/*
    * Copyright (C) 2012 The Guava Authors
    *
    * 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.google.common.cache;
  
  import com.google.common.annotations.GwtCompatible;
  import com.google.common.base.Supplier;
  
  import java.util.concurrent.atomic.AtomicLong;
  
  /**
   * Source of {@link LongAddable} objects that deals with GWT, Unsafe, and all
   * that.
   * 
   * @author Louis Wasserman
   */
  @GwtCompatible(emulated = true)
  final class LongAddables {
    private static final Supplier<LongAddable> SUPPLIER;
    
    static {
      Supplier<LongAddable> supplier;
      try {
        new LongAdder();
        supplier = new Supplier<LongAddable>() {
          @Override
          public LongAddable get() {
            return new LongAdder();
          }
        };
      } catch (Throwable t) { // we really want to catch *everything*
        supplier = new Supplier<LongAddable>() {
          @Override
          public LongAddable get() {
            return new PureJavaLongAddable();
          }
        };
      }
      SUPPLIER = supplier;
    }
    
    public static LongAddable create() {
      return SUPPLIER.get();
    }
    
    private static final class PureJavaLongAddable extends AtomicLong implements LongAddable {
      @Override
      public void increment() {
        getAndIncrement();
      }
  
      @Override
      public void add(long x) {
        getAndAdd(x);
      }
  
      @Override
      public long sum() {
        return get();
      }
    }
  }