C#中使用Parallel.ForEachAsync异步操作多线程的方法

public static Task ForEachAsync<TSource>(
    this IEnumerable<TSource> source,
    ParallelOptions parallelOptions,
    Func<TSource, CancellationToken, ValueTask> body
)

using System.Net.Http;
List<string> urls = GetUrls(); // 假设有 100 个 URL
using HttpClient client = new HttpClient();
// 配置并行选项：最大并发 10
var options = new ParallelOptions { MaxDegreeOfParallelism = 10 };
Console.WriteLine("开始并发下载...");
await Parallel.ForEachAsync(urls, options, async (url, ct) =>
{
    try
    {
        // 传入 ct，如果外部取消，当前请求会立即中止
        string content = await client.GetStringAsync(url, ct);
        Console.WriteLine($"成功下载 {url}，长度: {content.Length}");
    }
    catch (OperationCanceledException)
    {
        // 被取消
    }
    catch (Exception ex)
    {
        Console.WriteLine($"下载失败 {url}: {ex.Message}");
    }
});
Console.WriteLine("全部下载完成。");

using System.Collections.Concurrent;
using System.Diagnostics;

public static async Task Example_WithResultCollection()
{
    var inputs = Enumerable.Range(1, 10);
    var results = new ConcurrentBag<int>(); // 线程安全集合

    await Parallel.ForEachAsync(inputs, async i =>
    {
        await Task.Delay(100); // 模拟耗时操作
        int result = i * i;    // 计算逻辑
        results.Add(result);   // 并发添加结果（线程安全）
        
        Console.WriteLine($"{DateTime.Now:mm:ss:fff} - 处理 {i}");
    });

    Console.WriteLine($"结果数量: {results.Count}");
}

public static async Task Example_WithCancellation(CancellationToken cts)
{
    var range = Enumerable.Range(0, 1000);
    
    try
    {
        await Parallel.ForEachAsync(range, 
            new ParallelOptions { CancellationToken = cts, MaxDegreeOfParallelism = 10 }, 
            async (i, ct) =>
            {
                // 如果外部取消，这里会抛出 OperationCanceledException
                await Task.Delay(100, ct); 
                Console.WriteLine($"处理中: {i}");
            });
    }
    catch (OperationCanceledException)
    {
        Console.WriteLine("任务被用户取消。");
    }
}