[ViewVC] Diff of: cvs/AnyEvent-MP/MP.pm

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.27 by root, Tue Aug 4 22:13:45 2009 UTC vs.
Revision 1.119 by root, Sun Feb 26 10:29:59 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 noderef	9	$NODE # contains this node's node ID
10	NODE # returns this node's noderef	10	NODE # returns this node's node ID
11	NODE $port # returns the noderef of the port
12		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
13	snd $port, type => data...;	20	snd $port, type => data...;
		21	snd $port, @msg;
		22	snd @msg_with_first_element_being_a_port;
14		23
15	$SELF # receiving/own port id in rcv callbacks	24	# creating/using ports, the simple way
		25	my $simple_port = port { my @msg = @_ };
16		26
17	rcv $port, smartmatch => $cb->($port, @msg);	27	# creating/using ports, tagged message matching
18		28	my $port = port;
19	# examples:
20	rcv $port2, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
21	rcv $port1, pong => sub { warn "pong received\n" };	30	rcv $port, pong => sub { warn "pong received\n" };
22	snd $port2, ping => $port1;
23		31
24	# more, smarter, matches (_any_ is exported by this module)	32	# create a port on another node
25	rcv $port, [child_died => $pid] => sub { ...	33	my $port = spawn $node, $initfunc, @initdata;
26	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3	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.
27		59
28	=head1 DESCRIPTION	60	=head1 DESCRIPTION
29		61
30	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
31		63
32	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
33	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
34		66
35	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	67	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
36	manual page.	68	manual page and the examples under F<eg/>.
37
38	At the moment, this module family is severly broken and underdocumented,
39	so do not use. This was uploaded mainly to reserve the CPAN namespace -
40	stay tuned! The basic API should be finished, however.
41		69
42	=head1 CONCEPTS	70	=head1 CONCEPTS
43		71
44	=over 4	72	=over 4
45		73
46	=item port	74	=item port
47		75
48	A port is something you can send messages to with the C<snd> function, and	76	Not to be confused with a TCP port, a "port" is something you can send
49	you can register C<rcv> handlers with. All C<rcv> handlers will receive	77	messages to (with the C<snd> function).
50	messages they match, messages will not be queued.
51		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
52	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
53		86
54	A port id is always the noderef, a hash-mark (C<#>) as separator, followed	87	A port ID is the concatenation of a node ID, a hash-mark (C<#>) as
55	by a port name (a printable string of unspecified format).	88	separator, and a port name (a printable string of unspecified format).
56		89
57	=item node	90	=item node
58		91
59	A node is a single process containing at least one port - the node	92	A node is a single process containing at least one port - the node port,
60	port. You can send messages to node ports to let them create new ports,	93	which enables nodes to manage each other remotely, and to create new
61	among other things.	94	ports.
62		95
63	Initially, nodes are either private (single-process only) or hidden	96	Nodes are either public (have one or more listening ports) or private
64	(connected to a master node only). Only when they epxlicitly "become	97	(no listening ports). Private nodes cannot talk to other private nodes
65	public" can you send them messages from unrelated other nodes.	98	currently, but all nodes can talk to public nodes.
66		99
67	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	100	Nodes is represented by (printable) strings called "node IDs".
68		101
		102	=item node ID - C<[A-Za-z0-9_\-.:]*>
		103
69	A noderef is a string that either uniquely identifies a given node (for	104	A node ID is a string that uniquely identifies the node within a
70	private and hidden nodes), or contains a recipe on how to reach a given	105	network. Depending on the configuration used, node IDs can look like a
71	node (for public nodes).	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).
72		169
73	=back	170	=back
74		171
75	=head1 VARIABLES/FUNCTIONS	172	=head1 VARIABLES/FUNCTIONS
76		173
78		175
79	=cut	176	=cut
80		177
81	package AnyEvent::MP;	178	package AnyEvent::MP;
82		179
83	use AnyEvent::MP::Base;	180	use AnyEvent::MP::Kernel;
84		181
85	use common::sense;	182	use common::sense;
86		183
87	use Carp ();	184	use Carp ();
88		185
89	use AE ();	186	use AE ();
90		187
91	use base "Exporter";	188	use base "Exporter";
92		189
93	our $VERSION = '0.1';	190	our $VERSION = '1.30';
		191
94	our @EXPORT = qw(	192	our @EXPORT = qw(
95	NODE $NODE *SELF node_of _any_	193	NODE $NODE *SELF node_of after
96	become_slave become_public	194	configure
97	snd rcv mon kil reg psub	195	snd rcv mon mon_guard kil psub peval spawn cal
98	port	196	port
99	);	197	);
100		198
101	our $SELF;	199	our $SELF;
102		200
…		…
106	kil $SELF, die => $msg;	204	kil $SELF, die => $msg;
107	}	205	}
108		206
109	=item $thisnode = NODE / $NODE	207	=item $thisnode = NODE / $NODE
110		208
111	The C<NODE> function returns, and the C<$NODE> variable contains	209	The C<NODE> function returns, and the C<$NODE> variable contains, the node
112	the noderef of the local node. The value is initialised by a call	210	ID of the node running in the current process. This value is initialised by
113	to C<become_public> or C<become_slave>, after which all local port	211	a call to C<configure>.
114	identifiers become invalid.
115		212
116	=item $noderef = node_of $portid	213	=item $nodeid = node_of $port
117		214
118	Extracts and returns the noderef from a portid or a noderef.	215	Extracts and returns the node ID from a port ID or a node ID.
		216
		217	=item configure $profile, key => value...
		218
		219	=item configure key => value...
		220
		221	Before a node can talk to other nodes on the network (i.e. enter
		222	"distributed mode") it has to configure itself - the minimum a node needs
		223	to know is its own name, and optionally it should know the addresses of
		224	some other nodes in the network to discover other nodes.
		225
		226	The key/value pairs are basically the same ones as documented for the
		227	F<aemp> command line utility (sans the set/del prefix).
		228
		229	This function configures a node - it must be called exactly once (or
		230	never) before calling other AnyEvent::MP functions.
		231
		232	=over 4
		233
		234	=item step 1, gathering configuration from profiles
		235
		236	The function first looks up a profile in the aemp configuration (see the
		237	L<aemp> commandline utility). The profile name can be specified via the
		238	named C<profile> parameter or can simply be the first parameter). If it is
		239	missing, then the nodename (F<uname -n>) will be used as profile name.
		240
		241	The profile data is then gathered as follows:
		242
		243	First, all remaining key => value pairs (all of which are conveniently
		244	undocumented at the moment) will be interpreted as configuration
		245	data. Then they will be overwritten by any values specified in the global
		246	default configuration (see the F<aemp> utility), then the chain of
		247	profiles chosen by the profile name (and any C<parent> attributes).
		248
		249	That means that the values specified in the profile have highest priority
		250	and the values specified directly via C<configure> have lowest priority,
		251	and can only be used to specify defaults.
		252
		253	If the profile specifies a node ID, then this will become the node ID of
		254	this process. If not, then the profile name will be used as node ID. The
		255	special node ID of C<anon/> will be replaced by a random node ID.
		256
		257	=item step 2, bind listener sockets
		258
		259	The next step is to look up the binds in the profile, followed by binding
		260	aemp protocol listeners on all binds specified (it is possible and valid
		261	to have no binds, meaning that the node cannot be contacted form the
		262	outside. This means the node cannot talk to other nodes that also have no
		263	binds, but it can still talk to all "normal" nodes).
		264
		265	If the profile does not specify a binds list, then a default of C<*> is
		266	used, meaning the node will bind on a dynamically-assigned port on every
		267	local IP address it finds.
		268
		269	=item step 3, connect to seed nodes
		270
		271	As the last step, the seed ID list from the profile is passed to the
		272	L<AnyEvent::MP::Global> module, which will then use it to keep
		273	connectivity with at least one node at any point in time.
		274
		275	=back
		276
		277	Example: become a distributed node using the local node name as profile.
		278	This should be the most common form of invocation for "daemon"-type nodes.
		279
		280	configure
		281
		282	Example: become an anonymous node. This form is often used for commandline
		283	clients.
		284
		285	configure nodeid => "anon/";
		286
		287	Example: configure a node using a profile called seed, which si suitable
		288	for a seed node as it binds on all local addresses on a fixed port (4040,
		289	customary for aemp).
		290
		291	# use the aemp commandline utility
		292	# aemp profile seed nodeid anon/ binds '*:4040'
		293
		294	# then use it
		295	configure profile => "seed";
		296
		297	# or simply use aemp from the shell again:
		298	# aemp run profile seed
		299
		300	# or provide a nicer-to-remember nodeid
		301	# aemp run profile seed nodeid "$(hostname)"
119		302
120	=item $SELF	303	=item $SELF
121		304
122	Contains the current port id while executing C<rcv> callbacks or C<psub>	305	Contains the current port id while executing C<rcv> callbacks or C<psub>
123	blocks.	306	blocks.
124		307
125	=item SELF, %SELF, @SELF...	308	=item *SELF, SELF, %SELF, @SELF...
126		309
127	Due to some quirks in how perl exports variables, it is impossible to	310	Due to some quirks in how perl exports variables, it is impossible to
128	just export C<$SELF>, all the symbols called C<SELF> are exported by this	311	just export C<$SELF>, all the symbols named C<SELF> are exported by this
129	module, but only C<$SELF> is currently used.	312	module, but only C<$SELF> is currently used.
130		313
131	=item snd $portid, type => @data	314	=item snd $port, type => @data
132		315
133	=item snd $portid, @msg	316	=item snd $port, @msg
134		317
135	Send the given message to the given port ID, which can identify either	318	Send the given message to the given port, which can identify either a
136	a local or a remote port, and can be either a string or soemthignt hat	319	local or a remote port, and must be a port ID.
137	stringifies a sa port ID (such as a port object :).
138		320
139	While the message can be about anything, it is highly recommended to use a	321	While the message can be almost anything, it is highly recommended to
140	string as first element (a portid, or some word that indicates a request	322	use a string as first element (a port ID, or some word that indicates a
141	type etc.).	323	request type etc.) and to consist if only simple perl values (scalars,
		324	arrays, hashes) - if you think you need to pass an object, think again.
142		325
143	The message data effectively becomes read-only after a call to this	326	The message data logically becomes read-only after a call to this
144	function: modifying any argument is not allowed and can cause many	327	function: modifying any argument (or values referenced by them) is
145	problems.	328	forbidden, as there can be considerable time between the call to C<snd>
		329	and the time the message is actually being serialised - in fact, it might
		330	never be copied as within the same process it is simply handed to the
		331	receiving port.
146		332
147	The type of data you can transfer depends on the transport protocol: when	333	The type of data you can transfer depends on the transport protocol: when
148	JSON is used, then only strings, numbers and arrays and hashes consisting	334	JSON is used, then only strings, numbers and arrays and hashes consisting
149	of those are allowed (no objects). When Storable is used, then anything	335	of those are allowed (no objects). When Storable is used, then anything
150	that Storable can serialise and deserialise is allowed, and for the local	336	that Storable can serialise and deserialise is allowed, and for the local
151	node, anything can be passed.	337	node, anything can be passed. Best rely only on the common denominator of
		338	these.
152		339
153	=item kil $portid[, @reason]	340	=item $local_port = port
154		341
155	Kill the specified port with the given C<@reason>.	342	Create a new local port object and returns its port ID. Initially it has
		343	no callbacks set and will throw an error when it receives messages.
156		344
157	If no C<@reason> is specified, then the port is killed "normally" (linked	345	=item $local_port = port { my @msg = @_ }
158	ports will not be kileld, or even notified).
159		346
160	Otherwise, linked ports get killed with the same reason (second form of	347	Creates a new local port, and returns its ID. Semantically the same as
161	C<mon>, see below).	348	creating a port and calling C<rcv $port, $callback> on it.
162		349
163	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	350	The block will be called for every message received on the port, with the
164	will be reported as reason C<< die => $@ >>.	351	global variable C<$SELF> set to the port ID. Runtime errors will cause the
		352	port to be C<kil>ed. The message will be passed as-is, no extra argument
		353	(i.e. no port ID) will be passed to the callback.
165		354
166	Transport/communication errors are reported as C<< transport_error =>	355	If you want to stop/destroy the port, simply C<kil> it:
167	$message >>.
168		356
169	=item $guard = mon $portid, $cb->(@reason)	357	my $port = port {
		358	my @msg = @_;
		359	...
		360	kil $SELF;
		361	};
170		362
171	=item $guard = mon $portid, $otherport	363	=cut
172		364
173	=item $guard = mon $portid, $otherport, @msg	365	sub rcv($@);
174		366
		367	sub _kilme {
		368	die "received message on port without callback";
		369	}
		370
		371	sub port(;&) {
		372	my $id = "$UNIQ." . $ID++;
		373	my $port = "$NODE#$id";
		374
		375	rcv $port, shift \|\| \&_kilme;
		376
		377	$port
		378	}
		379
		380	=item rcv $local_port, $callback->(@msg)
		381
		382	Replaces the default callback on the specified port. There is no way to
		383	remove the default callback: use C<sub { }> to disable it, or better
		384	C<kil> the port when it is no longer needed.
		385
		386	The global C<$SELF> (exported by this module) contains C<$port> while
		387	executing the callback. Runtime errors during callback execution will
		388	result in the port being C<kil>ed.
		389
		390	The default callback received all messages not matched by a more specific
		391	C<tag> match.
		392
		393	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
		394
		395	Register (or replace) callbacks to be called on messages starting with the
		396	given tag on the given port (and return the port), or unregister it (when
		397	C<$callback> is C<$undef> or missing). There can only be one callback
		398	registered for each tag.
		399
		400	The original message will be passed to the callback, after the first
		401	element (the tag) has been removed. The callback will use the same
		402	environment as the default callback (see above).
		403
		404	Example: create a port and bind receivers on it in one go.
		405
		406	my $port = rcv port,
		407	msg1 => sub { ... },
		408	msg2 => sub { ... },
		409	;
		410
		411	Example: create a port, bind receivers and send it in a message elsewhere
		412	in one go:
		413
		414	snd $otherport, reply =>
		415	rcv port,
		416	msg1 => sub { ... },
		417	...
		418	;
		419
		420	Example: temporarily register a rcv callback for a tag matching some port
		421	(e.g. for an rpc reply) and unregister it after a message was received.
		422
		423	rcv $port, $otherport => sub {
		424	my @reply = @_;
		425
		426	rcv $SELF, $otherport;
		427	};
		428
		429	=cut
		430
		431	sub rcv($@) {
		432	my $port = shift;
		433	my ($nodeid, $portid) = split /#/, $port, 2;
		434
		435	$NODE{$nodeid} == $NODE{""}
		436	or Carp::croak "$port: rcv can only be called on local ports, caught";
		437
		438	while (@_) {
		439	if (ref $_[0]) {
		440	if (my $self = $PORT_DATA{$portid}) {
		441	"AnyEvent::MP::Port" eq ref $self
		442	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		443
		444	$self->[0] = shift;
		445	} else {
		446	my $cb = shift;
		447	$PORT{$portid} = sub {
		448	local $SELF = $port;
		449	eval { &$cb }; _self_die if $@;
		450	};
		451	}
		452	} elsif (defined $_[0]) {
		453	my $self = $PORT_DATA{$portid} \|\|= do {
		454	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
		455
		456	$PORT{$portid} = sub {
		457	local $SELF = $port;
		458
		459	if (my $cb = $self->[1]{$_[0]}) {
		460	shift;
		461	eval { &$cb }; _self_die if $@;
		462	} else {
		463	&{ $self->[0] };
		464	}
		465	};
		466
		467	$self
		468	};
		469
		470	"AnyEvent::MP::Port" eq ref $self
		471	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		472
		473	my ($tag, $cb) = splice @_, 0, 2;
		474
		475	if (defined $cb) {
		476	$self->[1]{$tag} = $cb;
		477	} else {
		478	delete $self->[1]{$tag};
		479	}
		480	}
		481	}
		482
		483	$port
		484	}
		485
		486	=item peval $port, $coderef[, @args]
		487
		488	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		489	when the code throews an exception the C<$port> will be killed.
		490
		491	Any remaining args will be passed to the callback. Any return values will
		492	be returned to the caller.
		493
		494	This is useful when you temporarily want to execute code in the context of
		495	a port.
		496
		497	Example: create a port and run some initialisation code in it's context.
		498
		499	my $port = port { ... };
		500
		501	peval $port, sub {
		502	init
		503	or die "unable to init";
		504	};
		505
		506	=cut
		507
		508	sub peval($$) {
		509	local $SELF = shift;
		510	my $cb = shift;
		511
		512	if (wantarray) {
		513	my @res = eval { &$cb };
		514	_self_die if $@;
		515	@res
		516	} else {
		517	my $res = eval { &$cb };
		518	_self_die if $@;
		519	$res
		520	}
		521	}
		522
		523	=item $closure = psub { BLOCK }
		524
		525	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
		526	closure is executed, sets up the environment in the same way as in C<rcv>
		527	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		528
		529	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		530	BLOCK }, @_ } >>.
		531
		532	This is useful when you register callbacks from C<rcv> callbacks:
		533
		534	rcv delayed_reply => sub {
		535	my ($delay, @reply) = @_;
		536	my $timer = AE::timer $delay, 0, psub {
		537	snd @reply, $SELF;
		538	};
		539	};
		540
		541	=cut
		542
		543	sub psub(&) {
		544	my $cb = shift;
		545
		546	my $port = $SELF
		547	or Carp::croak "psub can only be called from within rcv or psub callbacks, not";
		548
		549	sub {
		550	local $SELF = $port;
		551
		552	if (wantarray) {
		553	my @res = eval { &$cb };
		554	_self_die if $@;
		555	@res
		556	} else {
		557	my $res = eval { &$cb };
		558	_self_die if $@;
		559	$res
		560	}
		561	}
		562	}
		563
		564	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
		565
		566	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
		567
		568	=item $guard = mon $port # kill $SELF when $port dies
		569
		570	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		571
175	Monitor the given port and do something when the port is killed.	572	Monitor the given port and do something when the port is killed or
		573	messages to it were lost, and optionally return a guard that can be used
		574	to stop monitoring again.
176		575
177	In the first form, the callback is simply called with any number	576	In the first form (callback), the callback is simply called with any
178	of C<@reason> elements (no @reason means that the port was deleted	577	number of C<@reason> elements (no @reason means that the port was deleted
179	"normally"). Note also that I<< the callback B<must> never die >>, so use	578	"normally"). Note also that I<< the callback B<must> never die >>, so use
180	C<eval> if unsure.	579	C<eval> if unsure.
181		580
182	In the second form, the other port will be C<kil>'ed with C<@reason>, iff	581	In the second form (another port given), the other port (C<$rcvport>)
183	a @reason was specified, i.e. on "normal" kils nothing happens, while	582	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
184	under all other conditions, the other port is killed with the same reason.	583	"normal" kils nothing happens, while under all other conditions, the other
		584	port is killed with the same reason.
185		585
		586	The third form (kill self) is the same as the second form, except that
		587	C<$rvport> defaults to C<$SELF>.
		588
186	In the last form, a message of the form C<@msg, @reason> will be C<snd>.	589	In the last form (message), a message of the form C<@msg, @reason> will be
		590	C<snd>.
		591
		592	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		593	alert was raised), they are removed and will not trigger again.
		594
		595	As a rule of thumb, monitoring requests should always monitor a port from
		596	a local port (or callback). The reason is that kill messages might get
		597	lost, just like any other message. Another less obvious reason is that
		598	even monitoring requests can get lost (for example, when the connection
		599	to the other node goes down permanently). When monitoring a port locally
		600	these problems do not exist.
		601
		602	C<mon> effectively guarantees that, in the absence of hardware failures,
		603	after starting the monitor, either all messages sent to the port will
		604	arrive, or the monitoring action will be invoked after possible message
		605	loss has been detected. No messages will be lost "in between" (after
		606	the first lost message no further messages will be received by the
		607	port). After the monitoring action was invoked, further messages might get
		608	delivered again.
		609
		610	Inter-host-connection timeouts and monitoring depend on the transport
		611	used. The only transport currently implemented is TCP, and AnyEvent::MP
		612	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		613	non-idle connection, and usually around two hours for idle connections).
		614
		615	This means that monitoring is good for program errors and cleaning up
		616	stuff eventually, but they are no replacement for a timeout when you need
		617	to ensure some maximum latency.
187		618
188	Example: call a given callback when C<$port> is killed.	619	Example: call a given callback when C<$port> is killed.
189		620
190	mon $port, sub { warn "port died because of <@_>\n" };	621	mon $port, sub { warn "port died because of <@_>\n" };
191		622
192	Example: kill ourselves when C<$port> is killed abnormally.	623	Example: kill ourselves when C<$port> is killed abnormally.
193		624
194	mon $port, $self;	625	mon $port;
195		626
196	Example: send us a restart message another C<$port> is killed.	627	Example: send us a restart message when another C<$port> is killed.
197		628
198	mon $port, $self => "restart";	629	mon $port, $self => "restart";
199		630
200	=cut	631	=cut
201		632
202	sub mon {	633	sub mon {
203	my ($noderef, $port, $cb) = ((split /#/, shift, 2), shift);	634	my ($nodeid, $port) = split /#/, shift, 2;
204		635
205	my $node = $NODE{$noderef} \|\| add_node $noderef;	636	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
206		637
207	#TODO: ports must not be references	638	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
208	if (!ref $cb or "AnyEvent::MP::Port" eq ref $cb) {	639
		640	unless (ref $cb) {
209	if (@_) {	641	if (@_) {
210	# send a kill info message	642	# send a kill info message
211	my (@msg) = ($cb, @_);	643	my (@msg) = ($cb, @_);
212	$cb = sub { snd @msg, @_ };	644	$cb = sub { snd @msg, @_ };
213	} else {	645	} else {
…		…
218	}	650	}
219		651
220	$node->monitor ($port, $cb);	652	$node->monitor ($port, $cb);
221		653
222	defined wantarray	654	defined wantarray
223	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	655	and ($cb += 0, AnyEvent::Util::guard { $node->unmonitor ($port, $cb) })
224	}	656	}
225		657
226	=item $guard = mon_guard $port, $ref, $ref...	658	=item $guard = mon_guard $port, $ref, $ref...
227		659
228	Monitors the given C<$port> and keeps the passed references. When the port	660	Monitors the given C<$port> and keeps the passed references. When the port
229	is killed, the references will be freed.	661	is killed, the references will be freed.
230		662
231	Optionally returns a guard that will stop the monitoring.	663	Optionally returns a guard that will stop the monitoring.
232		664
233	This function is useful when you create e.g. timers or other watchers and	665	This function is useful when you create e.g. timers or other watchers and
234	want to free them when the port gets killed:	666	want to free them when the port gets killed (note the use of C<psub>):
235		667
236	$port->rcv (start => sub {	668	$port->rcv (start => sub {
237	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	669	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
238	undef $timer if 0.9 < rand;	670	undef $timer if 0.9 < rand;
239	});	671	});
240	});	672	});
241		673
242	=cut	674	=cut
243		675
244	sub mon_guard {	676	sub mon_guard {
245	my ($port, @refs) = @_;	677	my ($port, @refs) = @_;
246		678
		679	#TODO: mon-less form?
		680
247	mon $port, sub { 0 && @refs }	681	mon $port, sub { 0 && @refs }
248	}	682	}
249		683
250	=item lnk $port1, $port2	684	=item kil $port[, @reason]
251		685
252	Link two ports. This is simply a shorthand for:	686	Kill the specified port with the given C<@reason>.
253		687
254	mon $port1, $port2;	688	If no C<@reason> is specified, then the port is killed "normally" -
255	mon $port2, $port1;	689	monitor callback will be invoked, but the kil will not cause linked ports
		690	(C<mon $mport, $lport> form) to get killed.
256		691
257	It means that if either one is killed abnormally, the other one gets	692	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
258	killed as well.	693	form) get killed with the same reason.
259		694
260	=item $local_port = port	695	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		696	will be reported as reason C<< die => $@ >>.
261		697
262	Create a new local port object that supports message matching.	698	Transport/communication errors are reported as C<< transport_error =>
		699	$message >>.
263		700
264	=item $portid = port { my @msg = @_; $finished }	701	=cut
265		702
266	Creates a "mini port", that is, a very lightweight port without any	703	=item $port = spawn $node, $initfunc[, @initdata]
267	pattern matching behind it, and returns its ID.
268		704
269	The block will be called for every message received on the port. When the	705	Creates a port on the node C<$node> (which can also be a port ID, in which
270	callback returns a true value its job is considered "done" and the port	706	case it's the node where that port resides).
271	will be destroyed. Otherwise it will stay alive.
272		707
273	The message will be passed as-is, no extra argument (i.e. no port id) will	708	The port ID of the newly created port is returned immediately, and it is
274	be passed to the callback.	709	possible to immediately start sending messages or to monitor the port.
275		710
276	If you need the local port id in the callback, this works nicely:	711	After the port has been created, the init function is called on the remote
		712	node, in the same context as a C<rcv> callback. This function must be a
		713	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		714	specify a function in the main program, use C<::name>.
277		715
278	my $port; $port = miniport {	716	If the function doesn't exist, then the node tries to C<require>
279	snd $otherport, reply => $port;	717	the package, then the package above the package and so on (e.g.
		718	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		719	exists or it runs out of package names.
		720
		721	The init function is then called with the newly-created port as context
		722	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		723	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		724	the port might not get created.
		725
		726	A common idiom is to pass a local port, immediately monitor the spawned
		727	port, and in the remote init function, immediately monitor the passed
		728	local port. This two-way monitoring ensures that both ports get cleaned up
		729	when there is a problem.
		730
		731	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		732	caller before C<spawn> returns (by delaying invocation when spawn is
		733	called for the local node).
		734
		735	Example: spawn a chat server port on C<$othernode>.
		736
		737	# this node, executed from within a port context:
		738	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		739	mon $server;
		740
		741	# init function on C<$othernode>
		742	sub connect {
		743	my ($srcport) = @_;
		744
		745	mon $srcport;
		746
		747	rcv $SELF, sub {
		748	...
		749	};
		750	}
		751
		752	=cut
		753
		754	sub _spawn {
		755	my $port = shift;
		756	my $init = shift;
		757
		758	# rcv will create the actual port
		759	local $SELF = "$NODE#$port";
		760	eval {
		761	&{ load_func $init }
280	};	762	};
		763	_self_die if $@;
		764	}
281		765
282	=cut	766	sub spawn(@) {
		767	my ($nodeid, undef) = split /#/, shift, 2;
283		768
284	sub port(;&) {
285	my $id = "$UNIQ." . $ID++;	769	my $id = "$RUNIQ." . $ID++;
286	my $port = "$NODE#$id";
287		770
288	if (@_) {	771	$_[0] =~ /::/
289	my $cb = shift;	772	or Carp::croak "spawn init function must be a fully-qualified name, caught";
290	$PORT{$id} = sub {	773
291	local $SELF = $port;	774	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
292	eval {	775
293	&$cb	776	"$nodeid#$id"
294	and kil $id;	777	}
295	};	778
296	_self_die if $@;	779	=item after $timeout, @msg
		780
		781	=item after $timeout, $callback
		782
		783	Either sends the given message, or call the given callback, after the
		784	specified number of seconds.
		785
		786	This is simply a utility function that comes in handy at times - the
		787	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		788	so it may go away in the future.
		789
		790	=cut
		791
		792	sub after($@) {
		793	my ($timeout, @action) = @_;
		794
		795	my $t; $t = AE::timer $timeout, 0, sub {
		796	undef $t;
		797	ref $action[0]
		798	? $action[0]()
		799	: snd @action;
		800	};
		801	}
		802
		803	=item cal $port, @msg, $callback[, $timeout]
		804
		805	A simple form of RPC - sends a message to the given C<$port> with the
		806	given contents (C<@msg>), but adds a reply port to the message.
		807
		808	The reply port is created temporarily just for the purpose of receiving
		809	the reply, and will be C<kil>ed when no longer needed.
		810
		811	A reply message sent to the port is passed to the C<$callback> as-is.
		812
		813	If an optional time-out (in seconds) is given and it is not C<undef>,
		814	then the callback will be called without any arguments after the time-out
		815	elapsed and the port is C<kil>ed.
		816
		817	If no time-out is given (or it is C<undef>), then the local port will
		818	monitor the remote port instead, so it eventually gets cleaned-up.
		819
		820	Currently this function returns the temporary port, but this "feature"
		821	might go in future versions unless you can make a convincing case that
		822	this is indeed useful for something.
		823
		824	=cut
		825
		826	sub cal(@) {
		827	my $timeout = ref $_[-1] ? undef : pop;
		828	my $cb = pop;
		829
		830	my $port = port {
		831	undef $timeout;
		832	kil $SELF;
		833	&$cb;
		834	};
		835
		836	if (defined $timeout) {
		837	$timeout = AE::timer $timeout, 0, sub {
		838	undef $timeout;
		839	kil $port;
		840	$cb->();
297	};	841	};
298	} else {	842	} else {
299	my $self = bless {	843	mon $_[0], sub {
300	id => "$NODE#$id",	844	kil $port;
301	}, "AnyEvent::MP::Port";	845	$cb->();
302
303	$PORT_DATA{$id} = $self;
304	$PORT{$id} = sub {
305	local $SELF = $port;
306
307	eval {
308	for (@{ $self->{rc0}{$_[0]} }) {
309	$_ && &{$_->[0]}
310	&& undef $_;
311	}
312
313	for (@{ $self->{rcv}{$_[0]} }) {
314	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
315	&& &{$_->[0]}
316	&& undef $_;
317	}
318
319	for (@{ $self->{any} }) {
320	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
321	&& &{$_->[0]}
322	&& undef $_;
323	}
324	};
325	_self_die if $@;
326	};	846	};
327	}	847	}
328		848
		849	push @_, $port;
		850	&snd;
		851
329	$port	852	$port
330	}	853	}
331		854
332	=item reg $portid, $name
333
334	Registers the given port under the name C<$name>. If the name already
335	exists it is replaced.
336
337	A port can only be registered under one well known name.
338
339	A port automatically becomes unregistered when it is killed.
340
341	=cut
342
343	sub reg(@) {
344	my ($portid, $name) = @_;
345
346	$REG{$name} = $portid;
347	}
348
349	=item rcv $portid, tagstring => $callback->(@msg), ...
350
351	=item rcv $portid, $smartmatch => $callback->(@msg), ...
352
353	=item rcv $portid, [$smartmatch...] => $callback->(@msg), ...
354
355	Register callbacks to be called on matching messages on the given port.
356
357	The callback has to return a true value when its work is done, after
358	which is will be removed, or a false value in which case it will stay
359	registered.
360
361	The global C<$SELF> (exported by this module) contains C<$portid> while
362	executing the callback.
363
364	Runtime errors wdurign callback execution will result in the port being
365	C<kil>ed.
366
367	If the match is an array reference, then it will be matched against the
368	first elements of the message, otherwise only the first element is being
369	matched.
370
371	Any element in the match that is specified as C<_any_> (a function
372	exported by this module) matches any single element of the message.
373
374	While not required, it is highly recommended that the first matching
375	element is a string identifying the message. The one-string-only match is
376	also the most efficient match (by far).
377
378	=cut
379
380	sub rcv($@) {
381	my ($noderef, $port) = split /#/, shift, 2;
382
383	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}
384	or Carp::croak "$noderef#$port: rcv can only be called on local ports, caught";
385
386	my $self = $PORT_DATA{$port}
387	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";
388
389	"AnyEvent::MP::Port" eq ref $self
390	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";
391
392	while (@_) {
393	my ($match, $cb) = splice @_, 0, 2;
394
395	if (!ref $match) {
396	push @{ $self->{rc0}{$match} }, [$cb];
397	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
398	my ($type, @match) = @$match;
399	@match
400	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
401	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
402	} else {
403	push @{ $self->{any} }, [$cb, $match];
404	}
405	}
406	}
407
408	=item $closure = psub { BLOCK }
409
410	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
411	closure is executed, sets up the environment in the same way as in C<rcv>
412	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
413
414	This is useful when you register callbacks from C<rcv> callbacks:
415
416	rcv delayed_reply => sub {
417	my ($delay, @reply) = @_;
418	my $timer = AE::timer $delay, 0, psub {
419	snd @reply, $SELF;
420	};
421	};
422
423	=cut
424
425	sub psub(&) {
426	my $cb = shift;
427
428	my $port = $SELF
429	or Carp::croak "psub can only be called from within rcv or psub callbacks, not";
430
431	sub {
432	local $SELF = $port;
433
434	if (wantarray) {
435	my @res = eval { &$cb };
436	_self_die if $@;
437	@res
438	} else {
439	my $res = eval { &$cb };
440	_self_die if $@;
441	$res
442	}
443	}
444	}
445
446	=back	855	=back
447		856
448	=head1 FUNCTIONS FOR NODES
449
450	=over 4
451
452	=item become_public endpoint...
453
454	Tells the node to become a public node, i.e. reachable from other nodes.
455
456	If no arguments are given, or the first argument is C<undef>, then
457	AnyEvent::MP tries to bind on port C<4040> on all IP addresses that the
458	local nodename resolves to.
459
460	Otherwise the first argument must be an array-reference with transport
461	endpoints ("ip:port", "hostname:port") or port numbers (in which case the
462	local nodename is used as hostname). The endpoints are all resolved and
463	will become the node reference.
464
465	=cut
466
467	=back
468
469	=head1 NODE MESSAGES
470
471	Nodes understand the following messages sent to them. Many of them take
472	arguments called C<@reply>, which will simply be used to compose a reply
473	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
474	the remaining arguments are simply the message data.
475
476	=over 4
477
478	=cut
479
480	=item lookup => $name, @reply
481
482	Replies with the port ID of the specified well-known port, or C<undef>.
483
484	=item devnull => ...
485
486	Generic data sink/CPU heat conversion.
487
488	=item relay => $port, @msg
489
490	Simply forwards the message to the given port.
491
492	=item eval => $string[ @reply]
493
494	Evaluates the given string. If C<@reply> is given, then a message of the
495	form C<@reply, $@, @evalres> is sent.
496
497	Example: crash another node.
498
499	snd $othernode, eval => "exit";
500
501	=item time => @reply
502
503	Replies the the current node time to C<@reply>.
504
505	Example: tell the current node to send the current time to C<$myport> in a
506	C<timereply> message.
507
508	snd $NODE, time => $myport, timereply => 1, 2;
509	# => snd $myport, timereply => 1, 2, <time>
510
511	=back
512
513	=head1 AnyEvent::MP vs. Distributed Erlang	857	=head1 AnyEvent::MP vs. Distributed Erlang
514		858
515	AnyEvent::MP got lots of its ideas from distributed erlang (erlang node	859	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
516	== aemp node, erlang process == aemp port), so many of the documents and	860	== aemp node, Erlang process == aemp port), so many of the documents and
517	programming techniques employed by erlang apply to AnyEvent::MP. Here is a	861	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
518	sample:	862	sample:
519		863
520	http://www.erlang.se/doc/programming_rules.shtml	864	http://www.erlang.se/doc/programming_rules.shtml
521	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	865	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
522	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6	866	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
…		…
524		868
525	Despite the similarities, there are also some important differences:	869	Despite the similarities, there are also some important differences:
526		870
527	=over 4	871	=over 4
528		872
529	=item * Node references contain the recipe on how to contact them.	873	=item * Node IDs are arbitrary strings in AEMP.
530		874
531	Erlang relies on special naming and DNS to work everywhere in the	875	Erlang relies on special naming and DNS to work everywhere in the same
532	same way. AEMP relies on each node knowing it's own address(es), with	876	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
533	convenience functionality.	877	configuration or DNS), and possibly the addresses of some seed nodes, but
		878	will otherwise discover other nodes (and their IDs) itself.
534		879
535	This means that AEMP requires a less tightly controlled environment at the	880	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
536	cost of longer node references and a slightly higher management overhead.	881	uses "local ports are like remote ports".
		882
		883	The failure modes for local ports are quite different (runtime errors
		884	only) then for remote ports - when a local port dies, you I<know> it dies,
		885	when a connection to another node dies, you know nothing about the other
		886	port.
		887
		888	Erlang pretends remote ports are as reliable as local ports, even when
		889	they are not.
		890
		891	AEMP encourages a "treat remote ports differently" philosophy, with local
		892	ports being the special case/exception, where transport errors cannot
		893	occur.
537		894
538	=item * Erlang uses processes and a mailbox, AEMP does not queue.	895	=item * Erlang uses processes and a mailbox, AEMP does not queue.
539		896
540	Erlang uses processes that selctively receive messages, and therefore	897	Erlang uses processes that selectively receive messages out of order, and
541	needs a queue. AEMP is event based, queuing messages would serve no useful	898	therefore needs a queue. AEMP is event based, queuing messages would serve
542	purpose.	899	no useful purpose. For the same reason the pattern-matching abilities
		900	of AnyEvent::MP are more limited, as there is little need to be able to
		901	filter messages without dequeuing them.
543		902
544	(But see L<Coro::MP> for a more erlang-like process model on top of AEMP).	903	This is not a philosophical difference, but simply stems from AnyEvent::MP
		904	being event-based, while Erlang is process-based.
		905
		906	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		907	top of AEMP and Coro threads.
545		908
546	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	909	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
547		910
548	Sending messages in erlang is synchronous and blocks the process. AEMP	911	Sending messages in Erlang is synchronous and blocks the process until
549	sends are immediate, connection establishment is handled in the	912	a conenction has been established and the message sent (and so does not
550	background.	913	need a queue that can overflow). AEMP sends return immediately, connection
		914	establishment is handled in the background.
551		915
552	=item * Erlang can silently lose messages, AEMP cannot.	916	=item * Erlang suffers from silent message loss, AEMP does not.
553		917
554	Erlang makes few guarantees on messages delivery - messages can get lost	918	Erlang implements few guarantees on messages delivery - messages can get
555	without any of the processes realising it (i.e. you send messages a, b,	919	lost without any of the processes realising it (i.e. you send messages a,
556	and c, and the other side only receives messages a and c).	920	b, and c, and the other side only receives messages a and c).
557		921
558	AEMP guarantees correct ordering, and the guarantee that there are no	922	AEMP guarantees (modulo hardware errors) correct ordering, and the
		923	guarantee that after one message is lost, all following ones sent to the
		924	same port are lost as well, until monitoring raises an error, so there are
559	holes in the message sequence.	925	no silent "holes" in the message sequence.
560		926
561	=item * In erlang, processes can be declared dead and later be found to be	927	If you want your software to be very reliable, you have to cope with
562	alive.	928	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
563		929	simply tries to work better in common error cases, such as when a network
564	In erlang it can happen that a monitored process is declared dead and	930	link goes down.
565	linked processes get killed, but later it turns out that the process is
566	still alive - and can receive messages.
567
568	In AEMP, when port monitoring detects a port as dead, then that port will
569	eventually be killed - it cannot happen that a node detects a port as dead
570	and then later sends messages to it, finding it is still alive.
571		931
572	=item * Erlang can send messages to the wrong port, AEMP does not.	932	=item * Erlang can send messages to the wrong port, AEMP does not.
573		933
574	In erlang it is quite possible that a node that restarts reuses a process	934	In Erlang it is quite likely that a node that restarts reuses an Erlang
575	ID known to other nodes for a completely different process, causing	935	process ID known to other nodes for a completely different process,
576	messages destined for that process to end up in an unrelated process.	936	causing messages destined for that process to end up in an unrelated
		937	process.
577		938
578	AEMP never reuses port IDs, so old messages or old port IDs floating	939	AEMP does not reuse port IDs, so old messages or old port IDs floating
579	around in the network will not be sent to an unrelated port.	940	around in the network will not be sent to an unrelated port.
580		941
581	=item * Erlang uses unprotected connections, AEMP uses secure	942	=item * Erlang uses unprotected connections, AEMP uses secure
582	authentication and can use TLS.	943	authentication and can use TLS.
583		944
584	AEMP can use a proven protocol - SSL/TLS - to protect connections and	945	AEMP can use a proven protocol - TLS - to protect connections and
585	securely authenticate nodes.	946	securely authenticate nodes.
586		947
		948	=item * The AEMP protocol is optimised for both text-based and binary
		949	communications.
		950
		951	The AEMP protocol, unlike the Erlang protocol, supports both programming
		952	language independent text-only protocols (good for debugging), and binary,
		953	language-specific serialisers (e.g. Storable). By default, unless TLS is
		954	used, the protocol is actually completely text-based.
		955
		956	It has also been carefully designed to be implementable in other languages
		957	with a minimum of work while gracefully degrading functionality to make the
		958	protocol simple.
		959
		960	=item * AEMP has more flexible monitoring options than Erlang.
		961
		962	In Erlang, you can chose to receive I<all> exit signals as messages or
		963	I<none>, there is no in-between, so monitoring single Erlang processes is
		964	difficult to implement.
		965
		966	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		967	between automatic kill, exit message or callback on a per-port basis.
		968
		969	=item * Erlang tries to hide remote/local connections, AEMP does not.
		970
		971	Monitoring in Erlang is not an indicator of process death/crashes, in the
		972	same way as linking is (except linking is unreliable in Erlang).
		973
		974	In AEMP, you don't "look up" registered port names or send to named ports
		975	that might or might not be persistent. Instead, you normally spawn a port
		976	on the remote node. The init function monitors you, and you monitor the
		977	remote port. Since both monitors are local to the node, they are much more
		978	reliable (no need for C<spawn_link>).
		979
		980	This also saves round-trips and avoids sending messages to the wrong port
		981	(hard to do in Erlang).
		982
587	=back	983	=back
588		984
		985	=head1 RATIONALE
		986
		987	=over 4
		988
		989	=item Why strings for port and node IDs, why not objects?
		990
		991	We considered "objects", but found that the actual number of methods
		992	that can be called are quite low. Since port and node IDs travel over
		993	the network frequently, the serialising/deserialising would add lots of
		994	overhead, as well as having to keep a proxy object everywhere.
		995
		996	Strings can easily be printed, easily serialised etc. and need no special
		997	procedures to be "valid".
		998
		999	And as a result, a port with just a default receiver consists of a single
		1000	code reference stored in a global hash - it can't become much cheaper.
		1001
		1002	=item Why favour JSON, why not a real serialising format such as Storable?
		1003
		1004	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1005	format, but currently there is no way to make a node use Storable by
		1006	default (although all nodes will accept it).
		1007
		1008	The default framing protocol is JSON because a) JSON::XS is many times
		1009	faster for small messages and b) most importantly, after years of
		1010	experience we found that object serialisation is causing more problems
		1011	than it solves: Just like function calls, objects simply do not travel
		1012	easily over the network, mostly because they will always be a copy, so you
		1013	always have to re-think your design.
		1014
		1015	Keeping your messages simple, concentrating on data structures rather than
		1016	objects, will keep your messages clean, tidy and efficient.
		1017
		1018	=back
		1019
589	=head1 SEE ALSO	1020	=head1 SEE ALSO
		1021
		1022	L<AnyEvent::MP::Intro> - a gentle introduction.
		1023
		1024	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1025
		1026	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1027	your applications.
		1028
		1029	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1030
		1031	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1032	all nodes.
590		1033
591	L<AnyEvent>.	1034	L<AnyEvent>.
592		1035
593	=head1 AUTHOR	1036	=head1 AUTHOR
594		1037

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Revision 1.119 by root, Sun Feb 26 10:29:59 2012 UTC