com.datastax.oss.driver.internal.core.metadata.token.CanonicalNodeSetBuilder 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.oss.driver.internal.core.metadata.token;

import com.datastax.oss.driver.api.core.metadata.Node;
import com.datastax.oss.driver.shaded.guava.common.collect.ImmutableSet;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Set;
import net.jcip.annotations.NotThreadSafe;

/**
 * A reusable set builder that guarantees that identical sets (same elements in the same order) will
 * be represented by the same instance.
 */
@NotThreadSafe
class CanonicalNodeSetBuilder {

  private final Map, Set> canonicalSets = new HashMap<>();
  private final List elements = new ArrayList<>();

  void add(Node node) {
    // This is O(n), but the cardinality is low (max possible size is the replication factor).
    if (!elements.contains(node)) {
      elements.add(node);
    }
  }

  int size() {
    return elements.size();
  }

  Set build() {
    return canonicalSets.computeIfAbsent(elements, ImmutableSet::copyOf);
  }

  void clear() {
    elements.clear();
  }
}