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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.36 by root, Thu Aug 6 10:46:48 2009 UTC vs.
Revision 1.125 by root, Sat Mar 3 13:07:19 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
		12	$SELF # receiving/own port id in rcv callbacks
		13
		14	# initialise the node so it can send/receive messages
		15	configure;
		16
		17	# ports are message destinations
		18
		19	# sending messages
13	snd $port, type => data...;	20	snd $port, type => data...;
		21	snd $port, @msg;
		22	snd @msg_with_first_element_being_a_port;
14		23
15	$SELF # receiving/own port id in rcv callbacks	24	# creating/using ports, the simple way
		25	my $simple_port = port { my @msg = @_ };
16		26
17	rcv $port, smartmatch => $cb->($port, @msg);	27	# creating/using ports, tagged message matching
18		28	my $port = port;
19	# examples:
20	rcv $port2, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
21	rcv $port1, pong => sub { warn "pong received\n" };	30	rcv $port, pong => sub { warn "pong received\n" };
22	snd $port2, ping => $port1;
23		31
24	# more, smarter, matches (_any_ is exported by this module)	32	# create a port on another node
25	rcv $port, [child_died => $pid] => sub { ...	33	my $port = spawn $node, $initfunc, @initdata;
26	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3
27		34
28	# linking two ports, so they both crash together	35	# destroy a port again
29	lnk $port1, $port2;	36	kil $port; # "normal" kill
		37	kil $port, my_error => "everything is broken"; # error kill
30		38
31	# monitoring	39	# monitoring
32	mon $port, $cb->(@msg) # callback is invoked on death	40	mon $localport, $cb->(@msg) # callback is invoked on death
33	mon $port, $otherport # kill otherport on abnormal death	41	mon $localport, $otherport # kill otherport on abnormal death
34	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.
35		59
36	=head1 DESCRIPTION	60	=head1 DESCRIPTION
37		61
38	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
39		63
40	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
41	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
42		66
43	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>
44	manual page.	68	manual page and the examples under F<eg/>.
45
46	At the moment, this module family is severly broken and underdocumented,
47	so do not use. This was uploaded mainly to reserve the CPAN namespace -
48	stay tuned! The basic API should be finished, however.
49		69
50	=head1 CONCEPTS	70	=head1 CONCEPTS
51		71
52	=over 4	72	=over 4
53		73
54	=item port	74	=item port
55		75
56	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).
57		78
58	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
59	messages. All C<rcv> handlers will receive messages they match, messages	80	some messages. Messages send to ports will not be queued, regardless of
60	will not be queued.	81	anything was listening for them or not.
61		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
62	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
63		86
64	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<#>)
65	separator, and a port name (a printable string of unspecified format). An	88	as separator, and a port name (a printable string of unspecified
66	exception is the the node port, whose ID is identical to its node	89	format created by AnyEvent::MP).
67	reference.
68		90
69	=item node	91	=item node
70		92
71	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,
72	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
73	create new ports, among other things.	95	ports.
74		96
75	Nodes are either private (single-process only), slaves (connected to a	97	Nodes are either public (have one or more listening ports) or private
76	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.
77		100
78	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	101	Nodes is represented by (printable) strings called "node IDs".
79		102
80	A node reference is a string that either simply identifies the node (for	103	=item node ID - C<[A-Za-z0-9_\-.:]*>
81	private and slave nodes), or contains a recipe on how to reach a given
82	node (for public nodes).
83		104
84	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
85	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.
86		109
87	Node references come in two flavours: resolved (containing only numerical	110	=item binds - C<ip:port>
88	addresses) or unresolved (where hostnames are used instead of addresses).
89		111
90	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
91	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).
92		170
93	=back	171	=back
94		172
95	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
96		174
98		176
99	=cut	177	=cut
100		178
101	package AnyEvent::MP;	179	package AnyEvent::MP;
102		180
		181	use AnyEvent::MP::Config ();
103	use AnyEvent::MP::Base;	182	use AnyEvent::MP::Kernel;
		183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
104		184
105	use common::sense;	185	use common::sense;
106		186
107	use Carp ();	187	use Carp ();
108		188
109	use AE ();	189	use AE ();
		190	use Guard ();
110		191
111	use base "Exporter";	192	use base "Exporter";
112		193
113	our $VERSION = '0.1';	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
		195
114	our @EXPORT = qw(	196	our @EXPORT = qw(
115	NODE $NODE *SELF node_of _any_	197	NODE $NODE *SELF node_of after
116	resolve_node initialise_node	198	configure
117	snd rcv mon kil reg psub	199	snd rcv mon mon_guard kil psub peval spawn cal
118	port	200	port
		201	db_set db_del db_reg
119	);	202	);
120		203
121	our $SELF;	204	our $SELF;
122		205
123	sub _self_die() {	206	sub _self_die() {
…		…
126	kil $SELF, die => $msg;	209	kil $SELF, die => $msg;
127	}	210	}
128		211
129	=item $thisnode = NODE / $NODE	212	=item $thisnode = NODE / $NODE
130		213
131	The C<NODE> function returns, and the C<$NODE> variable contains	214	The C<NODE> function returns, and the C<$NODE> variable contains, the node
132	the noderef of the local node. The value is initialised by a call	215	ID of the node running in the current process. This value is initialised by
133	to C<become_public> or C<become_slave>, after which all local port	216	a call to C<configure>.
134	identifiers become invalid.
135		217
136	=item $noderef = node_of $port	218	=item $nodeid = node_of $port
137		219
138	Extracts and returns the noderef from a portid or a noderef.	220	Extracts and returns the node ID from a port ID or a node ID.
139		221
140	=item initialise_node $noderef, $seednode, $seednode...	222	=item configure $profile, key => value...
141		223
142	=item initialise_node "slave/", $master, $master...	224	=item configure key => value...
143		225
144	Before a node can talk to other nodes on the network it has to initialise	226	Before a node can talk to other nodes on the network (i.e. enter
145	itself - the minimum a node needs to know is it's own name, and optionally	227	"distributed mode") it has to configure itself - the minimum a node needs
146	it should know the noderefs of some other nodes in the network.	228	to know is its own name, and optionally it should know the addresses of
		229	some other nodes in the network to discover other nodes.
147		230
148	This function initialises a node - it must be called exactly once (or	231	This function configures a node - it must be called exactly once (or
149	never) before calling other AnyEvent::MP functions.	232	never) before calling other AnyEvent::MP functions.
150		233
151	All arguments are noderefs, which can be either resolved or unresolved.	234	The key/value pairs are basically the same ones as documented for the
152		235	F<aemp> command line utility (sans the set/del prefix), with two additions:
153	There are two types of networked nodes, public nodes and slave nodes:
154		236
155	=over 4	237	=over 4
156		238
157	=item public nodes	239	=item norc => $boolean (default false)
158		240
159	For public nodes, C<$noderef> must either be a (possibly unresolved)	241	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
160	noderef, in which case it will be resolved, or C<undef> (or missing), in	242	be consulted - all configuraiton options must be specified in the
161	which case the noderef will be guessed.	243	C<configure> call.
162		244
163	Afterwards, the node will bind itself on all endpoints and try to connect	245	=item force => $boolean (default false)
164	to all additional C<$seednodes> that are specified. Seednodes are optional
165	and can be used to quickly bootstrap the node into an existing network.
166		246
167	=item slave nodes	247	IF true, then the values specified in the C<configure> will take
168		248	precedence over any values configured via the rc file. The default is for
169	When the C<$noderef> is the special string C<slave/>, then the node will	249	the rc file to override any options specified in the program.
170	become a slave node. Slave nodes cannot be contacted from outside and will
171	route most of their traffic to the master node that they attach to.
172
173	At least one additional noderef is required: The node will try to connect
174	to all of them and will become a slave attached to the first node it can
175	successfully connect to.
176		250
177	=back	251	=back
178		252
179	This function will block until all nodes have been resolved and, for slave
180	nodes, until it has successfully established a connection to a master
181	server.
182
183	Example: become a public node listening on the default node.
184
185	initialise_node;
186
187	Example: become a public node, and try to contact some well-known master
188	servers to become part of the network.
189
190	initialise_node undef, "master1", "master2";
191
192	Example: become a public node listening on port C<4041>.
193
194	initialise_node 4041;
195
196	Example: become a public node, only visible on localhost port 4044.
197
198	initialise_node "locahost:4044";
199
200	Example: become a slave node to any of the specified master servers.
201
202	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
203
204	=item $cv = resolve_node $noderef
205
206	Takes an unresolved node reference that may contain hostnames and
207	abbreviated IDs, resolves all of them and returns a resolved node
208	reference.
209
210	In addition to C<address:port> pairs allowed in resolved noderefs, the
211	following forms are supported:
212
213	=over 4	253	=over 4
214		254
215	=item the empty string	255	=item step 1, gathering configuration from profiles
216		256
217	An empty-string component gets resolved as if the default port (4040) was	257	The function first looks up a profile in the aemp configuration (see the
218	specified.	258	L<aemp> commandline utility). The profile name can be specified via the
		259	named C<profile> parameter or can simply be the first parameter). If it is
		260	missing, then the nodename (F<uname -n>) will be used as profile name.
219		261
220	=item naked port numbers (e.g. C<1234>)	262	The profile data is then gathered as follows:
221		263
222	These are resolved by prepending the local nodename and a colon, to be	264	First, all remaining key => value pairs (all of which are conveniently
223	further resolved.	265	undocumented at the moment) will be interpreted as configuration
		266	data. Then they will be overwritten by any values specified in the global
		267	default configuration (see the F<aemp> utility), then the chain of
		268	profiles chosen by the profile name (and any C<parent> attributes).
224		269
225	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	270	That means that the values specified in the profile have highest priority
		271	and the values specified directly via C<configure> have lowest priority,
		272	and can only be used to specify defaults.
226		273
227	These are resolved by using AnyEvent::DNS to resolve them, optionally	274	If the profile specifies a node ID, then this will become the node ID of
228	looking up SRV records for the C<aemp=4040> port, if no port was	275	this process. If not, then the profile name will be used as node ID, with
229	specified.	276	a slash (C</>) attached.
		277
		278	If the node ID (or profile name) ends with a slash (C</>), then a random
		279	string is appended to make it unique.
		280
		281	=item step 2, bind listener sockets
		282
		283	The next step is to look up the binds in the profile, followed by binding
		284	aemp protocol listeners on all binds specified (it is possible and valid
		285	to have no binds, meaning that the node cannot be contacted form the
		286	outside. This means the node cannot talk to other nodes that also have no
		287	binds, but it can still talk to all "normal" nodes).
		288
		289	If the profile does not specify a binds list, then a default of C<*> is
		290	used, meaning the node will bind on a dynamically-assigned port on every
		291	local IP address it finds.
		292
		293	=item step 3, connect to seed nodes
		294
		295	As the last step, the seed ID list from the profile is passed to the
		296	L<AnyEvent::MP::Global> module, which will then use it to keep
		297	connectivity with at least one node at any point in time.
230		298
231	=back	299	=back
		300
		301	Example: become a distributed node using the local node name as profile.
		302	This should be the most common form of invocation for "daemon"-type nodes.
		303
		304	configure
		305
		306	Example: become an anonymous node. This form is often used for commandline
		307	clients.
		308
		309	configure nodeid => "anon/";
		310
		311	Example: configure a node using a profile called seed, which is suitable
		312	for a seed node as it binds on all local addresses on a fixed port (4040,
		313	customary for aemp).
		314
		315	# use the aemp commandline utility
		316	# aemp profile seed binds '*:4040'
		317
		318	# then use it
		319	configure profile => "seed";
		320
		321	# or simply use aemp from the shell again:
		322	# aemp run profile seed
		323
		324	# or provide a nicer-to-remember nodeid
		325	# aemp run profile seed nodeid "$(hostname)"
232		326
233	=item $SELF	327	=item $SELF
234		328
235	Contains the current port id while executing C<rcv> callbacks or C<psub>	329	Contains the current port id while executing C<rcv> callbacks or C<psub>
236	blocks.	330	blocks.
237		331
238	=item SELF, %SELF, @SELF...	332	=item *SELF, SELF, %SELF, @SELF...
239		333
240	Due to some quirks in how perl exports variables, it is impossible to	334	Due to some quirks in how perl exports variables, it is impossible to
241	just export C<$SELF>, all the symbols called C<SELF> are exported by this	335	just export C<$SELF>, all the symbols named C<SELF> are exported by this
242	module, but only C<$SELF> is currently used.	336	module, but only C<$SELF> is currently used.
243		337
244	=item snd $port, type => @data	338	=item snd $port, type => @data
245		339
246	=item snd $port, @msg	340	=item snd $port, @msg
247		341
248	Send the given message to the given port ID, which can identify either	342	Send the given message to the given port, which can identify either a
249	a local or a remote port, and can be either a string or soemthignt hat	343	local or a remote port, and must be a port ID.
250	stringifies a sa port ID (such as a port object :).
251		344
252	While the message can be about anything, it is highly recommended to use a	345	While the message can be almost anything, it is highly recommended to
253	string as first element (a portid, or some word that indicates a request	346	use a string as first element (a port ID, or some word that indicates a
254	type etc.).	347	request type etc.) and to consist if only simple perl values (scalars,
		348	arrays, hashes) - if you think you need to pass an object, think again.
255		349
256	The message data effectively becomes read-only after a call to this	350	The message data logically becomes read-only after a call to this
257	function: modifying any argument is not allowed and can cause many	351	function: modifying any argument (or values referenced by them) is
258	problems.	352	forbidden, as there can be considerable time between the call to C<snd>
		353	and the time the message is actually being serialised - in fact, it might
		354	never be copied as within the same process it is simply handed to the
		355	receiving port.
259		356
260	The type of data you can transfer depends on the transport protocol: when	357	The type of data you can transfer depends on the transport protocol: when
261	JSON is used, then only strings, numbers and arrays and hashes consisting	358	JSON is used, then only strings, numbers and arrays and hashes consisting
262	of those are allowed (no objects). When Storable is used, then anything	359	of those are allowed (no objects). When Storable is used, then anything
263	that Storable can serialise and deserialise is allowed, and for the local	360	that Storable can serialise and deserialise is allowed, and for the local
264	node, anything can be passed.	361	node, anything can be passed. Best rely only on the common denominator of
		362	these.
265		363
266	=item $local_port = port	364	=item $local_port = port
267		365
268	Create a new local port object that can be used either as a pattern	366	Create a new local port object and returns its port ID. Initially it has
269	matching port ("full port") or a single-callback port ("miniport"),	367	no callbacks set and will throw an error when it receives messages.
270	depending on how C<rcv> callbacks are bound to the object.
271		368
272	=item $port = port { my @msg = @_; $finished }	369	=item $local_port = port { my @msg = @_ }
273		370
274	Creates a "miniport", that is, a very lightweight port without any pattern	371	Creates a new local port, and returns its ID. Semantically the same as
275	matching behind it, and returns its ID. Semantically the same as creating
276	a port and calling C<rcv $port, $callback> on it.	372	creating a port and calling C<rcv $port, $callback> on it.
277		373
278	The block will be called for every message received on the port. When the	374	The block will be called for every message received on the port, with the
279	callback returns a true value its job is considered "done" and the port	375	global variable C<$SELF> set to the port ID. Runtime errors will cause the
280	will be destroyed. Otherwise it will stay alive.	376	port to be C<kil>ed. The message will be passed as-is, no extra argument
		377	(i.e. no port ID) will be passed to the callback.
281		378
282	The message will be passed as-is, no extra argument (i.e. no port id) will	379	If you want to stop/destroy the port, simply C<kil> it:
283	be passed to the callback.
284		380
285	If you need the local port id in the callback, this works nicely:	381	my $port = port {
286		382	my @msg = @_;
287	my $port; $port = port {	383	...
288	snd $otherport, reply => $port;	384	kil $SELF;
289	};	385	};
290		386
291	=cut	387	=cut
292		388
293	sub rcv($@);	389	sub rcv($@);
294		390
		391	sub _kilme {
		392	die "received message on port without callback";
		393	}
		394
295	sub port(;&) {	395	sub port(;&) {
296	my $id = "$UNIQ." . $ID++;	396	my $id = $UNIQ . ++$ID;
297	my $port = "$NODE#$id";	397	my $port = "$NODE#$id";
298		398
299	if (@_) {	399	rcv $port, shift \|\| \&_kilme;
300	rcv $port, shift;
301	} else {
302	$PORT{$id} = sub { }; # nop
303	}
304		400
305	$port	401	$port
306	}	402	}
307		403
308	=item reg $port, $name
309
310	=item reg $name
311
312	Registers the given port (or C<$SELF><<< if missing) under the name
313	C<$name>. If the name already exists it is replaced.
314
315	A port can only be registered under one well known name.
316
317	A port automatically becomes unregistered when it is killed.
318
319	=cut
320
321	sub reg(@) {
322	my $port = @_ > 1 ? shift : $SELF \|\| Carp::croak 'reg: called with one argument only, but $SELF not set,';
323
324	$REG{$_[0]} = $port;
325	}
326
327	=item rcv $port, $callback->(@msg)	404	=item rcv $local_port, $callback->(@msg)
328		405
329	Replaces the callback on the specified miniport (after converting it to	406	Replaces the default callback on the specified port. There is no way to
330	one if required).	407	remove the default callback: use C<sub { }> to disable it, or better
331		408	C<kil> the port when it is no longer needed.
332	=item rcv $port, tagstring => $callback->(@msg), ...
333
334	=item rcv $port, $smartmatch => $callback->(@msg), ...
335
336	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
337
338	Register callbacks to be called on matching messages on the given full
339	port (after converting it to one if required) and return the port.
340
341	The callback has to return a true value when its work is done, after
342	which is will be removed, or a false value in which case it will stay
343	registered.
344		409
345	The global C<$SELF> (exported by this module) contains C<$port> while	410	The global C<$SELF> (exported by this module) contains C<$port> while
346	executing the callback.	411	executing the callback. Runtime errors during callback execution will
		412	result in the port being C<kil>ed.
347		413
348	Runtime errors wdurign callback execution will result in the port being	414	The default callback received all messages not matched by a more specific
349	C<kil>ed.	415	C<tag> match.
350		416
351	If the match is an array reference, then it will be matched against the	417	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
352	first elements of the message, otherwise only the first element is being
353	matched.
354		418
355	Any element in the match that is specified as C<_any_> (a function	419	Register (or replace) callbacks to be called on messages starting with the
356	exported by this module) matches any single element of the message.	420	given tag on the given port (and return the port), or unregister it (when
		421	C<$callback> is C<$undef> or missing). There can only be one callback
		422	registered for each tag.
357		423
358	While not required, it is highly recommended that the first matching	424	The original message will be passed to the callback, after the first
359	element is a string identifying the message. The one-string-only match is	425	element (the tag) has been removed. The callback will use the same
360	also the most efficient match (by far).	426	environment as the default callback (see above).
361		427
362	Example: create a port and bind receivers on it in one go.	428	Example: create a port and bind receivers on it in one go.
363		429
364	my $port = rcv port,	430	my $port = rcv port,
365	msg1 => sub { ...; 0 },	431	msg1 => sub { ... },
366	msg2 => sub { ...; 0 },	432	msg2 => sub { ... },
367	;	433	;
368		434
369	Example: create a port, bind receivers and send it in a message elsewhere	435	Example: create a port, bind receivers and send it in a message elsewhere
370	in one go:	436	in one go:
371		437
372	snd $otherport, reply =>	438	snd $otherport, reply =>
373	rcv port,	439	rcv port,
374	msg1 => sub { ...; 0 },	440	msg1 => sub { ... },
375	...	441	...
376	;	442	;
377		443
		444	Example: temporarily register a rcv callback for a tag matching some port
		445	(e.g. for an rpc reply) and unregister it after a message was received.
		446
		447	rcv $port, $otherport => sub {
		448	my @reply = @_;
		449
		450	rcv $SELF, $otherport;
		451	};
		452
378	=cut	453	=cut
379		454
380	sub rcv($@) {	455	sub rcv($@) {
381	my $port = shift;	456	my $port = shift;
382	my ($noderef, $portid) = split /#/, $port, 2;	457	my ($nodeid, $portid) = split /#/, $port, 2;
383		458
384	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	459	$NODE{$nodeid} == $NODE{""}
385	or Carp::croak "$port: rcv can only be called on local ports, caught";	460	or Carp::croak "$port: rcv can only be called on local ports, caught";
386		461
387	if (@_ == 1) {	462	while (@_) {
		463	if (ref $_[0]) {
		464	if (my $self = $PORT_DATA{$portid}) {
		465	"AnyEvent::MP::Port" eq ref $self
		466	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		467
		468	$self->[0] = shift;
		469	} else {
388	my $cb = shift;	470	my $cb = shift;
389	delete $PORT_DATA{$portid};
390	$PORT{$portid} = sub {	471	$PORT{$portid} = sub {
391	local $SELF = $port;	472	local $SELF = $port;
392	eval {	473	eval { &$cb }; _self_die if $@;
393	&$cb	474	};
394	and kil $port;
395	};	475	}
396	_self_die if $@;	476	} elsif (defined $_[0]) {
397	};
398	} else {
399	my $self = $PORT_DATA{$portid} \|\|= do {	477	my $self = $PORT_DATA{$portid} \|\|= do {
400	my $self = bless {	478	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
401	id => $port,
402	}, "AnyEvent::MP::Port";
403		479
404	$PORT{$portid} = sub {	480	$PORT{$portid} = sub {
405	local $SELF = $port;	481	local $SELF = $port;
406		482
407	eval {
408	for (@{ $self->{rc0}{$_[0]} }) {	483	if (my $cb = $self->[1]{$_[0]}) {
409	$_ && &{$_->[0]}	484	shift;
410	&& undef $_;	485	eval { &$cb }; _self_die if $@;
411	}	486	} else {
412
413	for (@{ $self->{rcv}{$_[0]} }) {
414	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
415	&& &{$_->[0]}	487	&{ $self->[0] };
416	&& undef $_;
417	}
418
419	for (@{ $self->{any} }) {
420	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
421	&& &{$_->[0]}
422	&& undef $_;
423	}	488	}
424	};	489	};
425	_self_die if $@;	490
		491	$self
426	};	492	};
427		493
428	$self
429	};
430
431	"AnyEvent::MP::Port" eq ref $self	494	"AnyEvent::MP::Port" eq ref $self
432	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	495	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
433		496
434	while (@_) {
435	my ($match, $cb) = splice @_, 0, 2;	497	my ($tag, $cb) = splice @_, 0, 2;
436		498
437	if (!ref $match) {	499	if (defined $cb) {
438	push @{ $self->{rc0}{$match} }, [$cb];	500	$self->[1]{$tag} = $cb;
439	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
440	my ($type, @match) = @$match;
441	@match
442	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
443	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
444	} else {	501	} else {
445	push @{ $self->{any} }, [$cb, $match];	502	delete $self->[1]{$tag};
446	}	503	}
447	}	504	}
448	}	505	}
449		506
450	$port	507	$port
451	}	508	}
452		509
		510	=item peval $port, $coderef[, @args]
		511
		512	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		513	when the code throews an exception the C<$port> will be killed.
		514
		515	Any remaining args will be passed to the callback. Any return values will
		516	be returned to the caller.
		517
		518	This is useful when you temporarily want to execute code in the context of
		519	a port.
		520
		521	Example: create a port and run some initialisation code in it's context.
		522
		523	my $port = port { ... };
		524
		525	peval $port, sub {
		526	init
		527	or die "unable to init";
		528	};
		529
		530	=cut
		531
		532	sub peval($$) {
		533	local $SELF = shift;
		534	my $cb = shift;
		535
		536	if (wantarray) {
		537	my @res = eval { &$cb };
		538	_self_die if $@;
		539	@res
		540	} else {
		541	my $res = eval { &$cb };
		542	_self_die if $@;
		543	$res
		544	}
		545	}
		546
453	=item $closure = psub { BLOCK }	547	=item $closure = psub { BLOCK }
454		548
455	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	549	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
456	closure is executed, sets up the environment in the same way as in C<rcv>	550	closure is executed, sets up the environment in the same way as in C<rcv>
457	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.	551	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		552
		553	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		554	BLOCK }, @_ } >>.
458		555
459	This is useful when you register callbacks from C<rcv> callbacks:	556	This is useful when you register callbacks from C<rcv> callbacks:
460		557
461	rcv delayed_reply => sub {	558	rcv delayed_reply => sub {
462	my ($delay, @reply) = @_;	559	my ($delay, @reply) = @_;
…		…
486	$res	583	$res
487	}	584	}
488	}	585	}
489	}	586	}
490		587
491	=item $guard = mon $port, $cb->(@reason)	588	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
492		589
493	=item $guard = mon $port, $rcvport	590	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
494		591
495	=item $guard = mon $port	592	=item $guard = mon $port # kill $SELF when $port dies
496		593
497	=item $guard = mon $port, $rcvport, @msg	594	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
498		595
499	Monitor the given port and do something when the port is killed, and	596	Monitor the given port and do something when the port is killed or
500	optionally return a guard that can be used to stop monitoring again.	597	messages to it were lost, and optionally return a guard that can be used
		598	to stop monitoring again.
501		599
502	In the first form (callback), the callback is simply called with any	600	In the first form (callback), the callback is simply called with any
503	number of C<@reason> elements (no @reason means that the port was deleted	601	number of C<@reason> elements (no @reason means that the port was deleted
504	"normally"). Note also that I<< the callback B<must> never die >>, so use	602	"normally"). Note also that I<< the callback B<must> never die >>, so use
505	C<eval> if unsure.	603	C<eval> if unsure.
506		604
507	In the second form (another port given), the other port (C<$rcvport)	605	In the second form (another port given), the other port (C<$rcvport>)
508	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	606	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
509	"normal" kils nothing happens, while under all other conditions, the other	607	"normal" kils nothing happens, while under all other conditions, the other
510	port is killed with the same reason.	608	port is killed with the same reason.
511		609
512	The third form (kill self) is the same as the second form, except that	610	The third form (kill self) is the same as the second form, except that
513	C<$rvport> defaults to C<$SELF>.	611	C<$rvport> defaults to C<$SELF>.
514		612
515	In the last form (message), a message of the form C<@msg, @reason> will be	613	In the last form (message), a message of the form C<@msg, @reason> will be
516	C<snd>.	614	C<snd>.
517		615
		616	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		617	alert was raised), they are removed and will not trigger again.
		618
		619	As a rule of thumb, monitoring requests should always monitor a port from
		620	a local port (or callback). The reason is that kill messages might get
		621	lost, just like any other message. Another less obvious reason is that
		622	even monitoring requests can get lost (for example, when the connection
		623	to the other node goes down permanently). When monitoring a port locally
		624	these problems do not exist.
		625
		626	C<mon> effectively guarantees that, in the absence of hardware failures,
		627	after starting the monitor, either all messages sent to the port will
		628	arrive, or the monitoring action will be invoked after possible message
		629	loss has been detected. No messages will be lost "in between" (after
		630	the first lost message no further messages will be received by the
		631	port). After the monitoring action was invoked, further messages might get
		632	delivered again.
		633
		634	Inter-host-connection timeouts and monitoring depend on the transport
		635	used. The only transport currently implemented is TCP, and AnyEvent::MP
		636	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		637	non-idle connection, and usually around two hours for idle connections).
		638
		639	This means that monitoring is good for program errors and cleaning up
		640	stuff eventually, but they are no replacement for a timeout when you need
		641	to ensure some maximum latency.
		642
518	Example: call a given callback when C<$port> is killed.	643	Example: call a given callback when C<$port> is killed.
519		644
520	mon $port, sub { warn "port died because of <@_>\n" };	645	mon $port, sub { warn "port died because of <@_>\n" };
521		646
522	Example: kill ourselves when C<$port> is killed abnormally.	647	Example: kill ourselves when C<$port> is killed abnormally.
…		…
528	mon $port, $self => "restart";	653	mon $port, $self => "restart";
529		654
530	=cut	655	=cut
531		656
532	sub mon {	657	sub mon {
533	my ($noderef, $port) = split /#/, shift, 2;	658	my ($nodeid, $port) = split /#/, shift, 2;
534		659
535	my $node = $NODE{$noderef} \|\| add_node $noderef;	660	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
536		661
537	my $cb = @_ ? $_[0] : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';	662	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
538		663
539	unless (ref $cb) {	664	unless (ref $cb) {
540	if (@_) {	665	if (@_) {
541	# send a kill info message	666	# send a kill info message
542	my (@msg) = @_;	667	my (@msg) = ($cb, @_);
543	$cb = sub { snd @msg, @_ };	668	$cb = sub { snd @msg, @_ };
544	} else {	669	} else {
545	# simply kill other port	670	# simply kill other port
546	my $port = $cb;	671	my $port = $cb;
547	$cb = sub { kil $port, @_ if @_ };	672	$cb = sub { kil $port, @_ if @_ };
…		…
549	}	674	}
550		675
551	$node->monitor ($port, $cb);	676	$node->monitor ($port, $cb);
552		677
553	defined wantarray	678	defined wantarray
554	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	679	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
555	}	680	}
556		681
557	=item $guard = mon_guard $port, $ref, $ref...	682	=item $guard = mon_guard $port, $ref, $ref...
558		683
559	Monitors the given C<$port> and keeps the passed references. When the port	684	Monitors the given C<$port> and keeps the passed references. When the port
560	is killed, the references will be freed.	685	is killed, the references will be freed.
561		686
562	Optionally returns a guard that will stop the monitoring.	687	Optionally returns a guard that will stop the monitoring.
563		688
564	This function is useful when you create e.g. timers or other watchers and	689	This function is useful when you create e.g. timers or other watchers and
565	want to free them when the port gets killed:	690	want to free them when the port gets killed (note the use of C<psub>):
566		691
567	$port->rcv (start => sub {	692	$port->rcv (start => sub {
568	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	693	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
569	undef $timer if 0.9 < rand;	694	undef $timer if 0.9 < rand;
570	});	695	});
571	});	696	});
572		697
573	=cut	698	=cut
…		…
578	#TODO: mon-less form?	703	#TODO: mon-less form?
579		704
580	mon $port, sub { 0 && @refs }	705	mon $port, sub { 0 && @refs }
581	}	706	}
582		707
583	=item lnk $port1, $port2
584
585	=item lnk $otherport
586
587	Link two ports. This is simply a shorthand for:
588
589	mon $port1, $port2;
590	mon $port2, $port1;
591
592	It means that if either one is killed abnormally, the other one gets
593	killed as well.
594
595	The one-argument form assumes that one port is C<$SELF>.
596
597	=cut
598
599	sub lnk {
600	my $port1 = shift;
601	my $port2 = @_ ? shift : $SELF \|\| Carp::croak 'lnk: called with one argument only, but $SELF not set,';
602
603	mon $port1, $port2;
604	mon $port2, $port1;
605	}
606
607	=item kil $port[, @reason]	708	=item kil $port[, @reason]
608		709
609	Kill the specified port with the given C<@reason>.	710	Kill the specified port with the given C<@reason>.
610		711
611	If no C<@reason> is specified, then the port is killed "normally" (linked	712	If no C<@reason> is specified, then the port is killed "normally" -
612	ports will not be kileld, or even notified).	713	monitor callback will be invoked, but the kil will not cause linked ports
		714	(C<mon $mport, $lport> form) to get killed.
613		715
614	Otherwise, linked ports get killed with the same reason (second form of	716	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
615	C<mon>, see below).	717	form) get killed with the same reason.
616		718
617	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	719	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
618	will be reported as reason C<< die => $@ >>.	720	will be reported as reason C<< die => $@ >>.
619		721
620	Transport/communication errors are reported as C<< transport_error =>	722	Transport/communication errors are reported as C<< transport_error =>
621	$message >>.	723	$message >>.
622		724
		725	=cut
		726
		727	=item $port = spawn $node, $initfunc[, @initdata]
		728
		729	Creates a port on the node C<$node> (which can also be a port ID, in which
		730	case it's the node where that port resides).
		731
		732	The port ID of the newly created port is returned immediately, and it is
		733	possible to immediately start sending messages or to monitor the port.
		734
		735	After the port has been created, the init function is called on the remote
		736	node, in the same context as a C<rcv> callback. This function must be a
		737	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		738	specify a function in the main program, use C<::name>.
		739
		740	If the function doesn't exist, then the node tries to C<require>
		741	the package, then the package above the package and so on (e.g.
		742	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		743	exists or it runs out of package names.
		744
		745	The init function is then called with the newly-created port as context
		746	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		747	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		748	the port might not get created.
		749
		750	A common idiom is to pass a local port, immediately monitor the spawned
		751	port, and in the remote init function, immediately monitor the passed
		752	local port. This two-way monitoring ensures that both ports get cleaned up
		753	when there is a problem.
		754
		755	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		756	caller before C<spawn> returns (by delaying invocation when spawn is
		757	called for the local node).
		758
		759	Example: spawn a chat server port on C<$othernode>.
		760
		761	# this node, executed from within a port context:
		762	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		763	mon $server;
		764
		765	# init function on C<$othernode>
		766	sub connect {
		767	my ($srcport) = @_;
		768
		769	mon $srcport;
		770
		771	rcv $SELF, sub {
		772	...
		773	};
		774	}
		775
		776	=cut
		777
		778	sub _spawn {
		779	my $port = shift;
		780	my $init = shift;
		781
		782	# rcv will create the actual port
		783	local $SELF = "$NODE#$port";
		784	eval {
		785	&{ load_func $init }
		786	};
		787	_self_die if $@;
		788	}
		789
		790	sub spawn(@) {
		791	my ($nodeid, undef) = split /#/, shift, 2;
		792
		793	my $id = $RUNIQ . ++$ID;
		794
		795	$_[0] =~ /::/
		796	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		797
		798	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		799
		800	"$nodeid#$id"
		801	}
		802
		803
		804	=item after $timeout, @msg
		805
		806	=item after $timeout, $callback
		807
		808	Either sends the given message, or call the given callback, after the
		809	specified number of seconds.
		810
		811	This is simply a utility function that comes in handy at times - the
		812	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		813	so it may go away in the future.
		814
		815	=cut
		816
		817	sub after($@) {
		818	my ($timeout, @action) = @_;
		819
		820	my $t; $t = AE::timer $timeout, 0, sub {
		821	undef $t;
		822	ref $action[0]
		823	? $action[0]()
		824	: snd @action;
		825	};
		826	}
		827
		828	=item cal $port, @msg, $callback[, $timeout]
		829
		830	A simple form of RPC - sends a message to the given C<$port> with the
		831	given contents (C<@msg>), but adds a reply port to the message.
		832
		833	The reply port is created temporarily just for the purpose of receiving
		834	the reply, and will be C<kil>ed when no longer needed.
		835
		836	A reply message sent to the port is passed to the C<$callback> as-is.
		837
		838	If an optional time-out (in seconds) is given and it is not C<undef>,
		839	then the callback will be called without any arguments after the time-out
		840	elapsed and the port is C<kil>ed.
		841
		842	If no time-out is given (or it is C<undef>), then the local port will
		843	monitor the remote port instead, so it eventually gets cleaned-up.
		844
		845	Currently this function returns the temporary port, but this "feature"
		846	might go in future versions unless you can make a convincing case that
		847	this is indeed useful for something.
		848
		849	=cut
		850
		851	sub cal(@) {
		852	my $timeout = ref $_[-1] ? undef : pop;
		853	my $cb = pop;
		854
		855	my $port = port {
		856	undef $timeout;
		857	kil $SELF;
		858	&$cb;
		859	};
		860
		861	if (defined $timeout) {
		862	$timeout = AE::timer $timeout, 0, sub {
		863	undef $timeout;
		864	kil $port;
		865	$cb->();
		866	};
		867	} else {
		868	mon $_[0], sub {
		869	kil $port;
		870	$cb->();
		871	};
		872	}
		873
		874	push @_, $port;
		875	&snd;
		876
		877	$port
		878	}
		879
623	=back	880	=back
624		881
625	=head1 NODE MESSAGES	882	=head1 DISTRIBUTED DATABASE
626		883
627	Nodes understand the following messages sent to them. Many of them take	884	AnyEvent::MP comes with a simple distributed database. The database will
628	arguments called C<@reply>, which will simply be used to compose a reply	885	be mirrored asynchronously at all global nodes. Other nodes bind to one of
629	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and	886	the global nodes for their needs.
630	the remaining arguments are simply the message data.
631		887
632	While other messages exist, they are not public and subject to change.	888	The database consists of a two-level hash - a hash contains a hash which
		889	contains values.
633		890
634	=over 4	891	The top level hash key is called "family", and the second-level hash key
		892	is simply called "key".
635		893
636	=cut	894	The family must be alphanumeric, i.e. start with a letter and consist
		895	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		896	pretty much like Perl module names.
637		897
638	=item lookup => $name, @reply	898	As the family namespace is global, it is recommended to prefix family names
		899	with the name of the application or module using it.
639		900
640	Replies with the port ID of the specified well-known port, or C<undef>.	901	The keys must be strings, with no other limitations.
641		902
642	=item devnull => ...	903	The values should preferably be strings, but other perl scalars should
		904	work as well (such as undef, arrays and hashes).
643		905
644	Generic data sink/CPU heat conversion.	906	Every database entry is owned by one node - adding the same family/key
		907	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		908	but the result might be nondeterministic, i.e. the key might have
		909	different values on different nodes.
645		910
646	=item relay => $port, @msg	911	=item db_set $family => $key => $value
647		912
648	Simply forwards the message to the given port.	913	Sets (or replaces) a key to the database.
649		914
650	=item eval => $string[ @reply]	915	=item db_del $family => $key
651		916
652	Evaluates the given string. If C<@reply> is given, then a message of the	917	Deletes a key from the database.
653	form C<@reply, $@, @evalres> is sent.
654		918
655	Example: crash another node.	919	=item $guard = db_reg $family => $key [=> $value]
656		920
657	snd $othernode, eval => "exit";	921	Sets the key on the database and returns a guard. When the guard is
		922	destroyed, the key is deleted from the database. If C<$value> is missing,
		923	then C<undef> is used.
658		924
659	=item time => @reply	925	=cut
660
661	Replies the the current node time to C<@reply>.
662
663	Example: tell the current node to send the current time to C<$myport> in a
664	C<timereply> message.
665
666	snd $NODE, time => $myport, timereply => 1, 2;
667	# => snd $myport, timereply => 1, 2, <time>
668		926
669	=back	927	=back
670		928
671	=head1 AnyEvent::MP vs. Distributed Erlang	929	=head1 AnyEvent::MP vs. Distributed Erlang
672		930
673	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	931	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
674	== aemp node, Erlang process == aemp port), so many of the documents and	932	== aemp node, Erlang process == aemp port), so many of the documents and
675	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	933	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
676	sample:	934	sample:
677		935
678	http://www.Erlang.se/doc/programming_rules.shtml	936	http://www.erlang.se/doc/programming_rules.shtml
679	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	937	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
680	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	938	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
681	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	939	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
682		940
683	Despite the similarities, there are also some important differences:	941	Despite the similarities, there are also some important differences:
684		942
685	=over 4	943	=over 4
686		944
687	=item * Node references contain the recipe on how to contact them.	945	=item * Node IDs are arbitrary strings in AEMP.
688		946
689	Erlang relies on special naming and DNS to work everywhere in the	947	Erlang relies on special naming and DNS to work everywhere in the same
690	same way. AEMP relies on each node knowing it's own address(es), with	948	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
691	convenience functionality.	949	configuration or DNS), and possibly the addresses of some seed nodes, but
		950	will otherwise discover other nodes (and their IDs) itself.
692		951
693	This means that AEMP requires a less tightly controlled environment at the	952	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
694	cost of longer node references and a slightly higher management overhead.	953	uses "local ports are like remote ports".
		954
		955	The failure modes for local ports are quite different (runtime errors
		956	only) then for remote ports - when a local port dies, you I<know> it dies,
		957	when a connection to another node dies, you know nothing about the other
		958	port.
		959
		960	Erlang pretends remote ports are as reliable as local ports, even when
		961	they are not.
		962
		963	AEMP encourages a "treat remote ports differently" philosophy, with local
		964	ports being the special case/exception, where transport errors cannot
		965	occur.
695		966
696	=item * Erlang uses processes and a mailbox, AEMP does not queue.	967	=item * Erlang uses processes and a mailbox, AEMP does not queue.
697		968
698	Erlang uses processes that selctively receive messages, and therefore	969	Erlang uses processes that selectively receive messages out of order, and
699	needs a queue. AEMP is event based, queuing messages would serve no useful	970	therefore needs a queue. AEMP is event based, queuing messages would serve
700	purpose.	971	no useful purpose. For the same reason the pattern-matching abilities
		972	of AnyEvent::MP are more limited, as there is little need to be able to
		973	filter messages without dequeuing them.
701		974
702	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	975	This is not a philosophical difference, but simply stems from AnyEvent::MP
		976	being event-based, while Erlang is process-based.
		977
		978	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		979	top of AEMP and Coro threads.
703		980
704	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	981	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
705		982
706	Sending messages in Erlang is synchronous and blocks the process. AEMP	983	Sending messages in Erlang is synchronous and blocks the process until
707	sends are immediate, connection establishment is handled in the	984	a conenction has been established and the message sent (and so does not
708	background.	985	need a queue that can overflow). AEMP sends return immediately, connection
		986	establishment is handled in the background.
709		987
710	=item * Erlang can silently lose messages, AEMP cannot.	988	=item * Erlang suffers from silent message loss, AEMP does not.
711		989
712	Erlang makes few guarantees on messages delivery - messages can get lost	990	Erlang implements few guarantees on messages delivery - messages can get
713	without any of the processes realising it (i.e. you send messages a, b,	991	lost without any of the processes realising it (i.e. you send messages a,
714	and c, and the other side only receives messages a and c).	992	b, and c, and the other side only receives messages a and c).
715		993
716	AEMP guarantees correct ordering, and the guarantee that there are no	994	AEMP guarantees (modulo hardware errors) correct ordering, and the
		995	guarantee that after one message is lost, all following ones sent to the
		996	same port are lost as well, until monitoring raises an error, so there are
717	holes in the message sequence.	997	no silent "holes" in the message sequence.
718		998
719	=item * In Erlang, processes can be declared dead and later be found to be	999	If you want your software to be very reliable, you have to cope with
720	alive.	1000	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
721		1001	simply tries to work better in common error cases, such as when a network
722	In Erlang it can happen that a monitored process is declared dead and	1002	link goes down.
723	linked processes get killed, but later it turns out that the process is
724	still alive - and can receive messages.
725
726	In AEMP, when port monitoring detects a port as dead, then that port will
727	eventually be killed - it cannot happen that a node detects a port as dead
728	and then later sends messages to it, finding it is still alive.
729		1003
730	=item * Erlang can send messages to the wrong port, AEMP does not.	1004	=item * Erlang can send messages to the wrong port, AEMP does not.
731		1005
732	In Erlang it is quite possible that a node that restarts reuses a process	1006	In Erlang it is quite likely that a node that restarts reuses an Erlang
733	ID known to other nodes for a completely different process, causing	1007	process ID known to other nodes for a completely different process,
734	messages destined for that process to end up in an unrelated process.	1008	causing messages destined for that process to end up in an unrelated
		1009	process.
735		1010
736	AEMP never reuses port IDs, so old messages or old port IDs floating	1011	AEMP does not reuse port IDs, so old messages or old port IDs floating
737	around in the network will not be sent to an unrelated port.	1012	around in the network will not be sent to an unrelated port.
738		1013
739	=item * Erlang uses unprotected connections, AEMP uses secure	1014	=item * Erlang uses unprotected connections, AEMP uses secure
740	authentication and can use TLS.	1015	authentication and can use TLS.
741		1016
742	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1017	AEMP can use a proven protocol - TLS - to protect connections and
743	securely authenticate nodes.	1018	securely authenticate nodes.
744		1019
745	=item * The AEMP protocol is optimised for both text-based and binary	1020	=item * The AEMP protocol is optimised for both text-based and binary
746	communications.	1021	communications.
747		1022
748	The AEMP protocol, unlike the Erlang protocol, supports both	1023	The AEMP protocol, unlike the Erlang protocol, supports both programming
749	language-independent text-only protocols (good for debugging) and binary,	1024	language independent text-only protocols (good for debugging), and binary,
750	language-specific serialisers (e.g. Storable).	1025	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1026	used, the protocol is actually completely text-based.
751		1027
752	It has also been carefully designed to be implementable in other languages	1028	It has also been carefully designed to be implementable in other languages
753	with a minimum of work while gracefully degrading fucntionality to make the	1029	with a minimum of work while gracefully degrading functionality to make the
754	protocol simple.	1030	protocol simple.
755		1031
756	=item * AEMP has more flexible monitoring options than Erlang.	1032	=item * AEMP has more flexible monitoring options than Erlang.
757		1033
758	In Erlang, you can chose to receive I<all> exit signals as messages	1034	In Erlang, you can chose to receive I<all> exit signals as messages or
759	or I<none>, there is no in-between, so monitoring single processes is	1035	I<none>, there is no in-between, so monitoring single Erlang processes is
760	difficult to implement. Monitoring in AEMP is more flexible than in	1036	difficult to implement.
761	Erlang, as one can choose between automatic kill, exit message or callback
762	on a per-process basis.
763		1037
764	=item * Erlang has different semantics for monitoring and linking, AEMP has the same.	1038	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1039	between automatic kill, exit message or callback on a per-port basis.
765		1040
		1041	=item * Erlang tries to hide remote/local connections, AEMP does not.
		1042
766	Monitoring in Erlang is not an indicator of process death/crashes,	1043	Monitoring in Erlang is not an indicator of process death/crashes, in the
767	as linking is (except linking is unreliable in Erlang). In AEMP, the	1044	same way as linking is (except linking is unreliable in Erlang).
768	semantics of monitoring and linking are identical, linking is simply	1045
769	two-way monitoring with automatic kill.	1046	In AEMP, you don't "look up" registered port names or send to named ports
		1047	that might or might not be persistent. Instead, you normally spawn a port
		1048	on the remote node. The init function monitors you, and you monitor the
		1049	remote port. Since both monitors are local to the node, they are much more
		1050	reliable (no need for C<spawn_link>).
		1051
		1052	This also saves round-trips and avoids sending messages to the wrong port
		1053	(hard to do in Erlang).
770		1054
771	=back	1055	=back
772		1056
		1057	=head1 RATIONALE
		1058
		1059	=over 4
		1060
		1061	=item Why strings for port and node IDs, why not objects?
		1062
		1063	We considered "objects", but found that the actual number of methods
		1064	that can be called are quite low. Since port and node IDs travel over
		1065	the network frequently, the serialising/deserialising would add lots of
		1066	overhead, as well as having to keep a proxy object everywhere.
		1067
		1068	Strings can easily be printed, easily serialised etc. and need no special
		1069	procedures to be "valid".
		1070
		1071	And as a result, a port with just a default receiver consists of a single
		1072	code reference stored in a global hash - it can't become much cheaper.
		1073
		1074	=item Why favour JSON, why not a real serialising format such as Storable?
		1075
		1076	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1077	format, but currently there is no way to make a node use Storable by
		1078	default (although all nodes will accept it).
		1079
		1080	The default framing protocol is JSON because a) JSON::XS is many times
		1081	faster for small messages and b) most importantly, after years of
		1082	experience we found that object serialisation is causing more problems
		1083	than it solves: Just like function calls, objects simply do not travel
		1084	easily over the network, mostly because they will always be a copy, so you
		1085	always have to re-think your design.
		1086
		1087	Keeping your messages simple, concentrating on data structures rather than
		1088	objects, will keep your messages clean, tidy and efficient.
		1089
		1090	=back
		1091
773	=head1 SEE ALSO	1092	=head1 SEE ALSO
		1093
		1094	L<AnyEvent::MP::Intro> - a gentle introduction.
		1095
		1096	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1097
		1098	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1099	your applications.
		1100
		1101	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1102
		1103	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1104	all nodes.
774		1105
775	L<AnyEvent>.	1106	L<AnyEvent>.
776		1107
777	=head1 AUTHOR	1108	=head1 AUTHOR
778		1109

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Revision 1.125 by root, Sat Mar 3 13:07:19 2012 UTC