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Revision 1.26 by root, Tue Aug 4 22:05:43 2009 UTC vs.
Revision 1.139 by root, Thu Mar 22 20:07:31 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 $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.
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<#>)
55	by a port name (a printable string of unspecified format).	88	as separator, and a port name (a printable string of unspecified
		89	format created by AnyEvent::MP).
56		90
57	=item node	91	=item node
58		92
59	A node is a single process containing at least one port - the node	93	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,	94	which enables nodes to manage each other remotely, and to create new
61	among other things.	95	ports.
62		96
63	Initially, nodes are either private (single-process only) or hidden	97	Nodes are either public (have one or more listening ports) or private
64	(connected to a master node only). Only when they epxlicitly "become	98	(no listening ports). Private nodes cannot talk to other private nodes
65	public" can you send them messages from unrelated other nodes.	99	currently, but all nodes can talk to public nodes.
66		100
67	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	101	Nodes is represented by (printable) strings called "node IDs".
68		102
		103	=item node ID - C<[A-Za-z0-9_\-.:]*>
		104
69	A noderef is a string that either uniquely identifies a given node (for	105	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	106	network. Depending on the configuration used, node IDs can look like a
71	node (for public nodes).	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).
72		170
73	=back	171	=back
74		172
75	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
76		174
…		…
78		176
79	=cut	177	=cut
80		178
81	package AnyEvent::MP;	179	package AnyEvent::MP;
82		180
		181	use AnyEvent::MP::Config ();
83	use AnyEvent::MP::Base;	182	use AnyEvent::MP::Kernel;
		183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
84		184
85	use common::sense;	185	use common::sense;
86		186
87	use Carp ();	187	use Carp ();
88		188
89	use AE ();	189	use AE ();
		190	use Guard ();
90		191
91	use base "Exporter";	192	use base "Exporter";
92		193
93	our $VERSION = '0.1';	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
		195
94	our @EXPORT = qw(	196	our @EXPORT = qw(
95	NODE $NODE *SELF node_of _any_	197	NODE $NODE *SELF node_of after
96	become_slave become_public	198	configure
97	snd rcv mon kil reg psub	199	snd rcv mon mon_guard kil psub peval spawn cal
98	port	200	port
		201	db_set db_del db_reg
		202	db_mon db_family db_keys db_values
99	);	203	);
100		204
101	our $SELF;	205	our $SELF;
102		206
103	sub _self_die() {	207	sub _self_die() {
…		…
106	kil $SELF, die => $msg;	210	kil $SELF, die => $msg;
107	}	211	}
108		212
109	=item $thisnode = NODE / $NODE	213	=item $thisnode = NODE / $NODE
110		214
111	The C<NODE> function returns, and the C<$NODE> variable contains	215	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	216	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	217	a call to C<configure>.
114	identifiers become invalid.
115		218
116	=item $noderef = node_of $portid	219	=item $nodeid = node_of $port
117		220
118	Extracts and returns the noderef from a portid or a noderef.	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 => $pass->(@msg)
		253
		254	In addition to specifying a boolean, you can specify a code reference that
		255	is called for every code execution attempt - the execution request is
		256	granted iff the callback returns a true value.
		257
		258	Most of the time the callback should look only at
		259	C<$AnyEvent::MP::Kernel::SRCNODE> to make a decision, and not at the
		260	actual message (which can be about anything, and is mostly provided for
		261	diagnostic purposes).
		262
		263	See F<semp setsecure> for more info.
		264
		265	=back
		266
		267	=over 4
		268
		269	=item step 1, gathering configuration from profiles
		270
		271	The function first looks up a profile in the aemp configuration (see the
		272	L<aemp> commandline utility). The profile name can be specified via the
		273	named C<profile> parameter or can simply be the first parameter). If it is
		274	missing, then the nodename (F<uname -n>) will be used as profile name.
		275
		276	The profile data is then gathered as follows:
		277
		278	First, all remaining key => value pairs (all of which are conveniently
		279	undocumented at the moment) will be interpreted as configuration
		280	data. Then they will be overwritten by any values specified in the global
		281	default configuration (see the F<aemp> utility), then the chain of
		282	profiles chosen by the profile name (and any C<parent> attributes).
		283
		284	That means that the values specified in the profile have highest priority
		285	and the values specified directly via C<configure> have lowest priority,
		286	and can only be used to specify defaults.
		287
		288	If the profile specifies a node ID, then this will become the node ID of
		289	this process. If not, then the profile name will be used as node ID, with
		290	a unique randoms tring (C</%u>) appended.
		291
		292	The node ID can contain some C<%> sequences that are expanded: C<%n>
		293	is expanded to the local nodename, C<%u> is replaced by a random
		294	strign to make the node unique. For example, the F<aemp> commandline
		295	utility uses C<aemp/%n/%u> as nodename, which might expand to
		296	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		297
		298	=item step 2, bind listener sockets
		299
		300	The next step is to look up the binds in the profile, followed by binding
		301	aemp protocol listeners on all binds specified (it is possible and valid
		302	to have no binds, meaning that the node cannot be contacted form the
		303	outside. This means the node cannot talk to other nodes that also have no
		304	binds, but it can still talk to all "normal" nodes).
		305
		306	If the profile does not specify a binds list, then a default of C<*> is
		307	used, meaning the node will bind on a dynamically-assigned port on every
		308	local IP address it finds.
		309
		310	=item step 3, connect to seed nodes
		311
		312	As the last step, the seed ID list from the profile is passed to the
		313	L<AnyEvent::MP::Global> module, which will then use it to keep
		314	connectivity with at least one node at any point in time.
		315
		316	=back
		317
		318	Example: become a distributed node using the local node name as profile.
		319	This should be the most common form of invocation for "daemon"-type nodes.
		320
		321	configure
		322
		323	Example: become a semi-anonymous node. This form is often used for
		324	commandline clients.
		325
		326	configure nodeid => "myscript/%n/%u";
		327
		328	Example: configure a node using a profile called seed, which is suitable
		329	for a seed node as it binds on all local addresses on a fixed port (4040,
		330	customary for aemp).
		331
		332	# use the aemp commandline utility
		333	# aemp profile seed binds '*:4040'
		334
		335	# then use it
		336	configure profile => "seed";
		337
		338	# or simply use aemp from the shell again:
		339	# aemp run profile seed
		340
		341	# or provide a nicer-to-remember nodeid
		342	# aemp run profile seed nodeid "$(hostname)"
119		343
120	=item $SELF	344	=item $SELF
121		345
122	Contains the current port id while executing C<rcv> callbacks or C<psub>	346	Contains the current port id while executing C<rcv> callbacks or C<psub>
123	blocks.	347	blocks.
124		348
125	=item SELF, %SELF, @SELF...	349	=item *SELF, SELF, %SELF, @SELF...
126		350
127	Due to some quirks in how perl exports variables, it is impossible to	351	Due to some quirks in how perl exports variables, it is impossible to
128	just export C<$SELF>, all the symbols called C<SELF> are exported by this	352	just export C<$SELF>, all the symbols named C<SELF> are exported by this
129	module, but only C<$SELF> is currently used.	353	module, but only C<$SELF> is currently used.
130		354
131	=item snd $portid, type => @data	355	=item snd $port, type => @data
132		356
133	=item snd $portid, @msg	357	=item snd $port, @msg
134		358
135	Send the given message to the given port ID, which can identify either	359	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	360	local or a remote port, and must be a port ID.
137	stringifies a sa port ID (such as a port object :).
138		361
139	While the message can be about anything, it is highly recommended to use a	362	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	363	use a string as first element (a port ID, or some word that indicates a
141	type etc.).	364	request type etc.) and to consist if only simple perl values (scalars,
		365	arrays, hashes) - if you think you need to pass an object, think again.
142		366
143	The message data effectively becomes read-only after a call to this	367	The message data logically becomes read-only after a call to this
144	function: modifying any argument is not allowed and can cause many	368	function: modifying any argument (or values referenced by them) is
145	problems.	369	forbidden, as there can be considerable time between the call to C<snd>
		370	and the time the message is actually being serialised - in fact, it might
		371	never be copied as within the same process it is simply handed to the
		372	receiving port.
146		373
147	The type of data you can transfer depends on the transport protocol: when	374	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	375	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	376	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	377	that Storable can serialise and deserialise is allowed, and for the local
151	node, anything can be passed.	378	node, anything can be passed. Best rely only on the common denominator of
		379	these.
152		380
153	=item kil $portid[, @reason]	381	=item $local_port = port
154		382
155	Kill the specified port with the given C<@reason>.	383	Create a new local port object and returns its port ID. Initially it has
		384	no callbacks set and will throw an error when it receives messages.
156		385
157	If no C<@reason> is specified, then the port is killed "normally" (linked	386	=item $local_port = port { my @msg = @_ }
158	ports will not be kileld, or even notified).
159		387
160	Otherwise, linked ports get killed with the same reason (second form of	388	Creates a new local port, and returns its ID. Semantically the same as
161	C<mon>, see below).	389	creating a port and calling C<rcv $port, $callback> on it.
162		390
163	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	391	The block will be called for every message received on the port, with the
164	will be reported as reason C<< die => $@ >>.	392	global variable C<$SELF> set to the port ID. Runtime errors will cause the
		393	port to be C<kil>ed. The message will be passed as-is, no extra argument
		394	(i.e. no port ID) will be passed to the callback.
165		395
166	Transport/communication errors are reported as C<< transport_error =>	396	If you want to stop/destroy the port, simply C<kil> it:
167	$message >>.
168		397
169	=item $guard = mon $portid, $cb->(@reason)	398	my $port = port {
170		399	my @msg = @_;
171	=item $guard = mon $portid, $otherport	400	...
172		401	kil $SELF;
173	=item $guard = mon $portid, $otherport, @msg	402	};
174
175	Monitor the given port and do something when the port is killed.
176
177	In the first form, the callback is simply called with any number
178	of C<@reason> elements (no @reason means that the port was deleted
179	"normally"). Note also that I<< the callback B<must> never die >>, so use
180	C<eval> if unsure.
181
182	In the second form, the other port will be C<kil>'ed with C<@reason>, iff
183	a @reason was specified, i.e. on "normal" kils nothing happens, while
184	under all other conditions, the other port is killed with the same reason.
185
186	In the last form, a message of the form C<@msg, @reason> will be C<snd>.
187
188	Example: call a given callback when C<$port> is killed.
189
190	mon $port, sub { warn "port died because of <@_>\n" };
191
192	Example: kill ourselves when C<$port> is killed abnormally.
193
194	mon $port, $self;
195
196	Example: send us a restart message another C<$port> is killed.
197
198	mon $port, $self => "restart";
199		403
200	=cut	404	=cut
201		405
202	sub mon {	406	sub rcv($@);
203	my ($noderef, $port, $cb) = ((split /#/, shift, 2), shift);
204		407
205	my $node = $NODE{$noderef} || add_node $noderef;	408	my $KILME = sub {
		409	(my $tag = substr $_[0], 0, 30) =~ s/([\x20-\x7e])/./g;
		410	kil $SELF, unhandled_message => "no callback found for message '$tag'";
		411	};
206		412
207	#TODO: ports must not be references	413	sub port(;&) {
208	if (!ref $cb or "AnyEvent::MP::Port" eq ref $cb) {	414	my $id = $UNIQ . ++$ID;
		415	my $port = "$NODE#$id";
		416
		417	rcv $port, shift || $KILME;
		418
		419	$port
		420	}
		421
		422	=item rcv $local_port, $callback->(@msg)
		423
		424	Replaces the default callback on the specified port. There is no way to
		425	remove the default callback: use C<sub { }> to disable it, or better
		426	C<kil> the port when it is no longer needed.
		427
		428	The global C<$SELF> (exported by this module) contains C<$port> while
		429	executing the callback. Runtime errors during callback execution will
		430	result in the port being C<kil>ed.
		431
		432	The default callback receives all messages not matched by a more specific
		433	C<tag> match.
		434
		435	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
		436
		437	Register (or replace) callbacks to be called on messages starting with the
		438	given tag on the given port (and return the port), or unregister it (when
		439	C<$callback> is C<$undef> or missing). There can only be one callback
		440	registered for each tag.
		441
		442	The original message will be passed to the callback, after the first
		443	element (the tag) has been removed. The callback will use the same
		444	environment as the default callback (see above).
		445
		446	Example: create a port and bind receivers on it in one go.
		447
		448	my $port = rcv port,
		449	msg1 => sub { ... },
		450	msg2 => sub { ... },
		451	;
		452
		453	Example: create a port, bind receivers and send it in a message elsewhere
		454	in one go:
		455
		456	snd $otherport, reply =>
		457	rcv port,
		458	msg1 => sub { ... },
		459	...
		460	;
		461
		462	Example: temporarily register a rcv callback for a tag matching some port
		463	(e.g. for an rpc reply) and unregister it after a message was received.
		464
		465	rcv $port, $otherport => sub {
		466	my @reply = @_;
		467
		468	rcv $SELF, $otherport;
		469	};
		470
		471	=cut
		472
		473	sub rcv($@) {
		474	my $port = shift;
		475	my ($nodeid, $portid) = split /#/, $port, 2;
		476
		477	$NODE{$nodeid} == $NODE{""}
		478	or Carp::croak "$port: rcv can only be called on local ports, caught";
		479
		480	while (@_) {
209	if (@_) {	481	if (ref $_[0]) {
210	# send a kill info message	482	if (my $self = $PORT_DATA{$portid}) {
211	my (@msg) = ($cb, @_);	483	"AnyEvent::MP::Port" eq ref $self
212	$cb = sub { snd @msg, @_ };	484	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		485
		486	$self->[0] = shift;
213	} else {	487	} else {
214	# simply kill other port	488	my $cb = shift;
215	my $port = $cb;	489	$PORT{$portid} = sub {
216	$cb = sub { kil $port, @_ if @_ };	490	local $SELF = $port;
		491	eval { &$cb }; _self_die if $@;
		492	};
		493	}
		494	} elsif (defined $_[0]) {
		495	my $self = $PORT_DATA{$portid} ||= do {
		496	my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port";
		497
		498	$PORT{$portid} = sub {
		499	local $SELF = $port;
		500
		501	if (my $cb = $self->[1]{$_[0]}) {
		502	shift;
		503	eval { &$cb }; _self_die if $@;
		504	} else {
		505	&{ $self->[0] };
		506	}
		507	};
		508
		509	$self
		510	};
		511
		512	"AnyEvent::MP::Port" eq ref $self
		513	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		514
		515	my ($tag, $cb) = splice @_, 0, 2;
		516
		517	if (defined $cb) {
		518	$self->[1]{$tag} = $cb;
		519	} else {
		520	delete $self->[1]{$tag};
		521	}
217	}	522	}
218	}	523	}
219		524
220	$node->monitor ($port, $cb);
221
222	defined wantarray
223	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }
224	}
225
226	=item $guard = mon_guard $port, $ref, $ref...
227
228	Monitors the given C<$port> and keeps the passed references. When the port
229	is killed, the references will be freed.
230
231	Optionally returns a guard that will stop the monitoring.
232
233	This function is useful when you create e.g. timers or other watchers and
234	want to free them when the port gets killed:
235
236	$port->rcv (start => sub {
237	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {
238	undef $timer if 0.9 < rand;
239	});
240	});
241
242	=cut
243
244	sub mon_guard {
245	my ($port, @refs) = @_;
246
247	mon $port, sub { 0 && @refs }
248	}
249
250	=item lnk $port1, $port2
251
252	Link two ports. This is simply a shorthand for:
253
254	mon $port1, $port2;
255	mon $port2, $port1;
256
257	It means that if either one is killed abnormally, the other one gets
258	killed as well.
259
260	=item $local_port = port
261
262	Create a new local port object that supports message matching.
263
264	=item $portid = port { my @msg = @_; $finished }
265
266	Creates a "mini port", that is, a very lightweight port without any
267	pattern matching behind it, and returns its ID.
268
269	The block will be called for every message received on the port. When the
270	callback returns a true value its job is considered "done" and the port
271	will be destroyed. Otherwise it will stay alive.
272
273	The message will be passed as-is, no extra argument (i.e. no port id) will
274	be passed to the callback.
275
276	If you need the local port id in the callback, this works nicely:
277
278	my $port; $port = miniport {
279	snd $otherport, reply => $port;
280	};
281
282	=cut
283
284	sub port(;&) {
285	my $id = "$UNIQ." . $ID++;
286	my $port = "$NODE#$id";
287
288	if (@_) {
289	my $cb = shift;
290	$PORT{$id} = sub {
291	local $SELF = $port;
292	eval {
293	&$cb
294	and kil $id;
295	};
296	_self_die if $@;
297	};
298	} else {
299	my $self = bless {
300	id => "$NODE#$id",
301	}, "AnyEvent::MP::Port";
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	};
327	}
328
329	$port	525	$port
330	}	526	}
331		527
332	=item reg $portid, $name	528	=item peval $port, $coderef[, @args]
333		529
334	Registers the given port under the name C<$name>. If the name already	530	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
335	exists it is replaced.	531	when the code throews an exception the C<$port> will be killed.
336		532
337	A port can only be registered under one well known name.	533	Any remaining args will be passed to the callback. Any return values will
		534	be returned to the caller.
338		535
339	A port automatically becomes unregistered when it is killed.	536	This is useful when you temporarily want to execute code in the context of
		537	a port.
		538
		539	Example: create a port and run some initialisation code in it's context.
		540
		541	my $port = port { ... };
		542
		543	peval $port, sub {
		544	init
		545	or die "unable to init";
		546	};
340		547
341	=cut	548	=cut
342		549
343	sub reg(@) {	550	sub peval($$) {
344	my ($portid, $name) = @_;	551	local $SELF = shift;
		552	my $cb = shift;
345		553
346	$REG{$name} = $portid;	554	if (wantarray) {
347	}	555	my @res = eval { &$cb };
348		556	_self_die if $@;
349	=item rcv $portid, tagstring => $callback->(@msg), ...	557	@res
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 {	558	} else {
403	push @{ $self->{any} }, [$cb, $match];	559	my $res = eval { &$cb };
404	}	560	_self_die if $@;
		561	$res
405	}	562	}
406	}	563	}
407		564
408	=item $closure = psub { BLOCK }	565	=item $closure = psub { BLOCK }
409		566
410	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	567	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>	568	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.	569	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		570
		571	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		572	BLOCK }, @_ } >>.
413		573
414	This is useful when you register callbacks from C<rcv> callbacks:	574	This is useful when you register callbacks from C<rcv> callbacks:
415		575
416	rcv delayed_reply => sub {	576	rcv delayed_reply => sub {
417	my ($delay, @reply) = @_;	577	my ($delay, @reply) = @_;
…		…
441	$res	601	$res
442	}	602	}
443	}	603	}
444	}	604	}
445		605
		606	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
		607
		608	=item $guard = mon $port # kill $SELF when $port dies
		609
		610	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
		611
		612	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		613
		614	Monitor the given port and do something when the port is killed or
		615	messages to it were lost, and optionally return a guard that can be used
		616	to stop monitoring again.
		617
		618	The first two forms distinguish between "normal" and "abnormal" kil's:
		619
		620	In the first form (another port given), if the C<$port> is C<kil>'ed with
		621	a non-empty reason, the other port (C<$rcvport>) will be kil'ed with the
		622	same reason. That is, on "normal" kil's nothing happens, while under all
		623	other conditions, the other port is killed with the same reason.
		624
		625	The second form (kill self) is the same as the first form, except that
		626	C<$rvport> defaults to C<$SELF>.
		627
		628	The remaining forms don't distinguish between "normal" and "abnormal" kil's
		629	- it's up to the callback or receiver to check whether the C<@reason> is
		630	empty and act accordingly.
		631
		632	In the third form (callback), the callback is simply called with any
		633	number of C<@reason> elements (empty @reason means that the port was deleted
		634	"normally"). Note also that I<< the callback B<must> never die >>, so use
		635	C<eval> if unsure.
		636
		637	In the last form (message), a message of the form C<$rcvport, @msg,
		638	@reason> will be C<snd>.
		639
		640	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		641	alert was raised), they are removed and will not trigger again, even if it
		642	turns out that the port is still alive.
		643
		644	As a rule of thumb, monitoring requests should always monitor a remote
		645	port locally (using a local C<$rcvport> or a callback). The reason is that
		646	kill messages might get lost, just like any other message. Another less
		647	obvious reason is that even monitoring requests can get lost (for example,
		648	when the connection to the other node goes down permanently). When
		649	monitoring a port locally these problems do not exist.
		650
		651	C<mon> effectively guarantees that, in the absence of hardware failures,
		652	after starting the monitor, either all messages sent to the port will
		653	arrive, or the monitoring action will be invoked after possible message
		654	loss has been detected. No messages will be lost "in between" (after
		655	the first lost message no further messages will be received by the
		656	port). After the monitoring action was invoked, further messages might get
		657	delivered again.
		658
		659	Inter-host-connection timeouts and monitoring depend on the transport
		660	used. The only transport currently implemented is TCP, and AnyEvent::MP
		661	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		662	non-idle connection, and usually around two hours for idle connections).
		663
		664	This means that monitoring is good for program errors and cleaning up
		665	stuff eventually, but they are no replacement for a timeout when you need
		666	to ensure some maximum latency.
		667
		668	Example: call a given callback when C<$port> is killed.
		669
		670	mon $port, sub { warn "port died because of <@_>\n" };
		671
		672	Example: kill ourselves when C<$port> is killed abnormally.
		673
		674	mon $port;
		675
		676	Example: send us a restart message when another C<$port> is killed.
		677
		678	mon $port, $self => "restart";
		679
		680	=cut
		681
		682	sub mon {
		683	my ($nodeid, $port) = split /#/, shift, 2;
		684
		685	my $node = $NODE{$nodeid} || add_node $nodeid;
		686
		687	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
		688
		689	unless (ref $cb) {
		690	if (@_) {
		691	# send a kill info message
		692	my (@msg) = ($cb, @_);
		693	$cb = sub { snd @msg, @_ };
		694	} else {
		695	# simply kill other port
		696	my $port = $cb;
		697	$cb = sub { kil $port, @_ if @_ };
		698	}
		699	}
		700
		701	$node->monitor ($port, $cb);
		702
		703	defined wantarray
		704	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
		705	}
		706
		707	=item $guard = mon_guard $port, $ref, $ref...
		708
		709	Monitors the given C<$port> and keeps the passed references. When the port
		710	is killed, the references will be freed.
		711
		712	Optionally returns a guard that will stop the monitoring.
		713
		714	This function is useful when you create e.g. timers or other watchers and
		715	want to free them when the port gets killed (note the use of C<psub>):
		716
		717	$port->rcv (start => sub {
		718	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
		719	undef $timer if 0.9 < rand;
		720	});
		721	});
		722
		723	=cut
		724
		725	sub mon_guard {
		726	my ($port, @refs) = @_;
		727
		728	#TODO: mon-less form?
		729
		730	mon $port, sub { 0 && @refs }
		731	}
		732
		733	=item kil $port[, @reason]
		734
		735	Kill the specified port with the given C<@reason>.
		736
		737	If no C<@reason> is specified, then the port is killed "normally" -
		738	monitor callback will be invoked, but the kil will not cause linked ports
		739	(C<mon $mport, $lport> form) to get killed.
		740
		741	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
		742	form) get killed with the same reason.
		743
		744	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		745	will be reported as reason C<< die => $@ >>.
		746
		747	Transport/communication errors are reported as C<< transport_error =>
		748	$message >>.
		749
		750	Common idioms:
		751
		752	# silently remove yourself, do not kill linked ports
		753	kil $SELF;
		754
		755	# report a failure in some detail
		756	kil $SELF, failure_mode_1 => "it failed with too high temperature";
		757
		758	# do not waste much time with killing, just die when something goes wrong
		759	open my $fh, "<file"
		760	or die "file: $!";
		761
		762	=item $port = spawn $node, $initfunc[, @initdata]
		763
		764	Creates a port on the node C<$node> (which can also be a port ID, in which
		765	case it's the node where that port resides).
		766
		767	The port ID of the newly created port is returned immediately, and it is
		768	possible to immediately start sending messages or to monitor the port.
		769
		770	After the port has been created, the init function is called on the remote
		771	node, in the same context as a C<rcv> callback. This function must be a
		772	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		773	specify a function in the main program, use C<::name>.
		774
		775	If the function doesn't exist, then the node tries to C<require>
		776	the package, then the package above the package and so on (e.g.
		777	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		778	exists or it runs out of package names.
		779
		780	The init function is then called with the newly-created port as context
		781	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		782	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		783	the port might not get created.
		784
		785	A common idiom is to pass a local port, immediately monitor the spawned
		786	port, and in the remote init function, immediately monitor the passed
		787	local port. This two-way monitoring ensures that both ports get cleaned up
		788	when there is a problem.
		789
		790	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		791	caller before C<spawn> returns (by delaying invocation when spawn is
		792	called for the local node).
		793
		794	Example: spawn a chat server port on C<$othernode>.
		795
		796	# this node, executed from within a port context:
		797	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		798	mon $server;
		799
		800	# init function on C<$othernode>
		801	sub connect {
		802	my ($srcport) = @_;
		803
		804	mon $srcport;
		805
		806	rcv $SELF, sub {
		807	...
		808	};
		809	}
		810
		811	=cut
		812
		813	sub _spawn {
		814	my $port = shift;
		815	my $init = shift;
		816
		817	# rcv will create the actual port
		818	local $SELF = "$NODE#$port";
		819	eval {
		820	&{ load_func $init }
		821	};
		822	_self_die if $@;
		823	}
		824
		825	sub spawn(@) {
		826	my ($nodeid, undef) = split /#/, shift, 2;
		827
		828	my $id = $RUNIQ . ++$ID;
		829
		830	$_[0] =~ /::/
		831	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		832
		833	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		834
		835	"$nodeid#$id"
		836	}
		837
		838
		839	=item after $timeout, @msg
		840
		841	=item after $timeout, $callback
		842
		843	Either sends the given message, or call the given callback, after the
		844	specified number of seconds.
		845
		846	This is simply a utility function that comes in handy at times - the
		847	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		848	so it may go away in the future.
		849
		850	=cut
		851
		852	sub after($@) {
		853	my ($timeout, @action) = @_;
		854
		855	my $t; $t = AE::timer $timeout, 0, sub {
		856	undef $t;
		857	ref $action[0]
		858	? $action[0]()
		859	: snd @action;
		860	};
		861	}
		862
		863	#=item $cb2 = timeout $seconds, $cb[, @args]
		864
		865	=item cal $port, @msg, $callback[, $timeout]
		866
		867	A simple form of RPC - sends a message to the given C<$port> with the
		868	given contents (C<@msg>), but adds a reply port to the message.
		869
		870	The reply port is created temporarily just for the purpose of receiving
		871	the reply, and will be C<kil>ed when no longer needed.
		872
		873	A reply message sent to the port is passed to the C<$callback> as-is.
		874
		875	If an optional time-out (in seconds) is given and it is not C<undef>,
		876	then the callback will be called without any arguments after the time-out
		877	elapsed and the port is C<kil>ed.
		878
		879	If no time-out is given (or it is C<undef>), then the local port will
		880	monitor the remote port instead, so it eventually gets cleaned-up.
		881
		882	Currently this function returns the temporary port, but this "feature"
		883	might go in future versions unless you can make a convincing case that
		884	this is indeed useful for something.
		885
		886	=cut
		887
		888	sub cal(@) {
		889	my $timeout = ref $_[-1] ? undef : pop;
		890	my $cb = pop;
		891
		892	my $port = port {
		893	undef $timeout;
		894	kil $SELF;
		895	&$cb;
		896	};
		897
		898	if (defined $timeout) {
		899	$timeout = AE::timer $timeout, 0, sub {
		900	undef $timeout;
		901	kil $port;
		902	$cb->();
		903	};
		904	} else {
		905	mon $_[0], sub {
		906	kil $port;
		907	$cb->();
		908	};
		909	}
		910
		911	push @_, $port;
		912	&snd;
		913
		914	$port
		915	}
		916
446	=back	917	=back
447		918
448	=head1 FUNCTIONS FOR NODES	919	=head1 DISTRIBUTED DATABASE
		920
		921	AnyEvent::MP comes with a simple distributed database. The database will
		922	be mirrored asynchronously on all global nodes. Other nodes bind to one
		923	of the global nodes for their needs. Every node has a "local database"
		924	which contains all the values that are set locally. All local databases
		925	are merged together to form the global database, which can be queried.
		926
		927	The database structure is that of a two-level hash - the database hash
		928	contains hashes which contain values, similarly to a perl hash of hashes,
		929	i.e.:
		930
		931	$DATABASE{$family}{$subkey} = $value
		932
		933	The top level hash key is called "family", and the second-level hash key
		934	is called "subkey" or simply "key".
		935
		936	The family must be alphanumeric, i.e. start with a letter and consist
		937	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		938	pretty much like Perl module names.
		939
		940	As the family namespace is global, it is recommended to prefix family names
		941	with the name of the application or module using it.
		942
		943	The subkeys must be non-empty strings, with no further restrictions.
		944
		945	The values should preferably be strings, but other perl scalars should
		946	work as well (such as C<undef>, arrays and hashes).
		947
		948	Every database entry is owned by one node - adding the same family/subkey
		949	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		950	but the result might be nondeterministic, i.e. the key might have
		951	different values on different nodes.
		952
		953	Different subkeys in the same family can be owned by different nodes
		954	without problems, and in fact, this is the common method to create worker
		955	pools. For example, a worker port for image scaling might do this:
		956
		957	db_set my_image_scalers => $port;
		958
		959	And clients looking for an image scaler will want to get the
		960	C<my_image_scalers> keys from time to time:
		961
		962	db_keys my_image_scalers => sub {
		963	@ports = @{ $_[0] };
		964	};
		965
		966	Or better yet, they want to monitor the database family, so they always
		967	have a reasonable up-to-date copy:
		968
		969	db_mon my_image_scalers => sub {
		970	@ports = keys %{ $_[0] };
		971	};
		972
		973	In general, you can set or delete single subkeys, but query and monitor
		974	whole families only.
		975
		976	If you feel the need to monitor or query a single subkey, try giving it
		977	it's own family.
		978
		979	=over
		980
		981	=item $guard = db_set $family => $subkey [=> $value]
		982
		983	Sets (or replaces) a key to the database - if C<$value> is omitted,
		984	C<undef> is used instead.
		985
		986	When called in non-void context, C<db_set> returns a guard that
		987	automatically calls C<db_del> when it is destroyed.
		988
		989	=item db_del $family => $subkey...
		990
		991	Deletes one or more subkeys from the database family.
		992
		993	=item $guard = db_reg $family => $port => $value
		994
		995	=item $guard = db_reg $family => $port
		996
		997	=item $guard = db_reg $family
		998
		999	Registers a port in the given family and optionally returns a guard to
		1000	remove it.
		1001
		1002	This function basically does the same as:
		1003
		1004	db_set $family => $port => $value
		1005
		1006	Except that the port is monitored and automatically removed from the
		1007	database family when it is kil'ed.
		1008
		1009	If C<$value> is missing, C<undef> is used. If C<$port> is missing, then
		1010	C<$SELF> is used.
		1011
		1012	This function is most useful to register a port in some port group (which
		1013	is just another name for a database family), and have it removed when the
		1014	port is gone. This works best when the port is a local port.
		1015
		1016	=cut
		1017
		1018	sub db_reg($$;$) {
		1019	my $family = shift;
		1020	my $port = @_ ? shift : $SELF;
		1021
		1022	my $clr = sub { db_del $family => $port };
		1023	mon $port, $clr;
		1024
		1025	db_set $family => $port => $_[0];
		1026
		1027	defined wantarray
		1028	and &Guard::guard ($clr)
		1029	}
		1030
		1031	=item db_family $family => $cb->(\%familyhash)
		1032
		1033	Queries the named database C<$family> and call the callback with the
		1034	family represented as a hash. You can keep and freely modify the hash.
		1035
		1036	=item db_keys $family => $cb->(\@keys)
		1037
		1038	Same as C<db_family>, except it only queries the family I<subkeys> and passes
		1039	them as array reference to the callback.
		1040
		1041	=item db_values $family => $cb->(\@values)
		1042
		1043	Same as C<db_family>, except it only queries the family I<values> and passes them
		1044	as array reference to the callback.
		1045
		1046	=item $guard = db_mon $family => $cb->($familyhash, \@added, \@changed, \@deleted)
		1047
		1048	Creates a monitor on the given database family. Each time a key is set
		1049	or or is deleted the callback is called with a hash containing the
		1050	database family and three lists of added, changed and deleted subkeys,
		1051	respectively. If no keys have changed then the array reference might be
		1052	C<undef> or even missing.
		1053
		1054	If not called in void context, a guard object is returned that, when
		1055	destroyed, stops the monitor.
		1056
		1057	The family hash reference and the key arrays belong to AnyEvent::MP and
		1058	B<must not be modified or stored> by the callback. When in doubt, make a
		1059	copy.
		1060
		1061	As soon as possible after the monitoring starts, the callback will be
		1062	called with the intiial contents of the family, even if it is empty,
		1063	i.e. there will always be a timely call to the callback with the current
		1064	contents.
		1065
		1066	It is possible that the callback is called with a change event even though
		1067	the subkey is already present and the value has not changed.
		1068
		1069	The monitoring stops when the guard object is destroyed.
		1070
		1071	Example: on every change to the family "mygroup", print out all keys.
		1072
		1073	my $guard = db_mon mygroup => sub {
		1074	my ($family, $a, $c, $d) = @_;
		1075	print "mygroup members: ", (join " ", keys %$family), "\n";
		1076	};
		1077
		1078	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1079
		1080	my $guard; $guard = db_mon My::Module::workers => sub {
		1081	my ($family, $a, $c, $d) = @_;
		1082	return unless %$family;
		1083	undef $guard;
		1084	print "My::Module::workers now nonempty\n";
		1085	};
		1086
		1087	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		1088
		1089	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		1090	my ($family, $a, $c, $d) = @_;
		1091
		1092	print "+$_=$family->{$_}\n" for @$a;
		1093	print "*$_=$family->{$_}\n" for @$c;
		1094	print "-$_=$family->{$_}\n" for @$d;
		1095	};
		1096
		1097	=cut
		1098
		1099	=back
		1100
		1101	=head1 AnyEvent::MP vs. Distributed Erlang
		1102
		1103	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
		1104	== aemp node, Erlang process == aemp port), so many of the documents and
		1105	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
		1106	sample:
		1107
		1108	http://www.erlang.se/doc/programming_rules.shtml
		1109	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
		1110	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
		1111	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
		1112
		1113	Despite the similarities, there are also some important differences:
449		1114
450	=over 4	1115	=over 4
451		1116
452	=item become_public endpoint...	1117	=item * Node IDs are arbitrary strings in AEMP.
453		1118
454	Tells the node to become a public node, i.e. reachable from other nodes.
455
456	If no arguments are given, or the first argument is C<undef>, then
457	AnyEvent::MP tries to bind on port C<4040> on all IP addresses that the
458	local nodename resolves to.
459
460	Otherwise the first argument must be an array-reference with transport
461	endpoints ("ip:port", "hostname:port") or port numbers (in which case the
462	local nodename is used as hostname). The endpoints are all resolved and
463	will become the node reference.
464
465	=cut
466
467	=back
468
469	=head1 NODE MESSAGES
470
471	Nodes understand the following messages sent to them. Many of them take
472	arguments called C<@reply>, which will simply be used to compose a reply
473	message - C<$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
514
515	AnyEvent::MP got lots of its ideas from distributed erlang. Despite the
516	similarities (erlang node == aemp node, erlang process == aemp port and so
517	on), there are also some important differences:
518
519	=over 4
520
521	=item * Node references contain the recipe on how to contact them.
522
523	Erlang relies on special naming and DNS to work everywhere in the	1119	Erlang relies on special naming and DNS to work everywhere in the same
524	same way. AEMP relies on each node knowing it's own address(es), with	1120	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
525	convenience functionality.	1121	configuration or DNS), and possibly the addresses of some seed nodes, but
		1122	will otherwise discover other nodes (and their IDs) itself.
		1123
		1124	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
		1125	uses "local ports are like remote ports".
		1126
		1127	The failure modes for local ports are quite different (runtime errors
		1128	only) then for remote ports - when a local port dies, you I<know> it dies,
		1129	when a connection to another node dies, you know nothing about the other
		1130	port.
		1131
		1132	Erlang pretends remote ports are as reliable as local ports, even when
		1133	they are not.
		1134
		1135	AEMP encourages a "treat remote ports differently" philosophy, with local
		1136	ports being the special case/exception, where transport errors cannot
		1137	occur.
526		1138
527	=item * Erlang uses processes and a mailbox, AEMP does not queue.	1139	=item * Erlang uses processes and a mailbox, AEMP does not queue.
528		1140
529	Erlang uses processes that selctively receive messages, and therefore	1141	Erlang uses processes that selectively receive messages out of order, and
530	needs a queue. AEMP is event based, queuing messages would serve no useful	1142	therefore needs a queue. AEMP is event based, queuing messages would serve
531	purpose.	1143	no useful purpose. For the same reason the pattern-matching abilities
		1144	of AnyEvent::MP are more limited, as there is little need to be able to
		1145	filter messages without dequeuing them.
532		1146
533	(But see L<Coro::MP> for a more erlang-like process model on top of AEMP).	1147	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1148	being event-based, while Erlang is process-based.
		1149
		1150	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1151	top of AEMP and Coro threads.
534		1152
535	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1153	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
536		1154
537	Sending messages in erlang is synchronous and blocks the process. AEMP	1155	Sending messages in Erlang is synchronous and blocks the process until
538	sends are immediate, connection establishment is handled in the	1156	a conenction has been established and the message sent (and so does not
539	background.	1157	need a queue that can overflow). AEMP sends return immediately, connection
		1158	establishment is handled in the background.
540		1159
541	=item * Erlang can silently lose messages, AEMP cannot.	1160	=item * Erlang suffers from silent message loss, AEMP does not.
542		1161
543	Erlang makes few guarantees on messages delivery - messages can get lost	1162	Erlang implements few guarantees on messages delivery - messages can get
544	without any of the processes realising it (i.e. you send messages a, b,	1163	lost without any of the processes realising it (i.e. you send messages a,
545	and c, and the other side only receives messages a and c).	1164	b, and c, and the other side only receives messages a and c).
546		1165
547	AEMP guarantees correct ordering, and the guarantee that there are no	1166	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1167	guarantee that after one message is lost, all following ones sent to the
		1168	same port are lost as well, until monitoring raises an error, so there are
548	holes in the message sequence.	1169	no silent "holes" in the message sequence.
549		1170
550	=item * In erlang, processes can be declared dead and later be found to be	1171	If you want your software to be very reliable, you have to cope with
551	alive.	1172	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
552		1173	simply tries to work better in common error cases, such as when a network
553	In erlang it can happen that a monitored process is declared dead and	1174	link goes down.
554	linked processes get killed, but later it turns out that the process is
555	still alive - and can receive messages.
556
557	In AEMP, when port monitoring detects a port as dead, then that port will
558	eventually be killed - it cannot happen that a node detects a port as dead
559	and then later sends messages to it, finding it is still alive.
560		1175
561	=item * Erlang can send messages to the wrong port, AEMP does not.	1176	=item * Erlang can send messages to the wrong port, AEMP does not.
562		1177
563	In erlang it is quite possible that a node that restarts reuses a process	1178	In Erlang it is quite likely that a node that restarts reuses an Erlang
564	ID known to other nodes for a completely different process, causing	1179	process ID known to other nodes for a completely different process,
565	messages destined for that process to end up in an unrelated process.	1180	causing messages destined for that process to end up in an unrelated
		1181	process.
566		1182
567	AEMP never reuses port IDs, so old messages or old port IDs floating	1183	AEMP does not reuse port IDs, so old messages or old port IDs floating
568	around in the network will not be sent to an unrelated port.	1184	around in the network will not be sent to an unrelated port.
569		1185
570	=item * Erlang uses unprotected connections, AEMP uses secure	1186	=item * Erlang uses unprotected connections, AEMP uses secure
571	authentication and can use TLS.	1187	authentication and can use TLS.
572		1188
573	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1189	AEMP can use a proven protocol - TLS - to protect connections and
574	securely authenticate nodes.	1190	securely authenticate nodes.
575		1191
		1192	=item * The AEMP protocol is optimised for both text-based and binary
		1193	communications.
		1194
		1195	The AEMP protocol, unlike the Erlang protocol, supports both programming
		1196	language independent text-only protocols (good for debugging), and binary,
		1197	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1198	used, the protocol is actually completely text-based.
		1199
		1200	It has also been carefully designed to be implementable in other languages
		1201	with a minimum of work while gracefully degrading functionality to make the
		1202	protocol simple.
		1203
		1204	=item * AEMP has more flexible monitoring options than Erlang.
		1205
		1206	In Erlang, you can chose to receive I<all> exit signals as messages or
		1207	I<none>, there is no in-between, so monitoring single Erlang processes is
		1208	difficult to implement.
		1209
		1210	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1211	between automatic kill, exit message or callback on a per-port basis.
		1212
		1213	=item * Erlang tries to hide remote/local connections, AEMP does not.
		1214
		1215	Monitoring in Erlang is not an indicator of process death/crashes, in the
		1216	same way as linking is (except linking is unreliable in Erlang).
		1217
		1218	In AEMP, you don't "look up" registered port names or send to named ports
		1219	that might or might not be persistent. Instead, you normally spawn a port
		1220	on the remote node. The init function monitors you, and you monitor the
		1221	remote port. Since both monitors are local to the node, they are much more
		1222	reliable (no need for C<spawn_link>).
		1223
		1224	This also saves round-trips and avoids sending messages to the wrong port
		1225	(hard to do in Erlang).
		1226
576	=back	1227	=back
577		1228
		1229	=head1 RATIONALE
		1230
		1231	=over 4
		1232
		1233	=item Why strings for port and node IDs, why not objects?
		1234
		1235	We considered "objects", but found that the actual number of methods
		1236	that can be called are quite low. Since port and node IDs travel over
		1237	the network frequently, the serialising/deserialising would add lots of
		1238	overhead, as well as having to keep a proxy object everywhere.
		1239
		1240	Strings can easily be printed, easily serialised etc. and need no special
		1241	procedures to be "valid".
		1242
		1243	And as a result, a port with just a default receiver consists of a single
		1244	code reference stored in a global hash - it can't become much cheaper.
		1245
		1246	=item Why favour JSON, why not a real serialising format such as Storable?
		1247
		1248	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1249	format, but currently there is no way to make a node use Storable by
		1250	default (although all nodes will accept it).
		1251
		1252	The default framing protocol is JSON because a) JSON::XS is many times
		1253	faster for small messages and b) most importantly, after years of
		1254	experience we found that object serialisation is causing more problems
		1255	than it solves: Just like function calls, objects simply do not travel
		1256	easily over the network, mostly because they will always be a copy, so you
		1257	always have to re-think your design.
		1258
		1259	Keeping your messages simple, concentrating on data structures rather than
		1260	objects, will keep your messages clean, tidy and efficient.
		1261
		1262	=back
		1263
		1264	=head1 PORTING FROM AnyEvent::MP VERSION 1.X
		1265
		1266	AEMP version 2 has a few major incompatible changes compared to version 1:
		1267
		1268	=over 4
		1269
		1270	=item AnyEvent::MP::Global no longer has group management functions.
		1271
		1272	AnyEvent::MP now comes with a distributed database that is more
		1273	powerful. Its database families map closely to port groups, but the API
		1274	has changed (the functions are also now exported by AnyEvent::MP). Here is
		1275	a rough porting guide:
		1276
		1277	grp_reg $group, $port # old
		1278	db_reg $group, $port # new
		1279
		1280	$list = grp_get $group # old
		1281	db_keys $group, sub { my $list = shift } # new
		1282
		1283	grp_mon $group, $cb->(\@ports, $add, $del) # old
		1284	db_mon $group, $cb->(\%ports, $add, $change, $del) # new
		1285
		1286	C<grp_reg> is a no-brainer (just replace by C<db_reg>), but C<grp_get> is
		1287	no longer instant, because the local node might not have a copy of the
		1288	group. You can either modify your code to allow for a callback, or use
		1289	C<db_mon> to keep an updated copy of the group:
		1290
		1291	my $local_group_copy;
		1292	db_mon $group => sub { $local_group_copy = $_[0] };
		1293
		1294	# now "keys %$local_group_copy" always returns the most up-to-date
		1295	# list of ports in the group.
		1296
		1297	C<grp_mon> can be replaced by C<db_mon> with minor changes - C<db_mon>
		1298	passes a hash as first argument, and an extra C<$chg> argument that can be
		1299	ignored:
		1300
		1301	db_mon $group => sub {
		1302	my ($ports, $add, $chg, $lde) = @_;
		1303	$ports = [keys %$ports];
		1304
		1305	# now $ports, $add and $del are the same as
		1306	# were originally passed by grp_mon.
		1307	...
		1308	};
		1309
		1310	=item Nodes not longer connect to all other nodes.
		1311
		1312	In AEMP 1.x, every node automatically loads the L<AnyEvent::MP::Global>
		1313	module, which in turn would create connections to all other nodes in the
		1314	network (helped by the seed nodes).
		1315
		1316	In version 2.x, global nodes still connect to all other global nodes, but
		1317	other nodes don't - now every node either is a global node itself, or
		1318	attaches itself to another global node.
		1319
		1320	If a node isn't a global node itself, then it attaches itself to one
		1321	of its seed nodes. If that seed node isn't a global node yet, it will
		1322	automatically be upgraded to a global node.
		1323
		1324	So in many cases, nothing needs to be changed - one just has to make sure
		1325	that all seed nodes are meshed together with the other seed nodes (as with
		1326	AEMP 1.x), and other nodes specify them as seed nodes. This is most easily
		1327	achieved by specifying the same set of seed nodes for all nodes in the
		1328	network.
		1329
		1330	Not opening a connection to every other node is usually an advantage,
		1331	except when you need the lower latency of an already established
		1332	connection. To ensure a node establishes a connection to another node,
		1333	you can monitor the node port (C<mon $node, ...>), which will attempt to
		1334	create the connection (and notify you when the connection fails).
		1335
		1336	=item Listener-less nodes (nodes without binds) are gone.
		1337
		1338	And are not coming back, at least not in their old form. If no C<binds>
		1339	are specified for a node, AnyEvent::MP assumes a default of C<*:*>.
		1340
		1341	There are vague plans to implement some form of routing domains, which
		1342	might or might not bring back listener-less nodes, but don't count on it.
		1343
		1344	The fact that most connections are now optional somewhat mitigates this,
		1345	as a node can be effectively unreachable from the outside without any
		1346	problems, as long as it isn't a global node and only reaches out to other
		1347	nodes (as opposed to being contacted from other nodes).
		1348
		1349	=item $AnyEvent::MP::Kernel::WARN has gone.
		1350
		1351	AnyEvent has acquired a logging framework (L<AnyEvent::Log>), and AEMP now
		1352	uses this, and so should your programs.
		1353
		1354	Every module now documents what kinds of messages it generates, with
		1355	AnyEvent::MP acting as a catch all.
		1356
		1357	On the positive side, this means that instead of setting
		1358	C<PERL_ANYEVENT_MP_WARNLEVEL>, you can get away by setting C<AE_VERBOSE> -
		1359	much less to type.
		1360
		1361	=back
		1362
		1363	=head1 LOGGING
		1364
		1365	AnyEvent::MP does not normally log anything by itself, but sinc eit is the
		1366	root of the contetx hierarchy for AnyEvent::MP modules, it will receive
		1367	all log messages by submodules.
		1368
578	=head1 SEE ALSO	1369	=head1 SEE ALSO
		1370
		1371	L<AnyEvent::MP::Intro> - a gentle introduction.
		1372
		1373	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1374
		1375	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1376	your applications.
		1377
		1378	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1379
		1380	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1381	all nodes.
579		1382
580	L<AnyEvent>.	1383	L<AnyEvent>.
581		1384
582	=head1 AUTHOR	1385	=head1 AUTHOR
583		1386

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