Adding upstream version 86.0.1.upstream/86.0.1upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 808 insertions, 0 deletions

diff --git a/xpcom/ds/PLDHashTable.cpp b/xpcom/ds/PLDHashTable.cpp
new file mode 100644
index 0000000000..07a46c95ed
--- /dev/null
+++ b/xpcom/ds/PLDHashTable.cpp
@@ -0,0 +1,808 @@
+/* -*- 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 "mozilla/OperatorNewExtensions.h"
+#include "nsAlgorithm.h"
+#include "nsPointerHashKeys.h"
+#include "mozilla/Likely.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/ChaosMode.h"
+
+using namespace mozilla;
+
+#ifdef MOZ_HASH_TABLE_CHECKS_ENABLED
+
+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(const void* aKey) {
+  return HashString(static_cast<const char*>(aKey));
+}
+
+/* static */
+PLDHashNumber PLDHashTable::HashVoidPtrKeyStub(const void* aKey) {
+  return nsPtrHashKey<void>::HashKey(aKey);
+}
+
+/* static */
+bool PLDHashTable::MatchEntryStub(const PLDHashEntryHdr* aEntry,
+                                  const void* aKey) {
+  const PLDHashEntryStub* stub = (const PLDHashEntryStub*)aEntry;
+
+  return stub->key == aKey;
+}
+
+/* static */
+bool PLDHashTable::MatchStringKey(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) {
+  uint32_t slotSize = aEntrySize + sizeof(PLDHashNumber);
+  uint64_t nbytes64 = uint64_t(aCapacity) * uint64_t(slotSize);
+  *aNbytes = aCapacity * slotSize;
+  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) {
+  // Callers should ensure this is true.
+  MOZ_ASSERT(aLength <= PLDHashTable::kMaxInitialLength);
+
+  // 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 kPLDHashNumberBits - log2;
+}
+
+PLDHashTable::PLDHashTable(const PLDHashTableOps* aOps, uint32_t aEntrySize,
+                           uint32_t aLength)
+    : mOps(aOps),
+      mEntryStore(),
+      mGeneration(0),
+      mHashShift(HashShift(aEntrySize, aLength)),
+      mEntrySize(aEntrySize),
+      mEntryCount(0),
+      mRemovedCount(0) {
+  // An entry size greater than 0xff is unlikely, but let's check anyway. If
+  // you hit this, your hashtable would waste lots of space for unused entries
+  // and you should change your hash table's entries to pointers.
+  if (aEntrySize != uint32_t(mEntrySize)) {
+    MOZ_CRASH("Entry size is too large");
+  }
+}
+
+PLDHashTable& PLDHashTable::operator=(PLDHashTable&& aOther) {
+  if (this == &aOther) {
+    return *this;
+  }
+
+  // |mOps| and |mEntrySize| are required to stay the same, 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 || !mOps);
+  MOZ_RELEASE_ASSERT(mEntrySize == aOther.mEntrySize || !mEntrySize);
+
+  // Reconstruct |this|.
+  const PLDHashTableOps* ops = aOther.mOps;
+  this->~PLDHashTable();
+  new (KnownNotNull, this) PLDHashTable(ops, aOther.mEntrySize, 0);
+
+  // Move non-const pieces over.
+  mHashShift = std::move(aOther.mHashShift);
+  mEntryCount = std::move(aOther.mEntryCount);
+  mRemovedCount = std::move(aOther.mRemovedCount);
+  mEntryStore.Set(aOther.mEntryStore.Get(), &mGeneration);
+#ifdef MOZ_HASH_TABLE_CHECKS_ENABLED
+  mChecker = std::move(aOther.mChecker);
+#endif
+
+  // Clear up |aOther| so its destruction will be a no-op and it reports being
+  // empty.
+  {
+#ifdef MOZ_HASH_TABLE_CHECKS_ENABLED
+    AutoDestructorOp op(mChecker);
+#endif
+    aOther.mEntryCount = 0;
+    aOther.mEntryStore.Set(nullptr, &aOther.mGeneration);
+  }
+
+  return *this;
+}
+
+PLDHashNumber PLDHashTable::Hash1(PLDHashNumber aHash0) const {
+  return aHash0 >> mHashShift;
+}
+
+void PLDHashTable::Hash2(PLDHashNumber aHash0, uint32_t& aHash2Out,
+                         uint32_t& aSizeMaskOut) const {
+  uint32_t sizeLog2 = kPLDHashNumberBits - mHashShift;
+  uint32_t sizeMask = (PLDHashNumber(1) << sizeLog2) - 1;
+  aSizeMaskOut = sizeMask;
+
+  // The incoming aHash0 always has the low bit unset (since we leave it
+  // free for the collision flag), and should have reasonably random
+  // data in the other 31 bits.  We used the high bits of aHash0 for
+  // Hash1, so we use the low bits here.  If the table size is large,
+  // the bits we use may overlap, but that's still more random than
+  // filling with 0s.
+  //
+  // Double hashing needs the second hash code to be relatively prime to table
+  // size, so we simply make hash2 odd.
+  //
+  // This also conveniently covers up the fact that we have the low bit
+  // unset since aHash0 has the low bit unset.
+  aHash2Out = (aHash0 & sizeMask) | 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.
+
+// Match an entry's mKeyHash against an unstored one computed from a key.
+/* static */
+bool PLDHashTable::MatchSlotKeyhash(Slot& aSlot, const PLDHashNumber aKeyHash) {
+  return (aSlot.KeyHash() & ~kCollisionFlag) == aKeyHash;
+}
+
+// Compute the address of the indexed entry in table.
+auto PLDHashTable::SlotForIndex(uint32_t aIndex) const -> Slot {
+  return mEntryStore.SlotForIndex(aIndex, mEntrySize, CapacityFromHashShift());
+}
+
+PLDHashTable::~PLDHashTable() {
+#ifdef MOZ_HASH_TABLE_CHECKS_ENABLED
+  AutoDestructorOp op(mChecker);
+#endif
+
+  if (!mEntryStore.IsAllocated()) {
+    return;
+  }
+
+  // Clear any remaining live entries.
+  mEntryStore.ForEachSlot(Capacity(), mEntrySize, [&](const Slot& aSlot) {
+    if (aSlot.IsLive()) {
+      mOps->clearEntry(this, aSlot.ToEntry());
+    }
+  });
+
+  // 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 (KnownNotNull, this) PLDHashTable(ops, entrySize, aLength);
+}
+
+void PLDHashTable::Clear() { ClearAndPrepareForLength(kDefaultInitialLength); }
+
+// If |Reason| is |ForAdd|, the return value is always non-null and it may be
+// a previously-removed entry. If |Reason| is |ForSearchOrRemove|, 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. (It's also hot enough that
+// MOZ_ALWAYS_INLINE makes a significant difference.)
+template <PLDHashTable::SearchReason Reason, typename Success, typename Failure>
+MOZ_ALWAYS_INLINE auto PLDHashTable::SearchTable(const void* aKey,
+                                                 PLDHashNumber aKeyHash,
+                                                 Success&& aSuccess,
+                                                 Failure&& aFailure) const {
+  MOZ_ASSERT(mEntryStore.IsAllocated());
+  NS_ASSERTION(!(aKeyHash & kCollisionFlag), "!(aKeyHash & kCollisionFlag)");
+
+  // Compute the primary hash address.
+  PLDHashNumber hash1 = Hash1(aKeyHash);
+  Slot slot = SlotForIndex(hash1);
+
+  // Miss: return space for a new entry.
+  if (slot.IsFree()) {
+    return (Reason == ForAdd) ? aSuccess(slot) : aFailure();
+  }
+
+  // Hit: return entry.
+  PLDHashMatchEntry matchEntry = mOps->matchEntry;
+  if (MatchSlotKeyhash(slot, aKeyHash)) {
+    PLDHashEntryHdr* e = slot.ToEntry();
+    if (matchEntry(e, aKey)) {
+      return aSuccess(slot);
+    }
+  }
+
+  // Collision: double hash.
+  PLDHashNumber hash2;
+  uint32_t sizeMask;
+  Hash2(aKeyHash, hash2, sizeMask);
+
+  // Save the first removed entry slot so Add() can recycle it. (Only used
+  // if Reason==ForAdd.)
+  Maybe<Slot> firstRemoved;
+
+  for (;;) {
+    if (Reason == ForAdd && !firstRemoved) {
+      if (MOZ_UNLIKELY(slot.IsRemoved())) {
+        firstRemoved.emplace(slot);
+      } else {
+        slot.MarkColliding();
+      }
+    }
+
+    hash1 -= hash2;
+    hash1 &= sizeMask;
+
+    slot = SlotForIndex(hash1);
+    if (slot.IsFree()) {
+      if (Reason != ForAdd) {
+        return aFailure();
+      }
+      return aSuccess(firstRemoved.refOr(slot));
+    }
+
+    if (MatchSlotKeyhash(slot, aKeyHash)) {
+      PLDHashEntryHdr* e = slot.ToEntry();
+      if (matchEntry(e, aKey)) {
+        return aSuccess(slot);
+      }
+    }
+  }
+
+  // NOTREACHED
+  return aFailure();
+}
+
+// This is a copy of SearchTable(), used by ChangeTable(), hardcoded to
+//   1. assume |Reason| is |ForAdd|,
+//   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.
+MOZ_ALWAYS_INLINE auto PLDHashTable::FindFreeSlot(PLDHashNumber aKeyHash) const
+    -> Slot {
+  MOZ_ASSERT(mEntryStore.IsAllocated());
+  NS_ASSERTION(!(aKeyHash & kCollisionFlag), "!(aKeyHash & kCollisionFlag)");
+
+  // Compute the primary hash address.
+  PLDHashNumber hash1 = Hash1(aKeyHash);
+  Slot slot = SlotForIndex(hash1);
+
+  // Miss: return space for a new entry.
+  if (slot.IsFree()) {
+    return slot;
+  }
+
+  // Collision: double hash.
+  PLDHashNumber hash2;
+  uint32_t sizeMask;
+  Hash2(aKeyHash, hash2, sizeMask);
+
+  for (;;) {
+    MOZ_ASSERT(!slot.IsRemoved());
+    slot.MarkColliding();
+
+    hash1 -= hash2;
+    hash1 &= sizeMask;
+
+    slot = SlotForIndex(hash1);
+    if (slot.IsFree()) {
+      return slot;
+    }
+  }
+
+  // NOTREACHED
+}
+
+bool PLDHashTable::ChangeTable(int32_t aDeltaLog2) {
+  MOZ_ASSERT(mEntryStore.IsAllocated());
+
+  // Look, but don't touch, until we succeed in getting new entry store.
+  int32_t oldLog2 = kPLDHashNumberBits - 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*)calloc(1, nbytes);
+  if (!newEntryStore) {
+    return false;
+  }
+
+  // We can't fail from here on, so update table parameters.
+  mHashShift = kPLDHashNumberBits - newLog2;
+  mRemovedCount = 0;
+
+  // Assign the new entry store to table.
+  char* oldEntryStore = mEntryStore.Get();
+  mEntryStore.Set(newEntryStore, &mGeneration);
+  PLDHashMoveEntry moveEntry = mOps->moveEntry;
+
+  // Copy only live entries, leaving removed ones behind.
+  uint32_t oldCapacity = 1u << oldLog2;
+  EntryStore::ForEachSlot(
+      oldEntryStore, oldCapacity, mEntrySize, [&](const Slot& slot) {
+        if (slot.IsLive()) {
+          const PLDHashNumber key = slot.KeyHash() & ~kCollisionFlag;
+          Slot newSlot = FindFreeSlot(key);
+          MOZ_ASSERT(newSlot.IsFree());
+          moveEntry(this, slot.ToEntry(), newSlot.ToEntry());
+          newSlot.SetKeyHash(key);
+        }
+      });
+
+  free(oldEntryStore);
+  return true;
+}
+
+MOZ_ALWAYS_INLINE PLDHashNumber
+PLDHashTable::ComputeKeyHash(const void* aKey) const {
+  MOZ_ASSERT(mEntryStore.IsAllocated());
+
+  PLDHashNumber keyHash = mozilla::ScrambleHashCode(mOps->hashKey(aKey));
+
+  // 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) const {
+#ifdef MOZ_HASH_TABLE_CHECKS_ENABLED
+  AutoReadOp op(mChecker);
+#endif
+
+  if (!mEntryStore.IsAllocated()) {
+    return nullptr;
+  }
+
+  return SearchTable<ForSearchOrRemove>(
+      aKey, ComputeKeyHash(aKey),
+      [&](Slot& slot) -> PLDHashEntryHdr* { return slot.ToEntry(); },
+      [&]() -> PLDHashEntryHdr* { return nullptr; });
+}
+
+PLDHashEntryHdr* PLDHashTable::Add(const void* aKey,
+                                   const mozilla::fallible_t&) {
+#ifdef MOZ_HASH_TABLE_CHECKS_ENABLED
+  AutoWriteOp op(mChecker);
+#endif
+
+  // Allocate the entry storage if it hasn't already been allocated.
+  if (!mEntryStore.IsAllocated()) {
+    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*)calloc(1, nbytes), &mGeneration);
+    if (!mEntryStore.IsAllocated()) {
+      return nullptr;
+    }
+  }
+
+  // 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);
+  Slot slot = SearchTable<ForAdd>(
+      aKey, keyHash, [&](Slot& found) -> Slot { return found; },
+      [&]() -> Slot {
+        MOZ_CRASH("Nope");
+        return Slot(nullptr, nullptr);
+      });
+  if (!slot.IsLive()) {
+    // Initialize the slot, indicating that it's no longer free.
+    if (slot.IsRemoved()) {
+      mRemovedCount--;
+      keyHash |= kCollisionFlag;
+    }
+    if (mOps->initEntry) {
+      mOps->initEntry(slot.ToEntry(), aKey);
+    }
+    slot.SetKeyHash(keyHash);
+    mEntryCount++;
+  }
+
+  return slot.ToEntry();
+}
+
+PLDHashEntryHdr* PLDHashTable::Add(const void* aKey) {
+  PLDHashEntryHdr* entry = Add(aKey, fallible);
+  if (!entry) {
+    if (!mEntryStore.IsAllocated()) {
+      // 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 MOZ_HASH_TABLE_CHECKS_ENABLED
+  AutoWriteOp op(mChecker);
+#endif
+
+  if (!mEntryStore.IsAllocated()) {
+    return;
+  }
+
+  PLDHashNumber keyHash = ComputeKeyHash(aKey);
+  SearchTable<ForSearchOrRemove>(
+      aKey, keyHash,
+      [&](Slot& slot) {
+        RawRemove(slot);
+        ShrinkIfAppropriate();
+      },
+      [&]() {
+        // Do nothing.
+      });
+}
+
+void PLDHashTable::RemoveEntry(PLDHashEntryHdr* aEntry) {
+#ifdef MOZ_HASH_TABLE_CHECKS_ENABLED
+  AutoWriteOp op(mChecker);
+#endif
+
+  RawRemove(aEntry);
+  ShrinkIfAppropriate();
+}
+
+void PLDHashTable::RawRemove(PLDHashEntryHdr* aEntry) {
+  Slot slot(mEntryStore.SlotForPLDHashEntry(aEntry, Capacity(), mEntrySize));
+  RawRemove(slot);
+}
+
+void PLDHashTable::RawRemove(Slot& aSlot) {
+  // 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.IsAllocated());
+
+  MOZ_ASSERT(aSlot.IsLive());
+
+  // Load keyHash first in case clearEntry() goofs it.
+  PLDHashEntryHdr* entry = aSlot.ToEntry();
+  PLDHashNumber keyHash = aSlot.KeyHash();
+  mOps->clearEntry(this, entry);
+  if (keyHash & kCollisionFlag) {
+    aSlot.MarkRemoved();
+    mRemovedCount++;
+  } else {
+    aSlot.MarkFree();
+  }
+  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 - (kPLDHashNumberBits - mHashShift);
+    MOZ_ASSERT(deltaLog2 <= 0);
+
+    (void)ChangeTable(deltaLog2);
+  }
+}
+
+size_t PLDHashTable::ShallowSizeOfExcludingThis(
+    MallocSizeOf aMallocSizeOf) const {
+#ifdef MOZ_HASH_TABLE_CHECKS_ENABLED
+  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),
+      mCurrent(aOther.mCurrent),
+      mNexts(aOther.mNexts),
+      mNextsLimit(aOther.mNextsLimit),
+      mHaveRemoved(aOther.mHaveRemoved),
+      mEntrySize(aOther.mEntrySize) {
+  // No need to change |mChecker| here.
+  aOther.mTable = nullptr;
+  // We don't really have the concept of a null slot, so leave mCurrent.
+  aOther.mNexts = 0;
+  aOther.mNextsLimit = 0;
+  aOther.mHaveRemoved = false;
+  aOther.mEntrySize = 0;
+}
+
+PLDHashTable::Iterator::Iterator(PLDHashTable* aTable)
+    : mTable(aTable),
+      mCurrent(mTable->mEntryStore.SlotForIndex(0, mTable->mEntrySize,
+                                                mTable->Capacity())),
+      mNexts(0),
+      mNextsLimit(mTable->EntryCount()),
+      mHaveRemoved(false),
+      mEntrySize(aTable->mEntrySize) {
+#ifdef MOZ_HASH_TABLE_CHECKS_ENABLED
+  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.
+    uint32_t capacity = mTable->CapacityFromHashShift();
+    uint32_t i = ChaosMode::randomUint32LessThan(capacity);
+    mCurrent =
+        mTable->mEntryStore.SlotForIndex(i, mTable->mEntrySize, capacity);
+  }
+
+  // Advance to the first live entry, if there is one.
+  if (!Done() && IsOnNonLiveEntry()) {
+    MoveToNextLiveEntry();
+  }
+}
+
+PLDHashTable::Iterator::Iterator(PLDHashTable* aTable, EndIteratorTag aTag)
+    : mTable(aTable),
+      mCurrent(mTable->mEntryStore.SlotForIndex(0, mTable->mEntrySize,
+                                                mTable->Capacity())),
+      mNexts(mTable->EntryCount()),
+      mNextsLimit(mTable->EntryCount()),
+      mHaveRemoved(false),
+      mEntrySize(aTable->mEntrySize) {
+#ifdef MOZ_HASH_TABLE_CHECKS_ENABLED
+  mTable->mChecker.StartReadOp();
+#endif
+
+  MOZ_ASSERT(Done());
+}
+
+PLDHashTable::Iterator::Iterator(const Iterator& aOther)
+    : mTable(aOther.mTable),
+      mCurrent(aOther.mCurrent),
+      mNexts(aOther.mNexts),
+      mNextsLimit(aOther.mNextsLimit),
+      mHaveRemoved(aOther.mHaveRemoved),
+      mEntrySize(aOther.mEntrySize) {
+  // TODO: Is this necessary?
+  MOZ_ASSERT(!mHaveRemoved);
+
+#ifdef MOZ_HASH_TABLE_CHECKS_ENABLED
+  mTable->mChecker.StartReadOp();
+#endif
+}
+
+PLDHashTable::Iterator::~Iterator() {
+  if (mTable) {
+    if (mHaveRemoved) {
+      mTable->ShrinkIfAppropriate();
+    }
+#ifdef MOZ_HASH_TABLE_CHECKS_ENABLED
+    mTable->mChecker.EndReadOp();
+#endif
+  }
+}
+
+MOZ_ALWAYS_INLINE bool PLDHashTable::Iterator::IsOnNonLiveEntry() const {
+  MOZ_ASSERT(!Done());
+  return !mCurrent.IsLive();
+}
+
+void PLDHashTable::Iterator::Next() {
+  MOZ_ASSERT(!Done());
+
+  mNexts++;
+
+  // Advance to the next live entry, if there is one.
+  if (!Done()) {
+    MoveToNextLiveEntry();
+  }
+}
+
+MOZ_ALWAYS_INLINE void PLDHashTable::Iterator::MoveToNextLiveEntry() {
+  // Chaos mode requires wraparound to cover all possible entries, so we can't
+  // simply move to the next live entry and stop when we hit the end of the
+  // entry store. But we don't want to introduce extra branches into our inner
+  // loop. So we are going to exploit the structure of the entry store in this
+  // method to implement an efficient inner loop.
+  //
+  // The idea is that since we are really only iterating through the stored
+  // hashes and because we know that there are a power-of-two number of
+  // hashes, we can use masking to implement the wraparound for us. This
+  // method does have the downside of needing to recalculate where the
+  // associated entry is once we've found it, but that seems OK.
+
+  // Our current slot and its associated hash.
+  Slot slot = mCurrent;
+  PLDHashNumber* p = slot.HashPtr();
+  const uint32_t capacity = mTable->CapacityFromHashShift();
+  const uint32_t mask = capacity - 1;
+  auto hashes = reinterpret_cast<PLDHashNumber*>(mTable->mEntryStore.Get());
+  uint32_t slotIndex = p - hashes;
+
+  do {
+    slotIndex = (slotIndex + 1) & mask;
+  } while (!Slot::IsLiveHash(hashes[slotIndex]));
+
+  // slotIndex now indicates where a live slot is. Rematerialize the entry
+  // and the slot.
+  mCurrent = mTable->mEntryStore.SlotForIndex(slotIndex, mEntrySize, capacity);
+}
+
+void PLDHashTable::Iterator::Remove() {
+  mTable->RawRemove(mCurrent);
+  mHaveRemoved = true;
+}