Added a BufferedStream class that can be wrapped around an IOStream to

improve read performance when many small reads will be performed, e.g.
while reading directories and during housekeeping. (refs #3)

1 files changed, 207 insertions, 0 deletions

diff --git a/lib/common/BufferedStream.cpp b/lib/common/BufferedStream.cpp
new file mode 100644
index 00000000..288e1ed1
--- /dev/null
+++ b/lib/common/BufferedStream.cpp
@@ -0,0 +1,207 @@
+// --------------------------------------------------------------------------
+//
+// File
+//		Name:    BufferedStream.cpp
+//		Purpose: Buffering wrapper around IOStreams
+//		Created: 2007/01/16
+//
+// --------------------------------------------------------------------------
+
+#include "Box.h"
+#include "BufferedStream.h"
+#include "CommonException.h"
+
+#include <string.h>
+
+#include "MemLeakFindOn.h"
+
+// --------------------------------------------------------------------------
+//
+// Function
+//		Name:    BufferedStream::BufferedStream(const char *, int, int)
+//		Purpose: Constructor, set up buffer
+//		Created: 2007/01/16
+//
+// --------------------------------------------------------------------------
+BufferedStream::BufferedStream(IOStream& rSource)
+: mrSource(rSource), mBufferSize(0), mBufferPosition(0)
+{ }
+
+
+// --------------------------------------------------------------------------
+//
+// Function
+//		Name:    BufferedStream::Read(void *, int)
+//		Purpose: Reads bytes from the file
+//		Created: 2007/01/16
+//
+// --------------------------------------------------------------------------
+int BufferedStream::Read(void *pBuffer, int NBytes, int Timeout)
+{
+	if (mBufferSize == mBufferPosition)
+	{
+		// buffer is empty, fill it.
+
+		int numBytesRead = mrSource.Read(mBuffer, sizeof(mBuffer), 
+			Timeout);
+
+		if (numBytesRead < 0)
+		{
+			return numBytesRead;
+		}
+
+		mBufferSize = numBytesRead;
+	}
+
+	int sizeToReturn = mBufferSize - mBufferPosition;
+
+	if (sizeToReturn > NBytes)
+	{
+		sizeToReturn = NBytes;
+	}
+
+	memcpy(pBuffer, mBuffer + mBufferPosition, sizeToReturn);
+	mBufferPosition += sizeToReturn;
+
+	if (mBufferPosition == mBufferSize)
+	{
+		// clear out the buffer
+		mBufferSize = 0;
+		mBufferPosition = 0;
+	}
+
+	return sizeToReturn;
+}
+
+
+// --------------------------------------------------------------------------
+//
+// Function
+//		Name:    BufferedStream::BytesLeftToRead()
+//		Purpose: Returns number of bytes to read (may not be most efficient function ever)
+//		Created: 2007/01/16
+//
+// --------------------------------------------------------------------------
+IOStream::pos_type BufferedStream::BytesLeftToRead()
+{
+	return mrSource.BytesLeftToRead() + mBufferSize - mBufferPosition;
+}
+
+
+// --------------------------------------------------------------------------
+//
+// Function
+//		Name:    BufferedStream::Write(void *, int)
+//		Purpose: Writes bytes to the underlying stream (not supported)
+//		Created: 2003/07/31
+//
+// --------------------------------------------------------------------------
+void BufferedStream::Write(const void *pBuffer, int NBytes)
+{
+	THROW_EXCEPTION(CommonException, NotSupported);
+}
+
+
+// --------------------------------------------------------------------------
+//
+// Function
+//		Name:    BufferedStream::GetPosition()
+//		Purpose: Get position in stream
+//		Created: 2003/08/21
+//
+// --------------------------------------------------------------------------
+IOStream::pos_type BufferedStream::GetPosition() const
+{
+	return mrSource.GetPosition() - mBufferSize + mBufferPosition;
+}
+
+
+// --------------------------------------------------------------------------
+//
+// Function
+//		Name:    BufferedStream::Seek(pos_type, int)
+//		Purpose: Seeks within file, as lseek, invalidate buffer
+//		Created: 2003/07/31
+//
+// --------------------------------------------------------------------------
+void BufferedStream::Seek(IOStream::pos_type Offset, int SeekType)
+{
+	switch (SeekType)
+	{
+		case SeekType_Absolute:
+		{
+			// just go there
+			mrSource.Seek(Offset, SeekType);
+		}
+		break;
+
+		case SeekType_Relative:
+		{
+			// Actual underlying file position is 
+			// (mBufferSize - mBufferPosition) ahead of us.
+			// Need to subtract that amount from the seek
+			// to seek forward that much less, putting the 
+			// real pointer in the right place.
+			mrSource.Seek(Offset - mBufferSize + mBufferPosition, 
+				SeekType);
+		}
+		break;
+
+		case SeekType_End:
+		{
+			// Actual underlying file position is 
+			// (mBufferSize - mBufferPosition) ahead of us.
+			// Need to add that amount to the seek
+			// to seek backwards that much more, putting the 
+			// real pointer in the right place.
+			mrSource.Seek(Offset + mBufferSize - mBufferPosition, 
+				SeekType);
+		}
+	}
+
+	// always clear the buffer for now (may be slightly wasteful)
+	mBufferSize = 0;
+	mBufferPosition = 0;
+}
+
+
+// --------------------------------------------------------------------------
+//
+// Function
+//		Name:    BufferedStream::Close()
+//		Purpose: Closes the underlying stream (not needed)
+//		Created: 2003/07/31
+//
+// --------------------------------------------------------------------------
+void BufferedStream::Close()
+{
+	THROW_EXCEPTION(CommonException, NotSupported);
+}
+
+
+// --------------------------------------------------------------------------
+//
+// Function
+//		Name:    BufferedStream::StreamDataLeft()
+//		Purpose: Any data left to write?
+//		Created: 2003/08/02
+//
+// --------------------------------------------------------------------------
+bool BufferedStream::StreamDataLeft()
+{
+	return mrSource.StreamDataLeft();
+}
+
+// --------------------------------------------------------------------------
+//
+// Function
+//		Name:    BufferedStream::StreamClosed()
+//		Purpose: Is the stream closed?
+//		Created: 2003/08/02
+//
+// --------------------------------------------------------------------------
+bool BufferedStream::StreamClosed()
+{
+	return mrSource.StreamClosed();
+}
+