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

Comparing cvsroot/AnyEvent-MP/MP.pm (file contents):
Revision 1.33 by root, Wed Aug 5 22:40:51 2009 UTC vs.
Revision 1.49 by root, Thu Aug 13 15:29:58 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 miniports
		28	my $miniport = port { my @msg = @_; 0 };
16		29
		30	# creating/using full ports
		31	my $port = port;
17	rcv $port, smartmatch => $cb->($port, @msg);	32	rcv $port, smartmatch => $cb->(@msg);
18
19	# examples:
20	rcv $port2, ping => sub { snd $_[0], "pong"; 0 };	33	rcv $port, ping => sub { snd $_[0], "pong"; 0 };
21	rcv $port1, pong => sub { warn "pong received\n" };	34	rcv $port, pong => sub { warn "pong received\n"; 0 };
22	snd $port2, ping => $port1;
23		35
24	# more, smarter, matches (_any_ is exported by this module)	36	# more, smarter, matches (_any_ is exported by this module)
25	rcv $port, [child_died => $pid] => sub { ...	37	rcv $port, [child_died => $pid] => sub { ...
26	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3	38	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3
27		39
		40	# create a port on another node
		41	my $port = spawn $node, $initfunc, @initdata;
		42
		43	# monitoring
		44	mon $port, $cb->(@msg) # callback is invoked on death
		45	mon $port, $otherport # kill otherport on abnormal death
		46	mon $port, $otherport, @msg # send message on death
		47
		48	=head1 CURRENT STATUS
		49
		50	AnyEvent::MP - stable API, should work
		51	AnyEvent::MP::Intro - outdated
		52	AnyEvent::MP::Kernel - WIP
		53	AnyEvent::MP::Transport - mostly stable
		54
		55	stay tuned.
		56
28	=head1 DESCRIPTION	57	=head1 DESCRIPTION
29		58
30	This module (-family) implements a simple message passing framework.	59	This module (-family) implements a simple message passing framework.
31		60
32	Despite its simplicity, you can securely message other processes running	61	Despite its simplicity, you can securely message other processes running
…		…
35	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	64	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
36	manual page.	65	manual page.
37		66
38	At the moment, this module family is severly broken and underdocumented,	67	At the moment, this module family is severly broken and underdocumented,
39	so do not use. This was uploaded mainly to reserve the CPAN namespace -	68	so do not use. This was uploaded mainly to reserve the CPAN namespace -
40	stay tuned! The basic API should be finished, however.	69	stay tuned!
41		70
42	=head1 CONCEPTS	71	=head1 CONCEPTS
43		72
44	=over 4	73	=over 4
45		74
…		…
90		119
91	=cut	120	=cut
92		121
93	package AnyEvent::MP;	122	package AnyEvent::MP;
94		123
95	use AnyEvent::MP::Base;	124	use AnyEvent::MP::Kernel;
96		125
97	use common::sense;	126	use common::sense;
98		127
99	use Carp ();	128	use Carp ();
100		129
101	use AE ();	130	use AE ();
102		131
103	use base "Exporter";	132	use base "Exporter";
104		133
105	our $VERSION = '0.1';	134	our $VERSION = $AnyEvent::MP::Kernel::VERSION;
		135
106	our @EXPORT = qw(	136	our @EXPORT = qw(
107	NODE $NODE *SELF node_of _any_	137	NODE $NODE *SELF node_of _any_
108	resolve_node initialise_node	138	resolve_node initialise_node
109	snd rcv mon kil reg psub	139	snd rcv mon kil reg psub spawn
110	port	140	port
111	);	141	);
112		142
113	our $SELF;	143	our $SELF;
114		144
…		…
127		157
128	=item $noderef = node_of $port	158	=item $noderef = node_of $port
129		159
130	Extracts and returns the noderef from a portid or a noderef.	160	Extracts and returns the noderef from a portid or a noderef.
131		161
		162	=item initialise_node $noderef, $seednode, $seednode...
		163
		164	=item initialise_node "slave/", $master, $master...
		165
		166	Before a node can talk to other nodes on the network it has to initialise
		167	itself - the minimum a node needs to know is it's own name, and optionally
		168	it should know the noderefs of some other nodes in the network.
		169
		170	This function initialises a node - it must be called exactly once (or
		171	never) before calling other AnyEvent::MP functions.
		172
		173	All arguments (optionally except for the first) are noderefs, which can be
		174	either resolved or unresolved.
		175
		176	The first argument will be looked up in the configuration database first
		177	(if it is C<undef> then the current nodename will be used instead) to find
		178	the relevant configuration profile (see L<aemp>). If none is found then
		179	the default configuration is used. The configuration supplies additional
		180	seed/master nodes and can override the actual noderef.
		181
		182	There are two types of networked nodes, public nodes and slave nodes:
		183
		184	=over 4
		185
		186	=item public nodes
		187
		188	For public nodes, C<$noderef> (supplied either directly to
		189	C<initialise_node> or indirectly via a profile or the nodename) must be a
		190	noderef (possibly unresolved, in which case it will be resolved).
		191
		192	After resolving, the node will bind itself on all endpoints and try to
		193	connect to all additional C<$seednodes> that are specified. Seednodes are
		194	optional and can be used to quickly bootstrap the node into an existing
		195	network.
		196
		197	=item slave nodes
		198
		199	When the C<$noderef> (either as given or overriden by the config file)
		200	is the special string C<slave/>, then the node will become a slave
		201	node. Slave nodes cannot be contacted from outside and will route most of
		202	their traffic to the master node that they attach to.
		203
		204	At least one additional noderef is required (either by specifying it
		205	directly or because it is part of the configuration profile): The node
		206	will try to connect to all of them and will become a slave attached to the
		207	first node it can successfully connect to.
		208
		209	=back
		210
		211	This function will block until all nodes have been resolved and, for slave
		212	nodes, until it has successfully established a connection to a master
		213	server.
		214
		215	Example: become a public node listening on the guessed noderef, or the one
		216	specified via C<aemp> for the current node. This should be the most common
		217	form of invocation for "daemon"-type nodes.
		218
		219	initialise_node;
		220
		221	Example: become a slave node to any of the the seednodes specified via
		222	C<aemp>. This form is often used for commandline clients.
		223
		224	initialise_node "slave/";
		225
		226	Example: become a slave node to any of the specified master servers. This
		227	form is also often used for commandline clients.
		228
		229	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
		230
		231	Example: become a public node, and try to contact some well-known master
		232	servers to become part of the network.
		233
		234	initialise_node undef, "master1", "master2";
		235
		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
132	=item $cv = resolve_node $noderef	244	=item $cv = resolve_node $noderef
133		245
134	Takes an unresolved node reference that may contain hostnames and	246	Takes an unresolved node reference that may contain hostnames and
135	abbreviated IDs, resolves all of them and returns a resolved node	247	abbreviated IDs, resolves all of them and returns a resolved node
136	reference.	248	reference.
…		…
233	$port	345	$port
234	}	346	}
235		347
236	=item reg $port, $name	348	=item reg $port, $name
237		349
238	Registers the given port under the name C<$name>. If the name already	350	=item reg $name
239	exists it is replaced.	351
		352	Registers the given port (or C<$SELF><<< if missing) under the name
		353	C<$name>. If the name already exists it is replaced.
240		354
241	A port can only be registered under one well known name.	355	A port can only be registered under one well known name.
242		356
243	A port automatically becomes unregistered when it is killed.	357	A port automatically becomes unregistered when it is killed.
244		358
245	=cut	359	=cut
246		360
247	sub reg(@) {	361	sub reg(@) {
248	my ($port, $name) = @_;	362	my $port = @_ > 1 ? shift : $SELF \|\| Carp::croak 'reg: called with one argument only, but $SELF not set,';
249		363
250	$REG{$name} = $port;	364	$REG{$_[0]} = $port;
251	}	365	}
252		366
253	=item rcv $port, $callback->(@msg)	367	=item rcv $port, $callback->(@msg)
254		368
255	Replaces the callback on the specified miniport (after converting it to	369	Replaces the callback on the specified miniport (after converting it to
…		…
260	=item rcv $port, $smartmatch => $callback->(@msg), ...	374	=item rcv $port, $smartmatch => $callback->(@msg), ...
261		375
262	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...	376	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
263		377
264	Register callbacks to be called on matching messages on the given full	378	Register callbacks to be called on matching messages on the given full
265	port (after converting it to one if required).	379	port (after converting it to one if required) and return the port.
266		380
267	The callback has to return a true value when its work is done, after	381	The callback has to return a true value when its work is done, after
268	which is will be removed, or a false value in which case it will stay	382	which is will be removed, or a false value in which case it will stay
269	registered.	383	registered.
270		384
271	The global C<$SELF> (exported by this module) contains C<$port> while	385	The global C<$SELF> (exported by this module) contains C<$port> while
272	executing the callback.	386	executing the callback.
273		387
274	Runtime errors wdurign callback execution will result in the port being	388	Runtime errors during callback execution will result in the port being
275	C<kil>ed.	389	C<kil>ed.
276		390
277	If the match is an array reference, then it will be matched against the	391	If the match is an array reference, then it will be matched against the
278	first elements of the message, otherwise only the first element is being	392	first elements of the message, otherwise only the first element is being
279	matched.	393	matched.
…		…
282	exported by this module) matches any single element of the message.	396	exported by this module) matches any single element of the message.
283		397
284	While not required, it is highly recommended that the first matching	398	While not required, it is highly recommended that the first matching
285	element is a string identifying the message. The one-string-only match is	399	element is a string identifying the message. The one-string-only match is
286	also the most efficient match (by far).	400	also the most efficient match (by far).
		401
		402	Example: create a port and bind receivers on it in one go.
		403
		404	my $port = rcv port,
		405	msg1 => sub { ...; 0 },
		406	msg2 => sub { ...; 0 },
		407	;
		408
		409	Example: create a port, bind receivers and send it in a message elsewhere
		410	in one go:
		411
		412	snd $otherport, reply =>
		413	rcv port,
		414	msg1 => sub { ...; 0 },
		415	...
		416	;
287		417
288	=cut	418	=cut
289		419
290	sub rcv($@) {	420	sub rcv($@) {
291	my $port = shift;	421	my $port = shift;
…		…
398	}	528	}
399	}	529	}
400		530
401	=item $guard = mon $port, $cb->(@reason)	531	=item $guard = mon $port, $cb->(@reason)
402		532
403	=item $guard = mon $port, $otherport	533	=item $guard = mon $port, $rcvport
404		534
		535	=item $guard = mon $port
		536
405	=item $guard = mon $port, $otherport, @msg	537	=item $guard = mon $port, $rcvport, @msg
406		538
407	Monitor the given port and do something when the port is killed.	539	Monitor the given port and do something when the port is killed or
		540	messages to it were lost, and optionally return a guard that can be used
		541	to stop monitoring again.
408		542
		543	C<mon> effectively guarantees that, in the absence of hardware failures,
		544	that after starting the monitor, either all messages sent to the port
		545	will arrive, or the monitoring action will be invoked after possible
		546	message loss has been detected. No messages will be lost "in between"
		547	(after the first lost message no further messages will be received by the
		548	port). After the monitoring action was invoked, further messages might get
		549	delivered again.
		550
409	In the first form, the callback is simply called with any number	551	In the first form (callback), the callback is simply called with any
410	of C<@reason> elements (no @reason means that the port was deleted	552	number of C<@reason> elements (no @reason means that the port was deleted
411	"normally"). Note also that I<< the callback B<must> never die >>, so use	553	"normally"). Note also that I<< the callback B<must> never die >>, so use
412	C<eval> if unsure.	554	C<eval> if unsure.
413		555
414	In the second form, the other port will be C<kil>'ed with C<@reason>, iff	556	In the second form (another port given), the other port (C<$rcvport>)
415	a @reason was specified, i.e. on "normal" kils nothing happens, while	557	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on
416	under all other conditions, the other port is killed with the same reason.	558	"normal" kils nothing happens, while under all other conditions, the other
		559	port is killed with the same reason.
417		560
		561	The third form (kill self) is the same as the second form, except that
		562	C<$rvport> defaults to C<$SELF>.
		563
418	In the last form, a message of the form C<@msg, @reason> will be C<snd>.	564	In the last form (message), a message of the form C<@msg, @reason> will be
		565	C<snd>.
		566
		567	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
		569	lost, just like any other message. Another less obvious reason is that
		570	even monitoring requests can get lost (for exmaple, when the connection
		571	to the other node goes down permanently). When monitoring a port locally
		572	these problems do not exist.
419		573
420	Example: call a given callback when C<$port> is killed.	574	Example: call a given callback when C<$port> is killed.
421		575
422	mon $port, sub { warn "port died because of <@_>\n" };	576	mon $port, sub { warn "port died because of <@_>\n" };
423		577
424	Example: kill ourselves when C<$port> is killed abnormally.	578	Example: kill ourselves when C<$port> is killed abnormally.
425		579
426	mon $port, $self;	580	mon $port;
427		581
428	Example: send us a restart message another C<$port> is killed.	582	Example: send us a restart message when another C<$port> is killed.
429		583
430	mon $port, $self => "restart";	584	mon $port, $self => "restart";
431		585
432	=cut	586	=cut
433		587
434	sub mon {	588	sub mon {
435	my ($noderef, $port) = split /#/, shift, 2;	589	my ($noderef, $port) = split /#/, shift, 2;
436		590
437	my $node = $NODE{$noderef} \|\| add_node $noderef;	591	my $node = $NODE{$noderef} \|\| add_node $noderef;
438		592
439	my $cb = shift;	593	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
440		594
441	unless (ref $cb) {	595	unless (ref $cb) {
442	if (@_) {	596	if (@_) {
443	# send a kill info message	597	# send a kill info message
444	my (@msg) = ($cb, @_);	598	my (@msg) = ($cb, @_);
…		…
475	=cut	629	=cut
476		630
477	sub mon_guard {	631	sub mon_guard {
478	my ($port, @refs) = @_;	632	my ($port, @refs) = @_;
479		633
		634	#TODO: mon-less form?
		635
480	mon $port, sub { 0 && @refs }	636	mon $port, sub { 0 && @refs }
481	}	637	}
482		638
483	=item lnk $port1, $port2
484
485	Link two ports. This is simply a shorthand for:
486
487	mon $port1, $port2;
488	mon $port2, $port1;
489
490	It means that if either one is killed abnormally, the other one gets
491	killed as well.
492
493	=item kil $port[, @reason]	639	=item kil $port[, @reason]
494		640
495	Kill the specified port with the given C<@reason>.	641	Kill the specified port with the given C<@reason>.
496		642
497	If no C<@reason> is specified, then the port is killed "normally" (linked	643	If no C<@reason> is specified, then the port is killed "normally" (linked
…		…
504	will be reported as reason C<< die => $@ >>.	650	will be reported as reason C<< die => $@ >>.
505		651
506	Transport/communication errors are reported as C<< transport_error =>	652	Transport/communication errors are reported as C<< transport_error =>
507	$message >>.	653	$message >>.
508		654
509	=back
510
511	=head1 FUNCTIONS FOR NODES
512
513	=over 4
514
515	=item initialise_node $noderef, $seednode, $seednode...
516
517	=item initialise_node "slave/", $master, $master...
518
519	Initialises a node - must be called exactly once before calling other
520	AnyEvent::MP functions when talking to other nodes is required.
521
522	All arguments are noderefs, which can be either resolved or unresolved.
523
524	There are two types of networked nodes, public nodes and slave nodes:
525
526	=over 4
527
528	=item public nodes
529
530	For public nodes, C<$noderef> must either be a (possibly unresolved)
531	noderef, in which case it will be resolved, or C<undef> (or missing), in
532	which case the noderef will be guessed.
533
534	Afterwards, the node will bind itself on all endpoints and try to connect
535	to all additional C<$seednodes> that are specified. Seednodes are optional
536	and can be used to quickly bootstrap the node into an existing network.
537
538	=item slave nodes
539
540	When the C<$noderef> is the special string C<slave/>, then the node will
541	become a slave node. Slave nodes cannot be contacted from outside and will
542	route most of their traffic to the master node that they attach to.
543
544	At least one additional noderef is required: The node will try to connect
545	to all of them and will become a slave attached to the first node it can
546	successfully connect to.
547
548	=back
549
550	This function will block until all nodes have been resolved and, for slave
551	nodes, until it has successfully established a connection to a master
552	server.
553
554	Example: become a public node listening on the default node.
555
556	initialise_node;
557
558	Example: become a public node, and try to contact some well-known master
559	servers to become part of the network.
560
561	initialise_node undef, "master1", "master2";
562
563	Example: become a public node listening on port C<4041>.
564
565	initialise_node 4041;
566
567	Example: become a public node, only visible on localhost port 4044.
568
569	initialise_node "locahost:4044";
570
571	Example: become a slave node to any of the specified master servers.
572
573	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
574
575	=cut	655	=cut
		656
		657	=item $port = spawn $node, $initfunc[, @initdata]
		658
		659	Creates a port on the node C<$node> (which can also be a port ID, in which
		660	case it's the node where that port resides).
		661
		662	The port ID of the newly created port is return immediately, and it is
		663	permissible to immediately start sending messages or monitor the port.
		664
		665	After the port has been created, the init function is
		666	called. This function must be a fully-qualified function name
		667	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main
		668	program, use C<::name>.
		669
		670	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.
		672	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		673	exists or it runs out of package names.
		674
		675	The init function is then called with the newly-created port as context
		676	object (C<$SELF>) and the C<@initdata> values as arguments.
		677
		678	A common idiom is to pass your own port, monitor the spawned port, and
		679	in the init function, monitor the original port. This two-way monitoring
		680	ensures that both ports get cleaned up when there is a problem.
		681
		682	Example: spawn a chat server port on C<$othernode>.
		683
		684	# this node, executed from within a port context:
		685	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		686	mon $server;
		687
		688	# init function on C<$othernode>
		689	sub connect {
		690	my ($srcport) = @_;
		691
		692	mon $srcport;
		693
		694	rcv $SELF, sub {
		695	...
		696	};
		697	}
		698
		699	=cut
		700
		701	sub _spawn {
		702	my $port = shift;
		703	my $init = shift;
		704
		705	local $SELF = "$NODE#$port";
		706	eval {
		707	&{ load_func $init }
		708	};
		709	_self_die if $@;
		710	}
		711
		712	sub spawn(@) {
		713	my ($noderef, undef) = split /#/, shift, 2;
		714
		715	my $id = "$RUNIQ." . $ID++;
		716
		717	$_[0] =~ /::/
		718	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		719
		720	($NODE{$noderef} \|\| add_node $noderef)
		721	->send (["", "AnyEvent::MP::_spawn" => $id, @_]);
		722
		723	"$noderef#$id"
		724	}
576		725
577	=back	726	=back
578		727
579	=head1 NODE MESSAGES	728	=head1 NODE MESSAGES
580		729
…		…
622		771
623	=back	772	=back
624		773
625	=head1 AnyEvent::MP vs. Distributed Erlang	774	=head1 AnyEvent::MP vs. Distributed Erlang
626		775
627	AnyEvent::MP got lots of its ideas from distributed erlang (erlang node	776	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
628	== aemp node, erlang process == aemp port), so many of the documents and	777	== aemp node, Erlang process == aemp port), so many of the documents and
629	programming techniques employed by erlang apply to AnyEvent::MP. Here is a	778	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
630	sample:	779	sample:
631		780
632	http://www.erlang.se/doc/programming_rules.shtml	781	http://www.Erlang.se/doc/programming_rules.shtml
633	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	782	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
634	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6	783	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6
635	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	784	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
636		785
637	Despite the similarities, there are also some important differences:	786	Despite the similarities, there are also some important differences:
638		787
639	=over 4	788	=over 4
640		789
…		…
651		800
652	Erlang uses processes that selctively receive messages, and therefore	801	Erlang uses processes that selctively receive messages, and therefore
653	needs a queue. AEMP is event based, queuing messages would serve no useful	802	needs a queue. AEMP is event based, queuing messages would serve no useful
654	purpose.	803	purpose.
655		804
656	(But see L<Coro::MP> for a more erlang-like process model on top of AEMP).	805	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).
657		806
658	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	807	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
659		808
660	Sending messages in erlang is synchronous and blocks the process. AEMP	809	Sending messages in Erlang is synchronous and blocks the process. AEMP
661	sends are immediate, connection establishment is handled in the	810	sends are immediate, connection establishment is handled in the
662	background.	811	background.
663		812
664	=item * Erlang can silently lose messages, AEMP cannot.	813	=item * Erlang can silently lose messages, AEMP cannot.
665		814
…		…
668	and c, and the other side only receives messages a and c).	817	and c, and the other side only receives messages a and c).
669		818
670	AEMP guarantees correct ordering, and the guarantee that there are no	819	AEMP guarantees correct ordering, and the guarantee that there are no
671	holes in the message sequence.	820	holes in the message sequence.
672		821
673	=item * In erlang, processes can be declared dead and later be found to be	822	=item * In Erlang, processes can be declared dead and later be found to be
674	alive.	823	alive.
675		824
676	In erlang it can happen that a monitored process is declared dead and	825	In Erlang it can happen that a monitored process is declared dead and
677	linked processes get killed, but later it turns out that the process is	826	linked processes get killed, but later it turns out that the process is
678	still alive - and can receive messages.	827	still alive - and can receive messages.
679		828
680	In AEMP, when port monitoring detects a port as dead, then that port will	829	In AEMP, when port monitoring detects a port as dead, then that port will
681	eventually be killed - it cannot happen that a node detects a port as dead	830	eventually be killed - it cannot happen that a node detects a port as dead
682	and then later sends messages to it, finding it is still alive.	831	and then later sends messages to it, finding it is still alive.
683		832
684	=item * Erlang can send messages to the wrong port, AEMP does not.	833	=item * Erlang can send messages to the wrong port, AEMP does not.
685		834
686	In erlang it is quite possible that a node that restarts reuses a process	835	In Erlang it is quite possible that a node that restarts reuses a process
687	ID known to other nodes for a completely different process, causing	836	ID known to other nodes for a completely different process, causing
688	messages destined for that process to end up in an unrelated process.	837	messages destined for that process to end up in an unrelated process.
689		838
690	AEMP never reuses port IDs, so old messages or old port IDs floating	839	AEMP never reuses port IDs, so old messages or old port IDs floating
691	around in the network will not be sent to an unrelated port.	840	around in the network will not be sent to an unrelated port.
…		…
697	securely authenticate nodes.	846	securely authenticate nodes.
698		847
699	=item * The AEMP protocol is optimised for both text-based and binary	848	=item * The AEMP protocol is optimised for both text-based and binary
700	communications.	849	communications.
701		850
702	The AEMP protocol, unlike the erlang protocol, supports both	851	The AEMP protocol, unlike the Erlang protocol, supports both
703	language-independent text-only protocols (good for debugging) and binary,	852	language-independent text-only protocols (good for debugging) and binary,
704	language-specific serialisers (e.g. Storable).	853	language-specific serialisers (e.g. Storable).
705		854
706	It has also been carefully designed to be implementable in other languages	855	It has also been carefully designed to be implementable in other languages
707	with a minimum of work while gracefully degrading fucntionality to make the	856	with a minimum of work while gracefully degrading fucntionality to make the
708	protocol simple.	857	protocol simple.
709		858
		859	=item * AEMP has more flexible monitoring options than Erlang.
		860
		861	In Erlang, you can chose to receive I<all> exit signals as messages
		862	or I<none>, there is no in-between, so monitoring single processes is
		863	difficult to implement. Monitoring in AEMP is more flexible than in
		864	Erlang, as one can choose between automatic kill, exit message or callback
		865	on a per-process basis.
		866
		867	=item * Erlang tries to hide remote/local connections, AEMP does not.
		868
		869	Monitoring in Erlang is not an indicator of process death/crashes,
		870	as linking is (except linking is unreliable in Erlang).
		871
		872	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
		874	on the remote node. The init function monitors the you, and you monitor
		875	the remote port. Since both monitors are local to the node, they are much
		876	more reliable.
		877
		878	This also saves round-trips and avoids sending messages to the wrong port
		879	(hard to do in Erlang).
		880
		881	=back
		882
		883	=head1 RATIONALE
		884
		885	=over 4
		886
		887	=item Why strings for ports and noderefs, why not objects?
		888
		889	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
		891	the network frequently, the serialising/deserialising would add lots of
		892	overhead, as well as having to keep a proxy object.
		893
		894	Strings can easily be printed, easily serialised etc. and need no special
		895	procedures to be "valid".
		896
		897	And a a miniport consists of a single closure stored in a global hash - it
		898	can't become much cheaper.
		899
		900	=item Why favour JSON, why not real serialising format such as Storable?
		901
		902	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
		904	default.
		905
		906	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
		908	experience we found that object serialisation is causing more problems
		909	than it gains: Just like function calls, objects simply do not travel
		910	easily over the network, mostly because they will always be a copy, so you
		911	always have to re-think your design.
		912
		913	Keeping your messages simple, concentrating on data structures rather than
		914	objects, will keep your messages clean, tidy and efficient.
		915
710	=back	916	=back
711		917
712	=head1 SEE ALSO	918	=head1 SEE ALSO
713		919
714	L<AnyEvent>.	920	L<AnyEvent>.

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Revision 1.49 by root, Thu Aug 13 15:29:58 2009 UTC