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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.63 by root, Thu Aug 27 21:29:37 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;	15	configure;
17		16
18	# ports are message endpoints	17	# ports are message destinations
19		18
20	# sending messages	19	# sending messages
21	snd $port, type => data...;	20	snd $port, type => data...;
22	snd $port, @msg;	21	snd $port, @msg;
23	snd @msg_with_first_element_being_a_port;	22	snd @msg_with_first_element_being_a_port;
24		23
25	# creating/using ports, the simple way	24	# creating/using ports, the simple way
26	my $simple_port = port { my @msg = @_; 0 };	25	my $simple_port = port { my @msg = @_ };
27		26
28	# creating/using ports, tagged message matching	27	# creating/using ports, tagged message matching
29	my $port = port;	28	my $port = port;
30	rcv $port, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
31	rcv $port, pong => sub { warn "pong received\n"; 0 };	30	rcv $port, pong => sub { warn "pong received\n" };
32		31
33	# create a port on another node	32	# create a port on another node
34	my $port = spawn $node, $initfunc, @initdata;	33	my $port = spawn $node, $initfunc, @initdata;
35		34
		35	# destroy a port again
		36	kil $port; # "normal" kill
		37	kil $port, my_error => "everything is broken"; # error kill
		38
36	# monitoring	39	# monitoring
37	mon $port, $cb->(@msg) # callback is invoked on death	40	mon $localport, $cb->(@msg) # callback is invoked on death
38	mon $port, $otherport # kill otherport on abnormal death	41	mon $localport, $otherport # kill otherport on abnormal death
39	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	};
40		51
41	=head1 CURRENT STATUS	52	=head1 CURRENT STATUS
42		53
		54	bin/aemp - stable.
43	AnyEvent::MP - stable API, should work	55	AnyEvent::MP - stable API, should work.
44	AnyEvent::MP::Intro - outdated	56	AnyEvent::MP::Intro - explains most concepts.
45	AnyEvent::MP::Kernel - WIP
46	AnyEvent::MP::Transport - mostly stable	57	AnyEvent::MP::Kernel - mostly stable API.
47		58	AnyEvent::MP::Global - stable API.
48	stay tuned.
49		59
50	=head1 DESCRIPTION	60	=head1 DESCRIPTION
51		61
52	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
53		63
54	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
55	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
56		66
57	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>
58	manual page.	68	manual page and the examples under F<eg/>.
59
60	At the moment, this module family is severly broken and underdocumented,
61	so do not use. This was uploaded mainly to reserve the CPAN namespace -
62	stay tuned!
63		69
64	=head1 CONCEPTS	70	=head1 CONCEPTS
65		71
66	=over 4	72	=over 4
67		73
68	=item port	74	=item port
69		75
70	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).
71		78
72	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
73	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.
74		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
75	=item port ID - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
76		86
77	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<#>)
78	separator, and a port name (a printable string of unspecified format). An	88	as separator, and a port name (a printable string of unspecified
79	exception is the the node port, whose ID is identical to its node	89	format created by AnyEvent::MP).
80	reference.
81		90
82	=item node	91	=item node
83		92
84	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,
85	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
86	ports.	95	ports.
87		96
88	Nodes are either private (single-process only), slaves (can only talk to	97	Nodes are either public (have one or more listening ports) or private
89	public nodes, but do not need an open port) or public nodes (connectable	98	(no listening ports). Private nodes cannot talk to other private nodes
90	from any other node).	99	currently, but all nodes can talk to public nodes.
91		100
		101	Nodes is represented by (printable) strings called "node IDs".
		102
92	=item node ID - C<[a-za-Z0-9_\-.:]+>	103	=item node ID - C<[A-Za-z0-9_\-.:]*>
93		104
94	A node ID is a string that either simply identifies the node (for	105	A node ID is a string that uniquely identifies the node within a
95	private and slave nodes), or contains a recipe on how to reach a given	106	network. Depending on the configuration used, node IDs can look like a
96	node (for public nodes).	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.
97		109
98	This recipe is simply a comma-separated list of C<address:port> pairs (for	110	=item binds - C<ip:port>
99	TCP/IP, other protocols might look different).
100		111
101	Node references come in two flavours: resolved (containing only numerical	112	Nodes can only talk to each other by creating some kind of connection to
102	addresses) or unresolved (where hostnames are used instead of addresses).	113	each other. To do this, nodes should listen on one or more local transport
		114	endpoints - binds.
103		115
104	Before using an unresolved node reference in a message you first have to	116	Currently, only standard C<ip:port> specifications can be used, which
105	resolve it.	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).
106		170
107	=back	171	=back
108		172
109	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
110		174
112		176
113	=cut	177	=cut
114		178
115	package AnyEvent::MP;	179	package AnyEvent::MP;
116		180
		181	use AnyEvent::MP::Config ();
117	use AnyEvent::MP::Kernel;	182	use AnyEvent::MP::Kernel;
		183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
118		184
119	use common::sense;	185	use common::sense;
120		186
121	use Carp ();	187	use Carp ();
122		188
123	use AE ();	189	use AE ();
		190	use Guard ();
124		191
125	use base "Exporter";	192	use base "Exporter";
126		193
127	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
128		195
129	our @EXPORT = qw(	196	our @EXPORT = qw(
130	NODE $NODE *SELF node_of after	197	NODE $NODE *SELF node_of after
131	resolve_node initialise_node	198	configure
132	snd rcv mon mon_guard kil reg psub spawn	199	snd rcv mon mon_guard kil psub peval spawn cal
133	port	200	port
		201	db_set db_del db_reg
134	);	202	);
135		203
136	our $SELF;	204	our $SELF;
137		205
138	sub _self_die() {	206	sub _self_die() {
…		…
141	kil $SELF, die => $msg;	209	kil $SELF, die => $msg;
142	}	210	}
143		211
144	=item $thisnode = NODE / $NODE	212	=item $thisnode = NODE / $NODE
145		213
146	The C<NODE> function returns, and the C<$NODE> variable contains the	214	The C<NODE> function returns, and the C<$NODE> variable contains, the node
147	node id 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
148	C<initialise_node>.	216	a call to C<configure>.
149		217
150	=item $nodeid = node_of $port	218	=item $nodeid = node_of $port
151		219
152	Extracts and returns the noderef from a port ID or a node ID.	220	Extracts and returns the node ID from a port ID or a node ID.
153		221
154	=item initialise_node $profile_name	222	=item configure $profile, key => value...
155		223
		224	=item configure key => value...
		225
156	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
157	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
158	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.
159		230
160	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
161	never) before calling other AnyEvent::MP functions.	232	never) before calling other AnyEvent::MP functions.
162		233
163	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
164	either resolved or unresolved.	235	F<aemp> command line utility (sans the set/del prefix), with these additions:
165
166	The first argument will be looked up in the configuration database first
167	(if it is C<undef> then the current nodename will be used instead) to find
168	the relevant configuration profile (see L<aemp>). If none is found then
169	the default configuration is used. The configuration supplies additional
170	seed/master nodes and can override the actual noderef.
171
172	There are two types of networked nodes, public nodes and slave nodes:
173		236
174	=over 4	237	=over 4
175		238
176	=item public nodes	239	=item norc => $boolean (default false)
177		240
178	For public nodes, C<$noderef> (supplied either directly to	241	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
179	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
180	noderef (possibly unresolved, in which case it will be resolved).	243	C<configure> call.
181		244
182	After resolving, the node will bind itself on all endpoints.	245	=item force => $boolean (default false)
183		246
184	=item slave nodes	247	IF true, then the values specified in the C<configure> will take
		248	precedence over any values configured via the rc file. The default is for
		249	the rc file to override any options specified in the program.
185		250
186	When the C<$noderef> (either as given or overriden by the config file)	251	=item secure => $pass->($nodeid)
187	is the special string C<slave/>, then the node will become a slave
188	node. Slave nodes cannot be contacted from outside, and cannot talk to
189	each other (at least in this version of AnyEvent::MP).
190		252
191	Slave nodes work by creating connections to all public nodes, using the	253	In addition to specifying a boolean, you can specify a code reference that
192	L<AnyEvent::MP::Global> service.	254	is called for every remote execution attempt - the execution request is
		255	granted iff the callback returns a true value.
		256
		257	See F<semp setsecure> for more info.
193		258
194	=back	259	=back
195		260
196	After initialising itself, the node will connect to all additional
197	C<$seednodes> that are specified diretcly or via a profile. Seednodes are
198	optional and can be used to quickly bootstrap the node into an existing
199	network.
200
201	All the seednodes will also be specially marked to automatically retry
202	connecting to them indefinitely, so make sure that seednodes are really
203	reliable and up (this might also change in the future).
204
205	Example: become a public node listening on the guessed noderef, or the one
206	specified via C<aemp> for the current node. This should be the most common
207	form of invocation for "daemon"-type nodes.
208
209	initialise_node;
210
211	Example: become a slave node to any of the the seednodes specified via
212	C<aemp>. This form is often used for commandline clients.
213
214	initialise_node "slave/";
215
216	Example: become a public node, and try to contact some well-known master
217	servers to become part of the network.
218
219	initialise_node undef, "master1", "master2";
220
221	Example: become a public node listening on port C<4041>.
222
223	initialise_node 4041;
224
225	Example: become a public node, only visible on localhost port 4044.
226
227	initialise_node "localhost:4044";
228
229	=item $cv = resolve_node $noderef
230
231	Takes an unresolved node reference that may contain hostnames and
232	abbreviated IDs, resolves all of them and returns a resolved node
233	reference.
234
235	In addition to C<address:port> pairs allowed in resolved noderefs, the
236	following forms are supported:
237
238	=over 4	261	=over 4
239		262
240	=item the empty string	263	=item step 1, gathering configuration from profiles
241		264
242	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
243	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.
244		269
245	=item naked port numbers (e.g. C<1234>)	270	The profile data is then gathered as follows:
246		271
247	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
248	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).
249		277
250	=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.
251		281
252	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
253	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
254	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.
255		309
256	=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)"
257		337
258	=item $SELF	338	=item $SELF
259		339
260	Contains the current port id while executing C<rcv> callbacks or C<psub>	340	Contains the current port id while executing C<rcv> callbacks or C<psub>
261	blocks.	341	blocks.
262		342
263	=item SELF, %SELF, @SELF...	343	=item *SELF, SELF, %SELF, @SELF...
264		344
265	Due to some quirks in how perl exports variables, it is impossible to	345	Due to some quirks in how perl exports variables, it is impossible to
266	just export C<$SELF>, all the symbols called C<SELF> are exported by this	346	just export C<$SELF>, all the symbols named C<SELF> are exported by this
267	module, but only C<$SELF> is currently used.	347	module, but only C<$SELF> is currently used.
268		348
269	=item snd $port, type => @data	349	=item snd $port, type => @data
270		350
271	=item snd $port, @msg	351	=item snd $port, @msg
272		352
273	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
274	a local or a remote port, and must be a port ID.	354	local or a remote port, and must be a port ID.
275		355
276	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
277	string as first element (a port ID, or some word that indicates a request	357	use a string as first element (a port ID, or some word that indicates a
278	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.
279		360
280	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
281	function: modifying any argument is not allowed and can cause many	362	function: modifying any argument (or values referenced by them) is
282	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.
283		367
284	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
285	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
286	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
287	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
288	node, anything can be passed.	372	node, anything can be passed. Best rely only on the common denominator of
		373	these.
289		374
290	=item $local_port = port	375	=item $local_port = port
291		376
292	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
293	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.
…		…
317	sub _kilme {	402	sub _kilme {
318	die "received message on port without callback";	403	die "received message on port without callback";
319	}	404	}
320		405
321	sub port(;&) {	406	sub port(;&) {
322	my $id = "$UNIQ." . $ID++;	407	my $id = $UNIQ . ++$ID;
323	my $port = "$NODE#$id";	408	my $port = "$NODE#$id";
324		409
325	rcv $port, shift \|\| \&_kilme;	410	rcv $port, shift \|\| \&_kilme;
326		411
327	$port	412	$port
…		…
366	msg1 => sub { ... },	451	msg1 => sub { ... },
367	...	452	...
368	;	453	;
369		454
370	Example: temporarily register a rcv callback for a tag matching some port	455	Example: temporarily register a rcv callback for a tag matching some port
371	(e.g. for a rpc reply) and unregister it after a message was received.	456	(e.g. for an rpc reply) and unregister it after a message was received.
372		457
373	rcv $port, $otherport => sub {	458	rcv $port, $otherport => sub {
374	my @reply = @_;	459	my @reply = @_;
375		460
376	rcv $SELF, $otherport;	461	rcv $SELF, $otherport;
…		…
378		463
379	=cut	464	=cut
380		465
381	sub rcv($@) {	466	sub rcv($@) {
382	my $port = shift;	467	my $port = shift;
383	my ($noderef, $portid) = split /#/, $port, 2;	468	my ($nodeid, $portid) = split /#/, $port, 2;
384		469
385	$NODE{$noderef} == $NODE{""}	470	$NODE{$nodeid} == $NODE{""}
386	or Carp::croak "$port: rcv can only be called on local ports, caught";	471	or Carp::croak "$port: rcv can only be called on local ports, caught";
387		472
388	while (@_) {	473	while (@_) {
389	if (ref $_[0]) {	474	if (ref $_[0]) {
390	if (my $self = $PORT_DATA{$portid}) {	475	if (my $self = $PORT_DATA{$portid}) {
391	"AnyEvent::MP::Port" eq ref $self	476	"AnyEvent::MP::Port" eq ref $self
392	or Carp::croak "$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";
393		478
394	$self->[2] = shift;	479	$self->[0] = shift;
395	} else {	480	} else {
396	my $cb = shift;	481	my $cb = shift;
397	$PORT{$portid} = sub {	482	$PORT{$portid} = sub {
398	local $SELF = $port;	483	local $SELF = $port;
399	eval { &$cb }; _self_die if $@;	484	eval { &$cb }; _self_die if $@;
400	};	485	};
401	}	486	}
402	} elsif (defined $_[0]) {	487	} elsif (defined $_[0]) {
403	my $self = $PORT_DATA{$portid} \|\|= do {	488	my $self = $PORT_DATA{$portid} \|\|= do {
404	my $self = bless [$PORT{$port} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";	489	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
405		490
406	$PORT{$portid} = sub {	491	$PORT{$portid} = sub {
407	local $SELF = $port;	492	local $SELF = $port;
408		493
409	if (my $cb = $self->[1]{$_[0]}) {	494	if (my $cb = $self->[1]{$_[0]}) {
…		…
431	}	516	}
432		517
433	$port	518	$port
434	}	519	}
435		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
436	=item $closure = psub { BLOCK }	558	=item $closure = psub { BLOCK }
437		559
438	Remembers C<$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
439	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>
440	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 $SELF, sub {
		565	BLOCK }, @_ } >>.
441		566
442	This is useful when you register callbacks from C<rcv> callbacks:	567	This is useful when you register callbacks from C<rcv> callbacks:
443		568
444	rcv delayed_reply => sub {	569	rcv delayed_reply => sub {
445	my ($delay, @reply) = @_;	570	my ($delay, @reply) = @_;
…		…
469	$res	594	$res
470	}	595	}
471	}	596	}
472	}	597	}
473		598
474	=item $guard = mon $port, $cb->(@reason)	599	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
475		600
476	=item $guard = mon $port, $rcvport	601	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
477		602
478	=item $guard = mon $port	603	=item $guard = mon $port # kill $SELF when $port dies
479		604
480	=item $guard = mon $port, $rcvport, @msg	605	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
481		606
482	Monitor the given port and do something when the port is killed or	607	Monitor the given port and do something when the port is killed or
483	messages to it were lost, and optionally return a guard that can be used	608	messages to it were lost, and optionally return a guard that can be used
484	to stop monitoring again.	609	to stop monitoring again.
485
486	C<mon> effectively guarantees that, in the absence of hardware failures,
487	that after starting the monitor, either all messages sent to the port
488	will arrive, or the monitoring action will be invoked after possible
489	message loss has been detected. No messages will be lost "in between"
490	(after the first lost message no further messages will be received by the
491	port). After the monitoring action was invoked, further messages might get
492	delivered again.
493
494	Note that monitoring-actions are one-shot: once released, they are removed
495	and will not trigger again.
496		610
497	In the first form (callback), the callback is simply called with any	611	In the first form (callback), the callback is simply called with any
498	number of C<@reason> elements (no @reason means that the port was deleted	612	number of C<@reason> elements (no @reason means that the port was deleted
499	"normally"). Note also that I<< the callback B<must> never die >>, so use	613	"normally"). Note also that I<< the callback B<must> never die >>, so use
500	C<eval> if unsure.	614	C<eval> if unsure.
501		615
502	In the second form (another port given), the other port (C<$rcvport>)	616	In the second form (another port given), the other port (C<$rcvport>)
503	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	617	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
504	"normal" kils nothing happens, while under all other conditions, the other	618	"normal" kils nothing happens, while under all other conditions, the other
505	port is killed with the same reason.	619	port is killed with the same reason.
506		620
507	The third form (kill self) is the same as the second form, except that	621	The third form (kill self) is the same as the second form, except that
508	C<$rvport> defaults to C<$SELF>.	622	C<$rvport> defaults to C<$SELF>.
509		623
510	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
511	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.
512		629
513	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
514	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
515	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
516	even monitoring requests can get lost (for exmaple, when the connection	633	even monitoring requests can get lost (for example, when the connection
517	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
518	these problems do not exist.	635	these problems do not exist.
519		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
520	Example: call a given callback when C<$port> is killed.	654	Example: call a given callback when C<$port> is killed.
521		655
522	mon $port, sub { warn "port died because of <@_>\n" };	656	mon $port, sub { warn "port died because of <@_>\n" };
523		657
524	Example: kill ourselves when C<$port> is killed abnormally.	658	Example: kill ourselves when C<$port> is killed abnormally.
…		…
530	mon $port, $self => "restart";	664	mon $port, $self => "restart";
531		665
532	=cut	666	=cut
533		667
534	sub mon {	668	sub mon {
535	my ($noderef, $port) = split /#/, shift, 2;	669	my ($nodeid, $port) = split /#/, shift, 2;
536		670
537	my $node = $NODE{$noderef} \|\| add_node $noderef;	671	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
538		672
539	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,';
540		674
541	unless (ref $cb) {	675	unless (ref $cb) {
542	if (@_) {	676	if (@_) {
…		…
551	}	685	}
552		686
553	$node->monitor ($port, $cb);	687	$node->monitor ($port, $cb);
554		688
555	defined wantarray	689	defined wantarray
556	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	690	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
557	}	691	}
558		692
559	=item $guard = mon_guard $port, $ref, $ref...	693	=item $guard = mon_guard $port, $ref, $ref...
560		694
561	Monitors the given C<$port> and keeps the passed references. When the port	695	Monitors the given C<$port> and keeps the passed references. When the port
562	is killed, the references will be freed.	696	is killed, the references will be freed.
563		697
564	Optionally returns a guard that will stop the monitoring.	698	Optionally returns a guard that will stop the monitoring.
565		699
566	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
567	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>):
568		702
569	$port->rcv (start => sub {	703	$port->rcv (start => sub {
570	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	704	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
571	undef $timer if 0.9 < rand;	705	undef $timer if 0.9 < rand;
572	});	706	});
573	});	707	});
574		708
575	=cut	709	=cut
…		…
584		718
585	=item kil $port[, @reason]	719	=item kil $port[, @reason]
586		720
587	Kill the specified port with the given C<@reason>.	721	Kill the specified port with the given C<@reason>.
588		722
589	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" -
590	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.
591		726
592	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>
593	C<mon>, see below).	728	form) get killed with the same reason.
594		729
595	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
596	will be reported as reason C<< die => $@ >>.	731	will be reported as reason C<< die => $@ >>.
597		732
598	Transport/communication errors are reported as C<< transport_error =>	733	Transport/communication errors are reported as C<< transport_error =>
…		…
603	=item $port = spawn $node, $initfunc[, @initdata]	738	=item $port = spawn $node, $initfunc[, @initdata]
604		739
605	Creates a port on the node C<$node> (which can also be a port ID, in which	740	Creates a port on the node C<$node> (which can also be a port ID, in which
606	case it's the node where that port resides).	741	case it's the node where that port resides).
607		742
608	The port ID of the newly created port is return immediately, and it is	743	The port ID of the newly created port is returned immediately, and it is
609	permissible to immediately start sending messages or monitor the port.	744	possible to immediately start sending messages or to monitor the port.
610		745
611	After the port has been created, the init function is	746	After the port has been created, the init function is called on the remote
612	called. This function must be a fully-qualified function name	747	node, in the same context as a C<rcv> callback. This function must be a
613	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	748	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
614	program, use C<::name>.	749	specify a function in the main program, use C<::name>.
615		750
616	If the function doesn't exist, then the node tries to C<require>	751	If the function doesn't exist, then the node tries to C<require>
617	the package, then the package above the package and so on (e.g.	752	the package, then the package above the package and so on (e.g.
618	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	753	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
619	exists or it runs out of package names.	754	exists or it runs out of package names.
620		755
621	The init function is then called with the newly-created port as context	756	The init function is then called with the newly-created port as context
622	object (C<$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.
623		760
624	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
625	in the init function, monitor the original port. This two-way monitoring	762	port, and in the remote init function, immediately monitor the passed
626	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<$initfunc> has no visible effects on the
		767	caller before C<spawn> returns (by delaying invocation when spawn is
		768	called for the local node).
627		769
628	Example: spawn a chat server port on C<$othernode>.	770	Example: spawn a chat server port on C<$othernode>.
629		771
630	# this node, executed from within a port context:	772	# this node, executed from within a port context:
631	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	773	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
646		788
647	sub _spawn {	789	sub _spawn {
648	my $port = shift;	790	my $port = shift;
649	my $init = shift;	791	my $init = shift;
650		792
		793	# rcv will create the actual port
651	local $SELF = "$NODE#$port";	794	local $SELF = "$NODE#$port";
652	eval {	795	eval {
653	&{ load_func $init }	796	&{ load_func $init }
654	};	797	};
655	_self_die if $@;	798	_self_die if $@;
656	}	799	}
657		800
658	sub spawn(@) {	801	sub spawn(@) {
659	my ($noderef, undef) = split /#/, shift, 2;	802	my ($nodeid, undef) = split /#/, shift, 2;
660		803
661	my $id = "$RUNIQ." . $ID++;	804	my $id = $RUNIQ . ++$ID;
662		805
663	$_[0] =~ /::/	806	$_[0] =~ /::/
664	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";
665		808
666	snd_to_func $noderef, "AnyEvent::MP::_spawn" => $id, @_;	809	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
667		810
668	"$noderef#$id"	811	"$nodeid#$id"
669	}	812	}
		813
670		814
671	=item after $timeout, @msg	815	=item after $timeout, @msg
672		816
673	=item after $timeout, $callback	817	=item after $timeout, $callback
674		818
675	Either sends the given message, or call the given callback, after the	819	Either sends the given message, or call the given callback, after the
676	specified number of seconds.	820	specified number of seconds.
677		821
678	This is simply a utility function that come sin handy at times.	822	This is simply a utility function that comes in handy at times - the
		823	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		824	so it may go away in the future.
679		825
680	=cut	826	=cut
681		827
682	sub after($@) {	828	sub after($@) {
683	my ($timeout, @action) = @_;	829	my ($timeout, @action) = @_;
…		…
688	? $action[0]()	834	? $action[0]()
689	: snd @action;	835	: snd @action;
690	};	836	};
691	}	837	}
692		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
		891	=back
		892
		893	=head1 DISTRIBUTED DATABASE
		894
		895	AnyEvent::MP comes with a simple distributed database. The database will
		896	be mirrored asynchronously at all global nodes. Other nodes bind to one of
		897	the global nodes for their needs.
		898
		899	The database consists of a two-level hash - a hash contains a hash which
		900	contains values.
		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
		934	=over
		935
		936	=item db_set $family => $subkey [=> $value]
		937
		938	Sets (or replaces) a key to the database - if C<$value> is omitted,
		939	C<undef> is used instead.
		940
		941	=item db_del $family => $subkey
		942
		943	Deletes a key from the database.
		944
		945	=item $guard = db_reg $family => $subkey [=> $value]
		946
		947	Sets the key on the database and returns a guard. When the guard is
		948	destroyed, the key is deleted from the database. If C<$value> is missing,
		949	then C<undef> is used.
		950
		951	=cut
		952
693	=back	953	=back
694		954
695	=head1 AnyEvent::MP vs. Distributed Erlang	955	=head1 AnyEvent::MP vs. Distributed Erlang
696		956
697	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
698	== 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
699	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
700	sample:	960	sample:
701		961
702	http://www.Erlang.se/doc/programming_rules.shtml	962	http://www.erlang.se/doc/programming_rules.shtml
703	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
704	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
705	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
706		966
707	Despite the similarities, there are also some important differences:	967	Despite the similarities, there are also some important differences:
708		968
709	=over 4	969	=over 4
710		970
711	=item * Node references contain the recipe on how to contact them.	971	=item * Node IDs are arbitrary strings in AEMP.
712		972
713	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
714	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
715	convenience functionality.	975	configuration or DNS), and possibly the addresses of some seed nodes, but
716		976	will otherwise discover other nodes (and their IDs) itself.
717	This means that AEMP requires a less tightly controlled environment at the
718	cost of longer node references and a slightly higher management overhead.
719		977
720	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP	978	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
721	uses "local ports are like remote ports".	979	uses "local ports are like remote ports".
722		980
723	The failure modes for local ports are quite different (runtime errors	981	The failure modes for local ports are quite different (runtime errors
…		…
732	ports being the special case/exception, where transport errors cannot	990	ports being the special case/exception, where transport errors cannot
733	occur.	991	occur.
734		992
735	=item * Erlang uses processes and a mailbox, AEMP does not queue.	993	=item * Erlang uses processes and a mailbox, AEMP does not queue.
736		994
737	Erlang uses processes that selectively receive messages, and therefore	995	Erlang uses processes that selectively receive messages out of order, and
738	needs a queue. AEMP is event based, queuing messages would serve no	996	therefore needs a queue. AEMP is event based, queuing messages would serve
739	useful purpose. For the same reason the pattern-matching abilities of	997	no useful purpose. For the same reason the pattern-matching abilities
740	AnyEvent::MP are more limited, as there is little need to be able to	998	of AnyEvent::MP are more limited, as there is little need to be able to
741	filter messages without dequeing them.	999	filter messages without dequeuing them.
742		1000
743	(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.
744		1006
745	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1007	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
746		1008
747	Sending messages in Erlang is synchronous and blocks the process (and	1009	Sending messages in Erlang is synchronous and blocks the process until
		1010	a conenction has been established and the message sent (and so does not
748	so does not need a queue that can overflow). AEMP sends are immediate,	1011	need a queue that can overflow). AEMP sends return immediately, connection
749	connection establishment is handled in the background.	1012	establishment is handled in the background.
750		1013
751	=item * Erlang suffers from silent message loss, AEMP does not.	1014	=item * Erlang suffers from silent message loss, AEMP does not.
752		1015
753	Erlang makes few guarantees on messages delivery - messages can get lost	1016	Erlang implements few guarantees on messages delivery - messages can get
754	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,
755	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).
756		1019
757	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
758	holes in the message sequence.	1023	no silent "holes" in the message sequence.
759		1024
760	=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
761	alive.	1026	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
762		1027	simply tries to work better in common error cases, such as when a network
763	In Erlang it can happen that a monitored process is declared dead and	1028	link goes down.
764	linked processes get killed, but later it turns out that the process is
765	still alive - and can receive messages.
766
767	In AEMP, when port monitoring detects a port as dead, then that port will
768	eventually be killed - it cannot happen that a node detects a port as dead
769	and then later sends messages to it, finding it is still alive.
770		1029
771	=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.
772		1031
773	In Erlang it is quite likely that a node that restarts reuses a process ID	1032	In Erlang it is quite likely that a node that restarts reuses an Erlang
774	known to other nodes for a completely different process, causing messages	1033	process ID known to other nodes for a completely different process,
775	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.
776		1036
777	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
778	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.
779		1039
780	=item * Erlang uses unprotected connections, AEMP uses secure	1040	=item * Erlang uses unprotected connections, AEMP uses secure
781	authentication and can use TLS.	1041	authentication and can use TLS.
782		1042
783	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1043	AEMP can use a proven protocol - TLS - to protect connections and
784	securely authenticate nodes.	1044	securely authenticate nodes.
785		1045
786	=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
787	communications.	1047	communications.
788		1048
789	The AEMP protocol, unlike the Erlang protocol, supports both	1049	The AEMP protocol, unlike the Erlang protocol, supports both programming
790	language-independent text-only protocols (good for debugging) and binary,	1050	language independent text-only protocols (good for debugging), and binary,
791	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.
792		1053
793	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
794	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
795	protocol simple.	1056	protocol simple.
796		1057
797	=item * AEMP has more flexible monitoring options than Erlang.	1058	=item * AEMP has more flexible monitoring options than Erlang.
798		1059
799	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
800	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
801	difficult to implement. Monitoring in AEMP is more flexible than in	1062	difficult to implement.
802	Erlang, as one can choose between automatic kill, exit message or callback	1063
803	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.
804		1066
805	=item * Erlang tries to hide remote/local connections, AEMP does not.	1067	=item * Erlang tries to hide remote/local connections, AEMP does not.
806		1068
807	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
808	as linking is (except linking is unreliable in Erlang).	1070	same way as linking is (except linking is unreliable in Erlang).
809		1071
810	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
811	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
812	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
813	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
814	more reliable.	1076	reliable (no need for C<spawn_link>).
815		1077
816	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
817	(hard to do in Erlang).	1079	(hard to do in Erlang).
818		1080
819	=back	1081	=back
820		1082
821	=head1 RATIONALE	1083	=head1 RATIONALE
822		1084
823	=over 4	1085	=over 4
824		1086
825	=item Why strings for ports and noderefs, why not objects?	1087	=item Why strings for port and node IDs, why not objects?
826		1088
827	We considered "objects", but found that the actual number of methods	1089	We considered "objects", but found that the actual number of methods
828	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
829	the network frequently, the serialising/deserialising would add lots of	1091	the network frequently, the serialising/deserialising would add lots of
830	overhead, as well as having to keep a proxy object.	1092	overhead, as well as having to keep a proxy object everywhere.
831		1093
832	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
833	procedures to be "valid".	1095	procedures to be "valid".
834		1096
835	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
836	can't become much cheaper.	1098	code reference stored in a global hash - it can't become much cheaper.
837		1099
838	=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?
839		1101
840	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
841	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
842	default.	1104	default (although all nodes will accept it).
843		1105
844	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
845	faster for small messages and b) most importantly, after years of	1107	faster for small messages and b) most importantly, after years of
846	experience we found that object serialisation is causing more problems	1108	experience we found that object serialisation is causing more problems
847	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
848	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
849	always have to re-think your design.	1111	always have to re-think your design.
850		1112
851	Keeping your messages simple, concentrating on data structures rather than	1113	Keeping your messages simple, concentrating on data structures rather than
852	objects, will keep your messages clean, tidy and efficient.	1114	objects, will keep your messages clean, tidy and efficient.
853		1115
854	=back	1116	=back
855		1117
856	=head1 SEE ALSO	1118	=head1 SEE ALSO
857		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
858	L<AnyEvent>.	1132	L<AnyEvent>.
859		1133
860	=head1 AUTHOR	1134	=head1 AUTHOR
861		1135
862	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