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.

Header

Mercurial (dcc6d7a0dc00)

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 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603 604 605 606 607 608 609 610 611 612 613 614 615 616 617 618 619 620 621 622 623 624 625 626 627 628 629 630 631 632 633 634 635 636 637 638 639 640 641 642 643 644 645 646 647 648 649 650 651 652 653 654 655 656 657 658 659 660 661 662 663 664 665 666 667 668 669 670 671 672 673 674 675 676 677 678 679 680 681 682 683 684 685 686 687 688 689 690 691 692 693 694 695 696 697 698 699 700 701 702 703 704 705 706 707 708 709 710 711 712 713 714 715 716 717 718 719 720 721 722 723 724 725 726 727 728 729 730 731 732 733 734 735 736 737 738 739 740 741 742 743 744 745 746 747 748 749 750 751 752 753 754 755 756 757 758 759 760 761 762 763 764 765 766 767 768 769 770 771 772 773 774 775 776 777 778 779 780 781 782 783 784 785 786 787 788 789 790 791 792 793 794 795 796 797 798 799 800 801 802 803 804 805 806 807 808 809 810 811 812 813 814 815 816 817 818 819 820 821 822 823 824 825 826 827 828 829 830 831 832 833 834 835 836 837 838 839 840 841 842 843 844 845 846 847
/* -*- 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/. */

#include <new>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include "PLDHashTable.h"
#include "mozilla/HashFunctions.h"
#include "mozilla/MathAlgorithms.h"
#include "nsAlgorithm.h"
#include "mozilla/Likely.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/ChaosMode.h"

using namespace mozilla;

#ifdef DEBUG

class AutoReadOp
{
  Checker& mChk;
public:
  explicit AutoReadOp(Checker& aChk) : mChk(aChk) { mChk.StartReadOp(); }
  ~AutoReadOp() { mChk.EndReadOp(); }
};

class AutoWriteOp
{
  Checker& mChk;
public:
  explicit AutoWriteOp(Checker& aChk) : mChk(aChk) { mChk.StartWriteOp(); }
  ~AutoWriteOp() { mChk.EndWriteOp(); }
};

class AutoIteratorRemovalOp
{
  Checker& mChk;
public:
  explicit AutoIteratorRemovalOp(Checker& aChk)
    : mChk(aChk)
  {
    mChk.StartIteratorRemovalOp();
  }
  ~AutoIteratorRemovalOp() { mChk.EndIteratorRemovalOp(); }
};

class AutoDestructorOp
{
  Checker& mChk;
public:
  explicit AutoDestructorOp(Checker& aChk)
    : mChk(aChk)
  {
    mChk.StartDestructorOp();
  }
  ~AutoDestructorOp() { mChk.EndDestructorOp(); }
};

#endif

/* static */ PLDHashNumber
PLDHashTable::HashStringKey(PLDHashTable* aTable, const void* aKey)
{
  return HashString(static_cast<const char*>(aKey));
}

/* static */ PLDHashNumber
PLDHashTable::HashVoidPtrKeyStub(PLDHashTable* aTable, const void* aKey)
{
  return (PLDHashNumber)(ptrdiff_t)aKey >> 2;
}

/* static */ bool
PLDHashTable::MatchEntryStub(PLDHashTable* aTable,
                             const PLDHashEntryHdr* aEntry,
                             const void* aKey)
{
  const PLDHashEntryStub* stub = (const PLDHashEntryStub*)aEntry;

  return stub->key == aKey;
}

/* static */ bool
PLDHashTable::MatchStringKey(PLDHashTable* aTable,
                             const PLDHashEntryHdr* aEntry,
                             const void* aKey)
{
  const PLDHashEntryStub* stub = (const PLDHashEntryStub*)aEntry;

  // XXX tolerate null keys on account of sloppy Mozilla callers.
  return stub->key == aKey ||
         (stub->key && aKey &&
          strcmp((const char*)stub->key, (const char*)aKey) == 0);
}

/* static */ void
PLDHashTable::MoveEntryStub(PLDHashTable* aTable,
                            const PLDHashEntryHdr* aFrom,
                            PLDHashEntryHdr* aTo)
{
  memcpy(aTo, aFrom, aTable->mEntrySize);
}

/* static */ void
PLDHashTable::ClearEntryStub(PLDHashTable* aTable, PLDHashEntryHdr* aEntry)
{
  memset(aEntry, 0, aTable->mEntrySize);
}

static const PLDHashTableOps gStubOps = {
  PLDHashTable::HashVoidPtrKeyStub,
  PLDHashTable::MatchEntryStub,
  PLDHashTable::MoveEntryStub,
  PLDHashTable::ClearEntryStub,
  nullptr
};

/* static */ const PLDHashTableOps*
PLDHashTable::StubOps()
{
  return &gStubOps;
}

static bool
SizeOfEntryStore(uint32_t aCapacity, uint32_t aEntrySize, uint32_t* aNbytes)
{
  uint64_t nbytes64 = uint64_t(aCapacity) * uint64_t(aEntrySize);
  *aNbytes = aCapacity * aEntrySize;
  return uint64_t(*aNbytes) == nbytes64;   // returns false on overflow
}

// Compute max and min load numbers (entry counts). We have a secondary max
// that allows us to overload a table reasonably if it cannot be grown further
// (i.e. if ChangeTable() fails). The table slows down drastically if the
// secondary max is too close to 1, but 0.96875 gives only a slight slowdown
// while allowing 1.3x more elements.
static inline uint32_t
MaxLoad(uint32_t aCapacity)
{
  return aCapacity - (aCapacity >> 2);  // == aCapacity * 0.75
}
static inline uint32_t
MaxLoadOnGrowthFailure(uint32_t aCapacity)
{
  return aCapacity - (aCapacity >> 5);  // == aCapacity * 0.96875
}
static inline uint32_t
MinLoad(uint32_t aCapacity)
{
  return aCapacity >> 2;                // == aCapacity * 0.25
}

// Compute the minimum capacity (and the Log2 of that capacity) for a table
// containing |aLength| elements while respecting the following contraints:
// - table must be at most 75% full;
// - capacity must be a power of two;
// - capacity cannot be too small.
static inline void
BestCapacity(uint32_t aLength, uint32_t* aCapacityOut,
             uint32_t* aLog2CapacityOut)
{
  // Compute the smallest capacity allowing |aLength| elements to be inserted
  // without rehashing.
  uint32_t capacity = (aLength * 4 + (3 - 1)) / 3; // == ceil(aLength * 4 / 3)
  if (capacity < PLDHashTable::kMinCapacity) {
    capacity = PLDHashTable::kMinCapacity;
  }

  // Round up capacity to next power-of-two.
  uint32_t log2 = CeilingLog2(capacity);
  capacity = 1u << log2;
  MOZ_ASSERT(capacity <= PLDHashTable::kMaxCapacity);

  *aCapacityOut = capacity;
  *aLog2CapacityOut = log2;
}

/* static */ MOZ_ALWAYS_INLINE uint32_t
PLDHashTable::HashShift(uint32_t aEntrySize, uint32_t aLength)
{
  if (aLength > kMaxInitialLength) {
    MOZ_CRASH("Initial length is too large");
  }

  uint32_t capacity, log2;
  BestCapacity(aLength, &capacity, &log2);

  uint32_t nbytes;
  if (!SizeOfEntryStore(capacity, aEntrySize, &nbytes)) {
    MOZ_CRASH("Initial entry store size is too large");
  }

  // Compute the hashShift value.
  return kHashBits - log2;
}

PLDHashTable::PLDHashTable(const PLDHashTableOps* aOps, uint32_t aEntrySize,
                           uint32_t aLength)
  : mOps(aOps)
  , mHashShift(HashShift(aEntrySize, aLength))
  , mEntrySize(aEntrySize)
  , mEntryCount(0)
  , mRemovedCount(0)
  , mEntryStore()
#ifdef DEBUG
  , mChecker()
#endif
{
}

PLDHashTable&
PLDHashTable::operator=(PLDHashTable&& aOther)
{
  if (this == &aOther) {
    return *this;
  }

  // Destruct |this|.
  this->~PLDHashTable();

  // |mOps| and |mEntrySize| are const so we can't assign them. Instead, we
  // require that they are equal. The justification for this is that they're
  // conceptually part of the type -- indeed, if PLDHashTable was a templated
  // type like nsTHashtable, they *would* be part of the type -- so it only
  // makes sense to assign in cases where they match.
  MOZ_RELEASE_ASSERT(mOps == aOther.mOps);
  MOZ_RELEASE_ASSERT(mEntrySize == aOther.mEntrySize);

  // Move non-const pieces over.
  mHashShift = Move(aOther.mHashShift);
  mEntryCount = Move(aOther.mEntryCount);
  mRemovedCount = Move(aOther.mRemovedCount);
  mEntryStore = Move(aOther.mEntryStore);
#ifdef DEBUG
  mChecker = Move(aOther.mChecker);
#endif

  // Clear up |aOther| so its destruction will be a no-op.
  {
#ifdef DEBUG
    AutoDestructorOp op(mChecker);
#endif
    aOther.mEntryStore.Set(nullptr);
  }

  return *this;
}

PLDHashNumber
PLDHashTable::Hash1(PLDHashNumber aHash0)
{
  return aHash0 >> mHashShift;
}

// Double hashing needs the second hash code to be relatively prime to table
// size, so we simply make hash2 odd.
void
PLDHashTable::Hash2(PLDHashNumber aHash,
                    uint32_t& aHash2Out, uint32_t& aSizeMaskOut)
{
  uint32_t sizeLog2 = kHashBits - mHashShift;
  aHash2Out = ((aHash << sizeLog2) >> mHashShift) | 1;
  aSizeMaskOut = (PLDHashNumber(1) << sizeLog2) - 1;
}

// Reserve mKeyHash 0 for free entries and 1 for removed-entry sentinels. Note
// that a removed-entry sentinel need be stored only if the removed entry had
// a colliding entry added after it. Therefore we can use 1 as the collision
// flag in addition to the removed-entry sentinel value. Multiplicative hash
// uses the high order bits of mKeyHash, so this least-significant reservation
// should not hurt the hash function's effectiveness much.

/* static */ MOZ_ALWAYS_INLINE bool
PLDHashTable::EntryIsFree(PLDHashEntryHdr* aEntry)
{
  return aEntry->mKeyHash == 0;
}
/* static */ MOZ_ALWAYS_INLINE bool
PLDHashTable::EntryIsRemoved(PLDHashEntryHdr* aEntry)
{
  return aEntry->mKeyHash == 1;
}
/* static */ MOZ_ALWAYS_INLINE bool
PLDHashTable::EntryIsLive(PLDHashEntryHdr* aEntry)
{
  return aEntry->mKeyHash >= 2;
}

/* static */ MOZ_ALWAYS_INLINE void
PLDHashTable::MarkEntryFree(PLDHashEntryHdr* aEntry)
{
  aEntry->mKeyHash = 0;
}
/* static */ MOZ_ALWAYS_INLINE void
PLDHashTable::MarkEntryRemoved(PLDHashEntryHdr* aEntry)
{
  aEntry->mKeyHash = 1;
}

// Match an entry's mKeyHash against an unstored one computed from a key.
/* static */ bool
PLDHashTable::MatchEntryKeyhash(PLDHashEntryHdr* aEntry, PLDHashNumber aKeyHash)
{
  return (aEntry->mKeyHash & ~kCollisionFlag) == aKeyHash;
}

// Compute the address of the indexed entry in table.
PLDHashEntryHdr*
PLDHashTable::AddressEntry(uint32_t aIndex)
{
  return reinterpret_cast<PLDHashEntryHdr*>(
    mEntryStore.Get() + aIndex * mEntrySize);
}

PLDHashTable::~PLDHashTable()
{
#ifdef DEBUG
  AutoDestructorOp op(mChecker);
#endif

  if (!mEntryStore.Get()) {
    return;
  }

  // Clear any remaining live entries.
  char* entryAddr = mEntryStore.Get();
  char* entryLimit = entryAddr + Capacity() * mEntrySize;
  while (entryAddr < entryLimit) {
    PLDHashEntryHdr* entry = (PLDHashEntryHdr*)entryAddr;
    if (EntryIsLive(entry)) {
      mOps->clearEntry(this, entry);
    }
    entryAddr += mEntrySize;
  }

  // Entry storage is freed last, by ~EntryStore().
}

void
PLDHashTable::ClearAndPrepareForLength(uint32_t aLength)
{
  // Get these values before the destructor clobbers them.
  const PLDHashTableOps* ops = mOps;
  uint32_t entrySize = mEntrySize;

  this->~PLDHashTable();
  new (this) PLDHashTable(ops, entrySize, aLength);
}

void
PLDHashTable::Clear()
{
  ClearAndPrepareForLength(kDefaultInitialLength);
}

// If |IsAdd| is true, the return value is always non-null and it may be a
// previously-removed entry. If |IsAdd| is false, the return value is null on a
// miss, and will never be a previously-removed entry on a hit. This
// distinction is a bit grotty but this function is hot enough that these
// differences are worthwhile.
template <PLDHashTable::SearchReason Reason>
PLDHashEntryHdr* PL_DHASH_FASTCALL
PLDHashTable::SearchTable(const void* aKey, PLDHashNumber aKeyHash)
{
  MOZ_ASSERT(mEntryStore.Get());
  NS_ASSERTION(!(aKeyHash & kCollisionFlag),
               "!(aKeyHash & kCollisionFlag)");

  // Compute the primary hash address.
  PLDHashNumber hash1 = Hash1(aKeyHash);
  PLDHashEntryHdr* entry = AddressEntry(hash1);

  // Miss: return space for a new entry.
  if (EntryIsFree(entry)) {
    return (Reason == ForAdd) ? entry : nullptr;
  }

  // Hit: return entry.
  PLDHashMatchEntry matchEntry = mOps->matchEntry;
  if (MatchEntryKeyhash(entry, aKeyHash) &&
      matchEntry(this, entry, aKey)) {
    return entry;
  }

  // Collision: double hash.
  PLDHashNumber hash2;
  uint32_t sizeMask;
  Hash2(aKeyHash, hash2, sizeMask);

  // Save the first removed entry pointer so Add() can recycle it. (Only used
  // if Reason==ForAdd.)
  PLDHashEntryHdr* firstRemoved = nullptr;

  for (;;) {
    if (Reason == ForAdd) {
      if (MOZ_UNLIKELY(EntryIsRemoved(entry))) {
        if (!firstRemoved) {
          firstRemoved = entry;
        }
      } else {
        entry->mKeyHash |= kCollisionFlag;
      }
    }

    hash1 -= hash2;
    hash1 &= sizeMask;

    entry = AddressEntry(hash1);
    if (EntryIsFree(entry)) {
      return (Reason == ForAdd) ? (firstRemoved ? firstRemoved : entry)
                                : nullptr;
    }

    if (MatchEntryKeyhash(entry, aKeyHash) &&
        matchEntry(this, entry, aKey)) {
      return entry;
    }
  }

  // NOTREACHED
  return nullptr;
}

// This is a copy of SearchTable(), used by ChangeTable(), hardcoded to
//   1. assume |aIsAdd| is true,
//   2. assume that |aKey| will never match an existing entry, and
//   3. assume that no entries have been removed from the current table
//      structure.
// Avoiding the need for |aKey| means we can avoid needing a way to map entries
// to keys, which means callers can use complex key types more easily.
PLDHashEntryHdr* PL_DHASH_FASTCALL
PLDHashTable::FindFreeEntry(PLDHashNumber aKeyHash)
{
  MOZ_ASSERT(mEntryStore.Get());
  NS_ASSERTION(!(aKeyHash & kCollisionFlag),
               "!(aKeyHash & kCollisionFlag)");

  // Compute the primary hash address.
  PLDHashNumber hash1 = Hash1(aKeyHash);
  PLDHashEntryHdr* entry = AddressEntry(hash1);

  // Miss: return space for a new entry.
  if (EntryIsFree(entry)) {
    return entry;
  }

  // Collision: double hash.
  PLDHashNumber hash2;
  uint32_t sizeMask;
  Hash2(aKeyHash, hash2, sizeMask);

  for (;;) {
    NS_ASSERTION(!EntryIsRemoved(entry),
                 "!EntryIsRemoved(entry)");
    entry->mKeyHash |= kCollisionFlag;

    hash1 -= hash2;
    hash1 &= sizeMask;

    entry = AddressEntry(hash1);
    if (EntryIsFree(entry)) {
      return entry;
    }
  }

  // NOTREACHED
}

bool
PLDHashTable::ChangeTable(int32_t aDeltaLog2)
{
  MOZ_ASSERT(mEntryStore.Get());

  // Look, but don't touch, until we succeed in getting new entry store.
  int32_t oldLog2 = kHashBits - mHashShift;
  int32_t newLog2 = oldLog2 + aDeltaLog2;
  uint32_t newCapacity = 1u << newLog2;
  if (newCapacity > kMaxCapacity) {
    return false;
  }

  uint32_t nbytes;
  if (!SizeOfEntryStore(newCapacity, mEntrySize, &nbytes)) {
    return false;   // overflowed
  }

  char* newEntryStore = (char*)malloc(nbytes);
  if (!newEntryStore) {
    return false;
  }

  // We can't fail from here on, so update table parameters.
  mHashShift = kHashBits - newLog2;
  mRemovedCount = 0;

  // Assign the new entry store to table.
  memset(newEntryStore, 0, nbytes);
  char* oldEntryStore;
  char* oldEntryAddr;
  oldEntryAddr = oldEntryStore = mEntryStore.Get();
  mEntryStore.Set(newEntryStore);
  PLDHashMoveEntry moveEntry = mOps->moveEntry;

  // Copy only live entries, leaving removed ones behind.
  uint32_t oldCapacity = 1u << oldLog2;
  for (uint32_t i = 0; i < oldCapacity; ++i) {
    PLDHashEntryHdr* oldEntry = (PLDHashEntryHdr*)oldEntryAddr;
    if (EntryIsLive(oldEntry)) {
      oldEntry->mKeyHash &= ~kCollisionFlag;
      PLDHashEntryHdr* newEntry = FindFreeEntry(oldEntry->mKeyHash);
      NS_ASSERTION(EntryIsFree(newEntry), "EntryIsFree(newEntry)");
      moveEntry(this, oldEntry, newEntry);
      newEntry->mKeyHash = oldEntry->mKeyHash;
    }
    oldEntryAddr += mEntrySize;
  }

  free(oldEntryStore);
  return true;
}

MOZ_ALWAYS_INLINE PLDHashNumber
PLDHashTable::ComputeKeyHash(const void* aKey)
{
  MOZ_ASSERT(mEntryStore.Get());

  PLDHashNumber keyHash = mOps->hashKey(this, aKey);
  keyHash *= kGoldenRatio;

  // Avoid 0 and 1 hash codes, they indicate free and removed entries.
  if (keyHash < 2) {
    keyHash -= 2;
  }
  keyHash &= ~kCollisionFlag;

  return keyHash;
}

PLDHashEntryHdr*
PLDHashTable::Search(const void* aKey)
{
#ifdef DEBUG
  AutoReadOp op(mChecker);
#endif

  PLDHashEntryHdr* entry = mEntryStore.Get()
                         ? SearchTable<ForSearchOrRemove>(aKey,
                                                          ComputeKeyHash(aKey))
                         : nullptr;
  return entry;
}

PLDHashEntryHdr*
PLDHashTable::Add(const void* aKey, const mozilla::fallible_t&)
{
#ifdef DEBUG
  AutoWriteOp op(mChecker);
#endif

  // Allocate the entry storage if it hasn't already been allocated.
  if (!mEntryStore.Get()) {
    uint32_t nbytes;
    // We already checked this in the constructor, so it must still be true.
    MOZ_RELEASE_ASSERT(SizeOfEntryStore(CapacityFromHashShift(), mEntrySize,
                                        &nbytes));
    mEntryStore.Set((char*)malloc(nbytes));
    if (!mEntryStore.Get()) {
      return nullptr;
    }
    memset(mEntryStore.Get(), 0, nbytes);
  }

  // If alpha is >= .75, grow or compress the table. If aKey is already in the
  // table, we may grow once more than necessary, but only if we are on the
  // edge of being overloaded.
  uint32_t capacity = Capacity();
  if (mEntryCount + mRemovedCount >= MaxLoad(capacity)) {
    // Compress if a quarter or more of all entries are removed.
    int deltaLog2;
    if (mRemovedCount >= capacity >> 2) {
      deltaLog2 = 0;
    } else {
      deltaLog2 = 1;
    }

    // Grow or compress the table. If ChangeTable() fails, allow overloading up
    // to the secondary max. Once we hit the secondary max, return null.
    if (!ChangeTable(deltaLog2) &&
        mEntryCount + mRemovedCount >= MaxLoadOnGrowthFailure(capacity)) {
      return nullptr;
    }
  }

  // Look for entry after possibly growing, so we don't have to add it,
  // then skip it while growing the table and re-add it after.
  PLDHashNumber keyHash = ComputeKeyHash(aKey);
  PLDHashEntryHdr* entry = SearchTable<ForAdd>(aKey, keyHash);
  if (!EntryIsLive(entry)) {
    // Initialize the entry, indicating that it's no longer free.
    if (EntryIsRemoved(entry)) {
      mRemovedCount--;
      keyHash |= kCollisionFlag;
    }
    if (mOps->initEntry) {
      mOps->initEntry(entry, aKey);
    }
    entry->mKeyHash = keyHash;
    mEntryCount++;
  }

  return entry;
}

PLDHashEntryHdr*
PLDHashTable::Add(const void* aKey)
{
  PLDHashEntryHdr* entry = Add(aKey, fallible);
  if (!entry) {
    if (!mEntryStore.Get()) {
      // We OOM'd while allocating the initial entry storage.
      uint32_t nbytes;
      (void) SizeOfEntryStore(CapacityFromHashShift(), mEntrySize, &nbytes);
      NS_ABORT_OOM(nbytes);
    } else {
      // We failed to resize the existing entry storage, either due to OOM or
      // because we exceeded the maximum table capacity or size; report it as
      // an OOM. The multiplication by 2 gets us the size we tried to allocate,
      // which is double the current size.
      NS_ABORT_OOM(2 * EntrySize() * EntryCount());
    }
  }
  return entry;
}

void
PLDHashTable::Remove(const void* aKey)
{
#ifdef DEBUG
  AutoWriteOp op(mChecker);
#endif

  PLDHashEntryHdr* entry = mEntryStore.Get()
                         ? SearchTable<ForSearchOrRemove>(aKey,
                                                          ComputeKeyHash(aKey))
                         : nullptr;
  if (entry) {
    RawRemove(entry);
    ShrinkIfAppropriate();
  }
}

void
PLDHashTable::RemoveEntry(PLDHashEntryHdr* aEntry)
{
#ifdef DEBUG
  AutoWriteOp op(mChecker);
#endif

  RawRemove(aEntry);
  ShrinkIfAppropriate();
}

void
PLDHashTable::RawRemove(PLDHashEntryHdr* aEntry)
{
  // Unfortunately, we can only do weak checking here. That's because
  // RawRemove() can be called legitimately while an Enumerate() call is
  // active, which doesn't fit well into how Checker's mState variable works.
  MOZ_ASSERT(mChecker.IsWritable());

  MOZ_ASSERT(mEntryStore.Get());

  MOZ_ASSERT(EntryIsLive(aEntry), "EntryIsLive(aEntry)");

  // Load keyHash first in case clearEntry() goofs it.
  PLDHashNumber keyHash = aEntry->mKeyHash;
  mOps->clearEntry(this, aEntry);
  if (keyHash & kCollisionFlag) {
    MarkEntryRemoved(aEntry);
    mRemovedCount++;
  } else {
    MarkEntryFree(aEntry);
  }
  mEntryCount--;
}

// Shrink or compress if a quarter or more of all entries are removed, or if the
// table is underloaded according to the minimum alpha, and is not minimal-size
// already.
void
PLDHashTable::ShrinkIfAppropriate()
{
  uint32_t capacity = Capacity();
  if (mRemovedCount >= capacity >> 2 ||
      (capacity > kMinCapacity && mEntryCount <= MinLoad(capacity))) {
    uint32_t log2;
    BestCapacity(mEntryCount, &capacity, &log2);

    int32_t deltaLog2 = log2 - (kHashBits - mHashShift);
    MOZ_ASSERT(deltaLog2 <= 0);

    (void) ChangeTable(deltaLog2);
  }
}

size_t
PLDHashTable::ShallowSizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const
{
#ifdef DEBUG
  AutoReadOp op(mChecker);
#endif

  return aMallocSizeOf(mEntryStore.Get());
}

size_t
PLDHashTable::ShallowSizeOfIncludingThis(MallocSizeOf aMallocSizeOf) const
{
  return aMallocSizeOf(this) + ShallowSizeOfExcludingThis(aMallocSizeOf);
}

PLDHashTable::Iterator::Iterator(Iterator&& aOther)
  : mTable(aOther.mTable)
  , mStart(aOther.mStart)
  , mLimit(aOther.mLimit)
  , mCurrent(aOther.mCurrent)
  , mNexts(aOther.mNexts)
  , mNextsLimit(aOther.mNextsLimit)
  , mHaveRemoved(aOther.mHaveRemoved)
{
  // No need to change |mChecker| here.
  aOther.mTable = nullptr;
  aOther.mStart = nullptr;
  aOther.mLimit = nullptr;
  aOther.mCurrent = nullptr;
  aOther.mNexts = 0;
  aOther.mNextsLimit = 0;
  aOther.mHaveRemoved = false;
}

PLDHashTable::Iterator::Iterator(PLDHashTable* aTable)
  : mTable(aTable)
  , mStart(mTable->mEntryStore.Get())
  , mLimit(mTable->mEntryStore.Get() + mTable->Capacity() * mTable->mEntrySize)
  , mCurrent(mTable->mEntryStore.Get())
  , mNexts(0)
  , mNextsLimit(mTable->EntryCount())
  , mHaveRemoved(false)
{
#ifdef DEBUG
  mTable->mChecker.StartReadOp();
#endif

  if (ChaosMode::isActive(ChaosFeature::HashTableIteration) &&
      mTable->Capacity() > 0) {
    // Start iterating at a random entry. It would be even more chaotic to
    // iterate in fully random order, but that's harder.
    mCurrent += ChaosMode::randomUint32LessThan(mTable->Capacity()) *
                mTable->mEntrySize;
  }

  // Advance to the first live entry, if there is one.
  if (!Done()) {
    while (IsOnNonLiveEntry()) {
      MoveToNextEntry();
    }
  }
}

PLDHashTable::Iterator::~Iterator()
{
  if (mTable) {
    if (mHaveRemoved) {
      mTable->ShrinkIfAppropriate();
    }
#ifdef DEBUG
    mTable->mChecker.EndReadOp();
#endif
  }
}

bool
PLDHashTable::Iterator::Done() const
{
  return mNexts == mNextsLimit;
}

MOZ_ALWAYS_INLINE bool
PLDHashTable::Iterator::IsOnNonLiveEntry() const
{
  MOZ_ASSERT(!Done());
  return !EntryIsLive(reinterpret_cast<PLDHashEntryHdr*>(mCurrent));
}

MOZ_ALWAYS_INLINE void
PLDHashTable::Iterator::MoveToNextEntry()
{
  mCurrent += mTable->mEntrySize;
  if (mCurrent == mLimit) {
    mCurrent = mStart;  // Wrap-around. Possible due to Chaos Mode.
  }
}

PLDHashEntryHdr*
PLDHashTable::Iterator::Get() const
{
  MOZ_ASSERT(!Done());

  PLDHashEntryHdr* entry = reinterpret_cast<PLDHashEntryHdr*>(mCurrent);
  MOZ_ASSERT(EntryIsLive(entry));
  return entry;
}

void
PLDHashTable::Iterator::Next()
{
  MOZ_ASSERT(!Done());

  mNexts++;

  // Advance to the next live entry, if there is one.
  if (!Done()) {
    do {
      MoveToNextEntry();
    } while (IsOnNonLiveEntry());
  }
}

void
PLDHashTable::Iterator::Remove()
{
  // This cast is needed for the same reason as the one in the destructor.
  mTable->RawRemove(Get());
  mHaveRemoved = true;
}

#ifdef DEBUG
void
PLDHashTable::MarkImmutable()
{
  mChecker.SetNonWritable();
}
#endif