C#之并发字典

internal class Program
{
    const string Item = "Dictionary item";
    const int Iterations = 1000000;
    public static string CurrentItem;
    static void Main(string[] args)
    {
        var concurrentDict = new ConcurrentDictionary<int, string>();
        var dict=new Dictionary<int,string>();
        var sw = new Stopwatch();
        sw.Start();
        for(int i = 0; i < Iterations; i++)
        {
            lock(dict)
            {
                dict[i] = Item;
            }
        }
        sw.Stop();
        Console.WriteLine($"Writing to dict with a lock:{sw.Elapsed}");

        sw.Restart();
        for(int i = 0; i < Iterations; i++)
        {
            concurrentDict[i] = Item;
        }
        sw.Stop();
        Console.WriteLine($"Writing to concurrent dict:{sw.Elapsed}");


        sw.Restart();
        for(int i = 0; i < Iterations; i++)
        {
            lock (dict)
            {
                CurrentItem = dict[i];
            }
        }
        sw.Stop();
        Console.WriteLine($"Reading from dict with a lock:{sw.Elapsed}");

        sw.Restart();
        for(int i = 0; i < Iterations; i++)
        {
            CurrentItem = concurrentDict[i];
        }
        sw.Stop();
        Console.WriteLine($"Reading from concurrent dictionary:{sw.Elapsed}");

    }
}

通过这个demo，我们可以发现:并发字典写操作比使用锁的一般字典要慢，但读要快些。因此对于字典需要大量线程安全的读操作，并发字典是比较好的选择，但如果对字典只需要多线程访问只读元素，则没有必要执行线程安全的读操作，用一般的字典或者ReadOnlyDictionary就可以胜任。