marking.h 13.9 KB
Newer Older
1 2 3 4 5 6 7
// Copyright 2016 the V8 project authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef V8_MARKING_H
#define V8_MARKING_H

8
#include "src/base/atomic-utils.h"
9 10 11 12 13 14 15 16
#include "src/utils.h"

namespace v8 {
namespace internal {

class MarkBit {
 public:
  typedef uint32_t CellType;
17
  STATIC_ASSERT(sizeof(CellType) == sizeof(base::Atomic32));
18

19 20 21 22 23
  enum AccessMode { ATOMIC, NON_ATOMIC };

  inline MarkBit(base::Atomic32* cell, CellType mask) : cell_(cell) {
    mask_ = static_cast<base::Atomic32>(mask);
  }
24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40

#ifdef DEBUG
  bool operator==(const MarkBit& other) {
    return cell_ == other.cell_ && mask_ == other.mask_;
  }
#endif

 private:
  inline MarkBit Next() {
    CellType new_mask = mask_ << 1;
    if (new_mask == 0) {
      return MarkBit(cell_ + 1, 1);
    } else {
      return MarkBit(cell_, new_mask);
    }
  }

41
  template <AccessMode mode = NON_ATOMIC>
42
  inline bool Set();
43

44
  template <AccessMode mode = NON_ATOMIC>
45
  inline bool Get();
46 47

  template <AccessMode mode = NON_ATOMIC>
48
  inline bool Clear();
49 50 51

  base::Atomic32* cell_;
  base::Atomic32 mask_;
52 53

  friend class IncrementalMarking;
54
  friend class ConcurrentMarkingMarkbits;
55 56 57
  friend class Marking;
};

58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105
template <>
inline bool MarkBit::Set<MarkBit::NON_ATOMIC>() {
  *cell_ |= mask_;
  return true;
}

template <>
inline bool MarkBit::Set<MarkBit::ATOMIC>() {
  base::Atomic32 old_value;
  base::Atomic32 new_value;
  do {
    old_value = base::NoBarrier_Load(cell_);
    if (old_value & mask_) return false;
    new_value = old_value | mask_;
  } while (base::Release_CompareAndSwap(cell_, old_value, new_value) !=
           old_value);
  return true;
}

template <>
inline bool MarkBit::Get<MarkBit::NON_ATOMIC>() {
  return (base::NoBarrier_Load(cell_) & mask_) != 0;
}

template <>
inline bool MarkBit::Get<MarkBit::ATOMIC>() {
  return (base::Acquire_Load(cell_) & mask_) != 0;
}

template <>
inline bool MarkBit::Clear<MarkBit::NON_ATOMIC>() {
  *cell_ &= ~mask_;
  return true;
}

template <>
inline bool MarkBit::Clear<MarkBit::ATOMIC>() {
  base::Atomic32 old_value;
  base::Atomic32 new_value;
  do {
    old_value = base::NoBarrier_Load(cell_);
    if (!(old_value & mask_)) return false;
    new_value = old_value & ~mask_;
  } while (base::Release_CompareAndSwap(cell_, old_value, new_value) !=
           old_value);
  return true;
}

106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158
// Bitmap is a sequence of cells each containing fixed number of bits.
class Bitmap {
 public:
  static const uint32_t kBitsPerCell = 32;
  static const uint32_t kBitsPerCellLog2 = 5;
  static const uint32_t kBitIndexMask = kBitsPerCell - 1;
  static const uint32_t kBytesPerCell = kBitsPerCell / kBitsPerByte;
  static const uint32_t kBytesPerCellLog2 = kBitsPerCellLog2 - kBitsPerByteLog2;

  static const size_t kLength = (1 << kPageSizeBits) >> (kPointerSizeLog2);

  static const size_t kSize = (1 << kPageSizeBits) >>
                              (kPointerSizeLog2 + kBitsPerByteLog2);

  static int CellsForLength(int length) {
    return (length + kBitsPerCell - 1) >> kBitsPerCellLog2;
  }

  int CellsCount() { return CellsForLength(kLength); }

  static int SizeFor(int cells_count) {
    return sizeof(MarkBit::CellType) * cells_count;
  }

  INLINE(static uint32_t IndexToCell(uint32_t index)) {
    return index >> kBitsPerCellLog2;
  }

  V8_INLINE static uint32_t IndexInCell(uint32_t index) {
    return index & kBitIndexMask;
  }

  INLINE(static uint32_t CellToIndex(uint32_t index)) {
    return index << kBitsPerCellLog2;
  }

  INLINE(static uint32_t CellAlignIndex(uint32_t index)) {
    return (index + kBitIndexMask) & ~kBitIndexMask;
  }

  INLINE(MarkBit::CellType* cells()) {
    return reinterpret_cast<MarkBit::CellType*>(this);
  }

  INLINE(Address address()) { return reinterpret_cast<Address>(this); }

  INLINE(static Bitmap* FromAddress(Address addr)) {
    return reinterpret_cast<Bitmap*>(addr);
  }

  inline MarkBit MarkBitFromIndex(uint32_t index) {
    MarkBit::CellType mask = 1u << IndexInCell(index);
    MarkBit::CellType* cell = this->cells() + (index >> kBitsPerCellLog2);
159
    return MarkBit(reinterpret_cast<base::Atomic32*>(cell), mask);
160 161 162 163 164 165
  }

  void Clear() {
    for (int i = 0; i < CellsCount(); i++) cells()[i] = 0;
  }

166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257
  // Sets all bits in the range [start_index, end_index).
  void SetRange(uint32_t start_index, uint32_t end_index) {
    unsigned int start_cell_index = start_index >> Bitmap::kBitsPerCellLog2;
    MarkBit::CellType start_index_mask = 1u << Bitmap::IndexInCell(start_index);

    unsigned int end_cell_index = end_index >> Bitmap::kBitsPerCellLog2;
    MarkBit::CellType end_index_mask = 1u << Bitmap::IndexInCell(end_index);

    if (start_cell_index != end_cell_index) {
      // Firstly, fill all bits from the start address to the end of the first
      // cell with 1s.
      cells()[start_cell_index] |= ~(start_index_mask - 1);
      // Then fill all in between cells with 1s.
      for (unsigned int i = start_cell_index + 1; i < end_cell_index; i++) {
        cells()[i] = ~0u;
      }
      // Finally, fill all bits until the end address in the last cell with 1s.
      cells()[end_cell_index] |= (end_index_mask - 1);
    } else {
      cells()[start_cell_index] |= end_index_mask - start_index_mask;
    }
  }

  // Clears all bits in the range [start_index, end_index).
  void ClearRange(uint32_t start_index, uint32_t end_index) {
    unsigned int start_cell_index = start_index >> Bitmap::kBitsPerCellLog2;
    MarkBit::CellType start_index_mask = 1u << Bitmap::IndexInCell(start_index);

    unsigned int end_cell_index = end_index >> Bitmap::kBitsPerCellLog2;
    MarkBit::CellType end_index_mask = 1u << Bitmap::IndexInCell(end_index);

    if (start_cell_index != end_cell_index) {
      // Firstly, fill all bits from the start address to the end of the first
      // cell with 0s.
      cells()[start_cell_index] &= (start_index_mask - 1);
      // Then fill all in between cells with 0s.
      for (unsigned int i = start_cell_index + 1; i < end_cell_index; i++) {
        cells()[i] = 0;
      }
      // Finally, set all bits until the end address in the last cell with 0s.
      cells()[end_cell_index] &= ~(end_index_mask - 1);
    } else {
      cells()[start_cell_index] &= ~(end_index_mask - start_index_mask);
    }
  }

  // Returns true if all bits in the range [start_index, end_index) are set.
  bool AllBitsSetInRange(uint32_t start_index, uint32_t end_index) {
    unsigned int start_cell_index = start_index >> Bitmap::kBitsPerCellLog2;
    MarkBit::CellType start_index_mask = 1u << Bitmap::IndexInCell(start_index);

    unsigned int end_cell_index = end_index >> Bitmap::kBitsPerCellLog2;
    MarkBit::CellType end_index_mask = 1u << Bitmap::IndexInCell(end_index);

    MarkBit::CellType matching_mask;
    if (start_cell_index != end_cell_index) {
      matching_mask = ~(start_index_mask - 1);
      if ((cells()[start_cell_index] & matching_mask) != matching_mask) {
        return false;
      }
      for (unsigned int i = start_cell_index + 1; i < end_cell_index; i++) {
        if (cells()[i] != ~0u) return false;
      }
      matching_mask = (end_index_mask - 1);
      return ((cells()[end_cell_index] & matching_mask) == matching_mask);
    } else {
      matching_mask = end_index_mask - start_index_mask;
      return (cells()[end_cell_index] & matching_mask) == matching_mask;
    }
  }

  // Returns true if all bits in the range [start_index, end_index) are cleared.
  bool AllBitsClearInRange(uint32_t start_index, uint32_t end_index) {
    unsigned int start_cell_index = start_index >> Bitmap::kBitsPerCellLog2;
    MarkBit::CellType start_index_mask = 1u << Bitmap::IndexInCell(start_index);

    unsigned int end_cell_index = end_index >> Bitmap::kBitsPerCellLog2;
    MarkBit::CellType end_index_mask = 1u << Bitmap::IndexInCell(end_index);

    MarkBit::CellType matching_mask;
    if (start_cell_index != end_cell_index) {
      matching_mask = ~(start_index_mask - 1);
      if ((cells()[start_cell_index] & matching_mask)) return false;
      for (unsigned int i = start_cell_index + 1; i < end_cell_index; i++) {
        if (cells()[i]) return false;
      }
      matching_mask = (end_index_mask - 1);
      return !(cells()[end_cell_index] & matching_mask);
    } else {
      matching_mask = end_index_mask - start_index_mask;
      return !(cells()[end_cell_index] & matching_mask);
    }
258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328
  }

  static void PrintWord(uint32_t word, uint32_t himask = 0) {
    for (uint32_t mask = 1; mask != 0; mask <<= 1) {
      if ((mask & himask) != 0) PrintF("[");
      PrintF((mask & word) ? "1" : "0");
      if ((mask & himask) != 0) PrintF("]");
    }
  }

  class CellPrinter {
   public:
    CellPrinter() : seq_start(0), seq_type(0), seq_length(0) {}

    void Print(uint32_t pos, uint32_t cell) {
      if (cell == seq_type) {
        seq_length++;
        return;
      }

      Flush();

      if (IsSeq(cell)) {
        seq_start = pos;
        seq_length = 0;
        seq_type = cell;
        return;
      }

      PrintF("%d: ", pos);
      PrintWord(cell);
      PrintF("\n");
    }

    void Flush() {
      if (seq_length > 0) {
        PrintF("%d: %dx%d\n", seq_start, seq_type == 0 ? 0 : 1,
               seq_length * kBitsPerCell);
        seq_length = 0;
      }
    }

    static bool IsSeq(uint32_t cell) { return cell == 0 || cell == 0xFFFFFFFF; }

   private:
    uint32_t seq_start;
    uint32_t seq_type;
    uint32_t seq_length;
  };

  void Print() {
    CellPrinter printer;
    for (int i = 0; i < CellsCount(); i++) {
      printer.Print(i, cells()[i]);
    }
    printer.Flush();
    PrintF("\n");
  }

  bool IsClean() {
    for (int i = 0; i < CellsCount(); i++) {
      if (cells()[i] != 0) {
        return false;
      }
    }
    return true;
  }
};

class Marking : public AllStatic {
 public:
329 330 331 332
  // TODO(hpayer): The current mark bit operations use as default NON_ATOMIC
  // mode for access. We should remove the default value or switch it with
  // ATOMIC as soon we add concurrency.

333 334
  // Impossible markbits: 01
  static const char* kImpossibleBitPattern;
335
  template <MarkBit::AccessMode mode = MarkBit::NON_ATOMIC>
336
  INLINE(static bool IsImpossible(MarkBit mark_bit)) {
337 338 339 340 341 342 343 344 345 346 347 348
    if (mode == MarkBit::NON_ATOMIC) {
      return !mark_bit.Get<mode>() && mark_bit.Next().Get<mode>();
    }
    // If we are in concurrent mode we can only tell if an object has the
    // impossible bit pattern if we read the first bit again after reading
    // the first and the second bit. If the first bit is till zero and the
    // second bit is one then the object has the impossible bit pattern.
    bool is_impossible = !mark_bit.Get<mode>() && mark_bit.Next().Get<mode>();
    if (is_impossible) {
      return !mark_bit.Get<mode>();
    }
    return false;
349 350 351 352
  }

  // Black markbits: 11
  static const char* kBlackBitPattern;
353
  template <MarkBit::AccessMode mode = MarkBit::NON_ATOMIC>
354
  INLINE(static bool IsBlack(MarkBit mark_bit)) {
355
    return mark_bit.Get<mode>() && mark_bit.Next().Get<mode>();
356 357 358 359
  }

  // White markbits: 00 - this is required by the mark bit clearer.
  static const char* kWhiteBitPattern;
360
  template <MarkBit::AccessMode mode = MarkBit::NON_ATOMIC>
361 362
  INLINE(static bool IsWhite(MarkBit mark_bit)) {
    DCHECK(!IsImpossible(mark_bit));
363
    return !mark_bit.Get<mode>();
364 365 366 367
  }

  // Grey markbits: 10
  static const char* kGreyBitPattern;
368
  template <MarkBit::AccessMode mode = MarkBit::NON_ATOMIC>
369
  INLINE(static bool IsGrey(MarkBit mark_bit)) {
370
    return mark_bit.Get<mode>() && !mark_bit.Next().Get<mode>();
371 372 373 374
  }

  // IsBlackOrGrey assumes that the first bit is set for black or grey
  // objects.
375 376 377 378
  template <MarkBit::AccessMode mode = MarkBit::NON_ATOMIC>
  INLINE(static bool IsBlackOrGrey(MarkBit mark_bit)) {
    return mark_bit.Get<mode>();
  }
379

380
  template <MarkBit::AccessMode mode = MarkBit::NON_ATOMIC>
381
  INLINE(static void MarkWhite(MarkBit markbit)) {
382 383 384
    STATIC_ASSERT(mode == MarkBit::NON_ATOMIC);
    markbit.Clear<mode>();
    markbit.Next().Clear<mode>();
385 386
  }

387 388 389 390
  // Warning: this method is not safe in general in concurrent scenarios.
  // If you know that nobody else will change the bits on the given location
  // then you may use it.
  template <MarkBit::AccessMode mode = MarkBit::NON_ATOMIC>
391
  INLINE(static void MarkBlack(MarkBit markbit)) {
392 393
    markbit.Set<mode>();
    markbit.Next().Set<mode>();
394 395
  }

396 397 398
  template <MarkBit::AccessMode mode = MarkBit::NON_ATOMIC>
  INLINE(static bool BlackToGrey(MarkBit markbit)) {
    STATIC_ASSERT(mode == MarkBit::NON_ATOMIC);
399
    DCHECK(IsBlack(markbit));
400
    return markbit.Next().Clear<mode>();
401 402
  }

403 404 405 406
  template <MarkBit::AccessMode mode = MarkBit::NON_ATOMIC>
  INLINE(static bool WhiteToGrey(MarkBit markbit)) {
    DCHECK(mode == MarkBit::ATOMIC || IsWhite(markbit));
    return markbit.Set<mode>();
407 408
  }

409 410 411 412
  // Warning: this method is not safe in general in concurrent scenarios.
  // If you know that nobody else will change the bits on the given location
  // then you may use it.
  template <MarkBit::AccessMode mode = MarkBit::NON_ATOMIC>
413
  INLINE(static void WhiteToBlack(MarkBit markbit)) {
414 415 416
    DCHECK(mode == MarkBit::ATOMIC || IsWhite(markbit));
    markbit.Set<mode>();
    markbit.Next().Set<mode>();
417 418
  }

419 420 421 422
  template <MarkBit::AccessMode mode = MarkBit::NON_ATOMIC>
  INLINE(static bool GreyToBlack(MarkBit markbit)) {
    DCHECK(mode == MarkBit::ATOMIC || IsGrey(markbit));
    return markbit.Next().Set<mode>();
423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461
  }

  enum ObjectColor {
    BLACK_OBJECT,
    WHITE_OBJECT,
    GREY_OBJECT,
    IMPOSSIBLE_COLOR
  };

  static const char* ColorName(ObjectColor color) {
    switch (color) {
      case BLACK_OBJECT:
        return "black";
      case WHITE_OBJECT:
        return "white";
      case GREY_OBJECT:
        return "grey";
      case IMPOSSIBLE_COLOR:
        return "impossible";
    }
    return "error";
  }

  static ObjectColor Color(MarkBit mark_bit) {
    if (IsBlack(mark_bit)) return BLACK_OBJECT;
    if (IsWhite(mark_bit)) return WHITE_OBJECT;
    if (IsGrey(mark_bit)) return GREY_OBJECT;
    UNREACHABLE();
    return IMPOSSIBLE_COLOR;
  }

 private:
  DISALLOW_IMPLICIT_CONSTRUCTORS(Marking);
};

}  // namespace internal
}  // namespace v8

#endif  // V8_MARKING_H_