[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 1.73 by root, Mon Aug 31 11:08:25 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;	16	configure;
17		17
18	# ports are message endpoints	18	# ports are message endpoints
19		19
20	# sending messages	20	# sending messages
21	snd $port, type => data...;	21	snd $port, type => data...;
22	snd $port, @msg;	22	snd $port, @msg;
23	snd @msg_with_first_element_being_a_port;	23	snd @msg_with_first_element_being_a_port;
24		24
25	# creating/using ports, the simple way	25	# creating/using ports, the simple way
26	my $simple_port = port { my @msg = @_; 0 };	26	my $simple_port = port { my @msg = @_ };
27		27
28	# creating/using ports, tagged message matching	28	# creating/using ports, tagged message matching
29	my $port = port;	29	my $port = port;
30	rcv $port, ping => sub { snd $_[0], "pong"; 0 };	30	rcv $port, ping => sub { snd $_[0], "pong" };
31	rcv $port, pong => sub { warn "pong received\n"; 0 };	31	rcv $port, pong => sub { warn "pong received\n" };
32		32
33	# create a port on another node	33	# create a port on another node
34	my $port = spawn $node, $initfunc, @initdata;	34	my $port = spawn $node, $initfunc, @initdata;
35		35
36	# monitoring	36	# monitoring
…		…
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44	AnyEvent::MP::Intro - outdated	45	AnyEvent::MP::Intro - uptodate, but incomplete.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	configure
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<configure>.
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 $profile_name	166	=item configure key => value...
155		167
156	Before a node can talk to other nodes on the network it has to initialise	168	Before a node can talk to other nodes on the network (i.e. enter
157	itself - the minimum a node needs to know is it's own name, and optionally	169	"distributed mode") it has to configure itself - the minimum a node needs
158	it should know the noderefs of some other nodes in the network.	170	to know is its own name, and optionally it should know the addresses of
		171	some other nodes in the network to discover other nodes.
159		172
160	This function initialises a node - it must be called exactly once (or	173	This function configures a node - it must be called exactly once (or
161	never) before calling other AnyEvent::MP functions.	174	never) before calling other AnyEvent::MP functions.
162		175
163	All arguments (optionally except for the first) are noderefs, which can be
164	either resolved or unresolved.
165
166	The first argument will be looked up in the configuration database first
167	(if it is C<undef> then the current nodename will be used instead) to find
168	the relevant configuration profile (see L<aemp>). If none is found then
169	the default configuration is used. The configuration supplies additional
170	seed/master nodes and can override the actual noderef.
171
172	There are two types of networked nodes, public nodes and slave nodes:
173
174	=over 4	176	=over 4
175		177
176	=item public nodes	178	=item step 1, gathering configuration from profiles
177		179
178	For public nodes, C<$noderef> (supplied either directly to	180	The function first looks up a profile in the aemp configuration (see the
179	C<initialise_node> or indirectly via a profile or the nodename) must be a	181	L<aemp> commandline utility). The profile name can be specified via the
180	noderef (possibly unresolved, in which case it will be resolved).	182	named C<profile> parameter. If it is missing, then the nodename (F<uname
		183	-n>) will be used as profile name.
181		184
182	After resolving, the node will bind itself on all endpoints.	185	The profile data is then gathered as follows:
183		186
184	=item slave nodes	187	First, all remaining key => value pairs (all of which are conviniently
		188	undocumented at the moment) will be interpreted as configuration
		189	data. Then they will be overwritten by any values specified in the global
		190	default configuration (see the F<aemp> utility), then the chain of
		191	profiles chosen by the profile name (and any C<parent> attributes).
185		192
186	When the C<$noderef> (either as given or overriden by the config file)	193	That means that the values specified in the profile have highest priority
187	is the special string C<slave/>, then the node will become a slave	194	and the values specified directly via C<configure> have lowest priority,
188	node. Slave nodes cannot be contacted from outside, and cannot talk to	195	and can only be used to specify defaults.
189	each other (at least in this version of AnyEvent::MP).
190		196
191	Slave nodes work by creating connections to all public nodes, using the	197	If the profile specifies a node ID, then this will become the node ID of
192	L<AnyEvent::MP::Global> service.	198	this process. If not, then the profile name will be used as node ID. The
		199	special node ID of C<anon/> will be replaced by a random node ID.
		200
		201	=item step 2, bind listener sockets
		202
		203	The next step is to look up the binds in the profile, followed by binding
		204	aemp protocol listeners on all binds specified (it is possible and valid
		205	to have no binds, meaning that the node cannot be contacted form the
		206	outside. This means the node cannot talk to other nodes that also have no
		207	binds, but it can still talk to all "normal" nodes).
		208
		209	If the profile does not specify a binds list, then a default of C<*> is
		210	used, meaning the node will bind on a dynamically-assigned port on every
		211	local IP address it finds.
		212
		213	=item step 3, connect to seed nodes
		214
		215	As the last step, the seeds list from the profile is passed to the
		216	L<AnyEvent::MP::Global> module, which will then use it to keep
		217	connectivity with at least one node at any point in time.
193		218
194	=back	219	=back
195		220
196	After initialising itself, the node will connect to all additional	221	Example: become a distributed node using the locla node name as profile.
197	C<$seednodes> that are specified diretcly or via a profile. Seednodes are	222	This should be the most common form of invocation for "daemon"-type nodes.
198	optional and can be used to quickly bootstrap the node into an existing
199	network.
200		223
201	All the seednodes will also be specially marked to automatically retry	224	configure
202	connecting to them indefinitely, so make sure that seednodes are really
203	reliable and up (this might also change in the future).
204		225
205	Example: become a public node listening on the guessed noderef, or the one	226	Example: become an anonymous node. This form is often used for commandline
206	specified via C<aemp> for the current node. This should be the most common	227	clients.
207	form of invocation for "daemon"-type nodes.
208		228
209	initialise_node;	229	configure nodeid => "anon/";
210		230
211	Example: become a slave node to any of the the seednodes specified via	231	Example: configure a node using a profile called seed, which si suitable
212	C<aemp>. This form is often used for commandline clients.	232	for a seed node as it binds on all local addresses on a fixed port (4040,
		233	customary for aemp).
213		234
214	initialise_node "slave/";	235	# use the aemp commandline utility
		236	# aemp profile seed setnodeid anon/ setbinds '*:4040'
215		237
216	Example: become a public node, and try to contact some well-known master	238	# then use it
217	servers to become part of the network.	239	configure profile => "seed";
218		240
219	initialise_node undef, "master1", "master2";	241	# or simply use aemp from the shell again:
		242	# aemp run profile seed
220		243
221	Example: become a public node listening on port C<4041>.	244	# or provide a nicer-to-remember nodeid
222		245	# aemp run profile seed nodeid "$(hostname)"
223	initialise_node 4041;
224
225	Example: become a public node, only visible on localhost port 4044.
226
227	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		246
258	=item $SELF	247	=item $SELF
259		248
260	Contains the current port id while executing C<rcv> callbacks or C<psub>	249	Contains the current port id while executing C<rcv> callbacks or C<psub>
261	blocks.	250	blocks.
262		251
263	=item SELF, %SELF, @SELF...	252	=item *SELF, SELF, %SELF, @SELF...
264		253
265	Due to some quirks in how perl exports variables, it is impossible to	254	Due to some quirks in how perl exports variables, it is impossible to
266	just export C<$SELF>, all the symbols called C<SELF> are exported by this	255	just export C<$SELF>, all the symbols named C<SELF> are exported by this
267	module, but only C<$SELF> is currently used.	256	module, but only C<$SELF> is currently used.
268		257
269	=item snd $port, type => @data	258	=item snd $port, type => @data
270		259
271	=item snd $port, @msg	260	=item snd $port, @msg
272		261
273	Send the given message to the given port ID, which can identify either	262	Send the given message to the given port, which can identify either a
274	a local or a remote port, and must be a port ID.	263	local or a remote port, and must be a port ID.
275		264
276	While the message can be about anything, it is highly recommended to use a	265	While the message can be almost anything, it is highly recommended to
277	string as first element (a port ID, or some word that indicates a request	266	use a string as first element (a port ID, or some word that indicates a
278	type etc.).	267	request type etc.) and to consist if only simple perl values (scalars,
		268	arrays, hashes) - if you think you need to pass an object, think again.
279		269
280	The message data effectively becomes read-only after a call to this	270	The message data logically becomes read-only after a call to this
281	function: modifying any argument is not allowed and can cause many	271	function: modifying any argument (or values referenced by them) is
282	problems.	272	forbidden, as there can be considerable time between the call to C<snd>
		273	and the time the message is actually being serialised - in fact, it might
		274	never be copied as within the same process it is simply handed to the
		275	receiving port.
283		276
284	The type of data you can transfer depends on the transport protocol: when	277	The type of data you can transfer depends on the transport protocol: when
285	JSON is used, then only strings, numbers and arrays and hashes consisting	278	JSON is used, then only strings, numbers and arrays and hashes consisting
286	of those are allowed (no objects). When Storable is used, then anything	279	of those are allowed (no objects). When Storable is used, then anything
287	that Storable can serialise and deserialise is allowed, and for the local	280	that Storable can serialise and deserialise is allowed, and for the local
288	node, anything can be passed.	281	node, anything can be passed. Best rely only on the common denominator of
		282	these.
289		283
290	=item $local_port = port	284	=item $local_port = port
291		285
292	Create a new local port object and returns its port ID. Initially it has	286	Create a new local port object and returns its port ID. Initially it has
293	no callbacks set and will throw an error when it receives messages.	287	no callbacks set and will throw an error when it receives messages.
…		…
469	$res	463	$res
470	}	464	}
471	}	465	}
472	}	466	}
473		467
474	=item $guard = mon $port, $cb->(@reason)	468	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
475		469
476	=item $guard = mon $port, $rcvport	470	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
477		471
478	=item $guard = mon $port	472	=item $guard = mon $port # kill $SELF when $port dies
479		473
480	=item $guard = mon $port, $rcvport, @msg	474	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
481		475
482	Monitor the given port and do something when the port is killed or	476	Monitor the given port and do something when the port is killed or
483	messages to it were lost, and optionally return a guard that can be used	477	messages to it were lost, and optionally return a guard that can be used
484	to stop monitoring again.	478	to stop monitoring again.
485		479
486	C<mon> effectively guarantees that, in the absence of hardware failures,	480	C<mon> effectively guarantees that, in the absence of hardware failures,
487	that after starting the monitor, either all messages sent to the port	481	after starting the monitor, either all messages sent to the port will
488	will arrive, or the monitoring action will be invoked after possible	482	arrive, or the monitoring action will be invoked after possible message
489	message loss has been detected. No messages will be lost "in between"	483	loss has been detected. No messages will be lost "in between" (after
490	(after the first lost message no further messages will be received by the	484	the first lost message no further messages will be received by the
491	port). After the monitoring action was invoked, further messages might get	485	port). After the monitoring action was invoked, further messages might get
492	delivered again.	486	delivered again.
493		487
494	Note that monitoring-actions are one-shot: once released, they are removed	488	Note that monitoring-actions are one-shot: once messages are lost (and a
495	and will not trigger again.	489	monitoring alert was raised), they are removed and will not trigger again.
496		490
497	In the first form (callback), the callback is simply called with any	491	In the first form (callback), the callback is simply called with any
498	number of C<@reason> elements (no @reason means that the port was deleted	492	number of C<@reason> elements (no @reason means that the port was deleted
499	"normally"). Note also that I<< the callback B<must> never die >>, so use	493	"normally"). Note also that I<< the callback B<must> never die >>, so use
500	C<eval> if unsure.	494	C<eval> if unsure.
…		…
562	is killed, the references will be freed.	556	is killed, the references will be freed.
563		557
564	Optionally returns a guard that will stop the monitoring.	558	Optionally returns a guard that will stop the monitoring.
565		559
566	This function is useful when you create e.g. timers or other watchers and	560	This function is useful when you create e.g. timers or other watchers and
567	want to free them when the port gets killed:	561	want to free them when the port gets killed (note the use of C<psub>):
568		562
569	$port->rcv (start => sub {	563	$port->rcv (start => sub {
570	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	564	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
571	undef $timer if 0.9 < rand;	565	undef $timer if 0.9 < rand;
572	});	566	});
573	});	567	});
574		568
575	=cut	569	=cut
…		…
584		578
585	=item kil $port[, @reason]	579	=item kil $port[, @reason]
586		580
587	Kill the specified port with the given C<@reason>.	581	Kill the specified port with the given C<@reason>.
588		582
589	If no C<@reason> is specified, then the port is killed "normally" (linked	583	If no C<@reason> is specified, then the port is killed "normally" (ports
590	ports will not be kileld, or even notified).	584	monitoring other ports will not necessarily die because a port dies
		585	"normally").
591		586
592	Otherwise, linked ports get killed with the same reason (second form of	587	Otherwise, linked ports get killed with the same reason (second form of
593	C<mon>, see below).	588	C<mon>, see above).
594		589
595	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	590	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
596	will be reported as reason C<< die => $@ >>.	591	will be reported as reason C<< die => $@ >>.
597		592
598	Transport/communication errors are reported as C<< transport_error =>	593	Transport/communication errors are reported as C<< transport_error =>
…		…
603	=item $port = spawn $node, $initfunc[, @initdata]	598	=item $port = spawn $node, $initfunc[, @initdata]
604		599
605	Creates a port on the node C<$node> (which can also be a port ID, in which	600	Creates a port on the node C<$node> (which can also be a port ID, in which
606	case it's the node where that port resides).	601	case it's the node where that port resides).
607		602
608	The port ID of the newly created port is return immediately, and it is	603	The port ID of the newly created port is returned immediately, and it is
609	permissible to immediately start sending messages or monitor the port.	604	possible to immediately start sending messages or to monitor the port.
610		605
611	After the port has been created, the init function is	606	After the port has been created, the init function is called on the remote
612	called. This function must be a fully-qualified function name	607	node, in the same context as a C<rcv> callback. This function must be a
613	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	608	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
614	program, use C<::name>.	609	specify a function in the main program, use C<::name>.
615		610
616	If the function doesn't exist, then the node tries to C<require>	611	If the function doesn't exist, then the node tries to C<require>
617	the package, then the package above the package and so on (e.g.	612	the package, then the package above the package and so on (e.g.
618	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	613	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
619	exists or it runs out of package names.	614	exists or it runs out of package names.
620		615
621	The init function is then called with the newly-created port as context	616	The init function is then called with the newly-created port as context
622	object (C<$SELF>) and the C<@initdata> values as arguments.	617	object (C<$SELF>) and the C<@initdata> values as arguments.
623		618
624	A common idiom is to pass your own port, monitor the spawned port, and	619	A common idiom is to pass a local port, immediately monitor the spawned
625	in the init function, monitor the original port. This two-way monitoring	620	port, and in the remote init function, immediately monitor the passed
626	ensures that both ports get cleaned up when there is a problem.	621	local port. This two-way monitoring ensures that both ports get cleaned up
		622	when there is a problem.
627		623
628	Example: spawn a chat server port on C<$othernode>.	624	Example: spawn a chat server port on C<$othernode>.
629		625
630	# this node, executed from within a port context:	626	# this node, executed from within a port context:
631	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	627	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
673	=item after $timeout, $callback	669	=item after $timeout, $callback
674		670
675	Either sends the given message, or call the given callback, after the	671	Either sends the given message, or call the given callback, after the
676	specified number of seconds.	672	specified number of seconds.
677		673
678	This is simply a utility function that come sin handy at times.	674	This is simply a utility function that comes in handy at times - the
		675	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		676	so it may go away in the future.
679		677
680	=cut	678	=cut
681		679
682	sub after($@) {	680	sub after($@) {
683	my ($timeout, @action) = @_;	681	my ($timeout, @action) = @_;
…		…
706		704
707	Despite the similarities, there are also some important differences:	705	Despite the similarities, there are also some important differences:
708		706
709	=over 4	707	=over 4
710		708
711	=item * Node references contain the recipe on how to contact them.	709	=item * Node IDs are arbitrary strings in AEMP.
712		710
713	Erlang relies on special naming and DNS to work everywhere in the	711	Erlang relies on special naming and DNS to work everywhere in the same
714	same way. AEMP relies on each node knowing it's own address(es), with	712	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
715	convenience functionality.	713	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		714
720	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP	715	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
721	uses "local ports are like remote ports".	716	uses "local ports are like remote ports".
722		717
723	The failure modes for local ports are quite different (runtime errors	718	The failure modes for local ports are quite different (runtime errors
…		…
752		747
753	Erlang makes few guarantees on messages delivery - messages can get lost	748	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,	749	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).	750	and c, and the other side only receives messages a and c).
756		751
757	AEMP guarantees correct ordering, and the guarantee that there are no	752	AEMP guarantees correct ordering, and the guarantee that after one message
758	holes in the message sequence.	753	is lost, all following ones sent to the same port are lost as well, until
759		754	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	755	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		756
771	=item * Erlang can send messages to the wrong port, AEMP does not.	757	=item * Erlang can send messages to the wrong port, AEMP does not.
772		758
773	In Erlang it is quite likely that a node that restarts reuses a process ID	759	In Erlang it is quite likely that a node that restarts reuses a process ID
774	known to other nodes for a completely different process, causing messages	760	known to other nodes for a completely different process, causing messages
…		…
778	around in the network will not be sent to an unrelated port.	764	around in the network will not be sent to an unrelated port.
779		765
780	=item * Erlang uses unprotected connections, AEMP uses secure	766	=item * Erlang uses unprotected connections, AEMP uses secure
781	authentication and can use TLS.	767	authentication and can use TLS.
782		768
783	AEMP can use a proven protocol - SSL/TLS - to protect connections and	769	AEMP can use a proven protocol - TLS - to protect connections and
784	securely authenticate nodes.	770	securely authenticate nodes.
785		771
786	=item * The AEMP protocol is optimised for both text-based and binary	772	=item * The AEMP protocol is optimised for both text-based and binary
787	communications.	773	communications.
788		774
789	The AEMP protocol, unlike the Erlang protocol, supports both	775	The AEMP protocol, unlike the Erlang protocol, supports both programming
790	language-independent text-only protocols (good for debugging) and binary,	776	language independent text-only protocols (good for debugging) and binary,
791	language-specific serialisers (e.g. Storable).	777	language-specific serialisers (e.g. Storable). By default, unless TLS is
		778	used, the protocol is actually completely text-based.
792		779
793	It has also been carefully designed to be implementable in other languages	780	It has also been carefully designed to be implementable in other languages
794	with a minimum of work while gracefully degrading fucntionality to make the	781	with a minimum of work while gracefully degrading functionality to make the
795	protocol simple.	782	protocol simple.
796		783
797	=item * AEMP has more flexible monitoring options than Erlang.	784	=item * AEMP has more flexible monitoring options than Erlang.
798		785
799	In Erlang, you can chose to receive I<all> exit signals as messages	786	In Erlang, you can chose to receive I<all> exit signals as messages
…		…
802	Erlang, as one can choose between automatic kill, exit message or callback	789	Erlang, as one can choose between automatic kill, exit message or callback
803	on a per-process basis.	790	on a per-process basis.
804		791
805	=item * Erlang tries to hide remote/local connections, AEMP does not.	792	=item * Erlang tries to hide remote/local connections, AEMP does not.
806		793
807	Monitoring in Erlang is not an indicator of process death/crashes,	794	Monitoring in Erlang is not an indicator of process death/crashes, in the
808	as linking is (except linking is unreliable in Erlang).	795	same way as linking is (except linking is unreliable in Erlang).
809		796
810	In AEMP, you don't "look up" registered port names or send to named ports	797	In AEMP, you don't "look up" registered port names or send to named ports
811	that might or might not be persistent. Instead, you normally spawn a port	798	that might or might not be persistent. Instead, you normally spawn a port
812	on the remote node. The init function monitors the you, and you monitor	799	on the remote node. The init function monitors you, and you monitor the
813	the remote port. Since both monitors are local to the node, they are much	800	remote port. Since both monitors are local to the node, they are much more
814	more reliable.	801	reliable (no need for C<spawn_link>).
815		802
816	This also saves round-trips and avoids sending messages to the wrong port	803	This also saves round-trips and avoids sending messages to the wrong port
817	(hard to do in Erlang).	804	(hard to do in Erlang).
818		805
819	=back	806	=back
820		807
821	=head1 RATIONALE	808	=head1 RATIONALE
822		809
823	=over 4	810	=over 4
824		811
825	=item Why strings for ports and noderefs, why not objects?	812	=item Why strings for port and node IDs, why not objects?
826		813
827	We considered "objects", but found that the actual number of methods	814	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	815	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	816	the network frequently, the serialising/deserialising would add lots of
830	overhead, as well as having to keep a proxy object.	817	overhead, as well as having to keep a proxy object everywhere.
831		818
832	Strings can easily be printed, easily serialised etc. and need no special	819	Strings can easily be printed, easily serialised etc. and need no special
833	procedures to be "valid".	820	procedures to be "valid".
834		821
835	And a a miniport consists of a single closure stored in a global hash - it	822	And as a result, a miniport consists of a single closure stored in a
836	can't become much cheaper.	823	global hash - it can't become much cheaper.
837		824
838	=item Why favour JSON, why not real serialising format such as Storable?	825	=item Why favour JSON, why not a real serialising format such as Storable?
839		826
840	In fact, any AnyEvent::MP node will happily accept Storable as framing	827	In fact, any AnyEvent::MP node will happily accept Storable as framing
841	format, but currently there is no way to make a node use Storable by	828	format, but currently there is no way to make a node use Storable by
842	default.	829	default (although all nodes will accept it).
843		830
844	The default framing protocol is JSON because a) JSON::XS is many times	831	The default framing protocol is JSON because a) JSON::XS is many times
845	faster for small messages and b) most importantly, after years of	832	faster for small messages and b) most importantly, after years of
846	experience we found that object serialisation is causing more problems	833	experience we found that object serialisation is causing more problems
847	than it gains: Just like function calls, objects simply do not travel	834	than it solves: Just like function calls, objects simply do not travel
848	easily over the network, mostly because they will always be a copy, so you	835	easily over the network, mostly because they will always be a copy, so you
849	always have to re-think your design.	836	always have to re-think your design.
850		837
851	Keeping your messages simple, concentrating on data structures rather than	838	Keeping your messages simple, concentrating on data structures rather than
852	objects, will keep your messages clean, tidy and efficient.	839	objects, will keep your messages clean, tidy and efficient.
853		840
854	=back	841	=back
855		842
856	=head1 SEE ALSO	843	=head1 SEE ALSO
857		844
		845	L<AnyEvent::MP::Intro> - a gentle introduction.
		846
		847	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		848
		849	L<AnyEvent::MP::Global> - network maintainance and port groups, to find
		850	your applications.
		851
858	L<AnyEvent>.	852	L<AnyEvent>.
859		853
860	=head1 AUTHOR	854	=head1 AUTHOR
861		855
862	Marc Lehmann <schmorp@schmorp.de>	856	Marc Lehmann <schmorp@schmorp.de>

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Revision 1.63 by root, Thu Aug 27 21:29:37 2009 UTC vs.
Revision 1.73 by root, Mon Aug 31 11:08:25 2009 UTC