monitoring in Erlang is not an indicator of process death/crashes, in the
767	as linking is (except linking is unreliable in Erlang). In AEMP, the	1169	same way as linking is (except linking is unreliable in Erlang).
768	semantics of monitoring and linking are identical, linking is simply	1170
769	two-way monitoring with automatic kill.	1171	In AEMP, you don't "look up" registered port names or send to named ports
		1172	that might or might not be persistent. Instead, you normally spawn a port
		1173	on the remote node. The init function monitors you, and you monitor the
		1174	remote port. Since both monitors are local to the node, they are much more
		1175	reliable (no need for C<spawn_link>).
		1176
		1177	This also saves round-trips and avoids sending messages to the wrong port
		1178	(hard to do in Erlang).
770		1179
771	=back	1180	=back
772		1181
		1182	=head1 RATIONALE
		1183
		1184	=over 4
		1185
		1186	=item Why strings for port and node IDs, why not objects?
		1187
		1188	We considered "objects", but found that the actual number of methods
		1189	that can be called are quite low. Since port and node IDs travel over
		1190	the network frequently, the serialising/deserialising would add lots of
		1191	overhead, as well as having to keep a proxy object everywhere.
		1192
		1193	Strings can easily be printed, easily serialised etc. and need no special
		1194	procedures to be "valid".
		1195
		1196	And as a result, a port with just a default receiver consists of a single
		1197	code reference stored in a global hash - it can't become much cheaper.
		1198
		1199	=item Why favour JSON, why not a real serialising format such as Storable?
		1200
		1201	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1202	format, but currently there is no way to make a node use Storable by
		1203	default (although all nodes will accept it).
		1204
		1205	The default framing protocol is JSON because a) JSON::XS is many times
		1206	faster for small messages and b) most importantly, after years of
		1207	experience we found that object serialisation is causing more problems
		1208	than it solves: Just like function calls, objects simply do not travel
		1209	easily over the network, mostly because they will always be a copy, so you
		1210	always have to re-think your design.
		1211
		1212	Keeping your messages simple, concentrating on data structures rather than
		1213	objects, will keep your messages clean, tidy and efficient.
		1214
		1215	=back
		1216
773	=head1 SEE ALSO	1217	=head1 SEE ALSO
		1218
		1219	L<AnyEvent::MP::Intro> - a gentle introduction.
		1220
		1221	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1222
		1223	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1224	your applications.
		1225
		1226	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1227
		1228	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1229	all nodes.
774		1230
775	L<AnyEvent>.	1231	L<AnyEvent>.
776		1232
777	=head1 AUTHOR	1233	=head1 AUTHOR
778		1234

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