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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.33 by root, Wed Aug 5 22:40:51 2009 UTC vs.
Revision 1.118 by root, Thu Jun 30 09:31:58 2011 UTC

…		…
1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent::MP - multi-processing/message-passing framework	3	AnyEvent::MP - erlang-style multi-processing/message-passing framework
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::MP;	7	use AnyEvent::MP;
8		8
9	$NODE # contains this node's noderef	9	$NODE # contains this node's node ID
10	NODE # returns this node's noderef	10	NODE # returns this node's node ID
11	NODE $port # returns the noderef of the port
12		11
		12	$SELF # receiving/own port id in rcv callbacks
		13
		14	# initialise the node so it can send/receive messages
		15	configure;
		16
		17	# ports are message destinations
		18
		19	# sending messages
13	snd $port, type => data...;	20	snd $port, type => data...;
		21	snd $port, @msg;
		22	snd @msg_with_first_element_being_a_port;
14		23
15	$SELF # receiving/own port id in rcv callbacks	24	# creating/using ports, the simple way
		25	my $simple_port = port { my @msg = @_ };
16		26
17	rcv $port, smartmatch => $cb->($port, @msg);	27	# creating/using ports, tagged message matching
18		28	my $port = port;
19	# examples:
20	rcv $port2, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
21	rcv $port1, pong => sub { warn "pong received\n" };	30	rcv $port, pong => sub { warn "pong received\n" };
22	snd $port2, ping => $port1;
23		31
24	# more, smarter, matches (_any_ is exported by this module)	32	# create a port on another node
25	rcv $port, [child_died => $pid] => sub { ...	33	my $port = spawn $node, $initfunc, @initdata;
26	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3	34
		35	# destroy a port again
		36	kil $port; # "normal" kill
		37	kil $port, my_error => "everything is broken"; # error kill
		38
		39	# monitoring
		40	mon $localport, $cb->(@msg) # callback is invoked on death
		41	mon $localport, $otherport # kill otherport on abnormal 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.
27		59
28	=head1 DESCRIPTION	60	=head1 DESCRIPTION
29		61
30	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
31		63
32	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
33	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
34		66
35	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>
36	manual page.	68	manual page and the examples under F<eg/>.
37
38	At the moment, this module family is severly broken and underdocumented,
39	so do not use. This was uploaded mainly to reserve the CPAN namespace -
40	stay tuned! The basic API should be finished, however.
41		69
42	=head1 CONCEPTS	70	=head1 CONCEPTS
43		71
44	=over 4	72	=over 4
45		73
46	=item port	74	=item port
47		75
48	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).
49		78
50	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
51	messages. All C<rcv> handlers will receive messages they match, messages	80	some messages. Messages send to ports will not be queued, regardless of
52	will not be queued.	81	anything was listening for them or not.
53		82
54	=item port id - C<noderef#portname>	83	=item port ID - C<nodeid#portname>
55		84
56	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
57	separator, and a port name (a printable string of unspecified format). An	86	separator, and a port name (a printable string of unspecified format).
58	exception is the the node port, whose ID is identical to its node
59	reference.
60		87
61	=item node	88	=item node
62		89
63	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,
64	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
65	create new ports, among other things.	92	ports.
66		93
67	Nodes are either private (single-process only), slaves (connected to a	94	Nodes are either public (have one or more listening ports) or private
68	master node only) or public nodes (connectable from unrelated nodes).	95	(no listening ports). Private nodes cannot talk to other private nodes
		96	currently.
69		97
70	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	98	=item node ID - C<[A-Za-z0-9_\-.:]*>
71		99
72	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
73	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
74	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.
75		104
76	This recipe is simply a comma-separated list of C<address:port> pairs (for	105	=item binds - C<ip:port>
77	TCP/IP, other protocols might look different).
78		106
79	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
80	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.
81		111
82	Before using an unresolved node reference in a message you first have to	112	=item seed nodes
83	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.
84		139
85	=back	140	=back
86		141
87	=head1 VARIABLES/FUNCTIONS	142	=head1 VARIABLES/FUNCTIONS
88		143
90		145
91	=cut	146	=cut
92		147
93	package AnyEvent::MP;	148	package AnyEvent::MP;
94		149
95	use AnyEvent::MP::Base;	150	use AnyEvent::MP::Kernel;
96		151
97	use common::sense;	152	use common::sense;
98		153
99	use Carp ();	154	use Carp ();
100		155
101	use AE ();	156	use AE ();
102		157
103	use base "Exporter";	158	use base "Exporter";
104		159
105	our $VERSION = '0.1';	160	our $VERSION = '1.30';
		161
106	our @EXPORT = qw(	162	our @EXPORT = qw(
107	NODE $NODE *SELF node_of _any_	163	NODE $NODE *SELF node_of after
108	resolve_node initialise_node	164	configure
109	snd rcv mon kil reg psub	165	snd rcv mon mon_guard kil psub peval spawn cal
110	port	166	port
111	);	167	);
112		168
113	our $SELF;	169	our $SELF;
114		170
…		…
118	kil $SELF, die => $msg;	174	kil $SELF, die => $msg;
119	}	175	}
120		176
121	=item $thisnode = NODE / $NODE	177	=item $thisnode = NODE / $NODE
122		178
123	The C<NODE> function returns, and the C<$NODE> variable contains	179	The C<NODE> function returns, and the C<$NODE> variable contains, the node
124	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
125	to C<become_public> or C<become_slave>, after which all local port	181	a call to C<configure>.
126	identifiers become invalid.
127		182
128	=item $noderef = node_of $port	183	=item $nodeid = node_of $port
129		184
130	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.
131		186
132	=item $cv = resolve_node $noderef	187	=item configure $profile, key => value...
133		188
134	Takes an unresolved node reference that may contain hostnames and	189	=item configure key => value...
135	abbreviated IDs, resolves all of them and returns a resolved node
136	reference.
137		190
138	In addition to C<address:port> pairs allowed in resolved noderefs, the	191	Before a node can talk to other nodes on the network (i.e. enter
139	following forms are supported:	192	"distributed mode") it has to configure itself - the minimum a node needs
		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.
		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
		199	This function configures a node - it must be called exactly once (or
		200	never) before calling other AnyEvent::MP functions.
140		201
141	=over 4	202	=over 4
142		203
143	=item the empty string	204	=item step 1, gathering configuration from profiles
144		205
145	An empty-string component gets resolved as if the default port (4040) was	206	The function first looks up a profile in the aemp configuration (see the
146	specified.	207	L<aemp> commandline utility). The profile name can be specified via the
		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.
147		210
148	=item naked port numbers (e.g. C<1234>)	211	The profile data is then gathered as follows:
149		212
150	These are resolved by prepending the local nodename and a colon, to be	213	First, all remaining key => value pairs (all of which are conveniently
151	further resolved.	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).
152		218
153	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	219	That means that the values specified in the profile have highest priority
		220	and the values specified directly via C<configure> have lowest priority,
		221	and can only be used to specify defaults.
154		222
155	These are resolved by using AnyEvent::DNS to resolve them, optionally	223	If the profile specifies a node ID, then this will become the node ID of
156	looking up SRV records for the C<aemp=4040> port, if no port was	224	this process. If not, then the profile name will be used as node ID. The
157	specified.	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.
158		244
159	=back	245	=back
		246
		247	Example: become a distributed node using the local node name as profile.
		248	This should be the most common form of invocation for "daemon"-type nodes.
		249
		250	configure
		251
		252	Example: become an anonymous node. This form is often used for commandline
		253	clients.
		254
		255	configure nodeid => "anon/";
		256
		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).
		260
		261	# use the aemp commandline utility
		262	# aemp profile seed nodeid anon/ binds '*:4040'
		263
		264	# then use it
		265	configure profile => "seed";
		266
		267	# or simply use aemp from the shell again:
		268	# aemp run profile seed
		269
		270	# or provide a nicer-to-remember nodeid
		271	# aemp run profile seed nodeid "$(hostname)"
160		272
161	=item $SELF	273	=item $SELF
162		274
163	Contains the current port id while executing C<rcv> callbacks or C<psub>	275	Contains the current port id while executing C<rcv> callbacks or C<psub>
164	blocks.	276	blocks.
165		277
166	=item SELF, %SELF, @SELF...	278	=item *SELF, SELF, %SELF, @SELF...
167		279
168	Due to some quirks in how perl exports variables, it is impossible to	280	Due to some quirks in how perl exports variables, it is impossible to
169	just export C<$SELF>, all the symbols called C<SELF> are exported by this	281	just export C<$SELF>, all the symbols named C<SELF> are exported by this
170	module, but only C<$SELF> is currently used.	282	module, but only C<$SELF> is currently used.
171		283
172	=item snd $port, type => @data	284	=item snd $port, type => @data
173		285
174	=item snd $port, @msg	286	=item snd $port, @msg
175		287
176	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
177	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.
178	stringifies a sa port ID (such as a port object :).
179		290
180	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
181	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
182	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.
183		295
184	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
185	function: modifying any argument is not allowed and can cause many	297	function: modifying any argument (or values referenced by them) is
186	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.
187		302
188	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
189	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
190	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
191	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
192	node, anything can be passed.	307	node, anything can be passed. Best rely only on the common denominator of
		308	these.
193		309
194	=item $local_port = port	310	=item $local_port = port
195		311
196	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
197	matching port ("full port") or a single-callback port ("miniport"),	313	no callbacks set and will throw an error when it receives messages.
198	depending on how C<rcv> callbacks are bound to the object.
199		314
200	=item $port = port { my @msg = @_; $finished }	315	=item $local_port = port { my @msg = @_ }
201		316
202	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
203	matching behind it, and returns its ID. Semantically the same as creating
204	a port and calling C<rcv $port, $callback> on it.	318	creating a port and calling C<rcv $port, $callback> on it.
205		319
206	The block will be called for every message received on the port. When the	320	The block will be called for every message received on the port, with the
207	callback returns a true value its job is considered "done" and the port	321	global variable C<$SELF> set to the port ID. Runtime errors will cause the
208	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.
209		324
210	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:
211	be passed to the callback.
212		326
213	If you need the local port id in the callback, this works nicely:	327	my $port = port {
214		328	my @msg = @_;
215	my $port; $port = port {	329	...
216	snd $otherport, reply => $port;	330	kil $SELF;
217	};	331	};
218		332
219	=cut	333	=cut
220		334
221	sub rcv($@);	335	sub rcv($@);
		336
		337	sub _kilme {
		338	die "received message on port without callback";
		339	}
222		340
223	sub port(;&) {	341	sub port(;&) {
224	my $id = "$UNIQ." . $ID++;	342	my $id = "$UNIQ." . $ID++;
225	my $port = "$NODE#$id";	343	my $port = "$NODE#$id";
226		344
227	if (@_) {	345	rcv $port, shift \|\| \&_kilme;
228	rcv $port, shift;
229	} else {
230	$PORT{$id} = sub { }; # nop
231	}
232		346
233	$port	347	$port
234	}	348	}
235		349
236	=item reg $port, $name
237
238	Registers the given port under the name C<$name>. If the name already
239	exists it is replaced.
240
241	A port can only be registered under one well known name.
242
243	A port automatically becomes unregistered when it is killed.
244
245	=cut
246
247	sub reg(@) {
248	my ($port, $name) = @_;
249
250	$REG{$name} = $port;
251	}
252
253	=item rcv $port, $callback->(@msg)	350	=item rcv $local_port, $callback->(@msg)
254		351
255	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
256	one if required).	353	remove the default callback: use C<sub { }> to disable it, or better
257		354	C<kil> the port when it is no longer needed.
258	=item rcv $port, tagstring => $callback->(@msg), ...
259
260	=item rcv $port, $smartmatch => $callback->(@msg), ...
261
262	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
263
264	Register callbacks to be called on matching messages on the given full
265	port (after converting it to one if required).
266
267	The callback has to return a true value when its work is done, after
268	which is will be removed, or a false value in which case it will stay
269	registered.
270		355
271	The global C<$SELF> (exported by this module) contains C<$port> while	356	The global C<$SELF> (exported by this module) contains C<$port> while
272	executing the callback.	357	executing the callback. Runtime errors during callback execution will
		358	result in the port being C<kil>ed.
273		359
274	Runtime errors wdurign callback execution will result in the port being	360	The default callback received all messages not matched by a more specific
275	C<kil>ed.	361	C<tag> match.
276		362
277	If the match is an array reference, then it will be matched against the	363	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
278	first elements of the message, otherwise only the first element is being
279	matched.
280		364
281	Any element in the match that is specified as C<_any_> (a function	365	Register (or replace) callbacks to be called on messages starting with the
282	exported by this module) matches any single element of the message.	366	given tag on the given port (and return the port), or unregister it (when
		367	C<$callback> is C<$undef> or missing). There can only be one callback
		368	registered for each tag.
283		369
284	While not required, it is highly recommended that the first matching	370	The original message will be passed to the callback, after the first
285	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
286	also the most efficient match (by far).	372	environment as the default callback (see above).
		373
		374	Example: create a port and bind receivers on it in one go.
		375
		376	my $port = rcv port,
		377	msg1 => sub { ... },
		378	msg2 => sub { ... },
		379	;
		380
		381	Example: create a port, bind receivers and send it in a message elsewhere
		382	in one go:
		383
		384	snd $otherport, reply =>
		385	rcv port,
		386	msg1 => sub { ... },
		387	...
		388	;
		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, $otherport;
		397	};
287		398
288	=cut	399	=cut
289		400
290	sub rcv($@) {	401	sub rcv($@) {
291	my $port = shift;	402	my $port = shift;
292	my ($noderef, $portid) = split /#/, $port, 2;	403	my ($nodeid, $portid) = split /#/, $port, 2;
293		404
294	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	405	$NODE{$nodeid} == $NODE{""}
295	or Carp::croak "$port: rcv can only be called on local ports, caught";	406	or Carp::croak "$port: rcv can only be called on local ports, caught";
296		407
297	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 {
298	my $cb = shift;	416	my $cb = shift;
299	delete $PORT_DATA{$portid};
300	$PORT{$portid} = sub {	417	$PORT{$portid} = sub {
301	local $SELF = $port;	418	local $SELF = $port;
302	eval {	419	eval { &$cb }; _self_die if $@;
303	&$cb	420	};
304	and kil $port;
305	};	421	}
306	_self_die if $@;	422	} elsif (defined $_[0]) {
307	};
308	} else {
309	my $self = $PORT_DATA{$portid} \|\|= do {	423	my $self = $PORT_DATA{$portid} \|\|= do {
310	my $self = bless {	424	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
311	id => $port,
312	}, "AnyEvent::MP::Port";
313		425
314	$PORT{$portid} = sub {	426	$PORT{$portid} = sub {
315	local $SELF = $port;	427	local $SELF = $port;
316		428
317	eval {
318	for (@{ $self->{rc0}{$_[0]} }) {	429	if (my $cb = $self->[1]{$_[0]}) {
319	$_ && &{$_->[0]}	430	shift;
320	&& undef $_;	431	eval { &$cb }; _self_die if $@;
321	}	432	} else {
322
323	for (@{ $self->{rcv}{$_[0]} }) {
324	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
325	&& &{$_->[0]}	433	&{ $self->[0] };
326	&& undef $_;
327	}
328
329	for (@{ $self->{any} }) {
330	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
331	&& &{$_->[0]}
332	&& undef $_;
333	}	434	}
334	};	435	};
335	_self_die if $@;	436
		437	$self
336	};	438	};
337		439
338	$self
339	};
340
341	"AnyEvent::MP::Port" eq ref $self	440	"AnyEvent::MP::Port" eq ref $self
342	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	441	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
343		442
344	while (@_) {
345	my ($match, $cb) = splice @_, 0, 2;	443	my ($tag, $cb) = splice @_, 0, 2;
346		444
347	if (!ref $match) {	445	if (defined $cb) {
348	push @{ $self->{rc0}{$match} }, [$cb];	446	$self->[1]{$tag} = $cb;
349	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
350	my ($type, @match) = @$match;
351	@match
352	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
353	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
354	} else {	447	} else {
355	push @{ $self->{any} }, [$cb, $match];	448	delete $self->[1]{$tag};
356	}	449	}
357	}	450	}
358	}	451	}
359		452
360	$port	453	$port
361	}	454	}
362		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
363	=item $closure = psub { BLOCK }	493	=item $closure = psub { BLOCK }
364		494
365	Remembers C<$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
366	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>
367	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 $SELF, sub {
		500	BLOCK }, @_ } >>.
368		501
369	This is useful when you register callbacks from C<rcv> callbacks:	502	This is useful when you register callbacks from C<rcv> callbacks:
370		503
371	rcv delayed_reply => sub {	504	rcv delayed_reply => sub {
372	my ($delay, @reply) = @_;	505	my ($delay, @reply) = @_;
…		…
396	$res	529	$res
397	}	530	}
398	}	531	}
399	}	532	}
400		533
401	=item $guard = mon $port, $cb->(@reason)	534	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
402		535
403	=item $guard = mon $port, $otherport	536	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
404		537
405	=item $guard = mon $port, $otherport, @msg	538	=item $guard = mon $port # kill $SELF when $port dies
406		539
		540	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		541
407	Monitor the given port and do something when the port is killed.	542	Monitor the given port and do something when the port is killed or
		543	messages to it were lost, and optionally return a guard that can be used
		544	to stop monitoring again.
408		545
409	In the first form, the callback is simply called with any number	546	In the first form (callback), the callback is simply called with any
410	of C<@reason> elements (no @reason means that the port was deleted	547	number of C<@reason> elements (no @reason means that the port was deleted
411	"normally"). Note also that I<< the callback B<must> never die >>, so use	548	"normally"). Note also that I<< the callback B<must> never die >>, so use
412	C<eval> if unsure.	549	C<eval> if unsure.
413		550
414	In the second form, the other port will be C<kil>'ed with C<@reason>, iff	551	In the second form (another port given), the other port (C<$rcvport>)
415	a @reason was specified, i.e. on "normal" kils nothing happens, while	552	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
416	under all other conditions, the other port is killed with the same reason.	553	"normal" kils nothing happens, while under all other conditions, the other
		554	port is killed with the same reason.
417		555
		556	The third form (kill self) is the same as the second form, except that
		557	C<$rvport> defaults to C<$SELF>.
		558
418	In the last form, a message of the form C<@msg, @reason> will be C<snd>.	559	In the last form (message), a message of the form C<@msg, @reason> will be
		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.
		564
		565	As a rule of thumb, monitoring requests should always monitor a port from
		566	a local port (or callback). The reason is that kill messages might get
		567	lost, just like any other message. Another less obvious reason is that
		568	even monitoring requests can get lost (for example, when the connection
		569	to the other node goes down permanently). When monitoring a port locally
		570	these problems do not exist.
		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.
419		588
420	Example: call a given callback when C<$port> is killed.	589	Example: call a given callback when C<$port> is killed.
421		590
422	mon $port, sub { warn "port died because of <@_>\n" };	591	mon $port, sub { warn "port died because of <@_>\n" };
423		592
424	Example: kill ourselves when C<$port> is killed abnormally.	593	Example: kill ourselves when C<$port> is killed abnormally.
425		594
426	mon $port, $self;	595	mon $port;
427		596
428	Example: send us a restart message another C<$port> is killed.	597	Example: send us a restart message when another C<$port> is killed.
429		598
430	mon $port, $self => "restart";	599	mon $port, $self => "restart";
431		600
432	=cut	601	=cut
433		602
434	sub mon {	603	sub mon {
435	my ($noderef, $port) = split /#/, shift, 2;	604	my ($nodeid, $port) = split /#/, shift, 2;
436		605
437	my $node = $NODE{$noderef} \|\| add_node $noderef;	606	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
438		607
439	my $cb = shift;	608	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
440		609
441	unless (ref $cb) {	610	unless (ref $cb) {
442	if (@_) {	611	if (@_) {
443	# send a kill info message	612	# send a kill info message
444	my (@msg) = ($cb, @_);	613	my (@msg) = ($cb, @_);
…		…
451	}	620	}
452		621
453	$node->monitor ($port, $cb);	622	$node->monitor ($port, $cb);
454		623
455	defined wantarray	624	defined wantarray
456	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	625	and ($cb += 0, AnyEvent::Util::guard { $node->unmonitor ($port, $cb) })
457	}	626	}
458		627
459	=item $guard = mon_guard $port, $ref, $ref...	628	=item $guard = mon_guard $port, $ref, $ref...
460		629
461	Monitors the given C<$port> and keeps the passed references. When the port	630	Monitors the given C<$port> and keeps the passed references. When the port
462	is killed, the references will be freed.	631	is killed, the references will be freed.
463		632
464	Optionally returns a guard that will stop the monitoring.	633	Optionally returns a guard that will stop the monitoring.
465		634
466	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
467	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>):
468		637
469	$port->rcv (start => sub {	638	$port->rcv (start => sub {
470	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	639	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
471	undef $timer if 0.9 < rand;	640	undef $timer if 0.9 < rand;
472	});	641	});
473	});	642	});
474		643
475	=cut	644	=cut
476		645
477	sub mon_guard {	646	sub mon_guard {
478	my ($port, @refs) = @_;	647	my ($port, @refs) = @_;
479		648
		649	#TODO: mon-less form?
		650
480	mon $port, sub { 0 && @refs }	651	mon $port, sub { 0 && @refs }
481	}	652	}
482		653
483	=item lnk $port1, $port2
484
485	Link two ports. This is simply a shorthand for:
486
487	mon $port1, $port2;
488	mon $port2, $port1;
489
490	It means that if either one is killed abnormally, the other one gets
491	killed as well.
492
493	=item kil $port[, @reason]	654	=item kil $port[, @reason]
494		655
495	Kill the specified port with the given C<@reason>.	656	Kill the specified port with the given C<@reason>.
496		657
497	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" -
498	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.
499		661
500	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>
501	C<mon>, see below).	663	form) get killed with the same reason.
502		664
503	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
504	will be reported as reason C<< die => $@ >>.	666	will be reported as reason C<< die => $@ >>.
505		667
506	Transport/communication errors are reported as C<< transport_error =>	668	Transport/communication errors are reported as C<< transport_error =>
507	$message >>.	669	$message >>.
508		670
		671	=cut
		672
		673	=item $port = spawn $node, $initfunc[, @initdata]
		674
		675	Creates a port on the node C<$node> (which can also be a port ID, in which
		676	case it's the node where that port resides).
		677
		678	The port ID of the newly created port is returned immediately, and it is
		679	possible to immediately start sending messages or to monitor the port.
		680
		681	After the port has been created, the init function is called on the remote
		682	node, in the same context as a C<rcv> callback. This function must be a
		683	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		684	specify a function in the main program, use C<::name>.
		685
		686	If the function doesn't exist, then the node tries to C<require>
		687	the package, then the package above the package and so on (e.g.
		688	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		689	exists or it runs out of package names.
		690
		691	The init function is then called with the newly-created port as context
		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.
		695
		696	A common idiom is to pass a local port, immediately monitor the spawned
		697	port, and in the remote init function, immediately monitor the passed
		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<$initfunc> has no visible effects on the
		702	caller before C<spawn> returns (by delaying invocation when spawn is
		703	called for the local node).
		704
		705	Example: spawn a chat server port on C<$othernode>.
		706
		707	# this node, executed from within a port context:
		708	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		709	mon $server;
		710
		711	# init function on C<$othernode>
		712	sub connect {
		713	my ($srcport) = @_;
		714
		715	mon $srcport;
		716
		717	rcv $SELF, sub {
		718	...
		719	};
		720	}
		721
		722	=cut
		723
		724	sub _spawn {
		725	my $port = shift;
		726	my $init = shift;
		727
		728	# rcv will create the actual port
		729	local $SELF = "$NODE#$port";
		730	eval {
		731	&{ load_func $init }
		732	};
		733	_self_die if $@;
		734	}
		735
		736	sub spawn(@) {
		737	my ($nodeid, undef) = split /#/, shift, 2;
		738
		739	my $id = "$RUNIQ." . $ID++;
		740
		741	$_[0] =~ /::/
		742	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		743
		744	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		745
		746	"$nodeid#$id"
		747	}
		748
		749	=item after $timeout, @msg
		750
		751	=item after $timeout, $callback
		752
		753	Either sends the given message, or call the given callback, after the
		754	specified number of seconds.
		755
		756	This is simply a utility function that comes in handy at times - the
		757	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		758	so it may go away in the future.
		759
		760	=cut
		761
		762	sub after($@) {
		763	my ($timeout, @action) = @_;
		764
		765	my $t; $t = AE::timer $timeout, 0, sub {
		766	undef $t;
		767	ref $action[0]
		768	? $action[0]()
		769	: snd @action;
		770	};
		771	}
		772
		773	=item cal $port, @msg, $callback[, $timeout]
		774
		775	A simple form of RPC - sends a message to the given C<$port> with the
		776	given contents (C<@msg>), but adds a reply port to the message.
		777
		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.
		780
		781	A reply message sent to the port is passed to the C<$callback> as-is.
		782
		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.
		786
		787	If no time-out is given (or it is C<undef>), then the local port will
		788	monitor the remote port instead, so it eventually gets cleaned-up.
		789
		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.
		793
		794	=cut
		795
		796	sub cal(@) {
		797	my $timeout = ref $_[-1] ? undef : pop;
		798	my $cb = pop;
		799
		800	my $port = port {
		801	undef $timeout;
		802	kil $SELF;
		803	&$cb;
		804	};
		805
		806	if (defined $timeout) {
		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	}
		818
		819	push @_, $port;
		820	&snd;
		821
		822	$port
		823	}
		824
509	=back	825	=back
510		826
511	=head1 FUNCTIONS FOR NODES
512
513	=over 4
514
515	=item initialise_node $noderef, $seednode, $seednode...
516
517	=item initialise_node "slave/", $master, $master...
518
519	Initialises a node - must be called exactly once before calling other
520	AnyEvent::MP functions when talking to other nodes is required.
521
522	All arguments are noderefs, which can be either resolved or unresolved.
523
524	There are two types of networked nodes, public nodes and slave nodes:
525
526	=over 4
527
528	=item public nodes
529
530	For public nodes, C<$noderef> must either be a (possibly unresolved)
531	noderef, in which case it will be resolved, or C<undef> (or missing), in
532	which case the noderef will be guessed.
533
534	Afterwards, the node will bind itself on all endpoints and try to connect
535	to all additional C<$seednodes> that are specified. Seednodes are optional
536	and can be used to quickly bootstrap the node into an existing network.
537
538	=item slave nodes
539
540	When the C<$noderef> is the special string C<slave/>, then the node will
541	become a slave node. Slave nodes cannot be contacted from outside and will
542	route most of their traffic to the master node that they attach to.
543
544	At least one additional noderef is required: The node will try to connect
545	to all of them and will become a slave attached to the first node it can
546	successfully connect to.
547
548	=back
549
550	This function will block until all nodes have been resolved and, for slave
551	nodes, until it has successfully established a connection to a master
552	server.
553
554	Example: become a public node listening on the default node.
555
556	initialise_node;
557
558	Example: become a public node, and try to contact some well-known master
559	servers to become part of the network.
560
561	initialise_node undef, "master1", "master2";
562
563	Example: become a public node listening on port C<4041>.
564
565	initialise_node 4041;
566
567	Example: become a public node, only visible on localhost port 4044.
568
569	initialise_node "locahost:4044";
570
571	Example: become a slave node to any of the specified master servers.
572
573	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
574
575	=cut
576
577	=back
578
579	=head1 NODE MESSAGES
580
581	Nodes understand the following messages sent to them. Many of them take
582	arguments called C<@reply>, which will simply be used to compose a reply
583	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
584	the remaining arguments are simply the message data.
585
586	While other messages exist, they are not public and subject to change.
587
588	=over 4
589
590	=cut
591
592	=item lookup => $name, @reply
593
594	Replies with the port ID of the specified well-known port, or C<undef>.
595
596	=item devnull => ...
597
598	Generic data sink/CPU heat conversion.
599
600	=item relay => $port, @msg
601
602	Simply forwards the message to the given port.
603
604	=item eval => $string[ @reply]
605
606	Evaluates the given string. If C<@reply> is given, then a message of the
607	form C<@reply, $@, @evalres> is sent.
608
609	Example: crash another node.
610
611	snd $othernode, eval => "exit";
612
613	=item time => @reply
614
615	Replies the the current node time to C<@reply>.
616
617	Example: tell the current node to send the current time to C<$myport> in a
618	C<timereply> message.
619
620	snd $NODE, time => $myport, timereply => 1, 2;
621	# => snd $myport, timereply => 1, 2, <time>
622
623	=back
624
625	=head1 AnyEvent::MP vs. Distributed Erlang	827	=head1 AnyEvent::MP vs. Distributed Erlang
626		828
627	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
628	== 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
629	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
630	sample:	832	sample:
631		833
632	http://www.erlang.se/doc/programming_rules.shtml	834	http://www.erlang.se/doc/programming_rules.shtml
633	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
634	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
…		…
636		838
637	Despite the similarities, there are also some important differences:	839	Despite the similarities, there are also some important differences:
638		840
639	=over 4	841	=over 4
640		842
641	=item * Node references contain the recipe on how to contact them.	843	=item * Node IDs are arbitrary strings in AEMP.
642		844
643	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
644	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
645	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.
646		849
647	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
648	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.
649		864
650	=item * Erlang uses processes and a mailbox, AEMP does not queue.	865	=item * Erlang uses processes and a mailbox, AEMP does not queue.
651		866
652	Erlang uses processes that selctively receive messages, and therefore	867	Erlang uses processes that selectively receive messages, and therefore
653	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
654	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.
655		872
656	(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).
657		874
658	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	875	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
659		876
660	Sending messages in erlang is synchronous and blocks the process. AEMP	877	Sending messages in Erlang is synchronous and blocks the process (and
661	sends are immediate, connection establishment is handled in the	878	so does not need a queue that can overflow). AEMP sends are immediate,
662	background.	879	connection establishment is handled in the background.
663		880
664	=item * Erlang can silently lose messages, AEMP cannot.	881	=item * Erlang suffers from silent message loss, AEMP does not.
665		882
666	Erlang makes few guarantees on messages delivery - messages can get lost	883	Erlang implements few guarantees on messages delivery - messages can get
667	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,
668	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).
669		886
670	AEMP guarantees correct ordering, and the guarantee that there are no	887	AEMP guarantees (modulo hardware errors) correct ordering, and the
		888	guarantee that after one message is lost, all following ones sent to the
		889	same port are lost as well, until monitoring raises an error, so there are
671	holes in the message sequence.	890	no silent "holes" in the message sequence.
672
673	=item * In erlang, processes can be declared dead and later be found to be
674	alive.
675
676	In erlang it can happen that a monitored process is declared dead and
677	linked processes get killed, but later it turns out that the process is
678	still alive - and can receive messages.
679
680	In AEMP, when port monitoring detects a port as dead, then that port will
681	eventually be killed - it cannot happen that a node detects a port as dead
682	and then later sends messages to it, finding it is still alive.
683		891
684	=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.
685		893
686	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
687	ID known to other nodes for a completely different process, causing	895	known to other nodes for a completely different process, causing messages
688	messages destined for that process to end up in an unrelated process.	896	destined for that process to end up in an unrelated process.
689		897
690	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
691	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.
692		900
693	=item * Erlang uses unprotected connections, AEMP uses secure	901	=item * Erlang uses unprotected connections, AEMP uses secure
694	authentication and can use TLS.	902	authentication and can use TLS.
695		903
696	AEMP can use a proven protocol - SSL/TLS - to protect connections and	904	AEMP can use a proven protocol - TLS - to protect connections and
697	securely authenticate nodes.	905	securely authenticate nodes.
698		906
699	=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
700	communications.	908	communications.
701		909
702	The AEMP protocol, unlike the erlang protocol, supports both	910	The AEMP protocol, unlike the Erlang protocol, supports both programming
703	language-independent text-only protocols (good for debugging) and binary,	911	language independent text-only protocols (good for debugging) and binary,
704	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.
705		914
706	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
707	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
708	protocol simple.	917	protocol simple.
709		918
		919	=item * AEMP has more flexible monitoring options than Erlang.
		920
		921	In Erlang, you can chose to receive I<all> exit signals as messages
		922	or I<none>, there is no in-between, so monitoring single processes is
		923	difficult to implement. Monitoring in AEMP is more flexible than in
		924	Erlang, as one can choose between automatic kill, exit message or callback
		925	on a per-process basis.
		926
		927	=item * Erlang tries to hide remote/local connections, AEMP does not.
		928
		929	Monitoring in Erlang is not an indicator of process death/crashes, in the
		930	same way as linking is (except linking is unreliable in Erlang).
		931
		932	In AEMP, you don't "look up" registered port names or send to named ports
		933	that might or might not be persistent. Instead, you normally spawn a port
		934	on the remote node. The init function monitors you, and you monitor the
		935	remote port. Since both monitors are local to the node, they are much more
		936	reliable (no need for C<spawn_link>).
		937
		938	This also saves round-trips and avoids sending messages to the wrong port
		939	(hard to do in Erlang).
		940
710	=back	941	=back
711		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	code reference 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
712	=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 maintenance 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.
713		991
714	L<AnyEvent>.	992	L<AnyEvent>.
715		993
716	=head1 AUTHOR	994	=head1 AUTHOR
717		995

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Revision 1.118 by root, Thu Jun 30 09:31:58 2011 UTC