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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.38 by root, Fri Aug 7 22:55:18 2009 UTC vs.
Revision 1.119 by root, Sun Feb 26 10:29:59 2012 UTC

…		…
1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent::MP - multi-processing/message-passing framework	3	AnyEvent::MP - erlang-style multi-processing/message-passing framework
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::MP;	7	use AnyEvent::MP;
8		8
9	$NODE # contains this node's noderef	9	$NODE # contains this node's node ID
10	NODE # returns this node's noderef	10	NODE # returns this node's node ID
11	NODE $port # returns the noderef of the port
12		11
13	$SELF # receiving/own port id in rcv callbacks	12	$SELF # receiving/own port id in rcv callbacks
14		13
		14	# initialise the node so it can send/receive messages
		15	configure;
		16
15	# ports are message endpoints	17	# ports are message destinations
16		18
17	# sending messages	19	# sending messages
18	snd $port, type => data...;	20	snd $port, type => data...;
19	snd $port, @msg;	21	snd $port, @msg;
20	snd @msg_with_first_element_being_a_port;	22	snd @msg_with_first_element_being_a_port;
21		23
22	# miniports	24	# creating/using ports, the simple way
23	my $miniport = port { my @msg = @_; 0 };	25	my $simple_port = port { my @msg = @_ };
24		26
25	# full ports	27	# creating/using ports, tagged message matching
26	my $port = port;	28	my $port = port;
27	rcv $port, smartmatch => $cb->(@msg);
28	rcv $port, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
29	rcv $port, pong => sub { warn "pong received\n"; 0 };	30	rcv $port, pong => sub { warn "pong received\n" };
30		31
31	# remote ports	32	# create a port on another node
32	my $port = spawn $node, $initfunc, @initdata;	33	my $port = spawn $node, $initfunc, @initdata;
33		34
34	# more, smarter, matches (_any_ is exported by this module)	35	# destroy a port again
35	rcv $port, [child_died => $pid] => sub { ...	36	kil $port; # "normal" kill
36	rcv $port, [_any_, _any_, 3] => sub { .. $_[2] is 3	37	kil $port, my_error => "everything is broken"; # error kill
37		38
38	# monitoring	39	# monitoring
39	mon $port, $cb->(@msg) # callback is invoked on death	40	mon $localport, $cb->(@msg) # callback is invoked on death
40	mon $port, $otherport # kill otherport on abnormal death	41	mon $localport, $otherport # kill otherport on abnormal death
41	mon $port, $otherport, @msg # send message on death	42	mon $localport, $otherport, @msg # send message on death
		43
		44	# temporarily execute code in port context
		45	peval $port, sub { die "kill the port!" };
		46
		47	# execute callbacks in $SELF port context
		48	my $timer = AE::timer 1, 0, psub {
		49	die "kill the port, delayed";
		50	};
		51
		52	=head1 CURRENT STATUS
		53
		54	bin/aemp - stable.
		55	AnyEvent::MP - stable API, should work.
		56	AnyEvent::MP::Intro - explains most concepts.
		57	AnyEvent::MP::Kernel - mostly stable API.
		58	AnyEvent::MP::Global - stable API.
42		59
43	=head1 DESCRIPTION	60	=head1 DESCRIPTION
44		61
45	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
46		63
47	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
48	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
49		66
50	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	67	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
51	manual page.	68	manual page and the examples under F<eg/>.
52
53	At the moment, this module family is severly broken and underdocumented,
54	so do not use. This was uploaded mainly to reserve the CPAN namespace -
55	stay tuned! The basic API should be finished, however.
56		69
57	=head1 CONCEPTS	70	=head1 CONCEPTS
58		71
59	=over 4	72	=over 4
60		73
61	=item port	74	=item port
62		75
63	A port is something you can send messages to (with the C<snd> function).	76	Not to be confused with a TCP port, a "port" is something you can send
		77	messages to (with the C<snd> function).
64		78
65	Some ports allow you to register C<rcv> handlers that can match specific	79	Ports allow you to register C<rcv> handlers that can match all or just
66	messages. All C<rcv> handlers will receive messages they match, messages	80	some messages. Messages send to ports will not be queued, regardless of
67	will not be queued.	81	anything was listening for them or not.
68		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
69	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
70		86
71	A port id is normaly the concatenation of a noderef, a hash-mark (C<#>) as	87	A port ID is the concatenation of a node ID, a hash-mark (C<#>) as
72	separator, and a port name (a printable string of unspecified format). An	88	separator, and a port name (a printable string of unspecified format).
73	exception is the the node port, whose ID is identical to its node
74	reference.
75		89
76	=item node	90	=item node
77		91
78	A node is a single process containing at least one port - the node	92	A node is a single process containing at least one port - the node port,
79	port. You can send messages to node ports to find existing ports or to	93	which enables nodes to manage each other remotely, and to create new
80	create new ports, among other things.	94	ports.
81		95
82	Nodes are either private (single-process only), slaves (connected to a	96	Nodes are either public (have one or more listening ports) or private
83	master node only) or public nodes (connectable from unrelated nodes).	97	(no listening ports). Private nodes cannot talk to other private nodes
		98	currently, but all nodes can talk to public nodes.
84		99
85	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	100	Nodes is represented by (printable) strings called "node IDs".
86		101
87	A node reference is a string that either simply identifies the node (for	102	=item node ID - C<[A-Za-z0-9_\-.:]*>
88	private and slave nodes), or contains a recipe on how to reach a given
89	node (for public nodes).
90		103
91	This recipe is simply a comma-separated list of C<address:port> pairs (for	104	A node ID is a string that uniquely identifies the node within a
92	TCP/IP, other protocols might look different).	105	network. Depending on the configuration used, node IDs can look like a
		106	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		107	doesn't interpret node IDs in any way except to uniquely identify a node.
93		108
94	Node references come in two flavours: resolved (containing only numerical	109	=item binds - C<ip:port>
95	addresses) or unresolved (where hostnames are used instead of addresses).
96		110
97	Before using an unresolved node reference in a message you first have to	111	Nodes can only talk to each other by creating some kind of connection to
98	resolve it.	112	each other. To do this, nodes should listen on one or more local transport
		113	endpoints - binds.
		114
		115	Currently, only standard C<ip:port> specifications can be used, which
		116	specify TCP ports to listen on. So a bind is basically just a tcp socket
		117	in listening mode thta accepts conenctions form other nodes.
		118
		119	=item seed nodes
		120
		121	When a node starts, it knows nothing about the network it is in - it
		122	needs to connect to at least one other node that is already in the
		123	network. These other nodes are called "seed nodes".
		124
		125	Seed nodes themselves are not special - they are seed nodes only because
		126	some other node I<uses> them as such, but any node can be used as seed
		127	node for other nodes, and eahc node cna use a different set of seed nodes.
		128
		129	In addition to discovering the network, seed nodes are also used to
		130	maintain the network - all nodes using the same seed node form are part of
		131	the same network. If a network is split into multiple subnets because e.g.
		132	the network link between the parts goes down, then using the same seed
		133	nodes for all nodes ensures that eventually the subnets get merged again.
		134
		135	Seed nodes are expected to be long-running, and at least one seed node
		136	should always be available. They should also be relatively responsive - a
		137	seed node that blocks for long periods will slow down everybody else.
		138
		139	For small networks, it's best if every node uses the same set of seed
		140	nodes. For large networks, it can be useful to specify "regional" seed
		141	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		142	each other. What's important is that all seed nodes connections form a
		143	complete graph, so that the network cannot split into separate subnets
		144	forever.
		145
		146	Seed nodes are represented by seed IDs.
		147
		148	=item seed IDs - C<host:port>
		149
		150	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
		151	TCP port) of nodes that should be used as seed nodes.
		152
		153	=item global nodes
		154
		155	An AEMP network needs a discovery service - nodes need to know how to
		156	connect to other nodes they only know by name. In addition, AEMP offers a
		157	distributed "group database", which maps group names to a list of strings
		158	- for example, to register worker ports.
		159
		160	A network needs at least one global node to work, and allows every node to
		161	be a global node.
		162
		163	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		164	node and tries to keep connections to all other nodes. So while it can
		165	make sense to make every node "global" in small networks, it usually makes
		166	sense to only make seed nodes into global nodes in large networks (nodes
		167	keep connections to seed nodes and global nodes, so makign them the same
		168	reduces overhead).
99		169
100	=back	170	=back
101		171
102	=head1 VARIABLES/FUNCTIONS	172	=head1 VARIABLES/FUNCTIONS
103		173
105		175
106	=cut	176	=cut
107		177
108	package AnyEvent::MP;	178	package AnyEvent::MP;
109		179
110	use AnyEvent::MP::Base;	180	use AnyEvent::MP::Kernel;
111		181
112	use common::sense;	182	use common::sense;
113		183
114	use Carp ();	184	use Carp ();
115		185
116	use AE ();	186	use AE ();
117		187
118	use base "Exporter";	188	use base "Exporter";
119		189
120	our $VERSION = '0.1';	190	our $VERSION = '1.30';
		191
121	our @EXPORT = qw(	192	our @EXPORT = qw(
122	NODE $NODE *SELF node_of _any_	193	NODE $NODE *SELF node_of after
123	resolve_node initialise_node	194	configure
124	snd rcv mon kil reg psub spawn	195	snd rcv mon mon_guard kil psub peval spawn cal
125	port	196	port
126	);	197	);
127		198
128	our $SELF;	199	our $SELF;
129		200
…		…
133	kil $SELF, die => $msg;	204	kil $SELF, die => $msg;
134	}	205	}
135		206
136	=item $thisnode = NODE / $NODE	207	=item $thisnode = NODE / $NODE
137		208
138	The C<NODE> function returns, and the C<$NODE> variable contains	209	The C<NODE> function returns, and the C<$NODE> variable contains, the node
139	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
140	to C<become_public> or C<become_slave>, after which all local port	211	a call to C<configure>.
141	identifiers become invalid.
142		212
143	=item $noderef = node_of $port	213	=item $nodeid = node_of $port
144		214
145	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.
146		216
147	=item initialise_node $noderef, $seednode, $seednode...	217	=item configure $profile, key => value...
148		218
149	=item initialise_node "slave/", $master, $master...	219	=item configure key => value...
150		220
151	Before a node can talk to other nodes on the network it has to initialise	221	Before a node can talk to other nodes on the network (i.e. enter
152	itself - the minimum a node needs to know is it's own name, and optionally	222	"distributed mode") it has to configure itself - the minimum a node needs
153	it should know the noderefs of some other nodes in the network.	223	to know is its own name, and optionally it should know the addresses of
		224	some other nodes in the network to discover other nodes.
154		225
		226	The key/value pairs are basically the same ones as documented for the
		227	F<aemp> command line utility (sans the set/del prefix).
		228
155	This function initialises a node - it must be called exactly once (or	229	This function configures a node - it must be called exactly once (or
156	never) before calling other AnyEvent::MP functions.	230	never) before calling other AnyEvent::MP functions.
157		231
158	All arguments are noderefs, which can be either resolved or unresolved.
159
160	There are two types of networked nodes, public nodes and slave nodes:
161
162	=over 4	232	=over 4
163		233
164	=item public nodes	234	=item step 1, gathering configuration from profiles
165		235
166	For public nodes, C<$noderef> must either be a (possibly unresolved)	236	The function first looks up a profile in the aemp configuration (see the
167	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
168	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.
169		240
170	Afterwards, the node will bind itself on all endpoints and try to connect	241	The profile data is then gathered as follows:
171	to all additional C<$seednodes> that are specified. Seednodes are optional
172	and can be used to quickly bootstrap the node into an existing network.
173		242
174	=item slave nodes	243	First, all remaining key => value pairs (all of which are conveniently
		244	undocumented at the moment) will be interpreted as configuration
		245	data. Then they will be overwritten by any values specified in the global
		246	default configuration (see the F<aemp> utility), then the chain of
		247	profiles chosen by the profile name (and any C<parent> attributes).
175		248
176	When the C<$noderef> is the special string C<slave/>, then the node will	249	That means that the values specified in the profile have highest priority
177	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,
178	route most of their traffic to the master node that they attach to.	251	and can only be used to specify defaults.
179		252
180	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
181	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
182	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.
183		274
184	=back	275	=back
185		276
186	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.
187	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.
188	server.
189		279
190	Example: become a public node listening on the default node.	280	configure
191		281
192	initialise_node;	282	Example: become an anonymous node. This form is often used for commandline
		283	clients.
193		284
194	Example: become a public node, and try to contact some well-known master	285	configure nodeid => "anon/";
195	servers to become part of the network.
196		286
197	initialise_node undef, "master1", "master2";	287	Example: configure a node using a profile called seed, which si suitable
		288	for a seed node as it binds on all local addresses on a fixed port (4040,
		289	customary for aemp).
198		290
199	Example: become a public node listening on port C<4041>.	291	# use the aemp commandline utility
		292	# aemp profile seed nodeid anon/ binds '*:4040'
200		293
201	initialise_node 4041;	294	# then use it
		295	configure profile => "seed";
202		296
203	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
204		299
205	initialise_node "locahost:4044";	300	# or provide a nicer-to-remember nodeid
206		301	# aemp run profile seed nodeid "$(hostname)"
207	Example: become a slave node to any of the specified master servers.
208
209	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
210
211	=item $cv = resolve_node $noderef
212
213	Takes an unresolved node reference that may contain hostnames and
214	abbreviated IDs, resolves all of them and returns a resolved node
215	reference.
216
217	In addition to C<address:port> pairs allowed in resolved noderefs, the
218	following forms are supported:
219
220	=over 4
221
222	=item the empty string
223
224	An empty-string component gets resolved as if the default port (4040) was
225	specified.
226
227	=item naked port numbers (e.g. C<1234>)
228
229	These are resolved by prepending the local nodename and a colon, to be
230	further resolved.
231
232	=item hostnames (e.g. C<localhost:1234>, C<localhost>)
233
234	These are resolved by using AnyEvent::DNS to resolve them, optionally
235	looking up SRV records for the C<aemp=4040> port, if no port was
236	specified.
237
238	=back
239		302
240	=item $SELF	303	=item $SELF
241		304
242	Contains the current port id while executing C<rcv> callbacks or C<psub>	305	Contains the current port id while executing C<rcv> callbacks or C<psub>
243	blocks.	306	blocks.
244		307
245	=item SELF, %SELF, @SELF...	308	=item *SELF, SELF, %SELF, @SELF...
246		309
247	Due to some quirks in how perl exports variables, it is impossible to	310	Due to some quirks in how perl exports variables, it is impossible to
248	just export C<$SELF>, all the symbols called C<SELF> are exported by this	311	just export C<$SELF>, all the symbols named C<SELF> are exported by this
249	module, but only C<$SELF> is currently used.	312	module, but only C<$SELF> is currently used.
250		313
251	=item snd $port, type => @data	314	=item snd $port, type => @data
252		315
253	=item snd $port, @msg	316	=item snd $port, @msg
254		317
255	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
256	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.
257	stringifies a sa port ID (such as a port object :).
258		320
259	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
260	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
261	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.
262		325
263	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
264	function: modifying any argument is not allowed and can cause many	327	function: modifying any argument (or values referenced by them) is
265	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.
266		332
267	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
268	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
269	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
270	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
271	node, anything can be passed.	337	node, anything can be passed. Best rely only on the common denominator of
		338	these.
272		339
273	=item $local_port = port	340	=item $local_port = port
274		341
275	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
276	matching port ("full port") or a single-callback port ("miniport"),	343	no callbacks set and will throw an error when it receives messages.
277	depending on how C<rcv> callbacks are bound to the object.
278		344
279	=item $port = port { my @msg = @_; $finished }	345	=item $local_port = port { my @msg = @_ }
280		346
281	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
282	matching behind it, and returns its ID. Semantically the same as creating
283	a port and calling C<rcv $port, $callback> on it.	348	creating a port and calling C<rcv $port, $callback> on it.
284		349
285	The block will be called for every message received on the port. When the	350	The block will be called for every message received on the port, with the
286	callback returns a true value its job is considered "done" and the port	351	global variable C<$SELF> set to the port ID. Runtime errors will cause the
287	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.
288		354
289	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:
290	be passed to the callback.
291		356
292	If you need the local port id in the callback, this works nicely:	357	my $port = port {
293		358	my @msg = @_;
294	my $port; $port = port {	359	...
295	snd $otherport, reply => $port;	360	kil $SELF;
296	};	361	};
297		362
298	=cut	363	=cut
299		364
300	sub rcv($@);	365	sub rcv($@);
		366
		367	sub _kilme {
		368	die "received message on port without callback";
		369	}
301		370
302	sub port(;&) {	371	sub port(;&) {
303	my $id = "$UNIQ." . $ID++;	372	my $id = "$UNIQ." . $ID++;
304	my $port = "$NODE#$id";	373	my $port = "$NODE#$id";
305		374
306	if (@_) {	375	rcv $port, shift \|\| \&_kilme;
307	rcv $port, shift;
308	} else {
309	$PORT{$id} = sub { }; # nop
310	}
311		376
312	$port	377	$port
313	}	378	}
314		379
315	=item reg $port, $name
316
317	=item reg $name
318
319	Registers the given port (or C<$SELF><<< if missing) under the name
320	C<$name>. If the name already exists it is replaced.
321
322	A port can only be registered under one well known name.
323
324	A port automatically becomes unregistered when it is killed.
325
326	=cut
327
328	sub reg(@) {
329	my $port = @_ > 1 ? shift : $SELF \|\| Carp::croak 'reg: called with one argument only, but $SELF not set,';
330
331	$REG{$_[0]} = $port;
332	}
333
334	=item rcv $port, $callback->(@msg)	380	=item rcv $local_port, $callback->(@msg)
335		381
336	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
337	one if required).	383	remove the default callback: use C<sub { }> to disable it, or better
338		384	C<kil> the port when it is no longer needed.
339	=item rcv $port, tagstring => $callback->(@msg), ...
340
341	=item rcv $port, $smartmatch => $callback->(@msg), ...
342
343	=item rcv $port, [$smartmatch...] => $callback->(@msg), ...
344
345	Register callbacks to be called on matching messages on the given full
346	port (after converting it to one if required) and return the port.
347
348	The callback has to return a true value when its work is done, after
349	which is will be removed, or a false value in which case it will stay
350	registered.
351		385
352	The global C<$SELF> (exported by this module) contains C<$port> while	386	The global C<$SELF> (exported by this module) contains C<$port> while
353	executing the callback.	387	executing the callback. Runtime errors during callback execution will
		388	result in the port being C<kil>ed.
354		389
355	Runtime errors during callback execution will result in the port being	390	The default callback received all messages not matched by a more specific
356	C<kil>ed.	391	C<tag> match.
357		392
358	If the match is an array reference, then it will be matched against the	393	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
359	first elements of the message, otherwise only the first element is being
360	matched.
361		394
362	Any element in the match that is specified as C<_any_> (a function	395	Register (or replace) callbacks to be called on messages starting with the
363	exported by this module) matches any single element of the message.	396	given tag on the given port (and return the port), or unregister it (when
		397	C<$callback> is C<$undef> or missing). There can only be one callback
		398	registered for each tag.
364		399
365	While not required, it is highly recommended that the first matching	400	The original message will be passed to the callback, after the first
366	element is a string identifying the message. The one-string-only match is	401	element (the tag) has been removed. The callback will use the same
367	also the most efficient match (by far).	402	environment as the default callback (see above).
368		403
369	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.
370		405
371	my $port = rcv port,	406	my $port = rcv port,
372	msg1 => sub { ...; 0 },	407	msg1 => sub { ... },
373	msg2 => sub { ...; 0 },	408	msg2 => sub { ... },
374	;	409	;
375		410
376	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
377	in one go:	412	in one go:
378		413
379	snd $otherport, reply =>	414	snd $otherport, reply =>
380	rcv port,	415	rcv port,
381	msg1 => sub { ...; 0 },	416	msg1 => sub { ... },
382	...	417	...
383	;	418	;
384		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, $otherport;
		427	};
		428
385	=cut	429	=cut
386		430
387	sub rcv($@) {	431	sub rcv($@) {
388	my $port = shift;	432	my $port = shift;
389	my ($noderef, $portid) = split /#/, $port, 2;	433	my ($nodeid, $portid) = split /#/, $port, 2;
390		434
391	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	435	$NODE{$nodeid} == $NODE{""}
392	or Carp::croak "$port: rcv can only be called on local ports, caught";	436	or Carp::croak "$port: rcv can only be called on local ports, caught";
393		437
394	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 {
395	my $cb = shift;	446	my $cb = shift;
396	delete $PORT_DATA{$portid};
397	$PORT{$portid} = sub {	447	$PORT{$portid} = sub {
398	local $SELF = $port;	448	local $SELF = $port;
399	eval {	449	eval { &$cb }; _self_die if $@;
400	&$cb	450	};
401	and kil $port;
402	};	451	}
403	_self_die if $@;	452	} elsif (defined $_[0]) {
404	};
405	} else {
406	my $self = $PORT_DATA{$portid} \|\|= do {	453	my $self = $PORT_DATA{$portid} \|\|= do {
407	my $self = bless {	454	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
408	id => $port,
409	}, "AnyEvent::MP::Port";
410		455
411	$PORT{$portid} = sub {	456	$PORT{$portid} = sub {
412	local $SELF = $port;	457	local $SELF = $port;
413		458
414	eval {
415	for (@{ $self->{rc0}{$_[0]} }) {	459	if (my $cb = $self->[1]{$_[0]}) {
416	$_ && &{$_->[0]}	460	shift;
417	&& undef $_;	461	eval { &$cb }; _self_die if $@;
418	}	462	} else {
419
420	for (@{ $self->{rcv}{$_[0]} }) {
421	$_ && [@_[1 .. @{$_->[1]}]] ~~ $_->[1]
422	&& &{$_->[0]}	463	&{ $self->[0] };
423	&& undef $_;
424	}
425
426	for (@{ $self->{any} }) {
427	$_ && [@_[0 .. $#{$_->[1]}]] ~~ $_->[1]
428	&& &{$_->[0]}
429	&& undef $_;
430	}	464	}
431	};	465	};
432	_self_die if $@;	466
		467	$self
433	};	468	};
434		469
435	$self
436	};
437
438	"AnyEvent::MP::Port" eq ref $self	470	"AnyEvent::MP::Port" eq ref $self
439	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	471	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
440		472
441	while (@_) {
442	my ($match, $cb) = splice @_, 0, 2;	473	my ($tag, $cb) = splice @_, 0, 2;
443		474
444	if (!ref $match) {	475	if (defined $cb) {
445	push @{ $self->{rc0}{$match} }, [$cb];	476	$self->[1]{$tag} = $cb;
446	} elsif (("ARRAY" eq ref $match && !ref $match->[0])) {
447	my ($type, @match) = @$match;
448	@match
449	? push @{ $self->{rcv}{$match->[0]} }, [$cb, \@match]
450	: push @{ $self->{rc0}{$match->[0]} }, [$cb];
451	} else {	477	} else {
452	push @{ $self->{any} }, [$cb, $match];	478	delete $self->[1]{$tag};
453	}	479	}
454	}	480	}
455	}	481	}
456		482
457	$port	483	$port
458	}	484	}
459		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
460	=item $closure = psub { BLOCK }	523	=item $closure = psub { BLOCK }
461		524
462	Remembers C<$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
463	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>
464	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 $SELF, sub {
		530	BLOCK }, @_ } >>.
465		531
466	This is useful when you register callbacks from C<rcv> callbacks:	532	This is useful when you register callbacks from C<rcv> callbacks:
467		533
468	rcv delayed_reply => sub {	534	rcv delayed_reply => sub {
469	my ($delay, @reply) = @_;	535	my ($delay, @reply) = @_;
…		…
493	$res	559	$res
494	}	560	}
495	}	561	}
496	}	562	}
497		563
498	=item $guard = mon $port, $cb->(@reason)	564	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
499		565
500	=item $guard = mon $port, $rcvport	566	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
501		567
502	=item $guard = mon $port	568	=item $guard = mon $port # kill $SELF when $port dies
503		569
504	=item $guard = mon $port, $rcvport, @msg	570	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
505		571
506	Monitor the given port and do something when the port is killed, and	572	Monitor the given port and do something when the port is killed or
507	optionally return a guard that can be used to stop monitoring again.	573	messages to it were lost, and optionally return a guard that can be used
		574	to stop monitoring again.
508		575
509	In the first form (callback), the callback is simply called with any	576	In the first form (callback), the callback is simply called with any
510	number of C<@reason> elements (no @reason means that the port was deleted	577	number of C<@reason> elements (no @reason means that the port was deleted
511	"normally"). Note also that I<< the callback B<must> never die >>, so use	578	"normally"). Note also that I<< the callback B<must> never die >>, so use
512	C<eval> if unsure.	579	C<eval> if unsure.
513		580
514	In the second form (another port given), the other port (C<$rcvport)	581	In the second form (another port given), the other port (C<$rcvport>)
515	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	582	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
516	"normal" kils nothing happens, while under all other conditions, the other	583	"normal" kils nothing happens, while under all other conditions, the other
517	port is killed with the same reason.	584	port is killed with the same reason.
518		585
519	The third form (kill self) is the same as the second form, except that	586	The third form (kill self) is the same as the second form, except that
520	C<$rvport> defaults to C<$SELF>.	587	C<$rvport> defaults to C<$SELF>.
521		588
522	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
523	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.
524		594
525	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
526	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
527	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
528	even monitoring requests can get lost (for exmaple, when the connection	598	even monitoring requests can get lost (for example, when the connection
529	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
530	these problems do not exist.	600	these problems do not exist.
531		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
532	Example: call a given callback when C<$port> is killed.	619	Example: call a given callback when C<$port> is killed.
533		620
534	mon $port, sub { warn "port died because of <@_>\n" };	621	mon $port, sub { warn "port died because of <@_>\n" };
535		622
536	Example: kill ourselves when C<$port> is killed abnormally.	623	Example: kill ourselves when C<$port> is killed abnormally.
…		…
542	mon $port, $self => "restart";	629	mon $port, $self => "restart";
543		630
544	=cut	631	=cut
545		632
546	sub mon {	633	sub mon {
547	my ($noderef, $port) = split /#/, shift, 2;	634	my ($nodeid, $port) = split /#/, shift, 2;
548		635
549	my $node = $NODE{$noderef} \|\| add_node $noderef;	636	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
550		637
551	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,';
552		639
553	unless (ref $cb) {	640	unless (ref $cb) {
554	if (@_) {	641	if (@_) {
555	# send a kill info message	642	# send a kill info message
556	my (@msg) = @_;	643	my (@msg) = ($cb, @_);
557	$cb = sub { snd @msg, @_ };	644	$cb = sub { snd @msg, @_ };
558	} else {	645	} else {
559	# simply kill other port	646	# simply kill other port
560	my $port = $cb;	647	my $port = $cb;
561	$cb = sub { kil $port, @_ if @_ };	648	$cb = sub { kil $port, @_ if @_ };
…		…
563	}	650	}
564		651
565	$node->monitor ($port, $cb);	652	$node->monitor ($port, $cb);
566		653
567	defined wantarray	654	defined wantarray
568	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	655	and ($cb += 0, AnyEvent::Util::guard { $node->unmonitor ($port, $cb) })
569	}	656	}
570		657
571	=item $guard = mon_guard $port, $ref, $ref...	658	=item $guard = mon_guard $port, $ref, $ref...
572		659
573	Monitors the given C<$port> and keeps the passed references. When the port	660	Monitors the given C<$port> and keeps the passed references. When the port
574	is killed, the references will be freed.	661	is killed, the references will be freed.
575		662
576	Optionally returns a guard that will stop the monitoring.	663	Optionally returns a guard that will stop the monitoring.
577		664
578	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
579	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>):
580		667
581	$port->rcv (start => sub {	668	$port->rcv (start => sub {
582	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	669	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
583	undef $timer if 0.9 < rand;	670	undef $timer if 0.9 < rand;
584	});	671	});
585	});	672	});
586		673
587	=cut	674	=cut
…		…
596		683
597	=item kil $port[, @reason]	684	=item kil $port[, @reason]
598		685
599	Kill the specified port with the given C<@reason>.	686	Kill the specified port with the given C<@reason>.
600		687
601	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" -
602	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.
603		691
604	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>
605	C<mon>, see below).	693	form) get killed with the same reason.
606		694
607	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
608	will be reported as reason C<< die => $@ >>.	696	will be reported as reason C<< die => $@ >>.
609		697
610	Transport/communication errors are reported as C<< transport_error =>	698	Transport/communication errors are reported as C<< transport_error =>
…		…
615	=item $port = spawn $node, $initfunc[, @initdata]	703	=item $port = spawn $node, $initfunc[, @initdata]
616		704
617	Creates a port on the node C<$node> (which can also be a port ID, in which	705	Creates a port on the node C<$node> (which can also be a port ID, in which
618	case it's the node where that port resides).	706	case it's the node where that port resides).
619		707
620	The port ID of the newly created port is return immediately, and it is	708	The port ID of the newly created port is returned immediately, and it is
621	permissible to immediately start sending messages or monitor the port.	709	possible to immediately start sending messages or to monitor the port.
622		710
623	After the port has been created, the init function is	711	After the port has been created, the init function is called on the remote
624	called. This fucntion must be a fully-qualified function name	712	node, in the same context as a C<rcv> callback. This function must be a
625	(e.g. C<MyApp::Chat::Server::init>).	713	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
		714	specify a function in the main program, use C<::name>.
626		715
627	If the function doesn't exist, then the node tries to C<require>	716	If the function doesn't exist, then the node tries to C<require>
628	the package, then the package above the package and so on (e.g.	717	the package, then the package above the package and so on (e.g.
629	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	718	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
630	exists or it runs out of package names.	719	exists or it runs out of package names.
631		720
632	The init function is then called with the newly-created port as context	721	The init function is then called with the newly-created port as context
633	object (C<$SELF>) and the C<@initdata> values as arguments.	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.
634		725
635	A common idiom is to pass your own port, monitor the spawned port, and	726	A common idiom is to pass a local port, immediately monitor the spawned
636	in the init function, monitor the original port. This two-way monitoring	727	port, and in the remote init function, immediately monitor the passed
637	ensures that both ports get cleaned up when there is a problem.	728	local port. This two-way monitoring ensures that both ports get cleaned up
		729	when there is a problem.
		730
		731	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		732	caller before C<spawn> returns (by delaying invocation when spawn is
		733	called for the local node).
638		734
639	Example: spawn a chat server port on C<$othernode>.	735	Example: spawn a chat server port on C<$othernode>.
640		736
641	# this node, executed from within a port context:	737	# this node, executed from within a port context:
642	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	738	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
657		753
658	sub _spawn {	754	sub _spawn {
659	my $port = shift;	755	my $port = shift;
660	my $init = shift;	756	my $init = shift;
661		757
		758	# rcv will create the actual port
662	local $SELF = "$NODE#$port";	759	local $SELF = "$NODE#$port";
663	eval {	760	eval {
664	&{ load_func $init }	761	&{ load_func $init }
665	};	762	};
666	_self_die if $@;	763	_self_die if $@;
667	}	764	}
668		765
669	sub spawn(@) {	766	sub spawn(@) {
670	my ($noderef, undef) = split /#/, shift, 2;	767	my ($nodeid, undef) = split /#/, shift, 2;
671		768
672	my $id = "$RUNIQ." . $ID++;	769	my $id = "$RUNIQ." . $ID++;
673		770
674	($NODE{$noderef} \|\| add_node $noderef)	771	$_[0] =~ /::/
675	->send (["", "AnyEvent::MP::_spawn" => $id, @_]);	772	or Carp::croak "spawn init function must be a fully-qualified name, caught";
676		773
		774	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
		775
677	"$noderef#$id"	776	"$nodeid#$id"
678	}	777	}
679		778
680	=back	779	=item after $timeout, @msg
681		780
682	=head1 NODE MESSAGES	781	=item after $timeout, $callback
683		782
684	Nodes understand the following messages sent to them. Many of them take	783	Either sends the given message, or call the given callback, after the
685	arguments called C<@reply>, which will simply be used to compose a reply	784	specified number of seconds.
686	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and
687	the remaining arguments are simply the message data.
688		785
689	While other messages exist, they are not public and subject to change.	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.
690		789
691	=over 4
692
693	=cut	790	=cut
694		791
695	=item lookup => $name, @reply	792	sub after($@) {
		793	my ($timeout, @action) = @_;
696		794
697	Replies with the port ID of the specified well-known port, or C<undef>.	795	my $t; $t = AE::timer $timeout, 0, sub {
		796	undef $t;
		797	ref $action[0]
		798	? $action[0]()
		799	: snd @action;
		800	};
		801	}
698		802
699	=item devnull => ...	803	=item cal $port, @msg, $callback[, $timeout]
700		804
701	Generic data sink/CPU heat conversion.	805	A simple form of RPC - sends a message to the given C<$port> with the
		806	given contents (C<@msg>), but adds a reply port to the message.
702		807
703	=item relay => $port, @msg	808	The reply port is created temporarily just for the purpose of receiving
		809	the reply, and will be C<kil>ed when no longer needed.
704		810
705	Simply forwards the message to the given port.	811	A reply message sent to the port is passed to the C<$callback> as-is.
706		812
707	=item eval => $string[ @reply]	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.
708		816
709	Evaluates the given string. If C<@reply> is given, then a message of the	817	If no time-out is given (or it is C<undef>), then the local port will
710	form C<@reply, $@, @evalres> is sent.	818	monitor the remote port instead, so it eventually gets cleaned-up.
711		819
712	Example: crash another node.	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.
713		823
714	snd $othernode, eval => "exit";	824	=cut
715		825
716	=item time => @reply	826	sub cal(@) {
		827	my $timeout = ref $_[-1] ? undef : pop;
		828	my $cb = pop;
717		829
718	Replies the the current node time to C<@reply>.	830	my $port = port {
		831	undef $timeout;
		832	kil $SELF;
		833	&$cb;
		834	};
719		835
720	Example: tell the current node to send the current time to C<$myport> in a	836	if (defined $timeout) {
721	C<timereply> message.	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	}
722		848
723	snd $NODE, time => $myport, timereply => 1, 2;	849	push @_, $port;
724	# => snd $myport, timereply => 1, 2, <time>	850	&snd;
		851
		852	$port
		853	}
725		854
726	=back	855	=back
727		856
728	=head1 AnyEvent::MP vs. Distributed Erlang	857	=head1 AnyEvent::MP vs. Distributed Erlang
729		858
730	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
731	== 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
732	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
733	sample:	862	sample:
734		863
735	http://www.Erlang.se/doc/programming_rules.shtml	864	http://www.erlang.se/doc/programming_rules.shtml
736	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
737	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
738	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
739		868
740	Despite the similarities, there are also some important differences:	869	Despite the similarities, there are also some important differences:
741		870
742	=over 4	871	=over 4
743		872
744	=item * Node references contain the recipe on how to contact them.	873	=item * Node IDs are arbitrary strings in AEMP.
745		874
746	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
747	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
748	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.
749		879
750	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
751	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.
752		894
753	=item * Erlang uses processes and a mailbox, AEMP does not queue.	895	=item * Erlang uses processes and a mailbox, AEMP does not queue.
754		896
755	Erlang uses processes that selctively receive messages, and therefore	897	Erlang uses processes that selectively receive messages out of order, and
756	needs a queue. AEMP is event based, queuing messages would serve no useful	898	therefore needs a queue. AEMP is event based, queuing messages would serve
757	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.
758		902
759	(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.
760		908
761	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	909	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
762		910
763	Sending messages in Erlang is synchronous and blocks the process. AEMP	911	Sending messages in Erlang is synchronous and blocks the process until
764	sends are immediate, connection establishment is handled in the	912	a conenction has been established and the message sent (and so does not
765	background.	913	need a queue that can overflow). AEMP sends return immediately, connection
		914	establishment is handled in the background.
766		915
767	=item * Erlang can silently lose messages, AEMP cannot.	916	=item * Erlang suffers from silent message loss, AEMP does not.
768		917
769	Erlang makes few guarantees on messages delivery - messages can get lost	918	Erlang implements few guarantees on messages delivery - messages can get
770	without any of the processes realising it (i.e. you send messages a, b,	919	lost without any of the processes realising it (i.e. you send messages a,
771	and c, and the other side only receives messages a and c).	920	b, and c, and the other side only receives messages a and c).
772		921
773	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
774	holes in the message sequence.	925	no silent "holes" in the message sequence.
775		926
776	=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
777	alive.	928	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
778		929	simply tries to work better in common error cases, such as when a network
779	In Erlang it can happen that a monitored process is declared dead and	930	link goes down.
780	linked processes get killed, but later it turns out that the process is
781	still alive - and can receive messages.
782
783	In AEMP, when port monitoring detects a port as dead, then that port will
784	eventually be killed - it cannot happen that a node detects a port as dead
785	and then later sends messages to it, finding it is still alive.
786		931
787	=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.
788		933
789	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
790	ID known to other nodes for a completely different process, causing	935	process ID known to other nodes for a completely different process,
791	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.
792		938
793	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
794	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.
795		941
796	=item * Erlang uses unprotected connections, AEMP uses secure	942	=item * Erlang uses unprotected connections, AEMP uses secure
797	authentication and can use TLS.	943	authentication and can use TLS.
798		944
799	AEMP can use a proven protocol - SSL/TLS - to protect connections and	945	AEMP can use a proven protocol - TLS - to protect connections and
800	securely authenticate nodes.	946	securely authenticate nodes.
801		947
802	=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
803	communications.	949	communications.
804		950
805	The AEMP protocol, unlike the Erlang protocol, supports both	951	The AEMP protocol, unlike the Erlang protocol, supports both programming
806	language-independent text-only protocols (good for debugging) and binary,	952	language independent text-only protocols (good for debugging), and binary,
807	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.
808		955
809	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
810	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
811	protocol simple.	958	protocol simple.
812		959
813	=item * AEMP has more flexible monitoring options than Erlang.	960	=item * AEMP has more flexible monitoring options than Erlang.
814		961
815	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
816	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
817	difficult to implement. Monitoring in AEMP is more flexible than in	964	difficult to implement.
818	Erlang, as one can choose between automatic kill, exit message or callback	965
819	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.
820		968
821	=item * Erlang tries to hide remote/local connections, AEMP does not.	969	=item * Erlang tries to hide remote/local connections, AEMP does not.
822		970
823	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
824	as linking is (except linking is unreliable in Erlang).	972	same way as linking is (except linking is unreliable in Erlang).
825		973
826	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
827	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
828	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
829	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
830	more reliable.	978	reliable (no need for C<spawn_link>).
831		979
832	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
833	(hard to do in Erlang).	981	(hard to do in Erlang).
834		982
835	=back	983	=back
836		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
837	=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.
838		1033
839	L<AnyEvent>.	1034	L<AnyEvent>.
840		1035
841	=head1 AUTHOR	1036	=head1 AUTHOR
842		1037

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Revision 1.119 by root, Sun Feb 26 10:29:59 2012 UTC