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Revision 1.61 by root, Mon Aug 24 08:06:49 2009 UTC vs.
Revision 1.139 by root, Thu Mar 22 20:07:31 2012 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent::MP - multi-processing/message-passing framework	3	AnyEvent::MP - erlang-style multi-processing/message-passing framework
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::MP;	7	use AnyEvent::MP;
8		8
9	$NODE # contains this node's noderef	9	$NODE # contains this node's node ID
10	NODE # returns this node's noderef	10	NODE # returns this node's node ID
11	NODE $port # returns the noderef of the port
12		11
13	$SELF # receiving/own port id in rcv callbacks	12	$SELF # receiving/own port id in rcv callbacks
14		13
15	# initialise the node so it can send/receive messages	14	# initialise the node so it can send/receive messages
16	initialise_node; # -OR-	15	configure;
17	initialise_node "localhost:4040"; # -OR-
18	initialise_node "slave/", "localhost:4040"
19		16
20	# ports are message endpoints	17	# ports are message destinations
21		18
22	# sending messages	19	# sending messages
23	snd $port, type => data...;	20	snd $port, type => data...;
24	snd $port, @msg;	21	snd $port, @msg;
25	snd @msg_with_first_element_being_a_port;	22	snd @msg_with_first_element_being_a_port;
26		23
27	# creating/using ports, the simple way	24	# creating/using ports, the simple way
28	my $simple_port = port { my @msg = @_; 0 };	25	my $simple_port = port { my @msg = @_ };
29		26
30	# creating/using ports, tagged message matching	27	# creating/using ports, tagged message matching
31	my $port = port;	28	my $port = port;
32	rcv $port, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
33	rcv $port, pong => sub { warn "pong received\n"; 0 };	30	rcv $port, pong => sub { warn "pong received\n" };
34		31
35	# create a port on another node	32	# create a port on another node
36	my $port = spawn $node, $initfunc, @initdata;	33	my $port = spawn $node, $initfunc, @initdata;
37		34
		35	# destroy a port again
		36	kil $port; # "normal" kill
		37	kil $port, my_error => "everything is broken"; # error kill
		38
38	# monitoring	39	# monitoring
39	mon $port, $cb->(@msg) # callback is invoked on death	40	mon $port, $cb->(@msg) # callback is invoked on death
40	mon $port, $otherport # kill otherport on abnormal death	41	mon $port, $localport # kill localport on abnormal death
41	mon $port, $otherport, @msg # send message on death	42	mon $port, $localport, @msg # send message on death
		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 CURRENT STATUS	52	=head1 CURRENT STATUS
44		53
		54	bin/aemp - stable.
45	AnyEvent::MP - stable API, should work	55	AnyEvent::MP - stable API, should work.
46	AnyEvent::MP::Intro - outdated	56	AnyEvent::MP::Intro - explains most concepts.
47	AnyEvent::MP::Kernel - WIP
48	AnyEvent::MP::Transport - mostly stable	57	AnyEvent::MP::Kernel - mostly stable API.
49		58	AnyEvent::MP::Global - stable API.
50	stay tuned.
51		59
52	=head1 DESCRIPTION	60	=head1 DESCRIPTION
53		61
54	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
55		63
56	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
57	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
58		66
59	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	67	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
60	manual page.	68	manual page and the examples under F<eg/>.
61
62	At the moment, this module family is severly broken and underdocumented,
63	so do not use. This was uploaded mainly to reserve the CPAN namespace -
64	stay tuned!
65		69
66	=head1 CONCEPTS	70	=head1 CONCEPTS
67		71
68	=over 4	72	=over 4
69		73
70	=item port	74	=item port
71		75
72	A port is something you can send messages to (with the C<snd> function).	76	Not to be confused with a TCP port, a "port" is something you can send
		77	messages to (with the C<snd> function).
73		78
74	Ports allow you to register C<rcv> handlers that can match all or just	79	Ports allow you to register C<rcv> handlers that can match all or just
75	some messages. Messages will not be queued.	80	some messages. Messages send to ports will not be queued, regardless of
		81	anything was listening for them or not.
76		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
77	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
78		86
79	A port ID is the concatenation of a noderef, a hash-mark (C<#>) as	87	A port ID is the concatenation of a node ID, a hash-mark (C<#>)
80	separator, and a port name (a printable string of unspecified format). An	88	as separator, and a port name (a printable string of unspecified
81	exception is the the node port, whose ID is identical to its node	89	format created by AnyEvent::MP).
82	reference.
83		90
84	=item node	91	=item node
85		92
86	A node is a single process containing at least one port - the node port,	93	A node is a single process containing at least one port - the node port,
87	which provides nodes to manage each other remotely, and to create new	94	which enables nodes to manage each other remotely, and to create new
88	ports.	95	ports.
89		96
90	Nodes are either private (single-process only), slaves (connected to a	97	Nodes are either public (have one or more listening ports) or private
91	master node only) or public nodes (connectable from unrelated nodes).	98	(no listening ports). Private nodes cannot talk to other private nodes
		99	currently, but all nodes can talk to public nodes.
92		100
93	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	101	Nodes is represented by (printable) strings called "node IDs".
94		102
95	A node reference is a string that either simply identifies the node (for	103	=item node ID - C<[A-Za-z0-9_\-.:]*>
96	private and slave nodes), or contains a recipe on how to reach a given
97	node (for public nodes).
98		104
99	This recipe is simply a comma-separated list of C<address:port> pairs (for	105	A node ID is a string that uniquely identifies the node within a
100	TCP/IP, other protocols might look different).	106	network. Depending on the configuration used, node IDs can look like a
		107	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		108	doesn't interpret node IDs in any way except to uniquely identify a node.
101		109
102	Node references come in two flavours: resolved (containing only numerical	110	=item binds - C<ip:port>
103	addresses) or unresolved (where hostnames are used instead of addresses).
104		111
105	Before using an unresolved node reference in a message you first have to	112	Nodes can only talk to each other by creating some kind of connection to
106	resolve it.	113	each other. To do this, nodes should listen on one or more local transport
		114	endpoints - binds.
		115
		116	Currently, only standard C<ip:port> specifications can be used, which
		117	specify TCP ports to listen on. So a bind is basically just a tcp socket
		118	in listening mode thta accepts conenctions form other nodes.
		119
		120	=item seed nodes
		121
		122	When a node starts, it knows nothing about the network it is in - it
		123	needs to connect to at least one other node that is already in the
		124	network. These other nodes are called "seed nodes".
		125
		126	Seed nodes themselves are not special - they are seed nodes only because
		127	some other node I<uses> them as such, but any node can be used as seed
		128	node for other nodes, and eahc node cna use a different set of seed nodes.
		129
		130	In addition to discovering the network, seed nodes are also used to
		131	maintain the network - all nodes using the same seed node form are part of
		132	the same network. If a network is split into multiple subnets because e.g.
		133	the network link between the parts goes down, then using the same seed
		134	nodes for all nodes ensures that eventually the subnets get merged again.
		135
		136	Seed nodes are expected to be long-running, and at least one seed node
		137	should always be available. They should also be relatively responsive - a
		138	seed node that blocks for long periods will slow down everybody else.
		139
		140	For small networks, it's best if every node uses the same set of seed
		141	nodes. For large networks, it can be useful to specify "regional" seed
		142	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		143	each other. What's important is that all seed nodes connections form a
		144	complete graph, so that the network cannot split into separate subnets
		145	forever.
		146
		147	Seed nodes are represented by seed IDs.
		148
		149	=item seed IDs - C<host:port>
		150
		151	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
		152	TCP port) of nodes that should be used as seed nodes.
		153
		154	=item global nodes
		155
		156	An AEMP network needs a discovery service - nodes need to know how to
		157	connect to other nodes they only know by name. In addition, AEMP offers a
		158	distributed "group database", which maps group names to a list of strings
		159	- for example, to register worker ports.
		160
		161	A network needs at least one global node to work, and allows every node to
		162	be a global node.
		163
		164	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		165	node and tries to keep connections to all other nodes. So while it can
		166	make sense to make every node "global" in small networks, it usually makes
		167	sense to only make seed nodes into global nodes in large networks (nodes
		168	keep connections to seed nodes and global nodes, so makign them the same
		169	reduces overhead).
107		170
108	=back	171	=back
109		172
110	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
111		174
…		…
113		176
114	=cut	177	=cut
115		178
116	package AnyEvent::MP;	179	package AnyEvent::MP;
117		180
		181	use AnyEvent::MP::Config ();
118	use AnyEvent::MP::Kernel;	182	use AnyEvent::MP::Kernel;
		183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
119		184
120	use common::sense;	185	use common::sense;
121		186
122	use Carp ();	187	use Carp ();
123		188
124	use AE ();	189	use AE ();
		190	use Guard ();
125		191
126	use base "Exporter";	192	use base "Exporter";
127		193
128	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
129		195
130	our @EXPORT = qw(	196	our @EXPORT = qw(
131	NODE $NODE *SELF node_of after	197	NODE $NODE *SELF node_of after
132	resolve_node initialise_node	198	configure
133	snd rcv mon mon_guard kil reg psub spawn	199	snd rcv mon mon_guard kil psub peval spawn cal
134	port	200	port
		201	db_set db_del db_reg
		202	db_mon db_family db_keys db_values
135	);	203	);
136		204
137	our $SELF;	205	our $SELF;
138		206
139	sub _self_die() {	207	sub _self_die() {
…		…
142	kil $SELF, die => $msg;	210	kil $SELF, die => $msg;
143	}	211	}
144		212
145	=item $thisnode = NODE / $NODE	213	=item $thisnode = NODE / $NODE
146		214
147	The C<NODE> function returns, and the C<$NODE> variable contains the	215	The C<NODE> function returns, and the C<$NODE> variable contains, the node
148	noderef of the local node. The value is initialised by a call to	216	ID of the node running in the current process. This value is initialised by
149	C<initialise_node>.	217	a call to C<configure>.
150		218
151	=item $noderef = node_of $port	219	=item $nodeid = node_of $port
152		220
153	Extracts and returns the noderef from a port ID or a noderef.	221	Extracts and returns the node ID from a port ID or a node ID.
154		222
155	=item initialise_node $noderef, $seednode, $seednode...	223	=item configure $profile, key => value...
156		224
157	=item initialise_node "slave/", $master, $master...	225	=item configure key => value...
158		226
159	Before a node can talk to other nodes on the network it has to initialise	227	Before a node can talk to other nodes on the network (i.e. enter
160	itself - the minimum a node needs to know is it's own name, and optionally	228	"distributed mode") it has to configure itself - the minimum a node needs
161	it should know the noderefs of some other nodes in the network.	229	to know is its own name, and optionally it should know the addresses of
		230	some other nodes in the network to discover other nodes.
162		231
163	This function initialises a node - it must be called exactly once (or	232	This function configures a node - it must be called exactly once (or
164	never) before calling other AnyEvent::MP functions.	233	never) before calling other AnyEvent::MP functions.
165		234
166	All arguments (optionally except for the first) are noderefs, which can be	235	The key/value pairs are basically the same ones as documented for the
167	either resolved or unresolved.	236	F<aemp> command line utility (sans the set/del prefix), with these additions:
168
169	The first argument will be looked up in the configuration database first
170	(if it is C<undef> then the current nodename will be used instead) to find
171	the relevant configuration profile (see L<aemp>). If none is found then
172	the default configuration is used. The configuration supplies additional
173	seed/master nodes and can override the actual noderef.
174
175	There are two types of networked nodes, public nodes and slave nodes:
176		237
177	=over 4	238	=over 4
178		239
179	=item public nodes	240	=item norc => $boolean (default false)
180		241
181	For public nodes, C<$noderef> (supplied either directly to	242	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
182	C<initialise_node> or indirectly via a profile or the nodename) must be a	243	be consulted - all configuraiton options must be specified in the
183	noderef (possibly unresolved, in which case it will be resolved).	244	C<configure> call.
184		245
185	After resolving, the node will bind itself on all endpoints and try to	246	=item force => $boolean (default false)
186	connect to all additional C<$seednodes> that are specified. Seednodes are
187	optional and can be used to quickly bootstrap the node into an existing
188	network.
189		247
190	=item slave nodes	248	IF true, then the values specified in the C<configure> will take
		249	precedence over any values configured via the rc file. The default is for
		250	the rc file to override any options specified in the program.
191		251
192	When the C<$noderef> (either as given or overriden by the config file)	252	=item secure => $pass->(@msg)
193	is the special string C<slave/>, then the node will become a slave
194	node. Slave nodes cannot be contacted from outside and will route most of
195	their traffic to the master node that they attach to.
196		253
197	At least one additional noderef is required (either by specifying it	254	In addition to specifying a boolean, you can specify a code reference that
198	directly or because it is part of the configuration profile): The node	255	is called for every code execution attempt - the execution request is
199	will try to connect to all of them and will become a slave attached to the	256	granted iff the callback returns a true value.
200	first node it can successfully connect to.
201		257
202	Note that slave nodes cannot change their name, and consequently, their	258	Most of the time the callback should look only at
203	master, so if the master goes down, the slave node will not function well	259	C<$AnyEvent::MP::Kernel::SRCNODE> to make a decision, and not at the
204	anymore until it can re-establish conenciton to its master. This makes	260	actual message (which can be about anything, and is mostly provided for
205	slave nodes unsuitable for long-term nodes or fault-tolerant networks.	261	diagnostic purposes).
		262
		263	See F<semp setsecure> for more info.
206		264
207	=back	265	=back
208		266
209	This function will block until all nodes have been resolved and, for slave
210	nodes, until it has successfully established a connection to a master
211	server.
212
213	All the seednodes will also be specially marked to automatically retry
214	connecting to them infinitely.
215
216	Example: become a public node listening on the guessed noderef, or the one
217	specified via C<aemp> for the current node. This should be the most common
218	form of invocation for "daemon"-type nodes.
219
220	initialise_node;
221
222	Example: become a slave node to any of the the seednodes specified via
223	C<aemp>. This form is often used for commandline clients.
224
225	initialise_node "slave/";
226
227	Example: become a slave node to any of the specified master servers. This
228	form is also often used for commandline clients.
229
230	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
231
232	Example: become a public node, and try to contact some well-known master
233	servers to become part of the network.
234
235	initialise_node undef, "master1", "master2";
236
237	Example: become a public node listening on port C<4041>.
238
239	initialise_node 4041;
240
241	Example: become a public node, only visible on localhost port 4044.
242
243	initialise_node "localhost:4044";
244
245	=item $cv = resolve_node $noderef
246
247	Takes an unresolved node reference that may contain hostnames and
248	abbreviated IDs, resolves all of them and returns a resolved node
249	reference.
250
251	In addition to C<address:port> pairs allowed in resolved noderefs, the
252	following forms are supported:
253
254	=over 4	267	=over 4
255		268
256	=item the empty string	269	=item step 1, gathering configuration from profiles
257		270
258	An empty-string component gets resolved as if the default port (4040) was	271	The function first looks up a profile in the aemp configuration (see the
259	specified.	272	L<aemp> commandline utility). The profile name can be specified via the
		273	named C<profile> parameter or can simply be the first parameter). If it is
		274	missing, then the nodename (F<uname -n>) will be used as profile name.
260		275
261	=item naked port numbers (e.g. C<1234>)	276	The profile data is then gathered as follows:
262		277
263	These are resolved by prepending the local nodename and a colon, to be	278	First, all remaining key => value pairs (all of which are conveniently
264	further resolved.	279	undocumented at the moment) will be interpreted as configuration
		280	data. Then they will be overwritten by any values specified in the global
		281	default configuration (see the F<aemp> utility), then the chain of
		282	profiles chosen by the profile name (and any C<parent> attributes).
265		283
266	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	284	That means that the values specified in the profile have highest priority
		285	and the values specified directly via C<configure> have lowest priority,
		286	and can only be used to specify defaults.
267		287
268	These are resolved by using AnyEvent::DNS to resolve them, optionally	288	If the profile specifies a node ID, then this will become the node ID of
269	looking up SRV records for the C<aemp=4040> port, if no port was	289	this process. If not, then the profile name will be used as node ID, with
270	specified.	290	a unique randoms tring (C</%u>) appended.
		291
		292	The node ID can contain some C<%> sequences that are expanded: C<%n>
		293	is expanded to the local nodename, C<%u> is replaced by a random
		294	strign to make the node unique. For example, the F<aemp> commandline
		295	utility uses C<aemp/%n/%u> as nodename, which might expand to
		296	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		297
		298	=item step 2, bind listener sockets
		299
		300	The next step is to look up the binds in the profile, followed by binding
		301	aemp protocol listeners on all binds specified (it is possible and valid
		302	to have no binds, meaning that the node cannot be contacted form the
		303	outside. This means the node cannot talk to other nodes that also have no
		304	binds, but it can still talk to all "normal" nodes).
		305
		306	If the profile does not specify a binds list, then a default of C<*> is
		307	used, meaning the node will bind on a dynamically-assigned port on every
		308	local IP address it finds.
		309
		310	=item step 3, connect to seed nodes
		311
		312	As the last step, the seed ID list from the profile is passed to the
		313	L<AnyEvent::MP::Global> module, which will then use it to keep
		314	connectivity with at least one node at any point in time.
271		315
272	=back	316	=back
		317
		318	Example: become a distributed node using the local node name as profile.
		319	This should be the most common form of invocation for "daemon"-type nodes.
		320
		321	configure
		322
		323	Example: become a semi-anonymous node. This form is often used for
		324	commandline clients.
		325
		326	configure nodeid => "myscript/%n/%u";
		327
		328	Example: configure a node using a profile called seed, which is suitable
		329	for a seed node as it binds on all local addresses on a fixed port (4040,
		330	customary for aemp).
		331
		332	# use the aemp commandline utility
		333	# aemp profile seed binds '*:4040'
		334
		335	# then use it
		336	configure profile => "seed";
		337
		338	# or simply use aemp from the shell again:
		339	# aemp run profile seed
		340
		341	# or provide a nicer-to-remember nodeid
		342	# aemp run profile seed nodeid "$(hostname)"
273		343
274	=item $SELF	344	=item $SELF
275		345
276	Contains the current port id while executing C<rcv> callbacks or C<psub>	346	Contains the current port id while executing C<rcv> callbacks or C<psub>
277	blocks.	347	blocks.
278		348
279	=item SELF, %SELF, @SELF...	349	=item *SELF, SELF, %SELF, @SELF...
280		350
281	Due to some quirks in how perl exports variables, it is impossible to	351	Due to some quirks in how perl exports variables, it is impossible to
282	just export C<$SELF>, all the symbols called C<SELF> are exported by this	352	just export C<$SELF>, all the symbols named C<SELF> are exported by this
283	module, but only C<$SELF> is currently used.	353	module, but only C<$SELF> is currently used.
284		354
285	=item snd $port, type => @data	355	=item snd $port, type => @data
286		356
287	=item snd $port, @msg	357	=item snd $port, @msg
288		358
289	Send the given message to the given port ID, which can identify either	359	Send the given message to the given port, which can identify either a
290	a local or a remote port, and must be a port ID.	360	local or a remote port, and must be a port ID.
291		361
292	While the message can be about anything, it is highly recommended to use a	362	While the message can be almost anything, it is highly recommended to
293	string as first element (a port ID, or some word that indicates a request	363	use a string as first element (a port ID, or some word that indicates a
294	type etc.).	364	request type etc.) and to consist if only simple perl values (scalars,
		365	arrays, hashes) - if you think you need to pass an object, think again.
295		366
296	The message data effectively becomes read-only after a call to this	367	The message data logically becomes read-only after a call to this
297	function: modifying any argument is not allowed and can cause many	368	function: modifying any argument (or values referenced by them) is
298	problems.	369	forbidden, as there can be considerable time between the call to C<snd>
		370	and the time the message is actually being serialised - in fact, it might
		371	never be copied as within the same process it is simply handed to the
		372	receiving port.
299		373
300	The type of data you can transfer depends on the transport protocol: when	374	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	375	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	376	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	377	that Storable can serialise and deserialise is allowed, and for the local
304	node, anything can be passed.	378	node, anything can be passed. Best rely only on the common denominator of
		379	these.
305		380
306	=item $local_port = port	381	=item $local_port = port
307		382
308	Create a new local port object and returns its port ID. Initially it has	383	Create a new local port object and returns its port ID. Initially it has
309	no callbacks set and will throw an error when it receives messages.	384	no callbacks set and will throw an error when it receives messages.
…		…
328		403
329	=cut	404	=cut
330		405
331	sub rcv($@);	406	sub rcv($@);
332		407
333	sub _kilme {	408	my $KILME = sub {
334	die "received message on port without callback";	409	(my $tag = substr $_[0], 0, 30) =~ s/([\x20-\x7e])/./g;
335	}	410	kil $SELF, unhandled_message => "no callback found for message '$tag'";
		411	};
336		412
337	sub port(;&) {	413	sub port(;&) {
338	my $id = "$UNIQ." . $ID++;	414	my $id = $UNIQ . ++$ID;
339	my $port = "$NODE#$id";	415	my $port = "$NODE#$id";
340		416
341	rcv $port, shift || \&_kilme;	417	rcv $port, shift || $KILME;
342		418
343	$port	419	$port
344	}	420	}
345		421
346	=item rcv $local_port, $callback->(@msg)	422	=item rcv $local_port, $callback->(@msg)
…		…
351		427
352	The global C<$SELF> (exported by this module) contains C<$port> while	428	The global C<$SELF> (exported by this module) contains C<$port> while
353	executing the callback. Runtime errors during callback execution will	429	executing the callback. Runtime errors during callback execution will
354	result in the port being C<kil>ed.	430	result in the port being C<kil>ed.
355		431
356	The default callback received all messages not matched by a more specific	432	The default callback receives all messages not matched by a more specific
357	C<tag> match.	433	C<tag> match.
358		434
359	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...	435	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
360		436
361	Register (or replace) callbacks to be called on messages starting with the	437	Register (or replace) callbacks to be called on messages starting with the
…		…
382	msg1 => sub { ... },	458	msg1 => sub { ... },
383	...	459	...
384	;	460	;
385		461
386	Example: temporarily register a rcv callback for a tag matching some port	462	Example: temporarily register a rcv callback for a tag matching some port
387	(e.g. for a rpc reply) and unregister it after a message was received.	463	(e.g. for an rpc reply) and unregister it after a message was received.
388		464
389	rcv $port, $otherport => sub {	465	rcv $port, $otherport => sub {
390	my @reply = @_;	466	my @reply = @_;
391		467
392	rcv $SELF, $otherport;	468	rcv $SELF, $otherport;
…		…
394		470
395	=cut	471	=cut
396		472
397	sub rcv($@) {	473	sub rcv($@) {
398	my $port = shift;	474	my $port = shift;
399	my ($noderef, $portid) = split /#/, $port, 2;	475	my ($nodeid, $portid) = split /#/, $port, 2;
400		476
401	$NODE{$noderef} == $NODE{""}	477	$NODE{$nodeid} == $NODE{""}
402	or Carp::croak "$port: rcv can only be called on local ports, caught";	478	or Carp::croak "$port: rcv can only be called on local ports, caught";
403		479
404	while (@_) {	480	while (@_) {
405	if (ref $_[0]) {	481	if (ref $_[0]) {
406	if (my $self = $PORT_DATA{$portid}) {	482	if (my $self = $PORT_DATA{$portid}) {
407	"AnyEvent::MP::Port" eq ref $self	483	"AnyEvent::MP::Port" eq ref $self
408	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	484	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
409		485
410	$self->[2] = shift;	486	$self->[0] = shift;
411	} else {	487	} else {
412	my $cb = shift;	488	my $cb = shift;
413	$PORT{$portid} = sub {	489	$PORT{$portid} = sub {
414	local $SELF = $port;	490	local $SELF = $port;
415	eval { &$cb }; _self_die if $@;	491	eval { &$cb }; _self_die if $@;
416	};	492	};
417	}	493	}
418	} elsif (defined $_[0]) {	494	} elsif (defined $_[0]) {
419	my $self = $PORT_DATA{$portid} ||= do {	495	my $self = $PORT_DATA{$portid} ||= do {
420	my $self = bless [$PORT{$port} || sub { }, { }, $port], "AnyEvent::MP::Port";	496	my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port";
421		497
422	$PORT{$portid} = sub {	498	$PORT{$portid} = sub {
423	local $SELF = $port;	499	local $SELF = $port;
424		500
425	if (my $cb = $self->[1]{$_[0]}) {	501	if (my $cb = $self->[1]{$_[0]}) {
…		…
447	}	523	}
448		524
449	$port	525	$port
450	}	526	}
451		527
		528	=item peval $port, $coderef[, @args]
		529
		530	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		531	when the code throews an exception the C<$port> will be killed.
		532
		533	Any remaining args will be passed to the callback. Any return values will
		534	be returned to the caller.
		535
		536	This is useful when you temporarily want to execute code in the context of
		537	a port.
		538
		539	Example: create a port and run some initialisation code in it's context.
		540
		541	my $port = port { ... };
		542
		543	peval $port, sub {
		544	init
		545	or die "unable to init";
		546	};
		547
		548	=cut
		549
		550	sub peval($$) {
		551	local $SELF = shift;
		552	my $cb = shift;
		553
		554	if (wantarray) {
		555	my @res = eval { &$cb };
		556	_self_die if $@;
		557	@res
		558	} else {
		559	my $res = eval { &$cb };
		560	_self_die if $@;
		561	$res
		562	}
		563	}
		564
452	=item $closure = psub { BLOCK }	565	=item $closure = psub { BLOCK }
453		566
454	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	567	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
455	closure is executed, sets up the environment in the same way as in C<rcv>	568	closure is executed, sets up the environment in the same way as in C<rcv>
456	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.	569	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		570
		571	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		572	BLOCK }, @_ } >>.
457		573
458	This is useful when you register callbacks from C<rcv> callbacks:	574	This is useful when you register callbacks from C<rcv> callbacks:
459		575
460	rcv delayed_reply => sub {	576	rcv delayed_reply => sub {
461	my ($delay, @reply) = @_;	577	my ($delay, @reply) = @_;
…		…
485	$res	601	$res
486	}	602	}
487	}	603	}
488	}	604	}
489		605
490	=item $guard = mon $port, $cb->(@reason)	606	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
491		607
492	=item $guard = mon $port, $rcvport	608	=item $guard = mon $port # kill $SELF when $port dies
493		609
494	=item $guard = mon $port	610	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
495		611
496	=item $guard = mon $port, $rcvport, @msg	612	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
497		613
498	Monitor the given port and do something when the port is killed or	614	Monitor the given port and do something when the port is killed or
499	messages to it were lost, and optionally return a guard that can be used	615	messages to it were lost, and optionally return a guard that can be used
500	to stop monitoring again.	616	to stop monitoring again.
501		617
		618	The first two forms distinguish between "normal" and "abnormal" kil's:
		619
		620	In the first form (another port given), if the C<$port> is C<kil>'ed with
		621	a non-empty reason, the other port (C<$rcvport>) will be kil'ed with the
		622	same reason. That is, on "normal" kil's nothing happens, while under all
		623	other conditions, the other port is killed with the same reason.
		624
		625	The second form (kill self) is the same as the first form, except that
		626	C<$rvport> defaults to C<$SELF>.
		627
		628	The remaining forms don't distinguish between "normal" and "abnormal" kil's
		629	- it's up to the callback or receiver to check whether the C<@reason> is
		630	empty and act accordingly.
		631
		632	In the third form (callback), the callback is simply called with any
		633	number of C<@reason> elements (empty @reason means that the port was deleted
		634	"normally"). Note also that I<< the callback B<must> never die >>, so use
		635	C<eval> if unsure.
		636
		637	In the last form (message), a message of the form C<$rcvport, @msg,
		638	@reason> will be C<snd>.
		639
		640	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		641	alert was raised), they are removed and will not trigger again, even if it
		642	turns out that the port is still alive.
		643
		644	As a rule of thumb, monitoring requests should always monitor a remote
		645	port locally (using a local C<$rcvport> or a callback). The reason is that
		646	kill messages might get lost, just like any other message. Another less
		647	obvious reason is that even monitoring requests can get lost (for example,
		648	when the connection to the other node goes down permanently). When
		649	monitoring a port locally these problems do not exist.
		650
502	C<mon> effectively guarantees that, in the absence of hardware failures,	651	C<mon> effectively guarantees that, in the absence of hardware failures,
503	that after starting the monitor, either all messages sent to the port	652	after starting the monitor, either all messages sent to the port will
504	will arrive, or the monitoring action will be invoked after possible	653	arrive, or the monitoring action will be invoked after possible message
505	message loss has been detected. No messages will be lost "in between"	654	loss has been detected. No messages will be lost "in between" (after
506	(after the first lost message no further messages will be received by the	655	the first lost message no further messages will be received by the
507	port). After the monitoring action was invoked, further messages might get	656	port). After the monitoring action was invoked, further messages might get
508	delivered again.	657	delivered again.
509		658
510	Note that monitoring-actions are one-shot: once released, they are removed	659	Inter-host-connection timeouts and monitoring depend on the transport
511	and will not trigger again.	660	used. The only transport currently implemented is TCP, and AnyEvent::MP
		661	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		662	non-idle connection, and usually around two hours for idle connections).
512		663
513	In the first form (callback), the callback is simply called with any	664	This means that monitoring is good for program errors and cleaning up
514	number of C<@reason> elements (no @reason means that the port was deleted	665	stuff eventually, but they are no replacement for a timeout when you need
515	"normally"). Note also that I<< the callback B<must> never die >>, so use	666	to ensure some maximum latency.
516	C<eval> if unsure.
517
518	In the second form (another port given), the other port (C<$rcvport>)
519	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on
520	"normal" kils nothing happens, while under all other conditions, the other
521	port is killed with the same reason.
522
523	The third form (kill self) is the same as the second form, except that
524	C<$rvport> defaults to C<$SELF>.
525
526	In the last form (message), a message of the form C<@msg, @reason> will be
527	C<snd>.
528
529	As a rule of thumb, monitoring requests should always monitor a port from
530	a local port (or callback). The reason is that kill messages might get
531	lost, just like any other message. Another less obvious reason is that
532	even monitoring requests can get lost (for exmaple, when the connection
533	to the other node goes down permanently). When monitoring a port locally
534	these problems do not exist.
535		667
536	Example: call a given callback when C<$port> is killed.	668	Example: call a given callback when C<$port> is killed.
537		669
538	mon $port, sub { warn "port died because of <@_>\n" };	670	mon $port, sub { warn "port died because of <@_>\n" };
539		671
…		…
546	mon $port, $self => "restart";	678	mon $port, $self => "restart";
547		679
548	=cut	680	=cut
549		681
550	sub mon {	682	sub mon {
551	my ($noderef, $port) = split /#/, shift, 2;	683	my ($nodeid, $port) = split /#/, shift, 2;
552		684
553	my $node = $NODE{$noderef} || add_node $noderef;	685	my $node = $NODE{$nodeid} || add_node $nodeid;
554		686
555	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';	687	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
556		688
557	unless (ref $cb) {	689	unless (ref $cb) {
558	if (@_) {	690	if (@_) {
…		…
567	}	699	}
568		700
569	$node->monitor ($port, $cb);	701	$node->monitor ($port, $cb);
570		702
571	defined wantarray	703	defined wantarray
572	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	704	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
573	}	705	}
574		706
575	=item $guard = mon_guard $port, $ref, $ref...	707	=item $guard = mon_guard $port, $ref, $ref...
576		708
577	Monitors the given C<$port> and keeps the passed references. When the port	709	Monitors the given C<$port> and keeps the passed references. When the port
578	is killed, the references will be freed.	710	is killed, the references will be freed.
579		711
580	Optionally returns a guard that will stop the monitoring.	712	Optionally returns a guard that will stop the monitoring.
581		713
582	This function is useful when you create e.g. timers or other watchers and	714	This function is useful when you create e.g. timers or other watchers and
583	want to free them when the port gets killed:	715	want to free them when the port gets killed (note the use of C<psub>):
584		716
585	$port->rcv (start => sub {	717	$port->rcv (start => sub {
586	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	718	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
587	undef $timer if 0.9 < rand;	719	undef $timer if 0.9 < rand;
588	});	720	});
589	});	721	});
590		722
591	=cut	723	=cut
…		…
600		732
601	=item kil $port[, @reason]	733	=item kil $port[, @reason]
602		734
603	Kill the specified port with the given C<@reason>.	735	Kill the specified port with the given C<@reason>.
604		736
605	If no C<@reason> is specified, then the port is killed "normally" (linked	737	If no C<@reason> is specified, then the port is killed "normally" -
606	ports will not be kileld, or even notified).	738	monitor callback will be invoked, but the kil will not cause linked ports
		739	(C<mon $mport, $lport> form) to get killed.
607		740
608	Otherwise, linked ports get killed with the same reason (second form of	741	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
609	C<mon>, see below).	742	form) get killed with the same reason.
610		743
611	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	744	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
612	will be reported as reason C<< die => $@ >>.	745	will be reported as reason C<< die => $@ >>.
613		746
614	Transport/communication errors are reported as C<< transport_error =>	747	Transport/communication errors are reported as C<< transport_error =>
615	$message >>.	748	$message >>.
616		749
617	=cut	750	Common idioms:
		751
		752	# silently remove yourself, do not kill linked ports
		753	kil $SELF;
		754
		755	# report a failure in some detail
		756	kil $SELF, failure_mode_1 => "it failed with too high temperature";
		757
		758	# do not waste much time with killing, just die when something goes wrong
		759	open my $fh, "<file"
		760	or die "file: $!";
618		761
619	=item $port = spawn $node, $initfunc[, @initdata]	762	=item $port = spawn $node, $initfunc[, @initdata]
620		763
621	Creates a port on the node C<$node> (which can also be a port ID, in which	764	Creates a port on the node C<$node> (which can also be a port ID, in which
622	case it's the node where that port resides).	765	case it's the node where that port resides).
623		766
624	The port ID of the newly created port is return immediately, and it is	767	The port ID of the newly created port is returned immediately, and it is
625	permissible to immediately start sending messages or monitor the port.	768	possible to immediately start sending messages or to monitor the port.
626		769
627	After the port has been created, the init function is	770	After the port has been created, the init function is called on the remote
628	called. This function must be a fully-qualified function name	771	node, in the same context as a C<rcv> callback. This function must be a
629	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	772	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
630	program, use C<::name>.	773	specify a function in the main program, use C<::name>.
631		774
632	If the function doesn't exist, then the node tries to C<require>	775	If the function doesn't exist, then the node tries to C<require>
633	the package, then the package above the package and so on (e.g.	776	the package, then the package above the package and so on (e.g.
634	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	777	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
635	exists or it runs out of package names.	778	exists or it runs out of package names.
636		779
637	The init function is then called with the newly-created port as context	780	The init function is then called with the newly-created port as context
638	object (C<$SELF>) and the C<@initdata> values as arguments.	781	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		782	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		783	the port might not get created.
639		784
640	A common idiom is to pass your own port, monitor the spawned port, and	785	A common idiom is to pass a local port, immediately monitor the spawned
641	in the init function, monitor the original port. This two-way monitoring	786	port, and in the remote init function, immediately monitor the passed
642	ensures that both ports get cleaned up when there is a problem.	787	local port. This two-way monitoring ensures that both ports get cleaned up
		788	when there is a problem.
		789
		790	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		791	caller before C<spawn> returns (by delaying invocation when spawn is
		792	called for the local node).
643		793
644	Example: spawn a chat server port on C<$othernode>.	794	Example: spawn a chat server port on C<$othernode>.
645		795
646	# this node, executed from within a port context:	796	# this node, executed from within a port context:
647	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	797	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
662		812
663	sub _spawn {	813	sub _spawn {
664	my $port = shift;	814	my $port = shift;
665	my $init = shift;	815	my $init = shift;
666		816
		817	# rcv will create the actual port
667	local $SELF = "$NODE#$port";	818	local $SELF = "$NODE#$port";
668	eval {	819	eval {
669	&{ load_func $init }	820	&{ load_func $init }
670	};	821	};
671	_self_die if $@;	822	_self_die if $@;
672	}	823	}
673		824
674	sub spawn(@) {	825	sub spawn(@) {
675	my ($noderef, undef) = split /#/, shift, 2;	826	my ($nodeid, undef) = split /#/, shift, 2;
676		827
677	my $id = "$RUNIQ." . $ID++;	828	my $id = $RUNIQ . ++$ID;
678		829
679	$_[0] =~ /::/	830	$_[0] =~ /::/
680	or Carp::croak "spawn init function must be a fully-qualified name, caught";	831	or Carp::croak "spawn init function must be a fully-qualified name, caught";
681		832
682	snd_to_func $noderef, "AnyEvent::MP::_spawn" => $id, @_;	833	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
683		834
684	"$noderef#$id"	835	"$nodeid#$id"
685	}	836	}
		837
686		838
687	=item after $timeout, @msg	839	=item after $timeout, @msg
688		840
689	=item after $timeout, $callback	841	=item after $timeout, $callback
690		842
691	Either sends the given message, or call the given callback, after the	843	Either sends the given message, or call the given callback, after the
692	specified number of seconds.	844	specified number of seconds.
693		845
694	This is simply a utility function that come sin handy at times.	846	This is simply a utility function that comes in handy at times - the
		847	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		848	so it may go away in the future.
695		849
696	=cut	850	=cut
697		851
698	sub after($@) {	852	sub after($@) {
699	my ($timeout, @action) = @_;	853	my ($timeout, @action) = @_;
…		…
704	? $action[0]()	858	? $action[0]()
705	: snd @action;	859	: snd @action;
706	};	860	};
707	}	861	}
708		862
		863	#=item $cb2 = timeout $seconds, $cb[, @args]
		864
		865	=item cal $port, @msg, $callback[, $timeout]
		866
		867	A simple form of RPC - sends a message to the given C<$port> with the
		868	given contents (C<@msg>), but adds a reply port to the message.
		869
		870	The reply port is created temporarily just for the purpose of receiving
		871	the reply, and will be C<kil>ed when no longer needed.
		872
		873	A reply message sent to the port is passed to the C<$callback> as-is.
		874
		875	If an optional time-out (in seconds) is given and it is not C<undef>,
		876	then the callback will be called without any arguments after the time-out
		877	elapsed and the port is C<kil>ed.
		878
		879	If no time-out is given (or it is C<undef>), then the local port will
		880	monitor the remote port instead, so it eventually gets cleaned-up.
		881
		882	Currently this function returns the temporary port, but this "feature"
		883	might go in future versions unless you can make a convincing case that
		884	this is indeed useful for something.
		885
		886	=cut
		887
		888	sub cal(@) {
		889	my $timeout = ref $_[-1] ? undef : pop;
		890	my $cb = pop;
		891
		892	my $port = port {
		893	undef $timeout;
		894	kil $SELF;
		895	&$cb;
		896	};
		897
		898	if (defined $timeout) {
		899	$timeout = AE::timer $timeout, 0, sub {
		900	undef $timeout;
		901	kil $port;
		902	$cb->();
		903	};
		904	} else {
		905	mon $_[0], sub {
		906	kil $port;
		907	$cb->();
		908	};
		909	}
		910
		911	push @_, $port;
		912	&snd;
		913
		914	$port
		915	}
		916
		917	=back
		918
		919	=head1 DISTRIBUTED DATABASE
		920
		921	AnyEvent::MP comes with a simple distributed database. The database will
		922	be mirrored asynchronously on all global nodes. Other nodes bind to one
		923	of the global nodes for their needs. Every node has a "local database"
		924	which contains all the values that are set locally. All local databases
		925	are merged together to form the global database, which can be queried.
		926
		927	The database structure is that of a two-level hash - the database hash
		928	contains hashes which contain values, similarly to a perl hash of hashes,
		929	i.e.:
		930
		931	$DATABASE{$family}{$subkey} = $value
		932
		933	The top level hash key is called "family", and the second-level hash key
		934	is called "subkey" or simply "key".
		935
		936	The family must be alphanumeric, i.e. start with a letter and consist
		937	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		938	pretty much like Perl module names.
		939
		940	As the family namespace is global, it is recommended to prefix family names
		941	with the name of the application or module using it.
		942
		943	The subkeys must be non-empty strings, with no further restrictions.
		944
		945	The values should preferably be strings, but other perl scalars should
		946	work as well (such as C<undef>, arrays and hashes).
		947
		948	Every database entry is owned by one node - adding the same family/subkey
		949	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		950	but the result might be nondeterministic, i.e. the key might have
		951	different values on different nodes.
		952
		953	Different subkeys in the same family can be owned by different nodes
		954	without problems, and in fact, this is the common method to create worker
		955	pools. For example, a worker port for image scaling might do this:
		956
		957	db_set my_image_scalers => $port;
		958
		959	And clients looking for an image scaler will want to get the
		960	C<my_image_scalers> keys from time to time:
		961
		962	db_keys my_image_scalers => sub {
		963	@ports = @{ $_[0] };
		964	};
		965
		966	Or better yet, they want to monitor the database family, so they always
		967	have a reasonable up-to-date copy:
		968
		969	db_mon my_image_scalers => sub {
		970	@ports = keys %{ $_[0] };
		971	};
		972
		973	In general, you can set or delete single subkeys, but query and monitor
		974	whole families only.
		975
		976	If you feel the need to monitor or query a single subkey, try giving it
		977	it's own family.
		978
		979	=over
		980
		981	=item $guard = db_set $family => $subkey [=> $value]
		982
		983	Sets (or replaces) a key to the database - if C<$value> is omitted,
		984	C<undef> is used instead.
		985
		986	When called in non-void context, C<db_set> returns a guard that
		987	automatically calls C<db_del> when it is destroyed.
		988
		989	=item db_del $family => $subkey...
		990
		991	Deletes one or more subkeys from the database family.
		992
		993	=item $guard = db_reg $family => $port => $value
		994
		995	=item $guard = db_reg $family => $port
		996
		997	=item $guard = db_reg $family
		998
		999	Registers a port in the given family and optionally returns a guard to
		1000	remove it.
		1001
		1002	This function basically does the same as:
		1003
		1004	db_set $family => $port => $value
		1005
		1006	Except that the port is monitored and automatically removed from the
		1007	database family when it is kil'ed.
		1008
		1009	If C<$value> is missing, C<undef> is used. If C<$port> is missing, then
		1010	C<$SELF> is used.
		1011
		1012	This function is most useful to register a port in some port group (which
		1013	is just another name for a database family), and have it removed when the
		1014	port is gone. This works best when the port is a local port.
		1015
		1016	=cut
		1017
		1018	sub db_reg($$;$) {
		1019	my $family = shift;
		1020	my $port = @_ ? shift : $SELF;
		1021
		1022	my $clr = sub { db_del $family => $port };
		1023	mon $port, $clr;
		1024
		1025	db_set $family => $port => $_[0];
		1026
		1027	defined wantarray
		1028	and &Guard::guard ($clr)
		1029	}
		1030
		1031	=item db_family $family => $cb->(\%familyhash)
		1032
		1033	Queries the named database C<$family> and call the callback with the
		1034	family represented as a hash. You can keep and freely modify the hash.
		1035
		1036	=item db_keys $family => $cb->(\@keys)
		1037
		1038	Same as C<db_family>, except it only queries the family I<subkeys> and passes
		1039	them as array reference to the callback.
		1040
		1041	=item db_values $family => $cb->(\@values)
		1042
		1043	Same as C<db_family>, except it only queries the family I<values> and passes them
		1044	as array reference to the callback.
		1045
		1046	=item $guard = db_mon $family => $cb->($familyhash, \@added, \@changed, \@deleted)
		1047
		1048	Creates a monitor on the given database family. Each time a key is set
		1049	or or is deleted the callback is called with a hash containing the
		1050	database family and three lists of added, changed and deleted subkeys,
		1051	respectively. If no keys have changed then the array reference might be
		1052	C<undef> or even missing.
		1053
		1054	If not called in void context, a guard object is returned that, when
		1055	destroyed, stops the monitor.
		1056
		1057	The family hash reference and the key arrays belong to AnyEvent::MP and
		1058	B<must not be modified or stored> by the callback. When in doubt, make a
		1059	copy.
		1060
		1061	As soon as possible after the monitoring starts, the callback will be
		1062	called with the intiial contents of the family, even if it is empty,
		1063	i.e. there will always be a timely call to the callback with the current
		1064	contents.
		1065
		1066	It is possible that the callback is called with a change event even though
		1067	the subkey is already present and the value has not changed.
		1068
		1069	The monitoring stops when the guard object is destroyed.
		1070
		1071	Example: on every change to the family "mygroup", print out all keys.
		1072
		1073	my $guard = db_mon mygroup => sub {
		1074	my ($family, $a, $c, $d) = @_;
		1075	print "mygroup members: ", (join " ", keys %$family), "\n";
		1076	};
		1077
		1078	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1079
		1080	my $guard; $guard = db_mon My::Module::workers => sub {
		1081	my ($family, $a, $c, $d) = @_;
		1082	return unless %$family;
		1083	undef $guard;
		1084	print "My::Module::workers now nonempty\n";
		1085	};
		1086
		1087	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		1088
		1089	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		1090	my ($family, $a, $c, $d) = @_;
		1091
		1092	print "+$_=$family->{$_}\n" for @$a;
		1093	print "*$_=$family->{$_}\n" for @$c;
		1094	print "-$_=$family->{$_}\n" for @$d;
		1095	};
		1096
		1097	=cut
		1098
709	=back	1099	=back
710		1100
711	=head1 AnyEvent::MP vs. Distributed Erlang	1101	=head1 AnyEvent::MP vs. Distributed Erlang
712		1102
713	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	1103	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
714	== aemp node, Erlang process == aemp port), so many of the documents and	1104	== aemp node, Erlang process == aemp port), so many of the documents and
715	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	1105	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
716	sample:	1106	sample:
717		1107
718	http://www.Erlang.se/doc/programming_rules.shtml	1108	http://www.erlang.se/doc/programming_rules.shtml
719	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	1109	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
720	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	1110	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
721	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	1111	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
722		1112
723	Despite the similarities, there are also some important differences:	1113	Despite the similarities, there are also some important differences:
724		1114
725	=over 4	1115	=over 4
726		1116
727	=item * Node references contain the recipe on how to contact them.	1117	=item * Node IDs are arbitrary strings in AEMP.
728		1118
729	Erlang relies on special naming and DNS to work everywhere in the	1119	Erlang relies on special naming and DNS to work everywhere in the same
730	same way. AEMP relies on each node knowing it's own address(es), with	1120	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
731	convenience functionality.	1121	configuration or DNS), and possibly the addresses of some seed nodes, but
732		1122	will otherwise discover other nodes (and their IDs) itself.
733	This means that AEMP requires a less tightly controlled environment at the
734	cost of longer node references and a slightly higher management overhead.
735		1123
736	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP	1124	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
737	uses "local ports are like remote ports".	1125	uses "local ports are like remote ports".
738		1126
739	The failure modes for local ports are quite different (runtime errors	1127	The failure modes for local ports are quite different (runtime errors
…		…
748	ports being the special case/exception, where transport errors cannot	1136	ports being the special case/exception, where transport errors cannot
749	occur.	1137	occur.
750		1138
751	=item * Erlang uses processes and a mailbox, AEMP does not queue.	1139	=item * Erlang uses processes and a mailbox, AEMP does not queue.
752		1140
753	Erlang uses processes that selectively receive messages, and therefore	1141	Erlang uses processes that selectively receive messages out of order, and
754	needs a queue. AEMP is event based, queuing messages would serve no	1142	therefore needs a queue. AEMP is event based, queuing messages would serve
755	useful purpose. For the same reason the pattern-matching abilities of	1143	no useful purpose. For the same reason the pattern-matching abilities
756	AnyEvent::MP are more limited, as there is little need to be able to	1144	of AnyEvent::MP are more limited, as there is little need to be able to
757	filter messages without dequeing them.	1145	filter messages without dequeuing them.
758		1146
759	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	1147	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1148	being event-based, while Erlang is process-based.
		1149
		1150	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1151	top of AEMP and Coro threads.
760		1152
761	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1153	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
762		1154
763	Sending messages in Erlang is synchronous and blocks the process (and	1155	Sending messages in Erlang is synchronous and blocks the process until
		1156	a conenction has been established and the message sent (and so does not
764	so does not need a queue that can overflow). AEMP sends are immediate,	1157	need a queue that can overflow). AEMP sends return immediately, connection
765	connection establishment is handled in the background.	1158	establishment is handled in the background.
766		1159
767	=item * Erlang suffers from silent message loss, AEMP does not.	1160	=item * Erlang suffers from silent message loss, AEMP does not.
768		1161
769	Erlang makes few guarantees on messages delivery - messages can get lost	1162	Erlang implements few guarantees on messages delivery - messages can get
770	without any of the processes realising it (i.e. you send messages a, b,	1163	lost without any of the processes realising it (i.e. you send messages a,
771	and c, and the other side only receives messages a and c).	1164	b, and c, and the other side only receives messages a and c).
772		1165
773	AEMP guarantees correct ordering, and the guarantee that there are no	1166	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1167	guarantee that after one message is lost, all following ones sent to the
		1168	same port are lost as well, until monitoring raises an error, so there are
774	holes in the message sequence.	1169	no silent "holes" in the message sequence.
775		1170
776	=item * In Erlang, processes can be declared dead and later be found to be	1171	If you want your software to be very reliable, you have to cope with
777	alive.	1172	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
778		1173	simply tries to work better in common error cases, such as when a network
779	In Erlang it can happen that a monitored process is declared dead and	1174	link goes down.
780	linked processes get killed, but later it turns out that the process is
781	still alive - and can receive messages.
782
783	In AEMP, when port monitoring detects a port as dead, then that port will
784	eventually be killed - it cannot happen that a node detects a port as dead
785	and then later sends messages to it, finding it is still alive.
786		1175
787	=item * Erlang can send messages to the wrong port, AEMP does not.	1176	=item * Erlang can send messages to the wrong port, AEMP does not.
788		1177
789	In Erlang it is quite likely that a node that restarts reuses a process ID	1178	In Erlang it is quite likely that a node that restarts reuses an Erlang
790	known to other nodes for a completely different process, causing messages	1179	process ID known to other nodes for a completely different process,
791	destined for that process to end up in an unrelated process.	1180	causing messages destined for that process to end up in an unrelated
		1181	process.
792		1182
793	AEMP never reuses port IDs, so old messages or old port IDs floating	1183	AEMP does not reuse port IDs, so old messages or old port IDs floating
794	around in the network will not be sent to an unrelated port.	1184	around in the network will not be sent to an unrelated port.
795		1185
796	=item * Erlang uses unprotected connections, AEMP uses secure	1186	=item * Erlang uses unprotected connections, AEMP uses secure
797	authentication and can use TLS.	1187	authentication and can use TLS.
798		1188
799	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1189	AEMP can use a proven protocol - TLS - to protect connections and
800	securely authenticate nodes.	1190	securely authenticate nodes.
801		1191
802	=item * The AEMP protocol is optimised for both text-based and binary	1192	=item * The AEMP protocol is optimised for both text-based and binary
803	communications.	1193	communications.
804		1194
805	The AEMP protocol, unlike the Erlang protocol, supports both	1195	The AEMP protocol, unlike the Erlang protocol, supports both programming
806	language-independent text-only protocols (good for debugging) and binary,	1196	language independent text-only protocols (good for debugging), and binary,
807	language-specific serialisers (e.g. Storable).	1197	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1198	used, the protocol is actually completely text-based.
808		1199
809	It has also been carefully designed to be implementable in other languages	1200	It has also been carefully designed to be implementable in other languages
810	with a minimum of work while gracefully degrading fucntionality to make the	1201	with a minimum of work while gracefully degrading functionality to make the
811	protocol simple.	1202	protocol simple.
812		1203
813	=item * AEMP has more flexible monitoring options than Erlang.	1204	=item * AEMP has more flexible monitoring options than Erlang.
814		1205
815	In Erlang, you can chose to receive I<all> exit signals as messages	1206	In Erlang, you can chose to receive I<all> exit signals as messages or
816	or I<none>, there is no in-between, so monitoring single processes is	1207	I<none>, there is no in-between, so monitoring single Erlang processes is
817	difficult to implement. Monitoring in AEMP is more flexible than in	1208	difficult to implement.
818	Erlang, as one can choose between automatic kill, exit message or callback	1209
819	on a per-process basis.	1210	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1211	between automatic kill, exit message or callback on a per-port basis.
820		1212
821	=item * Erlang tries to hide remote/local connections, AEMP does not.	1213	=item * Erlang tries to hide remote/local connections, AEMP does not.
822		1214
823	Monitoring in Erlang is not an indicator of process death/crashes,	1215	Monitoring in Erlang is not an indicator of process death/crashes, in the
824	as linking is (except linking is unreliable in Erlang).	1216	same way as linking is (except linking is unreliable in Erlang).
825		1217
826	In AEMP, you don't "look up" registered port names or send to named ports	1218	In AEMP, you don't "look up" registered port names or send to named ports
827	that might or might not be persistent. Instead, you normally spawn a port	1219	that might or might not be persistent. Instead, you normally spawn a port
828	on the remote node. The init function monitors the you, and you monitor	1220	on the remote node. The init function monitors you, and you monitor the
829	the remote port. Since both monitors are local to the node, they are much	1221	remote port. Since both monitors are local to the node, they are much more
830	more reliable.	1222	reliable (no need for C<spawn_link>).
831		1223
832	This also saves round-trips and avoids sending messages to the wrong port	1224	This also saves round-trips and avoids sending messages to the wrong port
833	(hard to do in Erlang).	1225	(hard to do in Erlang).
834		1226
835	=back	1227	=back
836		1228
837	=head1 RATIONALE	1229	=head1 RATIONALE
838		1230
839	=over 4	1231	=over 4
840		1232
841	=item Why strings for ports and noderefs, why not objects?	1233	=item Why strings for port and node IDs, why not objects?
842		1234
843	We considered "objects", but found that the actual number of methods	1235	We considered "objects", but found that the actual number of methods
844	thatc an be called are very low. Since port IDs and noderefs travel over	1236	that can be called are quite low. Since port and node IDs travel over
845	the network frequently, the serialising/deserialising would add lots of	1237	the network frequently, the serialising/deserialising would add lots of
846	overhead, as well as having to keep a proxy object.	1238	overhead, as well as having to keep a proxy object everywhere.
847		1239
848	Strings can easily be printed, easily serialised etc. and need no special	1240	Strings can easily be printed, easily serialised etc. and need no special
849	procedures to be "valid".	1241	procedures to be "valid".
850		1242
851	And a a miniport consists of a single closure stored in a global hash - it	1243	And as a result, a port with just a default receiver consists of a single
852	can't become much cheaper.	1244	code reference stored in a global hash - it can't become much cheaper.
853		1245
854	=item Why favour JSON, why not real serialising format such as Storable?	1246	=item Why favour JSON, why not a real serialising format such as Storable?
855		1247
856	In fact, any AnyEvent::MP node will happily accept Storable as framing	1248	In fact, any AnyEvent::MP node will happily accept Storable as framing
857	format, but currently there is no way to make a node use Storable by	1249	format, but currently there is no way to make a node use Storable by
858	default.	1250	default (although all nodes will accept it).
859		1251
860	The default framing protocol is JSON because a) JSON::XS is many times	1252	The default framing protocol is JSON because a) JSON::XS is many times
861	faster for small messages and b) most importantly, after years of	1253	faster for small messages and b) most importantly, after years of
862	experience we found that object serialisation is causing more problems	1254	experience we found that object serialisation is causing more problems
863	than it gains: Just like function calls, objects simply do not travel	1255	than it solves: Just like function calls, objects simply do not travel
864	easily over the network, mostly because they will always be a copy, so you	1256	easily over the network, mostly because they will always be a copy, so you
865	always have to re-think your design.	1257	always have to re-think your design.
866		1258
867	Keeping your messages simple, concentrating on data structures rather than	1259	Keeping your messages simple, concentrating on data structures rather than
868	objects, will keep your messages clean, tidy and efficient.	1260	objects, will keep your messages clean, tidy and efficient.
869		1261
870	=back	1262	=back
871		1263
		1264	=head1 PORTING FROM AnyEvent::MP VERSION 1.X
		1265
		1266	AEMP version 2 has a few major incompatible changes compared to version 1:
		1267
		1268	=over 4
		1269
		1270	=item AnyEvent::MP::Global no longer has group management functions.
		1271
		1272	AnyEvent::MP now comes with a distributed database that is more
		1273	powerful. Its database families map closely to port groups, but the API
		1274	has changed (the functions are also now exported by AnyEvent::MP). Here is
		1275	a rough porting guide:
		1276
		1277	grp_reg $group, $port # old
		1278	db_reg $group, $port # new
		1279
		1280	$list = grp_get $group # old
		1281	db_keys $group, sub { my $list = shift } # new
		1282
		1283	grp_mon $group, $cb->(\@ports, $add, $del) # old
		1284	db_mon $group, $cb->(\%ports, $add, $change, $del) # new
		1285
		1286	C<grp_reg> is a no-brainer (just replace by C<db_reg>), but C<grp_get> is
		1287	no longer instant, because the local node might not have a copy of the
		1288	group. You can either modify your code to allow for a callback, or use
		1289	C<db_mon> to keep an updated copy of the group:
		1290
		1291	my $local_group_copy;
		1292	db_mon $group => sub { $local_group_copy = $_[0] };
		1293
		1294	# now "keys %$local_group_copy" always returns the most up-to-date
		1295	# list of ports in the group.
		1296
		1297	C<grp_mon> can be replaced by C<db_mon> with minor changes - C<db_mon>
		1298	passes a hash as first argument, and an extra C<$chg> argument that can be
		1299	ignored:
		1300
		1301	db_mon $group => sub {
		1302	my ($ports, $add, $chg, $lde) = @_;
		1303	$ports = [keys %$ports];
		1304
		1305	# now $ports, $add and $del are the same as
		1306	# were originally passed by grp_mon.
		1307	...
		1308	};
		1309
		1310	=item Nodes not longer connect to all other nodes.
		1311
		1312	In AEMP 1.x, every node automatically loads the L<AnyEvent::MP::Global>
		1313	module, which in turn would create connections to all other nodes in the
		1314	network (helped by the seed nodes).
		1315
		1316	In version 2.x, global nodes still connect to all other global nodes, but
		1317	other nodes don't - now every node either is a global node itself, or
		1318	attaches itself to another global node.
		1319
		1320	If a node isn't a global node itself, then it attaches itself to one
		1321	of its seed nodes. If that seed node isn't a global node yet, it will
		1322	automatically be upgraded to a global node.
		1323
		1324	So in many cases, nothing needs to be changed - one just has to make sure
		1325	that all seed nodes are meshed together with the other seed nodes (as with
		1326	AEMP 1.x), and other nodes specify them as seed nodes. This is most easily
		1327	achieved by specifying the same set of seed nodes for all nodes in the
		1328	network.
		1329
		1330	Not opening a connection to every other node is usually an advantage,
		1331	except when you need the lower latency of an already established
		1332	connection. To ensure a node establishes a connection to another node,
		1333	you can monitor the node port (C<mon $node, ...>), which will attempt to
		1334	create the connection (and notify you when the connection fails).
		1335
		1336	=item Listener-less nodes (nodes without binds) are gone.
		1337
		1338	And are not coming back, at least not in their old form. If no C<binds>
		1339	are specified for a node, AnyEvent::MP assumes a default of C<*:*>.
		1340
		1341	There are vague plans to implement some form of routing domains, which
		1342	might or might not bring back listener-less nodes, but don't count on it.
		1343
		1344	The fact that most connections are now optional somewhat mitigates this,
		1345	as a node can be effectively unreachable from the outside without any
		1346	problems, as long as it isn't a global node and only reaches out to other
		1347	nodes (as opposed to being contacted from other nodes).
		1348
		1349	=item $AnyEvent::MP::Kernel::WARN has gone.
		1350
		1351	AnyEvent has acquired a logging framework (L<AnyEvent::Log>), and AEMP now
		1352	uses this, and so should your programs.
		1353
		1354	Every module now documents what kinds of messages it generates, with
		1355	AnyEvent::MP acting as a catch all.
		1356
		1357	On the positive side, this means that instead of setting
		1358	C<PERL_ANYEVENT_MP_WARNLEVEL>, you can get away by setting C<AE_VERBOSE> -
		1359	much less to type.
		1360
		1361	=back
		1362
		1363	=head1 LOGGING
		1364
		1365	AnyEvent::MP does not normally log anything by itself, but sinc eit is the
		1366	root of the contetx hierarchy for AnyEvent::MP modules, it will receive
		1367	all log messages by submodules.
		1368
872	=head1 SEE ALSO	1369	=head1 SEE ALSO
		1370
		1371	L<AnyEvent::MP::Intro> - a gentle introduction.
		1372
		1373	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1374
		1375	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1376	your applications.
		1377
		1378	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1379
		1380	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1381	all nodes.
873		1382
874	L<AnyEvent>.	1383	L<AnyEvent>.
875		1384
876	=head1 AUTHOR	1385	=head1 AUTHOR
877		1386

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