ASP.NET 应用程序中任务的异常行为

Question

我正在尝试从所有分支机构的 Mysql 服务器异步连接并接收非常少量的数据，无需等待一个完成。

我有自己的事件驱动 .NET MySQL Connector Wrapper 库，无需异步即可正常工作。

看起来我在处理多项任务时遗漏了一些东西，但我不明白为什么。

public void GetALL()
    {
        TaskList = new Task[RemSQL.Count];

        Response.Write("<h1>starting..........</h1>");

        Task t;
        BranchInfo b;
        Wrapper w;

        for (int tx = 0; tx < RemSQL.Count; tx++)
        {
            int txx = tx; //strongly suggested on MSDN while using tasks/threads in loops
            b = RemSQL[txx];
            w = b.Wrapper;
            Response.Write("<h2>TASK #" + txx.ToString() + " branch.id #" + w.id + " starts...</h2>");

            w.Connecting += Wrapper_Connecting;            
            w.Connected += Wrapper_Connected;
            w.ConnectionError += Wrapper_ConnectionError;

            //w.Connect() //disabling multitasking works just fine

            t = new Task(() =>
            {
                w.Connect();
            });

            TaskList[txx] = t;
            t.Start();

        }

        Task.WaitAll(TaskList);

        Response.Write("<h1>Tasks completed</h1>");

        foreach(BranchInfo bb in RemSQL)
        {
            bb.Wrapper.Dispose();
        }

        Response.Flush();
        Response.End();

    }

    private void Wrapper_Connected(object sender)
    {
        Wrapper w = (Wrapper)sender;
        WriteScript("Connected('" + w.id + "');");
    }

    private void Wrapper_Connecting(object sender)
    {
        Wrapper w = (Wrapper)sender;
        WriteScript("Connecting('" + w.id + "');");
    }

    private void Wrapper_ConnectionError(object sender, Exception ex)
    {
        Wrapper w = (Wrapper)sender;
        WriteScript("ConnectionFailed('" + w.id + "', '" + ex.Message + "');");
    }

private void WriteScript(string scr)
{
    Response.Write("<script>" + scr + "</script>\n");
    Response.Flush();
}

这是输出：

<h1>starting..........</h1><h2>TASK #0 branch.id #2 starts...</h2>
<h2>TASK #1 branch.id #3 starts...</h2>
<h2>TASK #2 branch.id #4 starts...</h2>
<h2>TASK #3 branch.id #5 starts...</h2>
<h2>TASK #4 branch.id #6 starts...</h2>
<h2>TASK #5 branch.id #7 starts...</h2>
<h2>TASK #6 branch.id #8 starts...</h2>
<h2>TASK #7 branch.id #9 starts...</h2>
<h2>TASK #8 branch.id #10 starts...</h2>
<h2>TASK #9 branch.id #11 starts...</h2>
<h2>TASK #10 branch.id #13 starts...</h2>
<h2>TASK #11 branch.id #14 starts...</h2>
<h2>TASK #12 branch.id #15 starts...</h2>
<h2>TASK #13 branch.id #16 starts...</h2>
<h2>TASK #14 branch.id #17 starts...</h2>
<h2>TASK #15 branch.id #19 starts...</h2>
<h2>TASK #16 branch.id #20 starts...</h2>
<script>Connecting('20');</script>
<script>Connecting('20');</script>
<script>Connecting('20');</script>
<script>Connecting('20');</script>
<script>Connecting('20');</script>
<script>Connecting('20');</script>
<script>Connecting('20');</script>
<script>Connecting('20');</script>
<script>Connecting('20');</script>
<script>Connecting('20');</script>
<script>Connecting('20');</script>
<script>Connecting('20');</script>
<script>Connecting('20');</script>
<script>Connecting('20');</script>
<script>Connecting('20');</script>
<script>Connecting('20');</script>
<script>Connecting('20');</script>
<script>ConnectionFailed('20', 'There is already an open DataReader associated with this Connection which must be closed first.');</script>
<script>ConnectionFailed('20', 'There is already an open DataReader associated with this Connection which must be closed first.');</script>
<script>ConnectionFailed('20', 'There is already an open DataReader associated with this Connection which must be closed first.');</script>
<script>ConnectionFailed('20', 'There is already an open DataReader associated with this Connection which must be closed first.');</script>
<script>ConnectionFailed('20', 'There is already an open DataReader associated with this Connection which must be closed first.');</script>
<script>ConnectionFailed('20', 'There is already an open DataReader associated with this Connection which must be closed first.');</script>
<script>ConnectionFailed('20', 'There is already an open DataReader associated with this Connection which must be closed first.');</script>
<script>ConnectionFailed('20', 'There is already an open DataReader associated with this Connection which must be closed first.');</script>
<script>ConnectionFailed('20', 'There is already an open DataReader associated with this Connection which must be closed first.');</script>
<script>Connected('20');</script>
<script>ConnectionFailed('20', 'There is already an open DataReader associated with this Connection which must be closed first.');</script>
<script>ConnectionFailed('20', 'There is already an open DataReader associated with this Connection which must be closed first.');</script>
<script>ConnectionFailed('20', 'There is already an open DataReader associated with this Connection which must be closed first.');</script>
<script>ConnectionFailed('20', 'There is already an open DataReader associated with this Connection which must be closed first.');</script>
<script>ConnectionFailed('20', 'There is already an open DataReader associated with this Connection which must be closed first.');</script>
<script>ConnectionFailed('20', 'There is already an open DataReader associated with this Connection which must be closed first.');</script>
<script>Connected('20');</script>
<h1>Tasks completed</h1>

如您所见，我猜 Wrapper w 似乎总是在循环中获取最后一次调用的引用。但是当我注释掉任务部分并直接在循环中使用 w.Connect() 时，一切都会修复。

有什么想法吗？

Answer 1

您的问题是您正在关闭局部变量 w，稍后您将对其进行更改，因此，当您执行任务时，它已经包含运行.

解决方案很简单：在循环内声明 t、b 和 w。事实上，如果我是你，我会把它重写成简单的 Select:

Response.Write("<h1>starting..........</h1>");
Task.WaitAll(
  RemSQL.Select(b => b.Wrapper).Select(w => TaskFactory.Run(() => {
        Response.Write("<h2>TASK #" + txx.ToString() + " branch.id #" + w.id + " starts...</h2>");

        w.Connecting += Wrapper_Connecting;            
        w.Connected += Wrapper_Connected;
        w.ConnectionError += Wrapper_ConnectionError;

        w.Connect();
  })).ToArray());

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