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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.43 by root, Sun Aug 9 16:08:16 2009 UTC vs.
Revision 1.110 by root, Sun Mar 7 19:29:07 2010 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 prot 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
69	=item port id - C<noderef#portname>	83	=item port ID - C<nodeid#portname>
70		84
71	A port id is normaly the concatenation of a noderef, a hash-mark (C<#>) as	85	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	86	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		87
76	=item node	88	=item node
77		89
78	A node is a single process containing at least one port - the node	90	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	91	which enables nodes to manage each other remotely, and to create new
80	create new ports, among other things.	92	ports.
81		93
82	Nodes are either private (single-process only), slaves (connected to a	94	Nodes are either public (have one or more listening ports) or private
83	master node only) or public nodes (connectable from unrelated nodes).	95	(no listening ports). Private nodes cannot talk to other private nodes
		96	currently.
84		97
85	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	98	=item node ID - C<[A-Z_][a-zA-Z0-9_\-.:]*>
86		99
87	A node reference is a string that either simply identifies the node (for	100	A node ID is a string that uniquely identifies the node within a
88	private and slave nodes), or contains a recipe on how to reach a given	101	network. Depending on the configuration used, node IDs can look like a
89	node (for public nodes).	102	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		103	doesn't interpret node IDs in any way.
90		104
91	This recipe is simply a comma-separated list of C<address:port> pairs (for	105	=item binds - C<ip:port>
92	TCP/IP, other protocols might look different).
93		106
94	Node references come in two flavours: resolved (containing only numerical	107	Nodes can only talk to each other by creating some kind of connection to
95	addresses) or unresolved (where hostnames are used instead of addresses).	108	each other. To do this, nodes should listen on one or more local transport
		109	endpoints - binds. Currently, only standard C<ip:port> specifications can
		110	be used, which specify TCP ports to listen on.
96		111
97	Before using an unresolved node reference in a message you first have to	112	=item seed nodes
98	resolve it.	113
		114	When a node starts, it knows nothing about the network. To teach the node
		115	about the network it first has to contact some other node within the
		116	network. This node is called a seed.
		117
		118	Apart from the fact that other nodes know them as seed nodes and they have
		119	to have fixed listening addresses, seed nodes are perfectly normal nodes -
		120	any node can function as a seed node for others.
		121
		122	In addition to discovering the network, seed nodes are also used to
		123	maintain the network and to connect nodes that otherwise would have
		124	trouble connecting. They form the backbone of an AnyEvent::MP network.
		125
		126	Seed nodes are expected to be long-running, and at least one seed node
		127	should always be available. They should also be relatively responsive - a
		128	seed node that blocks for long periods will slow down everybody else.
		129
		130	=item seeds - C<host:port>
		131
		132	Seeds are transport endpoint(s) (usually a hostname/IP address and a
		133	TCP port) of nodes that should be used as seed nodes.
		134
		135	The nodes listening on those endpoints are expected to be long-running,
		136	and at least one of those should always be available. When nodes run out
		137	of connections (e.g. due to a network error), they try to re-establish
		138	connections to some seednodes again to join the network.
99		139
100	=back	140	=back
101		141
102	=head1 VARIABLES/FUNCTIONS	142	=head1 VARIABLES/FUNCTIONS
103		143
105		145
106	=cut	146	=cut
107		147
108	package AnyEvent::MP;	148	package AnyEvent::MP;
109		149
110	use AnyEvent::MP::Base;	150	use AnyEvent::MP::Kernel;
111		151
112	use common::sense;	152	use common::sense;
113		153
114	use Carp ();	154	use Carp ();
115		155
116	use AE ();	156	use AE ();
117		157
118	use base "Exporter";	158	use base "Exporter";
119		159
120	our $VERSION = $AnyEvent::MP::Base::VERSION;	160	our $VERSION = 1.26;
121		161
122	our @EXPORT = qw(	162	our @EXPORT = qw(
123	NODE $NODE *SELF node_of _any_	163	NODE $NODE *SELF node_of after
124	resolve_node initialise_node	164	configure
125	snd rcv mon kil reg psub spawn	165	snd rcv mon mon_guard kil psub peval spawn cal
126	port	166	port
127	);	167	);
128		168
129	our $SELF;	169	our $SELF;
130		170
…		…
134	kil $SELF, die => $msg;	174	kil $SELF, die => $msg;
135	}	175	}
136		176
137	=item $thisnode = NODE / $NODE	177	=item $thisnode = NODE / $NODE
138		178
139	The C<NODE> function returns, and the C<$NODE> variable contains	179	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	180	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	181	a call to C<configure>.
142	identifiers become invalid.
143		182
144	=item $noderef = node_of $port	183	=item $nodeid = node_of $port
145		184
146	Extracts and returns the noderef from a portid or a noderef.	185	Extracts and returns the node ID from a port ID or a node ID.
147		186
148	=item initialise_node $noderef, $seednode, $seednode...	187	=item configure $profile, key => value...
149		188
150	=item initialise_node "slave/", $master, $master...	189	=item configure key => value...
151		190
152	Before a node can talk to other nodes on the network it has to initialise	191	Before a node can talk to other nodes on the network (i.e. enter
153	itself - the minimum a node needs to know is it's own name, and optionally	192	"distributed mode") it has to configure itself - the minimum a node needs
154	it should know the noderefs of some other nodes in the network.	193	to know is its own name, and optionally it should know the addresses of
		194	some other nodes in the network to discover other nodes.
155		195
		196	The key/value pairs are basically the same ones as documented for the
		197	F<aemp> command line utility (sans the set/del prefix).
		198
156	This function initialises a node - it must be called exactly once (or	199	This function configures a node - it must be called exactly once (or
157	never) before calling other AnyEvent::MP functions.	200	never) before calling other AnyEvent::MP functions.
158		201
159	All arguments are noderefs, which can be either resolved or unresolved.
160
161	There are two types of networked nodes, public nodes and slave nodes:
162
163	=over 4	202	=over 4
164		203
165	=item public nodes	204	=item step 1, gathering configuration from profiles
166		205
167	For public nodes, C<$noderef> must either be a (possibly unresolved)	206	The function first looks up a profile in the aemp configuration (see the
168	noderef, in which case it will be resolved, or C<undef> (or missing), in	207	L<aemp> commandline utility). The profile name can be specified via the
169	which case the noderef will be guessed.	208	named C<profile> parameter or can simply be the first parameter). If it is
		209	missing, then the nodename (F<uname -n>) will be used as profile name.
170		210
171	Afterwards, the node will bind itself on all endpoints and try to connect	211	The profile data is then gathered as follows:
172	to all additional C<$seednodes> that are specified. Seednodes are optional
173	and can be used to quickly bootstrap the node into an existing network.
174		212
175	=item slave nodes	213	First, all remaining key => value pairs (all of which are conveniently
		214	undocumented at the moment) will be interpreted as configuration
		215	data. Then they will be overwritten by any values specified in the global
		216	default configuration (see the F<aemp> utility), then the chain of
		217	profiles chosen by the profile name (and any C<parent> attributes).
176		218
177	When the C<$noderef> is the special string C<slave/>, then the node will	219	That means that the values specified in the profile have highest priority
178	become a slave node. Slave nodes cannot be contacted from outside and will	220	and the values specified directly via C<configure> have lowest priority,
179	route most of their traffic to the master node that they attach to.	221	and can only be used to specify defaults.
180		222
181	At least one additional noderef is required: The node will try to connect	223	If the profile specifies a node ID, then this will become the node ID of
182	to all of them and will become a slave attached to the first node it can	224	this process. If not, then the profile name will be used as node ID. The
183	successfully connect to.	225	special node ID of C<anon/> will be replaced by a random node ID.
		226
		227	=item step 2, bind listener sockets
		228
		229	The next step is to look up the binds in the profile, followed by binding
		230	aemp protocol listeners on all binds specified (it is possible and valid
		231	to have no binds, meaning that the node cannot be contacted form the
		232	outside. This means the node cannot talk to other nodes that also have no
		233	binds, but it can still talk to all "normal" nodes).
		234
		235	If the profile does not specify a binds list, then a default of C<*> is
		236	used, meaning the node will bind on a dynamically-assigned port on every
		237	local IP address it finds.
		238
		239	=item step 3, connect to seed nodes
		240
		241	As the last step, the seeds list from the profile is passed to the
		242	L<AnyEvent::MP::Global> module, which will then use it to keep
		243	connectivity with at least one node at any point in time.
184		244
185	=back	245	=back
186		246
187	This function will block until all nodes have been resolved and, for slave	247	Example: become a distributed node using the local node name as profile.
188	nodes, until it has successfully established a connection to a master	248	This should be the most common form of invocation for "daemon"-type nodes.
189	server.
190		249
191	Example: become a public node listening on the default node.	250	configure
192		251
193	initialise_node;	252	Example: become an anonymous node. This form is often used for commandline
		253	clients.
194		254
195	Example: become a public node, and try to contact some well-known master	255	configure nodeid => "anon/";
196	servers to become part of the network.
197		256
198	initialise_node undef, "master1", "master2";	257	Example: configure a node using a profile called seed, which si suitable
		258	for a seed node as it binds on all local addresses on a fixed port (4040,
		259	customary for aemp).
199		260
200	Example: become a public node listening on port C<4041>.	261	# use the aemp commandline utility
		262	# aemp profile seed nodeid anon/ binds '*:4040'
201		263
202	initialise_node 4041;	264	# then use it
		265	configure profile => "seed";
203		266
204	Example: become a public node, only visible on localhost port 4044.	267	# or simply use aemp from the shell again:
		268	# aemp run profile seed
205		269
206	initialise_node "locahost:4044";	270	# or provide a nicer-to-remember nodeid
207		271	# aemp run profile seed nodeid "$(hostname)"
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
222
223	=item the empty string
224
225	An empty-string component gets resolved as if the default port (4040) was
226	specified.
227
228	=item naked port numbers (e.g. C<1234>)
229
230	These are resolved by prepending the local nodename and a colon, to be
231	further resolved.
232
233	=item hostnames (e.g. C<localhost:1234>, C<localhost>)
234
235	These are resolved by using AnyEvent::DNS to resolve them, optionally
236	looking up SRV records for the C<aemp=4040> port, if no port was
237	specified.
238
239	=back
240		272
241	=item $SELF	273	=item $SELF
242		274
243	Contains the current port id while executing C<rcv> callbacks or C<psub>	275	Contains the current port id while executing C<rcv> callbacks or C<psub>
244	blocks.	276	blocks.
245		277
246	=item SELF, %SELF, @SELF...	278	=item *SELF, SELF, %SELF, @SELF...
247		279
248	Due to some quirks in how perl exports variables, it is impossible to	280	Due to some quirks in how perl exports variables, it is impossible to
249	just export C<$SELF>, all the symbols called C<SELF> are exported by this	281	just export C<$SELF>, all the symbols named C<SELF> are exported by this
250	module, but only C<$SELF> is currently used.	282	module, but only C<$SELF> is currently used.
251		283
252	=item snd $port, type => @data	284	=item snd $port, type => @data
253		285
254	=item snd $port, @msg	286	=item snd $port, @msg
255		287
256	Send the given message to the given port ID, which can identify either	288	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	289	local or a remote port, and must be a port ID.
258	stringifies a sa port ID (such as a port object :).
259		290
260	While the message can be about anything, it is highly recommended to use a	291	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	292	use a string as first element (a port ID, or some word that indicates a
262	type etc.).	293	request type etc.) and to consist if only simple perl values (scalars,
		294	arrays, hashes) - if you think you need to pass an object, think again.
263		295
264	The message data effectively becomes read-only after a call to this	296	The message data logically becomes read-only after a call to this
265	function: modifying any argument is not allowed and can cause many	297	function: modifying any argument (or values referenced by them) is
266	problems.	298	forbidden, as there can be considerable time between the call to C<snd>
		299	and the time the message is actually being serialised - in fact, it might
		300	never be copied as within the same process it is simply handed to the
		301	receiving port.
267		302
268	The type of data you can transfer depends on the transport protocol: when	303	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	304	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	305	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	306	that Storable can serialise and deserialise is allowed, and for the local
272	node, anything can be passed.	307	node, anything can be passed. Best rely only on the common denominator of
		308	these.
273		309
274	=item $local_port = port	310	=item $local_port = port
275		311
276	Create a new local port object that can be used either as a pattern	312	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"),	313	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		314
280	=item $port = port { my @msg = @_; $finished }	315	=item $local_port = port { my @msg = @_ }
281		316
282	Creates a "miniport", that is, a very lightweight port without any pattern	317	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.	318	creating a port and calling C<rcv $port, $callback> on it.
285		319
286	The block will be called for every message received on the port. When the	320	The block will be called for every message received on the port, with the
287	callback returns a true value its job is considered "done" and the port	321	global variable C<$SELF> set to the port ID. Runtime errors will cause the
288	will be destroyed. Otherwise it will stay alive.	322	port to be C<kil>ed. The message will be passed as-is, no extra argument
		323	(i.e. no port ID) will be passed to the callback.
289		324
290	The message will be passed as-is, no extra argument (i.e. no port id) will	325	If you want to stop/destroy the port, simply C<kil> it:
291	be passed to the callback.
292		326
293	If you need the local port id in the callback, this works nicely:	327	my $port = port {
294		328	my @msg = @_;
295	my $port; $port = port {	329	...
296	snd $otherport, reply => $port;	330	kil $SELF;
297	};	331	};
298		332
299	=cut	333	=cut
300		334
301	sub rcv($@);	335	sub rcv($@);
		336
		337	sub _kilme {
		338	die "received message on port without callback";
		339	}
302		340
303	sub port(;&) {	341	sub port(;&) {
304	my $id = "$UNIQ." . $ID++;	342	my $id = "$UNIQ." . $ID++;
305	my $port = "$NODE#$id";	343	my $port = "$NODE#$id";
306		344
307	if (@_) {	345	rcv $port, shift \|\| \&_kilme;
308	rcv $port, shift;
309	} else {
310	$PORT{$id} = sub { }; # nop
311	}
312		346
313	$port	347	$port
314	}	348	}
315		349
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)	350	=item rcv $local_port, $callback->(@msg)
336		351
337	Replaces the callback on the specified miniport (after converting it to	352	Replaces the default callback on the specified port. There is no way to
338	one if required).	353	remove the default callback: use C<sub { }> to disable it, or better
339		354	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...] => $callback->(@msg), ...
345
346	Register callbacks to be called on matching messages on the given full
347	port (after converting it to one if required) and return the port.
348
349	The callback has to return a true value when its work is done, after
350	which is will be removed, or a false value in which case it will stay
351	registered.
352		355
353	The global C<$SELF> (exported by this module) contains C<$port> while	356	The global C<$SELF> (exported by this module) contains C<$port> while
354	executing the callback.	357	executing the callback. Runtime errors during callback execution will
		358	result in the port being C<kil>ed.
355		359
356	Runtime errors during callback execution will result in the port being	360	The default callback received all messages not matched by a more specific
357	C<kil>ed.	361	C<tag> match.
358		362
359	If the match is an array reference, then it will be matched against the	363	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
360	first elements of the message, otherwise only the first element is being
361	matched.
362		364
363	Any element in the match that is specified as C<_any_> (a function	365	Register (or replace) callbacks to be called on messages starting with the
364	exported by this module) matches any single element of the message.	366	given tag on the given port (and return the port), or unregister it (when
		367	C<$callback> is C<$undef> or missing). There can only be one callback
		368	registered for each tag.
365		369
366	While not required, it is highly recommended that the first matching	370	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	371	element (the tag) has been removed. The callback will use the same
368	also the most efficient match (by far).	372	environment as the default callback (see above).
369		373
370	Example: create a port and bind receivers on it in one go.	374	Example: create a port and bind receivers on it in one go.
371		375
372	my $port = rcv port,	376	my $port = rcv port,
373	msg1 => sub { ...; 0 },	377	msg1 => sub { ... },
374	msg2 => sub { ...; 0 },	378	msg2 => sub { ... },
375	;	379	;
376		380
377	Example: create a port, bind receivers and send it in a message elsewhere	381	Example: create a port, bind receivers and send it in a message elsewhere
378	in one go:	382	in one go:
379		383
380	snd $otherport, reply =>	384	snd $otherport, reply =>
381	rcv port,	385	rcv port,
382	msg1 => sub { ...; 0 },	386	msg1 => sub { ... },
383	...	387	...
384	;	388	;
385		389
		390	Example: temporarily register a rcv callback for a tag matching some port
		391	(e.g. for an rpc reply) and unregister it after a message was received.
		392
		393	rcv $port, $otherport => sub {
		394	my @reply = @_;
		395
		396	rcv $SELF, $otherport;
		397	};
		398
386	=cut	399	=cut
387		400
388	sub rcv($@) {	401	sub rcv($@) {
389	my $port = shift;	402	my $port = shift;
390	my ($noderef, $portid) = split /#/, $port, 2;	403	my ($nodeid, $portid) = split /#/, $port, 2;
391		404
392	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	405	$NODE{$nodeid} == $NODE{""}
393	or Carp::croak "$port: rcv can only be called on local ports, caught";	406	or Carp::croak "$port: rcv can only be called on local ports, caught";
394		407
395	if (@_ == 1) {	408	while (@_) {
		409	if (ref $_[0]) {
		410	if (my $self = $PORT_DATA{$portid}) {
		411	"AnyEvent::MP::Port" eq ref $self
		412	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		413
		414	$self->[0] = shift;
		415	} else {
396	my $cb = shift;	416	my $cb = shift;
397	delete $PORT_DATA{$portid};
398	$PORT{$portid} = sub {	417	$PORT{$portid} = sub {
399	local $SELF = $port;	418	local $SELF = $port;
400	eval {	419	eval { &$cb }; _self_die if $@;
401	&$cb	420	};
402	and kil $port;
403	};	421	}
404	_self_die if $@;	422	} elsif (defined $_[0]) {
405	};
406	} else {
407	my $self = $PORT_DATA{$portid} \|\|= do {	423	my $self = $PORT_DATA{$portid} \|\|= do {
408	my $self = bless {	424	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
409	id => $port,
410	}, "AnyEvent::MP::Port";
411		425
412	$PORT{$portid} = sub {	426	$PORT{$portid} = sub {
413	local $SELF = $port;	427	local $SELF = $port;
414		428
415	eval {
416	for (@{ $self->{rc0}{$_[0]} }) {	429	if (my $cb = $self->[1]{$_[0]}) {
417	$_ && &{$_->[0]}	430	shift;
418	&& undef $_;	431	eval { &$cb }; _self_die if $@;
419	}	432	} else {
420
421	for (@{ $self->{rcv}{$_[0]} }) {
422	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
423	&& &{$_->[0]}	433	&{ $self->[0] };
424	&& undef $_;
425	}
426
427	for (@{ $self->{any} }) {
428	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
429	&& &{$_->[0]}
430	&& undef $_;
431	}	434	}
432	};	435	};
433	_self_die if $@;	436
		437	$self
434	};	438	};
435		439
436	$self
437	};
438
439	"AnyEvent::MP::Port" eq ref $self	440	"AnyEvent::MP::Port" eq ref $self
440	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	441	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
441		442
442	while (@_) {
443	my ($match, $cb) = splice @_, 0, 2;	443	my ($tag, $cb) = splice @_, 0, 2;
444		444
445	if (!ref $match) {	445	if (defined $cb) {
446	push @{ $self->{rc0}{$match} }, [$cb];	446	$self->[1]{$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 {	447	} else {
453	push @{ $self->{any} }, [$cb, $match];	448	delete $self->[1]{$tag};
454	}	449	}
455	}	450	}
456	}	451	}
457		452
458	$port	453	$port
459	}	454	}
460		455
		456	=item peval $port, $coderef[, @args]
		457
		458	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		459	when the code throews an exception the C<$port> will be killed.
		460
		461	Any remaining args will be passed to the callback. Any return values will
		462	be returned to the caller.
		463
		464	This is useful when you temporarily want to execute code in the context of
		465	a port.
		466
		467	Example: create a port and run some initialisation code in it's context.
		468
		469	my $port = port { ... };
		470
		471	peval $port, sub {
		472	init
		473	or die "unable to init";
		474	};
		475
		476	=cut
		477
		478	sub peval($$) {
		479	local $SELF = shift;
		480	my $cb = shift;
		481
		482	if (wantarray) {
		483	my @res = eval { &$cb };
		484	_self_die if $@;
		485	@res
		486	} else {
		487	my $res = eval { &$cb };
		488	_self_die if $@;
		489	$res
		490	}
		491	}
		492
461	=item $closure = psub { BLOCK }	493	=item $closure = psub { BLOCK }
462		494
463	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	495	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>	496	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.	497	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		498
		499	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		500	BLOCK } } >>.
466		501
467	This is useful when you register callbacks from C<rcv> callbacks:	502	This is useful when you register callbacks from C<rcv> callbacks:
468		503
469	rcv delayed_reply => sub {	504	rcv delayed_reply => sub {
470	my ($delay, @reply) = @_;	505	my ($delay, @reply) = @_;
…		…
494	$res	529	$res
495	}	530	}
496	}	531	}
497	}	532	}
498		533
499	=item $guard = mon $port, $cb->(@reason)	534	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
500		535
501	=item $guard = mon $port, $rcvport	536	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
502		537
503	=item $guard = mon $port	538	=item $guard = mon $port # kill $SELF when $port dies
504		539
505	=item $guard = mon $port, $rcvport, @msg	540	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
506		541
507	Monitor the given port and do something when the port is killed or	542	Monitor the given port and do something when the port is killed or
508	messages to it were lost, and optionally return a guard that can be used	543	messages to it were lost, and optionally return a guard that can be used
509	to stop monitoring again.	544	to stop monitoring again.
510
511	C<mon> effectively guarantees that, in the absence of hardware failures,
512	that after starting the monitor, either all messages sent to the port
513	will arrive, or the monitoring action will be invoked after possible
514	message loss has been detected. No messages will be lost "in between"
515	(after the first lost message no further messages will be received by the
516	port). After the monitoring action was invoked, further messages might get
517	delivered again.
518		545
519	In the first form (callback), the callback is simply called with any	546	In the first form (callback), the callback is simply called with any
520	number of C<@reason> elements (no @reason means that the port was deleted	547	number of C<@reason> elements (no @reason means that the port was deleted
521	"normally"). Note also that I<< the callback B<must> never die >>, so use	548	"normally"). Note also that I<< the callback B<must> never die >>, so use
522	C<eval> if unsure.	549	C<eval> if unsure.
523		550
524	In the second form (another port given), the other port (C<$rcvport>)	551	In the second form (another port given), the other port (C<$rcvport>)
525	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	552	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
526	"normal" kils nothing happens, while under all other conditions, the other	553	"normal" kils nothing happens, while under all other conditions, the other
527	port is killed with the same reason.	554	port is killed with the same reason.
528		555
529	The third form (kill self) is the same as the second form, except that	556	The third form (kill self) is the same as the second form, except that
530	C<$rvport> defaults to C<$SELF>.	557	C<$rvport> defaults to C<$SELF>.
531		558
532	In the last form (message), a message of the form C<@msg, @reason> will be	559	In the last form (message), a message of the form C<@msg, @reason> will be
533	C<snd>.	560	C<snd>.
		561
		562	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		563	alert was raised), they are removed and will not trigger again.
534		564
535	As a rule of thumb, monitoring requests should always monitor a port from	565	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	566	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	567	lost, just like any other message. Another less obvious reason is that
538	even monitoring requests can get lost (for exmaple, when the connection	568	even monitoring requests can get lost (for example, when the connection
539	to the other node goes down permanently). When monitoring a port locally	569	to the other node goes down permanently). When monitoring a port locally
540	these problems do not exist.	570	these problems do not exist.
541		571
		572	C<mon> effectively guarantees that, in the absence of hardware failures,
		573	after starting the monitor, either all messages sent to the port will
		574	arrive, or the monitoring action will be invoked after possible message
		575	loss has been detected. No messages will be lost "in between" (after
		576	the first lost message no further messages will be received by the
		577	port). After the monitoring action was invoked, further messages might get
		578	delivered again.
		579
		580	Inter-host-connection timeouts and monitoring depend on the transport
		581	used. The only transport currently implemented is TCP, and AnyEvent::MP
		582	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		583	non-idle connection, and usually around two hours for idle connections).
		584
		585	This means that monitoring is good for program errors and cleaning up
		586	stuff eventually, but they are no replacement for a timeout when you need
		587	to ensure some maximum latency.
		588
542	Example: call a given callback when C<$port> is killed.	589	Example: call a given callback when C<$port> is killed.
543		590
544	mon $port, sub { warn "port died because of <@_>\n" };	591	mon $port, sub { warn "port died because of <@_>\n" };
545		592
546	Example: kill ourselves when C<$port> is killed abnormally.	593	Example: kill ourselves when C<$port> is killed abnormally.
…		…
552	mon $port, $self => "restart";	599	mon $port, $self => "restart";
553		600
554	=cut	601	=cut
555		602
556	sub mon {	603	sub mon {
557	my ($noderef, $port) = split /#/, shift, 2;	604	my ($nodeid, $port) = split /#/, shift, 2;
558		605
559	my $node = $NODE{$noderef} \|\| add_node $noderef;	606	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
560		607
561	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';	608	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
562		609
563	unless (ref $cb) {	610	unless (ref $cb) {
564	if (@_) {	611	if (@_) {
…		…
573	}	620	}
574		621
575	$node->monitor ($port, $cb);	622	$node->monitor ($port, $cb);
576		623
577	defined wantarray	624	defined wantarray
578	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	625	and ($cb += 0, AnyEvent::Util::guard { $node->unmonitor ($port, $cb) })
579	}	626	}
580		627
581	=item $guard = mon_guard $port, $ref, $ref...	628	=item $guard = mon_guard $port, $ref, $ref...
582		629
583	Monitors the given C<$port> and keeps the passed references. When the port	630	Monitors the given C<$port> and keeps the passed references. When the port
584	is killed, the references will be freed.	631	is killed, the references will be freed.
585		632
586	Optionally returns a guard that will stop the monitoring.	633	Optionally returns a guard that will stop the monitoring.
587		634
588	This function is useful when you create e.g. timers or other watchers and	635	This function is useful when you create e.g. timers or other watchers and
589	want to free them when the port gets killed:	636	want to free them when the port gets killed (note the use of C<psub>):
590		637
591	$port->rcv (start => sub {	638	$port->rcv (start => sub {
592	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	639	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
593	undef $timer if 0.9 < rand;	640	undef $timer if 0.9 < rand;
594	});	641	});
595	});	642	});
596		643
597	=cut	644	=cut
…		…
606		653
607	=item kil $port[, @reason]	654	=item kil $port[, @reason]
608		655
609	Kill the specified port with the given C<@reason>.	656	Kill the specified port with the given C<@reason>.
610		657
611	If no C<@reason> is specified, then the port is killed "normally" (linked	658	If no C<@reason> is specified, then the port is killed "normally" -
612	ports will not be kileld, or even notified).	659	monitor callback will be invoked, but the kil will not cause linked ports
		660	(C<mon $mport, $lport> form) to get killed.
613		661
614	Otherwise, linked ports get killed with the same reason (second form of	662	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
615	C<mon>, see below).	663	form) get killed with the same reason.
616		664
617	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	665	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
618	will be reported as reason C<< die => $@ >>.	666	will be reported as reason C<< die => $@ >>.
619		667
620	Transport/communication errors are reported as C<< transport_error =>	668	Transport/communication errors are reported as C<< transport_error =>
…		…
625	=item $port = spawn $node, $initfunc[, @initdata]	673	=item $port = spawn $node, $initfunc[, @initdata]
626		674
627	Creates a port on the node C<$node> (which can also be a port ID, in which	675	Creates a port on the node C<$node> (which can also be a port ID, in which
628	case it's the node where that port resides).	676	case it's the node where that port resides).
629		677
630	The port ID of the newly created port is return immediately, and it is	678	The port ID of the newly created port is returned immediately, and it is
631	permissible to immediately start sending messages or monitor the port.	679	possible to immediately start sending messages or to monitor the port.
632		680
633	After the port has been created, the init function is	681	After the port has been created, the init function is called on the remote
634	called. This function must be a fully-qualified function name	682	node, in the same context as a C<rcv> callback. This function must be a
635	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	683	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
636	program, use C<::name>.	684	specify a function in the main program, use C<::name>.
637		685
638	If the function doesn't exist, then the node tries to C<require>	686	If the function doesn't exist, then the node tries to C<require>
639	the package, then the package above the package and so on (e.g.	687	the package, then the package above the package and so on (e.g.
640	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	688	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
641	exists or it runs out of package names.	689	exists or it runs out of package names.
642		690
643	The init function is then called with the newly-created port as context	691	The init function is then called with the newly-created port as context
644	object (C<$SELF>) and the C<@initdata> values as arguments.	692	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		693	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		694	the port might not get created.
645		695
646	A common idiom is to pass your own port, monitor the spawned port, and	696	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	697	port, and in the remote init function, immediately monitor the passed
648	ensures that both ports get cleaned up when there is a problem.	698	local port. This two-way monitoring ensures that both ports get cleaned up
		699	when there is a problem.
		700
		701	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		702	caller before C<spawn> returns (by delaying invocation when spawn is
		703	called for the local node).
649		704
650	Example: spawn a chat server port on C<$othernode>.	705	Example: spawn a chat server port on C<$othernode>.
651		706
652	# this node, executed from within a port context:	707	# this node, executed from within a port context:
653	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	708	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
668		723
669	sub _spawn {	724	sub _spawn {
670	my $port = shift;	725	my $port = shift;
671	my $init = shift;	726	my $init = shift;
672		727
		728	# rcv will create the actual port
673	local $SELF = "$NODE#$port";	729	local $SELF = "$NODE#$port";
674	eval {	730	eval {
675	&{ load_func $init }	731	&{ load_func $init }
676	};	732	};
677	_self_die if $@;	733	_self_die if $@;
678	}	734	}
679		735
680	sub spawn(@) {	736	sub spawn(@) {
681	my ($noderef, undef) = split /#/, shift, 2;	737	my ($nodeid, undef) = split /#/, shift, 2;
682		738
683	my $id = "$RUNIQ." . $ID++;	739	my $id = "$RUNIQ." . $ID++;
684		740
685	$_[0] =~ /::/	741	$_[0] =~ /::/
686	or Carp::croak "spawn init function must be a fully-qualified name, caught";	742	or Carp::croak "spawn init function must be a fully-qualified name, caught";
687		743
688	($NODE{$noderef} \|\| add_node $noderef)	744	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
689	->send (["", "AnyEvent::MP::_spawn" => $id, @_]);
690		745
691	"$noderef#$id"	746	"$nodeid#$id"
692	}	747	}
693		748
694	=back	749	=item after $timeout, @msg
695		750
696	=head1 NODE MESSAGES	751	=item after $timeout, $callback
697		752
698	Nodes understand the following messages sent to them. Many of them take	753	Either sends the given message, or call the given callback, after the
699	arguments called C<@reply>, which will simply be used to compose a reply	754	specified number of seconds.
700	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
701	the remaining arguments are simply the message data.
702		755
703	While other messages exist, they are not public and subject to change.	756	This is simply a utility function that comes in handy at times - the
		757	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		758	so it may go away in the future.
704		759
705	=over 4
706
707	=cut	760	=cut
708		761
709	=item lookup => $name, @reply	762	sub after($@) {
		763	my ($timeout, @action) = @_;
710		764
711	Replies with the port ID of the specified well-known port, or C<undef>.	765	my $t; $t = AE::timer $timeout, 0, sub {
		766	undef $t;
		767	ref $action[0]
		768	? $action[0]()
		769	: snd @action;
		770	};
		771	}
712		772
713	=item devnull => ...	773	=item cal $port, @msg, $callback[, $timeout]
714		774
715	Generic data sink/CPU heat conversion.	775	A simple form of RPC - sends a message to the given C<$port> with the
		776	given contents (C<@msg>), but adds a reply port to the message.
716		777
717	=item relay => $port, @msg	778	The reply port is created temporarily just for the purpose of receiving
		779	the reply, and will be C<kil>ed when no longer needed.
718		780
719	Simply forwards the message to the given port.	781	A reply message sent to the port is passed to the C<$callback> as-is.
720		782
721	=item eval => $string[ @reply]	783	If an optional time-out (in seconds) is given and it is not C<undef>,
		784	then the callback will be called without any arguments after the time-out
		785	elapsed and the port is C<kil>ed.
722		786
723	Evaluates the given string. If C<@reply> is given, then a message of the	787	If no time-out is given (or it is C<undef>), then the local port will
724	form C<@reply, $@, @evalres> is sent.	788	monitor the remote port instead, so it eventually gets cleaned-up.
725		789
726	Example: crash another node.	790	Currently this function returns the temporary port, but this "feature"
		791	might go in future versions unless you can make a convincing case that
		792	this is indeed useful for something.
727		793
728	snd $othernode, eval => "exit";	794	=cut
729		795
730	=item time => @reply	796	sub cal(@) {
		797	my $timeout = ref $_[-1] ? undef : pop;
		798	my $cb = pop;
731		799
732	Replies the the current node time to C<@reply>.	800	my $port = port {
		801	undef $timeout;
		802	kil $SELF;
		803	&$cb;
		804	};
733		805
734	Example: tell the current node to send the current time to C<$myport> in a	806	if (defined $timeout) {
735	C<timereply> message.	807	$timeout = AE::timer $timeout, 0, sub {
		808	undef $timeout;
		809	kil $port;
		810	$cb->();
		811	};
		812	} else {
		813	mon $_[0], sub {
		814	kil $port;
		815	$cb->();
		816	};
		817	}
736		818
737	snd $NODE, time => $myport, timereply => 1, 2;	819	push @_, $port;
738	# => snd $myport, timereply => 1, 2, <time>	820	&snd;
		821
		822	$port
		823	}
739		824
740	=back	825	=back
741		826
742	=head1 AnyEvent::MP vs. Distributed Erlang	827	=head1 AnyEvent::MP vs. Distributed Erlang
743		828
744	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	829	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	830	== 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	831	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
747	sample:	832	sample:
748		833
749	http://www.Erlang.se/doc/programming_rules.shtml	834	http://www.erlang.se/doc/programming_rules.shtml
750	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	835	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	836	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	837	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
753		838
754	Despite the similarities, there are also some important differences:	839	Despite the similarities, there are also some important differences:
755		840
756	=over 4	841	=over 4
757		842
758	=item * Node references contain the recipe on how to contact them.	843	=item * Node IDs are arbitrary strings in AEMP.
759		844
760	Erlang relies on special naming and DNS to work everywhere in the	845	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	846	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
762	convenience functionality.	847	configuration or DNS), and possibly the addresses of some seed nodes, but
		848	will otherwise discover other nodes (and their IDs) itself.
763		849
764	This means that AEMP requires a less tightly controlled environment at the	850	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
765	cost of longer node references and a slightly higher management overhead.	851	uses "local ports are like remote ports".
		852
		853	The failure modes for local ports are quite different (runtime errors
		854	only) then for remote ports - when a local port dies, you I<know> it dies,
		855	when a connection to another node dies, you know nothing about the other
		856	port.
		857
		858	Erlang pretends remote ports are as reliable as local ports, even when
		859	they are not.
		860
		861	AEMP encourages a "treat remote ports differently" philosophy, with local
		862	ports being the special case/exception, where transport errors cannot
		863	occur.
766		864
767	=item * Erlang uses processes and a mailbox, AEMP does not queue.	865	=item * Erlang uses processes and a mailbox, AEMP does not queue.
768		866
769	Erlang uses processes that selctively receive messages, and therefore	867	Erlang uses processes that selectively receive messages, and therefore
770	needs a queue. AEMP is event based, queuing messages would serve no useful	868	needs a queue. AEMP is event based, queuing messages would serve no
771	purpose.	869	useful purpose. For the same reason the pattern-matching abilities of
		870	AnyEvent::MP are more limited, as there is little need to be able to
		871	filter messages without dequeuing them.
772		872
773	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	873	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).
774		874
775	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	875	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
776		876
777	Sending messages in Erlang is synchronous and blocks the process. AEMP	877	Sending messages in Erlang is synchronous and blocks the process (and
778	sends are immediate, connection establishment is handled in the	878	so does not need a queue that can overflow). AEMP sends are immediate,
779	background.	879	connection establishment is handled in the background.
780		880
781	=item * Erlang can silently lose messages, AEMP cannot.	881	=item * Erlang suffers from silent message loss, AEMP does not.
782		882
783	Erlang makes few guarantees on messages delivery - messages can get lost	883	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,	884	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).	885	b, and c, and the other side only receives messages a and c).
786		886
787	AEMP guarantees correct ordering, and the guarantee that there are no	887	AEMP guarantees correct ordering, and the guarantee that after one message
788	holes in the message sequence.	888	is lost, all following ones sent to the same port are lost as well, until
789		889	monitoring raises an error, so there are no silent "holes" in the message
790	=item * In Erlang, processes can be declared dead and later be found to be	890	sequence.
791	alive.
792
793	In Erlang it can happen that a monitored process is declared dead and
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		891
801	=item * Erlang can send messages to the wrong port, AEMP does not.	892	=item * Erlang can send messages to the wrong port, AEMP does not.
802		893
803	In Erlang it is quite possible that a node that restarts reuses a process	894	In Erlang it is quite likely that a node that restarts reuses a process ID
804	ID known to other nodes for a completely different process, causing	895	known to other nodes for a completely different process, causing messages
805	messages destined for that process to end up in an unrelated process.	896	destined for that process to end up in an unrelated process.
806		897
807	AEMP never reuses port IDs, so old messages or old port IDs floating	898	AEMP never reuses port IDs, so old messages or old port IDs floating
808	around in the network will not be sent to an unrelated port.	899	around in the network will not be sent to an unrelated port.
809		900
810	=item * Erlang uses unprotected connections, AEMP uses secure	901	=item * Erlang uses unprotected connections, AEMP uses secure
811	authentication and can use TLS.	902	authentication and can use TLS.
812		903
813	AEMP can use a proven protocol - SSL/TLS - to protect connections and	904	AEMP can use a proven protocol - TLS - to protect connections and
814	securely authenticate nodes.	905	securely authenticate nodes.
815		906
816	=item * The AEMP protocol is optimised for both text-based and binary	907	=item * The AEMP protocol is optimised for both text-based and binary
817	communications.	908	communications.
818		909
819	The AEMP protocol, unlike the Erlang protocol, supports both	910	The AEMP protocol, unlike the Erlang protocol, supports both programming
820	language-independent text-only protocols (good for debugging) and binary,	911	language independent text-only protocols (good for debugging) and binary,
821	language-specific serialisers (e.g. Storable).	912	language-specific serialisers (e.g. Storable). By default, unless TLS is
		913	used, the protocol is actually completely text-based.
822		914
823	It has also been carefully designed to be implementable in other languages	915	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	916	with a minimum of work while gracefully degrading functionality to make the
825	protocol simple.	917	protocol simple.
826		918
827	=item * AEMP has more flexible monitoring options than Erlang.	919	=item * AEMP has more flexible monitoring options than Erlang.
828		920
829	In Erlang, you can chose to receive I<all> exit signals as messages	921	In Erlang, you can chose to receive I<all> exit signals as messages
…		…
832	Erlang, as one can choose between automatic kill, exit message or callback	924	Erlang, as one can choose between automatic kill, exit message or callback
833	on a per-process basis.	925	on a per-process basis.
834		926
835	=item * Erlang tries to hide remote/local connections, AEMP does not.	927	=item * Erlang tries to hide remote/local connections, AEMP does not.
836		928
837	Monitoring in Erlang is not an indicator of process death/crashes,	929	Monitoring in Erlang is not an indicator of process death/crashes, in the
838	as linking is (except linking is unreliable in Erlang).	930	same way as linking is (except linking is unreliable in Erlang).
839		931
840	In AEMP, you don't "look up" registered port names or send to named ports	932	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	933	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	934	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	935	remote port. Since both monitors are local to the node, they are much more
844	more reliable.	936	reliable (no need for C<spawn_link>).
845		937
846	This also saves round-trips and avoids sending messages to the wrong port	938	This also saves round-trips and avoids sending messages to the wrong port
847	(hard to do in Erlang).	939	(hard to do in Erlang).
848		940
849	=back	941	=back
850		942
		943	=head1 RATIONALE
		944
		945	=over 4
		946
		947	=item Why strings for port and node IDs, why not objects?
		948
		949	We considered "objects", but found that the actual number of methods
		950	that can be called are quite low. Since port and node IDs travel over
		951	the network frequently, the serialising/deserialising would add lots of
		952	overhead, as well as having to keep a proxy object everywhere.
		953
		954	Strings can easily be printed, easily serialised etc. and need no special
		955	procedures to be "valid".
		956
		957	And as a result, a port with just a default receiver consists of a single
		958	closure stored in a global hash - it can't become much cheaper.
		959
		960	=item Why favour JSON, why not a real serialising format such as Storable?
		961
		962	In fact, any AnyEvent::MP node will happily accept Storable as framing
		963	format, but currently there is no way to make a node use Storable by
		964	default (although all nodes will accept it).
		965
		966	The default framing protocol is JSON because a) JSON::XS is many times
		967	faster for small messages and b) most importantly, after years of
		968	experience we found that object serialisation is causing more problems
		969	than it solves: Just like function calls, objects simply do not travel
		970	easily over the network, mostly because they will always be a copy, so you
		971	always have to re-think your design.
		972
		973	Keeping your messages simple, concentrating on data structures rather than
		974	objects, will keep your messages clean, tidy and efficient.
		975
		976	=back
		977
851	=head1 SEE ALSO	978	=head1 SEE ALSO
		979
		980	L<AnyEvent::MP::Intro> - a gentle introduction.
		981
		982	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		983
		984	L<AnyEvent::MP::Global> - network maintainance and port groups, to find
		985	your applications.
		986
		987	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		988
		989	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		990	all nodes.
852		991
853	L<AnyEvent>.	992	L<AnyEvent>.
854		993
855	=head1 AUTHOR	994	=head1 AUTHOR
856		995

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Revision 1.110 by root, Sun Mar 7 19:29:07 2010 UTC