EventPublisher.java

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package com.fermod.event;

import java.util.ArrayList;
import java.util.List;
import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import java.util.function.Consumer;

public abstract class EventPublisher<T> {

    private final ReadWriteLock readWriteLock = new ReentrantReadWriteLock(true);
    protected final Lock readLock = readWriteLock.readLock();
    protected final Lock writeLock = readWriteLock.writeLock();

    private List<T> listeners = new ArrayList<>();

    public T registerListener(T listener) {

        // Lock the list of listeners for writing
        this.writeLock.lock();

        try {
            // Add the listener to the list of registered listeners
            this.listeners.add(listener);
        } finally {
            // Unlock the writer lock
            this.writeLock.unlock();
        }

        return listener;
    }

    public void unregisterListener(T listener) {

        // Lock the list of listeners for writing
        this.writeLock.lock();

        try {
            // Remove the listener from the list of the registered listeners
            this.listeners.remove(listener);
        } finally {
            // Unlock the writer lock
            this.writeLock.unlock();
        }

    }

    public void unregisterAllListeners() {

        // Lock the list of listeners for writing
        this.writeLock.lock();

        try {
            // Remove all the listeners from the list of the registered listeners
            this.listeners.clear();
        } finally {
            // Unlock the writer lock
            this.writeLock.unlock();
        }

    }

    public void notifyListeners(Consumer<? super T> action) {

        // Lock the list of listeners for reading
        this.readLock.lock();

        try {
            // Execute some function on each of the listeners
            this.listeners.forEach(action);
        } finally {
            // Unlock the reader lock
            this.readLock.unlock();
        }

    }

}