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Revision 1.50 by root, Fri Aug 14 14:01:05 2009 UTC vs.
Revision 1.155 by root, Sat Sep 18 13:46:56 2021 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 $somple_port = port { my @msg = @_; 0 };	25	my $simple_port = port { my @msg = @_ };
29		26
30	# creating/using ports, type 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
42		43
43	=head1 CURRENT STATUS	44	# temporarily execute code in port context
		45	peval $port, sub { die "kill the port!" };
44		46
45	AnyEvent::MP - stable API, should work	47	# execute callbacks in $SELF port context
46	AnyEvent::MP::Intro - outdated	48	my $timer = AE::timer 1, 0, psub {
47	AnyEvent::MP::Kernel - WIP	49	die "kill the port, delayed";
48	AnyEvent::MP::Transport - mostly stable	50	};
49		51
50	stay tuned.	52	# distributed database - modification
		53	db_set $family => $subkey [=> $value] # add a subkey
		54	db_del $family => $subkey... # delete one or more subkeys
		55	db_reg $family => $port [=> $value] # register a port
		56
		57	# distributed database - queries
		58	db_family $family => $cb->(\%familyhash)
		59	db_keys $family => $cb->(\@keys)
		60	db_values $family => $cb->(\@values)
		61
		62	# distributed database - monitoring a family
		63	db_mon $family => $cb->(\%familyhash, \@added, \@changed, \@deleted)
51		64
52	=head1 DESCRIPTION	65	=head1 DESCRIPTION
53		66
54	This module (-family) implements a simple message passing framework.	67	This module (-family) implements a simple message passing framework.
55		68
56	Despite its simplicity, you can securely message other processes running	69	Despite its simplicity, you can securely message other processes running
57	on the same or other hosts.	70	on the same or other hosts, and you can supervise entities remotely.
58		71
59	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	72	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
60	manual page.	73	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		74
66	=head1 CONCEPTS	75	=head1 CONCEPTS
67		76
68	=over 4	77	=over 4
69		78
70	=item port	79	=item port
71		80
72	A port is something you can send messages to (with the C<snd> function).	81	Not to be confused with a TCP port, a "port" is something you can send
		82	messages to (with the C<snd> function).
73		83
74	Some ports allow you to register C<rcv> handlers that can match specific	84	Ports allow you to register C<rcv> handlers that can match all or just
75	messages. All C<rcv> handlers will receive messages they match, messages	85	some messages. Messages send to ports will not be queued, regardless of
76	will not be queued.	86	anything was listening for them or not.
77		87
		88	Ports are represented by (printable) strings called "port IDs".
		89
78	=item port id - C<noderef#portname>	90	=item port ID - C<nodeid#portname>
79		91
80	A port id is normaly the concatenation of a noderef, a hash-mark (C<#>) as	92	A port ID is the concatenation of a node ID, a hash-mark (C<#>)
81	separator, and a port name (a printable string of unspecified format). An	93	as separator, and a port name (a printable string of unspecified
82	exception is the the node port, whose ID is identical to its node	94	format created by AnyEvent::MP).
83	reference.
84		95
85	=item node	96	=item node
86		97
87	A node is a single process containing at least one port - the node	98	A node is a single process containing at least one port - the node port,
88	port. You can send messages to node ports to find existing ports or to	99	which enables nodes to manage each other remotely, and to create new
89	create new ports, among other things.	100	ports.
90		101
91	Nodes are either private (single-process only), slaves (connected to a	102	Nodes are either public (have one or more listening ports) or private
92	master node only) or public nodes (connectable from unrelated nodes).	103	(no listening ports). Private nodes cannot talk to other private nodes
		104	currently, but all nodes can talk to public nodes.
93		105
94	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	106	Nodes is represented by (printable) strings called "node IDs".
95		107
96	A node reference is a string that either simply identifies the node (for	108	=item node ID - C<[A-Za-z0-9_\-.:]*>
97	private and slave nodes), or contains a recipe on how to reach a given
98	node (for public nodes).
99		109
100	This recipe is simply a comma-separated list of C<address:port> pairs (for	110	A node ID is a string that uniquely identifies the node within a
101	TCP/IP, other protocols might look different).	111	network. Depending on the configuration used, node IDs can look like a
		112	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		113	doesn't interpret node IDs in any way except to uniquely identify a node.
102		114
103	Node references come in two flavours: resolved (containing only numerical	115	=item binds - C<ip:port>
104	addresses) or unresolved (where hostnames are used instead of addresses).
105		116
106	Before using an unresolved node reference in a message you first have to	117	Nodes can only talk to each other by creating some kind of connection to
107	resolve it.	118	each other. To do this, nodes should listen on one or more local transport
		119	endpoints - binds.
		120
		121	Currently, only standard C<ip:port> specifications can be used, which
		122	specify TCP ports to listen on. So a bind is basically just a tcp socket
		123	in listening mode that accepts connections from other nodes.
		124
		125	=item seed nodes
		126
		127	When a node starts, it knows nothing about the network it is in - it
		128	needs to connect to at least one other node that is already in the
		129	network. These other nodes are called "seed nodes".
		130
		131	Seed nodes themselves are not special - they are seed nodes only because
		132	some other node I<uses> them as such, but any node can be used as seed
		133	node for other nodes, and eahc node can use a different set of seed nodes.
		134
		135	In addition to discovering the network, seed nodes are also used to
		136	maintain the network - all nodes using the same seed node are part of the
		137	same network. If a network is split into multiple subnets because e.g. the
		138	network link between the parts goes down, then using the same seed nodes
		139	for all nodes ensures that eventually the subnets get merged again.
		140
		141	Seed nodes are expected to be long-running, and at least one seed node
		142	should always be available. They should also be relatively responsive - a
		143	seed node that blocks for long periods will slow down everybody else.
		144
		145	For small networks, it's best if every node uses the same set of seed
		146	nodes. For large networks, it can be useful to specify "regional" seed
		147	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		148	each other. What's important is that all seed nodes connections form a
		149	complete graph, so that the network cannot split into separate subnets
		150	forever.
		151
		152	Seed nodes are represented by seed IDs.
		153
		154	=item seed IDs - C<host:port>
		155
		156	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
		157	TCP port) of nodes that should be used as seed nodes.
		158
		159	=item global nodes
		160
		161	An AEMP network needs a discovery service - nodes need to know how to
		162	connect to other nodes they only know by name. In addition, AEMP offers a
		163	distributed "group database", which maps group names to a list of strings
		164	- for example, to register worker ports.
		165
		166	A network needs at least one global node to work, and allows every node to
		167	be a global node.
		168
		169	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		170	node and tries to keep connections to all other nodes. So while it can
		171	make sense to make every node "global" in small networks, it usually makes
		172	sense to only make seed nodes into global nodes in large networks (nodes
		173	keep connections to seed nodes and global nodes, so making them the same
		174	reduces overhead).
108		175
109	=back	176	=back
110		177
111	=head1 VARIABLES/FUNCTIONS	178	=head1 VARIABLES/FUNCTIONS
112		179
…		…
114		181
115	=cut	182	=cut
116		183
117	package AnyEvent::MP;	184	package AnyEvent::MP;
118		185
		186	use AnyEvent::MP::Config ();
119	use AnyEvent::MP::Kernel;	187	use AnyEvent::MP::Kernel;
		188	use AnyEvent::MP::Kernel qw(
		189	%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID
		190	add_node load_func
		191
		192	NODE $NODE
		193	configure
		194	node_of port_is_local
		195	snd kil
		196	db_set db_del
		197	db_mon db_family db_keys db_values
		198	);
120		199
121	use common::sense;	200	use common::sense;
122		201
123	use Carp ();	202	use Carp ();
124		203
125	use AE ();	204	use AnyEvent ();
		205	use Guard ();
126		206
127	use base "Exporter";	207	use base "Exporter";
128		208
129	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	209	our $VERSION = '2.02'; # also in MP/Config.pm
130		210
131	our @EXPORT = qw(	211	our @EXPORT = qw(
132	NODE $NODE *SELF node_of _any_	212	configure
133	resolve_node initialise_node	213
134	snd rcv mon kil reg psub spawn	214	NODE $NODE
135	port	215	*SELF
		216
		217	node_of port_is_local
		218
		219	snd kil
		220	port rcv mon mon_guard psub peval spawn cal
		221	db_set db_del db_reg
		222	db_mon db_family db_keys db_values
		223
		224	after
136	);	225	);
137		226
138	our $SELF;	227	our $SELF;
139		228
140	sub _self_die() {	229	sub _self_die() {
…		…
143	kil $SELF, die => $msg;	232	kil $SELF, die => $msg;
144	}	233	}
145		234
146	=item $thisnode = NODE / $NODE	235	=item $thisnode = NODE / $NODE
147		236
148	The C<NODE> function returns, and the C<$NODE> variable contains	237	The C<NODE> function returns, and the C<$NODE> variable contains, the node
149	the noderef of the local node. The value is initialised by a call	238	ID of the node running in the current process. This value is initialised by
150	to C<become_public> or C<become_slave>, after which all local port	239	a call to C<configure>.
151	identifiers become invalid.
152		240
153	=item $noderef = node_of $port	241	=item $nodeid = node_of $port
154		242
155	Extracts and returns the noderef from a portid or a noderef.	243	Extracts and returns the node ID from a port ID or a node ID.
156		244
157	=item initialise_node $noderef, $seednode, $seednode...	245	=item $is_local = port_is_local $port
158		246
159	=item initialise_node "slave/", $master, $master...	247	Returns true iff the port is a local port.
160		248
		249	=item configure $profile, key => value...
		250
		251	=item configure key => value...
		252
161	Before a node can talk to other nodes on the network it has to initialise	253	Before a node can talk to other nodes on the network (i.e. enter
162	itself - the minimum a node needs to know is it's own name, and optionally	254	"distributed mode") it has to configure itself - the minimum a node needs
163	it should know the noderefs of some other nodes in the network.	255	to know is its own name, and optionally it should know the addresses of
		256	some other nodes in the network to discover other nodes.
164		257
165	This function initialises a node - it must be called exactly once (or	258	This function configures a node - it must be called exactly once (or
166	never) before calling other AnyEvent::MP functions.	259	never) before calling other AnyEvent::MP functions.
167		260
168	All arguments (optionally except for the first) are noderefs, which can be	261	The key/value pairs are basically the same ones as documented for the
169	either resolved or unresolved.	262	F<aemp> command line utility (sans the set/del prefix), with these additions:
170
171	The first argument will be looked up in the configuration database first
172	(if it is C<undef> then the current nodename will be used instead) to find
173	the relevant configuration profile (see L<aemp>). If none is found then
174	the default configuration is used. The configuration supplies additional
175	seed/master nodes and can override the actual noderef.
176
177	There are two types of networked nodes, public nodes and slave nodes:
178		263
179	=over 4	264	=over 4
180		265
181	=item public nodes	266	=item norc => $boolean (default false)
182		267
183	For public nodes, C<$noderef> (supplied either directly to	268	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
184	C<initialise_node> or indirectly via a profile or the nodename) must be a	269	be consulted - all configuration options must be specified in the
185	noderef (possibly unresolved, in which case it will be resolved).	270	C<configure> call.
186		271
187	After resolving, the node will bind itself on all endpoints and try to	272	=item force => $boolean (default false)
188	connect to all additional C<$seednodes> that are specified. Seednodes are
189	optional and can be used to quickly bootstrap the node into an existing
190	network.
191		273
192	=item slave nodes	274	IF true, then the values specified in the C<configure> will take
193		275	precedence over any values configured via the rc file. The default is for
194	When the C<$noderef> (either as given or overriden by the config file)	276	the rc file to override any options specified in the program.
195	is the special string C<slave/>, then the node will become a slave
196	node. Slave nodes cannot be contacted from outside and will route most of
197	their traffic to the master node that they attach to.
198
199	At least one additional noderef is required (either by specifying it
200	directly or because it is part of the configuration profile): The node
201	will try to connect to all of them and will become a slave attached to the
202	first node it can successfully connect to.
203		277
204	=back	278	=back
205		279
206	This function will block until all nodes have been resolved and, for slave
207	nodes, until it has successfully established a connection to a master
208	server.
209
210	Example: become a public node listening on the guessed noderef, or the one
211	specified via C<aemp> for the current node. This should be the most common
212	form of invocation for "daemon"-type nodes.
213
214	initialise_node;
215
216	Example: become a slave node to any of the the seednodes specified via
217	C<aemp>. This form is often used for commandline clients.
218
219	initialise_node "slave/";
220
221	Example: become a slave node to any of the specified master servers. This
222	form is also often used for commandline clients.
223
224	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
225
226	Example: become a public node, and try to contact some well-known master
227	servers to become part of the network.
228
229	initialise_node undef, "master1", "master2";
230
231	Example: become a public node listening on port C<4041>.
232
233	initialise_node 4041;
234
235	Example: become a public node, only visible on localhost port 4044.
236
237	initialise_node "localhost:4044";
238
239	=item $cv = resolve_node $noderef
240
241	Takes an unresolved node reference that may contain hostnames and
242	abbreviated IDs, resolves all of them and returns a resolved node
243	reference.
244
245	In addition to C<address:port> pairs allowed in resolved noderefs, the
246	following forms are supported:
247
248	=over 4	280	=over 4
249		281
250	=item the empty string	282	=item step 1, gathering configuration from profiles
251		283
252	An empty-string component gets resolved as if the default port (4040) was	284	The function first looks up a profile in the aemp configuration (see the
253	specified.	285	L<aemp> commandline utility). The profile name can be specified via the
		286	named C<profile> parameter or can simply be the first parameter). If it is
		287	missing, then the nodename (F<uname -n>) will be used as profile name.
254		288
255	=item naked port numbers (e.g. C<1234>)	289	The profile data is then gathered as follows:
256		290
257	These are resolved by prepending the local nodename and a colon, to be	291	First, all remaining key => value pairs (all of which are conveniently
258	further resolved.	292	undocumented at the moment) will be interpreted as configuration
		293	data. Then they will be overwritten by any values specified in the global
		294	default configuration (see the F<aemp> utility), then the chain of
		295	profiles chosen by the profile name (and any C<parent> attributes).
259		296
260	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	297	That means that the values specified in the profile have highest priority
		298	and the values specified directly via C<configure> have lowest priority,
		299	and can only be used to specify defaults.
261		300
262	These are resolved by using AnyEvent::DNS to resolve them, optionally	301	If the profile specifies a node ID, then this will become the node ID of
263	looking up SRV records for the C<aemp=4040> port, if no port was	302	this process. If not, then the profile name will be used as node ID, with
264	specified.	303	a unique randoms tring (C</%u>) appended.
		304
		305	The node ID can contain some C<%> sequences that are expanded: C<%n>
		306	is expanded to the local nodename, C<%u> is replaced by a random
		307	string to make the node unique. For example, the F<aemp> commandline
		308	utility uses C<aemp/%n/%u> as nodename, which might expand to
		309	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		310
		311	=item step 2, bind listener sockets
		312
		313	The next step is to look up the binds in the profile, followed by binding
		314	aemp protocol listeners on all binds specified (it is possible and valid
		315	to have no binds, meaning that the node cannot be contacted from the
		316	outside. This means the node cannot talk to other nodes that also have no
		317	binds, but it can still talk to all "normal" nodes).
		318
		319	If the profile does not specify a binds list, then a default of C<*> is
		320	used, meaning the node will bind on a dynamically-assigned port on every
		321	local IP address it finds.
		322
		323	=item step 3, connect to seed nodes
		324
		325	As the last step, the seed ID list from the profile is passed to the
		326	L<AnyEvent::MP::Global> module, which will then use it to keep
		327	connectivity with at least one node at any point in time.
265		328
266	=back	329	=back
		330
		331	Example: become a distributed node using the local node name as profile.
		332	This should be the most common form of invocation for "daemon"-type nodes.
		333
		334	configure
		335
		336	Example: become a semi-anonymous node. This form is often used for
		337	commandline clients.
		338
		339	configure nodeid => "myscript/%n/%u";
		340
		341	Example: configure a node using a profile called seed, which is suitable
		342	for a seed node as it binds on all local addresses on a fixed port (4040,
		343	customary for aemp).
		344
		345	# use the aemp commandline utility
		346	# aemp profile seed binds '*:4040'
		347
		348	# then use it
		349	configure profile => "seed";
		350
		351	# or simply use aemp from the shell again:
		352	# aemp run profile seed
		353
		354	# or provide a nicer-to-remember nodeid
		355	# aemp run profile seed nodeid "$(hostname)"
267		356
268	=item $SELF	357	=item $SELF
269		358
270	Contains the current port id while executing C<rcv> callbacks or C<psub>	359	Contains the current port id while executing C<rcv> callbacks or C<psub>
271	blocks.	360	blocks.
272		361
273	=item SELF, %SELF, @SELF...	362	=item *SELF, SELF, %SELF, @SELF...
274		363
275	Due to some quirks in how perl exports variables, it is impossible to	364	Due to some quirks in how perl exports variables, it is impossible to
276	just export C<$SELF>, all the symbols called C<SELF> are exported by this	365	just export C<$SELF>, all the symbols named C<SELF> are exported by this
277	module, but only C<$SELF> is currently used.	366	module, but only C<$SELF> is currently used.
278		367
279	=item snd $port, type => @data	368	=item snd $port, type => @data
280		369
281	=item snd $port, @msg	370	=item snd $port, @msg
282		371
283	Send the given message to the given port ID, which can identify either	372	Send the given message to the given port, which can identify either a
284	a local or a remote port, and can be either a string or soemthignt hat	373	local or a remote port, and must be a port ID.
285	stringifies a sa port ID (such as a port object :).
286		374
287	While the message can be about anything, it is highly recommended to use a	375	While the message can be almost anything, it is highly recommended to
288	string as first element (a portid, or some word that indicates a request	376	use a string as first element (a port ID, or some word that indicates a
289	type etc.).	377	request type etc.) and to consist if only simple perl values (scalars,
		378	arrays, hashes) - if you think you need to pass an object, think again.
290		379
291	The message data effectively becomes read-only after a call to this	380	The message data logically becomes read-only after a call to this
292	function: modifying any argument is not allowed and can cause many	381	function: modifying any argument (or values referenced by them) is
293	problems.	382	forbidden, as there can be considerable time between the call to C<snd>
		383	and the time the message is actually being serialised - in fact, it might
		384	never be copied as within the same process it is simply handed to the
		385	receiving port.
294		386
295	The type of data you can transfer depends on the transport protocol: when	387	The type of data you can transfer depends on the transport protocol: when
296	JSON is used, then only strings, numbers and arrays and hashes consisting	388	JSON is used, then only strings, numbers and arrays and hashes consisting
297	of those are allowed (no objects). When Storable is used, then anything	389	of those are allowed (no objects). When Storable is used, then anything
298	that Storable can serialise and deserialise is allowed, and for the local	390	that Storable can serialise and deserialise is allowed, and for the local
299	node, anything can be passed.	391	node, anything can be passed. Best rely only on the common denominator of
		392	these.
300		393
301	=item $local_port = port	394	=item $local_port = port
302		395
303	Create a new local port object and returns its port ID. Initially it has	396	Create a new local port object and returns its port ID. Initially it has
304	no callbacks set and will throw an error when it receives messages.	397	no callbacks set and will throw an error when it receives messages.
…		…
323		416
324	=cut	417	=cut
325		418
326	sub rcv($@);	419	sub rcv($@);
327		420
328	sub _kilme {	421	my $KILME = sub {
329	die "received message on port without callback";	422	(my $tag = substr $_[0], 0, 30) =~ s/([^\x20-\x7e])/./g;
330	}	423	kil $SELF, unhandled_message => "no callback found for message '$tag'";
		424	};
331		425
332	sub port(;&) {	426	sub port(;&) {
333	my $id = "$UNIQ." . $ID++;	427	my $id = $UNIQ . ++$ID;
334	my $port = "$NODE#$id";	428	my $port = "$NODE#$id";
335		429
336	rcv $port, shift || \&_kilme;	430	rcv $port, shift || $KILME;
337		431
338	$port	432	$port
339	}	433	}
340		434
341	=item rcv $local_port, $callback->(@msg)	435	=item rcv $local_port, $callback->(@msg)
…		…
346		440
347	The global C<$SELF> (exported by this module) contains C<$port> while	441	The global C<$SELF> (exported by this module) contains C<$port> while
348	executing the callback. Runtime errors during callback execution will	442	executing the callback. Runtime errors during callback execution will
349	result in the port being C<kil>ed.	443	result in the port being C<kil>ed.
350		444
351	The default callback received all messages not matched by a more specific	445	The default callback receives all messages not matched by a more specific
352	C<tag> match.	446	C<tag> match.
353		447
354	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...	448	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
355		449
356	Register callbacks to be called on messages starting with the given tag on	450	Register (or replace) callbacks to be called on messages starting with the
357	the given port (and return the port), or unregister it (when C<$callback>	451	given tag on the given port (and return the port), or unregister it (when
358	is C<$undef>).	452	C<$callback> is C<$undef> or missing). There can only be one callback
		453	registered for each tag.
359		454
360	The original message will be passed to the callback, after the first	455	The original message will be passed to the callback, after the first
361	element (the tag) has been removed. The callback will use the same	456	element (the tag) has been removed. The callback will use the same
362	environment as the default callback (see above).	457	environment as the default callback (see above).
363		458
…		…
375	rcv port,	470	rcv port,
376	msg1 => sub { ... },	471	msg1 => sub { ... },
377	...	472	...
378	;	473	;
379		474
		475	Example: temporarily register a rcv callback for a tag matching some port
		476	(e.g. for an rpc reply) and unregister it after a message was received.
		477
		478	rcv $port, $otherport => sub {
		479	my @reply = @_;
		480
		481	rcv $SELF, $otherport;
		482	};
		483
380	=cut	484	=cut
381		485
382	sub rcv($@) {	486	sub rcv($@) {
383	my $port = shift;	487	my $port = shift;
384	my ($noderef, $portid) = split /#/, $port, 2;	488	my ($nodeid, $portid) = split /#/, $port, 2;
385		489
386	($NODE{$noderef} || add_node $noderef) == $NODE{""}	490	$nodeid eq $NODE
387	or Carp::croak "$port: rcv can only be called on local ports, caught";	491	or Carp::croak "$port: rcv can only be called on local ports, caught";
388		492
389	while (@_) {	493	while (@_) {
390	if (ref $_[0]) {	494	if (ref $_[0]) {
391	if (my $self = $PORT_DATA{$portid}) {	495	if (my $self = $PORT_DATA{$portid}) {
392	"AnyEvent::MP::Port" eq ref $self	496	"AnyEvent::MP::Port" eq ref $self
393	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	497	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
394		498
395	$self->[2] = shift;	499	$self->[0] = shift;
396	} else {	500	} else {
397	my $cb = shift;	501	my $cb = shift;
398	$PORT{$portid} = sub {	502	$PORT{$portid} = sub {
399	local $SELF = $port;	503	local $SELF = $port;
400	eval { &$cb }; _self_die if $@;	504	eval { &$cb }; _self_die if $@;
401	};	505	};
402	}	506	}
403	} elsif (defined $_[0]) {	507	} elsif (defined $_[0]) {
404	my $self = $PORT_DATA{$portid} ||= do {	508	my $self = $PORT_DATA{$portid} ||= do {
405	my $self = bless [$PORT{$port} || sub { }, { }, $port], "AnyEvent::MP::Port";	509	my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port";
406		510
407	$PORT{$portid} = sub {	511	$PORT{$portid} = sub {
408	local $SELF = $port;	512	local $SELF = $port;
409		513
410	if (my $cb = $self->[1]{$_[0]}) {	514	if (my $cb = $self->[1]{$_[0]}) {
…		…
432	}	536	}
433		537
434	$port	538	$port
435	}	539	}
436		540
		541	=item peval $port, $coderef[, @args]
		542
		543	Evaluates the given C<$codref> within the context of C<$port>, that is,
		544	when the code throws an exception the C<$port> will be killed.
		545
		546	Any remaining args will be passed to the callback. Any return values will
		547	be returned to the caller.
		548
		549	This is useful when you temporarily want to execute code in the context of
		550	a port.
		551
		552	Example: create a port and run some initialisation code in it's context.
		553
		554	my $port = port { ... };
		555
		556	peval $port, sub {
		557	init
		558	or die "unable to init";
		559	};
		560
		561	=cut
		562
		563	sub peval($$) {
		564	local $SELF = shift;
		565	my $cb = shift;
		566
		567	if (wantarray) {
		568	my @res = eval { &$cb };
		569	_self_die if $@;
		570	@res
		571	} else {
		572	my $res = eval { &$cb };
		573	_self_die if $@;
		574	$res
		575	}
		576	}
		577
437	=item $closure = psub { BLOCK }	578	=item $closure = psub { BLOCK }
438		579
439	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	580	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
440	closure is executed, sets up the environment in the same way as in C<rcv>	581	closure is executed, sets up the environment in the same way as in C<rcv>
441	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.	582	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		583
		584	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		585	BLOCK }, @_ } >>.
442		586
443	This is useful when you register callbacks from C<rcv> callbacks:	587	This is useful when you register callbacks from C<rcv> callbacks:
444		588
445	rcv delayed_reply => sub {	589	rcv delayed_reply => sub {
446	my ($delay, @reply) = @_;	590	my ($delay, @reply) = @_;
…		…
470	$res	614	$res
471	}	615	}
472	}	616	}
473	}	617	}
474		618
475	=item $guard = mon $port, $cb->(@reason)	619	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
476		620
477	=item $guard = mon $port, $rcvport	621	=item $guard = mon $port # kill $SELF when $port dies
478		622
479	=item $guard = mon $port	623	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
480		624
481	=item $guard = mon $port, $rcvport, @msg	625	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
482		626
483	Monitor the given port and do something when the port is killed or	627	Monitor the given port and do something when the port is killed or
484	messages to it were lost, and optionally return a guard that can be used	628	messages to it were lost, and optionally return a guard that can be used
485	to stop monitoring again.	629	to stop monitoring again.
486		630
		631	The first two forms distinguish between "normal" and "abnormal" kil's:
		632
		633	In the first form (another port given), if the C<$port> is C<kil>'ed with
		634	a non-empty reason, the other port (C<$rcvport>) will be kil'ed with the
		635	same reason. That is, on "normal" kil's nothing happens, while under all
		636	other conditions, the other port is killed with the same reason.
		637
		638	The second form (kill self) is the same as the first form, except that
		639	C<$rvport> defaults to C<$SELF>.
		640
		641	The remaining forms don't distinguish between "normal" and "abnormal" kil's
		642	- it's up to the callback or receiver to check whether the C<@reason> is
		643	empty and act accordingly.
		644
		645	In the third form (callback), the callback is simply called with any
		646	number of C<@reason> elements (empty @reason means that the port was deleted
		647	"normally"). Note also that I<< the callback B<must> never die >>, so use
		648	C<eval> if unsure.
		649
		650	In the last form (message), a message of the form C<$rcvport, @msg,
		651	@reason> will be C<snd>.
		652
		653	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		654	alert was raised), they are removed and will not trigger again, even if it
		655	turns out that the port is still alive (but monitoring actions added after
		656	that will again trigger).
		657
		658	As a rule of thumb, monitoring requests should always monitor a remote
		659	port locally (using a local C<$rcvport> or a callback). The reason is that
		660	kill messages might get lost, just like any other message. Another less
		661	obvious reason is that even monitoring requests can get lost (for example,
		662	when the connection to the other node goes down permanently). When
		663	monitoring a port locally these problems do not exist.
		664
487	C<mon> effectively guarantees that, in the absence of hardware failures,	665	C<mon> effectively guarantees that, in the absence of hardware failures,
488	that after starting the monitor, either all messages sent to the port	666	after starting the monitor, either all messages sent to the port will
489	will arrive, or the monitoring action will be invoked after possible	667	arrive, or the monitoring action will be invoked after possible message
490	message loss has been detected. No messages will be lost "in between"	668	loss has been detected. No messages will be lost "in between" (after
491	(after the first lost message no further messages will be received by the	669	the first lost message no further messages will be received by the
492	port). After the monitoring action was invoked, further messages might get	670	port). After the monitoring action was invoked, further messages might get
493	delivered again.	671	delivered again.
494		672
495	In the first form (callback), the callback is simply called with any	673	Inter-host-connection timeouts and monitoring depend on the transport
496	number of C<@reason> elements (no @reason means that the port was deleted	674	used. The only transport currently implemented is TCP, and AnyEvent::MP
497	"normally"). Note also that I<< the callback B<must> never die >>, so use	675	relies on TCP to detect node-downs (this can take 10-15 minutes on a
498	C<eval> if unsure.	676	non-idle connection, and usually around two hours for idle connections).
499		677
500	In the second form (another port given), the other port (C<$rcvport>)	678	This means that monitoring is good for program errors and cleaning up
501	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	679	stuff eventually, but they are no replacement for a timeout when you need
502	"normal" kils nothing happens, while under all other conditions, the other	680	to ensure some maximum latency.
503	port is killed with the same reason.
504
505	The third form (kill self) is the same as the second form, except that
506	C<$rvport> defaults to C<$SELF>.
507
508	In the last form (message), a message of the form C<@msg, @reason> will be
509	C<snd>.
510
511	As a rule of thumb, monitoring requests should always monitor a port from
512	a local port (or callback). The reason is that kill messages might get
513	lost, just like any other message. Another less obvious reason is that
514	even monitoring requests can get lost (for exmaple, when the connection
515	to the other node goes down permanently). When monitoring a port locally
516	these problems do not exist.
517		681
518	Example: call a given callback when C<$port> is killed.	682	Example: call a given callback when C<$port> is killed.
519		683
520	mon $port, sub { warn "port died because of <@_>\n" };	684	mon $port, sub { warn "port died because of <@_>\n" };
521		685
…		…
528	mon $port, $self => "restart";	692	mon $port, $self => "restart";
529		693
530	=cut	694	=cut
531		695
532	sub mon {	696	sub mon {
533	my ($noderef, $port) = split /#/, shift, 2;	697	my ($nodeid, $port) = split /#/, shift, 2;
534		698
535	my $node = $NODE{$noderef} || add_node $noderef;	699	my $node = $NODE{$nodeid} || add_node $nodeid;
536		700
537	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';	701	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
538		702
539	unless (ref $cb) {	703	unless (ref $cb) {
540	if (@_) {	704	if (@_) {
…		…
549	}	713	}
550		714
551	$node->monitor ($port, $cb);	715	$node->monitor ($port, $cb);
552		716
553	defined wantarray	717	defined wantarray
554	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	718	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
555	}	719	}
556		720
557	=item $guard = mon_guard $port, $ref, $ref...	721	=item $guard = mon_guard $port, $ref, $ref...
558		722
559	Monitors the given C<$port> and keeps the passed references. When the port	723	Monitors the given C<$port> and keeps the passed references. When the port
560	is killed, the references will be freed.	724	is killed, the references will be freed.
561		725
562	Optionally returns a guard that will stop the monitoring.	726	Optionally returns a guard that will stop the monitoring.
563		727
564	This function is useful when you create e.g. timers or other watchers and	728	This function is useful when you create e.g. timers or other watchers and
565	want to free them when the port gets killed:	729	want to free them when the port gets killed (note the use of C<psub>):
566		730
567	$port->rcv (start => sub {	731	$port->rcv (start => sub {
568	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	732	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
569	undef $timer if 0.9 < rand;	733	undef $timer if 0.9 < rand;
570	});	734	});
571	});	735	});
572		736
573	=cut	737	=cut
…		…
582		746
583	=item kil $port[, @reason]	747	=item kil $port[, @reason]
584		748
585	Kill the specified port with the given C<@reason>.	749	Kill the specified port with the given C<@reason>.
586		750
587	If no C<@reason> is specified, then the port is killed "normally" (linked	751	If no C<@reason> is specified, then the port is killed "normally" -
588	ports will not be kileld, or even notified).	752	monitor callback will be invoked, but the kil will not cause linked ports
		753	(C<mon $mport, $lport> form) to get killed.
589		754
590	Otherwise, linked ports get killed with the same reason (second form of	755	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
591	C<mon>, see below).	756	form) get killed with the same reason.
592		757
593	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	758	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
594	will be reported as reason C<< die => $@ >>.	759	will be reported as reason C<< die => $@ >>.
595		760
596	Transport/communication errors are reported as C<< transport_error =>	761	Transport/communication errors are reported as C<< transport_error =>
597	$message >>.	762	$message >>.
598		763
599	=cut	764	Common idioms:
		765
		766	# silently remove yourself, do not kill linked ports
		767	kil $SELF;
		768
		769	# report a failure in some detail
		770	kil $SELF, failure_mode_1 => "it failed with too high temperature";
		771
		772	# do not waste much time with killing, just die when something goes wrong
		773	open my $fh, "<file"
		774	or die "file: $!";
600		775
601	=item $port = spawn $node, $initfunc[, @initdata]	776	=item $port = spawn $node, $initfunc[, @initdata]
602		777
603	Creates a port on the node C<$node> (which can also be a port ID, in which	778	Creates a port on the node C<$node> (which can also be a port ID, in which
604	case it's the node where that port resides).	779	case it's the node where that port resides).
605		780
606	The port ID of the newly created port is return immediately, and it is	781	The port ID of the newly created port is returned immediately, and it is
607	permissible to immediately start sending messages or monitor the port.	782	possible to immediately start sending messages or to monitor the port.
608		783
609	After the port has been created, the init function is	784	After the port has been created, the init function is called on the remote
610	called. This function must be a fully-qualified function name	785	node, in the same context as a C<rcv> callback. This function must be a
611	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	786	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
612	program, use C<::name>.	787	specify a function in the main program, use C<::name>.
613		788
614	If the function doesn't exist, then the node tries to C<require>	789	If the function doesn't exist, then the node tries to C<require>
615	the package, then the package above the package and so on (e.g.	790	the package, then the package above the package and so on (e.g.
616	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	791	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
617	exists or it runs out of package names.	792	exists or it runs out of package names.
618		793
619	The init function is then called with the newly-created port as context	794	The init function is then called with the newly-created port as context
620	object (C<$SELF>) and the C<@initdata> values as arguments.	795	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		796	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		797	the port might not get created.
621		798
622	A common idiom is to pass your own port, monitor the spawned port, and	799	A common idiom is to pass a local port, immediately monitor the spawned
623	in the init function, monitor the original port. This two-way monitoring	800	port, and in the remote init function, immediately monitor the passed
624	ensures that both ports get cleaned up when there is a problem.	801	local port. This two-way monitoring ensures that both ports get cleaned up
		802	when there is a problem.
		803
		804	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		805	caller before C<spawn> returns (by delaying invocation when spawn is
		806	called for the local node).
625		807
626	Example: spawn a chat server port on C<$othernode>.	808	Example: spawn a chat server port on C<$othernode>.
627		809
628	# this node, executed from within a port context:	810	# this node, executed from within a port context:
629	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	811	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
644		826
645	sub _spawn {	827	sub _spawn {
646	my $port = shift;	828	my $port = shift;
647	my $init = shift;	829	my $init = shift;
648		830
		831	# rcv will create the actual port
649	local $SELF = "$NODE#$port";	832	local $SELF = "$NODE#$port";
650	eval {	833	eval {
651	&{ load_func $init }	834	&{ load_func $init }
652	};	835	};
653	_self_die if $@;	836	_self_die if $@;
654	}	837	}
655		838
656	sub spawn(@) {	839	sub spawn(@) {
657	my ($noderef, undef) = split /#/, shift, 2;	840	my ($nodeid, undef) = split /#/, shift, 2;
658		841
659	my $id = "$RUNIQ." . $ID++;	842	my $id = $RUNIQ . ++$ID;
660		843
661	$_[0] =~ /::/	844	$_[0] =~ /::/
662	or Carp::croak "spawn init function must be a fully-qualified name, caught";	845	or Carp::croak "spawn init function must be a fully-qualified name, caught";
663		846
664	($NODE{$noderef} || add_node $noderef)	847	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
665	->send (["", "AnyEvent::MP::_spawn" => $id, @_]);
666		848
667	"$noderef#$id"	849	"$nodeid#$id"
668	}	850	}
669		851
		852
		853	=item after $timeout, @msg
		854
		855	=item after $timeout, $callback
		856
		857	Either sends the given message, or call the given callback, after the
		858	specified number of seconds.
		859
		860	This is simply a utility function that comes in handy at times - the
		861	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		862	so it may go away in the future.
		863
		864	=cut
		865
		866	sub after($@) {
		867	my ($timeout, @action) = @_;
		868
		869	my $t; $t = AE::timer $timeout, 0, sub {
		870	undef $t;
		871	ref $action[0]
		872	? $action[0]()
		873	: snd @action;
		874	};
		875	}
		876
		877	#=item $cb2 = timeout $seconds, $cb[, @args]
		878
		879	=item cal $port, @msg, $callback[, $timeout]
		880
		881	A simple form of RPC - sends a message to the given C<$port> with the
		882	given contents (C<@msg>), but appends a reply port to the message.
		883
		884	The reply port is created temporarily just for the purpose of receiving
		885	the reply, and will be C<kil>ed when no longer needed.
		886
		887	A reply message sent to the port is passed to the C<$callback> as-is.
		888
		889	If an optional time-out (in seconds) is given and it is not C<undef>,
		890	then the callback will be called without any arguments after the time-out
		891	elapsed and the port is C<kil>ed.
		892
		893	If no time-out is given (or it is C<undef>), then the local port will
		894	monitor the remote port instead, so it eventually gets cleaned-up.
		895
		896	Currently this function returns the temporary port, but this "feature"
		897	might go in future versions unless you can make a convincing case that
		898	this is indeed useful for something.
		899
		900	=cut
		901
		902	sub cal(@) {
		903	my $timeout = ref $_[-1] ? undef : pop;
		904	my $cb = pop;
		905
		906	my $port = port {
		907	undef $timeout;
		908	kil $SELF;
		909	&$cb;
		910	};
		911
		912	if (defined $timeout) {
		913	$timeout = AE::timer $timeout, 0, sub {
		914	undef $timeout;
		915	kil $port;
		916	$cb->();
		917	};
		918	} else {
		919	mon $_[0], sub {
		920	kil $port;
		921	$cb->();
		922	};
		923	}
		924
		925	push @_, $port;
		926	&snd;
		927
		928	$port
		929	}
		930
670	=back	931	=back
671		932
672	=head1 NODE MESSAGES	933	=head1 DISTRIBUTED DATABASE
673		934
674	Nodes understand the following messages sent to them. Many of them take	935	AnyEvent::MP comes with a simple distributed database. The database will
675	arguments called C<@reply>, which will simply be used to compose a reply	936	be mirrored asynchronously on all global nodes. Other nodes bind to one
676	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and	937	of the global nodes for their needs. Every node has a "local database"
677	the remaining arguments are simply the message data.	938	which contains all the values that are set locally. All local databases
		939	are merged together to form the global database, which can be queried.
678		940
679	While other messages exist, they are not public and subject to change.	941	The database structure is that of a two-level hash - the database hash
		942	contains hashes which contain values, similarly to a perl hash of hashes,
		943	i.e.:
680		944
		945	$DATABASE{$family}{$subkey} = $value
		946
		947	The top level hash key is called "family", and the second-level hash key
		948	is called "subkey" or simply "key".
		949
		950	The family must be alphanumeric, i.e. start with a letter and consist
		951	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		952	pretty much like Perl module names.
		953
		954	As the family namespace is global, it is recommended to prefix family names
		955	with the name of the application or module using it.
		956
		957	The subkeys must be non-empty strings, with no further restrictions.
		958
		959	The values should preferably be strings, but other perl scalars should
		960	work as well (such as C<undef>, arrays and hashes).
		961
		962	Every database entry is owned by one node - adding the same family/subkey
		963	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		964	but the result might be nondeterministic, i.e. the key might have
		965	different values on different nodes.
		966
		967	Different subkeys in the same family can be owned by different nodes
		968	without problems, and in fact, this is the common method to create worker
		969	pools. For example, a worker port for image scaling might do this:
		970
		971	db_set my_image_scalers => $port;
		972
		973	And clients looking for an image scaler will want to get the
		974	C<my_image_scalers> keys from time to time:
		975
		976	db_keys my_image_scalers => sub {
		977	@ports = @{ $_[0] };
		978	};
		979
		980	Or better yet, they want to monitor the database family, so they always
		981	have a reasonable up-to-date copy:
		982
		983	db_mon my_image_scalers => sub {
		984	@ports = keys %{ $_[0] };
		985	};
		986
		987	In general, you can set or delete single subkeys, but query and monitor
		988	whole families only.
		989
		990	If you feel the need to monitor or query a single subkey, try giving it
		991	it's own family.
		992
681	=over 4	993	=over
		994
		995	=item $guard = db_set $family => $subkey [=> $value]
		996
		997	Sets (or replaces) a key to the database - if C<$value> is omitted,
		998	C<undef> is used instead.
		999
		1000	When called in non-void context, C<db_set> returns a guard that
		1001	automatically calls C<db_del> when it is destroyed.
		1002
		1003	=item db_del $family => $subkey...
		1004
		1005	Deletes one or more subkeys from the database family.
		1006
		1007	=item $guard = db_reg $family => $port => $value
		1008
		1009	=item $guard = db_reg $family => $port
		1010
		1011	=item $guard = db_reg $family
		1012
		1013	Registers a port in the given family and optionally returns a guard to
		1014	remove it.
		1015
		1016	This function basically does the same as:
		1017
		1018	db_set $family => $port => $value
		1019
		1020	Except that the port is monitored and automatically removed from the
		1021	database family when it is kil'ed.
		1022
		1023	If C<$value> is missing, C<undef> is used. If C<$port> is missing, then
		1024	C<$SELF> is used.
		1025
		1026	This function is most useful to register a port in some port group (which
		1027	is just another name for a database family), and have it removed when the
		1028	port is gone. This works best when the port is a local port.
682		1029
683	=cut	1030	=cut
684		1031
685	=item lookup => $name, @reply	1032	sub db_reg($$;$) {
		1033	my $family = shift;
		1034	my $port = @_ ? shift : $SELF;
686		1035
687	Replies with the port ID of the specified well-known port, or C<undef>.	1036	my $clr = sub { db_del $family => $port };
		1037	mon $port, $clr;
688		1038
689	=item devnull => ...	1039	db_set $family => $port => $_[0];
690		1040
691	Generic data sink/CPU heat conversion.	1041	defined wantarray
		1042	and &Guard::guard ($clr)
		1043	}
692		1044
693	=item relay => $port, @msg	1045	=item db_family $family => $cb->(\%familyhash)
694		1046
695	Simply forwards the message to the given port.	1047	Queries the named database C<$family> and call the callback with the
		1048	family represented as a hash. You can keep and freely modify the hash.
696		1049
697	=item eval => $string[ @reply]	1050	=item db_keys $family => $cb->(\@keys)
698		1051
699	Evaluates the given string. If C<@reply> is given, then a message of the	1052	Same as C<db_family>, except it only queries the family I<subkeys> and passes
700	form C<@reply, $@, @evalres> is sent.	1053	them as array reference to the callback.
701		1054
702	Example: crash another node.	1055	=item db_values $family => $cb->(\@values)
703		1056
704	snd $othernode, eval => "exit";	1057	Same as C<db_family>, except it only queries the family I<values> and passes them
		1058	as array reference to the callback.
705		1059
706	=item time => @reply	1060	=item $guard = db_mon $family => $cb->(\%familyhash, \@added, \@changed, \@deleted)
707		1061
708	Replies the the current node time to C<@reply>.	1062	Creates a monitor on the given database family. Each time a key is
		1063	set or is deleted the callback is called with a hash containing the
		1064	database family and three lists of added, changed and deleted subkeys,
		1065	respectively. If no keys have changed then the array reference might be
		1066	C<undef> or even missing.
709		1067
710	Example: tell the current node to send the current time to C<$myport> in a	1068	If not called in void context, a guard object is returned that, when
711	C<timereply> message.	1069	destroyed, stops the monitor.
712		1070
713	snd $NODE, time => $myport, timereply => 1, 2;	1071	The family hash reference and the key arrays belong to AnyEvent::MP and
714	# => snd $myport, timereply => 1, 2, <time>	1072	B<must not be modified or stored> by the callback. When in doubt, make a
		1073	copy.
		1074
		1075	As soon as possible after the monitoring starts, the callback will be
		1076	called with the intiial contents of the family, even if it is empty,
		1077	i.e. there will always be a timely call to the callback with the current
		1078	contents.
		1079
		1080	It is possible that the callback is called with a change event even though
		1081	the subkey is already present and the value has not changed.
		1082
		1083	The monitoring stops when the guard object is destroyed.
		1084
		1085	Example: on every change to the family "mygroup", print out all keys.
		1086
		1087	my $guard = db_mon mygroup => sub {
		1088	my ($family, $a, $c, $d) = @_;
		1089	print "mygroup members: ", (join " ", keys %$family), "\n";
		1090	};
		1091
		1092	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1093
		1094	my $guard; $guard = db_mon My::Module::workers => sub {
		1095	my ($family, $a, $c, $d) = @_;
		1096	return unless %$family;
		1097	undef $guard;
		1098	print "My::Module::workers now nonempty\n";
		1099	};
		1100
		1101	Example: print all changes to the family "AnyEvent::Fantasy::Module".
		1102
		1103	my $guard = db_mon AnyEvent::Fantasy::Module => sub {
		1104	my ($family, $a, $c, $d) = @_;
		1105
		1106	print "+$_=$family->{$_}\n" for @$a;
		1107	print "*$_=$family->{$_}\n" for @$c;
		1108	print "-$_=$family->{$_}\n" for @$d;
		1109	};
		1110
		1111	=cut
715		1112
716	=back	1113	=back
717		1114
718	=head1 AnyEvent::MP vs. Distributed Erlang	1115	=head1 AnyEvent::MP vs. Distributed Erlang
719		1116
720	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	1117	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
721	== aemp node, Erlang process == aemp port), so many of the documents and	1118	== aemp node, Erlang process == aemp port), so many of the documents and
722	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	1119	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
723	sample:	1120	sample:
724		1121
725	http://www.Erlang.se/doc/programming_rules.shtml	1122	http://www.erlang.se/doc/programming_rules.shtml
726	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	1123	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
727	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	1124	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
728	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	1125	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
729		1126
730	Despite the similarities, there are also some important differences:	1127	Despite the similarities, there are also some important differences:
731		1128
732	=over 4	1129	=over 4
733		1130
734	=item * Node references contain the recipe on how to contact them.	1131	=item * Node IDs are arbitrary strings in AEMP.
735		1132
736	Erlang relies on special naming and DNS to work everywhere in the	1133	Erlang relies on special naming and DNS to work everywhere in the same
737	same way. AEMP relies on each node knowing it's own address(es), with	1134	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
738	convenience functionality.	1135	configuration or DNS), and possibly the addresses of some seed nodes, but
		1136	will otherwise discover other nodes (and their IDs) itself.
739		1137
740	This means that AEMP requires a less tightly controlled environment at the	1138	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
741	cost of longer node references and a slightly higher management overhead.	1139	uses "local ports are like remote ports".
		1140
		1141	The failure modes for local ports are quite different (runtime errors
		1142	only) then for remote ports - when a local port dies, you I<know> it dies,
		1143	when a connection to another node dies, you know nothing about the other
		1144	port.
		1145
		1146	Erlang pretends remote ports are as reliable as local ports, even when
		1147	they are not.
		1148
		1149	AEMP encourages a "treat remote ports differently" philosophy, with local
		1150	ports being the special case/exception, where transport errors cannot
		1151	occur.
742		1152
743	=item * Erlang uses processes and a mailbox, AEMP does not queue.	1153	=item * Erlang uses processes and a mailbox, AEMP does not queue.
744		1154
745	Erlang uses processes that selctively receive messages, and therefore	1155	Erlang uses processes that selectively receive messages out of order, and
746	needs a queue. AEMP is event based, queuing messages would serve no useful	1156	therefore needs a queue. AEMP is event based, queuing messages would serve
747	purpose.	1157	no useful purpose. For the same reason the pattern-matching abilities
		1158	of AnyEvent::MP are more limited, as there is little need to be able to
		1159	filter messages without dequeuing them.
748		1160
749	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	1161	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1162	being event-based, while Erlang is process-based.
		1163
		1164	You can have a look at L<Coro::MP> for a more Erlang-like process model on
		1165	top of AEMP and Coro threads.
750		1166
751	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1167	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
752		1168
753	Sending messages in Erlang is synchronous and blocks the process. AEMP	1169	Sending messages in Erlang is synchronous and blocks the process until
754	sends are immediate, connection establishment is handled in the	1170	a connection has been established and the message sent (and so does not
755	background.	1171	need a queue that can overflow). AEMP sends return immediately, connection
		1172	establishment is handled in the background.
756		1173
757	=item * Erlang can silently lose messages, AEMP cannot.	1174	=item * Erlang suffers from silent message loss, AEMP does not.
758		1175
759	Erlang makes few guarantees on messages delivery - messages can get lost	1176	Erlang implements few guarantees on messages delivery - messages can get
760	without any of the processes realising it (i.e. you send messages a, b,	1177	lost without any of the processes realising it (i.e. you send messages a,
761	and c, and the other side only receives messages a and c).	1178	b, and c, and the other side only receives messages a and c).
762		1179
763	AEMP guarantees correct ordering, and the guarantee that there are no	1180	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1181	guarantee that after one message is lost, all following ones sent to the
		1182	same port are lost as well, until monitoring raises an error, so there are
764	holes in the message sequence.	1183	no silent "holes" in the message sequence.
765		1184
766	=item * In Erlang, processes can be declared dead and later be found to be	1185	If you want your software to be very reliable, you have to cope with
767	alive.	1186	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
768		1187	simply tries to work better in common error cases, such as when a network
769	In Erlang it can happen that a monitored process is declared dead and	1188	link goes down.
770	linked processes get killed, but later it turns out that the process is
771	still alive - and can receive messages.
772
773	In AEMP, when port monitoring detects a port as dead, then that port will
774	eventually be killed - it cannot happen that a node detects a port as dead
775	and then later sends messages to it, finding it is still alive.
776		1189
777	=item * Erlang can send messages to the wrong port, AEMP does not.	1190	=item * Erlang can send messages to the wrong port, AEMP does not.
778		1191
779	In Erlang it is quite possible that a node that restarts reuses a process	1192	In Erlang it is quite likely that a node that restarts reuses an Erlang
780	ID known to other nodes for a completely different process, causing	1193	process ID known to other nodes for a completely different process,
781	messages destined for that process to end up in an unrelated process.	1194	causing messages destined for that process to end up in an unrelated
		1195	process.
782		1196
783	AEMP never reuses port IDs, so old messages or old port IDs floating	1197	AEMP does not reuse port IDs, so old messages or old port IDs floating
784	around in the network will not be sent to an unrelated port.	1198	around in the network will not be sent to an unrelated port.
785		1199
786	=item * Erlang uses unprotected connections, AEMP uses secure	1200	=item * Erlang uses unprotected connections, AEMP uses secure
787	authentication and can use TLS.	1201	authentication and can use TLS.
788		1202
789	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1203	AEMP can use a proven protocol - TLS - to protect connections and
790	securely authenticate nodes.	1204	securely authenticate nodes.
791		1205
792	=item * The AEMP protocol is optimised for both text-based and binary	1206	=item * The AEMP protocol is optimised for both text-based and binary
793	communications.	1207	communications.
794		1208
795	The AEMP protocol, unlike the Erlang protocol, supports both	1209	The AEMP protocol, unlike the Erlang protocol, supports both programming
796	language-independent text-only protocols (good for debugging) and binary,	1210	language independent text-only protocols (good for debugging), and binary,
797	language-specific serialisers (e.g. Storable).	1211	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1212	used, the protocol is actually completely text-based.
798		1213
799	It has also been carefully designed to be implementable in other languages	1214	It has also been carefully designed to be implementable in other languages
800	with a minimum of work while gracefully degrading fucntionality to make the	1215	with a minimum of work while gracefully degrading functionality to make the
801	protocol simple.	1216	protocol simple.
802		1217
803	=item * AEMP has more flexible monitoring options than Erlang.	1218	=item * AEMP has more flexible monitoring options than Erlang.
804		1219
805	In Erlang, you can chose to receive I<all> exit signals as messages	1220	In Erlang, you can chose to receive I<all> exit signals as messages or
806	or I<none>, there is no in-between, so monitoring single processes is	1221	I<none>, there is no in-between, so monitoring single Erlang processes is
807	difficult to implement. Monitoring in AEMP is more flexible than in	1222	difficult to implement.
808	Erlang, as one can choose between automatic kill, exit message or callback	1223
809	on a per-process basis.	1224	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1225	between automatic kill, exit message or callback on a per-port basis.
810		1226
811	=item * Erlang tries to hide remote/local connections, AEMP does not.	1227	=item * Erlang tries to hide remote/local connections, AEMP does not.
812		1228
813	Monitoring in Erlang is not an indicator of process death/crashes,	1229	Monitoring in Erlang is not an indicator of process death/crashes, in the
814	as linking is (except linking is unreliable in Erlang).	1230	same way as linking is (except linking is unreliable in Erlang).
815		1231
816	In AEMP, you don't "look up" registered port names or send to named ports	1232	In AEMP, you don't "look up" registered port names or send to named ports
817	that might or might not be persistent. Instead, you normally spawn a port	1233	that might or might not be persistent. Instead, you normally spawn a port
818	on the remote node. The init function monitors the you, and you monitor	1234	on the remote node. The init function monitors you, and you monitor the
819	the remote port. Since both monitors are local to the node, they are much	1235	remote port. Since both monitors are local to the node, they are much more
820	more reliable.	1236	reliable (no need for C<spawn_link>).
821		1237
822	This also saves round-trips and avoids sending messages to the wrong port	1238	This also saves round-trips and avoids sending messages to the wrong port
823	(hard to do in Erlang).	1239	(hard to do in Erlang).
824		1240
825	=back	1241	=back
826		1242
827	=head1 RATIONALE	1243	=head1 RATIONALE
828		1244
829	=over 4	1245	=over 4
830		1246
831	=item Why strings for ports and noderefs, why not objects?	1247	=item Why strings for port and node IDs, why not objects?
832		1248
833	We considered "objects", but found that the actual number of methods	1249	We considered "objects", but found that the actual number of methods
834	thatc an be called are very low. Since port IDs and noderefs travel over	1250	that can be called are quite low. Since port and node IDs travel over
835	the network frequently, the serialising/deserialising would add lots of	1251	the network frequently, the serialising/deserialising would add lots of
836	overhead, as well as having to keep a proxy object.	1252	overhead, as well as having to keep a proxy object everywhere.
837		1253
838	Strings can easily be printed, easily serialised etc. and need no special	1254	Strings can easily be printed, easily serialised etc. and need no special
839	procedures to be "valid".	1255	procedures to be "valid".
840		1256
841	And a a miniport consists of a single closure stored in a global hash - it	1257	And as a result, a port with just a default receiver consists of a single
842	can't become much cheaper.	1258	code reference stored in a global hash - it can't become much cheaper.
843		1259
844	=item Why favour JSON, why not real serialising format such as Storable?	1260	=item Why favour JSON, why not a real serialising format such as Storable?
845		1261
846	In fact, any AnyEvent::MP node will happily accept Storable as framing	1262	In fact, any AnyEvent::MP node will happily accept Storable as framing
847	format, but currently there is no way to make a node use Storable by	1263	format, but currently there is no way to make a node use Storable by
848	default.	1264	default (although all nodes will accept it).
849		1265
850	The default framing protocol is JSON because a) JSON::XS is many times	1266	The default framing protocol is JSON because a) JSON::XS is many times
851	faster for small messages and b) most importantly, after years of	1267	faster for small messages and b) most importantly, after years of
852	experience we found that object serialisation is causing more problems	1268	experience we found that object serialisation is causing more problems
853	than it gains: Just like function calls, objects simply do not travel	1269	than it solves: Just like function calls, objects simply do not travel
854	easily over the network, mostly because they will always be a copy, so you	1270	easily over the network, mostly because they will always be a copy, so you
855	always have to re-think your design.	1271	always have to re-think your design.
856		1272
857	Keeping your messages simple, concentrating on data structures rather than	1273	Keeping your messages simple, concentrating on data structures rather than
858	objects, will keep your messages clean, tidy and efficient.	1274	objects, will keep your messages clean, tidy and efficient.
859		1275
860	=back	1276	=back
861		1277
		1278	=head1 PORTING FROM AnyEvent::MP VERSION 1.X
		1279
		1280	AEMP version 2 has a few major incompatible changes compared to version 1:
		1281
		1282	=over 4
		1283
		1284	=item AnyEvent::MP::Global no longer has group management functions.
		1285
		1286	At least not officially - the grp_* functions are still exported and might
		1287	work, but they will be removed in some later release.
		1288
		1289	AnyEvent::MP now comes with a distributed database that is more
		1290	powerful. Its database families map closely to port groups, but the API
		1291	has changed (the functions are also now exported by AnyEvent::MP). Here is
		1292	a rough porting guide:
		1293
		1294	grp_reg $group, $port # old
		1295	db_reg $group, $port # new
		1296
		1297	$list = grp_get $group # old
		1298	db_keys $group, sub { my $list = shift } # new
		1299
		1300	grp_mon $group, $cb->(\@ports, $add, $del) # old
		1301	db_mon $group, $cb->(\%ports, $add, $change, $del) # new
		1302
		1303	C<grp_reg> is a no-brainer (just replace by C<db_reg>), but C<grp_get> is
		1304	no longer instant, because the local node might not have a copy of the
		1305	group. You can either modify your code to allow for a callback, or use
		1306	C<db_mon> to keep an updated copy of the group:
		1307
		1308	my $local_group_copy;
		1309	db_mon $group => sub { $local_group_copy = $_[0] };
		1310
		1311	# now "keys %$local_group_copy" always returns the most up-to-date
		1312	# list of ports in the group.
		1313
		1314	C<grp_mon> can be replaced by C<db_mon> with minor changes - C<db_mon>
		1315	passes a hash as first argument, and an extra C<$chg> argument that can be
		1316	ignored:
		1317
		1318	db_mon $group => sub {
		1319	my ($ports, $add, $chg, $del) = @_;
		1320	$ports = [keys %$ports];
		1321
		1322	# now $ports, $add and $del are the same as
		1323	# were originally passed by grp_mon.
		1324	...
		1325	};
		1326
		1327	=item Nodes not longer connect to all other nodes.
		1328
		1329	In AEMP 1.x, every node automatically loads the L<AnyEvent::MP::Global>
		1330	module, which in turn would create connections to all other nodes in the
		1331	network (helped by the seed nodes).
		1332
		1333	In version 2.x, global nodes still connect to all other global nodes, but
		1334	other nodes don't - now every node either is a global node itself, or
		1335	attaches itself to another global node.
		1336
		1337	If a node isn't a global node itself, then it attaches itself to one
		1338	of its seed nodes. If that seed node isn't a global node yet, it will
		1339	automatically be upgraded to a global node.
		1340
		1341	So in many cases, nothing needs to be changed - one just has to make sure
		1342	that all seed nodes are meshed together with the other seed nodes (as with
		1343	AEMP 1.x), and other nodes specify them as seed nodes. This is most easily
		1344	achieved by specifying the same set of seed nodes for all nodes in the
		1345	network.
		1346
		1347	Not opening a connection to every other node is usually an advantage,
		1348	except when you need the lower latency of an already established
		1349	connection. To ensure a node establishes a connection to another node,
		1350	you can monitor the node port (C<mon $node, ...>), which will attempt to
		1351	create the connection (and notify you when the connection fails).
		1352
		1353	=item Listener-less nodes (nodes without binds) are gone.
		1354
		1355	And are not coming back, at least not in their old form. If no C<binds>
		1356	are specified for a node, AnyEvent::MP assumes a default of C<*:*>.
		1357
		1358	There are vague plans to implement some form of routing domains, which
		1359	might or might not bring back listener-less nodes, but don't count on it.
		1360
		1361	The fact that most connections are now optional somewhat mitigates this,
		1362	as a node can be effectively unreachable from the outside without any
		1363	problems, as long as it isn't a global node and only reaches out to other
		1364	nodes (as opposed to being contacted from other nodes).
		1365
		1366	=item $AnyEvent::MP::Kernel::WARN has gone.
		1367
		1368	AnyEvent has acquired a logging framework (L<AnyEvent::Log>), and AEMP now
		1369	uses this, and so should your programs.
		1370
		1371	Every module now documents what kinds of messages it generates, with
		1372	AnyEvent::MP acting as a catch all.
		1373
		1374	On the positive side, this means that instead of setting
		1375	C<PERL_ANYEVENT_MP_WARNLEVEL>, you can get away by setting C<AE_VERBOSE> -
		1376	much less to type.
		1377
		1378	=back
		1379
		1380	=head1 LOGGING
		1381
		1382	AnyEvent::MP does not normally log anything by itself, but since it is the
		1383	root of the context hierarchy for AnyEvent::MP modules, it will receive
		1384	all log messages by submodules.
		1385
862	=head1 SEE ALSO	1386	=head1 SEE ALSO
		1387
		1388	L<AnyEvent::MP::Intro> - a gentle introduction.
		1389
		1390	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1391
		1392	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1393	your applications.
		1394
		1395	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1396
		1397	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1398	all nodes.
863		1399
864	L<AnyEvent>.	1400	L<AnyEvent>.
865		1401
866	=head1 AUTHOR	1402	=head1 AUTHOR
867		1403

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