Concurrent access to MemoryBuffer leads to BufferUnderflowException

When same MemoryBuffer is accessed by multiple thread concurrently then it can lead to BufferUnderflowException.

MemoryManagerService.retrieve method performs following steps

1. Get MemoryBuffer associated with the Pointer
2. Set its readerIndex to 0
3. Call readBytes. Which for NioMemoryBuffer invokes following code

@Override
public int readBytes( byte[] bytes, int offset, int length )

{ byteBuffer.get( bytes, offset, length ); readerIndex += length; return length; }

So if multiple thread invoke retrieve with same Pointer then readerIndex might be set to wrong value leading to BufferUnderflowException

Refer to [1] for details

[1] http://markmail.org/thread/yvevhzddta2fyal6