org.hd.d.pg2k.webSvr.exhibit
Class DataSourceBean.EDVHObservable

java.lang.Object
  java.util.Observable
      org.hd.d.pg2k.webSvr.exhibit.DataSourceBean.EDVHObservable

Enclosing class:

DataSourceBean

private static final class DataSourceBean.EDVHObservable
extends java.util.Observable

An Observable that changes when its "currentEDVH" value changes. This currentEDVH is the hash over the exhibit data.

When we call notifyObserversInNewThread() we do so where possible with a single Integer argument carrying the current hash value. An Observer may ignore a call when the value matches its current hash in case it has already rebuilt its cache.

Note that we build this on top of the default Observable implementation which holds no locks while delivering notifications, which should help us avoid deadlocks.

currentEVDH

private int currentEVDH

The current hash of the exhibits: when this changes then the whole Observable hasChanged().

deliveryThread

private java.lang.Thread deliveryThread

Thread, if any, being used to deliver notifications. Private to notifyObserversInNewThread() and accessed under the instance lock.

DataSourceBean.EDVHObservable

private DataSourceBean.EDVHObservable()

setCurrentEDVH

final void setCurrentEDVH(int currentEVDH)

Set the currentEVDH; when changed hasChanged() returns true.

notifyObserversInNewThread

final void notifyObserversInNewThread(java.lang.Object arg)

Spins off background thread to call super.notifyObserversInNewThread(). Will not attempt to start a new thread to do this if the last one appears not to have died, so will in that case just not send any notifications.

No lock is held while notifications are delivered; the instance lock may be briefly held while the thread field is being examined and a thread launched.

Parameters:

arg - any object