如何将此foreach代码转换为Parallel.ForEach？-Java 学习之路

157

关于 Parallel.ForEach 我有点困惑 .
什么是 Parallel.ForEach ，它到底是做什么的？
请不要引用任何MSDN链接 .

这是一个简单的例子：

string[] lines = File.ReadAllLines(txtProxyListPath.Text);
List<string> list_lines = new List<string>(lines);

foreach (string line in list_lines)
{
    //My Stuff
}

如何用 Parallel.ForEach 重写这个例子？

4 回答

241

string[] lines = File.ReadAllLines(txtProxyListPath.Text);
List<string> list_lines = new List<string>(lines);
Parallel.ForEach(list_lines, line =>
{
    //Your stuff
});

回复于 2024-05-10T01:35:12+08:00

Foreach loop:

迭代按顺序进行，逐个循环从单个Thread运行 . 在每个.NET框架中都定义了foreach循环 . 慢速进程的执行速度可能较慢，因为它们是串行运行的 . 进程2在1完成之前无法启动 . 流程3在2和1完成之前无法启动...快速流程的执行速度更快，因为没有线程开销

Parallel.ForEach:

执行以并行方式进行 . Parallel.ForEach使用多个线程 . Parallel.ForEach在.Net 4.0及以上框架中定义 . 执行慢进程可以更快，因为它们可以并行运行进程1,2和3可以并发运行（参见下面示例中的重用线程）快速进程的执行速度较慢，因为额外的线程开销

以下示例清楚地演示了传统foreach循环与传统循环之间的区别

Parallel.ForEach() Example

using System;
using System.Diagnostics;
using System.Threading;
using System.Threading.Tasks;
namespace ParallelForEachExample
{
    class Program
    {
        static void Main()
        {
            string[] colors = {
                                  "1. Red",
                                  "2. Green",
                                  "3. Blue",
                                  "4. Yellow",
                                  "5. White",
                                  "6. Black",
                                  "7. Violet",
                                  "8. Brown",
                                  "9. Orange",
                                  "10. Pink"
                              };
            Console.WriteLine("Traditional foreach loop\n");
            //start the stopwatch for "for" loop
            var sw = Stopwatch.StartNew();
            foreach (string color in colors)
            {
                Console.WriteLine("{0}, Thread Id= {1}", color, Thread.CurrentThread.ManagedThreadId);
                Thread.Sleep(10);
            }
            Console.WriteLine("foreach loop execution time = {0} seconds\n", sw.Elapsed.TotalSeconds);
            Console.WriteLine("Using Parallel.ForEach");
            //start the stopwatch for "Parallel.ForEach"
             sw = Stopwatch.StartNew();
            Parallel.ForEach(colors, color =>
            {
                Console.WriteLine("{0}, Thread Id= {1}", color, Thread.CurrentThread.ManagedThreadId);
                Thread.Sleep(10);
            }
            );
            Console.WriteLine("Parallel.ForEach() execution time = {0} seconds", sw.Elapsed.TotalSeconds);
            Console.Read();
        }
    }
}

Output

Traditional foreach loop
1. Red, Thread Id= 10
2. Green, Thread Id= 10
3. Blue, Thread Id= 10
4. Yellow, Thread Id= 10
5. White, Thread Id= 10
6. Black, Thread Id= 10
7. Violet, Thread Id= 10
8. Brown, Thread Id= 10
9. Orange, Thread Id= 10
10. Pink, Thread Id= 10
foreach loop execution time = 0.1054376 seconds

Using Parallel.ForEach example

1. Red, Thread Id= 10
3. Blue, Thread Id= 11
4. Yellow, Thread Id= 11
2. Green, Thread Id= 10
5. White, Thread Id= 12
7. Violet, Thread Id= 14
9. Orange, Thread Id= 13
6. Black, Thread Id= 11
8. Brown, Thread Id= 10
10. Pink, Thread Id= 12
Parallel.ForEach() execution time = 0.055976 seconds

回复于 2024-05-10T01:35:12+08:00

6
```
string[] lines = File.ReadAllLines(txtProxyListPath.Text);

// No need for the list
// List<string> list_lines = new List<string>(lines); 

Parallel.ForEach(lines, line =>
{
    //My Stuff
});
```
这将导致在循环内并行解析行 . 如果你想要一个更详细的，更少的并行类的介绍，我写了一个关于TPL的系列，其中包括一个section on Parallel.ForEach .
回复于 2024-05-10T01:35:12+08:00
39
对于大文件使用以下代码（你的内存较少）
```
Parallel.ForEach(File.ReadLines(txtProxyListPath.Text), line => {
    //Your stuff
});
```
回复于 2024-05-10T01:35:12+08:00

如何将此foreach代码转换为Parallel.ForEach？

4 回答

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