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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.1 by root, Thu Jul 30 08:38:50 2009 UTC vs.
Revision 1.38 by root, Fri Aug 7 22:55:18 2009 UTC

…		…
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::MP;	7	use AnyEvent::MP;
8		8
		9	$NODE # contains this node's noderef
		10	NODE # returns this node's noderef
		11	NODE $port # returns the noderef of the port
		12
		13	$SELF # receiving/own port id in rcv callbacks
		14
		15	# ports are message endpoints
		16
		17	# sending messages
		18	snd $port, type => data...;
		19	snd $port, @msg;
		20	snd @msg_with_first_element_being_a_port;
		21
		22	# miniports
		23	my $miniport = port { my @msg = @_; 0 };
		24
		25	# full ports
		26	my $port = port;
		27	rcv $port, smartmatch => $cb->(@msg);
		28	rcv $port, ping => sub { snd $_[0], "pong"; 0 };
		29	rcv $port, pong => sub { warn "pong received\n"; 0 };
		30
		31	# remote ports
		32	my $port = spawn $node, $initfunc, @initdata;
		33
		34	# more, smarter, matches (_any_ is exported by this module)
		35	rcv $port, [child_died => $pid] => sub { ...
		36	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3
		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
9	=head1 DESCRIPTION	43	=head1 DESCRIPTION
10		44
		45	This module (-family) implements a simple message passing framework.
		46
		47	Despite its simplicity, you can securely message other processes running
		48	on the same or other hosts.
		49
		50	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
		51	manual page.
		52
		53	At the moment, this module family is severly broken and underdocumented,
		54	so do not use. This was uploaded mainly to reserve the CPAN namespace -
		55	stay tuned! The basic API should be finished, however.
		56
		57	=head1 CONCEPTS
		58
		59	=over 4
		60
		61	=item port
		62
		63	A port is something you can send messages to (with the C<snd> function).
		64
		65	Some ports allow you to register C<rcv> handlers that can match specific
		66	messages. All C<rcv> handlers will receive messages they match, messages
		67	will not be queued.
		68
		69	=item port id - C<noderef#portname>
		70
		71	A port id is normaly the concatenation of a noderef, a hash-mark (C<#>) as
		72	separator, and a port name (a printable string of unspecified format). An
		73	exception is the the node port, whose ID is identical to its node
		74	reference.
		75
		76	=item node
		77
		78	A node is a single process containing at least one port - the node
		79	port. You can send messages to node ports to find existing ports or to
		80	create new ports, among other things.
		81
		82	Nodes are either private (single-process only), slaves (connected to a
		83	master node only) or public nodes (connectable from unrelated nodes).
		84
		85	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>
		86
		87	A node reference is a string that either simply identifies the node (for
		88	private and slave nodes), or contains a recipe on how to reach a given
		89	node (for public nodes).
		90
		91	This recipe is simply a comma-separated list of C<address:port> pairs (for
		92	TCP/IP, other protocols might look different).
		93
		94	Node references come in two flavours: resolved (containing only numerical
		95	addresses) or unresolved (where hostnames are used instead of addresses).
		96
		97	Before using an unresolved node reference in a message you first have to
		98	resolve it.
		99
		100	=back
		101
		102	=head1 VARIABLES/FUNCTIONS
		103
		104	=over 4
		105
11	=cut	106	=cut
12		107
13	package AnyEvent::MP;	108	package AnyEvent::MP;
14		109
		110	use AnyEvent::MP::Base;
		111
15	use common::sense;	112	use common::sense;
16		113
		114	use Carp ();
		115
17	use AE ();	116	use AE ();
18		117
		118	use base "Exporter";
		119
19	our $VERSION = '0.0';	120	our $VERSION = '0.1';
		121	our @EXPORT = qw(
		122	NODE $NODE *SELF node_of _any_
		123	resolve_node initialise_node
		124	snd rcv mon kil reg psub spawn
		125	port
		126	);
20		127
21	sub nonce($) {	128	our $SELF;
22	my $nonce;
23		129
24	if (open my $fh, "</dev/urandom") {	130	sub _self_die() {
25	sysread $fh, $nonce, $_[0];	131	my $msg = $@;
		132	$msg =~ s/\n+$// unless ref $msg;
		133	kil $SELF, die => $msg;
		134	}
		135
		136	=item $thisnode = NODE / $NODE
		137
		138	The C<NODE> function returns, and the C<$NODE> variable contains
		139	the noderef of the local node. The value is initialised by a call
		140	to C<become_public> or C<become_slave>, after which all local port
		141	identifiers become invalid.
		142
		143	=item $noderef = node_of $port
		144
		145	Extracts and returns the noderef from a portid or a noderef.
		146
		147	=item initialise_node $noderef, $seednode, $seednode...
		148
		149	=item initialise_node "slave/", $master, $master...
		150
		151	Before a node can talk to other nodes on the network it has to initialise
		152	itself - the minimum a node needs to know is it's own name, and optionally
		153	it should know the noderefs of some other nodes in the network.
		154
		155	This function initialises a node - it must be called exactly once (or
		156	never) before calling other AnyEvent::MP functions.
		157
		158	All arguments are noderefs, which can be either resolved or unresolved.
		159
		160	There are two types of networked nodes, public nodes and slave nodes:
		161
		162	=over 4
		163
		164	=item public nodes
		165
		166	For public nodes, C<$noderef> must either be a (possibly unresolved)
		167	noderef, in which case it will be resolved, or C<undef> (or missing), in
		168	which case the noderef will be guessed.
		169
		170	Afterwards, the node will bind itself on all endpoints and try to connect
		171	to all additional C<$seednodes> that are specified. Seednodes are optional
		172	and can be used to quickly bootstrap the node into an existing network.
		173
		174	=item slave nodes
		175
		176	When the C<$noderef> is the special string C<slave/>, then the node will
		177	become a slave node. Slave nodes cannot be contacted from outside and will
		178	route most of their traffic to the master node that they attach to.
		179
		180	At least one additional noderef is required: The node will try to connect
		181	to all of them and will become a slave attached to the first node it can
		182	successfully connect to.
		183
		184	=back
		185
		186	This function will block until all nodes have been resolved and, for slave
		187	nodes, until it has successfully established a connection to a master
		188	server.
		189
		190	Example: become a public node listening on the default node.
		191
		192	initialise_node;
		193
		194	Example: become a public node, and try to contact some well-known master
		195	servers to become part of the network.
		196
		197	initialise_node undef, "master1", "master2";
		198
		199	Example: become a public node listening on port C<4041>.
		200
		201	initialise_node 4041;
		202
		203	Example: become a public node, only visible on localhost port 4044.
		204
		205	initialise_node "locahost:4044";
		206
		207	Example: become a slave node to any of the specified master servers.
		208
		209	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
		210
		211	=item $cv = resolve_node $noderef
		212
		213	Takes an unresolved node reference that may contain hostnames and
		214	abbreviated IDs, resolves all of them and returns a resolved node
		215	reference.
		216
		217	In addition to C<address:port> pairs allowed in resolved noderefs, the
		218	following forms are supported:
		219
		220	=over 4
		221
		222	=item the empty string
		223
		224	An empty-string component gets resolved as if the default port (4040) was
		225	specified.
		226
		227	=item naked port numbers (e.g. C<1234>)
		228
		229	These are resolved by prepending the local nodename and a colon, to be
		230	further resolved.
		231
		232	=item hostnames (e.g. C<localhost:1234>, C<localhost>)
		233
		234	These are resolved by using AnyEvent::DNS to resolve them, optionally
		235	looking up SRV records for the C<aemp=4040> port, if no port was
		236	specified.
		237
		238	=back
		239
		240	=item $SELF
		241
		242	Contains the current port id while executing C<rcv> callbacks or C<psub>
		243	blocks.
		244
		245	=item SELF, %SELF, @SELF...
		246
		247	Due to some quirks in how perl exports variables, it is impossible to
		248	just export C<$SELF>, all the symbols called C<SELF> are exported by this
		249	module, but only C<$SELF> is currently used.
		250
		251	=item snd $port, type => @data
		252
		253	=item snd $port, @msg
		254
		255	Send the given message to the given port ID, which can identify either
		256	a local or a remote port, and can be either a string or soemthignt hat
		257	stringifies a sa port ID (such as a port object :).
		258
		259	While the message can be about anything, it is highly recommended to use a
		260	string as first element (a portid, or some word that indicates a request
		261	type etc.).
		262
		263	The message data effectively becomes read-only after a call to this
		264	function: modifying any argument is not allowed and can cause many
		265	problems.
		266
		267	The type of data you can transfer depends on the transport protocol: when
		268	JSON is used, then only strings, numbers and arrays and hashes consisting
		269	of those are allowed (no objects). When Storable is used, then anything
		270	that Storable can serialise and deserialise is allowed, and for the local
		271	node, anything can be passed.
		272
		273	=item $local_port = port
		274
		275	Create a new local port object that can be used either as a pattern
		276	matching port ("full port") or a single-callback port ("miniport"),
		277	depending on how C<rcv> callbacks are bound to the object.
		278
		279	=item $port = port { my @msg = @_; $finished }
		280
		281	Creates a "miniport", that is, a very lightweight port without any pattern
		282	matching behind it, and returns its ID. Semantically the same as creating
		283	a port and calling C<rcv $port, $callback> on it.
		284
		285	The block will be called for every message received on the port. When the
		286	callback returns a true value its job is considered "done" and the port
		287	will be destroyed. Otherwise it will stay alive.
		288
		289	The message will be passed as-is, no extra argument (i.e. no port id) will
		290	be passed to the callback.
		291
		292	If you need the local port id in the callback, this works nicely:
		293
		294	my $port; $port = port {
		295	snd $otherport, reply => $port;
		296	};
		297
		298	=cut
		299
		300	sub rcv($@);
		301
		302	sub port(;&) {
		303	my $id = "$UNIQ." . $ID++;
		304	my $port = "$NODE#$id";
		305
		306	if (@_) {
		307	rcv $port, shift;
26	} else {	308	} else {
27	# shit...	309	$PORT{$id} = sub { }; # nop
28	our $nonce_init;
29	unless ($nonce_init++) {
30	srand time ^ $$ ^ unpack "%L*", qx"ps -edalf" . qx"ipconfig /all";
31	}
32
33	$nonce = join "", map +(chr rand 256), 1 .. $_[0]
34	}	310	}
35		311
36	$nonce	312	$port
37	}	313	}
38		314
39	our $DEFAULT_SECRET;	315	=item reg $port, $name
40		316
41	sub default_secret {	317	=item reg $name
42	unless (defined $DEFAULT_SECRET) {	318
43	if (open my $fh, "<$ENV{HOME}/.aemp-secret") {	319	Registers the given port (or C<$SELF><<< if missing) under the name
44	sysread $fh, $DEFAULT_SECRET, -s $fh;	320	C<$name>. If the name already exists it is replaced.
		321
		322	A port can only be registered under one well known name.
		323
		324	A port automatically becomes unregistered when it is killed.
		325
		326	=cut
		327
		328	sub reg(@) {
		329	my $port = @_ > 1 ? shift : $SELF \|\| Carp::croak 'reg: called with one argument only, but $SELF not set,';
		330
		331	$REG{$_[0]} = $port;
		332	}
		333
		334	=item rcv $port, $callback->(@msg)
		335
		336	Replaces the callback on the specified miniport (after converting it to
		337	one if required).
		338
		339	=item rcv $port, tagstring => $callback->(@msg), ...
		340
		341	=item rcv $port, $smartmatch => $callback->(@msg), ...
		342
		343	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
		344
		345	Register callbacks to be called on matching messages on the given full
		346	port (after converting it to one if required) and return the port.
		347
		348	The callback has to return a true value when its work is done, after
		349	which is will be removed, or a false value in which case it will stay
		350	registered.
		351
		352	The global C<$SELF> (exported by this module) contains C<$port> while
		353	executing the callback.
		354
		355	Runtime errors during callback execution will result in the port being
		356	C<kil>ed.
		357
		358	If the match is an array reference, then it will be matched against the
		359	first elements of the message, otherwise only the first element is being
		360	matched.
		361
		362	Any element in the match that is specified as C<_any_> (a function
		363	exported by this module) matches any single element of the message.
		364
		365	While not required, it is highly recommended that the first matching
		366	element is a string identifying the message. The one-string-only match is
		367	also the most efficient match (by far).
		368
		369	Example: create a port and bind receivers on it in one go.
		370
		371	my $port = rcv port,
		372	msg1 => sub { ...; 0 },
		373	msg2 => sub { ...; 0 },
		374	;
		375
		376	Example: create a port, bind receivers and send it in a message elsewhere
		377	in one go:
		378
		379	snd $otherport, reply =>
		380	rcv port,
		381	msg1 => sub { ...; 0 },
		382	...
		383	;
		384
		385	=cut
		386
		387	sub rcv($@) {
		388	my $port = shift;
		389	my ($noderef, $portid) = split /#/, $port, 2;
		390
		391	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}
		392	or Carp::croak "$port: rcv can only be called on local ports, caught";
		393
		394	if (@_ == 1) {
		395	my $cb = shift;
		396	delete $PORT_DATA{$portid};
		397	$PORT{$portid} = sub {
		398	local $SELF = $port;
		399	eval {
		400	&$cb
		401	and kil $port;
		402	};
		403	_self_die if $@;
		404	};
		405	} else {
		406	my $self = $PORT_DATA{$portid} \|\|= do {
		407	my $self = bless {
		408	id => $port,
		409	}, "AnyEvent::MP::Port";
		410
		411	$PORT{$portid} = sub {
		412	local $SELF = $port;
		413
		414	eval {
		415	for (@{ $self->{rc0}{$_[0]} }) {
		416	$_ && &{$_->[0]}
		417	&& undef $_;
		418	}
		419
		420	for (@{ $self->{rcv}{$_[0]} }) {
		421	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
		422	&& &{$_->[0]}
		423	&& undef $_;
		424	}
		425
		426	for (@{ $self->{any} }) {
		427	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
		428	&& &{$_->[0]}
		429	&& undef $_;
		430	}
		431	};
		432	_self_die if $@;
		433	};
		434
		435	$self
		436	};
		437
		438	"AnyEvent::MP::Port" eq ref $self
		439	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		440
		441	while (@_) {
		442	my ($match, $cb) = splice @_, 0, 2;
		443
		444	if (!ref $match) {
		445	push @{ $self->{rc0}{$match} }, [$cb];
		446	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
		447	my ($type, @match) = @$match;
		448	@match
		449	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
		450	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
45	} else {	451	} else {
46	$DEFAULT_SECRET = nonce 32;	452	push @{ $self->{any} }, [$cb, $match];
		453	}
47	}	454	}
48	}	455	}
49		456
50	$DEFAULT_SECRET	457	$port
51	}	458	}
		459
		460	=item $closure = psub { BLOCK }
		461
		462	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
		463	closure is executed, sets up the environment in the same way as in C<rcv>
		464	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		465
		466	This is useful when you register callbacks from C<rcv> callbacks:
		467
		468	rcv delayed_reply => sub {
		469	my ($delay, @reply) = @_;
		470	my $timer = AE::timer $delay, 0, psub {
		471	snd @reply, $SELF;
		472	};
		473	};
		474
		475	=cut
		476
		477	sub psub(&) {
		478	my $cb = shift;
		479
		480	my $port = $SELF
		481	or Carp::croak "psub can only be called from within rcv or psub callbacks, not";
		482
		483	sub {
		484	local $SELF = $port;
		485
		486	if (wantarray) {
		487	my @res = eval { &$cb };
		488	_self_die if $@;
		489	@res
		490	} else {
		491	my $res = eval { &$cb };
		492	_self_die if $@;
		493	$res
		494	}
		495	}
		496	}
		497
		498	=item $guard = mon $port, $cb->(@reason)
		499
		500	=item $guard = mon $port, $rcvport
		501
		502	=item $guard = mon $port
		503
		504	=item $guard = mon $port, $rcvport, @msg
		505
		506	Monitor the given port and do something when the port is killed, and
		507	optionally return a guard that can be used to stop monitoring again.
		508
		509	In the first form (callback), the callback is simply called with any
		510	number of C<@reason> elements (no @reason means that the port was deleted
		511	"normally"). Note also that I<< the callback B<must> never die >>, so use
		512	C<eval> if unsure.
		513
		514	In the second form (another port given), the other port (C<$rcvport)
		515	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on
		516	"normal" kils nothing happens, while under all other conditions, the other
		517	port is killed with the same reason.
		518
		519	The third form (kill self) is the same as the second form, except that
		520	C<$rvport> defaults to C<$SELF>.
		521
		522	In the last form (message), a message of the form C<@msg, @reason> will be
		523	C<snd>.
		524
		525	As a rule of thumb, monitoring requests should always monitor a port from
		526	a local port (or callback). The reason is that kill messages might get
		527	lost, just like any other message. Another less obvious reason is that
		528	even monitoring requests can get lost (for exmaple, when the connection
		529	to the other node goes down permanently). When monitoring a port locally
		530	these problems do not exist.
		531
		532	Example: call a given callback when C<$port> is killed.
		533
		534	mon $port, sub { warn "port died because of <@_>\n" };
		535
		536	Example: kill ourselves when C<$port> is killed abnormally.
		537
		538	mon $port;
		539
		540	Example: send us a restart message when another C<$port> is killed.
		541
		542	mon $port, $self => "restart";
		543
		544	=cut
		545
		546	sub mon {
		547	my ($noderef, $port) = split /#/, shift, 2;
		548
		549	my $node = $NODE{$noderef} \|\| add_node $noderef;
		550
		551	my $cb = @_ ? $_[0] : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
		552
		553	unless (ref $cb) {
		554	if (@_) {
		555	# send a kill info message
		556	my (@msg) = @_;
		557	$cb = sub { snd @msg, @_ };
		558	} else {
		559	# simply kill other port
		560	my $port = $cb;
		561	$cb = sub { kil $port, @_ if @_ };
		562	}
		563	}
		564
		565	$node->monitor ($port, $cb);
		566
		567	defined wantarray
		568	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }
		569	}
		570
		571	=item $guard = mon_guard $port, $ref, $ref...
		572
		573	Monitors the given C<$port> and keeps the passed references. When the port
		574	is killed, the references will be freed.
		575
		576	Optionally returns a guard that will stop the monitoring.
		577
		578	This function is useful when you create e.g. timers or other watchers and
		579	want to free them when the port gets killed:
		580
		581	$port->rcv (start => sub {
		582	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {
		583	undef $timer if 0.9 < rand;
		584	});
		585	});
		586
		587	=cut
		588
		589	sub mon_guard {
		590	my ($port, @refs) = @_;
		591
		592	#TODO: mon-less form?
		593
		594	mon $port, sub { 0 && @refs }
		595	}
		596
		597	=item kil $port[, @reason]
		598
		599	Kill the specified port with the given C<@reason>.
		600
		601	If no C<@reason> is specified, then the port is killed "normally" (linked
		602	ports will not be kileld, or even notified).
		603
		604	Otherwise, linked ports get killed with the same reason (second form of
		605	C<mon>, see below).
		606
		607	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		608	will be reported as reason C<< die => $@ >>.
		609
		610	Transport/communication errors are reported as C<< transport_error =>
		611	$message >>.
		612
		613	=cut
		614
		615	=item $port = spawn $node, $initfunc[, @initdata]
		616
		617	Creates a port on the node C<$node> (which can also be a port ID, in which
		618	case it's the node where that port resides).
		619
		620	The port ID of the newly created port is return immediately, and it is
		621	permissible to immediately start sending messages or monitor the port.
		622
		623	After the port has been created, the init function is
		624	called. This fucntion must be a fully-qualified function name
		625	(e.g. C<MyApp::Chat::Server::init>).
		626
		627	If the function doesn't exist, then the node tries to C<require>
		628	the package, then the package above the package and so on (e.g.
		629	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		630	exists or it runs out of package names.
		631
		632	The init function is then called with the newly-created port as context
		633	object (C<$SELF>) and the C<@initdata> values as arguments.
		634
		635	A common idiom is to pass your own port, monitor the spawned port, and
		636	in the init function, monitor the original port. This two-way monitoring
		637	ensures that both ports get cleaned up when there is a problem.
		638
		639	Example: spawn a chat server port on C<$othernode>.
		640
		641	# this node, executed from within a port context:
		642	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		643	mon $server;
		644
		645	# init function on C<$othernode>
		646	sub connect {
		647	my ($srcport) = @_;
		648
		649	mon $srcport;
		650
		651	rcv $SELF, sub {
		652	...
		653	};
		654	}
		655
		656	=cut
		657
		658	sub _spawn {
		659	my $port = shift;
		660	my $init = shift;
		661
		662	local $SELF = "$NODE#$port";
		663	eval {
		664	&{ load_func $init }
		665	};
		666	_self_die if $@;
		667	}
		668
		669	sub spawn(@) {
		670	my ($noderef, undef) = split /#/, shift, 2;
		671
		672	my $id = "$RUNIQ." . $ID++;
		673
		674	($NODE{$noderef} \|\| add_node $noderef)
		675	->send (["", "AnyEvent::MP::_spawn" => $id, @_]);
		676
		677	"$noderef#$id"
		678	}
		679
		680	=back
		681
		682	=head1 NODE MESSAGES
		683
		684	Nodes understand the following messages sent to them. Many of them take
		685	arguments called C<@reply>, which will simply be used to compose a reply
		686	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
		687	the remaining arguments are simply the message data.
		688
		689	While other messages exist, they are not public and subject to change.
		690
		691	=over 4
		692
		693	=cut
		694
		695	=item lookup => $name, @reply
		696
		697	Replies with the port ID of the specified well-known port, or C<undef>.
		698
		699	=item devnull => ...
		700
		701	Generic data sink/CPU heat conversion.
		702
		703	=item relay => $port, @msg
		704
		705	Simply forwards the message to the given port.
		706
		707	=item eval => $string[ @reply]
		708
		709	Evaluates the given string. If C<@reply> is given, then a message of the
		710	form C<@reply, $@, @evalres> is sent.
		711
		712	Example: crash another node.
		713
		714	snd $othernode, eval => "exit";
		715
		716	=item time => @reply
		717
		718	Replies the the current node time to C<@reply>.
		719
		720	Example: tell the current node to send the current time to C<$myport> in a
		721	C<timereply> message.
		722
		723	snd $NODE, time => $myport, timereply => 1, 2;
		724	# => snd $myport, timereply => 1, 2, <time>
		725
		726	=back
		727
		728	=head1 AnyEvent::MP vs. Distributed Erlang
		729
		730	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
		731	== aemp node, Erlang process == aemp port), so many of the documents and
		732	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
		733	sample:
		734
		735	http://www.Erlang.se/doc/programming_rules.shtml
		736	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
		737	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6
		738	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
		739
		740	Despite the similarities, there are also some important differences:
		741
		742	=over 4
		743
		744	=item * Node references contain the recipe on how to contact them.
		745
		746	Erlang relies on special naming and DNS to work everywhere in the
		747	same way. AEMP relies on each node knowing it's own address(es), with
		748	convenience functionality.
		749
		750	This means that AEMP requires a less tightly controlled environment at the
		751	cost of longer node references and a slightly higher management overhead.
		752
		753	=item * Erlang uses processes and a mailbox, AEMP does not queue.
		754
		755	Erlang uses processes that selctively receive messages, and therefore
		756	needs a queue. AEMP is event based, queuing messages would serve no useful
		757	purpose.
		758
		759	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).
		760
		761	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
		762
		763	Sending messages in Erlang is synchronous and blocks the process. AEMP
		764	sends are immediate, connection establishment is handled in the
		765	background.
		766
		767	=item * Erlang can silently lose messages, AEMP cannot.
		768
		769	Erlang makes few guarantees on messages delivery - messages can get lost
		770	without any of the processes realising it (i.e. you send messages a, b,
		771	and c, and the other side only receives messages a and c).
		772
		773	AEMP guarantees correct ordering, and the guarantee that there are no
		774	holes in the message sequence.
		775
		776	=item * In Erlang, processes can be declared dead and later be found to be
		777	alive.
		778
		779	In Erlang it can happen that a monitored process is declared dead and
		780	linked processes get killed, but later it turns out that the process is
		781	still alive - and can receive messages.
		782
		783	In AEMP, when port monitoring detects a port as dead, then that port will
		784	eventually be killed - it cannot happen that a node detects a port as dead
		785	and then later sends messages to it, finding it is still alive.
		786
		787	=item * Erlang can send messages to the wrong port, AEMP does not.
		788
		789	In Erlang it is quite possible that a node that restarts reuses a process
		790	ID known to other nodes for a completely different process, causing
		791	messages destined for that process to end up in an unrelated process.
		792
		793	AEMP never reuses port IDs, so old messages or old port IDs floating
		794	around in the network will not be sent to an unrelated port.
		795
		796	=item * Erlang uses unprotected connections, AEMP uses secure
		797	authentication and can use TLS.
		798
		799	AEMP can use a proven protocol - SSL/TLS - to protect connections and
		800	securely authenticate nodes.
		801
		802	=item * The AEMP protocol is optimised for both text-based and binary
		803	communications.
		804
		805	The AEMP protocol, unlike the Erlang protocol, supports both
		806	language-independent text-only protocols (good for debugging) and binary,
		807	language-specific serialisers (e.g. Storable).
		808
		809	It has also been carefully designed to be implementable in other languages
		810	with a minimum of work while gracefully degrading fucntionality to make the
		811	protocol simple.
		812
		813	=item * AEMP has more flexible monitoring options than Erlang.
		814
		815	In Erlang, you can chose to receive I<all> exit signals as messages
		816	or I<none>, there is no in-between, so monitoring single processes is
		817	difficult to implement. Monitoring in AEMP is more flexible than in
		818	Erlang, as one can choose between automatic kill, exit message or callback
		819	on a per-process basis.
		820
		821	=item * Erlang tries to hide remote/local connections, AEMP does not.
		822
		823	Monitoring in Erlang is not an indicator of process death/crashes,
		824	as linking is (except linking is unreliable in Erlang).
		825
		826	In AEMP, you don't "look up" registered port names or send to named ports
		827	that might or might not be persistent. Instead, you normally spawn a port
		828	on the remote node. The init function monitors the you, and you monitor
		829	the remote port. Since both monitors are local to the node, they are much
		830	more reliable.
		831
		832	This also saves round-trips and avoids sending messages to the wrong port
		833	(hard to do in Erlang).
		834
		835	=back
52		836
53	=head1 SEE ALSO	837	=head1 SEE ALSO
54		838
55	L<AnyEvent>.	839	L<AnyEvent>.
56		840

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Revision 1.38 by root, Fri Aug 7 22:55:18 2009 UTC