process.WaitForExit(int32) 异步

Question

我正在使用https://stackoverflow.com/a/19104345/2713516 中提供的解决方案来运行 WaitForExit 异步，但是，我想使用 Int32 参数重载 (https://msdn.microsoft.com/en-us/library/ty0d8k56(v=vs.110).aspx)，如 process.WaitForExit(10000)。

如何更改此扩展方法以使其与超时参数一起使用？

附带问题：我还看到有人提到 (https://stackoverflow.com/a/32994778/2713516) 我应该在某个时候处理 cancelToken，那么我不应该在方法中使用 dispose/using 吗？以及如何？

/// <summary>
/// Waits asynchronously for the process to exit.
/// </summary>
/// <param name="process">The process to wait for cancellation.</param>
/// <param name="cancellationToken">A cancellation token. If invoked, the task will return 
/// immediately as canceled.</param>
/// <returns>A Task representing waiting for the process to end.</returns>
public static Task WaitForExitAsync(this Process process, 
    CancellationToken cancellationToken = default(CancellationToken))
{
    var tcs = new TaskCompletionSource<object>();
    process.EnableRaisingEvents = true;
    process.Exited += (sender, args) => tcs.TrySetResult(null);
    if(cancellationToken != default(CancellationToken))
        cancellationToken.Register(tcs.SetCanceled);

    return tcs.Task;
}

Answer 1

您需要更改方法签名并应用流程本身的结果。例如考虑以下内容：

/// <summary>
/// Waits asynchronously for the process to exit.
/// </summary>
/// <param name="process">The process to wait for cancellation.</param>
/// <param name="cancellationToken">A cancellation token. If invoked, the task will return 
/// immediately as canceled.</param>
/// <returns>A Task representing waiting for the process to end.</returns>
public static Task WaitForExitAsync(this Process process, 
    int milliseconds,
    CancellationToken cancellationToken = default(CancellationToken))
{
    if (process.HasExited)
    {
        return Task.CompletedTask;
    }

    var tcs = new TaskCompletionSource<object>();
    process.EnableRaisingEvents = true;
    process.Exited += (sender, args) => tcs.TrySetResult(null);
    if (cancellationToken != default(CancellationToken))
    {
        cancellationToken.Register(tcs.SetCanceled);
    }

    return process.HasExited
        ? Task.CompletedTask
        : Task.WhenAny(tcs.Task, Task.Delay(milliseconds));
}

现在，如果进程还没有结束，任务仍然会在延迟后返回。另一种方法是使用Task.Run 调用所需的重载，如下所示：

/// <summary>
/// Waits asynchronously for the process to exit.
/// </summary>
/// <param name="process">The process to wait for cancellation.</param>
/// <param name="cancellationToken">A cancellation token. If invoked, the task will return 
/// immediately as canceled.</param>
/// <returns>A Task representing waiting for the process to end.</returns>
public static Task WaitForExitAsync(this Process process, 
    int milliseconds,
    CancellationToken cancellationToken = default(CancellationToken)) =>
    process.HasExited
        ? Task.CompletedTask
        : Task.Run(() => process.WaitForExit(milliseconds), cancellationToken);
}