[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 1.71 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46	AnyEvent::MP::Intro - outdated	45	AnyEvent::MP::Intro - uptodate, but incomplete.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
…		…
126	use base "Exporter";	137	use base "Exporter";
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 _any_	142	NODE $NODE *SELF node_of after
132	resolve_node initialise_node	143	initialise_node
133	snd rcv mon 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;
138		149
…		…
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	=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	206	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	207	the one specified via C<aemp> for the current node. This should be the
210	form of invocation for "daemon"-type nodes.	208	most common form of invocation for "daemon"-type nodes.
211		209
212	initialise_node;	210	initialise_node;
213		211
214	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
215	C<aemp>. This form is often used for commandline clients.	213	clients.
216		214
217	initialise_node "slave/";	215	initialise_node "anon/";
218		216
219	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
220	form is also often used for commandline clients.	218	name, or no binds list was specified, resolve C<localhost:4044> and bind
221		219	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		220
235	initialise_node "localhost:4044";	221	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		222
266	=item $SELF	223	=item $SELF
267		224
268	Contains the current port id while executing C<rcv> callbacks or C<psub>	225	Contains the current port id while executing C<rcv> callbacks or C<psub>
269	blocks.	226	blocks.
270		227
271	=item SELF, %SELF, @SELF...	228	=item *SELF, SELF, %SELF, @SELF...
272		229
273	Due to some quirks in how perl exports variables, it is impossible to	230	Due to some quirks in how perl exports variables, it is impossible to
274	just export C<$SELF>, all the symbols called C<SELF> are exported by this	231	just export C<$SELF>, all the symbols named C<SELF> are exported by this
275	module, but only C<$SELF> is currently used.	232	module, but only C<$SELF> is currently used.
276		233
277	=item snd $port, type => @data	234	=item snd $port, type => @data
278		235
279	=item snd $port, @msg	236	=item snd $port, @msg
280		237
281	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
282	a local or a remote port, and must be a port ID.	239	local or a remote port, and must be a port ID.
283		240
284	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
285	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
286	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.
287		245
288	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
289	function: modifying any argument is not allowed and can cause many	247	function: modifying any argument (or values referenced by them) is
290	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.
291		252
292	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
293	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
294	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
295	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
296	node, anything can be passed.	257	node, anything can be passed. Best rely only on the common denominator of
		258	these.
297		259
298	=item $local_port = port	260	=item $local_port = port
299		261
300	Create a new local port object and returns its port ID. Initially it has	262	Create a new local port object and returns its port ID. Initially it has
301	no callbacks set and will throw an error when it receives messages.	263	no callbacks set and will throw an error when it receives messages.
…		…
388		350
389	sub rcv($@) {	351	sub rcv($@) {
390	my $port = shift;	352	my $port = shift;
391	my ($noderef, $portid) = split /#/, $port, 2;	353	my ($noderef, $portid) = split /#/, $port, 2;
392		354
393	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	355	$NODE{$noderef} == $NODE{""}
394	or Carp::croak "$port: rcv can only be called on local ports, caught";	356	or Carp::croak "$port: rcv can only be called on local ports, caught";
395		357
396	while (@_) {	358	while (@_) {
397	if (ref $_[0]) {	359	if (ref $_[0]) {
398	if (my $self = $PORT_DATA{$portid}) {	360	if (my $self = $PORT_DATA{$portid}) {
…		…
477	$res	439	$res
478	}	440	}
479	}	441	}
480	}	442	}
481		443
482	=item $guard = mon $port, $cb->(@reason)	444	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
483		445
484	=item $guard = mon $port, $rcvport	446	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
485		447
486	=item $guard = mon $port	448	=item $guard = mon $port # kill $SELF when $port dies
487		449
488	=item $guard = mon $port, $rcvport, @msg	450	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
489		451
490	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
491	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
492	to stop monitoring again.	454	to stop monitoring again.
493		455
494	C<mon> effectively guarantees that, in the absence of hardware failures,	456	C<mon> effectively guarantees that, in the absence of hardware failures,
495	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
496	will arrive, or the monitoring action will be invoked after possible	458	arrive, or the monitoring action will be invoked after possible message
497	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
498	(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
499	port). After the monitoring action was invoked, further messages might get	461	port). After the monitoring action was invoked, further messages might get
500	delivered again.	462	delivered again.
		463
		464	Note that monitoring-actions are one-shot: once messages are lost (and a
		465	monitoring alert was raised), they are removed and will not trigger again.
501		466
502	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
503	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
504	"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
505	C<eval> if unsure.	470	C<eval> if unsure.
…		…
567	is killed, the references will be freed.	532	is killed, the references will be freed.
568		533
569	Optionally returns a guard that will stop the monitoring.	534	Optionally returns a guard that will stop the monitoring.
570		535
571	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
572	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>):
573		538
574	$port->rcv (start => sub {	539	$port->rcv (start => sub {
575	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	540	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
576	undef $timer if 0.9 < rand;	541	undef $timer if 0.9 < rand;
577	});	542	});
578	});	543	});
579		544
580	=cut	545	=cut
…		…
589		554
590	=item kil $port[, @reason]	555	=item kil $port[, @reason]
591		556
592	Kill the specified port with the given C<@reason>.	557	Kill the specified port with the given C<@reason>.
593		558
594	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
595	ports will not be kileld, or even notified).	560	monitoring other ports will not necessarily die because a port dies
		561	"normally").
596		562
597	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
598	C<mon>, see below).	564	C<mon>, see above).
599		565
600	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
601	will be reported as reason C<< die => $@ >>.	567	will be reported as reason C<< die => $@ >>.
602		568
603	Transport/communication errors are reported as C<< transport_error =>	569	Transport/communication errors are reported as C<< transport_error =>
…		…
608	=item $port = spawn $node, $initfunc[, @initdata]	574	=item $port = spawn $node, $initfunc[, @initdata]
609		575
610	Creates a port on the node C<$node> (which can also be a port ID, in which	576	Creates a port on the node C<$node> (which can also be a port ID, in which
611	case it's the node where that port resides).	577	case it's the node where that port resides).
612		578
613	The port ID of the newly created port is return immediately, and it is	579	The port ID of the newly created port is returned immediately, and it is
614	permissible to immediately start sending messages or monitor the port.	580	possible to immediately start sending messages or to monitor the port.
615		581
616	After the port has been created, the init function is	582	After the port has been created, the init function is called on the remote
617	called. This function must be a fully-qualified function name	583	node, in the same context as a C<rcv> callback. This function must be a
618	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	584	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
619	program, use C<::name>.	585	specify a function in the main program, use C<::name>.
620		586
621	If the function doesn't exist, then the node tries to C<require>	587	If the function doesn't exist, then the node tries to C<require>
622	the package, then the package above the package and so on (e.g.	588	the package, then the package above the package and so on (e.g.
623	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	589	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
624	exists or it runs out of package names.	590	exists or it runs out of package names.
625		591
626	The init function is then called with the newly-created port as context	592	The init function is then called with the newly-created port as context
627	object (C<$SELF>) and the C<@initdata> values as arguments.	593	object (C<$SELF>) and the C<@initdata> values as arguments.
628		594
629	A common idiom is to pass your own port, monitor the spawned port, and	595	A common idiom is to pass a local port, immediately monitor the spawned
630	in the init function, monitor the original port. This two-way monitoring	596	port, and in the remote init function, immediately monitor the passed
631	ensures that both ports get cleaned up when there is a problem.	597	local port. This two-way monitoring ensures that both ports get cleaned up
		598	when there is a problem.
632		599
633	Example: spawn a chat server port on C<$othernode>.	600	Example: spawn a chat server port on C<$othernode>.
634		601
635	# this node, executed from within a port context:	602	# this node, executed from within a port context:
636	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	603	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
671	snd_to_func $noderef, "AnyEvent::MP::_spawn" => $id, @_;	638	snd_to_func $noderef, "AnyEvent::MP::_spawn" => $id, @_;
672		639
673	"$noderef#$id"	640	"$noderef#$id"
674	}	641	}
675		642
676	=back	643	=item after $timeout, @msg
677		644
678	=head1 NODE MESSAGES	645	=item after $timeout, $callback
679		646
680	Nodes understand the following messages sent to them. Many of them take	647	Either sends the given message, or call the given callback, after the
681	arguments called C<@reply>, which will simply be used to compose a reply	648	specified number of seconds.
682	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
683	the remaining arguments are simply the message data.
684		649
685	While other messages exist, they are not public and subject to change.	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.
686		653
687	=over 4
688
689	=cut	654	=cut
690		655
691	=item lookup => $name, @reply	656	sub after($@) {
		657	my ($timeout, @action) = @_;
692		658
693	Replies with the port ID of the specified well-known port, or C<undef>.	659	my $t; $t = AE::timer $timeout, 0, sub {
694		660	undef $t;
695	=item devnull => ...	661	ref $action[0]
696		662	? $action[0]()
697	Generic data sink/CPU heat conversion.	663	: snd @action;
698		664	};
699	=item relay => $port, @msg	665	}
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		666
722	=back	667	=back
723		668
724	=head1 AnyEvent::MP vs. Distributed Erlang	669	=head1 AnyEvent::MP vs. Distributed Erlang
725		670
…		…
735		680
736	Despite the similarities, there are also some important differences:	681	Despite the similarities, there are also some important differences:
737		682
738	=over 4	683	=over 4
739		684
740	=item * Node references contain the recipe on how to contact them.	685	=item * Node IDs are arbitrary strings in AEMP.
741		686
742	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
743	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
744	convenience functionality.	689	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		690
749	=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
750	uses "local ports are like remote ports".	692	uses "local ports are like remote ports".
751		693
752	The failure modes for local ports are quite different (runtime errors	694	The failure modes for local ports are quite different (runtime errors
…		…
781		723
782	Erlang makes few guarantees on messages delivery - messages can get lost	724	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,	725	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).	726	and c, and the other side only receives messages a and c).
785		727
786	AEMP guarantees correct ordering, and the guarantee that there are no	728	AEMP guarantees correct ordering, and the guarantee that after one message
787	holes in the message sequence.	729	is lost, all following ones sent to the same port are lost as well, until
788		730	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	731	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		732
800	=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.
801		734
802	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
803	known to other nodes for a completely different process, causing messages	736	known to other nodes for a completely different process, causing messages
…		…
807	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.
808		741
809	=item * Erlang uses unprotected connections, AEMP uses secure	742	=item * Erlang uses unprotected connections, AEMP uses secure
810	authentication and can use TLS.	743	authentication and can use TLS.
811		744
812	AEMP can use a proven protocol - SSL/TLS - to protect connections and	745	AEMP can use a proven protocol - TLS - to protect connections and
813	securely authenticate nodes.	746	securely authenticate nodes.
814		747
815	=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
816	communications.	749	communications.
817		750
818	The AEMP protocol, unlike the Erlang protocol, supports both	751	The AEMP protocol, unlike the Erlang protocol, supports both programming
819	language-independent text-only protocols (good for debugging) and binary,	752	language independent text-only protocols (good for debugging) and binary,
820	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.
821		755
822	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
823	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
824	protocol simple.	758	protocol simple.
825		759
826	=item * AEMP has more flexible monitoring options than Erlang.	760	=item * AEMP has more flexible monitoring options than Erlang.
827		761
828	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
…		…
831	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
832	on a per-process basis.	766	on a per-process basis.
833		767
834	=item * Erlang tries to hide remote/local connections, AEMP does not.	768	=item * Erlang tries to hide remote/local connections, AEMP does not.
835		769
836	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
837	as linking is (except linking is unreliable in Erlang).	771	same way as linking is (except linking is unreliable in Erlang).
838		772
839	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
840	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
841	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
842	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
843	more reliable.	777	reliable (no need for C<spawn_link>).
844		778
845	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
846	(hard to do in Erlang).	780	(hard to do in Erlang).
847		781
848	=back	782	=back
849		783
850	=head1 RATIONALE	784	=head1 RATIONALE
851		785
852	=over 4	786	=over 4
853		787
854	=item Why strings for ports and noderefs, why not objects?	788	=item Why strings for port and node IDs, why not objects?
855		789
856	We considered "objects", but found that the actual number of methods	790	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	791	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	792	the network frequently, the serialising/deserialising would add lots of
859	overhead, as well as having to keep a proxy object.	793	overhead, as well as having to keep a proxy object everywhere.
860		794
861	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
862	procedures to be "valid".	796	procedures to be "valid".
863		797
864	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
865	can't become much cheaper.	799	global hash - it can't become much cheaper.
866		800
867	=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?
868		802
869	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
870	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
871	default.	805	default (although all nodes will accept it).
872		806
873	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
874	faster for small messages and b) most importantly, after years of	808	faster for small messages and b) most importantly, after years of
875	experience we found that object serialisation is causing more problems	809	experience we found that object serialisation is causing more problems
876	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
877	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
878	always have to re-think your design.	812	always have to re-think your design.
879		813
880	Keeping your messages simple, concentrating on data structures rather than	814	Keeping your messages simple, concentrating on data structures rather than
881	objects, will keep your messages clean, tidy and efficient.	815	objects, will keep your messages clean, tidy and efficient.
882		816
883	=back	817	=back
884		818
885	=head1 SEE ALSO	819	=head1 SEE ALSO
886		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
887	L<AnyEvent>.	828	L<AnyEvent>.
888		829
889	=head1 AUTHOR	830	=head1 AUTHOR
890		831
891	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