Csharp .NET并发词典交换值

此功能不包括在开箱即用中.GitHub DotNet/Runtime存储库中存在Transact方法的API proposal，这将提供此功能，但目前还没有产生太大的吸引力.不过，您可以使用基本的TryGetValue、TryAdd和TryUpdate方法手动实现它:

public static TValue AddOrUpdate<TKey, TValue>(
    this ConcurrentDictionary<TKey, TValue> source,
    TKey key,
    Func<TKey, TValue> addValueFactory,
    Func<TKey, TValue, TValue> updateValueFactory,
    out bool oldValueExists,
    out TValue oldValue) where TKey : notnull
{
    ArgumentNullException.ThrowIfNull(source);
    ArgumentNullException.ThrowIfNull(addValueFactory);
    ArgumentNullException.ThrowIfNull(updateValueFactory);
    while (true)
    {
        if (source.TryGetValue(key, out oldValue))
        {
            TValue newValue = updateValueFactory(key, oldValue);
            if (source.TryUpdate(key, newValue, oldValue))
            {
                oldValueExists = true;
                return newValue;
            }
        }
        else
        {
            TValue newValue = addValueFactory(key);
            if (source.TryAdd(key, addValueFactory(key)))
            {
                oldValueExists = false;
                oldValue = default;
                return newValue;
            }
        }
    }
}

上述实现是现有AddOrUpdate实现的修改版本.