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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.64 by root, Fri Aug 28 00:58:44 2009 UTC vs.
Revision 1.137 by root, Wed Mar 21 23:48:39 2012 UTC

…		…
1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent::MP - multi-processing/message-passing framework	3	AnyEvent::MP - erlang-style multi-processing/message-passing framework
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::MP;	7	use AnyEvent::MP;
8		8
9	$NODE # contains this node's noderef	9	$NODE # contains this node's node ID
10	NODE # returns this node's noderef	10	NODE # returns this node's node ID
11	NODE $port # returns the noderef of the port
12		11
13	$SELF # receiving/own port id in rcv callbacks	12	$SELF # receiving/own port id in rcv callbacks
14		13
15	# initialise the node so it can send/receive messages	14	# initialise the node so it can send/receive messages
16	initialise_node;	15	configure;
17		16
18	# ports are message endpoints	17	# ports are message destinations
19		18
20	# sending messages	19	# sending messages
21	snd $port, type => data...;	20	snd $port, type => data...;
22	snd $port, @msg;	21	snd $port, @msg;
23	snd @msg_with_first_element_being_a_port;	22	snd @msg_with_first_element_being_a_port;
24		23
25	# creating/using ports, the simple way	24	# creating/using ports, the simple way
26	my $simple_port = port { my @msg = @_; 0 };	25	my $simple_port = port { my @msg = @_ };
27		26
28	# creating/using ports, tagged message matching	27	# creating/using ports, tagged message matching
29	my $port = port;	28	my $port = port;
30	rcv $port, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
31	rcv $port, pong => sub { warn "pong received\n"; 0 };	30	rcv $port, pong => sub { warn "pong received\n" };
32		31
33	# create a port on another node	32	# create a port on another node
34	my $port = spawn $node, $initfunc, @initdata;	33	my $port = spawn $node, $initfunc, @initdata;
35		34
		35	# destroy a port again
		36	kil $port; # "normal" kill
		37	kil $port, my_error => "everything is broken"; # error kill
		38
36	# monitoring	39	# monitoring
37	mon $port, $cb->(@msg) # callback is invoked on death	40	mon $port, $cb->(@msg) # callback is invoked on death
38	mon $port, $otherport # kill otherport on abnormal death	41	mon $port, $localport # kill localport on abnormal death
39	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	};
40		51
41	=head1 CURRENT STATUS	52	=head1 CURRENT STATUS
42		53
		54	bin/aemp - stable.
43	AnyEvent::MP - stable API, should work	55	AnyEvent::MP - stable API, should work.
44	AnyEvent::MP::Intro - outdated	56	AnyEvent::MP::Intro - explains most concepts.
45	AnyEvent::MP::Kernel - WIP
46	AnyEvent::MP::Transport - mostly stable	57	AnyEvent::MP::Kernel - mostly stable API.
47		58	AnyEvent::MP::Global - stable API.
48	stay tuned.
49		59
50	=head1 DESCRIPTION	60	=head1 DESCRIPTION
51		61
52	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
53		63
54	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
55	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
56		66
57	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	67	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
58	manual page.	68	manual page and the examples under F<eg/>.
59
60	At the moment, this module family is severly broken and underdocumented,
61	so do not use. This was uploaded mainly to reserve the CPAN namespace -
62	stay tuned!
63		69
64	=head1 CONCEPTS	70	=head1 CONCEPTS
65		71
66	=over 4	72	=over 4
67		73
68	=item port	74	=item port
69		75
70	A port is something you can send messages to (with the C<snd> function).	76	Not to be confused with a TCP port, a "port" is something you can send
		77	messages to (with the C<snd> function).
71		78
72	Ports allow you to register C<rcv> handlers that can match all or just	79	Ports allow you to register C<rcv> handlers that can match all or just
73	some messages. Messages send to ports will not be queued, regardless of	80	some messages. Messages send to ports will not be queued, regardless of
74	anything was listening for them or not.	81	anything was listening for them or not.
75		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
76	=item port ID - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
77		86
78	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<#>)
79	separator, and a port name (a printable string of unspecified format). An	88	as separator, and a port name (a printable string of unspecified
80	exception is the the node port, whose ID is identical to its node	89	format created by AnyEvent::MP).
81	reference.
82		90
83	=item node	91	=item node
84		92
85	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,
86	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
87	ports.	95	ports.
88		96
89	Nodes are either private (single-process only), slaves (can only talk to	97	Nodes are either public (have one or more listening ports) or private
90	public nodes, but do not need an open port) or public nodes (connectable	98	(no listening ports). Private nodes cannot talk to other private nodes
91	from any other node).	99	currently, but all nodes can talk to public nodes.
92		100
		101	Nodes is represented by (printable) strings called "node IDs".
		102
93	=item node ID - C<[a-za-Z0-9_\-.:]+>	103	=item node ID - C<[A-Za-z0-9_\-.:]*>
94		104
95	A node ID is a string that uniquely identifies the node within a	105	A node ID is a string that uniquely identifies the node within a
96	network. Depending on the configuration used, node IDs can look like a	106	network. Depending on the configuration used, node IDs can look like a
97	hostname, a hostname and a port, or a random string. AnyEvent::MP itself	107	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
98	doesn't interpret node IDs in any way.	108	doesn't interpret node IDs in any way except to uniquely identify a node.
99		109
100	=item binds - C<ip:port>	110	=item binds - C<ip:port>
101		111
102	Nodes can only talk to each other by creating some kind of connection to	112	Nodes can only talk to each other by creating some kind of connection to
103	each other. To do this, nodes should listen on one or more local transport	113	each other. To do this, nodes should listen on one or more local transport
		114	endpoints - binds.
		115
104	endpoints - binds. Currently, only standard C<ip:port> specifications can	116	Currently, only standard C<ip:port> specifications can be used, which
105	be used, which specify TCP ports to listen on.	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.
106		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
107	=item seeds - C<host:port>	149	=item seed IDs - C<host:port>
108		150
109	When a node starts, it knows nothing about the network. To teach the node	151	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
110	about the network it first has to contact some other node within the	152	TCP port) of nodes that should be used as seed nodes.
111	network. This node is called a seed.
112		153
113	Seeds are transport endpoint(s) of as many nodes as one wants. Those nodes	154	=item global nodes
114	are expected to be long-running, and at least one of those should always	155
115	be available. When nodes run out of connections (e.g. due to a network	156	An AEMP network needs a discovery service - nodes need to know how to
116	error), they try to re-establish connections to some seednodes again to	157	connect to other nodes they only know by name. In addition, AEMP offers a
117	join the network.	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).
118		170
119	=back	171	=back
120		172
121	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
122		174
124		176
125	=cut	177	=cut
126		178
127	package AnyEvent::MP;	179	package AnyEvent::MP;
128		180
		181	use AnyEvent::MP::Config ();
129	use AnyEvent::MP::Kernel;	182	use AnyEvent::MP::Kernel;
		183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
130		184
131	use common::sense;	185	use common::sense;
132		186
133	use Carp ();	187	use Carp ();
134		188
135	use AE ();	189	use AE ();
		190	use Guard ();
136		191
137	use base "Exporter";	192	use base "Exporter";
138		193
139	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
140		195
141	our @EXPORT = qw(	196	our @EXPORT = qw(
142	NODE $NODE *SELF node_of after	197	NODE $NODE *SELF node_of after
143	resolve_node initialise_node	198	configure
144	snd rcv mon mon_guard kil reg psub spawn	199	snd rcv mon mon_guard kil psub peval spawn cal
145	port	200	port
		201	db_set db_del db_reg
		202	db_mon db_family db_keys db_values
146	);	203	);
147		204
148	our $SELF;	205	our $SELF;
149		206
150	sub _self_die() {	207	sub _self_die() {
…		…
153	kil $SELF, die => $msg;	210	kil $SELF, die => $msg;
154	}	211	}
155		212
156	=item $thisnode = NODE / $NODE	213	=item $thisnode = NODE / $NODE
157		214
158	The C<NODE> function returns, and the C<$NODE> variable contains the node	215	The C<NODE> function returns, and the C<$NODE> variable contains, the node
159	ID of the node running in the current process. This value is initialised by	216	ID of the node running in the current process. This value is initialised by
160	a call to C<initialise_node>.	217	a call to C<configure>.
161		218
162	=item $nodeid = node_of $port	219	=item $nodeid = node_of $port
163		220
164	Extracts and returns the node ID part from a port ID or a node ID.	221	Extracts and returns the node ID from a port ID or a node ID.
165		222
166	=item initialise_node $profile_name	223	=item configure $profile, key => value...
		224
		225	=item configure key => value...
167		226
168	Before a node can talk to other nodes on the network (i.e. enter	227	Before a node can talk to other nodes on the network (i.e. enter
169	"distributed mode") it has to initialise itself - the minimum a node needs	228	"distributed mode") it has to configure itself - the minimum a node needs
170	to know is its own name, and optionally it should know the addresses of	229	to know is its own name, and optionally it should know the addresses of
171	some other nodes in the network to discover other nodes.	230	some other nodes in the network to discover other nodes.
172		231
173	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
174	never) before calling other AnyEvent::MP functions.	233	never) before calling other AnyEvent::MP functions.
175		234
176	The first argument is a profile name. If it is C<undef> or missing, then	235	The key/value pairs are basically the same ones as documented for the
177	the current nodename will be used instead (i.e. F<uname -n>).	236	F<aemp> command line utility (sans the set/del prefix), with these additions:
178		237
		238	=over 4
		239
		240	=item norc => $boolean (default false)
		241
		242	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
		243	be consulted - all configuraiton options must be specified in the
		244	C<configure> call.
		245
		246	=item force => $boolean (default false)
		247
		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.
		251
		252	=item secure => $pass->(@msg)
		253
		254	In addition to specifying a boolean, you can specify a code reference that
		255	is called for every code execution attempt - the execution request is
		256	granted iff the callback returns a true value.
		257
		258	Most of the time the callback should look only at
		259	C<$AnyEvent::MP::Kernel::SRCNODE> to make a decision, and not at the
		260	actual message (which can be about anything, and is mostly provided for
		261	diagnostic purposes).
		262
		263	See F<semp setsecure> for more info.
		264
		265	=back
		266
		267	=over 4
		268
		269	=item step 1, gathering configuration from profiles
		270
179	The function then looks up the profile in the aemp configuration (see the	271	The function first looks up a profile in the aemp configuration (see the
180	L<aemp> commandline utility).	272	L<aemp> commandline utility). The profile name can be specified via the
		273	named C<profile> parameter or can simply be the first parameter). If it is
		274	missing, then the nodename (F<uname -n>) will be used as profile name.
		275
		276	The profile data is then gathered as follows:
		277
		278	First, all remaining key => value pairs (all of which are conveniently
		279	undocumented at the moment) will be interpreted as configuration
		280	data. Then they will be overwritten by any values specified in the global
		281	default configuration (see the F<aemp> utility), then the chain of
		282	profiles chosen by the profile name (and any C<parent> attributes).
		283
		284	That means that the values specified in the profile have highest priority
		285	and the values specified directly via C<configure> have lowest priority,
		286	and can only be used to specify defaults.
181		287
182	If the profile specifies a node ID, then this will become the node ID of	288	If the profile specifies a node ID, then this will become the node ID of
183	this process. If not, then the profile name will be used as node ID. The	289	this process. If not, then the profile name will be used as node ID, with
184	special node ID of C<anon/> will be replaced by a random node ID.	290	a unique randoms tring (C</%u>) appended.
		291
		292	The node ID can contain some C<%> sequences that are expanded: C<%n>
		293	is expanded to the local nodename, C<%u> is replaced by a random
		294	strign to make the node unique. For example, the F<aemp> commandline
		295	utility uses C<aemp/%n/%u> as nodename, which might expand to
		296	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		297
		298	=item step 2, bind listener sockets
185		299
186	The next step is to look up the binds in the profile, followed by binding	300	The next step is to look up the binds in the profile, followed by binding
187	aemp protocol listeners on all binds specified (it is possible and valid	301	aemp protocol listeners on all binds specified (it is possible and valid
188	to have no binds, meaning that the node cannot be contacted form the	302	to have no binds, meaning that the node cannot be contacted form the
189	outside. This means the node cannot talk to other nodes that also have no	303	outside. This means the node cannot talk to other nodes that also have no
190	binds, but it can still talk to all "normal" nodes).	304	binds, but it can still talk to all "normal" nodes).
191		305
192	If the profile does not specify a binds list, then the node ID will be	306	If the profile does not specify a binds list, then a default of C<*> is
193	treated as if it were of the form C<host:port>, which will be resolved and	307	used, meaning the node will bind on a dynamically-assigned port on every
194	used as binds list.	308	local IP address it finds.
195		309
		310	=item step 3, connect to seed nodes
		311
196	Lastly, the seeds list from the profile is passed to the	312	As the last step, the seed ID list from the profile is passed to the
197	L<AnyEvent::MP::Global> module, which will then use it to keep	313	L<AnyEvent::MP::Global> module, which will then use it to keep
198	connectivity with at least on of those seed nodes at any point in time.	314	connectivity with at least one node at any point in time.
199		315
200	Example: become a distributed node listening on the guessed noderef, or	316	=back
201	the one specified via C<aemp> for the current node. This should be the	317
		318	Example: become a distributed node using the local node name as profile.
202	most common form of invocation for "daemon"-type nodes.	319	This should be the most common form of invocation for "daemon"-type nodes.
203		320
204	initialise_node;	321	configure
205		322
206	Example: become an anonymous node. This form is often used for commandline	323	Example: become a semi-anonymous node. This form is often used for
207	clients.	324	commandline clients.
208		325
209	initialise_node "anon/";	326	configure nodeid => "myscript/%n/%u";
210		327
211	Example: become a distributed node. If there is no profile of the given	328	Example: configure a node using a profile called seed, which is suitable
212	name, or no binds list was specified, resolve C<localhost:4044> and bind	329	for a seed node as it binds on all local addresses on a fixed port (4040,
213	on the resulting addresses.	330	customary for aemp).
214		331
215	initialise_node "localhost:4044";	332	# use the aemp commandline utility
		333	# aemp profile seed binds '*:4040'
		334
		335	# then use it
		336	configure profile => "seed";
		337
		338	# or simply use aemp from the shell again:
		339	# aemp run profile seed
		340
		341	# or provide a nicer-to-remember nodeid
		342	# aemp run profile seed nodeid "$(hostname)"
216		343
217	=item $SELF	344	=item $SELF
218		345
219	Contains the current port id while executing C<rcv> callbacks or C<psub>	346	Contains the current port id while executing C<rcv> callbacks or C<psub>
220	blocks.	347	blocks.
221		348
222	=item SELF, %SELF, @SELF...	349	=item *SELF, SELF, %SELF, @SELF...
223		350
224	Due to some quirks in how perl exports variables, it is impossible to	351	Due to some quirks in how perl exports variables, it is impossible to
225	just export C<$SELF>, all the symbols called C<SELF> are exported by this	352	just export C<$SELF>, all the symbols named C<SELF> are exported by this
226	module, but only C<$SELF> is currently used.	353	module, but only C<$SELF> is currently used.
227		354
228	=item snd $port, type => @data	355	=item snd $port, type => @data
229		356
230	=item snd $port, @msg	357	=item snd $port, @msg
231		358
232	Send the given message to the given port ID, which can identify either	359	Send the given message to the given port, which can identify either a
233	a local or a remote port, and must be a port ID.	360	local or a remote port, and must be a port ID.
234		361
235	While the message can be about anything, it is highly recommended to use a	362	While the message can be almost anything, it is highly recommended to
236	string as first element (a port ID, or some word that indicates a request	363	use a string as first element (a port ID, or some word that indicates a
237	type etc.).	364	request type etc.) and to consist if only simple perl values (scalars,
		365	arrays, hashes) - if you think you need to pass an object, think again.
238		366
239	The message data effectively becomes read-only after a call to this	367	The message data logically becomes read-only after a call to this
240	function: modifying any argument is not allowed and can cause many	368	function: modifying any argument (or values referenced by them) is
241	problems.	369	forbidden, as there can be considerable time between the call to C<snd>
		370	and the time the message is actually being serialised - in fact, it might
		371	never be copied as within the same process it is simply handed to the
		372	receiving port.
242		373
243	The type of data you can transfer depends on the transport protocol: when	374	The type of data you can transfer depends on the transport protocol: when
244	JSON is used, then only strings, numbers and arrays and hashes consisting	375	JSON is used, then only strings, numbers and arrays and hashes consisting
245	of those are allowed (no objects). When Storable is used, then anything	376	of those are allowed (no objects). When Storable is used, then anything
246	that Storable can serialise and deserialise is allowed, and for the local	377	that Storable can serialise and deserialise is allowed, and for the local
247	node, anything can be passed.	378	node, anything can be passed. Best rely only on the common denominator of
		379	these.
248		380
249	=item $local_port = port	381	=item $local_port = port
250		382
251	Create a new local port object and returns its port ID. Initially it has	383	Create a new local port object and returns its port ID. Initially it has
252	no callbacks set and will throw an error when it receives messages.	384	no callbacks set and will throw an error when it receives messages.
…		…
271		403
272	=cut	404	=cut
273		405
274	sub rcv($@);	406	sub rcv($@);
275		407
276	sub _kilme {	408	my $KILME = sub {
277	die "received message on port without callback";	409	(my $tag = substr $_[0], 0, 30) =~ s/([\x20-\x7e])/./g;
278	}	410	kil $SELF, unhandled_message => "no callback found for message '$tag'";
		411	};
279		412
280	sub port(;&) {	413	sub port(;&) {
281	my $id = "$UNIQ." . $ID++;	414	my $id = $UNIQ . ++$ID;
282	my $port = "$NODE#$id";	415	my $port = "$NODE#$id";
283		416
284	rcv $port, shift \|\| \&_kilme;	417	rcv $port, shift \|\| $KILME;
285		418
286	$port	419	$port
287	}	420	}
288		421
289	=item rcv $local_port, $callback->(@msg)	422	=item rcv $local_port, $callback->(@msg)
…		…
294		427
295	The global C<$SELF> (exported by this module) contains C<$port> while	428	The global C<$SELF> (exported by this module) contains C<$port> while
296	executing the callback. Runtime errors during callback execution will	429	executing the callback. Runtime errors during callback execution will
297	result in the port being C<kil>ed.	430	result in the port being C<kil>ed.
298		431
299	The default callback received all messages not matched by a more specific	432	The default callback receives all messages not matched by a more specific
300	C<tag> match.	433	C<tag> match.
301		434
302	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...	435	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
303		436
304	Register (or replace) callbacks to be called on messages starting with the	437	Register (or replace) callbacks to be called on messages starting with the
…		…
325	msg1 => sub { ... },	458	msg1 => sub { ... },
326	...	459	...
327	;	460	;
328		461
329	Example: temporarily register a rcv callback for a tag matching some port	462	Example: temporarily register a rcv callback for a tag matching some port
330	(e.g. for a rpc reply) and unregister it after a message was received.	463	(e.g. for an rpc reply) and unregister it after a message was received.
331		464
332	rcv $port, $otherport => sub {	465	rcv $port, $otherport => sub {
333	my @reply = @_;	466	my @reply = @_;
334		467
335	rcv $SELF, $otherport;	468	rcv $SELF, $otherport;
…		…
337		470
338	=cut	471	=cut
339		472
340	sub rcv($@) {	473	sub rcv($@) {
341	my $port = shift;	474	my $port = shift;
342	my ($noderef, $portid) = split /#/, $port, 2;	475	my ($nodeid, $portid) = split /#/, $port, 2;
343		476
344	$NODE{$noderef} == $NODE{""}	477	$NODE{$nodeid} == $NODE{""}
345	or Carp::croak "$port: rcv can only be called on local ports, caught";	478	or Carp::croak "$port: rcv can only be called on local ports, caught";
346		479
347	while (@_) {	480	while (@_) {
348	if (ref $_[0]) {	481	if (ref $_[0]) {
349	if (my $self = $PORT_DATA{$portid}) {	482	if (my $self = $PORT_DATA{$portid}) {
350	"AnyEvent::MP::Port" eq ref $self	483	"AnyEvent::MP::Port" eq ref $self
351	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	484	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
352		485
353	$self->[2] = shift;	486	$self->[0] = shift;
354	} else {	487	} else {
355	my $cb = shift;	488	my $cb = shift;
356	$PORT{$portid} = sub {	489	$PORT{$portid} = sub {
357	local $SELF = $port;	490	local $SELF = $port;
358	eval { &$cb }; _self_die if $@;	491	eval { &$cb }; _self_die if $@;
359	};	492	};
360	}	493	}
361	} elsif (defined $_[0]) {	494	} elsif (defined $_[0]) {
362	my $self = $PORT_DATA{$portid} \|\|= do {	495	my $self = $PORT_DATA{$portid} \|\|= do {
363	my $self = bless [$PORT{$port} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";	496	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
364		497
365	$PORT{$portid} = sub {	498	$PORT{$portid} = sub {
366	local $SELF = $port;	499	local $SELF = $port;
367		500
368	if (my $cb = $self->[1]{$_[0]}) {	501	if (my $cb = $self->[1]{$_[0]}) {
…		…
390	}	523	}
391		524
392	$port	525	$port
393	}	526	}
394		527
		528	=item peval $port, $coderef[, @args]
		529
		530	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		531	when the code throews an exception the C<$port> will be killed.
		532
		533	Any remaining args will be passed to the callback. Any return values will
		534	be returned to the caller.
		535
		536	This is useful when you temporarily want to execute code in the context of
		537	a port.
		538
		539	Example: create a port and run some initialisation code in it's context.
		540
		541	my $port = port { ... };
		542
		543	peval $port, sub {
		544	init
		545	or die "unable to init";
		546	};
		547
		548	=cut
		549
		550	sub peval($$) {
		551	local $SELF = shift;
		552	my $cb = shift;
		553
		554	if (wantarray) {
		555	my @res = eval { &$cb };
		556	_self_die if $@;
		557	@res
		558	} else {
		559	my $res = eval { &$cb };
		560	_self_die if $@;
		561	$res
		562	}
		563	}
		564
395	=item $closure = psub { BLOCK }	565	=item $closure = psub { BLOCK }
396		566
397	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	567	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
398	closure is executed, sets up the environment in the same way as in C<rcv>	568	closure is executed, sets up the environment in the same way as in C<rcv>
399	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.	569	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		570
		571	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		572	BLOCK }, @_ } >>.
400		573
401	This is useful when you register callbacks from C<rcv> callbacks:	574	This is useful when you register callbacks from C<rcv> callbacks:
402		575
403	rcv delayed_reply => sub {	576	rcv delayed_reply => sub {
404	my ($delay, @reply) = @_;	577	my ($delay, @reply) = @_;
…		…
428	$res	601	$res
429	}	602	}
430	}	603	}
431	}	604	}
432		605
433	=item $guard = mon $port, $cb->(@reason)	606	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
434		607
435	=item $guard = mon $port, $rcvport	608	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
436		609
437	=item $guard = mon $port	610	=item $guard = mon $port # kill $SELF when $port dies
438		611
439	=item $guard = mon $port, $rcvport, @msg	612	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
440		613
441	Monitor the given port and do something when the port is killed or	614	Monitor the given port and do something when the port is killed or
442	messages to it were lost, and optionally return a guard that can be used	615	messages to it were lost, and optionally return a guard that can be used
443	to stop monitoring again.	616	to stop monitoring again.
444
445	C<mon> effectively guarantees that, in the absence of hardware failures,
446	that after starting the monitor, either all messages sent to the port
447	will arrive, or the monitoring action will be invoked after possible
448	message loss has been detected. No messages will be lost "in between"
449	(after the first lost message no further messages will be received by the
450	port). After the monitoring action was invoked, further messages might get
451	delivered again.
452
453	Note that monitoring-actions are one-shot: once released, they are removed
454	and will not trigger again.
455		617
456	In the first form (callback), the callback is simply called with any	618	In the first form (callback), the callback is simply called with any
457	number of C<@reason> elements (no @reason means that the port was deleted	619	number of C<@reason> elements (no @reason means that the port was deleted
458	"normally"). Note also that I<< the callback B<must> never die >>, so use	620	"normally"). Note also that I<< the callback B<must> never die >>, so use
459	C<eval> if unsure.	621	C<eval> if unsure.
460		622
461	In the second form (another port given), the other port (C<$rcvport>)	623	In the second form (another port given), the other port (C<$rcvport>)
462	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	624	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
463	"normal" kils nothing happens, while under all other conditions, the other	625	"normal" kils nothing happens, while under all other conditions, the other
464	port is killed with the same reason.	626	port is killed with the same reason.
465		627
466	The third form (kill self) is the same as the second form, except that	628	The third form (kill self) is the same as the second form, except that
467	C<$rvport> defaults to C<$SELF>.	629	C<$rvport> defaults to C<$SELF>.
468		630
469	In the last form (message), a message of the form C<@msg, @reason> will be	631	In the last form (message), a message of the form C<@msg, @reason> will be
470	C<snd>.	632	C<snd>.
		633
		634	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		635	alert was raised), they are removed and will not trigger again.
471		636
472	As a rule of thumb, monitoring requests should always monitor a port from	637	As a rule of thumb, monitoring requests should always monitor a port from
473	a local port (or callback). The reason is that kill messages might get	638	a local port (or callback). The reason is that kill messages might get
474	lost, just like any other message. Another less obvious reason is that	639	lost, just like any other message. Another less obvious reason is that
475	even monitoring requests can get lost (for exmaple, when the connection	640	even monitoring requests can get lost (for example, when the connection
476	to the other node goes down permanently). When monitoring a port locally	641	to the other node goes down permanently). When monitoring a port locally
477	these problems do not exist.	642	these problems do not exist.
478		643
		644	C<mon> effectively guarantees that, in the absence of hardware failures,
		645	after starting the monitor, either all messages sent to the port will
		646	arrive, or the monitoring action will be invoked after possible message
		647	loss has been detected. No messages will be lost "in between" (after
		648	the first lost message no further messages will be received by the
		649	port). After the monitoring action was invoked, further messages might get
		650	delivered again.
		651
		652	Inter-host-connection timeouts and monitoring depend on the transport
		653	used. The only transport currently implemented is TCP, and AnyEvent::MP
		654	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		655	non-idle connection, and usually around two hours for idle connections).
		656
		657	This means that monitoring is good for program errors and cleaning up
		658	stuff eventually, but they are no replacement for a timeout when you need
		659	to ensure some maximum latency.
		660
479	Example: call a given callback when C<$port> is killed.	661	Example: call a given callback when C<$port> is killed.
480		662
481	mon $port, sub { warn "port died because of <@_>\n" };	663	mon $port, sub { warn "port died because of <@_>\n" };
482		664
483	Example: kill ourselves when C<$port> is killed abnormally.	665	Example: kill ourselves when C<$port> is killed abnormally.
…		…
489	mon $port, $self => "restart";	671	mon $port, $self => "restart";
490		672
491	=cut	673	=cut
492		674
493	sub mon {	675	sub mon {
494	my ($noderef, $port) = split /#/, shift, 2;	676	my ($nodeid, $port) = split /#/, shift, 2;
495		677
496	my $node = $NODE{$noderef} \|\| add_node $noderef;	678	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
497		679
498	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';	680	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
499		681
500	unless (ref $cb) {	682	unless (ref $cb) {
501	if (@_) {	683	if (@_) {
…		…
510	}	692	}
511		693
512	$node->monitor ($port, $cb);	694	$node->monitor ($port, $cb);
513		695
514	defined wantarray	696	defined wantarray
515	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	697	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
516	}	698	}
517		699
518	=item $guard = mon_guard $port, $ref, $ref...	700	=item $guard = mon_guard $port, $ref, $ref...
519		701
520	Monitors the given C<$port> and keeps the passed references. When the port	702	Monitors the given C<$port> and keeps the passed references. When the port
521	is killed, the references will be freed.	703	is killed, the references will be freed.
522		704
523	Optionally returns a guard that will stop the monitoring.	705	Optionally returns a guard that will stop the monitoring.
524		706
525	This function is useful when you create e.g. timers or other watchers and	707	This function is useful when you create e.g. timers or other watchers and
526	want to free them when the port gets killed:	708	want to free them when the port gets killed (note the use of C<psub>):
527		709
528	$port->rcv (start => sub {	710	$port->rcv (start => sub {
529	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	711	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
530	undef $timer if 0.9 < rand;	712	undef $timer if 0.9 < rand;
531	});	713	});
532	});	714	});
533		715
534	=cut	716	=cut
…		…
543		725
544	=item kil $port[, @reason]	726	=item kil $port[, @reason]
545		727
546	Kill the specified port with the given C<@reason>.	728	Kill the specified port with the given C<@reason>.
547		729
548	If no C<@reason> is specified, then the port is killed "normally" (linked	730	If no C<@reason> is specified, then the port is killed "normally" -
549	ports will not be kileld, or even notified).	731	monitor callback will be invoked, but the kil will not cause linked ports
		732	(C<mon $mport, $lport> form) to get killed.
550		733
551	Otherwise, linked ports get killed with the same reason (second form of	734	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
552	C<mon>, see below).	735	form) get killed with the same reason.
553		736
554	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	737	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
555	will be reported as reason C<< die => $@ >>.	738	will be reported as reason C<< die => $@ >>.
556		739
557	Transport/communication errors are reported as C<< transport_error =>	740	Transport/communication errors are reported as C<< transport_error =>
558	$message >>.	741	$message >>.
559		742
560	=cut	743	Common idioms:
		744
		745	# silently remove yourself, do not kill linked ports
		746	kil $SELF;
		747
		748	# report a failure in some detail
		749	kil $SELF, failure_mode_1 => "it failed with too high temperature";
		750
		751	# do not waste much time with killing, just die when something goes wrong
		752	open my $fh, "<file"
		753	or die "file: $!";
561		754
562	=item $port = spawn $node, $initfunc[, @initdata]	755	=item $port = spawn $node, $initfunc[, @initdata]
563		756
564	Creates a port on the node C<$node> (which can also be a port ID, in which	757	Creates a port on the node C<$node> (which can also be a port ID, in which
565	case it's the node where that port resides).	758	case it's the node where that port resides).
566		759
567	The port ID of the newly created port is return immediately, and it is	760	The port ID of the newly created port is returned immediately, and it is
568	permissible to immediately start sending messages or monitor the port.	761	possible to immediately start sending messages or to monitor the port.
569		762
570	After the port has been created, the init function is	763	After the port has been created, the init function is called on the remote
571	called. This function must be a fully-qualified function name	764	node, in the same context as a C<rcv> callback. This function must be a
572	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	765	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
573	program, use C<::name>.	766	specify a function in the main program, use C<::name>.
574		767
575	If the function doesn't exist, then the node tries to C<require>	768	If the function doesn't exist, then the node tries to C<require>
576	the package, then the package above the package and so on (e.g.	769	the package, then the package above the package and so on (e.g.
577	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	770	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
578	exists or it runs out of package names.	771	exists or it runs out of package names.
579		772
580	The init function is then called with the newly-created port as context	773	The init function is then called with the newly-created port as context
581	object (C<$SELF>) and the C<@initdata> values as arguments.	774	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		775	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		776	the port might not get created.
582		777
583	A common idiom is to pass your own port, monitor the spawned port, and	778	A common idiom is to pass a local port, immediately monitor the spawned
584	in the init function, monitor the original port. This two-way monitoring	779	port, and in the remote init function, immediately monitor the passed
585	ensures that both ports get cleaned up when there is a problem.	780	local port. This two-way monitoring ensures that both ports get cleaned up
		781	when there is a problem.
		782
		783	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		784	caller before C<spawn> returns (by delaying invocation when spawn is
		785	called for the local node).
586		786
587	Example: spawn a chat server port on C<$othernode>.	787	Example: spawn a chat server port on C<$othernode>.
588		788
589	# this node, executed from within a port context:	789	# this node, executed from within a port context:
590	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	790	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
605		805
606	sub _spawn {	806	sub _spawn {
607	my $port = shift;	807	my $port = shift;
608	my $init = shift;	808	my $init = shift;
609		809
		810	# rcv will create the actual port
610	local $SELF = "$NODE#$port";	811	local $SELF = "$NODE#$port";
611	eval {	812	eval {
612	&{ load_func $init }	813	&{ load_func $init }
613	};	814	};
614	_self_die if $@;	815	_self_die if $@;
615	}	816	}
616		817
617	sub spawn(@) {	818	sub spawn(@) {
618	my ($noderef, undef) = split /#/, shift, 2;	819	my ($nodeid, undef) = split /#/, shift, 2;
619		820
620	my $id = "$RUNIQ." . $ID++;	821	my $id = $RUNIQ . ++$ID;
621		822
622	$_[0] =~ /::/	823	$_[0] =~ /::/
623	or Carp::croak "spawn init function must be a fully-qualified name, caught";	824	or Carp::croak "spawn init function must be a fully-qualified name, caught";
624		825
625	snd_to_func $noderef, "AnyEvent::MP::_spawn" => $id, @_;	826	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
626		827
627	"$noderef#$id"	828	"$nodeid#$id"
628	}	829	}
		830
629		831
630	=item after $timeout, @msg	832	=item after $timeout, @msg
631		833
632	=item after $timeout, $callback	834	=item after $timeout, $callback
633		835
634	Either sends the given message, or call the given callback, after the	836	Either sends the given message, or call the given callback, after the
635	specified number of seconds.	837	specified number of seconds.
636		838
637	This is simply a utility function that come sin handy at times.	839	This is simply a utility function that comes in handy at times - the
		840	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		841	so it may go away in the future.
638		842
639	=cut	843	=cut
640		844
641	sub after($@) {	845	sub after($@) {
642	my ($timeout, @action) = @_;	846	my ($timeout, @action) = @_;
…		…
647	? $action[0]()	851	? $action[0]()
648	: snd @action;	852	: snd @action;
649	};	853	};
650	}	854	}
651		855
		856	#=item $cb2 = timeout $seconds, $cb[, @args]
		857
		858	=item cal $port, @msg, $callback[, $timeout]
		859
		860	A simple form of RPC - sends a message to the given C<$port> with the
		861	given contents (C<@msg>), but adds a reply port to the message.
		862
		863	The reply port is created temporarily just for the purpose of receiving
		864	the reply, and will be C<kil>ed when no longer needed.
		865
		866	A reply message sent to the port is passed to the C<$callback> as-is.
		867
		868	If an optional time-out (in seconds) is given and it is not C<undef>,
		869	then the callback will be called without any arguments after the time-out
		870	elapsed and the port is C<kil>ed.
		871
		872	If no time-out is given (or it is C<undef>), then the local port will
		873	monitor the remote port instead, so it eventually gets cleaned-up.
		874
		875	Currently this function returns the temporary port, but this "feature"
		876	might go in future versions unless you can make a convincing case that
		877	this is indeed useful for something.
		878
		879	=cut
		880
		881	sub cal(@) {
		882	my $timeout = ref $_[-1] ? undef : pop;
		883	my $cb = pop;
		884
		885	my $port = port {
		886	undef $timeout;
		887	kil $SELF;
		888	&$cb;
		889	};
		890
		891	if (defined $timeout) {
		892	$timeout = AE::timer $timeout, 0, sub {
		893	undef $timeout;
		894	kil $port;
		895	$cb->();
		896	};
		897	} else {
		898	mon $_[0], sub {
		899	kil $port;
		900	$cb->();
		901	};
		902	}
		903
		904	push @_, $port;
		905	&snd;
		906
		907	$port
		908	}
		909
		910	=back
		911
		912	=head1 DISTRIBUTED DATABASE
		913
		914	AnyEvent::MP comes with a simple distributed database. The database will
		915	be mirrored asynchronously on all global nodes. Other nodes bind to one
		916	of the global nodes for their needs. Every node has a "local database"
		917	which contains all the values that are set locally. All local databases
		918	are merged together to form the global database, which can be queried.
		919
		920	The database structure is that of a two-level hash - the database hash
		921	contains hashes which contain values, similarly to a perl hash of hashes,
		922	i.e.:
		923
		924	$DATABASE{$family}{$subkey} = $value
		925
		926	The top level hash key is called "family", and the second-level hash key
		927	is called "subkey" or simply "key".
		928
		929	The family must be alphanumeric, i.e. start with a letter and consist
		930	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		931	pretty much like Perl module names.
		932
		933	As the family namespace is global, it is recommended to prefix family names
		934	with the name of the application or module using it.
		935
		936	The subkeys must be non-empty strings, with no further restrictions.
		937
		938	The values should preferably be strings, but other perl scalars should
		939	work as well (such as C<undef>, arrays and hashes).
		940
		941	Every database entry is owned by one node - adding the same family/subkey
		942	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		943	but the result might be nondeterministic, i.e. the key might have
		944	different values on different nodes.
		945
		946	Different subkeys in the same family can be owned by different nodes
		947	without problems, and in fact, this is the common method to create worker
		948	pools. For example, a worker port for image scaling might do this:
		949
		950	db_set my_image_scalers => $port;
		951
		952	And clients looking for an image scaler will want to get the
		953	C<my_image_scalers> keys from time to time:
		954
		955	db_keys my_image_scalers => sub {
		956	@ports = @{ $_[0] };
		957	};
		958
		959	Or better yet, they want to monitor the database family, so they always
		960	have a reasonable up-to-date copy:
		961
		962	db_mon my_image_scalers => sub {
		963	@ports = keys %{ $_[0] };
		964	};
		965
		966	In general, you can set or delete single subkeys, but query and monitor
		967	whole families only.
		968
		969	If you feel the need to monitor or query a single subkey, try giving it
		970	it's own family.
		971
		972	=over
		973
		974	=item $guard = db_set $family => $subkey [=> $value]
		975
		976	Sets (or replaces) a key to the database - if C<$value> is omitted,
		977	C<undef> is used instead.
		978
		979	When called in non-void context, C<db_set> returns a guard that
		980	automatically calls C<db_del> when it is destroyed.
		981
		982	=item db_del $family => $subkey...
		983
		984	Deletes one or more subkeys from the database family.
		985
		986	=item $guard = db_reg $family => $port => $value
		987
		988	=item $guard = db_reg $family => $port
		989
		990	=item $guard = db_reg $family
		991
		992	Registers a port in the given family and optionally returns a guard to
		993	remove it.
		994
		995	This function basically does the same as:
		996
		997	db_set $family => $port => $value
		998
		999	Except that the port is monitored and automatically removed from the
		1000	database family when it is kil'ed.
		1001
		1002	If C<$value> is missing, C<undef> is used. If C<$port> is missing, then
		1003	C<$SELF> is used.
		1004
		1005	This function is most useful to register a port in some port group (which
		1006	is just another name for a database family), and have it removed when the
		1007	port is gone. This works best when the port is a local port.
		1008
		1009	=cut
		1010
		1011	sub db_reg($$;$) {
		1012	my $family = shift;
		1013	my $port = @_ ? shift : $SELF;
		1014
		1015	my $clr = sub { db_del $family => $port };
		1016	mon $port, $clr;
		1017
		1018	db_set $family => $port => $_[0];
		1019
		1020	defined wantarray
		1021	and &Guard::guard ($clr)
		1022	}
		1023
		1024	=item db_family $family => $cb->(\%familyhash)
		1025
		1026	Queries the named database C<$family> and call the callback with the
		1027	family represented as a hash. You can keep and freely modify the hash.
		1028
		1029	=item db_keys $family => $cb->(\@keys)
		1030
		1031	Same as C<db_family>, except it only queries the family I<subkeys> and passes
		1032	them as array reference to the callback.
		1033
		1034	=item db_values $family => $cb->(\@values)
		1035
		1036	Same as C<db_family>, except it only queries the family I<values> and passes them
		1037	as array reference to the callback.
		1038
		1039	=item $guard = db_mon $family => $cb->($familyhash, \@added, \@changed, \@deleted)
		1040
		1041	Creates a monitor on the given database family. Each time a key is set
		1042	or or is deleted the callback is called with a hash containing the
		1043	database family and three lists of added, changed and deleted subkeys,
		1044	respectively. If no keys have changed then the array reference might be
		1045	C<undef> or even missing.
		1046
		1047	If not called in void context, a guard object is returned that, when
		1048	destroyed, stops the monitor.
		1049
		1050	The family hash reference and the key arrays belong to AnyEvent::MP and
		1051	B<must not be modified or stored> by the callback. When in doubt, make a
		1052	copy.
		1053
		1054	As soon as possible after the monitoring starts, the callback will be
		1055	called with the intiial contents of the family, even if it is empty,
		1056	i.e. there will always be a timely call to the callback with the current
		1057	contents.
		1058
		1059	It is possible that the callback is called with a change event even though
		1060	the subkey is already present and the value has not changed.
		1061
		1062	The monitoring stops when the guard object is destroyed.
		1063
		1064	Example: on every change to the family "mygroup", print out all keys.
		1065
		1066	my $guard = db_mon mygroup => sub {
		1067	my ($family, $a, $c, $d) = @_;
		1068	print "mygroup members: ", (join " ", keys %$family), "\n";
		1069	};
		1070
		1071	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1072
		1073	my $guard; $guard = db_mon My::Module::workers => sub {
		1074	my ($family, $a, $c, $d) = @_;
		1075	return unless %$family;
		1076	undef $guard;
		1077	print "My::Module::workers now nonempty\n";
		1078	};
		1079
		1080	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		1081
		1082	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		1083	my ($family, $a, $c, $d) = @_;
		1084
		1085	print "+$_=$family->{$_}\n" for @$a;
		1086	print "*$_=$family->{$_}\n" for @$c;
		1087	print "-$_=$family->{$_}\n" for @$d;
		1088	};
		1089
		1090	=cut
		1091
652	=back	1092	=back
653		1093
654	=head1 AnyEvent::MP vs. Distributed Erlang	1094	=head1 AnyEvent::MP vs. Distributed Erlang
655		1095
656	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	1096	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
657	== aemp node, Erlang process == aemp port), so many of the documents and	1097	== aemp node, Erlang process == aemp port), so many of the documents and
658	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	1098	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
659	sample:	1099	sample:
660		1100
661	http://www.Erlang.se/doc/programming_rules.shtml	1101	http://www.erlang.se/doc/programming_rules.shtml
662	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	1102	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
663	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	1103	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
664	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	1104	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
665		1105
666	Despite the similarities, there are also some important differences:	1106	Despite the similarities, there are also some important differences:
667		1107
668	=over 4	1108	=over 4
669		1109
670	=item * Node references contain the recipe on how to contact them.	1110	=item * Node IDs are arbitrary strings in AEMP.
671		1111
672	Erlang relies on special naming and DNS to work everywhere in the	1112	Erlang relies on special naming and DNS to work everywhere in the same
673	same way. AEMP relies on each node knowing it's own address(es), with	1113	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
674	convenience functionality.	1114	configuration or DNS), and possibly the addresses of some seed nodes, but
675		1115	will otherwise discover other nodes (and their IDs) itself.
676	This means that AEMP requires a less tightly controlled environment at the
677	cost of longer node references and a slightly higher management overhead.
678		1116
679	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP	1117	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
680	uses "local ports are like remote ports".	1118	uses "local ports are like remote ports".
681		1119
682	The failure modes for local ports are quite different (runtime errors	1120	The failure modes for local ports are quite different (runtime errors
…		…
691	ports being the special case/exception, where transport errors cannot	1129	ports being the special case/exception, where transport errors cannot
692	occur.	1130	occur.
693		1131
694	=item * Erlang uses processes and a mailbox, AEMP does not queue.	1132	=item * Erlang uses processes and a mailbox, AEMP does not queue.
695		1133
696	Erlang uses processes that selectively receive messages, and therefore	1134	Erlang uses processes that selectively receive messages out of order, and
697	needs a queue. AEMP is event based, queuing messages would serve no	1135	therefore needs a queue. AEMP is event based, queuing messages would serve
698	useful purpose. For the same reason the pattern-matching abilities of	1136	no useful purpose. For the same reason the pattern-matching abilities
699	AnyEvent::MP are more limited, as there is little need to be able to	1137	of AnyEvent::MP are more limited, as there is little need to be able to
700	filter messages without dequeing them.	1138	filter messages without dequeuing them.
701		1139
702	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	1140	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1141	being event-based, while Erlang is process-based.
		1142
		1143	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1144	top of AEMP and Coro threads.
703		1145
704	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1146	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
705		1147
706	Sending messages in Erlang is synchronous and blocks the process (and	1148	Sending messages in Erlang is synchronous and blocks the process until
		1149	a conenction has been established and the message sent (and so does not
707	so does not need a queue that can overflow). AEMP sends are immediate,	1150	need a queue that can overflow). AEMP sends return immediately, connection
708	connection establishment is handled in the background.	1151	establishment is handled in the background.
709		1152
710	=item * Erlang suffers from silent message loss, AEMP does not.	1153	=item * Erlang suffers from silent message loss, AEMP does not.
711		1154
712	Erlang makes few guarantees on messages delivery - messages can get lost	1155	Erlang implements few guarantees on messages delivery - messages can get
713	without any of the processes realising it (i.e. you send messages a, b,	1156	lost without any of the processes realising it (i.e. you send messages a,
714	and c, and the other side only receives messages a and c).	1157	b, and c, and the other side only receives messages a and c).
715		1158
716	AEMP guarantees correct ordering, and the guarantee that there are no	1159	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1160	guarantee that after one message is lost, all following ones sent to the
		1161	same port are lost as well, until monitoring raises an error, so there are
717	holes in the message sequence.	1162	no silent "holes" in the message sequence.
718		1163
719	=item * In Erlang, processes can be declared dead and later be found to be	1164	If you want your software to be very reliable, you have to cope with
720	alive.	1165	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
721		1166	simply tries to work better in common error cases, such as when a network
722	In Erlang it can happen that a monitored process is declared dead and	1167	link goes down.
723	linked processes get killed, but later it turns out that the process is
724	still alive - and can receive messages.
725
726	In AEMP, when port monitoring detects a port as dead, then that port will
727	eventually be killed - it cannot happen that a node detects a port as dead
728	and then later sends messages to it, finding it is still alive.
729		1168
730	=item * Erlang can send messages to the wrong port, AEMP does not.	1169	=item * Erlang can send messages to the wrong port, AEMP does not.
731		1170
732	In Erlang it is quite likely that a node that restarts reuses a process ID	1171	In Erlang it is quite likely that a node that restarts reuses an Erlang
733	known to other nodes for a completely different process, causing messages	1172	process ID known to other nodes for a completely different process,
734	destined for that process to end up in an unrelated process.	1173	causing messages destined for that process to end up in an unrelated
		1174	process.
735		1175
736	AEMP never reuses port IDs, so old messages or old port IDs floating	1176	AEMP does not reuse port IDs, so old messages or old port IDs floating
737	around in the network will not be sent to an unrelated port.	1177	around in the network will not be sent to an unrelated port.
738		1178
739	=item * Erlang uses unprotected connections, AEMP uses secure	1179	=item * Erlang uses unprotected connections, AEMP uses secure
740	authentication and can use TLS.	1180	authentication and can use TLS.
741		1181
742	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1182	AEMP can use a proven protocol - TLS - to protect connections and
743	securely authenticate nodes.	1183	securely authenticate nodes.
744		1184
745	=item * The AEMP protocol is optimised for both text-based and binary	1185	=item * The AEMP protocol is optimised for both text-based and binary
746	communications.	1186	communications.
747		1187
748	The AEMP protocol, unlike the Erlang protocol, supports both	1188	The AEMP protocol, unlike the Erlang protocol, supports both programming
749	language-independent text-only protocols (good for debugging) and binary,	1189	language independent text-only protocols (good for debugging), and binary,
750	language-specific serialisers (e.g. Storable).	1190	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1191	used, the protocol is actually completely text-based.
751		1192
752	It has also been carefully designed to be implementable in other languages	1193	It has also been carefully designed to be implementable in other languages
753	with a minimum of work while gracefully degrading fucntionality to make the	1194	with a minimum of work while gracefully degrading functionality to make the
754	protocol simple.	1195	protocol simple.
755		1196
756	=item * AEMP has more flexible monitoring options than Erlang.	1197	=item * AEMP has more flexible monitoring options than Erlang.
757		1198
758	In Erlang, you can chose to receive I<all> exit signals as messages	1199	In Erlang, you can chose to receive I<all> exit signals as messages or
759	or I<none>, there is no in-between, so monitoring single processes is	1200	I<none>, there is no in-between, so monitoring single Erlang processes is
760	difficult to implement. Monitoring in AEMP is more flexible than in	1201	difficult to implement.
761	Erlang, as one can choose between automatic kill, exit message or callback	1202
762	on a per-process basis.	1203	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1204	between automatic kill, exit message or callback on a per-port basis.
763		1205
764	=item * Erlang tries to hide remote/local connections, AEMP does not.	1206	=item * Erlang tries to hide remote/local connections, AEMP does not.
765		1207
766	Monitoring in Erlang is not an indicator of process death/crashes,	1208	Monitoring in Erlang is not an indicator of process death/crashes, in the
767	as linking is (except linking is unreliable in Erlang).	1209	same way as linking is (except linking is unreliable in Erlang).
768		1210
769	In AEMP, you don't "look up" registered port names or send to named ports	1211	In AEMP, you don't "look up" registered port names or send to named ports
770	that might or might not be persistent. Instead, you normally spawn a port	1212	that might or might not be persistent. Instead, you normally spawn a port
771	on the remote node. The init function monitors the you, and you monitor	1213	on the remote node. The init function monitors you, and you monitor the
772	the remote port. Since both monitors are local to the node, they are much	1214	remote port. Since both monitors are local to the node, they are much more
773	more reliable.	1215	reliable (no need for C<spawn_link>).
774		1216
775	This also saves round-trips and avoids sending messages to the wrong port	1217	This also saves round-trips and avoids sending messages to the wrong port
776	(hard to do in Erlang).	1218	(hard to do in Erlang).
777		1219
778	=back	1220	=back
779		1221
780	=head1 RATIONALE	1222	=head1 RATIONALE
781		1223
782	=over 4	1224	=over 4
783		1225
784	=item Why strings for ports and noderefs, why not objects?	1226	=item Why strings for port and node IDs, why not objects?
785		1227
786	We considered "objects", but found that the actual number of methods	1228	We considered "objects", but found that the actual number of methods
787	thatc an be called are very low. Since port IDs and noderefs travel over	1229	that can be called are quite low. Since port and node IDs travel over
788	the network frequently, the serialising/deserialising would add lots of	1230	the network frequently, the serialising/deserialising would add lots of
789	overhead, as well as having to keep a proxy object.	1231	overhead, as well as having to keep a proxy object everywhere.
790		1232
791	Strings can easily be printed, easily serialised etc. and need no special	1233	Strings can easily be printed, easily serialised etc. and need no special
792	procedures to be "valid".	1234	procedures to be "valid".
793		1235
794	And a a miniport consists of a single closure stored in a global hash - it	1236	And as a result, a port with just a default receiver consists of a single
795	can't become much cheaper.	1237	code reference stored in a global hash - it can't become much cheaper.
796		1238
797	=item Why favour JSON, why not real serialising format such as Storable?	1239	=item Why favour JSON, why not a real serialising format such as Storable?
798		1240
799	In fact, any AnyEvent::MP node will happily accept Storable as framing	1241	In fact, any AnyEvent::MP node will happily accept Storable as framing
800	format, but currently there is no way to make a node use Storable by	1242	format, but currently there is no way to make a node use Storable by
801	default.	1243	default (although all nodes will accept it).
802		1244
803	The default framing protocol is JSON because a) JSON::XS is many times	1245	The default framing protocol is JSON because a) JSON::XS is many times
804	faster for small messages and b) most importantly, after years of	1246	faster for small messages and b) most importantly, after years of
805	experience we found that object serialisation is causing more problems	1247	experience we found that object serialisation is causing more problems
806	than it gains: Just like function calls, objects simply do not travel	1248	than it solves: Just like function calls, objects simply do not travel
807	easily over the network, mostly because they will always be a copy, so you	1249	easily over the network, mostly because they will always be a copy, so you
808	always have to re-think your design.	1250	always have to re-think your design.
809		1251
810	Keeping your messages simple, concentrating on data structures rather than	1252	Keeping your messages simple, concentrating on data structures rather than
811	objects, will keep your messages clean, tidy and efficient.	1253	objects, will keep your messages clean, tidy and efficient.
812		1254
813	=back	1255	=back
814		1256
		1257	=head1 PORTING FROM AnyEvent::MP VERSION 1.X
		1258
		1259	AEMP version 2 has three major incompatible changes compared to version 1:
		1260
		1261	=over 4
		1262
		1263	=item AnyEvent::MP::Global no longer has group management functions.
		1264
		1265	AnyEvent::MP now comes with a distributed database that is more
		1266	powerful. It's database families map closely to ports, but the API has
		1267	minor differences:
		1268
		1269	grp_reg $group, $port # old
		1270	db_reg $group, $port # new
		1271
		1272	$list = grp_get $group # old
		1273	db_keys $group, sub { my $list = shift } # new
		1274
		1275	grp_mon $group, $cb->(\@ports, $add, $del) # old
		1276	db_mon $group, $cb->(\%ports, $add, $change, $del) # new
		1277
		1278	C<grp_reg> is a no-brainer (just replace by C<db_reg>), but C<grp_get>
		1279	is no longer instant, because the local node might not have a copy of
		1280	the group. This can be partially remedied by using C<db_mon> to keep an
		1281	updated copy of the group:
		1282
		1283	my $local_group_copy;
		1284	db_mon $group => sub { $local_group_copy = shift };
		1285
		1286	# no keys %$local_group_copy always returns the most up-to-date
		1287	# list of ports in the group.
		1288
		1289	C<grp_mon> can almost be replaced by C<db_mon>:
		1290
		1291	db_mon $group => sub {
		1292	my ($ports, $add, $chg, $lde) = @_;
		1293	$ports = [keys %$ports];
		1294
		1295	# now $ports, $add and $del are the same as
		1296	# were originally passed by grp_mon.
		1297	...
		1298	};
		1299
		1300	=item Nodes not longer connect to all other nodes.
		1301
		1302	In AEMP 1.x, every node automatically loads the L<AnyEvent::MP::Global>
		1303	module, which in turn would create connections to all other nodes in the
		1304	network (helped by the seed nodes).
		1305
		1306	In version 2.x, global nodes still connect to all other global nodes, but
		1307	other nodes don't - now every node either is a global node itself, or
		1308	attaches itself to another global node.
		1309
		1310	If a node isn't a global node itself, then it attaches itself to one
		1311	of its seed nodes. If that seed node isn't a global node yet, it will
		1312	automatically be upgraded to a global node.
		1313
		1314	So in many cases, nothing needs to be changed - one just has to make sure
		1315	that all seed nodes are meshed together with the other seed nodes (as with
		1316	AEMP 1.x), and other nodes specify them as seed nodes.
		1317
		1318	Not opening a connection to every other node is usually an advantage,
		1319	except when you need the lower latency of an already established
		1320	connection. To ensure a node establishes a connection to another node,
		1321	you can monitor the node port (C<mon $node, ...>), which will attempt to
		1322	create the connection (And notify you when the connection fails).
		1323
		1324	=item Listener-less nodes are gone.
		1325
		1326	And are not coming back, at least not in their old form.
		1327
		1328	There are vague plans to implement some form of routing domains, which
		1329	might or might not bring back listener-less nodes, but don't count on it.
		1330
		1331	The fact that most connections are now optional somewhat mitigates this,
		1332	as a node can be effectively unreachable from the outside without any
		1333	problems, as long as it isn't a global node and only reaches out to other
		1334	nodes (as opposed to being contacted from other nodes).
		1335
		1336	=back
		1337
815	=head1 SEE ALSO	1338	=head1 SEE ALSO
		1339
		1340	L<AnyEvent::MP::Intro> - a gentle introduction.
		1341
		1342	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1343
		1344	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1345	your applications.
		1346
		1347	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1348
		1349	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1350	all nodes.
816		1351
817	L<AnyEvent>.	1352	L<AnyEvent>.
818		1353
819	=head1 AUTHOR	1354	=head1 AUTHOR
820		1355

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Revision 1.137 by root, Wed Mar 21 23:48:39 2012 UTC