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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.34 by root, Wed Aug 5 23:50:46 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
		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	34
		35	# destroy a port again
		36	kil $port; # "normal" kill
		37	kil $port, my_error => "everything is broken"; # error kill
		38
		39	# monitoring
		40	mon $localport, $cb->(@msg) # callback is invoked on death
		41	mon $localport, $otherport # kill otherport on abnormal 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.
27		59
28	=head1 DESCRIPTION	60	=head1 DESCRIPTION
29		61
30	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
31		63
32	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
33	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
34		66
35	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>
36	manual page.	68	manual page and the examples under F<eg/>.
37
38	At the moment, this module family is severly broken and underdocumented,
39	so do not use. This was uploaded mainly to reserve the CPAN namespace -
40	stay tuned! The basic API should be finished, however.
41		69
42	=head1 CONCEPTS	70	=head1 CONCEPTS
43		71
44	=over 4	72	=over 4
45		73
46	=item port	74	=item port
47		75
48	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).
49		78
50	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
51	messages. All C<rcv> handlers will receive messages they match, messages	80	some messages. Messages send to ports will not be queued, regardless of
52	will not be queued.	81	anything was listening for them or not.
53		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
54	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
55		86
56	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
57	separator, and a port name (a printable string of unspecified format). An	88	separator, and a port name (a printable string of unspecified format).
58	exception is the the node port, whose ID is identical to its node
59	reference.
60		89
61	=item node	90	=item node
62		91
63	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,
64	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
65	create new ports, among other things.	94	ports.
66		95
67	Nodes are either private (single-process only), slaves (connected to a	96	Nodes are either public (have one or more listening ports) or private
68	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.
69		99
70	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	100	Nodes is represented by (printable) strings called "node IDs".
71		101
72	A node reference is a string that either simply identifies the node (for	102	=item node ID - C<[A-Za-z0-9_\-.:]*>
73	private and slave nodes), or contains a recipe on how to reach a given
74	node (for public nodes).
75		103
76	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
77	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.
78		108
79	Node references come in two flavours: resolved (containing only numerical	109	=item binds - C<ip:port>
80	addresses) or unresolved (where hostnames are used instead of addresses).
81		110
82	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
83	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).
84		169
85	=back	170	=back
86		171
87	=head1 VARIABLES/FUNCTIONS	172	=head1 VARIABLES/FUNCTIONS
88		173
90		175
91	=cut	176	=cut
92		177
93	package AnyEvent::MP;	178	package AnyEvent::MP;
94		179
		180	use AnyEvent::MP::Config ();
95	use AnyEvent::MP::Base;	181	use AnyEvent::MP::Kernel;
		182	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
96		183
97	use common::sense;	184	use common::sense;
98		185
99	use Carp ();	186	use Carp ();
100		187
101	use AE ();	188	use AE ();
102		189
103	use base "Exporter";	190	use base "Exporter";
104		191
105	our $VERSION = '0.1';	192	our $VERSION = $AnyEvent::MP::Config::VERSION;
		193
106	our @EXPORT = qw(	194	our @EXPORT = qw(
107	NODE $NODE *SELF node_of _any_	195	NODE $NODE *SELF node_of after
108	resolve_node initialise_node	196	configure
109	snd rcv mon kil reg psub	197	snd rcv mon mon_guard kil psub peval spawn cal
110	port	198	port
111	);	199	);
112		200
113	our $SELF;	201	our $SELF;
114		202
…		…
118	kil $SELF, die => $msg;	206	kil $SELF, die => $msg;
119	}	207	}
120		208
121	=item $thisnode = NODE / $NODE	209	=item $thisnode = NODE / $NODE
122		210
123	The C<NODE> function returns, and the C<$NODE> variable contains	211	The C<NODE> function returns, and the C<$NODE> variable contains, the node
124	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
125	to C<become_public> or C<become_slave>, after which all local port	213	a call to C<configure>.
126	identifiers become invalid.
127		214
128	=item $noderef = node_of $port	215	=item $nodeid = node_of $port
129		216
130	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.
131		218
132	=item initialise_node $noderef, $seednode, $seednode...	219	=item configure $profile, key => value...
133		220
134	=item initialise_node "slave/", $master, $master...	221	=item configure key => value...
135		222
136	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
137	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
138	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.
139		227
140	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
141	never) before calling other AnyEvent::MP functions.	229	never) before calling other AnyEvent::MP functions.
142		230
143	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
144		232	F<aemp> command line utility (sans the set/del prefix), with two additions:
145	There are two types of networked nodes, public nodes and slave nodes:
146		233
147	=over 4	234	=over 4
148		235
149	=item public nodes	236	=item norc => $boolean (default false)
150		237
151	For public nodes, C<$noderef> must either be a (possibly unresolved)	238	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
152	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
153	which case the noderef will be guessed.	240	C<configure> call.
154		241
155	Afterwards, the node will bind itself on all endpoints and try to connect	242	=item force => $boolean (default false)
156	to all additional C<$seednodes> that are specified. Seednodes are optional
157	and can be used to quickly bootstrap the node into an existing network.
158		243
159	=item slave nodes	244	IF true, then the values specified in the C<configure> will take
160		245	precedence over any values configured via the rc file. The default is for
161	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.
162	become a slave node. Slave nodes cannot be contacted from outside and will
163	route most of their traffic to the master node that they attach to.
164
165	At least one additional noderef is required: The node will try to connect
166	to all of them and will become a slave attached to the first node it can
167	successfully connect to.
168		247
169	=back	248	=back
170		249
171	This function will block until all nodes have been resolved and, for slave
172	nodes, until it has successfully established a connection to a master
173	server.
174
175	Example: become a public node listening on the default node.
176
177	initialise_node;
178
179	Example: become a public node, and try to contact some well-known master
180	servers to become part of the network.
181
182	initialise_node undef, "master1", "master2";
183
184	Example: become a public node listening on port C<4041>.
185
186	initialise_node 4041;
187
188	Example: become a public node, only visible on localhost port 4044.
189
190	initialise_node "locahost:4044";
191
192	Example: become a slave node to any of the specified master servers.
193
194	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
195
196	=item $cv = resolve_node $noderef
197
198	Takes an unresolved node reference that may contain hostnames and
199	abbreviated IDs, resolves all of them and returns a resolved node
200	reference.
201
202	In addition to C<address:port> pairs allowed in resolved noderefs, the
203	following forms are supported:
204
205	=over 4	250	=over 4
206		251
207	=item the empty string	252	=item step 1, gathering configuration from profiles
208		253
209	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
210	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.
211		258
212	=item naked port numbers (e.g. C<1234>)	259	The profile data is then gathered as follows:
213		260
214	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
215	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).
216		266
217	=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.
218		270
219	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
220	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
221	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.
222		295
223	=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)"
224		323
225	=item $SELF	324	=item $SELF
226		325
227	Contains the current port id while executing C<rcv> callbacks or C<psub>	326	Contains the current port id while executing C<rcv> callbacks or C<psub>
228	blocks.	327	blocks.
229		328
230	=item SELF, %SELF, @SELF...	329	=item *SELF, SELF, %SELF, @SELF...
231		330
232	Due to some quirks in how perl exports variables, it is impossible to	331	Due to some quirks in how perl exports variables, it is impossible to
233	just export C<$SELF>, all the symbols called C<SELF> are exported by this	332	just export C<$SELF>, all the symbols named C<SELF> are exported by this
234	module, but only C<$SELF> is currently used.	333	module, but only C<$SELF> is currently used.
235		334
236	=item snd $port, type => @data	335	=item snd $port, type => @data
237		336
238	=item snd $port, @msg	337	=item snd $port, @msg
239		338
240	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
241	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.
242	stringifies a sa port ID (such as a port object :).
243		341
244	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
245	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
246	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.
247		346
248	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
249	function: modifying any argument is not allowed and can cause many	348	function: modifying any argument (or values referenced by them) is
250	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.
251		353
252	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
253	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
254	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
255	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
256	node, anything can be passed.	358	node, anything can be passed. Best rely only on the common denominator of
		359	these.
257		360
258	=item $local_port = port	361	=item $local_port = port
259		362
260	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
261	matching port ("full port") or a single-callback port ("miniport"),	364	no callbacks set and will throw an error when it receives messages.
262	depending on how C<rcv> callbacks are bound to the object.
263		365
264	=item $port = port { my @msg = @_; $finished }	366	=item $local_port = port { my @msg = @_ }
265		367
266	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
267	matching behind it, and returns its ID. Semantically the same as creating
268	a port and calling C<rcv $port, $callback> on it.	369	creating a port and calling C<rcv $port, $callback> on it.
269		370
270	The block will be called for every message received on the port. When the	371	The block will be called for every message received on the port, with the
271	callback returns a true value its job is considered "done" and the port	372	global variable C<$SELF> set to the port ID. Runtime errors will cause the
272	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.
273		375
274	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:
275	be passed to the callback.
276		377
277	If you need the local port id in the callback, this works nicely:	378	my $port = port {
278		379	my @msg = @_;
279	my $port; $port = port {	380	...
280	snd $otherport, reply => $port;	381	kil $SELF;
281	};	382	};
282		383
283	=cut	384	=cut
284		385
285	sub rcv($@);	386	sub rcv($@);
286		387
		388	sub _kilme {
		389	die "received message on port without callback";
		390	}
		391
287	sub port(;&) {	392	sub port(;&) {
288	my $id = "$UNIQ." . $ID++;	393	my $id = "$UNIQ." . ++$ID;
289	my $port = "$NODE#$id";	394	my $port = "$NODE#$id";
290		395
291	if (@_) {	396	rcv $port, shift \|\| \&_kilme;
292	rcv $port, shift;
293	} else {
294	$PORT{$id} = sub { }; # nop
295	}
296		397
297	$port	398	$port
298	}	399	}
299		400
300	=item reg $port, $name
301
302	Registers the given port under the name C<$name>. If the name already
303	exists it is replaced.
304
305	A port can only be registered under one well known name.
306
307	A port automatically becomes unregistered when it is killed.
308
309	=cut
310
311	sub reg(@) {
312	my ($port, $name) = @_;
313
314	$REG{$name} = $port;
315	}
316
317	=item rcv $port, $callback->(@msg)	401	=item rcv $local_port, $callback->(@msg)
318		402
319	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
320	one if required).	404	remove the default callback: use C<sub { }> to disable it, or better
321		405	C<kil> the port when it is no longer needed.
322	=item rcv $port, tagstring => $callback->(@msg), ...
323
324	=item rcv $port, $smartmatch => $callback->(@msg), ...
325
326	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
327
328	Register callbacks to be called on matching messages on the given full
329	port (after converting it to one if required).
330
331	The callback has to return a true value when its work is done, after
332	which is will be removed, or a false value in which case it will stay
333	registered.
334		406
335	The global C<$SELF> (exported by this module) contains C<$port> while	407	The global C<$SELF> (exported by this module) contains C<$port> while
336	executing the callback.	408	executing the callback. Runtime errors during callback execution will
		409	result in the port being C<kil>ed.
337		410
338	Runtime errors wdurign callback execution will result in the port being	411	The default callback received all messages not matched by a more specific
339	C<kil>ed.	412	C<tag> match.
340		413
341	If the match is an array reference, then it will be matched against the	414	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
342	first elements of the message, otherwise only the first element is being
343	matched.
344		415
345	Any element in the match that is specified as C<_any_> (a function	416	Register (or replace) callbacks to be called on messages starting with the
346	exported by this module) matches any single element of the message.	417	given tag on the given port (and return the port), or unregister it (when
		418	C<$callback> is C<$undef> or missing). There can only be one callback
		419	registered for each tag.
347		420
348	While not required, it is highly recommended that the first matching	421	The original message will be passed to the callback, after the first
349	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
350	also the most efficient match (by far).	423	environment as the default callback (see above).
		424
		425	Example: create a port and bind receivers on it in one go.
		426
		427	my $port = rcv port,
		428	msg1 => sub { ... },
		429	msg2 => sub { ... },
		430	;
		431
		432	Example: create a port, bind receivers and send it in a message elsewhere
		433	in one go:
		434
		435	snd $otherport, reply =>
		436	rcv port,
		437	msg1 => sub { ... },
		438	...
		439	;
		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, $otherport;
		448	};
351		449
352	=cut	450	=cut
353		451
354	sub rcv($@) {	452	sub rcv($@) {
355	my $port = shift;	453	my $port = shift;
356	my ($noderef, $portid) = split /#/, $port, 2;	454	my ($nodeid, $portid) = split /#/, $port, 2;
357		455
358	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	456	$NODE{$nodeid} == $NODE{""}
359	or Carp::croak "$port: rcv can only be called on local ports, caught";	457	or Carp::croak "$port: rcv can only be called on local ports, caught";
360		458
361	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 {
362	my $cb = shift;	467	my $cb = shift;
363	delete $PORT_DATA{$portid};
364	$PORT{$portid} = sub {	468	$PORT{$portid} = sub {
365	local $SELF = $port;	469	local $SELF = $port;
366	eval {	470	eval { &$cb }; _self_die if $@;
367	&$cb	471	};
368	and kil $port;
369	};	472	}
370	_self_die if $@;	473	} elsif (defined $_[0]) {
371	};
372	} else {
373	my $self = $PORT_DATA{$portid} \|\|= do {	474	my $self = $PORT_DATA{$portid} \|\|= do {
374	my $self = bless {	475	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
375	id => $port,
376	}, "AnyEvent::MP::Port";
377		476
378	$PORT{$portid} = sub {	477	$PORT{$portid} = sub {
379	local $SELF = $port;	478	local $SELF = $port;
380		479
381	eval {
382	for (@{ $self->{rc0}{$_[0]} }) {	480	if (my $cb = $self->[1]{$_[0]}) {
383	$_ && &{$_->[0]}	481	shift;
384	&& undef $_;	482	eval { &$cb }; _self_die if $@;
385	}	483	} else {
386
387	for (@{ $self->{rcv}{$_[0]} }) {
388	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
389	&& &{$_->[0]}	484	&{ $self->[0] };
390	&& undef $_;
391	}
392
393	for (@{ $self->{any} }) {
394	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
395	&& &{$_->[0]}
396	&& undef $_;
397	}	485	}
398	};	486	};
399	_self_die if $@;	487
		488	$self
400	};	489	};
401		490
402	$self
403	};
404
405	"AnyEvent::MP::Port" eq ref $self	491	"AnyEvent::MP::Port" eq ref $self
406	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	492	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
407		493
408	while (@_) {
409	my ($match, $cb) = splice @_, 0, 2;	494	my ($tag, $cb) = splice @_, 0, 2;
410		495
411	if (!ref $match) {	496	if (defined $cb) {
412	push @{ $self->{rc0}{$match} }, [$cb];	497	$self->[1]{$tag} = $cb;
413	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
414	my ($type, @match) = @$match;
415	@match
416	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
417	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
418	} else {	498	} else {
419	push @{ $self->{any} }, [$cb, $match];	499	delete $self->[1]{$tag};
420	}	500	}
421	}	501	}
422	}	502	}
423		503
424	$port	504	$port
425	}	505	}
426		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
427	=item $closure = psub { BLOCK }	544	=item $closure = psub { BLOCK }
428		545
429	Remembers C<$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
430	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>
431	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 $SELF, sub {
		551	BLOCK }, @_ } >>.
432		552
433	This is useful when you register callbacks from C<rcv> callbacks:	553	This is useful when you register callbacks from C<rcv> callbacks:
434		554
435	rcv delayed_reply => sub {	555	rcv delayed_reply => sub {
436	my ($delay, @reply) = @_;	556	my ($delay, @reply) = @_;
…		…
460	$res	580	$res
461	}	581	}
462	}	582	}
463	}	583	}
464		584
465	=item $guard = mon $port, $cb->(@reason)	585	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
466		586
467	=item $guard = mon $port, $otherport	587	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
468		588
469	=item $guard = mon $port, $otherport, @msg	589	=item $guard = mon $port # kill $SELF when $port dies
470		590
		591	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
		592
471	Monitor the given port and do something when the port is killed.	593	Monitor the given port and do something when the port is killed or
		594	messages to it were lost, and optionally return a guard that can be used
		595	to stop monitoring again.
472		596
473	In the first form, the callback is simply called with any number	597	In the first form (callback), the callback is simply called with any
474	of C<@reason> elements (no @reason means that the port was deleted	598	number of C<@reason> elements (no @reason means that the port was deleted
475	"normally"). Note also that I<< the callback B<must> never die >>, so use	599	"normally"). Note also that I<< the callback B<must> never die >>, so use
476	C<eval> if unsure.	600	C<eval> if unsure.
477		601
478	In the second form, the other port will be C<kil>'ed with C<@reason>, iff	602	In the second form (another port given), the other port (C<$rcvport>)
479	a @reason was specified, i.e. on "normal" kils nothing happens, while	603	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
480	under all other conditions, the other port is killed with the same reason.	604	"normal" kils nothing happens, while under all other conditions, the other
		605	port is killed with the same reason.
481		606
		607	The third form (kill self) is the same as the second form, except that
		608	C<$rvport> defaults to C<$SELF>.
		609
482	In the last form, a message of the form C<@msg, @reason> will be C<snd>.	610	In the last form (message), a message of the form C<@msg, @reason> will be
		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.
		615
		616	As a rule of thumb, monitoring requests should always monitor a port from
		617	a local port (or callback). The reason is that kill messages might get
		618	lost, just like any other message. Another less obvious reason is that
		619	even monitoring requests can get lost (for example, when the connection
		620	to the other node goes down permanently). When monitoring a port locally
		621	these problems do not exist.
		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.
483		639
484	Example: call a given callback when C<$port> is killed.	640	Example: call a given callback when C<$port> is killed.
485		641
486	mon $port, sub { warn "port died because of <@_>\n" };	642	mon $port, sub { warn "port died because of <@_>\n" };
487		643
488	Example: kill ourselves when C<$port> is killed abnormally.	644	Example: kill ourselves when C<$port> is killed abnormally.
489		645
490	mon $port, $self;	646	mon $port;
491		647
492	Example: send us a restart message another C<$port> is killed.	648	Example: send us a restart message when another C<$port> is killed.
493		649
494	mon $port, $self => "restart";	650	mon $port, $self => "restart";
495		651
496	=cut	652	=cut
497		653
498	sub mon {	654	sub mon {
499	my ($noderef, $port) = split /#/, shift, 2;	655	my ($nodeid, $port) = split /#/, shift, 2;
500		656
501	my $node = $NODE{$noderef} \|\| add_node $noderef;	657	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
502		658
503	my $cb = shift;	659	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
504		660
505	unless (ref $cb) {	661	unless (ref $cb) {
506	if (@_) {	662	if (@_) {
507	# send a kill info message	663	# send a kill info message
508	my (@msg) = ($cb, @_);	664	my (@msg) = ($cb, @_);
…		…
515	}	671	}
516		672
517	$node->monitor ($port, $cb);	673	$node->monitor ($port, $cb);
518		674
519	defined wantarray	675	defined wantarray
520	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	676	and ($cb += 0, AnyEvent::Util::guard { $node->unmonitor ($port, $cb) })
521	}	677	}
522		678
523	=item $guard = mon_guard $port, $ref, $ref...	679	=item $guard = mon_guard $port, $ref, $ref...
524		680
525	Monitors the given C<$port> and keeps the passed references. When the port	681	Monitors the given C<$port> and keeps the passed references. When the port
526	is killed, the references will be freed.	682	is killed, the references will be freed.
527		683
528	Optionally returns a guard that will stop the monitoring.	684	Optionally returns a guard that will stop the monitoring.
529		685
530	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
531	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>):
532		688
533	$port->rcv (start => sub {	689	$port->rcv (start => sub {
534	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	690	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
535	undef $timer if 0.9 < rand;	691	undef $timer if 0.9 < rand;
536	});	692	});
537	});	693	});
538		694
539	=cut	695	=cut
540		696
541	sub mon_guard {	697	sub mon_guard {
542	my ($port, @refs) = @_;	698	my ($port, @refs) = @_;
543		699
		700	#TODO: mon-less form?
		701
544	mon $port, sub { 0 && @refs }	702	mon $port, sub { 0 && @refs }
545	}	703	}
546		704
547	=item lnk $port1, $port2
548
549	Link two ports. This is simply a shorthand for:
550
551	mon $port1, $port2;
552	mon $port2, $port1;
553
554	It means that if either one is killed abnormally, the other one gets
555	killed as well.
556
557	=item kil $port[, @reason]	705	=item kil $port[, @reason]
558		706
559	Kill the specified port with the given C<@reason>.	707	Kill the specified port with the given C<@reason>.
560		708
561	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" -
562	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.
563		712
564	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>
565	C<mon>, see below).	714	form) get killed with the same reason.
566		715
567	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
568	will be reported as reason C<< die => $@ >>.	717	will be reported as reason C<< die => $@ >>.
569		718
570	Transport/communication errors are reported as C<< transport_error =>	719	Transport/communication errors are reported as C<< transport_error =>
571	$message >>.	720	$message >>.
572		721
		722	=cut
		723
		724	=item $port = spawn $node, $initfunc[, @initdata]
		725
		726	Creates a port on the node C<$node> (which can also be a port ID, in which
		727	case it's the node where that port resides).
		728
		729	The port ID of the newly created port is returned immediately, and it is
		730	possible to immediately start sending messages or to monitor the port.
		731
		732	After the port has been created, the init function is called on the remote
		733	node, in the same context as a C<rcv> callback. This function must be a
		734	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		735	specify a function in the main program, use C<::name>.
		736
		737	If the function doesn't exist, then the node tries to C<require>
		738	the package, then the package above the package and so on (e.g.
		739	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		740	exists or it runs out of package names.
		741
		742	The init function is then called with the newly-created port as context
		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.
		746
		747	A common idiom is to pass a local port, immediately monitor the spawned
		748	port, and in the remote init function, immediately monitor the passed
		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<$initfunc> has no visible effects on the
		753	caller before C<spawn> returns (by delaying invocation when spawn is
		754	called for the local node).
		755
		756	Example: spawn a chat server port on C<$othernode>.
		757
		758	# this node, executed from within a port context:
		759	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		760	mon $server;
		761
		762	# init function on C<$othernode>
		763	sub connect {
		764	my ($srcport) = @_;
		765
		766	mon $srcport;
		767
		768	rcv $SELF, sub {
		769	...
		770	};
		771	}
		772
		773	=cut
		774
		775	sub _spawn {
		776	my $port = shift;
		777	my $init = shift;
		778
		779	# rcv will create the actual port
		780	local $SELF = "$NODE#$port";
		781	eval {
		782	&{ load_func $init }
		783	};
		784	_self_die if $@;
		785	}
		786
		787	sub spawn(@) {
		788	my ($nodeid, undef) = split /#/, shift, 2;
		789
		790	my $id = "$RUNIQ." . ++$ID;
		791
		792	$_[0] =~ /::/
		793	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		794
		795	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		796
		797	"$nodeid#$id"
		798	}
		799
		800
		801	=item after $timeout, @msg
		802
		803	=item after $timeout, $callback
		804
		805	Either sends the given message, or call the given callback, after the
		806	specified number of seconds.
		807
		808	This is simply a utility function that comes in handy at times - the
		809	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		810	so it may go away in the future.
		811
		812	=cut
		813
		814	sub after($@) {
		815	my ($timeout, @action) = @_;
		816
		817	my $t; $t = AE::timer $timeout, 0, sub {
		818	undef $t;
		819	ref $action[0]
		820	? $action[0]()
		821	: snd @action;
		822	};
		823	}
		824
		825	=item cal $port, @msg, $callback[, $timeout]
		826
		827	A simple form of RPC - sends a message to the given C<$port> with the
		828	given contents (C<@msg>), but adds a reply port to the message.
		829
		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.
		832
		833	A reply message sent to the port is passed to the C<$callback> as-is.
		834
		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.
		838
		839	If no time-out is given (or it is C<undef>), then the local port will
		840	monitor the remote port instead, so it eventually gets cleaned-up.
		841
		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.
		845
		846	=cut
		847
		848	sub cal(@) {
		849	my $timeout = ref $_[-1] ? undef : pop;
		850	my $cb = pop;
		851
		852	my $port = port {
		853	undef $timeout;
		854	kil $SELF;
		855	&$cb;
		856	};
		857
		858	if (defined $timeout) {
		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	}
		870
		871	push @_, $port;
		872	&snd;
		873
		874	$port
		875	}
		876
573	=back	877	=back
574		878
575	=head1 NODE MESSAGES
576
577	Nodes understand the following messages sent to them. Many of them take
578	arguments called C<@reply>, which will simply be used to compose a reply
579	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
580	the remaining arguments are simply the message data.
581
582	While other messages exist, they are not public and subject to change.
583
584	=over 4
585
586	=cut
587
588	=item lookup => $name, @reply
589
590	Replies with the port ID of the specified well-known port, or C<undef>.
591
592	=item devnull => ...
593
594	Generic data sink/CPU heat conversion.
595
596	=item relay => $port, @msg
597
598	Simply forwards the message to the given port.
599
600	=item eval => $string[ @reply]
601
602	Evaluates the given string. If C<@reply> is given, then a message of the
603	form C<@reply, $@, @evalres> is sent.
604
605	Example: crash another node.
606
607	snd $othernode, eval => "exit";
608
609	=item time => @reply
610
611	Replies the the current node time to C<@reply>.
612
613	Example: tell the current node to send the current time to C<$myport> in a
614	C<timereply> message.
615
616	snd $NODE, time => $myport, timereply => 1, 2;
617	# => snd $myport, timereply => 1, 2, <time>
618
619	=back
620
621	=head1 AnyEvent::MP vs. Distributed Erlang	879	=head1 AnyEvent::MP vs. Distributed Erlang
622		880
623	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
624	== 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
625	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
626	sample:	884	sample:
627		885
628	http://www.erlang.se/doc/programming_rules.shtml	886	http://www.erlang.se/doc/programming_rules.shtml
629	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
630	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
…		…
632		890
633	Despite the similarities, there are also some important differences:	891	Despite the similarities, there are also some important differences:
634		892
635	=over 4	893	=over 4
636		894
637	=item * Node references contain the recipe on how to contact them.	895	=item * Node IDs are arbitrary strings in AEMP.
638		896
639	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
640	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
641	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.
642		901
643	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
644	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.
645		916
646	=item * Erlang uses processes and a mailbox, AEMP does not queue.	917	=item * Erlang uses processes and a mailbox, AEMP does not queue.
647		918
648	Erlang uses processes that selctively receive messages, and therefore	919	Erlang uses processes that selectively receive messages out of order, and
649	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
650	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.
651		924
652	(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.
653		930
654	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	931	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
655		932
656	Sending messages in erlang is synchronous and blocks the process. AEMP	933	Sending messages in Erlang is synchronous and blocks the process until
657	sends are immediate, connection establishment is handled in the	934	a conenction has been established and the message sent (and so does not
658	background.	935	need a queue that can overflow). AEMP sends return immediately, connection
		936	establishment is handled in the background.
659		937
660	=item * Erlang can silently lose messages, AEMP cannot.	938	=item * Erlang suffers from silent message loss, AEMP does not.
661		939
662	Erlang makes few guarantees on messages delivery - messages can get lost	940	Erlang implements few guarantees on messages delivery - messages can get
663	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,
664	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).
665		943
666	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
667	holes in the message sequence.	947	no silent "holes" in the message sequence.
668		948
669	=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
670	alive.	950	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
671		951	simply tries to work better in common error cases, such as when a network
672	In erlang it can happen that a monitored process is declared dead and	952	link goes down.
673	linked processes get killed, but later it turns out that the process is
674	still alive - and can receive messages.
675
676	In AEMP, when port monitoring detects a port as dead, then that port will
677	eventually be killed - it cannot happen that a node detects a port as dead
678	and then later sends messages to it, finding it is still alive.
679		953
680	=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.
681		955
682	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
683	ID known to other nodes for a completely different process, causing	957	process ID known to other nodes for a completely different process,
684	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.
685		960
686	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
687	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.
688		963
689	=item * Erlang uses unprotected connections, AEMP uses secure	964	=item * Erlang uses unprotected connections, AEMP uses secure
690	authentication and can use TLS.	965	authentication and can use TLS.
691		966
692	AEMP can use a proven protocol - SSL/TLS - to protect connections and	967	AEMP can use a proven protocol - TLS - to protect connections and
693	securely authenticate nodes.	968	securely authenticate nodes.
694		969
695	=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
696	communications.	971	communications.
697		972
698	The AEMP protocol, unlike the erlang protocol, supports both	973	The AEMP protocol, unlike the Erlang protocol, supports both programming
699	language-independent text-only protocols (good for debugging) and binary,	974	language independent text-only protocols (good for debugging), and binary,
700	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.
701		977
702	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
703	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
704	protocol simple.	980	protocol simple.
705		981
		982	=item * AEMP has more flexible monitoring options than Erlang.
		983
		984	In Erlang, you can chose to receive I<all> exit signals as messages or
		985	I<none>, there is no in-between, so monitoring single Erlang processes is
		986	difficult to implement.
		987
		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.
		990
		991	=item * Erlang tries to hide remote/local connections, AEMP does not.
		992
		993	Monitoring in Erlang is not an indicator of process death/crashes, in the
		994	same way as linking is (except linking is unreliable in Erlang).
		995
		996	In AEMP, you don't "look up" registered port names or send to named ports
		997	that might or might not be persistent. Instead, you normally spawn a port
		998	on the remote node. The init function monitors you, and you monitor the
		999	remote port. Since both monitors are local to the node, they are much more
		1000	reliable (no need for C<spawn_link>).
		1001
		1002	This also saves round-trips and avoids sending messages to the wrong port
		1003	(hard to do in Erlang).
		1004
706	=back	1005	=back
707		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
708	=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.
709		1055
710	L<AnyEvent>.	1056	L<AnyEvent>.
711		1057
712	=head1 AUTHOR	1058	=head1 AUTHOR
713		1059

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