Difference between revisions of "The BPJ Library"

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Revision as of 13:26, 4 August 2013

See examples, e.g., BPJ/BPJCore110 -> bp.src.unittest.helloworld BPJ/Examples -> TicTacToe Events B-threads B-Program(s) A main method:


Events

  • Reflect the elements of behavior of your application (and its environment) – what you want to see in a trace.
  • Instantiate or extend Event class
  • Optional string name in constructor or in setName();
  • Optional data fields
  • See later on Event Sets

B-Threads

  • Contain the logic of your application
  • You code runBThread() method
  • Use events to affect system behavior
  • Call bSync() method to request, wait for or block events
  • You code import static bp.BProgram.bp
  • Use Java freely – but don’t wait for slow things (GUI interaction should be done separately).
  • Avoid or minimize side effects and external dependencies that are not event-driven
  • Events should be natural system behavior - minimize usage of events for pure inter-b-thread communication.
  • You may instantiate multiple instances of same b-thread class – possibly with constructor parameters
  • Parameters may be manually specified during instantiation or generated by the application - see Tic-Tac-Toe example.

The B-Program

  • A container and execution environment for b-threads.
  • You only need to instantiate it.
  • BProgram externalizes the public variable lastEvent that can be seen by b-threads.
  • Usually – there is just one BProgram per application, running all your b-threads, but you may have several b-programs in parallel.
  • You may change run-time parameters of the b-program by calling methods to set them.

The bSync() Method

  • bSync(RequestableEventInterface,EventSetInterface,EventSetInterface)
  • Three parameters:
    • Requested Events:
    • Waited-for events (a.k.a “watched events”)
    • Blocked events
  • Drives the collective execution mechanism:
    • Synchronizes the b-thread with the others – waits until all b-threads call bSync().
    • When all b-threads are waiting in bSync – the first event that is requested and is not blocked is selected. The search order is by b-thread priority, and within it – order of events in requestable event set.
    • All b-threads that have the selected event in their requested events set or in their waited-for event set are resumed.
    • B-threads can examine the event triggered by the last bSync in bp.lastEvent. Don’t modify this field; don’t rely on it past another bSync() call.
    • This synchronization assumes that all b-threads will be good citizens and will not wait long (e.g., will not be involved in GUI input)

Event Sets and Interfaces

  • The parameters to bSync are three sets of events, or sets of sets.
  • Nesting of set containment is allowed, and not limited.
  • RequestableEventInterface:
    • Required for requested event parameter of bSync();
    • Can be used also for waited-for and blocked.
    • Must contain an ordered set of concrete events, or ordered sets of requestableEventInterface (nesting of sets).
    • Implemented by RequestedEventsSet
  • EventSetInterface:
    • Can be used for waited-for and blocked events.
    • The method contains() determines membership in the EventSetInterface object.
    • This set can describe very large or infinite sets of events, or be used to filter events.
    • The set can contain another EventSetInterface (neesting of sets).
    • Cannot be used as the requested events parameter of bSync(), because it does not provide an interator over the concrete events.
    • Implemented by EventSet
  • RequestableEventSet: Implements both interfaces above
  • EventSet: implements only EventSetInterface
  • Event: The Event class implements the above interfaces. An individual event can be used instead of any of these sets. An event is also a set that contains the event.

Special Event Sets

  • None: the empty set - contains no event. Used in calls to bSync() when one of the three parameters should be empty.
  • All: contains all events. Most commonly used in bSync() when a b-thread such as a logger waits for all events.
  • EventsOfClass: all events of a given class.
  • Composable event sets
    • Available in BPJContrib (***ToDo: add BPJContrib to the package)
    • Allows specification of, e.g., theEventSet(A).and( not( theEventSet(B).or(C) ).xor( theEventSet(A).nand(c) ) )

anyOf( A, B, theEventSet(C).and(not(d)) )

The Application and the Main Method

  • In the main method insert the line BProgram.startBApplication(my-app-class, my-package);
  • You need to provide the method runBApplicatio. In it:
    • Instantiate and add b-threads to the b-program
    • Start the b-threads
    • You must assign unique real number priority to each b-thread. The smaller the value, the higher the priority.
    • Start any other parts (non-BP) of your application.
    • runBApplication may exit, or may wait for all b-threads to end.
  • Example (see BPJ package for more detail):
import static bp.BProgram.bp;
public class my-app-class implements BApplication {
   public void runBApplication() {
     bp.add(new my-Bthread-1(), mypriority1);
     bp.add(new my-Bthread-2(), mypriority2);
     . . .
     bp.startAll();
    }
   }

Dynamic B-Threads

  • New b-threads may be added by external (non behavioral) applications modules, or by b-threads
  • A running Java thread may be registered as a b-thread and subsequently deregistered as follows:...

See examples in...

Injecting External Events

ToDo: add text here

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