[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 1.131 by root, Fri Mar 9 19:07:53 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
		52	=head1 CURRENT STATUS
		53
		54	bin/aemp - stable.
		55	AnyEvent::MP - stable API, should work.
		56	AnyEvent::MP::Intro - explains most concepts.
		57	AnyEvent::MP::Kernel - mostly stable API.
		58	AnyEvent::MP::Global - stable API.
		59
9	=head1 DESCRIPTION	60	=head1 DESCRIPTION
10		61
		62	This module (-family) implements a simple message passing framework.
		63
		64	Despite its simplicity, you can securely message other processes running
		65	on the same or other hosts, and you can supervise entities remotely.
		66
		67	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
		68	manual page and the examples under F<eg/>.
		69
		70	=head1 CONCEPTS
		71
		72	=over 4
		73
		74	=item port
		75
		76	Not to be confused with a TCP port, a "port" is something you can send
		77	messages to (with the C<snd> function).
		78
		79	Ports allow you to register C<rcv> handlers that can match all or just
		80	some messages. Messages send to ports will not be queued, regardless of
		81	anything was listening for them or not.
		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
		85	=item port ID - C<nodeid#portname>
		86
		87	A port ID is the concatenation of a node ID, a hash-mark (C<#>)
		88	as separator, and a port name (a printable string of unspecified
		89	format created by AnyEvent::MP).
		90
		91	=item node
		92
		93	A node is a single process containing at least one port - the node port,
		94	which enables nodes to manage each other remotely, and to create new
		95	ports.
		96
		97	Nodes are either public (have one or more listening ports) or private
		98	(no listening ports). Private nodes cannot talk to other private nodes
		99	currently, but all nodes can talk to public nodes.
		100
		101	Nodes is represented by (printable) strings called "node IDs".
		102
		103	=item node ID - C<[A-Za-z0-9_\-.:]*>
		104
		105	A node ID is a string that uniquely identifies the node within a
		106	network. Depending on the configuration used, node IDs can look like a
		107	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		108	doesn't interpret node IDs in any way except to uniquely identify a node.
		109
		110	=item binds - C<ip:port>
		111
		112	Nodes can only talk to each other by creating some kind of connection to
		113	each other. To do this, nodes should listen on one or more local transport
		114	endpoints - binds.
		115
		116	Currently, only standard C<ip:port> specifications can be used, which
		117	specify TCP ports to listen on. So a bind is basically just a tcp socket
		118	in listening mode thta accepts conenctions form other nodes.
		119
		120	=item seed nodes
		121
		122	When a node starts, it knows nothing about the network it is in - it
		123	needs to connect to at least one other node that is already in the
		124	network. These other nodes are called "seed nodes".
		125
		126	Seed nodes themselves are not special - they are seed nodes only because
		127	some other node I<uses> them as such, but any node can be used as seed
		128	node for other nodes, and eahc node cna use a different set of seed nodes.
		129
		130	In addition to discovering the network, seed nodes are also used to
		131	maintain the network - all nodes using the same seed node form are part of
		132	the same network. If a network is split into multiple subnets because e.g.
		133	the network link between the parts goes down, then using the same seed
		134	nodes for all nodes ensures that eventually the subnets get merged again.
		135
		136	Seed nodes are expected to be long-running, and at least one seed node
		137	should always be available. They should also be relatively responsive - a
		138	seed node that blocks for long periods will slow down everybody else.
		139
		140	For small networks, it's best if every node uses the same set of seed
		141	nodes. For large networks, it can be useful to specify "regional" seed
		142	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		143	each other. What's important is that all seed nodes connections form a
		144	complete graph, so that the network cannot split into separate subnets
		145	forever.
		146
		147	Seed nodes are represented by seed IDs.
		148
		149	=item seed IDs - C<host:port>
		150
		151	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
		152	TCP port) of nodes that should be used as seed nodes.
		153
		154	=item global nodes
		155
		156	An AEMP network needs a discovery service - nodes need to know how to
		157	connect to other nodes they only know by name. In addition, AEMP offers a
		158	distributed "group database", which maps group names to a list of strings
		159	- for example, to register worker ports.
		160
		161	A network needs at least one global node to work, and allows every node to
		162	be a global node.
		163
		164	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		165	node and tries to keep connections to all other nodes. So while it can
		166	make sense to make every node "global" in small networks, it usually makes
		167	sense to only make seed nodes into global nodes in large networks (nodes
		168	keep connections to seed nodes and global nodes, so makign them the same
		169	reduces overhead).
		170
		171	=back
		172
		173	=head1 VARIABLES/FUNCTIONS
		174
		175	=over 4
		176
11	=cut	177	=cut
12		178
13	package AnyEvent::MP;	179	package AnyEvent::MP;
14		180
		181	use AnyEvent::MP::Config ();
		182	use AnyEvent::MP::Kernel;
		183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
		184
15	use common::sense;	185	use common::sense;
16		186
		187	use Carp ();
		188
17	use AE ();	189	use AE ();
		190	use Guard ();
18		191
19	our $VERSION = '0.0';	192	use base "Exporter";
20		193
21	sub nonce($) {	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
22	my $nonce;
23		195
24	if (open my $fh, "</dev/urandom") {	196	our @EXPORT = qw(
25	sysread $fh, $nonce, $_[0];	197	NODE $NODE *SELF node_of after
26	} else {	198	configure
27	# shit...	199	snd rcv mon mon_guard kil psub peval spawn cal
28	our $nonce_init;	200	port
29	unless ($nonce_init++) {	201	db_set db_del db_reg
30	srand time ^ $$ ^ unpack "%L*", qx"ps -edalf" . qx"ipconfig /all";	202	db_mon db_family db_keys db_values
31	}	203	);
32		204
33	$nonce = join "", map +(chr rand 256), 1 .. $_[0]	205	our $SELF;
34	}
35		206
36	$nonce	207	sub _self_die() {
		208	my $msg = $@;
		209	$msg =~ s/\n+$// unless ref $msg;
		210	kil $SELF, die => $msg;
37	}	211	}
38		212
39	our $DEFAULT_SECRET;	213	=item $thisnode = NODE / $NODE
40		214
41	sub default_secret {	215	The C<NODE> function returns, and the C<$NODE> variable contains, the node
42	unless (defined $DEFAULT_SECRET) {	216	ID of the node running in the current process. This value is initialised by
43	if (open my $fh, "<$ENV{HOME}/.aemp-secret") {	217	a call to C<configure>.
44	sysread $fh, $DEFAULT_SECRET, -s $fh;	218
		219	=item $nodeid = node_of $port
		220
		221	Extracts and returns the node ID from a port ID or a node ID.
		222
		223	=item configure $profile, key => value...
		224
		225	=item configure key => value...
		226
		227	Before a node can talk to other nodes on the network (i.e. enter
		228	"distributed mode") it has to configure itself - the minimum a node needs
		229	to know is its own name, and optionally it should know the addresses of
		230	some other nodes in the network to discover other nodes.
		231
		232	This function configures a node - it must be called exactly once (or
		233	never) before calling other AnyEvent::MP functions.
		234
		235	The key/value pairs are basically the same ones as documented for the
		236	F<aemp> command line utility (sans the set/del prefix), with these additions:
		237
		238	=over 4
		239
		240	=item norc => $boolean (default false)
		241
		242	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
		243	be consulted - all configuraiton options must be specified in the
		244	C<configure> call.
		245
		246	=item force => $boolean (default false)
		247
		248	IF true, then the values specified in the C<configure> will take
		249	precedence over any values configured via the rc file. The default is for
		250	the rc file to override any options specified in the program.
		251
		252	=item secure => $pass->($nodeid)
		253
		254	In addition to specifying a boolean, you can specify a code reference that
		255	is called for every remote execution attempt - the execution request is
		256	granted iff the callback returns a true value.
		257
		258	See F<semp setsecure> for more info.
		259
		260	=back
		261
		262	=over 4
		263
		264	=item step 1, gathering configuration from profiles
		265
		266	The function first looks up a profile in the aemp configuration (see the
		267	L<aemp> commandline utility). The profile name can be specified via the
		268	named C<profile> parameter or can simply be the first parameter). If it is
		269	missing, then the nodename (F<uname -n>) will be used as profile name.
		270
		271	The profile data is then gathered as follows:
		272
		273	First, all remaining key => value pairs (all of which are conveniently
		274	undocumented at the moment) will be interpreted as configuration
		275	data. Then they will be overwritten by any values specified in the global
		276	default configuration (see the F<aemp> utility), then the chain of
		277	profiles chosen by the profile name (and any C<parent> attributes).
		278
		279	That means that the values specified in the profile have highest priority
		280	and the values specified directly via C<configure> have lowest priority,
		281	and can only be used to specify defaults.
		282
		283	If the profile specifies a node ID, then this will become the node ID of
		284	this process. If not, then the profile name will be used as node ID, with
		285	a unique randoms tring (C</%u>) appended.
		286
		287	The node ID can contain some C<%> sequences that are expanded: C<%n>
		288	is expanded to the local nodename, C<%u> is replaced by a random
		289	strign to make the node unique. For example, the F<aemp> commandline
		290	utility uses C<aemp/%n/%u> as nodename, which might expand to
		291	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		292
		293	=item step 2, bind listener sockets
		294
		295	The next step is to look up the binds in the profile, followed by binding
		296	aemp protocol listeners on all binds specified (it is possible and valid
		297	to have no binds, meaning that the node cannot be contacted form the
		298	outside. This means the node cannot talk to other nodes that also have no
		299	binds, but it can still talk to all "normal" nodes).
		300
		301	If the profile does not specify a binds list, then a default of C<*> is
		302	used, meaning the node will bind on a dynamically-assigned port on every
		303	local IP address it finds.
		304
		305	=item step 3, connect to seed nodes
		306
		307	As the last step, the seed ID list from the profile is passed to the
		308	L<AnyEvent::MP::Global> module, which will then use it to keep
		309	connectivity with at least one node at any point in time.
		310
		311	=back
		312
		313	Example: become a distributed node using the local node name as profile.
		314	This should be the most common form of invocation for "daemon"-type nodes.
		315
		316	configure
		317
		318	Example: become a semi-anonymous node. This form is often used for
		319	commandline clients.
		320
		321	configure nodeid => "myscript/%n/%u";
		322
		323	Example: configure a node using a profile called seed, which is suitable
		324	for a seed node as it binds on all local addresses on a fixed port (4040,
		325	customary for aemp).
		326
		327	# use the aemp commandline utility
		328	# aemp profile seed binds '*:4040'
		329
		330	# then use it
		331	configure profile => "seed";
		332
		333	# or simply use aemp from the shell again:
		334	# aemp run profile seed
		335
		336	# or provide a nicer-to-remember nodeid
		337	# aemp run profile seed nodeid "$(hostname)"
		338
		339	=item $SELF
		340
		341	Contains the current port id while executing C<rcv> callbacks or C<psub>
		342	blocks.
		343
		344	=item *SELF, SELF, %SELF, @SELF...
		345
		346	Due to some quirks in how perl exports variables, it is impossible to
		347	just export C<$SELF>, all the symbols named C<SELF> are exported by this
		348	module, but only C<$SELF> is currently used.
		349
		350	=item snd $port, type => @data
		351
		352	=item snd $port, @msg
		353
		354	Send the given message to the given port, which can identify either a
		355	local or a remote port, and must be a port ID.
		356
		357	While the message can be almost anything, it is highly recommended to
		358	use a string as first element (a port ID, or some word that indicates a
		359	request type etc.) and to consist if only simple perl values (scalars,
		360	arrays, hashes) - if you think you need to pass an object, think again.
		361
		362	The message data logically becomes read-only after a call to this
		363	function: modifying any argument (or values referenced by them) is
		364	forbidden, as there can be considerable time between the call to C<snd>
		365	and the time the message is actually being serialised - in fact, it might
		366	never be copied as within the same process it is simply handed to the
		367	receiving port.
		368
		369	The type of data you can transfer depends on the transport protocol: when
		370	JSON is used, then only strings, numbers and arrays and hashes consisting
		371	of those are allowed (no objects). When Storable is used, then anything
		372	that Storable can serialise and deserialise is allowed, and for the local
		373	node, anything can be passed. Best rely only on the common denominator of
		374	these.
		375
		376	=item $local_port = port
		377
		378	Create a new local port object and returns its port ID. Initially it has
		379	no callbacks set and will throw an error when it receives messages.
		380
		381	=item $local_port = port { my @msg = @_ }
		382
		383	Creates a new local port, and returns its ID. Semantically the same as
		384	creating a port and calling C<rcv $port, $callback> on it.
		385
		386	The block will be called for every message received on the port, with the
		387	global variable C<$SELF> set to the port ID. Runtime errors will cause the
		388	port to be C<kil>ed. The message will be passed as-is, no extra argument
		389	(i.e. no port ID) will be passed to the callback.
		390
		391	If you want to stop/destroy the port, simply C<kil> it:
		392
		393	my $port = port {
		394	my @msg = @_;
		395	...
		396	kil $SELF;
		397	};
		398
		399	=cut
		400
		401	sub rcv($@);
		402
		403	sub _kilme {
		404	die "received message on port without callback";
		405	}
		406
		407	sub port(;&) {
		408	my $id = $UNIQ . ++$ID;
		409	my $port = "$NODE#$id";
		410
		411	rcv $port, shift \|\| \&_kilme;
		412
		413	$port
		414	}
		415
		416	=item rcv $local_port, $callback->(@msg)
		417
		418	Replaces the default callback on the specified port. There is no way to
		419	remove the default callback: use C<sub { }> to disable it, or better
		420	C<kil> the port when it is no longer needed.
		421
		422	The global C<$SELF> (exported by this module) contains C<$port> while
		423	executing the callback. Runtime errors during callback execution will
		424	result in the port being C<kil>ed.
		425
		426	The default callback received all messages not matched by a more specific
		427	C<tag> match.
		428
		429	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
		430
		431	Register (or replace) callbacks to be called on messages starting with the
		432	given tag on the given port (and return the port), or unregister it (when
		433	C<$callback> is C<$undef> or missing). There can only be one callback
		434	registered for each tag.
		435
		436	The original message will be passed to the callback, after the first
		437	element (the tag) has been removed. The callback will use the same
		438	environment as the default callback (see above).
		439
		440	Example: create a port and bind receivers on it in one go.
		441
		442	my $port = rcv port,
		443	msg1 => sub { ... },
		444	msg2 => sub { ... },
		445	;
		446
		447	Example: create a port, bind receivers and send it in a message elsewhere
		448	in one go:
		449
		450	snd $otherport, reply =>
		451	rcv port,
		452	msg1 => sub { ... },
		453	...
		454	;
		455
		456	Example: temporarily register a rcv callback for a tag matching some port
		457	(e.g. for an rpc reply) and unregister it after a message was received.
		458
		459	rcv $port, $otherport => sub {
		460	my @reply = @_;
		461
		462	rcv $SELF, $otherport;
		463	};
		464
		465	=cut
		466
		467	sub rcv($@) {
		468	my $port = shift;
		469	my ($nodeid, $portid) = split /#/, $port, 2;
		470
		471	$NODE{$nodeid} == $NODE{""}
		472	or Carp::croak "$port: rcv can only be called on local ports, caught";
		473
		474	while (@_) {
		475	if (ref $_[0]) {
		476	if (my $self = $PORT_DATA{$portid}) {
		477	"AnyEvent::MP::Port" eq ref $self
		478	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		479
		480	$self->[0] = shift;
45	} else {	481	} else {
46	$DEFAULT_SECRET = nonce 32;	482	my $cb = shift;
		483	$PORT{$portid} = sub {
		484	local $SELF = $port;
		485	eval { &$cb }; _self_die if $@;
		486	};
		487	}
		488	} elsif (defined $_[0]) {
		489	my $self = $PORT_DATA{$portid} \|\|= do {
		490	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
		491
		492	$PORT{$portid} = sub {
		493	local $SELF = $port;
		494
		495	if (my $cb = $self->[1]{$_[0]}) {
		496	shift;
		497	eval { &$cb }; _self_die if $@;
		498	} else {
		499	&{ $self->[0] };
		500	}
		501	};
		502
		503	$self
		504	};
		505
		506	"AnyEvent::MP::Port" eq ref $self
		507	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		508
		509	my ($tag, $cb) = splice @_, 0, 2;
		510
		511	if (defined $cb) {
		512	$self->[1]{$tag} = $cb;
		513	} else {
		514	delete $self->[1]{$tag};
		515	}
47	}	516	}
48	}	517	}
49		518
50	$DEFAULT_SECRET	519	$port
51	}	520	}
52		521
		522	=item peval $port, $coderef[, @args]
		523
		524	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		525	when the code throews an exception the C<$port> will be killed.
		526
		527	Any remaining args will be passed to the callback. Any return values will
		528	be returned to the caller.
		529
		530	This is useful when you temporarily want to execute code in the context of
		531	a port.
		532
		533	Example: create a port and run some initialisation code in it's context.
		534
		535	my $port = port { ... };
		536
		537	peval $port, sub {
		538	init
		539	or die "unable to init";
		540	};
		541
		542	=cut
		543
		544	sub peval($$) {
		545	local $SELF = shift;
		546	my $cb = shift;
		547
		548	if (wantarray) {
		549	my @res = eval { &$cb };
		550	_self_die if $@;
		551	@res
		552	} else {
		553	my $res = eval { &$cb };
		554	_self_die if $@;
		555	$res
		556	}
		557	}
		558
		559	=item $closure = psub { BLOCK }
		560
		561	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
		562	closure is executed, sets up the environment in the same way as in C<rcv>
		563	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		564
		565	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		566	BLOCK }, @_ } >>.
		567
		568	This is useful when you register callbacks from C<rcv> callbacks:
		569
		570	rcv delayed_reply => sub {
		571	my ($delay, @reply) = @_;
		572	my $timer = AE::timer $delay, 0, psub {
		573	snd @reply, $SELF;
		574	};
		575	};
		576
		577	=cut
		578
		579	sub psub(&) {
		580	my $cb = shift;
		581
		582	my $port = $SELF
		583	or Carp::croak "psub can only be called from within rcv or psub callbacks, not";
		584
		585	sub {
		586	local $SELF = $port;
		587
		588	if (wantarray) {
		589	my @res = eval { &$cb };
		590	_self_die if $@;
		591	@res
		592	} else {
		593	my $res = eval { &$cb };
		594	_self_die if $@;
		595	$res
		596	}
		597	}
		598	}
		599
		600	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
		601
		602	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
		603
		604	=item $guard = mon $port # kill $SELF when $port dies
		605
		606	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		607
		608	Monitor the given port and do something when the port is killed or
		609	messages to it were lost, and optionally return a guard that can be used
		610	to stop monitoring again.
		611
		612	In the first form (callback), the callback is simply called with any
		613	number of C<@reason> elements (no @reason means that the port was deleted
		614	"normally"). Note also that I<< the callback B<must> never die >>, so use
		615	C<eval> if unsure.
		616
		617	In the second form (another port given), the other port (C<$rcvport>)
		618	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
		619	"normal" kils nothing happens, while under all other conditions, the other
		620	port is killed with the same reason.
		621
		622	The third form (kill self) is the same as the second form, except that
		623	C<$rvport> defaults to C<$SELF>.
		624
		625	In the last form (message), a message of the form C<@msg, @reason> will be
		626	C<snd>.
		627
		628	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		629	alert was raised), they are removed and will not trigger again.
		630
		631	As a rule of thumb, monitoring requests should always monitor a port from
		632	a local port (or callback). The reason is that kill messages might get
		633	lost, just like any other message. Another less obvious reason is that
		634	even monitoring requests can get lost (for example, when the connection
		635	to the other node goes down permanently). When monitoring a port locally
		636	these problems do not exist.
		637
		638	C<mon> effectively guarantees that, in the absence of hardware failures,
		639	after starting the monitor, either all messages sent to the port will
		640	arrive, or the monitoring action will be invoked after possible message
		641	loss has been detected. No messages will be lost "in between" (after
		642	the first lost message no further messages will be received by the
		643	port). After the monitoring action was invoked, further messages might get
		644	delivered again.
		645
		646	Inter-host-connection timeouts and monitoring depend on the transport
		647	used. The only transport currently implemented is TCP, and AnyEvent::MP
		648	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		649	non-idle connection, and usually around two hours for idle connections).
		650
		651	This means that monitoring is good for program errors and cleaning up
		652	stuff eventually, but they are no replacement for a timeout when you need
		653	to ensure some maximum latency.
		654
		655	Example: call a given callback when C<$port> is killed.
		656
		657	mon $port, sub { warn "port died because of <@_>\n" };
		658
		659	Example: kill ourselves when C<$port> is killed abnormally.
		660
		661	mon $port;
		662
		663	Example: send us a restart message when another C<$port> is killed.
		664
		665	mon $port, $self => "restart";
		666
		667	=cut
		668
		669	sub mon {
		670	my ($nodeid, $port) = split /#/, shift, 2;
		671
		672	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
		673
		674	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
		675
		676	unless (ref $cb) {
		677	if (@_) {
		678	# send a kill info message
		679	my (@msg) = ($cb, @_);
		680	$cb = sub { snd @msg, @_ };
		681	} else {
		682	# simply kill other port
		683	my $port = $cb;
		684	$cb = sub { kil $port, @_ if @_ };
		685	}
		686	}
		687
		688	$node->monitor ($port, $cb);
		689
		690	defined wantarray
		691	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
		692	}
		693
		694	=item $guard = mon_guard $port, $ref, $ref...
		695
		696	Monitors the given C<$port> and keeps the passed references. When the port
		697	is killed, the references will be freed.
		698
		699	Optionally returns a guard that will stop the monitoring.
		700
		701	This function is useful when you create e.g. timers or other watchers and
		702	want to free them when the port gets killed (note the use of C<psub>):
		703
		704	$port->rcv (start => sub {
		705	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
		706	undef $timer if 0.9 < rand;
		707	});
		708	});
		709
		710	=cut
		711
		712	sub mon_guard {
		713	my ($port, @refs) = @_;
		714
		715	#TODO: mon-less form?
		716
		717	mon $port, sub { 0 && @refs }
		718	}
		719
		720	=item kil $port[, @reason]
		721
		722	Kill the specified port with the given C<@reason>.
		723
		724	If no C<@reason> is specified, then the port is killed "normally" -
		725	monitor callback will be invoked, but the kil will not cause linked ports
		726	(C<mon $mport, $lport> form) to get killed.
		727
		728	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
		729	form) get killed with the same reason.
		730
		731	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		732	will be reported as reason C<< die => $@ >>.
		733
		734	Transport/communication errors are reported as C<< transport_error =>
		735	$message >>.
		736
		737	=cut
		738
		739	=item $port = spawn $node, $initfunc[, @initdata]
		740
		741	Creates a port on the node C<$node> (which can also be a port ID, in which
		742	case it's the node where that port resides).
		743
		744	The port ID of the newly created port is returned immediately, and it is
		745	possible to immediately start sending messages or to monitor the port.
		746
		747	After the port has been created, the init function is called on the remote
		748	node, in the same context as a C<rcv> callback. This function must be a
		749	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		750	specify a function in the main program, use C<::name>.
		751
		752	If the function doesn't exist, then the node tries to C<require>
		753	the package, then the package above the package and so on (e.g.
		754	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		755	exists or it runs out of package names.
		756
		757	The init function is then called with the newly-created port as context
		758	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		759	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		760	the port might not get created.
		761
		762	A common idiom is to pass a local port, immediately monitor the spawned
		763	port, and in the remote init function, immediately monitor the passed
		764	local port. This two-way monitoring ensures that both ports get cleaned up
		765	when there is a problem.
		766
		767	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		768	caller before C<spawn> returns (by delaying invocation when spawn is
		769	called for the local node).
		770
		771	Example: spawn a chat server port on C<$othernode>.
		772
		773	# this node, executed from within a port context:
		774	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		775	mon $server;
		776
		777	# init function on C<$othernode>
		778	sub connect {
		779	my ($srcport) = @_;
		780
		781	mon $srcport;
		782
		783	rcv $SELF, sub {
		784	...
		785	};
		786	}
		787
		788	=cut
		789
		790	sub _spawn {
		791	my $port = shift;
		792	my $init = shift;
		793
		794	# rcv will create the actual port
		795	local $SELF = "$NODE#$port";
		796	eval {
		797	&{ load_func $init }
		798	};
		799	_self_die if $@;
		800	}
		801
		802	sub spawn(@) {
		803	my ($nodeid, undef) = split /#/, shift, 2;
		804
		805	my $id = $RUNIQ . ++$ID;
		806
		807	$_[0] =~ /::/
		808	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		809
		810	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		811
		812	"$nodeid#$id"
		813	}
		814
		815
		816	=item after $timeout, @msg
		817
		818	=item after $timeout, $callback
		819
		820	Either sends the given message, or call the given callback, after the
		821	specified number of seconds.
		822
		823	This is simply a utility function that comes in handy at times - the
		824	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		825	so it may go away in the future.
		826
		827	=cut
		828
		829	sub after($@) {
		830	my ($timeout, @action) = @_;
		831
		832	my $t; $t = AE::timer $timeout, 0, sub {
		833	undef $t;
		834	ref $action[0]
		835	? $action[0]()
		836	: snd @action;
		837	};
		838	}
		839
		840	#=item $cb2 = timeout $seconds, $cb[, @args]
		841
		842	=item cal $port, @msg, $callback[, $timeout]
		843
		844	A simple form of RPC - sends a message to the given C<$port> with the
		845	given contents (C<@msg>), but adds a reply port to the message.
		846
		847	The reply port is created temporarily just for the purpose of receiving
		848	the reply, and will be C<kil>ed when no longer needed.
		849
		850	A reply message sent to the port is passed to the C<$callback> as-is.
		851
		852	If an optional time-out (in seconds) is given and it is not C<undef>,
		853	then the callback will be called without any arguments after the time-out
		854	elapsed and the port is C<kil>ed.
		855
		856	If no time-out is given (or it is C<undef>), then the local port will
		857	monitor the remote port instead, so it eventually gets cleaned-up.
		858
		859	Currently this function returns the temporary port, but this "feature"
		860	might go in future versions unless you can make a convincing case that
		861	this is indeed useful for something.
		862
		863	=cut
		864
		865	sub cal(@) {
		866	my $timeout = ref $_[-1] ? undef : pop;
		867	my $cb = pop;
		868
		869	my $port = port {
		870	undef $timeout;
		871	kil $SELF;
		872	&$cb;
		873	};
		874
		875	if (defined $timeout) {
		876	$timeout = AE::timer $timeout, 0, sub {
		877	undef $timeout;
		878	kil $port;
		879	$cb->();
		880	};
		881	} else {
		882	mon $_[0], sub {
		883	kil $port;
		884	$cb->();
		885	};
		886	}
		887
		888	push @_, $port;
		889	&snd;
		890
		891	$port
		892	}
		893
		894	=back
		895
		896	=head1 DISTRIBUTED DATABASE
		897
		898	AnyEvent::MP comes with a simple distributed database. The database will
		899	be mirrored asynchronously on all global nodes. Other nodes bind to one
		900	of the global nodes for their needs. Every node has a "local database"
		901	which contains all the values that are set locally. All local databases
		902	are merged together to form the global database, which can be queried.
		903
		904	The database structure is that of a two-level hash - the database hash
		905	contains hashes which contain values, similarly to a perl hash of hashes,
		906	i.e.:
		907
		908	$DATABASE{$family}{$subkey} = $value
		909
		910	The top level hash key is called "family", and the second-level hash key
		911	is called "subkey" or simply "key".
		912
		913	The family must be alphanumeric, i.e. start with a letter and consist
		914	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		915	pretty much like Perl module names.
		916
		917	As the family namespace is global, it is recommended to prefix family names
		918	with the name of the application or module using it.
		919
		920	The subkeys must be non-empty strings, with no further restrictions.
		921
		922	The values should preferably be strings, but other perl scalars should
		923	work as well (such as C<undef>, arrays and hashes).
		924
		925	Every database entry is owned by one node - adding the same family/subkey
		926	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		927	but the result might be nondeterministic, i.e. the key might have
		928	different values on different nodes.
		929
		930	Different subkeys in the same family can be owned by different nodes
		931	without problems, and in fact, this is the common method to create worker
		932	pools. For example, a worker port for image scaling might do this:
		933
		934	db_set my_image_scalers => $port;
		935
		936	And clients looking for an image scaler will want to get the
		937	C<my_image_scalers> keys from time to time:
		938
		939	db_keys my_image_scalers => sub {
		940	@ports = @{ $_[0] };
		941	};
		942
		943	Or better yet, they want to monitor the database family, so they always
		944	have a reasonable up-to-date copy:
		945
		946	db_mon my_image_scalers => sub {
		947	@ports = keys %{ $_[0] };
		948	};
		949
		950	In general, you can set or delete single subkeys, but query and monitor
		951	whole families only.
		952
		953	If you feel the need to monitor or query a single subkey, try giving it
		954	it's own family.
		955
		956	=over
		957
		958	=item db_set $family => $subkey [=> $value]
		959
		960	Sets (or replaces) a key to the database - if C<$value> is omitted,
		961	C<undef> is used instead.
		962
		963	=item db_del $family => $subkey...
		964
		965	Deletes one or more subkeys from the database family.
		966
		967	=item $guard = db_reg $family => $subkey [=> $value]
		968
		969	Sets the key on the database and returns a guard. When the guard is
		970	destroyed, the key is deleted from the database. If C<$value> is missing,
		971	then C<undef> is used.
		972
		973	=item db_family $family => $cb->(\%familyhash)
		974
		975	Queries the named database C<$family> and call the callback with the
		976	family represented as a hash. You can keep and freely modify the hash.
		977
		978	=item db_keys $family => $cb->(\@keys)
		979
		980	Same as C<db_family>, except it only queries the family I<subkeys> and passes
		981	them as array reference to the callback.
		982
		983	=item db_values $family => $cb->(\@values)
		984
		985	Same as C<db_family>, except it only queries the family I<values> and passes them
		986	as array reference to the callback.
		987
		988	=item $guard = db_mon $family => $cb->($familyhash, \@added, \@changed, \@deleted)
		989
		990	Creates a monitor on the given database family. Each time a key is set
		991	or or is deleted the callback is called with a hash containing the
		992	database family and three lists of added, changed and deleted subkeys,
		993	respectively. If no keys have changed then the array reference might be
		994	C<undef> or even missing.
		995
		996	The family hash reference and the key arrays belong to AnyEvent::MP and
		997	B<must not be modified or stored> by the callback. When in doubt, make a
		998	copy.
		999
		1000	As soon as possible after the monitoring starts, the callback will be
		1001	called with the intiial contents of the family, even if it is empty,
		1002	i.e. there will always be a timely call to the callback with the current
		1003	contents.
		1004
		1005	It is possible that the callback is called with a change event even though
		1006	the subkey is already present and the value has not changed.
		1007
		1008	The monitoring stops when the guard object is destroyed.
		1009
		1010	Example: on every change to the family "mygroup", print out all keys.
		1011
		1012	my $guard = db_mon mygroup => sub {
		1013	my ($family, $a, $c, $d) = @_;
		1014	print "mygroup members: ", (join " ", keys %$family), "\n";
		1015	};
		1016
		1017	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1018
		1019	my $guard; $guard = db_mon My::Module::workers => sub {
		1020	my ($family, $a, $c, $d) = @_;
		1021	return unless %$family;
		1022	undef $guard;
		1023	print "My::Module::workers now nonempty\n";
		1024	};
		1025
		1026	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		1027
		1028	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		1029	my ($family, $a, $c, $d) = @_;
		1030
		1031	print "+$_=$family->{$_}\n" for @$a;
		1032	print "*$_=$family->{$_}\n" for @$c;
		1033	print "-$_=$family->{$_}\n" for @$d;
		1034	};
		1035
		1036	=cut
		1037
		1038	=back
		1039
		1040	=head1 AnyEvent::MP vs. Distributed Erlang
		1041
		1042	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
		1043	== aemp node, Erlang process == aemp port), so many of the documents and
		1044	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
		1045	sample:
		1046
		1047	http://www.erlang.se/doc/programming_rules.shtml
		1048	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
		1049	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
		1050	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
		1051
		1052	Despite the similarities, there are also some important differences:
		1053
		1054	=over 4
		1055
		1056	=item * Node IDs are arbitrary strings in AEMP.
		1057
		1058	Erlang relies on special naming and DNS to work everywhere in the same
		1059	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
		1060	configuration or DNS), and possibly the addresses of some seed nodes, but
		1061	will otherwise discover other nodes (and their IDs) itself.
		1062
		1063	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
		1064	uses "local ports are like remote ports".
		1065
		1066	The failure modes for local ports are quite different (runtime errors
		1067	only) then for remote ports - when a local port dies, you I<know> it dies,
		1068	when a connection to another node dies, you know nothing about the other
		1069	port.
		1070
		1071	Erlang pretends remote ports are as reliable as local ports, even when
		1072	they are not.
		1073
		1074	AEMP encourages a "treat remote ports differently" philosophy, with local
		1075	ports being the special case/exception, where transport errors cannot
		1076	occur.
		1077
		1078	=item * Erlang uses processes and a mailbox, AEMP does not queue.
		1079
		1080	Erlang uses processes that selectively receive messages out of order, and
		1081	therefore needs a queue. AEMP is event based, queuing messages would serve
		1082	no useful purpose. For the same reason the pattern-matching abilities
		1083	of AnyEvent::MP are more limited, as there is little need to be able to
		1084	filter messages without dequeuing them.
		1085
		1086	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1087	being event-based, while Erlang is process-based.
		1088
		1089	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1090	top of AEMP and Coro threads.
		1091
		1092	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
		1093
		1094	Sending messages in Erlang is synchronous and blocks the process until
		1095	a conenction has been established and the message sent (and so does not
		1096	need a queue that can overflow). AEMP sends return immediately, connection
		1097	establishment is handled in the background.
		1098
		1099	=item * Erlang suffers from silent message loss, AEMP does not.
		1100
		1101	Erlang implements few guarantees on messages delivery - messages can get
		1102	lost without any of the processes realising it (i.e. you send messages a,
		1103	b, and c, and the other side only receives messages a and c).
		1104
		1105	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1106	guarantee that after one message is lost, all following ones sent to the
		1107	same port are lost as well, until monitoring raises an error, so there are
		1108	no silent "holes" in the message sequence.
		1109
		1110	If you want your software to be very reliable, you have to cope with
		1111	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
		1112	simply tries to work better in common error cases, such as when a network
		1113	link goes down.
		1114
		1115	=item * Erlang can send messages to the wrong port, AEMP does not.
		1116
		1117	In Erlang it is quite likely that a node that restarts reuses an Erlang
		1118	process ID known to other nodes for a completely different process,
		1119	causing messages destined for that process to end up in an unrelated
		1120	process.
		1121
		1122	AEMP does not reuse port IDs, so old messages or old port IDs floating
		1123	around in the network will not be sent to an unrelated port.
		1124
		1125	=item * Erlang uses unprotected connections, AEMP uses secure
		1126	authentication and can use TLS.
		1127
		1128	AEMP can use a proven protocol - TLS - to protect connections and
		1129	securely authenticate nodes.
		1130
		1131	=item * The AEMP protocol is optimised for both text-based and binary
		1132	communications.
		1133
		1134	The AEMP protocol, unlike the Erlang protocol, supports both programming
		1135	language independent text-only protocols (good for debugging), and binary,
		1136	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1137	used, the protocol is actually completely text-based.
		1138
		1139	It has also been carefully designed to be implementable in other languages
		1140	with a minimum of work while gracefully degrading functionality to make the
		1141	protocol simple.
		1142
		1143	=item * AEMP has more flexible monitoring options than Erlang.
		1144
		1145	In Erlang, you can chose to receive I<all> exit signals as messages or
		1146	I<none>, there is no in-between, so monitoring single Erlang processes is
		1147	difficult to implement.
		1148
		1149	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1150	between automatic kill, exit message or callback on a per-port basis.
		1151
		1152	=item * Erlang tries to hide remote/local connections, AEMP does not.
		1153
		1154	Monitoring in Erlang is not an indicator of process death/crashes, in the
		1155	same way as linking is (except linking is unreliable in Erlang).
		1156
		1157	In AEMP, you don't "look up" registered port names or send to named ports
		1158	that might or might not be persistent. Instead, you normally spawn a port
		1159	on the remote node. The init function monitors you, and you monitor the
		1160	remote port. Since both monitors are local to the node, they are much more
		1161	reliable (no need for C<spawn_link>).
		1162
		1163	This also saves round-trips and avoids sending messages to the wrong port
		1164	(hard to do in Erlang).
		1165
		1166	=back
		1167
		1168	=head1 RATIONALE
		1169
		1170	=over 4
		1171
		1172	=item Why strings for port and node IDs, why not objects?
		1173
		1174	We considered "objects", but found that the actual number of methods
		1175	that can be called are quite low. Since port and node IDs travel over
		1176	the network frequently, the serialising/deserialising would add lots of
		1177	overhead, as well as having to keep a proxy object everywhere.
		1178
		1179	Strings can easily be printed, easily serialised etc. and need no special
		1180	procedures to be "valid".
		1181
		1182	And as a result, a port with just a default receiver consists of a single
		1183	code reference stored in a global hash - it can't become much cheaper.
		1184
		1185	=item Why favour JSON, why not a real serialising format such as Storable?
		1186
		1187	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1188	format, but currently there is no way to make a node use Storable by
		1189	default (although all nodes will accept it).
		1190
		1191	The default framing protocol is JSON because a) JSON::XS is many times
		1192	faster for small messages and b) most importantly, after years of
		1193	experience we found that object serialisation is causing more problems
		1194	than it solves: Just like function calls, objects simply do not travel
		1195	easily over the network, mostly because they will always be a copy, so you
		1196	always have to re-think your design.
		1197
		1198	Keeping your messages simple, concentrating on data structures rather than
		1199	objects, will keep your messages clean, tidy and efficient.
		1200
		1201	=back
		1202
53	=head1 SEE ALSO	1203	=head1 SEE ALSO
		1204
		1205	L<AnyEvent::MP::Intro> - a gentle introduction.
		1206
		1207	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1208
		1209	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1210	your applications.
		1211
		1212	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1213
		1214	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1215	all nodes.
54		1216
55	L<AnyEvent>.	1217	L<AnyEvent>.
56		1218
57	=head1 AUTHOR	1219	=head1 AUTHOR
58		1220

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Comparing AnyEvent-MP/MP.pm (file contents): Revision 1.1 by root, Thu Jul 30 08:38:50 2009 UTC vs. Revision 1.131 by root, Fri Mar 9 19:07:53 2012 UTC

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Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.1 by root, Thu Jul 30 08:38:50 2009 UTC vs.
Revision 1.131 by root, Fri Mar 9 19:07:53 2012 UTC