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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.61 by root, Mon Aug 24 08:06:49 2009 UTC vs.
Revision 1.71 by root, Sun Aug 30 19:52:56 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...;
…		…
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46	AnyEvent::MP::Intro - outdated	45	AnyEvent::MP::Intro - uptodate, but incomplete.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 (connected to a	86	Nodes are either public (have one or more listening ports) or private
91	master node only) or public nodes (connectable from unrelated nodes).	87	(no listening ports). Private nodes cannot talk to other private nodes
		88	currently.
92		89
93	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	90	=item node ID - C<[a-za-Z0-9_\-.:]+>
94		91
95	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
96	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
97	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.
98		96
99	This recipe is simply a comma-separated list of C<address:port> pairs (for	97	=item binds - C<ip:port>
100	TCP/IP, other protocols might look different).
101		98
102	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
103	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.
104		103
105	Before using an unresolved node reference in a message you first have to	104	=item seeds - C<host:port>
106	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.
107		118
108	=back	119	=back
109		120
110	=head1 VARIABLES/FUNCTIONS	121	=head1 VARIABLES/FUNCTIONS
111		122
…		…
127		138
128	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	139	our $VERSION = $AnyEvent::MP::Kernel::VERSION;
129		140
130	our @EXPORT = qw(	141	our @EXPORT = qw(
131	NODE $NODE *SELF node_of after	142	NODE $NODE *SELF node_of after
132	resolve_node initialise_node	143	initialise_node
133	snd rcv mon mon_guard kil reg psub spawn	144	snd rcv mon mon_guard kil reg psub spawn
134	port	145	port
135	);	146	);
136		147
137	our $SELF;	148	our $SELF;
…		…
142	kil $SELF, die => $msg;	153	kil $SELF, die => $msg;
143	}	154	}
144		155
145	=item $thisnode = NODE / $NODE	156	=item $thisnode = NODE / $NODE
146		157
147	The C<NODE> function returns, and the C<$NODE> variable contains the	158	The C<NODE> function returns, and the C<$NODE> variable contains, the node
148	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
149	C<initialise_node>.	160	a call to C<initialise_node>.
150		161
151	=item $noderef = node_of $port	162	=item $nodeid = node_of $port
152		163
153	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.
154		165
155	=item initialise_node $noderef, $seednode, $seednode...	166	=item initialise_node $profile_name, key => value...
156		167
157	=item initialise_node "slave/", $master, $master...
158
159	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
160	itself - the minimum a node needs to know is it's own name, and optionally	169	"distributed mode") it has to initialise itself - the minimum a node needs
161	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.
162		172
163	This function initialises a node - it must be called exactly once (or	173	This function initialises a node - it must be called exactly once (or
164	never) before calling other AnyEvent::MP functions.	174	never) before calling other AnyEvent::MP functions.
165		175
166	All arguments (optionally except for the first) are noderefs, which can be	176	The first argument is a profile name. If it is C<undef> or missing, then
167	either resolved or unresolved.	177	the current nodename will be used instead (i.e. F<uname -n>).
168		178
169	The first argument will be looked up in the configuration database first	179	The function first looks up the profile in the aemp configuration (see the
170	(if it is C<undef> then the current nodename will be used instead) to find	180	L<aemp> commandline utility). the profile is calculated as follows:
171	the relevant configuration profile (see L<aemp>). If none is found then
172	the default configuration is used. The configuration supplies additional
173	seed/master nodes and can override the actual noderef.
174		181
175	There are two types of networked nodes, public nodes and slave nodes:	182	First, all remaining key => value pairs (all of which are conviniently
		183	undocumented at the moment) will be used. Then they will be overwritten by
		184	any values specified in the global default configuration (see the F<aemp>
		185	utility), then the chain of profiles selected, if any. That means that
		186	the values specified in the profile have highest priority and the values
		187	specified via C<initialise_node> have lowest priority.
176		188
177	=over 4	189	If the profile specifies a node ID, then this will become the node ID of
		190	this process. If not, then the profile name will be used as node ID. The
		191	special node ID of C<anon/> will be replaced by a random node ID.
178		192
179	=item public nodes	193	The next step is to look up the binds in the profile, followed by binding
		194	aemp protocol listeners on all binds specified (it is possible and valid
		195	to have no binds, meaning that the node cannot be contacted form the
		196	outside. This means the node cannot talk to other nodes that also have no
		197	binds, but it can still talk to all "normal" nodes).
180		198
181	For public nodes, C<$noderef> (supplied either directly to	199	If the profile does not specify a binds list, then a default of C<*> is
182	C<initialise_node> or indirectly via a profile or the nodename) must be a	200	used.
183	noderef (possibly unresolved, in which case it will be resolved).
184		201
185	After resolving, the node will bind itself on all endpoints and try to	202	Lastly, the seeds list from the profile is passed to the
186	connect to all additional C<$seednodes> that are specified. Seednodes are	203	L<AnyEvent::MP::Global> module, which will then use it to keep
187	optional and can be used to quickly bootstrap the node into an existing	204	connectivity with at least on of those seed nodes at any point in time.
188	network.
189		205
190	=item slave nodes
191
192	When the C<$noderef> (either as given or overriden by the config file)
193	is the special string C<slave/>, then the node will become a slave
194	node. Slave nodes cannot be contacted from outside and will route most of
195	their traffic to the master node that they attach to.
196
197	At least one additional noderef is required (either by specifying it
198	directly or because it is part of the configuration profile): The node
199	will try to connect to all of them and will become a slave attached to the
200	first node it can successfully connect to.
201
202	Note that slave nodes cannot change their name, and consequently, their
203	master, so if the master goes down, the slave node will not function well
204	anymore until it can re-establish conenciton to its master. This makes
205	slave nodes unsuitable for long-term nodes or fault-tolerant networks.
206
207	=back
208
209	This function will block until all nodes have been resolved and, for slave
210	nodes, until it has successfully established a connection to a master
211	server.
212
213	All the seednodes will also be specially marked to automatically retry
214	connecting to them infinitely.
215
216	Example: become a public node listening on the guessed noderef, or the one	206	Example: become a distributed node listening on the guessed noderef, or
217	specified via C<aemp> for the current node. This should be the most common	207	the one specified via C<aemp> for the current node. This should be the
218	form of invocation for "daemon"-type nodes.	208	most common form of invocation for "daemon"-type nodes.
219		209
220	initialise_node;	210	initialise_node;
221		211
222	Example: become a slave node to any of the the seednodes specified via	212	Example: become an anonymous node. This form is often used for commandline
223	C<aemp>. This form is often used for commandline clients.	213	clients.
224		214
225	initialise_node "slave/";	215	initialise_node "anon/";
226		216
227	Example: become a slave node to any of the specified master servers. This	217	Example: become a distributed node. If there is no profile of the given
228	form is also often used for commandline clients.	218	name, or no binds list was specified, resolve C<localhost:4044> and bind
229		219	on the resulting addresses.
230	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
231
232	Example: become a public node, and try to contact some well-known master
233	servers to become part of the network.
234
235	initialise_node undef, "master1", "master2";
236
237	Example: become a public node listening on port C<4041>.
238
239	initialise_node 4041;
240
241	Example: become a public node, only visible on localhost port 4044.
242		220
243	initialise_node "localhost:4044";	221	initialise_node "localhost:4044";
244
245	=item $cv = resolve_node $noderef
246
247	Takes an unresolved node reference that may contain hostnames and
248	abbreviated IDs, resolves all of them and returns a resolved node
249	reference.
250
251	In addition to C<address:port> pairs allowed in resolved noderefs, the
252	following forms are supported:
253
254	=over 4
255
256	=item the empty string
257
258	An empty-string component gets resolved as if the default port (4040) was
259	specified.
260
261	=item naked port numbers (e.g. C<1234>)
262
263	These are resolved by prepending the local nodename and a colon, to be
264	further resolved.
265
266	=item hostnames (e.g. C<localhost:1234>, C<localhost>)
267
268	These are resolved by using AnyEvent::DNS to resolve them, optionally
269	looking up SRV records for the C<aemp=4040> port, if no port was
270	specified.
271
272	=back
273		222
274	=item $SELF	223	=item $SELF
275		224
276	Contains the current port id while executing C<rcv> callbacks or C<psub>	225	Contains the current port id while executing C<rcv> callbacks or C<psub>
277	blocks.	226	blocks.
278		227
279	=item SELF, %SELF, @SELF...	228	=item *SELF, SELF, %SELF, @SELF...
280		229
281	Due to some quirks in how perl exports variables, it is impossible to	230	Due to some quirks in how perl exports variables, it is impossible to
282	just export C<$SELF>, all the symbols called C<SELF> are exported by this	231	just export C<$SELF>, all the symbols named C<SELF> are exported by this
283	module, but only C<$SELF> is currently used.	232	module, but only C<$SELF> is currently used.
284		233
285	=item snd $port, type => @data	234	=item snd $port, type => @data
286		235
287	=item snd $port, @msg	236	=item snd $port, @msg
288		237
289	Send the given message to the given port ID, which can identify either	238	Send the given message to the given port, which can identify either a
290	a local or a remote port, and must be a port ID.	239	local or a remote port, and must be a port ID.
291		240
292	While the message can be about anything, it is highly recommended to use a	241	While the message can be almost anything, it is highly recommended to
293	string as first element (a port ID, or some word that indicates a request	242	use a string as first element (a port ID, or some word that indicates a
294	type etc.).	243	request type etc.) and to consist if only simple perl values (scalars,
		244	arrays, hashes) - if you think you need to pass an object, think again.
295		245
296	The message data effectively becomes read-only after a call to this	246	The message data logically becomes read-only after a call to this
297	function: modifying any argument is not allowed and can cause many	247	function: modifying any argument (or values referenced by them) is
298	problems.	248	forbidden, as there can be considerable time between the call to C<snd>
		249	and the time the message is actually being serialised - in fact, it might
		250	never be copied as within the same process it is simply handed to the
		251	receiving port.
299		252
300	The type of data you can transfer depends on the transport protocol: when	253	The type of data you can transfer depends on the transport protocol: when
301	JSON is used, then only strings, numbers and arrays and hashes consisting	254	JSON is used, then only strings, numbers and arrays and hashes consisting
302	of those are allowed (no objects). When Storable is used, then anything	255	of those are allowed (no objects). When Storable is used, then anything
303	that Storable can serialise and deserialise is allowed, and for the local	256	that Storable can serialise and deserialise is allowed, and for the local
304	node, anything can be passed.	257	node, anything can be passed. Best rely only on the common denominator of
		258	these.
305		259
306	=item $local_port = port	260	=item $local_port = port
307		261
308	Create a new local port object and returns its port ID. Initially it has	262	Create a new local port object and returns its port ID. Initially it has
309	no callbacks set and will throw an error when it receives messages.	263	no callbacks set and will throw an error when it receives messages.
…		…
485	$res	439	$res
486	}	440	}
487	}	441	}
488	}	442	}
489		443
490	=item $guard = mon $port, $cb->(@reason)	444	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
491		445
492	=item $guard = mon $port, $rcvport	446	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
493		447
494	=item $guard = mon $port	448	=item $guard = mon $port # kill $SELF when $port dies
495		449
496	=item $guard = mon $port, $rcvport, @msg	450	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
497		451
498	Monitor the given port and do something when the port is killed or	452	Monitor the given port and do something when the port is killed or
499	messages to it were lost, and optionally return a guard that can be used	453	messages to it were lost, and optionally return a guard that can be used
500	to stop monitoring again.	454	to stop monitoring again.
501		455
502	C<mon> effectively guarantees that, in the absence of hardware failures,	456	C<mon> effectively guarantees that, in the absence of hardware failures,
503	that after starting the monitor, either all messages sent to the port	457	after starting the monitor, either all messages sent to the port will
504	will arrive, or the monitoring action will be invoked after possible	458	arrive, or the monitoring action will be invoked after possible message
505	message loss has been detected. No messages will be lost "in between"	459	loss has been detected. No messages will be lost "in between" (after
506	(after the first lost message no further messages will be received by the	460	the first lost message no further messages will be received by the
507	port). After the monitoring action was invoked, further messages might get	461	port). After the monitoring action was invoked, further messages might get
508	delivered again.	462	delivered again.
509		463
510	Note that monitoring-actions are one-shot: once released, they are removed	464	Note that monitoring-actions are one-shot: once messages are lost (and a
511	and will not trigger again.	465	monitoring alert was raised), they are removed and will not trigger again.
512		466
513	In the first form (callback), the callback is simply called with any	467	In the first form (callback), the callback is simply called with any
514	number of C<@reason> elements (no @reason means that the port was deleted	468	number of C<@reason> elements (no @reason means that the port was deleted
515	"normally"). Note also that I<< the callback B<must> never die >>, so use	469	"normally"). Note also that I<< the callback B<must> never die >>, so use
516	C<eval> if unsure.	470	C<eval> if unsure.
…		…
578	is killed, the references will be freed.	532	is killed, the references will be freed.
579		533
580	Optionally returns a guard that will stop the monitoring.	534	Optionally returns a guard that will stop the monitoring.
581		535
582	This function is useful when you create e.g. timers or other watchers and	536	This function is useful when you create e.g. timers or other watchers and
583	want to free them when the port gets killed:	537	want to free them when the port gets killed (note the use of C<psub>):
584		538
585	$port->rcv (start => sub {	539	$port->rcv (start => sub {
586	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	540	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
587	undef $timer if 0.9 < rand;	541	undef $timer if 0.9 < rand;
588	});	542	});
589	});	543	});
590		544
591	=cut	545	=cut
…		…
600		554
601	=item kil $port[, @reason]	555	=item kil $port[, @reason]
602		556
603	Kill the specified port with the given C<@reason>.	557	Kill the specified port with the given C<@reason>.
604		558
605	If no C<@reason> is specified, then the port is killed "normally" (linked	559	If no C<@reason> is specified, then the port is killed "normally" (ports
606	ports will not be kileld, or even notified).	560	monitoring other ports will not necessarily die because a port dies
		561	"normally").
607		562
608	Otherwise, linked ports get killed with the same reason (second form of	563	Otherwise, linked ports get killed with the same reason (second form of
609	C<mon>, see below).	564	C<mon>, see above).
610		565
611	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	566	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
612	will be reported as reason C<< die => $@ >>.	567	will be reported as reason C<< die => $@ >>.
613		568
614	Transport/communication errors are reported as C<< transport_error =>	569	Transport/communication errors are reported as C<< transport_error =>
…		…
619	=item $port = spawn $node, $initfunc[, @initdata]	574	=item $port = spawn $node, $initfunc[, @initdata]
620		575
621	Creates a port on the node C<$node> (which can also be a port ID, in which	576	Creates a port on the node C<$node> (which can also be a port ID, in which
622	case it's the node where that port resides).	577	case it's the node where that port resides).
623		578
624	The port ID of the newly created port is return immediately, and it is	579	The port ID of the newly created port is returned immediately, and it is
625	permissible to immediately start sending messages or monitor the port.	580	possible to immediately start sending messages or to monitor the port.
626		581
627	After the port has been created, the init function is	582	After the port has been created, the init function is called on the remote
628	called. This function must be a fully-qualified function name	583	node, in the same context as a C<rcv> callback. This function must be a
629	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	584	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
630	program, use C<::name>.	585	specify a function in the main program, use C<::name>.
631		586
632	If the function doesn't exist, then the node tries to C<require>	587	If the function doesn't exist, then the node tries to C<require>
633	the package, then the package above the package and so on (e.g.	588	the package, then the package above the package and so on (e.g.
634	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	589	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
635	exists or it runs out of package names.	590	exists or it runs out of package names.
636		591
637	The init function is then called with the newly-created port as context	592	The init function is then called with the newly-created port as context
638	object (C<$SELF>) and the C<@initdata> values as arguments.	593	object (C<$SELF>) and the C<@initdata> values as arguments.
639		594
640	A common idiom is to pass your own port, monitor the spawned port, and	595	A common idiom is to pass a local port, immediately monitor the spawned
641	in the init function, monitor the original port. This two-way monitoring	596	port, and in the remote init function, immediately monitor the passed
642	ensures that both ports get cleaned up when there is a problem.	597	local port. This two-way monitoring ensures that both ports get cleaned up
		598	when there is a problem.
643		599
644	Example: spawn a chat server port on C<$othernode>.	600	Example: spawn a chat server port on C<$othernode>.
645		601
646	# this node, executed from within a port context:	602	# this node, executed from within a port context:
647	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	603	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
689	=item after $timeout, $callback	645	=item after $timeout, $callback
690		646
691	Either sends the given message, or call the given callback, after the	647	Either sends the given message, or call the given callback, after the
692	specified number of seconds.	648	specified number of seconds.
693		649
694	This is simply a utility function that come sin handy at times.	650	This is simply a utility function that comes in handy at times - the
		651	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		652	so it may go away in the future.
695		653
696	=cut	654	=cut
697		655
698	sub after($@) {	656	sub after($@) {
699	my ($timeout, @action) = @_;	657	my ($timeout, @action) = @_;
…		…
722		680
723	Despite the similarities, there are also some important differences:	681	Despite the similarities, there are also some important differences:
724		682
725	=over 4	683	=over 4
726		684
727	=item * Node references contain the recipe on how to contact them.	685	=item * Node IDs are arbitrary strings in AEMP.
728		686
729	Erlang relies on special naming and DNS to work everywhere in the	687	Erlang relies on special naming and DNS to work everywhere in the same
730	same way. AEMP relies on each node knowing it's own address(es), with	688	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
731	convenience functionality.	689	configuraiton or DNS), but will otherwise discover other odes itself.
732
733	This means that AEMP requires a less tightly controlled environment at the
734	cost of longer node references and a slightly higher management overhead.
735		690
736	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP	691	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
737	uses "local ports are like remote ports".	692	uses "local ports are like remote ports".
738		693
739	The failure modes for local ports are quite different (runtime errors	694	The failure modes for local ports are quite different (runtime errors
…		…
768		723
769	Erlang makes few guarantees on messages delivery - messages can get lost	724	Erlang makes few guarantees on messages delivery - messages can get lost
770	without any of the processes realising it (i.e. you send messages a, b,	725	without any of the processes realising it (i.e. you send messages a, b,
771	and c, and the other side only receives messages a and c).	726	and c, and the other side only receives messages a and c).
772		727
773	AEMP guarantees correct ordering, and the guarantee that there are no	728	AEMP guarantees correct ordering, and the guarantee that after one message
774	holes in the message sequence.	729	is lost, all following ones sent to the same port are lost as well, until
775		730	monitoring raises an error, so there are no silent "holes" in the message
776	=item * In Erlang, processes can be declared dead and later be found to be	731	sequence.
777	alive.
778
779	In Erlang it can happen that a monitored process is declared dead and
780	linked processes get killed, but later it turns out that the process is
781	still alive - and can receive messages.
782
783	In AEMP, when port monitoring detects a port as dead, then that port will
784	eventually be killed - it cannot happen that a node detects a port as dead
785	and then later sends messages to it, finding it is still alive.
786		732
787	=item * Erlang can send messages to the wrong port, AEMP does not.	733	=item * Erlang can send messages to the wrong port, AEMP does not.
788		734
789	In Erlang it is quite likely that a node that restarts reuses a process ID	735	In Erlang it is quite likely that a node that restarts reuses a process ID
790	known to other nodes for a completely different process, causing messages	736	known to other nodes for a completely different process, causing messages
…		…
794	around in the network will not be sent to an unrelated port.	740	around in the network will not be sent to an unrelated port.
795		741
796	=item * Erlang uses unprotected connections, AEMP uses secure	742	=item * Erlang uses unprotected connections, AEMP uses secure
797	authentication and can use TLS.	743	authentication and can use TLS.
798		744
799	AEMP can use a proven protocol - SSL/TLS - to protect connections and	745	AEMP can use a proven protocol - TLS - to protect connections and
800	securely authenticate nodes.	746	securely authenticate nodes.
801		747
802	=item * The AEMP protocol is optimised for both text-based and binary	748	=item * The AEMP protocol is optimised for both text-based and binary
803	communications.	749	communications.
804		750
805	The AEMP protocol, unlike the Erlang protocol, supports both	751	The AEMP protocol, unlike the Erlang protocol, supports both programming
806	language-independent text-only protocols (good for debugging) and binary,	752	language independent text-only protocols (good for debugging) and binary,
807	language-specific serialisers (e.g. Storable).	753	language-specific serialisers (e.g. Storable). By default, unless TLS is
		754	used, the protocol is actually completely text-based.
808		755
809	It has also been carefully designed to be implementable in other languages	756	It has also been carefully designed to be implementable in other languages
810	with a minimum of work while gracefully degrading fucntionality to make the	757	with a minimum of work while gracefully degrading functionality to make the
811	protocol simple.	758	protocol simple.
812		759
813	=item * AEMP has more flexible monitoring options than Erlang.	760	=item * AEMP has more flexible monitoring options than Erlang.
814		761
815	In Erlang, you can chose to receive I<all> exit signals as messages	762	In Erlang, you can chose to receive I<all> exit signals as messages
…		…
818	Erlang, as one can choose between automatic kill, exit message or callback	765	Erlang, as one can choose between automatic kill, exit message or callback
819	on a per-process basis.	766	on a per-process basis.
820		767
821	=item * Erlang tries to hide remote/local connections, AEMP does not.	768	=item * Erlang tries to hide remote/local connections, AEMP does not.
822		769
823	Monitoring in Erlang is not an indicator of process death/crashes,	770	Monitoring in Erlang is not an indicator of process death/crashes, in the
824	as linking is (except linking is unreliable in Erlang).	771	same way as linking is (except linking is unreliable in Erlang).
825		772
826	In AEMP, you don't "look up" registered port names or send to named ports	773	In AEMP, you don't "look up" registered port names or send to named ports
827	that might or might not be persistent. Instead, you normally spawn a port	774	that might or might not be persistent. Instead, you normally spawn a port
828	on the remote node. The init function monitors the you, and you monitor	775	on the remote node. The init function monitors you, and you monitor the
829	the remote port. Since both monitors are local to the node, they are much	776	remote port. Since both monitors are local to the node, they are much more
830	more reliable.	777	reliable (no need for C<spawn_link>).
831		778
832	This also saves round-trips and avoids sending messages to the wrong port	779	This also saves round-trips and avoids sending messages to the wrong port
833	(hard to do in Erlang).	780	(hard to do in Erlang).
834		781
835	=back	782	=back
836		783
837	=head1 RATIONALE	784	=head1 RATIONALE
838		785
839	=over 4	786	=over 4
840		787
841	=item Why strings for ports and noderefs, why not objects?	788	=item Why strings for port and node IDs, why not objects?
842		789
843	We considered "objects", but found that the actual number of methods	790	We considered "objects", but found that the actual number of methods
844	thatc an be called are very low. Since port IDs and noderefs travel over	791	that can be called are quite low. Since port and node IDs travel over
845	the network frequently, the serialising/deserialising would add lots of	792	the network frequently, the serialising/deserialising would add lots of
846	overhead, as well as having to keep a proxy object.	793	overhead, as well as having to keep a proxy object everywhere.
847		794
848	Strings can easily be printed, easily serialised etc. and need no special	795	Strings can easily be printed, easily serialised etc. and need no special
849	procedures to be "valid".	796	procedures to be "valid".
850		797
851	And a a miniport consists of a single closure stored in a global hash - it	798	And as a result, a miniport consists of a single closure stored in a
852	can't become much cheaper.	799	global hash - it can't become much cheaper.
853		800
854	=item Why favour JSON, why not real serialising format such as Storable?	801	=item Why favour JSON, why not a real serialising format such as Storable?
855		802
856	In fact, any AnyEvent::MP node will happily accept Storable as framing	803	In fact, any AnyEvent::MP node will happily accept Storable as framing
857	format, but currently there is no way to make a node use Storable by	804	format, but currently there is no way to make a node use Storable by
858	default.	805	default (although all nodes will accept it).
859		806
860	The default framing protocol is JSON because a) JSON::XS is many times	807	The default framing protocol is JSON because a) JSON::XS is many times
861	faster for small messages and b) most importantly, after years of	808	faster for small messages and b) most importantly, after years of
862	experience we found that object serialisation is causing more problems	809	experience we found that object serialisation is causing more problems
863	than it gains: Just like function calls, objects simply do not travel	810	than it solves: Just like function calls, objects simply do not travel
864	easily over the network, mostly because they will always be a copy, so you	811	easily over the network, mostly because they will always be a copy, so you
865	always have to re-think your design.	812	always have to re-think your design.
866		813
867	Keeping your messages simple, concentrating on data structures rather than	814	Keeping your messages simple, concentrating on data structures rather than
868	objects, will keep your messages clean, tidy and efficient.	815	objects, will keep your messages clean, tidy and efficient.
869		816
870	=back	817	=back
871		818
872	=head1 SEE ALSO	819	=head1 SEE ALSO
873		820
		821	L<AnyEvent::MP::Intro> - a gentle introduction.
		822
		823	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		824
		825	L<AnyEvent::MP::Global> - network maintainance and port groups, to find
		826	your applications.
		827
874	L<AnyEvent>.	828	L<AnyEvent>.
875		829
876	=head1 AUTHOR	830	=head1 AUTHOR
877		831
878	Marc Lehmann <schmorp@schmorp.de>	832	Marc Lehmann <schmorp@schmorp.de>

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