Task.WaitAll和Task.WaitAny

Task.WaitAll和Task.WaitAny

一、簡介

Task.WaitAll：等待所有提供的 Task 對象完成執行過程。Task.WaitAny：等待提供的任一 Task 對象完成執行過程。

二、代碼案例

Task.WaitAll

代碼：

   class Program
    {
        public class DownLoadTest
        {
            Stopwatch watch = new Stopwatch();
            public  DownLoadTest()
            {
                watch.Start();
            }
                
            public async Task DoRunTaskAsync(string url, CancellationToken ct)
            {
                if (ct.IsCancellationRequested)
                {
                    Console.WriteLine(string.Format("取消{0}的運行 :{1,4:N0}ms", url, watch.Elapsed.TotalMilliseconds));
                    return;
                }
                Console.WriteLine(string.Format("下載{0}開始運行 :{1,4:N0}ms", url, watch.Elapsed.TotalMilliseconds));
                WebClient wc = new WebClient();
                await Task.Run(() =>
                {
                    var task = wc.DownloadStringTaskAsync(url);
                    while (!task.IsCompleted)
                    {
                        if (ct.IsCancellationRequested)
                        {
                            Console.WriteLine(string.Format("取消{0}的運行 :{1,4:N0}ms", url, watch.Elapsed.TotalMilliseconds));
                            return;
                        }
                    }
                    if (task.IsCompleted)
                        Console.WriteLine(string.Format("下載{0}運行結束 :{1,4:N0}ms", url, watch.Elapsed.TotalMilliseconds));
                });
            }
        }

        static void Main(string[] args)
        {

            DownLoadTest dwtest = new DownLoadTest();
            CancellationTokenSource cts = new CancellationTokenSource();
            CancellationToken token = cts.Token;
            var task1 = dwtest.DoRunTaskAsync("https://www.baidu.com/", token);
            var task2 = dwtest.DoRunTaskAsync("https://www.taobao.com/", token);
            var task3 = dwtest.DoRunTaskAsync("https://www.cnblogs.com/", token);
            Task[] tasks = new Task[] { task1, task2, task3 };
            Console.WriteLine("task.Result等待結果打印");
            Task.WaitAll(tasks, 10000);
            cts.Cancel();//超過10s時間取消運行
            Console.WriteLine(task1.Status);
            Console.WriteLine(task2.Status);
            Console.WriteLine(task3.Status);
            Console.WriteLine(string.Format("主線程運行結束"));
            Console.ReadKey();
        }
    }

運行結果：

通過運行結果可以看出，可以看到Task.WaitAll(tasks)在等待超時的時間內，同步等待了所有的任務完成。

Task.WaitAny

代碼：

  class Program
    {
        public class DownLoadTest
        {
            Stopwatch watch = new Stopwatch();
            public  DownLoadTest()
            {
                watch.Start();
            }
                
            public async Task DoRunTaskAsync(string url, CancellationToken ct)
            {
                if (ct.IsCancellationRequested)
                {
                    Console.WriteLine(string.Format("取消{0}的運行 :{1,4:N0}ms", url, watch.Elapsed.TotalMilliseconds));
                    return;
                }
                Console.WriteLine(string.Format("下載{0}開始運行 :{1,4:N0}ms", url, watch.Elapsed.TotalMilliseconds));
                WebClient wc = new WebClient();
                await Task.Run(() =>
                {
                    var task = wc.DownloadStringTaskAsync(url);
                    while (!task.IsCompleted)
                    {
                        if (ct.IsCancellationRequested)
                        {
                            Console.WriteLine(string.Format("取消{0}的運行 :{1,4:N0}ms", url, watch.Elapsed.TotalMilliseconds));
                            return;
                        }
                    }
                    if (task.IsCompleted)
                        Console.WriteLine(string.Format("下載{0}運行結束 :{1,4:N0}ms", url, watch.Elapsed.TotalMilliseconds));
                });
            }
        }

        static void Main(string[] args)
        {

            DownLoadTest dwtest = new DownLoadTest();
            CancellationTokenSource cts = new CancellationTokenSource();
            CancellationToken token = cts.Token;
            var task1 = dwtest.DoRunTaskAsync("https://www.baidu.com/", token);
            var task2 = dwtest.DoRunTaskAsync("https://www.taobao.com/", token);
            var task3 = dwtest.DoRunTaskAsync("https://www.cnblogs.com/", token);
            Task[] tasks = new Task[] { task1, task2, task3 };
            Console.WriteLine("task.Result等待結果打印");
            Task.WaitAny(tasks, 4000);
            cts.Cancel();//超過4s時間取消運行
            Console.WriteLine(task1.Status);
            Console.WriteLine(task2.Status);
            Console.WriteLine(task3.Status);
            Console.WriteLine(string.Format("主線程運行結束"));
            Console.ReadKey();
        }
    }

運行結果：

通過運行結果截圖可以看出，可以看到，Task.WhenAny(tasks)至少等待了一個任務的完成。這里https://www.baidu.com/先下載完，就直接終止等待 。

 

三、總結

Task.WaitAll阻止當前線程，直到所有其他任務完成執行為止。Task.WaitAny阻止當前線程，至少等待一個任務完成執行為止。如果等待時長設置較長，上述案例結果會一樣。