[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 1.126 by root, Sat Mar 3 19:43:41 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 two 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 => $boolean (default false)
183		246
184	=item slave nodes	247	IF true, then the values specified in the C<configure> will take
185		248	precedence over any values configured via the rc file. The default is for
186	When the C<$noderef> (either as given or overriden by the config file)	249	the rc file to override any options specified in the program.
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
191	Slave nodes work by creating connections to all public nodes, using the
192	L<AnyEvent::MP::Global> service.
193		250
194	=back	251	=back
195		252
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	253	=over 4
239		254
240	=item the empty string	255	=item step 1, gathering configuration from profiles
241		256
242	An empty-string component gets resolved as if the default port (4040) was	257	The function first looks up a profile in the aemp configuration (see the
243	specified.	258	L<aemp> commandline utility). The profile name can be specified via the
		259	named C<profile> parameter or can simply be the first parameter). If it is
		260	missing, then the nodename (F<uname -n>) will be used as profile name.
244		261
245	=item naked port numbers (e.g. C<1234>)	262	The profile data is then gathered as follows:
246		263
247	These are resolved by prepending the local nodename and a colon, to be	264	First, all remaining key => value pairs (all of which are conveniently
248	further resolved.	265	undocumented at the moment) will be interpreted as configuration
		266	data. Then they will be overwritten by any values specified in the global
		267	default configuration (see the F<aemp> utility), then the chain of
		268	profiles chosen by the profile name (and any C<parent> attributes).
249		269
250	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	270	That means that the values specified in the profile have highest priority
		271	and the values specified directly via C<configure> have lowest priority,
		272	and can only be used to specify defaults.
251		273
252	These are resolved by using AnyEvent::DNS to resolve them, optionally	274	If the profile specifies a node ID, then this will become the node ID of
253	looking up SRV records for the C<aemp=4040> port, if no port was	275	this process. If not, then the profile name will be used as node ID, with
254	specified.	276	a unique randoms tring (C</%u>) appended.
		277
		278	The node ID can contain some C<%> sequences that are expanded: C<%n>
		279	is expanded to the local nodename, C<%u> is replaced by a random
		280	strign to make the node unique. For example, the F<aemp> commandline
		281	utility uses C<aemp/%n/%u> as nodename, which might expand to
		282	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		283
		284	=item step 2, bind listener sockets
		285
		286	The next step is to look up the binds in the profile, followed by binding
		287	aemp protocol listeners on all binds specified (it is possible and valid
		288	to have no binds, meaning that the node cannot be contacted form the
		289	outside. This means the node cannot talk to other nodes that also have no
		290	binds, but it can still talk to all "normal" nodes).
		291
		292	If the profile does not specify a binds list, then a default of C<*> is
		293	used, meaning the node will bind on a dynamically-assigned port on every
		294	local IP address it finds.
		295
		296	=item step 3, connect to seed nodes
		297
		298	As the last step, the seed ID list from the profile is passed to the
		299	L<AnyEvent::MP::Global> module, which will then use it to keep
		300	connectivity with at least one node at any point in time.
255		301
256	=back	302	=back
		303
		304	Example: become a distributed node using the local node name as profile.
		305	This should be the most common form of invocation for "daemon"-type nodes.
		306
		307	configure
		308
		309	Example: become a semi-anonymous node. This form is often used for
		310	commandline clients.
		311
		312	configure nodeid => "myscript/%n/%u";
		313
		314	Example: configure a node using a profile called seed, which is suitable
		315	for a seed node as it binds on all local addresses on a fixed port (4040,
		316	customary for aemp).
		317
		318	# use the aemp commandline utility
		319	# aemp profile seed binds '*:4040'
		320
		321	# then use it
		322	configure profile => "seed";
		323
		324	# or simply use aemp from the shell again:
		325	# aemp run profile seed
		326
		327	# or provide a nicer-to-remember nodeid
		328	# aemp run profile seed nodeid "$(hostname)"
257		329
258	=item $SELF	330	=item $SELF
259		331
260	Contains the current port id while executing C<rcv> callbacks or C<psub>	332	Contains the current port id while executing C<rcv> callbacks or C<psub>
261	blocks.	333	blocks.
262		334
263	=item SELF, %SELF, @SELF...	335	=item *SELF, SELF, %SELF, @SELF...
264		336
265	Due to some quirks in how perl exports variables, it is impossible to	337	Due to some quirks in how perl exports variables, it is impossible to
266	just export C<$SELF>, all the symbols called C<SELF> are exported by this	338	just export C<$SELF>, all the symbols named C<SELF> are exported by this
267	module, but only C<$SELF> is currently used.	339	module, but only C<$SELF> is currently used.
268		340
269	=item snd $port, type => @data	341	=item snd $port, type => @data
270		342
271	=item snd $port, @msg	343	=item snd $port, @msg
272		344
273	Send the given message to the given port ID, which can identify either	345	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.	346	local or a remote port, and must be a port ID.
275		347
276	While the message can be about anything, it is highly recommended to use a	348	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	349	use a string as first element (a port ID, or some word that indicates a
278	type etc.).	350	request type etc.) and to consist if only simple perl values (scalars,
		351	arrays, hashes) - if you think you need to pass an object, think again.
279		352
280	The message data effectively becomes read-only after a call to this	353	The message data logically becomes read-only after a call to this
281	function: modifying any argument is not allowed and can cause many	354	function: modifying any argument (or values referenced by them) is
282	problems.	355	forbidden, as there can be considerable time between the call to C<snd>
		356	and the time the message is actually being serialised - in fact, it might
		357	never be copied as within the same process it is simply handed to the
		358	receiving port.
283		359
284	The type of data you can transfer depends on the transport protocol: when	360	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	361	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	362	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	363	that Storable can serialise and deserialise is allowed, and for the local
288	node, anything can be passed.	364	node, anything can be passed. Best rely only on the common denominator of
		365	these.
289		366
290	=item $local_port = port	367	=item $local_port = port
291		368
292	Create a new local port object and returns its port ID. Initially it has	369	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.	370	no callbacks set and will throw an error when it receives messages.
…		…
317	sub _kilme {	394	sub _kilme {
318	die "received message on port without callback";	395	die "received message on port without callback";
319	}	396	}
320		397
321	sub port(;&) {	398	sub port(;&) {
322	my $id = "$UNIQ." . $ID++;	399	my $id = $UNIQ . ++$ID;
323	my $port = "$NODE#$id";	400	my $port = "$NODE#$id";
324		401
325	rcv $port, shift \|\| \&_kilme;	402	rcv $port, shift \|\| \&_kilme;
326		403
327	$port	404	$port
…		…
366	msg1 => sub { ... },	443	msg1 => sub { ... },
367	...	444	...
368	;	445	;
369		446
370	Example: temporarily register a rcv callback for a tag matching some port	447	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.	448	(e.g. for an rpc reply) and unregister it after a message was received.
372		449
373	rcv $port, $otherport => sub {	450	rcv $port, $otherport => sub {
374	my @reply = @_;	451	my @reply = @_;
375		452
376	rcv $SELF, $otherport;	453	rcv $SELF, $otherport;
…		…
378		455
379	=cut	456	=cut
380		457
381	sub rcv($@) {	458	sub rcv($@) {
382	my $port = shift;	459	my $port = shift;
383	my ($noderef, $portid) = split /#/, $port, 2;	460	my ($nodeid, $portid) = split /#/, $port, 2;
384		461
385	$NODE{$noderef} == $NODE{""}	462	$NODE{$nodeid} == $NODE{""}
386	or Carp::croak "$port: rcv can only be called on local ports, caught";	463	or Carp::croak "$port: rcv can only be called on local ports, caught";
387		464
388	while (@_) {	465	while (@_) {
389	if (ref $_[0]) {	466	if (ref $_[0]) {
390	if (my $self = $PORT_DATA{$portid}) {	467	if (my $self = $PORT_DATA{$portid}) {
391	"AnyEvent::MP::Port" eq ref $self	468	"AnyEvent::MP::Port" eq ref $self
392	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	469	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
393		470
394	$self->[2] = shift;	471	$self->[0] = shift;
395	} else {	472	} else {
396	my $cb = shift;	473	my $cb = shift;
397	$PORT{$portid} = sub {	474	$PORT{$portid} = sub {
398	local $SELF = $port;	475	local $SELF = $port;
399	eval { &$cb }; _self_die if $@;	476	eval { &$cb }; _self_die if $@;
400	};	477	};
401	}	478	}
402	} elsif (defined $_[0]) {	479	} elsif (defined $_[0]) {
403	my $self = $PORT_DATA{$portid} \|\|= do {	480	my $self = $PORT_DATA{$portid} \|\|= do {
404	my $self = bless [$PORT{$port} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";	481	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
405		482
406	$PORT{$portid} = sub {	483	$PORT{$portid} = sub {
407	local $SELF = $port;	484	local $SELF = $port;
408		485
409	if (my $cb = $self->[1]{$_[0]}) {	486	if (my $cb = $self->[1]{$_[0]}) {
…		…
431	}	508	}
432		509
433	$port	510	$port
434	}	511	}
435		512
		513	=item peval $port, $coderef[, @args]
		514
		515	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		516	when the code throews an exception the C<$port> will be killed.
		517
		518	Any remaining args will be passed to the callback. Any return values will
		519	be returned to the caller.
		520
		521	This is useful when you temporarily want to execute code in the context of
		522	a port.
		523
		524	Example: create a port and run some initialisation code in it's context.
		525
		526	my $port = port { ... };
		527
		528	peval $port, sub {
		529	init
		530	or die "unable to init";
		531	};
		532
		533	=cut
		534
		535	sub peval($$) {
		536	local $SELF = shift;
		537	my $cb = shift;
		538
		539	if (wantarray) {
		540	my @res = eval { &$cb };
		541	_self_die if $@;
		542	@res
		543	} else {
		544	my $res = eval { &$cb };
		545	_self_die if $@;
		546	$res
		547	}
		548	}
		549
436	=item $closure = psub { BLOCK }	550	=item $closure = psub { BLOCK }
437		551
438	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	552	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>	553	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.	554	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		555
		556	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		557	BLOCK }, @_ } >>.
441		558
442	This is useful when you register callbacks from C<rcv> callbacks:	559	This is useful when you register callbacks from C<rcv> callbacks:
443		560
444	rcv delayed_reply => sub {	561	rcv delayed_reply => sub {
445	my ($delay, @reply) = @_;	562	my ($delay, @reply) = @_;
…		…
469	$res	586	$res
470	}	587	}
471	}	588	}
472	}	589	}
473		590
474	=item $guard = mon $port, $cb->(@reason)	591	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
475		592
476	=item $guard = mon $port, $rcvport	593	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
477		594
478	=item $guard = mon $port	595	=item $guard = mon $port # kill $SELF when $port dies
479		596
480	=item $guard = mon $port, $rcvport, @msg	597	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
481		598
482	Monitor the given port and do something when the port is killed or	599	Monitor the given port and do something when the port is killed or
483	messages to it were lost, and optionally return a guard that can be used	600	messages to it were lost, and optionally return a guard that can be used
484	to stop monitoring again.	601	to stop monitoring again.
485
486	C<mon> effectively guarantees that, in the absence of hardware failures,
487	that after starting the monitor, either all messages sent to the port
488	will arrive, or the monitoring action will be invoked after possible
489	message loss has been detected. No messages will be lost "in between"
490	(after the first lost message no further messages will be received by the
491	port). After the monitoring action was invoked, further messages might get
492	delivered again.
493
494	Note that monitoring-actions are one-shot: once released, they are removed
495	and will not trigger again.
496		602
497	In the first form (callback), the callback is simply called with any	603	In the first form (callback), the callback is simply called with any
498	number of C<@reason> elements (no @reason means that the port was deleted	604	number of C<@reason> elements (no @reason means that the port was deleted
499	"normally"). Note also that I<< the callback B<must> never die >>, so use	605	"normally"). Note also that I<< the callback B<must> never die >>, so use
500	C<eval> if unsure.	606	C<eval> if unsure.
501		607
502	In the second form (another port given), the other port (C<$rcvport>)	608	In the second form (another port given), the other port (C<$rcvport>)
503	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	609	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
504	"normal" kils nothing happens, while under all other conditions, the other	610	"normal" kils nothing happens, while under all other conditions, the other
505	port is killed with the same reason.	611	port is killed with the same reason.
506		612
507	The third form (kill self) is the same as the second form, except that	613	The third form (kill self) is the same as the second form, except that
508	C<$rvport> defaults to C<$SELF>.	614	C<$rvport> defaults to C<$SELF>.
509		615
510	In the last form (message), a message of the form C<@msg, @reason> will be	616	In the last form (message), a message of the form C<@msg, @reason> will be
511	C<snd>.	617	C<snd>.
		618
		619	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		620	alert was raised), they are removed and will not trigger again.
512		621
513	As a rule of thumb, monitoring requests should always monitor a port from	622	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	623	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	624	lost, just like any other message. Another less obvious reason is that
516	even monitoring requests can get lost (for exmaple, when the connection	625	even monitoring requests can get lost (for example, when the connection
517	to the other node goes down permanently). When monitoring a port locally	626	to the other node goes down permanently). When monitoring a port locally
518	these problems do not exist.	627	these problems do not exist.
519		628
		629	C<mon> effectively guarantees that, in the absence of hardware failures,
		630	after starting the monitor, either all messages sent to the port will
		631	arrive, or the monitoring action will be invoked after possible message
		632	loss has been detected. No messages will be lost "in between" (after
		633	the first lost message no further messages will be received by the
		634	port). After the monitoring action was invoked, further messages might get
		635	delivered again.
		636
		637	Inter-host-connection timeouts and monitoring depend on the transport
		638	used. The only transport currently implemented is TCP, and AnyEvent::MP
		639	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		640	non-idle connection, and usually around two hours for idle connections).
		641
		642	This means that monitoring is good for program errors and cleaning up
		643	stuff eventually, but they are no replacement for a timeout when you need
		644	to ensure some maximum latency.
		645
520	Example: call a given callback when C<$port> is killed.	646	Example: call a given callback when C<$port> is killed.
521		647
522	mon $port, sub { warn "port died because of <@_>\n" };	648	mon $port, sub { warn "port died because of <@_>\n" };
523		649
524	Example: kill ourselves when C<$port> is killed abnormally.	650	Example: kill ourselves when C<$port> is killed abnormally.
…		…
530	mon $port, $self => "restart";	656	mon $port, $self => "restart";
531		657
532	=cut	658	=cut
533		659
534	sub mon {	660	sub mon {
535	my ($noderef, $port) = split /#/, shift, 2;	661	my ($nodeid, $port) = split /#/, shift, 2;
536		662
537	my $node = $NODE{$noderef} \|\| add_node $noderef;	663	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
538		664
539	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';	665	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
540		666
541	unless (ref $cb) {	667	unless (ref $cb) {
542	if (@_) {	668	if (@_) {
…		…
551	}	677	}
552		678
553	$node->monitor ($port, $cb);	679	$node->monitor ($port, $cb);
554		680
555	defined wantarray	681	defined wantarray
556	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	682	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
557	}	683	}
558		684
559	=item $guard = mon_guard $port, $ref, $ref...	685	=item $guard = mon_guard $port, $ref, $ref...
560		686
561	Monitors the given C<$port> and keeps the passed references. When the port	687	Monitors the given C<$port> and keeps the passed references. When the port
562	is killed, the references will be freed.	688	is killed, the references will be freed.
563		689
564	Optionally returns a guard that will stop the monitoring.	690	Optionally returns a guard that will stop the monitoring.
565		691
566	This function is useful when you create e.g. timers or other watchers and	692	This function is useful when you create e.g. timers or other watchers and
567	want to free them when the port gets killed:	693	want to free them when the port gets killed (note the use of C<psub>):
568		694
569	$port->rcv (start => sub {	695	$port->rcv (start => sub {
570	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	696	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
571	undef $timer if 0.9 < rand;	697	undef $timer if 0.9 < rand;
572	});	698	});
573	});	699	});
574		700
575	=cut	701	=cut
…		…
584		710
585	=item kil $port[, @reason]	711	=item kil $port[, @reason]
586		712
587	Kill the specified port with the given C<@reason>.	713	Kill the specified port with the given C<@reason>.
588		714
589	If no C<@reason> is specified, then the port is killed "normally" (linked	715	If no C<@reason> is specified, then the port is killed "normally" -
590	ports will not be kileld, or even notified).	716	monitor callback will be invoked, but the kil will not cause linked ports
		717	(C<mon $mport, $lport> form) to get killed.
591		718
592	Otherwise, linked ports get killed with the same reason (second form of	719	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
593	C<mon>, see below).	720	form) get killed with the same reason.
594		721
595	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	722	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
596	will be reported as reason C<< die => $@ >>.	723	will be reported as reason C<< die => $@ >>.
597		724
598	Transport/communication errors are reported as C<< transport_error =>	725	Transport/communication errors are reported as C<< transport_error =>
…		…
603	=item $port = spawn $node, $initfunc[, @initdata]	730	=item $port = spawn $node, $initfunc[, @initdata]
604		731
605	Creates a port on the node C<$node> (which can also be a port ID, in which	732	Creates a port on the node C<$node> (which can also be a port ID, in which
606	case it's the node where that port resides).	733	case it's the node where that port resides).
607		734
608	The port ID of the newly created port is return immediately, and it is	735	The port ID of the newly created port is returned immediately, and it is
609	permissible to immediately start sending messages or monitor the port.	736	possible to immediately start sending messages or to monitor the port.
610		737
611	After the port has been created, the init function is	738	After the port has been created, the init function is called on the remote
612	called. This function must be a fully-qualified function name	739	node, in the same context as a C<rcv> callback. This function must be a
613	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	740	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
614	program, use C<::name>.	741	specify a function in the main program, use C<::name>.
615		742
616	If the function doesn't exist, then the node tries to C<require>	743	If the function doesn't exist, then the node tries to C<require>
617	the package, then the package above the package and so on (e.g.	744	the package, then the package above the package and so on (e.g.
618	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	745	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
619	exists or it runs out of package names.	746	exists or it runs out of package names.
620		747
621	The init function is then called with the newly-created port as context	748	The init function is then called with the newly-created port as context
622	object (C<$SELF>) and the C<@initdata> values as arguments.	749	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		750	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		751	the port might not get created.
623		752
624	A common idiom is to pass your own port, monitor the spawned port, and	753	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	754	port, and in the remote init function, immediately monitor the passed
626	ensures that both ports get cleaned up when there is a problem.	755	local port. This two-way monitoring ensures that both ports get cleaned up
		756	when there is a problem.
		757
		758	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		759	caller before C<spawn> returns (by delaying invocation when spawn is
		760	called for the local node).
627		761
628	Example: spawn a chat server port on C<$othernode>.	762	Example: spawn a chat server port on C<$othernode>.
629		763
630	# this node, executed from within a port context:	764	# this node, executed from within a port context:
631	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	765	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
646		780
647	sub _spawn {	781	sub _spawn {
648	my $port = shift;	782	my $port = shift;
649	my $init = shift;	783	my $init = shift;
650		784
		785	# rcv will create the actual port
651	local $SELF = "$NODE#$port";	786	local $SELF = "$NODE#$port";
652	eval {	787	eval {
653	&{ load_func $init }	788	&{ load_func $init }
654	};	789	};
655	_self_die if $@;	790	_self_die if $@;
656	}	791	}
657		792
658	sub spawn(@) {	793	sub spawn(@) {
659	my ($noderef, undef) = split /#/, shift, 2;	794	my ($nodeid, undef) = split /#/, shift, 2;
660		795
661	my $id = "$RUNIQ." . $ID++;	796	my $id = $RUNIQ . ++$ID;
662		797
663	$_[0] =~ /::/	798	$_[0] =~ /::/
664	or Carp::croak "spawn init function must be a fully-qualified name, caught";	799	or Carp::croak "spawn init function must be a fully-qualified name, caught";
665		800
666	snd_to_func $noderef, "AnyEvent::MP::_spawn" => $id, @_;	801	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
667		802
668	"$noderef#$id"	803	"$nodeid#$id"
669	}	804	}
		805
670		806
671	=item after $timeout, @msg	807	=item after $timeout, @msg
672		808
673	=item after $timeout, $callback	809	=item after $timeout, $callback
674		810
675	Either sends the given message, or call the given callback, after the	811	Either sends the given message, or call the given callback, after the
676	specified number of seconds.	812	specified number of seconds.
677		813
678	This is simply a utility function that come sin handy at times.	814	This is simply a utility function that comes in handy at times - the
		815	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		816	so it may go away in the future.
679		817
680	=cut	818	=cut
681		819
682	sub after($@) {	820	sub after($@) {
683	my ($timeout, @action) = @_;	821	my ($timeout, @action) = @_;
…		…
688	? $action[0]()	826	? $action[0]()
689	: snd @action;	827	: snd @action;
690	};	828	};
691	}	829	}
692		830
		831	=item cal $port, @msg, $callback[, $timeout]
		832
		833	A simple form of RPC - sends a message to the given C<$port> with the
		834	given contents (C<@msg>), but adds a reply port to the message.
		835
		836	The reply port is created temporarily just for the purpose of receiving
		837	the reply, and will be C<kil>ed when no longer needed.
		838
		839	A reply message sent to the port is passed to the C<$callback> as-is.
		840
		841	If an optional time-out (in seconds) is given and it is not C<undef>,
		842	then the callback will be called without any arguments after the time-out
		843	elapsed and the port is C<kil>ed.
		844
		845	If no time-out is given (or it is C<undef>), then the local port will
		846	monitor the remote port instead, so it eventually gets cleaned-up.
		847
		848	Currently this function returns the temporary port, but this "feature"
		849	might go in future versions unless you can make a convincing case that
		850	this is indeed useful for something.
		851
		852	=cut
		853
		854	sub cal(@) {
		855	my $timeout = ref $_[-1] ? undef : pop;
		856	my $cb = pop;
		857
		858	my $port = port {
		859	undef $timeout;
		860	kil $SELF;
		861	&$cb;
		862	};
		863
		864	if (defined $timeout) {
		865	$timeout = AE::timer $timeout, 0, sub {
		866	undef $timeout;
		867	kil $port;
		868	$cb->();
		869	};
		870	} else {
		871	mon $_[0], sub {
		872	kil $port;
		873	$cb->();
		874	};
		875	}
		876
		877	push @_, $port;
		878	&snd;
		879
		880	$port
		881	}
		882
		883	=back
		884
		885	=head1 DISTRIBUTED DATABASE
		886
		887	AnyEvent::MP comes with a simple distributed database. The database will
		888	be mirrored asynchronously at all global nodes. Other nodes bind to one of
		889	the global nodes for their needs.
		890
		891	The database consists of a two-level hash - a hash contains a hash which
		892	contains values.
		893
		894	The top level hash key is called "family", and the second-level hash key
		895	is called "subkey" or simply "key".
		896
		897	The family must be alphanumeric, i.e. start with a letter and consist
		898	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		899	pretty much like Perl module names.
		900
		901	As the family namespace is global, it is recommended to prefix family names
		902	with the name of the application or module using it.
		903
		904	The subkeys must be non-empty strings, with no further restrictions.
		905
		906	The values should preferably be strings, but other perl scalars should
		907	work as well (such as undef, arrays and hashes).
		908
		909	Every database entry is owned by one node - adding the same family/subkey
		910	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		911	but the result might be nondeterministic, i.e. the key might have
		912	different values on different nodes.
		913
		914	Different subkeys in the same family can be owned by different nodes
		915	without problems, and in fact, this is the common method to create worker
		916	pools. For example, a worker port for image scaling might do this:
		917
		918	db_set my_image_scalers => $port;
		919
		920	And clients looking for an image scaler will want to get the
		921	C<my_image_scalers> keys:
		922
		923	db_keys "my_image_scalers" => 60 => sub {
		924	#d##TODO#
		925
		926	=over
		927
		928	=item db_set $family => $subkey [=> $value]
		929
		930	Sets (or replaces) a key to the database - if C<$value> is omitted,
		931	C<undef> is used instead.
		932
		933	=item db_del $family => $subkey
		934
		935	Deletes a key from the database.
		936
		937	=item $guard = db_reg $family => $subkey [=> $value]
		938
		939	Sets the key on the database and returns a guard. When the guard is
		940	destroyed, the key is deleted from the database. If C<$value> is missing,
		941	then C<undef> is used.
		942
		943	=cut
		944
693	=back	945	=back
694		946
695	=head1 AnyEvent::MP vs. Distributed Erlang	947	=head1 AnyEvent::MP vs. Distributed Erlang
696		948
697	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	949	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	950	== 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	951	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
700	sample:	952	sample:
701		953
702	http://www.Erlang.se/doc/programming_rules.shtml	954	http://www.erlang.se/doc/programming_rules.shtml
703	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	955	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	956	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	957	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
706		958
707	Despite the similarities, there are also some important differences:	959	Despite the similarities, there are also some important differences:
708		960
709	=over 4	961	=over 4
710		962
711	=item * Node references contain the recipe on how to contact them.	963	=item * Node IDs are arbitrary strings in AEMP.
712		964
713	Erlang relies on special naming and DNS to work everywhere in the	965	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	966	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
715	convenience functionality.	967	configuration or DNS), and possibly the addresses of some seed nodes, but
716		968	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		969
720	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP	970	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
721	uses "local ports are like remote ports".	971	uses "local ports are like remote ports".
722		972
723	The failure modes for local ports are quite different (runtime errors	973	The failure modes for local ports are quite different (runtime errors
…		…
732	ports being the special case/exception, where transport errors cannot	982	ports being the special case/exception, where transport errors cannot
733	occur.	983	occur.
734		984
735	=item * Erlang uses processes and a mailbox, AEMP does not queue.	985	=item * Erlang uses processes and a mailbox, AEMP does not queue.
736		986
737	Erlang uses processes that selectively receive messages, and therefore	987	Erlang uses processes that selectively receive messages out of order, and
738	needs a queue. AEMP is event based, queuing messages would serve no	988	therefore needs a queue. AEMP is event based, queuing messages would serve
739	useful purpose. For the same reason the pattern-matching abilities of	989	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	990	of AnyEvent::MP are more limited, as there is little need to be able to
741	filter messages without dequeing them.	991	filter messages without dequeuing them.
742		992
743	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	993	This is not a philosophical difference, but simply stems from AnyEvent::MP
		994	being event-based, while Erlang is process-based.
		995
		996	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		997	top of AEMP and Coro threads.
744		998
745	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	999	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
746		1000
747	Sending messages in Erlang is synchronous and blocks the process (and	1001	Sending messages in Erlang is synchronous and blocks the process until
		1002	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,	1003	need a queue that can overflow). AEMP sends return immediately, connection
749	connection establishment is handled in the background.	1004	establishment is handled in the background.
750		1005
751	=item * Erlang suffers from silent message loss, AEMP does not.	1006	=item * Erlang suffers from silent message loss, AEMP does not.
752		1007
753	Erlang makes few guarantees on messages delivery - messages can get lost	1008	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,	1009	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).	1010	b, and c, and the other side only receives messages a and c).
756		1011
757	AEMP guarantees correct ordering, and the guarantee that there are no	1012	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1013	guarantee that after one message is lost, all following ones sent to the
		1014	same port are lost as well, until monitoring raises an error, so there are
758	holes in the message sequence.	1015	no silent "holes" in the message sequence.
759		1016
760	=item * In Erlang, processes can be declared dead and later be found to be	1017	If you want your software to be very reliable, you have to cope with
761	alive.	1018	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
762		1019	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	1020	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		1021
771	=item * Erlang can send messages to the wrong port, AEMP does not.	1022	=item * Erlang can send messages to the wrong port, AEMP does not.
772		1023
773	In Erlang it is quite likely that a node that restarts reuses a process ID	1024	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	1025	process ID known to other nodes for a completely different process,
775	destined for that process to end up in an unrelated process.	1026	causing messages destined for that process to end up in an unrelated
		1027	process.
776		1028
777	AEMP never reuses port IDs, so old messages or old port IDs floating	1029	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.	1030	around in the network will not be sent to an unrelated port.
779		1031
780	=item * Erlang uses unprotected connections, AEMP uses secure	1032	=item * Erlang uses unprotected connections, AEMP uses secure
781	authentication and can use TLS.	1033	authentication and can use TLS.
782		1034
783	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1035	AEMP can use a proven protocol - TLS - to protect connections and
784	securely authenticate nodes.	1036	securely authenticate nodes.
785		1037
786	=item * The AEMP protocol is optimised for both text-based and binary	1038	=item * The AEMP protocol is optimised for both text-based and binary
787	communications.	1039	communications.
788		1040
789	The AEMP protocol, unlike the Erlang protocol, supports both	1041	The AEMP protocol, unlike the Erlang protocol, supports both programming
790	language-independent text-only protocols (good for debugging) and binary,	1042	language independent text-only protocols (good for debugging), and binary,
791	language-specific serialisers (e.g. Storable).	1043	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1044	used, the protocol is actually completely text-based.
792		1045
793	It has also been carefully designed to be implementable in other languages	1046	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	1047	with a minimum of work while gracefully degrading functionality to make the
795	protocol simple.	1048	protocol simple.
796		1049
797	=item * AEMP has more flexible monitoring options than Erlang.	1050	=item * AEMP has more flexible monitoring options than Erlang.
798		1051
799	In Erlang, you can chose to receive I<all> exit signals as messages	1052	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	1053	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	1054	difficult to implement.
802	Erlang, as one can choose between automatic kill, exit message or callback	1055
803	on a per-process basis.	1056	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1057	between automatic kill, exit message or callback on a per-port basis.
804		1058
805	=item * Erlang tries to hide remote/local connections, AEMP does not.	1059	=item * Erlang tries to hide remote/local connections, AEMP does not.
806		1060
807	Monitoring in Erlang is not an indicator of process death/crashes,	1061	Monitoring in Erlang is not an indicator of process death/crashes, in the
808	as linking is (except linking is unreliable in Erlang).	1062	same way as linking is (except linking is unreliable in Erlang).
809		1063
810	In AEMP, you don't "look up" registered port names or send to named ports	1064	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	1065	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	1066	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	1067	remote port. Since both monitors are local to the node, they are much more
814	more reliable.	1068	reliable (no need for C<spawn_link>).
815		1069
816	This also saves round-trips and avoids sending messages to the wrong port	1070	This also saves round-trips and avoids sending messages to the wrong port
817	(hard to do in Erlang).	1071	(hard to do in Erlang).
818		1072
819	=back	1073	=back
820		1074
821	=head1 RATIONALE	1075	=head1 RATIONALE
822		1076
823	=over 4	1077	=over 4
824		1078
825	=item Why strings for ports and noderefs, why not objects?	1079	=item Why strings for port and node IDs, why not objects?
826		1080
827	We considered "objects", but found that the actual number of methods	1081	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	1082	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	1083	the network frequently, the serialising/deserialising would add lots of
830	overhead, as well as having to keep a proxy object.	1084	overhead, as well as having to keep a proxy object everywhere.
831		1085
832	Strings can easily be printed, easily serialised etc. and need no special	1086	Strings can easily be printed, easily serialised etc. and need no special
833	procedures to be "valid".	1087	procedures to be "valid".
834		1088
835	And a a miniport consists of a single closure stored in a global hash - it	1089	And as a result, a port with just a default receiver consists of a single
836	can't become much cheaper.	1090	code reference stored in a global hash - it can't become much cheaper.
837		1091
838	=item Why favour JSON, why not real serialising format such as Storable?	1092	=item Why favour JSON, why not a real serialising format such as Storable?
839		1093
840	In fact, any AnyEvent::MP node will happily accept Storable as framing	1094	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	1095	format, but currently there is no way to make a node use Storable by
842	default.	1096	default (although all nodes will accept it).
843		1097
844	The default framing protocol is JSON because a) JSON::XS is many times	1098	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	1099	faster for small messages and b) most importantly, after years of
846	experience we found that object serialisation is causing more problems	1100	experience we found that object serialisation is causing more problems
847	than it gains: Just like function calls, objects simply do not travel	1101	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	1102	easily over the network, mostly because they will always be a copy, so you
849	always have to re-think your design.	1103	always have to re-think your design.
850		1104
851	Keeping your messages simple, concentrating on data structures rather than	1105	Keeping your messages simple, concentrating on data structures rather than
852	objects, will keep your messages clean, tidy and efficient.	1106	objects, will keep your messages clean, tidy and efficient.
853		1107
854	=back	1108	=back
855		1109
856	=head1 SEE ALSO	1110	=head1 SEE ALSO
857		1111
		1112	L<AnyEvent::MP::Intro> - a gentle introduction.
		1113
		1114	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1115
		1116	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1117	your applications.
		1118
		1119	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1120
		1121	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1122	all nodes.
		1123
858	L<AnyEvent>.	1124	L<AnyEvent>.
859		1125
860	=head1 AUTHOR	1126	=head1 AUTHOR
861		1127
862	Marc Lehmann <schmorp@schmorp.de>	1128	Marc Lehmann <schmorp@schmorp.de>

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Revision 1.63 by root, Thu Aug 27 21:29:37 2009 UTC vs.
Revision 1.126 by root, Sat Mar 3 19:43:41 2012 UTC