轉載自《C#多執行緒程式設計例項》

對於平行計算，我們需要使用適當的資料結構。這些結構具備可伸縮性，儘可能地避免鎖，並且還能提供執行緒安全的訪問。.Net Framework 引入了System.Collections.Concurrent 名稱空間，包含了一些資料結構。

const string Item = "Dictionary item";
public static string CurrentItem;

static void Main(string[] args)
{
var concurrentDictionary = new ConcurrentDictionary<int, string>();
var dictionary = new Dictionary<int, string>();
var sw = new Stopwatch();
sw.Start();
for (int i = 0; i < 1000000; i++)
{
lock (dictionary)
{
dictionary[i] = Item;
}
}
sw.Stop();
Console.WriteLine("Writing to dictionary with a lock: {0}", sw.Elapsed);

sw.Restart();
for (int i = 0; i < 1000000; i++)
{
concurrentDictionary[i] = Item;
}
sw.Stop();
Console.WriteLine("Writing to a concurrent dictionary: {0}", sw.Elapsed);

sw.Restart();
for (int i = 0; i < 1000000; i++)
{
lock (dictionary)
{
CurrentItem = dictionary[i];
}
}
sw.Stop();
Console.WriteLine("Reading from dictionary with a lock: {0}", sw.Elapsed);

sw.Restart();
for (int i = 0; i < 1000000; i++)
{
CurrentItem = concurrentDictionary[i];
}
sw.Stop();
Console.WriteLine("Reading from a concurrent dictionary: {0}", sw.Elapsed);

Console.Read();
}
 

可以明顯地看出使用lock配合Dictionary 與 ConcurrentDictionary 的效能差異：在“寫”操作上，lock配合Dictionary顯然快很多；而在“讀”操作上，ConcurrentDictionary更快一些。但是請注意，這裡使用的是單執行緒！如果執行緒數量上去，ConcurrentDictionary的效率會大大提升。