// Called by the transaction to initiate commit sequence
        public void SinglePhaseCommit(SysTx.SinglePhaseEnlistment enlistment) {
            Debug.Assert(null != enlistment, "null enlistment?");

            SqlInternalConnection connection = GetValidConnection();
            SqlConnection usersConnection = connection.Connection;

            Bid.Trace("<sc.SqlDelegatedTransaction.SinglePhaseCommit|RES|CPOOL> %d#, Connection %d#, committing transaction.\n", ObjectID, connection.ObjectID);

            RuntimeHelpers.PrepareConstrainedRegions();
            try {
#if DEBUG
                TdsParser.ReliabilitySection tdsReliabilitySection = new TdsParser.ReliabilitySection();

                RuntimeHelpers.PrepareConstrainedRegions();
                try {
                    tdsReliabilitySection.Start();
#else
                {
#endif //DEBUG
                    // If the connection is dooomed, we can be certain that the
                    // transaction will eventually be rolled back, and we shouldn't
                    // attempt to commit it.
                    if (connection.IsConnectionDoomed) {
                        lock (connection) {
                            _active = false; // set to inactive first, doesn't matter how the rest completes, this transaction is done.
                            _connection = null;
                        }

                        enlistment.Aborted(SQL.ConnectionDoomed());
                    }
                    else {
                        Exception commitException;
                        lock (connection) {
                            try {
                                // Now that we've acquired the lock, make sure we still have valid state for this operation.
                                ValidateActiveOnConnection(connection);

                                _active = false; // set to inactive first, doesn't matter how the rest completes, this transaction is done.
                                _connection = null;   // Set prior to ExecuteTransaction call in case this initiates a TransactionEnd event

                                connection.ExecuteTransaction(SqlInternalConnection.TransactionRequest.Commit, null, IsolationLevel.Unspecified, _internalTransaction, true);
                                commitException = null;
                            }
                            catch (SqlException e) {
                                commitException = e;

                                ADP.TraceExceptionWithoutRethrow(e);

                                // Doom the connection, to make sure that the transaction is
                                // eventually rolled back.
                                // VSTS 144562: doom the connection while having the lock on it to prevent race condition with "Transaction Ended" Event
                                connection.DoomThisConnection();
                            }
                            catch (InvalidOperationException e) {
                                commitException = e;
                                ADP.TraceExceptionWithoutRethrow(e);
                                connection.DoomThisConnection();
                            }
                        }
                        if (commitException != null) {
                            // connection.ExecuteTransaction failed with exception
                            if (_internalTransaction.IsCommitted) {
                                // Even though we got an exception, the transaction
                                // was committed by the server.
                                enlistment.Committed();
                            }
                            else if (_internalTransaction.IsAborted) {
                                // The transaction was aborted, report that to
                                // SysTx.
                                enlistment.Aborted(commitException);
                            }
                            else {
                                // The transaction is still active, we cannot
                                // know the state of the transaction.
                                enlistment.InDoubt(commitException);
                            }

                            // We eat the exception.  This is called on the SysTx
                            // thread, not the applications thread.  If we don't 
                            // eat the exception an UnhandledException will occur,
                            // causing the process to FailFast.
                        }

                        connection.CleanupConnectionOnTransactionCompletion(_atomicTransaction);
                        if (commitException == null) {
                            // connection.ExecuteTransaction succeeded
                            enlistment.Committed();
                        }
                    }
                }
#if DEBUG
                finally {
                    tdsReliabilitySection.Stop();
                }
#endif //DEBUG
            }
            catch (System.OutOfMemoryException e) {
                usersConnection.Abort(e);
                throw;
            }
            catch (System.StackOverflowException e) {
                usersConnection.Abort(e);
                throw;
            }
            catch (System.Threading.ThreadAbortException e)  {
                usersConnection.Abort(e);
                throw;
            }
        }
        // Called by transaction to initiate abort sequence
        public void Rollback(SysTx.SinglePhaseEnlistment enlistment) {
            Debug.Assert(null != enlistment, "null enlistment?");

            SqlInternalConnection connection = GetValidConnection();
            SqlConnection usersConnection = connection.Connection;

            Bid.Trace("<sc.SqlDelegatedTransaction.Rollback|RES|CPOOL> %d#, Connection %d#, aborting transaction.\n", ObjectID, connection.ObjectID);

            RuntimeHelpers.PrepareConstrainedRegions();
            try {
#if DEBUG
                TdsParser.ReliabilitySection tdsReliabilitySection = new TdsParser.ReliabilitySection();

                RuntimeHelpers.PrepareConstrainedRegions();
                try {
                    tdsReliabilitySection.Start();
#else
                {
#endif //DEBUG
                    lock (connection) {
                        try {
                            // Now that we've acquired the lock, make sure we still have valid state for this operation.
                            ValidateActiveOnConnection(connection);
                            _active = false; // set to inactive first, doesn't matter how the execute completes, this transaction is done.
                            _connection = null;  // Set prior to ExecuteTransaction call in case this initiates a TransactionEnd event

                            // If we haven't already rolled back (or aborted) then tell the SQL Server to roll back
                            if (!_internalTransaction.IsAborted) {
                                connection.ExecuteTransaction(SqlInternalConnection.TransactionRequest.Rollback, null, IsolationLevel.Unspecified, _internalTransaction, true);
                            }
                        }
                        catch (SqlException e) {
                            ADP.TraceExceptionWithoutRethrow(e);

                            // Doom the connection, to make sure that the transaction is
                            // eventually rolled back.
                            // VSTS 144562: doom the connection while having the lock on it to prevent race condition with "Transaction Ended" Event
                            connection.DoomThisConnection();

                            // Unlike SinglePhaseCommit, a rollback is a rollback, regardless 
                            // of how it happens, so SysTx won't throw an exception, and we
                            // don't want to throw an exception either, because SysTx isn't 
                            // handling it and it may create a fail fast scenario. In the end,
                            // there is no way for us to communicate to the consumer that this
                            // failed for more serious reasons than usual.
                            // 
                            // This is a bit like "should you throw if Close fails", however,
                            // it only matters when you really need to know.  In that case, 
                            // we have the tracing that we're doing to fallback on for the
                            // investigation.
                        }
                        catch (InvalidOperationException e) {
                            ADP.TraceExceptionWithoutRethrow(e);
                            connection.DoomThisConnection();
                        }
                    }

                    // it doesn't matter whether the rollback succeeded or not, we presume
                    // that the transaction is aborted, because it will be eventually.
                    connection.CleanupConnectionOnTransactionCompletion(_atomicTransaction);
                    enlistment.Aborted();
                }
#if DEBUG
                finally {
                    tdsReliabilitySection.Stop();
                }
#endif //DEBUG
            }
            catch (System.OutOfMemoryException e) {
                usersConnection.Abort(e);
                throw;
            }
            catch (System.StackOverflowException e) {
                usersConnection.Abort(e);
                throw;
            }
            catch (System.Threading.ThreadAbortException e)  {
                usersConnection.Abort(e);
                throw;
            }
        }