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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.38 by root, Fri Aug 7 22:55:18 2009 UTC vs.
Revision 1.121 by root, Tue Feb 28 18:37:24 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. The
236	specified.	273	special node ID of C<anon/> will be replaced by a random node ID.
		274
		275	=item step 2, bind listener sockets
		276
		277	The next step is to look up the binds in the profile, followed by binding
		278	aemp protocol listeners on all binds specified (it is possible and valid
		279	to have no binds, meaning that the node cannot be contacted form the
		280	outside. This means the node cannot talk to other nodes that also have no
		281	binds, but it can still talk to all "normal" nodes).
		282
		283	If the profile does not specify a binds list, then a default of C<*> is
		284	used, meaning the node will bind on a dynamically-assigned port on every
		285	local IP address it finds.
		286
		287	=item step 3, connect to seed nodes
		288
		289	As the last step, the seed ID list from the profile is passed to the
		290	L<AnyEvent::MP::Global> module, which will then use it to keep
		291	connectivity with at least one node at any point in time.
237		292
238	=back	293	=back
		294
		295	Example: become a distributed node using the local node name as profile.
		296	This should be the most common form of invocation for "daemon"-type nodes.
		297
		298	configure
		299
		300	Example: become an anonymous node. This form is often used for commandline
		301	clients.
		302
		303	configure nodeid => "anon/";
		304
		305	Example: configure a node using a profile called seed, which is suitable
		306	for a seed node as it binds on all local addresses on a fixed port (4040,
		307	customary for aemp).
		308
		309	# use the aemp commandline utility
		310	# aemp profile seed nodeid anon/ binds '*:4040'
		311
		312	# then use it
		313	configure profile => "seed";
		314
		315	# or simply use aemp from the shell again:
		316	# aemp run profile seed
		317
		318	# or provide a nicer-to-remember nodeid
		319	# aemp run profile seed nodeid "$(hostname)"
239		320
240	=item $SELF	321	=item $SELF
241		322
242	Contains the current port id while executing C<rcv> callbacks or C<psub>	323	Contains the current port id while executing C<rcv> callbacks or C<psub>
243	blocks.	324	blocks.
244		325
245	=item SELF, %SELF, @SELF...	326	=item *SELF, SELF, %SELF, @SELF...
246		327
247	Due to some quirks in how perl exports variables, it is impossible to	328	Due to some quirks in how perl exports variables, it is impossible to
248	just export C<$SELF>, all the symbols called C<SELF> are exported by this	329	just export C<$SELF>, all the symbols named C<SELF> are exported by this
249	module, but only C<$SELF> is currently used.	330	module, but only C<$SELF> is currently used.
250		331
251	=item snd $port, type => @data	332	=item snd $port, type => @data
252		333
253	=item snd $port, @msg	334	=item snd $port, @msg
254		335
255	Send the given message to the given port ID, which can identify either	336	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	337	local or a remote port, and must be a port ID.
257	stringifies a sa port ID (such as a port object :).
258		338
259	While the message can be about anything, it is highly recommended to use a	339	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	340	use a string as first element (a port ID, or some word that indicates a
261	type etc.).	341	request type etc.) and to consist if only simple perl values (scalars,
		342	arrays, hashes) - if you think you need to pass an object, think again.
262		343
263	The message data effectively becomes read-only after a call to this	344	The message data logically becomes read-only after a call to this
264	function: modifying any argument is not allowed and can cause many	345	function: modifying any argument (or values referenced by them) is
265	problems.	346	forbidden, as there can be considerable time between the call to C<snd>
		347	and the time the message is actually being serialised - in fact, it might
		348	never be copied as within the same process it is simply handed to the
		349	receiving port.
266		350
267	The type of data you can transfer depends on the transport protocol: when	351	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	352	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	353	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	354	that Storable can serialise and deserialise is allowed, and for the local
271	node, anything can be passed.	355	node, anything can be passed. Best rely only on the common denominator of
		356	these.
272		357
273	=item $local_port = port	358	=item $local_port = port
274		359
275	Create a new local port object that can be used either as a pattern	360	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"),	361	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		362
279	=item $port = port { my @msg = @_; $finished }	363	=item $local_port = port { my @msg = @_ }
280		364
281	Creates a "miniport", that is, a very lightweight port without any pattern	365	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.	366	creating a port and calling C<rcv $port, $callback> on it.
284		367
285	The block will be called for every message received on the port. When the	368	The block will be called for every message received on the port, with the
286	callback returns a true value its job is considered "done" and the port	369	global variable C<$SELF> set to the port ID. Runtime errors will cause the
287	will be destroyed. Otherwise it will stay alive.	370	port to be C<kil>ed. The message will be passed as-is, no extra argument
		371	(i.e. no port ID) will be passed to the callback.
288		372
289	The message will be passed as-is, no extra argument (i.e. no port id) will	373	If you want to stop/destroy the port, simply C<kil> it:
290	be passed to the callback.
291		374
292	If you need the local port id in the callback, this works nicely:	375	my $port = port {
293		376	my @msg = @_;
294	my $port; $port = port {	377	...
295	snd $otherport, reply => $port;	378	kil $SELF;
296	};	379	};
297		380
298	=cut	381	=cut
299		382
300	sub rcv($@);	383	sub rcv($@);
301		384
		385	sub _kilme {
		386	die "received message on port without callback";
		387	}
		388
302	sub port(;&) {	389	sub port(;&) {
303	my $id = "$UNIQ." . $ID++;	390	my $id = "$UNIQ." . ++$ID;
304	my $port = "$NODE#$id";	391	my $port = "$NODE#$id";
305		392
306	if (@_) {	393	rcv $port, shift \|\| \&_kilme;
307	rcv $port, shift;
308	} else {
309	$PORT{$id} = sub { }; # nop
310	}
311		394
312	$port	395	$port
313	}	396	}
314		397
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)	398	=item rcv $local_port, $callback->(@msg)
335		399
336	Replaces the callback on the specified miniport (after converting it to	400	Replaces the default callback on the specified port. There is no way to
337	one if required).	401	remove the default callback: use C<sub { }> to disable it, or better
338		402	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...] => $callback->(@msg), ...
344
345	Register callbacks to be called on matching messages on the given full
346	port (after converting it to one if required) and return the port.
347
348	The callback has to return a true value when its work is done, after
349	which is will be removed, or a false value in which case it will stay
350	registered.
351		403
352	The global C<$SELF> (exported by this module) contains C<$port> while	404	The global C<$SELF> (exported by this module) contains C<$port> while
353	executing the callback.	405	executing the callback. Runtime errors during callback execution will
		406	result in the port being C<kil>ed.
354		407
355	Runtime errors during callback execution will result in the port being	408	The default callback received all messages not matched by a more specific
356	C<kil>ed.	409	C<tag> match.
357		410
358	If the match is an array reference, then it will be matched against the	411	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
359	first elements of the message, otherwise only the first element is being
360	matched.
361		412
362	Any element in the match that is specified as C<_any_> (a function	413	Register (or replace) callbacks to be called on messages starting with the
363	exported by this module) matches any single element of the message.	414	given tag on the given port (and return the port), or unregister it (when
		415	C<$callback> is C<$undef> or missing). There can only be one callback
		416	registered for each tag.
364		417
365	While not required, it is highly recommended that the first matching	418	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	419	element (the tag) has been removed. The callback will use the same
367	also the most efficient match (by far).	420	environment as the default callback (see above).
368		421
369	Example: create a port and bind receivers on it in one go.	422	Example: create a port and bind receivers on it in one go.
370		423
371	my $port = rcv port,	424	my $port = rcv port,
372	msg1 => sub { ...; 0 },	425	msg1 => sub { ... },
373	msg2 => sub { ...; 0 },	426	msg2 => sub { ... },
374	;	427	;
375		428
376	Example: create a port, bind receivers and send it in a message elsewhere	429	Example: create a port, bind receivers and send it in a message elsewhere
377	in one go:	430	in one go:
378		431
379	snd $otherport, reply =>	432	snd $otherport, reply =>
380	rcv port,	433	rcv port,
381	msg1 => sub { ...; 0 },	434	msg1 => sub { ... },
382	...	435	...
383	;	436	;
384		437
		438	Example: temporarily register a rcv callback for a tag matching some port
		439	(e.g. for an rpc reply) and unregister it after a message was received.
		440
		441	rcv $port, $otherport => sub {
		442	my @reply = @_;
		443
		444	rcv $SELF, $otherport;
		445	};
		446
385	=cut	447	=cut
386		448
387	sub rcv($@) {	449	sub rcv($@) {
388	my $port = shift;	450	my $port = shift;
389	my ($noderef, $portid) = split /#/, $port, 2;	451	my ($nodeid, $portid) = split /#/, $port, 2;
390		452
391	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	453	$NODE{$nodeid} == $NODE{""}
392	or Carp::croak "$port: rcv can only be called on local ports, caught";	454	or Carp::croak "$port: rcv can only be called on local ports, caught";
393		455
394	if (@_ == 1) {	456	while (@_) {
		457	if (ref $_[0]) {
		458	if (my $self = $PORT_DATA{$portid}) {
		459	"AnyEvent::MP::Port" eq ref $self
		460	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		461
		462	$self->[0] = shift;
		463	} else {
395	my $cb = shift;	464	my $cb = shift;
396	delete $PORT_DATA{$portid};
397	$PORT{$portid} = sub {	465	$PORT{$portid} = sub {
398	local $SELF = $port;	466	local $SELF = $port;
399	eval {	467	eval { &$cb }; _self_die if $@;
400	&$cb	468	};
401	and kil $port;
402	};	469	}
403	_self_die if $@;	470	} elsif (defined $_[0]) {
404	};
405	} else {
406	my $self = $PORT_DATA{$portid} \|\|= do {	471	my $self = $PORT_DATA{$portid} \|\|= do {
407	my $self = bless {	472	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
408	id => $port,
409	}, "AnyEvent::MP::Port";
410		473
411	$PORT{$portid} = sub {	474	$PORT{$portid} = sub {
412	local $SELF = $port;	475	local $SELF = $port;
413		476
414	eval {
415	for (@{ $self->{rc0}{$_[0]} }) {	477	if (my $cb = $self->[1]{$_[0]}) {
416	$_ && &{$_->[0]}	478	shift;
417	&& undef $_;	479	eval { &$cb }; _self_die if $@;
418	}	480	} else {
419
420	for (@{ $self->{rcv}{$_[0]} }) {
421	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
422	&& &{$_->[0]}	481	&{ $self->[0] };
423	&& undef $_;
424	}
425
426	for (@{ $self->{any} }) {
427	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
428	&& &{$_->[0]}
429	&& undef $_;
430	}	482	}
431	};	483	};
432	_self_die if $@;	484
		485	$self
433	};	486	};
434		487
435	$self
436	};
437
438	"AnyEvent::MP::Port" eq ref $self	488	"AnyEvent::MP::Port" eq ref $self
439	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	489	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
440		490
441	while (@_) {
442	my ($match, $cb) = splice @_, 0, 2;	491	my ($tag, $cb) = splice @_, 0, 2;
443		492
444	if (!ref $match) {	493	if (defined $cb) {
445	push @{ $self->{rc0}{$match} }, [$cb];	494	$self->[1]{$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 {	495	} else {
452	push @{ $self->{any} }, [$cb, $match];	496	delete $self->[1]{$tag};
453	}	497	}
454	}	498	}
455	}	499	}
456		500
457	$port	501	$port
458	}	502	}
459		503
		504	=item peval $port, $coderef[, @args]
		505
		506	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		507	when the code throews an exception the C<$port> will be killed.
		508
		509	Any remaining args will be passed to the callback. Any return values will
		510	be returned to the caller.
		511
		512	This is useful when you temporarily want to execute code in the context of
		513	a port.
		514
		515	Example: create a port and run some initialisation code in it's context.
		516
		517	my $port = port { ... };
		518
		519	peval $port, sub {
		520	init
		521	or die "unable to init";
		522	};
		523
		524	=cut
		525
		526	sub peval($$) {
		527	local $SELF = shift;
		528	my $cb = shift;
		529
		530	if (wantarray) {
		531	my @res = eval { &$cb };
		532	_self_die if $@;
		533	@res
		534	} else {
		535	my $res = eval { &$cb };
		536	_self_die if $@;
		537	$res
		538	}
		539	}
		540
460	=item $closure = psub { BLOCK }	541	=item $closure = psub { BLOCK }
461		542
462	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	543	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>	544	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.	545	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		546
		547	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		548	BLOCK }, @_ } >>.
465		549
466	This is useful when you register callbacks from C<rcv> callbacks:	550	This is useful when you register callbacks from C<rcv> callbacks:
467		551
468	rcv delayed_reply => sub {	552	rcv delayed_reply => sub {
469	my ($delay, @reply) = @_;	553	my ($delay, @reply) = @_;
…		…
493	$res	577	$res
494	}	578	}
495	}	579	}
496	}	580	}
497		581
498	=item $guard = mon $port, $cb->(@reason)	582	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
499		583
500	=item $guard = mon $port, $rcvport	584	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
501		585
502	=item $guard = mon $port	586	=item $guard = mon $port # kill $SELF when $port dies
503		587
504	=item $guard = mon $port, $rcvport, @msg	588	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
505		589
506	Monitor the given port and do something when the port is killed, and	590	Monitor the given port and do something when the port is killed or
507	optionally return a guard that can be used to stop monitoring again.	591	messages to it were lost, and optionally return a guard that can be used
		592	to stop monitoring again.
508		593
509	In the first form (callback), the callback is simply called with any	594	In the first form (callback), the callback is simply called with any
510	number of C<@reason> elements (no @reason means that the port was deleted	595	number of C<@reason> elements (no @reason means that the port was deleted
511	"normally"). Note also that I<< the callback B<must> never die >>, so use	596	"normally"). Note also that I<< the callback B<must> never die >>, so use
512	C<eval> if unsure.	597	C<eval> if unsure.
513		598
514	In the second form (another port given), the other port (C<$rcvport)	599	In the second form (another port given), the other port (C<$rcvport>)
515	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	600	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
516	"normal" kils nothing happens, while under all other conditions, the other	601	"normal" kils nothing happens, while under all other conditions, the other
517	port is killed with the same reason.	602	port is killed with the same reason.
518		603
519	The third form (kill self) is the same as the second form, except that	604	The third form (kill self) is the same as the second form, except that
520	C<$rvport> defaults to C<$SELF>.	605	C<$rvport> defaults to C<$SELF>.
521		606
522	In the last form (message), a message of the form C<@msg, @reason> will be	607	In the last form (message), a message of the form C<@msg, @reason> will be
523	C<snd>.	608	C<snd>.
		609
		610	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		611	alert was raised), they are removed and will not trigger again.
524		612
525	As a rule of thumb, monitoring requests should always monitor a port from	613	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	614	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	615	lost, just like any other message. Another less obvious reason is that
528	even monitoring requests can get lost (for exmaple, when the connection	616	even monitoring requests can get lost (for example, when the connection
529	to the other node goes down permanently). When monitoring a port locally	617	to the other node goes down permanently). When monitoring a port locally
530	these problems do not exist.	618	these problems do not exist.
531		619
		620	C<mon> effectively guarantees that, in the absence of hardware failures,
		621	after starting the monitor, either all messages sent to the port will
		622	arrive, or the monitoring action will be invoked after possible message
		623	loss has been detected. No messages will be lost "in between" (after
		624	the first lost message no further messages will be received by the
		625	port). After the monitoring action was invoked, further messages might get
		626	delivered again.
		627
		628	Inter-host-connection timeouts and monitoring depend on the transport
		629	used. The only transport currently implemented is TCP, and AnyEvent::MP
		630	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		631	non-idle connection, and usually around two hours for idle connections).
		632
		633	This means that monitoring is good for program errors and cleaning up
		634	stuff eventually, but they are no replacement for a timeout when you need
		635	to ensure some maximum latency.
		636
532	Example: call a given callback when C<$port> is killed.	637	Example: call a given callback when C<$port> is killed.
533		638
534	mon $port, sub { warn "port died because of <@_>\n" };	639	mon $port, sub { warn "port died because of <@_>\n" };
535		640
536	Example: kill ourselves when C<$port> is killed abnormally.	641	Example: kill ourselves when C<$port> is killed abnormally.
…		…
542	mon $port, $self => "restart";	647	mon $port, $self => "restart";
543		648
544	=cut	649	=cut
545		650
546	sub mon {	651	sub mon {
547	my ($noderef, $port) = split /#/, shift, 2;	652	my ($nodeid, $port) = split /#/, shift, 2;
548		653
549	my $node = $NODE{$noderef} \|\| add_node $noderef;	654	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
550		655
551	my $cb = @_ ? $_[0] : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';	656	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
552		657
553	unless (ref $cb) {	658	unless (ref $cb) {
554	if (@_) {	659	if (@_) {
555	# send a kill info message	660	# send a kill info message
556	my (@msg) = @_;	661	my (@msg) = ($cb, @_);
557	$cb = sub { snd @msg, @_ };	662	$cb = sub { snd @msg, @_ };
558	} else {	663	} else {
559	# simply kill other port	664	# simply kill other port
560	my $port = $cb;	665	my $port = $cb;
561	$cb = sub { kil $port, @_ if @_ };	666	$cb = sub { kil $port, @_ if @_ };
…		…
563	}	668	}
564		669
565	$node->monitor ($port, $cb);	670	$node->monitor ($port, $cb);
566		671
567	defined wantarray	672	defined wantarray
568	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	673	and ($cb += 0, AnyEvent::Util::guard { $node->unmonitor ($port, $cb) })
569	}	674	}
570		675
571	=item $guard = mon_guard $port, $ref, $ref...	676	=item $guard = mon_guard $port, $ref, $ref...
572		677
573	Monitors the given C<$port> and keeps the passed references. When the port	678	Monitors the given C<$port> and keeps the passed references. When the port
574	is killed, the references will be freed.	679	is killed, the references will be freed.
575		680
576	Optionally returns a guard that will stop the monitoring.	681	Optionally returns a guard that will stop the monitoring.
577		682
578	This function is useful when you create e.g. timers or other watchers and	683	This function is useful when you create e.g. timers or other watchers and
579	want to free them when the port gets killed:	684	want to free them when the port gets killed (note the use of C<psub>):
580		685
581	$port->rcv (start => sub {	686	$port->rcv (start => sub {
582	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	687	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
583	undef $timer if 0.9 < rand;	688	undef $timer if 0.9 < rand;
584	});	689	});
585	});	690	});
586		691
587	=cut	692	=cut
…		…
596		701
597	=item kil $port[, @reason]	702	=item kil $port[, @reason]
598		703
599	Kill the specified port with the given C<@reason>.	704	Kill the specified port with the given C<@reason>.
600		705
601	If no C<@reason> is specified, then the port is killed "normally" (linked	706	If no C<@reason> is specified, then the port is killed "normally" -
602	ports will not be kileld, or even notified).	707	monitor callback will be invoked, but the kil will not cause linked ports
		708	(C<mon $mport, $lport> form) to get killed.
603		709
604	Otherwise, linked ports get killed with the same reason (second form of	710	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
605	C<mon>, see below).	711	form) get killed with the same reason.
606		712
607	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	713	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
608	will be reported as reason C<< die => $@ >>.	714	will be reported as reason C<< die => $@ >>.
609		715
610	Transport/communication errors are reported as C<< transport_error =>	716	Transport/communication errors are reported as C<< transport_error =>
…		…
615	=item $port = spawn $node, $initfunc[, @initdata]	721	=item $port = spawn $node, $initfunc[, @initdata]
616		722
617	Creates a port on the node C<$node> (which can also be a port ID, in which	723	Creates a port on the node C<$node> (which can also be a port ID, in which
618	case it's the node where that port resides).	724	case it's the node where that port resides).
619		725
620	The port ID of the newly created port is return immediately, and it is	726	The port ID of the newly created port is returned immediately, and it is
621	permissible to immediately start sending messages or monitor the port.	727	possible to immediately start sending messages or to monitor the port.
622		728
623	After the port has been created, the init function is	729	After the port has been created, the init function is called on the remote
624	called. This fucntion must be a fully-qualified function name	730	node, in the same context as a C<rcv> callback. This function must be a
625	(e.g. C<MyApp::Chat::Server::init>).	731	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		732	specify a function in the main program, use C<::name>.
626		733
627	If the function doesn't exist, then the node tries to C<require>	734	If the function doesn't exist, then the node tries to C<require>
628	the package, then the package above the package and so on (e.g.	735	the package, then the package above the package and so on (e.g.
629	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	736	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
630	exists or it runs out of package names.	737	exists or it runs out of package names.
631		738
632	The init function is then called with the newly-created port as context	739	The init function is then called with the newly-created port as context
633	object (C<$SELF>) and the C<@initdata> values as arguments.	740	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		741	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		742	the port might not get created.
634		743
635	A common idiom is to pass your own port, monitor the spawned port, and	744	A common idiom is to pass a local port, immediately monitor the spawned
636	in the init function, monitor the original port. This two-way monitoring	745	port, and in the remote init function, immediately monitor the passed
637	ensures that both ports get cleaned up when there is a problem.	746	local port. This two-way monitoring ensures that both ports get cleaned up
		747	when there is a problem.
		748
		749	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		750	caller before C<spawn> returns (by delaying invocation when spawn is
		751	called for the local node).
638		752
639	Example: spawn a chat server port on C<$othernode>.	753	Example: spawn a chat server port on C<$othernode>.
640		754
641	# this node, executed from within a port context:	755	# this node, executed from within a port context:
642	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	756	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
657		771
658	sub _spawn {	772	sub _spawn {
659	my $port = shift;	773	my $port = shift;
660	my $init = shift;	774	my $init = shift;
661		775
		776	# rcv will create the actual port
662	local $SELF = "$NODE#$port";	777	local $SELF = "$NODE#$port";
663	eval {	778	eval {
664	&{ load_func $init }	779	&{ load_func $init }
665	};	780	};
666	_self_die if $@;	781	_self_die if $@;
667	}	782	}
668		783
669	sub spawn(@) {	784	sub spawn(@) {
670	my ($noderef, undef) = split /#/, shift, 2;	785	my ($nodeid, undef) = split /#/, shift, 2;
671		786
672	my $id = "$RUNIQ." . $ID++;	787	my $id = "$RUNIQ." . ++$ID;
673		788
674	($NODE{$noderef} \|\| add_node $noderef)	789	$_[0] =~ /::/
675	->send (["", "AnyEvent::MP::_spawn" => $id, @_]);	790	or Carp::croak "spawn init function must be a fully-qualified name, caught";
676		791
		792	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		793
677	"$noderef#$id"	794	"$nodeid#$id"
678	}	795	}
679		796
680	=back
681		797
682	=head1 NODE MESSAGES	798	=item after $timeout, @msg
683		799
684	Nodes understand the following messages sent to them. Many of them take	800	=item after $timeout, $callback
685	arguments called C<@reply>, which will simply be used to compose a reply
686	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
687	the remaining arguments are simply the message data.
688		801
689	While other messages exist, they are not public and subject to change.	802	Either sends the given message, or call the given callback, after the
		803	specified number of seconds.
690		804
691	=over 4	805	This is simply a utility function that comes in handy at times - the
		806	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		807	so it may go away in the future.
692		808
693	=cut	809	=cut
694		810
695	=item lookup => $name, @reply	811	sub after($@) {
		812	my ($timeout, @action) = @_;
696		813
697	Replies with the port ID of the specified well-known port, or C<undef>.	814	my $t; $t = AE::timer $timeout, 0, sub {
		815	undef $t;
		816	ref $action[0]
		817	? $action[0]()
		818	: snd @action;
		819	};
		820	}
698		821
699	=item devnull => ...	822	=item cal $port, @msg, $callback[, $timeout]
700		823
701	Generic data sink/CPU heat conversion.	824	A simple form of RPC - sends a message to the given C<$port> with the
		825	given contents (C<@msg>), but adds a reply port to the message.
702		826
703	=item relay => $port, @msg	827	The reply port is created temporarily just for the purpose of receiving
		828	the reply, and will be C<kil>ed when no longer needed.
704		829
705	Simply forwards the message to the given port.	830	A reply message sent to the port is passed to the C<$callback> as-is.
706		831
707	=item eval => $string[ @reply]	832	If an optional time-out (in seconds) is given and it is not C<undef>,
		833	then the callback will be called without any arguments after the time-out
		834	elapsed and the port is C<kil>ed.
708		835
709	Evaluates the given string. If C<@reply> is given, then a message of the	836	If no time-out is given (or it is C<undef>), then the local port will
710	form C<@reply, $@, @evalres> is sent.	837	monitor the remote port instead, so it eventually gets cleaned-up.
711		838
712	Example: crash another node.	839	Currently this function returns the temporary port, but this "feature"
		840	might go in future versions unless you can make a convincing case that
		841	this is indeed useful for something.
713		842
714	snd $othernode, eval => "exit";	843	=cut
715		844
716	=item time => @reply	845	sub cal(@) {
		846	my $timeout = ref $_[-1] ? undef : pop;
		847	my $cb = pop;
717		848
718	Replies the the current node time to C<@reply>.	849	my $port = port {
		850	undef $timeout;
		851	kil $SELF;
		852	&$cb;
		853	};
719		854
720	Example: tell the current node to send the current time to C<$myport> in a	855	if (defined $timeout) {
721	C<timereply> message.	856	$timeout = AE::timer $timeout, 0, sub {
		857	undef $timeout;
		858	kil $port;
		859	$cb->();
		860	};
		861	} else {
		862	mon $_[0], sub {
		863	kil $port;
		864	$cb->();
		865	};
		866	}
722		867
723	snd $NODE, time => $myport, timereply => 1, 2;	868	push @_, $port;
724	# => snd $myport, timereply => 1, 2, <time>	869	&snd;
		870
		871	$port
		872	}
725		873
726	=back	874	=back
727		875
728	=head1 AnyEvent::MP vs. Distributed Erlang	876	=head1 AnyEvent::MP vs. Distributed Erlang
729		877
730	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	878	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
731	== aemp node, Erlang process == aemp port), so many of the documents and	879	== aemp node, Erlang process == aemp port), so many of the documents and
732	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	880	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
733	sample:	881	sample:
734		882
735	http://www.Erlang.se/doc/programming_rules.shtml	883	http://www.erlang.se/doc/programming_rules.shtml
736	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	884	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
737	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	885	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
738	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	886	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
739		887
740	Despite the similarities, there are also some important differences:	888	Despite the similarities, there are also some important differences:
741		889
742	=over 4	890	=over 4
743		891
744	=item * Node references contain the recipe on how to contact them.	892	=item * Node IDs are arbitrary strings in AEMP.
745		893
746	Erlang relies on special naming and DNS to work everywhere in the	894	Erlang relies on special naming and DNS to work everywhere in the same
747	same way. AEMP relies on each node knowing it's own address(es), with	895	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
748	convenience functionality.	896	configuration or DNS), and possibly the addresses of some seed nodes, but
		897	will otherwise discover other nodes (and their IDs) itself.
749		898
750	This means that AEMP requires a less tightly controlled environment at the	899	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
751	cost of longer node references and a slightly higher management overhead.	900	uses "local ports are like remote ports".
		901
		902	The failure modes for local ports are quite different (runtime errors
		903	only) then for remote ports - when a local port dies, you I<know> it dies,
		904	when a connection to another node dies, you know nothing about the other
		905	port.
		906
		907	Erlang pretends remote ports are as reliable as local ports, even when
		908	they are not.
		909
		910	AEMP encourages a "treat remote ports differently" philosophy, with local
		911	ports being the special case/exception, where transport errors cannot
		912	occur.
752		913
753	=item * Erlang uses processes and a mailbox, AEMP does not queue.	914	=item * Erlang uses processes and a mailbox, AEMP does not queue.
754		915
755	Erlang uses processes that selctively receive messages, and therefore	916	Erlang uses processes that selectively receive messages out of order, and
756	needs a queue. AEMP is event based, queuing messages would serve no useful	917	therefore needs a queue. AEMP is event based, queuing messages would serve
757	purpose.	918	no useful purpose. For the same reason the pattern-matching abilities
		919	of AnyEvent::MP are more limited, as there is little need to be able to
		920	filter messages without dequeuing them.
758		921
759	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	922	This is not a philosophical difference, but simply stems from AnyEvent::MP
		923	being event-based, while Erlang is process-based.
		924
		925	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		926	top of AEMP and Coro threads.
760		927
761	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	928	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
762		929
763	Sending messages in Erlang is synchronous and blocks the process. AEMP	930	Sending messages in Erlang is synchronous and blocks the process until
764	sends are immediate, connection establishment is handled in the	931	a conenction has been established and the message sent (and so does not
765	background.	932	need a queue that can overflow). AEMP sends return immediately, connection
		933	establishment is handled in the background.
766		934
767	=item * Erlang can silently lose messages, AEMP cannot.	935	=item * Erlang suffers from silent message loss, AEMP does not.
768		936
769	Erlang makes few guarantees on messages delivery - messages can get lost	937	Erlang implements few guarantees on messages delivery - messages can get
770	without any of the processes realising it (i.e. you send messages a, b,	938	lost without any of the processes realising it (i.e. you send messages a,
771	and c, and the other side only receives messages a and c).	939	b, and c, and the other side only receives messages a and c).
772		940
773	AEMP guarantees correct ordering, and the guarantee that there are no	941	AEMP guarantees (modulo hardware errors) correct ordering, and the
		942	guarantee that after one message is lost, all following ones sent to the
		943	same port are lost as well, until monitoring raises an error, so there are
774	holes in the message sequence.	944	no silent "holes" in the message sequence.
775		945
776	=item * In Erlang, processes can be declared dead and later be found to be	946	If you want your software to be very reliable, you have to cope with
777	alive.	947	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
778		948	simply tries to work better in common error cases, such as when a network
779	In Erlang it can happen that a monitored process is declared dead and	949	link goes down.
780	linked processes get killed, but later it turns out that the process is
781	still alive - and can receive messages.
782
783	In AEMP, when port monitoring detects a port as dead, then that port will
784	eventually be killed - it cannot happen that a node detects a port as dead
785	and then later sends messages to it, finding it is still alive.
786		950
787	=item * Erlang can send messages to the wrong port, AEMP does not.	951	=item * Erlang can send messages to the wrong port, AEMP does not.
788		952
789	In Erlang it is quite possible that a node that restarts reuses a process	953	In Erlang it is quite likely that a node that restarts reuses an Erlang
790	ID known to other nodes for a completely different process, causing	954	process ID known to other nodes for a completely different process,
791	messages destined for that process to end up in an unrelated process.	955	causing messages destined for that process to end up in an unrelated
		956	process.
792		957
793	AEMP never reuses port IDs, so old messages or old port IDs floating	958	AEMP does not reuse port IDs, so old messages or old port IDs floating
794	around in the network will not be sent to an unrelated port.	959	around in the network will not be sent to an unrelated port.
795		960
796	=item * Erlang uses unprotected connections, AEMP uses secure	961	=item * Erlang uses unprotected connections, AEMP uses secure
797	authentication and can use TLS.	962	authentication and can use TLS.
798		963
799	AEMP can use a proven protocol - SSL/TLS - to protect connections and	964	AEMP can use a proven protocol - TLS - to protect connections and
800	securely authenticate nodes.	965	securely authenticate nodes.
801		966
802	=item * The AEMP protocol is optimised for both text-based and binary	967	=item * The AEMP protocol is optimised for both text-based and binary
803	communications.	968	communications.
804		969
805	The AEMP protocol, unlike the Erlang protocol, supports both	970	The AEMP protocol, unlike the Erlang protocol, supports both programming
806	language-independent text-only protocols (good for debugging) and binary,	971	language independent text-only protocols (good for debugging), and binary,
807	language-specific serialisers (e.g. Storable).	972	language-specific serialisers (e.g. Storable). By default, unless TLS is
		973	used, the protocol is actually completely text-based.
808		974
809	It has also been carefully designed to be implementable in other languages	975	It has also been carefully designed to be implementable in other languages
810	with a minimum of work while gracefully degrading fucntionality to make the	976	with a minimum of work while gracefully degrading functionality to make the
811	protocol simple.	977	protocol simple.
812		978
813	=item * AEMP has more flexible monitoring options than Erlang.	979	=item * AEMP has more flexible monitoring options than Erlang.
814		980
815	In Erlang, you can chose to receive I<all> exit signals as messages	981	In Erlang, you can chose to receive I<all> exit signals as messages or
816	or I<none>, there is no in-between, so monitoring single processes is	982	I<none>, there is no in-between, so monitoring single Erlang processes is
817	difficult to implement. Monitoring in AEMP is more flexible than in	983	difficult to implement.
818	Erlang, as one can choose between automatic kill, exit message or callback	984
819	on a per-process basis.	985	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		986	between automatic kill, exit message or callback on a per-port basis.
820		987
821	=item * Erlang tries to hide remote/local connections, AEMP does not.	988	=item * Erlang tries to hide remote/local connections, AEMP does not.
822		989
823	Monitoring in Erlang is not an indicator of process death/crashes,	990	Monitoring in Erlang is not an indicator of process death/crashes, in the
824	as linking is (except linking is unreliable in Erlang).	991	same way as linking is (except linking is unreliable in Erlang).
825		992
826	In AEMP, you don't "look up" registered port names or send to named ports	993	In AEMP, you don't "look up" registered port names or send to named ports
827	that might or might not be persistent. Instead, you normally spawn a port	994	that might or might not be persistent. Instead, you normally spawn a port
828	on the remote node. The init function monitors the you, and you monitor	995	on the remote node. The init function monitors you, and you monitor the
829	the remote port. Since both monitors are local to the node, they are much	996	remote port. Since both monitors are local to the node, they are much more
830	more reliable.	997	reliable (no need for C<spawn_link>).
831		998
832	This also saves round-trips and avoids sending messages to the wrong port	999	This also saves round-trips and avoids sending messages to the wrong port
833	(hard to do in Erlang).	1000	(hard to do in Erlang).
834		1001
835	=back	1002	=back
836		1003
		1004	=head1 RATIONALE
		1005
		1006	=over 4
		1007
		1008	=item Why strings for port and node IDs, why not objects?
		1009
		1010	We considered "objects", but found that the actual number of methods
		1011	that can be called are quite low. Since port and node IDs travel over
		1012	the network frequently, the serialising/deserialising would add lots of
		1013	overhead, as well as having to keep a proxy object everywhere.
		1014
		1015	Strings can easily be printed, easily serialised etc. and need no special
		1016	procedures to be "valid".
		1017
		1018	And as a result, a port with just a default receiver consists of a single
		1019	code reference stored in a global hash - it can't become much cheaper.
		1020
		1021	=item Why favour JSON, why not a real serialising format such as Storable?
		1022
		1023	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1024	format, but currently there is no way to make a node use Storable by
		1025	default (although all nodes will accept it).
		1026
		1027	The default framing protocol is JSON because a) JSON::XS is many times
		1028	faster for small messages and b) most importantly, after years of
		1029	experience we found that object serialisation is causing more problems
		1030	than it solves: Just like function calls, objects simply do not travel
		1031	easily over the network, mostly because they will always be a copy, so you
		1032	always have to re-think your design.
		1033
		1034	Keeping your messages simple, concentrating on data structures rather than
		1035	objects, will keep your messages clean, tidy and efficient.
		1036
		1037	=back
		1038
837	=head1 SEE ALSO	1039	=head1 SEE ALSO
		1040
		1041	L<AnyEvent::MP::Intro> - a gentle introduction.
		1042
		1043	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1044
		1045	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1046	your applications.
		1047
		1048	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1049
		1050	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1051	all nodes.
838		1052
839	L<AnyEvent>.	1053	L<AnyEvent>.
840		1054
841	=head1 AUTHOR	1055	=head1 AUTHOR
842		1056

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Revision 1.121 by root, Tue Feb 28 18:37:24 2012 UTC