com.datastax.driver.core.policies.ConstantSpeculativeExecutionPolicy Maven / Gradle / Ivy

/*
 * 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.policies;

import com.datastax.driver.core.Cluster;
import com.datastax.driver.core.Host;
import com.datastax.driver.core.Statement;
import com.google.common.base.Preconditions;
import java.util.concurrent.atomic.AtomicInteger;

/**
 * A {@link SpeculativeExecutionPolicy} that schedules a given number of speculative executions,
 * separated by a fixed delay.
 */
public class ConstantSpeculativeExecutionPolicy implements SpeculativeExecutionPolicy {
  private final int maxSpeculativeExecutions;
  private final long constantDelayMillis;

  /**
   * Builds a new instance.
   *
   * @param constantDelayMillis the delay between each speculative execution. Must be >= 0. A zero
   *     delay means it should immediately send `maxSpeculativeExecutions` requests along with the
   *     original request.
   * @param maxSpeculativeExecutions the number of speculative executions. Must be strictly
   *     positive.
   * @throws IllegalArgumentException if one of the arguments does not respect the preconditions
   *     above.
   */
  public ConstantSpeculativeExecutionPolicy(
      final long constantDelayMillis, final int maxSpeculativeExecutions) {
    Preconditions.checkArgument(
        constantDelayMillis >= 0, "delay must be >= 0 (was %d)", constantDelayMillis);
    Preconditions.checkArgument(
        maxSpeculativeExecutions > 0,
        "number of speculative executions must be strictly positive (was %d)",
        maxSpeculativeExecutions);
    this.constantDelayMillis = constantDelayMillis;
    this.maxSpeculativeExecutions = maxSpeculativeExecutions;
  }

  @Override
  public SpeculativeExecutionPlan newPlan(String loggedKeyspace, Statement statement) {
    return new SpeculativeExecutionPlan() {
      private final AtomicInteger remaining = new AtomicInteger(maxSpeculativeExecutions);

      @Override
      public long nextExecution(Host lastQueried) {
        return (remaining.getAndDecrement() > 0) ? constantDelayMillis : -1;
      }
    };
  }

  @Override
  public void init(Cluster cluster) {
    // do nothing
  }

  @Override
  public void close() {
    // do nothing
  }
}