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Revision 1.40 by root, Sat Aug 8 00:22:16 2009 UTC vs.
Revision 1.140 by root, Thu Mar 22 23:47:01 2012 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent::MP - multi-processing/message-passing framework	3	AnyEvent::MP - erlang-style multi-processing/message-passing framework
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::MP;	7	use AnyEvent::MP;
8		8
9	$NODE # contains this node's noderef	9	$NODE # contains this node's node ID
10	NODE # returns this node's noderef	10	NODE # returns this node's node ID
11	NODE $port # returns the noderef of the port
12		11
13	$SELF # receiving/own port id in rcv callbacks	12	$SELF # receiving/own port id in rcv callbacks
14		13
		14	# initialise the node so it can send/receive messages
		15	configure;
		16
15	# ports are message endpoints	17	# ports are message destinations
16		18
17	# sending messages	19	# sending messages
18	snd $port, type => data...;	20	snd $port, type => data...;
19	snd $port, @msg;	21	snd $port, @msg;
20	snd @msg_with_first_element_being_a_port;	22	snd @msg_with_first_element_being_a_port;
21		23
22	# miniports	24	# creating/using ports, the simple way
23	my $miniport = port { my @msg = @_; 0 };	25	my $simple_port = port { my @msg = @_ };
24		26
25	# full ports	27	# creating/using ports, tagged message matching
26	my $port = port;	28	my $port = port;
27	rcv $port, smartmatch => $cb->(@msg);
28	rcv $port, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
29	rcv $port, pong => sub { warn "pong received\n"; 0 };	30	rcv $port, pong => sub { warn "pong received\n" };
30		31
31	# remote ports	32	# create a port on another node
32	my $port = spawn $node, $initfunc, @initdata;	33	my $port = spawn $node, $initfunc, @initdata;
33		34
34	# more, smarter, matches (_any_ is exported by this module)	35	# destroy a port again
35	rcv $port, [child_died => $pid] => sub { ...	36	kil $port; # "normal" kill
36	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3	37	kil $port, my_error => "everything is broken"; # error kill
37		38
38	# monitoring	39	# monitoring
39	mon $port, $cb->(@msg) # callback is invoked on death	40	mon $port, $cb->(@msg) # callback is invoked on death
40	mon $port, $otherport # kill otherport on abnormal death	41	mon $port, $localport # kill localport on abnormal death
41	mon $port, $otherport, @msg # send message on death	42	mon $port, $localport, @msg # send message on death
		43
		44	# temporarily execute code in port context
		45	peval $port, sub { die "kill the port!" };
		46
		47	# execute callbacks in $SELF port context
		48	my $timer = AE::timer 1, 0, psub {
		49	die "kill the port, delayed";
		50	};
42		51
43	=head1 DESCRIPTION	52	=head1 DESCRIPTION
44		53
45	This module (-family) implements a simple message passing framework.	54	This module (-family) implements a simple message passing framework.
46		55
47	Despite its simplicity, you can securely message other processes running	56	Despite its simplicity, you can securely message other processes running
48	on the same or other hosts.	57	on the same or other hosts, and you can supervise entities remotely.
49		58
50	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	59	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
51	manual page.	60	manual page and the examples under F<eg/>.
52
53	At the moment, this module family is severly broken and underdocumented,
54	so do not use. This was uploaded mainly to reserve the CPAN namespace -
55	stay tuned! The basic API should be finished, however.
56		61
57	=head1 CONCEPTS	62	=head1 CONCEPTS
58		63
59	=over 4	64	=over 4
60		65
61	=item port	66	=item port
62		67
63	A port is something you can send messages to (with the C<snd> function).	68	Not to be confused with a TCP port, a "port" is something you can send
		69	messages to (with the C<snd> function).
64		70
65	Some ports allow you to register C<rcv> handlers that can match specific	71	Ports allow you to register C<rcv> handlers that can match all or just
66	messages. All C<rcv> handlers will receive messages they match, messages	72	some messages. Messages send to ports will not be queued, regardless of
67	will not be queued.	73	anything was listening for them or not.
68		74
		75	Ports are represented by (printable) strings called "port IDs".
		76
69	=item port id - C<noderef#portname>	77	=item port ID - C<nodeid#portname>
70		78
71	A port id is normaly the concatenation of a noderef, a hash-mark (C<#>) as	79	A port ID is the concatenation of a node ID, a hash-mark (C<#>)
72	separator, and a port name (a printable string of unspecified format). An	80	as separator, and a port name (a printable string of unspecified
73	exception is the the node port, whose ID is identical to its node	81	format created by AnyEvent::MP).
74	reference.
75		82
76	=item node	83	=item node
77		84
78	A node is a single process containing at least one port - the node	85	A node is a single process containing at least one port - the node port,
79	port. You can send messages to node ports to find existing ports or to	86	which enables nodes to manage each other remotely, and to create new
80	create new ports, among other things.	87	ports.
81		88
82	Nodes are either private (single-process only), slaves (connected to a	89	Nodes are either public (have one or more listening ports) or private
83	master node only) or public nodes (connectable from unrelated nodes).	90	(no listening ports). Private nodes cannot talk to other private nodes
		91	currently, but all nodes can talk to public nodes.
84		92
85	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	93	Nodes is represented by (printable) strings called "node IDs".
86		94
87	A node reference is a string that either simply identifies the node (for	95	=item node ID - C<[A-Za-z0-9_\-.:]*>
88	private and slave nodes), or contains a recipe on how to reach a given
89	node (for public nodes).
90		96
91	This recipe is simply a comma-separated list of C<address:port> pairs (for	97	A node ID is a string that uniquely identifies the node within a
92	TCP/IP, other protocols might look different).	98	network. Depending on the configuration used, node IDs can look like a
		99	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		100	doesn't interpret node IDs in any way except to uniquely identify a node.
93		101
94	Node references come in two flavours: resolved (containing only numerical	102	=item binds - C<ip:port>
95	addresses) or unresolved (where hostnames are used instead of addresses).
96		103
97	Before using an unresolved node reference in a message you first have to	104	Nodes can only talk to each other by creating some kind of connection to
98	resolve it.	105	each other. To do this, nodes should listen on one or more local transport
		106	endpoints - binds.
		107
		108	Currently, only standard C<ip:port> specifications can be used, which
		109	specify TCP ports to listen on. So a bind is basically just a tcp socket
		110	in listening mode thta accepts conenctions form other nodes.
		111
		112	=item seed nodes
		113
		114	When a node starts, it knows nothing about the network it is in - it
		115	needs to connect to at least one other node that is already in the
		116	network. These other nodes are called "seed nodes".
		117
		118	Seed nodes themselves are not special - they are seed nodes only because
		119	some other node I<uses> them as such, but any node can be used as seed
		120	node for other nodes, and eahc node cna use a different set of seed nodes.
		121
		122	In addition to discovering the network, seed nodes are also used to
		123	maintain the network - all nodes using the same seed node form are part of
		124	the same network. If a network is split into multiple subnets because e.g.
		125	the network link between the parts goes down, then using the same seed
		126	nodes for all nodes ensures that eventually the subnets get merged again.
		127
		128	Seed nodes are expected to be long-running, and at least one seed node
		129	should always be available. They should also be relatively responsive - a
		130	seed node that blocks for long periods will slow down everybody else.
		131
		132	For small networks, it's best if every node uses the same set of seed
		133	nodes. For large networks, it can be useful to specify "regional" seed
		134	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		135	each other. What's important is that all seed nodes connections form a
		136	complete graph, so that the network cannot split into separate subnets
		137	forever.
		138
		139	Seed nodes are represented by seed IDs.
		140
		141	=item seed IDs - C<host:port>
		142
		143	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
		144	TCP port) of nodes that should be used as seed nodes.
		145
		146	=item global nodes
		147
		148	An AEMP network needs a discovery service - nodes need to know how to
		149	connect to other nodes they only know by name. In addition, AEMP offers a
		150	distributed "group database", which maps group names to a list of strings
		151	- for example, to register worker ports.
		152
		153	A network needs at least one global node to work, and allows every node to
		154	be a global node.
		155
		156	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		157	node and tries to keep connections to all other nodes. So while it can
		158	make sense to make every node "global" in small networks, it usually makes
		159	sense to only make seed nodes into global nodes in large networks (nodes
		160	keep connections to seed nodes and global nodes, so makign them the same
		161	reduces overhead).
99		162
100	=back	163	=back
101		164
102	=head1 VARIABLES/FUNCTIONS	165	=head1 VARIABLES/FUNCTIONS
103		166
…		…
105		168
106	=cut	169	=cut
107		170
108	package AnyEvent::MP;	171	package AnyEvent::MP;
109		172
		173	use AnyEvent::MP::Config ();
110	use AnyEvent::MP::Base;	174	use AnyEvent::MP::Kernel;
		175	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
111		176
112	use common::sense;	177	use common::sense;
113		178
114	use Carp ();	179	use Carp ();
115		180
116	use AE ();	181	use AE ();
		182	use Guard ();
117		183
118	use base "Exporter";	184	use base "Exporter";
119		185
120	our $VERSION = '0.1';	186	our $VERSION = $AnyEvent::MP::Config::VERSION;
		187
121	our @EXPORT = qw(	188	our @EXPORT = qw(
122	NODE $NODE *SELF node_of _any_	189	NODE $NODE *SELF node_of after
123	resolve_node initialise_node	190	configure
124	snd rcv mon kil reg psub spawn	191	snd rcv mon mon_guard kil psub peval spawn cal
125	port	192	port
		193	db_set db_del db_reg
		194	db_mon db_family db_keys db_values
126	);	195	);
127		196
128	our $SELF;	197	our $SELF;
129		198
130	sub _self_die() {	199	sub _self_die() {
…		…
133	kil $SELF, die => $msg;	202	kil $SELF, die => $msg;
134	}	203	}
135		204
136	=item $thisnode = NODE / $NODE	205	=item $thisnode = NODE / $NODE
137		206
138	The C<NODE> function returns, and the C<$NODE> variable contains	207	The C<NODE> function returns, and the C<$NODE> variable contains, the node
139	the noderef of the local node. The value is initialised by a call	208	ID of the node running in the current process. This value is initialised by
140	to C<become_public> or C<become_slave>, after which all local port	209	a call to C<configure>.
141	identifiers become invalid.
142		210
143	=item $noderef = node_of $port	211	=item $nodeid = node_of $port
144		212
145	Extracts and returns the noderef from a portid or a noderef.	213	Extracts and returns the node ID from a port ID or a node ID.
146		214
147	=item initialise_node $noderef, $seednode, $seednode...	215	=item configure $profile, key => value...
148		216
149	=item initialise_node "slave/", $master, $master...	217	=item configure key => value...
150		218
151	Before a node can talk to other nodes on the network it has to initialise	219	Before a node can talk to other nodes on the network (i.e. enter
152	itself - the minimum a node needs to know is it's own name, and optionally	220	"distributed mode") it has to configure itself - the minimum a node needs
153	it should know the noderefs of some other nodes in the network.	221	to know is its own name, and optionally it should know the addresses of
		222	some other nodes in the network to discover other nodes.
154		223
155	This function initialises a node - it must be called exactly once (or	224	This function configures a node - it must be called exactly once (or
156	never) before calling other AnyEvent::MP functions.	225	never) before calling other AnyEvent::MP functions.
157		226
158	All arguments are noderefs, which can be either resolved or unresolved.	227	The key/value pairs are basically the same ones as documented for the
159		228	F<aemp> command line utility (sans the set/del prefix), with these additions:
160	There are two types of networked nodes, public nodes and slave nodes:
161		229
162	=over 4	230	=over 4
163		231
164	=item public nodes	232	=item norc => $boolean (default false)
165		233
166	For public nodes, C<$noderef> must either be a (possibly unresolved)	234	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
167	noderef, in which case it will be resolved, or C<undef> (or missing), in	235	be consulted - all configuraiton options must be specified in the
168	which case the noderef will be guessed.	236	C<configure> call.
169		237
170	Afterwards, the node will bind itself on all endpoints and try to connect	238	=item force => $boolean (default false)
171	to all additional C<$seednodes> that are specified. Seednodes are optional
172	and can be used to quickly bootstrap the node into an existing network.
173		239
174	=item slave nodes	240	IF true, then the values specified in the C<configure> will take
		241	precedence over any values configured via the rc file. The default is for
		242	the rc file to override any options specified in the program.
175		243
176	When the C<$noderef> is the special string C<slave/>, then the node will	244	=item secure => $pass->(@msg)
177	become a slave node. Slave nodes cannot be contacted from outside and will
178	route most of their traffic to the master node that they attach to.
179		245
180	At least one additional noderef is required: The node will try to connect	246	In addition to specifying a boolean, you can specify a code reference that
181	to all of them and will become a slave attached to the first node it can	247	is called for every code execution attempt - the execution request is
182	successfully connect to.	248	granted iff the callback returns a true value.
		249
		250	Most of the time the callback should look only at
		251	C<$AnyEvent::MP::Kernel::SRCNODE> to make a decision, and not at the
		252	actual message (which can be about anything, and is mostly provided for
		253	diagnostic purposes).
		254
		255	See F<semp setsecure> for more info.
183		256
184	=back	257	=back
185		258
186	This function will block until all nodes have been resolved and, for slave
187	nodes, until it has successfully established a connection to a master
188	server.
189
190	Example: become a public node listening on the default node.
191
192	initialise_node;
193
194	Example: become a public node, and try to contact some well-known master
195	servers to become part of the network.
196
197	initialise_node undef, "master1", "master2";
198
199	Example: become a public node listening on port C<4041>.
200
201	initialise_node 4041;
202
203	Example: become a public node, only visible on localhost port 4044.
204
205	initialise_node "locahost:4044";
206
207	Example: become a slave node to any of the specified master servers.
208
209	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
210
211	=item $cv = resolve_node $noderef
212
213	Takes an unresolved node reference that may contain hostnames and
214	abbreviated IDs, resolves all of them and returns a resolved node
215	reference.
216
217	In addition to C<address:port> pairs allowed in resolved noderefs, the
218	following forms are supported:
219
220	=over 4	259	=over 4
221		260
222	=item the empty string	261	=item step 1, gathering configuration from profiles
223		262
224	An empty-string component gets resolved as if the default port (4040) was	263	The function first looks up a profile in the aemp configuration (see the
225	specified.	264	L<aemp> commandline utility). The profile name can be specified via the
		265	named C<profile> parameter or can simply be the first parameter). If it is
		266	missing, then the nodename (F<uname -n>) will be used as profile name.
226		267
227	=item naked port numbers (e.g. C<1234>)	268	The profile data is then gathered as follows:
228		269
229	These are resolved by prepending the local nodename and a colon, to be	270	First, all remaining key => value pairs (all of which are conveniently
230	further resolved.	271	undocumented at the moment) will be interpreted as configuration
		272	data. Then they will be overwritten by any values specified in the global
		273	default configuration (see the F<aemp> utility), then the chain of
		274	profiles chosen by the profile name (and any C<parent> attributes).
231		275
232	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	276	That means that the values specified in the profile have highest priority
		277	and the values specified directly via C<configure> have lowest priority,
		278	and can only be used to specify defaults.
233		279
234	These are resolved by using AnyEvent::DNS to resolve them, optionally	280	If the profile specifies a node ID, then this will become the node ID of
235	looking up SRV records for the C<aemp=4040> port, if no port was	281	this process. If not, then the profile name will be used as node ID, with
236	specified.	282	a unique randoms tring (C</%u>) appended.
		283
		284	The node ID can contain some C<%> sequences that are expanded: C<%n>
		285	is expanded to the local nodename, C<%u> is replaced by a random
		286	strign to make the node unique. For example, the F<aemp> commandline
		287	utility uses C<aemp/%n/%u> as nodename, which might expand to
		288	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		289
		290	=item step 2, bind listener sockets
		291
		292	The next step is to look up the binds in the profile, followed by binding
		293	aemp protocol listeners on all binds specified (it is possible and valid
		294	to have no binds, meaning that the node cannot be contacted form the
		295	outside. This means the node cannot talk to other nodes that also have no
		296	binds, but it can still talk to all "normal" nodes).
		297
		298	If the profile does not specify a binds list, then a default of C<*> is
		299	used, meaning the node will bind on a dynamically-assigned port on every
		300	local IP address it finds.
		301
		302	=item step 3, connect to seed nodes
		303
		304	As the last step, the seed ID list from the profile is passed to the
		305	L<AnyEvent::MP::Global> module, which will then use it to keep
		306	connectivity with at least one node at any point in time.
237		307
238	=back	308	=back
		309
		310	Example: become a distributed node using the local node name as profile.
		311	This should be the most common form of invocation for "daemon"-type nodes.
		312
		313	configure
		314
		315	Example: become a semi-anonymous node. This form is often used for
		316	commandline clients.
		317
		318	configure nodeid => "myscript/%n/%u";
		319
		320	Example: configure a node using a profile called seed, which is suitable
		321	for a seed node as it binds on all local addresses on a fixed port (4040,
		322	customary for aemp).
		323
		324	# use the aemp commandline utility
		325	# aemp profile seed binds '*:4040'
		326
		327	# then use it
		328	configure profile => "seed";
		329
		330	# or simply use aemp from the shell again:
		331	# aemp run profile seed
		332
		333	# or provide a nicer-to-remember nodeid
		334	# aemp run profile seed nodeid "$(hostname)"
239		335
240	=item $SELF	336	=item $SELF
241		337
242	Contains the current port id while executing C<rcv> callbacks or C<psub>	338	Contains the current port id while executing C<rcv> callbacks or C<psub>
243	blocks.	339	blocks.
244		340
245	=item SELF, %SELF, @SELF...	341	=item *SELF, SELF, %SELF, @SELF...
246		342
247	Due to some quirks in how perl exports variables, it is impossible to	343	Due to some quirks in how perl exports variables, it is impossible to
248	just export C<$SELF>, all the symbols called C<SELF> are exported by this	344	just export C<$SELF>, all the symbols named C<SELF> are exported by this
249	module, but only C<$SELF> is currently used.	345	module, but only C<$SELF> is currently used.
250		346
251	=item snd $port, type => @data	347	=item snd $port, type => @data
252		348
253	=item snd $port, @msg	349	=item snd $port, @msg
254		350
255	Send the given message to the given port ID, which can identify either	351	Send the given message to the given port, which can identify either a
256	a local or a remote port, and can be either a string or soemthignt hat	352	local or a remote port, and must be a port ID.
257	stringifies a sa port ID (such as a port object :).
258		353
259	While the message can be about anything, it is highly recommended to use a	354	While the message can be almost anything, it is highly recommended to
260	string as first element (a portid, or some word that indicates a request	355	use a string as first element (a port ID, or some word that indicates a
261	type etc.).	356	request type etc.) and to consist if only simple perl values (scalars,
		357	arrays, hashes) - if you think you need to pass an object, think again.
262		358
263	The message data effectively becomes read-only after a call to this	359	The message data logically becomes read-only after a call to this
264	function: modifying any argument is not allowed and can cause many	360	function: modifying any argument (or values referenced by them) is
265	problems.	361	forbidden, as there can be considerable time between the call to C<snd>
		362	and the time the message is actually being serialised - in fact, it might
		363	never be copied as within the same process it is simply handed to the
		364	receiving port.
266		365
267	The type of data you can transfer depends on the transport protocol: when	366	The type of data you can transfer depends on the transport protocol: when
268	JSON is used, then only strings, numbers and arrays and hashes consisting	367	JSON is used, then only strings, numbers and arrays and hashes consisting
269	of those are allowed (no objects). When Storable is used, then anything	368	of those are allowed (no objects). When Storable is used, then anything
270	that Storable can serialise and deserialise is allowed, and for the local	369	that Storable can serialise and deserialise is allowed, and for the local
271	node, anything can be passed.	370	node, anything can be passed. Best rely only on the common denominator of
		371	these.
272		372
273	=item $local_port = port	373	=item $local_port = port
274		374
275	Create a new local port object that can be used either as a pattern	375	Create a new local port object and returns its port ID. Initially it has
276	matching port ("full port") or a single-callback port ("miniport"),	376	no callbacks set and will throw an error when it receives messages.
277	depending on how C<rcv> callbacks are bound to the object.
278		377
279	=item $port = port { my @msg = @_; $finished }	378	=item $local_port = port { my @msg = @_ }
280		379
281	Creates a "miniport", that is, a very lightweight port without any pattern	380	Creates a new local port, and returns its ID. Semantically the same as
282	matching behind it, and returns its ID. Semantically the same as creating
283	a port and calling C<rcv $port, $callback> on it.	381	creating a port and calling C<rcv $port, $callback> on it.
284		382
285	The block will be called for every message received on the port. When the	383	The block will be called for every message received on the port, with the
286	callback returns a true value its job is considered "done" and the port	384	global variable C<$SELF> set to the port ID. Runtime errors will cause the
287	will be destroyed. Otherwise it will stay alive.	385	port to be C<kil>ed. The message will be passed as-is, no extra argument
		386	(i.e. no port ID) will be passed to the callback.
288		387
289	The message will be passed as-is, no extra argument (i.e. no port id) will	388	If you want to stop/destroy the port, simply C<kil> it:
290	be passed to the callback.
291		389
292	If you need the local port id in the callback, this works nicely:	390	my $port = port {
293		391	my @msg = @_;
294	my $port; $port = port {	392	...
295	snd $otherport, reply => $port;	393	kil $SELF;
296	};	394	};
297		395
298	=cut	396	=cut
299		397
300	sub rcv($@);	398	sub rcv($@);
301		399
		400	my $KILME = sub {
		401	(my $tag = substr $_[0], 0, 30) =~ s/([\x20-\x7e])/./g;
		402	kil $SELF, unhandled_message => "no callback found for message '$tag'";
		403	};
		404
302	sub port(;&) {	405	sub port(;&) {
303	my $id = "$UNIQ." . $ID++;	406	my $id = $UNIQ . ++$ID;
304	my $port = "$NODE#$id";	407	my $port = "$NODE#$id";
305		408
306	if (@_) {
307	rcv $port, shift;	409	rcv $port, shift || $KILME;
308	} else {
309	$PORT{$id} = sub { }; # nop
310	}
311		410
312	$port	411	$port
313	}	412	}
314		413
315	=item reg $port, $name
316
317	=item reg $name
318
319	Registers the given port (or C<$SELF><<< if missing) under the name
320	C<$name>. If the name already exists it is replaced.
321
322	A port can only be registered under one well known name.
323
324	A port automatically becomes unregistered when it is killed.
325
326	=cut
327
328	sub reg(@) {
329	my $port = @_ > 1 ? shift : $SELF || Carp::croak 'reg: called with one argument only, but $SELF not set,';
330
331	$REG{$_[0]} = $port;
332	}
333
334	=item rcv $port, $callback->(@msg)	414	=item rcv $local_port, $callback->(@msg)
335		415
336	Replaces the callback on the specified miniport (after converting it to	416	Replaces the default callback on the specified port. There is no way to
337	one if required).	417	remove the default callback: use C<sub { }> to disable it, or better
338		418	C<kil> the port when it is no longer needed.
339	=item rcv $port, tagstring => $callback->(@msg), ...
340
341	=item rcv $port, $smartmatch => $callback->(@msg), ...
342
343	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
344
345	Register callbacks to be called on matching messages on the given full
346	port (after converting it to one if required) and return the port.
347
348	The callback has to return a true value when its work is done, after
349	which is will be removed, or a false value in which case it will stay
350	registered.
351		419
352	The global C<$SELF> (exported by this module) contains C<$port> while	420	The global C<$SELF> (exported by this module) contains C<$port> while
353	executing the callback.	421	executing the callback. Runtime errors during callback execution will
		422	result in the port being C<kil>ed.
354		423
355	Runtime errors during callback execution will result in the port being	424	The default callback receives all messages not matched by a more specific
356	C<kil>ed.	425	C<tag> match.
357		426
358	If the match is an array reference, then it will be matched against the	427	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
359	first elements of the message, otherwise only the first element is being
360	matched.
361		428
362	Any element in the match that is specified as C<_any_> (a function	429	Register (or replace) callbacks to be called on messages starting with the
363	exported by this module) matches any single element of the message.	430	given tag on the given port (and return the port), or unregister it (when
		431	C<$callback> is C<$undef> or missing). There can only be one callback
		432	registered for each tag.
364		433
365	While not required, it is highly recommended that the first matching	434	The original message will be passed to the callback, after the first
366	element is a string identifying the message. The one-string-only match is	435	element (the tag) has been removed. The callback will use the same
367	also the most efficient match (by far).	436	environment as the default callback (see above).
368		437
369	Example: create a port and bind receivers on it in one go.	438	Example: create a port and bind receivers on it in one go.
370		439
371	my $port = rcv port,	440	my $port = rcv port,
372	msg1 => sub { ...; 0 },	441	msg1 => sub { ... },
373	msg2 => sub { ...; 0 },	442	msg2 => sub { ... },
374	;	443	;
375		444
376	Example: create a port, bind receivers and send it in a message elsewhere	445	Example: create a port, bind receivers and send it in a message elsewhere
377	in one go:	446	in one go:
378		447
379	snd $otherport, reply =>	448	snd $otherport, reply =>
380	rcv port,	449	rcv port,
381	msg1 => sub { ...; 0 },	450	msg1 => sub { ... },
382	...	451	...
383	;	452	;
384		453
		454	Example: temporarily register a rcv callback for a tag matching some port
		455	(e.g. for an rpc reply) and unregister it after a message was received.
		456
		457	rcv $port, $otherport => sub {
		458	my @reply = @_;
		459
		460	rcv $SELF, $otherport;
		461	};
		462
385	=cut	463	=cut
386		464
387	sub rcv($@) {	465	sub rcv($@) {
388	my $port = shift;	466	my $port = shift;
389	my ($noderef, $portid) = split /#/, $port, 2;	467	my ($nodeid, $portid) = split /#/, $port, 2;
390		468
391	($NODE{$noderef} || add_node $noderef) == $NODE{""}	469	$NODE{$nodeid} == $NODE{""}
392	or Carp::croak "$port: rcv can only be called on local ports, caught";	470	or Carp::croak "$port: rcv can only be called on local ports, caught";
393		471
394	if (@_ == 1) {	472	while (@_) {
		473	if (ref $_[0]) {
		474	if (my $self = $PORT_DATA{$portid}) {
		475	"AnyEvent::MP::Port" eq ref $self
		476	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		477
		478	$self->[0] = shift;
		479	} else {
395	my $cb = shift;	480	my $cb = shift;
396	delete $PORT_DATA{$portid};
397	$PORT{$portid} = sub {	481	$PORT{$portid} = sub {
398	local $SELF = $port;	482	local $SELF = $port;
399	eval {	483	eval { &$cb }; _self_die if $@;
400	&$cb	484	};
401	and kil $port;
402	};	485	}
403	_self_die if $@;	486	} elsif (defined $_[0]) {
404	};
405	} else {
406	my $self = $PORT_DATA{$portid} ||= do {	487	my $self = $PORT_DATA{$portid} ||= do {
407	my $self = bless {	488	my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port";
408	id => $port,
409	}, "AnyEvent::MP::Port";
410		489
411	$PORT{$portid} = sub {	490	$PORT{$portid} = sub {
412	local $SELF = $port;	491	local $SELF = $port;
413		492
414	eval {
415	for (@{ $self->{rc0}{$_[0]} }) {	493	if (my $cb = $self->[1]{$_[0]}) {
416	$_ && &{$_->[0]}	494	shift;
417	&& undef $_;	495	eval { &$cb }; _self_die if $@;
418	}	496	} else {
419
420	for (@{ $self->{rcv}{$_[0]} }) {
421	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
422	&& &{$_->[0]}	497	&{ $self->[0] };
423	&& undef $_;
424	}
425
426	for (@{ $self->{any} }) {
427	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
428	&& &{$_->[0]}
429	&& undef $_;
430	}	498	}
431	};	499	};
432	_self_die if $@;	500
		501	$self
433	};	502	};
434		503
435	$self
436	};
437
438	"AnyEvent::MP::Port" eq ref $self	504	"AnyEvent::MP::Port" eq ref $self
439	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	505	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
440		506
441	while (@_) {
442	my ($match, $cb) = splice @_, 0, 2;	507	my ($tag, $cb) = splice @_, 0, 2;
443		508
444	if (!ref $match) {	509	if (defined $cb) {
445	push @{ $self->{rc0}{$match} }, [$cb];	510	$self->[1]{$tag} = $cb;
446	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
447	my ($type, @match) = @$match;
448	@match
449	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
450	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
451	} else {	511	} else {
452	push @{ $self->{any} }, [$cb, $match];	512	delete $self->[1]{$tag};
453	}	513	}
454	}	514	}
455	}	515	}
456		516
457	$port	517	$port
458	}	518	}
459		519
		520	=item peval $port, $coderef[, @args]
		521
		522	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		523	when the code throews an exception the C<$port> will be killed.
		524
		525	Any remaining args will be passed to the callback. Any return values will
		526	be returned to the caller.
		527
		528	This is useful when you temporarily want to execute code in the context of
		529	a port.
		530
		531	Example: create a port and run some initialisation code in it's context.
		532
		533	my $port = port { ... };
		534
		535	peval $port, sub {
		536	init
		537	or die "unable to init";
		538	};
		539
		540	=cut
		541
		542	sub peval($$) {
		543	local $SELF = shift;
		544	my $cb = shift;
		545
		546	if (wantarray) {
		547	my @res = eval { &$cb };
		548	_self_die if $@;
		549	@res
		550	} else {
		551	my $res = eval { &$cb };
		552	_self_die if $@;
		553	$res
		554	}
		555	}
		556
460	=item $closure = psub { BLOCK }	557	=item $closure = psub { BLOCK }
461		558
462	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	559	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
463	closure is executed, sets up the environment in the same way as in C<rcv>	560	closure is executed, sets up the environment in the same way as in C<rcv>
464	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.	561	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		562
		563	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		564	BLOCK }, @_ } >>.
465		565
466	This is useful when you register callbacks from C<rcv> callbacks:	566	This is useful when you register callbacks from C<rcv> callbacks:
467		567
468	rcv delayed_reply => sub {	568	rcv delayed_reply => sub {
469	my ($delay, @reply) = @_;	569	my ($delay, @reply) = @_;
…		…
493	$res	593	$res
494	}	594	}
495	}	595	}
496	}	596	}
497		597
498	=item $guard = mon $port, $cb->(@reason)	598	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
499		599
500	=item $guard = mon $port, $rcvport	600	=item $guard = mon $port # kill $SELF when $port dies
501		601
502	=item $guard = mon $port	602	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
503		603
504	=item $guard = mon $port, $rcvport, @msg	604	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
505		605
506	Monitor the given port and do something when the port is killed, and	606	Monitor the given port and do something when the port is killed or
507	optionally return a guard that can be used to stop monitoring again.	607	messages to it were lost, and optionally return a guard that can be used
		608	to stop monitoring again.
508		609
		610	The first two forms distinguish between "normal" and "abnormal" kil's:
		611
		612	In the first form (another port given), if the C<$port> is C<kil>'ed with
		613	a non-empty reason, the other port (C<$rcvport>) will be kil'ed with the
		614	same reason. That is, on "normal" kil's nothing happens, while under all
		615	other conditions, the other port is killed with the same reason.
		616
		617	The second form (kill self) is the same as the first form, except that
		618	C<$rvport> defaults to C<$SELF>.
		619
		620	The remaining forms don't distinguish between "normal" and "abnormal" kil's
		621	- it's up to the callback or receiver to check whether the C<@reason> is
		622	empty and act accordingly.
		623
509	In the first form (callback), the callback is simply called with any	624	In the third form (callback), the callback is simply called with any
510	number of C<@reason> elements (no @reason means that the port was deleted	625	number of C<@reason> elements (empty @reason means that the port was deleted
511	"normally"). Note also that I<< the callback B<must> never die >>, so use	626	"normally"). Note also that I<< the callback B<must> never die >>, so use
512	C<eval> if unsure.	627	C<eval> if unsure.
513		628
514	In the second form (another port given), the other port (C<$rcvport)
515	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on
516	"normal" kils nothing happens, while under all other conditions, the other
517	port is killed with the same reason.
518
519	The third form (kill self) is the same as the second form, except that
520	C<$rvport> defaults to C<$SELF>.
521
522	In the last form (message), a message of the form C<@msg, @reason> will be	629	In the last form (message), a message of the form C<$rcvport, @msg,
523	C<snd>.	630	@reason> will be C<snd>.
524		631
		632	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		633	alert was raised), they are removed and will not trigger again, even if it
		634	turns out that the port is still alive.
		635
525	As a rule of thumb, monitoring requests should always monitor a port from	636	As a rule of thumb, monitoring requests should always monitor a remote
526	a local port (or callback). The reason is that kill messages might get	637	port locally (using a local C<$rcvport> or a callback). The reason is that
527	lost, just like any other message. Another less obvious reason is that	638	kill messages might get lost, just like any other message. Another less
528	even monitoring requests can get lost (for exmaple, when the connection	639	obvious reason is that even monitoring requests can get lost (for example,
529	to the other node goes down permanently). When monitoring a port locally	640	when the connection to the other node goes down permanently). When
530	these problems do not exist.	641	monitoring a port locally these problems do not exist.
		642
		643	C<mon> effectively guarantees that, in the absence of hardware failures,
		644	after starting the monitor, either all messages sent to the port will
		645	arrive, or the monitoring action will be invoked after possible message
		646	loss has been detected. No messages will be lost "in between" (after
		647	the first lost message no further messages will be received by the
		648	port). After the monitoring action was invoked, further messages might get
		649	delivered again.
		650
		651	Inter-host-connection timeouts and monitoring depend on the transport
		652	used. The only transport currently implemented is TCP, and AnyEvent::MP
		653	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		654	non-idle connection, and usually around two hours for idle connections).
		655
		656	This means that monitoring is good for program errors and cleaning up
		657	stuff eventually, but they are no replacement for a timeout when you need
		658	to ensure some maximum latency.
531		659
532	Example: call a given callback when C<$port> is killed.	660	Example: call a given callback when C<$port> is killed.
533		661
534	mon $port, sub { warn "port died because of <@_>\n" };	662	mon $port, sub { warn "port died because of <@_>\n" };
535		663
…		…
542	mon $port, $self => "restart";	670	mon $port, $self => "restart";
543		671
544	=cut	672	=cut
545		673
546	sub mon {	674	sub mon {
547	my ($noderef, $port) = split /#/, shift, 2;	675	my ($nodeid, $port) = split /#/, shift, 2;
548		676
549	my $node = $NODE{$noderef} || add_node $noderef;	677	my $node = $NODE{$nodeid} || add_node $nodeid;
550		678
551	my $cb = @_ ? $_[0] : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';	679	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
552		680
553	unless (ref $cb) {	681	unless (ref $cb) {
554	if (@_) {	682	if (@_) {
555	# send a kill info message	683	# send a kill info message
556	my (@msg) = @_;	684	my (@msg) = ($cb, @_);
557	$cb = sub { snd @msg, @_ };	685	$cb = sub { snd @msg, @_ };
558	} else {	686	} else {
559	# simply kill other port	687	# simply kill other port
560	my $port = $cb;	688	my $port = $cb;
561	$cb = sub { kil $port, @_ if @_ };	689	$cb = sub { kil $port, @_ if @_ };
…		…
563	}	691	}
564		692
565	$node->monitor ($port, $cb);	693	$node->monitor ($port, $cb);
566		694
567	defined wantarray	695	defined wantarray
568	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	696	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
569	}	697	}
570		698
571	=item $guard = mon_guard $port, $ref, $ref...	699	=item $guard = mon_guard $port, $ref, $ref...
572		700
573	Monitors the given C<$port> and keeps the passed references. When the port	701	Monitors the given C<$port> and keeps the passed references. When the port
574	is killed, the references will be freed.	702	is killed, the references will be freed.
575		703
576	Optionally returns a guard that will stop the monitoring.	704	Optionally returns a guard that will stop the monitoring.
577		705
578	This function is useful when you create e.g. timers or other watchers and	706	This function is useful when you create e.g. timers or other watchers and
579	want to free them when the port gets killed:	707	want to free them when the port gets killed (note the use of C<psub>):
580		708
581	$port->rcv (start => sub {	709	$port->rcv (start => sub {
582	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	710	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
583	undef $timer if 0.9 < rand;	711	undef $timer if 0.9 < rand;
584	});	712	});
585	});	713	});
586		714
587	=cut	715	=cut
…		…
596		724
597	=item kil $port[, @reason]	725	=item kil $port[, @reason]
598		726
599	Kill the specified port with the given C<@reason>.	727	Kill the specified port with the given C<@reason>.
600		728
601	If no C<@reason> is specified, then the port is killed "normally" (linked	729	If no C<@reason> is specified, then the port is killed "normally" -
602	ports will not be kileld, or even notified).	730	monitor callback will be invoked, but the kil will not cause linked ports
		731	(C<mon $mport, $lport> form) to get killed.
603		732
604	Otherwise, linked ports get killed with the same reason (second form of	733	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
605	C<mon>, see below).	734	form) get killed with the same reason.
606		735
607	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	736	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
608	will be reported as reason C<< die => $@ >>.	737	will be reported as reason C<< die => $@ >>.
609		738
610	Transport/communication errors are reported as C<< transport_error =>	739	Transport/communication errors are reported as C<< transport_error =>
611	$message >>.	740	$message >>.
612		741
613	=cut	742	Common idioms:
		743
		744	# silently remove yourself, do not kill linked ports
		745	kil $SELF;
		746
		747	# report a failure in some detail
		748	kil $SELF, failure_mode_1 => "it failed with too high temperature";
		749
		750	# do not waste much time with killing, just die when something goes wrong
		751	open my $fh, "<file"
		752	or die "file: $!";
614		753
615	=item $port = spawn $node, $initfunc[, @initdata]	754	=item $port = spawn $node, $initfunc[, @initdata]
616		755
617	Creates a port on the node C<$node> (which can also be a port ID, in which	756	Creates a port on the node C<$node> (which can also be a port ID, in which
618	case it's the node where that port resides).	757	case it's the node where that port resides).
619		758
620	The port ID of the newly created port is return immediately, and it is	759	The port ID of the newly created port is returned immediately, and it is
621	permissible to immediately start sending messages or monitor the port.	760	possible to immediately start sending messages or to monitor the port.
622		761
623	After the port has been created, the init function is	762	After the port has been created, the init function is called on the remote
624	called. This function must be a fully-qualified function name	763	node, in the same context as a C<rcv> callback. This function must be a
625	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	764	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
626	program, use C<::name>.	765	specify a function in the main program, use C<::name>.
627		766
628	If the function doesn't exist, then the node tries to C<require>	767	If the function doesn't exist, then the node tries to C<require>
629	the package, then the package above the package and so on (e.g.	768	the package, then the package above the package and so on (e.g.
630	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	769	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
631	exists or it runs out of package names.	770	exists or it runs out of package names.
632		771
633	The init function is then called with the newly-created port as context	772	The init function is then called with the newly-created port as context
634	object (C<$SELF>) and the C<@initdata> values as arguments.	773	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		774	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		775	the port might not get created.
635		776
636	A common idiom is to pass your own port, monitor the spawned port, and	777	A common idiom is to pass a local port, immediately monitor the spawned
637	in the init function, monitor the original port. This two-way monitoring	778	port, and in the remote init function, immediately monitor the passed
638	ensures that both ports get cleaned up when there is a problem.	779	local port. This two-way monitoring ensures that both ports get cleaned up
		780	when there is a problem.
		781
		782	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		783	caller before C<spawn> returns (by delaying invocation when spawn is
		784	called for the local node).
639		785
640	Example: spawn a chat server port on C<$othernode>.	786	Example: spawn a chat server port on C<$othernode>.
641		787
642	# this node, executed from within a port context:	788	# this node, executed from within a port context:
643	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	789	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
658		804
659	sub _spawn {	805	sub _spawn {
660	my $port = shift;	806	my $port = shift;
661	my $init = shift;	807	my $init = shift;
662		808
		809	# rcv will create the actual port
663	local $SELF = "$NODE#$port";	810	local $SELF = "$NODE#$port";
664	eval {	811	eval {
665	&{ load_func $init }	812	&{ load_func $init }
666	};	813	};
667	_self_die if $@;	814	_self_die if $@;
668	}	815	}
669		816
670	sub spawn(@) {	817	sub spawn(@) {
671	my ($noderef, undef) = split /#/, shift, 2;	818	my ($nodeid, undef) = split /#/, shift, 2;
672		819
673	my $id = "$RUNIQ." . $ID++;	820	my $id = $RUNIQ . ++$ID;
674		821
675	$_[0] =~ /::/	822	$_[0] =~ /::/
676	or Carp::croak "spawn init function must be a fully-qualified name, caught";	823	or Carp::croak "spawn init function must be a fully-qualified name, caught";
677		824
678	($NODE{$noderef} || add_node $noderef)	825	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
679	->send (["", "AnyEvent::MP::_spawn" => $id, @_]);
680		826
681	"$noderef#$id"	827	"$nodeid#$id"
682	}	828	}
683		829
		830
		831	=item after $timeout, @msg
		832
		833	=item after $timeout, $callback
		834
		835	Either sends the given message, or call the given callback, after the
		836	specified number of seconds.
		837
		838	This is simply a utility function that comes in handy at times - the
		839	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		840	so it may go away in the future.
		841
		842	=cut
		843
		844	sub after($@) {
		845	my ($timeout, @action) = @_;
		846
		847	my $t; $t = AE::timer $timeout, 0, sub {
		848	undef $t;
		849	ref $action[0]
		850	? $action[0]()
		851	: snd @action;
		852	};
		853	}
		854
		855	#=item $cb2 = timeout $seconds, $cb[, @args]
		856
		857	=item cal $port, @msg, $callback[, $timeout]
		858
		859	A simple form of RPC - sends a message to the given C<$port> with the
		860	given contents (C<@msg>), but adds a reply port to the message.
		861
		862	The reply port is created temporarily just for the purpose of receiving
		863	the reply, and will be C<kil>ed when no longer needed.
		864
		865	A reply message sent to the port is passed to the C<$callback> as-is.
		866
		867	If an optional time-out (in seconds) is given and it is not C<undef>,
		868	then the callback will be called without any arguments after the time-out
		869	elapsed and the port is C<kil>ed.
		870
		871	If no time-out is given (or it is C<undef>), then the local port will
		872	monitor the remote port instead, so it eventually gets cleaned-up.
		873
		874	Currently this function returns the temporary port, but this "feature"
		875	might go in future versions unless you can make a convincing case that
		876	this is indeed useful for something.
		877
		878	=cut
		879
		880	sub cal(@) {
		881	my $timeout = ref $_[-1] ? undef : pop;
		882	my $cb = pop;
		883
		884	my $port = port {
		885	undef $timeout;
		886	kil $SELF;
		887	&$cb;
		888	};
		889
		890	if (defined $timeout) {
		891	$timeout = AE::timer $timeout, 0, sub {
		892	undef $timeout;
		893	kil $port;
		894	$cb->();
		895	};
		896	} else {
		897	mon $_[0], sub {
		898	kil $port;
		899	$cb->();
		900	};
		901	}
		902
		903	push @_, $port;
		904	&snd;
		905
		906	$port
		907	}
		908
684	=back	909	=back
685		910
686	=head1 NODE MESSAGES	911	=head1 DISTRIBUTED DATABASE
687		912
688	Nodes understand the following messages sent to them. Many of them take	913	AnyEvent::MP comes with a simple distributed database. The database will
689	arguments called C<@reply>, which will simply be used to compose a reply	914	be mirrored asynchronously on all global nodes. Other nodes bind to one
690	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and	915	of the global nodes for their needs. Every node has a "local database"
691	the remaining arguments are simply the message data.	916	which contains all the values that are set locally. All local databases
		917	are merged together to form the global database, which can be queried.
692		918
693	While other messages exist, they are not public and subject to change.	919	The database structure is that of a two-level hash - the database hash
		920	contains hashes which contain values, similarly to a perl hash of hashes,
		921	i.e.:
694		922
		923	$DATABASE{$family}{$subkey} = $value
		924
		925	The top level hash key is called "family", and the second-level hash key
		926	is called "subkey" or simply "key".
		927
		928	The family must be alphanumeric, i.e. start with a letter and consist
		929	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		930	pretty much like Perl module names.
		931
		932	As the family namespace is global, it is recommended to prefix family names
		933	with the name of the application or module using it.
		934
		935	The subkeys must be non-empty strings, with no further restrictions.
		936
		937	The values should preferably be strings, but other perl scalars should
		938	work as well (such as C<undef>, arrays and hashes).
		939
		940	Every database entry is owned by one node - adding the same family/subkey
		941	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		942	but the result might be nondeterministic, i.e. the key might have
		943	different values on different nodes.
		944
		945	Different subkeys in the same family can be owned by different nodes
		946	without problems, and in fact, this is the common method to create worker
		947	pools. For example, a worker port for image scaling might do this:
		948
		949	db_set my_image_scalers => $port;
		950
		951	And clients looking for an image scaler will want to get the
		952	C<my_image_scalers> keys from time to time:
		953
		954	db_keys my_image_scalers => sub {
		955	@ports = @{ $_[0] };
		956	};
		957
		958	Or better yet, they want to monitor the database family, so they always
		959	have a reasonable up-to-date copy:
		960
		961	db_mon my_image_scalers => sub {
		962	@ports = keys %{ $_[0] };
		963	};
		964
		965	In general, you can set or delete single subkeys, but query and monitor
		966	whole families only.
		967
		968	If you feel the need to monitor or query a single subkey, try giving it
		969	it's own family.
		970
695	=over 4	971	=over
		972
		973	=item $guard = db_set $family => $subkey [=> $value]
		974
		975	Sets (or replaces) a key to the database - if C<$value> is omitted,
		976	C<undef> is used instead.
		977
		978	When called in non-void context, C<db_set> returns a guard that
		979	automatically calls C<db_del> when it is destroyed.
		980
		981	=item db_del $family => $subkey...
		982
		983	Deletes one or more subkeys from the database family.
		984
		985	=item $guard = db_reg $family => $port => $value
		986
		987	=item $guard = db_reg $family => $port
		988
		989	=item $guard = db_reg $family
		990
		991	Registers a port in the given family and optionally returns a guard to
		992	remove it.
		993
		994	This function basically does the same as:
		995
		996	db_set $family => $port => $value
		997
		998	Except that the port is monitored and automatically removed from the
		999	database family when it is kil'ed.
		1000
		1001	If C<$value> is missing, C<undef> is used. If C<$port> is missing, then
		1002	C<$SELF> is used.
		1003
		1004	This function is most useful to register a port in some port group (which
		1005	is just another name for a database family), and have it removed when the
		1006	port is gone. This works best when the port is a local port.
696		1007
697	=cut	1008	=cut
698		1009
699	=item lookup => $name, @reply	1010	sub db_reg($$;$) {
		1011	my $family = shift;
		1012	my $port = @_ ? shift : $SELF;
700		1013
701	Replies with the port ID of the specified well-known port, or C<undef>.	1014	my $clr = sub { db_del $family => $port };
		1015	mon $port, $clr;
702		1016
703	=item devnull => ...	1017	db_set $family => $port => $_[0];
704		1018
705	Generic data sink/CPU heat conversion.	1019	defined wantarray
		1020	and &Guard::guard ($clr)
		1021	}
706		1022
707	=item relay => $port, @msg	1023	=item db_family $family => $cb->(\%familyhash)
708		1024
709	Simply forwards the message to the given port.	1025	Queries the named database C<$family> and call the callback with the
		1026	family represented as a hash. You can keep and freely modify the hash.
710		1027
711	=item eval => $string[ @reply]	1028	=item db_keys $family => $cb->(\@keys)
712		1029
713	Evaluates the given string. If C<@reply> is given, then a message of the	1030	Same as C<db_family>, except it only queries the family I<subkeys> and passes
714	form C<@reply, $@, @evalres> is sent.	1031	them as array reference to the callback.
715		1032
716	Example: crash another node.	1033	=item db_values $family => $cb->(\@values)
717		1034
718	snd $othernode, eval => "exit";	1035	Same as C<db_family>, except it only queries the family I<values> and passes them
		1036	as array reference to the callback.
719		1037
720	=item time => @reply	1038	=item $guard = db_mon $family => $cb->($familyhash, \@added, \@changed, \@deleted)
721		1039
722	Replies the the current node time to C<@reply>.	1040	Creates a monitor on the given database family. Each time a key is set
		1041	or or is deleted the callback is called with a hash containing the
		1042	database family and three lists of added, changed and deleted subkeys,
		1043	respectively. If no keys have changed then the array reference might be
		1044	C<undef> or even missing.
723		1045
724	Example: tell the current node to send the current time to C<$myport> in a	1046	If not called in void context, a guard object is returned that, when
725	C<timereply> message.	1047	destroyed, stops the monitor.
726		1048
727	snd $NODE, time => $myport, timereply => 1, 2;	1049	The family hash reference and the key arrays belong to AnyEvent::MP and
728	# => snd $myport, timereply => 1, 2, <time>	1050	B<must not be modified or stored> by the callback. When in doubt, make a
		1051	copy.
		1052
		1053	As soon as possible after the monitoring starts, the callback will be
		1054	called with the intiial contents of the family, even if it is empty,
		1055	i.e. there will always be a timely call to the callback with the current
		1056	contents.
		1057
		1058	It is possible that the callback is called with a change event even though
		1059	the subkey is already present and the value has not changed.
		1060
		1061	The monitoring stops when the guard object is destroyed.
		1062
		1063	Example: on every change to the family "mygroup", print out all keys.
		1064
		1065	my $guard = db_mon mygroup => sub {
		1066	my ($family, $a, $c, $d) = @_;
		1067	print "mygroup members: ", (join " ", keys %$family), "\n";
		1068	};
		1069
		1070	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1071
		1072	my $guard; $guard = db_mon My::Module::workers => sub {
		1073	my ($family, $a, $c, $d) = @_;
		1074	return unless %$family;
		1075	undef $guard;
		1076	print "My::Module::workers now nonempty\n";
		1077	};
		1078
		1079	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		1080
		1081	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		1082	my ($family, $a, $c, $d) = @_;
		1083
		1084	print "+$_=$family->{$_}\n" for @$a;
		1085	print "*$_=$family->{$_}\n" for @$c;
		1086	print "-$_=$family->{$_}\n" for @$d;
		1087	};
		1088
		1089	=cut
729		1090
730	=back	1091	=back
731		1092
732	=head1 AnyEvent::MP vs. Distributed Erlang	1093	=head1 AnyEvent::MP vs. Distributed Erlang
733		1094
734	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	1095	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
735	== aemp node, Erlang process == aemp port), so many of the documents and	1096	== aemp node, Erlang process == aemp port), so many of the documents and
736	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	1097	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
737	sample:	1098	sample:
738		1099
739	http://www.Erlang.se/doc/programming_rules.shtml	1100	http://www.erlang.se/doc/programming_rules.shtml
740	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	1101	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
741	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	1102	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
742	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	1103	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
743		1104
744	Despite the similarities, there are also some important differences:	1105	Despite the similarities, there are also some important differences:
745		1106
746	=over 4	1107	=over 4
747		1108
748	=item * Node references contain the recipe on how to contact them.	1109	=item * Node IDs are arbitrary strings in AEMP.
749		1110
750	Erlang relies on special naming and DNS to work everywhere in the	1111	Erlang relies on special naming and DNS to work everywhere in the same
751	same way. AEMP relies on each node knowing it's own address(es), with	1112	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
752	convenience functionality.	1113	configuration or DNS), and possibly the addresses of some seed nodes, but
		1114	will otherwise discover other nodes (and their IDs) itself.
753		1115
754	This means that AEMP requires a less tightly controlled environment at the	1116	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
755	cost of longer node references and a slightly higher management overhead.	1117	uses "local ports are like remote ports".
		1118
		1119	The failure modes for local ports are quite different (runtime errors
		1120	only) then for remote ports - when a local port dies, you I<know> it dies,
		1121	when a connection to another node dies, you know nothing about the other
		1122	port.
		1123
		1124	Erlang pretends remote ports are as reliable as local ports, even when
		1125	they are not.
		1126
		1127	AEMP encourages a "treat remote ports differently" philosophy, with local
		1128	ports being the special case/exception, where transport errors cannot
		1129	occur.
756		1130
757	=item * Erlang uses processes and a mailbox, AEMP does not queue.	1131	=item * Erlang uses processes and a mailbox, AEMP does not queue.
758		1132
759	Erlang uses processes that selctively receive messages, and therefore	1133	Erlang uses processes that selectively receive messages out of order, and
760	needs a queue. AEMP is event based, queuing messages would serve no useful	1134	therefore needs a queue. AEMP is event based, queuing messages would serve
761	purpose.	1135	no useful purpose. For the same reason the pattern-matching abilities
		1136	of AnyEvent::MP are more limited, as there is little need to be able to
		1137	filter messages without dequeuing them.
762		1138
763	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	1139	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1140	being event-based, while Erlang is process-based.
		1141
		1142	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1143	top of AEMP and Coro threads.
764		1144
765	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1145	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
766		1146
767	Sending messages in Erlang is synchronous and blocks the process. AEMP	1147	Sending messages in Erlang is synchronous and blocks the process until
768	sends are immediate, connection establishment is handled in the	1148	a conenction has been established and the message sent (and so does not
769	background.	1149	need a queue that can overflow). AEMP sends return immediately, connection
		1150	establishment is handled in the background.
770		1151
771	=item * Erlang can silently lose messages, AEMP cannot.	1152	=item * Erlang suffers from silent message loss, AEMP does not.
772		1153
773	Erlang makes few guarantees on messages delivery - messages can get lost	1154	Erlang implements few guarantees on messages delivery - messages can get
774	without any of the processes realising it (i.e. you send messages a, b,	1155	lost without any of the processes realising it (i.e. you send messages a,
775	and c, and the other side only receives messages a and c).	1156	b, and c, and the other side only receives messages a and c).
776		1157
777	AEMP guarantees correct ordering, and the guarantee that there are no	1158	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1159	guarantee that after one message is lost, all following ones sent to the
		1160	same port are lost as well, until monitoring raises an error, so there are
778	holes in the message sequence.	1161	no silent "holes" in the message sequence.
779		1162
780	=item * In Erlang, processes can be declared dead and later be found to be	1163	If you want your software to be very reliable, you have to cope with
781	alive.	1164	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
782		1165	simply tries to work better in common error cases, such as when a network
783	In Erlang it can happen that a monitored process is declared dead and	1166	link goes down.
784	linked processes get killed, but later it turns out that the process is
785	still alive - and can receive messages.
786
787	In AEMP, when port monitoring detects a port as dead, then that port will
788	eventually be killed - it cannot happen that a node detects a port as dead
789	and then later sends messages to it, finding it is still alive.
790		1167
791	=item * Erlang can send messages to the wrong port, AEMP does not.	1168	=item * Erlang can send messages to the wrong port, AEMP does not.
792		1169
793	In Erlang it is quite possible that a node that restarts reuses a process	1170	In Erlang it is quite likely that a node that restarts reuses an Erlang
794	ID known to other nodes for a completely different process, causing	1171	process ID known to other nodes for a completely different process,
795	messages destined for that process to end up in an unrelated process.	1172	causing messages destined for that process to end up in an unrelated
		1173	process.
796		1174
797	AEMP never reuses port IDs, so old messages or old port IDs floating	1175	AEMP does not reuse port IDs, so old messages or old port IDs floating
798	around in the network will not be sent to an unrelated port.	1176	around in the network will not be sent to an unrelated port.
799		1177
800	=item * Erlang uses unprotected connections, AEMP uses secure	1178	=item * Erlang uses unprotected connections, AEMP uses secure
801	authentication and can use TLS.	1179	authentication and can use TLS.
802		1180
803	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1181	AEMP can use a proven protocol - TLS - to protect connections and
804	securely authenticate nodes.	1182	securely authenticate nodes.
805		1183
806	=item * The AEMP protocol is optimised for both text-based and binary	1184	=item * The AEMP protocol is optimised for both text-based and binary
807	communications.	1185	communications.
808		1186
809	The AEMP protocol, unlike the Erlang protocol, supports both	1187	The AEMP protocol, unlike the Erlang protocol, supports both programming
810	language-independent text-only protocols (good for debugging) and binary,	1188	language independent text-only protocols (good for debugging), and binary,
811	language-specific serialisers (e.g. Storable).	1189	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1190	used, the protocol is actually completely text-based.
812		1191
813	It has also been carefully designed to be implementable in other languages	1192	It has also been carefully designed to be implementable in other languages
814	with a minimum of work while gracefully degrading fucntionality to make the	1193	with a minimum of work while gracefully degrading functionality to make the
815	protocol simple.	1194	protocol simple.
816		1195
817	=item * AEMP has more flexible monitoring options than Erlang.	1196	=item * AEMP has more flexible monitoring options than Erlang.
818		1197
819	In Erlang, you can chose to receive I<all> exit signals as messages	1198	In Erlang, you can chose to receive I<all> exit signals as messages or
820	or I<none>, there is no in-between, so monitoring single processes is	1199	I<none>, there is no in-between, so monitoring single Erlang processes is
821	difficult to implement. Monitoring in AEMP is more flexible than in	1200	difficult to implement.
822	Erlang, as one can choose between automatic kill, exit message or callback	1201
823	on a per-process basis.	1202	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1203	between automatic kill, exit message or callback on a per-port basis.
824		1204
825	=item * Erlang tries to hide remote/local connections, AEMP does not.	1205	=item * Erlang tries to hide remote/local connections, AEMP does not.
826		1206
827	Monitoring in Erlang is not an indicator of process death/crashes,	1207	Monitoring in Erlang is not an indicator of process death/crashes, in the
828	as linking is (except linking is unreliable in Erlang).	1208	same way as linking is (except linking is unreliable in Erlang).
829		1209
830	In AEMP, you don't "look up" registered port names or send to named ports	1210	In AEMP, you don't "look up" registered port names or send to named ports
831	that might or might not be persistent. Instead, you normally spawn a port	1211	that might or might not be persistent. Instead, you normally spawn a port
832	on the remote node. The init function monitors the you, and you monitor	1212	on the remote node. The init function monitors you, and you monitor the
833	the remote port. Since both monitors are local to the node, they are much	1213	remote port. Since both monitors are local to the node, they are much more
834	more reliable.	1214	reliable (no need for C<spawn_link>).
835		1215
836	This also saves round-trips and avoids sending messages to the wrong port	1216	This also saves round-trips and avoids sending messages to the wrong port
837	(hard to do in Erlang).	1217	(hard to do in Erlang).
838		1218
839	=back	1219	=back
840		1220
		1221	=head1 RATIONALE
		1222
		1223	=over 4
		1224
		1225	=item Why strings for port and node IDs, why not objects?
		1226
		1227	We considered "objects", but found that the actual number of methods
		1228	that can be called are quite low. Since port and node IDs travel over
		1229	the network frequently, the serialising/deserialising would add lots of
		1230	overhead, as well as having to keep a proxy object everywhere.
		1231
		1232	Strings can easily be printed, easily serialised etc. and need no special
		1233	procedures to be "valid".
		1234
		1235	And as a result, a port with just a default receiver consists of a single
		1236	code reference stored in a global hash - it can't become much cheaper.
		1237
		1238	=item Why favour JSON, why not a real serialising format such as Storable?
		1239
		1240	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1241	format, but currently there is no way to make a node use Storable by
		1242	default (although all nodes will accept it).
		1243
		1244	The default framing protocol is JSON because a) JSON::XS is many times
		1245	faster for small messages and b) most importantly, after years of
		1246	experience we found that object serialisation is causing more problems
		1247	than it solves: Just like function calls, objects simply do not travel
		1248	easily over the network, mostly because they will always be a copy, so you
		1249	always have to re-think your design.
		1250
		1251	Keeping your messages simple, concentrating on data structures rather than
		1252	objects, will keep your messages clean, tidy and efficient.
		1253
		1254	=back
		1255
		1256	=head1 PORTING FROM AnyEvent::MP VERSION 1.X
		1257
		1258	AEMP version 2 has a few major incompatible changes compared to version 1:
		1259
		1260	=over 4
		1261
		1262	=item AnyEvent::MP::Global no longer has group management functions.
		1263
		1264	At least not officially - the grp_* functions are still exported and might
		1265	work, but they will be removed in some later release.
		1266
		1267	AnyEvent::MP now comes with a distributed database that is more
		1268	powerful. Its database families map closely to port groups, but the API
		1269	has changed (the functions are also now exported by AnyEvent::MP). Here is
		1270	a rough porting guide:
		1271
		1272	grp_reg $group, $port # old
		1273	db_reg $group, $port # new
		1274
		1275	$list = grp_get $group # old
		1276	db_keys $group, sub { my $list = shift } # new
		1277
		1278	grp_mon $group, $cb->(\@ports, $add, $del) # old
		1279	db_mon $group, $cb->(\%ports, $add, $change, $del) # new
		1280
		1281	C<grp_reg> is a no-brainer (just replace by C<db_reg>), but C<grp_get> is
		1282	no longer instant, because the local node might not have a copy of the
		1283	group. You can either modify your code to allow for a callback, or use
		1284	C<db_mon> to keep an updated copy of the group:
		1285
		1286	my $local_group_copy;
		1287	db_mon $group => sub { $local_group_copy = $_[0] };
		1288
		1289	# now "keys %$local_group_copy" always returns the most up-to-date
		1290	# list of ports in the group.
		1291
		1292	C<grp_mon> can be replaced by C<db_mon> with minor changes - C<db_mon>
		1293	passes a hash as first argument, and an extra C<$chg> argument that can be
		1294	ignored:
		1295
		1296	db_mon $group => sub {
		1297	my ($ports, $add, $chg, $lde) = @_;
		1298	$ports = [keys %$ports];
		1299
		1300	# now $ports, $add and $del are the same as
		1301	# were originally passed by grp_mon.
		1302	...
		1303	};
		1304
		1305	=item Nodes not longer connect to all other nodes.
		1306
		1307	In AEMP 1.x, every node automatically loads the L<AnyEvent::MP::Global>
		1308	module, which in turn would create connections to all other nodes in the
		1309	network (helped by the seed nodes).
		1310
		1311	In version 2.x, global nodes still connect to all other global nodes, but
		1312	other nodes don't - now every node either is a global node itself, or
		1313	attaches itself to another global node.
		1314
		1315	If a node isn't a global node itself, then it attaches itself to one
		1316	of its seed nodes. If that seed node isn't a global node yet, it will
		1317	automatically be upgraded to a global node.
		1318
		1319	So in many cases, nothing needs to be changed - one just has to make sure
		1320	that all seed nodes are meshed together with the other seed nodes (as with
		1321	AEMP 1.x), and other nodes specify them as seed nodes. This is most easily
		1322	achieved by specifying the same set of seed nodes for all nodes in the
		1323	network.
		1324
		1325	Not opening a connection to every other node is usually an advantage,
		1326	except when you need the lower latency of an already established
		1327	connection. To ensure a node establishes a connection to another node,
		1328	you can monitor the node port (C<mon $node, ...>), which will attempt to
		1329	create the connection (and notify you when the connection fails).
		1330
		1331	=item Listener-less nodes (nodes without binds) are gone.
		1332
		1333	And are not coming back, at least not in their old form. If no C<binds>
		1334	are specified for a node, AnyEvent::MP assumes a default of C<*:*>.
		1335
		1336	There are vague plans to implement some form of routing domains, which
		1337	might or might not bring back listener-less nodes, but don't count on it.
		1338
		1339	The fact that most connections are now optional somewhat mitigates this,
		1340	as a node can be effectively unreachable from the outside without any
		1341	problems, as long as it isn't a global node and only reaches out to other
		1342	nodes (as opposed to being contacted from other nodes).
		1343
		1344	=item $AnyEvent::MP::Kernel::WARN has gone.
		1345
		1346	AnyEvent has acquired a logging framework (L<AnyEvent::Log>), and AEMP now
		1347	uses this, and so should your programs.
		1348
		1349	Every module now documents what kinds of messages it generates, with
		1350	AnyEvent::MP acting as a catch all.
		1351
		1352	On the positive side, this means that instead of setting
		1353	C<PERL_ANYEVENT_MP_WARNLEVEL>, you can get away by setting C<AE_VERBOSE> -
		1354	much less to type.
		1355
		1356	=back
		1357
		1358	=head1 LOGGING
		1359
		1360	AnyEvent::MP does not normally log anything by itself, but sinc eit is the
		1361	root of the contetx hierarchy for AnyEvent::MP modules, it will receive
		1362	all log messages by submodules.
		1363
841	=head1 SEE ALSO	1364	=head1 SEE ALSO
		1365
		1366	L<AnyEvent::MP::Intro> - a gentle introduction.
		1367
		1368	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1369
		1370	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1371	your applications.
		1372
		1373	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1374
		1375	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1376	all nodes.
842		1377
843	L<AnyEvent>.	1378	L<AnyEvent>.
844		1379
845	=head1 AUTHOR	1380	=head1 AUTHOR
846		1381

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