Package com.tangosol.util

Class Daemon

java.lang.Object
com.tangosol.util.Base
com.tangosol.util.Daemon
All Implemented Interfaces:
Guardable, Runnable
Direct Known Subclasses:
AsyncBinaryStore.QueueDaemon, LoadBalancer.SocketHandler, ReadWriteBackingMap.ReadThread, ReadWriteBackingMap.WriteThread, RefreshableAddressProvider.RefreshThread, TaskDaemon
public abstract class Daemon extends Base implements Runnable, Guardable
A abstract Daemon thread handler. A sub-class need only provide an implementation of the run() method. When the Daemon is told to start, it will create a Java thread, which means that the number of Daemon instances within a system must be limited to a reasonable number. If an arbitrarily large number of conceptual daemons are necessary, consider using a TaskDaemon, which allows arbitrary tasks to be queued for execution.
Author:
cp 2000.08.02, cp 2006.02.23 (Coherence 3.2) added restartability, jh 2010.05.07 (Coherence 3.6) added shutdown

  • Constructor Details

    • Daemon

      public Daemon()
      Default constructor. Creates a Daemon using default settings. The daemon will not be automatically started.

    • Daemon

      public Daemon(String sName)
      Creates a Daemon with the specified name. The daemon will not be automatically started.
      Parameters:
      sName - the thread name (may be null)

    • Daemon

      public Daemon(String sName, int nPriority, boolean fStart)
      Creates a Daemon with a specified name and priority.

      Warning: If the implementation class is a inner non-static class that refers to its outer object ("MyOuterClass.this"), do not use the auto-start option. The reason is that the run() method of the Daemon may be invoked on the new thread before the construction of the Daemon object itself unwinds, which means that the outer object reference will not have been set yet, causing an inexplicable NullPointerException.

      Parameters:
      sName - the thread name (may be null)
      nPriority - the thread priority, between Thread.MIN_PRIORITY and Thread.MAX_PRIORITY inclusive
      fStart - pass true to auto-start the thread as part of its construction

  • Method Details

    • run

      public abstract void run()
      The daemon's implementation method. Override this method to implement a daemon.

      An example implementation is: 

      
   while (!isStopping())
       {
       // do some processing
       // ...

       synchronized (this)
           {
           // wait for notification of more work
           wait();
           }
       }
      Specified by:
      run in interface Runnable

    • setContext

      public void setContext(Guardian.GuardContext context)
      Set the guard context. Passing in null indicates that the Guardable is no longer being monitored by a Guardian.
      Specified by:
      setContext in interface Guardable
      Parameters:
      context - the context guarding this Guardable

    • recover

      public void recover()
      Attempt to recover this Guardable.

      In a common case where the Guardable has an associated thread, a suitable action would be to interrupt the thread.

      If this method does not return before the timeout expires, the Guardable will be considered unrecoverable and will be terminated.

      Specified by:
      recover in interface Guardable

    • terminate

      public void terminate()
      Terminate this Guardable.

      This is the final action taken by the Guardian before the Guardable is removed from its responsibility list.

      Specified by:
      terminate in interface Guardable

    • getContext

      public Guardian.GuardContext getContext()
      Return the guard context monitoring this guardable, or null if this Guardable is no longer being monitored.
      Specified by:
      getContext in interface Guardable
      Returns:
      the context guarding this Guardable

    • isGuarded

      public boolean isGuarded()
      Return true iff this Daemon's execution is guarded. See Guardian.
      Returns:
      true iff this Daemon is guarded

    • getMaxWaitMillis

      public long getMaxWaitMillis(long cDefaultMillis)
      If this Daemon is guarded, return the maximum wait time that the Daemon is allowed to wait for, according to its SLA.
      Parameters:
      cDefaultMillis - the default wait time to return if this Daemon is not Guarded
      Returns:
      the maximum wait time allowed, or cDefaultMillis if this Daemon is not guarded

    • heartbeat

      protected void heartbeat()
      If this Daemon is being guarded, issue a heartbeat to the Guardian.

    • heartbeat

      protected void heartbeat(long cMillis)
      If this Daemon is being guarded, issue a heartbeat to the Guardian.
      Parameters:
      cMillis - the number of milliseconds for which this Daemon should not be considered timed out

    • setGuardRegisterAction

      protected void setGuardRegisterAction(Runnable action)
      Set the Guardian registration action. This action is invoked when a new DaemonWorker thread is started to register the daemon with its Guardian.
      Parameters:
      action - the Guardian registration action

    • getGuardRegisterAction

      protected Runnable getGuardRegisterAction()
      Return the Guardian registration action.
      Returns:
      the Guardian registration action

    • setGuardPolicy

      protected void setGuardPolicy(Guardian guardian, long cTimeoutMillis, float flPctRecover)
      Set the Guardian and policy to guard this Daemon with. The Daemon is registered with the specified Guardian each time the Daemon is started, and is released each time the Daemon is stopped.
      Parameters:
      guardian - the Guardian that will be guarding this Daemon
      cTimeoutMillis - the timeout in ms for this Daemon, or 0 for the service guardian timeout
      flPctRecover - the recovery percentage for this Daemon

    • guardIfNeeded

      protected void guardIfNeeded()
      If this Daemon has a Guardian and SLA policy specified, ensure that it is registered with its Guardian.

    • getThread

      public Thread getThread()
      Accessor to obtain the Daemon thread object.

      The thread returned by this accessor will be null if the Daemon is stopped.

      Returns:
      the thread object

    • getWorker

      public Daemon.DaemonWorker getWorker()
      Accessor to obtain the Daemon worker object.

      The worker returned by this accessor will be null if the Daemon is stopped.

      Returns:
      the worker object

    • start

      public void start()
      Performs a synchronized start of the thread if the thread is not already started. This means that when control returns to the caller of this method, that the thread has started. This method has no effect if the daemon thread is already running, even if it is in the process of stopping. Note that a daemon can be re-started once it has stopped.

    • isRunning

      public boolean isRunning()
      Check if the daemon is running (has started and has not stopped).
      Returns:
      true if and only if the daemon is running

    • stop

      public void stop()
      Request the daemon to stop. This method will only have an effect if the daemon sub-class respects the value returned from isStopping().

    • shutdown

      public void shutdown(long cWait)
      Request the daemon to stop and wait up to the specified number of milliseconds for it to exit. This method will only have an effect if the daemon sub-class respects the value returned from isStopping().
      Parameters:
      cWait - the maximum number of milliseconds to wait for the daemon to exit; pass zero to return immediately; pass -1 to block the calling thread until the worker finishes stopping

    • isStopping

      public boolean isStopping()
      Check if the daemon is supposed to stop. This method is primarily used by the daemon thread itself to check if it should stop processing.
      Returns:
      true if and only if the worker thread is no longer supposed to be running

    • isOnWorkerThread

      public boolean isOnWorkerThread()
      Indicate if the current execution thread is a child of this daemon.
      Returns:
      true if the current thread is a child of the Daemon

    • getState

      protected int getState()
      Obtain the state of the daemon.
      Returns:
      one of the STATE_enums

    • finishStarting

      protected void finishStarting(Daemon.DaemonWorker worker)
      Wait for the specified worker to finish starting. This method is called while the daemon is in the STARTING state. The caller must be synchronized on this daemon object.
      Parameters:
      worker - a worker created by this daemon

    • finishStopping

      protected void finishStopping(Daemon.DaemonWorker worker, long cWait)
      Wait for the specified worker to finish stopping. This method is called while the daemon is in the STOPPING state. The caller must be synchronized on this daemon object.
      Parameters:
      worker - a worker created by this daemon
      cWait - the maximum number of milliseconds to wait for the specified worker to finish stopping; pass zero to return immediately; pass -1 to block the calling thread until the worker finishes stopping

    • changeState

      protected void changeState(int nState, Daemon.DaemonWorker worker)
      Change the state of the daemon.
      Parameters:
      nState - one of the STATE_enums
      worker - the new worker, if starting, otherwise the current worker

    • setConfiguredPriority

      protected void setConfiguredPriority(int nPriority)
      Configure the priority for the daemon.
      Parameters:
      nPriority - the thread priority for the daemon

    • getConfiguredPriority

      protected int getConfiguredPriority()
      Determine the configured priority for the daemon.
      Returns:
      the configured thread priority for the daemon

    • setConfiguredName

      protected void setConfiguredName(String sName)
      Configure the name for the daemon.
      Parameters:
      sName - the thread name for the daemon

    • getConfiguredName

      protected String getConfiguredName()
      Determine the configured name for the daemon.
      Returns:
      the configured thread name for the daemon

    • setThreadContextClassLoader

      public void setThreadContextClassLoader(ClassLoader loader)
      Configure the context ClassLoader for the daemon thread.

      If the daemon thread is not currently running, the specified ClassLoader will be associated with the daemon thread when it is started (or restarted). Otherwise, setContextClassLoader will be called on the daemon thread object immediately as well as during subsequent restarts.

      Parameters:
      loader - the context ClassLoader for the daemon thread

    • getThreadContextClassLoader

      public ClassLoader getThreadContextClassLoader()
      Determine the configured context ClassLoader for the daemon thread.
      Returns:
      the configured context ClassLoader for the daemon thread

    • instantiateWorker

      protected Daemon.DaemonWorker instantiateWorker()
      Instantiate a DaemonWorker that will be used as a daemon.
      Returns:
      a new instance of DaemonWorker or a sub-class thereof

    • configureWorker

      protected void configureWorker(Daemon.DaemonWorker worker)
      Configure a worker to use as a daemon.
      Parameters:
      worker - the DaemonWorker to configure

    • ensureThreadGroup

      protected ThreadGroup ensureThreadGroup()
      Obtain the existing ThreadGroup or create one if none exists or the current one is destroyed.
      Returns:
      the ThreadGroup that the worker will be part of

    • toString

      public String toString()
      Return a human-readable String representation of the Daemon.
      Overrides:
      toString in class Object
      Returns:
      a String describing the Daemon

    • getDescription

      protected String getDescription()
      Format the Daemon attributes into a String for inclusion in the String returned from the toString() method.
      Returns:
      a String listing the attributes of the Daemon

    • toStateString

      protected static String toStateString(int nState)
      Convert a state value to a human-readable String.
      Parameters:
      nState - a Daemon state, one of the STATE_* enums
      Returns:
      a human-readable name for the state