Serviceable

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org.apache.derby.iapi.services.daemon
Interface Serviceable

public interface Serviceable

To use a DaemonService, one implements the Serviceable interface. Only one DaemonService will call this at any given time. However, if this Serviceable object subscribes to or enqueues to the DeamonService multiple times, then multiple DaemonService threads may call this Serviceable object at the same time. The Serviceable object must decide what synchronization it needs to provide depending on what work it needs to do. The Serviceable interface does not provide a way to pass a work object to identify what work needs to be done, it is assumed that the Serviceable object knows that. If a Serviceable object has different work for the DaemonService to do, it must somehow encapsulate or identify the different work by an intermediary object which implements the Serviceable interface and which can an identify the different work and pass it along to the object that can deal with them.

Field Summary

static int DONE
          return status for performWork - only meaningful for enqueued client

static int REQUEUE


Method Summary

int performWork(org.apache.derby.iapi.services.context.ContextManager context)
          Do whatever it is that you want the daemon to do for you.

boolean serviceASAP()
          If this work should be done as soon as possible, then return true.

boolean serviceImmediately()
          If this work should be done immediately on the user thread then return true.

Field Detail

DONE

public static final int DONE

return status for performWork - only meaningful for enqueued client

See Also:: Constant Field Values

REQUEUE

public static final int REQUEUE

See Also:: Constant Field Values

Method Detail

performWork

public int performWork(org.apache.derby.iapi.services.context.ContextManager context)
                throws org.apache.derby.iapi.error.StandardException

Do whatever it is that you want the daemon to do for you. There may be multiple daemon objects on different thread calling performWork at the same time. The DaemonService will always call performWork with a context manager set up. the DaemonService will clean up the context if an exception is thrown. However, it is up to performWork to manage its own transaction. If you start a transaction in performWork, you must commit or abort it at the end. You may leave the transaction open so that other serviceable may use the transaction and context without starting a new one. On the same token, there may already be an opened transaction on the context. Serviceable performWork should always check the state of the context before use. A Serviceable object should be well behaved while it is performing the daemon work, i.e., it should not take too many resources or hog the CPU for too long or deadlock with anyone else.

serviceASAP

public boolean serviceASAP()

If this work should be done as soon as possible, then return true. If it doesn't make any difference if it is done sooner rather than later, then return false. The difference is whether or not the daemon service will be notified to work on this when this work is enqueued or subscribed, in case the serviceable work is put together but not sent to the daemon service directly, like in post commit processing

MT - MT safe

serviceImmediately

public boolean serviceImmediately()

If this work should be done immediately on the user thread then return true. If it doesn't make any difference if this work is done on a the user thread immediately or if it is performed by another thread asynchronously later, then return false.