.net async socket timeout check thread-safety

Question

http://msdn.microsoft.com/en-us/library/system.net.sockets.socketasynceventargs.aspx

Starting with the above msdn example I'm trying to write a timeout check which will close inactive client sockets and free up resources.

This is what I have come up with. But I'm not sure if its completely thread-safe and if there is a better way to do this. I hope someone can give some advices.

void IO_Completed(object sender, SocketAsyncEventArgs e)
{
    if (e.SocketError != SocketError.Success)
    {
        CloseClientSocket(e);
        return;
    }

    if (1 < Interlocked.CompareExchange(ref token.Status, 1, 0))
        return;

    switch (e.LastOperation)
    {
        case SocketAsyncOperation.Receive:
            ProcessReceive(e);
            break;
        ...
    }

    token.LastActive = Environment.TickCount;
    Interlocked.CompareExchange(ref token.Status, 0, 1);
}

void ProcessReceive(SocketAsyncEventArgs e)
{
    AsyncUserToken token = (AsyncUserToken)e.UserToken;
    if (e.BytesTransferred > 0)
        if (!token.Socket.SendAsync(e))
            ProcessSend(e);
    else
        CloseClientSocket(e);
}

void ProcessSend(SocketAsyncEventArgs e)
{
    AsyncUserToken token = (AsyncUserToken)e.UserToken;
    if (!token.Socket.ReceiveAsync(e))
        ProcessReceive(e);
}

TimeoutCheck will execute once each 20 seconds. allReadWriteArgs is an array with all SocketAsyncEventArgs. After closing the socket IO_Completed will be invoked with SocketError.OperationAborted.

void TimeoutCheck(object state)
{
    AsyncUserToken token;
    int timeout = Environment.TickCount - 20000;
    for (int i = 0; i < allReadWriteArgs.Length; i++)
    {
        token = (AsyncUserToken)allReadWriteArgs[i].UserToken;
        if (token.LastActive < timeout)
            if (0 == Interlocked.CompareExchange(ref token.Status, 2, 0))
                Interlocked.Exchange(ref token.Socket, null).Close();
    }
}


void CloseClientSocket(SocketAsyncEventArgs e)
{
    AsyncUserToken token = e.UserToken as AsyncUserToken;

    if (token.Socket != null)
    {
        try
        {
            token.Socket.Shutdown(SocketShutdown.Both);
        }
        catch (SocketException) { }
        token.Socket.Close();
    }

    token.Status = 2;
    bufferManager.FreeBuffer(e);
    readWritePool.Push(e);
    ...
}

Answer 1

Your code looks good. You can do something like this, as well:

void _connectionActivityCheck_Elapsed(object sender, System.Timers.ElapsedEventArgs e)
{
    _connectionActivityCheck.Stop();

    try
    {
        List<Guid> connectionsToRemove = new List<Guid>();

        lock (_connections.SyncRoot)
        {
            IncomingConnection conn;

            foreach (DictionaryEntry item in _connections)
            {
                conn = (IncomingConnection)item.Value;

                if (conn.LastIncomingActivity.HasValue && 
                    DateTime.Now.Subtract(conn.LastIncomingActivity.Value).TotalSeconds > MaximumInactivitySeconds)
                        connectionsToRemove.Add(conn.ConnectionId);
            }
        }

        if (connectionsToRemove.Count > 0)
        {
            int itemsToRemove = connectionsToRemove.Count;

            foreach (Guid item in connectionsToRemove)
            {
                RemoveConnection(item);
            }

            Context.Current.Logger.LogInfo(_loggerName, 
                string.Format("{0} connections were closed due to incoming traffic inactivity", itemsToRemove));
        }
    }
    catch (Exception ex)
    {
        Context.Current.Logger.LogFatal(_loggerName, "An error ocurred while checking incoming traffic.", ex);
    }
    finally
    {
        _connectionActivityCheck.Start();
    }
}



private void RemoveConnection(Guid connectionId)
{
    lock (_connections.SyncRoot)
    {
        try
        {
            IncomingConnection conn = _connections[connectionId] as IncomingConnection;

            if (conn != null)
            {
                try
                {
                    conn.Dispose();
                }
                catch { }

                _connections.Remove(connectionId);
            }
        }
        catch { }
    }
}