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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.45 by root, Thu Aug 13 01:16:24 2009 UTC vs.
Revision 1.122 by root, Wed Feb 29 18:44:59 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	};
42		51
43	=head1 CURRENT STATUS	52	=head1 CURRENT STATUS
44		53
		54	bin/aemp - stable.
45	AnyEvent::MP - stable API, should work	55	AnyEvent::MP - stable API, should work.
46	AnyEvent::MP::Intro - outdated	56	AnyEvent::MP::Intro - explains most concepts.
47	AnyEvent::MP::Kernel - WIP
48	AnyEvent::MP::Transport - mostly stable	57	AnyEvent::MP::Kernel - mostly stable API.
49		58	AnyEvent::MP::Global - stable API.
50	stay tuned.
51		59
52	=head1 DESCRIPTION	60	=head1 DESCRIPTION
53		61
54	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
55		63
56	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
57	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
58		66
59	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>
60	manual page.	68	manual page and the examples under F<eg/>.
61
62	At the moment, this module family is severly broken and underdocumented,
63	so do not use. This was uploaded mainly to reserve the CPAN namespace -
64	stay tuned!
65		69
66	=head1 CONCEPTS	70	=head1 CONCEPTS
67		71
68	=over 4	72	=over 4
69		73
70	=item port	74	=item port
71		75
72	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).
73		78
74	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
75	messages. All C<rcv> handlers will receive messages they match, messages	80	some messages. Messages send to ports will not be queued, regardless of
76	will not be queued.	81	anything was listening for them or not.
77		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
78	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
79		86
80	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<#>) as
81	separator, and a port name (a printable string of unspecified format). An	88	separator, and a port name (a printable string of unspecified format).
82	exception is the the node port, whose ID is identical to its node
83	reference.
84		89
85	=item node	90	=item node
86		91
87	A node is a single process containing at least one port - the node	92	A node is a single process containing at least one port - the node port,
88	port. You can send messages to node ports to find existing ports or to	93	which enables nodes to manage each other remotely, and to create new
89	create new ports, among other things.	94	ports.
90		95
91	Nodes are either private (single-process only), slaves (connected to a	96	Nodes are either public (have one or more listening ports) or private
92	master node only) or public nodes (connectable from unrelated nodes).	97	(no listening ports). Private nodes cannot talk to other private nodes
		98	currently, but all nodes can talk to public nodes.
93		99
94	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	100	Nodes is represented by (printable) strings called "node IDs".
95		101
96	A node reference is a string that either simply identifies the node (for	102	=item node ID - C<[A-Za-z0-9_\-.:]*>
97	private and slave nodes), or contains a recipe on how to reach a given
98	node (for public nodes).
99		103
100	This recipe is simply a comma-separated list of C<address:port> pairs (for	104	A node ID is a string that uniquely identifies the node within a
101	TCP/IP, other protocols might look different).	105	network. Depending on the configuration used, node IDs can look like a
		106	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		107	doesn't interpret node IDs in any way except to uniquely identify a node.
102		108
103	Node references come in two flavours: resolved (containing only numerical	109	=item binds - C<ip:port>
104	addresses) or unresolved (where hostnames are used instead of addresses).
105		110
106	Before using an unresolved node reference in a message you first have to	111	Nodes can only talk to each other by creating some kind of connection to
107	resolve it.	112	each other. To do this, nodes should listen on one or more local transport
		113	endpoints - binds.
		114
		115	Currently, only standard C<ip:port> specifications can be used, which
		116	specify TCP ports to listen on. So a bind is basically just a tcp socket
		117	in listening mode thta accepts conenctions form other nodes.
		118
		119	=item seed nodes
		120
		121	When a node starts, it knows nothing about the network it is in - it
		122	needs to connect to at least one other node that is already in the
		123	network. These other nodes are called "seed nodes".
		124
		125	Seed nodes themselves are not special - they are seed nodes only because
		126	some other node I<uses> them as such, but any node can be used as seed
		127	node for other nodes, and eahc node cna use a different set of seed nodes.
		128
		129	In addition to discovering the network, seed nodes are also used to
		130	maintain the network - all nodes using the same seed node form are part of
		131	the same network. If a network is split into multiple subnets because e.g.
		132	the network link between the parts goes down, then using the same seed
		133	nodes for all nodes ensures that eventually the subnets get merged again.
		134
		135	Seed nodes are expected to be long-running, and at least one seed node
		136	should always be available. They should also be relatively responsive - a
		137	seed node that blocks for long periods will slow down everybody else.
		138
		139	For small networks, it's best if every node uses the same set of seed
		140	nodes. For large networks, it can be useful to specify "regional" seed
		141	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		142	each other. What's important is that all seed nodes connections form a
		143	complete graph, so that the network cannot split into separate subnets
		144	forever.
		145
		146	Seed nodes are represented by seed IDs.
		147
		148	=item seed IDs - C<host:port>
		149
		150	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
		151	TCP port) of nodes that should be used as seed nodes.
		152
		153	=item global nodes
		154
		155	An AEMP network needs a discovery service - nodes need to know how to
		156	connect to other nodes they only know by name. In addition, AEMP offers a
		157	distributed "group database", which maps group names to a list of strings
		158	- for example, to register worker ports.
		159
		160	A network needs at least one global node to work, and allows every node to
		161	be a global node.
		162
		163	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		164	node and tries to keep connections to all other nodes. So while it can
		165	make sense to make every node "global" in small networks, it usually makes
		166	sense to only make seed nodes into global nodes in large networks (nodes
		167	keep connections to seed nodes and global nodes, so makign them the same
		168	reduces overhead).
108		169
109	=back	170	=back
110		171
111	=head1 VARIABLES/FUNCTIONS	172	=head1 VARIABLES/FUNCTIONS
112		173
114		175
115	=cut	176	=cut
116		177
117	package AnyEvent::MP;	178	package AnyEvent::MP;
118		179
		180	use AnyEvent::MP::Config ();
119	use AnyEvent::MP::Kernel;	181	use AnyEvent::MP::Kernel;
		182	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
120		183
121	use common::sense;	184	use common::sense;
122		185
123	use Carp ();	186	use Carp ();
124		187
125	use AE ();	188	use AE ();
126		189
127	use base "Exporter";	190	use base "Exporter";
128		191
129	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	192	our $VERSION = $AnyEvent::MP::Config::VERSION;
130		193
131	our @EXPORT = qw(	194	our @EXPORT = qw(
132	NODE $NODE *SELF node_of _any_	195	NODE $NODE *SELF node_of after
133	resolve_node initialise_node	196	configure
134	snd rcv mon kil reg psub spawn	197	snd rcv mon mon_guard kil psub peval spawn cal
135	port	198	port
136	);	199	);
137		200
138	our $SELF;	201	our $SELF;
139		202
…		…
143	kil $SELF, die => $msg;	206	kil $SELF, die => $msg;
144	}	207	}
145		208
146	=item $thisnode = NODE / $NODE	209	=item $thisnode = NODE / $NODE
147		210
148	The C<NODE> function returns, and the C<$NODE> variable contains	211	The C<NODE> function returns, and the C<$NODE> variable contains, the node
149	the noderef of the local node. The value is initialised by a call	212	ID of the node running in the current process. This value is initialised by
150	to C<become_public> or C<become_slave>, after which all local port	213	a call to C<configure>.
151	identifiers become invalid.
152		214
153	=item $noderef = node_of $port	215	=item $nodeid = node_of $port
154		216
155	Extracts and returns the noderef from a portid or a noderef.	217	Extracts and returns the node ID from a port ID or a node ID.
156		218
157	=item initialise_node $noderef, $seednode, $seednode...	219	=item configure $profile, key => value...
158		220
159	=item initialise_node "slave/", $master, $master...	221	=item configure key => value...
160		222
161	Before a node can talk to other nodes on the network it has to initialise	223	Before a node can talk to other nodes on the network (i.e. enter
162	itself - the minimum a node needs to know is it's own name, and optionally	224	"distributed mode") it has to configure itself - the minimum a node needs
163	it should know the noderefs of some other nodes in the network.	225	to know is its own name, and optionally it should know the addresses of
		226	some other nodes in the network to discover other nodes.
164		227
165	This function initialises a node - it must be called exactly once (or	228	This function configures a node - it must be called exactly once (or
166	never) before calling other AnyEvent::MP functions.	229	never) before calling other AnyEvent::MP functions.
167		230
168	All arguments are noderefs, which can be either resolved or unresolved.	231	The key/value pairs are basically the same ones as documented for the
169		232	F<aemp> command line utility (sans the set/del prefix), with two additions:
170	There are two types of networked nodes, public nodes and slave nodes:
171		233
172	=over 4	234	=over 4
173		235
174	=item public nodes	236	=item norc => $boolean (default false)
175		237
176	For public nodes, C<$noderef> must either be a (possibly unresolved)	238	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
177	noderef, in which case it will be resolved, or C<undef> (or missing), in	239	be consulted - all configuraiton options must be specified in the
178	which case the noderef will be guessed.	240	C<configure> call.
179		241
180	Afterwards, the node will bind itself on all endpoints and try to connect	242	=item force => $boolean (default false)
181	to all additional C<$seednodes> that are specified. Seednodes are optional
182	and can be used to quickly bootstrap the node into an existing network.
183		243
184	=item slave nodes	244	IF true, then the values specified in the C<configure> will take
185		245	precedence over any values configured via the rc file. The default is for
186	When the C<$noderef> is the special string C<slave/>, then the node will	246	the rc file to override any options specified in the program.
187	become a slave node. Slave nodes cannot be contacted from outside and will
188	route most of their traffic to the master node that they attach to.
189
190	At least one additional noderef is required: The node will try to connect
191	to all of them and will become a slave attached to the first node it can
192	successfully connect to.
193		247
194	=back	248	=back
195		249
196	This function will block until all nodes have been resolved and, for slave
197	nodes, until it has successfully established a connection to a master
198	server.
199
200	Example: become a public node listening on the default node.
201
202	initialise_node;
203
204	Example: become a public node, and try to contact some well-known master
205	servers to become part of the network.
206
207	initialise_node undef, "master1", "master2";
208
209	Example: become a public node listening on port C<4041>.
210
211	initialise_node 4041;
212
213	Example: become a public node, only visible on localhost port 4044.
214
215	initialise_node "locahost:4044";
216
217	Example: become a slave node to any of the specified master servers.
218
219	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
220
221	=item $cv = resolve_node $noderef
222
223	Takes an unresolved node reference that may contain hostnames and
224	abbreviated IDs, resolves all of them and returns a resolved node
225	reference.
226
227	In addition to C<address:port> pairs allowed in resolved noderefs, the
228	following forms are supported:
229
230	=over 4	250	=over 4
231		251
232	=item the empty string	252	=item step 1, gathering configuration from profiles
233		253
234	An empty-string component gets resolved as if the default port (4040) was	254	The function first looks up a profile in the aemp configuration (see the
235	specified.	255	L<aemp> commandline utility). The profile name can be specified via the
		256	named C<profile> parameter or can simply be the first parameter). If it is
		257	missing, then the nodename (F<uname -n>) will be used as profile name.
236		258
237	=item naked port numbers (e.g. C<1234>)	259	The profile data is then gathered as follows:
238		260
239	These are resolved by prepending the local nodename and a colon, to be	261	First, all remaining key => value pairs (all of which are conveniently
240	further resolved.	262	undocumented at the moment) will be interpreted as configuration
		263	data. Then they will be overwritten by any values specified in the global
		264	default configuration (see the F<aemp> utility), then the chain of
		265	profiles chosen by the profile name (and any C<parent> attributes).
241		266
242	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	267	That means that the values specified in the profile have highest priority
		268	and the values specified directly via C<configure> have lowest priority,
		269	and can only be used to specify defaults.
243		270
244	These are resolved by using AnyEvent::DNS to resolve them, optionally	271	If the profile specifies a node ID, then this will become the node ID of
245	looking up SRV records for the C<aemp=4040> port, if no port was	272	this process. If not, then the profile name will be used as node ID, with
246	specified.	273	a slash (C</>) attached.
		274
		275	If the node ID (or profile name) ends with a slash (C</>), then a random
		276	string is appended to make it unique.
		277
		278	=item step 2, bind listener sockets
		279
		280	The next step is to look up the binds in the profile, followed by binding
		281	aemp protocol listeners on all binds specified (it is possible and valid
		282	to have no binds, meaning that the node cannot be contacted form the
		283	outside. This means the node cannot talk to other nodes that also have no
		284	binds, but it can still talk to all "normal" nodes).
		285
		286	If the profile does not specify a binds list, then a default of C<*> is
		287	used, meaning the node will bind on a dynamically-assigned port on every
		288	local IP address it finds.
		289
		290	=item step 3, connect to seed nodes
		291
		292	As the last step, the seed ID list from the profile is passed to the
		293	L<AnyEvent::MP::Global> module, which will then use it to keep
		294	connectivity with at least one node at any point in time.
247		295
248	=back	296	=back
		297
		298	Example: become a distributed node using the local node name as profile.
		299	This should be the most common form of invocation for "daemon"-type nodes.
		300
		301	configure
		302
		303	Example: become an anonymous node. This form is often used for commandline
		304	clients.
		305
		306	configure nodeid => "anon/";
		307
		308	Example: configure a node using a profile called seed, which is suitable
		309	for a seed node as it binds on all local addresses on a fixed port (4040,
		310	customary for aemp).
		311
		312	# use the aemp commandline utility
		313	# aemp profile seed binds '*:4040'
		314
		315	# then use it
		316	configure profile => "seed";
		317
		318	# or simply use aemp from the shell again:
		319	# aemp run profile seed
		320
		321	# or provide a nicer-to-remember nodeid
		322	# aemp run profile seed nodeid "$(hostname)"
249		323
250	=item $SELF	324	=item $SELF
251		325
252	Contains the current port id while executing C<rcv> callbacks or C<psub>	326	Contains the current port id while executing C<rcv> callbacks or C<psub>
253	blocks.	327	blocks.
254		328
255	=item SELF, %SELF, @SELF...	329	=item *SELF, SELF, %SELF, @SELF...
256		330
257	Due to some quirks in how perl exports variables, it is impossible to	331	Due to some quirks in how perl exports variables, it is impossible to
258	just export C<$SELF>, all the symbols called C<SELF> are exported by this	332	just export C<$SELF>, all the symbols named C<SELF> are exported by this
259	module, but only C<$SELF> is currently used.	333	module, but only C<$SELF> is currently used.
260		334
261	=item snd $port, type => @data	335	=item snd $port, type => @data
262		336
263	=item snd $port, @msg	337	=item snd $port, @msg
264		338
265	Send the given message to the given port ID, which can identify either	339	Send the given message to the given port, which can identify either a
266	a local or a remote port, and can be either a string or soemthignt hat	340	local or a remote port, and must be a port ID.
267	stringifies a sa port ID (such as a port object :).
268		341
269	While the message can be about anything, it is highly recommended to use a	342	While the message can be almost anything, it is highly recommended to
270	string as first element (a portid, or some word that indicates a request	343	use a string as first element (a port ID, or some word that indicates a
271	type etc.).	344	request type etc.) and to consist if only simple perl values (scalars,
		345	arrays, hashes) - if you think you need to pass an object, think again.
272		346
273	The message data effectively becomes read-only after a call to this	347	The message data logically becomes read-only after a call to this
274	function: modifying any argument is not allowed and can cause many	348	function: modifying any argument (or values referenced by them) is
275	problems.	349	forbidden, as there can be considerable time between the call to C<snd>
		350	and the time the message is actually being serialised - in fact, it might
		351	never be copied as within the same process it is simply handed to the
		352	receiving port.
276		353
277	The type of data you can transfer depends on the transport protocol: when	354	The type of data you can transfer depends on the transport protocol: when
278	JSON is used, then only strings, numbers and arrays and hashes consisting	355	JSON is used, then only strings, numbers and arrays and hashes consisting
279	of those are allowed (no objects). When Storable is used, then anything	356	of those are allowed (no objects). When Storable is used, then anything
280	that Storable can serialise and deserialise is allowed, and for the local	357	that Storable can serialise and deserialise is allowed, and for the local
281	node, anything can be passed.	358	node, anything can be passed. Best rely only on the common denominator of
		359	these.
282		360
283	=item $local_port = port	361	=item $local_port = port
284		362
285	Create a new local port object that can be used either as a pattern	363	Create a new local port object and returns its port ID. Initially it has
286	matching port ("full port") or a single-callback port ("miniport"),	364	no callbacks set and will throw an error when it receives messages.
287	depending on how C<rcv> callbacks are bound to the object.
288		365
289	=item $port = port { my @msg = @_; $finished }	366	=item $local_port = port { my @msg = @_ }
290		367
291	Creates a "miniport", that is, a very lightweight port without any pattern	368	Creates a new local port, and returns its ID. Semantically the same as
292	matching behind it, and returns its ID. Semantically the same as creating
293	a port and calling C<rcv $port, $callback> on it.	369	creating a port and calling C<rcv $port, $callback> on it.
294		370
295	The block will be called for every message received on the port. When the	371	The block will be called for every message received on the port, with the
296	callback returns a true value its job is considered "done" and the port	372	global variable C<$SELF> set to the port ID. Runtime errors will cause the
297	will be destroyed. Otherwise it will stay alive.	373	port to be C<kil>ed. The message will be passed as-is, no extra argument
		374	(i.e. no port ID) will be passed to the callback.
298		375
299	The message will be passed as-is, no extra argument (i.e. no port id) will	376	If you want to stop/destroy the port, simply C<kil> it:
300	be passed to the callback.
301		377
302	If you need the local port id in the callback, this works nicely:	378	my $port = port {
303		379	my @msg = @_;
304	my $port; $port = port {	380	...
305	snd $otherport, reply => $port;	381	kil $SELF;
306	};	382	};
307		383
308	=cut	384	=cut
309		385
310	sub rcv($@);	386	sub rcv($@);
311		387
		388	sub _kilme {
		389	die "received message on port without callback";
		390	}
		391
312	sub port(;&) {	392	sub port(;&) {
313	my $id = "$UNIQ." . $ID++;	393	my $id = "$UNIQ." . ++$ID;
314	my $port = "$NODE#$id";	394	my $port = "$NODE#$id";
315		395
316	if (@_) {	396	rcv $port, shift \|\| \&_kilme;
317	rcv $port, shift;
318	} else {
319	$PORT{$id} = sub { }; # nop
320	}
321		397
322	$port	398	$port
323	}	399	}
324		400
325	=item reg $port, $name
326
327	=item reg $name
328
329	Registers the given port (or C<$SELF><<< if missing) under the name
330	C<$name>. If the name already exists it is replaced.
331
332	A port can only be registered under one well known name.
333
334	A port automatically becomes unregistered when it is killed.
335
336	=cut
337
338	sub reg(@) {
339	my $port = @_ > 1 ? shift : $SELF \|\| Carp::croak 'reg: called with one argument only, but $SELF not set,';
340
341	$REG{$_[0]} = $port;
342	}
343
344	=item rcv $port, $callback->(@msg)	401	=item rcv $local_port, $callback->(@msg)
345		402
346	Replaces the callback on the specified miniport (after converting it to	403	Replaces the default callback on the specified port. There is no way to
347	one if required).	404	remove the default callback: use C<sub { }> to disable it, or better
348		405	C<kil> the port when it is no longer needed.
349	=item rcv $port, tagstring => $callback->(@msg), ...
350
351	=item rcv $port, $smartmatch => $callback->(@msg), ...
352
353	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
354
355	Register callbacks to be called on matching messages on the given full
356	port (after converting it to one if required) and return the port.
357
358	The callback has to return a true value when its work is done, after
359	which is will be removed, or a false value in which case it will stay
360	registered.
361		406
362	The global C<$SELF> (exported by this module) contains C<$port> while	407	The global C<$SELF> (exported by this module) contains C<$port> while
363	executing the callback.	408	executing the callback. Runtime errors during callback execution will
		409	result in the port being C<kil>ed.
364		410
365	Runtime errors during callback execution will result in the port being	411	The default callback received all messages not matched by a more specific
366	C<kil>ed.	412	C<tag> match.
367		413
368	If the match is an array reference, then it will be matched against the	414	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
369	first elements of the message, otherwise only the first element is being
370	matched.
371		415
372	Any element in the match that is specified as C<_any_> (a function	416	Register (or replace) callbacks to be called on messages starting with the
373	exported by this module) matches any single element of the message.	417	given tag on the given port (and return the port), or unregister it (when
		418	C<$callback> is C<$undef> or missing). There can only be one callback
		419	registered for each tag.
374		420
375	While not required, it is highly recommended that the first matching	421	The original message will be passed to the callback, after the first
376	element is a string identifying the message. The one-string-only match is	422	element (the tag) has been removed. The callback will use the same
377	also the most efficient match (by far).	423	environment as the default callback (see above).
378		424
379	Example: create a port and bind receivers on it in one go.	425	Example: create a port and bind receivers on it in one go.
380		426
381	my $port = rcv port,	427	my $port = rcv port,
382	msg1 => sub { ...; 0 },	428	msg1 => sub { ... },
383	msg2 => sub { ...; 0 },	429	msg2 => sub { ... },
384	;	430	;
385		431
386	Example: create a port, bind receivers and send it in a message elsewhere	432	Example: create a port, bind receivers and send it in a message elsewhere
387	in one go:	433	in one go:
388		434
389	snd $otherport, reply =>	435	snd $otherport, reply =>
390	rcv port,	436	rcv port,
391	msg1 => sub { ...; 0 },	437	msg1 => sub { ... },
392	...	438	...
393	;	439	;
394		440
		441	Example: temporarily register a rcv callback for a tag matching some port
		442	(e.g. for an rpc reply) and unregister it after a message was received.
		443
		444	rcv $port, $otherport => sub {
		445	my @reply = @_;
		446
		447	rcv $SELF, $otherport;
		448	};
		449
395	=cut	450	=cut
396		451
397	sub rcv($@) {	452	sub rcv($@) {
398	my $port = shift;	453	my $port = shift;
399	my ($noderef, $portid) = split /#/, $port, 2;	454	my ($nodeid, $portid) = split /#/, $port, 2;
400		455
401	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	456	$NODE{$nodeid} == $NODE{""}
402	or Carp::croak "$port: rcv can only be called on local ports, caught";	457	or Carp::croak "$port: rcv can only be called on local ports, caught";
403		458
404	if (@_ == 1) {	459	while (@_) {
		460	if (ref $_[0]) {
		461	if (my $self = $PORT_DATA{$portid}) {
		462	"AnyEvent::MP::Port" eq ref $self
		463	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		464
		465	$self->[0] = shift;
		466	} else {
405	my $cb = shift;	467	my $cb = shift;
406	delete $PORT_DATA{$portid};
407	$PORT{$portid} = sub {	468	$PORT{$portid} = sub {
408	local $SELF = $port;	469	local $SELF = $port;
409	eval {	470	eval { &$cb }; _self_die if $@;
410	&$cb	471	};
411	and kil $port;
412	};	472	}
413	_self_die if $@;	473	} elsif (defined $_[0]) {
414	};
415	} else {
416	my $self = $PORT_DATA{$portid} \|\|= do {	474	my $self = $PORT_DATA{$portid} \|\|= do {
417	my $self = bless {	475	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
418	id => $port,
419	}, "AnyEvent::MP::Port";
420		476
421	$PORT{$portid} = sub {	477	$PORT{$portid} = sub {
422	local $SELF = $port;	478	local $SELF = $port;
423		479
424	eval {
425	for (@{ $self->{rc0}{$_[0]} }) {	480	if (my $cb = $self->[1]{$_[0]}) {
426	$_ && &{$_->[0]}	481	shift;
427	&& undef $_;	482	eval { &$cb }; _self_die if $@;
428	}	483	} else {
429
430	for (@{ $self->{rcv}{$_[0]} }) {
431	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
432	&& &{$_->[0]}	484	&{ $self->[0] };
433	&& undef $_;
434	}
435
436	for (@{ $self->{any} }) {
437	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
438	&& &{$_->[0]}
439	&& undef $_;
440	}	485	}
441	};	486	};
442	_self_die if $@;	487
		488	$self
443	};	489	};
444		490
445	$self
446	};
447
448	"AnyEvent::MP::Port" eq ref $self	491	"AnyEvent::MP::Port" eq ref $self
449	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	492	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
450		493
451	while (@_) {
452	my ($match, $cb) = splice @_, 0, 2;	494	my ($tag, $cb) = splice @_, 0, 2;
453		495
454	if (!ref $match) {	496	if (defined $cb) {
455	push @{ $self->{rc0}{$match} }, [$cb];	497	$self->[1]{$tag} = $cb;
456	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
457	my ($type, @match) = @$match;
458	@match
459	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
460	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
461	} else {	498	} else {
462	push @{ $self->{any} }, [$cb, $match];	499	delete $self->[1]{$tag};
463	}	500	}
464	}	501	}
465	}	502	}
466		503
467	$port	504	$port
468	}	505	}
469		506
		507	=item peval $port, $coderef[, @args]
		508
		509	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		510	when the code throews an exception the C<$port> will be killed.
		511
		512	Any remaining args will be passed to the callback. Any return values will
		513	be returned to the caller.
		514
		515	This is useful when you temporarily want to execute code in the context of
		516	a port.
		517
		518	Example: create a port and run some initialisation code in it's context.
		519
		520	my $port = port { ... };
		521
		522	peval $port, sub {
		523	init
		524	or die "unable to init";
		525	};
		526
		527	=cut
		528
		529	sub peval($$) {
		530	local $SELF = shift;
		531	my $cb = shift;
		532
		533	if (wantarray) {
		534	my @res = eval { &$cb };
		535	_self_die if $@;
		536	@res
		537	} else {
		538	my $res = eval { &$cb };
		539	_self_die if $@;
		540	$res
		541	}
		542	}
		543
470	=item $closure = psub { BLOCK }	544	=item $closure = psub { BLOCK }
471		545
472	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	546	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
473	closure is executed, sets up the environment in the same way as in C<rcv>	547	closure is executed, sets up the environment in the same way as in C<rcv>
474	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.	548	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		549
		550	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		551	BLOCK }, @_ } >>.
475		552
476	This is useful when you register callbacks from C<rcv> callbacks:	553	This is useful when you register callbacks from C<rcv> callbacks:
477		554
478	rcv delayed_reply => sub {	555	rcv delayed_reply => sub {
479	my ($delay, @reply) = @_;	556	my ($delay, @reply) = @_;
…		…
503	$res	580	$res
504	}	581	}
505	}	582	}
506	}	583	}
507		584
508	=item $guard = mon $port, $cb->(@reason)	585	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
509		586
510	=item $guard = mon $port, $rcvport	587	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
511		588
512	=item $guard = mon $port	589	=item $guard = mon $port # kill $SELF when $port dies
513		590
514	=item $guard = mon $port, $rcvport, @msg	591	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
515		592
516	Monitor the given port and do something when the port is killed or	593	Monitor the given port and do something when the port is killed or
517	messages to it were lost, and optionally return a guard that can be used	594	messages to it were lost, and optionally return a guard that can be used
518	to stop monitoring again.	595	to stop monitoring again.
519
520	C<mon> effectively guarantees that, in the absence of hardware failures,
521	that after starting the monitor, either all messages sent to the port
522	will arrive, or the monitoring action will be invoked after possible
523	message loss has been detected. No messages will be lost "in between"
524	(after the first lost message no further messages will be received by the
525	port). After the monitoring action was invoked, further messages might get
526	delivered again.
527		596
528	In the first form (callback), the callback is simply called with any	597	In the first form (callback), the callback is simply called with any
529	number of C<@reason> elements (no @reason means that the port was deleted	598	number of C<@reason> elements (no @reason means that the port was deleted
530	"normally"). Note also that I<< the callback B<must> never die >>, so use	599	"normally"). Note also that I<< the callback B<must> never die >>, so use
531	C<eval> if unsure.	600	C<eval> if unsure.
532		601
533	In the second form (another port given), the other port (C<$rcvport>)	602	In the second form (another port given), the other port (C<$rcvport>)
534	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	603	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
535	"normal" kils nothing happens, while under all other conditions, the other	604	"normal" kils nothing happens, while under all other conditions, the other
536	port is killed with the same reason.	605	port is killed with the same reason.
537		606
538	The third form (kill self) is the same as the second form, except that	607	The third form (kill self) is the same as the second form, except that
539	C<$rvport> defaults to C<$SELF>.	608	C<$rvport> defaults to C<$SELF>.
540		609
541	In the last form (message), a message of the form C<@msg, @reason> will be	610	In the last form (message), a message of the form C<@msg, @reason> will be
542	C<snd>.	611	C<snd>.
		612
		613	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		614	alert was raised), they are removed and will not trigger again.
543		615
544	As a rule of thumb, monitoring requests should always monitor a port from	616	As a rule of thumb, monitoring requests should always monitor a port from
545	a local port (or callback). The reason is that kill messages might get	617	a local port (or callback). The reason is that kill messages might get
546	lost, just like any other message. Another less obvious reason is that	618	lost, just like any other message. Another less obvious reason is that
547	even monitoring requests can get lost (for exmaple, when the connection	619	even monitoring requests can get lost (for example, when the connection
548	to the other node goes down permanently). When monitoring a port locally	620	to the other node goes down permanently). When monitoring a port locally
549	these problems do not exist.	621	these problems do not exist.
550		622
		623	C<mon> effectively guarantees that, in the absence of hardware failures,
		624	after starting the monitor, either all messages sent to the port will
		625	arrive, or the monitoring action will be invoked after possible message
		626	loss has been detected. No messages will be lost "in between" (after
		627	the first lost message no further messages will be received by the
		628	port). After the monitoring action was invoked, further messages might get
		629	delivered again.
		630
		631	Inter-host-connection timeouts and monitoring depend on the transport
		632	used. The only transport currently implemented is TCP, and AnyEvent::MP
		633	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		634	non-idle connection, and usually around two hours for idle connections).
		635
		636	This means that monitoring is good for program errors and cleaning up
		637	stuff eventually, but they are no replacement for a timeout when you need
		638	to ensure some maximum latency.
		639
551	Example: call a given callback when C<$port> is killed.	640	Example: call a given callback when C<$port> is killed.
552		641
553	mon $port, sub { warn "port died because of <@_>\n" };	642	mon $port, sub { warn "port died because of <@_>\n" };
554		643
555	Example: kill ourselves when C<$port> is killed abnormally.	644	Example: kill ourselves when C<$port> is killed abnormally.
…		…
561	mon $port, $self => "restart";	650	mon $port, $self => "restart";
562		651
563	=cut	652	=cut
564		653
565	sub mon {	654	sub mon {
566	my ($noderef, $port) = split /#/, shift, 2;	655	my ($nodeid, $port) = split /#/, shift, 2;
567		656
568	my $node = $NODE{$noderef} \|\| add_node $noderef;	657	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
569		658
570	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';	659	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
571		660
572	unless (ref $cb) {	661	unless (ref $cb) {
573	if (@_) {	662	if (@_) {
…		…
582	}	671	}
583		672
584	$node->monitor ($port, $cb);	673	$node->monitor ($port, $cb);
585		674
586	defined wantarray	675	defined wantarray
587	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	676	and ($cb += 0, AnyEvent::Util::guard { $node->unmonitor ($port, $cb) })
588	}	677	}
589		678
590	=item $guard = mon_guard $port, $ref, $ref...	679	=item $guard = mon_guard $port, $ref, $ref...
591		680
592	Monitors the given C<$port> and keeps the passed references. When the port	681	Monitors the given C<$port> and keeps the passed references. When the port
593	is killed, the references will be freed.	682	is killed, the references will be freed.
594		683
595	Optionally returns a guard that will stop the monitoring.	684	Optionally returns a guard that will stop the monitoring.
596		685
597	This function is useful when you create e.g. timers or other watchers and	686	This function is useful when you create e.g. timers or other watchers and
598	want to free them when the port gets killed:	687	want to free them when the port gets killed (note the use of C<psub>):
599		688
600	$port->rcv (start => sub {	689	$port->rcv (start => sub {
601	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	690	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
602	undef $timer if 0.9 < rand;	691	undef $timer if 0.9 < rand;
603	});	692	});
604	});	693	});
605		694
606	=cut	695	=cut
…		…
615		704
616	=item kil $port[, @reason]	705	=item kil $port[, @reason]
617		706
618	Kill the specified port with the given C<@reason>.	707	Kill the specified port with the given C<@reason>.
619		708
620	If no C<@reason> is specified, then the port is killed "normally" (linked	709	If no C<@reason> is specified, then the port is killed "normally" -
621	ports will not be kileld, or even notified).	710	monitor callback will be invoked, but the kil will not cause linked ports
		711	(C<mon $mport, $lport> form) to get killed.
622		712
623	Otherwise, linked ports get killed with the same reason (second form of	713	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
624	C<mon>, see below).	714	form) get killed with the same reason.
625		715
626	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	716	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
627	will be reported as reason C<< die => $@ >>.	717	will be reported as reason C<< die => $@ >>.
628		718
629	Transport/communication errors are reported as C<< transport_error =>	719	Transport/communication errors are reported as C<< transport_error =>
…		…
634	=item $port = spawn $node, $initfunc[, @initdata]	724	=item $port = spawn $node, $initfunc[, @initdata]
635		725
636	Creates a port on the node C<$node> (which can also be a port ID, in which	726	Creates a port on the node C<$node> (which can also be a port ID, in which
637	case it's the node where that port resides).	727	case it's the node where that port resides).
638		728
639	The port ID of the newly created port is return immediately, and it is	729	The port ID of the newly created port is returned immediately, and it is
640	permissible to immediately start sending messages or monitor the port.	730	possible to immediately start sending messages or to monitor the port.
641		731
642	After the port has been created, the init function is	732	After the port has been created, the init function is called on the remote
643	called. This function must be a fully-qualified function name	733	node, in the same context as a C<rcv> callback. This function must be a
644	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	734	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
645	program, use C<::name>.	735	specify a function in the main program, use C<::name>.
646		736
647	If the function doesn't exist, then the node tries to C<require>	737	If the function doesn't exist, then the node tries to C<require>
648	the package, then the package above the package and so on (e.g.	738	the package, then the package above the package and so on (e.g.
649	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	739	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
650	exists or it runs out of package names.	740	exists or it runs out of package names.
651		741
652	The init function is then called with the newly-created port as context	742	The init function is then called with the newly-created port as context
653	object (C<$SELF>) and the C<@initdata> values as arguments.	743	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		744	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		745	the port might not get created.
654		746
655	A common idiom is to pass your own port, monitor the spawned port, and	747	A common idiom is to pass a local port, immediately monitor the spawned
656	in the init function, monitor the original port. This two-way monitoring	748	port, and in the remote init function, immediately monitor the passed
657	ensures that both ports get cleaned up when there is a problem.	749	local port. This two-way monitoring ensures that both ports get cleaned up
		750	when there is a problem.
		751
		752	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		753	caller before C<spawn> returns (by delaying invocation when spawn is
		754	called for the local node).
658		755
659	Example: spawn a chat server port on C<$othernode>.	756	Example: spawn a chat server port on C<$othernode>.
660		757
661	# this node, executed from within a port context:	758	# this node, executed from within a port context:
662	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	759	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
677		774
678	sub _spawn {	775	sub _spawn {
679	my $port = shift;	776	my $port = shift;
680	my $init = shift;	777	my $init = shift;
681		778
		779	# rcv will create the actual port
682	local $SELF = "$NODE#$port";	780	local $SELF = "$NODE#$port";
683	eval {	781	eval {
684	&{ load_func $init }	782	&{ load_func $init }
685	};	783	};
686	_self_die if $@;	784	_self_die if $@;
687	}	785	}
688		786
689	sub spawn(@) {	787	sub spawn(@) {
690	my ($noderef, undef) = split /#/, shift, 2;	788	my ($nodeid, undef) = split /#/, shift, 2;
691		789
692	my $id = "$RUNIQ." . $ID++;	790	my $id = "$RUNIQ." . ++$ID;
693		791
694	$_[0] =~ /::/	792	$_[0] =~ /::/
695	or Carp::croak "spawn init function must be a fully-qualified name, caught";	793	or Carp::croak "spawn init function must be a fully-qualified name, caught";
696		794
697	($NODE{$noderef} \|\| add_node $noderef)	795	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
698	->send (["", "AnyEvent::MP::_spawn" => $id, @_]);
699		796
700	"$noderef#$id"	797	"$nodeid#$id"
701	}	798	}
702		799
703	=back
704		800
705	=head1 NODE MESSAGES	801	=item after $timeout, @msg
706		802
707	Nodes understand the following messages sent to them. Many of them take	803	=item after $timeout, $callback
708	arguments called C<@reply>, which will simply be used to compose a reply
709	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
710	the remaining arguments are simply the message data.
711		804
712	While other messages exist, they are not public and subject to change.	805	Either sends the given message, or call the given callback, after the
		806	specified number of seconds.
713		807
714	=over 4	808	This is simply a utility function that comes in handy at times - the
		809	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		810	so it may go away in the future.
715		811
716	=cut	812	=cut
717		813
718	=item lookup => $name, @reply	814	sub after($@) {
		815	my ($timeout, @action) = @_;
719		816
720	Replies with the port ID of the specified well-known port, or C<undef>.	817	my $t; $t = AE::timer $timeout, 0, sub {
		818	undef $t;
		819	ref $action[0]
		820	? $action[0]()
		821	: snd @action;
		822	};
		823	}
721		824
722	=item devnull => ...	825	=item cal $port, @msg, $callback[, $timeout]
723		826
724	Generic data sink/CPU heat conversion.	827	A simple form of RPC - sends a message to the given C<$port> with the
		828	given contents (C<@msg>), but adds a reply port to the message.
725		829
726	=item relay => $port, @msg	830	The reply port is created temporarily just for the purpose of receiving
		831	the reply, and will be C<kil>ed when no longer needed.
727		832
728	Simply forwards the message to the given port.	833	A reply message sent to the port is passed to the C<$callback> as-is.
729		834
730	=item eval => $string[ @reply]	835	If an optional time-out (in seconds) is given and it is not C<undef>,
		836	then the callback will be called without any arguments after the time-out
		837	elapsed and the port is C<kil>ed.
731		838
732	Evaluates the given string. If C<@reply> is given, then a message of the	839	If no time-out is given (or it is C<undef>), then the local port will
733	form C<@reply, $@, @evalres> is sent.	840	monitor the remote port instead, so it eventually gets cleaned-up.
734		841
735	Example: crash another node.	842	Currently this function returns the temporary port, but this "feature"
		843	might go in future versions unless you can make a convincing case that
		844	this is indeed useful for something.
736		845
737	snd $othernode, eval => "exit";	846	=cut
738		847
739	=item time => @reply	848	sub cal(@) {
		849	my $timeout = ref $_[-1] ? undef : pop;
		850	my $cb = pop;
740		851
741	Replies the the current node time to C<@reply>.	852	my $port = port {
		853	undef $timeout;
		854	kil $SELF;
		855	&$cb;
		856	};
742		857
743	Example: tell the current node to send the current time to C<$myport> in a	858	if (defined $timeout) {
744	C<timereply> message.	859	$timeout = AE::timer $timeout, 0, sub {
		860	undef $timeout;
		861	kil $port;
		862	$cb->();
		863	};
		864	} else {
		865	mon $_[0], sub {
		866	kil $port;
		867	$cb->();
		868	};
		869	}
745		870
746	snd $NODE, time => $myport, timereply => 1, 2;	871	push @_, $port;
747	# => snd $myport, timereply => 1, 2, <time>	872	&snd;
		873
		874	$port
		875	}
748		876
749	=back	877	=back
750		878
751	=head1 AnyEvent::MP vs. Distributed Erlang	879	=head1 AnyEvent::MP vs. Distributed Erlang
752		880
753	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	881	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
754	== aemp node, Erlang process == aemp port), so many of the documents and	882	== aemp node, Erlang process == aemp port), so many of the documents and
755	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	883	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
756	sample:	884	sample:
757		885
758	http://www.Erlang.se/doc/programming_rules.shtml	886	http://www.erlang.se/doc/programming_rules.shtml
759	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	887	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
760	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	888	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
761	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	889	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
762		890
763	Despite the similarities, there are also some important differences:	891	Despite the similarities, there are also some important differences:
764		892
765	=over 4	893	=over 4
766		894
767	=item * Node references contain the recipe on how to contact them.	895	=item * Node IDs are arbitrary strings in AEMP.
768		896
769	Erlang relies on special naming and DNS to work everywhere in the	897	Erlang relies on special naming and DNS to work everywhere in the same
770	same way. AEMP relies on each node knowing it's own address(es), with	898	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
771	convenience functionality.	899	configuration or DNS), and possibly the addresses of some seed nodes, but
		900	will otherwise discover other nodes (and their IDs) itself.
772		901
773	This means that AEMP requires a less tightly controlled environment at the	902	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
774	cost of longer node references and a slightly higher management overhead.	903	uses "local ports are like remote ports".
		904
		905	The failure modes for local ports are quite different (runtime errors
		906	only) then for remote ports - when a local port dies, you I<know> it dies,
		907	when a connection to another node dies, you know nothing about the other
		908	port.
		909
		910	Erlang pretends remote ports are as reliable as local ports, even when
		911	they are not.
		912
		913	AEMP encourages a "treat remote ports differently" philosophy, with local
		914	ports being the special case/exception, where transport errors cannot
		915	occur.
775		916
776	=item * Erlang uses processes and a mailbox, AEMP does not queue.	917	=item * Erlang uses processes and a mailbox, AEMP does not queue.
777		918
778	Erlang uses processes that selctively receive messages, and therefore	919	Erlang uses processes that selectively receive messages out of order, and
779	needs a queue. AEMP is event based, queuing messages would serve no useful	920	therefore needs a queue. AEMP is event based, queuing messages would serve
780	purpose.	921	no useful purpose. For the same reason the pattern-matching abilities
		922	of AnyEvent::MP are more limited, as there is little need to be able to
		923	filter messages without dequeuing them.
781		924
782	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	925	This is not a philosophical difference, but simply stems from AnyEvent::MP
		926	being event-based, while Erlang is process-based.
		927
		928	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		929	top of AEMP and Coro threads.
783		930
784	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	931	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
785		932
786	Sending messages in Erlang is synchronous and blocks the process. AEMP	933	Sending messages in Erlang is synchronous and blocks the process until
787	sends are immediate, connection establishment is handled in the	934	a conenction has been established and the message sent (and so does not
788	background.	935	need a queue that can overflow). AEMP sends return immediately, connection
		936	establishment is handled in the background.
789		937
790	=item * Erlang can silently lose messages, AEMP cannot.	938	=item * Erlang suffers from silent message loss, AEMP does not.
791		939
792	Erlang makes few guarantees on messages delivery - messages can get lost	940	Erlang implements few guarantees on messages delivery - messages can get
793	without any of the processes realising it (i.e. you send messages a, b,	941	lost without any of the processes realising it (i.e. you send messages a,
794	and c, and the other side only receives messages a and c).	942	b, and c, and the other side only receives messages a and c).
795		943
796	AEMP guarantees correct ordering, and the guarantee that there are no	944	AEMP guarantees (modulo hardware errors) correct ordering, and the
		945	guarantee that after one message is lost, all following ones sent to the
		946	same port are lost as well, until monitoring raises an error, so there are
797	holes in the message sequence.	947	no silent "holes" in the message sequence.
798		948
799	=item * In Erlang, processes can be declared dead and later be found to be	949	If you want your software to be very reliable, you have to cope with
800	alive.	950	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
801		951	simply tries to work better in common error cases, such as when a network
802	In Erlang it can happen that a monitored process is declared dead and	952	link goes down.
803	linked processes get killed, but later it turns out that the process is
804	still alive - and can receive messages.
805
806	In AEMP, when port monitoring detects a port as dead, then that port will
807	eventually be killed - it cannot happen that a node detects a port as dead
808	and then later sends messages to it, finding it is still alive.
809		953
810	=item * Erlang can send messages to the wrong port, AEMP does not.	954	=item * Erlang can send messages to the wrong port, AEMP does not.
811		955
812	In Erlang it is quite possible that a node that restarts reuses a process	956	In Erlang it is quite likely that a node that restarts reuses an Erlang
813	ID known to other nodes for a completely different process, causing	957	process ID known to other nodes for a completely different process,
814	messages destined for that process to end up in an unrelated process.	958	causing messages destined for that process to end up in an unrelated
		959	process.
815		960
816	AEMP never reuses port IDs, so old messages or old port IDs floating	961	AEMP does not reuse port IDs, so old messages or old port IDs floating
817	around in the network will not be sent to an unrelated port.	962	around in the network will not be sent to an unrelated port.
818		963
819	=item * Erlang uses unprotected connections, AEMP uses secure	964	=item * Erlang uses unprotected connections, AEMP uses secure
820	authentication and can use TLS.	965	authentication and can use TLS.
821		966
822	AEMP can use a proven protocol - SSL/TLS - to protect connections and	967	AEMP can use a proven protocol - TLS - to protect connections and
823	securely authenticate nodes.	968	securely authenticate nodes.
824		969
825	=item * The AEMP protocol is optimised for both text-based and binary	970	=item * The AEMP protocol is optimised for both text-based and binary
826	communications.	971	communications.
827		972
828	The AEMP protocol, unlike the Erlang protocol, supports both	973	The AEMP protocol, unlike the Erlang protocol, supports both programming
829	language-independent text-only protocols (good for debugging) and binary,	974	language independent text-only protocols (good for debugging), and binary,
830	language-specific serialisers (e.g. Storable).	975	language-specific serialisers (e.g. Storable). By default, unless TLS is
		976	used, the protocol is actually completely text-based.
831		977
832	It has also been carefully designed to be implementable in other languages	978	It has also been carefully designed to be implementable in other languages
833	with a minimum of work while gracefully degrading fucntionality to make the	979	with a minimum of work while gracefully degrading functionality to make the
834	protocol simple.	980	protocol simple.
835		981
836	=item * AEMP has more flexible monitoring options than Erlang.	982	=item * AEMP has more flexible monitoring options than Erlang.
837		983
838	In Erlang, you can chose to receive I<all> exit signals as messages	984	In Erlang, you can chose to receive I<all> exit signals as messages or
839	or I<none>, there is no in-between, so monitoring single processes is	985	I<none>, there is no in-between, so monitoring single Erlang processes is
840	difficult to implement. Monitoring in AEMP is more flexible than in	986	difficult to implement.
841	Erlang, as one can choose between automatic kill, exit message or callback	987
842	on a per-process basis.	988	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		989	between automatic kill, exit message or callback on a per-port basis.
843		990
844	=item * Erlang tries to hide remote/local connections, AEMP does not.	991	=item * Erlang tries to hide remote/local connections, AEMP does not.
845		992
846	Monitoring in Erlang is not an indicator of process death/crashes,	993	Monitoring in Erlang is not an indicator of process death/crashes, in the
847	as linking is (except linking is unreliable in Erlang).	994	same way as linking is (except linking is unreliable in Erlang).
848		995
849	In AEMP, you don't "look up" registered port names or send to named ports	996	In AEMP, you don't "look up" registered port names or send to named ports
850	that might or might not be persistent. Instead, you normally spawn a port	997	that might or might not be persistent. Instead, you normally spawn a port
851	on the remote node. The init function monitors the you, and you monitor	998	on the remote node. The init function monitors you, and you monitor the
852	the remote port. Since both monitors are local to the node, they are much	999	remote port. Since both monitors are local to the node, they are much more
853	more reliable.	1000	reliable (no need for C<spawn_link>).
854		1001
855	This also saves round-trips and avoids sending messages to the wrong port	1002	This also saves round-trips and avoids sending messages to the wrong port
856	(hard to do in Erlang).	1003	(hard to do in Erlang).
857		1004
858	=back	1005	=back
859		1006
		1007	=head1 RATIONALE
		1008
		1009	=over 4
		1010
		1011	=item Why strings for port and node IDs, why not objects?
		1012
		1013	We considered "objects", but found that the actual number of methods
		1014	that can be called are quite low. Since port and node IDs travel over
		1015	the network frequently, the serialising/deserialising would add lots of
		1016	overhead, as well as having to keep a proxy object everywhere.
		1017
		1018	Strings can easily be printed, easily serialised etc. and need no special
		1019	procedures to be "valid".
		1020
		1021	And as a result, a port with just a default receiver consists of a single
		1022	code reference stored in a global hash - it can't become much cheaper.
		1023
		1024	=item Why favour JSON, why not a real serialising format such as Storable?
		1025
		1026	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1027	format, but currently there is no way to make a node use Storable by
		1028	default (although all nodes will accept it).
		1029
		1030	The default framing protocol is JSON because a) JSON::XS is many times
		1031	faster for small messages and b) most importantly, after years of
		1032	experience we found that object serialisation is causing more problems
		1033	than it solves: Just like function calls, objects simply do not travel
		1034	easily over the network, mostly because they will always be a copy, so you
		1035	always have to re-think your design.
		1036
		1037	Keeping your messages simple, concentrating on data structures rather than
		1038	objects, will keep your messages clean, tidy and efficient.
		1039
		1040	=back
		1041
860	=head1 SEE ALSO	1042	=head1 SEE ALSO
		1043
		1044	L<AnyEvent::MP::Intro> - a gentle introduction.
		1045
		1046	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1047
		1048	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1049	your applications.
		1050
		1051	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1052
		1053	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1054	all nodes.
861		1055
862	L<AnyEvent>.	1056	L<AnyEvent>.
863		1057
864	=head1 AUTHOR	1058	=head1 AUTHOR
865		1059

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Revision 1.122 by root, Wed Feb 29 18:44:59 2012 UTC