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

Comparing cvsroot/AnyEvent-MP/MP.pm (file contents):
Revision 1.66 by root, Fri Aug 28 01:07:24 2009 UTC vs.
Revision 1.127 by root, Sat Mar 3 20:35:10 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
146	);	202	);
147		203
148	our $SELF;	204	our $SELF;
149		205
150	sub _self_die() {	206	sub _self_die() {
…		…
153	kil $SELF, die => $msg;	209	kil $SELF, die => $msg;
154	}	210	}
155		211
156	=item $thisnode = NODE / $NODE	212	=item $thisnode = NODE / $NODE
157		213
158	The C<NODE> function returns, and the C<$NODE> variable contains the node	214	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	215	ID of the node running in the current process. This value is initialised by
160	a call to C<initialise_node>.	216	a call to C<configure>.
161		217
162	=item $nodeid = node_of $port	218	=item $nodeid = node_of $port
163		219
164	Extracts and returns the node ID part from a port ID or a node ID.	220	Extracts and returns the node ID from a port ID or a node ID.
165		221
166	=item initialise_node $profile_name	222	=item configure $profile, key => value...
		223
		224	=item configure key => value...
167		225
168	Before a node can talk to other nodes on the network (i.e. enter	226	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	227	"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	228	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.	229	some other nodes in the network to discover other nodes.
172		230
173	This function initialises a node - it must be called exactly once (or	231	This function configures a node - it must be called exactly once (or
174	never) before calling other AnyEvent::MP functions.	232	never) before calling other AnyEvent::MP functions.
175		233
176	The first argument is a profile name. If it is C<undef> or missing, then	234	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>).	235	F<aemp> command line utility (sans the set/del prefix), with these additions:
178		236
		237	=over 4
		238
		239	=item norc => $boolean (default false)
		240
		241	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
		242	be consulted - all configuraiton options must be specified in the
		243	C<configure> call.
		244
		245	=item force => $boolean (default false)
		246
		247	IF true, then the values specified in the C<configure> will take
		248	precedence over any values configured via the rc file. The default is for
		249	the rc file to override any options specified in the program.
		250
		251	=item secure => $pass->($nodeid)
		252
		253	In addition to specifying a boolean, you can specify a code reference that
		254	is called for every remote execution attempt - the execution request is
		255	granted iff the callback returns a true value.
		256
		257	See F<semp setsecure> for more info.
		258
		259	=back
		260
		261	=over 4
		262
		263	=item step 1, gathering configuration from profiles
		264
179	The function then looks up the profile in the aemp configuration (see the	265	The function first looks up a profile in the aemp configuration (see the
180	L<aemp> commandline utility).	266	L<aemp> commandline utility). The profile name can be specified via the
		267	named C<profile> parameter or can simply be the first parameter). If it is
		268	missing, then the nodename (F<uname -n>) will be used as profile name.
		269
		270	The profile data is then gathered as follows:
		271
		272	First, all remaining key => value pairs (all of which are conveniently
		273	undocumented at the moment) will be interpreted as configuration
		274	data. Then they will be overwritten by any values specified in the global
		275	default configuration (see the F<aemp> utility), then the chain of
		276	profiles chosen by the profile name (and any C<parent> attributes).
		277
		278	That means that the values specified in the profile have highest priority
		279	and the values specified directly via C<configure> have lowest priority,
		280	and can only be used to specify defaults.
181		281
182	If the profile specifies a node ID, then this will become the node ID of	282	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	283	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.	284	a unique randoms tring (C</%u>) appended.
		285
		286	The node ID can contain some C<%> sequences that are expanded: C<%n>
		287	is expanded to the local nodename, C<%u> is replaced by a random
		288	strign to make the node unique. For example, the F<aemp> commandline
		289	utility uses C<aemp/%n/%u> as nodename, which might expand to
		290	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		291
		292	=item step 2, bind listener sockets
185		293
186	The next step is to look up the binds in the profile, followed by binding	294	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	295	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	296	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	297	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).	298	binds, but it can still talk to all "normal" nodes).
191		299
192	If the profile does not specify a binds list, then the node ID will be	300	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	301	used, meaning the node will bind on a dynamically-assigned port on every
194	used as binds list.	302	local IP address it finds.
195		303
		304	=item step 3, connect to seed nodes
		305
196	Lastly, the seeds list from the profile is passed to the	306	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	307	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.	308	connectivity with at least one node at any point in time.
199		309
200	Example: become a distributed node listening on the guessed noderef, or	310	=back
201	the one specified via C<aemp> for the current node. This should be the	311
		312	Example: become a distributed node using the local node name as profile.
202	most common form of invocation for "daemon"-type nodes.	313	This should be the most common form of invocation for "daemon"-type nodes.
203		314
204	initialise_node;	315	configure
205		316
206	Example: become an anonymous node. This form is often used for commandline	317	Example: become a semi-anonymous node. This form is often used for
207	clients.	318	commandline clients.
208		319
209	initialise_node "anon/";	320	configure nodeid => "myscript/%n/%u";
210		321
211	Example: become a distributed node. If there is no profile of the given	322	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	323	for a seed node as it binds on all local addresses on a fixed port (4040,
213	on the resulting addresses.	324	customary for aemp).
214		325
215	initialise_node "localhost:4044";	326	# use the aemp commandline utility
		327	# aemp profile seed binds '*:4040'
		328
		329	# then use it
		330	configure profile => "seed";
		331
		332	# or simply use aemp from the shell again:
		333	# aemp run profile seed
		334
		335	# or provide a nicer-to-remember nodeid
		336	# aemp run profile seed nodeid "$(hostname)"
216		337
217	=item $SELF	338	=item $SELF
218		339
219	Contains the current port id while executing C<rcv> callbacks or C<psub>	340	Contains the current port id while executing C<rcv> callbacks or C<psub>
220	blocks.	341	blocks.
221		342
222	=item SELF, %SELF, @SELF...	343	=item *SELF, SELF, %SELF, @SELF...
223		344
224	Due to some quirks in how perl exports variables, it is impossible to	345	Due to some quirks in how perl exports variables, it is impossible to
225	just export C<$SELF>, all the symbols called C<SELF> are exported by this	346	just export C<$SELF>, all the symbols named C<SELF> are exported by this
226	module, but only C<$SELF> is currently used.	347	module, but only C<$SELF> is currently used.
227		348
228	=item snd $port, type => @data	349	=item snd $port, type => @data
229		350
230	=item snd $port, @msg	351	=item snd $port, @msg
231		352
232	Send the given message to the given port ID, which can identify either	353	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.	354	local or a remote port, and must be a port ID.
234		355
235	While the message can be about anything, it is highly recommended to use a	356	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	357	use a string as first element (a port ID, or some word that indicates a
237	type etc.).	358	request type etc.) and to consist if only simple perl values (scalars,
		359	arrays, hashes) - if you think you need to pass an object, think again.
238		360
239	The message data effectively becomes read-only after a call to this	361	The message data logically becomes read-only after a call to this
240	function: modifying any argument is not allowed and can cause many	362	function: modifying any argument (or values referenced by them) is
241	problems.	363	forbidden, as there can be considerable time between the call to C<snd>
		364	and the time the message is actually being serialised - in fact, it might
		365	never be copied as within the same process it is simply handed to the
		366	receiving port.
242		367
243	The type of data you can transfer depends on the transport protocol: when	368	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	369	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	370	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	371	that Storable can serialise and deserialise is allowed, and for the local
247	node, anything can be passed.	372	node, anything can be passed. Best rely only on the common denominator of
		373	these.
248		374
249	=item $local_port = port	375	=item $local_port = port
250		376
251	Create a new local port object and returns its port ID. Initially it has	377	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.	378	no callbacks set and will throw an error when it receives messages.
…		…
276	sub _kilme {	402	sub _kilme {
277	die "received message on port without callback";	403	die "received message on port without callback";
278	}	404	}
279		405
280	sub port(;&) {	406	sub port(;&) {
281	my $id = "$UNIQ." . $ID++;	407	my $id = $UNIQ . ++$ID;
282	my $port = "$NODE#$id";	408	my $port = "$NODE#$id";
283		409
284	rcv $port, shift \|\| \&_kilme;	410	rcv $port, shift \|\| \&_kilme;
285		411
286	$port	412	$port
…		…
325	msg1 => sub { ... },	451	msg1 => sub { ... },
326	...	452	...
327	;	453	;
328		454
329	Example: temporarily register a rcv callback for a tag matching some port	455	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.	456	(e.g. for an rpc reply) and unregister it after a message was received.
331		457
332	rcv $port, $otherport => sub {	458	rcv $port, $otherport => sub {
333	my @reply = @_;	459	my @reply = @_;
334		460
335	rcv $SELF, $otherport;	461	rcv $SELF, $otherport;
…		…
337		463
338	=cut	464	=cut
339		465
340	sub rcv($@) {	466	sub rcv($@) {
341	my $port = shift;	467	my $port = shift;
342	my ($noderef, $portid) = split /#/, $port, 2;	468	my ($nodeid, $portid) = split /#/, $port, 2;
343		469
344	$NODE{$noderef} == $NODE{""}	470	$NODE{$nodeid} == $NODE{""}
345	or Carp::croak "$port: rcv can only be called on local ports, caught";	471	or Carp::croak "$port: rcv can only be called on local ports, caught";
346		472
347	while (@_) {	473	while (@_) {
348	if (ref $_[0]) {	474	if (ref $_[0]) {
349	if (my $self = $PORT_DATA{$portid}) {	475	if (my $self = $PORT_DATA{$portid}) {
350	"AnyEvent::MP::Port" eq ref $self	476	"AnyEvent::MP::Port" eq ref $self
351	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	477	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
352		478
353	$self->[2] = shift;	479	$self->[0] = shift;
354	} else {	480	} else {
355	my $cb = shift;	481	my $cb = shift;
356	$PORT{$portid} = sub {	482	$PORT{$portid} = sub {
357	local $SELF = $port;	483	local $SELF = $port;
358	eval { &$cb }; _self_die if $@;	484	eval { &$cb }; _self_die if $@;
359	};	485	};
360	}	486	}
361	} elsif (defined $_[0]) {	487	} elsif (defined $_[0]) {
362	my $self = $PORT_DATA{$portid} \|\|= do {	488	my $self = $PORT_DATA{$portid} \|\|= do {
363	my $self = bless [$PORT{$port} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";	489	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
364		490
365	$PORT{$portid} = sub {	491	$PORT{$portid} = sub {
366	local $SELF = $port;	492	local $SELF = $port;
367		493
368	if (my $cb = $self->[1]{$_[0]}) {	494	if (my $cb = $self->[1]{$_[0]}) {
…		…
390	}	516	}
391		517
392	$port	518	$port
393	}	519	}
394		520
		521	=item peval $port, $coderef[, @args]
		522
		523	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		524	when the code throews an exception the C<$port> will be killed.
		525
		526	Any remaining args will be passed to the callback. Any return values will
		527	be returned to the caller.
		528
		529	This is useful when you temporarily want to execute code in the context of
		530	a port.
		531
		532	Example: create a port and run some initialisation code in it's context.
		533
		534	my $port = port { ... };
		535
		536	peval $port, sub {
		537	init
		538	or die "unable to init";
		539	};
		540
		541	=cut
		542
		543	sub peval($$) {
		544	local $SELF = shift;
		545	my $cb = shift;
		546
		547	if (wantarray) {
		548	my @res = eval { &$cb };
		549	_self_die if $@;
		550	@res
		551	} else {
		552	my $res = eval { &$cb };
		553	_self_die if $@;
		554	$res
		555	}
		556	}
		557
395	=item $closure = psub { BLOCK }	558	=item $closure = psub { BLOCK }
396		559
397	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	560	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>	561	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.	562	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		563
		564	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		565	BLOCK }, @_ } >>.
400		566
401	This is useful when you register callbacks from C<rcv> callbacks:	567	This is useful when you register callbacks from C<rcv> callbacks:
402		568
403	rcv delayed_reply => sub {	569	rcv delayed_reply => sub {
404	my ($delay, @reply) = @_;	570	my ($delay, @reply) = @_;
…		…
428	$res	594	$res
429	}	595	}
430	}	596	}
431	}	597	}
432		598
433	=item $guard = mon $port, $cb->(@reason)	599	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
434		600
435	=item $guard = mon $port, $rcvport	601	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
436		602
437	=item $guard = mon $port	603	=item $guard = mon $port # kill $SELF when $port dies
438		604
439	=item $guard = mon $port, $rcvport, @msg	605	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
440		606
441	Monitor the given port and do something when the port is killed or	607	Monitor the given port and do something when the port is killed or
442	messages to it were lost, and optionally return a guard that can be used	608	messages to it were lost, and optionally return a guard that can be used
443	to stop monitoring again.	609	to stop monitoring again.
444
445	C<mon> effectively guarantees that, in the absence of hardware failures,
446	that after starting the monitor, either all messages sent to the port
447	will arrive, or the monitoring action will be invoked after possible
448	message loss has been detected. No messages will be lost "in between"
449	(after the first lost message no further messages will be received by the
450	port). After the monitoring action was invoked, further messages might get
451	delivered again.
452
453	Note that monitoring-actions are one-shot: once released, they are removed
454	and will not trigger again.
455		610
456	In the first form (callback), the callback is simply called with any	611	In the first form (callback), the callback is simply called with any
457	number of C<@reason> elements (no @reason means that the port was deleted	612	number of C<@reason> elements (no @reason means that the port was deleted
458	"normally"). Note also that I<< the callback B<must> never die >>, so use	613	"normally"). Note also that I<< the callback B<must> never die >>, so use
459	C<eval> if unsure.	614	C<eval> if unsure.
460		615
461	In the second form (another port given), the other port (C<$rcvport>)	616	In the second form (another port given), the other port (C<$rcvport>)
462	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	617	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
463	"normal" kils nothing happens, while under all other conditions, the other	618	"normal" kils nothing happens, while under all other conditions, the other
464	port is killed with the same reason.	619	port is killed with the same reason.
465		620
466	The third form (kill self) is the same as the second form, except that	621	The third form (kill self) is the same as the second form, except that
467	C<$rvport> defaults to C<$SELF>.	622	C<$rvport> defaults to C<$SELF>.
468		623
469	In the last form (message), a message of the form C<@msg, @reason> will be	624	In the last form (message), a message of the form C<@msg, @reason> will be
470	C<snd>.	625	C<snd>.
		626
		627	Monitoring-actions are one-shot: once messages are lost (and a monitoring
		628	alert was raised), they are removed and will not trigger again.
471		629
472	As a rule of thumb, monitoring requests should always monitor a port from	630	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	631	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	632	lost, just like any other message. Another less obvious reason is that
475	even monitoring requests can get lost (for exmaple, when the connection	633	even monitoring requests can get lost (for example, when the connection
476	to the other node goes down permanently). When monitoring a port locally	634	to the other node goes down permanently). When monitoring a port locally
477	these problems do not exist.	635	these problems do not exist.
478		636
		637	C<mon> effectively guarantees that, in the absence of hardware failures,
		638	after starting the monitor, either all messages sent to the port will
		639	arrive, or the monitoring action will be invoked after possible message
		640	loss has been detected. No messages will be lost "in between" (after
		641	the first lost message no further messages will be received by the
		642	port). After the monitoring action was invoked, further messages might get
		643	delivered again.
		644
		645	Inter-host-connection timeouts and monitoring depend on the transport
		646	used. The only transport currently implemented is TCP, and AnyEvent::MP
		647	relies on TCP to detect node-downs (this can take 10-15 minutes on a
		648	non-idle connection, and usually around two hours for idle connections).
		649
		650	This means that monitoring is good for program errors and cleaning up
		651	stuff eventually, but they are no replacement for a timeout when you need
		652	to ensure some maximum latency.
		653
479	Example: call a given callback when C<$port> is killed.	654	Example: call a given callback when C<$port> is killed.
480		655
481	mon $port, sub { warn "port died because of <@_>\n" };	656	mon $port, sub { warn "port died because of <@_>\n" };
482		657
483	Example: kill ourselves when C<$port> is killed abnormally.	658	Example: kill ourselves when C<$port> is killed abnormally.
…		…
489	mon $port, $self => "restart";	664	mon $port, $self => "restart";
490		665
491	=cut	666	=cut
492		667
493	sub mon {	668	sub mon {
494	my ($noderef, $port) = split /#/, shift, 2;	669	my ($nodeid, $port) = split /#/, shift, 2;
495		670
496	my $node = $NODE{$noderef} \|\| add_node $noderef;	671	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
497		672
498	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';	673	my $cb = @_ ? shift : $SELF \|\| Carp::croak 'mon: called with one argument only, but $SELF not set,';
499		674
500	unless (ref $cb) {	675	unless (ref $cb) {
501	if (@_) {	676	if (@_) {
…		…
510	}	685	}
511		686
512	$node->monitor ($port, $cb);	687	$node->monitor ($port, $cb);
513		688
514	defined wantarray	689	defined wantarray
515	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	690	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
516	}	691	}
517		692
518	=item $guard = mon_guard $port, $ref, $ref...	693	=item $guard = mon_guard $port, $ref, $ref...
519		694
520	Monitors the given C<$port> and keeps the passed references. When the port	695	Monitors the given C<$port> and keeps the passed references. When the port
521	is killed, the references will be freed.	696	is killed, the references will be freed.
522		697
523	Optionally returns a guard that will stop the monitoring.	698	Optionally returns a guard that will stop the monitoring.
524		699
525	This function is useful when you create e.g. timers or other watchers and	700	This function is useful when you create e.g. timers or other watchers and
526	want to free them when the port gets killed:	701	want to free them when the port gets killed (note the use of C<psub>):
527		702
528	$port->rcv (start => sub {	703	$port->rcv (start => sub {
529	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	704	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
530	undef $timer if 0.9 < rand;	705	undef $timer if 0.9 < rand;
531	});	706	});
532	});	707	});
533		708
534	=cut	709	=cut
…		…
543		718
544	=item kil $port[, @reason]	719	=item kil $port[, @reason]
545		720
546	Kill the specified port with the given C<@reason>.	721	Kill the specified port with the given C<@reason>.
547		722
548	If no C<@reason> is specified, then the port is killed "normally" (linked	723	If no C<@reason> is specified, then the port is killed "normally" -
549	ports will not be kileld, or even notified).	724	monitor callback will be invoked, but the kil will not cause linked ports
		725	(C<mon $mport, $lport> form) to get killed.
550		726
551	Otherwise, linked ports get killed with the same reason (second form of	727	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
552	C<mon>, see below).	728	form) get killed with the same reason.
553		729
554	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	730	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
555	will be reported as reason C<< die => $@ >>.	731	will be reported as reason C<< die => $@ >>.
556		732
557	Transport/communication errors are reported as C<< transport_error =>	733	Transport/communication errors are reported as C<< transport_error =>
…		…
562	=item $port = spawn $node, $initfunc[, @initdata]	738	=item $port = spawn $node, $initfunc[, @initdata]
563		739
564	Creates a port on the node C<$node> (which can also be a port ID, in which	740	Creates a port on the node C<$node> (which can also be a port ID, in which
565	case it's the node where that port resides).	741	case it's the node where that port resides).
566		742
567	The port ID of the newly created port is return immediately, and it is	743	The port ID of the newly created port is returned immediately, and it is
568	permissible to immediately start sending messages or monitor the port.	744	possible to immediately start sending messages or to monitor the port.
569		745
570	After the port has been created, the init function is	746	After the port has been created, the init function is called on the remote
571	called. This function must be a fully-qualified function name	747	node, in the same context as a C<rcv> callback. This function must be a
572	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	748	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
573	program, use C<::name>.	749	specify a function in the main program, use C<::name>.
574		750
575	If the function doesn't exist, then the node tries to C<require>	751	If the function doesn't exist, then the node tries to C<require>
576	the package, then the package above the package and so on (e.g.	752	the package, then the package above the package and so on (e.g.
577	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	753	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
578	exists or it runs out of package names.	754	exists or it runs out of package names.
579		755
580	The init function is then called with the newly-created port as context	756	The init function is then called with the newly-created port as context
581	object (C<$SELF>) and the C<@initdata> values as arguments.	757	object (C<$SELF>) and the C<@initdata> values as arguments. It I<must>
		758	call one of the C<rcv> functions to set callbacks on C<$SELF>, otherwise
		759	the port might not get created.
582		760
583	A common idiom is to pass your own port, monitor the spawned port, and	761	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	762	port, and in the remote init function, immediately monitor the passed
585	ensures that both ports get cleaned up when there is a problem.	763	local port. This two-way monitoring ensures that both ports get cleaned up
		764	when there is a problem.
		765
		766	C<spawn> guarantees that the C<$initfunc> has no visible effects on the
		767	caller before C<spawn> returns (by delaying invocation when spawn is
		768	called for the local node).
586		769
587	Example: spawn a chat server port on C<$othernode>.	770	Example: spawn a chat server port on C<$othernode>.
588		771
589	# this node, executed from within a port context:	772	# this node, executed from within a port context:
590	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	773	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
605		788
606	sub _spawn {	789	sub _spawn {
607	my $port = shift;	790	my $port = shift;
608	my $init = shift;	791	my $init = shift;
609		792
		793	# rcv will create the actual port
610	local $SELF = "$NODE#$port";	794	local $SELF = "$NODE#$port";
611	eval {	795	eval {
612	&{ load_func $init }	796	&{ load_func $init }
613	};	797	};
614	_self_die if $@;	798	_self_die if $@;
615	}	799	}
616		800
617	sub spawn(@) {	801	sub spawn(@) {
618	my ($noderef, undef) = split /#/, shift, 2;	802	my ($nodeid, undef) = split /#/, shift, 2;
619		803
620	my $id = "$RUNIQ." . $ID++;	804	my $id = $RUNIQ . ++$ID;
621		805
622	$_[0] =~ /::/	806	$_[0] =~ /::/
623	or Carp::croak "spawn init function must be a fully-qualified name, caught";	807	or Carp::croak "spawn init function must be a fully-qualified name, caught";
624		808
625	snd_to_func $noderef, "AnyEvent::MP::_spawn" => $id, @_;	809	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
626		810
627	"$noderef#$id"	811	"$nodeid#$id"
628	}	812	}
		813
629		814
630	=item after $timeout, @msg	815	=item after $timeout, @msg
631		816
632	=item after $timeout, $callback	817	=item after $timeout, $callback
633		818
634	Either sends the given message, or call the given callback, after the	819	Either sends the given message, or call the given callback, after the
635	specified number of seconds.	820	specified number of seconds.
636		821
637	This is simply a utility function that come sin handy at times.	822	This is simply a utility function that comes in handy at times - the
		823	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		824	so it may go away in the future.
638		825
639	=cut	826	=cut
640		827
641	sub after($@) {	828	sub after($@) {
642	my ($timeout, @action) = @_;	829	my ($timeout, @action) = @_;
…		…
647	? $action[0]()	834	? $action[0]()
648	: snd @action;	835	: snd @action;
649	};	836	};
650	}	837	}
651		838
		839	=item cal $port, @msg, $callback[, $timeout]
		840
		841	A simple form of RPC - sends a message to the given C<$port> with the
		842	given contents (C<@msg>), but adds a reply port to the message.
		843
		844	The reply port is created temporarily just for the purpose of receiving
		845	the reply, and will be C<kil>ed when no longer needed.
		846
		847	A reply message sent to the port is passed to the C<$callback> as-is.
		848
		849	If an optional time-out (in seconds) is given and it is not C<undef>,
		850	then the callback will be called without any arguments after the time-out
		851	elapsed and the port is C<kil>ed.
		852
		853	If no time-out is given (or it is C<undef>), then the local port will
		854	monitor the remote port instead, so it eventually gets cleaned-up.
		855
		856	Currently this function returns the temporary port, but this "feature"
		857	might go in future versions unless you can make a convincing case that
		858	this is indeed useful for something.
		859
		860	=cut
		861
		862	sub cal(@) {
		863	my $timeout = ref $_[-1] ? undef : pop;
		864	my $cb = pop;
		865
		866	my $port = port {
		867	undef $timeout;
		868	kil $SELF;
		869	&$cb;
		870	};
		871
		872	if (defined $timeout) {
		873	$timeout = AE::timer $timeout, 0, sub {
		874	undef $timeout;
		875	kil $port;
		876	$cb->();
		877	};
		878	} else {
		879	mon $_[0], sub {
		880	kil $port;
		881	$cb->();
		882	};
		883	}
		884
		885	push @_, $port;
		886	&snd;
		887
		888	$port
		889	}
		890
		891	=back
		892
		893	=head1 DISTRIBUTED DATABASE
		894
		895	AnyEvent::MP comes with a simple distributed database. The database will
		896	be mirrored asynchronously at all global nodes. Other nodes bind to one of
		897	the global nodes for their needs.
		898
		899	The database consists of a two-level hash - a hash contains a hash which
		900	contains values.
		901
		902	The top level hash key is called "family", and the second-level hash key
		903	is called "subkey" or simply "key".
		904
		905	The family must be alphanumeric, i.e. start with a letter and consist
		906	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		907	pretty much like Perl module names.
		908
		909	As the family namespace is global, it is recommended to prefix family names
		910	with the name of the application or module using it.
		911
		912	The subkeys must be non-empty strings, with no further restrictions.
		913
		914	The values should preferably be strings, but other perl scalars should
		915	work as well (such as undef, arrays and hashes).
		916
		917	Every database entry is owned by one node - adding the same family/subkey
		918	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		919	but the result might be nondeterministic, i.e. the key might have
		920	different values on different nodes.
		921
		922	Different subkeys in the same family can be owned by different nodes
		923	without problems, and in fact, this is the common method to create worker
		924	pools. For example, a worker port for image scaling might do this:
		925
		926	db_set my_image_scalers => $port;
		927
		928	And clients looking for an image scaler will want to get the
		929	C<my_image_scalers> keys:
		930
		931	db_keys "my_image_scalers" => 60 => sub {
		932	#d##TODO#
		933
		934	=over
		935
		936	=item db_set $family => $subkey [=> $value]
		937
		938	Sets (or replaces) a key to the database - if C<$value> is omitted,
		939	C<undef> is used instead.
		940
		941	=item db_del $family => $subkey
		942
		943	Deletes a key from the database.
		944
		945	=item $guard = db_reg $family => $subkey [=> $value]
		946
		947	Sets the key on the database and returns a guard. When the guard is
		948	destroyed, the key is deleted from the database. If C<$value> is missing,
		949	then C<undef> is used.
		950
		951	=cut
		952
652	=back	953	=back
653		954
654	=head1 AnyEvent::MP vs. Distributed Erlang	955	=head1 AnyEvent::MP vs. Distributed Erlang
655		956
656	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	957	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	958	== 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	959	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
659	sample:	960	sample:
660		961
661	http://www.Erlang.se/doc/programming_rules.shtml	962	http://www.erlang.se/doc/programming_rules.shtml
662	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	963	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	964	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	965	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
665		966
666	Despite the similarities, there are also some important differences:	967	Despite the similarities, there are also some important differences:
667		968
668	=over 4	969	=over 4
669		970
670	=item * Node IDs are arbitrary strings in AEMP.	971	=item * Node IDs are arbitrary strings in AEMP.
671		972
672	Erlang relies on special naming and DNS to work everywhere in the same	973	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	974	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.	975	configuration or DNS), and possibly the addresses of some seed nodes, but
		976	will otherwise discover other nodes (and their IDs) itself.
675		977
676	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP	978	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
677	uses "local ports are like remote ports".	979	uses "local ports are like remote ports".
678		980
679	The failure modes for local ports are quite different (runtime errors	981	The failure modes for local ports are quite different (runtime errors
…		…
688	ports being the special case/exception, where transport errors cannot	990	ports being the special case/exception, where transport errors cannot
689	occur.	991	occur.
690		992
691	=item * Erlang uses processes and a mailbox, AEMP does not queue.	993	=item * Erlang uses processes and a mailbox, AEMP does not queue.
692		994
693	Erlang uses processes that selectively receive messages, and therefore	995	Erlang uses processes that selectively receive messages out of order, and
694	needs a queue. AEMP is event based, queuing messages would serve no	996	therefore needs a queue. AEMP is event based, queuing messages would serve
695	useful purpose. For the same reason the pattern-matching abilities of	997	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	998	of AnyEvent::MP are more limited, as there is little need to be able to
697	filter messages without dequeing them.	999	filter messages without dequeuing them.
698		1000
699	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	1001	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1002	being event-based, while Erlang is process-based.
		1003
		1004	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1005	top of AEMP and Coro threads.
700		1006
701	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1007	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
702		1008
703	Sending messages in Erlang is synchronous and blocks the process (and	1009	Sending messages in Erlang is synchronous and blocks the process until
		1010	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,	1011	need a queue that can overflow). AEMP sends return immediately, connection
705	connection establishment is handled in the background.	1012	establishment is handled in the background.
706		1013
707	=item * Erlang suffers from silent message loss, AEMP does not.	1014	=item * Erlang suffers from silent message loss, AEMP does not.
708		1015
709	Erlang makes few guarantees on messages delivery - messages can get lost	1016	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,	1017	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).	1018	b, and c, and the other side only receives messages a and c).
712		1019
713	AEMP guarantees correct ordering, and the guarantee that after one message	1020	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	1021	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	1022	same port are lost as well, until monitoring raises an error, so there are
716	sequence.	1023	no silent "holes" in the message sequence.
		1024
		1025	If you want your software to be very reliable, you have to cope with
		1026	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
		1027	simply tries to work better in common error cases, such as when a network
		1028	link goes down.
717		1029
718	=item * Erlang can send messages to the wrong port, AEMP does not.	1030	=item * Erlang can send messages to the wrong port, AEMP does not.
719		1031
720	In Erlang it is quite likely that a node that restarts reuses a process ID	1032	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	1033	process ID known to other nodes for a completely different process,
722	destined for that process to end up in an unrelated process.	1034	causing messages destined for that process to end up in an unrelated
		1035	process.
723		1036
724	AEMP never reuses port IDs, so old messages or old port IDs floating	1037	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.	1038	around in the network will not be sent to an unrelated port.
726		1039
727	=item * Erlang uses unprotected connections, AEMP uses secure	1040	=item * Erlang uses unprotected connections, AEMP uses secure
728	authentication and can use TLS.	1041	authentication and can use TLS.
729		1042
…		…
732		1045
733	=item * The AEMP protocol is optimised for both text-based and binary	1046	=item * The AEMP protocol is optimised for both text-based and binary
734	communications.	1047	communications.
735		1048
736	The AEMP protocol, unlike the Erlang protocol, supports both programming	1049	The AEMP protocol, unlike the Erlang protocol, supports both programming
737	language independent text-only protocols (good for debugging) and binary,	1050	language independent text-only protocols (good for debugging), and binary,
738	language-specific serialisers (e.g. Storable).	1051	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1052	used, the protocol is actually completely text-based.
739		1053
740	It has also been carefully designed to be implementable in other languages	1054	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	1055	with a minimum of work while gracefully degrading functionality to make the
742	protocol simple.	1056	protocol simple.
743		1057
744	=item * AEMP has more flexible monitoring options than Erlang.	1058	=item * AEMP has more flexible monitoring options than Erlang.
745		1059
746	In Erlang, you can chose to receive I<all> exit signals as messages	1060	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	1061	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	1062	difficult to implement.
749	Erlang, as one can choose between automatic kill, exit message or callback	1063
750	on a per-process basis.	1064	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1065	between automatic kill, exit message or callback on a per-port basis.
751		1066
752	=item * Erlang tries to hide remote/local connections, AEMP does not.	1067	=item * Erlang tries to hide remote/local connections, AEMP does not.
753		1068
754	Monitoring in Erlang is not an indicator of process death/crashes,	1069	Monitoring in Erlang is not an indicator of process death/crashes, in the
755	as linking is (except linking is unreliable in Erlang).	1070	same way as linking is (except linking is unreliable in Erlang).
756		1071
757	In AEMP, you don't "look up" registered port names or send to named ports	1072	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	1073	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	1074	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	1075	remote port. Since both monitors are local to the node, they are much more
761	more reliable.	1076	reliable (no need for C<spawn_link>).
762		1077
763	This also saves round-trips and avoids sending messages to the wrong port	1078	This also saves round-trips and avoids sending messages to the wrong port
764	(hard to do in Erlang).	1079	(hard to do in Erlang).
765		1080
766	=back	1081	=back
767		1082
768	=head1 RATIONALE	1083	=head1 RATIONALE
769		1084
770	=over 4	1085	=over 4
771		1086
772	=item Why strings for ports and noderefs, why not objects?	1087	=item Why strings for port and node IDs, why not objects?
773		1088
774	We considered "objects", but found that the actual number of methods	1089	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	1090	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	1091	the network frequently, the serialising/deserialising would add lots of
777	overhead, as well as having to keep a proxy object.	1092	overhead, as well as having to keep a proxy object everywhere.
778		1093
779	Strings can easily be printed, easily serialised etc. and need no special	1094	Strings can easily be printed, easily serialised etc. and need no special
780	procedures to be "valid".	1095	procedures to be "valid".
781		1096
782	And a a miniport consists of a single closure stored in a global hash - it	1097	And as a result, a port with just a default receiver consists of a single
783	can't become much cheaper.	1098	code reference stored in a global hash - it can't become much cheaper.
784		1099
785	=item Why favour JSON, why not real serialising format such as Storable?	1100	=item Why favour JSON, why not a real serialising format such as Storable?
786		1101
787	In fact, any AnyEvent::MP node will happily accept Storable as framing	1102	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	1103	format, but currently there is no way to make a node use Storable by
789	default.	1104	default (although all nodes will accept it).
790		1105
791	The default framing protocol is JSON because a) JSON::XS is many times	1106	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	1107	faster for small messages and b) most importantly, after years of
793	experience we found that object serialisation is causing more problems	1108	experience we found that object serialisation is causing more problems
794	than it gains: Just like function calls, objects simply do not travel	1109	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	1110	easily over the network, mostly because they will always be a copy, so you
796	always have to re-think your design.	1111	always have to re-think your design.
797		1112
798	Keeping your messages simple, concentrating on data structures rather than	1113	Keeping your messages simple, concentrating on data structures rather than
799	objects, will keep your messages clean, tidy and efficient.	1114	objects, will keep your messages clean, tidy and efficient.
800		1115
801	=back	1116	=back
802		1117
803	=head1 SEE ALSO	1118	=head1 SEE ALSO
804		1119
		1120	L<AnyEvent::MP::Intro> - a gentle introduction.
		1121
		1122	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1123
		1124	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1125	your applications.
		1126
		1127	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1128
		1129	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1130	all nodes.
		1131
805	L<AnyEvent>.	1132	L<AnyEvent>.
806		1133
807	=head1 AUTHOR	1134	=head1 AUTHOR
808		1135
809	Marc Lehmann <schmorp@schmorp.de>	1136	Marc Lehmann <schmorp@schmorp.de>

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Revision 1.127 by root, Sat Mar 3 20:35:10 2012 UTC