[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 1.70 by root, Sun Aug 30 19:49:47 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46	AnyEvent::MP::Intro - outdated	44	AnyEvent::MP::Intro - outdated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 (all of which are conviniently
		184	undocumented at the moment) will be used. Then they will be overwritten by
		185	any values specified in the global default configuration (see the F<aemp>
		186	utility), then the chain of profiles selected, if any. That means that
		187	the values specified in the profile have highest priority and the values
		188	specified via C<initialise_node> have lowest 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 a default of C<*> is
183	C<initialise_node> or indirectly via a profile or the nodename) must be a	201	used.
184	noderef (possibly unresolved, in which case it will be resolved).
185		202
186	After resolving, the node will bind itself on all endpoints.	203	Lastly, the seeds list from the profile is passed to the
		204	L<AnyEvent::MP::Global> module, which will then use it to keep
		205	connectivity with at least on of those seed nodes at any point in time.
187		206
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	207	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	208	the one specified via C<aemp> for the current node. This should be the
211	form of invocation for "daemon"-type nodes.	209	most common form of invocation for "daemon"-type nodes.
212		210
213	initialise_node;	211	initialise_node;
214		212
215	Example: become a slave node to any of the the seednodes specified via	213	Example: become an anonymous node. This form is often used for commandline
216	C<aemp>. This form is often used for commandline clients.	214	clients.
217		215
218	initialise_node "slave/";	216	initialise_node "anon/";
219		217
220	Example: become a public node, and try to contact some well-known master	218	Example: become a distributed node. If there is no profile of the given
221	servers to become part of the network.	219	name, or no binds list was specified, resolve C<localhost:4044> and bind
222		220	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		221
231	initialise_node "localhost:4044";	222	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		223
262	=item $SELF	224	=item $SELF
263		225
264	Contains the current port id while executing C<rcv> callbacks or C<psub>	226	Contains the current port id while executing C<rcv> callbacks or C<psub>
265	blocks.	227	blocks.
266		228
267	=item SELF, %SELF, @SELF...	229	=item *SELF, SELF, %SELF, @SELF...
268		230
269	Due to some quirks in how perl exports variables, it is impossible to	231	Due to some quirks in how perl exports variables, it is impossible to
270	just export C<$SELF>, all the symbols called C<SELF> are exported by this	232	just export C<$SELF>, all the symbols named C<SELF> are exported by this
271	module, but only C<$SELF> is currently used.	233	module, but only C<$SELF> is currently used.
272		234
273	=item snd $port, type => @data	235	=item snd $port, type => @data
274		236
275	=item snd $port, @msg	237	=item snd $port, @msg
276		238
277	Send the given message to the given port ID, which can identify either	239	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.	240	local or a remote port, and must be a port ID.
279		241
280	While the message can be about anything, it is highly recommended to use a	242	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	243	use a string as first element (a port ID, or some word that indicates a
282	type etc.).	244	request type etc.) and to consist if only simple perl values (scalars,
		245	arrays, hashes) - if you think you need to pass an object, think again.
283		246
284	The message data effectively becomes read-only after a call to this	247	The message data logically becomes read-only after a call to this
285	function: modifying any argument is not allowed and can cause many	248	function: modifying any argument (or values referenced by them) is
286	problems.	249	forbidden, as there can be considerable time between the call to C<snd>
		250	and the time the message is actually being serialised - in fact, it might
		251	never be copied as within the same process it is simply handed to the
		252	receiving port.
287		253
288	The type of data you can transfer depends on the transport protocol: when	254	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	255	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	256	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	257	that Storable can serialise and deserialise is allowed, and for the local
292	node, anything can be passed.	258	node, anything can be passed. Best rely only on the common denominator of
		259	these.
293		260
294	=item $local_port = port	261	=item $local_port = port
295		262
296	Create a new local port object and returns its port ID. Initially it has	263	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.	264	no callbacks set and will throw an error when it receives messages.
…		…
473	$res	440	$res
474	}	441	}
475	}	442	}
476	}	443	}
477		444
478	=item $guard = mon $port, $cb->(@reason)	445	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
479		446
480	=item $guard = mon $port, $rcvport	447	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
481		448
482	=item $guard = mon $port	449	=item $guard = mon $port # kill $SELF when $port dies
483		450
484	=item $guard = mon $port, $rcvport, @msg	451	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
485		452
486	Monitor the given port and do something when the port is killed or	453	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	454	messages to it were lost, and optionally return a guard that can be used
488	to stop monitoring again.	455	to stop monitoring again.
489		456
490	C<mon> effectively guarantees that, in the absence of hardware failures,	457	C<mon> effectively guarantees that, in the absence of hardware failures,
491	that after starting the monitor, either all messages sent to the port	458	after starting the monitor, either all messages sent to the port will
492	will arrive, or the monitoring action will be invoked after possible	459	arrive, or the monitoring action will be invoked after possible message
493	message loss has been detected. No messages will be lost "in between"	460	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	461	the first lost message no further messages will be received by the
495	port). After the monitoring action was invoked, further messages might get	462	port). After the monitoring action was invoked, further messages might get
496	delivered again.	463	delivered again.
497		464
498	Note that monitoring-actions are one-shot: once released, they are removed	465	Note that monitoring-actions are one-shot: once messages are lost (and a
499	and will not trigger again.	466	monitoring alert was raised), they are removed and will not trigger again.
500		467
501	In the first form (callback), the callback is simply called with any	468	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	469	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	470	"normally"). Note also that I<< the callback B<must> never die >>, so use
504	C<eval> if unsure.	471	C<eval> if unsure.
…		…
566	is killed, the references will be freed.	533	is killed, the references will be freed.
567		534
568	Optionally returns a guard that will stop the monitoring.	535	Optionally returns a guard that will stop the monitoring.
569		536
570	This function is useful when you create e.g. timers or other watchers and	537	This function is useful when you create e.g. timers or other watchers and
571	want to free them when the port gets killed:	538	want to free them when the port gets killed (note the use of C<psub>):
572		539
573	$port->rcv (start => sub {	540	$port->rcv (start => sub {
574	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	541	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
575	undef $timer if 0.9 < rand;	542	undef $timer if 0.9 < rand;
576	});	543	});
577	});	544	});
578		545
579	=cut	546	=cut
…		…
588		555
589	=item kil $port[, @reason]	556	=item kil $port[, @reason]
590		557
591	Kill the specified port with the given C<@reason>.	558	Kill the specified port with the given C<@reason>.
592		559
593	If no C<@reason> is specified, then the port is killed "normally" (linked	560	If no C<@reason> is specified, then the port is killed "normally" (ports
594	ports will not be kileld, or even notified).	561	monitoring other ports will not necessarily die because a port dies
		562	"normally").
595		563
596	Otherwise, linked ports get killed with the same reason (second form of	564	Otherwise, linked ports get killed with the same reason (second form of
597	C<mon>, see below).	565	C<mon>, see above).
598		566
599	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	567	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
600	will be reported as reason C<< die => $@ >>.	568	will be reported as reason C<< die => $@ >>.
601		569
602	Transport/communication errors are reported as C<< transport_error =>	570	Transport/communication errors are reported as C<< transport_error =>
…		…
607	=item $port = spawn $node, $initfunc[, @initdata]	575	=item $port = spawn $node, $initfunc[, @initdata]
608		576
609	Creates a port on the node C<$node> (which can also be a port ID, in which	577	Creates a port on the node C<$node> (which can also be a port ID, in which
610	case it's the node where that port resides).	578	case it's the node where that port resides).
611		579
612	The port ID of the newly created port is return immediately, and it is	580	The port ID of the newly created port is returned immediately, and it is
613	permissible to immediately start sending messages or monitor the port.	581	possible to immediately start sending messages or to monitor the port.
614		582
615	After the port has been created, the init function is	583	After the port has been created, the init function is called on the remote
616	called. This function must be a fully-qualified function name	584	node, in the same context as a C<rcv> callback. This function must be a
617	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	585	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
618	program, use C<::name>.	586	specify a function in the main program, use C<::name>.
619		587
620	If the function doesn't exist, then the node tries to C<require>	588	If the function doesn't exist, then the node tries to C<require>
621	the package, then the package above the package and so on (e.g.	589	the package, then the package above the package and so on (e.g.
622	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	590	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
623	exists or it runs out of package names.	591	exists or it runs out of package names.
624		592
625	The init function is then called with the newly-created port as context	593	The init function is then called with the newly-created port as context
626	object (C<$SELF>) and the C<@initdata> values as arguments.	594	object (C<$SELF>) and the C<@initdata> values as arguments.
627		595
628	A common idiom is to pass your own port, monitor the spawned port, and	596	A common idiom is to pass a local port, immediately monitor the spawned
629	in the init function, monitor the original port. This two-way monitoring	597	port, and in the remote init function, immediately monitor the passed
630	ensures that both ports get cleaned up when there is a problem.	598	local port. This two-way monitoring ensures that both ports get cleaned up
		599	when there is a problem.
631		600
632	Example: spawn a chat server port on C<$othernode>.	601	Example: spawn a chat server port on C<$othernode>.
633		602
634	# this node, executed from within a port context:	603	# this node, executed from within a port context:
635	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	604	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
677	=item after $timeout, $callback	646	=item after $timeout, $callback
678		647
679	Either sends the given message, or call the given callback, after the	648	Either sends the given message, or call the given callback, after the
680	specified number of seconds.	649	specified number of seconds.
681		650
682	This is simply a utility function that come sin handy at times.	651	This is simply a utility function that comes in handy at times - the
		652	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		653	so it may go away in the future.
683		654
684	=cut	655	=cut
685		656
686	sub after($@) {	657	sub after($@) {
687	my ($timeout, @action) = @_;	658	my ($timeout, @action) = @_;
…		…
710		681
711	Despite the similarities, there are also some important differences:	682	Despite the similarities, there are also some important differences:
712		683
713	=over 4	684	=over 4
714		685
715	=item * Node references contain the recipe on how to contact them.	686	=item * Node IDs are arbitrary strings in AEMP.
716		687
717	Erlang relies on special naming and DNS to work everywhere in the	688	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	689	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
719	convenience functionality.	690	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		691
724	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP	692	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
725	uses "local ports are like remote ports".	693	uses "local ports are like remote ports".
726		694
727	The failure modes for local ports are quite different (runtime errors	695	The failure modes for local ports are quite different (runtime errors
…		…
756		724
757	Erlang makes few guarantees on messages delivery - messages can get lost	725	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,	726	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).	727	and c, and the other side only receives messages a and c).
760		728
761	AEMP guarantees correct ordering, and the guarantee that there are no	729	AEMP guarantees correct ordering, and the guarantee that after one message
762	holes in the message sequence.	730	is lost, all following ones sent to the same port are lost as well, until
763		731	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	732	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		733
775	=item * Erlang can send messages to the wrong port, AEMP does not.	734	=item * Erlang can send messages to the wrong port, AEMP does not.
776		735
777	In Erlang it is quite likely that a node that restarts reuses a process ID	736	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	737	known to other nodes for a completely different process, causing messages
…		…
782	around in the network will not be sent to an unrelated port.	741	around in the network will not be sent to an unrelated port.
783		742
784	=item * Erlang uses unprotected connections, AEMP uses secure	743	=item * Erlang uses unprotected connections, AEMP uses secure
785	authentication and can use TLS.	744	authentication and can use TLS.
786		745
787	AEMP can use a proven protocol - SSL/TLS - to protect connections and	746	AEMP can use a proven protocol - TLS - to protect connections and
788	securely authenticate nodes.	747	securely authenticate nodes.
789		748
790	=item * The AEMP protocol is optimised for both text-based and binary	749	=item * The AEMP protocol is optimised for both text-based and binary
791	communications.	750	communications.
792		751
793	The AEMP protocol, unlike the Erlang protocol, supports both	752	The AEMP protocol, unlike the Erlang protocol, supports both programming
794	language-independent text-only protocols (good for debugging) and binary,	753	language independent text-only protocols (good for debugging) and binary,
795	language-specific serialisers (e.g. Storable).	754	language-specific serialisers (e.g. Storable). By default, unless TLS is
		755	used, the protocol is actually completely text-based.
796		756
797	It has also been carefully designed to be implementable in other languages	757	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	758	with a minimum of work while gracefully degrading functionality to make the
799	protocol simple.	759	protocol simple.
800		760
801	=item * AEMP has more flexible monitoring options than Erlang.	761	=item * AEMP has more flexible monitoring options than Erlang.
802		762
803	In Erlang, you can chose to receive I<all> exit signals as messages	763	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	766	Erlang, as one can choose between automatic kill, exit message or callback
807	on a per-process basis.	767	on a per-process basis.
808		768
809	=item * Erlang tries to hide remote/local connections, AEMP does not.	769	=item * Erlang tries to hide remote/local connections, AEMP does not.
810		770
811	Monitoring in Erlang is not an indicator of process death/crashes,	771	Monitoring in Erlang is not an indicator of process death/crashes, in the
812	as linking is (except linking is unreliable in Erlang).	772	same way as linking is (except linking is unreliable in Erlang).
813		773
814	In AEMP, you don't "look up" registered port names or send to named ports	774	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	775	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	776	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	777	remote port. Since both monitors are local to the node, they are much more
818	more reliable.	778	reliable (no need for C<spawn_link>).
819		779
820	This also saves round-trips and avoids sending messages to the wrong port	780	This also saves round-trips and avoids sending messages to the wrong port
821	(hard to do in Erlang).	781	(hard to do in Erlang).
822		782
823	=back	783	=back
824		784
825	=head1 RATIONALE	785	=head1 RATIONALE
826		786
827	=over 4	787	=over 4
828		788
829	=item Why strings for ports and noderefs, why not objects?	789	=item Why strings for port and node IDs, why not objects?
830		790
831	We considered "objects", but found that the actual number of methods	791	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	792	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	793	the network frequently, the serialising/deserialising would add lots of
834	overhead, as well as having to keep a proxy object.	794	overhead, as well as having to keep a proxy object everywhere.
835		795
836	Strings can easily be printed, easily serialised etc. and need no special	796	Strings can easily be printed, easily serialised etc. and need no special
837	procedures to be "valid".	797	procedures to be "valid".
838		798
839	And a a miniport consists of a single closure stored in a global hash - it	799	And as a result, a miniport consists of a single closure stored in a
840	can't become much cheaper.	800	global hash - it can't become much cheaper.
841		801
842	=item Why favour JSON, why not real serialising format such as Storable?	802	=item Why favour JSON, why not a real serialising format such as Storable?
843		803
844	In fact, any AnyEvent::MP node will happily accept Storable as framing	804	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	805	format, but currently there is no way to make a node use Storable by
846	default.	806	default (although all nodes will accept it).
847		807
848	The default framing protocol is JSON because a) JSON::XS is many times	808	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	809	faster for small messages and b) most importantly, after years of
850	experience we found that object serialisation is causing more problems	810	experience we found that object serialisation is causing more problems
851	than it gains: Just like function calls, objects simply do not travel	811	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	812	easily over the network, mostly because they will always be a copy, so you
853	always have to re-think your design.	813	always have to re-think your design.
854		814
855	Keeping your messages simple, concentrating on data structures rather than	815	Keeping your messages simple, concentrating on data structures rather than
856	objects, will keep your messages clean, tidy and efficient.	816	objects, will keep your messages clean, tidy and efficient.
857		817
858	=back	818	=back
859		819
860	=head1 SEE ALSO	820	=head1 SEE ALSO
861		821
		822	L<AnyEvent::MP::Intro> - a gentle introduction.
		823
		824	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		825
		826	L<AnyEvent::MP::Global> - network maintainance and port groups, to find
		827	your applications.
		828
862	L<AnyEvent>.	829	L<AnyEvent>.
863		830
864	=head1 AUTHOR	831	=head1 AUTHOR
865		832
866	Marc Lehmann <schmorp@schmorp.de>	833	Marc Lehmann <schmorp@schmorp.de>

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Revision 1.70 by root, Sun Aug 30 19:49:47 2009 UTC