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Revision 1.30 by root, Tue Aug 4 23:35:51 2009 UTC vs.
Revision 1.128 by root, Sun Mar 4 14:28:44 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).	76	Not to be confused with a TCP port, a "port" is something you can send
		77	messages to (with the C<snd> function).
49		78
50	Some ports allow you to register C<rcv> handlers that can match specific	79	Ports allow you to register C<rcv> handlers that can match all or just
51	messages. All C<rcv> handlers will receive messages they match, messages	80	some messages. Messages send to ports will not be queued, regardless of
52	will not be queued.	81	anything was listening for them or not.
53		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
54	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
55		86
56	A port id is normaly the concatenation of a noderef, a hash-mark (C<#>) as	87	A port ID is the concatenation of a node ID, a hash-mark (C<#>)
57	separator, and a port name (a printable string of unspecified format). An	88	as separator, and a port name (a printable string of unspecified
58	exception is the the node port, whose ID is identical to its node	89	format created by AnyEvent::MP).
59	reference.
60		90
61	=item node	91	=item node
62		92
63	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,
64	port. You can send messages to node ports to find existing ports or to	94	which enables nodes to manage each other remotely, and to create new
65	create new ports, among other things.	95	ports.
66		96
67	Nodes are either private (single-process only), slaves (connected to a	97	Nodes are either public (have one or more listening ports) or private
68	master node only) or public nodes (connectable from unrelated nodes).	98	(no listening ports). Private nodes cannot talk to other private nodes
		99	currently, but all nodes can talk to public nodes.
69		100
70	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	101	Nodes is represented by (printable) strings called "node IDs".
71		102
72	A node reference is a string that either simply identifies the node (for	103	=item node ID - C<[A-Za-z0-9_\-.:]*>
73	private and slave nodes), or contains a recipe on how to reach a given
74	node (for public nodes).
75		104
76	This recipe is simply a comma-separated list of C<address:port> pairs (for	105	A node ID is a string that uniquely identifies the node within a
77	TCP/IP, other protocols might look different).	106	network. Depending on the configuration used, node IDs can look like a
		107	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		108	doesn't interpret node IDs in any way except to uniquely identify a node.
78		109
79	Node references come in two flavours: resolved (containing only numerical	110	=item binds - C<ip:port>
80	addresses) or unresolved (where hostnames are used instead of addresses).
81		111
82	Before using an unresolved node reference in a message you first have to	112	Nodes can only talk to each other by creating some kind of connection to
83	resolve it.	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).
84		170
85	=back	171	=back
86		172
87	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
88		174
…		…
90		176
91	=cut	177	=cut
92		178
93	package AnyEvent::MP;	179	package AnyEvent::MP;
94		180
		181	use AnyEvent::MP::Config ();
95	use AnyEvent::MP::Base;	182	use AnyEvent::MP::Kernel;
		183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
96		184
97	use common::sense;	185	use common::sense;
98		186
99	use Carp ();	187	use Carp ();
100		188
101	use AE ();	189	use AE ();
		190	use Guard ();
102		191
103	use base "Exporter";	192	use base "Exporter";
104		193
105	our $VERSION = '0.1';	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
		195
106	our @EXPORT = qw(	196	our @EXPORT = qw(
107	NODE $NODE *SELF node_of _any_	197	NODE $NODE *SELF node_of after
108	resolve_node	198	configure
109	become_slave become_public	199	snd rcv mon mon_guard kil psub peval spawn cal
110	snd rcv mon kil reg psub
111	port	200	port
		201	db_set db_del db_reg
		202	db_mon db_family db_keys db_values
112	);	203	);
113		204
114	our $SELF;	205	our $SELF;
115		206
116	sub _self_die() {	207	sub _self_die() {
…		…
119	kil $SELF, die => $msg;	210	kil $SELF, die => $msg;
120	}	211	}
121		212
122	=item $thisnode = NODE / $NODE	213	=item $thisnode = NODE / $NODE
123		214
124	The C<NODE> function returns, and the C<$NODE> variable contains	215	The C<NODE> function returns, and the C<$NODE> variable contains, the node
125	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
126	to C<become_public> or C<become_slave>, after which all local port	217	a call to C<configure>.
127	identifiers become invalid.
128		218
129	=item $noderef = node_of $portid	219	=item $nodeid = node_of $port
130		220
131	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.
132		222
133	=item $cv = resolve_node $noderef	223	=item configure $profile, key => value...
134		224
135	Takes an unresolved node reference that may contain hostnames and	225	=item configure key => value...
136	abbreviated IDs, resolves all of them and returns a resolved node
137	reference.
138		226
139	In addition to C<address:port> pairs allowed in resolved noderefs, the	227	Before a node can talk to other nodes on the network (i.e. enter
140	following forms are supported:	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:
141		237
142	=over 4	238	=over 4
143		239
144	=item the empty string	240	=item norc => $boolean (default false)
145		241
146	An empty-string component gets resolved as if the default port (4040) was	242	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
147	specified.	243	be consulted - all configuraiton options must be specified in the
		244	C<configure> call.
148		245
149	=item naked port numbers (e.g. C<1234>)	246	=item force => $boolean (default false)
150		247
151	These are resolved by prepending the local nodename and a colon, to be	248	IF true, then the values specified in the C<configure> will take
152	further resolved.	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.
153		251
154	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	252	=item secure => $pass->($nodeid)
155		253
156	These are resolved by using AnyEvent::DNS to resolve them, optionally	254	In addition to specifying a boolean, you can specify a code reference that
157	looking up SRV records for the C<aemp=4040> port, if no port was	255	is called for every remote execution attempt - the execution request is
158	specified.	256	granted iff the callback returns a true value.
		257
		258	See F<semp setsecure> for more info.
159		259
160	=back	260	=back
		261
		262	=over 4
		263
		264	=item step 1, gathering configuration from profiles
		265
		266	The function first looks up a profile in the aemp configuration (see the
		267	L<aemp> commandline utility). The profile name can be specified via the
		268	named C<profile> parameter or can simply be the first parameter). If it is
		269	missing, then the nodename (F<uname -n>) will be used as profile name.
		270
		271	The profile data is then gathered as follows:
		272
		273	First, all remaining key => value pairs (all of which are conveniently
		274	undocumented at the moment) will be interpreted as configuration
		275	data. Then they will be overwritten by any values specified in the global
		276	default configuration (see the F<aemp> utility), then the chain of
		277	profiles chosen by the profile name (and any C<parent> attributes).
		278
		279	That means that the values specified in the profile have highest priority
		280	and the values specified directly via C<configure> have lowest priority,
		281	and can only be used to specify defaults.
		282
		283	If the profile specifies a node ID, then this will become the node ID of
		284	this process. If not, then the profile name will be used as node ID, with
		285	a unique randoms tring (C</%u>) appended.
		286
		287	The node ID can contain some C<%> sequences that are expanded: C<%n>
		288	is expanded to the local nodename, C<%u> is replaced by a random
		289	strign to make the node unique. For example, the F<aemp> commandline
		290	utility uses C<aemp/%n/%u> as nodename, which might expand to
		291	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		292
		293	=item step 2, bind listener sockets
		294
		295	The next step is to look up the binds in the profile, followed by binding
		296	aemp protocol listeners on all binds specified (it is possible and valid
		297	to have no binds, meaning that the node cannot be contacted form the
		298	outside. This means the node cannot talk to other nodes that also have no
		299	binds, but it can still talk to all "normal" nodes).
		300
		301	If the profile does not specify a binds list, then a default of C<*> is
		302	used, meaning the node will bind on a dynamically-assigned port on every
		303	local IP address it finds.
		304
		305	=item step 3, connect to seed nodes
		306
		307	As the last step, the seed ID list from the profile is passed to the
		308	L<AnyEvent::MP::Global> module, which will then use it to keep
		309	connectivity with at least one node at any point in time.
		310
		311	=back
		312
		313	Example: become a distributed node using the local node name as profile.
		314	This should be the most common form of invocation for "daemon"-type nodes.
		315
		316	configure
		317
		318	Example: become a semi-anonymous node. This form is often used for
		319	commandline clients.
		320
		321	configure nodeid => "myscript/%n/%u";
		322
		323	Example: configure a node using a profile called seed, which is suitable
		324	for a seed node as it binds on all local addresses on a fixed port (4040,
		325	customary for aemp).
		326
		327	# use the aemp commandline utility
		328	# aemp profile seed binds '*:4040'
		329
		330	# then use it
		331	configure profile => "seed";
		332
		333	# or simply use aemp from the shell again:
		334	# aemp run profile seed
		335
		336	# or provide a nicer-to-remember nodeid
		337	# aemp run profile seed nodeid "$(hostname)"
161		338
162	=item $SELF	339	=item $SELF
163		340
164	Contains the current port id while executing C<rcv> callbacks or C<psub>	341	Contains the current port id while executing C<rcv> callbacks or C<psub>
165	blocks.	342	blocks.
166		343
167	=item SELF, %SELF, @SELF...	344	=item *SELF, SELF, %SELF, @SELF...
168		345
169	Due to some quirks in how perl exports variables, it is impossible to	346	Due to some quirks in how perl exports variables, it is impossible to
170	just export C<$SELF>, all the symbols called C<SELF> are exported by this	347	just export C<$SELF>, all the symbols named C<SELF> are exported by this
171	module, but only C<$SELF> is currently used.	348	module, but only C<$SELF> is currently used.
172		349
173	=item snd $portid, type => @data	350	=item snd $port, type => @data
174		351
175	=item snd $portid, @msg	352	=item snd $port, @msg
176		353
177	Send the given message to the given port ID, which can identify either	354	Send the given message to the given port, which can identify either a
178	a local or a remote port, and can be either a string or soemthignt hat	355	local or a remote port, and must be a port ID.
179	stringifies a sa port ID (such as a port object :).
180		356
181	While the message can be about anything, it is highly recommended to use a	357	While the message can be almost anything, it is highly recommended to
182	string as first element (a portid, or some word that indicates a request	358	use a string as first element (a port ID, or some word that indicates a
183	type etc.).	359	request type etc.) and to consist if only simple perl values (scalars,
		360	arrays, hashes) - if you think you need to pass an object, think again.
184		361
185	The message data effectively becomes read-only after a call to this	362	The message data logically becomes read-only after a call to this
186	function: modifying any argument is not allowed and can cause many	363	function: modifying any argument (or values referenced by them) is
187	problems.	364	forbidden, as there can be considerable time between the call to C<snd>
		365	and the time the message is actually being serialised - in fact, it might
		366	never be copied as within the same process it is simply handed to the
		367	receiving port.
188		368
189	The type of data you can transfer depends on the transport protocol: when	369	The type of data you can transfer depends on the transport protocol: when
190	JSON is used, then only strings, numbers and arrays and hashes consisting	370	JSON is used, then only strings, numbers and arrays and hashes consisting
191	of those are allowed (no objects). When Storable is used, then anything	371	of those are allowed (no objects). When Storable is used, then anything
192	that Storable can serialise and deserialise is allowed, and for the local	372	that Storable can serialise and deserialise is allowed, and for the local
193	node, anything can be passed.	373	node, anything can be passed. Best rely only on the common denominator of
		374	these.
194		375
195	=item kil $portid[, @reason]	376	=item $local_port = port
196		377
197	Kill the specified port with the given C<@reason>.	378	Create a new local port object and returns its port ID. Initially it has
		379	no callbacks set and will throw an error when it receives messages.
198		380
199	If no C<@reason> is specified, then the port is killed "normally" (linked	381	=item $local_port = port { my @msg = @_ }
200	ports will not be kileld, or even notified).
201		382
202	Otherwise, linked ports get killed with the same reason (second form of	383	Creates a new local port, and returns its ID. Semantically the same as
203	C<mon>, see below).	384	creating a port and calling C<rcv $port, $callback> on it.
204		385
205	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	386	The block will be called for every message received on the port, with the
206	will be reported as reason C<< die => $@ >>.	387	global variable C<$SELF> set to the port ID. Runtime errors will cause the
		388	port to be C<kil>ed. The message will be passed as-is, no extra argument
		389	(i.e. no port ID) will be passed to the callback.
207		390
208	Transport/communication errors are reported as C<< transport_error =>	391	If you want to stop/destroy the port, simply C<kil> it:
209	$message >>.
210		392
211	=item $guard = mon $portid, $cb->(@reason)	393	my $port = port {
		394	my @msg = @_;
		395	...
		396	kil $SELF;
		397	};
212		398
213	=item $guard = mon $portid, $otherport	399	=cut
214		400
215	=item $guard = mon $portid, $otherport, @msg	401	sub rcv($@);
216		402
		403	sub _kilme {
		404	die "received message on port without callback";
		405	}
		406
		407	sub port(;&) {
		408	my $id = $UNIQ . ++$ID;
		409	my $port = "$NODE#$id";
		410
		411	rcv $port, shift || \&_kilme;
		412
		413	$port
		414	}
		415
		416	=item rcv $local_port, $callback->(@msg)
		417
		418	Replaces the default callback on the specified port. There is no way to
		419	remove the default callback: use C<sub { }> to disable it, or better
		420	C<kil> the port when it is no longer needed.
		421
		422	The global C<$SELF> (exported by this module) contains C<$port> while
		423	executing the callback. Runtime errors during callback execution will
		424	result in the port being C<kil>ed.
		425
		426	The default callback received all messages not matched by a more specific
		427	C<tag> match.
		428
		429	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
		430
		431	Register (or replace) callbacks to be called on messages starting with the
		432	given tag on the given port (and return the port), or unregister it (when
		433	C<$callback> is C<$undef> or missing). There can only be one callback
		434	registered for each tag.
		435
		436	The original message will be passed to the callback, after the first
		437	element (the tag) has been removed. The callback will use the same
		438	environment as the default callback (see above).
		439
		440	Example: create a port and bind receivers on it in one go.
		441
		442	my $port = rcv port,
		443	msg1 => sub { ... },
		444	msg2 => sub { ... },
		445	;
		446
		447	Example: create a port, bind receivers and send it in a message elsewhere
		448	in one go:
		449
		450	snd $otherport, reply =>
		451	rcv port,
		452	msg1 => sub { ... },
		453	...
		454	;
		455
		456	Example: temporarily register a rcv callback for a tag matching some port
		457	(e.g. for an rpc reply) and unregister it after a message was received.
		458
		459	rcv $port, $otherport => sub {
		460	my @reply = @_;
		461
		462	rcv $SELF, $otherport;
		463	};
		464
		465	=cut
		466
		467	sub rcv($@) {
		468	my $port = shift;
		469	my ($nodeid, $portid) = split /#/, $port, 2;
		470
		471	$NODE{$nodeid} == $NODE{""}
		472	or Carp::croak "$port: rcv can only be called on local ports, caught";
		473
		474	while (@_) {
		475	if (ref $_[0]) {
		476	if (my $self = $PORT_DATA{$portid}) {
		477	"AnyEvent::MP::Port" eq ref $self
		478	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		479
		480	$self->[0] = shift;
		481	} else {
		482	my $cb = shift;
		483	$PORT{$portid} = sub {
		484	local $SELF = $port;
		485	eval { &$cb }; _self_die if $@;
		486	};
		487	}
		488	} elsif (defined $_[0]) {
		489	my $self = $PORT_DATA{$portid} ||= do {
		490	my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port";
		491
		492	$PORT{$portid} = sub {
		493	local $SELF = $port;
		494
		495	if (my $cb = $self->[1]{$_[0]}) {
		496	shift;
		497	eval { &$cb }; _self_die if $@;
		498	} else {
		499	&{ $self->[0] };
		500	}
		501	};
		502
		503	$self
		504	};
		505
		506	"AnyEvent::MP::Port" eq ref $self
		507	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		508
		509	my ($tag, $cb) = splice @_, 0, 2;
		510
		511	if (defined $cb) {
		512	$self->[1]{$tag} = $cb;
		513	} else {
		514	delete $self->[1]{$tag};
		515	}
		516	}
		517	}
		518
		519	$port
		520	}
		521
		522	=item peval $port, $coderef[, @args]
		523
		524	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		525	when the code throews an exception the C<$port> will be killed.
		526
		527	Any remaining args will be passed to the callback. Any return values will
		528	be returned to the caller.
		529
		530	This is useful when you temporarily want to execute code in the context of
		531	a port.
		532
		533	Example: create a port and run some initialisation code in it's context.
		534
		535	my $port = port { ... };
		536
		537	peval $port, sub {
		538	init
		539	or die "unable to init";
		540	};
		541
		542	=cut
		543
		544	sub peval($$) {
		545	local $SELF = shift;
		546	my $cb = shift;
		547
		548	if (wantarray) {
		549	my @res = eval { &$cb };
		550	_self_die if $@;
		551	@res
		552	} else {
		553	my $res = eval { &$cb };
		554	_self_die if $@;
		555	$res
		556	}
		557	}
		558
		559	=item $closure = psub { BLOCK }
		560
		561	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
		562	closure is executed, sets up the environment in the same way as in C<rcv>
		563	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		564
		565	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		566	BLOCK }, @_ } >>.
		567
		568	This is useful when you register callbacks from C<rcv> callbacks:
		569
		570	rcv delayed_reply => sub {
		571	my ($delay, @reply) = @_;
		572	my $timer = AE::timer $delay, 0, psub {
		573	snd @reply, $SELF;
		574	};
		575	};
		576
		577	=cut
		578
		579	sub psub(&) {
		580	my $cb = shift;
		581
		582	my $port = $SELF
		583	or Carp::croak "psub can only be called from within rcv or psub callbacks, not";
		584
		585	sub {
		586	local $SELF = $port;
		587
		588	if (wantarray) {
		589	my @res = eval { &$cb };
		590	_self_die if $@;
		591	@res
		592	} else {
		593	my $res = eval { &$cb };
		594	_self_die if $@;
		595	$res
		596	}
		597	}
		598	}
		599
		600	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
		601
		602	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
		603
		604	=item $guard = mon $port # kill $SELF when $port dies
		605
		606	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		607
217	Monitor the given port and do something when the port is killed.	608	Monitor the given port and do something when the port is killed or
		609	messages to it were lost, and optionally return a guard that can be used
		610	to stop monitoring again.
218		611
219	In the first form, the callback is simply called with any number	612	In the first form (callback), the callback is simply called with any
220	of C<@reason> elements (no @reason means that the port was deleted	613	number of C<@reason> elements (no @reason means that the port was deleted
221	"normally"). Note also that I<< the callback B<must> never die >>, so use	614	"normally"). Note also that I<< the callback B<must> never die >>, so use
222	C<eval> if unsure.	615	C<eval> if unsure.
223		616
224	In the second form, the other port will be C<kil>'ed with C<@reason>, iff	617	In the second form (another port given), the other port (C<$rcvport>)
225	a @reason was specified, i.e. on "normal" kils nothing happens, while	618	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
226	under all other conditions, the other port is killed with the same reason.	619	"normal" kils nothing happens, while under all other conditions, the other
		620	port is killed with the same reason.
227		621
		622	The third form (kill self) is the same as the second form, except that
		623	C<$rvport> defaults to C<$SELF>.
		624
228	In the last form, a message of the form C<@msg, @reason> will be C<snd>.	625	In the last form (message), a message of the form C<@msg, @reason> will be
		626	C<snd>.
		627
		628	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		629	alert was raised), they are removed and will not trigger again.
		630
		631	As a rule of thumb, monitoring requests should always monitor a port from
		632	a local port (or callback). The reason is that kill messages might get
		633	lost, just like any other message. Another less obvious reason is that
		634	even monitoring requests can get lost (for example, when the connection
		635	to the other node goes down permanently). When monitoring a port locally
		636	these problems do not exist.
		637
		638	C<mon> effectively guarantees that, in the absence of hardware failures,
		639	after starting the monitor, either all messages sent to the port will
		640	arrive, or the monitoring action will be invoked after possible message
		641	loss has been detected. No messages will be lost "in between" (after
		642	the first lost message no further messages will be received by the
		643	port). After the monitoring action was invoked, further messages might get
		644	delivered again.
		645
		646	Inter-host-connection timeouts and monitoring depend on the transport
		647	used. The only transport currently implemented is TCP, and AnyEvent::MP
		648	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		649	non-idle connection, and usually around two hours for idle connections).
		650
		651	This means that monitoring is good for program errors and cleaning up
		652	stuff eventually, but they are no replacement for a timeout when you need
		653	to ensure some maximum latency.
229		654
230	Example: call a given callback when C<$port> is killed.	655	Example: call a given callback when C<$port> is killed.
231		656
232	mon $port, sub { warn "port died because of <@_>\n" };	657	mon $port, sub { warn "port died because of <@_>\n" };
233		658
234	Example: kill ourselves when C<$port> is killed abnormally.	659	Example: kill ourselves when C<$port> is killed abnormally.
235		660
236	mon $port, $self;	661	mon $port;
237		662
238	Example: send us a restart message another C<$port> is killed.	663	Example: send us a restart message when another C<$port> is killed.
239		664
240	mon $port, $self => "restart";	665	mon $port, $self => "restart";
241		666
242	=cut	667	=cut
243		668
244	sub mon {	669	sub mon {
245	my ($noderef, $port) = split /#/, shift, 2;	670	my ($nodeid, $port) = split /#/, shift, 2;
246		671
247	my $node = $NODE{$noderef} || add_node $noderef;	672	my $node = $NODE{$nodeid} || add_node $nodeid;
248		673
249	my $cb = shift;	674	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
250		675
251	unless (ref $cb) {	676	unless (ref $cb) {
252	if (@_) {	677	if (@_) {
253	# send a kill info message	678	# send a kill info message
254	my (@msg) = ($cb, @_);	679	my (@msg) = ($cb, @_);
…		…
261	}	686	}
262		687
263	$node->monitor ($port, $cb);	688	$node->monitor ($port, $cb);
264		689
265	defined wantarray	690	defined wantarray
266	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	691	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
267	}	692	}
268		693
269	=item $guard = mon_guard $port, $ref, $ref...	694	=item $guard = mon_guard $port, $ref, $ref...
270		695
271	Monitors the given C<$port> and keeps the passed references. When the port	696	Monitors the given C<$port> and keeps the passed references. When the port
272	is killed, the references will be freed.	697	is killed, the references will be freed.
273		698
274	Optionally returns a guard that will stop the monitoring.	699	Optionally returns a guard that will stop the monitoring.
275		700
276	This function is useful when you create e.g. timers or other watchers and	701	This function is useful when you create e.g. timers or other watchers and
277	want to free them when the port gets killed:	702	want to free them when the port gets killed (note the use of C<psub>):
278		703
279	$port->rcv (start => sub {	704	$port->rcv (start => sub {
280	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	705	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
281	undef $timer if 0.9 < rand;	706	undef $timer if 0.9 < rand;
282	});	707	});
283	});	708	});
284		709
285	=cut	710	=cut
286		711
287	sub mon_guard {	712	sub mon_guard {
288	my ($port, @refs) = @_;	713	my ($port, @refs) = @_;
289		714
		715	#TODO: mon-less form?
		716
290	mon $port, sub { 0 && @refs }	717	mon $port, sub { 0 && @refs }
291	}	718	}
292		719
293	=item lnk $port1, $port2	720	=item kil $port[, @reason]
294		721
295	Link two ports. This is simply a shorthand for:	722	Kill the specified port with the given C<@reason>.
296		723
297	mon $port1, $port2;	724	If no C<@reason> is specified, then the port is killed "normally" -
298	mon $port2, $port1;	725	monitor callback will be invoked, but the kil will not cause linked ports
		726	(C<mon $mport, $lport> form) to get killed.
299		727
300	It means that if either one is killed abnormally, the other one gets	728	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
301	killed as well.	729	form) get killed with the same reason.
302		730
303	=item $local_port = port	731	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		732	will be reported as reason C<< die => $@ >>.
304		733
305	Create a new local port object that supports message matching.	734	Transport/communication errors are reported as C<< transport_error =>
		735	$message >>.
306		736
307	=item $portid = port { my @msg = @_; $finished }	737	=cut
308		738
309	Creates a "mini port", that is, a very lightweight port without any	739	=item $port = spawn $node, $initfunc[, @initdata]
310	pattern matching behind it, and returns its ID.
311		740
312	The block will be called for every message received on the port. When the	741	Creates a port on the node C<$node> (which can also be a port ID, in which
313	callback returns a true value its job is considered "done" and the port	742	case it's the node where that port resides).
314	will be destroyed. Otherwise it will stay alive.
315		743
316	The message will be passed as-is, no extra argument (i.e. no port id) will	744	The port ID of the newly created port is returned immediately, and it is
317	be passed to the callback.	745	possible to immediately start sending messages or to monitor the port.
318		746
319	If you need the local port id in the callback, this works nicely:	747	After the port has been created, the init function is called on the remote
		748	node, in the same context as a C<rcv> callback. This function must be a
		749	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		750	specify a function in the main program, use C<::name>.
320		751
321	my $port; $port = miniport {	752	If the function doesn't exist, then the node tries to C<require>
322	snd $otherport, reply => $port;	753	the package, then the package above the package and so on (e.g.
		754	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		755	exists or it runs out of package names.
		756
		757	The init function is then called with the newly-created port as context
		758	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		759	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		760	the port might not get created.
		761
		762	A common idiom is to pass a local port, immediately monitor the spawned
		763	port, and in the remote init function, immediately monitor the passed
		764	local port. This two-way monitoring ensures that both ports get cleaned up
		765	when there is a problem.
		766
		767	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		768	caller before C<spawn> returns (by delaying invocation when spawn is
		769	called for the local node).
		770
		771	Example: spawn a chat server port on C<$othernode>.
		772
		773	# this node, executed from within a port context:
		774	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		775	mon $server;
		776
		777	# init function on C<$othernode>
		778	sub connect {
		779	my ($srcport) = @_;
		780
		781	mon $srcport;
		782
		783	rcv $SELF, sub {
		784	...
		785	};
		786	}
		787
		788	=cut
		789
		790	sub _spawn {
		791	my $port = shift;
		792	my $init = shift;
		793
		794	# rcv will create the actual port
		795	local $SELF = "$NODE#$port";
		796	eval {
		797	&{ load_func $init }
323	};	798	};
324
325	=cut
326
327	sub port(;&) {
328	my $id = "$UNIQ." . $ID++;
329	my $port = "$NODE#$id";
330
331	if (@_) {
332	my $cb = shift;
333	$PORT{$id} = sub {
334	local $SELF = $port;
335	eval {
336	&$cb
337	and kil $id;
338	};
339	_self_die if $@;	799	_self_die if $@;
		800	}
		801
		802	sub spawn(@) {
		803	my ($nodeid, undef) = split /#/, shift, 2;
		804
		805	my $id = $RUNIQ . ++$ID;
		806
		807	$_[0] =~ /::/
		808	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		809
		810	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		811
		812	"$nodeid#$id"
		813	}
		814
		815
		816	=item after $timeout, @msg
		817
		818	=item after $timeout, $callback
		819
		820	Either sends the given message, or call the given callback, after the
		821	specified number of seconds.
		822
		823	This is simply a utility function that comes in handy at times - the
		824	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		825	so it may go away in the future.
		826
		827	=cut
		828
		829	sub after($@) {
		830	my ($timeout, @action) = @_;
		831
		832	my $t; $t = AE::timer $timeout, 0, sub {
		833	undef $t;
		834	ref $action[0]
		835	? $action[0]()
		836	: snd @action;
		837	};
		838	}
		839
		840	=item cal $port, @msg, $callback[, $timeout]
		841
		842	A simple form of RPC - sends a message to the given C<$port> with the
		843	given contents (C<@msg>), but adds a reply port to the message.
		844
		845	The reply port is created temporarily just for the purpose of receiving
		846	the reply, and will be C<kil>ed when no longer needed.
		847
		848	A reply message sent to the port is passed to the C<$callback> as-is.
		849
		850	If an optional time-out (in seconds) is given and it is not C<undef>,
		851	then the callback will be called without any arguments after the time-out
		852	elapsed and the port is C<kil>ed.
		853
		854	If no time-out is given (or it is C<undef>), then the local port will
		855	monitor the remote port instead, so it eventually gets cleaned-up.
		856
		857	Currently this function returns the temporary port, but this "feature"
		858	might go in future versions unless you can make a convincing case that
		859	this is indeed useful for something.
		860
		861	=cut
		862
		863	sub cal(@) {
		864	my $timeout = ref $_[-1] ? undef : pop;
		865	my $cb = pop;
		866
		867	my $port = port {
		868	undef $timeout;
		869	kil $SELF;
		870	&$cb;
		871	};
		872
		873	if (defined $timeout) {
		874	$timeout = AE::timer $timeout, 0, sub {
		875	undef $timeout;
		876	kil $port;
		877	$cb->();
340	};	878	};
341	} else {	879	} else {
342	my $self = bless {	880	mon $_[0], sub {
343	id => "$NODE#$id",	881	kil $port;
344	}, "AnyEvent::MP::Port";	882	$cb->();
345
346	$PORT_DATA{$id} = $self;
347	$PORT{$id} = sub {
348	local $SELF = $port;
349
350	eval {
351	for (@{ $self->{rc0}{$_[0]} }) {
352	$_ && &{$_->[0]}
353	&& undef $_;
354	}
355
356	for (@{ $self->{rcv}{$_[0]} }) {
357	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
358	&& &{$_->[0]}
359	&& undef $_;
360	}
361
362	for (@{ $self->{any} }) {
363	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
364	&& &{$_->[0]}
365	&& undef $_;
366	}
367	};
368	_self_die if $@;
369	};	883	};
370	}	884	}
371		885
		886	push @_, $port;
		887	&snd;
		888
372	$port	889	$port
373	}	890	}
374		891
375	=item reg $portid, $name	892	=back
376		893
377	Registers the given port under the name C<$name>. If the name already	894	=head1 DISTRIBUTED DATABASE
378	exists it is replaced.
379		895
380	A port can only be registered under one well known name.	896	AnyEvent::MP comes with a simple distributed database. The database will
		897	be mirrored asynchronously at all global nodes. Other nodes bind to one of
		898	the global nodes for their needs.
381		899
382	A port automatically becomes unregistered when it is killed.	900	The database consists of a two-level hash - a hash contains a hash which
		901	contains values.
383		902
384	=cut	903	The top level hash key is called "family", and the second-level hash key
		904	is called "subkey" or simply "key".
385		905
386	sub reg(@) {	906	The family must be alphanumeric, i.e. start with a letter and consist
387	my ($portid, $name) = @_;	907	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		908	pretty much like Perl module names.
388		909
389	$REG{$name} = $portid;	910	As the family namespace is global, it is recommended to prefix family names
390	}	911	with the name of the application or module using it.
391		912
392	=item rcv $portid, tagstring => $callback->(@msg), ...	913	The subkeys must be non-empty strings, with no further restrictions.
393		914
394	=item rcv $portid, $smartmatch => $callback->(@msg), ...	915	The values should preferably be strings, but other perl scalars should
		916	work as well (such as undef, arrays and hashes).
395		917
396	=item rcv $portid, [$smartmatch...] => $callback->(@msg), ...	918	Every database entry is owned by one node - adding the same family/subkey
		919	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		920	but the result might be nondeterministic, i.e. the key might have
		921	different values on different nodes.
397		922
398	Register callbacks to be called on matching messages on the given port.	923	Different subkeys in the same family can be owned by different nodes
		924	without problems, and in fact, this is the common method to create worker
		925	pools. For example, a worker port for image scaling might do this:
399		926
400	The callback has to return a true value when its work is done, after	927	db_set my_image_scalers => $port;
401	which is will be removed, or a false value in which case it will stay
402	registered.
403		928
404	The global C<$SELF> (exported by this module) contains C<$portid> while	929	And clients looking for an image scaler will want to get the
405	executing the callback.	930	C<my_image_scalers> keys:
406		931
407	Runtime errors wdurign callback execution will result in the port being	932	db_keys "my_image_scalers" => 60 => sub {
408	C<kil>ed.	933	#d##TODO#
409		934
410	If the match is an array reference, then it will be matched against the	935	=over
411	first elements of the message, otherwise only the first element is being
412	matched.
413		936
414	Any element in the match that is specified as C<_any_> (a function	937	=item db_set $family => $subkey [=> $value]
415	exported by this module) matches any single element of the message.
416		938
417	While not required, it is highly recommended that the first matching	939	Sets (or replaces) a key to the database - if C<$value> is omitted,
418	element is a string identifying the message. The one-string-only match is	940	C<undef> is used instead.
419	also the most efficient match (by far).
420		941
421	=cut	942	=item db_del $family => $subkey
422		943
423	sub rcv($@) {	944	Deletes a key from the database.
424	my ($noderef, $port) = split /#/, shift, 2;
425		945
426	($NODE{$noderef} || add_node $noderef) == $NODE{""}	946	=item $guard = db_reg $family => $subkey [=> $value]
427	or Carp::croak "$noderef#$port: rcv can only be called on local ports, caught";
428		947
429	my $self = $PORT_DATA{$port}	948	Sets the key on the database and returns a guard. When the guard is
430	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";	949	destroyed, the key is deleted from the database. If C<$value> is missing,
		950	then C<undef> is used.
431		951
432	"AnyEvent::MP::Port" eq ref $self	952	=item $guard = db_mon $family => $cb->($familyhash, \@subkeys...)
433	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";
434		953
435	while (@_) {	954	Creates a monitor on the given database family. Each time a key is set or
436	my ($match, $cb) = splice @_, 0, 2;	955	or is deleted the callback is called with a hash containing the database
		956	family and an arrayref with subkeys that have changed.
437		957
438	if (!ref $match) {	958	Specifically, if one of the passed subkeys exists in the $familyhash, then
439	push @{ $self->{rc0}{$match} }, [$cb];	959	it is currently set to the value in the $familyhash. Otherwise, it has
440	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {	960	been deleted.
441	my ($type, @match) = @$match;	961
442	@match	962	The first call will be with the current contents of the family and all
443	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]	963	keys, as if they were just added.
444	: push @{ $self->{rc0}{$match->[0]} }, [$cb];	964
445	} else {	965	It is possible that the callback is called with a change event even though
446	push @{ $self->{any} }, [$cb, $match];	966	the subkey is already present and the value has not changed.
		967
		968	The monitoring stops when the guard object is destroyed.
		969
		970	Example: on every change to the family "mygroup", print out all keys.
		971
		972	my $guard = db_mon mygroup => sub {
		973	my ($family, $keys) = @_;
		974	print "mygroup members: ", (join " ", keys %$family), "\n";
		975	};
		976
		977	Exmaple: wait until the family "My::Module::workers" is non-empty.
		978
		979	my $guard; $guard = db_mon My::Module::workers => sub {
		980	my ($family, $keys) = @_;
		981	return unless %$family;
		982	undef $guard;
		983	print "My::Module::workers now nonempty\n";
		984	};
		985
		986	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		987
		988	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		989	my ($family, $keys) = @_;
		990
		991	for (@$keys) {
		992	print "$_: ",
		993	(exists $family->{$_}
		994	? $family->{$_}
		995	: "(deleted)"),
		996	"\n";
447	}	997	}
448	}
449	}
450
451	=item $closure = psub { BLOCK }
452
453	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
454	closure is executed, sets up the environment in the same way as in C<rcv>
455	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
456
457	This is useful when you register callbacks from C<rcv> callbacks:
458
459	rcv delayed_reply => sub {
460	my ($delay, @reply) = @_;
461	my $timer = AE::timer $delay, 0, psub {
462	snd @reply, $SELF;
463	};
464	};	998	};
465		999
466	=cut	1000	=cut
467		1001
468	sub psub(&) {
469	my $cb = shift;
470
471	my $port = $SELF
472	or Carp::croak "psub can only be called from within rcv or psub callbacks, not";
473
474	sub {
475	local $SELF = $port;
476
477	if (wantarray) {
478	my @res = eval { &$cb };
479	_self_die if $@;
480	@res
481	} else {
482	my $res = eval { &$cb };
483	_self_die if $@;
484	$res
485	}
486	}
487	}
488
489	=back	1002	=back
490		1003
491	=head1 FUNCTIONS FOR NODES
492
493	=over 4
494
495	=item become_public $noderef
496
497	Tells the node to become a public node, i.e. reachable from other nodes.
498
499	The first argument is the (unresolved) node reference of the local node
500	(if missing then the empty string is used).
501
502	It is quite common to not specify anything, in which case the local node
503	tries to listen on the default port, or to only specify a port number, in
504	which case AnyEvent::MP tries to guess the local addresses.
505
506	=cut
507
508	=back
509
510	=head1 NODE MESSAGES
511
512	Nodes understand the following messages sent to them. Many of them take
513	arguments called C<@reply>, which will simply be used to compose a reply
514	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
515	the remaining arguments are simply the message data.
516
517	While other messages exist, they are not public and subject to change.
518
519	=over 4
520
521	=cut
522
523	=item lookup => $name, @reply
524
525	Replies with the port ID of the specified well-known port, or C<undef>.
526
527	=item devnull => ...
528
529	Generic data sink/CPU heat conversion.
530
531	=item relay => $port, @msg
532
533	Simply forwards the message to the given port.
534
535	=item eval => $string[ @reply]
536
537	Evaluates the given string. If C<@reply> is given, then a message of the
538	form C<@reply, $@, @evalres> is sent.
539
540	Example: crash another node.
541
542	snd $othernode, eval => "exit";
543
544	=item time => @reply
545
546	Replies the the current node time to C<@reply>.
547
548	Example: tell the current node to send the current time to C<$myport> in a
549	C<timereply> message.
550
551	snd $NODE, time => $myport, timereply => 1, 2;
552	# => snd $myport, timereply => 1, 2, <time>
553
554	=back
555
556	=head1 AnyEvent::MP vs. Distributed Erlang	1004	=head1 AnyEvent::MP vs. Distributed Erlang
557		1005
558	AnyEvent::MP got lots of its ideas from distributed erlang (erlang node	1006	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
559	== aemp node, erlang process == aemp port), so many of the documents and	1007	== aemp node, Erlang process == aemp port), so many of the documents and
560	programming techniques employed by erlang apply to AnyEvent::MP. Here is a	1008	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
561	sample:	1009	sample:
562		1010
563	http://www.erlang.se/doc/programming_rules.shtml	1011	http://www.erlang.se/doc/programming_rules.shtml
564	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	1012	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
565	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6	1013	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
…		…
567		1015
568	Despite the similarities, there are also some important differences:	1016	Despite the similarities, there are also some important differences:
569		1017
570	=over 4	1018	=over 4
571		1019
572	=item * Node references contain the recipe on how to contact them.	1020	=item * Node IDs are arbitrary strings in AEMP.
573		1021
574	Erlang relies on special naming and DNS to work everywhere in the	1022	Erlang relies on special naming and DNS to work everywhere in the same
575	same way. AEMP relies on each node knowing it's own address(es), with	1023	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
576	convenience functionality.	1024	configuration or DNS), and possibly the addresses of some seed nodes, but
		1025	will otherwise discover other nodes (and their IDs) itself.
577		1026
578	This means that AEMP requires a less tightly controlled environment at the	1027	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
579	cost of longer node references and a slightly higher management overhead.	1028	uses "local ports are like remote ports".
		1029
		1030	The failure modes for local ports are quite different (runtime errors
		1031	only) then for remote ports - when a local port dies, you I<know> it dies,
		1032	when a connection to another node dies, you know nothing about the other
		1033	port.
		1034
		1035	Erlang pretends remote ports are as reliable as local ports, even when
		1036	they are not.
		1037
		1038	AEMP encourages a "treat remote ports differently" philosophy, with local
		1039	ports being the special case/exception, where transport errors cannot
		1040	occur.
580		1041
581	=item * Erlang uses processes and a mailbox, AEMP does not queue.	1042	=item * Erlang uses processes and a mailbox, AEMP does not queue.
582		1043
583	Erlang uses processes that selctively receive messages, and therefore	1044	Erlang uses processes that selectively receive messages out of order, and
584	needs a queue. AEMP is event based, queuing messages would serve no useful	1045	therefore needs a queue. AEMP is event based, queuing messages would serve
585	purpose.	1046	no useful purpose. For the same reason the pattern-matching abilities
		1047	of AnyEvent::MP are more limited, as there is little need to be able to
		1048	filter messages without dequeuing them.
586		1049
587	(But see L<Coro::MP> for a more erlang-like process model on top of AEMP).	1050	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1051	being event-based, while Erlang is process-based.
		1052
		1053	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1054	top of AEMP and Coro threads.
588		1055
589	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1056	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
590		1057
591	Sending messages in erlang is synchronous and blocks the process. AEMP	1058	Sending messages in Erlang is synchronous and blocks the process until
592	sends are immediate, connection establishment is handled in the	1059	a conenction has been established and the message sent (and so does not
593	background.	1060	need a queue that can overflow). AEMP sends return immediately, connection
		1061	establishment is handled in the background.
594		1062
595	=item * Erlang can silently lose messages, AEMP cannot.	1063	=item * Erlang suffers from silent message loss, AEMP does not.
596		1064
597	Erlang makes few guarantees on messages delivery - messages can get lost	1065	Erlang implements few guarantees on messages delivery - messages can get
598	without any of the processes realising it (i.e. you send messages a, b,	1066	lost without any of the processes realising it (i.e. you send messages a,
599	and c, and the other side only receives messages a and c).	1067	b, and c, and the other side only receives messages a and c).
600		1068
601	AEMP guarantees correct ordering, and the guarantee that there are no	1069	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1070	guarantee that after one message is lost, all following ones sent to the
		1071	same port are lost as well, until monitoring raises an error, so there are
602	holes in the message sequence.	1072	no silent "holes" in the message sequence.
603		1073
604	=item * In erlang, processes can be declared dead and later be found to be	1074	If you want your software to be very reliable, you have to cope with
605	alive.	1075	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
606		1076	simply tries to work better in common error cases, such as when a network
607	In erlang it can happen that a monitored process is declared dead and	1077	link goes down.
608	linked processes get killed, but later it turns out that the process is
609	still alive - and can receive messages.
610
611	In AEMP, when port monitoring detects a port as dead, then that port will
612	eventually be killed - it cannot happen that a node detects a port as dead
613	and then later sends messages to it, finding it is still alive.
614		1078
615	=item * Erlang can send messages to the wrong port, AEMP does not.	1079	=item * Erlang can send messages to the wrong port, AEMP does not.
616		1080
617	In erlang it is quite possible that a node that restarts reuses a process	1081	In Erlang it is quite likely that a node that restarts reuses an Erlang
618	ID known to other nodes for a completely different process, causing	1082	process ID known to other nodes for a completely different process,
619	messages destined for that process to end up in an unrelated process.	1083	causing messages destined for that process to end up in an unrelated
		1084	process.
620		1085
621	AEMP never reuses port IDs, so old messages or old port IDs floating	1086	AEMP does not reuse port IDs, so old messages or old port IDs floating
622	around in the network will not be sent to an unrelated port.	1087	around in the network will not be sent to an unrelated port.
623		1088
624	=item * Erlang uses unprotected connections, AEMP uses secure	1089	=item * Erlang uses unprotected connections, AEMP uses secure
625	authentication and can use TLS.	1090	authentication and can use TLS.
626		1091
627	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1092	AEMP can use a proven protocol - TLS - to protect connections and
628	securely authenticate nodes.	1093	securely authenticate nodes.
629		1094
630	=item * The AEMP protocol is optimised for both text-based and binary	1095	=item * The AEMP protocol is optimised for both text-based and binary
631	communications.	1096	communications.
632		1097
633	The AEMP protocol, unlike the erlang protocol, supports both	1098	The AEMP protocol, unlike the Erlang protocol, supports both programming
634	language-independent text-only protocols (good for debugging) and binary,	1099	language independent text-only protocols (good for debugging), and binary,
635	language-specific serialisers (e.g. Storable).	1100	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1101	used, the protocol is actually completely text-based.
636		1102
637	It has also been carefully designed to be implementable in other languages	1103	It has also been carefully designed to be implementable in other languages
638	with a minimum of work while gracefully degrading fucntionality to make the	1104	with a minimum of work while gracefully degrading functionality to make the
639	protocol simple.	1105	protocol simple.
640		1106
		1107	=item * AEMP has more flexible monitoring options than Erlang.
		1108
		1109	In Erlang, you can chose to receive I<all> exit signals as messages or
		1110	I<none>, there is no in-between, so monitoring single Erlang processes is
		1111	difficult to implement.
		1112
		1113	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1114	between automatic kill, exit message or callback on a per-port basis.
		1115
		1116	=item * Erlang tries to hide remote/local connections, AEMP does not.
		1117
		1118	Monitoring in Erlang is not an indicator of process death/crashes, in the
		1119	same way as linking is (except linking is unreliable in Erlang).
		1120
		1121	In AEMP, you don't "look up" registered port names or send to named ports
		1122	that might or might not be persistent. Instead, you normally spawn a port
		1123	on the remote node. The init function monitors you, and you monitor the
		1124	remote port. Since both monitors are local to the node, they are much more
		1125	reliable (no need for C<spawn_link>).
		1126
		1127	This also saves round-trips and avoids sending messages to the wrong port
		1128	(hard to do in Erlang).
		1129
641	=back	1130	=back
642		1131
		1132	=head1 RATIONALE
		1133
		1134	=over 4
		1135
		1136	=item Why strings for port and node IDs, why not objects?
		1137
		1138	We considered "objects", but found that the actual number of methods
		1139	that can be called are quite low. Since port and node IDs travel over
		1140	the network frequently, the serialising/deserialising would add lots of
		1141	overhead, as well as having to keep a proxy object everywhere.
		1142
		1143	Strings can easily be printed, easily serialised etc. and need no special
		1144	procedures to be "valid".
		1145
		1146	And as a result, a port with just a default receiver consists of a single
		1147	code reference stored in a global hash - it can't become much cheaper.
		1148
		1149	=item Why favour JSON, why not a real serialising format such as Storable?
		1150
		1151	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1152	format, but currently there is no way to make a node use Storable by
		1153	default (although all nodes will accept it).
		1154
		1155	The default framing protocol is JSON because a) JSON::XS is many times
		1156	faster for small messages and b) most importantly, after years of
		1157	experience we found that object serialisation is causing more problems
		1158	than it solves: Just like function calls, objects simply do not travel
		1159	easily over the network, mostly because they will always be a copy, so you
		1160	always have to re-think your design.
		1161
		1162	Keeping your messages simple, concentrating on data structures rather than
		1163	objects, will keep your messages clean, tidy and efficient.
		1164
		1165	=back
		1166
643	=head1 SEE ALSO	1167	=head1 SEE ALSO
		1168
		1169	L<AnyEvent::MP::Intro> - a gentle introduction.
		1170
		1171	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1172
		1173	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1174	your applications.
		1175
		1176	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1177
		1178	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1179	all nodes.
644		1180
645	L<AnyEvent>.	1181	L<AnyEvent>.
646		1182
647	=head1 AUTHOR	1183	=head1 AUTHOR
648		1184

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