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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.37 by root, Fri Aug 7 16:47:23 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
		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
27		38
28	# monitoring	39	# monitoring
29	mon $port, $cb->(@msg) # callback is invoked on death	40	mon $localport, $cb->(@msg) # callback is invoked on death
30	mon $port, $otherport # kill otherport on abnormal death	41	mon $localport, $otherport # kill otherport on abnormal death
31	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.
32		59
33	=head1 DESCRIPTION	60	=head1 DESCRIPTION
34		61
35	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
36		63
37	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
38	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
39		66
40	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>
41	manual page.	68	manual page and the examples under F<eg/>.
42
43	At the moment, this module family is severly broken and underdocumented,
44	so do not use. This was uploaded mainly to reserve the CPAN namespace -
45	stay tuned! The basic API should be finished, however.
46		69
47	=head1 CONCEPTS	70	=head1 CONCEPTS
48		71
49	=over 4	72	=over 4
50		73
51	=item port	74	=item port
52		75
53	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).
54		78
55	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
56	messages. All C<rcv> handlers will receive messages they match, messages	80	some messages. Messages send to ports will not be queued, regardless of
57	will not be queued.	81	anything was listening for them or not.
58		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
59	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
60		86
61	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
62	separator, and a port name (a printable string of unspecified format). An	88	separator, and a port name (a printable string of unspecified format).
63	exception is the the node port, whose ID is identical to its node
64	reference.
65		89
66	=item node	90	=item node
67		91
68	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,
69	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
70	create new ports, among other things.	94	ports.
71		95
72	Nodes are either private (single-process only), slaves (connected to a	96	Nodes are either public (have one or more listening ports) or private
73	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.
74		99
75	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	100	Nodes is represented by (printable) strings called "node IDs".
76		101
77	A node reference is a string that either simply identifies the node (for	102	=item node ID - C<[A-Za-z0-9_\-.:]*>
78	private and slave nodes), or contains a recipe on how to reach a given
79	node (for public nodes).
80		103
81	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
82	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.
83		108
84	Node references come in two flavours: resolved (containing only numerical	109	=item binds - C<ip:port>
85	addresses) or unresolved (where hostnames are used instead of addresses).
86		110
87	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
88	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).
89		169
90	=back	170	=back
91		171
92	=head1 VARIABLES/FUNCTIONS	172	=head1 VARIABLES/FUNCTIONS
93		173
95		175
96	=cut	176	=cut
97		177
98	package AnyEvent::MP;	178	package AnyEvent::MP;
99		179
		180	use AnyEvent::MP::Config ();
100	use AnyEvent::MP::Base;	181	use AnyEvent::MP::Kernel;
		182	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
101		183
102	use common::sense;	184	use common::sense;
103		185
104	use Carp ();	186	use Carp ();
105		187
106	use AE ();	188	use AE ();
107		189
108	use base "Exporter";	190	use base "Exporter";
109		191
110	our $VERSION = '0.1';	192	our $VERSION = $AnyEvent::MP::Config::VERSION;
		193
111	our @EXPORT = qw(	194	our @EXPORT = qw(
112	NODE $NODE *SELF node_of _any_	195	NODE $NODE *SELF node_of after
113	resolve_node initialise_node	196	configure
114	snd rcv mon kil reg psub	197	snd rcv mon mon_guard kil psub peval spawn cal
115	port	198	port
116	);	199	);
117		200
118	our $SELF;	201	our $SELF;
119		202
…		…
123	kil $SELF, die => $msg;	206	kil $SELF, die => $msg;
124	}	207	}
125		208
126	=item $thisnode = NODE / $NODE	209	=item $thisnode = NODE / $NODE
127		210
128	The C<NODE> function returns, and the C<$NODE> variable contains	211	The C<NODE> function returns, and the C<$NODE> variable contains, the node
129	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
130	to C<become_public> or C<become_slave>, after which all local port	213	a call to C<configure>.
131	identifiers become invalid.
132		214
133	=item $noderef = node_of $port	215	=item $nodeid = node_of $port
134		216
135	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.
136		218
137	=item initialise_node $noderef, $seednode, $seednode...	219	=item configure $profile, key => value...
138		220
139	=item initialise_node "slave/", $master, $master...	221	=item configure key => value...
140		222
141	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
142	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
143	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.
144		227
145	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
146	never) before calling other AnyEvent::MP functions.	229	never) before calling other AnyEvent::MP functions.
147		230
148	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
149		232	F<aemp> command line utility (sans the set/del prefix), with two additions:
150	There are two types of networked nodes, public nodes and slave nodes:
151		233
152	=over 4	234	=over 4
153		235
154	=item public nodes	236	=item norc => $boolean (default false)
155		237
156	For public nodes, C<$noderef> must either be a (possibly unresolved)	238	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
157	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
158	which case the noderef will be guessed.	240	C<configure> call.
159		241
160	Afterwards, the node will bind itself on all endpoints and try to connect	242	=item force => $boolean (default false)
161	to all additional C<$seednodes> that are specified. Seednodes are optional
162	and can be used to quickly bootstrap the node into an existing network.
163		243
164	=item slave nodes	244	IF true, then the values specified in the C<configure> will take
165		245	precedence over any values configured via the rc file. The default is for
166	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.
167	become a slave node. Slave nodes cannot be contacted from outside and will
168	route most of their traffic to the master node that they attach to.
169
170	At least one additional noderef is required: The node will try to connect
171	to all of them and will become a slave attached to the first node it can
172	successfully connect to.
173		247
174	=back	248	=back
175		249
176	This function will block until all nodes have been resolved and, for slave
177	nodes, until it has successfully established a connection to a master
178	server.
179
180	Example: become a public node listening on the default node.
181
182	initialise_node;
183
184	Example: become a public node, and try to contact some well-known master
185	servers to become part of the network.
186
187	initialise_node undef, "master1", "master2";
188
189	Example: become a public node listening on port C<4041>.
190
191	initialise_node 4041;
192
193	Example: become a public node, only visible on localhost port 4044.
194
195	initialise_node "locahost:4044";
196
197	Example: become a slave node to any of the specified master servers.
198
199	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
200
201	=item $cv = resolve_node $noderef
202
203	Takes an unresolved node reference that may contain hostnames and
204	abbreviated IDs, resolves all of them and returns a resolved node
205	reference.
206
207	In addition to C<address:port> pairs allowed in resolved noderefs, the
208	following forms are supported:
209
210	=over 4	250	=over 4
211		251
212	=item the empty string	252	=item step 1, gathering configuration from profiles
213		253
214	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
215	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.
216		258
217	=item naked port numbers (e.g. C<1234>)	259	The profile data is then gathered as follows:
218		260
219	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
220	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).
221		266
222	=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.
223		270
224	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
225	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
226	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.
227		292
228	=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)"
229		320
230	=item $SELF	321	=item $SELF
231		322
232	Contains the current port id while executing C<rcv> callbacks or C<psub>	323	Contains the current port id while executing C<rcv> callbacks or C<psub>
233	blocks.	324	blocks.
234		325
235	=item SELF, %SELF, @SELF...	326	=item *SELF, SELF, %SELF, @SELF...
236		327
237	Due to some quirks in how perl exports variables, it is impossible to	328	Due to some quirks in how perl exports variables, it is impossible to
238	just export C<$SELF>, all the symbols called C<SELF> are exported by this	329	just export C<$SELF>, all the symbols named C<SELF> are exported by this
239	module, but only C<$SELF> is currently used.	330	module, but only C<$SELF> is currently used.
240		331
241	=item snd $port, type => @data	332	=item snd $port, type => @data
242		333
243	=item snd $port, @msg	334	=item snd $port, @msg
244		335
245	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
246	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.
247	stringifies a sa port ID (such as a port object :).
248		338
249	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
250	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
251	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.
252		343
253	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
254	function: modifying any argument is not allowed and can cause many	345	function: modifying any argument (or values referenced by them) is
255	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.
256		350
257	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
258	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
259	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
260	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
261	node, anything can be passed.	355	node, anything can be passed. Best rely only on the common denominator of
		356	these.
262		357
263	=item $local_port = port	358	=item $local_port = port
264		359
265	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
266	matching port ("full port") or a single-callback port ("miniport"),	361	no callbacks set and will throw an error when it receives messages.
267	depending on how C<rcv> callbacks are bound to the object.
268		362
269	=item $port = port { my @msg = @_; $finished }	363	=item $local_port = port { my @msg = @_ }
270		364
271	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
272	matching behind it, and returns its ID. Semantically the same as creating
273	a port and calling C<rcv $port, $callback> on it.	366	creating a port and calling C<rcv $port, $callback> on it.
274		367
275	The block will be called for every message received on the port. When the	368	The block will be called for every message received on the port, with the
276	callback returns a true value its job is considered "done" and the port	369	global variable C<$SELF> set to the port ID. Runtime errors will cause the
277	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.
278		372
279	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:
280	be passed to the callback.
281		374
282	If you need the local port id in the callback, this works nicely:	375	my $port = port {
283		376	my @msg = @_;
284	my $port; $port = port {	377	...
285	snd $otherport, reply => $port;	378	kil $SELF;
286	};	379	};
287		380
288	=cut	381	=cut
289		382
290	sub rcv($@);	383	sub rcv($@);
291		384
		385	sub _kilme {
		386	die "received message on port without callback";
		387	}
		388
292	sub port(;&) {	389	sub port(;&) {
293	my $id = "$UNIQ." . $ID++;	390	my $id = "$UNIQ." . ++$ID;
294	my $port = "$NODE#$id";	391	my $port = "$NODE#$id";
295		392
296	if (@_) {	393	rcv $port, shift \|\| \&_kilme;
297	rcv $port, shift;
298	} else {
299	$PORT{$id} = sub { }; # nop
300	}
301		394
302	$port	395	$port
303	}	396	}
304		397
305	=item reg $port, $name
306
307	=item reg $name
308
309	Registers the given port (or C<$SELF><<< if missing) under the name
310	C<$name>. If the name already exists it is replaced.
311
312	A port can only be registered under one well known name.
313
314	A port automatically becomes unregistered when it is killed.
315
316	=cut
317
318	sub reg(@) {
319	my $port = @_ > 1 ? shift : $SELF \|\| Carp::croak 'reg: called with one argument only, but $SELF not set,';
320
321	$REG{$_[0]} = $port;
322	}
323
324	=item rcv $port, $callback->(@msg)	398	=item rcv $local_port, $callback->(@msg)
325		399
326	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
327	one if required).	401	remove the default callback: use C<sub { }> to disable it, or better
328		402	C<kil> the port when it is no longer needed.
329	=item rcv $port, tagstring => $callback->(@msg), ...
330
331	=item rcv $port, $smartmatch => $callback->(@msg), ...
332
333	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
334
335	Register callbacks to be called on matching messages on the given full
336	port (after converting it to one if required) and return the port.
337
338	The callback has to return a true value when its work is done, after
339	which is will be removed, or a false value in which case it will stay
340	registered.
341		403
342	The global C<$SELF> (exported by this module) contains C<$port> while	404	The global C<$SELF> (exported by this module) contains C<$port> while
343	executing the callback.	405	executing the callback. Runtime errors during callback execution will
		406	result in the port being C<kil>ed.
344		407
345	Runtime errors wdurign callback execution will result in the port being	408	The default callback received all messages not matched by a more specific
346	C<kil>ed.	409	C<tag> match.
347		410
348	If the match is an array reference, then it will be matched against the	411	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
349	first elements of the message, otherwise only the first element is being
350	matched.
351		412
352	Any element in the match that is specified as C<_any_> (a function	413	Register (or replace) callbacks to be called on messages starting with the
353	exported by this module) matches any single element of the message.	414	given tag on the given port (and return the port), or unregister it (when
		415	C<$callback> is C<$undef> or missing). There can only be one callback
		416	registered for each tag.
354		417
355	While not required, it is highly recommended that the first matching	418	The original message will be passed to the callback, after the first
356	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
357	also the most efficient match (by far).	420	environment as the default callback (see above).
358		421
359	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.
360		423
361	my $port = rcv port,	424	my $port = rcv port,
362	msg1 => sub { ...; 0 },	425	msg1 => sub { ... },
363	msg2 => sub { ...; 0 },	426	msg2 => sub { ... },
364	;	427	;
365		428
366	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
367	in one go:	430	in one go:
368		431
369	snd $otherport, reply =>	432	snd $otherport, reply =>
370	rcv port,	433	rcv port,
371	msg1 => sub { ...; 0 },	434	msg1 => sub { ... },
372	...	435	...
373	;	436	;
374		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, $otherport;
		445	};
		446
375	=cut	447	=cut
376		448
377	sub rcv($@) {	449	sub rcv($@) {
378	my $port = shift;	450	my $port = shift;
379	my ($noderef, $portid) = split /#/, $port, 2;	451	my ($nodeid, $portid) = split /#/, $port, 2;
380		452
381	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	453	$NODE{$nodeid} == $NODE{""}
382	or Carp::croak "$port: rcv can only be called on local ports, caught";	454	or Carp::croak "$port: rcv can only be called on local ports, caught";
383		455
384	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 {
385	my $cb = shift;	464	my $cb = shift;
386	delete $PORT_DATA{$portid};
387	$PORT{$portid} = sub {	465	$PORT{$portid} = sub {
388	local $SELF = $port;	466	local $SELF = $port;
389	eval {	467	eval { &$cb }; _self_die if $@;
390	&$cb	468	};
391	and kil $port;
392	};	469	}
393	_self_die if $@;	470	} elsif (defined $_[0]) {
394	};
395	} else {
396	my $self = $PORT_DATA{$portid} \|\|= do {	471	my $self = $PORT_DATA{$portid} \|\|= do {
397	my $self = bless {	472	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
398	id => $port,
399	}, "AnyEvent::MP::Port";
400		473
401	$PORT{$portid} = sub {	474	$PORT{$portid} = sub {
402	local $SELF = $port;	475	local $SELF = $port;
403		476
404	eval {
405	for (@{ $self->{rc0}{$_[0]} }) {	477	if (my $cb = $self->[1]{$_[0]}) {
406	$_ && &{$_->[0]}	478	shift;
407	&& undef $_;	479	eval { &$cb }; _self_die if $@;
408	}	480	} else {
409
410	for (@{ $self->{rcv}{$_[0]} }) {
411	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
412	&& &{$_->[0]}	481	&{ $self->[0] };
413	&& undef $_;
414	}
415
416	for (@{ $self->{any} }) {
417	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
418	&& &{$_->[0]}
419	&& undef $_;
420	}	482	}
421	};	483	};
422	_self_die if $@;	484
		485	$self
423	};	486	};
424		487
425	$self
426	};
427
428	"AnyEvent::MP::Port" eq ref $self	488	"AnyEvent::MP::Port" eq ref $self
429	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	489	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
430		490
431	while (@_) {
432	my ($match, $cb) = splice @_, 0, 2;	491	my ($tag, $cb) = splice @_, 0, 2;
433		492
434	if (!ref $match) {	493	if (defined $cb) {
435	push @{ $self->{rc0}{$match} }, [$cb];	494	$self->[1]{$tag} = $cb;
436	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
437	my ($type, @match) = @$match;
438	@match
439	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
440	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
441	} else {	495	} else {
442	push @{ $self->{any} }, [$cb, $match];	496	delete $self->[1]{$tag};
443	}	497	}
444	}	498	}
445	}	499	}
446		500
447	$port	501	$port
448	}	502	}
449		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
450	=item $closure = psub { BLOCK }	541	=item $closure = psub { BLOCK }
451		542
452	Remembers C<$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
453	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>
454	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 $SELF, sub {
		548	BLOCK }, @_ } >>.
455		549
456	This is useful when you register callbacks from C<rcv> callbacks:	550	This is useful when you register callbacks from C<rcv> callbacks:
457		551
458	rcv delayed_reply => sub {	552	rcv delayed_reply => sub {
459	my ($delay, @reply) = @_;	553	my ($delay, @reply) = @_;
…		…
483	$res	577	$res
484	}	578	}
485	}	579	}
486	}	580	}
487		581
488	=item $guard = mon $port, $cb->(@reason)	582	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
489		583
490	=item $guard = mon $port, $rcvport	584	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
491		585
492	=item $guard = mon $port	586	=item $guard = mon $port # kill $SELF when $port dies
493		587
494	=item $guard = mon $port, $rcvport, @msg	588	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
495		589
496	Monitor the given port and do something when the port is killed, and	590	Monitor the given port and do something when the port is killed or
497	optionally return a guard that can be used to stop monitoring again.	591	messages to it were lost, and optionally return a guard that can be used
		592	to stop monitoring again.
498		593
499	In the first form (callback), the callback is simply called with any	594	In the first form (callback), the callback is simply called with any
500	number of C<@reason> elements (no @reason means that the port was deleted	595	number of C<@reason> elements (no @reason means that the port was deleted
501	"normally"). Note also that I<< the callback B<must> never die >>, so use	596	"normally"). Note also that I<< the callback B<must> never die >>, so use
502	C<eval> if unsure.	597	C<eval> if unsure.
503		598
504	In the second form (another port given), the other port (C<$rcvport)	599	In the second form (another port given), the other port (C<$rcvport>)
505	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	600	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
506	"normal" kils nothing happens, while under all other conditions, the other	601	"normal" kils nothing happens, while under all other conditions, the other
507	port is killed with the same reason.	602	port is killed with the same reason.
508		603
509	The third form (kill self) is the same as the second form, except that	604	The third form (kill self) is the same as the second form, except that
510	C<$rvport> defaults to C<$SELF>.	605	C<$rvport> defaults to C<$SELF>.
511		606
512	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
513	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.
514		612
515	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
516	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
517	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
518	even monitoring requests can get lost (for exmaple, when the connection	616	even monitoring requests can get lost (for example, when the connection
519	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
520	these problems do not exist.	618	these problems do not exist.
521		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
522	Example: call a given callback when C<$port> is killed.	637	Example: call a given callback when C<$port> is killed.
523		638
524	mon $port, sub { warn "port died because of <@_>\n" };	639	mon $port, sub { warn "port died because of <@_>\n" };
525		640
526	Example: kill ourselves when C<$port> is killed abnormally.	641	Example: kill ourselves when C<$port> is killed abnormally.
…		…
532	mon $port, $self => "restart";	647	mon $port, $self => "restart";
533		648
534	=cut	649	=cut
535		650
536	sub mon {	651	sub mon {
537	my ($noderef, $port) = split /#/, shift, 2;	652	my ($nodeid, $port) = split /#/, shift, 2;
538		653
539	my $node = $NODE{$noderef} \|\| add_node $noderef;	654	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
540		655
541	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,';
542		657
543	unless (ref $cb) {	658	unless (ref $cb) {
544	if (@_) {	659	if (@_) {
545	# send a kill info message	660	# send a kill info message
546	my (@msg) = @_;	661	my (@msg) = ($cb, @_);
547	$cb = sub { snd @msg, @_ };	662	$cb = sub { snd @msg, @_ };
548	} else {	663	} else {
549	# simply kill other port	664	# simply kill other port
550	my $port = $cb;	665	my $port = $cb;
551	$cb = sub { kil $port, @_ if @_ };	666	$cb = sub { kil $port, @_ if @_ };
…		…
553	}	668	}
554		669
555	$node->monitor ($port, $cb);	670	$node->monitor ($port, $cb);
556		671
557	defined wantarray	672	defined wantarray
558	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	673	and ($cb += 0, AnyEvent::Util::guard { $node->unmonitor ($port, $cb) })
559	}	674	}
560		675
561	=item $guard = mon_guard $port, $ref, $ref...	676	=item $guard = mon_guard $port, $ref, $ref...
562		677
563	Monitors the given C<$port> and keeps the passed references. When the port	678	Monitors the given C<$port> and keeps the passed references. When the port
564	is killed, the references will be freed.	679	is killed, the references will be freed.
565		680
566	Optionally returns a guard that will stop the monitoring.	681	Optionally returns a guard that will stop the monitoring.
567		682
568	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
569	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>):
570		685
571	$port->rcv (start => sub {	686	$port->rcv (start => sub {
572	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	687	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
573	undef $timer if 0.9 < rand;	688	undef $timer if 0.9 < rand;
574	});	689	});
575	});	690	});
576		691
577	=cut	692	=cut
…		…
586		701
587	=item kil $port[, @reason]	702	=item kil $port[, @reason]
588		703
589	Kill the specified port with the given C<@reason>.	704	Kill the specified port with the given C<@reason>.
590		705
591	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" -
592	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.
593		709
594	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>
595	C<mon>, see below).	711	form) get killed with the same reason.
596		712
597	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
598	will be reported as reason C<< die => $@ >>.	714	will be reported as reason C<< die => $@ >>.
599		715
600	Transport/communication errors are reported as C<< transport_error =>	716	Transport/communication errors are reported as C<< transport_error =>
601	$message >>.	717	$message >>.
602		718
603	=back
604
605	=head1 NODE MESSAGES
606
607	Nodes understand the following messages sent to them. Many of them take
608	arguments called C<@reply>, which will simply be used to compose a reply
609	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
610	the remaining arguments are simply the message data.
611
612	While other messages exist, they are not public and subject to change.
613
614	=over 4
615
616	=cut	719	=cut
617		720
618	=item lookup => $name, @reply	721	=item $port = spawn $node, $initfunc[, @initdata]
619		722
620	Replies with the port ID of the specified well-known port, or C<undef>.	723	Creates a port on the node C<$node> (which can also be a port ID, in which
		724	case it's the node where that port resides).
621		725
622	=item devnull => ...	726	The port ID of the newly created port is returned immediately, and it is
		727	possible to immediately start sending messages or to monitor the port.
623		728
624	Generic data sink/CPU heat conversion.	729	After the port has been created, the init function is called on the remote
		730	node, in the same context as a C<rcv> callback. This function must be a
		731	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		732	specify a function in the main program, use C<::name>.
625		733
626	=item relay => $port, @msg	734	If the function doesn't exist, then the node tries to C<require>
		735	the package, then the package above the package and so on (e.g.
		736	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		737	exists or it runs out of package names.
627		738
628	Simply forwards the message to the given port.	739	The init function is then called with the newly-created port as context
		740	object (C<$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.
629		743
630	=item eval => $string[ @reply]	744	A common idiom is to pass a local port, immediately monitor the spawned
		745	port, and in the remote init function, immediately monitor the passed
		746	local port. This two-way monitoring ensures that both ports get cleaned up
		747	when there is a problem.
631		748
632	Evaluates the given string. If C<@reply> is given, then a message of the	749	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
633	form C<@reply, $@, @evalres> is sent.	750	caller before C<spawn> returns (by delaying invocation when spawn is
		751	called for the local node).
634		752
635	Example: crash another node.	753	Example: spawn a chat server port on C<$othernode>.
636		754
637	snd $othernode, eval => "exit";	755	# this node, executed from within a port context:
		756	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		757	mon $server;
638		758
639	=item time => @reply	759	# init function on C<$othernode>
		760	sub connect {
		761	my ($srcport) = @_;
640		762
641	Replies the the current node time to C<@reply>.	763	mon $srcport;
642		764
643	Example: tell the current node to send the current time to C<$myport> in a	765	rcv $SELF, sub {
644	C<timereply> message.	766	...
		767	};
		768	}
645		769
646	snd $NODE, time => $myport, timereply => 1, 2;	770	=cut
647	# => snd $myport, timereply => 1, 2, <time>	771
		772	sub _spawn {
		773	my $port = shift;
		774	my $init = shift;
		775
		776	# rcv will create the actual port
		777	local $SELF = "$NODE#$port";
		778	eval {
		779	&{ load_func $init }
		780	};
		781	_self_die if $@;
		782	}
		783
		784	sub spawn(@) {
		785	my ($nodeid, undef) = split /#/, shift, 2;
		786
		787	my $id = "$RUNIQ." . ++$ID;
		788
		789	$_[0] =~ /::/
		790	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		791
		792	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		793
		794	"$nodeid#$id"
		795	}
		796
		797
		798	=item after $timeout, @msg
		799
		800	=item after $timeout, $callback
		801
		802	Either sends the given message, or call the given callback, after the
		803	specified number of seconds.
		804
		805	This is simply a utility function that comes in handy at times - the
		806	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		807	so it may go away in the future.
		808
		809	=cut
		810
		811	sub after($@) {
		812	my ($timeout, @action) = @_;
		813
		814	my $t; $t = AE::timer $timeout, 0, sub {
		815	undef $t;
		816	ref $action[0]
		817	? $action[0]()
		818	: snd @action;
		819	};
		820	}
		821
		822	=item cal $port, @msg, $callback[, $timeout]
		823
		824	A simple form of RPC - sends a message to the given C<$port> with the
		825	given contents (C<@msg>), but adds a reply port to the message.
		826
		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.
		829
		830	A reply message sent to the port is passed to the C<$callback> as-is.
		831
		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.
		835
		836	If no time-out is given (or it is C<undef>), then the local port will
		837	monitor the remote port instead, so it eventually gets cleaned-up.
		838
		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.
		842
		843	=cut
		844
		845	sub cal(@) {
		846	my $timeout = ref $_[-1] ? undef : pop;
		847	my $cb = pop;
		848
		849	my $port = port {
		850	undef $timeout;
		851	kil $SELF;
		852	&$cb;
		853	};
		854
		855	if (defined $timeout) {
		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	}
		867
		868	push @_, $port;
		869	&snd;
		870
		871	$port
		872	}
648		873
649	=back	874	=back
650		875
651	=head1 AnyEvent::MP vs. Distributed Erlang	876	=head1 AnyEvent::MP vs. Distributed Erlang
652		877
653	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
654	== 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
655	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
656	sample:	881	sample:
657		882
658	http://www.Erlang.se/doc/programming_rules.shtml	883	http://www.erlang.se/doc/programming_rules.shtml
659	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
660	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
661	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
662		887
663	Despite the similarities, there are also some important differences:	888	Despite the similarities, there are also some important differences:
664		889
665	=over 4	890	=over 4
666		891
667	=item * Node references contain the recipe on how to contact them.	892	=item * Node IDs are arbitrary strings in AEMP.
668		893
669	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
670	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
671	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.
672		898
673	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
674	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.
675		913
676	=item * Erlang uses processes and a mailbox, AEMP does not queue.	914	=item * Erlang uses processes and a mailbox, AEMP does not queue.
677		915
678	Erlang uses processes that selctively receive messages, and therefore	916	Erlang uses processes that selectively receive messages out of order, and
679	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
680	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.
681		921
682	(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.
683		927
684	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	928	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
685		929
686	Sending messages in Erlang is synchronous and blocks the process. AEMP	930	Sending messages in Erlang is synchronous and blocks the process until
687	sends are immediate, connection establishment is handled in the	931	a conenction has been established and the message sent (and so does not
688	background.	932	need a queue that can overflow). AEMP sends return immediately, connection
		933	establishment is handled in the background.
689		934
690	=item * Erlang can silently lose messages, AEMP cannot.	935	=item * Erlang suffers from silent message loss, AEMP does not.
691		936
692	Erlang makes few guarantees on messages delivery - messages can get lost	937	Erlang implements few guarantees on messages delivery - messages can get
693	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,
694	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).
695		940
696	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
697	holes in the message sequence.	944	no silent "holes" in the message sequence.
698		945
699	=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
700	alive.	947	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
701		948	simply tries to work better in common error cases, such as when a network
702	In Erlang it can happen that a monitored process is declared dead and	949	link goes down.
703	linked processes get killed, but later it turns out that the process is
704	still alive - and can receive messages.
705
706	In AEMP, when port monitoring detects a port as dead, then that port will
707	eventually be killed - it cannot happen that a node detects a port as dead
708	and then later sends messages to it, finding it is still alive.
709		950
710	=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.
711		952
712	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
713	ID known to other nodes for a completely different process, causing	954	process ID known to other nodes for a completely different process,
714	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.
715		957
716	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
717	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.
718		960
719	=item * Erlang uses unprotected connections, AEMP uses secure	961	=item * Erlang uses unprotected connections, AEMP uses secure
720	authentication and can use TLS.	962	authentication and can use TLS.
721		963
722	AEMP can use a proven protocol - SSL/TLS - to protect connections and	964	AEMP can use a proven protocol - TLS - to protect connections and
723	securely authenticate nodes.	965	securely authenticate nodes.
724		966
725	=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
726	communications.	968	communications.
727		969
728	The AEMP protocol, unlike the Erlang protocol, supports both	970	The AEMP protocol, unlike the Erlang protocol, supports both programming
729	language-independent text-only protocols (good for debugging) and binary,	971	language independent text-only protocols (good for debugging), and binary,
730	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.
731		974
732	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
733	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
734	protocol simple.	977	protocol simple.
735		978
736	=item * AEMP has more flexible monitoring options than Erlang.	979	=item * AEMP has more flexible monitoring options than Erlang.
737		980
738	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
739	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
740	difficult to implement. Monitoring in AEMP is more flexible than in	983	difficult to implement.
741	Erlang, as one can choose between automatic kill, exit message or callback	984
742	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.
743		987
744	=item * Erlang tries to hide remote/local connections, AEMP does not.	988	=item * Erlang tries to hide remote/local connections, AEMP does not.
745		989
746	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
747	as linking is (except linking is unreliable in Erlang).	991	same way as linking is (except linking is unreliable in Erlang).
748		992
749	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
750	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
751	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
752	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
753	more reliable.	997	reliable (no need for C<spawn_link>).
754		998
755	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
756	(hard to do in Erlang).	1000	(hard to do in Erlang).
757		1001
758	=back	1002	=back
759		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
760	=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.
761		1052
762	L<AnyEvent>.	1053	L<AnyEvent>.
763		1054
764	=head1 AUTHOR	1055	=head1 AUTHOR
765		1056

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