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+/* -*- 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/. */
+
+// See the comment at the top of mfbt/HashTable.h for a comparison between
+// PLDHashTable and mozilla::HashTable.
+
+#ifndef PLDHashTable_h
+#define PLDHashTable_h
+
+#include <utility>
+
+#include "mozilla/Assertions.h"
+#include "mozilla/Atomics.h"
+#include "mozilla/HashFunctions.h"
+#include "mozilla/Maybe.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/fallible.h"
+#include "nscore.h"
+
+using PLDHashNumber = mozilla::HashNumber;
+static const uint32_t kPLDHashNumberBits = mozilla::kHashNumberBits;
+
+#if defined(DEBUG) || defined(FUZZING)
+# define MOZ_HASH_TABLE_CHECKS_ENABLED 1
+#endif
+
+class PLDHashTable;
+struct PLDHashTableOps;
+
+// Table entry header structure.
+//
+// In order to allow in-line allocation of key and value, we do not declare
+// either here. Instead, the API uses const void *key as a formal parameter.
+// The key need not be stored in the entry; it may be part of the value, but
+// need not be stored at all.
+//
+// Callback types are defined below and grouped into the PLDHashTableOps
+// structure, for single static initialization per hash table sub-type.
+//
+// Each hash table sub-type should make its entry type a subclass of
+// PLDHashEntryHdr. PLDHashEntryHdr is merely a common superclass to present a
+// uniform interface to PLDHashTable clients. The zero-sized base class
+// optimization, employed by all of our supported C++ compilers, will ensure
+// that this abstraction does not make objects needlessly larger.
+struct PLDHashEntryHdr {
+ PLDHashEntryHdr() = default;
+ PLDHashEntryHdr(const PLDHashEntryHdr&) = delete;
+ PLDHashEntryHdr& operator=(const PLDHashEntryHdr&) = delete;
+ PLDHashEntryHdr(PLDHashEntryHdr&&) = default;
+ PLDHashEntryHdr& operator=(PLDHashEntryHdr&&) = default;
+
+ private:
+ friend class PLDHashTable;
+};
+
+#ifdef MOZ_HASH_TABLE_CHECKS_ENABLED
+
+// This class does three kinds of checking:
+//
+// - that calls to one of |mOps| or to an enumerator do not cause re-entry into
+// the table in an unsafe way;
+//
+// - that multiple threads do not access the table in an unsafe way;
+//
+// - that a table marked as immutable is not modified.
+//
+// "Safe" here means that multiple concurrent read operations are ok, but a
+// write operation (i.e. one that can cause the entry storage to be reallocated
+// or destroyed) cannot safely run concurrently with another read or write
+// operation. This meaning of "safe" is only partial; for example, it does not
+// cover whether a single entry in the table is modified by two separate
+// threads. (Doing such checking would be much harder.)
+//
+// It does this with two variables:
+//
+// - mState, which embodies a tri-stage tagged union with the following
+// variants:
+// - Idle
+// - Read(n), where 'n' is the number of concurrent read operations
+// - Write
+//
+// - mIsWritable, which indicates if the table is mutable.
+//
+class Checker {
+ public:
+ constexpr Checker() : mState(kIdle), mIsWritable(true) {}
+
+ Checker& operator=(Checker&& aOther) {
+ // Atomic<> doesn't have an |operator=(Atomic<>&&)|.
+ mState = uint32_t(aOther.mState);
+ mIsWritable = bool(aOther.mIsWritable);
+
+ aOther.mState = kIdle;
+ // XXX Shouldn't we set mIsWritable to true here for consistency?
+
+ return *this;
+ }
+
+ static bool IsIdle(uint32_t aState) { return aState == kIdle; }
+ static bool IsRead(uint32_t aState) {
+ return kRead1 <= aState && aState <= kReadMax;
+ }
+ static bool IsRead1(uint32_t aState) { return aState == kRead1; }
+ static bool IsWrite(uint32_t aState) { return aState == kWrite; }
+
+ bool IsIdle() const { return mState == kIdle; }
+
+ bool IsWritable() const { return mIsWritable; }
+
+ void SetNonWritable() { mIsWritable = false; }
+
+ // NOTE: the obvious way to implement these functions is to (a) check
+ // |mState| is reasonable, and then (b) update |mState|. But the lack of
+ // atomicity in such an implementation can cause problems if we get unlucky
+ // thread interleaving between (a) and (b).
+ //
+ // So instead for |mState| we are careful to (a) first get |mState|'s old
+ // value and assign it a new value in single atomic operation, and only then
+ // (b) check the old value was reasonable. This ensures we don't have
+ // interleaving problems.
+ //
+ // For |mIsWritable| we don't need to be as careful because it can only in
+ // transition in one direction (from writable to non-writable).
+
+ void StartReadOp() {
+ uint32_t oldState = mState++; // this is an atomic increment
+ MOZ_RELEASE_ASSERT(IsIdle(oldState) || IsRead(oldState));
+ MOZ_RELEASE_ASSERT(oldState < kReadMax); // check for overflow
+ }
+
+ void EndReadOp() {
+ uint32_t oldState = mState--; // this is an atomic decrement
+ MOZ_RELEASE_ASSERT(IsRead(oldState));
+ }
+
+ void StartWriteOp() {
+ MOZ_RELEASE_ASSERT(IsWritable());
+ uint32_t oldState = mState.exchange(kWrite);
+ MOZ_RELEASE_ASSERT(IsIdle(oldState));
+ }
+
+ void EndWriteOp() {
+ // Check again that the table is writable, in case it was marked as
+ // non-writable just after the IsWritable() assertion in StartWriteOp()
+ // occurred.
+ MOZ_RELEASE_ASSERT(IsWritable());
+ uint32_t oldState = mState.exchange(kIdle);
+ MOZ_RELEASE_ASSERT(IsWrite(oldState));
+ }
+
+ void StartIteratorRemovalOp() {
+ // When doing removals at the end of iteration, we go from Read1 state to
+ // Write and then back.
+ MOZ_RELEASE_ASSERT(IsWritable());
+ uint32_t oldState = mState.exchange(kWrite);
+ MOZ_RELEASE_ASSERT(IsRead1(oldState));
+ }
+
+ void EndIteratorRemovalOp() {
+ // Check again that the table is writable, in case it was marked as
+ // non-writable just after the IsWritable() assertion in
+ // StartIteratorRemovalOp() occurred.
+ MOZ_RELEASE_ASSERT(IsWritable());
+ uint32_t oldState = mState.exchange(kRead1);
+ MOZ_RELEASE_ASSERT(IsWrite(oldState));
+ }
+
+ void StartDestructorOp() {
+ // A destructor op is like a write, but the table doesn't need to be
+ // writable.
+ uint32_t oldState = mState.exchange(kWrite);
+ MOZ_RELEASE_ASSERT(IsIdle(oldState));
+ }
+
+ void EndDestructorOp() {
+ uint32_t oldState = mState.exchange(kIdle);
+ MOZ_RELEASE_ASSERT(IsWrite(oldState));
+ }
+
+ private:
+ // Things of note about the representation of |mState|.
+ // - The values between kRead1..kReadMax represent valid Read(n) values.
+ // - kIdle and kRead1 are deliberately chosen so that incrementing the -
+ // former gives the latter.
+ // - 9999 concurrent readers should be enough for anybody.
+ static const uint32_t kIdle = 0;
+ static const uint32_t kRead1 = 1;
+ static const uint32_t kReadMax = 9999;
+ static const uint32_t kWrite = 10000;
+
+ mozilla::Atomic<uint32_t, mozilla::SequentiallyConsistent> mState;
+ mozilla::Atomic<bool, mozilla::SequentiallyConsistent> mIsWritable;
+};
+#endif
+
+// A PLDHashTable may be allocated on the stack or within another structure or
+// class. No entry storage is allocated until the first element is added. This
+// means that empty hash tables are cheap, which is good because they are
+// common.
+//
+// There used to be a long, math-heavy comment here about the merits of
+// double hashing vs. chaining; it was removed in bug 1058335. In short, double
+// hashing is more space-efficient unless the element size gets large (in which
+// case you should keep using double hashing but switch to using pointer
+// elements). Also, with double hashing, you can't safely hold an entry pointer
+// and use it after an add or remove operation, unless you sample Generation()
+// before adding or removing, and compare the sample after, dereferencing the
+// entry pointer only if Generation() has not changed.
+class PLDHashTable {
+ private:
+ // A slot represents a cached hash value and its associated entry stored in
+ // the hash table. The hash value and the entry are not stored contiguously.
+ struct Slot {
+ Slot(PLDHashEntryHdr* aEntry, PLDHashNumber* aKeyHash)
+ : mEntry(aEntry), mKeyHash(aKeyHash) {}
+
+ Slot(const Slot&) = default;
+ Slot(Slot&& aOther) = default;
+
+ Slot& operator=(Slot&& aOther) = default;
+
+ bool operator==(const Slot& aOther) const {
+ return mEntry == aOther.mEntry;
+ }
+
+ PLDHashNumber KeyHash() const { return *HashPtr(); }
+ void SetKeyHash(PLDHashNumber aHash) { *HashPtr() = aHash; }
+
+ PLDHashEntryHdr* ToEntry() const { return mEntry; }
+
+ bool IsFree() const { return KeyHash() == 0; }
+ bool IsRemoved() const { return KeyHash() == 1; }
+ bool IsLive() const { return IsLiveHash(KeyHash()); }
+ static bool IsLiveHash(uint32_t aHash) { return aHash >= 2; }
+
+ void MarkFree() { *HashPtr() = 0; }
+ void MarkRemoved() { *HashPtr() = 1; }
+ void MarkColliding() { *HashPtr() |= kCollisionFlag; }
+
+ void Next(uint32_t aEntrySize) {
+ char* p = reinterpret_cast<char*>(mEntry);
+ p += aEntrySize;
+ mEntry = reinterpret_cast<PLDHashEntryHdr*>(p);
+ mKeyHash++;
+ }
+ PLDHashNumber* HashPtr() const { return mKeyHash; }
+
+ private:
+ PLDHashEntryHdr* mEntry;
+ PLDHashNumber* mKeyHash;
+ };
+
+ // This class maintains the invariant that every time the entry store is
+ // changed, the generation is updated.
+ //
+ // The data layout separates the cached hashes of entries and the entries
+ // themselves to save space. We could store the entries thusly:
+ //
+ // +--------+--------+---------+
+ // | entry0 | entry1 | ... |
+ // +--------+--------+---------+
+ //
+ // where the entries themselves contain the cached hash stored as their
+ // first member. PLDHashTable did this for a long time, with entries looking
+ // like:
+ //
+ // class PLDHashEntryHdr
+ // {
+ // PLDHashNumber mKeyHash;
+ // };
+ //
+ // class MyEntry : public PLDHashEntryHdr
+ // {
+ // ...
+ // };
+ //
+ // The problem with this setup is that, depending on the layout of
+ // `MyEntry`, there may be platform ABI-mandated padding between `mKeyHash`
+ // and the first member of `MyEntry`. This ABI-mandated padding is wasted
+ // space, and was surprisingly common, e.g. when MyEntry contained a single
+ // pointer on 64-bit platforms.
+ //
+ // As previously alluded to, the current setup stores things thusly:
+ //
+ // +-------+-------+-------+-------+--------+--------+---------+
+ // | hash0 | hash1 | ..... | hashN | entry0 | entry1 | ... |
+ // +-------+-------+-------+-------+--------+--------+---------+
+ //
+ // which contains no wasted space between the hashes themselves, and no
+ // wasted space between the entries themselves. malloc is guaranteed to
+ // return blocks of memory with at least word alignment on all of our major
+ // platforms. PLDHashTable mandates that the size of the hash table is
+ // always a power of two, so the alignment of the memory containing the
+ // first entry is always at least the alignment of the entire entry store.
+ // That means the alignment of `entry0` should be its natural alignment.
+ // Entries may have problems if they contain over-aligned members such as
+ // SIMD vector types, but this has not been a problem in practice.
+ //
+ // Note: It would be natural to store the generation within this class, but
+ // we can't do that without bloating sizeof(PLDHashTable) on 64-bit machines.
+ // So instead we store it outside this class, and Set() takes a pointer to it
+ // and ensures it is updated as necessary.
+ class EntryStore {
+ private:
+ char* mEntryStore;
+
+ static char* Entries(char* aStore, uint32_t aCapacity) {
+ return aStore + aCapacity * sizeof(PLDHashNumber);
+ }
+
+ char* Entries(uint32_t aCapacity) const {
+ return Entries(Get(), aCapacity);
+ }
+
+ public:
+ EntryStore() : mEntryStore(nullptr) {}
+
+ ~EntryStore() {
+ free(mEntryStore);
+ mEntryStore = nullptr;
+ }
+
+ char* Get() const { return mEntryStore; }
+ bool IsAllocated() const { return !!mEntryStore; }
+
+ Slot SlotForIndex(uint32_t aIndex, uint32_t aEntrySize,
+ uint32_t aCapacity) const {
+ char* entries = Entries(aCapacity);
+ auto entry =
+ reinterpret_cast<PLDHashEntryHdr*>(entries + aIndex * aEntrySize);
+ auto hashes = reinterpret_cast<PLDHashNumber*>(Get());
+ return Slot(entry, &hashes[aIndex]);
+ }
+
+ Slot SlotForPLDHashEntry(PLDHashEntryHdr* aEntry, uint32_t aCapacity,
+ uint32_t aEntrySize) {
+ char* entries = Entries(aCapacity);
+ char* entry = reinterpret_cast<char*>(aEntry);
+ uint32_t entryOffset = entry - entries;
+ uint32_t slotIndex = entryOffset / aEntrySize;
+ return SlotForIndex(slotIndex, aEntrySize, aCapacity);
+ }
+
+ template <typename F>
+ void ForEachSlot(uint32_t aCapacity, uint32_t aEntrySize, F&& aFunc) {
+ ForEachSlot(Get(), aCapacity, aEntrySize, std::move(aFunc));
+ }
+
+ template <typename F>
+ static void ForEachSlot(char* aStore, uint32_t aCapacity,
+ uint32_t aEntrySize, F&& aFunc) {
+ char* entries = Entries(aStore, aCapacity);
+ Slot slot(reinterpret_cast<PLDHashEntryHdr*>(entries),
+ reinterpret_cast<PLDHashNumber*>(aStore));
+ for (size_t i = 0; i < aCapacity; ++i) {
+ aFunc(slot);
+ slot.Next(aEntrySize);
+ }
+ }
+
+ void Set(char* aEntryStore, uint16_t* aGeneration) {
+ mEntryStore = aEntryStore;
+ *aGeneration += 1;
+ }
+ };
+
+ // These fields are packed carefully. On 32-bit platforms,
+ // sizeof(PLDHashTable) is 20. On 64-bit platforms, sizeof(PLDHashTable) is
+ // 32; 28 bytes of data followed by 4 bytes of padding for alignment.
+ const PLDHashTableOps* const mOps; // Virtual operations; see below.
+ EntryStore mEntryStore; // (Lazy) entry storage and generation.
+ uint16_t mGeneration; // The storage generation.
+ uint8_t mHashShift; // Multiplicative hash shift.
+ const uint8_t mEntrySize; // Number of bytes in an entry.
+ uint32_t mEntryCount; // Number of entries in table.
+ uint32_t mRemovedCount; // Removed entry sentinels in table.
+
+#ifdef MOZ_HASH_TABLE_CHECKS_ENABLED
+ mutable Checker mChecker;
+#endif
+
+ public:
+ // Table capacity limit; do not exceed. The max capacity used to be 1<<23 but
+ // that occasionally that wasn't enough. Making it much bigger than 1<<26
+ // probably isn't worthwhile -- tables that big are kind of ridiculous.
+ // Also, the growth operation will (deliberately) fail if |capacity *
+ // mEntrySize| overflows a uint32_t, and mEntrySize is always at least 8
+ // bytes.
+ static const uint32_t kMaxCapacity = ((uint32_t)1 << 26);
+
+ static const uint32_t kMinCapacity = 8;
+
+ // Making this half of kMaxCapacity ensures it'll fit. Nobody should need an
+ // initial length anywhere nearly this large, anyway.
+ static const uint32_t kMaxInitialLength = kMaxCapacity / 2;
+
+ // This gives a default initial capacity of 8.
+ static const uint32_t kDefaultInitialLength = 4;
+
+ // Initialize the table with |aOps| and |aEntrySize|. The table's initial
+ // capacity is chosen such that |aLength| elements can be inserted without
+ // rehashing; if |aLength| is a power-of-two, this capacity will be
+ // |2*length|. However, because entry storage is allocated lazily, this
+ // initial capacity won't be relevant until the first element is added; prior
+ // to that the capacity will be zero.
+ //
+ // This will crash if |aEntrySize| and/or |aLength| are too large.
+ PLDHashTable(const PLDHashTableOps* aOps, uint32_t aEntrySize,
+ uint32_t aLength = kDefaultInitialLength);
+
+ PLDHashTable(PLDHashTable&& aOther)
+ // Initialize fields which are checked by the move assignment operator
+ // and the destructor (which the move assignment operator calls).
+ : mOps(nullptr), mGeneration(0), mEntrySize(0) {
+ *this = std::move(aOther);
+ }
+
+ PLDHashTable& operator=(PLDHashTable&& aOther);
+
+ ~PLDHashTable();
+
+ // This should be used rarely.
+ const PLDHashTableOps* Ops() const { return mOps; }
+
+ // Size in entries (gross, not net of free and removed sentinels) for table.
+ // This can be zero if no elements have been added yet, in which case the
+ // entry storage will not have yet been allocated.
+ uint32_t Capacity() const {
+ return mEntryStore.IsAllocated() ? CapacityFromHashShift() : 0;
+ }
+
+ uint32_t EntrySize() const { return mEntrySize; }
+ uint32_t EntryCount() const { return mEntryCount; }
+ uint32_t Generation() const { return mGeneration; }
+
+ // To search for a |key| in |table|, call:
+ //
+ // entry = table.Search(key);
+ //
+ // If |entry| is non-null, |key| was found. If |entry| is null, key was not
+ // found.
+ PLDHashEntryHdr* Search(const void* aKey) const;
+
+ // To add an entry identified by |key| to table, call:
+ //
+ // entry = table.Add(key, mozilla::fallible);
+ //
+ // If |entry| is null upon return, then the table is severely overloaded and
+ // memory can't be allocated for entry storage.
+ //
+ // Otherwise, if the initEntry hook was provided, |entry| will be
+ // initialized. If the initEntry hook was not provided, the caller
+ // should initialize |entry| as appropriate.
+ PLDHashEntryHdr* Add(const void* aKey, const mozilla::fallible_t&);
+
+ // This is like the other Add() function, but infallible, and so never
+ // returns null.
+ PLDHashEntryHdr* Add(const void* aKey);
+
+ // To remove an entry identified by |key| from table, call:
+ //
+ // table.Remove(key);
+ //
+ // If |key|'s entry is found, it is cleared (via table->mOps->clearEntry).
+ // The table's capacity may be reduced afterwards.
+ void Remove(const void* aKey);
+
+ // To remove an entry found by a prior search, call:
+ //
+ // table.RemoveEntry(entry);
+ //
+ // The entry, which must be present and in use, is cleared (via
+ // table->mOps->clearEntry). The table's capacity may be reduced afterwards.
+ void RemoveEntry(PLDHashEntryHdr* aEntry);
+
+ // Remove an entry already accessed via Search() or Add().
+ //
+ // NB: this is a "raw" or low-level method. It does not shrink the table if
+ // it is underloaded. Don't use it unless necessary and you know what you are
+ // doing, and if so, please explain in a comment why it is necessary instead
+ // of RemoveEntry().
+ void RawRemove(PLDHashEntryHdr* aEntry);
+
+ // This function is equivalent to
+ // ClearAndPrepareForLength(kDefaultInitialLength).
+ void Clear();
+
+ // This function clears the table's contents and frees its entry storage,
+ // leaving it in a empty state ready to be used again. Afterwards, when the
+ // first element is added the entry storage that gets allocated will have a
+ // capacity large enough to fit |aLength| elements without rehashing.
+ //
+ // It's conceptually the same as calling the destructor and then re-calling
+ // the constructor with the original |aOps| and |aEntrySize| arguments, and
+ // a new |aLength| argument.
+ void ClearAndPrepareForLength(uint32_t aLength);
+
+ // Measure the size of the table's entry storage. If the entries contain
+ // pointers to other heap blocks, you have to iterate over the table and
+ // measure those separately; hence the "Shallow" prefix.
+ size_t ShallowSizeOfExcludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;
+
+ // Like ShallowSizeOfExcludingThis(), but includes sizeof(*this).
+ size_t ShallowSizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const;
+
+ // Mark a table as immutable for the remainder of its lifetime. This
+ // changes the implementation from asserting one set of invariants to
+ // asserting a different set.
+ void MarkImmutable() {
+#ifdef MOZ_HASH_TABLE_CHECKS_ENABLED
+ mChecker.SetNonWritable();
+#endif
+ }
+
+ // If you use PLDHashEntryStub or a subclass of it as your entry struct, and
+ // if your entries move via memcpy and clear via memset(0), you can use these
+ // stub operations.
+ static const PLDHashTableOps* StubOps();
+
+ // The individual stub operations in StubOps().
+ static PLDHashNumber HashVoidPtrKeyStub(const void* aKey);
+ static bool MatchEntryStub(const PLDHashEntryHdr* aEntry, const void* aKey);
+ static void MoveEntryStub(PLDHashTable* aTable, const PLDHashEntryHdr* aFrom,
+ PLDHashEntryHdr* aTo);
+ static void ClearEntryStub(PLDHashTable* aTable, PLDHashEntryHdr* aEntry);
+
+ // Hash/match operations for tables holding C strings.
+ static PLDHashNumber HashStringKey(const void* aKey);
+ static bool MatchStringKey(const PLDHashEntryHdr* aEntry, const void* aKey);
+
+ class EntryHandle {
+ public:
+ EntryHandle(EntryHandle&& aOther) noexcept;
+#ifdef MOZ_HASH_TABLE_CHECKS_ENABLED
+ ~EntryHandle();
+#endif
+
+ EntryHandle(const EntryHandle&) = delete;
+ EntryHandle& operator=(const EntryHandle&) = delete;
+ EntryHandle& operator=(EntryHandle&& aOther) = delete;
+
+ // Is this slot currently occupied?
+ bool HasEntry() const { return mSlot.IsLive(); }
+
+ explicit operator bool() const { return HasEntry(); }
+
+ // Get the entry stored in this slot. May not be called unless the slot is
+ // currently occupied.
+ PLDHashEntryHdr* Entry() {
+ MOZ_ASSERT(HasEntry());
+ return mSlot.ToEntry();
+ }
+
+ template <class F>
+ void Insert(F&& aInitEntry) {
+ MOZ_ASSERT(!HasEntry());
+ OccupySlot();
+ std::forward<F>(aInitEntry)(Entry());
+ }
+
+ // If the slot is currently vacant, the slot is occupied and `initEntry` is
+ // invoked to initialize the entry. Returns the entry stored in now-occupied
+ // slot.
+ template <class F>
+ PLDHashEntryHdr* OrInsert(F&& aInitEntry) {
+ if (!HasEntry()) {
+ Insert(std::forward<F>(aInitEntry));
+ }
+ return Entry();
+ }
+
+ /** Removes the entry. Note that the table won't shrink on destruction of
+ * the EntryHandle.
+ *
+ * \pre HasEntry()
+ * \post !HasEntry()
+ */
+ void Remove();
+
+ /** Removes the entry, if it exists. Note that the table won't shrink on
+ * destruction of the EntryHandle.
+ *
+ * \post !HasEntry()
+ */
+ void OrRemove();
+
+ private:
+ friend class PLDHashTable;
+
+ EntryHandle(PLDHashTable* aTable, PLDHashNumber aKeyHash, Slot aSlot);
+
+ void OccupySlot();
+
+ PLDHashTable* mTable;
+ PLDHashNumber mKeyHash;
+ Slot mSlot;
+ };
+
+ template <class F>
+ auto WithEntryHandle(const void* aKey, F&& aFunc)
+ -> std::invoke_result_t<F, EntryHandle&&> {
+ return std::forward<F>(aFunc)(MakeEntryHandle(aKey));
+ }
+
+ template <class F>
+ auto WithEntryHandle(const void* aKey, const mozilla::fallible_t& aFallible,
+ F&& aFunc)
+ -> std::invoke_result_t<F, mozilla::Maybe<EntryHandle>&&> {
+ return std::forward<F>(aFunc)(MakeEntryHandle(aKey, aFallible));
+ }
+
+ // This is an iterator for PLDHashtable. Assertions will detect some, but not
+ // all, mid-iteration table modifications that might invalidate (e.g.
+ // reallocate) the entry storage.
+ //
+ // Any element can be removed during iteration using Remove(). If any
+ // elements are removed, the table may be resized once iteration ends.
+ //
+ // Example usage:
+ //
+ // for (auto iter = table.Iter(); !iter.Done(); iter.Next()) {
+ // auto entry = static_cast<FooEntry*>(iter.Get());
+ // // ... do stuff with |entry| ...
+ // // ... possibly call iter.Remove() once ...
+ // }
+ //
+ // or:
+ //
+ // for (PLDHashTable::Iterator iter(&table); !iter.Done(); iter.Next()) {
+ // auto entry = static_cast<FooEntry*>(iter.Get());
+ // // ... do stuff with |entry| ...
+ // // ... possibly call iter.Remove() once ...
+ // }
+ //
+ // The latter form is more verbose but is easier to work with when
+ // making subclasses of Iterator.
+ //
+ class Iterator {
+ public:
+ explicit Iterator(PLDHashTable* aTable);
+ struct EndIteratorTag {};
+ Iterator(PLDHashTable* aTable, EndIteratorTag aTag);
+ Iterator(Iterator&& aOther);
+ ~Iterator();
+
+ // Have we finished?
+ bool Done() const { return mNexts == mNextsLimit; }
+
+ // Get the current entry.
+ PLDHashEntryHdr* Get() const {
+ MOZ_ASSERT(!Done());
+ MOZ_ASSERT(mCurrent.IsLive());
+ return mCurrent.ToEntry();
+ }
+
+ // Advance to the next entry.
+ void Next();
+
+ // Remove the current entry. Must only be called once per entry, and Get()
+ // must not be called on that entry afterwards.
+ void Remove();
+
+ bool operator==(const Iterator& aOther) const {
+ MOZ_ASSERT(mTable == aOther.mTable);
+ return mNexts == aOther.mNexts;
+ }
+
+ Iterator Clone() const { return {*this}; }
+
+ protected:
+ PLDHashTable* mTable; // Main table pointer.
+
+ private:
+ Slot mCurrent; // Pointer to the current entry.
+ uint32_t mNexts; // Number of Next() calls.
+ uint32_t mNextsLimit; // Next() call limit.
+
+ bool mHaveRemoved; // Have any elements been removed?
+ uint8_t mEntrySize; // Size of entries.
+
+ bool IsOnNonLiveEntry() const;
+
+ void MoveToNextLiveEntry();
+
+ Iterator() = delete;
+ Iterator(const Iterator&);
+ Iterator& operator=(const Iterator&) = delete;
+ Iterator& operator=(const Iterator&&) = delete;
+ };
+
+ Iterator Iter() { return Iterator(this); }
+
+ // Use this if you need to initialize an Iterator in a const method. If you
+ // use this case, you should not call Remove() on the iterator.
+ Iterator ConstIter() const {
+ return Iterator(const_cast<PLDHashTable*>(this));
+ }
+
+ private:
+ static uint32_t HashShift(uint32_t aEntrySize, uint32_t aLength);
+
+ static const PLDHashNumber kCollisionFlag = 1;
+
+ PLDHashNumber Hash1(PLDHashNumber aHash0) const;
+ void Hash2(PLDHashNumber aHash, uint32_t& aHash2Out,
+ uint32_t& aSizeMaskOut) const;
+
+ static bool MatchSlotKeyhash(Slot& aSlot, const PLDHashNumber aHash);
+ Slot SlotForIndex(uint32_t aIndex) const;
+
+ // We store mHashShift rather than sizeLog2 to optimize the collision-free
+ // case in SearchTable.
+ uint32_t CapacityFromHashShift() const {
+ return ((uint32_t)1 << (kPLDHashNumberBits - mHashShift));
+ }
+
+ PLDHashNumber ComputeKeyHash(const void* aKey) const;
+
+ enum SearchReason { ForSearchOrRemove, ForAdd };
+
+ // Avoid using bare `Success` and `Failure`, as those names are commonly
+ // defined as macros.
+ template <SearchReason Reason, typename PLDSuccess, typename PLDFailure>
+ auto SearchTable(const void* aKey, PLDHashNumber aKeyHash,
+ PLDSuccess&& aSucess, PLDFailure&& aFailure) const;
+
+ Slot FindFreeSlot(PLDHashNumber aKeyHash) const;
+
+ bool ChangeTable(int aDeltaLog2);
+
+ void RawRemove(Slot& aSlot);
+ void ShrinkIfAppropriate();
+
+ mozilla::Maybe<EntryHandle> MakeEntryHandle(const void* aKey,
+ const mozilla::fallible_t&);
+
+ EntryHandle MakeEntryHandle(const void* aKey);
+
+ PLDHashTable(const PLDHashTable& aOther) = delete;
+ PLDHashTable& operator=(const PLDHashTable& aOther) = delete;
+};
+
+// Compute the hash code for a given key to be looked up, added, or removed.
+// A hash code may have any PLDHashNumber value.
+typedef PLDHashNumber (*PLDHashHashKey)(const void* aKey);
+
+// Compare the key identifying aEntry with the provided key parameter. Return
+// true if keys match, false otherwise.
+typedef bool (*PLDHashMatchEntry)(const PLDHashEntryHdr* aEntry,
+ const void* aKey);
+
+// Copy the data starting at aFrom to the new entry storage at aTo. Do not add
+// reference counts for any strong references in the entry, however, as this
+// is a "move" operation: the old entry storage at from will be freed without
+// any reference-decrementing callback shortly.
+typedef void (*PLDHashMoveEntry)(PLDHashTable* aTable,
+ const PLDHashEntryHdr* aFrom,
+ PLDHashEntryHdr* aTo);
+
+// Clear the entry and drop any strong references it holds. This callback is
+// invoked by Remove(), but only if the given key is found in the table.
+typedef void (*PLDHashClearEntry)(PLDHashTable* aTable,
+ PLDHashEntryHdr* aEntry);
+
+// Initialize a new entry. This function is called when
+// Add() finds no existing entry for the given key, and must add a new one.
+typedef void (*PLDHashInitEntry)(PLDHashEntryHdr* aEntry, const void* aKey);
+
+// Finally, the "vtable" structure for PLDHashTable. The first four hooks
+// must be provided by implementations; they're called unconditionally by the
+// generic PLDHashTable.cpp code. Hooks after these may be null.
+//
+// Summary of allocation-related hook usage with C++ placement new emphasis:
+// initEntry Call placement new using default key-based ctor.
+// moveEntry Call placement new using copy ctor, run dtor on old
+// entry storage.
+// clearEntry Run dtor on entry.
+//
+// Note the reason why initEntry is optional: the default hooks (stubs) clear
+// entry storage. On a successful Add(tbl, key), the returned entry pointer
+// addresses an entry struct whose entry members are still clear (null). Add()
+// callers can test such members to see whether the entry was newly created by
+// the Add() call that just succeeded. If placement new or similar
+// initialization is required, define an |initEntry| hook. Of course, the
+// |clearEntry| hook must zero or null appropriately.
+//
+// XXX assumes 0 is null for pointer types.
+struct PLDHashTableOps {
+ // Mandatory hooks. All implementations must provide these.
+ PLDHashHashKey hashKey;
+ PLDHashMatchEntry matchEntry;
+ PLDHashMoveEntry moveEntry;
+
+ // Optional hooks start here. If null, these are not called.
+ PLDHashClearEntry clearEntry;
+ PLDHashInitEntry initEntry;
+};
+
+// A minimal entry is a subclass of PLDHashEntryHdr and has a void* key pointer.
+struct PLDHashEntryStub : public PLDHashEntryHdr {
+ const void* key;
+};
+
+#endif /* PLDHashTable_h */
generated by cgit v1.2.3 (git 2.39.1) at 2024-11-24 11:42:04 +0000