[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 1.135 by root, Mon Mar 12 14:55:55 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	my $KILME = sub {
		404	(my $tag = substr $_[0], 0, 30) =~ s/([\x20-\x7e])/./g;
		405	kil $SELF, unhandled_message => "no callback found for message '$tag'";
		406	};
		407
		408	sub port(;&) {
		409	my $id = $UNIQ . ++$ID;
		410	my $port = "$NODE#$id";
		411
		412	rcv $port, shift \|\| $KILME;
		413
		414	$port
		415	}
		416
		417	=item rcv $local_port, $callback->(@msg)
		418
		419	Replaces the default callback on the specified port. There is no way to
		420	remove the default callback: use C<sub { }> to disable it, or better
		421	C<kil> the port when it is no longer needed.
		422
		423	The global C<$SELF> (exported by this module) contains C<$port> while
		424	executing the callback. Runtime errors during callback execution will
		425	result in the port being C<kil>ed.
		426
		427	The default callback receives all messages not matched by a more specific
		428	C<tag> match.
		429
		430	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
		431
		432	Register (or replace) callbacks to be called on messages starting with the
		433	given tag on the given port (and return the port), or unregister it (when
		434	C<$callback> is C<$undef> or missing). There can only be one callback
		435	registered for each tag.
		436
		437	The original message will be passed to the callback, after the first
		438	element (the tag) has been removed. The callback will use the same
		439	environment as the default callback (see above).
		440
		441	Example: create a port and bind receivers on it in one go.
		442
		443	my $port = rcv port,
		444	msg1 => sub { ... },
		445	msg2 => sub { ... },
		446	;
		447
		448	Example: create a port, bind receivers and send it in a message elsewhere
		449	in one go:
		450
		451	snd $otherport, reply =>
		452	rcv port,
		453	msg1 => sub { ... },
		454	...
		455	;
		456
		457	Example: temporarily register a rcv callback for a tag matching some port
		458	(e.g. for an rpc reply) and unregister it after a message was received.
		459
		460	rcv $port, $otherport => sub {
		461	my @reply = @_;
		462
		463	rcv $SELF, $otherport;
		464	};
		465
		466	=cut
		467
		468	sub rcv($@) {
		469	my $port = shift;
		470	my ($nodeid, $portid) = split /#/, $port, 2;
		471
		472	$NODE{$nodeid} == $NODE{""}
		473	or Carp::croak "$port: rcv can only be called on local ports, caught";
		474
		475	while (@_) {
		476	if (ref $_[0]) {
		477	if (my $self = $PORT_DATA{$portid}) {
		478	"AnyEvent::MP::Port" eq ref $self
		479	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		480
		481	$self->[0] = shift;
45	} else {	482	} else {
46	$DEFAULT_SECRET = nonce 32;	483	my $cb = shift;
		484	$PORT{$portid} = sub {
		485	local $SELF = $port;
		486	eval { &$cb }; _self_die if $@;
		487	};
		488	}
		489	} elsif (defined $_[0]) {
		490	my $self = $PORT_DATA{$portid} \|\|= do {
		491	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
		492
		493	$PORT{$portid} = sub {
		494	local $SELF = $port;
		495
		496	if (my $cb = $self->[1]{$_[0]}) {
		497	shift;
		498	eval { &$cb }; _self_die if $@;
		499	} else {
		500	&{ $self->[0] };
		501	}
		502	};
		503
		504	$self
		505	};
		506
		507	"AnyEvent::MP::Port" eq ref $self
		508	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		509
		510	my ($tag, $cb) = splice @_, 0, 2;
		511
		512	if (defined $cb) {
		513	$self->[1]{$tag} = $cb;
		514	} else {
		515	delete $self->[1]{$tag};
		516	}
47	}	517	}
48	}	518	}
49		519
50	$DEFAULT_SECRET	520	$port
51	}	521	}
52		522
		523	=item peval $port, $coderef[, @args]
		524
		525	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		526	when the code throews an exception the C<$port> will be killed.
		527
		528	Any remaining args will be passed to the callback. Any return values will
		529	be returned to the caller.
		530
		531	This is useful when you temporarily want to execute code in the context of
		532	a port.
		533
		534	Example: create a port and run some initialisation code in it's context.
		535
		536	my $port = port { ... };
		537
		538	peval $port, sub {
		539	init
		540	or die "unable to init";
		541	};
		542
		543	=cut
		544
		545	sub peval($$) {
		546	local $SELF = shift;
		547	my $cb = shift;
		548
		549	if (wantarray) {
		550	my @res = eval { &$cb };
		551	_self_die if $@;
		552	@res
		553	} else {
		554	my $res = eval { &$cb };
		555	_self_die if $@;
		556	$res
		557	}
		558	}
		559
		560	=item $closure = psub { BLOCK }
		561
		562	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
		563	closure is executed, sets up the environment in the same way as in C<rcv>
		564	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		565
		566	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		567	BLOCK }, @_ } >>.
		568
		569	This is useful when you register callbacks from C<rcv> callbacks:
		570
		571	rcv delayed_reply => sub {
		572	my ($delay, @reply) = @_;
		573	my $timer = AE::timer $delay, 0, psub {
		574	snd @reply, $SELF;
		575	};
		576	};
		577
		578	=cut
		579
		580	sub psub(&) {
		581	my $cb = shift;
		582
		583	my $port = $SELF
		584	or Carp::croak "psub can only be called from within rcv or psub callbacks, not";
		585
		586	sub {
		587	local $SELF = $port;
		588
		589	if (wantarray) {
		590	my @res = eval { &$cb };
		591	_self_die if $@;
		592	@res
		593	} else {
		594	my $res = eval { &$cb };
		595	_self_die if $@;
		596	$res
		597	}
		598	}
		599	}
		600
		601	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
		602
		603	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
		604
		605	=item $guard = mon $port # kill $SELF when $port dies
		606
		607	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		608
		609	Monitor the given port and do something when the port is killed or
		610	messages to it were lost, and optionally return a guard that can be used
		611	to stop monitoring again.
		612
		613	In the first form (callback), the callback is simply called with any
		614	number of C<@reason> elements (no @reason means that the port was deleted
		615	"normally"). Note also that I<< the callback B<must> never die >>, so use
		616	C<eval> if unsure.
		617
		618	In the second form (another port given), the other port (C<$rcvport>)
		619	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
		620	"normal" kils nothing happens, while under all other conditions, the other
		621	port is killed with the same reason.
		622
		623	The third form (kill self) is the same as the second form, except that
		624	C<$rvport> defaults to C<$SELF>.
		625
		626	In the last form (message), a message of the form C<@msg, @reason> will be
		627	C<snd>.
		628
		629	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		630	alert was raised), they are removed and will not trigger again.
		631
		632	As a rule of thumb, monitoring requests should always monitor a port from
		633	a local port (or callback). The reason is that kill messages might get
		634	lost, just like any other message. Another less obvious reason is that
		635	even monitoring requests can get lost (for example, when the connection
		636	to the other node goes down permanently). When monitoring a port locally
		637	these problems do not exist.
		638
		639	C<mon> effectively guarantees that, in the absence of hardware failures,
		640	after starting the monitor, either all messages sent to the port will
		641	arrive, or the monitoring action will be invoked after possible message
		642	loss has been detected. No messages will be lost "in between" (after
		643	the first lost message no further messages will be received by the
		644	port). After the monitoring action was invoked, further messages might get
		645	delivered again.
		646
		647	Inter-host-connection timeouts and monitoring depend on the transport
		648	used. The only transport currently implemented is TCP, and AnyEvent::MP
		649	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		650	non-idle connection, and usually around two hours for idle connections).
		651
		652	This means that monitoring is good for program errors and cleaning up
		653	stuff eventually, but they are no replacement for a timeout when you need
		654	to ensure some maximum latency.
		655
		656	Example: call a given callback when C<$port> is killed.
		657
		658	mon $port, sub { warn "port died because of <@_>\n" };
		659
		660	Example: kill ourselves when C<$port> is killed abnormally.
		661
		662	mon $port;
		663
		664	Example: send us a restart message when another C<$port> is killed.
		665
		666	mon $port, $self => "restart";
		667
		668	=cut
		669
		670	sub mon {
		671	my ($nodeid, $port) = split /#/, shift, 2;
		672
		673	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
		674
		675	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
		676
		677	unless (ref $cb) {
		678	if (@_) {
		679	# send a kill info message
		680	my (@msg) = ($cb, @_);
		681	$cb = sub { snd @msg, @_ };
		682	} else {
		683	# simply kill other port
		684	my $port = $cb;
		685	$cb = sub { kil $port, @_ if @_ };
		686	}
		687	}
		688
		689	$node->monitor ($port, $cb);
		690
		691	defined wantarray
		692	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
		693	}
		694
		695	=item $guard = mon_guard $port, $ref, $ref...
		696
		697	Monitors the given C<$port> and keeps the passed references. When the port
		698	is killed, the references will be freed.
		699
		700	Optionally returns a guard that will stop the monitoring.
		701
		702	This function is useful when you create e.g. timers or other watchers and
		703	want to free them when the port gets killed (note the use of C<psub>):
		704
		705	$port->rcv (start => sub {
		706	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
		707	undef $timer if 0.9 < rand;
		708	});
		709	});
		710
		711	=cut
		712
		713	sub mon_guard {
		714	my ($port, @refs) = @_;
		715
		716	#TODO: mon-less form?
		717
		718	mon $port, sub { 0 && @refs }
		719	}
		720
		721	=item kil $port[, @reason]
		722
		723	Kill the specified port with the given C<@reason>.
		724
		725	If no C<@reason> is specified, then the port is killed "normally" -
		726	monitor callback will be invoked, but the kil will not cause linked ports
		727	(C<mon $mport, $lport> form) to get killed.
		728
		729	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
		730	form) get killed with the same reason.
		731
		732	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		733	will be reported as reason C<< die => $@ >>.
		734
		735	Transport/communication errors are reported as C<< transport_error =>
		736	$message >>.
		737
		738	Common idioms:
		739
		740	# silently remove yourself, do not kill linked ports
		741	kil $SELF;
		742
		743	# report a failure in some detail
		744	kil $SELF, failure_mode_1 => "it failed with too high temperature";
		745
		746	# do not waste much time with killing, just die when something goes wrong
		747	open my $fh, "<file"
		748	or die "file: $!";
		749
		750	=item $port = spawn $node, $initfunc[, @initdata]
		751
		752	Creates a port on the node C<$node> (which can also be a port ID, in which
		753	case it's the node where that port resides).
		754
		755	The port ID of the newly created port is returned immediately, and it is
		756	possible to immediately start sending messages or to monitor the port.
		757
		758	After the port has been created, the init function is called on the remote
		759	node, in the same context as a C<rcv> callback. This function must be a
		760	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		761	specify a function in the main program, use C<::name>.
		762
		763	If the function doesn't exist, then the node tries to C<require>
		764	the package, then the package above the package and so on (e.g.
		765	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		766	exists or it runs out of package names.
		767
		768	The init function is then called with the newly-created port as context
		769	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		770	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		771	the port might not get created.
		772
		773	A common idiom is to pass a local port, immediately monitor the spawned
		774	port, and in the remote init function, immediately monitor the passed
		775	local port. This two-way monitoring ensures that both ports get cleaned up
		776	when there is a problem.
		777
		778	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		779	caller before C<spawn> returns (by delaying invocation when spawn is
		780	called for the local node).
		781
		782	Example: spawn a chat server port on C<$othernode>.
		783
		784	# this node, executed from within a port context:
		785	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		786	mon $server;
		787
		788	# init function on C<$othernode>
		789	sub connect {
		790	my ($srcport) = @_;
		791
		792	mon $srcport;
		793
		794	rcv $SELF, sub {
		795	...
		796	};
		797	}
		798
		799	=cut
		800
		801	sub _spawn {
		802	my $port = shift;
		803	my $init = shift;
		804
		805	# rcv will create the actual port
		806	local $SELF = "$NODE#$port";
		807	eval {
		808	&{ load_func $init }
		809	};
		810	_self_die if $@;
		811	}
		812
		813	sub spawn(@) {
		814	my ($nodeid, undef) = split /#/, shift, 2;
		815
		816	my $id = $RUNIQ . ++$ID;
		817
		818	$_[0] =~ /::/
		819	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		820
		821	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		822
		823	"$nodeid#$id"
		824	}
		825
		826
		827	=item after $timeout, @msg
		828
		829	=item after $timeout, $callback
		830
		831	Either sends the given message, or call the given callback, after the
		832	specified number of seconds.
		833
		834	This is simply a utility function that comes in handy at times - the
		835	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		836	so it may go away in the future.
		837
		838	=cut
		839
		840	sub after($@) {
		841	my ($timeout, @action) = @_;
		842
		843	my $t; $t = AE::timer $timeout, 0, sub {
		844	undef $t;
		845	ref $action[0]
		846	? $action[0]()
		847	: snd @action;
		848	};
		849	}
		850
		851	#=item $cb2 = timeout $seconds, $cb[, @args]
		852
		853	=item cal $port, @msg, $callback[, $timeout]
		854
		855	A simple form of RPC - sends a message to the given C<$port> with the
		856	given contents (C<@msg>), but adds a reply port to the message.
		857
		858	The reply port is created temporarily just for the purpose of receiving
		859	the reply, and will be C<kil>ed when no longer needed.
		860
		861	A reply message sent to the port is passed to the C<$callback> as-is.
		862
		863	If an optional time-out (in seconds) is given and it is not C<undef>,
		864	then the callback will be called without any arguments after the time-out
		865	elapsed and the port is C<kil>ed.
		866
		867	If no time-out is given (or it is C<undef>), then the local port will
		868	monitor the remote port instead, so it eventually gets cleaned-up.
		869
		870	Currently this function returns the temporary port, but this "feature"
		871	might go in future versions unless you can make a convincing case that
		872	this is indeed useful for something.
		873
		874	=cut
		875
		876	sub cal(@) {
		877	my $timeout = ref $_[-1] ? undef : pop;
		878	my $cb = pop;
		879
		880	my $port = port {
		881	undef $timeout;
		882	kil $SELF;
		883	&$cb;
		884	};
		885
		886	if (defined $timeout) {
		887	$timeout = AE::timer $timeout, 0, sub {
		888	undef $timeout;
		889	kil $port;
		890	$cb->();
		891	};
		892	} else {
		893	mon $_[0], sub {
		894	kil $port;
		895	$cb->();
		896	};
		897	}
		898
		899	push @_, $port;
		900	&snd;
		901
		902	$port
		903	}
		904
		905	=back
		906
		907	=head1 DISTRIBUTED DATABASE
		908
		909	AnyEvent::MP comes with a simple distributed database. The database will
		910	be mirrored asynchronously on all global nodes. Other nodes bind to one
		911	of the global nodes for their needs. Every node has a "local database"
		912	which contains all the values that are set locally. All local databases
		913	are merged together to form the global database, which can be queried.
		914
		915	The database structure is that of a two-level hash - the database hash
		916	contains hashes which contain values, similarly to a perl hash of hashes,
		917	i.e.:
		918
		919	$DATABASE{$family}{$subkey} = $value
		920
		921	The top level hash key is called "family", and the second-level hash key
		922	is called "subkey" or simply "key".
		923
		924	The family must be alphanumeric, i.e. start with a letter and consist
		925	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		926	pretty much like Perl module names.
		927
		928	As the family namespace is global, it is recommended to prefix family names
		929	with the name of the application or module using it.
		930
		931	The subkeys must be non-empty strings, with no further restrictions.
		932
		933	The values should preferably be strings, but other perl scalars should
		934	work as well (such as C<undef>, arrays and hashes).
		935
		936	Every database entry is owned by one node - adding the same family/subkey
		937	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		938	but the result might be nondeterministic, i.e. the key might have
		939	different values on different nodes.
		940
		941	Different subkeys in the same family can be owned by different nodes
		942	without problems, and in fact, this is the common method to create worker
		943	pools. For example, a worker port for image scaling might do this:
		944
		945	db_set my_image_scalers => $port;
		946
		947	And clients looking for an image scaler will want to get the
		948	C<my_image_scalers> keys from time to time:
		949
		950	db_keys my_image_scalers => sub {
		951	@ports = @{ $_[0] };
		952	};
		953
		954	Or better yet, they want to monitor the database family, so they always
		955	have a reasonable up-to-date copy:
		956
		957	db_mon my_image_scalers => sub {
		958	@ports = keys %{ $_[0] };
		959	};
		960
		961	In general, you can set or delete single subkeys, but query and monitor
		962	whole families only.
		963
		964	If you feel the need to monitor or query a single subkey, try giving it
		965	it's own family.
		966
		967	=over
		968
		969	=item db_set $family => $subkey [=> $value]
		970
		971	Sets (or replaces) a key to the database - if C<$value> is omitted,
		972	C<undef> is used instead.
		973
		974	=item db_del $family => $subkey...
		975
		976	Deletes one or more subkeys from the database family.
		977
		978	=item $guard = db_reg $family => $subkey [=> $value]
		979
		980	Sets the key on the database and returns a guard. When the guard is
		981	destroyed, the key is deleted from the database. If C<$value> is missing,
		982	then C<undef> is used.
		983
		984	=item db_family $family => $cb->(\%familyhash)
		985
		986	Queries the named database C<$family> and call the callback with the
		987	family represented as a hash. You can keep and freely modify the hash.
		988
		989	=item db_keys $family => $cb->(\@keys)
		990
		991	Same as C<db_family>, except it only queries the family I<subkeys> and passes
		992	them as array reference to the callback.
		993
		994	=item db_values $family => $cb->(\@values)
		995
		996	Same as C<db_family>, except it only queries the family I<values> and passes them
		997	as array reference to the callback.
		998
		999	=item $guard = db_mon $family => $cb->($familyhash, \@added, \@changed, \@deleted)
		1000
		1001	Creates a monitor on the given database family. Each time a key is set
		1002	or or is deleted the callback is called with a hash containing the
		1003	database family and three lists of added, changed and deleted subkeys,
		1004	respectively. If no keys have changed then the array reference might be
		1005	C<undef> or even missing.
		1006
		1007	If not called in void context, a guard object is returned that, when
		1008	destroyed, stops the monitor.
		1009
		1010	The family hash reference and the key arrays belong to AnyEvent::MP and
		1011	B<must not be modified or stored> by the callback. When in doubt, make a
		1012	copy.
		1013
		1014	As soon as possible after the monitoring starts, the callback will be
		1015	called with the intiial contents of the family, even if it is empty,
		1016	i.e. there will always be a timely call to the callback with the current
		1017	contents.
		1018
		1019	It is possible that the callback is called with a change event even though
		1020	the subkey is already present and the value has not changed.
		1021
		1022	The monitoring stops when the guard object is destroyed.
		1023
		1024	Example: on every change to the family "mygroup", print out all keys.
		1025
		1026	my $guard = db_mon mygroup => sub {
		1027	my ($family, $a, $c, $d) = @_;
		1028	print "mygroup members: ", (join " ", keys %$family), "\n";
		1029	};
		1030
		1031	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1032
		1033	my $guard; $guard = db_mon My::Module::workers => sub {
		1034	my ($family, $a, $c, $d) = @_;
		1035	return unless %$family;
		1036	undef $guard;
		1037	print "My::Module::workers now nonempty\n";
		1038	};
		1039
		1040	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		1041
		1042	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		1043	my ($family, $a, $c, $d) = @_;
		1044
		1045	print "+$_=$family->{$_}\n" for @$a;
		1046	print "*$_=$family->{$_}\n" for @$c;
		1047	print "-$_=$family->{$_}\n" for @$d;
		1048	};
		1049
		1050	=cut
		1051
		1052	=back
		1053
		1054	=head1 AnyEvent::MP vs. Distributed Erlang
		1055
		1056	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
		1057	== aemp node, Erlang process == aemp port), so many of the documents and
		1058	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
		1059	sample:
		1060
		1061	http://www.erlang.se/doc/programming_rules.shtml
		1062	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
		1063	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
		1064	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
		1065
		1066	Despite the similarities, there are also some important differences:
		1067
		1068	=over 4
		1069
		1070	=item * Node IDs are arbitrary strings in AEMP.
		1071
		1072	Erlang relies on special naming and DNS to work everywhere in the same
		1073	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
		1074	configuration or DNS), and possibly the addresses of some seed nodes, but
		1075	will otherwise discover other nodes (and their IDs) itself.
		1076
		1077	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
		1078	uses "local ports are like remote ports".
		1079
		1080	The failure modes for local ports are quite different (runtime errors
		1081	only) then for remote ports - when a local port dies, you I<know> it dies,
		1082	when a connection to another node dies, you know nothing about the other
		1083	port.
		1084
		1085	Erlang pretends remote ports are as reliable as local ports, even when
		1086	they are not.
		1087
		1088	AEMP encourages a "treat remote ports differently" philosophy, with local
		1089	ports being the special case/exception, where transport errors cannot
		1090	occur.
		1091
		1092	=item * Erlang uses processes and a mailbox, AEMP does not queue.
		1093
		1094	Erlang uses processes that selectively receive messages out of order, and
		1095	therefore needs a queue. AEMP is event based, queuing messages would serve
		1096	no useful purpose. For the same reason the pattern-matching abilities
		1097	of AnyEvent::MP are more limited, as there is little need to be able to
		1098	filter messages without dequeuing them.
		1099
		1100	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1101	being event-based, while Erlang is process-based.
		1102
		1103	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1104	top of AEMP and Coro threads.
		1105
		1106	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
		1107
		1108	Sending messages in Erlang is synchronous and blocks the process until
		1109	a conenction has been established and the message sent (and so does not
		1110	need a queue that can overflow). AEMP sends return immediately, connection
		1111	establishment is handled in the background.
		1112
		1113	=item * Erlang suffers from silent message loss, AEMP does not.
		1114
		1115	Erlang implements few guarantees on messages delivery - messages can get
		1116	lost without any of the processes realising it (i.e. you send messages a,
		1117	b, and c, and the other side only receives messages a and c).
		1118
		1119	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1120	guarantee that after one message is lost, all following ones sent to the
		1121	same port are lost as well, until monitoring raises an error, so there are
		1122	no silent "holes" in the message sequence.
		1123
		1124	If you want your software to be very reliable, you have to cope with
		1125	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
		1126	simply tries to work better in common error cases, such as when a network
		1127	link goes down.
		1128
		1129	=item * Erlang can send messages to the wrong port, AEMP does not.
		1130
		1131	In Erlang it is quite likely that a node that restarts reuses an Erlang
		1132	process ID known to other nodes for a completely different process,
		1133	causing messages destined for that process to end up in an unrelated
		1134	process.
		1135
		1136	AEMP does not reuse port IDs, so old messages or old port IDs floating
		1137	around in the network will not be sent to an unrelated port.
		1138
		1139	=item * Erlang uses unprotected connections, AEMP uses secure
		1140	authentication and can use TLS.
		1141
		1142	AEMP can use a proven protocol - TLS - to protect connections and
		1143	securely authenticate nodes.
		1144
		1145	=item * The AEMP protocol is optimised for both text-based and binary
		1146	communications.
		1147
		1148	The AEMP protocol, unlike the Erlang protocol, supports both programming
		1149	language independent text-only protocols (good for debugging), and binary,
		1150	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1151	used, the protocol is actually completely text-based.
		1152
		1153	It has also been carefully designed to be implementable in other languages
		1154	with a minimum of work while gracefully degrading functionality to make the
		1155	protocol simple.
		1156
		1157	=item * AEMP has more flexible monitoring options than Erlang.
		1158
		1159	In Erlang, you can chose to receive I<all> exit signals as messages or
		1160	I<none>, there is no in-between, so monitoring single Erlang processes is
		1161	difficult to implement.
		1162
		1163	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1164	between automatic kill, exit message or callback on a per-port basis.
		1165
		1166	=item * Erlang tries to hide remote/local connections, AEMP does not.
		1167
		1168	Monitoring in Erlang is not an indicator of process death/crashes, in the
		1169	same way as linking is (except linking is unreliable in Erlang).
		1170
		1171	In AEMP, you don't "look up" registered port names or send to named ports
		1172	that might or might not be persistent. Instead, you normally spawn a port
		1173	on the remote node. The init function monitors you, and you monitor the
		1174	remote port. Since both monitors are local to the node, they are much more
		1175	reliable (no need for C<spawn_link>).
		1176
		1177	This also saves round-trips and avoids sending messages to the wrong port
		1178	(hard to do in Erlang).
		1179
		1180	=back
		1181
		1182	=head1 RATIONALE
		1183
		1184	=over 4
		1185
		1186	=item Why strings for port and node IDs, why not objects?
		1187
		1188	We considered "objects", but found that the actual number of methods
		1189	that can be called are quite low. Since port and node IDs travel over
		1190	the network frequently, the serialising/deserialising would add lots of
		1191	overhead, as well as having to keep a proxy object everywhere.
		1192
		1193	Strings can easily be printed, easily serialised etc. and need no special
		1194	procedures to be "valid".
		1195
		1196	And as a result, a port with just a default receiver consists of a single
		1197	code reference stored in a global hash - it can't become much cheaper.
		1198
		1199	=item Why favour JSON, why not a real serialising format such as Storable?
		1200
		1201	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1202	format, but currently there is no way to make a node use Storable by
		1203	default (although all nodes will accept it).
		1204
		1205	The default framing protocol is JSON because a) JSON::XS is many times
		1206	faster for small messages and b) most importantly, after years of
		1207	experience we found that object serialisation is causing more problems
		1208	than it solves: Just like function calls, objects simply do not travel
		1209	easily over the network, mostly because they will always be a copy, so you
		1210	always have to re-think your design.
		1211
		1212	Keeping your messages simple, concentrating on data structures rather than
		1213	objects, will keep your messages clean, tidy and efficient.
		1214
		1215	=back
		1216
53	=head1 SEE ALSO	1217	=head1 SEE ALSO
		1218
		1219	L<AnyEvent::MP::Intro> - a gentle introduction.
		1220
		1221	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1222
		1223	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1224	your applications.
		1225
		1226	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1227
		1228	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1229	all nodes.
54		1230
55	L<AnyEvent>.	1231	L<AnyEvent>.
56		1232
57	=head1 AUTHOR	1233	=head1 AUTHOR
58		1234

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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 1.135 by root, Mon Mar 12 14:55:55 2012 UTC

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Revision 1.1 by root, Thu Jul 30 08:38:50 2009 UTC vs.
Revision 1.135 by root, Mon Mar 12 14:55:55 2012 UTC