/// <summary>
/// Try to abort the transaction.
/// </summary>
///
/// <param name="transaction">
/// The transaction to abort.
/// </param>
/// <param name="cancellationToken">
/// A cancellation token that can be used by other objects or threads to receive notice of cancellation.
/// </param>
///
/// <returns>Whether the abort call has succeeded.</returns>
private async Task <bool> TryAbort(AsyncTransaction transaction, CancellationToken cancellationToken)
{
try
{
if (transaction != null)
{
await transaction.Abort();
}
else
{
await this.session.AbortTransactionAsync(cancellationToken);
}
}
catch (Exception e)
{
this.logger.LogWarning("This session is invalid on ABORT: {}", e);
return(false);
}
return(true);
}
/// <summary>
/// Initializes a new instance of the <see cref="AsyncTransactionExecutor"/> class.
/// </summary>
///
/// <param name="transaction">
/// The <see cref="AsyncTransaction"/> object the <see cref="AsyncTransactionExecutor"/> wraps.
/// </param>
/// <param name="serializer">The serializer to serialize and deserialize Ion data.</param>
internal AsyncTransactionExecutor(AsyncTransaction transaction, ISerializer serializer = null)
{
this.transaction = transaction;
this.serializer = serializer;
}
/// <summary>
/// Initializes a new instance of the <see cref="AsyncTransactionExecutor"/> class.
/// </summary>
///
/// <param name="transaction">
/// The <see cref="AsyncTransaction"/> object the <see cref="AsyncTransactionExecutor"/> wraps.
/// </param>
internal AsyncTransactionExecutor(AsyncTransaction transaction)
{
this.transaction = transaction;
}
/// <summary>
/// Execute the Executor lambda asynchronously against QLDB and retrieve the result within a transaction.
/// </summary>
///
/// <param name="func">The Executor lambda representing the block of code to be executed within the transaction.
/// This cannot have any side effects as it may be invoked multiple times, and the result cannot be trusted
/// until the transaction is committed.</param>
/// <param name="cancellationToken">A cancellation token that can be used by other objects or threads to receive
/// notice of cancellation.</param>
/// <typeparam name="T">The return type.</typeparam>
///
/// <returns>The return value of executing the executor. Note that if you directly return a
/// <see cref="IAsyncResult"/>, this will be automatically buffered in memory before the implicit commit to
/// allow reading, as the commit will close any open results. Any other <see cref="IAsyncResult"/> instances
/// created within the executor block will be invalidated, including if the return value is an object which
/// nests said <see cref="IAsyncResult"/> instances within it.
/// </returns>
///
/// <exception cref="TransactionAbortedException">
/// Thrown if the Executor lambda calls <see cref="AsyncTransactionExecutor.Abort"/>.
/// </exception>
/// <exception cref="AmazonServiceException">
/// Thrown when there is an error executing against QLDB.
/// </exception>
internal async Task <T> Execute <T>(
Func <AsyncTransactionExecutor, Task <T> > func,
CancellationToken cancellationToken)
{
ValidationUtils.AssertNotNull(func, "func");
AsyncTransaction transaction = null;
string transactionId = QldbTransactionException.DefaultTransactionId;
try
{
transaction = await this.StartTransaction(cancellationToken);
transactionId = transaction.Id;
T returnedValue = await func(new AsyncTransactionExecutor(transaction));
if (returnedValue is IAsyncResult result)
{
returnedValue = (T)(object)(await AsyncBufferedResult.BufferResultAsync(result));
}
await transaction.Commit();
return(returnedValue);
}
catch (TransactionAbortedException)
{
throw;
}
catch (InvalidSessionException ise)
{
if (IsTransactionExpiredException(ise))
{
throw new QldbTransactionException(
transactionId,
await this.TryAbort(transaction, cancellationToken),
ise);
}
else
{
throw new RetriableException(transactionId, false, ise);
}
}
catch (OccConflictException occ)
{
throw new RetriableException(transactionId, true, occ);
}
catch (AmazonServiceException ase)
{
if (ase.StatusCode == HttpStatusCode.InternalServerError ||
ase.StatusCode == HttpStatusCode.ServiceUnavailable)
{
throw new RetriableException(
transactionId,
await this.TryAbort(transaction, cancellationToken),
ase);
}
throw new QldbTransactionException(
transactionId,
await this.TryAbort(transaction, cancellationToken),
ase);
}
catch (Exception e)
{
throw new QldbTransactionException(
transactionId,
await this.TryAbort(transaction, cancellationToken),
e);
}
finally
{
transaction?.Dispose();
}
}