// Copies a section of data from master stream to the log stream
void BackupData(long location, int size)
{
logStream.Seek(0, SeekOrigin.End);
// Write segment header
SegmentMetadata sh = new SegmentMetadata
{
TransactionId = logStreamHeader.TransactionId,
Position = location,
Size = size
};
long metadataPos = logStream.Position;
sh.Save(logStream);
// Copy data
masterStream.Position = location;
int bytesCopied = CopyData(masterStream, size, logStream);
// If bytes copied differ from size in header, update the header
if (bytesCopied != size)
{
logStream.Position = metadataPos;
sh.Size = bytesCopied;
sh.Save(logStream);
}
logStream.Flush();
// Update log stream header
logStreamHeader.SegmentCount++;
logStreamHeader.Save(logStream);
logStream.Flush();
}
/// <summary>
/// Start transaction
/// </summary>
/// <param name="initialSegments">Areas in master stream which don't require backing up. Can be null.</param>
public Guid BeginTransaction(IEnumerable <Segment> initialSegments = null)
{
CheckState();
if (logStream == null)
{
throw new InvalidOperationException("Log stream not specified");
}
if (logStreamHeader != null)
{
throw new InvalidOperationException("Unable to start new transaction while existing transaction is in progress");
}
// Add custom segments that will not be backed up
segments.Clear();
if (initialSegments != null)
{
// <源码修改>
//IOrderedEnumerable<Segment> orderedList = initialSegments.OrderBy(x => x.Location);
var orderedList = new List <Segment>(initialSegments);
orderedList.Sort(SegmentComparer.Instance);
// </源码修改>
foreach (var segment in orderedList)
{
segments.AddLast(segment);
}
}
// Add unallocated space after the end of stream
segments.AddLast(new Segment(masterStream.Length, long.MaxValue - masterStream.Length));
CheckSegments();
// Truncate transaction log
logStream.SetLength(0);
logStream.Flush();
// Initialize transaction log
logStreamHeader = new TransactionLogStreamMetadata
{
TransactionId = Guid.NewGuid(),
StreamLength = masterStream.Length,
SegmentCount = 0,
TransactionCompleted = false
};
logStreamHeader.Save(logStream);
logStream.Flush();
return(logStreamHeader.TransactionId);
}