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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.30 by root, Tue Aug 4 23:35:51 2009 UTC vs.
Revision 1.123 by root, Thu Mar 1 19:37:59 2012 UTC

…		…
1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent::MP - multi-processing/message-passing framework	3	AnyEvent::MP - erlang-style multi-processing/message-passing framework
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::MP;	7	use AnyEvent::MP;
8		8
9	$NODE # contains this node's noderef	9	$NODE # contains this node's node ID
10	NODE # returns this node's noderef	10	NODE # returns this node's node ID
11	NODE $port # returns the noderef of the port
12		11
		12	$SELF # receiving/own port id in rcv callbacks
		13
		14	# initialise the node so it can send/receive messages
		15	configure;
		16
		17	# ports are message destinations
		18
		19	# sending messages
13	snd $port, type => data...;	20	snd $port, type => data...;
		21	snd $port, @msg;
		22	snd @msg_with_first_element_being_a_port;
14		23
15	$SELF # receiving/own port id in rcv callbacks	24	# creating/using ports, the simple way
		25	my $simple_port = port { my @msg = @_ };
16		26
17	rcv $port, smartmatch => $cb->($port, @msg);	27	# creating/using ports, tagged message matching
18		28	my $port = port;
19	# examples:
20	rcv $port2, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
21	rcv $port1, pong => sub { warn "pong received\n" };	30	rcv $port, pong => sub { warn "pong received\n" };
22	snd $port2, ping => $port1;
23		31
24	# more, smarter, matches (_any_ is exported by this module)	32	# create a port on another node
25	rcv $port, [child_died => $pid] => sub { ...	33	my $port = spawn $node, $initfunc, @initdata;
26	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3	34
		35	# destroy a port again
		36	kil $port; # "normal" kill
		37	kil $port, my_error => "everything is broken"; # error kill
		38
		39	# monitoring
		40	mon $localport, $cb->(@msg) # callback is invoked on death
		41	mon $localport, $otherport # kill otherport on abnormal death
		42	mon $localport, $otherport, @msg # send message on death
		43
		44	# temporarily execute code in port context
		45	peval $port, sub { die "kill the port!" };
		46
		47	# execute callbacks in $SELF port context
		48	my $timer = AE::timer 1, 0, psub {
		49	die "kill the port, delayed";
		50	};
		51
		52	=head1 CURRENT STATUS
		53
		54	bin/aemp - stable.
		55	AnyEvent::MP - stable API, should work.
		56	AnyEvent::MP::Intro - explains most concepts.
		57	AnyEvent::MP::Kernel - mostly stable API.
		58	AnyEvent::MP::Global - stable API.
27		59
28	=head1 DESCRIPTION	60	=head1 DESCRIPTION
29		61
30	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
31		63
32	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
33	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
34		66
35	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	67	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
36	manual page.	68	manual page and the examples under F<eg/>.
37
38	At the moment, this module family is severly broken and underdocumented,
39	so do not use. This was uploaded mainly to reserve the CPAN namespace -
40	stay tuned! The basic API should be finished, however.
41		69
42	=head1 CONCEPTS	70	=head1 CONCEPTS
43		71
44	=over 4	72	=over 4
45		73
46	=item port	74	=item port
47		75
48	A port is something you can send messages to (with the C<snd> function).	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 ();
102		190
103	use base "Exporter";	191	use base "Exporter";
104		192
105	our $VERSION = '0.1';	193	our $VERSION = $AnyEvent::MP::Config::VERSION;
		194
106	our @EXPORT = qw(	195	our @EXPORT = qw(
107	NODE $NODE *SELF node_of _any_	196	NODE $NODE *SELF node_of after
108	resolve_node	197	configure
109	become_slave become_public	198	snd rcv mon mon_guard kil psub peval spawn cal
110	snd rcv mon kil reg psub
111	port	199	port
112	);	200	);
113		201
114	our $SELF;	202	our $SELF;
115		203
…		…
119	kil $SELF, die => $msg;	207	kil $SELF, die => $msg;
120	}	208	}
121		209
122	=item $thisnode = NODE / $NODE	210	=item $thisnode = NODE / $NODE
123		211
124	The C<NODE> function returns, and the C<$NODE> variable contains	212	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	213	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	214	a call to C<configure>.
127	identifiers become invalid.
128		215
129	=item $noderef = node_of $portid	216	=item $nodeid = node_of $port
130		217
131	Extracts and returns the noderef from a portid or a noderef.	218	Extracts and returns the node ID from a port ID or a node ID.
132		219
133	=item $cv = resolve_node $noderef	220	=item configure $profile, key => value...
134		221
135	Takes an unresolved node reference that may contain hostnames and	222	=item configure key => value...
136	abbreviated IDs, resolves all of them and returns a resolved node
137	reference.
138		223
139	In addition to C<address:port> pairs allowed in resolved noderefs, the	224	Before a node can talk to other nodes on the network (i.e. enter
140	following forms are supported:	225	"distributed mode") it has to configure itself - the minimum a node needs
		226	to know is its own name, and optionally it should know the addresses of
		227	some other nodes in the network to discover other nodes.
		228
		229	This function configures a node - it must be called exactly once (or
		230	never) before calling other AnyEvent::MP functions.
		231
		232	The key/value pairs are basically the same ones as documented for the
		233	F<aemp> command line utility (sans the set/del prefix), with two additions:
141		234
142	=over 4	235	=over 4
143		236
144	=item the empty string	237	=item norc => $boolean (default false)
145		238
146	An empty-string component gets resolved as if the default port (4040) was	239	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
147	specified.	240	be consulted - all configuraiton options must be specified in the
		241	C<configure> call.
148		242
149	=item naked port numbers (e.g. C<1234>)	243	=item force => $boolean (default false)
150		244
151	These are resolved by prepending the local nodename and a colon, to be	245	IF true, then the values specified in the C<configure> will take
152	further resolved.	246	precedence over any values configured via the rc file. The default is for
153		247	the rc file to override any options specified in the program.
154	=item hostnames (e.g. C<localhost:1234>, C<localhost>)
155
156	These are resolved by using AnyEvent::DNS to resolve them, optionally
157	looking up SRV records for the C<aemp=4040> port, if no port was
158	specified.
159		248
160	=back	249	=back
		250
		251	=over 4
		252
		253	=item step 1, gathering configuration from profiles
		254
		255	The function first looks up a profile in the aemp configuration (see the
		256	L<aemp> commandline utility). The profile name can be specified via the
		257	named C<profile> parameter or can simply be the first parameter). If it is
		258	missing, then the nodename (F<uname -n>) will be used as profile name.
		259
		260	The profile data is then gathered as follows:
		261
		262	First, all remaining key => value pairs (all of which are conveniently
		263	undocumented at the moment) will be interpreted as configuration
		264	data. Then they will be overwritten by any values specified in the global
		265	default configuration (see the F<aemp> utility), then the chain of
		266	profiles chosen by the profile name (and any C<parent> attributes).
		267
		268	That means that the values specified in the profile have highest priority
		269	and the values specified directly via C<configure> have lowest priority,
		270	and can only be used to specify defaults.
		271
		272	If the profile specifies a node ID, then this will become the node ID of
		273	this process. If not, then the profile name will be used as node ID, with
		274	a slash (C</>) attached.
		275
		276	If the node ID (or profile name) ends with a slash (C</>), then a random
		277	string is appended to make it unique.
		278
		279	=item step 2, bind listener sockets
		280
		281	The next step is to look up the binds in the profile, followed by binding
		282	aemp protocol listeners on all binds specified (it is possible and valid
		283	to have no binds, meaning that the node cannot be contacted form the
		284	outside. This means the node cannot talk to other nodes that also have no
		285	binds, but it can still talk to all "normal" nodes).
		286
		287	If the profile does not specify a binds list, then a default of C<*> is
		288	used, meaning the node will bind on a dynamically-assigned port on every
		289	local IP address it finds.
		290
		291	=item step 3, connect to seed nodes
		292
		293	As the last step, the seed ID list from the profile is passed to the
		294	L<AnyEvent::MP::Global> module, which will then use it to keep
		295	connectivity with at least one node at any point in time.
		296
		297	=back
		298
		299	Example: become a distributed node using the local node name as profile.
		300	This should be the most common form of invocation for "daemon"-type nodes.
		301
		302	configure
		303
		304	Example: become an anonymous node. This form is often used for commandline
		305	clients.
		306
		307	configure nodeid => "anon/";
		308
		309	Example: configure a node using a profile called seed, which is suitable
		310	for a seed node as it binds on all local addresses on a fixed port (4040,
		311	customary for aemp).
		312
		313	# use the aemp commandline utility
		314	# aemp profile seed binds '*:4040'
		315
		316	# then use it
		317	configure profile => "seed";
		318
		319	# or simply use aemp from the shell again:
		320	# aemp run profile seed
		321
		322	# or provide a nicer-to-remember nodeid
		323	# aemp run profile seed nodeid "$(hostname)"
161		324
162	=item $SELF	325	=item $SELF
163		326
164	Contains the current port id while executing C<rcv> callbacks or C<psub>	327	Contains the current port id while executing C<rcv> callbacks or C<psub>
165	blocks.	328	blocks.
166		329
167	=item SELF, %SELF, @SELF...	330	=item *SELF, SELF, %SELF, @SELF...
168		331
169	Due to some quirks in how perl exports variables, it is impossible to	332	Due to some quirks in how perl exports variables, it is impossible to
170	just export C<$SELF>, all the symbols called C<SELF> are exported by this	333	just export C<$SELF>, all the symbols named C<SELF> are exported by this
171	module, but only C<$SELF> is currently used.	334	module, but only C<$SELF> is currently used.
172		335
173	=item snd $portid, type => @data	336	=item snd $port, type => @data
174		337
175	=item snd $portid, @msg	338	=item snd $port, @msg
176		339
177	Send the given message to the given port ID, which can identify either	340	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	341	local or a remote port, and must be a port ID.
179	stringifies a sa port ID (such as a port object :).
180		342
181	While the message can be about anything, it is highly recommended to use a	343	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	344	use a string as first element (a port ID, or some word that indicates a
183	type etc.).	345	request type etc.) and to consist if only simple perl values (scalars,
		346	arrays, hashes) - if you think you need to pass an object, think again.
184		347
185	The message data effectively becomes read-only after a call to this	348	The message data logically becomes read-only after a call to this
186	function: modifying any argument is not allowed and can cause many	349	function: modifying any argument (or values referenced by them) is
187	problems.	350	forbidden, as there can be considerable time between the call to C<snd>
		351	and the time the message is actually being serialised - in fact, it might
		352	never be copied as within the same process it is simply handed to the
		353	receiving port.
188		354
189	The type of data you can transfer depends on the transport protocol: when	355	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	356	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	357	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	358	that Storable can serialise and deserialise is allowed, and for the local
193	node, anything can be passed.	359	node, anything can be passed. Best rely only on the common denominator of
		360	these.
194		361
195	=item kil $portid[, @reason]	362	=item $local_port = port
196		363
197	Kill the specified port with the given C<@reason>.	364	Create a new local port object and returns its port ID. Initially it has
		365	no callbacks set and will throw an error when it receives messages.
198		366
199	If no C<@reason> is specified, then the port is killed "normally" (linked	367	=item $local_port = port { my @msg = @_ }
200	ports will not be kileld, or even notified).
201		368
202	Otherwise, linked ports get killed with the same reason (second form of	369	Creates a new local port, and returns its ID. Semantically the same as
203	C<mon>, see below).	370	creating a port and calling C<rcv $port, $callback> on it.
204		371
205	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	372	The block will be called for every message received on the port, with the
206	will be reported as reason C<< die => $@ >>.	373	global variable C<$SELF> set to the port ID. Runtime errors will cause the
		374	port to be C<kil>ed. The message will be passed as-is, no extra argument
		375	(i.e. no port ID) will be passed to the callback.
207		376
208	Transport/communication errors are reported as C<< transport_error =>	377	If you want to stop/destroy the port, simply C<kil> it:
209	$message >>.
210		378
211	=item $guard = mon $portid, $cb->(@reason)	379	my $port = port {
		380	my @msg = @_;
		381	...
		382	kil $SELF;
		383	};
212		384
213	=item $guard = mon $portid, $otherport	385	=cut
214		386
215	=item $guard = mon $portid, $otherport, @msg	387	sub rcv($@);
216		388
		389	sub _kilme {
		390	die "received message on port without callback";
		391	}
		392
		393	sub port(;&) {
		394	my $id = $UNIQ . ++$ID;
		395	my $port = "$NODE#$id";
		396
		397	rcv $port, shift \|\| \&_kilme;
		398
		399	$port
		400	}
		401
		402	=item rcv $local_port, $callback->(@msg)
		403
		404	Replaces the default callback on the specified port. There is no way to
		405	remove the default callback: use C<sub { }> to disable it, or better
		406	C<kil> the port when it is no longer needed.
		407
		408	The global C<$SELF> (exported by this module) contains C<$port> while
		409	executing the callback. Runtime errors during callback execution will
		410	result in the port being C<kil>ed.
		411
		412	The default callback received all messages not matched by a more specific
		413	C<tag> match.
		414
		415	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
		416
		417	Register (or replace) callbacks to be called on messages starting with the
		418	given tag on the given port (and return the port), or unregister it (when
		419	C<$callback> is C<$undef> or missing). There can only be one callback
		420	registered for each tag.
		421
		422	The original message will be passed to the callback, after the first
		423	element (the tag) has been removed. The callback will use the same
		424	environment as the default callback (see above).
		425
		426	Example: create a port and bind receivers on it in one go.
		427
		428	my $port = rcv port,
		429	msg1 => sub { ... },
		430	msg2 => sub { ... },
		431	;
		432
		433	Example: create a port, bind receivers and send it in a message elsewhere
		434	in one go:
		435
		436	snd $otherport, reply =>
		437	rcv port,
		438	msg1 => sub { ... },
		439	...
		440	;
		441
		442	Example: temporarily register a rcv callback for a tag matching some port
		443	(e.g. for an rpc reply) and unregister it after a message was received.
		444
		445	rcv $port, $otherport => sub {
		446	my @reply = @_;
		447
		448	rcv $SELF, $otherport;
		449	};
		450
		451	=cut
		452
		453	sub rcv($@) {
		454	my $port = shift;
		455	my ($nodeid, $portid) = split /#/, $port, 2;
		456
		457	$NODE{$nodeid} == $NODE{""}
		458	or Carp::croak "$port: rcv can only be called on local ports, caught";
		459
		460	while (@_) {
		461	if (ref $_[0]) {
		462	if (my $self = $PORT_DATA{$portid}) {
		463	"AnyEvent::MP::Port" eq ref $self
		464	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		465
		466	$self->[0] = shift;
		467	} else {
		468	my $cb = shift;
		469	$PORT{$portid} = sub {
		470	local $SELF = $port;
		471	eval { &$cb }; _self_die if $@;
		472	};
		473	}
		474	} elsif (defined $_[0]) {
		475	my $self = $PORT_DATA{$portid} \|\|= do {
		476	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
		477
		478	$PORT{$portid} = sub {
		479	local $SELF = $port;
		480
		481	if (my $cb = $self->[1]{$_[0]}) {
		482	shift;
		483	eval { &$cb }; _self_die if $@;
		484	} else {
		485	&{ $self->[0] };
		486	}
		487	};
		488
		489	$self
		490	};
		491
		492	"AnyEvent::MP::Port" eq ref $self
		493	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		494
		495	my ($tag, $cb) = splice @_, 0, 2;
		496
		497	if (defined $cb) {
		498	$self->[1]{$tag} = $cb;
		499	} else {
		500	delete $self->[1]{$tag};
		501	}
		502	}
		503	}
		504
		505	$port
		506	}
		507
		508	=item peval $port, $coderef[, @args]
		509
		510	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		511	when the code throews an exception the C<$port> will be killed.
		512
		513	Any remaining args will be passed to the callback. Any return values will
		514	be returned to the caller.
		515
		516	This is useful when you temporarily want to execute code in the context of
		517	a port.
		518
		519	Example: create a port and run some initialisation code in it's context.
		520
		521	my $port = port { ... };
		522
		523	peval $port, sub {
		524	init
		525	or die "unable to init";
		526	};
		527
		528	=cut
		529
		530	sub peval($$) {
		531	local $SELF = shift;
		532	my $cb = shift;
		533
		534	if (wantarray) {
		535	my @res = eval { &$cb };
		536	_self_die if $@;
		537	@res
		538	} else {
		539	my $res = eval { &$cb };
		540	_self_die if $@;
		541	$res
		542	}
		543	}
		544
		545	=item $closure = psub { BLOCK }
		546
		547	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
		548	closure is executed, sets up the environment in the same way as in C<rcv>
		549	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		550
		551	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		552	BLOCK }, @_ } >>.
		553
		554	This is useful when you register callbacks from C<rcv> callbacks:
		555
		556	rcv delayed_reply => sub {
		557	my ($delay, @reply) = @_;
		558	my $timer = AE::timer $delay, 0, psub {
		559	snd @reply, $SELF;
		560	};
		561	};
		562
		563	=cut
		564
		565	sub psub(&) {
		566	my $cb = shift;
		567
		568	my $port = $SELF
		569	or Carp::croak "psub can only be called from within rcv or psub callbacks, not";
		570
		571	sub {
		572	local $SELF = $port;
		573
		574	if (wantarray) {
		575	my @res = eval { &$cb };
		576	_self_die if $@;
		577	@res
		578	} else {
		579	my $res = eval { &$cb };
		580	_self_die if $@;
		581	$res
		582	}
		583	}
		584	}
		585
		586	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
		587
		588	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
		589
		590	=item $guard = mon $port # kill $SELF when $port dies
		591
		592	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		593
217	Monitor the given port and do something when the port is killed.	594	Monitor the given port and do something when the port is killed or
		595	messages to it were lost, and optionally return a guard that can be used
		596	to stop monitoring again.
218		597
219	In the first form, the callback is simply called with any number	598	In the first form (callback), the callback is simply called with any
220	of C<@reason> elements (no @reason means that the port was deleted	599	number of C<@reason> elements (no @reason means that the port was deleted
221	"normally"). Note also that I<< the callback B<must> never die >>, so use	600	"normally"). Note also that I<< the callback B<must> never die >>, so use
222	C<eval> if unsure.	601	C<eval> if unsure.
223		602
224	In the second form, the other port will be C<kil>'ed with C<@reason>, iff	603	In the second form (another port given), the other port (C<$rcvport>)
225	a @reason was specified, i.e. on "normal" kils nothing happens, while	604	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.	605	"normal" kils nothing happens, while under all other conditions, the other
		606	port is killed with the same reason.
227		607
		608	The third form (kill self) is the same as the second form, except that
		609	C<$rvport> defaults to C<$SELF>.
		610
228	In the last form, a message of the form C<@msg, @reason> will be C<snd>.	611	In the last form (message), a message of the form C<@msg, @reason> will be
		612	C<snd>.
		613
		614	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		615	alert was raised), they are removed and will not trigger again.
		616
		617	As a rule of thumb, monitoring requests should always monitor a port from
		618	a local port (or callback). The reason is that kill messages might get
		619	lost, just like any other message. Another less obvious reason is that
		620	even monitoring requests can get lost (for example, when the connection
		621	to the other node goes down permanently). When monitoring a port locally
		622	these problems do not exist.
		623
		624	C<mon> effectively guarantees that, in the absence of hardware failures,
		625	after starting the monitor, either all messages sent to the port will
		626	arrive, or the monitoring action will be invoked after possible message
		627	loss has been detected. No messages will be lost "in between" (after
		628	the first lost message no further messages will be received by the
		629	port). After the monitoring action was invoked, further messages might get
		630	delivered again.
		631
		632	Inter-host-connection timeouts and monitoring depend on the transport
		633	used. The only transport currently implemented is TCP, and AnyEvent::MP
		634	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		635	non-idle connection, and usually around two hours for idle connections).
		636
		637	This means that monitoring is good for program errors and cleaning up
		638	stuff eventually, but they are no replacement for a timeout when you need
		639	to ensure some maximum latency.
229		640
230	Example: call a given callback when C<$port> is killed.	641	Example: call a given callback when C<$port> is killed.
231		642
232	mon $port, sub { warn "port died because of <@_>\n" };	643	mon $port, sub { warn "port died because of <@_>\n" };
233		644
234	Example: kill ourselves when C<$port> is killed abnormally.	645	Example: kill ourselves when C<$port> is killed abnormally.
235		646
236	mon $port, $self;	647	mon $port;
237		648
238	Example: send us a restart message another C<$port> is killed.	649	Example: send us a restart message when another C<$port> is killed.
239		650
240	mon $port, $self => "restart";	651	mon $port, $self => "restart";
241		652
242	=cut	653	=cut
243		654
244	sub mon {	655	sub mon {
245	my ($noderef, $port) = split /#/, shift, 2;	656	my ($nodeid, $port) = split /#/, shift, 2;
246		657
247	my $node = $NODE{$noderef} \|\| add_node $noderef;	658	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
248		659
249	my $cb = shift;	660	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
250		661
251	unless (ref $cb) {	662	unless (ref $cb) {
252	if (@_) {	663	if (@_) {
253	# send a kill info message	664	# send a kill info message
254	my (@msg) = ($cb, @_);	665	my (@msg) = ($cb, @_);
…		…
261	}	672	}
262		673
263	$node->monitor ($port, $cb);	674	$node->monitor ($port, $cb);
264		675
265	defined wantarray	676	defined wantarray
266	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	677	and ($cb += 0, AnyEvent::Util::guard { $node->unmonitor ($port, $cb) })
267	}	678	}
268		679
269	=item $guard = mon_guard $port, $ref, $ref...	680	=item $guard = mon_guard $port, $ref, $ref...
270		681
271	Monitors the given C<$port> and keeps the passed references. When the port	682	Monitors the given C<$port> and keeps the passed references. When the port
272	is killed, the references will be freed.	683	is killed, the references will be freed.
273		684
274	Optionally returns a guard that will stop the monitoring.	685	Optionally returns a guard that will stop the monitoring.
275		686
276	This function is useful when you create e.g. timers or other watchers and	687	This function is useful when you create e.g. timers or other watchers and
277	want to free them when the port gets killed:	688	want to free them when the port gets killed (note the use of C<psub>):
278		689
279	$port->rcv (start => sub {	690	$port->rcv (start => sub {
280	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	691	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
281	undef $timer if 0.9 < rand;	692	undef $timer if 0.9 < rand;
282	});	693	});
283	});	694	});
284		695
285	=cut	696	=cut
286		697
287	sub mon_guard {	698	sub mon_guard {
288	my ($port, @refs) = @_;	699	my ($port, @refs) = @_;
289		700
		701	#TODO: mon-less form?
		702
290	mon $port, sub { 0 && @refs }	703	mon $port, sub { 0 && @refs }
291	}	704	}
292		705
293	=item lnk $port1, $port2	706	=item kil $port[, @reason]
294		707
295	Link two ports. This is simply a shorthand for:	708	Kill the specified port with the given C<@reason>.
296		709
297	mon $port1, $port2;	710	If no C<@reason> is specified, then the port is killed "normally" -
298	mon $port2, $port1;	711	monitor callback will be invoked, but the kil will not cause linked ports
		712	(C<mon $mport, $lport> form) to get killed.
299		713
300	It means that if either one is killed abnormally, the other one gets	714	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
301	killed as well.	715	form) get killed with the same reason.
302		716
303	=item $local_port = port	717	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
		718	will be reported as reason C<< die => $@ >>.
304		719
305	Create a new local port object that supports message matching.	720	Transport/communication errors are reported as C<< transport_error =>
		721	$message >>.
306		722
307	=item $portid = port { my @msg = @_; $finished }	723	=cut
308		724
309	Creates a "mini port", that is, a very lightweight port without any	725	=item $port = spawn $node, $initfunc[, @initdata]
310	pattern matching behind it, and returns its ID.
311		726
312	The block will be called for every message received on the port. When the	727	Creates a port on the node C<$node> (which can also be a port ID, in which
313	callback returns a true value its job is considered "done" and the port	728	case it's the node where that port resides).
314	will be destroyed. Otherwise it will stay alive.
315		729
316	The message will be passed as-is, no extra argument (i.e. no port id) will	730	The port ID of the newly created port is returned immediately, and it is
317	be passed to the callback.	731	possible to immediately start sending messages or to monitor the port.
318		732
319	If you need the local port id in the callback, this works nicely:	733	After the port has been created, the init function is called on the remote
		734	node, in the same context as a C<rcv> callback. This function must be a
		735	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		736	specify a function in the main program, use C<::name>.
320		737
321	my $port; $port = miniport {	738	If the function doesn't exist, then the node tries to C<require>
322	snd $otherport, reply => $port;	739	the package, then the package above the package and so on (e.g.
		740	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		741	exists or it runs out of package names.
		742
		743	The init function is then called with the newly-created port as context
		744	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		745	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		746	the port might not get created.
		747
		748	A common idiom is to pass a local port, immediately monitor the spawned
		749	port, and in the remote init function, immediately monitor the passed
		750	local port. This two-way monitoring ensures that both ports get cleaned up
		751	when there is a problem.
		752
		753	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		754	caller before C<spawn> returns (by delaying invocation when spawn is
		755	called for the local node).
		756
		757	Example: spawn a chat server port on C<$othernode>.
		758
		759	# this node, executed from within a port context:
		760	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		761	mon $server;
		762
		763	# init function on C<$othernode>
		764	sub connect {
		765	my ($srcport) = @_;
		766
		767	mon $srcport;
		768
		769	rcv $SELF, sub {
		770	...
		771	};
		772	}
		773
		774	=cut
		775
		776	sub _spawn {
		777	my $port = shift;
		778	my $init = shift;
		779
		780	# rcv will create the actual port
		781	local $SELF = "$NODE#$port";
		782	eval {
		783	&{ load_func $init }
323	};	784	};
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 $@;	785	_self_die if $@;
		786	}
		787
		788	sub spawn(@) {
		789	my ($nodeid, undef) = split /#/, shift, 2;
		790
		791	my $id = $RUNIQ . ++$ID;
		792
		793	$_[0] =~ /::/
		794	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		795
		796	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		797
		798	"$nodeid#$id"
		799	}
		800
		801
		802	=item after $timeout, @msg
		803
		804	=item after $timeout, $callback
		805
		806	Either sends the given message, or call the given callback, after the
		807	specified number of seconds.
		808
		809	This is simply a utility function that comes in handy at times - the
		810	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		811	so it may go away in the future.
		812
		813	=cut
		814
		815	sub after($@) {
		816	my ($timeout, @action) = @_;
		817
		818	my $t; $t = AE::timer $timeout, 0, sub {
		819	undef $t;
		820	ref $action[0]
		821	? $action[0]()
		822	: snd @action;
		823	};
		824	}
		825
		826	=item cal $port, @msg, $callback[, $timeout]
		827
		828	A simple form of RPC - sends a message to the given C<$port> with the
		829	given contents (C<@msg>), but adds a reply port to the message.
		830
		831	The reply port is created temporarily just for the purpose of receiving
		832	the reply, and will be C<kil>ed when no longer needed.
		833
		834	A reply message sent to the port is passed to the C<$callback> as-is.
		835
		836	If an optional time-out (in seconds) is given and it is not C<undef>,
		837	then the callback will be called without any arguments after the time-out
		838	elapsed and the port is C<kil>ed.
		839
		840	If no time-out is given (or it is C<undef>), then the local port will
		841	monitor the remote port instead, so it eventually gets cleaned-up.
		842
		843	Currently this function returns the temporary port, but this "feature"
		844	might go in future versions unless you can make a convincing case that
		845	this is indeed useful for something.
		846
		847	=cut
		848
		849	sub cal(@) {
		850	my $timeout = ref $_[-1] ? undef : pop;
		851	my $cb = pop;
		852
		853	my $port = port {
		854	undef $timeout;
		855	kil $SELF;
		856	&$cb;
		857	};
		858
		859	if (defined $timeout) {
		860	$timeout = AE::timer $timeout, 0, sub {
		861	undef $timeout;
		862	kil $port;
		863	$cb->();
340	};	864	};
341	} else {	865	} else {
342	my $self = bless {	866	mon $_[0], sub {
343	id => "$NODE#$id",	867	kil $port;
344	}, "AnyEvent::MP::Port";	868	$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	};	869	};
370	}	870	}
371		871
		872	push @_, $port;
		873	&snd;
		874
372	$port	875	$port
373	}	876	}
374		877
375	=item reg $portid, $name
376
377	Registers the given port under the name C<$name>. If the name already
378	exists it is replaced.
379
380	A port can only be registered under one well known name.
381
382	A port automatically becomes unregistered when it is killed.
383
384	=cut
385
386	sub reg(@) {
387	my ($portid, $name) = @_;
388
389	$REG{$name} = $portid;
390	}
391
392	=item rcv $portid, tagstring => $callback->(@msg), ...
393
394	=item rcv $portid, $smartmatch => $callback->(@msg), ...
395
396	=item rcv $portid, [$smartmatch...] => $callback->(@msg), ...
397
398	Register callbacks to be called on matching messages on the given port.
399
400	The callback has to return a true value when its work is done, after
401	which is will be removed, or a false value in which case it will stay
402	registered.
403
404	The global C<$SELF> (exported by this module) contains C<$portid> while
405	executing the callback.
406
407	Runtime errors wdurign callback execution will result in the port being
408	C<kil>ed.
409
410	If the match is an array reference, then it will be matched against the
411	first elements of the message, otherwise only the first element is being
412	matched.
413
414	Any element in the match that is specified as C<_any_> (a function
415	exported by this module) matches any single element of the message.
416
417	While not required, it is highly recommended that the first matching
418	element is a string identifying the message. The one-string-only match is
419	also the most efficient match (by far).
420
421	=cut
422
423	sub rcv($@) {
424	my ($noderef, $port) = split /#/, shift, 2;
425
426	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}
427	or Carp::croak "$noderef#$port: rcv can only be called on local ports, caught";
428
429	my $self = $PORT_DATA{$port}
430	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";
431
432	"AnyEvent::MP::Port" eq ref $self
433	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";
434
435	while (@_) {
436	my ($match, $cb) = splice @_, 0, 2;
437
438	if (!ref $match) {
439	push @{ $self->{rc0}{$match} }, [$cb];
440	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
441	my ($type, @match) = @$match;
442	@match
443	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
444	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
445	} else {
446	push @{ $self->{any} }, [$cb, $match];
447	}
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	};
465
466	=cut
467
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	878	=back
490		879
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	880	=head1 AnyEvent::MP vs. Distributed Erlang
557		881
558	AnyEvent::MP got lots of its ideas from distributed erlang (erlang node	882	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	883	== 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	884	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
561	sample:	885	sample:
562		886
563	http://www.erlang.se/doc/programming_rules.shtml	887	http://www.erlang.se/doc/programming_rules.shtml
564	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	888	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	889	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
…		…
567		891
568	Despite the similarities, there are also some important differences:	892	Despite the similarities, there are also some important differences:
569		893
570	=over 4	894	=over 4
571		895
572	=item * Node references contain the recipe on how to contact them.	896	=item * Node IDs are arbitrary strings in AEMP.
573		897
574	Erlang relies on special naming and DNS to work everywhere in the	898	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	899	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
576	convenience functionality.	900	configuration or DNS), and possibly the addresses of some seed nodes, but
		901	will otherwise discover other nodes (and their IDs) itself.
577		902
578	This means that AEMP requires a less tightly controlled environment at the	903	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
579	cost of longer node references and a slightly higher management overhead.	904	uses "local ports are like remote ports".
		905
		906	The failure modes for local ports are quite different (runtime errors
		907	only) then for remote ports - when a local port dies, you I<know> it dies,
		908	when a connection to another node dies, you know nothing about the other
		909	port.
		910
		911	Erlang pretends remote ports are as reliable as local ports, even when
		912	they are not.
		913
		914	AEMP encourages a "treat remote ports differently" philosophy, with local
		915	ports being the special case/exception, where transport errors cannot
		916	occur.
580		917
581	=item * Erlang uses processes and a mailbox, AEMP does not queue.	918	=item * Erlang uses processes and a mailbox, AEMP does not queue.
582		919
583	Erlang uses processes that selctively receive messages, and therefore	920	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	921	therefore needs a queue. AEMP is event based, queuing messages would serve
585	purpose.	922	no useful purpose. For the same reason the pattern-matching abilities
		923	of AnyEvent::MP are more limited, as there is little need to be able to
		924	filter messages without dequeuing them.
586		925
587	(But see L<Coro::MP> for a more erlang-like process model on top of AEMP).	926	This is not a philosophical difference, but simply stems from AnyEvent::MP
		927	being event-based, while Erlang is process-based.
		928
		929	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		930	top of AEMP and Coro threads.
588		931
589	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	932	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
590		933
591	Sending messages in erlang is synchronous and blocks the process. AEMP	934	Sending messages in Erlang is synchronous and blocks the process until
592	sends are immediate, connection establishment is handled in the	935	a conenction has been established and the message sent (and so does not
593	background.	936	need a queue that can overflow). AEMP sends return immediately, connection
		937	establishment is handled in the background.
594		938
595	=item * Erlang can silently lose messages, AEMP cannot.	939	=item * Erlang suffers from silent message loss, AEMP does not.
596		940
597	Erlang makes few guarantees on messages delivery - messages can get lost	941	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,	942	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).	943	b, and c, and the other side only receives messages a and c).
600		944
601	AEMP guarantees correct ordering, and the guarantee that there are no	945	AEMP guarantees (modulo hardware errors) correct ordering, and the
		946	guarantee that after one message is lost, all following ones sent to the
		947	same port are lost as well, until monitoring raises an error, so there are
602	holes in the message sequence.	948	no silent "holes" in the message sequence.
603		949
604	=item * In erlang, processes can be declared dead and later be found to be	950	If you want your software to be very reliable, you have to cope with
605	alive.	951	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
606		952	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	953	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		954
615	=item * Erlang can send messages to the wrong port, AEMP does not.	955	=item * Erlang can send messages to the wrong port, AEMP does not.
616		956
617	In erlang it is quite possible that a node that restarts reuses a process	957	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	958	process ID known to other nodes for a completely different process,
619	messages destined for that process to end up in an unrelated process.	959	causing messages destined for that process to end up in an unrelated
		960	process.
620		961
621	AEMP never reuses port IDs, so old messages or old port IDs floating	962	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.	963	around in the network will not be sent to an unrelated port.
623		964
624	=item * Erlang uses unprotected connections, AEMP uses secure	965	=item * Erlang uses unprotected connections, AEMP uses secure
625	authentication and can use TLS.	966	authentication and can use TLS.
626		967
627	AEMP can use a proven protocol - SSL/TLS - to protect connections and	968	AEMP can use a proven protocol - TLS - to protect connections and
628	securely authenticate nodes.	969	securely authenticate nodes.
629		970
630	=item * The AEMP protocol is optimised for both text-based and binary	971	=item * The AEMP protocol is optimised for both text-based and binary
631	communications.	972	communications.
632		973
633	The AEMP protocol, unlike the erlang protocol, supports both	974	The AEMP protocol, unlike the Erlang protocol, supports both programming
634	language-independent text-only protocols (good for debugging) and binary,	975	language independent text-only protocols (good for debugging), and binary,
635	language-specific serialisers (e.g. Storable).	976	language-specific serialisers (e.g. Storable). By default, unless TLS is
		977	used, the protocol is actually completely text-based.
636		978
637	It has also been carefully designed to be implementable in other languages	979	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	980	with a minimum of work while gracefully degrading functionality to make the
639	protocol simple.	981	protocol simple.
640		982
		983	=item * AEMP has more flexible monitoring options than Erlang.
		984
		985	In Erlang, you can chose to receive I<all> exit signals as messages or
		986	I<none>, there is no in-between, so monitoring single Erlang processes is
		987	difficult to implement.
		988
		989	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		990	between automatic kill, exit message or callback on a per-port basis.
		991
		992	=item * Erlang tries to hide remote/local connections, AEMP does not.
		993
		994	Monitoring in Erlang is not an indicator of process death/crashes, in the
		995	same way as linking is (except linking is unreliable in Erlang).
		996
		997	In AEMP, you don't "look up" registered port names or send to named ports
		998	that might or might not be persistent. Instead, you normally spawn a port
		999	on the remote node. The init function monitors you, and you monitor the
		1000	remote port. Since both monitors are local to the node, they are much more
		1001	reliable (no need for C<spawn_link>).
		1002
		1003	This also saves round-trips and avoids sending messages to the wrong port
		1004	(hard to do in Erlang).
		1005
641	=back	1006	=back
642		1007
		1008	=head1 RATIONALE
		1009
		1010	=over 4
		1011
		1012	=item Why strings for port and node IDs, why not objects?
		1013
		1014	We considered "objects", but found that the actual number of methods
		1015	that can be called are quite low. Since port and node IDs travel over
		1016	the network frequently, the serialising/deserialising would add lots of
		1017	overhead, as well as having to keep a proxy object everywhere.
		1018
		1019	Strings can easily be printed, easily serialised etc. and need no special
		1020	procedures to be "valid".
		1021
		1022	And as a result, a port with just a default receiver consists of a single
		1023	code reference stored in a global hash - it can't become much cheaper.
		1024
		1025	=item Why favour JSON, why not a real serialising format such as Storable?
		1026
		1027	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1028	format, but currently there is no way to make a node use Storable by
		1029	default (although all nodes will accept it).
		1030
		1031	The default framing protocol is JSON because a) JSON::XS is many times
		1032	faster for small messages and b) most importantly, after years of
		1033	experience we found that object serialisation is causing more problems
		1034	than it solves: Just like function calls, objects simply do not travel
		1035	easily over the network, mostly because they will always be a copy, so you
		1036	always have to re-think your design.
		1037
		1038	Keeping your messages simple, concentrating on data structures rather than
		1039	objects, will keep your messages clean, tidy and efficient.
		1040
		1041	=back
		1042
643	=head1 SEE ALSO	1043	=head1 SEE ALSO
		1044
		1045	L<AnyEvent::MP::Intro> - a gentle introduction.
		1046
		1047	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1048
		1049	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1050	your applications.
		1051
		1052	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1053
		1054	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1055	all nodes.
644		1056
645	L<AnyEvent>.	1057	L<AnyEvent>.
646		1058
647	=head1 AUTHOR	1059	=head1 AUTHOR
648		1060

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Revision 1.123 by root, Thu Mar 1 19:37:59 2012 UTC