[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 1.88 by root, Fri Sep 11 15:02:17 2009 UTC

…		…
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::MP;	7	use AnyEvent::MP;
8		8
		9	$NODE # contains this node's 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	# monitoring
		36	mon $port, $cb->(@msg) # callback is invoked on death
		37	mon $port, $otherport # kill otherport on abnormal death
		38	mon $port, $otherport, @msg # send message on death
		39
		40	=head1 CURRENT STATUS
		41
		42	bin/aemp - stable.
		43	AnyEvent::MP - stable API, should work.
		44	AnyEvent::MP::Intro - explains most concepts.
		45	AnyEvent::MP::Kernel - mostly stable API.
		46	AnyEvent::MP::Global - stable API.
		47
9	=head1 DESCRIPTION	48	=head1 DESCRIPTION
10		49
		50	This module (-family) implements a simple message passing framework.
		51
		52	Despite its simplicity, you can securely message other processes running
		53	on the same or other hosts, and you can supervise entities remotely.
		54
		55	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
		56	manual page and the examples under F<eg/>.
		57
		58	=head1 CONCEPTS
		59
		60	=over 4
		61
		62	=item port
		63
		64	Not to be confused with a TCP port, a "port" is something you can send
		65	messages to (with the C<snd> function).
		66
		67	Ports allow you to register C<rcv> handlers that can match all or just
		68	some messages. Messages send to ports will not be queued, regardless of
		69	anything was listening for them or not.
		70
		71	=item port ID - C<nodeid#portname>
		72
		73	A port ID is the concatenation of a node ID, a hash-mark (C<#>) as
		74	separator, and a port name (a printable string of unspecified format).
		75
		76	=item node
		77
		78	A node is a single process containing at least one port - the node port,
		79	which enables nodes to manage each other remotely, and to create new
		80	ports.
		81
		82	Nodes are either public (have one or more listening ports) or private
		83	(no listening ports). Private nodes cannot talk to other private nodes
		84	currently.
		85
		86	=item node ID - C<[A-Z_][a-zA-Z0-9_\-.:]*>
		87
		88	A node ID is a string that uniquely identifies the node within a
		89	network. Depending on the configuration used, node IDs can look like a
		90	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		91	doesn't interpret node IDs in any way.
		92
		93	=item binds - C<ip:port>
		94
		95	Nodes can only talk to each other by creating some kind of connection to
		96	each other. To do this, nodes should listen on one or more local transport
		97	endpoints - binds. Currently, only standard C<ip:port> specifications can
		98	be used, which specify TCP ports to listen on.
		99
		100	=item seed nodes
		101
		102	When a node starts, it knows nothing about the network. To teach the node
		103	about the network it first has to contact some other node within the
		104	network. This node is called a seed.
		105
		106	Apart from the fact that other nodes know them as seed nodes and they have
		107	to have fixed listening addresses, seed nodes are perfectly normal nodes -
		108	any node can function as a seed node for others.
		109
		110	In addition to discovering the network, seed nodes are also used to
		111	maintain the network and to connect nodes that otherwise would have
		112	trouble connecting. They form the backbone of an AnyEvent::MP network.
		113
		114	Seed nodes are expected to be long-running, and at least one seed node
		115	should always be available. They should also be relatively responsive - a
		116	seed node that blocks for long periods will slow down everybody else.
		117
		118	=item seeds - C<host:port>
		119
		120	Seeds are transport endpoint(s) (usually a hostname/IP address and a
		121	TCP port) of nodes thta should be used as seed nodes.
		122
		123	The nodes listening on those endpoints are expected to be long-running,
		124	and at least one of those should always be available. When nodes run out
		125	of connections (e.g. due to a network error), they try to re-establish
		126	connections to some seednodes again to join the network.
		127
		128	=back
		129
		130	=head1 VARIABLES/FUNCTIONS
		131
		132	=over 4
		133
11	=cut	134	=cut
12		135
13	package AnyEvent::MP;	136	package AnyEvent::MP;
14		137
		138	use AnyEvent::MP::Kernel;
		139
15	use common::sense;	140	use common::sense;
16		141
		142	use Carp ();
		143
17	use AE ();	144	use AE ();
18		145
19	our $VERSION = '0.0';	146	use base "Exporter";
20		147
21	sub nonce($) {	148	our $VERSION = $AnyEvent::MP::Kernel::VERSION;
22	my $nonce;
23		149
24	if (open my $fh, "</dev/urandom") {	150	our @EXPORT = qw(
25	sysread $fh, $nonce, $_[0];	151	NODE $NODE *SELF node_of after
26	} else {	152	configure
		153	snd rcv mon mon_guard kil reg psub spawn cal
		154	port
		155	);
		156
		157	our $SELF;
		158
		159	sub _self_die() {
		160	my $msg = $@;
		161	$msg =~ s/\n+$// unless ref $msg;
		162	kil $SELF, die => $msg;
		163	}
		164
		165	=item $thisnode = NODE / $NODE
		166
		167	The C<NODE> function returns, and the C<$NODE> variable contains, the node
		168	ID of the node running in the current process. This value is initialised by
		169	a call to C<configure>.
		170
		171	=item $nodeid = node_of $port
		172
		173	Extracts and returns the node ID from a port ID or a node ID.
		174
		175	=item configure $profile, key => value...
		176
		177	=item configure key => value...
		178
		179	Before a node can talk to other nodes on the network (i.e. enter
		180	"distributed mode") it has to configure itself - the minimum a node needs
		181	to know is its own name, and optionally it should know the addresses of
		182	some other nodes in the network to discover other nodes.
		183
		184	This function configures a node - it must be called exactly once (or
		185	never) before calling other AnyEvent::MP functions.
		186
		187	=over 4
		188
		189	=item step 1, gathering configuration from profiles
		190
		191	The function first looks up a profile in the aemp configuration (see the
		192	L<aemp> commandline utility). The profile name can be specified via the
		193	named C<profile> parameter or can simply be the first parameter). If it is
		194	missing, then the nodename (F<uname -n>) will be used as profile name.
		195
		196	The profile data is then gathered as follows:
		197
		198	First, all remaining key => value pairs (all of which are conveniently
		199	undocumented at the moment) will be interpreted as configuration
		200	data. Then they will be overwritten by any values specified in the global
		201	default configuration (see the F<aemp> utility), then the chain of
		202	profiles chosen by the profile name (and any C<parent> attributes).
		203
		204	That means that the values specified in the profile have highest priority
		205	and the values specified directly via C<configure> have lowest priority,
		206	and can only be used to specify defaults.
		207
		208	If the profile specifies a node ID, then this will become the node ID of
		209	this process. If not, then the profile name will be used as node ID. The
		210	special node ID of C<anon/> will be replaced by a random node ID.
		211
		212	=item step 2, bind listener sockets
		213
		214	The next step is to look up the binds in the profile, followed by binding
		215	aemp protocol listeners on all binds specified (it is possible and valid
		216	to have no binds, meaning that the node cannot be contacted form the
		217	outside. This means the node cannot talk to other nodes that also have no
		218	binds, but it can still talk to all "normal" nodes).
		219
		220	If the profile does not specify a binds list, then a default of C<*> is
		221	used, meaning the node will bind on a dynamically-assigned port on every
		222	local IP address it finds.
		223
		224	=item step 3, connect to seed nodes
		225
		226	As the last step, the seeds list from the profile is passed to the
		227	L<AnyEvent::MP::Global> module, which will then use it to keep
		228	connectivity with at least one node at any point in time.
		229
		230	=back
		231
		232	Example: become a distributed node using the local node name as profile.
		233	This should be the most common form of invocation for "daemon"-type nodes.
		234
		235	configure
		236
		237	Example: become an anonymous node. This form is often used for commandline
		238	clients.
		239
		240	configure nodeid => "anon/";
		241
		242	Example: configure a node using a profile called seed, which si suitable
		243	for a seed node as it binds on all local addresses on a fixed port (4040,
		244	customary for aemp).
		245
		246	# use the aemp commandline utility
		247	# aemp profile seed nodeid anon/ binds '*:4040'
		248
		249	# then use it
		250	configure profile => "seed";
		251
		252	# or simply use aemp from the shell again:
		253	# aemp run profile seed
		254
		255	# or provide a nicer-to-remember nodeid
		256	# aemp run profile seed nodeid "$(hostname)"
		257
		258	=item $SELF
		259
		260	Contains the current port id while executing C<rcv> callbacks or C<psub>
		261	blocks.
		262
		263	=item *SELF, SELF, %SELF, @SELF...
		264
		265	Due to some quirks in how perl exports variables, it is impossible to
		266	just export C<$SELF>, all the symbols named C<SELF> are exported by this
		267	module, but only C<$SELF> is currently used.
		268
		269	=item snd $port, type => @data
		270
		271	=item snd $port, @msg
		272
		273	Send the given message to the given port, which can identify either a
		274	local or a remote port, and must be a port ID.
		275
		276	While the message can be almost anything, it is highly recommended to
		277	use a string as first element (a port ID, or some word that indicates a
		278	request type etc.) and to consist if only simple perl values (scalars,
		279	arrays, hashes) - if you think you need to pass an object, think again.
		280
		281	The message data logically becomes read-only after a call to this
		282	function: modifying any argument (or values referenced by them) is
		283	forbidden, as there can be considerable time between the call to C<snd>
		284	and the time the message is actually being serialised - in fact, it might
		285	never be copied as within the same process it is simply handed to the
		286	receiving port.
		287
		288	The type of data you can transfer depends on the transport protocol: when
		289	JSON is used, then only strings, numbers and arrays and hashes consisting
		290	of those are allowed (no objects). When Storable is used, then anything
		291	that Storable can serialise and deserialise is allowed, and for the local
		292	node, anything can be passed. Best rely only on the common denominator of
		293	these.
		294
		295	=item $local_port = port
		296
		297	Create a new local port object and returns its port ID. Initially it has
		298	no callbacks set and will throw an error when it receives messages.
		299
		300	=item $local_port = port { my @msg = @_ }
		301
		302	Creates a new local port, and returns its ID. Semantically the same as
		303	creating a port and calling C<rcv $port, $callback> on it.
		304
		305	The block will be called for every message received on the port, with the
		306	global variable C<$SELF> set to the port ID. Runtime errors will cause the
		307	port to be C<kil>ed. The message will be passed as-is, no extra argument
		308	(i.e. no port ID) will be passed to the callback.
		309
		310	If you want to stop/destroy the port, simply C<kil> it:
		311
		312	my $port = port {
		313	my @msg = @_;
27	# shit...	314	...
28	our $nonce_init;	315	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	}	316	};
35		317
36	$nonce	318	=cut
37	}
38		319
39	our $DEFAULT_SECRET;	320	sub rcv($@);
40		321
41	sub default_secret {	322	sub _kilme {
42	unless (defined $DEFAULT_SECRET) {	323	die "received message on port without callback";
43	if (open my $fh, "<$ENV{HOME}/.aemp-secret") {	324	}
44	sysread $fh, $DEFAULT_SECRET, -s $fh;	325
		326	sub port(;&) {
		327	my $id = "$UNIQ." . $ID++;
		328	my $port = "$NODE#$id";
		329
		330	rcv $port, shift \|\| \&_kilme;
		331
		332	$port
		333	}
		334
		335	=item rcv $local_port, $callback->(@msg)
		336
		337	Replaces the default callback on the specified port. There is no way to
		338	remove the default callback: use C<sub { }> to disable it, or better
		339	C<kil> the port when it is no longer needed.
		340
		341	The global C<$SELF> (exported by this module) contains C<$port> while
		342	executing the callback. Runtime errors during callback execution will
		343	result in the port being C<kil>ed.
		344
		345	The default callback received all messages not matched by a more specific
		346	C<tag> match.
		347
		348	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
		349
		350	Register (or replace) callbacks to be called on messages starting with the
		351	given tag on the given port (and return the port), or unregister it (when
		352	C<$callback> is C<$undef> or missing). There can only be one callback
		353	registered for each tag.
		354
		355	The original message will be passed to the callback, after the first
		356	element (the tag) has been removed. The callback will use the same
		357	environment as the default callback (see above).
		358
		359	Example: create a port and bind receivers on it in one go.
		360
		361	my $port = rcv port,
		362	msg1 => sub { ... },
		363	msg2 => sub { ... },
		364	;
		365
		366	Example: create a port, bind receivers and send it in a message elsewhere
		367	in one go:
		368
		369	snd $otherport, reply =>
		370	rcv port,
		371	msg1 => sub { ... },
		372	...
		373	;
		374
		375	Example: temporarily register a rcv callback for a tag matching some port
		376	(e.g. for a rpc reply) and unregister it after a message was received.
		377
		378	rcv $port, $otherport => sub {
		379	my @reply = @_;
		380
		381	rcv $SELF, $otherport;
		382	};
		383
		384	=cut
		385
		386	sub rcv($@) {
		387	my $port = shift;
		388	my ($nodeid, $portid) = split /#/, $port, 2;
		389
		390	$NODE{$nodeid} == $NODE{""}
		391	or Carp::croak "$port: rcv can only be called on local ports, caught";
		392
		393	while (@_) {
		394	if (ref $_[0]) {
		395	if (my $self = $PORT_DATA{$portid}) {
		396	"AnyEvent::MP::Port" eq ref $self
		397	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		398
		399	$self->[2] = shift;
45	} else {	400	} else {
46	$DEFAULT_SECRET = nonce 32;	401	my $cb = shift;
		402	$PORT{$portid} = sub {
		403	local $SELF = $port;
		404	eval { &$cb }; _self_die if $@;
		405	};
		406	}
		407	} elsif (defined $_[0]) {
		408	my $self = $PORT_DATA{$portid} \|\|= do {
		409	my $self = bless [$PORT{$port} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
		410
		411	$PORT{$portid} = sub {
		412	local $SELF = $port;
		413
		414	if (my $cb = $self->[1]{$_[0]}) {
		415	shift;
		416	eval { &$cb }; _self_die if $@;
		417	} else {
		418	&{ $self->[0] };
		419	}
		420	};
		421
		422	$self
		423	};
		424
		425	"AnyEvent::MP::Port" eq ref $self
		426	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		427
		428	my ($tag, $cb) = splice @_, 0, 2;
		429
		430	if (defined $cb) {
		431	$self->[1]{$tag} = $cb;
		432	} else {
		433	delete $self->[1]{$tag};
		434	}
47	}	435	}
48	}	436	}
49		437
50	$DEFAULT_SECRET	438	$port
51	}	439	}
		440
		441	=item $closure = psub { BLOCK }
		442
		443	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
		444	closure is executed, sets up the environment in the same way as in C<rcv>
		445	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		446
		447	This is useful when you register callbacks from C<rcv> callbacks:
		448
		449	rcv delayed_reply => sub {
		450	my ($delay, @reply) = @_;
		451	my $timer = AE::timer $delay, 0, psub {
		452	snd @reply, $SELF;
		453	};
		454	};
		455
		456	=cut
		457
		458	sub psub(&) {
		459	my $cb = shift;
		460
		461	my $port = $SELF
		462	or Carp::croak "psub can only be called from within rcv or psub callbacks, not";
		463
		464	sub {
		465	local $SELF = $port;
		466
		467	if (wantarray) {
		468	my @res = eval { &$cb };
		469	_self_die if $@;
		470	@res
		471	} else {
		472	my $res = eval { &$cb };
		473	_self_die if $@;
		474	$res
		475	}
		476	}
		477	}
		478
		479	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
		480
		481	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
		482
		483	=item $guard = mon $port # kill $SELF when $port dies
		484
		485	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		486
		487	Monitor the given port and do something when the port is killed or
		488	messages to it were lost, and optionally return a guard that can be used
		489	to stop monitoring again.
		490
		491	In the first form (callback), the callback is simply called with any
		492	number of C<@reason> elements (no @reason means that the port was deleted
		493	"normally"). Note also that I<< the callback B<must> never die >>, so use
		494	C<eval> if unsure.
		495
		496	In the second form (another port given), the other port (C<$rcvport>)
		497	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
		498	"normal" kils nothing happens, while under all other conditions, the other
		499	port is killed with the same reason.
		500
		501	The third form (kill self) is the same as the second form, except that
		502	C<$rvport> defaults to C<$SELF>.
		503
		504	In the last form (message), a message of the form C<@msg, @reason> will be
		505	C<snd>.
		506
		507	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		508	alert was raised), they are removed and will not trigger again.
		509
		510	As a rule of thumb, monitoring requests should always monitor a port from
		511	a local port (or callback). The reason is that kill messages might get
		512	lost, just like any other message. Another less obvious reason is that
		513	even monitoring requests can get lost (for example, when the connection
		514	to the other node goes down permanently). When monitoring a port locally
		515	these problems do not exist.
		516
		517	C<mon> effectively guarantees that, in the absence of hardware failures,
		518	after starting the monitor, either all messages sent to the port will
		519	arrive, or the monitoring action will be invoked after possible message
		520	loss has been detected. No messages will be lost "in between" (after
		521	the first lost message no further messages will be received by the
		522	port). After the monitoring action was invoked, further messages might get
		523	delivered again.
		524
		525	Inter-host-connection timeouts and monitoring depend on the transport
		526	used. The only transport currently implemented is TCP, and AnyEvent::MP
		527	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		528	non-idle connection, and usually around two hours for idle conenctions).
		529
		530	This means that monitoring is good for program errors and cleaning up
		531	stuff eventually, but they are no replacement for a timeout when you need
		532	to ensure some maximum latency.
		533
		534	Example: call a given callback when C<$port> is killed.
		535
		536	mon $port, sub { warn "port died because of <@_>\n" };
		537
		538	Example: kill ourselves when C<$port> is killed abnormally.
		539
		540	mon $port;
		541
		542	Example: send us a restart message when another C<$port> is killed.
		543
		544	mon $port, $self => "restart";
		545
		546	=cut
		547
		548	sub mon {
		549	my ($nodeid, $port) = split /#/, shift, 2;
		550
		551	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
		552
		553	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
		554
		555	unless (ref $cb) {
		556	if (@_) {
		557	# send a kill info message
		558	my (@msg) = ($cb, @_);
		559	$cb = sub { snd @msg, @_ };
		560	} else {
		561	# simply kill other port
		562	my $port = $cb;
		563	$cb = sub { kil $port, @_ if @_ };
		564	}
		565	}
		566
		567	$node->monitor ($port, $cb);
		568
		569	defined wantarray
		570	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }
		571	}
		572
		573	=item $guard = mon_guard $port, $ref, $ref...
		574
		575	Monitors the given C<$port> and keeps the passed references. When the port
		576	is killed, the references will be freed.
		577
		578	Optionally returns a guard that will stop the monitoring.
		579
		580	This function is useful when you create e.g. timers or other watchers and
		581	want to free them when the port gets killed (note the use of C<psub>):
		582
		583	$port->rcv (start => sub {
		584	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
		585	undef $timer if 0.9 < rand;
		586	});
		587	});
		588
		589	=cut
		590
		591	sub mon_guard {
		592	my ($port, @refs) = @_;
		593
		594	#TODO: mon-less form?
		595
		596	mon $port, sub { 0 && @refs }
		597	}
		598
		599	=item kil $port[, @reason]
		600
		601	Kill the specified port with the given C<@reason>.
		602
		603	If no C<@reason> is specified, then the port is killed "normally" (ports
		604	monitoring other ports will not necessarily die because a port dies
		605	"normally").
		606
		607	Otherwise, linked ports get killed with the same reason (second form of
		608	C<mon>, see above).
		609
		610	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		611	will be reported as reason C<< die => $@ >>.
		612
		613	Transport/communication errors are reported as C<< transport_error =>
		614	$message >>.
		615
		616	=cut
		617
		618	=item $port = spawn $node, $initfunc[, @initdata]
		619
		620	Creates a port on the node C<$node> (which can also be a port ID, in which
		621	case it's the node where that port resides).
		622
		623	The port ID of the newly created port is returned immediately, and it is
		624	possible to immediately start sending messages or to monitor the port.
		625
		626	After the port has been created, the init function is called on the remote
		627	node, in the same context as a C<rcv> callback. This function must be a
		628	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		629	specify a function in the main program, use C<::name>.
		630
		631	If the function doesn't exist, then the node tries to C<require>
		632	the package, then the package above the package and so on (e.g.
		633	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		634	exists or it runs out of package names.
		635
		636	The init function is then called with the newly-created port as context
		637	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		638	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		639	the port might not get created.
		640
		641	A common idiom is to pass a local port, immediately monitor the spawned
		642	port, and in the remote init function, immediately monitor the passed
		643	local port. This two-way monitoring ensures that both ports get cleaned up
		644	when there is a problem.
		645
		646	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		647	caller before C<spawn> returns (by delaying invocation when spawn is
		648	called for the local node).
		649
		650	Example: spawn a chat server port on C<$othernode>.
		651
		652	# this node, executed from within a port context:
		653	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		654	mon $server;
		655
		656	# init function on C<$othernode>
		657	sub connect {
		658	my ($srcport) = @_;
		659
		660	mon $srcport;
		661
		662	rcv $SELF, sub {
		663	...
		664	};
		665	}
		666
		667	=cut
		668
		669	sub _spawn {
		670	my $port = shift;
		671	my $init = shift;
		672
		673	# rcv will create the actual port
		674	local $SELF = "$NODE#$port";
		675	eval {
		676	&{ load_func $init }
		677	};
		678	_self_die if $@;
		679	}
		680
		681	sub spawn(@) {
		682	my ($nodeid, undef) = split /#/, shift, 2;
		683
		684	my $id = "$RUNIQ." . $ID++;
		685
		686	$_[0] =~ /::/
		687	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		688
		689	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		690
		691	"$nodeid#$id"
		692	}
		693
		694	=item after $timeout, @msg
		695
		696	=item after $timeout, $callback
		697
		698	Either sends the given message, or call the given callback, after the
		699	specified number of seconds.
		700
		701	This is simply a utility function that comes in handy at times - the
		702	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		703	so it may go away in the future.
		704
		705	=cut
		706
		707	sub after($@) {
		708	my ($timeout, @action) = @_;
		709
		710	my $t; $t = AE::timer $timeout, 0, sub {
		711	undef $t;
		712	ref $action[0]
		713	? $action[0]()
		714	: snd @action;
		715	};
		716	}
		717
		718	=item cal $port, @msg, $callback[, $timeout]
		719
		720	A simple form of RPC - sends a message to the given C<$port> with the
		721	given contents (C<@msg>), but adds a reply port to the message.
		722
		723	The reply port is created temporarily just for the purpose of receiving
		724	the reply, and will be C<kil>ed when no longer needed.
		725
		726	A reply message sent to the port is passed to the C<$callback> as-is.
		727
		728	If an optional time-out (in seconds) is given and it is not C<undef>,
		729	then the callback will be called without any arguments after the time-out
		730	elapsed and the port is C<kil>ed.
		731
		732	If no time-out is given, then the local port will monitor the remote port
		733	instead, so it eventually gets cleaned-up.
		734
		735	Currently this function returns the temporary port, but this "feature"
		736	might go in future versions unless you can make a convincing case that
		737	this is indeed useful for something.
		738
		739	=cut
		740
		741	sub cal(@) {
		742	my $timeout = ref $_[-1] ? undef : pop;
		743	my $cb = pop;
		744
		745	my $port = port {
		746	undef $timeout;
		747	kil $SELF;
		748	&$cb;
		749	};
		750
		751	if (defined $timeout) {
		752	$timeout = AE::timer $timeout, 0, sub {
		753	undef $timeout;
		754	kil $port;
		755	$cb->();
		756	};
		757	} else {
		758	mon $_[0], sub {
		759	kil $port;
		760	$cb->();
		761	};
		762	}
		763
		764	push @_, $port;
		765	&snd;
		766
		767	$port
		768	}
		769
		770	=back
		771
		772	=head1 AnyEvent::MP vs. Distributed Erlang
		773
		774	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
		775	== aemp node, Erlang process == aemp port), so many of the documents and
		776	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
		777	sample:
		778
		779	http://www.Erlang.se/doc/programming_rules.shtml
		780	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
		781	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6
		782	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
		783
		784	Despite the similarities, there are also some important differences:
		785
		786	=over 4
		787
		788	=item * Node IDs are arbitrary strings in AEMP.
		789
		790	Erlang relies on special naming and DNS to work everywhere in the same
		791	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
		792	configuration or DNS), but will otherwise discover other odes itself.
		793
		794	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
		795	uses "local ports are like remote ports".
		796
		797	The failure modes for local ports are quite different (runtime errors
		798	only) then for remote ports - when a local port dies, you I<know> it dies,
		799	when a connection to another node dies, you know nothing about the other
		800	port.
		801
		802	Erlang pretends remote ports are as reliable as local ports, even when
		803	they are not.
		804
		805	AEMP encourages a "treat remote ports differently" philosophy, with local
		806	ports being the special case/exception, where transport errors cannot
		807	occur.
		808
		809	=item * Erlang uses processes and a mailbox, AEMP does not queue.
		810
		811	Erlang uses processes that selectively receive messages, and therefore
		812	needs a queue. AEMP is event based, queuing messages would serve no
		813	useful purpose. For the same reason the pattern-matching abilities of
		814	AnyEvent::MP are more limited, as there is little need to be able to
		815	filter messages without dequeuing them.
		816
		817	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).
		818
		819	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
		820
		821	Sending messages in Erlang is synchronous and blocks the process (and
		822	so does not need a queue that can overflow). AEMP sends are immediate,
		823	connection establishment is handled in the background.
		824
		825	=item * Erlang suffers from silent message loss, AEMP does not.
		826
		827	Erlang makes few guarantees on messages delivery - messages can get lost
		828	without any of the processes realising it (i.e. you send messages a, b,
		829	and c, and the other side only receives messages a and c).
		830
		831	AEMP guarantees correct ordering, and the guarantee that after one message
		832	is lost, all following ones sent to the same port are lost as well, until
		833	monitoring raises an error, so there are no silent "holes" in the message
		834	sequence.
		835
		836	=item * Erlang can send messages to the wrong port, AEMP does not.
		837
		838	In Erlang it is quite likely that a node that restarts reuses a process ID
		839	known to other nodes for a completely different process, causing messages
		840	destined for that process to end up in an unrelated process.
		841
		842	AEMP never reuses port IDs, so old messages or old port IDs floating
		843	around in the network will not be sent to an unrelated port.
		844
		845	=item * Erlang uses unprotected connections, AEMP uses secure
		846	authentication and can use TLS.
		847
		848	AEMP can use a proven protocol - TLS - to protect connections and
		849	securely authenticate nodes.
		850
		851	=item * The AEMP protocol is optimised for both text-based and binary
		852	communications.
		853
		854	The AEMP protocol, unlike the Erlang protocol, supports both programming
		855	language independent text-only protocols (good for debugging) and binary,
		856	language-specific serialisers (e.g. Storable). By default, unless TLS is
		857	used, the protocol is actually completely text-based.
		858
		859	It has also been carefully designed to be implementable in other languages
		860	with a minimum of work while gracefully degrading functionality to make the
		861	protocol simple.
		862
		863	=item * AEMP has more flexible monitoring options than Erlang.
		864
		865	In Erlang, you can chose to receive I<all> exit signals as messages
		866	or I<none>, there is no in-between, so monitoring single processes is
		867	difficult to implement. Monitoring in AEMP is more flexible than in
		868	Erlang, as one can choose between automatic kill, exit message or callback
		869	on a per-process basis.
		870
		871	=item * Erlang tries to hide remote/local connections, AEMP does not.
		872
		873	Monitoring in Erlang is not an indicator of process death/crashes, in the
		874	same way as linking is (except linking is unreliable in Erlang).
		875
		876	In AEMP, you don't "look up" registered port names or send to named ports
		877	that might or might not be persistent. Instead, you normally spawn a port
		878	on the remote node. The init function monitors you, and you monitor the
		879	remote port. Since both monitors are local to the node, they are much more
		880	reliable (no need for C<spawn_link>).
		881
		882	This also saves round-trips and avoids sending messages to the wrong port
		883	(hard to do in Erlang).
		884
		885	=back
		886
		887	=head1 RATIONALE
		888
		889	=over 4
		890
		891	=item Why strings for port and node IDs, why not objects?
		892
		893	We considered "objects", but found that the actual number of methods
		894	that can be called are quite low. Since port and node IDs travel over
		895	the network frequently, the serialising/deserialising would add lots of
		896	overhead, as well as having to keep a proxy object everywhere.
		897
		898	Strings can easily be printed, easily serialised etc. and need no special
		899	procedures to be "valid".
		900
		901	And as a result, a miniport consists of a single closure stored in a
		902	global hash - it can't become much cheaper.
		903
		904	=item Why favour JSON, why not a real serialising format such as Storable?
		905
		906	In fact, any AnyEvent::MP node will happily accept Storable as framing
		907	format, but currently there is no way to make a node use Storable by
		908	default (although all nodes will accept it).
		909
		910	The default framing protocol is JSON because a) JSON::XS is many times
		911	faster for small messages and b) most importantly, after years of
		912	experience we found that object serialisation is causing more problems
		913	than it solves: Just like function calls, objects simply do not travel
		914	easily over the network, mostly because they will always be a copy, so you
		915	always have to re-think your design.
		916
		917	Keeping your messages simple, concentrating on data structures rather than
		918	objects, will keep your messages clean, tidy and efficient.
		919
		920	=back
52		921
53	=head1 SEE ALSO	922	=head1 SEE ALSO
		923
		924	L<AnyEvent::MP::Intro> - a gentle introduction.
		925
		926	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		927
		928	L<AnyEvent::MP::Global> - network maintainance and port groups, to find
		929	your applications.
		930
		931	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		932	all nodes.
54		933
55	L<AnyEvent>.	934	L<AnyEvent>.
56		935
57	=head1 AUTHOR	936	=head1 AUTHOR
58		937

Diff Legend

-–
+Removed lines
-+
+Added lines
-<
+Changed lines
->
+Changed lines

Comparing AnyEvent-MP/MP.pm (file contents): Revision 1.1 by root, Thu Jul 30 08:38:50 2009 UTC vs. Revision 1.88 by root, Fri Sep 11 15:02:17 2009 UTC

Diff Legend

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.1 by root, Thu Jul 30 08:38:50 2009 UTC vs.
Revision 1.88 by root, Fri Sep 11 15:02:17 2009 UTC