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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.57 by root, Sat Aug 15 04:34:34 2009 UTC vs.
Revision 1.134 by root, Mon Mar 12 14:47:23 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 $port, $cb->(@msg) # callback is invoked on death
40	mon $port, $otherport # kill otherport on abnormal death	41	mon $port, $localport # kill localport on abnormal death
41	mon $port, $otherport, @msg # send message on death	42	mon $port, $localport, @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
		202	db_mon db_family db_keys db_values
135	);	203	);
136		204
137	our $SELF;	205	our $SELF;
138		206
139	sub _self_die() {	207	sub _self_die() {
…		…
142	kil $SELF, die => $msg;	210	kil $SELF, die => $msg;
143	}	211	}
144		212
145	=item $thisnode = NODE / $NODE	213	=item $thisnode = NODE / $NODE
146		214
147	The C<NODE> function returns, and the C<$NODE> variable contains the	215	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	216	ID of the node running in the current process. This value is initialised by
149	C<initialise_node>.	217	a call to C<configure>.
150		218
151	=item $noderef = node_of $port	219	=item $nodeid = node_of $port
152		220
153	Extracts and returns the noderef from a port ID or a noderef.	221	Extracts and returns the node ID from a port ID or a node ID.
154		222
155	=item initialise_node $noderef, $seednode, $seednode...	223	=item configure $profile, key => value...
156		224
157	=item initialise_node "slave/", $master, $master...	225	=item configure key => value...
158		226
159	Before a node can talk to other nodes on the network it has to initialise	227	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	228	"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.	229	to know is its own name, and optionally it should know the addresses of
		230	some other nodes in the network to discover other nodes.
162		231
163	This function initialises a node - it must be called exactly once (or	232	This function configures a node - it must be called exactly once (or
164	never) before calling other AnyEvent::MP functions.	233	never) before calling other AnyEvent::MP functions.
165		234
166	All arguments (optionally except for the first) are noderefs, which can be	235	The key/value pairs are basically the same ones as documented for the
167	either resolved or unresolved.	236	F<aemp> command line utility (sans the set/del prefix), with these 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		237
177	=over 4	238	=over 4
178		239
179	=item public nodes	240	=item norc => $boolean (default false)
180		241
181	For public nodes, C<$noderef> (supplied either directly to	242	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	243	be consulted - all configuraiton options must be specified in the
183	noderef (possibly unresolved, in which case it will be resolved).	244	C<configure> call.
184		245
185	After resolving, the node will bind itself on all endpoints and try to	246	=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		247
190	=item slave nodes	248	IF true, then the values specified in the C<configure> will take
		249	precedence over any values configured via the rc file. The default is for
		250	the rc file to override any options specified in the program.
191		251
192	When the C<$noderef> (either as given or overriden by the config file)	252	=item secure => $pass->($nodeid)
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		253
197	At least one additional noderef is required (either by specifying it	254	In addition to specifying a boolean, you can specify a code reference that
198	directly or because it is part of the configuration profile): The node	255	is called for every remote execution attempt - the execution request is
199	will try to connect to all of them and will become a slave attached to the	256	granted iff the callback returns a true value.
200	first node it can successfully connect to.
201		257
202	Note that slave nodes cannot change their name, and consequently, their	258	See F<semp setsecure> for more info.
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		259
207	=back	260	=back
208		261
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	262	=over 4
255		263
256	=item the empty string	264	=item step 1, gathering configuration from profiles
257		265
258	An empty-string component gets resolved as if the default port (4040) was	266	The function first looks up a profile in the aemp configuration (see the
259	specified.	267	L<aemp> commandline utility). The profile name can be specified via the
		268	named C<profile> parameter or can simply be the first parameter). If it is
		269	missing, then the nodename (F<uname -n>) will be used as profile name.
260		270
261	=item naked port numbers (e.g. C<1234>)	271	The profile data is then gathered as follows:
262		272
263	These are resolved by prepending the local nodename and a colon, to be	273	First, all remaining key => value pairs (all of which are conveniently
264	further resolved.	274	undocumented at the moment) will be interpreted as configuration
		275	data. Then they will be overwritten by any values specified in the global
		276	default configuration (see the F<aemp> utility), then the chain of
		277	profiles chosen by the profile name (and any C<parent> attributes).
265		278
266	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	279	That means that the values specified in the profile have highest priority
		280	and the values specified directly via C<configure> have lowest priority,
		281	and can only be used to specify defaults.
267		282
268	These are resolved by using AnyEvent::DNS to resolve them, optionally	283	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	284	this process. If not, then the profile name will be used as node ID, with
270	specified.	285	a unique randoms tring (C</%u>) appended.
		286
		287	The node ID can contain some C<%> sequences that are expanded: C<%n>
		288	is expanded to the local nodename, C<%u> is replaced by a random
		289	strign to make the node unique. For example, the F<aemp> commandline
		290	utility uses C<aemp/%n/%u> as nodename, which might expand to
		291	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		292
		293	=item step 2, bind listener sockets
		294
		295	The next step is to look up the binds in the profile, followed by binding
		296	aemp protocol listeners on all binds specified (it is possible and valid
		297	to have no binds, meaning that the node cannot be contacted form the
		298	outside. This means the node cannot talk to other nodes that also have no
		299	binds, but it can still talk to all "normal" nodes).
		300
		301	If the profile does not specify a binds list, then a default of C<*> is
		302	used, meaning the node will bind on a dynamically-assigned port on every
		303	local IP address it finds.
		304
		305	=item step 3, connect to seed nodes
		306
		307	As the last step, the seed ID list from the profile is passed to the
		308	L<AnyEvent::MP::Global> module, which will then use it to keep
		309	connectivity with at least one node at any point in time.
271		310
272	=back	311	=back
		312
		313	Example: become a distributed node using the local node name as profile.
		314	This should be the most common form of invocation for "daemon"-type nodes.
		315
		316	configure
		317
		318	Example: become a semi-anonymous node. This form is often used for
		319	commandline clients.
		320
		321	configure nodeid => "myscript/%n/%u";
		322
		323	Example: configure a node using a profile called seed, which is suitable
		324	for a seed node as it binds on all local addresses on a fixed port (4040,
		325	customary for aemp).
		326
		327	# use the aemp commandline utility
		328	# aemp profile seed binds '*:4040'
		329
		330	# then use it
		331	configure profile => "seed";
		332
		333	# or simply use aemp from the shell again:
		334	# aemp run profile seed
		335
		336	# or provide a nicer-to-remember nodeid
		337	# aemp run profile seed nodeid "$(hostname)"
273		338
274	=item $SELF	339	=item $SELF
275		340
276	Contains the current port id while executing C<rcv> callbacks or C<psub>	341	Contains the current port id while executing C<rcv> callbacks or C<psub>
277	blocks.	342	blocks.
278		343
279	=item SELF, %SELF, @SELF...	344	=item *SELF, SELF, %SELF, @SELF...
280		345
281	Due to some quirks in how perl exports variables, it is impossible to	346	Due to some quirks in how perl exports variables, it is impossible to
282	just export C<$SELF>, all the symbols called C<SELF> are exported by this	347	just export C<$SELF>, all the symbols named C<SELF> are exported by this
283	module, but only C<$SELF> is currently used.	348	module, but only C<$SELF> is currently used.
284		349
285	=item snd $port, type => @data	350	=item snd $port, type => @data
286		351
287	=item snd $port, @msg	352	=item snd $port, @msg
288		353
289	Send the given message to the given port ID, which can identify either	354	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.	355	local or a remote port, and must be a port ID.
291		356
292	While the message can be about anything, it is highly recommended to use a	357	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	358	use a string as first element (a port ID, or some word that indicates a
294	type etc.).	359	request type etc.) and to consist if only simple perl values (scalars,
		360	arrays, hashes) - if you think you need to pass an object, think again.
295		361
296	The message data effectively becomes read-only after a call to this	362	The message data logically becomes read-only after a call to this
297	function: modifying any argument is not allowed and can cause many	363	function: modifying any argument (or values referenced by them) is
298	problems.	364	forbidden, as there can be considerable time between the call to C<snd>
		365	and the time the message is actually being serialised - in fact, it might
		366	never be copied as within the same process it is simply handed to the
		367	receiving port.
299		368
300	The type of data you can transfer depends on the transport protocol: when	369	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	370	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	371	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	372	that Storable can serialise and deserialise is allowed, and for the local
304	node, anything can be passed.	373	node, anything can be passed. Best rely only on the common denominator of
		374	these.
305		375
306	=item $local_port = port	376	=item $local_port = port
307		377
308	Create a new local port object and returns its port ID. Initially it has	378	Create a new local port object and returns its port ID. Initially it has
309	no callbacks set and will throw an error when it receives messages.	379	no callbacks set and will throw an error when it receives messages.
…		…
328		398
329	=cut	399	=cut
330		400
331	sub rcv($@);	401	sub rcv($@);
332		402
333	sub _kilme {	403	my $KILME = sub {
334	die "received message on port without callback";	404	(my $tag = substr $_[0], 0, 30) =~ s/([\x20-\x7e])/./g;
335	}	405	kil $SELF, unhandled_message => "missing (tag or fallback) callback for message '$tag'";
		406	};
336		407
337	sub port(;&) {	408	sub port(;&) {
338	my $id = "$UNIQ." . $ID++;	409	my $id = $UNIQ . ++$ID;
339	my $port = "$NODE#$id";	410	my $port = "$NODE#$id";
340		411
341	rcv $port, shift \|\| \&_kilme;	412	rcv $port, shift \|\| $KILME;
342		413
343	$port	414	$port
344	}	415	}
345		416
346	=item rcv $local_port, $callback->(@msg)	417	=item rcv $local_port, $callback->(@msg)
…		…
351		422
352	The global C<$SELF> (exported by this module) contains C<$port> while	423	The global C<$SELF> (exported by this module) contains C<$port> while
353	executing the callback. Runtime errors during callback execution will	424	executing the callback. Runtime errors during callback execution will
354	result in the port being C<kil>ed.	425	result in the port being C<kil>ed.
355		426
356	The default callback received all messages not matched by a more specific	427	The default callback receives all messages not matched by a more specific
357	C<tag> match.	428	C<tag> match.
358		429
359	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...	430	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
360		431
361	Register (or replace) callbacks to be called on messages starting with the	432	Register (or replace) callbacks to be called on messages starting with the
…		…
382	msg1 => sub { ... },	453	msg1 => sub { ... },
383	...	454	...
384	;	455	;
385		456
386	Example: temporarily register a rcv callback for a tag matching some port	457	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.	458	(e.g. for an rpc reply) and unregister it after a message was received.
388		459
389	rcv $port, $otherport => sub {	460	rcv $port, $otherport => sub {
390	my @reply = @_;	461	my @reply = @_;
391		462
392	rcv $SELF, $otherport;	463	rcv $SELF, $otherport;
…		…
394		465
395	=cut	466	=cut
396		467
397	sub rcv($@) {	468	sub rcv($@) {
398	my $port = shift;	469	my $port = shift;
399	my ($noderef, $portid) = split /#/, $port, 2;	470	my ($nodeid, $portid) = split /#/, $port, 2;
400		471
401	($NODE{$noderef} \|\| add_node $noderef) == $NODE{""}	472	$NODE{$nodeid} == $NODE{""}
402	or Carp::croak "$port: rcv can only be called on local ports, caught";	473	or Carp::croak "$port: rcv can only be called on local ports, caught";
403		474
404	while (@_) {	475	while (@_) {
405	if (ref $_[0]) {	476	if (ref $_[0]) {
406	if (my $self = $PORT_DATA{$portid}) {	477	if (my $self = $PORT_DATA{$portid}) {
407	"AnyEvent::MP::Port" eq ref $self	478	"AnyEvent::MP::Port" eq ref $self
408	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	479	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
409		480
410	$self->[2] = shift;	481	$self->[0] = shift;
411	} else {	482	} else {
412	my $cb = shift;	483	my $cb = shift;
413	$PORT{$portid} = sub {	484	$PORT{$portid} = sub {
414	local $SELF = $port;	485	local $SELF = $port;
415	eval { &$cb }; _self_die if $@;	486	eval { &$cb }; _self_die if $@;
416	};	487	};
417	}	488	}
418	} elsif (defined $_[0]) {	489	} elsif (defined $_[0]) {
419	my $self = $PORT_DATA{$portid} \|\|= do {	490	my $self = $PORT_DATA{$portid} \|\|= do {
420	my $self = bless [$PORT{$port} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";	491	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
421		492
422	$PORT{$portid} = sub {	493	$PORT{$portid} = sub {
423	local $SELF = $port;	494	local $SELF = $port;
424		495
425	if (my $cb = $self->[1]{$_[0]}) {	496	if (my $cb = $self->[1]{$_[0]}) {
…		…
447	}	518	}
448		519
449	$port	520	$port
450	}	521	}
451		522
		523	=item peval $port, $coderef[, @args]
		524
		525	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		526	when the code throews an exception the C<$port> will be killed.
		527
		528	Any remaining args will be passed to the callback. Any return values will
		529	be returned to the caller.
		530
		531	This is useful when you temporarily want to execute code in the context of
		532	a port.
		533
		534	Example: create a port and run some initialisation code in it's context.
		535
		536	my $port = port { ... };
		537
		538	peval $port, sub {
		539	init
		540	or die "unable to init";
		541	};
		542
		543	=cut
		544
		545	sub peval($$) {
		546	local $SELF = shift;
		547	my $cb = shift;
		548
		549	if (wantarray) {
		550	my @res = eval { &$cb };
		551	_self_die if $@;
		552	@res
		553	} else {
		554	my $res = eval { &$cb };
		555	_self_die if $@;
		556	$res
		557	}
		558	}
		559
452	=item $closure = psub { BLOCK }	560	=item $closure = psub { BLOCK }
453		561
454	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	562	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>	563	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.	564	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		565
		566	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		567	BLOCK }, @_ } >>.
457		568
458	This is useful when you register callbacks from C<rcv> callbacks:	569	This is useful when you register callbacks from C<rcv> callbacks:
459		570
460	rcv delayed_reply => sub {	571	rcv delayed_reply => sub {
461	my ($delay, @reply) = @_;	572	my ($delay, @reply) = @_;
…		…
485	$res	596	$res
486	}	597	}
487	}	598	}
488	}	599	}
489		600
490	=item $guard = mon $port, $cb->(@reason)	601	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
491		602
492	=item $guard = mon $port, $rcvport	603	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
493		604
494	=item $guard = mon $port	605	=item $guard = mon $port # kill $SELF when $port dies
495		606
496	=item $guard = mon $port, $rcvport, @msg	607	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
497		608
498	Monitor the given port and do something when the port is killed or	609	Monitor the given port and do something when the port is killed or
499	messages to it were lost, and optionally return a guard that can be used	610	messages to it were lost, and optionally return a guard that can be used
500	to stop monitoring again.	611	to stop monitoring again.
501
502	C<mon> effectively guarantees that, in the absence of hardware failures,
503	that after starting the monitor, either all messages sent to the port
504	will arrive, or the monitoring action will be invoked after possible
505	message loss has been detected. No messages will be lost "in between"
506	(after the first lost message no further messages will be received by the
507	port). After the monitoring action was invoked, further messages might get
508	delivered again.
509		612
510	In the first form (callback), the callback is simply called with any	613	In the first form (callback), the callback is simply called with any
511	number of C<@reason> elements (no @reason means that the port was deleted	614	number of C<@reason> elements (no @reason means that the port was deleted
512	"normally"). Note also that I<< the callback B<must> never die >>, so use	615	"normally"). Note also that I<< the callback B<must> never die >>, so use
513	C<eval> if unsure.	616	C<eval> if unsure.
514		617
515	In the second form (another port given), the other port (C<$rcvport>)	618	In the second form (another port given), the other port (C<$rcvport>)
516	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	619	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
517	"normal" kils nothing happens, while under all other conditions, the other	620	"normal" kils nothing happens, while under all other conditions, the other
518	port is killed with the same reason.	621	port is killed with the same reason.
519		622
520	The third form (kill self) is the same as the second form, except that	623	The third form (kill self) is the same as the second form, except that
521	C<$rvport> defaults to C<$SELF>.	624	C<$rvport> defaults to C<$SELF>.
522		625
523	In the last form (message), a message of the form C<@msg, @reason> will be	626	In the last form (message), a message of the form C<@msg, @reason> will be
524	C<snd>.	627	C<snd>.
		628
		629	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		630	alert was raised), they are removed and will not trigger again.
525		631
526	As a rule of thumb, monitoring requests should always monitor a port from	632	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	633	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	634	lost, just like any other message. Another less obvious reason is that
529	even monitoring requests can get lost (for exmaple, when the connection	635	even monitoring requests can get lost (for example, when the connection
530	to the other node goes down permanently). When monitoring a port locally	636	to the other node goes down permanently). When monitoring a port locally
531	these problems do not exist.	637	these problems do not exist.
532		638
		639	C<mon> effectively guarantees that, in the absence of hardware failures,
		640	after starting the monitor, either all messages sent to the port will
		641	arrive, or the monitoring action will be invoked after possible message
		642	loss has been detected. No messages will be lost "in between" (after
		643	the first lost message no further messages will be received by the
		644	port). After the monitoring action was invoked, further messages might get
		645	delivered again.
		646
		647	Inter-host-connection timeouts and monitoring depend on the transport
		648	used. The only transport currently implemented is TCP, and AnyEvent::MP
		649	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		650	non-idle connection, and usually around two hours for idle connections).
		651
		652	This means that monitoring is good for program errors and cleaning up
		653	stuff eventually, but they are no replacement for a timeout when you need
		654	to ensure some maximum latency.
		655
533	Example: call a given callback when C<$port> is killed.	656	Example: call a given callback when C<$port> is killed.
534		657
535	mon $port, sub { warn "port died because of <@_>\n" };	658	mon $port, sub { warn "port died because of <@_>\n" };
536		659
537	Example: kill ourselves when C<$port> is killed abnormally.	660	Example: kill ourselves when C<$port> is killed abnormally.
…		…
543	mon $port, $self => "restart";	666	mon $port, $self => "restart";
544		667
545	=cut	668	=cut
546		669
547	sub mon {	670	sub mon {
548	my ($noderef, $port) = split /#/, shift, 2;	671	my ($nodeid, $port) = split /#/, shift, 2;
549		672
550	my $node = $NODE{$noderef} \|\| add_node $noderef;	673	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
551		674
552	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';	675	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
553		676
554	unless (ref $cb) {	677	unless (ref $cb) {
555	if (@_) {	678	if (@_) {
…		…
564	}	687	}
565		688
566	$node->monitor ($port, $cb);	689	$node->monitor ($port, $cb);
567		690
568	defined wantarray	691	defined wantarray
569	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	692	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
570	}	693	}
571		694
572	=item $guard = mon_guard $port, $ref, $ref...	695	=item $guard = mon_guard $port, $ref, $ref...
573		696
574	Monitors the given C<$port> and keeps the passed references. When the port	697	Monitors the given C<$port> and keeps the passed references. When the port
575	is killed, the references will be freed.	698	is killed, the references will be freed.
576		699
577	Optionally returns a guard that will stop the monitoring.	700	Optionally returns a guard that will stop the monitoring.
578		701
579	This function is useful when you create e.g. timers or other watchers and	702	This function is useful when you create e.g. timers or other watchers and
580	want to free them when the port gets killed:	703	want to free them when the port gets killed (note the use of C<psub>):
581		704
582	$port->rcv (start => sub {	705	$port->rcv (start => sub {
583	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	706	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
584	undef $timer if 0.9 < rand;	707	undef $timer if 0.9 < rand;
585	});	708	});
586	});	709	});
587		710
588	=cut	711	=cut
…		…
597		720
598	=item kil $port[, @reason]	721	=item kil $port[, @reason]
599		722
600	Kill the specified port with the given C<@reason>.	723	Kill the specified port with the given C<@reason>.
601		724
602	If no C<@reason> is specified, then the port is killed "normally" (linked	725	If no C<@reason> is specified, then the port is killed "normally" -
603	ports will not be kileld, or even notified).	726	monitor callback will be invoked, but the kil will not cause linked ports
		727	(C<mon $mport, $lport> form) to get killed.
604		728
605	Otherwise, linked ports get killed with the same reason (second form of	729	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
606	C<mon>, see below).	730	form) get killed with the same reason.
607		731
608	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	732	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
609	will be reported as reason C<< die => $@ >>.	733	will be reported as reason C<< die => $@ >>.
610		734
611	Transport/communication errors are reported as C<< transport_error =>	735	Transport/communication errors are reported as C<< transport_error =>
612	$message >>.	736	$message >>.
613		737
614	=cut	738	Common idioms:
		739
		740	# silently remove yourself, do not kill linked ports
		741	kil $SELF;
		742
		743	# report a failure in some detail
		744	kil $SELF, failure_mode_1 => "it failed with too high temperature";
		745
		746	# do not waste much time with killing, just die when something goes wrong
		747	open my $fh, "<file"
		748	or die "file: $!";
615		749
616	=item $port = spawn $node, $initfunc[, @initdata]	750	=item $port = spawn $node, $initfunc[, @initdata]
617		751
618	Creates a port on the node C<$node> (which can also be a port ID, in which	752	Creates a port on the node C<$node> (which can also be a port ID, in which
619	case it's the node where that port resides).	753	case it's the node where that port resides).
620		754
621	The port ID of the newly created port is return immediately, and it is	755	The port ID of the newly created port is returned immediately, and it is
622	permissible to immediately start sending messages or monitor the port.	756	possible to immediately start sending messages or to monitor the port.
623		757
624	After the port has been created, the init function is	758	After the port has been created, the init function is called on the remote
625	called. This function must be a fully-qualified function name	759	node, in the same context as a C<rcv> callback. This function must be a
626	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	760	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
627	program, use C<::name>.	761	specify a function in the main program, use C<::name>.
628		762
629	If the function doesn't exist, then the node tries to C<require>	763	If the function doesn't exist, then the node tries to C<require>
630	the package, then the package above the package and so on (e.g.	764	the package, then the package above the package and so on (e.g.
631	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	765	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
632	exists or it runs out of package names.	766	exists or it runs out of package names.
633		767
634	The init function is then called with the newly-created port as context	768	The init function is then called with the newly-created port as context
635	object (C<$SELF>) and the C<@initdata> values as arguments.	769	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		770	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		771	the port might not get created.
636		772
637	A common idiom is to pass your own port, monitor the spawned port, and	773	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	774	port, and in the remote init function, immediately monitor the passed
639	ensures that both ports get cleaned up when there is a problem.	775	local port. This two-way monitoring ensures that both ports get cleaned up
		776	when there is a problem.
		777
		778	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		779	caller before C<spawn> returns (by delaying invocation when spawn is
		780	called for the local node).
640		781
641	Example: spawn a chat server port on C<$othernode>.	782	Example: spawn a chat server port on C<$othernode>.
642		783
643	# this node, executed from within a port context:	784	# this node, executed from within a port context:
644	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	785	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
659		800
660	sub _spawn {	801	sub _spawn {
661	my $port = shift;	802	my $port = shift;
662	my $init = shift;	803	my $init = shift;
663		804
		805	# rcv will create the actual port
664	local $SELF = "$NODE#$port";	806	local $SELF = "$NODE#$port";
665	eval {	807	eval {
666	&{ load_func $init }	808	&{ load_func $init }
667	};	809	};
668	_self_die if $@;	810	_self_die if $@;
669	}	811	}
670		812
671	sub spawn(@) {	813	sub spawn(@) {
672	my ($noderef, undef) = split /#/, shift, 2;	814	my ($nodeid, undef) = split /#/, shift, 2;
673		815
674	my $id = "$RUNIQ." . $ID++;	816	my $id = $RUNIQ . ++$ID;
675		817
676	$_[0] =~ /::/	818	$_[0] =~ /::/
677	or Carp::croak "spawn init function must be a fully-qualified name, caught";	819	or Carp::croak "spawn init function must be a fully-qualified name, caught";
678		820
679	snd_to_func $noderef, "AnyEvent::MP::_spawn" => $id, @_;	821	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
680		822
681	"$noderef#$id"	823	"$nodeid#$id"
682	}	824	}
		825
		826
		827	=item after $timeout, @msg
		828
		829	=item after $timeout, $callback
		830
		831	Either sends the given message, or call the given callback, after the
		832	specified number of seconds.
		833
		834	This is simply a utility function that comes in handy at times - the
		835	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		836	so it may go away in the future.
		837
		838	=cut
		839
		840	sub after($@) {
		841	my ($timeout, @action) = @_;
		842
		843	my $t; $t = AE::timer $timeout, 0, sub {
		844	undef $t;
		845	ref $action[0]
		846	? $action[0]()
		847	: snd @action;
		848	};
		849	}
		850
		851	#=item $cb2 = timeout $seconds, $cb[, @args]
		852
		853	=item cal $port, @msg, $callback[, $timeout]
		854
		855	A simple form of RPC - sends a message to the given C<$port> with the
		856	given contents (C<@msg>), but adds a reply port to the message.
		857
		858	The reply port is created temporarily just for the purpose of receiving
		859	the reply, and will be C<kil>ed when no longer needed.
		860
		861	A reply message sent to the port is passed to the C<$callback> as-is.
		862
		863	If an optional time-out (in seconds) is given and it is not C<undef>,
		864	then the callback will be called without any arguments after the time-out
		865	elapsed and the port is C<kil>ed.
		866
		867	If no time-out is given (or it is C<undef>), then the local port will
		868	monitor the remote port instead, so it eventually gets cleaned-up.
		869
		870	Currently this function returns the temporary port, but this "feature"
		871	might go in future versions unless you can make a convincing case that
		872	this is indeed useful for something.
		873
		874	=cut
		875
		876	sub cal(@) {
		877	my $timeout = ref $_[-1] ? undef : pop;
		878	my $cb = pop;
		879
		880	my $port = port {
		881	undef $timeout;
		882	kil $SELF;
		883	&$cb;
		884	};
		885
		886	if (defined $timeout) {
		887	$timeout = AE::timer $timeout, 0, sub {
		888	undef $timeout;
		889	kil $port;
		890	$cb->();
		891	};
		892	} else {
		893	mon $_[0], sub {
		894	kil $port;
		895	$cb->();
		896	};
		897	}
		898
		899	push @_, $port;
		900	&snd;
		901
		902	$port
		903	}
		904
		905	=back
		906
		907	=head1 DISTRIBUTED DATABASE
		908
		909	AnyEvent::MP comes with a simple distributed database. The database will
		910	be mirrored asynchronously on all global nodes. Other nodes bind to one
		911	of the global nodes for their needs. Every node has a "local database"
		912	which contains all the values that are set locally. All local databases
		913	are merged together to form the global database, which can be queried.
		914
		915	The database structure is that of a two-level hash - the database hash
		916	contains hashes which contain values, similarly to a perl hash of hashes,
		917	i.e.:
		918
		919	$DATABASE{$family}{$subkey} = $value
		920
		921	The top level hash key is called "family", and the second-level hash key
		922	is called "subkey" or simply "key".
		923
		924	The family must be alphanumeric, i.e. start with a letter and consist
		925	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		926	pretty much like Perl module names.
		927
		928	As the family namespace is global, it is recommended to prefix family names
		929	with the name of the application or module using it.
		930
		931	The subkeys must be non-empty strings, with no further restrictions.
		932
		933	The values should preferably be strings, but other perl scalars should
		934	work as well (such as C<undef>, arrays and hashes).
		935
		936	Every database entry is owned by one node - adding the same family/subkey
		937	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		938	but the result might be nondeterministic, i.e. the key might have
		939	different values on different nodes.
		940
		941	Different subkeys in the same family can be owned by different nodes
		942	without problems, and in fact, this is the common method to create worker
		943	pools. For example, a worker port for image scaling might do this:
		944
		945	db_set my_image_scalers => $port;
		946
		947	And clients looking for an image scaler will want to get the
		948	C<my_image_scalers> keys from time to time:
		949
		950	db_keys my_image_scalers => sub {
		951	@ports = @{ $_[0] };
		952	};
		953
		954	Or better yet, they want to monitor the database family, so they always
		955	have a reasonable up-to-date copy:
		956
		957	db_mon my_image_scalers => sub {
		958	@ports = keys %{ $_[0] };
		959	};
		960
		961	In general, you can set or delete single subkeys, but query and monitor
		962	whole families only.
		963
		964	If you feel the need to monitor or query a single subkey, try giving it
		965	it's own family.
		966
		967	=over
		968
		969	=item db_set $family => $subkey [=> $value]
		970
		971	Sets (or replaces) a key to the database - if C<$value> is omitted,
		972	C<undef> is used instead.
		973
		974	=item db_del $family => $subkey...
		975
		976	Deletes one or more subkeys from the database family.
		977
		978	=item $guard = db_reg $family => $subkey [=> $value]
		979
		980	Sets the key on the database and returns a guard. When the guard is
		981	destroyed, the key is deleted from the database. If C<$value> is missing,
		982	then C<undef> is used.
		983
		984	=item db_family $family => $cb->(\%familyhash)
		985
		986	Queries the named database C<$family> and call the callback with the
		987	family represented as a hash. You can keep and freely modify the hash.
		988
		989	=item db_keys $family => $cb->(\@keys)
		990
		991	Same as C<db_family>, except it only queries the family I<subkeys> and passes
		992	them as array reference to the callback.
		993
		994	=item db_values $family => $cb->(\@values)
		995
		996	Same as C<db_family>, except it only queries the family I<values> and passes them
		997	as array reference to the callback.
		998
		999	=item $guard = db_mon $family => $cb->($familyhash, \@added, \@changed, \@deleted)
		1000
		1001	Creates a monitor on the given database family. Each time a key is set
		1002	or or is deleted the callback is called with a hash containing the
		1003	database family and three lists of added, changed and deleted subkeys,
		1004	respectively. If no keys have changed then the array reference might be
		1005	C<undef> or even missing.
		1006
		1007	If not called in void context, a guard object is returned that, when
		1008	destroyed, stops the monitor.
		1009
		1010	The family hash reference and the key arrays belong to AnyEvent::MP and
		1011	B<must not be modified or stored> by the callback. When in doubt, make a
		1012	copy.
		1013
		1014	As soon as possible after the monitoring starts, the callback will be
		1015	called with the intiial contents of the family, even if it is empty,
		1016	i.e. there will always be a timely call to the callback with the current
		1017	contents.
		1018
		1019	It is possible that the callback is called with a change event even though
		1020	the subkey is already present and the value has not changed.
		1021
		1022	The monitoring stops when the guard object is destroyed.
		1023
		1024	Example: on every change to the family "mygroup", print out all keys.
		1025
		1026	my $guard = db_mon mygroup => sub {
		1027	my ($family, $a, $c, $d) = @_;
		1028	print "mygroup members: ", (join " ", keys %$family), "\n";
		1029	};
		1030
		1031	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1032
		1033	my $guard; $guard = db_mon My::Module::workers => sub {
		1034	my ($family, $a, $c, $d) = @_;
		1035	return unless %$family;
		1036	undef $guard;
		1037	print "My::Module::workers now nonempty\n";
		1038	};
		1039
		1040	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		1041
		1042	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		1043	my ($family, $a, $c, $d) = @_;
		1044
		1045	print "+$_=$family->{$_}\n" for @$a;
		1046	print "*$_=$family->{$_}\n" for @$c;
		1047	print "-$_=$family->{$_}\n" for @$d;
		1048	};
		1049
		1050	=cut
683		1051
684	=back	1052	=back
685		1053
686	=head1 AnyEvent::MP vs. Distributed Erlang	1054	=head1 AnyEvent::MP vs. Distributed Erlang
687		1055
688	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	1056	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
689	== aemp node, Erlang process == aemp port), so many of the documents and	1057	== aemp node, Erlang process == aemp port), so many of the documents and
690	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	1058	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
691	sample:	1059	sample:
692		1060
693	http://www.Erlang.se/doc/programming_rules.shtml	1061	http://www.erlang.se/doc/programming_rules.shtml
694	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	1062	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
695	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	1063	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
696	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	1064	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
697		1065
698	Despite the similarities, there are also some important differences:	1066	Despite the similarities, there are also some important differences:
699		1067
700	=over 4	1068	=over 4
701		1069
702	=item * Node references contain the recipe on how to contact them.	1070	=item * Node IDs are arbitrary strings in AEMP.
703		1071
704	Erlang relies on special naming and DNS to work everywhere in the	1072	Erlang relies on special naming and DNS to work everywhere in the same
705	same way. AEMP relies on each node knowing it's own address(es), with	1073	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
706	convenience functionality.	1074	configuration or DNS), and possibly the addresses of some seed nodes, but
707		1075	will otherwise discover other nodes (and their IDs) itself.
708	This means that AEMP requires a less tightly controlled environment at the
709	cost of longer node references and a slightly higher management overhead.
710		1076
711	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP	1077	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
712	uses "local ports are like remote ports".	1078	uses "local ports are like remote ports".
713		1079
714	The failure modes for local ports are quite different (runtime errors	1080	The failure modes for local ports are quite different (runtime errors
…		…
723	ports being the special case/exception, where transport errors cannot	1089	ports being the special case/exception, where transport errors cannot
724	occur.	1090	occur.
725		1091
726	=item * Erlang uses processes and a mailbox, AEMP does not queue.	1092	=item * Erlang uses processes and a mailbox, AEMP does not queue.
727		1093
728	Erlang uses processes that selectively receive messages, and therefore	1094	Erlang uses processes that selectively receive messages out of order, and
729	needs a queue. AEMP is event based, queuing messages would serve no	1095	therefore needs a queue. AEMP is event based, queuing messages would serve
730	useful purpose. For the same reason the pattern-matching abilities of	1096	no useful purpose. For the same reason the pattern-matching abilities
731	AnyEvent::MP are more limited, as there is little need to be able to	1097	of AnyEvent::MP are more limited, as there is little need to be able to
732	filter messages without dequeing them.	1098	filter messages without dequeuing them.
733		1099
734	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	1100	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1101	being event-based, while Erlang is process-based.
		1102
		1103	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1104	top of AEMP and Coro threads.
735		1105
736	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1106	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
737		1107
738	Sending messages in Erlang is synchronous and blocks the process (and	1108	Sending messages in Erlang is synchronous and blocks the process until
		1109	a conenction has been established and the message sent (and so does not
739	so does not need a queue that can overflow). AEMP sends are immediate,	1110	need a queue that can overflow). AEMP sends return immediately, connection
740	connection establishment is handled in the background.	1111	establishment is handled in the background.
741		1112
742	=item * Erlang suffers from silent message loss, AEMP does not.	1113	=item * Erlang suffers from silent message loss, AEMP does not.
743		1114
744	Erlang makes few guarantees on messages delivery - messages can get lost	1115	Erlang implements few guarantees on messages delivery - messages can get
745	without any of the processes realising it (i.e. you send messages a, b,	1116	lost without any of the processes realising it (i.e. you send messages a,
746	and c, and the other side only receives messages a and c).	1117	b, and c, and the other side only receives messages a and c).
747		1118
748	AEMP guarantees correct ordering, and the guarantee that there are no	1119	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1120	guarantee that after one message is lost, all following ones sent to the
		1121	same port are lost as well, until monitoring raises an error, so there are
749	holes in the message sequence.	1122	no silent "holes" in the message sequence.
750		1123
751	=item * In Erlang, processes can be declared dead and later be found to be	1124	If you want your software to be very reliable, you have to cope with
752	alive.	1125	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
753		1126	simply tries to work better in common error cases, such as when a network
754	In Erlang it can happen that a monitored process is declared dead and	1127	link goes down.
755	linked processes get killed, but later it turns out that the process is
756	still alive - and can receive messages.
757
758	In AEMP, when port monitoring detects a port as dead, then that port will
759	eventually be killed - it cannot happen that a node detects a port as dead
760	and then later sends messages to it, finding it is still alive.
761		1128
762	=item * Erlang can send messages to the wrong port, AEMP does not.	1129	=item * Erlang can send messages to the wrong port, AEMP does not.
763		1130
764	In Erlang it is quite likely that a node that restarts reuses a process ID	1131	In Erlang it is quite likely that a node that restarts reuses an Erlang
765	known to other nodes for a completely different process, causing messages	1132	process ID known to other nodes for a completely different process,
766	destined for that process to end up in an unrelated process.	1133	causing messages destined for that process to end up in an unrelated
		1134	process.
767		1135
768	AEMP never reuses port IDs, so old messages or old port IDs floating	1136	AEMP does not reuse port IDs, so old messages or old port IDs floating
769	around in the network will not be sent to an unrelated port.	1137	around in the network will not be sent to an unrelated port.
770		1138
771	=item * Erlang uses unprotected connections, AEMP uses secure	1139	=item * Erlang uses unprotected connections, AEMP uses secure
772	authentication and can use TLS.	1140	authentication and can use TLS.
773		1141
774	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1142	AEMP can use a proven protocol - TLS - to protect connections and
775	securely authenticate nodes.	1143	securely authenticate nodes.
776		1144
777	=item * The AEMP protocol is optimised for both text-based and binary	1145	=item * The AEMP protocol is optimised for both text-based and binary
778	communications.	1146	communications.
779		1147
780	The AEMP protocol, unlike the Erlang protocol, supports both	1148	The AEMP protocol, unlike the Erlang protocol, supports both programming
781	language-independent text-only protocols (good for debugging) and binary,	1149	language independent text-only protocols (good for debugging), and binary,
782	language-specific serialisers (e.g. Storable).	1150	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1151	used, the protocol is actually completely text-based.
783		1152
784	It has also been carefully designed to be implementable in other languages	1153	It has also been carefully designed to be implementable in other languages
785	with a minimum of work while gracefully degrading fucntionality to make the	1154	with a minimum of work while gracefully degrading functionality to make the
786	protocol simple.	1155	protocol simple.
787		1156
788	=item * AEMP has more flexible monitoring options than Erlang.	1157	=item * AEMP has more flexible monitoring options than Erlang.
789		1158
790	In Erlang, you can chose to receive I<all> exit signals as messages	1159	In Erlang, you can chose to receive I<all> exit signals as messages or
791	or I<none>, there is no in-between, so monitoring single processes is	1160	I<none>, there is no in-between, so monitoring single Erlang processes is
792	difficult to implement. Monitoring in AEMP is more flexible than in	1161	difficult to implement.
793	Erlang, as one can choose between automatic kill, exit message or callback	1162
794	on a per-process basis.	1163	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1164	between automatic kill, exit message or callback on a per-port basis.
795		1165
796	=item * Erlang tries to hide remote/local connections, AEMP does not.	1166	=item * Erlang tries to hide remote/local connections, AEMP does not.
797		1167
798	Monitoring in Erlang is not an indicator of process death/crashes,	1168	Monitoring in Erlang is not an indicator of process death/crashes, in the
799	as linking is (except linking is unreliable in Erlang).	1169	same way as linking is (except linking is unreliable in Erlang).
800		1170
801	In AEMP, you don't "look up" registered port names or send to named ports	1171	In AEMP, you don't "look up" registered port names or send to named ports
802	that might or might not be persistent. Instead, you normally spawn a port	1172	that might or might not be persistent. Instead, you normally spawn a port
803	on the remote node. The init function monitors the you, and you monitor	1173	on the remote node. The init function monitors you, and you monitor the
804	the remote port. Since both monitors are local to the node, they are much	1174	remote port. Since both monitors are local to the node, they are much more
805	more reliable.	1175	reliable (no need for C<spawn_link>).
806		1176
807	This also saves round-trips and avoids sending messages to the wrong port	1177	This also saves round-trips and avoids sending messages to the wrong port
808	(hard to do in Erlang).	1178	(hard to do in Erlang).
809		1179
810	=back	1180	=back
811		1181
812	=head1 RATIONALE	1182	=head1 RATIONALE
813		1183
814	=over 4	1184	=over 4
815		1185
816	=item Why strings for ports and noderefs, why not objects?	1186	=item Why strings for port and node IDs, why not objects?
817		1187
818	We considered "objects", but found that the actual number of methods	1188	We considered "objects", but found that the actual number of methods
819	thatc an be called are very low. Since port IDs and noderefs travel over	1189	that can be called are quite low. Since port and node IDs travel over
820	the network frequently, the serialising/deserialising would add lots of	1190	the network frequently, the serialising/deserialising would add lots of
821	overhead, as well as having to keep a proxy object.	1191	overhead, as well as having to keep a proxy object everywhere.
822		1192
823	Strings can easily be printed, easily serialised etc. and need no special	1193	Strings can easily be printed, easily serialised etc. and need no special
824	procedures to be "valid".	1194	procedures to be "valid".
825		1195
826	And a a miniport consists of a single closure stored in a global hash - it	1196	And as a result, a port with just a default receiver consists of a single
827	can't become much cheaper.	1197	code reference stored in a global hash - it can't become much cheaper.
828		1198
829	=item Why favour JSON, why not real serialising format such as Storable?	1199	=item Why favour JSON, why not a real serialising format such as Storable?
830		1200
831	In fact, any AnyEvent::MP node will happily accept Storable as framing	1201	In fact, any AnyEvent::MP node will happily accept Storable as framing
832	format, but currently there is no way to make a node use Storable by	1202	format, but currently there is no way to make a node use Storable by
833	default.	1203	default (although all nodes will accept it).
834		1204
835	The default framing protocol is JSON because a) JSON::XS is many times	1205	The default framing protocol is JSON because a) JSON::XS is many times
836	faster for small messages and b) most importantly, after years of	1206	faster for small messages and b) most importantly, after years of
837	experience we found that object serialisation is causing more problems	1207	experience we found that object serialisation is causing more problems
838	than it gains: Just like function calls, objects simply do not travel	1208	than it solves: Just like function calls, objects simply do not travel
839	easily over the network, mostly because they will always be a copy, so you	1209	easily over the network, mostly because they will always be a copy, so you
840	always have to re-think your design.	1210	always have to re-think your design.
841		1211
842	Keeping your messages simple, concentrating on data structures rather than	1212	Keeping your messages simple, concentrating on data structures rather than
843	objects, will keep your messages clean, tidy and efficient.	1213	objects, will keep your messages clean, tidy and efficient.
844		1214
845	=back	1215	=back
846		1216
847	=head1 SEE ALSO	1217	=head1 SEE ALSO
848		1218
		1219	L<AnyEvent::MP::Intro> - a gentle introduction.
		1220
		1221	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1222
		1223	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1224	your applications.
		1225
		1226	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1227
		1228	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1229	all nodes.
		1230
849	L<AnyEvent>.	1231	L<AnyEvent>.
850		1232
851	=head1 AUTHOR	1233	=head1 AUTHOR
852		1234
853	Marc Lehmann <schmorp@schmorp.de>	1235	Marc Lehmann <schmorp@schmorp.de>

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Revision 1.134 by root, Mon Mar 12 14:47:23 2012 UTC