Avoid thrust vector initialization. (#10544)

* Avoid thrust vector initialization.

- Add a wrapper for rmm device uvector.
- Split up the `Resize` method for HDV.

tests/cpp/common/test_device_vector.cu

@@ -0,0 +1,21 @@
+/**
+ * Copyright 2024, XGBoost Contributors
+ */
+#include <gtest/gtest.h>
+
+#include "../../../src/common/device_vector.cuh"
+#include "xgboost/global_config.h"  // for GlobalConfigThreadLocalStore
+
+namespace dh {
+TEST(DeviceUVector, Basic) {
+  GlobalMemoryLogger().Clear();
+  std::int32_t verbosity{3};
+  std::swap(verbosity, xgboost::GlobalConfigThreadLocalStore::Get()->verbosity);
+  DeviceUVector<float> uvec;
+  uvec.Resize(12);
+  auto peak = GlobalMemoryLogger().PeakMemory();
+  auto n_bytes = sizeof(decltype(uvec)::value_type) * uvec.size();
+  ASSERT_EQ(peak, n_bytes);
+  std::swap(verbosity, xgboost::GlobalConfigThreadLocalStore::Get()->verbosity);
+}
+}  // namespace dh

tests/cpp/common/test_host_device_vector.cu

@@ -1,5 +1,5 @@
 /**
- * Copyright 2018-2023 XGBoost contributors
+ * Copyright 2018-2024, XGBoost contributors
  */
 #include <gtest/gtest.h>
 #include <thrust/equal.h>
@@ -181,4 +181,41 @@ TEST(HostDeviceVector, Empty) {
   ASSERT_FALSE(another.Empty());
   ASSERT_TRUE(vec.Empty());
 }
+
+TEST(HostDeviceVector, Resize) {
+  auto check = [&](HostDeviceVector<float> const& vec) {
+    auto const& h_vec = vec.ConstHostSpan();
+    for (std::size_t i = 0; i < 4; ++i) {
+      ASSERT_EQ(h_vec[i], i + 1);
+    }
+    for (std::size_t i = 4; i < vec.Size(); ++i) {
+      ASSERT_EQ(h_vec[i], 3.0);
+    }
+  };
+  {
+    HostDeviceVector<float> vec{1.0f, 2.0f, 3.0f, 4.0f};
+    vec.SetDevice(DeviceOrd::CUDA(0));
+    vec.ConstDeviceSpan();
+    ASSERT_TRUE(vec.DeviceCanRead());
+    ASSERT_FALSE(vec.DeviceCanWrite());
+    vec.DeviceSpan();
+    vec.Resize(7, 3.0f);
+    ASSERT_TRUE(vec.DeviceCanWrite());
+    check(vec);
+  }
+  {
+    HostDeviceVector<float> vec{{1.0f, 2.0f, 3.0f, 4.0f}, DeviceOrd::CUDA(0)};
+    ASSERT_TRUE(vec.DeviceCanWrite());
+    vec.Resize(7, 3.0f);
+    ASSERT_TRUE(vec.DeviceCanWrite());
+    check(vec);
+  }
+  {
+    HostDeviceVector<float> vec{1.0f, 2.0f, 3.0f, 4.0f};
+    ASSERT_TRUE(vec.HostCanWrite());
+    vec.Resize(7, 3.0f);
+    ASSERT_TRUE(vec.HostCanWrite());
+    check(vec);
+  }
+}
 }  // namespace xgboost::common