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

  • how quickly and how often the clients should expect to be be serviced
  • how the clients are prioritized
  • whether the clients need to tolerate spurious services

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

See Also:
  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static final String
    Trace flag that can be used to turn off background daemons If DaemonOff is set, background Daemon will not attempt to do anything.
    static final String
    Trace flag that can be used by Daemons to print stuff out
    static final int
     
  • Method Summary

    Modifier and Type
    Method
    Description
    void
    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.
    void
    Resume service after a pause
    void
    serviceNow(int clientNumber)
    Service this subscription ASAP.
    void
    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
     
  • Field Details

    • TIMER_DELAY

      static final int TIMER_DELAY
      See Also:
    • DaemonTrace

      static final String DaemonTrace
      Trace flag that can be used by Daemons to print stuff out
    • DaemonOff

      static final 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 Details

    • 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()