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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.63 by root, Thu Aug 27 21:29:37 2009 UTC vs.
Revision 1.68 by root, Fri Aug 28 23:06:33 2009 UTC

…		…
40		40
41	=head1 CURRENT STATUS	41	=head1 CURRENT STATUS
42		42
43	AnyEvent::MP - stable API, should work	43	AnyEvent::MP - stable API, should work
44	AnyEvent::MP::Intro - outdated	44	AnyEvent::MP::Intro - outdated
45	AnyEvent::MP::Kernel - WIP
46	AnyEvent::MP::Transport - mostly stable	45	AnyEvent::MP::Kernel - mostly stable
		46	AnyEvent::MP::Global - mostly stable
		47	AnyEvent::MP::Node - mostly stable, but internal anyways
		48	AnyEvent::MP::Transport - mostly stable, but internal anyways
47		49
48	stay tuned.	50	stay tuned.
49		51
50	=head1 DESCRIPTION	52	=head1 DESCRIPTION
51		53
52	This module (-family) implements a simple message passing framework.	54	This module (-family) implements a simple message passing framework.
53		55
54	Despite its simplicity, you can securely message other processes running	56	Despite its simplicity, you can securely message other processes running
55	on the same or other hosts.	57	on the same or other hosts, and you can supervise entities remotely.
56		58
57	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	59	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
58	manual page.	60	manual page and the examples under F<eg/>.
59		61
60	At the moment, this module family is severly broken and underdocumented,	62	At the moment, this module family is a bit underdocumented.
61	so do not use. This was uploaded mainly to reserve the CPAN namespace -
62	stay tuned!
63		63
64	=head1 CONCEPTS	64	=head1 CONCEPTS
65		65
66	=over 4	66	=over 4
67		67
68	=item port	68	=item port
69		69
70	A port is something you can send messages to (with the C<snd> function).	70	A port is something you can send messages to (with the C<snd> function).
71		71
72	Ports allow you to register C<rcv> handlers that can match all or just	72	Ports allow you to register C<rcv> handlers that can match all or just
73	some messages. Messages will not be queued.	73	some messages. Messages send to ports will not be queued, regardless of
		74	anything was listening for them or not.
74		75
75	=item port ID - C<noderef#portname>	76	=item port ID - C<nodeid#portname>
76		77
77	A port ID is the concatenation of a noderef, a hash-mark (C<#>) as	78	A port ID is the concatenation of a node ID, a hash-mark (C<#>) as
78	separator, and a port name (a printable string of unspecified format). An	79	separator, and a port name (a printable string of unspecified format).
79	exception is the the node port, whose ID is identical to its node
80	reference.
81		80
82	=item node	81	=item node
83		82
84	A node is a single process containing at least one port - the node port,	83	A node is a single process containing at least one port - the node port,
85	which provides nodes to manage each other remotely, and to create new	84	which enables nodes to manage each other remotely, and to create new
86	ports.	85	ports.
87		86
88	Nodes are either private (single-process only), slaves (can only talk to	87	Nodes are either public (have one or more listening ports) or private
89	public nodes, but do not need an open port) or public nodes (connectable	88	(no listening ports). Private nodes cannot talk to other private nodes
90	from any other node).	89	currently.
91		90
92	=item node ID - C<[a-za-Z0-9_\-.:]+>	91	=item node ID - C<[a-za-Z0-9_\-.:]+>
93		92
94	A node ID is a string that either simply identifies the node (for	93	A node ID is a string that uniquely identifies the node within a
95	private and slave nodes), or contains a recipe on how to reach a given	94	network. Depending on the configuration used, node IDs can look like a
96	node (for public nodes).	95	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		96	doesn't interpret node IDs in any way.
97		97
98	This recipe is simply a comma-separated list of C<address:port> pairs (for	98	=item binds - C<ip:port>
99	TCP/IP, other protocols might look different).
100		99
101	Node references come in two flavours: resolved (containing only numerical	100	Nodes can only talk to each other by creating some kind of connection to
102	addresses) or unresolved (where hostnames are used instead of addresses).	101	each other. To do this, nodes should listen on one or more local transport
		102	endpoints - binds. Currently, only standard C<ip:port> specifications can
		103	be used, which specify TCP ports to listen on.
103		104
104	Before using an unresolved node reference in a message you first have to	105	=item seeds - C<host:port>
105	resolve it.	106
		107	When a node starts, it knows nothing about the network. To teach the node
		108	about the network it first has to contact some other node within the
		109	network. This node is called a seed.
		110
		111	Seeds are transport endpoint(s) of as many nodes as one wants. Those nodes
		112	are expected to be long-running, and at least one of those should always
		113	be available. When nodes run out of connections (e.g. due to a network
		114	error), they try to re-establish connections to some seednodes again to
		115	join the network.
		116
		117	Apart from being sued for seeding, seednodes are not special in any way -
		118	every public node can be a seednode.
106		119
107	=back	120	=back
108		121
109	=head1 VARIABLES/FUNCTIONS	122	=head1 VARIABLES/FUNCTIONS
110		123
…		…
126		139
127	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	140	our $VERSION = $AnyEvent::MP::Kernel::VERSION;
128		141
129	our @EXPORT = qw(	142	our @EXPORT = qw(
130	NODE $NODE *SELF node_of after	143	NODE $NODE *SELF node_of after
131	resolve_node initialise_node	144	initialise_node
132	snd rcv mon mon_guard kil reg psub spawn	145	snd rcv mon mon_guard kil reg psub spawn
133	port	146	port
134	);	147	);
135		148
136	our $SELF;	149	our $SELF;
…		…
141	kil $SELF, die => $msg;	154	kil $SELF, die => $msg;
142	}	155	}
143		156
144	=item $thisnode = NODE / $NODE	157	=item $thisnode = NODE / $NODE
145		158
146	The C<NODE> function returns, and the C<$NODE> variable contains the	159	The C<NODE> function returns, and the C<$NODE> variable contains, the node
147	node id of the local node. The value is initialised by a call to	160	ID of the node running in the current process. This value is initialised by
148	C<initialise_node>.	161	a call to C<initialise_node>.
149		162
150	=item $nodeid = node_of $port	163	=item $nodeid = node_of $port
151		164
152	Extracts and returns the noderef from a port ID or a node ID.	165	Extracts and returns the node ID from a port ID or a node ID.
153		166
154	=item initialise_node $profile_name	167	=item initialise_node $profile_name
155		168
156	Before a node can talk to other nodes on the network it has to initialise	169	Before a node can talk to other nodes on the network (i.e. enter
157	itself - the minimum a node needs to know is it's own name, and optionally	170	"distributed mode") it has to initialise itself - the minimum a node needs
158	it should know the noderefs of some other nodes in the network.	171	to know is its own name, and optionally it should know the addresses of
		172	some other nodes in the network to discover other nodes.
159		173
160	This function initialises a node - it must be called exactly once (or	174	This function initialises a node - it must be called exactly once (or
161	never) before calling other AnyEvent::MP functions.	175	never) before calling other AnyEvent::MP functions.
162		176
163	All arguments (optionally except for the first) are noderefs, which can be	177	The first argument is a profile name. If it is C<undef> or missing, then
164	either resolved or unresolved.	178	the current nodename will be used instead (i.e. F<uname -n>).
165		179
166	The first argument will be looked up in the configuration database first	180	The function then looks up the profile in the aemp configuration (see the
167	(if it is C<undef> then the current nodename will be used instead) to find	181	L<aemp> commandline utility).
168	the relevant configuration profile (see L<aemp>). If none is found then
169	the default configuration is used. The configuration supplies additional
170	seed/master nodes and can override the actual noderef.
171		182
172	There are two types of networked nodes, public nodes and slave nodes:	183	If the profile specifies a node ID, then this will become the node ID of
		184	this process. If not, then the profile name will be used as node ID. The
		185	special node ID of C<anon/> will be replaced by a random node ID.
173		186
174	=over 4	187	The next step is to look up the binds in the profile, followed by binding
		188	aemp protocol listeners on all binds specified (it is possible and valid
		189	to have no binds, meaning that the node cannot be contacted form the
		190	outside. This means the node cannot talk to other nodes that also have no
		191	binds, but it can still talk to all "normal" nodes).
175		192
176	=item public nodes	193	If the profile does not specify a binds list, then the node ID will be
		194	treated as if it were of the form C<host:port>, which will be resolved and
		195	used as binds list.
177		196
178	For public nodes, C<$noderef> (supplied either directly to	197	Lastly, the seeds list from the profile is passed to the
179	C<initialise_node> or indirectly via a profile or the nodename) must be a	198	L<AnyEvent::MP::Global> module, which will then use it to keep
180	noderef (possibly unresolved, in which case it will be resolved).	199	connectivity with at least on of those seed nodes at any point in time.
181		200
182	After resolving, the node will bind itself on all endpoints.
183
184	=item slave nodes
185
186	When the C<$noderef> (either as given or overriden by the config file)
187	is the special string C<slave/>, then the node will become a slave
188	node. Slave nodes cannot be contacted from outside, and cannot talk to
189	each other (at least in this version of AnyEvent::MP).
190
191	Slave nodes work by creating connections to all public nodes, using the
192	L<AnyEvent::MP::Global> service.
193
194	=back
195
196	After initialising itself, the node will connect to all additional
197	C<$seednodes> that are specified diretcly or via a profile. Seednodes are
198	optional and can be used to quickly bootstrap the node into an existing
199	network.
200
201	All the seednodes will also be specially marked to automatically retry
202	connecting to them indefinitely, so make sure that seednodes are really
203	reliable and up (this might also change in the future).
204
205	Example: become a public node listening on the guessed noderef, or the one	201	Example: become a distributed node listening on the guessed noderef, or
206	specified via C<aemp> for the current node. This should be the most common	202	the one specified via C<aemp> for the current node. This should be the
207	form of invocation for "daemon"-type nodes.	203	most common form of invocation for "daemon"-type nodes.
208		204
209	initialise_node;	205	initialise_node;
210		206
211	Example: become a slave node to any of the the seednodes specified via	207	Example: become an anonymous node. This form is often used for commandline
212	C<aemp>. This form is often used for commandline clients.	208	clients.
213		209
214	initialise_node "slave/";	210	initialise_node "anon/";
215		211
216	Example: become a public node, and try to contact some well-known master	212	Example: become a distributed node. If there is no profile of the given
217	servers to become part of the network.	213	name, or no binds list was specified, resolve C<localhost:4044> and bind
218		214	on the resulting addresses.
219	initialise_node undef, "master1", "master2";
220
221	Example: become a public node listening on port C<4041>.
222
223	initialise_node 4041;
224
225	Example: become a public node, only visible on localhost port 4044.
226		215
227	initialise_node "localhost:4044";	216	initialise_node "localhost:4044";
228
229	=item $cv = resolve_node $noderef
230
231	Takes an unresolved node reference that may contain hostnames and
232	abbreviated IDs, resolves all of them and returns a resolved node
233	reference.
234
235	In addition to C<address:port> pairs allowed in resolved noderefs, the
236	following forms are supported:
237
238	=over 4
239
240	=item the empty string
241
242	An empty-string component gets resolved as if the default port (4040) was
243	specified.
244
245	=item naked port numbers (e.g. C<1234>)
246
247	These are resolved by prepending the local nodename and a colon, to be
248	further resolved.
249
250	=item hostnames (e.g. C<localhost:1234>, C<localhost>)
251
252	These are resolved by using AnyEvent::DNS to resolve them, optionally
253	looking up SRV records for the C<aemp=4040> port, if no port was
254	specified.
255
256	=back
257		217
258	=item $SELF	218	=item $SELF
259		219
260	Contains the current port id while executing C<rcv> callbacks or C<psub>	220	Contains the current port id while executing C<rcv> callbacks or C<psub>
261	blocks.	221	blocks.
262		222
263	=item SELF, %SELF, @SELF...	223	=item *SELF, SELF, %SELF, @SELF...
264		224
265	Due to some quirks in how perl exports variables, it is impossible to	225	Due to some quirks in how perl exports variables, it is impossible to
266	just export C<$SELF>, all the symbols called C<SELF> are exported by this	226	just export C<$SELF>, all the symbols named C<SELF> are exported by this
267	module, but only C<$SELF> is currently used.	227	module, but only C<$SELF> is currently used.
268		228
269	=item snd $port, type => @data	229	=item snd $port, type => @data
270		230
271	=item snd $port, @msg	231	=item snd $port, @msg
272		232
273	Send the given message to the given port ID, which can identify either	233	Send the given message to the given port, which can identify either a
274	a local or a remote port, and must be a port ID.	234	local or a remote port, and must be a port ID.
275		235
276	While the message can be about anything, it is highly recommended to use a	236	While the message can be almost anything, it is highly recommended to
277	string as first element (a port ID, or some word that indicates a request	237	use a string as first element (a port ID, or some word that indicates a
278	type etc.).	238	request type etc.) and to consist if only simple perl values (scalars,
		239	arrays, hashes) - if you think you need to pass an object, think again.
279		240
280	The message data effectively becomes read-only after a call to this	241	The message data logically becomes read-only after a call to this
281	function: modifying any argument is not allowed and can cause many	242	function: modifying any argument (or values referenced by them) is
282	problems.	243	forbidden, as there can be considerable time between the call to C<snd>
		244	and the time the message is actually being serialised - in fact, it might
		245	never be copied as within the same process it is simply handed to the
		246	receiving port.
283		247
284	The type of data you can transfer depends on the transport protocol: when	248	The type of data you can transfer depends on the transport protocol: when
285	JSON is used, then only strings, numbers and arrays and hashes consisting	249	JSON is used, then only strings, numbers and arrays and hashes consisting
286	of those are allowed (no objects). When Storable is used, then anything	250	of those are allowed (no objects). When Storable is used, then anything
287	that Storable can serialise and deserialise is allowed, and for the local	251	that Storable can serialise and deserialise is allowed, and for the local
288	node, anything can be passed.	252	node, anything can be passed. Best rely only on the common denominator of
		253	these.
289		254
290	=item $local_port = port	255	=item $local_port = port
291		256
292	Create a new local port object and returns its port ID. Initially it has	257	Create a new local port object and returns its port ID. Initially it has
293	no callbacks set and will throw an error when it receives messages.	258	no callbacks set and will throw an error when it receives messages.
…		…
469	$res	434	$res
470	}	435	}
471	}	436	}
472	}	437	}
473		438
474	=item $guard = mon $port, $cb->(@reason)	439	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
475		440
476	=item $guard = mon $port, $rcvport	441	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
477		442
478	=item $guard = mon $port	443	=item $guard = mon $port # kill $SELF when $port dies
479		444
480	=item $guard = mon $port, $rcvport, @msg	445	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
481		446
482	Monitor the given port and do something when the port is killed or	447	Monitor the given port and do something when the port is killed or
483	messages to it were lost, and optionally return a guard that can be used	448	messages to it were lost, and optionally return a guard that can be used
484	to stop monitoring again.	449	to stop monitoring again.
485		450
486	C<mon> effectively guarantees that, in the absence of hardware failures,	451	C<mon> effectively guarantees that, in the absence of hardware failures,
487	that after starting the monitor, either all messages sent to the port	452	after starting the monitor, either all messages sent to the port will
488	will arrive, or the monitoring action will be invoked after possible	453	arrive, or the monitoring action will be invoked after possible message
489	message loss has been detected. No messages will be lost "in between"	454	loss has been detected. No messages will be lost "in between" (after
490	(after the first lost message no further messages will be received by the	455	the first lost message no further messages will be received by the
491	port). After the monitoring action was invoked, further messages might get	456	port). After the monitoring action was invoked, further messages might get
492	delivered again.	457	delivered again.
493		458
494	Note that monitoring-actions are one-shot: once released, they are removed	459	Note that monitoring-actions are one-shot: once messages are lost (and a
495	and will not trigger again.	460	monitoring alert was raised), they are removed and will not trigger again.
496		461
497	In the first form (callback), the callback is simply called with any	462	In the first form (callback), the callback is simply called with any
498	number of C<@reason> elements (no @reason means that the port was deleted	463	number of C<@reason> elements (no @reason means that the port was deleted
499	"normally"). Note also that I<< the callback B<must> never die >>, so use	464	"normally"). Note also that I<< the callback B<must> never die >>, so use
500	C<eval> if unsure.	465	C<eval> if unsure.
…		…
562	is killed, the references will be freed.	527	is killed, the references will be freed.
563		528
564	Optionally returns a guard that will stop the monitoring.	529	Optionally returns a guard that will stop the monitoring.
565		530
566	This function is useful when you create e.g. timers or other watchers and	531	This function is useful when you create e.g. timers or other watchers and
567	want to free them when the port gets killed:	532	want to free them when the port gets killed (note the use of C<psub>):
568		533
569	$port->rcv (start => sub {	534	$port->rcv (start => sub {
570	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	535	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
571	undef $timer if 0.9 < rand;	536	undef $timer if 0.9 < rand;
572	});	537	});
573	});	538	});
574		539
575	=cut	540	=cut
…		…
584		549
585	=item kil $port[, @reason]	550	=item kil $port[, @reason]
586		551
587	Kill the specified port with the given C<@reason>.	552	Kill the specified port with the given C<@reason>.
588		553
589	If no C<@reason> is specified, then the port is killed "normally" (linked	554	If no C<@reason> is specified, then the port is killed "normally" (ports
590	ports will not be kileld, or even notified).	555	monitoring other ports will not necessarily die because a port dies
		556	"normally").
591		557
592	Otherwise, linked ports get killed with the same reason (second form of	558	Otherwise, linked ports get killed with the same reason (second form of
593	C<mon>, see below).	559	C<mon>, see above).
594		560
595	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	561	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
596	will be reported as reason C<< die => $@ >>.	562	will be reported as reason C<< die => $@ >>.
597		563
598	Transport/communication errors are reported as C<< transport_error =>	564	Transport/communication errors are reported as C<< transport_error =>
…		…
603	=item $port = spawn $node, $initfunc[, @initdata]	569	=item $port = spawn $node, $initfunc[, @initdata]
604		570
605	Creates a port on the node C<$node> (which can also be a port ID, in which	571	Creates a port on the node C<$node> (which can also be a port ID, in which
606	case it's the node where that port resides).	572	case it's the node where that port resides).
607		573
608	The port ID of the newly created port is return immediately, and it is	574	The port ID of the newly created port is returned immediately, and it is
609	permissible to immediately start sending messages or monitor the port.	575	possible to immediately start sending messages or to monitor the port.
610		576
611	After the port has been created, the init function is	577	After the port has been created, the init function is called on the remote
612	called. This function must be a fully-qualified function name	578	node, in the same context as a C<rcv> callback. This function must be a
613	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	579	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
614	program, use C<::name>.	580	specify a function in the main program, use C<::name>.
615		581
616	If the function doesn't exist, then the node tries to C<require>	582	If the function doesn't exist, then the node tries to C<require>
617	the package, then the package above the package and so on (e.g.	583	the package, then the package above the package and so on (e.g.
618	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	584	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
619	exists or it runs out of package names.	585	exists or it runs out of package names.
620		586
621	The init function is then called with the newly-created port as context	587	The init function is then called with the newly-created port as context
622	object (C<$SELF>) and the C<@initdata> values as arguments.	588	object (C<$SELF>) and the C<@initdata> values as arguments.
623		589
624	A common idiom is to pass your own port, monitor the spawned port, and	590	A common idiom is to pass a local port, immediately monitor the spawned
625	in the init function, monitor the original port. This two-way monitoring	591	port, and in the remote init function, immediately monitor the passed
626	ensures that both ports get cleaned up when there is a problem.	592	local port. This two-way monitoring ensures that both ports get cleaned up
		593	when there is a problem.
627		594
628	Example: spawn a chat server port on C<$othernode>.	595	Example: spawn a chat server port on C<$othernode>.
629		596
630	# this node, executed from within a port context:	597	# this node, executed from within a port context:
631	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	598	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
673	=item after $timeout, $callback	640	=item after $timeout, $callback
674		641
675	Either sends the given message, or call the given callback, after the	642	Either sends the given message, or call the given callback, after the
676	specified number of seconds.	643	specified number of seconds.
677		644
678	This is simply a utility function that come sin handy at times.	645	This is simply a utility function that comes in handy at times - the
		646	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		647	so it may go away in the future.
679		648
680	=cut	649	=cut
681		650
682	sub after($@) {	651	sub after($@) {
683	my ($timeout, @action) = @_;	652	my ($timeout, @action) = @_;
…		…
706		675
707	Despite the similarities, there are also some important differences:	676	Despite the similarities, there are also some important differences:
708		677
709	=over 4	678	=over 4
710		679
711	=item * Node references contain the recipe on how to contact them.	680	=item * Node IDs are arbitrary strings in AEMP.
712		681
713	Erlang relies on special naming and DNS to work everywhere in the	682	Erlang relies on special naming and DNS to work everywhere in the same
714	same way. AEMP relies on each node knowing it's own address(es), with	683	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
715	convenience functionality.	684	configuraiton or DNS), but will otherwise discover other odes itself.
716
717	This means that AEMP requires a less tightly controlled environment at the
718	cost of longer node references and a slightly higher management overhead.
719		685
720	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP	686	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
721	uses "local ports are like remote ports".	687	uses "local ports are like remote ports".
722		688
723	The failure modes for local ports are quite different (runtime errors	689	The failure modes for local ports are quite different (runtime errors
…		…
752		718
753	Erlang makes few guarantees on messages delivery - messages can get lost	719	Erlang makes few guarantees on messages delivery - messages can get lost
754	without any of the processes realising it (i.e. you send messages a, b,	720	without any of the processes realising it (i.e. you send messages a, b,
755	and c, and the other side only receives messages a and c).	721	and c, and the other side only receives messages a and c).
756		722
757	AEMP guarantees correct ordering, and the guarantee that there are no	723	AEMP guarantees correct ordering, and the guarantee that after one message
758	holes in the message sequence.	724	is lost, all following ones sent to the same port are lost as well, until
759		725	monitoring raises an error, so there are no silent "holes" in the message
760	=item * In Erlang, processes can be declared dead and later be found to be	726	sequence.
761	alive.
762
763	In Erlang it can happen that a monitored process is declared dead and
764	linked processes get killed, but later it turns out that the process is
765	still alive - and can receive messages.
766
767	In AEMP, when port monitoring detects a port as dead, then that port will
768	eventually be killed - it cannot happen that a node detects a port as dead
769	and then later sends messages to it, finding it is still alive.
770		727
771	=item * Erlang can send messages to the wrong port, AEMP does not.	728	=item * Erlang can send messages to the wrong port, AEMP does not.
772		729
773	In Erlang it is quite likely that a node that restarts reuses a process ID	730	In Erlang it is quite likely that a node that restarts reuses a process ID
774	known to other nodes for a completely different process, causing messages	731	known to other nodes for a completely different process, causing messages
…		…
778	around in the network will not be sent to an unrelated port.	735	around in the network will not be sent to an unrelated port.
779		736
780	=item * Erlang uses unprotected connections, AEMP uses secure	737	=item * Erlang uses unprotected connections, AEMP uses secure
781	authentication and can use TLS.	738	authentication and can use TLS.
782		739
783	AEMP can use a proven protocol - SSL/TLS - to protect connections and	740	AEMP can use a proven protocol - TLS - to protect connections and
784	securely authenticate nodes.	741	securely authenticate nodes.
785		742
786	=item * The AEMP protocol is optimised for both text-based and binary	743	=item * The AEMP protocol is optimised for both text-based and binary
787	communications.	744	communications.
788		745
789	The AEMP protocol, unlike the Erlang protocol, supports both	746	The AEMP protocol, unlike the Erlang protocol, supports both programming
790	language-independent text-only protocols (good for debugging) and binary,	747	language independent text-only protocols (good for debugging) and binary,
791	language-specific serialisers (e.g. Storable).	748	language-specific serialisers (e.g. Storable). By default, unless TLS is
		749	used, the protocol is actually completely text-based.
792		750
793	It has also been carefully designed to be implementable in other languages	751	It has also been carefully designed to be implementable in other languages
794	with a minimum of work while gracefully degrading fucntionality to make the	752	with a minimum of work while gracefully degrading functionality to make the
795	protocol simple.	753	protocol simple.
796		754
797	=item * AEMP has more flexible monitoring options than Erlang.	755	=item * AEMP has more flexible monitoring options than Erlang.
798		756
799	In Erlang, you can chose to receive I<all> exit signals as messages	757	In Erlang, you can chose to receive I<all> exit signals as messages
…		…
802	Erlang, as one can choose between automatic kill, exit message or callback	760	Erlang, as one can choose between automatic kill, exit message or callback
803	on a per-process basis.	761	on a per-process basis.
804		762
805	=item * Erlang tries to hide remote/local connections, AEMP does not.	763	=item * Erlang tries to hide remote/local connections, AEMP does not.
806		764
807	Monitoring in Erlang is not an indicator of process death/crashes,	765	Monitoring in Erlang is not an indicator of process death/crashes, in the
808	as linking is (except linking is unreliable in Erlang).	766	same way as linking is (except linking is unreliable in Erlang).
809		767
810	In AEMP, you don't "look up" registered port names or send to named ports	768	In AEMP, you don't "look up" registered port names or send to named ports
811	that might or might not be persistent. Instead, you normally spawn a port	769	that might or might not be persistent. Instead, you normally spawn a port
812	on the remote node. The init function monitors the you, and you monitor	770	on the remote node. The init function monitors you, and you monitor the
813	the remote port. Since both monitors are local to the node, they are much	771	remote port. Since both monitors are local to the node, they are much more
814	more reliable.	772	reliable (no need for C<spawn_link>).
815		773
816	This also saves round-trips and avoids sending messages to the wrong port	774	This also saves round-trips and avoids sending messages to the wrong port
817	(hard to do in Erlang).	775	(hard to do in Erlang).
818		776
819	=back	777	=back
820		778
821	=head1 RATIONALE	779	=head1 RATIONALE
822		780
823	=over 4	781	=over 4
824		782
825	=item Why strings for ports and noderefs, why not objects?	783	=item Why strings for port and node IDs, why not objects?
826		784
827	We considered "objects", but found that the actual number of methods	785	We considered "objects", but found that the actual number of methods
828	thatc an be called are very low. Since port IDs and noderefs travel over	786	that can be called are quite low. Since port and node IDs travel over
829	the network frequently, the serialising/deserialising would add lots of	787	the network frequently, the serialising/deserialising would add lots of
830	overhead, as well as having to keep a proxy object.	788	overhead, as well as having to keep a proxy object everywhere.
831		789
832	Strings can easily be printed, easily serialised etc. and need no special	790	Strings can easily be printed, easily serialised etc. and need no special
833	procedures to be "valid".	791	procedures to be "valid".
834		792
835	And a a miniport consists of a single closure stored in a global hash - it	793	And as a result, a miniport consists of a single closure stored in a
836	can't become much cheaper.	794	global hash - it can't become much cheaper.
837		795
838	=item Why favour JSON, why not real serialising format such as Storable?	796	=item Why favour JSON, why not a real serialising format such as Storable?
839		797
840	In fact, any AnyEvent::MP node will happily accept Storable as framing	798	In fact, any AnyEvent::MP node will happily accept Storable as framing
841	format, but currently there is no way to make a node use Storable by	799	format, but currently there is no way to make a node use Storable by
842	default.	800	default (although all nodes will accept it).
843		801
844	The default framing protocol is JSON because a) JSON::XS is many times	802	The default framing protocol is JSON because a) JSON::XS is many times
845	faster for small messages and b) most importantly, after years of	803	faster for small messages and b) most importantly, after years of
846	experience we found that object serialisation is causing more problems	804	experience we found that object serialisation is causing more problems
847	than it gains: Just like function calls, objects simply do not travel	805	than it solves: Just like function calls, objects simply do not travel
848	easily over the network, mostly because they will always be a copy, so you	806	easily over the network, mostly because they will always be a copy, so you
849	always have to re-think your design.	807	always have to re-think your design.
850		808
851	Keeping your messages simple, concentrating on data structures rather than	809	Keeping your messages simple, concentrating on data structures rather than
852	objects, will keep your messages clean, tidy and efficient.	810	objects, will keep your messages clean, tidy and efficient.
853		811
854	=back	812	=back
855		813
856	=head1 SEE ALSO	814	=head1 SEE ALSO
857		815
		816	L<AnyEvent::MP::Intro> - a gentle introduction.
		817
		818	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		819
		820	L<AnyEvent::MP::Global> - network maintainance and port groups, to find
		821	your applications.
		822
858	L<AnyEvent>.	823	L<AnyEvent>.
859		824
860	=head1 AUTHOR	825	=head1 AUTHOR
861		826
862	Marc Lehmann <schmorp@schmorp.de>	827	Marc Lehmann <schmorp@schmorp.de>

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Revision 1.68 by root, Fri Aug 28 23:06:33 2009 UTC