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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.44 by root, Wed Aug 12 21:39:58 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
13	$SELF # receiving/own port id in rcv callbacks	12	$SELF # receiving/own port id in rcv callbacks
14		13
		14	# initialise the node so it can send/receive messages
		15	configure;
		16
15	# ports are message endpoints	17	# ports are message destinations
16		18
17	# sending messages	19	# sending messages
18	snd $port, type => data...;	20	snd $port, type => data...;
19	snd $port, @msg;	21	snd $port, @msg;
20	snd @msg_with_first_element_being_a_port;	22	snd @msg_with_first_element_being_a_port;
21		23
22	# miniports	24	# creating/using ports, the simple way
23	my $miniport = port { my @msg = @_; 0 };	25	my $simple_port = port { my @msg = @_ };
24		26
25	# full ports	27	# creating/using ports, tagged message matching
26	my $port = port;	28	my $port = port;
27	rcv $port, smartmatch => $cb->(@msg);
28	rcv $port, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
29	rcv $port, pong => sub { warn "pong received\n"; 0 };	30	rcv $port, pong => sub { warn "pong received\n" };
30		31
31	# remote ports	32	# create a port on another node
32	my $port = spawn $node, $initfunc, @initdata;	33	my $port = spawn $node, $initfunc, @initdata;
33		34
34	# more, smarter, matches (_any_ is exported by this module)	35	# destroy a port again
35	rcv $port, [child_died => $pid] => sub { ...	36	kil $port; # "normal" kill
36	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3	37	kil $port, my_error => "everything is broken"; # error kill
37		38
38	# monitoring	39	# monitoring
39	mon $port, $cb->(@msg) # callback is invoked on death	40	mon $localport, $cb->(@msg) # callback is invoked on death
40	mon $port, $otherport # kill otherport on abnormal death	41	mon $localport, $otherport # kill otherport on abnormal death
41	mon $port, $otherport, @msg # send message on death	42	mon $localport, $otherport, @msg # send message on death
		43
		44	# temporarily execute code in port context
		45	peval $port, sub { die "kill the port!" };
		46
		47	# execute callbacks in $SELF port context
		48	my $timer = AE::timer 1, 0, psub {
		49	die "kill the port, delayed";
		50	};
		51
		52	=head1 CURRENT STATUS
		53
		54	bin/aemp - stable.
		55	AnyEvent::MP - stable API, should work.
		56	AnyEvent::MP::Intro - explains most concepts.
		57	AnyEvent::MP::Kernel - mostly stable API.
		58	AnyEvent::MP::Global - stable API.
42		59
43	=head1 DESCRIPTION	60	=head1 DESCRIPTION
44		61
45	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
46		63
47	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
48	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
49		66
50	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	67	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
51	manual page.	68	manual page and the examples under F<eg/>.
52
53	At the moment, this module family is severly broken and underdocumented,
54	so do not use. This was uploaded mainly to reserve the CPAN namespace -
55	stay tuned! The basic API should be finished, however.
56		69
57	=head1 CONCEPTS	70	=head1 CONCEPTS
58		71
59	=over 4	72	=over 4
60		73
61	=item port	74	=item port
62		75
63	A port is something you can send messages to (with the C<snd> function).	76	Not to be confused with a TCP port, a "port" is something you can send
		77	messages to (with the C<snd> function).
64		78
65	Some ports allow you to register C<rcv> handlers that can match specific	79	Ports allow you to register C<rcv> handlers that can match all or just
66	messages. All C<rcv> handlers will receive messages they match, messages	80	some messages. Messages send to ports will not be queued, regardless of
67	will not be queued.	81	anything was listening for them or not.
68		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
69	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
70		86
71	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
72	separator, and a port name (a printable string of unspecified format). An	88	separator, and a port name (a printable string of unspecified format).
73	exception is the the node port, whose ID is identical to its node
74	reference.
75		89
76	=item node	90	=item node
77		91
78	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,
79	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
80	create new ports, among other things.	94	ports.
81		95
82	Nodes are either private (single-process only), slaves (connected to a	96	Nodes are either public (have one or more listening ports) or private
83	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.
84		99
85	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	100	Nodes is represented by (printable) strings called "node IDs".
86		101
87	A node reference is a string that either simply identifies the node (for	102	=item node ID - C<[A-Za-z0-9_\-.:]*>
88	private and slave nodes), or contains a recipe on how to reach a given
89	node (for public nodes).
90		103
91	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
92	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.
93		108
94	Node references come in two flavours: resolved (containing only numerical	109	=item binds - C<ip:port>
95	addresses) or unresolved (where hostnames are used instead of addresses).
96		110
97	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
98	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).
99		169
100	=back	170	=back
101		171
102	=head1 VARIABLES/FUNCTIONS	172	=head1 VARIABLES/FUNCTIONS
103		173
115		185
116	use AE ();	186	use AE ();
117		187
118	use base "Exporter";	188	use base "Exporter";
119		189
120	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	190	our $VERSION = '1.30';
121		191
122	our @EXPORT = qw(	192	our @EXPORT = qw(
123	NODE $NODE *SELF node_of _any_	193	NODE $NODE *SELF node_of after
124	resolve_node initialise_node	194	configure
125	snd rcv mon kil reg psub spawn	195	snd rcv mon mon_guard kil psub peval spawn cal
126	port	196	port
127	);	197	);
128		198
129	our $SELF;	199	our $SELF;
130		200
…		…
134	kil $SELF, die => $msg;	204	kil $SELF, die => $msg;
135	}	205	}
136		206
137	=item $thisnode = NODE / $NODE	207	=item $thisnode = NODE / $NODE
138		208
139	The C<NODE> function returns, and the C<$NODE> variable contains	209	The C<NODE> function returns, and the C<$NODE> variable contains, the node
140	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
141	to C<become_public> or C<become_slave>, after which all local port	211	a call to C<configure>.
142	identifiers become invalid.
143		212
144	=item $noderef = node_of $port	213	=item $nodeid = node_of $port
145		214
146	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.
147		216
148	=item initialise_node $noderef, $seednode, $seednode...	217	=item configure $profile, key => value...
149		218
150	=item initialise_node "slave/", $master, $master...	219	=item configure key => value...
151		220
152	Before a node can talk to other nodes on the network it has to initialise	221	Before a node can talk to other nodes on the network (i.e. enter
153	itself - the minimum a node needs to know is it's own name, and optionally	222	"distributed mode") it has to configure itself - the minimum a node needs
154	it should know the noderefs of some other nodes in the network.	223	to know is its own name, and optionally it should know the addresses of
		224	some other nodes in the network to discover other nodes.
155		225
		226	The key/value pairs are basically the same ones as documented for the
		227	F<aemp> command line utility (sans the set/del prefix).
		228
156	This function initialises a node - it must be called exactly once (or	229	This function configures a node - it must be called exactly once (or
157	never) before calling other AnyEvent::MP functions.	230	never) before calling other AnyEvent::MP functions.
158		231
159	All arguments are noderefs, which can be either resolved or unresolved.
160
161	There are two types of networked nodes, public nodes and slave nodes:
162
163	=over 4	232	=over 4
164		233
165	=item public nodes	234	=item step 1, gathering configuration from profiles
166		235
167	For public nodes, C<$noderef> must either be a (possibly unresolved)	236	The function first looks up a profile in the aemp configuration (see the
168	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
169	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.
170		240
171	Afterwards, the node will bind itself on all endpoints and try to connect	241	The profile data is then gathered as follows:
172	to all additional C<$seednodes> that are specified. Seednodes are optional
173	and can be used to quickly bootstrap the node into an existing network.
174		242
175	=item slave nodes	243	First, all remaining key => value pairs (all of which are conveniently
		244	undocumented at the moment) will be interpreted as configuration
		245	data. Then they will be overwritten by any values specified in the global
		246	default configuration (see the F<aemp> utility), then the chain of
		247	profiles chosen by the profile name (and any C<parent> attributes).
176		248
177	When the C<$noderef> is the special string C<slave/>, then the node will	249	That means that the values specified in the profile have highest priority
178	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,
179	route most of their traffic to the master node that they attach to.	251	and can only be used to specify defaults.
180		252
181	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
182	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
183	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.
184		274
185	=back	275	=back
186		276
187	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.
188	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.
189	server.
190		279
191	Example: become a public node listening on the default node.	280	configure
192		281
193	initialise_node;	282	Example: become an anonymous node. This form is often used for commandline
		283	clients.
194		284
195	Example: become a public node, and try to contact some well-known master	285	configure nodeid => "anon/";
196	servers to become part of the network.
197		286
198	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).
199		290
200	Example: become a public node listening on port C<4041>.	291	# use the aemp commandline utility
		292	# aemp profile seed nodeid anon/ binds '*:4040'
201		293
202	initialise_node 4041;	294	# then use it
		295	configure profile => "seed";
203		296
204	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
205		299
206	initialise_node "locahost:4044";	300	# or provide a nicer-to-remember nodeid
207		301	# aemp run profile seed nodeid "$(hostname)"
208	Example: become a slave node to any of the specified master servers.
209
210	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
211
212	=item $cv = resolve_node $noderef
213
214	Takes an unresolved node reference that may contain hostnames and
215	abbreviated IDs, resolves all of them and returns a resolved node
216	reference.
217
218	In addition to C<address:port> pairs allowed in resolved noderefs, the
219	following forms are supported:
220
221	=over 4
222
223	=item the empty string
224
225	An empty-string component gets resolved as if the default port (4040) was
226	specified.
227
228	=item naked port numbers (e.g. C<1234>)
229
230	These are resolved by prepending the local nodename and a colon, to be
231	further resolved.
232
233	=item hostnames (e.g. C<localhost:1234>, C<localhost>)
234
235	These are resolved by using AnyEvent::DNS to resolve them, optionally
236	looking up SRV records for the C<aemp=4040> port, if no port was
237	specified.
238
239	=back
240		302
241	=item $SELF	303	=item $SELF
242		304
243	Contains the current port id while executing C<rcv> callbacks or C<psub>	305	Contains the current port id while executing C<rcv> callbacks or C<psub>
244	blocks.	306	blocks.
245		307
246	=item SELF, %SELF, @SELF...	308	=item *SELF, SELF, %SELF, @SELF...
247		309
248	Due to some quirks in how perl exports variables, it is impossible to	310	Due to some quirks in how perl exports variables, it is impossible to
249	just export C<$SELF>, all the symbols called C<SELF> are exported by this	311	just export C<$SELF>, all the symbols named C<SELF> are exported by this
250	module, but only C<$SELF> is currently used.	312	module, but only C<$SELF> is currently used.
251		313
252	=item snd $port, type => @data	314	=item snd $port, type => @data
253		315
254	=item snd $port, @msg	316	=item snd $port, @msg
255		317
256	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
257	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.
258	stringifies a sa port ID (such as a port object :).
259		320
260	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
261	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
262	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.
263		325
264	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
265	function: modifying any argument is not allowed and can cause many	327	function: modifying any argument (or values referenced by them) is
266	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.
267		332
268	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
269	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
270	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
271	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
272	node, anything can be passed.	337	node, anything can be passed. Best rely only on the common denominator of
		338	these.
273		339
274	=item $local_port = port	340	=item $local_port = port
275		341
276	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
277	matching port ("full port") or a single-callback port ("miniport"),	343	no callbacks set and will throw an error when it receives messages.
278	depending on how C<rcv> callbacks are bound to the object.
279		344
280	=item $port = port { my @msg = @_; $finished }	345	=item $local_port = port { my @msg = @_ }
281		346
282	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
283	matching behind it, and returns its ID. Semantically the same as creating
284	a port and calling C<rcv $port, $callback> on it.	348	creating a port and calling C<rcv $port, $callback> on it.
285		349
286	The block will be called for every message received on the port. When the	350	The block will be called for every message received on the port, with the
287	callback returns a true value its job is considered "done" and the port	351	global variable C<$SELF> set to the port ID. Runtime errors will cause the
288	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.
289		354
290	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:
291	be passed to the callback.
292		356
293	If you need the local port id in the callback, this works nicely:	357	my $port = port {
294		358	my @msg = @_;
295	my $port; $port = port {	359	...
296	snd $otherport, reply => $port;	360	kil $SELF;
297	};	361	};
298		362
299	=cut	363	=cut
300		364
301	sub rcv($@);	365	sub rcv($@);
		366
		367	sub _kilme {
		368	die "received message on port without callback";
		369	}
302		370
303	sub port(;&) {	371	sub port(;&) {
304	my $id = "$UNIQ." . $ID++;	372	my $id = "$UNIQ." . $ID++;
305	my $port = "$NODE#$id";	373	my $port = "$NODE#$id";
306		374
307	if (@_) {	375	rcv $port, shift \|\| \&_kilme;
308	rcv $port, shift;
309	} else {
310	$PORT{$id} = sub { }; # nop
311	}
312		376
313	$port	377	$port
314	}	378	}
315		379
316	=item reg $port, $name
317
318	=item reg $name
319
320	Registers the given port (or C<$SELF><<< if missing) under the name
321	C<$name>. If the name already exists it is replaced.
322
323	A port can only be registered under one well known name.
324
325	A port automatically becomes unregistered when it is killed.
326
327	=cut
328
329	sub reg(@) {
330	my $port = @_ > 1 ? shift : $SELF \|\| Carp::croak 'reg: called with one argument only, but $SELF not set,';
331
332	$REG{$_[0]} = $port;
333	}
334
335	=item rcv $port, $callback->(@msg)	380	=item rcv $local_port, $callback->(@msg)
336		381
337	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
338	one if required).	383	remove the default callback: use C<sub { }> to disable it, or better
339		384	C<kil> the port when it is no longer needed.
340	=item rcv $port, tagstring => $callback->(@msg), ...
341
342	=item rcv $port, $smartmatch => $callback->(@msg), ...
343
344	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
345
346	Register callbacks to be called on matching messages on the given full
347	port (after converting it to one if required) and return the port.
348
349	The callback has to return a true value when its work is done, after
350	which is will be removed, or a false value in which case it will stay
351	registered.
352		385
353	The global C<$SELF> (exported by this module) contains C<$port> while	386	The global C<$SELF> (exported by this module) contains C<$port> while
354	executing the callback.	387	executing the callback. Runtime errors during callback execution will
		388	result in the port being C<kil>ed.
355		389
356	Runtime errors during callback execution will result in the port being	390	The default callback received all messages not matched by a more specific
357	C<kil>ed.	391	C<tag> match.
358		392
359	If the match is an array reference, then it will be matched against the	393	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
360	first elements of the message, otherwise only the first element is being
361	matched.
362		394
363	Any element in the match that is specified as C<_any_> (a function	395	Register (or replace) callbacks to be called on messages starting with the
364	exported by this module) matches any single element of the message.	396	given tag on the given port (and return the port), or unregister it (when
		397	C<$callback> is C<$undef> or missing). There can only be one callback
		398	registered for each tag.
365		399
366	While not required, it is highly recommended that the first matching	400	The original message will be passed to the callback, after the first
367	element is a string identifying the message. The one-string-only match is	401	element (the tag) has been removed. The callback will use the same
368	also the most efficient match (by far).	402	environment as the default callback (see above).
369		403
370	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.
371		405
372	my $port = rcv port,	406	my $port = rcv port,
373	msg1 => sub { ...; 0 },	407	msg1 => sub { ... },
374	msg2 => sub { ...; 0 },	408	msg2 => sub { ... },
375	;	409	;
376		410
377	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
378	in one go:	412	in one go:
379		413
380	snd $otherport, reply =>	414	snd $otherport, reply =>
381	rcv port,	415	rcv port,
382	msg1 => sub { ...; 0 },	416	msg1 => sub { ... },
383	...	417	...
384	;	418	;
385		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, $otherport;
		427	};
		428
386	=cut	429	=cut
387		430
388	sub rcv($@) {	431	sub rcv($@) {
389	my $port = shift;	432	my $port = shift;
390	my ($noderef, $portid) = split /#/, $port, 2;	433	my ($nodeid, $portid) = split /#/, $port, 2;
391		434
392	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	435	$NODE{$nodeid} == $NODE{""}
393	or Carp::croak "$port: rcv can only be called on local ports, caught";	436	or Carp::croak "$port: rcv can only be called on local ports, caught";
394		437
395	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 {
396	my $cb = shift;	446	my $cb = shift;
397	delete $PORT_DATA{$portid};
398	$PORT{$portid} = sub {	447	$PORT{$portid} = sub {
399	local $SELF = $port;	448	local $SELF = $port;
400	eval {	449	eval { &$cb }; _self_die if $@;
401	&$cb	450	};
402	and kil $port;
403	};	451	}
404	_self_die if $@;	452	} elsif (defined $_[0]) {
405	};
406	} else {
407	my $self = $PORT_DATA{$portid} \|\|= do {	453	my $self = $PORT_DATA{$portid} \|\|= do {
408	my $self = bless {	454	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
409	id => $port,
410	}, "AnyEvent::MP::Port";
411		455
412	$PORT{$portid} = sub {	456	$PORT{$portid} = sub {
413	local $SELF = $port;	457	local $SELF = $port;
414		458
415	eval {
416	for (@{ $self->{rc0}{$_[0]} }) {	459	if (my $cb = $self->[1]{$_[0]}) {
417	$_ && &{$_->[0]}	460	shift;
418	&& undef $_;	461	eval { &$cb }; _self_die if $@;
419	}	462	} else {
420
421	for (@{ $self->{rcv}{$_[0]} }) {
422	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
423	&& &{$_->[0]}	463	&{ $self->[0] };
424	&& undef $_;
425	}
426
427	for (@{ $self->{any} }) {
428	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
429	&& &{$_->[0]}
430	&& undef $_;
431	}	464	}
432	};	465	};
433	_self_die if $@;	466
		467	$self
434	};	468	};
435		469
436	$self
437	};
438
439	"AnyEvent::MP::Port" eq ref $self	470	"AnyEvent::MP::Port" eq ref $self
440	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	471	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
441		472
442	while (@_) {
443	my ($match, $cb) = splice @_, 0, 2;	473	my ($tag, $cb) = splice @_, 0, 2;
444		474
445	if (!ref $match) {	475	if (defined $cb) {
446	push @{ $self->{rc0}{$match} }, [$cb];	476	$self->[1]{$tag} = $cb;
447	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
448	my ($type, @match) = @$match;
449	@match
450	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
451	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
452	} else {	477	} else {
453	push @{ $self->{any} }, [$cb, $match];	478	delete $self->[1]{$tag};
454	}	479	}
455	}	480	}
456	}	481	}
457		482
458	$port	483	$port
459	}	484	}
460		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
461	=item $closure = psub { BLOCK }	523	=item $closure = psub { BLOCK }
462		524
463	Remembers C<$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
464	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>
465	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 $SELF, sub {
		530	BLOCK }, @_ } >>.
466		531
467	This is useful when you register callbacks from C<rcv> callbacks:	532	This is useful when you register callbacks from C<rcv> callbacks:
468		533
469	rcv delayed_reply => sub {	534	rcv delayed_reply => sub {
470	my ($delay, @reply) = @_;	535	my ($delay, @reply) = @_;
…		…
494	$res	559	$res
495	}	560	}
496	}	561	}
497	}	562	}
498		563
499	=item $guard = mon $port, $cb->(@reason)	564	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
500		565
501	=item $guard = mon $port, $rcvport	566	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
502		567
503	=item $guard = mon $port	568	=item $guard = mon $port # kill $SELF when $port dies
504		569
505	=item $guard = mon $port, $rcvport, @msg	570	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
506		571
507	Monitor the given port and do something when the port is killed or	572	Monitor the given port and do something when the port is killed or
508	messages to it were lost, and optionally return a guard that can be used	573	messages to it were lost, and optionally return a guard that can be used
509	to stop monitoring again.	574	to stop monitoring again.
510
511	C<mon> effectively guarantees that, in the absence of hardware failures,
512	that after starting the monitor, either all messages sent to the port
513	will arrive, or the monitoring action will be invoked after possible
514	message loss has been detected. No messages will be lost "in between"
515	(after the first lost message no further messages will be received by the
516	port). After the monitoring action was invoked, further messages might get
517	delivered again.
518		575
519	In the first form (callback), the callback is simply called with any	576	In the first form (callback), the callback is simply called with any
520	number of C<@reason> elements (no @reason means that the port was deleted	577	number of C<@reason> elements (no @reason means that the port was deleted
521	"normally"). Note also that I<< the callback B<must> never die >>, so use	578	"normally"). Note also that I<< the callback B<must> never die >>, so use
522	C<eval> if unsure.	579	C<eval> if unsure.
523		580
524	In the second form (another port given), the other port (C<$rcvport>)	581	In the second form (another port given), the other port (C<$rcvport>)
525	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	582	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
526	"normal" kils nothing happens, while under all other conditions, the other	583	"normal" kils nothing happens, while under all other conditions, the other
527	port is killed with the same reason.	584	port is killed with the same reason.
528		585
529	The third form (kill self) is the same as the second form, except that	586	The third form (kill self) is the same as the second form, except that
530	C<$rvport> defaults to C<$SELF>.	587	C<$rvport> defaults to C<$SELF>.
531		588
532	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
533	C<snd>.	590	C<snd>.
		591
		592	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		593	alert was raised), they are removed and will not trigger again.
534		594
535	As a rule of thumb, monitoring requests should always monitor a port from	595	As a rule of thumb, monitoring requests should always monitor a port from
536	a local port (or callback). The reason is that kill messages might get	596	a local port (or callback). The reason is that kill messages might get
537	lost, just like any other message. Another less obvious reason is that	597	lost, just like any other message. Another less obvious reason is that
538	even monitoring requests can get lost (for exmaple, when the connection	598	even monitoring requests can get lost (for example, when the connection
539	to the other node goes down permanently). When monitoring a port locally	599	to the other node goes down permanently). When monitoring a port locally
540	these problems do not exist.	600	these problems do not exist.
541		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
542	Example: call a given callback when C<$port> is killed.	619	Example: call a given callback when C<$port> is killed.
543		620
544	mon $port, sub { warn "port died because of <@_>\n" };	621	mon $port, sub { warn "port died because of <@_>\n" };
545		622
546	Example: kill ourselves when C<$port> is killed abnormally.	623	Example: kill ourselves when C<$port> is killed abnormally.
…		…
552	mon $port, $self => "restart";	629	mon $port, $self => "restart";
553		630
554	=cut	631	=cut
555		632
556	sub mon {	633	sub mon {
557	my ($noderef, $port) = split /#/, shift, 2;	634	my ($nodeid, $port) = split /#/, shift, 2;
558		635
559	my $node = $NODE{$noderef} \|\| add_node $noderef;	636	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
560		637
561	my $cb = @_ ? shift : $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,';
562		639
563	unless (ref $cb) {	640	unless (ref $cb) {
564	if (@_) {	641	if (@_) {
…		…
573	}	650	}
574		651
575	$node->monitor ($port, $cb);	652	$node->monitor ($port, $cb);
576		653
577	defined wantarray	654	defined wantarray
578	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	655	and ($cb += 0, AnyEvent::Util::guard { $node->unmonitor ($port, $cb) })
579	}	656	}
580		657
581	=item $guard = mon_guard $port, $ref, $ref...	658	=item $guard = mon_guard $port, $ref, $ref...
582		659
583	Monitors the given C<$port> and keeps the passed references. When the port	660	Monitors the given C<$port> and keeps the passed references. When the port
584	is killed, the references will be freed.	661	is killed, the references will be freed.
585		662
586	Optionally returns a guard that will stop the monitoring.	663	Optionally returns a guard that will stop the monitoring.
587		664
588	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
589	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>):
590		667
591	$port->rcv (start => sub {	668	$port->rcv (start => sub {
592	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	669	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
593	undef $timer if 0.9 < rand;	670	undef $timer if 0.9 < rand;
594	});	671	});
595	});	672	});
596		673
597	=cut	674	=cut
…		…
606		683
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 =>
…		…
625	=item $port = spawn $node, $initfunc[, @initdata]	703	=item $port = spawn $node, $initfunc[, @initdata]
626		704
627	Creates a port on the node C<$node> (which can also be a port ID, in which	705	Creates a port on the node C<$node> (which can also be a port ID, in which
628	case it's the node where that port resides).	706	case it's the node where that port resides).
629		707
630	The port ID of the newly created port is return immediately, and it is	708	The port ID of the newly created port is returned immediately, and it is
631	permissible to immediately start sending messages or monitor the port.	709	possible to immediately start sending messages or to monitor the port.
632		710
633	After the port has been created, the init function is	711	After the port has been created, the init function is called on the remote
634	called. This function must be a fully-qualified function name	712	node, in the same context as a C<rcv> callback. This function must be a
635	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	713	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
636	program, use C<::name>.	714	specify a function in the main program, use C<::name>.
637		715
638	If the function doesn't exist, then the node tries to C<require>	716	If the function doesn't exist, then the node tries to C<require>
639	the package, then the package above the package and so on (e.g.	717	the package, then the package above the package and so on (e.g.
640	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	718	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
641	exists or it runs out of package names.	719	exists or it runs out of package names.
642		720
643	The init function is then called with the newly-created port as context	721	The init function is then called with the newly-created port as context
644	object (C<$SELF>) and the C<@initdata> values as arguments.	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.
645		725
646	A common idiom is to pass your own port, monitor the spawned port, and	726	A common idiom is to pass a local port, immediately monitor the spawned
647	in the init function, monitor the original port. This two-way monitoring	727	port, and in the remote init function, immediately monitor the passed
648	ensures that both ports get cleaned up when there is a problem.	728	local port. This two-way monitoring ensures that both ports get cleaned up
		729	when there is a problem.
		730
		731	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		732	caller before C<spawn> returns (by delaying invocation when spawn is
		733	called for the local node).
649		734
650	Example: spawn a chat server port on C<$othernode>.	735	Example: spawn a chat server port on C<$othernode>.
651		736
652	# this node, executed from within a port context:	737	# this node, executed from within a port context:
653	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	738	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
668		753
669	sub _spawn {	754	sub _spawn {
670	my $port = shift;	755	my $port = shift;
671	my $init = shift;	756	my $init = shift;
672		757
		758	# rcv will create the actual port
673	local $SELF = "$NODE#$port";	759	local $SELF = "$NODE#$port";
674	eval {	760	eval {
675	&{ load_func $init }	761	&{ load_func $init }
676	};	762	};
677	_self_die if $@;	763	_self_die if $@;
678	}	764	}
679		765
680	sub spawn(@) {	766	sub spawn(@) {
681	my ($noderef, undef) = split /#/, shift, 2;	767	my ($nodeid, undef) = split /#/, shift, 2;
682		768
683	my $id = "$RUNIQ." . $ID++;	769	my $id = "$RUNIQ." . $ID++;
684		770
685	$_[0] =~ /::/	771	$_[0] =~ /::/
686	or Carp::croak "spawn init function must be a fully-qualified name, caught";	772	or Carp::croak "spawn init function must be a fully-qualified name, caught";
687		773
688	($NODE{$noderef} \|\| add_node $noderef)	774	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
689	->send (["", "AnyEvent::MP::_spawn" => $id, @_]);
690		775
691	"$noderef#$id"	776	"$nodeid#$id"
692	}	777	}
693		778
694	=back	779	=item after $timeout, @msg
695		780
696	=head1 NODE MESSAGES	781	=item after $timeout, $callback
697		782
698	Nodes understand the following messages sent to them. Many of them take	783	Either sends the given message, or call the given callback, after the
699	arguments called C<@reply>, which will simply be used to compose a reply	784	specified number of seconds.
700	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
701	the remaining arguments are simply the message data.
702		785
703	While other messages exist, they are not public and subject to change.	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.
704		789
705	=over 4
706
707	=cut	790	=cut
708		791
709	=item lookup => $name, @reply	792	sub after($@) {
		793	my ($timeout, @action) = @_;
710		794
711	Replies with the port ID of the specified well-known port, or C<undef>.	795	my $t; $t = AE::timer $timeout, 0, sub {
		796	undef $t;
		797	ref $action[0]
		798	? $action[0]()
		799	: snd @action;
		800	};
		801	}
712		802
713	=item devnull => ...	803	=item cal $port, @msg, $callback[, $timeout]
714		804
715	Generic data sink/CPU heat conversion.	805	A simple form of RPC - sends a message to the given C<$port> with the
		806	given contents (C<@msg>), but adds a reply port to the message.
716		807
717	=item relay => $port, @msg	808	The reply port is created temporarily just for the purpose of receiving
		809	the reply, and will be C<kil>ed when no longer needed.
718		810
719	Simply forwards the message to the given port.	811	A reply message sent to the port is passed to the C<$callback> as-is.
720		812
721	=item eval => $string[ @reply]	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.
722		816
723	Evaluates the given string. If C<@reply> is given, then a message of the	817	If no time-out is given (or it is C<undef>), then the local port will
724	form C<@reply, $@, @evalres> is sent.	818	monitor the remote port instead, so it eventually gets cleaned-up.
725		819
726	Example: crash another node.	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.
727		823
728	snd $othernode, eval => "exit";	824	=cut
729		825
730	=item time => @reply	826	sub cal(@) {
		827	my $timeout = ref $_[-1] ? undef : pop;
		828	my $cb = pop;
731		829
732	Replies the the current node time to C<@reply>.	830	my $port = port {
		831	undef $timeout;
		832	kil $SELF;
		833	&$cb;
		834	};
733		835
734	Example: tell the current node to send the current time to C<$myport> in a	836	if (defined $timeout) {
735	C<timereply> message.	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	}
736		848
737	snd $NODE, time => $myport, timereply => 1, 2;	849	push @_, $port;
738	# => snd $myport, timereply => 1, 2, <time>	850	&snd;
		851
		852	$port
		853	}
739		854
740	=back	855	=back
741		856
742	=head1 AnyEvent::MP vs. Distributed Erlang	857	=head1 AnyEvent::MP vs. Distributed Erlang
743		858
744	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
745	== 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
746	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
747	sample:	862	sample:
748		863
749	http://www.Erlang.se/doc/programming_rules.shtml	864	http://www.erlang.se/doc/programming_rules.shtml
750	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
751	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
752	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
753		868
754	Despite the similarities, there are also some important differences:	869	Despite the similarities, there are also some important differences:
755		870
756	=over 4	871	=over 4
757		872
758	=item * Node references contain the recipe on how to contact them.	873	=item * Node IDs are arbitrary strings in AEMP.
759		874
760	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
761	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
762	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.
763		879
764	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
765	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.
766		894
767	=item * Erlang uses processes and a mailbox, AEMP does not queue.	895	=item * Erlang uses processes and a mailbox, AEMP does not queue.
768		896
769	Erlang uses processes that selctively receive messages, and therefore	897	Erlang uses processes that selectively receive messages out of order, and
770	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
771	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.
772		902
773	(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.
774		908
775	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	909	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
776		910
777	Sending messages in Erlang is synchronous and blocks the process. AEMP	911	Sending messages in Erlang is synchronous and blocks the process until
778	sends are immediate, connection establishment is handled in the	912	a conenction has been established and the message sent (and so does not
779	background.	913	need a queue that can overflow). AEMP sends return immediately, connection
		914	establishment is handled in the background.
780		915
781	=item * Erlang can silently lose messages, AEMP cannot.	916	=item * Erlang suffers from silent message loss, AEMP does not.
782		917
783	Erlang makes few guarantees on messages delivery - messages can get lost	918	Erlang implements few guarantees on messages delivery - messages can get
784	without any of the processes realising it (i.e. you send messages a, b,	919	lost without any of the processes realising it (i.e. you send messages a,
785	and c, and the other side only receives messages a and c).	920	b, and c, and the other side only receives messages a and c).
786		921
787	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
788	holes in the message sequence.	925	no silent "holes" in the message sequence.
789		926
790	=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
791	alive.	928	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
792		929	simply tries to work better in common error cases, such as when a network
793	In Erlang it can happen that a monitored process is declared dead and	930	link goes down.
794	linked processes get killed, but later it turns out that the process is
795	still alive - and can receive messages.
796
797	In AEMP, when port monitoring detects a port as dead, then that port will
798	eventually be killed - it cannot happen that a node detects a port as dead
799	and then later sends messages to it, finding it is still alive.
800		931
801	=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.
802		933
803	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
804	ID known to other nodes for a completely different process, causing	935	process ID known to other nodes for a completely different process,
805	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.
806		938
807	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
808	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.
809		941
810	=item * Erlang uses unprotected connections, AEMP uses secure	942	=item * Erlang uses unprotected connections, AEMP uses secure
811	authentication and can use TLS.	943	authentication and can use TLS.
812		944
813	AEMP can use a proven protocol - SSL/TLS - to protect connections and	945	AEMP can use a proven protocol - TLS - to protect connections and
814	securely authenticate nodes.	946	securely authenticate nodes.
815		947
816	=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
817	communications.	949	communications.
818		950
819	The AEMP protocol, unlike the Erlang protocol, supports both	951	The AEMP protocol, unlike the Erlang protocol, supports both programming
820	language-independent text-only protocols (good for debugging) and binary,	952	language independent text-only protocols (good for debugging), and binary,
821	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.
822		955
823	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
824	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
825	protocol simple.	958	protocol simple.
826		959
827	=item * AEMP has more flexible monitoring options than Erlang.	960	=item * AEMP has more flexible monitoring options than Erlang.
828		961
829	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
830	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
831	difficult to implement. Monitoring in AEMP is more flexible than in	964	difficult to implement.
832	Erlang, as one can choose between automatic kill, exit message or callback	965
833	on a per-process basis.	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.
834		968
835	=item * Erlang tries to hide remote/local connections, AEMP does not.	969	=item * Erlang tries to hide remote/local connections, AEMP does not.
836		970
837	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
838	as linking is (except linking is unreliable in Erlang).	972	same way as linking is (except linking is unreliable in Erlang).
839		973
840	In AEMP, you don't "look up" registered port names or send to named ports	974	In AEMP, you don't "look up" registered port names or send to named ports
841	that might or might not be persistent. Instead, you normally spawn a port	975	that might or might not be persistent. Instead, you normally spawn a port
842	on the remote node. The init function monitors the you, and you monitor	976	on the remote node. The init function monitors you, and you monitor the
843	the remote port. Since both monitors are local to the node, they are much	977	remote port. Since both monitors are local to the node, they are much more
844	more reliable.	978	reliable (no need for C<spawn_link>).
845		979
846	This also saves round-trips and avoids sending messages to the wrong port	980	This also saves round-trips and avoids sending messages to the wrong port
847	(hard to do in Erlang).	981	(hard to do in Erlang).
848		982
849	=back	983	=back
850		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
851	=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.
852		1033
853	L<AnyEvent>.	1034	L<AnyEvent>.
854		1035
855	=head1 AUTHOR	1036	=head1 AUTHOR
856		1037

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