/// <summary>
/// After advancing current position to next item in online queue
/// check the offline queue and open top reader if it contains
/// items with timestamp lower or equal to the <see cref="TopReader"/>
/// or just open the first file in the queue if the online queue
/// is empty
/// </summary>
/// <remarks>
/// Call it after returning item from top online reader or after
/// initial seek populating the offline queue.
/// </remarks>
private void SyncOfflineQueueForReading()
{
// need to repeat because FirstTimestampInOfflineQueue is not necessarily what we will get after loading the file
// because it's potential; the actual item timestamp may be further from the seek time but we only find it out
// after loading the file
while (_offlineQueue.Count > 0 &&
(
TopReader == null || // whatever is in the offline queue is is better than nothing
TimestampComparer.Compare(CurrentItemTimestamp, this.FirstTimestampInOfflineQueue) >= 0 // offline is potentially prior to top reader
))
{
DateTime firstOfflineTimestamp = this.FirstTimestampInOfflineQueue;
// if DataItemComparer is set we need to load all readers with the top timestamp
// to enforce order
do
{
RepositoryFolderReader readerToGoOnline = _offlineQueue.First.Value;
if (readerToGoOnline.LoadNextFile())
{
_onlineQueue.AddFirst(readerToGoOnline);
// may need to update position when timestamps are equal and the DataItemComparer is set
UpdateTopReaderPosition();
}
else
{
AddToExhaustedImpl(readerToGoOnline);
}
_offlineQueue.RemoveFirst();
}while (this.FirstTimestampInOfflineQueue == firstOfflineTimestamp && this.DataItemComparer != null);
}
}
/// <summary>
/// <see cref="IRepositoryReader.RemoveFolder"/>
/// </summary>
/// <exception cref="ObjectDisposedException">
/// The reader has been disposed.
/// </exception>
public void RemoveFolder(IRepositoryFolder folder)
{
CheckNotDisposed();
Util.Check.DoRequireArgumentNotNull(folder, "folder");
Exceptions.DifferentRepositoriesExceptionHelper.Check(folder.Repository, Repository);
RepositoryFolderReader reader = GetExistingReader(folder.FolderKey);
Util.Check.DoRequire(reader != null, "The folder is not being read by the reader");
_position.Remove(reader.Position);
reader.Unload();
bool topReaderRemoved = this.HasData && TopReader == reader;
bool success = !(!_exhaustedReaders.Remove(reader) && !_offlineQueue.Remove(reader) && !_onlineQueue.Remove(reader));
Util.Check.Ensure(success, "Internal error: reader not found.");
success = _readers.Remove(folder.FolderKey);
Util.Check.Ensure(success);
if (topReaderRemoved)
{
SyncOfflineQueueForReading();
}
Invariant();
}
/// <summary>
/// Add folder to read and optionally prepare it for reading
/// </summary>
/// <param name="folder">
/// Folder to add
/// </param>
/// <param name="position">
/// <see langword="null"/> means do not prepare it for reading
/// </param>
/// <returns>
/// <see langword="false"/> - the folder is already being read
/// <see langword="true"/> otherwise
/// </returns>
/// <remarks>
/// If reader has data (<see cref="HasData"/>) <paramref name="position"/> must have value
/// </remarks>
private bool AddFolderImpl(IRepositoryFolder folder, IFolderReadingPosition position)
{
Check.RequireArgumentNotNull(folder, "folder");
IFolder folderTyped = RepositoryFolder.CastFolder(folder);
Check.Require(object.ReferenceEquals(folder.Repository, Repository));
Check.Require(!HasData || position != null, "If we have data we cannot leave a reader unpositioned");
if (IsAccessing(folder, false))
{
return(false);
}
Check.Require(!_position.FolderPositions.ContainsKey(folder.FolderKey)
, "Folder position found in repository reader position for a folder not being read");
RepositoryFolderReader reader = new RepositoryFolderReader(folderTyped, this);
reader.Direction = this.Direction;
_readers.Add(folder.FolderKey, reader);
if (position != null)
{
SeekFolderReader(reader, position);
}
return(true);
}
/// <summary>
/// Add a positioned offline reader to an appropriate queue
/// </summary>
/// <param name="reader">
/// The reader must be added to all readers collection as necessary; not added here
/// </param>
/// <remarks>
/// The reader will go into either offline queue or exhausted readers collection
/// </remarks>
private void AddPositionedOfflineReaderToAQueue(RepositoryFolderReader reader)
{
if (reader.NextFileFound)
{
AddReaderToOfflineQueue(reader);
}
else
{
AddToExhaustedImpl(reader);
}
}
/// <summary>
/// Initiate reading from the <paramref name="reader"/>.
/// It must not be in any of the 2 queues (online, offline) or exhausted list.
/// If the file contains data since <paramref name="seekTime"/> the reader will
/// be placed into offline queue. Otherwise it will go into exhausted readers list.
/// </summary>
/// <param name="reader">
/// Reader to initiate. It must not be in any of the 2 queues (online, offline) or exhausted list.
/// </param>
/// <param name="position">
/// Position to start reading from.
/// </param>
/// <remarks>
/// The method ensures that currently loaded reader's data is unloaded first.
/// Seeking is done lazily - all go to offline queue and loaded immediately
/// before reading.
/// </remarks>
private void SeekFolderReader(RepositoryFolderReader reader, IFolderReadingPosition position)
{
Check.RequireArgumentNotNull(position, "position");
Check.RequireArgumentNotNull(reader, "reader");
Check.Require(!_offlineQueue.Contains(reader) && !_exhaustedReaders.Contains(reader) && !_onlineQueue.Contains(reader));
reader.Unload();
reader.SeekDataFile(position);
AddPositionedOfflineReaderToAQueue(reader);
// as reader.Position is singleton, changes to the reader's position do not require modifying _position
_position.SetFolderPosition(reader.Position);
}
/// <summary>
/// Add the specified reader to the offline queue
/// </summary>
/// <param name="reader">
/// The reader to add. Its <see cref="RepositoryFolderReader.NextFileFound"/>
/// must equal <see langword="true"/>.
/// </param>
private void AddReaderToOfflineQueue(RepositoryFolderReader reader)
{
Util.Check.Require(reader.NextFileFound, "Internal error: reader unsuitable for offline queue");
// free memory
reader.Unload();
LinkedListNode <RepositoryFolderReader> predecessor = null;
if (_offlineQueue.Count > 0)
{
predecessor = FindPredecessorInQueue(_offlineQueue.First, reader, _offlineReaderComparer);
}
if (null == predecessor)
{
_offlineQueue.AddFirst(reader);
}
else
{
_offlineQueue.AddAfter(predecessor, reader);
}
}
/// <summary>
/// Find predecessor for the <paramref name="reader"/> in the queue
/// of readers sorted by <paramref name="readerComparer"/> ascending starting
/// from <paramref name="queueStart"/>
/// </summary>
/// <param name="queueStart">
/// The first element in the queue to start lookup from; all readers
/// in the queue must have current item
/// </param>
/// <param name="reader">
/// The reader to find place for in the queue
/// </param>
/// <returns>
/// <see langword="null"/> if the <paramref name="queueStart"/> is
/// positioned to a greater item than <paramref name="reader"/>
/// i.e. <paramref name="reader"/> must be before <paramref name="queueStart"/>
/// otherwise the first element in the queue which is less than the
/// <paramref name="reader"/>
/// </returns>
private LinkedListNode <RepositoryFolderReader> FindPredecessorInQueue(
LinkedListNode <RepositoryFolderReader> queueStart
, RepositoryFolderReader reader
, IComparer <RepositoryFolderReader> readerComparer)
{
LinkedListNode <RepositoryFolderReader> retval;
if (readerComparer.Compare(queueStart.Value, reader) >= 0)
{
// the reader must be before the first item in the queue
return(null);
}
for (
retval = queueStart
; retval.Next != null && readerComparer.Compare(retval.Next.Value, reader) < 0
; retval = retval.Next)
{
Util.Check.Ensure(readerComparer.Compare(retval.Value, reader) < 0
, "Internal logic error; queue may not be sorted properly");
}
return(retval);
}
private void AddToExhaustedImpl(RepositoryFolderReader reader)
{
reader.Unload();
_exhaustedReaders.AddLast(reader);
}