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gecko-dev/modules/libpref/SharedPrefMap.h
Kris Maglione 667653bbb3 Bug 1471025: Part 5 - Add a range iterator helper for iterating both static and dynamic preferences. r=njn 
For memory efficiency in content processes, we need to be able to store
changed preferences in a separate dynamic hashtable when their values don't
match the snapshot values.

That makes iteration over the full set of preferences somewhat more
complicated, since not only do we need to iterate over two tables, but we also
need to ignore preferences in the snapshot table if they also exist in the
dynamic hashtable.

This patch solves that problem by adding an iterator helper which iterates
over values in both tables, and skips values in the static table if they also
exist in the dynamic table.

In order to support completely deleting preferences that exist in the base
table, it also ignores all dynamic entries with the None type, so that they
can completely mask deleted base table values.

MozReview-Commit-ID: LCIwyPJMByj

--HG--
extra : intermediate-source : f9362cf1add47c2f62529e42764ed6088d274170
extra : absorb_source : fdaf890e85af43271cffd2371cf6fbf408c6cc50
extra : source : d344247b870668f53fa645e72bda4bb4309346c8
extra : histedit_source : 6cd565727eff617eeba386b563477ce4d4bfbd0a
2018-07-02 18:17:48 -07:00

896 lines
36 KiB
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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
/* vim: set ts=8 sts=4 et sw=4 tw=99: */
/* 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 "nsDataHashtable.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 lenghts.
//
// 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;
};
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 IsSticky() const { return mEntry->mIsSticky; }
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 entry in the map. This should
// not be attempted unless Index() is less than the map's Count().
Pref& operator++()
{
mEntry++;
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 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 { return UncheckedGetValueAt(0); }
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;
};
void Add(const char* aKey,
const Flags& aFlags,
bool aDefaultValue,
bool aUserValue);
void Add(const char* aKey,
const Flags& aFlags,
int32_t aDefaultValue,
int32_t aUserValue);
void Add(const char* 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());
auto entry = mDefaultEntries.LookupForAdd(aDefaultValue).OrInsert([&]() {
return Entry{ index, false, aDefaultValue };
});
return { 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 (auto iter = mDefaultEntries.ConstIter(); !iter.Done(); iter.Next()) {
const auto& entry = iter.Data();
buffer[defaultsOffset + entry.mIndex] = entry.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;
nsDataHashtable<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 CharType* aKey)
{
auto entry =
mEntries.AppendElement(Entry{ mSize, uint32_t(strlen(aKey)), aKey });
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;
};
// 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 };
};
} // mozilla
#endif // dom_ipc_SharedPrefMap_h
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