[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 1.71 by root, Sun Aug 30 19:52:56 2009 UTC

…		…
38	mon $port, $otherport # kill otherport on abnormal death	38	mon $port, $otherport # kill otherport on abnormal death
39	mon $port, $otherport, @msg # send message on death	39	mon $port, $otherport, @msg # send message on death
40		40
41	=head1 CURRENT STATUS	41	=head1 CURRENT STATUS
42		42
		43	bin/aemp - stable.
43	AnyEvent::MP - stable API, should work	44	AnyEvent::MP - stable API, should work.
44	AnyEvent::MP::Intro - outdated	45	AnyEvent::MP::Intro - uptodate, but incomplete.
45	AnyEvent::MP::Kernel - WIP
46	AnyEvent::MP::Transport - mostly stable	46	AnyEvent::MP::Kernel - mostly stable.
		47	AnyEvent::MP::Global - stable API, protocol not yet final.
47		48
48	stay tuned.	49	stay tuned.
49		50
50	=head1 DESCRIPTION	51	=head1 DESCRIPTION
51		52
52	This module (-family) implements a simple message passing framework.	53	This module (-family) implements a simple message passing framework.
53		54
54	Despite its simplicity, you can securely message other processes running	55	Despite its simplicity, you can securely message other processes running
55	on the same or other hosts.	56	on the same or other hosts, and you can supervise entities remotely.
56		57
57	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>
58	manual page.	59	manual page and the examples under F<eg/>.
59		60
60	At the moment, this module family is severly broken and underdocumented,	61	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		62
64	=head1 CONCEPTS	63	=head1 CONCEPTS
65		64
66	=over 4	65	=over 4
67		66
68	=item port	67	=item port
69		68
70	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).
71		70
72	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
73	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.
74		74
75	=item port ID - C<noderef#portname>	75	=item port ID - C<nodeid#portname>
76		76
77	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
78	separator, and a port name (a printable string of unspecified format). An	78	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		79
82	=item node	80	=item node
83		81
84	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,
85	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
86	ports.	84	ports.
87		85
88	Nodes are either private (single-process only), slaves (can only talk to	86	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	87	(no listening ports). Private nodes cannot talk to other private nodes
90	from any other node).	88	currently.
91		89
92	=item node ID - C<[a-za-Z0-9_\-.:]+>	90	=item node ID - C<[a-za-Z0-9_\-.:]+>
93		91
94	A node ID is a string that either simply identifies the node (for	92	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	93	network. Depending on the configuration used, node IDs can look like a
96	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.
97		96
98	This recipe is simply a comma-separated list of C<address:port> pairs (for	97	=item binds - C<ip:port>
99	TCP/IP, other protocols might look different).
100		98
101	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
102	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.
103		103
104	Before using an unresolved node reference in a message you first have to	104	=item seeds - C<host:port>
105	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.
106		118
107	=back	119	=back
108		120
109	=head1 VARIABLES/FUNCTIONS	121	=head1 VARIABLES/FUNCTIONS
110		122
…		…
126		138
127	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	139	our $VERSION = $AnyEvent::MP::Kernel::VERSION;
128		140
129	our @EXPORT = qw(	141	our @EXPORT = qw(
130	NODE $NODE *SELF node_of after	142	NODE $NODE *SELF node_of after
131	resolve_node initialise_node	143	initialise_node
132	snd rcv mon mon_guard kil reg psub spawn	144	snd rcv mon mon_guard kil reg psub spawn
133	port	145	port
134	);	146	);
135		147
136	our $SELF;	148	our $SELF;
…		…
141	kil $SELF, die => $msg;	153	kil $SELF, die => $msg;
142	}	154	}
143		155
144	=item $thisnode = NODE / $NODE	156	=item $thisnode = NODE / $NODE
145		157
146	The C<NODE> function returns, and the C<$NODE> variable contains the	158	The C<NODE> function returns, and the C<$NODE> variable contains, the node
147	node id 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
148	C<initialise_node>.	160	a call to C<initialise_node>.
149		161
150	=item $nodeid = node_of $port	162	=item $nodeid = node_of $port
151		163
152	Extracts and returns the noderef from a port ID or a node ID.	164	Extracts and returns the node ID from a port ID or a node ID.
153		165
154	=item initialise_node $profile_name	166	=item initialise_node $profile_name, key => value...
155		167
156	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
157	itself - the minimum a node needs to know is it's own name, and optionally	169	"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.	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.
159		172
160	This function initialises a node - it must be called exactly once (or	173	This function initialises a node - it must be called exactly once (or
161	never) before calling other AnyEvent::MP functions.	174	never) before calling other AnyEvent::MP functions.
162		175
163	All arguments (optionally except for the first) are noderefs, which can be	176	The first argument is a profile name. If it is C<undef> or missing, then
164	either resolved or unresolved.	177	the current nodename will be used instead (i.e. F<uname -n>).
165		178
166	The first argument will be looked up in the configuration database first	179	The function first 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	180	L<aemp> commandline utility). the profile is calculated as follows:
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		181
172	There are two types of networked nodes, public nodes and slave nodes:	182	First, all remaining key => value pairs (all of which are conviniently
		183	undocumented at the moment) will be used. Then they will be overwritten by
		184	any values specified in the global default configuration (see the F<aemp>
		185	utility), then the chain of profiles selected, if any. That means that
		186	the values specified in the profile have highest priority and the values
		187	specified via C<initialise_node> have lowest priority.
173		188
174	=over 4	189	If the profile specifies a node ID, then this will become the node ID of
		190	this process. If not, then the profile name will be used as node ID. The
		191	special node ID of C<anon/> will be replaced by a random node ID.
175		192
176	=item public nodes	193	The next step is to look up the binds in the profile, followed by binding
		194	aemp protocol listeners on all binds specified (it is possible and valid
		195	to have no binds, meaning that the node cannot be contacted form the
		196	outside. This means the node cannot talk to other nodes that also have no
		197	binds, but it can still talk to all "normal" nodes).
177		198
178	For public nodes, C<$noderef> (supplied either directly to	199	If the profile does not specify a binds list, then a default of C<*> is
179	C<initialise_node> or indirectly via a profile or the nodename) must be a	200	used.
180	noderef (possibly unresolved, in which case it will be resolved).
181		201
182	After resolving, the node will bind itself on all endpoints.	202	Lastly, the seeds list from the profile is passed to the
		203	L<AnyEvent::MP::Global> module, which will then use it to keep
		204	connectivity with at least on of those seed nodes at any point in time.
183		205
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	206	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	207	the one specified via C<aemp> for the current node. This should be the
207	form of invocation for "daemon"-type nodes.	208	most common form of invocation for "daemon"-type nodes.
208		209
209	initialise_node;	210	initialise_node;
210		211
211	Example: become a slave node to any of the the seednodes specified via	212	Example: become an anonymous node. This form is often used for commandline
212	C<aemp>. This form is often used for commandline clients.	213	clients.
213		214
214	initialise_node "slave/";	215	initialise_node "anon/";
215		216
216	Example: become a public node, and try to contact some well-known master	217	Example: become a distributed node. If there is no profile of the given
217	servers to become part of the network.	218	name, or no binds list was specified, resolve C<localhost:4044> and bind
218		219	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		220
227	initialise_node "localhost:4044";	221	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		222
258	=item $SELF	223	=item $SELF
259		224
260	Contains the current port id while executing C<rcv> callbacks or C<psub>	225	Contains the current port id while executing C<rcv> callbacks or C<psub>
261	blocks.	226	blocks.
262		227
263	=item SELF, %SELF, @SELF...	228	=item *SELF, SELF, %SELF, @SELF...
264		229
265	Due to some quirks in how perl exports variables, it is impossible to	230	Due to some quirks in how perl exports variables, it is impossible to
266	just export C<$SELF>, all the symbols called C<SELF> are exported by this	231	just export C<$SELF>, all the symbols named C<SELF> are exported by this
267	module, but only C<$SELF> is currently used.	232	module, but only C<$SELF> is currently used.
268		233
269	=item snd $port, type => @data	234	=item snd $port, type => @data
270		235
271	=item snd $port, @msg	236	=item snd $port, @msg
272		237
273	Send the given message to the given port ID, which can identify either	238	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.	239	local or a remote port, and must be a port ID.
275		240
276	While the message can be about anything, it is highly recommended to use a	241	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	242	use a string as first element (a port ID, or some word that indicates a
278	type etc.).	243	request type etc.) and to consist if only simple perl values (scalars,
		244	arrays, hashes) - if you think you need to pass an object, think again.
279		245
280	The message data effectively becomes read-only after a call to this	246	The message data logically becomes read-only after a call to this
281	function: modifying any argument is not allowed and can cause many	247	function: modifying any argument (or values referenced by them) is
282	problems.	248	forbidden, as there can be considerable time between the call to C<snd>
		249	and the time the message is actually being serialised - in fact, it might
		250	never be copied as within the same process it is simply handed to the
		251	receiving port.
283		252
284	The type of data you can transfer depends on the transport protocol: when	253	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	254	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	255	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	256	that Storable can serialise and deserialise is allowed, and for the local
288	node, anything can be passed.	257	node, anything can be passed. Best rely only on the common denominator of
		258	these.
289		259
290	=item $local_port = port	260	=item $local_port = port
291		261
292	Create a new local port object and returns its port ID. Initially it has	262	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.	263	no callbacks set and will throw an error when it receives messages.
…		…
469	$res	439	$res
470	}	440	}
471	}	441	}
472	}	442	}
473		443
474	=item $guard = mon $port, $cb->(@reason)	444	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
475		445
476	=item $guard = mon $port, $rcvport	446	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
477		447
478	=item $guard = mon $port	448	=item $guard = mon $port # kill $SELF when $port dies
479		449
480	=item $guard = mon $port, $rcvport, @msg	450	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
481		451
482	Monitor the given port and do something when the port is killed or	452	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	453	messages to it were lost, and optionally return a guard that can be used
484	to stop monitoring again.	454	to stop monitoring again.
485		455
486	C<mon> effectively guarantees that, in the absence of hardware failures,	456	C<mon> effectively guarantees that, in the absence of hardware failures,
487	that after starting the monitor, either all messages sent to the port	457	after starting the monitor, either all messages sent to the port will
488	will arrive, or the monitoring action will be invoked after possible	458	arrive, or the monitoring action will be invoked after possible message
489	message loss has been detected. No messages will be lost "in between"	459	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	460	the first lost message no further messages will be received by the
491	port). After the monitoring action was invoked, further messages might get	461	port). After the monitoring action was invoked, further messages might get
492	delivered again.	462	delivered again.
493		463
494	Note that monitoring-actions are one-shot: once released, they are removed	464	Note that monitoring-actions are one-shot: once messages are lost (and a
495	and will not trigger again.	465	monitoring alert was raised), they are removed and will not trigger again.
496		466
497	In the first form (callback), the callback is simply called with any	467	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	468	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	469	"normally"). Note also that I<< the callback B<must> never die >>, so use
500	C<eval> if unsure.	470	C<eval> if unsure.
…		…
562	is killed, the references will be freed.	532	is killed, the references will be freed.
563		533
564	Optionally returns a guard that will stop the monitoring.	534	Optionally returns a guard that will stop the monitoring.
565		535
566	This function is useful when you create e.g. timers or other watchers and	536	This function is useful when you create e.g. timers or other watchers and
567	want to free them when the port gets killed:	537	want to free them when the port gets killed (note the use of C<psub>):
568		538
569	$port->rcv (start => sub {	539	$port->rcv (start => sub {
570	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	540	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
571	undef $timer if 0.9 < rand;	541	undef $timer if 0.9 < rand;
572	});	542	});
573	});	543	});
574		544
575	=cut	545	=cut
…		…
584		554
585	=item kil $port[, @reason]	555	=item kil $port[, @reason]
586		556
587	Kill the specified port with the given C<@reason>.	557	Kill the specified port with the given C<@reason>.
588		558
589	If no C<@reason> is specified, then the port is killed "normally" (linked	559	If no C<@reason> is specified, then the port is killed "normally" (ports
590	ports will not be kileld, or even notified).	560	monitoring other ports will not necessarily die because a port dies
		561	"normally").
591		562
592	Otherwise, linked ports get killed with the same reason (second form of	563	Otherwise, linked ports get killed with the same reason (second form of
593	C<mon>, see below).	564	C<mon>, see above).
594		565
595	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	566	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
596	will be reported as reason C<< die => $@ >>.	567	will be reported as reason C<< die => $@ >>.
597		568
598	Transport/communication errors are reported as C<< transport_error =>	569	Transport/communication errors are reported as C<< transport_error =>
…		…
603	=item $port = spawn $node, $initfunc[, @initdata]	574	=item $port = spawn $node, $initfunc[, @initdata]
604		575
605	Creates a port on the node C<$node> (which can also be a port ID, in which	576	Creates a port on the node C<$node> (which can also be a port ID, in which
606	case it's the node where that port resides).	577	case it's the node where that port resides).
607		578
608	The port ID of the newly created port is return immediately, and it is	579	The port ID of the newly created port is returned immediately, and it is
609	permissible to immediately start sending messages or monitor the port.	580	possible to immediately start sending messages or to monitor the port.
610		581
611	After the port has been created, the init function is	582	After the port has been created, the init function is called on the remote
612	called. This function must be a fully-qualified function name	583	node, in the same context as a C<rcv> callback. This function must be a
613	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	584	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
614	program, use C<::name>.	585	specify a function in the main program, use C<::name>.
615		586
616	If the function doesn't exist, then the node tries to C<require>	587	If the function doesn't exist, then the node tries to C<require>
617	the package, then the package above the package and so on (e.g.	588	the package, then the package above the package and so on (e.g.
618	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	589	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
619	exists or it runs out of package names.	590	exists or it runs out of package names.
620		591
621	The init function is then called with the newly-created port as context	592	The init function is then called with the newly-created port as context
622	object (C<$SELF>) and the C<@initdata> values as arguments.	593	object (C<$SELF>) and the C<@initdata> values as arguments.
623		594
624	A common idiom is to pass your own port, monitor the spawned port, and	595	A common idiom is to pass a local port, immediately monitor the spawned
625	in the init function, monitor the original port. This two-way monitoring	596	port, and in the remote init function, immediately monitor the passed
626	ensures that both ports get cleaned up when there is a problem.	597	local port. This two-way monitoring ensures that both ports get cleaned up
		598	when there is a problem.
627		599
628	Example: spawn a chat server port on C<$othernode>.	600	Example: spawn a chat server port on C<$othernode>.
629		601
630	# this node, executed from within a port context:	602	# this node, executed from within a port context:
631	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	603	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
673	=item after $timeout, $callback	645	=item after $timeout, $callback
674		646
675	Either sends the given message, or call the given callback, after the	647	Either sends the given message, or call the given callback, after the
676	specified number of seconds.	648	specified number of seconds.
677		649
678	This is simply a utility function that come sin handy at times.	650	This is simply a utility function that comes in handy at times - the
		651	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		652	so it may go away in the future.
679		653
680	=cut	654	=cut
681		655
682	sub after($@) {	656	sub after($@) {
683	my ($timeout, @action) = @_;	657	my ($timeout, @action) = @_;
…		…
706		680
707	Despite the similarities, there are also some important differences:	681	Despite the similarities, there are also some important differences:
708		682
709	=over 4	683	=over 4
710		684
711	=item * Node references contain the recipe on how to contact them.	685	=item * Node IDs are arbitrary strings in AEMP.
712		686
713	Erlang relies on special naming and DNS to work everywhere in the	687	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	688	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
715	convenience functionality.	689	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		690
720	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP	691	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
721	uses "local ports are like remote ports".	692	uses "local ports are like remote ports".
722		693
723	The failure modes for local ports are quite different (runtime errors	694	The failure modes for local ports are quite different (runtime errors
…		…
752		723
753	Erlang makes few guarantees on messages delivery - messages can get lost	724	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,	725	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).	726	and c, and the other side only receives messages a and c).
756		727
757	AEMP guarantees correct ordering, and the guarantee that there are no	728	AEMP guarantees correct ordering, and the guarantee that after one message
758	holes in the message sequence.	729	is lost, all following ones sent to the same port are lost as well, until
759		730	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	731	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		732
771	=item * Erlang can send messages to the wrong port, AEMP does not.	733	=item * Erlang can send messages to the wrong port, AEMP does not.
772		734
773	In Erlang it is quite likely that a node that restarts reuses a process ID	735	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	736	known to other nodes for a completely different process, causing messages
…		…
778	around in the network will not be sent to an unrelated port.	740	around in the network will not be sent to an unrelated port.
779		741
780	=item * Erlang uses unprotected connections, AEMP uses secure	742	=item * Erlang uses unprotected connections, AEMP uses secure
781	authentication and can use TLS.	743	authentication and can use TLS.
782		744
783	AEMP can use a proven protocol - SSL/TLS - to protect connections and	745	AEMP can use a proven protocol - TLS - to protect connections and
784	securely authenticate nodes.	746	securely authenticate nodes.
785		747
786	=item * The AEMP protocol is optimised for both text-based and binary	748	=item * The AEMP protocol is optimised for both text-based and binary
787	communications.	749	communications.
788		750
789	The AEMP protocol, unlike the Erlang protocol, supports both	751	The AEMP protocol, unlike the Erlang protocol, supports both programming
790	language-independent text-only protocols (good for debugging) and binary,	752	language independent text-only protocols (good for debugging) and binary,
791	language-specific serialisers (e.g. Storable).	753	language-specific serialisers (e.g. Storable). By default, unless TLS is
		754	used, the protocol is actually completely text-based.
792		755
793	It has also been carefully designed to be implementable in other languages	756	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	757	with a minimum of work while gracefully degrading functionality to make the
795	protocol simple.	758	protocol simple.
796		759
797	=item * AEMP has more flexible monitoring options than Erlang.	760	=item * AEMP has more flexible monitoring options than Erlang.
798		761
799	In Erlang, you can chose to receive I<all> exit signals as messages	762	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	765	Erlang, as one can choose between automatic kill, exit message or callback
803	on a per-process basis.	766	on a per-process basis.
804		767
805	=item * Erlang tries to hide remote/local connections, AEMP does not.	768	=item * Erlang tries to hide remote/local connections, AEMP does not.
806		769
807	Monitoring in Erlang is not an indicator of process death/crashes,	770	Monitoring in Erlang is not an indicator of process death/crashes, in the
808	as linking is (except linking is unreliable in Erlang).	771	same way as linking is (except linking is unreliable in Erlang).
809		772
810	In AEMP, you don't "look up" registered port names or send to named ports	773	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	774	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	775	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	776	remote port. Since both monitors are local to the node, they are much more
814	more reliable.	777	reliable (no need for C<spawn_link>).
815		778
816	This also saves round-trips and avoids sending messages to the wrong port	779	This also saves round-trips and avoids sending messages to the wrong port
817	(hard to do in Erlang).	780	(hard to do in Erlang).
818		781
819	=back	782	=back
820		783
821	=head1 RATIONALE	784	=head1 RATIONALE
822		785
823	=over 4	786	=over 4
824		787
825	=item Why strings for ports and noderefs, why not objects?	788	=item Why strings for port and node IDs, why not objects?
826		789
827	We considered "objects", but found that the actual number of methods	790	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	791	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	792	the network frequently, the serialising/deserialising would add lots of
830	overhead, as well as having to keep a proxy object.	793	overhead, as well as having to keep a proxy object everywhere.
831		794
832	Strings can easily be printed, easily serialised etc. and need no special	795	Strings can easily be printed, easily serialised etc. and need no special
833	procedures to be "valid".	796	procedures to be "valid".
834		797
835	And a a miniport consists of a single closure stored in a global hash - it	798	And as a result, a miniport consists of a single closure stored in a
836	can't become much cheaper.	799	global hash - it can't become much cheaper.
837		800
838	=item Why favour JSON, why not real serialising format such as Storable?	801	=item Why favour JSON, why not a real serialising format such as Storable?
839		802
840	In fact, any AnyEvent::MP node will happily accept Storable as framing	803	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	804	format, but currently there is no way to make a node use Storable by
842	default.	805	default (although all nodes will accept it).
843		806
844	The default framing protocol is JSON because a) JSON::XS is many times	807	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	808	faster for small messages and b) most importantly, after years of
846	experience we found that object serialisation is causing more problems	809	experience we found that object serialisation is causing more problems
847	than it gains: Just like function calls, objects simply do not travel	810	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	811	easily over the network, mostly because they will always be a copy, so you
849	always have to re-think your design.	812	always have to re-think your design.
850		813
851	Keeping your messages simple, concentrating on data structures rather than	814	Keeping your messages simple, concentrating on data structures rather than
852	objects, will keep your messages clean, tidy and efficient.	815	objects, will keep your messages clean, tidy and efficient.
853		816
854	=back	817	=back
855		818
856	=head1 SEE ALSO	819	=head1 SEE ALSO
857		820
		821	L<AnyEvent::MP::Intro> - a gentle introduction.
		822
		823	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		824
		825	L<AnyEvent::MP::Global> - network maintainance and port groups, to find
		826	your applications.
		827
858	L<AnyEvent>.	828	L<AnyEvent>.
859		829
860	=head1 AUTHOR	830	=head1 AUTHOR
861		831
862	Marc Lehmann <schmorp@schmorp.de>	832	Marc Lehmann <schmorp@schmorp.de>

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Revision 1.71 by root, Sun Aug 30 19:52:56 2009 UTC