[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 1.36 by root, Thu Aug 6 10:46:48 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	snd $port, type => data...;
		14
		15	$SELF # receiving/own port id in rcv callbacks
		16
		17	rcv $port, smartmatch => $cb->($port, @msg);
		18
		19	# examples:
		20	rcv $port2, ping => sub { snd $_[0], "pong"; 0 };
		21	rcv $port1, pong => sub { warn "pong received\n" };
		22	snd $port2, ping => $port1;
		23
		24	# more, smarter, matches (_any_ is exported by this module)
		25	rcv $port, [child_died => $pid] => sub { ...
		26	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3
		27
		28	# linking two ports, so they both crash together
		29	lnk $port1, $port2;
		30
		31	# monitoring
		32	mon $port, $cb->(@msg) # callback is invoked on death
		33	mon $port, $otherport # kill otherport on abnormal death
		34	mon $port, $otherport, @msg # send message on death
		35
9	=head1 DESCRIPTION	36	=head1 DESCRIPTION
10		37
		38	This module (-family) implements a simple message passing framework.
		39
		40	Despite its simplicity, you can securely message other processes running
		41	on the same or other hosts.
		42
		43	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
		44	manual page.
		45
		46	At the moment, this module family is severly broken and underdocumented,
		47	so do not use. This was uploaded mainly to reserve the CPAN namespace -
		48	stay tuned! The basic API should be finished, however.
		49
		50	=head1 CONCEPTS
		51
		52	=over 4
		53
		54	=item port
		55
		56	A port is something you can send messages to (with the C<snd> function).
		57
		58	Some ports allow you to register C<rcv> handlers that can match specific
		59	messages. All C<rcv> handlers will receive messages they match, messages
		60	will not be queued.
		61
		62	=item port id - C<noderef#portname>
		63
		64	A port id is normaly the concatenation of a noderef, a hash-mark (C<#>) as
		65	separator, and a port name (a printable string of unspecified format). An
		66	exception is the the node port, whose ID is identical to its node
		67	reference.
		68
		69	=item node
		70
		71	A node is a single process containing at least one port - the node
		72	port. You can send messages to node ports to find existing ports or to
		73	create new ports, among other things.
		74
		75	Nodes are either private (single-process only), slaves (connected to a
		76	master node only) or public nodes (connectable from unrelated nodes).
		77
		78	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>
		79
		80	A node reference is a string that either simply identifies the node (for
		81	private and slave nodes), or contains a recipe on how to reach a given
		82	node (for public nodes).
		83
		84	This recipe is simply a comma-separated list of C<address:port> pairs (for
		85	TCP/IP, other protocols might look different).
		86
		87	Node references come in two flavours: resolved (containing only numerical
		88	addresses) or unresolved (where hostnames are used instead of addresses).
		89
		90	Before using an unresolved node reference in a message you first have to
		91	resolve it.
		92
		93	=back
		94
		95	=head1 VARIABLES/FUNCTIONS
		96
		97	=over 4
		98
11	=cut	99	=cut
12		100
13	package AnyEvent::MP;	101	package AnyEvent::MP;
14		102
		103	use AnyEvent::MP::Base;
		104
15	use common::sense;	105	use common::sense;
16		106
		107	use Carp ();
		108
17	use AE ();	109	use AE ();
18		110
		111	use base "Exporter";
		112
19	our $VERSION = '0.0';	113	our $VERSION = '0.1';
		114	our @EXPORT = qw(
		115	NODE $NODE *SELF node_of _any_
		116	resolve_node initialise_node
		117	snd rcv mon kil reg psub
		118	port
		119	);
20		120
21	sub nonce($) {	121	our $SELF;
22	my $nonce;
23		122
24	if (open my $fh, "</dev/urandom") {	123	sub _self_die() {
25	sysread $fh, $nonce, $_[0];	124	my $msg = $@;
		125	$msg =~ s/\n+$// unless ref $msg;
		126	kil $SELF, die => $msg;
		127	}
		128
		129	=item $thisnode = NODE / $NODE
		130
		131	The C<NODE> function returns, and the C<$NODE> variable contains
		132	the noderef of the local node. The value is initialised by a call
		133	to C<become_public> or C<become_slave>, after which all local port
		134	identifiers become invalid.
		135
		136	=item $noderef = node_of $port
		137
		138	Extracts and returns the noderef from a portid or a noderef.
		139
		140	=item initialise_node $noderef, $seednode, $seednode...
		141
		142	=item initialise_node "slave/", $master, $master...
		143
		144	Before a node can talk to other nodes on the network it has to initialise
		145	itself - the minimum a node needs to know is it's own name, and optionally
		146	it should know the noderefs of some other nodes in the network.
		147
		148	This function initialises a node - it must be called exactly once (or
		149	never) before calling other AnyEvent::MP functions.
		150
		151	All arguments are noderefs, which can be either resolved or unresolved.
		152
		153	There are two types of networked nodes, public nodes and slave nodes:
		154
		155	=over 4
		156
		157	=item public nodes
		158
		159	For public nodes, C<$noderef> must either be a (possibly unresolved)
		160	noderef, in which case it will be resolved, or C<undef> (or missing), in
		161	which case the noderef will be guessed.
		162
		163	Afterwards, the node will bind itself on all endpoints and try to connect
		164	to all additional C<$seednodes> that are specified. Seednodes are optional
		165	and can be used to quickly bootstrap the node into an existing network.
		166
		167	=item slave nodes
		168
		169	When the C<$noderef> is the special string C<slave/>, then the node will
		170	become a slave node. Slave nodes cannot be contacted from outside and will
		171	route most of their traffic to the master node that they attach to.
		172
		173	At least one additional noderef is required: The node will try to connect
		174	to all of them and will become a slave attached to the first node it can
		175	successfully connect to.
		176
		177	=back
		178
		179	This function will block until all nodes have been resolved and, for slave
		180	nodes, until it has successfully established a connection to a master
		181	server.
		182
		183	Example: become a public node listening on the default node.
		184
		185	initialise_node;
		186
		187	Example: become a public node, and try to contact some well-known master
		188	servers to become part of the network.
		189
		190	initialise_node undef, "master1", "master2";
		191
		192	Example: become a public node listening on port C<4041>.
		193
		194	initialise_node 4041;
		195
		196	Example: become a public node, only visible on localhost port 4044.
		197
		198	initialise_node "locahost:4044";
		199
		200	Example: become a slave node to any of the specified master servers.
		201
		202	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
		203
		204	=item $cv = resolve_node $noderef
		205
		206	Takes an unresolved node reference that may contain hostnames and
		207	abbreviated IDs, resolves all of them and returns a resolved node
		208	reference.
		209
		210	In addition to C<address:port> pairs allowed in resolved noderefs, the
		211	following forms are supported:
		212
		213	=over 4
		214
		215	=item the empty string
		216
		217	An empty-string component gets resolved as if the default port (4040) was
		218	specified.
		219
		220	=item naked port numbers (e.g. C<1234>)
		221
		222	These are resolved by prepending the local nodename and a colon, to be
		223	further resolved.
		224
		225	=item hostnames (e.g. C<localhost:1234>, C<localhost>)
		226
		227	These are resolved by using AnyEvent::DNS to resolve them, optionally
		228	looking up SRV records for the C<aemp=4040> port, if no port was
		229	specified.
		230
		231	=back
		232
		233	=item $SELF
		234
		235	Contains the current port id while executing C<rcv> callbacks or C<psub>
		236	blocks.
		237
		238	=item SELF, %SELF, @SELF...
		239
		240	Due to some quirks in how perl exports variables, it is impossible to
		241	just export C<$SELF>, all the symbols called C<SELF> are exported by this
		242	module, but only C<$SELF> is currently used.
		243
		244	=item snd $port, type => @data
		245
		246	=item snd $port, @msg
		247
		248	Send the given message to the given port ID, which can identify either
		249	a local or a remote port, and can be either a string or soemthignt hat
		250	stringifies a sa port ID (such as a port object :).
		251
		252	While the message can be about anything, it is highly recommended to use a
		253	string as first element (a portid, or some word that indicates a request
		254	type etc.).
		255
		256	The message data effectively becomes read-only after a call to this
		257	function: modifying any argument is not allowed and can cause many
		258	problems.
		259
		260	The type of data you can transfer depends on the transport protocol: when
		261	JSON is used, then only strings, numbers and arrays and hashes consisting
		262	of those are allowed (no objects). When Storable is used, then anything
		263	that Storable can serialise and deserialise is allowed, and for the local
		264	node, anything can be passed.
		265
		266	=item $local_port = port
		267
		268	Create a new local port object that can be used either as a pattern
		269	matching port ("full port") or a single-callback port ("miniport"),
		270	depending on how C<rcv> callbacks are bound to the object.
		271
		272	=item $port = port { my @msg = @_; $finished }
		273
		274	Creates a "miniport", that is, a very lightweight port without any pattern
		275	matching behind it, and returns its ID. Semantically the same as creating
		276	a port and calling C<rcv $port, $callback> on it.
		277
		278	The block will be called for every message received on the port. When the
		279	callback returns a true value its job is considered "done" and the port
		280	will be destroyed. Otherwise it will stay alive.
		281
		282	The message will be passed as-is, no extra argument (i.e. no port id) will
		283	be passed to the callback.
		284
		285	If you need the local port id in the callback, this works nicely:
		286
		287	my $port; $port = port {
		288	snd $otherport, reply => $port;
		289	};
		290
		291	=cut
		292
		293	sub rcv($@);
		294
		295	sub port(;&) {
		296	my $id = "$UNIQ." . $ID++;
		297	my $port = "$NODE#$id";
		298
		299	if (@_) {
		300	rcv $port, shift;
26	} else {	301	} else {
27	# shit...	302	$PORT{$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	}	303	}
35		304
36	$nonce	305	$port
37	}	306	}
38		307
39	our $DEFAULT_SECRET;	308	=item reg $port, $name
40		309
41	sub default_secret {	310	=item reg $name
42	unless (defined $DEFAULT_SECRET) {	311
43	if (open my $fh, "<$ENV{HOME}/.aemp-secret") {	312	Registers the given port (or C<$SELF><<< if missing) under the name
44	sysread $fh, $DEFAULT_SECRET, -s $fh;	313	C<$name>. If the name already exists it is replaced.
		314
		315	A port can only be registered under one well known name.
		316
		317	A port automatically becomes unregistered when it is killed.
		318
		319	=cut
		320
		321	sub reg(@) {
		322	my $port = @_ > 1 ? shift : $SELF \|\| Carp::croak 'reg: called with one argument only, but $SELF not set,';
		323
		324	$REG{$_[0]} = $port;
		325	}
		326
		327	=item rcv $port, $callback->(@msg)
		328
		329	Replaces the callback on the specified miniport (after converting it to
		330	one if required).
		331
		332	=item rcv $port, tagstring => $callback->(@msg), ...
		333
		334	=item rcv $port, $smartmatch => $callback->(@msg), ...
		335
		336	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
		337
		338	Register callbacks to be called on matching messages on the given full
		339	port (after converting it to one if required) and return the port.
		340
		341	The callback has to return a true value when its work is done, after
		342	which is will be removed, or a false value in which case it will stay
		343	registered.
		344
		345	The global C<$SELF> (exported by this module) contains C<$port> while
		346	executing the callback.
		347
		348	Runtime errors wdurign callback execution will result in the port being
		349	C<kil>ed.
		350
		351	If the match is an array reference, then it will be matched against the
		352	first elements of the message, otherwise only the first element is being
		353	matched.
		354
		355	Any element in the match that is specified as C<_any_> (a function
		356	exported by this module) matches any single element of the message.
		357
		358	While not required, it is highly recommended that the first matching
		359	element is a string identifying the message. The one-string-only match is
		360	also the most efficient match (by far).
		361
		362	Example: create a port and bind receivers on it in one go.
		363
		364	my $port = rcv port,
		365	msg1 => sub { ...; 0 },
		366	msg2 => sub { ...; 0 },
		367	;
		368
		369	Example: create a port, bind receivers and send it in a message elsewhere
		370	in one go:
		371
		372	snd $otherport, reply =>
		373	rcv port,
		374	msg1 => sub { ...; 0 },
		375	...
		376	;
		377
		378	=cut
		379
		380	sub rcv($@) {
		381	my $port = shift;
		382	my ($noderef, $portid) = split /#/, $port, 2;
		383
		384	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}
		385	or Carp::croak "$port: rcv can only be called on local ports, caught";
		386
		387	if (@_ == 1) {
		388	my $cb = shift;
		389	delete $PORT_DATA{$portid};
		390	$PORT{$portid} = sub {
		391	local $SELF = $port;
		392	eval {
		393	&$cb
		394	and kil $port;
		395	};
		396	_self_die if $@;
		397	};
		398	} else {
		399	my $self = $PORT_DATA{$portid} \|\|= do {
		400	my $self = bless {
		401	id => $port,
		402	}, "AnyEvent::MP::Port";
		403
		404	$PORT{$portid} = sub {
		405	local $SELF = $port;
		406
		407	eval {
		408	for (@{ $self->{rc0}{$_[0]} }) {
		409	$_ && &{$_->[0]}
		410	&& undef $_;
		411	}
		412
		413	for (@{ $self->{rcv}{$_[0]} }) {
		414	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
		415	&& &{$_->[0]}
		416	&& undef $_;
		417	}
		418
		419	for (@{ $self->{any} }) {
		420	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
		421	&& &{$_->[0]}
		422	&& undef $_;
		423	}
		424	};
		425	_self_die if $@;
		426	};
		427
		428	$self
		429	};
		430
		431	"AnyEvent::MP::Port" eq ref $self
		432	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		433
		434	while (@_) {
		435	my ($match, $cb) = splice @_, 0, 2;
		436
		437	if (!ref $match) {
		438	push @{ $self->{rc0}{$match} }, [$cb];
		439	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
		440	my ($type, @match) = @$match;
		441	@match
		442	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
		443	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
45	} else {	444	} else {
46	$DEFAULT_SECRET = nonce 32;	445	push @{ $self->{any} }, [$cb, $match];
		446	}
47	}	447	}
48	}	448	}
49		449
50	$DEFAULT_SECRET	450	$port
51	}	451	}
		452
		453	=item $closure = psub { BLOCK }
		454
		455	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
		456	closure is executed, sets up the environment in the same way as in C<rcv>
		457	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		458
		459	This is useful when you register callbacks from C<rcv> callbacks:
		460
		461	rcv delayed_reply => sub {
		462	my ($delay, @reply) = @_;
		463	my $timer = AE::timer $delay, 0, psub {
		464	snd @reply, $SELF;
		465	};
		466	};
		467
		468	=cut
		469
		470	sub psub(&) {
		471	my $cb = shift;
		472
		473	my $port = $SELF
		474	or Carp::croak "psub can only be called from within rcv or psub callbacks, not";
		475
		476	sub {
		477	local $SELF = $port;
		478
		479	if (wantarray) {
		480	my @res = eval { &$cb };
		481	_self_die if $@;
		482	@res
		483	} else {
		484	my $res = eval { &$cb };
		485	_self_die if $@;
		486	$res
		487	}
		488	}
		489	}
		490
		491	=item $guard = mon $port, $cb->(@reason)
		492
		493	=item $guard = mon $port, $rcvport
		494
		495	=item $guard = mon $port
		496
		497	=item $guard = mon $port, $rcvport, @msg
		498
		499	Monitor the given port and do something when the port is killed, and
		500	optionally return a guard that can be used to stop monitoring again.
		501
		502	In the first form (callback), the callback is simply called with any
		503	number of C<@reason> elements (no @reason means that the port was deleted
		504	"normally"). Note also that I<< the callback B<must> never die >>, so use
		505	C<eval> if unsure.
		506
		507	In the second form (another port given), the other port (C<$rcvport)
		508	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on
		509	"normal" kils nothing happens, while under all other conditions, the other
		510	port is killed with the same reason.
		511
		512	The third form (kill self) is the same as the second form, except that
		513	C<$rvport> defaults to C<$SELF>.
		514
		515	In the last form (message), a message of the form C<@msg, @reason> will be
		516	C<snd>.
		517
		518	Example: call a given callback when C<$port> is killed.
		519
		520	mon $port, sub { warn "port died because of <@_>\n" };
		521
		522	Example: kill ourselves when C<$port> is killed abnormally.
		523
		524	mon $port;
		525
		526	Example: send us a restart message when another C<$port> is killed.
		527
		528	mon $port, $self => "restart";
		529
		530	=cut
		531
		532	sub mon {
		533	my ($noderef, $port) = split /#/, shift, 2;
		534
		535	my $node = $NODE{$noderef} \|\| add_node $noderef;
		536
		537	my $cb = @_ ? $_[0] : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
		538
		539	unless (ref $cb) {
		540	if (@_) {
		541	# send a kill info message
		542	my (@msg) = @_;
		543	$cb = sub { snd @msg, @_ };
		544	} else {
		545	# simply kill other port
		546	my $port = $cb;
		547	$cb = sub { kil $port, @_ if @_ };
		548	}
		549	}
		550
		551	$node->monitor ($port, $cb);
		552
		553	defined wantarray
		554	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }
		555	}
		556
		557	=item $guard = mon_guard $port, $ref, $ref...
		558
		559	Monitors the given C<$port> and keeps the passed references. When the port
		560	is killed, the references will be freed.
		561
		562	Optionally returns a guard that will stop the monitoring.
		563
		564	This function is useful when you create e.g. timers or other watchers and
		565	want to free them when the port gets killed:
		566
		567	$port->rcv (start => sub {
		568	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {
		569	undef $timer if 0.9 < rand;
		570	});
		571	});
		572
		573	=cut
		574
		575	sub mon_guard {
		576	my ($port, @refs) = @_;
		577
		578	#TODO: mon-less form?
		579
		580	mon $port, sub { 0 && @refs }
		581	}
		582
		583	=item lnk $port1, $port2
		584
		585	=item lnk $otherport
		586
		587	Link two ports. This is simply a shorthand for:
		588
		589	mon $port1, $port2;
		590	mon $port2, $port1;
		591
		592	It means that if either one is killed abnormally, the other one gets
		593	killed as well.
		594
		595	The one-argument form assumes that one port is C<$SELF>.
		596
		597	=cut
		598
		599	sub lnk {
		600	my $port1 = shift;
		601	my $port2 = @_ ? shift : $SELF \|\| Carp::croak 'lnk: called with one argument only, but $SELF not set,';
		602
		603	mon $port1, $port2;
		604	mon $port2, $port1;
		605	}
		606
		607	=item kil $port[, @reason]
		608
		609	Kill the specified port with the given C<@reason>.
		610
		611	If no C<@reason> is specified, then the port is killed "normally" (linked
		612	ports will not be kileld, or even notified).
		613
		614	Otherwise, linked ports get killed with the same reason (second form of
		615	C<mon>, see below).
		616
		617	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		618	will be reported as reason C<< die => $@ >>.
		619
		620	Transport/communication errors are reported as C<< transport_error =>
		621	$message >>.
		622
		623	=back
		624
		625	=head1 NODE MESSAGES
		626
		627	Nodes understand the following messages sent to them. Many of them take
		628	arguments called C<@reply>, which will simply be used to compose a reply
		629	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
		630	the remaining arguments are simply the message data.
		631
		632	While other messages exist, they are not public and subject to change.
		633
		634	=over 4
		635
		636	=cut
		637
		638	=item lookup => $name, @reply
		639
		640	Replies with the port ID of the specified well-known port, or C<undef>.
		641
		642	=item devnull => ...
		643
		644	Generic data sink/CPU heat conversion.
		645
		646	=item relay => $port, @msg
		647
		648	Simply forwards the message to the given port.
		649
		650	=item eval => $string[ @reply]
		651
		652	Evaluates the given string. If C<@reply> is given, then a message of the
		653	form C<@reply, $@, @evalres> is sent.
		654
		655	Example: crash another node.
		656
		657	snd $othernode, eval => "exit";
		658
		659	=item time => @reply
		660
		661	Replies the the current node time to C<@reply>.
		662
		663	Example: tell the current node to send the current time to C<$myport> in a
		664	C<timereply> message.
		665
		666	snd $NODE, time => $myport, timereply => 1, 2;
		667	# => snd $myport, timereply => 1, 2, <time>
		668
		669	=back
		670
		671	=head1 AnyEvent::MP vs. Distributed Erlang
		672
		673	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
		674	== aemp node, Erlang process == aemp port), so many of the documents and
		675	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
		676	sample:
		677
		678	http://www.Erlang.se/doc/programming_rules.shtml
		679	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
		680	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6
		681	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
		682
		683	Despite the similarities, there are also some important differences:
		684
		685	=over 4
		686
		687	=item * Node references contain the recipe on how to contact them.
		688
		689	Erlang relies on special naming and DNS to work everywhere in the
		690	same way. AEMP relies on each node knowing it's own address(es), with
		691	convenience functionality.
		692
		693	This means that AEMP requires a less tightly controlled environment at the
		694	cost of longer node references and a slightly higher management overhead.
		695
		696	=item * Erlang uses processes and a mailbox, AEMP does not queue.
		697
		698	Erlang uses processes that selctively receive messages, and therefore
		699	needs a queue. AEMP is event based, queuing messages would serve no useful
		700	purpose.
		701
		702	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).
		703
		704	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
		705
		706	Sending messages in Erlang is synchronous and blocks the process. AEMP
		707	sends are immediate, connection establishment is handled in the
		708	background.
		709
		710	=item * Erlang can silently lose messages, AEMP cannot.
		711
		712	Erlang makes few guarantees on messages delivery - messages can get lost
		713	without any of the processes realising it (i.e. you send messages a, b,
		714	and c, and the other side only receives messages a and c).
		715
		716	AEMP guarantees correct ordering, and the guarantee that there are no
		717	holes in the message sequence.
		718
		719	=item * In Erlang, processes can be declared dead and later be found to be
		720	alive.
		721
		722	In Erlang it can happen that a monitored process is declared dead and
		723	linked processes get killed, but later it turns out that the process is
		724	still alive - and can receive messages.
		725
		726	In AEMP, when port monitoring detects a port as dead, then that port will
		727	eventually be killed - it cannot happen that a node detects a port as dead
		728	and then later sends messages to it, finding it is still alive.
		729
		730	=item * Erlang can send messages to the wrong port, AEMP does not.
		731
		732	In Erlang it is quite possible that a node that restarts reuses a process
		733	ID known to other nodes for a completely different process, causing
		734	messages destined for that process to end up in an unrelated process.
		735
		736	AEMP never reuses port IDs, so old messages or old port IDs floating
		737	around in the network will not be sent to an unrelated port.
		738
		739	=item * Erlang uses unprotected connections, AEMP uses secure
		740	authentication and can use TLS.
		741
		742	AEMP can use a proven protocol - SSL/TLS - to protect connections and
		743	securely authenticate nodes.
		744
		745	=item * The AEMP protocol is optimised for both text-based and binary
		746	communications.
		747
		748	The AEMP protocol, unlike the Erlang protocol, supports both
		749	language-independent text-only protocols (good for debugging) and binary,
		750	language-specific serialisers (e.g. Storable).
		751
		752	It has also been carefully designed to be implementable in other languages
		753	with a minimum of work while gracefully degrading fucntionality to make the
		754	protocol simple.
		755
		756	=item * AEMP has more flexible monitoring options than Erlang.
		757
		758	In Erlang, you can chose to receive I<all> exit signals as messages
		759	or I<none>, there is no in-between, so monitoring single processes is
		760	difficult to implement. Monitoring in AEMP is more flexible than in
		761	Erlang, as one can choose between automatic kill, exit message or callback
		762	on a per-process basis.
		763
		764	=item * Erlang has different semantics for monitoring and linking, AEMP has the same.
		765
		766	Monitoring in Erlang is not an indicator of process death/crashes,
		767	as linking is (except linking is unreliable in Erlang). In AEMP, the
		768	semantics of monitoring and linking are identical, linking is simply
		769	two-way monitoring with automatic kill.
		770
		771	=back
52		772
53	=head1 SEE ALSO	773	=head1 SEE ALSO
54		774
55	L<AnyEvent>.	775	L<AnyEvent>.
56		776

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Revision 1.36 by root, Thu Aug 6 10:46:48 2009 UTC