Newtonsoft.Json\Utilities\ThreadSafeStore.cs

using System;

using System.Collections.Generic;

namespace Newtonsoft.Json.Utilities

{

  internal class ThreadSafeStore<TKey, TValue>

  {

    private readonly object _lock = new object();

    private Dictionary<TKey, TValue> _store;

    private readonly Func<TKey, TValue> _creator;

    public ThreadSafeStore(Func<TKey, TValue> creator)

    {

      if (creator == null)

        throw new ArgumentNullException("creator");

      _creator = creator;

    }

    public TValue Get(TKey key)

    {

      if (_store == null)

        return AddValue(key);

      TValue value;

      if (!_store.TryGetValue(key, out value))

        return AddValue(key);

      return value;

    }

    private TValue AddValue(TKey key)

    {

      TValue value = _creator(key);

      lock (_lock)

      {

        if (_store == null)

        {

          _store = new Dictionary<TKey, TValue>();

          _store[key] = value;

        }

        else

        {

          // double check locking

          TValue checkValue;

          if (_store.TryGetValue(key, out checkValue))

            return checkValue;

          Dictionary<TKey, TValue> newStore = new Dictionary<TKey, TValue>(_store);

          newStore[key] = value;

          _store = newStore;

        }

        return value;

      }

    }

  }

}