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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.62 by root, Thu Aug 27 07:12:48 2009 UTC vs.
Revision 1.69 by root, Sun Aug 30 18:51:49 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	initialise_node;
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...;
…		…
42		40
43	=head1 CURRENT STATUS	41	=head1 CURRENT STATUS
44		42
45	AnyEvent::MP - stable API, should work	43	AnyEvent::MP - stable API, should work
46	AnyEvent::MP::Intro - outdated	44	AnyEvent::MP::Intro - outdated
47	AnyEvent::MP::Kernel - WIP
48	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
49		49
50	stay tuned.	50	stay tuned.
51		51
52	=head1 DESCRIPTION	52	=head1 DESCRIPTION
53		53
54	This module (-family) implements a simple message passing framework.	54	This module (-family) implements a simple message passing framework.
55		55
56	Despite its simplicity, you can securely message other processes running	56	Despite its simplicity, you can securely message other processes running
57	on the same or other hosts.	57	on the same or other hosts, and you can supervise entities remotely.
58		58
59	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>
60	manual page.	60	manual page and the examples under F<eg/>.
61		61
62	At the moment, this module family is severly broken and underdocumented,	62	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		63
66	=head1 CONCEPTS	64	=head1 CONCEPTS
67		65
68	=over 4	66	=over 4
69		67
70	=item port	68	=item port
71		69
72	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).
73		71
74	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
75	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.
76		75
77	=item port id - C<noderef#portname>	76	=item port ID - C<nodeid#portname>
78		77
79	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
80	separator, and a port name (a printable string of unspecified format). An	79	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		80
84	=item node	81	=item node
85		82
86	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,
87	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
88	ports.	85	ports.
89		86
90	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
91	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
92	from any other node).	89	currently.
93		90
94	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	91	=item node ID - C<[a-za-Z0-9_\-.:]+>
95		92
96	A node reference is a string that either simply identifies the node (for	93	A node ID is a string that uniquely identifies the node within a
97	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
98	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.
99		97
100	This recipe is simply a comma-separated list of C<address:port> pairs (for	98	=item binds - C<ip:port>
101	TCP/IP, other protocols might look different).
102		99
103	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
104	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.
105		104
106	Before using an unresolved node reference in a message you first have to	105	=item seeds - C<host:port>
107	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.
108		119
109	=back	120	=back
110		121
111	=head1 VARIABLES/FUNCTIONS	122	=head1 VARIABLES/FUNCTIONS
112		123
…		…
128		139
129	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	140	our $VERSION = $AnyEvent::MP::Kernel::VERSION;
130		141
131	our @EXPORT = qw(	142	our @EXPORT = qw(
132	NODE $NODE *SELF node_of after	143	NODE $NODE *SELF node_of after
133	resolve_node initialise_node	144	initialise_node
134	snd rcv mon mon_guard kil reg psub spawn	145	snd rcv mon mon_guard kil reg psub spawn
135	port	146	port
136	);	147	);
137		148
138	our $SELF;	149	our $SELF;
…		…
143	kil $SELF, die => $msg;	154	kil $SELF, die => $msg;
144	}	155	}
145		156
146	=item $thisnode = NODE / $NODE	157	=item $thisnode = NODE / $NODE
147		158
148	The C<NODE> function returns, and the C<$NODE> variable contains the	159	The C<NODE> function returns, and the C<$NODE> variable contains, the node
149	noderef 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
150	C<initialise_node>.	161	a call to C<initialise_node>.
151		162
152	=item $noderef = node_of $port	163	=item $nodeid = node_of $port
153		164
154	Extracts and returns the noderef from a port ID or a noderef.	165	Extracts and returns the node ID from a port ID or a node ID.
155		166
156	=item initialise_node $noderef, $seednode, $seednode...	167	=item initialise_node $profile_name, key => value...
157		168
158	=item initialise_node "slave/", $master, $master...
159
160	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
161	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
162	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.
163		173
164	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
165	never) before calling other AnyEvent::MP functions.	175	never) before calling other AnyEvent::MP functions.
166		176
167	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
168	either resolved or unresolved.	178	the current nodename will be used instead (i.e. F<uname -n>).
169		179
170	The first argument will be looked up in the configuration database first	180	The function first looks up the profile in the aemp configuration (see the
171	(if it is C<undef> then the current nodename will be used instead) to find	181	L<aemp> commandline utility). the profile is calculated as follows:
172	the relevant configuration profile (see L<aemp>). If none is found then
173	the default configuration is used. The configuration supplies additional
174	seed/master nodes and can override the actual noderef.
175		182
176	There are two types of networked nodes, public nodes and slave nodes:	183	First, all remaining key => value pairs will be used. Then they will be
		184	overwritten by any values specified in the global default configuration
		185	(see the F<aemp> utility), then the chain of profiles selected, if
		186	any. That means that the values specified in the profile have highest
		187	priority and the values specified via C<initialise_node> have lowest
		188	priority.
177		189
178	=over 4	190	If the profile specifies a node ID, then this will become the node ID of
		191	this process. If not, then the profile name will be used as node ID. The
		192	special node ID of C<anon/> will be replaced by a random node ID.
179		193
180	=item public nodes	194	The next step is to look up the binds in the profile, followed by binding
		195	aemp protocol listeners on all binds specified (it is possible and valid
		196	to have no binds, meaning that the node cannot be contacted form the
		197	outside. This means the node cannot talk to other nodes that also have no
		198	binds, but it can still talk to all "normal" nodes).
181		199
182	For public nodes, C<$noderef> (supplied either directly to	200	If the profile does not specify a binds list, then the node ID will be
183	C<initialise_node> or indirectly via a profile or the nodename) must be a	201	treated as if it were of the form C<host:port>, which will be resolved and
184	noderef (possibly unresolved, in which case it will be resolved).	202	used as binds list.
185		203
186	After resolving, the node will bind itself on all endpoints.	204	Lastly, the seeds list from the profile is passed to the
		205	L<AnyEvent::MP::Global> module, which will then use it to keep
		206	connectivity with at least on of those seed nodes at any point in time.
187		207
188	=item slave nodes
189
190	When the C<$noderef> (either as given or overriden by the config file)
191	is the special string C<slave/>, then the node will become a slave
192	node. Slave nodes cannot be contacted from outside, and cannot talk to
193	each other (at least in this version of AnyEvent::MP).
194
195	Slave nodes work by creating connections to all public nodes, using the
196	L<AnyEvent::MP::Global> service.
197
198	=back
199
200	After initialising itself, the node will connect to all additional
201	C<$seednodes> that are specified diretcly or via a profile. Seednodes are
202	optional and can be used to quickly bootstrap the node into an existing
203	network.
204
205	All the seednodes will also be specially marked to automatically retry
206	connecting to them indefinitely, so make sure that seednodes are really
207	reliable and up (this might also change in the future).
208
209	Example: become a public node listening on the guessed noderef, or the one	208	Example: become a distributed node listening on the guessed noderef, or
210	specified via C<aemp> for the current node. This should be the most common	209	the one specified via C<aemp> for the current node. This should be the
211	form of invocation for "daemon"-type nodes.	210	most common form of invocation for "daemon"-type nodes.
212		211
213	initialise_node;	212	initialise_node;
214		213
215	Example: become a slave node to any of the the seednodes specified via	214	Example: become an anonymous node. This form is often used for commandline
216	C<aemp>. This form is often used for commandline clients.	215	clients.
217		216
218	initialise_node "slave/";	217	initialise_node "anon/";
219		218
220	Example: become a public node, and try to contact some well-known master	219	Example: become a distributed node. If there is no profile of the given
221	servers to become part of the network.	220	name, or no binds list was specified, resolve C<localhost:4044> and bind
222		221	on the resulting addresses.
223	initialise_node undef, "master1", "master2";
224
225	Example: become a public node listening on port C<4041>.
226
227	initialise_node 4041;
228
229	Example: become a public node, only visible on localhost port 4044.
230		222
231	initialise_node "localhost:4044";	223	initialise_node "localhost:4044";
232
233	=item $cv = resolve_node $noderef
234
235	Takes an unresolved node reference that may contain hostnames and
236	abbreviated IDs, resolves all of them and returns a resolved node
237	reference.
238
239	In addition to C<address:port> pairs allowed in resolved noderefs, the
240	following forms are supported:
241
242	=over 4
243
244	=item the empty string
245
246	An empty-string component gets resolved as if the default port (4040) was
247	specified.
248
249	=item naked port numbers (e.g. C<1234>)
250
251	These are resolved by prepending the local nodename and a colon, to be
252	further resolved.
253
254	=item hostnames (e.g. C<localhost:1234>, C<localhost>)
255
256	These are resolved by using AnyEvent::DNS to resolve them, optionally
257	looking up SRV records for the C<aemp=4040> port, if no port was
258	specified.
259
260	=back
261		224
262	=item $SELF	225	=item $SELF
263		226
264	Contains the current port id while executing C<rcv> callbacks or C<psub>	227	Contains the current port id while executing C<rcv> callbacks or C<psub>
265	blocks.	228	blocks.
266		229
267	=item SELF, %SELF, @SELF...	230	=item *SELF, SELF, %SELF, @SELF...
268		231
269	Due to some quirks in how perl exports variables, it is impossible to	232	Due to some quirks in how perl exports variables, it is impossible to
270	just export C<$SELF>, all the symbols called C<SELF> are exported by this	233	just export C<$SELF>, all the symbols named C<SELF> are exported by this
271	module, but only C<$SELF> is currently used.	234	module, but only C<$SELF> is currently used.
272		235
273	=item snd $port, type => @data	236	=item snd $port, type => @data
274		237
275	=item snd $port, @msg	238	=item snd $port, @msg
276		239
277	Send the given message to the given port ID, which can identify either	240	Send the given message to the given port, which can identify either a
278	a local or a remote port, and must be a port ID.	241	local or a remote port, and must be a port ID.
279		242
280	While the message can be about anything, it is highly recommended to use a	243	While the message can be almost anything, it is highly recommended to
281	string as first element (a port ID, or some word that indicates a request	244	use a string as first element (a port ID, or some word that indicates a
282	type etc.).	245	request type etc.) and to consist if only simple perl values (scalars,
		246	arrays, hashes) - if you think you need to pass an object, think again.
283		247
284	The message data effectively becomes read-only after a call to this	248	The message data logically becomes read-only after a call to this
285	function: modifying any argument is not allowed and can cause many	249	function: modifying any argument (or values referenced by them) is
286	problems.	250	forbidden, as there can be considerable time between the call to C<snd>
		251	and the time the message is actually being serialised - in fact, it might
		252	never be copied as within the same process it is simply handed to the
		253	receiving port.
287		254
288	The type of data you can transfer depends on the transport protocol: when	255	The type of data you can transfer depends on the transport protocol: when
289	JSON is used, then only strings, numbers and arrays and hashes consisting	256	JSON is used, then only strings, numbers and arrays and hashes consisting
290	of those are allowed (no objects). When Storable is used, then anything	257	of those are allowed (no objects). When Storable is used, then anything
291	that Storable can serialise and deserialise is allowed, and for the local	258	that Storable can serialise and deserialise is allowed, and for the local
292	node, anything can be passed.	259	node, anything can be passed. Best rely only on the common denominator of
		260	these.
293		261
294	=item $local_port = port	262	=item $local_port = port
295		263
296	Create a new local port object and returns its port ID. Initially it has	264	Create a new local port object and returns its port ID. Initially it has
297	no callbacks set and will throw an error when it receives messages.	265	no callbacks set and will throw an error when it receives messages.
…		…
473	$res	441	$res
474	}	442	}
475	}	443	}
476	}	444	}
477		445
478	=item $guard = mon $port, $cb->(@reason)	446	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
479		447
480	=item $guard = mon $port, $rcvport	448	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
481		449
482	=item $guard = mon $port	450	=item $guard = mon $port # kill $SELF when $port dies
483		451
484	=item $guard = mon $port, $rcvport, @msg	452	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
485		453
486	Monitor the given port and do something when the port is killed or	454	Monitor the given port and do something when the port is killed or
487	messages to it were lost, and optionally return a guard that can be used	455	messages to it were lost, and optionally return a guard that can be used
488	to stop monitoring again.	456	to stop monitoring again.
489		457
490	C<mon> effectively guarantees that, in the absence of hardware failures,	458	C<mon> effectively guarantees that, in the absence of hardware failures,
491	that after starting the monitor, either all messages sent to the port	459	after starting the monitor, either all messages sent to the port will
492	will arrive, or the monitoring action will be invoked after possible	460	arrive, or the monitoring action will be invoked after possible message
493	message loss has been detected. No messages will be lost "in between"	461	loss has been detected. No messages will be lost "in between" (after
494	(after the first lost message no further messages will be received by the	462	the first lost message no further messages will be received by the
495	port). After the monitoring action was invoked, further messages might get	463	port). After the monitoring action was invoked, further messages might get
496	delivered again.	464	delivered again.
497		465
498	Note that monitoring-actions are one-shot: once released, they are removed	466	Note that monitoring-actions are one-shot: once messages are lost (and a
499	and will not trigger again.	467	monitoring alert was raised), they are removed and will not trigger again.
500		468
501	In the first form (callback), the callback is simply called with any	469	In the first form (callback), the callback is simply called with any
502	number of C<@reason> elements (no @reason means that the port was deleted	470	number of C<@reason> elements (no @reason means that the port was deleted
503	"normally"). Note also that I<< the callback B<must> never die >>, so use	471	"normally"). Note also that I<< the callback B<must> never die >>, so use
504	C<eval> if unsure.	472	C<eval> if unsure.
…		…
566	is killed, the references will be freed.	534	is killed, the references will be freed.
567		535
568	Optionally returns a guard that will stop the monitoring.	536	Optionally returns a guard that will stop the monitoring.
569		537
570	This function is useful when you create e.g. timers or other watchers and	538	This function is useful when you create e.g. timers or other watchers and
571	want to free them when the port gets killed:	539	want to free them when the port gets killed (note the use of C<psub>):
572		540
573	$port->rcv (start => sub {	541	$port->rcv (start => sub {
574	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	542	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
575	undef $timer if 0.9 < rand;	543	undef $timer if 0.9 < rand;
576	});	544	});
577	});	545	});
578		546
579	=cut	547	=cut
…		…
588		556
589	=item kil $port[, @reason]	557	=item kil $port[, @reason]
590		558
591	Kill the specified port with the given C<@reason>.	559	Kill the specified port with the given C<@reason>.
592		560
593	If no C<@reason> is specified, then the port is killed "normally" (linked	561	If no C<@reason> is specified, then the port is killed "normally" (ports
594	ports will not be kileld, or even notified).	562	monitoring other ports will not necessarily die because a port dies
		563	"normally").
595		564
596	Otherwise, linked ports get killed with the same reason (second form of	565	Otherwise, linked ports get killed with the same reason (second form of
597	C<mon>, see below).	566	C<mon>, see above).
598		567
599	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	568	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
600	will be reported as reason C<< die => $@ >>.	569	will be reported as reason C<< die => $@ >>.
601		570
602	Transport/communication errors are reported as C<< transport_error =>	571	Transport/communication errors are reported as C<< transport_error =>
…		…
607	=item $port = spawn $node, $initfunc[, @initdata]	576	=item $port = spawn $node, $initfunc[, @initdata]
608		577
609	Creates a port on the node C<$node> (which can also be a port ID, in which	578	Creates a port on the node C<$node> (which can also be a port ID, in which
610	case it's the node where that port resides).	579	case it's the node where that port resides).
611		580
612	The port ID of the newly created port is return immediately, and it is	581	The port ID of the newly created port is returned immediately, and it is
613	permissible to immediately start sending messages or monitor the port.	582	possible to immediately start sending messages or to monitor the port.
614		583
615	After the port has been created, the init function is	584	After the port has been created, the init function is called on the remote
616	called. This function must be a fully-qualified function name	585	node, in the same context as a C<rcv> callback. This function must be a
617	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	586	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
618	program, use C<::name>.	587	specify a function in the main program, use C<::name>.
619		588
620	If the function doesn't exist, then the node tries to C<require>	589	If the function doesn't exist, then the node tries to C<require>
621	the package, then the package above the package and so on (e.g.	590	the package, then the package above the package and so on (e.g.
622	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	591	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
623	exists or it runs out of package names.	592	exists or it runs out of package names.
624		593
625	The init function is then called with the newly-created port as context	594	The init function is then called with the newly-created port as context
626	object (C<$SELF>) and the C<@initdata> values as arguments.	595	object (C<$SELF>) and the C<@initdata> values as arguments.
627		596
628	A common idiom is to pass your own port, monitor the spawned port, and	597	A common idiom is to pass a local port, immediately monitor the spawned
629	in the init function, monitor the original port. This two-way monitoring	598	port, and in the remote init function, immediately monitor the passed
630	ensures that both ports get cleaned up when there is a problem.	599	local port. This two-way monitoring ensures that both ports get cleaned up
		600	when there is a problem.
631		601
632	Example: spawn a chat server port on C<$othernode>.	602	Example: spawn a chat server port on C<$othernode>.
633		603
634	# this node, executed from within a port context:	604	# this node, executed from within a port context:
635	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	605	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
677	=item after $timeout, $callback	647	=item after $timeout, $callback
678		648
679	Either sends the given message, or call the given callback, after the	649	Either sends the given message, or call the given callback, after the
680	specified number of seconds.	650	specified number of seconds.
681		651
682	This is simply a utility function that come sin handy at times.	652	This is simply a utility function that comes in handy at times - the
		653	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		654	so it may go away in the future.
683		655
684	=cut	656	=cut
685		657
686	sub after($@) {	658	sub after($@) {
687	my ($timeout, @action) = @_;	659	my ($timeout, @action) = @_;
…		…
710		682
711	Despite the similarities, there are also some important differences:	683	Despite the similarities, there are also some important differences:
712		684
713	=over 4	685	=over 4
714		686
715	=item * Node references contain the recipe on how to contact them.	687	=item * Node IDs are arbitrary strings in AEMP.
716		688
717	Erlang relies on special naming and DNS to work everywhere in the	689	Erlang relies on special naming and DNS to work everywhere in the same
718	same way. AEMP relies on each node knowing it's own address(es), with	690	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
719	convenience functionality.	691	configuraiton or DNS), but will otherwise discover other odes itself.
720
721	This means that AEMP requires a less tightly controlled environment at the
722	cost of longer node references and a slightly higher management overhead.
723		692
724	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP	693	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
725	uses "local ports are like remote ports".	694	uses "local ports are like remote ports".
726		695
727	The failure modes for local ports are quite different (runtime errors	696	The failure modes for local ports are quite different (runtime errors
…		…
756		725
757	Erlang makes few guarantees on messages delivery - messages can get lost	726	Erlang makes few guarantees on messages delivery - messages can get lost
758	without any of the processes realising it (i.e. you send messages a, b,	727	without any of the processes realising it (i.e. you send messages a, b,
759	and c, and the other side only receives messages a and c).	728	and c, and the other side only receives messages a and c).
760		729
761	AEMP guarantees correct ordering, and the guarantee that there are no	730	AEMP guarantees correct ordering, and the guarantee that after one message
762	holes in the message sequence.	731	is lost, all following ones sent to the same port are lost as well, until
763		732	monitoring raises an error, so there are no silent "holes" in the message
764	=item * In Erlang, processes can be declared dead and later be found to be	733	sequence.
765	alive.
766
767	In Erlang it can happen that a monitored process is declared dead and
768	linked processes get killed, but later it turns out that the process is
769	still alive - and can receive messages.
770
771	In AEMP, when port monitoring detects a port as dead, then that port will
772	eventually be killed - it cannot happen that a node detects a port as dead
773	and then later sends messages to it, finding it is still alive.
774		734
775	=item * Erlang can send messages to the wrong port, AEMP does not.	735	=item * Erlang can send messages to the wrong port, AEMP does not.
776		736
777	In Erlang it is quite likely that a node that restarts reuses a process ID	737	In Erlang it is quite likely that a node that restarts reuses a process ID
778	known to other nodes for a completely different process, causing messages	738	known to other nodes for a completely different process, causing messages
…		…
782	around in the network will not be sent to an unrelated port.	742	around in the network will not be sent to an unrelated port.
783		743
784	=item * Erlang uses unprotected connections, AEMP uses secure	744	=item * Erlang uses unprotected connections, AEMP uses secure
785	authentication and can use TLS.	745	authentication and can use TLS.
786		746
787	AEMP can use a proven protocol - SSL/TLS - to protect connections and	747	AEMP can use a proven protocol - TLS - to protect connections and
788	securely authenticate nodes.	748	securely authenticate nodes.
789		749
790	=item * The AEMP protocol is optimised for both text-based and binary	750	=item * The AEMP protocol is optimised for both text-based and binary
791	communications.	751	communications.
792		752
793	The AEMP protocol, unlike the Erlang protocol, supports both	753	The AEMP protocol, unlike the Erlang protocol, supports both programming
794	language-independent text-only protocols (good for debugging) and binary,	754	language independent text-only protocols (good for debugging) and binary,
795	language-specific serialisers (e.g. Storable).	755	language-specific serialisers (e.g. Storable). By default, unless TLS is
		756	used, the protocol is actually completely text-based.
796		757
797	It has also been carefully designed to be implementable in other languages	758	It has also been carefully designed to be implementable in other languages
798	with a minimum of work while gracefully degrading fucntionality to make the	759	with a minimum of work while gracefully degrading functionality to make the
799	protocol simple.	760	protocol simple.
800		761
801	=item * AEMP has more flexible monitoring options than Erlang.	762	=item * AEMP has more flexible monitoring options than Erlang.
802		763
803	In Erlang, you can chose to receive I<all> exit signals as messages	764	In Erlang, you can chose to receive I<all> exit signals as messages
…		…
806	Erlang, as one can choose between automatic kill, exit message or callback	767	Erlang, as one can choose between automatic kill, exit message or callback
807	on a per-process basis.	768	on a per-process basis.
808		769
809	=item * Erlang tries to hide remote/local connections, AEMP does not.	770	=item * Erlang tries to hide remote/local connections, AEMP does not.
810		771
811	Monitoring in Erlang is not an indicator of process death/crashes,	772	Monitoring in Erlang is not an indicator of process death/crashes, in the
812	as linking is (except linking is unreliable in Erlang).	773	same way as linking is (except linking is unreliable in Erlang).
813		774
814	In AEMP, you don't "look up" registered port names or send to named ports	775	In AEMP, you don't "look up" registered port names or send to named ports
815	that might or might not be persistent. Instead, you normally spawn a port	776	that might or might not be persistent. Instead, you normally spawn a port
816	on the remote node. The init function monitors the you, and you monitor	777	on the remote node. The init function monitors you, and you monitor the
817	the remote port. Since both monitors are local to the node, they are much	778	remote port. Since both monitors are local to the node, they are much more
818	more reliable.	779	reliable (no need for C<spawn_link>).
819		780
820	This also saves round-trips and avoids sending messages to the wrong port	781	This also saves round-trips and avoids sending messages to the wrong port
821	(hard to do in Erlang).	782	(hard to do in Erlang).
822		783
823	=back	784	=back
824		785
825	=head1 RATIONALE	786	=head1 RATIONALE
826		787
827	=over 4	788	=over 4
828		789
829	=item Why strings for ports and noderefs, why not objects?	790	=item Why strings for port and node IDs, why not objects?
830		791
831	We considered "objects", but found that the actual number of methods	792	We considered "objects", but found that the actual number of methods
832	thatc an be called are very low. Since port IDs and noderefs travel over	793	that can be called are quite low. Since port and node IDs travel over
833	the network frequently, the serialising/deserialising would add lots of	794	the network frequently, the serialising/deserialising would add lots of
834	overhead, as well as having to keep a proxy object.	795	overhead, as well as having to keep a proxy object everywhere.
835		796
836	Strings can easily be printed, easily serialised etc. and need no special	797	Strings can easily be printed, easily serialised etc. and need no special
837	procedures to be "valid".	798	procedures to be "valid".
838		799
839	And a a miniport consists of a single closure stored in a global hash - it	800	And as a result, a miniport consists of a single closure stored in a
840	can't become much cheaper.	801	global hash - it can't become much cheaper.
841		802
842	=item Why favour JSON, why not real serialising format such as Storable?	803	=item Why favour JSON, why not a real serialising format such as Storable?
843		804
844	In fact, any AnyEvent::MP node will happily accept Storable as framing	805	In fact, any AnyEvent::MP node will happily accept Storable as framing
845	format, but currently there is no way to make a node use Storable by	806	format, but currently there is no way to make a node use Storable by
846	default.	807	default (although all nodes will accept it).
847		808
848	The default framing protocol is JSON because a) JSON::XS is many times	809	The default framing protocol is JSON because a) JSON::XS is many times
849	faster for small messages and b) most importantly, after years of	810	faster for small messages and b) most importantly, after years of
850	experience we found that object serialisation is causing more problems	811	experience we found that object serialisation is causing more problems
851	than it gains: Just like function calls, objects simply do not travel	812	than it solves: Just like function calls, objects simply do not travel
852	easily over the network, mostly because they will always be a copy, so you	813	easily over the network, mostly because they will always be a copy, so you
853	always have to re-think your design.	814	always have to re-think your design.
854		815
855	Keeping your messages simple, concentrating on data structures rather than	816	Keeping your messages simple, concentrating on data structures rather than
856	objects, will keep your messages clean, tidy and efficient.	817	objects, will keep your messages clean, tidy and efficient.
857		818
858	=back	819	=back
859		820
860	=head1 SEE ALSO	821	=head1 SEE ALSO
861		822
		823	L<AnyEvent::MP::Intro> - a gentle introduction.
		824
		825	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		826
		827	L<AnyEvent::MP::Global> - network maintainance and port groups, to find
		828	your applications.
		829
862	L<AnyEvent>.	830	L<AnyEvent>.
863		831
864	=head1 AUTHOR	832	=head1 AUTHOR
865		833
866	Marc Lehmann <schmorp@schmorp.de>	834	Marc Lehmann <schmorp@schmorp.de>

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Revision 1.69 by root, Sun Aug 30 18:51:49 2009 UTC