/// <summary>
/// <see cref="ProducerThreadMethod"/> works in parallel with RPM's <see cref="RequestProcessingManager.WriteTo"/>.
/// RPM supplies empty buffers to be filled with data into <see cref="RequestExecutionContext.BuffersRing"/> and consumes them on the other end.
/// The data ring has very limited number of buffers.
/// RPM is limited by network throughput and Producer's speed.
/// Producer is limited by underlying storage driver, local processing speed and RPM's consumption of complete buffers.
/// The difference between the two: RPM <see cref="RequestProcessingManager.WriteTo"/> is scheduled for execution by service infrastructure (WCF),
/// whereas <see cref="DataEngine.ProducerThreadMethod"/> is scheduled by RPM itself, when it invokes <see cref="IDataEngine.BeginExecution"/>.
/// </summary>
void ProducerThreadMethod(RequestExecutionContext context)
{
PqlEngineSecurityContext.Set(new PqlClientSecurityContext(
context.AuthContext.UserId, "dummy", context.AuthContext.TenantId, context.AuthContext.ContextId));
var executionPending = true;
IDriverDataEnumerator sourceEnumerator = null;
try
{
// row number is needed for "rownum()" Pql function
context.ClauseEvaluationContext.RowNumber = 0;
// Our production is limited by the network throughput.
// Production will also be aborted if the destination sink stops accepting.
// In that case, ConsumingEnumerable will either throw or stop yielding.
bool havePendingDriverRow = false;
foreach (var buffer in context.BuffersRing.ConsumeProcessingTasks(context.CancellationTokenSource.Token)
)
{
buffer.Cleanup();
try
{
if (executionPending)
{
executionPending = false;
// read network protocol message
// parse-compile expressions and collect information for execution plan
// generate response headers and fetch data from Redis
// this place fails most often, because of Pql compilation or storage driver connectivity failures
StartProduction(context, buffer, out sourceEnumerator);
if (context.Request.ReturnDataset)
{
// write response headers BEFORE the query processing is completed
// records affected and whatever other stats will be zero
Serializer.SerializeWithLengthPrefix(buffer.Stream, context.ResponseHeaders, PrefixStyle.Base128);
}
}
// go through retrieved data
havePendingDriverRow = ((DataEngine)context.Engine).WriteItems(
context, buffer, sourceEnumerator, havePendingDriverRow);
// some consistency checks
if (context.Request.ReturnDataset)
{
if (havePendingDriverRow && buffer.RowsOutput == 0)
{
throw new Exception("Internal error: should not have pending row when no data is produced");
}
}
else
{
if (havePendingDriverRow)
{
throw new Exception("Internal error: should not have pending row when no dataset is requested");
}
if (buffer.Stream.Length > 0)
{
throw new Exception("Internal error: should not have written anything to stream when no dataset is requested");
}
}
// time to quit?
// no dataset requested, don't have any more data, or enough rows accumulated for requested page of results?
if (buffer.RowsOutput == 0 || buffer.IsFailed || !context.Request.ReturnDataset)
{
if (!context.Request.ReturnDataset)
{
// if there is no dataset sent, write response headers AFTER processing the query
// records affected and whatever other stats are meaningful
context.ResponseHeaders.RecordsAffected = context.RecordsAffected;
Serializer.SerializeWithLengthPrefix(buffer.Stream, context.ResponseHeaders, PrefixStyle.Base128);
}
break;
}
}
catch (Exception e)
{
buffer.Error = e;
context.TrySetLastError(e);
m_tracer.Exception(e);
// this will go to client, and overwrite whatever we managed to put into buffer before failure
using (var writer = new PqlErrorDataWriter(1, e, false))
{
buffer.Stream.SetLength(0);
writer.WriteTo(buffer.Stream);
}
return;
}
finally
{
// return the buffer back to the ring in any case
context.BuffersRing.ReturnCompletedTask(buffer);
}
}
}
catch (OperationCanceledException e)
{
context.Cancel(e);
}
catch (Exception e)
{
if (Environment.HasShutdownStarted)
{
// nobody cares now
return;
}
var cts = context.CancellationTokenSource;
if (cts != null && !cts.IsCancellationRequested)
{
m_tracer.Exception(e);
context.Cancel(e);
}
}
finally
{
var ring = context.BuffersRing;
if (ring != null)
{
ring.CompleteAddingCompletedTasks();
}
if (sourceEnumerator != null)
{
// release driver-level resources & locks
sourceEnumerator.Dispose();
}
}
}