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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.34 by root, Wed Aug 5 23:50:46 2009 UTC vs.
Revision 1.127 by root, Sat Mar 3 20:35:10 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
111	);	202	);
112		203
113	our $SELF;	204	our $SELF;
114		205
115	sub _self_die() {	206	sub _self_die() {
…		…
118	kil $SELF, die => $msg;	209	kil $SELF, die => $msg;
119	}	210	}
120		211
121	=item $thisnode = NODE / $NODE	212	=item $thisnode = NODE / $NODE
122		213
123	The C<NODE> function returns, and the C<$NODE> variable contains	214	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	215	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	216	a call to C<configure>.
126	identifiers become invalid.
127		217
128	=item $noderef = node_of $port	218	=item $nodeid = node_of $port
129		219
130	Extracts and returns the noderef from a portid or a noderef.	220	Extracts and returns the node ID from a port ID or a node ID.
131		221
132	=item initialise_node $noderef, $seednode, $seednode...	222	=item configure $profile, key => value...
133		223
134	=item initialise_node "slave/", $master, $master...	224	=item configure key => value...
135		225
136	Before a node can talk to other nodes on the network it has to initialise	226	Before a node can talk to other nodes on the network (i.e. enter
137	itself - the minimum a node needs to know is it's own name, and optionally	227	"distributed mode") it has to configure itself - the minimum a node needs
138	it should know the noderefs of some other nodes in the network.	228	to know is its own name, and optionally it should know the addresses of
		229	some other nodes in the network to discover other nodes.
139		230
140	This function initialises a node - it must be called exactly once (or	231	This function configures a node - it must be called exactly once (or
141	never) before calling other AnyEvent::MP functions.	232	never) before calling other AnyEvent::MP functions.
142		233
143	All arguments are noderefs, which can be either resolved or unresolved.	234	The key/value pairs are basically the same ones as documented for the
144		235	F<aemp> command line utility (sans the set/del prefix), with these additions:
145	There are two types of networked nodes, public nodes and slave nodes:
146		236
147	=over 4	237	=over 4
148		238
149	=item public nodes	239	=item norc => $boolean (default false)
150		240
151	For public nodes, C<$noderef> must either be a (possibly unresolved)	241	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
152	noderef, in which case it will be resolved, or C<undef> (or missing), in	242	be consulted - all configuraiton options must be specified in the
153	which case the noderef will be guessed.	243	C<configure> call.
154		244
155	Afterwards, the node will bind itself on all endpoints and try to connect	245	=item force => $boolean (default false)
156	to all additional C<$seednodes> that are specified. Seednodes are optional
157	and can be used to quickly bootstrap the node into an existing network.
158		246
159	=item slave nodes	247	IF true, then the values specified in the C<configure> will take
		248	precedence over any values configured via the rc file. The default is for
		249	the rc file to override any options specified in the program.
160		250
161	When the C<$noderef> is the special string C<slave/>, then the node will	251	=item secure => $pass->($nodeid)
162	become a slave node. Slave nodes cannot be contacted from outside and will
163	route most of their traffic to the master node that they attach to.
164		252
165	At least one additional noderef is required: The node will try to connect	253	In addition to specifying a boolean, you can specify a code reference that
166	to all of them and will become a slave attached to the first node it can	254	is called for every remote execution attempt - the execution request is
167	successfully connect to.	255	granted iff the callback returns a true value.
		256
		257	See F<semp setsecure> for more info.
168		258
169	=back	259	=back
170		260
171	This function will block until all nodes have been resolved and, for slave
172	nodes, until it has successfully established a connection to a master
173	server.
174
175	Example: become a public node listening on the default node.
176
177	initialise_node;
178
179	Example: become a public node, and try to contact some well-known master
180	servers to become part of the network.
181
182	initialise_node undef, "master1", "master2";
183
184	Example: become a public node listening on port C<4041>.
185
186	initialise_node 4041;
187
188	Example: become a public node, only visible on localhost port 4044.
189
190	initialise_node "locahost:4044";
191
192	Example: become a slave node to any of the specified master servers.
193
194	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
195
196	=item $cv = resolve_node $noderef
197
198	Takes an unresolved node reference that may contain hostnames and
199	abbreviated IDs, resolves all of them and returns a resolved node
200	reference.
201
202	In addition to C<address:port> pairs allowed in resolved noderefs, the
203	following forms are supported:
204
205	=over 4	261	=over 4
206		262
207	=item the empty string	263	=item step 1, gathering configuration from profiles
208		264
209	An empty-string component gets resolved as if the default port (4040) was	265	The function first looks up a profile in the aemp configuration (see the
210	specified.	266	L<aemp> commandline utility). The profile name can be specified via the
		267	named C<profile> parameter or can simply be the first parameter). If it is
		268	missing, then the nodename (F<uname -n>) will be used as profile name.
211		269
212	=item naked port numbers (e.g. C<1234>)	270	The profile data is then gathered as follows:
213		271
214	These are resolved by prepending the local nodename and a colon, to be	272	First, all remaining key => value pairs (all of which are conveniently
215	further resolved.	273	undocumented at the moment) will be interpreted as configuration
		274	data. Then they will be overwritten by any values specified in the global
		275	default configuration (see the F<aemp> utility), then the chain of
		276	profiles chosen by the profile name (and any C<parent> attributes).
216		277
217	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	278	That means that the values specified in the profile have highest priority
		279	and the values specified directly via C<configure> have lowest priority,
		280	and can only be used to specify defaults.
218		281
219	These are resolved by using AnyEvent::DNS to resolve them, optionally	282	If the profile specifies a node ID, then this will become the node ID of
220	looking up SRV records for the C<aemp=4040> port, if no port was	283	this process. If not, then the profile name will be used as node ID, with
221	specified.	284	a unique randoms tring (C</%u>) appended.
		285
		286	The node ID can contain some C<%> sequences that are expanded: C<%n>
		287	is expanded to the local nodename, C<%u> is replaced by a random
		288	strign to make the node unique. For example, the F<aemp> commandline
		289	utility uses C<aemp/%n/%u> as nodename, which might expand to
		290	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		291
		292	=item step 2, bind listener sockets
		293
		294	The next step is to look up the binds in the profile, followed by binding
		295	aemp protocol listeners on all binds specified (it is possible and valid
		296	to have no binds, meaning that the node cannot be contacted form the
		297	outside. This means the node cannot talk to other nodes that also have no
		298	binds, but it can still talk to all "normal" nodes).
		299
		300	If the profile does not specify a binds list, then a default of C<*> is
		301	used, meaning the node will bind on a dynamically-assigned port on every
		302	local IP address it finds.
		303
		304	=item step 3, connect to seed nodes
		305
		306	As the last step, the seed ID list from the profile is passed to the
		307	L<AnyEvent::MP::Global> module, which will then use it to keep
		308	connectivity with at least one node at any point in time.
222		309
223	=back	310	=back
		311
		312	Example: become a distributed node using the local node name as profile.
		313	This should be the most common form of invocation for "daemon"-type nodes.
		314
		315	configure
		316
		317	Example: become a semi-anonymous node. This form is often used for
		318	commandline clients.
		319
		320	configure nodeid => "myscript/%n/%u";
		321
		322	Example: configure a node using a profile called seed, which is suitable
		323	for a seed node as it binds on all local addresses on a fixed port (4040,
		324	customary for aemp).
		325
		326	# use the aemp commandline utility
		327	# aemp profile seed binds '*:4040'
		328
		329	# then use it
		330	configure profile => "seed";
		331
		332	# or simply use aemp from the shell again:
		333	# aemp run profile seed
		334
		335	# or provide a nicer-to-remember nodeid
		336	# aemp run profile seed nodeid "$(hostname)"
224		337
225	=item $SELF	338	=item $SELF
226		339
227	Contains the current port id while executing C<rcv> callbacks or C<psub>	340	Contains the current port id while executing C<rcv> callbacks or C<psub>
228	blocks.	341	blocks.
229		342
230	=item SELF, %SELF, @SELF...	343	=item *SELF, SELF, %SELF, @SELF...
231		344
232	Due to some quirks in how perl exports variables, it is impossible to	345	Due to some quirks in how perl exports variables, it is impossible to
233	just export C<$SELF>, all the symbols called C<SELF> are exported by this	346	just export C<$SELF>, all the symbols named C<SELF> are exported by this
234	module, but only C<$SELF> is currently used.	347	module, but only C<$SELF> is currently used.
235		348
236	=item snd $port, type => @data	349	=item snd $port, type => @data
237		350
238	=item snd $port, @msg	351	=item snd $port, @msg
239		352
240	Send the given message to the given port ID, which can identify either	353	Send the given message to the given port, which can identify either a
241	a local or a remote port, and can be either a string or soemthignt hat	354	local or a remote port, and must be a port ID.
242	stringifies a sa port ID (such as a port object :).
243		355
244	While the message can be about anything, it is highly recommended to use a	356	While the message can be almost anything, it is highly recommended to
245	string as first element (a portid, or some word that indicates a request	357	use a string as first element (a port ID, or some word that indicates a
246	type etc.).	358	request type etc.) and to consist if only simple perl values (scalars,
		359	arrays, hashes) - if you think you need to pass an object, think again.
247		360
248	The message data effectively becomes read-only after a call to this	361	The message data logically becomes read-only after a call to this
249	function: modifying any argument is not allowed and can cause many	362	function: modifying any argument (or values referenced by them) is
250	problems.	363	forbidden, as there can be considerable time between the call to C<snd>
		364	and the time the message is actually being serialised - in fact, it might
		365	never be copied as within the same process it is simply handed to the
		366	receiving port.
251		367
252	The type of data you can transfer depends on the transport protocol: when	368	The type of data you can transfer depends on the transport protocol: when
253	JSON is used, then only strings, numbers and arrays and hashes consisting	369	JSON is used, then only strings, numbers and arrays and hashes consisting
254	of those are allowed (no objects). When Storable is used, then anything	370	of those are allowed (no objects). When Storable is used, then anything
255	that Storable can serialise and deserialise is allowed, and for the local	371	that Storable can serialise and deserialise is allowed, and for the local
256	node, anything can be passed.	372	node, anything can be passed. Best rely only on the common denominator of
		373	these.
257		374
258	=item $local_port = port	375	=item $local_port = port
259		376
260	Create a new local port object that can be used either as a pattern	377	Create a new local port object and returns its port ID. Initially it has
261	matching port ("full port") or a single-callback port ("miniport"),	378	no callbacks set and will throw an error when it receives messages.
262	depending on how C<rcv> callbacks are bound to the object.
263		379
264	=item $port = port { my @msg = @_; $finished }	380	=item $local_port = port { my @msg = @_ }
265		381
266	Creates a "miniport", that is, a very lightweight port without any pattern	382	Creates a new local port, and returns its ID. Semantically the same as
267	matching behind it, and returns its ID. Semantically the same as creating
268	a port and calling C<rcv $port, $callback> on it.	383	creating a port and calling C<rcv $port, $callback> on it.
269		384
270	The block will be called for every message received on the port. When the	385	The block will be called for every message received on the port, with the
271	callback returns a true value its job is considered "done" and the port	386	global variable C<$SELF> set to the port ID. Runtime errors will cause the
272	will be destroyed. Otherwise it will stay alive.	387	port to be C<kil>ed. The message will be passed as-is, no extra argument
		388	(i.e. no port ID) will be passed to the callback.
273		389
274	The message will be passed as-is, no extra argument (i.e. no port id) will	390	If you want to stop/destroy the port, simply C<kil> it:
275	be passed to the callback.
276		391
277	If you need the local port id in the callback, this works nicely:	392	my $port = port {
278		393	my @msg = @_;
279	my $port; $port = port {	394	...
280	snd $otherport, reply => $port;	395	kil $SELF;
281	};	396	};
282		397
283	=cut	398	=cut
284		399
285	sub rcv($@);	400	sub rcv($@);
286		401
		402	sub _kilme {
		403	die "received message on port without callback";
		404	}
		405
287	sub port(;&) {	406	sub port(;&) {
288	my $id = "$UNIQ." . $ID++;	407	my $id = $UNIQ . ++$ID;
289	my $port = "$NODE#$id";	408	my $port = "$NODE#$id";
290		409
291	if (@_) {	410	rcv $port, shift \|\| \&_kilme;
292	rcv $port, shift;
293	} else {
294	$PORT{$id} = sub { }; # nop
295	}
296		411
297	$port	412	$port
298	}	413	}
299		414
300	=item reg $port, $name
301
302	Registers the given port under the name C<$name>. If the name already
303	exists it is replaced.
304
305	A port can only be registered under one well known name.
306
307	A port automatically becomes unregistered when it is killed.
308
309	=cut
310
311	sub reg(@) {
312	my ($port, $name) = @_;
313
314	$REG{$name} = $port;
315	}
316
317	=item rcv $port, $callback->(@msg)	415	=item rcv $local_port, $callback->(@msg)
318		416
319	Replaces the callback on the specified miniport (after converting it to	417	Replaces the default callback on the specified port. There is no way to
320	one if required).	418	remove the default callback: use C<sub { }> to disable it, or better
321		419	C<kil> the port when it is no longer needed.
322	=item rcv $port, tagstring => $callback->(@msg), ...
323
324	=item rcv $port, $smartmatch => $callback->(@msg), ...
325
326	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
327
328	Register callbacks to be called on matching messages on the given full
329	port (after converting it to one if required).
330
331	The callback has to return a true value when its work is done, after
332	which is will be removed, or a false value in which case it will stay
333	registered.
334		420
335	The global C<$SELF> (exported by this module) contains C<$port> while	421	The global C<$SELF> (exported by this module) contains C<$port> while
336	executing the callback.	422	executing the callback. Runtime errors during callback execution will
		423	result in the port being C<kil>ed.
337		424
338	Runtime errors wdurign callback execution will result in the port being	425	The default callback received all messages not matched by a more specific
339	C<kil>ed.	426	C<tag> match.
340		427
341	If the match is an array reference, then it will be matched against the	428	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
342	first elements of the message, otherwise only the first element is being
343	matched.
344		429
345	Any element in the match that is specified as C<_any_> (a function	430	Register (or replace) callbacks to be called on messages starting with the
346	exported by this module) matches any single element of the message.	431	given tag on the given port (and return the port), or unregister it (when
		432	C<$callback> is C<$undef> or missing). There can only be one callback
		433	registered for each tag.
347		434
348	While not required, it is highly recommended that the first matching	435	The original message will be passed to the callback, after the first
349	element is a string identifying the message. The one-string-only match is	436	element (the tag) has been removed. The callback will use the same
350	also the most efficient match (by far).	437	environment as the default callback (see above).
		438
		439	Example: create a port and bind receivers on it in one go.
		440
		441	my $port = rcv port,
		442	msg1 => sub { ... },
		443	msg2 => sub { ... },
		444	;
		445
		446	Example: create a port, bind receivers and send it in a message elsewhere
		447	in one go:
		448
		449	snd $otherport, reply =>
		450	rcv port,
		451	msg1 => sub { ... },
		452	...
		453	;
		454
		455	Example: temporarily register a rcv callback for a tag matching some port
		456	(e.g. for an rpc reply) and unregister it after a message was received.
		457
		458	rcv $port, $otherport => sub {
		459	my @reply = @_;
		460
		461	rcv $SELF, $otherport;
		462	};
351		463
352	=cut	464	=cut
353		465
354	sub rcv($@) {	466	sub rcv($@) {
355	my $port = shift;	467	my $port = shift;
356	my ($noderef, $portid) = split /#/, $port, 2;	468	my ($nodeid, $portid) = split /#/, $port, 2;
357		469
358	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	470	$NODE{$nodeid} == $NODE{""}
359	or Carp::croak "$port: rcv can only be called on local ports, caught";	471	or Carp::croak "$port: rcv can only be called on local ports, caught";
360		472
361	if (@_ == 1) {	473	while (@_) {
		474	if (ref $_[0]) {
		475	if (my $self = $PORT_DATA{$portid}) {
		476	"AnyEvent::MP::Port" eq ref $self
		477	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		478
		479	$self->[0] = shift;
		480	} else {
362	my $cb = shift;	481	my $cb = shift;
363	delete $PORT_DATA{$portid};
364	$PORT{$portid} = sub {	482	$PORT{$portid} = sub {
365	local $SELF = $port;	483	local $SELF = $port;
366	eval {	484	eval { &$cb }; _self_die if $@;
367	&$cb	485	};
368	and kil $port;
369	};	486	}
370	_self_die if $@;	487	} elsif (defined $_[0]) {
371	};
372	} else {
373	my $self = $PORT_DATA{$portid} \|\|= do {	488	my $self = $PORT_DATA{$portid} \|\|= do {
374	my $self = bless {	489	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
375	id => $port,
376	}, "AnyEvent::MP::Port";
377		490
378	$PORT{$portid} = sub {	491	$PORT{$portid} = sub {
379	local $SELF = $port;	492	local $SELF = $port;
380		493
381	eval {
382	for (@{ $self->{rc0}{$_[0]} }) {	494	if (my $cb = $self->[1]{$_[0]}) {
383	$_ && &{$_->[0]}	495	shift;
384	&& undef $_;	496	eval { &$cb }; _self_die if $@;
385	}	497	} else {
386
387	for (@{ $self->{rcv}{$_[0]} }) {
388	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
389	&& &{$_->[0]}	498	&{ $self->[0] };
390	&& undef $_;
391	}
392
393	for (@{ $self->{any} }) {
394	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
395	&& &{$_->[0]}
396	&& undef $_;
397	}	499	}
398	};	500	};
399	_self_die if $@;	501
		502	$self
400	};	503	};
401		504
402	$self
403	};
404
405	"AnyEvent::MP::Port" eq ref $self	505	"AnyEvent::MP::Port" eq ref $self
406	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	506	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
407		507
408	while (@_) {
409	my ($match, $cb) = splice @_, 0, 2;	508	my ($tag, $cb) = splice @_, 0, 2;
410		509
411	if (!ref $match) {	510	if (defined $cb) {
412	push @{ $self->{rc0}{$match} }, [$cb];	511	$self->[1]{$tag} = $cb;
413	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
414	my ($type, @match) = @$match;
415	@match
416	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
417	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
418	} else {	512	} else {
419	push @{ $self->{any} }, [$cb, $match];	513	delete $self->[1]{$tag};
420	}	514	}
421	}	515	}
422	}	516	}
423		517
424	$port	518	$port
425	}	519	}
426		520
		521	=item peval $port, $coderef[, @args]
		522
		523	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		524	when the code throews an exception the C<$port> will be killed.
		525
		526	Any remaining args will be passed to the callback. Any return values will
		527	be returned to the caller.
		528
		529	This is useful when you temporarily want to execute code in the context of
		530	a port.
		531
		532	Example: create a port and run some initialisation code in it's context.
		533
		534	my $port = port { ... };
		535
		536	peval $port, sub {
		537	init
		538	or die "unable to init";
		539	};
		540
		541	=cut
		542
		543	sub peval($$) {
		544	local $SELF = shift;
		545	my $cb = shift;
		546
		547	if (wantarray) {
		548	my @res = eval { &$cb };
		549	_self_die if $@;
		550	@res
		551	} else {
		552	my $res = eval { &$cb };
		553	_self_die if $@;
		554	$res
		555	}
		556	}
		557
427	=item $closure = psub { BLOCK }	558	=item $closure = psub { BLOCK }
428		559
429	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	560	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
430	closure is executed, sets up the environment in the same way as in C<rcv>	561	closure is executed, sets up the environment in the same way as in C<rcv>
431	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.	562	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		563
		564	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		565	BLOCK }, @_ } >>.
432		566
433	This is useful when you register callbacks from C<rcv> callbacks:	567	This is useful when you register callbacks from C<rcv> callbacks:
434		568
435	rcv delayed_reply => sub {	569	rcv delayed_reply => sub {
436	my ($delay, @reply) = @_;	570	my ($delay, @reply) = @_;
…		…
460	$res	594	$res
461	}	595	}
462	}	596	}
463	}	597	}
464		598
465	=item $guard = mon $port, $cb->(@reason)	599	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
466		600
467	=item $guard = mon $port, $otherport	601	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
468		602
469	=item $guard = mon $port, $otherport, @msg	603	=item $guard = mon $port # kill $SELF when $port dies
470		604
		605	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		606
471	Monitor the given port and do something when the port is killed.	607	Monitor the given port and do something when the port is killed or
		608	messages to it were lost, and optionally return a guard that can be used
		609	to stop monitoring again.
472		610
473	In the first form, the callback is simply called with any number	611	In the first form (callback), the callback is simply called with any
474	of C<@reason> elements (no @reason means that the port was deleted	612	number of C<@reason> elements (no @reason means that the port was deleted
475	"normally"). Note also that I<< the callback B<must> never die >>, so use	613	"normally"). Note also that I<< the callback B<must> never die >>, so use
476	C<eval> if unsure.	614	C<eval> if unsure.
477		615
478	In the second form, the other port will be C<kil>'ed with C<@reason>, iff	616	In the second form (another port given), the other port (C<$rcvport>)
479	a @reason was specified, i.e. on "normal" kils nothing happens, while	617	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
480	under all other conditions, the other port is killed with the same reason.	618	"normal" kils nothing happens, while under all other conditions, the other
		619	port is killed with the same reason.
481		620
		621	The third form (kill self) is the same as the second form, except that
		622	C<$rvport> defaults to C<$SELF>.
		623
482	In the last form, a message of the form C<@msg, @reason> will be C<snd>.	624	In the last form (message), a message of the form C<@msg, @reason> will be
		625	C<snd>.
		626
		627	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		628	alert was raised), they are removed and will not trigger again.
		629
		630	As a rule of thumb, monitoring requests should always monitor a port from
		631	a local port (or callback). The reason is that kill messages might get
		632	lost, just like any other message. Another less obvious reason is that
		633	even monitoring requests can get lost (for example, when the connection
		634	to the other node goes down permanently). When monitoring a port locally
		635	these problems do not exist.
		636
		637	C<mon> effectively guarantees that, in the absence of hardware failures,
		638	after starting the monitor, either all messages sent to the port will
		639	arrive, or the monitoring action will be invoked after possible message
		640	loss has been detected. No messages will be lost "in between" (after
		641	the first lost message no further messages will be received by the
		642	port). After the monitoring action was invoked, further messages might get
		643	delivered again.
		644
		645	Inter-host-connection timeouts and monitoring depend on the transport
		646	used. The only transport currently implemented is TCP, and AnyEvent::MP
		647	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		648	non-idle connection, and usually around two hours for idle connections).
		649
		650	This means that monitoring is good for program errors and cleaning up
		651	stuff eventually, but they are no replacement for a timeout when you need
		652	to ensure some maximum latency.
483		653
484	Example: call a given callback when C<$port> is killed.	654	Example: call a given callback when C<$port> is killed.
485		655
486	mon $port, sub { warn "port died because of <@_>\n" };	656	mon $port, sub { warn "port died because of <@_>\n" };
487		657
488	Example: kill ourselves when C<$port> is killed abnormally.	658	Example: kill ourselves when C<$port> is killed abnormally.
489		659
490	mon $port, $self;	660	mon $port;
491		661
492	Example: send us a restart message another C<$port> is killed.	662	Example: send us a restart message when another C<$port> is killed.
493		663
494	mon $port, $self => "restart";	664	mon $port, $self => "restart";
495		665
496	=cut	666	=cut
497		667
498	sub mon {	668	sub mon {
499	my ($noderef, $port) = split /#/, shift, 2;	669	my ($nodeid, $port) = split /#/, shift, 2;
500		670
501	my $node = $NODE{$noderef} \|\| add_node $noderef;	671	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
502		672
503	my $cb = shift;	673	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
504		674
505	unless (ref $cb) {	675	unless (ref $cb) {
506	if (@_) {	676	if (@_) {
507	# send a kill info message	677	# send a kill info message
508	my (@msg) = ($cb, @_);	678	my (@msg) = ($cb, @_);
…		…
515	}	685	}
516		686
517	$node->monitor ($port, $cb);	687	$node->monitor ($port, $cb);
518		688
519	defined wantarray	689	defined wantarray
520	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	690	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
521	}	691	}
522		692
523	=item $guard = mon_guard $port, $ref, $ref...	693	=item $guard = mon_guard $port, $ref, $ref...
524		694
525	Monitors the given C<$port> and keeps the passed references. When the port	695	Monitors the given C<$port> and keeps the passed references. When the port
526	is killed, the references will be freed.	696	is killed, the references will be freed.
527		697
528	Optionally returns a guard that will stop the monitoring.	698	Optionally returns a guard that will stop the monitoring.
529		699
530	This function is useful when you create e.g. timers or other watchers and	700	This function is useful when you create e.g. timers or other watchers and
531	want to free them when the port gets killed:	701	want to free them when the port gets killed (note the use of C<psub>):
532		702
533	$port->rcv (start => sub {	703	$port->rcv (start => sub {
534	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	704	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
535	undef $timer if 0.9 < rand;	705	undef $timer if 0.9 < rand;
536	});	706	});
537	});	707	});
538		708
539	=cut	709	=cut
540		710
541	sub mon_guard {	711	sub mon_guard {
542	my ($port, @refs) = @_;	712	my ($port, @refs) = @_;
543		713
		714	#TODO: mon-less form?
		715
544	mon $port, sub { 0 && @refs }	716	mon $port, sub { 0 && @refs }
545	}	717	}
546		718
547	=item lnk $port1, $port2
548
549	Link two ports. This is simply a shorthand for:
550
551	mon $port1, $port2;
552	mon $port2, $port1;
553
554	It means that if either one is killed abnormally, the other one gets
555	killed as well.
556
557	=item kil $port[, @reason]	719	=item kil $port[, @reason]
558		720
559	Kill the specified port with the given C<@reason>.	721	Kill the specified port with the given C<@reason>.
560		722
561	If no C<@reason> is specified, then the port is killed "normally" (linked	723	If no C<@reason> is specified, then the port is killed "normally" -
562	ports will not be kileld, or even notified).	724	monitor callback will be invoked, but the kil will not cause linked ports
		725	(C<mon $mport, $lport> form) to get killed.
563		726
564	Otherwise, linked ports get killed with the same reason (second form of	727	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
565	C<mon>, see below).	728	form) get killed with the same reason.
566		729
567	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	730	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
568	will be reported as reason C<< die => $@ >>.	731	will be reported as reason C<< die => $@ >>.
569		732
570	Transport/communication errors are reported as C<< transport_error =>	733	Transport/communication errors are reported as C<< transport_error =>
571	$message >>.	734	$message >>.
572		735
		736	=cut
		737
		738	=item $port = spawn $node, $initfunc[, @initdata]
		739
		740	Creates a port on the node C<$node> (which can also be a port ID, in which
		741	case it's the node where that port resides).
		742
		743	The port ID of the newly created port is returned immediately, and it is
		744	possible to immediately start sending messages or to monitor the port.
		745
		746	After the port has been created, the init function is called on the remote
		747	node, in the same context as a C<rcv> callback. This function must be a
		748	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		749	specify a function in the main program, use C<::name>.
		750
		751	If the function doesn't exist, then the node tries to C<require>
		752	the package, then the package above the package and so on (e.g.
		753	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		754	exists or it runs out of package names.
		755
		756	The init function is then called with the newly-created port as context
		757	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		758	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		759	the port might not get created.
		760
		761	A common idiom is to pass a local port, immediately monitor the spawned
		762	port, and in the remote init function, immediately monitor the passed
		763	local port. This two-way monitoring ensures that both ports get cleaned up
		764	when there is a problem.
		765
		766	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		767	caller before C<spawn> returns (by delaying invocation when spawn is
		768	called for the local node).
		769
		770	Example: spawn a chat server port on C<$othernode>.
		771
		772	# this node, executed from within a port context:
		773	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		774	mon $server;
		775
		776	# init function on C<$othernode>
		777	sub connect {
		778	my ($srcport) = @_;
		779
		780	mon $srcport;
		781
		782	rcv $SELF, sub {
		783	...
		784	};
		785	}
		786
		787	=cut
		788
		789	sub _spawn {
		790	my $port = shift;
		791	my $init = shift;
		792
		793	# rcv will create the actual port
		794	local $SELF = "$NODE#$port";
		795	eval {
		796	&{ load_func $init }
		797	};
		798	_self_die if $@;
		799	}
		800
		801	sub spawn(@) {
		802	my ($nodeid, undef) = split /#/, shift, 2;
		803
		804	my $id = $RUNIQ . ++$ID;
		805
		806	$_[0] =~ /::/
		807	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		808
		809	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		810
		811	"$nodeid#$id"
		812	}
		813
		814
		815	=item after $timeout, @msg
		816
		817	=item after $timeout, $callback
		818
		819	Either sends the given message, or call the given callback, after the
		820	specified number of seconds.
		821
		822	This is simply a utility function that comes in handy at times - the
		823	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		824	so it may go away in the future.
		825
		826	=cut
		827
		828	sub after($@) {
		829	my ($timeout, @action) = @_;
		830
		831	my $t; $t = AE::timer $timeout, 0, sub {
		832	undef $t;
		833	ref $action[0]
		834	? $action[0]()
		835	: snd @action;
		836	};
		837	}
		838
		839	=item cal $port, @msg, $callback[, $timeout]
		840
		841	A simple form of RPC - sends a message to the given C<$port> with the
		842	given contents (C<@msg>), but adds a reply port to the message.
		843
		844	The reply port is created temporarily just for the purpose of receiving
		845	the reply, and will be C<kil>ed when no longer needed.
		846
		847	A reply message sent to the port is passed to the C<$callback> as-is.
		848
		849	If an optional time-out (in seconds) is given and it is not C<undef>,
		850	then the callback will be called without any arguments after the time-out
		851	elapsed and the port is C<kil>ed.
		852
		853	If no time-out is given (or it is C<undef>), then the local port will
		854	monitor the remote port instead, so it eventually gets cleaned-up.
		855
		856	Currently this function returns the temporary port, but this "feature"
		857	might go in future versions unless you can make a convincing case that
		858	this is indeed useful for something.
		859
		860	=cut
		861
		862	sub cal(@) {
		863	my $timeout = ref $_[-1] ? undef : pop;
		864	my $cb = pop;
		865
		866	my $port = port {
		867	undef $timeout;
		868	kil $SELF;
		869	&$cb;
		870	};
		871
		872	if (defined $timeout) {
		873	$timeout = AE::timer $timeout, 0, sub {
		874	undef $timeout;
		875	kil $port;
		876	$cb->();
		877	};
		878	} else {
		879	mon $_[0], sub {
		880	kil $port;
		881	$cb->();
		882	};
		883	}
		884
		885	push @_, $port;
		886	&snd;
		887
		888	$port
		889	}
		890
573	=back	891	=back
574		892
575	=head1 NODE MESSAGES	893	=head1 DISTRIBUTED DATABASE
576		894
577	Nodes understand the following messages sent to them. Many of them take	895	AnyEvent::MP comes with a simple distributed database. The database will
578	arguments called C<@reply>, which will simply be used to compose a reply	896	be mirrored asynchronously at all global nodes. Other nodes bind to one of
579	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and	897	the global nodes for their needs.
580	the remaining arguments are simply the message data.
581		898
582	While other messages exist, they are not public and subject to change.	899	The database consists of a two-level hash - a hash contains a hash which
		900	contains values.
583		901
		902	The top level hash key is called "family", and the second-level hash key
		903	is called "subkey" or simply "key".
		904
		905	The family must be alphanumeric, i.e. start with a letter and consist
		906	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		907	pretty much like Perl module names.
		908
		909	As the family namespace is global, it is recommended to prefix family names
		910	with the name of the application or module using it.
		911
		912	The subkeys must be non-empty strings, with no further restrictions.
		913
		914	The values should preferably be strings, but other perl scalars should
		915	work as well (such as undef, arrays and hashes).
		916
		917	Every database entry is owned by one node - adding the same family/subkey
		918	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		919	but the result might be nondeterministic, i.e. the key might have
		920	different values on different nodes.
		921
		922	Different subkeys in the same family can be owned by different nodes
		923	without problems, and in fact, this is the common method to create worker
		924	pools. For example, a worker port for image scaling might do this:
		925
		926	db_set my_image_scalers => $port;
		927
		928	And clients looking for an image scaler will want to get the
		929	C<my_image_scalers> keys:
		930
		931	db_keys "my_image_scalers" => 60 => sub {
		932	#d##TODO#
		933
584	=over 4	934	=over
585		935
586	=cut	936	=item db_set $family => $subkey [=> $value]
587		937
588	=item lookup => $name, @reply	938	Sets (or replaces) a key to the database - if C<$value> is omitted,
		939	C<undef> is used instead.
589		940
590	Replies with the port ID of the specified well-known port, or C<undef>.	941	=item db_del $family => $subkey
591		942
592	=item devnull => ...	943	Deletes a key from the database.
593		944
594	Generic data sink/CPU heat conversion.	945	=item $guard = db_reg $family => $subkey [=> $value]
595		946
596	=item relay => $port, @msg	947	Sets the key on the database and returns a guard. When the guard is
		948	destroyed, the key is deleted from the database. If C<$value> is missing,
		949	then C<undef> is used.
597		950
598	Simply forwards the message to the given port.	951	=cut
599
600	=item eval => $string[ @reply]
601
602	Evaluates the given string. If C<@reply> is given, then a message of the
603	form C<@reply, $@, @evalres> is sent.
604
605	Example: crash another node.
606
607	snd $othernode, eval => "exit";
608
609	=item time => @reply
610
611	Replies the the current node time to C<@reply>.
612
613	Example: tell the current node to send the current time to C<$myport> in a
614	C<timereply> message.
615
616	snd $NODE, time => $myport, timereply => 1, 2;
617	# => snd $myport, timereply => 1, 2, <time>
618		952
619	=back	953	=back
620		954
621	=head1 AnyEvent::MP vs. Distributed Erlang	955	=head1 AnyEvent::MP vs. Distributed Erlang
622		956
623	AnyEvent::MP got lots of its ideas from distributed erlang (erlang node	957	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
624	== aemp node, erlang process == aemp port), so many of the documents and	958	== aemp node, Erlang process == aemp port), so many of the documents and
625	programming techniques employed by erlang apply to AnyEvent::MP. Here is a	959	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
626	sample:	960	sample:
627		961
628	http://www.erlang.se/doc/programming_rules.shtml	962	http://www.erlang.se/doc/programming_rules.shtml
629	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	963	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
630	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6	964	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
…		…
632		966
633	Despite the similarities, there are also some important differences:	967	Despite the similarities, there are also some important differences:
634		968
635	=over 4	969	=over 4
636		970
637	=item * Node references contain the recipe on how to contact them.	971	=item * Node IDs are arbitrary strings in AEMP.
638		972
639	Erlang relies on special naming and DNS to work everywhere in the	973	Erlang relies on special naming and DNS to work everywhere in the same
640	same way. AEMP relies on each node knowing it's own address(es), with	974	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
641	convenience functionality.	975	configuration or DNS), and possibly the addresses of some seed nodes, but
		976	will otherwise discover other nodes (and their IDs) itself.
642		977
643	This means that AEMP requires a less tightly controlled environment at the	978	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
644	cost of longer node references and a slightly higher management overhead.	979	uses "local ports are like remote ports".
		980
		981	The failure modes for local ports are quite different (runtime errors
		982	only) then for remote ports - when a local port dies, you I<know> it dies,
		983	when a connection to another node dies, you know nothing about the other
		984	port.
		985
		986	Erlang pretends remote ports are as reliable as local ports, even when
		987	they are not.
		988
		989	AEMP encourages a "treat remote ports differently" philosophy, with local
		990	ports being the special case/exception, where transport errors cannot
		991	occur.
645		992
646	=item * Erlang uses processes and a mailbox, AEMP does not queue.	993	=item * Erlang uses processes and a mailbox, AEMP does not queue.
647		994
648	Erlang uses processes that selctively receive messages, and therefore	995	Erlang uses processes that selectively receive messages out of order, and
649	needs a queue. AEMP is event based, queuing messages would serve no useful	996	therefore needs a queue. AEMP is event based, queuing messages would serve
650	purpose.	997	no useful purpose. For the same reason the pattern-matching abilities
		998	of AnyEvent::MP are more limited, as there is little need to be able to
		999	filter messages without dequeuing them.
651		1000
652	(But see L<Coro::MP> for a more erlang-like process model on top of AEMP).	1001	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1002	being event-based, while Erlang is process-based.
		1003
		1004	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1005	top of AEMP and Coro threads.
653		1006
654	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1007	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
655		1008
656	Sending messages in erlang is synchronous and blocks the process. AEMP	1009	Sending messages in Erlang is synchronous and blocks the process until
657	sends are immediate, connection establishment is handled in the	1010	a conenction has been established and the message sent (and so does not
658	background.	1011	need a queue that can overflow). AEMP sends return immediately, connection
		1012	establishment is handled in the background.
659		1013
660	=item * Erlang can silently lose messages, AEMP cannot.	1014	=item * Erlang suffers from silent message loss, AEMP does not.
661		1015
662	Erlang makes few guarantees on messages delivery - messages can get lost	1016	Erlang implements few guarantees on messages delivery - messages can get
663	without any of the processes realising it (i.e. you send messages a, b,	1017	lost without any of the processes realising it (i.e. you send messages a,
664	and c, and the other side only receives messages a and c).	1018	b, and c, and the other side only receives messages a and c).
665		1019
666	AEMP guarantees correct ordering, and the guarantee that there are no	1020	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1021	guarantee that after one message is lost, all following ones sent to the
		1022	same port are lost as well, until monitoring raises an error, so there are
667	holes in the message sequence.	1023	no silent "holes" in the message sequence.
668		1024
669	=item * In erlang, processes can be declared dead and later be found to be	1025	If you want your software to be very reliable, you have to cope with
670	alive.	1026	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
671		1027	simply tries to work better in common error cases, such as when a network
672	In erlang it can happen that a monitored process is declared dead and	1028	link goes down.
673	linked processes get killed, but later it turns out that the process is
674	still alive - and can receive messages.
675
676	In AEMP, when port monitoring detects a port as dead, then that port will
677	eventually be killed - it cannot happen that a node detects a port as dead
678	and then later sends messages to it, finding it is still alive.
679		1029
680	=item * Erlang can send messages to the wrong port, AEMP does not.	1030	=item * Erlang can send messages to the wrong port, AEMP does not.
681		1031
682	In erlang it is quite possible that a node that restarts reuses a process	1032	In Erlang it is quite likely that a node that restarts reuses an Erlang
683	ID known to other nodes for a completely different process, causing	1033	process ID known to other nodes for a completely different process,
684	messages destined for that process to end up in an unrelated process.	1034	causing messages destined for that process to end up in an unrelated
		1035	process.
685		1036
686	AEMP never reuses port IDs, so old messages or old port IDs floating	1037	AEMP does not reuse port IDs, so old messages or old port IDs floating
687	around in the network will not be sent to an unrelated port.	1038	around in the network will not be sent to an unrelated port.
688		1039
689	=item * Erlang uses unprotected connections, AEMP uses secure	1040	=item * Erlang uses unprotected connections, AEMP uses secure
690	authentication and can use TLS.	1041	authentication and can use TLS.
691		1042
692	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1043	AEMP can use a proven protocol - TLS - to protect connections and
693	securely authenticate nodes.	1044	securely authenticate nodes.
694		1045
695	=item * The AEMP protocol is optimised for both text-based and binary	1046	=item * The AEMP protocol is optimised for both text-based and binary
696	communications.	1047	communications.
697		1048
698	The AEMP protocol, unlike the erlang protocol, supports both	1049	The AEMP protocol, unlike the Erlang protocol, supports both programming
699	language-independent text-only protocols (good for debugging) and binary,	1050	language independent text-only protocols (good for debugging), and binary,
700	language-specific serialisers (e.g. Storable).	1051	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1052	used, the protocol is actually completely text-based.
701		1053
702	It has also been carefully designed to be implementable in other languages	1054	It has also been carefully designed to be implementable in other languages
703	with a minimum of work while gracefully degrading fucntionality to make the	1055	with a minimum of work while gracefully degrading functionality to make the
704	protocol simple.	1056	protocol simple.
705		1057
		1058	=item * AEMP has more flexible monitoring options than Erlang.
		1059
		1060	In Erlang, you can chose to receive I<all> exit signals as messages or
		1061	I<none>, there is no in-between, so monitoring single Erlang processes is
		1062	difficult to implement.
		1063
		1064	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1065	between automatic kill, exit message or callback on a per-port basis.
		1066
		1067	=item * Erlang tries to hide remote/local connections, AEMP does not.
		1068
		1069	Monitoring in Erlang is not an indicator of process death/crashes, in the
		1070	same way as linking is (except linking is unreliable in Erlang).
		1071
		1072	In AEMP, you don't "look up" registered port names or send to named ports
		1073	that might or might not be persistent. Instead, you normally spawn a port
		1074	on the remote node. The init function monitors you, and you monitor the
		1075	remote port. Since both monitors are local to the node, they are much more
		1076	reliable (no need for C<spawn_link>).
		1077
		1078	This also saves round-trips and avoids sending messages to the wrong port
		1079	(hard to do in Erlang).
		1080
706	=back	1081	=back
707		1082
		1083	=head1 RATIONALE
		1084
		1085	=over 4
		1086
		1087	=item Why strings for port and node IDs, why not objects?
		1088
		1089	We considered "objects", but found that the actual number of methods
		1090	that can be called are quite low. Since port and node IDs travel over
		1091	the network frequently, the serialising/deserialising would add lots of
		1092	overhead, as well as having to keep a proxy object everywhere.
		1093
		1094	Strings can easily be printed, easily serialised etc. and need no special
		1095	procedures to be "valid".
		1096
		1097	And as a result, a port with just a default receiver consists of a single
		1098	code reference stored in a global hash - it can't become much cheaper.
		1099
		1100	=item Why favour JSON, why not a real serialising format such as Storable?
		1101
		1102	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1103	format, but currently there is no way to make a node use Storable by
		1104	default (although all nodes will accept it).
		1105
		1106	The default framing protocol is JSON because a) JSON::XS is many times
		1107	faster for small messages and b) most importantly, after years of
		1108	experience we found that object serialisation is causing more problems
		1109	than it solves: Just like function calls, objects simply do not travel
		1110	easily over the network, mostly because they will always be a copy, so you
		1111	always have to re-think your design.
		1112
		1113	Keeping your messages simple, concentrating on data structures rather than
		1114	objects, will keep your messages clean, tidy and efficient.
		1115
		1116	=back
		1117
708	=head1 SEE ALSO	1118	=head1 SEE ALSO
		1119
		1120	L<AnyEvent::MP::Intro> - a gentle introduction.
		1121
		1122	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1123
		1124	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1125	your applications.
		1126
		1127	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1128
		1129	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1130	all nodes.
709		1131
710	L<AnyEvent>.	1132	L<AnyEvent>.
711		1133
712	=head1 AUTHOR	1134	=head1 AUTHOR
713		1135

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Revision 1.127 by root, Sat Mar 3 20:35:10 2012 UTC