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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.32 by root, Wed Aug 5 19:58:46 2009 UTC vs.
Revision 1.119 by root, Sun Feb 26 10:29:59 2012 UTC

…		…
1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent::MP - multi-processing/message-passing framework	3	AnyEvent::MP - erlang-style multi-processing/message-passing framework
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::MP;	7	use AnyEvent::MP;
8		8
9	$NODE # contains this node's noderef	9	$NODE # contains this node's node ID
10	NODE # returns this node's noderef	10	NODE # returns this node's node ID
11	NODE $port # returns the noderef of the port
12		11
		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
		83	Ports are represented by (printable) strings called "port IDs".
		84
54	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
55		86
56	A port id is normaly the concatenation of a noderef, a hash-mark (C<#>) as	87	A port ID is the concatenation of a node ID, a hash-mark (C<#>) as
57	separator, and a port name (a printable string of unspecified format). An	88	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		89
61	=item node	90	=item node
62		91
63	A node is a single process containing at least one port - the node	92	A node is a single process containing at least one port - the node port,
64	port. You can send messages to node ports to find existing ports or to	93	which enables nodes to manage each other remotely, and to create new
65	create new ports, among other things.	94	ports.
66		95
67	Nodes are either private (single-process only), slaves (connected to a	96	Nodes are either public (have one or more listening ports) or private
68	master node only) or public nodes (connectable from unrelated nodes).	97	(no listening ports). Private nodes cannot talk to other private nodes
		98	currently, but all nodes can talk to public nodes.
69		99
70	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	100	Nodes is represented by (printable) strings called "node IDs".
71		101
72	A node reference is a string that either simply identifies the node (for	102	=item node ID - C<[A-Za-z0-9_\-.:]*>
73	private and slave nodes), or contains a recipe on how to reach a given
74	node (for public nodes).
75		103
76	This recipe is simply a comma-separated list of C<address:port> pairs (for	104	A node ID is a string that uniquely identifies the node within a
77	TCP/IP, other protocols might look different).	105	network. Depending on the configuration used, node IDs can look like a
		106	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		107	doesn't interpret node IDs in any way except to uniquely identify a node.
78		108
79	Node references come in two flavours: resolved (containing only numerical	109	=item binds - C<ip:port>
80	addresses) or unresolved (where hostnames are used instead of addresses).
81		110
82	Before using an unresolved node reference in a message you first have to	111	Nodes can only talk to each other by creating some kind of connection to
83	resolve it.	112	each other. To do this, nodes should listen on one or more local transport
		113	endpoints - binds.
		114
		115	Currently, only standard C<ip:port> specifications can be used, which
		116	specify TCP ports to listen on. So a bind is basically just a tcp socket
		117	in listening mode thta accepts conenctions form other nodes.
		118
		119	=item seed nodes
		120
		121	When a node starts, it knows nothing about the network it is in - it
		122	needs to connect to at least one other node that is already in the
		123	network. These other nodes are called "seed nodes".
		124
		125	Seed nodes themselves are not special - they are seed nodes only because
		126	some other node I<uses> them as such, but any node can be used as seed
		127	node for other nodes, and eahc node cna use a different set of seed nodes.
		128
		129	In addition to discovering the network, seed nodes are also used to
		130	maintain the network - all nodes using the same seed node form are part of
		131	the same network. If a network is split into multiple subnets because e.g.
		132	the network link between the parts goes down, then using the same seed
		133	nodes for all nodes ensures that eventually the subnets get merged again.
		134
		135	Seed nodes are expected to be long-running, and at least one seed node
		136	should always be available. They should also be relatively responsive - a
		137	seed node that blocks for long periods will slow down everybody else.
		138
		139	For small networks, it's best if every node uses the same set of seed
		140	nodes. For large networks, it can be useful to specify "regional" seed
		141	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		142	each other. What's important is that all seed nodes connections form a
		143	complete graph, so that the network cannot split into separate subnets
		144	forever.
		145
		146	Seed nodes are represented by seed IDs.
		147
		148	=item seed IDs - C<host:port>
		149
		150	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
		151	TCP port) of nodes that should be used as seed nodes.
		152
		153	=item global nodes
		154
		155	An AEMP network needs a discovery service - nodes need to know how to
		156	connect to other nodes they only know by name. In addition, AEMP offers a
		157	distributed "group database", which maps group names to a list of strings
		158	- for example, to register worker ports.
		159
		160	A network needs at least one global node to work, and allows every node to
		161	be a global node.
		162
		163	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		164	node and tries to keep connections to all other nodes. So while it can
		165	make sense to make every node "global" in small networks, it usually makes
		166	sense to only make seed nodes into global nodes in large networks (nodes
		167	keep connections to seed nodes and global nodes, so makign them the same
		168	reduces overhead).
84		169
85	=back	170	=back
86		171
87	=head1 VARIABLES/FUNCTIONS	172	=head1 VARIABLES/FUNCTIONS
88		173
90		175
91	=cut	176	=cut
92		177
93	package AnyEvent::MP;	178	package AnyEvent::MP;
94		179
95	use AnyEvent::MP::Base;	180	use AnyEvent::MP::Kernel;
96		181
97	use common::sense;	182	use common::sense;
98		183
99	use Carp ();	184	use Carp ();
100		185
101	use AE ();	186	use AE ();
102		187
103	use base "Exporter";	188	use base "Exporter";
104		189
105	our $VERSION = '0.1';	190	our $VERSION = '1.30';
		191
106	our @EXPORT = qw(	192	our @EXPORT = qw(
107	NODE $NODE *SELF node_of _any_	193	NODE $NODE *SELF node_of after
108	resolve_node initialise_node	194	configure
109	snd rcv mon kil reg psub	195	snd rcv mon mon_guard kil psub peval spawn cal
110	port	196	port
111	);	197	);
112		198
113	our $SELF;	199	our $SELF;
114		200
…		…
118	kil $SELF, die => $msg;	204	kil $SELF, die => $msg;
119	}	205	}
120		206
121	=item $thisnode = NODE / $NODE	207	=item $thisnode = NODE / $NODE
122		208
123	The C<NODE> function returns, and the C<$NODE> variable contains	209	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	210	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	211	a call to C<configure>.
126	identifiers become invalid.
127		212
128	=item $noderef = node_of $portid	213	=item $nodeid = node_of $port
129		214
130	Extracts and returns the noderef from a portid or a noderef.	215	Extracts and returns the node ID from a port ID or a node ID.
131		216
132	=item $cv = resolve_node $noderef	217	=item configure $profile, key => value...
133		218
134	Takes an unresolved node reference that may contain hostnames and	219	=item configure key => value...
135	abbreviated IDs, resolves all of them and returns a resolved node
136	reference.
137		220
138	In addition to C<address:port> pairs allowed in resolved noderefs, the	221	Before a node can talk to other nodes on the network (i.e. enter
139	following forms are supported:	222	"distributed mode") it has to configure itself - the minimum a node needs
		223	to know is its own name, and optionally it should know the addresses of
		224	some other nodes in the network to discover other nodes.
		225
		226	The key/value pairs are basically the same ones as documented for the
		227	F<aemp> command line utility (sans the set/del prefix).
		228
		229	This function configures a node - it must be called exactly once (or
		230	never) before calling other AnyEvent::MP functions.
140		231
141	=over 4	232	=over 4
142		233
143	=item the empty string	234	=item step 1, gathering configuration from profiles
144		235
145	An empty-string component gets resolved as if the default port (4040) was	236	The function first looks up a profile in the aemp configuration (see the
146	specified.	237	L<aemp> commandline utility). The profile name can be specified via the
		238	named C<profile> parameter or can simply be the first parameter). If it is
		239	missing, then the nodename (F<uname -n>) will be used as profile name.
147		240
148	=item naked port numbers (e.g. C<1234>)	241	The profile data is then gathered as follows:
149		242
150	These are resolved by prepending the local nodename and a colon, to be	243	First, all remaining key => value pairs (all of which are conveniently
151	further resolved.	244	undocumented at the moment) will be interpreted as configuration
		245	data. Then they will be overwritten by any values specified in the global
		246	default configuration (see the F<aemp> utility), then the chain of
		247	profiles chosen by the profile name (and any C<parent> attributes).
152		248
153	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	249	That means that the values specified in the profile have highest priority
		250	and the values specified directly via C<configure> have lowest priority,
		251	and can only be used to specify defaults.
154		252
155	These are resolved by using AnyEvent::DNS to resolve them, optionally	253	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	254	this process. If not, then the profile name will be used as node ID. The
157	specified.	255	special node ID of C<anon/> will be replaced by a random node ID.
		256
		257	=item step 2, bind listener sockets
		258
		259	The next step is to look up the binds in the profile, followed by binding
		260	aemp protocol listeners on all binds specified (it is possible and valid
		261	to have no binds, meaning that the node cannot be contacted form the
		262	outside. This means the node cannot talk to other nodes that also have no
		263	binds, but it can still talk to all "normal" nodes).
		264
		265	If the profile does not specify a binds list, then a default of C<*> is
		266	used, meaning the node will bind on a dynamically-assigned port on every
		267	local IP address it finds.
		268
		269	=item step 3, connect to seed nodes
		270
		271	As the last step, the seed ID list from the profile is passed to the
		272	L<AnyEvent::MP::Global> module, which will then use it to keep
		273	connectivity with at least one node at any point in time.
158		274
159	=back	275	=back
		276
		277	Example: become a distributed node using the local node name as profile.
		278	This should be the most common form of invocation for "daemon"-type nodes.
		279
		280	configure
		281
		282	Example: become an anonymous node. This form is often used for commandline
		283	clients.
		284
		285	configure nodeid => "anon/";
		286
		287	Example: configure a node using a profile called seed, which si suitable
		288	for a seed node as it binds on all local addresses on a fixed port (4040,
		289	customary for aemp).
		290
		291	# use the aemp commandline utility
		292	# aemp profile seed nodeid anon/ binds '*:4040'
		293
		294	# then use it
		295	configure profile => "seed";
		296
		297	# or simply use aemp from the shell again:
		298	# aemp run profile seed
		299
		300	# or provide a nicer-to-remember nodeid
		301	# aemp run profile seed nodeid "$(hostname)"
160		302
161	=item $SELF	303	=item $SELF
162		304
163	Contains the current port id while executing C<rcv> callbacks or C<psub>	305	Contains the current port id while executing C<rcv> callbacks or C<psub>
164	blocks.	306	blocks.
165		307
166	=item SELF, %SELF, @SELF...	308	=item *SELF, SELF, %SELF, @SELF...
167		309
168	Due to some quirks in how perl exports variables, it is impossible to	310	Due to some quirks in how perl exports variables, it is impossible to
169	just export C<$SELF>, all the symbols called C<SELF> are exported by this	311	just export C<$SELF>, all the symbols named C<SELF> are exported by this
170	module, but only C<$SELF> is currently used.	312	module, but only C<$SELF> is currently used.
171		313
172	=item snd $portid, type => @data	314	=item snd $port, type => @data
173		315
174	=item snd $portid, @msg	316	=item snd $port, @msg
175		317
176	Send the given message to the given port ID, which can identify either	318	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	319	local or a remote port, and must be a port ID.
178	stringifies a sa port ID (such as a port object :).
179		320
180	While the message can be about anything, it is highly recommended to use a	321	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	322	use a string as first element (a port ID, or some word that indicates a
182	type etc.).	323	request type etc.) and to consist if only simple perl values (scalars,
		324	arrays, hashes) - if you think you need to pass an object, think again.
183		325
184	The message data effectively becomes read-only after a call to this	326	The message data logically becomes read-only after a call to this
185	function: modifying any argument is not allowed and can cause many	327	function: modifying any argument (or values referenced by them) is
186	problems.	328	forbidden, as there can be considerable time between the call to C<snd>
		329	and the time the message is actually being serialised - in fact, it might
		330	never be copied as within the same process it is simply handed to the
		331	receiving port.
187		332
188	The type of data you can transfer depends on the transport protocol: when	333	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	334	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	335	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	336	that Storable can serialise and deserialise is allowed, and for the local
192	node, anything can be passed.	337	node, anything can be passed. Best rely only on the common denominator of
		338	these.
193		339
194	=item $local_port = port	340	=item $local_port = port
195		341
196	Create a new local port object that can be used either as a pattern	342	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"),	343	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		344
200	=item $portid = port { my @msg = @_; $finished }	345	=item $local_port = port { my @msg = @_ }
201		346
202	Creates a "mini port", that is, a very lightweight port without any	347	Creates a new local port, and returns its ID. Semantically the same as
203	pattern matching behind it, and returns its ID.	348	creating a port and calling C<rcv $port, $callback> on it.
204		349
205	The block will be called for every message received on the port. When the	350	The block will be called for every message received on the port, with the
206	callback returns a true value its job is considered "done" and the port	351	global variable C<$SELF> set to the port ID. Runtime errors will cause the
207	will be destroyed. Otherwise it will stay alive.	352	port to be C<kil>ed. The message will be passed as-is, no extra argument
		353	(i.e. no port ID) will be passed to the callback.
208		354
209	The message will be passed as-is, no extra argument (i.e. no port id) will	355	If you want to stop/destroy the port, simply C<kil> it:
210	be passed to the callback.
211		356
212	If you need the local port id in the callback, this works nicely:	357	my $port = port {
213		358	my @msg = @_;
214	my $port; $port = port {	359	...
215	snd $otherport, reply => $port;	360	kil $SELF;
216	};	361	};
217		362
218	=cut	363	=cut
		364
		365	sub rcv($@);
		366
		367	sub _kilme {
		368	die "received message on port without callback";
		369	}
219		370
220	sub port(;&) {	371	sub port(;&) {
221	my $id = "$UNIQ." . $ID++;	372	my $id = "$UNIQ." . $ID++;
222	my $port = "$NODE#$id";	373	my $port = "$NODE#$id";
223		374
		375	rcv $port, shift \|\| \&_kilme;
		376
		377	$port
		378	}
		379
		380	=item rcv $local_port, $callback->(@msg)
		381
		382	Replaces the default callback on the specified port. There is no way to
		383	remove the default callback: use C<sub { }> to disable it, or better
		384	C<kil> the port when it is no longer needed.
		385
		386	The global C<$SELF> (exported by this module) contains C<$port> while
		387	executing the callback. Runtime errors during callback execution will
		388	result in the port being C<kil>ed.
		389
		390	The default callback received all messages not matched by a more specific
		391	C<tag> match.
		392
		393	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
		394
		395	Register (or replace) callbacks to be called on messages starting with the
		396	given tag on the given port (and return the port), or unregister it (when
		397	C<$callback> is C<$undef> or missing). There can only be one callback
		398	registered for each tag.
		399
		400	The original message will be passed to the callback, after the first
		401	element (the tag) has been removed. The callback will use the same
		402	environment as the default callback (see above).
		403
		404	Example: create a port and bind receivers on it in one go.
		405
		406	my $port = rcv port,
		407	msg1 => sub { ... },
		408	msg2 => sub { ... },
		409	;
		410
		411	Example: create a port, bind receivers and send it in a message elsewhere
		412	in one go:
		413
		414	snd $otherport, reply =>
		415	rcv port,
		416	msg1 => sub { ... },
		417	...
		418	;
		419
		420	Example: temporarily register a rcv callback for a tag matching some port
		421	(e.g. for an rpc reply) and unregister it after a message was received.
		422
		423	rcv $port, $otherport => sub {
		424	my @reply = @_;
		425
		426	rcv $SELF, $otherport;
		427	};
		428
		429	=cut
		430
		431	sub rcv($@) {
		432	my $port = shift;
		433	my ($nodeid, $portid) = split /#/, $port, 2;
		434
		435	$NODE{$nodeid} == $NODE{""}
		436	or Carp::croak "$port: rcv can only be called on local ports, caught";
		437
224	if (@_) {	438	while (@_) {
		439	if (ref $_[0]) {
		440	if (my $self = $PORT_DATA{$portid}) {
		441	"AnyEvent::MP::Port" eq ref $self
		442	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		443
		444	$self->[0] = shift;
		445	} else {
225	my $cb = shift;	446	my $cb = shift;
226	$PORT{$id} = sub {	447	$PORT{$portid} = sub {
227	local $SELF = $port;	448	local $SELF = $port;
228	eval {	449	eval { &$cb }; _self_die if $@;
229	&$cb	450	};
230	and kil $id;	451	}
		452	} elsif (defined $_[0]) {
		453	my $self = $PORT_DATA{$portid} \|\|= do {
		454	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
		455
		456	$PORT{$portid} = sub {
		457	local $SELF = $port;
		458
		459	if (my $cb = $self->[1]{$_[0]}) {
		460	shift;
		461	eval { &$cb }; _self_die if $@;
		462	} else {
		463	&{ $self->[0] };
		464	}
		465	};
		466
		467	$self
231	};	468	};
232	_self_die if $@;	469
233	};
234	} else {
235	my $self = bless {
236	id => "$NODE#$id",
237	}, "AnyEvent::MP::Port";	470	"AnyEvent::MP::Port" eq ref $self
		471	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
238		472
239	$PORT_DATA{$id} = $self;	473	my ($tag, $cb) = splice @_, 0, 2;
240	$PORT{$id} = sub {
241	local $SELF = $port;
242		474
		475	if (defined $cb) {
		476	$self->[1]{$tag} = $cb;
243	eval {	477	} else {
244	for (@{ $self->{rc0}{$_[0]} }) {	478	delete $self->[1]{$tag};
245	$_ && &{$_->[0]}
246	&& undef $_;
247	}
248
249	for (@{ $self->{rcv}{$_[0]} }) {
250	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
251	&& &{$_->[0]}
252	&& undef $_;
253	}
254
255	for (@{ $self->{any} }) {
256	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
257	&& &{$_->[0]}
258	&& undef $_;
259	}
260	};	479	}
261	_self_die if $@;
262	};
263	}
264
265	$port
266	}
267
268	=item reg $portid, $name
269
270	Registers the given port under the name C<$name>. If the name already
271	exists it is replaced.
272
273	A port can only be registered under one well known name.
274
275	A port automatically becomes unregistered when it is killed.
276
277	=cut
278
279	sub reg(@) {
280	my ($portid, $name) = @_;
281
282	$REG{$name} = $portid;
283	}
284
285	=item rcv $portid, $callback->(@msg)
286
287	Replaces the callback on the specified miniport (or newly created port
288	object, see C<port>). Full ports are configured with the following calls:
289
290	=item rcv $portid, tagstring => $callback->(@msg), ...
291
292	=item rcv $portid, $smartmatch => $callback->(@msg), ...
293
294	=item rcv $portid, [$smartmatch...] => $callback->(@msg), ...
295
296	Register callbacks to be called on matching messages on the given full
297	port (or newly created port).
298
299	The callback has to return a true value when its work is done, after
300	which is will be removed, or a false value in which case it will stay
301	registered.
302
303	The global C<$SELF> (exported by this module) contains C<$portid> while
304	executing the callback.
305
306	Runtime errors wdurign callback execution will result in the port being
307	C<kil>ed.
308
309	If the match is an array reference, then it will be matched against the
310	first elements of the message, otherwise only the first element is being
311	matched.
312
313	Any element in the match that is specified as C<_any_> (a function
314	exported by this module) matches any single element of the message.
315
316	While not required, it is highly recommended that the first matching
317	element is a string identifying the message. The one-string-only match is
318	also the most efficient match (by far).
319
320	=cut
321
322	sub rcv($@) {
323	my $portid = shift;
324	my ($noderef, $port) = split /#/, $port, 2;
325
326	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}
327	or Carp::croak "$noderef#$port: rcv can only be called on local ports, caught";
328
329	my $self = $PORT_DATA{$port}
330	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";
331
332	"AnyEvent::MP::Port" eq ref $self
333	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";
334
335	while (@_) {
336	my ($match, $cb) = splice @_, 0, 2;
337
338	if (!ref $match) {
339	push @{ $self->{rc0}{$match} }, [$cb];
340	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
341	my ($type, @match) = @$match;
342	@match
343	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
344	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
345	} else {
346	push @{ $self->{any} }, [$cb, $match];
347	}	480	}
348	}	481	}
349		482
350	$portid	483	$port
		484	}
		485
		486	=item peval $port, $coderef[, @args]
		487
		488	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		489	when the code throews an exception the C<$port> will be killed.
		490
		491	Any remaining args will be passed to the callback. Any return values will
		492	be returned to the caller.
		493
		494	This is useful when you temporarily want to execute code in the context of
		495	a port.
		496
		497	Example: create a port and run some initialisation code in it's context.
		498
		499	my $port = port { ... };
		500
		501	peval $port, sub {
		502	init
		503	or die "unable to init";
		504	};
		505
		506	=cut
		507
		508	sub peval($$) {
		509	local $SELF = shift;
		510	my $cb = shift;
		511
		512	if (wantarray) {
		513	my @res = eval { &$cb };
		514	_self_die if $@;
		515	@res
		516	} else {
		517	my $res = eval { &$cb };
		518	_self_die if $@;
		519	$res
		520	}
351	}	521	}
352		522
353	=item $closure = psub { BLOCK }	523	=item $closure = psub { BLOCK }
354		524
355	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	525	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
356	closure is executed, sets up the environment in the same way as in C<rcv>	526	closure is executed, sets up the environment in the same way as in C<rcv>
357	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.	527	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		528
		529	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		530	BLOCK }, @_ } >>.
358		531
359	This is useful when you register callbacks from C<rcv> callbacks:	532	This is useful when you register callbacks from C<rcv> callbacks:
360		533
361	rcv delayed_reply => sub {	534	rcv delayed_reply => sub {
362	my ($delay, @reply) = @_;	535	my ($delay, @reply) = @_;
…		…
386	$res	559	$res
387	}	560	}
388	}	561	}
389	}	562	}
390		563
391	=item $guard = mon $portid, $cb->(@reason)	564	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
392		565
393	=item $guard = mon $portid, $otherport	566	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
394		567
395	=item $guard = mon $portid, $otherport, @msg	568	=item $guard = mon $port # kill $SELF when $port dies
396		569
		570	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		571
397	Monitor the given port and do something when the port is killed.	572	Monitor the given port and do something when the port is killed or
		573	messages to it were lost, and optionally return a guard that can be used
		574	to stop monitoring again.
398		575
399	In the first form, the callback is simply called with any number	576	In the first form (callback), the callback is simply called with any
400	of C<@reason> elements (no @reason means that the port was deleted	577	number of C<@reason> elements (no @reason means that the port was deleted
401	"normally"). Note also that I<< the callback B<must> never die >>, so use	578	"normally"). Note also that I<< the callback B<must> never die >>, so use
402	C<eval> if unsure.	579	C<eval> if unsure.
403		580
404	In the second form, the other port will be C<kil>'ed with C<@reason>, iff	581	In the second form (another port given), the other port (C<$rcvport>)
405	a @reason was specified, i.e. on "normal" kils nothing happens, while	582	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
406	under all other conditions, the other port is killed with the same reason.	583	"normal" kils nothing happens, while under all other conditions, the other
		584	port is killed with the same reason.
407		585
		586	The third form (kill self) is the same as the second form, except that
		587	C<$rvport> defaults to C<$SELF>.
		588
408	In the last form, a message of the form C<@msg, @reason> will be C<snd>.	589	In the last form (message), a message of the form C<@msg, @reason> will be
		590	C<snd>.
		591
		592	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		593	alert was raised), they are removed and will not trigger again.
		594
		595	As a rule of thumb, monitoring requests should always monitor a port from
		596	a local port (or callback). The reason is that kill messages might get
		597	lost, just like any other message. Another less obvious reason is that
		598	even monitoring requests can get lost (for example, when the connection
		599	to the other node goes down permanently). When monitoring a port locally
		600	these problems do not exist.
		601
		602	C<mon> effectively guarantees that, in the absence of hardware failures,
		603	after starting the monitor, either all messages sent to the port will
		604	arrive, or the monitoring action will be invoked after possible message
		605	loss has been detected. No messages will be lost "in between" (after
		606	the first lost message no further messages will be received by the
		607	port). After the monitoring action was invoked, further messages might get
		608	delivered again.
		609
		610	Inter-host-connection timeouts and monitoring depend on the transport
		611	used. The only transport currently implemented is TCP, and AnyEvent::MP
		612	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		613	non-idle connection, and usually around two hours for idle connections).
		614
		615	This means that monitoring is good for program errors and cleaning up
		616	stuff eventually, but they are no replacement for a timeout when you need
		617	to ensure some maximum latency.
409		618
410	Example: call a given callback when C<$port> is killed.	619	Example: call a given callback when C<$port> is killed.
411		620
412	mon $port, sub { warn "port died because of <@_>\n" };	621	mon $port, sub { warn "port died because of <@_>\n" };
413		622
414	Example: kill ourselves when C<$port> is killed abnormally.	623	Example: kill ourselves when C<$port> is killed abnormally.
415		624
416	mon $port, $self;	625	mon $port;
417		626
418	Example: send us a restart message another C<$port> is killed.	627	Example: send us a restart message when another C<$port> is killed.
419		628
420	mon $port, $self => "restart";	629	mon $port, $self => "restart";
421		630
422	=cut	631	=cut
423		632
424	sub mon {	633	sub mon {
425	my ($noderef, $port) = split /#/, shift, 2;	634	my ($nodeid, $port) = split /#/, shift, 2;
426		635
427	my $node = $NODE{$noderef} \|\| add_node $noderef;	636	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
428		637
429	my $cb = shift;	638	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
430		639
431	unless (ref $cb) {	640	unless (ref $cb) {
432	if (@_) {	641	if (@_) {
433	# send a kill info message	642	# send a kill info message
434	my (@msg) = ($cb, @_);	643	my (@msg) = ($cb, @_);
…		…
441	}	650	}
442		651
443	$node->monitor ($port, $cb);	652	$node->monitor ($port, $cb);
444		653
445	defined wantarray	654	defined wantarray
446	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	655	and ($cb += 0, AnyEvent::Util::guard { $node->unmonitor ($port, $cb) })
447	}	656	}
448		657
449	=item $guard = mon_guard $port, $ref, $ref...	658	=item $guard = mon_guard $port, $ref, $ref...
450		659
451	Monitors the given C<$port> and keeps the passed references. When the port	660	Monitors the given C<$port> and keeps the passed references. When the port
452	is killed, the references will be freed.	661	is killed, the references will be freed.
453		662
454	Optionally returns a guard that will stop the monitoring.	663	Optionally returns a guard that will stop the monitoring.
455		664
456	This function is useful when you create e.g. timers or other watchers and	665	This function is useful when you create e.g. timers or other watchers and
457	want to free them when the port gets killed:	666	want to free them when the port gets killed (note the use of C<psub>):
458		667
459	$port->rcv (start => sub {	668	$port->rcv (start => sub {
460	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	669	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
461	undef $timer if 0.9 < rand;	670	undef $timer if 0.9 < rand;
462	});	671	});
463	});	672	});
464		673
465	=cut	674	=cut
466		675
467	sub mon_guard {	676	sub mon_guard {
468	my ($port, @refs) = @_;	677	my ($port, @refs) = @_;
469		678
		679	#TODO: mon-less form?
		680
470	mon $port, sub { 0 && @refs }	681	mon $port, sub { 0 && @refs }
471	}	682	}
472		683
473	=item lnk $port1, $port2
474
475	Link two ports. This is simply a shorthand for:
476
477	mon $port1, $port2;
478	mon $port2, $port1;
479
480	It means that if either one is killed abnormally, the other one gets
481	killed as well.
482
483	=item kil $portid[, @reason]	684	=item kil $port[, @reason]
484		685
485	Kill the specified port with the given C<@reason>.	686	Kill the specified port with the given C<@reason>.
486		687
487	If no C<@reason> is specified, then the port is killed "normally" (linked	688	If no C<@reason> is specified, then the port is killed "normally" -
488	ports will not be kileld, or even notified).	689	monitor callback will be invoked, but the kil will not cause linked ports
		690	(C<mon $mport, $lport> form) to get killed.
489		691
490	Otherwise, linked ports get killed with the same reason (second form of	692	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
491	C<mon>, see below).	693	form) get killed with the same reason.
492		694
493	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	695	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
494	will be reported as reason C<< die => $@ >>.	696	will be reported as reason C<< die => $@ >>.
495		697
496	Transport/communication errors are reported as C<< transport_error =>	698	Transport/communication errors are reported as C<< transport_error =>
497	$message >>.	699	$message >>.
498		700
		701	=cut
		702
		703	=item $port = spawn $node, $initfunc[, @initdata]
		704
		705	Creates a port on the node C<$node> (which can also be a port ID, in which
		706	case it's the node where that port resides).
		707
		708	The port ID of the newly created port is returned immediately, and it is
		709	possible to immediately start sending messages or to monitor the port.
		710
		711	After the port has been created, the init function is called on the remote
		712	node, in the same context as a C<rcv> callback. This function must be a
		713	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		714	specify a function in the main program, use C<::name>.
		715
		716	If the function doesn't exist, then the node tries to C<require>
		717	the package, then the package above the package and so on (e.g.
		718	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		719	exists or it runs out of package names.
		720
		721	The init function is then called with the newly-created port as context
		722	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		723	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		724	the port might not get created.
		725
		726	A common idiom is to pass a local port, immediately monitor the spawned
		727	port, and in the remote init function, immediately monitor the passed
		728	local port. This two-way monitoring ensures that both ports get cleaned up
		729	when there is a problem.
		730
		731	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		732	caller before C<spawn> returns (by delaying invocation when spawn is
		733	called for the local node).
		734
		735	Example: spawn a chat server port on C<$othernode>.
		736
		737	# this node, executed from within a port context:
		738	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		739	mon $server;
		740
		741	# init function on C<$othernode>
		742	sub connect {
		743	my ($srcport) = @_;
		744
		745	mon $srcport;
		746
		747	rcv $SELF, sub {
		748	...
		749	};
		750	}
		751
		752	=cut
		753
		754	sub _spawn {
		755	my $port = shift;
		756	my $init = shift;
		757
		758	# rcv will create the actual port
		759	local $SELF = "$NODE#$port";
		760	eval {
		761	&{ load_func $init }
		762	};
		763	_self_die if $@;
		764	}
		765
		766	sub spawn(@) {
		767	my ($nodeid, undef) = split /#/, shift, 2;
		768
		769	my $id = "$RUNIQ." . $ID++;
		770
		771	$_[0] =~ /::/
		772	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		773
		774	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		775
		776	"$nodeid#$id"
		777	}
		778
		779	=item after $timeout, @msg
		780
		781	=item after $timeout, $callback
		782
		783	Either sends the given message, or call the given callback, after the
		784	specified number of seconds.
		785
		786	This is simply a utility function that comes in handy at times - the
		787	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		788	so it may go away in the future.
		789
		790	=cut
		791
		792	sub after($@) {
		793	my ($timeout, @action) = @_;
		794
		795	my $t; $t = AE::timer $timeout, 0, sub {
		796	undef $t;
		797	ref $action[0]
		798	? $action[0]()
		799	: snd @action;
		800	};
		801	}
		802
		803	=item cal $port, @msg, $callback[, $timeout]
		804
		805	A simple form of RPC - sends a message to the given C<$port> with the
		806	given contents (C<@msg>), but adds a reply port to the message.
		807
		808	The reply port is created temporarily just for the purpose of receiving
		809	the reply, and will be C<kil>ed when no longer needed.
		810
		811	A reply message sent to the port is passed to the C<$callback> as-is.
		812
		813	If an optional time-out (in seconds) is given and it is not C<undef>,
		814	then the callback will be called without any arguments after the time-out
		815	elapsed and the port is C<kil>ed.
		816
		817	If no time-out is given (or it is C<undef>), then the local port will
		818	monitor the remote port instead, so it eventually gets cleaned-up.
		819
		820	Currently this function returns the temporary port, but this "feature"
		821	might go in future versions unless you can make a convincing case that
		822	this is indeed useful for something.
		823
		824	=cut
		825
		826	sub cal(@) {
		827	my $timeout = ref $_[-1] ? undef : pop;
		828	my $cb = pop;
		829
		830	my $port = port {
		831	undef $timeout;
		832	kil $SELF;
		833	&$cb;
		834	};
		835
		836	if (defined $timeout) {
		837	$timeout = AE::timer $timeout, 0, sub {
		838	undef $timeout;
		839	kil $port;
		840	$cb->();
		841	};
		842	} else {
		843	mon $_[0], sub {
		844	kil $port;
		845	$cb->();
		846	};
		847	}
		848
		849	push @_, $port;
		850	&snd;
		851
		852	$port
		853	}
		854
499	=back	855	=back
500		856
501	=head1 FUNCTIONS FOR NODES
502
503	=over 4
504
505	=item become_public $noderef
506
507	Tells the node to become a public node, i.e. reachable from other nodes.
508
509	The first argument is the (unresolved) node reference of the local node
510	(if missing then the empty string is used).
511
512	It is quite common to not specify anything, in which case the local node
513	tries to listen on the default port, or to only specify a port number, in
514	which case AnyEvent::MP tries to guess the local addresses.
515
516	=cut
517
518	=back
519
520	=head1 NODE MESSAGES
521
522	Nodes understand the following messages sent to them. Many of them take
523	arguments called C<@reply>, which will simply be used to compose a reply
524	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
525	the remaining arguments are simply the message data.
526
527	While other messages exist, they are not public and subject to change.
528
529	=over 4
530
531	=cut
532
533	=item lookup => $name, @reply
534
535	Replies with the port ID of the specified well-known port, or C<undef>.
536
537	=item devnull => ...
538
539	Generic data sink/CPU heat conversion.
540
541	=item relay => $port, @msg
542
543	Simply forwards the message to the given port.
544
545	=item eval => $string[ @reply]
546
547	Evaluates the given string. If C<@reply> is given, then a message of the
548	form C<@reply, $@, @evalres> is sent.
549
550	Example: crash another node.
551
552	snd $othernode, eval => "exit";
553
554	=item time => @reply
555
556	Replies the the current node time to C<@reply>.
557
558	Example: tell the current node to send the current time to C<$myport> in a
559	C<timereply> message.
560
561	snd $NODE, time => $myport, timereply => 1, 2;
562	# => snd $myport, timereply => 1, 2, <time>
563
564	=back
565
566	=head1 AnyEvent::MP vs. Distributed Erlang	857	=head1 AnyEvent::MP vs. Distributed Erlang
567		858
568	AnyEvent::MP got lots of its ideas from distributed erlang (erlang node	859	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
569	== aemp node, erlang process == aemp port), so many of the documents and	860	== aemp node, Erlang process == aemp port), so many of the documents and
570	programming techniques employed by erlang apply to AnyEvent::MP. Here is a	861	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
571	sample:	862	sample:
572		863
573	http://www.erlang.se/doc/programming_rules.shtml	864	http://www.erlang.se/doc/programming_rules.shtml
574	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	865	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
575	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6	866	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
…		…
577		868
578	Despite the similarities, there are also some important differences:	869	Despite the similarities, there are also some important differences:
579		870
580	=over 4	871	=over 4
581		872
582	=item * Node references contain the recipe on how to contact them.	873	=item * Node IDs are arbitrary strings in AEMP.
583		874
584	Erlang relies on special naming and DNS to work everywhere in the	875	Erlang relies on special naming and DNS to work everywhere in the same
585	same way. AEMP relies on each node knowing it's own address(es), with	876	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
586	convenience functionality.	877	configuration or DNS), and possibly the addresses of some seed nodes, but
		878	will otherwise discover other nodes (and their IDs) itself.
587		879
588	This means that AEMP requires a less tightly controlled environment at the	880	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
589	cost of longer node references and a slightly higher management overhead.	881	uses "local ports are like remote ports".
		882
		883	The failure modes for local ports are quite different (runtime errors
		884	only) then for remote ports - when a local port dies, you I<know> it dies,
		885	when a connection to another node dies, you know nothing about the other
		886	port.
		887
		888	Erlang pretends remote ports are as reliable as local ports, even when
		889	they are not.
		890
		891	AEMP encourages a "treat remote ports differently" philosophy, with local
		892	ports being the special case/exception, where transport errors cannot
		893	occur.
590		894
591	=item * Erlang uses processes and a mailbox, AEMP does not queue.	895	=item * Erlang uses processes and a mailbox, AEMP does not queue.
592		896
593	Erlang uses processes that selctively receive messages, and therefore	897	Erlang uses processes that selectively receive messages out of order, and
594	needs a queue. AEMP is event based, queuing messages would serve no useful	898	therefore needs a queue. AEMP is event based, queuing messages would serve
595	purpose.	899	no useful purpose. For the same reason the pattern-matching abilities
		900	of AnyEvent::MP are more limited, as there is little need to be able to
		901	filter messages without dequeuing them.
596		902
597	(But see L<Coro::MP> for a more erlang-like process model on top of AEMP).	903	This is not a philosophical difference, but simply stems from AnyEvent::MP
		904	being event-based, while Erlang is process-based.
		905
		906	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		907	top of AEMP and Coro threads.
598		908
599	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	909	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
600		910
601	Sending messages in erlang is synchronous and blocks the process. AEMP	911	Sending messages in Erlang is synchronous and blocks the process until
602	sends are immediate, connection establishment is handled in the	912	a conenction has been established and the message sent (and so does not
603	background.	913	need a queue that can overflow). AEMP sends return immediately, connection
		914	establishment is handled in the background.
604		915
605	=item * Erlang can silently lose messages, AEMP cannot.	916	=item * Erlang suffers from silent message loss, AEMP does not.
606		917
607	Erlang makes few guarantees on messages delivery - messages can get lost	918	Erlang implements few guarantees on messages delivery - messages can get
608	without any of the processes realising it (i.e. you send messages a, b,	919	lost without any of the processes realising it (i.e. you send messages a,
609	and c, and the other side only receives messages a and c).	920	b, and c, and the other side only receives messages a and c).
610		921
611	AEMP guarantees correct ordering, and the guarantee that there are no	922	AEMP guarantees (modulo hardware errors) correct ordering, and the
		923	guarantee that after one message is lost, all following ones sent to the
		924	same port are lost as well, until monitoring raises an error, so there are
612	holes in the message sequence.	925	no silent "holes" in the message sequence.
613		926
614	=item * In erlang, processes can be declared dead and later be found to be	927	If you want your software to be very reliable, you have to cope with
615	alive.	928	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
616		929	simply tries to work better in common error cases, such as when a network
617	In erlang it can happen that a monitored process is declared dead and	930	link goes down.
618	linked processes get killed, but later it turns out that the process is
619	still alive - and can receive messages.
620
621	In AEMP, when port monitoring detects a port as dead, then that port will
622	eventually be killed - it cannot happen that a node detects a port as dead
623	and then later sends messages to it, finding it is still alive.
624		931
625	=item * Erlang can send messages to the wrong port, AEMP does not.	932	=item * Erlang can send messages to the wrong port, AEMP does not.
626		933
627	In erlang it is quite possible that a node that restarts reuses a process	934	In Erlang it is quite likely that a node that restarts reuses an Erlang
628	ID known to other nodes for a completely different process, causing	935	process ID known to other nodes for a completely different process,
629	messages destined for that process to end up in an unrelated process.	936	causing messages destined for that process to end up in an unrelated
		937	process.
630		938
631	AEMP never reuses port IDs, so old messages or old port IDs floating	939	AEMP does not reuse port IDs, so old messages or old port IDs floating
632	around in the network will not be sent to an unrelated port.	940	around in the network will not be sent to an unrelated port.
633		941
634	=item * Erlang uses unprotected connections, AEMP uses secure	942	=item * Erlang uses unprotected connections, AEMP uses secure
635	authentication and can use TLS.	943	authentication and can use TLS.
636		944
637	AEMP can use a proven protocol - SSL/TLS - to protect connections and	945	AEMP can use a proven protocol - TLS - to protect connections and
638	securely authenticate nodes.	946	securely authenticate nodes.
639		947
640	=item * The AEMP protocol is optimised for both text-based and binary	948	=item * The AEMP protocol is optimised for both text-based and binary
641	communications.	949	communications.
642		950
643	The AEMP protocol, unlike the erlang protocol, supports both	951	The AEMP protocol, unlike the Erlang protocol, supports both programming
644	language-independent text-only protocols (good for debugging) and binary,	952	language independent text-only protocols (good for debugging), and binary,
645	language-specific serialisers (e.g. Storable).	953	language-specific serialisers (e.g. Storable). By default, unless TLS is
		954	used, the protocol is actually completely text-based.
646		955
647	It has also been carefully designed to be implementable in other languages	956	It has also been carefully designed to be implementable in other languages
648	with a minimum of work while gracefully degrading fucntionality to make the	957	with a minimum of work while gracefully degrading functionality to make the
649	protocol simple.	958	protocol simple.
650		959
		960	=item * AEMP has more flexible monitoring options than Erlang.
		961
		962	In Erlang, you can chose to receive I<all> exit signals as messages or
		963	I<none>, there is no in-between, so monitoring single Erlang processes is
		964	difficult to implement.
		965
		966	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		967	between automatic kill, exit message or callback on a per-port basis.
		968
		969	=item * Erlang tries to hide remote/local connections, AEMP does not.
		970
		971	Monitoring in Erlang is not an indicator of process death/crashes, in the
		972	same way as linking is (except linking is unreliable in Erlang).
		973
		974	In AEMP, you don't "look up" registered port names or send to named ports
		975	that might or might not be persistent. Instead, you normally spawn a port
		976	on the remote node. The init function monitors you, and you monitor the
		977	remote port. Since both monitors are local to the node, they are much more
		978	reliable (no need for C<spawn_link>).
		979
		980	This also saves round-trips and avoids sending messages to the wrong port
		981	(hard to do in Erlang).
		982
651	=back	983	=back
652		984
		985	=head1 RATIONALE
		986
		987	=over 4
		988
		989	=item Why strings for port and node IDs, why not objects?
		990
		991	We considered "objects", but found that the actual number of methods
		992	that can be called are quite low. Since port and node IDs travel over
		993	the network frequently, the serialising/deserialising would add lots of
		994	overhead, as well as having to keep a proxy object everywhere.
		995
		996	Strings can easily be printed, easily serialised etc. and need no special
		997	procedures to be "valid".
		998
		999	And as a result, a port with just a default receiver consists of a single
		1000	code reference stored in a global hash - it can't become much cheaper.
		1001
		1002	=item Why favour JSON, why not a real serialising format such as Storable?
		1003
		1004	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1005	format, but currently there is no way to make a node use Storable by
		1006	default (although all nodes will accept it).
		1007
		1008	The default framing protocol is JSON because a) JSON::XS is many times
		1009	faster for small messages and b) most importantly, after years of
		1010	experience we found that object serialisation is causing more problems
		1011	than it solves: Just like function calls, objects simply do not travel
		1012	easily over the network, mostly because they will always be a copy, so you
		1013	always have to re-think your design.
		1014
		1015	Keeping your messages simple, concentrating on data structures rather than
		1016	objects, will keep your messages clean, tidy and efficient.
		1017
		1018	=back
		1019
653	=head1 SEE ALSO	1020	=head1 SEE ALSO
		1021
		1022	L<AnyEvent::MP::Intro> - a gentle introduction.
		1023
		1024	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1025
		1026	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1027	your applications.
		1028
		1029	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1030
		1031	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1032	all nodes.
654		1033
655	L<AnyEvent>.	1034	L<AnyEvent>.
656		1035
657	=head1 AUTHOR	1036	=head1 AUTHOR
658		1037

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Revision 1.119 by root, Sun Feb 26 10:29:59 2012 UTC