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Cancellation: "Multiple simultaneous connections ... not supported when UseXaTransactions=False" #1001
Description
With UseXaTransactions=False and TransactionScope, triggering the cancellation token during ExecuteReaderAsync leads to the following exception:
System.NotSupportedException: Multiple simultaneous connections or connections with different connection strings
inside the same transaction are not supported when UseXaTransactions=False.
at MySqlConnector.MySqlConnection.FindExistingEnlistedSession(Transaction transaction) in /_/src/MySqlConnector/MySqlConnection.cs:line 289
at MySqlConnector.MySqlConnection.OpenAsync(Nullable`1 ioBehavior, CancellationToken cancellationToken) in /_/src/MySqlConnector/MySqlConnection.cs:line 435
at MySqlConnector.MySqlConnection.Open() in /_/src/MySqlConnector/MySqlConnection.cs:line 380
at MySqlConnector.MySqlConnection.Cancel(ICancellableCommand command, Int32 commandId, Boolean isCancel) in /_/src/MySqlConnector/MySqlConnection.cs:line 719
at MySqlConnector.MySqlCommand.Cancel() in /_/src/MySqlConnector/MySqlCommand.cs:line 98
at System.Threading.CancellationToken.<>c.<.cctor>b__26_0(Object obj)
at System.Threading.CancellationTokenSource.InternalRegister(Action`1 callback, Object stateForCallback, SynchronizationContext syncContext, ExecutionContext executionContext)
at System.Threading.CancellationToken.Register(Action`1 callback, Object state, Boolean useSynchronizationContext, Boolean useExecutionContext)
at MySqlConnector.MySqlCommand.MySqlConnector.Core.ICancellableCommand.RegisterCancel(CancellationToken cancellationToken) in /_/src/MySqlConnector/MySqlCommand.cs:line 364
at MySqlConnector.MySqlDataReader.ReadAsync(CancellationToken cancellationToken) in /_/src/MySqlConnector/MySqlDataReader.cs:line 43The cancellation token was triggered due to application shutdown (SIGTERM).
The flow was as follows:
- Construct
TransactionsScopeinusing, with async flows enabled. ExecuteReaderAsync, withCancellationToken.CancellationTokenrequests cancellation.
I have a theory. Is it possible that the logic that handles cancellation fails to return the connection to the pool? Perhaps a rollback is then attempted, but the connection that was bound to the transaction is not available, so a new connection is attempted to be used. That would explain the exception.
I also wonder if this could be related to #745.
Activity
bgrainger commentedon Jun 14, 2021
It looks like the background connection being opened to cancel the command is automatically enlisting in the current
TransactionScope.This is not desirable, and should be trivial to bypass with
AutoEnlist=false.Don't AutoEnlist cancellation connection. Fixes #1001
Timovzl commentedon Jun 15, 2021
Nice! As always, your fast response is greatly appreciated.
bgrainger commentedon Jun 16, 2021
Fixed in 1.3.10.