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/*
* 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 {@link AbstractCircuitBreaker}. It also creates an internal {@link 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
* {@link 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();
}
}
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