问题
Possible Duplicate:
Entity framework 4 not closing connection in sql server 2005 profiler
Well, lots of developers on stackoverflow are saying that I should not worry to close my connection: my using statement will close the connection for me, here and here and all over the site. Unfortunately, I do not see it happening. Here is my code:
[Test, Explicit]
public void ReconnectTest()
{
const string connString = "Initial Catalog=MyDb;Data Source=MyServer;Integrated Security=SSPI;Application Name=ReconnectTest;";
for (int i = 0; i < 2000; i++)
{
try
{
using (var conn = new SqlConnection(connString))
{
conn.Open();
using (var command = conn.CreateCommand())
{
command.CommandText = "SELECT 1 as a";
command.CommandType = CommandType.Text;
command.ExecuteNonQuery();
}
//conn.Close();
// optional breakpoint 1 below
}
}
catch(SqlException e)
{
// breakpoint 2 below
Console.WriteLine(e);
}
// breakpoint 3 below
}
}
When I enable all breakpoints and start my test, the first iteration succeeds, and I hit breakpoint 3. At this point, the connection is still open: I see it in the Profiler, and sp_who2 outputs it too.
Let's suppose that at this time I am out for a lunch, and my connection is idle. As such, our production server kills it. To imitate it, I am killing the connection from SSMS.
So, when I hit F5 and run the second iteration, my connection is killed. Unfortunately, it does not reopen automatically, so ExecuteNonQuery throws the following exception: "transport-level error has occurred". When I run the third iteration, my connection actually opens: I see it as an event in Profiler, and sp_who2 outputs it as well.
Even when I have uncommented my conn.Close() command, the connection still does not close, and when I kill it from SSMS, the next iteration still blows up.
What am I missing? Why can't using statement close my connection? Why can't Open() actually open it the first time, but succeeds the next time?
This question has originated from my previous one
回答1:
When you call SqlConnection.Dispose(), which you do because of the using block, the connection is not closed, per-se. It is released back to the connection pool.
In order to avoid constantly building/tearing down connections, the connection pool will keep connections open for your application to use. So it makes perfect sense that the connection would still show as being open.
What's happening after that, I can't explain offhand - I know that keeping a random connection open would not cause that, though, because your application can certainly make more than a single concurrent connection.
来源：https://stackoverflow.com/questions/9133473/why-is-my-using-statement-not-closing-connection