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