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Revision 1.29 by root, Tue Aug 4 23:16:57 2009 UTC vs.
Revision 1.150 by root, Wed Aug 17 19:45:18 2016 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	34
		35	# destroy a port again
		36	kil $port; # "normal" kill
		37	kil $port, my_error => "everything is broken"; # error kill
		38
		39	# monitoring
		40	mon $port, $cb->(@msg) # callback is invoked on death
		41	mon $port, $localport # kill localport on abnormal 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	# distributed database - modification
		53	db_set $family => $subkey [=> $value] # add a subkey
		54	db_del $family => $subkey... # delete one or more subkeys
		55	db_reg $family => $port [=> $value] # register a port
		56
		57	# distributed database - queries
		58	db_family $family => $cb->(\%familyhash)
		59	db_keys $family => $cb->(\@keys)
		60	db_values $family => $cb->(\@values)
		61
		62	# distributed database - monitoring a family
		63	db_mon $family => $cb->(\%familyhash, \@added, \@changed, \@deleted)
27		64
28	=head1 DESCRIPTION	65	=head1 DESCRIPTION
29		66
30	This module (-family) implements a simple message passing framework.	67	This module (-family) implements a simple message passing framework.
31		68
32	Despite its simplicity, you can securely message other processes running	69	Despite its simplicity, you can securely message other processes running
33	on the same or other hosts.	70	on the same or other hosts, and you can supervise entities remotely.
34		71
35	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	72	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
36	manual page.	73	manual page and the examples under F<eg/>.
37
38	At the moment, this module family is severly broken and underdocumented,
39	so do not use. This was uploaded mainly to reserve the CPAN namespace -
40	stay tuned! The basic API should be finished, however.
41		74
42	=head1 CONCEPTS	75	=head1 CONCEPTS
43		76
44	=over 4	77	=over 4
45		78
46	=item port	79	=item port
47		80
48	A port is something you can send messages to (with the C<snd> function).	81	Not to be confused with a TCP port, a "port" is something you can send
		82	messages to (with the C<snd> function).
49		83
50	Some ports allow you to register C<rcv> handlers that can match specific	84	Ports allow you to register C<rcv> handlers that can match all or just
51	messages. All C<rcv> handlers will receive messages they match, messages	85	some messages. Messages send to ports will not be queued, regardless of
52	will not be queued.	86	anything was listening for them or not.
53		87
		88	Ports are represented by (printable) strings called "port IDs".
		89
54	=item port id - C<noderef#portname>	90	=item port ID - C<nodeid#portname>
55		91
56	A port id is normaly the concatenation of a noderef, a hash-mark (C<#>) as	92	A port ID is the concatenation of a node ID, a hash-mark (C<#>)
57	separator, and a port name (a printable string of unspecified format). An	93	as separator, and a port name (a printable string of unspecified
58	exception is the the node port, whose ID is identical to it's node	94	format created by AnyEvent::MP).
59	reference.
60		95
61	=item node	96	=item node
62		97
63	A node is a single process containing at least one port - the node	98	A node is a single process containing at least one port - the node port,
64	port. You can send messages to node ports to find existing ports or to	99	which enables nodes to manage each other remotely, and to create new
65	create new ports, among other things.	100	ports.
66		101
67	Nodes are either private (single-process only), slaves (connected to a	102	Nodes are either public (have one or more listening ports) or private
68	master node only) or public nodes (connectable from unrelated nodes).	103	(no listening ports). Private nodes cannot talk to other private nodes
		104	currently, but all nodes can talk to public nodes.
69		105
70	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	106	Nodes is represented by (printable) strings called "node IDs".
71		107
72	A node reference is a string that either simply identifies the node (for	108	=item node ID - C<[A-Za-z0-9_\-.:]*>
73	private and slave nodes), or contains a recipe on how to reach a given
74	node (for public nodes).
75		109
76	This recipe is simply a comma-separated list of C<address:port> pairs (for	110	A node ID is a string that uniquely identifies the node within a
77	TCP/IP, other protocols might look different).	111	network. Depending on the configuration used, node IDs can look like a
		112	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		113	doesn't interpret node IDs in any way except to uniquely identify a node.
78		114
79	Node references come in two flavours: resolved (containing only numerical	115	=item binds - C<ip:port>
80	addresses) or unresolved (where hostnames are used instead of addresses).
81		116
82	Before using an unresolved node reference in a message you first have to	117	Nodes can only talk to each other by creating some kind of connection to
83	resolve it.	118	each other. To do this, nodes should listen on one or more local transport
		119	endpoints - binds.
		120
		121	Currently, only standard C<ip:port> specifications can be used, which
		122	specify TCP ports to listen on. So a bind is basically just a tcp socket
		123	in listening mode that accepts connections from other nodes.
		124
		125	=item seed nodes
		126
		127	When a node starts, it knows nothing about the network it is in - it
		128	needs to connect to at least one other node that is already in the
		129	network. These other nodes are called "seed nodes".
		130
		131	Seed nodes themselves are not special - they are seed nodes only because
		132	some other node I<uses> them as such, but any node can be used as seed
		133	node for other nodes, and eahc node can use a different set of seed nodes.
		134
		135	In addition to discovering the network, seed nodes are also used to
		136	maintain the network - all nodes using the same seed node are part of the
		137	same network. If a network is split into multiple subnets because e.g. the
		138	network link between the parts goes down, then using the same seed nodes
		139	for all nodes ensures that eventually the subnets get merged again.
		140
		141	Seed nodes are expected to be long-running, and at least one seed node
		142	should always be available. They should also be relatively responsive - a
		143	seed node that blocks for long periods will slow down everybody else.
		144
		145	For small networks, it's best if every node uses the same set of seed
		146	nodes. For large networks, it can be useful to specify "regional" seed
		147	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		148	each other. What's important is that all seed nodes connections form a
		149	complete graph, so that the network cannot split into separate subnets
		150	forever.
		151
		152	Seed nodes are represented by seed IDs.
		153
		154	=item seed IDs - C<host:port>
		155
		156	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
		157	TCP port) of nodes that should be used as seed nodes.
		158
		159	=item global nodes
		160
		161	An AEMP network needs a discovery service - nodes need to know how to
		162	connect to other nodes they only know by name. In addition, AEMP offers a
		163	distributed "group database", which maps group names to a list of strings
		164	- for example, to register worker ports.
		165
		166	A network needs at least one global node to work, and allows every node to
		167	be a global node.
		168
		169	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		170	node and tries to keep connections to all other nodes. So while it can
		171	make sense to make every node "global" in small networks, it usually makes
		172	sense to only make seed nodes into global nodes in large networks (nodes
		173	keep connections to seed nodes and global nodes, so making them the same
		174	reduces overhead).
84		175
85	=back	176	=back
86		177
87	=head1 VARIABLES/FUNCTIONS	178	=head1 VARIABLES/FUNCTIONS
88		179
…		…
90		181
91	=cut	182	=cut
92		183
93	package AnyEvent::MP;	184	package AnyEvent::MP;
94		185
		186	use AnyEvent::MP::Config ();
95	use AnyEvent::MP::Base;	187	use AnyEvent::MP::Kernel;
		188	use AnyEvent::MP::Kernel qw(
		189	%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID
		190	add_node load_func
		191
		192	NODE $NODE
		193	configure
		194	node_of port_is_local
		195	snd kil
		196	db_set db_del
		197	db_mon db_family db_keys db_values
		198	);
96		199
97	use common::sense;	200	use common::sense;
98		201
99	use Carp ();	202	use Carp ();
100		203
101	use AE ();	204	use AnyEvent ();
		205	use Guard ();
102		206
103	use base "Exporter";	207	use base "Exporter";
104		208
105	our $VERSION = '0.1';	209	our $VERSION = $AnyEvent::MP::Config::VERSION;
		210
106	our @EXPORT = qw(	211	our @EXPORT = qw(
107	NODE $NODE *SELF node_of _any_	212	NODE $NODE
108	resolve_node	213	configure
109	become_slave become_public	214	node_of port_is_local
110	snd rcv mon kil reg psub	215	snd kil
111	port	216	db_set db_del
		217	db_mon db_family db_keys db_values
		218
		219	*SELF
		220
		221	port rcv mon mon_guard psub peval spawn cal
		222	db_set db_del db_reg
		223	db_mon db_family db_keys db_values
		224
		225	after
112	);	226	);
113		227
114	our $SELF;	228	our $SELF;
115		229
116	sub _self_die() {	230	sub _self_die() {
…		…
119	kil $SELF, die => $msg;	233	kil $SELF, die => $msg;
120	}	234	}
121		235
122	=item $thisnode = NODE / $NODE	236	=item $thisnode = NODE / $NODE
123		237
124	The C<NODE> function returns, and the C<$NODE> variable contains	238	The C<NODE> function returns, and the C<$NODE> variable contains, the node
125	the noderef of the local node. The value is initialised by a call	239	ID of the node running in the current process. This value is initialised by
126	to C<become_public> or C<become_slave>, after which all local port	240	a call to C<configure>.
127	identifiers become invalid.
128		241
129	=item $noderef = node_of $portid	242	=item $nodeid = node_of $port
130		243
131	Extracts and returns the noderef from a portid or a noderef.	244	Extracts and returns the node ID from a port ID or a node ID.
132		245
133	=item $cv = resolve_node $noderef	246	=item $is_local = port_is_local $port
134		247
135	Takes an unresolved node reference that may contain hostnames and	248	Returns true iff the port is a local port.
136	abbreviated IDs, resolves all of them and returns a resolved node
137	reference.
138		249
139	In addition to C<address:port> pairs allowed in resolved noderefs, the	250	=item configure $profile, key => value...
140	following forms are supported:	251
		252	=item configure key => value...
		253
		254	Before a node can talk to other nodes on the network (i.e. enter
		255	"distributed mode") it has to configure itself - the minimum a node needs
		256	to know is its own name, and optionally it should know the addresses of
		257	some other nodes in the network to discover other nodes.
		258
		259	This function configures a node - it must be called exactly once (or
		260	never) before calling other AnyEvent::MP functions.
		261
		262	The key/value pairs are basically the same ones as documented for the
		263	F<aemp> command line utility (sans the set/del prefix), with these additions:
141		264
142	=over 4	265	=over 4
143		266
144	=item the empty string	267	=item norc => $boolean (default false)
145		268
146	An empty-string component gets resolved as if the default port (4040) was	269	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
147	specified.	270	be consulted - all configuration options must be specified in the
		271	C<configure> call.
148		272
149	=item naked port numbers (e.g. C<1234>)	273	=item force => $boolean (default false)
150		274
151	These are resolved by prepending the local nodename and a colon, to be	275	IF true, then the values specified in the C<configure> will take
152	further resolved.	276	precedence over any values configured via the rc file. The default is for
153		277	the rc file to override any options specified in the program.
154	=item hostnames (e.g. C<localhost:1234>, C<localhost>)
155
156	These are resolved by using AnyEvent::DNS to resolve them, optionally
157	looking up SRV records for the C<aemp=4040> port, if no port was
158	specified.
159		278
160	=back	279	=back
		280
		281	=over 4
		282
		283	=item step 1, gathering configuration from profiles
		284
		285	The function first looks up a profile in the aemp configuration (see the
		286	L<aemp> commandline utility). The profile name can be specified via the
		287	named C<profile> parameter or can simply be the first parameter). If it is
		288	missing, then the nodename (F<uname -n>) will be used as profile name.
		289
		290	The profile data is then gathered as follows:
		291
		292	First, all remaining key => value pairs (all of which are conveniently
		293	undocumented at the moment) will be interpreted as configuration
		294	data. Then they will be overwritten by any values specified in the global
		295	default configuration (see the F<aemp> utility), then the chain of
		296	profiles chosen by the profile name (and any C<parent> attributes).
		297
		298	That means that the values specified in the profile have highest priority
		299	and the values specified directly via C<configure> have lowest priority,
		300	and can only be used to specify defaults.
		301
		302	If the profile specifies a node ID, then this will become the node ID of
		303	this process. If not, then the profile name will be used as node ID, with
		304	a unique randoms tring (C</%u>) appended.
		305
		306	The node ID can contain some C<%> sequences that are expanded: C<%n>
		307	is expanded to the local nodename, C<%u> is replaced by a random
		308	strign to make the node unique. For example, the F<aemp> commandline
		309	utility uses C<aemp/%n/%u> as nodename, which might expand to
		310	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		311
		312	=item step 2, bind listener sockets
		313
		314	The next step is to look up the binds in the profile, followed by binding
		315	aemp protocol listeners on all binds specified (it is possible and valid
		316	to have no binds, meaning that the node cannot be contacted from the
		317	outside. This means the node cannot talk to other nodes that also have no
		318	binds, but it can still talk to all "normal" nodes).
		319
		320	If the profile does not specify a binds list, then a default of C<*> is
		321	used, meaning the node will bind on a dynamically-assigned port on every
		322	local IP address it finds.
		323
		324	=item step 3, connect to seed nodes
		325
		326	As the last step, the seed ID list from the profile is passed to the
		327	L<AnyEvent::MP::Global> module, which will then use it to keep
		328	connectivity with at least one node at any point in time.
		329
		330	=back
		331
		332	Example: become a distributed node using the local node name as profile.
		333	This should be the most common form of invocation for "daemon"-type nodes.
		334
		335	configure
		336
		337	Example: become a semi-anonymous node. This form is often used for
		338	commandline clients.
		339
		340	configure nodeid => "myscript/%n/%u";
		341
		342	Example: configure a node using a profile called seed, which is suitable
		343	for a seed node as it binds on all local addresses on a fixed port (4040,
		344	customary for aemp).
		345
		346	# use the aemp commandline utility
		347	# aemp profile seed binds '*:4040'
		348
		349	# then use it
		350	configure profile => "seed";
		351
		352	# or simply use aemp from the shell again:
		353	# aemp run profile seed
		354
		355	# or provide a nicer-to-remember nodeid
		356	# aemp run profile seed nodeid "$(hostname)"
161		357
162	=item $SELF	358	=item $SELF
163		359
164	Contains the current port id while executing C<rcv> callbacks or C<psub>	360	Contains the current port id while executing C<rcv> callbacks or C<psub>
165	blocks.	361	blocks.
166		362
167	=item SELF, %SELF, @SELF...	363	=item *SELF, SELF, %SELF, @SELF...
168		364
169	Due to some quirks in how perl exports variables, it is impossible to	365	Due to some quirks in how perl exports variables, it is impossible to
170	just export C<$SELF>, all the symbols called C<SELF> are exported by this	366	just export C<$SELF>, all the symbols named C<SELF> are exported by this
171	module, but only C<$SELF> is currently used.	367	module, but only C<$SELF> is currently used.
172		368
173	=item snd $portid, type => @data	369	=item snd $port, type => @data
174		370
175	=item snd $portid, @msg	371	=item snd $port, @msg
176		372
177	Send the given message to the given port ID, which can identify either	373	Send the given message to the given port, which can identify either a
178	a local or a remote port, and can be either a string or soemthignt hat	374	local or a remote port, and must be a port ID.
179	stringifies a sa port ID (such as a port object :).
180		375
181	While the message can be about anything, it is highly recommended to use a	376	While the message can be almost anything, it is highly recommended to
182	string as first element (a portid, or some word that indicates a request	377	use a string as first element (a port ID, or some word that indicates a
183	type etc.).	378	request type etc.) and to consist if only simple perl values (scalars,
		379	arrays, hashes) - if you think you need to pass an object, think again.
184		380
185	The message data effectively becomes read-only after a call to this	381	The message data logically becomes read-only after a call to this
186	function: modifying any argument is not allowed and can cause many	382	function: modifying any argument (or values referenced by them) is
187	problems.	383	forbidden, as there can be considerable time between the call to C<snd>
		384	and the time the message is actually being serialised - in fact, it might
		385	never be copied as within the same process it is simply handed to the
		386	receiving port.
188		387
189	The type of data you can transfer depends on the transport protocol: when	388	The type of data you can transfer depends on the transport protocol: when
190	JSON is used, then only strings, numbers and arrays and hashes consisting	389	JSON is used, then only strings, numbers and arrays and hashes consisting
191	of those are allowed (no objects). When Storable is used, then anything	390	of those are allowed (no objects). When Storable is used, then anything
192	that Storable can serialise and deserialise is allowed, and for the local	391	that Storable can serialise and deserialise is allowed, and for the local
193	node, anything can be passed.	392	node, anything can be passed. Best rely only on the common denominator of
		393	these.
194		394
195	=item kil $portid[, @reason]	395	=item $local_port = port
196		396
197	Kill the specified port with the given C<@reason>.	397	Create a new local port object and returns its port ID. Initially it has
		398	no callbacks set and will throw an error when it receives messages.
198		399
199	If no C<@reason> is specified, then the port is killed "normally" (linked	400	=item $local_port = port { my @msg = @_ }
200	ports will not be kileld, or even notified).
201		401
202	Otherwise, linked ports get killed with the same reason (second form of	402	Creates a new local port, and returns its ID. Semantically the same as
203	C<mon>, see below).	403	creating a port and calling C<rcv $port, $callback> on it.
204		404
205	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	405	The block will be called for every message received on the port, with the
206	will be reported as reason C<< die => $@ >>.	406	global variable C<$SELF> set to the port ID. Runtime errors will cause the
		407	port to be C<kil>ed. The message will be passed as-is, no extra argument
		408	(i.e. no port ID) will be passed to the callback.
207		409
208	Transport/communication errors are reported as C<< transport_error =>	410	If you want to stop/destroy the port, simply C<kil> it:
209	$message >>.
210		411
211	=item $guard = mon $portid, $cb->(@reason)	412	my $port = port {
212		413	my @msg = @_;
213	=item $guard = mon $portid, $otherport	414	...
214		415	kil $SELF;
215	=item $guard = mon $portid, $otherport, @msg	416	};
216
217	Monitor the given port and do something when the port is killed.
218
219	In the first form, the callback is simply called with any number
220	of C<@reason> elements (no @reason means that the port was deleted
221	"normally"). Note also that I<< the callback B<must> never die >>, so use
222	C<eval> if unsure.
223
224	In the second form, the other port will be C<kil>'ed with C<@reason>, iff
225	a @reason was specified, i.e. on "normal" kils nothing happens, while
226	under all other conditions, the other port is killed with the same reason.
227
228	In the last form, a message of the form C<@msg, @reason> will be C<snd>.
229
230	Example: call a given callback when C<$port> is killed.
231
232	mon $port, sub { warn "port died because of <@_>\n" };
233
234	Example: kill ourselves when C<$port> is killed abnormally.
235
236	mon $port, $self;
237
238	Example: send us a restart message another C<$port> is killed.
239
240	mon $port, $self => "restart";
241		417
242	=cut	418	=cut
243		419
244	sub mon {	420	sub rcv($@);
245	my ($noderef, $port, $cb) = ((split /#/, shift, 2), shift);
246		421
247	my $node = $NODE{$noderef} || add_node $noderef;	422	my $KILME = sub {
		423	(my $tag = substr $_[0], 0, 30) =~ s/([^\x20-\x7e])/./g;
		424	kil $SELF, unhandled_message => "no callback found for message '$tag'";
		425	};
248		426
249	#TODO: ports must not be references	427	sub port(;&) {
250	if (!ref $cb or "AnyEvent::MP::Port" eq ref $cb) {	428	my $id = $UNIQ . ++$ID;
		429	my $port = "$NODE#$id";
		430
		431	rcv $port, shift || $KILME;
		432
		433	$port
		434	}
		435
		436	=item rcv $local_port, $callback->(@msg)
		437
		438	Replaces the default callback on the specified port. There is no way to
		439	remove the default callback: use C<sub { }> to disable it, or better
		440	C<kil> the port when it is no longer needed.
		441
		442	The global C<$SELF> (exported by this module) contains C<$port> while
		443	executing the callback. Runtime errors during callback execution will
		444	result in the port being C<kil>ed.
		445
		446	The default callback receives all messages not matched by a more specific
		447	C<tag> match.
		448
		449	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
		450
		451	Register (or replace) callbacks to be called on messages starting with the
		452	given tag on the given port (and return the port), or unregister it (when
		453	C<$callback> is C<$undef> or missing). There can only be one callback
		454	registered for each tag.
		455
		456	The original message will be passed to the callback, after the first
		457	element (the tag) has been removed. The callback will use the same
		458	environment as the default callback (see above).
		459
		460	Example: create a port and bind receivers on it in one go.
		461
		462	my $port = rcv port,
		463	msg1 => sub { ... },
		464	msg2 => sub { ... },
		465	;
		466
		467	Example: create a port, bind receivers and send it in a message elsewhere
		468	in one go:
		469
		470	snd $otherport, reply =>
		471	rcv port,
		472	msg1 => sub { ... },
		473	...
		474	;
		475
		476	Example: temporarily register a rcv callback for a tag matching some port
		477	(e.g. for an rpc reply) and unregister it after a message was received.
		478
		479	rcv $port, $otherport => sub {
		480	my @reply = @_;
		481
		482	rcv $SELF, $otherport;
		483	};
		484
		485	=cut
		486
		487	sub rcv($@) {
		488	my $port = shift;
		489	my ($nodeid, $portid) = split /#/, $port, 2;
		490
		491	$nodeid eq $NODE
		492	or Carp::croak "$port: rcv can only be called on local ports, caught";
		493
		494	while (@_) {
251	if (@_) {	495	if (ref $_[0]) {
252	# send a kill info message	496	if (my $self = $PORT_DATA{$portid}) {
253	my (@msg) = ($cb, @_);	497	"AnyEvent::MP::Port" eq ref $self
254	$cb = sub { snd @msg, @_ };	498	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		499
		500	$self->[0] = shift;
255	} else {	501	} else {
256	# simply kill other port	502	my $cb = shift;
257	my $port = $cb;	503	$PORT{$portid} = sub {
258	$cb = sub { kil $port, @_ if @_ };	504	local $SELF = $port;
		505	eval { &$cb }; _self_die if $@;
		506	};
		507	}
		508	} elsif (defined $_[0]) {
		509	my $self = $PORT_DATA{$portid} ||= do {
		510	my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port";
		511
		512	$PORT{$portid} = sub {
		513	local $SELF = $port;
		514
		515	if (my $cb = $self->[1]{$_[0]}) {
		516	shift;
		517	eval { &$cb }; _self_die if $@;
		518	} else {
		519	&{ $self->[0] };
		520	}
		521	};
		522
		523	$self
		524	};
		525
		526	"AnyEvent::MP::Port" eq ref $self
		527	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		528
		529	my ($tag, $cb) = splice @_, 0, 2;
		530
		531	if (defined $cb) {
		532	$self->[1]{$tag} = $cb;
		533	} else {
		534	delete $self->[1]{$tag};
		535	}
259	}	536	}
260	}	537	}
261		538
262	$node->monitor ($port, $cb);
263
264	defined wantarray
265	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }
266	}
267
268	=item $guard = mon_guard $port, $ref, $ref...
269
270	Monitors the given C<$port> and keeps the passed references. When the port
271	is killed, the references will be freed.
272
273	Optionally returns a guard that will stop the monitoring.
274
275	This function is useful when you create e.g. timers or other watchers and
276	want to free them when the port gets killed:
277
278	$port->rcv (start => sub {
279	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {
280	undef $timer if 0.9 < rand;
281	});
282	});
283
284	=cut
285
286	sub mon_guard {
287	my ($port, @refs) = @_;
288
289	mon $port, sub { 0 && @refs }
290	}
291
292	=item lnk $port1, $port2
293
294	Link two ports. This is simply a shorthand for:
295
296	mon $port1, $port2;
297	mon $port2, $port1;
298
299	It means that if either one is killed abnormally, the other one gets
300	killed as well.
301
302	=item $local_port = port
303
304	Create a new local port object that supports message matching.
305
306	=item $portid = port { my @msg = @_; $finished }
307
308	Creates a "mini port", that is, a very lightweight port without any
309	pattern matching behind it, and returns its ID.
310
311	The block will be called for every message received on the port. When the
312	callback returns a true value its job is considered "done" and the port
313	will be destroyed. Otherwise it will stay alive.
314
315	The message will be passed as-is, no extra argument (i.e. no port id) will
316	be passed to the callback.
317
318	If you need the local port id in the callback, this works nicely:
319
320	my $port; $port = miniport {
321	snd $otherport, reply => $port;
322	};
323
324	=cut
325
326	sub port(;&) {
327	my $id = "$UNIQ." . $ID++;
328	my $port = "$NODE#$id";
329
330	if (@_) {
331	my $cb = shift;
332	$PORT{$id} = sub {
333	local $SELF = $port;
334	eval {
335	&$cb
336	and kil $id;
337	};
338	_self_die if $@;
339	};
340	} else {
341	my $self = bless {
342	id => "$NODE#$id",
343	}, "AnyEvent::MP::Port";
344
345	$PORT_DATA{$id} = $self;
346	$PORT{$id} = sub {
347	local $SELF = $port;
348
349	eval {
350	for (@{ $self->{rc0}{$_[0]} }) {
351	$_ && &{$_->[0]}
352	&& undef $_;
353	}
354
355	for (@{ $self->{rcv}{$_[0]} }) {
356	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
357	&& &{$_->[0]}
358	&& undef $_;
359	}
360
361	for (@{ $self->{any} }) {
362	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
363	&& &{$_->[0]}
364	&& undef $_;
365	}
366	};
367	_self_die if $@;
368	};
369	}
370
371	$port	539	$port
372	}	540	}
373		541
374	=item reg $portid, $name	542	=item peval $port, $coderef[, @args]
375		543
376	Registers the given port under the name C<$name>. If the name already	544	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
377	exists it is replaced.	545	when the code throws an exception the C<$port> will be killed.
378		546
379	A port can only be registered under one well known name.	547	Any remaining args will be passed to the callback. Any return values will
		548	be returned to the caller.
380		549
381	A port automatically becomes unregistered when it is killed.	550	This is useful when you temporarily want to execute code in the context of
		551	a port.
		552
		553	Example: create a port and run some initialisation code in it's context.
		554
		555	my $port = port { ... };
		556
		557	peval $port, sub {
		558	init
		559	or die "unable to init";
		560	};
382		561
383	=cut	562	=cut
384		563
385	sub reg(@) {	564	sub peval($$) {
386	my ($portid, $name) = @_;	565	local $SELF = shift;
		566	my $cb = shift;
387		567
388	$REG{$name} = $portid;	568	if (wantarray) {
389	}	569	my @res = eval { &$cb };
390		570	_self_die if $@;
391	=item rcv $portid, tagstring => $callback->(@msg), ...	571	@res
392
393	=item rcv $portid, $smartmatch => $callback->(@msg), ...
394
395	=item rcv $portid, [$smartmatch...] => $callback->(@msg), ...
396
397	Register callbacks to be called on matching messages on the given port.
398
399	The callback has to return a true value when its work is done, after
400	which is will be removed, or a false value in which case it will stay
401	registered.
402
403	The global C<$SELF> (exported by this module) contains C<$portid> while
404	executing the callback.
405
406	Runtime errors wdurign callback execution will result in the port being
407	C<kil>ed.
408
409	If the match is an array reference, then it will be matched against the
410	first elements of the message, otherwise only the first element is being
411	matched.
412
413	Any element in the match that is specified as C<_any_> (a function
414	exported by this module) matches any single element of the message.
415
416	While not required, it is highly recommended that the first matching
417	element is a string identifying the message. The one-string-only match is
418	also the most efficient match (by far).
419
420	=cut
421
422	sub rcv($@) {
423	my ($noderef, $port) = split /#/, shift, 2;
424
425	($NODE{$noderef} || add_node $noderef) == $NODE{""}
426	or Carp::croak "$noderef#$port: rcv can only be called on local ports, caught";
427
428	my $self = $PORT_DATA{$port}
429	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";
430
431	"AnyEvent::MP::Port" eq ref $self
432	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";
433
434	while (@_) {
435	my ($match, $cb) = splice @_, 0, 2;
436
437	if (!ref $match) {
438	push @{ $self->{rc0}{$match} }, [$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 {	572	} else {
445	push @{ $self->{any} }, [$cb, $match];	573	my $res = eval { &$cb };
446	}	574	_self_die if $@;
		575	$res
447	}	576	}
448	}	577	}
449		578
450	=item $closure = psub { BLOCK }	579	=item $closure = psub { BLOCK }
451		580
452	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	581	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
453	closure is executed, sets up the environment in the same way as in C<rcv>	582	closure is executed, sets up the environment in the same way as in C<rcv>
454	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.	583	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		584
		585	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		586	BLOCK }, @_ } >>.
455		587
456	This is useful when you register callbacks from C<rcv> callbacks:	588	This is useful when you register callbacks from C<rcv> callbacks:
457		589
458	rcv delayed_reply => sub {	590	rcv delayed_reply => sub {
459	my ($delay, @reply) = @_;	591	my ($delay, @reply) = @_;
…		…
483	$res	615	$res
484	}	616	}
485	}	617	}
486	}	618	}
487		619
		620	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
		621
		622	=item $guard = mon $port # kill $SELF when $port dies
		623
		624	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
		625
		626	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		627
		628	Monitor the given port and do something when the port is killed or
		629	messages to it were lost, and optionally return a guard that can be used
		630	to stop monitoring again.
		631
		632	The first two forms distinguish between "normal" and "abnormal" kil's:
		633
		634	In the first form (another port given), if the C<$port> is C<kil>'ed with
		635	a non-empty reason, the other port (C<$rcvport>) will be kil'ed with the
		636	same reason. That is, on "normal" kil's nothing happens, while under all
		637	other conditions, the other port is killed with the same reason.
		638
		639	The second form (kill self) is the same as the first form, except that
		640	C<$rvport> defaults to C<$SELF>.
		641
		642	The remaining forms don't distinguish between "normal" and "abnormal" kil's
		643	- it's up to the callback or receiver to check whether the C<@reason> is
		644	empty and act accordingly.
		645
		646	In the third form (callback), the callback is simply called with any
		647	number of C<@reason> elements (empty @reason means that the port was deleted
		648	"normally"). Note also that I<< the callback B<must> never die >>, so use
		649	C<eval> if unsure.
		650
		651	In the last form (message), a message of the form C<$rcvport, @msg,
		652	@reason> will be C<snd>.
		653
		654	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		655	alert was raised), they are removed and will not trigger again, even if it
		656	turns out that the port is still alive.
		657
		658	As a rule of thumb, monitoring requests should always monitor a remote
		659	port locally (using a local C<$rcvport> or a callback). The reason is that
		660	kill messages might get lost, just like any other message. Another less
		661	obvious reason is that even monitoring requests can get lost (for example,
		662	when the connection to the other node goes down permanently). When
		663	monitoring a port locally these problems do not exist.
		664
		665	C<mon> effectively guarantees that, in the absence of hardware failures,
		666	after starting the monitor, either all messages sent to the port will
		667	arrive, or the monitoring action will be invoked after possible message
		668	loss has been detected. No messages will be lost "in between" (after
		669	the first lost message no further messages will be received by the
		670	port). After the monitoring action was invoked, further messages might get
		671	delivered again.
		672
		673	Inter-host-connection timeouts and monitoring depend on the transport
		674	used. The only transport currently implemented is TCP, and AnyEvent::MP
		675	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		676	non-idle connection, and usually around two hours for idle connections).
		677
		678	This means that monitoring is good for program errors and cleaning up
		679	stuff eventually, but they are no replacement for a timeout when you need
		680	to ensure some maximum latency.
		681
		682	Example: call a given callback when C<$port> is killed.
		683
		684	mon $port, sub { warn "port died because of <@_>\n" };
		685
		686	Example: kill ourselves when C<$port> is killed abnormally.
		687
		688	mon $port;
		689
		690	Example: send us a restart message when another C<$port> is killed.
		691
		692	mon $port, $self => "restart";
		693
		694	=cut
		695
		696	sub mon {
		697	my ($nodeid, $port) = split /#/, shift, 2;
		698
		699	my $node = $NODE{$nodeid} || add_node $nodeid;
		700
		701	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
		702
		703	unless (ref $cb) {
		704	if (@_) {
		705	# send a kill info message
		706	my (@msg) = ($cb, @_);
		707	$cb = sub { snd @msg, @_ };
		708	} else {
		709	# simply kill other port
		710	my $port = $cb;
		711	$cb = sub { kil $port, @_ if @_ };
		712	}
		713	}
		714
		715	$node->monitor ($port, $cb);
		716
		717	defined wantarray
		718	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
		719	}
		720
		721	=item $guard = mon_guard $port, $ref, $ref...
		722
		723	Monitors the given C<$port> and keeps the passed references. When the port
		724	is killed, the references will be freed.
		725
		726	Optionally returns a guard that will stop the monitoring.
		727
		728	This function is useful when you create e.g. timers or other watchers and
		729	want to free them when the port gets killed (note the use of C<psub>):
		730
		731	$port->rcv (start => sub {
		732	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
		733	undef $timer if 0.9 < rand;
		734	});
		735	});
		736
		737	=cut
		738
		739	sub mon_guard {
		740	my ($port, @refs) = @_;
		741
		742	#TODO: mon-less form?
		743
		744	mon $port, sub { 0 && @refs }
		745	}
		746
		747	=item kil $port[, @reason]
		748
		749	Kill the specified port with the given C<@reason>.
		750
		751	If no C<@reason> is specified, then the port is killed "normally" -
		752	monitor callback will be invoked, but the kil will not cause linked ports
		753	(C<mon $mport, $lport> form) to get killed.
		754
		755	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
		756	form) get killed with the same reason.
		757
		758	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		759	will be reported as reason C<< die => $@ >>.
		760
		761	Transport/communication errors are reported as C<< transport_error =>
		762	$message >>.
		763
		764	Common idioms:
		765
		766	# silently remove yourself, do not kill linked ports
		767	kil $SELF;
		768
		769	# report a failure in some detail
		770	kil $SELF, failure_mode_1 => "it failed with too high temperature";
		771
		772	# do not waste much time with killing, just die when something goes wrong
		773	open my $fh, "<file"
		774	or die "file: $!";
		775
		776	=item $port = spawn $node, $initfunc[, @initdata]
		777
		778	Creates a port on the node C<$node> (which can also be a port ID, in which
		779	case it's the node where that port resides).
		780
		781	The port ID of the newly created port is returned immediately, and it is
		782	possible to immediately start sending messages or to monitor the port.
		783
		784	After the port has been created, the init function is called on the remote
		785	node, in the same context as a C<rcv> callback. This function must be a
		786	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		787	specify a function in the main program, use C<::name>.
		788
		789	If the function doesn't exist, then the node tries to C<require>
		790	the package, then the package above the package and so on (e.g.
		791	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		792	exists or it runs out of package names.
		793
		794	The init function is then called with the newly-created port as context
		795	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		796	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		797	the port might not get created.
		798
		799	A common idiom is to pass a local port, immediately monitor the spawned
		800	port, and in the remote init function, immediately monitor the passed
		801	local port. This two-way monitoring ensures that both ports get cleaned up
		802	when there is a problem.
		803
		804	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		805	caller before C<spawn> returns (by delaying invocation when spawn is
		806	called for the local node).
		807
		808	Example: spawn a chat server port on C<$othernode>.
		809
		810	# this node, executed from within a port context:
		811	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		812	mon $server;
		813
		814	# init function on C<$othernode>
		815	sub connect {
		816	my ($srcport) = @_;
		817
		818	mon $srcport;
		819
		820	rcv $SELF, sub {
		821	...
		822	};
		823	}
		824
		825	=cut
		826
		827	sub _spawn {
		828	my $port = shift;
		829	my $init = shift;
		830
		831	# rcv will create the actual port
		832	local $SELF = "$NODE#$port";
		833	eval {
		834	&{ load_func $init }
		835	};
		836	_self_die if $@;
		837	}
		838
		839	sub spawn(@) {
		840	my ($nodeid, undef) = split /#/, shift, 2;
		841
		842	my $id = $RUNIQ . ++$ID;
		843
		844	$_[0] =~ /::/
		845	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		846
		847	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		848
		849	"$nodeid#$id"
		850	}
		851
		852
		853	=item after $timeout, @msg
		854
		855	=item after $timeout, $callback
		856
		857	Either sends the given message, or call the given callback, after the
		858	specified number of seconds.
		859
		860	This is simply a utility function that comes in handy at times - the
		861	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		862	so it may go away in the future.
		863
		864	=cut
		865
		866	sub after($@) {
		867	my ($timeout, @action) = @_;
		868
		869	my $t; $t = AE::timer $timeout, 0, sub {
		870	undef $t;
		871	ref $action[0]
		872	? $action[0]()
		873	: snd @action;
		874	};
		875	}
		876
		877	#=item $cb2 = timeout $seconds, $cb[, @args]
		878
		879	=item cal $port, @msg, $callback[, $timeout]
		880
		881	A simple form of RPC - sends a message to the given C<$port> with the
		882	given contents (C<@msg>), but adds a reply port to the message.
		883
		884	The reply port is created temporarily just for the purpose of receiving
		885	the reply, and will be C<kil>ed when no longer needed.
		886
		887	A reply message sent to the port is passed to the C<$callback> as-is.
		888
		889	If an optional time-out (in seconds) is given and it is not C<undef>,
		890	then the callback will be called without any arguments after the time-out
		891	elapsed and the port is C<kil>ed.
		892
		893	If no time-out is given (or it is C<undef>), then the local port will
		894	monitor the remote port instead, so it eventually gets cleaned-up.
		895
		896	Currently this function returns the temporary port, but this "feature"
		897	might go in future versions unless you can make a convincing case that
		898	this is indeed useful for something.
		899
		900	=cut
		901
		902	sub cal(@) {
		903	my $timeout = ref $_[-1] ? undef : pop;
		904	my $cb = pop;
		905
		906	my $port = port {
		907	undef $timeout;
		908	kil $SELF;
		909	&$cb;
		910	};
		911
		912	if (defined $timeout) {
		913	$timeout = AE::timer $timeout, 0, sub {
		914	undef $timeout;
		915	kil $port;
		916	$cb->();
		917	};
		918	} else {
		919	mon $_[0], sub {
		920	kil $port;
		921	$cb->();
		922	};
		923	}
		924
		925	push @_, $port;
		926	&snd;
		927
		928	$port
		929	}
		930
488	=back	931	=back
489		932
490	=head1 FUNCTIONS FOR NODES	933	=head1 DISTRIBUTED DATABASE
491		934
		935	AnyEvent::MP comes with a simple distributed database. The database will
		936	be mirrored asynchronously on all global nodes. Other nodes bind to one
		937	of the global nodes for their needs. Every node has a "local database"
		938	which contains all the values that are set locally. All local databases
		939	are merged together to form the global database, which can be queried.
		940
		941	The database structure is that of a two-level hash - the database hash
		942	contains hashes which contain values, similarly to a perl hash of hashes,
		943	i.e.:
		944
		945	$DATABASE{$family}{$subkey} = $value
		946
		947	The top level hash key is called "family", and the second-level hash key
		948	is called "subkey" or simply "key".
		949
		950	The family must be alphanumeric, i.e. start with a letter and consist
		951	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		952	pretty much like Perl module names.
		953
		954	As the family namespace is global, it is recommended to prefix family names
		955	with the name of the application or module using it.
		956
		957	The subkeys must be non-empty strings, with no further restrictions.
		958
		959	The values should preferably be strings, but other perl scalars should
		960	work as well (such as C<undef>, arrays and hashes).
		961
		962	Every database entry is owned by one node - adding the same family/subkey
		963	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		964	but the result might be nondeterministic, i.e. the key might have
		965	different values on different nodes.
		966
		967	Different subkeys in the same family can be owned by different nodes
		968	without problems, and in fact, this is the common method to create worker
		969	pools. For example, a worker port for image scaling might do this:
		970
		971	db_set my_image_scalers => $port;
		972
		973	And clients looking for an image scaler will want to get the
		974	C<my_image_scalers> keys from time to time:
		975
		976	db_keys my_image_scalers => sub {
		977	@ports = @{ $_[0] };
		978	};
		979
		980	Or better yet, they want to monitor the database family, so they always
		981	have a reasonable up-to-date copy:
		982
		983	db_mon my_image_scalers => sub {
		984	@ports = keys %{ $_[0] };
		985	};
		986
		987	In general, you can set or delete single subkeys, but query and monitor
		988	whole families only.
		989
		990	If you feel the need to monitor or query a single subkey, try giving it
		991	it's own family.
		992
492	=over 4	993	=over
493		994
494	=item become_public $noderef	995	=item $guard = db_set $family => $subkey [=> $value]
495		996
496	Tells the node to become a public node, i.e. reachable from other nodes.	997	Sets (or replaces) a key to the database - if C<$value> is omitted,
		998	C<undef> is used instead.
497		999
498	The first argument is the (unresolved) node reference of the local node	1000	When called in non-void context, C<db_set> returns a guard that
499	(if missing then the empty string is used).	1001	automatically calls C<db_del> when it is destroyed.
500		1002
501	It is quite common to not specify anything, in which case the local node	1003	=item db_del $family => $subkey...
502	tries to listen on the default port, or to only specify a port number, in	1004
503	which case AnyEvent::MP tries to guess the local addresses.	1005	Deletes one or more subkeys from the database family.
		1006
		1007	=item $guard = db_reg $family => $port => $value
		1008
		1009	=item $guard = db_reg $family => $port
		1010
		1011	=item $guard = db_reg $family
		1012
		1013	Registers a port in the given family and optionally returns a guard to
		1014	remove it.
		1015
		1016	This function basically does the same as:
		1017
		1018	db_set $family => $port => $value
		1019
		1020	Except that the port is monitored and automatically removed from the
		1021	database family when it is kil'ed.
		1022
		1023	If C<$value> is missing, C<undef> is used. If C<$port> is missing, then
		1024	C<$SELF> is used.
		1025
		1026	This function is most useful to register a port in some port group (which
		1027	is just another name for a database family), and have it removed when the
		1028	port is gone. This works best when the port is a local port.
504		1029
505	=cut	1030	=cut
506		1031
		1032	sub db_reg($$;$) {
		1033	my $family = shift;
		1034	my $port = @_ ? shift : $SELF;
		1035
		1036	my $clr = sub { db_del $family => $port };
		1037	mon $port, $clr;
		1038
		1039	db_set $family => $port => $_[0];
		1040
		1041	defined wantarray
		1042	and &Guard::guard ($clr)
		1043	}
		1044
		1045	=item db_family $family => $cb->(\%familyhash)
		1046
		1047	Queries the named database C<$family> and call the callback with the
		1048	family represented as a hash. You can keep and freely modify the hash.
		1049
		1050	=item db_keys $family => $cb->(\@keys)
		1051
		1052	Same as C<db_family>, except it only queries the family I<subkeys> and passes
		1053	them as array reference to the callback.
		1054
		1055	=item db_values $family => $cb->(\@values)
		1056
		1057	Same as C<db_family>, except it only queries the family I<values> and passes them
		1058	as array reference to the callback.
		1059
		1060	=item $guard = db_mon $family => $cb->(\%familyhash, \@added, \@changed, \@deleted)
		1061
		1062	Creates a monitor on the given database family. Each time a key is
		1063	set or is deleted the callback is called with a hash containing the
		1064	database family and three lists of added, changed and deleted subkeys,
		1065	respectively. If no keys have changed then the array reference might be
		1066	C<undef> or even missing.
		1067
		1068	If not called in void context, a guard object is returned that, when
		1069	destroyed, stops the monitor.
		1070
		1071	The family hash reference and the key arrays belong to AnyEvent::MP and
		1072	B<must not be modified or stored> by the callback. When in doubt, make a
		1073	copy.
		1074
		1075	As soon as possible after the monitoring starts, the callback will be
		1076	called with the intiial contents of the family, even if it is empty,
		1077	i.e. there will always be a timely call to the callback with the current
		1078	contents.
		1079
		1080	It is possible that the callback is called with a change event even though
		1081	the subkey is already present and the value has not changed.
		1082
		1083	The monitoring stops when the guard object is destroyed.
		1084
		1085	Example: on every change to the family "mygroup", print out all keys.
		1086
		1087	my $guard = db_mon mygroup => sub {
		1088	my ($family, $a, $c, $d) = @_;
		1089	print "mygroup members: ", (join " ", keys %$family), "\n";
		1090	};
		1091
		1092	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1093
		1094	my $guard; $guard = db_mon My::Module::workers => sub {
		1095	my ($family, $a, $c, $d) = @_;
		1096	return unless %$family;
		1097	undef $guard;
		1098	print "My::Module::workers now nonempty\n";
		1099	};
		1100
		1101	Example: print all changes to the family "AnyEvent::Fantasy::Module".
		1102
		1103	my $guard = db_mon AnyEvent::Fantasy::Module => sub {
		1104	my ($family, $a, $c, $d) = @_;
		1105
		1106	print "+$_=$family->{$_}\n" for @$a;
		1107	print "*$_=$family->{$_}\n" for @$c;
		1108	print "-$_=$family->{$_}\n" for @$d;
		1109	};
		1110
		1111	=cut
		1112
507	=back	1113	=back
508		1114
509	=head1 NODE MESSAGES
510
511	Nodes understand the following messages sent to them. Many of them take
512	arguments called C<@reply>, which will simply be used to compose a reply
513	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
514	the remaining arguments are simply the message data.
515
516	While other messages exist, they are not public and subject to change.
517
518	=over 4
519
520	=cut
521
522	=item lookup => $name, @reply
523
524	Replies with the port ID of the specified well-known port, or C<undef>.
525
526	=item devnull => ...
527
528	Generic data sink/CPU heat conversion.
529
530	=item relay => $port, @msg
531
532	Simply forwards the message to the given port.
533
534	=item eval => $string[ @reply]
535
536	Evaluates the given string. If C<@reply> is given, then a message of the
537	form C<@reply, $@, @evalres> is sent.
538
539	Example: crash another node.
540
541	snd $othernode, eval => "exit";
542
543	=item time => @reply
544
545	Replies the the current node time to C<@reply>.
546
547	Example: tell the current node to send the current time to C<$myport> in a
548	C<timereply> message.
549
550	snd $NODE, time => $myport, timereply => 1, 2;
551	# => snd $myport, timereply => 1, 2, <time>
552
553	=back
554
555	=head1 AnyEvent::MP vs. Distributed Erlang	1115	=head1 AnyEvent::MP vs. Distributed Erlang
556		1116
557	AnyEvent::MP got lots of its ideas from distributed erlang (erlang node	1117	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
558	== aemp node, erlang process == aemp port), so many of the documents and	1118	== aemp node, Erlang process == aemp port), so many of the documents and
559	programming techniques employed by erlang apply to AnyEvent::MP. Here is a	1119	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
560	sample:	1120	sample:
561		1121
562	http://www.erlang.se/doc/programming_rules.shtml	1122	http://www.erlang.se/doc/programming_rules.shtml
563	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	1123	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
564	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6	1124	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
…		…
566		1126
567	Despite the similarities, there are also some important differences:	1127	Despite the similarities, there are also some important differences:
568		1128
569	=over 4	1129	=over 4
570		1130
571	=item * Node references contain the recipe on how to contact them.	1131	=item * Node IDs are arbitrary strings in AEMP.
572		1132
573	Erlang relies on special naming and DNS to work everywhere in the	1133	Erlang relies on special naming and DNS to work everywhere in the same
574	same way. AEMP relies on each node knowing it's own address(es), with	1134	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
575	convenience functionality.	1135	configuration or DNS), and possibly the addresses of some seed nodes, but
		1136	will otherwise discover other nodes (and their IDs) itself.
576		1137
577	This means that AEMP requires a less tightly controlled environment at the	1138	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
578	cost of longer node references and a slightly higher management overhead.	1139	uses "local ports are like remote ports".
		1140
		1141	The failure modes for local ports are quite different (runtime errors
		1142	only) then for remote ports - when a local port dies, you I<know> it dies,
		1143	when a connection to another node dies, you know nothing about the other
		1144	port.
		1145
		1146	Erlang pretends remote ports are as reliable as local ports, even when
		1147	they are not.
		1148
		1149	AEMP encourages a "treat remote ports differently" philosophy, with local
		1150	ports being the special case/exception, where transport errors cannot
		1151	occur.
579		1152
580	=item * Erlang uses processes and a mailbox, AEMP does not queue.	1153	=item * Erlang uses processes and a mailbox, AEMP does not queue.
581		1154
582	Erlang uses processes that selctively receive messages, and therefore	1155	Erlang uses processes that selectively receive messages out of order, and
583	needs a queue. AEMP is event based, queuing messages would serve no useful	1156	therefore needs a queue. AEMP is event based, queuing messages would serve
584	purpose.	1157	no useful purpose. For the same reason the pattern-matching abilities
		1158	of AnyEvent::MP are more limited, as there is little need to be able to
		1159	filter messages without dequeuing them.
585		1160
586	(But see L<Coro::MP> for a more erlang-like process model on top of AEMP).	1161	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1162	being event-based, while Erlang is process-based.
		1163
		1164	You can have a look at L<Coro::MP> for a more Erlang-like process model on
		1165	top of AEMP and Coro threads.
587		1166
588	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1167	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
589		1168
590	Sending messages in erlang is synchronous and blocks the process. AEMP	1169	Sending messages in Erlang is synchronous and blocks the process until
591	sends are immediate, connection establishment is handled in the	1170	a connection has been established and the message sent (and so does not
592	background.	1171	need a queue that can overflow). AEMP sends return immediately, connection
		1172	establishment is handled in the background.
593		1173
594	=item * Erlang can silently lose messages, AEMP cannot.	1174	=item * Erlang suffers from silent message loss, AEMP does not.
595		1175
596	Erlang makes few guarantees on messages delivery - messages can get lost	1176	Erlang implements few guarantees on messages delivery - messages can get
597	without any of the processes realising it (i.e. you send messages a, b,	1177	lost without any of the processes realising it (i.e. you send messages a,
598	and c, and the other side only receives messages a and c).	1178	b, and c, and the other side only receives messages a and c).
599		1179
600	AEMP guarantees correct ordering, and the guarantee that there are no	1180	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1181	guarantee that after one message is lost, all following ones sent to the
		1182	same port are lost as well, until monitoring raises an error, so there are
601	holes in the message sequence.	1183	no silent "holes" in the message sequence.
602		1184
603	=item * In erlang, processes can be declared dead and later be found to be	1185	If you want your software to be very reliable, you have to cope with
604	alive.	1186	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
605		1187	simply tries to work better in common error cases, such as when a network
606	In erlang it can happen that a monitored process is declared dead and	1188	link goes down.
607	linked processes get killed, but later it turns out that the process is
608	still alive - and can receive messages.
609
610	In AEMP, when port monitoring detects a port as dead, then that port will
611	eventually be killed - it cannot happen that a node detects a port as dead
612	and then later sends messages to it, finding it is still alive.
613		1189
614	=item * Erlang can send messages to the wrong port, AEMP does not.	1190	=item * Erlang can send messages to the wrong port, AEMP does not.
615		1191
616	In erlang it is quite possible that a node that restarts reuses a process	1192	In Erlang it is quite likely that a node that restarts reuses an Erlang
617	ID known to other nodes for a completely different process, causing	1193	process ID known to other nodes for a completely different process,
618	messages destined for that process to end up in an unrelated process.	1194	causing messages destined for that process to end up in an unrelated
		1195	process.
619		1196
620	AEMP never reuses port IDs, so old messages or old port IDs floating	1197	AEMP does not reuse port IDs, so old messages or old port IDs floating
621	around in the network will not be sent to an unrelated port.	1198	around in the network will not be sent to an unrelated port.
622		1199
623	=item * Erlang uses unprotected connections, AEMP uses secure	1200	=item * Erlang uses unprotected connections, AEMP uses secure
624	authentication and can use TLS.	1201	authentication and can use TLS.
625		1202
626	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1203	AEMP can use a proven protocol - TLS - to protect connections and
627	securely authenticate nodes.	1204	securely authenticate nodes.
628		1205
629	=item * The AEMP protocol is optimised for both text-based and binary	1206	=item * The AEMP protocol is optimised for both text-based and binary
630	communications.	1207	communications.
631		1208
632	The AEMP protocol, unlike the erlang protocol, supports both	1209	The AEMP protocol, unlike the Erlang protocol, supports both programming
633	language-independent text-only protocols (good for debugging) and binary,	1210	language independent text-only protocols (good for debugging), and binary,
634	language-specific serialisers (e.g. Storable).	1211	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1212	used, the protocol is actually completely text-based.
635		1213
636	It has also been carefully designed to be implementable in other languages	1214	It has also been carefully designed to be implementable in other languages
637	with a minimum of work while gracefully degrading fucntionality to make the	1215	with a minimum of work while gracefully degrading functionality to make the
638	protocol simple.	1216	protocol simple.
639		1217
		1218	=item * AEMP has more flexible monitoring options than Erlang.
		1219
		1220	In Erlang, you can chose to receive I<all> exit signals as messages or
		1221	I<none>, there is no in-between, so monitoring single Erlang processes is
		1222	difficult to implement.
		1223
		1224	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1225	between automatic kill, exit message or callback on a per-port basis.
		1226
		1227	=item * Erlang tries to hide remote/local connections, AEMP does not.
		1228
		1229	Monitoring in Erlang is not an indicator of process death/crashes, in the
		1230	same way as linking is (except linking is unreliable in Erlang).
		1231
		1232	In AEMP, you don't "look up" registered port names or send to named ports
		1233	that might or might not be persistent. Instead, you normally spawn a port
		1234	on the remote node. The init function monitors you, and you monitor the
		1235	remote port. Since both monitors are local to the node, they are much more
		1236	reliable (no need for C<spawn_link>).
		1237
		1238	This also saves round-trips and avoids sending messages to the wrong port
		1239	(hard to do in Erlang).
		1240
640	=back	1241	=back
641		1242
		1243	=head1 RATIONALE
		1244
		1245	=over 4
		1246
		1247	=item Why strings for port and node IDs, why not objects?
		1248
		1249	We considered "objects", but found that the actual number of methods
		1250	that can be called are quite low. Since port and node IDs travel over
		1251	the network frequently, the serialising/deserialising would add lots of
		1252	overhead, as well as having to keep a proxy object everywhere.
		1253
		1254	Strings can easily be printed, easily serialised etc. and need no special
		1255	procedures to be "valid".
		1256
		1257	And as a result, a port with just a default receiver consists of a single
		1258	code reference stored in a global hash - it can't become much cheaper.
		1259
		1260	=item Why favour JSON, why not a real serialising format such as Storable?
		1261
		1262	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1263	format, but currently there is no way to make a node use Storable by
		1264	default (although all nodes will accept it).
		1265
		1266	The default framing protocol is JSON because a) JSON::XS is many times
		1267	faster for small messages and b) most importantly, after years of
		1268	experience we found that object serialisation is causing more problems
		1269	than it solves: Just like function calls, objects simply do not travel
		1270	easily over the network, mostly because they will always be a copy, so you
		1271	always have to re-think your design.
		1272
		1273	Keeping your messages simple, concentrating on data structures rather than
		1274	objects, will keep your messages clean, tidy and efficient.
		1275
		1276	=back
		1277
		1278	=head1 PORTING FROM AnyEvent::MP VERSION 1.X
		1279
		1280	AEMP version 2 has a few major incompatible changes compared to version 1:
		1281
		1282	=over 4
		1283
		1284	=item AnyEvent::MP::Global no longer has group management functions.
		1285
		1286	At least not officially - the grp_* functions are still exported and might
		1287	work, but they will be removed in some later release.
		1288
		1289	AnyEvent::MP now comes with a distributed database that is more
		1290	powerful. Its database families map closely to port groups, but the API
		1291	has changed (the functions are also now exported by AnyEvent::MP). Here is
		1292	a rough porting guide:
		1293
		1294	grp_reg $group, $port # old
		1295	db_reg $group, $port # new
		1296
		1297	$list = grp_get $group # old
		1298	db_keys $group, sub { my $list = shift } # new
		1299
		1300	grp_mon $group, $cb->(\@ports, $add, $del) # old
		1301	db_mon $group, $cb->(\%ports, $add, $change, $del) # new
		1302
		1303	C<grp_reg> is a no-brainer (just replace by C<db_reg>), but C<grp_get> is
		1304	no longer instant, because the local node might not have a copy of the
		1305	group. You can either modify your code to allow for a callback, or use
		1306	C<db_mon> to keep an updated copy of the group:
		1307
		1308	my $local_group_copy;
		1309	db_mon $group => sub { $local_group_copy = $_[0] };
		1310
		1311	# now "keys %$local_group_copy" always returns the most up-to-date
		1312	# list of ports in the group.
		1313
		1314	C<grp_mon> can be replaced by C<db_mon> with minor changes - C<db_mon>
		1315	passes a hash as first argument, and an extra C<$chg> argument that can be
		1316	ignored:
		1317
		1318	db_mon $group => sub {
		1319	my ($ports, $add, $chg, $del) = @_;
		1320	$ports = [keys %$ports];
		1321
		1322	# now $ports, $add and $del are the same as
		1323	# were originally passed by grp_mon.
		1324	...
		1325	};
		1326
		1327	=item Nodes not longer connect to all other nodes.
		1328
		1329	In AEMP 1.x, every node automatically loads the L<AnyEvent::MP::Global>
		1330	module, which in turn would create connections to all other nodes in the
		1331	network (helped by the seed nodes).
		1332
		1333	In version 2.x, global nodes still connect to all other global nodes, but
		1334	other nodes don't - now every node either is a global node itself, or
		1335	attaches itself to another global node.
		1336
		1337	If a node isn't a global node itself, then it attaches itself to one
		1338	of its seed nodes. If that seed node isn't a global node yet, it will
		1339	automatically be upgraded to a global node.
		1340
		1341	So in many cases, nothing needs to be changed - one just has to make sure
		1342	that all seed nodes are meshed together with the other seed nodes (as with
		1343	AEMP 1.x), and other nodes specify them as seed nodes. This is most easily
		1344	achieved by specifying the same set of seed nodes for all nodes in the
		1345	network.
		1346
		1347	Not opening a connection to every other node is usually an advantage,
		1348	except when you need the lower latency of an already established
		1349	connection. To ensure a node establishes a connection to another node,
		1350	you can monitor the node port (C<mon $node, ...>), which will attempt to
		1351	create the connection (and notify you when the connection fails).
		1352
		1353	=item Listener-less nodes (nodes without binds) are gone.
		1354
		1355	And are not coming back, at least not in their old form. If no C<binds>
		1356	are specified for a node, AnyEvent::MP assumes a default of C<*:*>.
		1357
		1358	There are vague plans to implement some form of routing domains, which
		1359	might or might not bring back listener-less nodes, but don't count on it.
		1360
		1361	The fact that most connections are now optional somewhat mitigates this,
		1362	as a node can be effectively unreachable from the outside without any
		1363	problems, as long as it isn't a global node and only reaches out to other
		1364	nodes (as opposed to being contacted from other nodes).
		1365
		1366	=item $AnyEvent::MP::Kernel::WARN has gone.
		1367
		1368	AnyEvent has acquired a logging framework (L<AnyEvent::Log>), and AEMP now
		1369	uses this, and so should your programs.
		1370
		1371	Every module now documents what kinds of messages it generates, with
		1372	AnyEvent::MP acting as a catch all.
		1373
		1374	On the positive side, this means that instead of setting
		1375	C<PERL_ANYEVENT_MP_WARNLEVEL>, you can get away by setting C<AE_VERBOSE> -
		1376	much less to type.
		1377
		1378	=back
		1379
		1380	=head1 LOGGING
		1381
		1382	AnyEvent::MP does not normally log anything by itself, but since it is the
		1383	root of the contetx hierarchy for AnyEvent::MP modules, it will receive
		1384	all log messages by submodules.
		1385
642	=head1 SEE ALSO	1386	=head1 SEE ALSO
		1387
		1388	L<AnyEvent::MP::Intro> - a gentle introduction.
		1389
		1390	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1391
		1392	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1393	your applications.
		1394
		1395	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1396
		1397	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1398	all nodes.
643		1399
644	L<AnyEvent>.	1400	L<AnyEvent>.
645		1401
646	=head1 AUTHOR	1402	=head1 AUTHOR
647		1403

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