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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.63 by root, Thu Aug 27 21:29:37 2009 UTC vs.
Revision 1.130 by root, Fri Mar 9 17:05:26 2012 UTC

…		…
1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent::MP - multi-processing/message-passing framework	3	AnyEvent::MP - erlang-style multi-processing/message-passing framework
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::MP;	7	use AnyEvent::MP;
8		8
9	$NODE # contains this node's noderef	9	$NODE # contains this node's node ID
10	NODE # returns this node's noderef	10	NODE # returns this node's node ID
11	NODE $port # returns the noderef of the port
12		11
13	$SELF # receiving/own port id in rcv callbacks	12	$SELF # receiving/own port id in rcv callbacks
14		13
15	# initialise the node so it can send/receive messages	14	# initialise the node so it can send/receive messages
16	initialise_node;	15	configure;
17		16
18	# ports are message endpoints	17	# ports are message destinations
19		18
20	# sending messages	19	# sending messages
21	snd $port, type => data...;	20	snd $port, type => data...;
22	snd $port, @msg;	21	snd $port, @msg;
23	snd @msg_with_first_element_being_a_port;	22	snd @msg_with_first_element_being_a_port;
24		23
25	# creating/using ports, the simple way	24	# creating/using ports, the simple way
26	my $simple_port = port { my @msg = @_; 0 };	25	my $simple_port = port { my @msg = @_ };
27		26
28	# creating/using ports, tagged message matching	27	# creating/using ports, tagged message matching
29	my $port = port;	28	my $port = port;
30	rcv $port, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
31	rcv $port, pong => sub { warn "pong received\n"; 0 };	30	rcv $port, pong => sub { warn "pong received\n" };
32		31
33	# create a port on another node	32	# create a port on another node
34	my $port = spawn $node, $initfunc, @initdata;	33	my $port = spawn $node, $initfunc, @initdata;
35		34
		35	# destroy a port again
		36	kil $port; # "normal" kill
		37	kil $port, my_error => "everything is broken"; # error kill
		38
36	# monitoring	39	# monitoring
37	mon $port, $cb->(@msg) # callback is invoked on death	40	mon $port, $cb->(@msg) # callback is invoked on death
38	mon $port, $otherport # kill otherport on abnormal death	41	mon $port, $localport # kill localport on abnormal death
39	mon $port, $otherport, @msg # send message on death	42	mon $port, $localport, @msg # send message on death
		43
		44	# temporarily execute code in port context
		45	peval $port, sub { die "kill the port!" };
		46
		47	# execute callbacks in $SELF port context
		48	my $timer = AE::timer 1, 0, psub {
		49	die "kill the port, delayed";
		50	};
40		51
41	=head1 CURRENT STATUS	52	=head1 CURRENT STATUS
42		53
		54	bin/aemp - stable.
43	AnyEvent::MP - stable API, should work	55	AnyEvent::MP - stable API, should work.
44	AnyEvent::MP::Intro - outdated	56	AnyEvent::MP::Intro - explains most concepts.
45	AnyEvent::MP::Kernel - WIP
46	AnyEvent::MP::Transport - mostly stable	57	AnyEvent::MP::Kernel - mostly stable API.
47		58	AnyEvent::MP::Global - stable API.
48	stay tuned.
49		59
50	=head1 DESCRIPTION	60	=head1 DESCRIPTION
51		61
52	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
53		63
54	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
55	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
56		66
57	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	67	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
58	manual page.	68	manual page and the examples under F<eg/>.
59
60	At the moment, this module family is severly broken and underdocumented,
61	so do not use. This was uploaded mainly to reserve the CPAN namespace -
62	stay tuned!
63		69
64	=head1 CONCEPTS	70	=head1 CONCEPTS
65		71
66	=over 4	72	=over 4
67		73
68	=item port	74	=item port
69		75
70	A port is something you can send messages to (with the C<snd> function).	76	Not to be confused with a TCP port, a "port" is something you can send
		77	messages to (with the C<snd> function).
71		78
72	Ports allow you to register C<rcv> handlers that can match all or just	79	Ports allow you to register C<rcv> handlers that can match all or just
73	some messages. Messages 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.
74		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
75	=item port ID - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
76		86
77	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<#>)
78	separator, and a port name (a printable string of unspecified format). An	88	as separator, and a port name (a printable string of unspecified
79	exception is the the node port, whose ID is identical to its node	89	format created by AnyEvent::MP).
80	reference.
81		90
82	=item node	91	=item node
83		92
84	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,
85	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
86	ports.	95	ports.
87		96
88	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
89	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
90	from any other node).	99	currently, but all nodes can talk to public nodes.
91		100
		101	Nodes is represented by (printable) strings called "node IDs".
		102
92	=item node ID - C<[a-za-Z0-9_\-.:]+>	103	=item node ID - C<[A-Za-z0-9_\-.:]*>
93		104
94	A node ID is a string that either simply identifies the node (for	105	A node ID is a string that uniquely identifies the node within a
95	private and slave nodes), or contains a recipe on how to reach a given	106	network. Depending on the configuration used, node IDs can look like a
96	node (for public nodes).	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.
97		109
98	This recipe is simply a comma-separated list of C<address:port> pairs (for	110	=item binds - C<ip:port>
99	TCP/IP, other protocols might look different).
100		111
101	Node references come in two flavours: resolved (containing only numerical	112	Nodes can only talk to each other by creating some kind of connection to
102	addresses) or unresolved (where hostnames are used instead of addresses).	113	each other. To do this, nodes should listen on one or more local transport
		114	endpoints - binds.
103		115
104	Before using an unresolved node reference in a message you first have to	116	Currently, only standard C<ip:port> specifications can be used, which
105	resolve it.	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).
106		170
107	=back	171	=back
108		172
109	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
110		174
112		176
113	=cut	177	=cut
114		178
115	package AnyEvent::MP;	179	package AnyEvent::MP;
116		180
		181	use AnyEvent::MP::Config ();
117	use AnyEvent::MP::Kernel;	182	use AnyEvent::MP::Kernel;
		183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
118		184
119	use common::sense;	185	use common::sense;
120		186
121	use Carp ();	187	use Carp ();
122		188
123	use AE ();	189	use AE ();
		190	use Guard ();
124		191
125	use base "Exporter";	192	use base "Exporter";
126		193
127	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
128		195
129	our @EXPORT = qw(	196	our @EXPORT = qw(
130	NODE $NODE *SELF node_of after	197	NODE $NODE *SELF node_of after
131	resolve_node initialise_node	198	configure
132	snd rcv mon mon_guard kil reg psub spawn	199	snd rcv mon mon_guard kil psub peval spawn cal
133	port	200	port
		201	db_set db_del db_reg
		202	db_mon db_family db_keys db_values
134	);	203	);
135		204
136	our $SELF;	205	our $SELF;
137		206
138	sub _self_die() {	207	sub _self_die() {
…		…
141	kil $SELF, die => $msg;	210	kil $SELF, die => $msg;
142	}	211	}
143		212
144	=item $thisnode = NODE / $NODE	213	=item $thisnode = NODE / $NODE
145		214
146	The C<NODE> function returns, and the C<$NODE> variable contains the	215	The C<NODE> function returns, and the C<$NODE> variable contains, the node
147	node id 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
148	C<initialise_node>.	217	a call to C<configure>.
149		218
150	=item $nodeid = node_of $port	219	=item $nodeid = node_of $port
151		220
152	Extracts and returns the noderef from a port ID or a node ID.	221	Extracts and returns the node ID from a port ID or a node ID.
153		222
154	=item initialise_node $profile_name	223	=item configure $profile, key => value...
155		224
		225	=item configure key => value...
		226
156	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
157	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
158	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.
159		231
160	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
161	never) before calling other AnyEvent::MP functions.	233	never) before calling other AnyEvent::MP functions.
162		234
163	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
164	either resolved or unresolved.	236	F<aemp> command line utility (sans the set/del prefix), with these additions:
165
166	The first argument will be looked up in the configuration database first
167	(if it is C<undef> then the current nodename will be used instead) to find
168	the relevant configuration profile (see L<aemp>). If none is found then
169	the default configuration is used. The configuration supplies additional
170	seed/master nodes and can override the actual noderef.
171
172	There are two types of networked nodes, public nodes and slave nodes:
173		237
174	=over 4	238	=over 4
175		239
176	=item public nodes	240	=item norc => $boolean (default false)
177		241
178	For public nodes, C<$noderef> (supplied either directly to	242	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
179	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
180	noderef (possibly unresolved, in which case it will be resolved).	244	C<configure> call.
181		245
182	After resolving, the node will bind itself on all endpoints.	246	=item force => $boolean (default false)
183		247
184	=item slave nodes	248	IF true, then the values specified in the C<configure> will take
		249	precedence over any values configured via the rc file. The default is for
		250	the rc file to override any options specified in the program.
185		251
186	When the C<$noderef> (either as given or overriden by the config file)	252	=item secure => $pass->($nodeid)
187	is the special string C<slave/>, then the node will become a slave
188	node. Slave nodes cannot be contacted from outside, and cannot talk to
189	each other (at least in this version of AnyEvent::MP).
190		253
191	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
192	L<AnyEvent::MP::Global> service.	255	is called for every remote execution attempt - the execution request is
		256	granted iff the callback returns a true value.
		257
		258	See F<semp setsecure> for more info.
193		259
194	=back	260	=back
195		261
196	After initialising itself, the node will connect to all additional
197	C<$seednodes> that are specified diretcly or via a profile. Seednodes are
198	optional and can be used to quickly bootstrap the node into an existing
199	network.
200
201	All the seednodes will also be specially marked to automatically retry
202	connecting to them indefinitely, so make sure that seednodes are really
203	reliable and up (this might also change in the future).
204
205	Example: become a public node listening on the guessed noderef, or the one
206	specified via C<aemp> for the current node. This should be the most common
207	form of invocation for "daemon"-type nodes.
208
209	initialise_node;
210
211	Example: become a slave node to any of the the seednodes specified via
212	C<aemp>. This form is often used for commandline clients.
213
214	initialise_node "slave/";
215
216	Example: become a public node, and try to contact some well-known master
217	servers to become part of the network.
218
219	initialise_node undef, "master1", "master2";
220
221	Example: become a public node listening on port C<4041>.
222
223	initialise_node 4041;
224
225	Example: become a public node, only visible on localhost port 4044.
226
227	initialise_node "localhost:4044";
228
229	=item $cv = resolve_node $noderef
230
231	Takes an unresolved node reference that may contain hostnames and
232	abbreviated IDs, resolves all of them and returns a resolved node
233	reference.
234
235	In addition to C<address:port> pairs allowed in resolved noderefs, the
236	following forms are supported:
237
238	=over 4	262	=over 4
239		263
240	=item the empty string	264	=item step 1, gathering configuration from profiles
241		265
242	An empty-string component gets resolved as if the default port (4040) was	266	The function first looks up a profile in the aemp configuration (see the
243	specified.	267	L<aemp> commandline utility). The profile name can be specified via the
		268	named C<profile> parameter or can simply be the first parameter). If it is
		269	missing, then the nodename (F<uname -n>) will be used as profile name.
244		270
245	=item naked port numbers (e.g. C<1234>)	271	The profile data is then gathered as follows:
246		272
247	These are resolved by prepending the local nodename and a colon, to be	273	First, all remaining key => value pairs (all of which are conveniently
248	further resolved.	274	undocumented at the moment) will be interpreted as configuration
		275	data. Then they will be overwritten by any values specified in the global
		276	default configuration (see the F<aemp> utility), then the chain of
		277	profiles chosen by the profile name (and any C<parent> attributes).
249		278
250	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	279	That means that the values specified in the profile have highest priority
		280	and the values specified directly via C<configure> have lowest priority,
		281	and can only be used to specify defaults.
251		282
252	These are resolved by using AnyEvent::DNS to resolve them, optionally	283	If the profile specifies a node ID, then this will become the node ID of
253	looking up SRV records for the C<aemp=4040> port, if no port was	284	this process. If not, then the profile name will be used as node ID, with
254	specified.	285	a unique randoms tring (C</%u>) appended.
		286
		287	The node ID can contain some C<%> sequences that are expanded: C<%n>
		288	is expanded to the local nodename, C<%u> is replaced by a random
		289	strign to make the node unique. For example, the F<aemp> commandline
		290	utility uses C<aemp/%n/%u> as nodename, which might expand to
		291	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		292
		293	=item step 2, bind listener sockets
		294
		295	The next step is to look up the binds in the profile, followed by binding
		296	aemp protocol listeners on all binds specified (it is possible and valid
		297	to have no binds, meaning that the node cannot be contacted form the
		298	outside. This means the node cannot talk to other nodes that also have no
		299	binds, but it can still talk to all "normal" nodes).
		300
		301	If the profile does not specify a binds list, then a default of C<*> is
		302	used, meaning the node will bind on a dynamically-assigned port on every
		303	local IP address it finds.
		304
		305	=item step 3, connect to seed nodes
		306
		307	As the last step, the seed ID list from the profile is passed to the
		308	L<AnyEvent::MP::Global> module, which will then use it to keep
		309	connectivity with at least one node at any point in time.
255		310
256	=back	311	=back
		312
		313	Example: become a distributed node using the local node name as profile.
		314	This should be the most common form of invocation for "daemon"-type nodes.
		315
		316	configure
		317
		318	Example: become a semi-anonymous node. This form is often used for
		319	commandline clients.
		320
		321	configure nodeid => "myscript/%n/%u";
		322
		323	Example: configure a node using a profile called seed, which is suitable
		324	for a seed node as it binds on all local addresses on a fixed port (4040,
		325	customary for aemp).
		326
		327	# use the aemp commandline utility
		328	# aemp profile seed binds '*:4040'
		329
		330	# then use it
		331	configure profile => "seed";
		332
		333	# or simply use aemp from the shell again:
		334	# aemp run profile seed
		335
		336	# or provide a nicer-to-remember nodeid
		337	# aemp run profile seed nodeid "$(hostname)"
257		338
258	=item $SELF	339	=item $SELF
259		340
260	Contains the current port id while executing C<rcv> callbacks or C<psub>	341	Contains the current port id while executing C<rcv> callbacks or C<psub>
261	blocks.	342	blocks.
262		343
263	=item SELF, %SELF, @SELF...	344	=item *SELF, SELF, %SELF, @SELF...
264		345
265	Due to some quirks in how perl exports variables, it is impossible to	346	Due to some quirks in how perl exports variables, it is impossible to
266	just export C<$SELF>, all the symbols called C<SELF> are exported by this	347	just export C<$SELF>, all the symbols named C<SELF> are exported by this
267	module, but only C<$SELF> is currently used.	348	module, but only C<$SELF> is currently used.
268		349
269	=item snd $port, type => @data	350	=item snd $port, type => @data
270		351
271	=item snd $port, @msg	352	=item snd $port, @msg
272		353
273	Send the given message to the given port ID, which can identify either	354	Send the given message to the given port, which can identify either a
274	a local or a remote port, and must be a port ID.	355	local or a remote port, and must be a port ID.
275		356
276	While the message can be about anything, it is highly recommended to use a	357	While the message can be almost anything, it is highly recommended to
277	string as first element (a port ID, or some word that indicates a request	358	use a string as first element (a port ID, or some word that indicates a
278	type etc.).	359	request type etc.) and to consist if only simple perl values (scalars,
		360	arrays, hashes) - if you think you need to pass an object, think again.
279		361
280	The message data effectively becomes read-only after a call to this	362	The message data logically becomes read-only after a call to this
281	function: modifying any argument is not allowed and can cause many	363	function: modifying any argument (or values referenced by them) is
282	problems.	364	forbidden, as there can be considerable time between the call to C<snd>
		365	and the time the message is actually being serialised - in fact, it might
		366	never be copied as within the same process it is simply handed to the
		367	receiving port.
283		368
284	The type of data you can transfer depends on the transport protocol: when	369	The type of data you can transfer depends on the transport protocol: when
285	JSON is used, then only strings, numbers and arrays and hashes consisting	370	JSON is used, then only strings, numbers and arrays and hashes consisting
286	of those are allowed (no objects). When Storable is used, then anything	371	of those are allowed (no objects). When Storable is used, then anything
287	that Storable can serialise and deserialise is allowed, and for the local	372	that Storable can serialise and deserialise is allowed, and for the local
288	node, anything can be passed.	373	node, anything can be passed. Best rely only on the common denominator of
		374	these.
289		375
290	=item $local_port = port	376	=item $local_port = port
291		377
292	Create a new local port object and returns its port ID. Initially it has	378	Create a new local port object and returns its port ID. Initially it has
293	no callbacks set and will throw an error when it receives messages.	379	no callbacks set and will throw an error when it receives messages.
…		…
317	sub _kilme {	403	sub _kilme {
318	die "received message on port without callback";	404	die "received message on port without callback";
319	}	405	}
320		406
321	sub port(;&) {	407	sub port(;&) {
322	my $id = "$UNIQ." . $ID++;	408	my $id = $UNIQ . ++$ID;
323	my $port = "$NODE#$id";	409	my $port = "$NODE#$id";
324		410
325	rcv $port, shift \|\| \&_kilme;	411	rcv $port, shift \|\| \&_kilme;
326		412
327	$port	413	$port
…		…
366	msg1 => sub { ... },	452	msg1 => sub { ... },
367	...	453	...
368	;	454	;
369		455
370	Example: temporarily register a rcv callback for a tag matching some port	456	Example: temporarily register a rcv callback for a tag matching some port
371	(e.g. for a rpc reply) and unregister it after a message was received.	457	(e.g. for an rpc reply) and unregister it after a message was received.
372		458
373	rcv $port, $otherport => sub {	459	rcv $port, $otherport => sub {
374	my @reply = @_;	460	my @reply = @_;
375		461
376	rcv $SELF, $otherport;	462	rcv $SELF, $otherport;
…		…
378		464
379	=cut	465	=cut
380		466
381	sub rcv($@) {	467	sub rcv($@) {
382	my $port = shift;	468	my $port = shift;
383	my ($noderef, $portid) = split /#/, $port, 2;	469	my ($nodeid, $portid) = split /#/, $port, 2;
384		470
385	$NODE{$noderef} == $NODE{""}	471	$NODE{$nodeid} == $NODE{""}
386	or Carp::croak "$port: rcv can only be called on local ports, caught";	472	or Carp::croak "$port: rcv can only be called on local ports, caught";
387		473
388	while (@_) {	474	while (@_) {
389	if (ref $_[0]) {	475	if (ref $_[0]) {
390	if (my $self = $PORT_DATA{$portid}) {	476	if (my $self = $PORT_DATA{$portid}) {
391	"AnyEvent::MP::Port" eq ref $self	477	"AnyEvent::MP::Port" eq ref $self
392	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	478	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
393		479
394	$self->[2] = shift;	480	$self->[0] = shift;
395	} else {	481	} else {
396	my $cb = shift;	482	my $cb = shift;
397	$PORT{$portid} = sub {	483	$PORT{$portid} = sub {
398	local $SELF = $port;	484	local $SELF = $port;
399	eval { &$cb }; _self_die if $@;	485	eval { &$cb }; _self_die if $@;
400	};	486	};
401	}	487	}
402	} elsif (defined $_[0]) {	488	} elsif (defined $_[0]) {
403	my $self = $PORT_DATA{$portid} \|\|= do {	489	my $self = $PORT_DATA{$portid} \|\|= do {
404	my $self = bless [$PORT{$port} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";	490	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
405		491
406	$PORT{$portid} = sub {	492	$PORT{$portid} = sub {
407	local $SELF = $port;	493	local $SELF = $port;
408		494
409	if (my $cb = $self->[1]{$_[0]}) {	495	if (my $cb = $self->[1]{$_[0]}) {
…		…
431	}	517	}
432		518
433	$port	519	$port
434	}	520	}
435		521
		522	=item peval $port, $coderef[, @args]
		523
		524	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		525	when the code throews an exception the C<$port> will be killed.
		526
		527	Any remaining args will be passed to the callback. Any return values will
		528	be returned to the caller.
		529
		530	This is useful when you temporarily want to execute code in the context of
		531	a port.
		532
		533	Example: create a port and run some initialisation code in it's context.
		534
		535	my $port = port { ... };
		536
		537	peval $port, sub {
		538	init
		539	or die "unable to init";
		540	};
		541
		542	=cut
		543
		544	sub peval($$) {
		545	local $SELF = shift;
		546	my $cb = shift;
		547
		548	if (wantarray) {
		549	my @res = eval { &$cb };
		550	_self_die if $@;
		551	@res
		552	} else {
		553	my $res = eval { &$cb };
		554	_self_die if $@;
		555	$res
		556	}
		557	}
		558
436	=item $closure = psub { BLOCK }	559	=item $closure = psub { BLOCK }
437		560
438	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	561	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
439	closure is executed, sets up the environment in the same way as in C<rcv>	562	closure is executed, sets up the environment in the same way as in C<rcv>
440	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.	563	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		564
		565	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		566	BLOCK }, @_ } >>.
441		567
442	This is useful when you register callbacks from C<rcv> callbacks:	568	This is useful when you register callbacks from C<rcv> callbacks:
443		569
444	rcv delayed_reply => sub {	570	rcv delayed_reply => sub {
445	my ($delay, @reply) = @_;	571	my ($delay, @reply) = @_;
…		…
469	$res	595	$res
470	}	596	}
471	}	597	}
472	}	598	}
473		599
474	=item $guard = mon $port, $cb->(@reason)	600	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
475		601
476	=item $guard = mon $port, $rcvport	602	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
477		603
478	=item $guard = mon $port	604	=item $guard = mon $port # kill $SELF when $port dies
479		605
480	=item $guard = mon $port, $rcvport, @msg	606	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
481		607
482	Monitor the given port and do something when the port is killed or	608	Monitor the given port and do something when the port is killed or
483	messages to it were lost, and optionally return a guard that can be used	609	messages to it were lost, and optionally return a guard that can be used
484	to stop monitoring again.	610	to stop monitoring again.
485
486	C<mon> effectively guarantees that, in the absence of hardware failures,
487	that after starting the monitor, either all messages sent to the port
488	will arrive, or the monitoring action will be invoked after possible
489	message loss has been detected. No messages will be lost "in between"
490	(after the first lost message no further messages will be received by the
491	port). After the monitoring action was invoked, further messages might get
492	delivered again.
493
494	Note that monitoring-actions are one-shot: once released, they are removed
495	and will not trigger again.
496		611
497	In the first form (callback), the callback is simply called with any	612	In the first form (callback), the callback is simply called with any
498	number of C<@reason> elements (no @reason means that the port was deleted	613	number of C<@reason> elements (no @reason means that the port was deleted
499	"normally"). Note also that I<< the callback B<must> never die >>, so use	614	"normally"). Note also that I<< the callback B<must> never die >>, so use
500	C<eval> if unsure.	615	C<eval> if unsure.
501		616
502	In the second form (another port given), the other port (C<$rcvport>)	617	In the second form (another port given), the other port (C<$rcvport>)
503	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	618	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
504	"normal" kils nothing happens, while under all other conditions, the other	619	"normal" kils nothing happens, while under all other conditions, the other
505	port is killed with the same reason.	620	port is killed with the same reason.
506		621
507	The third form (kill self) is the same as the second form, except that	622	The third form (kill self) is the same as the second form, except that
508	C<$rvport> defaults to C<$SELF>.	623	C<$rvport> defaults to C<$SELF>.
509		624
510	In the last form (message), a message of the form C<@msg, @reason> will be	625	In the last form (message), a message of the form C<@msg, @reason> will be
511	C<snd>.	626	C<snd>.
		627
		628	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		629	alert was raised), they are removed and will not trigger again.
512		630
513	As a rule of thumb, monitoring requests should always monitor a port from	631	As a rule of thumb, monitoring requests should always monitor a port from
514	a local port (or callback). The reason is that kill messages might get	632	a local port (or callback). The reason is that kill messages might get
515	lost, just like any other message. Another less obvious reason is that	633	lost, just like any other message. Another less obvious reason is that
516	even monitoring requests can get lost (for exmaple, when the connection	634	even monitoring requests can get lost (for example, when the connection
517	to the other node goes down permanently). When monitoring a port locally	635	to the other node goes down permanently). When monitoring a port locally
518	these problems do not exist.	636	these problems do not exist.
519		637
		638	C<mon> effectively guarantees that, in the absence of hardware failures,
		639	after starting the monitor, either all messages sent to the port will
		640	arrive, or the monitoring action will be invoked after possible message
		641	loss has been detected. No messages will be lost "in between" (after
		642	the first lost message no further messages will be received by the
		643	port). After the monitoring action was invoked, further messages might get
		644	delivered again.
		645
		646	Inter-host-connection timeouts and monitoring depend on the transport
		647	used. The only transport currently implemented is TCP, and AnyEvent::MP
		648	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		649	non-idle connection, and usually around two hours for idle connections).
		650
		651	This means that monitoring is good for program errors and cleaning up
		652	stuff eventually, but they are no replacement for a timeout when you need
		653	to ensure some maximum latency.
		654
520	Example: call a given callback when C<$port> is killed.	655	Example: call a given callback when C<$port> is killed.
521		656
522	mon $port, sub { warn "port died because of <@_>\n" };	657	mon $port, sub { warn "port died because of <@_>\n" };
523		658
524	Example: kill ourselves when C<$port> is killed abnormally.	659	Example: kill ourselves when C<$port> is killed abnormally.
…		…
530	mon $port, $self => "restart";	665	mon $port, $self => "restart";
531		666
532	=cut	667	=cut
533		668
534	sub mon {	669	sub mon {
535	my ($noderef, $port) = split /#/, shift, 2;	670	my ($nodeid, $port) = split /#/, shift, 2;
536		671
537	my $node = $NODE{$noderef} \|\| add_node $noderef;	672	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
538		673
539	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';	674	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
540		675
541	unless (ref $cb) {	676	unless (ref $cb) {
542	if (@_) {	677	if (@_) {
…		…
551	}	686	}
552		687
553	$node->monitor ($port, $cb);	688	$node->monitor ($port, $cb);
554		689
555	defined wantarray	690	defined wantarray
556	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	691	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
557	}	692	}
558		693
559	=item $guard = mon_guard $port, $ref, $ref...	694	=item $guard = mon_guard $port, $ref, $ref...
560		695
561	Monitors the given C<$port> and keeps the passed references. When the port	696	Monitors the given C<$port> and keeps the passed references. When the port
562	is killed, the references will be freed.	697	is killed, the references will be freed.
563		698
564	Optionally returns a guard that will stop the monitoring.	699	Optionally returns a guard that will stop the monitoring.
565		700
566	This function is useful when you create e.g. timers or other watchers and	701	This function is useful when you create e.g. timers or other watchers and
567	want to free them when the port gets killed:	702	want to free them when the port gets killed (note the use of C<psub>):
568		703
569	$port->rcv (start => sub {	704	$port->rcv (start => sub {
570	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	705	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
571	undef $timer if 0.9 < rand;	706	undef $timer if 0.9 < rand;
572	});	707	});
573	});	708	});
574		709
575	=cut	710	=cut
…		…
584		719
585	=item kil $port[, @reason]	720	=item kil $port[, @reason]
586		721
587	Kill the specified port with the given C<@reason>.	722	Kill the specified port with the given C<@reason>.
588		723
589	If no C<@reason> is specified, then the port is killed "normally" (linked	724	If no C<@reason> is specified, then the port is killed "normally" -
590	ports will not be kileld, or even notified).	725	monitor callback will be invoked, but the kil will not cause linked ports
		726	(C<mon $mport, $lport> form) to get killed.
591		727
592	Otherwise, linked ports get killed with the same reason (second form of	728	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
593	C<mon>, see below).	729	form) get killed with the same reason.
594		730
595	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	731	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
596	will be reported as reason C<< die => $@ >>.	732	will be reported as reason C<< die => $@ >>.
597		733
598	Transport/communication errors are reported as C<< transport_error =>	734	Transport/communication errors are reported as C<< transport_error =>
…		…
603	=item $port = spawn $node, $initfunc[, @initdata]	739	=item $port = spawn $node, $initfunc[, @initdata]
604		740
605	Creates a port on the node C<$node> (which can also be a port ID, in which	741	Creates a port on the node C<$node> (which can also be a port ID, in which
606	case it's the node where that port resides).	742	case it's the node where that port resides).
607		743
608	The port ID of the newly created port is return immediately, and it is	744	The port ID of the newly created port is returned immediately, and it is
609	permissible to immediately start sending messages or monitor the port.	745	possible to immediately start sending messages or to monitor the port.
610		746
611	After the port has been created, the init function is	747	After the port has been created, the init function is called on the remote
612	called. This function must be a fully-qualified function name	748	node, in the same context as a C<rcv> callback. This function must be a
613	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	749	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
614	program, use C<::name>.	750	specify a function in the main program, use C<::name>.
615		751
616	If the function doesn't exist, then the node tries to C<require>	752	If the function doesn't exist, then the node tries to C<require>
617	the package, then the package above the package and so on (e.g.	753	the package, then the package above the package and so on (e.g.
618	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	754	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
619	exists or it runs out of package names.	755	exists or it runs out of package names.
620		756
621	The init function is then called with the newly-created port as context	757	The init function is then called with the newly-created port as context
622	object (C<$SELF>) and the C<@initdata> values as arguments.	758	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		759	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		760	the port might not get created.
623		761
624	A common idiom is to pass your own port, monitor the spawned port, and	762	A common idiom is to pass a local port, immediately monitor the spawned
625	in the init function, monitor the original port. This two-way monitoring	763	port, and in the remote init function, immediately monitor the passed
626	ensures that both ports get cleaned up when there is a problem.	764	local port. This two-way monitoring ensures that both ports get cleaned up
		765	when there is a problem.
		766
		767	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		768	caller before C<spawn> returns (by delaying invocation when spawn is
		769	called for the local node).
627		770
628	Example: spawn a chat server port on C<$othernode>.	771	Example: spawn a chat server port on C<$othernode>.
629		772
630	# this node, executed from within a port context:	773	# this node, executed from within a port context:
631	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	774	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
646		789
647	sub _spawn {	790	sub _spawn {
648	my $port = shift;	791	my $port = shift;
649	my $init = shift;	792	my $init = shift;
650		793
		794	# rcv will create the actual port
651	local $SELF = "$NODE#$port";	795	local $SELF = "$NODE#$port";
652	eval {	796	eval {
653	&{ load_func $init }	797	&{ load_func $init }
654	};	798	};
655	_self_die if $@;	799	_self_die if $@;
656	}	800	}
657		801
658	sub spawn(@) {	802	sub spawn(@) {
659	my ($noderef, undef) = split /#/, shift, 2;	803	my ($nodeid, undef) = split /#/, shift, 2;
660		804
661	my $id = "$RUNIQ." . $ID++;	805	my $id = $RUNIQ . ++$ID;
662		806
663	$_[0] =~ /::/	807	$_[0] =~ /::/
664	or Carp::croak "spawn init function must be a fully-qualified name, caught";	808	or Carp::croak "spawn init function must be a fully-qualified name, caught";
665		809
666	snd_to_func $noderef, "AnyEvent::MP::_spawn" => $id, @_;	810	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
667		811
668	"$noderef#$id"	812	"$nodeid#$id"
669	}	813	}
		814
670		815
671	=item after $timeout, @msg	816	=item after $timeout, @msg
672		817
673	=item after $timeout, $callback	818	=item after $timeout, $callback
674		819
675	Either sends the given message, or call the given callback, after the	820	Either sends the given message, or call the given callback, after the
676	specified number of seconds.	821	specified number of seconds.
677		822
678	This is simply a utility function that come sin handy at times.	823	This is simply a utility function that comes in handy at times - the
		824	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		825	so it may go away in the future.
679		826
680	=cut	827	=cut
681		828
682	sub after($@) {	829	sub after($@) {
683	my ($timeout, @action) = @_;	830	my ($timeout, @action) = @_;
…		…
688	? $action[0]()	835	? $action[0]()
689	: snd @action;	836	: snd @action;
690	};	837	};
691	}	838	}
692		839
		840	#=item $cb2 = timeout $seconds, $cb[, @args]
		841
		842	=item cal $port, @msg, $callback[, $timeout]
		843
		844	A simple form of RPC - sends a message to the given C<$port> with the
		845	given contents (C<@msg>), but adds a reply port to the message.
		846
		847	The reply port is created temporarily just for the purpose of receiving
		848	the reply, and will be C<kil>ed when no longer needed.
		849
		850	A reply message sent to the port is passed to the C<$callback> as-is.
		851
		852	If an optional time-out (in seconds) is given and it is not C<undef>,
		853	then the callback will be called without any arguments after the time-out
		854	elapsed and the port is C<kil>ed.
		855
		856	If no time-out is given (or it is C<undef>), then the local port will
		857	monitor the remote port instead, so it eventually gets cleaned-up.
		858
		859	Currently this function returns the temporary port, but this "feature"
		860	might go in future versions unless you can make a convincing case that
		861	this is indeed useful for something.
		862
		863	=cut
		864
		865	sub cal(@) {
		866	my $timeout = ref $_[-1] ? undef : pop;
		867	my $cb = pop;
		868
		869	my $port = port {
		870	undef $timeout;
		871	kil $SELF;
		872	&$cb;
		873	};
		874
		875	if (defined $timeout) {
		876	$timeout = AE::timer $timeout, 0, sub {
		877	undef $timeout;
		878	kil $port;
		879	$cb->();
		880	};
		881	} else {
		882	mon $_[0], sub {
		883	kil $port;
		884	$cb->();
		885	};
		886	}
		887
		888	push @_, $port;
		889	&snd;
		890
		891	$port
		892	}
		893
		894	=back
		895
		896	=head1 DISTRIBUTED DATABASE
		897
		898	AnyEvent::MP comes with a simple distributed database. The database will
		899	be mirrored asynchronously at all global nodes. Other nodes bind to one of
		900	the global nodes for their needs.
		901
		902	The database consists of a two-level hash - a hash contains a hash which
		903	contains values.
		904
		905	The top level hash key is called "family", and the second-level hash key
		906	is called "subkey" or simply "key".
		907
		908	The family must be alphanumeric, i.e. start with a letter and consist
		909	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		910	pretty much like Perl module names.
		911
		912	As the family namespace is global, it is recommended to prefix family names
		913	with the name of the application or module using it.
		914
		915	The subkeys must be non-empty strings, with no further restrictions.
		916
		917	The values should preferably be strings, but other perl scalars should
		918	work as well (such as undef, arrays and hashes).
		919
		920	Every database entry is owned by one node - adding the same family/subkey
		921	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		922	but the result might be nondeterministic, i.e. the key might have
		923	different values on different nodes.
		924
		925	Different subkeys in the same family can be owned by different nodes
		926	without problems, and in fact, this is the common method to create worker
		927	pools. For example, a worker port for image scaling might do this:
		928
		929	db_set my_image_scalers => $port;
		930
		931	And clients looking for an image scaler will want to get the
		932	C<my_image_scalers> keys from time to time:
		933
		934	db_keys my_image_scalers => sub {
		935	@ports = @{ $_[0] };
		936	};
		937
		938	Or better yet, they want to monitor the database family, so they always
		939	have a reasonable up-to-date copy:
		940
		941	db_mon my_image_scalers => sub {
		942	@ports = keys %{ $_[0] };
		943	};
		944
		945	In general, you can set or delete single subkeys, but query and monitor
		946	whole families only.
		947
		948	If you feel the need to monitor or query a single subkey, try giving it
		949	it's own family.
		950
		951	=over
		952
		953	=item db_set $family => $subkey [=> $value]
		954
		955	Sets (or replaces) a key to the database - if C<$value> is omitted,
		956	C<undef> is used instead.
		957
		958	=item db_del $family => $subkey...
		959
		960	Deletes one or more subkeys from the database family.
		961
		962	=item $guard = db_reg $family => $subkey [=> $value]
		963
		964	Sets the key on the database and returns a guard. When the guard is
		965	destroyed, the key is deleted from the database. If C<$value> is missing,
		966	then C<undef> is used.
		967
		968	=item db_family $family => $cb->(\%familyhash)
		969
		970	Queries the named database C<$family> and call the callback with the
		971	family represented as a hash. You can keep and freely modify the hash.
		972
		973	=item db_keys $family => $cb->(\@keys)
		974
		975	Same as C<db_family>, except it only queries the family I<subkeys> and passes
		976	them as array reference to the callback.
		977
		978	=item db_values $family => $cb->(\@values)
		979
		980	Same as C<db_family>, except it only queries the family I<values> and passes them
		981	as array reference to the callback.
		982
		983	=item $guard = db_mon $family => $cb->($familyhash, \@added, \@changed, \@deleted)
		984
		985	Creates a monitor on the given database family. Each time a key is set
		986	or or is deleted the callback is called with a hash containing the
		987	database family and three lists of added, changed and deleted subkeys,
		988	respectively. If no keys have changed then the array reference might be
		989	C<undef> or even missing.
		990
		991	The family hash reference and the key arrays belong to AnyEvent::MP and
		992	B<must not be modified or stored> by the callback. When in doubt, make a
		993	copy.
		994
		995	As soon as possible after the monitoring starts, the callback will be
		996	called with the intiial contents of the family, even if it is empty,
		997	i.e. there will always be a timely call to the callback with the current
		998	contents.
		999
		1000	It is possible that the callback is called with a change event even though
		1001	the subkey is already present and the value has not changed.
		1002
		1003	The monitoring stops when the guard object is destroyed.
		1004
		1005	Example: on every change to the family "mygroup", print out all keys.
		1006
		1007	my $guard = db_mon mygroup => sub {
		1008	my ($family, $a, $c, $d) = @_;
		1009	print "mygroup members: ", (join " ", keys %$family), "\n";
		1010	};
		1011
		1012	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1013
		1014	my $guard; $guard = db_mon My::Module::workers => sub {
		1015	my ($family, $a, $c, $d) = @_;
		1016	return unless %$family;
		1017	undef $guard;
		1018	print "My::Module::workers now nonempty\n";
		1019	};
		1020
		1021	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		1022
		1023	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		1024	my ($family, $a, $c, $d) = @_;
		1025
		1026	print "+$_=$family->{$_}\n" for @$a;
		1027	print "*$_=$family->{$_}\n" for @$c;
		1028	print "-$_=$family->{$_}\n" for @$d;
		1029	};
		1030
		1031	=cut
		1032
693	=back	1033	=back
694		1034
695	=head1 AnyEvent::MP vs. Distributed Erlang	1035	=head1 AnyEvent::MP vs. Distributed Erlang
696		1036
697	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	1037	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
698	== aemp node, Erlang process == aemp port), so many of the documents and	1038	== aemp node, Erlang process == aemp port), so many of the documents and
699	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	1039	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
700	sample:	1040	sample:
701		1041
702	http://www.Erlang.se/doc/programming_rules.shtml	1042	http://www.erlang.se/doc/programming_rules.shtml
703	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	1043	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
704	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	1044	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
705	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	1045	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
706		1046
707	Despite the similarities, there are also some important differences:	1047	Despite the similarities, there are also some important differences:
708		1048
709	=over 4	1049	=over 4
710		1050
711	=item * Node references contain the recipe on how to contact them.	1051	=item * Node IDs are arbitrary strings in AEMP.
712		1052
713	Erlang relies on special naming and DNS to work everywhere in the	1053	Erlang relies on special naming and DNS to work everywhere in the same
714	same way. AEMP relies on each node knowing it's own address(es), with	1054	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
715	convenience functionality.	1055	configuration or DNS), and possibly the addresses of some seed nodes, but
716		1056	will otherwise discover other nodes (and their IDs) itself.
717	This means that AEMP requires a less tightly controlled environment at the
718	cost of longer node references and a slightly higher management overhead.
719		1057
720	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP	1058	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
721	uses "local ports are like remote ports".	1059	uses "local ports are like remote ports".
722		1060
723	The failure modes for local ports are quite different (runtime errors	1061	The failure modes for local ports are quite different (runtime errors
…		…
732	ports being the special case/exception, where transport errors cannot	1070	ports being the special case/exception, where transport errors cannot
733	occur.	1071	occur.
734		1072
735	=item * Erlang uses processes and a mailbox, AEMP does not queue.	1073	=item * Erlang uses processes and a mailbox, AEMP does not queue.
736		1074
737	Erlang uses processes that selectively receive messages, and therefore	1075	Erlang uses processes that selectively receive messages out of order, and
738	needs a queue. AEMP is event based, queuing messages would serve no	1076	therefore needs a queue. AEMP is event based, queuing messages would serve
739	useful purpose. For the same reason the pattern-matching abilities of	1077	no useful purpose. For the same reason the pattern-matching abilities
740	AnyEvent::MP are more limited, as there is little need to be able to	1078	of AnyEvent::MP are more limited, as there is little need to be able to
741	filter messages without dequeing them.	1079	filter messages without dequeuing them.
742		1080
743	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	1081	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1082	being event-based, while Erlang is process-based.
		1083
		1084	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1085	top of AEMP and Coro threads.
744		1086
745	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1087	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
746		1088
747	Sending messages in Erlang is synchronous and blocks the process (and	1089	Sending messages in Erlang is synchronous and blocks the process until
		1090	a conenction has been established and the message sent (and so does not
748	so does not need a queue that can overflow). AEMP sends are immediate,	1091	need a queue that can overflow). AEMP sends return immediately, connection
749	connection establishment is handled in the background.	1092	establishment is handled in the background.
750		1093
751	=item * Erlang suffers from silent message loss, AEMP does not.	1094	=item * Erlang suffers from silent message loss, AEMP does not.
752		1095
753	Erlang makes few guarantees on messages delivery - messages can get lost	1096	Erlang implements few guarantees on messages delivery - messages can get
754	without any of the processes realising it (i.e. you send messages a, b,	1097	lost without any of the processes realising it (i.e. you send messages a,
755	and c, and the other side only receives messages a and c).	1098	b, and c, and the other side only receives messages a and c).
756		1099
757	AEMP guarantees correct ordering, and the guarantee that there are no	1100	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1101	guarantee that after one message is lost, all following ones sent to the
		1102	same port are lost as well, until monitoring raises an error, so there are
758	holes in the message sequence.	1103	no silent "holes" in the message sequence.
759		1104
760	=item * In Erlang, processes can be declared dead and later be found to be	1105	If you want your software to be very reliable, you have to cope with
761	alive.	1106	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
762		1107	simply tries to work better in common error cases, such as when a network
763	In Erlang it can happen that a monitored process is declared dead and	1108	link goes down.
764	linked processes get killed, but later it turns out that the process is
765	still alive - and can receive messages.
766
767	In AEMP, when port monitoring detects a port as dead, then that port will
768	eventually be killed - it cannot happen that a node detects a port as dead
769	and then later sends messages to it, finding it is still alive.
770		1109
771	=item * Erlang can send messages to the wrong port, AEMP does not.	1110	=item * Erlang can send messages to the wrong port, AEMP does not.
772		1111
773	In Erlang it is quite likely that a node that restarts reuses a process ID	1112	In Erlang it is quite likely that a node that restarts reuses an Erlang
774	known to other nodes for a completely different process, causing messages	1113	process ID known to other nodes for a completely different process,
775	destined for that process to end up in an unrelated process.	1114	causing messages destined for that process to end up in an unrelated
		1115	process.
776		1116
777	AEMP never reuses port IDs, so old messages or old port IDs floating	1117	AEMP does not reuse port IDs, so old messages or old port IDs floating
778	around in the network will not be sent to an unrelated port.	1118	around in the network will not be sent to an unrelated port.
779		1119
780	=item * Erlang uses unprotected connections, AEMP uses secure	1120	=item * Erlang uses unprotected connections, AEMP uses secure
781	authentication and can use TLS.	1121	authentication and can use TLS.
782		1122
783	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1123	AEMP can use a proven protocol - TLS - to protect connections and
784	securely authenticate nodes.	1124	securely authenticate nodes.
785		1125
786	=item * The AEMP protocol is optimised for both text-based and binary	1126	=item * The AEMP protocol is optimised for both text-based and binary
787	communications.	1127	communications.
788		1128
789	The AEMP protocol, unlike the Erlang protocol, supports both	1129	The AEMP protocol, unlike the Erlang protocol, supports both programming
790	language-independent text-only protocols (good for debugging) and binary,	1130	language independent text-only protocols (good for debugging), and binary,
791	language-specific serialisers (e.g. Storable).	1131	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1132	used, the protocol is actually completely text-based.
792		1133
793	It has also been carefully designed to be implementable in other languages	1134	It has also been carefully designed to be implementable in other languages
794	with a minimum of work while gracefully degrading fucntionality to make the	1135	with a minimum of work while gracefully degrading functionality to make the
795	protocol simple.	1136	protocol simple.
796		1137
797	=item * AEMP has more flexible monitoring options than Erlang.	1138	=item * AEMP has more flexible monitoring options than Erlang.
798		1139
799	In Erlang, you can chose to receive I<all> exit signals as messages	1140	In Erlang, you can chose to receive I<all> exit signals as messages or
800	or I<none>, there is no in-between, so monitoring single processes is	1141	I<none>, there is no in-between, so monitoring single Erlang processes is
801	difficult to implement. Monitoring in AEMP is more flexible than in	1142	difficult to implement.
802	Erlang, as one can choose between automatic kill, exit message or callback	1143
803	on a per-process basis.	1144	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1145	between automatic kill, exit message or callback on a per-port basis.
804		1146
805	=item * Erlang tries to hide remote/local connections, AEMP does not.	1147	=item * Erlang tries to hide remote/local connections, AEMP does not.
806		1148
807	Monitoring in Erlang is not an indicator of process death/crashes,	1149	Monitoring in Erlang is not an indicator of process death/crashes, in the
808	as linking is (except linking is unreliable in Erlang).	1150	same way as linking is (except linking is unreliable in Erlang).
809		1151
810	In AEMP, you don't "look up" registered port names or send to named ports	1152	In AEMP, you don't "look up" registered port names or send to named ports
811	that might or might not be persistent. Instead, you normally spawn a port	1153	that might or might not be persistent. Instead, you normally spawn a port
812	on the remote node. The init function monitors the you, and you monitor	1154	on the remote node. The init function monitors you, and you monitor the
813	the remote port. Since both monitors are local to the node, they are much	1155	remote port. Since both monitors are local to the node, they are much more
814	more reliable.	1156	reliable (no need for C<spawn_link>).
815		1157
816	This also saves round-trips and avoids sending messages to the wrong port	1158	This also saves round-trips and avoids sending messages to the wrong port
817	(hard to do in Erlang).	1159	(hard to do in Erlang).
818		1160
819	=back	1161	=back
820		1162
821	=head1 RATIONALE	1163	=head1 RATIONALE
822		1164
823	=over 4	1165	=over 4
824		1166
825	=item Why strings for ports and noderefs, why not objects?	1167	=item Why strings for port and node IDs, why not objects?
826		1168
827	We considered "objects", but found that the actual number of methods	1169	We considered "objects", but found that the actual number of methods
828	thatc an be called are very low. Since port IDs and noderefs travel over	1170	that can be called are quite low. Since port and node IDs travel over
829	the network frequently, the serialising/deserialising would add lots of	1171	the network frequently, the serialising/deserialising would add lots of
830	overhead, as well as having to keep a proxy object.	1172	overhead, as well as having to keep a proxy object everywhere.
831		1173
832	Strings can easily be printed, easily serialised etc. and need no special	1174	Strings can easily be printed, easily serialised etc. and need no special
833	procedures to be "valid".	1175	procedures to be "valid".
834		1176
835	And a a miniport consists of a single closure stored in a global hash - it	1177	And as a result, a port with just a default receiver consists of a single
836	can't become much cheaper.	1178	code reference stored in a global hash - it can't become much cheaper.
837		1179
838	=item Why favour JSON, why not real serialising format such as Storable?	1180	=item Why favour JSON, why not a real serialising format such as Storable?
839		1181
840	In fact, any AnyEvent::MP node will happily accept Storable as framing	1182	In fact, any AnyEvent::MP node will happily accept Storable as framing
841	format, but currently there is no way to make a node use Storable by	1183	format, but currently there is no way to make a node use Storable by
842	default.	1184	default (although all nodes will accept it).
843		1185
844	The default framing protocol is JSON because a) JSON::XS is many times	1186	The default framing protocol is JSON because a) JSON::XS is many times
845	faster for small messages and b) most importantly, after years of	1187	faster for small messages and b) most importantly, after years of
846	experience we found that object serialisation is causing more problems	1188	experience we found that object serialisation is causing more problems
847	than it gains: Just like function calls, objects simply do not travel	1189	than it solves: Just like function calls, objects simply do not travel
848	easily over the network, mostly because they will always be a copy, so you	1190	easily over the network, mostly because they will always be a copy, so you
849	always have to re-think your design.	1191	always have to re-think your design.
850		1192
851	Keeping your messages simple, concentrating on data structures rather than	1193	Keeping your messages simple, concentrating on data structures rather than
852	objects, will keep your messages clean, tidy and efficient.	1194	objects, will keep your messages clean, tidy and efficient.
853		1195
854	=back	1196	=back
855		1197
856	=head1 SEE ALSO	1198	=head1 SEE ALSO
857		1199
		1200	L<AnyEvent::MP::Intro> - a gentle introduction.
		1201
		1202	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1203
		1204	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1205	your applications.
		1206
		1207	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1208
		1209	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1210	all nodes.
		1211
858	L<AnyEvent>.	1212	L<AnyEvent>.
859		1213
860	=head1 AUTHOR	1214	=head1 AUTHOR
861		1215
862	Marc Lehmann <schmorp@schmorp.de>	1216	Marc Lehmann <schmorp@schmorp.de>

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Revision 1.130 by root, Fri Mar 9 17:05:26 2012 UTC