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

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.118 by root, Thu Jun 30 09:31:58 2011 UTC vs.
Revision 1.119 by root, Sun Feb 26 10:29:59 2012 UTC

…		…
78		78
79	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
80	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
81	anything was listening for them or not.	81	anything was listening for them or not.
82		82
		83	Ports are represented by (printable) strings called "port IDs".
		84
83	=item port ID - C<nodeid#portname>	85	=item port ID - C<nodeid#portname>
84		86
85	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<#>) as
86	separator, and a port name (a printable string of unspecified format).	88	separator, and a port name (a printable string of unspecified format).
87		89
…		…
91	which enables nodes to manage each other remotely, and to create new	93	which enables nodes to manage each other remotely, and to create new
92	ports.	94	ports.
93		95
94	Nodes are either public (have one or more listening ports) or private	96	Nodes are either public (have one or more listening ports) or private
95	(no listening ports). Private nodes cannot talk to other private nodes	97	(no listening ports). Private nodes cannot talk to other private nodes
96	currently.	98	currently, but all nodes can talk to public nodes.
		99
		100	Nodes is represented by (printable) strings called "node IDs".
97		101
98	=item node ID - C<[A-Za-z0-9_\-.:]*>	102	=item node ID - C<[A-Za-z0-9_\-.:]*>
99		103
100	A node ID is a string that uniquely identifies the node within a	104	A node ID is a string that uniquely identifies the node within a
101	network. Depending on the configuration used, node IDs can look like a	105	network. Depending on the configuration used, node IDs can look like a
102	hostname, a hostname and a port, or a random string. AnyEvent::MP itself	106	hostname, a hostname and a port, or a random string. AnyEvent::MP itself
103	doesn't interpret node IDs in any way.	107	doesn't interpret node IDs in any way except to uniquely identify a node.
104		108
105	=item binds - C<ip:port>	109	=item binds - C<ip:port>
106		110
107	Nodes can only talk to each other by creating some kind of connection to	111	Nodes can only talk to each other by creating some kind of connection to
108	each other. To do this, nodes should listen on one or more local transport	112	each other. To do this, nodes should listen on one or more local transport
		113	endpoints - binds.
		114
109	endpoints - binds. Currently, only standard C<ip:port> specifications can	115	Currently, only standard C<ip:port> specifications can be used, which
110	be used, which specify TCP ports to listen on.	116	specify TCP ports to listen on. So a bind is basically just a tcp socket
		117	in listening mode thta accepts conenctions form other nodes.
111		118
112	=item seed nodes	119	=item seed nodes
113		120
114	When a node starts, it knows nothing about the network. To teach the node	121	When a node starts, it knows nothing about the network it is in - it
115	about the network it first has to contact some other node within the	122	needs to connect to at least one other node that is already in the
116	network. This node is called a seed.	123	network. These other nodes are called "seed nodes".
117		124
118	Apart from the fact that other nodes know them as seed nodes and they have	125	Seed nodes themselves are not special - they are seed nodes only because
119	to have fixed listening addresses, seed nodes are perfectly normal nodes -	126	some other node I<uses> them as such, but any node can be used as seed
120	any node can function as a seed node for others.	127	node for other nodes, and eahc node cna use a different set of seed nodes.
121		128
122	In addition to discovering the network, seed nodes are also used to	129	In addition to discovering the network, seed nodes are also used to
123	maintain the network and to connect nodes that otherwise would have	130	maintain the network - all nodes using the same seed node form are part of
124	trouble connecting. They form the backbone of an AnyEvent::MP network.	131	the same network. If a network is split into multiple subnets because e.g.
		132	the network link between the parts goes down, then using the same seed
		133	nodes for all nodes ensures that eventually the subnets get merged again.
125		134
126	Seed nodes are expected to be long-running, and at least one seed node	135	Seed nodes are expected to be long-running, and at least one seed node
127	should always be available. They should also be relatively responsive - a	136	should always be available. They should also be relatively responsive - a
128	seed node that blocks for long periods will slow down everybody else.	137	seed node that blocks for long periods will slow down everybody else.
129		138
		139	For small networks, it's best if every node uses the same set of seed
		140	nodes. For large networks, it can be useful to specify "regional" seed
		141	nodes for most nodes in an area, and use all seed nodes as seed nodes for
		142	each other. What's important is that all seed nodes connections form a
		143	complete graph, so that the network cannot split into separate subnets
		144	forever.
		145
		146	Seed nodes are represented by seed IDs.
		147
130	=item seeds - C<host:port>	148	=item seed IDs - C<host:port>
131		149
132	Seeds are transport endpoint(s) (usually a hostname/IP address and a	150	Seed IDs are transport endpoint(s) (usually a hostname/IP address and a
133	TCP port) of nodes that should be used as seed nodes.	151	TCP port) of nodes that should be used as seed nodes.
134		152
135	The nodes listening on those endpoints are expected to be long-running,	153	=item global nodes
136	and at least one of those should always be available. When nodes run out	154
137	of connections (e.g. due to a network error), they try to re-establish	155	An AEMP network needs a discovery service - nodes need to know how to
138	connections to some seednodes again to join the network.	156	connect to other nodes they only know by name. In addition, AEMP offers a
		157	distributed "group database", which maps group names to a list of strings
		158	- for example, to register worker ports.
		159
		160	A network needs at least one global node to work, and allows every node to
		161	be a global node.
		162
		163	Any node that loads the L<AnyEvent::MP::Global> module becomes a global
		164	node and tries to keep connections to all other nodes. So while it can
		165	make sense to make every node "global" in small networks, it usually makes
		166	sense to only make seed nodes into global nodes in large networks (nodes
		167	keep connections to seed nodes and global nodes, so makign them the same
		168	reduces overhead).
139		169
140	=back	170	=back
141		171
142	=head1 VARIABLES/FUNCTIONS	172	=head1 VARIABLES/FUNCTIONS
143		173
…		…
236	used, meaning the node will bind on a dynamically-assigned port on every	266	used, meaning the node will bind on a dynamically-assigned port on every
237	local IP address it finds.	267	local IP address it finds.
238		268
239	=item step 3, connect to seed nodes	269	=item step 3, connect to seed nodes
240		270
241	As the last step, the seeds list from the profile is passed to the	271	As the last step, the seed ID list from the profile is passed to the
242	L<AnyEvent::MP::Global> module, which will then use it to keep	272	L<AnyEvent::MP::Global> module, which will then use it to keep
243	connectivity with at least one node at any point in time.	273	connectivity with at least one node at any point in time.
244		274
245	=back	275	=back
246		276
…		…
862	ports being the special case/exception, where transport errors cannot	892	ports being the special case/exception, where transport errors cannot
863	occur.	893	occur.
864		894
865	=item * Erlang uses processes and a mailbox, AEMP does not queue.	895	=item * Erlang uses processes and a mailbox, AEMP does not queue.
866		896
867	Erlang uses processes that selectively receive messages, and therefore	897	Erlang uses processes that selectively receive messages out of order, and
868	needs a queue. AEMP is event based, queuing messages would serve no	898	therefore needs a queue. AEMP is event based, queuing messages would serve
869	useful purpose. For the same reason the pattern-matching abilities of	899	no useful purpose. For the same reason the pattern-matching abilities
870	AnyEvent::MP are more limited, as there is little need to be able to	900	of AnyEvent::MP are more limited, as there is little need to be able to
871	filter messages without dequeuing them.	901	filter messages without dequeuing them.
872		902
873	(But see L<Coro::MP> for a more Erlang-like process model on top of AEMP).	903	This is not a philosophical difference, but simply stems from AnyEvent::MP
		904	being event-based, while Erlang is process-based.
		905
		906	You cna have a look at L<Coro::MP> for a more Erlang-like process model on
		907	top of AEMP and Coro threads.
874		908
875	=item * Erlang sends are synchronous, AEMP sends are asynchronous.	909	=item * Erlang sends are synchronous, AEMP sends are asynchronous.
876		910
877	Sending messages in Erlang is synchronous and blocks the process (and	911	Sending messages in Erlang is synchronous and blocks the process until
		912	a conenction has been established and the message sent (and so does not
878	so does not need a queue that can overflow). AEMP sends are immediate,	913	need a queue that can overflow). AEMP sends return immediately, connection
879	connection establishment is handled in the background.	914	establishment is handled in the background.
880		915
881	=item * Erlang suffers from silent message loss, AEMP does not.	916	=item * Erlang suffers from silent message loss, AEMP does not.
882		917
883	Erlang implements few guarantees on messages delivery - messages can get	918	Erlang implements few guarantees on messages delivery - messages can get
884	lost without any of the processes realising it (i.e. you send messages a,	919	lost without any of the processes realising it (i.e. you send messages a,
…		…
887	AEMP guarantees (modulo hardware errors) correct ordering, and the	922	AEMP guarantees (modulo hardware errors) correct ordering, and the
888	guarantee that after one message is lost, all following ones sent to the	923	guarantee that after one message is lost, all following ones sent to the
889	same port are lost as well, until monitoring raises an error, so there are	924	same port are lost as well, until monitoring raises an error, so there are
890	no silent "holes" in the message sequence.	925	no silent "holes" in the message sequence.
891		926
		927	If you want your software to be very reliable, you have to cope with
		928	corrupted and even out-of-order messages in both Erlang and AEMP. AEMP
		929	simply tries to work better in common error cases, such as when a network
		930	link goes down.
		931
892	=item * Erlang can send messages to the wrong port, AEMP does not.	932	=item * Erlang can send messages to the wrong port, AEMP does not.
893		933
894	In Erlang it is quite likely that a node that restarts reuses a process ID	934	In Erlang it is quite likely that a node that restarts reuses an Erlang
895	known to other nodes for a completely different process, causing messages	935	process ID known to other nodes for a completely different process,
896	destined for that process to end up in an unrelated process.	936	causing messages destined for that process to end up in an unrelated
		937	process.
897		938
898	AEMP never reuses port IDs, so old messages or old port IDs floating	939	AEMP does not reuse port IDs, so old messages or old port IDs floating
899	around in the network will not be sent to an unrelated port.	940	around in the network will not be sent to an unrelated port.
900		941
901	=item * Erlang uses unprotected connections, AEMP uses secure	942	=item * Erlang uses unprotected connections, AEMP uses secure
902	authentication and can use TLS.	943	authentication and can use TLS.
903		944
…		…
906		947
907	=item * The AEMP protocol is optimised for both text-based and binary	948	=item * The AEMP protocol is optimised for both text-based and binary
908	communications.	949	communications.
909		950
910	The AEMP protocol, unlike the Erlang protocol, supports both programming	951	The AEMP protocol, unlike the Erlang protocol, supports both programming
911	language independent text-only protocols (good for debugging) and binary,	952	language independent text-only protocols (good for debugging), and binary,
912	language-specific serialisers (e.g. Storable). By default, unless TLS is	953	language-specific serialisers (e.g. Storable). By default, unless TLS is
913	used, the protocol is actually completely text-based.	954	used, the protocol is actually completely text-based.
914		955
915	It has also been carefully designed to be implementable in other languages	956	It has also been carefully designed to be implementable in other languages
916	with a minimum of work while gracefully degrading functionality to make the	957	with a minimum of work while gracefully degrading functionality to make the
917	protocol simple.	958	protocol simple.
918		959
919	=item * AEMP has more flexible monitoring options than Erlang.	960	=item * AEMP has more flexible monitoring options than Erlang.
920		961
921	In Erlang, you can chose to receive I<all> exit signals as messages	962	In Erlang, you can chose to receive I<all> exit signals as messages or
922	or I<none>, there is no in-between, so monitoring single processes is	963	I<none>, there is no in-between, so monitoring single Erlang processes is
923	difficult to implement. Monitoring in AEMP is more flexible than in	964	difficult to implement.
924	Erlang, as one can choose between automatic kill, exit message or callback	965
925	on a per-process basis.	966	Monitoring in AEMP is more flexible than in Erlang, as one can choose
		967	between automatic kill, exit message or callback on a per-port basis.
926		968
927	=item * Erlang tries to hide remote/local connections, AEMP does not.	969	=item * Erlang tries to hide remote/local connections, AEMP does not.
928		970
929	Monitoring in Erlang is not an indicator of process death/crashes, in the	971	Monitoring in Erlang is not an indicator of process death/crashes, in the
930	same way as linking is (except linking is unreliable in Erlang).	972	same way as linking is (except linking is unreliable in Erlang).

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Comparing AnyEvent-MP/MP.pm (file contents): Revision 1.118 by root, Thu Jun 30 09:31:58 2011 UTC vs. Revision 1.119 by root, Sun Feb 26 10:29:59 2012 UTC

Diff Legend

Comparing AnyEvent-MP/MP.pm (file contents):
Revision 1.118 by root, Thu Jun 30 09:31:58 2011 UTC vs.
Revision 1.119 by root, Sun Feb 26 10:29:59 2012 UTC