content: /*
   * 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 com.datastax.oss.driver.internal.core.connection;
  
  import com.datastax.oss.driver.api.core.config.DefaultDriverOption;
  import com.datastax.oss.driver.api.core.config.DriverExecutionProfile;
  import com.datastax.oss.driver.api.core.connection.ReconnectionPolicy;
  import com.datastax.oss.driver.api.core.context.DriverContext;
  import com.datastax.oss.driver.api.core.metadata.Node;
  import com.datastax.oss.driver.shaded.guava.common.base.Preconditions;
  import edu.umd.cs.findbugs.annotations.NonNull;
  import java.time.Duration;
  import java.util.concurrent.ThreadLocalRandom;
  import net.jcip.annotations.ThreadSafe;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * A reconnection policy that waits exponentially longer between each reconnection attempt (but
   * keeps a constant delay once a maximum delay is reached).
   *
   * <p>It uses the same schedule implementation for individual nodes or the control connection:
   * reconnection attempt {@code i} will be tried {@code Math.min(2^(i-1) * getBaseDelayMs(),
   * getMaxDelayMs())} milliseconds after the previous one. A random amount of jitter (+/- 15%) will
   * be added to the pure exponential delay value to avoid situations where many clients are in the
   * reconnection process at exactly the same time. The jitter will never cause the delay to be less
   * than the base delay, or more than the max delay.
   *
   * <p>To activate this policy, modify the {@code advanced.reconnection-policy} section in the driver
   * configuration, for example:
   *
   * <pre>
   * datastax-java-driver {
   *   advanced.reconnection-policy {
   *     class = ExponentialReconnectionPolicy
   *     base-delay = 1 second
   *     max-delay = 60 seconds
   *   }
   * }
   * </pre>
   *
   * See {@code reference.conf} (in the manual or core driver JAR) for more details.
   */
  @ThreadSafe
  public class ExponentialReconnectionPolicy implements ReconnectionPolicy {
  
    private static final Logger LOG = LoggerFactory.getLogger(ExponentialReconnectionPolicy.class);
  
    private final String logPrefix;
    private final long baseDelayMs;
    private final long maxDelayMs;
    private final long maxAttempts;
  
    /** Builds a new instance. */
    public ExponentialReconnectionPolicy(DriverContext context) {
      this.logPrefix = context.getSessionName();
  
      DriverExecutionProfile config = context.getConfig().getDefaultProfile();
  
      this.baseDelayMs = config.getDuration(DefaultDriverOption.RECONNECTION_BASE_DELAY).toMillis();
      this.maxDelayMs = config.getDuration(DefaultDriverOption.RECONNECTION_MAX_DELAY).toMillis();
  
      Preconditions.checkArgument(
          baseDelayMs > 0,
          "%s must be strictly positive (got %s)",
          DefaultDriverOption.RECONNECTION_BASE_DELAY.getPath(),
          baseDelayMs);
      Preconditions.checkArgument(
          maxDelayMs >= 0,
          "%s must be positive (got %s)",
          DefaultDriverOption.RECONNECTION_MAX_DELAY.getPath(),
          maxDelayMs);
      Preconditions.checkArgument(
          maxDelayMs >= baseDelayMs,
          "%s must be bigger than %s (got %s, %s)",
          DefaultDriverOption.RECONNECTION_MAX_DELAY.getPath(),
          DefaultDriverOption.RECONNECTION_BASE_DELAY.getPath(),
          maxDelayMs,
          baseDelayMs);
  
      // Maximum number of attempts after which we overflow
      int ceil = (baseDelayMs & (baseDelayMs - 1)) == 0 ? 0 : 1;
      this.maxAttempts = 64L - Long.numberOfLeadingZeros(Long.MAX_VALUE / baseDelayMs) - ceil;
    }
  
    /**
     * The base delay in milliseconds for this policy (e.g. the delay before the first reconnection
     * attempt).
     *
     * @return the base delay in milliseconds for this policy.
     */
    public long getBaseDelayMs() {
      return baseDelayMs;
    }
  
    /**
     * The maximum delay in milliseconds between reconnection attempts for this policy.
     *
     * @return the maximum delay in milliseconds between reconnection attempts for this policy.
     */
    public long getMaxDelayMs() {
      return maxDelayMs;
    }
  
    @NonNull
    @Override
    public ReconnectionSchedule newNodeSchedule(@NonNull Node node) {
      LOG.debug("[{}] Creating new schedule for {}", logPrefix, node);
      return new ExponentialSchedule();
    }
  
    @NonNull
    @Override
    public ReconnectionSchedule newControlConnectionSchedule(
        @SuppressWarnings("ignored") boolean isInitialConnection) {
      LOG.debug("[{}] Creating new schedule for the control connection", logPrefix);
      return new ExponentialSchedule();
    }
  
    @Override
    public void close() {
      // nothing to do
    }
  
    private class ExponentialSchedule implements ReconnectionSchedule {
  
      private int attempts;
  
      @NonNull
      @Override
      public Duration nextDelay() {
        long delay = (attempts > maxAttempts) ? maxDelayMs : calculateDelayWithJitter();
        return Duration.ofMillis(delay);
      }
  
      private long calculateDelayWithJitter() {
        // assert we haven't hit the max attempts
        assert attempts <= maxAttempts;
        // get the pure exponential delay based on the attempt count
        long delay = Math.min(baseDelayMs * (1L << attempts++), maxDelayMs);
        // calculate up to 15% jitter, plus or minus (i.e. 85 - 115% of the pure value)
        int jitter = ThreadLocalRandom.current().nextInt(85, 116);
        // apply jitter
        delay = (jitter * delay) / 100;
        // ensure the final delay is between the base and max
        delay = Math.min(maxDelayMs, Math.max(baseDelayMs, delay));
        return delay;
      }
    }
  
    public long getMaxAttempts() {
      return maxAttempts;
    }
  }
  