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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.64 by root, Fri Aug 28 00:58:44 2009 UTC vs.
Revision 1.130 by root, Fri Mar 9 17:05:26 2012 UTC

…		…
1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent::MP - multi-processing/message-passing framework	3	AnyEvent::MP - erlang-style multi-processing/message-passing framework
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::MP;	7	use AnyEvent::MP;
8		8
9	$NODE # contains this node's noderef	9	$NODE # contains this node's node ID
10	NODE # returns this node's noderef	10	NODE # returns this node's node ID
11	NODE $port # returns the noderef of the port
12		11
13	$SELF # receiving/own port id in rcv callbacks	12	$SELF # receiving/own port id in rcv callbacks
14		13
15	# initialise the node so it can send/receive messages	14	# initialise the node so it can send/receive messages
16	initialise_node;	15	configure;
17		16
18	# ports are message endpoints	17	# ports are message destinations
19		18
20	# sending messages	19	# sending messages
21	snd $port, type => data...;	20	snd $port, type => data...;
22	snd $port, @msg;	21	snd $port, @msg;
23	snd @msg_with_first_element_being_a_port;	22	snd @msg_with_first_element_being_a_port;
24		23
25	# creating/using ports, the simple way	24	# creating/using ports, the simple way
26	my $simple_port = port { my @msg = @_; 0 };	25	my $simple_port = port { my @msg = @_ };
27		26
28	# creating/using ports, tagged message matching	27	# creating/using ports, tagged message matching
29	my $port = port;	28	my $port = port;
30	rcv $port, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
31	rcv $port, pong => sub { warn "pong received\n"; 0 };	30	rcv $port, pong => sub { warn "pong received\n" };
32		31
33	# create a port on another node	32	# create a port on another node
34	my $port = spawn $node, $initfunc, @initdata;	33	my $port = spawn $node, $initfunc, @initdata;
35		34
		35	# destroy a port again
		36	kil $port; # "normal" kill
		37	kil $port, my_error => "everything is broken"; # error kill
		38
36	# monitoring	39	# monitoring
37	mon $port, $cb->(@msg) # callback is invoked on death	40	mon $port, $cb->(@msg) # callback is invoked on death
38	mon $port, $otherport # kill otherport on abnormal death	41	mon $port, $localport # kill localport on abnormal death
39	mon $port, $otherport, @msg # send message on death	42	mon $port, $localport, @msg # send message on death
		43
		44	# temporarily execute code in port context
		45	peval $port, sub { die "kill the port!" };
		46
		47	# execute callbacks in $SELF port context
		48	my $timer = AE::timer 1, 0, psub {
		49	die "kill the port, delayed";
		50	};
40		51
41	=head1 CURRENT STATUS	52	=head1 CURRENT STATUS
42		53
		54	bin/aemp - stable.
43	AnyEvent::MP - stable API, should work	55	AnyEvent::MP - stable API, should work.
44	AnyEvent::MP::Intro - outdated	56	AnyEvent::MP::Intro - explains most concepts.
45	AnyEvent::MP::Kernel - WIP
46	AnyEvent::MP::Transport - mostly stable	57	AnyEvent::MP::Kernel - mostly stable API.
47		58	AnyEvent::MP::Global - stable API.
48	stay tuned.
49		59
50	=head1 DESCRIPTION	60	=head1 DESCRIPTION
51		61
52	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
53		63
54	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
55	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
56		66
57	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	67	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
58	manual page.	68	manual page and the examples under F<eg/>.
59
60	At the moment, this module family is severly broken and underdocumented,
61	so do not use. This was uploaded mainly to reserve the CPAN namespace -
62	stay tuned!
63		69
64	=head1 CONCEPTS	70	=head1 CONCEPTS
65		71
66	=over 4	72	=over 4
67		73
68	=item port	74	=item port
69		75
70	A port is something you can send messages to (with the C<snd> function).	76	Not to be confused with a TCP port, a "port" is something you can send
		77	messages to (with the C<snd> function).
71		78
72	Ports allow you to register C<rcv> handlers that can match all or just	79	Ports allow you to register C<rcv> handlers that can match all or just
73	some messages. Messages 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 $cb2 = timeout $seconds, $cb[, @args]
		841
		842	=item cal $port, @msg, $callback[, $timeout]
		843
		844	A simple form of RPC - sends a message to the given C<$port> with the
		845	given contents (C<@msg>), but adds a reply port to the message.
		846
		847	The reply port is created temporarily just for the purpose of receiving
		848	the reply, and will be C<kil>ed when no longer needed.
		849
		850	A reply message sent to the port is passed to the C<$callback> as-is.
		851
		852	If an optional time-out (in seconds) is given and it is not C<undef>,
		853	then the callback will be called without any arguments after the time-out
		854	elapsed and the port is C<kil>ed.
		855
		856	If no time-out is given (or it is C<undef>), then the local port will
		857	monitor the remote port instead, so it eventually gets cleaned-up.
		858
		859	Currently this function returns the temporary port, but this "feature"
		860	might go in future versions unless you can make a convincing case that
		861	this is indeed useful for something.
		862
		863	=cut
		864
		865	sub cal(@) {
		866	my $timeout = ref $_[-1] ? undef : pop;
		867	my $cb = pop;
		868
		869	my $port = port {
		870	undef $timeout;
		871	kil $SELF;
		872	&$cb;
		873	};
		874
		875	if (defined $timeout) {
		876	$timeout = AE::timer $timeout, 0, sub {
		877	undef $timeout;
		878	kil $port;
		879	$cb->();
		880	};
		881	} else {
		882	mon $_[0], sub {
		883	kil $port;
		884	$cb->();
		885	};
		886	}
		887
		888	push @_, $port;
		889	&snd;
		890
		891	$port
		892	}
		893
		894	=back
		895
		896	=head1 DISTRIBUTED DATABASE
		897
		898	AnyEvent::MP comes with a simple distributed database. The database will
		899	be mirrored asynchronously at all global nodes. Other nodes bind to one of
		900	the global nodes for their needs.
		901
		902	The database consists of a two-level hash - a hash contains a hash which
		903	contains values.
		904
		905	The top level hash key is called "family", and the second-level hash key
		906	is called "subkey" or simply "key".
		907
		908	The family must be alphanumeric, i.e. start with a letter and consist
		909	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		910	pretty much like Perl module names.
		911
		912	As the family namespace is global, it is recommended to prefix family names
		913	with the name of the application or module using it.
		914
		915	The subkeys must be non-empty strings, with no further restrictions.
		916
		917	The values should preferably be strings, but other perl scalars should
		918	work as well (such as undef, arrays and hashes).
		919
		920	Every database entry is owned by one node - adding the same family/subkey
		921	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		922	but the result might be nondeterministic, i.e. the key might have
		923	different values on different nodes.
		924
		925	Different subkeys in the same family can be owned by different nodes
		926	without problems, and in fact, this is the common method to create worker
		927	pools. For example, a worker port for image scaling might do this:
		928
		929	db_set my_image_scalers => $port;
		930
		931	And clients looking for an image scaler will want to get the
		932	C<my_image_scalers> keys from time to time:
		933
		934	db_keys my_image_scalers => sub {
		935	@ports = @{ $_[0] };
		936	};
		937
		938	Or better yet, they want to monitor the database family, so they always
		939	have a reasonable up-to-date copy:
		940
		941	db_mon my_image_scalers => sub {
		942	@ports = keys %{ $_[0] };
		943	};
		944
		945	In general, you can set or delete single subkeys, but query and monitor
		946	whole families only.
		947
		948	If you feel the need to monitor or query a single subkey, try giving it
		949	it's own family.
		950
		951	=over
		952
		953	=item db_set $family => $subkey [=> $value]
		954
		955	Sets (or replaces) a key to the database - if C<$value> is omitted,
		956	C<undef> is used instead.
		957
		958	=item db_del $family => $subkey...
		959
		960	Deletes one or more subkeys from the database family.
		961
		962	=item $guard = db_reg $family => $subkey [=> $value]
		963
		964	Sets the key on the database and returns a guard. When the guard is
		965	destroyed, the key is deleted from the database. If C<$value> is missing,
		966	then C<undef> is used.
		967
		968	=item db_family $family => $cb->(\%familyhash)
		969
		970	Queries the named database C<$family> and call the callback with the
		971	family represented as a hash. You can keep and freely modify the hash.
		972
		973	=item db_keys $family => $cb->(\@keys)
		974
		975	Same as C<db_family>, except it only queries the family I<subkeys> and passes
		976	them as array reference to the callback.
		977
		978	=item db_values $family => $cb->(\@values)
		979
		980	Same as C<db_family>, except it only queries the family I<values> and passes them
		981	as array reference to the callback.
		982
		983	=item $guard = db_mon $family => $cb->($familyhash, \@added, \@changed, \@deleted)
		984
		985	Creates a monitor on the given database family. Each time a key is set
		986	or or is deleted the callback is called with a hash containing the
		987	database family and three lists of added, changed and deleted subkeys,
		988	respectively. If no keys have changed then the array reference might be
		989	C<undef> or even missing.
		990
		991	The family hash reference and the key arrays belong to AnyEvent::MP and
		992	B<must not be modified or stored> by the callback. When in doubt, make a
		993	copy.
		994
		995	As soon as possible after the monitoring starts, the callback will be
		996	called with the intiial contents of the family, even if it is empty,
		997	i.e. there will always be a timely call to the callback with the current
		998	contents.
		999
		1000	It is possible that the callback is called with a change event even though
		1001	the subkey is already present and the value has not changed.
		1002
		1003	The monitoring stops when the guard object is destroyed.
		1004
		1005	Example: on every change to the family "mygroup", print out all keys.
		1006
		1007	my $guard = db_mon mygroup => sub {
		1008	my ($family, $a, $c, $d) = @_;
		1009	print "mygroup members: ", (join " ", keys %$family), "\n";
		1010	};
		1011
		1012	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1013
		1014	my $guard; $guard = db_mon My::Module::workers => sub {
		1015	my ($family, $a, $c, $d) = @_;
		1016	return unless %$family;
		1017	undef $guard;
		1018	print "My::Module::workers now nonempty\n";
		1019	};
		1020
		1021	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		1022
		1023	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		1024	my ($family, $a, $c, $d) = @_;
		1025
		1026	print "+$_=$family->{$_}\n" for @$a;
		1027	print "*$_=$family->{$_}\n" for @$c;
		1028	print "-$_=$family->{$_}\n" for @$d;
		1029	};
		1030
		1031	=cut
		1032
652	=back	1033	=back
653		1034
654	=head1 AnyEvent::MP vs. Distributed Erlang	1035	=head1 AnyEvent::MP vs. Distributed Erlang
655		1036
656	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	1037	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
657	== aemp node, Erlang process == aemp port), so many of the documents and	1038	== aemp node, Erlang process == aemp port), so many of the documents and
658	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	1039	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
659	sample:	1040	sample:
660		1041
661	http://www.Erlang.se/doc/programming_rules.shtml	1042	http://www.erlang.se/doc/programming_rules.shtml
662	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	1043	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
663	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	1044	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
664	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	1045	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
665		1046
666	Despite the similarities, there are also some important differences:	1047	Despite the similarities, there are also some important differences:
667		1048
668	=over 4	1049	=over 4
669		1050
670	=item * Node references contain the recipe on how to contact them.	1051	=item * Node IDs are arbitrary strings in AEMP.
671		1052
672	Erlang relies on special naming and DNS to work everywhere in the	1053	Erlang relies on special naming and DNS to work everywhere in the same
673	same way. AEMP relies on each node knowing it's own address(es), with	1054	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
674	convenience functionality.	1055	configuration or DNS), and possibly the addresses of some seed nodes, but
675		1056	will otherwise discover other nodes (and their IDs) itself.
676	This means that AEMP requires a less tightly controlled environment at the
677	cost of longer node references and a slightly higher management overhead.
678		1057
679	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP	1058	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
680	uses "local ports are like remote ports".	1059	uses "local ports are like remote ports".
681		1060
682	The failure modes for local ports are quite different (runtime errors	1061	The failure modes for local ports are quite different (runtime errors
…		…
691	ports being the special case/exception, where transport errors cannot	1070	ports being the special case/exception, where transport errors cannot
692	occur.	1071	occur.
693		1072
694	=item * Erlang uses processes and a mailbox, AEMP does not queue.	1073	=item * Erlang uses processes and a mailbox, AEMP does not queue.
695		1074
696	Erlang uses processes that selectively receive messages, and therefore	1075	Erlang uses processes that selectively receive messages out of order, and
697	needs a queue. AEMP is event based, queuing messages would serve no	1076	therefore needs a queue. AEMP is event based, queuing messages would serve
698	useful purpose. For the same reason the pattern-matching abilities of	1077	no useful purpose. For the same reason the pattern-matching abilities
699	AnyEvent::MP are more limited, as there is little need to be able to	1078	of AnyEvent::MP are more limited, as there is little need to be able to
700	filter messages without dequeing them.	1079	filter messages without dequeuing them.
701		1080
702	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	1081	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1082	being event-based, while Erlang is process-based.
		1083
		1084	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1085	top of AEMP and Coro threads.
703		1086
704	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1087	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
705		1088
706	Sending messages in Erlang is synchronous and blocks the process (and	1089	Sending messages in Erlang is synchronous and blocks the process until
		1090	a conenction has been established and the message sent (and so does not
707	so does not need a queue that can overflow). AEMP sends are immediate,	1091	need a queue that can overflow). AEMP sends return immediately, connection
708	connection establishment is handled in the background.	1092	establishment is handled in the background.
709		1093
710	=item * Erlang suffers from silent message loss, AEMP does not.	1094	=item * Erlang suffers from silent message loss, AEMP does not.
711		1095
712	Erlang makes few guarantees on messages delivery - messages can get lost	1096	Erlang implements few guarantees on messages delivery - messages can get
713	without any of the processes realising it (i.e. you send messages a, b,	1097	lost without any of the processes realising it (i.e. you send messages a,
714	and c, and the other side only receives messages a and c).	1098	b, and c, and the other side only receives messages a and c).
715		1099
716	AEMP guarantees correct ordering, and the guarantee that there are no	1100	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1101	guarantee that after one message is lost, all following ones sent to the
		1102	same port are lost as well, until monitoring raises an error, so there are
717	holes in the message sequence.	1103	no silent "holes" in the message sequence.
718		1104
719	=item * In Erlang, processes can be declared dead and later be found to be	1105	If you want your software to be very reliable, you have to cope with
720	alive.	1106	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
721		1107	simply tries to work better in common error cases, such as when a network
722	In Erlang it can happen that a monitored process is declared dead and	1108	link goes down.
723	linked processes get killed, but later it turns out that the process is
724	still alive - and can receive messages.
725
726	In AEMP, when port monitoring detects a port as dead, then that port will
727	eventually be killed - it cannot happen that a node detects a port as dead
728	and then later sends messages to it, finding it is still alive.
729		1109
730	=item * Erlang can send messages to the wrong port, AEMP does not.	1110	=item * Erlang can send messages to the wrong port, AEMP does not.
731		1111
732	In Erlang it is quite likely that a node that restarts reuses a process ID	1112	In Erlang it is quite likely that a node that restarts reuses an Erlang
733	known to other nodes for a completely different process, causing messages	1113	process ID known to other nodes for a completely different process,
734	destined for that process to end up in an unrelated process.	1114	causing messages destined for that process to end up in an unrelated
		1115	process.
735		1116
736	AEMP never reuses port IDs, so old messages or old port IDs floating	1117	AEMP does not reuse port IDs, so old messages or old port IDs floating
737	around in the network will not be sent to an unrelated port.	1118	around in the network will not be sent to an unrelated port.
738		1119
739	=item * Erlang uses unprotected connections, AEMP uses secure	1120	=item * Erlang uses unprotected connections, AEMP uses secure
740	authentication and can use TLS.	1121	authentication and can use TLS.
741		1122
742	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1123	AEMP can use a proven protocol - TLS - to protect connections and
743	securely authenticate nodes.	1124	securely authenticate nodes.
744		1125
745	=item * The AEMP protocol is optimised for both text-based and binary	1126	=item * The AEMP protocol is optimised for both text-based and binary
746	communications.	1127	communications.
747		1128
748	The AEMP protocol, unlike the Erlang protocol, supports both	1129	The AEMP protocol, unlike the Erlang protocol, supports both programming
749	language-independent text-only protocols (good for debugging) and binary,	1130	language independent text-only protocols (good for debugging), and binary,
750	language-specific serialisers (e.g. Storable).	1131	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1132	used, the protocol is actually completely text-based.
751		1133
752	It has also been carefully designed to be implementable in other languages	1134	It has also been carefully designed to be implementable in other languages
753	with a minimum of work while gracefully degrading fucntionality to make the	1135	with a minimum of work while gracefully degrading functionality to make the
754	protocol simple.	1136	protocol simple.
755		1137
756	=item * AEMP has more flexible monitoring options than Erlang.	1138	=item * AEMP has more flexible monitoring options than Erlang.
757		1139
758	In Erlang, you can chose to receive I<all> exit signals as messages	1140	In Erlang, you can chose to receive I<all> exit signals as messages or
759	or I<none>, there is no in-between, so monitoring single processes is	1141	I<none>, there is no in-between, so monitoring single Erlang processes is
760	difficult to implement. Monitoring in AEMP is more flexible than in	1142	difficult to implement.
761	Erlang, as one can choose between automatic kill, exit message or callback	1143
762	on a per-process basis.	1144	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1145	between automatic kill, exit message or callback on a per-port basis.
763		1146
764	=item * Erlang tries to hide remote/local connections, AEMP does not.	1147	=item * Erlang tries to hide remote/local connections, AEMP does not.
765		1148
766	Monitoring in Erlang is not an indicator of process death/crashes,	1149	Monitoring in Erlang is not an indicator of process death/crashes, in the
767	as linking is (except linking is unreliable in Erlang).	1150	same way as linking is (except linking is unreliable in Erlang).
768		1151
769	In AEMP, you don't "look up" registered port names or send to named ports	1152	In AEMP, you don't "look up" registered port names or send to named ports
770	that might or might not be persistent. Instead, you normally spawn a port	1153	that might or might not be persistent. Instead, you normally spawn a port
771	on the remote node. The init function monitors the you, and you monitor	1154	on the remote node. The init function monitors you, and you monitor the
772	the remote port. Since both monitors are local to the node, they are much	1155	remote port. Since both monitors are local to the node, they are much more
773	more reliable.	1156	reliable (no need for C<spawn_link>).
774		1157
775	This also saves round-trips and avoids sending messages to the wrong port	1158	This also saves round-trips and avoids sending messages to the wrong port
776	(hard to do in Erlang).	1159	(hard to do in Erlang).
777		1160
778	=back	1161	=back
779		1162
780	=head1 RATIONALE	1163	=head1 RATIONALE
781		1164
782	=over 4	1165	=over 4
783		1166
784	=item Why strings for ports and noderefs, why not objects?	1167	=item Why strings for port and node IDs, why not objects?
785		1168
786	We considered "objects", but found that the actual number of methods	1169	We considered "objects", but found that the actual number of methods
787	thatc an be called are very low. Since port IDs and noderefs travel over	1170	that can be called are quite low. Since port and node IDs travel over
788	the network frequently, the serialising/deserialising would add lots of	1171	the network frequently, the serialising/deserialising would add lots of
789	overhead, as well as having to keep a proxy object.	1172	overhead, as well as having to keep a proxy object everywhere.
790		1173
791	Strings can easily be printed, easily serialised etc. and need no special	1174	Strings can easily be printed, easily serialised etc. and need no special
792	procedures to be "valid".	1175	procedures to be "valid".
793		1176
794	And a a miniport consists of a single closure stored in a global hash - it	1177	And as a result, a port with just a default receiver consists of a single
795	can't become much cheaper.	1178	code reference stored in a global hash - it can't become much cheaper.
796		1179
797	=item Why favour JSON, why not real serialising format such as Storable?	1180	=item Why favour JSON, why not a real serialising format such as Storable?
798		1181
799	In fact, any AnyEvent::MP node will happily accept Storable as framing	1182	In fact, any AnyEvent::MP node will happily accept Storable as framing
800	format, but currently there is no way to make a node use Storable by	1183	format, but currently there is no way to make a node use Storable by
801	default.	1184	default (although all nodes will accept it).
802		1185
803	The default framing protocol is JSON because a) JSON::XS is many times	1186	The default framing protocol is JSON because a) JSON::XS is many times
804	faster for small messages and b) most importantly, after years of	1187	faster for small messages and b) most importantly, after years of
805	experience we found that object serialisation is causing more problems	1188	experience we found that object serialisation is causing more problems
806	than it gains: Just like function calls, objects simply do not travel	1189	than it solves: Just like function calls, objects simply do not travel
807	easily over the network, mostly because they will always be a copy, so you	1190	easily over the network, mostly because they will always be a copy, so you
808	always have to re-think your design.	1191	always have to re-think your design.
809		1192
810	Keeping your messages simple, concentrating on data structures rather than	1193	Keeping your messages simple, concentrating on data structures rather than
811	objects, will keep your messages clean, tidy and efficient.	1194	objects, will keep your messages clean, tidy and efficient.
812		1195
813	=back	1196	=back
814		1197
815	=head1 SEE ALSO	1198	=head1 SEE ALSO
816		1199
		1200	L<AnyEvent::MP::Intro> - a gentle introduction.
		1201
		1202	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1203
		1204	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1205	your applications.
		1206
		1207	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1208
		1209	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1210	all nodes.
		1211
817	L<AnyEvent>.	1212	L<AnyEvent>.
818		1213
819	=head1 AUTHOR	1214	=head1 AUTHOR
820		1215
821	Marc Lehmann <schmorp@schmorp.de>	1216	Marc Lehmann <schmorp@schmorp.de>

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