com.twineworks.collections.shapemap.ShapeKey Maven / Gradle / Ivy

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Special purpose collections for Java.
There is a newer version: 1.2.1
/*
 * The MIT License (MIT)
 *
 * Copyright (c) 2017 Twineworks GmbH
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in all
 * copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
 * SOFTWARE.
 */

package com.twineworks.collections.shapemap;

import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.WeakReference;
import java.util.Collection;
import java.util.HashSet;
import java.util.Set;
import java.util.concurrent.ConcurrentHashMap;

public class ShapeKey {

  // keeps interned weak references of keys
  private static final ConcurrentHashMap> table = new ConcurrentHashMap<>();
  private static final ReferenceQueue rq = new ReferenceQueue<>();

  // cached hashcode of the key
  public final int hashCode;

  // string the key is for
  public final String sym;

  private static ShapeKey intern(String sym){

    Reference existingRef = table.get(sym);

    if(existingRef == null) {
      purgeCache();

      ShapeKey k = new ShapeKey(sym);
      existingRef = table.putIfAbsent(sym, new WeakReference<>(k, rq));

      if(existingRef == null)
        return k;

    }

    ShapeKey existingKey = existingRef.get();

    if(existingKey != null)
      return existingKey;

    // entry was gc'd in the interim, retry
    table.remove(sym, existingRef);
    return intern(sym);
  }

  public static void purgeCache(){
    WeakRefCacheUtil.clear(rq, table);
  }

  public static ShapeKey get(String symbol){
    return intern(symbol);
  }

  public static Set getAll(String ... symbols){
    HashSet keys = new HashSet<>(symbols.length);
    for (String sym : symbols) {
      keys.add(get(sym));
    }

    return keys;
  }

  public static Set getAll(Collection symbols){
    HashSet keys = new HashSet<>(symbols.size());
    for (String sym : symbols) {
      keys.add(get(sym));
    }

    return keys;
  }

  public static Set getAll(ShapeKey ... inputs){
    HashSet keys = new HashSet<>(inputs.length);
    for (ShapeKey k : inputs) {
      keys.add(k);
    }
    return keys;
  }

  private ShapeKey(String symbol){
    this.sym = symbol;
    this.hashCode = symbol.hashCode();
  }

  @Override
  public boolean equals(Object obj) {
    // all instances are interned, using object identity
    return this == obj;
  }

  @Override
  public final int hashCode(){
    return hashCode;
  }

  @Override
  public String toString(){
    return sym;
  }

}