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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.39 by root, Fri Aug 7 23:21:48 2009 UTC vs.
Revision 1.134 by root, Mon Mar 12 14:47:23 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::Base;	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 = '0.1';	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
		195
121	our @EXPORT = qw(	196	our @EXPORT = qw(
122	NODE $NODE *SELF node_of _any_	197	NODE $NODE *SELF node_of after
123	resolve_node initialise_node	198	configure
124	snd rcv mon kil reg psub spawn	199	snd rcv mon mon_guard kil psub peval spawn cal
125	port	200	port
		201	db_set db_del db_reg
		202	db_mon db_family db_keys db_values
126	);	203	);
127		204
128	our $SELF;	205	our $SELF;
129		206
130	sub _self_die() {	207	sub _self_die() {
…		…
133	kil $SELF, die => $msg;	210	kil $SELF, die => $msg;
134	}	211	}
135		212
136	=item $thisnode = NODE / $NODE	213	=item $thisnode = NODE / $NODE
137		214
138	The C<NODE> function returns, and the C<$NODE> variable contains	215	The C<NODE> function returns, and the C<$NODE> variable contains, the node
139	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
140	to C<become_public> or C<become_slave>, after which all local port	217	a call to C<configure>.
141	identifiers become invalid.
142		218
143	=item $noderef = node_of $port	219	=item $nodeid = node_of $port
144		220
145	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.
146		222
147	=item initialise_node $noderef, $seednode, $seednode...	223	=item configure $profile, key => value...
148		224
149	=item initialise_node "slave/", $master, $master...	225	=item configure key => value...
150		226
151	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
152	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
153	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.
154		231
155	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
156	never) before calling other AnyEvent::MP functions.	233	never) before calling other AnyEvent::MP functions.
157		234
158	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
159		236	F<aemp> command line utility (sans the set/del prefix), with these additions:
160	There are two types of networked nodes, public nodes and slave nodes:
161		237
162	=over 4	238	=over 4
163		239
164	=item public nodes	240	=item norc => $boolean (default false)
165		241
166	For public nodes, C<$noderef> must either be a (possibly unresolved)	242	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
167	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
168	which case the noderef will be guessed.	244	C<configure> call.
169		245
170	Afterwards, the node will bind itself on all endpoints and try to connect	246	=item force => $boolean (default false)
171	to all additional C<$seednodes> that are specified. Seednodes are optional
172	and can be used to quickly bootstrap the node into an existing network.
173		247
174	=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.
175		251
176	When the C<$noderef> is the special string C<slave/>, then the node will	252	=item secure => $pass->($nodeid)
177	become a slave node. Slave nodes cannot be contacted from outside and will
178	route most of their traffic to the master node that they attach to.
179		253
180	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
181	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
182	successfully connect to.	256	granted iff the callback returns a true value.
		257
		258	See F<semp setsecure> for more info.
183		259
184	=back	260	=back
185		261
186	This function will block until all nodes have been resolved and, for slave
187	nodes, until it has successfully established a connection to a master
188	server.
189
190	Example: become a public node listening on the default node.
191
192	initialise_node;
193
194	Example: become a public node, and try to contact some well-known master
195	servers to become part of the network.
196
197	initialise_node undef, "master1", "master2";
198
199	Example: become a public node listening on port C<4041>.
200
201	initialise_node 4041;
202
203	Example: become a public node, only visible on localhost port 4044.
204
205	initialise_node "locahost:4044";
206
207	Example: become a slave node to any of the specified master servers.
208
209	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
210
211	=item $cv = resolve_node $noderef
212
213	Takes an unresolved node reference that may contain hostnames and
214	abbreviated IDs, resolves all of them and returns a resolved node
215	reference.
216
217	In addition to C<address:port> pairs allowed in resolved noderefs, the
218	following forms are supported:
219
220	=over 4	262	=over 4
221		263
222	=item the empty string	264	=item step 1, gathering configuration from profiles
223		265
224	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
225	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.
226		270
227	=item naked port numbers (e.g. C<1234>)	271	The profile data is then gathered as follows:
228		272
229	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
230	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).
231		278
232	=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.
233		282
234	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
235	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
236	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.
237		310
238	=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)"
239		338
240	=item $SELF	339	=item $SELF
241		340
242	Contains the current port id while executing C<rcv> callbacks or C<psub>	341	Contains the current port id while executing C<rcv> callbacks or C<psub>
243	blocks.	342	blocks.
244		343
245	=item SELF, %SELF, @SELF...	344	=item *SELF, SELF, %SELF, @SELF...
246		345
247	Due to some quirks in how perl exports variables, it is impossible to	346	Due to some quirks in how perl exports variables, it is impossible to
248	just export C<$SELF>, all the symbols called C<SELF> are exported by this	347	just export C<$SELF>, all the symbols named C<SELF> are exported by this
249	module, but only C<$SELF> is currently used.	348	module, but only C<$SELF> is currently used.
250		349
251	=item snd $port, type => @data	350	=item snd $port, type => @data
252		351
253	=item snd $port, @msg	352	=item snd $port, @msg
254		353
255	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
256	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.
257	stringifies a sa port ID (such as a port object :).
258		356
259	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
260	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
261	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.
262		361
263	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
264	function: modifying any argument is not allowed and can cause many	363	function: modifying any argument (or values referenced by them) is
265	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.
266		368
267	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
268	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
269	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
270	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
271	node, anything can be passed.	373	node, anything can be passed. Best rely only on the common denominator of
		374	these.
272		375
273	=item $local_port = port	376	=item $local_port = port
274		377
275	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
276	matching port ("full port") or a single-callback port ("miniport"),	379	no callbacks set and will throw an error when it receives messages.
277	depending on how C<rcv> callbacks are bound to the object.
278		380
279	=item $port = port { my @msg = @_; $finished }	381	=item $local_port = port { my @msg = @_ }
280		382
281	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
282	matching behind it, and returns its ID. Semantically the same as creating
283	a port and calling C<rcv $port, $callback> on it.	384	creating a port and calling C<rcv $port, $callback> on it.
284		385
285	The block will be called for every message received on the port. When the	386	The block will be called for every message received on the port, with the
286	callback returns a true value its job is considered "done" and the port	387	global variable C<$SELF> set to the port ID. Runtime errors will cause the
287	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.
288		390
289	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:
290	be passed to the callback.
291		392
292	If you need the local port id in the callback, this works nicely:	393	my $port = port {
293		394	my @msg = @_;
294	my $port; $port = port {	395	...
295	snd $otherport, reply => $port;	396	kil $SELF;
296	};	397	};
297		398
298	=cut	399	=cut
299		400
300	sub rcv($@);	401	sub rcv($@);
301		402
		403	my $KILME = sub {
		404	(my $tag = substr $_[0], 0, 30) =~ s/([\x20-\x7e])/./g;
		405	kil $SELF, unhandled_message => "missing (tag or fallback) callback for message '$tag'";
		406	};
		407
302	sub port(;&) {	408	sub port(;&) {
303	my $id = "$UNIQ." . $ID++;	409	my $id = $UNIQ . ++$ID;
304	my $port = "$NODE#$id";	410	my $port = "$NODE#$id";
305		411
306	if (@_) {
307	rcv $port, shift;	412	rcv $port, shift \|\| $KILME;
308	} else {
309	$PORT{$id} = sub { }; # nop
310	}
311		413
312	$port	414	$port
313	}	415	}
314		416
315	=item reg $port, $name
316
317	=item reg $name
318
319	Registers the given port (or C<$SELF><<< if missing) under the name
320	C<$name>. If the name already exists it is replaced.
321
322	A port can only be registered under one well known name.
323
324	A port automatically becomes unregistered when it is killed.
325
326	=cut
327
328	sub reg(@) {
329	my $port = @_ > 1 ? shift : $SELF \|\| Carp::croak 'reg: called with one argument only, but $SELF not set,';
330
331	$REG{$_[0]} = $port;
332	}
333
334	=item rcv $port, $callback->(@msg)	417	=item rcv $local_port, $callback->(@msg)
335		418
336	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
337	one if required).	420	remove the default callback: use C<sub { }> to disable it, or better
338		421	C<kil> the port when it is no longer needed.
339	=item rcv $port, tagstring => $callback->(@msg), ...
340
341	=item rcv $port, $smartmatch => $callback->(@msg), ...
342
343	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
344
345	Register callbacks to be called on matching messages on the given full
346	port (after converting it to one if required) and return the port.
347
348	The callback has to return a true value when its work is done, after
349	which is will be removed, or a false value in which case it will stay
350	registered.
351		422
352	The global C<$SELF> (exported by this module) contains C<$port> while	423	The global C<$SELF> (exported by this module) contains C<$port> while
353	executing the callback.	424	executing the callback. Runtime errors during callback execution will
		425	result in the port being C<kil>ed.
354		426
355	Runtime errors during callback execution will result in the port being	427	The default callback receives all messages not matched by a more specific
356	C<kil>ed.	428	C<tag> match.
357		429
358	If the match is an array reference, then it will be matched against the	430	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
359	first elements of the message, otherwise only the first element is being
360	matched.
361		431
362	Any element in the match that is specified as C<_any_> (a function	432	Register (or replace) callbacks to be called on messages starting with the
363	exported by this module) matches any single element of the message.	433	given tag on the given port (and return the port), or unregister it (when
		434	C<$callback> is C<$undef> or missing). There can only be one callback
		435	registered for each tag.
364		436
365	While not required, it is highly recommended that the first matching	437	The original message will be passed to the callback, after the first
366	element is a string identifying the message. The one-string-only match is	438	element (the tag) has been removed. The callback will use the same
367	also the most efficient match (by far).	439	environment as the default callback (see above).
368		440
369	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.
370		442
371	my $port = rcv port,	443	my $port = rcv port,
372	msg1 => sub { ...; 0 },	444	msg1 => sub { ... },
373	msg2 => sub { ...; 0 },	445	msg2 => sub { ... },
374	;	446	;
375		447
376	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
377	in one go:	449	in one go:
378		450
379	snd $otherport, reply =>	451	snd $otherport, reply =>
380	rcv port,	452	rcv port,
381	msg1 => sub { ...; 0 },	453	msg1 => sub { ... },
382	...	454	...
383	;	455	;
384		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, $otherport;
		464	};
		465
385	=cut	466	=cut
386		467
387	sub rcv($@) {	468	sub rcv($@) {
388	my $port = shift;	469	my $port = shift;
389	my ($noderef, $portid) = split /#/, $port, 2;	470	my ($nodeid, $portid) = split /#/, $port, 2;
390		471
391	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	472	$NODE{$nodeid} == $NODE{""}
392	or Carp::croak "$port: rcv can only be called on local ports, caught";	473	or Carp::croak "$port: rcv can only be called on local ports, caught";
393		474
394	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 {
395	my $cb = shift;	483	my $cb = shift;
396	delete $PORT_DATA{$portid};
397	$PORT{$portid} = sub {	484	$PORT{$portid} = sub {
398	local $SELF = $port;	485	local $SELF = $port;
399	eval {	486	eval { &$cb }; _self_die if $@;
400	&$cb	487	};
401	and kil $port;
402	};	488	}
403	_self_die if $@;	489	} elsif (defined $_[0]) {
404	};
405	} else {
406	my $self = $PORT_DATA{$portid} \|\|= do {	490	my $self = $PORT_DATA{$portid} \|\|= do {
407	my $self = bless {	491	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
408	id => $port,
409	}, "AnyEvent::MP::Port";
410		492
411	$PORT{$portid} = sub {	493	$PORT{$portid} = sub {
412	local $SELF = $port;	494	local $SELF = $port;
413		495
414	eval {
415	for (@{ $self->{rc0}{$_[0]} }) {	496	if (my $cb = $self->[1]{$_[0]}) {
416	$_ && &{$_->[0]}	497	shift;
417	&& undef $_;	498	eval { &$cb }; _self_die if $@;
418	}	499	} else {
419
420	for (@{ $self->{rcv}{$_[0]} }) {
421	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
422	&& &{$_->[0]}	500	&{ $self->[0] };
423	&& undef $_;
424	}
425
426	for (@{ $self->{any} }) {
427	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
428	&& &{$_->[0]}
429	&& undef $_;
430	}	501	}
431	};	502	};
432	_self_die if $@;	503
		504	$self
433	};	505	};
434		506
435	$self
436	};
437
438	"AnyEvent::MP::Port" eq ref $self	507	"AnyEvent::MP::Port" eq ref $self
439	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	508	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
440		509
441	while (@_) {
442	my ($match, $cb) = splice @_, 0, 2;	510	my ($tag, $cb) = splice @_, 0, 2;
443		511
444	if (!ref $match) {	512	if (defined $cb) {
445	push @{ $self->{rc0}{$match} }, [$cb];	513	$self->[1]{$tag} = $cb;
446	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
447	my ($type, @match) = @$match;
448	@match
449	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
450	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
451	} else {	514	} else {
452	push @{ $self->{any} }, [$cb, $match];	515	delete $self->[1]{$tag};
453	}	516	}
454	}	517	}
455	}	518	}
456		519
457	$port	520	$port
458	}	521	}
459		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
460	=item $closure = psub { BLOCK }	560	=item $closure = psub { BLOCK }
461		561
462	Remembers C<$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
463	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>
464	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 $SELF, sub {
		567	BLOCK }, @_ } >>.
465		568
466	This is useful when you register callbacks from C<rcv> callbacks:	569	This is useful when you register callbacks from C<rcv> callbacks:
467		570
468	rcv delayed_reply => sub {	571	rcv delayed_reply => sub {
469	my ($delay, @reply) = @_;	572	my ($delay, @reply) = @_;
…		…
493	$res	596	$res
494	}	597	}
495	}	598	}
496	}	599	}
497		600
498	=item $guard = mon $port, $cb->(@reason)	601	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
499		602
500	=item $guard = mon $port, $rcvport	603	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
501		604
502	=item $guard = mon $port	605	=item $guard = mon $port # kill $SELF when $port dies
503		606
504	=item $guard = mon $port, $rcvport, @msg	607	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
505		608
506	Monitor the given port and do something when the port is killed, and	609	Monitor the given port and do something when the port is killed or
507	optionally return a guard that can be used to stop monitoring again.	610	messages to it were lost, and optionally return a guard that can be used
		611	to stop monitoring again.
508		612
509	In the first form (callback), the callback is simply called with any	613	In the first form (callback), the callback is simply called with any
510	number of C<@reason> elements (no @reason means that the port was deleted	614	number of C<@reason> elements (no @reason means that the port was deleted
511	"normally"). Note also that I<< the callback B<must> never die >>, so use	615	"normally"). Note also that I<< the callback B<must> never die >>, so use
512	C<eval> if unsure.	616	C<eval> if unsure.
513		617
514	In the second form (another port given), the other port (C<$rcvport)	618	In the second form (another port given), the other port (C<$rcvport>)
515	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	619	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
516	"normal" kils nothing happens, while under all other conditions, the other	620	"normal" kils nothing happens, while under all other conditions, the other
517	port is killed with the same reason.	621	port is killed with the same reason.
518		622
519	The third form (kill self) is the same as the second form, except that	623	The third form (kill self) is the same as the second form, except that
520	C<$rvport> defaults to C<$SELF>.	624	C<$rvport> defaults to C<$SELF>.
521		625
522	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
523	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.
524		631
525	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
526	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
527	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
528	even monitoring requests can get lost (for exmaple, when the connection	635	even monitoring requests can get lost (for example, when the connection
529	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
530	these problems do not exist.	637	these problems do not exist.
531		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
532	Example: call a given callback when C<$port> is killed.	656	Example: call a given callback when C<$port> is killed.
533		657
534	mon $port, sub { warn "port died because of <@_>\n" };	658	mon $port, sub { warn "port died because of <@_>\n" };
535		659
536	Example: kill ourselves when C<$port> is killed abnormally.	660	Example: kill ourselves when C<$port> is killed abnormally.
…		…
542	mon $port, $self => "restart";	666	mon $port, $self => "restart";
543		667
544	=cut	668	=cut
545		669
546	sub mon {	670	sub mon {
547	my ($noderef, $port) = split /#/, shift, 2;	671	my ($nodeid, $port) = split /#/, shift, 2;
548		672
549	my $node = $NODE{$noderef} \|\| add_node $noderef;	673	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
550		674
551	my $cb = @_ ? $_[0] : $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,';
552		676
553	unless (ref $cb) {	677	unless (ref $cb) {
554	if (@_) {	678	if (@_) {
555	# send a kill info message	679	# send a kill info message
556	my (@msg) = @_;	680	my (@msg) = ($cb, @_);
557	$cb = sub { snd @msg, @_ };	681	$cb = sub { snd @msg, @_ };
558	} else {	682	} else {
559	# simply kill other port	683	# simply kill other port
560	my $port = $cb;	684	my $port = $cb;
561	$cb = sub { kil $port, @_ if @_ };	685	$cb = sub { kil $port, @_ if @_ };
…		…
563	}	687	}
564		688
565	$node->monitor ($port, $cb);	689	$node->monitor ($port, $cb);
566		690
567	defined wantarray	691	defined wantarray
568	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	692	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
569	}	693	}
570		694
571	=item $guard = mon_guard $port, $ref, $ref...	695	=item $guard = mon_guard $port, $ref, $ref...
572		696
573	Monitors the given C<$port> and keeps the passed references. When the port	697	Monitors the given C<$port> and keeps the passed references. When the port
574	is killed, the references will be freed.	698	is killed, the references will be freed.
575		699
576	Optionally returns a guard that will stop the monitoring.	700	Optionally returns a guard that will stop the monitoring.
577		701
578	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
579	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>):
580		704
581	$port->rcv (start => sub {	705	$port->rcv (start => sub {
582	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	706	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
583	undef $timer if 0.9 < rand;	707	undef $timer if 0.9 < rand;
584	});	708	});
585	});	709	});
586		710
587	=cut	711	=cut
…		…
596		720
597	=item kil $port[, @reason]	721	=item kil $port[, @reason]
598		722
599	Kill the specified port with the given C<@reason>.	723	Kill the specified port with the given C<@reason>.
600		724
601	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" -
602	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.
603		728
604	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>
605	C<mon>, see below).	730	form) get killed with the same reason.
606		731
607	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
608	will be reported as reason C<< die => $@ >>.	733	will be reported as reason C<< die => $@ >>.
609		734
610	Transport/communication errors are reported as C<< transport_error =>	735	Transport/communication errors are reported as C<< transport_error =>
611	$message >>.	736	$message >>.
612		737
613	=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: $!";
614		749
615	=item $port = spawn $node, $initfunc[, @initdata]	750	=item $port = spawn $node, $initfunc[, @initdata]
616		751
617	Creates a port on the node C<$node> (which can also be a port ID, in which	752	Creates a port on the node C<$node> (which can also be a port ID, in which
618	case it's the node where that port resides).	753	case it's the node where that port resides).
619		754
620	The port ID of the newly created port is return immediately, and it is	755	The port ID of the newly created port is returned immediately, and it is
621	permissible to immediately start sending messages or monitor the port.	756	possible to immediately start sending messages or to monitor the port.
622		757
623	After the port has been created, the init function is	758	After the port has been created, the init function is called on the remote
624	called. This function must be a fully-qualified function name	759	node, in the same context as a C<rcv> callback. This function must be a
625	(e.g. C<MyApp::Chat::Server::init>).	760	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		761	specify a function in the main program, use C<::name>.
626		762
627	If the function doesn't exist, then the node tries to C<require>	763	If the function doesn't exist, then the node tries to C<require>
628	the package, then the package above the package and so on (e.g.	764	the package, then the package above the package and so on (e.g.
629	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	765	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
630	exists or it runs out of package names.	766	exists or it runs out of package names.
631		767
632	The init function is then called with the newly-created port as context	768	The init function is then called with the newly-created port as context
633	object (C<$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.
634		772
635	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
636	in the init function, monitor the original port. This two-way monitoring	774	port, and in the remote init function, immediately monitor the passed
637	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<$initfunc> has no visible effects on the
		779	caller before C<spawn> returns (by delaying invocation when spawn is
		780	called for the local node).
638		781
639	Example: spawn a chat server port on C<$othernode>.	782	Example: spawn a chat server port on C<$othernode>.
640		783
641	# this node, executed from within a port context:	784	# this node, executed from within a port context:
642	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	785	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
657		800
658	sub _spawn {	801	sub _spawn {
659	my $port = shift;	802	my $port = shift;
660	my $init = shift;	803	my $init = shift;
661		804
		805	# rcv will create the actual port
662	local $SELF = "$NODE#$port";	806	local $SELF = "$NODE#$port";
663	eval {	807	eval {
664	&{ load_func $init }	808	&{ load_func $init }
665	};	809	};
666	_self_die if $@;	810	_self_die if $@;
667	}	811	}
668		812
669	sub spawn(@) {	813	sub spawn(@) {
670	my ($noderef, undef) = split /#/, shift, 2;	814	my ($nodeid, undef) = split /#/, shift, 2;
671		815
672	my $id = "$RUNIQ." . $ID++;	816	my $id = $RUNIQ . ++$ID;
673		817
674	$_[0] =~ /::/	818	$_[0] =~ /::/
675	or Carp::croak "spawn init function must be a fully-qualified name, caught";	819	or Carp::croak "spawn init function must be a fully-qualified name, caught";
676		820
677	($NODE{$noderef} \|\| add_node $noderef)	821	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
678	->send (["", "AnyEvent::MP::_spawn" => $id, @_]);
679		822
680	"$noderef#$id"	823	"$nodeid#$id"
681	}	824	}
682		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	$port
		903	}
		904
683	=back	905	=back
684		906
685	=head1 NODE MESSAGES	907	=head1 DISTRIBUTED DATABASE
686		908
687	Nodes understand the following messages sent to them. Many of them take	909	AnyEvent::MP comes with a simple distributed database. The database will
688	arguments called C<@reply>, which will simply be used to compose a reply	910	be mirrored asynchronously on all global nodes. Other nodes bind to one
689	message - C<$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"
690	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.
691		914
692	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.:
693		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
694	=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	};
695		1049
696	=cut	1050	=cut
697
698	=item lookup => $name, @reply
699
700	Replies with the port ID of the specified well-known port, or C<undef>.
701
702	=item devnull => ...
703
704	Generic data sink/CPU heat conversion.
705
706	=item relay => $port, @msg
707
708	Simply forwards the message to the given port.
709
710	=item eval => $string[ @reply]
711
712	Evaluates the given string. If C<@reply> is given, then a message of the
713	form C<@reply, $@, @evalres> is sent.
714
715	Example: crash another node.
716
717	snd $othernode, eval => "exit";
718
719	=item time => @reply
720
721	Replies the the current node time to C<@reply>.
722
723	Example: tell the current node to send the current time to C<$myport> in a
724	C<timereply> message.
725
726	snd $NODE, time => $myport, timereply => 1, 2;
727	# => snd $myport, timereply => 1, 2, <time>
728		1051
729	=back	1052	=back
730		1053
731	=head1 AnyEvent::MP vs. Distributed Erlang	1054	=head1 AnyEvent::MP vs. Distributed Erlang
732		1055
733	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
734	== 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
735	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
736	sample:	1059	sample:
737		1060
738	http://www.Erlang.se/doc/programming_rules.shtml	1061	http://www.erlang.se/doc/programming_rules.shtml
739	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
740	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
741	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
742		1065
743	Despite the similarities, there are also some important differences:	1066	Despite the similarities, there are also some important differences:
744		1067
745	=over 4	1068	=over 4
746		1069
747	=item * Node references contain the recipe on how to contact them.	1070	=item * Node IDs are arbitrary strings in AEMP.
748		1071
749	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
750	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
751	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.
752		1076
753	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
754	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.
755		1091
756	=item * Erlang uses processes and a mailbox, AEMP does not queue.	1092	=item * Erlang uses processes and a mailbox, AEMP does not queue.
757		1093
758	Erlang uses processes that selctively receive messages, and therefore	1094	Erlang uses processes that selectively receive messages out of order, and
759	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
760	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.
761		1099
762	(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.
763		1105
764	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1106	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
765		1107
766	Sending messages in Erlang is synchronous and blocks the process. AEMP	1108	Sending messages in Erlang is synchronous and blocks the process until
767	sends are immediate, connection establishment is handled in the	1109	a conenction has been established and the message sent (and so does not
768	background.	1110	need a queue that can overflow). AEMP sends return immediately, connection
		1111	establishment is handled in the background.
769		1112
770	=item * Erlang can silently lose messages, AEMP cannot.	1113	=item * Erlang suffers from silent message loss, AEMP does not.
771		1114
772	Erlang makes few guarantees on messages delivery - messages can get lost	1115	Erlang implements few guarantees on messages delivery - messages can get
773	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,
774	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).
775		1118
776	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
777	holes in the message sequence.	1122	no silent "holes" in the message sequence.
778		1123
779	=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
780	alive.	1125	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
781		1126	simply tries to work better in common error cases, such as when a network
782	In Erlang it can happen that a monitored process is declared dead and	1127	link goes down.
783	linked processes get killed, but later it turns out that the process is
784	still alive - and can receive messages.
785
786	In AEMP, when port monitoring detects a port as dead, then that port will
787	eventually be killed - it cannot happen that a node detects a port as dead
788	and then later sends messages to it, finding it is still alive.
789		1128
790	=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.
791		1130
792	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
793	ID known to other nodes for a completely different process, causing	1132	process ID known to other nodes for a completely different process,
794	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.
795		1135
796	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
797	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.
798		1138
799	=item * Erlang uses unprotected connections, AEMP uses secure	1139	=item * Erlang uses unprotected connections, AEMP uses secure
800	authentication and can use TLS.	1140	authentication and can use TLS.
801		1141
802	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1142	AEMP can use a proven protocol - TLS - to protect connections and
803	securely authenticate nodes.	1143	securely authenticate nodes.
804		1144
805	=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
806	communications.	1146	communications.
807		1147
808	The AEMP protocol, unlike the Erlang protocol, supports both	1148	The AEMP protocol, unlike the Erlang protocol, supports both programming
809	language-independent text-only protocols (good for debugging) and binary,	1149	language independent text-only protocols (good for debugging), and binary,
810	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.
811		1152
812	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
813	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
814	protocol simple.	1155	protocol simple.
815		1156
816	=item * AEMP has more flexible monitoring options than Erlang.	1157	=item * AEMP has more flexible monitoring options than Erlang.
817		1158
818	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
819	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
820	difficult to implement. Monitoring in AEMP is more flexible than in	1161	difficult to implement.
821	Erlang, as one can choose between automatic kill, exit message or callback	1162
822	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.
823		1165
824	=item * Erlang tries to hide remote/local connections, AEMP does not.	1166	=item * Erlang tries to hide remote/local connections, AEMP does not.
825		1167
826	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
827	as linking is (except linking is unreliable in Erlang).	1169	same way as linking is (except linking is unreliable in Erlang).
828		1170
829	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
830	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
831	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
832	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
833	more reliable.	1175	reliable (no need for C<spawn_link>).
834		1176
835	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
836	(hard to do in Erlang).	1178	(hard to do in Erlang).
837		1179
838	=back	1180	=back
839		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
840	=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.
841		1230
842	L<AnyEvent>.	1231	L<AnyEvent>.
843		1232
844	=head1 AUTHOR	1233	=head1 AUTHOR
845		1234

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Revision 1.134 by root, Mon Mar 12 14:47:23 2012 UTC