【C#】【多线程】【04-使用任务平行库】08-并行运行任务

## 并行运行任务

```csharp
/// <summary>
/// 并行运行任务
/// </summary>
/// <param name="args"></param>
static void Main(string[] args)
{
    // 创建两个任务
    var firstTask = new Task<int>(() => TaskMethod("First Task", 3));
    var secondTask = new Task<int>(() => TaskMethod("Second Task", 2));
    // 使用Task.WhenAll创建第三个任务，该任务将在所有任务完成后执行
    // 该任务的结果提供了一个结果数组
    var whenAllTask = Task.WhenAll(firstTask, secondTask);
    whenAllTask.ContinueWith(
        t => Console.WriteLine($"The first answer is {t.Result[0]}, the second is {t.Result[1]}"),
        TaskContinuationOptions.OnlyOnRanToCompletion);

firstTask.Start();
    secondTask.Start();

Thread.Sleep(TimeSpan.FromSeconds(4));

// 创建一个任务列表
    var tasks = new List<Task<int>>();
    for (int i = 0; i < 4; i++)
    {
        int counter = i;
        var task = new Task<int>(() => TaskMethod($"Task {counter}", counter));
        tasks.Add(task);
        task.Start();
    }

while (tasks.Count > 0)
    {
        // 通过Task.WhenAny方法等待任何一个任务完成
        var completedTask = Task.WhenAny(tasks).Result;
        tasks.Remove(completedTask);
        Console.WriteLine($"A task has been completed with result {completedTask.Result}.");
    }

Thread.Sleep(TimeSpan.FromSeconds(1));
    Console.ReadLine();
}

static int TaskMethod(string name, int seconds)
{
    Console.WriteLine($"Task {name} is running on a thread id {Thread.CurrentThread.ManagedThreadId}. " +
        $"Is thread pool thread: {Thread.CurrentThread.IsThreadPoolThread}");
    Thread.Sleep(TimeSpan.FromSeconds(seconds));
    return 42 * seconds;
}
```

打印结果

```
Task First Task is running on a thread id 3. Is thread pool thread: True
Task Second Task is running on a thread id 4. Is thread pool thread: True
The first answer is 126, the second is 84
Task Task 0 is running on a thread id 5. Is thread pool thread: True
Task Task 3 is running on a thread id 3. Is thread pool thread: True
Task Task 2 is running on a thread id 6. Is thread pool thread: True
Task Task 1 is running on a thread id 4. Is thread pool thread: True
A task has been completed with result 0.
A task has been completed with result 42.
A task has been completed with result 84.
A task has been completed with result 126.
```

【C#】【多线程】【04-使用任务平行库】08-并行运行任务

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