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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.56 by root, Sat Aug 15 04:12:38 2009 UTC vs.
Revision 1.72 by root, Mon Aug 31 10:07:04 2009 UTC

…		…
11	NODE $port # returns the noderef of the port	11	NODE $port # returns the noderef of the port
12		12
13	$SELF # receiving/own port id in rcv callbacks	13	$SELF # receiving/own port id in rcv callbacks
14		14
15	# initialise the node so it can send/receive messages	15	# initialise the node so it can send/receive messages
16	initialise_node; # -OR-	16	configure;
17	initialise_node "localhost:4040"; # -OR-
18	initialise_node "slave/", "localhost:4040"
19		17
20	# ports are message endpoints	18	# ports are message endpoints
21		19
22	# sending messages	20	# sending messages
23	snd $port, type => data...;	21	snd $port, type => data...;
…		…
40	mon $port, $otherport # kill otherport on abnormal death	38	mon $port, $otherport # kill otherport on abnormal death
41	mon $port, $otherport, @msg # send message on death	39	mon $port, $otherport, @msg # send message on death
42		40
43	=head1 CURRENT STATUS	41	=head1 CURRENT STATUS
44		42
		43	bin/aemp - stable.
45	AnyEvent::MP - stable API, should work	44	AnyEvent::MP - stable API, should work.
46	AnyEvent::MP::Intro - outdated	45	AnyEvent::MP::Intro - uptodate, but incomplete.
47	AnyEvent::MP::Kernel - WIP
48	AnyEvent::MP::Transport - mostly stable	46	AnyEvent::MP::Kernel - mostly stable.
		47	AnyEvent::MP::Global - stable API, protocol not yet final.
49		48
50	stay tuned.	49	stay tuned.
51		50
52	=head1 DESCRIPTION	51	=head1 DESCRIPTION
53		52
54	This module (-family) implements a simple message passing framework.	53	This module (-family) implements a simple message passing framework.
55		54
56	Despite its simplicity, you can securely message other processes running	55	Despite its simplicity, you can securely message other processes running
57	on the same or other hosts.	56	on the same or other hosts, and you can supervise entities remotely.
58		57
59	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	58	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
60	manual page.	59	manual page and the examples under F<eg/>.
61		60
62	At the moment, this module family is severly broken and underdocumented,	61	At the moment, this module family is a bit underdocumented.
63	so do not use. This was uploaded mainly to reserve the CPAN namespace -
64	stay tuned!
65		62
66	=head1 CONCEPTS	63	=head1 CONCEPTS
67		64
68	=over 4	65	=over 4
69		66
70	=item port	67	=item port
71		68
72	A port is something you can send messages to (with the C<snd> function).	69	A port is something you can send messages to (with the C<snd> function).
73		70
74	Ports allow you to register C<rcv> handlers that can match all or just	71	Ports allow you to register C<rcv> handlers that can match all or just
75	some messages. Messages will not be queued.	72	some messages. Messages send to ports will not be queued, regardless of
		73	anything was listening for them or not.
76		74
77	=item port id - C<noderef#portname>	75	=item port ID - C<nodeid#portname>
78		76
79	A port ID is the concatenation of a noderef, a hash-mark (C<#>) as	77	A port ID is the concatenation of a node ID, a hash-mark (C<#>) as
80	separator, and a port name (a printable string of unspecified format). An	78	separator, and a port name (a printable string of unspecified format).
81	exception is the the node port, whose ID is identical to its node
82	reference.
83		79
84	=item node	80	=item node
85		81
86	A node is a single process containing at least one port - the node port,	82	A node is a single process containing at least one port - the node port,
87	which provides nodes to manage each other remotely, and to create new	83	which enables nodes to manage each other remotely, and to create new
88	ports.	84	ports.
89		85
90	Nodes are either private (single-process only), slaves (connected to a	86	Nodes are either public (have one or more listening ports) or private
91	master node only) or public nodes (connectable from unrelated nodes).	87	(no listening ports). Private nodes cannot talk to other private nodes
		88	currently.
92		89
93	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	90	=item node ID - C<[a-za-Z0-9_\-.:]+>
94		91
95	A node reference is a string that either simply identifies the node (for	92	A node ID is a string that uniquely identifies the node within a
96	private and slave nodes), or contains a recipe on how to reach a given	93	network. Depending on the configuration used, node IDs can look like a
97	node (for public nodes).	94	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		95	doesn't interpret node IDs in any way.
98		96
99	This recipe is simply a comma-separated list of C<address:port> pairs (for	97	=item binds - C<ip:port>
100	TCP/IP, other protocols might look different).
101		98
102	Node references come in two flavours: resolved (containing only numerical	99	Nodes can only talk to each other by creating some kind of connection to
103	addresses) or unresolved (where hostnames are used instead of addresses).	100	each other. To do this, nodes should listen on one or more local transport
		101	endpoints - binds. Currently, only standard C<ip:port> specifications can
		102	be used, which specify TCP ports to listen on.
104		103
105	Before using an unresolved node reference in a message you first have to	104	=item seeds - C<host:port>
106	resolve it.	105
		106	When a node starts, it knows nothing about the network. To teach the node
		107	about the network it first has to contact some other node within the
		108	network. This node is called a seed.
		109
		110	Seeds are transport endpoint(s) of as many nodes as one wants. Those nodes
		111	are expected to be long-running, and at least one of those should always
		112	be available. When nodes run out of connections (e.g. due to a network
		113	error), they try to re-establish connections to some seednodes again to
		114	join the network.
		115
		116	Apart from being sued for seeding, seednodes are not special in any way -
		117	every public node can be a seednode.
107		118
108	=back	119	=back
109		120
110	=head1 VARIABLES/FUNCTIONS	121	=head1 VARIABLES/FUNCTIONS
111		122
…		…
126	use base "Exporter";	137	use base "Exporter";
127		138
128	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	139	our $VERSION = $AnyEvent::MP::Kernel::VERSION;
129		140
130	our @EXPORT = qw(	141	our @EXPORT = qw(
131	NODE $NODE *SELF node_of _any_	142	NODE $NODE *SELF node_of after
132	resolve_node initialise_node	143	configure
133	snd rcv mon kil reg psub spawn	144	snd rcv mon mon_guard kil reg psub spawn
134	port	145	port
135	);	146	);
136		147
137	our $SELF;	148	our $SELF;
138		149
…		…
142	kil $SELF, die => $msg;	153	kil $SELF, die => $msg;
143	}	154	}
144		155
145	=item $thisnode = NODE / $NODE	156	=item $thisnode = NODE / $NODE
146		157
147	The C<NODE> function returns, and the C<$NODE> variable contains the	158	The C<NODE> function returns, and the C<$NODE> variable contains, the node
148	noderef of the local node. The value is initialised by a call to	159	ID of the node running in the current process. This value is initialised by
149	C<initialise_node>.	160	a call to C<configure>.
150		161
151	=item $noderef = node_of $port	162	=item $nodeid = node_of $port
152		163
153	Extracts and returns the noderef from a port ID or a noderef.	164	Extracts and returns the node ID from a port ID or a node ID.
154		165
155	=item initialise_node $noderef, $seednode, $seednode...	166	=item configure key => value...
156		167
157	=item initialise_node "slave/", $master, $master...
158
159	Before a node can talk to other nodes on the network it has to initialise	168	Before a node can talk to other nodes on the network (i.e. enter
160	itself - the minimum a node needs to know is it's own name, and optionally	169	"distributed mode") it has to configure itself - the minimum a node needs
161	it should know the noderefs of some other nodes in the network.	170	to know is its own name, and optionally it should know the addresses of
		171	some other nodes in the network to discover other nodes.
162		172
163	This function initialises a node - it must be called exactly once (or	173	This function configures a node - it must be called exactly once (or
164	never) before calling other AnyEvent::MP functions.	174	never) before calling other AnyEvent::MP functions.
165		175
166	All arguments (optionally except for the first) are noderefs, which can be
167	either resolved or unresolved.
168
169	The first argument will be looked up in the configuration database first
170	(if it is C<undef> then the current nodename will be used instead) to find
171	the relevant configuration profile (see L<aemp>). If none is found then
172	the default configuration is used. The configuration supplies additional
173	seed/master nodes and can override the actual noderef.
174
175	There are two types of networked nodes, public nodes and slave nodes:
176
177	=over 4	176	=over 4
178		177
179	=item public nodes	178	=item step 1, gathering configuration from profiles
180		179
181	For public nodes, C<$noderef> (supplied either directly to	180	The function first looks up a profile in the aemp configuration (see the
182	C<initialise_node> or indirectly via a profile or the nodename) must be a	181	L<aemp> commandline utility). The profile name can be specified via the
183	noderef (possibly unresolved, in which case it will be resolved).	182	named C<profile> parameter. If it is missing, then the nodename (F<uname
		183	-n>) will be used as profile name.
184		184
185	After resolving, the node will bind itself on all endpoints and try to	185	The profile data is then gathered as follows:
186	connect to all additional C<$seednodes> that are specified. Seednodes are
187	optional and can be used to quickly bootstrap the node into an existing
188	network.
189		186
190	=item slave nodes	187	First, all remaining key => value pairs (all of which are conviniently
		188	undocumented at the moment) will be interpreted as configuration
		189	data. Then they will be overwritten by any values specified in the global
		190	default configuration (see the F<aemp> utility), then the chain of
		191	profiles chosen by the profile name (and any C<parent> attributes).
191		192
192	When the C<$noderef> (either as given or overriden by the config file)	193	That means that the values specified in the profile have highest priority
193	is the special string C<slave/>, then the node will become a slave	194	and the values specified directly via C<configure> have lowest priority,
194	node. Slave nodes cannot be contacted from outside and will route most of	195	and can only be used to specify defaults.
195	their traffic to the master node that they attach to.
196		196
197	At least one additional noderef is required (either by specifying it	197	If the profile specifies a node ID, then this will become the node ID of
198	directly or because it is part of the configuration profile): The node	198	this process. If not, then the profile name will be used as node ID. The
199	will try to connect to all of them and will become a slave attached to the	199	special node ID of C<anon/> will be replaced by a random node ID.
200	first node it can successfully connect to.
201		200
202	Note that slave nodes cannot change their name, and consequently, their	201	=item step 2, bind listener sockets
203	master, so if the master goes down, the slave node will not function well	202
204	anymore until it can re-establish conenciton to its master. This makes	203	The next step is to look up the binds in the profile, followed by binding
205	slave nodes unsuitable for long-term nodes or fault-tolerant networks.	204	aemp protocol listeners on all binds specified (it is possible and valid
		205	to have no binds, meaning that the node cannot be contacted form the
		206	outside. This means the node cannot talk to other nodes that also have no
		207	binds, but it can still talk to all "normal" nodes).
		208
		209	If the profile does not specify a binds list, then a default of C<*> is
		210	used, meaning the node will bind on a dynamically-assigned port on every
		211	local IP address it finds.
		212
		213	=item step 3, connect to seed nodes
		214
		215	As the last step, the seeds list from the profile is passed to the
		216	L<AnyEvent::MP::Global> module, which will then use it to keep
		217	connectivity with at least one node at any point in time.
206		218
207	=back	219	=back
208		220
209	This function will block until all nodes have been resolved and, for slave	221	Example: become a distributed node using the locla node name as profile.
210	nodes, until it has successfully established a connection to a master	222	This should be the most common form of invocation for "daemon"-type nodes.
211	server.
212		223
213	All the seednodes will also be specially marked to automatically retry	224	configure
214	connecting to them infinitely.
215		225
216	Example: become a public node listening on the guessed noderef, or the one	226	Example: become an anonymous node. This form is often used for commandline
217	specified via C<aemp> for the current node. This should be the most common	227	clients.
218	form of invocation for "daemon"-type nodes.
219		228
220	initialise_node;	229	configure nodeid => "anon/";
221		230
222	Example: become a slave node to any of the the seednodes specified via	231	Example: configure a node using a profile called seed, which si suitable
223	C<aemp>. This form is often used for commandline clients.	232	for a seed node as it binds on all local addresses on a fixed port (4040,
		233	customary for aemp).
224		234
225	initialise_node "slave/";	235	# use the aemp commandline utility
		236	# aemp profile seed setnodeid anon/ setbinds '*:4040'
226		237
227	Example: become a slave node to any of the specified master servers. This	238	# then use it
228	form is also often used for commandline clients.	239	configure profile => "seed";
229		240
230	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";	241	# or simply use aemp from the shell again:
		242	# aemp run profile seed
231		243
232	Example: become a public node, and try to contact some well-known master	244	# or provide a nicer-to-remember nodeid
233	servers to become part of the network.	245	# aemp run profile seed nodeid "$(hostname)"
234
235	initialise_node undef, "master1", "master2";
236
237	Example: become a public node listening on port C<4041>.
238
239	initialise_node 4041;
240
241	Example: become a public node, only visible on localhost port 4044.
242
243	initialise_node "localhost:4044";
244
245	=item $cv = resolve_node $noderef
246
247	Takes an unresolved node reference that may contain hostnames and
248	abbreviated IDs, resolves all of them and returns a resolved node
249	reference.
250
251	In addition to C<address:port> pairs allowed in resolved noderefs, the
252	following forms are supported:
253
254	=over 4
255
256	=item the empty string
257
258	An empty-string component gets resolved as if the default port (4040) was
259	specified.
260
261	=item naked port numbers (e.g. C<1234>)
262
263	These are resolved by prepending the local nodename and a colon, to be
264	further resolved.
265
266	=item hostnames (e.g. C<localhost:1234>, C<localhost>)
267
268	These are resolved by using AnyEvent::DNS to resolve them, optionally
269	looking up SRV records for the C<aemp=4040> port, if no port was
270	specified.
271
272	=back
273		246
274	=item $SELF	247	=item $SELF
275		248
276	Contains the current port id while executing C<rcv> callbacks or C<psub>	249	Contains the current port id while executing C<rcv> callbacks or C<psub>
277	blocks.	250	blocks.
278		251
279	=item SELF, %SELF, @SELF...	252	=item *SELF, SELF, %SELF, @SELF...
280		253
281	Due to some quirks in how perl exports variables, it is impossible to	254	Due to some quirks in how perl exports variables, it is impossible to
282	just export C<$SELF>, all the symbols called C<SELF> are exported by this	255	just export C<$SELF>, all the symbols named C<SELF> are exported by this
283	module, but only C<$SELF> is currently used.	256	module, but only C<$SELF> is currently used.
284		257
285	=item snd $port, type => @data	258	=item snd $port, type => @data
286		259
287	=item snd $port, @msg	260	=item snd $port, @msg
288		261
289	Send the given message to the given port ID, which can identify either	262	Send the given message to the given port, which can identify either a
290	a local or a remote port, and must be a port ID.	263	local or a remote port, and must be a port ID.
291		264
292	While the message can be about anything, it is highly recommended to use a	265	While the message can be almost anything, it is highly recommended to
293	string as first element (a port ID, or some word that indicates a request	266	use a string as first element (a port ID, or some word that indicates a
294	type etc.).	267	request type etc.) and to consist if only simple perl values (scalars,
		268	arrays, hashes) - if you think you need to pass an object, think again.
295		269
296	The message data effectively becomes read-only after a call to this	270	The message data logically becomes read-only after a call to this
297	function: modifying any argument is not allowed and can cause many	271	function: modifying any argument (or values referenced by them) is
298	problems.	272	forbidden, as there can be considerable time between the call to C<snd>
		273	and the time the message is actually being serialised - in fact, it might
		274	never be copied as within the same process it is simply handed to the
		275	receiving port.
299		276
300	The type of data you can transfer depends on the transport protocol: when	277	The type of data you can transfer depends on the transport protocol: when
301	JSON is used, then only strings, numbers and arrays and hashes consisting	278	JSON is used, then only strings, numbers and arrays and hashes consisting
302	of those are allowed (no objects). When Storable is used, then anything	279	of those are allowed (no objects). When Storable is used, then anything
303	that Storable can serialise and deserialise is allowed, and for the local	280	that Storable can serialise and deserialise is allowed, and for the local
304	node, anything can be passed.	281	node, anything can be passed. Best rely only on the common denominator of
		282	these.
305		283
306	=item $local_port = port	284	=item $local_port = port
307		285
308	Create a new local port object and returns its port ID. Initially it has	286	Create a new local port object and returns its port ID. Initially it has
309	no callbacks set and will throw an error when it receives messages.	287	no callbacks set and will throw an error when it receives messages.
…		…
396		374
397	sub rcv($@) {	375	sub rcv($@) {
398	my $port = shift;	376	my $port = shift;
399	my ($noderef, $portid) = split /#/, $port, 2;	377	my ($noderef, $portid) = split /#/, $port, 2;
400		378
401	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	379	$NODE{$noderef} == $NODE{""}
402	or Carp::croak "$port: rcv can only be called on local ports, caught";	380	or Carp::croak "$port: rcv can only be called on local ports, caught";
403		381
404	while (@_) {	382	while (@_) {
405	if (ref $_[0]) {	383	if (ref $_[0]) {
406	if (my $self = $PORT_DATA{$portid}) {	384	if (my $self = $PORT_DATA{$portid}) {
…		…
485	$res	463	$res
486	}	464	}
487	}	465	}
488	}	466	}
489		467
490	=item $guard = mon $port, $cb->(@reason)	468	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
491		469
492	=item $guard = mon $port, $rcvport	470	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
493		471
494	=item $guard = mon $port	472	=item $guard = mon $port # kill $SELF when $port dies
495		473
496	=item $guard = mon $port, $rcvport, @msg	474	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
497		475
498	Monitor the given port and do something when the port is killed or	476	Monitor the given port and do something when the port is killed or
499	messages to it were lost, and optionally return a guard that can be used	477	messages to it were lost, and optionally return a guard that can be used
500	to stop monitoring again.	478	to stop monitoring again.
501		479
502	C<mon> effectively guarantees that, in the absence of hardware failures,	480	C<mon> effectively guarantees that, in the absence of hardware failures,
503	that after starting the monitor, either all messages sent to the port	481	after starting the monitor, either all messages sent to the port will
504	will arrive, or the monitoring action will be invoked after possible	482	arrive, or the monitoring action will be invoked after possible message
505	message loss has been detected. No messages will be lost "in between"	483	loss has been detected. No messages will be lost "in between" (after
506	(after the first lost message no further messages will be received by the	484	the first lost message no further messages will be received by the
507	port). After the monitoring action was invoked, further messages might get	485	port). After the monitoring action was invoked, further messages might get
508	delivered again.	486	delivered again.
		487
		488	Note that monitoring-actions are one-shot: once messages are lost (and a
		489	monitoring alert was raised), they are removed and will not trigger again.
509		490
510	In the first form (callback), the callback is simply called with any	491	In the first form (callback), the callback is simply called with any
511	number of C<@reason> elements (no @reason means that the port was deleted	492	number of C<@reason> elements (no @reason means that the port was deleted
512	"normally"). Note also that I<< the callback B<must> never die >>, so use	493	"normally"). Note also that I<< the callback B<must> never die >>, so use
513	C<eval> if unsure.	494	C<eval> if unsure.
…		…
575	is killed, the references will be freed.	556	is killed, the references will be freed.
576		557
577	Optionally returns a guard that will stop the monitoring.	558	Optionally returns a guard that will stop the monitoring.
578		559
579	This function is useful when you create e.g. timers or other watchers and	560	This function is useful when you create e.g. timers or other watchers and
580	want to free them when the port gets killed:	561	want to free them when the port gets killed (note the use of C<psub>):
581		562
582	$port->rcv (start => sub {	563	$port->rcv (start => sub {
583	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	564	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
584	undef $timer if 0.9 < rand;	565	undef $timer if 0.9 < rand;
585	});	566	});
586	});	567	});
587		568
588	=cut	569	=cut
…		…
597		578
598	=item kil $port[, @reason]	579	=item kil $port[, @reason]
599		580
600	Kill the specified port with the given C<@reason>.	581	Kill the specified port with the given C<@reason>.
601		582
602	If no C<@reason> is specified, then the port is killed "normally" (linked	583	If no C<@reason> is specified, then the port is killed "normally" (ports
603	ports will not be kileld, or even notified).	584	monitoring other ports will not necessarily die because a port dies
		585	"normally").
604		586
605	Otherwise, linked ports get killed with the same reason (second form of	587	Otherwise, linked ports get killed with the same reason (second form of
606	C<mon>, see below).	588	C<mon>, see above).
607		589
608	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	590	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
609	will be reported as reason C<< die => $@ >>.	591	will be reported as reason C<< die => $@ >>.
610		592
611	Transport/communication errors are reported as C<< transport_error =>	593	Transport/communication errors are reported as C<< transport_error =>
…		…
616	=item $port = spawn $node, $initfunc[, @initdata]	598	=item $port = spawn $node, $initfunc[, @initdata]
617		599
618	Creates a port on the node C<$node> (which can also be a port ID, in which	600	Creates a port on the node C<$node> (which can also be a port ID, in which
619	case it's the node where that port resides).	601	case it's the node where that port resides).
620		602
621	The port ID of the newly created port is return immediately, and it is	603	The port ID of the newly created port is returned immediately, and it is
622	permissible to immediately start sending messages or monitor the port.	604	possible to immediately start sending messages or to monitor the port.
623		605
624	After the port has been created, the init function is	606	After the port has been created, the init function is called on the remote
625	called. This function must be a fully-qualified function name	607	node, in the same context as a C<rcv> callback. This function must be a
626	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	608	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
627	program, use C<::name>.	609	specify a function in the main program, use C<::name>.
628		610
629	If the function doesn't exist, then the node tries to C<require>	611	If the function doesn't exist, then the node tries to C<require>
630	the package, then the package above the package and so on (e.g.	612	the package, then the package above the package and so on (e.g.
631	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	613	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
632	exists or it runs out of package names.	614	exists or it runs out of package names.
633		615
634	The init function is then called with the newly-created port as context	616	The init function is then called with the newly-created port as context
635	object (C<$SELF>) and the C<@initdata> values as arguments.	617	object (C<$SELF>) and the C<@initdata> values as arguments.
636		618
637	A common idiom is to pass your own port, monitor the spawned port, and	619	A common idiom is to pass a local port, immediately monitor the spawned
638	in the init function, monitor the original port. This two-way monitoring	620	port, and in the remote init function, immediately monitor the passed
639	ensures that both ports get cleaned up when there is a problem.	621	local port. This two-way monitoring ensures that both ports get cleaned up
		622	when there is a problem.
640		623
641	Example: spawn a chat server port on C<$othernode>.	624	Example: spawn a chat server port on C<$othernode>.
642		625
643	# this node, executed from within a port context:	626	# this node, executed from within a port context:
644	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	627	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
679	snd_to_func $noderef, "AnyEvent::MP::_spawn" => $id, @_;	662	snd_to_func $noderef, "AnyEvent::MP::_spawn" => $id, @_;
680		663
681	"$noderef#$id"	664	"$noderef#$id"
682	}	665	}
683		666
684	=back	667	=item after $timeout, @msg
685		668
686	=head1 NODE MESSAGES	669	=item after $timeout, $callback
687		670
688	Nodes understand the following messages sent to them. Many of them take	671	Either sends the given message, or call the given callback, after the
689	arguments called C<@reply>, which will simply be used to compose a reply	672	specified number of seconds.
690	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
691	the remaining arguments are simply the message data.
692		673
693	While other messages exist, they are not public and subject to change.	674	This is simply a utility function that comes in handy at times - the
		675	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		676	so it may go away in the future.
694		677
695	=over 4
696
697	=cut	678	=cut
698		679
699	=item lookup => $name, @reply	680	sub after($@) {
		681	my ($timeout, @action) = @_;
700		682
701	Replies with the port ID of the specified well-known port, or C<undef>.	683	my $t; $t = AE::timer $timeout, 0, sub {
702		684	undef $t;
703	=item devnull => ...	685	ref $action[0]
704		686	? $action[0]()
705	Generic data sink/CPU heat conversion.	687	: snd @action;
706		688	};
707	=item relay => $port, @msg	689	}
708
709	Simply forwards the message to the given port.
710
711	=item eval => $string[ @reply]
712
713	Evaluates the given string. If C<@reply> is given, then a message of the
714	form C<@reply, $@, @evalres> is sent.
715
716	Example: crash another node.
717
718	snd $othernode, eval => "exit";
719
720	=item time => @reply
721
722	Replies the the current node time to C<@reply>.
723
724	Example: tell the current node to send the current time to C<$myport> in a
725	C<timereply> message.
726
727	snd $NODE, time => $myport, timereply => 1, 2;
728	# => snd $myport, timereply => 1, 2, <time>
729		690
730	=back	691	=back
731		692
732	=head1 AnyEvent::MP vs. Distributed Erlang	693	=head1 AnyEvent::MP vs. Distributed Erlang
733		694
…		…
743		704
744	Despite the similarities, there are also some important differences:	705	Despite the similarities, there are also some important differences:
745		706
746	=over 4	707	=over 4
747		708
748	=item * Node references contain the recipe on how to contact them.	709	=item * Node IDs are arbitrary strings in AEMP.
749		710
750	Erlang relies on special naming and DNS to work everywhere in the	711	Erlang relies on special naming and DNS to work everywhere in the same
751	same way. AEMP relies on each node knowing it's own address(es), with	712	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
752	convenience functionality.	713	configuraiton or DNS), but will otherwise discover other odes itself.
753
754	This means that AEMP requires a less tightly controlled environment at the
755	cost of longer node references and a slightly higher management overhead.
756		714
757	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP	715	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
758	uses "local ports are like remote ports".	716	uses "local ports are like remote ports".
759		717
760	The failure modes for local ports are quite different (runtime errors	718	The failure modes for local ports are quite different (runtime errors
…		…
789		747
790	Erlang makes few guarantees on messages delivery - messages can get lost	748	Erlang makes few guarantees on messages delivery - messages can get lost
791	without any of the processes realising it (i.e. you send messages a, b,	749	without any of the processes realising it (i.e. you send messages a, b,
792	and c, and the other side only receives messages a and c).	750	and c, and the other side only receives messages a and c).
793		751
794	AEMP guarantees correct ordering, and the guarantee that there are no	752	AEMP guarantees correct ordering, and the guarantee that after one message
795	holes in the message sequence.	753	is lost, all following ones sent to the same port are lost as well, until
796		754	monitoring raises an error, so there are no silent "holes" in the message
797	=item * In Erlang, processes can be declared dead and later be found to be	755	sequence.
798	alive.
799
800	In Erlang it can happen that a monitored process is declared dead and
801	linked processes get killed, but later it turns out that the process is
802	still alive - and can receive messages.
803
804	In AEMP, when port monitoring detects a port as dead, then that port will
805	eventually be killed - it cannot happen that a node detects a port as dead
806	and then later sends messages to it, finding it is still alive.
807		756
808	=item * Erlang can send messages to the wrong port, AEMP does not.	757	=item * Erlang can send messages to the wrong port, AEMP does not.
809		758
810	In Erlang it is quite likely that a node that restarts reuses a process ID	759	In Erlang it is quite likely that a node that restarts reuses a process ID
811	known to other nodes for a completely different process, causing messages	760	known to other nodes for a completely different process, causing messages
…		…
815	around in the network will not be sent to an unrelated port.	764	around in the network will not be sent to an unrelated port.
816		765
817	=item * Erlang uses unprotected connections, AEMP uses secure	766	=item * Erlang uses unprotected connections, AEMP uses secure
818	authentication and can use TLS.	767	authentication and can use TLS.
819		768
820	AEMP can use a proven protocol - SSL/TLS - to protect connections and	769	AEMP can use a proven protocol - TLS - to protect connections and
821	securely authenticate nodes.	770	securely authenticate nodes.
822		771
823	=item * The AEMP protocol is optimised for both text-based and binary	772	=item * The AEMP protocol is optimised for both text-based and binary
824	communications.	773	communications.
825		774
826	The AEMP protocol, unlike the Erlang protocol, supports both	775	The AEMP protocol, unlike the Erlang protocol, supports both programming
827	language-independent text-only protocols (good for debugging) and binary,	776	language independent text-only protocols (good for debugging) and binary,
828	language-specific serialisers (e.g. Storable).	777	language-specific serialisers (e.g. Storable). By default, unless TLS is
		778	used, the protocol is actually completely text-based.
829		779
830	It has also been carefully designed to be implementable in other languages	780	It has also been carefully designed to be implementable in other languages
831	with a minimum of work while gracefully degrading fucntionality to make the	781	with a minimum of work while gracefully degrading functionality to make the
832	protocol simple.	782	protocol simple.
833		783
834	=item * AEMP has more flexible monitoring options than Erlang.	784	=item * AEMP has more flexible monitoring options than Erlang.
835		785
836	In Erlang, you can chose to receive I<all> exit signals as messages	786	In Erlang, you can chose to receive I<all> exit signals as messages
…		…
839	Erlang, as one can choose between automatic kill, exit message or callback	789	Erlang, as one can choose between automatic kill, exit message or callback
840	on a per-process basis.	790	on a per-process basis.
841		791
842	=item * Erlang tries to hide remote/local connections, AEMP does not.	792	=item * Erlang tries to hide remote/local connections, AEMP does not.
843		793
844	Monitoring in Erlang is not an indicator of process death/crashes,	794	Monitoring in Erlang is not an indicator of process death/crashes, in the
845	as linking is (except linking is unreliable in Erlang).	795	same way as linking is (except linking is unreliable in Erlang).
846		796
847	In AEMP, you don't "look up" registered port names or send to named ports	797	In AEMP, you don't "look up" registered port names or send to named ports
848	that might or might not be persistent. Instead, you normally spawn a port	798	that might or might not be persistent. Instead, you normally spawn a port
849	on the remote node. The init function monitors the you, and you monitor	799	on the remote node. The init function monitors you, and you monitor the
850	the remote port. Since both monitors are local to the node, they are much	800	remote port. Since both monitors are local to the node, they are much more
851	more reliable.	801	reliable (no need for C<spawn_link>).
852		802
853	This also saves round-trips and avoids sending messages to the wrong port	803	This also saves round-trips and avoids sending messages to the wrong port
854	(hard to do in Erlang).	804	(hard to do in Erlang).
855		805
856	=back	806	=back
857		807
858	=head1 RATIONALE	808	=head1 RATIONALE
859		809
860	=over 4	810	=over 4
861		811
862	=item Why strings for ports and noderefs, why not objects?	812	=item Why strings for port and node IDs, why not objects?
863		813
864	We considered "objects", but found that the actual number of methods	814	We considered "objects", but found that the actual number of methods
865	thatc an be called are very low. Since port IDs and noderefs travel over	815	that can be called are quite low. Since port and node IDs travel over
866	the network frequently, the serialising/deserialising would add lots of	816	the network frequently, the serialising/deserialising would add lots of
867	overhead, as well as having to keep a proxy object.	817	overhead, as well as having to keep a proxy object everywhere.
868		818
869	Strings can easily be printed, easily serialised etc. and need no special	819	Strings can easily be printed, easily serialised etc. and need no special
870	procedures to be "valid".	820	procedures to be "valid".
871		821
872	And a a miniport consists of a single closure stored in a global hash - it	822	And as a result, a miniport consists of a single closure stored in a
873	can't become much cheaper.	823	global hash - it can't become much cheaper.
874		824
875	=item Why favour JSON, why not real serialising format such as Storable?	825	=item Why favour JSON, why not a real serialising format such as Storable?
876		826
877	In fact, any AnyEvent::MP node will happily accept Storable as framing	827	In fact, any AnyEvent::MP node will happily accept Storable as framing
878	format, but currently there is no way to make a node use Storable by	828	format, but currently there is no way to make a node use Storable by
879	default.	829	default (although all nodes will accept it).
880		830
881	The default framing protocol is JSON because a) JSON::XS is many times	831	The default framing protocol is JSON because a) JSON::XS is many times
882	faster for small messages and b) most importantly, after years of	832	faster for small messages and b) most importantly, after years of
883	experience we found that object serialisation is causing more problems	833	experience we found that object serialisation is causing more problems
884	than it gains: Just like function calls, objects simply do not travel	834	than it solves: Just like function calls, objects simply do not travel
885	easily over the network, mostly because they will always be a copy, so you	835	easily over the network, mostly because they will always be a copy, so you
886	always have to re-think your design.	836	always have to re-think your design.
887		837
888	Keeping your messages simple, concentrating on data structures rather than	838	Keeping your messages simple, concentrating on data structures rather than
889	objects, will keep your messages clean, tidy and efficient.	839	objects, will keep your messages clean, tidy and efficient.
890		840
891	=back	841	=back
892		842
893	=head1 SEE ALSO	843	=head1 SEE ALSO
894		844
		845	L<AnyEvent::MP::Intro> - a gentle introduction.
		846
		847	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		848
		849	L<AnyEvent::MP::Global> - network maintainance and port groups, to find
		850	your applications.
		851
895	L<AnyEvent>.	852	L<AnyEvent>.
896		853
897	=head1 AUTHOR	854	=head1 AUTHOR
898		855
899	Marc Lehmann <schmorp@schmorp.de>	856	Marc Lehmann <schmorp@schmorp.de>

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Revision 1.72 by root, Mon Aug 31 10:07:04 2009 UTC