[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 1.125 by root, Sat Mar 3 13:07:19 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<#>)
62	separator, and a port name (a printable string of unspecified format). An	88	as separator, and a port name (a printable string of unspecified
63	exception is the the node port, whose ID is identical to its node	89	format created by AnyEvent::MP).
64	reference.
65		90
66	=item node	91	=item node
67		92
68	A node is a single process containing at least one port - the node	93	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	94	which enables nodes to manage each other remotely, and to create new
70	create new ports, among other things.	95	ports.
71		96
72	Nodes are either private (single-process only), slaves (connected to a	97	Nodes are either public (have one or more listening ports) or private
73	master node only) or public nodes (connectable from unrelated nodes).	98	(no listening ports). Private nodes cannot talk to other private nodes
		99	currently, but all nodes can talk to public nodes.
74		100
75	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	101	Nodes is represented by (printable) strings called "node IDs".
76		102
77	A node reference is a string that either simply identifies the node (for	103	=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		104
81	This recipe is simply a comma-separated list of C<address:port> pairs (for	105	A node ID is a string that uniquely identifies the node within a
82	TCP/IP, other protocols might look different).	106	network. Depending on the configuration used, node IDs can look like a
		107	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		108	doesn't interpret node IDs in any way except to uniquely identify a node.
83		109
84	Node references come in two flavours: resolved (containing only numerical	110	=item binds - C<ip:port>
85	addresses) or unresolved (where hostnames are used instead of addresses).
86		111
87	Before using an unresolved node reference in a message you first have to	112	Nodes can only talk to each other by creating some kind of connection to
88	resolve it.	113	each other. To do this, nodes should listen on one or more local transport
		114	endpoints - binds.
		115
		116	Currently, only standard C<ip:port> specifications can be used, which
		117	specify TCP ports to listen on. So a bind is basically just a tcp socket
		118	in listening mode thta accepts conenctions form other nodes.
		119
		120	=item seed nodes
		121
		122	When a node starts, it knows nothing about the network it is in - it
		123	needs to connect to at least one other node that is already in the
		124	network. These other nodes are called "seed nodes".
		125
		126	Seed nodes themselves are not special - they are seed nodes only because
		127	some other node I<uses> them as such, but any node can be used as seed
		128	node for other nodes, and eahc node cna use a different set of seed nodes.
		129
		130	In addition to discovering the network, seed nodes are also used to
		131	maintain the network - all nodes using the same seed node form are part of
		132	the same network. If a network is split into multiple subnets because e.g.
		133	the network link between the parts goes down, then using the same seed
		134	nodes for all nodes ensures that eventually the subnets get merged again.
		135
		136	Seed nodes are expected to be long-running, and at least one seed node
		137	should always be available. They should also be relatively responsive - a
		138	seed node that blocks for long periods will slow down everybody else.
		139
		140	For small networks, it's best if every node uses the same set of seed
		141	nodes. For large networks, it can be useful to specify "regional" seed
		142	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		143	each other. What's important is that all seed nodes connections form a
		144	complete graph, so that the network cannot split into separate subnets
		145	forever.
		146
		147	Seed nodes are represented by seed IDs.
		148
		149	=item seed IDs - C<host:port>
		150
		151	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
		152	TCP port) of nodes that should be used as seed nodes.
		153
		154	=item global nodes
		155
		156	An AEMP network needs a discovery service - nodes need to know how to
		157	connect to other nodes they only know by name. In addition, AEMP offers a
		158	distributed "group database", which maps group names to a list of strings
		159	- for example, to register worker ports.
		160
		161	A network needs at least one global node to work, and allows every node to
		162	be a global node.
		163
		164	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		165	node and tries to keep connections to all other nodes. So while it can
		166	make sense to make every node "global" in small networks, it usually makes
		167	sense to only make seed nodes into global nodes in large networks (nodes
		168	keep connections to seed nodes and global nodes, so makign them the same
		169	reduces overhead).
89		170
90	=back	171	=back
91		172
92	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
93		174
95		176
96	=cut	177	=cut
97		178
98	package AnyEvent::MP;	179	package AnyEvent::MP;
99		180
		181	use AnyEvent::MP::Config ();
100	use AnyEvent::MP::Base;	182	use AnyEvent::MP::Kernel;
		183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
101		184
102	use common::sense;	185	use common::sense;
103		186
104	use Carp ();	187	use Carp ();
105		188
106	use AE ();	189	use AE ();
		190	use Guard ();
107		191
108	use base "Exporter";	192	use base "Exporter";
109		193
110	our $VERSION = '0.1';	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
		195
111	our @EXPORT = qw(	196	our @EXPORT = qw(
112	NODE $NODE *SELF node_of _any_	197	NODE $NODE *SELF node_of after
113	resolve_node initialise_node	198	configure
114	snd rcv mon kil reg psub	199	snd rcv mon mon_guard kil psub peval spawn cal
115	port	200	port
		201	db_set db_del db_reg
116	);	202	);
117		203
118	our $SELF;	204	our $SELF;
119		205
120	sub _self_die() {	206	sub _self_die() {
…		…
123	kil $SELF, die => $msg;	209	kil $SELF, die => $msg;
124	}	210	}
125		211
126	=item $thisnode = NODE / $NODE	212	=item $thisnode = NODE / $NODE
127		213
128	The C<NODE> function returns, and the C<$NODE> variable contains	214	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	215	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	216	a call to C<configure>.
131	identifiers become invalid.
132		217
133	=item $noderef = node_of $port	218	=item $nodeid = node_of $port
134		219
135	Extracts and returns the noderef from a portid or a noderef.	220	Extracts and returns the node ID from a port ID or a node ID.
136		221
137	=item initialise_node $noderef, $seednode, $seednode...	222	=item configure $profile, key => value...
138		223
139	=item initialise_node "slave/", $master, $master...	224	=item configure key => value...
140		225
141	Before a node can talk to other nodes on the network it has to initialise	226	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	227	"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.	228	to know is its own name, and optionally it should know the addresses of
		229	some other nodes in the network to discover other nodes.
144		230
145	This function initialises a node - it must be called exactly once (or	231	This function configures a node - it must be called exactly once (or
146	never) before calling other AnyEvent::MP functions.	232	never) before calling other AnyEvent::MP functions.
147		233
148	All arguments are noderefs, which can be either resolved or unresolved.	234	The key/value pairs are basically the same ones as documented for the
149		235	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		236
152	=over 4	237	=over 4
153		238
154	=item public nodes	239	=item norc => $boolean (default false)
155		240
156	For public nodes, C<$noderef> must either be a (possibly unresolved)	241	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	242	be consulted - all configuraiton options must be specified in the
158	which case the noderef will be guessed.	243	C<configure> call.
159		244
160	Afterwards, the node will bind itself on all endpoints and try to connect	245	=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		246
164	=item slave nodes	247	IF true, then the values specified in the C<configure> will take
165		248	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	249	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		250
174	=back	251	=back
175		252
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	253	=over 4
211		254
212	=item the empty string	255	=item step 1, gathering configuration from profiles
213		256
214	An empty-string component gets resolved as if the default port (4040) was	257	The function first looks up a profile in the aemp configuration (see the
215	specified.	258	L<aemp> commandline utility). The profile name can be specified via the
		259	named C<profile> parameter or can simply be the first parameter). If it is
		260	missing, then the nodename (F<uname -n>) will be used as profile name.
216		261
217	=item naked port numbers (e.g. C<1234>)	262	The profile data is then gathered as follows:
218		263
219	These are resolved by prepending the local nodename and a colon, to be	264	First, all remaining key => value pairs (all of which are conveniently
220	further resolved.	265	undocumented at the moment) will be interpreted as configuration
		266	data. Then they will be overwritten by any values specified in the global
		267	default configuration (see the F<aemp> utility), then the chain of
		268	profiles chosen by the profile name (and any C<parent> attributes).
221		269
222	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	270	That means that the values specified in the profile have highest priority
		271	and the values specified directly via C<configure> have lowest priority,
		272	and can only be used to specify defaults.
223		273
224	These are resolved by using AnyEvent::DNS to resolve them, optionally	274	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	275	this process. If not, then the profile name will be used as node ID, with
226	specified.	276	a slash (C</>) attached.
		277
		278	If the node ID (or profile name) ends with a slash (C</>), then a random
		279	string is appended to make it unique.
		280
		281	=item step 2, bind listener sockets
		282
		283	The next step is to look up the binds in the profile, followed by binding
		284	aemp protocol listeners on all binds specified (it is possible and valid
		285	to have no binds, meaning that the node cannot be contacted form the
		286	outside. This means the node cannot talk to other nodes that also have no
		287	binds, but it can still talk to all "normal" nodes).
		288
		289	If the profile does not specify a binds list, then a default of C<*> is
		290	used, meaning the node will bind on a dynamically-assigned port on every
		291	local IP address it finds.
		292
		293	=item step 3, connect to seed nodes
		294
		295	As the last step, the seed ID list from the profile is passed to the
		296	L<AnyEvent::MP::Global> module, which will then use it to keep
		297	connectivity with at least one node at any point in time.
227		298
228	=back	299	=back
		300
		301	Example: become a distributed node using the local node name as profile.
		302	This should be the most common form of invocation for "daemon"-type nodes.
		303
		304	configure
		305
		306	Example: become an anonymous node. This form is often used for commandline
		307	clients.
		308
		309	configure nodeid => "anon/";
		310
		311	Example: configure a node using a profile called seed, which is suitable
		312	for a seed node as it binds on all local addresses on a fixed port (4040,
		313	customary for aemp).
		314
		315	# use the aemp commandline utility
		316	# aemp profile seed binds '*:4040'
		317
		318	# then use it
		319	configure profile => "seed";
		320
		321	# or simply use aemp from the shell again:
		322	# aemp run profile seed
		323
		324	# or provide a nicer-to-remember nodeid
		325	# aemp run profile seed nodeid "$(hostname)"
229		326
230	=item $SELF	327	=item $SELF
231		328
232	Contains the current port id while executing C<rcv> callbacks or C<psub>	329	Contains the current port id while executing C<rcv> callbacks or C<psub>
233	blocks.	330	blocks.
234		331
235	=item SELF, %SELF, @SELF...	332	=item *SELF, SELF, %SELF, @SELF...
236		333
237	Due to some quirks in how perl exports variables, it is impossible to	334	Due to some quirks in how perl exports variables, it is impossible to
238	just export C<$SELF>, all the symbols called C<SELF> are exported by this	335	just export C<$SELF>, all the symbols named C<SELF> are exported by this
239	module, but only C<$SELF> is currently used.	336	module, but only C<$SELF> is currently used.
240		337
241	=item snd $port, type => @data	338	=item snd $port, type => @data
242		339
243	=item snd $port, @msg	340	=item snd $port, @msg
244		341
245	Send the given message to the given port ID, which can identify either	342	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	343	local or a remote port, and must be a port ID.
247	stringifies a sa port ID (such as a port object :).
248		344
249	While the message can be about anything, it is highly recommended to use a	345	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	346	use a string as first element (a port ID, or some word that indicates a
251	type etc.).	347	request type etc.) and to consist if only simple perl values (scalars,
		348	arrays, hashes) - if you think you need to pass an object, think again.
252		349
253	The message data effectively becomes read-only after a call to this	350	The message data logically becomes read-only after a call to this
254	function: modifying any argument is not allowed and can cause many	351	function: modifying any argument (or values referenced by them) is
255	problems.	352	forbidden, as there can be considerable time between the call to C<snd>
		353	and the time the message is actually being serialised - in fact, it might
		354	never be copied as within the same process it is simply handed to the
		355	receiving port.
256		356
257	The type of data you can transfer depends on the transport protocol: when	357	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	358	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	359	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	360	that Storable can serialise and deserialise is allowed, and for the local
261	node, anything can be passed.	361	node, anything can be passed. Best rely only on the common denominator of
		362	these.
262		363
263	=item $local_port = port	364	=item $local_port = port
264		365
265	Create a new local port object that can be used either as a pattern	366	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"),	367	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		368
269	=item $port = port { my @msg = @_; $finished }	369	=item $local_port = port { my @msg = @_ }
270		370
271	Creates a "miniport", that is, a very lightweight port without any pattern	371	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.	372	creating a port and calling C<rcv $port, $callback> on it.
274		373
275	The block will be called for every message received on the port. When the	374	The block will be called for every message received on the port, with the
276	callback returns a true value its job is considered "done" and the port	375	global variable C<$SELF> set to the port ID. Runtime errors will cause the
277	will be destroyed. Otherwise it will stay alive.	376	port to be C<kil>ed. The message will be passed as-is, no extra argument
		377	(i.e. no port ID) will be passed to the callback.
278		378
279	The message will be passed as-is, no extra argument (i.e. no port id) will	379	If you want to stop/destroy the port, simply C<kil> it:
280	be passed to the callback.
281		380
282	If you need the local port id in the callback, this works nicely:	381	my $port = port {
283		382	my @msg = @_;
284	my $port; $port = port {	383	...
285	snd $otherport, reply => $port;	384	kil $SELF;
286	};	385	};
287		386
288	=cut	387	=cut
289		388
290	sub rcv($@);	389	sub rcv($@);
291		390
		391	sub _kilme {
		392	die "received message on port without callback";
		393	}
		394
292	sub port(;&) {	395	sub port(;&) {
293	my $id = "$UNIQ." . $ID++;	396	my $id = $UNIQ . ++$ID;
294	my $port = "$NODE#$id";	397	my $port = "$NODE#$id";
295		398
296	if (@_) {	399	rcv $port, shift \|\| \&_kilme;
297	rcv $port, shift;
298	} else {
299	$PORT{$id} = sub { }; # nop
300	}
301		400
302	$port	401	$port
303	}	402	}
304		403
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)	404	=item rcv $local_port, $callback->(@msg)
325		405
326	Replaces the callback on the specified miniport (after converting it to	406	Replaces the default callback on the specified port. There is no way to
327	one if required).	407	remove the default callback: use C<sub { }> to disable it, or better
328		408	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...] => $callback->(@msg), ...
334
335	Register callbacks to be called on matching messages on the given full
336	port (after converting it to one if required) and return the port.
337
338	The callback has to return a true value when its work is done, after
339	which is will be removed, or a false value in which case it will stay
340	registered.
341		409
342	The global C<$SELF> (exported by this module) contains C<$port> while	410	The global C<$SELF> (exported by this module) contains C<$port> while
343	executing the callback.	411	executing the callback. Runtime errors during callback execution will
		412	result in the port being C<kil>ed.
344		413
345	Runtime errors wdurign callback execution will result in the port being	414	The default callback received all messages not matched by a more specific
346	C<kil>ed.	415	C<tag> match.
347		416
348	If the match is an array reference, then it will be matched against the	417	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
349	first elements of the message, otherwise only the first element is being
350	matched.
351		418
352	Any element in the match that is specified as C<_any_> (a function	419	Register (or replace) callbacks to be called on messages starting with the
353	exported by this module) matches any single element of the message.	420	given tag on the given port (and return the port), or unregister it (when
		421	C<$callback> is C<$undef> or missing). There can only be one callback
		422	registered for each tag.
354		423
355	While not required, it is highly recommended that the first matching	424	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	425	element (the tag) has been removed. The callback will use the same
357	also the most efficient match (by far).	426	environment as the default callback (see above).
358		427
359	Example: create a port and bind receivers on it in one go.	428	Example: create a port and bind receivers on it in one go.
360		429
361	my $port = rcv port,	430	my $port = rcv port,
362	msg1 => sub { ...; 0 },	431	msg1 => sub { ... },
363	msg2 => sub { ...; 0 },	432	msg2 => sub { ... },
364	;	433	;
365		434
366	Example: create a port, bind receivers and send it in a message elsewhere	435	Example: create a port, bind receivers and send it in a message elsewhere
367	in one go:	436	in one go:
368		437
369	snd $otherport, reply =>	438	snd $otherport, reply =>
370	rcv port,	439	rcv port,
371	msg1 => sub { ...; 0 },	440	msg1 => sub { ... },
372	...	441	...
373	;	442	;
374		443
		444	Example: temporarily register a rcv callback for a tag matching some port
		445	(e.g. for an rpc reply) and unregister it after a message was received.
		446
		447	rcv $port, $otherport => sub {
		448	my @reply = @_;
		449
		450	rcv $SELF, $otherport;
		451	};
		452
375	=cut	453	=cut
376		454
377	sub rcv($@) {	455	sub rcv($@) {
378	my $port = shift;	456	my $port = shift;
379	my ($noderef, $portid) = split /#/, $port, 2;	457	my ($nodeid, $portid) = split /#/, $port, 2;
380		458
381	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	459	$NODE{$nodeid} == $NODE{""}
382	or Carp::croak "$port: rcv can only be called on local ports, caught";	460	or Carp::croak "$port: rcv can only be called on local ports, caught";
383		461
384	if (@_ == 1) {	462	while (@_) {
		463	if (ref $_[0]) {
		464	if (my $self = $PORT_DATA{$portid}) {
		465	"AnyEvent::MP::Port" eq ref $self
		466	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
		467
		468	$self->[0] = shift;
		469	} else {
385	my $cb = shift;	470	my $cb = shift;
386	delete $PORT_DATA{$portid};
387	$PORT{$portid} = sub {	471	$PORT{$portid} = sub {
388	local $SELF = $port;	472	local $SELF = $port;
389	eval {	473	eval { &$cb }; _self_die if $@;
390	&$cb	474	};
391	and kil $port;
392	};	475	}
393	_self_die if $@;	476	} elsif (defined $_[0]) {
394	};
395	} else {
396	my $self = $PORT_DATA{$portid} \|\|= do {	477	my $self = $PORT_DATA{$portid} \|\|= do {
397	my $self = bless {	478	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
398	id => $port,
399	}, "AnyEvent::MP::Port";
400		479
401	$PORT{$portid} = sub {	480	$PORT{$portid} = sub {
402	local $SELF = $port;	481	local $SELF = $port;
403		482
404	eval {
405	for (@{ $self->{rc0}{$_[0]} }) {	483	if (my $cb = $self->[1]{$_[0]}) {
406	$_ && &{$_->[0]}	484	shift;
407	&& undef $_;	485	eval { &$cb }; _self_die if $@;
408	}	486	} else {
409
410	for (@{ $self->{rcv}{$_[0]} }) {
411	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
412	&& &{$_->[0]}	487	&{ $self->[0] };
413	&& undef $_;
414	}
415
416	for (@{ $self->{any} }) {
417	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
418	&& &{$_->[0]}
419	&& undef $_;
420	}	488	}
421	};	489	};
422	_self_die if $@;	490
		491	$self
423	};	492	};
424		493
425	$self
426	};
427
428	"AnyEvent::MP::Port" eq ref $self	494	"AnyEvent::MP::Port" eq ref $self
429	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	495	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
430		496
431	while (@_) {
432	my ($match, $cb) = splice @_, 0, 2;	497	my ($tag, $cb) = splice @_, 0, 2;
433		498
434	if (!ref $match) {	499	if (defined $cb) {
435	push @{ $self->{rc0}{$match} }, [$cb];	500	$self->[1]{$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 {	501	} else {
442	push @{ $self->{any} }, [$cb, $match];	502	delete $self->[1]{$tag};
443	}	503	}
444	}	504	}
445	}	505	}
446		506
447	$port	507	$port
448	}	508	}
449		509
		510	=item peval $port, $coderef[, @args]
		511
		512	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		513	when the code throews an exception the C<$port> will be killed.
		514
		515	Any remaining args will be passed to the callback. Any return values will
		516	be returned to the caller.
		517
		518	This is useful when you temporarily want to execute code in the context of
		519	a port.
		520
		521	Example: create a port and run some initialisation code in it's context.
		522
		523	my $port = port { ... };
		524
		525	peval $port, sub {
		526	init
		527	or die "unable to init";
		528	};
		529
		530	=cut
		531
		532	sub peval($$) {
		533	local $SELF = shift;
		534	my $cb = shift;
		535
		536	if (wantarray) {
		537	my @res = eval { &$cb };
		538	_self_die if $@;
		539	@res
		540	} else {
		541	my $res = eval { &$cb };
		542	_self_die if $@;
		543	$res
		544	}
		545	}
		546
450	=item $closure = psub { BLOCK }	547	=item $closure = psub { BLOCK }
451		548
452	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	549	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>	550	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.	551	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		552
		553	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		554	BLOCK }, @_ } >>.
455		555
456	This is useful when you register callbacks from C<rcv> callbacks:	556	This is useful when you register callbacks from C<rcv> callbacks:
457		557
458	rcv delayed_reply => sub {	558	rcv delayed_reply => sub {
459	my ($delay, @reply) = @_;	559	my ($delay, @reply) = @_;
…		…
483	$res	583	$res
484	}	584	}
485	}	585	}
486	}	586	}
487		587
488	=item $guard = mon $port, $cb->(@reason)	588	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
489		589
490	=item $guard = mon $port, $rcvport	590	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
491		591
492	=item $guard = mon $port	592	=item $guard = mon $port # kill $SELF when $port dies
493		593
494	=item $guard = mon $port, $rcvport, @msg	594	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
495		595
496	Monitor the given port and do something when the port is killed, and	596	Monitor the given port and do something when the port is killed or
497	optionally return a guard that can be used to stop monitoring again.	597	messages to it were lost, and optionally return a guard that can be used
		598	to stop monitoring again.
498		599
499	In the first form (callback), the callback is simply called with any	600	In the first form (callback), the callback is simply called with any
500	number of C<@reason> elements (no @reason means that the port was deleted	601	number of C<@reason> elements (no @reason means that the port was deleted
501	"normally"). Note also that I<< the callback B<must> never die >>, so use	602	"normally"). Note also that I<< the callback B<must> never die >>, so use
502	C<eval> if unsure.	603	C<eval> if unsure.
503		604
504	In the second form (another port given), the other port (C<$rcvport)	605	In the second form (another port given), the other port (C<$rcvport>)
505	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	606	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
506	"normal" kils nothing happens, while under all other conditions, the other	607	"normal" kils nothing happens, while under all other conditions, the other
507	port is killed with the same reason.	608	port is killed with the same reason.
508		609
509	The third form (kill self) is the same as the second form, except that	610	The third form (kill self) is the same as the second form, except that
510	C<$rvport> defaults to C<$SELF>.	611	C<$rvport> defaults to C<$SELF>.
511		612
512	In the last form (message), a message of the form C<@msg, @reason> will be	613	In the last form (message), a message of the form C<@msg, @reason> will be
513	C<snd>.	614	C<snd>.
		615
		616	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		617	alert was raised), they are removed and will not trigger again.
514		618
515	As a rule of thumb, monitoring requests should always monitor a port from	619	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	620	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	621	lost, just like any other message. Another less obvious reason is that
518	even monitoring requests can get lost (for exmaple, when the connection	622	even monitoring requests can get lost (for example, when the connection
519	to the other node goes down permanently). When monitoring a port locally	623	to the other node goes down permanently). When monitoring a port locally
520	these problems do not exist.	624	these problems do not exist.
521		625
		626	C<mon> effectively guarantees that, in the absence of hardware failures,
		627	after starting the monitor, either all messages sent to the port will
		628	arrive, or the monitoring action will be invoked after possible message
		629	loss has been detected. No messages will be lost "in between" (after
		630	the first lost message no further messages will be received by the
		631	port). After the monitoring action was invoked, further messages might get
		632	delivered again.
		633
		634	Inter-host-connection timeouts and monitoring depend on the transport
		635	used. The only transport currently implemented is TCP, and AnyEvent::MP
		636	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		637	non-idle connection, and usually around two hours for idle connections).
		638
		639	This means that monitoring is good for program errors and cleaning up
		640	stuff eventually, but they are no replacement for a timeout when you need
		641	to ensure some maximum latency.
		642
522	Example: call a given callback when C<$port> is killed.	643	Example: call a given callback when C<$port> is killed.
523		644
524	mon $port, sub { warn "port died because of <@_>\n" };	645	mon $port, sub { warn "port died because of <@_>\n" };
525		646
526	Example: kill ourselves when C<$port> is killed abnormally.	647	Example: kill ourselves when C<$port> is killed abnormally.
…		…
532	mon $port, $self => "restart";	653	mon $port, $self => "restart";
533		654
534	=cut	655	=cut
535		656
536	sub mon {	657	sub mon {
537	my ($noderef, $port) = split /#/, shift, 2;	658	my ($nodeid, $port) = split /#/, shift, 2;
538		659
539	my $node = $NODE{$noderef} \|\| add_node $noderef;	660	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
540		661
541	my $cb = @_ ? $_[0] : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';	662	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
542		663
543	unless (ref $cb) {	664	unless (ref $cb) {
544	if (@_) {	665	if (@_) {
545	# send a kill info message	666	# send a kill info message
546	my (@msg) = @_;	667	my (@msg) = ($cb, @_);
547	$cb = sub { snd @msg, @_ };	668	$cb = sub { snd @msg, @_ };
548	} else {	669	} else {
549	# simply kill other port	670	# simply kill other port
550	my $port = $cb;	671	my $port = $cb;
551	$cb = sub { kil $port, @_ if @_ };	672	$cb = sub { kil $port, @_ if @_ };
…		…
553	}	674	}
554		675
555	$node->monitor ($port, $cb);	676	$node->monitor ($port, $cb);
556		677
557	defined wantarray	678	defined wantarray
558	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	679	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
559	}	680	}
560		681
561	=item $guard = mon_guard $port, $ref, $ref...	682	=item $guard = mon_guard $port, $ref, $ref...
562		683
563	Monitors the given C<$port> and keeps the passed references. When the port	684	Monitors the given C<$port> and keeps the passed references. When the port
564	is killed, the references will be freed.	685	is killed, the references will be freed.
565		686
566	Optionally returns a guard that will stop the monitoring.	687	Optionally returns a guard that will stop the monitoring.
567		688
568	This function is useful when you create e.g. timers or other watchers and	689	This function is useful when you create e.g. timers or other watchers and
569	want to free them when the port gets killed:	690	want to free them when the port gets killed (note the use of C<psub>):
570		691
571	$port->rcv (start => sub {	692	$port->rcv (start => sub {
572	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	693	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
573	undef $timer if 0.9 < rand;	694	undef $timer if 0.9 < rand;
574	});	695	});
575	});	696	});
576		697
577	=cut	698	=cut
…		…
586		707
587	=item kil $port[, @reason]	708	=item kil $port[, @reason]
588		709
589	Kill the specified port with the given C<@reason>.	710	Kill the specified port with the given C<@reason>.
590		711
591	If no C<@reason> is specified, then the port is killed "normally" (linked	712	If no C<@reason> is specified, then the port is killed "normally" -
592	ports will not be kileld, or even notified).	713	monitor callback will be invoked, but the kil will not cause linked ports
		714	(C<mon $mport, $lport> form) to get killed.
593		715
594	Otherwise, linked ports get killed with the same reason (second form of	716	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
595	C<mon>, see below).	717	form) get killed with the same reason.
596		718
597	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	719	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
598	will be reported as reason C<< die => $@ >>.	720	will be reported as reason C<< die => $@ >>.
599		721
600	Transport/communication errors are reported as C<< transport_error =>	722	Transport/communication errors are reported as C<< transport_error =>
601	$message >>.	723	$message >>.
602		724
		725	=cut
		726
		727	=item $port = spawn $node, $initfunc[, @initdata]
		728
		729	Creates a port on the node C<$node> (which can also be a port ID, in which
		730	case it's the node where that port resides).
		731
		732	The port ID of the newly created port is returned immediately, and it is
		733	possible to immediately start sending messages or to monitor the port.
		734
		735	After the port has been created, the init function is called on the remote
		736	node, in the same context as a C<rcv> callback. This function must be a
		737	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		738	specify a function in the main program, use C<::name>.
		739
		740	If the function doesn't exist, then the node tries to C<require>
		741	the package, then the package above the package and so on (e.g.
		742	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
		743	exists or it runs out of package names.
		744
		745	The init function is then called with the newly-created port as context
		746	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		747	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		748	the port might not get created.
		749
		750	A common idiom is to pass a local port, immediately monitor the spawned
		751	port, and in the remote init function, immediately monitor the passed
		752	local port. This two-way monitoring ensures that both ports get cleaned up
		753	when there is a problem.
		754
		755	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		756	caller before C<spawn> returns (by delaying invocation when spawn is
		757	called for the local node).
		758
		759	Example: spawn a chat server port on C<$othernode>.
		760
		761	# this node, executed from within a port context:
		762	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
		763	mon $server;
		764
		765	# init function on C<$othernode>
		766	sub connect {
		767	my ($srcport) = @_;
		768
		769	mon $srcport;
		770
		771	rcv $SELF, sub {
		772	...
		773	};
		774	}
		775
		776	=cut
		777
		778	sub _spawn {
		779	my $port = shift;
		780	my $init = shift;
		781
		782	# rcv will create the actual port
		783	local $SELF = "$NODE#$port";
		784	eval {
		785	&{ load_func $init }
		786	};
		787	_self_die if $@;
		788	}
		789
		790	sub spawn(@) {
		791	my ($nodeid, undef) = split /#/, shift, 2;
		792
		793	my $id = $RUNIQ . ++$ID;
		794
		795	$_[0] =~ /::/
		796	or Carp::croak "spawn init function must be a fully-qualified name, caught";
		797
		798	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		799
		800	"$nodeid#$id"
		801	}
		802
		803
		804	=item after $timeout, @msg
		805
		806	=item after $timeout, $callback
		807
		808	Either sends the given message, or call the given callback, after the
		809	specified number of seconds.
		810
		811	This is simply a utility function that comes in handy at times - the
		812	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		813	so it may go away in the future.
		814
		815	=cut
		816
		817	sub after($@) {
		818	my ($timeout, @action) = @_;
		819
		820	my $t; $t = AE::timer $timeout, 0, sub {
		821	undef $t;
		822	ref $action[0]
		823	? $action[0]()
		824	: snd @action;
		825	};
		826	}
		827
		828	=item cal $port, @msg, $callback[, $timeout]
		829
		830	A simple form of RPC - sends a message to the given C<$port> with the
		831	given contents (C<@msg>), but adds a reply port to the message.
		832
		833	The reply port is created temporarily just for the purpose of receiving
		834	the reply, and will be C<kil>ed when no longer needed.
		835
		836	A reply message sent to the port is passed to the C<$callback> as-is.
		837
		838	If an optional time-out (in seconds) is given and it is not C<undef>,
		839	then the callback will be called without any arguments after the time-out
		840	elapsed and the port is C<kil>ed.
		841
		842	If no time-out is given (or it is C<undef>), then the local port will
		843	monitor the remote port instead, so it eventually gets cleaned-up.
		844
		845	Currently this function returns the temporary port, but this "feature"
		846	might go in future versions unless you can make a convincing case that
		847	this is indeed useful for something.
		848
		849	=cut
		850
		851	sub cal(@) {
		852	my $timeout = ref $_[-1] ? undef : pop;
		853	my $cb = pop;
		854
		855	my $port = port {
		856	undef $timeout;
		857	kil $SELF;
		858	&$cb;
		859	};
		860
		861	if (defined $timeout) {
		862	$timeout = AE::timer $timeout, 0, sub {
		863	undef $timeout;
		864	kil $port;
		865	$cb->();
		866	};
		867	} else {
		868	mon $_[0], sub {
		869	kil $port;
		870	$cb->();
		871	};
		872	}
		873
		874	push @_, $port;
		875	&snd;
		876
		877	$port
		878	}
		879
603	=back	880	=back
604		881
605	=head1 NODE MESSAGES	882	=head1 DISTRIBUTED DATABASE
606		883
607	Nodes understand the following messages sent to them. Many of them take	884	AnyEvent::MP comes with a simple distributed database. The database will
608	arguments called C<@reply>, which will simply be used to compose a reply	885	be mirrored asynchronously at all global nodes. Other nodes bind to one of
609	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and	886	the global nodes for their needs.
610	the remaining arguments are simply the message data.
611		887
612	While other messages exist, they are not public and subject to change.	888	The database consists of a two-level hash - a hash contains a hash which
		889	contains values.
613		890
614	=over 4	891	The top level hash key is called "family", and the second-level hash key
		892	is simply called "key".
615		893
616	=cut	894	The family must be alphanumeric, i.e. start with a letter and consist
		895	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		896	pretty much like Perl module names.
617		897
618	=item lookup => $name, @reply	898	As the family namespace is global, it is recommended to prefix family names
		899	with the name of the application or module using it.
619		900
620	Replies with the port ID of the specified well-known port, or C<undef>.	901	The keys must be strings, with no other limitations.
621		902
622	=item devnull => ...	903	The values should preferably be strings, but other perl scalars should
		904	work as well (such as undef, arrays and hashes).
623		905
624	Generic data sink/CPU heat conversion.	906	Every database entry is owned by one node - adding the same family/key
		907	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		908	but the result might be nondeterministic, i.e. the key might have
		909	different values on different nodes.
625		910
626	=item relay => $port, @msg	911	=item db_set $family => $key => $value
627		912
628	Simply forwards the message to the given port.	913	Sets (or replaces) a key to the database.
629		914
630	=item eval => $string[ @reply]	915	=item db_del $family => $key
631		916
632	Evaluates the given string. If C<@reply> is given, then a message of the	917	Deletes a key from the database.
633	form C<@reply, $@, @evalres> is sent.
634		918
635	Example: crash another node.	919	=item $guard = db_reg $family => $key [=> $value]
636		920
637	snd $othernode, eval => "exit";	921	Sets the key on the database and returns a guard. When the guard is
		922	destroyed, the key is deleted from the database. If C<$value> is missing,
		923	then C<undef> is used.
638		924
639	=item time => @reply	925	=cut
640
641	Replies the the current node time to C<@reply>.
642
643	Example: tell the current node to send the current time to C<$myport> in a
644	C<timereply> message.
645
646	snd $NODE, time => $myport, timereply => 1, 2;
647	# => snd $myport, timereply => 1, 2, <time>
648		926
649	=back	927	=back
650		928
651	=head1 AnyEvent::MP vs. Distributed Erlang	929	=head1 AnyEvent::MP vs. Distributed Erlang
652		930
653	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	931	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	932	== 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	933	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
656	sample:	934	sample:
657		935
658	http://www.Erlang.se/doc/programming_rules.shtml	936	http://www.erlang.se/doc/programming_rules.shtml
659	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	937	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	938	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	939	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
662		940
663	Despite the similarities, there are also some important differences:	941	Despite the similarities, there are also some important differences:
664		942
665	=over 4	943	=over 4
666		944
667	=item * Node references contain the recipe on how to contact them.	945	=item * Node IDs are arbitrary strings in AEMP.
668		946
669	Erlang relies on special naming and DNS to work everywhere in the	947	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	948	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
671	convenience functionality.	949	configuration or DNS), and possibly the addresses of some seed nodes, but
		950	will otherwise discover other nodes (and their IDs) itself.
672		951
673	This means that AEMP requires a less tightly controlled environment at the	952	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
674	cost of longer node references and a slightly higher management overhead.	953	uses "local ports are like remote ports".
		954
		955	The failure modes for local ports are quite different (runtime errors
		956	only) then for remote ports - when a local port dies, you I<know> it dies,
		957	when a connection to another node dies, you know nothing about the other
		958	port.
		959
		960	Erlang pretends remote ports are as reliable as local ports, even when
		961	they are not.
		962
		963	AEMP encourages a "treat remote ports differently" philosophy, with local
		964	ports being the special case/exception, where transport errors cannot
		965	occur.
675		966
676	=item * Erlang uses processes and a mailbox, AEMP does not queue.	967	=item * Erlang uses processes and a mailbox, AEMP does not queue.
677		968
678	Erlang uses processes that selctively receive messages, and therefore	969	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	970	therefore needs a queue. AEMP is event based, queuing messages would serve
680	purpose.	971	no useful purpose. For the same reason the pattern-matching abilities
		972	of AnyEvent::MP are more limited, as there is little need to be able to
		973	filter messages without dequeuing them.
681		974
682	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	975	This is not a philosophical difference, but simply stems from AnyEvent::MP
		976	being event-based, while Erlang is process-based.
		977
		978	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		979	top of AEMP and Coro threads.
683		980
684	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	981	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
685		982
686	Sending messages in Erlang is synchronous and blocks the process. AEMP	983	Sending messages in Erlang is synchronous and blocks the process until
687	sends are immediate, connection establishment is handled in the	984	a conenction has been established and the message sent (and so does not
688	background.	985	need a queue that can overflow). AEMP sends return immediately, connection
		986	establishment is handled in the background.
689		987
690	=item * Erlang can silently lose messages, AEMP cannot.	988	=item * Erlang suffers from silent message loss, AEMP does not.
691		989
692	Erlang makes few guarantees on messages delivery - messages can get lost	990	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,	991	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).	992	b, and c, and the other side only receives messages a and c).
695		993
696	AEMP guarantees correct ordering, and the guarantee that there are no	994	AEMP guarantees (modulo hardware errors) correct ordering, and the
		995	guarantee that after one message is lost, all following ones sent to the
		996	same port are lost as well, until monitoring raises an error, so there are
697	holes in the message sequence.	997	no silent "holes" in the message sequence.
698		998
699	=item * In Erlang, processes can be declared dead and later be found to be	999	If you want your software to be very reliable, you have to cope with
700	alive.	1000	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
701		1001	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	1002	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		1003
710	=item * Erlang can send messages to the wrong port, AEMP does not.	1004	=item * Erlang can send messages to the wrong port, AEMP does not.
711		1005
712	In Erlang it is quite possible that a node that restarts reuses a process	1006	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	1007	process ID known to other nodes for a completely different process,
714	messages destined for that process to end up in an unrelated process.	1008	causing messages destined for that process to end up in an unrelated
		1009	process.
715		1010
716	AEMP never reuses port IDs, so old messages or old port IDs floating	1011	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.	1012	around in the network will not be sent to an unrelated port.
718		1013
719	=item * Erlang uses unprotected connections, AEMP uses secure	1014	=item * Erlang uses unprotected connections, AEMP uses secure
720	authentication and can use TLS.	1015	authentication and can use TLS.
721		1016
722	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1017	AEMP can use a proven protocol - TLS - to protect connections and
723	securely authenticate nodes.	1018	securely authenticate nodes.
724		1019
725	=item * The AEMP protocol is optimised for both text-based and binary	1020	=item * The AEMP protocol is optimised for both text-based and binary
726	communications.	1021	communications.
727		1022
728	The AEMP protocol, unlike the Erlang protocol, supports both	1023	The AEMP protocol, unlike the Erlang protocol, supports both programming
729	language-independent text-only protocols (good for debugging) and binary,	1024	language independent text-only protocols (good for debugging), and binary,
730	language-specific serialisers (e.g. Storable).	1025	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1026	used, the protocol is actually completely text-based.
731		1027
732	It has also been carefully designed to be implementable in other languages	1028	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	1029	with a minimum of work while gracefully degrading functionality to make the
734	protocol simple.	1030	protocol simple.
735		1031
736	=item * AEMP has more flexible monitoring options than Erlang.	1032	=item * AEMP has more flexible monitoring options than Erlang.
737		1033
738	In Erlang, you can chose to receive I<all> exit signals as messages	1034	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	1035	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	1036	difficult to implement.
741	Erlang, as one can choose between automatic kill, exit message or callback	1037
742	on a per-process basis.	1038	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1039	between automatic kill, exit message or callback on a per-port basis.
743		1040
744	=item * Erlang tries to hide remote/local connections, AEMP does not.	1041	=item * Erlang tries to hide remote/local connections, AEMP does not.
745		1042
746	Monitoring in Erlang is not an indicator of process death/crashes,	1043	Monitoring in Erlang is not an indicator of process death/crashes, in the
747	as linking is (except linking is unreliable in Erlang).	1044	same way as linking is (except linking is unreliable in Erlang).
748		1045
749	In AEMP, you don't "look up" registered port names or send to named ports	1046	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	1047	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	1048	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	1049	remote port. Since both monitors are local to the node, they are much more
753	more reliable.	1050	reliable (no need for C<spawn_link>).
754		1051
755	This also saves round-trips and avoids sending messages to the wrong port	1052	This also saves round-trips and avoids sending messages to the wrong port
756	(hard to do in Erlang).	1053	(hard to do in Erlang).
757		1054
758	=back	1055	=back
759		1056
		1057	=head1 RATIONALE
		1058
		1059	=over 4
		1060
		1061	=item Why strings for port and node IDs, why not objects?
		1062
		1063	We considered "objects", but found that the actual number of methods
		1064	that can be called are quite low. Since port and node IDs travel over
		1065	the network frequently, the serialising/deserialising would add lots of
		1066	overhead, as well as having to keep a proxy object everywhere.
		1067
		1068	Strings can easily be printed, easily serialised etc. and need no special
		1069	procedures to be "valid".
		1070
		1071	And as a result, a port with just a default receiver consists of a single
		1072	code reference stored in a global hash - it can't become much cheaper.
		1073
		1074	=item Why favour JSON, why not a real serialising format such as Storable?
		1075
		1076	In fact, any AnyEvent::MP node will happily accept Storable as framing
		1077	format, but currently there is no way to make a node use Storable by
		1078	default (although all nodes will accept it).
		1079
		1080	The default framing protocol is JSON because a) JSON::XS is many times
		1081	faster for small messages and b) most importantly, after years of
		1082	experience we found that object serialisation is causing more problems
		1083	than it solves: Just like function calls, objects simply do not travel
		1084	easily over the network, mostly because they will always be a copy, so you
		1085	always have to re-think your design.
		1086
		1087	Keeping your messages simple, concentrating on data structures rather than
		1088	objects, will keep your messages clean, tidy and efficient.
		1089
		1090	=back
		1091
760	=head1 SEE ALSO	1092	=head1 SEE ALSO
		1093
		1094	L<AnyEvent::MP::Intro> - a gentle introduction.
		1095
		1096	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1097
		1098	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1099	your applications.
		1100
		1101	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1102
		1103	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1104	all nodes.
761		1105
762	L<AnyEvent>.	1106	L<AnyEvent>.
763		1107
764	=head1 AUTHOR	1108	=head1 AUTHOR
765		1109

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Revision 1.125 by root, Sat Mar 3 13:07:19 2012 UTC