1 //===- llvm/Support/Parallel.h - Parallel algorithms ----------------------===//
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
7 //===----------------------------------------------------------------------===//
9 #ifndef LLVM_SUPPORT_PARALLEL_H
10 #define LLVM_SUPPORT_PARALLEL_H
12 #include "llvm/ADT/STLExtras.h"
13 #include "llvm/Config/llvm-config.h"
14 #include "llvm/Support/MathExtras.h"
17 #include <condition_variable>
24 struct sequential_execution_policy {};
25 struct parallel_execution_policy {};
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> {};
33 constexpr sequential_execution_policy seq{};
34 constexpr parallel_execution_policy par{};
38 #if LLVM_ENABLE_THREADS
42 mutable std::mutex Mutex;
43 mutable std::condition_variable Cond;
46 explicit Latch(uint32_t Count = 0) : Count(Count) {}
50 std::lock_guard<std::mutex> lock(Mutex);
55 std::lock_guard<std::mutex> lock(Mutex);
61 std::unique_lock<std::mutex> lock(Mutex);
62 Cond.wait(lock, [&] { return Count == 0; });
74 void spawn(std::function<void()> f);
76 void sync() const { L.sync(); }
79 const ptrdiff_t MinParallelSize = 1024;
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)
90 : (Comp(*Mid, *Start) ? (Comp(*(End - 1), *Mid) ? Mid : End - 1)
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);
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));
110 // Move Pivot to middle of partition.
111 std::swap(*Pivot, *(End - 1));
114 TG.spawn([=, &Comp, &TG] {
115 parallel_quick_sort(Start, Pivot, Comp, TG, Depth - 1);
117 parallel_quick_sort(Pivot + 1, End, Comp, TG, Depth - 1);
120 template <class RandomAccessIterator, class Comparator>
121 void parallel_sort(RandomAccessIterator Start, RandomAccessIterator End,
122 const Comparator &Comp) {
124 parallel_quick_sort(Start, End, Comp, TG,
125 llvm::Log2_64(std::distance(Start, End)) + 1);
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;
139 while (TaskSize < std::distance(Begin, End)) {
140 TG.spawn([=, &Fn] { std::for_each(Begin, Begin + TaskSize, Fn); });
143 std::for_each(Begin, End, Fn);
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;
154 for (; I + TaskSize < End; I += TaskSize) {
156 for (IndexTy J = I, E = I + TaskSize; J != E; ++J)
160 for (IndexTy J = I; J < End; ++J)
166 template <typename Iter>
167 using DefComparator =
168 std::less<typename std::iterator_traits<Iter>::value_type>;
170 } // namespace detail
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);
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);
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)
197 // Parallel algorithm implementations, only available when LLVM_ENABLE_THREADS
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);
207 template <class IterTy, class FuncTy>
208 void for_each(parallel_execution_policy policy, IterTy Begin, IterTy End,
210 detail::parallel_for_each(Begin, End, Fn);
213 template <class IndexTy, class FuncTy>
214 void for_each_n(parallel_execution_policy policy, IndexTy Begin, IndexTy End,
216 detail::parallel_for_each_n(Begin, End, Fn);
220 } // namespace parallel
223 #endif // LLVM_SUPPORT_PARALLEL_H