presto-main/src/main/java/io/prestosql/operator/JoinProbe.java/JoinProbe/JoinProbe
class JoinProbe:    private JoinProbe(int[] probeOutputChannels, Page page, List<Integer> probeJoinChannels, OptionalInt probeHashChannel)
    {
        this.probeOutputChannels = probeOutputChannels;
        this.positionCount = page.getPositionCount();
        this.probeBlocks = new Block[probeJoinChannels.size()];

        for (int i = 0; i < probeJoinChannels.size(); i++) {
            probeBlocks[i] = page.getBlock(probeJoinChannels.get(i));
        }
        this.page = page;
        this.probePage = new Page(page.getPositionCount(), probeBlocks);
        this.probeHashBlock = probeHashChannel.isPresent() ? Optional.of(page.getBlock(probeHashChannel.getAsInt())) : Optional.empty();
    }