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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.36 by root, Thu Aug 6 10:46:48 2009 UTC vs.
Revision 1.120 by root, Sun Feb 26 11:12:54 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<#>) as
65	separator, and a port name (a printable string of unspecified format). An	88	separator, and a port name (a printable string of unspecified format).
66	exception is the the node port, whose ID is identical to its node
67	reference.
68		89
69	=item node	90	=item node
70		91
71	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,
72	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
73	create new ports, among other things.	94	ports.
74		95
75	Nodes are either private (single-process only), slaves (connected to a	96	Nodes are either public (have one or more listening ports) or private
76	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.
77		99
78	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	100	Nodes is represented by (printable) strings called "node IDs".
79		101
80	A node reference is a string that either simply identifies the node (for	102	=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		103
84	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
85	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.
86		108
87	Node references come in two flavours: resolved (containing only numerical	109	=item binds - C<ip:port>
88	addresses) or unresolved (where hostnames are used instead of addresses).
89		110
90	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
91	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).
92		169
93	=back	170	=back
94		171
95	=head1 VARIABLES/FUNCTIONS	172	=head1 VARIABLES/FUNCTIONS
96		173
98		175
99	=cut	176	=cut
100		177
101	package AnyEvent::MP;	178	package AnyEvent::MP;
102		179
103	use AnyEvent::MP::Base;	180	use AnyEvent::MP::Kernel;
104		181
105	use common::sense;	182	use common::sense;
106		183
107	use Carp ();	184	use Carp ();
108		185
109	use AE ();	186	use AE ();
110		187
111	use base "Exporter";	188	use base "Exporter";
112		189
113	our $VERSION = '0.1';	190	our $VERSION = '1.30';
		191
114	our @EXPORT = qw(	192	our @EXPORT = qw(
115	NODE $NODE *SELF node_of _any_	193	NODE $NODE *SELF node_of after
116	resolve_node initialise_node	194	configure
117	snd rcv mon kil reg psub	195	snd rcv mon mon_guard kil psub peval spawn cal
118	port	196	port
119	);	197	);
120		198
121	our $SELF;	199	our $SELF;
122		200
…		…
126	kil $SELF, die => $msg;	204	kil $SELF, die => $msg;
127	}	205	}
128		206
129	=item $thisnode = NODE / $NODE	207	=item $thisnode = NODE / $NODE
130		208
131	The C<NODE> function returns, and the C<$NODE> variable contains	209	The C<NODE> function returns, and the C<$NODE> variable contains, the node
132	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
133	to C<become_public> or C<become_slave>, after which all local port	211	a call to C<configure>.
134	identifiers become invalid.
135		212
136	=item $noderef = node_of $port	213	=item $nodeid = node_of $port
137		214
138	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.
139		216
140	=item initialise_node $noderef, $seednode, $seednode...	217	=item configure $profile, key => value...
141		218
142	=item initialise_node "slave/", $master, $master...	219	=item configure key => value...
143		220
144	Before a node can talk to other nodes on the network it has to initialise	221	Before a node can talk to other nodes on the network (i.e. enter
145	itself - the minimum a node needs to know is it's own name, and optionally	222	"distributed mode") it has to configure itself - the minimum a node needs
146	it should know the noderefs of some other nodes in the network.	223	to know is its own name, and optionally it should know the addresses of
		224	some other nodes in the network to discover other nodes.
147		225
		226	The key/value pairs are basically the same ones as documented for the
		227	F<aemp> command line utility (sans the set/del prefix).
		228
148	This function initialises a node - it must be called exactly once (or	229	This function configures a node - it must be called exactly once (or
149	never) before calling other AnyEvent::MP functions.	230	never) before calling other AnyEvent::MP functions.
150		231
151	All arguments are noderefs, which can be either resolved or unresolved.
152
153	There are two types of networked nodes, public nodes and slave nodes:
154
155	=over 4	232	=over 4
156		233
157	=item public nodes	234	=item step 1, gathering configuration from profiles
158		235
159	For public nodes, C<$noderef> must either be a (possibly unresolved)	236	The function first looks up a profile in the aemp configuration (see the
160	noderef, in which case it will be resolved, or C<undef> (or missing), in	237	L<aemp> commandline utility). The profile name can be specified via the
161	which case the noderef will be guessed.	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.
162		240
163	Afterwards, the node will bind itself on all endpoints and try to connect	241	The profile data is then gathered as follows:
164	to all additional C<$seednodes> that are specified. Seednodes are optional
165	and can be used to quickly bootstrap the node into an existing network.
166		242
167	=item slave nodes	243	First, all remaining key => value pairs (all of which are conveniently
		244	undocumented at the moment) will be interpreted as configuration
		245	data. Then they will be overwritten by any values specified in the global
		246	default configuration (see the F<aemp> utility), then the chain of
		247	profiles chosen by the profile name (and any C<parent> attributes).
168		248
169	When the C<$noderef> is the special string C<slave/>, then the node will	249	That means that the values specified in the profile have highest priority
170	become a slave node. Slave nodes cannot be contacted from outside and will	250	and the values specified directly via C<configure> have lowest priority,
171	route most of their traffic to the master node that they attach to.	251	and can only be used to specify defaults.
172		252
173	At least one additional noderef is required: The node will try to connect	253	If the profile specifies a node ID, then this will become the node ID of
174	to all of them and will become a slave attached to the first node it can	254	this process. If not, then the profile name will be used as node ID. The
175	successfully connect to.	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.
176		274
177	=back	275	=back
178		276
179	This function will block until all nodes have been resolved and, for slave	277	Example: become a distributed node using the local node name as profile.
180	nodes, until it has successfully established a connection to a master	278	This should be the most common form of invocation for "daemon"-type nodes.
181	server.
182		279
183	Example: become a public node listening on the default node.	280	configure
184		281
185	initialise_node;	282	Example: become an anonymous node. This form is often used for commandline
		283	clients.
186		284
187	Example: become a public node, and try to contact some well-known master	285	configure nodeid => "anon/";
188	servers to become part of the network.
189		286
190	initialise_node undef, "master1", "master2";	287	Example: configure a node using a profile called seed, which is suitable
		288	for a seed node as it binds on all local addresses on a fixed port (4040,
		289	customary for aemp).
191		290
192	Example: become a public node listening on port C<4041>.	291	# use the aemp commandline utility
		292	# aemp profile seed nodeid anon/ binds '*:4040'
193		293
194	initialise_node 4041;	294	# then use it
		295	configure profile => "seed";
195		296
196	Example: become a public node, only visible on localhost port 4044.	297	# or simply use aemp from the shell again:
		298	# aemp run profile seed
197		299
198	initialise_node "locahost:4044";	300	# or provide a nicer-to-remember nodeid
199		301	# aemp run profile seed nodeid "$(hostname)"
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
214
215	=item the empty string
216
217	An empty-string component gets resolved as if the default port (4040) was
218	specified.
219
220	=item naked port numbers (e.g. C<1234>)
221
222	These are resolved by prepending the local nodename and a colon, to be
223	further resolved.
224
225	=item hostnames (e.g. C<localhost:1234>, C<localhost>)
226
227	These are resolved by using AnyEvent::DNS to resolve them, optionally
228	looking up SRV records for the C<aemp=4040> port, if no port was
229	specified.
230
231	=back
232		302
233	=item $SELF	303	=item $SELF
234		304
235	Contains the current port id while executing C<rcv> callbacks or C<psub>	305	Contains the current port id while executing C<rcv> callbacks or C<psub>
236	blocks.	306	blocks.
237		307
238	=item SELF, %SELF, @SELF...	308	=item *SELF, SELF, %SELF, @SELF...
239		309
240	Due to some quirks in how perl exports variables, it is impossible to	310	Due to some quirks in how perl exports variables, it is impossible to
241	just export C<$SELF>, all the symbols called C<SELF> are exported by this	311	just export C<$SELF>, all the symbols named C<SELF> are exported by this
242	module, but only C<$SELF> is currently used.	312	module, but only C<$SELF> is currently used.
243		313
244	=item snd $port, type => @data	314	=item snd $port, type => @data
245		315
246	=item snd $port, @msg	316	=item snd $port, @msg
247		317
248	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
249	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.
250	stringifies a sa port ID (such as a port object :).
251		320
252	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
253	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
254	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.
255		325
256	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
257	function: modifying any argument is not allowed and can cause many	327	function: modifying any argument (or values referenced by them) is
258	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.
259		332
260	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
261	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
262	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
263	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
264	node, anything can be passed.	337	node, anything can be passed. Best rely only on the common denominator of
		338	these.
265		339
266	=item $local_port = port	340	=item $local_port = port
267		341
268	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
269	matching port ("full port") or a single-callback port ("miniport"),	343	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		344
272	=item $port = port { my @msg = @_; $finished }	345	=item $local_port = port { my @msg = @_ }
273		346
274	Creates a "miniport", that is, a very lightweight port without any pattern	347	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.	348	creating a port and calling C<rcv $port, $callback> on it.
277		349
278	The block will be called for every message received on the port. When the	350	The block will be called for every message received on the port, with the
279	callback returns a true value its job is considered "done" and the port	351	global variable C<$SELF> set to the port ID. Runtime errors will cause the
280	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.
281		354
282	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:
283	be passed to the callback.
284		356
285	If you need the local port id in the callback, this works nicely:	357	my $port = port {
286		358	my @msg = @_;
287	my $port; $port = port {	359	...
288	snd $otherport, reply => $port;	360	kil $SELF;
289	};	361	};
290		362
291	=cut	363	=cut
292		364
293	sub rcv($@);	365	sub rcv($@);
		366
		367	sub _kilme {
		368	die "received message on port without callback";
		369	}
294		370
295	sub port(;&) {	371	sub port(;&) {
296	my $id = "$UNIQ." . $ID++;	372	my $id = "$UNIQ." . $ID++;
297	my $port = "$NODE#$id";	373	my $port = "$NODE#$id";
298		374
299	if (@_) {	375	rcv $port, shift \|\| \&_kilme;
300	rcv $port, shift;
301	} else {
302	$PORT{$id} = sub { }; # nop
303	}
304		376
305	$port	377	$port
306	}	378	}
307		379
308	=item reg $port, $name
309
310	=item reg $name
311
312	Registers the given port (or C<$SELF><<< if missing) under the name
313	C<$name>. If the name already exists it is replaced.
314
315	A port can only be registered under one well known name.
316
317	A port automatically becomes unregistered when it is killed.
318
319	=cut
320
321	sub reg(@) {
322	my $port = @_ > 1 ? shift : $SELF \|\| Carp::croak 'reg: called with one argument only, but $SELF not set,';
323
324	$REG{$_[0]} = $port;
325	}
326
327	=item rcv $port, $callback->(@msg)	380	=item rcv $local_port, $callback->(@msg)
328		381
329	Replaces the callback on the specified miniport (after converting it to	382	Replaces the default callback on the specified port. There is no way to
330	one if required).	383	remove the default callback: use C<sub { }> to disable it, or better
331		384	C<kil> the port when it is no longer needed.
332	=item rcv $port, tagstring => $callback->(@msg), ...
333
334	=item rcv $port, $smartmatch => $callback->(@msg), ...
335
336	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
337
338	Register callbacks to be called on matching messages on the given full
339	port (after converting it to one if required) and return the port.
340
341	The callback has to return a true value when its work is done, after
342	which is will be removed, or a false value in which case it will stay
343	registered.
344		385
345	The global C<$SELF> (exported by this module) contains C<$port> while	386	The global C<$SELF> (exported by this module) contains C<$port> while
346	executing the callback.	387	executing the callback. Runtime errors during callback execution will
		388	result in the port being C<kil>ed.
347		389
348	Runtime errors wdurign callback execution will result in the port being	390	The default callback received all messages not matched by a more specific
349	C<kil>ed.	391	C<tag> match.
350		392
351	If the match is an array reference, then it will be matched against the	393	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
352	first elements of the message, otherwise only the first element is being
353	matched.
354		394
355	Any element in the match that is specified as C<_any_> (a function	395	Register (or replace) callbacks to be called on messages starting with the
356	exported by this module) matches any single element of the message.	396	given tag on the given port (and return the port), or unregister it (when
		397	C<$callback> is C<$undef> or missing). There can only be one callback
		398	registered for each tag.
357		399
358	While not required, it is highly recommended that the first matching	400	The original message will be passed to the callback, after the first
359	element is a string identifying the message. The one-string-only match is	401	element (the tag) has been removed. The callback will use the same
360	also the most efficient match (by far).	402	environment as the default callback (see above).
361		403
362	Example: create a port and bind receivers on it in one go.	404	Example: create a port and bind receivers on it in one go.
363		405
364	my $port = rcv port,	406	my $port = rcv port,
365	msg1 => sub { ...; 0 },	407	msg1 => sub { ... },
366	msg2 => sub { ...; 0 },	408	msg2 => sub { ... },
367	;	409	;
368		410
369	Example: create a port, bind receivers and send it in a message elsewhere	411	Example: create a port, bind receivers and send it in a message elsewhere
370	in one go:	412	in one go:
371		413
372	snd $otherport, reply =>	414	snd $otherport, reply =>
373	rcv port,	415	rcv port,
374	msg1 => sub { ...; 0 },	416	msg1 => sub { ... },
375	...	417	...
376	;	418	;
377		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, $otherport;
		427	};
		428
378	=cut	429	=cut
379		430
380	sub rcv($@) {	431	sub rcv($@) {
381	my $port = shift;	432	my $port = shift;
382	my ($noderef, $portid) = split /#/, $port, 2;	433	my ($nodeid, $portid) = split /#/, $port, 2;
383		434
384	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	435	$NODE{$nodeid} == $NODE{""}
385	or Carp::croak "$port: rcv can only be called on local ports, caught";	436	or Carp::croak "$port: rcv can only be called on local ports, caught";
386		437
387	if (@_ == 1) {	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 {
388	my $cb = shift;	446	my $cb = shift;
389	delete $PORT_DATA{$portid};
390	$PORT{$portid} = sub {	447	$PORT{$portid} = sub {
391	local $SELF = $port;	448	local $SELF = $port;
392	eval {	449	eval { &$cb }; _self_die if $@;
393	&$cb	450	};
394	and kil $port;
395	};	451	}
396	_self_die if $@;	452	} elsif (defined $_[0]) {
397	};
398	} else {
399	my $self = $PORT_DATA{$portid} \|\|= do {	453	my $self = $PORT_DATA{$portid} \|\|= do {
400	my $self = bless {	454	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
401	id => $port,
402	}, "AnyEvent::MP::Port";
403		455
404	$PORT{$portid} = sub {	456	$PORT{$portid} = sub {
405	local $SELF = $port;	457	local $SELF = $port;
406		458
407	eval {
408	for (@{ $self->{rc0}{$_[0]} }) {	459	if (my $cb = $self->[1]{$_[0]}) {
409	$_ && &{$_->[0]}	460	shift;
410	&& undef $_;	461	eval { &$cb }; _self_die if $@;
411	}	462	} else {
412
413	for (@{ $self->{rcv}{$_[0]} }) {
414	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
415	&& &{$_->[0]}	463	&{ $self->[0] };
416	&& undef $_;
417	}
418
419	for (@{ $self->{any} }) {
420	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
421	&& &{$_->[0]}
422	&& undef $_;
423	}	464	}
424	};	465	};
425	_self_die if $@;	466
		467	$self
426	};	468	};
427		469
428	$self
429	};
430
431	"AnyEvent::MP::Port" eq ref $self	470	"AnyEvent::MP::Port" eq ref $self
432	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	471	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
433		472
434	while (@_) {
435	my ($match, $cb) = splice @_, 0, 2;	473	my ($tag, $cb) = splice @_, 0, 2;
436		474
437	if (!ref $match) {	475	if (defined $cb) {
438	push @{ $self->{rc0}{$match} }, [$cb];	476	$self->[1]{$tag} = $cb;
439	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
440	my ($type, @match) = @$match;
441	@match
442	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
443	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
444	} else {	477	} else {
445	push @{ $self->{any} }, [$cb, $match];	478	delete $self->[1]{$tag};
446	}	479	}
447	}	480	}
448	}	481	}
449		482
450	$port	483	$port
451	}	484	}
452		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	}
		521	}
		522
453	=item $closure = psub { BLOCK }	523	=item $closure = psub { BLOCK }
454		524
455	Remembers C<$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
456	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>
457	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 $SELF, sub {
		530	BLOCK }, @_ } >>.
458		531
459	This is useful when you register callbacks from C<rcv> callbacks:	532	This is useful when you register callbacks from C<rcv> callbacks:
460		533
461	rcv delayed_reply => sub {	534	rcv delayed_reply => sub {
462	my ($delay, @reply) = @_;	535	my ($delay, @reply) = @_;
…		…
486	$res	559	$res
487	}	560	}
488	}	561	}
489	}	562	}
490		563
491	=item $guard = mon $port, $cb->(@reason)	564	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
492		565
493	=item $guard = mon $port, $rcvport	566	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
494		567
495	=item $guard = mon $port	568	=item $guard = mon $port # kill $SELF when $port dies
496		569
497	=item $guard = mon $port, $rcvport, @msg	570	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
498		571
499	Monitor the given port and do something when the port is killed, and	572	Monitor the given port and do something when the port is killed or
500	optionally return a guard that can be used to stop monitoring again.	573	messages to it were lost, and optionally return a guard that can be used
		574	to stop monitoring again.
501		575
502	In the first form (callback), the callback is simply called with any	576	In the first form (callback), the callback is simply called with any
503	number of C<@reason> elements (no @reason means that the port was deleted	577	number of C<@reason> elements (no @reason means that the port was deleted
504	"normally"). Note also that I<< the callback B<must> never die >>, so use	578	"normally"). Note also that I<< the callback B<must> never die >>, so use
505	C<eval> if unsure.	579	C<eval> if unsure.
506		580
507	In the second form (another port given), the other port (C<$rcvport)	581	In the second form (another port given), the other port (C<$rcvport>)
508	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	582	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
509	"normal" kils nothing happens, while under all other conditions, the other	583	"normal" kils nothing happens, while under all other conditions, the other
510	port is killed with the same reason.	584	port is killed with the same reason.
511		585
512	The third form (kill self) is the same as the second form, except that	586	The third form (kill self) is the same as the second form, except that
513	C<$rvport> defaults to C<$SELF>.	587	C<$rvport> defaults to C<$SELF>.
514		588
515	In the last form (message), a message of the form C<@msg, @reason> will be	589	In the last form (message), a message of the form C<@msg, @reason> will be
516	C<snd>.	590	C<snd>.
517		591
		592	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		593	alert was raised), they are removed and will not trigger again.
		594
		595	As a rule of thumb, monitoring requests should always monitor a port from
		596	a local port (or callback). The reason is that kill messages might get
		597	lost, just like any other message. Another less obvious reason is that
		598	even monitoring requests can get lost (for example, when the connection
		599	to the other node goes down permanently). When monitoring a port locally
		600	these problems do not exist.
		601
		602	C<mon> effectively guarantees that, in the absence of hardware failures,
		603	after starting the monitor, either all messages sent to the port will
		604	arrive, or the monitoring action will be invoked after possible message
		605	loss has been detected. No messages will be lost "in between" (after
		606	the first lost message no further messages will be received by the
		607	port). After the monitoring action was invoked, further messages might get
		608	delivered again.
		609
		610	Inter-host-connection timeouts and monitoring depend on the transport
		611	used. The only transport currently implemented is TCP, and AnyEvent::MP
		612	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		613	non-idle connection, and usually around two hours for idle connections).
		614
		615	This means that monitoring is good for program errors and cleaning up
		616	stuff eventually, but they are no replacement for a timeout when you need
		617	to ensure some maximum latency.
		618
518	Example: call a given callback when C<$port> is killed.	619	Example: call a given callback when C<$port> is killed.
519		620
520	mon $port, sub { warn "port died because of <@_>\n" };	621	mon $port, sub { warn "port died because of <@_>\n" };
521		622
522	Example: kill ourselves when C<$port> is killed abnormally.	623	Example: kill ourselves when C<$port> is killed abnormally.
…		…
528	mon $port, $self => "restart";	629	mon $port, $self => "restart";
529		630
530	=cut	631	=cut
531		632
532	sub mon {	633	sub mon {
533	my ($noderef, $port) = split /#/, shift, 2;	634	my ($nodeid, $port) = split /#/, shift, 2;
534		635
535	my $node = $NODE{$noderef} \|\| add_node $noderef;	636	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
536		637
537	my $cb = @_ ? $_[0] : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';	638	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
538		639
539	unless (ref $cb) {	640	unless (ref $cb) {
540	if (@_) {	641	if (@_) {
541	# send a kill info message	642	# send a kill info message
542	my (@msg) = @_;	643	my (@msg) = ($cb, @_);
543	$cb = sub { snd @msg, @_ };	644	$cb = sub { snd @msg, @_ };
544	} else {	645	} else {
545	# simply kill other port	646	# simply kill other port
546	my $port = $cb;	647	my $port = $cb;
547	$cb = sub { kil $port, @_ if @_ };	648	$cb = sub { kil $port, @_ if @_ };
…		…
549	}	650	}
550		651
551	$node->monitor ($port, $cb);	652	$node->monitor ($port, $cb);
552		653
553	defined wantarray	654	defined wantarray
554	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	655	and ($cb += 0, AnyEvent::Util::guard { $node->unmonitor ($port, $cb) })
555	}	656	}
556		657
557	=item $guard = mon_guard $port, $ref, $ref...	658	=item $guard = mon_guard $port, $ref, $ref...
558		659
559	Monitors the given C<$port> and keeps the passed references. When the port	660	Monitors the given C<$port> and keeps the passed references. When the port
560	is killed, the references will be freed.	661	is killed, the references will be freed.
561		662
562	Optionally returns a guard that will stop the monitoring.	663	Optionally returns a guard that will stop the monitoring.
563		664
564	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
565	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>):
566		667
567	$port->rcv (start => sub {	668	$port->rcv (start => sub {
568	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	669	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
569	undef $timer if 0.9 < rand;	670	undef $timer if 0.9 < rand;
570	});	671	});
571	});	672	});
572		673
573	=cut	674	=cut
…		…
578	#TODO: mon-less form?	679	#TODO: mon-less form?
579		680
580	mon $port, sub { 0 && @refs }	681	mon $port, sub { 0 && @refs }
581	}	682	}
582		683
583	=item lnk $port1, $port2
584
585	=item lnk $otherport
586
587	Link two ports. This is simply a shorthand for:
588
589	mon $port1, $port2;
590	mon $port2, $port1;
591
592	It means that if either one is killed abnormally, the other one gets
593	killed as well.
594
595	The one-argument form assumes that one port is C<$SELF>.
596
597	=cut
598
599	sub lnk {
600	my $port1 = shift;
601	my $port2 = @_ ? shift : $SELF \|\| Carp::croak 'lnk: called with one argument only, but $SELF not set,';
602
603	mon $port1, $port2;
604	mon $port2, $port1;
605	}
606
607	=item kil $port[, @reason]	684	=item kil $port[, @reason]
608		685
609	Kill the specified port with the given C<@reason>.	686	Kill the specified port with the given C<@reason>.
610		687
611	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" -
612	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.
613		691
614	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>
615	C<mon>, see below).	693	form) get killed with the same reason.
616		694
617	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
618	will be reported as reason C<< die => $@ >>.	696	will be reported as reason C<< die => $@ >>.
619		697
620	Transport/communication errors are reported as C<< transport_error =>	698	Transport/communication errors are reported as C<< transport_error =>
621	$message >>.	699	$message >>.
622		700
623	=back
624
625	=head1 NODE MESSAGES
626
627	Nodes understand the following messages sent to them. Many of them take
628	arguments called C<@reply>, which will simply be used to compose a reply
629	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
630	the remaining arguments are simply the message data.
631
632	While other messages exist, they are not public and subject to change.
633
634	=over 4
635
636	=cut	701	=cut
637		702
638	=item lookup => $name, @reply	703	=item $port = spawn $node, $initfunc[, @initdata]
639		704
640	Replies with the port ID of the specified well-known port, or C<undef>.	705	Creates a port on the node C<$node> (which can also be a port ID, in which
		706	case it's the node where that port resides).
641		707
642	=item devnull => ...	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.
643		710
644	Generic data sink/CPU heat conversion.	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>.
645		715
646	=item relay => $port, @msg	716	If the function doesn't exist, then the node tries to C<require>
		717	the package, then the package above the package and so on (e.g.
		718	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		719	exists or it runs out of package names.
647		720
648	Simply forwards the message to the given port.	721	The init function is then called with the newly-created port as context
		722	object (C<$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.
649		725
650	=item eval => $string[ @reply]	726	A common idiom is to pass a local port, immediately monitor the spawned
		727	port, and in the remote init function, immediately monitor the passed
		728	local port. This two-way monitoring ensures that both ports get cleaned up
		729	when there is a problem.
651		730
652	Evaluates the given string. If C<@reply> is given, then a message of the	731	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
653	form C<@reply, $@, @evalres> is sent.	732	caller before C<spawn> returns (by delaying invocation when spawn is
		733	called for the local node).
654		734
655	Example: crash another node.	735	Example: spawn a chat server port on C<$othernode>.
656		736
657	snd $othernode, eval => "exit";	737	# this node, executed from within a port context:
		738	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		739	mon $server;
658		740
659	=item time => @reply	741	# init function on C<$othernode>
		742	sub connect {
		743	my ($srcport) = @_;
660		744
661	Replies the the current node time to C<@reply>.	745	mon $srcport;
662		746
663	Example: tell the current node to send the current time to C<$myport> in a	747	rcv $SELF, sub {
664	C<timereply> message.	748	...
		749	};
		750	}
665		751
666	snd $NODE, time => $myport, timereply => 1, 2;	752	=cut
667	# => snd $myport, timereply => 1, 2, <time>	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	}
668		854
669	=back	855	=back
670		856
671	=head1 AnyEvent::MP vs. Distributed Erlang	857	=head1 AnyEvent::MP vs. Distributed Erlang
672		858
673	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
674	== 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
675	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
676	sample:	862	sample:
677		863
678	http://www.Erlang.se/doc/programming_rules.shtml	864	http://www.erlang.se/doc/programming_rules.shtml
679	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
680	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
681	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	867	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
682		868
683	Despite the similarities, there are also some important differences:	869	Despite the similarities, there are also some important differences:
684		870
685	=over 4	871	=over 4
686		872
687	=item * Node references contain the recipe on how to contact them.	873	=item * Node IDs are arbitrary strings in AEMP.
688		874
689	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
690	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
691	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.
692		879
693	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
694	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.
695		894
696	=item * Erlang uses processes and a mailbox, AEMP does not queue.	895	=item * Erlang uses processes and a mailbox, AEMP does not queue.
697		896
698	Erlang uses processes that selctively receive messages, and therefore	897	Erlang uses processes that selectively receive messages out of order, and
699	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
700	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.
701		902
702	(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.
703		908
704	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	909	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
705		910
706	Sending messages in Erlang is synchronous and blocks the process. AEMP	911	Sending messages in Erlang is synchronous and blocks the process until
707	sends are immediate, connection establishment is handled in the	912	a conenction has been established and the message sent (and so does not
708	background.	913	need a queue that can overflow). AEMP sends return immediately, connection
		914	establishment is handled in the background.
709		915
710	=item * Erlang can silently lose messages, AEMP cannot.	916	=item * Erlang suffers from silent message loss, AEMP does not.
711		917
712	Erlang makes few guarantees on messages delivery - messages can get lost	918	Erlang implements few guarantees on messages delivery - messages can get
713	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,
714	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).
715		921
716	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
717	holes in the message sequence.	925	no silent "holes" in the message sequence.
718		926
719	=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
720	alive.	928	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
721		929	simply tries to work better in common error cases, such as when a network
722	In Erlang it can happen that a monitored process is declared dead and	930	link goes down.
723	linked processes get killed, but later it turns out that the process is
724	still alive - and can receive messages.
725
726	In AEMP, when port monitoring detects a port as dead, then that port will
727	eventually be killed - it cannot happen that a node detects a port as dead
728	and then later sends messages to it, finding it is still alive.
729		931
730	=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.
731		933
732	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
733	ID known to other nodes for a completely different process, causing	935	process ID known to other nodes for a completely different process,
734	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.
735		938
736	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
737	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.
738		941
739	=item * Erlang uses unprotected connections, AEMP uses secure	942	=item * Erlang uses unprotected connections, AEMP uses secure
740	authentication and can use TLS.	943	authentication and can use TLS.
741		944
742	AEMP can use a proven protocol - SSL/TLS - to protect connections and	945	AEMP can use a proven protocol - TLS - to protect connections and
743	securely authenticate nodes.	946	securely authenticate nodes.
744		947
745	=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
746	communications.	949	communications.
747		950
748	The AEMP protocol, unlike the Erlang protocol, supports both	951	The AEMP protocol, unlike the Erlang protocol, supports both programming
749	language-independent text-only protocols (good for debugging) and binary,	952	language independent text-only protocols (good for debugging), and binary,
750	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.
751		955
752	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
753	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
754	protocol simple.	958	protocol simple.
755		959
756	=item * AEMP has more flexible monitoring options than Erlang.	960	=item * AEMP has more flexible monitoring options than Erlang.
757		961
758	In Erlang, you can chose to receive I<all> exit signals as messages	962	In Erlang, you can chose to receive I<all> exit signals as messages or
759	or I<none>, there is no in-between, so monitoring single processes is	963	I<none>, there is no in-between, so monitoring single Erlang processes is
760	difficult to implement. Monitoring in AEMP is more flexible than in	964	difficult to implement.
761	Erlang, as one can choose between automatic kill, exit message or callback
762	on a per-process basis.
763		965
764	=item * Erlang has different semantics for monitoring and linking, AEMP has the same.	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.
765		968
		969	=item * Erlang tries to hide remote/local connections, AEMP does not.
		970
766	Monitoring in Erlang is not an indicator of process death/crashes,	971	Monitoring in Erlang is not an indicator of process death/crashes, in the
767	as linking is (except linking is unreliable in Erlang). In AEMP, the	972	same way as linking is (except linking is unreliable in Erlang).
768	semantics of monitoring and linking are identical, linking is simply	973
769	two-way monitoring with automatic kill.	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).
770		982
771	=back	983	=back
772		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
773	=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.
774		1033
775	L<AnyEvent>.	1034	L<AnyEvent>.
776		1035
777	=head1 AUTHOR	1036	=head1 AUTHOR
778		1037

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Revision 1.120 by root, Sun Feb 26 11:12:54 2012 UTC