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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.91 by root, Tue Sep 22 09:54:42 2009 UTC vs.
Revision 1.126 by root, Sat Mar 3 19:43:41 2012 UTC

…		…
30	rcv $port, pong => sub { warn "pong received\n" };	30	rcv $port, pong => sub { warn "pong received\n" };
31		31
32	# create a port on another node	32	# create a port on another node
33	my $port = spawn $node, $initfunc, @initdata;	33	my $port = spawn $node, $initfunc, @initdata;
34		34
		35	# destroy a port again
		36	kil $port; # "normal" kill
		37	kil $port, my_error => "everything is broken"; # error kill
		38
35	# monitoring	39	# monitoring
36	mon $localport, $cb->(@msg) # callback is invoked on death	40	mon $localport, $cb->(@msg) # callback is invoked on death
37	mon $localport, $otherport # kill otherport on abnormal death	41	mon $localport, $otherport # kill otherport on abnormal death
38	mon $localport, $otherport, @msg # send message on death	42	mon $localport, $otherport, @msg # send message on death
		43
		44	# temporarily execute code in port context
		45	peval $port, sub { die "kill the port!" };
		46
		47	# execute callbacks in $SELF port context
		48	my $timer = AE::timer 1, 0, psub {
		49	die "kill the port, delayed";
		50	};
39		51
40	=head1 CURRENT STATUS	52	=head1 CURRENT STATUS
41		53
42	bin/aemp - stable.	54	bin/aemp - stable.
43	AnyEvent::MP - stable API, should work.	55	AnyEvent::MP - stable API, should work.
…		…
66		78
67	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
68	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
69	anything was listening for them or not.	81	anything was listening for them or not.
70		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
71	=item port ID - C<nodeid#portname>	85	=item port ID - C<nodeid#portname>
72		86
73	A port ID is the concatenation of a node ID, a hash-mark (C<#>) as	87	A port ID is the concatenation of a node ID, a hash-mark (C<#>)
74	separator, and a port name (a printable string of unspecified format).	88	as separator, and a port name (a printable string of unspecified
		89	format created by AnyEvent::MP).
75		90
76	=item node	91	=item node
77		92
78	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,
79	which enables nodes to manage each other remotely, and to create new	94	which enables nodes to manage each other remotely, and to create new
80	ports.	95	ports.
81		96
82	Nodes are either public (have one or more listening ports) or private	97	Nodes are either public (have one or more listening ports) or private
83	(no listening ports). Private nodes cannot talk to other private nodes	98	(no listening ports). Private nodes cannot talk to other private nodes
84	currently.	99	currently, but all nodes can talk to public nodes.
85		100
		101	Nodes is represented by (printable) strings called "node IDs".
		102
86	=item node ID - C<[A-Z_][a-zA-Z0-9_\-.:]*>	103	=item node ID - C<[A-Za-z0-9_\-.:]*>
87		104
88	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
89	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
90	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
91	doesn't interpret node IDs in any way.	108	doesn't interpret node IDs in any way except to uniquely identify a node.
92		109
93	=item binds - C<ip:port>	110	=item binds - C<ip:port>
94		111
95	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
96	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
97	endpoints - binds. Currently, only standard C<ip:port> specifications can	116	Currently, only standard C<ip:port> specifications can be used, which
98	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.
99		119
100	=item seed nodes	120	=item seed nodes
101		121
102	When a node starts, it knows nothing about the network. To teach the node	122	When a node starts, it knows nothing about the network it is in - it
103	about the network it first has to contact some other node within the	123	needs to connect to at least one other node that is already in the
104	network. This node is called a seed.	124	network. These other nodes are called "seed nodes".
105		125
106	Apart from the fact that other nodes know them as seed nodes and they have	126	Seed nodes themselves are not special - they are seed nodes only because
107	to have fixed listening addresses, seed nodes are perfectly normal nodes -	127	some other node I<uses> them as such, but any node can be used as seed
108	any node can function as a seed node for others.	128	node for other nodes, and eahc node cna use a different set of seed nodes.
109		129
110	In addition to discovering the network, seed nodes are also used to	130	In addition to discovering the network, seed nodes are also used to
111	maintain the network and to connect nodes that otherwise would have	131	maintain the network - all nodes using the same seed node form are part of
112	trouble connecting. They form the backbone of an AnyEvent::MP network.	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.
113		135
114	Seed nodes are expected to be long-running, and at least one seed node	136	Seed nodes are expected to be long-running, and at least one seed node
115	should always be available. They should also be relatively responsive - a	137	should always be available. They should also be relatively responsive - a
116	seed node that blocks for long periods will slow down everybody else.	138	seed node that blocks for long periods will slow down everybody else.
117		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
118	=item seeds - C<host:port>	149	=item seed IDs - C<host:port>
119		150
120	Seeds are transport endpoint(s) (usually a hostname/IP address and a	151	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
121	TCP port) of nodes thta should be used as seed nodes.	152	TCP port) of nodes that should be used as seed nodes.
122		153
123	The nodes listening on those endpoints are expected to be long-running,	154	=item global nodes
124	and at least one of those should always be available. When nodes run out	155
125	of connections (e.g. due to a network error), they try to re-establish	156	An AEMP network needs a discovery service - nodes need to know how to
126	connections to some seednodes again to join the network.	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).
127		170
128	=back	171	=back
129		172
130	=head1 VARIABLES/FUNCTIONS	173	=head1 VARIABLES/FUNCTIONS
131		174
…		…
133		176
134	=cut	177	=cut
135		178
136	package AnyEvent::MP;	179	package AnyEvent::MP;
137		180
		181	use AnyEvent::MP::Config ();
138	use AnyEvent::MP::Kernel;	182	use AnyEvent::MP::Kernel;
		183	use AnyEvent::MP::Kernel qw(%NODE %PORT %PORT_DATA $UNIQ $RUNIQ $ID);
139		184
140	use common::sense;	185	use common::sense;
141		186
142	use Carp ();	187	use Carp ();
143		188
144	use AE ();	189	use AE ();
		190	use Guard ();
145		191
146	use base "Exporter";	192	use base "Exporter";
147		193
148	our $VERSION = $AnyEvent::MP::Kernel::VERSION;	194	our $VERSION = $AnyEvent::MP::Config::VERSION;
149		195
150	our @EXPORT = qw(	196	our @EXPORT = qw(
151	NODE $NODE *SELF node_of after	197	NODE $NODE *SELF node_of after
152	configure	198	configure
153	snd rcv mon mon_guard kil psub spawn cal	199	snd rcv mon mon_guard kil psub peval spawn cal
154	port	200	port
		201	db_set db_del db_reg
155	);	202	);
156		203
157	our $SELF;	204	our $SELF;
158		205
159	sub _self_die() {	206	sub _self_die() {
…		…
182	some other nodes in the network to discover other nodes.	229	some other nodes in the network to discover other nodes.
183		230
184	This function configures a node - it must be called exactly once (or	231	This function configures a node - it must be called exactly once (or
185	never) before calling other AnyEvent::MP functions.	232	never) before calling other AnyEvent::MP functions.
186		233
		234	The key/value pairs are basically the same ones as documented for the
		235	F<aemp> command line utility (sans the set/del prefix), with two additions:
		236
		237	=over 4
		238
		239	=item norc => $boolean (default false)
		240
		241	If true, then the rc file (e.g. F<~/.perl-anyevent-mp>) will I<not>
		242	be consulted - all configuraiton options must be specified in the
		243	C<configure> call.
		244
		245	=item force => $boolean (default false)
		246
		247	IF true, then the values specified in the C<configure> will take
		248	precedence over any values configured via the rc file. The default is for
		249	the rc file to override any options specified in the program.
		250
		251	=back
		252
187	=over 4	253	=over 4
188		254
189	=item step 1, gathering configuration from profiles	255	=item step 1, gathering configuration from profiles
190		256
191	The function first looks up a profile in the aemp configuration (see the	257	The function first looks up a profile in the aemp configuration (see the
…		…
204	That means that the values specified in the profile have highest priority	270	That means that the values specified in the profile have highest priority
205	and the values specified directly via C<configure> have lowest priority,	271	and the values specified directly via C<configure> have lowest priority,
206	and can only be used to specify defaults.	272	and can only be used to specify defaults.
207		273
208	If the profile specifies a node ID, then this will become the node ID of	274	If the profile specifies a node ID, then this will become the node ID of
209	this process. If not, then the profile name will be used as node ID. The	275	this process. If not, then the profile name will be used as node ID, with
210	special node ID of C<anon/> will be replaced by a random node ID.	276	a unique randoms tring (C</%u>) appended.
		277
		278	The node ID can contain some C<%> sequences that are expanded: C<%n>
		279	is expanded to the local nodename, C<%u> is replaced by a random
		280	strign to make the node unique. For example, the F<aemp> commandline
		281	utility uses C<aemp/%n/%u> as nodename, which might expand to
		282	C<aemp/cerebro/ZQDGSIkRhEZQDGSIkRhE>.
211		283
212	=item step 2, bind listener sockets	284	=item step 2, bind listener sockets
213		285
214	The next step is to look up the binds in the profile, followed by binding	286	The next step is to look up the binds in the profile, followed by binding
215	aemp protocol listeners on all binds specified (it is possible and valid	287	aemp protocol listeners on all binds specified (it is possible and valid
…		…
221	used, meaning the node will bind on a dynamically-assigned port on every	293	used, meaning the node will bind on a dynamically-assigned port on every
222	local IP address it finds.	294	local IP address it finds.
223		295
224	=item step 3, connect to seed nodes	296	=item step 3, connect to seed nodes
225		297
226	As the last step, the seeds list from the profile is passed to the	298	As the last step, the seed ID list from the profile is passed to the
227	L<AnyEvent::MP::Global> module, which will then use it to keep	299	L<AnyEvent::MP::Global> module, which will then use it to keep
228	connectivity with at least one node at any point in time.	300	connectivity with at least one node at any point in time.
229		301
230	=back	302	=back
231		303
232	Example: become a distributed node using the local node name as profile.	304	Example: become a distributed node using the local node name as profile.
233	This should be the most common form of invocation for "daemon"-type nodes.	305	This should be the most common form of invocation for "daemon"-type nodes.
234		306
235	configure	307	configure
236		308
237	Example: become an anonymous node. This form is often used for commandline	309	Example: become a semi-anonymous node. This form is often used for
238	clients.	310	commandline clients.
239		311
240	configure nodeid => "anon/";	312	configure nodeid => "myscript/%n/%u";
241		313
242	Example: configure a node using a profile called seed, which si suitable	314	Example: configure a node using a profile called seed, which is suitable
243	for a seed node as it binds on all local addresses on a fixed port (4040,	315	for a seed node as it binds on all local addresses on a fixed port (4040,
244	customary for aemp).	316	customary for aemp).
245		317
246	# use the aemp commandline utility	318	# use the aemp commandline utility
247	# aemp profile seed nodeid anon/ binds '*:4040'	319	# aemp profile seed binds '*:4040'
248		320
249	# then use it	321	# then use it
250	configure profile => "seed";	322	configure profile => "seed";
251		323
252	# or simply use aemp from the shell again:	324	# or simply use aemp from the shell again:
…		…
322	sub _kilme {	394	sub _kilme {
323	die "received message on port without callback";	395	die "received message on port without callback";
324	}	396	}
325		397
326	sub port(;&) {	398	sub port(;&) {
327	my $id = "$UNIQ." . $ID++;	399	my $id = $UNIQ . ++$ID;
328	my $port = "$NODE#$id";	400	my $port = "$NODE#$id";
329		401
330	rcv $port, shift \|\| \&_kilme;	402	rcv $port, shift \|\| \&_kilme;
331		403
332	$port	404	$port
…		…
371	msg1 => sub { ... },	443	msg1 => sub { ... },
372	...	444	...
373	;	445	;
374		446
375	Example: temporarily register a rcv callback for a tag matching some port	447	Example: temporarily register a rcv callback for a tag matching some port
376	(e.g. for a rpc reply) and unregister it after a message was received.	448	(e.g. for an rpc reply) and unregister it after a message was received.
377		449
378	rcv $port, $otherport => sub {	450	rcv $port, $otherport => sub {
379	my @reply = @_;	451	my @reply = @_;
380		452
381	rcv $SELF, $otherport;	453	rcv $SELF, $otherport;
…		…
394	if (ref $_[0]) {	466	if (ref $_[0]) {
395	if (my $self = $PORT_DATA{$portid}) {	467	if (my $self = $PORT_DATA{$portid}) {
396	"AnyEvent::MP::Port" eq ref $self	468	"AnyEvent::MP::Port" eq ref $self
397	or Carp::croak "$port: rcv can only be called on message matching ports, caught";	469	or Carp::croak "$port: rcv can only be called on message matching ports, caught";
398		470
399	$self->[2] = shift;	471	$self->[0] = shift;
400	} else {	472	} else {
401	my $cb = shift;	473	my $cb = shift;
402	$PORT{$portid} = sub {	474	$PORT{$portid} = sub {
403	local $SELF = $port;	475	local $SELF = $port;
404	eval { &$cb }; _self_die if $@;	476	eval { &$cb }; _self_die if $@;
405	};	477	};
406	}	478	}
407	} elsif (defined $_[0]) {	479	} elsif (defined $_[0]) {
408	my $self = $PORT_DATA{$portid} \|\|= do {	480	my $self = $PORT_DATA{$portid} \|\|= do {
409	my $self = bless [$PORT{$port} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";	481	my $self = bless [$PORT{$portid} \|\| sub { }, { }, $port], "AnyEvent::MP::Port";
410		482
411	$PORT{$portid} = sub {	483	$PORT{$portid} = sub {
412	local $SELF = $port;	484	local $SELF = $port;
413		485
414	if (my $cb = $self->[1]{$_[0]}) {	486	if (my $cb = $self->[1]{$_[0]}) {
…		…
436	}	508	}
437		509
438	$port	510	$port
439	}	511	}
440		512
		513	=item peval $port, $coderef[, @args]
		514
		515	Evaluates the given C<$codref> within the contetx of C<$port>, that is,
		516	when the code throews an exception the C<$port> will be killed.
		517
		518	Any remaining args will be passed to the callback. Any return values will
		519	be returned to the caller.
		520
		521	This is useful when you temporarily want to execute code in the context of
		522	a port.
		523
		524	Example: create a port and run some initialisation code in it's context.
		525
		526	my $port = port { ... };
		527
		528	peval $port, sub {
		529	init
		530	or die "unable to init";
		531	};
		532
		533	=cut
		534
		535	sub peval($$) {
		536	local $SELF = shift;
		537	my $cb = shift;
		538
		539	if (wantarray) {
		540	my @res = eval { &$cb };
		541	_self_die if $@;
		542	@res
		543	} else {
		544	my $res = eval { &$cb };
		545	_self_die if $@;
		546	$res
		547	}
		548	}
		549
441	=item $closure = psub { BLOCK }	550	=item $closure = psub { BLOCK }
442		551
443	Remembers C<$SELF> and creates a closure out of the BLOCK. When the	552	Remembers C<$SELF> and creates a closure out of the BLOCK. When the
444	closure is executed, sets up the environment in the same way as in C<rcv>	553	closure is executed, sets up the environment in the same way as in C<rcv>
445	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.	554	callbacks, i.e. runtime errors will cause the port to get C<kil>ed.
		555
		556	The effect is basically as if it returned C<< sub { peval $SELF, sub {
		557	BLOCK }, @_ } >>.
446		558
447	This is useful when you register callbacks from C<rcv> callbacks:	559	This is useful when you register callbacks from C<rcv> callbacks:
448		560
449	rcv delayed_reply => sub {	561	rcv delayed_reply => sub {
450	my ($delay, @reply) = @_;	562	my ($delay, @reply) = @_;
…		…
523	delivered again.	635	delivered again.
524		636
525	Inter-host-connection timeouts and monitoring depend on the transport	637	Inter-host-connection timeouts and monitoring depend on the transport
526	used. The only transport currently implemented is TCP, and AnyEvent::MP	638	used. The only transport currently implemented is TCP, and AnyEvent::MP
527	relies on TCP to detect node-downs (this can take 10-15 minutes on a	639	relies on TCP to detect node-downs (this can take 10-15 minutes on a
528	non-idle connection, and usually around two hours for idle conenctions).	640	non-idle connection, and usually around two hours for idle connections).
529		641
530	This means that monitoring is good for program errors and cleaning up	642	This means that monitoring is good for program errors and cleaning up
531	stuff eventually, but they are no replacement for a timeout when you need	643	stuff eventually, but they are no replacement for a timeout when you need
532	to ensure some maximum latency.	644	to ensure some maximum latency.
533		645
…		…
565	}	677	}
566		678
567	$node->monitor ($port, $cb);	679	$node->monitor ($port, $cb);
568		680
569	defined wantarray	681	defined wantarray
570	and AnyEvent::Util::guard { $node->unmonitor ($port, $cb) }	682	and ($cb += 0, Guard::guard { $node->unmonitor ($port, $cb) })
571	}	683	}
572		684
573	=item $guard = mon_guard $port, $ref, $ref...	685	=item $guard = mon_guard $port, $ref, $ref...
574		686
575	Monitors the given C<$port> and keeps the passed references. When the port	687	Monitors the given C<$port> and keeps the passed references. When the port
…		…
598		710
599	=item kil $port[, @reason]	711	=item kil $port[, @reason]
600		712
601	Kill the specified port with the given C<@reason>.	713	Kill the specified port with the given C<@reason>.
602		714
603	If no C<@reason> is specified, then the port is killed "normally" (ports	715	If no C<@reason> is specified, then the port is killed "normally" -
604	monitoring other ports will not necessarily die because a port dies	716	monitor callback will be invoked, but the kil will not cause linked ports
605	"normally").	717	(C<mon $mport, $lport> form) to get killed.
606		718
607	Otherwise, linked ports get killed with the same reason (second form of	719	If a C<@reason> is specified, then linked ports (C<mon $mport, $lport>
608	C<mon>, see above).	720	form) get killed with the same reason.
609		721
610	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks	722	Runtime errors while evaluating C<rcv> callbacks or inside C<psub> blocks
611	will be reported as reason C<< die => $@ >>.	723	will be reported as reason C<< die => $@ >>.
612		724
613	Transport/communication errors are reported as C<< transport_error =>	725	Transport/communication errors are reported as C<< transport_error =>
…		…
679	}	791	}
680		792
681	sub spawn(@) {	793	sub spawn(@) {
682	my ($nodeid, undef) = split /#/, shift, 2;	794	my ($nodeid, undef) = split /#/, shift, 2;
683		795
684	my $id = "$RUNIQ." . $ID++;	796	my $id = $RUNIQ . ++$ID;
685		797
686	$_[0] =~ /::/	798	$_[0] =~ /::/
687	or Carp::croak "spawn init function must be a fully-qualified name, caught";	799	or Carp::croak "spawn init function must be a fully-qualified name, caught";
688		800
689	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;	801	snd_to_func $nodeid, "AnyEvent::MP::_spawn" => $id, @_;
690		802
691	"$nodeid#$id"	803	"$nodeid#$id"
692	}	804	}
		805
693		806
694	=item after $timeout, @msg	807	=item after $timeout, @msg
695		808
696	=item after $timeout, $callback	809	=item after $timeout, $callback
697		810
…		…
727		840
728	If an optional time-out (in seconds) is given and it is not C<undef>,	841	If an optional time-out (in seconds) is given and it is not C<undef>,
729	then the callback will be called without any arguments after the time-out	842	then the callback will be called without any arguments after the time-out
730	elapsed and the port is C<kil>ed.	843	elapsed and the port is C<kil>ed.
731		844
732	If no time-out is given, then the local port will monitor the remote port	845	If no time-out is given (or it is C<undef>), then the local port will
733	instead, so it eventually gets cleaned-up.	846	monitor the remote port instead, so it eventually gets cleaned-up.
734		847
735	Currently this function returns the temporary port, but this "feature"	848	Currently this function returns the temporary port, but this "feature"
736	might go in future versions unless you can make a convincing case that	849	might go in future versions unless you can make a convincing case that
737	this is indeed useful for something.	850	this is indeed useful for something.
738		851
…		…
767	$port	880	$port
768	}	881	}
769		882
770	=back	883	=back
771		884
		885	=head1 DISTRIBUTED DATABASE
		886
		887	AnyEvent::MP comes with a simple distributed database. The database will
		888	be mirrored asynchronously at all global nodes. Other nodes bind to one of
		889	the global nodes for their needs.
		890
		891	The database consists of a two-level hash - a hash contains a hash which
		892	contains values.
		893
		894	The top level hash key is called "family", and the second-level hash key
		895	is called "subkey" or simply "key".
		896
		897	The family must be alphanumeric, i.e. start with a letter and consist
		898	of letters, digits, underscores and colons (C<[A-Za-z][A-Za-z0-9_:]*>,
		899	pretty much like Perl module names.
		900
		901	As the family namespace is global, it is recommended to prefix family names
		902	with the name of the application or module using it.
		903
		904	The subkeys must be non-empty strings, with no further restrictions.
		905
		906	The values should preferably be strings, but other perl scalars should
		907	work as well (such as undef, arrays and hashes).
		908
		909	Every database entry is owned by one node - adding the same family/subkey
		910	combination on multiple nodes will not cause discomfort for AnyEvent::MP,
		911	but the result might be nondeterministic, i.e. the key might have
		912	different values on different nodes.
		913
		914	Different subkeys in the same family can be owned by different nodes
		915	without problems, and in fact, this is the common method to create worker
		916	pools. For example, a worker port for image scaling might do this:
		917
		918	db_set my_image_scalers => $port;
		919
		920	And clients looking for an image scaler will want to get the
		921	C<my_image_scalers> keys:
		922
		923	db_keys "my_image_scalers" => 60 => sub {
		924	#d##TODO#
		925
		926	=over
		927
		928	=item db_set $family => $subkey [=> $value]
		929
		930	Sets (or replaces) a key to the database - if C<$value> is omitted,
		931	C<undef> is used instead.
		932
		933	=item db_del $family => $subkey
		934
		935	Deletes a key from the database.
		936
		937	=item $guard = db_reg $family => $subkey [=> $value]
		938
		939	Sets the key on the database and returns a guard. When the guard is
		940	destroyed, the key is deleted from the database. If C<$value> is missing,
		941	then C<undef> is used.
		942
		943	=cut
		944
		945	=back
		946
772	=head1 AnyEvent::MP vs. Distributed Erlang	947	=head1 AnyEvent::MP vs. Distributed Erlang
773		948
774	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node	949	AnyEvent::MP got lots of its ideas from distributed Erlang (Erlang node
775	== aemp node, Erlang process == aemp port), so many of the documents and	950	== aemp node, Erlang process == aemp port), so many of the documents and
776	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a	951	programming techniques employed by Erlang apply to AnyEvent::MP. Here is a
777	sample:	952	sample:
778		953
779	http://www.Erlang.se/doc/programming_rules.shtml	954	http://www.erlang.se/doc/programming_rules.shtml
780	http://Erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4	955	http://erlang.org/doc/getting_started/part_frame.html # chapters 3 and 4
781	http://Erlang.org/download/Erlang-book-part1.pdf # chapters 5 and 6	956	http://erlang.org/download/erlang-book-part1.pdf # chapters 5 and 6
782	http://Erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5	957	http://erlang.org/download/armstrong_thesis_2003.pdf # chapters 4 and 5
783		958
784	Despite the similarities, there are also some important differences:	959	Despite the similarities, there are also some important differences:
785		960
786	=over 4	961	=over 4
787		962
788	=item * Node IDs are arbitrary strings in AEMP.	963	=item * Node IDs are arbitrary strings in AEMP.
789		964
790	Erlang relies on special naming and DNS to work everywhere in the same	965	Erlang relies on special naming and DNS to work everywhere in the same
791	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by	966	way. AEMP relies on each node somehow knowing its own address(es) (e.g. by
792	configuration or DNS), but will otherwise discover other odes itself.	967	configuration or DNS), and possibly the addresses of some seed nodes, but
		968	will otherwise discover other nodes (and their IDs) itself.
793		969
794	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP	970	=item * Erlang has a "remote ports are like local ports" philosophy, AEMP
795	uses "local ports are like remote ports".	971	uses "local ports are like remote ports".
796		972
797	The failure modes for local ports are quite different (runtime errors	973	The failure modes for local ports are quite different (runtime errors
…		…
806	ports being the special case/exception, where transport errors cannot	982	ports being the special case/exception, where transport errors cannot
807	occur.	983	occur.
808		984
809	=item * Erlang uses processes and a mailbox, AEMP does not queue.	985	=item * Erlang uses processes and a mailbox, AEMP does not queue.
810		986
811	Erlang uses processes that selectively receive messages, and therefore	987	Erlang uses processes that selectively receive messages out of order, and
812	needs a queue. AEMP is event based, queuing messages would serve no	988	therefore needs a queue. AEMP is event based, queuing messages would serve
813	useful purpose. For the same reason the pattern-matching abilities of	989	no useful purpose. For the same reason the pattern-matching abilities
814	AnyEvent::MP are more limited, as there is little need to be able to	990	of AnyEvent::MP are more limited, as there is little need to be able to
815	filter messages without dequeuing them.	991	filter messages without dequeuing them.
816		992
817	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	993	This is not a philosophical difference, but simply stems from AnyEvent::MP
		994	being event-based, while Erlang is process-based.
		995
		996	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		997	top of AEMP and Coro threads.
818		998
819	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	999	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
820		1000
821	Sending messages in Erlang is synchronous and blocks the process (and	1001	Sending messages in Erlang is synchronous and blocks the process until
		1002	a conenction has been established and the message sent (and so does not
822	so does not need a queue that can overflow). AEMP sends are immediate,	1003	need a queue that can overflow). AEMP sends return immediately, connection
823	connection establishment is handled in the background.	1004	establishment is handled in the background.
824		1005
825	=item * Erlang suffers from silent message loss, AEMP does not.	1006	=item * Erlang suffers from silent message loss, AEMP does not.
826		1007
827	Erlang makes few guarantees on messages delivery - messages can get lost	1008	Erlang implements few guarantees on messages delivery - messages can get
828	without any of the processes realising it (i.e. you send messages a, b,	1009	lost without any of the processes realising it (i.e. you send messages a,
829	and c, and the other side only receives messages a and c).	1010	b, and c, and the other side only receives messages a and c).
830		1011
831	AEMP guarantees correct ordering, and the guarantee that after one message	1012	AEMP guarantees (modulo hardware errors) correct ordering, and the
832	is lost, all following ones sent to the same port are lost as well, until	1013	guarantee that after one message is lost, all following ones sent to the
833	monitoring raises an error, so there are no silent "holes" in the message	1014	same port are lost as well, until monitoring raises an error, so there are
834	sequence.	1015	no silent "holes" in the message sequence.
		1016
		1017	If you want your software to be very reliable, you have to cope with
		1018	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
		1019	simply tries to work better in common error cases, such as when a network
		1020	link goes down.
835		1021
836	=item * Erlang can send messages to the wrong port, AEMP does not.	1022	=item * Erlang can send messages to the wrong port, AEMP does not.
837		1023
838	In Erlang it is quite likely that a node that restarts reuses a process ID	1024	In Erlang it is quite likely that a node that restarts reuses an Erlang
839	known to other nodes for a completely different process, causing messages	1025	process ID known to other nodes for a completely different process,
840	destined for that process to end up in an unrelated process.	1026	causing messages destined for that process to end up in an unrelated
		1027	process.
841		1028
842	AEMP never reuses port IDs, so old messages or old port IDs floating	1029	AEMP does not reuse port IDs, so old messages or old port IDs floating
843	around in the network will not be sent to an unrelated port.	1030	around in the network will not be sent to an unrelated port.
844		1031
845	=item * Erlang uses unprotected connections, AEMP uses secure	1032	=item * Erlang uses unprotected connections, AEMP uses secure
846	authentication and can use TLS.	1033	authentication and can use TLS.
847		1034
…		…
850		1037
851	=item * The AEMP protocol is optimised for both text-based and binary	1038	=item * The AEMP protocol is optimised for both text-based and binary
852	communications.	1039	communications.
853		1040
854	The AEMP protocol, unlike the Erlang protocol, supports both programming	1041	The AEMP protocol, unlike the Erlang protocol, supports both programming
855	language independent text-only protocols (good for debugging) and binary,	1042	language independent text-only protocols (good for debugging), and binary,
856	language-specific serialisers (e.g. Storable). By default, unless TLS is	1043	language-specific serialisers (e.g. Storable). By default, unless TLS is
857	used, the protocol is actually completely text-based.	1044	used, the protocol is actually completely text-based.
858		1045
859	It has also been carefully designed to be implementable in other languages	1046	It has also been carefully designed to be implementable in other languages
860	with a minimum of work while gracefully degrading functionality to make the	1047	with a minimum of work while gracefully degrading functionality to make the
861	protocol simple.	1048	protocol simple.
862		1049
863	=item * AEMP has more flexible monitoring options than Erlang.	1050	=item * AEMP has more flexible monitoring options than Erlang.
864		1051
865	In Erlang, you can chose to receive I<all> exit signals as messages	1052	In Erlang, you can chose to receive I<all> exit signals as messages or
866	or I<none>, there is no in-between, so monitoring single processes is	1053	I<none>, there is no in-between, so monitoring single Erlang processes is
867	difficult to implement. Monitoring in AEMP is more flexible than in	1054	difficult to implement.
868	Erlang, as one can choose between automatic kill, exit message or callback	1055
869	on a per-process basis.	1056	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		1057	between automatic kill, exit message or callback on a per-port basis.
870		1058
871	=item * Erlang tries to hide remote/local connections, AEMP does not.	1059	=item * Erlang tries to hide remote/local connections, AEMP does not.
872		1060
873	Monitoring in Erlang is not an indicator of process death/crashes, in the	1061	Monitoring in Erlang is not an indicator of process death/crashes, in the
874	same way as linking is (except linking is unreliable in Erlang).	1062	same way as linking is (except linking is unreliable in Erlang).
…		…
896	overhead, as well as having to keep a proxy object everywhere.	1084	overhead, as well as having to keep a proxy object everywhere.
897		1085
898	Strings can easily be printed, easily serialised etc. and need no special	1086	Strings can easily be printed, easily serialised etc. and need no special
899	procedures to be "valid".	1087	procedures to be "valid".
900		1088
901	And as a result, a miniport consists of a single closure stored in a	1089	And as a result, a port with just a default receiver consists of a single
902	global hash - it can't become much cheaper.	1090	code reference stored in a global hash - it can't become much cheaper.
903		1091
904	=item Why favour JSON, why not a real serialising format such as Storable?	1092	=item Why favour JSON, why not a real serialising format such as Storable?
905		1093
906	In fact, any AnyEvent::MP node will happily accept Storable as framing	1094	In fact, any AnyEvent::MP node will happily accept Storable as framing
907	format, but currently there is no way to make a node use Storable by	1095	format, but currently there is no way to make a node use Storable by
…		…
923		1111
924	L<AnyEvent::MP::Intro> - a gentle introduction.	1112	L<AnyEvent::MP::Intro> - a gentle introduction.
925		1113
926	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.	1114	L<AnyEvent::MP::Kernel> - more, lower-level, stuff.
927		1115
928	L<AnyEvent::MP::Global> - network maintainance and port groups, to find	1116	L<AnyEvent::MP::Global> - network maintenance and port groups, to find
929	your applications.	1117	your applications.
		1118
		1119	L<AnyEvent::MP::DataConn> - establish data connections between nodes.
930		1120
931	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from	1121	L<AnyEvent::MP::LogCatcher> - simple service to display log messages from
932	all nodes.	1122	all nodes.
933		1123
934	L<AnyEvent>.	1124	L<AnyEvent>.

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Comparing AnyEvent-MP/MP.pm (file contents): Revision 1.91 by root, Tue Sep 22 09:54:42 2009 UTC vs. Revision 1.126 by root, Sat Mar 3 19:43:41 2012 UTC

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Revision 1.91 by root, Tue Sep 22 09:54:42 2009 UTC vs.
Revision 1.126 by root, Sat Mar 3 19:43:41 2012 UTC