System.Net.Cache.CombinedReadStream.BeginRead C# (CSharp) Method

        public override IAsyncResult BeginRead(byte[] buffer, int offset, int count, AsyncCallback callback, Object state) {
            try {
                if (Interlocked.Increment(ref m_ReadNesting) != 1) {
                    throw new NotSupportedException(SR.GetString(SR.net_io_invalidnestedcall, "BeginRead", "read"));
                }

                if (m_ReadCallback == null) {
                    m_ReadCallback = new AsyncCallback(ReadCallback);
                }

                if (m_HeadEOF) {
                    return m_TailStream.BeginRead(buffer, offset, count, callback, state);
                }
                else {
                    InnerAsyncResult userResult = new InnerAsyncResult(state, callback, buffer, offset, count);
                    IAsyncResult ar = m_HeadStream.BeginRead(buffer, offset, count, m_ReadCallback, userResult);

                    if (!ar.CompletedSynchronously)
                    {
                        return userResult;
                    }

                    int bytes = m_HeadStream.EndRead(ar);
                    m_HeadLength += bytes;

                    //check on EOF condition
                    if (bytes == 0 && userResult.Count != 0) {
                        //Got a first stream EOF
                        m_HeadEOF = true;
                        m_HeadStream.Close();
                        return m_TailStream.BeginRead(buffer, offset, count, callback, state);
                    }
                    else {
                        // just complete user IO
                        userResult.Buffer = null;
                        userResult.InvokeCallback(count);
                        return userResult;
                    }

                }
            }
            catch {
                Interlocked.Decrement(ref m_ReadNesting);
                throw;
            }
        }