org.cougaar.core.blackboard

The standard agent contains a {@link org.cougaar.core.blackboard.StandardBlackboard} component that provides the {@link org.cougaar.core.service.BlackboardService}, which is a wrapper around the {@link org.cougaar.core.blackboard.Subscriber} class. The StandardBlackboard creates the {@link org.cougaar.core.blackboard.Distributor}, which manages the subscribers, and the special {@link org.cougaar.core.blackboard.Blackboard} subscriber to maintain a view of all blackboard objects and invoke {@link org.cougaar.core.domain.Domain} {@link org.cougaar.core.domain.LogicProvider}s. Each subscriber has a set of {@link org.cougaar.core.blackboard.Subscription}s that are known only to that subscriber. A subscriber registers with the distributor to receive blackboard add/change/remove notification "tuples". When a subscriber wishes to modify the blackboard contents, it must start a distributor transaction, fill an envelope with add/change/remove tuples, and finish the distributor transaction. The distributor also coordinates periodic persistence and ensures that blackboard updates are thread-safe.

For more detail, see the Cougaar Developers' Guide.

This is similar to a BitSet, but has a shifting base index.

Plugins are the most common example of such components.
ComponentPlugin is an extension of this class.

Create a derived class by implementing setupSubscriptions() and execute().

Note that both "precycle()" and "cycle()" will be run by the scheduler.

All operations are backed by the org.cougaar.core.blackboard.Distributor .

ChangeReports are published by using org.cougaar.core.service.BlackboardService.publishChange(ObjectCollection) and are viewed by using CollectionSubscription.getChangeReports(Object) .

Subclasses describe specific types of changes.

The hashCode and equals methods should compute their return values based on the type and not any specific (old) value which may be stored in the object.

See CollectionSubscription for a system property that identifies subscriptions that could potentially be changed to DeltaSubscriptions.

We subclass IncrementalSubscription to both reuse code and to make it easy for existing plugins to switch over to this class.

Any transaction envelopes received by the client for a newly created subscription prior to this envelope are ignored.

Note that Claim warnings are currently just warnings, regardless of how scary looking they are.

NOTE: at some point, only Publishable objects will be admitted to the blackboard.

The QM tracks which blackboard clients we care about quiescence for, and numbers incoming and outgoing messsages for those we care about.

Persistence reservations indicate that a persistence instance wishes to take a snapshot of its agent.

On the SubscriptionWatcher.signalNotify callback, the watcher should schedule itself to run in a separate thread, e.g.

TodoSubscriptions are typically used for Alarm callbacks, for example:

 public class MyPlugin extends ComponentPlugin {
 private TodoSubscription expiredAlarms;
 protected void setupSubscriptions() {
 expiredAlarms = (TodoSubscription) 
 blackboard.subscribe(new TodoSubscription("x"));
 // wake up in 10 seconds
 getAlarmService().addRealTimeAlarm(
 new MyAlarm(System.currentTimeMillis() + 10000));
 }
 protected void execute() {
 if (expiredAlarms.hasChanged()) {
 System.out.println("Due alarms: "+expiredAlarms.getAddedCollection());
 }
 }
 private class MyAlarm extends AlarmBase {
 // optionally add fields here, e.g.