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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.62 by root, Thu Aug 27 07:12:48 2009 UTC vs.
Revision 1.136 by root, Wed Mar 21 15:22:16 2012 UTC

…		…
1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent::MP - multi-processing/message-passing framework	3	AnyEvent::MP - erlang-style multi-processing/message-passing framework
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::MP;	7	use AnyEvent::MP;
8		8
9	$NODE # contains this node's noderef	9	$NODE # contains this node's node ID
10	NODE # returns this node's noderef	10	NODE # returns this node's node ID
11	NODE $port # returns the noderef of the port
12		11
13	$SELF # receiving/own port id in rcv callbacks	12	$SELF # receiving/own port id in rcv callbacks
14		13
15	# initialise the node so it can send/receive messages	14	# initialise the node so it can send/receive messages
16	initialise_node; # -OR-	15	configure;
17	initialise_node "localhost:4040"; # -OR-
18	initialise_node "slave/", "localhost:4040"
19		16
20	# ports are message endpoints	17	# ports are message destinations
21		18
22	# sending messages	19	# sending messages
23	snd $port, type => data...;	20	snd $port, type => data...;
24	snd $port, @msg;	21	snd $port, @msg;
25	snd @msg_with_first_element_being_a_port;	22	snd @msg_with_first_element_being_a_port;
26		23
27	# creating/using ports, the simple way	24	# creating/using ports, the simple way
28	my $simple_port = port { my @msg = @_; 0 };	25	my $simple_port = port { my @msg = @_ };
29		26
30	# creating/using ports, tagged message matching	27	# creating/using ports, tagged message matching
31	my $port = port;	28	my $port = port;
32	rcv $port, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
33	rcv $port, pong => sub { warn "pong received\n"; 0 };	30	rcv $port, pong => sub { warn "pong received\n" };
34		31
35	# create a port on another node	32	# create a port on another node
36	my $port = spawn $node, $initfunc, @initdata;	33	my $port = spawn $node, $initfunc, @initdata;
37		34
		35	# destroy a port again
		36	kil $port; # "normal" kill
		37	kil $port, my_error => "everything is broken"; # error kill
		38
38	# monitoring	39	# monitoring
39	mon $port, $cb->(@msg) # callback is invoked on death	40	mon $port, $cb->(@msg) # callback is invoked on death
40	mon $port, $otherport # kill otherport on abnormal death	41	mon $port, $localport # kill localport on abnormal death
41	mon $port, $otherport, @msg # send message on death	42	mon $port, $localport, @msg # send message on death
		43
		44	# temporarily execute code in port context
		45	peval $port, sub { die "kill the port!" };
		46
		47	# execute callbacks in $SELF port context
		48	my $timer = AE::timer 1, 0, psub {
		49	die "kill the port, delayed";
		50	};
42		51
43	=head1 CURRENT STATUS	52	=head1 CURRENT STATUS
44		53
		54	bin/aemp - stable.
45	AnyEvent::MP - stable API, should work	55	AnyEvent::MP - stable API, should work.
46	AnyEvent::MP::Intro - outdated	56	AnyEvent::MP::Intro - explains most concepts.
47	AnyEvent::MP::Kernel - WIP
48	AnyEvent::MP::Transport - mostly stable	57	AnyEvent::MP::Kernel - mostly stable API.
49		58	AnyEvent::MP::Global - stable API.
50	stay tuned.
51		59
52	=head1 DESCRIPTION	60	=head1 DESCRIPTION
53		61
54	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
55		63
56	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
57	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
58		66
59	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	67	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
60	manual page.	68	manual page and the examples under F<eg/>.
61
62	At the moment, this module family is severly broken and underdocumented,
63	so do not use. This was uploaded mainly to reserve the CPAN namespace -
64	stay tuned!
65		69
66	=head1 CONCEPTS	70	=head1 CONCEPTS
67		71
68	=over 4	72	=over 4
69		73
70	=item port	74	=item port
71		75
72	A port is something you can send messages to (with the C<snd> function).	76	Not to be confused with a TCP port, a "port" is something you can send
		77	messages to (with the C<snd> function).
73		78
74	Ports allow you to register C<rcv> handlers that can match all or just	79	Ports allow you to register C<rcv> handlers that can match all or just
75	some messages. Messages will not be queued.	80	some messages. Messages send to ports will not be queued, regardless of
		81	anything was listening for them or not.
76		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
77	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
78		86
79	A port ID is the concatenation of a noderef, a hash-mark (C<#>) as	87	A port ID is the concatenation of a node ID, a hash-mark (C<#>)
80	separator, and a port name (a printable string of unspecified format). An	88	as separator, and a port name (a printable string of unspecified
81	exception is the the node port, whose ID is identical to its node	89	format created by AnyEvent::MP).
82	reference.
83		90
84	=item node	91	=item node
85		92
86	A node is a single process containing at least one port - the node port,	93	A node is a single process containing at least one port - the node port,
87	which provides nodes to manage each other remotely, and to create new	94	which enables nodes to manage each other remotely, and to create new
88	ports.	95	ports.
89		96
90	Nodes are either private (single-process only), slaves (can only talk to	97	Nodes are either public (have one or more listening ports) or private
91	public nodes, but do not need an open port) or public nodes (connectable	98	(no listening ports). Private nodes cannot talk to other private nodes
92	from any other node).	99	currently, but all nodes can talk to public nodes.
93		100
94	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	101	Nodes is represented by (printable) strings called "node IDs".
95		102
96	A node reference is a string that either simply identifies the node (for	103	=item node ID - C<[A-Za-z0-9_\-.:]*>
97	private and slave nodes), or contains a recipe on how to reach a given
98	node (for public nodes).
99		104
100	This recipe is simply a comma-separated list of C<address:port> pairs (for	105	A node ID is a string that uniquely identifies the node within a
101	TCP/IP, other protocols might look different).	106	network. Depending on the configuration used, node IDs can look like a
		107	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		108	doesn't interpret node IDs in any way except to uniquely identify a node.
102		109
103	Node references come in two flavours: resolved (containing only numerical	110	=item binds - C<ip:port>
104	addresses) or unresolved (where hostnames are used instead of addresses).
105		111
106	Before using an unresolved node reference in a message you first have to	112	Nodes can only talk to each other by creating some kind of connection to
107	resolve it.	113	each other. To do this, nodes should listen on one or more local transport
		114	endpoints - binds.
		115
		116	Currently, only standard C<ip:port> specifications can be used, which
		117	specify TCP ports to listen on. So a bind is basically just a tcp socket
		118	in listening mode thta accepts conenctions form other nodes.
		119
		120	=item seed nodes
		121
		122	When a node starts, it knows nothing about the network it is in - it
		123	needs to connect to at least one other node that is already in the
		124	network. These other nodes are called "seed nodes".
		125
		126	Seed nodes themselves are not special - they are seed nodes only because
		127	some other node I<uses> them as such, but any node can be used as seed
		128	node for other nodes, and eahc node cna use a different set of seed nodes.
		129
		130	In addition to discovering the network, seed nodes are also used to
		131	maintain the network - all nodes using the same seed node form are part of
		132	the same network. If a network is split into multiple subnets because e.g.
		133	the network link between the parts goes down, then using the same seed
		134	nodes for all nodes ensures that eventually the subnets get merged again.
		135
		136	Seed nodes are expected to be long-running, and at least one seed node
		137	should always be available. They should also be relatively responsive - a
		138	seed node that blocks for long periods will slow down everybody else.
		139
		140	For small networks, it's best if every node uses the same set of seed
		141	nodes. For large networks, it can be useful to specify "regional" seed
		142	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		143	each other. What's important is that all seed nodes connections form a
		144	complete graph, so that the network cannot split into separate subnets
		145	forever.
		146
		147	Seed nodes are represented by seed IDs.
		148
		149	=item seed IDs - C<host:port>
		150
		151	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
		152	TCP port) of nodes that should be used as seed nodes.
		153
		154	=item global nodes
		155
		156	An AEMP network needs a discovery service - nodes need to know how to
		157	connect to other nodes they only know by name. In addition, AEMP offers a
		158	distributed "group database", which maps group names to a list of strings
		159	- for example, to register worker ports.
		160
		161	A network needs at least one global node to work, and allows every node to
		162	be a global node.
		163
		164	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		165	node and tries to keep connections to all other nodes. So while it can
		166	make sense to make every node "global" in small networks, it usually makes
		167	sense to only make seed nodes into global nodes in large networks (nodes
		168	keep connections to seed nodes and global nodes, so makign them the same
		169	reduces overhead).
108		170
109	=back	171	=back
110		172
111	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
112		174
114		176
115	=cut	177	=cut
116		178
117	package AnyEvent::MP;	179	package AnyEvent::MP;
118		180
		181	use AnyEvent::MP::Config ();
119	use AnyEvent::MP::Kernel;	182	use AnyEvent::MP::Kernel;
		183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
120		184
121	use common::sense;	185	use common::sense;
122		186
123	use Carp ();	187	use Carp ();
124		188
125	use AE ();	189	use AE ();
		190	use Guard ();
126		191
127	use base "Exporter";	192	use base "Exporter";
128		193
129	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
130		195
131	our @EXPORT = qw(	196	our @EXPORT = qw(
132	NODE $NODE *SELF node_of after	197	NODE $NODE *SELF node_of after
133	resolve_node initialise_node	198	configure
134	snd rcv mon mon_guard kil reg psub spawn	199	snd rcv mon mon_guard kil psub peval spawn cal
135	port	200	port
		201	db_set db_del db_reg
		202	db_mon db_family db_keys db_values
136	);	203	);
137		204
138	our $SELF;	205	our $SELF;
139		206
140	sub _self_die() {	207	sub _self_die() {
…		…
143	kil $SELF, die => $msg;	210	kil $SELF, die => $msg;
144	}	211	}
145		212
146	=item $thisnode = NODE / $NODE	213	=item $thisnode = NODE / $NODE
147		214
148	The C<NODE> function returns, and the C<$NODE> variable contains the	215	The C<NODE> function returns, and the C<$NODE> variable contains, the node
149	noderef of the local node. The value is initialised by a call to	216	ID of the node running in the current process. This value is initialised by
150	C<initialise_node>.	217	a call to C<configure>.
151		218
152	=item $noderef = node_of $port	219	=item $nodeid = node_of $port
153		220
154	Extracts and returns the noderef from a port ID or a noderef.	221	Extracts and returns the node ID from a port ID or a node ID.
155		222
156	=item initialise_node $noderef, $seednode, $seednode...	223	=item configure $profile, key => value...
157		224
158	=item initialise_node "slave/", $master, $master...	225	=item configure key => value...
159		226
160	Before a node can talk to other nodes on the network it has to initialise	227	Before a node can talk to other nodes on the network (i.e. enter
161	itself - the minimum a node needs to know is it's own name, and optionally	228	"distributed mode") it has to configure itself - the minimum a node needs
162	it should know the noderefs of some other nodes in the network.	229	to know is its own name, and optionally it should know the addresses of
		230	some other nodes in the network to discover other nodes.
163		231
164	This function initialises a node - it must be called exactly once (or	232	This function configures a node - it must be called exactly once (or
165	never) before calling other AnyEvent::MP functions.	233	never) before calling other AnyEvent::MP functions.
166		234
167	All arguments (optionally except for the first) are noderefs, which can be	235	The key/value pairs are basically the same ones as documented for the
168	either resolved or unresolved.	236	F<aemp> command line utility (sans the set/del prefix), with these additions:
169
170	The first argument will be looked up in the configuration database first
171	(if it is C<undef> then the current nodename will be used instead) to find
172	the relevant configuration profile (see L<aemp>). If none is found then
173	the default configuration is used. The configuration supplies additional
174	seed/master nodes and can override the actual noderef.
175
176	There are two types of networked nodes, public nodes and slave nodes:
177		237
178	=over 4	238	=over 4
179		239
180	=item public nodes	240	=item norc => $boolean (default false)
181		241
182	For public nodes, C<$noderef> (supplied either directly to	242	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
183	C<initialise_node> or indirectly via a profile or the nodename) must be a	243	be consulted - all configuraiton options must be specified in the
184	noderef (possibly unresolved, in which case it will be resolved).	244	C<configure> call.
185		245
186	After resolving, the node will bind itself on all endpoints.	246	=item force => $boolean (default false)
187		247
188	=item slave nodes	248	IF true, then the values specified in the C<configure> will take
		249	precedence over any values configured via the rc file. The default is for
		250	the rc file to override any options specified in the program.
189		251
190	When the C<$noderef> (either as given or overriden by the config file)	252	=item secure => $pass->(@msg)
191	is the special string C<slave/>, then the node will become a slave
192	node. Slave nodes cannot be contacted from outside, and cannot talk to
193	each other (at least in this version of AnyEvent::MP).
194		253
195	Slave nodes work by creating connections to all public nodes, using the	254	In addition to specifying a boolean, you can specify a code reference that
196	L<AnyEvent::MP::Global> service.	255	is called for every code execution attempt - the execution request is
		256	granted iff the callback returns a true value.
		257
		258	Most of the time the callback should look only at
		259	C<$AnyEvent::MP::Kernel::SRCNODE> to make a decision, and not at the
		260	actual message (which can be about anything, and is mostly provided for
		261	diagnostic purposes).
		262
		263	See F<semp setsecure> for more info.
197		264
198	=back	265	=back
199		266
200	After initialising itself, the node will connect to all additional
201	C<$seednodes> that are specified diretcly or via a profile. Seednodes are
202	optional and can be used to quickly bootstrap the node into an existing
203	network.
204
205	All the seednodes will also be specially marked to automatically retry
206	connecting to them indefinitely, so make sure that seednodes are really
207	reliable and up (this might also change in the future).
208
209	Example: become a public node listening on the guessed noderef, or the one
210	specified via C<aemp> for the current node. This should be the most common
211	form of invocation for "daemon"-type nodes.
212
213	initialise_node;
214
215	Example: become a slave node to any of the the seednodes specified via
216	C<aemp>. This form is often used for commandline clients.
217
218	initialise_node "slave/";
219
220	Example: become a public node, and try to contact some well-known master
221	servers to become part of the network.
222
223	initialise_node undef, "master1", "master2";
224
225	Example: become a public node listening on port C<4041>.
226
227	initialise_node 4041;
228
229	Example: become a public node, only visible on localhost port 4044.
230
231	initialise_node "localhost:4044";
232
233	=item $cv = resolve_node $noderef
234
235	Takes an unresolved node reference that may contain hostnames and
236	abbreviated IDs, resolves all of them and returns a resolved node
237	reference.
238
239	In addition to C<address:port> pairs allowed in resolved noderefs, the
240	following forms are supported:
241
242	=over 4	267	=over 4
243		268
244	=item the empty string	269	=item step 1, gathering configuration from profiles
245		270
246	An empty-string component gets resolved as if the default port (4040) was	271	The function first looks up a profile in the aemp configuration (see the
247	specified.	272	L<aemp> commandline utility). The profile name can be specified via the
		273	named C<profile> parameter or can simply be the first parameter). If it is
		274	missing, then the nodename (F<uname -n>) will be used as profile name.
248		275
249	=item naked port numbers (e.g. C<1234>)	276	The profile data is then gathered as follows:
250		277
251	These are resolved by prepending the local nodename and a colon, to be	278	First, all remaining key => value pairs (all of which are conveniently
252	further resolved.	279	undocumented at the moment) will be interpreted as configuration
		280	data. Then they will be overwritten by any values specified in the global
		281	default configuration (see the F<aemp> utility), then the chain of
		282	profiles chosen by the profile name (and any C<parent> attributes).
253		283
254	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	284	That means that the values specified in the profile have highest priority
		285	and the values specified directly via C<configure> have lowest priority,
		286	and can only be used to specify defaults.
255		287
256	These are resolved by using AnyEvent::DNS to resolve them, optionally	288	If the profile specifies a node ID, then this will become the node ID of
257	looking up SRV records for the C<aemp=4040> port, if no port was	289	this process. If not, then the profile name will be used as node ID, with
258	specified.	290	a unique randoms tring (C</%u>) appended.
		291
		292	The node ID can contain some C<%> sequences that are expanded: C<%n>
		293	is expanded to the local nodename, C<%u> is replaced by a random
		294	strign to make the node unique. For example, the F<aemp> commandline
		295	utility uses C<aemp/%n/%u> as nodename, which might expand to
		296	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		297
		298	=item step 2, bind listener sockets
		299
		300	The next step is to look up the binds in the profile, followed by binding
		301	aemp protocol listeners on all binds specified (it is possible and valid
		302	to have no binds, meaning that the node cannot be contacted form the
		303	outside. This means the node cannot talk to other nodes that also have no
		304	binds, but it can still talk to all "normal" nodes).
		305
		306	If the profile does not specify a binds list, then a default of C<*> is
		307	used, meaning the node will bind on a dynamically-assigned port on every
		308	local IP address it finds.
		309
		310	=item step 3, connect to seed nodes
		311
		312	As the last step, the seed ID list from the profile is passed to the
		313	L<AnyEvent::MP::Global> module, which will then use it to keep
		314	connectivity with at least one node at any point in time.
259		315
260	=back	316	=back
		317
		318	Example: become a distributed node using the local node name as profile.
		319	This should be the most common form of invocation for "daemon"-type nodes.
		320
		321	configure
		322
		323	Example: become a semi-anonymous node. This form is often used for
		324	commandline clients.
		325
		326	configure nodeid => "myscript/%n/%u";
		327
		328	Example: configure a node using a profile called seed, which is suitable
		329	for a seed node as it binds on all local addresses on a fixed port (4040,
		330	customary for aemp).
		331
		332	# use the aemp commandline utility
		333	# aemp profile seed binds '*:4040'
		334
		335	# then use it
		336	configure profile => "seed";
		337
		338	# or simply use aemp from the shell again:
		339	# aemp run profile seed
		340
		341	# or provide a nicer-to-remember nodeid
		342	# aemp run profile seed nodeid "$(hostname)"
261		343
262	=item $SELF	344	=item $SELF
263		345
264	Contains the current port id while executing C<rcv> callbacks or C<psub>	346	Contains the current port id while executing C<rcv> callbacks or C<psub>
265	blocks.	347	blocks.
266		348
267	=item SELF, %SELF, @SELF...	349	=item *SELF, SELF, %SELF, @SELF...
268		350
269	Due to some quirks in how perl exports variables, it is impossible to	351	Due to some quirks in how perl exports variables, it is impossible to
270	just export C<$SELF>, all the symbols called C<SELF> are exported by this	352	just export C<$SELF>, all the symbols named C<SELF> are exported by this
271	module, but only C<$SELF> is currently used.	353	module, but only C<$SELF> is currently used.
272		354
273	=item snd $port, type => @data	355	=item snd $port, type => @data
274		356
275	=item snd $port, @msg	357	=item snd $port, @msg
276		358
277	Send the given message to the given port ID, which can identify either	359	Send the given message to the given port, which can identify either a
278	a local or a remote port, and must be a port ID.	360	local or a remote port, and must be a port ID.
279		361
280	While the message can be about anything, it is highly recommended to use a	362	While the message can be almost anything, it is highly recommended to
281	string as first element (a port ID, or some word that indicates a request	363	use a string as first element (a port ID, or some word that indicates a
282	type etc.).	364	request type etc.) and to consist if only simple perl values (scalars,
		365	arrays, hashes) - if you think you need to pass an object, think again.
283		366
284	The message data effectively becomes read-only after a call to this	367	The message data logically becomes read-only after a call to this
285	function: modifying any argument is not allowed and can cause many	368	function: modifying any argument (or values referenced by them) is
286	problems.	369	forbidden, as there can be considerable time between the call to C<snd>
		370	and the time the message is actually being serialised - in fact, it might
		371	never be copied as within the same process it is simply handed to the
		372	receiving port.
287		373
288	The type of data you can transfer depends on the transport protocol: when	374	The type of data you can transfer depends on the transport protocol: when
289	JSON is used, then only strings, numbers and arrays and hashes consisting	375	JSON is used, then only strings, numbers and arrays and hashes consisting
290	of those are allowed (no objects). When Storable is used, then anything	376	of those are allowed (no objects). When Storable is used, then anything
291	that Storable can serialise and deserialise is allowed, and for the local	377	that Storable can serialise and deserialise is allowed, and for the local
292	node, anything can be passed.	378	node, anything can be passed. Best rely only on the common denominator of
		379	these.
293		380
294	=item $local_port = port	381	=item $local_port = port
295		382
296	Create a new local port object and returns its port ID. Initially it has	383	Create a new local port object and returns its port ID. Initially it has
297	no callbacks set and will throw an error when it receives messages.	384	no callbacks set and will throw an error when it receives messages.
…		…
316		403
317	=cut	404	=cut
318		405
319	sub rcv($@);	406	sub rcv($@);
320		407
321	sub _kilme {	408	my $KILME = sub {
322	die "received message on port without callback";	409	(my $tag = substr $_[0], 0, 30) =~ s/([\x20-\x7e])/./g;
323	}	410	kil $SELF, unhandled_message => "no callback found for message '$tag'";
		411	};
324		412
325	sub port(;&) {	413	sub port(;&) {
326	my $id = "$UNIQ." . $ID++;	414	my $id = $UNIQ . ++$ID;
327	my $port = "$NODE#$id";	415	my $port = "$NODE#$id";
328		416
329	rcv $port, shift \|\| \&_kilme;	417	rcv $port, shift \|\| $KILME;
330		418
331	$port	419	$port
332	}	420	}
333		421
334	=item rcv $local_port, $callback->(@msg)	422	=item rcv $local_port, $callback->(@msg)
…		…
339		427
340	The global C<$SELF> (exported by this module) contains C<$port> while	428	The global C<$SELF> (exported by this module) contains C<$port> while
341	executing the callback. Runtime errors during callback execution will	429	executing the callback. Runtime errors during callback execution will
342	result in the port being C<kil>ed.	430	result in the port being C<kil>ed.
343		431
344	The default callback received all messages not matched by a more specific	432	The default callback receives all messages not matched by a more specific
345	C<tag> match.	433	C<tag> match.
346		434
347	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...	435	=item rcv $local_port, tag => $callback->(@msg_without_tag), ...
348		436
349	Register (or replace) callbacks to be called on messages starting with the	437	Register (or replace) callbacks to be called on messages starting with the
…		…
370	msg1 => sub { ... },	458	msg1 => sub { ... },
371	...	459	...
372	;	460	;
373		461
374	Example: temporarily register a rcv callback for a tag matching some port	462	Example: temporarily register a rcv callback for a tag matching some port
375	(e.g. for a rpc reply) and unregister it after a message was received.	463	(e.g. for an rpc reply) and unregister it after a message was received.
376		464
377	rcv $port, $otherport => sub {	465	rcv $port, $otherport => sub {
378	my @reply = @_;	466	my @reply = @_;
379		467
380	rcv $SELF, $otherport;	468	rcv $SELF, $otherport;
…		…
382		470
383	=cut	471	=cut
384		472
385	sub rcv($@) {	473	sub rcv($@) {
386	my $port = shift;	474	my $port = shift;
387	my ($noderef, $portid) = split /#/, $port, 2;	475	my ($nodeid, $portid) = split /#/, $port, 2;
388		476
389	$NODE{$noderef} == $NODE{""}	477	$NODE{$nodeid} == $NODE{""}
390	or Carp::croak "$port: rcv can only be called on local ports, caught";	478	or Carp::croak "$port: rcv can only be called on local ports, caught";
391		479
392	while (@_) {	480	while (@_) {
393	if (ref $_[0]) {	481	if (ref $_[0]) {
394	if (my $self = $PORT_DATA{$portid}) {	482	if (my $self = $PORT_DATA{$portid}) {
395	"AnyEvent::MP::Port" eq ref $self	483	"AnyEvent::MP::Port" eq ref $self
396	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	484	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
397		485
398	$self->[2] = shift;	486	$self->[0] = shift;
399	} else {	487	} else {
400	my $cb = shift;	488	my $cb = shift;
401	$PORT{$portid} = sub {	489	$PORT{$portid} = sub {
402	local $SELF = $port;	490	local $SELF = $port;
403	eval { &$cb }; _self_die if $@;	491	eval { &$cb }; _self_die if $@;
404	};	492	};
405	}	493	}
406	} elsif (defined $_[0]) {	494	} elsif (defined $_[0]) {
407	my $self = $PORT_DATA{$portid} \|\|= do {	495	my $self = $PORT_DATA{$portid} \|\|= do {
408	my $self = bless [$PORT{$port} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";	496	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
409		497
410	$PORT{$portid} = sub {	498	$PORT{$portid} = sub {
411	local $SELF = $port;	499	local $SELF = $port;
412		500
413	if (my $cb = $self->[1]{$_[0]}) {	501	if (my $cb = $self->[1]{$_[0]}) {
…		…
435	}	523	}
436		524
437	$port	525	$port
438	}	526	}
439		527
		528	=item peval $port, $coderef[, @args]
		529
		530	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		531	when the code throews an exception the C<$port> will be killed.
		532
		533	Any remaining args will be passed to the callback. Any return values will
		534	be returned to the caller.
		535
		536	This is useful when you temporarily want to execute code in the context of
		537	a port.
		538
		539	Example: create a port and run some initialisation code in it's context.
		540
		541	my $port = port { ... };
		542
		543	peval $port, sub {
		544	init
		545	or die "unable to init";
		546	};
		547
		548	=cut
		549
		550	sub peval($$) {
		551	local $SELF = shift;
		552	my $cb = shift;
		553
		554	if (wantarray) {
		555	my @res = eval { &$cb };
		556	_self_die if $@;
		557	@res
		558	} else {
		559	my $res = eval { &$cb };
		560	_self_die if $@;
		561	$res
		562	}
		563	}
		564
440	=item $closure = psub { BLOCK }	565	=item $closure = psub { BLOCK }
441		566
442	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	567	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
443	closure is executed, sets up the environment in the same way as in C<rcv>	568	closure is executed, sets up the environment in the same way as in C<rcv>
444	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.	569	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		570
		571	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		572	BLOCK }, @_ } >>.
445		573
446	This is useful when you register callbacks from C<rcv> callbacks:	574	This is useful when you register callbacks from C<rcv> callbacks:
447		575
448	rcv delayed_reply => sub {	576	rcv delayed_reply => sub {
449	my ($delay, @reply) = @_;	577	my ($delay, @reply) = @_;
…		…
473	$res	601	$res
474	}	602	}
475	}	603	}
476	}	604	}
477		605
478	=item $guard = mon $port, $cb->(@reason)	606	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
479		607
480	=item $guard = mon $port, $rcvport	608	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
481		609
482	=item $guard = mon $port	610	=item $guard = mon $port # kill $SELF when $port dies
483		611
484	=item $guard = mon $port, $rcvport, @msg	612	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
485		613
486	Monitor the given port and do something when the port is killed or	614	Monitor the given port and do something when the port is killed or
487	messages to it were lost, and optionally return a guard that can be used	615	messages to it were lost, and optionally return a guard that can be used
488	to stop monitoring again.	616	to stop monitoring again.
489
490	C<mon> effectively guarantees that, in the absence of hardware failures,
491	that after starting the monitor, either all messages sent to the port
492	will arrive, or the monitoring action will be invoked after possible
493	message loss has been detected. No messages will be lost "in between"
494	(after the first lost message no further messages will be received by the
495	port). After the monitoring action was invoked, further messages might get
496	delivered again.
497
498	Note that monitoring-actions are one-shot: once released, they are removed
499	and will not trigger again.
500		617
501	In the first form (callback), the callback is simply called with any	618	In the first form (callback), the callback is simply called with any
502	number of C<@reason> elements (no @reason means that the port was deleted	619	number of C<@reason> elements (no @reason means that the port was deleted
503	"normally"). Note also that I<< the callback B<must> never die >>, so use	620	"normally"). Note also that I<< the callback B<must> never die >>, so use
504	C<eval> if unsure.	621	C<eval> if unsure.
505		622
506	In the second form (another port given), the other port (C<$rcvport>)	623	In the second form (another port given), the other port (C<$rcvport>)
507	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	624	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
508	"normal" kils nothing happens, while under all other conditions, the other	625	"normal" kils nothing happens, while under all other conditions, the other
509	port is killed with the same reason.	626	port is killed with the same reason.
510		627
511	The third form (kill self) is the same as the second form, except that	628	The third form (kill self) is the same as the second form, except that
512	C<$rvport> defaults to C<$SELF>.	629	C<$rvport> defaults to C<$SELF>.
513		630
514	In the last form (message), a message of the form C<@msg, @reason> will be	631	In the last form (message), a message of the form C<@msg, @reason> will be
515	C<snd>.	632	C<snd>.
		633
		634	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		635	alert was raised), they are removed and will not trigger again.
516		636
517	As a rule of thumb, monitoring requests should always monitor a port from	637	As a rule of thumb, monitoring requests should always monitor a port from
518	a local port (or callback). The reason is that kill messages might get	638	a local port (or callback). The reason is that kill messages might get
519	lost, just like any other message. Another less obvious reason is that	639	lost, just like any other message. Another less obvious reason is that
520	even monitoring requests can get lost (for exmaple, when the connection	640	even monitoring requests can get lost (for example, when the connection
521	to the other node goes down permanently). When monitoring a port locally	641	to the other node goes down permanently). When monitoring a port locally
522	these problems do not exist.	642	these problems do not exist.
523		643
		644	C<mon> effectively guarantees that, in the absence of hardware failures,
		645	after starting the monitor, either all messages sent to the port will
		646	arrive, or the monitoring action will be invoked after possible message
		647	loss has been detected. No messages will be lost "in between" (after
		648	the first lost message no further messages will be received by the
		649	port). After the monitoring action was invoked, further messages might get
		650	delivered again.
		651
		652	Inter-host-connection timeouts and monitoring depend on the transport
		653	used. The only transport currently implemented is TCP, and AnyEvent::MP
		654	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		655	non-idle connection, and usually around two hours for idle connections).
		656
		657	This means that monitoring is good for program errors and cleaning up
		658	stuff eventually, but they are no replacement for a timeout when you need
		659	to ensure some maximum latency.
		660
524	Example: call a given callback when C<$port> is killed.	661	Example: call a given callback when C<$port> is killed.
525		662
526	mon $port, sub { warn "port died because of <@_>\n" };	663	mon $port, sub { warn "port died because of <@_>\n" };
527		664
528	Example: kill ourselves when C<$port> is killed abnormally.	665	Example: kill ourselves when C<$port> is killed abnormally.
…		…
534	mon $port, $self => "restart";	671	mon $port, $self => "restart";
535		672
536	=cut	673	=cut
537		674
538	sub mon {	675	sub mon {
539	my ($noderef, $port) = split /#/, shift, 2;	676	my ($nodeid, $port) = split /#/, shift, 2;
540		677
541	my $node = $NODE{$noderef} \|\| add_node $noderef;	678	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
542		679
543	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';	680	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
544		681
545	unless (ref $cb) {	682	unless (ref $cb) {
546	if (@_) {	683	if (@_) {
…		…
555	}	692	}
556		693
557	$node->monitor ($port, $cb);	694	$node->monitor ($port, $cb);
558		695
559	defined wantarray	696	defined wantarray
560	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	697	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
561	}	698	}
562		699
563	=item $guard = mon_guard $port, $ref, $ref...	700	=item $guard = mon_guard $port, $ref, $ref...
564		701
565	Monitors the given C<$port> and keeps the passed references. When the port	702	Monitors the given C<$port> and keeps the passed references. When the port
566	is killed, the references will be freed.	703	is killed, the references will be freed.
567		704
568	Optionally returns a guard that will stop the monitoring.	705	Optionally returns a guard that will stop the monitoring.
569		706
570	This function is useful when you create e.g. timers or other watchers and	707	This function is useful when you create e.g. timers or other watchers and
571	want to free them when the port gets killed:	708	want to free them when the port gets killed (note the use of C<psub>):
572		709
573	$port->rcv (start => sub {	710	$port->rcv (start => sub {
574	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	711	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
575	undef $timer if 0.9 < rand;	712	undef $timer if 0.9 < rand;
576	});	713	});
577	});	714	});
578		715
579	=cut	716	=cut
…		…
588		725
589	=item kil $port[, @reason]	726	=item kil $port[, @reason]
590		727
591	Kill the specified port with the given C<@reason>.	728	Kill the specified port with the given C<@reason>.
592		729
593	If no C<@reason> is specified, then the port is killed "normally" (linked	730	If no C<@reason> is specified, then the port is killed "normally" -
594	ports will not be kileld, or even notified).	731	monitor callback will be invoked, but the kil will not cause linked ports
		732	(C<mon $mport, $lport> form) to get killed.
595		733
596	Otherwise, linked ports get killed with the same reason (second form of	734	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
597	C<mon>, see below).	735	form) get killed with the same reason.
598		736
599	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	737	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
600	will be reported as reason C<< die => $@ >>.	738	will be reported as reason C<< die => $@ >>.
601		739
602	Transport/communication errors are reported as C<< transport_error =>	740	Transport/communication errors are reported as C<< transport_error =>
603	$message >>.	741	$message >>.
604		742
605	=cut	743	Common idioms:
		744
		745	# silently remove yourself, do not kill linked ports
		746	kil $SELF;
		747
		748	# report a failure in some detail
		749	kil $SELF, failure_mode_1 => "it failed with too high temperature";
		750
		751	# do not waste much time with killing, just die when something goes wrong
		752	open my $fh, "<file"
		753	or die "file: $!";
606		754
607	=item $port = spawn $node, $initfunc[, @initdata]	755	=item $port = spawn $node, $initfunc[, @initdata]
608		756
609	Creates a port on the node C<$node> (which can also be a port ID, in which	757	Creates a port on the node C<$node> (which can also be a port ID, in which
610	case it's the node where that port resides).	758	case it's the node where that port resides).
611		759
612	The port ID of the newly created port is return immediately, and it is	760	The port ID of the newly created port is returned immediately, and it is
613	permissible to immediately start sending messages or monitor the port.	761	possible to immediately start sending messages or to monitor the port.
614		762
615	After the port has been created, the init function is	763	After the port has been created, the init function is called on the remote
616	called. This function must be a fully-qualified function name	764	node, in the same context as a C<rcv> callback. This function must be a
617	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	765	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
618	program, use C<::name>.	766	specify a function in the main program, use C<::name>.
619		767
620	If the function doesn't exist, then the node tries to C<require>	768	If the function doesn't exist, then the node tries to C<require>
621	the package, then the package above the package and so on (e.g.	769	the package, then the package above the package and so on (e.g.
622	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	770	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
623	exists or it runs out of package names.	771	exists or it runs out of package names.
624		772
625	The init function is then called with the newly-created port as context	773	The init function is then called with the newly-created port as context
626	object (C<$SELF>) and the C<@initdata> values as arguments.	774	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		775	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		776	the port might not get created.
627		777
628	A common idiom is to pass your own port, monitor the spawned port, and	778	A common idiom is to pass a local port, immediately monitor the spawned
629	in the init function, monitor the original port. This two-way monitoring	779	port, and in the remote init function, immediately monitor the passed
630	ensures that both ports get cleaned up when there is a problem.	780	local port. This two-way monitoring ensures that both ports get cleaned up
		781	when there is a problem.
		782
		783	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		784	caller before C<spawn> returns (by delaying invocation when spawn is
		785	called for the local node).
631		786
632	Example: spawn a chat server port on C<$othernode>.	787	Example: spawn a chat server port on C<$othernode>.
633		788
634	# this node, executed from within a port context:	789	# this node, executed from within a port context:
635	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	790	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
650		805
651	sub _spawn {	806	sub _spawn {
652	my $port = shift;	807	my $port = shift;
653	my $init = shift;	808	my $init = shift;
654		809
		810	# rcv will create the actual port
655	local $SELF = "$NODE#$port";	811	local $SELF = "$NODE#$port";
656	eval {	812	eval {
657	&{ load_func $init }	813	&{ load_func $init }
658	};	814	};
659	_self_die if $@;	815	_self_die if $@;
660	}	816	}
661		817
662	sub spawn(@) {	818	sub spawn(@) {
663	my ($noderef, undef) = split /#/, shift, 2;	819	my ($nodeid, undef) = split /#/, shift, 2;
664		820
665	my $id = "$RUNIQ." . $ID++;	821	my $id = $RUNIQ . ++$ID;
666		822
667	$_[0] =~ /::/	823	$_[0] =~ /::/
668	or Carp::croak "spawn init function must be a fully-qualified name, caught";	824	or Carp::croak "spawn init function must be a fully-qualified name, caught";
669		825
670	snd_to_func $noderef, "AnyEvent::MP::_spawn" => $id, @_;	826	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
671		827
672	"$noderef#$id"	828	"$nodeid#$id"
673	}	829	}
		830
674		831
675	=item after $timeout, @msg	832	=item after $timeout, @msg
676		833
677	=item after $timeout, $callback	834	=item after $timeout, $callback
678		835
679	Either sends the given message, or call the given callback, after the	836	Either sends the given message, or call the given callback, after the
680	specified number of seconds.	837	specified number of seconds.
681		838
682	This is simply a utility function that come sin handy at times.	839	This is simply a utility function that comes in handy at times - the
		840	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		841	so it may go away in the future.
683		842
684	=cut	843	=cut
685		844
686	sub after($@) {	845	sub after($@) {
687	my ($timeout, @action) = @_;	846	my ($timeout, @action) = @_;
…		…
692	? $action[0]()	851	? $action[0]()
693	: snd @action;	852	: snd @action;
694	};	853	};
695	}	854	}
696		855
		856	#=item $cb2 = timeout $seconds, $cb[, @args]
		857
		858	=item cal $port, @msg, $callback[, $timeout]
		859
		860	A simple form of RPC - sends a message to the given C<$port> with the
		861	given contents (C<@msg>), but adds a reply port to the message.
		862
		863	The reply port is created temporarily just for the purpose of receiving
		864	the reply, and will be C<kil>ed when no longer needed.
		865
		866	A reply message sent to the port is passed to the C<$callback> as-is.
		867
		868	If an optional time-out (in seconds) is given and it is not C<undef>,
		869	then the callback will be called without any arguments after the time-out
		870	elapsed and the port is C<kil>ed.
		871
		872	If no time-out is given (or it is C<undef>), then the local port will
		873	monitor the remote port instead, so it eventually gets cleaned-up.
		874
		875	Currently this function returns the temporary port, but this "feature"
		876	might go in future versions unless you can make a convincing case that
		877	this is indeed useful for something.
		878
		879	=cut
		880
		881	sub cal(@) {
		882	my $timeout = ref $_[-1] ? undef : pop;
		883	my $cb = pop;
		884
		885	my $port = port {
		886	undef $timeout;
		887	kil $SELF;
		888	&$cb;
		889	};
		890
		891	if (defined $timeout) {
		892	$timeout = AE::timer $timeout, 0, sub {
		893	undef $timeout;
		894	kil $port;
		895	$cb->();
		896	};
		897	} else {
		898	mon $_[0], sub {
		899	kil $port;
		900	$cb->();
		901	};
		902	}
		903
		904	push @_, $port;
		905	&snd;
		906
		907	$port
		908	}
		909
		910	=back
		911
		912	=head1 DISTRIBUTED DATABASE
		913
		914	AnyEvent::MP comes with a simple distributed database. The database will
		915	be mirrored asynchronously on all global nodes. Other nodes bind to one
		916	of the global nodes for their needs. Every node has a "local database"
		917	which contains all the values that are set locally. All local databases
		918	are merged together to form the global database, which can be queried.
		919
		920	The database structure is that of a two-level hash - the database hash
		921	contains hashes which contain values, similarly to a perl hash of hashes,
		922	i.e.:
		923
		924	$DATABASE{$family}{$subkey} = $value
		925
		926	The top level hash key is called "family", and the second-level hash key
		927	is called "subkey" or simply "key".
		928
		929	The family must be alphanumeric, i.e. start with a letter and consist
		930	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		931	pretty much like Perl module names.
		932
		933	As the family namespace is global, it is recommended to prefix family names
		934	with the name of the application or module using it.
		935
		936	The subkeys must be non-empty strings, with no further restrictions.
		937
		938	The values should preferably be strings, but other perl scalars should
		939	work as well (such as C<undef>, arrays and hashes).
		940
		941	Every database entry is owned by one node - adding the same family/subkey
		942	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		943	but the result might be nondeterministic, i.e. the key might have
		944	different values on different nodes.
		945
		946	Different subkeys in the same family can be owned by different nodes
		947	without problems, and in fact, this is the common method to create worker
		948	pools. For example, a worker port for image scaling might do this:
		949
		950	db_set my_image_scalers => $port;
		951
		952	And clients looking for an image scaler will want to get the
		953	C<my_image_scalers> keys from time to time:
		954
		955	db_keys my_image_scalers => sub {
		956	@ports = @{ $_[0] };
		957	};
		958
		959	Or better yet, they want to monitor the database family, so they always
		960	have a reasonable up-to-date copy:
		961
		962	db_mon my_image_scalers => sub {
		963	@ports = keys %{ $_[0] };
		964	};
		965
		966	In general, you can set or delete single subkeys, but query and monitor
		967	whole families only.
		968
		969	If you feel the need to monitor or query a single subkey, try giving it
		970	it's own family.
		971
		972	=over
		973
		974	=item db_set $family => $subkey [=> $value]
		975
		976	Sets (or replaces) a key to the database - if C<$value> is omitted,
		977	C<undef> is used instead.
		978
		979	=item db_del $family => $subkey...
		980
		981	Deletes one or more subkeys from the database family.
		982
		983	=item $guard = db_reg $family => $subkey [=> $value]
		984
		985	Sets the key on the database and returns a guard. When the guard is
		986	destroyed, the key is deleted from the database. If C<$value> is missing,
		987	then C<undef> is used.
		988
		989	=item db_family $family => $cb->(\%familyhash)
		990
		991	Queries the named database C<$family> and call the callback with the
		992	family represented as a hash. You can keep and freely modify the hash.
		993
		994	=item db_keys $family => $cb->(\@keys)
		995
		996	Same as C<db_family>, except it only queries the family I<subkeys> and passes
		997	them as array reference to the callback.
		998
		999	=item db_values $family => $cb->(\@values)
		1000
		1001	Same as C<db_family>, except it only queries the family I<values> and passes them
		1002	as array reference to the callback.
		1003
		1004	=item $guard = db_mon $family => $cb->($familyhash, \@added, \@changed, \@deleted)
		1005
		1006	Creates a monitor on the given database family. Each time a key is set
		1007	or or is deleted the callback is called with a hash containing the
		1008	database family and three lists of added, changed and deleted subkeys,
		1009	respectively. If no keys have changed then the array reference might be
		1010	C<undef> or even missing.
		1011
		1012	If not called in void context, a guard object is returned that, when
		1013	destroyed, stops the monitor.
		1014
		1015	The family hash reference and the key arrays belong to AnyEvent::MP and
		1016	B<must not be modified or stored> by the callback. When in doubt, make a
		1017	copy.
		1018
		1019	As soon as possible after the monitoring starts, the callback will be
		1020	called with the intiial contents of the family, even if it is empty,
		1021	i.e. there will always be a timely call to the callback with the current
		1022	contents.
		1023
		1024	It is possible that the callback is called with a change event even though
		1025	the subkey is already present and the value has not changed.
		1026
		1027	The monitoring stops when the guard object is destroyed.
		1028
		1029	Example: on every change to the family "mygroup", print out all keys.
		1030
		1031	my $guard = db_mon mygroup => sub {
		1032	my ($family, $a, $c, $d) = @_;
		1033	print "mygroup members: ", (join " ", keys %$family), "\n";
		1034	};
		1035
		1036	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1037
		1038	my $guard; $guard = db_mon My::Module::workers => sub {
		1039	my ($family, $a, $c, $d) = @_;
		1040	return unless %$family;
		1041	undef $guard;
		1042	print "My::Module::workers now nonempty\n";
		1043	};
		1044
		1045	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		1046
		1047	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		1048	my ($family, $a, $c, $d) = @_;
		1049
		1050	print "+$_=$family->{$_}\n" for @$a;
		1051	print "*$_=$family->{$_}\n" for @$c;
		1052	print "-$_=$family->{$_}\n" for @$d;
		1053	};
		1054
		1055	=cut
		1056
697	=back	1057	=back
698		1058
699	=head1 AnyEvent::MP vs. Distributed Erlang	1059	=head1 AnyEvent::MP vs. Distributed Erlang
700		1060
701	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	1061	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
702	== aemp node, Erlang process == aemp port), so many of the documents and	1062	== aemp node, Erlang process == aemp port), so many of the documents and
703	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	1063	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
704	sample:	1064	sample:
705		1065
706	http://www.Erlang.se/doc/programming_rules.shtml	1066	http://www.erlang.se/doc/programming_rules.shtml
707	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	1067	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
708	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	1068	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
709	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	1069	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
710		1070
711	Despite the similarities, there are also some important differences:	1071	Despite the similarities, there are also some important differences:
712		1072
713	=over 4	1073	=over 4
714		1074
715	=item * Node references contain the recipe on how to contact them.	1075	=item * Node IDs are arbitrary strings in AEMP.
716		1076
717	Erlang relies on special naming and DNS to work everywhere in the	1077	Erlang relies on special naming and DNS to work everywhere in the same
718	same way. AEMP relies on each node knowing it's own address(es), with	1078	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
719	convenience functionality.	1079	configuration or DNS), and possibly the addresses of some seed nodes, but
720		1080	will otherwise discover other nodes (and their IDs) itself.
721	This means that AEMP requires a less tightly controlled environment at the
722	cost of longer node references and a slightly higher management overhead.
723		1081
724	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP	1082	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
725	uses "local ports are like remote ports".	1083	uses "local ports are like remote ports".
726		1084
727	The failure modes for local ports are quite different (runtime errors	1085	The failure modes for local ports are quite different (runtime errors
…		…
736	ports being the special case/exception, where transport errors cannot	1094	ports being the special case/exception, where transport errors cannot
737	occur.	1095	occur.
738		1096
739	=item * Erlang uses processes and a mailbox, AEMP does not queue.	1097	=item * Erlang uses processes and a mailbox, AEMP does not queue.
740		1098
741	Erlang uses processes that selectively receive messages, and therefore	1099	Erlang uses processes that selectively receive messages out of order, and
742	needs a queue. AEMP is event based, queuing messages would serve no	1100	therefore needs a queue. AEMP is event based, queuing messages would serve
743	useful purpose. For the same reason the pattern-matching abilities of	1101	no useful purpose. For the same reason the pattern-matching abilities
744	AnyEvent::MP are more limited, as there is little need to be able to	1102	of AnyEvent::MP are more limited, as there is little need to be able to
745	filter messages without dequeing them.	1103	filter messages without dequeuing them.
746		1104
747	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	1105	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1106	being event-based, while Erlang is process-based.
		1107
		1108	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1109	top of AEMP and Coro threads.
748		1110
749	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1111	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
750		1112
751	Sending messages in Erlang is synchronous and blocks the process (and	1113	Sending messages in Erlang is synchronous and blocks the process until
		1114	a conenction has been established and the message sent (and so does not
752	so does not need a queue that can overflow). AEMP sends are immediate,	1115	need a queue that can overflow). AEMP sends return immediately, connection
753	connection establishment is handled in the background.	1116	establishment is handled in the background.
754		1117
755	=item * Erlang suffers from silent message loss, AEMP does not.	1118	=item * Erlang suffers from silent message loss, AEMP does not.
756		1119
757	Erlang makes few guarantees on messages delivery - messages can get lost	1120	Erlang implements few guarantees on messages delivery - messages can get
758	without any of the processes realising it (i.e. you send messages a, b,	1121	lost without any of the processes realising it (i.e. you send messages a,
759	and c, and the other side only receives messages a and c).	1122	b, and c, and the other side only receives messages a and c).
760		1123
761	AEMP guarantees correct ordering, and the guarantee that there are no	1124	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1125	guarantee that after one message is lost, all following ones sent to the
		1126	same port are lost as well, until monitoring raises an error, so there are
762	holes in the message sequence.	1127	no silent "holes" in the message sequence.
763		1128
764	=item * In Erlang, processes can be declared dead and later be found to be	1129	If you want your software to be very reliable, you have to cope with
765	alive.	1130	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
766		1131	simply tries to work better in common error cases, such as when a network
767	In Erlang it can happen that a monitored process is declared dead and	1132	link goes down.
768	linked processes get killed, but later it turns out that the process is
769	still alive - and can receive messages.
770
771	In AEMP, when port monitoring detects a port as dead, then that port will
772	eventually be killed - it cannot happen that a node detects a port as dead
773	and then later sends messages to it, finding it is still alive.
774		1133
775	=item * Erlang can send messages to the wrong port, AEMP does not.	1134	=item * Erlang can send messages to the wrong port, AEMP does not.
776		1135
777	In Erlang it is quite likely that a node that restarts reuses a process ID	1136	In Erlang it is quite likely that a node that restarts reuses an Erlang
778	known to other nodes for a completely different process, causing messages	1137	process ID known to other nodes for a completely different process,
779	destined for that process to end up in an unrelated process.	1138	causing messages destined for that process to end up in an unrelated
		1139	process.
780		1140
781	AEMP never reuses port IDs, so old messages or old port IDs floating	1141	AEMP does not reuse port IDs, so old messages or old port IDs floating
782	around in the network will not be sent to an unrelated port.	1142	around in the network will not be sent to an unrelated port.
783		1143
784	=item * Erlang uses unprotected connections, AEMP uses secure	1144	=item * Erlang uses unprotected connections, AEMP uses secure
785	authentication and can use TLS.	1145	authentication and can use TLS.
786		1146
787	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1147	AEMP can use a proven protocol - TLS - to protect connections and
788	securely authenticate nodes.	1148	securely authenticate nodes.
789		1149
790	=item * The AEMP protocol is optimised for both text-based and binary	1150	=item * The AEMP protocol is optimised for both text-based and binary
791	communications.	1151	communications.
792		1152
793	The AEMP protocol, unlike the Erlang protocol, supports both	1153	The AEMP protocol, unlike the Erlang protocol, supports both programming
794	language-independent text-only protocols (good for debugging) and binary,	1154	language independent text-only protocols (good for debugging), and binary,
795	language-specific serialisers (e.g. Storable).	1155	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1156	used, the protocol is actually completely text-based.
796		1157
797	It has also been carefully designed to be implementable in other languages	1158	It has also been carefully designed to be implementable in other languages
798	with a minimum of work while gracefully degrading fucntionality to make the	1159	with a minimum of work while gracefully degrading functionality to make the
799	protocol simple.	1160	protocol simple.
800		1161
801	=item * AEMP has more flexible monitoring options than Erlang.	1162	=item * AEMP has more flexible monitoring options than Erlang.
802		1163
803	In Erlang, you can chose to receive I<all> exit signals as messages	1164	In Erlang, you can chose to receive I<all> exit signals as messages or
804	or I<none>, there is no in-between, so monitoring single processes is	1165	I<none>, there is no in-between, so monitoring single Erlang processes is
805	difficult to implement. Monitoring in AEMP is more flexible than in	1166	difficult to implement.
806	Erlang, as one can choose between automatic kill, exit message or callback	1167
807	on a per-process basis.	1168	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1169	between automatic kill, exit message or callback on a per-port basis.
808		1170
809	=item * Erlang tries to hide remote/local connections, AEMP does not.	1171	=item * Erlang tries to hide remote/local connections, AEMP does not.
810		1172
811	Monitoring in Erlang is not an indicator of process death/crashes,	1173	Monitoring in Erlang is not an indicator of process death/crashes, in the
812	as linking is (except linking is unreliable in Erlang).	1174	same way as linking is (except linking is unreliable in Erlang).
813		1175
814	In AEMP, you don't "look up" registered port names or send to named ports	1176	In AEMP, you don't "look up" registered port names or send to named ports
815	that might or might not be persistent. Instead, you normally spawn a port	1177	that might or might not be persistent. Instead, you normally spawn a port
816	on the remote node. The init function monitors the you, and you monitor	1178	on the remote node. The init function monitors you, and you monitor the
817	the remote port. Since both monitors are local to the node, they are much	1179	remote port. Since both monitors are local to the node, they are much more
818	more reliable.	1180	reliable (no need for C<spawn_link>).
819		1181
820	This also saves round-trips and avoids sending messages to the wrong port	1182	This also saves round-trips and avoids sending messages to the wrong port
821	(hard to do in Erlang).	1183	(hard to do in Erlang).
822		1184
823	=back	1185	=back
824		1186
825	=head1 RATIONALE	1187	=head1 RATIONALE
826		1188
827	=over 4	1189	=over 4
828		1190
829	=item Why strings for ports and noderefs, why not objects?	1191	=item Why strings for port and node IDs, why not objects?
830		1192
831	We considered "objects", but found that the actual number of methods	1193	We considered "objects", but found that the actual number of methods
832	thatc an be called are very low. Since port IDs and noderefs travel over	1194	that can be called are quite low. Since port and node IDs travel over
833	the network frequently, the serialising/deserialising would add lots of	1195	the network frequently, the serialising/deserialising would add lots of
834	overhead, as well as having to keep a proxy object.	1196	overhead, as well as having to keep a proxy object everywhere.
835		1197
836	Strings can easily be printed, easily serialised etc. and need no special	1198	Strings can easily be printed, easily serialised etc. and need no special
837	procedures to be "valid".	1199	procedures to be "valid".
838		1200
839	And a a miniport consists of a single closure stored in a global hash - it	1201	And as a result, a port with just a default receiver consists of a single
840	can't become much cheaper.	1202	code reference stored in a global hash - it can't become much cheaper.
841		1203
842	=item Why favour JSON, why not real serialising format such as Storable?	1204	=item Why favour JSON, why not a real serialising format such as Storable?
843		1205
844	In fact, any AnyEvent::MP node will happily accept Storable as framing	1206	In fact, any AnyEvent::MP node will happily accept Storable as framing
845	format, but currently there is no way to make a node use Storable by	1207	format, but currently there is no way to make a node use Storable by
846	default.	1208	default (although all nodes will accept it).
847		1209
848	The default framing protocol is JSON because a) JSON::XS is many times	1210	The default framing protocol is JSON because a) JSON::XS is many times
849	faster for small messages and b) most importantly, after years of	1211	faster for small messages and b) most importantly, after years of
850	experience we found that object serialisation is causing more problems	1212	experience we found that object serialisation is causing more problems
851	than it gains: Just like function calls, objects simply do not travel	1213	than it solves: Just like function calls, objects simply do not travel
852	easily over the network, mostly because they will always be a copy, so you	1214	easily over the network, mostly because they will always be a copy, so you
853	always have to re-think your design.	1215	always have to re-think your design.
854		1216
855	Keeping your messages simple, concentrating on data structures rather than	1217	Keeping your messages simple, concentrating on data structures rather than
856	objects, will keep your messages clean, tidy and efficient.	1218	objects, will keep your messages clean, tidy and efficient.
857		1219
858	=back	1220	=back
859		1221
860	=head1 SEE ALSO	1222	=head1 SEE ALSO
861		1223
		1224	L<AnyEvent::MP::Intro> - a gentle introduction.
		1225
		1226	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1227
		1228	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1229	your applications.
		1230
		1231	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1232
		1233	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1234	all nodes.
		1235
862	L<AnyEvent>.	1236	L<AnyEvent>.
863		1237
864	=head1 AUTHOR	1238	=head1 AUTHOR
865		1239
866	Marc Lehmann <schmorp@schmorp.de>	1240	Marc Lehmann <schmorp@schmorp.de>

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Revision 1.136 by root, Wed Mar 21 15:22:16 2012 UTC