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

Comparing cvsroot/AnyEvent-MP/MP.pm (file contents):
Revision 1.35 by root, Thu Aug 6 10:21:48 2009 UTC vs.
Revision 1.127 by root, Sat Mar 3 20:35:10 2012 UTC

…		…
1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent::MP - multi-processing/message-passing framework	3	AnyEvent::MP - erlang-style multi-processing/message-passing framework
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::MP;	7	use AnyEvent::MP;
8		8
9	$NODE # contains this node's noderef	9	$NODE # contains this node's node ID
10	NODE # returns this node's noderef	10	NODE # returns this node's node ID
11	NODE $port # returns the noderef of the port
12		11
		12	$SELF # receiving/own port id in rcv callbacks
		13
		14	# initialise the node so it can send/receive messages
		15	configure;
		16
		17	# ports are message destinations
		18
		19	# sending messages
13	snd $port, type => data...;	20	snd $port, type => data...;
		21	snd $port, @msg;
		22	snd @msg_with_first_element_being_a_port;
14		23
15	$SELF # receiving/own port id in rcv callbacks	24	# creating/using ports, the simple way
		25	my $simple_port = port { my @msg = @_ };
16		26
17	rcv $port, smartmatch => $cb->($port, @msg);	27	# creating/using ports, tagged message matching
18		28	my $port = port;
19	# examples:
20	rcv $port2, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
21	rcv $port1, pong => sub { warn "pong received\n" };	30	rcv $port, pong => sub { warn "pong received\n" };
22	snd $port2, ping => $port1;
23		31
24	# more, smarter, matches (_any_ is exported by this module)	32	# create a port on another node
25	rcv $port, [child_died => $pid] => sub { ...	33	my $port = spawn $node, $initfunc, @initdata;
26	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3
27		34
28	# linking two ports, so they both crash together	35	# destroy a port again
29	lnk $port1, $port2;	36	kil $port; # "normal" kill
		37	kil $port, my_error => "everything is broken"; # error kill
30		38
31	# monitoring	39	# monitoring
32	mon $port, $cb->(@msg) # callback is invoked on death	40	mon $localport, $cb->(@msg) # callback is invoked on death
33	mon $port, $otherport # kill otherport on abnormal death	41	mon $localport, $otherport # kill otherport on abnormal death
34	mon $port, $otherport, @msg # send message on death	42	mon $localport, $otherport, @msg # send message on death
		43
		44	# temporarily execute code in port context
		45	peval $port, sub { die "kill the port!" };
		46
		47	# execute callbacks in $SELF port context
		48	my $timer = AE::timer 1, 0, psub {
		49	die "kill the port, delayed";
		50	};
		51
		52	=head1 CURRENT STATUS
		53
		54	bin/aemp - stable.
		55	AnyEvent::MP - stable API, should work.
		56	AnyEvent::MP::Intro - explains most concepts.
		57	AnyEvent::MP::Kernel - mostly stable API.
		58	AnyEvent::MP::Global - stable API.
35		59
36	=head1 DESCRIPTION	60	=head1 DESCRIPTION
37		61
38	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
39		63
40	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
41	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
42		66
43	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	67	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
44	manual page.	68	manual page and the examples under F<eg/>.
45
46	At the moment, this module family is severly broken and underdocumented,
47	so do not use. This was uploaded mainly to reserve the CPAN namespace -
48	stay tuned! The basic API should be finished, however.
49		69
50	=head1 CONCEPTS	70	=head1 CONCEPTS
51		71
52	=over 4	72	=over 4
53		73
54	=item port	74	=item port
55		75
56	A port is something you can send messages to (with the C<snd> function).	76	Not to be confused with a TCP port, a "port" is something you can send
		77	messages to (with the C<snd> function).
57		78
58	Some ports allow you to register C<rcv> handlers that can match specific	79	Ports allow you to register C<rcv> handlers that can match all or just
59	messages. All C<rcv> handlers will receive messages they match, messages	80	some messages. Messages send to ports will not be queued, regardless of
60	will not be queued.	81	anything was listening for them or not.
61		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
62	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
63		86
64	A port id is normaly the concatenation of a noderef, a hash-mark (C<#>) as	87	A port ID is the concatenation of a node ID, a hash-mark (C<#>)
65	separator, and a port name (a printable string of unspecified format). An	88	as separator, and a port name (a printable string of unspecified
66	exception is the the node port, whose ID is identical to its node	89	format created by AnyEvent::MP).
67	reference.
68		90
69	=item node	91	=item node
70		92
71	A node is a single process containing at least one port - the node	93	A node is a single process containing at least one port - the node port,
72	port. You can send messages to node ports to find existing ports or to	94	which enables nodes to manage each other remotely, and to create new
73	create new ports, among other things.	95	ports.
74		96
75	Nodes are either private (single-process only), slaves (connected to a	97	Nodes are either public (have one or more listening ports) or private
76	master node only) or public nodes (connectable from unrelated nodes).	98	(no listening ports). Private nodes cannot talk to other private nodes
		99	currently, but all nodes can talk to public nodes.
77		100
78	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	101	Nodes is represented by (printable) strings called "node IDs".
79		102
80	A node reference is a string that either simply identifies the node (for	103	=item node ID - C<[A-Za-z0-9_\-.:]*>
81	private and slave nodes), or contains a recipe on how to reach a given
82	node (for public nodes).
83		104
84	This recipe is simply a comma-separated list of C<address:port> pairs (for	105	A node ID is a string that uniquely identifies the node within a
85	TCP/IP, other protocols might look different).	106	network. Depending on the configuration used, node IDs can look like a
		107	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		108	doesn't interpret node IDs in any way except to uniquely identify a node.
86		109
87	Node references come in two flavours: resolved (containing only numerical	110	=item binds - C<ip:port>
88	addresses) or unresolved (where hostnames are used instead of addresses).
89		111
90	Before using an unresolved node reference in a message you first have to	112	Nodes can only talk to each other by creating some kind of connection to
91	resolve it.	113	each other. To do this, nodes should listen on one or more local transport
		114	endpoints - binds.
		115
		116	Currently, only standard C<ip:port> specifications can be used, which
		117	specify TCP ports to listen on. So a bind is basically just a tcp socket
		118	in listening mode thta accepts conenctions form other nodes.
		119
		120	=item seed nodes
		121
		122	When a node starts, it knows nothing about the network it is in - it
		123	needs to connect to at least one other node that is already in the
		124	network. These other nodes are called "seed nodes".
		125
		126	Seed nodes themselves are not special - they are seed nodes only because
		127	some other node I<uses> them as such, but any node can be used as seed
		128	node for other nodes, and eahc node cna use a different set of seed nodes.
		129
		130	In addition to discovering the network, seed nodes are also used to
		131	maintain the network - all nodes using the same seed node form are part of
		132	the same network. If a network is split into multiple subnets because e.g.
		133	the network link between the parts goes down, then using the same seed
		134	nodes for all nodes ensures that eventually the subnets get merged again.
		135
		136	Seed nodes are expected to be long-running, and at least one seed node
		137	should always be available. They should also be relatively responsive - a
		138	seed node that blocks for long periods will slow down everybody else.
		139
		140	For small networks, it's best if every node uses the same set of seed
		141	nodes. For large networks, it can be useful to specify "regional" seed
		142	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		143	each other. What's important is that all seed nodes connections form a
		144	complete graph, so that the network cannot split into separate subnets
		145	forever.
		146
		147	Seed nodes are represented by seed IDs.
		148
		149	=item seed IDs - C<host:port>
		150
		151	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
		152	TCP port) of nodes that should be used as seed nodes.
		153
		154	=item global nodes
		155
		156	An AEMP network needs a discovery service - nodes need to know how to
		157	connect to other nodes they only know by name. In addition, AEMP offers a
		158	distributed "group database", which maps group names to a list of strings
		159	- for example, to register worker ports.
		160
		161	A network needs at least one global node to work, and allows every node to
		162	be a global node.
		163
		164	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		165	node and tries to keep connections to all other nodes. So while it can
		166	make sense to make every node "global" in small networks, it usually makes
		167	sense to only make seed nodes into global nodes in large networks (nodes
		168	keep connections to seed nodes and global nodes, so makign them the same
		169	reduces overhead).
92		170
93	=back	171	=back
94		172
95	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
96		174
98		176
99	=cut	177	=cut
100		178
101	package AnyEvent::MP;	179	package AnyEvent::MP;
102		180
		181	use AnyEvent::MP::Config ();
103	use AnyEvent::MP::Base;	182	use AnyEvent::MP::Kernel;
		183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
104		184
105	use common::sense;	185	use common::sense;
106		186
107	use Carp ();	187	use Carp ();
108		188
109	use AE ();	189	use AE ();
		190	use Guard ();
110		191
111	use base "Exporter";	192	use base "Exporter";
112		193
113	our $VERSION = '0.1';	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
		195
114	our @EXPORT = qw(	196	our @EXPORT = qw(
115	NODE $NODE *SELF node_of _any_	197	NODE $NODE *SELF node_of after
116	resolve_node initialise_node	198	configure
117	snd rcv mon kil reg psub	199	snd rcv mon mon_guard kil psub peval spawn cal
118	port	200	port
		201	db_set db_del db_reg
119	);	202	);
120		203
121	our $SELF;	204	our $SELF;
122		205
123	sub _self_die() {	206	sub _self_die() {
…		…
126	kil $SELF, die => $msg;	209	kil $SELF, die => $msg;
127	}	210	}
128		211
129	=item $thisnode = NODE / $NODE	212	=item $thisnode = NODE / $NODE
130		213
131	The C<NODE> function returns, and the C<$NODE> variable contains	214	The C<NODE> function returns, and the C<$NODE> variable contains, the node
132	the noderef of the local node. The value is initialised by a call	215	ID of the node running in the current process. This value is initialised by
133	to C<become_public> or C<become_slave>, after which all local port	216	a call to C<configure>.
134	identifiers become invalid.
135		217
136	=item $noderef = node_of $port	218	=item $nodeid = node_of $port
137		219
138	Extracts and returns the noderef from a portid or a noderef.	220	Extracts and returns the node ID from a port ID or a node ID.
139		221
140	=item initialise_node $noderef, $seednode, $seednode...	222	=item configure $profile, key => value...
141		223
142	=item initialise_node "slave/", $master, $master...	224	=item configure key => value...
143		225
144	Before a node can talk to other nodes on the network it has to initialise	226	Before a node can talk to other nodes on the network (i.e. enter
145	itself - the minimum a node needs to know is it's own name, and optionally	227	"distributed mode") it has to configure itself - the minimum a node needs
146	it should know the noderefs of some other nodes in the network.	228	to know is its own name, and optionally it should know the addresses of
		229	some other nodes in the network to discover other nodes.
147		230
148	This function initialises a node - it must be called exactly once (or	231	This function configures a node - it must be called exactly once (or
149	never) before calling other AnyEvent::MP functions.	232	never) before calling other AnyEvent::MP functions.
150		233
151	All arguments are noderefs, which can be either resolved or unresolved.	234	The key/value pairs are basically the same ones as documented for the
152		235	F<aemp> command line utility (sans the set/del prefix), with these additions:
153	There are two types of networked nodes, public nodes and slave nodes:
154		236
155	=over 4	237	=over 4
156		238
157	=item public nodes	239	=item norc => $boolean (default false)
158		240
159	For public nodes, C<$noderef> must either be a (possibly unresolved)	241	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
160	noderef, in which case it will be resolved, or C<undef> (or missing), in	242	be consulted - all configuraiton options must be specified in the
161	which case the noderef will be guessed.	243	C<configure> call.
162		244
163	Afterwards, the node will bind itself on all endpoints and try to connect	245	=item force => $boolean (default false)
164	to all additional C<$seednodes> that are specified. Seednodes are optional
165	and can be used to quickly bootstrap the node into an existing network.
166		246
167	=item slave nodes	247	IF true, then the values specified in the C<configure> will take
		248	precedence over any values configured via the rc file. The default is for
		249	the rc file to override any options specified in the program.
168		250
169	When the C<$noderef> is the special string C<slave/>, then the node will	251	=item secure => $pass->($nodeid)
170	become a slave node. Slave nodes cannot be contacted from outside and will
171	route most of their traffic to the master node that they attach to.
172		252
173	At least one additional noderef is required: The node will try to connect	253	In addition to specifying a boolean, you can specify a code reference that
174	to all of them and will become a slave attached to the first node it can	254	is called for every remote execution attempt - the execution request is
175	successfully connect to.	255	granted iff the callback returns a true value.
		256
		257	See F<semp setsecure> for more info.
176		258
177	=back	259	=back
178		260
179	This function will block until all nodes have been resolved and, for slave
180	nodes, until it has successfully established a connection to a master
181	server.
182
183	Example: become a public node listening on the default node.
184
185	initialise_node;
186
187	Example: become a public node, and try to contact some well-known master
188	servers to become part of the network.
189
190	initialise_node undef, "master1", "master2";
191
192	Example: become a public node listening on port C<4041>.
193
194	initialise_node 4041;
195
196	Example: become a public node, only visible on localhost port 4044.
197
198	initialise_node "locahost:4044";
199
200	Example: become a slave node to any of the specified master servers.
201
202	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
203
204	=item $cv = resolve_node $noderef
205
206	Takes an unresolved node reference that may contain hostnames and
207	abbreviated IDs, resolves all of them and returns a resolved node
208	reference.
209
210	In addition to C<address:port> pairs allowed in resolved noderefs, the
211	following forms are supported:
212
213	=over 4	261	=over 4
214		262
215	=item the empty string	263	=item step 1, gathering configuration from profiles
216		264
217	An empty-string component gets resolved as if the default port (4040) was	265	The function first looks up a profile in the aemp configuration (see the
218	specified.	266	L<aemp> commandline utility). The profile name can be specified via the
		267	named C<profile> parameter or can simply be the first parameter). If it is
		268	missing, then the nodename (F<uname -n>) will be used as profile name.
219		269
220	=item naked port numbers (e.g. C<1234>)	270	The profile data is then gathered as follows:
221		271
222	These are resolved by prepending the local nodename and a colon, to be	272	First, all remaining key => value pairs (all of which are conveniently
223	further resolved.	273	undocumented at the moment) will be interpreted as configuration
		274	data. Then they will be overwritten by any values specified in the global
		275	default configuration (see the F<aemp> utility), then the chain of
		276	profiles chosen by the profile name (and any C<parent> attributes).
224		277
225	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	278	That means that the values specified in the profile have highest priority
		279	and the values specified directly via C<configure> have lowest priority,
		280	and can only be used to specify defaults.
226		281
227	These are resolved by using AnyEvent::DNS to resolve them, optionally	282	If the profile specifies a node ID, then this will become the node ID of
228	looking up SRV records for the C<aemp=4040> port, if no port was	283	this process. If not, then the profile name will be used as node ID, with
229	specified.	284	a unique randoms tring (C</%u>) appended.
		285
		286	The node ID can contain some C<%> sequences that are expanded: C<%n>
		287	is expanded to the local nodename, C<%u> is replaced by a random
		288	strign to make the node unique. For example, the F<aemp> commandline
		289	utility uses C<aemp/%n/%u> as nodename, which might expand to
		290	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		291
		292	=item step 2, bind listener sockets
		293
		294	The next step is to look up the binds in the profile, followed by binding
		295	aemp protocol listeners on all binds specified (it is possible and valid
		296	to have no binds, meaning that the node cannot be contacted form the
		297	outside. This means the node cannot talk to other nodes that also have no
		298	binds, but it can still talk to all "normal" nodes).
		299
		300	If the profile does not specify a binds list, then a default of C<*> is
		301	used, meaning the node will bind on a dynamically-assigned port on every
		302	local IP address it finds.
		303
		304	=item step 3, connect to seed nodes
		305
		306	As the last step, the seed ID list from the profile is passed to the
		307	L<AnyEvent::MP::Global> module, which will then use it to keep
		308	connectivity with at least one node at any point in time.
230		309
231	=back	310	=back
		311
		312	Example: become a distributed node using the local node name as profile.
		313	This should be the most common form of invocation for "daemon"-type nodes.
		314
		315	configure
		316
		317	Example: become a semi-anonymous node. This form is often used for
		318	commandline clients.
		319
		320	configure nodeid => "myscript/%n/%u";
		321
		322	Example: configure a node using a profile called seed, which is suitable
		323	for a seed node as it binds on all local addresses on a fixed port (4040,
		324	customary for aemp).
		325
		326	# use the aemp commandline utility
		327	# aemp profile seed binds '*:4040'
		328
		329	# then use it
		330	configure profile => "seed";
		331
		332	# or simply use aemp from the shell again:
		333	# aemp run profile seed
		334
		335	# or provide a nicer-to-remember nodeid
		336	# aemp run profile seed nodeid "$(hostname)"
232		337
233	=item $SELF	338	=item $SELF
234		339
235	Contains the current port id while executing C<rcv> callbacks or C<psub>	340	Contains the current port id while executing C<rcv> callbacks or C<psub>
236	blocks.	341	blocks.
237		342
238	=item SELF, %SELF, @SELF...	343	=item *SELF, SELF, %SELF, @SELF...
239		344
240	Due to some quirks in how perl exports variables, it is impossible to	345	Due to some quirks in how perl exports variables, it is impossible to
241	just export C<$SELF>, all the symbols called C<SELF> are exported by this	346	just export C<$SELF>, all the symbols named C<SELF> are exported by this
242	module, but only C<$SELF> is currently used.	347	module, but only C<$SELF> is currently used.
243		348
244	=item snd $port, type => @data	349	=item snd $port, type => @data
245		350
246	=item snd $port, @msg	351	=item snd $port, @msg
247		352
248	Send the given message to the given port ID, which can identify either	353	Send the given message to the given port, which can identify either a
249	a local or a remote port, and can be either a string or soemthignt hat	354	local or a remote port, and must be a port ID.
250	stringifies a sa port ID (such as a port object :).
251		355
252	While the message can be about anything, it is highly recommended to use a	356	While the message can be almost anything, it is highly recommended to
253	string as first element (a portid, or some word that indicates a request	357	use a string as first element (a port ID, or some word that indicates a
254	type etc.).	358	request type etc.) and to consist if only simple perl values (scalars,
		359	arrays, hashes) - if you think you need to pass an object, think again.
255		360
256	The message data effectively becomes read-only after a call to this	361	The message data logically becomes read-only after a call to this
257	function: modifying any argument is not allowed and can cause many	362	function: modifying any argument (or values referenced by them) is
258	problems.	363	forbidden, as there can be considerable time between the call to C<snd>
		364	and the time the message is actually being serialised - in fact, it might
		365	never be copied as within the same process it is simply handed to the
		366	receiving port.
259		367
260	The type of data you can transfer depends on the transport protocol: when	368	The type of data you can transfer depends on the transport protocol: when
261	JSON is used, then only strings, numbers and arrays and hashes consisting	369	JSON is used, then only strings, numbers and arrays and hashes consisting
262	of those are allowed (no objects). When Storable is used, then anything	370	of those are allowed (no objects). When Storable is used, then anything
263	that Storable can serialise and deserialise is allowed, and for the local	371	that Storable can serialise and deserialise is allowed, and for the local
264	node, anything can be passed.	372	node, anything can be passed. Best rely only on the common denominator of
		373	these.
265		374
266	=item $local_port = port	375	=item $local_port = port
267		376
268	Create a new local port object that can be used either as a pattern	377	Create a new local port object and returns its port ID. Initially it has
269	matching port ("full port") or a single-callback port ("miniport"),	378	no callbacks set and will throw an error when it receives messages.
270	depending on how C<rcv> callbacks are bound to the object.
271		379
272	=item $port = port { my @msg = @_; $finished }	380	=item $local_port = port { my @msg = @_ }
273		381
274	Creates a "miniport", that is, a very lightweight port without any pattern	382	Creates a new local port, and returns its ID. Semantically the same as
275	matching behind it, and returns its ID. Semantically the same as creating
276	a port and calling C<rcv $port, $callback> on it.	383	creating a port and calling C<rcv $port, $callback> on it.
277		384
278	The block will be called for every message received on the port. When the	385	The block will be called for every message received on the port, with the
279	callback returns a true value its job is considered "done" and the port	386	global variable C<$SELF> set to the port ID. Runtime errors will cause the
280	will be destroyed. Otherwise it will stay alive.	387	port to be C<kil>ed. The message will be passed as-is, no extra argument
		388	(i.e. no port ID) will be passed to the callback.
281		389
282	The message will be passed as-is, no extra argument (i.e. no port id) will	390	If you want to stop/destroy the port, simply C<kil> it:
283	be passed to the callback.
284		391
285	If you need the local port id in the callback, this works nicely:	392	my $port = port {
286		393	my @msg = @_;
287	my $port; $port = port {	394	...
288	snd $otherport, reply => $port;	395	kil $SELF;
289	};	396	};
290		397
291	=cut	398	=cut
292		399
293	sub rcv($@);	400	sub rcv($@);
294		401
		402	sub _kilme {
		403	die "received message on port without callback";
		404	}
		405
295	sub port(;&) {	406	sub port(;&) {
296	my $id = "$UNIQ." . $ID++;	407	my $id = $UNIQ . ++$ID;
297	my $port = "$NODE#$id";	408	my $port = "$NODE#$id";
298		409
299	if (@_) {	410	rcv $port, shift \|\| \&_kilme;
300	rcv $port, shift;
301	} else {
302	$PORT{$id} = sub { }; # nop
303	}
304		411
305	$port	412	$port
306	}	413	}
307		414
308	=item reg $port, $name
309
310	Registers the given port under the name C<$name>. If the name already
311	exists it is replaced.
312
313	A port can only be registered under one well known name.
314
315	A port automatically becomes unregistered when it is killed.
316
317	=cut
318
319	sub reg(@) {
320	my ($port, $name) = @_;
321
322	$REG{$name} = $port;
323	}
324
325	=item rcv $port, $callback->(@msg)	415	=item rcv $local_port, $callback->(@msg)
326		416
327	Replaces the callback on the specified miniport (after converting it to	417	Replaces the default callback on the specified port. There is no way to
328	one if required).	418	remove the default callback: use C<sub { }> to disable it, or better
329		419	C<kil> the port when it is no longer needed.
330	=item rcv $port, tagstring => $callback->(@msg), ...
331
332	=item rcv $port, $smartmatch => $callback->(@msg), ...
333
334	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
335
336	Register callbacks to be called on matching messages on the given full
337	port (after converting it to one if required).
338
339	The callback has to return a true value when its work is done, after
340	which is will be removed, or a false value in which case it will stay
341	registered.
342		420
343	The global C<$SELF> (exported by this module) contains C<$port> while	421	The global C<$SELF> (exported by this module) contains C<$port> while
344	executing the callback.	422	executing the callback. Runtime errors during callback execution will
		423	result in the port being C<kil>ed.
345		424
346	Runtime errors wdurign callback execution will result in the port being	425	The default callback received all messages not matched by a more specific
347	C<kil>ed.	426	C<tag> match.
348		427
349	If the match is an array reference, then it will be matched against the	428	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
350	first elements of the message, otherwise only the first element is being
351	matched.
352		429
353	Any element in the match that is specified as C<_any_> (a function	430	Register (or replace) callbacks to be called on messages starting with the
354	exported by this module) matches any single element of the message.	431	given tag on the given port (and return the port), or unregister it (when
		432	C<$callback> is C<$undef> or missing). There can only be one callback
		433	registered for each tag.
355		434
356	While not required, it is highly recommended that the first matching	435	The original message will be passed to the callback, after the first
357	element is a string identifying the message. The one-string-only match is	436	element (the tag) has been removed. The callback will use the same
358	also the most efficient match (by far).	437	environment as the default callback (see above).
		438
		439	Example: create a port and bind receivers on it in one go.
		440
		441	my $port = rcv port,
		442	msg1 => sub { ... },
		443	msg2 => sub { ... },
		444	;
		445
		446	Example: create a port, bind receivers and send it in a message elsewhere
		447	in one go:
		448
		449	snd $otherport, reply =>
		450	rcv port,
		451	msg1 => sub { ... },
		452	...
		453	;
		454
		455	Example: temporarily register a rcv callback for a tag matching some port
		456	(e.g. for an rpc reply) and unregister it after a message was received.
		457
		458	rcv $port, $otherport => sub {
		459	my @reply = @_;
		460
		461	rcv $SELF, $otherport;
		462	};
359		463
360	=cut	464	=cut
361		465
362	sub rcv($@) {	466	sub rcv($@) {
363	my $port = shift;	467	my $port = shift;
364	my ($noderef, $portid) = split /#/, $port, 2;	468	my ($nodeid, $portid) = split /#/, $port, 2;
365		469
366	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	470	$NODE{$nodeid} == $NODE{""}
367	or Carp::croak "$port: rcv can only be called on local ports, caught";	471	or Carp::croak "$port: rcv can only be called on local ports, caught";
368		472
369	if (@_ == 1) {	473	while (@_) {
		474	if (ref $_[0]) {
		475	if (my $self = $PORT_DATA{$portid}) {
		476	"AnyEvent::MP::Port" eq ref $self
		477	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		478
		479	$self->[0] = shift;
		480	} else {
370	my $cb = shift;	481	my $cb = shift;
371	delete $PORT_DATA{$portid};
372	$PORT{$portid} = sub {	482	$PORT{$portid} = sub {
373	local $SELF = $port;	483	local $SELF = $port;
374	eval {	484	eval { &$cb }; _self_die if $@;
375	&$cb	485	};
376	and kil $port;
377	};	486	}
378	_self_die if $@;	487	} elsif (defined $_[0]) {
379	};
380	} else {
381	my $self = $PORT_DATA{$portid} \|\|= do {	488	my $self = $PORT_DATA{$portid} \|\|= do {
382	my $self = bless {	489	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
383	id => $port,
384	}, "AnyEvent::MP::Port";
385		490
386	$PORT{$portid} = sub {	491	$PORT{$portid} = sub {
387	local $SELF = $port;	492	local $SELF = $port;
388		493
389	eval {
390	for (@{ $self->{rc0}{$_[0]} }) {	494	if (my $cb = $self->[1]{$_[0]}) {
391	$_ && &{$_->[0]}	495	shift;
392	&& undef $_;	496	eval { &$cb }; _self_die if $@;
393	}	497	} else {
394
395	for (@{ $self->{rcv}{$_[0]} }) {
396	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
397	&& &{$_->[0]}	498	&{ $self->[0] };
398	&& undef $_;
399	}
400
401	for (@{ $self->{any} }) {
402	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
403	&& &{$_->[0]}
404	&& undef $_;
405	}	499	}
406	};	500	};
407	_self_die if $@;	501
		502	$self
408	};	503	};
409		504
410	$self
411	};
412
413	"AnyEvent::MP::Port" eq ref $self	505	"AnyEvent::MP::Port" eq ref $self
414	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	506	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
415		507
416	while (@_) {
417	my ($match, $cb) = splice @_, 0, 2;	508	my ($tag, $cb) = splice @_, 0, 2;
418		509
419	if (!ref $match) {	510	if (defined $cb) {
420	push @{ $self->{rc0}{$match} }, [$cb];	511	$self->[1]{$tag} = $cb;
421	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
422	my ($type, @match) = @$match;
423	@match
424	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
425	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
426	} else {	512	} else {
427	push @{ $self->{any} }, [$cb, $match];	513	delete $self->[1]{$tag};
428	}	514	}
429	}	515	}
430	}	516	}
431		517
432	$port	518	$port
433	}	519	}
434		520
		521	=item peval $port, $coderef[, @args]
		522
		523	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		524	when the code throews an exception the C<$port> will be killed.
		525
		526	Any remaining args will be passed to the callback. Any return values will
		527	be returned to the caller.
		528
		529	This is useful when you temporarily want to execute code in the context of
		530	a port.
		531
		532	Example: create a port and run some initialisation code in it's context.
		533
		534	my $port = port { ... };
		535
		536	peval $port, sub {
		537	init
		538	or die "unable to init";
		539	};
		540
		541	=cut
		542
		543	sub peval($$) {
		544	local $SELF = shift;
		545	my $cb = shift;
		546
		547	if (wantarray) {
		548	my @res = eval { &$cb };
		549	_self_die if $@;
		550	@res
		551	} else {
		552	my $res = eval { &$cb };
		553	_self_die if $@;
		554	$res
		555	}
		556	}
		557
435	=item $closure = psub { BLOCK }	558	=item $closure = psub { BLOCK }
436		559
437	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	560	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
438	closure is executed, sets up the environment in the same way as in C<rcv>	561	closure is executed, sets up the environment in the same way as in C<rcv>
439	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.	562	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		563
		564	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		565	BLOCK }, @_ } >>.
440		566
441	This is useful when you register callbacks from C<rcv> callbacks:	567	This is useful when you register callbacks from C<rcv> callbacks:
442		568
443	rcv delayed_reply => sub {	569	rcv delayed_reply => sub {
444	my ($delay, @reply) = @_;	570	my ($delay, @reply) = @_;
…		…
468	$res	594	$res
469	}	595	}
470	}	596	}
471	}	597	}
472		598
473	=item $guard = mon $port, $cb->(@reason)	599	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
474		600
475	=item $guard = mon $port, $otherport	601	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
476		602
477	=item $guard = mon $port, $otherport, @msg	603	=item $guard = mon $port # kill $SELF when $port dies
478		604
		605	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		606
479	Monitor the given port and do something when the port is killed.	607	Monitor the given port and do something when the port is killed or
		608	messages to it were lost, and optionally return a guard that can be used
		609	to stop monitoring again.
480		610
481	In the first form, the callback is simply called with any number	611	In the first form (callback), the callback is simply called with any
482	of C<@reason> elements (no @reason means that the port was deleted	612	number of C<@reason> elements (no @reason means that the port was deleted
483	"normally"). Note also that I<< the callback B<must> never die >>, so use	613	"normally"). Note also that I<< the callback B<must> never die >>, so use
484	C<eval> if unsure.	614	C<eval> if unsure.
485		615
486	In the second form, the other port will be C<kil>'ed with C<@reason>, iff	616	In the second form (another port given), the other port (C<$rcvport>)
487	a @reason was specified, i.e. on "normal" kils nothing happens, while	617	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
488	under all other conditions, the other port is killed with the same reason.	618	"normal" kils nothing happens, while under all other conditions, the other
		619	port is killed with the same reason.
489		620
		621	The third form (kill self) is the same as the second form, except that
		622	C<$rvport> defaults to C<$SELF>.
		623
490	In the last form, a message of the form C<@msg, @reason> will be C<snd>.	624	In the last form (message), a message of the form C<@msg, @reason> will be
		625	C<snd>.
		626
		627	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		628	alert was raised), they are removed and will not trigger again.
		629
		630	As a rule of thumb, monitoring requests should always monitor a port from
		631	a local port (or callback). The reason is that kill messages might get
		632	lost, just like any other message. Another less obvious reason is that
		633	even monitoring requests can get lost (for example, when the connection
		634	to the other node goes down permanently). When monitoring a port locally
		635	these problems do not exist.
		636
		637	C<mon> effectively guarantees that, in the absence of hardware failures,
		638	after starting the monitor, either all messages sent to the port will
		639	arrive, or the monitoring action will be invoked after possible message
		640	loss has been detected. No messages will be lost "in between" (after
		641	the first lost message no further messages will be received by the
		642	port). After the monitoring action was invoked, further messages might get
		643	delivered again.
		644
		645	Inter-host-connection timeouts and monitoring depend on the transport
		646	used. The only transport currently implemented is TCP, and AnyEvent::MP
		647	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		648	non-idle connection, and usually around two hours for idle connections).
		649
		650	This means that monitoring is good for program errors and cleaning up
		651	stuff eventually, but they are no replacement for a timeout when you need
		652	to ensure some maximum latency.
491		653
492	Example: call a given callback when C<$port> is killed.	654	Example: call a given callback when C<$port> is killed.
493		655
494	mon $port, sub { warn "port died because of <@_>\n" };	656	mon $port, sub { warn "port died because of <@_>\n" };
495		657
496	Example: kill ourselves when C<$port> is killed abnormally.	658	Example: kill ourselves when C<$port> is killed abnormally.
497		659
498	mon $port, $self;	660	mon $port;
499		661
500	Example: send us a restart message another C<$port> is killed.	662	Example: send us a restart message when another C<$port> is killed.
501		663
502	mon $port, $self => "restart";	664	mon $port, $self => "restart";
503		665
504	=cut	666	=cut
505		667
506	sub mon {	668	sub mon {
507	my ($noderef, $port) = split /#/, shift, 2;	669	my ($nodeid, $port) = split /#/, shift, 2;
508		670
509	my $node = $NODE{$noderef} \|\| add_node $noderef;	671	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
510		672
511	my $cb = shift;	673	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
512		674
513	unless (ref $cb) {	675	unless (ref $cb) {
514	if (@_) {	676	if (@_) {
515	# send a kill info message	677	# send a kill info message
516	my (@msg) = ($cb, @_);	678	my (@msg) = ($cb, @_);
…		…
523	}	685	}
524		686
525	$node->monitor ($port, $cb);	687	$node->monitor ($port, $cb);
526		688
527	defined wantarray	689	defined wantarray
528	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	690	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
529	}	691	}
530		692
531	=item $guard = mon_guard $port, $ref, $ref...	693	=item $guard = mon_guard $port, $ref, $ref...
532		694
533	Monitors the given C<$port> and keeps the passed references. When the port	695	Monitors the given C<$port> and keeps the passed references. When the port
534	is killed, the references will be freed.	696	is killed, the references will be freed.
535		697
536	Optionally returns a guard that will stop the monitoring.	698	Optionally returns a guard that will stop the monitoring.
537		699
538	This function is useful when you create e.g. timers or other watchers and	700	This function is useful when you create e.g. timers or other watchers and
539	want to free them when the port gets killed:	701	want to free them when the port gets killed (note the use of C<psub>):
540		702
541	$port->rcv (start => sub {	703	$port->rcv (start => sub {
542	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	704	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
543	undef $timer if 0.9 < rand;	705	undef $timer if 0.9 < rand;
544	});	706	});
545	});	707	});
546		708
547	=cut	709	=cut
548		710
549	sub mon_guard {	711	sub mon_guard {
550	my ($port, @refs) = @_;	712	my ($port, @refs) = @_;
551		713
		714	#TODO: mon-less form?
		715
552	mon $port, sub { 0 && @refs }	716	mon $port, sub { 0 && @refs }
553	}	717	}
554		718
555	=item lnk $port1, $port2
556
557	Link two ports. This is simply a shorthand for:
558
559	mon $port1, $port2;
560	mon $port2, $port1;
561
562	It means that if either one is killed abnormally, the other one gets
563	killed as well.
564
565	=item kil $port[, @reason]	719	=item kil $port[, @reason]
566		720
567	Kill the specified port with the given C<@reason>.	721	Kill the specified port with the given C<@reason>.
568		722
569	If no C<@reason> is specified, then the port is killed "normally" (linked	723	If no C<@reason> is specified, then the port is killed "normally" -
570	ports will not be kileld, or even notified).	724	monitor callback will be invoked, but the kil will not cause linked ports
		725	(C<mon $mport, $lport> form) to get killed.
571		726
572	Otherwise, linked ports get killed with the same reason (second form of	727	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
573	C<mon>, see below).	728	form) get killed with the same reason.
574		729
575	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	730	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
576	will be reported as reason C<< die => $@ >>.	731	will be reported as reason C<< die => $@ >>.
577		732
578	Transport/communication errors are reported as C<< transport_error =>	733	Transport/communication errors are reported as C<< transport_error =>
579	$message >>.	734	$message >>.
580		735
		736	=cut
		737
		738	=item $port = spawn $node, $initfunc[, @initdata]
		739
		740	Creates a port on the node C<$node> (which can also be a port ID, in which
		741	case it's the node where that port resides).
		742
		743	The port ID of the newly created port is returned immediately, and it is
		744	possible to immediately start sending messages or to monitor the port.
		745
		746	After the port has been created, the init function is called on the remote
		747	node, in the same context as a C<rcv> callback. This function must be a
		748	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		749	specify a function in the main program, use C<::name>.
		750
		751	If the function doesn't exist, then the node tries to C<require>
		752	the package, then the package above the package and so on (e.g.
		753	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		754	exists or it runs out of package names.
		755
		756	The init function is then called with the newly-created port as context
		757	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		758	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		759	the port might not get created.
		760
		761	A common idiom is to pass a local port, immediately monitor the spawned
		762	port, and in the remote init function, immediately monitor the passed
		763	local port. This two-way monitoring ensures that both ports get cleaned up
		764	when there is a problem.
		765
		766	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		767	caller before C<spawn> returns (by delaying invocation when spawn is
		768	called for the local node).
		769
		770	Example: spawn a chat server port on C<$othernode>.
		771
		772	# this node, executed from within a port context:
		773	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		774	mon $server;
		775
		776	# init function on C<$othernode>
		777	sub connect {
		778	my ($srcport) = @_;
		779
		780	mon $srcport;
		781
		782	rcv $SELF, sub {
		783	...
		784	};
		785	}
		786
		787	=cut
		788
		789	sub _spawn {
		790	my $port = shift;
		791	my $init = shift;
		792
		793	# rcv will create the actual port
		794	local $SELF = "$NODE#$port";
		795	eval {
		796	&{ load_func $init }
		797	};
		798	_self_die if $@;
		799	}
		800
		801	sub spawn(@) {
		802	my ($nodeid, undef) = split /#/, shift, 2;
		803
		804	my $id = $RUNIQ . ++$ID;
		805
		806	$_[0] =~ /::/
		807	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		808
		809	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		810
		811	"$nodeid#$id"
		812	}
		813
		814
		815	=item after $timeout, @msg
		816
		817	=item after $timeout, $callback
		818
		819	Either sends the given message, or call the given callback, after the
		820	specified number of seconds.
		821
		822	This is simply a utility function that comes in handy at times - the
		823	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		824	so it may go away in the future.
		825
		826	=cut
		827
		828	sub after($@) {
		829	my ($timeout, @action) = @_;
		830
		831	my $t; $t = AE::timer $timeout, 0, sub {
		832	undef $t;
		833	ref $action[0]
		834	? $action[0]()
		835	: snd @action;
		836	};
		837	}
		838
		839	=item cal $port, @msg, $callback[, $timeout]
		840
		841	A simple form of RPC - sends a message to the given C<$port> with the
		842	given contents (C<@msg>), but adds a reply port to the message.
		843
		844	The reply port is created temporarily just for the purpose of receiving
		845	the reply, and will be C<kil>ed when no longer needed.
		846
		847	A reply message sent to the port is passed to the C<$callback> as-is.
		848
		849	If an optional time-out (in seconds) is given and it is not C<undef>,
		850	then the callback will be called without any arguments after the time-out
		851	elapsed and the port is C<kil>ed.
		852
		853	If no time-out is given (or it is C<undef>), then the local port will
		854	monitor the remote port instead, so it eventually gets cleaned-up.
		855
		856	Currently this function returns the temporary port, but this "feature"
		857	might go in future versions unless you can make a convincing case that
		858	this is indeed useful for something.
		859
		860	=cut
		861
		862	sub cal(@) {
		863	my $timeout = ref $_[-1] ? undef : pop;
		864	my $cb = pop;
		865
		866	my $port = port {
		867	undef $timeout;
		868	kil $SELF;
		869	&$cb;
		870	};
		871
		872	if (defined $timeout) {
		873	$timeout = AE::timer $timeout, 0, sub {
		874	undef $timeout;
		875	kil $port;
		876	$cb->();
		877	};
		878	} else {
		879	mon $_[0], sub {
		880	kil $port;
		881	$cb->();
		882	};
		883	}
		884
		885	push @_, $port;
		886	&snd;
		887
		888	$port
		889	}
		890
581	=back	891	=back
582		892
583	=head1 NODE MESSAGES	893	=head1 DISTRIBUTED DATABASE
584		894
585	Nodes understand the following messages sent to them. Many of them take	895	AnyEvent::MP comes with a simple distributed database. The database will
586	arguments called C<@reply>, which will simply be used to compose a reply	896	be mirrored asynchronously at all global nodes. Other nodes bind to one of
587	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and	897	the global nodes for their needs.
588	the remaining arguments are simply the message data.
589		898
590	While other messages exist, they are not public and subject to change.	899	The database consists of a two-level hash - a hash contains a hash which
		900	contains values.
591		901
		902	The top level hash key is called "family", and the second-level hash key
		903	is called "subkey" or simply "key".
		904
		905	The family must be alphanumeric, i.e. start with a letter and consist
		906	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		907	pretty much like Perl module names.
		908
		909	As the family namespace is global, it is recommended to prefix family names
		910	with the name of the application or module using it.
		911
		912	The subkeys must be non-empty strings, with no further restrictions.
		913
		914	The values should preferably be strings, but other perl scalars should
		915	work as well (such as undef, arrays and hashes).
		916
		917	Every database entry is owned by one node - adding the same family/subkey
		918	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		919	but the result might be nondeterministic, i.e. the key might have
		920	different values on different nodes.
		921
		922	Different subkeys in the same family can be owned by different nodes
		923	without problems, and in fact, this is the common method to create worker
		924	pools. For example, a worker port for image scaling might do this:
		925
		926	db_set my_image_scalers => $port;
		927
		928	And clients looking for an image scaler will want to get the
		929	C<my_image_scalers> keys:
		930
		931	db_keys "my_image_scalers" => 60 => sub {
		932	#d##TODO#
		933
592	=over 4	934	=over
593		935
594	=cut	936	=item db_set $family => $subkey [=> $value]
595		937
596	=item lookup => $name, @reply	938	Sets (or replaces) a key to the database - if C<$value> is omitted,
		939	C<undef> is used instead.
597		940
598	Replies with the port ID of the specified well-known port, or C<undef>.	941	=item db_del $family => $subkey
599		942
600	=item devnull => ...	943	Deletes a key from the database.
601		944
602	Generic data sink/CPU heat conversion.	945	=item $guard = db_reg $family => $subkey [=> $value]
603		946
604	=item relay => $port, @msg	947	Sets the key on the database and returns a guard. When the guard is
		948	destroyed, the key is deleted from the database. If C<$value> is missing,
		949	then C<undef> is used.
605		950
606	Simply forwards the message to the given port.	951	=cut
607
608	=item eval => $string[ @reply]
609
610	Evaluates the given string. If C<@reply> is given, then a message of the
611	form C<@reply, $@, @evalres> is sent.
612
613	Example: crash another node.
614
615	snd $othernode, eval => "exit";
616
617	=item time => @reply
618
619	Replies the the current node time to C<@reply>.
620
621	Example: tell the current node to send the current time to C<$myport> in a
622	C<timereply> message.
623
624	snd $NODE, time => $myport, timereply => 1, 2;
625	# => snd $myport, timereply => 1, 2, <time>
626		952
627	=back	953	=back
628		954
629	=head1 AnyEvent::MP vs. Distributed Erlang	955	=head1 AnyEvent::MP vs. Distributed Erlang
630		956
631	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	957	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
632	== aemp node, Erlang process == aemp port), so many of the documents and	958	== aemp node, Erlang process == aemp port), so many of the documents and
633	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	959	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
634	sample:	960	sample:
635		961
636	http://www.Erlang.se/doc/programming_rules.shtml	962	http://www.erlang.se/doc/programming_rules.shtml
637	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	963	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
638	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	964	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
639	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	965	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
640		966
641	Despite the similarities, there are also some important differences:	967	Despite the similarities, there are also some important differences:
642		968
643	=over 4	969	=over 4
644		970
645	=item * Node references contain the recipe on how to contact them.	971	=item * Node IDs are arbitrary strings in AEMP.
646		972
647	Erlang relies on special naming and DNS to work everywhere in the	973	Erlang relies on special naming and DNS to work everywhere in the same
648	same way. AEMP relies on each node knowing it's own address(es), with	974	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
649	convenience functionality.	975	configuration or DNS), and possibly the addresses of some seed nodes, but
		976	will otherwise discover other nodes (and their IDs) itself.
650		977
651	This means that AEMP requires a less tightly controlled environment at the	978	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
652	cost of longer node references and a slightly higher management overhead.	979	uses "local ports are like remote ports".
		980
		981	The failure modes for local ports are quite different (runtime errors
		982	only) then for remote ports - when a local port dies, you I<know> it dies,
		983	when a connection to another node dies, you know nothing about the other
		984	port.
		985
		986	Erlang pretends remote ports are as reliable as local ports, even when
		987	they are not.
		988
		989	AEMP encourages a "treat remote ports differently" philosophy, with local
		990	ports being the special case/exception, where transport errors cannot
		991	occur.
653		992
654	=item * Erlang uses processes and a mailbox, AEMP does not queue.	993	=item * Erlang uses processes and a mailbox, AEMP does not queue.
655		994
656	Erlang uses processes that selctively receive messages, and therefore	995	Erlang uses processes that selectively receive messages out of order, and
657	needs a queue. AEMP is event based, queuing messages would serve no useful	996	therefore needs a queue. AEMP is event based, queuing messages would serve
658	purpose.	997	no useful purpose. For the same reason the pattern-matching abilities
		998	of AnyEvent::MP are more limited, as there is little need to be able to
		999	filter messages without dequeuing them.
659		1000
660	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	1001	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1002	being event-based, while Erlang is process-based.
		1003
		1004	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1005	top of AEMP and Coro threads.
661		1006
662	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1007	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
663		1008
664	Sending messages in Erlang is synchronous and blocks the process. AEMP	1009	Sending messages in Erlang is synchronous and blocks the process until
665	sends are immediate, connection establishment is handled in the	1010	a conenction has been established and the message sent (and so does not
666	background.	1011	need a queue that can overflow). AEMP sends return immediately, connection
		1012	establishment is handled in the background.
667		1013
668	=item * Erlang can silently lose messages, AEMP cannot.	1014	=item * Erlang suffers from silent message loss, AEMP does not.
669		1015
670	Erlang makes few guarantees on messages delivery - messages can get lost	1016	Erlang implements few guarantees on messages delivery - messages can get
671	without any of the processes realising it (i.e. you send messages a, b,	1017	lost without any of the processes realising it (i.e. you send messages a,
672	and c, and the other side only receives messages a and c).	1018	b, and c, and the other side only receives messages a and c).
673		1019
674	AEMP guarantees correct ordering, and the guarantee that there are no	1020	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1021	guarantee that after one message is lost, all following ones sent to the
		1022	same port are lost as well, until monitoring raises an error, so there are
675	holes in the message sequence.	1023	no silent "holes" in the message sequence.
676		1024
677	=item * In Erlang, processes can be declared dead and later be found to be	1025	If you want your software to be very reliable, you have to cope with
678	alive.	1026	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
679		1027	simply tries to work better in common error cases, such as when a network
680	In Erlang it can happen that a monitored process is declared dead and	1028	link goes down.
681	linked processes get killed, but later it turns out that the process is
682	still alive - and can receive messages.
683
684	In AEMP, when port monitoring detects a port as dead, then that port will
685	eventually be killed - it cannot happen that a node detects a port as dead
686	and then later sends messages to it, finding it is still alive.
687		1029
688	=item * Erlang can send messages to the wrong port, AEMP does not.	1030	=item * Erlang can send messages to the wrong port, AEMP does not.
689		1031
690	In Erlang it is quite possible that a node that restarts reuses a process	1032	In Erlang it is quite likely that a node that restarts reuses an Erlang
691	ID known to other nodes for a completely different process, causing	1033	process ID known to other nodes for a completely different process,
692	messages destined for that process to end up in an unrelated process.	1034	causing messages destined for that process to end up in an unrelated
		1035	process.
693		1036
694	AEMP never reuses port IDs, so old messages or old port IDs floating	1037	AEMP does not reuse port IDs, so old messages or old port IDs floating
695	around in the network will not be sent to an unrelated port.	1038	around in the network will not be sent to an unrelated port.
696		1039
697	=item * Erlang uses unprotected connections, AEMP uses secure	1040	=item * Erlang uses unprotected connections, AEMP uses secure
698	authentication and can use TLS.	1041	authentication and can use TLS.
699		1042
700	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1043	AEMP can use a proven protocol - TLS - to protect connections and
701	securely authenticate nodes.	1044	securely authenticate nodes.
702		1045
703	=item * The AEMP protocol is optimised for both text-based and binary	1046	=item * The AEMP protocol is optimised for both text-based and binary
704	communications.	1047	communications.
705		1048
706	The AEMP protocol, unlike the Erlang protocol, supports both	1049	The AEMP protocol, unlike the Erlang protocol, supports both programming
707	language-independent text-only protocols (good for debugging) and binary,	1050	language independent text-only protocols (good for debugging), and binary,
708	language-specific serialisers (e.g. Storable).	1051	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1052	used, the protocol is actually completely text-based.
709		1053
710	It has also been carefully designed to be implementable in other languages	1054	It has also been carefully designed to be implementable in other languages
711	with a minimum of work while gracefully degrading fucntionality to make the	1055	with a minimum of work while gracefully degrading functionality to make the
712	protocol simple.	1056	protocol simple.
713		1057
714	=item * AEMP has more flexible monitoring options than Erlang.	1058	=item * AEMP has more flexible monitoring options than Erlang.
715		1059
716	In Erlang, you can chose to receive I<all> exit signals as messages	1060	In Erlang, you can chose to receive I<all> exit signals as messages or
717	or I<none>, there is no in-between, so monitoring single processes is	1061	I<none>, there is no in-between, so monitoring single Erlang processes is
718	difficult to implement. Monitoring in AEMP is more flexible than in	1062	difficult to implement.
719	Erlang, as one can choose between automatic kill, exit message or callback
720	on a per-process basis.
721		1063
722	=item * Erlang has different semantics for monitoring and linking, AEMP has the same.	1064	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1065	between automatic kill, exit message or callback on a per-port basis.
723		1066
		1067	=item * Erlang tries to hide remote/local connections, AEMP does not.
		1068
724	Monitoring in Erlang is not an indicator of process death/crashes,	1069	Monitoring in Erlang is not an indicator of process death/crashes, in the
725	as linking is (except linking is unreliable in Erlang). In AEMP, the	1070	same way as linking is (except linking is unreliable in Erlang).
726	semantics of monitoring and linking are identical, linking is simply	1071
727	two-way monitoring with automatic kill.	1072	In AEMP, you don't "look up" registered port names or send to named ports
		1073	that might or might not be persistent. Instead, you normally spawn a port
		1074	on the remote node. The init function monitors you, and you monitor the
		1075	remote port. Since both monitors are local to the node, they are much more
		1076	reliable (no need for C<spawn_link>).
		1077
		1078	This also saves round-trips and avoids sending messages to the wrong port
		1079	(hard to do in Erlang).
728		1080
729	=back	1081	=back
730		1082
		1083	=head1 RATIONALE
		1084
		1085	=over 4
		1086
		1087	=item Why strings for port and node IDs, why not objects?
		1088
		1089	We considered "objects", but found that the actual number of methods
		1090	that can be called are quite low. Since port and node IDs travel over
		1091	the network frequently, the serialising/deserialising would add lots of
		1092	overhead, as well as having to keep a proxy object everywhere.
		1093
		1094	Strings can easily be printed, easily serialised etc. and need no special
		1095	procedures to be "valid".
		1096
		1097	And as a result, a port with just a default receiver consists of a single
		1098	code reference stored in a global hash - it can't become much cheaper.
		1099
		1100	=item Why favour JSON, why not a real serialising format such as Storable?
		1101
		1102	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1103	format, but currently there is no way to make a node use Storable by
		1104	default (although all nodes will accept it).
		1105
		1106	The default framing protocol is JSON because a) JSON::XS is many times
		1107	faster for small messages and b) most importantly, after years of
		1108	experience we found that object serialisation is causing more problems
		1109	than it solves: Just like function calls, objects simply do not travel
		1110	easily over the network, mostly because they will always be a copy, so you
		1111	always have to re-think your design.
		1112
		1113	Keeping your messages simple, concentrating on data structures rather than
		1114	objects, will keep your messages clean, tidy and efficient.
		1115
		1116	=back
		1117
731	=head1 SEE ALSO	1118	=head1 SEE ALSO
		1119
		1120	L<AnyEvent::MP::Intro> - a gentle introduction.
		1121
		1122	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1123
		1124	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1125	your applications.
		1126
		1127	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1128
		1129	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1130	all nodes.
732		1131
733	L<AnyEvent>.	1132	L<AnyEvent>.
734		1133
735	=head1 AUTHOR	1134	=head1 AUTHOR
736		1135

Diff Legend

-–
+Removed lines
-+
+Added lines
-<
+Changed lines
->
+Changed lines

Comparing cvsroot/AnyEvent-MP/MP.pm (file contents): Revision 1.35 by root, Thu Aug 6 10:21:48 2009 UTC vs. Revision 1.127 by root, Sat Mar 3 20:35:10 2012 UTC

Diff Legend

Comparing cvsroot/AnyEvent-MP/MP.pm (file contents):
Revision 1.35 by root, Thu Aug 6 10:21:48 2009 UTC vs.
Revision 1.127 by root, Sat Mar 3 20:35:10 2012 UTC