1. middleware a guide to middleware construction (roughly) based on Boris
(roughly) geared towards Java
Simon Lynch

2. what is middleware?
a substrate to support system components / subsystems
an interface between subsystems
an additional level of abstraction

3. what does middleware do?
handles data/message passing between subsystems
provides clean subsystem interfacing
allowing greater encapsulation & interoperability
adding a new level of abstraction
“glues (sub)systems together”

4. what may it also do? facilitate easier concurrency for subsystems
allow distribution
provide system diagnostics
allow dynamic reconfiguration
manage resources

5. building middleware NB: these notes based on Boris philosophy
meta-agents / meta-actors
building blocks
blocking queue  (spooler)  meta-agent  Portal agent, socket agent, interface agent
PS: assume (here) all messages are Strings

6. messages & threads see example… message sending message receiving
clones
non-clones

7. a meta-agent subsystem

8. the blocking queue eg: class LinkedBlockingQueue<E>
extends AbstractQueue<E>
implements BlockingQueue<E>, Serializable
 void put(E e) Inserts element at the tail of queue, waiting if necessary for space to become available.
 E take() Retrieves and removes the head of this queue, waiting if necessary until an element becomes available.

9. meta-agent meta-agent extends blocking-queue variables: name, portal
constructor method( args... )
| super.constructor( args... )
| thread{ loop-forever
| msgHandler ( dequeue() )}
void msgHandler( String msg )
| ... msg processing code goes here...

10. msgs via portals (i) agents sharing a portal
(ii) agents with their own portal

11. portal portal extends meta-agent variables: routing-table
void msg-handler(msg)
| routing-table.get(
| recipient-of(msg)).enqueue(msg)
void add-agent( name, agent )
| routing-table.set( name, agent )
so... meta-agent.send-message(recipient, msg)
| portal.enqueue(
| wrap(name, recipient, msg)

12. comms with sockets

13. name mapping #1
P1 : { A1  | A1| , A2  | A2| }

14. name mapping #2
P1 : { A1  | A1| , A2  | P2| } P2 : { A1  | P1| , A2  | A2| }

15. name mapping #3
P1 : { A1  | A1| , A2  | S1| } P2 : { A1  | S2| , A2  | A2| }

16. usr-agent #1 usr-agent variables: metaAgent, msgHandler
constructor method( args... )
| metaAgent = new MetaAgent( args... )
| ...other stuff...
void sendMessage( String to, String msg)
| ... add who from & send ...
...other methods...

17. usr-agent #2 usr-agent variables: metaAgent, msgHandler
constructor method( args... )
| metaAgent = new MetaAgent( args... )
| ...other stuff...
void msg-handler(msg)
| if msgHandler != null
| msgHandler.processMsg( ...un-wrapped msg...)
void addMsgHandler( MsgHandler m )...
NB: MsgHandler is an Interface with a method...
void processMsg( String )