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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.35 by root, Thu Aug 6 10:21:48 2009 UTC vs.
Revision 1.123 by root, Thu Mar 1 19:37:59 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
27		34
28	# linking two ports, so they both crash together	35	# destroy a port again
29	lnk $port1, $port2;	36	kil $port; # "normal" kill
		37	kil $port, my_error => "everything is broken"; # error kill
30		38
31	# monitoring	39	# monitoring
32	mon $port, $cb->(@msg) # callback is invoked on death	40	mon $localport, $cb->(@msg) # callback is invoked on death
33	mon $port, $otherport # kill otherport on abnormal death	41	mon $localport, $otherport # kill otherport on abnormal death
34	mon $port, $otherport, @msg # send message on death	42	mon $localport, $otherport, @msg # send message on death
		43
		44	# temporarily execute code in port context
		45	peval $port, sub { die "kill the port!" };
		46
		47	# execute callbacks in $SELF port context
		48	my $timer = AE::timer 1, 0, psub {
		49	die "kill the port, delayed";
		50	};
		51
		52	=head1 CURRENT STATUS
		53
		54	bin/aemp - stable.
		55	AnyEvent::MP - stable API, should work.
		56	AnyEvent::MP::Intro - explains most concepts.
		57	AnyEvent::MP::Kernel - mostly stable API.
		58	AnyEvent::MP::Global - stable API.
35		59
36	=head1 DESCRIPTION	60	=head1 DESCRIPTION
37		61
38	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
39		63
40	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
41	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
42		66
43	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>
44	manual page.	68	manual page and the examples under F<eg/>.
45
46	At the moment, this module family is severly broken and underdocumented,
47	so do not use. This was uploaded mainly to reserve the CPAN namespace -
48	stay tuned! The basic API should be finished, however.
49		69
50	=head1 CONCEPTS	70	=head1 CONCEPTS
51		71
52	=over 4	72	=over 4
53		73
54	=item port	74	=item port
55		75
56	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).
57		78
58	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
59	messages. All C<rcv> handlers will receive messages they match, messages	80	some messages. Messages send to ports will not be queued, regardless of
60	will not be queued.	81	anything was listening for them or not.
61		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
62	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
63		86
64	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<#>)
65	separator, and a port name (a printable string of unspecified format). An	88	as separator, and a port name (a printable string of unspecified
66	exception is the the node port, whose ID is identical to its node	89	format created by AnyEvent::MP).
67	reference.
68		90
69	=item node	91	=item node
70		92
71	A node is a single process containing at least one port - the node	93	A node is a single process containing at least one port - the node port,
72	port. You can send messages to node ports to find existing ports or to	94	which enables nodes to manage each other remotely, and to create new
73	create new ports, among other things.	95	ports.
74		96
75	Nodes are either private (single-process only), slaves (connected to a	97	Nodes are either public (have one or more listening ports) or private
76	master node only) or public nodes (connectable from unrelated nodes).	98	(no listening ports). Private nodes cannot talk to other private nodes
		99	currently, but all nodes can talk to public nodes.
77		100
78	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	101	Nodes is represented by (printable) strings called "node IDs".
79		102
80	A node reference is a string that either simply identifies the node (for	103	=item node ID - C<[A-Za-z0-9_\-.:]*>
81	private and slave nodes), or contains a recipe on how to reach a given
82	node (for public nodes).
83		104
84	This recipe is simply a comma-separated list of C<address:port> pairs (for	105	A node ID is a string that uniquely identifies the node within a
85	TCP/IP, other protocols might look different).	106	network. Depending on the configuration used, node IDs can look like a
		107	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		108	doesn't interpret node IDs in any way except to uniquely identify a node.
86		109
87	Node references come in two flavours: resolved (containing only numerical	110	=item binds - C<ip:port>
88	addresses) or unresolved (where hostnames are used instead of addresses).
89		111
90	Before using an unresolved node reference in a message you first have to	112	Nodes can only talk to each other by creating some kind of connection to
91	resolve it.	113	each other. To do this, nodes should listen on one or more local transport
		114	endpoints - binds.
		115
		116	Currently, only standard C<ip:port> specifications can be used, which
		117	specify TCP ports to listen on. So a bind is basically just a tcp socket
		118	in listening mode thta accepts conenctions form other nodes.
		119
		120	=item seed nodes
		121
		122	When a node starts, it knows nothing about the network it is in - it
		123	needs to connect to at least one other node that is already in the
		124	network. These other nodes are called "seed nodes".
		125
		126	Seed nodes themselves are not special - they are seed nodes only because
		127	some other node I<uses> them as such, but any node can be used as seed
		128	node for other nodes, and eahc node cna use a different set of seed nodes.
		129
		130	In addition to discovering the network, seed nodes are also used to
		131	maintain the network - all nodes using the same seed node form are part of
		132	the same network. If a network is split into multiple subnets because e.g.
		133	the network link between the parts goes down, then using the same seed
		134	nodes for all nodes ensures that eventually the subnets get merged again.
		135
		136	Seed nodes are expected to be long-running, and at least one seed node
		137	should always be available. They should also be relatively responsive - a
		138	seed node that blocks for long periods will slow down everybody else.
		139
		140	For small networks, it's best if every node uses the same set of seed
		141	nodes. For large networks, it can be useful to specify "regional" seed
		142	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		143	each other. What's important is that all seed nodes connections form a
		144	complete graph, so that the network cannot split into separate subnets
		145	forever.
		146
		147	Seed nodes are represented by seed IDs.
		148
		149	=item seed IDs - C<host:port>
		150
		151	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
		152	TCP port) of nodes that should be used as seed nodes.
		153
		154	=item global nodes
		155
		156	An AEMP network needs a discovery service - nodes need to know how to
		157	connect to other nodes they only know by name. In addition, AEMP offers a
		158	distributed "group database", which maps group names to a list of strings
		159	- for example, to register worker ports.
		160
		161	A network needs at least one global node to work, and allows every node to
		162	be a global node.
		163
		164	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		165	node and tries to keep connections to all other nodes. So while it can
		166	make sense to make every node "global" in small networks, it usually makes
		167	sense to only make seed nodes into global nodes in large networks (nodes
		168	keep connections to seed nodes and global nodes, so makign them the same
		169	reduces overhead).
92		170
93	=back	171	=back
94		172
95	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
96		174
98		176
99	=cut	177	=cut
100		178
101	package AnyEvent::MP;	179	package AnyEvent::MP;
102		180
		181	use AnyEvent::MP::Config ();
103	use AnyEvent::MP::Base;	182	use AnyEvent::MP::Kernel;
		183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
104		184
105	use common::sense;	185	use common::sense;
106		186
107	use Carp ();	187	use Carp ();
108		188
109	use AE ();	189	use AE ();
110		190
111	use base "Exporter";	191	use base "Exporter";
112		192
113	our $VERSION = '0.1';	193	our $VERSION = $AnyEvent::MP::Config::VERSION;
		194
114	our @EXPORT = qw(	195	our @EXPORT = qw(
115	NODE $NODE *SELF node_of _any_	196	NODE $NODE *SELF node_of after
116	resolve_node initialise_node	197	configure
117	snd rcv mon kil reg psub	198	snd rcv mon mon_guard kil psub peval spawn cal
118	port	199	port
119	);	200	);
120		201
121	our $SELF;	202	our $SELF;
122		203
…		…
126	kil $SELF, die => $msg;	207	kil $SELF, die => $msg;
127	}	208	}
128		209
129	=item $thisnode = NODE / $NODE	210	=item $thisnode = NODE / $NODE
130		211
131	The C<NODE> function returns, and the C<$NODE> variable contains	212	The C<NODE> function returns, and the C<$NODE> variable contains, the node
132	the noderef of the local node. The value is initialised by a call	213	ID of the node running in the current process. This value is initialised by
133	to C<become_public> or C<become_slave>, after which all local port	214	a call to C<configure>.
134	identifiers become invalid.
135		215
136	=item $noderef = node_of $port	216	=item $nodeid = node_of $port
137		217
138	Extracts and returns the noderef from a portid or a noderef.	218	Extracts and returns the node ID from a port ID or a node ID.
139		219
140	=item initialise_node $noderef, $seednode, $seednode...	220	=item configure $profile, key => value...
141		221
142	=item initialise_node "slave/", $master, $master...	222	=item configure key => value...
143		223
144	Before a node can talk to other nodes on the network it has to initialise	224	Before a node can talk to other nodes on the network (i.e. enter
145	itself - the minimum a node needs to know is it's own name, and optionally	225	"distributed mode") it has to configure itself - the minimum a node needs
146	it should know the noderefs of some other nodes in the network.	226	to know is its own name, and optionally it should know the addresses of
		227	some other nodes in the network to discover other nodes.
147		228
148	This function initialises a node - it must be called exactly once (or	229	This function configures a node - it must be called exactly once (or
149	never) before calling other AnyEvent::MP functions.	230	never) before calling other AnyEvent::MP functions.
150		231
151	All arguments are noderefs, which can be either resolved or unresolved.	232	The key/value pairs are basically the same ones as documented for the
152		233	F<aemp> command line utility (sans the set/del prefix), with two additions:
153	There are two types of networked nodes, public nodes and slave nodes:
154		234
155	=over 4	235	=over 4
156		236
157	=item public nodes	237	=item norc => $boolean (default false)
158		238
159	For public nodes, C<$noderef> must either be a (possibly unresolved)	239	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
160	noderef, in which case it will be resolved, or C<undef> (or missing), in	240	be consulted - all configuraiton options must be specified in the
161	which case the noderef will be guessed.	241	C<configure> call.
162		242
163	Afterwards, the node will bind itself on all endpoints and try to connect	243	=item force => $boolean (default false)
164	to all additional C<$seednodes> that are specified. Seednodes are optional
165	and can be used to quickly bootstrap the node into an existing network.
166		244
167	=item slave nodes	245	IF true, then the values specified in the C<configure> will take
168		246	precedence over any values configured via the rc file. The default is for
169	When the C<$noderef> is the special string C<slave/>, then the node will	247	the rc file to override any options specified in the program.
170	become a slave node. Slave nodes cannot be contacted from outside and will
171	route most of their traffic to the master node that they attach to.
172
173	At least one additional noderef is required: The node will try to connect
174	to all of them and will become a slave attached to the first node it can
175	successfully connect to.
176		248
177	=back	249	=back
178		250
179	This function will block until all nodes have been resolved and, for slave
180	nodes, until it has successfully established a connection to a master
181	server.
182
183	Example: become a public node listening on the default node.
184
185	initialise_node;
186
187	Example: become a public node, and try to contact some well-known master
188	servers to become part of the network.
189
190	initialise_node undef, "master1", "master2";
191
192	Example: become a public node listening on port C<4041>.
193
194	initialise_node 4041;
195
196	Example: become a public node, only visible on localhost port 4044.
197
198	initialise_node "locahost:4044";
199
200	Example: become a slave node to any of the specified master servers.
201
202	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
203
204	=item $cv = resolve_node $noderef
205
206	Takes an unresolved node reference that may contain hostnames and
207	abbreviated IDs, resolves all of them and returns a resolved node
208	reference.
209
210	In addition to C<address:port> pairs allowed in resolved noderefs, the
211	following forms are supported:
212
213	=over 4	251	=over 4
214		252
215	=item the empty string	253	=item step 1, gathering configuration from profiles
216		254
217	An empty-string component gets resolved as if the default port (4040) was	255	The function first looks up a profile in the aemp configuration (see the
218	specified.	256	L<aemp> commandline utility). The profile name can be specified via the
		257	named C<profile> parameter or can simply be the first parameter). If it is
		258	missing, then the nodename (F<uname -n>) will be used as profile name.
219		259
220	=item naked port numbers (e.g. C<1234>)	260	The profile data is then gathered as follows:
221		261
222	These are resolved by prepending the local nodename and a colon, to be	262	First, all remaining key => value pairs (all of which are conveniently
223	further resolved.	263	undocumented at the moment) will be interpreted as configuration
		264	data. Then they will be overwritten by any values specified in the global
		265	default configuration (see the F<aemp> utility), then the chain of
		266	profiles chosen by the profile name (and any C<parent> attributes).
224		267
225	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	268	That means that the values specified in the profile have highest priority
		269	and the values specified directly via C<configure> have lowest priority,
		270	and can only be used to specify defaults.
226		271
227	These are resolved by using AnyEvent::DNS to resolve them, optionally	272	If the profile specifies a node ID, then this will become the node ID of
228	looking up SRV records for the C<aemp=4040> port, if no port was	273	this process. If not, then the profile name will be used as node ID, with
229	specified.	274	a slash (C</>) attached.
		275
		276	If the node ID (or profile name) ends with a slash (C</>), then a random
		277	string is appended to make it unique.
		278
		279	=item step 2, bind listener sockets
		280
		281	The next step is to look up the binds in the profile, followed by binding
		282	aemp protocol listeners on all binds specified (it is possible and valid
		283	to have no binds, meaning that the node cannot be contacted form the
		284	outside. This means the node cannot talk to other nodes that also have no
		285	binds, but it can still talk to all "normal" nodes).
		286
		287	If the profile does not specify a binds list, then a default of C<*> is
		288	used, meaning the node will bind on a dynamically-assigned port on every
		289	local IP address it finds.
		290
		291	=item step 3, connect to seed nodes
		292
		293	As the last step, the seed ID list from the profile is passed to the
		294	L<AnyEvent::MP::Global> module, which will then use it to keep
		295	connectivity with at least one node at any point in time.
230		296
231	=back	297	=back
		298
		299	Example: become a distributed node using the local node name as profile.
		300	This should be the most common form of invocation for "daemon"-type nodes.
		301
		302	configure
		303
		304	Example: become an anonymous node. This form is often used for commandline
		305	clients.
		306
		307	configure nodeid => "anon/";
		308
		309	Example: configure a node using a profile called seed, which is suitable
		310	for a seed node as it binds on all local addresses on a fixed port (4040,
		311	customary for aemp).
		312
		313	# use the aemp commandline utility
		314	# aemp profile seed binds '*:4040'
		315
		316	# then use it
		317	configure profile => "seed";
		318
		319	# or simply use aemp from the shell again:
		320	# aemp run profile seed
		321
		322	# or provide a nicer-to-remember nodeid
		323	# aemp run profile seed nodeid "$(hostname)"
232		324
233	=item $SELF	325	=item $SELF
234		326
235	Contains the current port id while executing C<rcv> callbacks or C<psub>	327	Contains the current port id while executing C<rcv> callbacks or C<psub>
236	blocks.	328	blocks.
237		329
238	=item SELF, %SELF, @SELF...	330	=item *SELF, SELF, %SELF, @SELF...
239		331
240	Due to some quirks in how perl exports variables, it is impossible to	332	Due to some quirks in how perl exports variables, it is impossible to
241	just export C<$SELF>, all the symbols called C<SELF> are exported by this	333	just export C<$SELF>, all the symbols named C<SELF> are exported by this
242	module, but only C<$SELF> is currently used.	334	module, but only C<$SELF> is currently used.
243		335
244	=item snd $port, type => @data	336	=item snd $port, type => @data
245		337
246	=item snd $port, @msg	338	=item snd $port, @msg
247		339
248	Send the given message to the given port ID, which can identify either	340	Send the given message to the given port, which can identify either a
249	a local or a remote port, and can be either a string or soemthignt hat	341	local or a remote port, and must be a port ID.
250	stringifies a sa port ID (such as a port object :).
251		342
252	While the message can be about anything, it is highly recommended to use a	343	While the message can be almost anything, it is highly recommended to
253	string as first element (a portid, or some word that indicates a request	344	use a string as first element (a port ID, or some word that indicates a
254	type etc.).	345	request type etc.) and to consist if only simple perl values (scalars,
		346	arrays, hashes) - if you think you need to pass an object, think again.
255		347
256	The message data effectively becomes read-only after a call to this	348	The message data logically becomes read-only after a call to this
257	function: modifying any argument is not allowed and can cause many	349	function: modifying any argument (or values referenced by them) is
258	problems.	350	forbidden, as there can be considerable time between the call to C<snd>
		351	and the time the message is actually being serialised - in fact, it might
		352	never be copied as within the same process it is simply handed to the
		353	receiving port.
259		354
260	The type of data you can transfer depends on the transport protocol: when	355	The type of data you can transfer depends on the transport protocol: when
261	JSON is used, then only strings, numbers and arrays and hashes consisting	356	JSON is used, then only strings, numbers and arrays and hashes consisting
262	of those are allowed (no objects). When Storable is used, then anything	357	of those are allowed (no objects). When Storable is used, then anything
263	that Storable can serialise and deserialise is allowed, and for the local	358	that Storable can serialise and deserialise is allowed, and for the local
264	node, anything can be passed.	359	node, anything can be passed. Best rely only on the common denominator of
		360	these.
265		361
266	=item $local_port = port	362	=item $local_port = port
267		363
268	Create a new local port object that can be used either as a pattern	364	Create a new local port object and returns its port ID. Initially it has
269	matching port ("full port") or a single-callback port ("miniport"),	365	no callbacks set and will throw an error when it receives messages.
270	depending on how C<rcv> callbacks are bound to the object.
271		366
272	=item $port = port { my @msg = @_; $finished }	367	=item $local_port = port { my @msg = @_ }
273		368
274	Creates a "miniport", that is, a very lightweight port without any pattern	369	Creates a new local port, and returns its ID. Semantically the same as
275	matching behind it, and returns its ID. Semantically the same as creating
276	a port and calling C<rcv $port, $callback> on it.	370	creating a port and calling C<rcv $port, $callback> on it.
277		371
278	The block will be called for every message received on the port. When the	372	The block will be called for every message received on the port, with the
279	callback returns a true value its job is considered "done" and the port	373	global variable C<$SELF> set to the port ID. Runtime errors will cause the
280	will be destroyed. Otherwise it will stay alive.	374	port to be C<kil>ed. The message will be passed as-is, no extra argument
		375	(i.e. no port ID) will be passed to the callback.
281		376
282	The message will be passed as-is, no extra argument (i.e. no port id) will	377	If you want to stop/destroy the port, simply C<kil> it:
283	be passed to the callback.
284		378
285	If you need the local port id in the callback, this works nicely:	379	my $port = port {
286		380	my @msg = @_;
287	my $port; $port = port {	381	...
288	snd $otherport, reply => $port;	382	kil $SELF;
289	};	383	};
290		384
291	=cut	385	=cut
292		386
293	sub rcv($@);	387	sub rcv($@);
294		388
		389	sub _kilme {
		390	die "received message on port without callback";
		391	}
		392
295	sub port(;&) {	393	sub port(;&) {
296	my $id = "$UNIQ." . $ID++;	394	my $id = $UNIQ . ++$ID;
297	my $port = "$NODE#$id";	395	my $port = "$NODE#$id";
298		396
299	if (@_) {	397	rcv $port, shift \|\| \&_kilme;
300	rcv $port, shift;
301	} else {
302	$PORT{$id} = sub { }; # nop
303	}
304		398
305	$port	399	$port
306	}	400	}
307		401
308	=item reg $port, $name
309
310	Registers the given port under the name C<$name>. If the name already
311	exists it is replaced.
312
313	A port can only be registered under one well known name.
314
315	A port automatically becomes unregistered when it is killed.
316
317	=cut
318
319	sub reg(@) {
320	my ($port, $name) = @_;
321
322	$REG{$name} = $port;
323	}
324
325	=item rcv $port, $callback->(@msg)	402	=item rcv $local_port, $callback->(@msg)
326		403
327	Replaces the callback on the specified miniport (after converting it to	404	Replaces the default callback on the specified port. There is no way to
328	one if required).	405	remove the default callback: use C<sub { }> to disable it, or better
329		406	C<kil> the port when it is no longer needed.
330	=item rcv $port, tagstring => $callback->(@msg), ...
331
332	=item rcv $port, $smartmatch => $callback->(@msg), ...
333
334	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
335
336	Register callbacks to be called on matching messages on the given full
337	port (after converting it to one if required).
338
339	The callback has to return a true value when its work is done, after
340	which is will be removed, or a false value in which case it will stay
341	registered.
342		407
343	The global C<$SELF> (exported by this module) contains C<$port> while	408	The global C<$SELF> (exported by this module) contains C<$port> while
344	executing the callback.	409	executing the callback. Runtime errors during callback execution will
		410	result in the port being C<kil>ed.
345		411
346	Runtime errors wdurign callback execution will result in the port being	412	The default callback received all messages not matched by a more specific
347	C<kil>ed.	413	C<tag> match.
348		414
349	If the match is an array reference, then it will be matched against the	415	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
350	first elements of the message, otherwise only the first element is being
351	matched.
352		416
353	Any element in the match that is specified as C<_any_> (a function	417	Register (or replace) callbacks to be called on messages starting with the
354	exported by this module) matches any single element of the message.	418	given tag on the given port (and return the port), or unregister it (when
		419	C<$callback> is C<$undef> or missing). There can only be one callback
		420	registered for each tag.
355		421
356	While not required, it is highly recommended that the first matching	422	The original message will be passed to the callback, after the first
357	element is a string identifying the message. The one-string-only match is	423	element (the tag) has been removed. The callback will use the same
358	also the most efficient match (by far).	424	environment as the default callback (see above).
		425
		426	Example: create a port and bind receivers on it in one go.
		427
		428	my $port = rcv port,
		429	msg1 => sub { ... },
		430	msg2 => sub { ... },
		431	;
		432
		433	Example: create a port, bind receivers and send it in a message elsewhere
		434	in one go:
		435
		436	snd $otherport, reply =>
		437	rcv port,
		438	msg1 => sub { ... },
		439	...
		440	;
		441
		442	Example: temporarily register a rcv callback for a tag matching some port
		443	(e.g. for an rpc reply) and unregister it after a message was received.
		444
		445	rcv $port, $otherport => sub {
		446	my @reply = @_;
		447
		448	rcv $SELF, $otherport;
		449	};
359		450
360	=cut	451	=cut
361		452
362	sub rcv($@) {	453	sub rcv($@) {
363	my $port = shift;	454	my $port = shift;
364	my ($noderef, $portid) = split /#/, $port, 2;	455	my ($nodeid, $portid) = split /#/, $port, 2;
365		456
366	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	457	$NODE{$nodeid} == $NODE{""}
367	or Carp::croak "$port: rcv can only be called on local ports, caught";	458	or Carp::croak "$port: rcv can only be called on local ports, caught";
368		459
369	if (@_ == 1) {	460	while (@_) {
		461	if (ref $_[0]) {
		462	if (my $self = $PORT_DATA{$portid}) {
		463	"AnyEvent::MP::Port" eq ref $self
		464	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		465
		466	$self->[0] = shift;
		467	} else {
370	my $cb = shift;	468	my $cb = shift;
371	delete $PORT_DATA{$portid};
372	$PORT{$portid} = sub {	469	$PORT{$portid} = sub {
373	local $SELF = $port;	470	local $SELF = $port;
374	eval {	471	eval { &$cb }; _self_die if $@;
375	&$cb	472	};
376	and kil $port;
377	};	473	}
378	_self_die if $@;	474	} elsif (defined $_[0]) {
379	};
380	} else {
381	my $self = $PORT_DATA{$portid} \|\|= do {	475	my $self = $PORT_DATA{$portid} \|\|= do {
382	my $self = bless {	476	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
383	id => $port,
384	}, "AnyEvent::MP::Port";
385		477
386	$PORT{$portid} = sub {	478	$PORT{$portid} = sub {
387	local $SELF = $port;	479	local $SELF = $port;
388		480
389	eval {
390	for (@{ $self->{rc0}{$_[0]} }) {	481	if (my $cb = $self->[1]{$_[0]}) {
391	$_ && &{$_->[0]}	482	shift;
392	&& undef $_;	483	eval { &$cb }; _self_die if $@;
393	}	484	} else {
394
395	for (@{ $self->{rcv}{$_[0]} }) {
396	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
397	&& &{$_->[0]}	485	&{ $self->[0] };
398	&& undef $_;
399	}
400
401	for (@{ $self->{any} }) {
402	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
403	&& &{$_->[0]}
404	&& undef $_;
405	}	486	}
406	};	487	};
407	_self_die if $@;	488
		489	$self
408	};	490	};
409		491
410	$self
411	};
412
413	"AnyEvent::MP::Port" eq ref $self	492	"AnyEvent::MP::Port" eq ref $self
414	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	493	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
415		494
416	while (@_) {
417	my ($match, $cb) = splice @_, 0, 2;	495	my ($tag, $cb) = splice @_, 0, 2;
418		496
419	if (!ref $match) {	497	if (defined $cb) {
420	push @{ $self->{rc0}{$match} }, [$cb];	498	$self->[1]{$tag} = $cb;
421	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
422	my ($type, @match) = @$match;
423	@match
424	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
425	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
426	} else {	499	} else {
427	push @{ $self->{any} }, [$cb, $match];	500	delete $self->[1]{$tag};
428	}	501	}
429	}	502	}
430	}	503	}
431		504
432	$port	505	$port
433	}	506	}
434		507
		508	=item peval $port, $coderef[, @args]
		509
		510	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		511	when the code throews an exception the C<$port> will be killed.
		512
		513	Any remaining args will be passed to the callback. Any return values will
		514	be returned to the caller.
		515
		516	This is useful when you temporarily want to execute code in the context of
		517	a port.
		518
		519	Example: create a port and run some initialisation code in it's context.
		520
		521	my $port = port { ... };
		522
		523	peval $port, sub {
		524	init
		525	or die "unable to init";
		526	};
		527
		528	=cut
		529
		530	sub peval($$) {
		531	local $SELF = shift;
		532	my $cb = shift;
		533
		534	if (wantarray) {
		535	my @res = eval { &$cb };
		536	_self_die if $@;
		537	@res
		538	} else {
		539	my $res = eval { &$cb };
		540	_self_die if $@;
		541	$res
		542	}
		543	}
		544
435	=item $closure = psub { BLOCK }	545	=item $closure = psub { BLOCK }
436		546
437	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	547	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
438	closure is executed, sets up the environment in the same way as in C<rcv>	548	closure is executed, sets up the environment in the same way as in C<rcv>
439	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.	549	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		550
		551	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		552	BLOCK }, @_ } >>.
440		553
441	This is useful when you register callbacks from C<rcv> callbacks:	554	This is useful when you register callbacks from C<rcv> callbacks:
442		555
443	rcv delayed_reply => sub {	556	rcv delayed_reply => sub {
444	my ($delay, @reply) = @_;	557	my ($delay, @reply) = @_;
…		…
468	$res	581	$res
469	}	582	}
470	}	583	}
471	}	584	}
472		585
473	=item $guard = mon $port, $cb->(@reason)	586	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
474		587
475	=item $guard = mon $port, $otherport	588	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
476		589
477	=item $guard = mon $port, $otherport, @msg	590	=item $guard = mon $port # kill $SELF when $port dies
478		591
		592	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		593
479	Monitor the given port and do something when the port is killed.	594	Monitor the given port and do something when the port is killed or
		595	messages to it were lost, and optionally return a guard that can be used
		596	to stop monitoring again.
480		597
481	In the first form, the callback is simply called with any number	598	In the first form (callback), the callback is simply called with any
482	of C<@reason> elements (no @reason means that the port was deleted	599	number of C<@reason> elements (no @reason means that the port was deleted
483	"normally"). Note also that I<< the callback B<must> never die >>, so use	600	"normally"). Note also that I<< the callback B<must> never die >>, so use
484	C<eval> if unsure.	601	C<eval> if unsure.
485		602
486	In the second form, the other port will be C<kil>'ed with C<@reason>, iff	603	In the second form (another port given), the other port (C<$rcvport>)
487	a @reason was specified, i.e. on "normal" kils nothing happens, while	604	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
488	under all other conditions, the other port is killed with the same reason.	605	"normal" kils nothing happens, while under all other conditions, the other
		606	port is killed with the same reason.
489		607
		608	The third form (kill self) is the same as the second form, except that
		609	C<$rvport> defaults to C<$SELF>.
		610
490	In the last form, a message of the form C<@msg, @reason> will be C<snd>.	611	In the last form (message), a message of the form C<@msg, @reason> will be
		612	C<snd>.
		613
		614	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		615	alert was raised), they are removed and will not trigger again.
		616
		617	As a rule of thumb, monitoring requests should always monitor a port from
		618	a local port (or callback). The reason is that kill messages might get
		619	lost, just like any other message. Another less obvious reason is that
		620	even monitoring requests can get lost (for example, when the connection
		621	to the other node goes down permanently). When monitoring a port locally
		622	these problems do not exist.
		623
		624	C<mon> effectively guarantees that, in the absence of hardware failures,
		625	after starting the monitor, either all messages sent to the port will
		626	arrive, or the monitoring action will be invoked after possible message
		627	loss has been detected. No messages will be lost "in between" (after
		628	the first lost message no further messages will be received by the
		629	port). After the monitoring action was invoked, further messages might get
		630	delivered again.
		631
		632	Inter-host-connection timeouts and monitoring depend on the transport
		633	used. The only transport currently implemented is TCP, and AnyEvent::MP
		634	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		635	non-idle connection, and usually around two hours for idle connections).
		636
		637	This means that monitoring is good for program errors and cleaning up
		638	stuff eventually, but they are no replacement for a timeout when you need
		639	to ensure some maximum latency.
491		640
492	Example: call a given callback when C<$port> is killed.	641	Example: call a given callback when C<$port> is killed.
493		642
494	mon $port, sub { warn "port died because of <@_>\n" };	643	mon $port, sub { warn "port died because of <@_>\n" };
495		644
496	Example: kill ourselves when C<$port> is killed abnormally.	645	Example: kill ourselves when C<$port> is killed abnormally.
497		646
498	mon $port, $self;	647	mon $port;
499		648
500	Example: send us a restart message another C<$port> is killed.	649	Example: send us a restart message when another C<$port> is killed.
501		650
502	mon $port, $self => "restart";	651	mon $port, $self => "restart";
503		652
504	=cut	653	=cut
505		654
506	sub mon {	655	sub mon {
507	my ($noderef, $port) = split /#/, shift, 2;	656	my ($nodeid, $port) = split /#/, shift, 2;
508		657
509	my $node = $NODE{$noderef} \|\| add_node $noderef;	658	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
510		659
511	my $cb = shift;	660	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
512		661
513	unless (ref $cb) {	662	unless (ref $cb) {
514	if (@_) {	663	if (@_) {
515	# send a kill info message	664	# send a kill info message
516	my (@msg) = ($cb, @_);	665	my (@msg) = ($cb, @_);
…		…
523	}	672	}
524		673
525	$node->monitor ($port, $cb);	674	$node->monitor ($port, $cb);
526		675
527	defined wantarray	676	defined wantarray
528	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	677	and ($cb += 0, AnyEvent::Util::guard { $node->unmonitor ($port, $cb) })
529	}	678	}
530		679
531	=item $guard = mon_guard $port, $ref, $ref...	680	=item $guard = mon_guard $port, $ref, $ref...
532		681
533	Monitors the given C<$port> and keeps the passed references. When the port	682	Monitors the given C<$port> and keeps the passed references. When the port
534	is killed, the references will be freed.	683	is killed, the references will be freed.
535		684
536	Optionally returns a guard that will stop the monitoring.	685	Optionally returns a guard that will stop the monitoring.
537		686
538	This function is useful when you create e.g. timers or other watchers and	687	This function is useful when you create e.g. timers or other watchers and
539	want to free them when the port gets killed:	688	want to free them when the port gets killed (note the use of C<psub>):
540		689
541	$port->rcv (start => sub {	690	$port->rcv (start => sub {
542	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	691	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
543	undef $timer if 0.9 < rand;	692	undef $timer if 0.9 < rand;
544	});	693	});
545	});	694	});
546		695
547	=cut	696	=cut
548		697
549	sub mon_guard {	698	sub mon_guard {
550	my ($port, @refs) = @_;	699	my ($port, @refs) = @_;
551		700
		701	#TODO: mon-less form?
		702
552	mon $port, sub { 0 && @refs }	703	mon $port, sub { 0 && @refs }
553	}	704	}
554		705
555	=item lnk $port1, $port2
556
557	Link two ports. This is simply a shorthand for:
558
559	mon $port1, $port2;
560	mon $port2, $port1;
561
562	It means that if either one is killed abnormally, the other one gets
563	killed as well.
564
565	=item kil $port[, @reason]	706	=item kil $port[, @reason]
566		707
567	Kill the specified port with the given C<@reason>.	708	Kill the specified port with the given C<@reason>.
568		709
569	If no C<@reason> is specified, then the port is killed "normally" (linked	710	If no C<@reason> is specified, then the port is killed "normally" -
570	ports will not be kileld, or even notified).	711	monitor callback will be invoked, but the kil will not cause linked ports
		712	(C<mon $mport, $lport> form) to get killed.
571		713
572	Otherwise, linked ports get killed with the same reason (second form of	714	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
573	C<mon>, see below).	715	form) get killed with the same reason.
574		716
575	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	717	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
576	will be reported as reason C<< die => $@ >>.	718	will be reported as reason C<< die => $@ >>.
577		719
578	Transport/communication errors are reported as C<< transport_error =>	720	Transport/communication errors are reported as C<< transport_error =>
579	$message >>.	721	$message >>.
580		722
581	=back
582
583	=head1 NODE MESSAGES
584
585	Nodes understand the following messages sent to them. Many of them take
586	arguments called C<@reply>, which will simply be used to compose a reply
587	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
588	the remaining arguments are simply the message data.
589
590	While other messages exist, they are not public and subject to change.
591
592	=over 4
593
594	=cut	723	=cut
595		724
596	=item lookup => $name, @reply	725	=item $port = spawn $node, $initfunc[, @initdata]
597		726
598	Replies with the port ID of the specified well-known port, or C<undef>.	727	Creates a port on the node C<$node> (which can also be a port ID, in which
		728	case it's the node where that port resides).
599		729
600	=item devnull => ...	730	The port ID of the newly created port is returned immediately, and it is
		731	possible to immediately start sending messages or to monitor the port.
601		732
602	Generic data sink/CPU heat conversion.	733	After the port has been created, the init function is called on the remote
		734	node, in the same context as a C<rcv> callback. This function must be a
		735	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		736	specify a function in the main program, use C<::name>.
603		737
604	=item relay => $port, @msg	738	If the function doesn't exist, then the node tries to C<require>
		739	the package, then the package above the package and so on (e.g.
		740	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		741	exists or it runs out of package names.
605		742
606	Simply forwards the message to the given port.	743	The init function is then called with the newly-created port as context
		744	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		745	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		746	the port might not get created.
607		747
608	=item eval => $string[ @reply]	748	A common idiom is to pass a local port, immediately monitor the spawned
		749	port, and in the remote init function, immediately monitor the passed
		750	local port. This two-way monitoring ensures that both ports get cleaned up
		751	when there is a problem.
609		752
610	Evaluates the given string. If C<@reply> is given, then a message of the	753	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
611	form C<@reply, $@, @evalres> is sent.	754	caller before C<spawn> returns (by delaying invocation when spawn is
		755	called for the local node).
612		756
613	Example: crash another node.	757	Example: spawn a chat server port on C<$othernode>.
614		758
615	snd $othernode, eval => "exit";	759	# this node, executed from within a port context:
		760	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		761	mon $server;
616		762
617	=item time => @reply	763	# init function on C<$othernode>
		764	sub connect {
		765	my ($srcport) = @_;
618		766
619	Replies the the current node time to C<@reply>.	767	mon $srcport;
620		768
621	Example: tell the current node to send the current time to C<$myport> in a	769	rcv $SELF, sub {
622	C<timereply> message.	770	...
		771	};
		772	}
623		773
624	snd $NODE, time => $myport, timereply => 1, 2;	774	=cut
625	# => snd $myport, timereply => 1, 2, <time>	775
		776	sub _spawn {
		777	my $port = shift;
		778	my $init = shift;
		779
		780	# rcv will create the actual port
		781	local $SELF = "$NODE#$port";
		782	eval {
		783	&{ load_func $init }
		784	};
		785	_self_die if $@;
		786	}
		787
		788	sub spawn(@) {
		789	my ($nodeid, undef) = split /#/, shift, 2;
		790
		791	my $id = $RUNIQ . ++$ID;
		792
		793	$_[0] =~ /::/
		794	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		795
		796	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		797
		798	"$nodeid#$id"
		799	}
		800
		801
		802	=item after $timeout, @msg
		803
		804	=item after $timeout, $callback
		805
		806	Either sends the given message, or call the given callback, after the
		807	specified number of seconds.
		808
		809	This is simply a utility function that comes in handy at times - the
		810	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		811	so it may go away in the future.
		812
		813	=cut
		814
		815	sub after($@) {
		816	my ($timeout, @action) = @_;
		817
		818	my $t; $t = AE::timer $timeout, 0, sub {
		819	undef $t;
		820	ref $action[0]
		821	? $action[0]()
		822	: snd @action;
		823	};
		824	}
		825
		826	=item cal $port, @msg, $callback[, $timeout]
		827
		828	A simple form of RPC - sends a message to the given C<$port> with the
		829	given contents (C<@msg>), but adds a reply port to the message.
		830
		831	The reply port is created temporarily just for the purpose of receiving
		832	the reply, and will be C<kil>ed when no longer needed.
		833
		834	A reply message sent to the port is passed to the C<$callback> as-is.
		835
		836	If an optional time-out (in seconds) is given and it is not C<undef>,
		837	then the callback will be called without any arguments after the time-out
		838	elapsed and the port is C<kil>ed.
		839
		840	If no time-out is given (or it is C<undef>), then the local port will
		841	monitor the remote port instead, so it eventually gets cleaned-up.
		842
		843	Currently this function returns the temporary port, but this "feature"
		844	might go in future versions unless you can make a convincing case that
		845	this is indeed useful for something.
		846
		847	=cut
		848
		849	sub cal(@) {
		850	my $timeout = ref $_[-1] ? undef : pop;
		851	my $cb = pop;
		852
		853	my $port = port {
		854	undef $timeout;
		855	kil $SELF;
		856	&$cb;
		857	};
		858
		859	if (defined $timeout) {
		860	$timeout = AE::timer $timeout, 0, sub {
		861	undef $timeout;
		862	kil $port;
		863	$cb->();
		864	};
		865	} else {
		866	mon $_[0], sub {
		867	kil $port;
		868	$cb->();
		869	};
		870	}
		871
		872	push @_, $port;
		873	&snd;
		874
		875	$port
		876	}
626		877
627	=back	878	=back
628		879
629	=head1 AnyEvent::MP vs. Distributed Erlang	880	=head1 AnyEvent::MP vs. Distributed Erlang
630		881
631	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	882	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
632	== aemp node, Erlang process == aemp port), so many of the documents and	883	== aemp node, Erlang process == aemp port), so many of the documents and
633	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	884	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
634	sample:	885	sample:
635		886
636	http://www.Erlang.se/doc/programming_rules.shtml	887	http://www.erlang.se/doc/programming_rules.shtml
637	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	888	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
638	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	889	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
639	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	890	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
640		891
641	Despite the similarities, there are also some important differences:	892	Despite the similarities, there are also some important differences:
642		893
643	=over 4	894	=over 4
644		895
645	=item * Node references contain the recipe on how to contact them.	896	=item * Node IDs are arbitrary strings in AEMP.
646		897
647	Erlang relies on special naming and DNS to work everywhere in the	898	Erlang relies on special naming and DNS to work everywhere in the same
648	same way. AEMP relies on each node knowing it's own address(es), with	899	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
649	convenience functionality.	900	configuration or DNS), and possibly the addresses of some seed nodes, but
		901	will otherwise discover other nodes (and their IDs) itself.
650		902
651	This means that AEMP requires a less tightly controlled environment at the	903	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
652	cost of longer node references and a slightly higher management overhead.	904	uses "local ports are like remote ports".
		905
		906	The failure modes for local ports are quite different (runtime errors
		907	only) then for remote ports - when a local port dies, you I<know> it dies,
		908	when a connection to another node dies, you know nothing about the other
		909	port.
		910
		911	Erlang pretends remote ports are as reliable as local ports, even when
		912	they are not.
		913
		914	AEMP encourages a "treat remote ports differently" philosophy, with local
		915	ports being the special case/exception, where transport errors cannot
		916	occur.
653		917
654	=item * Erlang uses processes and a mailbox, AEMP does not queue.	918	=item * Erlang uses processes and a mailbox, AEMP does not queue.
655		919
656	Erlang uses processes that selctively receive messages, and therefore	920	Erlang uses processes that selectively receive messages out of order, and
657	needs a queue. AEMP is event based, queuing messages would serve no useful	921	therefore needs a queue. AEMP is event based, queuing messages would serve
658	purpose.	922	no useful purpose. For the same reason the pattern-matching abilities
		923	of AnyEvent::MP are more limited, as there is little need to be able to
		924	filter messages without dequeuing them.
659		925
660	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	926	This is not a philosophical difference, but simply stems from AnyEvent::MP
		927	being event-based, while Erlang is process-based.
		928
		929	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		930	top of AEMP and Coro threads.
661		931
662	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	932	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
663		933
664	Sending messages in Erlang is synchronous and blocks the process. AEMP	934	Sending messages in Erlang is synchronous and blocks the process until
665	sends are immediate, connection establishment is handled in the	935	a conenction has been established and the message sent (and so does not
666	background.	936	need a queue that can overflow). AEMP sends return immediately, connection
		937	establishment is handled in the background.
667		938
668	=item * Erlang can silently lose messages, AEMP cannot.	939	=item * Erlang suffers from silent message loss, AEMP does not.
669		940
670	Erlang makes few guarantees on messages delivery - messages can get lost	941	Erlang implements few guarantees on messages delivery - messages can get
671	without any of the processes realising it (i.e. you send messages a, b,	942	lost without any of the processes realising it (i.e. you send messages a,
672	and c, and the other side only receives messages a and c).	943	b, and c, and the other side only receives messages a and c).
673		944
674	AEMP guarantees correct ordering, and the guarantee that there are no	945	AEMP guarantees (modulo hardware errors) correct ordering, and the
		946	guarantee that after one message is lost, all following ones sent to the
		947	same port are lost as well, until monitoring raises an error, so there are
675	holes in the message sequence.	948	no silent "holes" in the message sequence.
676		949
677	=item * In Erlang, processes can be declared dead and later be found to be	950	If you want your software to be very reliable, you have to cope with
678	alive.	951	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
679		952	simply tries to work better in common error cases, such as when a network
680	In Erlang it can happen that a monitored process is declared dead and	953	link goes down.
681	linked processes get killed, but later it turns out that the process is
682	still alive - and can receive messages.
683
684	In AEMP, when port monitoring detects a port as dead, then that port will
685	eventually be killed - it cannot happen that a node detects a port as dead
686	and then later sends messages to it, finding it is still alive.
687		954
688	=item * Erlang can send messages to the wrong port, AEMP does not.	955	=item * Erlang can send messages to the wrong port, AEMP does not.
689		956
690	In Erlang it is quite possible that a node that restarts reuses a process	957	In Erlang it is quite likely that a node that restarts reuses an Erlang
691	ID known to other nodes for a completely different process, causing	958	process ID known to other nodes for a completely different process,
692	messages destined for that process to end up in an unrelated process.	959	causing messages destined for that process to end up in an unrelated
		960	process.
693		961
694	AEMP never reuses port IDs, so old messages or old port IDs floating	962	AEMP does not reuse port IDs, so old messages or old port IDs floating
695	around in the network will not be sent to an unrelated port.	963	around in the network will not be sent to an unrelated port.
696		964
697	=item * Erlang uses unprotected connections, AEMP uses secure	965	=item * Erlang uses unprotected connections, AEMP uses secure
698	authentication and can use TLS.	966	authentication and can use TLS.
699		967
700	AEMP can use a proven protocol - SSL/TLS - to protect connections and	968	AEMP can use a proven protocol - TLS - to protect connections and
701	securely authenticate nodes.	969	securely authenticate nodes.
702		970
703	=item * The AEMP protocol is optimised for both text-based and binary	971	=item * The AEMP protocol is optimised for both text-based and binary
704	communications.	972	communications.
705		973
706	The AEMP protocol, unlike the Erlang protocol, supports both	974	The AEMP protocol, unlike the Erlang protocol, supports both programming
707	language-independent text-only protocols (good for debugging) and binary,	975	language independent text-only protocols (good for debugging), and binary,
708	language-specific serialisers (e.g. Storable).	976	language-specific serialisers (e.g. Storable). By default, unless TLS is
		977	used, the protocol is actually completely text-based.
709		978
710	It has also been carefully designed to be implementable in other languages	979	It has also been carefully designed to be implementable in other languages
711	with a minimum of work while gracefully degrading fucntionality to make the	980	with a minimum of work while gracefully degrading functionality to make the
712	protocol simple.	981	protocol simple.
713		982
714	=item * AEMP has more flexible monitoring options than Erlang.	983	=item * AEMP has more flexible monitoring options than Erlang.
715		984
716	In Erlang, you can chose to receive I<all> exit signals as messages	985	In Erlang, you can chose to receive I<all> exit signals as messages or
717	or I<none>, there is no in-between, so monitoring single processes is	986	I<none>, there is no in-between, so monitoring single Erlang processes is
718	difficult to implement. Monitoring in AEMP is more flexible than in	987	difficult to implement.
719	Erlang, as one can choose between automatic kill, exit message or callback
720	on a per-process basis.
721		988
722	=item * Erlang has different semantics for monitoring and linking, AEMP has the same.	989	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		990	between automatic kill, exit message or callback on a per-port basis.
723		991
		992	=item * Erlang tries to hide remote/local connections, AEMP does not.
		993
724	Monitoring in Erlang is not an indicator of process death/crashes,	994	Monitoring in Erlang is not an indicator of process death/crashes, in the
725	as linking is (except linking is unreliable in Erlang). In AEMP, the	995	same way as linking is (except linking is unreliable in Erlang).
726	semantics of monitoring and linking are identical, linking is simply	996
727	two-way monitoring with automatic kill.	997	In AEMP, you don't "look up" registered port names or send to named ports
		998	that might or might not be persistent. Instead, you normally spawn a port
		999	on the remote node. The init function monitors you, and you monitor the
		1000	remote port. Since both monitors are local to the node, they are much more
		1001	reliable (no need for C<spawn_link>).
		1002
		1003	This also saves round-trips and avoids sending messages to the wrong port
		1004	(hard to do in Erlang).
728		1005
729	=back	1006	=back
730		1007
		1008	=head1 RATIONALE
		1009
		1010	=over 4
		1011
		1012	=item Why strings for port and node IDs, why not objects?
		1013
		1014	We considered "objects", but found that the actual number of methods
		1015	that can be called are quite low. Since port and node IDs travel over
		1016	the network frequently, the serialising/deserialising would add lots of
		1017	overhead, as well as having to keep a proxy object everywhere.
		1018
		1019	Strings can easily be printed, easily serialised etc. and need no special
		1020	procedures to be "valid".
		1021
		1022	And as a result, a port with just a default receiver consists of a single
		1023	code reference stored in a global hash - it can't become much cheaper.
		1024
		1025	=item Why favour JSON, why not a real serialising format such as Storable?
		1026
		1027	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1028	format, but currently there is no way to make a node use Storable by
		1029	default (although all nodes will accept it).
		1030
		1031	The default framing protocol is JSON because a) JSON::XS is many times
		1032	faster for small messages and b) most importantly, after years of
		1033	experience we found that object serialisation is causing more problems
		1034	than it solves: Just like function calls, objects simply do not travel
		1035	easily over the network, mostly because they will always be a copy, so you
		1036	always have to re-think your design.
		1037
		1038	Keeping your messages simple, concentrating on data structures rather than
		1039	objects, will keep your messages clean, tidy and efficient.
		1040
		1041	=back
		1042
731	=head1 SEE ALSO	1043	=head1 SEE ALSO
		1044
		1045	L<AnyEvent::MP::Intro> - a gentle introduction.
		1046
		1047	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1048
		1049	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1050	your applications.
		1051
		1052	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1053
		1054	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1055	all nodes.
732		1056
733	L<AnyEvent>.	1057	L<AnyEvent>.
734		1058
735	=head1 AUTHOR	1059	=head1 AUTHOR
736		1060

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Revision 1.123 by root, Thu Mar 1 19:37:59 2012 UTC