Some Async Socket Code - Help with Garbage Collection?

Question

I think this question is really about my understanding of Garbage collection and variable references. But I will go ahead and throw out some code for you to look at.

// Please note do not use this code for async sockets, just to highlight my question

// SocketTransport
// This is a simple wrapper class that is used as the 'state' object
// when performing Async Socket Reads/Writes
public class SocketTransport
{
    public Socket Socket;
    public byte[] Buffer;
    public SocketTransport(Socket socket, byte[] buffer)
    {
        this.Socket = socket;
        this.Buffer = buffer;
    }
}

// Entry point - creates a SocketTransport, then passes it as the state
// object when Asyncly reading from the socket.
public void ReadOne(Socket socket)
{
    SocketTransport socketTransport_One =
        new SocketTransport(socket, new byte[10]);

    socketTransport_One.Socket.BeginRecieve
        (
        socketTransport_One.Buffer,    // Buffer to store data
        0,                             // Buffer offset
        10,                            // Read Length
        SocketFlags.None               // SocketFlags
        new AsyncCallback(OnReadOne),  // Callback when BeginRead completes
        socketTransport_One            // 'state' object to pass to Callback.
        );
}

public void OnReadOne(IAsyncResult ar)
{
    SocketTransport socketTransport_One = ar.asyncState as SocketTransport;
    ProcessReadOneBuffer(socketTransport_One.Buffer);  // Do processing

    // New Read
    // Create another! SocketTransport (what happens to first one?)
    SocketTransport socketTransport_Two =
        new SocketTransport(socket, new byte[10]);

    socketTransport_Two.Socket.BeginRecieve
        (
        socketTransport_One.Buffer,
        0,
        10,
        SocketFlags.None
        new AsyncCallback(OnReadTwo),
        socketTransport_Two
        );
}

public void OnReadTwo(IAsyncResult ar)
{
    SocketTransport socketTransport_Two = ar.asyncState as SocketTransport;
    ..............

So my question is:

• The first SocketTransport to be created (socketTransport_One) has a strong reference to a Socket object (lets call is ~SocketA~).

• Once the async read is completed, a new SocketTransport object is created (socketTransport_Two) also with a strong reference to ~SocketA~.

  Q1. Will socketTransport_One be collected by the garbage collector when method OnReadOne exits? Even though it still contains a strong reference to ~SocketA~

Thanks all!

Answer 1

In your example, socketTransport_One should be garbage-collected, because no other objects have a strong reference to it. Just because it has a strong reference to another object doesn't mean it's ineligible for garbage collection.