libcxx/include/__cxx03/__pstl/backends/libdispatch.h

   1 //===----------------------------------------------------------------------===//
   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 _LIBCPP___PSTL_BACKENDS_LIBDISPATCH_H
  10 #define _LIBCPP___PSTL_BACKENDS_LIBDISPATCH_H
  11
  12 #include <__cxx03/__algorithm/inplace_merge.h>
  13 #include <__cxx03/__algorithm/lower_bound.h>
  14 #include <__cxx03/__algorithm/max.h>
  15 #include <__cxx03/__algorithm/merge.h>
  16 #include <__cxx03/__algorithm/upper_bound.h>
  17 #include <__cxx03/__atomic/atomic.h>
  18 #include <__cxx03/__config>
  19 #include <__cxx03/__exception/terminate.h>
  20 #include <__cxx03/__iterator/iterator_traits.h>
  21 #include <__cxx03/__iterator/move_iterator.h>
  22 #include <__cxx03/__memory/allocator.h>
  23 #include <__cxx03/__memory/construct_at.h>
  24 #include <__cxx03/__memory/unique_ptr.h>
  25 #include <__cxx03/__numeric/reduce.h>
  26 #include <__cxx03/__pstl/backend_fwd.h>
  27 #include <__cxx03/__pstl/cpu_algos/any_of.h>
  28 #include <__cxx03/__pstl/cpu_algos/cpu_traits.h>
  29 #include <__cxx03/__pstl/cpu_algos/fill.h>
  30 #include <__cxx03/__pstl/cpu_algos/find_if.h>
  31 #include <__cxx03/__pstl/cpu_algos/for_each.h>
  32 #include <__cxx03/__pstl/cpu_algos/merge.h>
  33 #include <__cxx03/__pstl/cpu_algos/stable_sort.h>
  34 #include <__cxx03/__pstl/cpu_algos/transform.h>
  35 #include <__cxx03/__pstl/cpu_algos/transform_reduce.h>
  36 #include <__cxx03/__utility/empty.h>
  37 #include <__cxx03/__utility/exception_guard.h>
  38 #include <__cxx03/__utility/move.h>
  39 #include <__cxx03/__utility/pair.h>
  40 #include <__cxx03/cstddef>
  41 #include <__cxx03/new>
  42 #include <__cxx03/optional>
  43
  44 _LIBCPP_PUSH_MACROS
  45 #include <__cxx03/__undef_macros>
  46
  47 _LIBCPP_BEGIN_NAMESPACE_STD
  48 namespace __pstl {
  49
  50 namespace __libdispatch {
  51 // ::dispatch_apply is marked as __attribute__((nothrow)) because it doesn't let exceptions propagate, and neither do
  52 // we.
  53 // TODO: Do we want to add [[_Clang::__callback__(__func, __context, __)]]?
  54 _LIBCPP_EXPORTED_FROM_ABI void
  55 __dispatch_apply(size_t __chunk_count, void* __context, void (*__func)(void* __context, size_t __chunk)) noexcept;
  56
  57 template <class _Func>
  58 _LIBCPP_HIDE_FROM_ABI void __dispatch_apply(size_t __chunk_count, _Func __func) noexcept {
  59   __libdispatch::__dispatch_apply(__chunk_count, &__func, [](void* __context, size_t __chunk) {
  60     (*static_cast<_Func*>(__context))(__chunk);
  61   });
  62 }
  63
  64 struct __chunk_partitions {
  65   ptrdiff_t __chunk_count_; // includes the first chunk
  66   ptrdiff_t __chunk_size_;
  67   ptrdiff_t __first_chunk_size_;
  68 };
  69
  70 [[__gnu__::__const__]] _LIBCPP_EXPORTED_FROM_ABI __chunk_partitions __partition_chunks(ptrdiff_t __size) noexcept;
  71
  72 template <class _RandomAccessIterator, class _Functor>
  73 _LIBCPP_HIDE_FROM_ABI optional<__empty>
  74 __dispatch_parallel_for(__chunk_partitions __partitions, _RandomAccessIterator __first, _Functor __func) {
  75   // Perform the chunked execution.
  76   __libdispatch::__dispatch_apply(__partitions.__chunk_count_, [&](size_t __chunk) {
  77     auto __this_chunk_size = __chunk == 0 ? __partitions.__first_chunk_size_ : __partitions.__chunk_size_;
  78     auto __index =
  79         __chunk == 0
  80             ? 0
  81             : (__chunk * __partitions.__chunk_size_) + (__partitions.__first_chunk_size_ - __partitions.__chunk_size_);
  82     __func(__first + __index, __first + __index + __this_chunk_size);
  83   });
  84
  85   return __empty{};
  86 }
  87 } // namespace __libdispatch
  88
  89 template <>
  90 struct __cpu_traits<__libdispatch_backend_tag> {
  91   template <class _RandomAccessIterator, class _Functor>
  92   _LIBCPP_HIDE_FROM_ABI static optional<__empty>
  93   __for_each(_RandomAccessIterator __first, _RandomAccessIterator __last, _Functor __func) {
  94     return __libdispatch::__dispatch_parallel_for(
  95         __libdispatch::__partition_chunks(__last - __first), std::move(__first), std::move(__func));
  96   }
  97
  98   template <class _RandomAccessIterator1, class _RandomAccessIterator2, class _RandomAccessIteratorOut>
  99   struct __merge_range {
 100     __merge_range(_RandomAccessIterator1 __mid1, _RandomAccessIterator2 __mid2, _RandomAccessIteratorOut __result)
 101         : __mid1_(__mid1), __mid2_(__mid2), __result_(__result) {}
 102
 103     _RandomAccessIterator1 __mid1_;
 104     _RandomAccessIterator2 __mid2_;
 105     _RandomAccessIteratorOut __result_;
 106   };
 107
 108   template <typename _RandomAccessIterator1,
 109             typename _RandomAccessIterator2,
 110             typename _RandomAccessIterator3,
 111             typename _Compare,
 112             typename _LeafMerge>
 113   _LIBCPP_HIDE_FROM_ABI static optional<__empty>
 114   __merge(_RandomAccessIterator1 __first1,
 115           _RandomAccessIterator1 __last1,
 116           _RandomAccessIterator2 __first2,
 117           _RandomAccessIterator2 __last2,
 118           _RandomAccessIterator3 __result,
 119           _Compare __comp,
 120           _LeafMerge __leaf_merge) noexcept {
 121     __libdispatch::__chunk_partitions __partitions =
 122         __libdispatch::__partition_chunks(std::max<ptrdiff_t>(__last1 - __first1, __last2 - __first2));
 123
 124     if (__partitions.__chunk_count_ == 0)
 125       return __empty{};
 126
 127     if (__partitions.__chunk_count_ == 1) {
 128       __leaf_merge(__first1, __last1, __first2, __last2, __result, __comp);
 129       return __empty{};
 130     }
 131
 132     using __merge_range_t = __merge_range<_RandomAccessIterator1, _RandomAccessIterator2, _RandomAccessIterator3>;
 133     auto const __n_ranges = __partitions.__chunk_count_ + 1;
 134
 135     // TODO: use __uninitialized_buffer
 136     auto __destroy = [=](__merge_range_t* __ptr) {
 137       std::destroy_n(__ptr, __n_ranges);
 138       std::allocator<__merge_range_t>().deallocate(__ptr, __n_ranges);
 139     };
 140
 141     unique_ptr<__merge_range_t[], decltype(__destroy)> __ranges(
 142         [&]() -> __merge_range_t* {
 143 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
 144           try {
 145 #endif
 146             return std::allocator<__merge_range_t>().allocate(__n_ranges);
 147 #ifndef _LIBCPP_HAS_NO_EXCEPTIONS
 148           } catch (const std::bad_alloc&) {
 149             return nullptr;
 150           }
 151 #endif
 152         }(),
 153         __destroy);
 154
 155     if (!__ranges)
 156       return nullopt;
 157
 158     // TODO: Improve the case where the smaller range is merged into just a few (or even one) chunks of the larger case
 159     __merge_range_t* __r = __ranges.get();
 160     std::__construct_at(__r++, __first1, __first2, __result);
 161
 162     bool __iterate_first_range = __last1 - __first1 > __last2 - __first2;
 163
 164     auto __compute_chunk = [&](size_t __chunk_size) -> __merge_range_t {
 165       auto [__mid1, __mid2] = [&] {
 166         if (__iterate_first_range) {
 167           auto __m1 = __first1 + __chunk_size;
 168           auto __m2 = std::lower_bound(__first2, __last2, __m1[-1], __comp);
 169           return std::make_pair(__m1, __m2);
 170         } else {
 171           auto __m2 = __first2 + __chunk_size;
 172           auto __m1 = std::lower_bound(__first1, __last1, __m2[-1], __comp);
 173           return std::make_pair(__m1, __m2);
 174         }
 175       }();
 176
 177       __result += (__mid1 - __first1) + (__mid2 - __first2);
 178       __first1 = __mid1;
 179       __first2 = __mid2;
 180       return {std::move(__mid1), std::move(__mid2), __result};
 181     };
 182
 183     // handle first chunk
 184     std::__construct_at(__r++, __compute_chunk(__partitions.__first_chunk_size_));
 185
 186     // handle 2 -> N - 1 chunks
 187     for (ptrdiff_t __i = 0; __i != __partitions.__chunk_count_ - 2; ++__i)
 188       std::__construct_at(__r++, __compute_chunk(__partitions.__chunk_size_));
 189
 190     // handle last chunk
 191     std::__construct_at(__r, __last1, __last2, __result);
 192
 193     __libdispatch::__dispatch_apply(__partitions.__chunk_count_, [&](size_t __index) {
 194       auto __first_iters = __ranges[__index];
 195       auto __last_iters  = __ranges[__index + 1];
 196       __leaf_merge(
 197           __first_iters.__mid1_,
 198           __last_iters.__mid1_,
 199           __first_iters.__mid2_,
 200           __last_iters.__mid2_,
 201           __first_iters.__result_,
 202           __comp);
 203     });
 204
 205     return __empty{};
 206   }
 207
 208   template <class _RandomAccessIterator, class _Transform, class _Value, class _Combiner, class _Reduction>
 209   _LIBCPP_HIDE_FROM_ABI static optional<_Value> __transform_reduce(
 210       _RandomAccessIterator __first,
 211       _RandomAccessIterator __last,
 212       _Transform __transform,
 213       _Value __init,
 214       _Combiner __combiner,
 215       _Reduction __reduction) {
 216     if (__first == __last)
 217       return __init;
 218
 219     auto __partitions = __libdispatch::__partition_chunks(__last - __first);
 220
 221     auto __destroy = [__count = __partitions.__chunk_count_](_Value* __ptr) {
 222       std::destroy_n(__ptr, __count);
 223       std::allocator<_Value>().deallocate(__ptr, __count);
 224     };
 225
 226     // TODO: use __uninitialized_buffer
 227     // TODO: allocate one element per worker instead of one element per chunk
 228     unique_ptr<_Value[], decltype(__destroy)> __values(
 229         std::allocator<_Value>().allocate(__partitions.__chunk_count_), __destroy);
 230
 231     // __dispatch_apply is noexcept
 232     __libdispatch::__dispatch_apply(__partitions.__chunk_count_, [&](size_t __chunk) {
 233       auto __this_chunk_size = __chunk == 0 ? __partitions.__first_chunk_size_ : __partitions.__chunk_size_;
 234       auto __index           = __chunk == 0 ? 0
 235                                             : (__chunk * __partitions.__chunk_size_) +
 236                                         (__partitions.__first_chunk_size_ - __partitions.__chunk_size_);
 237       if (__this_chunk_size != 1) {
 238         std::__construct_at(
 239             __values.get() + __chunk,
 240             __reduction(__first + __index + 2,
 241                         __first + __index + __this_chunk_size,
 242                         __combiner(__transform(__first + __index), __transform(__first + __index + 1))));
 243       } else {
 244         std::__construct_at(__values.get() + __chunk, __transform(__first + __index));
 245       }
 246     });
 247
 248     return std::reduce(
 249         std::make_move_iterator(__values.get()),
 250         std::make_move_iterator(__values.get() + __partitions.__chunk_count_),
 251         std::move(__init),
 252         __combiner);
 253   }
 254
 255   template <class _RandomAccessIterator, class _Comp, class _LeafSort>
 256   _LIBCPP_HIDE_FROM_ABI static optional<__empty>
 257   __stable_sort(_RandomAccessIterator __first, _RandomAccessIterator __last, _Comp __comp, _LeafSort __leaf_sort) {
 258     const auto __size = __last - __first;
 259     auto __partitions = __libdispatch::__partition_chunks(__size);
 260
 261     if (__partitions.__chunk_count_ == 0)
 262       return __empty{};
 263
 264     if (__partitions.__chunk_count_ == 1) {
 265       __leaf_sort(__first, __last, __comp);
 266       return __empty{};
 267     }
 268
 269     using _Value = __iter_value_type<_RandomAccessIterator>;
 270
 271     auto __destroy = [__size](_Value* __ptr) {
 272       std::destroy_n(__ptr, __size);
 273       std::allocator<_Value>().deallocate(__ptr, __size);
 274     };
 275
 276     // TODO: use __uninitialized_buffer
 277     unique_ptr<_Value[], decltype(__destroy)> __values(std::allocator<_Value>().allocate(__size), __destroy);
 278
 279     // Initialize all elements to a moved-from state
 280     // TODO: Don't do this - this can be done in the first merge - see https://llvm.org/PR63928
 281     std::__construct_at(__values.get(), std::move(*__first));
 282     for (__iter_diff_t<_RandomAccessIterator> __i = 1; __i != __size; ++__i) {
 283       std::__construct_at(__values.get() + __i, std::move(__values.get()[__i - 1]));
 284     }
 285     *__first = std::move(__values.get()[__size - 1]);
 286
 287     __libdispatch::__dispatch_parallel_for(
 288         __partitions,
 289         __first,
 290         [&__leaf_sort, &__comp](_RandomAccessIterator __chunk_first, _RandomAccessIterator __chunk_last) {
 291           __leaf_sort(std::move(__chunk_first), std::move(__chunk_last), __comp);
 292         });
 293
 294     bool __objects_are_in_buffer = false;
 295     do {
 296       const auto __old_chunk_size = __partitions.__chunk_size_;
 297       if (__partitions.__chunk_count_ % 2 == 1) {
 298         auto __inplace_merge_chunks = [&__comp, &__partitions](auto __first_chunk_begin) {
 299           std::inplace_merge(
 300               __first_chunk_begin,
 301               __first_chunk_begin + __partitions.__first_chunk_size_,
 302               __first_chunk_begin + __partitions.__first_chunk_size_ + __partitions.__chunk_size_,
 303               __comp);
 304         };
 305         if (__objects_are_in_buffer)
 306           __inplace_merge_chunks(__values.get());
 307         else
 308           __inplace_merge_chunks(__first);
 309         __partitions.__first_chunk_size_ += 2 * __partitions.__chunk_size_;
 310       } else {
 311         __partitions.__first_chunk_size_ += __partitions.__chunk_size_;
 312       }
 313
 314       __partitions.__chunk_size_ *= 2;
 315       __partitions.__chunk_count_ /= 2;
 316
 317       auto __merge_chunks = [__partitions, __old_chunk_size, &__comp](auto __from_first, auto __to_first) {
 318         __libdispatch::__dispatch_parallel_for(
 319             __partitions,
 320             __from_first,
 321             [__old_chunk_size, &__from_first, &__to_first, &__comp](auto __chunk_first, auto __chunk_last) {
 322               std::merge(std::make_move_iterator(__chunk_first),
 323                          std::make_move_iterator(__chunk_last - __old_chunk_size),
 324                          std::make_move_iterator(__chunk_last - __old_chunk_size),
 325                          std::make_move_iterator(__chunk_last),
 326                          __to_first + (__chunk_first - __from_first),
 327                          __comp);
 328             });
 329       };
 330
 331       if (__objects_are_in_buffer)
 332         __merge_chunks(__values.get(), __first);
 333       else
 334         __merge_chunks(__first, __values.get());
 335       __objects_are_in_buffer = !__objects_are_in_buffer;
 336     } while (__partitions.__chunk_count_ > 1);
 337
 338     if (__objects_are_in_buffer) {
 339       std::move(__values.get(), __values.get() + __size, __first);
 340     }
 341
 342     return __empty{};
 343   }
 344
 345   _LIBCPP_HIDE_FROM_ABI static void __cancel_execution() {}
 346
 347   static constexpr size_t __lane_size = 64;
 348 };
 349
 350 // Mandatory implementations of the computational basis
 351 template <class _ExecutionPolicy>
 352 struct __find_if<__libdispatch_backend_tag, _ExecutionPolicy>
 353     : __cpu_parallel_find_if<__libdispatch_backend_tag, _ExecutionPolicy> {};
 354
 355 template <class _ExecutionPolicy>
 356 struct __for_each<__libdispatch_backend_tag, _ExecutionPolicy>
 357     : __cpu_parallel_for_each<__libdispatch_backend_tag, _ExecutionPolicy> {};
 358
 359 template <class _ExecutionPolicy>
 360 struct __merge<__libdispatch_backend_tag, _ExecutionPolicy>
 361     : __cpu_parallel_merge<__libdispatch_backend_tag, _ExecutionPolicy> {};
 362
 363 template <class _ExecutionPolicy>
 364 struct __stable_sort<__libdispatch_backend_tag, _ExecutionPolicy>
 365     : __cpu_parallel_stable_sort<__libdispatch_backend_tag, _ExecutionPolicy> {};
 366
 367 template <class _ExecutionPolicy>
 368 struct __transform<__libdispatch_backend_tag, _ExecutionPolicy>
 369     : __cpu_parallel_transform<__libdispatch_backend_tag, _ExecutionPolicy> {};
 370
 371 template <class _ExecutionPolicy>
 372 struct __transform_binary<__libdispatch_backend_tag, _ExecutionPolicy>
 373     : __cpu_parallel_transform_binary<__libdispatch_backend_tag, _ExecutionPolicy> {};
 374
 375 template <class _ExecutionPolicy>
 376 struct __transform_reduce<__libdispatch_backend_tag, _ExecutionPolicy>
 377     : __cpu_parallel_transform_reduce<__libdispatch_backend_tag, _ExecutionPolicy> {};
 378
 379 template <class _ExecutionPolicy>
 380 struct __transform_reduce_binary<__libdispatch_backend_tag, _ExecutionPolicy>
 381     : __cpu_parallel_transform_reduce_binary<__libdispatch_backend_tag, _ExecutionPolicy> {};
 382
 383 // Not mandatory, but better optimized
 384 template <class _ExecutionPolicy>
 385 struct __any_of<__libdispatch_backend_tag, _ExecutionPolicy>
 386     : __cpu_parallel_any_of<__libdispatch_backend_tag, _ExecutionPolicy> {};
 387
 388 template <class _ExecutionPolicy>
 389 struct __fill<__libdispatch_backend_tag, _ExecutionPolicy>
 390     : __cpu_parallel_fill<__libdispatch_backend_tag, _ExecutionPolicy> {};
 391
 392 } // namespace __pstl
 393 _LIBCPP_END_NAMESPACE_STD
 394
 395 _LIBCPP_POP_MACROS
 396
 397 #endif // _LIBCPP___PSTL_BACKENDS_LIBDISPATCH_H