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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.33 by root, Wed Aug 5 22:40:51 2009 UTC vs.
Revision 1.46 by root, Thu Aug 13 01:46:10 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	# ports are message endpoints
		16
		17	# sending messages
13	snd $port, type => data...;	18	snd $port, type => data...;
		19	snd $port, @msg;
		20	snd @msg_with_first_element_being_a_port;
14		21
15	$SELF # receiving/own port id in rcv callbacks	22	# miniports
		23	my $miniport = port { my @msg = @_; 0 };
16		24
		25	# full ports
		26	my $port = port;
17	rcv $port, smartmatch => $cb->($port, @msg);	27	rcv $port, smartmatch => $cb->(@msg);
18
19	# examples:
20	rcv $port2, ping => sub { snd $_[0], "pong"; 0 };	28	rcv $port, ping => sub { snd $_[0], "pong"; 0 };
21	rcv $port1, pong => sub { warn "pong received\n" };	29	rcv $port, pong => sub { warn "pong received\n"; 0 };
22	snd $port2, ping => $port1;	30
		31	# remote ports
		32	my $port = spawn $node, $initfunc, @initdata;
23		33
24	# more, smarter, matches (_any_ is exported by this module)	34	# more, smarter, matches (_any_ is exported by this module)
25	rcv $port, [child_died => $pid] => sub { ...	35	rcv $port, [child_died => $pid] => sub { ...
26	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3	36	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3
27		37
		38	# monitoring
		39	mon $port, $cb->(@msg) # callback is invoked on death
		40	mon $port, $otherport # kill otherport on abnormal death
		41	mon $port, $otherport, @msg # send message on death
		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		46	AnyEvent::MP::Intro - outdated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
28	=head1 DESCRIPTION	52	=head1 DESCRIPTION
29		53
30	This module (-family) implements a simple message passing framework.	54	This module (-family) implements a simple message passing framework.
31		55
32	Despite its simplicity, you can securely message other processes running	56	Despite its simplicity, you can securely message other processes running
…		…
35	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>
36	manual page.	60	manual page.
37		61
38	At the moment, this module family is severly broken and underdocumented,	62	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 -	63	so do not use. This was uploaded mainly to reserve the CPAN namespace -
40	stay tuned! The basic API should be finished, however.	64	stay tuned!
41		65
42	=head1 CONCEPTS	66	=head1 CONCEPTS
43		67
44	=over 4	68	=over 4
45		69
…		…
90		114
91	=cut	115	=cut
92		116
93	package AnyEvent::MP;	117	package AnyEvent::MP;
94		118
95	use AnyEvent::MP::Base;	119	use AnyEvent::MP::Kernel;
96		120
97	use common::sense;	121	use common::sense;
98		122
99	use Carp ();	123	use Carp ();
100		124
101	use AE ();	125	use AE ();
102		126
103	use base "Exporter";	127	use base "Exporter";
104		128
105	our $VERSION = '0.1';	129	our $VERSION = $AnyEvent::MP::Kernel::VERSION;
		130
106	our @EXPORT = qw(	131	our @EXPORT = qw(
107	NODE $NODE *SELF node_of _any_	132	NODE $NODE *SELF node_of _any_
108	resolve_node initialise_node	133	resolve_node initialise_node
109	snd rcv mon kil reg psub	134	snd rcv mon kil reg psub spawn
110	port	135	port
111	);	136	);
112		137
113	our $SELF;	138	our $SELF;
114		139
…		…
127		152
128	=item $noderef = node_of $port	153	=item $noderef = node_of $port
129		154
130	Extracts and returns the noderef from a portid or a noderef.	155	Extracts and returns the noderef from a portid or a noderef.
131		156
		157	=item initialise_node $noderef, $seednode, $seednode...
		158
		159	=item initialise_node "slave/", $master, $master...
		160
		161	Before a node can talk to other nodes on the network it has to initialise
		162	itself - the minimum a node needs to know is it's own name, and optionally
		163	it should know the noderefs of some other nodes in the network.
		164
		165	This function initialises a node - it must be called exactly once (or
		166	never) before calling other AnyEvent::MP functions.
		167
		168	All arguments are noderefs, which can be either resolved or unresolved.
		169
		170	There are two types of networked nodes, public nodes and slave nodes:
		171
		172	=over 4
		173
		174	=item public nodes
		175
		176	For public nodes, C<$noderef> must either be a (possibly unresolved)
		177	noderef, in which case it will be resolved, or C<undef> (or missing), in
		178	which case the noderef will be guessed.
		179
		180	Afterwards, the node will bind itself on all endpoints and try to connect
		181	to all additional C<$seednodes> that are specified. Seednodes are optional
		182	and can be used to quickly bootstrap the node into an existing network.
		183
		184	=item slave nodes
		185
		186	When the C<$noderef> is the special string C<slave/>, then the node will
		187	become a slave node. Slave nodes cannot be contacted from outside and will
		188	route most of their traffic to the master node that they attach to.
		189
		190	At least one additional noderef is required: The node will try to connect
		191	to all of them and will become a slave attached to the first node it can
		192	successfully connect to.
		193
		194	=back
		195
		196	This function will block until all nodes have been resolved and, for slave
		197	nodes, until it has successfully established a connection to a master
		198	server.
		199
		200	Example: become a public node listening on the default node.
		201
		202	initialise_node;
		203
		204	Example: become a public node, and try to contact some well-known master
		205	servers to become part of the network.
		206
		207	initialise_node undef, "master1", "master2";
		208
		209	Example: become a public node listening on port C<4041>.
		210
		211	initialise_node 4041;
		212
		213	Example: become a public node, only visible on localhost port 4044.
		214
		215	initialise_node "locahost:4044";
		216
		217	Example: become a slave node to any of the specified master servers.
		218
		219	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
		220
132	=item $cv = resolve_node $noderef	221	=item $cv = resolve_node $noderef
133		222
134	Takes an unresolved node reference that may contain hostnames and	223	Takes an unresolved node reference that may contain hostnames and
135	abbreviated IDs, resolves all of them and returns a resolved node	224	abbreviated IDs, resolves all of them and returns a resolved node
136	reference.	225	reference.
…		…
233	$port	322	$port
234	}	323	}
235		324
236	=item reg $port, $name	325	=item reg $port, $name
237		326
238	Registers the given port under the name C<$name>. If the name already	327	=item reg $name
239	exists it is replaced.	328
		329	Registers the given port (or C<$SELF><<< if missing) under the name
		330	C<$name>. If the name already exists it is replaced.
240		331
241	A port can only be registered under one well known name.	332	A port can only be registered under one well known name.
242		333
243	A port automatically becomes unregistered when it is killed.	334	A port automatically becomes unregistered when it is killed.
244		335
245	=cut	336	=cut
246		337
247	sub reg(@) {	338	sub reg(@) {
248	my ($port, $name) = @_;	339	my $port = @_ > 1 ? shift : $SELF \|\| Carp::croak 'reg: called with one argument only, but $SELF not set,';
249		340
250	$REG{$name} = $port;	341	$REG{$_[0]} = $port;
251	}	342	}
252		343
253	=item rcv $port, $callback->(@msg)	344	=item rcv $port, $callback->(@msg)
254		345
255	Replaces the callback on the specified miniport (after converting it to	346	Replaces the callback on the specified miniport (after converting it to
…		…
260	=item rcv $port, $smartmatch => $callback->(@msg), ...	351	=item rcv $port, $smartmatch => $callback->(@msg), ...
261		352
262	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...	353	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
263		354
264	Register callbacks to be called on matching messages on the given full	355	Register callbacks to be called on matching messages on the given full
265	port (after converting it to one if required).	356	port (after converting it to one if required) and return the port.
266		357
267	The callback has to return a true value when its work is done, after	358	The callback has to return a true value when its work is done, after
268	which is will be removed, or a false value in which case it will stay	359	which is will be removed, or a false value in which case it will stay
269	registered.	360	registered.
270		361
271	The global C<$SELF> (exported by this module) contains C<$port> while	362	The global C<$SELF> (exported by this module) contains C<$port> while
272	executing the callback.	363	executing the callback.
273		364
274	Runtime errors wdurign callback execution will result in the port being	365	Runtime errors during callback execution will result in the port being
275	C<kil>ed.	366	C<kil>ed.
276		367
277	If the match is an array reference, then it will be matched against the	368	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	369	first elements of the message, otherwise only the first element is being
279	matched.	370	matched.
…		…
282	exported by this module) matches any single element of the message.	373	exported by this module) matches any single element of the message.
283		374
284	While not required, it is highly recommended that the first matching	375	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	376	element is a string identifying the message. The one-string-only match is
286	also the most efficient match (by far).	377	also the most efficient match (by far).
		378
		379	Example: create a port and bind receivers on it in one go.
		380
		381	my $port = rcv port,
		382	msg1 => sub { ...; 0 },
		383	msg2 => sub { ...; 0 },
		384	;
		385
		386	Example: create a port, bind receivers and send it in a message elsewhere
		387	in one go:
		388
		389	snd $otherport, reply =>
		390	rcv port,
		391	msg1 => sub { ...; 0 },
		392	...
		393	;
287		394
288	=cut	395	=cut
289		396
290	sub rcv($@) {	397	sub rcv($@) {
291	my $port = shift;	398	my $port = shift;
…		…
398	}	505	}
399	}	506	}
400		507
401	=item $guard = mon $port, $cb->(@reason)	508	=item $guard = mon $port, $cb->(@reason)
402		509
403	=item $guard = mon $port, $otherport	510	=item $guard = mon $port, $rcvport
404		511
		512	=item $guard = mon $port
		513
405	=item $guard = mon $port, $otherport, @msg	514	=item $guard = mon $port, $rcvport, @msg
406		515
407	Monitor the given port and do something when the port is killed.	516	Monitor the given port and do something when the port is killed or
		517	messages to it were lost, and optionally return a guard that can be used
		518	to stop monitoring again.
408		519
		520	C<mon> effectively guarantees that, in the absence of hardware failures,
		521	that after starting the monitor, either all messages sent to the port
		522	will arrive, or the monitoring action will be invoked after possible
		523	message loss has been detected. No messages will be lost "in between"
		524	(after the first lost message no further messages will be received by the
		525	port). After the monitoring action was invoked, further messages might get
		526	delivered again.
		527
409	In the first form, the callback is simply called with any number	528	In the first form (callback), the callback is simply called with any
410	of C<@reason> elements (no @reason means that the port was deleted	529	number of C<@reason> elements (no @reason means that the port was deleted
411	"normally"). Note also that I<< the callback B<must> never die >>, so use	530	"normally"). Note also that I<< the callback B<must> never die >>, so use
412	C<eval> if unsure.	531	C<eval> if unsure.
413		532
414	In the second form, the other port will be C<kil>'ed with C<@reason>, iff	533	In the second form (another port given), the other port (C<$rcvport>)
415	a @reason was specified, i.e. on "normal" kils nothing happens, while	534	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.	535	"normal" kils nothing happens, while under all other conditions, the other
		536	port is killed with the same reason.
417		537
		538	The third form (kill self) is the same as the second form, except that
		539	C<$rvport> defaults to C<$SELF>.
		540
418	In the last form, a message of the form C<@msg, @reason> will be C<snd>.	541	In the last form (message), a message of the form C<@msg, @reason> will be
		542	C<snd>.
		543
		544	As a rule of thumb, monitoring requests should always monitor a port from
		545	a local port (or callback). The reason is that kill messages might get
		546	lost, just like any other message. Another less obvious reason is that
		547	even monitoring requests can get lost (for exmaple, when the connection
		548	to the other node goes down permanently). When monitoring a port locally
		549	these problems do not exist.
419		550
420	Example: call a given callback when C<$port> is killed.	551	Example: call a given callback when C<$port> is killed.
421		552
422	mon $port, sub { warn "port died because of <@_>\n" };	553	mon $port, sub { warn "port died because of <@_>\n" };
423		554
424	Example: kill ourselves when C<$port> is killed abnormally.	555	Example: kill ourselves when C<$port> is killed abnormally.
425		556
426	mon $port, $self;	557	mon $port;
427		558
428	Example: send us a restart message another C<$port> is killed.	559	Example: send us a restart message when another C<$port> is killed.
429		560
430	mon $port, $self => "restart";	561	mon $port, $self => "restart";
431		562
432	=cut	563	=cut
433		564
434	sub mon {	565	sub mon {
435	my ($noderef, $port) = split /#/, shift, 2;	566	my ($noderef, $port) = split /#/, shift, 2;
436		567
437	my $node = $NODE{$noderef} \|\| add_node $noderef;	568	my $node = $NODE{$noderef} \|\| add_node $noderef;
438		569
439	my $cb = shift;	570	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
440		571
441	unless (ref $cb) {	572	unless (ref $cb) {
442	if (@_) {	573	if (@_) {
443	# send a kill info message	574	# send a kill info message
444	my (@msg) = ($cb, @_);	575	my (@msg) = ($cb, @_);
…		…
475	=cut	606	=cut
476		607
477	sub mon_guard {	608	sub mon_guard {
478	my ($port, @refs) = @_;	609	my ($port, @refs) = @_;
479		610
		611	#TODO: mon-less form?
		612
480	mon $port, sub { 0 && @refs }	613	mon $port, sub { 0 && @refs }
481	}	614	}
482		615
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]	616	=item kil $port[, @reason]
494		617
495	Kill the specified port with the given C<@reason>.	618	Kill the specified port with the given C<@reason>.
496		619
497	If no C<@reason> is specified, then the port is killed "normally" (linked	620	If no C<@reason> is specified, then the port is killed "normally" (linked
…		…
504	will be reported as reason C<< die => $@ >>.	627	will be reported as reason C<< die => $@ >>.
505		628
506	Transport/communication errors are reported as C<< transport_error =>	629	Transport/communication errors are reported as C<< transport_error =>
507	$message >>.	630	$message >>.
508		631
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	632	=cut
		633
		634	=item $port = spawn $node, $initfunc[, @initdata]
		635
		636	Creates a port on the node C<$node> (which can also be a port ID, in which
		637	case it's the node where that port resides).
		638
		639	The port ID of the newly created port is return immediately, and it is
		640	permissible to immediately start sending messages or monitor the port.
		641
		642	After the port has been created, the init function is
		643	called. This function must be a fully-qualified function name
		644	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main
		645	program, use C<::name>.
		646
		647	If the function doesn't exist, then the node tries to C<require>
		648	the package, then the package above the package and so on (e.g.
		649	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		650	exists or it runs out of package names.
		651
		652	The init function is then called with the newly-created port as context
		653	object (C<$SELF>) and the C<@initdata> values as arguments.
		654
		655	A common idiom is to pass your own port, monitor the spawned port, and
		656	in the init function, monitor the original port. This two-way monitoring
		657	ensures that both ports get cleaned up when there is a problem.
		658
		659	Example: spawn a chat server port on C<$othernode>.
		660
		661	# this node, executed from within a port context:
		662	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		663	mon $server;
		664
		665	# init function on C<$othernode>
		666	sub connect {
		667	my ($srcport) = @_;
		668
		669	mon $srcport;
		670
		671	rcv $SELF, sub {
		672	...
		673	};
		674	}
		675
		676	=cut
		677
		678	sub _spawn {
		679	my $port = shift;
		680	my $init = shift;
		681
		682	local $SELF = "$NODE#$port";
		683	eval {
		684	&{ load_func $init }
		685	};
		686	_self_die if $@;
		687	}
		688
		689	sub spawn(@) {
		690	my ($noderef, undef) = split /#/, shift, 2;
		691
		692	my $id = "$RUNIQ." . $ID++;
		693
		694	$_[0] =~ /::/
		695	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		696
		697	($NODE{$noderef} \|\| add_node $noderef)
		698	->send (["", "AnyEvent::MP::_spawn" => $id, @_]);
		699
		700	"$noderef#$id"
		701	}
576		702
577	=back	703	=back
578		704
579	=head1 NODE MESSAGES	705	=head1 NODE MESSAGES
580		706
…		…
622		748
623	=back	749	=back
624		750
625	=head1 AnyEvent::MP vs. Distributed Erlang	751	=head1 AnyEvent::MP vs. Distributed Erlang
626		752
627	AnyEvent::MP got lots of its ideas from distributed erlang (erlang node	753	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	754	== 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	755	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
630	sample:	756	sample:
631		757
632	http://www.erlang.se/doc/programming_rules.shtml	758	http://www.Erlang.se/doc/programming_rules.shtml
633	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	759	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	760	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	761	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
636		762
637	Despite the similarities, there are also some important differences:	763	Despite the similarities, there are also some important differences:
638		764
639	=over 4	765	=over 4
640		766
…		…
651		777
652	Erlang uses processes that selctively receive messages, and therefore	778	Erlang uses processes that selctively receive messages, and therefore
653	needs a queue. AEMP is event based, queuing messages would serve no useful	779	needs a queue. AEMP is event based, queuing messages would serve no useful
654	purpose.	780	purpose.
655		781
656	(But see L<Coro::MP> for a more erlang-like process model on top of AEMP).	782	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).
657		783
658	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	784	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
659		785
660	Sending messages in erlang is synchronous and blocks the process. AEMP	786	Sending messages in Erlang is synchronous and blocks the process. AEMP
661	sends are immediate, connection establishment is handled in the	787	sends are immediate, connection establishment is handled in the
662	background.	788	background.
663		789
664	=item * Erlang can silently lose messages, AEMP cannot.	790	=item * Erlang can silently lose messages, AEMP cannot.
665		791
…		…
668	and c, and the other side only receives messages a and c).	794	and c, and the other side only receives messages a and c).
669		795
670	AEMP guarantees correct ordering, and the guarantee that there are no	796	AEMP guarantees correct ordering, and the guarantee that there are no
671	holes in the message sequence.	797	holes in the message sequence.
672		798
673	=item * In erlang, processes can be declared dead and later be found to be	799	=item * In Erlang, processes can be declared dead and later be found to be
674	alive.	800	alive.
675		801
676	In erlang it can happen that a monitored process is declared dead and	802	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	803	linked processes get killed, but later it turns out that the process is
678	still alive - and can receive messages.	804	still alive - and can receive messages.
679		805
680	In AEMP, when port monitoring detects a port as dead, then that port will	806	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	807	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.	808	and then later sends messages to it, finding it is still alive.
683		809
684	=item * Erlang can send messages to the wrong port, AEMP does not.	810	=item * Erlang can send messages to the wrong port, AEMP does not.
685		811
686	In erlang it is quite possible that a node that restarts reuses a process	812	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	813	ID known to other nodes for a completely different process, causing
688	messages destined for that process to end up in an unrelated process.	814	messages destined for that process to end up in an unrelated process.
689		815
690	AEMP never reuses port IDs, so old messages or old port IDs floating	816	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.	817	around in the network will not be sent to an unrelated port.
…		…
697	securely authenticate nodes.	823	securely authenticate nodes.
698		824
699	=item * The AEMP protocol is optimised for both text-based and binary	825	=item * The AEMP protocol is optimised for both text-based and binary
700	communications.	826	communications.
701		827
702	The AEMP protocol, unlike the erlang protocol, supports both	828	The AEMP protocol, unlike the Erlang protocol, supports both
703	language-independent text-only protocols (good for debugging) and binary,	829	language-independent text-only protocols (good for debugging) and binary,
704	language-specific serialisers (e.g. Storable).	830	language-specific serialisers (e.g. Storable).
705		831
706	It has also been carefully designed to be implementable in other languages	832	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	833	with a minimum of work while gracefully degrading fucntionality to make the
708	protocol simple.	834	protocol simple.
709		835
		836	=item * AEMP has more flexible monitoring options than Erlang.
		837
		838	In Erlang, you can chose to receive I<all> exit signals as messages
		839	or I<none>, there is no in-between, so monitoring single processes is
		840	difficult to implement. Monitoring in AEMP is more flexible than in
		841	Erlang, as one can choose between automatic kill, exit message or callback
		842	on a per-process basis.
		843
		844	=item * Erlang tries to hide remote/local connections, AEMP does not.
		845
		846	Monitoring in Erlang is not an indicator of process death/crashes,
		847	as linking is (except linking is unreliable in Erlang).
		848
		849	In AEMP, you don't "look up" registered port names or send to named ports
		850	that might or might not be persistent. Instead, you normally spawn a port
		851	on the remote node. The init function monitors the you, and you monitor
		852	the remote port. Since both monitors are local to the node, they are much
		853	more reliable.
		854
		855	This also saves round-trips and avoids sending messages to the wrong port
		856	(hard to do in Erlang).
		857
		858	=back
		859
		860	=head1 RATIONALE
		861
		862	=over 4
		863
		864	=item Why strings for ports and noderefs, why not objects?
		865
		866	We considered "objects", but found that the actual number of methods
		867	thatc an be called are very low. Since port IDs and noderefs travel over
		868	the network frequently, the serialising/deserialising would add lots of
		869	overhead, as well as having to keep a proxy object.
		870
		871	Strings can easily be printed, easily serialised etc. and need no special
		872	procedures to be "valid".
		873
		874	=item Why favour JSON, why not real serialising format such as Storable?
		875
		876	In fact, any AnyEvent::MP node will happily accept Storable as framing
		877	format, but currently there is no way to make a node use Storable by
		878	default.
		879
		880	The default framing protocol is JSON because a) JSON::XS is many times
		881	faster for small messages and b) most importantly, after years of
		882	experience we found that object serialisation is causing more problems
		883	than it gains: Just like function calls, objects simply do not travel
		884	easily over the network, mostly because they will always be a copy, so you
		885	always have to re-think your design.
		886
		887	Keeping your messages simple, concentrating on data structures rather than
		888	objects, will keep your messages clean, tidy and efficient.
		889
710	=back	890	=back
711		891
712	=head1 SEE ALSO	892	=head1 SEE ALSO
713		893
714	L<AnyEvent>.	894	L<AnyEvent>.

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Revision 1.46 by root, Thu Aug 13 01:46:10 2009 UTC