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 org.apache.cassandra.simulator;
  
  import com.google.common.base.Preconditions;
  
  import org.apache.cassandra.utils.Shared;
  
  import static org.apache.cassandra.utils.Shared.Scope.SIMULATION;
  
  /**
   * A token representing some ordering property of the system.
   * Most notably this is used to implement executor services where a number of tasks may be run concurrently,
   * particularly single threaded executors where causality is a strict requirement of correctness.
   *
   * This is also used to denote "strict" ordering on any suitably annotated {@link Action}.
   *
   * For convenience, efficiency and simplicity we have OrderOn represent a singleton collection of OrderOns.
   */
  @Shared(scope = SIMULATION)
  public interface OrderOn extends OrderOns
  {
      /**
       * The number of {@link Action} in the provided sequence that may be executed at once,
       * before any ordering takes effect.
       */
      int concurrency();
  
      /**
       * If true then all child actions (and their children, etc) must be ordered together, i.e. the next
       * {@link Action} ordered by this sequence may not run until the present {@link Action} and all actions
       * started by it, directly or indirectly, have completed.
       */
      default boolean isStrict() { return false; }
  
      /**
       * Whether the ordering is imposed immediately, occupying a slot in the sequence prior to any Action being scheduled
       * (e.g. in the case of {@code executor.execute()}), or if it applies only after the scheduled time elapsed
       * (e.g. in the case of {@code executor.schedule()}).
       *
       * This may be modified and still refer to the same {@code OrderOn} as another {@code OrderOn} by overriding
       * the {@code unwrap()} method
       */
      default boolean appliesBeforeScheduling() { return true; }
  
      /**
       * {@code this} may be a thin wrapper around another {@code OrderOn} with a different {@code appliesBeforeScheduling()}.
       * In this case this method returns the underlying {@code OrderOn} to impose the order upon.
       */
      default OrderOn unwrap() { return this; }
  
      /**
       * A convenience method to indicate if this {@code OrderOn} imposes any ordering
       */
      @Override
      default boolean isOrdered() { return concurrency() < Integer.MAX_VALUE; }
  
      @Override
      default OrderOns with(OrderOn add)
      {
          return new TwoOrderOns(this, add);
      }
  
      @Override
      default int size()
      {
          return 1;
      }
  
      @Override
      default OrderOn get(int i)
      {
          Preconditions.checkArgument(i == 0);
          return this;
      }
  
      abstract class OrderOnId implements OrderOn
      {
          public final Object id;
  
          public OrderOnId(Object id)
          {
              this.id = id;
          }
  
          @Override
          public int hashCode()
          {
              return id.hashCode();
          }
  
          @Override
          public boolean equals(Object that)
          {
              return that instanceof OrderOnId && id.equals(((OrderOnId) that).id);
          }
  
          public String toString()
          {
              return id.toString();
          }
      }
  
      public class Sequential extends OrderOnId
      {
          public Sequential(Object id)
          {
              super(id);
          }
  
          public int concurrency() { return 1; }
      }
  
      public class StrictSequential extends Sequential
      {
          public StrictSequential(Object id)
          {
              super(id);
          }
  
          @Override
          public boolean isStrict()
          {
              return true;
          }
      }
  
      public class Strict extends Sequential
      {
          final int concurrency;
  
          public Strict(Object id, int concurrency)
          {
              super(id);
              this.concurrency = concurrency;
          }
  
          @Override
          public int concurrency()
          {
              return concurrency;
          }
  
          @Override
          public boolean isStrict()
          {
              return true;
          }
      }
  
      public class OrderAppliesAfterScheduling implements OrderOn
      {
          final OrderOn inner;
  
          public OrderAppliesAfterScheduling(OrderOn inner) { this.inner = inner; }
          @Override public int concurrency() { return inner.concurrency(); }
          @Override public boolean isStrict() { return inner.isStrict(); }
          @Override public boolean isOrdered() { return inner.isOrdered(); }
  
          @Override public boolean appliesBeforeScheduling() { return false; }
          @Override public OrderOn unwrap() { return inner; }
          @Override public String toString() { return inner.toString(); }
      }
  }
  