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| -rw-r--r-- | modules/libpref/SharedPrefMap.h | 848 |
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diff --git a/modules/libpref/SharedPrefMap.h b/modules/libpref/SharedPrefMap.h new file mode 100644 index 0000000000..7c949e137d --- /dev/null +++ b/modules/libpref/SharedPrefMap.h @@ -0,0 +1,848 @@ +/* -*- 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/. */ + +#ifndef dom_ipc_SharedPrefMap_h +#define dom_ipc_SharedPrefMap_h + +#include "mozilla/AutoMemMap.h" +#include "mozilla/HashFunctions.h" +#include "mozilla/Preferences.h" +#include "mozilla/Result.h" +#include "mozilla/dom/ipc/StringTable.h" +#include "nsTHashMap.h" + +namespace mozilla { + +// The approximate number of preferences expected to be in an ordinary +// preferences database. +// +// This number is used to determine initial allocation sizes for data structures +// when building the shared preference map, and should be slightly higher than +// the expected number of preferences in an ordinary database to avoid +// unnecessary reallocations/rehashes. +constexpr size_t kExpectedPrefCount = 4000; + +class SharedPrefMapBuilder; + +// This class provides access to a compact, read-only copy of a preference +// database, backed by a shared memory buffer which can be shared between +// processes. All state data for the database is stored in the shared memory +// region, so individual instances require no dynamic memory allocation. +// +// Further, all strings returned from this API are nsLiteralCStrings with +// pointers into the shared memory region, which means that they can be copied +// into new nsCString instances without additional allocations. For instance, +// the following (where `pref` is a Pref object) will not cause any string +// copies, memory allocations, or atomic refcount changes: +// +// nsCString prefName(pref.NameString()); +// +// whereas if we returned a nsDependentCString or a dynamically allocated +// nsCString, it would. +// +// The set of entries is stored in sorted order by preference name, so look-ups +// are done by binary search. This means that look-ups have O(log n) complexity, +// rather than the O(1) complexity of a dynamic hashtable. Consumers should keep +// this in mind when planning their accesses. +// +// Important: The mapped memory created by this class is persistent. Once an +// instance has been initialized, the memory that it allocates can never be +// freed before process shutdown. Do not use it for short-lived mappings. +class SharedPrefMap { + using FileDescriptor = mozilla::ipc::FileDescriptor; + + friend class SharedPrefMapBuilder; + + // Describes a block of memory within the shared memory region. + struct DataBlock { + // The byte offset from the start of the shared memory region to the start + // of the block. + size_t mOffset; + // The size of the block, in bytes. This is typically used only for bounds + // checking in debug builds. + size_t mSize; + }; + + // Describes the contents of the shared memory region, which is laid-out as + // follows: + // + // - The Header struct + // + // - An array of Entry structs with mEntryCount elements, lexicographically + // sorted by preference name. + // + // - A set of data blocks, with offsets and sizes described by the DataBlock + // entries in the header, described below. + // + // Each entry stores its name string and values as indices into these blocks, + // as documented in the Entry struct, but with some important optimizations: + // + // - Boolean values are always stored inline. Both the default and user + // values can be retrieved directly from the entry. Other types have only + // one value index, and their values appear at the same indices in the + // default and user value arrays. + // + // Aside from reducing our memory footprint, this space-efficiency means + // that we can fit more entries in the CPU cache at once, and reduces the + // number of likely cache misses during lookups. + // + // - Key strings are stored in a separate string table from value strings. As + // above, this makes it more likely that the strings we need will be + // available in the CPU cache during lookups by not interleaving them with + // extraneous data. + // + // - Default and user values are stored in separate arrays. Entries with user + // values always appear before entries with default values in the value + // arrays, and entries without user values do not have entries in the user + // array at all. Since the same index is used for both arrays, this means + // that entries with a default value but no user value do not allocate any + // space to store their user value. + // + // - For preferences with no user value, the entries in the default value are + // de-duplicated. All preferences with the same default value (and no user + // value) point to the same index in the default value array. + // + // + // For example, a preference database containing: + // + // +---------+-------------------------------+-------------------------------+ + // | Name | Default Value | User Value | | + // +---------+---------------+---------------+-------------------------------+ + // | string1 | "meh" | "hem" | | + // | string2 | | "b" | | + // | string3 | "a" | | | + // | string4 | "foo" | | | + // | string5 | "foo" | | | + // | string6 | "meh" | | | + // +---------+---------------+---------------+-------------------------------+ + // | bool1 | false | true | | + // | bool2 | | false | | + // | bool3 | true | | | + // +---------+---------------+---------------+-------------------------------+ + // | int1 | 18 | 16 | | + // | int2 | | 24 | | + // | int3 | 42 | | | + // | int4 | 12 | | | + // | int5 | 12 | | | + // | int6 | 18 | | | + // +---------+---------------+---------------+-------------------------------+ + // + // Results in a database that looks like: + // + // +-------------------------------------------------------------------------+ + // | Header: | + // +-------------------------------------------------------------------------+ + // | mEntryCount = 15 | + // | ... | + // +-------------------------------------------------------------------------+ + // + // +-------------------------------------------------------------------------+ + // | Key strings: | + // +--------+----------------------------------------------------------------+ + // | Offset | Value | + // +--------+----------------------------------------------------------------+ + // | 0 | string1\0 | + // | 8 | string2\0 | + // | 16 | string3\0 | + // | 24 | string4\0 | + // | 32 | string5\0 | + // | 40 | string6\0 | + // | 48 | bool1\0 | + // | 54 | bool2\0 | + // | 60 | bool3\0 | + // | 66 | int1\0 | + // | 71 | int2\0 | + // | 76 | int3\0 | + // | 81 | int4\0 | + // | 86 | int6\0 | + // | 91 | int6\0 | + // +--------+----------------------------------------------------------------+ + // + // +-------------------------------------------------------------------------+ + // | Entries: | + // +---------------------+------+------------+------------+------------------+ + // | Key[1] | Type | HasDefault | HasUser | Value | + // +---------------------+------+------------+------------+------------------+ + // | K["bool1", 48, 5] | 3 | true | true | { false, true } | + // | K["bool2", 54, 5] | 3 | false | true | { 0, false } | + // | K["bool3", 60, 5] | 3 | true | false | { true, 0 } | + // | K["int1", 66, 4] | 2 | true | true | 0 | + // | K["int2", 71, 4] | 2 | false | true | 1 | + // | K["int3", 76, 4] | 2 | true | false | 2 | + // | K["int4", 81, 4] | 2 | true | false | 3 | + // | K["int5", 86, 4] | 2 | true | false | 3 | + // | K["int6", 91, 4] | 2 | true | false | 4 | + // | K["string1", 0, 6] | 1 | true | true | 0 | + // | K["string2", 8, 6] | 1 | false | true | 1 | + // | K["string3", 16, 6] | 1 | true | false | 2 | + // | K["string4", 24, 6] | 1 | true | false | 3 | + // | K["string5", 32, 6] | 1 | true | false | 3 | + // | K["string6", 40, 6] | 1 | true | false | 4 | + // +---------------------+------+------------+------------+------------------+ + // | [1]: Encoded as an offset into the key table and a length. Specified | + // | as K[string, offset, length] for clarity. | + // +-------------------------------------------------------------------------+ + // + // +------------------------------------+------------------------------------+ + // | User integer values | Default integer values | + // +-------+----------------------------+-------+----------------------------+ + // | Index | Contents | Index | Contents | + // +-------+----------------------------+-------+----------------------------+ + // | 0 | 16 | 0 | 18 | + // | 1 | 24 | 1 | | + // | | | 2 | 42 | + // | | | 3 | 12 | + // | | | 4 | 18 | + // +-------+----------------------------+-------+----------------------------+ + // | * Note: Tables are laid out sequentially in memory, but displayed | + // | here side-by-side for clarity. | + // +-------------------------------------------------------------------------+ + // + // +------------------------------------+------------------------------------+ + // | User string values | Default string values | + // +-------+----------------------------+-------+----------------------------+ + // | Index | Contents[1] | Index | Contents[1] | + // +-------+----------------------------+-------+----------------------------+ + // | 0 | V["hem", 0, 3] | 0 | V["meh", 4, 3] | + // | 1 | V["b", 8, 1] | 1 | | + // | | | 2 | V["a", 10, 1] | + // | | | 3 | V["foo", 12, 3] | + // | | | 4 | V["meh", 4, 3] | + // |-------+----------------------------+-------+----------------------------+ + // | [1]: Encoded as an offset into the value table and a length. Specified | + // | as V[string, offset, length] for clarity. | + // +-------------------------------------------------------------------------+ + // | * Note: Tables are laid out sequentially in memory, but displayed | + // | here side-by-side for clarity. | + // +-------------------------------------------------------------------------+ + // + // +-------------------------------------------------------------------------+ + // | Value strings: | + // +--------+----------------------------------------------------------------+ + // | Offset | Value | + // +--------+----------------------------------------------------------------+ + // | 0 | hem\0 | + // | 4 | meh\0 | + // | 8 | b\0 | + // | 10 | a\0 | + // | 12 | foo\0 | + // +--------+----------------------------------------------------------------+ + struct Header { + // The number of entries in this map. + uint32_t mEntryCount; + + // The StringTable data block for preference name strings, which act as keys + // in the map. + DataBlock mKeyStrings; + + // The int32_t arrays of user and default int preference values. Entries in + // the map store their values as indices into these arrays. + DataBlock mUserIntValues; + DataBlock mDefaultIntValues; + + // The StringTableEntry arrays of user and default string preference values. + // + // Strings are stored as StringTableEntry structs with character offsets + // into the mValueStrings string table and their corresponding lengths. + // + // Entries in the map, likewise, store their string values as indices into + // these arrays. + DataBlock mUserStringValues; + DataBlock mDefaultStringValues; + + // The StringTable data block for string preference values, referenced by + // the above two data blocks. + DataBlock mValueStrings; + }; + + using StringTableEntry = mozilla::dom::ipc::StringTableEntry; + + // Represents a preference value, as either a pair of boolean values, or an + // index into one of the above value arrays. + union Value { + Value(bool aDefaultValue, bool aUserValue) + : mDefaultBool(aDefaultValue), mUserBool(aUserValue) {} + + MOZ_IMPLICIT Value(uint16_t aIndex) : mIndex(aIndex) {} + + // The index of this entry in the value arrays. + // + // User and default preference values have the same indices in their + // respective arrays. However, entries without a user value are not + // guaranteed to have space allocated for them in the user value array, and + // likewise for preferences without default values in the default value + // array. This means that callers must only access value entries for entries + // which claim to have a value of that type. + uint16_t mIndex; + struct { + bool mDefaultBool; + bool mUserBool; + }; + }; + + // Represents a preference entry in the map, containing its name, type info, + // flags, and a reference to its value. + struct Entry { + // A pointer to the preference name in the KeyTable string table. + StringTableEntry mKey; + + // The preference's value, either as a pair of booleans, or an index into + // the value arrays. Please see the documentation for the Value struct + // above. + Value mValue; + + // The preference's type, as a PrefType enum value. This must *never* be + // PrefType::None for values in a shared array. + uint8_t mType : 2; + // True if the preference has a default value. Callers must not attempt to + // access the entry's default value if this is false. + uint8_t mHasDefaultValue : 1; + // True if the preference has a user value. Callers must not attempt to + // access the entry's user value if this is false. + uint8_t mHasUserValue : 1; + // True if the preference is sticky, as defined by the preference service. + uint8_t mIsSticky : 1; + // True if the preference is locked, as defined by the preference service. + uint8_t mIsLocked : 1; + // True if the preference is sanitized, as defined by the preference + // service. + uint8_t mIsSanitized : 1; + // True if the preference should be skipped while iterating over the + // SharedPrefMap. This is used to internally store Once StaticPrefs. + // This property is not visible to users the way sticky and locked are. + uint8_t mIsSkippedByIteration : 1; + }; + + public: + NS_INLINE_DECL_REFCOUNTING(SharedPrefMap) + + // A temporary wrapper class for accessing entries in the array. Instances of + // this class are valid as long as SharedPrefMap instance is alive, but + // generally should not be stored long term, or allocated on the heap. + // + // The class is implemented as two pointers, one to the SharedPrefMap + // instance, and one to the Entry that corresponds to the preference, and is + // meant to be cheaply returned by value from preference lookups and + // iterators. All property accessors lazily fetch the appropriate values from + // the shared memory region. + class MOZ_STACK_CLASS Pref final { + public: + const char* Name() const { return mMap->KeyTable().GetBare(mEntry->mKey); } + + nsCString NameString() const { return mMap->KeyTable().Get(mEntry->mKey); } + + PrefType Type() const { + MOZ_ASSERT(PrefType(mEntry->mType) != PrefType::None); + return PrefType(mEntry->mType); + } + + bool HasDefaultValue() const { return mEntry->mHasDefaultValue; } + bool HasUserValue() const { return mEntry->mHasUserValue; } + bool IsLocked() const { return mEntry->mIsLocked; } + bool IsSanitized() const { return mEntry->mIsSanitized; } + bool IsSticky() const { return mEntry->mIsSticky; } + bool IsSkippedByIteration() const { return mEntry->mIsSkippedByIteration; } + + bool GetBoolValue(PrefValueKind aKind = PrefValueKind::User) const { + MOZ_ASSERT(Type() == PrefType::Bool); + MOZ_ASSERT(aKind == PrefValueKind::Default ? HasDefaultValue() + : HasUserValue()); + + return aKind == PrefValueKind::Default ? mEntry->mValue.mDefaultBool + : mEntry->mValue.mUserBool; + } + + int32_t GetIntValue(PrefValueKind aKind = PrefValueKind::User) const { + MOZ_ASSERT(Type() == PrefType::Int); + MOZ_ASSERT(aKind == PrefValueKind::Default ? HasDefaultValue() + : HasUserValue()); + + return aKind == PrefValueKind::Default + ? mMap->DefaultIntValues()[mEntry->mValue.mIndex] + : mMap->UserIntValues()[mEntry->mValue.mIndex]; + } + + private: + const StringTableEntry& GetStringEntry(PrefValueKind aKind) const { + MOZ_ASSERT(Type() == PrefType::String); + MOZ_ASSERT(aKind == PrefValueKind::Default ? HasDefaultValue() + : HasUserValue()); + + return aKind == PrefValueKind::Default + ? mMap->DefaultStringValues()[mEntry->mValue.mIndex] + : mMap->UserStringValues()[mEntry->mValue.mIndex]; + } + + public: + nsCString GetStringValue(PrefValueKind aKind = PrefValueKind::User) const { + return mMap->ValueTable().Get(GetStringEntry(aKind)); + } + + const char* GetBareStringValue( + PrefValueKind aKind = PrefValueKind::User) const { + return mMap->ValueTable().GetBare(GetStringEntry(aKind)); + } + + // Returns the entry's index in the map, as understood by GetKeyAt() and + // GetValueAt(). + size_t Index() const { return mEntry - mMap->Entries().get(); } + + bool operator==(const Pref& aPref) const { return mEntry == aPref.mEntry; } + bool operator!=(const Pref& aPref) const { return !(*this == aPref); } + + // This is odd, but necessary in order for the C++ range iterator protocol + // to work here. + Pref& operator*() { return *this; } + + // Updates this wrapper to point to the next visible entry in the map. This + // should not be attempted unless Index() is less than the map's Count(). + Pref& operator++() { + do { + mEntry++; + } while (mEntry->mIsSkippedByIteration && Index() < mMap->Count()); + return *this; + } + + Pref(const Pref& aPref) = default; + + protected: + friend class SharedPrefMap; + + Pref(const SharedPrefMap* aPrefMap, const Entry* aEntry) + : mMap(aPrefMap), mEntry(aEntry) {} + + private: + const SharedPrefMap* const mMap; + const Entry* mEntry; + }; + + // Note: These constructors are infallible, because the preference database is + // critical to platform functionality, and we cannot operate without it. + SharedPrefMap(const FileDescriptor&, size_t); + explicit SharedPrefMap(SharedPrefMapBuilder&&); + + // Searches for the given preference in the map, and returns true if it + // exists. + bool Has(const char* aKey) const; + + bool Has(const nsCString& aKey) const { return Has(aKey.get()); } + + // Searches for the given preference in the map, and if it exists, returns + // a Some<Pref> containing its details. + Maybe<const Pref> Get(const char* aKey) const; + + Maybe<const Pref> Get(const nsCString& aKey) const { return Get(aKey.get()); } + + private: + // Searches for an entry for the given key. If found, returns true, and + // places its index in the entry array in aIndex. + bool Find(const char* aKey, size_t* aIndex) const; + + public: + // Returns the number of entries in the map. + uint32_t Count() const { return EntryCount(); } + + // Returns the string entry at the given index. Keys are guaranteed to be + // sorted lexicographically. + // + // The given index *must* be less than the value returned by Count(). + // + // The returned value is a literal string which references the mapped memory + // region. + nsCString GetKeyAt(uint32_t aIndex) const { + MOZ_ASSERT(aIndex < Count()); + return KeyTable().Get(Entries()[aIndex].mKey); + } + + // Returns the value for the entry at the given index. + // + // The given index *must* be less than the value returned by Count(). + // + // The returned value is valid for the lifetime of this map instance. + const Pref GetValueAt(uint32_t aIndex) const { + MOZ_ASSERT(aIndex < Count()); + return UncheckedGetValueAt(aIndex); + } + + private: + // Returns a wrapper with a pointer to an entry without checking its bounds. + // This should only be used by range iterators, to check their end positions. + // + // Note: In debug builds, the RangePtr returned by entries will still assert + // that aIndex is no more than 1 past the last element in the array, since it + // also takes into account the ranged iteration use case. + Pref UncheckedGetValueAt(uint32_t aIndex) const { + return {this, (Entries() + aIndex).get()}; + } + + public: + // C++ range iterator protocol. begin() and end() return references to the + // first (non-skippable) and last entries in the array. The begin wrapper + // can be incremented until it matches the last element in the array, at which + // point it becomes invalid and the iteration is over. + Pref begin() const { + for (uint32_t aIndex = 0; aIndex < Count(); aIndex++) { + Pref pref = UncheckedGetValueAt(aIndex); + if (!pref.IsSkippedByIteration()) { + return pref; + } + } + return end(); + } + Pref end() const { return UncheckedGetValueAt(Count()); } + + // A cosmetic helper for range iteration. Returns a reference value from a + // pointer to this instance so that its .begin() and .end() methods can be + // accessed in a ranged for loop. `map->Iter()` is equivalent to `*map`, but + // makes its purpose slightly clearer. + const SharedPrefMap& Iter() const { return *this; } + + // Returns a copy of the read-only file descriptor which backs the shared + // memory region for this map. The file descriptor may be passed between + // processes, and used to construct new instances of SharedPrefMap with + // the same data as this instance. + FileDescriptor CloneFileDescriptor() const; + + // Returns the size of the mapped memory region. This size must be passed to + // the constructor when mapping the shared region in another process. + size_t MapSize() const { return mMap.size(); } + + protected: + ~SharedPrefMap() = default; + + private: + template <typename T> + using StringTable = mozilla::dom::ipc::StringTable<T>; + + // Type-safe getters for values in the shared memory region: + const Header& GetHeader() const { return mMap.get<Header>()[0]; } + + RangedPtr<const Entry> Entries() const { + return {reinterpret_cast<const Entry*>(&GetHeader() + 1), EntryCount()}; + } + + uint32_t EntryCount() const { return GetHeader().mEntryCount; } + + template <typename T> + RangedPtr<const T> GetBlock(const DataBlock& aBlock) const { + return RangedPtr<uint8_t>(&mMap.get<uint8_t>()[aBlock.mOffset], + aBlock.mSize) + .ReinterpretCast<const T>(); + } + + RangedPtr<const int32_t> DefaultIntValues() const { + return GetBlock<int32_t>(GetHeader().mDefaultIntValues); + } + RangedPtr<const int32_t> UserIntValues() const { + return GetBlock<int32_t>(GetHeader().mUserIntValues); + } + + RangedPtr<const StringTableEntry> DefaultStringValues() const { + return GetBlock<StringTableEntry>(GetHeader().mDefaultStringValues); + } + RangedPtr<const StringTableEntry> UserStringValues() const { + return GetBlock<StringTableEntry>(GetHeader().mUserStringValues); + } + + StringTable<nsCString> KeyTable() const { + auto& block = GetHeader().mKeyStrings; + return {{&mMap.get<uint8_t>()[block.mOffset], block.mSize}}; + } + + StringTable<nsCString> ValueTable() const { + auto& block = GetHeader().mValueStrings; + return {{&mMap.get<uint8_t>()[block.mOffset], block.mSize}}; + } + + loader::AutoMemMap mMap; +}; + +// A helper class which builds the contiguous look-up table used by +// SharedPrefMap. Each preference in the final map is added to the builder, +// before it is finalized and transformed into a read-only snapshot. +class MOZ_RAII SharedPrefMapBuilder { + public: + SharedPrefMapBuilder() = default; + + // The set of flags for the preference, as documented in SharedPrefMap::Entry. + struct Flags { + uint8_t mHasDefaultValue : 1; + uint8_t mHasUserValue : 1; + uint8_t mIsSticky : 1; + uint8_t mIsLocked : 1; + uint8_t mIsSanitized : 1; + uint8_t mIsSkippedByIteration : 1; + }; + + void Add(const nsCString& aKey, const Flags& aFlags, bool aDefaultValue, + bool aUserValue); + + void Add(const nsCString& aKey, const Flags& aFlags, int32_t aDefaultValue, + int32_t aUserValue); + + void Add(const nsCString& aKey, const Flags& aFlags, + const nsCString& aDefaultValue, const nsCString& aUserValue); + + // Finalizes the binary representation of the map, writes it to a shared + // memory region, and then initializes the given AutoMemMap with a reference + // to the read-only copy of it. + // + // This should generally not be used directly by callers. The + // SharedPrefMapBuilder instance should instead be passed to the SharedPrefMap + // constructor as a move reference. + Result<Ok, nsresult> Finalize(loader::AutoMemMap& aMap); + + private: + using StringTableEntry = mozilla::dom::ipc::StringTableEntry; + template <typename T, typename U> + using StringTableBuilder = mozilla::dom::ipc::StringTableBuilder<T, U>; + + // An opaque descriptor of the index of a preference entry in a value array, + // which can be converted numeric index after the ValueTableBuilder is + // finalized. + struct ValueIdx { + // The relative index of the entry, based on its class. Entries for + // preferences with user values appear at the value arrays. Entries with + // only default values begin after the last entry with a user value. + uint16_t mIndex; + bool mHasUserValue; + }; + + // A helper class for building default and user value arrays for preferences. + // + // As described in the SharedPrefMap class, this helper optimizes the way that + // it builds its value arrays, in that: + // + // - It stores value entries for all preferences with user values before + // entries for preferences with only default values, and allocates no + // entries for preferences with only default values in the user value array. + // Since most preferences have only default values, this dramatically + // reduces the space required for value storage. + // + // - For preferences with only default values, it de-duplicates value entries, + // and returns the same indices for all preferences with the same value. + // + // One important complication of this approach is that it means we cannot know + // the final index of any entry with only a default value until all entries + // have been added to the builder, since it depends on the final number of + // user entries in the output. + // + // To deal with this, when entries are added, we return an opaque ValueIndex + // struct, from which we can calculate the final index after the map has been + // finalized. + template <typename HashKey, typename ValueType_> + class ValueTableBuilder { + public: + using ValueType = ValueType_; + + // Adds an entry for a preference with only a default value to the array, + // and returns an opaque descriptor for its index. + ValueIdx Add(const ValueType& aDefaultValue) { + auto index = uint16_t(mDefaultEntries.Count()); + + return mDefaultEntries.WithEntryHandle(aDefaultValue, [&](auto&& entry) { + entry.OrInsertWith([&] { return Entry{index, false, aDefaultValue}; }); + + return ValueIdx{entry->mIndex, false}; + }); + } + + // Adds an entry for a preference with a user value to the array. Regardless + // of whether the preference has a default value, space must be allocated + // for it. For preferences with no default value, the actual value which + // appears in the array at its value index is ignored. + ValueIdx Add(const ValueType& aDefaultValue, const ValueType& aUserValue) { + auto index = uint16_t(mUserEntries.Length()); + + mUserEntries.AppendElement(Entry{index, true, aDefaultValue, aUserValue}); + + return {index, true}; + } + + // Returns the final index for an entry based on its opaque index + // descriptor. This must only be called after the caller has finished adding + // entries to the builder. + uint16_t GetIndex(const ValueIdx& aIndex) const { + uint16_t base = aIndex.mHasUserValue ? 0 : UserCount(); + return base + aIndex.mIndex; + } + + // Writes out the array of default values at the block beginning at the + // given pointer. The block must be at least as large as the value returned + // by DefaultSize(). + void WriteDefaultValues(const RangedPtr<uint8_t>& aBuffer) const { + auto buffer = aBuffer.ReinterpretCast<ValueType>(); + + for (const auto& entry : mUserEntries) { + buffer[entry.mIndex] = entry.mDefaultValue; + } + + size_t defaultsOffset = UserCount(); + for (const auto& data : mDefaultEntries.Values()) { + buffer[defaultsOffset + data.mIndex] = data.mDefaultValue; + } + } + + // Writes out the array of user values at the block beginning at the + // given pointer. The block must be at least as large as the value returned + // by UserSize(). + void WriteUserValues(const RangedPtr<uint8_t>& aBuffer) const { + auto buffer = aBuffer.ReinterpretCast<ValueType>(); + + for (const auto& entry : mUserEntries) { + buffer[entry.mIndex] = entry.mUserValue; + } + } + + // These return the number of entries in the default and user value arrays, + // respectively. + uint32_t DefaultCount() const { + return UserCount() + mDefaultEntries.Count(); + } + uint32_t UserCount() const { return mUserEntries.Length(); } + + // These return the byte sizes of the default and user value arrays, + // respectively. + uint32_t DefaultSize() const { return DefaultCount() * sizeof(ValueType); } + uint32_t UserSize() const { return UserCount() * sizeof(ValueType); } + + void Clear() { + mUserEntries.Clear(); + mDefaultEntries.Clear(); + } + + static constexpr size_t Alignment() { return alignof(ValueType); } + + private: + struct Entry { + uint16_t mIndex; + bool mHasUserValue; + ValueType mDefaultValue; + ValueType mUserValue{}; + }; + + AutoTArray<Entry, 256> mUserEntries; + + nsTHashMap<HashKey, Entry> mDefaultEntries; + }; + + // A special-purpose string table builder for keys which are already + // guaranteed to be unique. Duplicate values will not be detected or + // de-duplicated. + template <typename CharType> + class UniqueStringTableBuilder { + public: + using ElemType = CharType; + + explicit UniqueStringTableBuilder(size_t aCapacity) : mEntries(aCapacity) {} + + StringTableEntry Add(const nsTString<CharType>& aKey) { + auto entry = mEntries.AppendElement( + Entry{mSize, uint32_t(aKey.Length()), aKey.get()}); + + mSize += entry->mLength + 1; + + return {entry->mOffset, entry->mLength}; + } + + void Write(const RangedPtr<uint8_t>& aBuffer) { + auto buffer = aBuffer.ReinterpretCast<ElemType>(); + + for (auto& entry : mEntries) { + memcpy(&buffer[entry.mOffset], entry.mValue, + sizeof(ElemType) * (entry.mLength + 1)); + } + } + + uint32_t Count() const { return mEntries.Length(); } + + uint32_t Size() const { return mSize * sizeof(ElemType); } + + void Clear() { mEntries.Clear(); } + + static constexpr size_t Alignment() { return alignof(ElemType); } + + private: + struct Entry { + uint32_t mOffset; + uint32_t mLength; + const CharType* mValue; + }; + + nsTArray<Entry> mEntries; + uint32_t mSize = 0; + }; + + // A preference value entry, roughly corresponding to the + // SharedPrefMap::Value struct, but with a temporary place-holder value rather + // than a final value index. + union Value { + Value(bool aDefaultValue, bool aUserValue) + : mDefaultBool(aDefaultValue), mUserBool(aUserValue) {} + + MOZ_IMPLICIT Value(const ValueIdx& aIndex) : mIndex(aIndex) {} + + // For Bool preferences, their default and user bool values. + struct { + bool mDefaultBool; + bool mUserBool; + }; + // For Int and String preferences, an opaque descriptor for their entries in + // their value arrays. This must be passed to the appropriate + // ValueTableBuilder to obtain the final index when the entry is serialized. + ValueIdx mIndex; + }; + + // A preference entry, to be converted to a SharedPrefMap::Entry struct during + // serialization. + struct Entry { + // The entry's preference name, as passed to Add(). The caller is + // responsible for keeping this pointer alive until the builder is + // finalized. + const char* mKeyString; + // The entry in mKeyTable corresponding to mKeyString. + StringTableEntry mKey; + Value mValue; + + uint8_t mType : 2; + uint8_t mHasDefaultValue : 1; + uint8_t mHasUserValue : 1; + uint8_t mIsSticky : 1; + uint8_t mIsLocked : 1; + uint8_t mIsSanitized : 1; + uint8_t mIsSkippedByIteration : 1; + }; + + // Converts a builder Value struct to a SharedPrefMap::Value struct for + // serialization. This must not be called before callers have finished adding + // entries to the value array builders. + SharedPrefMap::Value GetValue(const Entry& aEntry) const { + switch (PrefType(aEntry.mType)) { + case PrefType::Bool: + return {aEntry.mValue.mDefaultBool, aEntry.mValue.mUserBool}; + case PrefType::Int: + return {mIntValueTable.GetIndex(aEntry.mValue.mIndex)}; + case PrefType::String: + return {mStringValueTable.GetIndex(aEntry.mValue.mIndex)}; + default: + MOZ_ASSERT_UNREACHABLE("Invalid pref type"); + return {false, false}; + } + } + + UniqueStringTableBuilder<char> mKeyTable{kExpectedPrefCount}; + StringTableBuilder<nsCStringHashKey, nsCString> mValueStringTable; + + ValueTableBuilder<nsUint32HashKey, uint32_t> mIntValueTable; + ValueTableBuilder<nsGenericHashKey<StringTableEntry>, StringTableEntry> + mStringValueTable; + + nsTArray<Entry> mEntries{kExpectedPrefCount}; +}; + +} // namespace mozilla + +#endif // dom_ipc_SharedPrefMap_h |