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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.66 by root, Fri Aug 28 01:07:24 2009 UTC vs.
Revision 1.128 by root, Sun Mar 4 14:28:44 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 $localport, $cb->(@msg) # callback is invoked on death
38	mon $port, $otherport # kill otherport on abnormal death	41	mon $localport, $otherport # kill otherport on abnormal death
39	mon $port, $otherport, @msg # send message on death	42	mon $localport, $otherport, @msg # send message on death
		43
		44	# temporarily execute code in port context
		45	peval $port, sub { die "kill the port!" };
		46
		47	# execute callbacks in $SELF port context
		48	my $timer = AE::timer 1, 0, psub {
		49	die "kill the port, delayed";
		50	};
40		51
41	=head1 CURRENT STATUS	52	=head1 CURRENT STATUS
42		53
		54	bin/aemp - stable.
43	AnyEvent::MP - stable API, should work	55	AnyEvent::MP - stable API, should work.
44	AnyEvent::MP::Intro - outdated	56	AnyEvent::MP::Intro - explains most concepts.
45	AnyEvent::MP::Kernel - WIP
46	AnyEvent::MP::Transport - mostly stable	57	AnyEvent::MP::Kernel - mostly stable API.
47		58	AnyEvent::MP::Global - stable API.
48	stay tuned.
49		59
50	=head1 DESCRIPTION	60	=head1 DESCRIPTION
51		61
52	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
53		63
54	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
55	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
56		66
57	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	67	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
58	manual page.	68	manual page and the examples under F<eg/>.
59
60	At the moment, this module family is severly broken and underdocumented,
61	so do not use. This was uploaded mainly to reserve the CPAN namespace -
62	stay tuned!
63		69
64	=head1 CONCEPTS	70	=head1 CONCEPTS
65		71
66	=over 4	72	=over 4
67		73
68	=item port	74	=item port
69		75
70	A port is something you can send messages to (with the C<snd> function).	76	Not to be confused with a TCP port, a "port" is something you can send
		77	messages to (with the C<snd> function).
71		78
72	Ports allow you to register C<rcv> handlers that can match all or just	79	Ports allow you to register C<rcv> handlers that can match all or just
73	some messages. Messages send to ports will not be queued, regardless of	80	some messages. Messages send to ports will not be queued, regardless of
74	anything was listening for them or not.	81	anything was listening for them or not.
75		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
76	=item port ID - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
77		86
78	A port ID is the concatenation of a noderef, a hash-mark (C<#>) as	87	A port ID is the concatenation of a node ID, a hash-mark (C<#>)
79	separator, and a port name (a printable string of unspecified format). An	88	as separator, and a port name (a printable string of unspecified
80	exception is the the node port, whose ID is identical to its node	89	format created by AnyEvent::MP).
81	reference.
82		90
83	=item node	91	=item node
84		92
85	A node is a single process containing at least one port - the node port,	93	A node is a single process containing at least one port - the node port,
86	which provides nodes to manage each other remotely, and to create new	94	which enables nodes to manage each other remotely, and to create new
87	ports.	95	ports.
88		96
89	Nodes are either private (single-process only), slaves (can only talk to	97	Nodes are either public (have one or more listening ports) or private
90	public nodes, but do not need an open port) or public nodes (connectable	98	(no listening ports). Private nodes cannot talk to other private nodes
91	from any other node).	99	currently, but all nodes can talk to public nodes.
92		100
		101	Nodes is represented by (printable) strings called "node IDs".
		102
93	=item node ID - C<[a-za-Z0-9_\-.:]+>	103	=item node ID - C<[A-Za-z0-9_\-.:]*>
94		104
95	A node ID is a string that uniquely identifies the node within a	105	A node ID is a string that uniquely identifies the node within a
96	network. Depending on the configuration used, node IDs can look like a	106	network. Depending on the configuration used, node IDs can look like a
97	hostname, a hostname and a port, or a random string. AnyEvent::MP itself	107	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
98	doesn't interpret node IDs in any way.	108	doesn't interpret node IDs in any way except to uniquely identify a node.
99		109
100	=item binds - C<ip:port>	110	=item binds - C<ip:port>
101		111
102	Nodes can only talk to each other by creating some kind of connection to	112	Nodes can only talk to each other by creating some kind of connection to
103	each other. To do this, nodes should listen on one or more local transport	113	each other. To do this, nodes should listen on one or more local transport
		114	endpoints - binds.
		115
104	endpoints - binds. Currently, only standard C<ip:port> specifications can	116	Currently, only standard C<ip:port> specifications can be used, which
105	be used, which specify TCP ports to listen on.	117	specify TCP ports to listen on. So a bind is basically just a tcp socket
		118	in listening mode thta accepts conenctions form other nodes.
106		119
		120	=item seed nodes
		121
		122	When a node starts, it knows nothing about the network it is in - it
		123	needs to connect to at least one other node that is already in the
		124	network. These other nodes are called "seed nodes".
		125
		126	Seed nodes themselves are not special - they are seed nodes only because
		127	some other node I<uses> them as such, but any node can be used as seed
		128	node for other nodes, and eahc node cna use a different set of seed nodes.
		129
		130	In addition to discovering the network, seed nodes are also used to
		131	maintain the network - all nodes using the same seed node form are part of
		132	the same network. If a network is split into multiple subnets because e.g.
		133	the network link between the parts goes down, then using the same seed
		134	nodes for all nodes ensures that eventually the subnets get merged again.
		135
		136	Seed nodes are expected to be long-running, and at least one seed node
		137	should always be available. They should also be relatively responsive - a
		138	seed node that blocks for long periods will slow down everybody else.
		139
		140	For small networks, it's best if every node uses the same set of seed
		141	nodes. For large networks, it can be useful to specify "regional" seed
		142	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		143	each other. What's important is that all seed nodes connections form a
		144	complete graph, so that the network cannot split into separate subnets
		145	forever.
		146
		147	Seed nodes are represented by seed IDs.
		148
107	=item seeds - C<host:port>	149	=item seed IDs - C<host:port>
108		150
109	When a node starts, it knows nothing about the network. To teach the node	151	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
110	about the network it first has to contact some other node within the	152	TCP port) of nodes that should be used as seed nodes.
111	network. This node is called a seed.
112		153
113	Seeds are transport endpoint(s) of as many nodes as one wants. Those nodes	154	=item global nodes
114	are expected to be long-running, and at least one of those should always	155
115	be available. When nodes run out of connections (e.g. due to a network	156	An AEMP network needs a discovery service - nodes need to know how to
116	error), they try to re-establish connections to some seednodes again to	157	connect to other nodes they only know by name. In addition, AEMP offers a
117	join the network.	158	distributed "group database", which maps group names to a list of strings
		159	- for example, to register worker ports.
		160
		161	A network needs at least one global node to work, and allows every node to
		162	be a global node.
		163
		164	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		165	node and tries to keep connections to all other nodes. So while it can
		166	make sense to make every node "global" in small networks, it usually makes
		167	sense to only make seed nodes into global nodes in large networks (nodes
		168	keep connections to seed nodes and global nodes, so makign them the same
		169	reduces overhead).
118		170
119	=back	171	=back
120		172
121	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
122		174
124		176
125	=cut	177	=cut
126		178
127	package AnyEvent::MP;	179	package AnyEvent::MP;
128		180
		181	use AnyEvent::MP::Config ();
129	use AnyEvent::MP::Kernel;	182	use AnyEvent::MP::Kernel;
		183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
130		184
131	use common::sense;	185	use common::sense;
132		186
133	use Carp ();	187	use Carp ();
134		188
135	use AE ();	189	use AE ();
		190	use Guard ();
136		191
137	use base "Exporter";	192	use base "Exporter";
138		193
139	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
140		195
141	our @EXPORT = qw(	196	our @EXPORT = qw(
142	NODE $NODE *SELF node_of after	197	NODE $NODE *SELF node_of after
143	resolve_node initialise_node	198	configure
144	snd rcv mon mon_guard kil reg psub spawn	199	snd rcv mon mon_guard kil psub peval spawn cal
145	port	200	port
		201	db_set db_del db_reg
		202	db_mon db_family db_keys db_values
146	);	203	);
147		204
148	our $SELF;	205	our $SELF;
149		206
150	sub _self_die() {	207	sub _self_die() {
…		…
153	kil $SELF, die => $msg;	210	kil $SELF, die => $msg;
154	}	211	}
155		212
156	=item $thisnode = NODE / $NODE	213	=item $thisnode = NODE / $NODE
157		214
158	The C<NODE> function returns, and the C<$NODE> variable contains the node	215	The C<NODE> function returns, and the C<$NODE> variable contains, the node
159	ID of the node running in the current process. This value is initialised by	216	ID of the node running in the current process. This value is initialised by
160	a call to C<initialise_node>.	217	a call to C<configure>.
161		218
162	=item $nodeid = node_of $port	219	=item $nodeid = node_of $port
163		220
164	Extracts and returns the node ID part from a port ID or a node ID.	221	Extracts and returns the node ID from a port ID or a node ID.
165		222
166	=item initialise_node $profile_name	223	=item configure $profile, key => value...
		224
		225	=item configure key => value...
167		226
168	Before a node can talk to other nodes on the network (i.e. enter	227	Before a node can talk to other nodes on the network (i.e. enter
169	"distributed mode") it has to initialise itself - the minimum a node needs	228	"distributed mode") it has to configure itself - the minimum a node needs
170	to know is its own name, and optionally it should know the addresses of	229	to know is its own name, and optionally it should know the addresses of
171	some other nodes in the network to discover other nodes.	230	some other nodes in the network to discover other nodes.
172		231
173	This function initialises a node - it must be called exactly once (or	232	This function configures a node - it must be called exactly once (or
174	never) before calling other AnyEvent::MP functions.	233	never) before calling other AnyEvent::MP functions.
175		234
176	The first argument is a profile name. If it is C<undef> or missing, then	235	The key/value pairs are basically the same ones as documented for the
177	the current nodename will be used instead (i.e. F<uname -n>).	236	F<aemp> command line utility (sans the set/del prefix), with these additions:
178		237
		238	=over 4
		239
		240	=item norc => $boolean (default false)
		241
		242	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
		243	be consulted - all configuraiton options must be specified in the
		244	C<configure> call.
		245
		246	=item force => $boolean (default false)
		247
		248	IF true, then the values specified in the C<configure> will take
		249	precedence over any values configured via the rc file. The default is for
		250	the rc file to override any options specified in the program.
		251
		252	=item secure => $pass->($nodeid)
		253
		254	In addition to specifying a boolean, you can specify a code reference that
		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.
		259
		260	=back
		261
		262	=over 4
		263
		264	=item step 1, gathering configuration from profiles
		265
179	The function then looks up the profile in the aemp configuration (see the	266	The function first looks up a profile in the aemp configuration (see the
180	L<aemp> commandline utility).	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.
		270
		271	The profile data is then gathered as follows:
		272
		273	First, all remaining key => value pairs (all of which are conveniently
		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).
		278
		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.
181		282
182	If the profile specifies a node ID, then this will become the node ID of	283	If the profile specifies a node ID, then this will become the node ID of
183	this process. If not, then the profile name will be used as node ID. The	284	this process. If not, then the profile name will be used as node ID, with
184	special node ID of C<anon/> will be replaced by a random node ID.	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
185		294
186	The next step is to look up the binds in the profile, followed by binding	295	The next step is to look up the binds in the profile, followed by binding
187	aemp protocol listeners on all binds specified (it is possible and valid	296	aemp protocol listeners on all binds specified (it is possible and valid
188	to have no binds, meaning that the node cannot be contacted form the	297	to have no binds, meaning that the node cannot be contacted form the
189	outside. This means the node cannot talk to other nodes that also have no	298	outside. This means the node cannot talk to other nodes that also have no
190	binds, but it can still talk to all "normal" nodes).	299	binds, but it can still talk to all "normal" nodes).
191		300
192	If the profile does not specify a binds list, then the node ID will be	301	If the profile does not specify a binds list, then a default of C<*> is
193	treated as if it were of the form C<host:port>, which will be resolved and	302	used, meaning the node will bind on a dynamically-assigned port on every
194	used as binds list.	303	local IP address it finds.
195		304
		305	=item step 3, connect to seed nodes
		306
196	Lastly, the seeds list from the profile is passed to the	307	As the last step, the seed ID list from the profile is passed to the
197	L<AnyEvent::MP::Global> module, which will then use it to keep	308	L<AnyEvent::MP::Global> module, which will then use it to keep
198	connectivity with at least on of those seed nodes at any point in time.	309	connectivity with at least one node at any point in time.
199		310
200	Example: become a distributed node listening on the guessed noderef, or	311	=back
201	the one specified via C<aemp> for the current node. This should be the	312
		313	Example: become a distributed node using the local node name as profile.
202	most common form of invocation for "daemon"-type nodes.	314	This should be the most common form of invocation for "daemon"-type nodes.
203		315
204	initialise_node;	316	configure
205		317
206	Example: become an anonymous node. This form is often used for commandline	318	Example: become a semi-anonymous node. This form is often used for
207	clients.	319	commandline clients.
208		320
209	initialise_node "anon/";	321	configure nodeid => "myscript/%n/%u";
210		322
211	Example: become a distributed node. If there is no profile of the given	323	Example: configure a node using a profile called seed, which is suitable
212	name, or no binds list was specified, resolve C<localhost:4044> and bind	324	for a seed node as it binds on all local addresses on a fixed port (4040,
213	on the resulting addresses.	325	customary for aemp).
214		326
215	initialise_node "localhost:4044";	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)"
216		338
217	=item $SELF	339	=item $SELF
218		340
219	Contains the current port id while executing C<rcv> callbacks or C<psub>	341	Contains the current port id while executing C<rcv> callbacks or C<psub>
220	blocks.	342	blocks.
221		343
222	=item SELF, %SELF, @SELF...	344	=item *SELF, SELF, %SELF, @SELF...
223		345
224	Due to some quirks in how perl exports variables, it is impossible to	346	Due to some quirks in how perl exports variables, it is impossible to
225	just export C<$SELF>, all the symbols called C<SELF> are exported by this	347	just export C<$SELF>, all the symbols named C<SELF> are exported by this
226	module, but only C<$SELF> is currently used.	348	module, but only C<$SELF> is currently used.
227		349
228	=item snd $port, type => @data	350	=item snd $port, type => @data
229		351
230	=item snd $port, @msg	352	=item snd $port, @msg
231		353
232	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
233	a local or a remote port, and must be a port ID.	355	local or a remote port, and must be a port ID.
234		356
235	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
236	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
237	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.
238		361
239	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
240	function: modifying any argument is not allowed and can cause many	363	function: modifying any argument (or values referenced by them) is
241	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.
242		368
243	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
244	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
245	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
246	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
247	node, anything can be passed.	373	node, anything can be passed. Best rely only on the common denominator of
		374	these.
248		375
249	=item $local_port = port	376	=item $local_port = port
250		377
251	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
252	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.
…		…
276	sub _kilme {	403	sub _kilme {
277	die "received message on port without callback";	404	die "received message on port without callback";
278	}	405	}
279		406
280	sub port(;&) {	407	sub port(;&) {
281	my $id = "$UNIQ." . $ID++;	408	my $id = $UNIQ . ++$ID;
282	my $port = "$NODE#$id";	409	my $port = "$NODE#$id";
283		410
284	rcv $port, shift \|\| \&_kilme;	411	rcv $port, shift \|\| \&_kilme;
285		412
286	$port	413	$port
…		…
325	msg1 => sub { ... },	452	msg1 => sub { ... },
326	...	453	...
327	;	454	;
328		455
329	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
330	(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.
331		458
332	rcv $port, $otherport => sub {	459	rcv $port, $otherport => sub {
333	my @reply = @_;	460	my @reply = @_;
334		461
335	rcv $SELF, $otherport;	462	rcv $SELF, $otherport;
…		…
337		464
338	=cut	465	=cut
339		466
340	sub rcv($@) {	467	sub rcv($@) {
341	my $port = shift;	468	my $port = shift;
342	my ($noderef, $portid) = split /#/, $port, 2;	469	my ($nodeid, $portid) = split /#/, $port, 2;
343		470
344	$NODE{$noderef} == $NODE{""}	471	$NODE{$nodeid} == $NODE{""}
345	or Carp::croak "$port: rcv can only be called on local ports, caught";	472	or Carp::croak "$port: rcv can only be called on local ports, caught";
346		473
347	while (@_) {	474	while (@_) {
348	if (ref $_[0]) {	475	if (ref $_[0]) {
349	if (my $self = $PORT_DATA{$portid}) {	476	if (my $self = $PORT_DATA{$portid}) {
350	"AnyEvent::MP::Port" eq ref $self	477	"AnyEvent::MP::Port" eq ref $self
351	or Carp::croak "$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";
352		479
353	$self->[2] = shift;	480	$self->[0] = shift;
354	} else {	481	} else {
355	my $cb = shift;	482	my $cb = shift;
356	$PORT{$portid} = sub {	483	$PORT{$portid} = sub {
357	local $SELF = $port;	484	local $SELF = $port;
358	eval { &$cb }; _self_die if $@;	485	eval { &$cb }; _self_die if $@;
359	};	486	};
360	}	487	}
361	} elsif (defined $_[0]) {	488	} elsif (defined $_[0]) {
362	my $self = $PORT_DATA{$portid} \|\|= do {	489	my $self = $PORT_DATA{$portid} \|\|= do {
363	my $self = bless [$PORT{$port} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";	490	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
364		491
365	$PORT{$portid} = sub {	492	$PORT{$portid} = sub {
366	local $SELF = $port;	493	local $SELF = $port;
367		494
368	if (my $cb = $self->[1]{$_[0]}) {	495	if (my $cb = $self->[1]{$_[0]}) {
…		…
390	}	517	}
391		518
392	$port	519	$port
393	}	520	}
394		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
395	=item $closure = psub { BLOCK }	559	=item $closure = psub { BLOCK }
396		560
397	Remembers C<$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
398	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>
399	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 $SELF, sub {
		566	BLOCK }, @_ } >>.
400		567
401	This is useful when you register callbacks from C<rcv> callbacks:	568	This is useful when you register callbacks from C<rcv> callbacks:
402		569
403	rcv delayed_reply => sub {	570	rcv delayed_reply => sub {
404	my ($delay, @reply) = @_;	571	my ($delay, @reply) = @_;
…		…
428	$res	595	$res
429	}	596	}
430	}	597	}
431	}	598	}
432		599
433	=item $guard = mon $port, $cb->(@reason)	600	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
434		601
435	=item $guard = mon $port, $rcvport	602	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
436		603
437	=item $guard = mon $port	604	=item $guard = mon $port # kill $SELF when $port dies
438		605
439	=item $guard = mon $port, $rcvport, @msg	606	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
440		607
441	Monitor the given port and do something when the port is killed or	608	Monitor the given port and do something when the port is killed or
442	messages to it were lost, and optionally return a guard that can be used	609	messages to it were lost, and optionally return a guard that can be used
443	to stop monitoring again.	610	to stop monitoring again.
444
445	C<mon> effectively guarantees that, in the absence of hardware failures,
446	that after starting the monitor, either all messages sent to the port
447	will arrive, or the monitoring action will be invoked after possible
448	message loss has been detected. No messages will be lost "in between"
449	(after the first lost message no further messages will be received by the
450	port). After the monitoring action was invoked, further messages might get
451	delivered again.
452
453	Note that monitoring-actions are one-shot: once released, they are removed
454	and will not trigger again.
455		611
456	In the first form (callback), the callback is simply called with any	612	In the first form (callback), the callback is simply called with any
457	number of C<@reason> elements (no @reason means that the port was deleted	613	number of C<@reason> elements (no @reason means that the port was deleted
458	"normally"). Note also that I<< the callback B<must> never die >>, so use	614	"normally"). Note also that I<< the callback B<must> never die >>, so use
459	C<eval> if unsure.	615	C<eval> if unsure.
460		616
461	In the second form (another port given), the other port (C<$rcvport>)	617	In the second form (another port given), the other port (C<$rcvport>)
462	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	618	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
463	"normal" kils nothing happens, while under all other conditions, the other	619	"normal" kils nothing happens, while under all other conditions, the other
464	port is killed with the same reason.	620	port is killed with the same reason.
465		621
466	The third form (kill self) is the same as the second form, except that	622	The third form (kill self) is the same as the second form, except that
467	C<$rvport> defaults to C<$SELF>.	623	C<$rvport> defaults to C<$SELF>.
468		624
469	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
470	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.
471		630
472	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
473	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
474	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
475	even monitoring requests can get lost (for exmaple, when the connection	634	even monitoring requests can get lost (for example, when the connection
476	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
477	these problems do not exist.	636	these problems do not exist.
478		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
479	Example: call a given callback when C<$port> is killed.	655	Example: call a given callback when C<$port> is killed.
480		656
481	mon $port, sub { warn "port died because of <@_>\n" };	657	mon $port, sub { warn "port died because of <@_>\n" };
482		658
483	Example: kill ourselves when C<$port> is killed abnormally.	659	Example: kill ourselves when C<$port> is killed abnormally.
…		…
489	mon $port, $self => "restart";	665	mon $port, $self => "restart";
490		666
491	=cut	667	=cut
492		668
493	sub mon {	669	sub mon {
494	my ($noderef, $port) = split /#/, shift, 2;	670	my ($nodeid, $port) = split /#/, shift, 2;
495		671
496	my $node = $NODE{$noderef} \|\| add_node $noderef;	672	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
497		673
498	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,';
499		675
500	unless (ref $cb) {	676	unless (ref $cb) {
501	if (@_) {	677	if (@_) {
…		…
510	}	686	}
511		687
512	$node->monitor ($port, $cb);	688	$node->monitor ($port, $cb);
513		689
514	defined wantarray	690	defined wantarray
515	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	691	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
516	}	692	}
517		693
518	=item $guard = mon_guard $port, $ref, $ref...	694	=item $guard = mon_guard $port, $ref, $ref...
519		695
520	Monitors the given C<$port> and keeps the passed references. When the port	696	Monitors the given C<$port> and keeps the passed references. When the port
521	is killed, the references will be freed.	697	is killed, the references will be freed.
522		698
523	Optionally returns a guard that will stop the monitoring.	699	Optionally returns a guard that will stop the monitoring.
524		700
525	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
526	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>):
527		703
528	$port->rcv (start => sub {	704	$port->rcv (start => sub {
529	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	705	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
530	undef $timer if 0.9 < rand;	706	undef $timer if 0.9 < rand;
531	});	707	});
532	});	708	});
533		709
534	=cut	710	=cut
…		…
543		719
544	=item kil $port[, @reason]	720	=item kil $port[, @reason]
545		721
546	Kill the specified port with the given C<@reason>.	722	Kill the specified port with the given C<@reason>.
547		723
548	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" -
549	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.
550		727
551	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>
552	C<mon>, see below).	729	form) get killed with the same reason.
553		730
554	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
555	will be reported as reason C<< die => $@ >>.	732	will be reported as reason C<< die => $@ >>.
556		733
557	Transport/communication errors are reported as C<< transport_error =>	734	Transport/communication errors are reported as C<< transport_error =>
…		…
562	=item $port = spawn $node, $initfunc[, @initdata]	739	=item $port = spawn $node, $initfunc[, @initdata]
563		740
564	Creates a port on the node C<$node> (which can also be a port ID, in which	741	Creates a port on the node C<$node> (which can also be a port ID, in which
565	case it's the node where that port resides).	742	case it's the node where that port resides).
566		743
567	The port ID of the newly created port is return immediately, and it is	744	The port ID of the newly created port is returned immediately, and it is
568	permissible to immediately start sending messages or monitor the port.	745	possible to immediately start sending messages or to monitor the port.
569		746
570	After the port has been created, the init function is	747	After the port has been created, the init function is called on the remote
571	called. This function must be a fully-qualified function name	748	node, in the same context as a C<rcv> callback. This function must be a
572	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	749	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
573	program, use C<::name>.	750	specify a function in the main program, use C<::name>.
574		751
575	If the function doesn't exist, then the node tries to C<require>	752	If the function doesn't exist, then the node tries to C<require>
576	the package, then the package above the package and so on (e.g.	753	the package, then the package above the package and so on (e.g.
577	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	754	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
578	exists or it runs out of package names.	755	exists or it runs out of package names.
579		756
580	The init function is then called with the newly-created port as context	757	The init function is then called with the newly-created port as context
581	object (C<$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.
582		761
583	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
584	in the init function, monitor the original port. This two-way monitoring	763	port, and in the remote init function, immediately monitor the passed
585	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<$initfunc> has no visible effects on the
		768	caller before C<spawn> returns (by delaying invocation when spawn is
		769	called for the local node).
586		770
587	Example: spawn a chat server port on C<$othernode>.	771	Example: spawn a chat server port on C<$othernode>.
588		772
589	# this node, executed from within a port context:	773	# this node, executed from within a port context:
590	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	774	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
605		789
606	sub _spawn {	790	sub _spawn {
607	my $port = shift;	791	my $port = shift;
608	my $init = shift;	792	my $init = shift;
609		793
		794	# rcv will create the actual port
610	local $SELF = "$NODE#$port";	795	local $SELF = "$NODE#$port";
611	eval {	796	eval {
612	&{ load_func $init }	797	&{ load_func $init }
613	};	798	};
614	_self_die if $@;	799	_self_die if $@;
615	}	800	}
616		801
617	sub spawn(@) {	802	sub spawn(@) {
618	my ($noderef, undef) = split /#/, shift, 2;	803	my ($nodeid, undef) = split /#/, shift, 2;
619		804
620	my $id = "$RUNIQ." . $ID++;	805	my $id = $RUNIQ . ++$ID;
621		806
622	$_[0] =~ /::/	807	$_[0] =~ /::/
623	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";
624		809
625	snd_to_func $noderef, "AnyEvent::MP::_spawn" => $id, @_;	810	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
626		811
627	"$noderef#$id"	812	"$nodeid#$id"
628	}	813	}
		814
629		815
630	=item after $timeout, @msg	816	=item after $timeout, @msg
631		817
632	=item after $timeout, $callback	818	=item after $timeout, $callback
633		819
634	Either sends the given message, or call the given callback, after the	820	Either sends the given message, or call the given callback, after the
635	specified number of seconds.	821	specified number of seconds.
636		822
637	This is simply a utility function that come sin handy at times.	823	This is simply a utility function that comes in handy at times - the
		824	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		825	so it may go away in the future.
638		826
639	=cut	827	=cut
640		828
641	sub after($@) {	829	sub after($@) {
642	my ($timeout, @action) = @_;	830	my ($timeout, @action) = @_;
…		…
647	? $action[0]()	835	? $action[0]()
648	: snd @action;	836	: snd @action;
649	};	837	};
650	}	838	}
651		839
		840	=item cal $port, @msg, $callback[, $timeout]
		841
		842	A simple form of RPC - sends a message to the given C<$port> with the
		843	given contents (C<@msg>), but adds a reply port to the message.
		844
		845	The reply port is created temporarily just for the purpose of receiving
		846	the reply, and will be C<kil>ed when no longer needed.
		847
		848	A reply message sent to the port is passed to the C<$callback> as-is.
		849
		850	If an optional time-out (in seconds) is given and it is not C<undef>,
		851	then the callback will be called without any arguments after the time-out
		852	elapsed and the port is C<kil>ed.
		853
		854	If no time-out is given (or it is C<undef>), then the local port will
		855	monitor the remote port instead, so it eventually gets cleaned-up.
		856
		857	Currently this function returns the temporary port, but this "feature"
		858	might go in future versions unless you can make a convincing case that
		859	this is indeed useful for something.
		860
		861	=cut
		862
		863	sub cal(@) {
		864	my $timeout = ref $_[-1] ? undef : pop;
		865	my $cb = pop;
		866
		867	my $port = port {
		868	undef $timeout;
		869	kil $SELF;
		870	&$cb;
		871	};
		872
		873	if (defined $timeout) {
		874	$timeout = AE::timer $timeout, 0, sub {
		875	undef $timeout;
		876	kil $port;
		877	$cb->();
		878	};
		879	} else {
		880	mon $_[0], sub {
		881	kil $port;
		882	$cb->();
		883	};
		884	}
		885
		886	push @_, $port;
		887	&snd;
		888
		889	$port
		890	}
		891
		892	=back
		893
		894	=head1 DISTRIBUTED DATABASE
		895
		896	AnyEvent::MP comes with a simple distributed database. The database will
		897	be mirrored asynchronously at all global nodes. Other nodes bind to one of
		898	the global nodes for their needs.
		899
		900	The database consists of a two-level hash - a hash contains a hash which
		901	contains values.
		902
		903	The top level hash key is called "family", and the second-level hash key
		904	is called "subkey" or simply "key".
		905
		906	The family must be alphanumeric, i.e. start with a letter and consist
		907	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		908	pretty much like Perl module names.
		909
		910	As the family namespace is global, it is recommended to prefix family names
		911	with the name of the application or module using it.
		912
		913	The subkeys must be non-empty strings, with no further restrictions.
		914
		915	The values should preferably be strings, but other perl scalars should
		916	work as well (such as undef, arrays and hashes).
		917
		918	Every database entry is owned by one node - adding the same family/subkey
		919	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		920	but the result might be nondeterministic, i.e. the key might have
		921	different values on different nodes.
		922
		923	Different subkeys in the same family can be owned by different nodes
		924	without problems, and in fact, this is the common method to create worker
		925	pools. For example, a worker port for image scaling might do this:
		926
		927	db_set my_image_scalers => $port;
		928
		929	And clients looking for an image scaler will want to get the
		930	C<my_image_scalers> keys:
		931
		932	db_keys "my_image_scalers" => 60 => sub {
		933	#d##TODO#
		934
		935	=over
		936
		937	=item db_set $family => $subkey [=> $value]
		938
		939	Sets (or replaces) a key to the database - if C<$value> is omitted,
		940	C<undef> is used instead.
		941
		942	=item db_del $family => $subkey
		943
		944	Deletes a key from the database.
		945
		946	=item $guard = db_reg $family => $subkey [=> $value]
		947
		948	Sets the key on the database and returns a guard. When the guard is
		949	destroyed, the key is deleted from the database. If C<$value> is missing,
		950	then C<undef> is used.
		951
		952	=item $guard = db_mon $family => $cb->($familyhash, \@subkeys...)
		953
		954	Creates a monitor on the given database family. Each time a key is set or
		955	or is deleted the callback is called with a hash containing the database
		956	family and an arrayref with subkeys that have changed.
		957
		958	Specifically, if one of the passed subkeys exists in the $familyhash, then
		959	it is currently set to the value in the $familyhash. Otherwise, it has
		960	been deleted.
		961
		962	The first call will be with the current contents of the family and all
		963	keys, as if they were just added.
		964
		965	It is possible that the callback is called with a change event even though
		966	the subkey is already present and the value has not changed.
		967
		968	The monitoring stops when the guard object is destroyed.
		969
		970	Example: on every change to the family "mygroup", print out all keys.
		971
		972	my $guard = db_mon mygroup => sub {
		973	my ($family, $keys) = @_;
		974	print "mygroup members: ", (join " ", keys %$family), "\n";
		975	};
		976
		977	Exmaple: wait until the family "My::Module::workers" is non-empty.
		978
		979	my $guard; $guard = db_mon My::Module::workers => sub {
		980	my ($family, $keys) = @_;
		981	return unless %$family;
		982	undef $guard;
		983	print "My::Module::workers now nonempty\n";
		984	};
		985
		986	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		987
		988	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		989	my ($family, $keys) = @_;
		990
		991	for (@$keys) {
		992	print "$_: ",
		993	(exists $family->{$_}
		994	? $family->{$_}
		995	: "(deleted)"),
		996	"\n";
		997	}
		998	};
		999
		1000	=cut
		1001
652	=back	1002	=back
653		1003
654	=head1 AnyEvent::MP vs. Distributed Erlang	1004	=head1 AnyEvent::MP vs. Distributed Erlang
655		1005
656	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	1006	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
657	== aemp node, Erlang process == aemp port), so many of the documents and	1007	== aemp node, Erlang process == aemp port), so many of the documents and
658	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	1008	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
659	sample:	1009	sample:
660		1010
661	http://www.Erlang.se/doc/programming_rules.shtml	1011	http://www.erlang.se/doc/programming_rules.shtml
662	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	1012	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
663	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	1013	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
664	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	1014	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
665		1015
666	Despite the similarities, there are also some important differences:	1016	Despite the similarities, there are also some important differences:
667		1017
668	=over 4	1018	=over 4
669		1019
670	=item * Node IDs are arbitrary strings in AEMP.	1020	=item * Node IDs are arbitrary strings in AEMP.
671		1021
672	Erlang relies on special naming and DNS to work everywhere in the same	1022	Erlang relies on special naming and DNS to work everywhere in the same
673	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by	1023	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
674	configuraiton or DNS), but will otherwise discover other odes itself.	1024	configuration or DNS), and possibly the addresses of some seed nodes, but
		1025	will otherwise discover other nodes (and their IDs) itself.
675		1026
676	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP	1027	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
677	uses "local ports are like remote ports".	1028	uses "local ports are like remote ports".
678		1029
679	The failure modes for local ports are quite different (runtime errors	1030	The failure modes for local ports are quite different (runtime errors
…		…
688	ports being the special case/exception, where transport errors cannot	1039	ports being the special case/exception, where transport errors cannot
689	occur.	1040	occur.
690		1041
691	=item * Erlang uses processes and a mailbox, AEMP does not queue.	1042	=item * Erlang uses processes and a mailbox, AEMP does not queue.
692		1043
693	Erlang uses processes that selectively receive messages, and therefore	1044	Erlang uses processes that selectively receive messages out of order, and
694	needs a queue. AEMP is event based, queuing messages would serve no	1045	therefore needs a queue. AEMP is event based, queuing messages would serve
695	useful purpose. For the same reason the pattern-matching abilities of	1046	no useful purpose. For the same reason the pattern-matching abilities
696	AnyEvent::MP are more limited, as there is little need to be able to	1047	of AnyEvent::MP are more limited, as there is little need to be able to
697	filter messages without dequeing them.	1048	filter messages without dequeuing them.
698		1049
699	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	1050	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1051	being event-based, while Erlang is process-based.
		1052
		1053	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1054	top of AEMP and Coro threads.
700		1055
701	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1056	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
702		1057
703	Sending messages in Erlang is synchronous and blocks the process (and	1058	Sending messages in Erlang is synchronous and blocks the process until
		1059	a conenction has been established and the message sent (and so does not
704	so does not need a queue that can overflow). AEMP sends are immediate,	1060	need a queue that can overflow). AEMP sends return immediately, connection
705	connection establishment is handled in the background.	1061	establishment is handled in the background.
706		1062
707	=item * Erlang suffers from silent message loss, AEMP does not.	1063	=item * Erlang suffers from silent message loss, AEMP does not.
708		1064
709	Erlang makes few guarantees on messages delivery - messages can get lost	1065	Erlang implements few guarantees on messages delivery - messages can get
710	without any of the processes realising it (i.e. you send messages a, b,	1066	lost without any of the processes realising it (i.e. you send messages a,
711	and c, and the other side only receives messages a and c).	1067	b, and c, and the other side only receives messages a and c).
712		1068
713	AEMP guarantees correct ordering, and the guarantee that after one message	1069	AEMP guarantees (modulo hardware errors) correct ordering, and the
714	is lost, all following ones sent to the same port are lost as well, until	1070	guarantee that after one message is lost, all following ones sent to the
715	monitoring raises an error, so there are no silent "holes" in the message	1071	same port are lost as well, until monitoring raises an error, so there are
716	sequence.	1072	no silent "holes" in the message sequence.
		1073
		1074	If you want your software to be very reliable, you have to cope with
		1075	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
		1076	simply tries to work better in common error cases, such as when a network
		1077	link goes down.
717		1078
718	=item * Erlang can send messages to the wrong port, AEMP does not.	1079	=item * Erlang can send messages to the wrong port, AEMP does not.
719		1080
720	In Erlang it is quite likely that a node that restarts reuses a process ID	1081	In Erlang it is quite likely that a node that restarts reuses an Erlang
721	known to other nodes for a completely different process, causing messages	1082	process ID known to other nodes for a completely different process,
722	destined for that process to end up in an unrelated process.	1083	causing messages destined for that process to end up in an unrelated
		1084	process.
723		1085
724	AEMP never reuses port IDs, so old messages or old port IDs floating	1086	AEMP does not reuse port IDs, so old messages or old port IDs floating
725	around in the network will not be sent to an unrelated port.	1087	around in the network will not be sent to an unrelated port.
726		1088
727	=item * Erlang uses unprotected connections, AEMP uses secure	1089	=item * Erlang uses unprotected connections, AEMP uses secure
728	authentication and can use TLS.	1090	authentication and can use TLS.
729		1091
…		…
732		1094
733	=item * The AEMP protocol is optimised for both text-based and binary	1095	=item * The AEMP protocol is optimised for both text-based and binary
734	communications.	1096	communications.
735		1097
736	The AEMP protocol, unlike the Erlang protocol, supports both programming	1098	The AEMP protocol, unlike the Erlang protocol, supports both programming
737	language independent text-only protocols (good for debugging) and binary,	1099	language independent text-only protocols (good for debugging), and binary,
738	language-specific serialisers (e.g. Storable).	1100	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1101	used, the protocol is actually completely text-based.
739		1102
740	It has also been carefully designed to be implementable in other languages	1103	It has also been carefully designed to be implementable in other languages
741	with a minimum of work while gracefully degrading functionality to make the	1104	with a minimum of work while gracefully degrading functionality to make the
742	protocol simple.	1105	protocol simple.
743		1106
744	=item * AEMP has more flexible monitoring options than Erlang.	1107	=item * AEMP has more flexible monitoring options than Erlang.
745		1108
746	In Erlang, you can chose to receive I<all> exit signals as messages	1109	In Erlang, you can chose to receive I<all> exit signals as messages or
747	or I<none>, there is no in-between, so monitoring single processes is	1110	I<none>, there is no in-between, so monitoring single Erlang processes is
748	difficult to implement. Monitoring in AEMP is more flexible than in	1111	difficult to implement.
749	Erlang, as one can choose between automatic kill, exit message or callback	1112
750	on a per-process basis.	1113	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1114	between automatic kill, exit message or callback on a per-port basis.
751		1115
752	=item * Erlang tries to hide remote/local connections, AEMP does not.	1116	=item * Erlang tries to hide remote/local connections, AEMP does not.
753		1117
754	Monitoring in Erlang is not an indicator of process death/crashes,	1118	Monitoring in Erlang is not an indicator of process death/crashes, in the
755	as linking is (except linking is unreliable in Erlang).	1119	same way as linking is (except linking is unreliable in Erlang).
756		1120
757	In AEMP, you don't "look up" registered port names or send to named ports	1121	In AEMP, you don't "look up" registered port names or send to named ports
758	that might or might not be persistent. Instead, you normally spawn a port	1122	that might or might not be persistent. Instead, you normally spawn a port
759	on the remote node. The init function monitors the you, and you monitor	1123	on the remote node. The init function monitors you, and you monitor the
760	the remote port. Since both monitors are local to the node, they are much	1124	remote port. Since both monitors are local to the node, they are much more
761	more reliable.	1125	reliable (no need for C<spawn_link>).
762		1126
763	This also saves round-trips and avoids sending messages to the wrong port	1127	This also saves round-trips and avoids sending messages to the wrong port
764	(hard to do in Erlang).	1128	(hard to do in Erlang).
765		1129
766	=back	1130	=back
767		1131
768	=head1 RATIONALE	1132	=head1 RATIONALE
769		1133
770	=over 4	1134	=over 4
771		1135
772	=item Why strings for ports and noderefs, why not objects?	1136	=item Why strings for port and node IDs, why not objects?
773		1137
774	We considered "objects", but found that the actual number of methods	1138	We considered "objects", but found that the actual number of methods
775	thatc an be called are very low. Since port IDs and noderefs travel over	1139	that can be called are quite low. Since port and node IDs travel over
776	the network frequently, the serialising/deserialising would add lots of	1140	the network frequently, the serialising/deserialising would add lots of
777	overhead, as well as having to keep a proxy object.	1141	overhead, as well as having to keep a proxy object everywhere.
778		1142
779	Strings can easily be printed, easily serialised etc. and need no special	1143	Strings can easily be printed, easily serialised etc. and need no special
780	procedures to be "valid".	1144	procedures to be "valid".
781		1145
782	And a a miniport consists of a single closure stored in a global hash - it	1146	And as a result, a port with just a default receiver consists of a single
783	can't become much cheaper.	1147	code reference stored in a global hash - it can't become much cheaper.
784		1148
785	=item Why favour JSON, why not real serialising format such as Storable?	1149	=item Why favour JSON, why not a real serialising format such as Storable?
786		1150
787	In fact, any AnyEvent::MP node will happily accept Storable as framing	1151	In fact, any AnyEvent::MP node will happily accept Storable as framing
788	format, but currently there is no way to make a node use Storable by	1152	format, but currently there is no way to make a node use Storable by
789	default.	1153	default (although all nodes will accept it).
790		1154
791	The default framing protocol is JSON because a) JSON::XS is many times	1155	The default framing protocol is JSON because a) JSON::XS is many times
792	faster for small messages and b) most importantly, after years of	1156	faster for small messages and b) most importantly, after years of
793	experience we found that object serialisation is causing more problems	1157	experience we found that object serialisation is causing more problems
794	than it gains: Just like function calls, objects simply do not travel	1158	than it solves: Just like function calls, objects simply do not travel
795	easily over the network, mostly because they will always be a copy, so you	1159	easily over the network, mostly because they will always be a copy, so you
796	always have to re-think your design.	1160	always have to re-think your design.
797		1161
798	Keeping your messages simple, concentrating on data structures rather than	1162	Keeping your messages simple, concentrating on data structures rather than
799	objects, will keep your messages clean, tidy and efficient.	1163	objects, will keep your messages clean, tidy and efficient.
800		1164
801	=back	1165	=back
802		1166
803	=head1 SEE ALSO	1167	=head1 SEE ALSO
804		1168
		1169	L<AnyEvent::MP::Intro> - a gentle introduction.
		1170
		1171	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1172
		1173	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1174	your applications.
		1175
		1176	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1177
		1178	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1179	all nodes.
		1180
805	L<AnyEvent>.	1181	L<AnyEvent>.
806		1182
807	=head1 AUTHOR	1183	=head1 AUTHOR
808		1184
809	Marc Lehmann <schmorp@schmorp.de>	1185	Marc Lehmann <schmorp@schmorp.de>

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Revision 1.128 by root, Sun Mar 4 14:28:44 2012 UTC