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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.2 by root, Fri Jul 31 20:55:46 2009 UTC vs.
Revision 1.30 by root, Tue Aug 4 23:35:51 2009 UTC

…		…
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::MP;	7	use AnyEvent::MP;
8		8
9	NODE # returns this node identifier
10	$NODE # contains this node identifier	9	$NODE # contains this node's noderef
		10	NODE # returns this node's noderef
		11	NODE $port # returns the noderef of the port
11		12
12	snd $port, type => data...;	13	snd $port, type => data...;
		14
		15	$SELF # receiving/own port id in rcv callbacks
13		16
14	rcv $port, smartmatch => $cb->($port, @msg);	17	rcv $port, smartmatch => $cb->($port, @msg);
15		18
16	# examples:	19	# examples:
17	rcv $port2, ping => sub { snd $_[0], "pong"; 0 };	20	rcv $port2, ping => sub { snd $_[0], "pong"; 0 };
…		…
27	This module (-family) implements a simple message passing framework.	30	This module (-family) implements a simple message passing framework.
28		31
29	Despite its simplicity, you can securely message other processes running	32	Despite its simplicity, you can securely message other processes running
30	on the same or other hosts.	33	on the same or other hosts.
31		34
		35	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
		36	manual page.
		37
		38	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 -
		40	stay tuned! The basic API should be finished, however.
		41
32	=head1 CONCEPTS	42	=head1 CONCEPTS
33		43
34	=over 4	44	=over 4
35		45
36	=item port	46	=item port
37		47
38	A port is something you can send messages to with the C<snd> function, and	48	A port is something you can send messages to (with the C<snd> function).
39	you can register C<rcv> handlers with. All C<rcv> handlers will receive
40	messages they match, messages will not be queued.
41		49
		50	Some ports allow you to register C<rcv> handlers that can match specific
		51	messages. All C<rcv> handlers will receive messages they match, messages
		52	will not be queued.
		53
42	=item port id - C<pid@host#portname>	54	=item port id - C<noderef#portname>
43		55
44	A port id is always the node id, a hash-mark (C<#>) as separator, followed	56	A port id is normaly the concatenation of a noderef, a hash-mark (C<#>) as
45	by a port name.	57	separator, and a port name (a printable string of unspecified format). An
46		58	exception is the the node port, whose ID is identical to its node
47	A port name can be a well known port (basically an identifier/bareword),	59	reference.
48	or a generated name, consisting of node id, a dot (C<.>), and an
49	identifier.
50		60
51	=item node	61	=item node
52		62
53	A node is a single process containing at least one port - the node	63	A node is a single process containing at least one port - the node
54	port. You can send messages to node ports to let them create new ports,	64	port. You can send messages to node ports to find existing ports or to
55	among other things.	65	create new ports, among other things.
56		66
57	Initially, nodes are either private (single-process only) or hidden	67	Nodes are either private (single-process only), slaves (connected to a
58	(connected to a father node only). Only when they epxlicitly "go public"	68	master node only) or public nodes (connectable from unrelated nodes).
59	can you send them messages form unrelated other nodes.
60		69
61	Public nodes automatically connect to all other public nodes in a network	70	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>
62	when they connect, creating a full mesh.
63		71
64	=item node id - C<host:port>, C<id@host>, C<id>
65
66	A node ID is a string that either uniquely identifies a given node (For	72	A node reference is a string that either simply identifies the node (for
67	private and hidden nodes), or contains a recipe on how to reach a given	73	private and slave nodes), or contains a recipe on how to reach a given
68	node (for public nodes).	74	node (for public nodes).
69		75
		76	This recipe is simply a comma-separated list of C<address:port> pairs (for
		77	TCP/IP, other protocols might look different).
		78
		79	Node references come in two flavours: resolved (containing only numerical
		80	addresses) or unresolved (where hostnames are used instead of addresses).
		81
		82	Before using an unresolved node reference in a message you first have to
		83	resolve it.
		84
70	=back	85	=back
71		86
72	=head1 FUNCTIONS	87	=head1 VARIABLES/FUNCTIONS
73		88
74	=over 4	89	=over 4
75		90
76	=cut	91	=cut
77		92
78	package AnyEvent::MP;	93	package AnyEvent::MP;
79		94
80	use AnyEvent::MP::Util ();
81	use AnyEvent::MP::Node;	95	use AnyEvent::MP::Base;
82	use AnyEvent::MP::Transport;
83		96
84	use utf8;
85	use common::sense;	97	use common::sense;
86		98
87	use Carp ();	99	use Carp ();
88		100
89	use AE ();	101	use AE ();
90		102
91	use base "Exporter";	103	use base "Exporter";
92		104
93	our $VERSION = '0.0';	105	our $VERSION = '0.1';
94	our @EXPORT = qw(NODE $NODE $PORT snd rcv _any_);	106	our @EXPORT = qw(
		107	NODE $NODE *SELF node_of _any_
		108	resolve_node
		109	become_slave become_public
		110	snd rcv mon kil reg psub
		111	port
		112	);
95		113
96	our $DEFAULT_SECRET;	114	our $SELF;
97	our $DEFAULT_PORT = "4040";
98		115
99	our $CONNECT_INTERVAL = 5; # new connect every 5s, at least	116	sub _self_die() {
100	our $CONNECT_TIMEOUT = 30; # includes handshake	117	my $msg = $@;
		118	$msg =~ s/\n+$// unless ref $msg;
		119	kil $SELF, die => $msg;
		120	}
101		121
102	sub default_secret {	122	=item $thisnode = NODE / $NODE
103	unless (defined $DEFAULT_SECRET) {	123
104	if (open my $fh, "<$ENV{HOME}/.aemp-secret") {	124	The C<NODE> function returns, and the C<$NODE> variable contains
105	sysread $fh, $DEFAULT_SECRET, -s $fh;	125	the noderef of the local node. The value is initialised by a call
		126	to C<become_public> or C<become_slave>, after which all local port
		127	identifiers become invalid.
		128
		129	=item $noderef = node_of $portid
		130
		131	Extracts and returns the noderef from a portid or a noderef.
		132
		133	=item $cv = resolve_node $noderef
		134
		135	Takes an unresolved node reference that may contain hostnames and
		136	abbreviated IDs, resolves all of them and returns a resolved node
		137	reference.
		138
		139	In addition to C<address:port> pairs allowed in resolved noderefs, the
		140	following forms are supported:
		141
		142	=over 4
		143
		144	=item the empty string
		145
		146	An empty-string component gets resolved as if the default port (4040) was
		147	specified.
		148
		149	=item naked port numbers (e.g. C<1234>)
		150
		151	These are resolved by prepending the local nodename and a colon, to be
		152	further resolved.
		153
		154	=item hostnames (e.g. C<localhost:1234>, C<localhost>)
		155
		156	These are resolved by using AnyEvent::DNS to resolve them, optionally
		157	looking up SRV records for the C<aemp=4040> port, if no port was
		158	specified.
		159
		160	=back
		161
		162	=item $SELF
		163
		164	Contains the current port id while executing C<rcv> callbacks or C<psub>
		165	blocks.
		166
		167	=item SELF, %SELF, @SELF...
		168
		169	Due to some quirks in how perl exports variables, it is impossible to
		170	just export C<$SELF>, all the symbols called C<SELF> are exported by this
		171	module, but only C<$SELF> is currently used.
		172
		173	=item snd $portid, type => @data
		174
		175	=item snd $portid, @msg
		176
		177	Send the given message to the given port ID, which can identify either
		178	a local or a remote port, and can be either a string or soemthignt hat
		179	stringifies a sa port ID (such as a port object :).
		180
		181	While the message can be about anything, it is highly recommended to use a
		182	string as first element (a portid, or some word that indicates a request
		183	type etc.).
		184
		185	The message data effectively becomes read-only after a call to this
		186	function: modifying any argument is not allowed and can cause many
		187	problems.
		188
		189	The type of data you can transfer depends on the transport protocol: when
		190	JSON is used, then only strings, numbers and arrays and hashes consisting
		191	of those are allowed (no objects). When Storable is used, then anything
		192	that Storable can serialise and deserialise is allowed, and for the local
		193	node, anything can be passed.
		194
		195	=item kil $portid[, @reason]
		196
		197	Kill the specified port with the given C<@reason>.
		198
		199	If no C<@reason> is specified, then the port is killed "normally" (linked
		200	ports will not be kileld, or even notified).
		201
		202	Otherwise, linked ports get killed with the same reason (second form of
		203	C<mon>, see below).
		204
		205	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		206	will be reported as reason C<< die => $@ >>.
		207
		208	Transport/communication errors are reported as C<< transport_error =>
		209	$message >>.
		210
		211	=item $guard = mon $portid, $cb->(@reason)
		212
		213	=item $guard = mon $portid, $otherport
		214
		215	=item $guard = mon $portid, $otherport, @msg
		216
		217	Monitor the given port and do something when the port is killed.
		218
		219	In the first form, the callback is simply called with any number
		220	of C<@reason> elements (no @reason means that the port was deleted
		221	"normally"). Note also that I<< the callback B<must> never die >>, so use
		222	C<eval> if unsure.
		223
		224	In the second form, the other port will be C<kil>'ed with C<@reason>, iff
		225	a @reason was specified, i.e. on "normal" kils nothing happens, while
		226	under all other conditions, the other port is killed with the same reason.
		227
		228	In the last form, a message of the form C<@msg, @reason> will be C<snd>.
		229
		230	Example: call a given callback when C<$port> is killed.
		231
		232	mon $port, sub { warn "port died because of <@_>\n" };
		233
		234	Example: kill ourselves when C<$port> is killed abnormally.
		235
		236	mon $port, $self;
		237
		238	Example: send us a restart message another C<$port> is killed.
		239
		240	mon $port, $self => "restart";
		241
		242	=cut
		243
		244	sub mon {
		245	my ($noderef, $port) = split /#/, shift, 2;
		246
		247	my $node = $NODE{$noderef} \|\| add_node $noderef;
		248
		249	my $cb = shift;
		250
		251	unless (ref $cb) {
		252	if (@_) {
		253	# send a kill info message
		254	my (@msg) = ($cb, @_);
		255	$cb = sub { snd @msg, @_ };
106	} else {	256	} else {
107	$DEFAULT_SECRET = AnyEvent::MP::Util::nonce 32;	257	# simply kill other port
		258	my $port = $cb;
		259	$cb = sub { kil $port, @_ if @_ };
108	}	260	}
109	}	261	}
110		262
111	$DEFAULT_SECRET	263	$node->monitor ($port, $cb);
		264
		265	defined wantarray
		266	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }
112	}	267	}
113		268
114	our $UNIQ = sprintf "%x.%x", $$, time; # per-process/node unique cookie	269	=item $guard = mon_guard $port, $ref, $ref...
115	our $PUBLIC = 0;
116	our $NODE;
117	our $PORT;
118		270
119	our %NODE; # node id to transport mapping, or "undef", for local node	271	Monitors the given C<$port> and keeps the passed references. When the port
120	our %PORT; # local ports	272	is killed, the references will be freed.
121	our %LISTENER; # local transports
122		273
123	sub NODE() { $NODE }	274	Optionally returns a guard that will stop the monitoring.
124		275
125	{	276	This function is useful when you create e.g. timers or other watchers and
126	use POSIX ();	277	want to free them when the port gets killed:
127	my $nodename = (POSIX::uname)[1];	278
128	$NODE = "$$\@$nodename";	279	$port->rcv (start => sub {
		280	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {
		281	undef $timer if 0.9 < rand;
		282	});
		283	});
		284
		285	=cut
		286
		287	sub mon_guard {
		288	my ($port, @refs) = @_;
		289
		290	mon $port, sub { 0 && @refs }
129	}	291	}
130		292
131	sub _ANY_() { 1 }	293	=item lnk $port1, $port2
132	sub _any_() { \&_ANY_ }
133		294
134	sub add_node {	295	Link two ports. This is simply a shorthand for:
135	my ($noderef) = @_;
136		296
137	return $NODE{$noderef}	297	mon $port1, $port2;
138	if exists $NODE{$noderef};	298	mon $port2, $port1;
139		299
140	for (split /,/, $noderef) {	300	It means that if either one is killed abnormally, the other one gets
141	return $NODE{$noderef} = $NODE{$_}	301	killed as well.
142	if exists $NODE{$_};	302
		303	=item $local_port = port
		304
		305	Create a new local port object that supports message matching.
		306
		307	=item $portid = port { my @msg = @_; $finished }
		308
		309	Creates a "mini port", that is, a very lightweight port without any
		310	pattern matching behind it, and returns its ID.
		311
		312	The block will be called for every message received on the port. When the
		313	callback returns a true value its job is considered "done" and the port
		314	will be destroyed. Otherwise it will stay alive.
		315
		316	The message will be passed as-is, no extra argument (i.e. no port id) will
		317	be passed to the callback.
		318
		319	If you need the local port id in the callback, this works nicely:
		320
		321	my $port; $port = miniport {
		322	snd $otherport, reply => $port;
		323	};
		324
		325	=cut
		326
		327	sub port(;&) {
		328	my $id = "$UNIQ." . $ID++;
		329	my $port = "$NODE#$id";
		330
		331	if (@_) {
		332	my $cb = shift;
		333	$PORT{$id} = sub {
		334	local $SELF = $port;
		335	eval {
		336	&$cb
		337	and kil $id;
		338	};
		339	_self_die if $@;
		340	};
		341	} else {
		342	my $self = bless {
		343	id => "$NODE#$id",
		344	}, "AnyEvent::MP::Port";
		345
		346	$PORT_DATA{$id} = $self;
		347	$PORT{$id} = sub {
		348	local $SELF = $port;
		349
		350	eval {
		351	for (@{ $self->{rc0}{$_[0]} }) {
		352	$_ && &{$_->[0]}
		353	&& undef $_;
		354	}
		355
		356	for (@{ $self->{rcv}{$_[0]} }) {
		357	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
		358	&& &{$_->[0]}
		359	&& undef $_;
		360	}
		361
		362	for (@{ $self->{any} }) {
		363	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
		364	&& &{$_->[0]}
		365	&& undef $_;
		366	}
		367	};
		368	_self_die if $@;
		369	};
143	}	370	}
144		371
145	# for indirect sends, use a different class	372	$port
146	my $node = new AnyEvent::MP::Node::Direct $noderef;
147
148	$NODE{$_} = $node
149	for $noderef, split /,/, $noderef;
150
151	$node
152	}	373	}
153		374
		375	=item reg $portid, $name
		376
		377	Registers the given port under the name C<$name>. If the name already
		378	exists it is replaced.
		379
		380	A port can only be registered under one well known name.
		381
		382	A port automatically becomes unregistered when it is killed.
		383
		384	=cut
		385
		386	sub reg(@) {
		387	my ($portid, $name) = @_;
		388
		389	$REG{$name} = $portid;
		390	}
		391
		392	=item rcv $portid, tagstring => $callback->(@msg), ...
		393
		394	=item rcv $portid, $smartmatch => $callback->(@msg), ...
		395
		396	=item rcv $portid, [$smartmatch...] => $callback->(@msg), ...
		397
		398	Register callbacks to be called on matching messages on the given port.
		399
		400	The callback has to return a true value when its work is done, after
		401	which is will be removed, or a false value in which case it will stay
		402	registered.
		403
		404	The global C<$SELF> (exported by this module) contains C<$portid> while
		405	executing the callback.
		406
		407	Runtime errors wdurign callback execution will result in the port being
		408	C<kil>ed.
		409
		410	If the match is an array reference, then it will be matched against the
		411	first elements of the message, otherwise only the first element is being
		412	matched.
		413
		414	Any element in the match that is specified as C<_any_> (a function
		415	exported by this module) matches any single element of the message.
		416
		417	While not required, it is highly recommended that the first matching
		418	element is a string identifying the message. The one-string-only match is
		419	also the most efficient match (by far).
		420
		421	=cut
		422
154	sub snd($@) {	423	sub rcv($@) {
155	my ($noderef, $port) = split /#/, shift, 2;	424	my ($noderef, $port) = split /#/, shift, 2;
156		425
157	add_node $noderef	426	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}
158	unless exists $NODE{$noderef};	427	or Carp::croak "$noderef#$port: rcv can only be called on local ports, caught";
159		428
160	$NODE{$noderef}->send ([$port, [@_]]);	429	my $self = $PORT_DATA{$port}
161	}	430	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";
162		431
163	sub _inject {	432	"AnyEvent::MP::Port" eq ref $self
164	my ($port, $msg) = @{+shift};	433	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";
165		434
166	$port = $PORT{$port}	435	while (@_) {
167	or return;	436	my ($match, $cb) = splice @_, 0, 2;
168		437
169	use Data::Dumper;	438	if (!ref $match) {
170	warn Dumper $msg;	439	push @{ $self->{rc0}{$match} }, [$cb];
171	}	440	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
172		441	my ($type, @match) = @$match;
173	sub normalise_noderef($) {	442	@match
174	my ($noderef) = @_;	443	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
175		444	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
176	my $cv = AE::cv;
177	my @res;
178
179	$cv->begin (sub {
180	my %seen;
181	my @refs;
182	for (sort { $a->[0] <=> $b->[0] } @res) {
183	push @refs, $_->[1] unless $seen{$_->[1]}++
184	}
185	shift->send (join ",", @refs);
186	});
187
188	$noderef = $DEFAULT_PORT unless length $noderef;
189
190	my $idx;
191	for my $t (split /,/, $noderef) {
192	my $pri = ++$idx;
193
194	#TODO: this should be outside normalise_noderef and in become_public
195	if ($t =~ /^\d*$/) {
196	my $nodename = (POSIX::uname)[1];
197
198	$cv->begin;
199	AnyEvent::Socket::resolve_sockaddr $nodename, $t \|\| "aemp=$DEFAULT_PORT", "tcp", 0, undef, sub {
200	for (@_) {
201	my ($service, $host) = AnyEvent::Socket::unpack_sockaddr $_->[3];
202	push @res, [
203	$pri += 1e-5,
204	AnyEvent::Socket::format_hostport AnyEvent::Socket::format_address $host, $service
205	];
206	}
207	$cv->end;
208	};
209
210	# my (undef, undef, undef, undef, @ipv4) = gethostbyname $nodename;
211	#
212	# for (@ipv4) {
213	# push @res, [
214	# $pri,
215	# AnyEvent::Socket::format_hostport AnyEvent::Socket::format_address $_, $t \|\| $DEFAULT_PORT,
216	# ];
217	# }
218	} else {	445	} else {
219	my ($host, $port) = AnyEvent::Socket::parse_hostport $t, "aemp=$DEFAULT_PORT"	446	push @{ $self->{any} }, [$cb, $match];
220	or Carp::croak "$t: unparsable transport descriptor";
221
222	$cv->begin;
223	AnyEvent::Socket::resolve_sockaddr $host, $port, "tcp", 0, undef, sub {
224	for (@_) {
225	my ($service, $host) = AnyEvent::Socket::unpack_sockaddr $_->[3];
226	push @res, [
227	$pri += 1e-5,
228	AnyEvent::Socket::format_hostport AnyEvent::Socket::format_address $host, $service
229	];
230	}
231	$cv->end;
232	}
233	}	447	}
234	}	448	}
235
236	$cv->end;
237
238	$cv
239	}	449	}
240		450
241	sub become_public {	451	=item $closure = psub { BLOCK }
242	return if $PUBLIC;
243		452
244	my $noderef = join ",", ref $_[0] ? @{+shift} : shift;	453	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
245	my @args = @_;	454	closure is executed, sets up the environment in the same way as in C<rcv>
		455	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
246		456
247	$NODE = (normalise_noderef $noderef)->recv;	457	This is useful when you register callbacks from C<rcv> callbacks:
248		458
249	my $self = new AnyEvent::MP::Node::Self noderef => $NODE;	459	rcv delayed_reply => sub {
250		460	my ($delay, @reply) = @_;
251	$NODE{""} = $self; # empty string == local node	461	my $timer = AE::timer $delay, 0, psub {
252		462	snd @reply, $SELF;
253	for my $t (split /,/, $NODE) {
254	$NODE{$t} = $self;
255
256	my ($host, $port) = AnyEvent::Socket::parse_hostport $t;
257
258	$LISTENER{$t} = AnyEvent::MP::Transport::mp_server $host, $port,
259	@args,
260	on_error => sub {
261	die "on_error<@_>\n";#d#
262	},
263	on_connect => sub {
264	my ($tp) = @_;
265
266	$NODE{$tp->{remote_id}} = $_[0];
267	},
268	sub {
269	my ($tp) = @_;
270
271	$NODE{"$tp->{peerhost}:$tp->{peerport}"} = $tp;
272	},
273	;	463	};
		464	};
		465
		466	=cut
		467
		468	sub psub(&) {
		469	my $cb = shift;
		470
		471	my $port = $SELF
		472	or Carp::croak "psub can only be called from within rcv or psub callbacks, not";
		473
		474	sub {
		475	local $SELF = $port;
		476
		477	if (wantarray) {
		478	my @res = eval { &$cb };
		479	_self_die if $@;
		480	@res
		481	} else {
		482	my $res = eval { &$cb };
		483	_self_die if $@;
		484	$res
		485	}
274	}	486	}
275
276	$PUBLIC = 1;
277	}	487	}
		488
		489	=back
		490
		491	=head1 FUNCTIONS FOR NODES
		492
		493	=over 4
		494
		495	=item become_public $noderef
		496
		497	Tells the node to become a public node, i.e. reachable from other nodes.
		498
		499	The first argument is the (unresolved) node reference of the local node
		500	(if missing then the empty string is used).
		501
		502	It is quite common to not specify anything, in which case the local node
		503	tries to listen on the default port, or to only specify a port number, in
		504	which case AnyEvent::MP tries to guess the local addresses.
		505
		506	=cut
		507
		508	=back
		509
		510	=head1 NODE MESSAGES
		511
		512	Nodes understand the following messages sent to them. Many of them take
		513	arguments called C<@reply>, which will simply be used to compose a reply
		514	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
		515	the remaining arguments are simply the message data.
		516
		517	While other messages exist, they are not public and subject to change.
		518
		519	=over 4
		520
		521	=cut
		522
		523	=item lookup => $name, @reply
		524
		525	Replies with the port ID of the specified well-known port, or C<undef>.
		526
		527	=item devnull => ...
		528
		529	Generic data sink/CPU heat conversion.
		530
		531	=item relay => $port, @msg
		532
		533	Simply forwards the message to the given port.
		534
		535	=item eval => $string[ @reply]
		536
		537	Evaluates the given string. If C<@reply> is given, then a message of the
		538	form C<@reply, $@, @evalres> is sent.
		539
		540	Example: crash another node.
		541
		542	snd $othernode, eval => "exit";
		543
		544	=item time => @reply
		545
		546	Replies the the current node time to C<@reply>.
		547
		548	Example: tell the current node to send the current time to C<$myport> in a
		549	C<timereply> message.
		550
		551	snd $NODE, time => $myport, timereply => 1, 2;
		552	# => snd $myport, timereply => 1, 2, <time>
		553
		554	=back
		555
		556	=head1 AnyEvent::MP vs. Distributed Erlang
		557
		558	AnyEvent::MP got lots of its ideas from distributed erlang (erlang node
		559	== aemp node, erlang process == aemp port), so many of the documents and
		560	programming techniques employed by erlang apply to AnyEvent::MP. Here is a
		561	sample:
		562
		563	http://www.erlang.se/doc/programming_rules.shtml
		564	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
		565	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
		566	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
		567
		568	Despite the similarities, there are also some important differences:
		569
		570	=over 4
		571
		572	=item * Node references contain the recipe on how to contact them.
		573
		574	Erlang relies on special naming and DNS to work everywhere in the
		575	same way. AEMP relies on each node knowing it's own address(es), with
		576	convenience functionality.
		577
		578	This means that AEMP requires a less tightly controlled environment at the
		579	cost of longer node references and a slightly higher management overhead.
		580
		581	=item * Erlang uses processes and a mailbox, AEMP does not queue.
		582
		583	Erlang uses processes that selctively receive messages, and therefore
		584	needs a queue. AEMP is event based, queuing messages would serve no useful
		585	purpose.
		586
		587	(But see L<Coro::MP> for a more erlang-like process model on top of AEMP).
		588
		589	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
		590
		591	Sending messages in erlang is synchronous and blocks the process. AEMP
		592	sends are immediate, connection establishment is handled in the
		593	background.
		594
		595	=item * Erlang can silently lose messages, AEMP cannot.
		596
		597	Erlang makes few guarantees on messages delivery - messages can get lost
		598	without any of the processes realising it (i.e. you send messages a, b,
		599	and c, and the other side only receives messages a and c).
		600
		601	AEMP guarantees correct ordering, and the guarantee that there are no
		602	holes in the message sequence.
		603
		604	=item * In erlang, processes can be declared dead and later be found to be
		605	alive.
		606
		607	In erlang it can happen that a monitored process is declared dead and
		608	linked processes get killed, but later it turns out that the process is
		609	still alive - and can receive messages.
		610
		611	In AEMP, when port monitoring detects a port as dead, then that port will
		612	eventually be killed - it cannot happen that a node detects a port as dead
		613	and then later sends messages to it, finding it is still alive.
		614
		615	=item * Erlang can send messages to the wrong port, AEMP does not.
		616
		617	In erlang it is quite possible that a node that restarts reuses a process
		618	ID known to other nodes for a completely different process, causing
		619	messages destined for that process to end up in an unrelated process.
		620
		621	AEMP never reuses port IDs, so old messages or old port IDs floating
		622	around in the network will not be sent to an unrelated port.
		623
		624	=item * Erlang uses unprotected connections, AEMP uses secure
		625	authentication and can use TLS.
		626
		627	AEMP can use a proven protocol - SSL/TLS - to protect connections and
		628	securely authenticate nodes.
		629
		630	=item * The AEMP protocol is optimised for both text-based and binary
		631	communications.
		632
		633	The AEMP protocol, unlike the erlang protocol, supports both
		634	language-independent text-only protocols (good for debugging) and binary,
		635	language-specific serialisers (e.g. Storable).
		636
		637	It has also been carefully designed to be implementable in other languages
		638	with a minimum of work while gracefully degrading fucntionality to make the
		639	protocol simple.
278		640
279	=back	641	=back
280		642
281	=head1 SEE ALSO	643	=head1 SEE ALSO
282		644

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Revision 1.30 by root, Tue Aug 4 23:35:51 2009 UTC