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

…		…
11	NODE $port # returns the noderef of the port	11	NODE $port # returns the noderef of the port
12		12
13	$SELF # receiving/own port id in rcv callbacks	13	$SELF # receiving/own port id in rcv callbacks
14		14
15	# initialise the node so it can send/receive messages	15	# initialise the node so it can send/receive messages
16	initialise_node; # -OR-	16	initialise_node;
17	initialise_node "localhost:4040"; # -OR-
18	initialise_node "slave/", "localhost:4040"
19		17
20	# ports are message endpoints	18	# ports are message endpoints
21		19
22	# sending messages	20	# sending messages
23	snd $port, type => data...;	21	snd $port, type => data...;
…		…
42		40
43	=head1 CURRENT STATUS	41	=head1 CURRENT STATUS
44		42
45	AnyEvent::MP - stable API, should work	43	AnyEvent::MP - stable API, should work
46	AnyEvent::MP::Intro - outdated	44	AnyEvent::MP::Intro - outdated
47	AnyEvent::MP::Kernel - WIP
48	AnyEvent::MP::Transport - mostly stable	45	AnyEvent::MP::Kernel - mostly stable
		46	AnyEvent::MP::Global - mostly stable
		47	AnyEvent::MP::Node - mostly stable, but internal anyways
		48	AnyEvent::MP::Transport - mostly stable, but internal anyways
49		49
50	stay tuned.	50	stay tuned.
51		51
52	=head1 DESCRIPTION	52	=head1 DESCRIPTION
53		53
54	This module (-family) implements a simple message passing framework.	54	This module (-family) implements a simple message passing framework.
55		55
56	Despite its simplicity, you can securely message other processes running	56	Despite its simplicity, you can securely message other processes running
57	on the same or other hosts.	57	on the same or other hosts, and you can supervise entities remotely.
58		58
59	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	59	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
60	manual page.	60	manual page and the examples under F<eg/>.
61		61
62	At the moment, this module family is severly broken and underdocumented,	62	At the moment, this module family is a bit underdocumented.
63	so do not use. This was uploaded mainly to reserve the CPAN namespace -
64	stay tuned!
65		63
66	=head1 CONCEPTS	64	=head1 CONCEPTS
67		65
68	=over 4	66	=over 4
69		67
70	=item port	68	=item port
71		69
72	A port is something you can send messages to (with the C<snd> function).	70	A port is something you can send messages to (with the C<snd> function).
73		71
74	Ports allow you to register C<rcv> handlers that can match all or just	72	Ports allow you to register C<rcv> handlers that can match all or just
75	some messages. Messages will not be queued.	73	some messages. Messages send to ports will not be queued, regardless of
		74	anything was listening for them or not.
76		75
77	=item port id - C<noderef#portname>	76	=item port ID - C<nodeid#portname>
78		77
79	A port ID is the concatenation of a noderef, a hash-mark (C<#>) as	78	A port ID is the concatenation of a node ID, a hash-mark (C<#>) as
80	separator, and a port name (a printable string of unspecified format). An	79	separator, and a port name (a printable string of unspecified format).
81	exception is the the node port, whose ID is identical to its node
82	reference.
83		80
84	=item node	81	=item node
85		82
86	A node is a single process containing at least one port - the node port,	83	A node is a single process containing at least one port - the node port,
87	which provides nodes to manage each other remotely, and to create new	84	which enables nodes to manage each other remotely, and to create new
88	ports.	85	ports.
89		86
90	Nodes are either private (single-process only), slaves (connected to a	87	Nodes are either public (have one or more listening ports) or private
91	master node only) or public nodes (connectable from unrelated nodes).	88	(no listening ports). Private nodes cannot talk to other private nodes
		89	currently.
92		90
93	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	91	=item node ID - C<[a-za-Z0-9_\-.:]+>
94		92
95	A node reference is a string that either simply identifies the node (for	93	A node ID is a string that uniquely identifies the node within a
96	private and slave nodes), or contains a recipe on how to reach a given	94	network. Depending on the configuration used, node IDs can look like a
97	node (for public nodes).	95	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		96	doesn't interpret node IDs in any way.
98		97
99	This recipe is simply a comma-separated list of C<address:port> pairs (for	98	=item binds - C<ip:port>
100	TCP/IP, other protocols might look different).
101		99
102	Node references come in two flavours: resolved (containing only numerical	100	Nodes can only talk to each other by creating some kind of connection to
103	addresses) or unresolved (where hostnames are used instead of addresses).	101	each other. To do this, nodes should listen on one or more local transport
		102	endpoints - binds. Currently, only standard C<ip:port> specifications can
		103	be used, which specify TCP ports to listen on.
104		104
105	Before using an unresolved node reference in a message you first have to	105	=item seeds - C<host:port>
106	resolve it.	106
		107	When a node starts, it knows nothing about the network. To teach the node
		108	about the network it first has to contact some other node within the
		109	network. This node is called a seed.
		110
		111	Seeds are transport endpoint(s) of as many nodes as one wants. Those nodes
		112	are expected to be long-running, and at least one of those should always
		113	be available. When nodes run out of connections (e.g. due to a network
		114	error), they try to re-establish connections to some seednodes again to
		115	join the network.
		116
		117	Apart from being sued for seeding, seednodes are not special in any way -
		118	every public node can be a seednode.
107		119
108	=back	120	=back
109		121
110	=head1 VARIABLES/FUNCTIONS	122	=head1 VARIABLES/FUNCTIONS
111		123
…		…
127		139
128	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	140	our $VERSION = $AnyEvent::MP::Kernel::VERSION;
129		141
130	our @EXPORT = qw(	142	our @EXPORT = qw(
131	NODE $NODE *SELF node_of after	143	NODE $NODE *SELF node_of after
132	resolve_node initialise_node	144	initialise_node
133	snd rcv mon mon_guard kil reg psub spawn	145	snd rcv mon mon_guard kil reg psub spawn
134	port	146	port
135	);	147	);
136		148
137	our $SELF;	149	our $SELF;
…		…
142	kil $SELF, die => $msg;	154	kil $SELF, die => $msg;
143	}	155	}
144		156
145	=item $thisnode = NODE / $NODE	157	=item $thisnode = NODE / $NODE
146		158
147	The C<NODE> function returns, and the C<$NODE> variable contains the	159	The C<NODE> function returns, and the C<$NODE> variable contains, the node
148	noderef of the local node. The value is initialised by a call to	160	ID of the node running in the current process. This value is initialised by
149	C<initialise_node>.	161	a call to C<initialise_node>.
150		162
151	=item $noderef = node_of $port	163	=item $nodeid = node_of $port
152		164
153	Extracts and returns the noderef from a port ID or a noderef.	165	Extracts and returns the node ID from a port ID or a node ID.
154		166
155	=item initialise_node $noderef, $seednode, $seednode...	167	=item initialise_node $profile_name, key => value...
156		168
157	=item initialise_node "slave/", $master, $master...
158
159	Before a node can talk to other nodes on the network it has to initialise	169	Before a node can talk to other nodes on the network (i.e. enter
160	itself - the minimum a node needs to know is it's own name, and optionally	170	"distributed mode") it has to initialise itself - the minimum a node needs
161	it should know the noderefs of some other nodes in the network.	171	to know is its own name, and optionally it should know the addresses of
		172	some other nodes in the network to discover other nodes.
162		173
163	This function initialises a node - it must be called exactly once (or	174	This function initialises a node - it must be called exactly once (or
164	never) before calling other AnyEvent::MP functions.	175	never) before calling other AnyEvent::MP functions.
165		176
166	All arguments (optionally except for the first) are noderefs, which can be	177	The first argument is a profile name. If it is C<undef> or missing, then
167	either resolved or unresolved.	178	the current nodename will be used instead (i.e. F<uname -n>).
168		179
169	The first argument will be looked up in the configuration database first	180	The function first looks up the profile in the aemp configuration (see the
170	(if it is C<undef> then the current nodename will be used instead) to find	181	L<aemp> commandline utility). the profile is calculated as follows:
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		182
175	There are two types of networked nodes, public nodes and slave nodes:	183	First, all remaining key => value pairs will be used. Then they will be
		184	overwritten by any values specified in the global default configuration
		185	(see the F<aemp> utility), then the chain of profiles selected, if
		186	any. That means that the values specified in the profile have highest
		187	priority and the values specified via C<initialise_node> have lowest
		188	priority.
176		189
177	=over 4	190	If the profile specifies a node ID, then this will become the node ID of
		191	this process. If not, then the profile name will be used as node ID. The
		192	special node ID of C<anon/> will be replaced by a random node ID.
178		193
179	=item public nodes	194	The next step is to look up the binds in the profile, followed by binding
		195	aemp protocol listeners on all binds specified (it is possible and valid
		196	to have no binds, meaning that the node cannot be contacted form the
		197	outside. This means the node cannot talk to other nodes that also have no
		198	binds, but it can still talk to all "normal" nodes).
180		199
181	For public nodes, C<$noderef> (supplied either directly to	200	If the profile does not specify a binds list, then the node ID will be
182	C<initialise_node> or indirectly via a profile or the nodename) must be a	201	treated as if it were of the form C<host:port>, which will be resolved and
183	noderef (possibly unresolved, in which case it will be resolved).	202	used as binds list.
184		203
185	After resolving, the node will bind itself on all endpoints and try to	204	Lastly, the seeds list from the profile is passed to the
186	connect to all additional C<$seednodes> that are specified. Seednodes are	205	L<AnyEvent::MP::Global> module, which will then use it to keep
187	optional and can be used to quickly bootstrap the node into an existing	206	connectivity with at least on of those seed nodes at any point in time.
188	network.
189		207
190	=item slave nodes
191
192	When the C<$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	208	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	209	the one specified via C<aemp> for the current node. This should be the
218	form of invocation for "daemon"-type nodes.	210	most common form of invocation for "daemon"-type nodes.
219		211
220	initialise_node;	212	initialise_node;
221		213
222	Example: become a slave node to any of the the seednodes specified via	214	Example: become an anonymous node. This form is often used for commandline
223	C<aemp>. This form is often used for commandline clients.	215	clients.
224		216
225	initialise_node "slave/";	217	initialise_node "anon/";
226		218
227	Example: become a slave node to any of the specified master servers. This	219	Example: become a distributed node. If there is no profile of the given
228	form is also often used for commandline clients.	220	name, or no binds list was specified, resolve C<localhost:4044> and bind
229		221	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		222
243	initialise_node "localhost:4044";	223	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		224
274	=item $SELF	225	=item $SELF
275		226
276	Contains the current port id while executing C<rcv> callbacks or C<psub>	227	Contains the current port id while executing C<rcv> callbacks or C<psub>
277	blocks.	228	blocks.
278		229
279	=item SELF, %SELF, @SELF...	230	=item *SELF, SELF, %SELF, @SELF...
280		231
281	Due to some quirks in how perl exports variables, it is impossible to	232	Due to some quirks in how perl exports variables, it is impossible to
282	just export C<$SELF>, all the symbols called C<SELF> are exported by this	233	just export C<$SELF>, all the symbols named C<SELF> are exported by this
283	module, but only C<$SELF> is currently used.	234	module, but only C<$SELF> is currently used.
284		235
285	=item snd $port, type => @data	236	=item snd $port, type => @data
286		237
287	=item snd $port, @msg	238	=item snd $port, @msg
288		239
289	Send the given message to the given port ID, which can identify either	240	Send the given message to the given port, which can identify either a
290	a local or a remote port, and must be a port ID.	241	local or a remote port, and must be a port ID.
291		242
292	While the message can be about anything, it is highly recommended to use a	243	While the message can be almost anything, it is highly recommended to
293	string as first element (a port ID, or some word that indicates a request	244	use a string as first element (a port ID, or some word that indicates a
294	type etc.).	245	request type etc.) and to consist if only simple perl values (scalars,
		246	arrays, hashes) - if you think you need to pass an object, think again.
295		247
296	The message data effectively becomes read-only after a call to this	248	The message data logically becomes read-only after a call to this
297	function: modifying any argument is not allowed and can cause many	249	function: modifying any argument (or values referenced by them) is
298	problems.	250	forbidden, as there can be considerable time between the call to C<snd>
		251	and the time the message is actually being serialised - in fact, it might
		252	never be copied as within the same process it is simply handed to the
		253	receiving port.
299		254
300	The type of data you can transfer depends on the transport protocol: when	255	The type of data you can transfer depends on the transport protocol: when
301	JSON is used, then only strings, numbers and arrays and hashes consisting	256	JSON is used, then only strings, numbers and arrays and hashes consisting
302	of those are allowed (no objects). When Storable is used, then anything	257	of those are allowed (no objects). When Storable is used, then anything
303	that Storable can serialise and deserialise is allowed, and for the local	258	that Storable can serialise and deserialise is allowed, and for the local
304	node, anything can be passed.	259	node, anything can be passed. Best rely only on the common denominator of
		260	these.
305		261
306	=item $local_port = port	262	=item $local_port = port
307		263
308	Create a new local port object and returns its port ID. Initially it has	264	Create a new local port object and returns its port ID. Initially it has
309	no callbacks set and will throw an error when it receives messages.	265	no callbacks set and will throw an error when it receives messages.
…		…
485	$res	441	$res
486	}	442	}
487	}	443	}
488	}	444	}
489		445
490	=item $guard = mon $port, $cb->(@reason)	446	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
491		447
492	=item $guard = mon $port, $rcvport	448	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
493		449
494	=item $guard = mon $port	450	=item $guard = mon $port # kill $SELF when $port dies
495		451
496	=item $guard = mon $port, $rcvport, @msg	452	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
497		453
498	Monitor the given port and do something when the port is killed or	454	Monitor the given port and do something when the port is killed or
499	messages to it were lost, and optionally return a guard that can be used	455	messages to it were lost, and optionally return a guard that can be used
500	to stop monitoring again.	456	to stop monitoring again.
501		457
502	C<mon> effectively guarantees that, in the absence of hardware failures,	458	C<mon> effectively guarantees that, in the absence of hardware failures,
503	that after starting the monitor, either all messages sent to the port	459	after starting the monitor, either all messages sent to the port will
504	will arrive, or the monitoring action will be invoked after possible	460	arrive, or the monitoring action will be invoked after possible message
505	message loss has been detected. No messages will be lost "in between"	461	loss has been detected. No messages will be lost "in between" (after
506	(after the first lost message no further messages will be received by the	462	the first lost message no further messages will be received by the
507	port). After the monitoring action was invoked, further messages might get	463	port). After the monitoring action was invoked, further messages might get
508	delivered again.	464	delivered again.
509		465
510	Note that monitoring-actions are one-shot: once released, they are removed	466	Note that monitoring-actions are one-shot: once messages are lost (and a
511	and will not trigger again.	467	monitoring alert was raised), they are removed and will not trigger again.
512		468
513	In the first form (callback), the callback is simply called with any	469	In the first form (callback), the callback is simply called with any
514	number of C<@reason> elements (no @reason means that the port was deleted	470	number of C<@reason> elements (no @reason means that the port was deleted
515	"normally"). Note also that I<< the callback B<must> never die >>, so use	471	"normally"). Note also that I<< the callback B<must> never die >>, so use
516	C<eval> if unsure.	472	C<eval> if unsure.
…		…
578	is killed, the references will be freed.	534	is killed, the references will be freed.
579		535
580	Optionally returns a guard that will stop the monitoring.	536	Optionally returns a guard that will stop the monitoring.
581		537
582	This function is useful when you create e.g. timers or other watchers and	538	This function is useful when you create e.g. timers or other watchers and
583	want to free them when the port gets killed:	539	want to free them when the port gets killed (note the use of C<psub>):
584		540
585	$port->rcv (start => sub {	541	$port->rcv (start => sub {
586	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	542	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
587	undef $timer if 0.9 < rand;	543	undef $timer if 0.9 < rand;
588	});	544	});
589	});	545	});
590		546
591	=cut	547	=cut
…		…
600		556
601	=item kil $port[, @reason]	557	=item kil $port[, @reason]
602		558
603	Kill the specified port with the given C<@reason>.	559	Kill the specified port with the given C<@reason>.
604		560
605	If no C<@reason> is specified, then the port is killed "normally" (linked	561	If no C<@reason> is specified, then the port is killed "normally" (ports
606	ports will not be kileld, or even notified).	562	monitoring other ports will not necessarily die because a port dies
		563	"normally").
607		564
608	Otherwise, linked ports get killed with the same reason (second form of	565	Otherwise, linked ports get killed with the same reason (second form of
609	C<mon>, see below).	566	C<mon>, see above).
610		567
611	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	568	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
612	will be reported as reason C<< die => $@ >>.	569	will be reported as reason C<< die => $@ >>.
613		570
614	Transport/communication errors are reported as C<< transport_error =>	571	Transport/communication errors are reported as C<< transport_error =>
…		…
619	=item $port = spawn $node, $initfunc[, @initdata]	576	=item $port = spawn $node, $initfunc[, @initdata]
620		577
621	Creates a port on the node C<$node> (which can also be a port ID, in which	578	Creates a port on the node C<$node> (which can also be a port ID, in which
622	case it's the node where that port resides).	579	case it's the node where that port resides).
623		580
624	The port ID of the newly created port is return immediately, and it is	581	The port ID of the newly created port is returned immediately, and it is
625	permissible to immediately start sending messages or monitor the port.	582	possible to immediately start sending messages or to monitor the port.
626		583
627	After the port has been created, the init function is	584	After the port has been created, the init function is called on the remote
628	called. This function must be a fully-qualified function name	585	node, in the same context as a C<rcv> callback. This function must be a
629	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	586	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
630	program, use C<::name>.	587	specify a function in the main program, use C<::name>.
631		588
632	If the function doesn't exist, then the node tries to C<require>	589	If the function doesn't exist, then the node tries to C<require>
633	the package, then the package above the package and so on (e.g.	590	the package, then the package above the package and so on (e.g.
634	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	591	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
635	exists or it runs out of package names.	592	exists or it runs out of package names.
636		593
637	The init function is then called with the newly-created port as context	594	The init function is then called with the newly-created port as context
638	object (C<$SELF>) and the C<@initdata> values as arguments.	595	object (C<$SELF>) and the C<@initdata> values as arguments.
639		596
640	A common idiom is to pass your own port, monitor the spawned port, and	597	A common idiom is to pass a local port, immediately monitor the spawned
641	in the init function, monitor the original port. This two-way monitoring	598	port, and in the remote init function, immediately monitor the passed
642	ensures that both ports get cleaned up when there is a problem.	599	local port. This two-way monitoring ensures that both ports get cleaned up
		600	when there is a problem.
643		601
644	Example: spawn a chat server port on C<$othernode>.	602	Example: spawn a chat server port on C<$othernode>.
645		603
646	# this node, executed from within a port context:	604	# this node, executed from within a port context:
647	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	605	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
689	=item after $timeout, $callback	647	=item after $timeout, $callback
690		648
691	Either sends the given message, or call the given callback, after the	649	Either sends the given message, or call the given callback, after the
692	specified number of seconds.	650	specified number of seconds.
693		651
694	This is simply a utility function that come sin handy at times.	652	This is simply a utility function that comes in handy at times - the
		653	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		654	so it may go away in the future.
695		655
696	=cut	656	=cut
697		657
698	sub after($@) {	658	sub after($@) {
699	my ($timeout, @action) = @_;	659	my ($timeout, @action) = @_;
…		…
722		682
723	Despite the similarities, there are also some important differences:	683	Despite the similarities, there are also some important differences:
724		684
725	=over 4	685	=over 4
726		686
727	=item * Node references contain the recipe on how to contact them.	687	=item * Node IDs are arbitrary strings in AEMP.
728		688
729	Erlang relies on special naming and DNS to work everywhere in the	689	Erlang relies on special naming and DNS to work everywhere in the same
730	same way. AEMP relies on each node knowing it's own address(es), with	690	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
731	convenience functionality.	691	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		692
736	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP	693	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
737	uses "local ports are like remote ports".	694	uses "local ports are like remote ports".
738		695
739	The failure modes for local ports are quite different (runtime errors	696	The failure modes for local ports are quite different (runtime errors
…		…
768		725
769	Erlang makes few guarantees on messages delivery - messages can get lost	726	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,	727	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).	728	and c, and the other side only receives messages a and c).
772		729
773	AEMP guarantees correct ordering, and the guarantee that there are no	730	AEMP guarantees correct ordering, and the guarantee that after one message
774	holes in the message sequence.	731	is lost, all following ones sent to the same port are lost as well, until
775		732	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	733	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		734
787	=item * Erlang can send messages to the wrong port, AEMP does not.	735	=item * Erlang can send messages to the wrong port, AEMP does not.
788		736
789	In Erlang it is quite likely that a node that restarts reuses a process ID	737	In Erlang it is quite likely that a node that restarts reuses a process ID
790	known to other nodes for a completely different process, causing messages	738	known to other nodes for a completely different process, causing messages
…		…
794	around in the network will not be sent to an unrelated port.	742	around in the network will not be sent to an unrelated port.
795		743
796	=item * Erlang uses unprotected connections, AEMP uses secure	744	=item * Erlang uses unprotected connections, AEMP uses secure
797	authentication and can use TLS.	745	authentication and can use TLS.
798		746
799	AEMP can use a proven protocol - SSL/TLS - to protect connections and	747	AEMP can use a proven protocol - TLS - to protect connections and
800	securely authenticate nodes.	748	securely authenticate nodes.
801		749
802	=item * The AEMP protocol is optimised for both text-based and binary	750	=item * The AEMP protocol is optimised for both text-based and binary
803	communications.	751	communications.
804		752
805	The AEMP protocol, unlike the Erlang protocol, supports both	753	The AEMP protocol, unlike the Erlang protocol, supports both programming
806	language-independent text-only protocols (good for debugging) and binary,	754	language independent text-only protocols (good for debugging) and binary,
807	language-specific serialisers (e.g. Storable).	755	language-specific serialisers (e.g. Storable). By default, unless TLS is
		756	used, the protocol is actually completely text-based.
808		757
809	It has also been carefully designed to be implementable in other languages	758	It has also been carefully designed to be implementable in other languages
810	with a minimum of work while gracefully degrading fucntionality to make the	759	with a minimum of work while gracefully degrading functionality to make the
811	protocol simple.	760	protocol simple.
812		761
813	=item * AEMP has more flexible monitoring options than Erlang.	762	=item * AEMP has more flexible monitoring options than Erlang.
814		763
815	In Erlang, you can chose to receive I<all> exit signals as messages	764	In Erlang, you can chose to receive I<all> exit signals as messages
…		…
818	Erlang, as one can choose between automatic kill, exit message or callback	767	Erlang, as one can choose between automatic kill, exit message or callback
819	on a per-process basis.	768	on a per-process basis.
820		769
821	=item * Erlang tries to hide remote/local connections, AEMP does not.	770	=item * Erlang tries to hide remote/local connections, AEMP does not.
822		771
823	Monitoring in Erlang is not an indicator of process death/crashes,	772	Monitoring in Erlang is not an indicator of process death/crashes, in the
824	as linking is (except linking is unreliable in Erlang).	773	same way as linking is (except linking is unreliable in Erlang).
825		774
826	In AEMP, you don't "look up" registered port names or send to named ports	775	In AEMP, you don't "look up" registered port names or send to named ports
827	that might or might not be persistent. Instead, you normally spawn a port	776	that might or might not be persistent. Instead, you normally spawn a port
828	on the remote node. The init function monitors the you, and you monitor	777	on the remote node. The init function monitors you, and you monitor the
829	the remote port. Since both monitors are local to the node, they are much	778	remote port. Since both monitors are local to the node, they are much more
830	more reliable.	779	reliable (no need for C<spawn_link>).
831		780
832	This also saves round-trips and avoids sending messages to the wrong port	781	This also saves round-trips and avoids sending messages to the wrong port
833	(hard to do in Erlang).	782	(hard to do in Erlang).
834		783
835	=back	784	=back
836		785
837	=head1 RATIONALE	786	=head1 RATIONALE
838		787
839	=over 4	788	=over 4
840		789
841	=item Why strings for ports and noderefs, why not objects?	790	=item Why strings for port and node IDs, why not objects?
842		791
843	We considered "objects", but found that the actual number of methods	792	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	793	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	794	the network frequently, the serialising/deserialising would add lots of
846	overhead, as well as having to keep a proxy object.	795	overhead, as well as having to keep a proxy object everywhere.
847		796
848	Strings can easily be printed, easily serialised etc. and need no special	797	Strings can easily be printed, easily serialised etc. and need no special
849	procedures to be "valid".	798	procedures to be "valid".
850		799
851	And a a miniport consists of a single closure stored in a global hash - it	800	And as a result, a miniport consists of a single closure stored in a
852	can't become much cheaper.	801	global hash - it can't become much cheaper.
853		802
854	=item Why favour JSON, why not real serialising format such as Storable?	803	=item Why favour JSON, why not a real serialising format such as Storable?
855		804
856	In fact, any AnyEvent::MP node will happily accept Storable as framing	805	In fact, any AnyEvent::MP node will happily accept Storable as framing
857	format, but currently there is no way to make a node use Storable by	806	format, but currently there is no way to make a node use Storable by
858	default.	807	default (although all nodes will accept it).
859		808
860	The default framing protocol is JSON because a) JSON::XS is many times	809	The default framing protocol is JSON because a) JSON::XS is many times
861	faster for small messages and b) most importantly, after years of	810	faster for small messages and b) most importantly, after years of
862	experience we found that object serialisation is causing more problems	811	experience we found that object serialisation is causing more problems
863	than it gains: Just like function calls, objects simply do not travel	812	than it solves: Just like function calls, objects simply do not travel
864	easily over the network, mostly because they will always be a copy, so you	813	easily over the network, mostly because they will always be a copy, so you
865	always have to re-think your design.	814	always have to re-think your design.
866		815
867	Keeping your messages simple, concentrating on data structures rather than	816	Keeping your messages simple, concentrating on data structures rather than
868	objects, will keep your messages clean, tidy and efficient.	817	objects, will keep your messages clean, tidy and efficient.
869		818
870	=back	819	=back
871		820
872	=head1 SEE ALSO	821	=head1 SEE ALSO
873		822
		823	L<AnyEvent::MP::Intro> - a gentle introduction.
		824
		825	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		826
		827	L<AnyEvent::MP::Global> - network maintainance and port groups, to find
		828	your applications.
		829
874	L<AnyEvent>.	830	L<AnyEvent>.
875		831
876	=head1 AUTHOR	832	=head1 AUTHOR
877		833
878	Marc Lehmann <schmorp@schmorp.de>	834	Marc Lehmann <schmorp@schmorp.de>

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