Prevent copying SimpleDMatrix. (#5453)

* Set default dtor for SimpleDMatrix to initialize default copy ctor, which is
deleted due to unique ptr.

* Remove commented code.
* Remove warning for calling host function (std::max).
* Remove warning for initialization order.
* Remove warning for unused variables.

src/common/common.h

@@ -64,6 +64,11 @@ inline std::vector<std::string> Split(const std::string& s, char delim) {
   return ret;
 }
 
+template <typename T>
+XGBOOST_DEVICE T Max(T a, T b) {
+  return a < b ? b : a;
+}
+
 // simple routine to convert any data to string
 template<typename T>
 inline std::string ToString(const T& data) {

src/common/compressed_iterator.h

@@ -8,6 +8,8 @@
 #include <cstddef>
 #include <algorithm>
 
+#include "common.h"
+
 #ifdef __CUDACC__
 #include "device_helpers.cuh"
 #endif  // __CUDACC__
@@ -29,12 +31,12 @@ inline void ClearBit(CompressedByteT *byte, int bit_idx) {
   *byte &= ~(1 << bit_idx);
 }
 static const int kPadding = 4;  // Assign padding so we can read slightly off
-                               // the beginning of the array
+                                // the beginning of the array
 
 // The number of bits required to represent a given unsigned range
 inline XGBOOST_DEVICE size_t SymbolBits(size_t num_symbols) {
   auto bits = std::ceil(log2(static_cast<double>(num_symbols)));
-  return std::max(static_cast<size_t>(bits), size_t(1));
+  return common::Max(static_cast<size_t>(bits), size_t(1));
 }
 }  // namespace detail
 

src/common/hist_util.h

@@ -297,9 +297,9 @@ struct Index {
   std::vector<uint8_t> data_;
   std::vector<uint32_t> offset_;  // size of this field is equal to number of features
   void* data_ptr_;
-  uint32_t* offset_ptr_;
-  size_t p_;
   BinTypeSize binTypeSize_;
+  size_t p_;
+  uint32_t* offset_ptr_;
   Func func_;
 };
 

src/common/quantile.h

@@ -710,7 +710,7 @@ class QuantileSketchTemplate {
     // check invariant
     size_t n = (1ULL << nlevel);
     CHECK(n * limit_size >= maxn) << "invalid init parameter";
-    CHECK(nlevel <= std::max(1, static_cast<int>(limit_size * eps)))
+    CHECK(nlevel <= std::max(static_cast<size_t>(1), static_cast<size_t>(limit_size * eps)))
         << "invalid init parameter";
   }
 

src/data/data.cc

@@ -427,25 +427,6 @@ DMatrix* DMatrix::Load(const std::string& uri,
   return dmat;
 }
 
-
-/*
-DMatrix* DMatrix::Create(std::unique_ptr<DataSource<SparsePage>>&& source,
-                         const std::string& cache_prefix) {
-  if (cache_prefix.length() == 0) {
-    // Data split mode is fixed to be row right now.
-    rabit::Allreduce<rabit::op::Max>(&source->info.num_col_, 1);
-    return new data::SimpleDMatrix(std::move(source));
-  } else {
-#if DMLC_ENABLE_STD_THREAD
-    return new data::SparsePageDMatrix(std::move(source), cache_prefix);
-#else
-    LOG(FATAL) << "External memory is not enabled in mingw";
-    return nullptr;
-#endif  // DMLC_ENABLE_STD_THREAD
-  }
-}
-*/
-
 template <typename AdapterT>
 DMatrix* DMatrix::Create(AdapterT* adapter, float missing, int nthread,
                          const std::string& cache_prefix,  size_t page_size ) {

src/data/simple_dmatrix.h

@@ -23,6 +23,7 @@ class SimpleDMatrix : public DMatrix {
   explicit SimpleDMatrix(AdapterT* adapter, float missing, int nthread);
 
   explicit SimpleDMatrix(dmlc::Stream* in_stream);
+  ~SimpleDMatrix() override = default;
 
   void SaveToLocalFile(const std::string& fname);
 

src/data/sparse_page_dmatrix.h

@@ -30,7 +30,6 @@ class SparsePageDMatrix : public DMatrix {
     row_source_.reset(new data::SparsePageSource(adapter, missing, nthread,
                                                  cache_prefix, page_size));
   }
-  // Set number of threads but keep old value so we can reset it after
   ~SparsePageDMatrix() override = default;
 
   MetaInfo& Info() override;

tests/cpp/common/test_hist_util.cc

@@ -403,7 +403,6 @@ TEST(hist_util, IndexBinData) {
   size_t constexpr kRows = 100;
   size_t constexpr kCols = 10;
 
-  size_t bin_id = 0;
   for (auto max_bin : kBinSizes) {
     auto p_fmat = RandomDataGenerator(kRows, kCols, 0).GenerateDMatix();
     common::GHistIndexMatrix hmat;
@@ -434,7 +433,6 @@ TEST(hist_util, SparseIndexBinData) {
   size_t constexpr kRows = 100;
   size_t constexpr kCols = 10;
 
-  size_t bin_id = 0;
   for (auto max_bin : bin_sizes) {
     auto p_fmat = RandomDataGenerator(kRows, kCols, 0.2).GenerateDMatix();
     common::GHistIndexMatrix hmat;

tests/cpp/data/test_simple_dmatrix.cc

@@ -72,32 +72,32 @@ TEST(SimpleDMatrix, Empty) {
 
   data::CSRAdapter csr_adapter(row_ptr.data(), feature_idx.data(), data.data(),
                                0, 0, 0);
-  data::SimpleDMatrix dmat(&csr_adapter,
-                           std::numeric_limits<float>::quiet_NaN(), 1);
-  CHECK_EQ(dmat.Info().num_nonzero_, 0);
-  CHECK_EQ(dmat.Info().num_row_, 0);
-  CHECK_EQ(dmat.Info().num_col_, 0);
-  for (auto &batch : dmat.GetBatches<SparsePage>()) {
+  std::unique_ptr<data::SimpleDMatrix> dmat(new data::SimpleDMatrix(
+      &csr_adapter, std::numeric_limits<float>::quiet_NaN(), 1));
+  CHECK_EQ(dmat->Info().num_nonzero_, 0);
+  CHECK_EQ(dmat->Info().num_row_, 0);
+  CHECK_EQ(dmat->Info().num_col_, 0);
+  for (auto &batch : dmat->GetBatches<SparsePage>()) {
     CHECK_EQ(batch.Size(), 0);
   }
 
   data::DenseAdapter dense_adapter(nullptr, 0, 0);
-  dmat = data::SimpleDMatrix(&dense_adapter,
-                             std::numeric_limits<float>::quiet_NaN(), 1);
-  CHECK_EQ(dmat.Info().num_nonzero_, 0);
-  CHECK_EQ(dmat.Info().num_row_, 0);
-  CHECK_EQ(dmat.Info().num_col_, 0);
-  for (auto &batch : dmat.GetBatches<SparsePage>()) {
+  dmat.reset( new data::SimpleDMatrix(&dense_adapter,
+                                      std::numeric_limits<float>::quiet_NaN(), 1) );
+  CHECK_EQ(dmat->Info().num_nonzero_, 0);
+  CHECK_EQ(dmat->Info().num_row_, 0);
+  CHECK_EQ(dmat->Info().num_col_, 0);
+  for (auto &batch : dmat->GetBatches<SparsePage>()) {
     CHECK_EQ(batch.Size(), 0);
   }
 
   data::CSCAdapter csc_adapter(nullptr, nullptr, nullptr, 0, 0);
-  dmat = data::SimpleDMatrix(&csc_adapter,
-                             std::numeric_limits<float>::quiet_NaN(), 1);
-  CHECK_EQ(dmat.Info().num_nonzero_, 0);
-  CHECK_EQ(dmat.Info().num_row_, 0);
-  CHECK_EQ(dmat.Info().num_col_, 0);
-  for (auto &batch : dmat.GetBatches<SparsePage>()) {
+  dmat.reset(new data::SimpleDMatrix(
+      &csc_adapter, std::numeric_limits<float>::quiet_NaN(), 1));
+  CHECK_EQ(dmat->Info().num_nonzero_, 0);
+  CHECK_EQ(dmat->Info().num_row_, 0);
+  CHECK_EQ(dmat->Info().num_col_, 0);
+  for (auto &batch : dmat->GetBatches<SparsePage>()) {
     CHECK_EQ(batch.Size(), 0);
   }
 }
@@ -109,11 +109,11 @@ TEST(SimpleDMatrix, MissingData) {
 
   data::CSRAdapter adapter(row_ptr.data(), feature_idx.data(), data.data(), 2,
                            3, 2);
-  data::SimpleDMatrix dmat(&adapter, std::numeric_limits<float>::quiet_NaN(),
-                           1);
-  CHECK_EQ(dmat.Info().num_nonzero_, 2);
-  dmat = data::SimpleDMatrix(&adapter, 1.0, 1);
-  CHECK_EQ(dmat.Info().num_nonzero_, 1);
+  std::unique_ptr<data::SimpleDMatrix> dmat{new data::SimpleDMatrix{
+      &adapter, std::numeric_limits<float>::quiet_NaN(), 1}};
+  CHECK_EQ(dmat->Info().num_nonzero_, 2);
+  dmat.reset(new data::SimpleDMatrix(&adapter, 1.0, 1));
+  CHECK_EQ(dmat->Info().num_nonzero_, 1);
 }
 
 TEST(SimpleDMatrix, EmptyRow) {