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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.32 by root, Wed Aug 5 19:58:46 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 initialise_node	198	configure
109	snd rcv mon kil reg psub	199	snd rcv mon mon_guard kil psub peval spawn cal
110	port	200	port
		201	db_set db_del db_reg
		202	db_mon db_family db_keys db_values
111	);	203	);
112		204
113	our $SELF;	205	our $SELF;
114		206
115	sub _self_die() {	207	sub _self_die() {
…		…
118	kil $SELF, die => $msg;	210	kil $SELF, die => $msg;
119	}	211	}
120		212
121	=item $thisnode = NODE / $NODE	213	=item $thisnode = NODE / $NODE
122		214
123	The C<NODE> function returns, and the C<$NODE> variable contains	215	The C<NODE> function returns, and the C<$NODE> variable contains, the node
124	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
125	to C<become_public> or C<become_slave>, after which all local port	217	a call to C<configure>.
126	identifiers become invalid.
127		218
128	=item $noderef = node_of $portid	219	=item $nodeid = node_of $port
129		220
130	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.
131		222
132	=item $cv = resolve_node $noderef	223	=item configure $profile, key => value...
133		224
134	Takes an unresolved node reference that may contain hostnames and	225	=item configure key => value...
135	abbreviated IDs, resolves all of them and returns a resolved node
136	reference.
137		226
138	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
139	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:
140		237
141	=over 4	238	=over 4
142		239
143	=item the empty string	240	=item norc => $boolean (default false)
144		241
145	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>
146	specified.	243	be consulted - all configuraiton options must be specified in the
		244	C<configure> call.
147		245
148	=item naked port numbers (e.g. C<1234>)	246	=item force => $boolean (default false)
149		247
150	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
151	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.
152		251
153	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	252	=item secure => $pass->($nodeid)
154		253
155	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
156	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
157	specified.	256	granted iff the callback returns a true value.
		257
		258	See F<semp setsecure> for more info.
158		259
159	=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)"
160		338
161	=item $SELF	339	=item $SELF
162		340
163	Contains the current port id while executing C<rcv> callbacks or C<psub>	341	Contains the current port id while executing C<rcv> callbacks or C<psub>
164	blocks.	342	blocks.
165		343
166	=item SELF, %SELF, @SELF...	344	=item *SELF, SELF, %SELF, @SELF...
167		345
168	Due to some quirks in how perl exports variables, it is impossible to	346	Due to some quirks in how perl exports variables, it is impossible to
169	just export C<$SELF>, all the symbols called C<SELF> are exported by this	347	just export C<$SELF>, all the symbols named C<SELF> are exported by this
170	module, but only C<$SELF> is currently used.	348	module, but only C<$SELF> is currently used.
171		349
172	=item snd $portid, type => @data	350	=item snd $port, type => @data
173		351
174	=item snd $portid, @msg	352	=item snd $port, @msg
175		353
176	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
177	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.
178	stringifies a sa port ID (such as a port object :).
179		356
180	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
181	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
182	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.
183		361
184	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
185	function: modifying any argument is not allowed and can cause many	363	function: modifying any argument (or values referenced by them) is
186	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.
187		368
188	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
189	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
190	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
191	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
192	node, anything can be passed.	373	node, anything can be passed. Best rely only on the common denominator of
		374	these.
193		375
194	=item $local_port = port	376	=item $local_port = port
195		377
196	Create a new local port object that can be used either as a pattern	378	Create a new local port object and returns its port ID. Initially it has
197	matching port ("full port") or a single-callback port ("miniport"),	379	no callbacks set and will throw an error when it receives messages.
198	depending on how C<rcv> callbacks are bound to the object.
199		380
200	=item $portid = port { my @msg = @_; $finished }	381	=item $local_port = port { my @msg = @_ }
201		382
202	Creates a "mini port", that is, a very lightweight port without any	383	Creates a new local port, and returns its ID. Semantically the same as
203	pattern matching behind it, and returns its ID.	384	creating a port and calling C<rcv $port, $callback> on it.
204		385
205	The block will be called for every message received on the port. When the	386	The block will be called for every message received on the port, with the
206	callback returns a true value its job is considered "done" and the port	387	global variable C<$SELF> set to the port ID. Runtime errors will cause the
207	will be destroyed. Otherwise it will stay alive.	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.
208		390
209	The message will be passed as-is, no extra argument (i.e. no port id) will	391	If you want to stop/destroy the port, simply C<kil> it:
210	be passed to the callback.
211		392
212	If you need the local port id in the callback, this works nicely:	393	my $port = port {
213		394	my @msg = @_;
214	my $port; $port = port {	395	...
215	snd $otherport, reply => $port;	396	kil $SELF;
216	};	397	};
217		398
218	=cut	399	=cut
219		400
		401	sub rcv($@);
		402
		403	sub _kilme {
		404	die "received message on port without callback";
		405	}
		406
220	sub port(;&) {	407	sub port(;&) {
221	my $id = "$UNIQ." . $ID++;	408	my $id = $UNIQ . ++$ID;
222	my $port = "$NODE#$id";	409	my $port = "$NODE#$id";
223		410
224	if (@_) {	411	rcv $port, shift \|\| \&_kilme;
225	my $cb = shift;
226	$PORT{$id} = sub {
227	local $SELF = $port;
228	eval {
229	&$cb
230	and kil $id;
231	};
232	_self_die if $@;
233	};
234	} else {
235	my $self = bless {
236	id => "$NODE#$id",
237	}, "AnyEvent::MP::Port";
238
239	$PORT_DATA{$id} = $self;
240	$PORT{$id} = sub {
241	local $SELF = $port;
242
243	eval {
244	for (@{ $self->{rc0}{$_[0]} }) {
245	$_ && &{$_->[0]}
246	&& undef $_;
247	}
248
249	for (@{ $self->{rcv}{$_[0]} }) {
250	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
251	&& &{$_->[0]}
252	&& undef $_;
253	}
254
255	for (@{ $self->{any} }) {
256	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
257	&& &{$_->[0]}
258	&& undef $_;
259	}
260	};
261	_self_die if $@;
262	};
263	}
264		412
265	$port	413	$port
266	}	414	}
267		415
268	=item reg $portid, $name
269
270	Registers the given port under the name C<$name>. If the name already
271	exists it is replaced.
272
273	A port can only be registered under one well known name.
274
275	A port automatically becomes unregistered when it is killed.
276
277	=cut
278
279	sub reg(@) {
280	my ($portid, $name) = @_;
281
282	$REG{$name} = $portid;
283	}
284
285	=item rcv $portid, $callback->(@msg)	416	=item rcv $local_port, $callback->(@msg)
286		417
287	Replaces the callback on the specified miniport (or newly created port	418	Replaces the default callback on the specified port. There is no way to
288	object, see C<port>). Full ports are configured with the following calls:	419	remove the default callback: use C<sub { }> to disable it, or better
		420	C<kil> the port when it is no longer needed.
289		421
290	=item rcv $portid, tagstring => $callback->(@msg), ...
291
292	=item rcv $portid, $smartmatch => $callback->(@msg), ...
293
294	=item rcv $portid, [$smartmatch...] => $callback->(@msg), ...
295
296	Register callbacks to be called on matching messages on the given full
297	port (or newly created port).
298
299	The callback has to return a true value when its work is done, after
300	which is will be removed, or a false value in which case it will stay
301	registered.
302
303	The global C<$SELF> (exported by this module) contains C<$portid> while	422	The global C<$SELF> (exported by this module) contains C<$port> while
304	executing the callback.	423	executing the callback. Runtime errors during callback execution will
		424	result in the port being C<kil>ed.
305		425
306	Runtime errors wdurign callback execution will result in the port being	426	The default callback received all messages not matched by a more specific
307	C<kil>ed.	427	C<tag> match.
308		428
309	If the match is an array reference, then it will be matched against the	429	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
310	first elements of the message, otherwise only the first element is being
311	matched.
312		430
313	Any element in the match that is specified as C<_any_> (a function	431	Register (or replace) callbacks to be called on messages starting with the
314	exported by this module) matches any single element of the message.	432	given tag on the given port (and return the port), or unregister it (when
		433	C<$callback> is C<$undef> or missing). There can only be one callback
		434	registered for each tag.
315		435
316	While not required, it is highly recommended that the first matching	436	The original message will be passed to the callback, after the first
317	element is a string identifying the message. The one-string-only match is	437	element (the tag) has been removed. The callback will use the same
318	also the most efficient match (by far).	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, $otherport;
		463	};
319		464
320	=cut	465	=cut
321		466
322	sub rcv($@) {	467	sub rcv($@) {
323	my $portid = shift;	468	my $port = shift;
324	my ($noderef, $port) = split /#/, $port, 2;	469	my ($nodeid, $portid) = split /#/, $port, 2;
325		470
326	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	471	$NODE{$nodeid} == $NODE{""}
327	or Carp::croak "$noderef#$port: rcv can only be called on local ports, caught";	472	or Carp::croak "$port: rcv can only be called on local ports, caught";
328
329	my $self = $PORT_DATA{$port}
330	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";
331
332	"AnyEvent::MP::Port" eq ref $self
333	or Carp::croak "$noderef#$port: rcv can only be called on message matching ports, caught";
334		473
335	while (@_) {	474	while (@_) {
336	my ($match, $cb) = splice @_, 0, 2;
337
338	if (!ref $match) {	475	if (ref $_[0]) {
339	push @{ $self->{rc0}{$match} }, [$cb];	476	if (my $self = $PORT_DATA{$portid}) {
340	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {	477	"AnyEvent::MP::Port" eq ref $self
341	my ($type, @match) = @$match;	478	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
342	@match	479
343	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]	480	$self->[0] = shift;
344	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
345	} else {	481	} else {
346	push @{ $self->{any} }, [$cb, $match];	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	}
347	}	516	}
348	}	517	}
349		518
350	$portid	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	}
351	}	557	}
352		558
353	=item $closure = psub { BLOCK }	559	=item $closure = psub { BLOCK }
354		560
355	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	561	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
356	closure is executed, sets up the environment in the same way as in C<rcv>	562	closure is executed, sets up the environment in the same way as in C<rcv>
357	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.	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 $SELF, sub {
		566	BLOCK }, @_ } >>.
358		567
359	This is useful when you register callbacks from C<rcv> callbacks:	568	This is useful when you register callbacks from C<rcv> callbacks:
360		569
361	rcv delayed_reply => sub {	570	rcv delayed_reply => sub {
362	my ($delay, @reply) = @_;	571	my ($delay, @reply) = @_;
…		…
386	$res	595	$res
387	}	596	}
388	}	597	}
389	}	598	}
390		599
391	=item $guard = mon $portid, $cb->(@reason)	600	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
392		601
393	=item $guard = mon $portid, $otherport	602	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
394		603
395	=item $guard = mon $portid, $otherport, @msg	604	=item $guard = mon $port # kill $SELF when $port dies
396		605
		606	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		607
397	Monitor the given port and do something when the port is killed.	608	Monitor the given port and do something when the port is killed or
		609	messages to it were lost, and optionally return a guard that can be used
		610	to stop monitoring again.
398		611
399	In the first form, the callback is simply called with any number	612	In the first form (callback), the callback is simply called with any
400	of C<@reason> elements (no @reason means that the port was deleted	613	number of C<@reason> elements (no @reason means that the port was deleted
401	"normally"). Note also that I<< the callback B<must> never die >>, so use	614	"normally"). Note also that I<< the callback B<must> never die >>, so use
402	C<eval> if unsure.	615	C<eval> if unsure.
403		616
404	In the second form, the other port will be C<kil>'ed with C<@reason>, iff	617	In the second form (another port given), the other port (C<$rcvport>)
405	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
406	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.
407		621
		622	The third form (kill self) is the same as the second form, except that
		623	C<$rvport> defaults to C<$SELF>.
		624
408	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.
409		654
410	Example: call a given callback when C<$port> is killed.	655	Example: call a given callback when C<$port> is killed.
411		656
412	mon $port, sub { warn "port died because of <@_>\n" };	657	mon $port, sub { warn "port died because of <@_>\n" };
413		658
414	Example: kill ourselves when C<$port> is killed abnormally.	659	Example: kill ourselves when C<$port> is killed abnormally.
415		660
416	mon $port, $self;	661	mon $port;
417		662
418	Example: send us a restart message another C<$port> is killed.	663	Example: send us a restart message when another C<$port> is killed.
419		664
420	mon $port, $self => "restart";	665	mon $port, $self => "restart";
421		666
422	=cut	667	=cut
423		668
424	sub mon {	669	sub mon {
425	my ($noderef, $port) = split /#/, shift, 2;	670	my ($nodeid, $port) = split /#/, shift, 2;
426		671
427	my $node = $NODE{$noderef} \|\| add_node $noderef;	672	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
428		673
429	my $cb = shift;	674	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
430		675
431	unless (ref $cb) {	676	unless (ref $cb) {
432	if (@_) {	677	if (@_) {
433	# send a kill info message	678	# send a kill info message
434	my (@msg) = ($cb, @_);	679	my (@msg) = ($cb, @_);
…		…
441	}	686	}
442		687
443	$node->monitor ($port, $cb);	688	$node->monitor ($port, $cb);
444		689
445	defined wantarray	690	defined wantarray
446	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	691	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
447	}	692	}
448		693
449	=item $guard = mon_guard $port, $ref, $ref...	694	=item $guard = mon_guard $port, $ref, $ref...
450		695
451	Monitors the given C<$port> and keeps the passed references. When the port	696	Monitors the given C<$port> and keeps the passed references. When the port
452	is killed, the references will be freed.	697	is killed, the references will be freed.
453		698
454	Optionally returns a guard that will stop the monitoring.	699	Optionally returns a guard that will stop the monitoring.
455		700
456	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
457	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>):
458		703
459	$port->rcv (start => sub {	704	$port->rcv (start => sub {
460	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	705	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
461	undef $timer if 0.9 < rand;	706	undef $timer if 0.9 < rand;
462	});	707	});
463	});	708	});
464		709
465	=cut	710	=cut
466		711
467	sub mon_guard {	712	sub mon_guard {
468	my ($port, @refs) = @_;	713	my ($port, @refs) = @_;
469		714
		715	#TODO: mon-less form?
		716
470	mon $port, sub { 0 && @refs }	717	mon $port, sub { 0 && @refs }
471	}	718	}
472		719
473	=item lnk $port1, $port2
474
475	Link two ports. This is simply a shorthand for:
476
477	mon $port1, $port2;
478	mon $port2, $port1;
479
480	It means that if either one is killed abnormally, the other one gets
481	killed as well.
482
483	=item kil $portid[, @reason]	720	=item kil $port[, @reason]
484		721
485	Kill the specified port with the given C<@reason>.	722	Kill the specified port with the given C<@reason>.
486		723
487	If no C<@reason> is specified, then the port is killed "normally" (linked	724	If no C<@reason> is specified, then the port is killed "normally" -
488	ports will not be kileld, or even notified).	725	monitor callback will be invoked, but the kil will not cause linked ports
		726	(C<mon $mport, $lport> form) to get killed.
489		727
490	Otherwise, linked ports get killed with the same reason (second form of	728	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
491	C<mon>, see below).	729	form) get killed with the same reason.
492		730
493	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	731	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
494	will be reported as reason C<< die => $@ >>.	732	will be reported as reason C<< die => $@ >>.
495		733
496	Transport/communication errors are reported as C<< transport_error =>	734	Transport/communication errors are reported as C<< transport_error =>
497	$message >>.	735	$message >>.
498		736
		737	=cut
		738
		739	=item $port = spawn $node, $initfunc[, @initdata]
		740
		741	Creates a port on the node C<$node> (which can also be a port ID, in which
		742	case it's the node where that port resides).
		743
		744	The port ID of the newly created port is returned immediately, and it is
		745	possible to immediately start sending messages or to monitor the port.
		746
		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>.
		751
		752	If the function doesn't exist, then the node tries to C<require>
		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 }
		798	};
		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->();
		878	};
		879	} else {
		880	mon $_[0], sub {
		881	kil $port;
		882	$cb->();
		883	};
		884	}
		885
		886	push @_, $port;
		887	&snd;
		888
		889	$port
		890	}
		891
499	=back	892	=back
500		893
501	=head1 FUNCTIONS FOR NODES	894	=head1 DISTRIBUTED DATABASE
502		895
		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.
		899
		900	The database consists of a two-level hash - a hash contains a hash which
		901	contains values.
		902
		903	The top level hash key is called "family", and the second-level hash key
		904	is called "subkey" or simply "key".
		905
		906	The family must be alphanumeric, i.e. start with a letter and consist
		907	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		908	pretty much like Perl module names.
		909
		910	As the family namespace is global, it is recommended to prefix family names
		911	with the name of the application or module using it.
		912
		913	The subkeys must be non-empty strings, with no further restrictions.
		914
		915	The values should preferably be strings, but other perl scalars should
		916	work as well (such as undef, arrays and hashes).
		917
		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.
		922
		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:
		926
		927	db_set my_image_scalers => $port;
		928
		929	And clients looking for an image scaler will want to get the
		930	C<my_image_scalers> keys:
		931
		932	db_keys "my_image_scalers" => 60 => sub {
		933	#d##TODO#
		934
503	=over 4	935	=over
504		936
505	=item become_public $noderef	937	=item db_set $family => $subkey [=> $value]
506		938
507	Tells the node to become a public node, i.e. reachable from other nodes.	939	Sets (or replaces) a key to the database - if C<$value> is omitted,
		940	C<undef> is used instead.
508		941
509	The first argument is the (unresolved) node reference of the local node	942	=item db_del $family => $subkey
510	(if missing then the empty string is used).
511		943
512	It is quite common to not specify anything, in which case the local node	944	Deletes a key from the database.
513	tries to listen on the default port, or to only specify a port number, in	945
514	which case AnyEvent::MP tries to guess the local addresses.	946	=item $guard = db_reg $family => $subkey [=> $value]
		947
		948	Sets the key on the database and returns a guard. When the guard is
		949	destroyed, the key is deleted from the database. If C<$value> is missing,
		950	then C<undef> is used.
		951
		952	=item $guard = db_mon $family => $cb->($familyhash, \@subkeys...)
		953
		954	Creates a monitor on the given database family. Each time a key is set or
		955	or is deleted the callback is called with a hash containing the database
		956	family and an arrayref with subkeys that have changed.
		957
		958	Specifically, if one of the passed subkeys exists in the $familyhash, then
		959	it is currently set to the value in the $familyhash. Otherwise, it has
		960	been deleted.
		961
		962	The first call will be with the current contents of the family and all
		963	keys, as if they were just added.
		964
		965	It is possible that the callback is called with a change event even though
		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";
		997	}
		998	};
515		999
516	=cut	1000	=cut
517		1001
518	=back	1002	=back
519		1003
520	=head1 NODE MESSAGES
521
522	Nodes understand the following messages sent to them. Many of them take
523	arguments called C<@reply>, which will simply be used to compose a reply
524	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
525	the remaining arguments are simply the message data.
526
527	While other messages exist, they are not public and subject to change.
528
529	=over 4
530
531	=cut
532
533	=item lookup => $name, @reply
534
535	Replies with the port ID of the specified well-known port, or C<undef>.
536
537	=item devnull => ...
538
539	Generic data sink/CPU heat conversion.
540
541	=item relay => $port, @msg
542
543	Simply forwards the message to the given port.
544
545	=item eval => $string[ @reply]
546
547	Evaluates the given string. If C<@reply> is given, then a message of the
548	form C<@reply, $@, @evalres> is sent.
549
550	Example: crash another node.
551
552	snd $othernode, eval => "exit";
553
554	=item time => @reply
555
556	Replies the the current node time to C<@reply>.
557
558	Example: tell the current node to send the current time to C<$myport> in a
559	C<timereply> message.
560
561	snd $NODE, time => $myport, timereply => 1, 2;
562	# => snd $myport, timereply => 1, 2, <time>
563
564	=back
565
566	=head1 AnyEvent::MP vs. Distributed Erlang	1004	=head1 AnyEvent::MP vs. Distributed Erlang
567		1005
568	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
569	== 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
570	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
571	sample:	1009	sample:
572		1010
573	http://www.erlang.se/doc/programming_rules.shtml	1011	http://www.erlang.se/doc/programming_rules.shtml
574	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
575	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
…		…
577		1015
578	Despite the similarities, there are also some important differences:	1016	Despite the similarities, there are also some important differences:
579		1017
580	=over 4	1018	=over 4
581		1019
582	=item * Node references contain the recipe on how to contact them.	1020	=item * Node IDs are arbitrary strings in AEMP.
583		1021
584	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
585	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
586	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.
587		1026
588	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
589	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.
590		1041
591	=item * Erlang uses processes and a mailbox, AEMP does not queue.	1042	=item * Erlang uses processes and a mailbox, AEMP does not queue.
592		1043
593	Erlang uses processes that selctively receive messages, and therefore	1044	Erlang uses processes that selectively receive messages out of order, and
594	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
595	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.
596		1049
597	(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.
598		1055
599	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1056	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
600		1057
601	Sending messages in erlang is synchronous and blocks the process. AEMP	1058	Sending messages in Erlang is synchronous and blocks the process until
602	sends are immediate, connection establishment is handled in the	1059	a conenction has been established and the message sent (and so does not
603	background.	1060	need a queue that can overflow). AEMP sends return immediately, connection
		1061	establishment is handled in the background.
604		1062
605	=item * Erlang can silently lose messages, AEMP cannot.	1063	=item * Erlang suffers from silent message loss, AEMP does not.
606		1064
607	Erlang makes few guarantees on messages delivery - messages can get lost	1065	Erlang implements few guarantees on messages delivery - messages can get
608	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,
609	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).
610		1068
611	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
612	holes in the message sequence.	1072	no silent "holes" in the message sequence.
613		1073
614	=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
615	alive.	1075	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
616		1076	simply tries to work better in common error cases, such as when a network
617	In erlang it can happen that a monitored process is declared dead and	1077	link goes down.
618	linked processes get killed, but later it turns out that the process is
619	still alive - and can receive messages.
620
621	In AEMP, when port monitoring detects a port as dead, then that port will
622	eventually be killed - it cannot happen that a node detects a port as dead
623	and then later sends messages to it, finding it is still alive.
624		1078
625	=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.
626		1080
627	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
628	ID known to other nodes for a completely different process, causing	1082	process ID known to other nodes for a completely different process,
629	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.
630		1085
631	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
632	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.
633		1088
634	=item * Erlang uses unprotected connections, AEMP uses secure	1089	=item * Erlang uses unprotected connections, AEMP uses secure
635	authentication and can use TLS.	1090	authentication and can use TLS.
636		1091
637	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1092	AEMP can use a proven protocol - TLS - to protect connections and
638	securely authenticate nodes.	1093	securely authenticate nodes.
639		1094
640	=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
641	communications.	1096	communications.
642		1097
643	The AEMP protocol, unlike the erlang protocol, supports both	1098	The AEMP protocol, unlike the Erlang protocol, supports both programming
644	language-independent text-only protocols (good for debugging) and binary,	1099	language independent text-only protocols (good for debugging), and binary,
645	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.
646		1102
647	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
648	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
649	protocol simple.	1105	protocol simple.
650		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
651	=back	1130	=back
652		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
653	=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.
654		1180
655	L<AnyEvent>.	1181	L<AnyEvent>.
656		1182
657	=head1 AUTHOR	1183	=head1 AUTHOR
658		1184

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Revision 1.128 by root, Sun Mar 4 14:28:44 2012 UTC