1 //===- llvm/Support/Parallel.h - Parallel algorithms ----------------------===// 2 // 3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions. 4 // See https://llvm.org/LICENSE.txt for license information. 5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception 6 // 7 //===----------------------------------------------------------------------===// 8 9 #ifndef LLVM_SUPPORT_PARALLEL_H 10 #define LLVM_SUPPORT_PARALLEL_H 11 12 #include "llvm/ADT/STLExtras.h" 13 #include "llvm/Config/llvm-config.h" 14 #include "llvm/Support/MathExtras.h" 15 16 #include <algorithm> 17 #include <condition_variable> 18 #include <functional> 19 #include <mutex> 20 21 namespace llvm { 22 23 namespace parallel { 24 struct sequential_execution_policy {}; 25 struct parallel_execution_policy {}; 26 27 template <typename T> 28 struct is_execution_policy 29 : public std::integral_constant< 30 bool, llvm::is_one_of<T, sequential_execution_policy, 31 parallel_execution_policy>::value> {}; 32 33 constexpr sequential_execution_policy seq{}; 34 constexpr parallel_execution_policy par{}; 35 36 namespace detail { 37 38 #if LLVM_ENABLE_THREADS 39 40 class Latch { 41 uint32_t Count; 42 mutable std::mutex Mutex; 43 mutable std::condition_variable Cond; 44 45 public: 46 explicit Latch(uint32_t Count = 0) : Count(Count) {} 47 ~Latch() { sync(); } 48 49 void inc() { 50 std::lock_guard<std::mutex> lock(Mutex); 51 ++Count; 52 } 53 54 void dec() { 55 std::lock_guard<std::mutex> lock(Mutex); 56 if (--Count == 0) 57 Cond.notify_all(); 58 } 59 60 void sync() const { 61 std::unique_lock<std::mutex> lock(Mutex); 62 Cond.wait(lock, [&] { return Count == 0; }); 63 } 64 }; 65 66 class TaskGroup { 67 Latch L; 68 bool Parallel; 69 70 public: 71 TaskGroup(); 72 ~TaskGroup(); 73 74 void spawn(std::function<void()> f); 75 76 void sync() const { L.sync(); } 77 }; 78 79 const ptrdiff_t MinParallelSize = 1024; 80 81 /// Inclusive median. 82 template <class RandomAccessIterator, class Comparator> 83 RandomAccessIterator medianOf3(RandomAccessIterator Start, 84 RandomAccessIterator End, 85 const Comparator &Comp) { 86 RandomAccessIterator Mid = Start + (std::distance(Start, End) / 2); 87 return Comp(*Start, *(End - 1)) 88 ? (Comp(*Mid, *(End - 1)) ? (Comp(*Start, *Mid) ? Mid : Start) 89 : End - 1) 90 : (Comp(*Mid, *Start) ? (Comp(*(End - 1), *Mid) ? Mid : End - 1) 91 : Start); 92 } 93 94 template <class RandomAccessIterator, class Comparator> 95 void parallel_quick_sort(RandomAccessIterator Start, RandomAccessIterator End, 96 const Comparator &Comp, TaskGroup &TG, size_t Depth) { 97 // Do a sequential sort for small inputs. 98 if (std::distance(Start, End) < detail::MinParallelSize || Depth == 0) { 99 llvm::sort(Start, End, Comp); 100 return; 101 } 102 103 // Partition. 104 auto Pivot = medianOf3(Start, End, Comp); 105 // Move Pivot to End. 106 std::swap(*(End - 1), *Pivot); 107 Pivot = std::partition(Start, End - 1, [&Comp, End](decltype(*Start) V) { 108 return Comp(V, *(End - 1)); 109 }); 110 // Move Pivot to middle of partition. 111 std::swap(*Pivot, *(End - 1)); 112 113 // Recurse. 114 TG.spawn([=, &Comp, &TG] { 115 parallel_quick_sort(Start, Pivot, Comp, TG, Depth - 1); 116 }); 117 parallel_quick_sort(Pivot + 1, End, Comp, TG, Depth - 1); 118 } 119 120 template <class RandomAccessIterator, class Comparator> 121 void parallel_sort(RandomAccessIterator Start, RandomAccessIterator End, 122 const Comparator &Comp) { 123 TaskGroup TG; 124 parallel_quick_sort(Start, End, Comp, TG, 125 llvm::Log2_64(std::distance(Start, End)) + 1); 126 } 127 128 template <class IterTy, class FuncTy> 129 void parallel_for_each(IterTy Begin, IterTy End, FuncTy Fn) { 130 // TaskGroup has a relatively high overhead, so we want to reduce 131 // the number of spawn() calls. We'll create up to 1024 tasks here. 132 // (Note that 1024 is an arbitrary number. This code probably needs 133 // improving to take the number of available cores into account.) 134 ptrdiff_t TaskSize = std::distance(Begin, End) / 1024; 135 if (TaskSize == 0) 136 TaskSize = 1; 137 138 TaskGroup TG; 139 while (TaskSize < std::distance(Begin, End)) { 140 TG.spawn([=, &Fn] { std::for_each(Begin, Begin + TaskSize, Fn); }); 141 Begin += TaskSize; 142 } 143 std::for_each(Begin, End, Fn); 144 } 145 146 template <class IndexTy, class FuncTy> 147 void parallel_for_each_n(IndexTy Begin, IndexTy End, FuncTy Fn) { 148 ptrdiff_t TaskSize = (End - Begin) / 1024; 149 if (TaskSize == 0) 150 TaskSize = 1; 151 152 TaskGroup TG; 153 IndexTy I = Begin; 154 for (; I + TaskSize < End; I += TaskSize) { 155 TG.spawn([=, &Fn] { 156 for (IndexTy J = I, E = I + TaskSize; J != E; ++J) 157 Fn(J); 158 }); 159 } 160 for (IndexTy J = I; J < End; ++J) 161 Fn(J); 162 } 163 164 #endif 165 166 template <typename Iter> 167 using DefComparator = 168 std::less<typename std::iterator_traits<Iter>::value_type>; 169 170 } // namespace detail 171 172 // sequential algorithm implementations. 173 template <class Policy, class RandomAccessIterator, 174 class Comparator = detail::DefComparator<RandomAccessIterator>> 175 void sort(Policy policy, RandomAccessIterator Start, RandomAccessIterator End, 176 const Comparator &Comp = Comparator()) { 177 static_assert(is_execution_policy<Policy>::value, 178 "Invalid execution policy!"); 179 llvm::sort(Start, End, Comp); 180 } 181 182 template <class Policy, class IterTy, class FuncTy> 183 void for_each(Policy policy, IterTy Begin, IterTy End, FuncTy Fn) { 184 static_assert(is_execution_policy<Policy>::value, 185 "Invalid execution policy!"); 186 std::for_each(Begin, End, Fn); 187 } 188 189 template <class Policy, class IndexTy, class FuncTy> 190 void for_each_n(Policy policy, IndexTy Begin, IndexTy End, FuncTy Fn) { 191 static_assert(is_execution_policy<Policy>::value, 192 "Invalid execution policy!"); 193 for (IndexTy I = Begin; I != End; ++I) 194 Fn(I); 195 } 196 197 // Parallel algorithm implementations, only available when LLVM_ENABLE_THREADS 198 // is true. 199 #if LLVM_ENABLE_THREADS 200 template <class RandomAccessIterator, 201 class Comparator = detail::DefComparator<RandomAccessIterator>> 202 void sort(parallel_execution_policy policy, RandomAccessIterator Start, 203 RandomAccessIterator End, const Comparator &Comp = Comparator()) { 204 detail::parallel_sort(Start, End, Comp); 205 } 206 207 template <class IterTy, class FuncTy> 208 void for_each(parallel_execution_policy policy, IterTy Begin, IterTy End, 209 FuncTy Fn) { 210 detail::parallel_for_each(Begin, End, Fn); 211 } 212 213 template <class IndexTy, class FuncTy> 214 void for_each_n(parallel_execution_policy policy, IndexTy Begin, IndexTy End, 215 FuncTy Fn) { 216 detail::parallel_for_each_n(Begin, End, Fn); 217 } 218 #endif 219 220 } // namespace parallel 221 } // namespace llvm 222 223 #endif // LLVM_SUPPORT_PARALLEL_H 224