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| /*! | ||
| * Copyright 2015-2019 by Contributors | ||
| * \file common.h | ||
| * \brief Threading utilities | ||
| */ | ||
| #ifndef XGBOOST_COMMON_THREADING_UTILS_H_ | ||
| #define XGBOOST_COMMON_THREADING_UTILS_H_ | ||
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| #include <vector> | ||
| #include <algorithm> | ||
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| namespace xgboost { | ||
| namespace common { | ||
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| // Represent simple range of indexes [begin, end) | ||
| // Inspired by tbb::blocked_range | ||
| class Range1d { | ||
| public: | ||
| Range1d(size_t begin, size_t end): begin_(begin), end_(end) { | ||
| CHECK_LT(begin, end); | ||
| } | ||
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| size_t begin() { | ||
| return begin_; | ||
| } | ||
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| size_t end() { | ||
| return end_; | ||
| } | ||
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| private: | ||
| size_t begin_; | ||
| size_t end_; | ||
| }; | ||
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| // Split 2d space to balanced blocks | ||
| // Implementation of the class is inspired by tbb::blocked_range2d | ||
| // However, TBB provides only (n x m) 2d range (matrix) separated by blocks. Example: | ||
| // [ 1,2,3 ] | ||
| // [ 4,5,6 ] | ||
| // [ 7,8,9 ] | ||
| // But the class is able to work with different sizes in each 'row'. Example: | ||
| // [ 1,2 ] | ||
| // [ 3,4,5,6 ] | ||
| // [ 7,8,9] | ||
| // If grain_size is 2: It produces following blocks: | ||
| // [1,2], [3,4], [5,6], [7,8], [9] | ||
| // The class helps to process data in several tree nodes (non-balanced usually) in parallel | ||
| // Using nested parallelism (by nodes and by data in each node) | ||
| // it helps to improve CPU resources utilization | ||
| class BlockedSpace2d { | ||
| public: | ||
| // Example of space: | ||
| // [ 1,2 ] | ||
| // [ 3,4,5,6 ] | ||
| // [ 7,8,9] | ||
| // BlockedSpace2d will create following blocks (tasks) if grain_size=2: | ||
| // 1-block: first_dimension = 0, range of indexes in a 'row' = [0,2) (includes [1,2] values) | ||
| // 2-block: first_dimension = 1, range of indexes in a 'row' = [0,2) (includes [3,4] values) | ||
| // 3-block: first_dimension = 1, range of indexes in a 'row' = [2,4) (includes [5,6] values) | ||
| // 4-block: first_dimension = 2, range of indexes in a 'row' = [0,2) (includes [7,8] values) | ||
| // 5-block: first_dimension = 2, range of indexes in a 'row' = [2,3) (includes [9] values) | ||
| // Arguments: | ||
| // dim1 - size of the first dimension in the space | ||
| // getter_size_dim2 - functor to get the second dimensions for each 'row' by row-index | ||
| // grain_size - max size of produced blocks | ||
| template<typename Func> | ||
| BlockedSpace2d(size_t dim1, Func getter_size_dim2, size_t grain_size) { | ||
| for (size_t i = 0; i < dim1; ++i) { | ||
| const size_t size = getter_size_dim2(i); | ||
| const size_t n_blocks = size/grain_size + !!(size % grain_size); | ||
| for (size_t iblock = 0; iblock < n_blocks; ++iblock) { | ||
| const size_t begin = iblock * grain_size; | ||
| const size_t end = std::min(begin + grain_size, size); | ||
| AddBlock(i, begin, end); | ||
| } | ||
| } | ||
| } | ||
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| // Amount of blocks(tasks) in a space | ||
| size_t Size() const { | ||
| return ranges_.size(); | ||
| } | ||
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| // get index of the first dimension of i-th block(task) | ||
| size_t GetFirstDimension(size_t i) const { | ||
| CHECK_LT(i, first_dimension_.size()); | ||
| return first_dimension_[i]; | ||
| } | ||
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| // get a range of indexes for the second dimension of i-th block(task) | ||
| Range1d GetRange(size_t i) const { | ||
| CHECK_LT(i, ranges_.size()); | ||
| return ranges_[i]; | ||
| } | ||
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| private: | ||
| void AddBlock(size_t first_dimension, size_t begin, size_t end) { | ||
| first_dimension_.push_back(first_dimension); | ||
| ranges_.emplace_back(begin, end); | ||
| } | ||
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| std::vector<Range1d> ranges_; | ||
| std::vector<size_t> first_dimension_; | ||
| }; | ||
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| // Wrapper to implement nested parallelism with simple omp parallel for | ||
| template<typename Func> | ||
| void ParallelFor2d(const BlockedSpace2d& space, Func func) { | ||
| const int num_blocks_in_space = static_cast<int>(space.Size()); | ||
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| #pragma omp parallel for | ||
| for (auto i = 0; i < num_blocks_in_space; i++) { | ||
| func(space.GetFirstDimension(i), space.GetRange(i)); | ||
| } | ||
| } | ||
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| } // namespace common | ||
| } // namespace xgboost | ||
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| #endif // XGBOOST_COMMON_THREADING_UTILS_H_ |
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