Why DefaultMappedFile::appendMessageInner() call ByteBuffer::position() after ByteBuffer::slice()

[yao-wenbin]

The code looks like this:

    public AppendMessageResult appendMessagesInner(final MessageExt messageExt, final AppendMessageCallback cb,
        PutMessageContext putMessageContext) {
        int currentPos = WROTE_POSITION_UPDATER.get(this);

        if (currentPos < this.fileSize) {
            ByteBuffer byteBuffer = appendMessageBuffer().slice();
            byteBuffer.position(currentPos);
    ....

In my opinion, the slice() methods will return the new Rerecence of ByteBuffer with position is 0, and limit is remainning size.
And then The call to position() will resets current to the original ByteBuffer's position(which is currentPos) and starts writing, so isn't the space between the new ByteBuffer's 0 and currentPos wasted