无法使用异步方法从 C# 应用程序读取子进程的输出？

Question

我正在尝试使用 C# 和 Visual Studio 2013 Update 4 在我的 Windows 8.1 机器上为 EXE 编写我自己的交互式 shell。代码运行时没有任何错误，但我在任何一个中的读取调用中都看不到任何返回从 stdout 读取的循环或读取 stderr 的循环。读取调用永远不会返回。我的方法有什么问题？

我看到了这个相关的 SO 帖子，但我根本没有收到任何异常：

C# Read stdout of child process asynchronously

public partial class frmMain : Form
{
    private const string DIR_CHILDPROCESS = @"C:\Users\Robert\Documents\Visual Studio 2012\ChildProcess-5.3.1 - IDAvatars\";
    private const string EXE_NAME = @"childprocess.exe";

    Process _childProcess = null;

    public frmMain()
    {
        InitializeComponent();
    }

    private async Task ReadOutputFromChildProcess()
    {
        char[] aryC = new char[1];

        while (true)
        {
            // Get output from ChildProcess.
            int count = await this._childProcess.StandardOutput.ReadAsync(aryC, 0, 1);

            Debug.Write(aryC[0]);

            // await Task.Delay(50);
        }
    }

    private async Task ReadFromErrorsChildProcess()
    {
        char[] aryC = new char[1];

        while (true)
        {
            // Get output from ChildProcess.
            int count = await this._childProcess.StandardError.ReadAsync(aryC, 0, 1);

            Debug.Write(aryC[0]);

            // await Task.Delay(50);
        }
    }

    private void frmShell_Load(object sender, EventArgs e)
    {
        string target = Path.Combine(DIR_CHILDPROCESS, EXE_NAME);

        this._childProcess = new Process();

        this._childProcess.StartInfo.UseShellExecute = false;
        this._childProcess.StartInfo.RedirectStandardOutput = true;
        this._childProcess.StartInfo.RedirectStandardError = true;
        this._childProcess.StartInfo.RedirectStandardInput = true;
        this._childProcess.StartInfo.CreateNoWindow = true; 

        this._childProcess.EnableRaisingEvents = true;

        this._childProcess.StartInfo.FileName = target;

        this._childProcess.Exited += this._childProcess_Exited;

        // this._childProcess.StartInfo.Arguments = arguments;
        // this._childProcess.StartInfo.
        this._childProcess.StartInfo.WorkingDirectory = DIR_CHILDPROCESS;
        //this._childProcess.StartInfo.FileName = Path.Combine(DIR_CHILDPROCESS, EXE_NAME);
        //this._childProcess.StartInfo.UseShellExecute = false;
        //this._childProcess.StartInfo.RedirectStandardOutput = true;
        //this._childProcess.StartInfo.RedirectStandardError = true;
        //this._childProcess.StartInfo.RedirectStandardInput = true;
        //this._childProcess.StartInfo.CreateNoWindow = true;


        if (!this._childProcess.Start())
            MessageBox.Show("ChildProcess failed to start.", "Error");

        // Start the loop that reads output from ChildProcess.
        this.ReadOutputFromChildProcess();

        // Start the loop that reads error messages from ChildProcess.
        this.ReadFromErrorsChildProcess();

        Debug.WriteLine("ChildProcess launched successfully.");

        // this._childProcess.WaitForExit();

    }

    void _childProcess_Exited(object sender, EventArgs e)
    {
        Debug.WriteLine("Child process exited with exit code: " + this._childProcess.ExitCode.ToString());
    }

    private void frmMain_FormClosing(object sender, FormClosingEventArgs e)
    {
        this._childProcess.Kill();
    }
}

Answer 1

我看到了这个相关的 SO 帖子，但没有抛出任何异常 完全没有

从任何异步方法传播的任何异常都将被两个 Task 对象吞没，您无需等待任何对象。如果您想观察任何异常，您可以同时执行两个异步操作并使用Task.WhenAll 等待它们：

private async void frmShell_Load(object sender, EventArgs e)
{
    var readOutputTask = this.ReadOutputFromChildProcess();
    var readErrorTask = this.ReadFromErrorsChildProcess();

    await Task.WhenAll(readOutputTask, readErrorTask);
}

否则，如果你想让这两个操作顺序执行，你可以await每一个单独执行：

private async void frmShell_Load(object sender, EventArgs e)
{
    await ReadOutputFromChildProcess();
    await ReadFromErrorsChildProcess();
}