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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.43 by root, Sun Aug 9 16:08:16 2009 UTC vs.
Revision 1.128 by root, Sun Mar 4 14:28:44 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 $localport, $cb->(@msg) # callback is invoked on death
40	mon $port, $otherport # kill otherport on abnormal death	41	mon $localport, $otherport # kill otherport on abnormal death
41	mon $port, $otherport, @msg # send message on death	42	mon $localport, $otherport, @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 = $AnyEvent::MP::Base::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	sub _kilme {
		404	die "received message on port without callback";
		405	}
		406
303	sub port(;&) {	407	sub port(;&) {
304	my $id = "$UNIQ." . $ID++;	408	my $id = $UNIQ . ++$ID;
305	my $port = "$NODE#$id";	409	my $port = "$NODE#$id";
306		410
307	if (@_) {	411	rcv $port, shift \|\| \&_kilme;
308	rcv $port, shift;
309	} else {
310	$PORT{$id} = sub { }; # nop
311	}
312		412
313	$port	413	$port
314	}	414	}
315		415
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)	416	=item rcv $local_port, $callback->(@msg)
336		417
337	Replaces the callback on the specified miniport (after converting it to	418	Replaces the default callback on the specified port. There is no way to
338	one if required).	419	remove the default callback: use C<sub { }> to disable it, or better
339		420	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...] => $callback->(@msg), ...
345
346	Register callbacks to be called on matching messages on the given full
347	port (after converting it to one if required) and return the port.
348
349	The callback has to return a true value when its work is done, after
350	which is will be removed, or a false value in which case it will stay
351	registered.
352		421
353	The global C<$SELF> (exported by this module) contains C<$port> while	422	The global C<$SELF> (exported by this module) contains C<$port> while
354	executing the callback.	423	executing the callback. Runtime errors during callback execution will
		424	result in the port being C<kil>ed.
355		425
356	Runtime errors during callback execution will result in the port being	426	The default callback received all messages not matched by a more specific
357	C<kil>ed.	427	C<tag> match.
358		428
359	If the match is an array reference, then it will be matched against the	429	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
360	first elements of the message, otherwise only the first element is being
361	matched.
362		430
363	Any element in the match that is specified as C<_any_> (a function	431	Register (or replace) callbacks to be called on messages starting with the
364	exported by this module) matches any single element of the message.	432	given tag on the given port (and return the port), or unregister it (when
		433	C<$callback> is C<$undef> or missing). There can only be one callback
		434	registered for each tag.
365		435
366	While not required, it is highly recommended that the first matching	436	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	437	element (the tag) has been removed. The callback will use the same
368	also the most efficient match (by far).	438	environment as the default callback (see above).
369		439
370	Example: create a port and bind receivers on it in one go.	440	Example: create a port and bind receivers on it in one go.
371		441
372	my $port = rcv port,	442	my $port = rcv port,
373	msg1 => sub { ...; 0 },	443	msg1 => sub { ... },
374	msg2 => sub { ...; 0 },	444	msg2 => sub { ... },
375	;	445	;
376		446
377	Example: create a port, bind receivers and send it in a message elsewhere	447	Example: create a port, bind receivers and send it in a message elsewhere
378	in one go:	448	in one go:
379		449
380	snd $otherport, reply =>	450	snd $otherport, reply =>
381	rcv port,	451	rcv port,
382	msg1 => sub { ...; 0 },	452	msg1 => sub { ... },
383	...	453	...
384	;	454	;
385		455
		456	Example: temporarily register a rcv callback for a tag matching some port
		457	(e.g. for an rpc reply) and unregister it after a message was received.
		458
		459	rcv $port, $otherport => sub {
		460	my @reply = @_;
		461
		462	rcv $SELF, $otherport;
		463	};
		464
386	=cut	465	=cut
387		466
388	sub rcv($@) {	467	sub rcv($@) {
389	my $port = shift;	468	my $port = shift;
390	my ($noderef, $portid) = split /#/, $port, 2;	469	my ($nodeid, $portid) = split /#/, $port, 2;
391		470
392	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	471	$NODE{$nodeid} == $NODE{""}
393	or Carp::croak "$port: rcv can only be called on local ports, caught";	472	or Carp::croak "$port: rcv can only be called on local ports, caught";
394		473
395	if (@_ == 1) {	474	while (@_) {
		475	if (ref $_[0]) {
		476	if (my $self = $PORT_DATA{$portid}) {
		477	"AnyEvent::MP::Port" eq ref $self
		478	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		479
		480	$self->[0] = shift;
		481	} else {
396	my $cb = shift;	482	my $cb = shift;
397	delete $PORT_DATA{$portid};
398	$PORT{$portid} = sub {	483	$PORT{$portid} = sub {
399	local $SELF = $port;	484	local $SELF = $port;
400	eval {	485	eval { &$cb }; _self_die if $@;
401	&$cb	486	};
402	and kil $port;
403	};	487	}
404	_self_die if $@;	488	} elsif (defined $_[0]) {
405	};
406	} else {
407	my $self = $PORT_DATA{$portid} \|\|= do {	489	my $self = $PORT_DATA{$portid} \|\|= do {
408	my $self = bless {	490	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
409	id => $port,
410	}, "AnyEvent::MP::Port";
411		491
412	$PORT{$portid} = sub {	492	$PORT{$portid} = sub {
413	local $SELF = $port;	493	local $SELF = $port;
414		494
415	eval {
416	for (@{ $self->{rc0}{$_[0]} }) {	495	if (my $cb = $self->[1]{$_[0]}) {
417	$_ && &{$_->[0]}	496	shift;
418	&& undef $_;	497	eval { &$cb }; _self_die if $@;
419	}	498	} else {
420
421	for (@{ $self->{rcv}{$_[0]} }) {
422	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
423	&& &{$_->[0]}	499	&{ $self->[0] };
424	&& undef $_;
425	}
426
427	for (@{ $self->{any} }) {
428	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
429	&& &{$_->[0]}
430	&& undef $_;
431	}	500	}
432	};	501	};
433	_self_die if $@;	502
		503	$self
434	};	504	};
435		505
436	$self
437	};
438
439	"AnyEvent::MP::Port" eq ref $self	506	"AnyEvent::MP::Port" eq ref $self
440	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	507	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
441		508
442	while (@_) {
443	my ($match, $cb) = splice @_, 0, 2;	509	my ($tag, $cb) = splice @_, 0, 2;
444		510
445	if (!ref $match) {	511	if (defined $cb) {
446	push @{ $self->{rc0}{$match} }, [$cb];	512	$self->[1]{$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 {	513	} else {
453	push @{ $self->{any} }, [$cb, $match];	514	delete $self->[1]{$tag};
454	}	515	}
455	}	516	}
456	}	517	}
457		518
458	$port	519	$port
459	}	520	}
460		521
		522	=item peval $port, $coderef[, @args]
		523
		524	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		525	when the code throews an exception the C<$port> will be killed.
		526
		527	Any remaining args will be passed to the callback. Any return values will
		528	be returned to the caller.
		529
		530	This is useful when you temporarily want to execute code in the context of
		531	a port.
		532
		533	Example: create a port and run some initialisation code in it's context.
		534
		535	my $port = port { ... };
		536
		537	peval $port, sub {
		538	init
		539	or die "unable to init";
		540	};
		541
		542	=cut
		543
		544	sub peval($$) {
		545	local $SELF = shift;
		546	my $cb = shift;
		547
		548	if (wantarray) {
		549	my @res = eval { &$cb };
		550	_self_die if $@;
		551	@res
		552	} else {
		553	my $res = eval { &$cb };
		554	_self_die if $@;
		555	$res
		556	}
		557	}
		558
461	=item $closure = psub { BLOCK }	559	=item $closure = psub { BLOCK }
462		560
463	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	561	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>	562	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.	563	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		564
		565	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		566	BLOCK }, @_ } >>.
466		567
467	This is useful when you register callbacks from C<rcv> callbacks:	568	This is useful when you register callbacks from C<rcv> callbacks:
468		569
469	rcv delayed_reply => sub {	570	rcv delayed_reply => sub {
470	my ($delay, @reply) = @_;	571	my ($delay, @reply) = @_;
…		…
494	$res	595	$res
495	}	596	}
496	}	597	}
497	}	598	}
498		599
499	=item $guard = mon $port, $cb->(@reason)	600	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
500		601
501	=item $guard = mon $port, $rcvport	602	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
502		603
503	=item $guard = mon $port	604	=item $guard = mon $port # kill $SELF when $port dies
504		605
505	=item $guard = mon $port, $rcvport, @msg	606	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
506		607
507	Monitor the given port and do something when the port is killed or	608	Monitor the given port and do something when the port is killed or
508	messages to it were lost, and optionally return a guard that can be used	609	messages to it were lost, and optionally return a guard that can be used
509	to stop monitoring again.	610	to stop monitoring again.
510
511	C<mon> effectively guarantees that, in the absence of hardware failures,
512	that after starting the monitor, either all messages sent to the port
513	will arrive, or the monitoring action will be invoked after possible
514	message loss has been detected. No messages will be lost "in between"
515	(after the first lost message no further messages will be received by the
516	port). After the monitoring action was invoked, further messages might get
517	delivered again.
518		611
519	In the first form (callback), the callback is simply called with any	612	In the first form (callback), the callback is simply called with any
520	number of C<@reason> elements (no @reason means that the port was deleted	613	number of C<@reason> elements (no @reason means that the port was deleted
521	"normally"). Note also that I<< the callback B<must> never die >>, so use	614	"normally"). Note also that I<< the callback B<must> never die >>, so use
522	C<eval> if unsure.	615	C<eval> if unsure.
523		616
524	In the second form (another port given), the other port (C<$rcvport>)	617	In the second form (another port given), the other port (C<$rcvport>)
525	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	618	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
526	"normal" kils nothing happens, while under all other conditions, the other	619	"normal" kils nothing happens, while under all other conditions, the other
527	port is killed with the same reason.	620	port is killed with the same reason.
528		621
529	The third form (kill self) is the same as the second form, except that	622	The third form (kill self) is the same as the second form, except that
530	C<$rvport> defaults to C<$SELF>.	623	C<$rvport> defaults to C<$SELF>.
531		624
532	In the last form (message), a message of the form C<@msg, @reason> will be	625	In the last form (message), a message of the form C<@msg, @reason> will be
533	C<snd>.	626	C<snd>.
		627
		628	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		629	alert was raised), they are removed and will not trigger again.
534		630
535	As a rule of thumb, monitoring requests should always monitor a port from	631	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	632	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	633	lost, just like any other message. Another less obvious reason is that
538	even monitoring requests can get lost (for exmaple, when the connection	634	even monitoring requests can get lost (for example, when the connection
539	to the other node goes down permanently). When monitoring a port locally	635	to the other node goes down permanently). When monitoring a port locally
540	these problems do not exist.	636	these problems do not exist.
541		637
		638	C<mon> effectively guarantees that, in the absence of hardware failures,
		639	after starting the monitor, either all messages sent to the port will
		640	arrive, or the monitoring action will be invoked after possible message
		641	loss has been detected. No messages will be lost "in between" (after
		642	the first lost message no further messages will be received by the
		643	port). After the monitoring action was invoked, further messages might get
		644	delivered again.
		645
		646	Inter-host-connection timeouts and monitoring depend on the transport
		647	used. The only transport currently implemented is TCP, and AnyEvent::MP
		648	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		649	non-idle connection, and usually around two hours for idle connections).
		650
		651	This means that monitoring is good for program errors and cleaning up
		652	stuff eventually, but they are no replacement for a timeout when you need
		653	to ensure some maximum latency.
		654
542	Example: call a given callback when C<$port> is killed.	655	Example: call a given callback when C<$port> is killed.
543		656
544	mon $port, sub { warn "port died because of <@_>\n" };	657	mon $port, sub { warn "port died because of <@_>\n" };
545		658
546	Example: kill ourselves when C<$port> is killed abnormally.	659	Example: kill ourselves when C<$port> is killed abnormally.
…		…
552	mon $port, $self => "restart";	665	mon $port, $self => "restart";
553		666
554	=cut	667	=cut
555		668
556	sub mon {	669	sub mon {
557	my ($noderef, $port) = split /#/, shift, 2;	670	my ($nodeid, $port) = split /#/, shift, 2;
558		671
559	my $node = $NODE{$noderef} \|\| add_node $noderef;	672	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
560		673
561	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';	674	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
562		675
563	unless (ref $cb) {	676	unless (ref $cb) {
564	if (@_) {	677	if (@_) {
…		…
573	}	686	}
574		687
575	$node->monitor ($port, $cb);	688	$node->monitor ($port, $cb);
576		689
577	defined wantarray	690	defined wantarray
578	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	691	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
579	}	692	}
580		693
581	=item $guard = mon_guard $port, $ref, $ref...	694	=item $guard = mon_guard $port, $ref, $ref...
582		695
583	Monitors the given C<$port> and keeps the passed references. When the port	696	Monitors the given C<$port> and keeps the passed references. When the port
584	is killed, the references will be freed.	697	is killed, the references will be freed.
585		698
586	Optionally returns a guard that will stop the monitoring.	699	Optionally returns a guard that will stop the monitoring.
587		700
588	This function is useful when you create e.g. timers or other watchers and	701	This function is useful when you create e.g. timers or other watchers and
589	want to free them when the port gets killed:	702	want to free them when the port gets killed (note the use of C<psub>):
590		703
591	$port->rcv (start => sub {	704	$port->rcv (start => sub {
592	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	705	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
593	undef $timer if 0.9 < rand;	706	undef $timer if 0.9 < rand;
594	});	707	});
595	});	708	});
596		709
597	=cut	710	=cut
…		…
606		719
607	=item kil $port[, @reason]	720	=item kil $port[, @reason]
608		721
609	Kill the specified port with the given C<@reason>.	722	Kill the specified port with the given C<@reason>.
610		723
611	If no C<@reason> is specified, then the port is killed "normally" (linked	724	If no C<@reason> is specified, then the port is killed "normally" -
612	ports will not be kileld, or even notified).	725	monitor callback will be invoked, but the kil will not cause linked ports
		726	(C<mon $mport, $lport> form) to get killed.
613		727
614	Otherwise, linked ports get killed with the same reason (second form of	728	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
615	C<mon>, see below).	729	form) get killed with the same reason.
616		730
617	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	731	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
618	will be reported as reason C<< die => $@ >>.	732	will be reported as reason C<< die => $@ >>.
619		733
620	Transport/communication errors are reported as C<< transport_error =>	734	Transport/communication errors are reported as C<< transport_error =>
…		…
625	=item $port = spawn $node, $initfunc[, @initdata]	739	=item $port = spawn $node, $initfunc[, @initdata]
626		740
627	Creates a port on the node C<$node> (which can also be a port ID, in which	741	Creates a port on the node C<$node> (which can also be a port ID, in which
628	case it's the node where that port resides).	742	case it's the node where that port resides).
629		743
630	The port ID of the newly created port is return immediately, and it is	744	The port ID of the newly created port is returned immediately, and it is
631	permissible to immediately start sending messages or monitor the port.	745	possible to immediately start sending messages or to monitor the port.
632		746
633	After the port has been created, the init function is	747	After the port has been created, the init function is called on the remote
634	called. This function must be a fully-qualified function name	748	node, in the same context as a C<rcv> callback. This function must be a
635	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	749	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
636	program, use C<::name>.	750	specify a function in the main program, use C<::name>.
637		751
638	If the function doesn't exist, then the node tries to C<require>	752	If the function doesn't exist, then the node tries to C<require>
639	the package, then the package above the package and so on (e.g.	753	the package, then the package above the package and so on (e.g.
640	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	754	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
641	exists or it runs out of package names.	755	exists or it runs out of package names.
642		756
643	The init function is then called with the newly-created port as context	757	The init function is then called with the newly-created port as context
644	object (C<$SELF>) and the C<@initdata> values as arguments.	758	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		759	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		760	the port might not get created.
645		761
646	A common idiom is to pass your own port, monitor the spawned port, and	762	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	763	port, and in the remote init function, immediately monitor the passed
648	ensures that both ports get cleaned up when there is a problem.	764	local port. This two-way monitoring ensures that both ports get cleaned up
		765	when there is a problem.
		766
		767	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		768	caller before C<spawn> returns (by delaying invocation when spawn is
		769	called for the local node).
649		770
650	Example: spawn a chat server port on C<$othernode>.	771	Example: spawn a chat server port on C<$othernode>.
651		772
652	# this node, executed from within a port context:	773	# this node, executed from within a port context:
653	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	774	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
668		789
669	sub _spawn {	790	sub _spawn {
670	my $port = shift;	791	my $port = shift;
671	my $init = shift;	792	my $init = shift;
672		793
		794	# rcv will create the actual port
673	local $SELF = "$NODE#$port";	795	local $SELF = "$NODE#$port";
674	eval {	796	eval {
675	&{ load_func $init }	797	&{ load_func $init }
676	};	798	};
677	_self_die if $@;	799	_self_die if $@;
678	}	800	}
679		801
680	sub spawn(@) {	802	sub spawn(@) {
681	my ($noderef, undef) = split /#/, shift, 2;	803	my ($nodeid, undef) = split /#/, shift, 2;
682		804
683	my $id = "$RUNIQ." . $ID++;	805	my $id = $RUNIQ . ++$ID;
684		806
685	$_[0] =~ /::/	807	$_[0] =~ /::/
686	or Carp::croak "spawn init function must be a fully-qualified name, caught";	808	or Carp::croak "spawn init function must be a fully-qualified name, caught";
687		809
688	($NODE{$noderef} \|\| add_node $noderef)	810	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
689	->send (["", "AnyEvent::MP::_spawn" => $id, @_]);
690		811
691	"$noderef#$id"	812	"$nodeid#$id"
692	}	813	}
693		814
		815
		816	=item after $timeout, @msg
		817
		818	=item after $timeout, $callback
		819
		820	Either sends the given message, or call the given callback, after the
		821	specified number of seconds.
		822
		823	This is simply a utility function that comes in handy at times - the
		824	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		825	so it may go away in the future.
		826
		827	=cut
		828
		829	sub after($@) {
		830	my ($timeout, @action) = @_;
		831
		832	my $t; $t = AE::timer $timeout, 0, sub {
		833	undef $t;
		834	ref $action[0]
		835	? $action[0]()
		836	: snd @action;
		837	};
		838	}
		839
		840	=item cal $port, @msg, $callback[, $timeout]
		841
		842	A simple form of RPC - sends a message to the given C<$port> with the
		843	given contents (C<@msg>), but adds a reply port to the message.
		844
		845	The reply port is created temporarily just for the purpose of receiving
		846	the reply, and will be C<kil>ed when no longer needed.
		847
		848	A reply message sent to the port is passed to the C<$callback> as-is.
		849
		850	If an optional time-out (in seconds) is given and it is not C<undef>,
		851	then the callback will be called without any arguments after the time-out
		852	elapsed and the port is C<kil>ed.
		853
		854	If no time-out is given (or it is C<undef>), then the local port will
		855	monitor the remote port instead, so it eventually gets cleaned-up.
		856
		857	Currently this function returns the temporary port, but this "feature"
		858	might go in future versions unless you can make a convincing case that
		859	this is indeed useful for something.
		860
		861	=cut
		862
		863	sub cal(@) {
		864	my $timeout = ref $_[-1] ? undef : pop;
		865	my $cb = pop;
		866
		867	my $port = port {
		868	undef $timeout;
		869	kil $SELF;
		870	&$cb;
		871	};
		872
		873	if (defined $timeout) {
		874	$timeout = AE::timer $timeout, 0, sub {
		875	undef $timeout;
		876	kil $port;
		877	$cb->();
		878	};
		879	} else {
		880	mon $_[0], sub {
		881	kil $port;
		882	$cb->();
		883	};
		884	}
		885
		886	push @_, $port;
		887	&snd;
		888
		889	$port
		890	}
		891
694	=back	892	=back
695		893
696	=head1 NODE MESSAGES	894	=head1 DISTRIBUTED DATABASE
697		895
698	Nodes understand the following messages sent to them. Many of them take	896	AnyEvent::MP comes with a simple distributed database. The database will
699	arguments called C<@reply>, which will simply be used to compose a reply	897	be mirrored asynchronously at all global nodes. Other nodes bind to one of
700	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and	898	the global nodes for their needs.
701	the remaining arguments are simply the message data.
702		899
703	While other messages exist, they are not public and subject to change.	900	The database consists of a two-level hash - a hash contains a hash which
		901	contains values.
704		902
		903	The top level hash key is called "family", and the second-level hash key
		904	is called "subkey" or simply "key".
		905
		906	The family must be alphanumeric, i.e. start with a letter and consist
		907	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		908	pretty much like Perl module names.
		909
		910	As the family namespace is global, it is recommended to prefix family names
		911	with the name of the application or module using it.
		912
		913	The subkeys must be non-empty strings, with no further restrictions.
		914
		915	The values should preferably be strings, but other perl scalars should
		916	work as well (such as undef, arrays and hashes).
		917
		918	Every database entry is owned by one node - adding the same family/subkey
		919	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		920	but the result might be nondeterministic, i.e. the key might have
		921	different values on different nodes.
		922
		923	Different subkeys in the same family can be owned by different nodes
		924	without problems, and in fact, this is the common method to create worker
		925	pools. For example, a worker port for image scaling might do this:
		926
		927	db_set my_image_scalers => $port;
		928
		929	And clients looking for an image scaler will want to get the
		930	C<my_image_scalers> keys:
		931
		932	db_keys "my_image_scalers" => 60 => sub {
		933	#d##TODO#
		934
705	=over 4	935	=over
706		936
707	=cut	937	=item db_set $family => $subkey [=> $value]
708		938
709	=item lookup => $name, @reply	939	Sets (or replaces) a key to the database - if C<$value> is omitted,
		940	C<undef> is used instead.
710		941
711	Replies with the port ID of the specified well-known port, or C<undef>.	942	=item db_del $family => $subkey
712		943
713	=item devnull => ...	944	Deletes a key from the database.
714		945
715	Generic data sink/CPU heat conversion.	946	=item $guard = db_reg $family => $subkey [=> $value]
716		947
717	=item relay => $port, @msg	948	Sets the key on the database and returns a guard. When the guard is
		949	destroyed, the key is deleted from the database. If C<$value> is missing,
		950	then C<undef> is used.
718		951
719	Simply forwards the message to the given port.	952	=item $guard = db_mon $family => $cb->($familyhash, \@subkeys...)
720		953
721	=item eval => $string[ @reply]	954	Creates a monitor on the given database family. Each time a key is set or
		955	or is deleted the callback is called with a hash containing the database
		956	family and an arrayref with subkeys that have changed.
722		957
723	Evaluates the given string. If C<@reply> is given, then a message of the	958	Specifically, if one of the passed subkeys exists in the $familyhash, then
724	form C<@reply, $@, @evalres> is sent.	959	it is currently set to the value in the $familyhash. Otherwise, it has
		960	been deleted.
725		961
726	Example: crash another node.	962	The first call will be with the current contents of the family and all
		963	keys, as if they were just added.
727		964
728	snd $othernode, eval => "exit";	965	It is possible that the callback is called with a change event even though
		966	the subkey is already present and the value has not changed.
729		967
730	=item time => @reply	968	The monitoring stops when the guard object is destroyed.
731		969
732	Replies the the current node time to C<@reply>.	970	Example: on every change to the family "mygroup", print out all keys.
733		971
734	Example: tell the current node to send the current time to C<$myport> in a	972	my $guard = db_mon mygroup => sub {
735	C<timereply> message.	973	my ($family, $keys) = @_;
		974	print "mygroup members: ", (join " ", keys %$family), "\n";
		975	};
736		976
737	snd $NODE, time => $myport, timereply => 1, 2;	977	Exmaple: wait until the family "My::Module::workers" is non-empty.
738	# => snd $myport, timereply => 1, 2, <time>	978
		979	my $guard; $guard = db_mon My::Module::workers => sub {
		980	my ($family, $keys) = @_;
		981	return unless %$family;
		982	undef $guard;
		983	print "My::Module::workers now nonempty\n";
		984	};
		985
		986	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		987
		988	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		989	my ($family, $keys) = @_;
		990
		991	for (@$keys) {
		992	print "$_: ",
		993	(exists $family->{$_}
		994	? $family->{$_}
		995	: "(deleted)"),
		996	"\n";
		997	}
		998	};
		999
		1000	=cut
739		1001
740	=back	1002	=back
741		1003
742	=head1 AnyEvent::MP vs. Distributed Erlang	1004	=head1 AnyEvent::MP vs. Distributed Erlang
743		1005
744	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	1006	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	1007	== 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	1008	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
747	sample:	1009	sample:
748		1010
749	http://www.Erlang.se/doc/programming_rules.shtml	1011	http://www.erlang.se/doc/programming_rules.shtml
750	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	1012	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	1013	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	1014	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
753		1015
754	Despite the similarities, there are also some important differences:	1016	Despite the similarities, there are also some important differences:
755		1017
756	=over 4	1018	=over 4
757		1019
758	=item * Node references contain the recipe on how to contact them.	1020	=item * Node IDs are arbitrary strings in AEMP.
759		1021
760	Erlang relies on special naming and DNS to work everywhere in the	1022	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	1023	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
762	convenience functionality.	1024	configuration or DNS), and possibly the addresses of some seed nodes, but
		1025	will otherwise discover other nodes (and their IDs) itself.
763		1026
764	This means that AEMP requires a less tightly controlled environment at the	1027	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
765	cost of longer node references and a slightly higher management overhead.	1028	uses "local ports are like remote ports".
		1029
		1030	The failure modes for local ports are quite different (runtime errors
		1031	only) then for remote ports - when a local port dies, you I<know> it dies,
		1032	when a connection to another node dies, you know nothing about the other
		1033	port.
		1034
		1035	Erlang pretends remote ports are as reliable as local ports, even when
		1036	they are not.
		1037
		1038	AEMP encourages a "treat remote ports differently" philosophy, with local
		1039	ports being the special case/exception, where transport errors cannot
		1040	occur.
766		1041
767	=item * Erlang uses processes and a mailbox, AEMP does not queue.	1042	=item * Erlang uses processes and a mailbox, AEMP does not queue.
768		1043
769	Erlang uses processes that selctively receive messages, and therefore	1044	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	1045	therefore needs a queue. AEMP is event based, queuing messages would serve
771	purpose.	1046	no useful purpose. For the same reason the pattern-matching abilities
		1047	of AnyEvent::MP are more limited, as there is little need to be able to
		1048	filter messages without dequeuing them.
772		1049
773	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	1050	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1051	being event-based, while Erlang is process-based.
		1052
		1053	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1054	top of AEMP and Coro threads.
774		1055
775	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1056	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
776		1057
777	Sending messages in Erlang is synchronous and blocks the process. AEMP	1058	Sending messages in Erlang is synchronous and blocks the process until
778	sends are immediate, connection establishment is handled in the	1059	a conenction has been established and the message sent (and so does not
779	background.	1060	need a queue that can overflow). AEMP sends return immediately, connection
		1061	establishment is handled in the background.
780		1062
781	=item * Erlang can silently lose messages, AEMP cannot.	1063	=item * Erlang suffers from silent message loss, AEMP does not.
782		1064
783	Erlang makes few guarantees on messages delivery - messages can get lost	1065	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,	1066	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).	1067	b, and c, and the other side only receives messages a and c).
786		1068
787	AEMP guarantees correct ordering, and the guarantee that there are no	1069	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1070	guarantee that after one message is lost, all following ones sent to the
		1071	same port are lost as well, until monitoring raises an error, so there are
788	holes in the message sequence.	1072	no silent "holes" in the message sequence.
789		1073
790	=item * In Erlang, processes can be declared dead and later be found to be	1074	If you want your software to be very reliable, you have to cope with
791	alive.	1075	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
792		1076	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	1077	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		1078
801	=item * Erlang can send messages to the wrong port, AEMP does not.	1079	=item * Erlang can send messages to the wrong port, AEMP does not.
802		1080
803	In Erlang it is quite possible that a node that restarts reuses a process	1081	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	1082	process ID known to other nodes for a completely different process,
805	messages destined for that process to end up in an unrelated process.	1083	causing messages destined for that process to end up in an unrelated
		1084	process.
806		1085
807	AEMP never reuses port IDs, so old messages or old port IDs floating	1086	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.	1087	around in the network will not be sent to an unrelated port.
809		1088
810	=item * Erlang uses unprotected connections, AEMP uses secure	1089	=item * Erlang uses unprotected connections, AEMP uses secure
811	authentication and can use TLS.	1090	authentication and can use TLS.
812		1091
813	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1092	AEMP can use a proven protocol - TLS - to protect connections and
814	securely authenticate nodes.	1093	securely authenticate nodes.
815		1094
816	=item * The AEMP protocol is optimised for both text-based and binary	1095	=item * The AEMP protocol is optimised for both text-based and binary
817	communications.	1096	communications.
818		1097
819	The AEMP protocol, unlike the Erlang protocol, supports both	1098	The AEMP protocol, unlike the Erlang protocol, supports both programming
820	language-independent text-only protocols (good for debugging) and binary,	1099	language independent text-only protocols (good for debugging), and binary,
821	language-specific serialisers (e.g. Storable).	1100	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1101	used, the protocol is actually completely text-based.
822		1102
823	It has also been carefully designed to be implementable in other languages	1103	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	1104	with a minimum of work while gracefully degrading functionality to make the
825	protocol simple.	1105	protocol simple.
826		1106
827	=item * AEMP has more flexible monitoring options than Erlang.	1107	=item * AEMP has more flexible monitoring options than Erlang.
828		1108
829	In Erlang, you can chose to receive I<all> exit signals as messages	1109	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	1110	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	1111	difficult to implement.
832	Erlang, as one can choose between automatic kill, exit message or callback	1112
833	on a per-process basis.	1113	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1114	between automatic kill, exit message or callback on a per-port basis.
834		1115
835	=item * Erlang tries to hide remote/local connections, AEMP does not.	1116	=item * Erlang tries to hide remote/local connections, AEMP does not.
836		1117
837	Monitoring in Erlang is not an indicator of process death/crashes,	1118	Monitoring in Erlang is not an indicator of process death/crashes, in the
838	as linking is (except linking is unreliable in Erlang).	1119	same way as linking is (except linking is unreliable in Erlang).
839		1120
840	In AEMP, you don't "look up" registered port names or send to named ports	1121	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	1122	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	1123	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	1124	remote port. Since both monitors are local to the node, they are much more
844	more reliable.	1125	reliable (no need for C<spawn_link>).
845		1126
846	This also saves round-trips and avoids sending messages to the wrong port	1127	This also saves round-trips and avoids sending messages to the wrong port
847	(hard to do in Erlang).	1128	(hard to do in Erlang).
848		1129
849	=back	1130	=back
850		1131
		1132	=head1 RATIONALE
		1133
		1134	=over 4
		1135
		1136	=item Why strings for port and node IDs, why not objects?
		1137
		1138	We considered "objects", but found that the actual number of methods
		1139	that can be called are quite low. Since port and node IDs travel over
		1140	the network frequently, the serialising/deserialising would add lots of
		1141	overhead, as well as having to keep a proxy object everywhere.
		1142
		1143	Strings can easily be printed, easily serialised etc. and need no special
		1144	procedures to be "valid".
		1145
		1146	And as a result, a port with just a default receiver consists of a single
		1147	code reference stored in a global hash - it can't become much cheaper.
		1148
		1149	=item Why favour JSON, why not a real serialising format such as Storable?
		1150
		1151	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1152	format, but currently there is no way to make a node use Storable by
		1153	default (although all nodes will accept it).
		1154
		1155	The default framing protocol is JSON because a) JSON::XS is many times
		1156	faster for small messages and b) most importantly, after years of
		1157	experience we found that object serialisation is causing more problems
		1158	than it solves: Just like function calls, objects simply do not travel
		1159	easily over the network, mostly because they will always be a copy, so you
		1160	always have to re-think your design.
		1161
		1162	Keeping your messages simple, concentrating on data structures rather than
		1163	objects, will keep your messages clean, tidy and efficient.
		1164
		1165	=back
		1166
851	=head1 SEE ALSO	1167	=head1 SEE ALSO
		1168
		1169	L<AnyEvent::MP::Intro> - a gentle introduction.
		1170
		1171	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1172
		1173	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1174	your applications.
		1175
		1176	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1177
		1178	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1179	all nodes.
852		1180
853	L<AnyEvent>.	1181	L<AnyEvent>.
854		1182
855	=head1 AUTHOR	1183	=head1 AUTHOR
856		1184

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Revision 1.43 by root, Sun Aug 9 16:08:16 2009 UTC vs.
Revision 1.128 by root, Sun Mar 4 14:28:44 2012 UTC