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Revision 1.142 by root, Fri Mar 23 13:44:01 2012 UTC

1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent::MP - multi-processing/message-passing framework	3	AnyEvent::MP - erlang-style multi-processing/message-passing framework
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 node ID
		10	NODE # returns this node's node ID
		11
		12	$SELF # receiving/own port id in rcv callbacks
		13
		14	# initialise the node so it can send/receive messages
		15	configure;
		16
		17	# ports are message destinations
		18
		19	# sending messages
		20	snd $port, type => data...;
		21	snd $port, @msg;
		22	snd @msg_with_first_element_being_a_port;
		23
		24	# creating/using ports, the simple way
		25	my $simple_port = port { my @msg = @_ };
		26
		27	# creating/using ports, tagged message matching
		28	my $port = port;
		29	rcv $port, ping => sub { snd $_[0], "pong" };
		30	rcv $port, pong => sub { warn "pong received\n" };
		31
		32	# create a port on another node
		33	my $port = spawn $node, $initfunc, @initdata;
		34
		35	# destroy a port again
		36	kil $port; # "normal" kill
		37	kil $port, my_error => "everything is broken"; # error kill
		38
		39	# monitoring
		40	mon $port, $cb->(@msg) # callback is invoked on death
		41	mon $port, $localport # kill localport on abnormal death
		42	mon $port, $localport, @msg # send message on death
		43
		44	# temporarily execute code in port context
		45	peval $port, sub { die "kill the port!" };
		46
		47	# execute callbacks in $SELF port context
		48	my $timer = AE::timer 1, 0, psub {
		49	die "kill the port, delayed";
		50	};
		51
9	=head1 DESCRIPTION	52	=head1 DESCRIPTION
10		53
		54	This module (-family) implements a simple message passing framework.
		55
		56	Despite its simplicity, you can securely message other processes running
		57	on the same or other hosts, and you can supervise entities remotely.
		58
		59	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
		60	manual page and the examples under F<eg/>.
		61
		62	=head1 CONCEPTS
		63
		64	=over 4
		65
		66	=item port
		67
		68	Not to be confused with a TCP port, a "port" is something you can send
		69	messages to (with the C<snd> function).
		70
		71	Ports allow you to register C<rcv> handlers that can match all or just
		72	some messages. Messages send to ports will not be queued, regardless of
		73	anything was listening for them or not.
		74
		75	Ports are represented by (printable) strings called "port IDs".
		76
		77	=item port ID - C<nodeid#portname>
		78
		79	A port ID is the concatenation of a node ID, a hash-mark (C<#>)
		80	as separator, and a port name (a printable string of unspecified
		81	format created by AnyEvent::MP).
		82
		83	=item node
		84
		85	A node is a single process containing at least one port - the node port,
		86	which enables nodes to manage each other remotely, and to create new
		87	ports.
		88
		89	Nodes are either public (have one or more listening ports) or private
		90	(no listening ports). Private nodes cannot talk to other private nodes
		91	currently, but all nodes can talk to public nodes.
		92
		93	Nodes is represented by (printable) strings called "node IDs".
		94
		95	=item node ID - C<[A-Za-z0-9_\-.:]*>
		96
		97	A node ID is a string that uniquely identifies the node within a
		98	network. Depending on the configuration used, node IDs can look like a
		99	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		100	doesn't interpret node IDs in any way except to uniquely identify a node.
		101
		102	=item binds - C<ip:port>
		103
		104	Nodes can only talk to each other by creating some kind of connection to
		105	each other. To do this, nodes should listen on one or more local transport
		106	endpoints - binds.
		107
		108	Currently, only standard C<ip:port> specifications can be used, which
		109	specify TCP ports to listen on. So a bind is basically just a tcp socket
		110	in listening mode thta accepts conenctions form other nodes.
		111
		112	=item seed nodes
		113
		114	When a node starts, it knows nothing about the network it is in - it
		115	needs to connect to at least one other node that is already in the
		116	network. These other nodes are called "seed nodes".
		117
		118	Seed nodes themselves are not special - they are seed nodes only because
		119	some other node I<uses> them as such, but any node can be used as seed
		120	node for other nodes, and eahc node cna use a different set of seed nodes.
		121
		122	In addition to discovering the network, seed nodes are also used to
		123	maintain the network - all nodes using the same seed node form are part of
		124	the same network. If a network is split into multiple subnets because e.g.
		125	the network link between the parts goes down, then using the same seed
		126	nodes for all nodes ensures that eventually the subnets get merged again.
		127
		128	Seed nodes are expected to be long-running, and at least one seed node
		129	should always be available. They should also be relatively responsive - a
		130	seed node that blocks for long periods will slow down everybody else.
		131
		132	For small networks, it's best if every node uses the same set of seed
		133	nodes. For large networks, it can be useful to specify "regional" seed
		134	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		135	each other. What's important is that all seed nodes connections form a
		136	complete graph, so that the network cannot split into separate subnets
		137	forever.
		138
		139	Seed nodes are represented by seed IDs.
		140
		141	=item seed IDs - C<host:port>
		142
		143	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
		144	TCP port) of nodes that should be used as seed nodes.
		145
		146	=item global nodes
		147
		148	An AEMP network needs a discovery service - nodes need to know how to
		149	connect to other nodes they only know by name. In addition, AEMP offers a
		150	distributed "group database", which maps group names to a list of strings
		151	- for example, to register worker ports.
		152
		153	A network needs at least one global node to work, and allows every node to
		154	be a global node.
		155
		156	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		157	node and tries to keep connections to all other nodes. So while it can
		158	make sense to make every node "global" in small networks, it usually makes
		159	sense to only make seed nodes into global nodes in large networks (nodes
		160	keep connections to seed nodes and global nodes, so makign them the same
		161	reduces overhead).
		162
		163	=back
		164
		165	=head1 VARIABLES/FUNCTIONS
		166
		167	=over 4
		168
11	=cut	169	=cut
12		170
13	package AnyEvent::MP;	171	package AnyEvent::MP;
14		172
		173	use AnyEvent::MP::Config ();
		174	use AnyEvent::MP::Kernel;
		175	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
		176
15	use common::sense;	177	use common::sense;
16		178
		179	use Carp ();
		180
17	use AE ();	181	use AnyEvent ();
		182	use Guard ();
18		183
19	our $VERSION = '0.0';	184	use base "Exporter";
20		185
21	sub nonce($) {	186	our $VERSION = $AnyEvent::MP::Config::VERSION;
22	my $nonce;
23		187
24	if (open my $fh, "</dev/urandom") {	188	our @EXPORT = qw(
25	sysread $fh, $nonce, $_[0];	189	NODE $NODE *SELF node_of after
26	} else {	190	configure
27	# shit...	191	snd rcv mon mon_guard kil psub peval spawn cal
28	our $nonce_init;	192	port
29	unless ($nonce_init++) {	193	db_set db_del db_reg
30	srand time ^ $$ ^ unpack "%L*", qx"ps -edalf" . qx"ipconfig /all";	194	db_mon db_family db_keys db_values
31	}	195	);
32		196
33	$nonce = join "", map +(chr rand 256), 1 .. $_[0]	197	our $SELF;
34	}
35		198
36	$nonce	199	sub _self_die() {
		200	my $msg = $@;
		201	$msg =~ s/\n+$// unless ref $msg;
		202	kil $SELF, die => $msg;
37	}	203	}
38		204
39	our $DEFAULT_SECRET;	205	=item $thisnode = NODE / $NODE
40		206
41	sub default_secret {	207	The C<NODE> function returns, and the C<$NODE> variable contains, the node
42	unless (defined $DEFAULT_SECRET) {	208	ID of the node running in the current process. This value is initialised by
43	if (open my $fh, "<$ENV{HOME}/.aemp-secret") {	209	a call to C<configure>.
44	sysread $fh, $DEFAULT_SECRET, -s $fh;	210
		211	=item $nodeid = node_of $port
		212
		213	Extracts and returns the node ID from a port ID or a node ID.
		214
		215	=item configure $profile, key => value...
		216
		217	=item configure key => value...
		218
		219	Before a node can talk to other nodes on the network (i.e. enter
		220	"distributed mode") it has to configure itself - the minimum a node needs
		221	to know is its own name, and optionally it should know the addresses of
		222	some other nodes in the network to discover other nodes.
		223
		224	This function configures a node - it must be called exactly once (or
		225	never) before calling other AnyEvent::MP functions.
		226
		227	The key/value pairs are basically the same ones as documented for the
		228	F<aemp> command line utility (sans the set/del prefix), with these additions:
		229
		230	=over 4
		231
		232	=item norc => $boolean (default false)
		233
		234	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
		235	be consulted - all configuraiton options must be specified in the
		236	C<configure> call.
		237
		238	=item force => $boolean (default false)
		239
		240	IF true, then the values specified in the C<configure> will take
		241	precedence over any values configured via the rc file. The default is for
		242	the rc file to override any options specified in the program.
		243
		244	=back
		245
		246	=over 4
		247
		248	=item step 1, gathering configuration from profiles
		249
		250	The function first looks up a profile in the aemp configuration (see the
		251	L<aemp> commandline utility). The profile name can be specified via the
		252	named C<profile> parameter or can simply be the first parameter). If it is
		253	missing, then the nodename (F<uname -n>) will be used as profile name.
		254
		255	The profile data is then gathered as follows:
		256
		257	First, all remaining key => value pairs (all of which are conveniently
		258	undocumented at the moment) will be interpreted as configuration
		259	data. Then they will be overwritten by any values specified in the global
		260	default configuration (see the F<aemp> utility), then the chain of
		261	profiles chosen by the profile name (and any C<parent> attributes).
		262
		263	That means that the values specified in the profile have highest priority
		264	and the values specified directly via C<configure> have lowest priority,
		265	and can only be used to specify defaults.
		266
		267	If the profile specifies a node ID, then this will become the node ID of
		268	this process. If not, then the profile name will be used as node ID, with
		269	a unique randoms tring (C</%u>) appended.
		270
		271	The node ID can contain some C<%> sequences that are expanded: C<%n>
		272	is expanded to the local nodename, C<%u> is replaced by a random
		273	strign to make the node unique. For example, the F<aemp> commandline
		274	utility uses C<aemp/%n/%u> as nodename, which might expand to
		275	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		276
		277	=item step 2, bind listener sockets
		278
		279	The next step is to look up the binds in the profile, followed by binding
		280	aemp protocol listeners on all binds specified (it is possible and valid
		281	to have no binds, meaning that the node cannot be contacted form the
		282	outside. This means the node cannot talk to other nodes that also have no
		283	binds, but it can still talk to all "normal" nodes).
		284
		285	If the profile does not specify a binds list, then a default of C<*> is
		286	used, meaning the node will bind on a dynamically-assigned port on every
		287	local IP address it finds.
		288
		289	=item step 3, connect to seed nodes
		290
		291	As the last step, the seed ID list from the profile is passed to the
		292	L<AnyEvent::MP::Global> module, which will then use it to keep
		293	connectivity with at least one node at any point in time.
		294
		295	=back
		296
		297	Example: become a distributed node using the local node name as profile.
		298	This should be the most common form of invocation for "daemon"-type nodes.
		299
		300	configure
		301
		302	Example: become a semi-anonymous node. This form is often used for
		303	commandline clients.
		304
		305	configure nodeid => "myscript/%n/%u";
		306
		307	Example: configure a node using a profile called seed, which is suitable
		308	for a seed node as it binds on all local addresses on a fixed port (4040,
		309	customary for aemp).
		310
		311	# use the aemp commandline utility
		312	# aemp profile seed binds '*:4040'
		313
		314	# then use it
		315	configure profile => "seed";
		316
		317	# or simply use aemp from the shell again:
		318	# aemp run profile seed
		319
		320	# or provide a nicer-to-remember nodeid
		321	# aemp run profile seed nodeid "$(hostname)"
		322
		323	=item $SELF
		324
		325	Contains the current port id while executing C<rcv> callbacks or C<psub>
		326	blocks.
		327
		328	=item *SELF, SELF, %SELF, @SELF...
		329
		330	Due to some quirks in how perl exports variables, it is impossible to
		331	just export C<$SELF>, all the symbols named C<SELF> are exported by this
		332	module, but only C<$SELF> is currently used.
		333
		334	=item snd $port, type => @data
		335
		336	=item snd $port, @msg
		337
		338	Send the given message to the given port, which can identify either a
		339	local or a remote port, and must be a port ID.
		340
		341	While the message can be almost anything, it is highly recommended to
		342	use a string as first element (a port ID, or some word that indicates a
		343	request type etc.) and to consist if only simple perl values (scalars,
		344	arrays, hashes) - if you think you need to pass an object, think again.
		345
		346	The message data logically becomes read-only after a call to this
		347	function: modifying any argument (or values referenced by them) is
		348	forbidden, as there can be considerable time between the call to C<snd>
		349	and the time the message is actually being serialised - in fact, it might
		350	never be copied as within the same process it is simply handed to the
		351	receiving port.
		352
		353	The type of data you can transfer depends on the transport protocol: when
		354	JSON is used, then only strings, numbers and arrays and hashes consisting
		355	of those are allowed (no objects). When Storable is used, then anything
		356	that Storable can serialise and deserialise is allowed, and for the local
		357	node, anything can be passed. Best rely only on the common denominator of
		358	these.
		359
		360	=item $local_port = port
		361
		362	Create a new local port object and returns its port ID. Initially it has
		363	no callbacks set and will throw an error when it receives messages.
		364
		365	=item $local_port = port { my @msg = @_ }
		366
		367	Creates a new local port, and returns its ID. Semantically the same as
		368	creating a port and calling C<rcv $port, $callback> on it.
		369
		370	The block will be called for every message received on the port, with the
		371	global variable C<$SELF> set to the port ID. Runtime errors will cause the
		372	port to be C<kil>ed. The message will be passed as-is, no extra argument
		373	(i.e. no port ID) will be passed to the callback.
		374
		375	If you want to stop/destroy the port, simply C<kil> it:
		376
		377	my $port = port {
		378	my @msg = @_;
		379	...
		380	kil $SELF;
		381	};
		382
		383	=cut
		384
		385	sub rcv($@);
		386
		387	my $KILME = sub {
		388	(my $tag = substr $_[0], 0, 30) =~ s/([\x20-\x7e])/./g;
		389	kil $SELF, unhandled_message => "no callback found for message '$tag'";
		390	};
		391
		392	sub port(;&) {
		393	my $id = $UNIQ . ++$ID;
		394	my $port = "$NODE#$id";
		395
		396	rcv $port, shift || $KILME;
		397
		398	$port
		399	}
		400
		401	=item rcv $local_port, $callback->(@msg)
		402
		403	Replaces the default callback on the specified port. There is no way to
		404	remove the default callback: use C<sub { }> to disable it, or better
		405	C<kil> the port when it is no longer needed.
		406
		407	The global C<$SELF> (exported by this module) contains C<$port> while
		408	executing the callback. Runtime errors during callback execution will
		409	result in the port being C<kil>ed.
		410
		411	The default callback receives all messages not matched by a more specific
		412	C<tag> match.
		413
		414	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
		415
		416	Register (or replace) callbacks to be called on messages starting with the
		417	given tag on the given port (and return the port), or unregister it (when
		418	C<$callback> is C<$undef> or missing). There can only be one callback
		419	registered for each tag.
		420
		421	The original message will be passed to the callback, after the first
		422	element (the tag) has been removed. The callback will use the same
		423	environment as the default callback (see above).
		424
		425	Example: create a port and bind receivers on it in one go.
		426
		427	my $port = rcv port,
		428	msg1 => sub { ... },
		429	msg2 => sub { ... },
		430	;
		431
		432	Example: create a port, bind receivers and send it in a message elsewhere
		433	in one go:
		434
		435	snd $otherport, reply =>
		436	rcv port,
		437	msg1 => sub { ... },
		438	...
		439	;
		440
		441	Example: temporarily register a rcv callback for a tag matching some port
		442	(e.g. for an rpc reply) and unregister it after a message was received.
		443
		444	rcv $port, $otherport => sub {
		445	my @reply = @_;
		446
		447	rcv $SELF, $otherport;
		448	};
		449
		450	=cut
		451
		452	sub rcv($@) {
		453	my $port = shift;
		454	my ($nodeid, $portid) = split /#/, $port, 2;
		455
		456	$NODE{$nodeid} == $NODE{""}
		457	or Carp::croak "$port: rcv can only be called on local ports, caught";
		458
		459	while (@_) {
		460	if (ref $_[0]) {
		461	if (my $self = $PORT_DATA{$portid}) {
		462	"AnyEvent::MP::Port" eq ref $self
		463	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		464
		465	$self->[0] = shift;
45	} else {	466	} else {
46	$DEFAULT_SECRET = nonce 32;	467	my $cb = shift;
		468	$PORT{$portid} = sub {
		469	local $SELF = $port;
		470	eval { &$cb }; _self_die if $@;
		471	};
		472	}
		473	} elsif (defined $_[0]) {
		474	my $self = $PORT_DATA{$portid} ||= do {
		475	my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port";
		476
		477	$PORT{$portid} = sub {
		478	local $SELF = $port;
		479
		480	if (my $cb = $self->[1]{$_[0]}) {
		481	shift;
		482	eval { &$cb }; _self_die if $@;
		483	} else {
		484	&{ $self->[0] };
		485	}
		486	};
		487
		488	$self
		489	};
		490
		491	"AnyEvent::MP::Port" eq ref $self
		492	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		493
		494	my ($tag, $cb) = splice @_, 0, 2;
		495
		496	if (defined $cb) {
		497	$self->[1]{$tag} = $cb;
		498	} else {
		499	delete $self->[1]{$tag};
		500	}
47	}	501	}
48	}	502	}
49		503
50	$DEFAULT_SECRET	504	$port
51	}	505	}
52		506
		507	=item peval $port, $coderef[, @args]
		508
		509	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		510	when the code throews an exception the C<$port> will be killed.
		511
		512	Any remaining args will be passed to the callback. Any return values will
		513	be returned to the caller.
		514
		515	This is useful when you temporarily want to execute code in the context of
		516	a port.
		517
		518	Example: create a port and run some initialisation code in it's context.
		519
		520	my $port = port { ... };
		521
		522	peval $port, sub {
		523	init
		524	or die "unable to init";
		525	};
		526
		527	=cut
		528
		529	sub peval($$) {
		530	local $SELF = shift;
		531	my $cb = shift;
		532
		533	if (wantarray) {
		534	my @res = eval { &$cb };
		535	_self_die if $@;
		536	@res
		537	} else {
		538	my $res = eval { &$cb };
		539	_self_die if $@;
		540	$res
		541	}
		542	}
		543
		544	=item $closure = psub { BLOCK }
		545
		546	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
		547	closure is executed, sets up the environment in the same way as in C<rcv>
		548	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		549
		550	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		551	BLOCK }, @_ } >>.
		552
		553	This is useful when you register callbacks from C<rcv> callbacks:
		554
		555	rcv delayed_reply => sub {
		556	my ($delay, @reply) = @_;
		557	my $timer = AE::timer $delay, 0, psub {
		558	snd @reply, $SELF;
		559	};
		560	};
		561
		562	=cut
		563
		564	sub psub(&) {
		565	my $cb = shift;
		566
		567	my $port = $SELF
		568	or Carp::croak "psub can only be called from within rcv or psub callbacks, not";
		569
		570	sub {
		571	local $SELF = $port;
		572
		573	if (wantarray) {
		574	my @res = eval { &$cb };
		575	_self_die if $@;
		576	@res
		577	} else {
		578	my $res = eval { &$cb };
		579	_self_die if $@;
		580	$res
		581	}
		582	}
		583	}
		584
		585	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
		586
		587	=item $guard = mon $port # kill $SELF when $port dies
		588
		589	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
		590
		591	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		592
		593	Monitor the given port and do something when the port is killed or
		594	messages to it were lost, and optionally return a guard that can be used
		595	to stop monitoring again.
		596
		597	The first two forms distinguish between "normal" and "abnormal" kil's:
		598
		599	In the first form (another port given), if the C<$port> is C<kil>'ed with
		600	a non-empty reason, the other port (C<$rcvport>) will be kil'ed with the
		601	same reason. That is, on "normal" kil's nothing happens, while under all
		602	other conditions, the other port is killed with the same reason.
		603
		604	The second form (kill self) is the same as the first form, except that
		605	C<$rvport> defaults to C<$SELF>.
		606
		607	The remaining forms don't distinguish between "normal" and "abnormal" kil's
		608	- it's up to the callback or receiver to check whether the C<@reason> is
		609	empty and act accordingly.
		610
		611	In the third form (callback), the callback is simply called with any
		612	number of C<@reason> elements (empty @reason means that the port was deleted
		613	"normally"). Note also that I<< the callback B<must> never die >>, so use
		614	C<eval> if unsure.
		615
		616	In the last form (message), a message of the form C<$rcvport, @msg,
		617	@reason> will be C<snd>.
		618
		619	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		620	alert was raised), they are removed and will not trigger again, even if it
		621	turns out that the port is still alive.
		622
		623	As a rule of thumb, monitoring requests should always monitor a remote
		624	port locally (using a local C<$rcvport> or a callback). The reason is that
		625	kill messages might get lost, just like any other message. Another less
		626	obvious reason is that even monitoring requests can get lost (for example,
		627	when the connection to the other node goes down permanently). When
		628	monitoring a port locally these problems do not exist.
		629
		630	C<mon> effectively guarantees that, in the absence of hardware failures,
		631	after starting the monitor, either all messages sent to the port will
		632	arrive, or the monitoring action will be invoked after possible message
		633	loss has been detected. No messages will be lost "in between" (after
		634	the first lost message no further messages will be received by the
		635	port). After the monitoring action was invoked, further messages might get
		636	delivered again.
		637
		638	Inter-host-connection timeouts and monitoring depend on the transport
		639	used. The only transport currently implemented is TCP, and AnyEvent::MP
		640	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		641	non-idle connection, and usually around two hours for idle connections).
		642
		643	This means that monitoring is good for program errors and cleaning up
		644	stuff eventually, but they are no replacement for a timeout when you need
		645	to ensure some maximum latency.
		646
		647	Example: call a given callback when C<$port> is killed.
		648
		649	mon $port, sub { warn "port died because of <@_>\n" };
		650
		651	Example: kill ourselves when C<$port> is killed abnormally.
		652
		653	mon $port;
		654
		655	Example: send us a restart message when another C<$port> is killed.
		656
		657	mon $port, $self => "restart";
		658
		659	=cut
		660
		661	sub mon {
		662	my ($nodeid, $port) = split /#/, shift, 2;
		663
		664	my $node = $NODE{$nodeid} || add_node $nodeid;
		665
		666	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
		667
		668	unless (ref $cb) {
		669	if (@_) {
		670	# send a kill info message
		671	my (@msg) = ($cb, @_);
		672	$cb = sub { snd @msg, @_ };
		673	} else {
		674	# simply kill other port
		675	my $port = $cb;
		676	$cb = sub { kil $port, @_ if @_ };
		677	}
		678	}
		679
		680	$node->monitor ($port, $cb);
		681
		682	defined wantarray
		683	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
		684	}
		685
		686	=item $guard = mon_guard $port, $ref, $ref...
		687
		688	Monitors the given C<$port> and keeps the passed references. When the port
		689	is killed, the references will be freed.
		690
		691	Optionally returns a guard that will stop the monitoring.
		692
		693	This function is useful when you create e.g. timers or other watchers and
		694	want to free them when the port gets killed (note the use of C<psub>):
		695
		696	$port->rcv (start => sub {
		697	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
		698	undef $timer if 0.9 < rand;
		699	});
		700	});
		701
		702	=cut
		703
		704	sub mon_guard {
		705	my ($port, @refs) = @_;
		706
		707	#TODO: mon-less form?
		708
		709	mon $port, sub { 0 && @refs }
		710	}
		711
		712	=item kil $port[, @reason]
		713
		714	Kill the specified port with the given C<@reason>.
		715
		716	If no C<@reason> is specified, then the port is killed "normally" -
		717	monitor callback will be invoked, but the kil will not cause linked ports
		718	(C<mon $mport, $lport> form) to get killed.
		719
		720	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
		721	form) get killed with the same reason.
		722
		723	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		724	will be reported as reason C<< die => $@ >>.
		725
		726	Transport/communication errors are reported as C<< transport_error =>
		727	$message >>.
		728
		729	Common idioms:
		730
		731	# silently remove yourself, do not kill linked ports
		732	kil $SELF;
		733
		734	# report a failure in some detail
		735	kil $SELF, failure_mode_1 => "it failed with too high temperature";
		736
		737	# do not waste much time with killing, just die when something goes wrong
		738	open my $fh, "<file"
		739	or die "file: $!";
		740
		741	=item $port = spawn $node, $initfunc[, @initdata]
		742
		743	Creates a port on the node C<$node> (which can also be a port ID, in which
		744	case it's the node where that port resides).
		745
		746	The port ID of the newly created port is returned immediately, and it is
		747	possible to immediately start sending messages or to monitor the port.
		748
		749	After the port has been created, the init function is called on the remote
		750	node, in the same context as a C<rcv> callback. This function must be a
		751	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		752	specify a function in the main program, use C<::name>.
		753
		754	If the function doesn't exist, then the node tries to C<require>
		755	the package, then the package above the package and so on (e.g.
		756	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		757	exists or it runs out of package names.
		758
		759	The init function is then called with the newly-created port as context
		760	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		761	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		762	the port might not get created.
		763
		764	A common idiom is to pass a local port, immediately monitor the spawned
		765	port, and in the remote init function, immediately monitor the passed
		766	local port. This two-way monitoring ensures that both ports get cleaned up
		767	when there is a problem.
		768
		769	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		770	caller before C<spawn> returns (by delaying invocation when spawn is
		771	called for the local node).
		772
		773	Example: spawn a chat server port on C<$othernode>.
		774
		775	# this node, executed from within a port context:
		776	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		777	mon $server;
		778
		779	# init function on C<$othernode>
		780	sub connect {
		781	my ($srcport) = @_;
		782
		783	mon $srcport;
		784
		785	rcv $SELF, sub {
		786	...
		787	};
		788	}
		789
		790	=cut
		791
		792	sub _spawn {
		793	my $port = shift;
		794	my $init = shift;
		795
		796	# rcv will create the actual port
		797	local $SELF = "$NODE#$port";
		798	eval {
		799	&{ load_func $init }
		800	};
		801	_self_die if $@;
		802	}
		803
		804	sub spawn(@) {
		805	my ($nodeid, undef) = split /#/, shift, 2;
		806
		807	my $id = $RUNIQ . ++$ID;
		808
		809	$_[0] =~ /::/
		810	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		811
		812	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		813
		814	"$nodeid#$id"
		815	}
		816
		817
		818	=item after $timeout, @msg
		819
		820	=item after $timeout, $callback
		821
		822	Either sends the given message, or call the given callback, after the
		823	specified number of seconds.
		824
		825	This is simply a utility function that comes in handy at times - the
		826	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		827	so it may go away in the future.
		828
		829	=cut
		830
		831	sub after($@) {
		832	my ($timeout, @action) = @_;
		833
		834	my $t; $t = AE::timer $timeout, 0, sub {
		835	undef $t;
		836	ref $action[0]
		837	? $action[0]()
		838	: snd @action;
		839	};
		840	}
		841
		842	#=item $cb2 = timeout $seconds, $cb[, @args]
		843
		844	=item cal $port, @msg, $callback[, $timeout]
		845
		846	A simple form of RPC - sends a message to the given C<$port> with the
		847	given contents (C<@msg>), but adds a reply port to the message.
		848
		849	The reply port is created temporarily just for the purpose of receiving
		850	the reply, and will be C<kil>ed when no longer needed.
		851
		852	A reply message sent to the port is passed to the C<$callback> as-is.
		853
		854	If an optional time-out (in seconds) is given and it is not C<undef>,
		855	then the callback will be called without any arguments after the time-out
		856	elapsed and the port is C<kil>ed.
		857
		858	If no time-out is given (or it is C<undef>), then the local port will
		859	monitor the remote port instead, so it eventually gets cleaned-up.
		860
		861	Currently this function returns the temporary port, but this "feature"
		862	might go in future versions unless you can make a convincing case that
		863	this is indeed useful for something.
		864
		865	=cut
		866
		867	sub cal(@) {
		868	my $timeout = ref $_[-1] ? undef : pop;
		869	my $cb = pop;
		870
		871	my $port = port {
		872	undef $timeout;
		873	kil $SELF;
		874	&$cb;
		875	};
		876
		877	if (defined $timeout) {
		878	$timeout = AE::timer $timeout, 0, sub {
		879	undef $timeout;
		880	kil $port;
		881	$cb->();
		882	};
		883	} else {
		884	mon $_[0], sub {
		885	kil $port;
		886	$cb->();
		887	};
		888	}
		889
		890	push @_, $port;
		891	&snd;
		892
		893	$port
		894	}
		895
		896	=back
		897
		898	=head1 DISTRIBUTED DATABASE
		899
		900	AnyEvent::MP comes with a simple distributed database. The database will
		901	be mirrored asynchronously on all global nodes. Other nodes bind to one
		902	of the global nodes for their needs. Every node has a "local database"
		903	which contains all the values that are set locally. All local databases
		904	are merged together to form the global database, which can be queried.
		905
		906	The database structure is that of a two-level hash - the database hash
		907	contains hashes which contain values, similarly to a perl hash of hashes,
		908	i.e.:
		909
		910	$DATABASE{$family}{$subkey} = $value
		911
		912	The top level hash key is called "family", and the second-level hash key
		913	is called "subkey" or simply "key".
		914
		915	The family must be alphanumeric, i.e. start with a letter and consist
		916	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		917	pretty much like Perl module names.
		918
		919	As the family namespace is global, it is recommended to prefix family names
		920	with the name of the application or module using it.
		921
		922	The subkeys must be non-empty strings, with no further restrictions.
		923
		924	The values should preferably be strings, but other perl scalars should
		925	work as well (such as C<undef>, arrays and hashes).
		926
		927	Every database entry is owned by one node - adding the same family/subkey
		928	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		929	but the result might be nondeterministic, i.e. the key might have
		930	different values on different nodes.
		931
		932	Different subkeys in the same family can be owned by different nodes
		933	without problems, and in fact, this is the common method to create worker
		934	pools. For example, a worker port for image scaling might do this:
		935
		936	db_set my_image_scalers => $port;
		937
		938	And clients looking for an image scaler will want to get the
		939	C<my_image_scalers> keys from time to time:
		940
		941	db_keys my_image_scalers => sub {
		942	@ports = @{ $_[0] };
		943	};
		944
		945	Or better yet, they want to monitor the database family, so they always
		946	have a reasonable up-to-date copy:
		947
		948	db_mon my_image_scalers => sub {
		949	@ports = keys %{ $_[0] };
		950	};
		951
		952	In general, you can set or delete single subkeys, but query and monitor
		953	whole families only.
		954
		955	If you feel the need to monitor or query a single subkey, try giving it
		956	it's own family.
		957
		958	=over
		959
		960	=item $guard = db_set $family => $subkey [=> $value]
		961
		962	Sets (or replaces) a key to the database - if C<$value> is omitted,
		963	C<undef> is used instead.
		964
		965	When called in non-void context, C<db_set> returns a guard that
		966	automatically calls C<db_del> when it is destroyed.
		967
		968	=item db_del $family => $subkey...
		969
		970	Deletes one or more subkeys from the database family.
		971
		972	=item $guard = db_reg $family => $port => $value
		973
		974	=item $guard = db_reg $family => $port
		975
		976	=item $guard = db_reg $family
		977
		978	Registers a port in the given family and optionally returns a guard to
		979	remove it.
		980
		981	This function basically does the same as:
		982
		983	db_set $family => $port => $value
		984
		985	Except that the port is monitored and automatically removed from the
		986	database family when it is kil'ed.
		987
		988	If C<$value> is missing, C<undef> is used. If C<$port> is missing, then
		989	C<$SELF> is used.
		990
		991	This function is most useful to register a port in some port group (which
		992	is just another name for a database family), and have it removed when the
		993	port is gone. This works best when the port is a local port.
		994
		995	=cut
		996
		997	sub db_reg($$;$) {
		998	my $family = shift;
		999	my $port = @_ ? shift : $SELF;
		1000
		1001	my $clr = sub { db_del $family => $port };
		1002	mon $port, $clr;
		1003
		1004	db_set $family => $port => $_[0];
		1005
		1006	defined wantarray
		1007	and &Guard::guard ($clr)
		1008	}
		1009
		1010	=item db_family $family => $cb->(\%familyhash)
		1011
		1012	Queries the named database C<$family> and call the callback with the
		1013	family represented as a hash. You can keep and freely modify the hash.
		1014
		1015	=item db_keys $family => $cb->(\@keys)
		1016
		1017	Same as C<db_family>, except it only queries the family I<subkeys> and passes
		1018	them as array reference to the callback.
		1019
		1020	=item db_values $family => $cb->(\@values)
		1021
		1022	Same as C<db_family>, except it only queries the family I<values> and passes them
		1023	as array reference to the callback.
		1024
		1025	=item $guard = db_mon $family => $cb->($familyhash, \@added, \@changed, \@deleted)
		1026
		1027	Creates a monitor on the given database family. Each time a key is set
		1028	or or is deleted the callback is called with a hash containing the
		1029	database family and three lists of added, changed and deleted subkeys,
		1030	respectively. If no keys have changed then the array reference might be
		1031	C<undef> or even missing.
		1032
		1033	If not called in void context, a guard object is returned that, when
		1034	destroyed, stops the monitor.
		1035
		1036	The family hash reference and the key arrays belong to AnyEvent::MP and
		1037	B<must not be modified or stored> by the callback. When in doubt, make a
		1038	copy.
		1039
		1040	As soon as possible after the monitoring starts, the callback will be
		1041	called with the intiial contents of the family, even if it is empty,
		1042	i.e. there will always be a timely call to the callback with the current
		1043	contents.
		1044
		1045	It is possible that the callback is called with a change event even though
		1046	the subkey is already present and the value has not changed.
		1047
		1048	The monitoring stops when the guard object is destroyed.
		1049
		1050	Example: on every change to the family "mygroup", print out all keys.
		1051
		1052	my $guard = db_mon mygroup => sub {
		1053	my ($family, $a, $c, $d) = @_;
		1054	print "mygroup members: ", (join " ", keys %$family), "\n";
		1055	};
		1056
		1057	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1058
		1059	my $guard; $guard = db_mon My::Module::workers => sub {
		1060	my ($family, $a, $c, $d) = @_;
		1061	return unless %$family;
		1062	undef $guard;
		1063	print "My::Module::workers now nonempty\n";
		1064	};
		1065
		1066	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		1067
		1068	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		1069	my ($family, $a, $c, $d) = @_;
		1070
		1071	print "+$_=$family->{$_}\n" for @$a;
		1072	print "*$_=$family->{$_}\n" for @$c;
		1073	print "-$_=$family->{$_}\n" for @$d;
		1074	};
		1075
		1076	=cut
		1077
		1078	=back
		1079
		1080	=head1 AnyEvent::MP vs. Distributed Erlang
		1081
		1082	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
		1083	== aemp node, Erlang process == aemp port), so many of the documents and
		1084	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
		1085	sample:
		1086
		1087	http://www.erlang.se/doc/programming_rules.shtml
		1088	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
		1089	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
		1090	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
		1091
		1092	Despite the similarities, there are also some important differences:
		1093
		1094	=over 4
		1095
		1096	=item * Node IDs are arbitrary strings in AEMP.
		1097
		1098	Erlang relies on special naming and DNS to work everywhere in the same
		1099	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
		1100	configuration or DNS), and possibly the addresses of some seed nodes, but
		1101	will otherwise discover other nodes (and their IDs) itself.
		1102
		1103	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
		1104	uses "local ports are like remote ports".
		1105
		1106	The failure modes for local ports are quite different (runtime errors
		1107	only) then for remote ports - when a local port dies, you I<know> it dies,
		1108	when a connection to another node dies, you know nothing about the other
		1109	port.
		1110
		1111	Erlang pretends remote ports are as reliable as local ports, even when
		1112	they are not.
		1113
		1114	AEMP encourages a "treat remote ports differently" philosophy, with local
		1115	ports being the special case/exception, where transport errors cannot
		1116	occur.
		1117
		1118	=item * Erlang uses processes and a mailbox, AEMP does not queue.
		1119
		1120	Erlang uses processes that selectively receive messages out of order, and
		1121	therefore needs a queue. AEMP is event based, queuing messages would serve
		1122	no useful purpose. For the same reason the pattern-matching abilities
		1123	of AnyEvent::MP are more limited, as there is little need to be able to
		1124	filter messages without dequeuing them.
		1125
		1126	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1127	being event-based, while Erlang is process-based.
		1128
		1129	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1130	top of AEMP and Coro threads.
		1131
		1132	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
		1133
		1134	Sending messages in Erlang is synchronous and blocks the process until
		1135	a conenction has been established and the message sent (and so does not
		1136	need a queue that can overflow). AEMP sends return immediately, connection
		1137	establishment is handled in the background.
		1138
		1139	=item * Erlang suffers from silent message loss, AEMP does not.
		1140
		1141	Erlang implements few guarantees on messages delivery - messages can get
		1142	lost without any of the processes realising it (i.e. you send messages a,
		1143	b, and c, and the other side only receives messages a and c).
		1144
		1145	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1146	guarantee that after one message is lost, all following ones sent to the
		1147	same port are lost as well, until monitoring raises an error, so there are
		1148	no silent "holes" in the message sequence.
		1149
		1150	If you want your software to be very reliable, you have to cope with
		1151	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
		1152	simply tries to work better in common error cases, such as when a network
		1153	link goes down.
		1154
		1155	=item * Erlang can send messages to the wrong port, AEMP does not.
		1156
		1157	In Erlang it is quite likely that a node that restarts reuses an Erlang
		1158	process ID known to other nodes for a completely different process,
		1159	causing messages destined for that process to end up in an unrelated
		1160	process.
		1161
		1162	AEMP does not reuse port IDs, so old messages or old port IDs floating
		1163	around in the network will not be sent to an unrelated port.
		1164
		1165	=item * Erlang uses unprotected connections, AEMP uses secure
		1166	authentication and can use TLS.
		1167
		1168	AEMP can use a proven protocol - TLS - to protect connections and
		1169	securely authenticate nodes.
		1170
		1171	=item * The AEMP protocol is optimised for both text-based and binary
		1172	communications.
		1173
		1174	The AEMP protocol, unlike the Erlang protocol, supports both programming
		1175	language independent text-only protocols (good for debugging), and binary,
		1176	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1177	used, the protocol is actually completely text-based.
		1178
		1179	It has also been carefully designed to be implementable in other languages
		1180	with a minimum of work while gracefully degrading functionality to make the
		1181	protocol simple.
		1182
		1183	=item * AEMP has more flexible monitoring options than Erlang.
		1184
		1185	In Erlang, you can chose to receive I<all> exit signals as messages or
		1186	I<none>, there is no in-between, so monitoring single Erlang processes is
		1187	difficult to implement.
		1188
		1189	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1190	between automatic kill, exit message or callback on a per-port basis.
		1191
		1192	=item * Erlang tries to hide remote/local connections, AEMP does not.
		1193
		1194	Monitoring in Erlang is not an indicator of process death/crashes, in the
		1195	same way as linking is (except linking is unreliable in Erlang).
		1196
		1197	In AEMP, you don't "look up" registered port names or send to named ports
		1198	that might or might not be persistent. Instead, you normally spawn a port
		1199	on the remote node. The init function monitors you, and you monitor the
		1200	remote port. Since both monitors are local to the node, they are much more
		1201	reliable (no need for C<spawn_link>).
		1202
		1203	This also saves round-trips and avoids sending messages to the wrong port
		1204	(hard to do in Erlang).
		1205
		1206	=back
		1207
		1208	=head1 RATIONALE
		1209
		1210	=over 4
		1211
		1212	=item Why strings for port and node IDs, why not objects?
		1213
		1214	We considered "objects", but found that the actual number of methods
		1215	that can be called are quite low. Since port and node IDs travel over
		1216	the network frequently, the serialising/deserialising would add lots of
		1217	overhead, as well as having to keep a proxy object everywhere.
		1218
		1219	Strings can easily be printed, easily serialised etc. and need no special
		1220	procedures to be "valid".
		1221
		1222	And as a result, a port with just a default receiver consists of a single
		1223	code reference stored in a global hash - it can't become much cheaper.
		1224
		1225	=item Why favour JSON, why not a real serialising format such as Storable?
		1226
		1227	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1228	format, but currently there is no way to make a node use Storable by
		1229	default (although all nodes will accept it).
		1230
		1231	The default framing protocol is JSON because a) JSON::XS is many times
		1232	faster for small messages and b) most importantly, after years of
		1233	experience we found that object serialisation is causing more problems
		1234	than it solves: Just like function calls, objects simply do not travel
		1235	easily over the network, mostly because they will always be a copy, so you
		1236	always have to re-think your design.
		1237
		1238	Keeping your messages simple, concentrating on data structures rather than
		1239	objects, will keep your messages clean, tidy and efficient.
		1240
		1241	=back
		1242
		1243	=head1 PORTING FROM AnyEvent::MP VERSION 1.X
		1244
		1245	AEMP version 2 has a few major incompatible changes compared to version 1:
		1246
		1247	=over 4
		1248
		1249	=item AnyEvent::MP::Global no longer has group management functions.
		1250
		1251	At least not officially - the grp_* functions are still exported and might
		1252	work, but they will be removed in some later release.
		1253
		1254	AnyEvent::MP now comes with a distributed database that is more
		1255	powerful. Its database families map closely to port groups, but the API
		1256	has changed (the functions are also now exported by AnyEvent::MP). Here is
		1257	a rough porting guide:
		1258
		1259	grp_reg $group, $port # old
		1260	db_reg $group, $port # new
		1261
		1262	$list = grp_get $group # old
		1263	db_keys $group, sub { my $list = shift } # new
		1264
		1265	grp_mon $group, $cb->(\@ports, $add, $del) # old
		1266	db_mon $group, $cb->(\%ports, $add, $change, $del) # new
		1267
		1268	C<grp_reg> is a no-brainer (just replace by C<db_reg>), but C<grp_get> is
		1269	no longer instant, because the local node might not have a copy of the
		1270	group. You can either modify your code to allow for a callback, or use
		1271	C<db_mon> to keep an updated copy of the group:
		1272
		1273	my $local_group_copy;
		1274	db_mon $group => sub { $local_group_copy = $_[0] };
		1275
		1276	# now "keys %$local_group_copy" always returns the most up-to-date
		1277	# list of ports in the group.
		1278
		1279	C<grp_mon> can be replaced by C<db_mon> with minor changes - C<db_mon>
		1280	passes a hash as first argument, and an extra C<$chg> argument that can be
		1281	ignored:
		1282
		1283	db_mon $group => sub {
		1284	my ($ports, $add, $chg, $lde) = @_;
		1285	$ports = [keys %$ports];
		1286
		1287	# now $ports, $add and $del are the same as
		1288	# were originally passed by grp_mon.
		1289	...
		1290	};
		1291
		1292	=item Nodes not longer connect to all other nodes.
		1293
		1294	In AEMP 1.x, every node automatically loads the L<AnyEvent::MP::Global>
		1295	module, which in turn would create connections to all other nodes in the
		1296	network (helped by the seed nodes).
		1297
		1298	In version 2.x, global nodes still connect to all other global nodes, but
		1299	other nodes don't - now every node either is a global node itself, or
		1300	attaches itself to another global node.
		1301
		1302	If a node isn't a global node itself, then it attaches itself to one
		1303	of its seed nodes. If that seed node isn't a global node yet, it will
		1304	automatically be upgraded to a global node.
		1305
		1306	So in many cases, nothing needs to be changed - one just has to make sure
		1307	that all seed nodes are meshed together with the other seed nodes (as with
		1308	AEMP 1.x), and other nodes specify them as seed nodes. This is most easily
		1309	achieved by specifying the same set of seed nodes for all nodes in the
		1310	network.
		1311
		1312	Not opening a connection to every other node is usually an advantage,
		1313	except when you need the lower latency of an already established
		1314	connection. To ensure a node establishes a connection to another node,
		1315	you can monitor the node port (C<mon $node, ...>), which will attempt to
		1316	create the connection (and notify you when the connection fails).
		1317
		1318	=item Listener-less nodes (nodes without binds) are gone.
		1319
		1320	And are not coming back, at least not in their old form. If no C<binds>
		1321	are specified for a node, AnyEvent::MP assumes a default of C<*:*>.
		1322
		1323	There are vague plans to implement some form of routing domains, which
		1324	might or might not bring back listener-less nodes, but don't count on it.
		1325
		1326	The fact that most connections are now optional somewhat mitigates this,
		1327	as a node can be effectively unreachable from the outside without any
		1328	problems, as long as it isn't a global node and only reaches out to other
		1329	nodes (as opposed to being contacted from other nodes).
		1330
		1331	=item $AnyEvent::MP::Kernel::WARN has gone.
		1332
		1333	AnyEvent has acquired a logging framework (L<AnyEvent::Log>), and AEMP now
		1334	uses this, and so should your programs.
		1335
		1336	Every module now documents what kinds of messages it generates, with
		1337	AnyEvent::MP acting as a catch all.
		1338
		1339	On the positive side, this means that instead of setting
		1340	C<PERL_ANYEVENT_MP_WARNLEVEL>, you can get away by setting C<AE_VERBOSE> -
		1341	much less to type.
		1342
		1343	=back
		1344
		1345	=head1 LOGGING
		1346
		1347	AnyEvent::MP does not normally log anything by itself, but sinc eit is the
		1348	root of the contetx hierarchy for AnyEvent::MP modules, it will receive
		1349	all log messages by submodules.
		1350
53	=head1 SEE ALSO	1351	=head1 SEE ALSO
		1352
		1353	L<AnyEvent::MP::Intro> - a gentle introduction.
		1354
		1355	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1356
		1357	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1358	your applications.
		1359
		1360	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1361
		1362	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1363	all nodes.
54		1364
55	L<AnyEvent>.	1365	L<AnyEvent>.
56		1366
57	=head1 AUTHOR	1367	=head1 AUTHOR
58		1368

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