Replaced std::vector-based interfaces with HostDeviceVector-based interfaces. (#3116)

* Replaced std::vector-based interfaces with HostDeviceVector-based interfaces.

- replacement was performed in the learner, boosters, predictors,
  updaters, and objective functions
- only interfaces used in training were replaced;
  interfaces like PredictInstance() still use std::vector
- refactoring necessary for replacement of interfaces was also performed,
  such as using HostDeviceVector in prediction cache

* HostDeviceVector-based interfaces for custom objective function example plugin.

src/common/host_device_vector.cc

@@ -12,13 +12,27 @@ namespace xgboost {
 
 template <typename T>
 struct HostDeviceVectorImpl {
-  explicit HostDeviceVectorImpl(size_t size) : data_h_(size) {}
+  explicit HostDeviceVectorImpl(size_t size, T v) : data_h_(size, v) {}
+  explicit HostDeviceVectorImpl(std::initializer_list<T> init) : data_h_(init) {}
+  explicit HostDeviceVectorImpl(const std::vector<T>& init) : data_h_(init) {}
   std::vector<T> data_h_;
 };
 
 template <typename T>
-HostDeviceVector<T>::HostDeviceVector(size_t size, int device) : impl_(nullptr) {
-  impl_ = new HostDeviceVectorImpl<T>(size);
+HostDeviceVector<T>::HostDeviceVector(size_t size, T v, int device) : impl_(nullptr) {
+  impl_ = new HostDeviceVectorImpl<T>(size, v);
+}
+
+template <typename T>
+HostDeviceVector<T>::HostDeviceVector(std::initializer_list<T> init, int device)
+  : impl_(nullptr) {
+  impl_ = new HostDeviceVectorImpl<T>(init);
+}
+
+template <typename T>
+HostDeviceVector<T>::HostDeviceVector(const std::vector<T>& init, int device)
+  : impl_(nullptr) {
+  impl_ = new HostDeviceVectorImpl<T>(init);
 }
 
 template <typename T>
@@ -41,8 +55,8 @@ template <typename T>
 std::vector<T>& HostDeviceVector<T>::data_h() { return impl_->data_h_; }
 
 template <typename T>
-void HostDeviceVector<T>::resize(size_t new_size, int new_device) {
-  impl_->data_h_.resize(new_size);
+void HostDeviceVector<T>::resize(size_t new_size, T v, int new_device) {
+  impl_->data_h_.resize(new_size, v);
 }
 
 // explicit instantiations are required, as HostDeviceVector isn't header-only

src/common/host_device_vector.cu

@@ -1,6 +1,7 @@
 /*!
  * Copyright 2017 XGBoost contributors
  */
+
 #include "./host_device_vector.h"
 #include "./device_helpers.cuh"
 
@@ -8,13 +9,25 @@ namespace xgboost {
 
 template <typename T>
 struct HostDeviceVectorImpl {
-  HostDeviceVectorImpl(size_t size, int device)
+  HostDeviceVectorImpl(size_t size, T v, int device)
     : device_(device), on_d_(device >= 0) {
     if (on_d_) {
       dh::safe_cuda(cudaSetDevice(device_));
-      data_d_.resize(size);
+      data_d_.resize(size, v);
     } else {
-      data_h_.resize(size);
+      data_h_.resize(size, v);
+    }
+  }
+  // Init can be std::vector<T> or std::initializer_list<T>
+  template <class Init>
+  HostDeviceVectorImpl(const Init& init, int device)
+    : device_(device), on_d_(device >= 0) {
+    if (on_d_) {
+      dh::safe_cuda(cudaSetDevice(device_));
+      data_d_.resize(init.size());
+      thrust::copy(init.begin(), init.end(), data_d_.begin());
+    } else {
+      data_h_ = init;
     }
   }
   HostDeviceVectorImpl(const HostDeviceVectorImpl<T>&) = delete;
@@ -41,17 +54,18 @@ struct HostDeviceVectorImpl {
     lazy_sync_host();
     return data_h_;
   }
-  void resize(size_t new_size, int new_device) {
+  void resize(size_t new_size, T v, int new_device) {
     if (new_size == this->size() && new_device == device_)
       return;
-    device_ = new_device;
+    if (new_device != -1)
+      device_ = new_device;
     // if !on_d_, but the data size is 0 and the device is set,
     // resize the data on device instead
     if (!on_d_ && (data_h_.size() > 0 || device_ == -1)) {
-      data_h_.resize(new_size);
+      data_h_.resize(new_size, v);
     } else {
       dh::safe_cuda(cudaSetDevice(device_));
-      data_d_.resize(new_size);
+      data_d_.resize(new_size, v);
       on_d_ = true;
     }
   }
@@ -90,8 +104,20 @@ struct HostDeviceVectorImpl {
 };
 
 template <typename T>
-HostDeviceVector<T>::HostDeviceVector(size_t size, int device) : impl_(nullptr) {
-  impl_ = new HostDeviceVectorImpl<T>(size, device);
+HostDeviceVector<T>::HostDeviceVector(size_t size, T v, int device) : impl_(nullptr) {
+  impl_ = new HostDeviceVectorImpl<T>(size, v, device);
+}
+
+template <typename T>
+HostDeviceVector<T>::HostDeviceVector(std::initializer_list<T> init, int device)
+  : impl_(nullptr) {
+  impl_ = new HostDeviceVectorImpl<T>(init, device);
+}
+
+template <typename T>
+HostDeviceVector<T>::HostDeviceVector(const std::vector<T>& init, int device)
+  : impl_(nullptr) {
+  impl_ = new HostDeviceVectorImpl<T>(init, device);
 }
 
 template <typename T>
@@ -124,8 +150,8 @@ template <typename T>
 std::vector<T>& HostDeviceVector<T>::data_h() { return impl_->data_h(); }
 
 template <typename T>
-void HostDeviceVector<T>::resize(size_t new_size, int new_device) {
-  impl_->resize(new_size, new_device);
+void HostDeviceVector<T>::resize(size_t new_size, T v, int new_device) {
+  impl_->resize(new_size, v, new_device);
 }
 
 // explicit instantiations are required, as HostDeviceVector isn't header-only

src/common/host_device_vector.h

@@ -5,6 +5,7 @@
 #define XGBOOST_COMMON_HOST_DEVICE_VECTOR_H_
 
 #include <cstdlib>
+#include <initializer_list>
 #include <vector>
 
 // only include thrust-related files if host_device_vector.h
@@ -61,7 +62,9 @@ template <typename T> struct HostDeviceVectorImpl;
 template <typename T>
 class HostDeviceVector {
  public:
-  explicit HostDeviceVector(size_t size = 0, int device = -1);
+  explicit HostDeviceVector(size_t size = 0, T v = T(), int device = -1);
+  HostDeviceVector(std::initializer_list<T> init, int device = -1);
+  explicit HostDeviceVector(const std::vector<T>& init, int device = -1);
   ~HostDeviceVector();
   HostDeviceVector(const HostDeviceVector<T>&) = delete;
   HostDeviceVector(HostDeviceVector<T>&&) = delete;
@@ -70,6 +73,7 @@ class HostDeviceVector {
   size_t size() const;
   int device() const;
   T* ptr_d(int device);
+  T* ptr_h() { return data_h().data(); }
 
   // only define functions returning device_ptr
   // if HostDeviceVector.h is included from a .cu file
@@ -79,17 +83,9 @@ class HostDeviceVector {
 #endif
 
   std::vector<T>& data_h();
-  void resize(size_t new_size, int new_device);
 
-  // helper functions in case a function needs to be templated
-  // to work for both HostDeviceVector and std::vector
-  static std::vector<T>& data_h(HostDeviceVector<T>* v) {
-    return v->data_h();
-  }
-
-  static std::vector<T>& data_h(std::vector<T>* v) {
-    return *v;
-  }
+  // passing in new_device == -1 keeps the device as is
+  void resize(size_t new_size, T v = T(), int new_device = -1);
 
  private:
   HostDeviceVectorImpl<T>* impl_;