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Revision 1.142 by root, Fri Mar 23 13:44:01 2012 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent::MP - multi-processing/message-passing framework	3	AnyEvent::MP - erlang-style multi-processing/message-passing framework
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::MP;	7	use AnyEvent::MP;
8		8
9	$NODE # contains this node's noderef	9	$NODE # contains this node's node ID
10	NODE # returns this node's noderef	10	NODE # returns this node's node ID
11	NODE $port # returns the noderef of the port
12		11
13	$SELF # receiving/own port id in rcv callbacks	12	$SELF # receiving/own port id in rcv callbacks
14		13
15	# initialise the node so it can send/receive messages	14	# initialise the node so it can send/receive messages
16	initialise_node; # -OR-	15	configure;
17	initialise_node "localhost:4040"; # -OR-
18	initialise_node "slave/", "localhost:4040"
19		16
20	# ports are message endpoints	17	# ports are message destinations
21		18
22	# sending messages	19	# sending messages
23	snd $port, type => data...;	20	snd $port, type => data...;
24	snd $port, @msg;	21	snd $port, @msg;
25	snd @msg_with_first_element_being_a_port;	22	snd @msg_with_first_element_being_a_port;
26		23
27	# creating/using miniports	24	# creating/using ports, the simple way
28	my $miniport = port { my @msg = @_; 0 };	25	my $simple_port = port { my @msg = @_ };
29		26
30	# creating/using full ports	27	# creating/using ports, tagged message matching
31	my $port = port;	28	my $port = port;
32	rcv $port, smartmatch => $cb->(@msg);
33	rcv $port, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
34	rcv $port, pong => sub { warn "pong received\n"; 0 };	30	rcv $port, pong => sub { warn "pong received\n" };
35
36	# more, smarter, matches (_any_ is exported by this module)
37	rcv $port, [child_died => $pid] => sub { ...
38	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3
39		31
40	# create a port on another node	32	# create a port on another node
41	my $port = spawn $node, $initfunc, @initdata;	33	my $port = spawn $node, $initfunc, @initdata;
42		34
		35	# destroy a port again
		36	kil $port; # "normal" kill
		37	kil $port, my_error => "everything is broken"; # error kill
		38
43	# monitoring	39	# monitoring
44	mon $port, $cb->(@msg) # callback is invoked on death	40	mon $port, $cb->(@msg) # callback is invoked on death
45	mon $port, $otherport # kill otherport on abnormal death	41	mon $port, $localport # kill localport on abnormal death
46	mon $port, $otherport, @msg # send message on death	42	mon $port, $localport, @msg # send message on death
47		43
48	=head1 CURRENT STATUS	44	# temporarily execute code in port context
		45	peval $port, sub { die "kill the port!" };
49		46
50	AnyEvent::MP - stable API, should work	47	# execute callbacks in $SELF port context
51	AnyEvent::MP::Intro - outdated	48	my $timer = AE::timer 1, 0, psub {
52	AnyEvent::MP::Kernel - WIP	49	die "kill the port, delayed";
53	AnyEvent::MP::Transport - mostly stable	50	};
54
55	stay tuned.
56		51
57	=head1 DESCRIPTION	52	=head1 DESCRIPTION
58		53
59	This module (-family) implements a simple message passing framework.	54	This module (-family) implements a simple message passing framework.
60		55
61	Despite its simplicity, you can securely message other processes running	56	Despite its simplicity, you can securely message other processes running
62	on the same or other hosts.	57	on the same or other hosts, and you can supervise entities remotely.
63		58
64	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>
65	manual page.	60	manual page and the examples under F<eg/>.
66
67	At the moment, this module family is severly broken and underdocumented,
68	so do not use. This was uploaded mainly to reserve the CPAN namespace -
69	stay tuned!
70		61
71	=head1 CONCEPTS	62	=head1 CONCEPTS
72		63
73	=over 4	64	=over 4
74		65
75	=item port	66	=item port
76		67
77	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).
78		70
79	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
80	messages. All C<rcv> handlers will receive messages they match, messages	72	some messages. Messages send to ports will not be queued, regardless of
81	will not be queued.	73	anything was listening for them or not.
82		74
		75	Ports are represented by (printable) strings called "port IDs".
		76
83	=item port id - C<noderef#portname>	77	=item port ID - C<nodeid#portname>
84		78
85	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<#>)
86	separator, and a port name (a printable string of unspecified format). An	80	as separator, and a port name (a printable string of unspecified
87	exception is the the node port, whose ID is identical to its node	81	format created by AnyEvent::MP).
88	reference.
89		82
90	=item node	83	=item node
91		84
92	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,
93	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
94	create new ports, among other things.	87	ports.
95		88
96	Nodes are either private (single-process only), slaves (connected to a	89	Nodes are either public (have one or more listening ports) or private
97	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.
98		92
99	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	93	Nodes is represented by (printable) strings called "node IDs".
100		94
101	A node reference is a string that either simply identifies the node (for	95	=item node ID - C<[A-Za-z0-9_\-.:]*>
102	private and slave nodes), or contains a recipe on how to reach a given
103	node (for public nodes).
104		96
105	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
106	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.
107		101
108	Node references come in two flavours: resolved (containing only numerical	102	=item binds - C<ip:port>
109	addresses) or unresolved (where hostnames are used instead of addresses).
110		103
111	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
112	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).
113		162
114	=back	163	=back
115		164
116	=head1 VARIABLES/FUNCTIONS	165	=head1 VARIABLES/FUNCTIONS
117		166
…		…
119		168
120	=cut	169	=cut
121		170
122	package AnyEvent::MP;	171	package AnyEvent::MP;
123		172
		173	use AnyEvent::MP::Config ();
124	use AnyEvent::MP::Kernel;	174	use AnyEvent::MP::Kernel;
		175	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
125		176
126	use common::sense;	177	use common::sense;
127		178
128	use Carp ();	179	use Carp ();
129		180
130	use AE ();	181	use AnyEvent ();
		182	use Guard ();
131		183
132	use base "Exporter";	184	use base "Exporter";
133		185
134	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	186	our $VERSION = $AnyEvent::MP::Config::VERSION;
135		187
136	our @EXPORT = qw(	188	our @EXPORT = qw(
137	NODE $NODE *SELF node_of _any_	189	NODE $NODE *SELF node_of after
138	resolve_node initialise_node	190	configure
139	snd rcv mon kil reg psub spawn	191	snd rcv mon mon_guard kil psub peval spawn cal
140	port	192	port
		193	db_set db_del db_reg
		194	db_mon db_family db_keys db_values
141	);	195	);
142		196
143	our $SELF;	197	our $SELF;
144		198
145	sub _self_die() {	199	sub _self_die() {
…		…
148	kil $SELF, die => $msg;	202	kil $SELF, die => $msg;
149	}	203	}
150		204
151	=item $thisnode = NODE / $NODE	205	=item $thisnode = NODE / $NODE
152		206
153	The C<NODE> function returns, and the C<$NODE> variable contains	207	The C<NODE> function returns, and the C<$NODE> variable contains, the node
154	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
155	to C<become_public> or C<become_slave>, after which all local port	209	a call to C<configure>.
156	identifiers become invalid.
157		210
158	=item $noderef = node_of $port	211	=item $nodeid = node_of $port
159		212
160	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.
161		214
162	=item initialise_node $noderef, $seednode, $seednode...	215	=item configure $profile, key => value...
163		216
164	=item initialise_node "slave/", $master, $master...	217	=item configure key => value...
165		218
166	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
167	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
168	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.
169		223
170	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
171	never) before calling other AnyEvent::MP functions.	225	never) before calling other AnyEvent::MP functions.
172		226
173	All arguments (optionally except for the first) are noderefs, which can be	227	The key/value pairs are basically the same ones as documented for the
174	either resolved or unresolved.	228	F<aemp> command line utility (sans the set/del prefix), with these additions:
175
176	The first argument will be looked up in the configuration database first
177	(if it is C<undef> then the current nodename will be used instead) to find
178	the relevant configuration profile (see L<aemp>). If none is found then
179	the default configuration is used. The configuration supplies additional
180	seed/master nodes and can override the actual noderef.
181
182	There are two types of networked nodes, public nodes and slave nodes:
183		229
184	=over 4	230	=over 4
185		231
186	=item public nodes	232	=item norc => $boolean (default false)
187		233
188	For public nodes, C<$noderef> (supplied either directly to	234	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
189	C<initialise_node> or indirectly via a profile or the nodename) must be a	235	be consulted - all configuraiton options must be specified in the
190	noderef (possibly unresolved, in which case it will be resolved).	236	C<configure> call.
191		237
192	After resolving, the node will bind itself on all endpoints and try to	238	=item force => $boolean (default false)
193	connect to all additional C<$seednodes> that are specified. Seednodes are
194	optional and can be used to quickly bootstrap the node into an existing
195	network.
196		239
197	=item slave nodes	240	IF true, then the values specified in the C<configure> will take
198		241	precedence over any values configured via the rc file. The default is for
199	When the C<$noderef> (either as given or overriden by the config file)	242	the rc file to override any options specified in the program.
200	is the special string C<slave/>, then the node will become a slave
201	node. Slave nodes cannot be contacted from outside and will route most of
202	their traffic to the master node that they attach to.
203
204	At least one additional noderef is required (either by specifying it
205	directly or because it is part of the configuration profile): The node
206	will try to connect to all of them and will become a slave attached to the
207	first node it can successfully connect to.
208		243
209	=back	244	=back
210		245
211	This function will block until all nodes have been resolved and, for slave
212	nodes, until it has successfully established a connection to a master
213	server.
214
215	Example: become a public node listening on the guessed noderef, or the one
216	specified via C<aemp> for the current node. This should be the most common
217	form of invocation for "daemon"-type nodes.
218
219	initialise_node;
220
221	Example: become a slave node to any of the the seednodes specified via
222	C<aemp>. This form is often used for commandline clients.
223
224	initialise_node "slave/";
225
226	Example: become a slave node to any of the specified master servers. This
227	form is also often used for commandline clients.
228
229	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
230
231	Example: become a public node, and try to contact some well-known master
232	servers to become part of the network.
233
234	initialise_node undef, "master1", "master2";
235
236	Example: become a public node listening on port C<4041>.
237
238	initialise_node 4041;
239
240	Example: become a public node, only visible on localhost port 4044.
241
242	initialise_node "localhost:4044";
243
244	=item $cv = resolve_node $noderef
245
246	Takes an unresolved node reference that may contain hostnames and
247	abbreviated IDs, resolves all of them and returns a resolved node
248	reference.
249
250	In addition to C<address:port> pairs allowed in resolved noderefs, the
251	following forms are supported:
252
253	=over 4	246	=over 4
254		247
255	=item the empty string	248	=item step 1, gathering configuration from profiles
256		249
257	An empty-string component gets resolved as if the default port (4040) was	250	The function first looks up a profile in the aemp configuration (see the
258	specified.	251	L<aemp> commandline utility). The profile name can be specified via the
		252	named C<profile> parameter or can simply be the first parameter). If it is
		253	missing, then the nodename (F<uname -n>) will be used as profile name.
259		254
260	=item naked port numbers (e.g. C<1234>)	255	The profile data is then gathered as follows:
261		256
262	These are resolved by prepending the local nodename and a colon, to be	257	First, all remaining key => value pairs (all of which are conveniently
263	further resolved.	258	undocumented at the moment) will be interpreted as configuration
		259	data. Then they will be overwritten by any values specified in the global
		260	default configuration (see the F<aemp> utility), then the chain of
		261	profiles chosen by the profile name (and any C<parent> attributes).
264		262
265	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	263	That means that the values specified in the profile have highest priority
		264	and the values specified directly via C<configure> have lowest priority,
		265	and can only be used to specify defaults.
266		266
267	These are resolved by using AnyEvent::DNS to resolve them, optionally	267	If the profile specifies a node ID, then this will become the node ID of
268	looking up SRV records for the C<aemp=4040> port, if no port was	268	this process. If not, then the profile name will be used as node ID, with
269	specified.	269	a unique randoms tring (C</%u>) appended.
		270
		271	The node ID can contain some C<%> sequences that are expanded: C<%n>
		272	is expanded to the local nodename, C<%u> is replaced by a random
		273	strign to make the node unique. For example, the F<aemp> commandline
		274	utility uses C<aemp/%n/%u> as nodename, which might expand to
		275	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		276
		277	=item step 2, bind listener sockets
		278
		279	The next step is to look up the binds in the profile, followed by binding
		280	aemp protocol listeners on all binds specified (it is possible and valid
		281	to have no binds, meaning that the node cannot be contacted form the
		282	outside. This means the node cannot talk to other nodes that also have no
		283	binds, but it can still talk to all "normal" nodes).
		284
		285	If the profile does not specify a binds list, then a default of C<*> is
		286	used, meaning the node will bind on a dynamically-assigned port on every
		287	local IP address it finds.
		288
		289	=item step 3, connect to seed nodes
		290
		291	As the last step, the seed ID list from the profile is passed to the
		292	L<AnyEvent::MP::Global> module, which will then use it to keep
		293	connectivity with at least one node at any point in time.
270		294
271	=back	295	=back
		296
		297	Example: become a distributed node using the local node name as profile.
		298	This should be the most common form of invocation for "daemon"-type nodes.
		299
		300	configure
		301
		302	Example: become a semi-anonymous node. This form is often used for
		303	commandline clients.
		304
		305	configure nodeid => "myscript/%n/%u";
		306
		307	Example: configure a node using a profile called seed, which is suitable
		308	for a seed node as it binds on all local addresses on a fixed port (4040,
		309	customary for aemp).
		310
		311	# use the aemp commandline utility
		312	# aemp profile seed binds '*:4040'
		313
		314	# then use it
		315	configure profile => "seed";
		316
		317	# or simply use aemp from the shell again:
		318	# aemp run profile seed
		319
		320	# or provide a nicer-to-remember nodeid
		321	# aemp run profile seed nodeid "$(hostname)"
272		322
273	=item $SELF	323	=item $SELF
274		324
275	Contains the current port id while executing C<rcv> callbacks or C<psub>	325	Contains the current port id while executing C<rcv> callbacks or C<psub>
276	blocks.	326	blocks.
277		327
278	=item SELF, %SELF, @SELF...	328	=item *SELF, SELF, %SELF, @SELF...
279		329
280	Due to some quirks in how perl exports variables, it is impossible to	330	Due to some quirks in how perl exports variables, it is impossible to
281	just export C<$SELF>, all the symbols called C<SELF> are exported by this	331	just export C<$SELF>, all the symbols named C<SELF> are exported by this
282	module, but only C<$SELF> is currently used.	332	module, but only C<$SELF> is currently used.
283		333
284	=item snd $port, type => @data	334	=item snd $port, type => @data
285		335
286	=item snd $port, @msg	336	=item snd $port, @msg
287		337
288	Send the given message to the given port ID, which can identify either	338	Send the given message to the given port, which can identify either a
289	a local or a remote port, and can be either a string or soemthignt hat	339	local or a remote port, and must be a port ID.
290	stringifies a sa port ID (such as a port object :).
291		340
292	While the message can be about anything, it is highly recommended to use a	341	While the message can be almost anything, it is highly recommended to
293	string as first element (a portid, or some word that indicates a request	342	use a string as first element (a port ID, or some word that indicates a
294	type etc.).	343	request type etc.) and to consist if only simple perl values (scalars,
		344	arrays, hashes) - if you think you need to pass an object, think again.
295		345
296	The message data effectively becomes read-only after a call to this	346	The message data logically becomes read-only after a call to this
297	function: modifying any argument is not allowed and can cause many	347	function: modifying any argument (or values referenced by them) is
298	problems.	348	forbidden, as there can be considerable time between the call to C<snd>
		349	and the time the message is actually being serialised - in fact, it might
		350	never be copied as within the same process it is simply handed to the
		351	receiving port.
299		352
300	The type of data you can transfer depends on the transport protocol: when	353	The type of data you can transfer depends on the transport protocol: when
301	JSON is used, then only strings, numbers and arrays and hashes consisting	354	JSON is used, then only strings, numbers and arrays and hashes consisting
302	of those are allowed (no objects). When Storable is used, then anything	355	of those are allowed (no objects). When Storable is used, then anything
303	that Storable can serialise and deserialise is allowed, and for the local	356	that Storable can serialise and deserialise is allowed, and for the local
304	node, anything can be passed.	357	node, anything can be passed. Best rely only on the common denominator of
		358	these.
305		359
306	=item $local_port = port	360	=item $local_port = port
307		361
308	Create a new local port object that can be used either as a pattern	362	Create a new local port object and returns its port ID. Initially it has
309	matching port ("full port") or a single-callback port ("miniport"),	363	no callbacks set and will throw an error when it receives messages.
310	depending on how C<rcv> callbacks are bound to the object.
311		364
312	=item $port = port { my @msg = @_; $finished }	365	=item $local_port = port { my @msg = @_ }
313		366
314	Creates a "miniport", that is, a very lightweight port without any pattern	367	Creates a new local port, and returns its ID. Semantically the same as
315	matching behind it, and returns its ID. Semantically the same as creating
316	a port and calling C<rcv $port, $callback> on it.	368	creating a port and calling C<rcv $port, $callback> on it.
317		369
318	The block will be called for every message received on the port. When the	370	The block will be called for every message received on the port, with the
319	callback returns a true value its job is considered "done" and the port	371	global variable C<$SELF> set to the port ID. Runtime errors will cause the
320	will be destroyed. Otherwise it will stay alive.	372	port to be C<kil>ed. The message will be passed as-is, no extra argument
		373	(i.e. no port ID) will be passed to the callback.
321		374
322	The message will be passed as-is, no extra argument (i.e. no port id) will	375	If you want to stop/destroy the port, simply C<kil> it:
323	be passed to the callback.
324		376
325	If you need the local port id in the callback, this works nicely:	377	my $port = port {
326		378	my @msg = @_;
327	my $port; $port = port {	379	...
328	snd $otherport, reply => $port;	380	kil $SELF;
329	};	381	};
330		382
331	=cut	383	=cut
332		384
333	sub rcv($@);	385	sub rcv($@);
334		386
		387	my $KILME = sub {
		388	(my $tag = substr $_[0], 0, 30) =~ s/([\x20-\x7e])/./g;
		389	kil $SELF, unhandled_message => "no callback found for message '$tag'";
		390	};
		391
335	sub port(;&) {	392	sub port(;&) {
336	my $id = "$UNIQ." . $ID++;	393	my $id = $UNIQ . ++$ID;
337	my $port = "$NODE#$id";	394	my $port = "$NODE#$id";
338		395
339	if (@_) {
340	rcv $port, shift;	396	rcv $port, shift || $KILME;
341	} else {
342	$PORT{$id} = sub { }; # nop
343	}
344		397
345	$port	398	$port
346	}	399	}
347		400
348	=item reg $port, $name
349
350	=item reg $name
351
352	Registers the given port (or C<$SELF><<< if missing) under the name
353	C<$name>. If the name already exists it is replaced.
354
355	A port can only be registered under one well known name.
356
357	A port automatically becomes unregistered when it is killed.
358
359	=cut
360
361	sub reg(@) {
362	my $port = @_ > 1 ? shift : $SELF || Carp::croak 'reg: called with one argument only, but $SELF not set,';
363
364	$REG{$_[0]} = $port;
365	}
366
367	=item rcv $port, $callback->(@msg)	401	=item rcv $local_port, $callback->(@msg)
368		402
369	Replaces the callback on the specified miniport (after converting it to	403	Replaces the default callback on the specified port. There is no way to
370	one if required).	404	remove the default callback: use C<sub { }> to disable it, or better
371		405	C<kil> the port when it is no longer needed.
372	=item rcv $port, tagstring => $callback->(@msg), ...
373
374	=item rcv $port, $smartmatch => $callback->(@msg), ...
375
376	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
377
378	Register callbacks to be called on matching messages on the given full
379	port (after converting it to one if required) and return the port.
380
381	The callback has to return a true value when its work is done, after
382	which is will be removed, or a false value in which case it will stay
383	registered.
384		406
385	The global C<$SELF> (exported by this module) contains C<$port> while	407	The global C<$SELF> (exported by this module) contains C<$port> while
386	executing the callback.	408	executing the callback. Runtime errors during callback execution will
		409	result in the port being C<kil>ed.
387		410
388	Runtime errors during callback execution will result in the port being	411	The default callback receives all messages not matched by a more specific
389	C<kil>ed.	412	C<tag> match.
390		413
391	If the match is an array reference, then it will be matched against the	414	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
392	first elements of the message, otherwise only the first element is being
393	matched.
394		415
395	Any element in the match that is specified as C<_any_> (a function	416	Register (or replace) callbacks to be called on messages starting with the
396	exported by this module) matches any single element of the message.	417	given tag on the given port (and return the port), or unregister it (when
		418	C<$callback> is C<$undef> or missing). There can only be one callback
		419	registered for each tag.
397		420
398	While not required, it is highly recommended that the first matching	421	The original message will be passed to the callback, after the first
399	element is a string identifying the message. The one-string-only match is	422	element (the tag) has been removed. The callback will use the same
400	also the most efficient match (by far).	423	environment as the default callback (see above).
401		424
402	Example: create a port and bind receivers on it in one go.	425	Example: create a port and bind receivers on it in one go.
403		426
404	my $port = rcv port,	427	my $port = rcv port,
405	msg1 => sub { ...; 0 },	428	msg1 => sub { ... },
406	msg2 => sub { ...; 0 },	429	msg2 => sub { ... },
407	;	430	;
408		431
409	Example: create a port, bind receivers and send it in a message elsewhere	432	Example: create a port, bind receivers and send it in a message elsewhere
410	in one go:	433	in one go:
411		434
412	snd $otherport, reply =>	435	snd $otherport, reply =>
413	rcv port,	436	rcv port,
414	msg1 => sub { ...; 0 },	437	msg1 => sub { ... },
415	...	438	...
416	;	439	;
417		440
		441	Example: temporarily register a rcv callback for a tag matching some port
		442	(e.g. for an rpc reply) and unregister it after a message was received.
		443
		444	rcv $port, $otherport => sub {
		445	my @reply = @_;
		446
		447	rcv $SELF, $otherport;
		448	};
		449
418	=cut	450	=cut
419		451
420	sub rcv($@) {	452	sub rcv($@) {
421	my $port = shift;	453	my $port = shift;
422	my ($noderef, $portid) = split /#/, $port, 2;	454	my ($nodeid, $portid) = split /#/, $port, 2;
423		455
424	($NODE{$noderef} || add_node $noderef) == $NODE{""}	456	$NODE{$nodeid} == $NODE{""}
425	or Carp::croak "$port: rcv can only be called on local ports, caught";	457	or Carp::croak "$port: rcv can only be called on local ports, caught";
426		458
427	if (@_ == 1) {	459	while (@_) {
		460	if (ref $_[0]) {
		461	if (my $self = $PORT_DATA{$portid}) {
		462	"AnyEvent::MP::Port" eq ref $self
		463	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		464
		465	$self->[0] = shift;
		466	} else {
428	my $cb = shift;	467	my $cb = shift;
429	delete $PORT_DATA{$portid};
430	$PORT{$portid} = sub {	468	$PORT{$portid} = sub {
431	local $SELF = $port;	469	local $SELF = $port;
432	eval {	470	eval { &$cb }; _self_die if $@;
433	&$cb	471	};
434	and kil $port;
435	};	472	}
436	_self_die if $@;	473	} elsif (defined $_[0]) {
437	};
438	} else {
439	my $self = $PORT_DATA{$portid} ||= do {	474	my $self = $PORT_DATA{$portid} ||= do {
440	my $self = bless {	475	my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port";
441	id => $port,
442	}, "AnyEvent::MP::Port";
443		476
444	$PORT{$portid} = sub {	477	$PORT{$portid} = sub {
445	local $SELF = $port;	478	local $SELF = $port;
446		479
447	eval {
448	for (@{ $self->{rc0}{$_[0]} }) {	480	if (my $cb = $self->[1]{$_[0]}) {
449	$_ && &{$_->[0]}	481	shift;
450	&& undef $_;	482	eval { &$cb }; _self_die if $@;
451	}	483	} else {
452
453	for (@{ $self->{rcv}{$_[0]} }) {
454	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
455	&& &{$_->[0]}	484	&{ $self->[0] };
456	&& undef $_;
457	}
458
459	for (@{ $self->{any} }) {
460	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
461	&& &{$_->[0]}
462	&& undef $_;
463	}	485	}
464	};	486	};
465	_self_die if $@;	487
		488	$self
466	};	489	};
467		490
468	$self
469	};
470
471	"AnyEvent::MP::Port" eq ref $self	491	"AnyEvent::MP::Port" eq ref $self
472	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	492	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
473		493
474	while (@_) {
475	my ($match, $cb) = splice @_, 0, 2;	494	my ($tag, $cb) = splice @_, 0, 2;
476		495
477	if (!ref $match) {	496	if (defined $cb) {
478	push @{ $self->{rc0}{$match} }, [$cb];	497	$self->[1]{$tag} = $cb;
479	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
480	my ($type, @match) = @$match;
481	@match
482	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
483	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
484	} else {	498	} else {
485	push @{ $self->{any} }, [$cb, $match];	499	delete $self->[1]{$tag};
486	}	500	}
487	}	501	}
488	}	502	}
489		503
490	$port	504	$port
491	}	505	}
492		506
		507	=item peval $port, $coderef[, @args]
		508
		509	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		510	when the code throews an exception the C<$port> will be killed.
		511
		512	Any remaining args will be passed to the callback. Any return values will
		513	be returned to the caller.
		514
		515	This is useful when you temporarily want to execute code in the context of
		516	a port.
		517
		518	Example: create a port and run some initialisation code in it's context.
		519
		520	my $port = port { ... };
		521
		522	peval $port, sub {
		523	init
		524	or die "unable to init";
		525	};
		526
		527	=cut
		528
		529	sub peval($$) {
		530	local $SELF = shift;
		531	my $cb = shift;
		532
		533	if (wantarray) {
		534	my @res = eval { &$cb };
		535	_self_die if $@;
		536	@res
		537	} else {
		538	my $res = eval { &$cb };
		539	_self_die if $@;
		540	$res
		541	}
		542	}
		543
493	=item $closure = psub { BLOCK }	544	=item $closure = psub { BLOCK }
494		545
495	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	546	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
496	closure is executed, sets up the environment in the same way as in C<rcv>	547	closure is executed, sets up the environment in the same way as in C<rcv>
497	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.	548	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		549
		550	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		551	BLOCK }, @_ } >>.
498		552
499	This is useful when you register callbacks from C<rcv> callbacks:	553	This is useful when you register callbacks from C<rcv> callbacks:
500		554
501	rcv delayed_reply => sub {	555	rcv delayed_reply => sub {
502	my ($delay, @reply) = @_;	556	my ($delay, @reply) = @_;
…		…
526	$res	580	$res
527	}	581	}
528	}	582	}
529	}	583	}
530		584
531	=item $guard = mon $port, $cb->(@reason)	585	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
532		586
533	=item $guard = mon $port, $rcvport	587	=item $guard = mon $port # kill $SELF when $port dies
534		588
535	=item $guard = mon $port	589	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
536		590
537	=item $guard = mon $port, $rcvport, @msg	591	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
538		592
539	Monitor the given port and do something when the port is killed or	593	Monitor the given port and do something when the port is killed or
540	messages to it were lost, and optionally return a guard that can be used	594	messages to it were lost, and optionally return a guard that can be used
541	to stop monitoring again.	595	to stop monitoring again.
542		596
		597	The first two forms distinguish between "normal" and "abnormal" kil's:
		598
		599	In the first form (another port given), if the C<$port> is C<kil>'ed with
		600	a non-empty reason, the other port (C<$rcvport>) will be kil'ed with the
		601	same reason. That is, on "normal" kil's nothing happens, while under all
		602	other conditions, the other port is killed with the same reason.
		603
		604	The second form (kill self) is the same as the first form, except that
		605	C<$rvport> defaults to C<$SELF>.
		606
		607	The remaining forms don't distinguish between "normal" and "abnormal" kil's
		608	- it's up to the callback or receiver to check whether the C<@reason> is
		609	empty and act accordingly.
		610
		611	In the third form (callback), the callback is simply called with any
		612	number of C<@reason> elements (empty @reason means that the port was deleted
		613	"normally"). Note also that I<< the callback B<must> never die >>, so use
		614	C<eval> if unsure.
		615
		616	In the last form (message), a message of the form C<$rcvport, @msg,
		617	@reason> will be C<snd>.
		618
		619	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		620	alert was raised), they are removed and will not trigger again, even if it
		621	turns out that the port is still alive.
		622
		623	As a rule of thumb, monitoring requests should always monitor a remote
		624	port locally (using a local C<$rcvport> or a callback). The reason is that
		625	kill messages might get lost, just like any other message. Another less
		626	obvious reason is that even monitoring requests can get lost (for example,
		627	when the connection to the other node goes down permanently). When
		628	monitoring a port locally these problems do not exist.
		629
543	C<mon> effectively guarantees that, in the absence of hardware failures,	630	C<mon> effectively guarantees that, in the absence of hardware failures,
544	that after starting the monitor, either all messages sent to the port	631	after starting the monitor, either all messages sent to the port will
545	will arrive, or the monitoring action will be invoked after possible	632	arrive, or the monitoring action will be invoked after possible message
546	message loss has been detected. No messages will be lost "in between"	633	loss has been detected. No messages will be lost "in between" (after
547	(after the first lost message no further messages will be received by the	634	the first lost message no further messages will be received by the
548	port). After the monitoring action was invoked, further messages might get	635	port). After the monitoring action was invoked, further messages might get
549	delivered again.	636	delivered again.
550		637
551	In the first form (callback), the callback is simply called with any	638	Inter-host-connection timeouts and monitoring depend on the transport
552	number of C<@reason> elements (no @reason means that the port was deleted	639	used. The only transport currently implemented is TCP, and AnyEvent::MP
553	"normally"). Note also that I<< the callback B<must> never die >>, so use	640	relies on TCP to detect node-downs (this can take 10-15 minutes on a
554	C<eval> if unsure.	641	non-idle connection, and usually around two hours for idle connections).
555		642
556	In the second form (another port given), the other port (C<$rcvport>)	643	This means that monitoring is good for program errors and cleaning up
557	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	644	stuff eventually, but they are no replacement for a timeout when you need
558	"normal" kils nothing happens, while under all other conditions, the other	645	to ensure some maximum latency.
559	port is killed with the same reason.
560
561	The third form (kill self) is the same as the second form, except that
562	C<$rvport> defaults to C<$SELF>.
563
564	In the last form (message), a message of the form C<@msg, @reason> will be
565	C<snd>.
566
567	As a rule of thumb, monitoring requests should always monitor a port from
568	a local port (or callback). The reason is that kill messages might get
569	lost, just like any other message. Another less obvious reason is that
570	even monitoring requests can get lost (for exmaple, when the connection
571	to the other node goes down permanently). When monitoring a port locally
572	these problems do not exist.
573		646
574	Example: call a given callback when C<$port> is killed.	647	Example: call a given callback when C<$port> is killed.
575		648
576	mon $port, sub { warn "port died because of <@_>\n" };	649	mon $port, sub { warn "port died because of <@_>\n" };
577		650
…		…
584	mon $port, $self => "restart";	657	mon $port, $self => "restart";
585		658
586	=cut	659	=cut
587		660
588	sub mon {	661	sub mon {
589	my ($noderef, $port) = split /#/, shift, 2;	662	my ($nodeid, $port) = split /#/, shift, 2;
590		663
591	my $node = $NODE{$noderef} || add_node $noderef;	664	my $node = $NODE{$nodeid} || add_node $nodeid;
592		665
593	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';	666	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
594		667
595	unless (ref $cb) {	668	unless (ref $cb) {
596	if (@_) {	669	if (@_) {
…		…
605	}	678	}
606		679
607	$node->monitor ($port, $cb);	680	$node->monitor ($port, $cb);
608		681
609	defined wantarray	682	defined wantarray
610	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	683	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
611	}	684	}
612		685
613	=item $guard = mon_guard $port, $ref, $ref...	686	=item $guard = mon_guard $port, $ref, $ref...
614		687
615	Monitors the given C<$port> and keeps the passed references. When the port	688	Monitors the given C<$port> and keeps the passed references. When the port
616	is killed, the references will be freed.	689	is killed, the references will be freed.
617		690
618	Optionally returns a guard that will stop the monitoring.	691	Optionally returns a guard that will stop the monitoring.
619		692
620	This function is useful when you create e.g. timers or other watchers and	693	This function is useful when you create e.g. timers or other watchers and
621	want to free them when the port gets killed:	694	want to free them when the port gets killed (note the use of C<psub>):
622		695
623	$port->rcv (start => sub {	696	$port->rcv (start => sub {
624	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	697	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
625	undef $timer if 0.9 < rand;	698	undef $timer if 0.9 < rand;
626	});	699	});
627	});	700	});
628		701
629	=cut	702	=cut
…		…
638		711
639	=item kil $port[, @reason]	712	=item kil $port[, @reason]
640		713
641	Kill the specified port with the given C<@reason>.	714	Kill the specified port with the given C<@reason>.
642		715
643	If no C<@reason> is specified, then the port is killed "normally" (linked	716	If no C<@reason> is specified, then the port is killed "normally" -
644	ports will not be kileld, or even notified).	717	monitor callback will be invoked, but the kil will not cause linked ports
		718	(C<mon $mport, $lport> form) to get killed.
645		719
646	Otherwise, linked ports get killed with the same reason (second form of	720	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
647	C<mon>, see below).	721	form) get killed with the same reason.
648		722
649	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	723	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
650	will be reported as reason C<< die => $@ >>.	724	will be reported as reason C<< die => $@ >>.
651		725
652	Transport/communication errors are reported as C<< transport_error =>	726	Transport/communication errors are reported as C<< transport_error =>
653	$message >>.	727	$message >>.
654		728
655	=cut	729	Common idioms:
		730
		731	# silently remove yourself, do not kill linked ports
		732	kil $SELF;
		733
		734	# report a failure in some detail
		735	kil $SELF, failure_mode_1 => "it failed with too high temperature";
		736
		737	# do not waste much time with killing, just die when something goes wrong
		738	open my $fh, "<file"
		739	or die "file: $!";
656		740
657	=item $port = spawn $node, $initfunc[, @initdata]	741	=item $port = spawn $node, $initfunc[, @initdata]
658		742
659	Creates a port on the node C<$node> (which can also be a port ID, in which	743	Creates a port on the node C<$node> (which can also be a port ID, in which
660	case it's the node where that port resides).	744	case it's the node where that port resides).
661		745
662	The port ID of the newly created port is return immediately, and it is	746	The port ID of the newly created port is returned immediately, and it is
663	permissible to immediately start sending messages or monitor the port.	747	possible to immediately start sending messages or to monitor the port.
664		748
665	After the port has been created, the init function is	749	After the port has been created, the init function is called on the remote
666	called. This function must be a fully-qualified function name	750	node, in the same context as a C<rcv> callback. This function must be a
667	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	751	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
668	program, use C<::name>.	752	specify a function in the main program, use C<::name>.
669		753
670	If the function doesn't exist, then the node tries to C<require>	754	If the function doesn't exist, then the node tries to C<require>
671	the package, then the package above the package and so on (e.g.	755	the package, then the package above the package and so on (e.g.
672	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	756	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
673	exists or it runs out of package names.	757	exists or it runs out of package names.
674		758
675	The init function is then called with the newly-created port as context	759	The init function is then called with the newly-created port as context
676	object (C<$SELF>) and the C<@initdata> values as arguments.	760	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		761	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		762	the port might not get created.
677		763
678	A common idiom is to pass your own port, monitor the spawned port, and	764	A common idiom is to pass a local port, immediately monitor the spawned
679	in the init function, monitor the original port. This two-way monitoring	765	port, and in the remote init function, immediately monitor the passed
680	ensures that both ports get cleaned up when there is a problem.	766	local port. This two-way monitoring ensures that both ports get cleaned up
		767	when there is a problem.
		768
		769	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		770	caller before C<spawn> returns (by delaying invocation when spawn is
		771	called for the local node).
681		772
682	Example: spawn a chat server port on C<$othernode>.	773	Example: spawn a chat server port on C<$othernode>.
683		774
684	# this node, executed from within a port context:	775	# this node, executed from within a port context:
685	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	776	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
700		791
701	sub _spawn {	792	sub _spawn {
702	my $port = shift;	793	my $port = shift;
703	my $init = shift;	794	my $init = shift;
704		795
		796	# rcv will create the actual port
705	local $SELF = "$NODE#$port";	797	local $SELF = "$NODE#$port";
706	eval {	798	eval {
707	&{ load_func $init }	799	&{ load_func $init }
708	};	800	};
709	_self_die if $@;	801	_self_die if $@;
710	}	802	}
711		803
712	sub spawn(@) {	804	sub spawn(@) {
713	my ($noderef, undef) = split /#/, shift, 2;	805	my ($nodeid, undef) = split /#/, shift, 2;
714		806
715	my $id = "$RUNIQ." . $ID++;	807	my $id = $RUNIQ . ++$ID;
716		808
717	$_[0] =~ /::/	809	$_[0] =~ /::/
718	or Carp::croak "spawn init function must be a fully-qualified name, caught";	810	or Carp::croak "spawn init function must be a fully-qualified name, caught";
719		811
720	($NODE{$noderef} || add_node $noderef)	812	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
721	->send (["", "AnyEvent::MP::_spawn" => $id, @_]);
722		813
723	"$noderef#$id"	814	"$nodeid#$id"
724	}	815	}
725		816
		817
		818	=item after $timeout, @msg
		819
		820	=item after $timeout, $callback
		821
		822	Either sends the given message, or call the given callback, after the
		823	specified number of seconds.
		824
		825	This is simply a utility function that comes in handy at times - the
		826	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		827	so it may go away in the future.
		828
		829	=cut
		830
		831	sub after($@) {
		832	my ($timeout, @action) = @_;
		833
		834	my $t; $t = AE::timer $timeout, 0, sub {
		835	undef $t;
		836	ref $action[0]
		837	? $action[0]()
		838	: snd @action;
		839	};
		840	}
		841
		842	#=item $cb2 = timeout $seconds, $cb[, @args]
		843
		844	=item cal $port, @msg, $callback[, $timeout]
		845
		846	A simple form of RPC - sends a message to the given C<$port> with the
		847	given contents (C<@msg>), but adds a reply port to the message.
		848
		849	The reply port is created temporarily just for the purpose of receiving
		850	the reply, and will be C<kil>ed when no longer needed.
		851
		852	A reply message sent to the port is passed to the C<$callback> as-is.
		853
		854	If an optional time-out (in seconds) is given and it is not C<undef>,
		855	then the callback will be called without any arguments after the time-out
		856	elapsed and the port is C<kil>ed.
		857
		858	If no time-out is given (or it is C<undef>), then the local port will
		859	monitor the remote port instead, so it eventually gets cleaned-up.
		860
		861	Currently this function returns the temporary port, but this "feature"
		862	might go in future versions unless you can make a convincing case that
		863	this is indeed useful for something.
		864
		865	=cut
		866
		867	sub cal(@) {
		868	my $timeout = ref $_[-1] ? undef : pop;
		869	my $cb = pop;
		870
		871	my $port = port {
		872	undef $timeout;
		873	kil $SELF;
		874	&$cb;
		875	};
		876
		877	if (defined $timeout) {
		878	$timeout = AE::timer $timeout, 0, sub {
		879	undef $timeout;
		880	kil $port;
		881	$cb->();
		882	};
		883	} else {
		884	mon $_[0], sub {
		885	kil $port;
		886	$cb->();
		887	};
		888	}
		889
		890	push @_, $port;
		891	&snd;
		892
		893	$port
		894	}
		895
726	=back	896	=back
727		897
728	=head1 NODE MESSAGES	898	=head1 DISTRIBUTED DATABASE
729		899
730	Nodes understand the following messages sent to them. Many of them take	900	AnyEvent::MP comes with a simple distributed database. The database will
731	arguments called C<@reply>, which will simply be used to compose a reply	901	be mirrored asynchronously on all global nodes. Other nodes bind to one
732	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and	902	of the global nodes for their needs. Every node has a "local database"
733	the remaining arguments are simply the message data.	903	which contains all the values that are set locally. All local databases
		904	are merged together to form the global database, which can be queried.
734		905
735	While other messages exist, they are not public and subject to change.	906	The database structure is that of a two-level hash - the database hash
		907	contains hashes which contain values, similarly to a perl hash of hashes,
		908	i.e.:
736		909
		910	$DATABASE{$family}{$subkey} = $value
		911
		912	The top level hash key is called "family", and the second-level hash key
		913	is called "subkey" or simply "key".
		914
		915	The family must be alphanumeric, i.e. start with a letter and consist
		916	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		917	pretty much like Perl module names.
		918
		919	As the family namespace is global, it is recommended to prefix family names
		920	with the name of the application or module using it.
		921
		922	The subkeys must be non-empty strings, with no further restrictions.
		923
		924	The values should preferably be strings, but other perl scalars should
		925	work as well (such as C<undef>, arrays and hashes).
		926
		927	Every database entry is owned by one node - adding the same family/subkey
		928	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		929	but the result might be nondeterministic, i.e. the key might have
		930	different values on different nodes.
		931
		932	Different subkeys in the same family can be owned by different nodes
		933	without problems, and in fact, this is the common method to create worker
		934	pools. For example, a worker port for image scaling might do this:
		935
		936	db_set my_image_scalers => $port;
		937
		938	And clients looking for an image scaler will want to get the
		939	C<my_image_scalers> keys from time to time:
		940
		941	db_keys my_image_scalers => sub {
		942	@ports = @{ $_[0] };
		943	};
		944
		945	Or better yet, they want to monitor the database family, so they always
		946	have a reasonable up-to-date copy:
		947
		948	db_mon my_image_scalers => sub {
		949	@ports = keys %{ $_[0] };
		950	};
		951
		952	In general, you can set or delete single subkeys, but query and monitor
		953	whole families only.
		954
		955	If you feel the need to monitor or query a single subkey, try giving it
		956	it's own family.
		957
737	=over 4	958	=over
		959
		960	=item $guard = db_set $family => $subkey [=> $value]
		961
		962	Sets (or replaces) a key to the database - if C<$value> is omitted,
		963	C<undef> is used instead.
		964
		965	When called in non-void context, C<db_set> returns a guard that
		966	automatically calls C<db_del> when it is destroyed.
		967
		968	=item db_del $family => $subkey...
		969
		970	Deletes one or more subkeys from the database family.
		971
		972	=item $guard = db_reg $family => $port => $value
		973
		974	=item $guard = db_reg $family => $port
		975
		976	=item $guard = db_reg $family
		977
		978	Registers a port in the given family and optionally returns a guard to
		979	remove it.
		980
		981	This function basically does the same as:
		982
		983	db_set $family => $port => $value
		984
		985	Except that the port is monitored and automatically removed from the
		986	database family when it is kil'ed.
		987
		988	If C<$value> is missing, C<undef> is used. If C<$port> is missing, then
		989	C<$SELF> is used.
		990
		991	This function is most useful to register a port in some port group (which
		992	is just another name for a database family), and have it removed when the
		993	port is gone. This works best when the port is a local port.
738		994
739	=cut	995	=cut
740		996
741	=item lookup => $name, @reply	997	sub db_reg($$;$) {
		998	my $family = shift;
		999	my $port = @_ ? shift : $SELF;
742		1000
743	Replies with the port ID of the specified well-known port, or C<undef>.	1001	my $clr = sub { db_del $family => $port };
		1002	mon $port, $clr;
744		1003
745	=item devnull => ...	1004	db_set $family => $port => $_[0];
746		1005
747	Generic data sink/CPU heat conversion.	1006	defined wantarray
		1007	and &Guard::guard ($clr)
		1008	}
748		1009
749	=item relay => $port, @msg	1010	=item db_family $family => $cb->(\%familyhash)
750		1011
751	Simply forwards the message to the given port.	1012	Queries the named database C<$family> and call the callback with the
		1013	family represented as a hash. You can keep and freely modify the hash.
752		1014
753	=item eval => $string[ @reply]	1015	=item db_keys $family => $cb->(\@keys)
754		1016
755	Evaluates the given string. If C<@reply> is given, then a message of the	1017	Same as C<db_family>, except it only queries the family I<subkeys> and passes
756	form C<@reply, $@, @evalres> is sent.	1018	them as array reference to the callback.
757		1019
758	Example: crash another node.	1020	=item db_values $family => $cb->(\@values)
759		1021
760	snd $othernode, eval => "exit";	1022	Same as C<db_family>, except it only queries the family I<values> and passes them
		1023	as array reference to the callback.
761		1024
762	=item time => @reply	1025	=item $guard = db_mon $family => $cb->($familyhash, \@added, \@changed, \@deleted)
763		1026
764	Replies the the current node time to C<@reply>.	1027	Creates a monitor on the given database family. Each time a key is set
		1028	or or is deleted the callback is called with a hash containing the
		1029	database family and three lists of added, changed and deleted subkeys,
		1030	respectively. If no keys have changed then the array reference might be
		1031	C<undef> or even missing.
765		1032
766	Example: tell the current node to send the current time to C<$myport> in a	1033	If not called in void context, a guard object is returned that, when
767	C<timereply> message.	1034	destroyed, stops the monitor.
768		1035
769	snd $NODE, time => $myport, timereply => 1, 2;	1036	The family hash reference and the key arrays belong to AnyEvent::MP and
770	# => snd $myport, timereply => 1, 2, <time>	1037	B<must not be modified or stored> by the callback. When in doubt, make a
		1038	copy.
		1039
		1040	As soon as possible after the monitoring starts, the callback will be
		1041	called with the intiial contents of the family, even if it is empty,
		1042	i.e. there will always be a timely call to the callback with the current
		1043	contents.
		1044
		1045	It is possible that the callback is called with a change event even though
		1046	the subkey is already present and the value has not changed.
		1047
		1048	The monitoring stops when the guard object is destroyed.
		1049
		1050	Example: on every change to the family "mygroup", print out all keys.
		1051
		1052	my $guard = db_mon mygroup => sub {
		1053	my ($family, $a, $c, $d) = @_;
		1054	print "mygroup members: ", (join " ", keys %$family), "\n";
		1055	};
		1056
		1057	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1058
		1059	my $guard; $guard = db_mon My::Module::workers => sub {
		1060	my ($family, $a, $c, $d) = @_;
		1061	return unless %$family;
		1062	undef $guard;
		1063	print "My::Module::workers now nonempty\n";
		1064	};
		1065
		1066	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		1067
		1068	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		1069	my ($family, $a, $c, $d) = @_;
		1070
		1071	print "+$_=$family->{$_}\n" for @$a;
		1072	print "*$_=$family->{$_}\n" for @$c;
		1073	print "-$_=$family->{$_}\n" for @$d;
		1074	};
		1075
		1076	=cut
771		1077
772	=back	1078	=back
773		1079
774	=head1 AnyEvent::MP vs. Distributed Erlang	1080	=head1 AnyEvent::MP vs. Distributed Erlang
775		1081
776	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	1082	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
777	== aemp node, Erlang process == aemp port), so many of the documents and	1083	== aemp node, Erlang process == aemp port), so many of the documents and
778	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	1084	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
779	sample:	1085	sample:
780		1086
781	http://www.Erlang.se/doc/programming_rules.shtml	1087	http://www.erlang.se/doc/programming_rules.shtml
782	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	1088	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
783	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	1089	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
784	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	1090	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
785		1091
786	Despite the similarities, there are also some important differences:	1092	Despite the similarities, there are also some important differences:
787		1093
788	=over 4	1094	=over 4
789		1095
790	=item * Node references contain the recipe on how to contact them.	1096	=item * Node IDs are arbitrary strings in AEMP.
791		1097
792	Erlang relies on special naming and DNS to work everywhere in the	1098	Erlang relies on special naming and DNS to work everywhere in the same
793	same way. AEMP relies on each node knowing it's own address(es), with	1099	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
794	convenience functionality.	1100	configuration or DNS), and possibly the addresses of some seed nodes, but
		1101	will otherwise discover other nodes (and their IDs) itself.
795		1102
796	This means that AEMP requires a less tightly controlled environment at the	1103	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
797	cost of longer node references and a slightly higher management overhead.	1104	uses "local ports are like remote ports".
		1105
		1106	The failure modes for local ports are quite different (runtime errors
		1107	only) then for remote ports - when a local port dies, you I<know> it dies,
		1108	when a connection to another node dies, you know nothing about the other
		1109	port.
		1110
		1111	Erlang pretends remote ports are as reliable as local ports, even when
		1112	they are not.
		1113
		1114	AEMP encourages a "treat remote ports differently" philosophy, with local
		1115	ports being the special case/exception, where transport errors cannot
		1116	occur.
798		1117
799	=item * Erlang uses processes and a mailbox, AEMP does not queue.	1118	=item * Erlang uses processes and a mailbox, AEMP does not queue.
800		1119
801	Erlang uses processes that selctively receive messages, and therefore	1120	Erlang uses processes that selectively receive messages out of order, and
802	needs a queue. AEMP is event based, queuing messages would serve no useful	1121	therefore needs a queue. AEMP is event based, queuing messages would serve
803	purpose.	1122	no useful purpose. For the same reason the pattern-matching abilities
		1123	of AnyEvent::MP are more limited, as there is little need to be able to
		1124	filter messages without dequeuing them.
804		1125
805	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	1126	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1127	being event-based, while Erlang is process-based.
		1128
		1129	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1130	top of AEMP and Coro threads.
806		1131
807	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1132	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
808		1133
809	Sending messages in Erlang is synchronous and blocks the process. AEMP	1134	Sending messages in Erlang is synchronous and blocks the process until
810	sends are immediate, connection establishment is handled in the	1135	a conenction has been established and the message sent (and so does not
811	background.	1136	need a queue that can overflow). AEMP sends return immediately, connection
		1137	establishment is handled in the background.
812		1138
813	=item * Erlang can silently lose messages, AEMP cannot.	1139	=item * Erlang suffers from silent message loss, AEMP does not.
814		1140
815	Erlang makes few guarantees on messages delivery - messages can get lost	1141	Erlang implements few guarantees on messages delivery - messages can get
816	without any of the processes realising it (i.e. you send messages a, b,	1142	lost without any of the processes realising it (i.e. you send messages a,
817	and c, and the other side only receives messages a and c).	1143	b, and c, and the other side only receives messages a and c).
818		1144
819	AEMP guarantees correct ordering, and the guarantee that there are no	1145	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1146	guarantee that after one message is lost, all following ones sent to the
		1147	same port are lost as well, until monitoring raises an error, so there are
820	holes in the message sequence.	1148	no silent "holes" in the message sequence.
821		1149
822	=item * In Erlang, processes can be declared dead and later be found to be	1150	If you want your software to be very reliable, you have to cope with
823	alive.	1151	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
824		1152	simply tries to work better in common error cases, such as when a network
825	In Erlang it can happen that a monitored process is declared dead and	1153	link goes down.
826	linked processes get killed, but later it turns out that the process is
827	still alive - and can receive messages.
828
829	In AEMP, when port monitoring detects a port as dead, then that port will
830	eventually be killed - it cannot happen that a node detects a port as dead
831	and then later sends messages to it, finding it is still alive.
832		1154
833	=item * Erlang can send messages to the wrong port, AEMP does not.	1155	=item * Erlang can send messages to the wrong port, AEMP does not.
834		1156
835	In Erlang it is quite possible that a node that restarts reuses a process	1157	In Erlang it is quite likely that a node that restarts reuses an Erlang
836	ID known to other nodes for a completely different process, causing	1158	process ID known to other nodes for a completely different process,
837	messages destined for that process to end up in an unrelated process.	1159	causing messages destined for that process to end up in an unrelated
		1160	process.
838		1161
839	AEMP never reuses port IDs, so old messages or old port IDs floating	1162	AEMP does not reuse port IDs, so old messages or old port IDs floating
840	around in the network will not be sent to an unrelated port.	1163	around in the network will not be sent to an unrelated port.
841		1164
842	=item * Erlang uses unprotected connections, AEMP uses secure	1165	=item * Erlang uses unprotected connections, AEMP uses secure
843	authentication and can use TLS.	1166	authentication and can use TLS.
844		1167
845	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1168	AEMP can use a proven protocol - TLS - to protect connections and
846	securely authenticate nodes.	1169	securely authenticate nodes.
847		1170
848	=item * The AEMP protocol is optimised for both text-based and binary	1171	=item * The AEMP protocol is optimised for both text-based and binary
849	communications.	1172	communications.
850		1173
851	The AEMP protocol, unlike the Erlang protocol, supports both	1174	The AEMP protocol, unlike the Erlang protocol, supports both programming
852	language-independent text-only protocols (good for debugging) and binary,	1175	language independent text-only protocols (good for debugging), and binary,
853	language-specific serialisers (e.g. Storable).	1176	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1177	used, the protocol is actually completely text-based.
854		1178
855	It has also been carefully designed to be implementable in other languages	1179	It has also been carefully designed to be implementable in other languages
856	with a minimum of work while gracefully degrading fucntionality to make the	1180	with a minimum of work while gracefully degrading functionality to make the
857	protocol simple.	1181	protocol simple.
858		1182
859	=item * AEMP has more flexible monitoring options than Erlang.	1183	=item * AEMP has more flexible monitoring options than Erlang.
860		1184
861	In Erlang, you can chose to receive I<all> exit signals as messages	1185	In Erlang, you can chose to receive I<all> exit signals as messages or
862	or I<none>, there is no in-between, so monitoring single processes is	1186	I<none>, there is no in-between, so monitoring single Erlang processes is
863	difficult to implement. Monitoring in AEMP is more flexible than in	1187	difficult to implement.
864	Erlang, as one can choose between automatic kill, exit message or callback	1188
865	on a per-process basis.	1189	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1190	between automatic kill, exit message or callback on a per-port basis.
866		1191
867	=item * Erlang tries to hide remote/local connections, AEMP does not.	1192	=item * Erlang tries to hide remote/local connections, AEMP does not.
868		1193
869	Monitoring in Erlang is not an indicator of process death/crashes,	1194	Monitoring in Erlang is not an indicator of process death/crashes, in the
870	as linking is (except linking is unreliable in Erlang).	1195	same way as linking is (except linking is unreliable in Erlang).
871		1196
872	In AEMP, you don't "look up" registered port names or send to named ports	1197	In AEMP, you don't "look up" registered port names or send to named ports
873	that might or might not be persistent. Instead, you normally spawn a port	1198	that might or might not be persistent. Instead, you normally spawn a port
874	on the remote node. The init function monitors the you, and you monitor	1199	on the remote node. The init function monitors you, and you monitor the
875	the remote port. Since both monitors are local to the node, they are much	1200	remote port. Since both monitors are local to the node, they are much more
876	more reliable.	1201	reliable (no need for C<spawn_link>).
877		1202
878	This also saves round-trips and avoids sending messages to the wrong port	1203	This also saves round-trips and avoids sending messages to the wrong port
879	(hard to do in Erlang).	1204	(hard to do in Erlang).
880		1205
881	=back	1206	=back
882		1207
883	=head1 RATIONALE	1208	=head1 RATIONALE
884		1209
885	=over 4	1210	=over 4
886		1211
887	=item Why strings for ports and noderefs, why not objects?	1212	=item Why strings for port and node IDs, why not objects?
888		1213
889	We considered "objects", but found that the actual number of methods	1214	We considered "objects", but found that the actual number of methods
890	thatc an be called are very low. Since port IDs and noderefs travel over	1215	that can be called are quite low. Since port and node IDs travel over
891	the network frequently, the serialising/deserialising would add lots of	1216	the network frequently, the serialising/deserialising would add lots of
892	overhead, as well as having to keep a proxy object.	1217	overhead, as well as having to keep a proxy object everywhere.
893		1218
894	Strings can easily be printed, easily serialised etc. and need no special	1219	Strings can easily be printed, easily serialised etc. and need no special
895	procedures to be "valid".	1220	procedures to be "valid".
896		1221
897	And a a miniport consists of a single closure stored in a global hash - it	1222	And as a result, a port with just a default receiver consists of a single
898	can't become much cheaper.	1223	code reference stored in a global hash - it can't become much cheaper.
899		1224
900	=item Why favour JSON, why not real serialising format such as Storable?	1225	=item Why favour JSON, why not a real serialising format such as Storable?
901		1226
902	In fact, any AnyEvent::MP node will happily accept Storable as framing	1227	In fact, any AnyEvent::MP node will happily accept Storable as framing
903	format, but currently there is no way to make a node use Storable by	1228	format, but currently there is no way to make a node use Storable by
904	default.	1229	default (although all nodes will accept it).
905		1230
906	The default framing protocol is JSON because a) JSON::XS is many times	1231	The default framing protocol is JSON because a) JSON::XS is many times
907	faster for small messages and b) most importantly, after years of	1232	faster for small messages and b) most importantly, after years of
908	experience we found that object serialisation is causing more problems	1233	experience we found that object serialisation is causing more problems
909	than it gains: Just like function calls, objects simply do not travel	1234	than it solves: Just like function calls, objects simply do not travel
910	easily over the network, mostly because they will always be a copy, so you	1235	easily over the network, mostly because they will always be a copy, so you
911	always have to re-think your design.	1236	always have to re-think your design.
912		1237
913	Keeping your messages simple, concentrating on data structures rather than	1238	Keeping your messages simple, concentrating on data structures rather than
914	objects, will keep your messages clean, tidy and efficient.	1239	objects, will keep your messages clean, tidy and efficient.
915		1240
916	=back	1241	=back
917		1242
		1243	=head1 PORTING FROM AnyEvent::MP VERSION 1.X
		1244
		1245	AEMP version 2 has a few major incompatible changes compared to version 1:
		1246
		1247	=over 4
		1248
		1249	=item AnyEvent::MP::Global no longer has group management functions.
		1250
		1251	At least not officially - the grp_* functions are still exported and might
		1252	work, but they will be removed in some later release.
		1253
		1254	AnyEvent::MP now comes with a distributed database that is more
		1255	powerful. Its database families map closely to port groups, but the API
		1256	has changed (the functions are also now exported by AnyEvent::MP). Here is
		1257	a rough porting guide:
		1258
		1259	grp_reg $group, $port # old
		1260	db_reg $group, $port # new
		1261
		1262	$list = grp_get $group # old
		1263	db_keys $group, sub { my $list = shift } # new
		1264
		1265	grp_mon $group, $cb->(\@ports, $add, $del) # old
		1266	db_mon $group, $cb->(\%ports, $add, $change, $del) # new
		1267
		1268	C<grp_reg> is a no-brainer (just replace by C<db_reg>), but C<grp_get> is
		1269	no longer instant, because the local node might not have a copy of the
		1270	group. You can either modify your code to allow for a callback, or use
		1271	C<db_mon> to keep an updated copy of the group:
		1272
		1273	my $local_group_copy;
		1274	db_mon $group => sub { $local_group_copy = $_[0] };
		1275
		1276	# now "keys %$local_group_copy" always returns the most up-to-date
		1277	# list of ports in the group.
		1278
		1279	C<grp_mon> can be replaced by C<db_mon> with minor changes - C<db_mon>
		1280	passes a hash as first argument, and an extra C<$chg> argument that can be
		1281	ignored:
		1282
		1283	db_mon $group => sub {
		1284	my ($ports, $add, $chg, $lde) = @_;
		1285	$ports = [keys %$ports];
		1286
		1287	# now $ports, $add and $del are the same as
		1288	# were originally passed by grp_mon.
		1289	...
		1290	};
		1291
		1292	=item Nodes not longer connect to all other nodes.
		1293
		1294	In AEMP 1.x, every node automatically loads the L<AnyEvent::MP::Global>
		1295	module, which in turn would create connections to all other nodes in the
		1296	network (helped by the seed nodes).
		1297
		1298	In version 2.x, global nodes still connect to all other global nodes, but
		1299	other nodes don't - now every node either is a global node itself, or
		1300	attaches itself to another global node.
		1301
		1302	If a node isn't a global node itself, then it attaches itself to one
		1303	of its seed nodes. If that seed node isn't a global node yet, it will
		1304	automatically be upgraded to a global node.
		1305
		1306	So in many cases, nothing needs to be changed - one just has to make sure
		1307	that all seed nodes are meshed together with the other seed nodes (as with
		1308	AEMP 1.x), and other nodes specify them as seed nodes. This is most easily
		1309	achieved by specifying the same set of seed nodes for all nodes in the
		1310	network.
		1311
		1312	Not opening a connection to every other node is usually an advantage,
		1313	except when you need the lower latency of an already established
		1314	connection. To ensure a node establishes a connection to another node,
		1315	you can monitor the node port (C<mon $node, ...>), which will attempt to
		1316	create the connection (and notify you when the connection fails).
		1317
		1318	=item Listener-less nodes (nodes without binds) are gone.
		1319
		1320	And are not coming back, at least not in their old form. If no C<binds>
		1321	are specified for a node, AnyEvent::MP assumes a default of C<*:*>.
		1322
		1323	There are vague plans to implement some form of routing domains, which
		1324	might or might not bring back listener-less nodes, but don't count on it.
		1325
		1326	The fact that most connections are now optional somewhat mitigates this,
		1327	as a node can be effectively unreachable from the outside without any
		1328	problems, as long as it isn't a global node and only reaches out to other
		1329	nodes (as opposed to being contacted from other nodes).
		1330
		1331	=item $AnyEvent::MP::Kernel::WARN has gone.
		1332
		1333	AnyEvent has acquired a logging framework (L<AnyEvent::Log>), and AEMP now
		1334	uses this, and so should your programs.
		1335
		1336	Every module now documents what kinds of messages it generates, with
		1337	AnyEvent::MP acting as a catch all.
		1338
		1339	On the positive side, this means that instead of setting
		1340	C<PERL_ANYEVENT_MP_WARNLEVEL>, you can get away by setting C<AE_VERBOSE> -
		1341	much less to type.
		1342
		1343	=back
		1344
		1345	=head1 LOGGING
		1346
		1347	AnyEvent::MP does not normally log anything by itself, but sinc eit is the
		1348	root of the contetx hierarchy for AnyEvent::MP modules, it will receive
		1349	all log messages by submodules.
		1350
918	=head1 SEE ALSO	1351	=head1 SEE ALSO
		1352
		1353	L<AnyEvent::MP::Intro> - a gentle introduction.
		1354
		1355	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1356
		1357	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1358	your applications.
		1359
		1360	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1361
		1362	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1363	all nodes.
919		1364
920	L<AnyEvent>.	1365	L<AnyEvent>.
921		1366
922	=head1 AUTHOR	1367	=head1 AUTHOR
923		1368

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