[英]Weird behaviour of task in ASP.NET application
我試圖異步地從所有分支的Mysql服務器連接並接收非常少量的數據,而不必等待一個完成。
我有我自己的事件驅動的.NET MySQL Connector Wrapper庫,它可以正常工作而無需異步。
看起來我在執行多任務處理時缺少某些東西,但我不知道為什么。
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();
}
這是輸出:
<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>
如您所見,我想包裝器w總是會得到循環中最后一次調用的引用。 但是,當我注釋掉任務部分並直接在循環中使用w.Connect()時,一切都已修復。
有任何想法嗎 ?
您的問題是您正在關閉稍后要更改的局部變量w
,因此,當您執行任務時,它已經包含運行時的其他值。
解決方案很簡單:在循環內聲明t
, b
和w
。 實際上,如果我是您,我會將其重寫為簡單的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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