Package org.threadly.concurrent.event

Class AsyncCallListenerHelper<T>

  • Type Parameters:
    T - Interface for listeners to implement and called into with
    public class AsyncCallListenerHelper<T>
extends ListenerHelper<T>
    This class changes the behavior of how listeners are called from the parent class ListenerHelper. In this implementation when listeners are invoked with the ListenerHelper.call() function, the invocation of all the listeners will occur on the Executor that was provided at construction. If the listener was added without a provided executor it will then run on the provided executor (in the thread doing the ListenerHelper.call() invocation, AKA it will run that listener before executing other listeners). If the listener was added with a provided executor, that listener will still execute on the provided executor (so not necessarily the executor provided at construction time).

    If it is desired that all listeners are executed asynchronously from each other, you should actually use the normal ListenerHelper, and instead just ensure that an executor is provided when each listener is added. If you want listeners to execute concurrently from each other, but not concurrently for any single listener, DefaultExecutorListenerHelper is likely a better choice. This class is only designed to ensure that ListenerHelper.call() invocations will never block.

    To better clarify when this implementation makes sense compared to ListenerHelper and DefaultExecutorListenerHelper. If you have a LOT of quick running listeners, this is the right class for you. If you have few listeners that execute quickly, then the normal ListenerHelper is likely a better choice. If you have long running/complex listeners, DefaultExecutorListenerHelper is possibly the better choice. Alternative for the last condition you could use the normal ListenerHelper, and just ensure that an executor is provided for every listener (but if you want to ensure a given listener is not executed concurrently the DefaultExecutorListenerHelper will handle this for you).

    It is important to note that this class does not ensure ordering of how listeners are called. For example if you provided a multi-threaded executor, and are calling the listeners twice, those listeners call order is non-deterministic. If this is important to you, you must ensure that the Executor provided is single threaded (ie 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).

    Since:
    2.2.0

    • Constructor Detail

      • AsyncCallListenerHelper

        public AsyncCallListenerHelper​(java.lang.Class<? super T> listenerInterface,
                               java.util.concurrent.Executor executor)
        Constructs a new AsyncCallListenerHelper that will handle listeners with the provided interface. The provided class MUST be an interface. All ListenerHelper.call() invocations will occur on the provided executor, but listeners may run on different executors if they are added with their respective executors.
        Parameters:
        listenerInterface - Interface that listeners need to implement
        executor - Executor that ListenerHelper.call() invocation will occur on