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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.56 by root, Sat Aug 15 04:12:38 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; # -OR-	15	configure;
17	initialise_node "localhost:4040"; # -OR-
18	initialise_node "slave/", "localhost:4040"
19		16
20	# ports are message endpoints	17	# ports are message destinations
21		18
22	# sending messages	19	# sending messages
23	snd $port, type => data...;	20	snd $port, type => data...;
24	snd $port, @msg;	21	snd $port, @msg;
25	snd @msg_with_first_element_being_a_port;	22	snd @msg_with_first_element_being_a_port;
26		23
27	# creating/using ports, the simple way	24	# creating/using ports, the simple way
28	my $simple_port = port { my @msg = @_; 0 };	25	my $simple_port = port { my @msg = @_ };
29		26
30	# creating/using ports, tagged message matching	27	# creating/using ports, tagged message matching
31	my $port = port;	28	my $port = port;
32	rcv $port, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
33	rcv $port, pong => sub { warn "pong received\n"; 0 };	30	rcv $port, pong => sub { warn "pong received\n" };
34		31
35	# create a port on another node	32	# create a port on another node
36	my $port = spawn $node, $initfunc, @initdata;	33	my $port = spawn $node, $initfunc, @initdata;
37		34
		35	# destroy a port again
		36	kil $port; # "normal" kill
		37	kil $port, my_error => "everything is broken"; # error kill
		38
38	# monitoring	39	# monitoring
39	mon $port, $cb->(@msg) # callback is invoked on death	40	mon $localport, $cb->(@msg) # callback is invoked on death
40	mon $port, $otherport # kill otherport on abnormal death	41	mon $localport, $otherport # kill otherport on abnormal death
41	mon $port, $otherport, @msg # send message on death	42	mon $localport, $otherport, @msg # send message on death
		43
		44	# temporarily execute code in port context
		45	peval $port, sub { die "kill the port!" };
		46
		47	# execute callbacks in $SELF port context
		48	my $timer = AE::timer 1, 0, psub {
		49	die "kill the port, delayed";
		50	};
42		51
43	=head1 CURRENT STATUS	52	=head1 CURRENT STATUS
44		53
		54	bin/aemp - stable.
45	AnyEvent::MP - stable API, should work	55	AnyEvent::MP - stable API, should work.
46	AnyEvent::MP::Intro - outdated	56	AnyEvent::MP::Intro - explains most concepts.
47	AnyEvent::MP::Kernel - WIP
48	AnyEvent::MP::Transport - mostly stable	57	AnyEvent::MP::Kernel - mostly stable API.
49		58	AnyEvent::MP::Global - stable API.
50	stay tuned.
51		59
52	=head1 DESCRIPTION	60	=head1 DESCRIPTION
53		61
54	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
55		63
56	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
57	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
58		66
59	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	67	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
60	manual page.	68	manual page and the examples under F<eg/>.
61
62	At the moment, this module family is severly broken and underdocumented,
63	so do not use. This was uploaded mainly to reserve the CPAN namespace -
64	stay tuned!
65		69
66	=head1 CONCEPTS	70	=head1 CONCEPTS
67		71
68	=over 4	72	=over 4
69		73
70	=item port	74	=item port
71		75
72	A port is something you can send messages to (with the C<snd> function).	76	Not to be confused with a TCP port, a "port" is something you can send
		77	messages to (with the C<snd> function).
73		78
74	Ports allow you to register C<rcv> handlers that can match all or just	79	Ports allow you to register C<rcv> handlers that can match all or just
75	some messages. Messages will not be queued.	80	some messages. Messages send to ports will not be queued, regardless of
		81	anything was listening for them or not.
76		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
77	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
78		86
79	A port ID is the concatenation of a noderef, a hash-mark (C<#>) as	87	A port ID is the concatenation of a node ID, a hash-mark (C<#>)
80	separator, and a port name (a printable string of unspecified format). An	88	as separator, and a port name (a printable string of unspecified
81	exception is the the node port, whose ID is identical to its node	89	format created by AnyEvent::MP).
82	reference.
83		90
84	=item node	91	=item node
85		92
86	A node is a single process containing at least one port - the node port,	93	A node is a single process containing at least one port - the node port,
87	which provides nodes to manage each other remotely, and to create new	94	which enables nodes to manage each other remotely, and to create new
88	ports.	95	ports.
89		96
90	Nodes are either private (single-process only), slaves (connected to a	97	Nodes are either public (have one or more listening ports) or private
91	master node only) or public nodes (connectable from unrelated nodes).	98	(no listening ports). Private nodes cannot talk to other private nodes
		99	currently, but all nodes can talk to public nodes.
92		100
93	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	101	Nodes is represented by (printable) strings called "node IDs".
94		102
95	A node reference is a string that either simply identifies the node (for	103	=item node ID - C<[A-Za-z0-9_\-.:]*>
96	private and slave nodes), or contains a recipe on how to reach a given
97	node (for public nodes).
98		104
99	This recipe is simply a comma-separated list of C<address:port> pairs (for	105	A node ID is a string that uniquely identifies the node within a
100	TCP/IP, other protocols might look different).	106	network. Depending on the configuration used, node IDs can look like a
		107	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		108	doesn't interpret node IDs in any way except to uniquely identify a node.
101		109
102	Node references come in two flavours: resolved (containing only numerical	110	=item binds - C<ip:port>
103	addresses) or unresolved (where hostnames are used instead of addresses).
104		111
105	Before using an unresolved node reference in a message you first have to	112	Nodes can only talk to each other by creating some kind of connection to
106	resolve it.	113	each other. To do this, nodes should listen on one or more local transport
		114	endpoints - binds.
		115
		116	Currently, only standard C<ip:port> specifications can be used, which
		117	specify TCP ports to listen on. So a bind is basically just a tcp socket
		118	in listening mode thta accepts conenctions form other nodes.
		119
		120	=item seed nodes
		121
		122	When a node starts, it knows nothing about the network it is in - it
		123	needs to connect to at least one other node that is already in the
		124	network. These other nodes are called "seed nodes".
		125
		126	Seed nodes themselves are not special - they are seed nodes only because
		127	some other node I<uses> them as such, but any node can be used as seed
		128	node for other nodes, and eahc node cna use a different set of seed nodes.
		129
		130	In addition to discovering the network, seed nodes are also used to
		131	maintain the network - all nodes using the same seed node form are part of
		132	the same network. If a network is split into multiple subnets because e.g.
		133	the network link between the parts goes down, then using the same seed
		134	nodes for all nodes ensures that eventually the subnets get merged again.
		135
		136	Seed nodes are expected to be long-running, and at least one seed node
		137	should always be available. They should also be relatively responsive - a
		138	seed node that blocks for long periods will slow down everybody else.
		139
		140	For small networks, it's best if every node uses the same set of seed
		141	nodes. For large networks, it can be useful to specify "regional" seed
		142	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		143	each other. What's important is that all seed nodes connections form a
		144	complete graph, so that the network cannot split into separate subnets
		145	forever.
		146
		147	Seed nodes are represented by seed IDs.
		148
		149	=item seed IDs - C<host:port>
		150
		151	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
		152	TCP port) of nodes that should be used as seed nodes.
		153
		154	=item global nodes
		155
		156	An AEMP network needs a discovery service - nodes need to know how to
		157	connect to other nodes they only know by name. In addition, AEMP offers a
		158	distributed "group database", which maps group names to a list of strings
		159	- for example, to register worker ports.
		160
		161	A network needs at least one global node to work, and allows every node to
		162	be a global node.
		163
		164	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		165	node and tries to keep connections to all other nodes. So while it can
		166	make sense to make every node "global" in small networks, it usually makes
		167	sense to only make seed nodes into global nodes in large networks (nodes
		168	keep connections to seed nodes and global nodes, so makign them the same
		169	reduces overhead).
107		170
108	=back	171	=back
109		172
110	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
111		174
113		176
114	=cut	177	=cut
115		178
116	package AnyEvent::MP;	179	package AnyEvent::MP;
117		180
		181	use AnyEvent::MP::Config ();
118	use AnyEvent::MP::Kernel;	182	use AnyEvent::MP::Kernel;
		183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
119		184
120	use common::sense;	185	use common::sense;
121		186
122	use Carp ();	187	use Carp ();
123		188
124	use AE ();	189	use AE ();
		190	use Guard ();
125		191
126	use base "Exporter";	192	use base "Exporter";
127		193
128	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
129		195
130	our @EXPORT = qw(	196	our @EXPORT = qw(
131	NODE $NODE *SELF node_of _any_	197	NODE $NODE *SELF node_of after
132	resolve_node initialise_node	198	configure
133	snd rcv mon kil reg psub spawn	199	snd rcv mon mon_guard kil psub peval spawn cal
134	port	200	port
		201	db_set db_del db_reg
135	);	202	);
136		203
137	our $SELF;	204	our $SELF;
138		205
139	sub _self_die() {	206	sub _self_die() {
…		…
142	kil $SELF, die => $msg;	209	kil $SELF, die => $msg;
143	}	210	}
144		211
145	=item $thisnode = NODE / $NODE	212	=item $thisnode = NODE / $NODE
146		213
147	The C<NODE> function returns, and the C<$NODE> variable contains the	214	The C<NODE> function returns, and the C<$NODE> variable contains, the node
148	noderef of the local node. The value is initialised by a call to	215	ID of the node running in the current process. This value is initialised by
149	C<initialise_node>.	216	a call to C<configure>.
150		217
151	=item $noderef = node_of $port	218	=item $nodeid = node_of $port
152		219
153	Extracts and returns the noderef from a port ID or a noderef.	220	Extracts and returns the node ID from a port ID or a node ID.
154		221
155	=item initialise_node $noderef, $seednode, $seednode...	222	=item configure $profile, key => value...
156		223
157	=item initialise_node "slave/", $master, $master...	224	=item configure key => value...
158		225
159	Before a node can talk to other nodes on the network it has to initialise	226	Before a node can talk to other nodes on the network (i.e. enter
160	itself - the minimum a node needs to know is it's own name, and optionally	227	"distributed mode") it has to configure itself - the minimum a node needs
161	it should know the noderefs of some other nodes in the network.	228	to know is its own name, and optionally it should know the addresses of
		229	some other nodes in the network to discover other nodes.
162		230
163	This function initialises a node - it must be called exactly once (or	231	This function configures a node - it must be called exactly once (or
164	never) before calling other AnyEvent::MP functions.	232	never) before calling other AnyEvent::MP functions.
165		233
166	All arguments (optionally except for the first) are noderefs, which can be	234	The key/value pairs are basically the same ones as documented for the
167	either resolved or unresolved.	235	F<aemp> command line utility (sans the set/del prefix), with two additions:
168
169	The first argument will be looked up in the configuration database first
170	(if it is C<undef> then the current nodename will be used instead) to find
171	the relevant configuration profile (see L<aemp>). If none is found then
172	the default configuration is used. The configuration supplies additional
173	seed/master nodes and can override the actual noderef.
174
175	There are two types of networked nodes, public nodes and slave nodes:
176		236
177	=over 4	237	=over 4
178		238
179	=item public nodes	239	=item norc => $boolean (default false)
180		240
181	For public nodes, C<$noderef> (supplied either directly to	241	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
182	C<initialise_node> or indirectly via a profile or the nodename) must be a	242	be consulted - all configuraiton options must be specified in the
183	noderef (possibly unresolved, in which case it will be resolved).	243	C<configure> call.
184		244
185	After resolving, the node will bind itself on all endpoints and try to	245	=item force => $boolean (default false)
186	connect to all additional C<$seednodes> that are specified. Seednodes are
187	optional and can be used to quickly bootstrap the node into an existing
188	network.
189		246
190	=item slave nodes	247	IF true, then the values specified in the C<configure> will take
191		248	precedence over any values configured via the rc file. The default is for
192	When the C<$noderef> (either as given or overriden by the config file)	249	the rc file to override any options specified in the program.
193	is the special string C<slave/>, then the node will become a slave
194	node. Slave nodes cannot be contacted from outside and will route most of
195	their traffic to the master node that they attach to.
196
197	At least one additional noderef is required (either by specifying it
198	directly or because it is part of the configuration profile): The node
199	will try to connect to all of them and will become a slave attached to the
200	first node it can successfully connect to.
201
202	Note that slave nodes cannot change their name, and consequently, their
203	master, so if the master goes down, the slave node will not function well
204	anymore until it can re-establish conenciton to its master. This makes
205	slave nodes unsuitable for long-term nodes or fault-tolerant networks.
206		250
207	=back	251	=back
208		252
209	This function will block until all nodes have been resolved and, for slave
210	nodes, until it has successfully established a connection to a master
211	server.
212
213	All the seednodes will also be specially marked to automatically retry
214	connecting to them infinitely.
215
216	Example: become a public node listening on the guessed noderef, or the one
217	specified via C<aemp> for the current node. This should be the most common
218	form of invocation for "daemon"-type nodes.
219
220	initialise_node;
221
222	Example: become a slave node to any of the the seednodes specified via
223	C<aemp>. This form is often used for commandline clients.
224
225	initialise_node "slave/";
226
227	Example: become a slave node to any of the specified master servers. This
228	form is also often used for commandline clients.
229
230	initialise_node "slave/", "master1", "192.168.13.17", "mp.example.net";
231
232	Example: become a public node, and try to contact some well-known master
233	servers to become part of the network.
234
235	initialise_node undef, "master1", "master2";
236
237	Example: become a public node listening on port C<4041>.
238
239	initialise_node 4041;
240
241	Example: become a public node, only visible on localhost port 4044.
242
243	initialise_node "localhost:4044";
244
245	=item $cv = resolve_node $noderef
246
247	Takes an unresolved node reference that may contain hostnames and
248	abbreviated IDs, resolves all of them and returns a resolved node
249	reference.
250
251	In addition to C<address:port> pairs allowed in resolved noderefs, the
252	following forms are supported:
253
254	=over 4	253	=over 4
255		254
256	=item the empty string	255	=item step 1, gathering configuration from profiles
257		256
258	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
259	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.
260		261
261	=item naked port numbers (e.g. C<1234>)	262	The profile data is then gathered as follows:
262		263
263	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
264	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).
265		269
266	=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.
267		273
268	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
269	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
270	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.
271		301
272	=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)"
273		329
274	=item $SELF	330	=item $SELF
275		331
276	Contains the current port id while executing C<rcv> callbacks or C<psub>	332	Contains the current port id while executing C<rcv> callbacks or C<psub>
277	blocks.	333	blocks.
278		334
279	=item SELF, %SELF, @SELF...	335	=item *SELF, SELF, %SELF, @SELF...
280		336
281	Due to some quirks in how perl exports variables, it is impossible to	337	Due to some quirks in how perl exports variables, it is impossible to
282	just export C<$SELF>, all the symbols called C<SELF> are exported by this	338	just export C<$SELF>, all the symbols named C<SELF> are exported by this
283	module, but only C<$SELF> is currently used.	339	module, but only C<$SELF> is currently used.
284		340
285	=item snd $port, type => @data	341	=item snd $port, type => @data
286		342
287	=item snd $port, @msg	343	=item snd $port, @msg
288		344
289	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
290	a local or a remote port, and must be a port ID.	346	local or a remote port, and must be a port ID.
291		347
292	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
293	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
294	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.
295		352
296	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
297	function: modifying any argument is not allowed and can cause many	354	function: modifying any argument (or values referenced by them) is
298	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.
299		359
300	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
301	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
302	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
303	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
304	node, anything can be passed.	364	node, anything can be passed. Best rely only on the common denominator of
		365	these.
305		366
306	=item $local_port = port	367	=item $local_port = port
307		368
308	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
309	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.
…		…
333	sub _kilme {	394	sub _kilme {
334	die "received message on port without callback";	395	die "received message on port without callback";
335	}	396	}
336		397
337	sub port(;&) {	398	sub port(;&) {
338	my $id = "$UNIQ." . $ID++;	399	my $id = $UNIQ . ++$ID;
339	my $port = "$NODE#$id";	400	my $port = "$NODE#$id";
340		401
341	rcv $port, shift \|\| \&_kilme;	402	rcv $port, shift \|\| \&_kilme;
342		403
343	$port	404	$port
…		…
382	msg1 => sub { ... },	443	msg1 => sub { ... },
383	...	444	...
384	;	445	;
385		446
386	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
387	(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.
388		449
389	rcv $port, $otherport => sub {	450	rcv $port, $otherport => sub {
390	my @reply = @_;	451	my @reply = @_;
391		452
392	rcv $SELF, $otherport;	453	rcv $SELF, $otherport;
…		…
394		455
395	=cut	456	=cut
396		457
397	sub rcv($@) {	458	sub rcv($@) {
398	my $port = shift;	459	my $port = shift;
399	my ($noderef, $portid) = split /#/, $port, 2;	460	my ($nodeid, $portid) = split /#/, $port, 2;
400		461
401	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	462	$NODE{$nodeid} == $NODE{""}
402	or Carp::croak "$port: rcv can only be called on local ports, caught";	463	or Carp::croak "$port: rcv can only be called on local ports, caught";
403		464
404	while (@_) {	465	while (@_) {
405	if (ref $_[0]) {	466	if (ref $_[0]) {
406	if (my $self = $PORT_DATA{$portid}) {	467	if (my $self = $PORT_DATA{$portid}) {
407	"AnyEvent::MP::Port" eq ref $self	468	"AnyEvent::MP::Port" eq ref $self
408	or Carp::croak "$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";
409		470
410	$self->[2] = shift;	471	$self->[0] = shift;
411	} else {	472	} else {
412	my $cb = shift;	473	my $cb = shift;
413	$PORT{$portid} = sub {	474	$PORT{$portid} = sub {
414	local $SELF = $port;	475	local $SELF = $port;
415	eval { &$cb }; _self_die if $@;	476	eval { &$cb }; _self_die if $@;
416	};	477	};
417	}	478	}
418	} elsif (defined $_[0]) {	479	} elsif (defined $_[0]) {
419	my $self = $PORT_DATA{$portid} \|\|= do {	480	my $self = $PORT_DATA{$portid} \|\|= do {
420	my $self = bless [$PORT{$port} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";	481	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
421		482
422	$PORT{$portid} = sub {	483	$PORT{$portid} = sub {
423	local $SELF = $port;	484	local $SELF = $port;
424		485
425	if (my $cb = $self->[1]{$_[0]}) {	486	if (my $cb = $self->[1]{$_[0]}) {
…		…
447	}	508	}
448		509
449	$port	510	$port
450	}	511	}
451		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
452	=item $closure = psub { BLOCK }	550	=item $closure = psub { BLOCK }
453		551
454	Remembers C<$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
455	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>
456	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 $SELF, sub {
		557	BLOCK }, @_ } >>.
457		558
458	This is useful when you register callbacks from C<rcv> callbacks:	559	This is useful when you register callbacks from C<rcv> callbacks:
459		560
460	rcv delayed_reply => sub {	561	rcv delayed_reply => sub {
461	my ($delay, @reply) = @_;	562	my ($delay, @reply) = @_;
…		…
485	$res	586	$res
486	}	587	}
487	}	588	}
488	}	589	}
489		590
490	=item $guard = mon $port, $cb->(@reason)	591	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
491		592
492	=item $guard = mon $port, $rcvport	593	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
493		594
494	=item $guard = mon $port	595	=item $guard = mon $port # kill $SELF when $port dies
495		596
496	=item $guard = mon $port, $rcvport, @msg	597	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
497		598
498	Monitor the given port and do something when the port is killed or	599	Monitor the given port and do something when the port is killed or
499	messages to it were lost, and optionally return a guard that can be used	600	messages to it were lost, and optionally return a guard that can be used
500	to stop monitoring again.	601	to stop monitoring again.
501
502	C<mon> effectively guarantees that, in the absence of hardware failures,
503	that after starting the monitor, either all messages sent to the port
504	will arrive, or the monitoring action will be invoked after possible
505	message loss has been detected. No messages will be lost "in between"
506	(after the first lost message no further messages will be received by the
507	port). After the monitoring action was invoked, further messages might get
508	delivered again.
509		602
510	In the first form (callback), the callback is simply called with any	603	In the first form (callback), the callback is simply called with any
511	number of C<@reason> elements (no @reason means that the port was deleted	604	number of C<@reason> elements (no @reason means that the port was deleted
512	"normally"). Note also that I<< the callback B<must> never die >>, so use	605	"normally"). Note also that I<< the callback B<must> never die >>, so use
513	C<eval> if unsure.	606	C<eval> if unsure.
514		607
515	In the second form (another port given), the other port (C<$rcvport>)	608	In the second form (another port given), the other port (C<$rcvport>)
516	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	609	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
517	"normal" kils nothing happens, while under all other conditions, the other	610	"normal" kils nothing happens, while under all other conditions, the other
518	port is killed with the same reason.	611	port is killed with the same reason.
519		612
520	The third form (kill self) is the same as the second form, except that	613	The third form (kill self) is the same as the second form, except that
521	C<$rvport> defaults to C<$SELF>.	614	C<$rvport> defaults to C<$SELF>.
522		615
523	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
524	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.
525		621
526	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
527	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
528	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
529	even monitoring requests can get lost (for exmaple, when the connection	625	even monitoring requests can get lost (for example, when the connection
530	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
531	these problems do not exist.	627	these problems do not exist.
532		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
533	Example: call a given callback when C<$port> is killed.	646	Example: call a given callback when C<$port> is killed.
534		647
535	mon $port, sub { warn "port died because of <@_>\n" };	648	mon $port, sub { warn "port died because of <@_>\n" };
536		649
537	Example: kill ourselves when C<$port> is killed abnormally.	650	Example: kill ourselves when C<$port> is killed abnormally.
…		…
543	mon $port, $self => "restart";	656	mon $port, $self => "restart";
544		657
545	=cut	658	=cut
546		659
547	sub mon {	660	sub mon {
548	my ($noderef, $port) = split /#/, shift, 2;	661	my ($nodeid, $port) = split /#/, shift, 2;
549		662
550	my $node = $NODE{$noderef} \|\| add_node $noderef;	663	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
551		664
552	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,';
553		666
554	unless (ref $cb) {	667	unless (ref $cb) {
555	if (@_) {	668	if (@_) {
…		…
564	}	677	}
565		678
566	$node->monitor ($port, $cb);	679	$node->monitor ($port, $cb);
567		680
568	defined wantarray	681	defined wantarray
569	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	682	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
570	}	683	}
571		684
572	=item $guard = mon_guard $port, $ref, $ref...	685	=item $guard = mon_guard $port, $ref, $ref...
573		686
574	Monitors the given C<$port> and keeps the passed references. When the port	687	Monitors the given C<$port> and keeps the passed references. When the port
575	is killed, the references will be freed.	688	is killed, the references will be freed.
576		689
577	Optionally returns a guard that will stop the monitoring.	690	Optionally returns a guard that will stop the monitoring.
578		691
579	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
580	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>):
581		694
582	$port->rcv (start => sub {	695	$port->rcv (start => sub {
583	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	696	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
584	undef $timer if 0.9 < rand;	697	undef $timer if 0.9 < rand;
585	});	698	});
586	});	699	});
587		700
588	=cut	701	=cut
…		…
597		710
598	=item kil $port[, @reason]	711	=item kil $port[, @reason]
599		712
600	Kill the specified port with the given C<@reason>.	713	Kill the specified port with the given C<@reason>.
601		714
602	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" -
603	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.
604		718
605	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>
606	C<mon>, see below).	720	form) get killed with the same reason.
607		721
608	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
609	will be reported as reason C<< die => $@ >>.	723	will be reported as reason C<< die => $@ >>.
610		724
611	Transport/communication errors are reported as C<< transport_error =>	725	Transport/communication errors are reported as C<< transport_error =>
…		…
616	=item $port = spawn $node, $initfunc[, @initdata]	730	=item $port = spawn $node, $initfunc[, @initdata]
617		731
618	Creates a port on the node C<$node> (which can also be a port ID, in which	732	Creates a port on the node C<$node> (which can also be a port ID, in which
619	case it's the node where that port resides).	733	case it's the node where that port resides).
620		734
621	The port ID of the newly created port is return immediately, and it is	735	The port ID of the newly created port is returned immediately, and it is
622	permissible to immediately start sending messages or monitor the port.	736	possible to immediately start sending messages or to monitor the port.
623		737
624	After the port has been created, the init function is	738	After the port has been created, the init function is called on the remote
625	called. This function must be a fully-qualified function name	739	node, in the same context as a C<rcv> callback. This function must be a
626	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	740	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
627	program, use C<::name>.	741	specify a function in the main program, use C<::name>.
628		742
629	If the function doesn't exist, then the node tries to C<require>	743	If the function doesn't exist, then the node tries to C<require>
630	the package, then the package above the package and so on (e.g.	744	the package, then the package above the package and so on (e.g.
631	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	745	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
632	exists or it runs out of package names.	746	exists or it runs out of package names.
633		747
634	The init function is then called with the newly-created port as context	748	The init function is then called with the newly-created port as context
635	object (C<$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.
636		752
637	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
638	in the init function, monitor the original port. This two-way monitoring	754	port, and in the remote init function, immediately monitor the passed
639	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<$initfunc> has no visible effects on the
		759	caller before C<spawn> returns (by delaying invocation when spawn is
		760	called for the local node).
640		761
641	Example: spawn a chat server port on C<$othernode>.	762	Example: spawn a chat server port on C<$othernode>.
642		763
643	# this node, executed from within a port context:	764	# this node, executed from within a port context:
644	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	765	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
659		780
660	sub _spawn {	781	sub _spawn {
661	my $port = shift;	782	my $port = shift;
662	my $init = shift;	783	my $init = shift;
663		784
		785	# rcv will create the actual port
664	local $SELF = "$NODE#$port";	786	local $SELF = "$NODE#$port";
665	eval {	787	eval {
666	&{ load_func $init }	788	&{ load_func $init }
667	};	789	};
668	_self_die if $@;	790	_self_die if $@;
669	}	791	}
670		792
671	sub spawn(@) {	793	sub spawn(@) {
672	my ($noderef, undef) = split /#/, shift, 2;	794	my ($nodeid, undef) = split /#/, shift, 2;
673		795
674	my $id = "$RUNIQ." . $ID++;	796	my $id = $RUNIQ . ++$ID;
675		797
676	$_[0] =~ /::/	798	$_[0] =~ /::/
677	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";
678		800
679	snd_to_func $noderef, "AnyEvent::MP::_spawn" => $id, @_;	801	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
680		802
681	"$noderef#$id"	803	"$nodeid#$id"
682	}	804	}
683		805
		806
		807	=item after $timeout, @msg
		808
		809	=item after $timeout, $callback
		810
		811	Either sends the given message, or call the given callback, after the
		812	specified number of seconds.
		813
		814	This is simply a utility function that comes in handy at times - the
		815	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		816	so it may go away in the future.
		817
		818	=cut
		819
		820	sub after($@) {
		821	my ($timeout, @action) = @_;
		822
		823	my $t; $t = AE::timer $timeout, 0, sub {
		824	undef $t;
		825	ref $action[0]
		826	? $action[0]()
		827	: snd @action;
		828	};
		829	}
		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	$port
		881	}
		882
684	=back	883	=back
685		884
686	=head1 NODE MESSAGES	885	=head1 DISTRIBUTED DATABASE
687		886
688	Nodes understand the following messages sent to them. Many of them take	887	AnyEvent::MP comes with a simple distributed database. The database will
689	arguments called C<@reply>, which will simply be used to compose a reply	888	be mirrored asynchronously at all global nodes. Other nodes bind to one of
690	message - C<$reply[0]> is the port to reply to, C<$reply[1]> the type and	889	the global nodes for their needs.
691	the remaining arguments are simply the message data.
692		890
693	While other messages exist, they are not public and subject to change.	891	The database consists of a two-level hash - a hash contains a hash which
		892	contains values.
694		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
695	=over 4	926	=over
696		927
697	=cut	928	=item db_set $family => $subkey [=> $value]
698		929
699	=item lookup => $name, @reply	930	Sets (or replaces) a key to the database - if C<$value> is omitted,
		931	C<undef> is used instead.
700		932
701	Replies with the port ID of the specified well-known port, or C<undef>.	933	=item db_del $family => $subkey
702		934
703	=item devnull => ...	935	Deletes a key from the database.
704		936
705	Generic data sink/CPU heat conversion.	937	=item $guard = db_reg $family => $subkey [=> $value]
706		938
707	=item relay => $port, @msg	939	Sets the key on the database and returns a guard. When the guard is
		940	destroyed, the key is deleted from the database. If C<$value> is missing,
		941	then C<undef> is used.
708		942
709	Simply forwards the message to the given port.	943	=cut
710
711	=item eval => $string[ @reply]
712
713	Evaluates the given string. If C<@reply> is given, then a message of the
714	form C<@reply, $@, @evalres> is sent.
715
716	Example: crash another node.
717
718	snd $othernode, eval => "exit";
719
720	=item time => @reply
721
722	Replies the the current node time to C<@reply>.
723
724	Example: tell the current node to send the current time to C<$myport> in a
725	C<timereply> message.
726
727	snd $NODE, time => $myport, timereply => 1, 2;
728	# => snd $myport, timereply => 1, 2, <time>
729		944
730	=back	945	=back
731		946
732	=head1 AnyEvent::MP vs. Distributed Erlang	947	=head1 AnyEvent::MP vs. Distributed Erlang
733		948
734	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
735	== 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
736	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
737	sample:	952	sample:
738		953
739	http://www.Erlang.se/doc/programming_rules.shtml	954	http://www.erlang.se/doc/programming_rules.shtml
740	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
741	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
742	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
743		958
744	Despite the similarities, there are also some important differences:	959	Despite the similarities, there are also some important differences:
745		960
746	=over 4	961	=over 4
747		962
748	=item * Node references contain the recipe on how to contact them.	963	=item * Node IDs are arbitrary strings in AEMP.
749		964
750	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
751	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
752	convenience functionality.	967	configuration or DNS), and possibly the addresses of some seed nodes, but
753		968	will otherwise discover other nodes (and their IDs) itself.
754	This means that AEMP requires a less tightly controlled environment at the
755	cost of longer node references and a slightly higher management overhead.
756		969
757	=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
758	uses "local ports are like remote ports".	971	uses "local ports are like remote ports".
759		972
760	The failure modes for local ports are quite different (runtime errors	973	The failure modes for local ports are quite different (runtime errors
…		…
769	ports being the special case/exception, where transport errors cannot	982	ports being the special case/exception, where transport errors cannot
770	occur.	983	occur.
771		984
772	=item * Erlang uses processes and a mailbox, AEMP does not queue.	985	=item * Erlang uses processes and a mailbox, AEMP does not queue.
773		986
774	Erlang uses processes that selectively receive messages, and therefore	987	Erlang uses processes that selectively receive messages out of order, and
775	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
776	useful purpose. For the same reason the pattern-matching abilities of	989	no useful purpose. For the same reason the pattern-matching abilities
777	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
778	filter messages without dequeing them.	991	filter messages without dequeuing them.
779		992
780	(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.
781		998
782	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	999	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
783		1000
784	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
785	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
786	connection establishment is handled in the background.	1004	establishment is handled in the background.
787		1005
788	=item * Erlang suffers from silent message loss, AEMP does not.	1006	=item * Erlang suffers from silent message loss, AEMP does not.
789		1007
790	Erlang makes few guarantees on messages delivery - messages can get lost	1008	Erlang implements few guarantees on messages delivery - messages can get
791	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,
792	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).
793		1011
794	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
795	holes in the message sequence.	1015	no silent "holes" in the message sequence.
796		1016
797	=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
798	alive.	1018	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
799		1019	simply tries to work better in common error cases, such as when a network
800	In Erlang it can happen that a monitored process is declared dead and	1020	link goes down.
801	linked processes get killed, but later it turns out that the process is
802	still alive - and can receive messages.
803
804	In AEMP, when port monitoring detects a port as dead, then that port will
805	eventually be killed - it cannot happen that a node detects a port as dead
806	and then later sends messages to it, finding it is still alive.
807		1021
808	=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.
809		1023
810	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
811	known to other nodes for a completely different process, causing messages	1025	process ID known to other nodes for a completely different process,
812	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.
813		1028
814	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
815	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.
816		1031
817	=item * Erlang uses unprotected connections, AEMP uses secure	1032	=item * Erlang uses unprotected connections, AEMP uses secure
818	authentication and can use TLS.	1033	authentication and can use TLS.
819		1034
820	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1035	AEMP can use a proven protocol - TLS - to protect connections and
821	securely authenticate nodes.	1036	securely authenticate nodes.
822		1037
823	=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
824	communications.	1039	communications.
825		1040
826	The AEMP protocol, unlike the Erlang protocol, supports both	1041	The AEMP protocol, unlike the Erlang protocol, supports both programming
827	language-independent text-only protocols (good for debugging) and binary,	1042	language independent text-only protocols (good for debugging), and binary,
828	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.
829		1045
830	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
831	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
832	protocol simple.	1048	protocol simple.
833		1049
834	=item * AEMP has more flexible monitoring options than Erlang.	1050	=item * AEMP has more flexible monitoring options than Erlang.
835		1051
836	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
837	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
838	difficult to implement. Monitoring in AEMP is more flexible than in	1054	difficult to implement.
839	Erlang, as one can choose between automatic kill, exit message or callback	1055
840	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.
841		1058
842	=item * Erlang tries to hide remote/local connections, AEMP does not.	1059	=item * Erlang tries to hide remote/local connections, AEMP does not.
843		1060
844	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
845	as linking is (except linking is unreliable in Erlang).	1062	same way as linking is (except linking is unreliable in Erlang).
846		1063
847	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
848	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
849	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
850	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
851	more reliable.	1068	reliable (no need for C<spawn_link>).
852		1069
853	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
854	(hard to do in Erlang).	1071	(hard to do in Erlang).
855		1072
856	=back	1073	=back
857		1074
858	=head1 RATIONALE	1075	=head1 RATIONALE
859		1076
860	=over 4	1077	=over 4
861		1078
862	=item Why strings for ports and noderefs, why not objects?	1079	=item Why strings for port and node IDs, why not objects?
863		1080
864	We considered "objects", but found that the actual number of methods	1081	We considered "objects", but found that the actual number of methods
865	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
866	the network frequently, the serialising/deserialising would add lots of	1083	the network frequently, the serialising/deserialising would add lots of
867	overhead, as well as having to keep a proxy object.	1084	overhead, as well as having to keep a proxy object everywhere.
868		1085
869	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
870	procedures to be "valid".	1087	procedures to be "valid".
871		1088
872	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
873	can't become much cheaper.	1090	code reference stored in a global hash - it can't become much cheaper.
874		1091
875	=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?
876		1093
877	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
878	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
879	default.	1096	default (although all nodes will accept it).
880		1097
881	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
882	faster for small messages and b) most importantly, after years of	1099	faster for small messages and b) most importantly, after years of
883	experience we found that object serialisation is causing more problems	1100	experience we found that object serialisation is causing more problems
884	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
885	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
886	always have to re-think your design.	1103	always have to re-think your design.
887		1104
888	Keeping your messages simple, concentrating on data structures rather than	1105	Keeping your messages simple, concentrating on data structures rather than
889	objects, will keep your messages clean, tidy and efficient.	1106	objects, will keep your messages clean, tidy and efficient.
890		1107
891	=back	1108	=back
892		1109
893	=head1 SEE ALSO	1110	=head1 SEE ALSO
894		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
895	L<AnyEvent>.	1124	L<AnyEvent>.
896		1125
897	=head1 AUTHOR	1126	=head1 AUTHOR
898		1127
899	Marc Lehmann <schmorp@schmorp.de>	1128	Marc Lehmann <schmorp@schmorp.de>

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Revision 1.126 by root, Sat Mar 3 19:43:41 2012 UTC