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 *      http://www.apache.org/licenses/LICENSE-2.0
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package org.apache.commons.lang3.concurrent;


An interface describing a Circuit Breaker component.


A circuit breaker can be used to protect an application against unreliable
services or unexpected load. It typically monitors a specific resource. As long as this
resource works as expected, it stays in state closed, meaning that the
resource can be used. If problems are encountered when using the resource, the circuit
breaker can switch into state open; then access to this resource is
prohibited. Depending on a concrete implementation, it is possible that the circuit
breaker switches back to state closed when the resource becomes available
again.


This interface defines a generic protocol of a circuit breaker component. It should be
sufficiently generic to be applied to multiple different use cases.

Type parameters:
<T> – the type of the value monitored by this circuit breaker
Since:
3.5/**
 * <p>
 * An interface describing a <a
 * href="http://martinfowler.com/bliki/CircuitBreaker.html">Circuit Breaker</a> component.
 * </p>
 * <p>
 * A <em>circuit breaker</em> can be used to protect an application against unreliable
 * services or unexpected load. It typically monitors a specific resource. As long as this
 * resource works as expected, it stays in state <em>closed</em>, meaning that the
 * resource can be used. If problems are encountered when using the resource, the circuit
 * breaker can switch into state <em>open</em>; then access to this resource is
 * prohibited. Depending on a concrete implementation, it is possible that the circuit
 * breaker switches back to state <em>closed</em> when the resource becomes available
 * again.
 * </p>
 * <p>
 * This interface defines a generic protocol of a circuit breaker component. It should be
 * sufficiently generic to be applied to multiple different use cases.
 * </p>
 *
 * @param <T> the type of the value monitored by this circuit breaker
 * @since 3.5
 */
public interface CircuitBreaker<T> {
    
Returns the current open state of this circuit breaker. A return value of
true means that the circuit breaker is currently open indicating a
problem in the monitored sub system.
Returns:
the current open state of this circuit breaker/**
     * Returns the current open state of this circuit breaker. A return value of
     * <strong>true</strong> means that the circuit breaker is currently open indicating a
     * problem in the monitored sub system.
     *
     * @return the current open state of this circuit breaker
     */
    boolean isOpen();

    
Returns the current closed state of this circuit breaker. A return value of
true means that the circuit breaker is currently closed. This
means that everything is okay with the monitored sub system.
Returns:
the current closed state of this circuit breaker/**
     * Returns the current closed state of this circuit breaker. A return value of
     * <strong>true</strong> means that the circuit breaker is currently closed. This
     * means that everything is okay with the monitored sub system.
     *
     * @return the current closed state of this circuit breaker
     */
    boolean isClosed();

    
Checks the state of this circuit breaker and changes it if necessary. The return value indicates whether the circuit breaker is now in state CLOSED; a value of true typically means that the current operation can continue.
Returns:
true if the circuit breaker is now closed;
false otherwise/**
     * Checks the state of this circuit breaker and changes it if necessary. The return
     * value indicates whether the circuit breaker is now in state {@code CLOSED}; a value
     * of <strong>true</strong> typically means that the current operation can continue.
     *
     * @return <strong>true</strong> if the circuit breaker is now closed;
     * <strong>false</strong> otherwise
     */
    boolean checkState();

    
Closes this circuit breaker. Its state is changed to closed. If this circuit
breaker is already closed, this method has no effect.
/**
     * Closes this circuit breaker. Its state is changed to closed. If this circuit
     * breaker is already closed, this method has no effect.
     */
    void close();

    
Opens this circuit breaker. Its state is changed to open. Depending on a concrete
implementation, it may close itself again if the monitored sub system becomes
available. If this circuit breaker is already open, this method has no effect.
/**
     * Opens this circuit breaker. Its state is changed to open. Depending on a concrete
     * implementation, it may close itself again if the monitored sub system becomes
     * available. If this circuit breaker is already open, this method has no effect.
     */
    void open();

    
Increments the monitored value and performs a check of the current state of this circuit breaker. This method works like checkState(), but the monitored value is incremented before the state check is performed. 
Params:
increment – value to increment in the monitored value of the circuit breaker
Returns:
true if the circuit breaker is now closed;
false otherwise/**
     * Increments the monitored value and performs a check of the current state of this
     * circuit breaker. This method works like {@link #checkState()}, but the monitored
     * value is incremented before the state check is performed.
     *
     * @param increment value to increment in the monitored value of the circuit breaker
     * @return <strong>true</strong> if the circuit breaker is now closed;
     * <strong>false</strong> otherwise
     */
    boolean incrementAndCheckState(T increment);
}