Memory Problems in C# using while(true)

Question

i would like to write an Client in C# which checks if a User is logged in on different Clients. The Client should run 24/7 and refreshes a Database with some State Information for each Client.

My Problem is: The Command Line Tool takes more and more Memory, so ill think that there is a Problem that i allocate Memory which never gets released.

I think it is that i am creating a ManagementScope, but i cannot all the Dispose() Method for it.

Here is my Code:

static void Main(string[] args)
    {

        Ping pingSender = new Ping();
        PingOptions options = new PingOptions();

        string sqlconnectionstring = "Data Source=(local)\\SQLEXPRESS;Initial Catalog=clientstat;User ID=...;Password=....;Integrated Security=SSPI";
        SqlConnection clientread = new SqlConnection(sqlconnectionstring);
        clientread.Open();

        // Use the default Ttl value which is 128,
        // but change the fragmentation behavior.
        options.DontFragment = true;

        string username = "";

        // Create a buffer of 32 bytes of data to be transmitted.
        string data = "aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa";
        byte[] buffer = Encoding.ASCII.GetBytes(data);
        int timeout = 120;

        while (true)
        {

            SqlCommand clientcommand = new SqlCommand("SELECT * FROM Client WHERE StateID = @stateid", clientread);
            clientcommand.Parameters.Add(new SqlParameter("stateid", 1));

            SqlDataReader clientreader = clientcommand.ExecuteReader();
            while (clientreader.Read())
            {
                string ipadress = Convert.ToString(clientreader["IP"]);
                string clientid = Convert.ToString(clientreader["ID"]);

                if (ipadress != string.Empty && clientid != string.Empty)
                {
                    // First Try To Ping Computer

                    PingReply reply = pingSender.Send(ipadress, timeout, buffer, options);
                    if (reply.Status == IPStatus.Success)
                    {

                        try
                        {

                            ManagementScope managementScope = new ManagementScope((@"\\" + ipadress + @"\root\cimv2"));
                            managementScope.Options.Username = "....";
                            managementScope.Options.Password = "...";
                            managementScope.Options.EnablePrivileges = true;
                            // ObjectQuery to Check if User is logged on
                            ObjectQuery objectQuery = new ObjectQuery("SELECT * FROM Win32_ComputerSystem");
                            ManagementObjectSearcher managementObjectSearcher = new ManagementObjectSearcher(managementScope, objectQuery);
                            ManagementObjectCollection querycollection = managementObjectSearcher.Get();

                            foreach (ManagementObject mo in querycollection)
                            {
                                // Check Here UserName
                                username = Convert.ToString(mo["UserName"]);
                                if (username != "")
                                {
                                    Console.WriteLine(ipadress + " " + username);

                                }

                            }
                            querycollection.Dispose();
                            managementObjectSearcher.Dispose();
                        }
                        catch (Exception x)
                        {
                            Console.WriteLine(x.Message);
                        }
                    }
                }
                else
                {
                    Console.WriteLine(clientid + " has no IP-Adress in Database");
                }
            }
            clientcommand.Dispose();
            clientreader.Close();
            clientreader.Dispose();
        }

    }

}

Any Ideas or Suggestions what i can improve here? Or what exactly could be a Problem?

Thanks in advance

Answer 1

Idea 1:

You have to Dispose the ManagementObject to release the unmanaged COM resources.

Unfortunately, there is a bug in the Dispose implementation of it. Here are more details about it.

Credits should go to this answer that provides a workaround using GC.Collect(). Unfortunately, it costs.

That's why it is better to use a counter to perform the GC.Collect every n loops, with a n value you will manually tune until the performances are acceptable.

Anyway, I would try to invoke the ManagementObject Dispose() using reflection.

Idea 2:

In general, re-using a opened connection for several queries is not good since it prevents the connection pooling mechanism to work as optimal. Therefore, the sqlconnection may retain resources if used so.

Instead, please include the SqlConnection create/open and close/dispose in the loop, as related to this question.

Answer 2

You should use using (and not invoke Dispose(), it's not needed). The "new" issue would be the nesting, which will look like this:

using (SqlConnection ...) 
{
    using (SqlCommand ...)
    {
        using (SqlDataReader ...) 
        {
           ...
        }
    }
}

Basically, if you are instancing something which implements IDisposable, put a using there and be assured that .NET will handle memory for you (at least, it will try to).

Answer 3

Try to add a GC.Collect() call after each top level iteration (just to diagnose the issue). See if the memory behaves the same. If not then you don't have an issue, the GC might just be optimistic and delay collections.

Each iteration uses a non trivial amount of space due to the data reader buffers and what not so if those are just not collected you will observe memory just increasing.

It is just a false alarm though. If your system becomes memory constrained or the app triggers some kind of internal GC threshold collection will happen just fine.

Answer 4

I'm not sure why you're creating a new SqlCommand on each loop iteration.

Just parameterize the SqlCommand, and in the loop iteration, and set the parameters, rather than creating a new SqlCommand.

Do that, and let me know how the memory looks. Remember one more thing - the GC won't kick in until it kicks in (i.e. non-determinism rules are in effect). Unless you really want to run a GC.Collect in your loop (that's sheer madness, IMHO). Another words, the constant creation/disposal of the objects is probably making the memory grow. Remember that a naive Dispose isn't going to make the memory magically shrink. Also keep in mind the memory management model of .NET and you should be all right.

Answer 5

The reason you are getting this exception is you are using while(true) statement and you are not using break; anywhere in a loop to break it explicitly. So the while loop is executing in infinite times and thus taking whole lot of memory. I think you should use Windows Service instead of while(true) to run it 24/7 and do it's operation without exception.