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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.48 by root, Thu Aug 13 02:59:42 2009 UTC vs.
Revision 1.109 by root, Wed Dec 30 15:49:05 2009 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
15	# initialise the node so it can send/receive messages	14	# initialise the node so it can send/receive messages
16	initialise_node; # -OR-	15	configure;
17	initialise_node "localhost:4040"; # -OR-
18	initialise_node "slave/", "localhost:4040"
19		16
20	# ports are message endpoints	17	# ports are message destinations
21		18
22	# sending messages	19	# sending messages
23	snd $port, type => data...;	20	snd $port, type => data...;
24	snd $port, @msg;	21	snd $port, @msg;
25	snd @msg_with_first_element_being_a_port;	22	snd @msg_with_first_element_being_a_port;
26		23
27	# creating/using miniports	24	# creating/using ports, the simple way
28	my $miniport = port { my @msg = @_; 0 };	25	my $simple_port = port { my @msg = @_ };
29		26
30	# creating/using full ports	27	# creating/using ports, tagged message matching
31	my $port = port;	28	my $port = port;
32	rcv $port, smartmatch => $cb->(@msg);
33	rcv $port, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
34	rcv $port, pong => sub { warn "pong received\n"; 0 };	30	rcv $port, pong => sub { warn "pong received\n" };
35
36	# more, smarter, matches (_any_ is exported by this module)
37	rcv $port, [child_died => $pid] => sub { ...
38	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3
39		31
40	# create a port on another node	32	# create a port on another node
41	my $port = spawn $node, $initfunc, @initdata;	33	my $port = spawn $node, $initfunc, @initdata;
42		34
		35	# destroy a prot again
		36	kil $port; # "normal" kill
		37	kil $port, my_error => "everything is broken"; # error kill
		38
43	# monitoring	39	# monitoring
44	mon $port, $cb->(@msg) # callback is invoked on death	40	mon $localport, $cb->(@msg) # callback is invoked on death
45	mon $port, $otherport # kill otherport on abnormal death	41	mon $localport, $otherport # kill otherport on abnormal death
46	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	};
47		51
48	=head1 CURRENT STATUS	52	=head1 CURRENT STATUS
49		53
		54	bin/aemp - stable.
50	AnyEvent::MP - stable API, should work	55	AnyEvent::MP - stable API, should work.
51	AnyEvent::MP::Intro - outdated	56	AnyEvent::MP::Intro - explains most concepts.
52	AnyEvent::MP::Kernel - WIP
53	AnyEvent::MP::Transport - mostly stable	57	AnyEvent::MP::Kernel - mostly stable API.
54		58	AnyEvent::MP::Global - stable API.
55	stay tuned.
56		59
57	=head1 DESCRIPTION	60	=head1 DESCRIPTION
58		61
59	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
60		63
61	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
62	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
63		66
64	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>
65	manual page.	68	manual page and the examples under F<eg/>.
66
67	At the moment, this module family is severly broken and underdocumented,
68	so do not use. This was uploaded mainly to reserve the CPAN namespace -
69	stay tuned!
70		69
71	=head1 CONCEPTS	70	=head1 CONCEPTS
72		71
73	=over 4	72	=over 4
74		73
75	=item port	74	=item port
76		75
77	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).
78		78
79	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
80	messages. All C<rcv> handlers will receive messages they match, messages	80	some messages. Messages send to ports will not be queued, regardless of
81	will not be queued.	81	anything was listening for them or not.
82		82
83	=item port id - C<noderef#portname>	83	=item port ID - C<nodeid#portname>
84		84
85	A port id is normaly the concatenation of a noderef, a hash-mark (C<#>) as	85	A port ID is the concatenation of a node ID, a hash-mark (C<#>) as
86	separator, and a port name (a printable string of unspecified format). An	86	separator, and a port name (a printable string of unspecified format).
87	exception is the the node port, whose ID is identical to its node
88	reference.
89		87
90	=item node	88	=item node
91		89
92	A node is a single process containing at least one port - the node	90	A node is a single process containing at least one port - the node port,
93	port. You can send messages to node ports to find existing ports or to	91	which enables nodes to manage each other remotely, and to create new
94	create new ports, among other things.	92	ports.
95		93
96	Nodes are either private (single-process only), slaves (connected to a	94	Nodes are either public (have one or more listening ports) or private
97	master node only) or public nodes (connectable from unrelated nodes).	95	(no listening ports). Private nodes cannot talk to other private nodes
		96	currently.
98		97
99	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	98	=item node ID - C<[A-Z_][a-zA-Z0-9_\-.:]*>
100		99
101	A node reference is a string that either simply identifies the node (for	100	A node ID is a string that uniquely identifies the node within a
102	private and slave nodes), or contains a recipe on how to reach a given	101	network. Depending on the configuration used, node IDs can look like a
103	node (for public nodes).	102	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		103	doesn't interpret node IDs in any way.
104		104
105	This recipe is simply a comma-separated list of C<address:port> pairs (for	105	=item binds - C<ip:port>
106	TCP/IP, other protocols might look different).
107		106
108	Node references come in two flavours: resolved (containing only numerical	107	Nodes can only talk to each other by creating some kind of connection to
109	addresses) or unresolved (where hostnames are used instead of addresses).	108	each other. To do this, nodes should listen on one or more local transport
		109	endpoints - binds. Currently, only standard C<ip:port> specifications can
		110	be used, which specify TCP ports to listen on.
110		111
111	Before using an unresolved node reference in a message you first have to	112	=item seed nodes
112	resolve it.	113
		114	When a node starts, it knows nothing about the network. To teach the node
		115	about the network it first has to contact some other node within the
		116	network. This node is called a seed.
		117
		118	Apart from the fact that other nodes know them as seed nodes and they have
		119	to have fixed listening addresses, seed nodes are perfectly normal nodes -
		120	any node can function as a seed node for others.
		121
		122	In addition to discovering the network, seed nodes are also used to
		123	maintain the network and to connect nodes that otherwise would have
		124	trouble connecting. They form the backbone of an AnyEvent::MP network.
		125
		126	Seed nodes are expected to be long-running, and at least one seed node
		127	should always be available. They should also be relatively responsive - a
		128	seed node that blocks for long periods will slow down everybody else.
		129
		130	=item seeds - C<host:port>
		131
		132	Seeds are transport endpoint(s) (usually a hostname/IP address and a
		133	TCP port) of nodes that should be used as seed nodes.
		134
		135	The nodes listening on those endpoints are expected to be long-running,
		136	and at least one of those should always be available. When nodes run out
		137	of connections (e.g. due to a network error), they try to re-establish
		138	connections to some seednodes again to join the network.
113		139
114	=back	140	=back
115		141
116	=head1 VARIABLES/FUNCTIONS	142	=head1 VARIABLES/FUNCTIONS
117		143
129		155
130	use AE ();	156	use AE ();
131		157
132	use base "Exporter";	158	use base "Exporter";
133		159
134	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	160	our $VERSION = 1.26;
135		161
136	our @EXPORT = qw(	162	our @EXPORT = qw(
137	NODE $NODE *SELF node_of _any_	163	NODE $NODE *SELF node_of after
138	resolve_node initialise_node	164	configure
139	snd rcv mon kil reg psub spawn	165	snd rcv mon mon_guard kil psub peval spawn cal
140	port	166	port
141	);	167	);
142		168
143	our $SELF;	169	our $SELF;
144		170
…		…
148	kil $SELF, die => $msg;	174	kil $SELF, die => $msg;
149	}	175	}
150		176
151	=item $thisnode = NODE / $NODE	177	=item $thisnode = NODE / $NODE
152		178
153	The C<NODE> function returns, and the C<$NODE> variable contains	179	The C<NODE> function returns, and the C<$NODE> variable contains, the node
154	the noderef of the local node. The value is initialised by a call	180	ID of the node running in the current process. This value is initialised by
155	to C<become_public> or C<become_slave>, after which all local port	181	a call to C<configure>.
156	identifiers become invalid.
157		182
158	=item $noderef = node_of $port	183	=item $nodeid = node_of $port
159		184
160	Extracts and returns the noderef from a portid or a noderef.	185	Extracts and returns the node ID from a port ID or a node ID.
161		186
162	=item initialise_node $noderef, $seednode, $seednode...	187	=item configure $profile, key => value...
163		188
164	=item initialise_node "slave/", $master, $master...	189	=item configure key => value...
165		190
166	Before a node can talk to other nodes on the network it has to initialise	191	Before a node can talk to other nodes on the network (i.e. enter
167	itself - the minimum a node needs to know is it's own name, and optionally	192	"distributed mode") it has to configure itself - the minimum a node needs
168	it should know the noderefs of some other nodes in the network.	193	to know is its own name, and optionally it should know the addresses of
		194	some other nodes in the network to discover other nodes.
169		195
		196	The key/value pairs are basically the same ones as documented for the
		197	F<aemp> command line utility (sans the set/del prefix).
		198
170	This function initialises a node - it must be called exactly once (or	199	This function configures a node - it must be called exactly once (or
171	never) before calling other AnyEvent::MP functions.	200	never) before calling other AnyEvent::MP functions.
172		201
173	All arguments are noderefs, which can be either resolved or unresolved.
174
175	There are two types of networked nodes, public nodes and slave nodes:
176
177	=over 4	202	=over 4
178		203
179	=item public nodes	204	=item step 1, gathering configuration from profiles
180		205
181	For public nodes, C<$noderef> must either be a (possibly unresolved)	206	The function first looks up a profile in the aemp configuration (see the
182	noderef, in which case it will be resolved, or C<undef> (or missing), in	207	L<aemp> commandline utility). The profile name can be specified via the
183	which case the noderef will be guessed.	208	named C<profile> parameter or can simply be the first parameter). If it is
		209	missing, then the nodename (F<uname -n>) will be used as profile name.
184		210
185	Afterwards, the node will bind itself on all endpoints and try to connect	211	The profile data is then gathered as follows:
186	to all additional C<$seednodes> that are specified. Seednodes are optional
187	and can be used to quickly bootstrap the node into an existing network.
188		212
189	=item slave nodes	213	First, all remaining key => value pairs (all of which are conveniently
		214	undocumented at the moment) will be interpreted as configuration
		215	data. Then they will be overwritten by any values specified in the global
		216	default configuration (see the F<aemp> utility), then the chain of
		217	profiles chosen by the profile name (and any C<parent> attributes).
190		218
191	When the C<$noderef> is the special string C<slave/>, then the node will	219	That means that the values specified in the profile have highest priority
192	become a slave node. Slave nodes cannot be contacted from outside and will	220	and the values specified directly via C<configure> have lowest priority,
193	route most of their traffic to the master node that they attach to.	221	and can only be used to specify defaults.
194		222
195	At least one additional noderef is required: The node will try to connect	223	If the profile specifies a node ID, then this will become the node ID of
196	to all of them and will become a slave attached to the first node it can	224	this process. If not, then the profile name will be used as node ID. The
197	successfully connect to.	225	special node ID of C<anon/> will be replaced by a random node ID.
		226
		227	=item step 2, bind listener sockets
		228
		229	The next step is to look up the binds in the profile, followed by binding
		230	aemp protocol listeners on all binds specified (it is possible and valid
		231	to have no binds, meaning that the node cannot be contacted form the
		232	outside. This means the node cannot talk to other nodes that also have no
		233	binds, but it can still talk to all "normal" nodes).
		234
		235	If the profile does not specify a binds list, then a default of C<*> is
		236	used, meaning the node will bind on a dynamically-assigned port on every
		237	local IP address it finds.
		238
		239	=item step 3, connect to seed nodes
		240
		241	As the last step, the seeds list from the profile is passed to the
		242	L<AnyEvent::MP::Global> module, which will then use it to keep
		243	connectivity with at least one node at any point in time.
198		244
199	=back	245	=back
200		246
201	This function will block until all nodes have been resolved and, for slave	247	Example: become a distributed node using the local node name as profile.
202	nodes, until it has successfully established a connection to a master	248	This should be the most common form of invocation for "daemon"-type nodes.
203	server.
204		249
205	Example: become a public node listening on the default node.	250	configure
206		251
207	initialise_node;	252	Example: become an anonymous node. This form is often used for commandline
		253	clients.
208		254
209	Example: become a public node, and try to contact some well-known master	255	configure nodeid => "anon/";
210	servers to become part of the network.
211		256
212	initialise_node undef, "master1", "master2";	257	Example: configure a node using a profile called seed, which si suitable
		258	for a seed node as it binds on all local addresses on a fixed port (4040,
		259	customary for aemp).
213		260
214	Example: become a public node listening on port C<4041>.	261	# use the aemp commandline utility
		262	# aemp profile seed nodeid anon/ binds '*:4040'
215		263
216	initialise_node 4041;	264	# then use it
		265	configure profile => "seed";
217		266
218	Example: become a public node, only visible on localhost port 4044.	267	# or simply use aemp from the shell again:
		268	# aemp run profile seed
219		269
220	initialise_node "locahost:4044";	270	# or provide a nicer-to-remember nodeid
221		271	# aemp run profile seed nodeid "$(hostname)"
222	Example: become a slave node to any of the specified master servers.
223
224	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
225
226	=item $cv = resolve_node $noderef
227
228	Takes an unresolved node reference that may contain hostnames and
229	abbreviated IDs, resolves all of them and returns a resolved node
230	reference.
231
232	In addition to C<address:port> pairs allowed in resolved noderefs, the
233	following forms are supported:
234
235	=over 4
236
237	=item the empty string
238
239	An empty-string component gets resolved as if the default port (4040) was
240	specified.
241
242	=item naked port numbers (e.g. C<1234>)
243
244	These are resolved by prepending the local nodename and a colon, to be
245	further resolved.
246
247	=item hostnames (e.g. C<localhost:1234>, C<localhost>)
248
249	These are resolved by using AnyEvent::DNS to resolve them, optionally
250	looking up SRV records for the C<aemp=4040> port, if no port was
251	specified.
252
253	=back
254		272
255	=item $SELF	273	=item $SELF
256		274
257	Contains the current port id while executing C<rcv> callbacks or C<psub>	275	Contains the current port id while executing C<rcv> callbacks or C<psub>
258	blocks.	276	blocks.
259		277
260	=item SELF, %SELF, @SELF...	278	=item *SELF, SELF, %SELF, @SELF...
261		279
262	Due to some quirks in how perl exports variables, it is impossible to	280	Due to some quirks in how perl exports variables, it is impossible to
263	just export C<$SELF>, all the symbols called C<SELF> are exported by this	281	just export C<$SELF>, all the symbols named C<SELF> are exported by this
264	module, but only C<$SELF> is currently used.	282	module, but only C<$SELF> is currently used.
265		283
266	=item snd $port, type => @data	284	=item snd $port, type => @data
267		285
268	=item snd $port, @msg	286	=item snd $port, @msg
269		287
270	Send the given message to the given port ID, which can identify either	288	Send the given message to the given port, which can identify either a
271	a local or a remote port, and can be either a string or soemthignt hat	289	local or a remote port, and must be a port ID.
272	stringifies a sa port ID (such as a port object :).
273		290
274	While the message can be about anything, it is highly recommended to use a	291	While the message can be almost anything, it is highly recommended to
275	string as first element (a portid, or some word that indicates a request	292	use a string as first element (a port ID, or some word that indicates a
276	type etc.).	293	request type etc.) and to consist if only simple perl values (scalars,
		294	arrays, hashes) - if you think you need to pass an object, think again.
277		295
278	The message data effectively becomes read-only after a call to this	296	The message data logically becomes read-only after a call to this
279	function: modifying any argument is not allowed and can cause many	297	function: modifying any argument (or values referenced by them) is
280	problems.	298	forbidden, as there can be considerable time between the call to C<snd>
		299	and the time the message is actually being serialised - in fact, it might
		300	never be copied as within the same process it is simply handed to the
		301	receiving port.
281		302
282	The type of data you can transfer depends on the transport protocol: when	303	The type of data you can transfer depends on the transport protocol: when
283	JSON is used, then only strings, numbers and arrays and hashes consisting	304	JSON is used, then only strings, numbers and arrays and hashes consisting
284	of those are allowed (no objects). When Storable is used, then anything	305	of those are allowed (no objects). When Storable is used, then anything
285	that Storable can serialise and deserialise is allowed, and for the local	306	that Storable can serialise and deserialise is allowed, and for the local
286	node, anything can be passed.	307	node, anything can be passed. Best rely only on the common denominator of
		308	these.
287		309
288	=item $local_port = port	310	=item $local_port = port
289		311
290	Create a new local port object that can be used either as a pattern	312	Create a new local port object and returns its port ID. Initially it has
291	matching port ("full port") or a single-callback port ("miniport"),	313	no callbacks set and will throw an error when it receives messages.
292	depending on how C<rcv> callbacks are bound to the object.
293		314
294	=item $port = port { my @msg = @_; $finished }	315	=item $local_port = port { my @msg = @_ }
295		316
296	Creates a "miniport", that is, a very lightweight port without any pattern	317	Creates a new local port, and returns its ID. Semantically the same as
297	matching behind it, and returns its ID. Semantically the same as creating
298	a port and calling C<rcv $port, $callback> on it.	318	creating a port and calling C<rcv $port, $callback> on it.
299		319
300	The block will be called for every message received on the port. When the	320	The block will be called for every message received on the port, with the
301	callback returns a true value its job is considered "done" and the port	321	global variable C<$SELF> set to the port ID. Runtime errors will cause the
302	will be destroyed. Otherwise it will stay alive.	322	port to be C<kil>ed. The message will be passed as-is, no extra argument
		323	(i.e. no port ID) will be passed to the callback.
303		324
304	The message will be passed as-is, no extra argument (i.e. no port id) will	325	If you want to stop/destroy the port, simply C<kil> it:
305	be passed to the callback.
306		326
307	If you need the local port id in the callback, this works nicely:	327	my $port = port {
308		328	my @msg = @_;
309	my $port; $port = port {	329	...
310	snd $otherport, reply => $port;	330	kil $SELF;
311	};	331	};
312		332
313	=cut	333	=cut
314		334
315	sub rcv($@);	335	sub rcv($@);
		336
		337	sub _kilme {
		338	die "received message on port without callback";
		339	}
316		340
317	sub port(;&) {	341	sub port(;&) {
318	my $id = "$UNIQ." . $ID++;	342	my $id = "$UNIQ." . $ID++;
319	my $port = "$NODE#$id";	343	my $port = "$NODE#$id";
320		344
321	if (@_) {	345	rcv $port, shift \|\| \&_kilme;
322	rcv $port, shift;
323	} else {
324	$PORT{$id} = sub { }; # nop
325	}
326		346
327	$port	347	$port
328	}	348	}
329		349
330	=item reg $port, $name
331
332	=item reg $name
333
334	Registers the given port (or C<$SELF><<< if missing) under the name
335	C<$name>. If the name already exists it is replaced.
336
337	A port can only be registered under one well known name.
338
339	A port automatically becomes unregistered when it is killed.
340
341	=cut
342
343	sub reg(@) {
344	my $port = @_ > 1 ? shift : $SELF \|\| Carp::croak 'reg: called with one argument only, but $SELF not set,';
345
346	$REG{$_[0]} = $port;
347	}
348
349	=item rcv $port, $callback->(@msg)	350	=item rcv $local_port, $callback->(@msg)
350		351
351	Replaces the callback on the specified miniport (after converting it to	352	Replaces the default callback on the specified port. There is no way to
352	one if required).	353	remove the default callback: use C<sub { }> to disable it, or better
353		354	C<kil> the port when it is no longer needed.
354	=item rcv $port, tagstring => $callback->(@msg), ...
355
356	=item rcv $port, $smartmatch => $callback->(@msg), ...
357
358	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
359
360	Register callbacks to be called on matching messages on the given full
361	port (after converting it to one if required) and return the port.
362
363	The callback has to return a true value when its work is done, after
364	which is will be removed, or a false value in which case it will stay
365	registered.
366		355
367	The global C<$SELF> (exported by this module) contains C<$port> while	356	The global C<$SELF> (exported by this module) contains C<$port> while
368	executing the callback.	357	executing the callback. Runtime errors during callback execution will
		358	result in the port being C<kil>ed.
369		359
370	Runtime errors during callback execution will result in the port being	360	The default callback received all messages not matched by a more specific
371	C<kil>ed.	361	C<tag> match.
372		362
373	If the match is an array reference, then it will be matched against the	363	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
374	first elements of the message, otherwise only the first element is being
375	matched.
376		364
377	Any element in the match that is specified as C<_any_> (a function	365	Register (or replace) callbacks to be called on messages starting with the
378	exported by this module) matches any single element of the message.	366	given tag on the given port (and return the port), or unregister it (when
		367	C<$callback> is C<$undef> or missing). There can only be one callback
		368	registered for each tag.
379		369
380	While not required, it is highly recommended that the first matching	370	The original message will be passed to the callback, after the first
381	element is a string identifying the message. The one-string-only match is	371	element (the tag) has been removed. The callback will use the same
382	also the most efficient match (by far).	372	environment as the default callback (see above).
383		373
384	Example: create a port and bind receivers on it in one go.	374	Example: create a port and bind receivers on it in one go.
385		375
386	my $port = rcv port,	376	my $port = rcv port,
387	msg1 => sub { ...; 0 },	377	msg1 => sub { ... },
388	msg2 => sub { ...; 0 },	378	msg2 => sub { ... },
389	;	379	;
390		380
391	Example: create a port, bind receivers and send it in a message elsewhere	381	Example: create a port, bind receivers and send it in a message elsewhere
392	in one go:	382	in one go:
393		383
394	snd $otherport, reply =>	384	snd $otherport, reply =>
395	rcv port,	385	rcv port,
396	msg1 => sub { ...; 0 },	386	msg1 => sub { ... },
397	...	387	...
398	;	388	;
399		389
		390	Example: temporarily register a rcv callback for a tag matching some port
		391	(e.g. for an rpc reply) and unregister it after a message was received.
		392
		393	rcv $port, $otherport => sub {
		394	my @reply = @_;
		395
		396	rcv $SELF, $otherport;
		397	};
		398
400	=cut	399	=cut
401		400
402	sub rcv($@) {	401	sub rcv($@) {
403	my $port = shift;	402	my $port = shift;
404	my ($noderef, $portid) = split /#/, $port, 2;	403	my ($nodeid, $portid) = split /#/, $port, 2;
405		404
406	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	405	$NODE{$nodeid} == $NODE{""}
407	or Carp::croak "$port: rcv can only be called on local ports, caught";	406	or Carp::croak "$port: rcv can only be called on local ports, caught";
408		407
409	if (@_ == 1) {	408	while (@_) {
		409	if (ref $_[0]) {
		410	if (my $self = $PORT_DATA{$portid}) {
		411	"AnyEvent::MP::Port" eq ref $self
		412	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		413
		414	$self->[0] = shift;
		415	} else {
410	my $cb = shift;	416	my $cb = shift;
411	delete $PORT_DATA{$portid};
412	$PORT{$portid} = sub {	417	$PORT{$portid} = sub {
413	local $SELF = $port;	418	local $SELF = $port;
414	eval {	419	eval { &$cb }; _self_die if $@;
415	&$cb	420	};
416	and kil $port;
417	};	421	}
418	_self_die if $@;	422	} elsif (defined $_[0]) {
419	};
420	} else {
421	my $self = $PORT_DATA{$portid} \|\|= do {	423	my $self = $PORT_DATA{$portid} \|\|= do {
422	my $self = bless {	424	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
423	id => $port,
424	}, "AnyEvent::MP::Port";
425		425
426	$PORT{$portid} = sub {	426	$PORT{$portid} = sub {
427	local $SELF = $port;	427	local $SELF = $port;
428		428
429	eval {
430	for (@{ $self->{rc0}{$_[0]} }) {	429	if (my $cb = $self->[1]{$_[0]}) {
431	$_ && &{$_->[0]}	430	shift;
432	&& undef $_;	431	eval { &$cb }; _self_die if $@;
433	}	432	} else {
434
435	for (@{ $self->{rcv}{$_[0]} }) {
436	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
437	&& &{$_->[0]}	433	&{ $self->[0] };
438	&& undef $_;
439	}
440
441	for (@{ $self->{any} }) {
442	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
443	&& &{$_->[0]}
444	&& undef $_;
445	}	434	}
446	};	435	};
447	_self_die if $@;	436
		437	$self
448	};	438	};
449		439
450	$self
451	};
452
453	"AnyEvent::MP::Port" eq ref $self	440	"AnyEvent::MP::Port" eq ref $self
454	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	441	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
455		442
456	while (@_) {
457	my ($match, $cb) = splice @_, 0, 2;	443	my ($tag, $cb) = splice @_, 0, 2;
458		444
459	if (!ref $match) {	445	if (defined $cb) {
460	push @{ $self->{rc0}{$match} }, [$cb];	446	$self->[1]{$tag} = $cb;
461	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
462	my ($type, @match) = @$match;
463	@match
464	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
465	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
466	} else {	447	} else {
467	push @{ $self->{any} }, [$cb, $match];	448	delete $self->[1]{$tag};
468	}	449	}
469	}	450	}
470	}	451	}
471		452
472	$port	453	$port
473	}	454	}
474		455
		456	=item peval $port, $coderef[, @args]
		457
		458	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		459	when the code throews an exception the C<$port> will be killed.
		460
		461	Any remaining args will be passed to the callback. Any return values will
		462	be returned to the caller.
		463
		464	This is useful when you temporarily want to execute code in the context of
		465	a port.
		466
		467	Example: create a port and run some initialisation code in it's context.
		468
		469	my $port = port { ... };
		470
		471	peval $port, sub {
		472	init
		473	or die "unable to init";
		474	};
		475
		476	=cut
		477
		478	sub peval($$) {
		479	local $SELF = shift;
		480	my $cb = shift;
		481
		482	if (wantarray) {
		483	my @res = eval { &$cb };
		484	_self_die if $@;
		485	@res
		486	} else {
		487	my $res = eval { &$cb };
		488	_self_die if $@;
		489	$res
		490	}
		491	}
		492
475	=item $closure = psub { BLOCK }	493	=item $closure = psub { BLOCK }
476		494
477	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	495	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
478	closure is executed, sets up the environment in the same way as in C<rcv>	496	closure is executed, sets up the environment in the same way as in C<rcv>
479	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.	497	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		498
		499	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		500	BLOCK } } >>.
480		501
481	This is useful when you register callbacks from C<rcv> callbacks:	502	This is useful when you register callbacks from C<rcv> callbacks:
482		503
483	rcv delayed_reply => sub {	504	rcv delayed_reply => sub {
484	my ($delay, @reply) = @_;	505	my ($delay, @reply) = @_;
…		…
508	$res	529	$res
509	}	530	}
510	}	531	}
511	}	532	}
512		533
513	=item $guard = mon $port, $cb->(@reason)	534	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
514		535
515	=item $guard = mon $port, $rcvport	536	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
516		537
517	=item $guard = mon $port	538	=item $guard = mon $port # kill $SELF when $port dies
518		539
519	=item $guard = mon $port, $rcvport, @msg	540	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
520		541
521	Monitor the given port and do something when the port is killed or	542	Monitor the given port and do something when the port is killed or
522	messages to it were lost, and optionally return a guard that can be used	543	messages to it were lost, and optionally return a guard that can be used
523	to stop monitoring again.	544	to stop monitoring again.
524
525	C<mon> effectively guarantees that, in the absence of hardware failures,
526	that after starting the monitor, either all messages sent to the port
527	will arrive, or the monitoring action will be invoked after possible
528	message loss has been detected. No messages will be lost "in between"
529	(after the first lost message no further messages will be received by the
530	port). After the monitoring action was invoked, further messages might get
531	delivered again.
532		545
533	In the first form (callback), the callback is simply called with any	546	In the first form (callback), the callback is simply called with any
534	number of C<@reason> elements (no @reason means that the port was deleted	547	number of C<@reason> elements (no @reason means that the port was deleted
535	"normally"). Note also that I<< the callback B<must> never die >>, so use	548	"normally"). Note also that I<< the callback B<must> never die >>, so use
536	C<eval> if unsure.	549	C<eval> if unsure.
537		550
538	In the second form (another port given), the other port (C<$rcvport>)	551	In the second form (another port given), the other port (C<$rcvport>)
539	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	552	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
540	"normal" kils nothing happens, while under all other conditions, the other	553	"normal" kils nothing happens, while under all other conditions, the other
541	port is killed with the same reason.	554	port is killed with the same reason.
542		555
543	The third form (kill self) is the same as the second form, except that	556	The third form (kill self) is the same as the second form, except that
544	C<$rvport> defaults to C<$SELF>.	557	C<$rvport> defaults to C<$SELF>.
545		558
546	In the last form (message), a message of the form C<@msg, @reason> will be	559	In the last form (message), a message of the form C<@msg, @reason> will be
547	C<snd>.	560	C<snd>.
		561
		562	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		563	alert was raised), they are removed and will not trigger again.
548		564
549	As a rule of thumb, monitoring requests should always monitor a port from	565	As a rule of thumb, monitoring requests should always monitor a port from
550	a local port (or callback). The reason is that kill messages might get	566	a local port (or callback). The reason is that kill messages might get
551	lost, just like any other message. Another less obvious reason is that	567	lost, just like any other message. Another less obvious reason is that
552	even monitoring requests can get lost (for exmaple, when the connection	568	even monitoring requests can get lost (for example, when the connection
553	to the other node goes down permanently). When monitoring a port locally	569	to the other node goes down permanently). When monitoring a port locally
554	these problems do not exist.	570	these problems do not exist.
555		571
		572	C<mon> effectively guarantees that, in the absence of hardware failures,
		573	after starting the monitor, either all messages sent to the port will
		574	arrive, or the monitoring action will be invoked after possible message
		575	loss has been detected. No messages will be lost "in between" (after
		576	the first lost message no further messages will be received by the
		577	port). After the monitoring action was invoked, further messages might get
		578	delivered again.
		579
		580	Inter-host-connection timeouts and monitoring depend on the transport
		581	used. The only transport currently implemented is TCP, and AnyEvent::MP
		582	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		583	non-idle connection, and usually around two hours for idle connections).
		584
		585	This means that monitoring is good for program errors and cleaning up
		586	stuff eventually, but they are no replacement for a timeout when you need
		587	to ensure some maximum latency.
		588
556	Example: call a given callback when C<$port> is killed.	589	Example: call a given callback when C<$port> is killed.
557		590
558	mon $port, sub { warn "port died because of <@_>\n" };	591	mon $port, sub { warn "port died because of <@_>\n" };
559		592
560	Example: kill ourselves when C<$port> is killed abnormally.	593	Example: kill ourselves when C<$port> is killed abnormally.
…		…
566	mon $port, $self => "restart";	599	mon $port, $self => "restart";
567		600
568	=cut	601	=cut
569		602
570	sub mon {	603	sub mon {
571	my ($noderef, $port) = split /#/, shift, 2;	604	my ($nodeid, $port) = split /#/, shift, 2;
572		605
573	my $node = $NODE{$noderef} \|\| add_node $noderef;	606	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
574		607
575	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';	608	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
576		609
577	unless (ref $cb) {	610	unless (ref $cb) {
578	if (@_) {	611	if (@_) {
…		…
587	}	620	}
588		621
589	$node->monitor ($port, $cb);	622	$node->monitor ($port, $cb);
590		623
591	defined wantarray	624	defined wantarray
592	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	625	and ($cb += 0, AnyEvent::Util::guard { $node->unmonitor ($port, $cb) })
593	}	626	}
594		627
595	=item $guard = mon_guard $port, $ref, $ref...	628	=item $guard = mon_guard $port, $ref, $ref...
596		629
597	Monitors the given C<$port> and keeps the passed references. When the port	630	Monitors the given C<$port> and keeps the passed references. When the port
598	is killed, the references will be freed.	631	is killed, the references will be freed.
599		632
600	Optionally returns a guard that will stop the monitoring.	633	Optionally returns a guard that will stop the monitoring.
601		634
602	This function is useful when you create e.g. timers or other watchers and	635	This function is useful when you create e.g. timers or other watchers and
603	want to free them when the port gets killed:	636	want to free them when the port gets killed (note the use of C<psub>):
604		637
605	$port->rcv (start => sub {	638	$port->rcv (start => sub {
606	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	639	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
607	undef $timer if 0.9 < rand;	640	undef $timer if 0.9 < rand;
608	});	641	});
609	});	642	});
610		643
611	=cut	644	=cut
…		…
620		653
621	=item kil $port[, @reason]	654	=item kil $port[, @reason]
622		655
623	Kill the specified port with the given C<@reason>.	656	Kill the specified port with the given C<@reason>.
624		657
625	If no C<@reason> is specified, then the port is killed "normally" (linked	658	If no C<@reason> is specified, then the port is killed "normally" -
626	ports will not be kileld, or even notified).	659	monitor callback will be invoked, but the kil will not cause linked ports
		660	(C<mon $mport, $lport> form) to get killed.
627		661
628	Otherwise, linked ports get killed with the same reason (second form of	662	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
629	C<mon>, see below).	663	form) get killed with the same reason.
630		664
631	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	665	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
632	will be reported as reason C<< die => $@ >>.	666	will be reported as reason C<< die => $@ >>.
633		667
634	Transport/communication errors are reported as C<< transport_error =>	668	Transport/communication errors are reported as C<< transport_error =>
…		…
639	=item $port = spawn $node, $initfunc[, @initdata]	673	=item $port = spawn $node, $initfunc[, @initdata]
640		674
641	Creates a port on the node C<$node> (which can also be a port ID, in which	675	Creates a port on the node C<$node> (which can also be a port ID, in which
642	case it's the node where that port resides).	676	case it's the node where that port resides).
643		677
644	The port ID of the newly created port is return immediately, and it is	678	The port ID of the newly created port is returned immediately, and it is
645	permissible to immediately start sending messages or monitor the port.	679	possible to immediately start sending messages or to monitor the port.
646		680
647	After the port has been created, the init function is	681	After the port has been created, the init function is called on the remote
648	called. This function must be a fully-qualified function name	682	node, in the same context as a C<rcv> callback. This function must be a
649	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	683	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
650	program, use C<::name>.	684	specify a function in the main program, use C<::name>.
651		685
652	If the function doesn't exist, then the node tries to C<require>	686	If the function doesn't exist, then the node tries to C<require>
653	the package, then the package above the package and so on (e.g.	687	the package, then the package above the package and so on (e.g.
654	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	688	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
655	exists or it runs out of package names.	689	exists or it runs out of package names.
656		690
657	The init function is then called with the newly-created port as context	691	The init function is then called with the newly-created port as context
658	object (C<$SELF>) and the C<@initdata> values as arguments.	692	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		693	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		694	the port might not get created.
659		695
660	A common idiom is to pass your own port, monitor the spawned port, and	696	A common idiom is to pass a local port, immediately monitor the spawned
661	in the init function, monitor the original port. This two-way monitoring	697	port, and in the remote init function, immediately monitor the passed
662	ensures that both ports get cleaned up when there is a problem.	698	local port. This two-way monitoring ensures that both ports get cleaned up
		699	when there is a problem.
		700
		701	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		702	caller before C<spawn> returns (by delaying invocation when spawn is
		703	called for the local node).
663		704
664	Example: spawn a chat server port on C<$othernode>.	705	Example: spawn a chat server port on C<$othernode>.
665		706
666	# this node, executed from within a port context:	707	# this node, executed from within a port context:
667	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	708	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
682		723
683	sub _spawn {	724	sub _spawn {
684	my $port = shift;	725	my $port = shift;
685	my $init = shift;	726	my $init = shift;
686		727
		728	# rcv will create the actual port
687	local $SELF = "$NODE#$port";	729	local $SELF = "$NODE#$port";
688	eval {	730	eval {
689	&{ load_func $init }	731	&{ load_func $init }
690	};	732	};
691	_self_die if $@;	733	_self_die if $@;
692	}	734	}
693		735
694	sub spawn(@) {	736	sub spawn(@) {
695	my ($noderef, undef) = split /#/, shift, 2;	737	my ($nodeid, undef) = split /#/, shift, 2;
696		738
697	my $id = "$RUNIQ." . $ID++;	739	my $id = "$RUNIQ." . $ID++;
698		740
699	$_[0] =~ /::/	741	$_[0] =~ /::/
700	or Carp::croak "spawn init function must be a fully-qualified name, caught";	742	or Carp::croak "spawn init function must be a fully-qualified name, caught";
701		743
702	($NODE{$noderef} \|\| add_node $noderef)	744	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
703	->send (["", "AnyEvent::MP::_spawn" => $id, @_]);
704		745
705	"$noderef#$id"	746	"$nodeid#$id"
706	}	747	}
707		748
708	=back	749	=item after $timeout, @msg
709		750
710	=head1 NODE MESSAGES	751	=item after $timeout, $callback
711		752
712	Nodes understand the following messages sent to them. Many of them take	753	Either sends the given message, or call the given callback, after the
713	arguments called C<@reply>, which will simply be used to compose a reply	754	specified number of seconds.
714	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
715	the remaining arguments are simply the message data.
716		755
717	While other messages exist, they are not public and subject to change.	756	This is simply a utility function that comes in handy at times - the
		757	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		758	so it may go away in the future.
718		759
719	=over 4
720
721	=cut	760	=cut
722		761
723	=item lookup => $name, @reply	762	sub after($@) {
		763	my ($timeout, @action) = @_;
724		764
725	Replies with the port ID of the specified well-known port, or C<undef>.	765	my $t; $t = AE::timer $timeout, 0, sub {
		766	undef $t;
		767	ref $action[0]
		768	? $action[0]()
		769	: snd @action;
		770	};
		771	}
726		772
727	=item devnull => ...	773	=item cal $port, @msg, $callback[, $timeout]
728		774
729	Generic data sink/CPU heat conversion.	775	A simple form of RPC - sends a message to the given C<$port> with the
		776	given contents (C<@msg>), but adds a reply port to the message.
730		777
731	=item relay => $port, @msg	778	The reply port is created temporarily just for the purpose of receiving
		779	the reply, and will be C<kil>ed when no longer needed.
732		780
733	Simply forwards the message to the given port.	781	A reply message sent to the port is passed to the C<$callback> as-is.
734		782
735	=item eval => $string[ @reply]	783	If an optional time-out (in seconds) is given and it is not C<undef>,
		784	then the callback will be called without any arguments after the time-out
		785	elapsed and the port is C<kil>ed.
736		786
737	Evaluates the given string. If C<@reply> is given, then a message of the	787	If no time-out is given (or it is C<undef>), then the local port will
738	form C<@reply, $@, @evalres> is sent.	788	monitor the remote port instead, so it eventually gets cleaned-up.
739		789
740	Example: crash another node.	790	Currently this function returns the temporary port, but this "feature"
		791	might go in future versions unless you can make a convincing case that
		792	this is indeed useful for something.
741		793
742	snd $othernode, eval => "exit";	794	=cut
743		795
744	=item time => @reply	796	sub cal(@) {
		797	my $timeout = ref $_[-1] ? undef : pop;
		798	my $cb = pop;
745		799
746	Replies the the current node time to C<@reply>.	800	my $port = port {
		801	undef $timeout;
		802	kil $SELF;
		803	&$cb;
		804	};
747		805
748	Example: tell the current node to send the current time to C<$myport> in a	806	if (defined $timeout) {
749	C<timereply> message.	807	$timeout = AE::timer $timeout, 0, sub {
		808	undef $timeout;
		809	kil $port;
		810	$cb->();
		811	};
		812	} else {
		813	mon $_[0], sub {
		814	kil $port;
		815	$cb->();
		816	};
		817	}
750		818
751	snd $NODE, time => $myport, timereply => 1, 2;	819	push @_, $port;
752	# => snd $myport, timereply => 1, 2, <time>	820	&snd;
		821
		822	$port
		823	}
753		824
754	=back	825	=back
755		826
756	=head1 AnyEvent::MP vs. Distributed Erlang	827	=head1 AnyEvent::MP vs. Distributed Erlang
757		828
758	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	829	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
759	== aemp node, Erlang process == aemp port), so many of the documents and	830	== aemp node, Erlang process == aemp port), so many of the documents and
760	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	831	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
761	sample:	832	sample:
762		833
763	http://www.Erlang.se/doc/programming_rules.shtml	834	http://www.erlang.se/doc/programming_rules.shtml
764	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	835	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
765	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	836	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
766	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	837	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
767		838
768	Despite the similarities, there are also some important differences:	839	Despite the similarities, there are also some important differences:
769		840
770	=over 4	841	=over 4
771		842
772	=item * Node references contain the recipe on how to contact them.	843	=item * Node IDs are arbitrary strings in AEMP.
773		844
774	Erlang relies on special naming and DNS to work everywhere in the	845	Erlang relies on special naming and DNS to work everywhere in the same
775	same way. AEMP relies on each node knowing it's own address(es), with	846	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
776	convenience functionality.	847	configuration or DNS), and possibly the addresses of some seed nodes, but
		848	will otherwise discover other nodes (and their IDs) itself.
777		849
778	This means that AEMP requires a less tightly controlled environment at the	850	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
779	cost of longer node references and a slightly higher management overhead.	851	uses "local ports are like remote ports".
		852
		853	The failure modes for local ports are quite different (runtime errors
		854	only) then for remote ports - when a local port dies, you I<know> it dies,
		855	when a connection to another node dies, you know nothing about the other
		856	port.
		857
		858	Erlang pretends remote ports are as reliable as local ports, even when
		859	they are not.
		860
		861	AEMP encourages a "treat remote ports differently" philosophy, with local
		862	ports being the special case/exception, where transport errors cannot
		863	occur.
780		864
781	=item * Erlang uses processes and a mailbox, AEMP does not queue.	865	=item * Erlang uses processes and a mailbox, AEMP does not queue.
782		866
783	Erlang uses processes that selctively receive messages, and therefore	867	Erlang uses processes that selectively receive messages, and therefore
784	needs a queue. AEMP is event based, queuing messages would serve no useful	868	needs a queue. AEMP is event based, queuing messages would serve no
785	purpose.	869	useful purpose. For the same reason the pattern-matching abilities of
		870	AnyEvent::MP are more limited, as there is little need to be able to
		871	filter messages without dequeuing them.
786		872
787	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	873	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).
788		874
789	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	875	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
790		876
791	Sending messages in Erlang is synchronous and blocks the process. AEMP	877	Sending messages in Erlang is synchronous and blocks the process (and
792	sends are immediate, connection establishment is handled in the	878	so does not need a queue that can overflow). AEMP sends are immediate,
793	background.	879	connection establishment is handled in the background.
794		880
795	=item * Erlang can silently lose messages, AEMP cannot.	881	=item * Erlang suffers from silent message loss, AEMP does not.
796		882
797	Erlang makes few guarantees on messages delivery - messages can get lost	883	Erlang implements few guarantees on messages delivery - messages can get
798	without any of the processes realising it (i.e. you send messages a, b,	884	lost without any of the processes realising it (i.e. you send messages a,
799	and c, and the other side only receives messages a and c).	885	b, and c, and the other side only receives messages a and c).
800		886
801	AEMP guarantees correct ordering, and the guarantee that there are no	887	AEMP guarantees correct ordering, and the guarantee that after one message
802	holes in the message sequence.	888	is lost, all following ones sent to the same port are lost as well, until
803		889	monitoring raises an error, so there are no silent "holes" in the message
804	=item * In Erlang, processes can be declared dead and later be found to be	890	sequence.
805	alive.
806
807	In Erlang it can happen that a monitored process is declared dead and
808	linked processes get killed, but later it turns out that the process is
809	still alive - and can receive messages.
810
811	In AEMP, when port monitoring detects a port as dead, then that port will
812	eventually be killed - it cannot happen that a node detects a port as dead
813	and then later sends messages to it, finding it is still alive.
814		891
815	=item * Erlang can send messages to the wrong port, AEMP does not.	892	=item * Erlang can send messages to the wrong port, AEMP does not.
816		893
817	In Erlang it is quite possible that a node that restarts reuses a process	894	In Erlang it is quite likely that a node that restarts reuses a process ID
818	ID known to other nodes for a completely different process, causing	895	known to other nodes for a completely different process, causing messages
819	messages destined for that process to end up in an unrelated process.	896	destined for that process to end up in an unrelated process.
820		897
821	AEMP never reuses port IDs, so old messages or old port IDs floating	898	AEMP never reuses port IDs, so old messages or old port IDs floating
822	around in the network will not be sent to an unrelated port.	899	around in the network will not be sent to an unrelated port.
823		900
824	=item * Erlang uses unprotected connections, AEMP uses secure	901	=item * Erlang uses unprotected connections, AEMP uses secure
825	authentication and can use TLS.	902	authentication and can use TLS.
826		903
827	AEMP can use a proven protocol - SSL/TLS - to protect connections and	904	AEMP can use a proven protocol - TLS - to protect connections and
828	securely authenticate nodes.	905	securely authenticate nodes.
829		906
830	=item * The AEMP protocol is optimised for both text-based and binary	907	=item * The AEMP protocol is optimised for both text-based and binary
831	communications.	908	communications.
832		909
833	The AEMP protocol, unlike the Erlang protocol, supports both	910	The AEMP protocol, unlike the Erlang protocol, supports both programming
834	language-independent text-only protocols (good for debugging) and binary,	911	language independent text-only protocols (good for debugging) and binary,
835	language-specific serialisers (e.g. Storable).	912	language-specific serialisers (e.g. Storable). By default, unless TLS is
		913	used, the protocol is actually completely text-based.
836		914
837	It has also been carefully designed to be implementable in other languages	915	It has also been carefully designed to be implementable in other languages
838	with a minimum of work while gracefully degrading fucntionality to make the	916	with a minimum of work while gracefully degrading functionality to make the
839	protocol simple.	917	protocol simple.
840		918
841	=item * AEMP has more flexible monitoring options than Erlang.	919	=item * AEMP has more flexible monitoring options than Erlang.
842		920
843	In Erlang, you can chose to receive I<all> exit signals as messages	921	In Erlang, you can chose to receive I<all> exit signals as messages
…		…
846	Erlang, as one can choose between automatic kill, exit message or callback	924	Erlang, as one can choose between automatic kill, exit message or callback
847	on a per-process basis.	925	on a per-process basis.
848		926
849	=item * Erlang tries to hide remote/local connections, AEMP does not.	927	=item * Erlang tries to hide remote/local connections, AEMP does not.
850		928
851	Monitoring in Erlang is not an indicator of process death/crashes,	929	Monitoring in Erlang is not an indicator of process death/crashes, in the
852	as linking is (except linking is unreliable in Erlang).	930	same way as linking is (except linking is unreliable in Erlang).
853		931
854	In AEMP, you don't "look up" registered port names or send to named ports	932	In AEMP, you don't "look up" registered port names or send to named ports
855	that might or might not be persistent. Instead, you normally spawn a port	933	that might or might not be persistent. Instead, you normally spawn a port
856	on the remote node. The init function monitors the you, and you monitor	934	on the remote node. The init function monitors you, and you monitor the
857	the remote port. Since both monitors are local to the node, they are much	935	remote port. Since both monitors are local to the node, they are much more
858	more reliable.	936	reliable (no need for C<spawn_link>).
859		937
860	This also saves round-trips and avoids sending messages to the wrong port	938	This also saves round-trips and avoids sending messages to the wrong port
861	(hard to do in Erlang).	939	(hard to do in Erlang).
862		940
863	=back	941	=back
864		942
865	=head1 RATIONALE	943	=head1 RATIONALE
866		944
867	=over 4	945	=over 4
868		946
869	=item Why strings for ports and noderefs, why not objects?	947	=item Why strings for port and node IDs, why not objects?
870		948
871	We considered "objects", but found that the actual number of methods	949	We considered "objects", but found that the actual number of methods
872	thatc an be called are very low. Since port IDs and noderefs travel over	950	that can be called are quite low. Since port and node IDs travel over
873	the network frequently, the serialising/deserialising would add lots of	951	the network frequently, the serialising/deserialising would add lots of
874	overhead, as well as having to keep a proxy object.	952	overhead, as well as having to keep a proxy object everywhere.
875		953
876	Strings can easily be printed, easily serialised etc. and need no special	954	Strings can easily be printed, easily serialised etc. and need no special
877	procedures to be "valid".	955	procedures to be "valid".
878		956
879	And a a miniport consists of a single closure stored in a global hash - it	957	And as a result, a miniport consists of a single closure stored in a
880	can't become much cheaper.	958	global hash - it can't become much cheaper.
881		959
882	=item Why favour JSON, why not real serialising format such as Storable?	960	=item Why favour JSON, why not a real serialising format such as Storable?
883		961
884	In fact, any AnyEvent::MP node will happily accept Storable as framing	962	In fact, any AnyEvent::MP node will happily accept Storable as framing
885	format, but currently there is no way to make a node use Storable by	963	format, but currently there is no way to make a node use Storable by
886	default.	964	default (although all nodes will accept it).
887		965
888	The default framing protocol is JSON because a) JSON::XS is many times	966	The default framing protocol is JSON because a) JSON::XS is many times
889	faster for small messages and b) most importantly, after years of	967	faster for small messages and b) most importantly, after years of
890	experience we found that object serialisation is causing more problems	968	experience we found that object serialisation is causing more problems
891	than it gains: Just like function calls, objects simply do not travel	969	than it solves: Just like function calls, objects simply do not travel
892	easily over the network, mostly because they will always be a copy, so you	970	easily over the network, mostly because they will always be a copy, so you
893	always have to re-think your design.	971	always have to re-think your design.
894		972
895	Keeping your messages simple, concentrating on data structures rather than	973	Keeping your messages simple, concentrating on data structures rather than
896	objects, will keep your messages clean, tidy and efficient.	974	objects, will keep your messages clean, tidy and efficient.
897		975
898	=back	976	=back
899		977
900	=head1 SEE ALSO	978	=head1 SEE ALSO
901		979
		980	L<AnyEvent::MP::Intro> - a gentle introduction.
		981
		982	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		983
		984	L<AnyEvent::MP::Global> - network maintainance and port groups, to find
		985	your applications.
		986
		987	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		988
		989	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		990	all nodes.
		991
902	L<AnyEvent>.	992	L<AnyEvent>.
903		993
904	=head1 AUTHOR	994	=head1 AUTHOR
905		995
906	Marc Lehmann <schmorp@schmorp.de>	996	Marc Lehmann <schmorp@schmorp.de>

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Revision 1.109 by root, Wed Dec 30 15:49:05 2009 UTC