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:
    Serviceable
    • Field Summary

      Fields 
      Modifier and Type Field Description
      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  
    • Field Detail

      • 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()