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

Comparing cvsroot/AnyEvent-MP/MP.pm (file contents):
Revision 1.37 by root, Fri Aug 7 16:47:23 2009 UTC vs.
Revision 1.120 by root, Sun Feb 26 11:12:54 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
100	use AnyEvent::MP::Base;	180	use AnyEvent::MP::Kernel;
101		181
102	use common::sense;	182	use common::sense;
103		183
104	use Carp ();	184	use Carp ();
105		185
106	use AE ();	186	use AE ();
107		187
108	use base "Exporter";	188	use base "Exporter";
109		189
110	our $VERSION = '0.1';	190	our $VERSION = '1.30';
		191
111	our @EXPORT = qw(	192	our @EXPORT = qw(
112	NODE $NODE *SELF node_of _any_	193	NODE $NODE *SELF node_of after
113	resolve_node initialise_node	194	configure
114	snd rcv mon kil reg psub	195	snd rcv mon mon_guard kil psub peval spawn cal
115	port	196	port
116	);	197	);
117		198
118	our $SELF;	199	our $SELF;
119		200
…		…
123	kil $SELF, die => $msg;	204	kil $SELF, die => $msg;
124	}	205	}
125		206
126	=item $thisnode = NODE / $NODE	207	=item $thisnode = NODE / $NODE
127		208
128	The C<NODE> function returns, and the C<$NODE> variable contains	209	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	210	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	211	a call to C<configure>.
131	identifiers become invalid.
132		212
133	=item $noderef = node_of $port	213	=item $nodeid = node_of $port
134		214
135	Extracts and returns the noderef from a portid or a noderef.	215	Extracts and returns the node ID from a port ID or a node ID.
136		216
137	=item initialise_node $noderef, $seednode, $seednode...	217	=item configure $profile, key => value...
138		218
139	=item initialise_node "slave/", $master, $master...	219	=item configure key => value...
140		220
141	Before a node can talk to other nodes on the network it has to initialise	221	Before a node can talk to other nodes on the network (i.e. enter
142	itself - the minimum a node needs to know is it's own name, and optionally	222	"distributed mode") it has to configure itself - the minimum a node needs
143	it should know the noderefs of some other nodes in the network.	223	to know is its own name, and optionally it should know the addresses of
		224	some other nodes in the network to discover other nodes.
144		225
		226	The key/value pairs are basically the same ones as documented for the
		227	F<aemp> command line utility (sans the set/del prefix).
		228
145	This function initialises a node - it must be called exactly once (or	229	This function configures a node - it must be called exactly once (or
146	never) before calling other AnyEvent::MP functions.	230	never) before calling other AnyEvent::MP functions.
147		231
148	All arguments are noderefs, which can be either resolved or unresolved.
149
150	There are two types of networked nodes, public nodes and slave nodes:
151
152	=over 4	232	=over 4
153		233
154	=item public nodes	234	=item step 1, gathering configuration from profiles
155		235
156	For public nodes, C<$noderef> must either be a (possibly unresolved)	236	The function first looks up a profile in the aemp configuration (see the
157	noderef, in which case it will be resolved, or C<undef> (or missing), in	237	L<aemp> commandline utility). The profile name can be specified via the
158	which case the noderef will be guessed.	238	named C<profile> parameter or can simply be the first parameter). If it is
		239	missing, then the nodename (F<uname -n>) will be used as profile name.
159		240
160	Afterwards, the node will bind itself on all endpoints and try to connect	241	The profile data is then gathered as follows:
161	to all additional C<$seednodes> that are specified. Seednodes are optional
162	and can be used to quickly bootstrap the node into an existing network.
163		242
164	=item slave nodes	243	First, all remaining key => value pairs (all of which are conveniently
		244	undocumented at the moment) will be interpreted as configuration
		245	data. Then they will be overwritten by any values specified in the global
		246	default configuration (see the F<aemp> utility), then the chain of
		247	profiles chosen by the profile name (and any C<parent> attributes).
165		248
166	When the C<$noderef> is the special string C<slave/>, then the node will	249	That means that the values specified in the profile have highest priority
167	become a slave node. Slave nodes cannot be contacted from outside and will	250	and the values specified directly via C<configure> have lowest priority,
168	route most of their traffic to the master node that they attach to.	251	and can only be used to specify defaults.
169		252
170	At least one additional noderef is required: The node will try to connect	253	If the profile specifies a node ID, then this will become the node ID of
171	to all of them and will become a slave attached to the first node it can	254	this process. If not, then the profile name will be used as node ID. The
172	successfully connect to.	255	special node ID of C<anon/> will be replaced by a random node ID.
		256
		257	=item step 2, bind listener sockets
		258
		259	The next step is to look up the binds in the profile, followed by binding
		260	aemp protocol listeners on all binds specified (it is possible and valid
		261	to have no binds, meaning that the node cannot be contacted form the
		262	outside. This means the node cannot talk to other nodes that also have no
		263	binds, but it can still talk to all "normal" nodes).
		264
		265	If the profile does not specify a binds list, then a default of C<*> is
		266	used, meaning the node will bind on a dynamically-assigned port on every
		267	local IP address it finds.
		268
		269	=item step 3, connect to seed nodes
		270
		271	As the last step, the seed ID list from the profile is passed to the
		272	L<AnyEvent::MP::Global> module, which will then use it to keep
		273	connectivity with at least one node at any point in time.
173		274
174	=back	275	=back
175		276
176	This function will block until all nodes have been resolved and, for slave	277	Example: become a distributed node using the local node name as profile.
177	nodes, until it has successfully established a connection to a master	278	This should be the most common form of invocation for "daemon"-type nodes.
178	server.
179		279
180	Example: become a public node listening on the default node.	280	configure
181		281
182	initialise_node;	282	Example: become an anonymous node. This form is often used for commandline
		283	clients.
183		284
184	Example: become a public node, and try to contact some well-known master	285	configure nodeid => "anon/";
185	servers to become part of the network.
186		286
187	initialise_node undef, "master1", "master2";	287	Example: configure a node using a profile called seed, which is suitable
		288	for a seed node as it binds on all local addresses on a fixed port (4040,
		289	customary for aemp).
188		290
189	Example: become a public node listening on port C<4041>.	291	# use the aemp commandline utility
		292	# aemp profile seed nodeid anon/ binds '*:4040'
190		293
191	initialise_node 4041;	294	# then use it
		295	configure profile => "seed";
192		296
193	Example: become a public node, only visible on localhost port 4044.	297	# or simply use aemp from the shell again:
		298	# aemp run profile seed
194		299
195	initialise_node "locahost:4044";	300	# or provide a nicer-to-remember nodeid
196		301	# aemp run profile seed nodeid "$(hostname)"
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
211
212	=item the empty string
213
214	An empty-string component gets resolved as if the default port (4040) was
215	specified.
216
217	=item naked port numbers (e.g. C<1234>)
218
219	These are resolved by prepending the local nodename and a colon, to be
220	further resolved.
221
222	=item hostnames (e.g. C<localhost:1234>, C<localhost>)
223
224	These are resolved by using AnyEvent::DNS to resolve them, optionally
225	looking up SRV records for the C<aemp=4040> port, if no port was
226	specified.
227
228	=back
229		302
230	=item $SELF	303	=item $SELF
231		304
232	Contains the current port id while executing C<rcv> callbacks or C<psub>	305	Contains the current port id while executing C<rcv> callbacks or C<psub>
233	blocks.	306	blocks.
234		307
235	=item SELF, %SELF, @SELF...	308	=item *SELF, SELF, %SELF, @SELF...
236		309
237	Due to some quirks in how perl exports variables, it is impossible to	310	Due to some quirks in how perl exports variables, it is impossible to
238	just export C<$SELF>, all the symbols called C<SELF> are exported by this	311	just export C<$SELF>, all the symbols named C<SELF> are exported by this
239	module, but only C<$SELF> is currently used.	312	module, but only C<$SELF> is currently used.
240		313
241	=item snd $port, type => @data	314	=item snd $port, type => @data
242		315
243	=item snd $port, @msg	316	=item snd $port, @msg
244		317
245	Send the given message to the given port ID, which can identify either	318	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	319	local or a remote port, and must be a port ID.
247	stringifies a sa port ID (such as a port object :).
248		320
249	While the message can be about anything, it is highly recommended to use a	321	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	322	use a string as first element (a port ID, or some word that indicates a
251	type etc.).	323	request type etc.) and to consist if only simple perl values (scalars,
		324	arrays, hashes) - if you think you need to pass an object, think again.
252		325
253	The message data effectively becomes read-only after a call to this	326	The message data logically becomes read-only after a call to this
254	function: modifying any argument is not allowed and can cause many	327	function: modifying any argument (or values referenced by them) is
255	problems.	328	forbidden, as there can be considerable time between the call to C<snd>
		329	and the time the message is actually being serialised - in fact, it might
		330	never be copied as within the same process it is simply handed to the
		331	receiving port.
256		332
257	The type of data you can transfer depends on the transport protocol: when	333	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	334	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	335	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	336	that Storable can serialise and deserialise is allowed, and for the local
261	node, anything can be passed.	337	node, anything can be passed. Best rely only on the common denominator of
		338	these.
262		339
263	=item $local_port = port	340	=item $local_port = port
264		341
265	Create a new local port object that can be used either as a pattern	342	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"),	343	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		344
269	=item $port = port { my @msg = @_; $finished }	345	=item $local_port = port { my @msg = @_ }
270		346
271	Creates a "miniport", that is, a very lightweight port without any pattern	347	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.	348	creating a port and calling C<rcv $port, $callback> on it.
274		349
275	The block will be called for every message received on the port. When the	350	The block will be called for every message received on the port, with the
276	callback returns a true value its job is considered "done" and the port	351	global variable C<$SELF> set to the port ID. Runtime errors will cause the
277	will be destroyed. Otherwise it will stay alive.	352	port to be C<kil>ed. The message will be passed as-is, no extra argument
		353	(i.e. no port ID) will be passed to the callback.
278		354
279	The message will be passed as-is, no extra argument (i.e. no port id) will	355	If you want to stop/destroy the port, simply C<kil> it:
280	be passed to the callback.
281		356
282	If you need the local port id in the callback, this works nicely:	357	my $port = port {
283		358	my @msg = @_;
284	my $port; $port = port {	359	...
285	snd $otherport, reply => $port;	360	kil $SELF;
286	};	361	};
287		362
288	=cut	363	=cut
289		364
290	sub rcv($@);	365	sub rcv($@);
		366
		367	sub _kilme {
		368	die "received message on port without callback";
		369	}
291		370
292	sub port(;&) {	371	sub port(;&) {
293	my $id = "$UNIQ." . $ID++;	372	my $id = "$UNIQ." . $ID++;
294	my $port = "$NODE#$id";	373	my $port = "$NODE#$id";
295		374
296	if (@_) {	375	rcv $port, shift \|\| \&_kilme;
297	rcv $port, shift;
298	} else {
299	$PORT{$id} = sub { }; # nop
300	}
301		376
302	$port	377	$port
303	}	378	}
304		379
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)	380	=item rcv $local_port, $callback->(@msg)
325		381
326	Replaces the callback on the specified miniport (after converting it to	382	Replaces the default callback on the specified port. There is no way to
327	one if required).	383	remove the default callback: use C<sub { }> to disable it, or better
328		384	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...] => $callback->(@msg), ...
334
335	Register callbacks to be called on matching messages on the given full
336	port (after converting it to one if required) and return the port.
337
338	The callback has to return a true value when its work is done, after
339	which is will be removed, or a false value in which case it will stay
340	registered.
341		385
342	The global C<$SELF> (exported by this module) contains C<$port> while	386	The global C<$SELF> (exported by this module) contains C<$port> while
343	executing the callback.	387	executing the callback. Runtime errors during callback execution will
		388	result in the port being C<kil>ed.
344		389
345	Runtime errors wdurign callback execution will result in the port being	390	The default callback received all messages not matched by a more specific
346	C<kil>ed.	391	C<tag> match.
347		392
348	If the match is an array reference, then it will be matched against the	393	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
349	first elements of the message, otherwise only the first element is being
350	matched.
351		394
352	Any element in the match that is specified as C<_any_> (a function	395	Register (or replace) callbacks to be called on messages starting with the
353	exported by this module) matches any single element of the message.	396	given tag on the given port (and return the port), or unregister it (when
		397	C<$callback> is C<$undef> or missing). There can only be one callback
		398	registered for each tag.
354		399
355	While not required, it is highly recommended that the first matching	400	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	401	element (the tag) has been removed. The callback will use the same
357	also the most efficient match (by far).	402	environment as the default callback (see above).
358		403
359	Example: create a port and bind receivers on it in one go.	404	Example: create a port and bind receivers on it in one go.
360		405
361	my $port = rcv port,	406	my $port = rcv port,
362	msg1 => sub { ...; 0 },	407	msg1 => sub { ... },
363	msg2 => sub { ...; 0 },	408	msg2 => sub { ... },
364	;	409	;
365		410
366	Example: create a port, bind receivers and send it in a message elsewhere	411	Example: create a port, bind receivers and send it in a message elsewhere
367	in one go:	412	in one go:
368		413
369	snd $otherport, reply =>	414	snd $otherport, reply =>
370	rcv port,	415	rcv port,
371	msg1 => sub { ...; 0 },	416	msg1 => sub { ... },
372	...	417	...
373	;	418	;
374		419
		420	Example: temporarily register a rcv callback for a tag matching some port
		421	(e.g. for an rpc reply) and unregister it after a message was received.
		422
		423	rcv $port, $otherport => sub {
		424	my @reply = @_;
		425
		426	rcv $SELF, $otherport;
		427	};
		428
375	=cut	429	=cut
376		430
377	sub rcv($@) {	431	sub rcv($@) {
378	my $port = shift;	432	my $port = shift;
379	my ($noderef, $portid) = split /#/, $port, 2;	433	my ($nodeid, $portid) = split /#/, $port, 2;
380		434
381	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	435	$NODE{$nodeid} == $NODE{""}
382	or Carp::croak "$port: rcv can only be called on local ports, caught";	436	or Carp::croak "$port: rcv can only be called on local ports, caught";
383		437
384	if (@_ == 1) {	438	while (@_) {
		439	if (ref $_[0]) {
		440	if (my $self = $PORT_DATA{$portid}) {
		441	"AnyEvent::MP::Port" eq ref $self
		442	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		443
		444	$self->[0] = shift;
		445	} else {
385	my $cb = shift;	446	my $cb = shift;
386	delete $PORT_DATA{$portid};
387	$PORT{$portid} = sub {	447	$PORT{$portid} = sub {
388	local $SELF = $port;	448	local $SELF = $port;
389	eval {	449	eval { &$cb }; _self_die if $@;
390	&$cb	450	};
391	and kil $port;
392	};	451	}
393	_self_die if $@;	452	} elsif (defined $_[0]) {
394	};
395	} else {
396	my $self = $PORT_DATA{$portid} \|\|= do {	453	my $self = $PORT_DATA{$portid} \|\|= do {
397	my $self = bless {	454	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
398	id => $port,
399	}, "AnyEvent::MP::Port";
400		455
401	$PORT{$portid} = sub {	456	$PORT{$portid} = sub {
402	local $SELF = $port;	457	local $SELF = $port;
403		458
404	eval {
405	for (@{ $self->{rc0}{$_[0]} }) {	459	if (my $cb = $self->[1]{$_[0]}) {
406	$_ && &{$_->[0]}	460	shift;
407	&& undef $_;	461	eval { &$cb }; _self_die if $@;
408	}	462	} else {
409
410	for (@{ $self->{rcv}{$_[0]} }) {
411	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
412	&& &{$_->[0]}	463	&{ $self->[0] };
413	&& undef $_;
414	}
415
416	for (@{ $self->{any} }) {
417	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
418	&& &{$_->[0]}
419	&& undef $_;
420	}	464	}
421	};	465	};
422	_self_die if $@;	466
		467	$self
423	};	468	};
424		469
425	$self
426	};
427
428	"AnyEvent::MP::Port" eq ref $self	470	"AnyEvent::MP::Port" eq ref $self
429	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	471	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
430		472
431	while (@_) {
432	my ($match, $cb) = splice @_, 0, 2;	473	my ($tag, $cb) = splice @_, 0, 2;
433		474
434	if (!ref $match) {	475	if (defined $cb) {
435	push @{ $self->{rc0}{$match} }, [$cb];	476	$self->[1]{$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 {	477	} else {
442	push @{ $self->{any} }, [$cb, $match];	478	delete $self->[1]{$tag};
443	}	479	}
444	}	480	}
445	}	481	}
446		482
447	$port	483	$port
448	}	484	}
449		485
		486	=item peval $port, $coderef[, @args]
		487
		488	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		489	when the code throews an exception the C<$port> will be killed.
		490
		491	Any remaining args will be passed to the callback. Any return values will
		492	be returned to the caller.
		493
		494	This is useful when you temporarily want to execute code in the context of
		495	a port.
		496
		497	Example: create a port and run some initialisation code in it's context.
		498
		499	my $port = port { ... };
		500
		501	peval $port, sub {
		502	init
		503	or die "unable to init";
		504	};
		505
		506	=cut
		507
		508	sub peval($$) {
		509	local $SELF = shift;
		510	my $cb = shift;
		511
		512	if (wantarray) {
		513	my @res = eval { &$cb };
		514	_self_die if $@;
		515	@res
		516	} else {
		517	my $res = eval { &$cb };
		518	_self_die if $@;
		519	$res
		520	}
		521	}
		522
450	=item $closure = psub { BLOCK }	523	=item $closure = psub { BLOCK }
451		524
452	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	525	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>	526	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.	527	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		528
		529	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		530	BLOCK }, @_ } >>.
455		531
456	This is useful when you register callbacks from C<rcv> callbacks:	532	This is useful when you register callbacks from C<rcv> callbacks:
457		533
458	rcv delayed_reply => sub {	534	rcv delayed_reply => sub {
459	my ($delay, @reply) = @_;	535	my ($delay, @reply) = @_;
…		…
483	$res	559	$res
484	}	560	}
485	}	561	}
486	}	562	}
487		563
488	=item $guard = mon $port, $cb->(@reason)	564	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
489		565
490	=item $guard = mon $port, $rcvport	566	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
491		567
492	=item $guard = mon $port	568	=item $guard = mon $port # kill $SELF when $port dies
493		569
494	=item $guard = mon $port, $rcvport, @msg	570	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
495		571
496	Monitor the given port and do something when the port is killed, and	572	Monitor the given port and do something when the port is killed or
497	optionally return a guard that can be used to stop monitoring again.	573	messages to it were lost, and optionally return a guard that can be used
		574	to stop monitoring again.
498		575
499	In the first form (callback), the callback is simply called with any	576	In the first form (callback), the callback is simply called with any
500	number of C<@reason> elements (no @reason means that the port was deleted	577	number of C<@reason> elements (no @reason means that the port was deleted
501	"normally"). Note also that I<< the callback B<must> never die >>, so use	578	"normally"). Note also that I<< the callback B<must> never die >>, so use
502	C<eval> if unsure.	579	C<eval> if unsure.
503		580
504	In the second form (another port given), the other port (C<$rcvport)	581	In the second form (another port given), the other port (C<$rcvport>)
505	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	582	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
506	"normal" kils nothing happens, while under all other conditions, the other	583	"normal" kils nothing happens, while under all other conditions, the other
507	port is killed with the same reason.	584	port is killed with the same reason.
508		585
509	The third form (kill self) is the same as the second form, except that	586	The third form (kill self) is the same as the second form, except that
510	C<$rvport> defaults to C<$SELF>.	587	C<$rvport> defaults to C<$SELF>.
511		588
512	In the last form (message), a message of the form C<@msg, @reason> will be	589	In the last form (message), a message of the form C<@msg, @reason> will be
513	C<snd>.	590	C<snd>.
		591
		592	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		593	alert was raised), they are removed and will not trigger again.
514		594
515	As a rule of thumb, monitoring requests should always monitor a port from	595	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	596	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	597	lost, just like any other message. Another less obvious reason is that
518	even monitoring requests can get lost (for exmaple, when the connection	598	even monitoring requests can get lost (for example, when the connection
519	to the other node goes down permanently). When monitoring a port locally	599	to the other node goes down permanently). When monitoring a port locally
520	these problems do not exist.	600	these problems do not exist.
521		601
		602	C<mon> effectively guarantees that, in the absence of hardware failures,
		603	after starting the monitor, either all messages sent to the port will
		604	arrive, or the monitoring action will be invoked after possible message
		605	loss has been detected. No messages will be lost "in between" (after
		606	the first lost message no further messages will be received by the
		607	port). After the monitoring action was invoked, further messages might get
		608	delivered again.
		609
		610	Inter-host-connection timeouts and monitoring depend on the transport
		611	used. The only transport currently implemented is TCP, and AnyEvent::MP
		612	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		613	non-idle connection, and usually around two hours for idle connections).
		614
		615	This means that monitoring is good for program errors and cleaning up
		616	stuff eventually, but they are no replacement for a timeout when you need
		617	to ensure some maximum latency.
		618
522	Example: call a given callback when C<$port> is killed.	619	Example: call a given callback when C<$port> is killed.
523		620
524	mon $port, sub { warn "port died because of <@_>\n" };	621	mon $port, sub { warn "port died because of <@_>\n" };
525		622
526	Example: kill ourselves when C<$port> is killed abnormally.	623	Example: kill ourselves when C<$port> is killed abnormally.
…		…
532	mon $port, $self => "restart";	629	mon $port, $self => "restart";
533		630
534	=cut	631	=cut
535		632
536	sub mon {	633	sub mon {
537	my ($noderef, $port) = split /#/, shift, 2;	634	my ($nodeid, $port) = split /#/, shift, 2;
538		635
539	my $node = $NODE{$noderef} \|\| add_node $noderef;	636	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
540		637
541	my $cb = @_ ? $_[0] : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';	638	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
542		639
543	unless (ref $cb) {	640	unless (ref $cb) {
544	if (@_) {	641	if (@_) {
545	# send a kill info message	642	# send a kill info message
546	my (@msg) = @_;	643	my (@msg) = ($cb, @_);
547	$cb = sub { snd @msg, @_ };	644	$cb = sub { snd @msg, @_ };
548	} else {	645	} else {
549	# simply kill other port	646	# simply kill other port
550	my $port = $cb;	647	my $port = $cb;
551	$cb = sub { kil $port, @_ if @_ };	648	$cb = sub { kil $port, @_ if @_ };
…		…
553	}	650	}
554		651
555	$node->monitor ($port, $cb);	652	$node->monitor ($port, $cb);
556		653
557	defined wantarray	654	defined wantarray
558	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	655	and ($cb += 0, AnyEvent::Util::guard { $node->unmonitor ($port, $cb) })
559	}	656	}
560		657
561	=item $guard = mon_guard $port, $ref, $ref...	658	=item $guard = mon_guard $port, $ref, $ref...
562		659
563	Monitors the given C<$port> and keeps the passed references. When the port	660	Monitors the given C<$port> and keeps the passed references. When the port
564	is killed, the references will be freed.	661	is killed, the references will be freed.
565		662
566	Optionally returns a guard that will stop the monitoring.	663	Optionally returns a guard that will stop the monitoring.
567		664
568	This function is useful when you create e.g. timers or other watchers and	665	This function is useful when you create e.g. timers or other watchers and
569	want to free them when the port gets killed:	666	want to free them when the port gets killed (note the use of C<psub>):
570		667
571	$port->rcv (start => sub {	668	$port->rcv (start => sub {
572	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	669	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
573	undef $timer if 0.9 < rand;	670	undef $timer if 0.9 < rand;
574	});	671	});
575	});	672	});
576		673
577	=cut	674	=cut
…		…
586		683
587	=item kil $port[, @reason]	684	=item kil $port[, @reason]
588		685
589	Kill the specified port with the given C<@reason>.	686	Kill the specified port with the given C<@reason>.
590		687
591	If no C<@reason> is specified, then the port is killed "normally" (linked	688	If no C<@reason> is specified, then the port is killed "normally" -
592	ports will not be kileld, or even notified).	689	monitor callback will be invoked, but the kil will not cause linked ports
		690	(C<mon $mport, $lport> form) to get killed.
593		691
594	Otherwise, linked ports get killed with the same reason (second form of	692	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
595	C<mon>, see below).	693	form) get killed with the same reason.
596		694
597	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	695	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
598	will be reported as reason C<< die => $@ >>.	696	will be reported as reason C<< die => $@ >>.
599		697
600	Transport/communication errors are reported as C<< transport_error =>	698	Transport/communication errors are reported as C<< transport_error =>
601	$message >>.	699	$message >>.
602		700
603	=back
604
605	=head1 NODE MESSAGES
606
607	Nodes understand the following messages sent to them. Many of them take
608	arguments called C<@reply>, which will simply be used to compose a reply
609	message - C<$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	701	=cut
617		702
618	=item lookup => $name, @reply	703	=item $port = spawn $node, $initfunc[, @initdata]
619		704
620	Replies with the port ID of the specified well-known port, or C<undef>.	705	Creates a port on the node C<$node> (which can also be a port ID, in which
		706	case it's the node where that port resides).
621		707
622	=item devnull => ...	708	The port ID of the newly created port is returned immediately, and it is
		709	possible to immediately start sending messages or to monitor the port.
623		710
624	Generic data sink/CPU heat conversion.	711	After the port has been created, the init function is called on the remote
		712	node, in the same context as a C<rcv> callback. This function must be a
		713	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		714	specify a function in the main program, use C<::name>.
625		715
626	=item relay => $port, @msg	716	If the function doesn't exist, then the node tries to C<require>
		717	the package, then the package above the package and so on (e.g.
		718	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		719	exists or it runs out of package names.
627		720
628	Simply forwards the message to the given port.	721	The init function is then called with the newly-created port as context
		722	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		723	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		724	the port might not get created.
629		725
630	=item eval => $string[ @reply]	726	A common idiom is to pass a local port, immediately monitor the spawned
		727	port, and in the remote init function, immediately monitor the passed
		728	local port. This two-way monitoring ensures that both ports get cleaned up
		729	when there is a problem.
631		730
632	Evaluates the given string. If C<@reply> is given, then a message of the	731	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
633	form C<@reply, $@, @evalres> is sent.	732	caller before C<spawn> returns (by delaying invocation when spawn is
		733	called for the local node).
634		734
635	Example: crash another node.	735	Example: spawn a chat server port on C<$othernode>.
636		736
637	snd $othernode, eval => "exit";	737	# this node, executed from within a port context:
		738	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		739	mon $server;
638		740
639	=item time => @reply	741	# init function on C<$othernode>
		742	sub connect {
		743	my ($srcport) = @_;
640		744
641	Replies the the current node time to C<@reply>.	745	mon $srcport;
642		746
643	Example: tell the current node to send the current time to C<$myport> in a	747	rcv $SELF, sub {
644	C<timereply> message.	748	...
		749	};
		750	}
645		751
646	snd $NODE, time => $myport, timereply => 1, 2;	752	=cut
647	# => snd $myport, timereply => 1, 2, <time>	753
		754	sub _spawn {
		755	my $port = shift;
		756	my $init = shift;
		757
		758	# rcv will create the actual port
		759	local $SELF = "$NODE#$port";
		760	eval {
		761	&{ load_func $init }
		762	};
		763	_self_die if $@;
		764	}
		765
		766	sub spawn(@) {
		767	my ($nodeid, undef) = split /#/, shift, 2;
		768
		769	my $id = "$RUNIQ." . $ID++;
		770
		771	$_[0] =~ /::/
		772	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		773
		774	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		775
		776	"$nodeid#$id"
		777	}
		778
		779	=item after $timeout, @msg
		780
		781	=item after $timeout, $callback
		782
		783	Either sends the given message, or call the given callback, after the
		784	specified number of seconds.
		785
		786	This is simply a utility function that comes in handy at times - the
		787	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		788	so it may go away in the future.
		789
		790	=cut
		791
		792	sub after($@) {
		793	my ($timeout, @action) = @_;
		794
		795	my $t; $t = AE::timer $timeout, 0, sub {
		796	undef $t;
		797	ref $action[0]
		798	? $action[0]()
		799	: snd @action;
		800	};
		801	}
		802
		803	=item cal $port, @msg, $callback[, $timeout]
		804
		805	A simple form of RPC - sends a message to the given C<$port> with the
		806	given contents (C<@msg>), but adds a reply port to the message.
		807
		808	The reply port is created temporarily just for the purpose of receiving
		809	the reply, and will be C<kil>ed when no longer needed.
		810
		811	A reply message sent to the port is passed to the C<$callback> as-is.
		812
		813	If an optional time-out (in seconds) is given and it is not C<undef>,
		814	then the callback will be called without any arguments after the time-out
		815	elapsed and the port is C<kil>ed.
		816
		817	If no time-out is given (or it is C<undef>), then the local port will
		818	monitor the remote port instead, so it eventually gets cleaned-up.
		819
		820	Currently this function returns the temporary port, but this "feature"
		821	might go in future versions unless you can make a convincing case that
		822	this is indeed useful for something.
		823
		824	=cut
		825
		826	sub cal(@) {
		827	my $timeout = ref $_[-1] ? undef : pop;
		828	my $cb = pop;
		829
		830	my $port = port {
		831	undef $timeout;
		832	kil $SELF;
		833	&$cb;
		834	};
		835
		836	if (defined $timeout) {
		837	$timeout = AE::timer $timeout, 0, sub {
		838	undef $timeout;
		839	kil $port;
		840	$cb->();
		841	};
		842	} else {
		843	mon $_[0], sub {
		844	kil $port;
		845	$cb->();
		846	};
		847	}
		848
		849	push @_, $port;
		850	&snd;
		851
		852	$port
		853	}
648		854
649	=back	855	=back
650		856
651	=head1 AnyEvent::MP vs. Distributed Erlang	857	=head1 AnyEvent::MP vs. Distributed Erlang
652		858
653	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	859	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	860	== 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	861	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
656	sample:	862	sample:
657		863
658	http://www.Erlang.se/doc/programming_rules.shtml	864	http://www.erlang.se/doc/programming_rules.shtml
659	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	865	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	866	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	867	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
662		868
663	Despite the similarities, there are also some important differences:	869	Despite the similarities, there are also some important differences:
664		870
665	=over 4	871	=over 4
666		872
667	=item * Node references contain the recipe on how to contact them.	873	=item * Node IDs are arbitrary strings in AEMP.
668		874
669	Erlang relies on special naming and DNS to work everywhere in the	875	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	876	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
671	convenience functionality.	877	configuration or DNS), and possibly the addresses of some seed nodes, but
		878	will otherwise discover other nodes (and their IDs) itself.
672		879
673	This means that AEMP requires a less tightly controlled environment at the	880	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
674	cost of longer node references and a slightly higher management overhead.	881	uses "local ports are like remote ports".
		882
		883	The failure modes for local ports are quite different (runtime errors
		884	only) then for remote ports - when a local port dies, you I<know> it dies,
		885	when a connection to another node dies, you know nothing about the other
		886	port.
		887
		888	Erlang pretends remote ports are as reliable as local ports, even when
		889	they are not.
		890
		891	AEMP encourages a "treat remote ports differently" philosophy, with local
		892	ports being the special case/exception, where transport errors cannot
		893	occur.
675		894
676	=item * Erlang uses processes and a mailbox, AEMP does not queue.	895	=item * Erlang uses processes and a mailbox, AEMP does not queue.
677		896
678	Erlang uses processes that selctively receive messages, and therefore	897	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	898	therefore needs a queue. AEMP is event based, queuing messages would serve
680	purpose.	899	no useful purpose. For the same reason the pattern-matching abilities
		900	of AnyEvent::MP are more limited, as there is little need to be able to
		901	filter messages without dequeuing them.
681		902
682	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	903	This is not a philosophical difference, but simply stems from AnyEvent::MP
		904	being event-based, while Erlang is process-based.
		905
		906	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		907	top of AEMP and Coro threads.
683		908
684	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	909	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
685		910
686	Sending messages in Erlang is synchronous and blocks the process. AEMP	911	Sending messages in Erlang is synchronous and blocks the process until
687	sends are immediate, connection establishment is handled in the	912	a conenction has been established and the message sent (and so does not
688	background.	913	need a queue that can overflow). AEMP sends return immediately, connection
		914	establishment is handled in the background.
689		915
690	=item * Erlang can silently lose messages, AEMP cannot.	916	=item * Erlang suffers from silent message loss, AEMP does not.
691		917
692	Erlang makes few guarantees on messages delivery - messages can get lost	918	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,	919	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).	920	b, and c, and the other side only receives messages a and c).
695		921
696	AEMP guarantees correct ordering, and the guarantee that there are no	922	AEMP guarantees (modulo hardware errors) correct ordering, and the
		923	guarantee that after one message is lost, all following ones sent to the
		924	same port are lost as well, until monitoring raises an error, so there are
697	holes in the message sequence.	925	no silent "holes" in the message sequence.
698		926
699	=item * In Erlang, processes can be declared dead and later be found to be	927	If you want your software to be very reliable, you have to cope with
700	alive.	928	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
701		929	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	930	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		931
710	=item * Erlang can send messages to the wrong port, AEMP does not.	932	=item * Erlang can send messages to the wrong port, AEMP does not.
711		933
712	In Erlang it is quite possible that a node that restarts reuses a process	934	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	935	process ID known to other nodes for a completely different process,
714	messages destined for that process to end up in an unrelated process.	936	causing messages destined for that process to end up in an unrelated
		937	process.
715		938
716	AEMP never reuses port IDs, so old messages or old port IDs floating	939	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.	940	around in the network will not be sent to an unrelated port.
718		941
719	=item * Erlang uses unprotected connections, AEMP uses secure	942	=item * Erlang uses unprotected connections, AEMP uses secure
720	authentication and can use TLS.	943	authentication and can use TLS.
721		944
722	AEMP can use a proven protocol - SSL/TLS - to protect connections and	945	AEMP can use a proven protocol - TLS - to protect connections and
723	securely authenticate nodes.	946	securely authenticate nodes.
724		947
725	=item * The AEMP protocol is optimised for both text-based and binary	948	=item * The AEMP protocol is optimised for both text-based and binary
726	communications.	949	communications.
727		950
728	The AEMP protocol, unlike the Erlang protocol, supports both	951	The AEMP protocol, unlike the Erlang protocol, supports both programming
729	language-independent text-only protocols (good for debugging) and binary,	952	language independent text-only protocols (good for debugging), and binary,
730	language-specific serialisers (e.g. Storable).	953	language-specific serialisers (e.g. Storable). By default, unless TLS is
		954	used, the protocol is actually completely text-based.
731		955
732	It has also been carefully designed to be implementable in other languages	956	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	957	with a minimum of work while gracefully degrading functionality to make the
734	protocol simple.	958	protocol simple.
735		959
736	=item * AEMP has more flexible monitoring options than Erlang.	960	=item * AEMP has more flexible monitoring options than Erlang.
737		961
738	In Erlang, you can chose to receive I<all> exit signals as messages	962	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	963	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	964	difficult to implement.
741	Erlang, as one can choose between automatic kill, exit message or callback	965
742	on a per-process basis.	966	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		967	between automatic kill, exit message or callback on a per-port basis.
743		968
744	=item * Erlang tries to hide remote/local connections, AEMP does not.	969	=item * Erlang tries to hide remote/local connections, AEMP does not.
745		970
746	Monitoring in Erlang is not an indicator of process death/crashes,	971	Monitoring in Erlang is not an indicator of process death/crashes, in the
747	as linking is (except linking is unreliable in Erlang).	972	same way as linking is (except linking is unreliable in Erlang).
748		973
749	In AEMP, you don't "look up" registered port names or send to named ports	974	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	975	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	976	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	977	remote port. Since both monitors are local to the node, they are much more
753	more reliable.	978	reliable (no need for C<spawn_link>).
754		979
755	This also saves round-trips and avoids sending messages to the wrong port	980	This also saves round-trips and avoids sending messages to the wrong port
756	(hard to do in Erlang).	981	(hard to do in Erlang).
757		982
758	=back	983	=back
759		984
		985	=head1 RATIONALE
		986
		987	=over 4
		988
		989	=item Why strings for port and node IDs, why not objects?
		990
		991	We considered "objects", but found that the actual number of methods
		992	that can be called are quite low. Since port and node IDs travel over
		993	the network frequently, the serialising/deserialising would add lots of
		994	overhead, as well as having to keep a proxy object everywhere.
		995
		996	Strings can easily be printed, easily serialised etc. and need no special
		997	procedures to be "valid".
		998
		999	And as a result, a port with just a default receiver consists of a single
		1000	code reference stored in a global hash - it can't become much cheaper.
		1001
		1002	=item Why favour JSON, why not a real serialising format such as Storable?
		1003
		1004	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1005	format, but currently there is no way to make a node use Storable by
		1006	default (although all nodes will accept it).
		1007
		1008	The default framing protocol is JSON because a) JSON::XS is many times
		1009	faster for small messages and b) most importantly, after years of
		1010	experience we found that object serialisation is causing more problems
		1011	than it solves: Just like function calls, objects simply do not travel
		1012	easily over the network, mostly because they will always be a copy, so you
		1013	always have to re-think your design.
		1014
		1015	Keeping your messages simple, concentrating on data structures rather than
		1016	objects, will keep your messages clean, tidy and efficient.
		1017
		1018	=back
		1019
760	=head1 SEE ALSO	1020	=head1 SEE ALSO
		1021
		1022	L<AnyEvent::MP::Intro> - a gentle introduction.
		1023
		1024	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1025
		1026	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1027	your applications.
		1028
		1029	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1030
		1031	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1032	all nodes.
761		1033
762	L<AnyEvent>.	1034	L<AnyEvent>.
763		1035
764	=head1 AUTHOR	1036	=head1 AUTHOR
765		1037

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Revision 1.120 by root, Sun Feb 26 11:12:54 2012 UTC