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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.49 by root, Thu Aug 13 15:29:58 2009 UTC vs.
Revision 1.102 by root, Tue Oct 6 13:37:52 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 = 1.21;
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, $master...	189	=item configure key => value...
165		190
166	Before a node can talk to other nodes on the network it has to initialise	191	Before a node can talk to other nodes on the network (i.e. enter
167	itself - the minimum a node needs to know is it's own name, and optionally	192	"distributed mode") it has to configure itself - the minimum a node needs
168	it should know the noderefs of some other nodes in the network.	193	to know is its own name, and optionally it should know the addresses of
		194	some other nodes in the network to discover other nodes.
169		195
170	This function initialises a node - it must be called exactly once (or	196	This function configures a node - it must be called exactly once (or
171	never) before calling other AnyEvent::MP functions.	197	never) before calling other AnyEvent::MP functions.
172		198
173	All arguments (optionally except for the first) are noderefs, which can be
174	either resolved or unresolved.
175
176	The first argument will be looked up in the configuration database first
177	(if it is C<undef> then the current nodename will be used instead) to find
178	the relevant configuration profile (see L<aemp>). If none is found then
179	the default configuration is used. The configuration supplies additional
180	seed/master nodes and can override the actual noderef.
181
182	There are two types of networked nodes, public nodes and slave nodes:
183
184	=over 4	199	=over 4
185		200
186	=item public nodes	201	=item step 1, gathering configuration from profiles
187		202
188	For public nodes, C<$noderef> (supplied either directly to	203	The function first looks up a profile in the aemp configuration (see the
189	C<initialise_node> or indirectly via a profile or the nodename) must be a	204	L<aemp> commandline utility). The profile name can be specified via the
190	noderef (possibly unresolved, in which case it will be resolved).	205	named C<profile> parameter or can simply be the first parameter). If it is
		206	missing, then the nodename (F<uname -n>) will be used as profile name.
191		207
192	After resolving, the node will bind itself on all endpoints and try to	208	The profile data is then gathered as follows:
193	connect to all additional C<$seednodes> that are specified. Seednodes are
194	optional and can be used to quickly bootstrap the node into an existing
195	network.
196		209
197	=item slave nodes	210	First, all remaining key => value pairs (all of which are conveniently
		211	undocumented at the moment) will be interpreted as configuration
		212	data. Then they will be overwritten by any values specified in the global
		213	default configuration (see the F<aemp> utility), then the chain of
		214	profiles chosen by the profile name (and any C<parent> attributes).
198		215
199	When the C<$noderef> (either as given or overriden by the config file)	216	That means that the values specified in the profile have highest priority
200	is the special string C<slave/>, then the node will become a slave	217	and the values specified directly via C<configure> have lowest priority,
201	node. Slave nodes cannot be contacted from outside and will route most of	218	and can only be used to specify defaults.
202	their traffic to the master node that they attach to.
203		219
204	At least one additional noderef is required (either by specifying it	220	If the profile specifies a node ID, then this will become the node ID of
205	directly or because it is part of the configuration profile): The node	221	this process. If not, then the profile name will be used as node ID. The
206	will try to connect to all of them and will become a slave attached to the	222	special node ID of C<anon/> will be replaced by a random node ID.
207	first node it can successfully connect to.	223
		224	=item step 2, bind listener sockets
		225
		226	The next step is to look up the binds in the profile, followed by binding
		227	aemp protocol listeners on all binds specified (it is possible and valid
		228	to have no binds, meaning that the node cannot be contacted form the
		229	outside. This means the node cannot talk to other nodes that also have no
		230	binds, but it can still talk to all "normal" nodes).
		231
		232	If the profile does not specify a binds list, then a default of C<*> is
		233	used, meaning the node will bind on a dynamically-assigned port on every
		234	local IP address it finds.
		235
		236	=item step 3, connect to seed nodes
		237
		238	As the last step, the seeds list from the profile is passed to the
		239	L<AnyEvent::MP::Global> module, which will then use it to keep
		240	connectivity with at least one node at any point in time.
208		241
209	=back	242	=back
210		243
211	This function will block until all nodes have been resolved and, for slave	244	Example: become a distributed node using the local node name as profile.
212	nodes, until it has successfully established a connection to a master	245	This should be the most common form of invocation for "daemon"-type nodes.
213	server.
214		246
215	Example: become a public node listening on the guessed noderef, or the one	247	configure
216	specified via C<aemp> for the current node. This should be the most common
217	form of invocation for "daemon"-type nodes.
218		248
219	initialise_node;	249	Example: become an anonymous node. This form is often used for commandline
		250	clients.
220		251
221	Example: become a slave node to any of the the seednodes specified via	252	configure nodeid => "anon/";
222	C<aemp>. This form is often used for commandline clients.
223		253
224	initialise_node "slave/";	254	Example: configure a node using a profile called seed, which si suitable
		255	for a seed node as it binds on all local addresses on a fixed port (4040,
		256	customary for aemp).
225		257
226	Example: become a slave node to any of the specified master servers. This	258	# use the aemp commandline utility
227	form is also often used for commandline clients.	259	# aemp profile seed nodeid anon/ binds '*:4040'
228		260
229	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";	261	# then use it
		262	configure profile => "seed";
230		263
231	Example: become a public node, and try to contact some well-known master	264	# or simply use aemp from the shell again:
232	servers to become part of the network.	265	# aemp run profile seed
233		266
234	initialise_node undef, "master1", "master2";	267	# or provide a nicer-to-remember nodeid
235		268	# aemp run profile seed nodeid "$(hostname)"
236	Example: become a public node listening on port C<4041>.
237
238	initialise_node 4041;
239
240	Example: become a public node, only visible on localhost port 4044.
241
242	initialise_node "localhost:4044";
243
244	=item $cv = resolve_node $noderef
245
246	Takes an unresolved node reference that may contain hostnames and
247	abbreviated IDs, resolves all of them and returns a resolved node
248	reference.
249
250	In addition to C<address:port> pairs allowed in resolved noderefs, the
251	following forms are supported:
252
253	=over 4
254
255	=item the empty string
256
257	An empty-string component gets resolved as if the default port (4040) was
258	specified.
259
260	=item naked port numbers (e.g. C<1234>)
261
262	These are resolved by prepending the local nodename and a colon, to be
263	further resolved.
264
265	=item hostnames (e.g. C<localhost:1234>, C<localhost>)
266
267	These are resolved by using AnyEvent::DNS to resolve them, optionally
268	looking up SRV records for the C<aemp=4040> port, if no port was
269	specified.
270
271	=back
272		269
273	=item $SELF	270	=item $SELF
274		271
275	Contains the current port id while executing C<rcv> callbacks or C<psub>	272	Contains the current port id while executing C<rcv> callbacks or C<psub>
276	blocks.	273	blocks.
277		274
278	=item SELF, %SELF, @SELF...	275	=item *SELF, SELF, %SELF, @SELF...
279		276
280	Due to some quirks in how perl exports variables, it is impossible to	277	Due to some quirks in how perl exports variables, it is impossible to
281	just export C<$SELF>, all the symbols called C<SELF> are exported by this	278	just export C<$SELF>, all the symbols named C<SELF> are exported by this
282	module, but only C<$SELF> is currently used.	279	module, but only C<$SELF> is currently used.
283		280
284	=item snd $port, type => @data	281	=item snd $port, type => @data
285		282
286	=item snd $port, @msg	283	=item snd $port, @msg
287		284
288	Send the given message to the given port ID, which can identify either	285	Send the given message to the given port, which can identify either a
289	a local or a remote port, and can be either a string or soemthignt hat	286	local or a remote port, and must be a port ID.
290	stringifies a sa port ID (such as a port object :).
291		287
292	While the message can be about anything, it is highly recommended to use a	288	While the message can be almost anything, it is highly recommended to
293	string as first element (a portid, or some word that indicates a request	289	use a string as first element (a port ID, or some word that indicates a
294	type etc.).	290	request type etc.) and to consist if only simple perl values (scalars,
		291	arrays, hashes) - if you think you need to pass an object, think again.
295		292
296	The message data effectively becomes read-only after a call to this	293	The message data logically becomes read-only after a call to this
297	function: modifying any argument is not allowed and can cause many	294	function: modifying any argument (or values referenced by them) is
298	problems.	295	forbidden, as there can be considerable time between the call to C<snd>
		296	and the time the message is actually being serialised - in fact, it might
		297	never be copied as within the same process it is simply handed to the
		298	receiving port.
299		299
300	The type of data you can transfer depends on the transport protocol: when	300	The type of data you can transfer depends on the transport protocol: when
301	JSON is used, then only strings, numbers and arrays and hashes consisting	301	JSON is used, then only strings, numbers and arrays and hashes consisting
302	of those are allowed (no objects). When Storable is used, then anything	302	of those are allowed (no objects). When Storable is used, then anything
303	that Storable can serialise and deserialise is allowed, and for the local	303	that Storable can serialise and deserialise is allowed, and for the local
304	node, anything can be passed.	304	node, anything can be passed. Best rely only on the common denominator of
		305	these.
305		306
306	=item $local_port = port	307	=item $local_port = port
307		308
308	Create a new local port object that can be used either as a pattern	309	Create a new local port object and returns its port ID. Initially it has
309	matching port ("full port") or a single-callback port ("miniport"),	310	no callbacks set and will throw an error when it receives messages.
310	depending on how C<rcv> callbacks are bound to the object.
311		311
312	=item $port = port { my @msg = @_; $finished }	312	=item $local_port = port { my @msg = @_ }
313		313
314	Creates a "miniport", that is, a very lightweight port without any pattern	314	Creates a new local port, and returns its ID. Semantically the same as
315	matching behind it, and returns its ID. Semantically the same as creating
316	a port and calling C<rcv $port, $callback> on it.	315	creating a port and calling C<rcv $port, $callback> on it.
317		316
318	The block will be called for every message received on the port. When the	317	The block will be called for every message received on the port, with the
319	callback returns a true value its job is considered "done" and the port	318	global variable C<$SELF> set to the port ID. Runtime errors will cause the
320	will be destroyed. Otherwise it will stay alive.	319	port to be C<kil>ed. The message will be passed as-is, no extra argument
		320	(i.e. no port ID) will be passed to the callback.
321		321
322	The message will be passed as-is, no extra argument (i.e. no port id) will	322	If you want to stop/destroy the port, simply C<kil> it:
323	be passed to the callback.
324		323
325	If you need the local port id in the callback, this works nicely:	324	my $port = port {
326		325	my @msg = @_;
327	my $port; $port = port {	326	...
328	snd $otherport, reply => $port;	327	kil $SELF;
329	};	328	};
330		329
331	=cut	330	=cut
332		331
333	sub rcv($@);	332	sub rcv($@);
		333
		334	sub _kilme {
		335	die "received message on port without callback";
		336	}
334		337
335	sub port(;&) {	338	sub port(;&) {
336	my $id = "$UNIQ." . $ID++;	339	my $id = "$UNIQ." . $ID++;
337	my $port = "$NODE#$id";	340	my $port = "$NODE#$id";
338		341
339	if (@_) {	342	rcv $port, shift \|\| \&_kilme;
340	rcv $port, shift;
341	} else {
342	$PORT{$id} = sub { }; # nop
343	}
344		343
345	$port	344	$port
346	}	345	}
347		346
348	=item reg $port, $name
349
350	=item reg $name
351
352	Registers the given port (or C<$SELF><<< if missing) under the name
353	C<$name>. If the name already exists it is replaced.
354
355	A port can only be registered under one well known name.
356
357	A port automatically becomes unregistered when it is killed.
358
359	=cut
360
361	sub reg(@) {
362	my $port = @_ > 1 ? shift : $SELF \|\| Carp::croak 'reg: called with one argument only, but $SELF not set,';
363
364	$REG{$_[0]} = $port;
365	}
366
367	=item rcv $port, $callback->(@msg)	347	=item rcv $local_port, $callback->(@msg)
368		348
369	Replaces the callback on the specified miniport (after converting it to	349	Replaces the default callback on the specified port. There is no way to
370	one if required).	350	remove the default callback: use C<sub { }> to disable it, or better
371		351	C<kil> the port when it is no longer needed.
372	=item rcv $port, tagstring => $callback->(@msg), ...
373
374	=item rcv $port, $smartmatch => $callback->(@msg), ...
375
376	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
377
378	Register callbacks to be called on matching messages on the given full
379	port (after converting it to one if required) and return the port.
380
381	The callback has to return a true value when its work is done, after
382	which is will be removed, or a false value in which case it will stay
383	registered.
384		352
385	The global C<$SELF> (exported by this module) contains C<$port> while	353	The global C<$SELF> (exported by this module) contains C<$port> while
386	executing the callback.	354	executing the callback. Runtime errors during callback execution will
		355	result in the port being C<kil>ed.
387		356
388	Runtime errors during callback execution will result in the port being	357	The default callback received all messages not matched by a more specific
389	C<kil>ed.	358	C<tag> match.
390		359
391	If the match is an array reference, then it will be matched against the	360	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
392	first elements of the message, otherwise only the first element is being
393	matched.
394		361
395	Any element in the match that is specified as C<_any_> (a function	362	Register (or replace) callbacks to be called on messages starting with the
396	exported by this module) matches any single element of the message.	363	given tag on the given port (and return the port), or unregister it (when
		364	C<$callback> is C<$undef> or missing). There can only be one callback
		365	registered for each tag.
397		366
398	While not required, it is highly recommended that the first matching	367	The original message will be passed to the callback, after the first
399	element is a string identifying the message. The one-string-only match is	368	element (the tag) has been removed. The callback will use the same
400	also the most efficient match (by far).	369	environment as the default callback (see above).
401		370
402	Example: create a port and bind receivers on it in one go.	371	Example: create a port and bind receivers on it in one go.
403		372
404	my $port = rcv port,	373	my $port = rcv port,
405	msg1 => sub { ...; 0 },	374	msg1 => sub { ... },
406	msg2 => sub { ...; 0 },	375	msg2 => sub { ... },
407	;	376	;
408		377
409	Example: create a port, bind receivers and send it in a message elsewhere	378	Example: create a port, bind receivers and send it in a message elsewhere
410	in one go:	379	in one go:
411		380
412	snd $otherport, reply =>	381	snd $otherport, reply =>
413	rcv port,	382	rcv port,
414	msg1 => sub { ...; 0 },	383	msg1 => sub { ... },
415	...	384	...
416	;	385	;
417		386
		387	Example: temporarily register a rcv callback for a tag matching some port
		388	(e.g. for an rpc reply) and unregister it after a message was received.
		389
		390	rcv $port, $otherport => sub {
		391	my @reply = @_;
		392
		393	rcv $SELF, $otherport;
		394	};
		395
418	=cut	396	=cut
419		397
420	sub rcv($@) {	398	sub rcv($@) {
421	my $port = shift;	399	my $port = shift;
422	my ($noderef, $portid) = split /#/, $port, 2;	400	my ($nodeid, $portid) = split /#/, $port, 2;
423		401
424	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	402	$NODE{$nodeid} == $NODE{""}
425	or Carp::croak "$port: rcv can only be called on local ports, caught";	403	or Carp::croak "$port: rcv can only be called on local ports, caught";
426		404
427	if (@_ == 1) {	405	while (@_) {
		406	if (ref $_[0]) {
		407	if (my $self = $PORT_DATA{$portid}) {
		408	"AnyEvent::MP::Port" eq ref $self
		409	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		410
		411	$self->[2] = shift;
		412	} else {
428	my $cb = shift;	413	my $cb = shift;
429	delete $PORT_DATA{$portid};
430	$PORT{$portid} = sub {	414	$PORT{$portid} = sub {
431	local $SELF = $port;	415	local $SELF = $port;
432	eval {	416	eval { &$cb }; _self_die if $@;
433	&$cb	417	};
434	and kil $port;
435	};	418	}
436	_self_die if $@;	419	} elsif (defined $_[0]) {
437	};
438	} else {
439	my $self = $PORT_DATA{$portid} \|\|= do {	420	my $self = $PORT_DATA{$portid} \|\|= do {
440	my $self = bless {	421	my $self = bless [$PORT{$port} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
441	id => $port,
442	}, "AnyEvent::MP::Port";
443		422
444	$PORT{$portid} = sub {	423	$PORT{$portid} = sub {
445	local $SELF = $port;	424	local $SELF = $port;
446		425
447	eval {
448	for (@{ $self->{rc0}{$_[0]} }) {	426	if (my $cb = $self->[1]{$_[0]}) {
449	$_ && &{$_->[0]}	427	shift;
450	&& undef $_;	428	eval { &$cb }; _self_die if $@;
451	}	429	} else {
452
453	for (@{ $self->{rcv}{$_[0]} }) {
454	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
455	&& &{$_->[0]}	430	&{ $self->[0] };
456	&& undef $_;
457	}
458
459	for (@{ $self->{any} }) {
460	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
461	&& &{$_->[0]}
462	&& undef $_;
463	}	431	}
464	};	432	};
465	_self_die if $@;	433
		434	$self
466	};	435	};
467		436
468	$self
469	};
470
471	"AnyEvent::MP::Port" eq ref $self	437	"AnyEvent::MP::Port" eq ref $self
472	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	438	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
473		439
474	while (@_) {
475	my ($match, $cb) = splice @_, 0, 2;	440	my ($tag, $cb) = splice @_, 0, 2;
476		441
477	if (!ref $match) {	442	if (defined $cb) {
478	push @{ $self->{rc0}{$match} }, [$cb];	443	$self->[1]{$tag} = $cb;
479	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
480	my ($type, @match) = @$match;
481	@match
482	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
483	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
484	} else {	444	} else {
485	push @{ $self->{any} }, [$cb, $match];	445	delete $self->[1]{$tag};
486	}	446	}
487	}	447	}
488	}	448	}
489		449
490	$port	450	$port
491	}	451	}
492		452
		453	=item peval $port, $coderef[, @args]
		454
		455	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		456	when the code throews an exception the C<$port> will be killed.
		457
		458	Any remaining args will be passed to the callback. Any return values will
		459	be returned to the caller.
		460
		461	This is useful when you temporarily want to execute code in the context of
		462	a port.
		463
		464	Example: create a port and run some initialisation code in it's context.
		465
		466	my $port = port { ... };
		467
		468	peval $port, sub {
		469	init
		470	or die "unable to init";
		471	};
		472
		473	=cut
		474
		475	sub peval($$) {
		476	local $SELF = shift;
		477	my $cb = shift;
		478
		479	if (wantarray) {
		480	my @res = eval { &$cb };
		481	_self_die if $@;
		482	@res
		483	} else {
		484	my $res = eval { &$cb };
		485	_self_die if $@;
		486	$res
		487	}
		488	}
		489
493	=item $closure = psub { BLOCK }	490	=item $closure = psub { BLOCK }
494		491
495	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	492	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
496	closure is executed, sets up the environment in the same way as in C<rcv>	493	closure is executed, sets up the environment in the same way as in C<rcv>
497	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.	494	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		495
		496	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		497	BLOCK } } >>.
498		498
499	This is useful when you register callbacks from C<rcv> callbacks:	499	This is useful when you register callbacks from C<rcv> callbacks:
500		500
501	rcv delayed_reply => sub {	501	rcv delayed_reply => sub {
502	my ($delay, @reply) = @_;	502	my ($delay, @reply) = @_;
…		…
526	$res	526	$res
527	}	527	}
528	}	528	}
529	}	529	}
530		530
531	=item $guard = mon $port, $cb->(@reason)	531	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
532		532
533	=item $guard = mon $port, $rcvport	533	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
534		534
535	=item $guard = mon $port	535	=item $guard = mon $port # kill $SELF when $port dies
536		536
537	=item $guard = mon $port, $rcvport, @msg	537	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
538		538
539	Monitor the given port and do something when the port is killed or	539	Monitor the given port and do something when the port is killed or
540	messages to it were lost, and optionally return a guard that can be used	540	messages to it were lost, and optionally return a guard that can be used
541	to stop monitoring again.	541	to stop monitoring again.
542
543	C<mon> effectively guarantees that, in the absence of hardware failures,
544	that after starting the monitor, either all messages sent to the port
545	will arrive, or the monitoring action will be invoked after possible
546	message loss has been detected. No messages will be lost "in between"
547	(after the first lost message no further messages will be received by the
548	port). After the monitoring action was invoked, further messages might get
549	delivered again.
550		542
551	In the first form (callback), the callback is simply called with any	543	In the first form (callback), the callback is simply called with any
552	number of C<@reason> elements (no @reason means that the port was deleted	544	number of C<@reason> elements (no @reason means that the port was deleted
553	"normally"). Note also that I<< the callback B<must> never die >>, so use	545	"normally"). Note also that I<< the callback B<must> never die >>, so use
554	C<eval> if unsure.	546	C<eval> if unsure.
555		547
556	In the second form (another port given), the other port (C<$rcvport>)	548	In the second form (another port given), the other port (C<$rcvport>)
557	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	549	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
558	"normal" kils nothing happens, while under all other conditions, the other	550	"normal" kils nothing happens, while under all other conditions, the other
559	port is killed with the same reason.	551	port is killed with the same reason.
560		552
561	The third form (kill self) is the same as the second form, except that	553	The third form (kill self) is the same as the second form, except that
562	C<$rvport> defaults to C<$SELF>.	554	C<$rvport> defaults to C<$SELF>.
563		555
564	In the last form (message), a message of the form C<@msg, @reason> will be	556	In the last form (message), a message of the form C<@msg, @reason> will be
565	C<snd>.	557	C<snd>.
		558
		559	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		560	alert was raised), they are removed and will not trigger again.
566		561
567	As a rule of thumb, monitoring requests should always monitor a port from	562	As a rule of thumb, monitoring requests should always monitor a port from
568	a local port (or callback). The reason is that kill messages might get	563	a local port (or callback). The reason is that kill messages might get
569	lost, just like any other message. Another less obvious reason is that	564	lost, just like any other message. Another less obvious reason is that
570	even monitoring requests can get lost (for exmaple, when the connection	565	even monitoring requests can get lost (for example, when the connection
571	to the other node goes down permanently). When monitoring a port locally	566	to the other node goes down permanently). When monitoring a port locally
572	these problems do not exist.	567	these problems do not exist.
573		568
		569	C<mon> effectively guarantees that, in the absence of hardware failures,
		570	after starting the monitor, either all messages sent to the port will
		571	arrive, or the monitoring action will be invoked after possible message
		572	loss has been detected. No messages will be lost "in between" (after
		573	the first lost message no further messages will be received by the
		574	port). After the monitoring action was invoked, further messages might get
		575	delivered again.
		576
		577	Inter-host-connection timeouts and monitoring depend on the transport
		578	used. The only transport currently implemented is TCP, and AnyEvent::MP
		579	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		580	non-idle connection, and usually around two hours for idle connections).
		581
		582	This means that monitoring is good for program errors and cleaning up
		583	stuff eventually, but they are no replacement for a timeout when you need
		584	to ensure some maximum latency.
		585
574	Example: call a given callback when C<$port> is killed.	586	Example: call a given callback when C<$port> is killed.
575		587
576	mon $port, sub { warn "port died because of <@_>\n" };	588	mon $port, sub { warn "port died because of <@_>\n" };
577		589
578	Example: kill ourselves when C<$port> is killed abnormally.	590	Example: kill ourselves when C<$port> is killed abnormally.
…		…
584	mon $port, $self => "restart";	596	mon $port, $self => "restart";
585		597
586	=cut	598	=cut
587		599
588	sub mon {	600	sub mon {
589	my ($noderef, $port) = split /#/, shift, 2;	601	my ($nodeid, $port) = split /#/, shift, 2;
590		602
591	my $node = $NODE{$noderef} \|\| add_node $noderef;	603	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
592		604
593	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';	605	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
594		606
595	unless (ref $cb) {	607	unless (ref $cb) {
596	if (@_) {	608	if (@_) {
…		…
605	}	617	}
606		618
607	$node->monitor ($port, $cb);	619	$node->monitor ($port, $cb);
608		620
609	defined wantarray	621	defined wantarray
610	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	622	and ($cb += 0, AnyEvent::Util::guard { $node->unmonitor ($port, $cb) })
611	}	623	}
612		624
613	=item $guard = mon_guard $port, $ref, $ref...	625	=item $guard = mon_guard $port, $ref, $ref...
614		626
615	Monitors the given C<$port> and keeps the passed references. When the port	627	Monitors the given C<$port> and keeps the passed references. When the port
616	is killed, the references will be freed.	628	is killed, the references will be freed.
617		629
618	Optionally returns a guard that will stop the monitoring.	630	Optionally returns a guard that will stop the monitoring.
619		631
620	This function is useful when you create e.g. timers or other watchers and	632	This function is useful when you create e.g. timers or other watchers and
621	want to free them when the port gets killed:	633	want to free them when the port gets killed (note the use of C<psub>):
622		634
623	$port->rcv (start => sub {	635	$port->rcv (start => sub {
624	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	636	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
625	undef $timer if 0.9 < rand;	637	undef $timer if 0.9 < rand;
626	});	638	});
627	});	639	});
628		640
629	=cut	641	=cut
…		…
638		650
639	=item kil $port[, @reason]	651	=item kil $port[, @reason]
640		652
641	Kill the specified port with the given C<@reason>.	653	Kill the specified port with the given C<@reason>.
642		654
643	If no C<@reason> is specified, then the port is killed "normally" (linked	655	If no C<@reason> is specified, then the port is killed "normally" (ports
644	ports will not be kileld, or even notified).	656	monitoring other ports will not necessarily die because a port dies
		657	"normally").
645		658
646	Otherwise, linked ports get killed with the same reason (second form of	659	Otherwise, linked ports get killed with the same reason (second form of
647	C<mon>, see below).	660	C<mon>, see above).
648		661
649	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	662	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
650	will be reported as reason C<< die => $@ >>.	663	will be reported as reason C<< die => $@ >>.
651		664
652	Transport/communication errors are reported as C<< transport_error =>	665	Transport/communication errors are reported as C<< transport_error =>
…		…
657	=item $port = spawn $node, $initfunc[, @initdata]	670	=item $port = spawn $node, $initfunc[, @initdata]
658		671
659	Creates a port on the node C<$node> (which can also be a port ID, in which	672	Creates a port on the node C<$node> (which can also be a port ID, in which
660	case it's the node where that port resides).	673	case it's the node where that port resides).
661		674
662	The port ID of the newly created port is return immediately, and it is	675	The port ID of the newly created port is returned immediately, and it is
663	permissible to immediately start sending messages or monitor the port.	676	possible to immediately start sending messages or to monitor the port.
664		677
665	After the port has been created, the init function is	678	After the port has been created, the init function is called on the remote
666	called. This function must be a fully-qualified function name	679	node, in the same context as a C<rcv> callback. This function must be a
667	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	680	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
668	program, use C<::name>.	681	specify a function in the main program, use C<::name>.
669		682
670	If the function doesn't exist, then the node tries to C<require>	683	If the function doesn't exist, then the node tries to C<require>
671	the package, then the package above the package and so on (e.g.	684	the package, then the package above the package and so on (e.g.
672	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	685	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
673	exists or it runs out of package names.	686	exists or it runs out of package names.
674		687
675	The init function is then called with the newly-created port as context	688	The init function is then called with the newly-created port as context
676	object (C<$SELF>) and the C<@initdata> values as arguments.	689	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		690	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		691	the port might not get created.
677		692
678	A common idiom is to pass your own port, monitor the spawned port, and	693	A common idiom is to pass a local port, immediately monitor the spawned
679	in the init function, monitor the original port. This two-way monitoring	694	port, and in the remote init function, immediately monitor the passed
680	ensures that both ports get cleaned up when there is a problem.	695	local port. This two-way monitoring ensures that both ports get cleaned up
		696	when there is a problem.
		697
		698	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		699	caller before C<spawn> returns (by delaying invocation when spawn is
		700	called for the local node).
681		701
682	Example: spawn a chat server port on C<$othernode>.	702	Example: spawn a chat server port on C<$othernode>.
683		703
684	# this node, executed from within a port context:	704	# this node, executed from within a port context:
685	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	705	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
700		720
701	sub _spawn {	721	sub _spawn {
702	my $port = shift;	722	my $port = shift;
703	my $init = shift;	723	my $init = shift;
704		724
		725	# rcv will create the actual port
705	local $SELF = "$NODE#$port";	726	local $SELF = "$NODE#$port";
706	eval {	727	eval {
707	&{ load_func $init }	728	&{ load_func $init }
708	};	729	};
709	_self_die if $@;	730	_self_die if $@;
710	}	731	}
711		732
712	sub spawn(@) {	733	sub spawn(@) {
713	my ($noderef, undef) = split /#/, shift, 2;	734	my ($nodeid, undef) = split /#/, shift, 2;
714		735
715	my $id = "$RUNIQ." . $ID++;	736	my $id = "$RUNIQ." . $ID++;
716		737
717	$_[0] =~ /::/	738	$_[0] =~ /::/
718	or Carp::croak "spawn init function must be a fully-qualified name, caught";	739	or Carp::croak "spawn init function must be a fully-qualified name, caught";
719		740
720	($NODE{$noderef} \|\| add_node $noderef)	741	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
721	->send (["", "AnyEvent::MP::_spawn" => $id, @_]);
722		742
723	"$noderef#$id"	743	"$nodeid#$id"
724	}	744	}
725		745
726	=back	746	=item after $timeout, @msg
727		747
728	=head1 NODE MESSAGES	748	=item after $timeout, $callback
729		749
730	Nodes understand the following messages sent to them. Many of them take	750	Either sends the given message, or call the given callback, after the
731	arguments called C<@reply>, which will simply be used to compose a reply	751	specified number of seconds.
732	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
733	the remaining arguments are simply the message data.
734		752
735	While other messages exist, they are not public and subject to change.	753	This is simply a utility function that comes in handy at times - the
		754	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		755	so it may go away in the future.
736		756
737	=over 4
738
739	=cut	757	=cut
740		758
741	=item lookup => $name, @reply	759	sub after($@) {
		760	my ($timeout, @action) = @_;
742		761
743	Replies with the port ID of the specified well-known port, or C<undef>.	762	my $t; $t = AE::timer $timeout, 0, sub {
		763	undef $t;
		764	ref $action[0]
		765	? $action[0]()
		766	: snd @action;
		767	};
		768	}
744		769
745	=item devnull => ...	770	=item cal $port, @msg, $callback[, $timeout]
746		771
747	Generic data sink/CPU heat conversion.	772	A simple form of RPC - sends a message to the given C<$port> with the
		773	given contents (C<@msg>), but adds a reply port to the message.
748		774
749	=item relay => $port, @msg	775	The reply port is created temporarily just for the purpose of receiving
		776	the reply, and will be C<kil>ed when no longer needed.
750		777
751	Simply forwards the message to the given port.	778	A reply message sent to the port is passed to the C<$callback> as-is.
752		779
753	=item eval => $string[ @reply]	780	If an optional time-out (in seconds) is given and it is not C<undef>,
		781	then the callback will be called without any arguments after the time-out
		782	elapsed and the port is C<kil>ed.
754		783
755	Evaluates the given string. If C<@reply> is given, then a message of the	784	If no time-out is given (or it is C<undef>), then the local port will
756	form C<@reply, $@, @evalres> is sent.	785	monitor the remote port instead, so it eventually gets cleaned-up.
757		786
758	Example: crash another node.	787	Currently this function returns the temporary port, but this "feature"
		788	might go in future versions unless you can make a convincing case that
		789	this is indeed useful for something.
759		790
760	snd $othernode, eval => "exit";	791	=cut
761		792
762	=item time => @reply	793	sub cal(@) {
		794	my $timeout = ref $_[-1] ? undef : pop;
		795	my $cb = pop;
763		796
764	Replies the the current node time to C<@reply>.	797	my $port = port {
		798	undef $timeout;
		799	kil $SELF;
		800	&$cb;
		801	};
765		802
766	Example: tell the current node to send the current time to C<$myport> in a	803	if (defined $timeout) {
767	C<timereply> message.	804	$timeout = AE::timer $timeout, 0, sub {
		805	undef $timeout;
		806	kil $port;
		807	$cb->();
		808	};
		809	} else {
		810	mon $_[0], sub {
		811	kil $port;
		812	$cb->();
		813	};
		814	}
768		815
769	snd $NODE, time => $myport, timereply => 1, 2;	816	push @_, $port;
770	# => snd $myport, timereply => 1, 2, <time>	817	&snd;
		818
		819	$port
		820	}
771		821
772	=back	822	=back
773		823
774	=head1 AnyEvent::MP vs. Distributed Erlang	824	=head1 AnyEvent::MP vs. Distributed Erlang
775		825
776	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	826	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
777	== aemp node, Erlang process == aemp port), so many of the documents and	827	== aemp node, Erlang process == aemp port), so many of the documents and
778	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	828	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
779	sample:	829	sample:
780		830
781	http://www.Erlang.se/doc/programming_rules.shtml	831	http://www.erlang.se/doc/programming_rules.shtml
782	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	832	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
783	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	833	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
784	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	834	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
785		835
786	Despite the similarities, there are also some important differences:	836	Despite the similarities, there are also some important differences:
787		837
788	=over 4	838	=over 4
789		839
790	=item * Node references contain the recipe on how to contact them.	840	=item * Node IDs are arbitrary strings in AEMP.
791		841
792	Erlang relies on special naming and DNS to work everywhere in the	842	Erlang relies on special naming and DNS to work everywhere in the same
793	same way. AEMP relies on each node knowing it's own address(es), with	843	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
794	convenience functionality.	844	configuration or DNS), and possibly the addresses of some seed nodes, but
		845	will otherwise discover other nodes (and their IDs) itself.
795		846
796	This means that AEMP requires a less tightly controlled environment at the	847	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
797	cost of longer node references and a slightly higher management overhead.	848	uses "local ports are like remote ports".
		849
		850	The failure modes for local ports are quite different (runtime errors
		851	only) then for remote ports - when a local port dies, you I<know> it dies,
		852	when a connection to another node dies, you know nothing about the other
		853	port.
		854
		855	Erlang pretends remote ports are as reliable as local ports, even when
		856	they are not.
		857
		858	AEMP encourages a "treat remote ports differently" philosophy, with local
		859	ports being the special case/exception, where transport errors cannot
		860	occur.
798		861
799	=item * Erlang uses processes and a mailbox, AEMP does not queue.	862	=item * Erlang uses processes and a mailbox, AEMP does not queue.
800		863
801	Erlang uses processes that selctively receive messages, and therefore	864	Erlang uses processes that selectively receive messages, and therefore
802	needs a queue. AEMP is event based, queuing messages would serve no useful	865	needs a queue. AEMP is event based, queuing messages would serve no
803	purpose.	866	useful purpose. For the same reason the pattern-matching abilities of
		867	AnyEvent::MP are more limited, as there is little need to be able to
		868	filter messages without dequeuing them.
804		869
805	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	870	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).
806		871
807	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	872	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
808		873
809	Sending messages in Erlang is synchronous and blocks the process. AEMP	874	Sending messages in Erlang is synchronous and blocks the process (and
810	sends are immediate, connection establishment is handled in the	875	so does not need a queue that can overflow). AEMP sends are immediate,
811	background.	876	connection establishment is handled in the background.
812		877
813	=item * Erlang can silently lose messages, AEMP cannot.	878	=item * Erlang suffers from silent message loss, AEMP does not.
814		879
815	Erlang makes few guarantees on messages delivery - messages can get lost	880	Erlang implements few guarantees on messages delivery - messages can get
816	without any of the processes realising it (i.e. you send messages a, b,	881	lost without any of the processes realising it (i.e. you send messages a,
817	and c, and the other side only receives messages a and c).	882	b, and c, and the other side only receives messages a and c).
818		883
819	AEMP guarantees correct ordering, and the guarantee that there are no	884	AEMP guarantees correct ordering, and the guarantee that after one message
820	holes in the message sequence.	885	is lost, all following ones sent to the same port are lost as well, until
821		886	monitoring raises an error, so there are no silent "holes" in the message
822	=item * In Erlang, processes can be declared dead and later be found to be	887	sequence.
823	alive.
824
825	In Erlang it can happen that a monitored process is declared dead and
826	linked processes get killed, but later it turns out that the process is
827	still alive - and can receive messages.
828
829	In AEMP, when port monitoring detects a port as dead, then that port will
830	eventually be killed - it cannot happen that a node detects a port as dead
831	and then later sends messages to it, finding it is still alive.
832		888
833	=item * Erlang can send messages to the wrong port, AEMP does not.	889	=item * Erlang can send messages to the wrong port, AEMP does not.
834		890
835	In Erlang it is quite possible that a node that restarts reuses a process	891	In Erlang it is quite likely that a node that restarts reuses a process ID
836	ID known to other nodes for a completely different process, causing	892	known to other nodes for a completely different process, causing messages
837	messages destined for that process to end up in an unrelated process.	893	destined for that process to end up in an unrelated process.
838		894
839	AEMP never reuses port IDs, so old messages or old port IDs floating	895	AEMP never reuses port IDs, so old messages or old port IDs floating
840	around in the network will not be sent to an unrelated port.	896	around in the network will not be sent to an unrelated port.
841		897
842	=item * Erlang uses unprotected connections, AEMP uses secure	898	=item * Erlang uses unprotected connections, AEMP uses secure
843	authentication and can use TLS.	899	authentication and can use TLS.
844		900
845	AEMP can use a proven protocol - SSL/TLS - to protect connections and	901	AEMP can use a proven protocol - TLS - to protect connections and
846	securely authenticate nodes.	902	securely authenticate nodes.
847		903
848	=item * The AEMP protocol is optimised for both text-based and binary	904	=item * The AEMP protocol is optimised for both text-based and binary
849	communications.	905	communications.
850		906
851	The AEMP protocol, unlike the Erlang protocol, supports both	907	The AEMP protocol, unlike the Erlang protocol, supports both programming
852	language-independent text-only protocols (good for debugging) and binary,	908	language independent text-only protocols (good for debugging) and binary,
853	language-specific serialisers (e.g. Storable).	909	language-specific serialisers (e.g. Storable). By default, unless TLS is
		910	used, the protocol is actually completely text-based.
854		911
855	It has also been carefully designed to be implementable in other languages	912	It has also been carefully designed to be implementable in other languages
856	with a minimum of work while gracefully degrading fucntionality to make the	913	with a minimum of work while gracefully degrading functionality to make the
857	protocol simple.	914	protocol simple.
858		915
859	=item * AEMP has more flexible monitoring options than Erlang.	916	=item * AEMP has more flexible monitoring options than Erlang.
860		917
861	In Erlang, you can chose to receive I<all> exit signals as messages	918	In Erlang, you can chose to receive I<all> exit signals as messages
…		…
864	Erlang, as one can choose between automatic kill, exit message or callback	921	Erlang, as one can choose between automatic kill, exit message or callback
865	on a per-process basis.	922	on a per-process basis.
866		923
867	=item * Erlang tries to hide remote/local connections, AEMP does not.	924	=item * Erlang tries to hide remote/local connections, AEMP does not.
868		925
869	Monitoring in Erlang is not an indicator of process death/crashes,	926	Monitoring in Erlang is not an indicator of process death/crashes, in the
870	as linking is (except linking is unreliable in Erlang).	927	same way as linking is (except linking is unreliable in Erlang).
871		928
872	In AEMP, you don't "look up" registered port names or send to named ports	929	In AEMP, you don't "look up" registered port names or send to named ports
873	that might or might not be persistent. Instead, you normally spawn a port	930	that might or might not be persistent. Instead, you normally spawn a port
874	on the remote node. The init function monitors the you, and you monitor	931	on the remote node. The init function monitors you, and you monitor the
875	the remote port. Since both monitors are local to the node, they are much	932	remote port. Since both monitors are local to the node, they are much more
876	more reliable.	933	reliable (no need for C<spawn_link>).
877		934
878	This also saves round-trips and avoids sending messages to the wrong port	935	This also saves round-trips and avoids sending messages to the wrong port
879	(hard to do in Erlang).	936	(hard to do in Erlang).
880		937
881	=back	938	=back
882		939
883	=head1 RATIONALE	940	=head1 RATIONALE
884		941
885	=over 4	942	=over 4
886		943
887	=item Why strings for ports and noderefs, why not objects?	944	=item Why strings for port and node IDs, why not objects?
888		945
889	We considered "objects", but found that the actual number of methods	946	We considered "objects", but found that the actual number of methods
890	thatc an be called are very low. Since port IDs and noderefs travel over	947	that can be called are quite low. Since port and node IDs travel over
891	the network frequently, the serialising/deserialising would add lots of	948	the network frequently, the serialising/deserialising would add lots of
892	overhead, as well as having to keep a proxy object.	949	overhead, as well as having to keep a proxy object everywhere.
893		950
894	Strings can easily be printed, easily serialised etc. and need no special	951	Strings can easily be printed, easily serialised etc. and need no special
895	procedures to be "valid".	952	procedures to be "valid".
896		953
897	And a a miniport consists of a single closure stored in a global hash - it	954	And as a result, a miniport consists of a single closure stored in a
898	can't become much cheaper.	955	global hash - it can't become much cheaper.
899		956
900	=item Why favour JSON, why not real serialising format such as Storable?	957	=item Why favour JSON, why not a real serialising format such as Storable?
901		958
902	In fact, any AnyEvent::MP node will happily accept Storable as framing	959	In fact, any AnyEvent::MP node will happily accept Storable as framing
903	format, but currently there is no way to make a node use Storable by	960	format, but currently there is no way to make a node use Storable by
904	default.	961	default (although all nodes will accept it).
905		962
906	The default framing protocol is JSON because a) JSON::XS is many times	963	The default framing protocol is JSON because a) JSON::XS is many times
907	faster for small messages and b) most importantly, after years of	964	faster for small messages and b) most importantly, after years of
908	experience we found that object serialisation is causing more problems	965	experience we found that object serialisation is causing more problems
909	than it gains: Just like function calls, objects simply do not travel	966	than it solves: Just like function calls, objects simply do not travel
910	easily over the network, mostly because they will always be a copy, so you	967	easily over the network, mostly because they will always be a copy, so you
911	always have to re-think your design.	968	always have to re-think your design.
912		969
913	Keeping your messages simple, concentrating on data structures rather than	970	Keeping your messages simple, concentrating on data structures rather than
914	objects, will keep your messages clean, tidy and efficient.	971	objects, will keep your messages clean, tidy and efficient.
915		972
916	=back	973	=back
917		974
918	=head1 SEE ALSO	975	=head1 SEE ALSO
919		976
		977	L<AnyEvent::MP::Intro> - a gentle introduction.
		978
		979	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		980
		981	L<AnyEvent::MP::Global> - network maintainance and port groups, to find
		982	your applications.
		983
		984	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		985	all nodes.
		986
920	L<AnyEvent>.	987	L<AnyEvent>.
921		988
922	=head1 AUTHOR	989	=head1 AUTHOR
923		990
924	Marc Lehmann <schmorp@schmorp.de>	991	Marc Lehmann <schmorp@schmorp.de>

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Revision 1.102 by root, Tue Oct 6 13:37:52 2009 UTC