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

All Known Implementing Classes:
BasicDaemon

public interface DaemonService

A DaemonService provides a background service which is suitable for asynchronous I/O and general clean up. It should not be used as a general worker thread for parallel execution. A DaemonService can be subscribe to by many Serviceable objects and a DaemonService will call that object's performWork from time to time. The performWork method is defined by the client object and should be well behaved - in other words, it should not take too long or hog too many resources or deadlock with anyone else. And it cannot (should not) error out.

It is up to each DaemonService implementation to define its level of service, including

MT - all routines on the interface must be MT-safe.

See Also:
Serviceable

Field Summary
static java.lang.String DaemonOff
          Trace flag that can be used to turn off background daemons If DaemonOff is set, background Daemon will not attempt to do anything.
static java.lang.String DaemonTrace
          Trace flag that can be used by Daemons to print stuff out
static int TIMER_DELAY
           
 
Method Summary
 void clear()
          Clear all the queued up work from this daemon.
 boolean enqueue(Serviceable newClient, boolean serviceNow)
          Request a one time service from the Daemon.
 void pause()
          Pause.
 void resume()
          Resume service after a pause
 void serviceNow(int clientNumber)
          Service this subscription ASAP.
 void stop()
          End this daemon service
 int subscribe(Serviceable newClient, boolean onDemandOnly)
          Add a new client that this daemon needs to service
 void unsubscribe(int clientNumber)
          Get rid of a client from the daemon.
 void waitUntilQueueIsEmpty()
           
 

Field Detail

TIMER_DELAY

static final int TIMER_DELAY
See Also:
Constant Field Values

DaemonTrace

static final java.lang.String DaemonTrace
Trace flag that can be used by Daemons to print stuff out


DaemonOff

static final java.lang.String DaemonOff
Trace flag that can be used to turn off background daemons If DaemonOff is set, background Daemon will not attempt to do anything.

Method Detail

subscribe

int subscribe(Serviceable newClient,
              boolean onDemandOnly)
Add a new client that this daemon needs to service

Parameters:
newClient - a Serviceable object this daemon will service from time to time
onDemandOnly - only service this client when it ask for service with a serviceNow request
Returns:
a client number that uniquely identifies this client (this subscription)

unsubscribe

void unsubscribe(int clientNumber)
Get rid of a client from the daemon. If a client is being serviced when the call is made, the implementation may choose whether or not the call should block until the client has completed its work. If the call does not block, the client must be prepared to handle calls to its performWork() method even after unsubscribe() has returned.

Parameters:
clientNumber - the number that uniquely identify the client

serviceNow

void serviceNow(int clientNumber)
Service this subscription ASAP. When this method is called, the subscriber's performWork() method is guaranteed to be invoked at some point in the future. However, there is no guarantee that a subscriber's performWork() is called the same number of times as the subscriber calls this method. More precisely, if a subscriber is waiting for this daemon service to invoke its performWork() method, the daemon service may, but is not required to, ignore requests from that subscriber until the performWork() method has been invoked.

Parameters:
clientNumber - the number that uniquely identifies the client

enqueue

boolean enqueue(Serviceable newClient,
                boolean serviceNow)
Request a one time service from the Daemon. Unless performWork returns REQUEUE (see Serviceable), the daemon will service this client once and then it will get rid of this client. Since no client number is associated with this client, it cannot request to be serviced or be unsubscribed. The work is always added to the deamon, regardless of the state it returns.

Parameters:
newClient - the object that needs a one time service
serviceNow - if true, this client should be serviced ASAP, as if a serviceNow has been issued. If false, then this client will be serviced with the normal scheduled.
Returns:
true if the daemon indicates it is being overloaded, false it's happy.

pause

void pause()
Pause. No new service is performed until a resume is issued.


resume

void resume()
Resume service after a pause


stop

void stop()
End this daemon service


clear

void clear()
Clear all the queued up work from this daemon. Subscriptions are not affected.


waitUntilQueueIsEmpty

void waitUntilQueueIsEmpty()

Built on Thu 2012-03-29 21:53:33+0000, from revision ???

Apache Derby V10.6 Internals - Copyright © 2004,2007 The Apache Software Foundation. All Rights Reserved.