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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.53 by root, Fri Aug 14 15:31:21 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
13	$SELF # receiving/own port id in rcv callbacks	12	$SELF # receiving/own port id in rcv callbacks
14		13
15	# initialise the node so it can send/receive messages	14	# initialise the node so it can send/receive messages
16	initialise_node; # -OR-	15	configure;
17	initialise_node "localhost:4040"; # -OR-
18	initialise_node "slave/", "localhost:4040"
19		16
20	# ports are message endpoints	17	# ports are message destinations
21		18
22	# sending messages	19	# sending messages
23	snd $port, type => data...;	20	snd $port, type => data...;
24	snd $port, @msg;	21	snd $port, @msg;
25	snd @msg_with_first_element_being_a_port;	22	snd @msg_with_first_element_being_a_port;
26		23
27	# creating/using ports, the simple way	24	# creating/using ports, the simple way
28	my $simple_port = port { my @msg = @_; 0 };	25	my $simple_port = port { my @msg = @_ };
29		26
30	# creating/using ports, tagged message matching	27	# creating/using ports, tagged message matching
31	my $port = port;	28	my $port = port;
32	rcv $port, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
33	rcv $port, pong => sub { warn "pong received\n"; 0 };	30	rcv $port, pong => sub { warn "pong received\n" };
34		31
35	# create a port on another node	32	# create a port on another node
36	my $port = spawn $node, $initfunc, @initdata;	33	my $port = spawn $node, $initfunc, @initdata;
37		34
		35	# destroy a port again
		36	kil $port; # "normal" kill
		37	kil $port, my_error => "everything is broken"; # error kill
		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	};
42		51
43	=head1 CURRENT STATUS	52	=head1 CURRENT STATUS
44		53
		54	bin/aemp - stable.
45	AnyEvent::MP - stable API, should work	55	AnyEvent::MP - stable API, should work.
46	AnyEvent::MP::Intro - outdated	56	AnyEvent::MP::Intro - explains most concepts.
47	AnyEvent::MP::Kernel - WIP
48	AnyEvent::MP::Transport - mostly stable	57	AnyEvent::MP::Kernel - mostly stable API.
49		58	AnyEvent::MP::Global - stable API.
50	stay tuned.
51		59
52	=head1 DESCRIPTION	60	=head1 DESCRIPTION
53		61
54	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
55		63
56	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
57	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
58		66
59	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>
60	manual page.	68	manual page and the examples under F<eg/>.
61
62	At the moment, this module family is severly broken and underdocumented,
63	so do not use. This was uploaded mainly to reserve the CPAN namespace -
64	stay tuned!
65		69
66	=head1 CONCEPTS	70	=head1 CONCEPTS
67		71
68	=over 4	72	=over 4
69		73
70	=item port	74	=item port
71		75
72	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).
73		78
74	Ports allow you to register C<rcv> handlers that can match all or just	79	Ports allow you to register C<rcv> handlers that can match all or just
75	some messages. Messages will not be queued.	80	some messages. Messages send to ports will not be queued, regardless of
		81	anything was listening for them or not.
76		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
77	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
78		86
79	A port ID is 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<#>)
80	separator, and a port name (a printable string of unspecified format). An	88	as separator, and a port name (a printable string of unspecified
81	exception is the the node port, whose ID is identical to its node	89	format created by AnyEvent::MP).
82	reference.
83		90
84	=item node	91	=item node
85		92
86	A node is a single process containing at least one port - the node port,	93	A node is a single process containing at least one port - the node port,
87	which provides nodes to manage each other remotely, and to create new	94	which enables nodes to manage each other remotely, and to create new
88	ports.	95	ports.
89		96
90	Nodes are either private (single-process only), slaves (connected to a	97	Nodes are either public (have one or more listening ports) or private
91	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.
92		100
93	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	101	Nodes is represented by (printable) strings called "node IDs".
94		102
95	A node reference is a string that either simply identifies the node (for	103	=item node ID - C<[A-Za-z0-9_\-.:]*>
96	private and slave nodes), or contains a recipe on how to reach a given
97	node (for public nodes).
98		104
99	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
100	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.
101		109
102	Node references come in two flavours: resolved (containing only numerical	110	=item binds - C<ip:port>
103	addresses) or unresolved (where hostnames are used instead of addresses).
104		111
105	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
106	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).
107		170
108	=back	171	=back
109		172
110	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
111		174
113		176
114	=cut	177	=cut
115		178
116	package AnyEvent::MP;	179	package AnyEvent::MP;
117		180
		181	use AnyEvent::MP::Config ();
118	use AnyEvent::MP::Kernel;	182	use AnyEvent::MP::Kernel;
		183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
119		184
120	use common::sense;	185	use common::sense;
121		186
122	use Carp ();	187	use Carp ();
123		188
124	use AE ();	189	use AE ();
		190	use Guard ();
125		191
126	use base "Exporter";	192	use base "Exporter";
127		193
128	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
129		195
130	our @EXPORT = qw(	196	our @EXPORT = qw(
131	NODE $NODE *SELF node_of _any_	197	NODE $NODE *SELF node_of after
132	resolve_node initialise_node	198	configure
133	snd rcv mon kil reg psub spawn	199	snd rcv mon mon_guard kil psub peval spawn cal
134	port	200	port
		201	db_set db_del db_reg
135	);	202	);
136		203
137	our $SELF;	204	our $SELF;
138		205
139	sub _self_die() {	206	sub _self_die() {
…		…
142	kil $SELF, die => $msg;	209	kil $SELF, die => $msg;
143	}	210	}
144		211
145	=item $thisnode = NODE / $NODE	212	=item $thisnode = NODE / $NODE
146		213
147	The C<NODE> function returns, and the C<$NODE> variable contains the	214	The C<NODE> function returns, and the C<$NODE> variable contains, the node
148	noderef of the local node. The value is initialised by a call to	215	ID of the node running in the current process. This value is initialised by
149	C<initialise_node>.	216	a call to C<configure>.
150		217
151	=item $noderef = node_of $port	218	=item $nodeid = node_of $port
152		219
153	Extracts and returns the noderef from a port ID or a noderef.	220	Extracts and returns the node ID from a port ID or a node ID.
154		221
155	=item initialise_node $noderef, $seednode, $seednode...	222	=item configure $profile, key => value...
156		223
157	=item initialise_node "slave/", $master, $master...	224	=item configure key => value...
158		225
159	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
160	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
161	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.
162		230
163	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
164	never) before calling other AnyEvent::MP functions.	232	never) before calling other AnyEvent::MP functions.
165		233
166	All arguments (optionally except for the first) are noderefs, which can be	234	The key/value pairs are basically the same ones as documented for the
167	either resolved or unresolved.	235	F<aemp> command line utility (sans the set/del prefix), with two additions:
168
169	The first argument will be looked up in the configuration database first
170	(if it is C<undef> then the current nodename will be used instead) to find
171	the relevant configuration profile (see L<aemp>). If none is found then
172	the default configuration is used. The configuration supplies additional
173	seed/master nodes and can override the actual noderef.
174
175	There are two types of networked nodes, public nodes and slave nodes:
176		236
177	=over 4	237	=over 4
178		238
179	=item public nodes	239	=item norc => $boolean (default false)
180		240
181	For public nodes, C<$noderef> (supplied either directly to	241	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
182	C<initialise_node> or indirectly via a profile or the nodename) must be a	242	be consulted - all configuraiton options must be specified in the
183	noderef (possibly unresolved, in which case it will be resolved).	243	C<configure> call.
184		244
185	After resolving, the node will bind itself on all endpoints and try to	245	=item force => $boolean (default false)
186	connect to all additional C<$seednodes> that are specified. Seednodes are
187	optional and can be used to quickly bootstrap the node into an existing
188	network.
189		246
190	=item slave nodes	247	IF true, then the values specified in the C<configure> will take
191		248	precedence over any values configured via the rc file. The default is for
192	When the C<$noderef> (either as given or overriden by the config file)	249	the rc file to override any options specified in the program.
193	is the special string C<slave/>, then the node will become a slave
194	node. Slave nodes cannot be contacted from outside and will route most of
195	their traffic to the master node that they attach to.
196
197	At least one additional noderef is required (either by specifying it
198	directly or because it is part of the configuration profile): The node
199	will try to connect to all of them and will become a slave attached to the
200	first node it can successfully connect to.
201		250
202	=back	251	=back
203		252
204	This function will block until all nodes have been resolved and, for slave
205	nodes, until it has successfully established a connection to a master
206	server.
207
208	Example: become a public node listening on the guessed noderef, or the one
209	specified via C<aemp> for the current node. This should be the most common
210	form of invocation for "daemon"-type nodes.
211
212	initialise_node;
213
214	Example: become a slave node to any of the the seednodes specified via
215	C<aemp>. This form is often used for commandline clients.
216
217	initialise_node "slave/";
218
219	Example: become a slave node to any of the specified master servers. This
220	form is also often used for commandline clients.
221
222	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
223
224	Example: become a public node, and try to contact some well-known master
225	servers to become part of the network.
226
227	initialise_node undef, "master1", "master2";
228
229	Example: become a public node listening on port C<4041>.
230
231	initialise_node 4041;
232
233	Example: become a public node, only visible on localhost port 4044.
234
235	initialise_node "localhost:4044";
236
237	=item $cv = resolve_node $noderef
238
239	Takes an unresolved node reference that may contain hostnames and
240	abbreviated IDs, resolves all of them and returns a resolved node
241	reference.
242
243	In addition to C<address:port> pairs allowed in resolved noderefs, the
244	following forms are supported:
245
246	=over 4	253	=over 4
247		254
248	=item the empty string	255	=item step 1, gathering configuration from profiles
249		256
250	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
251	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.
252		261
253	=item naked port numbers (e.g. C<1234>)	262	The profile data is then gathered as follows:
254		263
255	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
256	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).
257		269
258	=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.
259		273
260	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
261	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
262	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.
263		298
264	=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)"
265		326
266	=item $SELF	327	=item $SELF
267		328
268	Contains the current port id while executing C<rcv> callbacks or C<psub>	329	Contains the current port id while executing C<rcv> callbacks or C<psub>
269	blocks.	330	blocks.
270		331
271	=item SELF, %SELF, @SELF...	332	=item *SELF, SELF, %SELF, @SELF...
272		333
273	Due to some quirks in how perl exports variables, it is impossible to	334	Due to some quirks in how perl exports variables, it is impossible to
274	just export C<$SELF>, all the symbols called C<SELF> are exported by this	335	just export C<$SELF>, all the symbols named C<SELF> are exported by this
275	module, but only C<$SELF> is currently used.	336	module, but only C<$SELF> is currently used.
276		337
277	=item snd $port, type => @data	338	=item snd $port, type => @data
278		339
279	=item snd $port, @msg	340	=item snd $port, @msg
280		341
281	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
282	a local or a remote port, and must be a port ID.	343	local or a remote port, and must be a port ID.
283		344
284	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
285	string as first element (a port ID, or some word that indicates a request	346	use a string as first element (a port ID, or some word that indicates a
286	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.
287		349
288	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
289	function: modifying any argument is not allowed and can cause many	351	function: modifying any argument (or values referenced by them) is
290	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.
291		356
292	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
293	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
294	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
295	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
296	node, anything can be passed.	361	node, anything can be passed. Best rely only on the common denominator of
		362	these.
297		363
298	=item $local_port = port	364	=item $local_port = port
299		365
300	Create a new local port object and returns its port ID. Initially it has	366	Create a new local port object and returns its port ID. Initially it has
301	no callbacks set and will throw an error when it receives messages.	367	no callbacks set and will throw an error when it receives messages.
…		…
325	sub _kilme {	391	sub _kilme {
326	die "received message on port without callback";	392	die "received message on port without callback";
327	}	393	}
328		394
329	sub port(;&) {	395	sub port(;&) {
330	my $id = "$UNIQ." . $ID++;	396	my $id = $UNIQ . ++$ID;
331	my $port = "$NODE#$id";	397	my $port = "$NODE#$id";
332		398
333	rcv $port, shift \|\| \&_kilme;	399	rcv $port, shift \|\| \&_kilme;
334		400
335	$port	401	$port
…		…
348	The default callback received all messages not matched by a more specific	414	The default callback received all messages not matched by a more specific
349	C<tag> match.	415	C<tag> match.
350		416
351	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...	417	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
352		418
353	Register callbacks to be called on messages starting with the given tag on	419	Register (or replace) callbacks to be called on messages starting with the
354	the given port (and return the port), or unregister it (when C<$callback>	420	given tag on the given port (and return the port), or unregister it (when
355	is C<$undef>).	421	C<$callback> is C<$undef> or missing). There can only be one callback
		422	registered for each tag.
356		423
357	The original message will be passed to the callback, after the first	424	The original message will be passed to the callback, after the first
358	element (the tag) has been removed. The callback will use the same	425	element (the tag) has been removed. The callback will use the same
359	environment as the default callback (see above).	426	environment as the default callback (see above).
360		427
…		…
372	rcv port,	439	rcv port,
373	msg1 => sub { ... },	440	msg1 => sub { ... },
374	...	441	...
375	;	442	;
376		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, $otherport;
		451	};
		452
377	=cut	453	=cut
378		454
379	sub rcv($@) {	455	sub rcv($@) {
380	my $port = shift;	456	my $port = shift;
381	my ($noderef, $portid) = split /#/, $port, 2;	457	my ($nodeid, $portid) = split /#/, $port, 2;
382		458
383	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	459	$NODE{$nodeid} == $NODE{""}
384	or Carp::croak "$port: rcv can only be called on local ports, caught";	460	or Carp::croak "$port: rcv can only be called on local ports, caught";
385		461
386	while (@_) {	462	while (@_) {
387	if (ref $_[0]) {	463	if (ref $_[0]) {
388	if (my $self = $PORT_DATA{$portid}) {	464	if (my $self = $PORT_DATA{$portid}) {
389	"AnyEvent::MP::Port" eq ref $self	465	"AnyEvent::MP::Port" eq ref $self
390	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	466	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
391		467
392	$self->[2] = shift;	468	$self->[0] = shift;
393	} else {	469	} else {
394	my $cb = shift;	470	my $cb = shift;
395	$PORT{$portid} = sub {	471	$PORT{$portid} = sub {
396	local $SELF = $port;	472	local $SELF = $port;
397	eval { &$cb }; _self_die if $@;	473	eval { &$cb }; _self_die if $@;
398	};	474	};
399	}	475	}
400	} elsif (defined $_[0]) {	476	} elsif (defined $_[0]) {
401	my $self = $PORT_DATA{$portid} \|\|= do {	477	my $self = $PORT_DATA{$portid} \|\|= do {
402	my $self = bless [$PORT{$port} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";	478	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
403		479
404	$PORT{$portid} = sub {	480	$PORT{$portid} = sub {
405	local $SELF = $port;	481	local $SELF = $port;
406		482
407	if (my $cb = $self->[1]{$_[0]}) {	483	if (my $cb = $self->[1]{$_[0]}) {
…		…
429	}	505	}
430		506
431	$port	507	$port
432	}	508	}
433		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
434	=item $closure = psub { BLOCK }	547	=item $closure = psub { BLOCK }
435		548
436	Remembers C<$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
437	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>
438	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 $SELF, sub {
		554	BLOCK }, @_ } >>.
439		555
440	This is useful when you register callbacks from C<rcv> callbacks:	556	This is useful when you register callbacks from C<rcv> callbacks:
441		557
442	rcv delayed_reply => sub {	558	rcv delayed_reply => sub {
443	my ($delay, @reply) = @_;	559	my ($delay, @reply) = @_;
…		…
467	$res	583	$res
468	}	584	}
469	}	585	}
470	}	586	}
471		587
472	=item $guard = mon $port, $cb->(@reason)	588	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
473		589
474	=item $guard = mon $port, $rcvport	590	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
475		591
476	=item $guard = mon $port	592	=item $guard = mon $port # kill $SELF when $port dies
477		593
478	=item $guard = mon $port, $rcvport, @msg	594	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
479		595
480	Monitor the given port and do something when the port is killed or	596	Monitor the given port and do something when the port is killed or
481	messages to it were lost, and optionally return a guard that can be used	597	messages to it were lost, and optionally return a guard that can be used
482	to stop monitoring again.	598	to stop monitoring again.
483
484	C<mon> effectively guarantees that, in the absence of hardware failures,
485	that after starting the monitor, either all messages sent to the port
486	will arrive, or the monitoring action will be invoked after possible
487	message loss has been detected. No messages will be lost "in between"
488	(after the first lost message no further messages will be received by the
489	port). After the monitoring action was invoked, further messages might get
490	delivered again.
491		599
492	In the first form (callback), the callback is simply called with any	600	In the first form (callback), the callback is simply called with any
493	number of C<@reason> elements (no @reason means that the port was deleted	601	number of C<@reason> elements (no @reason means that the port was deleted
494	"normally"). Note also that I<< the callback B<must> never die >>, so use	602	"normally"). Note also that I<< the callback B<must> never die >>, so use
495	C<eval> if unsure.	603	C<eval> if unsure.
496		604
497	In the second form (another port given), the other port (C<$rcvport>)	605	In the second form (another port given), the other port (C<$rcvport>)
498	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	606	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
499	"normal" kils nothing happens, while under all other conditions, the other	607	"normal" kils nothing happens, while under all other conditions, the other
500	port is killed with the same reason.	608	port is killed with the same reason.
501		609
502	The third form (kill self) is the same as the second form, except that	610	The third form (kill self) is the same as the second form, except that
503	C<$rvport> defaults to C<$SELF>.	611	C<$rvport> defaults to C<$SELF>.
504		612
505	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
506	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.
507		618
508	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
509	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
510	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
511	even monitoring requests can get lost (for exmaple, when the connection	622	even monitoring requests can get lost (for example, when the connection
512	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
513	these problems do not exist.	624	these problems do not exist.
514		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
515	Example: call a given callback when C<$port> is killed.	643	Example: call a given callback when C<$port> is killed.
516		644
517	mon $port, sub { warn "port died because of <@_>\n" };	645	mon $port, sub { warn "port died because of <@_>\n" };
518		646
519	Example: kill ourselves when C<$port> is killed abnormally.	647	Example: kill ourselves when C<$port> is killed abnormally.
…		…
525	mon $port, $self => "restart";	653	mon $port, $self => "restart";
526		654
527	=cut	655	=cut
528		656
529	sub mon {	657	sub mon {
530	my ($noderef, $port) = split /#/, shift, 2;	658	my ($nodeid, $port) = split /#/, shift, 2;
531		659
532	my $node = $NODE{$noderef} \|\| add_node $noderef;	660	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
533		661
534	my $cb = @_ ? shift : $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,';
535		663
536	unless (ref $cb) {	664	unless (ref $cb) {
537	if (@_) {	665	if (@_) {
…		…
546	}	674	}
547		675
548	$node->monitor ($port, $cb);	676	$node->monitor ($port, $cb);
549		677
550	defined wantarray	678	defined wantarray
551	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	679	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
552	}	680	}
553		681
554	=item $guard = mon_guard $port, $ref, $ref...	682	=item $guard = mon_guard $port, $ref, $ref...
555		683
556	Monitors the given C<$port> and keeps the passed references. When the port	684	Monitors the given C<$port> and keeps the passed references. When the port
557	is killed, the references will be freed.	685	is killed, the references will be freed.
558		686
559	Optionally returns a guard that will stop the monitoring.	687	Optionally returns a guard that will stop the monitoring.
560		688
561	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
562	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>):
563		691
564	$port->rcv (start => sub {	692	$port->rcv (start => sub {
565	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	693	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
566	undef $timer if 0.9 < rand;	694	undef $timer if 0.9 < rand;
567	});	695	});
568	});	696	});
569		697
570	=cut	698	=cut
…		…
579		707
580	=item kil $port[, @reason]	708	=item kil $port[, @reason]
581		709
582	Kill the specified port with the given C<@reason>.	710	Kill the specified port with the given C<@reason>.
583		711
584	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" -
585	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.
586		715
587	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>
588	C<mon>, see below).	717	form) get killed with the same reason.
589		718
590	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
591	will be reported as reason C<< die => $@ >>.	720	will be reported as reason C<< die => $@ >>.
592		721
593	Transport/communication errors are reported as C<< transport_error =>	722	Transport/communication errors are reported as C<< transport_error =>
…		…
598	=item $port = spawn $node, $initfunc[, @initdata]	727	=item $port = spawn $node, $initfunc[, @initdata]
599		728
600	Creates a port on the node C<$node> (which can also be a port ID, in which	729	Creates a port on the node C<$node> (which can also be a port ID, in which
601	case it's the node where that port resides).	730	case it's the node where that port resides).
602		731
603	The port ID of the newly created port is return immediately, and it is	732	The port ID of the newly created port is returned immediately, and it is
604	permissible to immediately start sending messages or monitor the port.	733	possible to immediately start sending messages or to monitor the port.
605		734
606	After the port has been created, the init function is	735	After the port has been created, the init function is called on the remote
607	called. This function must be a fully-qualified function name	736	node, in the same context as a C<rcv> callback. This function must be a
608	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	737	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
609	program, use C<::name>.	738	specify a function in the main program, use C<::name>.
610		739
611	If the function doesn't exist, then the node tries to C<require>	740	If the function doesn't exist, then the node tries to C<require>
612	the package, then the package above the package and so on (e.g.	741	the package, then the package above the package and so on (e.g.
613	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	742	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
614	exists or it runs out of package names.	743	exists or it runs out of package names.
615		744
616	The init function is then called with the newly-created port as context	745	The init function is then called with the newly-created port as context
617	object (C<$SELF>) and the C<@initdata> values as arguments.	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.
618		749
619	A common idiom is to pass your own port, monitor the spawned port, and	750	A common idiom is to pass a local port, immediately monitor the spawned
620	in the init function, monitor the original port. This two-way monitoring	751	port, and in the remote init function, immediately monitor the passed
621	ensures that both ports get cleaned up when there is a problem.	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<$initfunc> has no visible effects on the
		756	caller before C<spawn> returns (by delaying invocation when spawn is
		757	called for the local node).
622		758
623	Example: spawn a chat server port on C<$othernode>.	759	Example: spawn a chat server port on C<$othernode>.
624		760
625	# this node, executed from within a port context:	761	# this node, executed from within a port context:
626	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	762	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
641		777
642	sub _spawn {	778	sub _spawn {
643	my $port = shift;	779	my $port = shift;
644	my $init = shift;	780	my $init = shift;
645		781
		782	# rcv will create the actual port
646	local $SELF = "$NODE#$port";	783	local $SELF = "$NODE#$port";
647	eval {	784	eval {
648	&{ load_func $init }	785	&{ load_func $init }
649	};	786	};
650	_self_die if $@;	787	_self_die if $@;
651	}	788	}
652		789
653	sub spawn(@) {	790	sub spawn(@) {
654	my ($noderef, undef) = split /#/, shift, 2;	791	my ($nodeid, undef) = split /#/, shift, 2;
655		792
656	my $id = "$RUNIQ." . $ID++;	793	my $id = $RUNIQ . ++$ID;
657		794
658	$_[0] =~ /::/	795	$_[0] =~ /::/
659	or Carp::croak "spawn init function must be a fully-qualified name, caught";	796	or Carp::croak "spawn init function must be a fully-qualified name, caught";
660		797
661	($NODE{$noderef} \|\| add_node $noderef)	798	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
662	->send (["", "AnyEvent::MP::_spawn" => $id, @_]);
663		799
664	"$noderef#$id"	800	"$nodeid#$id"
665	}	801	}
666		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	$port
		878	}
		879
667	=back	880	=back
668		881
669	=head1 NODE MESSAGES	882	=head1 DISTRIBUTED DATABASE
670		883
671	Nodes understand the following messages sent to them. Many of them take	884	AnyEvent::MP comes with a simple distributed database. The database will
672	arguments called C<@reply>, which will simply be used to compose a reply	885	be mirrored asynchronously at all global nodes. Other nodes bind to one of
673	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and	886	the global nodes for their needs.
674	the remaining arguments are simply the message data.
675		887
676	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.
677		890
678	=over 4	891	The top level hash key is called "family", and the second-level hash key
		892	is simply called "key".
679		893
680	=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.
681		897
682	=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.
683		900
684	Replies with the port ID of the specified well-known port, or C<undef>.	901	The keys must be strings, with no other limitations.
685		902
686	=item devnull => ...	903	The values should preferably be strings, but other perl scalars should
		904	work as well (such as undef, arrays and hashes).
687		905
688	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.
689		910
690	=item relay => $port, @msg	911	=item db_set $family => $key => $value
691		912
692	Simply forwards the message to the given port.	913	Sets (or replaces) a key to the database.
693		914
694	=item eval => $string[ @reply]	915	=item db_del $family => $key
695		916
696	Evaluates the given string. If C<@reply> is given, then a message of the	917	Deletes a key from the database.
697	form C<@reply, $@, @evalres> is sent.
698		918
699	Example: crash another node.	919	=item $guard = db_reg $family => $key [=> $value]
700		920
701	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.
702		924
703	=item time => @reply	925	=cut
704
705	Replies the the current node time to C<@reply>.
706
707	Example: tell the current node to send the current time to C<$myport> in a
708	C<timereply> message.
709
710	snd $NODE, time => $myport, timereply => 1, 2;
711	# => snd $myport, timereply => 1, 2, <time>
712		926
713	=back	927	=back
714		928
715	=head1 AnyEvent::MP vs. Distributed Erlang	929	=head1 AnyEvent::MP vs. Distributed Erlang
716		930
717	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
718	== 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
719	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
720	sample:	934	sample:
721		935
722	http://www.Erlang.se/doc/programming_rules.shtml	936	http://www.erlang.se/doc/programming_rules.shtml
723	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
724	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
725	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
726		940
727	Despite the similarities, there are also some important differences:	941	Despite the similarities, there are also some important differences:
728		942
729	=over 4	943	=over 4
730		944
731	=item * Node references contain the recipe on how to contact them.	945	=item * Node IDs are arbitrary strings in AEMP.
732		946
733	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
734	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
735	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.
736		951
737	This means that AEMP requires a less tightly controlled environment at the
738	cost of longer node references and a slightly higher management overhead.
739
740	=item Erlang has a "remote ports are like local ports" philosophy, AEMP	952	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
741	uses "local ports are like remote ports".	953	uses "local ports are like remote ports".
742		954
743	The failure modes for local ports are quite different (runtime errors	955	The failure modes for local ports are quite different (runtime errors
744	only) then for remote ports - when a local port dies, you I<know> it dies,	956	only) then for remote ports - when a local port dies, you I<know> it dies,
745	when a connection to another node dies, you know nothing about the other	957	when a connection to another node dies, you know nothing about the other
…		…
752	ports being the special case/exception, where transport errors cannot	964	ports being the special case/exception, where transport errors cannot
753	occur.	965	occur.
754		966
755	=item * Erlang uses processes and a mailbox, AEMP does not queue.	967	=item * Erlang uses processes and a mailbox, AEMP does not queue.
756		968
757	Erlang uses processes that selectively receive messages, and therefore	969	Erlang uses processes that selectively receive messages out of order, and
758	needs a queue. AEMP is event based, queuing messages would serve no	970	therefore needs a queue. AEMP is event based, queuing messages would serve
759	useful purpose. For the same reason the pattern-matching abilities of	971	no useful purpose. For the same reason the pattern-matching abilities
760	AnyEvent::MP are more limited, as there is little need to be able to	972	of AnyEvent::MP are more limited, as there is little need to be able to
761	filter messages without dequeing them.	973	filter messages without dequeuing them.
762		974
763	(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.
764		980
765	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	981	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
766		982
767	Sending messages in Erlang is synchronous and blocks the process (and	983	Sending messages in Erlang is synchronous and blocks the process until
		984	a conenction has been established and the message sent (and so does not
768	so does not need a queue that can overflow). AEMP sends are immediate,	985	need a queue that can overflow). AEMP sends return immediately, connection
769	connection establishment is handled in the background.	986	establishment is handled in the background.
770		987
771	=item * Erlang suffers from silent message loss, AEMP does not.	988	=item * Erlang suffers from silent message loss, AEMP does not.
772		989
773	Erlang makes few guarantees on messages delivery - messages can get lost	990	Erlang implements few guarantees on messages delivery - messages can get
774	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,
775	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).
776		993
777	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
778	holes in the message sequence.	997	no silent "holes" in the message sequence.
779		998
780	=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
781	alive.	1000	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
782		1001	simply tries to work better in common error cases, such as when a network
783	In Erlang it can happen that a monitored process is declared dead and	1002	link goes down.
784	linked processes get killed, but later it turns out that the process is
785	still alive - and can receive messages.
786
787	In AEMP, when port monitoring detects a port as dead, then that port will
788	eventually be killed - it cannot happen that a node detects a port as dead
789	and then later sends messages to it, finding it is still alive.
790		1003
791	=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.
792		1005
793	In Erlang it is quite likely that a node that restarts reuses a process ID	1006	In Erlang it is quite likely that a node that restarts reuses an Erlang
794	known to other nodes for a completely different process, causing messages	1007	process ID known to other nodes for a completely different process,
795	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.
796		1010
797	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
798	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.
799		1013
800	=item * Erlang uses unprotected connections, AEMP uses secure	1014	=item * Erlang uses unprotected connections, AEMP uses secure
801	authentication and can use TLS.	1015	authentication and can use TLS.
802		1016
803	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1017	AEMP can use a proven protocol - TLS - to protect connections and
804	securely authenticate nodes.	1018	securely authenticate nodes.
805		1019
806	=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
807	communications.	1021	communications.
808		1022
809	The AEMP protocol, unlike the Erlang protocol, supports both	1023	The AEMP protocol, unlike the Erlang protocol, supports both programming
810	language-independent text-only protocols (good for debugging) and binary,	1024	language independent text-only protocols (good for debugging), and binary,
811	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.
812		1027
813	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
814	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
815	protocol simple.	1030	protocol simple.
816		1031
817	=item * AEMP has more flexible monitoring options than Erlang.	1032	=item * AEMP has more flexible monitoring options than Erlang.
818		1033
819	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
820	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
821	difficult to implement. Monitoring in AEMP is more flexible than in	1036	difficult to implement.
822	Erlang, as one can choose between automatic kill, exit message or callback	1037
823	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.
824		1040
825	=item * Erlang tries to hide remote/local connections, AEMP does not.	1041	=item * Erlang tries to hide remote/local connections, AEMP does not.
826		1042
827	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
828	as linking is (except linking is unreliable in Erlang).	1044	same way as linking is (except linking is unreliable in Erlang).
829		1045
830	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
831	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
832	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
833	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
834	more reliable.	1050	reliable (no need for C<spawn_link>).
835		1051
836	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
837	(hard to do in Erlang).	1053	(hard to do in Erlang).
838		1054
839	=back	1055	=back
840		1056
841	=head1 RATIONALE	1057	=head1 RATIONALE
842		1058
843	=over 4	1059	=over 4
844		1060
845	=item Why strings for ports and noderefs, why not objects?	1061	=item Why strings for port and node IDs, why not objects?
846		1062
847	We considered "objects", but found that the actual number of methods	1063	We considered "objects", but found that the actual number of methods
848	thatc an be called are very low. Since port IDs and noderefs travel over	1064	that can be called are quite low. Since port and node IDs travel over
849	the network frequently, the serialising/deserialising would add lots of	1065	the network frequently, the serialising/deserialising would add lots of
850	overhead, as well as having to keep a proxy object.	1066	overhead, as well as having to keep a proxy object everywhere.
851		1067
852	Strings can easily be printed, easily serialised etc. and need no special	1068	Strings can easily be printed, easily serialised etc. and need no special
853	procedures to be "valid".	1069	procedures to be "valid".
854		1070
855	And a a miniport consists of a single closure stored in a global hash - it	1071	And as a result, a port with just a default receiver consists of a single
856	can't become much cheaper.	1072	code reference stored in a global hash - it can't become much cheaper.
857		1073
858	=item Why favour JSON, why not real serialising format such as Storable?	1074	=item Why favour JSON, why not a real serialising format such as Storable?
859		1075
860	In fact, any AnyEvent::MP node will happily accept Storable as framing	1076	In fact, any AnyEvent::MP node will happily accept Storable as framing
861	format, but currently there is no way to make a node use Storable by	1077	format, but currently there is no way to make a node use Storable by
862	default.	1078	default (although all nodes will accept it).
863		1079
864	The default framing protocol is JSON because a) JSON::XS is many times	1080	The default framing protocol is JSON because a) JSON::XS is many times
865	faster for small messages and b) most importantly, after years of	1081	faster for small messages and b) most importantly, after years of
866	experience we found that object serialisation is causing more problems	1082	experience we found that object serialisation is causing more problems
867	than it gains: Just like function calls, objects simply do not travel	1083	than it solves: Just like function calls, objects simply do not travel
868	easily over the network, mostly because they will always be a copy, so you	1084	easily over the network, mostly because they will always be a copy, so you
869	always have to re-think your design.	1085	always have to re-think your design.
870		1086
871	Keeping your messages simple, concentrating on data structures rather than	1087	Keeping your messages simple, concentrating on data structures rather than
872	objects, will keep your messages clean, tidy and efficient.	1088	objects, will keep your messages clean, tidy and efficient.
873		1089
874	=back	1090	=back
875		1091
876	=head1 SEE ALSO	1092	=head1 SEE ALSO
877		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.
		1105
878	L<AnyEvent>.	1106	L<AnyEvent>.
879		1107
880	=head1 AUTHOR	1108	=head1 AUTHOR
881		1109
882	Marc Lehmann <schmorp@schmorp.de>	1110	Marc Lehmann <schmorp@schmorp.de>

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