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

Comparing cvsroot/AnyEvent-MP/MP.pm (file contents):
Revision 1.50 by root, Fri Aug 14 14:01:05 2009 UTC vs.
Revision 1.127 by root, Sat Mar 3 20:35:10 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 $somple_port = port { my @msg = @_; 0 };	25	my $simple_port = port { my @msg = @_ };
29		26
30	# creating/using ports, type 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	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
75	messages. All C<rcv> handlers will receive messages they match, messages	80	some messages. Messages send to ports will not be queued, regardless of
76	will not be queued.	81	anything was listening for them or not.
77		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
78	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
79		86
80	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<#>)
81	separator, and a port name (a printable string of unspecified format). An	88	as separator, and a port name (a printable string of unspecified
82	exception is the the node port, whose ID is identical to its node	89	format created by AnyEvent::MP).
83	reference.
84		90
85	=item node	91	=item node
86		92
87	A node is a single process containing at least one port - the node	93	A node is a single process containing at least one port - the node port,
88	port. You can send messages to node ports to find existing ports or to	94	which enables nodes to manage each other remotely, and to create new
89	create new ports, among other things.	95	ports.
90		96
91	Nodes are either private (single-process only), slaves (connected to a	97	Nodes are either public (have one or more listening ports) or private
92	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.
93		100
94	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	101	Nodes is represented by (printable) strings called "node IDs".
95		102
96	A node reference is a string that either simply identifies the node (for	103	=item node ID - C<[A-Za-z0-9_\-.:]*>
97	private and slave nodes), or contains a recipe on how to reach a given
98	node (for public nodes).
99		104
100	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
101	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.
102		109
103	Node references come in two flavours: resolved (containing only numerical	110	=item binds - C<ip:port>
104	addresses) or unresolved (where hostnames are used instead of addresses).
105		111
106	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
107	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).
108		170
109	=back	171	=back
110		172
111	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
112		174
114		176
115	=cut	177	=cut
116		178
117	package AnyEvent::MP;	179	package AnyEvent::MP;
118		180
		181	use AnyEvent::MP::Config ();
119	use AnyEvent::MP::Kernel;	182	use AnyEvent::MP::Kernel;
		183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
120		184
121	use common::sense;	185	use common::sense;
122		186
123	use Carp ();	187	use Carp ();
124		188
125	use AE ();	189	use AE ();
		190	use Guard ();
126		191
127	use base "Exporter";	192	use base "Exporter";
128		193
129	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
130		195
131	our @EXPORT = qw(	196	our @EXPORT = qw(
132	NODE $NODE *SELF node_of _any_	197	NODE $NODE *SELF node_of after
133	resolve_node initialise_node	198	configure
134	snd rcv mon kil reg psub spawn	199	snd rcv mon mon_guard kil psub peval spawn cal
135	port	200	port
		201	db_set db_del db_reg
136	);	202	);
137		203
138	our $SELF;	204	our $SELF;
139		205
140	sub _self_die() {	206	sub _self_die() {
…		…
143	kil $SELF, die => $msg;	209	kil $SELF, die => $msg;
144	}	210	}
145		211
146	=item $thisnode = NODE / $NODE	212	=item $thisnode = NODE / $NODE
147		213
148	The C<NODE> function returns, and the C<$NODE> variable contains	214	The C<NODE> function returns, and the C<$NODE> variable contains, the node
149	the noderef of the local node. The value is initialised by a call	215	ID of the node running in the current process. This value is initialised by
150	to C<become_public> or C<become_slave>, after which all local port	216	a call to C<configure>.
151	identifiers become invalid.
152		217
153	=item $noderef = node_of $port	218	=item $nodeid = node_of $port
154		219
155	Extracts and returns the noderef from a portid or a noderef.	220	Extracts and returns the node ID from a port ID or a node ID.
156		221
157	=item initialise_node $noderef, $seednode, $seednode...	222	=item configure $profile, key => value...
158		223
159	=item initialise_node "slave/", $master, $master...	224	=item configure key => value...
160		225
161	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
162	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
163	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.
164		230
165	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
166	never) before calling other AnyEvent::MP functions.	232	never) before calling other AnyEvent::MP functions.
167		233
168	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
169	either resolved or unresolved.	235	F<aemp> command line utility (sans the set/del prefix), with these additions:
170
171	The first argument will be looked up in the configuration database first
172	(if it is C<undef> then the current nodename will be used instead) to find
173	the relevant configuration profile (see L<aemp>). If none is found then
174	the default configuration is used. The configuration supplies additional
175	seed/master nodes and can override the actual noderef.
176
177	There are two types of networked nodes, public nodes and slave nodes:
178		236
179	=over 4	237	=over 4
180		238
181	=item public nodes	239	=item norc => $boolean (default false)
182		240
183	For public nodes, C<$noderef> (supplied either directly to	241	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
184	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
185	noderef (possibly unresolved, in which case it will be resolved).	243	C<configure> call.
186		244
187	After resolving, the node will bind itself on all endpoints and try to	245	=item force => $boolean (default false)
188	connect to all additional C<$seednodes> that are specified. Seednodes are
189	optional and can be used to quickly bootstrap the node into an existing
190	network.
191		246
192	=item slave nodes	247	IF true, then the values specified in the C<configure> will take
		248	precedence over any values configured via the rc file. The default is for
		249	the rc file to override any options specified in the program.
193		250
194	When the C<$noderef> (either as given or overriden by the config file)	251	=item secure => $pass->($nodeid)
195	is the special string C<slave/>, then the node will become a slave
196	node. Slave nodes cannot be contacted from outside and will route most of
197	their traffic to the master node that they attach to.
198		252
199	At least one additional noderef is required (either by specifying it	253	In addition to specifying a boolean, you can specify a code reference that
200	directly or because it is part of the configuration profile): The node	254	is called for every remote execution attempt - the execution request is
201	will try to connect to all of them and will become a slave attached to the	255	granted iff the callback returns a true value.
202	first node it can successfully connect to.	256
		257	See F<semp setsecure> for more info.
203		258
204	=back	259	=back
205		260
206	This function will block until all nodes have been resolved and, for slave
207	nodes, until it has successfully established a connection to a master
208	server.
209
210	Example: become a public node listening on the guessed noderef, or the one
211	specified via C<aemp> for the current node. This should be the most common
212	form of invocation for "daemon"-type nodes.
213
214	initialise_node;
215
216	Example: become a slave node to any of the the seednodes specified via
217	C<aemp>. This form is often used for commandline clients.
218
219	initialise_node "slave/";
220
221	Example: become a slave node to any of the specified master servers. This
222	form is also often used for commandline clients.
223
224	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
225
226	Example: become a public node, and try to contact some well-known master
227	servers to become part of the network.
228
229	initialise_node undef, "master1", "master2";
230
231	Example: become a public node listening on port C<4041>.
232
233	initialise_node 4041;
234
235	Example: become a public node, only visible on localhost port 4044.
236
237	initialise_node "localhost:4044";
238
239	=item $cv = resolve_node $noderef
240
241	Takes an unresolved node reference that may contain hostnames and
242	abbreviated IDs, resolves all of them and returns a resolved node
243	reference.
244
245	In addition to C<address:port> pairs allowed in resolved noderefs, the
246	following forms are supported:
247
248	=over 4	261	=over 4
249		262
250	=item the empty string	263	=item step 1, gathering configuration from profiles
251		264
252	An empty-string component gets resolved as if the default port (4040) was	265	The function first looks up a profile in the aemp configuration (see the
253	specified.	266	L<aemp> commandline utility). The profile name can be specified via the
		267	named C<profile> parameter or can simply be the first parameter). If it is
		268	missing, then the nodename (F<uname -n>) will be used as profile name.
254		269
255	=item naked port numbers (e.g. C<1234>)	270	The profile data is then gathered as follows:
256		271
257	These are resolved by prepending the local nodename and a colon, to be	272	First, all remaining key => value pairs (all of which are conveniently
258	further resolved.	273	undocumented at the moment) will be interpreted as configuration
		274	data. Then they will be overwritten by any values specified in the global
		275	default configuration (see the F<aemp> utility), then the chain of
		276	profiles chosen by the profile name (and any C<parent> attributes).
259		277
260	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	278	That means that the values specified in the profile have highest priority
		279	and the values specified directly via C<configure> have lowest priority,
		280	and can only be used to specify defaults.
261		281
262	These are resolved by using AnyEvent::DNS to resolve them, optionally	282	If the profile specifies a node ID, then this will become the node ID of
263	looking up SRV records for the C<aemp=4040> port, if no port was	283	this process. If not, then the profile name will be used as node ID, with
264	specified.	284	a unique randoms tring (C</%u>) appended.
		285
		286	The node ID can contain some C<%> sequences that are expanded: C<%n>
		287	is expanded to the local nodename, C<%u> is replaced by a random
		288	strign to make the node unique. For example, the F<aemp> commandline
		289	utility uses C<aemp/%n/%u> as nodename, which might expand to
		290	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		291
		292	=item step 2, bind listener sockets
		293
		294	The next step is to look up the binds in the profile, followed by binding
		295	aemp protocol listeners on all binds specified (it is possible and valid
		296	to have no binds, meaning that the node cannot be contacted form the
		297	outside. This means the node cannot talk to other nodes that also have no
		298	binds, but it can still talk to all "normal" nodes).
		299
		300	If the profile does not specify a binds list, then a default of C<*> is
		301	used, meaning the node will bind on a dynamically-assigned port on every
		302	local IP address it finds.
		303
		304	=item step 3, connect to seed nodes
		305
		306	As the last step, the seed ID list from the profile is passed to the
		307	L<AnyEvent::MP::Global> module, which will then use it to keep
		308	connectivity with at least one node at any point in time.
265		309
266	=back	310	=back
		311
		312	Example: become a distributed node using the local node name as profile.
		313	This should be the most common form of invocation for "daemon"-type nodes.
		314
		315	configure
		316
		317	Example: become a semi-anonymous node. This form is often used for
		318	commandline clients.
		319
		320	configure nodeid => "myscript/%n/%u";
		321
		322	Example: configure a node using a profile called seed, which is suitable
		323	for a seed node as it binds on all local addresses on a fixed port (4040,
		324	customary for aemp).
		325
		326	# use the aemp commandline utility
		327	# aemp profile seed binds '*:4040'
		328
		329	# then use it
		330	configure profile => "seed";
		331
		332	# or simply use aemp from the shell again:
		333	# aemp run profile seed
		334
		335	# or provide a nicer-to-remember nodeid
		336	# aemp run profile seed nodeid "$(hostname)"
267		337
268	=item $SELF	338	=item $SELF
269		339
270	Contains the current port id while executing C<rcv> callbacks or C<psub>	340	Contains the current port id while executing C<rcv> callbacks or C<psub>
271	blocks.	341	blocks.
272		342
273	=item SELF, %SELF, @SELF...	343	=item *SELF, SELF, %SELF, @SELF...
274		344
275	Due to some quirks in how perl exports variables, it is impossible to	345	Due to some quirks in how perl exports variables, it is impossible to
276	just export C<$SELF>, all the symbols called C<SELF> are exported by this	346	just export C<$SELF>, all the symbols named C<SELF> are exported by this
277	module, but only C<$SELF> is currently used.	347	module, but only C<$SELF> is currently used.
278		348
279	=item snd $port, type => @data	349	=item snd $port, type => @data
280		350
281	=item snd $port, @msg	351	=item snd $port, @msg
282		352
283	Send the given message to the given port ID, which can identify either	353	Send the given message to the given port, which can identify either a
284	a local or a remote port, and can be either a string or soemthignt hat	354	local or a remote port, and must be a port ID.
285	stringifies a sa port ID (such as a port object :).
286		355
287	While the message can be about anything, it is highly recommended to use a	356	While the message can be almost anything, it is highly recommended to
288	string as first element (a portid, or some word that indicates a request	357	use a string as first element (a port ID, or some word that indicates a
289	type etc.).	358	request type etc.) and to consist if only simple perl values (scalars,
		359	arrays, hashes) - if you think you need to pass an object, think again.
290		360
291	The message data effectively becomes read-only after a call to this	361	The message data logically becomes read-only after a call to this
292	function: modifying any argument is not allowed and can cause many	362	function: modifying any argument (or values referenced by them) is
293	problems.	363	forbidden, as there can be considerable time between the call to C<snd>
		364	and the time the message is actually being serialised - in fact, it might
		365	never be copied as within the same process it is simply handed to the
		366	receiving port.
294		367
295	The type of data you can transfer depends on the transport protocol: when	368	The type of data you can transfer depends on the transport protocol: when
296	JSON is used, then only strings, numbers and arrays and hashes consisting	369	JSON is used, then only strings, numbers and arrays and hashes consisting
297	of those are allowed (no objects). When Storable is used, then anything	370	of those are allowed (no objects). When Storable is used, then anything
298	that Storable can serialise and deserialise is allowed, and for the local	371	that Storable can serialise and deserialise is allowed, and for the local
299	node, anything can be passed.	372	node, anything can be passed. Best rely only on the common denominator of
		373	these.
300		374
301	=item $local_port = port	375	=item $local_port = port
302		376
303	Create a new local port object and returns its port ID. Initially it has	377	Create a new local port object and returns its port ID. Initially it has
304	no callbacks set and will throw an error when it receives messages.	378	no callbacks set and will throw an error when it receives messages.
…		…
328	sub _kilme {	402	sub _kilme {
329	die "received message on port without callback";	403	die "received message on port without callback";
330	}	404	}
331		405
332	sub port(;&) {	406	sub port(;&) {
333	my $id = "$UNIQ." . $ID++;	407	my $id = $UNIQ . ++$ID;
334	my $port = "$NODE#$id";	408	my $port = "$NODE#$id";
335		409
336	rcv $port, shift \|\| \&_kilme;	410	rcv $port, shift \|\| \&_kilme;
337		411
338	$port	412	$port
…		…
351	The default callback received all messages not matched by a more specific	425	The default callback received all messages not matched by a more specific
352	C<tag> match.	426	C<tag> match.
353		427
354	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...	428	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
355		429
356	Register callbacks to be called on messages starting with the given tag on	430	Register (or replace) callbacks to be called on messages starting with the
357	the given port (and return the port), or unregister it (when C<$callback>	431	given tag on the given port (and return the port), or unregister it (when
358	is C<$undef>).	432	C<$callback> is C<$undef> or missing). There can only be one callback
		433	registered for each tag.
359		434
360	The original message will be passed to the callback, after the first	435	The original message will be passed to the callback, after the first
361	element (the tag) has been removed. The callback will use the same	436	element (the tag) has been removed. The callback will use the same
362	environment as the default callback (see above).	437	environment as the default callback (see above).
363		438
…		…
375	rcv port,	450	rcv port,
376	msg1 => sub { ... },	451	msg1 => sub { ... },
377	...	452	...
378	;	453	;
379		454
		455	Example: temporarily register a rcv callback for a tag matching some port
		456	(e.g. for an rpc reply) and unregister it after a message was received.
		457
		458	rcv $port, $otherport => sub {
		459	my @reply = @_;
		460
		461	rcv $SELF, $otherport;
		462	};
		463
380	=cut	464	=cut
381		465
382	sub rcv($@) {	466	sub rcv($@) {
383	my $port = shift;	467	my $port = shift;
384	my ($noderef, $portid) = split /#/, $port, 2;	468	my ($nodeid, $portid) = split /#/, $port, 2;
385		469
386	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	470	$NODE{$nodeid} == $NODE{""}
387	or Carp::croak "$port: rcv can only be called on local ports, caught";	471	or Carp::croak "$port: rcv can only be called on local ports, caught";
388		472
389	while (@_) {	473	while (@_) {
390	if (ref $_[0]) {	474	if (ref $_[0]) {
391	if (my $self = $PORT_DATA{$portid}) {	475	if (my $self = $PORT_DATA{$portid}) {
392	"AnyEvent::MP::Port" eq ref $self	476	"AnyEvent::MP::Port" eq ref $self
393	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	477	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
394		478
395	$self->[2] = shift;	479	$self->[0] = shift;
396	} else {	480	} else {
397	my $cb = shift;	481	my $cb = shift;
398	$PORT{$portid} = sub {	482	$PORT{$portid} = sub {
399	local $SELF = $port;	483	local $SELF = $port;
400	eval { &$cb }; _self_die if $@;	484	eval { &$cb }; _self_die if $@;
401	};	485	};
402	}	486	}
403	} elsif (defined $_[0]) {	487	} elsif (defined $_[0]) {
404	my $self = $PORT_DATA{$portid} \|\|= do {	488	my $self = $PORT_DATA{$portid} \|\|= do {
405	my $self = bless [$PORT{$port} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";	489	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
406		490
407	$PORT{$portid} = sub {	491	$PORT{$portid} = sub {
408	local $SELF = $port;	492	local $SELF = $port;
409		493
410	if (my $cb = $self->[1]{$_[0]}) {	494	if (my $cb = $self->[1]{$_[0]}) {
…		…
432	}	516	}
433		517
434	$port	518	$port
435	}	519	}
436		520
		521	=item peval $port, $coderef[, @args]
		522
		523	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		524	when the code throews an exception the C<$port> will be killed.
		525
		526	Any remaining args will be passed to the callback. Any return values will
		527	be returned to the caller.
		528
		529	This is useful when you temporarily want to execute code in the context of
		530	a port.
		531
		532	Example: create a port and run some initialisation code in it's context.
		533
		534	my $port = port { ... };
		535
		536	peval $port, sub {
		537	init
		538	or die "unable to init";
		539	};
		540
		541	=cut
		542
		543	sub peval($$) {
		544	local $SELF = shift;
		545	my $cb = shift;
		546
		547	if (wantarray) {
		548	my @res = eval { &$cb };
		549	_self_die if $@;
		550	@res
		551	} else {
		552	my $res = eval { &$cb };
		553	_self_die if $@;
		554	$res
		555	}
		556	}
		557
437	=item $closure = psub { BLOCK }	558	=item $closure = psub { BLOCK }
438		559
439	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	560	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
440	closure is executed, sets up the environment in the same way as in C<rcv>	561	closure is executed, sets up the environment in the same way as in C<rcv>
441	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.	562	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		563
		564	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		565	BLOCK }, @_ } >>.
442		566
443	This is useful when you register callbacks from C<rcv> callbacks:	567	This is useful when you register callbacks from C<rcv> callbacks:
444		568
445	rcv delayed_reply => sub {	569	rcv delayed_reply => sub {
446	my ($delay, @reply) = @_;	570	my ($delay, @reply) = @_;
…		…
470	$res	594	$res
471	}	595	}
472	}	596	}
473	}	597	}
474		598
475	=item $guard = mon $port, $cb->(@reason)	599	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
476		600
477	=item $guard = mon $port, $rcvport	601	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
478		602
479	=item $guard = mon $port	603	=item $guard = mon $port # kill $SELF when $port dies
480		604
481	=item $guard = mon $port, $rcvport, @msg	605	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
482		606
483	Monitor the given port and do something when the port is killed or	607	Monitor the given port and do something when the port is killed or
484	messages to it were lost, and optionally return a guard that can be used	608	messages to it were lost, and optionally return a guard that can be used
485	to stop monitoring again.	609	to stop monitoring again.
486
487	C<mon> effectively guarantees that, in the absence of hardware failures,
488	that after starting the monitor, either all messages sent to the port
489	will arrive, or the monitoring action will be invoked after possible
490	message loss has been detected. No messages will be lost "in between"
491	(after the first lost message no further messages will be received by the
492	port). After the monitoring action was invoked, further messages might get
493	delivered again.
494		610
495	In the first form (callback), the callback is simply called with any	611	In the first form (callback), the callback is simply called with any
496	number of C<@reason> elements (no @reason means that the port was deleted	612	number of C<@reason> elements (no @reason means that the port was deleted
497	"normally"). Note also that I<< the callback B<must> never die >>, so use	613	"normally"). Note also that I<< the callback B<must> never die >>, so use
498	C<eval> if unsure.	614	C<eval> if unsure.
499		615
500	In the second form (another port given), the other port (C<$rcvport>)	616	In the second form (another port given), the other port (C<$rcvport>)
501	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	617	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
502	"normal" kils nothing happens, while under all other conditions, the other	618	"normal" kils nothing happens, while under all other conditions, the other
503	port is killed with the same reason.	619	port is killed with the same reason.
504		620
505	The third form (kill self) is the same as the second form, except that	621	The third form (kill self) is the same as the second form, except that
506	C<$rvport> defaults to C<$SELF>.	622	C<$rvport> defaults to C<$SELF>.
507		623
508	In the last form (message), a message of the form C<@msg, @reason> will be	624	In the last form (message), a message of the form C<@msg, @reason> will be
509	C<snd>.	625	C<snd>.
		626
		627	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		628	alert was raised), they are removed and will not trigger again.
510		629
511	As a rule of thumb, monitoring requests should always monitor a port from	630	As a rule of thumb, monitoring requests should always monitor a port from
512	a local port (or callback). The reason is that kill messages might get	631	a local port (or callback). The reason is that kill messages might get
513	lost, just like any other message. Another less obvious reason is that	632	lost, just like any other message. Another less obvious reason is that
514	even monitoring requests can get lost (for exmaple, when the connection	633	even monitoring requests can get lost (for example, when the connection
515	to the other node goes down permanently). When monitoring a port locally	634	to the other node goes down permanently). When monitoring a port locally
516	these problems do not exist.	635	these problems do not exist.
517		636
		637	C<mon> effectively guarantees that, in the absence of hardware failures,
		638	after starting the monitor, either all messages sent to the port will
		639	arrive, or the monitoring action will be invoked after possible message
		640	loss has been detected. No messages will be lost "in between" (after
		641	the first lost message no further messages will be received by the
		642	port). After the monitoring action was invoked, further messages might get
		643	delivered again.
		644
		645	Inter-host-connection timeouts and monitoring depend on the transport
		646	used. The only transport currently implemented is TCP, and AnyEvent::MP
		647	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		648	non-idle connection, and usually around two hours for idle connections).
		649
		650	This means that monitoring is good for program errors and cleaning up
		651	stuff eventually, but they are no replacement for a timeout when you need
		652	to ensure some maximum latency.
		653
518	Example: call a given callback when C<$port> is killed.	654	Example: call a given callback when C<$port> is killed.
519		655
520	mon $port, sub { warn "port died because of <@_>\n" };	656	mon $port, sub { warn "port died because of <@_>\n" };
521		657
522	Example: kill ourselves when C<$port> is killed abnormally.	658	Example: kill ourselves when C<$port> is killed abnormally.
…		…
528	mon $port, $self => "restart";	664	mon $port, $self => "restart";
529		665
530	=cut	666	=cut
531		667
532	sub mon {	668	sub mon {
533	my ($noderef, $port) = split /#/, shift, 2;	669	my ($nodeid, $port) = split /#/, shift, 2;
534		670
535	my $node = $NODE{$noderef} \|\| add_node $noderef;	671	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
536		672
537	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';	673	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
538		674
539	unless (ref $cb) {	675	unless (ref $cb) {
540	if (@_) {	676	if (@_) {
…		…
549	}	685	}
550		686
551	$node->monitor ($port, $cb);	687	$node->monitor ($port, $cb);
552		688
553	defined wantarray	689	defined wantarray
554	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	690	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
555	}	691	}
556		692
557	=item $guard = mon_guard $port, $ref, $ref...	693	=item $guard = mon_guard $port, $ref, $ref...
558		694
559	Monitors the given C<$port> and keeps the passed references. When the port	695	Monitors the given C<$port> and keeps the passed references. When the port
560	is killed, the references will be freed.	696	is killed, the references will be freed.
561		697
562	Optionally returns a guard that will stop the monitoring.	698	Optionally returns a guard that will stop the monitoring.
563		699
564	This function is useful when you create e.g. timers or other watchers and	700	This function is useful when you create e.g. timers or other watchers and
565	want to free them when the port gets killed:	701	want to free them when the port gets killed (note the use of C<psub>):
566		702
567	$port->rcv (start => sub {	703	$port->rcv (start => sub {
568	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	704	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
569	undef $timer if 0.9 < rand;	705	undef $timer if 0.9 < rand;
570	});	706	});
571	});	707	});
572		708
573	=cut	709	=cut
…		…
582		718
583	=item kil $port[, @reason]	719	=item kil $port[, @reason]
584		720
585	Kill the specified port with the given C<@reason>.	721	Kill the specified port with the given C<@reason>.
586		722
587	If no C<@reason> is specified, then the port is killed "normally" (linked	723	If no C<@reason> is specified, then the port is killed "normally" -
588	ports will not be kileld, or even notified).	724	monitor callback will be invoked, but the kil will not cause linked ports
		725	(C<mon $mport, $lport> form) to get killed.
589		726
590	Otherwise, linked ports get killed with the same reason (second form of	727	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
591	C<mon>, see below).	728	form) get killed with the same reason.
592		729
593	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	730	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
594	will be reported as reason C<< die => $@ >>.	731	will be reported as reason C<< die => $@ >>.
595		732
596	Transport/communication errors are reported as C<< transport_error =>	733	Transport/communication errors are reported as C<< transport_error =>
…		…
601	=item $port = spawn $node, $initfunc[, @initdata]	738	=item $port = spawn $node, $initfunc[, @initdata]
602		739
603	Creates a port on the node C<$node> (which can also be a port ID, in which	740	Creates a port on the node C<$node> (which can also be a port ID, in which
604	case it's the node where that port resides).	741	case it's the node where that port resides).
605		742
606	The port ID of the newly created port is return immediately, and it is	743	The port ID of the newly created port is returned immediately, and it is
607	permissible to immediately start sending messages or monitor the port.	744	possible to immediately start sending messages or to monitor the port.
608		745
609	After the port has been created, the init function is	746	After the port has been created, the init function is called on the remote
610	called. This function must be a fully-qualified function name	747	node, in the same context as a C<rcv> callback. This function must be a
611	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	748	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
612	program, use C<::name>.	749	specify a function in the main program, use C<::name>.
613		750
614	If the function doesn't exist, then the node tries to C<require>	751	If the function doesn't exist, then the node tries to C<require>
615	the package, then the package above the package and so on (e.g.	752	the package, then the package above the package and so on (e.g.
616	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	753	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
617	exists or it runs out of package names.	754	exists or it runs out of package names.
618		755
619	The init function is then called with the newly-created port as context	756	The init function is then called with the newly-created port as context
620	object (C<$SELF>) and the C<@initdata> values as arguments.	757	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		758	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		759	the port might not get created.
621		760
622	A common idiom is to pass your own port, monitor the spawned port, and	761	A common idiom is to pass a local port, immediately monitor the spawned
623	in the init function, monitor the original port. This two-way monitoring	762	port, and in the remote init function, immediately monitor the passed
624	ensures that both ports get cleaned up when there is a problem.	763	local port. This two-way monitoring ensures that both ports get cleaned up
		764	when there is a problem.
		765
		766	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		767	caller before C<spawn> returns (by delaying invocation when spawn is
		768	called for the local node).
625		769
626	Example: spawn a chat server port on C<$othernode>.	770	Example: spawn a chat server port on C<$othernode>.
627		771
628	# this node, executed from within a port context:	772	# this node, executed from within a port context:
629	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	773	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
644		788
645	sub _spawn {	789	sub _spawn {
646	my $port = shift;	790	my $port = shift;
647	my $init = shift;	791	my $init = shift;
648		792
		793	# rcv will create the actual port
649	local $SELF = "$NODE#$port";	794	local $SELF = "$NODE#$port";
650	eval {	795	eval {
651	&{ load_func $init }	796	&{ load_func $init }
652	};	797	};
653	_self_die if $@;	798	_self_die if $@;
654	}	799	}
655		800
656	sub spawn(@) {	801	sub spawn(@) {
657	my ($noderef, undef) = split /#/, shift, 2;	802	my ($nodeid, undef) = split /#/, shift, 2;
658		803
659	my $id = "$RUNIQ." . $ID++;	804	my $id = $RUNIQ . ++$ID;
660		805
661	$_[0] =~ /::/	806	$_[0] =~ /::/
662	or Carp::croak "spawn init function must be a fully-qualified name, caught";	807	or Carp::croak "spawn init function must be a fully-qualified name, caught";
663		808
664	($NODE{$noderef} \|\| add_node $noderef)	809	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
665	->send (["", "AnyEvent::MP::_spawn" => $id, @_]);
666		810
667	"$noderef#$id"	811	"$nodeid#$id"
668	}	812	}
669		813
		814
		815	=item after $timeout, @msg
		816
		817	=item after $timeout, $callback
		818
		819	Either sends the given message, or call the given callback, after the
		820	specified number of seconds.
		821
		822	This is simply a utility function that comes in handy at times - the
		823	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		824	so it may go away in the future.
		825
		826	=cut
		827
		828	sub after($@) {
		829	my ($timeout, @action) = @_;
		830
		831	my $t; $t = AE::timer $timeout, 0, sub {
		832	undef $t;
		833	ref $action[0]
		834	? $action[0]()
		835	: snd @action;
		836	};
		837	}
		838
		839	=item cal $port, @msg, $callback[, $timeout]
		840
		841	A simple form of RPC - sends a message to the given C<$port> with the
		842	given contents (C<@msg>), but adds a reply port to the message.
		843
		844	The reply port is created temporarily just for the purpose of receiving
		845	the reply, and will be C<kil>ed when no longer needed.
		846
		847	A reply message sent to the port is passed to the C<$callback> as-is.
		848
		849	If an optional time-out (in seconds) is given and it is not C<undef>,
		850	then the callback will be called without any arguments after the time-out
		851	elapsed and the port is C<kil>ed.
		852
		853	If no time-out is given (or it is C<undef>), then the local port will
		854	monitor the remote port instead, so it eventually gets cleaned-up.
		855
		856	Currently this function returns the temporary port, but this "feature"
		857	might go in future versions unless you can make a convincing case that
		858	this is indeed useful for something.
		859
		860	=cut
		861
		862	sub cal(@) {
		863	my $timeout = ref $_[-1] ? undef : pop;
		864	my $cb = pop;
		865
		866	my $port = port {
		867	undef $timeout;
		868	kil $SELF;
		869	&$cb;
		870	};
		871
		872	if (defined $timeout) {
		873	$timeout = AE::timer $timeout, 0, sub {
		874	undef $timeout;
		875	kil $port;
		876	$cb->();
		877	};
		878	} else {
		879	mon $_[0], sub {
		880	kil $port;
		881	$cb->();
		882	};
		883	}
		884
		885	push @_, $port;
		886	&snd;
		887
		888	$port
		889	}
		890
670	=back	891	=back
671		892
672	=head1 NODE MESSAGES	893	=head1 DISTRIBUTED DATABASE
673		894
674	Nodes understand the following messages sent to them. Many of them take	895	AnyEvent::MP comes with a simple distributed database. The database will
675	arguments called C<@reply>, which will simply be used to compose a reply	896	be mirrored asynchronously at all global nodes. Other nodes bind to one of
676	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and	897	the global nodes for their needs.
677	the remaining arguments are simply the message data.
678		898
679	While other messages exist, they are not public and subject to change.	899	The database consists of a two-level hash - a hash contains a hash which
		900	contains values.
680		901
		902	The top level hash key is called "family", and the second-level hash key
		903	is called "subkey" or simply "key".
		904
		905	The family must be alphanumeric, i.e. start with a letter and consist
		906	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		907	pretty much like Perl module names.
		908
		909	As the family namespace is global, it is recommended to prefix family names
		910	with the name of the application or module using it.
		911
		912	The subkeys must be non-empty strings, with no further restrictions.
		913
		914	The values should preferably be strings, but other perl scalars should
		915	work as well (such as undef, arrays and hashes).
		916
		917	Every database entry is owned by one node - adding the same family/subkey
		918	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		919	but the result might be nondeterministic, i.e. the key might have
		920	different values on different nodes.
		921
		922	Different subkeys in the same family can be owned by different nodes
		923	without problems, and in fact, this is the common method to create worker
		924	pools. For example, a worker port for image scaling might do this:
		925
		926	db_set my_image_scalers => $port;
		927
		928	And clients looking for an image scaler will want to get the
		929	C<my_image_scalers> keys:
		930
		931	db_keys "my_image_scalers" => 60 => sub {
		932	#d##TODO#
		933
681	=over 4	934	=over
682		935
683	=cut	936	=item db_set $family => $subkey [=> $value]
684		937
685	=item lookup => $name, @reply	938	Sets (or replaces) a key to the database - if C<$value> is omitted,
		939	C<undef> is used instead.
686		940
687	Replies with the port ID of the specified well-known port, or C<undef>.	941	=item db_del $family => $subkey
688		942
689	=item devnull => ...	943	Deletes a key from the database.
690		944
691	Generic data sink/CPU heat conversion.	945	=item $guard = db_reg $family => $subkey [=> $value]
692		946
693	=item relay => $port, @msg	947	Sets the key on the database and returns a guard. When the guard is
		948	destroyed, the key is deleted from the database. If C<$value> is missing,
		949	then C<undef> is used.
694		950
695	Simply forwards the message to the given port.	951	=cut
696
697	=item eval => $string[ @reply]
698
699	Evaluates the given string. If C<@reply> is given, then a message of the
700	form C<@reply, $@, @evalres> is sent.
701
702	Example: crash another node.
703
704	snd $othernode, eval => "exit";
705
706	=item time => @reply
707
708	Replies the the current node time to C<@reply>.
709
710	Example: tell the current node to send the current time to C<$myport> in a
711	C<timereply> message.
712
713	snd $NODE, time => $myport, timereply => 1, 2;
714	# => snd $myport, timereply => 1, 2, <time>
715		952
716	=back	953	=back
717		954
718	=head1 AnyEvent::MP vs. Distributed Erlang	955	=head1 AnyEvent::MP vs. Distributed Erlang
719		956
720	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	957	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
721	== aemp node, Erlang process == aemp port), so many of the documents and	958	== aemp node, Erlang process == aemp port), so many of the documents and
722	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	959	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
723	sample:	960	sample:
724		961
725	http://www.Erlang.se/doc/programming_rules.shtml	962	http://www.erlang.se/doc/programming_rules.shtml
726	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	963	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
727	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	964	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
728	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	965	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
729		966
730	Despite the similarities, there are also some important differences:	967	Despite the similarities, there are also some important differences:
731		968
732	=over 4	969	=over 4
733		970
734	=item * Node references contain the recipe on how to contact them.	971	=item * Node IDs are arbitrary strings in AEMP.
735		972
736	Erlang relies on special naming and DNS to work everywhere in the	973	Erlang relies on special naming and DNS to work everywhere in the same
737	same way. AEMP relies on each node knowing it's own address(es), with	974	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
738	convenience functionality.	975	configuration or DNS), and possibly the addresses of some seed nodes, but
		976	will otherwise discover other nodes (and their IDs) itself.
739		977
740	This means that AEMP requires a less tightly controlled environment at the	978	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
741	cost of longer node references and a slightly higher management overhead.	979	uses "local ports are like remote ports".
		980
		981	The failure modes for local ports are quite different (runtime errors
		982	only) then for remote ports - when a local port dies, you I<know> it dies,
		983	when a connection to another node dies, you know nothing about the other
		984	port.
		985
		986	Erlang pretends remote ports are as reliable as local ports, even when
		987	they are not.
		988
		989	AEMP encourages a "treat remote ports differently" philosophy, with local
		990	ports being the special case/exception, where transport errors cannot
		991	occur.
742		992
743	=item * Erlang uses processes and a mailbox, AEMP does not queue.	993	=item * Erlang uses processes and a mailbox, AEMP does not queue.
744		994
745	Erlang uses processes that selctively receive messages, and therefore	995	Erlang uses processes that selectively receive messages out of order, and
746	needs a queue. AEMP is event based, queuing messages would serve no useful	996	therefore needs a queue. AEMP is event based, queuing messages would serve
747	purpose.	997	no useful purpose. For the same reason the pattern-matching abilities
		998	of AnyEvent::MP are more limited, as there is little need to be able to
		999	filter messages without dequeuing them.
748		1000
749	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	1001	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1002	being event-based, while Erlang is process-based.
		1003
		1004	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1005	top of AEMP and Coro threads.
750		1006
751	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1007	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
752		1008
753	Sending messages in Erlang is synchronous and blocks the process. AEMP	1009	Sending messages in Erlang is synchronous and blocks the process until
754	sends are immediate, connection establishment is handled in the	1010	a conenction has been established and the message sent (and so does not
755	background.	1011	need a queue that can overflow). AEMP sends return immediately, connection
		1012	establishment is handled in the background.
756		1013
757	=item * Erlang can silently lose messages, AEMP cannot.	1014	=item * Erlang suffers from silent message loss, AEMP does not.
758		1015
759	Erlang makes few guarantees on messages delivery - messages can get lost	1016	Erlang implements few guarantees on messages delivery - messages can get
760	without any of the processes realising it (i.e. you send messages a, b,	1017	lost without any of the processes realising it (i.e. you send messages a,
761	and c, and the other side only receives messages a and c).	1018	b, and c, and the other side only receives messages a and c).
762		1019
763	AEMP guarantees correct ordering, and the guarantee that there are no	1020	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1021	guarantee that after one message is lost, all following ones sent to the
		1022	same port are lost as well, until monitoring raises an error, so there are
764	holes in the message sequence.	1023	no silent "holes" in the message sequence.
765		1024
766	=item * In Erlang, processes can be declared dead and later be found to be	1025	If you want your software to be very reliable, you have to cope with
767	alive.	1026	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
768		1027	simply tries to work better in common error cases, such as when a network
769	In Erlang it can happen that a monitored process is declared dead and	1028	link goes down.
770	linked processes get killed, but later it turns out that the process is
771	still alive - and can receive messages.
772
773	In AEMP, when port monitoring detects a port as dead, then that port will
774	eventually be killed - it cannot happen that a node detects a port as dead
775	and then later sends messages to it, finding it is still alive.
776		1029
777	=item * Erlang can send messages to the wrong port, AEMP does not.	1030	=item * Erlang can send messages to the wrong port, AEMP does not.
778		1031
779	In Erlang it is quite possible that a node that restarts reuses a process	1032	In Erlang it is quite likely that a node that restarts reuses an Erlang
780	ID known to other nodes for a completely different process, causing	1033	process ID known to other nodes for a completely different process,
781	messages destined for that process to end up in an unrelated process.	1034	causing messages destined for that process to end up in an unrelated
		1035	process.
782		1036
783	AEMP never reuses port IDs, so old messages or old port IDs floating	1037	AEMP does not reuse port IDs, so old messages or old port IDs floating
784	around in the network will not be sent to an unrelated port.	1038	around in the network will not be sent to an unrelated port.
785		1039
786	=item * Erlang uses unprotected connections, AEMP uses secure	1040	=item * Erlang uses unprotected connections, AEMP uses secure
787	authentication and can use TLS.	1041	authentication and can use TLS.
788		1042
789	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1043	AEMP can use a proven protocol - TLS - to protect connections and
790	securely authenticate nodes.	1044	securely authenticate nodes.
791		1045
792	=item * The AEMP protocol is optimised for both text-based and binary	1046	=item * The AEMP protocol is optimised for both text-based and binary
793	communications.	1047	communications.
794		1048
795	The AEMP protocol, unlike the Erlang protocol, supports both	1049	The AEMP protocol, unlike the Erlang protocol, supports both programming
796	language-independent text-only protocols (good for debugging) and binary,	1050	language independent text-only protocols (good for debugging), and binary,
797	language-specific serialisers (e.g. Storable).	1051	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1052	used, the protocol is actually completely text-based.
798		1053
799	It has also been carefully designed to be implementable in other languages	1054	It has also been carefully designed to be implementable in other languages
800	with a minimum of work while gracefully degrading fucntionality to make the	1055	with a minimum of work while gracefully degrading functionality to make the
801	protocol simple.	1056	protocol simple.
802		1057
803	=item * AEMP has more flexible monitoring options than Erlang.	1058	=item * AEMP has more flexible monitoring options than Erlang.
804		1059
805	In Erlang, you can chose to receive I<all> exit signals as messages	1060	In Erlang, you can chose to receive I<all> exit signals as messages or
806	or I<none>, there is no in-between, so monitoring single processes is	1061	I<none>, there is no in-between, so monitoring single Erlang processes is
807	difficult to implement. Monitoring in AEMP is more flexible than in	1062	difficult to implement.
808	Erlang, as one can choose between automatic kill, exit message or callback	1063
809	on a per-process basis.	1064	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1065	between automatic kill, exit message or callback on a per-port basis.
810		1066
811	=item * Erlang tries to hide remote/local connections, AEMP does not.	1067	=item * Erlang tries to hide remote/local connections, AEMP does not.
812		1068
813	Monitoring in Erlang is not an indicator of process death/crashes,	1069	Monitoring in Erlang is not an indicator of process death/crashes, in the
814	as linking is (except linking is unreliable in Erlang).	1070	same way as linking is (except linking is unreliable in Erlang).
815		1071
816	In AEMP, you don't "look up" registered port names or send to named ports	1072	In AEMP, you don't "look up" registered port names or send to named ports
817	that might or might not be persistent. Instead, you normally spawn a port	1073	that might or might not be persistent. Instead, you normally spawn a port
818	on the remote node. The init function monitors the you, and you monitor	1074	on the remote node. The init function monitors you, and you monitor the
819	the remote port. Since both monitors are local to the node, they are much	1075	remote port. Since both monitors are local to the node, they are much more
820	more reliable.	1076	reliable (no need for C<spawn_link>).
821		1077
822	This also saves round-trips and avoids sending messages to the wrong port	1078	This also saves round-trips and avoids sending messages to the wrong port
823	(hard to do in Erlang).	1079	(hard to do in Erlang).
824		1080
825	=back	1081	=back
826		1082
827	=head1 RATIONALE	1083	=head1 RATIONALE
828		1084
829	=over 4	1085	=over 4
830		1086
831	=item Why strings for ports and noderefs, why not objects?	1087	=item Why strings for port and node IDs, why not objects?
832		1088
833	We considered "objects", but found that the actual number of methods	1089	We considered "objects", but found that the actual number of methods
834	thatc an be called are very low. Since port IDs and noderefs travel over	1090	that can be called are quite low. Since port and node IDs travel over
835	the network frequently, the serialising/deserialising would add lots of	1091	the network frequently, the serialising/deserialising would add lots of
836	overhead, as well as having to keep a proxy object.	1092	overhead, as well as having to keep a proxy object everywhere.
837		1093
838	Strings can easily be printed, easily serialised etc. and need no special	1094	Strings can easily be printed, easily serialised etc. and need no special
839	procedures to be "valid".	1095	procedures to be "valid".
840		1096
841	And a a miniport consists of a single closure stored in a global hash - it	1097	And as a result, a port with just a default receiver consists of a single
842	can't become much cheaper.	1098	code reference stored in a global hash - it can't become much cheaper.
843		1099
844	=item Why favour JSON, why not real serialising format such as Storable?	1100	=item Why favour JSON, why not a real serialising format such as Storable?
845		1101
846	In fact, any AnyEvent::MP node will happily accept Storable as framing	1102	In fact, any AnyEvent::MP node will happily accept Storable as framing
847	format, but currently there is no way to make a node use Storable by	1103	format, but currently there is no way to make a node use Storable by
848	default.	1104	default (although all nodes will accept it).
849		1105
850	The default framing protocol is JSON because a) JSON::XS is many times	1106	The default framing protocol is JSON because a) JSON::XS is many times
851	faster for small messages and b) most importantly, after years of	1107	faster for small messages and b) most importantly, after years of
852	experience we found that object serialisation is causing more problems	1108	experience we found that object serialisation is causing more problems
853	than it gains: Just like function calls, objects simply do not travel	1109	than it solves: Just like function calls, objects simply do not travel
854	easily over the network, mostly because they will always be a copy, so you	1110	easily over the network, mostly because they will always be a copy, so you
855	always have to re-think your design.	1111	always have to re-think your design.
856		1112
857	Keeping your messages simple, concentrating on data structures rather than	1113	Keeping your messages simple, concentrating on data structures rather than
858	objects, will keep your messages clean, tidy and efficient.	1114	objects, will keep your messages clean, tidy and efficient.
859		1115
860	=back	1116	=back
861		1117
862	=head1 SEE ALSO	1118	=head1 SEE ALSO
863		1119
		1120	L<AnyEvent::MP::Intro> - a gentle introduction.
		1121
		1122	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1123
		1124	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1125	your applications.
		1126
		1127	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1128
		1129	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1130	all nodes.
		1131
864	L<AnyEvent>.	1132	L<AnyEvent>.
865		1133
866	=head1 AUTHOR	1134	=head1 AUTHOR
867		1135
868	Marc Lehmann <schmorp@schmorp.de>	1136	Marc Lehmann <schmorp@schmorp.de>

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Revision 1.127 by root, Sat Mar 3 20:35:10 2012 UTC