Class DefaultExecutorRunnableListenerHelper

  • public class DefaultExecutorRunnableListenerHelper
    extends RunnableListenerHelper
    This class ensures that listener execution will never happen on the thread that invokes RunnableListenerHelper.callListeners(). It does this in a different way from how the AsyncCallRunnableListenerHelper does it. In this implementation the iteration of the listeners still occurs on the thread executing the RunnableListenerHelper.callListeners(), but as listeners are added, it is ensured that they are provided an executor to execute on (so listener execution will actually happen on the executor). If a listener is provided with an executor, that provided Executor will NOT be overridden, and instead it will be used for the listeners execution.

    Internally this class uses the KeyDistributedExecutor, using the listener as the execution key, to ensure that any single listener will NEVER execute concurrently with itself.

    In general, this implementation is most efficient when there are few listeners, but the listeners are high complexity, or take a long time to execute. If you have few listeners AND they execute quickly, the normal RunnableListenerHelper is likely a better choice. If you have MANY listeners, but they execute very quickly, AsyncCallRunnableListenerHelper is possibly a better choice.

    Unlike AsyncCallRunnableListenerHelper, even if the executor provided here is multi-threaded, order of listener call's are preserved. So there is no need to provide a single threaded executor into this class.

    • Constructor Detail

      • DefaultExecutorRunnableListenerHelper

        public DefaultExecutorRunnableListenerHelper​(boolean callListenersOnce,
                                                     java.util.concurrent.Executor executor)
        Constructs a new DefaultExecutorRunnableListenerHelper. If any listeners are not provided an executor, they will execute on the provided executor.
        callListenersOnce - true if listeners should only be called once
        executor - Executor to execute listeners which were not provided one by default
    • Method Detail

      • addListener

        public void addListener​(java.lang.Runnable listener,
                                java.util.concurrent.Executor executor)
        Description copied from class: RunnableListenerHelper
        Adds a listener to be called. If the RunnableListenerHelper was constructed with true (listeners can only be called once) then this listener will be called immediately. If the executor is null it will be called either on this thread or the thread calling RunnableListenerHelper.callListeners() (depending on the previous condition).

        If an Executor is provided, and that Executor is NOT single threaded, the listener may be called concurrently. You can ensure this wont happen by using the KeyDistributedExecutor to get an executor from a single key, or by using the ExecutorLimiter with a limit of one, or an instance of the SingleThreadScheduler.

        addListener in class RunnableListenerHelper
        listener - runnable to call when trigger event called
        executor - executor listener should run on, or null