一、简介
Task.WhenAll()、Task.WhenAny()这两个与Task.WaitALL()、Task.WaitAny()是有区别的，When是异步的，Wait是同步的。
Task.WhenAll()：所有提供的任务已完成时，创建将完成的任务。
Task.WhenAny()：任何提供的任务已完成时，创建将完成的任务。.
二、代码案例
Task.WhenAll
代码：
class Program{public class DownLoadTest{Stopwatch watch = new Stopwatch();public DownLoadTest(){watch.Start();}public string DownLoadString(string url){Console.WriteLine(string.Format("下載{0}開始運行 :{1,4:N0}ms", url, watch.Elapsed.TotalMilliseconds));WebClient wc = new WebClient();string str = wc.DownloadString(url);Console.WriteLine(string.Format("下載{0}運行結束 :{1,4:N0}ms", url, watch.Elapsed.TotalMilliseconds));return str;}public async Task<string> DoRunStringAsync(string url){Console.WriteLine(string.Format("異步程序獲取{0}開始運行:{1,4:N0}ms", url, watch.Elapsed.TotalMilliseconds));var task = await DownLoadStringAsync(url);Console.WriteLine(string.Format("異步程序獲取{0運行結束:{1,4:N0}ms", url, watch.Elapsed.TotalMilliseconds));return task;}public async Task<string> DownLoadStringAsync(string url){string str = await Task.Run(() => DownLoadString(url));return str;}}static void Main(string[] args){string[] urls = { "https://www.baidu.com/", "https://www.taobao.com/", "https://www.cnblogs.com/" };var task = DoRunsAsync(urls);//task.Wait(3000);Console.WriteLine(string.Format("主線程運行結束."));Console.ReadKey();}private static async Task<string> DoRunsAsync(IEnumerable<string> urls){DownLoadTest dwtest = new DownLoadTest();List<Task> tasks = new List<Task>();foreach (var url in urls){var task = dwtest.DoRunStringAsync(url);Console.WriteLine("task.Id =" + task.Id + " url=" + url);tasks.Add(task);}await Task.WhenAll(tasks);foreach (var task in tasks){Console.WriteLine("task.Id =" + task.Id + " task.Status=" + task.Status);}return "";}}
运行结果：
可以看到await Task.WhenAll(tasks);异步等待了所有的任务完成。
Task.WhenAny
代码：
class Program{public class DownLoadTest{Stopwatch watch = new Stopwatch();public DownLoadTest(){watch.Start();}public string DownLoadString(string url){Console.WriteLine(string.Format("下載{0}開始運行 :{1,4:N0}ms", url, watch.Elapsed.TotalMilliseconds));WebClient wc = new WebClient();string str = wc.DownloadString(url);Console.WriteLine(string.Format("下載{0}運行結束 :{1,4:N0}ms", url, watch.Elapsed.TotalMilliseconds));return str;}public async Task<string> DoRunStringAsync(string url){Console.WriteLine(string.Format("異步程序獲取{0}開始運行:{1,4:N0}ms", url, watch.Elapsed.TotalMilliseconds));var task = await DownLoadStringAsync(url);Console.WriteLine(string.Format("異步程序獲取{0運行結束:{1,4:N0}ms", url, watch.Elapsed.TotalMilliseconds));return task;}public async Task<string> DownLoadStringAsync(string url){string str = await Task.Run(() => DownLoadString(url));return str;}}static void Main(string[] args){string[] urls = { "https://www.baidu.com/", "https://www.taobao.com/", "https://www.cnblogs.com/" };var task = DoRunsAsync(urls);task.Wait(1000);Console.WriteLine(string.Format("主線程運行結束."));Console.ReadKey();}private static async Task<string> DoRunsAsync(IEnumerable<string> urls){DownLoadTest dwtest = new DownLoadTest();List<Task> tasks = new List<Task>();foreach (var url in urls){var task = dwtest.DoRunStringAsync(url);Console.WriteLine("task.Id =" + task.Id + " url=" + url);tasks.Add(task);}await Task.WhenAny(tasks);foreach (var task in tasks){Console.WriteLine("task.Id =" + task.Id + " task.Status=" + task.Status);}return "";}}
运行结果：
Task.WhenAny(tasks)至少等待了一个任务的完成。这里https://www.baidu.com/先下载完，就直接终止等待 。
