Object Not Garbage Collected

Question

Hello All,

I have a third party component I'm using and I'm seeing some issues with resources not being released. The component causes windows to create a handle to a UDP socket ("\Device\Udp" as well as "\Device\Afd"). If I allow the program to execute and dereference the third party object, I assumed that like all .NET objects I've worked with in the past, the object will get garbage collected. However, Process Explorer is showing that the "\Device\Udp" handles are being kept indefinitely until the actual process is killed (or in the case of the app in question: app pool is recycled.

Furthermore, if I manually call the Dispose() method of the object, then the handles are released. This is the fix I have in place, but I'm just curious about why it is needed. Is it possible that the builders of the componenet have done something or set some attribute which prevents the garbage collector from calling the destructing on the object?

If it helps, I have posted the code below. The code was used in a Forms application, so the process does not end after the while loop completes.

Code that does not work (100 handles created indefinitely):

        for (int i = 0; i < n; i++)
        {
            Snmpmgr mgr = new Snmpmgr();
            mgr.Timeout = 10;

            mgr.ObjCount = 1;
            mgr.ObjId[1] = ".1.3.6.1.2.1.1.1.0";

            try
            {
                mgr.SendGetRequest();  // Handle shows up in ProcExplorer after this call
            }
            catch (Exception ex)
            {
                throw new TimeoutException("Error contacting CMTS.");
            }
        }  // end of for...  obj referenced by mgr never garbage collected

Code that does work (handles created and released):

        for (int i = 0; i < n; i++)
        {
            Snmpmgr mgr = new Snmpmgr();
            mgr.Timeout = 10;

            mgr.ObjCount = 1;
            mgr.ObjId[1] = ".1.3.6.1.2.1.1.1.0";

            try
            {
                mgr.SendGetRequest();  // Handle shows up in ProcExplorer after this 
            }
            catch (Exception ex)
            {
                throw new TimeoutException("Error contacting CMTS.");
            }
            mgr.Dispose();  // UDP Socket Handle freed...  not sure that's how to spell free + ed :)
        }

Thanks in advance for your help.

Chris

Answer 1

You used a mgr.Dispose call in the second example. I'll take it mgr is an IDisposable?

In that case, you need to use a using block:

for (int i = 0; i < n; i++)
{
    using(Snmpmgr mgr = new Snmpmgr())
    {
        // Your Code
    }
}

Answer 2

Calling Dispose is the proper thing to do. Some objects use unmanaged resources (and if you're working with sockets, it's likely the case). The Dispose method is exposed precisely so that the object can properly deallocate its unmanaged resources. Any time you use an object that implements IDisposable, you should call Dispose when you're done with it.

For more detail about IDisposable: http://stackoverflow.com/questions/12368/how-to-dispose-a-class-in-net

Answer 3

That's the point about the Dipose() method. Since one can never know when the destructor will be called, you should use Dispose to release unmanaged resources. As MiffTheFox said, you should put your code inside an 'using' block. When the code execution reaches the end of the 'using' block, Dipose() will be called automatically.

Answer 4

Perhaps you can put mgr.Dispose() in your "finally" clause, after your try/catch block.

Answer 5

You did in fact implement a destructor on the Snmpmgr class to release the socket handle, right? ... otherwise the GC does not know there is some work to be done to release resources if you do not do it explicitly through Dispose().