[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 1.122 by root, Wed Feb 29 18:44:59 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 $localport, $cb->(@msg) # callback is invoked on death
		41	mon $localport, $otherport # kill otherport on abnormal death
		42	mon $localport, $otherport, @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<#>) as
		88	separator, and a port name (a printable string of unspecified format).
		89
		90	=item node
		91
		92	A node is a single process containing at least one port - the node port,
		93	which enables nodes to manage each other remotely, and to create new
		94	ports.
		95
		96	Nodes are either public (have one or more listening ports) or private
		97	(no listening ports). Private nodes cannot talk to other private nodes
		98	currently, but all nodes can talk to public nodes.
		99
		100	Nodes is represented by (printable) strings called "node IDs".
		101
		102	=item node ID - C<[A-Za-z0-9_\-.:]*>
		103
		104	A node ID is a string that uniquely identifies the node within a
		105	network. Depending on the configuration used, node IDs can look like a
		106	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		107	doesn't interpret node IDs in any way except to uniquely identify a node.
		108
		109	=item binds - C<ip:port>
		110
		111	Nodes can only talk to each other by creating some kind of connection to
		112	each other. To do this, nodes should listen on one or more local transport
		113	endpoints - binds.
		114
		115	Currently, only standard C<ip:port> specifications can be used, which
		116	specify TCP ports to listen on. So a bind is basically just a tcp socket
		117	in listening mode thta accepts conenctions form other nodes.
		118
		119	=item seed nodes
		120
		121	When a node starts, it knows nothing about the network it is in - it
		122	needs to connect to at least one other node that is already in the
		123	network. These other nodes are called "seed nodes".
		124
		125	Seed nodes themselves are not special - they are seed nodes only because
		126	some other node I<uses> them as such, but any node can be used as seed
		127	node for other nodes, and eahc node cna use a different set of seed nodes.
		128
		129	In addition to discovering the network, seed nodes are also used to
		130	maintain the network - all nodes using the same seed node form are part of
		131	the same network. If a network is split into multiple subnets because e.g.
		132	the network link between the parts goes down, then using the same seed
		133	nodes for all nodes ensures that eventually the subnets get merged again.
		134
		135	Seed nodes are expected to be long-running, and at least one seed node
		136	should always be available. They should also be relatively responsive - a
		137	seed node that blocks for long periods will slow down everybody else.
		138
		139	For small networks, it's best if every node uses the same set of seed
		140	nodes. For large networks, it can be useful to specify "regional" seed
		141	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		142	each other. What's important is that all seed nodes connections form a
		143	complete graph, so that the network cannot split into separate subnets
		144	forever.
		145
		146	Seed nodes are represented by seed IDs.
		147
		148	=item seed IDs - C<host:port>
		149
		150	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
		151	TCP port) of nodes that should be used as seed nodes.
		152
		153	=item global nodes
		154
		155	An AEMP network needs a discovery service - nodes need to know how to
		156	connect to other nodes they only know by name. In addition, AEMP offers a
		157	distributed "group database", which maps group names to a list of strings
		158	- for example, to register worker ports.
		159
		160	A network needs at least one global node to work, and allows every node to
		161	be a global node.
		162
		163	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		164	node and tries to keep connections to all other nodes. So while it can
		165	make sense to make every node "global" in small networks, it usually makes
		166	sense to only make seed nodes into global nodes in large networks (nodes
		167	keep connections to seed nodes and global nodes, so makign them the same
		168	reduces overhead).
		169
		170	=back
		171
		172	=head1 VARIABLES/FUNCTIONS
		173
		174	=over 4
		175
11	=cut	176	=cut
12		177
13	package AnyEvent::MP;	178	package AnyEvent::MP;
14		179
		180	use AnyEvent::MP::Config ();
		181	use AnyEvent::MP::Kernel;
		182	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
		183
15	use common::sense;	184	use common::sense;
16		185
		186	use Carp ();
		187
17	use AE ();	188	use AE ();
18		189
19	our $VERSION = '0.0';	190	use base "Exporter";
20		191
21	sub nonce($) {	192	our $VERSION = $AnyEvent::MP::Config::VERSION;
22	my $nonce;
23		193
24	if (open my $fh, "</dev/urandom") {	194	our @EXPORT = qw(
25	sysread $fh, $nonce, $_[0];	195	NODE $NODE *SELF node_of after
26	} else {	196	configure
		197	snd rcv mon mon_guard kil psub peval spawn cal
		198	port
		199	);
		200
		201	our $SELF;
		202
		203	sub _self_die() {
		204	my $msg = $@;
		205	$msg =~ s/\n+$// unless ref $msg;
		206	kil $SELF, die => $msg;
		207	}
		208
		209	=item $thisnode = NODE / $NODE
		210
		211	The C<NODE> function returns, and the C<$NODE> variable contains, the node
		212	ID of the node running in the current process. This value is initialised by
		213	a call to C<configure>.
		214
		215	=item $nodeid = node_of $port
		216
		217	Extracts and returns the node ID from a port ID or a node ID.
		218
		219	=item configure $profile, key => value...
		220
		221	=item configure key => value...
		222
		223	Before a node can talk to other nodes on the network (i.e. enter
		224	"distributed mode") it has to configure itself - the minimum a node needs
		225	to know is its own name, and optionally it should know the addresses of
		226	some other nodes in the network to discover other nodes.
		227
		228	This function configures a node - it must be called exactly once (or
		229	never) before calling other AnyEvent::MP functions.
		230
		231	The key/value pairs are basically the same ones as documented for the
		232	F<aemp> command line utility (sans the set/del prefix), with two additions:
		233
		234	=over 4
		235
		236	=item norc => $boolean (default false)
		237
		238	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
		239	be consulted - all configuraiton options must be specified in the
		240	C<configure> call.
		241
		242	=item force => $boolean (default false)
		243
		244	IF true, then the values specified in the C<configure> will take
		245	precedence over any values configured via the rc file. The default is for
		246	the rc file to override any options specified in the program.
		247
		248	=back
		249
		250	=over 4
		251
		252	=item step 1, gathering configuration from profiles
		253
		254	The function first looks up a profile in the aemp configuration (see the
		255	L<aemp> commandline utility). The profile name can be specified via the
		256	named C<profile> parameter or can simply be the first parameter). If it is
		257	missing, then the nodename (F<uname -n>) will be used as profile name.
		258
		259	The profile data is then gathered as follows:
		260
		261	First, all remaining key => value pairs (all of which are conveniently
		262	undocumented at the moment) will be interpreted as configuration
		263	data. Then they will be overwritten by any values specified in the global
		264	default configuration (see the F<aemp> utility), then the chain of
		265	profiles chosen by the profile name (and any C<parent> attributes).
		266
		267	That means that the values specified in the profile have highest priority
		268	and the values specified directly via C<configure> have lowest priority,
		269	and can only be used to specify defaults.
		270
		271	If the profile specifies a node ID, then this will become the node ID of
		272	this process. If not, then the profile name will be used as node ID, with
		273	a slash (C</>) attached.
		274
		275	If the node ID (or profile name) ends with a slash (C</>), then a random
		276	string is appended to make it unique.
		277
		278	=item step 2, bind listener sockets
		279
		280	The next step is to look up the binds in the profile, followed by binding
		281	aemp protocol listeners on all binds specified (it is possible and valid
		282	to have no binds, meaning that the node cannot be contacted form the
		283	outside. This means the node cannot talk to other nodes that also have no
		284	binds, but it can still talk to all "normal" nodes).
		285
		286	If the profile does not specify a binds list, then a default of C<*> is
		287	used, meaning the node will bind on a dynamically-assigned port on every
		288	local IP address it finds.
		289
		290	=item step 3, connect to seed nodes
		291
		292	As the last step, the seed ID list from the profile is passed to the
		293	L<AnyEvent::MP::Global> module, which will then use it to keep
		294	connectivity with at least one node at any point in time.
		295
		296	=back
		297
		298	Example: become a distributed node using the local node name as profile.
		299	This should be the most common form of invocation for "daemon"-type nodes.
		300
		301	configure
		302
		303	Example: become an anonymous node. This form is often used for commandline
		304	clients.
		305
		306	configure nodeid => "anon/";
		307
		308	Example: configure a node using a profile called seed, which is suitable
		309	for a seed node as it binds on all local addresses on a fixed port (4040,
		310	customary for aemp).
		311
		312	# use the aemp commandline utility
		313	# aemp profile seed binds '*:4040'
		314
		315	# then use it
		316	configure profile => "seed";
		317
		318	# or simply use aemp from the shell again:
		319	# aemp run profile seed
		320
		321	# or provide a nicer-to-remember nodeid
		322	# aemp run profile seed nodeid "$(hostname)"
		323
		324	=item $SELF
		325
		326	Contains the current port id while executing C<rcv> callbacks or C<psub>
		327	blocks.
		328
		329	=item *SELF, SELF, %SELF, @SELF...
		330
		331	Due to some quirks in how perl exports variables, it is impossible to
		332	just export C<$SELF>, all the symbols named C<SELF> are exported by this
		333	module, but only C<$SELF> is currently used.
		334
		335	=item snd $port, type => @data
		336
		337	=item snd $port, @msg
		338
		339	Send the given message to the given port, which can identify either a
		340	local or a remote port, and must be a port ID.
		341
		342	While the message can be almost anything, it is highly recommended to
		343	use a string as first element (a port ID, or some word that indicates a
		344	request type etc.) and to consist if only simple perl values (scalars,
		345	arrays, hashes) - if you think you need to pass an object, think again.
		346
		347	The message data logically becomes read-only after a call to this
		348	function: modifying any argument (or values referenced by them) is
		349	forbidden, as there can be considerable time between the call to C<snd>
		350	and the time the message is actually being serialised - in fact, it might
		351	never be copied as within the same process it is simply handed to the
		352	receiving port.
		353
		354	The type of data you can transfer depends on the transport protocol: when
		355	JSON is used, then only strings, numbers and arrays and hashes consisting
		356	of those are allowed (no objects). When Storable is used, then anything
		357	that Storable can serialise and deserialise is allowed, and for the local
		358	node, anything can be passed. Best rely only on the common denominator of
		359	these.
		360
		361	=item $local_port = port
		362
		363	Create a new local port object and returns its port ID. Initially it has
		364	no callbacks set and will throw an error when it receives messages.
		365
		366	=item $local_port = port { my @msg = @_ }
		367
		368	Creates a new local port, and returns its ID. Semantically the same as
		369	creating a port and calling C<rcv $port, $callback> on it.
		370
		371	The block will be called for every message received on the port, with the
		372	global variable C<$SELF> set to the port ID. Runtime errors will cause the
		373	port to be C<kil>ed. The message will be passed as-is, no extra argument
		374	(i.e. no port ID) will be passed to the callback.
		375
		376	If you want to stop/destroy the port, simply C<kil> it:
		377
		378	my $port = port {
		379	my @msg = @_;
27	# shit...	380	...
28	our $nonce_init;	381	kil $SELF;
29	unless ($nonce_init++) {
30	srand time ^ $$ ^ unpack "%L*", qx"ps -edalf" . qx"ipconfig /all";
31	}
32
33	$nonce = join "", map +(chr rand 256), 1 .. $_[0]
34	}	382	};
35		383
36	$nonce	384	=cut
37	}
38		385
39	our $DEFAULT_SECRET;	386	sub rcv($@);
40		387
41	sub default_secret {	388	sub _kilme {
42	unless (defined $DEFAULT_SECRET) {	389	die "received message on port without callback";
43	if (open my $fh, "<$ENV{HOME}/.aemp-secret") {	390	}
44	sysread $fh, $DEFAULT_SECRET, -s $fh;	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 received 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	}
		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, $cb->(@reason) # call $cb when $port dies
		586
		587	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
		588
		589	=item $guard = mon $port # kill $SELF when $port dies
		590
		591	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		592
		593	Monitor the given port and do something when the port is killed or
		594	messages to it were lost, and optionally return a guard that can be used
		595	to stop monitoring again.
		596
		597	In the first form (callback), the callback is simply called with any
		598	number of C<@reason> elements (no @reason means that the port was deleted
		599	"normally"). Note also that I<< the callback B<must> never die >>, so use
		600	C<eval> if unsure.
		601
		602	In the second form (another port given), the other port (C<$rcvport>)
		603	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
		604	"normal" kils nothing happens, while under all other conditions, the other
		605	port is killed with the same reason.
		606
		607	The third form (kill self) is the same as the second form, except that
		608	C<$rvport> defaults to C<$SELF>.
		609
		610	In the last form (message), a message of the form C<@msg, @reason> will be
		611	C<snd>.
		612
		613	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		614	alert was raised), they are removed and will not trigger again.
		615
		616	As a rule of thumb, monitoring requests should always monitor a port from
		617	a local port (or callback). The reason is that kill messages might get
		618	lost, just like any other message. Another less obvious reason is that
		619	even monitoring requests can get lost (for example, when the connection
		620	to the other node goes down permanently). When monitoring a port locally
		621	these problems do not exist.
		622
		623	C<mon> effectively guarantees that, in the absence of hardware failures,
		624	after starting the monitor, either all messages sent to the port will
		625	arrive, or the monitoring action will be invoked after possible message
		626	loss has been detected. No messages will be lost "in between" (after
		627	the first lost message no further messages will be received by the
		628	port). After the monitoring action was invoked, further messages might get
		629	delivered again.
		630
		631	Inter-host-connection timeouts and monitoring depend on the transport
		632	used. The only transport currently implemented is TCP, and AnyEvent::MP
		633	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		634	non-idle connection, and usually around two hours for idle connections).
		635
		636	This means that monitoring is good for program errors and cleaning up
		637	stuff eventually, but they are no replacement for a timeout when you need
		638	to ensure some maximum latency.
		639
		640	Example: call a given callback when C<$port> is killed.
		641
		642	mon $port, sub { warn "port died because of <@_>\n" };
		643
		644	Example: kill ourselves when C<$port> is killed abnormally.
		645
		646	mon $port;
		647
		648	Example: send us a restart message when another C<$port> is killed.
		649
		650	mon $port, $self => "restart";
		651
		652	=cut
		653
		654	sub mon {
		655	my ($nodeid, $port) = split /#/, shift, 2;
		656
		657	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
		658
		659	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
		660
		661	unless (ref $cb) {
		662	if (@_) {
		663	# send a kill info message
		664	my (@msg) = ($cb, @_);
		665	$cb = sub { snd @msg, @_ };
		666	} else {
		667	# simply kill other port
		668	my $port = $cb;
		669	$cb = sub { kil $port, @_ if @_ };
		670	}
		671	}
		672
		673	$node->monitor ($port, $cb);
		674
		675	defined wantarray
		676	and ($cb += 0, AnyEvent::Util::guard { $node->unmonitor ($port, $cb) })
		677	}
		678
		679	=item $guard = mon_guard $port, $ref, $ref...
		680
		681	Monitors the given C<$port> and keeps the passed references. When the port
		682	is killed, the references will be freed.
		683
		684	Optionally returns a guard that will stop the monitoring.
		685
		686	This function is useful when you create e.g. timers or other watchers and
		687	want to free them when the port gets killed (note the use of C<psub>):
		688
		689	$port->rcv (start => sub {
		690	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
		691	undef $timer if 0.9 < rand;
		692	});
		693	});
		694
		695	=cut
		696
		697	sub mon_guard {
		698	my ($port, @refs) = @_;
		699
		700	#TODO: mon-less form?
		701
		702	mon $port, sub { 0 && @refs }
		703	}
		704
		705	=item kil $port[, @reason]
		706
		707	Kill the specified port with the given C<@reason>.
		708
		709	If no C<@reason> is specified, then the port is killed "normally" -
		710	monitor callback will be invoked, but the kil will not cause linked ports
		711	(C<mon $mport, $lport> form) to get killed.
		712
		713	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
		714	form) get killed with the same reason.
		715
		716	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		717	will be reported as reason C<< die => $@ >>.
		718
		719	Transport/communication errors are reported as C<< transport_error =>
		720	$message >>.
		721
		722	=cut
		723
		724	=item $port = spawn $node, $initfunc[, @initdata]
		725
		726	Creates a port on the node C<$node> (which can also be a port ID, in which
		727	case it's the node where that port resides).
		728
		729	The port ID of the newly created port is returned immediately, and it is
		730	possible to immediately start sending messages or to monitor the port.
		731
		732	After the port has been created, the init function is called on the remote
		733	node, in the same context as a C<rcv> callback. This function must be a
		734	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		735	specify a function in the main program, use C<::name>.
		736
		737	If the function doesn't exist, then the node tries to C<require>
		738	the package, then the package above the package and so on (e.g.
		739	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		740	exists or it runs out of package names.
		741
		742	The init function is then called with the newly-created port as context
		743	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		744	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		745	the port might not get created.
		746
		747	A common idiom is to pass a local port, immediately monitor the spawned
		748	port, and in the remote init function, immediately monitor the passed
		749	local port. This two-way monitoring ensures that both ports get cleaned up
		750	when there is a problem.
		751
		752	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		753	caller before C<spawn> returns (by delaying invocation when spawn is
		754	called for the local node).
		755
		756	Example: spawn a chat server port on C<$othernode>.
		757
		758	# this node, executed from within a port context:
		759	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		760	mon $server;
		761
		762	# init function on C<$othernode>
		763	sub connect {
		764	my ($srcport) = @_;
		765
		766	mon $srcport;
		767
		768	rcv $SELF, sub {
		769	...
		770	};
		771	}
		772
		773	=cut
		774
		775	sub _spawn {
		776	my $port = shift;
		777	my $init = shift;
		778
		779	# rcv will create the actual port
		780	local $SELF = "$NODE#$port";
		781	eval {
		782	&{ load_func $init }
		783	};
		784	_self_die if $@;
		785	}
		786
		787	sub spawn(@) {
		788	my ($nodeid, undef) = split /#/, shift, 2;
		789
		790	my $id = "$RUNIQ." . ++$ID;
		791
		792	$_[0] =~ /::/
		793	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		794
		795	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		796
		797	"$nodeid#$id"
		798	}
		799
		800
		801	=item after $timeout, @msg
		802
		803	=item after $timeout, $callback
		804
		805	Either sends the given message, or call the given callback, after the
		806	specified number of seconds.
		807
		808	This is simply a utility function that comes in handy at times - the
		809	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		810	so it may go away in the future.
		811
		812	=cut
		813
		814	sub after($@) {
		815	my ($timeout, @action) = @_;
		816
		817	my $t; $t = AE::timer $timeout, 0, sub {
		818	undef $t;
		819	ref $action[0]
		820	? $action[0]()
		821	: snd @action;
		822	};
		823	}
		824
		825	=item cal $port, @msg, $callback[, $timeout]
		826
		827	A simple form of RPC - sends a message to the given C<$port> with the
		828	given contents (C<@msg>), but adds a reply port to the message.
		829
		830	The reply port is created temporarily just for the purpose of receiving
		831	the reply, and will be C<kil>ed when no longer needed.
		832
		833	A reply message sent to the port is passed to the C<$callback> as-is.
		834
		835	If an optional time-out (in seconds) is given and it is not C<undef>,
		836	then the callback will be called without any arguments after the time-out
		837	elapsed and the port is C<kil>ed.
		838
		839	If no time-out is given (or it is C<undef>), then the local port will
		840	monitor the remote port instead, so it eventually gets cleaned-up.
		841
		842	Currently this function returns the temporary port, but this "feature"
		843	might go in future versions unless you can make a convincing case that
		844	this is indeed useful for something.
		845
		846	=cut
		847
		848	sub cal(@) {
		849	my $timeout = ref $_[-1] ? undef : pop;
		850	my $cb = pop;
		851
		852	my $port = port {
		853	undef $timeout;
		854	kil $SELF;
		855	&$cb;
		856	};
		857
		858	if (defined $timeout) {
		859	$timeout = AE::timer $timeout, 0, sub {
		860	undef $timeout;
		861	kil $port;
		862	$cb->();
		863	};
		864	} else {
		865	mon $_[0], sub {
		866	kil $port;
		867	$cb->();
		868	};
		869	}
		870
		871	push @_, $port;
		872	&snd;
		873
		874	$port
		875	}
		876
		877	=back
		878
		879	=head1 AnyEvent::MP vs. Distributed Erlang
		880
		881	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
		882	== aemp node, Erlang process == aemp port), so many of the documents and
		883	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
		884	sample:
		885
		886	http://www.erlang.se/doc/programming_rules.shtml
		887	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
		888	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
		889	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
		890
		891	Despite the similarities, there are also some important differences:
		892
		893	=over 4
		894
		895	=item * Node IDs are arbitrary strings in AEMP.
		896
		897	Erlang relies on special naming and DNS to work everywhere in the same
		898	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
		899	configuration or DNS), and possibly the addresses of some seed nodes, but
		900	will otherwise discover other nodes (and their IDs) itself.
		901
		902	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
		903	uses "local ports are like remote ports".
		904
		905	The failure modes for local ports are quite different (runtime errors
		906	only) then for remote ports - when a local port dies, you I<know> it dies,
		907	when a connection to another node dies, you know nothing about the other
		908	port.
		909
		910	Erlang pretends remote ports are as reliable as local ports, even when
		911	they are not.
		912
		913	AEMP encourages a "treat remote ports differently" philosophy, with local
		914	ports being the special case/exception, where transport errors cannot
		915	occur.
		916
		917	=item * Erlang uses processes and a mailbox, AEMP does not queue.
		918
		919	Erlang uses processes that selectively receive messages out of order, and
		920	therefore needs a queue. AEMP is event based, queuing messages would serve
		921	no useful purpose. For the same reason the pattern-matching abilities
		922	of AnyEvent::MP are more limited, as there is little need to be able to
		923	filter messages without dequeuing them.
		924
		925	This is not a philosophical difference, but simply stems from AnyEvent::MP
		926	being event-based, while Erlang is process-based.
		927
		928	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		929	top of AEMP and Coro threads.
		930
		931	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
		932
		933	Sending messages in Erlang is synchronous and blocks the process until
		934	a conenction has been established and the message sent (and so does not
		935	need a queue that can overflow). AEMP sends return immediately, connection
		936	establishment is handled in the background.
		937
		938	=item * Erlang suffers from silent message loss, AEMP does not.
		939
		940	Erlang implements few guarantees on messages delivery - messages can get
		941	lost without any of the processes realising it (i.e. you send messages a,
		942	b, and c, and the other side only receives messages a and c).
		943
		944	AEMP guarantees (modulo hardware errors) correct ordering, and the
		945	guarantee that after one message is lost, all following ones sent to the
		946	same port are lost as well, until monitoring raises an error, so there are
		947	no silent "holes" in the message sequence.
		948
		949	If you want your software to be very reliable, you have to cope with
		950	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
		951	simply tries to work better in common error cases, such as when a network
		952	link goes down.
		953
		954	=item * Erlang can send messages to the wrong port, AEMP does not.
		955
		956	In Erlang it is quite likely that a node that restarts reuses an Erlang
		957	process ID known to other nodes for a completely different process,
		958	causing messages destined for that process to end up in an unrelated
		959	process.
		960
		961	AEMP does not reuse port IDs, so old messages or old port IDs floating
		962	around in the network will not be sent to an unrelated port.
		963
		964	=item * Erlang uses unprotected connections, AEMP uses secure
		965	authentication and can use TLS.
		966
		967	AEMP can use a proven protocol - TLS - to protect connections and
		968	securely authenticate nodes.
		969
		970	=item * The AEMP protocol is optimised for both text-based and binary
		971	communications.
		972
		973	The AEMP protocol, unlike the Erlang protocol, supports both programming
		974	language independent text-only protocols (good for debugging), and binary,
		975	language-specific serialisers (e.g. Storable). By default, unless TLS is
		976	used, the protocol is actually completely text-based.
		977
		978	It has also been carefully designed to be implementable in other languages
		979	with a minimum of work while gracefully degrading functionality to make the
		980	protocol simple.
		981
		982	=item * AEMP has more flexible monitoring options than Erlang.
		983
		984	In Erlang, you can chose to receive I<all> exit signals as messages or
		985	I<none>, there is no in-between, so monitoring single Erlang processes is
		986	difficult to implement.
		987
		988	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		989	between automatic kill, exit message or callback on a per-port basis.
		990
		991	=item * Erlang tries to hide remote/local connections, AEMP does not.
		992
		993	Monitoring in Erlang is not an indicator of process death/crashes, in the
		994	same way as linking is (except linking is unreliable in Erlang).
		995
		996	In AEMP, you don't "look up" registered port names or send to named ports
		997	that might or might not be persistent. Instead, you normally spawn a port
		998	on the remote node. The init function monitors you, and you monitor the
		999	remote port. Since both monitors are local to the node, they are much more
		1000	reliable (no need for C<spawn_link>).
		1001
		1002	This also saves round-trips and avoids sending messages to the wrong port
		1003	(hard to do in Erlang).
		1004
		1005	=back
		1006
		1007	=head1 RATIONALE
		1008
		1009	=over 4
		1010
		1011	=item Why strings for port and node IDs, why not objects?
		1012
		1013	We considered "objects", but found that the actual number of methods
		1014	that can be called are quite low. Since port and node IDs travel over
		1015	the network frequently, the serialising/deserialising would add lots of
		1016	overhead, as well as having to keep a proxy object everywhere.
		1017
		1018	Strings can easily be printed, easily serialised etc. and need no special
		1019	procedures to be "valid".
		1020
		1021	And as a result, a port with just a default receiver consists of a single
		1022	code reference stored in a global hash - it can't become much cheaper.
		1023
		1024	=item Why favour JSON, why not a real serialising format such as Storable?
		1025
		1026	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1027	format, but currently there is no way to make a node use Storable by
		1028	default (although all nodes will accept it).
		1029
		1030	The default framing protocol is JSON because a) JSON::XS is many times
		1031	faster for small messages and b) most importantly, after years of
		1032	experience we found that object serialisation is causing more problems
		1033	than it solves: Just like function calls, objects simply do not travel
		1034	easily over the network, mostly because they will always be a copy, so you
		1035	always have to re-think your design.
		1036
		1037	Keeping your messages simple, concentrating on data structures rather than
		1038	objects, will keep your messages clean, tidy and efficient.
		1039
		1040	=back
52		1041
53	=head1 SEE ALSO	1042	=head1 SEE ALSO
		1043
		1044	L<AnyEvent::MP::Intro> - a gentle introduction.
		1045
		1046	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1047
		1048	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1049	your applications.
		1050
		1051	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1052
		1053	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1054	all nodes.
54		1055
55	L<AnyEvent>.	1056	L<AnyEvent>.
56		1057
57	=head1 AUTHOR	1058	=head1 AUTHOR
58		1059

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Revision 1.122 by root, Wed Feb 29 18:44:59 2012 UTC