[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 1.48 by root, Thu Aug 13 02:59:42 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		51	AnyEvent::MP::Intro - outdated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, $master...
		165
		166	Before a node can talk to other nodes on the network it has to initialise
		167	itself - the minimum a node needs to know is it's own name, and optionally
		168	it should know the noderefs of some other nodes in the network.
		169
		170	This function initialises a node - it must be called exactly once (or
		171	never) before calling other AnyEvent::MP functions.
		172
		173	All arguments are noderefs, which can be either resolved or unresolved.
		174
		175	There are two types of networked nodes, public nodes and slave nodes:
		176
		177	=over 4
		178
		179	=item public nodes
		180
		181	For public nodes, C<$noderef> must either be a (possibly unresolved)
		182	noderef, in which case it will be resolved, or C<undef> (or missing), in
		183	which case the noderef will be guessed.
		184
		185	Afterwards, the node will bind itself on all endpoints and try to connect
		186	to all additional C<$seednodes> that are specified. Seednodes are optional
		187	and can be used to quickly bootstrap the node into an existing network.
		188
		189	=item slave nodes
		190
		191	When the C<$noderef> is the special string C<slave/>, then the node will
		192	become a slave node. Slave nodes cannot be contacted from outside and will
		193	route most of their traffic to the master node that they attach to.
		194
		195	At least one additional noderef is required: The node will try to connect
		196	to all of them and will become a slave attached to the first node it can
		197	successfully connect to.
		198
		199	=back
		200
		201	This function will block until all nodes have been resolved and, for slave
		202	nodes, until it has successfully established a connection to a master
		203	server.
		204
		205	Example: become a public node listening on the default node.
		206
		207	initialise_node;
		208
		209	Example: become a public node, and try to contact some well-known master
		210	servers to become part of the network.
		211
		212	initialise_node undef, "master1", "master2";
		213
		214	Example: become a public node listening on port C<4041>.
		215
		216	initialise_node 4041;
		217
		218	Example: become a public node, only visible on localhost port 4044.
		219
		220	initialise_node "locahost:4044";
		221
		222	Example: become a slave node to any of the specified master servers.
		223
		224	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
		225
132	=item $cv = resolve_node $noderef	226	=item $cv = resolve_node $noderef
133		227
134	Takes an unresolved node reference that may contain hostnames and	228	Takes an unresolved node reference that may contain hostnames and
135	abbreviated IDs, resolves all of them and returns a resolved node	229	abbreviated IDs, resolves all of them and returns a resolved node
136	reference.	230	reference.
…		…
233	$port	327	$port
234	}	328	}
235		329
236	=item reg $port, $name	330	=item reg $port, $name
237		331
238	Registers the given port under the name C<$name>. If the name already	332	=item reg $name
239	exists it is replaced.	333
		334	Registers the given port (or C<$SELF><<< if missing) under the name
		335	C<$name>. If the name already exists it is replaced.
240		336
241	A port can only be registered under one well known name.	337	A port can only be registered under one well known name.
242		338
243	A port automatically becomes unregistered when it is killed.	339	A port automatically becomes unregistered when it is killed.
244		340
245	=cut	341	=cut
246		342
247	sub reg(@) {	343	sub reg(@) {
248	my ($port, $name) = @_;	344	my $port = @_ > 1 ? shift : $SELF \|\| Carp::croak 'reg: called with one argument only, but $SELF not set,';
249		345
250	$REG{$name} = $port;	346	$REG{$_[0]} = $port;
251	}	347	}
252		348
253	=item rcv $port, $callback->(@msg)	349	=item rcv $port, $callback->(@msg)
254		350
255	Replaces the callback on the specified miniport (after converting it to	351	Replaces the callback on the specified miniport (after converting it to
…		…
260	=item rcv $port, $smartmatch => $callback->(@msg), ...	356	=item rcv $port, $smartmatch => $callback->(@msg), ...
261		357
262	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...	358	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
263		359
264	Register callbacks to be called on matching messages on the given full	360	Register callbacks to be called on matching messages on the given full
265	port (after converting it to one if required).	361	port (after converting it to one if required) and return the port.
266		362
267	The callback has to return a true value when its work is done, after	363	The callback has to return a true value when its work is done, after
268	which is will be removed, or a false value in which case it will stay	364	which is will be removed, or a false value in which case it will stay
269	registered.	365	registered.
270		366
271	The global C<$SELF> (exported by this module) contains C<$port> while	367	The global C<$SELF> (exported by this module) contains C<$port> while
272	executing the callback.	368	executing the callback.
273		369
274	Runtime errors wdurign callback execution will result in the port being	370	Runtime errors during callback execution will result in the port being
275	C<kil>ed.	371	C<kil>ed.
276		372
277	If the match is an array reference, then it will be matched against the	373	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	374	first elements of the message, otherwise only the first element is being
279	matched.	375	matched.
…		…
282	exported by this module) matches any single element of the message.	378	exported by this module) matches any single element of the message.
283		379
284	While not required, it is highly recommended that the first matching	380	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	381	element is a string identifying the message. The one-string-only match is
286	also the most efficient match (by far).	382	also the most efficient match (by far).
		383
		384	Example: create a port and bind receivers on it in one go.
		385
		386	my $port = rcv port,
		387	msg1 => sub { ...; 0 },
		388	msg2 => sub { ...; 0 },
		389	;
		390
		391	Example: create a port, bind receivers and send it in a message elsewhere
		392	in one go:
		393
		394	snd $otherport, reply =>
		395	rcv port,
		396	msg1 => sub { ...; 0 },
		397	...
		398	;
287		399
288	=cut	400	=cut
289		401
290	sub rcv($@) {	402	sub rcv($@) {
291	my $port = shift;	403	my $port = shift;
…		…
398	}	510	}
399	}	511	}
400		512
401	=item $guard = mon $port, $cb->(@reason)	513	=item $guard = mon $port, $cb->(@reason)
402		514
403	=item $guard = mon $port, $otherport	515	=item $guard = mon $port, $rcvport
404		516
		517	=item $guard = mon $port
		518
405	=item $guard = mon $port, $otherport, @msg	519	=item $guard = mon $port, $rcvport, @msg
406		520
407	Monitor the given port and do something when the port is killed.	521	Monitor the given port and do something when the port is killed or
		522	messages to it were lost, and optionally return a guard that can be used
		523	to stop monitoring again.
408		524
		525	C<mon> effectively guarantees that, in the absence of hardware failures,
		526	that after starting the monitor, either all messages sent to the port
		527	will arrive, or the monitoring action will be invoked after possible
		528	message loss has been detected. No messages will be lost "in between"
		529	(after the first lost message no further messages will be received by the
		530	port). After the monitoring action was invoked, further messages might get
		531	delivered again.
		532
409	In the first form, the callback is simply called with any number	533	In the first form (callback), the callback is simply called with any
410	of C<@reason> elements (no @reason means that the port was deleted	534	number of C<@reason> elements (no @reason means that the port was deleted
411	"normally"). Note also that I<< the callback B<must> never die >>, so use	535	"normally"). Note also that I<< the callback B<must> never die >>, so use
412	C<eval> if unsure.	536	C<eval> if unsure.
413		537
414	In the second form, the other port will be C<kil>'ed with C<@reason>, iff	538	In the second form (another port given), the other port (C<$rcvport>)
415	a @reason was specified, i.e. on "normal" kils nothing happens, while	539	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.	540	"normal" kils nothing happens, while under all other conditions, the other
		541	port is killed with the same reason.
417		542
		543	The third form (kill self) is the same as the second form, except that
		544	C<$rvport> defaults to C<$SELF>.
		545
418	In the last form, a message of the form C<@msg, @reason> will be C<snd>.	546	In the last form (message), a message of the form C<@msg, @reason> will be
		547	C<snd>.
		548
		549	As a rule of thumb, monitoring requests should always monitor a port from
		550	a local port (or callback). The reason is that kill messages might get
		551	lost, just like any other message. Another less obvious reason is that
		552	even monitoring requests can get lost (for exmaple, when the connection
		553	to the other node goes down permanently). When monitoring a port locally
		554	these problems do not exist.
419		555
420	Example: call a given callback when C<$port> is killed.	556	Example: call a given callback when C<$port> is killed.
421		557
422	mon $port, sub { warn "port died because of <@_>\n" };	558	mon $port, sub { warn "port died because of <@_>\n" };
423		559
424	Example: kill ourselves when C<$port> is killed abnormally.	560	Example: kill ourselves when C<$port> is killed abnormally.
425		561
426	mon $port, $self;	562	mon $port;
427		563
428	Example: send us a restart message another C<$port> is killed.	564	Example: send us a restart message when another C<$port> is killed.
429		565
430	mon $port, $self => "restart";	566	mon $port, $self => "restart";
431		567
432	=cut	568	=cut
433		569
434	sub mon {	570	sub mon {
435	my ($noderef, $port) = split /#/, shift, 2;	571	my ($noderef, $port) = split /#/, shift, 2;
436		572
437	my $node = $NODE{$noderef} \|\| add_node $noderef;	573	my $node = $NODE{$noderef} \|\| add_node $noderef;
438		574
439	my $cb = shift;	575	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
440		576
441	unless (ref $cb) {	577	unless (ref $cb) {
442	if (@_) {	578	if (@_) {
443	# send a kill info message	579	# send a kill info message
444	my (@msg) = ($cb, @_);	580	my (@msg) = ($cb, @_);
…		…
475	=cut	611	=cut
476		612
477	sub mon_guard {	613	sub mon_guard {
478	my ($port, @refs) = @_;	614	my ($port, @refs) = @_;
479		615
		616	#TODO: mon-less form?
		617
480	mon $port, sub { 0 && @refs }	618	mon $port, sub { 0 && @refs }
481	}	619	}
482		620
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]	621	=item kil $port[, @reason]
494		622
495	Kill the specified port with the given C<@reason>.	623	Kill the specified port with the given C<@reason>.
496		624
497	If no C<@reason> is specified, then the port is killed "normally" (linked	625	If no C<@reason> is specified, then the port is killed "normally" (linked
…		…
504	will be reported as reason C<< die => $@ >>.	632	will be reported as reason C<< die => $@ >>.
505		633
506	Transport/communication errors are reported as C<< transport_error =>	634	Transport/communication errors are reported as C<< transport_error =>
507	$message >>.	635	$message >>.
508		636
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	637	=cut
		638
		639	=item $port = spawn $node, $initfunc[, @initdata]
		640
		641	Creates a port on the node C<$node> (which can also be a port ID, in which
		642	case it's the node where that port resides).
		643
		644	The port ID of the newly created port is return immediately, and it is
		645	permissible to immediately start sending messages or monitor the port.
		646
		647	After the port has been created, the init function is
		648	called. This function must be a fully-qualified function name
		649	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main
		650	program, use C<::name>.
		651
		652	If the function doesn't exist, then the node tries to C<require>
		653	the package, then the package above the package and so on (e.g.
		654	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		655	exists or it runs out of package names.
		656
		657	The init function is then called with the newly-created port as context
		658	object (C<$SELF>) and the C<@initdata> values as arguments.
		659
		660	A common idiom is to pass your own port, monitor the spawned port, and
		661	in the init function, monitor the original port. This two-way monitoring
		662	ensures that both ports get cleaned up when there is a problem.
		663
		664	Example: spawn a chat server port on C<$othernode>.
		665
		666	# this node, executed from within a port context:
		667	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		668	mon $server;
		669
		670	# init function on C<$othernode>
		671	sub connect {
		672	my ($srcport) = @_;
		673
		674	mon $srcport;
		675
		676	rcv $SELF, sub {
		677	...
		678	};
		679	}
		680
		681	=cut
		682
		683	sub _spawn {
		684	my $port = shift;
		685	my $init = shift;
		686
		687	local $SELF = "$NODE#$port";
		688	eval {
		689	&{ load_func $init }
		690	};
		691	_self_die if $@;
		692	}
		693
		694	sub spawn(@) {
		695	my ($noderef, undef) = split /#/, shift, 2;
		696
		697	my $id = "$RUNIQ." . $ID++;
		698
		699	$_[0] =~ /::/
		700	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		701
		702	($NODE{$noderef} \|\| add_node $noderef)
		703	->send (["", "AnyEvent::MP::_spawn" => $id, @_]);
		704
		705	"$noderef#$id"
		706	}
576		707
577	=back	708	=back
578		709
579	=head1 NODE MESSAGES	710	=head1 NODE MESSAGES
580		711
…		…
622		753
623	=back	754	=back
624		755
625	=head1 AnyEvent::MP vs. Distributed Erlang	756	=head1 AnyEvent::MP vs. Distributed Erlang
626		757
627	AnyEvent::MP got lots of its ideas from distributed erlang (erlang node	758	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	759	== 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	760	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
630	sample:	761	sample:
631		762
632	http://www.erlang.se/doc/programming_rules.shtml	763	http://www.Erlang.se/doc/programming_rules.shtml
633	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	764	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	765	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	766	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
636		767
637	Despite the similarities, there are also some important differences:	768	Despite the similarities, there are also some important differences:
638		769
639	=over 4	770	=over 4
640		771
…		…
651		782
652	Erlang uses processes that selctively receive messages, and therefore	783	Erlang uses processes that selctively receive messages, and therefore
653	needs a queue. AEMP is event based, queuing messages would serve no useful	784	needs a queue. AEMP is event based, queuing messages would serve no useful
654	purpose.	785	purpose.
655		786
656	(But see L<Coro::MP> for a more erlang-like process model on top of AEMP).	787	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).
657		788
658	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	789	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
659		790
660	Sending messages in erlang is synchronous and blocks the process. AEMP	791	Sending messages in Erlang is synchronous and blocks the process. AEMP
661	sends are immediate, connection establishment is handled in the	792	sends are immediate, connection establishment is handled in the
662	background.	793	background.
663		794
664	=item * Erlang can silently lose messages, AEMP cannot.	795	=item * Erlang can silently lose messages, AEMP cannot.
665		796
…		…
668	and c, and the other side only receives messages a and c).	799	and c, and the other side only receives messages a and c).
669		800
670	AEMP guarantees correct ordering, and the guarantee that there are no	801	AEMP guarantees correct ordering, and the guarantee that there are no
671	holes in the message sequence.	802	holes in the message sequence.
672		803
673	=item * In erlang, processes can be declared dead and later be found to be	804	=item * In Erlang, processes can be declared dead and later be found to be
674	alive.	805	alive.
675		806
676	In erlang it can happen that a monitored process is declared dead and	807	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	808	linked processes get killed, but later it turns out that the process is
678	still alive - and can receive messages.	809	still alive - and can receive messages.
679		810
680	In AEMP, when port monitoring detects a port as dead, then that port will	811	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	812	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.	813	and then later sends messages to it, finding it is still alive.
683		814
684	=item * Erlang can send messages to the wrong port, AEMP does not.	815	=item * Erlang can send messages to the wrong port, AEMP does not.
685		816
686	In erlang it is quite possible that a node that restarts reuses a process	817	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	818	ID known to other nodes for a completely different process, causing
688	messages destined for that process to end up in an unrelated process.	819	messages destined for that process to end up in an unrelated process.
689		820
690	AEMP never reuses port IDs, so old messages or old port IDs floating	821	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.	822	around in the network will not be sent to an unrelated port.
…		…
697	securely authenticate nodes.	828	securely authenticate nodes.
698		829
699	=item * The AEMP protocol is optimised for both text-based and binary	830	=item * The AEMP protocol is optimised for both text-based and binary
700	communications.	831	communications.
701		832
702	The AEMP protocol, unlike the erlang protocol, supports both	833	The AEMP protocol, unlike the Erlang protocol, supports both
703	language-independent text-only protocols (good for debugging) and binary,	834	language-independent text-only protocols (good for debugging) and binary,
704	language-specific serialisers (e.g. Storable).	835	language-specific serialisers (e.g. Storable).
705		836
706	It has also been carefully designed to be implementable in other languages	837	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	838	with a minimum of work while gracefully degrading fucntionality to make the
708	protocol simple.	839	protocol simple.
709		840
		841	=item * AEMP has more flexible monitoring options than Erlang.
		842
		843	In Erlang, you can chose to receive I<all> exit signals as messages
		844	or I<none>, there is no in-between, so monitoring single processes is
		845	difficult to implement. Monitoring in AEMP is more flexible than in
		846	Erlang, as one can choose between automatic kill, exit message or callback
		847	on a per-process basis.
		848
		849	=item * Erlang tries to hide remote/local connections, AEMP does not.
		850
		851	Monitoring in Erlang is not an indicator of process death/crashes,
		852	as linking is (except linking is unreliable in Erlang).
		853
		854	In AEMP, you don't "look up" registered port names or send to named ports
		855	that might or might not be persistent. Instead, you normally spawn a port
		856	on the remote node. The init function monitors the you, and you monitor
		857	the remote port. Since both monitors are local to the node, they are much
		858	more reliable.
		859
		860	This also saves round-trips and avoids sending messages to the wrong port
		861	(hard to do in Erlang).
		862
		863	=back
		864
		865	=head1 RATIONALE
		866
		867	=over 4
		868
		869	=item Why strings for ports and noderefs, why not objects?
		870
		871	We considered "objects", but found that the actual number of methods
		872	thatc an be called are very low. Since port IDs and noderefs travel over
		873	the network frequently, the serialising/deserialising would add lots of
		874	overhead, as well as having to keep a proxy object.
		875
		876	Strings can easily be printed, easily serialised etc. and need no special
		877	procedures to be "valid".
		878
		879	And a a miniport consists of a single closure stored in a global hash - it
		880	can't become much cheaper.
		881
		882	=item Why favour JSON, why not real serialising format such as Storable?
		883
		884	In fact, any AnyEvent::MP node will happily accept Storable as framing
		885	format, but currently there is no way to make a node use Storable by
		886	default.
		887
		888	The default framing protocol is JSON because a) JSON::XS is many times
		889	faster for small messages and b) most importantly, after years of
		890	experience we found that object serialisation is causing more problems
		891	than it gains: Just like function calls, objects simply do not travel
		892	easily over the network, mostly because they will always be a copy, so you
		893	always have to re-think your design.
		894
		895	Keeping your messages simple, concentrating on data structures rather than
		896	objects, will keep your messages clean, tidy and efficient.
		897
710	=back	898	=back
711		899
712	=head1 SEE ALSO	900	=head1 SEE ALSO
713		901
714	L<AnyEvent>.	902	L<AnyEvent>.

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Revision 1.48 by root, Thu Aug 13 02:59:42 2009 UTC