ViewVC Help

View File | Revision Log | Show Annotations | Download File

/cvs/AnyEvent-MP/MP.pm

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.61 by root, Mon Aug 24 08:06:49 2009 UTC vs.
Revision 1.144 by root, Fri Mar 23 21:16:25 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
42		43
43	=head1 CURRENT STATUS	44	# temporarily execute code in port context
		45	peval $port, sub { die "kill the port!" };
44		46
45	AnyEvent::MP - stable API, should work	47	# execute callbacks in $SELF port context
46	AnyEvent::MP::Intro - outdated	48	my $timer = AE::timer 1, 0, psub {
47	AnyEvent::MP::Kernel - WIP	49	die "kill the port, delayed";
48	AnyEvent::MP::Transport - mostly stable	50	};
49		51
50	stay tuned.	52	# distributed database - modification
		53	db_set $family => $subkey [=> $value] # add a subkey
		54	db_del $family => $subkey... # delete one or more subkeys
		55	db_reg $family => $port [=> $value] # register a port
		56
		57	# distributed database - queries
		58	db_family $family => $cb->(\%familyhash)
		59	db_keys $family => $cb->(\@keys)
		60	db_values $family => $cb->(\@values)
		61
		62	# distributed database - monitoring a family
		63	db_mon $family => $cb->(\%familyhash, \@added, \@changed, \@deleted)
51		64
52	=head1 DESCRIPTION	65	=head1 DESCRIPTION
53		66
54	This module (-family) implements a simple message passing framework.	67	This module (-family) implements a simple message passing framework.
55		68
56	Despite its simplicity, you can securely message other processes running	69	Despite its simplicity, you can securely message other processes running
57	on the same or other hosts.	70	on the same or other hosts, and you can supervise entities remotely.
58		71
59	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	72	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
60	manual page.	73	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		74
66	=head1 CONCEPTS	75	=head1 CONCEPTS
67		76
68	=over 4	77	=over 4
69		78
70	=item port	79	=item port
71		80
72	A port is something you can send messages to (with the C<snd> function).	81	Not to be confused with a TCP port, a "port" is something you can send
		82	messages to (with the C<snd> function).
73		83
74	Ports allow you to register C<rcv> handlers that can match all or just	84	Ports allow you to register C<rcv> handlers that can match all or just
75	some messages. Messages will not be queued.	85	some messages. Messages send to ports will not be queued, regardless of
		86	anything was listening for them or not.
76		87
		88	Ports are represented by (printable) strings called "port IDs".
		89
77	=item port id - C<noderef#portname>	90	=item port ID - C<nodeid#portname>
78		91
79	A port ID is the concatenation of a noderef, a hash-mark (C<#>) as	92	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	93	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	94	format created by AnyEvent::MP).
82	reference.
83		95
84	=item node	96	=item node
85		97
86	A node is a single process containing at least one port - the node port,	98	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	99	which enables nodes to manage each other remotely, and to create new
88	ports.	100	ports.
89		101
90	Nodes are either private (single-process only), slaves (connected to a	102	Nodes are either public (have one or more listening ports) or private
91	master node only) or public nodes (connectable from unrelated nodes).	103	(no listening ports). Private nodes cannot talk to other private nodes
		104	currently, but all nodes can talk to public nodes.
92		105
93	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	106	Nodes is represented by (printable) strings called "node IDs".
94		107
95	A node reference is a string that either simply identifies the node (for	108	=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		109
99	This recipe is simply a comma-separated list of C<address:port> pairs (for	110	A node ID is a string that uniquely identifies the node within a
100	TCP/IP, other protocols might look different).	111	network. Depending on the configuration used, node IDs can look like a
		112	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		113	doesn't interpret node IDs in any way except to uniquely identify a node.
101		114
102	Node references come in two flavours: resolved (containing only numerical	115	=item binds - C<ip:port>
103	addresses) or unresolved (where hostnames are used instead of addresses).
104		116
105	Before using an unresolved node reference in a message you first have to	117	Nodes can only talk to each other by creating some kind of connection to
106	resolve it.	118	each other. To do this, nodes should listen on one or more local transport
		119	endpoints - binds.
		120
		121	Currently, only standard C<ip:port> specifications can be used, which
		122	specify TCP ports to listen on. So a bind is basically just a tcp socket
		123	in listening mode thta accepts conenctions form other nodes.
		124
		125	=item seed nodes
		126
		127	When a node starts, it knows nothing about the network it is in - it
		128	needs to connect to at least one other node that is already in the
		129	network. These other nodes are called "seed nodes".
		130
		131	Seed nodes themselves are not special - they are seed nodes only because
		132	some other node I<uses> them as such, but any node can be used as seed
		133	node for other nodes, and eahc node cna use a different set of seed nodes.
		134
		135	In addition to discovering the network, seed nodes are also used to
		136	maintain the network - all nodes using the same seed node form are part of
		137	the same network. If a network is split into multiple subnets because e.g.
		138	the network link between the parts goes down, then using the same seed
		139	nodes for all nodes ensures that eventually the subnets get merged again.
		140
		141	Seed nodes are expected to be long-running, and at least one seed node
		142	should always be available. They should also be relatively responsive - a
		143	seed node that blocks for long periods will slow down everybody else.
		144
		145	For small networks, it's best if every node uses the same set of seed
		146	nodes. For large networks, it can be useful to specify "regional" seed
		147	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		148	each other. What's important is that all seed nodes connections form a
		149	complete graph, so that the network cannot split into separate subnets
		150	forever.
		151
		152	Seed nodes are represented by seed IDs.
		153
		154	=item seed IDs - C<host:port>
		155
		156	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
		157	TCP port) of nodes that should be used as seed nodes.
		158
		159	=item global nodes
		160
		161	An AEMP network needs a discovery service - nodes need to know how to
		162	connect to other nodes they only know by name. In addition, AEMP offers a
		163	distributed "group database", which maps group names to a list of strings
		164	- for example, to register worker ports.
		165
		166	A network needs at least one global node to work, and allows every node to
		167	be a global node.
		168
		169	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		170	node and tries to keep connections to all other nodes. So while it can
		171	make sense to make every node "global" in small networks, it usually makes
		172	sense to only make seed nodes into global nodes in large networks (nodes
		173	keep connections to seed nodes and global nodes, so makign them the same
		174	reduces overhead).
107		175
108	=back	176	=back
109		177
110	=head1 VARIABLES/FUNCTIONS	178	=head1 VARIABLES/FUNCTIONS
111		179
…		…
113		181
114	=cut	182	=cut
115		183
116	package AnyEvent::MP;	184	package AnyEvent::MP;
117		185
		186	use AnyEvent::MP::Config ();
118	use AnyEvent::MP::Kernel;	187	use AnyEvent::MP::Kernel;
		188	use AnyEvent::MP::Kernel qw(
		189	%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID
		190	add_node load_func
		191
		192	NODE $NODE
		193	configure
		194	node_of port_is_local
		195	snd kil
		196	db_set db_del
		197	db_mon db_family db_keys db_values
		198	);
119		199
120	use common::sense;	200	use common::sense;
121		201
122	use Carp ();	202	use Carp ();
123		203
124	use AE ();	204	use AnyEvent ();
		205	use Guard ();
125		206
126	use base "Exporter";	207	use base "Exporter";
127		208
128	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	209	our $VERSION = $AnyEvent::MP::Config::VERSION;
129		210
130	our @EXPORT = qw(	211	our @EXPORT = qw(
131	NODE $NODE *SELF node_of after	212	NODE $NODE
132	resolve_node initialise_node	213	configure
133	snd rcv mon mon_guard kil reg psub spawn	214	node_of port_is_local
134	port	215	snd kil
		216	db_set db_del
		217	db_mon db_family db_keys db_values
		218
		219	*SELF
		220
		221	port rcv mon mon_guard psub peval spawn cal
		222	db_set db_del db_reg
		223	db_mon db_family db_keys db_values
		224
		225	after
135	);	226	);
136		227
137	our $SELF;	228	our $SELF;
138		229
139	sub _self_die() {	230	sub _self_die() {
…		…
142	kil $SELF, die => $msg;	233	kil $SELF, die => $msg;
143	}	234	}
144		235
145	=item $thisnode = NODE / $NODE	236	=item $thisnode = NODE / $NODE
146		237
147	The C<NODE> function returns, and the C<$NODE> variable contains the	238	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	239	ID of the node running in the current process. This value is initialised by
149	C<initialise_node>.	240	a call to C<configure>.
150		241
151	=item $noderef = node_of $port	242	=item $nodeid = node_of $port
152		243
153	Extracts and returns the noderef from a port ID or a noderef.	244	Extracts and returns the node ID from a port ID or a node ID.
154		245
155	=item initialise_node $noderef, $seednode, $seednode...	246	=item $is_local = port_is_local $port
156		247
157	=item initialise_node "slave/", $master, $master...	248	Returns true iff the port is a local port.
158		249
		250	=item configure $profile, key => value...
		251
		252	=item configure key => value...
		253
159	Before a node can talk to other nodes on the network it has to initialise	254	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	255	"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.	256	to know is its own name, and optionally it should know the addresses of
		257	some other nodes in the network to discover other nodes.
162		258
163	This function initialises a node - it must be called exactly once (or	259	This function configures a node - it must be called exactly once (or
164	never) before calling other AnyEvent::MP functions.	260	never) before calling other AnyEvent::MP functions.
165		261
166	All arguments (optionally except for the first) are noderefs, which can be	262	The key/value pairs are basically the same ones as documented for the
167	either resolved or unresolved.	263	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		264
177	=over 4	265	=over 4
178		266
179	=item public nodes	267	=item norc => $boolean (default false)
180		268
181	For public nodes, C<$noderef> (supplied either directly to	269	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	270	be consulted - all configuraiton options must be specified in the
183	noderef (possibly unresolved, in which case it will be resolved).	271	C<configure> call.
184		272
185	After resolving, the node will bind itself on all endpoints and try to	273	=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		274
190	=item slave nodes	275	IF true, then the values specified in the C<configure> will take
191		276	precedence over any values configured via the rc file. The default is for
192	When the C<$noderef> (either as given or overriden by the config file)	277	the rc file to override any options specified in the program.
193	is the special string C<slave/>, then the node will become a slave
194	node. Slave nodes cannot be contacted from outside and will route most of
195	their traffic to the master node that they attach to.
196
197	At least one additional noderef is required (either by specifying it
198	directly or because it is part of the configuration profile): The node
199	will try to connect to all of them and will become a slave attached to the
200	first node it can successfully connect to.
201
202	Note that slave nodes cannot change their name, and consequently, their
203	master, so if the master goes down, the slave node will not function well
204	anymore until it can re-establish conenciton to its master. This makes
205	slave nodes unsuitable for long-term nodes or fault-tolerant networks.
206		278
207	=back	279	=back
208		280
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	281	=over 4
255		282
256	=item the empty string	283	=item step 1, gathering configuration from profiles
257		284
258	An empty-string component gets resolved as if the default port (4040) was	285	The function first looks up a profile in the aemp configuration (see the
259	specified.	286	L<aemp> commandline utility). The profile name can be specified via the
		287	named C<profile> parameter or can simply be the first parameter). If it is
		288	missing, then the nodename (F<uname -n>) will be used as profile name.
260		289
261	=item naked port numbers (e.g. C<1234>)	290	The profile data is then gathered as follows:
262		291
263	These are resolved by prepending the local nodename and a colon, to be	292	First, all remaining key => value pairs (all of which are conveniently
264	further resolved.	293	undocumented at the moment) will be interpreted as configuration
		294	data. Then they will be overwritten by any values specified in the global
		295	default configuration (see the F<aemp> utility), then the chain of
		296	profiles chosen by the profile name (and any C<parent> attributes).
265		297
266	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	298	That means that the values specified in the profile have highest priority
		299	and the values specified directly via C<configure> have lowest priority,
		300	and can only be used to specify defaults.
267		301
268	These are resolved by using AnyEvent::DNS to resolve them, optionally	302	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	303	this process. If not, then the profile name will be used as node ID, with
270	specified.	304	a unique randoms tring (C</%u>) appended.
		305
		306	The node ID can contain some C<%> sequences that are expanded: C<%n>
		307	is expanded to the local nodename, C<%u> is replaced by a random
		308	strign to make the node unique. For example, the F<aemp> commandline
		309	utility uses C<aemp/%n/%u> as nodename, which might expand to
		310	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		311
		312	=item step 2, bind listener sockets
		313
		314	The next step is to look up the binds in the profile, followed by binding
		315	aemp protocol listeners on all binds specified (it is possible and valid
		316	to have no binds, meaning that the node cannot be contacted form the
		317	outside. This means the node cannot talk to other nodes that also have no
		318	binds, but it can still talk to all "normal" nodes).
		319
		320	If the profile does not specify a binds list, then a default of C<*> is
		321	used, meaning the node will bind on a dynamically-assigned port on every
		322	local IP address it finds.
		323
		324	=item step 3, connect to seed nodes
		325
		326	As the last step, the seed ID list from the profile is passed to the
		327	L<AnyEvent::MP::Global> module, which will then use it to keep
		328	connectivity with at least one node at any point in time.
271		329
272	=back	330	=back
		331
		332	Example: become a distributed node using the local node name as profile.
		333	This should be the most common form of invocation for "daemon"-type nodes.
		334
		335	configure
		336
		337	Example: become a semi-anonymous node. This form is often used for
		338	commandline clients.
		339
		340	configure nodeid => "myscript/%n/%u";
		341
		342	Example: configure a node using a profile called seed, which is suitable
		343	for a seed node as it binds on all local addresses on a fixed port (4040,
		344	customary for aemp).
		345
		346	# use the aemp commandline utility
		347	# aemp profile seed binds '*:4040'
		348
		349	# then use it
		350	configure profile => "seed";
		351
		352	# or simply use aemp from the shell again:
		353	# aemp run profile seed
		354
		355	# or provide a nicer-to-remember nodeid
		356	# aemp run profile seed nodeid "$(hostname)"
273		357
274	=item $SELF	358	=item $SELF
275		359
276	Contains the current port id while executing C<rcv> callbacks or C<psub>	360	Contains the current port id while executing C<rcv> callbacks or C<psub>
277	blocks.	361	blocks.
278		362
279	=item SELF, %SELF, @SELF...	363	=item *SELF, SELF, %SELF, @SELF...
280		364
281	Due to some quirks in how perl exports variables, it is impossible to	365	Due to some quirks in how perl exports variables, it is impossible to
282	just export C<$SELF>, all the symbols called C<SELF> are exported by this	366	just export C<$SELF>, all the symbols named C<SELF> are exported by this
283	module, but only C<$SELF> is currently used.	367	module, but only C<$SELF> is currently used.
284		368
285	=item snd $port, type => @data	369	=item snd $port, type => @data
286		370
287	=item snd $port, @msg	371	=item snd $port, @msg
288		372
289	Send the given message to the given port ID, which can identify either	373	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.	374	local or a remote port, and must be a port ID.
291		375
292	While the message can be about anything, it is highly recommended to use a	376	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	377	use a string as first element (a port ID, or some word that indicates a
294	type etc.).	378	request type etc.) and to consist if only simple perl values (scalars,
		379	arrays, hashes) - if you think you need to pass an object, think again.
295		380
296	The message data effectively becomes read-only after a call to this	381	The message data logically becomes read-only after a call to this
297	function: modifying any argument is not allowed and can cause many	382	function: modifying any argument (or values referenced by them) is
298	problems.	383	forbidden, as there can be considerable time between the call to C<snd>
		384	and the time the message is actually being serialised - in fact, it might
		385	never be copied as within the same process it is simply handed to the
		386	receiving port.
299		387
300	The type of data you can transfer depends on the transport protocol: when	388	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	389	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	390	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	391	that Storable can serialise and deserialise is allowed, and for the local
304	node, anything can be passed.	392	node, anything can be passed. Best rely only on the common denominator of
		393	these.
305		394
306	=item $local_port = port	395	=item $local_port = port
307		396
308	Create a new local port object and returns its port ID. Initially it has	397	Create a new local port object and returns its port ID. Initially it has
309	no callbacks set and will throw an error when it receives messages.	398	no callbacks set and will throw an error when it receives messages.
…		…
328		417
329	=cut	418	=cut
330		419
331	sub rcv($@);	420	sub rcv($@);
332		421
333	sub _kilme {	422	my $KILME = sub {
334	die "received message on port without callback";	423	(my $tag = substr $_[0], 0, 30) =~ s/([\x20-\x7e])/./g;
335	}	424	kil $SELF, unhandled_message => "no callback found for message '$tag'";
		425	};
336		426
337	sub port(;&) {	427	sub port(;&) {
338	my $id = "$UNIQ." . $ID++;	428	my $id = $UNIQ . ++$ID;
339	my $port = "$NODE#$id";	429	my $port = "$NODE#$id";
340		430
341	rcv $port, shift || \&_kilme;	431	rcv $port, shift || $KILME;
342		432
343	$port	433	$port
344	}	434	}
345		435
346	=item rcv $local_port, $callback->(@msg)	436	=item rcv $local_port, $callback->(@msg)
…		…
351		441
352	The global C<$SELF> (exported by this module) contains C<$port> while	442	The global C<$SELF> (exported by this module) contains C<$port> while
353	executing the callback. Runtime errors during callback execution will	443	executing the callback. Runtime errors during callback execution will
354	result in the port being C<kil>ed.	444	result in the port being C<kil>ed.
355		445
356	The default callback received all messages not matched by a more specific	446	The default callback receives all messages not matched by a more specific
357	C<tag> match.	447	C<tag> match.
358		448
359	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...	449	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
360		450
361	Register (or replace) callbacks to be called on messages starting with the	451	Register (or replace) callbacks to be called on messages starting with the
…		…
382	msg1 => sub { ... },	472	msg1 => sub { ... },
383	...	473	...
384	;	474	;
385		475
386	Example: temporarily register a rcv callback for a tag matching some port	476	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.	477	(e.g. for an rpc reply) and unregister it after a message was received.
388		478
389	rcv $port, $otherport => sub {	479	rcv $port, $otherport => sub {
390	my @reply = @_;	480	my @reply = @_;
391		481
392	rcv $SELF, $otherport;	482	rcv $SELF, $otherport;
…		…
394		484
395	=cut	485	=cut
396		486
397	sub rcv($@) {	487	sub rcv($@) {
398	my $port = shift;	488	my $port = shift;
399	my ($noderef, $portid) = split /#/, $port, 2;	489	my ($nodeid, $portid) = split /#/, $port, 2;
400		490
401	$NODE{$noderef} == $NODE{""}	491	$nodeid eq $NODE
402	or Carp::croak "$port: rcv can only be called on local ports, caught";	492	or Carp::croak "$port: rcv can only be called on local ports, caught";
403		493
404	while (@_) {	494	while (@_) {
405	if (ref $_[0]) {	495	if (ref $_[0]) {
406	if (my $self = $PORT_DATA{$portid}) {	496	if (my $self = $PORT_DATA{$portid}) {
407	"AnyEvent::MP::Port" eq ref $self	497	"AnyEvent::MP::Port" eq ref $self
408	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	498	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
409		499
410	$self->[2] = shift;	500	$self->[0] = shift;
411	} else {	501	} else {
412	my $cb = shift;	502	my $cb = shift;
413	$PORT{$portid} = sub {	503	$PORT{$portid} = sub {
414	local $SELF = $port;	504	local $SELF = $port;
415	eval { &$cb }; _self_die if $@;	505	eval { &$cb }; _self_die if $@;
416	};	506	};
417	}	507	}
418	} elsif (defined $_[0]) {	508	} elsif (defined $_[0]) {
419	my $self = $PORT_DATA{$portid} ||= do {	509	my $self = $PORT_DATA{$portid} ||= do {
420	my $self = bless [$PORT{$port} || sub { }, { }, $port], "AnyEvent::MP::Port";	510	my $self = bless [$PORT{$portid} || sub { }, { }, $port], "AnyEvent::MP::Port";
421		511
422	$PORT{$portid} = sub {	512	$PORT{$portid} = sub {
423	local $SELF = $port;	513	local $SELF = $port;
424		514
425	if (my $cb = $self->[1]{$_[0]}) {	515	if (my $cb = $self->[1]{$_[0]}) {
…		…
447	}	537	}
448		538
449	$port	539	$port
450	}	540	}
451		541
		542	=item peval $port, $coderef[, @args]
		543
		544	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		545	when the code throews an exception the C<$port> will be killed.
		546
		547	Any remaining args will be passed to the callback. Any return values will
		548	be returned to the caller.
		549
		550	This is useful when you temporarily want to execute code in the context of
		551	a port.
		552
		553	Example: create a port and run some initialisation code in it's context.
		554
		555	my $port = port { ... };
		556
		557	peval $port, sub {
		558	init
		559	or die "unable to init";
		560	};
		561
		562	=cut
		563
		564	sub peval($$) {
		565	local $SELF = shift;
		566	my $cb = shift;
		567
		568	if (wantarray) {
		569	my @res = eval { &$cb };
		570	_self_die if $@;
		571	@res
		572	} else {
		573	my $res = eval { &$cb };
		574	_self_die if $@;
		575	$res
		576	}
		577	}
		578
452	=item $closure = psub { BLOCK }	579	=item $closure = psub { BLOCK }
453		580
454	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	581	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>	582	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.	583	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		584
		585	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		586	BLOCK }, @_ } >>.
457		587
458	This is useful when you register callbacks from C<rcv> callbacks:	588	This is useful when you register callbacks from C<rcv> callbacks:
459		589
460	rcv delayed_reply => sub {	590	rcv delayed_reply => sub {
461	my ($delay, @reply) = @_;	591	my ($delay, @reply) = @_;
…		…
485	$res	615	$res
486	}	616	}
487	}	617	}
488	}	618	}
489		619
490	=item $guard = mon $port, $cb->(@reason)	620	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
491		621
492	=item $guard = mon $port, $rcvport	622	=item $guard = mon $port # kill $SELF when $port dies
493		623
494	=item $guard = mon $port	624	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
495		625
496	=item $guard = mon $port, $rcvport, @msg	626	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
497		627
498	Monitor the given port and do something when the port is killed or	628	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	629	messages to it were lost, and optionally return a guard that can be used
500	to stop monitoring again.	630	to stop monitoring again.
501		631
		632	The first two forms distinguish between "normal" and "abnormal" kil's:
		633
		634	In the first form (another port given), if the C<$port> is C<kil>'ed with
		635	a non-empty reason, the other port (C<$rcvport>) will be kil'ed with the
		636	same reason. That is, on "normal" kil's nothing happens, while under all
		637	other conditions, the other port is killed with the same reason.
		638
		639	The second form (kill self) is the same as the first form, except that
		640	C<$rvport> defaults to C<$SELF>.
		641
		642	The remaining forms don't distinguish between "normal" and "abnormal" kil's
		643	- it's up to the callback or receiver to check whether the C<@reason> is
		644	empty and act accordingly.
		645
		646	In the third form (callback), the callback is simply called with any
		647	number of C<@reason> elements (empty @reason means that the port was deleted
		648	"normally"). Note also that I<< the callback B<must> never die >>, so use
		649	C<eval> if unsure.
		650
		651	In the last form (message), a message of the form C<$rcvport, @msg,
		652	@reason> will be C<snd>.
		653
		654	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		655	alert was raised), they are removed and will not trigger again, even if it
		656	turns out that the port is still alive.
		657
		658	As a rule of thumb, monitoring requests should always monitor a remote
		659	port locally (using a local C<$rcvport> or a callback). The reason is that
		660	kill messages might get lost, just like any other message. Another less
		661	obvious reason is that even monitoring requests can get lost (for example,
		662	when the connection to the other node goes down permanently). When
		663	monitoring a port locally these problems do not exist.
		664
502	C<mon> effectively guarantees that, in the absence of hardware failures,	665	C<mon> effectively guarantees that, in the absence of hardware failures,
503	that after starting the monitor, either all messages sent to the port	666	after starting the monitor, either all messages sent to the port will
504	will arrive, or the monitoring action will be invoked after possible	667	arrive, or the monitoring action will be invoked after possible message
505	message loss has been detected. No messages will be lost "in between"	668	loss has been detected. No messages will be lost "in between" (after
506	(after the first lost message no further messages will be received by the	669	the first lost message no further messages will be received by the
507	port). After the monitoring action was invoked, further messages might get	670	port). After the monitoring action was invoked, further messages might get
508	delivered again.	671	delivered again.
509		672
510	Note that monitoring-actions are one-shot: once released, they are removed	673	Inter-host-connection timeouts and monitoring depend on the transport
511	and will not trigger again.	674	used. The only transport currently implemented is TCP, and AnyEvent::MP
		675	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		676	non-idle connection, and usually around two hours for idle connections).
512		677
513	In the first form (callback), the callback is simply called with any	678	This means that monitoring is good for program errors and cleaning up
514	number of C<@reason> elements (no @reason means that the port was deleted	679	stuff eventually, but they are no replacement for a timeout when you need
515	"normally"). Note also that I<< the callback B<must> never die >>, so use	680	to ensure some maximum latency.
516	C<eval> if unsure.
517
518	In the second form (another port given), the other port (C<$rcvport>)
519	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on
520	"normal" kils nothing happens, while under all other conditions, the other
521	port is killed with the same reason.
522
523	The third form (kill self) is the same as the second form, except that
524	C<$rvport> defaults to C<$SELF>.
525
526	In the last form (message), a message of the form C<@msg, @reason> will be
527	C<snd>.
528
529	As a rule of thumb, monitoring requests should always monitor a port from
530	a local port (or callback). The reason is that kill messages might get
531	lost, just like any other message. Another less obvious reason is that
532	even monitoring requests can get lost (for exmaple, when the connection
533	to the other node goes down permanently). When monitoring a port locally
534	these problems do not exist.
535		681
536	Example: call a given callback when C<$port> is killed.	682	Example: call a given callback when C<$port> is killed.
537		683
538	mon $port, sub { warn "port died because of <@_>\n" };	684	mon $port, sub { warn "port died because of <@_>\n" };
539		685
…		…
546	mon $port, $self => "restart";	692	mon $port, $self => "restart";
547		693
548	=cut	694	=cut
549		695
550	sub mon {	696	sub mon {
551	my ($noderef, $port) = split /#/, shift, 2;	697	my ($nodeid, $port) = split /#/, shift, 2;
552		698
553	my $node = $NODE{$noderef} || add_node $noderef;	699	my $node = $NODE{$nodeid} || add_node $nodeid;
554		700
555	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';	701	my $cb = @_ ? shift : $SELF || Carp::croak 'mon: called with one argument only, but $SELF not set,';
556		702
557	unless (ref $cb) {	703	unless (ref $cb) {
558	if (@_) {	704	if (@_) {
…		…
567	}	713	}
568		714
569	$node->monitor ($port, $cb);	715	$node->monitor ($port, $cb);
570		716
571	defined wantarray	717	defined wantarray
572	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	718	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
573	}	719	}
574		720
575	=item $guard = mon_guard $port, $ref, $ref...	721	=item $guard = mon_guard $port, $ref, $ref...
576		722
577	Monitors the given C<$port> and keeps the passed references. When the port	723	Monitors the given C<$port> and keeps the passed references. When the port
578	is killed, the references will be freed.	724	is killed, the references will be freed.
579		725
580	Optionally returns a guard that will stop the monitoring.	726	Optionally returns a guard that will stop the monitoring.
581		727
582	This function is useful when you create e.g. timers or other watchers and	728	This function is useful when you create e.g. timers or other watchers and
583	want to free them when the port gets killed:	729	want to free them when the port gets killed (note the use of C<psub>):
584		730
585	$port->rcv (start => sub {	731	$port->rcv (start => sub {
586	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	732	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
587	undef $timer if 0.9 < rand;	733	undef $timer if 0.9 < rand;
588	});	734	});
589	});	735	});
590		736
591	=cut	737	=cut
…		…
600		746
601	=item kil $port[, @reason]	747	=item kil $port[, @reason]
602		748
603	Kill the specified port with the given C<@reason>.	749	Kill the specified port with the given C<@reason>.
604		750
605	If no C<@reason> is specified, then the port is killed "normally" (linked	751	If no C<@reason> is specified, then the port is killed "normally" -
606	ports will not be kileld, or even notified).	752	monitor callback will be invoked, but the kil will not cause linked ports
		753	(C<mon $mport, $lport> form) to get killed.
607		754
608	Otherwise, linked ports get killed with the same reason (second form of	755	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
609	C<mon>, see below).	756	form) get killed with the same reason.
610		757
611	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	758	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
612	will be reported as reason C<< die => $@ >>.	759	will be reported as reason C<< die => $@ >>.
613		760
614	Transport/communication errors are reported as C<< transport_error =>	761	Transport/communication errors are reported as C<< transport_error =>
615	$message >>.	762	$message >>.
616		763
617	=cut	764	Common idioms:
		765
		766	# silently remove yourself, do not kill linked ports
		767	kil $SELF;
		768
		769	# report a failure in some detail
		770	kil $SELF, failure_mode_1 => "it failed with too high temperature";
		771
		772	# do not waste much time with killing, just die when something goes wrong
		773	open my $fh, "<file"
		774	or die "file: $!";
618		775
619	=item $port = spawn $node, $initfunc[, @initdata]	776	=item $port = spawn $node, $initfunc[, @initdata]
620		777
621	Creates a port on the node C<$node> (which can also be a port ID, in which	778	Creates a port on the node C<$node> (which can also be a port ID, in which
622	case it's the node where that port resides).	779	case it's the node where that port resides).
623		780
624	The port ID of the newly created port is return immediately, and it is	781	The port ID of the newly created port is returned immediately, and it is
625	permissible to immediately start sending messages or monitor the port.	782	possible to immediately start sending messages or to monitor the port.
626		783
627	After the port has been created, the init function is	784	After the port has been created, the init function is called on the remote
628	called. This function must be a fully-qualified function name	785	node, in the same context as a C<rcv> callback. This function must be a
629	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	786	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
630	program, use C<::name>.	787	specify a function in the main program, use C<::name>.
631		788
632	If the function doesn't exist, then the node tries to C<require>	789	If the function doesn't exist, then the node tries to C<require>
633	the package, then the package above the package and so on (e.g.	790	the package, then the package above the package and so on (e.g.
634	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	791	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
635	exists or it runs out of package names.	792	exists or it runs out of package names.
636		793
637	The init function is then called with the newly-created port as context	794	The init function is then called with the newly-created port as context
638	object (C<$SELF>) and the C<@initdata> values as arguments.	795	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		796	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		797	the port might not get created.
639		798
640	A common idiom is to pass your own port, monitor the spawned port, and	799	A common idiom is to pass a local port, immediately monitor the spawned
641	in the init function, monitor the original port. This two-way monitoring	800	port, and in the remote init function, immediately monitor the passed
642	ensures that both ports get cleaned up when there is a problem.	801	local port. This two-way monitoring ensures that both ports get cleaned up
		802	when there is a problem.
		803
		804	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		805	caller before C<spawn> returns (by delaying invocation when spawn is
		806	called for the local node).
643		807
644	Example: spawn a chat server port on C<$othernode>.	808	Example: spawn a chat server port on C<$othernode>.
645		809
646	# this node, executed from within a port context:	810	# this node, executed from within a port context:
647	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	811	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
662		826
663	sub _spawn {	827	sub _spawn {
664	my $port = shift;	828	my $port = shift;
665	my $init = shift;	829	my $init = shift;
666		830
		831	# rcv will create the actual port
667	local $SELF = "$NODE#$port";	832	local $SELF = "$NODE#$port";
668	eval {	833	eval {
669	&{ load_func $init }	834	&{ load_func $init }
670	};	835	};
671	_self_die if $@;	836	_self_die if $@;
672	}	837	}
673		838
674	sub spawn(@) {	839	sub spawn(@) {
675	my ($noderef, undef) = split /#/, shift, 2;	840	my ($nodeid, undef) = split /#/, shift, 2;
676		841
677	my $id = "$RUNIQ." . $ID++;	842	my $id = $RUNIQ . ++$ID;
678		843
679	$_[0] =~ /::/	844	$_[0] =~ /::/
680	or Carp::croak "spawn init function must be a fully-qualified name, caught";	845	or Carp::croak "spawn init function must be a fully-qualified name, caught";
681		846
682	snd_to_func $noderef, "AnyEvent::MP::_spawn" => $id, @_;	847	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
683		848
684	"$noderef#$id"	849	"$nodeid#$id"
685	}	850	}
		851
686		852
687	=item after $timeout, @msg	853	=item after $timeout, @msg
688		854
689	=item after $timeout, $callback	855	=item after $timeout, $callback
690		856
691	Either sends the given message, or call the given callback, after the	857	Either sends the given message, or call the given callback, after the
692	specified number of seconds.	858	specified number of seconds.
693		859
694	This is simply a utility function that come sin handy at times.	860	This is simply a utility function that comes in handy at times - the
		861	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		862	so it may go away in the future.
695		863
696	=cut	864	=cut
697		865
698	sub after($@) {	866	sub after($@) {
699	my ($timeout, @action) = @_;	867	my ($timeout, @action) = @_;
…		…
704	? $action[0]()	872	? $action[0]()
705	: snd @action;	873	: snd @action;
706	};	874	};
707	}	875	}
708		876
		877	#=item $cb2 = timeout $seconds, $cb[, @args]
		878
		879	=item cal $port, @msg, $callback[, $timeout]
		880
		881	A simple form of RPC - sends a message to the given C<$port> with the
		882	given contents (C<@msg>), but adds a reply port to the message.
		883
		884	The reply port is created temporarily just for the purpose of receiving
		885	the reply, and will be C<kil>ed when no longer needed.
		886
		887	A reply message sent to the port is passed to the C<$callback> as-is.
		888
		889	If an optional time-out (in seconds) is given and it is not C<undef>,
		890	then the callback will be called without any arguments after the time-out
		891	elapsed and the port is C<kil>ed.
		892
		893	If no time-out is given (or it is C<undef>), then the local port will
		894	monitor the remote port instead, so it eventually gets cleaned-up.
		895
		896	Currently this function returns the temporary port, but this "feature"
		897	might go in future versions unless you can make a convincing case that
		898	this is indeed useful for something.
		899
		900	=cut
		901
		902	sub cal(@) {
		903	my $timeout = ref $_[-1] ? undef : pop;
		904	my $cb = pop;
		905
		906	my $port = port {
		907	undef $timeout;
		908	kil $SELF;
		909	&$cb;
		910	};
		911
		912	if (defined $timeout) {
		913	$timeout = AE::timer $timeout, 0, sub {
		914	undef $timeout;
		915	kil $port;
		916	$cb->();
		917	};
		918	} else {
		919	mon $_[0], sub {
		920	kil $port;
		921	$cb->();
		922	};
		923	}
		924
		925	push @_, $port;
		926	&snd;
		927
		928	$port
		929	}
		930
		931	=back
		932
		933	=head1 DISTRIBUTED DATABASE
		934
		935	AnyEvent::MP comes with a simple distributed database. The database will
		936	be mirrored asynchronously on all global nodes. Other nodes bind to one
		937	of the global nodes for their needs. Every node has a "local database"
		938	which contains all the values that are set locally. All local databases
		939	are merged together to form the global database, which can be queried.
		940
		941	The database structure is that of a two-level hash - the database hash
		942	contains hashes which contain values, similarly to a perl hash of hashes,
		943	i.e.:
		944
		945	$DATABASE{$family}{$subkey} = $value
		946
		947	The top level hash key is called "family", and the second-level hash key
		948	is called "subkey" or simply "key".
		949
		950	The family must be alphanumeric, i.e. start with a letter and consist
		951	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		952	pretty much like Perl module names.
		953
		954	As the family namespace is global, it is recommended to prefix family names
		955	with the name of the application or module using it.
		956
		957	The subkeys must be non-empty strings, with no further restrictions.
		958
		959	The values should preferably be strings, but other perl scalars should
		960	work as well (such as C<undef>, arrays and hashes).
		961
		962	Every database entry is owned by one node - adding the same family/subkey
		963	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		964	but the result might be nondeterministic, i.e. the key might have
		965	different values on different nodes.
		966
		967	Different subkeys in the same family can be owned by different nodes
		968	without problems, and in fact, this is the common method to create worker
		969	pools. For example, a worker port for image scaling might do this:
		970
		971	db_set my_image_scalers => $port;
		972
		973	And clients looking for an image scaler will want to get the
		974	C<my_image_scalers> keys from time to time:
		975
		976	db_keys my_image_scalers => sub {
		977	@ports = @{ $_[0] };
		978	};
		979
		980	Or better yet, they want to monitor the database family, so they always
		981	have a reasonable up-to-date copy:
		982
		983	db_mon my_image_scalers => sub {
		984	@ports = keys %{ $_[0] };
		985	};
		986
		987	In general, you can set or delete single subkeys, but query and monitor
		988	whole families only.
		989
		990	If you feel the need to monitor or query a single subkey, try giving it
		991	it's own family.
		992
		993	=over
		994
		995	=item $guard = db_set $family => $subkey [=> $value]
		996
		997	Sets (or replaces) a key to the database - if C<$value> is omitted,
		998	C<undef> is used instead.
		999
		1000	When called in non-void context, C<db_set> returns a guard that
		1001	automatically calls C<db_del> when it is destroyed.
		1002
		1003	=item db_del $family => $subkey...
		1004
		1005	Deletes one or more subkeys from the database family.
		1006
		1007	=item $guard = db_reg $family => $port => $value
		1008
		1009	=item $guard = db_reg $family => $port
		1010
		1011	=item $guard = db_reg $family
		1012
		1013	Registers a port in the given family and optionally returns a guard to
		1014	remove it.
		1015
		1016	This function basically does the same as:
		1017
		1018	db_set $family => $port => $value
		1019
		1020	Except that the port is monitored and automatically removed from the
		1021	database family when it is kil'ed.
		1022
		1023	If C<$value> is missing, C<undef> is used. If C<$port> is missing, then
		1024	C<$SELF> is used.
		1025
		1026	This function is most useful to register a port in some port group (which
		1027	is just another name for a database family), and have it removed when the
		1028	port is gone. This works best when the port is a local port.
		1029
		1030	=cut
		1031
		1032	sub db_reg($$;$) {
		1033	my $family = shift;
		1034	my $port = @_ ? shift : $SELF;
		1035
		1036	my $clr = sub { db_del $family => $port };
		1037	mon $port, $clr;
		1038
		1039	db_set $family => $port => $_[0];
		1040
		1041	defined wantarray
		1042	and &Guard::guard ($clr)
		1043	}
		1044
		1045	=item db_family $family => $cb->(\%familyhash)
		1046
		1047	Queries the named database C<$family> and call the callback with the
		1048	family represented as a hash. You can keep and freely modify the hash.
		1049
		1050	=item db_keys $family => $cb->(\@keys)
		1051
		1052	Same as C<db_family>, except it only queries the family I<subkeys> and passes
		1053	them as array reference to the callback.
		1054
		1055	=item db_values $family => $cb->(\@values)
		1056
		1057	Same as C<db_family>, except it only queries the family I<values> and passes them
		1058	as array reference to the callback.
		1059
		1060	=item $guard = db_mon $family => $cb->(\%familyhash, \@added, \@changed, \@deleted)
		1061
		1062	Creates a monitor on the given database family. Each time a key is set
		1063	or or is deleted the callback is called with a hash containing the
		1064	database family and three lists of added, changed and deleted subkeys,
		1065	respectively. If no keys have changed then the array reference might be
		1066	C<undef> or even missing.
		1067
		1068	If not called in void context, a guard object is returned that, when
		1069	destroyed, stops the monitor.
		1070
		1071	The family hash reference and the key arrays belong to AnyEvent::MP and
		1072	B<must not be modified or stored> by the callback. When in doubt, make a
		1073	copy.
		1074
		1075	As soon as possible after the monitoring starts, the callback will be
		1076	called with the intiial contents of the family, even if it is empty,
		1077	i.e. there will always be a timely call to the callback with the current
		1078	contents.
		1079
		1080	It is possible that the callback is called with a change event even though
		1081	the subkey is already present and the value has not changed.
		1082
		1083	The monitoring stops when the guard object is destroyed.
		1084
		1085	Example: on every change to the family "mygroup", print out all keys.
		1086
		1087	my $guard = db_mon mygroup => sub {
		1088	my ($family, $a, $c, $d) = @_;
		1089	print "mygroup members: ", (join " ", keys %$family), "\n";
		1090	};
		1091
		1092	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1093
		1094	my $guard; $guard = db_mon My::Module::workers => sub {
		1095	my ($family, $a, $c, $d) = @_;
		1096	return unless %$family;
		1097	undef $guard;
		1098	print "My::Module::workers now nonempty\n";
		1099	};
		1100
		1101	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		1102
		1103	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		1104	my ($family, $a, $c, $d) = @_;
		1105
		1106	print "+$_=$family->{$_}\n" for @$a;
		1107	print "*$_=$family->{$_}\n" for @$c;
		1108	print "-$_=$family->{$_}\n" for @$d;
		1109	};
		1110
		1111	=cut
		1112
709	=back	1113	=back
710		1114
711	=head1 AnyEvent::MP vs. Distributed Erlang	1115	=head1 AnyEvent::MP vs. Distributed Erlang
712		1116
713	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	1117	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
714	== aemp node, Erlang process == aemp port), so many of the documents and	1118	== aemp node, Erlang process == aemp port), so many of the documents and
715	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	1119	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
716	sample:	1120	sample:
717		1121
718	http://www.Erlang.se/doc/programming_rules.shtml	1122	http://www.erlang.se/doc/programming_rules.shtml
719	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	1123	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
720	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	1124	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
721	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	1125	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
722		1126
723	Despite the similarities, there are also some important differences:	1127	Despite the similarities, there are also some important differences:
724		1128
725	=over 4	1129	=over 4
726		1130
727	=item * Node references contain the recipe on how to contact them.	1131	=item * Node IDs are arbitrary strings in AEMP.
728		1132
729	Erlang relies on special naming and DNS to work everywhere in the	1133	Erlang relies on special naming and DNS to work everywhere in the same
730	same way. AEMP relies on each node knowing it's own address(es), with	1134	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
731	convenience functionality.	1135	configuration or DNS), and possibly the addresses of some seed nodes, but
732		1136	will otherwise discover other nodes (and their IDs) itself.
733	This means that AEMP requires a less tightly controlled environment at the
734	cost of longer node references and a slightly higher management overhead.
735		1137
736	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP	1138	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
737	uses "local ports are like remote ports".	1139	uses "local ports are like remote ports".
738		1140
739	The failure modes for local ports are quite different (runtime errors	1141	The failure modes for local ports are quite different (runtime errors
…		…
748	ports being the special case/exception, where transport errors cannot	1150	ports being the special case/exception, where transport errors cannot
749	occur.	1151	occur.
750		1152
751	=item * Erlang uses processes and a mailbox, AEMP does not queue.	1153	=item * Erlang uses processes and a mailbox, AEMP does not queue.
752		1154
753	Erlang uses processes that selectively receive messages, and therefore	1155	Erlang uses processes that selectively receive messages out of order, and
754	needs a queue. AEMP is event based, queuing messages would serve no	1156	therefore needs a queue. AEMP is event based, queuing messages would serve
755	useful purpose. For the same reason the pattern-matching abilities of	1157	no useful purpose. For the same reason the pattern-matching abilities
756	AnyEvent::MP are more limited, as there is little need to be able to	1158	of AnyEvent::MP are more limited, as there is little need to be able to
757	filter messages without dequeing them.	1159	filter messages without dequeuing them.
758		1160
759	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	1161	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1162	being event-based, while Erlang is process-based.
		1163
		1164	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1165	top of AEMP and Coro threads.
760		1166
761	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1167	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
762		1168
763	Sending messages in Erlang is synchronous and blocks the process (and	1169	Sending messages in Erlang is synchronous and blocks the process until
		1170	a conenction has been established and the message sent (and so does not
764	so does not need a queue that can overflow). AEMP sends are immediate,	1171	need a queue that can overflow). AEMP sends return immediately, connection
765	connection establishment is handled in the background.	1172	establishment is handled in the background.
766		1173
767	=item * Erlang suffers from silent message loss, AEMP does not.	1174	=item * Erlang suffers from silent message loss, AEMP does not.
768		1175
769	Erlang makes few guarantees on messages delivery - messages can get lost	1176	Erlang implements few guarantees on messages delivery - messages can get
770	without any of the processes realising it (i.e. you send messages a, b,	1177	lost without any of the processes realising it (i.e. you send messages a,
771	and c, and the other side only receives messages a and c).	1178	b, and c, and the other side only receives messages a and c).
772		1179
773	AEMP guarantees correct ordering, and the guarantee that there are no	1180	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1181	guarantee that after one message is lost, all following ones sent to the
		1182	same port are lost as well, until monitoring raises an error, so there are
774	holes in the message sequence.	1183	no silent "holes" in the message sequence.
775		1184
776	=item * In Erlang, processes can be declared dead and later be found to be	1185	If you want your software to be very reliable, you have to cope with
777	alive.	1186	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
778		1187	simply tries to work better in common error cases, such as when a network
779	In Erlang it can happen that a monitored process is declared dead and	1188	link goes down.
780	linked processes get killed, but later it turns out that the process is
781	still alive - and can receive messages.
782
783	In AEMP, when port monitoring detects a port as dead, then that port will
784	eventually be killed - it cannot happen that a node detects a port as dead
785	and then later sends messages to it, finding it is still alive.
786		1189
787	=item * Erlang can send messages to the wrong port, AEMP does not.	1190	=item * Erlang can send messages to the wrong port, AEMP does not.
788		1191
789	In Erlang it is quite likely that a node that restarts reuses a process ID	1192	In Erlang it is quite likely that a node that restarts reuses an Erlang
790	known to other nodes for a completely different process, causing messages	1193	process ID known to other nodes for a completely different process,
791	destined for that process to end up in an unrelated process.	1194	causing messages destined for that process to end up in an unrelated
		1195	process.
792		1196
793	AEMP never reuses port IDs, so old messages or old port IDs floating	1197	AEMP does not reuse port IDs, so old messages or old port IDs floating
794	around in the network will not be sent to an unrelated port.	1198	around in the network will not be sent to an unrelated port.
795		1199
796	=item * Erlang uses unprotected connections, AEMP uses secure	1200	=item * Erlang uses unprotected connections, AEMP uses secure
797	authentication and can use TLS.	1201	authentication and can use TLS.
798		1202
799	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1203	AEMP can use a proven protocol - TLS - to protect connections and
800	securely authenticate nodes.	1204	securely authenticate nodes.
801		1205
802	=item * The AEMP protocol is optimised for both text-based and binary	1206	=item * The AEMP protocol is optimised for both text-based and binary
803	communications.	1207	communications.
804		1208
805	The AEMP protocol, unlike the Erlang protocol, supports both	1209	The AEMP protocol, unlike the Erlang protocol, supports both programming
806	language-independent text-only protocols (good for debugging) and binary,	1210	language independent text-only protocols (good for debugging), and binary,
807	language-specific serialisers (e.g. Storable).	1211	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1212	used, the protocol is actually completely text-based.
808		1213
809	It has also been carefully designed to be implementable in other languages	1214	It has also been carefully designed to be implementable in other languages
810	with a minimum of work while gracefully degrading fucntionality to make the	1215	with a minimum of work while gracefully degrading functionality to make the
811	protocol simple.	1216	protocol simple.
812		1217
813	=item * AEMP has more flexible monitoring options than Erlang.	1218	=item * AEMP has more flexible monitoring options than Erlang.
814		1219
815	In Erlang, you can chose to receive I<all> exit signals as messages	1220	In Erlang, you can chose to receive I<all> exit signals as messages or
816	or I<none>, there is no in-between, so monitoring single processes is	1221	I<none>, there is no in-between, so monitoring single Erlang processes is
817	difficult to implement. Monitoring in AEMP is more flexible than in	1222	difficult to implement.
818	Erlang, as one can choose between automatic kill, exit message or callback	1223
819	on a per-process basis.	1224	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1225	between automatic kill, exit message or callback on a per-port basis.
820		1226
821	=item * Erlang tries to hide remote/local connections, AEMP does not.	1227	=item * Erlang tries to hide remote/local connections, AEMP does not.
822		1228
823	Monitoring in Erlang is not an indicator of process death/crashes,	1229	Monitoring in Erlang is not an indicator of process death/crashes, in the
824	as linking is (except linking is unreliable in Erlang).	1230	same way as linking is (except linking is unreliable in Erlang).
825		1231
826	In AEMP, you don't "look up" registered port names or send to named ports	1232	In AEMP, you don't "look up" registered port names or send to named ports
827	that might or might not be persistent. Instead, you normally spawn a port	1233	that might or might not be persistent. Instead, you normally spawn a port
828	on the remote node. The init function monitors the you, and you monitor	1234	on the remote node. The init function monitors you, and you monitor the
829	the remote port. Since both monitors are local to the node, they are much	1235	remote port. Since both monitors are local to the node, they are much more
830	more reliable.	1236	reliable (no need for C<spawn_link>).
831		1237
832	This also saves round-trips and avoids sending messages to the wrong port	1238	This also saves round-trips and avoids sending messages to the wrong port
833	(hard to do in Erlang).	1239	(hard to do in Erlang).
834		1240
835	=back	1241	=back
836		1242
837	=head1 RATIONALE	1243	=head1 RATIONALE
838		1244
839	=over 4	1245	=over 4
840		1246
841	=item Why strings for ports and noderefs, why not objects?	1247	=item Why strings for port and node IDs, why not objects?
842		1248
843	We considered "objects", but found that the actual number of methods	1249	We considered "objects", but found that the actual number of methods
844	thatc an be called are very low. Since port IDs and noderefs travel over	1250	that can be called are quite low. Since port and node IDs travel over
845	the network frequently, the serialising/deserialising would add lots of	1251	the network frequently, the serialising/deserialising would add lots of
846	overhead, as well as having to keep a proxy object.	1252	overhead, as well as having to keep a proxy object everywhere.
847		1253
848	Strings can easily be printed, easily serialised etc. and need no special	1254	Strings can easily be printed, easily serialised etc. and need no special
849	procedures to be "valid".	1255	procedures to be "valid".
850		1256
851	And a a miniport consists of a single closure stored in a global hash - it	1257	And as a result, a port with just a default receiver consists of a single
852	can't become much cheaper.	1258	code reference stored in a global hash - it can't become much cheaper.
853		1259
854	=item Why favour JSON, why not real serialising format such as Storable?	1260	=item Why favour JSON, why not a real serialising format such as Storable?
855		1261
856	In fact, any AnyEvent::MP node will happily accept Storable as framing	1262	In fact, any AnyEvent::MP node will happily accept Storable as framing
857	format, but currently there is no way to make a node use Storable by	1263	format, but currently there is no way to make a node use Storable by
858	default.	1264	default (although all nodes will accept it).
859		1265
860	The default framing protocol is JSON because a) JSON::XS is many times	1266	The default framing protocol is JSON because a) JSON::XS is many times
861	faster for small messages and b) most importantly, after years of	1267	faster for small messages and b) most importantly, after years of
862	experience we found that object serialisation is causing more problems	1268	experience we found that object serialisation is causing more problems
863	than it gains: Just like function calls, objects simply do not travel	1269	than it solves: Just like function calls, objects simply do not travel
864	easily over the network, mostly because they will always be a copy, so you	1270	easily over the network, mostly because they will always be a copy, so you
865	always have to re-think your design.	1271	always have to re-think your design.
866		1272
867	Keeping your messages simple, concentrating on data structures rather than	1273	Keeping your messages simple, concentrating on data structures rather than
868	objects, will keep your messages clean, tidy and efficient.	1274	objects, will keep your messages clean, tidy and efficient.
869		1275
870	=back	1276	=back
871		1277
		1278	=head1 PORTING FROM AnyEvent::MP VERSION 1.X
		1279
		1280	AEMP version 2 has a few major incompatible changes compared to version 1:
		1281
		1282	=over 4
		1283
		1284	=item AnyEvent::MP::Global no longer has group management functions.
		1285
		1286	At least not officially - the grp_* functions are still exported and might
		1287	work, but they will be removed in some later release.
		1288
		1289	AnyEvent::MP now comes with a distributed database that is more
		1290	powerful. Its database families map closely to port groups, but the API
		1291	has changed (the functions are also now exported by AnyEvent::MP). Here is
		1292	a rough porting guide:
		1293
		1294	grp_reg $group, $port # old
		1295	db_reg $group, $port # new
		1296
		1297	$list = grp_get $group # old
		1298	db_keys $group, sub { my $list = shift } # new
		1299
		1300	grp_mon $group, $cb->(\@ports, $add, $del) # old
		1301	db_mon $group, $cb->(\%ports, $add, $change, $del) # new
		1302
		1303	C<grp_reg> is a no-brainer (just replace by C<db_reg>), but C<grp_get> is
		1304	no longer instant, because the local node might not have a copy of the
		1305	group. You can either modify your code to allow for a callback, or use
		1306	C<db_mon> to keep an updated copy of the group:
		1307
		1308	my $local_group_copy;
		1309	db_mon $group => sub { $local_group_copy = $_[0] };
		1310
		1311	# now "keys %$local_group_copy" always returns the most up-to-date
		1312	# list of ports in the group.
		1313
		1314	C<grp_mon> can be replaced by C<db_mon> with minor changes - C<db_mon>
		1315	passes a hash as first argument, and an extra C<$chg> argument that can be
		1316	ignored:
		1317
		1318	db_mon $group => sub {
		1319	my ($ports, $add, $chg, $lde) = @_;
		1320	$ports = [keys %$ports];
		1321
		1322	# now $ports, $add and $del are the same as
		1323	# were originally passed by grp_mon.
		1324	...
		1325	};
		1326
		1327	=item Nodes not longer connect to all other nodes.
		1328
		1329	In AEMP 1.x, every node automatically loads the L<AnyEvent::MP::Global>
		1330	module, which in turn would create connections to all other nodes in the
		1331	network (helped by the seed nodes).
		1332
		1333	In version 2.x, global nodes still connect to all other global nodes, but
		1334	other nodes don't - now every node either is a global node itself, or
		1335	attaches itself to another global node.
		1336
		1337	If a node isn't a global node itself, then it attaches itself to one
		1338	of its seed nodes. If that seed node isn't a global node yet, it will
		1339	automatically be upgraded to a global node.
		1340
		1341	So in many cases, nothing needs to be changed - one just has to make sure
		1342	that all seed nodes are meshed together with the other seed nodes (as with
		1343	AEMP 1.x), and other nodes specify them as seed nodes. This is most easily
		1344	achieved by specifying the same set of seed nodes for all nodes in the
		1345	network.
		1346
		1347	Not opening a connection to every other node is usually an advantage,
		1348	except when you need the lower latency of an already established
		1349	connection. To ensure a node establishes a connection to another node,
		1350	you can monitor the node port (C<mon $node, ...>), which will attempt to
		1351	create the connection (and notify you when the connection fails).
		1352
		1353	=item Listener-less nodes (nodes without binds) are gone.
		1354
		1355	And are not coming back, at least not in their old form. If no C<binds>
		1356	are specified for a node, AnyEvent::MP assumes a default of C<*:*>.
		1357
		1358	There are vague plans to implement some form of routing domains, which
		1359	might or might not bring back listener-less nodes, but don't count on it.
		1360
		1361	The fact that most connections are now optional somewhat mitigates this,
		1362	as a node can be effectively unreachable from the outside without any
		1363	problems, as long as it isn't a global node and only reaches out to other
		1364	nodes (as opposed to being contacted from other nodes).
		1365
		1366	=item $AnyEvent::MP::Kernel::WARN has gone.
		1367
		1368	AnyEvent has acquired a logging framework (L<AnyEvent::Log>), and AEMP now
		1369	uses this, and so should your programs.
		1370
		1371	Every module now documents what kinds of messages it generates, with
		1372	AnyEvent::MP acting as a catch all.
		1373
		1374	On the positive side, this means that instead of setting
		1375	C<PERL_ANYEVENT_MP_WARNLEVEL>, you can get away by setting C<AE_VERBOSE> -
		1376	much less to type.
		1377
		1378	=back
		1379
		1380	=head1 LOGGING
		1381
		1382	AnyEvent::MP does not normally log anything by itself, but sinc eit is the
		1383	root of the contetx hierarchy for AnyEvent::MP modules, it will receive
		1384	all log messages by submodules.
		1385
872	=head1 SEE ALSO	1386	=head1 SEE ALSO
		1387
		1388	L<AnyEvent::MP::Intro> - a gentle introduction.
		1389
		1390	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1391
		1392	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1393	your applications.
		1394
		1395	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1396
		1397	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1398	all nodes.
873		1399
874	L<AnyEvent>.	1400	L<AnyEvent>.
875		1401
876	=head1 AUTHOR	1402	=head1 AUTHOR
877		1403

Diff Legend

–	Removed lines
+	Added lines
<	Changed lines
>	Changed lines