[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 1.74 by root, Mon Aug 31 11:11:27 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	configure;
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...;
24	snd $port, @msg;	22	snd $port, @msg;
25	snd @msg_with_first_element_being_a_port;	23	snd @msg_with_first_element_being_a_port;
26		24
27	# creating/using ports, the simple way	25	# creating/using ports, the simple way
28	my $simple_port = port { my @msg = @_; 0 };	26	my $simple_port = port { my @msg = @_ };
29		27
30	# creating/using ports, tagged message matching	28	# creating/using ports, tagged message matching
31	my $port = port;	29	my $port = port;
32	rcv $port, ping => sub { snd $_[0], "pong"; 0 };	30	rcv $port, ping => sub { snd $_[0], "pong" };
33	rcv $port, pong => sub { warn "pong received\n"; 0 };	31	rcv $port, pong => sub { warn "pong received\n" };
34		32
35	# create a port on another node	33	# create a port on another node
36	my $port = spawn $node, $initfunc, @initdata;	34	my $port = spawn $node, $initfunc, @initdata;
37		35
38	# monitoring	36	# monitoring
…		…
40	mon $port, $otherport # kill otherport on abnormal death	38	mon $port, $otherport # kill otherport on abnormal death
41	mon $port, $otherport, @msg # send message on death	39	mon $port, $otherport, @msg # send message on death
42		40
43	=head1 CURRENT STATUS	41	=head1 CURRENT STATUS
44		42
		43	bin/aemp - stable.
45	AnyEvent::MP - stable API, should work	44	AnyEvent::MP - stable API, should work.
46	AnyEvent::MP::Intro - outdated	45	AnyEvent::MP::Intro - uptodate, but incomplete.
47	AnyEvent::MP::Kernel - WIP
48	AnyEvent::MP::Transport - mostly stable	46	AnyEvent::MP::Kernel - mostly stable.
		47	AnyEvent::MP::Global - stable API, protocol not yet final.
49		48
50	stay tuned.	49	stay tuned.
51		50
52	=head1 DESCRIPTION	51	=head1 DESCRIPTION
53		52
54	This module (-family) implements a simple message passing framework.	53	This module (-family) implements a simple message passing framework.
55		54
56	Despite its simplicity, you can securely message other processes running	55	Despite its simplicity, you can securely message other processes running
57	on the same or other hosts.	56	on the same or other hosts, and you can supervise entities remotely.
58		57
59	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>
60	manual page.	59	manual page and the examples under F<eg/>.
61		60
62	At the moment, this module family is severly broken and underdocumented,	61	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		62
66	=head1 CONCEPTS	63	=head1 CONCEPTS
67		64
68	=over 4	65	=over 4
69		66
70	=item port	67	=item port
71		68
72	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).
73		70
74	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
75	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.
76		74
77	=item port id - C<noderef#portname>	75	=item port ID - C<nodeid#portname>
78		76
79	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
80	separator, and a port name (a printable string of unspecified format). An	78	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		79
84	=item node	80	=item node
85		81
86	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,
87	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
88	ports.	84	ports.
89		85
90	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
91	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
92	from any other node).	88	currently.
93		89
94	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	90	=item node ID - C<[a-za-Z0-9_\-.:]+>
95		91
96	A node reference is a string that either simply identifies the node (for	92	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	93	network. Depending on the configuration used, node IDs can look like a
98	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.
99		96
100	This recipe is simply a comma-separated list of C<address:port> pairs (for	97	=item binds - C<ip:port>
101	TCP/IP, other protocols might look different).
102		98
103	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
104	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.
105		103
106	Before using an unresolved node reference in a message you first have to	104	=item seeds - C<host:port>
107	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.
108		118
109	=back	119	=back
110		120
111	=head1 VARIABLES/FUNCTIONS	121	=head1 VARIABLES/FUNCTIONS
112		122
…		…
128		138
129	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	139	our $VERSION = $AnyEvent::MP::Kernel::VERSION;
130		140
131	our @EXPORT = qw(	141	our @EXPORT = qw(
132	NODE $NODE *SELF node_of after	142	NODE $NODE *SELF node_of after
133	resolve_node initialise_node	143	configure
134	snd rcv mon mon_guard kil reg psub spawn	144	snd rcv mon mon_guard kil reg psub spawn
135	port	145	port
136	);	146	);
137		147
138	our $SELF;	148	our $SELF;
…		…
143	kil $SELF, die => $msg;	153	kil $SELF, die => $msg;
144	}	154	}
145		155
146	=item $thisnode = NODE / $NODE	156	=item $thisnode = NODE / $NODE
147		157
148	The C<NODE> function returns, and the C<$NODE> variable contains the	158	The C<NODE> function returns, and the C<$NODE> variable contains, the node
149	noderef 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
150	C<initialise_node>.	160	a call to C<configure>.
151		161
152	=item $noderef = node_of $port	162	=item $nodeid = node_of $port
153		163
154	Extracts and returns the noderef from a port ID or a noderef.	164	Extracts and returns the node ID from a port ID or a node ID.
155		165
156	=item initialise_node $noderef, $seednode, $seednode...	166	=item configure key => value...
157		167
158	=item initialise_node "slave/", $master, $master...
159
160	Before a node can talk to other nodes on the network it has to initialise	168	Before a node can talk to other nodes on the network (i.e. enter
161	itself - the minimum a node needs to know is it's own name, and optionally	169	"distributed mode") it has to configure itself - the minimum a node needs
162	it should know the noderefs of some other nodes in the network.	170	to know is its own name, and optionally it should know the addresses of
		171	some other nodes in the network to discover other nodes.
163		172
164	This function initialises a node - it must be called exactly once (or	173	This function configures a node - it must be called exactly once (or
165	never) before calling other AnyEvent::MP functions.	174	never) before calling other AnyEvent::MP functions.
166		175
167	All arguments (optionally except for the first) are noderefs, which can be
168	either resolved or unresolved.
169
170	The first argument will be looked up in the configuration database first
171	(if it is C<undef> then the current nodename will be used instead) to find
172	the relevant configuration profile (see L<aemp>). If none is found then
173	the default configuration is used. The configuration supplies additional
174	seed/master nodes and can override the actual noderef.
175
176	There are two types of networked nodes, public nodes and slave nodes:
177
178	=over 4	176	=over 4
179		177
180	=item public nodes	178	=item step 1, gathering configuration from profiles
181		179
182	For public nodes, C<$noderef> (supplied either directly to	180	The function first looks up a profile in the aemp configuration (see the
183	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
184	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.
185		184
186	After resolving, the node will bind itself on all endpoints.	185	The profile data is then gathered as follows:
187		186
188	=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).
189		192
190	When the C<$noderef> (either as given or overriden by the config file)	193	That means that the values specified in the profile have highest priority
191	is the special string C<slave/>, then the node will become a slave	194	and the values specified directly via C<configure> have lowest priority,
192	node. Slave nodes cannot be contacted from outside, and cannot talk to	195	and can only be used to specify defaults.
193	each other (at least in this version of AnyEvent::MP).
194		196
195	Slave nodes work by creating connections to all public nodes, using the	197	If the profile specifies a node ID, then this will become the node ID of
196	L<AnyEvent::MP::Global> service.	198	this process. If not, then the profile name will be used as node ID. The
		199	special node ID of C<anon/> will be replaced by a random node ID.
		200
		201	=item step 2, bind listener sockets
		202
		203	The next step is to look up the binds in the profile, followed by binding
		204	aemp protocol listeners on all binds specified (it is possible and valid
		205	to have no binds, meaning that the node cannot be contacted form the
		206	outside. This means the node cannot talk to other nodes that also have no
		207	binds, but it can still talk to all "normal" nodes).
		208
		209	If the profile does not specify a binds list, then a default of C<*> is
		210	used, meaning the node will bind on a dynamically-assigned port on every
		211	local IP address it finds.
		212
		213	=item step 3, connect to seed nodes
		214
		215	As the last step, the seeds list from the profile is passed to the
		216	L<AnyEvent::MP::Global> module, which will then use it to keep
		217	connectivity with at least one node at any point in time.
197		218
198	=back	219	=back
199		220
200	After initialising itself, the node will connect to all additional	221	Example: become a distributed node using the locla node name as profile.
201	C<$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.
202	optional and can be used to quickly bootstrap the node into an existing
203	network.
204		223
205	All the seednodes will also be specially marked to automatically retry	224	configure
206	connecting to them indefinitely, so make sure that seednodes are really
207	reliable and up (this might also change in the future).
208		225
209	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
210	specified via C<aemp> for the current node. This should be the most common	227	clients.
211	form of invocation for "daemon"-type nodes.
212		228
213	initialise_node;	229	configure nodeid => "anon/";
214		230
215	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
216	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).
217		234
218	initialise_node "slave/";	235	# use the aemp commandline utility
		236	# aemp profile seed nodeid anon/ binds '*:4040'
219		237
220	Example: become a public node, and try to contact some well-known master	238	# then use it
221	servers to become part of the network.	239	configure profile => "seed";
222		240
223	initialise_node undef, "master1", "master2";	241	# or simply use aemp from the shell again:
		242	# aemp run profile seed
224		243
225	Example: become a public node listening on port C<4041>.	244	# or provide a nicer-to-remember nodeid
226		245	# aemp run profile seed nodeid "$(hostname)"
227	initialise_node 4041;
228
229	Example: become a public node, only visible on localhost port 4044.
230
231	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		246
262	=item $SELF	247	=item $SELF
263		248
264	Contains the current port id while executing C<rcv> callbacks or C<psub>	249	Contains the current port id while executing C<rcv> callbacks or C<psub>
265	blocks.	250	blocks.
266		251
267	=item SELF, %SELF, @SELF...	252	=item *SELF, SELF, %SELF, @SELF...
268		253
269	Due to some quirks in how perl exports variables, it is impossible to	254	Due to some quirks in how perl exports variables, it is impossible to
270	just export C<$SELF>, all the symbols called C<SELF> are exported by this	255	just export C<$SELF>, all the symbols named C<SELF> are exported by this
271	module, but only C<$SELF> is currently used.	256	module, but only C<$SELF> is currently used.
272		257
273	=item snd $port, type => @data	258	=item snd $port, type => @data
274		259
275	=item snd $port, @msg	260	=item snd $port, @msg
276		261
277	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
278	a local or a remote port, and must be a port ID.	263	local or a remote port, and must be a port ID.
279		264
280	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
281	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
282	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.
283		269
284	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
285	function: modifying any argument is not allowed and can cause many	271	function: modifying any argument (or values referenced by them) is
286	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.
287		276
288	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
289	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
290	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
291	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
292	node, anything can be passed.	281	node, anything can be passed. Best rely only on the common denominator of
		282	these.
293		283
294	=item $local_port = port	284	=item $local_port = port
295		285
296	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
297	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.
…		…
473	$res	463	$res
474	}	464	}
475	}	465	}
476	}	466	}
477		467
478	=item $guard = mon $port, $cb->(@reason)	468	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
479		469
480	=item $guard = mon $port, $rcvport	470	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
481		471
482	=item $guard = mon $port	472	=item $guard = mon $port # kill $SELF when $port dies
483		473
484	=item $guard = mon $port, $rcvport, @msg	474	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
485		475
486	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
487	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
488	to stop monitoring again.	478	to stop monitoring again.
489		479
490	C<mon> effectively guarantees that, in the absence of hardware failures,	480	C<mon> effectively guarantees that, in the absence of hardware failures,
491	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
492	will arrive, or the monitoring action will be invoked after possible	482	arrive, or the monitoring action will be invoked after possible message
493	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
494	(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
495	port). After the monitoring action was invoked, further messages might get	485	port). After the monitoring action was invoked, further messages might get
496	delivered again.	486	delivered again.
497		487
498	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
499	and will not trigger again.	489	monitoring alert was raised), they are removed and will not trigger again.
500		490
501	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
502	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
503	"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
504	C<eval> if unsure.	494	C<eval> if unsure.
…		…
566	is killed, the references will be freed.	556	is killed, the references will be freed.
567		557
568	Optionally returns a guard that will stop the monitoring.	558	Optionally returns a guard that will stop the monitoring.
569		559
570	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
571	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>):
572		562
573	$port->rcv (start => sub {	563	$port->rcv (start => sub {
574	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	564	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
575	undef $timer if 0.9 < rand;	565	undef $timer if 0.9 < rand;
576	});	566	});
577	});	567	});
578		568
579	=cut	569	=cut
…		…
588		578
589	=item kil $port[, @reason]	579	=item kil $port[, @reason]
590		580
591	Kill the specified port with the given C<@reason>.	581	Kill the specified port with the given C<@reason>.
592		582
593	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
594	ports will not be kileld, or even notified).	584	monitoring other ports will not necessarily die because a port dies
		585	"normally").
595		586
596	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
597	C<mon>, see below).	588	C<mon>, see above).
598		589
599	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
600	will be reported as reason C<< die => $@ >>.	591	will be reported as reason C<< die => $@ >>.
601		592
602	Transport/communication errors are reported as C<< transport_error =>	593	Transport/communication errors are reported as C<< transport_error =>
…		…
607	=item $port = spawn $node, $initfunc[, @initdata]	598	=item $port = spawn $node, $initfunc[, @initdata]
608		599
609	Creates a port on the node C<$node> (which can also be a port ID, in which	600	Creates a port on the node C<$node> (which can also be a port ID, in which
610	case it's the node where that port resides).	601	case it's the node where that port resides).
611		602
612	The port ID of the newly created port is return immediately, and it is	603	The port ID of the newly created port is returned immediately, and it is
613	permissible to immediately start sending messages or monitor the port.	604	possible to immediately start sending messages or to monitor the port.
614		605
615	After the port has been created, the init function is	606	After the port has been created, the init function is called on the remote
616	called. This function must be a fully-qualified function name	607	node, in the same context as a C<rcv> callback. This function must be a
617	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	608	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
618	program, use C<::name>.	609	specify a function in the main program, use C<::name>.
619		610
620	If the function doesn't exist, then the node tries to C<require>	611	If the function doesn't exist, then the node tries to C<require>
621	the package, then the package above the package and so on (e.g.	612	the package, then the package above the package and so on (e.g.
622	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	613	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
623	exists or it runs out of package names.	614	exists or it runs out of package names.
624		615
625	The init function is then called with the newly-created port as context	616	The init function is then called with the newly-created port as context
626	object (C<$SELF>) and the C<@initdata> values as arguments.	617	object (C<$SELF>) and the C<@initdata> values as arguments.
627		618
628	A common idiom is to pass your own port, monitor the spawned port, and	619	A common idiom is to pass a local port, immediately monitor the spawned
629	in the init function, monitor the original port. This two-way monitoring	620	port, and in the remote init function, immediately monitor the passed
630	ensures that both ports get cleaned up when there is a problem.	621	local port. This two-way monitoring ensures that both ports get cleaned up
		622	when there is a problem.
631		623
632	Example: spawn a chat server port on C<$othernode>.	624	Example: spawn a chat server port on C<$othernode>.
633		625
634	# this node, executed from within a port context:	626	# this node, executed from within a port context:
635	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	627	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
677	=item after $timeout, $callback	669	=item after $timeout, $callback
678		670
679	Either sends the given message, or call the given callback, after the	671	Either sends the given message, or call the given callback, after the
680	specified number of seconds.	672	specified number of seconds.
681		673
682	This is simply a utility function that come sin handy at times.	674	This is simply a utility function that comes in handy at times - the
		675	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		676	so it may go away in the future.
683		677
684	=cut	678	=cut
685		679
686	sub after($@) {	680	sub after($@) {
687	my ($timeout, @action) = @_;	681	my ($timeout, @action) = @_;
…		…
710		704
711	Despite the similarities, there are also some important differences:	705	Despite the similarities, there are also some important differences:
712		706
713	=over 4	707	=over 4
714		708
715	=item * Node references contain the recipe on how to contact them.	709	=item * Node IDs are arbitrary strings in AEMP.
716		710
717	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
718	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
719	convenience functionality.	713	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		714
724	=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
725	uses "local ports are like remote ports".	716	uses "local ports are like remote ports".
726		717
727	The failure modes for local ports are quite different (runtime errors	718	The failure modes for local ports are quite different (runtime errors
…		…
756		747
757	Erlang makes few guarantees on messages delivery - messages can get lost	748	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,	749	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).	750	and c, and the other side only receives messages a and c).
760		751
761	AEMP guarantees correct ordering, and the guarantee that there are no	752	AEMP guarantees correct ordering, and the guarantee that after one message
762	holes in the message sequence.	753	is lost, all following ones sent to the same port are lost as well, until
763		754	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	755	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		756
775	=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.
776		758
777	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
778	known to other nodes for a completely different process, causing messages	760	known to other nodes for a completely different process, causing messages
…		…
782	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.
783		765
784	=item * Erlang uses unprotected connections, AEMP uses secure	766	=item * Erlang uses unprotected connections, AEMP uses secure
785	authentication and can use TLS.	767	authentication and can use TLS.
786		768
787	AEMP can use a proven protocol - SSL/TLS - to protect connections and	769	AEMP can use a proven protocol - TLS - to protect connections and
788	securely authenticate nodes.	770	securely authenticate nodes.
789		771
790	=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
791	communications.	773	communications.
792		774
793	The AEMP protocol, unlike the Erlang protocol, supports both	775	The AEMP protocol, unlike the Erlang protocol, supports both programming
794	language-independent text-only protocols (good for debugging) and binary,	776	language independent text-only protocols (good for debugging) and binary,
795	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.
796		779
797	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
798	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
799	protocol simple.	782	protocol simple.
800		783
801	=item * AEMP has more flexible monitoring options than Erlang.	784	=item * AEMP has more flexible monitoring options than Erlang.
802		785
803	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
…		…
806	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
807	on a per-process basis.	790	on a per-process basis.
808		791
809	=item * Erlang tries to hide remote/local connections, AEMP does not.	792	=item * Erlang tries to hide remote/local connections, AEMP does not.
810		793
811	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
812	as linking is (except linking is unreliable in Erlang).	795	same way as linking is (except linking is unreliable in Erlang).
813		796
814	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
815	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
816	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
817	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
818	more reliable.	801	reliable (no need for C<spawn_link>).
819		802
820	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
821	(hard to do in Erlang).	804	(hard to do in Erlang).
822		805
823	=back	806	=back
824		807
825	=head1 RATIONALE	808	=head1 RATIONALE
826		809
827	=over 4	810	=over 4
828		811
829	=item Why strings for ports and noderefs, why not objects?	812	=item Why strings for port and node IDs, why not objects?
830		813
831	We considered "objects", but found that the actual number of methods	814	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	815	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	816	the network frequently, the serialising/deserialising would add lots of
834	overhead, as well as having to keep a proxy object.	817	overhead, as well as having to keep a proxy object everywhere.
835		818
836	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
837	procedures to be "valid".	820	procedures to be "valid".
838		821
839	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
840	can't become much cheaper.	823	global hash - it can't become much cheaper.
841		824
842	=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?
843		826
844	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
845	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
846	default.	829	default (although all nodes will accept it).
847		830
848	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
849	faster for small messages and b) most importantly, after years of	832	faster for small messages and b) most importantly, after years of
850	experience we found that object serialisation is causing more problems	833	experience we found that object serialisation is causing more problems
851	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
852	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
853	always have to re-think your design.	836	always have to re-think your design.
854		837
855	Keeping your messages simple, concentrating on data structures rather than	838	Keeping your messages simple, concentrating on data structures rather than
856	objects, will keep your messages clean, tidy and efficient.	839	objects, will keep your messages clean, tidy and efficient.
857		840
858	=back	841	=back
859		842
860	=head1 SEE ALSO	843	=head1 SEE ALSO
861		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
862	L<AnyEvent>.	852	L<AnyEvent>.
863		853
864	=head1 AUTHOR	854	=head1 AUTHOR
865		855
866	Marc Lehmann <schmorp@schmorp.de>	856	Marc Lehmann <schmorp@schmorp.de>

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Revision 1.62 by root, Thu Aug 27 07:12:48 2009 UTC vs.
Revision 1.74 by root, Mon Aug 31 11:11:27 2009 UTC