[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 1.31 by root, Wed Aug 5 19:55:58 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 initialise_node
		109	snd rcv mon kil reg psub
		110	port
		111	);
95		112
96	our $DEFAULT_SECRET;	113	our $SELF;
97	our $DEFAULT_PORT = "4040";
98		114
99	our $CONNECT_INTERVAL = 5; # new connect every 5s, at least	115	sub _self_die() {
100	our $CONNECT_TIMEOUT = 30; # includes handshake	116	my $msg = $@;
		117	$msg =~ s/\n+$// unless ref $msg;
		118	kil $SELF, die => $msg;
		119	}
101		120
102	sub default_secret {	121	=item $thisnode = NODE / $NODE
103	unless (defined $DEFAULT_SECRET) {	122
104	if (open my $fh, "<$ENV{HOME}/.aemp-secret") {	123	The C<NODE> function returns, and the C<$NODE> variable contains
105	sysread $fh, $DEFAULT_SECRET, -s $fh;	124	the noderef of the local node. The value is initialised by a call
		125	to C<become_public> or C<become_slave>, after which all local port
		126	identifiers become invalid.
		127
		128	=item $noderef = node_of $portid
		129
		130	Extracts and returns the noderef from a portid or a noderef.
		131
		132	=item $cv = resolve_node $noderef
		133
		134	Takes an unresolved node reference that may contain hostnames and
		135	abbreviated IDs, resolves all of them and returns a resolved node
		136	reference.
		137
		138	In addition to C<address:port> pairs allowed in resolved noderefs, the
		139	following forms are supported:
		140
		141	=over 4
		142
		143	=item the empty string
		144
		145	An empty-string component gets resolved as if the default port (4040) was
		146	specified.
		147
		148	=item naked port numbers (e.g. C<1234>)
		149
		150	These are resolved by prepending the local nodename and a colon, to be
		151	further resolved.
		152
		153	=item hostnames (e.g. C<localhost:1234>, C<localhost>)
		154
		155	These are resolved by using AnyEvent::DNS to resolve them, optionally
		156	looking up SRV records for the C<aemp=4040> port, if no port was
		157	specified.
		158
		159	=back
		160
		161	=item $SELF
		162
		163	Contains the current port id while executing C<rcv> callbacks or C<psub>
		164	blocks.
		165
		166	=item SELF, %SELF, @SELF...
		167
		168	Due to some quirks in how perl exports variables, it is impossible to
		169	just export C<$SELF>, all the symbols called C<SELF> are exported by this
		170	module, but only C<$SELF> is currently used.
		171
		172	=item snd $portid, type => @data
		173
		174	=item snd $portid, @msg
		175
		176	Send the given message to the given port ID, which can identify either
		177	a local or a remote port, and can be either a string or soemthignt hat
		178	stringifies a sa port ID (such as a port object :).
		179
		180	While the message can be about anything, it is highly recommended to use a
		181	string as first element (a portid, or some word that indicates a request
		182	type etc.).
		183
		184	The message data effectively becomes read-only after a call to this
		185	function: modifying any argument is not allowed and can cause many
		186	problems.
		187
		188	The type of data you can transfer depends on the transport protocol: when
		189	JSON is used, then only strings, numbers and arrays and hashes consisting
		190	of those are allowed (no objects). When Storable is used, then anything
		191	that Storable can serialise and deserialise is allowed, and for the local
		192	node, anything can be passed.
		193
		194	=item kil $portid[, @reason]
		195
		196	Kill the specified port with the given C<@reason>.
		197
		198	If no C<@reason> is specified, then the port is killed "normally" (linked
		199	ports will not be kileld, or even notified).
		200
		201	Otherwise, linked ports get killed with the same reason (second form of
		202	C<mon>, see below).
		203
		204	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		205	will be reported as reason C<< die => $@ >>.
		206
		207	Transport/communication errors are reported as C<< transport_error =>
		208	$message >>.
		209
		210	=item $guard = mon $portid, $cb->(@reason)
		211
		212	=item $guard = mon $portid, $otherport
		213
		214	=item $guard = mon $portid, $otherport, @msg
		215
		216	Monitor the given port and do something when the port is killed.
		217
		218	In the first form, the callback is simply called with any number
		219	of C<@reason> elements (no @reason means that the port was deleted
		220	"normally"). Note also that I<< the callback B<must> never die >>, so use
		221	C<eval> if unsure.
		222
		223	In the second form, the other port will be C<kil>'ed with C<@reason>, iff
		224	a @reason was specified, i.e. on "normal" kils nothing happens, while
		225	under all other conditions, the other port is killed with the same reason.
		226
		227	In the last form, a message of the form C<@msg, @reason> will be C<snd>.
		228
		229	Example: call a given callback when C<$port> is killed.
		230
		231	mon $port, sub { warn "port died because of <@_>\n" };
		232
		233	Example: kill ourselves when C<$port> is killed abnormally.
		234
		235	mon $port, $self;
		236
		237	Example: send us a restart message another C<$port> is killed.
		238
		239	mon $port, $self => "restart";
		240
		241	=cut
		242
		243	sub mon {
		244	my ($noderef, $port) = split /#/, shift, 2;
		245
		246	my $node = $NODE{$noderef} \|\| add_node $noderef;
		247
		248	my $cb = shift;
		249
		250	unless (ref $cb) {
		251	if (@_) {
		252	# send a kill info message
		253	my (@msg) = ($cb, @_);
		254	$cb = sub { snd @msg, @_ };
106	} else {	255	} else {
107	$DEFAULT_SECRET = AnyEvent::MP::Util::nonce 32;	256	# simply kill other port
		257	my $port = $cb;
		258	$cb = sub { kil $port, @_ if @_ };
108	}	259	}
109	}	260	}
110		261
111	$DEFAULT_SECRET	262	$node->monitor ($port, $cb);
		263
		264	defined wantarray
		265	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }
112	}	266	}
113		267
114	our $UNIQ = sprintf "%x.%x", $$, time; # per-process/node unique cookie	268	=item $guard = mon_guard $port, $ref, $ref...
115	our $PUBLIC = 0;
116	our $NODE;
117	our $PORT;
118		269
119	our %NODE; # node id to transport mapping, or "undef", for local node	270	Monitors the given C<$port> and keeps the passed references. When the port
120	our %PORT; # local ports	271	is killed, the references will be freed.
121	our %LISTENER; # local transports
122		272
123	sub NODE() { $NODE }	273	Optionally returns a guard that will stop the monitoring.
124		274
125	{	275	This function is useful when you create e.g. timers or other watchers and
126	use POSIX ();	276	want to free them when the port gets killed:
127	my $nodename = (POSIX::uname)[1];	277
128	$NODE = "$$\@$nodename";	278	$port->rcv (start => sub {
		279	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {
		280	undef $timer if 0.9 < rand;
		281	});
		282	});
		283
		284	=cut
		285
		286	sub mon_guard {
		287	my ($port, @refs) = @_;
		288
		289	mon $port, sub { 0 && @refs }
129	}	290	}
130		291
131	sub _ANY_() { 1 }	292	=item lnk $port1, $port2
132	sub _any_() { \&_ANY_ }
133		293
134	sub add_node {	294	Link two ports. This is simply a shorthand for:
135	my ($noderef) = @_;
136		295
137	return $NODE{$noderef}	296	mon $port1, $port2;
138	if exists $NODE{$noderef};	297	mon $port2, $port1;
139		298
140	for (split /,/, $noderef) {	299	It means that if either one is killed abnormally, the other one gets
141	return $NODE{$noderef} = $NODE{$_}	300	killed as well.
142	if exists $NODE{$_};	301
		302	=item $local_port = port
		303
		304	Create a new local port object that can be used either as a pattern
		305	matching port ("full port") or a single-callback port ("miniport"),
		306	depending on how C<rcv> callbacks are bound to the object.
		307
		308	=item $portid = port { my @msg = @_; $finished }
		309
		310	Creates a "mini port", that is, a very lightweight port without any
		311	pattern matching behind it, and returns its ID.
		312
		313	The block will be called for every message received on the port. When the
		314	callback returns a true value its job is considered "done" and the port
		315	will be destroyed. Otherwise it will stay alive.
		316
		317	The message will be passed as-is, no extra argument (i.e. no port id) will
		318	be passed to the callback.
		319
		320	If you need the local port id in the callback, this works nicely:
		321
		322	my $port; $port = port {
		323	snd $otherport, reply => $port;
		324	};
		325
		326	=cut
		327
		328	sub port(;&) {
		329	my $id = "$UNIQ." . $ID++;
		330	my $port = "$NODE#$id";
		331
		332	if (@_) {
		333	my $cb = shift;
		334	$PORT{$id} = sub {
		335	local $SELF = $port;
		336	eval {
		337	&$cb
		338	and kil $id;
		339	};
		340	_self_die if $@;
		341	};
		342	} else {
		343	my $self = bless {
		344	id => "$NODE#$id",
		345	}, "AnyEvent::MP::Port";
		346
		347	$PORT_DATA{$id} = $self;
		348	$PORT{$id} = sub {
		349	local $SELF = $port;
		350
		351	eval {
		352	for (@{ $self->{rc0}{$_[0]} }) {
		353	$_ && &{$_->[0]}
		354	&& undef $_;
		355	}
		356
		357	for (@{ $self->{rcv}{$_[0]} }) {
		358	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
		359	&& &{$_->[0]}
		360	&& undef $_;
		361	}
		362
		363	for (@{ $self->{any} }) {
		364	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
		365	&& &{$_->[0]}
		366	&& undef $_;
		367	}
		368	};
		369	_self_die if $@;
		370	};
143	}	371	}
144		372
145	# for indirect sends, use a different class	373	$port
146	my $node = new AnyEvent::MP::Node::Direct $noderef;
147
148	$NODE{$_} = $node
149	for $noderef, split /,/, $noderef;
150
151	$node
152	}	374	}
153		375
154	sub snd($@) {	376	=item reg $portid, $name
155	my ($noderef, $port) = split /#/, shift, 2;
156		377
157	add_node $noderef	378	Registers the given port under the name C<$name>. If the name already
158	unless exists $NODE{$noderef};	379	exists it is replaced.
159		380
160	$NODE{$noderef}->send ([$port, [@_]]);	381	A port can only be registered under one well known name.
		382
		383	A port automatically becomes unregistered when it is killed.
		384
		385	=cut
		386
		387	sub reg(@) {
		388	my ($portid, $name) = @_;
		389
		390	$REG{$name} = $portid;
161	}	391	}
162		392
163	sub _inject {	393	=item rcv $portid, $callback->(@msg)
164	my ($port, $msg) = @{+shift};
165		394
166	$port = $PORT{$port}	395	Replaces the callback on the specified miniport (or newly created port
167	or return;	396	object, see C<port>). Full ports are configured with the following calls:
168		397
169	use Data::Dumper;	398	=item rcv $portid, tagstring => $callback->(@msg), ...
170	warn Dumper $msg;
171	}
172		399
173	sub normalise_noderef($) {	400	=item rcv $portid, $smartmatch => $callback->(@msg), ...
174	my ($noderef) = @_;
175		401
176	my $cv = AE::cv;	402	=item rcv $portid, [$smartmatch...] => $callback->(@msg), ...
177	my @res;
178		403
179	$cv->begin (sub {	404	Register callbacks to be called on matching messages on the given port.
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		405
188	$noderef = $DEFAULT_PORT unless length $noderef;	406	The callback has to return a true value when its work is done, after
		407	which is will be removed, or a false value in which case it will stay
		408	registered.
189		409
190	my $idx;	410	The global C<$SELF> (exported by this module) contains C<$portid> while
191	for my $t (split /,/, $noderef) {	411	executing the callback.
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		412
198	$cv->begin;	413	Runtime errors wdurign callback execution will result in the port being
199	AnyEvent::Socket::resolve_sockaddr $nodename, $t \|\| "aemp=$DEFAULT_PORT", "tcp", 0, undef, sub {	414	C<kil>ed.
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		415
210	# my (undef, undef, undef, undef, @ipv4) = gethostbyname $nodename;	416	If the match is an array reference, then it will be matched against the
211	#	417	first elements of the message, otherwise only the first element is being
212	# for (@ipv4) {	418	matched.
213	# push @res, [	419
214	# $pri,	420	Any element in the match that is specified as C<_any_> (a function
215	# AnyEvent::Socket::format_hostport AnyEvent::Socket::format_address $_, $t \|\| $DEFAULT_PORT,	421	exported by this module) matches any single element of the message.
216	# ];	422
217	# }	423	While not required, it is highly recommended that the first matching
		424	element is a string identifying the message. The one-string-only match is
		425	also the most efficient match (by far).
		426
		427	=cut
		428
		429	sub rcv($@) {
		430	my $portid = shift;
		431	my ($noderef, $port) = split /#/, $port, 2;
		432
		433	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}
		434	or Carp::croak "$noderef#$port: rcv can only be called on local ports, caught";
		435
		436	my $self = $PORT_DATA{$port}
		437	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";
		438
		439	"AnyEvent::MP::Port" eq ref $self
		440	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";
		441
		442	while (@_) {
		443	my ($match, $cb) = splice @_, 0, 2;
		444
		445	if (!ref $match) {
		446	push @{ $self->{rc0}{$match} }, [$cb];
		447	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
		448	my ($type, @match) = @$match;
		449	@match
		450	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
		451	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
218	} else {	452	} else {
219	my ($host, $port) = AnyEvent::Socket::parse_hostport $t, "aemp=$DEFAULT_PORT"	453	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	}	454	}
234	}	455	}
235		456
236	$cv->end;	457	$portid
237
238	$cv
239	}	458	}
240		459
241	sub become_public {	460	=item $closure = psub { BLOCK }
242	return if $PUBLIC;
243		461
244	my $noderef = join ",", ref $_[0] ? @{+shift} : shift;	462	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
245	my @args = @_;	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.
246		465
247	$NODE = (normalise_noderef $noderef)->recv;	466	This is useful when you register callbacks from C<rcv> callbacks:
248		467
249	my $self = new AnyEvent::MP::Node::Self noderef => $NODE;	468	rcv delayed_reply => sub {
250		469	my ($delay, @reply) = @_;
251	$NODE{""} = $self; # empty string == local node	470	my $timer = AE::timer $delay, 0, psub {
252		471	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	;	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	}
274	}	495	}
275
276	$PUBLIC = 1;
277	}	496	}
		497
		498	=back
		499
		500	=head1 FUNCTIONS FOR NODES
		501
		502	=over 4
		503
		504	=item become_public $noderef
		505
		506	Tells the node to become a public node, i.e. reachable from other nodes.
		507
		508	The first argument is the (unresolved) node reference of the local node
		509	(if missing then the empty string is used).
		510
		511	It is quite common to not specify anything, in which case the local node
		512	tries to listen on the default port, or to only specify a port number, in
		513	which case AnyEvent::MP tries to guess the local addresses.
		514
		515	=cut
		516
		517	=back
		518
		519	=head1 NODE MESSAGES
		520
		521	Nodes understand the following messages sent to them. Many of them take
		522	arguments called C<@reply>, which will simply be used to compose a reply
		523	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
		524	the remaining arguments are simply the message data.
		525
		526	While other messages exist, they are not public and subject to change.
		527
		528	=over 4
		529
		530	=cut
		531
		532	=item lookup => $name, @reply
		533
		534	Replies with the port ID of the specified well-known port, or C<undef>.
		535
		536	=item devnull => ...
		537
		538	Generic data sink/CPU heat conversion.
		539
		540	=item relay => $port, @msg
		541
		542	Simply forwards the message to the given port.
		543
		544	=item eval => $string[ @reply]
		545
		546	Evaluates the given string. If C<@reply> is given, then a message of the
		547	form C<@reply, $@, @evalres> is sent.
		548
		549	Example: crash another node.
		550
		551	snd $othernode, eval => "exit";
		552
		553	=item time => @reply
		554
		555	Replies the the current node time to C<@reply>.
		556
		557	Example: tell the current node to send the current time to C<$myport> in a
		558	C<timereply> message.
		559
		560	snd $NODE, time => $myport, timereply => 1, 2;
		561	# => snd $myport, timereply => 1, 2, <time>
		562
		563	=back
		564
		565	=head1 AnyEvent::MP vs. Distributed Erlang
		566
		567	AnyEvent::MP got lots of its ideas from distributed erlang (erlang node
		568	== aemp node, erlang process == aemp port), so many of the documents and
		569	programming techniques employed by erlang apply to AnyEvent::MP. Here is a
		570	sample:
		571
		572	http://www.erlang.se/doc/programming_rules.shtml
		573	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
		574	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
		575	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
		576
		577	Despite the similarities, there are also some important differences:
		578
		579	=over 4
		580
		581	=item * Node references contain the recipe on how to contact them.
		582
		583	Erlang relies on special naming and DNS to work everywhere in the
		584	same way. AEMP relies on each node knowing it's own address(es), with
		585	convenience functionality.
		586
		587	This means that AEMP requires a less tightly controlled environment at the
		588	cost of longer node references and a slightly higher management overhead.
		589
		590	=item * Erlang uses processes and a mailbox, AEMP does not queue.
		591
		592	Erlang uses processes that selctively receive messages, and therefore
		593	needs a queue. AEMP is event based, queuing messages would serve no useful
		594	purpose.
		595
		596	(But see L<Coro::MP> for a more erlang-like process model on top of AEMP).
		597
		598	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
		599
		600	Sending messages in erlang is synchronous and blocks the process. AEMP
		601	sends are immediate, connection establishment is handled in the
		602	background.
		603
		604	=item * Erlang can silently lose messages, AEMP cannot.
		605
		606	Erlang makes few guarantees on messages delivery - messages can get lost
		607	without any of the processes realising it (i.e. you send messages a, b,
		608	and c, and the other side only receives messages a and c).
		609
		610	AEMP guarantees correct ordering, and the guarantee that there are no
		611	holes in the message sequence.
		612
		613	=item * In erlang, processes can be declared dead and later be found to be
		614	alive.
		615
		616	In erlang it can happen that a monitored process is declared dead and
		617	linked processes get killed, but later it turns out that the process is
		618	still alive - and can receive messages.
		619
		620	In AEMP, when port monitoring detects a port as dead, then that port will
		621	eventually be killed - it cannot happen that a node detects a port as dead
		622	and then later sends messages to it, finding it is still alive.
		623
		624	=item * Erlang can send messages to the wrong port, AEMP does not.
		625
		626	In erlang it is quite possible that a node that restarts reuses a process
		627	ID known to other nodes for a completely different process, causing
		628	messages destined for that process to end up in an unrelated process.
		629
		630	AEMP never reuses port IDs, so old messages or old port IDs floating
		631	around in the network will not be sent to an unrelated port.
		632
		633	=item * Erlang uses unprotected connections, AEMP uses secure
		634	authentication and can use TLS.
		635
		636	AEMP can use a proven protocol - SSL/TLS - to protect connections and
		637	securely authenticate nodes.
		638
		639	=item * The AEMP protocol is optimised for both text-based and binary
		640	communications.
		641
		642	The AEMP protocol, unlike the erlang protocol, supports both
		643	language-independent text-only protocols (good for debugging) and binary,
		644	language-specific serialisers (e.g. Storable).
		645
		646	It has also been carefully designed to be implementable in other languages
		647	with a minimum of work while gracefully degrading fucntionality to make the
		648	protocol simple.
278		649
279	=back	650	=back
280		651
281	=head1 SEE ALSO	652	=head1 SEE ALSO
282		653

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Revision 1.31 by root, Wed Aug 5 19:55:58 2009 UTC