如何在C#中限制Parallel.ForEach？
并行Foreach
C#中的Parallel.ForEach循环在多个线程上运行，并且处理以并行方式进行。Parallel.ForEach循环不是C#的基本功能，并且在C#4.0及更高版本中可用。要使用Parallel.ForEach循环，我们需要在using指令中导入System.Threading.Tasks命名空间。
Foreach
C#中的Foreach循环在单个线程上运行，并且处理过程是一个接一个地进行的。Foreach循环是C#的基本功能，可从C#1.0中获得。在大多数情况下，它的执行要比Parallel.Foreach慢。
例子1
static void Main(string[] args){
List<string> alphabets = new List<string>();
alphabets.Add("A");
alphabets.Add("B");
alphabets.Add("C");
alphabets.Add("D");
alphabets.Add("E");
alphabets.Add("F");
alphabets.Add("G");
alphabets.Add("H");
alphabets.Add("I");
alphabets.Add("J");
alphabets.Add("K");
alphabets.Add("L");
alphabets.Add("M");
alphabets.Add("N");
alphabets.Add("O");
alphabets.Add("P");
alphabets.Add("Q");
alphabets.Add("R");
alphabets.Add("S");
alphabets.Add("T");
alphabets.Add("U");
alphabets.Add("V");
alphabets.Add("W");
alphabets.Add("X");
alphabets.Add("Y");
alphabets.Add("Z");
Console.WriteLine("使用foreach循环打印列表\n");
var stopWatch = Stopwatch.StartNew();
foreach (string alphabet in alphabets){
Console.WriteLine("alphabet Name: {0}, Thread Id= {1}", alphabet,Thread.CurrentThread.ManagedThreadId);
}
Console.WriteLine("foreach循环执行时间 = {0} seconds\n", stopWatch.Elapsed.TotalSeconds);
Console.WriteLine("打印列表使用Parallel.ForEach");
stopWatch = Stopwatch.StartNew();
Parallel.ForEach(alphabets, alphabet =>
{
Console.WriteLine("alphabet Name: {0}, Thread Id= {1}", alphabet,Thread.CurrentThread.ManagedThreadId);
}
);
Console.WriteLine("Parallel.ForEach() execution time = {0} seconds",stopWatch.Elapsed.TotalSeconds);
Console.Read();
Console.ReadLine();
}输出结果
使用foreach循环打印列表
alphabet Name: A, Thread Id= 1 alphabet Name: B, Thread Id= 1 alphabet Name: C, Thread Id= 1 alphabet Name: D, Thread Id= 1 alphabet Name: E, Thread Id= 1 alphabet Name: F, Thread Id= 1 alphabet Name: G, Thread Id= 1 alphabet Name: H, Thread Id= 1 alphabet Name: I, Thread Id= 1 alphabet Name: J, Thread Id= 1 alphabet Name: K, Thread Id= 1 alphabet Name: L, Thread Id= 1 alphabet Name: M, Thread Id= 1 alphabet Name: N, Thread Id= 1 alphabet Name: O, Thread Id= 1 alphabet Name: P, Thread Id= 1 alphabet Name: Q, Thread Id= 1 alphabet Name: R, Thread Id= 1 alphabet Name: S, Thread Id= 1 alphabet Name: T, Thread Id= 1 alphabet Name: U, Thread Id= 1 alphabet Name: V, Thread Id= 1 alphabet Name: W, Thread Id= 1 alphabet Name: X, Thread Id= 1 alphabet Name: Y, Thread Id= 1 alphabet Name: Z, Thread Id= 1 foreach loop execution time = 0.0223421 seconds
使用Parallel.ForEach打印列表
alphabet Name: A, Thread Id= 1 alphabet Name: G, Thread Id= 4 alphabet Name: H, Thread Id= 4 alphabet Name: I, Thread Id= 4 alphabet Name: J, Thread Id= 4 alphabet Name: K, Thread Id= 4 alphabet Name: L, Thread Id= 4 alphabet Name: N, Thread Id= 4 alphabet Name: O, Thread Id= 4 alphabet Name: P, Thread Id= 4 alphabet Name: Q, Thread Id= 4 alphabet Name: Y, Thread Id= 6 alphabet Name: Z, Thread Id= 6 alphabet Name: D, Thread Id= 6 alphabet Name: E, Thread Id= 6 alphabet Name: F, Thread Id= 6 alphabet Name: T, Thread Id= 6 alphabet Name: U, Thread Id= 6 alphabet Name: V, Thread Id= 6 alphabet Name: R, Thread Id= 4 alphabet Name: M, Thread Id= 5 alphabet Name: S, Thread Id= 7 alphabet Name: B, Thread Id= 1 alphabet Name: C, Thread Id= 1 alphabet Name: W, Thread Id= 6 alphabet Name: X, Thread Id= 6 Parallel.ForEach() execution time = 0.0559777 seconds
例子2
在parallel.foreach中限制并行
static class Program{
static void Main(string[] args){
List<string> alphabets = new List<string>();
alphabets.Add("A");
alphabets.Add("B");
alphabets.Add("C");
alphabets.Add("D");
alphabets.Add("E");
alphabets.Add("F");
alphabets.Add("G");
alphabets.Add("H");
alphabets.Add("I");
alphabets.Add("J");
alphabets.Add("K");
alphabets.Add("L");
alphabets.Add("M");
alphabets.Add("N");
alphabets.Add("O");
alphabets.Add("P");
alphabets.Add("Q");
alphabets.Add("R");
alphabets.Add("S");
alphabets.Add("T");
alphabets.Add("U");
alphabets.Add("V");
alphabets.Add("W");
alphabets.Add("X");
alphabets.Add("Y");
alphabets.Add("Z");
Parallel.ForEach(
alphabets,
new ParallelOptions { MaxDegreeOfParallelism = 2 },
alphabet => { Console.WriteLine("alphabet Name: {0}, Thread Id= {1}", alphabet,Thread.CurrentThread.ManagedThreadId); }
);
}
}输出结果
alphabet Name: N, Thread Id= 4 alphabet Name: O, Thread Id= 4 alphabet Name: P, Thread Id= 4 alphabet Name: A, Thread Id= 1 alphabet Name: B, Thread Id= 1 alphabet Name: C, Thread Id= 1 alphabet Name: Q, Thread Id= 4 alphabet Name: R, Thread Id= 4 alphabet Name: S, Thread Id= 4 alphabet Name: T, Thread Id= 4 alphabet Name: U, Thread Id= 4 alphabet Name: V, Thread Id= 4 alphabet Name: W, Thread Id= 4 alphabet Name: X, Thread Id= 4 alphabet Name: Y, Thread Id= 4 alphabet Name: Z, Thread Id= 4 alphabet Name: H, Thread Id= 4 alphabet Name: I, Thread Id= 4 alphabet Name: J, Thread Id= 4 alphabet Name: K, Thread Id= 4 alphabet Name: D, Thread Id= 1 alphabet Name: L, Thread Id= 4 alphabet Name: E, Thread Id= 1 alphabet Name: F, Thread Id= 1 alphabet Name: G, Thread Id= 1 alphabet Name: M, Thread Id= 4