Fix cpplint. (#4157)

* Add comment after #endif.
* Add missing headers.

src/data/data.cc

@@ -15,7 +15,7 @@
 #if DMLC_ENABLE_STD_THREAD
 #include "./sparse_page_source.h"
 #include "./sparse_page_dmatrix.h"
-#endif
+#endif  // DMLC_ENABLE_STD_THREAD
 
 namespace dmlc {
 DMLC_REGISTRY_ENABLE(::xgboost::data::SparsePageFormatReg);
@@ -264,7 +264,7 @@ DMatrix* DMatrix::Create(dmlc::Parser<uint32_t>* parser,
 #else
     LOG(FATAL) << "External memory is not enabled in mingw";
     return nullptr;
-#endif
+#endif  // DMLC_ENABLE_STD_THREAD
   }
 }
 
@@ -285,7 +285,7 @@ DMatrix* DMatrix::Create(std::unique_ptr<DataSource>&& source,
 #else
     LOG(FATAL) << "External memory is not enabled in mingw";
     return nullptr;
-#endif
+#endif  // DMLC_ENABLE_STD_THREAD
   }
 }
 }  // namespace xgboost

src/data/simple_dmatrix.h

@@ -9,9 +9,13 @@
 
 #include <xgboost/base.h>
 #include <xgboost/data.h>
+
 #include <algorithm>
 #include <cstring>
+#include <memory>
+#include <utility>
 #include <vector>
+
 #include "simple_csr_source.h"
 
 namespace xgboost {

src/data/sparse_page_dmatrix.cc

@@ -100,4 +100,4 @@ bool SparsePageDMatrix::SingleColBlock() const {
 }
 }  // namespace data
 }  // namespace xgboost
-#endif
+#endif  // DMLC_ENABLE_STD_THREAD

src/data/sparse_page_dmatrix.h

@@ -9,9 +9,11 @@
 
 #include <xgboost/data.h>
 #include <algorithm>
+#include <memory>
 #include <string>
 #include <utility>
 #include <vector>
+
 #include "sparse_page_source.h"
 
 namespace xgboost {

src/data/sparse_page_source.cc

@@ -29,7 +29,7 @@ GetCacheShards(const std::string& cache_info) {
     cache_shards[0] = cache_info.substr(0, 2) + cache_shards[0];
     return cache_shards;
   }
-#endif
+#endif  // (defined _WIN32) || (defined __CYGWIN__)
   return xgboost::common::Split(cache_info, ':');
 }
 
@@ -291,4 +291,4 @@ void SparsePageSource::CreateColumnPage(DMatrix* src,
 }
 }  // namespace data
 }  // namespace xgboost
-#endif
+#endif  // DMLC_ENABLE_STD_THREAD

src/data/sparse_page_source.h

@@ -10,9 +10,12 @@
 #include <xgboost/base.h>
 #include <xgboost/data.h>
 #include <dmlc/threadediter.h>
-#include <vector>
+
 #include <algorithm>
+#include <memory>
 #include <string>
+#include <vector>
+
 #include "sparse_page_writer.h"
 
 namespace xgboost {

src/data/sparse_page_writer.h

@@ -19,7 +19,7 @@
 #if DMLC_ENABLE_STD_THREAD
 #include <dmlc/concurrency.h>
 #include <thread>
-#endif
+#endif  // DMLC_ENABLE_STD_THREAD
 
 namespace xgboost {
 namespace data {