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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.37 by root, Fri Aug 7 16:47:23 2009 UTC vs.
Revision 1.51 by root, Fri Aug 14 14:07:44 2009 UTC

…		…
8		8
9	$NODE # contains this node's noderef	9	$NODE # contains this node's noderef
10	NODE # returns this node's noderef	10	NODE # returns this node's noderef
11	NODE $port # returns the noderef of the port	11	NODE $port # returns the noderef of the port
12		12
		13	$SELF # receiving/own port id in rcv callbacks
		14
		15	# initialise the node so it can send/receive messages
		16	initialise_node; # -OR-
		17	initialise_node "localhost:4040"; # -OR-
		18	initialise_node "slave/", "localhost:4040"
		19
		20	# ports are message endpoints
		21
		22	# sending messages
13	snd $port, type => data...;	23	snd $port, type => data...;
		24	snd $port, @msg;
		25	snd @msg_with_first_element_being_a_port;
14		26
15	$SELF # receiving/own port id in rcv callbacks	27	# creating/using ports, the simple way
		28	my $somple_port = port { my @msg = @_; 0 };
16		29
17	rcv $port, smartmatch => $cb->($port, @msg);	30	# creating/using ports, type matching
18		31	my $port = port;
19	# examples:
20	rcv $port2, ping => sub { snd $_[0], "pong"; 0 };	32	rcv $port, ping => sub { snd $_[0], "pong"; 0 };
21	rcv $port1, pong => sub { warn "pong received\n" };	33	rcv $port, pong => sub { warn "pong received\n"; 0 };
22	snd $port2, ping => $port1;
23		34
24	# more, smarter, matches (_any_ is exported by this module)	35	# create a port on another node
25	rcv $port, [child_died => $pid] => sub { ...	36	my $port = spawn $node, $initfunc, @initdata;
26	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3
27		37
28	# monitoring	38	# monitoring
29	mon $port, $cb->(@msg) # callback is invoked on death	39	mon $port, $cb->(@msg) # callback is invoked on death
30	mon $port, $otherport # kill otherport on abnormal death	40	mon $port, $otherport # kill otherport on abnormal death
31	mon $port, $otherport, @msg # send message on death	41	mon $port, $otherport, @msg # send message on death
32		42
		43	=head1 CURRENT STATUS
		44
		45	AnyEvent::MP - stable API, should work
		46	AnyEvent::MP::Intro - outdated
		47	AnyEvent::MP::Kernel - WIP
		48	AnyEvent::MP::Transport - mostly stable
		49
		50	stay tuned.
		51
33	=head1 DESCRIPTION	52	=head1 DESCRIPTION
34		53
35	This module (-family) implements a simple message passing framework.	54	This module (-family) implements a simple message passing framework.
36		55
37	Despite its simplicity, you can securely message other processes running	56	Despite its simplicity, you can securely message other processes running
…		…
40	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	59	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
41	manual page.	60	manual page.
42		61
43	At the moment, this module family is severly broken and underdocumented,	62	At the moment, this module family is severly broken and underdocumented,
44	so do not use. This was uploaded mainly to reserve the CPAN namespace -	63	so do not use. This was uploaded mainly to reserve the CPAN namespace -
45	stay tuned! The basic API should be finished, however.	64	stay tuned!
46		65
47	=head1 CONCEPTS	66	=head1 CONCEPTS
48		67
49	=over 4	68	=over 4
50		69
…		…
95		114
96	=cut	115	=cut
97		116
98	package AnyEvent::MP;	117	package AnyEvent::MP;
99		118
100	use AnyEvent::MP::Base;	119	use AnyEvent::MP::Kernel;
101		120
102	use common::sense;	121	use common::sense;
103		122
104	use Carp ();	123	use Carp ();
105		124
106	use AE ();	125	use AE ();
107		126
108	use base "Exporter";	127	use base "Exporter";
109		128
110	our $VERSION = '0.1';	129	our $VERSION = $AnyEvent::MP::Kernel::VERSION;
		130
111	our @EXPORT = qw(	131	our @EXPORT = qw(
112	NODE $NODE *SELF node_of _any_	132	NODE $NODE *SELF node_of _any_
113	resolve_node initialise_node	133	resolve_node initialise_node
114	snd rcv mon kil reg psub	134	snd rcv mon kil reg psub spawn
115	port	135	port
116	);	136	);
117		137
118	our $SELF;	138	our $SELF;
119		139
…		…
143	it should know the noderefs of some other nodes in the network.	163	it should know the noderefs of some other nodes in the network.
144		164
145	This function initialises a node - it must be called exactly once (or	165	This function initialises a node - it must be called exactly once (or
146	never) before calling other AnyEvent::MP functions.	166	never) before calling other AnyEvent::MP functions.
147		167
148	All arguments are noderefs, which can be either resolved or unresolved.	168	All arguments (optionally except for the first) are noderefs, which can be
		169	either resolved or unresolved.
		170
		171	The first argument will be looked up in the configuration database first
		172	(if it is C<undef> then the current nodename will be used instead) to find
		173	the relevant configuration profile (see L<aemp>). If none is found then
		174	the default configuration is used. The configuration supplies additional
		175	seed/master nodes and can override the actual noderef.
149		176
150	There are two types of networked nodes, public nodes and slave nodes:	177	There are two types of networked nodes, public nodes and slave nodes:
151		178
152	=over 4	179	=over 4
153		180
154	=item public nodes	181	=item public nodes
155		182
156	For public nodes, C<$noderef> must either be a (possibly unresolved)	183	For public nodes, C<$noderef> (supplied either directly to
157	noderef, in which case it will be resolved, or C<undef> (or missing), in	184	C<initialise_node> or indirectly via a profile or the nodename) must be a
158	which case the noderef will be guessed.	185	noderef (possibly unresolved, in which case it will be resolved).
159		186
160	Afterwards, the node will bind itself on all endpoints and try to connect	187	After resolving, the node will bind itself on all endpoints and try to
161	to all additional C<$seednodes> that are specified. Seednodes are optional	188	connect to all additional C<$seednodes> that are specified. Seednodes are
162	and can be used to quickly bootstrap the node into an existing network.	189	optional and can be used to quickly bootstrap the node into an existing
		190	network.
163		191
164	=item slave nodes	192	=item slave nodes
165		193
166	When the C<$noderef> is the special string C<slave/>, then the node will	194	When the C<$noderef> (either as given or overriden by the config file)
		195	is the special string C<slave/>, then the node will become a slave
167	become a slave node. Slave nodes cannot be contacted from outside and will	196	node. Slave nodes cannot be contacted from outside and will route most of
168	route most of their traffic to the master node that they attach to.	197	their traffic to the master node that they attach to.
169		198
170	At least one additional noderef is required: The node will try to connect	199	At least one additional noderef is required (either by specifying it
171	to all of them and will become a slave attached to the first node it can	200	directly or because it is part of the configuration profile): The node
172	successfully connect to.	201	will try to connect to all of them and will become a slave attached to the
		202	first node it can successfully connect to.
173		203
174	=back	204	=back
175		205
176	This function will block until all nodes have been resolved and, for slave	206	This function will block until all nodes have been resolved and, for slave
177	nodes, until it has successfully established a connection to a master	207	nodes, until it has successfully established a connection to a master
178	server.	208	server.
179		209
180	Example: become a public node listening on the default node.	210	Example: become a public node listening on the guessed noderef, or the one
		211	specified via C<aemp> for the current node. This should be the most common
		212	form of invocation for "daemon"-type nodes.
181		213
182	initialise_node;	214	initialise_node;
		215
		216	Example: become a slave node to any of the the seednodes specified via
		217	C<aemp>. This form is often used for commandline clients.
		218
		219	initialise_node "slave/";
		220
		221	Example: become a slave node to any of the specified master servers. This
		222	form is also often used for commandline clients.
		223
		224	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
183		225
184	Example: become a public node, and try to contact some well-known master	226	Example: become a public node, and try to contact some well-known master
185	servers to become part of the network.	227	servers to become part of the network.
186		228
187	initialise_node undef, "master1", "master2";	229	initialise_node undef, "master1", "master2";
…		…
190		232
191	initialise_node 4041;	233	initialise_node 4041;
192		234
193	Example: become a public node, only visible on localhost port 4044.	235	Example: become a public node, only visible on localhost port 4044.
194		236
195	initialise_node "locahost:4044";	237	initialise_node "localhost:4044";
196
197	Example: become a slave node to any of the specified master servers.
198
199	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
200		238
201	=item $cv = resolve_node $noderef	239	=item $cv = resolve_node $noderef
202		240
203	Takes an unresolved node reference that may contain hostnames and	241	Takes an unresolved node reference that may contain hostnames and
204	abbreviated IDs, resolves all of them and returns a resolved node	242	abbreviated IDs, resolves all of them and returns a resolved node
…		…
260	that Storable can serialise and deserialise is allowed, and for the local	298	that Storable can serialise and deserialise is allowed, and for the local
261	node, anything can be passed.	299	node, anything can be passed.
262		300
263	=item $local_port = port	301	=item $local_port = port
264		302
265	Create a new local port object that can be used either as a pattern	303	Create a new local port object and returns its port ID. Initially it has
266	matching port ("full port") or a single-callback port ("miniport"),	304	no callbacks set and will throw an error when it receives messages.
267	depending on how C<rcv> callbacks are bound to the object.
268		305
269	=item $port = port { my @msg = @_; $finished }	306	=item $local_port = port { my @msg = @_ }
270		307
271	Creates a "miniport", that is, a very lightweight port without any pattern	308	Creates a new local port, and returns its ID. Semantically the same as
272	matching behind it, and returns its ID. Semantically the same as creating
273	a port and calling C<rcv $port, $callback> on it.	309	creating a port and calling C<rcv $port, $callback> on it.
274		310
275	The block will be called for every message received on the port. When the	311	The block will be called for every message received on the port, with the
276	callback returns a true value its job is considered "done" and the port	312	global variable C<$SELF> set to the port ID. Runtime errors will cause the
277	will be destroyed. Otherwise it will stay alive.	313	port to be C<kil>ed. The message will be passed as-is, no extra argument
		314	(i.e. no port ID) will be passed to the callback.
278		315
279	The message will be passed as-is, no extra argument (i.e. no port id) will	316	If you want to stop/destroy the port, simply C<kil> it:
280	be passed to the callback.
281		317
282	If you need the local port id in the callback, this works nicely:	318	my $port = port {
283		319	my @msg = @_;
284	my $port; $port = port {	320	...
285	snd $otherport, reply => $port;	321	kil $SELF;
286	};	322	};
287		323
288	=cut	324	=cut
289		325
290	sub rcv($@);	326	sub rcv($@);
		327
		328	sub _kilme {
		329	die "received message on port without callback";
		330	}
291		331
292	sub port(;&) {	332	sub port(;&) {
293	my $id = "$UNIQ." . $ID++;	333	my $id = "$UNIQ." . $ID++;
294	my $port = "$NODE#$id";	334	my $port = "$NODE#$id";
295		335
296	if (@_) {	336	rcv $port, shift \|\| \&_kilme;
297	rcv $port, shift;
298	} else {
299	$PORT{$id} = sub { }; # nop
300	}
301		337
302	$port	338	$port
303	}	339	}
304		340
305	=item reg $port, $name
306
307	=item reg $name
308
309	Registers the given port (or C<$SELF><<< if missing) under the name
310	C<$name>. If the name already exists it is replaced.
311
312	A port can only be registered under one well known name.
313
314	A port automatically becomes unregistered when it is killed.
315
316	=cut
317
318	sub reg(@) {
319	my $port = @_ > 1 ? shift : $SELF \|\| Carp::croak 'reg: called with one argument only, but $SELF not set,';
320
321	$REG{$_[0]} = $port;
322	}
323
324	=item rcv $port, $callback->(@msg)	341	=item rcv $local_port, $callback->(@msg)
325		342
326	Replaces the callback on the specified miniport (after converting it to	343	Replaces the default callback on the specified port. There is no way to
327	one if required).	344	remove the default callback: use C<sub { }> to disable it, or better
328		345	C<kil> the port when it is no longer needed.
329	=item rcv $port, tagstring => $callback->(@msg), ...
330
331	=item rcv $port, $smartmatch => $callback->(@msg), ...
332
333	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
334
335	Register callbacks to be called on matching messages on the given full
336	port (after converting it to one if required) and return the port.
337
338	The callback has to return a true value when its work is done, after
339	which is will be removed, or a false value in which case it will stay
340	registered.
341		346
342	The global C<$SELF> (exported by this module) contains C<$port> while	347	The global C<$SELF> (exported by this module) contains C<$port> while
343	executing the callback.	348	executing the callback. Runtime errors during callback execution will
		349	result in the port being C<kil>ed.
344		350
345	Runtime errors wdurign callback execution will result in the port being	351	The default callback received all messages not matched by a more specific
346	C<kil>ed.	352	C<tag> match.
347		353
348	If the match is an array reference, then it will be matched against the	354	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
349	first elements of the message, otherwise only the first element is being
350	matched.
351		355
352	Any element in the match that is specified as C<_any_> (a function	356	Register callbacks to be called on messages starting with the given tag on
353	exported by this module) matches any single element of the message.	357	the given port (and return the port), or unregister it (when C<$callback>
		358	is C<$undef>).
354		359
355	While not required, it is highly recommended that the first matching	360	The original message will be passed to the callback, after the first
356	element is a string identifying the message. The one-string-only match is	361	element (the tag) has been removed. The callback will use the same
357	also the most efficient match (by far).	362	environment as the default callback (see above).
358		363
359	Example: create a port and bind receivers on it in one go.	364	Example: create a port and bind receivers on it in one go.
360		365
361	my $port = rcv port,	366	my $port = rcv port,
362	msg1 => sub { ...; 0 },	367	msg1 => sub { ... },
363	msg2 => sub { ...; 0 },	368	msg2 => sub { ... },
364	;	369	;
365		370
366	Example: create a port, bind receivers and send it in a message elsewhere	371	Example: create a port, bind receivers and send it in a message elsewhere
367	in one go:	372	in one go:
368		373
369	snd $otherport, reply =>	374	snd $otherport, reply =>
370	rcv port,	375	rcv port,
371	msg1 => sub { ...; 0 },	376	msg1 => sub { ... },
372	...	377	...
373	;	378	;
374		379
375	=cut	380	=cut
376		381
…		…
379	my ($noderef, $portid) = split /#/, $port, 2;	384	my ($noderef, $portid) = split /#/, $port, 2;
380		385
381	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	386	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}
382	or Carp::croak "$port: rcv can only be called on local ports, caught";	387	or Carp::croak "$port: rcv can only be called on local ports, caught";
383		388
384	if (@_ == 1) {	389	while (@_) {
		390	if (ref $_[0]) {
		391	if (my $self = $PORT_DATA{$portid}) {
		392	"AnyEvent::MP::Port" eq ref $self
		393	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		394
		395	$self->[2] = shift;
		396	} else {
385	my $cb = shift;	397	my $cb = shift;
386	delete $PORT_DATA{$portid};
387	$PORT{$portid} = sub {	398	$PORT{$portid} = sub {
388	local $SELF = $port;	399	local $SELF = $port;
389	eval {	400	eval { &$cb }; _self_die if $@;
390	&$cb	401	};
391	and kil $port;
392	};	402	}
393	_self_die if $@;	403	} elsif (defined $_[0]) {
394	};
395	} else {
396	my $self = $PORT_DATA{$portid} \|\|= do {	404	my $self = $PORT_DATA{$portid} \|\|= do {
397	my $self = bless {	405	my $self = bless [$PORT{$port} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
398	id => $port,
399	}, "AnyEvent::MP::Port";
400		406
401	$PORT{$portid} = sub {	407	$PORT{$portid} = sub {
402	local $SELF = $port;	408	local $SELF = $port;
403		409
404	eval {
405	for (@{ $self->{rc0}{$_[0]} }) {	410	if (my $cb = $self->[1]{$_[0]}) {
406	$_ && &{$_->[0]}	411	shift;
407	&& undef $_;	412	eval { &$cb }; _self_die if $@;
408	}	413	} else {
409
410	for (@{ $self->{rcv}{$_[0]} }) {
411	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
412	&& &{$_->[0]}	414	&{ $self->[0] };
413	&& undef $_;
414	}
415
416	for (@{ $self->{any} }) {
417	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
418	&& &{$_->[0]}
419	&& undef $_;
420	}	415	}
421	};	416	};
422	_self_die if $@;	417
		418	$self
423	};	419	};
424		420
425	$self
426	};
427
428	"AnyEvent::MP::Port" eq ref $self	421	"AnyEvent::MP::Port" eq ref $self
429	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	422	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
430		423
431	while (@_) {
432	my ($match, $cb) = splice @_, 0, 2;	424	my ($tag, $cb) = splice @_, 0, 2;
433		425
434	if (!ref $match) {	426	if (defined $cb) {
435	push @{ $self->{rc0}{$match} }, [$cb];	427	$self->[1]{$tag} = $cb;
436	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
437	my ($type, @match) = @$match;
438	@match
439	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
440	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
441	} else {	428	} else {
442	push @{ $self->{any} }, [$cb, $match];	429	delete $self->[1]{$tag};
443	}	430	}
444	}	431	}
445	}	432	}
446		433
447	$port	434	$port
…		…
491		478
492	=item $guard = mon $port	479	=item $guard = mon $port
493		480
494	=item $guard = mon $port, $rcvport, @msg	481	=item $guard = mon $port, $rcvport, @msg
495		482
496	Monitor the given port and do something when the port is killed, and	483	Monitor the given port and do something when the port is killed or
497	optionally return a guard that can be used to stop monitoring again.	484	messages to it were lost, and optionally return a guard that can be used
		485	to stop monitoring again.
		486
		487	C<mon> effectively guarantees that, in the absence of hardware failures,
		488	that after starting the monitor, either all messages sent to the port
		489	will arrive, or the monitoring action will be invoked after possible
		490	message loss has been detected. No messages will be lost "in between"
		491	(after the first lost message no further messages will be received by the
		492	port). After the monitoring action was invoked, further messages might get
		493	delivered again.
498		494
499	In the first form (callback), the callback is simply called with any	495	In the first form (callback), the callback is simply called with any
500	number of C<@reason> elements (no @reason means that the port was deleted	496	number of C<@reason> elements (no @reason means that the port was deleted
501	"normally"). Note also that I<< the callback B<must> never die >>, so use	497	"normally"). Note also that I<< the callback B<must> never die >>, so use
502	C<eval> if unsure.	498	C<eval> if unsure.
503		499
504	In the second form (another port given), the other port (C<$rcvport)	500	In the second form (another port given), the other port (C<$rcvport>)
505	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	501	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on
506	"normal" kils nothing happens, while under all other conditions, the other	502	"normal" kils nothing happens, while under all other conditions, the other
507	port is killed with the same reason.	503	port is killed with the same reason.
508		504
509	The third form (kill self) is the same as the second form, except that	505	The third form (kill self) is the same as the second form, except that
…		…
536	sub mon {	532	sub mon {
537	my ($noderef, $port) = split /#/, shift, 2;	533	my ($noderef, $port) = split /#/, shift, 2;
538		534
539	my $node = $NODE{$noderef} \|\| add_node $noderef;	535	my $node = $NODE{$noderef} \|\| add_node $noderef;
540		536
541	my $cb = @_ ? $_[0] : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';	537	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
542		538
543	unless (ref $cb) {	539	unless (ref $cb) {
544	if (@_) {	540	if (@_) {
545	# send a kill info message	541	# send a kill info message
546	my (@msg) = @_;	542	my (@msg) = ($cb, @_);
547	$cb = sub { snd @msg, @_ };	543	$cb = sub { snd @msg, @_ };
548	} else {	544	} else {
549	# simply kill other port	545	# simply kill other port
550	my $port = $cb;	546	my $port = $cb;
551	$cb = sub { kil $port, @_ if @_ };	547	$cb = sub { kil $port, @_ if @_ };
…		…
598	will be reported as reason C<< die => $@ >>.	594	will be reported as reason C<< die => $@ >>.
599		595
600	Transport/communication errors are reported as C<< transport_error =>	596	Transport/communication errors are reported as C<< transport_error =>
601	$message >>.	597	$message >>.
602		598
		599	=cut
		600
		601	=item $port = spawn $node, $initfunc[, @initdata]
		602
		603	Creates a port on the node C<$node> (which can also be a port ID, in which
		604	case it's the node where that port resides).
		605
		606	The port ID of the newly created port is return immediately, and it is
		607	permissible to immediately start sending messages or monitor the port.
		608
		609	After the port has been created, the init function is
		610	called. This function must be a fully-qualified function name
		611	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main
		612	program, use C<::name>.
		613
		614	If the function doesn't exist, then the node tries to C<require>
		615	the package, then the package above the package and so on (e.g.
		616	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		617	exists or it runs out of package names.
		618
		619	The init function is then called with the newly-created port as context
		620	object (C<$SELF>) and the C<@initdata> values as arguments.
		621
		622	A common idiom is to pass your own port, monitor the spawned port, and
		623	in the init function, monitor the original port. This two-way monitoring
		624	ensures that both ports get cleaned up when there is a problem.
		625
		626	Example: spawn a chat server port on C<$othernode>.
		627
		628	# this node, executed from within a port context:
		629	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		630	mon $server;
		631
		632	# init function on C<$othernode>
		633	sub connect {
		634	my ($srcport) = @_;
		635
		636	mon $srcport;
		637
		638	rcv $SELF, sub {
		639	...
		640	};
		641	}
		642
		643	=cut
		644
		645	sub _spawn {
		646	my $port = shift;
		647	my $init = shift;
		648
		649	local $SELF = "$NODE#$port";
		650	eval {
		651	&{ load_func $init }
		652	};
		653	_self_die if $@;
		654	}
		655
		656	sub spawn(@) {
		657	my ($noderef, undef) = split /#/, shift, 2;
		658
		659	my $id = "$RUNIQ." . $ID++;
		660
		661	$_[0] =~ /::/
		662	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		663
		664	($NODE{$noderef} \|\| add_node $noderef)
		665	->send (["", "AnyEvent::MP::_spawn" => $id, @_]);
		666
		667	"$noderef#$id"
		668	}
		669
603	=back	670	=back
604		671
605	=head1 NODE MESSAGES	672	=head1 NODE MESSAGES
606		673
607	Nodes understand the following messages sent to them. Many of them take	674	Nodes understand the following messages sent to them. Many of them take
…		…
671	convenience functionality.	738	convenience functionality.
672		739
673	This means that AEMP requires a less tightly controlled environment at the	740	This means that AEMP requires a less tightly controlled environment at the
674	cost of longer node references and a slightly higher management overhead.	741	cost of longer node references and a slightly higher management overhead.
675		742
		743	=item Erlang has a "remote ports are like local ports" philosophy, AEMP
		744	uses "local ports are like remote ports".
		745
		746	The failure modes for local ports are quite different (runtime errors
		747	only) then for remote ports - when a local port dies, you I<know> it dies,
		748	when a connection to another node dies, you know nothing about the other
		749	port.
		750
		751	Erlang pretends remote ports are as reliable as local ports, even when
		752	they are not.
		753
		754	AEMP encourages a "treat remote ports differently" philosophy, with local
		755	ports being the special case/exception, where transport errors cannot
		756	occur.
		757
676	=item * Erlang uses processes and a mailbox, AEMP does not queue.	758	=item * Erlang uses processes and a mailbox, AEMP does not queue.
677		759
678	Erlang uses processes that selctively receive messages, and therefore	760	Erlang uses processes that selectively receive messages, and therefore
679	needs a queue. AEMP is event based, queuing messages would serve no useful	761	needs a queue. AEMP is event based, queuing messages would serve no
680	purpose.	762	useful purpose. For the same reason the pattern-matching abilities of
		763	AnyEvent::MP are more limited, as there is little need to be able to
		764	filter messages without dequeing them.
681		765
682	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	766	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).
683		767
684	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	768	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
685		769
686	Sending messages in Erlang is synchronous and blocks the process. AEMP	770	Sending messages in Erlang is synchronous and blocks the process (and
687	sends are immediate, connection establishment is handled in the	771	so does not need a queue that can overflow). AEMP sends are immediate,
688	background.	772	connection establishment is handled in the background.
689		773
690	=item * Erlang can silently lose messages, AEMP cannot.	774	=item * Erlang suffers from silent message loss, AEMP does not.
691		775
692	Erlang makes few guarantees on messages delivery - messages can get lost	776	Erlang makes few guarantees on messages delivery - messages can get lost
693	without any of the processes realising it (i.e. you send messages a, b,	777	without any of the processes realising it (i.e. you send messages a, b,
694	and c, and the other side only receives messages a and c).	778	and c, and the other side only receives messages a and c).
695		779
…		…
707	eventually be killed - it cannot happen that a node detects a port as dead	791	eventually be killed - it cannot happen that a node detects a port as dead
708	and then later sends messages to it, finding it is still alive.	792	and then later sends messages to it, finding it is still alive.
709		793
710	=item * Erlang can send messages to the wrong port, AEMP does not.	794	=item * Erlang can send messages to the wrong port, AEMP does not.
711		795
712	In Erlang it is quite possible that a node that restarts reuses a process	796	In Erlang it is quite likely that a node that restarts reuses a process ID
713	ID known to other nodes for a completely different process, causing	797	known to other nodes for a completely different process, causing messages
714	messages destined for that process to end up in an unrelated process.	798	destined for that process to end up in an unrelated process.
715		799
716	AEMP never reuses port IDs, so old messages or old port IDs floating	800	AEMP never reuses port IDs, so old messages or old port IDs floating
717	around in the network will not be sent to an unrelated port.	801	around in the network will not be sent to an unrelated port.
718		802
719	=item * Erlang uses unprotected connections, AEMP uses secure	803	=item * Erlang uses unprotected connections, AEMP uses secure
…		…
755	This also saves round-trips and avoids sending messages to the wrong port	839	This also saves round-trips and avoids sending messages to the wrong port
756	(hard to do in Erlang).	840	(hard to do in Erlang).
757		841
758	=back	842	=back
759		843
		844	=head1 RATIONALE
		845
		846	=over 4
		847
		848	=item Why strings for ports and noderefs, why not objects?
		849
		850	We considered "objects", but found that the actual number of methods
		851	thatc an be called are very low. Since port IDs and noderefs travel over
		852	the network frequently, the serialising/deserialising would add lots of
		853	overhead, as well as having to keep a proxy object.
		854
		855	Strings can easily be printed, easily serialised etc. and need no special
		856	procedures to be "valid".
		857
		858	And a a miniport consists of a single closure stored in a global hash - it
		859	can't become much cheaper.
		860
		861	=item Why favour JSON, why not real serialising format such as Storable?
		862
		863	In fact, any AnyEvent::MP node will happily accept Storable as framing
		864	format, but currently there is no way to make a node use Storable by
		865	default.
		866
		867	The default framing protocol is JSON because a) JSON::XS is many times
		868	faster for small messages and b) most importantly, after years of
		869	experience we found that object serialisation is causing more problems
		870	than it gains: Just like function calls, objects simply do not travel
		871	easily over the network, mostly because they will always be a copy, so you
		872	always have to re-think your design.
		873
		874	Keeping your messages simple, concentrating on data structures rather than
		875	objects, will keep your messages clean, tidy and efficient.
		876
		877	=back
		878
760	=head1 SEE ALSO	879	=head1 SEE ALSO
761		880
762	L<AnyEvent>.	881	L<AnyEvent>.
763		882
764	=head1 AUTHOR	883	=head1 AUTHOR

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Revision 1.37 by root, Fri Aug 7 16:47:23 2009 UTC vs.
Revision 1.51 by root, Fri Aug 14 14:07:44 2009 UTC