presto-main/src/main/java/io/prestosql/operator/project/InputChannels.java/InputChannels/getInputChannels
class InputChannels:    public Page getInputChannels(Page page)
    {
        Block[] blocks = new Block[inputChannels.length];
        for (int i = 0; i < inputChannels.length; i++) {
            blocks[i] = page.getBlock(inputChannels[i]);
        }
        return new Page(page.getPositionCount(), blocks);
    }