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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.55 by root, Fri Aug 14 23:17:17 2009 UTC vs.
Revision 1.68 by root, Fri Aug 28 23:06:33 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46	AnyEvent::MP::Intro - outdated	44	AnyEvent::MP::Intro - outdated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
…		…
126	use base "Exporter";	138	use base "Exporter";
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 _any_	143	NODE $NODE *SELF node_of after
132	resolve_node initialise_node	144	initialise_node
133	snd rcv mon 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;
138		150
…		…
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
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 then 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).
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	If the profile specifies a node ID, then this will become the node ID of
		184	this process. If not, then the profile name will be used as node ID. The
		185	special node ID of C<anon/> will be replaced by a random node ID.
176		186
177	=over 4	187	The next step is to look up the binds in the profile, followed by binding
		188	aemp protocol listeners on all binds specified (it is possible and valid
		189	to have no binds, meaning that the node cannot be contacted form the
		190	outside. This means the node cannot talk to other nodes that also have no
		191	binds, but it can still talk to all "normal" nodes).
178		192
179	=item public nodes	193	If the profile does not specify a binds list, then the node ID will be
		194	treated as if it were of the form C<host:port>, which will be resolved and
		195	used as binds list.
180		196
181	For public nodes, C<$noderef> (supplied either directly to	197	Lastly, the seeds list from the profile is passed to the
182	C<initialise_node> or indirectly via a profile or the nodename) must be a	198	L<AnyEvent::MP::Global> module, which will then use it to keep
183	noderef (possibly unresolved, in which case it will be resolved).	199	connectivity with at least on of those seed nodes at any point in time.
184		200
185	After resolving, the node will bind itself on all endpoints and try to
186	connect to all additional C<$seednodes> that are specified. Seednodes are
187	optional and can be used to quickly bootstrap the node into an existing
188	network.
189
190	=item slave nodes
191
192	When the C<$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	=back
203
204	This function will block until all nodes have been resolved and, for slave
205	nodes, until it has successfully established a connection to a master
206	server.
207
208	Example: become a public node listening on the guessed noderef, or the one	201	Example: become a distributed node listening on the guessed noderef, or
209	specified via C<aemp> for the current node. This should be the most common	202	the one specified via C<aemp> for the current node. This should be the
210	form of invocation for "daemon"-type nodes.	203	most common form of invocation for "daemon"-type nodes.
211		204
212	initialise_node;	205	initialise_node;
213		206
214	Example: become a slave node to any of the the seednodes specified via	207	Example: become an anonymous node. This form is often used for commandline
215	C<aemp>. This form is often used for commandline clients.	208	clients.
216		209
217	initialise_node "slave/";	210	initialise_node "anon/";
218		211
219	Example: become a slave node to any of the specified master servers. This	212	Example: become a distributed node. If there is no profile of the given
220	form is also often used for commandline clients.	213	name, or no binds list was specified, resolve C<localhost:4044> and bind
221		214	on the resulting addresses.
222	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
223
224	Example: become a public node, and try to contact some well-known master
225	servers to become part of the network.
226
227	initialise_node undef, "master1", "master2";
228
229	Example: become a public node listening on port C<4041>.
230
231	initialise_node 4041;
232
233	Example: become a public node, only visible on localhost port 4044.
234		215
235	initialise_node "localhost:4044";	216	initialise_node "localhost:4044";
236
237	=item $cv = resolve_node $noderef
238
239	Takes an unresolved node reference that may contain hostnames and
240	abbreviated IDs, resolves all of them and returns a resolved node
241	reference.
242
243	In addition to C<address:port> pairs allowed in resolved noderefs, the
244	following forms are supported:
245
246	=over 4
247
248	=item the empty string
249
250	An empty-string component gets resolved as if the default port (4040) was
251	specified.
252
253	=item naked port numbers (e.g. C<1234>)
254
255	These are resolved by prepending the local nodename and a colon, to be
256	further resolved.
257
258	=item hostnames (e.g. C<localhost:1234>, C<localhost>)
259
260	These are resolved by using AnyEvent::DNS to resolve them, optionally
261	looking up SRV records for the C<aemp=4040> port, if no port was
262	specified.
263
264	=back
265		217
266	=item $SELF	218	=item $SELF
267		219
268	Contains the current port id while executing C<rcv> callbacks or C<psub>	220	Contains the current port id while executing C<rcv> callbacks or C<psub>
269	blocks.	221	blocks.
270		222
271	=item SELF, %SELF, @SELF...	223	=item *SELF, SELF, %SELF, @SELF...
272		224
273	Due to some quirks in how perl exports variables, it is impossible to	225	Due to some quirks in how perl exports variables, it is impossible to
274	just export C<$SELF>, all the symbols called C<SELF> are exported by this	226	just export C<$SELF>, all the symbols named C<SELF> are exported by this
275	module, but only C<$SELF> is currently used.	227	module, but only C<$SELF> is currently used.
276		228
277	=item snd $port, type => @data	229	=item snd $port, type => @data
278		230
279	=item snd $port, @msg	231	=item snd $port, @msg
280		232
281	Send the given message to the given port ID, which can identify either	233	Send the given message to the given port, which can identify either a
282	a local or a remote port, and must be a port ID.	234	local or a remote port, and must be a port ID.
283		235
284	While the message can be about anything, it is highly recommended to use a	236	While the message can be almost anything, it is highly recommended to
285	string as first element (a port ID, or some word that indicates a request	237	use a string as first element (a port ID, or some word that indicates a
286	type etc.).	238	request type etc.) and to consist if only simple perl values (scalars,
		239	arrays, hashes) - if you think you need to pass an object, think again.
287		240
288	The message data effectively becomes read-only after a call to this	241	The message data logically becomes read-only after a call to this
289	function: modifying any argument is not allowed and can cause many	242	function: modifying any argument (or values referenced by them) is
290	problems.	243	forbidden, as there can be considerable time between the call to C<snd>
		244	and the time the message is actually being serialised - in fact, it might
		245	never be copied as within the same process it is simply handed to the
		246	receiving port.
291		247
292	The type of data you can transfer depends on the transport protocol: when	248	The type of data you can transfer depends on the transport protocol: when
293	JSON is used, then only strings, numbers and arrays and hashes consisting	249	JSON is used, then only strings, numbers and arrays and hashes consisting
294	of those are allowed (no objects). When Storable is used, then anything	250	of those are allowed (no objects). When Storable is used, then anything
295	that Storable can serialise and deserialise is allowed, and for the local	251	that Storable can serialise and deserialise is allowed, and for the local
296	node, anything can be passed.	252	node, anything can be passed. Best rely only on the common denominator of
		253	these.
297		254
298	=item $local_port = port	255	=item $local_port = port
299		256
300	Create a new local port object and returns its port ID. Initially it has	257	Create a new local port object and returns its port ID. Initially it has
301	no callbacks set and will throw an error when it receives messages.	258	no callbacks set and will throw an error when it receives messages.
…		…
388		345
389	sub rcv($@) {	346	sub rcv($@) {
390	my $port = shift;	347	my $port = shift;
391	my ($noderef, $portid) = split /#/, $port, 2;	348	my ($noderef, $portid) = split /#/, $port, 2;
392		349
393	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	350	$NODE{$noderef} == $NODE{""}
394	or Carp::croak "$port: rcv can only be called on local ports, caught";	351	or Carp::croak "$port: rcv can only be called on local ports, caught";
395		352
396	while (@_) {	353	while (@_) {
397	if (ref $_[0]) {	354	if (ref $_[0]) {
398	if (my $self = $PORT_DATA{$portid}) {	355	if (my $self = $PORT_DATA{$portid}) {
…		…
477	$res	434	$res
478	}	435	}
479	}	436	}
480	}	437	}
481		438
482	=item $guard = mon $port, $cb->(@reason)	439	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
483		440
484	=item $guard = mon $port, $rcvport	441	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
485		442
486	=item $guard = mon $port	443	=item $guard = mon $port # kill $SELF when $port dies
487		444
488	=item $guard = mon $port, $rcvport, @msg	445	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
489		446
490	Monitor the given port and do something when the port is killed or	447	Monitor the given port and do something when the port is killed or
491	messages to it were lost, and optionally return a guard that can be used	448	messages to it were lost, and optionally return a guard that can be used
492	to stop monitoring again.	449	to stop monitoring again.
493		450
494	C<mon> effectively guarantees that, in the absence of hardware failures,	451	C<mon> effectively guarantees that, in the absence of hardware failures,
495	that after starting the monitor, either all messages sent to the port	452	after starting the monitor, either all messages sent to the port will
496	will arrive, or the monitoring action will be invoked after possible	453	arrive, or the monitoring action will be invoked after possible message
497	message loss has been detected. No messages will be lost "in between"	454	loss has been detected. No messages will be lost "in between" (after
498	(after the first lost message no further messages will be received by the	455	the first lost message no further messages will be received by the
499	port). After the monitoring action was invoked, further messages might get	456	port). After the monitoring action was invoked, further messages might get
500	delivered again.	457	delivered again.
		458
		459	Note that monitoring-actions are one-shot: once messages are lost (and a
		460	monitoring alert was raised), they are removed and will not trigger again.
501		461
502	In the first form (callback), the callback is simply called with any	462	In the first form (callback), the callback is simply called with any
503	number of C<@reason> elements (no @reason means that the port was deleted	463	number of C<@reason> elements (no @reason means that the port was deleted
504	"normally"). Note also that I<< the callback B<must> never die >>, so use	464	"normally"). Note also that I<< the callback B<must> never die >>, so use
505	C<eval> if unsure.	465	C<eval> if unsure.
…		…
567	is killed, the references will be freed.	527	is killed, the references will be freed.
568		528
569	Optionally returns a guard that will stop the monitoring.	529	Optionally returns a guard that will stop the monitoring.
570		530
571	This function is useful when you create e.g. timers or other watchers and	531	This function is useful when you create e.g. timers or other watchers and
572	want to free them when the port gets killed:	532	want to free them when the port gets killed (note the use of C<psub>):
573		533
574	$port->rcv (start => sub {	534	$port->rcv (start => sub {
575	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	535	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
576	undef $timer if 0.9 < rand;	536	undef $timer if 0.9 < rand;
577	});	537	});
578	});	538	});
579		539
580	=cut	540	=cut
…		…
589		549
590	=item kil $port[, @reason]	550	=item kil $port[, @reason]
591		551
592	Kill the specified port with the given C<@reason>.	552	Kill the specified port with the given C<@reason>.
593		553
594	If no C<@reason> is specified, then the port is killed "normally" (linked	554	If no C<@reason> is specified, then the port is killed "normally" (ports
595	ports will not be kileld, or even notified).	555	monitoring other ports will not necessarily die because a port dies
		556	"normally").
596		557
597	Otherwise, linked ports get killed with the same reason (second form of	558	Otherwise, linked ports get killed with the same reason (second form of
598	C<mon>, see below).	559	C<mon>, see above).
599		560
600	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	561	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
601	will be reported as reason C<< die => $@ >>.	562	will be reported as reason C<< die => $@ >>.
602		563
603	Transport/communication errors are reported as C<< transport_error =>	564	Transport/communication errors are reported as C<< transport_error =>
…		…
608	=item $port = spawn $node, $initfunc[, @initdata]	569	=item $port = spawn $node, $initfunc[, @initdata]
609		570
610	Creates a port on the node C<$node> (which can also be a port ID, in which	571	Creates a port on the node C<$node> (which can also be a port ID, in which
611	case it's the node where that port resides).	572	case it's the node where that port resides).
612		573
613	The port ID of the newly created port is return immediately, and it is	574	The port ID of the newly created port is returned immediately, and it is
614	permissible to immediately start sending messages or monitor the port.	575	possible to immediately start sending messages or to monitor the port.
615		576
616	After the port has been created, the init function is	577	After the port has been created, the init function is called on the remote
617	called. This function must be a fully-qualified function name	578	node, in the same context as a C<rcv> callback. This function must be a
618	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	579	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
619	program, use C<::name>.	580	specify a function in the main program, use C<::name>.
620		581
621	If the function doesn't exist, then the node tries to C<require>	582	If the function doesn't exist, then the node tries to C<require>
622	the package, then the package above the package and so on (e.g.	583	the package, then the package above the package and so on (e.g.
623	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	584	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
624	exists or it runs out of package names.	585	exists or it runs out of package names.
625		586
626	The init function is then called with the newly-created port as context	587	The init function is then called with the newly-created port as context
627	object (C<$SELF>) and the C<@initdata> values as arguments.	588	object (C<$SELF>) and the C<@initdata> values as arguments.
628		589
629	A common idiom is to pass your own port, monitor the spawned port, and	590	A common idiom is to pass a local port, immediately monitor the spawned
630	in the init function, monitor the original port. This two-way monitoring	591	port, and in the remote init function, immediately monitor the passed
631	ensures that both ports get cleaned up when there is a problem.	592	local port. This two-way monitoring ensures that both ports get cleaned up
		593	when there is a problem.
632		594
633	Example: spawn a chat server port on C<$othernode>.	595	Example: spawn a chat server port on C<$othernode>.
634		596
635	# this node, executed from within a port context:	597	# this node, executed from within a port context:
636	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	598	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
671	snd_to_func $noderef, "AnyEvent::MP::_spawn" => $id, @_;	633	snd_to_func $noderef, "AnyEvent::MP::_spawn" => $id, @_;
672		634
673	"$noderef#$id"	635	"$noderef#$id"
674	}	636	}
675		637
676	=back	638	=item after $timeout, @msg
677		639
678	=head1 NODE MESSAGES	640	=item after $timeout, $callback
679		641
680	Nodes understand the following messages sent to them. Many of them take	642	Either sends the given message, or call the given callback, after the
681	arguments called C<@reply>, which will simply be used to compose a reply	643	specified number of seconds.
682	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
683	the remaining arguments are simply the message data.
684		644
685	While other messages exist, they are not public and subject to change.	645	This is simply a utility function that comes in handy at times - the
		646	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		647	so it may go away in the future.
686		648
687	=over 4
688
689	=cut	649	=cut
690		650
691	=item lookup => $name, @reply	651	sub after($@) {
		652	my ($timeout, @action) = @_;
692		653
693	Replies with the port ID of the specified well-known port, or C<undef>.	654	my $t; $t = AE::timer $timeout, 0, sub {
694		655	undef $t;
695	=item devnull => ...	656	ref $action[0]
696		657	? $action[0]()
697	Generic data sink/CPU heat conversion.	658	: snd @action;
698		659	};
699	=item relay => $port, @msg	660	}
700
701	Simply forwards the message to the given port.
702
703	=item eval => $string[ @reply]
704
705	Evaluates the given string. If C<@reply> is given, then a message of the
706	form C<@reply, $@, @evalres> is sent.
707
708	Example: crash another node.
709
710	snd $othernode, eval => "exit";
711
712	=item time => @reply
713
714	Replies the the current node time to C<@reply>.
715
716	Example: tell the current node to send the current time to C<$myport> in a
717	C<timereply> message.
718
719	snd $NODE, time => $myport, timereply => 1, 2;
720	# => snd $myport, timereply => 1, 2, <time>
721		661
722	=back	662	=back
723		663
724	=head1 AnyEvent::MP vs. Distributed Erlang	664	=head1 AnyEvent::MP vs. Distributed Erlang
725		665
…		…
735		675
736	Despite the similarities, there are also some important differences:	676	Despite the similarities, there are also some important differences:
737		677
738	=over 4	678	=over 4
739		679
740	=item * Node references contain the recipe on how to contact them.	680	=item * Node IDs are arbitrary strings in AEMP.
741		681
742	Erlang relies on special naming and DNS to work everywhere in the	682	Erlang relies on special naming and DNS to work everywhere in the same
743	same way. AEMP relies on each node knowing it's own address(es), with	683	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
744	convenience functionality.	684	configuraiton or DNS), but will otherwise discover other odes itself.
745
746	This means that AEMP requires a less tightly controlled environment at the
747	cost of longer node references and a slightly higher management overhead.
748		685
749	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP	686	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
750	uses "local ports are like remote ports".	687	uses "local ports are like remote ports".
751		688
752	The failure modes for local ports are quite different (runtime errors	689	The failure modes for local ports are quite different (runtime errors
…		…
781		718
782	Erlang makes few guarantees on messages delivery - messages can get lost	719	Erlang makes few guarantees on messages delivery - messages can get lost
783	without any of the processes realising it (i.e. you send messages a, b,	720	without any of the processes realising it (i.e. you send messages a, b,
784	and c, and the other side only receives messages a and c).	721	and c, and the other side only receives messages a and c).
785		722
786	AEMP guarantees correct ordering, and the guarantee that there are no	723	AEMP guarantees correct ordering, and the guarantee that after one message
787	holes in the message sequence.	724	is lost, all following ones sent to the same port are lost as well, until
788		725	monitoring raises an error, so there are no silent "holes" in the message
789	=item * In Erlang, processes can be declared dead and later be found to be	726	sequence.
790	alive.
791
792	In Erlang it can happen that a monitored process is declared dead and
793	linked processes get killed, but later it turns out that the process is
794	still alive - and can receive messages.
795
796	In AEMP, when port monitoring detects a port as dead, then that port will
797	eventually be killed - it cannot happen that a node detects a port as dead
798	and then later sends messages to it, finding it is still alive.
799		727
800	=item * Erlang can send messages to the wrong port, AEMP does not.	728	=item * Erlang can send messages to the wrong port, AEMP does not.
801		729
802	In Erlang it is quite likely that a node that restarts reuses a process ID	730	In Erlang it is quite likely that a node that restarts reuses a process ID
803	known to other nodes for a completely different process, causing messages	731	known to other nodes for a completely different process, causing messages
…		…
807	around in the network will not be sent to an unrelated port.	735	around in the network will not be sent to an unrelated port.
808		736
809	=item * Erlang uses unprotected connections, AEMP uses secure	737	=item * Erlang uses unprotected connections, AEMP uses secure
810	authentication and can use TLS.	738	authentication and can use TLS.
811		739
812	AEMP can use a proven protocol - SSL/TLS - to protect connections and	740	AEMP can use a proven protocol - TLS - to protect connections and
813	securely authenticate nodes.	741	securely authenticate nodes.
814		742
815	=item * The AEMP protocol is optimised for both text-based and binary	743	=item * The AEMP protocol is optimised for both text-based and binary
816	communications.	744	communications.
817		745
818	The AEMP protocol, unlike the Erlang protocol, supports both	746	The AEMP protocol, unlike the Erlang protocol, supports both programming
819	language-independent text-only protocols (good for debugging) and binary,	747	language independent text-only protocols (good for debugging) and binary,
820	language-specific serialisers (e.g. Storable).	748	language-specific serialisers (e.g. Storable). By default, unless TLS is
		749	used, the protocol is actually completely text-based.
821		750
822	It has also been carefully designed to be implementable in other languages	751	It has also been carefully designed to be implementable in other languages
823	with a minimum of work while gracefully degrading fucntionality to make the	752	with a minimum of work while gracefully degrading functionality to make the
824	protocol simple.	753	protocol simple.
825		754
826	=item * AEMP has more flexible monitoring options than Erlang.	755	=item * AEMP has more flexible monitoring options than Erlang.
827		756
828	In Erlang, you can chose to receive I<all> exit signals as messages	757	In Erlang, you can chose to receive I<all> exit signals as messages
…		…
831	Erlang, as one can choose between automatic kill, exit message or callback	760	Erlang, as one can choose between automatic kill, exit message or callback
832	on a per-process basis.	761	on a per-process basis.
833		762
834	=item * Erlang tries to hide remote/local connections, AEMP does not.	763	=item * Erlang tries to hide remote/local connections, AEMP does not.
835		764
836	Monitoring in Erlang is not an indicator of process death/crashes,	765	Monitoring in Erlang is not an indicator of process death/crashes, in the
837	as linking is (except linking is unreliable in Erlang).	766	same way as linking is (except linking is unreliable in Erlang).
838		767
839	In AEMP, you don't "look up" registered port names or send to named ports	768	In AEMP, you don't "look up" registered port names or send to named ports
840	that might or might not be persistent. Instead, you normally spawn a port	769	that might or might not be persistent. Instead, you normally spawn a port
841	on the remote node. The init function monitors the you, and you monitor	770	on the remote node. The init function monitors you, and you monitor the
842	the remote port. Since both monitors are local to the node, they are much	771	remote port. Since both monitors are local to the node, they are much more
843	more reliable.	772	reliable (no need for C<spawn_link>).
844		773
845	This also saves round-trips and avoids sending messages to the wrong port	774	This also saves round-trips and avoids sending messages to the wrong port
846	(hard to do in Erlang).	775	(hard to do in Erlang).
847		776
848	=back	777	=back
849		778
850	=head1 RATIONALE	779	=head1 RATIONALE
851		780
852	=over 4	781	=over 4
853		782
854	=item Why strings for ports and noderefs, why not objects?	783	=item Why strings for port and node IDs, why not objects?
855		784
856	We considered "objects", but found that the actual number of methods	785	We considered "objects", but found that the actual number of methods
857	thatc an be called are very low. Since port IDs and noderefs travel over	786	that can be called are quite low. Since port and node IDs travel over
858	the network frequently, the serialising/deserialising would add lots of	787	the network frequently, the serialising/deserialising would add lots of
859	overhead, as well as having to keep a proxy object.	788	overhead, as well as having to keep a proxy object everywhere.
860		789
861	Strings can easily be printed, easily serialised etc. and need no special	790	Strings can easily be printed, easily serialised etc. and need no special
862	procedures to be "valid".	791	procedures to be "valid".
863		792
864	And a a miniport consists of a single closure stored in a global hash - it	793	And as a result, a miniport consists of a single closure stored in a
865	can't become much cheaper.	794	global hash - it can't become much cheaper.
866		795
867	=item Why favour JSON, why not real serialising format such as Storable?	796	=item Why favour JSON, why not a real serialising format such as Storable?
868		797
869	In fact, any AnyEvent::MP node will happily accept Storable as framing	798	In fact, any AnyEvent::MP node will happily accept Storable as framing
870	format, but currently there is no way to make a node use Storable by	799	format, but currently there is no way to make a node use Storable by
871	default.	800	default (although all nodes will accept it).
872		801
873	The default framing protocol is JSON because a) JSON::XS is many times	802	The default framing protocol is JSON because a) JSON::XS is many times
874	faster for small messages and b) most importantly, after years of	803	faster for small messages and b) most importantly, after years of
875	experience we found that object serialisation is causing more problems	804	experience we found that object serialisation is causing more problems
876	than it gains: Just like function calls, objects simply do not travel	805	than it solves: Just like function calls, objects simply do not travel
877	easily over the network, mostly because they will always be a copy, so you	806	easily over the network, mostly because they will always be a copy, so you
878	always have to re-think your design.	807	always have to re-think your design.
879		808
880	Keeping your messages simple, concentrating on data structures rather than	809	Keeping your messages simple, concentrating on data structures rather than
881	objects, will keep your messages clean, tidy and efficient.	810	objects, will keep your messages clean, tidy and efficient.
882		811
883	=back	812	=back
884		813
885	=head1 SEE ALSO	814	=head1 SEE ALSO
886		815
		816	L<AnyEvent::MP::Intro> - a gentle introduction.
		817
		818	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		819
		820	L<AnyEvent::MP::Global> - network maintainance and port groups, to find
		821	your applications.
		822
887	L<AnyEvent>.	823	L<AnyEvent>.
888		824
889	=head1 AUTHOR	825	=head1 AUTHOR
890		826
891	Marc Lehmann <schmorp@schmorp.de>	827	Marc Lehmann <schmorp@schmorp.de>

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Revision 1.68 by root, Fri Aug 28 23:06:33 2009 UTC