/// <summary>
/// After top reader returned last data item in a file
/// </summary>
private void OnTopReaderFileFinished()
{
if (!this.TopReader.EndReached)
{
if (_onlineQueue.First.Next == null ||
TimestampComparer.Compare(
_onlineQueue.First.Next.Value.CurrentItem.DateTime
, TopReader.NextFileFirstTimestampToRead.Value) >= 0)
{
// there's no next reader or it contains older or equal item as the first item in
// the top reader's next file
// second in the queue must remain second; load next data file in the top reader
TopReader.LoadNextFile();
// update may be required because if data item timestamps are equal the DataItemComparer may change the order
UpdateTopReaderPosition();
}
else
{
// second reader is present and it has to move to the top
MoveTopReaderToOfflineQueue();
}
}
else
{
MoveTopReaderToExhaustedList();
}
}
/// <summary>
/// Read next available data item
/// </summary>
/// <returns>
/// <see cref="IDataItemRead"/>
/// <see langword="null"/> if the end is reached (<see cref="HasData"/> will return <see langword="false"/>)
/// </returns>
/// <remarks>
/// The order of data items coming from multiple folders is guaranteed only if item timestamps are different.
/// If more than one folder being read contains data item with a particular timestamp
/// the order in which those data items are read may change next time you read same data from those same folders.
/// Use <see cref="IRepositoryFolder.LastTimestamp"/> to position precisely every single data source.
/// <seealso cref="IRepositoryReader.GetLastItemTimestamp"/>
/// <seealso cref="IDataItemRead.RepositoryFolder"/>
/// </remarks>
/// <exception cref="ObjectDisposedException">
/// The reader has been disposed.
/// </exception>
public IDataItemRead Read()
{
CheckNotDisposed();
IDataItemRead retval = null;
if (this.HasData)
{
retval = new DataItemRead
{
DataItem = TopReader.CurrentItem,
RepositoryFolder = TopReader.TargetFolder
};
TopReader.UpdatePosition();
_position.Update(retval.DataItem);
MoveTopReaderToNextItem();
}
return(retval);
}
