Apache Derby Database Engine and Embedded JDBC Driver 10.17.1.0 · org.apache.derby.iapi.services.daemon.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

Modifier and Type	Field and Description
public static final int	DONE return status for performWork - only meaningful for enqueued client
public static final int	REQUEUE

Method Summary

Modifier and Type	Method and Description
public int	Returns: the return status is only significant if the Serviceable client was enqueued instead of subscribed. For subscribed client, the return status is ignored. For enqueue client, it returns DONE or REQUEUE. If a REQUEUEd is returned, it would be desirable if this should not be serviceASAP, although no harm is done if this still maintains that this should be serviced ASAP ... performWork(ContextManager the contextManager set up by the DaemonService. There may or may not be the necessary context on it, depending on which other Serviceable object it has done work for. context) Do whatever it is that you want the daemon to do for you.
public boolean	Returns: true if this should work as soon as possible serviceASAP() If this work should be done as soon as possible, then return true.
public boolean	Returns: true if this work shold happen immediately on the user thread serviceImmediately() If this work should be done immediately on the user thread then return true.

Field Detail

DONE	back to summary
public static final int DONE return status for performWork - only meaningful for enqueued client

REQUEUE	back to summary
public static final int REQUEUE

Method Detail

performWork	back to summary
public int performWork(ContextManager context) throws 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. Parameters context:ContextManager the contextManager set up by the DaemonService. There may or may not be the necessary context on it, depending on which other Serviceable object it has done work for. Returns:int the return status is only significant if the Serviceable client was enqueued instead of subscribed. For subscribed client, the return status is ignored. For enqueue client, it returns DONE or REQUEUE. If a REQUEUEd is returned, it would be desirable if this should not be serviceASAP, although no harm is done if this still maintains that this should be serviced ASAP ... Exceptions StandardException: Standard Derby exception policy MT - depends on the work. Be wary of multiple DaemonService thread calling at the same time if you subscribe or enqueue multiple times.

performWork

back to summary

public int performWork(ContextManager context) throws 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.

Parameters

context:ContextManager: the contextManager set up by the DaemonService. There may or may not be the necessary context on it, depending on which other Serviceable object it has done work for.

Returns:int

the return status is only significant if the Serviceable client was enqueued instead of subscribed. For subscribed client, the return status is ignored. For enqueue client, it returns DONE or REQUEUE. If a REQUEUEd is returned, it would be desirable if this should not be serviceASAP, although no harm is done if this still maintains that this should be serviced ASAP ...

Exceptions

StandardException:: Standard Derby exception policy
MT - depends on the work. Be wary of multiple DaemonService thread calling at the same time if you subscribe or enqueue multiple times.

serviceASAP	back to summary
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 Returns:boolean true if this should work as soon as possible

serviceASAP

back to summary

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

Returns:boolean: true if this should work as soon as possible

serviceImmediately	back to summary
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. Returns:boolean true if this work shold happen immediately on the user thread

serviceImmediately

back to summary

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.

Returns:boolean: true if this work shold happen immediately on the user thread

public Interface Serviceable

Field Summary

Method Summary

Field Detail

Method Detail