DXR is a code search and navigation tool aimed at making sense of large projects. It supports full-text and regex searches as well as structural queries.

Mercurial (b6d82b1a6b02)

VCS Links

Line Code
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
 * vim: set ts=8 sts=2 et sw=2 tw=80:
 * This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

/*
 * GC-internal definitions of ArenaList and associated heap data structures.
 */

#ifndef gc_ArenaList_h
#define gc_ArenaList_h

#include "gc/AllocKind.h"
#include "js/SliceBudget.h"
#include "js/TypeDecls.h"
#include "threading/ProtectedData.h"

namespace js {

class Nursery;
class TenuringTracer;

namespace gcstats {
struct Statistics;
}

namespace gc {

class Arena;
struct FinalizePhase;
class FreeSpan;
class TenuredCell;

/*
 * A single segment of a SortedArenaList. Each segment has a head and a tail,
 * which track the start and end of a segment for O(1) append and concatenation.
 */
struct SortedArenaListSegment {
  Arena* head;
  Arena** tailp;

  void clear() {
    head = nullptr;
    tailp = &head;
  }

  bool isEmpty() const { return tailp == &head; }

  // Appends |arena| to this segment.
  inline void append(Arena* arena);

  // Points the tail of this segment at |arena|, which may be null. Note
  // that this does not change the tail itself, but merely which arena
  // follows it. This essentially turns the tail into a cursor (see also the
  // description of ArenaList), but from the perspective of a SortedArenaList
  // this makes no difference.
  void linkTo(Arena* arena) { *tailp = arena; }
};

/*
 * Arena lists have a head and a cursor. The cursor conceptually lies on arena
 * boundaries, i.e. before the first arena, between two arenas, or after the
 * last arena.
 *
 * Arenas are usually sorted in order of increasing free space, with the cursor
 * following the Arena currently being allocated from. This ordering should not
 * be treated as an invariant, however, as the free lists may be cleared,
 * leaving arenas previously used for allocation partially full. Sorting order
 * is restored during sweeping.

 * Arenas following the cursor should not be full.
 */
class ArenaList {
  // The cursor is implemented via an indirect pointer, |cursorp_|, to allow
  // for efficient list insertion at the cursor point and other list
  // manipulations.
  //
  // - If the list is empty: |head| is null, |cursorp_| points to |head|, and
  //   therefore |*cursorp_| is null.
  //
  // - If the list is not empty: |head| is non-null, and...
  //
  //   - If the cursor is at the start of the list: |cursorp_| points to
  //     |head|, and therefore |*cursorp_| points to the first arena.
  //
  //   - If cursor is at the end of the list: |cursorp_| points to the |next|
  //     field of the last arena, and therefore |*cursorp_| is null.
  //
  //   - If the cursor is at neither the start nor the end of the list:
  //     |cursorp_| points to the |next| field of the arena preceding the
  //     cursor, and therefore |*cursorp_| points to the arena following the
  //     cursor.
  //
  // |cursorp_| is never null.
  //
  Arena* head_;
  Arena** cursorp_;

  inline void copy(const ArenaList& other);

 public:
  inline ArenaList();
  inline ArenaList(const ArenaList& other);

  inline ArenaList& operator=(const ArenaList& other);

  inline explicit ArenaList(const SortedArenaListSegment& segment);

  inline void check() const;

  inline void clear();
  inline ArenaList copyAndClear();
  inline bool isEmpty() const;

  // This returns nullptr if the list is empty.
  inline Arena* head() const;

  inline bool isCursorAtHead() const;
  inline bool isCursorAtEnd() const;

  inline void moveCursorToEnd();

  // This can return nullptr.
  inline Arena* arenaAfterCursor() const;

  // This returns the arena after the cursor and moves the cursor past it.
  inline Arena* takeNextArena();

  // This does two things.
  // - Inserts |a| at the cursor.
  // - Leaves the cursor sitting just before |a|, if |a| is not full, or just
  //   after |a|, if |a| is full.
  inline void insertAtCursor(Arena* a);

  // Inserts |a| at the cursor, then moves the cursor past it.
  inline void insertBeforeCursor(Arena* a);

  // This inserts |other|, which must be full, at the cursor of |this|.
  inline ArenaList& insertListWithCursorAtEnd(const ArenaList& other);

  Arena* removeRemainingArenas(Arena** arenap);
  Arena** pickArenasToRelocate(size_t& arenaTotalOut, size_t& relocTotalOut);
  Arena* relocateArenas(Arena* toRelocate, Arena* relocated,
                        js::SliceBudget& sliceBudget,
                        gcstats::Statistics& stats);
};

/*
 * A class that holds arenas in sorted order by appending arenas to specific
 * segments. Each segment has a head and a tail, which can be linked up to
 * other segments to create a contiguous ArenaList.
 */
class SortedArenaList {
 public:
  // The minimum size, in bytes, of a GC thing.
  static const size_t MinThingSize = 16;

  static_assert(ArenaSize <= 4096,
                "When increasing the Arena size, please consider how"
                " this will affect the size of a SortedArenaList.");

  static_assert(MinThingSize >= 16,
                "When decreasing the minimum thing size, please consider"
                " how this will affect the size of a SortedArenaList.");

 private:
  // The maximum number of GC things that an arena can hold.
  static const size_t MaxThingsPerArena =
      (ArenaSize - ArenaHeaderSize) / MinThingSize;

  size_t thingsPerArena_;
  SortedArenaListSegment segments[MaxThingsPerArena + 1];

  // Convenience functions to get the nth head and tail.
  Arena* headAt(size_t n) { return segments[n].head; }
  Arena** tailAt(size_t n) { return segments[n].tailp; }

 public:
  inline explicit SortedArenaList(size_t thingsPerArena = MaxThingsPerArena);

  inline void setThingsPerArena(size_t thingsPerArena);

  // Resets the first |thingsPerArena| segments of this list for further use.
  inline void reset(size_t thingsPerArena = MaxThingsPerArena);

  // Inserts an arena, which has room for |nfree| more things, in its segment.
  inline void insertAt(Arena* arena, size_t nfree);

  // Remove all empty arenas, inserting them as a linked list.
  inline void extractEmpty(Arena** empty);

  // Links up the tail of each non-empty segment to the head of the next
  // non-empty segment, creating a contiguous list that is returned as an
  // ArenaList. This is not a destructive operation: neither the head nor tail
  // of any segment is modified. However, note that the Arenas in the
  // resulting ArenaList should be treated as read-only unless the
  // SortedArenaList is no longer needed: inserting or removing arenas would
  // invalidate the SortedArenaList.
  inline ArenaList toArenaList();
};

enum class ShouldCheckThresholds {
  DontCheckThresholds = 0,
  CheckThresholds = 1
};

// For each arena kind its free list is represented as the first span with free
// things. Initially all the spans are initialized as empty. After we find a new
// arena with available things we move its first free span into the list and set
// the arena as fully allocated. That way we do not need to update the arena
// after the initial allocation. When starting the GC we only move the head of
// the of the list of spans back to the arena only for the arena that was not
// fully allocated.
class FreeLists {
  AllAllocKindArray<FreeSpan*> freeLists_;

 public:
  // Because the JITs can allocate from the free lists, they cannot be null.
  // We use a placeholder FreeSpan that is empty (and wihout an associated
  // Arena) so the JITs can fall back gracefully.
  static FreeSpan emptySentinel;

  FreeLists();

#ifdef DEBUG
  inline bool allEmpty() const;
  inline bool isEmpty(AllocKind kind) const;
#endif

  inline void clear();

  MOZ_ALWAYS_INLINE TenuredCell* allocate(AllocKind kind);

  inline TenuredCell* setArenaAndAllocate(Arena* arena, AllocKind kind);

  inline void unmarkPreMarkedFreeCells(AllocKind kind);

  FreeSpan** addressOfFreeList(AllocKind thingKind) {
    return &freeLists_[thingKind];
  }
};

class ArenaLists {
  JS::Zone* zone_;

  ZoneData<FreeLists> freeLists_;

  ArenaListData<AllAllocKindArray<ArenaList>> arenaLists_;

  ArenaList& arenaLists(AllocKind i) { return arenaLists_.ref()[i]; }
  const ArenaList& arenaLists(AllocKind i) const {
    return arenaLists_.ref()[i];
  }

  enum class ConcurrentUse : uint32_t {
    None,
    BackgroundFinalize,
    ParallelAlloc
  };

  using ConcurrentUseState =
      mozilla::Atomic<ConcurrentUse, mozilla::SequentiallyConsistent,
                      mozilla::recordreplay::Behavior::DontPreserve>;

  // Whether this structure can be accessed by other threads.
  UnprotectedData<AllAllocKindArray<ConcurrentUseState>> concurrentUseState_;

  ConcurrentUseState& concurrentUse(AllocKind i) {
    return concurrentUseState_.ref()[i];
  }
  ConcurrentUse concurrentUse(AllocKind i) const {
    return concurrentUseState_.ref()[i];
  }

  /* For each arena kind, a list of arenas remaining to be swept. */
  MainThreadOrGCTaskData<AllAllocKindArray<Arena*>> arenaListsToSweep_;
  Arena*& arenaListsToSweep(AllocKind i) { return arenaListsToSweep_.ref()[i]; }
  Arena* arenaListsToSweep(AllocKind i) const {
    return arenaListsToSweep_.ref()[i];
  }

  /* During incremental sweeping, a list of the arenas already swept. */
  ZoneOrGCTaskData<AllocKind> incrementalSweptArenaKind;
  ZoneOrGCTaskData<ArenaList> incrementalSweptArenas;

  // Arena lists which have yet to be swept, but need additional foreground
  // processing before they are swept.
  ZoneData<Arena*> gcShapeArenasToUpdate;
  ZoneData<Arena*> gcAccessorShapeArenasToUpdate;
  ZoneData<Arena*> gcScriptArenasToUpdate;
  ZoneData<Arena*> gcObjectGroupArenasToUpdate;

  // The list of empty arenas which are collected during the sweep phase and
  // released at the end of sweeping every sweep group.
  ZoneData<Arena*> savedEmptyArenas;

 public:
  explicit ArenaLists(JS::Zone* zone);
  ~ArenaLists();

  FreeLists& freeLists() { return freeLists_.ref(); }
  const FreeLists& freeLists() const { return freeLists_.ref(); }

  FreeSpan** addressOfFreeList(AllocKind thingKind) {
    return freeLists_.refNoCheck().addressOfFreeList(thingKind);
  }

  inline Arena* getFirstArena(AllocKind thingKind) const;
  inline Arena* getFirstArenaToSweep(AllocKind thingKind) const;
  inline Arena* getFirstSweptArena(AllocKind thingKind) const;
  inline Arena* getArenaAfterCursor(AllocKind thingKind) const;

  inline bool arenaListsAreEmpty() const;

  inline void unmarkAll();

  inline bool doneBackgroundFinalize(AllocKind kind) const;
  inline bool needBackgroundFinalizeWait(AllocKind kind) const;

  /* Clear the free lists so we won't try to allocate from swept arenas. */
  inline void clearFreeLists();

  inline void unmarkPreMarkedFreeCells();

  MOZ_ALWAYS_INLINE TenuredCell* allocateFromFreeList(AllocKind thingKind);

  /* Moves all arenas from |fromArenaLists| into |this|. */
  void adoptArenas(ArenaLists* fromArenaLists, bool targetZoneIsCollecting);

  inline void checkEmptyFreeLists();
  inline void checkEmptyArenaLists();
  inline void checkEmptyFreeList(AllocKind kind);

  void checkEmptyArenaList(AllocKind kind);

  bool relocateArenas(Arena*& relocatedListOut, JS::GCReason reason,
                      js::SliceBudget& sliceBudget, gcstats::Statistics& stats);

  void queueForegroundObjectsForSweep(JSFreeOp* fop);
  void queueForegroundThingsForSweep();

  void releaseForegroundSweptEmptyArenas();

  bool foregroundFinalize(JSFreeOp* fop, AllocKind thingKind,
                          js::SliceBudget& sliceBudget,
                          SortedArenaList& sweepList);
  static void backgroundFinalize(JSFreeOp* fop, Arena* listHead, Arena** empty);

  void setParallelAllocEnabled(bool enabled);

 private:
  inline JSRuntime* runtime();
  inline JSRuntime* runtimeFromAnyThread();

  inline void queueForForegroundSweep(JSFreeOp* fop,
                                      const FinalizePhase& phase);
  inline void queueForBackgroundSweep(JSFreeOp* fop,
                                      const FinalizePhase& phase);
  inline void queueForForegroundSweep(AllocKind thingKind);
  inline void queueForBackgroundSweep(AllocKind thingKind);

  TenuredCell* refillFreeListAndAllocate(FreeLists& freeLists,
                                         AllocKind thingKind,
                                         ShouldCheckThresholds checkThresholds);

  friend class GCRuntime;
  friend class js::Nursery;
  friend class js::TenuringTracer;
};

} /* namespace gc */
} /* namespace js */

#endif /* gc_ArenaList_h */