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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.65 by root, Fri Aug 28 01:00:34 2009 UTC vs.
Revision 1.142 by root, Fri Mar 23 13:44:01 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
40		43
41	=head1 CURRENT STATUS	44	# temporarily execute code in port context
		45	peval $port, sub { die "kill the port!" };
42		46
43	AnyEvent::MP - stable API, should work	47	# execute callbacks in $SELF port context
44	AnyEvent::MP::Intro - outdated	48	my $timer = AE::timer 1, 0, psub {
45	AnyEvent::MP::Kernel - WIP	49	die "kill the port, delayed";
46	AnyEvent::MP::Transport - mostly stable	50	};
47
48	stay tuned.
49		51
50	=head1 DESCRIPTION	52	=head1 DESCRIPTION
51		53
52	This module (-family) implements a simple message passing framework.	54	This module (-family) implements a simple message passing framework.
53		55
54	Despite its simplicity, you can securely message other processes running	56	Despite its simplicity, you can securely message other processes running
55	on the same or other hosts.	57	on the same or other hosts, and you can supervise entities remotely.
56		58
57	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	59	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
58	manual page.	60	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		61
64	=head1 CONCEPTS	62	=head1 CONCEPTS
65		63
66	=over 4	64	=over 4
67		65
68	=item port	66	=item port
69		67
70	A port is something you can send messages to (with the C<snd> function).	68	Not to be confused with a TCP port, a "port" is something you can send
		69	messages to (with the C<snd> function).
71		70
72	Ports allow you to register C<rcv> handlers that can match all or just	71	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	72	some messages. Messages send to ports will not be queued, regardless of
74	anything was listening for them or not.	73	anything was listening for them or not.
75		74
		75	Ports are represented by (printable) strings called "port IDs".
		76
76	=item port ID - C<noderef#portname>	77	=item port ID - C<nodeid#portname>
77		78
78	A port ID is the concatenation of a noderef, a hash-mark (C<#>) as	79	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	80	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	81	format created by AnyEvent::MP).
81	reference.
82		82
83	=item node	83	=item node
84		84
85	A node is a single process containing at least one port - the node port,	85	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	86	which enables nodes to manage each other remotely, and to create new
87	ports.	87	ports.
88		88
89	Nodes are either private (single-process only), slaves (can only talk to	89	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	90	(no listening ports). Private nodes cannot talk to other private nodes
91	from any other node).	91	currently, but all nodes can talk to public nodes.
92		92
		93	Nodes is represented by (printable) strings called "node IDs".
		94
93	=item node ID - C<[a-za-Z0-9_\-.:]+>	95	=item node ID - C<[A-Za-z0-9_\-.:]*>
94		96
95	A node ID is a string that uniquely identifies the node within a	97	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	98	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	99	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
98	doesn't interpret node IDs in any way.	100	doesn't interpret node IDs in any way except to uniquely identify a node.
99		101
100	=item binds - C<ip:port>	102	=item binds - C<ip:port>
101		103
102	Nodes can only talk to each other by creating some kind of connection to	104	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	105	each other. To do this, nodes should listen on one or more local transport
		106	endpoints - binds.
		107
104	endpoints - binds. Currently, only standard C<ip:port> specifications can	108	Currently, only standard C<ip:port> specifications can be used, which
105	be used, which specify TCP ports to listen on.	109	specify TCP ports to listen on. So a bind is basically just a tcp socket
		110	in listening mode thta accepts conenctions form other nodes.
106		111
		112	=item seed nodes
		113
		114	When a node starts, it knows nothing about the network it is in - it
		115	needs to connect to at least one other node that is already in the
		116	network. These other nodes are called "seed nodes".
		117
		118	Seed nodes themselves are not special - they are seed nodes only because
		119	some other node I<uses> them as such, but any node can be used as seed
		120	node for other nodes, and eahc node cna use a different set of seed nodes.
		121
		122	In addition to discovering the network, seed nodes are also used to
		123	maintain the network - all nodes using the same seed node form are part of
		124	the same network. If a network is split into multiple subnets because e.g.
		125	the network link between the parts goes down, then using the same seed
		126	nodes for all nodes ensures that eventually the subnets get merged again.
		127
		128	Seed nodes are expected to be long-running, and at least one seed node
		129	should always be available. They should also be relatively responsive - a
		130	seed node that blocks for long periods will slow down everybody else.
		131
		132	For small networks, it's best if every node uses the same set of seed
		133	nodes. For large networks, it can be useful to specify "regional" seed
		134	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		135	each other. What's important is that all seed nodes connections form a
		136	complete graph, so that the network cannot split into separate subnets
		137	forever.
		138
		139	Seed nodes are represented by seed IDs.
		140
107	=item seeds - C<host:port>	141	=item seed IDs - C<host:port>
108		142
109	When a node starts, it knows nothing about the network. To teach the node	143	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	144	TCP port) of nodes that should be used as seed nodes.
111	network. This node is called a seed.
112		145
113	Seeds are transport endpoint(s) of as many nodes as one wants. Those nodes	146	=item global nodes
114	are expected to be long-running, and at least one of those should always	147
115	be available. When nodes run out of connections (e.g. due to a network	148	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	149	connect to other nodes they only know by name. In addition, AEMP offers a
117	join the network.	150	distributed "group database", which maps group names to a list of strings
		151	- for example, to register worker ports.
		152
		153	A network needs at least one global node to work, and allows every node to
		154	be a global node.
		155
		156	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		157	node and tries to keep connections to all other nodes. So while it can
		158	make sense to make every node "global" in small networks, it usually makes
		159	sense to only make seed nodes into global nodes in large networks (nodes
		160	keep connections to seed nodes and global nodes, so makign them the same
		161	reduces overhead).
118		162
119	=back	163	=back
120		164
121	=head1 VARIABLES/FUNCTIONS	165	=head1 VARIABLES/FUNCTIONS
122		166
124		168
125	=cut	169	=cut
126		170
127	package AnyEvent::MP;	171	package AnyEvent::MP;
128		172
		173	use AnyEvent::MP::Config ();
129	use AnyEvent::MP::Kernel;	174	use AnyEvent::MP::Kernel;
		175	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
130		176
131	use common::sense;	177	use common::sense;
132		178
133	use Carp ();	179	use Carp ();
134		180
135	use AE ();	181	use AnyEvent ();
		182	use Guard ();
136		183
137	use base "Exporter";	184	use base "Exporter";
138		185
139	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	186	our $VERSION = $AnyEvent::MP::Config::VERSION;
140		187
141	our @EXPORT = qw(	188	our @EXPORT = qw(
142	NODE $NODE *SELF node_of after	189	NODE $NODE *SELF node_of after
143	resolve_node initialise_node	190	configure
144	snd rcv mon mon_guard kil reg psub spawn	191	snd rcv mon mon_guard kil psub peval spawn cal
145	port	192	port
		193	db_set db_del db_reg
		194	db_mon db_family db_keys db_values
146	);	195	);
147		196
148	our $SELF;	197	our $SELF;
149		198
150	sub _self_die() {	199	sub _self_die() {
…		…
153	kil $SELF, die => $msg;	202	kil $SELF, die => $msg;
154	}	203	}
155		204
156	=item $thisnode = NODE / $NODE	205	=item $thisnode = NODE / $NODE
157		206
158	The C<NODE> function returns, and the C<$NODE> variable contains the node	207	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	208	ID of the node running in the current process. This value is initialised by
160	a call to C<initialise_node>.	209	a call to C<configure>.
161		210
162	=item $nodeid = node_of $port	211	=item $nodeid = node_of $port
163		212
164	Extracts and returns the node ID part from a port ID or a node ID.	213	Extracts and returns the node ID from a port ID or a node ID.
165		214
166	=item initialise_node $profile_name	215	=item configure $profile, key => value...
		216
		217	=item configure key => value...
167		218
168	Before a node can talk to other nodes on the network (i.e. enter	219	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	220	"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	221	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.	222	some other nodes in the network to discover other nodes.
172		223
173	This function initialises a node - it must be called exactly once (or	224	This function configures a node - it must be called exactly once (or
174	never) before calling other AnyEvent::MP functions.	225	never) before calling other AnyEvent::MP functions.
175		226
176	The first argument is a profile name. If it is C<undef> or missing, then	227	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>).	228	F<aemp> command line utility (sans the set/del prefix), with these additions:
178		229
		230	=over 4
		231
		232	=item norc => $boolean (default false)
		233
		234	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
		235	be consulted - all configuraiton options must be specified in the
		236	C<configure> call.
		237
		238	=item force => $boolean (default false)
		239
		240	IF true, then the values specified in the C<configure> will take
		241	precedence over any values configured via the rc file. The default is for
		242	the rc file to override any options specified in the program.
		243
		244	=back
		245
		246	=over 4
		247
		248	=item step 1, gathering configuration from profiles
		249
179	The function then looks up the profile in the aemp configuration (see the	250	The function first looks up a profile in the aemp configuration (see the
180	L<aemp> commandline utility).	251	L<aemp> commandline utility). The profile name can be specified via the
		252	named C<profile> parameter or can simply be the first parameter). If it is
		253	missing, then the nodename (F<uname -n>) will be used as profile name.
		254
		255	The profile data is then gathered as follows:
		256
		257	First, all remaining key => value pairs (all of which are conveniently
		258	undocumented at the moment) will be interpreted as configuration
		259	data. Then they will be overwritten by any values specified in the global
		260	default configuration (see the F<aemp> utility), then the chain of
		261	profiles chosen by the profile name (and any C<parent> attributes).
		262
		263	That means that the values specified in the profile have highest priority
		264	and the values specified directly via C<configure> have lowest priority,
		265	and can only be used to specify defaults.
181		266
182	If the profile specifies a node ID, then this will become the node ID of	267	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	268	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.	269	a unique randoms tring (C</%u>) appended.
		270
		271	The node ID can contain some C<%> sequences that are expanded: C<%n>
		272	is expanded to the local nodename, C<%u> is replaced by a random
		273	strign to make the node unique. For example, the F<aemp> commandline
		274	utility uses C<aemp/%n/%u> as nodename, which might expand to
		275	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		276
		277	=item step 2, bind listener sockets
185		278
186	The next step is to look up the binds in the profile, followed by binding	279	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	280	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	281	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	282	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).	283	binds, but it can still talk to all "normal" nodes).
191		284
192	If the profile does not specify a binds list, then the node ID will be	285	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	286	used, meaning the node will bind on a dynamically-assigned port on every
194	used as binds list.	287	local IP address it finds.
195		288
		289	=item step 3, connect to seed nodes
		290
196	Lastly, the seeds list from the profile is passed to the	291	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	292	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.	293	connectivity with at least one node at any point in time.
199		294
200	Example: become a distributed node listening on the guessed noderef, or	295	=back
201	the one specified via C<aemp> for the current node. This should be the	296
		297	Example: become a distributed node using the local node name as profile.
202	most common form of invocation for "daemon"-type nodes.	298	This should be the most common form of invocation for "daemon"-type nodes.
203		299
204	initialise_node;	300	configure
205		301
206	Example: become an anonymous node. This form is often used for commandline	302	Example: become a semi-anonymous node. This form is often used for
207	clients.	303	commandline clients.
208		304
209	initialise_node "anon/";	305	configure nodeid => "myscript/%n/%u";
210		306
211	Example: become a distributed node. If there is no profile of the given	307	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	308	for a seed node as it binds on all local addresses on a fixed port (4040,
213	on the resulting addresses.	309	customary for aemp).
214		310
215	initialise_node "localhost:4044";	311	# use the aemp commandline utility
		312	# aemp profile seed binds '*:4040'
		313
		314	# then use it
		315	configure profile => "seed";
		316
		317	# or simply use aemp from the shell again:
		318	# aemp run profile seed
		319
		320	# or provide a nicer-to-remember nodeid
		321	# aemp run profile seed nodeid "$(hostname)"
216		322
217	=item $SELF	323	=item $SELF
218		324
219	Contains the current port id while executing C<rcv> callbacks or C<psub>	325	Contains the current port id while executing C<rcv> callbacks or C<psub>
220	blocks.	326	blocks.
221		327
222	=item SELF, %SELF, @SELF...	328	=item *SELF, SELF, %SELF, @SELF...
223		329
224	Due to some quirks in how perl exports variables, it is impossible to	330	Due to some quirks in how perl exports variables, it is impossible to
225	just export C<$SELF>, all the symbols called C<SELF> are exported by this	331	just export C<$SELF>, all the symbols named C<SELF> are exported by this
226	module, but only C<$SELF> is currently used.	332	module, but only C<$SELF> is currently used.
227		333
228	=item snd $port, type => @data	334	=item snd $port, type => @data
229		335
230	=item snd $port, @msg	336	=item snd $port, @msg
231		337
232	Send the given message to the given port ID, which can identify either	338	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.	339	local or a remote port, and must be a port ID.
234		340
235	While the message can be about anything, it is highly recommended to use a	341	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	342	use a string as first element (a port ID, or some word that indicates a
237	type etc.).	343	request type etc.) and to consist if only simple perl values (scalars,
		344	arrays, hashes) - if you think you need to pass an object, think again.
238		345
239	The message data effectively becomes read-only after a call to this	346	The message data logically becomes read-only after a call to this
240	function: modifying any argument is not allowed and can cause many	347	function: modifying any argument (or values referenced by them) is
241	problems.	348	forbidden, as there can be considerable time between the call to C<snd>
		349	and the time the message is actually being serialised - in fact, it might
		350	never be copied as within the same process it is simply handed to the
		351	receiving port.
242		352
243	The type of data you can transfer depends on the transport protocol: when	353	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	354	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	355	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	356	that Storable can serialise and deserialise is allowed, and for the local
247	node, anything can be passed.	357	node, anything can be passed. Best rely only on the common denominator of
		358	these.
248		359
249	=item $local_port = port	360	=item $local_port = port
250		361
251	Create a new local port object and returns its port ID. Initially it has	362	Create a new local port object and returns its port ID. Initially it has
252	no callbacks set and will throw an error when it receives messages.	363	no callbacks set and will throw an error when it receives messages.
…		…
271		382
272	=cut	383	=cut
273		384
274	sub rcv($@);	385	sub rcv($@);
275		386
276	sub _kilme {	387	my $KILME = sub {
277	die "received message on port without callback";	388	(my $tag = substr $_[0], 0, 30) =~ s/([\x20-\x7e])/./g;
278	}	389	kil $SELF, unhandled_message => "no callback found for message '$tag'";
		390	};
279		391
280	sub port(;&) {	392	sub port(;&) {
281	my $id = "$UNIQ." . $ID++;	393	my $id = $UNIQ . ++$ID;
282	my $port = "$NODE#$id";	394	my $port = "$NODE#$id";
283		395
284	rcv $port, shift \|\| \&_kilme;	396	rcv $port, shift \|\| $KILME;
285		397
286	$port	398	$port
287	}	399	}
288		400
289	=item rcv $local_port, $callback->(@msg)	401	=item rcv $local_port, $callback->(@msg)
…		…
294		406
295	The global C<$SELF> (exported by this module) contains C<$port> while	407	The global C<$SELF> (exported by this module) contains C<$port> while
296	executing the callback. Runtime errors during callback execution will	408	executing the callback. Runtime errors during callback execution will
297	result in the port being C<kil>ed.	409	result in the port being C<kil>ed.
298		410
299	The default callback received all messages not matched by a more specific	411	The default callback receives all messages not matched by a more specific
300	C<tag> match.	412	C<tag> match.
301		413
302	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...	414	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
303		415
304	Register (or replace) callbacks to be called on messages starting with the	416	Register (or replace) callbacks to be called on messages starting with the
…		…
325	msg1 => sub { ... },	437	msg1 => sub { ... },
326	...	438	...
327	;	439	;
328		440
329	Example: temporarily register a rcv callback for a tag matching some port	441	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.	442	(e.g. for an rpc reply) and unregister it after a message was received.
331		443
332	rcv $port, $otherport => sub {	444	rcv $port, $otherport => sub {
333	my @reply = @_;	445	my @reply = @_;
334		446
335	rcv $SELF, $otherport;	447	rcv $SELF, $otherport;
…		…
337		449
338	=cut	450	=cut
339		451
340	sub rcv($@) {	452	sub rcv($@) {
341	my $port = shift;	453	my $port = shift;
342	my ($noderef, $portid) = split /#/, $port, 2;	454	my ($nodeid, $portid) = split /#/, $port, 2;
343		455
344	$NODE{$noderef} == $NODE{""}	456	$NODE{$nodeid} == $NODE{""}
345	or Carp::croak "$port: rcv can only be called on local ports, caught";	457	or Carp::croak "$port: rcv can only be called on local ports, caught";
346		458
347	while (@_) {	459	while (@_) {
348	if (ref $_[0]) {	460	if (ref $_[0]) {
349	if (my $self = $PORT_DATA{$portid}) {	461	if (my $self = $PORT_DATA{$portid}) {
350	"AnyEvent::MP::Port" eq ref $self	462	"AnyEvent::MP::Port" eq ref $self
351	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	463	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
352		464
353	$self->[2] = shift;	465	$self->[0] = shift;
354	} else {	466	} else {
355	my $cb = shift;	467	my $cb = shift;
356	$PORT{$portid} = sub {	468	$PORT{$portid} = sub {
357	local $SELF = $port;	469	local $SELF = $port;
358	eval { &$cb }; _self_die if $@;	470	eval { &$cb }; _self_die if $@;
359	};	471	};
360	}	472	}
361	} elsif (defined $_[0]) {	473	} elsif (defined $_[0]) {
362	my $self = $PORT_DATA{$portid} \|\|= do {	474	my $self = $PORT_DATA{$portid} \|\|= do {
363	my $self = bless [$PORT{$port} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";	475	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
364		476
365	$PORT{$portid} = sub {	477	$PORT{$portid} = sub {
366	local $SELF = $port;	478	local $SELF = $port;
367		479
368	if (my $cb = $self->[1]{$_[0]}) {	480	if (my $cb = $self->[1]{$_[0]}) {
…		…
390	}	502	}
391		503
392	$port	504	$port
393	}	505	}
394		506
		507	=item peval $port, $coderef[, @args]
		508
		509	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		510	when the code throews an exception the C<$port> will be killed.
		511
		512	Any remaining args will be passed to the callback. Any return values will
		513	be returned to the caller.
		514
		515	This is useful when you temporarily want to execute code in the context of
		516	a port.
		517
		518	Example: create a port and run some initialisation code in it's context.
		519
		520	my $port = port { ... };
		521
		522	peval $port, sub {
		523	init
		524	or die "unable to init";
		525	};
		526
		527	=cut
		528
		529	sub peval($$) {
		530	local $SELF = shift;
		531	my $cb = shift;
		532
		533	if (wantarray) {
		534	my @res = eval { &$cb };
		535	_self_die if $@;
		536	@res
		537	} else {
		538	my $res = eval { &$cb };
		539	_self_die if $@;
		540	$res
		541	}
		542	}
		543
395	=item $closure = psub { BLOCK }	544	=item $closure = psub { BLOCK }
396		545
397	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	546	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>	547	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.	548	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		549
		550	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		551	BLOCK }, @_ } >>.
400		552
401	This is useful when you register callbacks from C<rcv> callbacks:	553	This is useful when you register callbacks from C<rcv> callbacks:
402		554
403	rcv delayed_reply => sub {	555	rcv delayed_reply => sub {
404	my ($delay, @reply) = @_;	556	my ($delay, @reply) = @_;
…		…
428	$res	580	$res
429	}	581	}
430	}	582	}
431	}	583	}
432		584
433	=item $guard = mon $port, $cb->(@reason)	585	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
434		586
435	=item $guard = mon $port, $rcvport	587	=item $guard = mon $port # kill $SELF when $port dies
436		588
437	=item $guard = mon $port	589	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
438		590
439	=item $guard = mon $port, $rcvport, @msg	591	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
440		592
441	Monitor the given port and do something when the port is killed or	593	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	594	messages to it were lost, and optionally return a guard that can be used
443	to stop monitoring again.	595	to stop monitoring again.
444		596
		597	The first two forms distinguish between "normal" and "abnormal" kil's:
		598
		599	In the first form (another port given), if the C<$port> is C<kil>'ed with
		600	a non-empty reason, the other port (C<$rcvport>) will be kil'ed with the
		601	same reason. That is, on "normal" kil's nothing happens, while under all
		602	other conditions, the other port is killed with the same reason.
		603
		604	The second form (kill self) is the same as the first form, except that
		605	C<$rvport> defaults to C<$SELF>.
		606
		607	The remaining forms don't distinguish between "normal" and "abnormal" kil's
		608	- it's up to the callback or receiver to check whether the C<@reason> is
		609	empty and act accordingly.
		610
		611	In the third form (callback), the callback is simply called with any
		612	number of C<@reason> elements (empty @reason means that the port was deleted
		613	"normally"). Note also that I<< the callback B<must> never die >>, so use
		614	C<eval> if unsure.
		615
		616	In the last form (message), a message of the form C<$rcvport, @msg,
		617	@reason> will be C<snd>.
		618
		619	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		620	alert was raised), they are removed and will not trigger again, even if it
		621	turns out that the port is still alive.
		622
		623	As a rule of thumb, monitoring requests should always monitor a remote
		624	port locally (using a local C<$rcvport> or a callback). The reason is that
		625	kill messages might get lost, just like any other message. Another less
		626	obvious reason is that even monitoring requests can get lost (for example,
		627	when the connection to the other node goes down permanently). When
		628	monitoring a port locally these problems do not exist.
		629
445	C<mon> effectively guarantees that, in the absence of hardware failures,	630	C<mon> effectively guarantees that, in the absence of hardware failures,
446	that after starting the monitor, either all messages sent to the port	631	after starting the monitor, either all messages sent to the port will
447	will arrive, or the monitoring action will be invoked after possible	632	arrive, or the monitoring action will be invoked after possible message
448	message loss has been detected. No messages will be lost "in between"	633	loss has been detected. No messages will be lost "in between" (after
449	(after the first lost message no further messages will be received by the	634	the first lost message no further messages will be received by the
450	port). After the monitoring action was invoked, further messages might get	635	port). After the monitoring action was invoked, further messages might get
451	delivered again.	636	delivered again.
452		637
453	Note that monitoring-actions are one-shot: once released, they are removed	638	Inter-host-connection timeouts and monitoring depend on the transport
454	and will not trigger again.	639	used. The only transport currently implemented is TCP, and AnyEvent::MP
		640	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		641	non-idle connection, and usually around two hours for idle connections).
455		642
456	In the first form (callback), the callback is simply called with any	643	This means that monitoring is good for program errors and cleaning up
457	number of C<@reason> elements (no @reason means that the port was deleted	644	stuff eventually, but they are no replacement for a timeout when you need
458	"normally"). Note also that I<< the callback B<must> never die >>, so use	645	to ensure some maximum latency.
459	C<eval> if unsure.
460
461	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
463	"normal" kils nothing happens, while under all other conditions, the other
464	port is killed with the same reason.
465
466	The third form (kill self) is the same as the second form, except that
467	C<$rvport> defaults to C<$SELF>.
468
469	In the last form (message), a message of the form C<@msg, @reason> will be
470	C<snd>.
471
472	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
474	lost, just like any other message. Another less obvious reason is that
475	even monitoring requests can get lost (for exmaple, when the connection
476	to the other node goes down permanently). When monitoring a port locally
477	these problems do not exist.
478		646
479	Example: call a given callback when C<$port> is killed.	647	Example: call a given callback when C<$port> is killed.
480		648
481	mon $port, sub { warn "port died because of <@_>\n" };	649	mon $port, sub { warn "port died because of <@_>\n" };
482		650
…		…
489	mon $port, $self => "restart";	657	mon $port, $self => "restart";
490		658
491	=cut	659	=cut
492		660
493	sub mon {	661	sub mon {
494	my ($noderef, $port) = split /#/, shift, 2;	662	my ($nodeid, $port) = split /#/, shift, 2;
495		663
496	my $node = $NODE{$noderef} \|\| add_node $noderef;	664	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
497		665
498	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';	666	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
499		667
500	unless (ref $cb) {	668	unless (ref $cb) {
501	if (@_) {	669	if (@_) {
…		…
510	}	678	}
511		679
512	$node->monitor ($port, $cb);	680	$node->monitor ($port, $cb);
513		681
514	defined wantarray	682	defined wantarray
515	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	683	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
516	}	684	}
517		685
518	=item $guard = mon_guard $port, $ref, $ref...	686	=item $guard = mon_guard $port, $ref, $ref...
519		687
520	Monitors the given C<$port> and keeps the passed references. When the port	688	Monitors the given C<$port> and keeps the passed references. When the port
521	is killed, the references will be freed.	689	is killed, the references will be freed.
522		690
523	Optionally returns a guard that will stop the monitoring.	691	Optionally returns a guard that will stop the monitoring.
524		692
525	This function is useful when you create e.g. timers or other watchers and	693	This function is useful when you create e.g. timers or other watchers and
526	want to free them when the port gets killed:	694	want to free them when the port gets killed (note the use of C<psub>):
527		695
528	$port->rcv (start => sub {	696	$port->rcv (start => sub {
529	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	697	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
530	undef $timer if 0.9 < rand;	698	undef $timer if 0.9 < rand;
531	});	699	});
532	});	700	});
533		701
534	=cut	702	=cut
…		…
543		711
544	=item kil $port[, @reason]	712	=item kil $port[, @reason]
545		713
546	Kill the specified port with the given C<@reason>.	714	Kill the specified port with the given C<@reason>.
547		715
548	If no C<@reason> is specified, then the port is killed "normally" (linked	716	If no C<@reason> is specified, then the port is killed "normally" -
549	ports will not be kileld, or even notified).	717	monitor callback will be invoked, but the kil will not cause linked ports
		718	(C<mon $mport, $lport> form) to get killed.
550		719
551	Otherwise, linked ports get killed with the same reason (second form of	720	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
552	C<mon>, see below).	721	form) get killed with the same reason.
553		722
554	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	723	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
555	will be reported as reason C<< die => $@ >>.	724	will be reported as reason C<< die => $@ >>.
556		725
557	Transport/communication errors are reported as C<< transport_error =>	726	Transport/communication errors are reported as C<< transport_error =>
558	$message >>.	727	$message >>.
559		728
560	=cut	729	Common idioms:
		730
		731	# silently remove yourself, do not kill linked ports
		732	kil $SELF;
		733
		734	# report a failure in some detail
		735	kil $SELF, failure_mode_1 => "it failed with too high temperature";
		736
		737	# do not waste much time with killing, just die when something goes wrong
		738	open my $fh, "<file"
		739	or die "file: $!";
561		740
562	=item $port = spawn $node, $initfunc[, @initdata]	741	=item $port = spawn $node, $initfunc[, @initdata]
563		742
564	Creates a port on the node C<$node> (which can also be a port ID, in which	743	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).	744	case it's the node where that port resides).
566		745
567	The port ID of the newly created port is return immediately, and it is	746	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.	747	possible to immediately start sending messages or to monitor the port.
569		748
570	After the port has been created, the init function is	749	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	750	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	751	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
573	program, use C<::name>.	752	specify a function in the main program, use C<::name>.
574		753
575	If the function doesn't exist, then the node tries to C<require>	754	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.	755	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	756	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
578	exists or it runs out of package names.	757	exists or it runs out of package names.
579		758
580	The init function is then called with the newly-created port as context	759	The init function is then called with the newly-created port as context
581	object (C<$SELF>) and the C<@initdata> values as arguments.	760	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		761	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		762	the port might not get created.
582		763
583	A common idiom is to pass your own port, monitor the spawned port, and	764	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	765	port, and in the remote init function, immediately monitor the passed
585	ensures that both ports get cleaned up when there is a problem.	766	local port. This two-way monitoring ensures that both ports get cleaned up
		767	when there is a problem.
		768
		769	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		770	caller before C<spawn> returns (by delaying invocation when spawn is
		771	called for the local node).
586		772
587	Example: spawn a chat server port on C<$othernode>.	773	Example: spawn a chat server port on C<$othernode>.
588		774
589	# this node, executed from within a port context:	775	# this node, executed from within a port context:
590	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	776	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
605		791
606	sub _spawn {	792	sub _spawn {
607	my $port = shift;	793	my $port = shift;
608	my $init = shift;	794	my $init = shift;
609		795
		796	# rcv will create the actual port
610	local $SELF = "$NODE#$port";	797	local $SELF = "$NODE#$port";
611	eval {	798	eval {
612	&{ load_func $init }	799	&{ load_func $init }
613	};	800	};
614	_self_die if $@;	801	_self_die if $@;
615	}	802	}
616		803
617	sub spawn(@) {	804	sub spawn(@) {
618	my ($noderef, undef) = split /#/, shift, 2;	805	my ($nodeid, undef) = split /#/, shift, 2;
619		806
620	my $id = "$RUNIQ." . $ID++;	807	my $id = $RUNIQ . ++$ID;
621		808
622	$_[0] =~ /::/	809	$_[0] =~ /::/
623	or Carp::croak "spawn init function must be a fully-qualified name, caught";	810	or Carp::croak "spawn init function must be a fully-qualified name, caught";
624		811
625	snd_to_func $noderef, "AnyEvent::MP::_spawn" => $id, @_;	812	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
626		813
627	"$noderef#$id"	814	"$nodeid#$id"
628	}	815	}
		816
629		817
630	=item after $timeout, @msg	818	=item after $timeout, @msg
631		819
632	=item after $timeout, $callback	820	=item after $timeout, $callback
633		821
634	Either sends the given message, or call the given callback, after the	822	Either sends the given message, or call the given callback, after the
635	specified number of seconds.	823	specified number of seconds.
636		824
637	This is simply a utility function that come sin handy at times.	825	This is simply a utility function that comes in handy at times - the
		826	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		827	so it may go away in the future.
638		828
639	=cut	829	=cut
640		830
641	sub after($@) {	831	sub after($@) {
642	my ($timeout, @action) = @_;	832	my ($timeout, @action) = @_;
…		…
647	? $action[0]()	837	? $action[0]()
648	: snd @action;	838	: snd @action;
649	};	839	};
650	}	840	}
651		841
		842	#=item $cb2 = timeout $seconds, $cb[, @args]
		843
		844	=item cal $port, @msg, $callback[, $timeout]
		845
		846	A simple form of RPC - sends a message to the given C<$port> with the
		847	given contents (C<@msg>), but adds a reply port to the message.
		848
		849	The reply port is created temporarily just for the purpose of receiving
		850	the reply, and will be C<kil>ed when no longer needed.
		851
		852	A reply message sent to the port is passed to the C<$callback> as-is.
		853
		854	If an optional time-out (in seconds) is given and it is not C<undef>,
		855	then the callback will be called without any arguments after the time-out
		856	elapsed and the port is C<kil>ed.
		857
		858	If no time-out is given (or it is C<undef>), then the local port will
		859	monitor the remote port instead, so it eventually gets cleaned-up.
		860
		861	Currently this function returns the temporary port, but this "feature"
		862	might go in future versions unless you can make a convincing case that
		863	this is indeed useful for something.
		864
		865	=cut
		866
		867	sub cal(@) {
		868	my $timeout = ref $_[-1] ? undef : pop;
		869	my $cb = pop;
		870
		871	my $port = port {
		872	undef $timeout;
		873	kil $SELF;
		874	&$cb;
		875	};
		876
		877	if (defined $timeout) {
		878	$timeout = AE::timer $timeout, 0, sub {
		879	undef $timeout;
		880	kil $port;
		881	$cb->();
		882	};
		883	} else {
		884	mon $_[0], sub {
		885	kil $port;
		886	$cb->();
		887	};
		888	}
		889
		890	push @_, $port;
		891	&snd;
		892
		893	$port
		894	}
		895
		896	=back
		897
		898	=head1 DISTRIBUTED DATABASE
		899
		900	AnyEvent::MP comes with a simple distributed database. The database will
		901	be mirrored asynchronously on all global nodes. Other nodes bind to one
		902	of the global nodes for their needs. Every node has a "local database"
		903	which contains all the values that are set locally. All local databases
		904	are merged together to form the global database, which can be queried.
		905
		906	The database structure is that of a two-level hash - the database hash
		907	contains hashes which contain values, similarly to a perl hash of hashes,
		908	i.e.:
		909
		910	$DATABASE{$family}{$subkey} = $value
		911
		912	The top level hash key is called "family", and the second-level hash key
		913	is called "subkey" or simply "key".
		914
		915	The family must be alphanumeric, i.e. start with a letter and consist
		916	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		917	pretty much like Perl module names.
		918
		919	As the family namespace is global, it is recommended to prefix family names
		920	with the name of the application or module using it.
		921
		922	The subkeys must be non-empty strings, with no further restrictions.
		923
		924	The values should preferably be strings, but other perl scalars should
		925	work as well (such as C<undef>, arrays and hashes).
		926
		927	Every database entry is owned by one node - adding the same family/subkey
		928	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		929	but the result might be nondeterministic, i.e. the key might have
		930	different values on different nodes.
		931
		932	Different subkeys in the same family can be owned by different nodes
		933	without problems, and in fact, this is the common method to create worker
		934	pools. For example, a worker port for image scaling might do this:
		935
		936	db_set my_image_scalers => $port;
		937
		938	And clients looking for an image scaler will want to get the
		939	C<my_image_scalers> keys from time to time:
		940
		941	db_keys my_image_scalers => sub {
		942	@ports = @{ $_[0] };
		943	};
		944
		945	Or better yet, they want to monitor the database family, so they always
		946	have a reasonable up-to-date copy:
		947
		948	db_mon my_image_scalers => sub {
		949	@ports = keys %{ $_[0] };
		950	};
		951
		952	In general, you can set or delete single subkeys, but query and monitor
		953	whole families only.
		954
		955	If you feel the need to monitor or query a single subkey, try giving it
		956	it's own family.
		957
		958	=over
		959
		960	=item $guard = db_set $family => $subkey [=> $value]
		961
		962	Sets (or replaces) a key to the database - if C<$value> is omitted,
		963	C<undef> is used instead.
		964
		965	When called in non-void context, C<db_set> returns a guard that
		966	automatically calls C<db_del> when it is destroyed.
		967
		968	=item db_del $family => $subkey...
		969
		970	Deletes one or more subkeys from the database family.
		971
		972	=item $guard = db_reg $family => $port => $value
		973
		974	=item $guard = db_reg $family => $port
		975
		976	=item $guard = db_reg $family
		977
		978	Registers a port in the given family and optionally returns a guard to
		979	remove it.
		980
		981	This function basically does the same as:
		982
		983	db_set $family => $port => $value
		984
		985	Except that the port is monitored and automatically removed from the
		986	database family when it is kil'ed.
		987
		988	If C<$value> is missing, C<undef> is used. If C<$port> is missing, then
		989	C<$SELF> is used.
		990
		991	This function is most useful to register a port in some port group (which
		992	is just another name for a database family), and have it removed when the
		993	port is gone. This works best when the port is a local port.
		994
		995	=cut
		996
		997	sub db_reg($$;$) {
		998	my $family = shift;
		999	my $port = @_ ? shift : $SELF;
		1000
		1001	my $clr = sub { db_del $family => $port };
		1002	mon $port, $clr;
		1003
		1004	db_set $family => $port => $_[0];
		1005
		1006	defined wantarray
		1007	and &Guard::guard ($clr)
		1008	}
		1009
		1010	=item db_family $family => $cb->(\%familyhash)
		1011
		1012	Queries the named database C<$family> and call the callback with the
		1013	family represented as a hash. You can keep and freely modify the hash.
		1014
		1015	=item db_keys $family => $cb->(\@keys)
		1016
		1017	Same as C<db_family>, except it only queries the family I<subkeys> and passes
		1018	them as array reference to the callback.
		1019
		1020	=item db_values $family => $cb->(\@values)
		1021
		1022	Same as C<db_family>, except it only queries the family I<values> and passes them
		1023	as array reference to the callback.
		1024
		1025	=item $guard = db_mon $family => $cb->($familyhash, \@added, \@changed, \@deleted)
		1026
		1027	Creates a monitor on the given database family. Each time a key is set
		1028	or or is deleted the callback is called with a hash containing the
		1029	database family and three lists of added, changed and deleted subkeys,
		1030	respectively. If no keys have changed then the array reference might be
		1031	C<undef> or even missing.
		1032
		1033	If not called in void context, a guard object is returned that, when
		1034	destroyed, stops the monitor.
		1035
		1036	The family hash reference and the key arrays belong to AnyEvent::MP and
		1037	B<must not be modified or stored> by the callback. When in doubt, make a
		1038	copy.
		1039
		1040	As soon as possible after the monitoring starts, the callback will be
		1041	called with the intiial contents of the family, even if it is empty,
		1042	i.e. there will always be a timely call to the callback with the current
		1043	contents.
		1044
		1045	It is possible that the callback is called with a change event even though
		1046	the subkey is already present and the value has not changed.
		1047
		1048	The monitoring stops when the guard object is destroyed.
		1049
		1050	Example: on every change to the family "mygroup", print out all keys.
		1051
		1052	my $guard = db_mon mygroup => sub {
		1053	my ($family, $a, $c, $d) = @_;
		1054	print "mygroup members: ", (join " ", keys %$family), "\n";
		1055	};
		1056
		1057	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1058
		1059	my $guard; $guard = db_mon My::Module::workers => sub {
		1060	my ($family, $a, $c, $d) = @_;
		1061	return unless %$family;
		1062	undef $guard;
		1063	print "My::Module::workers now nonempty\n";
		1064	};
		1065
		1066	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		1067
		1068	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		1069	my ($family, $a, $c, $d) = @_;
		1070
		1071	print "+$_=$family->{$_}\n" for @$a;
		1072	print "*$_=$family->{$_}\n" for @$c;
		1073	print "-$_=$family->{$_}\n" for @$d;
		1074	};
		1075
		1076	=cut
		1077
652	=back	1078	=back
653		1079
654	=head1 AnyEvent::MP vs. Distributed Erlang	1080	=head1 AnyEvent::MP vs. Distributed Erlang
655		1081
656	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	1082	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	1083	== 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	1084	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
659	sample:	1085	sample:
660		1086
661	http://www.Erlang.se/doc/programming_rules.shtml	1087	http://www.erlang.se/doc/programming_rules.shtml
662	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	1088	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	1089	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	1090	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
665		1091
666	Despite the similarities, there are also some important differences:	1092	Despite the similarities, there are also some important differences:
667		1093
668	=over 4	1094	=over 4
669		1095
670	=item * Node IDs are arbitrary strings in AEMP.	1096	=item * Node IDs are arbitrary strings in AEMP.
671		1097
672	Erlang relies on special naming and DNS to work everywhere in the same	1098	Erlang relies on special naming and DNS to work everywhere in the same
673	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by	1099	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
674	configuraiton or DNS), but will otherwise discover other odes itself.	1100	configuration or DNS), and possibly the addresses of some seed nodes, but
		1101	will otherwise discover other nodes (and their IDs) itself.
675		1102
676	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP	1103	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
677	uses "local ports are like remote ports".	1104	uses "local ports are like remote ports".
678		1105
679	The failure modes for local ports are quite different (runtime errors	1106	The failure modes for local ports are quite different (runtime errors
…		…
688	ports being the special case/exception, where transport errors cannot	1115	ports being the special case/exception, where transport errors cannot
689	occur.	1116	occur.
690		1117
691	=item * Erlang uses processes and a mailbox, AEMP does not queue.	1118	=item * Erlang uses processes and a mailbox, AEMP does not queue.
692		1119
693	Erlang uses processes that selectively receive messages, and therefore	1120	Erlang uses processes that selectively receive messages out of order, and
694	needs a queue. AEMP is event based, queuing messages would serve no	1121	therefore needs a queue. AEMP is event based, queuing messages would serve
695	useful purpose. For the same reason the pattern-matching abilities of	1122	no useful purpose. For the same reason the pattern-matching abilities
696	AnyEvent::MP are more limited, as there is little need to be able to	1123	of AnyEvent::MP are more limited, as there is little need to be able to
697	filter messages without dequeing them.	1124	filter messages without dequeuing them.
698		1125
699	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	1126	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1127	being event-based, while Erlang is process-based.
		1128
		1129	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1130	top of AEMP and Coro threads.
700		1131
701	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1132	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
702		1133
703	Sending messages in Erlang is synchronous and blocks the process (and	1134	Sending messages in Erlang is synchronous and blocks the process until
		1135	a conenction has been established and the message sent (and so does not
704	so does not need a queue that can overflow). AEMP sends are immediate,	1136	need a queue that can overflow). AEMP sends return immediately, connection
705	connection establishment is handled in the background.	1137	establishment is handled in the background.
706		1138
707	=item * Erlang suffers from silent message loss, AEMP does not.	1139	=item * Erlang suffers from silent message loss, AEMP does not.
708		1140
709	Erlang makes few guarantees on messages delivery - messages can get lost	1141	Erlang implements few guarantees on messages delivery - messages can get
710	without any of the processes realising it (i.e. you send messages a, b,	1142	lost without any of the processes realising it (i.e. you send messages a,
711	and c, and the other side only receives messages a and c).	1143	b, and c, and the other side only receives messages a and c).
712		1144
713	AEMP guarantees correct ordering, and the guarantee that there are no	1145	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1146	guarantee that after one message is lost, all following ones sent to the
		1147	same port are lost as well, until monitoring raises an error, so there are
714	holes in the message sequence.	1148	no silent "holes" in the message sequence.
715		1149
716	=item * In Erlang, processes can be declared dead and later be found to be	1150	If you want your software to be very reliable, you have to cope with
717	alive.	1151	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
718		1152	simply tries to work better in common error cases, such as when a network
719	In Erlang it can happen that a monitored process is declared dead and	1153	link goes down.
720	linked processes get killed, but later it turns out that the process is
721	still alive - and can receive messages.
722
723	In AEMP, when port monitoring detects a port as dead, then that port will
724	eventually be killed - it cannot happen that a node detects a port as dead
725	and then later sends messages to it, finding it is still alive.
726		1154
727	=item * Erlang can send messages to the wrong port, AEMP does not.	1155	=item * Erlang can send messages to the wrong port, AEMP does not.
728		1156
729	In Erlang it is quite likely that a node that restarts reuses a process ID	1157	In Erlang it is quite likely that a node that restarts reuses an Erlang
730	known to other nodes for a completely different process, causing messages	1158	process ID known to other nodes for a completely different process,
731	destined for that process to end up in an unrelated process.	1159	causing messages destined for that process to end up in an unrelated
		1160	process.
732		1161
733	AEMP never reuses port IDs, so old messages or old port IDs floating	1162	AEMP does not reuse port IDs, so old messages or old port IDs floating
734	around in the network will not be sent to an unrelated port.	1163	around in the network will not be sent to an unrelated port.
735		1164
736	=item * Erlang uses unprotected connections, AEMP uses secure	1165	=item * Erlang uses unprotected connections, AEMP uses secure
737	authentication and can use TLS.	1166	authentication and can use TLS.
738		1167
739	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1168	AEMP can use a proven protocol - TLS - to protect connections and
740	securely authenticate nodes.	1169	securely authenticate nodes.
741		1170
742	=item * The AEMP protocol is optimised for both text-based and binary	1171	=item * The AEMP protocol is optimised for both text-based and binary
743	communications.	1172	communications.
744		1173
745	The AEMP protocol, unlike the Erlang protocol, supports both	1174	The AEMP protocol, unlike the Erlang protocol, supports both programming
746	language-independent text-only protocols (good for debugging) and binary,	1175	language independent text-only protocols (good for debugging), and binary,
747	language-specific serialisers (e.g. Storable).	1176	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1177	used, the protocol is actually completely text-based.
748		1178
749	It has also been carefully designed to be implementable in other languages	1179	It has also been carefully designed to be implementable in other languages
750	with a minimum of work while gracefully degrading fucntionality to make the	1180	with a minimum of work while gracefully degrading functionality to make the
751	protocol simple.	1181	protocol simple.
752		1182
753	=item * AEMP has more flexible monitoring options than Erlang.	1183	=item * AEMP has more flexible monitoring options than Erlang.
754		1184
755	In Erlang, you can chose to receive I<all> exit signals as messages	1185	In Erlang, you can chose to receive I<all> exit signals as messages or
756	or I<none>, there is no in-between, so monitoring single processes is	1186	I<none>, there is no in-between, so monitoring single Erlang processes is
757	difficult to implement. Monitoring in AEMP is more flexible than in	1187	difficult to implement.
758	Erlang, as one can choose between automatic kill, exit message or callback	1188
759	on a per-process basis.	1189	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1190	between automatic kill, exit message or callback on a per-port basis.
760		1191
761	=item * Erlang tries to hide remote/local connections, AEMP does not.	1192	=item * Erlang tries to hide remote/local connections, AEMP does not.
762		1193
763	Monitoring in Erlang is not an indicator of process death/crashes,	1194	Monitoring in Erlang is not an indicator of process death/crashes, in the
764	as linking is (except linking is unreliable in Erlang).	1195	same way as linking is (except linking is unreliable in Erlang).
765		1196
766	In AEMP, you don't "look up" registered port names or send to named ports	1197	In AEMP, you don't "look up" registered port names or send to named ports
767	that might or might not be persistent. Instead, you normally spawn a port	1198	that might or might not be persistent. Instead, you normally spawn a port
768	on the remote node. The init function monitors the you, and you monitor	1199	on the remote node. The init function monitors you, and you monitor the
769	the remote port. Since both monitors are local to the node, they are much	1200	remote port. Since both monitors are local to the node, they are much more
770	more reliable.	1201	reliable (no need for C<spawn_link>).
771		1202
772	This also saves round-trips and avoids sending messages to the wrong port	1203	This also saves round-trips and avoids sending messages to the wrong port
773	(hard to do in Erlang).	1204	(hard to do in Erlang).
774		1205
775	=back	1206	=back
776		1207
777	=head1 RATIONALE	1208	=head1 RATIONALE
778		1209
779	=over 4	1210	=over 4
780		1211
781	=item Why strings for ports and noderefs, why not objects?	1212	=item Why strings for port and node IDs, why not objects?
782		1213
783	We considered "objects", but found that the actual number of methods	1214	We considered "objects", but found that the actual number of methods
784	thatc an be called are very low. Since port IDs and noderefs travel over	1215	that can be called are quite low. Since port and node IDs travel over
785	the network frequently, the serialising/deserialising would add lots of	1216	the network frequently, the serialising/deserialising would add lots of
786	overhead, as well as having to keep a proxy object.	1217	overhead, as well as having to keep a proxy object everywhere.
787		1218
788	Strings can easily be printed, easily serialised etc. and need no special	1219	Strings can easily be printed, easily serialised etc. and need no special
789	procedures to be "valid".	1220	procedures to be "valid".
790		1221
791	And a a miniport consists of a single closure stored in a global hash - it	1222	And as a result, a port with just a default receiver consists of a single
792	can't become much cheaper.	1223	code reference stored in a global hash - it can't become much cheaper.
793		1224
794	=item Why favour JSON, why not real serialising format such as Storable?	1225	=item Why favour JSON, why not a real serialising format such as Storable?
795		1226
796	In fact, any AnyEvent::MP node will happily accept Storable as framing	1227	In fact, any AnyEvent::MP node will happily accept Storable as framing
797	format, but currently there is no way to make a node use Storable by	1228	format, but currently there is no way to make a node use Storable by
798	default.	1229	default (although all nodes will accept it).
799		1230
800	The default framing protocol is JSON because a) JSON::XS is many times	1231	The default framing protocol is JSON because a) JSON::XS is many times
801	faster for small messages and b) most importantly, after years of	1232	faster for small messages and b) most importantly, after years of
802	experience we found that object serialisation is causing more problems	1233	experience we found that object serialisation is causing more problems
803	than it gains: Just like function calls, objects simply do not travel	1234	than it solves: Just like function calls, objects simply do not travel
804	easily over the network, mostly because they will always be a copy, so you	1235	easily over the network, mostly because they will always be a copy, so you
805	always have to re-think your design.	1236	always have to re-think your design.
806		1237
807	Keeping your messages simple, concentrating on data structures rather than	1238	Keeping your messages simple, concentrating on data structures rather than
808	objects, will keep your messages clean, tidy and efficient.	1239	objects, will keep your messages clean, tidy and efficient.
809		1240
810	=back	1241	=back
811		1242
		1243	=head1 PORTING FROM AnyEvent::MP VERSION 1.X
		1244
		1245	AEMP version 2 has a few major incompatible changes compared to version 1:
		1246
		1247	=over 4
		1248
		1249	=item AnyEvent::MP::Global no longer has group management functions.
		1250
		1251	At least not officially - the grp_* functions are still exported and might
		1252	work, but they will be removed in some later release.
		1253
		1254	AnyEvent::MP now comes with a distributed database that is more
		1255	powerful. Its database families map closely to port groups, but the API
		1256	has changed (the functions are also now exported by AnyEvent::MP). Here is
		1257	a rough porting guide:
		1258
		1259	grp_reg $group, $port # old
		1260	db_reg $group, $port # new
		1261
		1262	$list = grp_get $group # old
		1263	db_keys $group, sub { my $list = shift } # new
		1264
		1265	grp_mon $group, $cb->(\@ports, $add, $del) # old
		1266	db_mon $group, $cb->(\%ports, $add, $change, $del) # new
		1267
		1268	C<grp_reg> is a no-brainer (just replace by C<db_reg>), but C<grp_get> is
		1269	no longer instant, because the local node might not have a copy of the
		1270	group. You can either modify your code to allow for a callback, or use
		1271	C<db_mon> to keep an updated copy of the group:
		1272
		1273	my $local_group_copy;
		1274	db_mon $group => sub { $local_group_copy = $_[0] };
		1275
		1276	# now "keys %$local_group_copy" always returns the most up-to-date
		1277	# list of ports in the group.
		1278
		1279	C<grp_mon> can be replaced by C<db_mon> with minor changes - C<db_mon>
		1280	passes a hash as first argument, and an extra C<$chg> argument that can be
		1281	ignored:
		1282
		1283	db_mon $group => sub {
		1284	my ($ports, $add, $chg, $lde) = @_;
		1285	$ports = [keys %$ports];
		1286
		1287	# now $ports, $add and $del are the same as
		1288	# were originally passed by grp_mon.
		1289	...
		1290	};
		1291
		1292	=item Nodes not longer connect to all other nodes.
		1293
		1294	In AEMP 1.x, every node automatically loads the L<AnyEvent::MP::Global>
		1295	module, which in turn would create connections to all other nodes in the
		1296	network (helped by the seed nodes).
		1297
		1298	In version 2.x, global nodes still connect to all other global nodes, but
		1299	other nodes don't - now every node either is a global node itself, or
		1300	attaches itself to another global node.
		1301
		1302	If a node isn't a global node itself, then it attaches itself to one
		1303	of its seed nodes. If that seed node isn't a global node yet, it will
		1304	automatically be upgraded to a global node.
		1305
		1306	So in many cases, nothing needs to be changed - one just has to make sure
		1307	that all seed nodes are meshed together with the other seed nodes (as with
		1308	AEMP 1.x), and other nodes specify them as seed nodes. This is most easily
		1309	achieved by specifying the same set of seed nodes for all nodes in the
		1310	network.
		1311
		1312	Not opening a connection to every other node is usually an advantage,
		1313	except when you need the lower latency of an already established
		1314	connection. To ensure a node establishes a connection to another node,
		1315	you can monitor the node port (C<mon $node, ...>), which will attempt to
		1316	create the connection (and notify you when the connection fails).
		1317
		1318	=item Listener-less nodes (nodes without binds) are gone.
		1319
		1320	And are not coming back, at least not in their old form. If no C<binds>
		1321	are specified for a node, AnyEvent::MP assumes a default of C<:>.
		1322
		1323	There are vague plans to implement some form of routing domains, which
		1324	might or might not bring back listener-less nodes, but don't count on it.
		1325
		1326	The fact that most connections are now optional somewhat mitigates this,
		1327	as a node can be effectively unreachable from the outside without any
		1328	problems, as long as it isn't a global node and only reaches out to other
		1329	nodes (as opposed to being contacted from other nodes).
		1330
		1331	=item $AnyEvent::MP::Kernel::WARN has gone.
		1332
		1333	AnyEvent has acquired a logging framework (L<AnyEvent::Log>), and AEMP now
		1334	uses this, and so should your programs.
		1335
		1336	Every module now documents what kinds of messages it generates, with
		1337	AnyEvent::MP acting as a catch all.
		1338
		1339	On the positive side, this means that instead of setting
		1340	C<PERL_ANYEVENT_MP_WARNLEVEL>, you can get away by setting C<AE_VERBOSE> -
		1341	much less to type.
		1342
		1343	=back
		1344
		1345	=head1 LOGGING
		1346
		1347	AnyEvent::MP does not normally log anything by itself, but sinc eit is the
		1348	root of the contetx hierarchy for AnyEvent::MP modules, it will receive
		1349	all log messages by submodules.
		1350
812	=head1 SEE ALSO	1351	=head1 SEE ALSO
		1352
		1353	L<AnyEvent::MP::Intro> - a gentle introduction.
		1354
		1355	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1356
		1357	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1358	your applications.
		1359
		1360	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1361
		1362	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1363	all nodes.
813		1364
814	L<AnyEvent>.	1365	L<AnyEvent>.
815		1366
816	=head1 AUTHOR	1367	=head1 AUTHOR
817		1368

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Revision 1.142 by root, Fri Mar 23 13:44:01 2012 UTC