<filename>driver-core/src/main/java/com/datastax/driver/core/LatencyTracker.java
/*
 * Copyright DataStax, Inc.
 *
 * Licensed 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 com.datastax.driver.core;

/**
 * Interface for objects that are interested in tracking the latencies of the driver queries to each
 * Cassandra nodes.
 *
 * <p>An implementation of this interface can be registered against a Cluster object trough the
 * {@link Cluster#register} method, after which the {@link #update(Host, Statement, Exception,
 * long)} method will be called after each query of the driver to a Cassandra host with the
 * latency/duration (in nanoseconds) of this operation.
 */
public interface LatencyTracker {

  /**
   * A method that is called after each request to a Cassandra node with the duration of that
   * operation.
   *
   * <p>Note that there is no guarantee that this method won't be called concurrently by multiple
   * threads, so implementations should synchronize internally if need be.
   *
   * @param host The Cassandra host on which a request has been performed. This parameter is never
   *     {@code null}.
   * @param statement The {@link com.datastax.driver.core.Statement} that has been executed. This
   *     parameter is never {@code null}.
   * @param exception An {@link Exception} thrown when receiving the response, or {@code null} if
   *     the response was successful.
   * @param newLatencyNanos the latency in nanoseconds of the operation. This latency corresponds to
   *     the time elapsed between when the query was sent to {@code host} and when the response was
   *     received by the driver (or the operation timed out, in which {@code newLatencyNanos} will
   *     approximately be the timeout value).
   */
  public void update(Host host, Statement statement, Exception exception, long newLatencyNanos);

  /**
   * Gets invoked when the tracker is registered with a cluster, or at cluster startup if the
   * tracker was registered at initialization with {@link
   * com.datastax.driver.core.Cluster.Initializer#register(LatencyTracker)}.
   *
   * @param cluster the cluster that this tracker is registered with.
   */
  void onRegister(Cluster cluster);

  /**
   * Gets invoked when the tracker is unregistered from a cluster, or at cluster shutdown if the
   * tracker was not unregistered.
   *
   * @param cluster the cluster that this tracker was registered with.
   */
  void onUnregister(Cluster cluster);
}
