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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.62 by root, Thu Aug 27 07:12:48 2009 UTC vs.
Revision 1.129 by root, Thu Mar 8 21:37:51 2012 UTC

…		…
1	=head1 NAME	1	=head1 NAME
2		2
3	AnyEvent::MP - multi-processing/message-passing framework	3	AnyEvent::MP - erlang-style multi-processing/message-passing framework
4		4
5	=head1 SYNOPSIS	5	=head1 SYNOPSIS
6		6
7	use AnyEvent::MP;	7	use AnyEvent::MP;
8		8
9	$NODE # contains this node's noderef	9	$NODE # contains this node's node ID
10	NODE # returns this node's noderef	10	NODE # returns this node's node ID
11	NODE $port # returns the noderef of the port
12		11
13	$SELF # receiving/own port id in rcv callbacks	12	$SELF # receiving/own port id in rcv callbacks
14		13
15	# initialise the node so it can send/receive messages	14	# initialise the node so it can send/receive messages
16	initialise_node; # -OR-	15	configure;
17	initialise_node "localhost:4040"; # -OR-
18	initialise_node "slave/", "localhost:4040"
19		16
20	# ports are message endpoints	17	# ports are message destinations
21		18
22	# sending messages	19	# sending messages
23	snd $port, type => data...;	20	snd $port, type => data...;
24	snd $port, @msg;	21	snd $port, @msg;
25	snd @msg_with_first_element_being_a_port;	22	snd @msg_with_first_element_being_a_port;
26		23
27	# creating/using ports, the simple way	24	# creating/using ports, the simple way
28	my $simple_port = port { my @msg = @_; 0 };	25	my $simple_port = port { my @msg = @_ };
29		26
30	# creating/using ports, tagged message matching	27	# creating/using ports, tagged message matching
31	my $port = port;	28	my $port = port;
32	rcv $port, ping => sub { snd $_[0], "pong"; 0 };	29	rcv $port, ping => sub { snd $_[0], "pong" };
33	rcv $port, pong => sub { warn "pong received\n"; 0 };	30	rcv $port, pong => sub { warn "pong received\n" };
34		31
35	# create a port on another node	32	# create a port on another node
36	my $port = spawn $node, $initfunc, @initdata;	33	my $port = spawn $node, $initfunc, @initdata;
37		34
		35	# destroy a port again
		36	kil $port; # "normal" kill
		37	kil $port, my_error => "everything is broken"; # error kill
		38
38	# monitoring	39	# monitoring
39	mon $port, $cb->(@msg) # callback is invoked on death	40	mon $port, $cb->(@msg) # callback is invoked on death
40	mon $port, $otherport # kill otherport on abnormal death	41	mon $port, $localport # kill localport on abnormal death
41	mon $port, $otherport, @msg # send message on death	42	mon $port, $localport, @msg # send message on death
		43
		44	# temporarily execute code in port context
		45	peval $port, sub { die "kill the port!" };
		46
		47	# execute callbacks in $SELF port context
		48	my $timer = AE::timer 1, 0, psub {
		49	die "kill the port, delayed";
		50	};
42		51
43	=head1 CURRENT STATUS	52	=head1 CURRENT STATUS
44		53
		54	bin/aemp - stable.
45	AnyEvent::MP - stable API, should work	55	AnyEvent::MP - stable API, should work.
46	AnyEvent::MP::Intro - outdated	56	AnyEvent::MP::Intro - explains most concepts.
47	AnyEvent::MP::Kernel - WIP
48	AnyEvent::MP::Transport - mostly stable	57	AnyEvent::MP::Kernel - mostly stable API.
49		58	AnyEvent::MP::Global - stable API.
50	stay tuned.
51		59
52	=head1 DESCRIPTION	60	=head1 DESCRIPTION
53		61
54	This module (-family) implements a simple message passing framework.	62	This module (-family) implements a simple message passing framework.
55		63
56	Despite its simplicity, you can securely message other processes running	64	Despite its simplicity, you can securely message other processes running
57	on the same or other hosts.	65	on the same or other hosts, and you can supervise entities remotely.
58		66
59	For an introduction to this module family, see the L<AnyEvent::MP::Intro>	67	For an introduction to this module family, see the L<AnyEvent::MP::Intro>
60	manual page.	68	manual page and the examples under F<eg/>.
61
62	At the moment, this module family is severly broken and underdocumented,
63	so do not use. This was uploaded mainly to reserve the CPAN namespace -
64	stay tuned!
65		69
66	=head1 CONCEPTS	70	=head1 CONCEPTS
67		71
68	=over 4	72	=over 4
69		73
70	=item port	74	=item port
71		75
72	A port is something you can send messages to (with the C<snd> function).	76	Not to be confused with a TCP port, a "port" is something you can send
		77	messages to (with the C<snd> function).
73		78
74	Ports allow you to register C<rcv> handlers that can match all or just	79	Ports allow you to register C<rcv> handlers that can match all or just
75	some messages. Messages will not be queued.	80	some messages. Messages send to ports will not be queued, regardless of
		81	anything was listening for them or not.
76		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
77	=item port id - C<noderef#portname>	85	=item port ID - C<nodeid#portname>
78		86
79	A port ID is the concatenation of a noderef, a hash-mark (C<#>) as	87	A port ID is the concatenation of a node ID, a hash-mark (C<#>)
80	separator, and a port name (a printable string of unspecified format). An	88	as separator, and a port name (a printable string of unspecified
81	exception is the the node port, whose ID is identical to its node	89	format created by AnyEvent::MP).
82	reference.
83		90
84	=item node	91	=item node
85		92
86	A node is a single process containing at least one port - the node port,	93	A node is a single process containing at least one port - the node port,
87	which provides nodes to manage each other remotely, and to create new	94	which enables nodes to manage each other remotely, and to create new
88	ports.	95	ports.
89		96
90	Nodes are either private (single-process only), slaves (can only talk to	97	Nodes are either public (have one or more listening ports) or private
91	public nodes, but do not need an open port) or public nodes (connectable	98	(no listening ports). Private nodes cannot talk to other private nodes
92	from any other node).	99	currently, but all nodes can talk to public nodes.
93		100
94	=item noderef - C<host:port,host:port...>, C<id@noderef>, C<id>	101	Nodes is represented by (printable) strings called "node IDs".
95		102
96	A node reference is a string that either simply identifies the node (for	103	=item node ID - C<[A-Za-z0-9_\-.:]*>
97	private and slave nodes), or contains a recipe on how to reach a given
98	node (for public nodes).
99		104
100	This recipe is simply a comma-separated list of C<address:port> pairs (for	105	A node ID is a string that uniquely identifies the node within a
101	TCP/IP, other protocols might look different).	106	network. Depending on the configuration used, node IDs can look like a
		107	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
		108	doesn't interpret node IDs in any way except to uniquely identify a node.
102		109
103	Node references come in two flavours: resolved (containing only numerical	110	=item binds - C<ip:port>
104	addresses) or unresolved (where hostnames are used instead of addresses).
105		111
106	Before using an unresolved node reference in a message you first have to	112	Nodes can only talk to each other by creating some kind of connection to
107	resolve it.	113	each other. To do this, nodes should listen on one or more local transport
		114	endpoints - binds.
		115
		116	Currently, only standard C<ip:port> specifications can be used, which
		117	specify TCP ports to listen on. So a bind is basically just a tcp socket
		118	in listening mode thta accepts conenctions form other nodes.
		119
		120	=item seed nodes
		121
		122	When a node starts, it knows nothing about the network it is in - it
		123	needs to connect to at least one other node that is already in the
		124	network. These other nodes are called "seed nodes".
		125
		126	Seed nodes themselves are not special - they are seed nodes only because
		127	some other node I<uses> them as such, but any node can be used as seed
		128	node for other nodes, and eahc node cna use a different set of seed nodes.
		129
		130	In addition to discovering the network, seed nodes are also used to
		131	maintain the network - all nodes using the same seed node form are part of
		132	the same network. If a network is split into multiple subnets because e.g.
		133	the network link between the parts goes down, then using the same seed
		134	nodes for all nodes ensures that eventually the subnets get merged again.
		135
		136	Seed nodes are expected to be long-running, and at least one seed node
		137	should always be available. They should also be relatively responsive - a
		138	seed node that blocks for long periods will slow down everybody else.
		139
		140	For small networks, it's best if every node uses the same set of seed
		141	nodes. For large networks, it can be useful to specify "regional" seed
		142	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		143	each other. What's important is that all seed nodes connections form a
		144	complete graph, so that the network cannot split into separate subnets
		145	forever.
		146
		147	Seed nodes are represented by seed IDs.
		148
		149	=item seed IDs - C<host:port>
		150
		151	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
		152	TCP port) of nodes that should be used as seed nodes.
		153
		154	=item global nodes
		155
		156	An AEMP network needs a discovery service - nodes need to know how to
		157	connect to other nodes they only know by name. In addition, AEMP offers a
		158	distributed "group database", which maps group names to a list of strings
		159	- for example, to register worker ports.
		160
		161	A network needs at least one global node to work, and allows every node to
		162	be a global node.
		163
		164	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		165	node and tries to keep connections to all other nodes. So while it can
		166	make sense to make every node "global" in small networks, it usually makes
		167	sense to only make seed nodes into global nodes in large networks (nodes
		168	keep connections to seed nodes and global nodes, so makign them the same
		169	reduces overhead).
108		170
109	=back	171	=back
110		172
111	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
112		174
114		176
115	=cut	177	=cut
116		178
117	package AnyEvent::MP;	179	package AnyEvent::MP;
118		180
		181	use AnyEvent::MP::Config ();
119	use AnyEvent::MP::Kernel;	182	use AnyEvent::MP::Kernel;
		183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
120		184
121	use common::sense;	185	use common::sense;
122		186
123	use Carp ();	187	use Carp ();
124		188
125	use AE ();	189	use AE ();
		190	use Guard ();
126		191
127	use base "Exporter";	192	use base "Exporter";
128		193
129	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
130		195
131	our @EXPORT = qw(	196	our @EXPORT = qw(
132	NODE $NODE *SELF node_of after	197	NODE $NODE *SELF node_of after
133	resolve_node initialise_node	198	configure
134	snd rcv mon mon_guard kil reg psub spawn	199	snd rcv mon mon_guard kil psub peval spawn cal
135	port	200	port
		201	db_set db_del db_reg
		202	db_mon db_family db_keys db_values
136	);	203	);
137		204
138	our $SELF;	205	our $SELF;
139		206
140	sub _self_die() {	207	sub _self_die() {
…		…
143	kil $SELF, die => $msg;	210	kil $SELF, die => $msg;
144	}	211	}
145		212
146	=item $thisnode = NODE / $NODE	213	=item $thisnode = NODE / $NODE
147		214
148	The C<NODE> function returns, and the C<$NODE> variable contains the	215	The C<NODE> function returns, and the C<$NODE> variable contains, the node
149	noderef of the local node. The value is initialised by a call to	216	ID of the node running in the current process. This value is initialised by
150	C<initialise_node>.	217	a call to C<configure>.
151		218
152	=item $noderef = node_of $port	219	=item $nodeid = node_of $port
153		220
154	Extracts and returns the noderef from a port ID or a noderef.	221	Extracts and returns the node ID from a port ID or a node ID.
155		222
156	=item initialise_node $noderef, $seednode, $seednode...	223	=item configure $profile, key => value...
157		224
158	=item initialise_node "slave/", $master, $master...	225	=item configure key => value...
159		226
160	Before a node can talk to other nodes on the network it has to initialise	227	Before a node can talk to other nodes on the network (i.e. enter
161	itself - the minimum a node needs to know is it's own name, and optionally	228	"distributed mode") it has to configure itself - the minimum a node needs
162	it should know the noderefs of some other nodes in the network.	229	to know is its own name, and optionally it should know the addresses of
		230	some other nodes in the network to discover other nodes.
163		231
164	This function initialises a node - it must be called exactly once (or	232	This function configures a node - it must be called exactly once (or
165	never) before calling other AnyEvent::MP functions.	233	never) before calling other AnyEvent::MP functions.
166		234
167	All arguments (optionally except for the first) are noderefs, which can be	235	The key/value pairs are basically the same ones as documented for the
168	either resolved or unresolved.	236	F<aemp> command line utility (sans the set/del prefix), with these additions:
169
170	The first argument will be looked up in the configuration database first
171	(if it is C<undef> then the current nodename will be used instead) to find
172	the relevant configuration profile (see L<aemp>). If none is found then
173	the default configuration is used. The configuration supplies additional
174	seed/master nodes and can override the actual noderef.
175
176	There are two types of networked nodes, public nodes and slave nodes:
177		237
178	=over 4	238	=over 4
179		239
180	=item public nodes	240	=item norc => $boolean (default false)
181		241
182	For public nodes, C<$noderef> (supplied either directly to	242	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
183	C<initialise_node> or indirectly via a profile or the nodename) must be a	243	be consulted - all configuraiton options must be specified in the
184	noderef (possibly unresolved, in which case it will be resolved).	244	C<configure> call.
185		245
186	After resolving, the node will bind itself on all endpoints.	246	=item force => $boolean (default false)
187		247
188	=item slave nodes	248	IF true, then the values specified in the C<configure> will take
		249	precedence over any values configured via the rc file. The default is for
		250	the rc file to override any options specified in the program.
189		251
190	When the C<$noderef> (either as given or overriden by the config file)	252	=item secure => $pass->($nodeid)
191	is the special string C<slave/>, then the node will become a slave
192	node. Slave nodes cannot be contacted from outside, and cannot talk to
193	each other (at least in this version of AnyEvent::MP).
194		253
195	Slave nodes work by creating connections to all public nodes, using the	254	In addition to specifying a boolean, you can specify a code reference that
196	L<AnyEvent::MP::Global> service.	255	is called for every 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.
197		259
198	=back	260	=back
199		261
200	After initialising itself, the node will connect to all additional
201	C<$seednodes> that are specified diretcly or via a profile. Seednodes are
202	optional and can be used to quickly bootstrap the node into an existing
203	network.
204
205	All the seednodes will also be specially marked to automatically retry
206	connecting to them indefinitely, so make sure that seednodes are really
207	reliable and up (this might also change in the future).
208
209	Example: become a public node listening on the guessed noderef, or the one
210	specified via C<aemp> for the current node. This should be the most common
211	form of invocation for "daemon"-type nodes.
212
213	initialise_node;
214
215	Example: become a slave node to any of the the seednodes specified via
216	C<aemp>. This form is often used for commandline clients.
217
218	initialise_node "slave/";
219
220	Example: become a public node, and try to contact some well-known master
221	servers to become part of the network.
222
223	initialise_node undef, "master1", "master2";
224
225	Example: become a public node listening on port C<4041>.
226
227	initialise_node 4041;
228
229	Example: become a public node, only visible on localhost port 4044.
230
231	initialise_node "localhost:4044";
232
233	=item $cv = resolve_node $noderef
234
235	Takes an unresolved node reference that may contain hostnames and
236	abbreviated IDs, resolves all of them and returns a resolved node
237	reference.
238
239	In addition to C<address:port> pairs allowed in resolved noderefs, the
240	following forms are supported:
241
242	=over 4	262	=over 4
243		263
244	=item the empty string	264	=item step 1, gathering configuration from profiles
245		265
246	An empty-string component gets resolved as if the default port (4040) was	266	The function first looks up a profile in the aemp configuration (see the
247	specified.	267	L<aemp> commandline utility). The profile name can be specified via the
		268	named C<profile> parameter or can simply be the first parameter). If it is
		269	missing, then the nodename (F<uname -n>) will be used as profile name.
248		270
249	=item naked port numbers (e.g. C<1234>)	271	The profile data is then gathered as follows:
250		272
251	These are resolved by prepending the local nodename and a colon, to be	273	First, all remaining key => value pairs (all of which are conveniently
252	further resolved.	274	undocumented at the moment) will be interpreted as configuration
		275	data. Then they will be overwritten by any values specified in the global
		276	default configuration (see the F<aemp> utility), then the chain of
		277	profiles chosen by the profile name (and any C<parent> attributes).
253		278
254	=item hostnames (e.g. C<localhost:1234>, C<localhost>)	279	That means that the values specified in the profile have highest priority
		280	and the values specified directly via C<configure> have lowest priority,
		281	and can only be used to specify defaults.
255		282
256	These are resolved by using AnyEvent::DNS to resolve them, optionally	283	If the profile specifies a node ID, then this will become the node ID of
257	looking up SRV records for the C<aemp=4040> port, if no port was	284	this process. If not, then the profile name will be used as node ID, with
258	specified.	285	a unique randoms tring (C</%u>) appended.
		286
		287	The node ID can contain some C<%> sequences that are expanded: C<%n>
		288	is expanded to the local nodename, C<%u> is replaced by a random
		289	strign to make the node unique. For example, the F<aemp> commandline
		290	utility uses C<aemp/%n/%u> as nodename, which might expand to
		291	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
		292
		293	=item step 2, bind listener sockets
		294
		295	The next step is to look up the binds in the profile, followed by binding
		296	aemp protocol listeners on all binds specified (it is possible and valid
		297	to have no binds, meaning that the node cannot be contacted form the
		298	outside. This means the node cannot talk to other nodes that also have no
		299	binds, but it can still talk to all "normal" nodes).
		300
		301	If the profile does not specify a binds list, then a default of C<*> is
		302	used, meaning the node will bind on a dynamically-assigned port on every
		303	local IP address it finds.
		304
		305	=item step 3, connect to seed nodes
		306
		307	As the last step, the seed ID list from the profile is passed to the
		308	L<AnyEvent::MP::Global> module, which will then use it to keep
		309	connectivity with at least one node at any point in time.
259		310
260	=back	311	=back
		312
		313	Example: become a distributed node using the local node name as profile.
		314	This should be the most common form of invocation for "daemon"-type nodes.
		315
		316	configure
		317
		318	Example: become a semi-anonymous node. This form is often used for
		319	commandline clients.
		320
		321	configure nodeid => "myscript/%n/%u";
		322
		323	Example: configure a node using a profile called seed, which is suitable
		324	for a seed node as it binds on all local addresses on a fixed port (4040,
		325	customary for aemp).
		326
		327	# use the aemp commandline utility
		328	# aemp profile seed binds '*:4040'
		329
		330	# then use it
		331	configure profile => "seed";
		332
		333	# or simply use aemp from the shell again:
		334	# aemp run profile seed
		335
		336	# or provide a nicer-to-remember nodeid
		337	# aemp run profile seed nodeid "$(hostname)"
261		338
262	=item $SELF	339	=item $SELF
263		340
264	Contains the current port id while executing C<rcv> callbacks or C<psub>	341	Contains the current port id while executing C<rcv> callbacks or C<psub>
265	blocks.	342	blocks.
266		343
267	=item SELF, %SELF, @SELF...	344	=item *SELF, SELF, %SELF, @SELF...
268		345
269	Due to some quirks in how perl exports variables, it is impossible to	346	Due to some quirks in how perl exports variables, it is impossible to
270	just export C<$SELF>, all the symbols called C<SELF> are exported by this	347	just export C<$SELF>, all the symbols named C<SELF> are exported by this
271	module, but only C<$SELF> is currently used.	348	module, but only C<$SELF> is currently used.
272		349
273	=item snd $port, type => @data	350	=item snd $port, type => @data
274		351
275	=item snd $port, @msg	352	=item snd $port, @msg
276		353
277	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
278	a local or a remote port, and must be a port ID.	355	local or a remote port, and must be a port ID.
279		356
280	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
281	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
282	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.
283		361
284	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
285	function: modifying any argument is not allowed and can cause many	363	function: modifying any argument (or values referenced by them) is
286	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.
287		368
288	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
289	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
290	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
291	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
292	node, anything can be passed.	373	node, anything can be passed. Best rely only on the common denominator of
		374	these.
293		375
294	=item $local_port = port	376	=item $local_port = port
295		377
296	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
297	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.
…		…
321	sub _kilme {	403	sub _kilme {
322	die "received message on port without callback";	404	die "received message on port without callback";
323	}	405	}
324		406
325	sub port(;&) {	407	sub port(;&) {
326	my $id = "$UNIQ." . $ID++;	408	my $id = $UNIQ . ++$ID;
327	my $port = "$NODE#$id";	409	my $port = "$NODE#$id";
328		410
329	rcv $port, shift \|\| \&_kilme;	411	rcv $port, shift \|\| \&_kilme;
330		412
331	$port	413	$port
…		…
370	msg1 => sub { ... },	452	msg1 => sub { ... },
371	...	453	...
372	;	454	;
373		455
374	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
375	(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.
376		458
377	rcv $port, $otherport => sub {	459	rcv $port, $otherport => sub {
378	my @reply = @_;	460	my @reply = @_;
379		461
380	rcv $SELF, $otherport;	462	rcv $SELF, $otherport;
…		…
382		464
383	=cut	465	=cut
384		466
385	sub rcv($@) {	467	sub rcv($@) {
386	my $port = shift;	468	my $port = shift;
387	my ($noderef, $portid) = split /#/, $port, 2;	469	my ($nodeid, $portid) = split /#/, $port, 2;
388		470
389	$NODE{$noderef} == $NODE{""}	471	$NODE{$nodeid} == $NODE{""}
390	or Carp::croak "$port: rcv can only be called on local ports, caught";	472	or Carp::croak "$port: rcv can only be called on local ports, caught";
391		473
392	while (@_) {	474	while (@_) {
393	if (ref $_[0]) {	475	if (ref $_[0]) {
394	if (my $self = $PORT_DATA{$portid}) {	476	if (my $self = $PORT_DATA{$portid}) {
395	"AnyEvent::MP::Port" eq ref $self	477	"AnyEvent::MP::Port" eq ref $self
396	or Carp::croak "$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";
397		479
398	$self->[2] = shift;	480	$self->[0] = shift;
399	} else {	481	} else {
400	my $cb = shift;	482	my $cb = shift;
401	$PORT{$portid} = sub {	483	$PORT{$portid} = sub {
402	local $SELF = $port;	484	local $SELF = $port;
403	eval { &$cb }; _self_die if $@;	485	eval { &$cb }; _self_die if $@;
404	};	486	};
405	}	487	}
406	} elsif (defined $_[0]) {	488	} elsif (defined $_[0]) {
407	my $self = $PORT_DATA{$portid} \|\|= do {	489	my $self = $PORT_DATA{$portid} \|\|= do {
408	my $self = bless [$PORT{$port} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";	490	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
409		491
410	$PORT{$portid} = sub {	492	$PORT{$portid} = sub {
411	local $SELF = $port;	493	local $SELF = $port;
412		494
413	if (my $cb = $self->[1]{$_[0]}) {	495	if (my $cb = $self->[1]{$_[0]}) {
…		…
435	}	517	}
436		518
437	$port	519	$port
438	}	520	}
439		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
440	=item $closure = psub { BLOCK }	559	=item $closure = psub { BLOCK }
441		560
442	Remembers C<$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
443	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>
444	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 $SELF, sub {
		566	BLOCK }, @_ } >>.
445		567
446	This is useful when you register callbacks from C<rcv> callbacks:	568	This is useful when you register callbacks from C<rcv> callbacks:
447		569
448	rcv delayed_reply => sub {	570	rcv delayed_reply => sub {
449	my ($delay, @reply) = @_;	571	my ($delay, @reply) = @_;
…		…
473	$res	595	$res
474	}	596	}
475	}	597	}
476	}	598	}
477		599
478	=item $guard = mon $port, $cb->(@reason)	600	=item $guard = mon $port, $cb->(@reason) # call $cb when $port dies
479		601
480	=item $guard = mon $port, $rcvport	602	=item $guard = mon $port, $rcvport # kill $rcvport when $port dies
481		603
482	=item $guard = mon $port	604	=item $guard = mon $port # kill $SELF when $port dies
483		605
484	=item $guard = mon $port, $rcvport, @msg	606	=item $guard = mon $port, $rcvport, @msg # send a message when $port dies
485		607
486	Monitor the given port and do something when the port is killed or	608	Monitor the given port and do something when the port is killed or
487	messages to it were lost, and optionally return a guard that can be used	609	messages to it were lost, and optionally return a guard that can be used
488	to stop monitoring again.	610	to stop monitoring again.
489
490	C<mon> effectively guarantees that, in the absence of hardware failures,
491	that after starting the monitor, either all messages sent to the port
492	will arrive, or the monitoring action will be invoked after possible
493	message loss has been detected. No messages will be lost "in between"
494	(after the first lost message no further messages will be received by the
495	port). After the monitoring action was invoked, further messages might get
496	delivered again.
497
498	Note that monitoring-actions are one-shot: once released, they are removed
499	and will not trigger again.
500		611
501	In the first form (callback), the callback is simply called with any	612	In the first form (callback), the callback is simply called with any
502	number of C<@reason> elements (no @reason means that the port was deleted	613	number of C<@reason> elements (no @reason means that the port was deleted
503	"normally"). Note also that I<< the callback B<must> never die >>, so use	614	"normally"). Note also that I<< the callback B<must> never die >>, so use
504	C<eval> if unsure.	615	C<eval> if unsure.
505		616
506	In the second form (another port given), the other port (C<$rcvport>)	617	In the second form (another port given), the other port (C<$rcvport>)
507	will be C<kil>'ed with C<@reason>, iff a @reason was specified, i.e. on	618	will be C<kil>'ed with C<@reason>, if a @reason was specified, i.e. on
508	"normal" kils nothing happens, while under all other conditions, the other	619	"normal" kils nothing happens, while under all other conditions, the other
509	port is killed with the same reason.	620	port is killed with the same reason.
510		621
511	The third form (kill self) is the same as the second form, except that	622	The third form (kill self) is the same as the second form, except that
512	C<$rvport> defaults to C<$SELF>.	623	C<$rvport> defaults to C<$SELF>.
513		624
514	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
515	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.
516		630
517	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
518	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
519	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
520	even monitoring requests can get lost (for exmaple, when the connection	634	even monitoring requests can get lost (for example, when the connection
521	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
522	these problems do not exist.	636	these problems do not exist.
523		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
524	Example: call a given callback when C<$port> is killed.	655	Example: call a given callback when C<$port> is killed.
525		656
526	mon $port, sub { warn "port died because of <@_>\n" };	657	mon $port, sub { warn "port died because of <@_>\n" };
527		658
528	Example: kill ourselves when C<$port> is killed abnormally.	659	Example: kill ourselves when C<$port> is killed abnormally.
…		…
534	mon $port, $self => "restart";	665	mon $port, $self => "restart";
535		666
536	=cut	667	=cut
537		668
538	sub mon {	669	sub mon {
539	my ($noderef, $port) = split /#/, shift, 2;	670	my ($nodeid, $port) = split /#/, shift, 2;
540		671
541	my $node = $NODE{$noderef} \|\| add_node $noderef;	672	my $node = $NODE{$nodeid} \|\| add_node $nodeid;
542		673
543	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,';
544		675
545	unless (ref $cb) {	676	unless (ref $cb) {
546	if (@_) {	677	if (@_) {
…		…
555	}	686	}
556		687
557	$node->monitor ($port, $cb);	688	$node->monitor ($port, $cb);
558		689
559	defined wantarray	690	defined wantarray
560	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	691	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
561	}	692	}
562		693
563	=item $guard = mon_guard $port, $ref, $ref...	694	=item $guard = mon_guard $port, $ref, $ref...
564		695
565	Monitors the given C<$port> and keeps the passed references. When the port	696	Monitors the given C<$port> and keeps the passed references. When the port
566	is killed, the references will be freed.	697	is killed, the references will be freed.
567		698
568	Optionally returns a guard that will stop the monitoring.	699	Optionally returns a guard that will stop the monitoring.
569		700
570	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
571	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>):
572		703
573	$port->rcv (start => sub {	704	$port->rcv (start => sub {
574	my $timer; $timer = mon_guard $port, AE::timer 1, 1, sub {	705	my $timer; $timer = mon_guard $port, AE::timer 1, 1, psub {
575	undef $timer if 0.9 < rand;	706	undef $timer if 0.9 < rand;
576	});	707	});
577	});	708	});
578		709
579	=cut	710	=cut
…		…
588		719
589	=item kil $port[, @reason]	720	=item kil $port[, @reason]
590		721
591	Kill the specified port with the given C<@reason>.	722	Kill the specified port with the given C<@reason>.
592		723
593	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" -
594	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.
595		727
596	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>
597	C<mon>, see below).	729	form) get killed with the same reason.
598		730
599	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
600	will be reported as reason C<< die => $@ >>.	732	will be reported as reason C<< die => $@ >>.
601		733
602	Transport/communication errors are reported as C<< transport_error =>	734	Transport/communication errors are reported as C<< transport_error =>
…		…
607	=item $port = spawn $node, $initfunc[, @initdata]	739	=item $port = spawn $node, $initfunc[, @initdata]
608		740
609	Creates a port on the node C<$node> (which can also be a port ID, in which	741	Creates a port on the node C<$node> (which can also be a port ID, in which
610	case it's the node where that port resides).	742	case it's the node where that port resides).
611		743
612	The port ID of the newly created port is return immediately, and it is	744	The port ID of the newly created port is returned immediately, and it is
613	permissible to immediately start sending messages or monitor the port.	745	possible to immediately start sending messages or to monitor the port.
614		746
615	After the port has been created, the init function is	747	After the port has been created, the init function is called on the remote
616	called. This function must be a fully-qualified function name	748	node, in the same context as a C<rcv> callback. This function must be a
617	(e.g. C<MyApp::Chat::Server::init>). To specify a function in the main	749	fully-qualified function name (e.g. C<MyApp::Chat::Server::init>). To
618	program, use C<::name>.	750	specify a function in the main program, use C<::name>.
619		751
620	If the function doesn't exist, then the node tries to C<require>	752	If the function doesn't exist, then the node tries to C<require>
621	the package, then the package above the package and so on (e.g.	753	the package, then the package above the package and so on (e.g.
622	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function	754	C<MyApp::Chat::Server>, C<MyApp::Chat>, C<MyApp>) until the function
623	exists or it runs out of package names.	755	exists or it runs out of package names.
624		756
625	The init function is then called with the newly-created port as context	757	The init function is then called with the newly-created port as context
626	object (C<$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.
627		761
628	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
629	in the init function, monitor the original port. This two-way monitoring	763	port, and in the remote init function, immediately monitor the passed
630	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<$initfunc> has no visible effects on the
		768	caller before C<spawn> returns (by delaying invocation when spawn is
		769	called for the local node).
631		770
632	Example: spawn a chat server port on C<$othernode>.	771	Example: spawn a chat server port on C<$othernode>.
633		772
634	# this node, executed from within a port context:	773	# this node, executed from within a port context:
635	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;	774	my $server = spawn $othernode, "MyApp::Chat::Server::connect", $SELF;
…		…
650		789
651	sub _spawn {	790	sub _spawn {
652	my $port = shift;	791	my $port = shift;
653	my $init = shift;	792	my $init = shift;
654		793
		794	# rcv will create the actual port
655	local $SELF = "$NODE#$port";	795	local $SELF = "$NODE#$port";
656	eval {	796	eval {
657	&{ load_func $init }	797	&{ load_func $init }
658	};	798	};
659	_self_die if $@;	799	_self_die if $@;
660	}	800	}
661		801
662	sub spawn(@) {	802	sub spawn(@) {
663	my ($noderef, undef) = split /#/, shift, 2;	803	my ($nodeid, undef) = split /#/, shift, 2;
664		804
665	my $id = "$RUNIQ." . $ID++;	805	my $id = $RUNIQ . ++$ID;
666		806
667	$_[0] =~ /::/	807	$_[0] =~ /::/
668	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";
669		809
670	snd_to_func $noderef, "AnyEvent::MP::_spawn" => $id, @_;	810	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
671		811
672	"$noderef#$id"	812	"$nodeid#$id"
673	}	813	}
		814
674		815
675	=item after $timeout, @msg	816	=item after $timeout, @msg
676		817
677	=item after $timeout, $callback	818	=item after $timeout, $callback
678		819
679	Either sends the given message, or call the given callback, after the	820	Either sends the given message, or call the given callback, after the
680	specified number of seconds.	821	specified number of seconds.
681		822
682	This is simply a utility function that come sin handy at times.	823	This is simply a utility function that comes in handy at times - the
		824	AnyEvent::MP author is not convinced of the wisdom of having it, though,
		825	so it may go away in the future.
683		826
684	=cut	827	=cut
685		828
686	sub after($@) {	829	sub after($@) {
687	my ($timeout, @action) = @_;	830	my ($timeout, @action) = @_;
…		…
692	? $action[0]()	835	? $action[0]()
693	: snd @action;	836	: snd @action;
694	};	837	};
695	}	838	}
696		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 a key from the database.
		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, \@subkeys...)
		984
		985	Creates a monitor on the given database family. Each time a key is set or
		986	or is deleted the callback is called with a hash containing the database
		987	family and an arrayref with subkeys that have changed.
		988
		989	Specifically, if one of the passed subkeys exists in the $familyhash, then
		990	it is currently set to the value in the $familyhash. Otherwise, it has
		991	been deleted.
		992
		993	The family hash reference belongs to AnyEvent::MP and B<must not be
		994	modified or stored> by the callback. When in doubt, make a copy.
		995
		996	The first call will be with the current contents of the family and all
		997	keys, as if they were just added.
		998
		999	It is possible that the callback is called with a change event even though
		1000	the subkey is already present and the value has not changed.
		1001
		1002	The monitoring stops when the guard object is destroyed.
		1003
		1004	Example: on every change to the family "mygroup", print out all keys.
		1005
		1006	my $guard = db_mon mygroup => sub {
		1007	my ($family, $keys) = @_;
		1008	print "mygroup members: ", (join " ", keys %$family), "\n";
		1009	};
		1010
		1011	Exmaple: wait until the family "My::Module::workers" is non-empty.
		1012
		1013	my $guard; $guard = db_mon My::Module::workers => sub {
		1014	my ($family, $keys) = @_;
		1015	return unless %$family;
		1016	undef $guard;
		1017	print "My::Module::workers now nonempty\n";
		1018	};
		1019
		1020	Example: print all changes to the family "AnyRvent::Fantasy::Module".
		1021
		1022	my $guard = db_mon AnyRvent::Fantasy::Module => sub {
		1023	my ($family, $keys) = @_;
		1024
		1025	for (@$keys) {
		1026	print "$_: ",
		1027	(exists $family->{$_}
		1028	? $family->{$_}
		1029	: "(deleted)"),
		1030	"\n";
		1031	}
		1032	};
		1033
		1034	=cut
		1035
697	=back	1036	=back
698		1037
699	=head1 AnyEvent::MP vs. Distributed Erlang	1038	=head1 AnyEvent::MP vs. Distributed Erlang
700		1039
701	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	1040	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
702	== aemp node, Erlang process == aemp port), so many of the documents and	1041	== aemp node, Erlang process == aemp port), so many of the documents and
703	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	1042	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
704	sample:	1043	sample:
705		1044
706	http://www.Erlang.se/doc/programming_rules.shtml	1045	http://www.erlang.se/doc/programming_rules.shtml
707	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	1046	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
708	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	1047	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
709	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	1048	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
710		1049
711	Despite the similarities, there are also some important differences:	1050	Despite the similarities, there are also some important differences:
712		1051
713	=over 4	1052	=over 4
714		1053
715	=item * Node references contain the recipe on how to contact them.	1054	=item * Node IDs are arbitrary strings in AEMP.
716		1055
717	Erlang relies on special naming and DNS to work everywhere in the	1056	Erlang relies on special naming and DNS to work everywhere in the same
718	same way. AEMP relies on each node knowing it's own address(es), with	1057	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
719	convenience functionality.	1058	configuration or DNS), and possibly the addresses of some seed nodes, but
720		1059	will otherwise discover other nodes (and their IDs) itself.
721	This means that AEMP requires a less tightly controlled environment at the
722	cost of longer node references and a slightly higher management overhead.
723		1060
724	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP	1061	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
725	uses "local ports are like remote ports".	1062	uses "local ports are like remote ports".
726		1063
727	The failure modes for local ports are quite different (runtime errors	1064	The failure modes for local ports are quite different (runtime errors
…		…
736	ports being the special case/exception, where transport errors cannot	1073	ports being the special case/exception, where transport errors cannot
737	occur.	1074	occur.
738		1075
739	=item * Erlang uses processes and a mailbox, AEMP does not queue.	1076	=item * Erlang uses processes and a mailbox, AEMP does not queue.
740		1077
741	Erlang uses processes that selectively receive messages, and therefore	1078	Erlang uses processes that selectively receive messages out of order, and
742	needs a queue. AEMP is event based, queuing messages would serve no	1079	therefore needs a queue. AEMP is event based, queuing messages would serve
743	useful purpose. For the same reason the pattern-matching abilities of	1080	no useful purpose. For the same reason the pattern-matching abilities
744	AnyEvent::MP are more limited, as there is little need to be able to	1081	of AnyEvent::MP are more limited, as there is little need to be able to
745	filter messages without dequeing them.	1082	filter messages without dequeuing them.
746		1083
747	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	1084	This is not a philosophical difference, but simply stems from AnyEvent::MP
		1085	being event-based, while Erlang is process-based.
		1086
		1087	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		1088	top of AEMP and Coro threads.
748		1089
749	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	1090	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
750		1091
751	Sending messages in Erlang is synchronous and blocks the process (and	1092	Sending messages in Erlang is synchronous and blocks the process until
		1093	a conenction has been established and the message sent (and so does not
752	so does not need a queue that can overflow). AEMP sends are immediate,	1094	need a queue that can overflow). AEMP sends return immediately, connection
753	connection establishment is handled in the background.	1095	establishment is handled in the background.
754		1096
755	=item * Erlang suffers from silent message loss, AEMP does not.	1097	=item * Erlang suffers from silent message loss, AEMP does not.
756		1098
757	Erlang makes few guarantees on messages delivery - messages can get lost	1099	Erlang implements few guarantees on messages delivery - messages can get
758	without any of the processes realising it (i.e. you send messages a, b,	1100	lost without any of the processes realising it (i.e. you send messages a,
759	and c, and the other side only receives messages a and c).	1101	b, and c, and the other side only receives messages a and c).
760		1102
761	AEMP guarantees correct ordering, and the guarantee that there are no	1103	AEMP guarantees (modulo hardware errors) correct ordering, and the
		1104	guarantee that after one message is lost, all following ones sent to the
		1105	same port are lost as well, until monitoring raises an error, so there are
762	holes in the message sequence.	1106	no silent "holes" in the message sequence.
763		1107
764	=item * In Erlang, processes can be declared dead and later be found to be	1108	If you want your software to be very reliable, you have to cope with
765	alive.	1109	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
766		1110	simply tries to work better in common error cases, such as when a network
767	In Erlang it can happen that a monitored process is declared dead and	1111	link goes down.
768	linked processes get killed, but later it turns out that the process is
769	still alive - and can receive messages.
770
771	In AEMP, when port monitoring detects a port as dead, then that port will
772	eventually be killed - it cannot happen that a node detects a port as dead
773	and then later sends messages to it, finding it is still alive.
774		1112
775	=item * Erlang can send messages to the wrong port, AEMP does not.	1113	=item * Erlang can send messages to the wrong port, AEMP does not.
776		1114
777	In Erlang it is quite likely that a node that restarts reuses a process ID	1115	In Erlang it is quite likely that a node that restarts reuses an Erlang
778	known to other nodes for a completely different process, causing messages	1116	process ID known to other nodes for a completely different process,
779	destined for that process to end up in an unrelated process.	1117	causing messages destined for that process to end up in an unrelated
		1118	process.
780		1119
781	AEMP never reuses port IDs, so old messages or old port IDs floating	1120	AEMP does not reuse port IDs, so old messages or old port IDs floating
782	around in the network will not be sent to an unrelated port.	1121	around in the network will not be sent to an unrelated port.
783		1122
784	=item * Erlang uses unprotected connections, AEMP uses secure	1123	=item * Erlang uses unprotected connections, AEMP uses secure
785	authentication and can use TLS.	1124	authentication and can use TLS.
786		1125
787	AEMP can use a proven protocol - SSL/TLS - to protect connections and	1126	AEMP can use a proven protocol - TLS - to protect connections and
788	securely authenticate nodes.	1127	securely authenticate nodes.
789		1128
790	=item * The AEMP protocol is optimised for both text-based and binary	1129	=item * The AEMP protocol is optimised for both text-based and binary
791	communications.	1130	communications.
792		1131
793	The AEMP protocol, unlike the Erlang protocol, supports both	1132	The AEMP protocol, unlike the Erlang protocol, supports both programming
794	language-independent text-only protocols (good for debugging) and binary,	1133	language independent text-only protocols (good for debugging), and binary,
795	language-specific serialisers (e.g. Storable).	1134	language-specific serialisers (e.g. Storable). By default, unless TLS is
		1135	used, the protocol is actually completely text-based.
796		1136
797	It has also been carefully designed to be implementable in other languages	1137	It has also been carefully designed to be implementable in other languages
798	with a minimum of work while gracefully degrading fucntionality to make the	1138	with a minimum of work while gracefully degrading functionality to make the
799	protocol simple.	1139	protocol simple.
800		1140
801	=item * AEMP has more flexible monitoring options than Erlang.	1141	=item * AEMP has more flexible monitoring options than Erlang.
802		1142
803	In Erlang, you can chose to receive I<all> exit signals as messages	1143	In Erlang, you can chose to receive I<all> exit signals as messages or
804	or I<none>, there is no in-between, so monitoring single processes is	1144	I<none>, there is no in-between, so monitoring single Erlang processes is
805	difficult to implement. Monitoring in AEMP is more flexible than in	1145	difficult to implement.
806	Erlang, as one can choose between automatic kill, exit message or callback	1146
807	on a per-process basis.	1147	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1148	between automatic kill, exit message or callback on a per-port basis.
808		1149
809	=item * Erlang tries to hide remote/local connections, AEMP does not.	1150	=item * Erlang tries to hide remote/local connections, AEMP does not.
810		1151
811	Monitoring in Erlang is not an indicator of process death/crashes,	1152	Monitoring in Erlang is not an indicator of process death/crashes, in the
812	as linking is (except linking is unreliable in Erlang).	1153	same way as linking is (except linking is unreliable in Erlang).
813		1154
814	In AEMP, you don't "look up" registered port names or send to named ports	1155	In AEMP, you don't "look up" registered port names or send to named ports
815	that might or might not be persistent. Instead, you normally spawn a port	1156	that might or might not be persistent. Instead, you normally spawn a port
816	on the remote node. The init function monitors the you, and you monitor	1157	on the remote node. The init function monitors you, and you monitor the
817	the remote port. Since both monitors are local to the node, they are much	1158	remote port. Since both monitors are local to the node, they are much more
818	more reliable.	1159	reliable (no need for C<spawn_link>).
819		1160
820	This also saves round-trips and avoids sending messages to the wrong port	1161	This also saves round-trips and avoids sending messages to the wrong port
821	(hard to do in Erlang).	1162	(hard to do in Erlang).
822		1163
823	=back	1164	=back
824		1165
825	=head1 RATIONALE	1166	=head1 RATIONALE
826		1167
827	=over 4	1168	=over 4
828		1169
829	=item Why strings for ports and noderefs, why not objects?	1170	=item Why strings for port and node IDs, why not objects?
830		1171
831	We considered "objects", but found that the actual number of methods	1172	We considered "objects", but found that the actual number of methods
832	thatc an be called are very low. Since port IDs and noderefs travel over	1173	that can be called are quite low. Since port and node IDs travel over
833	the network frequently, the serialising/deserialising would add lots of	1174	the network frequently, the serialising/deserialising would add lots of
834	overhead, as well as having to keep a proxy object.	1175	overhead, as well as having to keep a proxy object everywhere.
835		1176
836	Strings can easily be printed, easily serialised etc. and need no special	1177	Strings can easily be printed, easily serialised etc. and need no special
837	procedures to be "valid".	1178	procedures to be "valid".
838		1179
839	And a a miniport consists of a single closure stored in a global hash - it	1180	And as a result, a port with just a default receiver consists of a single
840	can't become much cheaper.	1181	code reference stored in a global hash - it can't become much cheaper.
841		1182
842	=item Why favour JSON, why not real serialising format such as Storable?	1183	=item Why favour JSON, why not a real serialising format such as Storable?
843		1184
844	In fact, any AnyEvent::MP node will happily accept Storable as framing	1185	In fact, any AnyEvent::MP node will happily accept Storable as framing
845	format, but currently there is no way to make a node use Storable by	1186	format, but currently there is no way to make a node use Storable by
846	default.	1187	default (although all nodes will accept it).
847		1188
848	The default framing protocol is JSON because a) JSON::XS is many times	1189	The default framing protocol is JSON because a) JSON::XS is many times
849	faster for small messages and b) most importantly, after years of	1190	faster for small messages and b) most importantly, after years of
850	experience we found that object serialisation is causing more problems	1191	experience we found that object serialisation is causing more problems
851	than it gains: Just like function calls, objects simply do not travel	1192	than it solves: Just like function calls, objects simply do not travel
852	easily over the network, mostly because they will always be a copy, so you	1193	easily over the network, mostly because they will always be a copy, so you
853	always have to re-think your design.	1194	always have to re-think your design.
854		1195
855	Keeping your messages simple, concentrating on data structures rather than	1196	Keeping your messages simple, concentrating on data structures rather than
856	objects, will keep your messages clean, tidy and efficient.	1197	objects, will keep your messages clean, tidy and efficient.
857		1198
858	=back	1199	=back
859		1200
860	=head1 SEE ALSO	1201	=head1 SEE ALSO
861		1202
		1203	L<AnyEvent::MP::Intro> - a gentle introduction.
		1204
		1205	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
		1206
		1207	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
		1208	your applications.
		1209
		1210	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
		1211
		1212	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
		1213	all nodes.
		1214
862	L<AnyEvent>.	1215	L<AnyEvent>.
863		1216
864	=head1 AUTHOR	1217	=head1 AUTHOR
865		1218
866	Marc Lehmann <schmorp@schmorp.de>	1219	Marc Lehmann <schmorp@schmorp.de>

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Revision 1.129 by root, Thu Mar 8 21:37:51 2012 UTC