diff options
Diffstat (limited to '')
| -rw-r--r-- | xpcom/ds/PLDHashTable.cpp | 870 |
1 files changed, 870 insertions, 0 deletions
diff --git a/xpcom/ds/PLDHashTable.cpp b/xpcom/ds/PLDHashTable.cpp new file mode 100644 index 0000000000..2814813f68 --- /dev/null +++ b/xpcom/ds/PLDHashTable.cpp @@ -0,0 +1,870 @@ +/* -*- 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 "nsDebug.h" +#include "mozilla/HashFunctions.h" +#include "mozilla/MathAlgorithms.h" +#include "mozilla/OperatorNewExtensions.h" +#include "mozilla/ScopeExit.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 (if not trivially destructible). + if (mOps->clearEntry) { + 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& aFallible) { + auto maybeEntryHandle = MakeEntryHandle(aKey, aFallible); + if (!maybeEntryHandle) { + return nullptr; + } + return maybeEntryHandle->OrInsert([&aKey, this](PLDHashEntryHdr* entry) { + if (mOps->initEntry) { + mOps->initEntry(entry, aKey); + } + }); +} + +PLDHashEntryHdr* PLDHashTable::Add(const void* aKey) { + return MakeEntryHandle(aKey).OrInsert([&aKey, this](PLDHashEntryHdr* entry) { + if (mOps->initEntry) { + mOps->initEntry(entry, aKey); + } + }); +} + +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. + PLDHashNumber keyHash = aSlot.KeyHash(); + if (mOps->clearEntry) { + PLDHashEntryHdr* entry = aSlot.ToEntry(); + 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); +} + +mozilla::Maybe<PLDHashTable::EntryHandle> PLDHashTable::MakeEntryHandle( + const void* aKey, const mozilla::fallible_t&) { +#ifdef MOZ_HASH_TABLE_CHECKS_ENABLED + mChecker.StartWriteOp(); + auto endWriteOp = MakeScopeExit([&] { mChecker.EndWriteOp(); }); +#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 Nothing(); + } + } + + // 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 = 1; + if (mRemovedCount >= capacity >> 2) { + deltaLog2 = 0; + } + + // 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 Nothing(); + } + } + + // 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); + }); + + // The `EntryHandle` will handle ending the write op when it is destroyed. +#ifdef MOZ_HASH_TABLE_CHECKS_ENABLED + endWriteOp.release(); +#endif + + return Some(EntryHandle{this, keyHash, slot}); +} + +PLDHashTable::EntryHandle PLDHashTable::MakeEntryHandle(const void* aKey) { + auto res = MakeEntryHandle(aKey, fallible); + if (!res) { + 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 res.extract(); +} + +PLDHashTable::EntryHandle::EntryHandle(PLDHashTable* aTable, + PLDHashNumber aKeyHash, Slot aSlot) + : mTable(aTable), mKeyHash(aKeyHash), mSlot(aSlot) {} + +PLDHashTable::EntryHandle::EntryHandle(EntryHandle&& aOther) noexcept + : mTable(std::exchange(aOther.mTable, nullptr)), + mKeyHash(aOther.mKeyHash), + mSlot(aOther.mSlot) {} + +#ifdef MOZ_HASH_TABLE_CHECKS_ENABLED +PLDHashTable::EntryHandle::~EntryHandle() { + if (!mTable) { + return; + } + + mTable->mChecker.EndWriteOp(); +} +#endif + +void PLDHashTable::EntryHandle::Remove() { + MOZ_ASSERT(HasEntry()); + + mTable->RawRemove(mSlot); +} + +void PLDHashTable::EntryHandle::OrRemove() { + if (HasEntry()) { + Remove(); + } +} + +void PLDHashTable::EntryHandle::OccupySlot() { + MOZ_ASSERT(!HasEntry()); + + PLDHashNumber keyHash = mKeyHash; + if (mSlot.IsRemoved()) { + mTable->mRemovedCount--; + keyHash |= kCollisionFlag; + } + mSlot.SetKeyHash(keyHash); + mTable->mEntryCount++; +} + +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; +} |