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

Comparing cvsroot/AnyEvent-MP/MP.pm (file contents):
Revision 1.43 by root, Sun Aug 9 16:08:16 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	};
		51
		52	=head1 CURRENT STATUS
		53
		54	bin/aemp - stable.
		55	AnyEvent::MP - stable API, should work.
		56	AnyEvent::MP::Intro - explains most concepts.
		57	AnyEvent::MP::Kernel - mostly stable API.
		58	AnyEvent::MP::Global - stable API.
42		59
43	=head1 DESCRIPTION	60	=head1 DESCRIPTION
44		61
45	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
46		63
47	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
48	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
49		66
50	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	67	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
51	manual page.	68	manual page and the examples under F<eg/>.
52
53	At the moment, this module family is severly broken and underdocumented,
54	so do not use. This was uploaded mainly to reserve the CPAN namespace -
55	stay tuned! The basic API should be finished, however.
56		69
57	=head1 CONCEPTS	70	=head1 CONCEPTS
58		71
59	=over 4	72	=over 4
60		73
61	=item port	74	=item port
62		75
63	A port is something you can send messages to (with the C<snd> function).	76	Not to be confused with a TCP port, a "port" is something you can send
		77	messages to (with the C<snd> function).
64		78
65	Some ports allow you to register C<rcv> handlers that can match specific	79	Ports allow you to register C<rcv> handlers that can match all or just
66	messages. All C<rcv> handlers will receive messages they match, messages	80	some messages. Messages send to ports will not be queued, regardless of
67	will not be queued.	81	anything was listening for them or not.
68		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
69	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
70		86
71	A port id is normaly the concatenation of a noderef, a hash-mark (C<#>) as	87	A port ID is the concatenation of a node ID, a hash-mark (C<#>) as
72	separator, and a port name (a printable string of unspecified format). An	88	separator, and a port name (a printable string of unspecified format).
73	exception is the the node port, whose ID is identical to its node
74	reference.
75		89
76	=item node	90	=item node
77		91
78	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,
79	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
80	create new ports, among other things.	94	ports.
81		95
82	Nodes are either private (single-process only), slaves (connected to a	96	Nodes are either public (have one or more listening ports) or private
83	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.
84		99
85	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	100	Nodes is represented by (printable) strings called "node IDs".
86		101
87	A node reference is a string that either simply identifies the node (for	102	=item node ID - C<[A-Za-z0-9_\-.:]*>
88	private and slave nodes), or contains a recipe on how to reach a given
89	node (for public nodes).
90		103
91	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
92	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.
93		108
94	Node references come in two flavours: resolved (containing only numerical	109	=item binds - C<ip:port>
95	addresses) or unresolved (where hostnames are used instead of addresses).
96		110
97	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
98	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).
99		169
100	=back	170	=back
101		171
102	=head1 VARIABLES/FUNCTIONS	172	=head1 VARIABLES/FUNCTIONS
103		173
105		175
106	=cut	176	=cut
107		177
108	package AnyEvent::MP;	178	package AnyEvent::MP;
109		179
		180	use AnyEvent::MP::Config ();
110	use AnyEvent::MP::Base;	181	use AnyEvent::MP::Kernel;
		182	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
111		183
112	use common::sense;	184	use common::sense;
113		185
114	use Carp ();	186	use Carp ();
115		187
116	use AE ();	188	use AE ();
117		189
118	use base "Exporter";	190	use base "Exporter";
119		191
120	our $VERSION = $AnyEvent::MP::Base::VERSION;	192	our $VERSION = $AnyEvent::MP::Config::VERSION;
121		193
122	our @EXPORT = qw(	194	our @EXPORT = qw(
123	NODE $NODE *SELF node_of _any_	195	NODE $NODE *SELF node_of after
124	resolve_node initialise_node	196	configure
125	snd rcv mon kil reg psub spawn	197	snd rcv mon mon_guard kil psub peval spawn cal
126	port	198	port
127	);	199	);
128		200
129	our $SELF;	201	our $SELF;
130		202
…		…
134	kil $SELF, die => $msg;	206	kil $SELF, die => $msg;
135	}	207	}
136		208
137	=item $thisnode = NODE / $NODE	209	=item $thisnode = NODE / $NODE
138		210
139	The C<NODE> function returns, and the C<$NODE> variable contains	211	The C<NODE> function returns, and the C<$NODE> variable contains, the node
140	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
141	to C<become_public> or C<become_slave>, after which all local port	213	a call to C<configure>.
142	identifiers become invalid.
143		214
144	=item $noderef = node_of $port	215	=item $nodeid = node_of $port
145		216
146	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.
147		218
148	=item initialise_node $noderef, $seednode, $seednode...	219	=item configure $profile, key => value...
149		220
150	=item initialise_node "slave/", $master, $master...	221	=item configure key => value...
151		222
152	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
153	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
154	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.
155		227
156	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
157	never) before calling other AnyEvent::MP functions.	229	never) before calling other AnyEvent::MP functions.
158		230
159	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
160		232	F<aemp> command line utility (sans the set/del prefix), with two additions:
161	There are two types of networked nodes, public nodes and slave nodes:
162		233
163	=over 4	234	=over 4
164		235
165	=item public nodes	236	=item norc => $boolean (default false)
166		237
167	For public nodes, C<$noderef> must either be a (possibly unresolved)	238	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
168	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
169	which case the noderef will be guessed.	240	C<configure> call.
170		241
171	Afterwards, the node will bind itself on all endpoints and try to connect	242	=item force => $boolean (default false)
172	to all additional C<$seednodes> that are specified. Seednodes are optional
173	and can be used to quickly bootstrap the node into an existing network.
174		243
175	=item slave nodes	244	IF true, then the values specified in the C<configure> will take
176		245	precedence over any values configured via the rc file. The default is for
177	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.
178	become a slave node. Slave nodes cannot be contacted from outside and will
179	route most of their traffic to the master node that they attach to.
180
181	At least one additional noderef is required: The node will try to connect
182	to all of them and will become a slave attached to the first node it can
183	successfully connect to.
184		247
185	=back	248	=back
186		249
187	This function will block until all nodes have been resolved and, for slave
188	nodes, until it has successfully established a connection to a master
189	server.
190
191	Example: become a public node listening on the default node.
192
193	initialise_node;
194
195	Example: become a public node, and try to contact some well-known master
196	servers to become part of the network.
197
198	initialise_node undef, "master1", "master2";
199
200	Example: become a public node listening on port C<4041>.
201
202	initialise_node 4041;
203
204	Example: become a public node, only visible on localhost port 4044.
205
206	initialise_node "locahost:4044";
207
208	Example: become a slave node to any of the specified master servers.
209
210	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
211
212	=item $cv = resolve_node $noderef
213
214	Takes an unresolved node reference that may contain hostnames and
215	abbreviated IDs, resolves all of them and returns a resolved node
216	reference.
217
218	In addition to C<address:port> pairs allowed in resolved noderefs, the
219	following forms are supported:
220
221	=over 4	250	=over 4
222		251
223	=item the empty string	252	=item step 1, gathering configuration from profiles
224		253
225	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
226	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.
227		258
228	=item naked port numbers (e.g. C<1234>)	259	The profile data is then gathered as follows:
229		260
230	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
231	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).
232		266
233	=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.
234		270
235	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
236	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
237	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.
238		295
239	=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)"
240		323
241	=item $SELF	324	=item $SELF
242		325
243	Contains the current port id while executing C<rcv> callbacks or C<psub>	326	Contains the current port id while executing C<rcv> callbacks or C<psub>
244	blocks.	327	blocks.
245		328
246	=item SELF, %SELF, @SELF...	329	=item *SELF, SELF, %SELF, @SELF...
247		330
248	Due to some quirks in how perl exports variables, it is impossible to	331	Due to some quirks in how perl exports variables, it is impossible to
249	just export C<$SELF>, all the symbols called C<SELF> are exported by this	332	just export C<$SELF>, all the symbols named C<SELF> are exported by this
250	module, but only C<$SELF> is currently used.	333	module, but only C<$SELF> is currently used.
251		334
252	=item snd $port, type => @data	335	=item snd $port, type => @data
253		336
254	=item snd $port, @msg	337	=item snd $port, @msg
255		338
256	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
257	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.
258	stringifies a sa port ID (such as a port object :).
259		341
260	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
261	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
262	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.
263		346
264	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
265	function: modifying any argument is not allowed and can cause many	348	function: modifying any argument (or values referenced by them) is
266	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.
267		353
268	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
269	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
270	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
271	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
272	node, anything can be passed.	358	node, anything can be passed. Best rely only on the common denominator of
		359	these.
273		360
274	=item $local_port = port	361	=item $local_port = port
275		362
276	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
277	matching port ("full port") or a single-callback port ("miniport"),	364	no callbacks set and will throw an error when it receives messages.
278	depending on how C<rcv> callbacks are bound to the object.
279		365
280	=item $port = port { my @msg = @_; $finished }	366	=item $local_port = port { my @msg = @_ }
281		367
282	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
283	matching behind it, and returns its ID. Semantically the same as creating
284	a port and calling C<rcv $port, $callback> on it.	369	creating a port and calling C<rcv $port, $callback> on it.
285		370
286	The block will be called for every message received on the port. When the	371	The block will be called for every message received on the port, with the
287	callback returns a true value its job is considered "done" and the port	372	global variable C<$SELF> set to the port ID. Runtime errors will cause the
288	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.
289		375
290	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:
291	be passed to the callback.
292		377
293	If you need the local port id in the callback, this works nicely:	378	my $port = port {
294		379	my @msg = @_;
295	my $port; $port = port {	380	...
296	snd $otherport, reply => $port;	381	kil $SELF;
297	};	382	};
298		383
299	=cut	384	=cut
300		385
301	sub rcv($@);	386	sub rcv($@);
302		387
		388	sub _kilme {
		389	die "received message on port without callback";
		390	}
		391
303	sub port(;&) {	392	sub port(;&) {
304	my $id = "$UNIQ." . $ID++;	393	my $id = "$UNIQ." . ++$ID;
305	my $port = "$NODE#$id";	394	my $port = "$NODE#$id";
306		395
307	if (@_) {	396	rcv $port, shift \|\| \&_kilme;
308	rcv $port, shift;
309	} else {
310	$PORT{$id} = sub { }; # nop
311	}
312		397
313	$port	398	$port
314	}	399	}
315		400
316	=item reg $port, $name
317
318	=item reg $name
319
320	Registers the given port (or C<$SELF><<< if missing) under the name
321	C<$name>. If the name already exists it is replaced.
322
323	A port can only be registered under one well known name.
324
325	A port automatically becomes unregistered when it is killed.
326
327	=cut
328
329	sub reg(@) {
330	my $port = @_ > 1 ? shift : $SELF \|\| Carp::croak 'reg: called with one argument only, but $SELF not set,';
331
332	$REG{$_[0]} = $port;
333	}
334
335	=item rcv $port, $callback->(@msg)	401	=item rcv $local_port, $callback->(@msg)
336		402
337	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
338	one if required).	404	remove the default callback: use C<sub { }> to disable it, or better
339		405	C<kil> the port when it is no longer needed.
340	=item rcv $port, tagstring => $callback->(@msg), ...
341
342	=item rcv $port, $smartmatch => $callback->(@msg), ...
343
344	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
345
346	Register callbacks to be called on matching messages on the given full
347	port (after converting it to one if required) and return the port.
348
349	The callback has to return a true value when its work is done, after
350	which is will be removed, or a false value in which case it will stay
351	registered.
352		406
353	The global C<$SELF> (exported by this module) contains C<$port> while	407	The global C<$SELF> (exported by this module) contains C<$port> while
354	executing the callback.	408	executing the callback. Runtime errors during callback execution will
		409	result in the port being C<kil>ed.
355		410
356	Runtime errors during callback execution will result in the port being	411	The default callback received all messages not matched by a more specific
357	C<kil>ed.	412	C<tag> match.
358		413
359	If the match is an array reference, then it will be matched against the	414	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
360	first elements of the message, otherwise only the first element is being
361	matched.
362		415
363	Any element in the match that is specified as C<_any_> (a function	416	Register (or replace) callbacks to be called on messages starting with the
364	exported by this module) matches any single element of the message.	417	given tag on the given port (and return the port), or unregister it (when
		418	C<$callback> is C<$undef> or missing). There can only be one callback
		419	registered for each tag.
365		420
366	While not required, it is highly recommended that the first matching	421	The original message will be passed to the callback, after the first
367	element is a string identifying the message. The one-string-only match is	422	element (the tag) has been removed. The callback will use the same
368	also the most efficient match (by far).	423	environment as the default callback (see above).
369		424
370	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.
371		426
372	my $port = rcv port,	427	my $port = rcv port,
373	msg1 => sub { ...; 0 },	428	msg1 => sub { ... },
374	msg2 => sub { ...; 0 },	429	msg2 => sub { ... },
375	;	430	;
376		431
377	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
378	in one go:	433	in one go:
379		434
380	snd $otherport, reply =>	435	snd $otherport, reply =>
381	rcv port,	436	rcv port,
382	msg1 => sub { ...; 0 },	437	msg1 => sub { ... },
383	...	438	...
384	;	439	;
385		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, $otherport;
		448	};
		449
386	=cut	450	=cut
387		451
388	sub rcv($@) {	452	sub rcv($@) {
389	my $port = shift;	453	my $port = shift;
390	my ($noderef, $portid) = split /#/, $port, 2;	454	my ($nodeid, $portid) = split /#/, $port, 2;
391		455
392	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	456	$NODE{$nodeid} == $NODE{""}
393	or Carp::croak "$port: rcv can only be called on local ports, caught";	457	or Carp::croak "$port: rcv can only be called on local ports, caught";
394		458
395	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 {
396	my $cb = shift;	467	my $cb = shift;
397	delete $PORT_DATA{$portid};
398	$PORT{$portid} = sub {	468	$PORT{$portid} = sub {
399	local $SELF = $port;	469	local $SELF = $port;
400	eval {	470	eval { &$cb }; _self_die if $@;
401	&$cb	471	};
402	and kil $port;
403	};	472	}
404	_self_die if $@;	473	} elsif (defined $_[0]) {
405	};
406	} else {
407	my $self = $PORT_DATA{$portid} \|\|= do {	474	my $self = $PORT_DATA{$portid} \|\|= do {
408	my $self = bless {	475	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
409	id => $port,
410	}, "AnyEvent::MP::Port";
411		476
412	$PORT{$portid} = sub {	477	$PORT{$portid} = sub {
413	local $SELF = $port;	478	local $SELF = $port;
414		479
415	eval {
416	for (@{ $self->{rc0}{$_[0]} }) {	480	if (my $cb = $self->[1]{$_[0]}) {
417	$_ && &{$_->[0]}	481	shift;
418	&& undef $_;	482	eval { &$cb }; _self_die if $@;
419	}	483	} else {
420
421	for (@{ $self->{rcv}{$_[0]} }) {
422	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
423	&& &{$_->[0]}	484	&{ $self->[0] };
424	&& undef $_;
425	}
426
427	for (@{ $self->{any} }) {
428	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
429	&& &{$_->[0]}
430	&& undef $_;
431	}	485	}
432	};	486	};
433	_self_die if $@;	487
		488	$self
434	};	489	};
435		490
436	$self
437	};
438
439	"AnyEvent::MP::Port" eq ref $self	491	"AnyEvent::MP::Port" eq ref $self
440	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	492	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
441		493
442	while (@_) {
443	my ($match, $cb) = splice @_, 0, 2;	494	my ($tag, $cb) = splice @_, 0, 2;
444		495
445	if (!ref $match) {	496	if (defined $cb) {
446	push @{ $self->{rc0}{$match} }, [$cb];	497	$self->[1]{$tag} = $cb;
447	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
448	my ($type, @match) = @$match;
449	@match
450	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
451	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
452	} else {	498	} else {
453	push @{ $self->{any} }, [$cb, $match];	499	delete $self->[1]{$tag};
454	}	500	}
455	}	501	}
456	}	502	}
457		503
458	$port	504	$port
459	}	505	}
460		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
461	=item $closure = psub { BLOCK }	544	=item $closure = psub { BLOCK }
462		545
463	Remembers C<$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
464	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>
465	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 $SELF, sub {
		551	BLOCK }, @_ } >>.
466		552
467	This is useful when you register callbacks from C<rcv> callbacks:	553	This is useful when you register callbacks from C<rcv> callbacks:
468		554
469	rcv delayed_reply => sub {	555	rcv delayed_reply => sub {
470	my ($delay, @reply) = @_;	556	my ($delay, @reply) = @_;
…		…
494	$res	580	$res
495	}	581	}
496	}	582	}
497	}	583	}
498		584
499	=item $guard = mon $port, $cb->(@reason)	585	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
500		586
501	=item $guard = mon $port, $rcvport	587	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
502		588
503	=item $guard = mon $port	589	=item $guard = mon $port # kill $SELF when $port dies
504		590
505	=item $guard = mon $port, $rcvport, @msg	591	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
506		592
507	Monitor the given port and do something when the port is killed or	593	Monitor the given port and do something when the port is killed or
508	messages to it were lost, and optionally return a guard that can be used	594	messages to it were lost, and optionally return a guard that can be used
509	to stop monitoring again.	595	to stop monitoring again.
510
511	C<mon> effectively guarantees that, in the absence of hardware failures,
512	that after starting the monitor, either all messages sent to the port
513	will arrive, or the monitoring action will be invoked after possible
514	message loss has been detected. No messages will be lost "in between"
515	(after the first lost message no further messages will be received by the
516	port). After the monitoring action was invoked, further messages might get
517	delivered again.
518		596
519	In the first form (callback), the callback is simply called with any	597	In the first form (callback), the callback is simply called with any
520	number of C<@reason> elements (no @reason means that the port was deleted	598	number of C<@reason> elements (no @reason means that the port was deleted
521	"normally"). Note also that I<< the callback B<must> never die >>, so use	599	"normally"). Note also that I<< the callback B<must> never die >>, so use
522	C<eval> if unsure.	600	C<eval> if unsure.
523		601
524	In the second form (another port given), the other port (C<$rcvport>)	602	In the second form (another port given), the other port (C<$rcvport>)
525	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	603	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
526	"normal" kils nothing happens, while under all other conditions, the other	604	"normal" kils nothing happens, while under all other conditions, the other
527	port is killed with the same reason.	605	port is killed with the same reason.
528		606
529	The third form (kill self) is the same as the second form, except that	607	The third form (kill self) is the same as the second form, except that
530	C<$rvport> defaults to C<$SELF>.	608	C<$rvport> defaults to C<$SELF>.
531		609
532	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
533	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.
534		615
535	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
536	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
537	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
538	even monitoring requests can get lost (for exmaple, when the connection	619	even monitoring requests can get lost (for example, when the connection
539	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
540	these problems do not exist.	621	these problems do not exist.
541		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
542	Example: call a given callback when C<$port> is killed.	640	Example: call a given callback when C<$port> is killed.
543		641
544	mon $port, sub { warn "port died because of <@_>\n" };	642	mon $port, sub { warn "port died because of <@_>\n" };
545		643
546	Example: kill ourselves when C<$port> is killed abnormally.	644	Example: kill ourselves when C<$port> is killed abnormally.
…		…
552	mon $port, $self => "restart";	650	mon $port, $self => "restart";
553		651
554	=cut	652	=cut
555		653
556	sub mon {	654	sub mon {
557	my ($noderef, $port) = split /#/, shift, 2;	655	my ($nodeid, $port) = split /#/, shift, 2;
558		656
559	my $node = $NODE{$noderef} \|\| add_node $noderef;	657	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
560		658
561	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,';
562		660
563	unless (ref $cb) {	661	unless (ref $cb) {
564	if (@_) {	662	if (@_) {
…		…
573	}	671	}
574		672
575	$node->monitor ($port, $cb);	673	$node->monitor ($port, $cb);
576		674
577	defined wantarray	675	defined wantarray
578	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	676	and ($cb += 0, AnyEvent::Util::guard { $node->unmonitor ($port, $cb) })
579	}	677	}
580		678
581	=item $guard = mon_guard $port, $ref, $ref...	679	=item $guard = mon_guard $port, $ref, $ref...
582		680
583	Monitors the given C<$port> and keeps the passed references. When the port	681	Monitors the given C<$port> and keeps the passed references. When the port
584	is killed, the references will be freed.	682	is killed, the references will be freed.
585		683
586	Optionally returns a guard that will stop the monitoring.	684	Optionally returns a guard that will stop the monitoring.
587		685
588	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
589	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>):
590		688
591	$port->rcv (start => sub {	689	$port->rcv (start => sub {
592	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	690	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
593	undef $timer if 0.9 < rand;	691	undef $timer if 0.9 < rand;
594	});	692	});
595	});	693	});
596		694
597	=cut	695	=cut
…		…
606		704
607	=item kil $port[, @reason]	705	=item kil $port[, @reason]
608		706
609	Kill the specified port with the given C<@reason>.	707	Kill the specified port with the given C<@reason>.
610		708
611	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" -
612	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.
613		712
614	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>
615	C<mon>, see below).	714	form) get killed with the same reason.
616		715
617	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
618	will be reported as reason C<< die => $@ >>.	717	will be reported as reason C<< die => $@ >>.
619		718
620	Transport/communication errors are reported as C<< transport_error =>	719	Transport/communication errors are reported as C<< transport_error =>
…		…
625	=item $port = spawn $node, $initfunc[, @initdata]	724	=item $port = spawn $node, $initfunc[, @initdata]
626		725
627	Creates a port on the node C<$node> (which can also be a port ID, in which	726	Creates a port on the node C<$node> (which can also be a port ID, in which
628	case it's the node where that port resides).	727	case it's the node where that port resides).
629		728
630	The port ID of the newly created port is return immediately, and it is	729	The port ID of the newly created port is returned immediately, and it is
631	permissible to immediately start sending messages or monitor the port.	730	possible to immediately start sending messages or to monitor the port.
632		731
633	After the port has been created, the init function is	732	After the port has been created, the init function is called on the remote
634	called. This function must be a fully-qualified function name	733	node, in the same context as a C<rcv> callback. This function must be a
635	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	734	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
636	program, use C<::name>.	735	specify a function in the main program, use C<::name>.
637		736
638	If the function doesn't exist, then the node tries to C<require>	737	If the function doesn't exist, then the node tries to C<require>
639	the package, then the package above the package and so on (e.g.	738	the package, then the package above the package and so on (e.g.
640	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	739	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
641	exists or it runs out of package names.	740	exists or it runs out of package names.
642		741
643	The init function is then called with the newly-created port as context	742	The init function is then called with the newly-created port as context
644	object (C<$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.
645		746
646	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
647	in the init function, monitor the original port. This two-way monitoring	748	port, and in the remote init function, immediately monitor the passed
648	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<$initfunc> has no visible effects on the
		753	caller before C<spawn> returns (by delaying invocation when spawn is
		754	called for the local node).
649		755
650	Example: spawn a chat server port on C<$othernode>.	756	Example: spawn a chat server port on C<$othernode>.
651		757
652	# this node, executed from within a port context:	758	# this node, executed from within a port context:
653	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	759	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
668		774
669	sub _spawn {	775	sub _spawn {
670	my $port = shift;	776	my $port = shift;
671	my $init = shift;	777	my $init = shift;
672		778
		779	# rcv will create the actual port
673	local $SELF = "$NODE#$port";	780	local $SELF = "$NODE#$port";
674	eval {	781	eval {
675	&{ load_func $init }	782	&{ load_func $init }
676	};	783	};
677	_self_die if $@;	784	_self_die if $@;
678	}	785	}
679		786
680	sub spawn(@) {	787	sub spawn(@) {
681	my ($noderef, undef) = split /#/, shift, 2;	788	my ($nodeid, undef) = split /#/, shift, 2;
682		789
683	my $id = "$RUNIQ." . $ID++;	790	my $id = "$RUNIQ." . ++$ID;
684		791
685	$_[0] =~ /::/	792	$_[0] =~ /::/
686	or Carp::croak "spawn init function must be a fully-qualified name, caught";	793	or Carp::croak "spawn init function must be a fully-qualified name, caught";
687		794
688	($NODE{$noderef} \|\| add_node $noderef)	795	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
689	->send (["", "AnyEvent::MP::_spawn" => $id, @_]);
690		796
691	"$noderef#$id"	797	"$nodeid#$id"
692	}	798	}
693		799
694	=back
695		800
696	=head1 NODE MESSAGES	801	=item after $timeout, @msg
697		802
698	Nodes understand the following messages sent to them. Many of them take	803	=item after $timeout, $callback
699	arguments called C<@reply>, which will simply be used to compose a reply
700	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
701	the remaining arguments are simply the message data.
702		804
703	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.
704		807
705	=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.
706		811
707	=cut	812	=cut
708		813
709	=item lookup => $name, @reply	814	sub after($@) {
		815	my ($timeout, @action) = @_;
710		816
711	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	}
712		824
713	=item devnull => ...	825	=item cal $port, @msg, $callback[, $timeout]
714		826
715	Generic data sink/CPU heat conversion.	827	A simple form of RPC - sends a message to the given C<$port> with the
		828	given contents (C<@msg>), but adds a reply port to the message.
716		829
717	=item relay => $port, @msg	830	The reply port is created temporarily just for the purpose of receiving
		831	the reply, and will be C<kil>ed when no longer needed.
718		832
719	Simply forwards the message to the given port.	833	A reply message sent to the port is passed to the C<$callback> as-is.
720		834
721	=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.
722		838
723	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
724	form C<@reply, $@, @evalres> is sent.	840	monitor the remote port instead, so it eventually gets cleaned-up.
725		841
726	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.
727		845
728	snd $othernode, eval => "exit";	846	=cut
729		847
730	=item time => @reply	848	sub cal(@) {
		849	my $timeout = ref $_[-1] ? undef : pop;
		850	my $cb = pop;
731		851
732	Replies the the current node time to C<@reply>.	852	my $port = port {
		853	undef $timeout;
		854	kil $SELF;
		855	&$cb;
		856	};
733		857
734	Example: tell the current node to send the current time to C<$myport> in a	858	if (defined $timeout) {
735	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	}
736		870
737	snd $NODE, time => $myport, timereply => 1, 2;	871	push @_, $port;
738	# => snd $myport, timereply => 1, 2, <time>	872	&snd;
		873
		874	$port
		875	}
739		876
740	=back	877	=back
741		878
742	=head1 AnyEvent::MP vs. Distributed Erlang	879	=head1 AnyEvent::MP vs. Distributed Erlang
743		880
744	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
745	== 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
746	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
747	sample:	884	sample:
748		885
749	http://www.Erlang.se/doc/programming_rules.shtml	886	http://www.erlang.se/doc/programming_rules.shtml
750	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
751	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
752	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
753		890
754	Despite the similarities, there are also some important differences:	891	Despite the similarities, there are also some important differences:
755		892
756	=over 4	893	=over 4
757		894
758	=item * Node references contain the recipe on how to contact them.	895	=item * Node IDs are arbitrary strings in AEMP.
759		896
760	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
761	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
762	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.
763		901
764	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
765	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.
766		916
767	=item * Erlang uses processes and a mailbox, AEMP does not queue.	917	=item * Erlang uses processes and a mailbox, AEMP does not queue.
768		918
769	Erlang uses processes that selctively receive messages, and therefore	919	Erlang uses processes that selectively receive messages out of order, and
770	needs a queue. AEMP is event based, queuing messages would serve no useful	920	therefore needs a queue. AEMP is event based, queuing messages would serve
771	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.
772		924
773	(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.
774		930
775	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	931	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
776		932
777	Sending messages in Erlang is synchronous and blocks the process. AEMP	933	Sending messages in Erlang is synchronous and blocks the process until
778	sends are immediate, connection establishment is handled in the	934	a conenction has been established and the message sent (and so does not
779	background.	935	need a queue that can overflow). AEMP sends return immediately, connection
		936	establishment is handled in the background.
780		937
781	=item * Erlang can silently lose messages, AEMP cannot.	938	=item * Erlang suffers from silent message loss, AEMP does not.
782		939
783	Erlang makes few guarantees on messages delivery - messages can get lost	940	Erlang implements few guarantees on messages delivery - messages can get
784	without any of the processes realising it (i.e. you send messages a, b,	941	lost without any of the processes realising it (i.e. you send messages a,
785	and c, and the other side only receives messages a and c).	942	b, and c, and the other side only receives messages a and c).
786		943
787	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
788	holes in the message sequence.	947	no silent "holes" in the message sequence.
789		948
790	=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
791	alive.	950	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
792		951	simply tries to work better in common error cases, such as when a network
793	In Erlang it can happen that a monitored process is declared dead and	952	link goes down.
794	linked processes get killed, but later it turns out that the process is
795	still alive - and can receive messages.
796
797	In AEMP, when port monitoring detects a port as dead, then that port will
798	eventually be killed - it cannot happen that a node detects a port as dead
799	and then later sends messages to it, finding it is still alive.
800		953
801	=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.
802		955
803	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
804	ID known to other nodes for a completely different process, causing	957	process ID known to other nodes for a completely different process,
805	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.
806		960
807	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
808	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.
809		963
810	=item * Erlang uses unprotected connections, AEMP uses secure	964	=item * Erlang uses unprotected connections, AEMP uses secure
811	authentication and can use TLS.	965	authentication and can use TLS.
812		966
813	AEMP can use a proven protocol - SSL/TLS - to protect connections and	967	AEMP can use a proven protocol - TLS - to protect connections and
814	securely authenticate nodes.	968	securely authenticate nodes.
815		969
816	=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
817	communications.	971	communications.
818		972
819	The AEMP protocol, unlike the Erlang protocol, supports both	973	The AEMP protocol, unlike the Erlang protocol, supports both programming
820	language-independent text-only protocols (good for debugging) and binary,	974	language independent text-only protocols (good for debugging), and binary,
821	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.
822		977
823	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
824	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
825	protocol simple.	980	protocol simple.
826		981
827	=item * AEMP has more flexible monitoring options than Erlang.	982	=item * AEMP has more flexible monitoring options than Erlang.
828		983
829	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
830	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
831	difficult to implement. Monitoring in AEMP is more flexible than in	986	difficult to implement.
832	Erlang, as one can choose between automatic kill, exit message or callback	987
833	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.
834		990
835	=item * Erlang tries to hide remote/local connections, AEMP does not.	991	=item * Erlang tries to hide remote/local connections, AEMP does not.
836		992
837	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
838	as linking is (except linking is unreliable in Erlang).	994	same way as linking is (except linking is unreliable in Erlang).
839		995
840	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
841	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
842	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
843	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
844	more reliable.	1000	reliable (no need for C<spawn_link>).
845		1001
846	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
847	(hard to do in Erlang).	1003	(hard to do in Erlang).
848		1004
849	=back	1005	=back
850		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
851	=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.
852		1055
853	L<AnyEvent>.	1056	L<AnyEvent>.
854		1057
855	=head1 AUTHOR	1058	=head1 AUTHOR
856		1059

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