| /* |
| * Licensed to the Apache Software Foundation (ASF) under one or more |
| * contributor license agreements. See the NOTICE file distributed with |
| * this work for additional information regarding copyright ownership. |
| * The ASF licenses this file to You under the Apache License, Version 2.0 |
| * (the "License"); you may not use this file except in compliance with |
| * the License. You may obtain a copy of the License at |
| * |
| * http://www.apache.org/licenses/LICENSE-2.0 |
| * |
| * Unless required by applicable law or agreed to in writing, software |
| * distributed under the License is distributed on an "AS IS" BASIS, |
| * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| * See the License for the specific language governing permissions and |
| * limitations under the License. |
| */ |
| package org.apache.commons.lang3.concurrent; |
| |
| import java.beans.PropertyChangeListener; |
| import java.beans.PropertyChangeSupport; |
| import java.util.concurrent.atomic.AtomicReference; |
| |
| /** |
| * Base class for circuit breakers. |
| * |
| * @param <T> the type of the value monitored by this circuit breaker |
| * @since 3.5 |
| */ |
| public abstract class AbstractCircuitBreaker<T> implements CircuitBreaker<T> { |
| |
| /** |
| * The name of the <em>open</em> property as it is passed to registered |
| * change listeners. |
| */ |
| public static final String PROPERTY_NAME = "open"; |
| |
| /** The current state of this circuit breaker. */ |
| protected final AtomicReference<State> state = new AtomicReference<>(State.CLOSED); |
| |
| /** An object for managing change listeners registered at this instance. */ |
| private final PropertyChangeSupport changeSupport; |
| |
| /** |
| * Creates an {@code AbstractCircuitBreaker}. It also creates an internal {@code PropertyChangeSupport}. |
| */ |
| public AbstractCircuitBreaker() { |
| changeSupport = new PropertyChangeSupport(this); |
| } |
| |
| /** |
| * {@inheritDoc} |
| */ |
| @Override |
| public boolean isOpen() { |
| return isOpen(state.get()); |
| } |
| |
| /** |
| * {@inheritDoc} |
| */ |
| @Override |
| public boolean isClosed() { |
| return !isOpen(); |
| } |
| |
| /** |
| * {@inheritDoc} |
| */ |
| @Override |
| public abstract boolean checkState(); |
| |
| /** |
| * {@inheritDoc} |
| */ |
| @Override |
| public abstract boolean incrementAndCheckState(T increment); |
| |
| /** |
| * {@inheritDoc} |
| */ |
| @Override |
| public void close() { |
| changeState(State.CLOSED); |
| } |
| |
| /** |
| * {@inheritDoc} |
| */ |
| @Override |
| public void open() { |
| changeState(State.OPEN); |
| } |
| |
| /** |
| * Converts the given state value to a boolean <em>open</em> property. |
| * |
| * @param state the state to be converted |
| * @return the boolean open flag |
| */ |
| protected static boolean isOpen(final State state) { |
| return state == State.OPEN; |
| } |
| |
| /** |
| * Changes the internal state of this circuit breaker. If there is actually a change |
| * of the state value, all registered change listeners are notified. |
| * |
| * @param newState the new state to be set |
| */ |
| protected void changeState(final State newState) { |
| if (state.compareAndSet(newState.oppositeState(), newState)) { |
| changeSupport.firePropertyChange(PROPERTY_NAME, !isOpen(newState), isOpen(newState)); |
| } |
| } |
| |
| /** |
| * Adds a change listener to this circuit breaker. This listener is notified whenever |
| * the state of this circuit breaker changes. If the listener is |
| * <strong>null</strong>, it is silently ignored. |
| * |
| * @param listener the listener to be added |
| */ |
| public void addChangeListener(final PropertyChangeListener listener) { |
| changeSupport.addPropertyChangeListener(listener); |
| } |
| |
| /** |
| * Removes the specified change listener from this circuit breaker. |
| * |
| * @param listener the listener to be removed |
| */ |
| public void removeChangeListener(final PropertyChangeListener listener) { |
| changeSupport.removePropertyChangeListener(listener); |
| } |
| |
| /** |
| * An internal enumeration representing the different states of a circuit |
| * breaker. This class also contains some logic for performing state |
| * transitions. This is done to avoid complex if-conditions in the code of |
| * {@code CircuitBreaker}. |
| */ |
| protected enum State { |
| |
| /** The closed state. */ |
| CLOSED { |
| /** |
| * {@inheritDoc} |
| */ |
| @Override |
| public State oppositeState() { |
| return OPEN; |
| } |
| }, |
| |
| /** The open state. */ |
| OPEN { |
| /** |
| * {@inheritDoc} |
| */ |
| @Override |
| public State oppositeState() { |
| return CLOSED; |
| } |
| }; |
| |
| /** |
| * Returns the opposite state to the represented state. This is useful |
| * for flipping the current state. |
| * |
| * @return the opposite state |
| */ |
| public abstract State oppositeState(); |
| } |
| |
| } |