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POWhy does my multithreaded code to fill grids sometimes fail?
 

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  1. POWhy does my multithreaded code to fill grids sometimes fail?
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    <p>I read documents about thread pooling and I wrote test code to load data into two grids from different threads. Sometimes, though, only one grid fills, and the other remains empty. And sometimes everything's ok. Why? when i use waitall i get this exception:WaitAll for multiple handles on a STA thread is not supported.</p> <pre><code> private void button1_Click(object sender, EventArgs e) { ManualResetEvent[] mre = new ManualResetEvent[2]; mre[0] = new ManualResetEvent(false); multhread ml = new multhread(mre[0]); ThreadPool.QueueUserWorkItem(ml.setdatabase,1); mre[1] = new ManualResetEvent(false); // multhread ml2 = new multhread(mre[1]); ThreadPool.QueueUserWorkItem(ml.setdatabase2, 2); WaitHandle.WaitAll(mre); dataGridView1.DataSource = ml.propdt; dataGridView2.DataSource = ml.propdt2; } public DataTable propdt2 { get; set; } public void s() { string constring = "DATA SOURCE=.; database=test;integrated security= true; USER ID=sa;password=123456789"; SqlCommand com = new SqlCommand(); SqlConnection con = new SqlConnection(constring); com.Connection = con; com.CommandText = " select * from imgtable"; SqlDataAdapter adapt = new SqlDataAdapter(com); DataTable dt2 = new DataTable(); adapt.Fill(dt2); propdt2 = dt2; } } public class multhread { private ManualResetEvent _doneEvent; public multhread(ManualResetEvent doevent) { _doneEvent = doevent; } public static DataTable dt; public static DataTable dt2; public DataTable propdt { get; set; } public DataTable propdt2 { get; set; } public void setdatabase(Object threadContext) { string constring = "DATA SOURCE=.; database=test;integrated security= true; USER ID=sa;password=123456789"; SqlCommand com = new SqlCommand(); SqlConnection con = new SqlConnection(constring); com.Connection = con; com.CommandText = " select * from imgtable"; SqlDataAdapter adapt = new SqlDataAdapter(com); dt2 = new DataTable(); adapt.Fill(dt2); propdt2 = dt2; _doneEvent.Set(); // return dt2; } public void setdatabase2(Object threadContext) { string constring = "DATA SOURCE=.; database=test;integrated security= true; USER ID=sa;password=123456789"; SqlCommand com = new SqlCommand(); SqlConnection con = new SqlConnection(constring); com.Connection = con; com.CommandText = " select * from imgtable order by id desc "; SqlDataAdapter adapt = new SqlDataAdapter(com); dt = new DataTable(); adapt.Fill(dt); propdt = dt; _doneEvent.Set(); } </code></pre>
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    1. This table or related slice is empty.
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    1. USheavy
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    1. This table or related slice is empty.
    1. This table or related slice is empty.
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      1. POWhy does my multithreaded code to fill grids sometimes fail?
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    1. COIs this code in a web application?
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      1. POWhy does my multithreaded code to fill grids sometimes fail?
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    2. COno its win application.
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      1. POWhy does my multithreaded code to fill grids sometimes fail?
      1. USheavy
    3. COAre you asking this in an attempt to understand the theory, or is this intended to be actual production code? While it's possible to make simultaneous SQL Server commands work this way, it's definitely not the recommended approach. Are you using .NET 4.5?
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      1. POWhy does my multithreaded code to fill grids sometimes fail?
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