[ViewVC] Diff of: cvs/AnyEvent-MP/MP.pm

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.44 by root, Wed Aug 12 21:39:58 2009 UTC vs.
Revision 1.135 by root, Mon Mar 12 14:55:55 2012 UTC

…		…
1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent::MP - multi-processing/message-passing framework	3	AnyEvent::MP - erlang-style multi-processing/message-passing framework
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::MP;	7	use AnyEvent::MP;
8		8
9	$NODE # contains this node's noderef	9	$NODE # contains this node's node ID
10	NODE # returns this node's noderef	10	NODE # returns this node's node ID
11	NODE $port # returns the noderef of the port
12		11
13	$SELF # receiving/own port id in rcv callbacks	12	$SELF # receiving/own port id in rcv callbacks
14		13
		14	# initialise the node so it can send/receive messages
		15	configure;
		16
15	# ports are message endpoints	17	# ports are message destinations
16		18
17	# sending messages	19	# sending messages
18	snd $port, type => data...;	20	snd $port, type => data...;
19	snd $port, @msg;	21	snd $port, @msg;
20	snd @msg_with_first_element_being_a_port;	22	snd @msg_with_first_element_being_a_port;
21		23
22	# miniports	24	# creating/using ports, the simple way
23	my $miniport = port { my @msg = @_; 0 };	25	my $simple_port = port { my @msg = @_ };
24		26
25	# full ports	27	# creating/using ports, tagged message matching
26	my $port = port;	28	my $port = port;
27	rcv $port, smartmatch => $cb->(@msg);
28	rcv $port, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
29	rcv $port, pong => sub { warn "pong received\n"; 0 };	30	rcv $port, pong => sub { warn "pong received\n" };
30		31
31	# remote ports	32	# create a port on another node
32	my $port = spawn $node, $initfunc, @initdata;	33	my $port = spawn $node, $initfunc, @initdata;
33		34
34	# more, smarter, matches (_any_ is exported by this module)	35	# destroy a port again
35	rcv $port, [child_died => $pid] => sub { ...	36	kil $port; # "normal" kill
36	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3	37	kil $port, my_error => "everything is broken"; # error kill
37		38
38	# monitoring	39	# monitoring
39	mon $port, $cb->(@msg) # callback is invoked on death	40	mon $port, $cb->(@msg) # callback is invoked on death
40	mon $port, $otherport # kill otherport on abnormal death	41	mon $port, $localport # kill localport on abnormal death
41	mon $port, $otherport, @msg # send message on death	42	mon $port, $localport, @msg # send message on death
		43
		44	# temporarily execute code in port context
		45	peval $port, sub { die "kill the port!" };
		46
		47	# execute callbacks in $SELF port context
		48	my $timer = AE::timer 1, 0, psub {
		49	die "kill the port, delayed";
		50	};
		51
		52	=head1 CURRENT STATUS
		53
		54	bin/aemp - stable.
		55	AnyEvent::MP - stable API, should work.
		56	AnyEvent::MP::Intro - explains most concepts.
		57	AnyEvent::MP::Kernel - mostly stable API.
		58	AnyEvent::MP::Global - stable API.
42		59
43	=head1 DESCRIPTION	60	=head1 DESCRIPTION
44		61
45	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
46		63
47	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
48	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
49		66
50	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>
51	manual page.	68	manual page and the examples under F<eg/>.
52
53	At the moment, this module family is severly broken and underdocumented,
54	so do not use. This was uploaded mainly to reserve the CPAN namespace -
55	stay tuned! The basic API should be finished, however.
56		69
57	=head1 CONCEPTS	70	=head1 CONCEPTS
58		71
59	=over 4	72	=over 4
60		73
61	=item port	74	=item port
62		75
63	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).
64		78
65	Some ports allow you to register C<rcv> handlers that can match specific	79	Ports allow you to register C<rcv> handlers that can match all or just
66	messages. All C<rcv> handlers will receive messages they match, messages	80	some messages. Messages send to ports will not be queued, regardless of
67	will not be queued.	81	anything was listening for them or not.
68		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
69	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
70		86
71	A port id is normaly 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<#>)
72	separator, and a port name (a printable string of unspecified format). An	88	as separator, and a port name (a printable string of unspecified
73	exception is the the node port, whose ID is identical to its node	89	format created by AnyEvent::MP).
74	reference.
75		90
76	=item node	91	=item node
77		92
78	A node is a single process containing at least one port - the node	93	A node is a single process containing at least one port - the node port,
79	port. You can send messages to node ports to find existing ports or to	94	which enables nodes to manage each other remotely, and to create new
80	create new ports, among other things.	95	ports.
81		96
82	Nodes are either private (single-process only), slaves (connected to a	97	Nodes are either public (have one or more listening ports) or private
83	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.
84		100
85	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	101	Nodes is represented by (printable) strings called "node IDs".
86		102
87	A node reference is a string that either simply identifies the node (for	103	=item node ID - C<[A-Za-z0-9_\-.:]*>
88	private and slave nodes), or contains a recipe on how to reach a given
89	node (for public nodes).
90		104
91	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
92	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.
93		109
94	Node references come in two flavours: resolved (containing only numerical	110	=item binds - C<ip:port>
95	addresses) or unresolved (where hostnames are used instead of addresses).
96		111
97	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
98	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).
99		170
100	=back	171	=back
101		172
102	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
103		174
105		176
106	=cut	177	=cut
107		178
108	package AnyEvent::MP;	179	package AnyEvent::MP;
109		180
		181	use AnyEvent::MP::Config ();
110	use AnyEvent::MP::Kernel;	182	use AnyEvent::MP::Kernel;
		183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
111		184
112	use common::sense;	185	use common::sense;
113		186
114	use Carp ();	187	use Carp ();
115		188
116	use AE ();	189	use AE ();
		190	use Guard ();
117		191
118	use base "Exporter";	192	use base "Exporter";
119		193
120	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
121		195
122	our @EXPORT = qw(	196	our @EXPORT = qw(
123	NODE $NODE *SELF node_of _any_	197	NODE $NODE *SELF node_of after
124	resolve_node initialise_node	198	configure
125	snd rcv mon kil reg psub spawn	199	snd rcv mon mon_guard kil psub peval spawn cal
126	port	200	port
		201	db_set db_del db_reg
		202	db_mon db_family db_keys db_values
127	);	203	);
128		204
129	our $SELF;	205	our $SELF;
130		206
131	sub _self_die() {	207	sub _self_die() {
…		…
134	kil $SELF, die => $msg;	210	kil $SELF, die => $msg;
135	}	211	}
136		212
137	=item $thisnode = NODE / $NODE	213	=item $thisnode = NODE / $NODE
138		214
139	The C<NODE> function returns, and the C<$NODE> variable contains	215	The C<NODE> function returns, and the C<$NODE> variable contains, the node
140	the noderef of the local node. The value is initialised by a call	216	ID of the node running in the current process. This value is initialised by
141	to C<become_public> or C<become_slave>, after which all local port	217	a call to C<configure>.
142	identifiers become invalid.
143		218
144	=item $noderef = node_of $port	219	=item $nodeid = node_of $port
145		220
146	Extracts and returns the noderef from a portid or a noderef.	221	Extracts and returns the node ID from a port ID or a node ID.
147		222
148	=item initialise_node $noderef, $seednode, $seednode...	223	=item configure $profile, key => value...
149		224
150	=item initialise_node "slave/", $master, $master...	225	=item configure key => value...
151		226
152	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
153	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
154	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.
155		231
156	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
157	never) before calling other AnyEvent::MP functions.	233	never) before calling other AnyEvent::MP functions.
158		234
159	All arguments are noderefs, which can be either resolved or unresolved.	235	The key/value pairs are basically the same ones as documented for the
160		236	F<aemp> command line utility (sans the set/del prefix), with these additions:
161	There are two types of networked nodes, public nodes and slave nodes:
162		237
163	=over 4	238	=over 4
164		239
165	=item public nodes	240	=item norc => $boolean (default false)
166		241
167	For public nodes, C<$noderef> must either be a (possibly unresolved)	242	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
168	noderef, in which case it will be resolved, or C<undef> (or missing), in	243	be consulted - all configuraiton options must be specified in the
169	which case the noderef will be guessed.	244	C<configure> call.
170		245
171	Afterwards, the node will bind itself on all endpoints and try to connect	246	=item force => $boolean (default false)
172	to all additional C<$seednodes> that are specified. Seednodes are optional
173	and can be used to quickly bootstrap the node into an existing network.
174		247
175	=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.
176		251
177	When the C<$noderef> is the special string C<slave/>, then the node will	252	=item secure => $pass->($nodeid)
178	become a slave node. Slave nodes cannot be contacted from outside and will
179	route most of their traffic to the master node that they attach to.
180		253
181	At least one additional noderef is required: The node will try to connect	254	In addition to specifying a boolean, you can specify a code reference that
182	to all of them and will become a slave attached to the first node it can	255	is called for every remote execution attempt - the execution request is
183	successfully connect to.	256	granted iff the callback returns a true value.
		257
		258	See F<semp setsecure> for more info.
184		259
185	=back	260	=back
186		261
187	This function will block until all nodes have been resolved and, for slave
188	nodes, until it has successfully established a connection to a master
189	server.
190
191	Example: become a public node listening on the default node.
192
193	initialise_node;
194
195	Example: become a public node, and try to contact some well-known master
196	servers to become part of the network.
197
198	initialise_node undef, "master1", "master2";
199
200	Example: become a public node listening on port C<4041>.
201
202	initialise_node 4041;
203
204	Example: become a public node, only visible on localhost port 4044.
205
206	initialise_node "locahost:4044";
207
208	Example: become a slave node to any of the specified master servers.
209
210	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
211
212	=item $cv = resolve_node $noderef
213
214	Takes an unresolved node reference that may contain hostnames and
215	abbreviated IDs, resolves all of them and returns a resolved node
216	reference.
217
218	In addition to C<address:port> pairs allowed in resolved noderefs, the
219	following forms are supported:
220
221	=over 4	262	=over 4
222		263
223	=item the empty string	264	=item step 1, gathering configuration from profiles
224		265
225	An empty-string component gets resolved as if the default port (4040) was	266	The function first looks up a profile in the aemp configuration (see the
226	specified.	267	L<aemp> commandline utility). The profile name can be specified via the
		268	named C<profile> parameter or can simply be the first parameter). If it is
		269	missing, then the nodename (F<uname -n>) will be used as profile name.
227		270
228	=item naked port numbers (e.g. C<1234>)	271	The profile data is then gathered as follows:
229		272
230	These are resolved by prepending the local nodename and a colon, to be	273	First, all remaining key => value pairs (all of which are conveniently
231	further resolved.	274	undocumented at the moment) will be interpreted as configuration
		275	data. Then they will be overwritten by any values specified in the global
		276	default configuration (see the F<aemp> utility), then the chain of
		277	profiles chosen by the profile name (and any C<parent> attributes).
232		278
233	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	279	That means that the values specified in the profile have highest priority
		280	and the values specified directly via C<configure> have lowest priority,
		281	and can only be used to specify defaults.
234		282
235	These are resolved by using AnyEvent::DNS to resolve them, optionally	283	If the profile specifies a node ID, then this will become the node ID of
236	looking up SRV records for the C<aemp=4040> port, if no port was	284	this process. If not, then the profile name will be used as node ID, with
237	specified.	285	a unique randoms tring (C</%u>) appended.
		286
		287	The node ID can contain some C<%> sequences that are expanded: C<%n>
		288	is expanded to the local nodename, C<%u> is replaced by a random
		289	strign to make the node unique. For example, the F<aemp> commandline
		290	utility uses C<aemp/%n/%u> as nodename, which might expand to
		291	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		292
		293	=item step 2, bind listener sockets
		294
		295	The next step is to look up the binds in the profile, followed by binding
		296	aemp protocol listeners on all binds specified (it is possible and valid
		297	to have no binds, meaning that the node cannot be contacted form the
		298	outside. This means the node cannot talk to other nodes that also have no
		299	binds, but it can still talk to all "normal" nodes).
		300
		301	If the profile does not specify a binds list, then a default of C<*> is
		302	used, meaning the node will bind on a dynamically-assigned port on every
		303	local IP address it finds.
		304
		305	=item step 3, connect to seed nodes
		306
		307	As the last step, the seed ID list from the profile is passed to the
		308	L<AnyEvent::MP::Global> module, which will then use it to keep
		309	connectivity with at least one node at any point in time.
238		310
239	=back	311	=back
		312
		313	Example: become a distributed node using the local node name as profile.
		314	This should be the most common form of invocation for "daemon"-type nodes.
		315
		316	configure
		317
		318	Example: become a semi-anonymous node. This form is often used for
		319	commandline clients.
		320
		321	configure nodeid => "myscript/%n/%u";
		322
		323	Example: configure a node using a profile called seed, which is suitable
		324	for a seed node as it binds on all local addresses on a fixed port (4040,
		325	customary for aemp).
		326
		327	# use the aemp commandline utility
		328	# aemp profile seed binds '*:4040'
		329
		330	# then use it
		331	configure profile => "seed";
		332
		333	# or simply use aemp from the shell again:
		334	# aemp run profile seed
		335
		336	# or provide a nicer-to-remember nodeid
		337	# aemp run profile seed nodeid "$(hostname)"
240		338
241	=item $SELF	339	=item $SELF
242		340
243	Contains the current port id while executing C<rcv> callbacks or C<psub>	341	Contains the current port id while executing C<rcv> callbacks or C<psub>
244	blocks.	342	blocks.
245		343
246	=item SELF, %SELF, @SELF...	344	=item *SELF, SELF, %SELF, @SELF...
247		345
248	Due to some quirks in how perl exports variables, it is impossible to	346	Due to some quirks in how perl exports variables, it is impossible to
249	just export C<$SELF>, all the symbols called C<SELF> are exported by this	347	just export C<$SELF>, all the symbols named C<SELF> are exported by this
250	module, but only C<$SELF> is currently used.	348	module, but only C<$SELF> is currently used.
251		349
252	=item snd $port, type => @data	350	=item snd $port, type => @data
253		351
254	=item snd $port, @msg	352	=item snd $port, @msg
255		353
256	Send the given message to the given port ID, which can identify either	354	Send the given message to the given port, which can identify either a
257	a local or a remote port, and can be either a string or soemthignt hat	355	local or a remote port, and must be a port ID.
258	stringifies a sa port ID (such as a port object :).
259		356
260	While the message can be about anything, it is highly recommended to use a	357	While the message can be almost anything, it is highly recommended to
261	string as first element (a portid, or some word that indicates a request	358	use a string as first element (a port ID, or some word that indicates a
262	type etc.).	359	request type etc.) and to consist if only simple perl values (scalars,
		360	arrays, hashes) - if you think you need to pass an object, think again.
263		361
264	The message data effectively becomes read-only after a call to this	362	The message data logically becomes read-only after a call to this
265	function: modifying any argument is not allowed and can cause many	363	function: modifying any argument (or values referenced by them) is
266	problems.	364	forbidden, as there can be considerable time between the call to C<snd>
		365	and the time the message is actually being serialised - in fact, it might
		366	never be copied as within the same process it is simply handed to the
		367	receiving port.
267		368
268	The type of data you can transfer depends on the transport protocol: when	369	The type of data you can transfer depends on the transport protocol: when
269	JSON is used, then only strings, numbers and arrays and hashes consisting	370	JSON is used, then only strings, numbers and arrays and hashes consisting
270	of those are allowed (no objects). When Storable is used, then anything	371	of those are allowed (no objects). When Storable is used, then anything
271	that Storable can serialise and deserialise is allowed, and for the local	372	that Storable can serialise and deserialise is allowed, and for the local
272	node, anything can be passed.	373	node, anything can be passed. Best rely only on the common denominator of
		374	these.
273		375
274	=item $local_port = port	376	=item $local_port = port
275		377
276	Create a new local port object that can be used either as a pattern	378	Create a new local port object and returns its port ID. Initially it has
277	matching port ("full port") or a single-callback port ("miniport"),	379	no callbacks set and will throw an error when it receives messages.
278	depending on how C<rcv> callbacks are bound to the object.
279		380
280	=item $port = port { my @msg = @_; $finished }	381	=item $local_port = port { my @msg = @_ }
281		382
282	Creates a "miniport", that is, a very lightweight port without any pattern	383	Creates a new local port, and returns its ID. Semantically the same as
283	matching behind it, and returns its ID. Semantically the same as creating
284	a port and calling C<rcv $port, $callback> on it.	384	creating a port and calling C<rcv $port, $callback> on it.
285		385
286	The block will be called for every message received on the port. When the	386	The block will be called for every message received on the port, with the
287	callback returns a true value its job is considered "done" and the port	387	global variable C<$SELF> set to the port ID. Runtime errors will cause the
288	will be destroyed. Otherwise it will stay alive.	388	port to be C<kil>ed. The message will be passed as-is, no extra argument
		389	(i.e. no port ID) will be passed to the callback.
289		390
290	The message will be passed as-is, no extra argument (i.e. no port id) will	391	If you want to stop/destroy the port, simply C<kil> it:
291	be passed to the callback.
292		392
293	If you need the local port id in the callback, this works nicely:	393	my $port = port {
294		394	my @msg = @_;
295	my $port; $port = port {	395	...
296	snd $otherport, reply => $port;	396	kil $SELF;
297	};	397	};
298		398
299	=cut	399	=cut
300		400
301	sub rcv($@);	401	sub rcv($@);
302		402
		403	my $KILME = sub {
		404	(my $tag = substr $_[0], 0, 30) =~ s/([\x20-\x7e])/./g;
		405	kil $SELF, unhandled_message => "no callback found for message '$tag'";
		406	};
		407
303	sub port(;&) {	408	sub port(;&) {
304	my $id = "$UNIQ." . $ID++;	409	my $id = $UNIQ . ++$ID;
305	my $port = "$NODE#$id";	410	my $port = "$NODE#$id";
306		411
307	if (@_) {
308	rcv $port, shift;	412	rcv $port, shift \|\| $KILME;
309	} else {
310	$PORT{$id} = sub { }; # nop
311	}
312		413
313	$port	414	$port
314	}	415	}
315		416
316	=item reg $port, $name
317
318	=item reg $name
319
320	Registers the given port (or C<$SELF><<< if missing) under the name
321	C<$name>. If the name already exists it is replaced.
322
323	A port can only be registered under one well known name.
324
325	A port automatically becomes unregistered when it is killed.
326
327	=cut
328
329	sub reg(@) {
330	my $port = @_ > 1 ? shift : $SELF \|\| Carp::croak 'reg: called with one argument only, but $SELF not set,';
331
332	$REG{$_[0]} = $port;
333	}
334
335	=item rcv $port, $callback->(@msg)	417	=item rcv $local_port, $callback->(@msg)
336		418
337	Replaces the callback on the specified miniport (after converting it to	419	Replaces the default callback on the specified port. There is no way to
338	one if required).	420	remove the default callback: use C<sub { }> to disable it, or better
339		421	C<kil> the port when it is no longer needed.
340	=item rcv $port, tagstring => $callback->(@msg), ...
341
342	=item rcv $port, $smartmatch => $callback->(@msg), ...
343
344	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
345
346	Register callbacks to be called on matching messages on the given full
347	port (after converting it to one if required) and return the port.
348
349	The callback has to return a true value when its work is done, after
350	which is will be removed, or a false value in which case it will stay
351	registered.
352		422
353	The global C<$SELF> (exported by this module) contains C<$port> while	423	The global C<$SELF> (exported by this module) contains C<$port> while
354	executing the callback.	424	executing the callback. Runtime errors during callback execution will
		425	result in the port being C<kil>ed.
355		426
356	Runtime errors during callback execution will result in the port being	427	The default callback receives all messages not matched by a more specific
357	C<kil>ed.	428	C<tag> match.
358		429
359	If the match is an array reference, then it will be matched against the	430	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
360	first elements of the message, otherwise only the first element is being
361	matched.
362		431
363	Any element in the match that is specified as C<_any_> (a function	432	Register (or replace) callbacks to be called on messages starting with the
364	exported by this module) matches any single element of the message.	433	given tag on the given port (and return the port), or unregister it (when
		434	C<$callback> is C<$undef> or missing). There can only be one callback
		435	registered for each tag.
365		436
366	While not required, it is highly recommended that the first matching	437	The original message will be passed to the callback, after the first
367	element is a string identifying the message. The one-string-only match is	438	element (the tag) has been removed. The callback will use the same
368	also the most efficient match (by far).	439	environment as the default callback (see above).
369		440
370	Example: create a port and bind receivers on it in one go.	441	Example: create a port and bind receivers on it in one go.
371		442
372	my $port = rcv port,	443	my $port = rcv port,
373	msg1 => sub { ...; 0 },	444	msg1 => sub { ... },
374	msg2 => sub { ...; 0 },	445	msg2 => sub { ... },
375	;	446	;
376		447
377	Example: create a port, bind receivers and send it in a message elsewhere	448	Example: create a port, bind receivers and send it in a message elsewhere
378	in one go:	449	in one go:
379		450
380	snd $otherport, reply =>	451	snd $otherport, reply =>
381	rcv port,	452	rcv port,
382	msg1 => sub { ...; 0 },	453	msg1 => sub { ... },
383	...	454	...
384	;	455	;
385		456
		457	Example: temporarily register a rcv callback for a tag matching some port
		458	(e.g. for an rpc reply) and unregister it after a message was received.
		459
		460	rcv $port, $otherport => sub {
		461	my @reply = @_;
		462
		463	rcv $SELF, $otherport;
		464	};
		465
386	=cut	466	=cut
387		467
388	sub rcv($@) {	468	sub rcv($@) {
389	my $port = shift;	469	my $port = shift;
390	my ($noderef, $portid) = split /#/, $port, 2;	470	my ($nodeid, $portid) = split /#/, $port, 2;
391		471
392	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	472	$NODE{$nodeid} == $NODE{""}
393	or Carp::croak "$port: rcv can only be called on local ports, caught";	473	or Carp::croak "$port: rcv can only be called on local ports, caught";
394		474
395	if (@_ == 1) {	475	while (@_) {
		476	if (ref $_[0]) {
		477	if (my $self = $PORT_DATA{$portid}) {
		478	"AnyEvent::MP::Port" eq ref $self
		479	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		480
		481	$self->[0] = shift;
		482	} else {
396	my $cb = shift;	483	my $cb = shift;
397	delete $PORT_DATA{$portid};
398	$PORT{$portid} = sub {	484	$PORT{$portid} = sub {
399	local $SELF = $port;	485	local $SELF = $port;
400	eval {	486	eval { &$cb }; _self_die if $@;
401	&$cb	487	};
402	and kil $port;
403	};	488	}
404	_self_die if $@;	489	} elsif (defined $_[0]) {
405	};
406	} else {
407	my $self = $PORT_DATA{$portid} \|\|= do {	490	my $self = $PORT_DATA{$portid} \|\|= do {
408	my $self = bless {	491	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
409	id => $port,
410	}, "AnyEvent::MP::Port";
411		492
412	$PORT{$portid} = sub {	493	$PORT{$portid} = sub {
413	local $SELF = $port;	494	local $SELF = $port;
414		495
415	eval {
416	for (@{ $self->{rc0}{$_[0]} }) {	496	if (my $cb = $self->[1]{$_[0]}) {
417	$_ && &{$_->[0]}	497	shift;
418	&& undef $_;	498	eval { &$cb }; _self_die if $@;
419	}	499	} else {
420
421	for (@{ $self->{rcv}{$_[0]} }) {
422	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
423	&& &{$_->[0]}	500	&{ $self->[0] };
424	&& undef $_;
425	}
426
427	for (@{ $self->{any} }) {
428	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
429	&& &{$_->[0]}
430	&& undef $_;
431	}	501	}
432	};	502	};
433	_self_die if $@;	503
		504	$self
434	};	505	};
435		506
436	$self
437	};
438
439	"AnyEvent::MP::Port" eq ref $self	507	"AnyEvent::MP::Port" eq ref $self
440	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	508	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
441		509
442	while (@_) {
443	my ($match, $cb) = splice @_, 0, 2;	510	my ($tag, $cb) = splice @_, 0, 2;
444		511
445	if (!ref $match) {	512	if (defined $cb) {
446	push @{ $self->{rc0}{$match} }, [$cb];	513	$self->[1]{$tag} = $cb;
447	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
448	my ($type, @match) = @$match;
449	@match
450	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
451	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
452	} else {	514	} else {
453	push @{ $self->{any} }, [$cb, $match];	515	delete $self->[1]{$tag};
454	}	516	}
455	}	517	}
456	}	518	}
457		519
458	$port	520	$port
459	}	521	}
460		522
		523	=item peval $port, $coderef[, @args]
		524
		525	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		526	when the code throews an exception the C<$port> will be killed.
		527
		528	Any remaining args will be passed to the callback. Any return values will
		529	be returned to the caller.
		530
		531	This is useful when you temporarily want to execute code in the context of
		532	a port.
		533
		534	Example: create a port and run some initialisation code in it's context.
		535
		536	my $port = port { ... };
		537
		538	peval $port, sub {
		539	init
		540	or die "unable to init";
		541	};
		542
		543	=cut
		544
		545	sub peval($$) {
		546	local $SELF = shift;
		547	my $cb = shift;
		548
		549	if (wantarray) {
		550	my @res = eval { &$cb };
		551	_self_die if $@;
		552	@res
		553	} else {
		554	my $res = eval { &$cb };
		555	_self_die if $@;
		556	$res
		557	}
		558	}
		559
461	=item $closure = psub { BLOCK }	560	=item $closure = psub { BLOCK }
462		561
463	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	562	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
464	closure is executed, sets up the environment in the same way as in C<rcv>	563	closure is executed, sets up the environment in the same way as in C<rcv>
465	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.	564	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		565
		566	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		567	BLOCK }, @_ } >>.
466		568
467	This is useful when you register callbacks from C<rcv> callbacks:	569	This is useful when you register callbacks from C<rcv> callbacks:
468		570
469	rcv delayed_reply => sub {	571	rcv delayed_reply => sub {
470	my ($delay, @reply) = @_;	572	my ($delay, @reply) = @_;
…		…
494	$res	596	$res
495	}	597	}
496	}	598	}
497	}	599	}
498		600
499	=item $guard = mon $port, $cb->(@reason)	601	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
500		602
501	=item $guard = mon $port, $rcvport	603	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
502		604
503	=item $guard = mon $port	605	=item $guard = mon $port # kill $SELF when $port dies
504		606
505	=item $guard = mon $port, $rcvport, @msg	607	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
506		608
507	Monitor the given port and do something when the port is killed or	609	Monitor the given port and do something when the port is killed or
508	messages to it were lost, and optionally return a guard that can be used	610	messages to it were lost, and optionally return a guard that can be used
509	to stop monitoring again.	611	to stop monitoring again.
510
511	C<mon> effectively guarantees that, in the absence of hardware failures,
512	that after starting the monitor, either all messages sent to the port
513	will arrive, or the monitoring action will be invoked after possible
514	message loss has been detected. No messages will be lost "in between"
515	(after the first lost message no further messages will be received by the
516	port). After the monitoring action was invoked, further messages might get
517	delivered again.
518		612
519	In the first form (callback), the callback is simply called with any	613	In the first form (callback), the callback is simply called with any
520	number of C<@reason> elements (no @reason means that the port was deleted	614	number of C<@reason> elements (no @reason means that the port was deleted
521	"normally"). Note also that I<< the callback B<must> never die >>, so use	615	"normally"). Note also that I<< the callback B<must> never die >>, so use
522	C<eval> if unsure.	616	C<eval> if unsure.
523		617
524	In the second form (another port given), the other port (C<$rcvport>)	618	In the second form (another port given), the other port (C<$rcvport>)
525	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	619	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
526	"normal" kils nothing happens, while under all other conditions, the other	620	"normal" kils nothing happens, while under all other conditions, the other
527	port is killed with the same reason.	621	port is killed with the same reason.
528		622
529	The third form (kill self) is the same as the second form, except that	623	The third form (kill self) is the same as the second form, except that
530	C<$rvport> defaults to C<$SELF>.	624	C<$rvport> defaults to C<$SELF>.
531		625
532	In the last form (message), a message of the form C<@msg, @reason> will be	626	In the last form (message), a message of the form C<@msg, @reason> will be
533	C<snd>.	627	C<snd>.
		628
		629	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		630	alert was raised), they are removed and will not trigger again.
534		631
535	As a rule of thumb, monitoring requests should always monitor a port from	632	As a rule of thumb, monitoring requests should always monitor a port from
536	a local port (or callback). The reason is that kill messages might get	633	a local port (or callback). The reason is that kill messages might get
537	lost, just like any other message. Another less obvious reason is that	634	lost, just like any other message. Another less obvious reason is that
538	even monitoring requests can get lost (for exmaple, when the connection	635	even monitoring requests can get lost (for example, when the connection
539	to the other node goes down permanently). When monitoring a port locally	636	to the other node goes down permanently). When monitoring a port locally
540	these problems do not exist.	637	these problems do not exist.
541		638
		639	C<mon> effectively guarantees that, in the absence of hardware failures,
		640	after starting the monitor, either all messages sent to the port will
		641	arrive, or the monitoring action will be invoked after possible message
		642	loss has been detected. No messages will be lost "in between" (after
		643	the first lost message no further messages will be received by the
		644	port). After the monitoring action was invoked, further messages might get
		645	delivered again.
		646
		647	Inter-host-connection timeouts and monitoring depend on the transport
		648	used. The only transport currently implemented is TCP, and AnyEvent::MP
		649	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		650	non-idle connection, and usually around two hours for idle connections).
		651
		652	This means that monitoring is good for program errors and cleaning up
		653	stuff eventually, but they are no replacement for a timeout when you need
		654	to ensure some maximum latency.
		655
542	Example: call a given callback when C<$port> is killed.	656	Example: call a given callback when C<$port> is killed.
543		657
544	mon $port, sub { warn "port died because of <@_>\n" };	658	mon $port, sub { warn "port died because of <@_>\n" };
545		659
546	Example: kill ourselves when C<$port> is killed abnormally.	660	Example: kill ourselves when C<$port> is killed abnormally.
…		…
552	mon $port, $self => "restart";	666	mon $port, $self => "restart";
553		667
554	=cut	668	=cut
555		669
556	sub mon {	670	sub mon {
557	my ($noderef, $port) = split /#/, shift, 2;	671	my ($nodeid, $port) = split /#/, shift, 2;
558		672
559	my $node = $NODE{$noderef} \|\| add_node $noderef;	673	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
560		674
561	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';	675	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
562		676
563	unless (ref $cb) {	677	unless (ref $cb) {
564	if (@_) {	678	if (@_) {
…		…
573	}	687	}
574		688
575	$node->monitor ($port, $cb);	689	$node->monitor ($port, $cb);
576		690
577	defined wantarray	691	defined wantarray
578	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	692	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
579	}	693	}
580		694
581	=item $guard = mon_guard $port, $ref, $ref...	695	=item $guard = mon_guard $port, $ref, $ref...
582		696
583	Monitors the given C<$port> and keeps the passed references. When the port	697	Monitors the given C<$port> and keeps the passed references. When the port
584	is killed, the references will be freed.	698	is killed, the references will be freed.
585		699
586	Optionally returns a guard that will stop the monitoring.	700	Optionally returns a guard that will stop the monitoring.
587		701
588	This function is useful when you create e.g. timers or other watchers and	702	This function is useful when you create e.g. timers or other watchers and
589	want to free them when the port gets killed:	703	want to free them when the port gets killed (note the use of C<psub>):
590		704
591	$port->rcv (start => sub {	705	$port->rcv (start => sub {
592	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	706	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
593	undef $timer if 0.9 < rand;	707	undef $timer if 0.9 < rand;
594	});	708	});
595	});	709	});
596		710
597	=cut	711	=cut
…		…
606		720
607	=item kil $port[, @reason]	721	=item kil $port[, @reason]
608		722
609	Kill the specified port with the given C<@reason>.	723	Kill the specified port with the given C<@reason>.
610		724
611	If no C<@reason> is specified, then the port is killed "normally" (linked	725	If no C<@reason> is specified, then the port is killed "normally" -
612	ports will not be kileld, or even notified).	726	monitor callback will be invoked, but the kil will not cause linked ports
		727	(C<mon $mport, $lport> form) to get killed.
613		728
614	Otherwise, linked ports get killed with the same reason (second form of	729	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
615	C<mon>, see below).	730	form) get killed with the same reason.
616		731
617	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	732	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
618	will be reported as reason C<< die => $@ >>.	733	will be reported as reason C<< die => $@ >>.
619		734
620	Transport/communication errors are reported as C<< transport_error =>	735	Transport/communication errors are reported as C<< transport_error =>
621	$message >>.	736	$message >>.
622		737
623	=cut	738	Common idioms:
		739
		740	# silently remove yourself, do not kill linked ports
		741	kil $SELF;
		742
		743	# report a failure in some detail
		744	kil $SELF, failure_mode_1 => "it failed with too high temperature";
		745
		746	# do not waste much time with killing, just die when something goes wrong
		747	open my $fh, "<file"
		748	or die "file: $!";
624		749
625	=item $port = spawn $node, $initfunc[, @initdata]	750	=item $port = spawn $node, $initfunc[, @initdata]
626		751
627	Creates a port on the node C<$node> (which can also be a port ID, in which	752	Creates a port on the node C<$node> (which can also be a port ID, in which
628	case it's the node where that port resides).	753	case it's the node where that port resides).
629		754
630	The port ID of the newly created port is return immediately, and it is	755	The port ID of the newly created port is returned immediately, and it is
631	permissible to immediately start sending messages or monitor the port.	756	possible to immediately start sending messages or to monitor the port.
632		757
633	After the port has been created, the init function is	758	After the port has been created, the init function is called on the remote
634	called. This function must be a fully-qualified function name	759	node, in the same context as a C<rcv> callback. This function must be a
635	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	760	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
636	program, use C<::name>.	761	specify a function in the main program, use C<::name>.
637		762
638	If the function doesn't exist, then the node tries to C<require>	763	If the function doesn't exist, then the node tries to C<require>
639	the package, then the package above the package and so on (e.g.	764	the package, then the package above the package and so on (e.g.
640	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	765	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
641	exists or it runs out of package names.	766	exists or it runs out of package names.
642		767
643	The init function is then called with the newly-created port as context	768	The init function is then called with the newly-created port as context
644	object (C<$SELF>) and the C<@initdata> values as arguments.	769	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		770	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		771	the port might not get created.
645		772
646	A common idiom is to pass your own port, monitor the spawned port, and	773	A common idiom is to pass a local port, immediately monitor the spawned
647	in the init function, monitor the original port. This two-way monitoring	774	port, and in the remote init function, immediately monitor the passed
648	ensures that both ports get cleaned up when there is a problem.	775	local port. This two-way monitoring ensures that both ports get cleaned up
		776	when there is a problem.
		777
		778	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		779	caller before C<spawn> returns (by delaying invocation when spawn is
		780	called for the local node).
649		781
650	Example: spawn a chat server port on C<$othernode>.	782	Example: spawn a chat server port on C<$othernode>.
651		783
652	# this node, executed from within a port context:	784	# this node, executed from within a port context:
653	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	785	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
668		800
669	sub _spawn {	801	sub _spawn {
670	my $port = shift;	802	my $port = shift;
671	my $init = shift;	803	my $init = shift;
672		804
		805	# rcv will create the actual port
673	local $SELF = "$NODE#$port";	806	local $SELF = "$NODE#$port";
674	eval {	807	eval {
675	&{ load_func $init }	808	&{ load_func $init }
676	};	809	};
677	_self_die if $@;	810	_self_die if $@;
678	}	811	}
679		812
680	sub spawn(@) {	813	sub spawn(@) {
681	my ($noderef, undef) = split /#/, shift, 2;	814	my ($nodeid, undef) = split /#/, shift, 2;
682		815
683	my $id = "$RUNIQ." . $ID++;	816	my $id = $RUNIQ . ++$ID;
684		817
685	$_[0] =~ /::/	818	$_[0] =~ /::/
686	or Carp::croak "spawn init function must be a fully-qualified name, caught";	819	or Carp::croak "spawn init function must be a fully-qualified name, caught";
687		820
688	($NODE{$noderef} \|\| add_node $noderef)	821	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
689	->send (["", "AnyEvent::MP::_spawn" => $id, @_]);
690		822
691	"$noderef#$id"	823	"$nodeid#$id"
692	}	824	}
693		825
		826
		827	=item after $timeout, @msg
		828
		829	=item after $timeout, $callback
		830
		831	Either sends the given message, or call the given callback, after the
		832	specified number of seconds.
		833
		834	This is simply a utility function that comes in handy at times - the
		835	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		836	so it may go away in the future.
		837
		838	=cut
		839
		840	sub after($@) {
		841	my ($timeout, @action) = @_;
		842
		843	my $t; $t = AE::timer $timeout, 0, sub {
		844	undef $t;
		845	ref $action[0]
		846	? $action[0]()
		847	: snd @action;
		848	};
		849	}
		850
		851	#=item $cb2 = timeout $seconds, $cb[, @args]
		852
		853	=item cal $port, @msg, $callback[, $timeout]
		854
		855	A simple form of RPC - sends a message to the given C<$port> with the
		856	given contents (C<@msg>), but adds a reply port to the message.
		857
		858	The reply port is created temporarily just for the purpose of receiving
		859	the reply, and will be C<kil>ed when no longer needed.
		860
		861	A reply message sent to the port is passed to the C<$callback> as-is.
		862
		863	If an optional time-out (in seconds) is given and it is not C<undef>,
		864	then the callback will be called without any arguments after the time-out
		865	elapsed and the port is C<kil>ed.
		866
		867	If no time-out is given (or it is C<undef>), then the local port will
		868	monitor the remote port instead, so it eventually gets cleaned-up.
		869
		870	Currently this function returns the temporary port, but this "feature"
		871	might go in future versions unless you can make a convincing case that
		872	this is indeed useful for something.
		873
		874	=cut
		875
		876	sub cal(@) {
		877	my $timeout = ref $_[-1] ? undef : pop;
		878	my $cb = pop;
		879
		880	my $port = port {
		881	undef $timeout;
		882	kil $SELF;
		883	&$cb;
		884	};
		885
		886	if (defined $timeout) {
		887	$timeout = AE::timer $timeout, 0, sub {
		888	undef $timeout;
		889	kil $port;
		890	$cb->();
		891	};
		892	} else {
		893	mon $_[0], sub {
		894	kil $port;
		895	$cb->();
		896	};
		897	}
		898
		899	push @_, $port;
		900	&snd;
		901
		902	$port
		903	}
		904
694	=back	905	=back
695		906
696	=head1 NODE MESSAGES	907	=head1 DISTRIBUTED DATABASE
697		908
698	Nodes understand the following messages sent to them. Many of them take	909	AnyEvent::MP comes with a simple distributed database. The database will
699	arguments called C<@reply>, which will simply be used to compose a reply	910	be mirrored asynchronously on all global nodes. Other nodes bind to one
700	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and	911	of the global nodes for their needs. Every node has a "local database"
701	the remaining arguments are simply the message data.	912	which contains all the values that are set locally. All local databases
		913	are merged together to form the global database, which can be queried.
702		914
703	While other messages exist, they are not public and subject to change.	915	The database structure is that of a two-level hash - the database hash
		916	contains hashes which contain values, similarly to a perl hash of hashes,
		917	i.e.:
704		918
		919	$DATABASE{$family}{$subkey} = $value
		920
		921	The top level hash key is called "family", and the second-level hash key
		922	is called "subkey" or simply "key".
		923
		924	The family must be alphanumeric, i.e. start with a letter and consist
		925	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		926	pretty much like Perl module names.
		927
		928	As the family namespace is global, it is recommended to prefix family names
		929	with the name of the application or module using it.
		930
		931	The subkeys must be non-empty strings, with no further restrictions.
		932
		933	The values should preferably be strings, but other perl scalars should
		934	work as well (such as C<undef>, arrays and hashes).
		935
		936	Every database entry is owned by one node - adding the same family/subkey
		937	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		938	but the result might be nondeterministic, i.e. the key might have
		939	different values on different nodes.
		940
		941	Different subkeys in the same family can be owned by different nodes
		942	without problems, and in fact, this is the common method to create worker
		943	pools. For example, a worker port for image scaling might do this:
		944
		945	db_set my_image_scalers => $port;
		946
		947	And clients looking for an image scaler will want to get the
		948	C<my_image_scalers> keys from time to time:
		949
		950	db_keys my_image_scalers => sub {
		951	@ports = @{ $_[0] };
		952	};
		953
		954	Or better yet, they want to monitor the database family, so they always
		955	have a reasonable up-to-date copy:
		956
		957	db_mon my_image_scalers => sub {
		958	@ports = keys %{ $_[0] };
		959	};
		960
		961	In general, you can set or delete single subkeys, but query and monitor
		962	whole families only.
		963
		964	If you feel the need to monitor or query a single subkey, try giving it
		965	it's own family.
		966
705	=over 4	967	=over
		968
		969	=item db_set $family => $subkey [=> $value]
		970
		971	Sets (or replaces) a key to the database - if C<$value> is omitted,
		972	C<undef> is used instead.
		973
		974	=item db_del $family => $subkey...
		975
		976	Deletes one or more subkeys from the database family.
		977
		978	=item $guard = db_reg $family => $subkey [=> $value]
		979
		980	Sets the key on the database and returns a guard. When the guard is
		981	destroyed, the key is deleted from the database. If C<$value> is missing,
		982	then C<undef> is used.
		983
		984	=item db_family $family => $cb->(\%familyhash)
		985
		986	Queries the named database C<$family> and call the callback with the
		987	family represented as a hash. You can keep and freely modify the hash.
		988
		989	=item db_keys $family => $cb->(\@keys)
		990
		991	Same as C<db_family>, except it only queries the family I<subkeys> and passes
		992	them as array reference to the callback.
		993
		994	=item db_values $family => $cb->(\@values)
		995
		996	Same as C<db_family>, except it only queries the family I<values> and passes them
		997	as array reference to the callback.
		998
		999	=item $guard = db_mon $family => $cb->($familyhash, \@added, \@changed, \@deleted)
		1000
		1001	Creates a monitor on the given database family. Each time a key is set
		1002	or or is deleted the callback is called with a hash containing the
		1003	database family and three lists of added, changed and deleted subkeys,
		1004	respectively. If no keys have changed then the array reference might be
		1005	C<undef> or even missing.
		1006
		1007	If not called in void context, a guard object is returned that, when
		1008	destroyed, stops the monitor.
		1009
		1010	The family hash reference and the key arrays belong to AnyEvent::MP and
		1011	B<must not be modified or stored> by the callback. When in doubt, make a
		1012	copy.
		1013
		1014	As soon as possible after the monitoring starts, the callback will be
		1015	called with the intiial contents of the family, even if it is empty,
		1016	i.e. there will always be a timely call to the callback with the current
		1017	contents.
		1018
		1019	It is possible that the callback is called with a change event even though
		1020	the subkey is already present and the value has not changed.
		1021
		1022	The monitoring stops when the guard object is destroyed.
		1023
		1024	Example: on every change to the family "mygroup", print out all keys.
		1025
		1026	my $guard = db_mon mygroup => sub {
		1027	my ($family, $a, $c, $d) = @_;
		1028	print "mygroup members: ", (join " ", keys %$family), "\n";
		1029	};
		1030
		1031	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1032
		1033	my $guard; $guard = db_mon My::Module::workers => sub {
		1034	my ($family, $a, $c, $d) = @_;
		1035	return unless %$family;
		1036	undef $guard;
		1037	print "My::Module::workers now nonempty\n";
		1038	};
		1039
		1040	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		1041
		1042	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		1043	my ($family, $a, $c, $d) = @_;
		1044
		1045	print "+$_=$family->{$_}\n" for @$a;
		1046	print "*$_=$family->{$_}\n" for @$c;
		1047	print "-$_=$family->{$_}\n" for @$d;
		1048	};
706		1049
707	=cut	1050	=cut
708
709	=item lookup => $name, @reply
710
711	Replies with the port ID of the specified well-known port, or C<undef>.
712
713	=item devnull => ...
714
715	Generic data sink/CPU heat conversion.
716
717	=item relay => $port, @msg
718
719	Simply forwards the message to the given port.
720
721	=item eval => $string[ @reply]
722
723	Evaluates the given string. If C<@reply> is given, then a message of the
724	form C<@reply, $@, @evalres> is sent.
725
726	Example: crash another node.
727
728	snd $othernode, eval => "exit";
729
730	=item time => @reply
731
732	Replies the the current node time to C<@reply>.
733
734	Example: tell the current node to send the current time to C<$myport> in a
735	C<timereply> message.
736
737	snd $NODE, time => $myport, timereply => 1, 2;
738	# => snd $myport, timereply => 1, 2, <time>
739		1051
740	=back	1052	=back
741		1053
742	=head1 AnyEvent::MP vs. Distributed Erlang	1054	=head1 AnyEvent::MP vs. Distributed Erlang
743		1055
744	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	1056	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
745	== aemp node, Erlang process == aemp port), so many of the documents and	1057	== aemp node, Erlang process == aemp port), so many of the documents and
746	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	1058	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
747	sample:	1059	sample:
748		1060
749	http://www.Erlang.se/doc/programming_rules.shtml	1061	http://www.erlang.se/doc/programming_rules.shtml
750	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	1062	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
751	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	1063	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
752	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	1064	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
753		1065
754	Despite the similarities, there are also some important differences:	1066	Despite the similarities, there are also some important differences:
755		1067
756	=over 4	1068	=over 4
757		1069
758	=item * Node references contain the recipe on how to contact them.	1070	=item * Node IDs are arbitrary strings in AEMP.
759		1071
760	Erlang relies on special naming and DNS to work everywhere in the	1072	Erlang relies on special naming and DNS to work everywhere in the same
761	same way. AEMP relies on each node knowing it's own address(es), with	1073	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
762	convenience functionality.	1074	configuration or DNS), and possibly the addresses of some seed nodes, but
		1075	will otherwise discover other nodes (and their IDs) itself.
763		1076
764	This means that AEMP requires a less tightly controlled environment at the	1077	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
765	cost of longer node references and a slightly higher management overhead.	1078	uses "local ports are like remote ports".
		1079
		1080	The failure modes for local ports are quite different (runtime errors
		1081	only) then for remote ports - when a local port dies, you I<know> it dies,
		1082	when a connection to another node dies, you know nothing about the other
		1083	port.
		1084
		1085	Erlang pretends remote ports are as reliable as local ports, even when
		1086	they are not.
		1087
		1088	AEMP encourages a "treat remote ports differently" philosophy, with local
		1089	ports being the special case/exception, where transport errors cannot
		1090	occur.
766		1091
767	=item * Erlang uses processes and a mailbox, AEMP does not queue.	1092	=item * Erlang uses processes and a mailbox, AEMP does not queue.
768		1093
769	Erlang uses processes that selctively receive messages, and therefore	1094	Erlang uses processes that selectively receive messages out of order, and
770	needs a queue. AEMP is event based, queuing messages would serve no useful	1095	therefore needs a queue. AEMP is event based, queuing messages would serve
771	purpose.	1096	no useful purpose. For the same reason the pattern-matching abilities
		1097	of AnyEvent::MP are more limited, as there is little need to be able to
		1098	filter messages without dequeuing them.
772		1099
773	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	1100	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1101	being event-based, while Erlang is process-based.
		1102
		1103	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1104	top of AEMP and Coro threads.
774		1105
775	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1106	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
776		1107
777	Sending messages in Erlang is synchronous and blocks the process. AEMP	1108	Sending messages in Erlang is synchronous and blocks the process until
778	sends are immediate, connection establishment is handled in the	1109	a conenction has been established and the message sent (and so does not
779	background.	1110	need a queue that can overflow). AEMP sends return immediately, connection
		1111	establishment is handled in the background.
780		1112
781	=item * Erlang can silently lose messages, AEMP cannot.	1113	=item * Erlang suffers from silent message loss, AEMP does not.
782		1114
783	Erlang makes few guarantees on messages delivery - messages can get lost	1115	Erlang implements few guarantees on messages delivery - messages can get
784	without any of the processes realising it (i.e. you send messages a, b,	1116	lost without any of the processes realising it (i.e. you send messages a,
785	and c, and the other side only receives messages a and c).	1117	b, and c, and the other side only receives messages a and c).
786		1118
787	AEMP guarantees correct ordering, and the guarantee that there are no	1119	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1120	guarantee that after one message is lost, all following ones sent to the
		1121	same port are lost as well, until monitoring raises an error, so there are
788	holes in the message sequence.	1122	no silent "holes" in the message sequence.
789		1123
790	=item * In Erlang, processes can be declared dead and later be found to be	1124	If you want your software to be very reliable, you have to cope with
791	alive.	1125	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
792		1126	simply tries to work better in common error cases, such as when a network
793	In Erlang it can happen that a monitored process is declared dead and	1127	link goes down.
794	linked processes get killed, but later it turns out that the process is
795	still alive - and can receive messages.
796
797	In AEMP, when port monitoring detects a port as dead, then that port will
798	eventually be killed - it cannot happen that a node detects a port as dead
799	and then later sends messages to it, finding it is still alive.
800		1128
801	=item * Erlang can send messages to the wrong port, AEMP does not.	1129	=item * Erlang can send messages to the wrong port, AEMP does not.
802		1130
803	In Erlang it is quite possible that a node that restarts reuses a process	1131	In Erlang it is quite likely that a node that restarts reuses an Erlang
804	ID known to other nodes for a completely different process, causing	1132	process ID known to other nodes for a completely different process,
805	messages destined for that process to end up in an unrelated process.	1133	causing messages destined for that process to end up in an unrelated
		1134	process.
806		1135
807	AEMP never reuses port IDs, so old messages or old port IDs floating	1136	AEMP does not reuse port IDs, so old messages or old port IDs floating
808	around in the network will not be sent to an unrelated port.	1137	around in the network will not be sent to an unrelated port.
809		1138
810	=item * Erlang uses unprotected connections, AEMP uses secure	1139	=item * Erlang uses unprotected connections, AEMP uses secure
811	authentication and can use TLS.	1140	authentication and can use TLS.
812		1141
813	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1142	AEMP can use a proven protocol - TLS - to protect connections and
814	securely authenticate nodes.	1143	securely authenticate nodes.
815		1144
816	=item * The AEMP protocol is optimised for both text-based and binary	1145	=item * The AEMP protocol is optimised for both text-based and binary
817	communications.	1146	communications.
818		1147
819	The AEMP protocol, unlike the Erlang protocol, supports both	1148	The AEMP protocol, unlike the Erlang protocol, supports both programming
820	language-independent text-only protocols (good for debugging) and binary,	1149	language independent text-only protocols (good for debugging), and binary,
821	language-specific serialisers (e.g. Storable).	1150	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1151	used, the protocol is actually completely text-based.
822		1152
823	It has also been carefully designed to be implementable in other languages	1153	It has also been carefully designed to be implementable in other languages
824	with a minimum of work while gracefully degrading fucntionality to make the	1154	with a minimum of work while gracefully degrading functionality to make the
825	protocol simple.	1155	protocol simple.
826		1156
827	=item * AEMP has more flexible monitoring options than Erlang.	1157	=item * AEMP has more flexible monitoring options than Erlang.
828		1158
829	In Erlang, you can chose to receive I<all> exit signals as messages	1159	In Erlang, you can chose to receive I<all> exit signals as messages or
830	or I<none>, there is no in-between, so monitoring single processes is	1160	I<none>, there is no in-between, so monitoring single Erlang processes is
831	difficult to implement. Monitoring in AEMP is more flexible than in	1161	difficult to implement.
832	Erlang, as one can choose between automatic kill, exit message or callback	1162
833	on a per-process basis.	1163	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1164	between automatic kill, exit message or callback on a per-port basis.
834		1165
835	=item * Erlang tries to hide remote/local connections, AEMP does not.	1166	=item * Erlang tries to hide remote/local connections, AEMP does not.
836		1167
837	Monitoring in Erlang is not an indicator of process death/crashes,	1168	Monitoring in Erlang is not an indicator of process death/crashes, in the
838	as linking is (except linking is unreliable in Erlang).	1169	same way as linking is (except linking is unreliable in Erlang).
839		1170
840	In AEMP, you don't "look up" registered port names or send to named ports	1171	In AEMP, you don't "look up" registered port names or send to named ports
841	that might or might not be persistent. Instead, you normally spawn a port	1172	that might or might not be persistent. Instead, you normally spawn a port
842	on the remote node. The init function monitors the you, and you monitor	1173	on the remote node. The init function monitors you, and you monitor the
843	the remote port. Since both monitors are local to the node, they are much	1174	remote port. Since both monitors are local to the node, they are much more
844	more reliable.	1175	reliable (no need for C<spawn_link>).
845		1176
846	This also saves round-trips and avoids sending messages to the wrong port	1177	This also saves round-trips and avoids sending messages to the wrong port
847	(hard to do in Erlang).	1178	(hard to do in Erlang).
848		1179
849	=back	1180	=back
850		1181
		1182	=head1 RATIONALE
		1183
		1184	=over 4
		1185
		1186	=item Why strings for port and node IDs, why not objects?
		1187
		1188	We considered "objects", but found that the actual number of methods
		1189	that can be called are quite low. Since port and node IDs travel over
		1190	the network frequently, the serialising/deserialising would add lots of
		1191	overhead, as well as having to keep a proxy object everywhere.
		1192
		1193	Strings can easily be printed, easily serialised etc. and need no special
		1194	procedures to be "valid".
		1195
		1196	And as a result, a port with just a default receiver consists of a single
		1197	code reference stored in a global hash - it can't become much cheaper.
		1198
		1199	=item Why favour JSON, why not a real serialising format such as Storable?
		1200
		1201	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1202	format, but currently there is no way to make a node use Storable by
		1203	default (although all nodes will accept it).
		1204
		1205	The default framing protocol is JSON because a) JSON::XS is many times
		1206	faster for small messages and b) most importantly, after years of
		1207	experience we found that object serialisation is causing more problems
		1208	than it solves: Just like function calls, objects simply do not travel
		1209	easily over the network, mostly because they will always be a copy, so you
		1210	always have to re-think your design.
		1211
		1212	Keeping your messages simple, concentrating on data structures rather than
		1213	objects, will keep your messages clean, tidy and efficient.
		1214
		1215	=back
		1216
851	=head1 SEE ALSO	1217	=head1 SEE ALSO
		1218
		1219	L<AnyEvent::MP::Intro> - a gentle introduction.
		1220
		1221	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1222
		1223	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1224	your applications.
		1225
		1226	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1227
		1228	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1229	all nodes.
852		1230
853	L<AnyEvent>.	1231	L<AnyEvent>.
854		1232
855	=head1 AUTHOR	1233	=head1 AUTHOR
856		1234

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Revision 1.135 by root, Mon Mar 12 14:55:55 2012 UTC