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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.40 by root, Sat Aug 8 00:22:16 2009 UTC vs.
Revision 1.122 by root, Wed Feb 29 18:44:59 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
13	$SELF # receiving/own port id in rcv callbacks	12	$SELF # receiving/own port id in rcv callbacks
14		13
		14	# initialise the node so it can send/receive messages
		15	configure;
		16
15	# ports are message endpoints	17	# ports are message destinations
16		18
17	# sending messages	19	# sending messages
18	snd $port, type => data...;	20	snd $port, type => data...;
19	snd $port, @msg;	21	snd $port, @msg;
20	snd @msg_with_first_element_being_a_port;	22	snd @msg_with_first_element_being_a_port;
21		23
22	# miniports	24	# creating/using ports, the simple way
23	my $miniport = port { my @msg = @_; 0 };	25	my $simple_port = port { my @msg = @_ };
24		26
25	# full ports	27	# creating/using ports, tagged message matching
26	my $port = port;	28	my $port = port;
27	rcv $port, smartmatch => $cb->(@msg);
28	rcv $port, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
29	rcv $port, pong => sub { warn "pong received\n"; 0 };	30	rcv $port, pong => sub { warn "pong received\n" };
30		31
31	# remote ports	32	# create a port on another node
32	my $port = spawn $node, $initfunc, @initdata;	33	my $port = spawn $node, $initfunc, @initdata;
33		34
34	# more, smarter, matches (_any_ is exported by this module)	35	# destroy a port again
35	rcv $port, [child_died => $pid] => sub { ...	36	kil $port; # "normal" kill
36	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3	37	kil $port, my_error => "everything is broken"; # error kill
37		38
38	# monitoring	39	# monitoring
39	mon $port, $cb->(@msg) # callback is invoked on death	40	mon $localport, $cb->(@msg) # callback is invoked on death
40	mon $port, $otherport # kill otherport on abnormal death	41	mon $localport, $otherport # kill otherport on abnormal death
41	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.
42		59
43	=head1 DESCRIPTION	60	=head1 DESCRIPTION
44		61
45	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
46		63
47	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
48	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
49		66
50	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>
51	manual page.	68	manual page and the examples under F<eg/>.
52
53	At the moment, this module family is severly broken and underdocumented,
54	so do not use. This was uploaded mainly to reserve the CPAN namespace -
55	stay tuned! The basic API should be finished, however.
56		69
57	=head1 CONCEPTS	70	=head1 CONCEPTS
58		71
59	=over 4	72	=over 4
60		73
61	=item port	74	=item port
62		75
63	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).
64		78
65	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
66	messages. All C<rcv> handlers will receive messages they match, messages	80	some messages. Messages send to ports will not be queued, regardless of
67	will not be queued.	81	anything was listening for them or not.
68		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
69	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
70		86
71	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<#>) as
72	separator, and a port name (a printable string of unspecified format). An	88	separator, and a port name (a printable string of unspecified format).
73	exception is the the node port, whose ID is identical to its node
74	reference.
75		89
76	=item node	90	=item node
77		91
78	A node is a single process containing at least one port - the node	92	A node is a single process containing at least one port - the node port,
79	port. You can send messages to node ports to find existing ports or to	93	which enables nodes to manage each other remotely, and to create new
80	create new ports, among other things.	94	ports.
81		95
82	Nodes are either private (single-process only), slaves (connected to a	96	Nodes are either public (have one or more listening ports) or private
83	master node only) or public nodes (connectable from unrelated nodes).	97	(no listening ports). Private nodes cannot talk to other private nodes
		98	currently, but all nodes can talk to public nodes.
84		99
85	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	100	Nodes is represented by (printable) strings called "node IDs".
86		101
87	A node reference is a string that either simply identifies the node (for	102	=item node ID - C<[A-Za-z0-9_\-.:]*>
88	private and slave nodes), or contains a recipe on how to reach a given
89	node (for public nodes).
90		103
91	This recipe is simply a comma-separated list of C<address:port> pairs (for	104	A node ID is a string that uniquely identifies the node within a
92	TCP/IP, other protocols might look different).	105	network. Depending on the configuration used, node IDs can look like a
		106	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		107	doesn't interpret node IDs in any way except to uniquely identify a node.
93		108
94	Node references come in two flavours: resolved (containing only numerical	109	=item binds - C<ip:port>
95	addresses) or unresolved (where hostnames are used instead of addresses).
96		110
97	Before using an unresolved node reference in a message you first have to	111	Nodes can only talk to each other by creating some kind of connection to
98	resolve it.	112	each other. To do this, nodes should listen on one or more local transport
		113	endpoints - binds.
		114
		115	Currently, only standard C<ip:port> specifications can be used, which
		116	specify TCP ports to listen on. So a bind is basically just a tcp socket
		117	in listening mode thta accepts conenctions form other nodes.
		118
		119	=item seed nodes
		120
		121	When a node starts, it knows nothing about the network it is in - it
		122	needs to connect to at least one other node that is already in the
		123	network. These other nodes are called "seed nodes".
		124
		125	Seed nodes themselves are not special - they are seed nodes only because
		126	some other node I<uses> them as such, but any node can be used as seed
		127	node for other nodes, and eahc node cna use a different set of seed nodes.
		128
		129	In addition to discovering the network, seed nodes are also used to
		130	maintain the network - all nodes using the same seed node form are part of
		131	the same network. If a network is split into multiple subnets because e.g.
		132	the network link between the parts goes down, then using the same seed
		133	nodes for all nodes ensures that eventually the subnets get merged again.
		134
		135	Seed nodes are expected to be long-running, and at least one seed node
		136	should always be available. They should also be relatively responsive - a
		137	seed node that blocks for long periods will slow down everybody else.
		138
		139	For small networks, it's best if every node uses the same set of seed
		140	nodes. For large networks, it can be useful to specify "regional" seed
		141	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		142	each other. What's important is that all seed nodes connections form a
		143	complete graph, so that the network cannot split into separate subnets
		144	forever.
		145
		146	Seed nodes are represented by seed IDs.
		147
		148	=item seed IDs - C<host:port>
		149
		150	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
		151	TCP port) of nodes that should be used as seed nodes.
		152
		153	=item global nodes
		154
		155	An AEMP network needs a discovery service - nodes need to know how to
		156	connect to other nodes they only know by name. In addition, AEMP offers a
		157	distributed "group database", which maps group names to a list of strings
		158	- for example, to register worker ports.
		159
		160	A network needs at least one global node to work, and allows every node to
		161	be a global node.
		162
		163	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		164	node and tries to keep connections to all other nodes. So while it can
		165	make sense to make every node "global" in small networks, it usually makes
		166	sense to only make seed nodes into global nodes in large networks (nodes
		167	keep connections to seed nodes and global nodes, so makign them the same
		168	reduces overhead).
99		169
100	=back	170	=back
101		171
102	=head1 VARIABLES/FUNCTIONS	172	=head1 VARIABLES/FUNCTIONS
103		173
105		175
106	=cut	176	=cut
107		177
108	package AnyEvent::MP;	178	package AnyEvent::MP;
109		179
		180	use AnyEvent::MP::Config ();
110	use AnyEvent::MP::Base;	181	use AnyEvent::MP::Kernel;
		182	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
111		183
112	use common::sense;	184	use common::sense;
113		185
114	use Carp ();	186	use Carp ();
115		187
116	use AE ();	188	use AE ();
117		189
118	use base "Exporter";	190	use base "Exporter";
119		191
120	our $VERSION = '0.1';	192	our $VERSION = $AnyEvent::MP::Config::VERSION;
		193
121	our @EXPORT = qw(	194	our @EXPORT = qw(
122	NODE $NODE *SELF node_of _any_	195	NODE $NODE *SELF node_of after
123	resolve_node initialise_node	196	configure
124	snd rcv mon kil reg psub spawn	197	snd rcv mon mon_guard kil psub peval spawn cal
125	port	198	port
126	);	199	);
127		200
128	our $SELF;	201	our $SELF;
129		202
…		…
133	kil $SELF, die => $msg;	206	kil $SELF, die => $msg;
134	}	207	}
135		208
136	=item $thisnode = NODE / $NODE	209	=item $thisnode = NODE / $NODE
137		210
138	The C<NODE> function returns, and the C<$NODE> variable contains	211	The C<NODE> function returns, and the C<$NODE> variable contains, the node
139	the noderef of the local node. The value is initialised by a call	212	ID of the node running in the current process. This value is initialised by
140	to C<become_public> or C<become_slave>, after which all local port	213	a call to C<configure>.
141	identifiers become invalid.
142		214
143	=item $noderef = node_of $port	215	=item $nodeid = node_of $port
144		216
145	Extracts and returns the noderef from a portid or a noderef.	217	Extracts and returns the node ID from a port ID or a node ID.
146		218
147	=item initialise_node $noderef, $seednode, $seednode...	219	=item configure $profile, key => value...
148		220
149	=item initialise_node "slave/", $master, $master...	221	=item configure key => value...
150		222
151	Before a node can talk to other nodes on the network it has to initialise	223	Before a node can talk to other nodes on the network (i.e. enter
152	itself - the minimum a node needs to know is it's own name, and optionally	224	"distributed mode") it has to configure itself - the minimum a node needs
153	it should know the noderefs of some other nodes in the network.	225	to know is its own name, and optionally it should know the addresses of
		226	some other nodes in the network to discover other nodes.
154		227
155	This function initialises a node - it must be called exactly once (or	228	This function configures a node - it must be called exactly once (or
156	never) before calling other AnyEvent::MP functions.	229	never) before calling other AnyEvent::MP functions.
157		230
158	All arguments are noderefs, which can be either resolved or unresolved.	231	The key/value pairs are basically the same ones as documented for the
159		232	F<aemp> command line utility (sans the set/del prefix), with two additions:
160	There are two types of networked nodes, public nodes and slave nodes:
161		233
162	=over 4	234	=over 4
163		235
164	=item public nodes	236	=item norc => $boolean (default false)
165		237
166	For public nodes, C<$noderef> must either be a (possibly unresolved)	238	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
167	noderef, in which case it will be resolved, or C<undef> (or missing), in	239	be consulted - all configuraiton options must be specified in the
168	which case the noderef will be guessed.	240	C<configure> call.
169		241
170	Afterwards, the node will bind itself on all endpoints and try to connect	242	=item force => $boolean (default false)
171	to all additional C<$seednodes> that are specified. Seednodes are optional
172	and can be used to quickly bootstrap the node into an existing network.
173		243
174	=item slave nodes	244	IF true, then the values specified in the C<configure> will take
175		245	precedence over any values configured via the rc file. The default is for
176	When the C<$noderef> is the special string C<slave/>, then the node will	246	the rc file to override any options specified in the program.
177	become a slave node. Slave nodes cannot be contacted from outside and will
178	route most of their traffic to the master node that they attach to.
179
180	At least one additional noderef is required: The node will try to connect
181	to all of them and will become a slave attached to the first node it can
182	successfully connect to.
183		247
184	=back	248	=back
185		249
186	This function will block until all nodes have been resolved and, for slave
187	nodes, until it has successfully established a connection to a master
188	server.
189
190	Example: become a public node listening on the default node.
191
192	initialise_node;
193
194	Example: become a public node, and try to contact some well-known master
195	servers to become part of the network.
196
197	initialise_node undef, "master1", "master2";
198
199	Example: become a public node listening on port C<4041>.
200
201	initialise_node 4041;
202
203	Example: become a public node, only visible on localhost port 4044.
204
205	initialise_node "locahost:4044";
206
207	Example: become a slave node to any of the specified master servers.
208
209	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
210
211	=item $cv = resolve_node $noderef
212
213	Takes an unresolved node reference that may contain hostnames and
214	abbreviated IDs, resolves all of them and returns a resolved node
215	reference.
216
217	In addition to C<address:port> pairs allowed in resolved noderefs, the
218	following forms are supported:
219
220	=over 4	250	=over 4
221		251
222	=item the empty string	252	=item step 1, gathering configuration from profiles
223		253
224	An empty-string component gets resolved as if the default port (4040) was	254	The function first looks up a profile in the aemp configuration (see the
225	specified.	255	L<aemp> commandline utility). The profile name can be specified via the
		256	named C<profile> parameter or can simply be the first parameter). If it is
		257	missing, then the nodename (F<uname -n>) will be used as profile name.
226		258
227	=item naked port numbers (e.g. C<1234>)	259	The profile data is then gathered as follows:
228		260
229	These are resolved by prepending the local nodename and a colon, to be	261	First, all remaining key => value pairs (all of which are conveniently
230	further resolved.	262	undocumented at the moment) will be interpreted as configuration
		263	data. Then they will be overwritten by any values specified in the global
		264	default configuration (see the F<aemp> utility), then the chain of
		265	profiles chosen by the profile name (and any C<parent> attributes).
231		266
232	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	267	That means that the values specified in the profile have highest priority
		268	and the values specified directly via C<configure> have lowest priority,
		269	and can only be used to specify defaults.
233		270
234	These are resolved by using AnyEvent::DNS to resolve them, optionally	271	If the profile specifies a node ID, then this will become the node ID of
235	looking up SRV records for the C<aemp=4040> port, if no port was	272	this process. If not, then the profile name will be used as node ID, with
236	specified.	273	a slash (C</>) attached.
		274
		275	If the node ID (or profile name) ends with a slash (C</>), then a random
		276	string is appended to make it unique.
		277
		278	=item step 2, bind listener sockets
		279
		280	The next step is to look up the binds in the profile, followed by binding
		281	aemp protocol listeners on all binds specified (it is possible and valid
		282	to have no binds, meaning that the node cannot be contacted form the
		283	outside. This means the node cannot talk to other nodes that also have no
		284	binds, but it can still talk to all "normal" nodes).
		285
		286	If the profile does not specify a binds list, then a default of C<*> is
		287	used, meaning the node will bind on a dynamically-assigned port on every
		288	local IP address it finds.
		289
		290	=item step 3, connect to seed nodes
		291
		292	As the last step, the seed ID list from the profile is passed to the
		293	L<AnyEvent::MP::Global> module, which will then use it to keep
		294	connectivity with at least one node at any point in time.
237		295
238	=back	296	=back
		297
		298	Example: become a distributed node using the local node name as profile.
		299	This should be the most common form of invocation for "daemon"-type nodes.
		300
		301	configure
		302
		303	Example: become an anonymous node. This form is often used for commandline
		304	clients.
		305
		306	configure nodeid => "anon/";
		307
		308	Example: configure a node using a profile called seed, which is suitable
		309	for a seed node as it binds on all local addresses on a fixed port (4040,
		310	customary for aemp).
		311
		312	# use the aemp commandline utility
		313	# aemp profile seed binds '*:4040'
		314
		315	# then use it
		316	configure profile => "seed";
		317
		318	# or simply use aemp from the shell again:
		319	# aemp run profile seed
		320
		321	# or provide a nicer-to-remember nodeid
		322	# aemp run profile seed nodeid "$(hostname)"
239		323
240	=item $SELF	324	=item $SELF
241		325
242	Contains the current port id while executing C<rcv> callbacks or C<psub>	326	Contains the current port id while executing C<rcv> callbacks or C<psub>
243	blocks.	327	blocks.
244		328
245	=item SELF, %SELF, @SELF...	329	=item *SELF, SELF, %SELF, @SELF...
246		330
247	Due to some quirks in how perl exports variables, it is impossible to	331	Due to some quirks in how perl exports variables, it is impossible to
248	just export C<$SELF>, all the symbols called C<SELF> are exported by this	332	just export C<$SELF>, all the symbols named C<SELF> are exported by this
249	module, but only C<$SELF> is currently used.	333	module, but only C<$SELF> is currently used.
250		334
251	=item snd $port, type => @data	335	=item snd $port, type => @data
252		336
253	=item snd $port, @msg	337	=item snd $port, @msg
254		338
255	Send the given message to the given port ID, which can identify either	339	Send the given message to the given port, which can identify either a
256	a local or a remote port, and can be either a string or soemthignt hat	340	local or a remote port, and must be a port ID.
257	stringifies a sa port ID (such as a port object :).
258		341
259	While the message can be about anything, it is highly recommended to use a	342	While the message can be almost anything, it is highly recommended to
260	string as first element (a portid, or some word that indicates a request	343	use a string as first element (a port ID, or some word that indicates a
261	type etc.).	344	request type etc.) and to consist if only simple perl values (scalars,
		345	arrays, hashes) - if you think you need to pass an object, think again.
262		346
263	The message data effectively becomes read-only after a call to this	347	The message data logically becomes read-only after a call to this
264	function: modifying any argument is not allowed and can cause many	348	function: modifying any argument (or values referenced by them) is
265	problems.	349	forbidden, as there can be considerable time between the call to C<snd>
		350	and the time the message is actually being serialised - in fact, it might
		351	never be copied as within the same process it is simply handed to the
		352	receiving port.
266		353
267	The type of data you can transfer depends on the transport protocol: when	354	The type of data you can transfer depends on the transport protocol: when
268	JSON is used, then only strings, numbers and arrays and hashes consisting	355	JSON is used, then only strings, numbers and arrays and hashes consisting
269	of those are allowed (no objects). When Storable is used, then anything	356	of those are allowed (no objects). When Storable is used, then anything
270	that Storable can serialise and deserialise is allowed, and for the local	357	that Storable can serialise and deserialise is allowed, and for the local
271	node, anything can be passed.	358	node, anything can be passed. Best rely only on the common denominator of
		359	these.
272		360
273	=item $local_port = port	361	=item $local_port = port
274		362
275	Create a new local port object that can be used either as a pattern	363	Create a new local port object and returns its port ID. Initially it has
276	matching port ("full port") or a single-callback port ("miniport"),	364	no callbacks set and will throw an error when it receives messages.
277	depending on how C<rcv> callbacks are bound to the object.
278		365
279	=item $port = port { my @msg = @_; $finished }	366	=item $local_port = port { my @msg = @_ }
280		367
281	Creates a "miniport", that is, a very lightweight port without any pattern	368	Creates a new local port, and returns its ID. Semantically the same as
282	matching behind it, and returns its ID. Semantically the same as creating
283	a port and calling C<rcv $port, $callback> on it.	369	creating a port and calling C<rcv $port, $callback> on it.
284		370
285	The block will be called for every message received on the port. When the	371	The block will be called for every message received on the port, with the
286	callback returns a true value its job is considered "done" and the port	372	global variable C<$SELF> set to the port ID. Runtime errors will cause the
287	will be destroyed. Otherwise it will stay alive.	373	port to be C<kil>ed. The message will be passed as-is, no extra argument
		374	(i.e. no port ID) will be passed to the callback.
288		375
289	The message will be passed as-is, no extra argument (i.e. no port id) will	376	If you want to stop/destroy the port, simply C<kil> it:
290	be passed to the callback.
291		377
292	If you need the local port id in the callback, this works nicely:	378	my $port = port {
293		379	my @msg = @_;
294	my $port; $port = port {	380	...
295	snd $otherport, reply => $port;	381	kil $SELF;
296	};	382	};
297		383
298	=cut	384	=cut
299		385
300	sub rcv($@);	386	sub rcv($@);
301		387
		388	sub _kilme {
		389	die "received message on port without callback";
		390	}
		391
302	sub port(;&) {	392	sub port(;&) {
303	my $id = "$UNIQ." . $ID++;	393	my $id = "$UNIQ." . ++$ID;
304	my $port = "$NODE#$id";	394	my $port = "$NODE#$id";
305		395
306	if (@_) {	396	rcv $port, shift \|\| \&_kilme;
307	rcv $port, shift;
308	} else {
309	$PORT{$id} = sub { }; # nop
310	}
311		397
312	$port	398	$port
313	}	399	}
314		400
315	=item reg $port, $name
316
317	=item reg $name
318
319	Registers the given port (or C<$SELF><<< if missing) under the name
320	C<$name>. If the name already exists it is replaced.
321
322	A port can only be registered under one well known name.
323
324	A port automatically becomes unregistered when it is killed.
325
326	=cut
327
328	sub reg(@) {
329	my $port = @_ > 1 ? shift : $SELF \|\| Carp::croak 'reg: called with one argument only, but $SELF not set,';
330
331	$REG{$_[0]} = $port;
332	}
333
334	=item rcv $port, $callback->(@msg)	401	=item rcv $local_port, $callback->(@msg)
335		402
336	Replaces the callback on the specified miniport (after converting it to	403	Replaces the default callback on the specified port. There is no way to
337	one if required).	404	remove the default callback: use C<sub { }> to disable it, or better
338		405	C<kil> the port when it is no longer needed.
339	=item rcv $port, tagstring => $callback->(@msg), ...
340
341	=item rcv $port, $smartmatch => $callback->(@msg), ...
342
343	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
344
345	Register callbacks to be called on matching messages on the given full
346	port (after converting it to one if required) and return the port.
347
348	The callback has to return a true value when its work is done, after
349	which is will be removed, or a false value in which case it will stay
350	registered.
351		406
352	The global C<$SELF> (exported by this module) contains C<$port> while	407	The global C<$SELF> (exported by this module) contains C<$port> while
353	executing the callback.	408	executing the callback. Runtime errors during callback execution will
		409	result in the port being C<kil>ed.
354		410
355	Runtime errors during callback execution will result in the port being	411	The default callback received all messages not matched by a more specific
356	C<kil>ed.	412	C<tag> match.
357		413
358	If the match is an array reference, then it will be matched against the	414	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
359	first elements of the message, otherwise only the first element is being
360	matched.
361		415
362	Any element in the match that is specified as C<_any_> (a function	416	Register (or replace) callbacks to be called on messages starting with the
363	exported by this module) matches any single element of the message.	417	given tag on the given port (and return the port), or unregister it (when
		418	C<$callback> is C<$undef> or missing). There can only be one callback
		419	registered for each tag.
364		420
365	While not required, it is highly recommended that the first matching	421	The original message will be passed to the callback, after the first
366	element is a string identifying the message. The one-string-only match is	422	element (the tag) has been removed. The callback will use the same
367	also the most efficient match (by far).	423	environment as the default callback (see above).
368		424
369	Example: create a port and bind receivers on it in one go.	425	Example: create a port and bind receivers on it in one go.
370		426
371	my $port = rcv port,	427	my $port = rcv port,
372	msg1 => sub { ...; 0 },	428	msg1 => sub { ... },
373	msg2 => sub { ...; 0 },	429	msg2 => sub { ... },
374	;	430	;
375		431
376	Example: create a port, bind receivers and send it in a message elsewhere	432	Example: create a port, bind receivers and send it in a message elsewhere
377	in one go:	433	in one go:
378		434
379	snd $otherport, reply =>	435	snd $otherport, reply =>
380	rcv port,	436	rcv port,
381	msg1 => sub { ...; 0 },	437	msg1 => sub { ... },
382	...	438	...
383	;	439	;
384		440
		441	Example: temporarily register a rcv callback for a tag matching some port
		442	(e.g. for an rpc reply) and unregister it after a message was received.
		443
		444	rcv $port, $otherport => sub {
		445	my @reply = @_;
		446
		447	rcv $SELF, $otherport;
		448	};
		449
385	=cut	450	=cut
386		451
387	sub rcv($@) {	452	sub rcv($@) {
388	my $port = shift;	453	my $port = shift;
389	my ($noderef, $portid) = split /#/, $port, 2;	454	my ($nodeid, $portid) = split /#/, $port, 2;
390		455
391	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	456	$NODE{$nodeid} == $NODE{""}
392	or Carp::croak "$port: rcv can only be called on local ports, caught";	457	or Carp::croak "$port: rcv can only be called on local ports, caught";
393		458
394	if (@_ == 1) {	459	while (@_) {
		460	if (ref $_[0]) {
		461	if (my $self = $PORT_DATA{$portid}) {
		462	"AnyEvent::MP::Port" eq ref $self
		463	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		464
		465	$self->[0] = shift;
		466	} else {
395	my $cb = shift;	467	my $cb = shift;
396	delete $PORT_DATA{$portid};
397	$PORT{$portid} = sub {	468	$PORT{$portid} = sub {
398	local $SELF = $port;	469	local $SELF = $port;
399	eval {	470	eval { &$cb }; _self_die if $@;
400	&$cb	471	};
401	and kil $port;
402	};	472	}
403	_self_die if $@;	473	} elsif (defined $_[0]) {
404	};
405	} else {
406	my $self = $PORT_DATA{$portid} \|\|= do {	474	my $self = $PORT_DATA{$portid} \|\|= do {
407	my $self = bless {	475	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
408	id => $port,
409	}, "AnyEvent::MP::Port";
410		476
411	$PORT{$portid} = sub {	477	$PORT{$portid} = sub {
412	local $SELF = $port;	478	local $SELF = $port;
413		479
414	eval {
415	for (@{ $self->{rc0}{$_[0]} }) {	480	if (my $cb = $self->[1]{$_[0]}) {
416	$_ && &{$_->[0]}	481	shift;
417	&& undef $_;	482	eval { &$cb }; _self_die if $@;
418	}	483	} else {
419
420	for (@{ $self->{rcv}{$_[0]} }) {
421	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
422	&& &{$_->[0]}	484	&{ $self->[0] };
423	&& undef $_;
424	}
425
426	for (@{ $self->{any} }) {
427	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
428	&& &{$_->[0]}
429	&& undef $_;
430	}	485	}
431	};	486	};
432	_self_die if $@;	487
		488	$self
433	};	489	};
434		490
435	$self
436	};
437
438	"AnyEvent::MP::Port" eq ref $self	491	"AnyEvent::MP::Port" eq ref $self
439	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	492	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
440		493
441	while (@_) {
442	my ($match, $cb) = splice @_, 0, 2;	494	my ($tag, $cb) = splice @_, 0, 2;
443		495
444	if (!ref $match) {	496	if (defined $cb) {
445	push @{ $self->{rc0}{$match} }, [$cb];	497	$self->[1]{$tag} = $cb;
446	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
447	my ($type, @match) = @$match;
448	@match
449	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
450	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
451	} else {	498	} else {
452	push @{ $self->{any} }, [$cb, $match];	499	delete $self->[1]{$tag};
453	}	500	}
454	}	501	}
455	}	502	}
456		503
457	$port	504	$port
458	}	505	}
459		506
		507	=item peval $port, $coderef[, @args]
		508
		509	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		510	when the code throews an exception the C<$port> will be killed.
		511
		512	Any remaining args will be passed to the callback. Any return values will
		513	be returned to the caller.
		514
		515	This is useful when you temporarily want to execute code in the context of
		516	a port.
		517
		518	Example: create a port and run some initialisation code in it's context.
		519
		520	my $port = port { ... };
		521
		522	peval $port, sub {
		523	init
		524	or die "unable to init";
		525	};
		526
		527	=cut
		528
		529	sub peval($$) {
		530	local $SELF = shift;
		531	my $cb = shift;
		532
		533	if (wantarray) {
		534	my @res = eval { &$cb };
		535	_self_die if $@;
		536	@res
		537	} else {
		538	my $res = eval { &$cb };
		539	_self_die if $@;
		540	$res
		541	}
		542	}
		543
460	=item $closure = psub { BLOCK }	544	=item $closure = psub { BLOCK }
461		545
462	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	546	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
463	closure is executed, sets up the environment in the same way as in C<rcv>	547	closure is executed, sets up the environment in the same way as in C<rcv>
464	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.	548	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		549
		550	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		551	BLOCK }, @_ } >>.
465		552
466	This is useful when you register callbacks from C<rcv> callbacks:	553	This is useful when you register callbacks from C<rcv> callbacks:
467		554
468	rcv delayed_reply => sub {	555	rcv delayed_reply => sub {
469	my ($delay, @reply) = @_;	556	my ($delay, @reply) = @_;
…		…
493	$res	580	$res
494	}	581	}
495	}	582	}
496	}	583	}
497		584
498	=item $guard = mon $port, $cb->(@reason)	585	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
499		586
500	=item $guard = mon $port, $rcvport	587	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
501		588
502	=item $guard = mon $port	589	=item $guard = mon $port # kill $SELF when $port dies
503		590
504	=item $guard = mon $port, $rcvport, @msg	591	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
505		592
506	Monitor the given port and do something when the port is killed, and	593	Monitor the given port and do something when the port is killed or
507	optionally return a guard that can be used to stop monitoring again.	594	messages to it were lost, and optionally return a guard that can be used
		595	to stop monitoring again.
508		596
509	In the first form (callback), the callback is simply called with any	597	In the first form (callback), the callback is simply called with any
510	number of C<@reason> elements (no @reason means that the port was deleted	598	number of C<@reason> elements (no @reason means that the port was deleted
511	"normally"). Note also that I<< the callback B<must> never die >>, so use	599	"normally"). Note also that I<< the callback B<must> never die >>, so use
512	C<eval> if unsure.	600	C<eval> if unsure.
513		601
514	In the second form (another port given), the other port (C<$rcvport)	602	In the second form (another port given), the other port (C<$rcvport>)
515	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	603	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
516	"normal" kils nothing happens, while under all other conditions, the other	604	"normal" kils nothing happens, while under all other conditions, the other
517	port is killed with the same reason.	605	port is killed with the same reason.
518		606
519	The third form (kill self) is the same as the second form, except that	607	The third form (kill self) is the same as the second form, except that
520	C<$rvport> defaults to C<$SELF>.	608	C<$rvport> defaults to C<$SELF>.
521		609
522	In the last form (message), a message of the form C<@msg, @reason> will be	610	In the last form (message), a message of the form C<@msg, @reason> will be
523	C<snd>.	611	C<snd>.
		612
		613	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		614	alert was raised), they are removed and will not trigger again.
524		615
525	As a rule of thumb, monitoring requests should always monitor a port from	616	As a rule of thumb, monitoring requests should always monitor a port from
526	a local port (or callback). The reason is that kill messages might get	617	a local port (or callback). The reason is that kill messages might get
527	lost, just like any other message. Another less obvious reason is that	618	lost, just like any other message. Another less obvious reason is that
528	even monitoring requests can get lost (for exmaple, when the connection	619	even monitoring requests can get lost (for example, when the connection
529	to the other node goes down permanently). When monitoring a port locally	620	to the other node goes down permanently). When monitoring a port locally
530	these problems do not exist.	621	these problems do not exist.
531		622
		623	C<mon> effectively guarantees that, in the absence of hardware failures,
		624	after starting the monitor, either all messages sent to the port will
		625	arrive, or the monitoring action will be invoked after possible message
		626	loss has been detected. No messages will be lost "in between" (after
		627	the first lost message no further messages will be received by the
		628	port). After the monitoring action was invoked, further messages might get
		629	delivered again.
		630
		631	Inter-host-connection timeouts and monitoring depend on the transport
		632	used. The only transport currently implemented is TCP, and AnyEvent::MP
		633	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		634	non-idle connection, and usually around two hours for idle connections).
		635
		636	This means that monitoring is good for program errors and cleaning up
		637	stuff eventually, but they are no replacement for a timeout when you need
		638	to ensure some maximum latency.
		639
532	Example: call a given callback when C<$port> is killed.	640	Example: call a given callback when C<$port> is killed.
533		641
534	mon $port, sub { warn "port died because of <@_>\n" };	642	mon $port, sub { warn "port died because of <@_>\n" };
535		643
536	Example: kill ourselves when C<$port> is killed abnormally.	644	Example: kill ourselves when C<$port> is killed abnormally.
…		…
542	mon $port, $self => "restart";	650	mon $port, $self => "restart";
543		651
544	=cut	652	=cut
545		653
546	sub mon {	654	sub mon {
547	my ($noderef, $port) = split /#/, shift, 2;	655	my ($nodeid, $port) = split /#/, shift, 2;
548		656
549	my $node = $NODE{$noderef} \|\| add_node $noderef;	657	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
550		658
551	my $cb = @_ ? $_[0] : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';	659	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
552		660
553	unless (ref $cb) {	661	unless (ref $cb) {
554	if (@_) {	662	if (@_) {
555	# send a kill info message	663	# send a kill info message
556	my (@msg) = @_;	664	my (@msg) = ($cb, @_);
557	$cb = sub { snd @msg, @_ };	665	$cb = sub { snd @msg, @_ };
558	} else {	666	} else {
559	# simply kill other port	667	# simply kill other port
560	my $port = $cb;	668	my $port = $cb;
561	$cb = sub { kil $port, @_ if @_ };	669	$cb = sub { kil $port, @_ if @_ };
…		…
563	}	671	}
564		672
565	$node->monitor ($port, $cb);	673	$node->monitor ($port, $cb);
566		674
567	defined wantarray	675	defined wantarray
568	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	676	and ($cb += 0, AnyEvent::Util::guard { $node->unmonitor ($port, $cb) })
569	}	677	}
570		678
571	=item $guard = mon_guard $port, $ref, $ref...	679	=item $guard = mon_guard $port, $ref, $ref...
572		680
573	Monitors the given C<$port> and keeps the passed references. When the port	681	Monitors the given C<$port> and keeps the passed references. When the port
574	is killed, the references will be freed.	682	is killed, the references will be freed.
575		683
576	Optionally returns a guard that will stop the monitoring.	684	Optionally returns a guard that will stop the monitoring.
577		685
578	This function is useful when you create e.g. timers or other watchers and	686	This function is useful when you create e.g. timers or other watchers and
579	want to free them when the port gets killed:	687	want to free them when the port gets killed (note the use of C<psub>):
580		688
581	$port->rcv (start => sub {	689	$port->rcv (start => sub {
582	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	690	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
583	undef $timer if 0.9 < rand;	691	undef $timer if 0.9 < rand;
584	});	692	});
585	});	693	});
586		694
587	=cut	695	=cut
…		…
596		704
597	=item kil $port[, @reason]	705	=item kil $port[, @reason]
598		706
599	Kill the specified port with the given C<@reason>.	707	Kill the specified port with the given C<@reason>.
600		708
601	If no C<@reason> is specified, then the port is killed "normally" (linked	709	If no C<@reason> is specified, then the port is killed "normally" -
602	ports will not be kileld, or even notified).	710	monitor callback will be invoked, but the kil will not cause linked ports
		711	(C<mon $mport, $lport> form) to get killed.
603		712
604	Otherwise, linked ports get killed with the same reason (second form of	713	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
605	C<mon>, see below).	714	form) get killed with the same reason.
606		715
607	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	716	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
608	will be reported as reason C<< die => $@ >>.	717	will be reported as reason C<< die => $@ >>.
609		718
610	Transport/communication errors are reported as C<< transport_error =>	719	Transport/communication errors are reported as C<< transport_error =>
…		…
615	=item $port = spawn $node, $initfunc[, @initdata]	724	=item $port = spawn $node, $initfunc[, @initdata]
616		725
617	Creates a port on the node C<$node> (which can also be a port ID, in which	726	Creates a port on the node C<$node> (which can also be a port ID, in which
618	case it's the node where that port resides).	727	case it's the node where that port resides).
619		728
620	The port ID of the newly created port is return immediately, and it is	729	The port ID of the newly created port is returned immediately, and it is
621	permissible to immediately start sending messages or monitor the port.	730	possible to immediately start sending messages or to monitor the port.
622		731
623	After the port has been created, the init function is	732	After the port has been created, the init function is called on the remote
624	called. This function must be a fully-qualified function name	733	node, in the same context as a C<rcv> callback. This function must be a
625	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	734	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
626	program, use C<::name>.	735	specify a function in the main program, use C<::name>.
627		736
628	If the function doesn't exist, then the node tries to C<require>	737	If the function doesn't exist, then the node tries to C<require>
629	the package, then the package above the package and so on (e.g.	738	the package, then the package above the package and so on (e.g.
630	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	739	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
631	exists or it runs out of package names.	740	exists or it runs out of package names.
632		741
633	The init function is then called with the newly-created port as context	742	The init function is then called with the newly-created port as context
634	object (C<$SELF>) and the C<@initdata> values as arguments.	743	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		744	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		745	the port might not get created.
635		746
636	A common idiom is to pass your own port, monitor the spawned port, and	747	A common idiom is to pass a local port, immediately monitor the spawned
637	in the init function, monitor the original port. This two-way monitoring	748	port, and in the remote init function, immediately monitor the passed
638	ensures that both ports get cleaned up when there is a problem.	749	local port. This two-way monitoring ensures that both ports get cleaned up
		750	when there is a problem.
		751
		752	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		753	caller before C<spawn> returns (by delaying invocation when spawn is
		754	called for the local node).
639		755
640	Example: spawn a chat server port on C<$othernode>.	756	Example: spawn a chat server port on C<$othernode>.
641		757
642	# this node, executed from within a port context:	758	# this node, executed from within a port context:
643	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	759	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
658		774
659	sub _spawn {	775	sub _spawn {
660	my $port = shift;	776	my $port = shift;
661	my $init = shift;	777	my $init = shift;
662		778
		779	# rcv will create the actual port
663	local $SELF = "$NODE#$port";	780	local $SELF = "$NODE#$port";
664	eval {	781	eval {
665	&{ load_func $init }	782	&{ load_func $init }
666	};	783	};
667	_self_die if $@;	784	_self_die if $@;
668	}	785	}
669		786
670	sub spawn(@) {	787	sub spawn(@) {
671	my ($noderef, undef) = split /#/, shift, 2;	788	my ($nodeid, undef) = split /#/, shift, 2;
672		789
673	my $id = "$RUNIQ." . $ID++;	790	my $id = "$RUNIQ." . ++$ID;
674		791
675	$_[0] =~ /::/	792	$_[0] =~ /::/
676	or Carp::croak "spawn init function must be a fully-qualified name, caught";	793	or Carp::croak "spawn init function must be a fully-qualified name, caught";
677		794
678	($NODE{$noderef} \|\| add_node $noderef)	795	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
679	->send (["", "AnyEvent::MP::_spawn" => $id, @_]);
680		796
681	"$noderef#$id"	797	"$nodeid#$id"
682	}	798	}
683		799
684	=back
685		800
686	=head1 NODE MESSAGES	801	=item after $timeout, @msg
687		802
688	Nodes understand the following messages sent to them. Many of them take	803	=item after $timeout, $callback
689	arguments called C<@reply>, which will simply be used to compose a reply
690	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
691	the remaining arguments are simply the message data.
692		804
693	While other messages exist, they are not public and subject to change.	805	Either sends the given message, or call the given callback, after the
		806	specified number of seconds.
694		807
695	=over 4	808	This is simply a utility function that comes in handy at times - the
		809	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		810	so it may go away in the future.
696		811
697	=cut	812	=cut
698		813
699	=item lookup => $name, @reply	814	sub after($@) {
		815	my ($timeout, @action) = @_;
700		816
701	Replies with the port ID of the specified well-known port, or C<undef>.	817	my $t; $t = AE::timer $timeout, 0, sub {
		818	undef $t;
		819	ref $action[0]
		820	? $action[0]()
		821	: snd @action;
		822	};
		823	}
702		824
703	=item devnull => ...	825	=item cal $port, @msg, $callback[, $timeout]
704		826
705	Generic data sink/CPU heat conversion.	827	A simple form of RPC - sends a message to the given C<$port> with the
		828	given contents (C<@msg>), but adds a reply port to the message.
706		829
707	=item relay => $port, @msg	830	The reply port is created temporarily just for the purpose of receiving
		831	the reply, and will be C<kil>ed when no longer needed.
708		832
709	Simply forwards the message to the given port.	833	A reply message sent to the port is passed to the C<$callback> as-is.
710		834
711	=item eval => $string[ @reply]	835	If an optional time-out (in seconds) is given and it is not C<undef>,
		836	then the callback will be called without any arguments after the time-out
		837	elapsed and the port is C<kil>ed.
712		838
713	Evaluates the given string. If C<@reply> is given, then a message of the	839	If no time-out is given (or it is C<undef>), then the local port will
714	form C<@reply, $@, @evalres> is sent.	840	monitor the remote port instead, so it eventually gets cleaned-up.
715		841
716	Example: crash another node.	842	Currently this function returns the temporary port, but this "feature"
		843	might go in future versions unless you can make a convincing case that
		844	this is indeed useful for something.
717		845
718	snd $othernode, eval => "exit";	846	=cut
719		847
720	=item time => @reply	848	sub cal(@) {
		849	my $timeout = ref $_[-1] ? undef : pop;
		850	my $cb = pop;
721		851
722	Replies the the current node time to C<@reply>.	852	my $port = port {
		853	undef $timeout;
		854	kil $SELF;
		855	&$cb;
		856	};
723		857
724	Example: tell the current node to send the current time to C<$myport> in a	858	if (defined $timeout) {
725	C<timereply> message.	859	$timeout = AE::timer $timeout, 0, sub {
		860	undef $timeout;
		861	kil $port;
		862	$cb->();
		863	};
		864	} else {
		865	mon $_[0], sub {
		866	kil $port;
		867	$cb->();
		868	};
		869	}
726		870
727	snd $NODE, time => $myport, timereply => 1, 2;	871	push @_, $port;
728	# => snd $myport, timereply => 1, 2, <time>	872	&snd;
		873
		874	$port
		875	}
729		876
730	=back	877	=back
731		878
732	=head1 AnyEvent::MP vs. Distributed Erlang	879	=head1 AnyEvent::MP vs. Distributed Erlang
733		880
734	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	881	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
735	== aemp node, Erlang process == aemp port), so many of the documents and	882	== aemp node, Erlang process == aemp port), so many of the documents and
736	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	883	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
737	sample:	884	sample:
738		885
739	http://www.Erlang.se/doc/programming_rules.shtml	886	http://www.erlang.se/doc/programming_rules.shtml
740	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	887	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
741	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	888	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
742	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	889	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
743		890
744	Despite the similarities, there are also some important differences:	891	Despite the similarities, there are also some important differences:
745		892
746	=over 4	893	=over 4
747		894
748	=item * Node references contain the recipe on how to contact them.	895	=item * Node IDs are arbitrary strings in AEMP.
749		896
750	Erlang relies on special naming and DNS to work everywhere in the	897	Erlang relies on special naming and DNS to work everywhere in the same
751	same way. AEMP relies on each node knowing it's own address(es), with	898	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
752	convenience functionality.	899	configuration or DNS), and possibly the addresses of some seed nodes, but
		900	will otherwise discover other nodes (and their IDs) itself.
753		901
754	This means that AEMP requires a less tightly controlled environment at the	902	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
755	cost of longer node references and a slightly higher management overhead.	903	uses "local ports are like remote ports".
		904
		905	The failure modes for local ports are quite different (runtime errors
		906	only) then for remote ports - when a local port dies, you I<know> it dies,
		907	when a connection to another node dies, you know nothing about the other
		908	port.
		909
		910	Erlang pretends remote ports are as reliable as local ports, even when
		911	they are not.
		912
		913	AEMP encourages a "treat remote ports differently" philosophy, with local
		914	ports being the special case/exception, where transport errors cannot
		915	occur.
756		916
757	=item * Erlang uses processes and a mailbox, AEMP does not queue.	917	=item * Erlang uses processes and a mailbox, AEMP does not queue.
758		918
759	Erlang uses processes that selctively receive messages, and therefore	919	Erlang uses processes that selectively receive messages out of order, and
760	needs a queue. AEMP is event based, queuing messages would serve no useful	920	therefore needs a queue. AEMP is event based, queuing messages would serve
761	purpose.	921	no useful purpose. For the same reason the pattern-matching abilities
		922	of AnyEvent::MP are more limited, as there is little need to be able to
		923	filter messages without dequeuing them.
762		924
763	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	925	This is not a philosophical difference, but simply stems from AnyEvent::MP
		926	being event-based, while Erlang is process-based.
		927
		928	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		929	top of AEMP and Coro threads.
764		930
765	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	931	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
766		932
767	Sending messages in Erlang is synchronous and blocks the process. AEMP	933	Sending messages in Erlang is synchronous and blocks the process until
768	sends are immediate, connection establishment is handled in the	934	a conenction has been established and the message sent (and so does not
769	background.	935	need a queue that can overflow). AEMP sends return immediately, connection
		936	establishment is handled in the background.
770		937
771	=item * Erlang can silently lose messages, AEMP cannot.	938	=item * Erlang suffers from silent message loss, AEMP does not.
772		939
773	Erlang makes few guarantees on messages delivery - messages can get lost	940	Erlang implements few guarantees on messages delivery - messages can get
774	without any of the processes realising it (i.e. you send messages a, b,	941	lost without any of the processes realising it (i.e. you send messages a,
775	and c, and the other side only receives messages a and c).	942	b, and c, and the other side only receives messages a and c).
776		943
777	AEMP guarantees correct ordering, and the guarantee that there are no	944	AEMP guarantees (modulo hardware errors) correct ordering, and the
		945	guarantee that after one message is lost, all following ones sent to the
		946	same port are lost as well, until monitoring raises an error, so there are
778	holes in the message sequence.	947	no silent "holes" in the message sequence.
779		948
780	=item * In Erlang, processes can be declared dead and later be found to be	949	If you want your software to be very reliable, you have to cope with
781	alive.	950	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
782		951	simply tries to work better in common error cases, such as when a network
783	In Erlang it can happen that a monitored process is declared dead and	952	link goes down.
784	linked processes get killed, but later it turns out that the process is
785	still alive - and can receive messages.
786
787	In AEMP, when port monitoring detects a port as dead, then that port will
788	eventually be killed - it cannot happen that a node detects a port as dead
789	and then later sends messages to it, finding it is still alive.
790		953
791	=item * Erlang can send messages to the wrong port, AEMP does not.	954	=item * Erlang can send messages to the wrong port, AEMP does not.
792		955
793	In Erlang it is quite possible that a node that restarts reuses a process	956	In Erlang it is quite likely that a node that restarts reuses an Erlang
794	ID known to other nodes for a completely different process, causing	957	process ID known to other nodes for a completely different process,
795	messages destined for that process to end up in an unrelated process.	958	causing messages destined for that process to end up in an unrelated
		959	process.
796		960
797	AEMP never reuses port IDs, so old messages or old port IDs floating	961	AEMP does not reuse port IDs, so old messages or old port IDs floating
798	around in the network will not be sent to an unrelated port.	962	around in the network will not be sent to an unrelated port.
799		963
800	=item * Erlang uses unprotected connections, AEMP uses secure	964	=item * Erlang uses unprotected connections, AEMP uses secure
801	authentication and can use TLS.	965	authentication and can use TLS.
802		966
803	AEMP can use a proven protocol - SSL/TLS - to protect connections and	967	AEMP can use a proven protocol - TLS - to protect connections and
804	securely authenticate nodes.	968	securely authenticate nodes.
805		969
806	=item * The AEMP protocol is optimised for both text-based and binary	970	=item * The AEMP protocol is optimised for both text-based and binary
807	communications.	971	communications.
808		972
809	The AEMP protocol, unlike the Erlang protocol, supports both	973	The AEMP protocol, unlike the Erlang protocol, supports both programming
810	language-independent text-only protocols (good for debugging) and binary,	974	language independent text-only protocols (good for debugging), and binary,
811	language-specific serialisers (e.g. Storable).	975	language-specific serialisers (e.g. Storable). By default, unless TLS is
		976	used, the protocol is actually completely text-based.
812		977
813	It has also been carefully designed to be implementable in other languages	978	It has also been carefully designed to be implementable in other languages
814	with a minimum of work while gracefully degrading fucntionality to make the	979	with a minimum of work while gracefully degrading functionality to make the
815	protocol simple.	980	protocol simple.
816		981
817	=item * AEMP has more flexible monitoring options than Erlang.	982	=item * AEMP has more flexible monitoring options than Erlang.
818		983
819	In Erlang, you can chose to receive I<all> exit signals as messages	984	In Erlang, you can chose to receive I<all> exit signals as messages or
820	or I<none>, there is no in-between, so monitoring single processes is	985	I<none>, there is no in-between, so monitoring single Erlang processes is
821	difficult to implement. Monitoring in AEMP is more flexible than in	986	difficult to implement.
822	Erlang, as one can choose between automatic kill, exit message or callback	987
823	on a per-process basis.	988	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		989	between automatic kill, exit message or callback on a per-port basis.
824		990
825	=item * Erlang tries to hide remote/local connections, AEMP does not.	991	=item * Erlang tries to hide remote/local connections, AEMP does not.
826		992
827	Monitoring in Erlang is not an indicator of process death/crashes,	993	Monitoring in Erlang is not an indicator of process death/crashes, in the
828	as linking is (except linking is unreliable in Erlang).	994	same way as linking is (except linking is unreliable in Erlang).
829		995
830	In AEMP, you don't "look up" registered port names or send to named ports	996	In AEMP, you don't "look up" registered port names or send to named ports
831	that might or might not be persistent. Instead, you normally spawn a port	997	that might or might not be persistent. Instead, you normally spawn a port
832	on the remote node. The init function monitors the you, and you monitor	998	on the remote node. The init function monitors you, and you monitor the
833	the remote port. Since both monitors are local to the node, they are much	999	remote port. Since both monitors are local to the node, they are much more
834	more reliable.	1000	reliable (no need for C<spawn_link>).
835		1001
836	This also saves round-trips and avoids sending messages to the wrong port	1002	This also saves round-trips and avoids sending messages to the wrong port
837	(hard to do in Erlang).	1003	(hard to do in Erlang).
838		1004
839	=back	1005	=back
840		1006
		1007	=head1 RATIONALE
		1008
		1009	=over 4
		1010
		1011	=item Why strings for port and node IDs, why not objects?
		1012
		1013	We considered "objects", but found that the actual number of methods
		1014	that can be called are quite low. Since port and node IDs travel over
		1015	the network frequently, the serialising/deserialising would add lots of
		1016	overhead, as well as having to keep a proxy object everywhere.
		1017
		1018	Strings can easily be printed, easily serialised etc. and need no special
		1019	procedures to be "valid".
		1020
		1021	And as a result, a port with just a default receiver consists of a single
		1022	code reference stored in a global hash - it can't become much cheaper.
		1023
		1024	=item Why favour JSON, why not a real serialising format such as Storable?
		1025
		1026	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1027	format, but currently there is no way to make a node use Storable by
		1028	default (although all nodes will accept it).
		1029
		1030	The default framing protocol is JSON because a) JSON::XS is many times
		1031	faster for small messages and b) most importantly, after years of
		1032	experience we found that object serialisation is causing more problems
		1033	than it solves: Just like function calls, objects simply do not travel
		1034	easily over the network, mostly because they will always be a copy, so you
		1035	always have to re-think your design.
		1036
		1037	Keeping your messages simple, concentrating on data structures rather than
		1038	objects, will keep your messages clean, tidy and efficient.
		1039
		1040	=back
		1041
841	=head1 SEE ALSO	1042	=head1 SEE ALSO
		1043
		1044	L<AnyEvent::MP::Intro> - a gentle introduction.
		1045
		1046	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1047
		1048	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1049	your applications.
		1050
		1051	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1052
		1053	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1054	all nodes.
842		1055
843	L<AnyEvent>.	1056	L<AnyEvent>.
844		1057
845	=head1 AUTHOR	1058	=head1 AUTHOR
846		1059

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Revision 1.122 by root, Wed Feb 29 18:44:59 2012 UTC