Function GetSubsetWithScheduling

catboost/libs/data/objects.cpp:680–738

template <class TColumn, class TGetAggregatedColumn>
static void GetSubsetWithScheduling(
    TConstArrayRef<THolder<TColumn>> src,
    const TFeaturesArraySubsetIndexing* subsetIndexing,

    // needed only for sparse features
    const TMaybe<TFeaturesArraySubsetInvertedIndexing>& subsetInvertedIndexing,

    /* flatFeatureIdx -> THolder<TColumn>
     * returns packed or bundled or grouped column data, returns nullptr if not packed or bundled or grouped
     */
    TGetAggregatedColumn&& getAggregatedData,
    //std::function<THolder<TColumn>(ui32)> getAggregatedData,
    TResourceConstrainedExecutor* resourceConstrainedExecutor,
    TVector<THolder<TColumn>>* dst
) {

    dst->clear(); // cleanup old data
    dst->resize(src.size());

    TCloningParams cloningParams;
    cloningParams.MakeConsecutive = false;
    cloningParams.SubsetIndexing = subsetIndexing;
    if (subsetInvertedIndexing.Defined()) {
        cloningParams.InvertedSubsetIndexing = subsetInvertedIndexing.Get();
    }

    auto localExecutor = resourceConstrainedExecutor->GetExecutorPtr();
    for (auto i : xrange(src.size())) {
        auto* srcDataPtr = src[i].Get();
        if (!srcDataPtr) {
            continue;
        }

        (*dst)[i] = getAggregatedData(srcDataPtr->GetId());
        if ((*dst)[i]) {
            continue;
        }
        auto dstHolderPtr = &(*dst)[i];
        // TODO(kirillovs): add shortcut here for zero-cost cloneable columns
        resourceConstrainedExecutor->Add(
            {
                srcDataPtr->EstimateMemoryForCloning(cloningParams),
                [srcDataPtr, dstHolderPtr, localExecutor, cloningParams] () {
                    auto clonedColumn = srcDataPtr->CloneWithNewSubsetIndexing(
                        cloningParams,
                        localExecutor
                    );
                    *dstHolderPtr = DynamicHolderCast<TColumn>(
                        srcDataPtr->CloneWithNewSubsetIndexing(
                            cloningParams,
                            localExecutor
                        ),
                        "Column type changed after cloning"
                    );
                }
            }
        );
    }