/// <summary>
/// Executes the query, either sequentially or in parallel, depending on the query execution mode and
/// whether a premature merge was inserted by this ElementAt operator.
/// </summary>
/// <param name="result">result</param>
/// <param name="withDefaultValue">withDefaultValue</param>
/// <returns>whether an element with this index exists</returns>
internal bool Aggregate(out TSource result, bool withDefaultValue)
{
// If we were to insert a premature merge before this ElementAt, and we are executing in conservative mode, run the whole query
// sequentially.
if (LimitsParallelism && SpecifiedQuerySettings.WithDefaults().ExecutionMode.Value != ParallelExecutionMode.ForceParallelism)
{
CancellationState cancelState = SpecifiedQuerySettings.CancellationState;
if (withDefaultValue)
{
IEnumerable <TSource> childAsSequential = Child.AsSequentialQuery(cancelState.ExternalCancellationToken);
IEnumerable <TSource> childWithCancelChecks = CancellableEnumerable.Wrap(childAsSequential, cancelState.ExternalCancellationToken);
result = ExceptionAggregator.WrapEnumerable(childWithCancelChecks, cancelState).ElementAtOrDefault(_index);
}
else
{
IEnumerable <TSource> childAsSequential = Child.AsSequentialQuery(cancelState.ExternalCancellationToken);
IEnumerable <TSource> childWithCancelChecks = CancellableEnumerable.Wrap(childAsSequential, cancelState.ExternalCancellationToken);
result = ExceptionAggregator.WrapEnumerable(childWithCancelChecks, cancelState).ElementAt(_index);
}
return(true);
}
using (IEnumerator <TSource> e = GetEnumerator(ParallelMergeOptions.FullyBuffered))
{
if (e.MoveNext())
{
TSource current = e.Current;
Debug.Assert(!e.MoveNext(), "expected enumerator to be empty");
result = current;
return(true);
}
}
result = default(TSource);
return(false);
}
//---------------------------------------------------------------------------------------
// Executes the query and returns the results in an array.
//
internal TOutput[] ExecuteAndGetResultsAsArray()
{
QuerySettings querySettings =
SpecifiedQuerySettings
.WithPerExecutionSettings()
.WithDefaults();
QueryLifecycle.LogicalQueryExecutionBegin(querySettings.QueryId);
try
{
if (querySettings.ExecutionMode.Value == ParallelExecutionMode.Default && LimitsParallelism)
{
IEnumerable <TOutput> opSequential = AsSequentialQuery(querySettings.CancellationState.ExternalCancellationToken);
IEnumerable <TOutput> opSequentialWithCancelChecks = CancellableEnumerable.Wrap(opSequential, querySettings.CancellationState.ExternalCancellationToken);
return(ExceptionAggregator.WrapEnumerable(opSequentialWithCancelChecks, querySettings.CancellationState).ToArray());
}
QueryResults <TOutput> results = GetQueryResults(querySettings);
// Top-level preemptive cancellation test.
// This handles situations where cancellation has occurred before execution commences
// The handling for in-execution occurs in QueryTaskGroupState.QueryEnd()
if (querySettings.CancellationState.MergedCancellationToken.IsCancellationRequested)
{
if (querySettings.CancellationState.ExternalCancellationToken.IsCancellationRequested)
{
throw new OperationCanceledException(querySettings.CancellationState.ExternalCancellationToken);
}
else
{
throw new OperationCanceledException();
}
}
if (results.IsIndexible && OutputOrdered)
{
// The special array-based merge performs better if the output is ordered, because
// it does not have to pay for ordering. In the unordered case, we it appears that
// the stop-and-go merge performs a little better.
ArrayMergeHelper <TOutput> merger = new ArrayMergeHelper <TOutput>(SpecifiedQuerySettings, results);
merger.Execute();
TOutput[] output = merger.GetResultsAsArray();
querySettings.CleanStateAtQueryEnd();
return(output);
}
else
{
PartitionedStreamMerger <TOutput> merger =
new PartitionedStreamMerger <TOutput>(false, ParallelMergeOptions.FullyBuffered, querySettings.TaskScheduler,
OutputOrdered, querySettings.CancellationState, querySettings.QueryId);
results.GivePartitionedStream(merger);
TOutput[] output = merger.MergeExecutor.GetResultsAsArray();
querySettings.CleanStateAtQueryEnd();
return(output);
}
}
finally
{
QueryLifecycle.LogicalQueryExecutionEnd(querySettings.QueryId);
}
}