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Bug 1471025: Part 2 - Add a helper class creating and accessing shared preference map snapshots. r=njn,erahm 

This is based on the SharedStringMap that's currently used for shared memory
string bundles.

When the parent process is ready to launch its first content process, it
creates a snapshot of the current state of the preference database, maps that
as read-only, and shares it with each content process. Look-ups in the
snapshotted map are done entirely using data in the shared memory region. It
doesn't require any additional per-process state data.

MozReview-Commit-ID: BdTUhak7dmS

--HG--
extra : intermediate-source : 434106f1b75e3ba900912f261bd22a1b7f5c931d
extra : absorb_source : 647ad37590448ad3c1eb8eb512bf671f262fa96e
extra : source : 68bb03c63b3cee1d47cbddfd3abf919f5783c04b
extra : histedit_source : 2228a9f8395929f5072a3c5ebda6ae3221e4a62d
This commit is contained in:
Kris Maglione 2018-07-01 18:28:31 -07:00
Родитель 9b5cf7e9da
Коммит 82bc4d713f
10 изменённых файлов: 1363 добавлений и 100 удалений
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2
dom/ipc/MemMapSnapshot.h
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@ -7,7 +7,7 @@
#ifndef dom_ipc_MemMapSnapshot_h
#define dom_ipc_MemMapSnapshot_h
#include "AutoMemMap.h"
#include "mozilla/AutoMemMap.h"
#include "mozilla/Attributes.h"
#include "mozilla/Maybe.h"
#include "mozilla/RangedPtr.h"

3
dom/ipc/SharedStringMap.cpp
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@ -90,8 +90,7 @@ SharedStringMap::Find(const nsCString& aKey, size_t* aIndex)
void
SharedStringMapBuilder::Add(const nsCString& aKey, const nsString& aValue)
{
mEntries.Put(aKey, {{mKeyTable.Add(aKey), aKey.Length()},
{mValueTable.Add(aValue), aValue.Length()}});
mEntries.Put(aKey, {mKeyTable.Add(aKey), mValueTable.Add(aValue)});
}
Result<Ok, nsresult>

91
dom/ipc/SharedStringMap.h
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@ -9,7 +9,7 @@
#include "mozilla/AutoMemMap.h"
#include "mozilla/Result.h"
#include "mozilla/TypeTraits.h"
#include "mozilla/dom/ipc/StringTable.h"
#include "nsDataHashtable.h"
namespace mozilla {
@ -75,25 +75,15 @@ public:
size_t mValueStringsSize;
};
/**
* Contains the character offset and character length of an entry in a string
* table. This may be used for either 8-bit or 16-bit strings, and is required
* to retrieve an entry from a string table.
*/
struct StringEntry {
uint32_t mOffset;
uint32_t mLength;
};
/**
* Describes a value in the string map, as offsets into the key and value
* string tables.
*/
struct Entry {
// The offset and size of the entry's UTF-8 key in the key string table.
StringEntry mKey;
StringTableEntry mKey;
// The offset and size of the entry's UTF-16 value in the value string table.
StringEntry mValue;
StringTableEntry mValue;
};
NS_INLINE_DECL_REFCOUNTING(SharedStringMap)
@ -174,35 +164,6 @@ protected:
~SharedStringMap() = default;
private:
template <typename StringType>
class StringTable
{
using ElemType = decltype(DeclVal<StringType>()[0]);
public:
MOZ_IMPLICIT StringTable(const RangedPtr<uint8_t>& aBuffer)
: mBuffer(aBuffer.ReinterpretCast<ElemType>())
{
MOZ_ASSERT(uintptr_t(aBuffer.get()) % alignof(ElemType) == 0,
"Got misalinged buffer");
}
StringType Get(const StringEntry& aEntry) const
{
StringType res;
res.AssignLiteral(GetBare(aEntry), aEntry.mLength);
return res;
}
const ElemType* GetBare(const StringEntry& aEntry) const
{
return &mBuffer[aEntry.mOffset];
}
private:
RangedPtr<ElemType> mBuffer;
};
// Type-safe getters for values in the shared memory region:
const Header& GetHeader() const
@ -262,52 +223,6 @@ public:
Result<Ok, nsresult> Finalize(loader::AutoMemMap& aMap);
private:
template <typename KeyType, typename StringType>
class StringTableBuilder
{
public:
using ElemType = typename StringType::char_type;
uint32_t Add(const StringType& aKey)
{
auto entry = mEntries.LookupForAdd(aKey).OrInsert([&] () {
Entry newEntry { mSize, aKey };
mSize += aKey.Length() + 1;
return newEntry;
});
return entry.mOffset;
}
void Write(const RangedPtr<uint8_t>& aBuffer)
{
auto buffer = aBuffer.ReinterpretCast<ElemType>();
for (auto iter = mEntries.Iter(); !iter.Done(); iter.Next()) {
auto& entry = iter.Data();
memcpy(&buffer[entry.mOffset], entry.mValue.BeginReading(),
sizeof(ElemType) * (entry.mValue.Length() + 1));
}
}
uint32_t Count() const { return mEntries.Count(); }
uint32_t Size() const { return mSize * sizeof(ElemType); }
void Clear() { mEntries.Clear(); }
private:
struct Entry
{
uint32_t mOffset;
StringType mValue;
};
nsDataHashtable<KeyType, Entry> mEntries;
uint32_t mSize = 0;
};
using Entry = SharedStringMap::Entry;
StringTableBuilder<nsCStringHashKey, nsCString> mKeyTable;

127
dom/ipc/StringTable.h Normal file
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@ -0,0 +1,127 @@
/* -*- 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_StringTable_h
#define dom_ipc_StringTable_h
#include "mozilla/RangedPtr.h"
#include "nsDataHashtable.h"
/**
* This file contains helper classes for creating and accessing compact string
* tables, which can be used as the building blocks of shared memory databases.
* Each string table a de-duplicated set of strings which can be referenced
* using their character offsets within a data block and their lengths. The
* string tables, once created, cannot be modified, and are primarily useful in
* read-only shared memory or memory mapped files.
*/
namespace mozilla {
namespace dom {
namespace ipc {
/**
* Contains the character offset and character length of an entry in a string
* table. This may be used for either 8-bit or 16-bit strings, and is required
* to retrieve an entry from a string table.
*/
struct StringTableEntry
{
uint32_t mOffset;
uint32_t mLength;
// Ignore mLength. It must be the same for any two strings with the same
// offset.
uint32_t Hash() const { return mOffset; }
bool operator==(const StringTableEntry& aOther) const
{
return mOffset == aOther.mOffset;
}
};
template <typename StringType>
class StringTable
{
using ElemType = typename StringType::char_type;
public:
MOZ_IMPLICIT StringTable(const RangedPtr<uint8_t>& aBuffer)
: mBuffer(aBuffer.ReinterpretCast<ElemType>())
{
MOZ_ASSERT(uintptr_t(aBuffer.get()) % alignof(ElemType) == 0,
"Got misalinged buffer");
}
StringType Get(const StringTableEntry& aEntry) const
{
StringType res;
res.AssignLiteral(GetBare(aEntry), aEntry.mLength);
return res;
}
const ElemType* GetBare(const StringTableEntry& aEntry) const
{
return &mBuffer[aEntry.mOffset];
}
private:
RangedPtr<ElemType> mBuffer;
};
template <typename KeyType, typename StringType>
class StringTableBuilder
{
public:
using ElemType = typename StringType::char_type;
StringTableEntry Add(const StringType& aKey)
{
const auto& entry = mEntries.LookupForAdd(aKey).OrInsert([&] () {
Entry newEntry { mSize, aKey };
mSize += aKey.Length() + 1;
return newEntry;
});
return { entry.mOffset, aKey.Length() };
}
void Write(const RangedPtr<uint8_t>& aBuffer)
{
auto buffer = aBuffer.ReinterpretCast<ElemType>();
for (auto iter = mEntries.Iter(); !iter.Done(); iter.Next()) {
auto& entry = iter.Data();
memcpy(&buffer[entry.mOffset], entry.mValue.BeginReading(),
sizeof(ElemType) * (entry.mValue.Length() + 1));
}
}
uint32_t Count() const { return mEntries.Count(); }
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;
StringType mValue;
};
nsDataHashtable<KeyType, Entry> mEntries;
uint32_t mSize = 0;
};
} // namespace ipc
} // namespace dom
} // namespace mozilla
#endif

2
dom/ipc/moz.build
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@ -15,9 +15,11 @@ XPIDL_MODULE = 'dom'
EXPORTS.mozilla.dom.ipc += [
'IdType.h',
'MemMapSnapshot.h',
'SharedMap.h',
'SharedMapChangeEvent.h',
'SharedStringMap.h',
'StringTable.h',
'StructuredCloneData.h',
]

109
modules/libpref/Preferences.cpp
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@ -8,6 +8,8 @@
#include <stdlib.h>
#include <string.h>
#include "SharedPrefMap.h"
#include "base/basictypes.h"
#include "GeckoProfiler.h"
#include "MainThreadUtils.h"
@ -93,6 +95,8 @@
using namespace mozilla;
using mozilla::ipc::FileDescriptor;
#ifdef DEBUG
#define ENSURE_PARENT_PROCESS(func, pref) \
@ -127,15 +131,6 @@ static const uint32_t MAX_PREF_LENGTH = 1 * 1024 * 1024;
// Actually, 4kb should be enough for everyone.
static const uint32_t MAX_ADVISABLE_PREF_LENGTH = 4 * 1024;
// Keep this in sync with PrefType in parser/src/lib.rs.
enum class PrefType : uint8_t
{
None = 0, // only used when neither the default nor user value is set
String = 1,
Int = 2,
Bool = 3,
};
// This is used for pref names and string pref values. We encode the string
// length, then a '/', then the string chars. This encoding means there are no
// special chars that are forbidden or require escaping.
@ -189,6 +184,9 @@ union PrefValue {
}
}
template<typename T>
T Get() const;
void Init(PrefType aNewType, PrefValue aNewValue)
{
if (aNewType == PrefType::String) {
@ -318,6 +316,27 @@ union PrefValue {
}
};
template<>
bool
PrefValue::Get() const
{
return mBoolVal;
}
template<>
int32_t
PrefValue::Get() const
{
return mIntVal;
}
template<>
nsDependentCString
PrefValue::Get() const
{
return nsDependentCString(mStringVal);
}
#ifdef DEBUG
const char*
PrefTypeToString(PrefType aType)
@ -468,6 +487,29 @@ public:
bool HasDefaultValue() const { return mHasDefaultValue; }
bool HasUserValue() const { return mHasUserValue; }
template<typename T>
void AddToMap(SharedPrefMapBuilder& aMap)
{
aMap.Add(
Name(),
{ HasDefaultValue(), HasUserValue(), uint8_t(mIsSticky), IsLocked() },
HasDefaultValue() ? mDefaultValue.Get<T>() : T(),
HasUserValue() ? mUserValue.Get<T>() : T());
}
void AddToMap(SharedPrefMapBuilder& aMap)
{
if (IsTypeBool()) {
AddToMap<bool>(aMap);
} else if (IsTypeInt()) {
AddToMap<int32_t>(aMap);
} else if (IsTypeString()) {
AddToMap<nsDependentCString>(aMap);
} else {
MOZ_ASSERT_UNREACHABLE("Unexpected preference type");
}
}
// When a content process is created we could tell it about every pref. But
// the content process also initializes prefs from file, so we save a lot of
// IPC if we only tell it about prefs that have changed since initialization.
@ -1064,6 +1106,8 @@ private:
static PLDHashTable* gHashTable;
static StaticRefPtr<SharedPrefMap> gSharedMap;
// The callback list contains all the priority callbacks followed by the
// non-priority callbacks. gLastPriorityNode records where the first part ends.
static CallbackNode* gFirstCallback = nullptr;
@ -3018,6 +3062,10 @@ PreferenceServiceReporter::CollectReports(
node->AddSizeOfIncludingThis(mallocSizeOf, sizes);
}
if (gSharedMap) {
sizes.mMisc += mallocSizeOf(gSharedMap);
}
MOZ_COLLECT_REPORT("explicit/preferences/hash-table",
KIND_HEAP,
UNITS_BYTES,
@ -3073,6 +3121,17 @@ PreferenceServiceReporter::CollectReports(
sizes.mMisc,
"Miscellaneous memory used by libpref.");
if (gSharedMap) {
if (XRE_IsParentProcess()) {
MOZ_COLLECT_REPORT("explicit/preferences/shared-memory-map",
KIND_NONHEAP,
UNITS_BYTES,
gSharedMap->MapSize(),
"The shared memory mapping used to share a "
"snapshot of preference values across processes.");
}
}
nsPrefBranch* rootBranch =
static_cast<nsPrefBranch*>(Preferences::GetRootBranch());
if (!rootBranch) {
@ -3445,6 +3504,8 @@ Preferences::~Preferences()
delete gAccessCounts;
#endif
gSharedMap = nullptr;
gPrefNameArena.Clear();
}
@ -3496,6 +3557,36 @@ Preferences::DeserializePreferences(char* aStr, size_t aPrefsLen)
#endif
}
/* static */ FileDescriptor
Preferences::EnsureSnapshot(size_t* aSize)
{
MOZ_ASSERT(XRE_IsParentProcess());
if (!gSharedMap) {
SharedPrefMapBuilder builder;
for (auto iter = gHashTable->Iter(); !iter.Done(); iter.Next()) {
Pref* pref = static_cast<PrefEntry*>(iter.Get())->mPref;
pref->AddToMap(builder);
}
gSharedMap = new SharedPrefMap(std::move(builder));
}
*aSize = gSharedMap->MapSize();
return gSharedMap->CloneFileDescriptor();
}
/* static */ void
Preferences::InitSnapshot(const FileDescriptor& aHandle, size_t aSize)
{
MOZ_ASSERT(!XRE_IsParentProcess());
MOZ_ASSERT(!gSharedMap);
gSharedMap = new SharedPrefMap(aHandle, aSize);
}
/* static */ void
Preferences::InitializeUserPrefs()
{

22
modules/libpref/Preferences.h
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@ -39,8 +39,27 @@ class Pref;
class PrefValue;
} // namespace dom
namespace ipc {
class FileDescriptor;
} // namespace ipc
struct PrefsSizes;
// Xlib.h defines Bool as a macro constant. Don't try to define this enum if
// it's already been included.
#ifndef Bool
// Keep this in sync with PrefType in parser/src/lib.rs.
enum class PrefType : uint8_t
{
None = 0, // only used when neither the default nor user value is set
String = 1,
Int = 2,
Bool = 3,
};
#endif
#ifdef XP_UNIX
// XXX: bug 1440207 is about improving how fixed fds such as this are used.
static const int kPrefsFileDescriptor = 8;
@ -481,6 +500,9 @@ public:
static void SerializePreferences(nsCString& aStr);
static void DeserializePreferences(char* aStr, size_t aPrefsLen);
static mozilla::ipc::FileDescriptor EnsureSnapshot(size_t* aSize);
static void InitSnapshot(const mozilla::ipc::FileDescriptor&, size_t aSize);
// When a single pref is changed in the parent process, these methods are
// used to pass the update to content processes.
static void GetPreference(dom::Pref* aPref);

252
modules/libpref/SharedPrefMap.cpp Normal file
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@ -0,0 +1,252 @@
/* -*- 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/. */
#include "SharedPrefMap.h"
#include "mozilla/dom/ipc/MemMapSnapshot.h"
#include "mozilla/BinarySearch.h"
#include "mozilla/ResultExtensions.h"
#include "mozilla/ipc/FileDescriptor.h"
using namespace mozilla::loader;
namespace mozilla {
using namespace ipc;
static inline size_t
GetAlignmentOffset(size_t aOffset, size_t aAlign)
{
auto mod = aOffset % aAlign;
return mod ? aAlign - mod : 0;
}
SharedPrefMap::SharedPrefMap(const FileDescriptor& aMapFile, size_t aMapSize)
{
auto result = mMap.initWithHandle(aMapFile, aMapSize);
MOZ_RELEASE_ASSERT(result.isOk());
// We return literal nsCStrings pointing to the mapped data for preference
// names and string values, which means that we may still have references to
// the mapped data even after this instance is destroyed. That means that we
// need to keep the mapping alive until process shutdown, in order to be safe.
mMap.setPersistent();
}
SharedPrefMap::SharedPrefMap(SharedPrefMapBuilder&& aBuilder)
{
auto result = aBuilder.Finalize(mMap);
MOZ_RELEASE_ASSERT(result.isOk());
mMap.setPersistent();
}
mozilla::ipc::FileDescriptor
SharedPrefMap::CloneFileDescriptor() const
{
return mMap.cloneHandle();
}
bool
SharedPrefMap::Has(const char* aKey) const
{
size_t index;
return Find(aKey, &index);
}
Maybe<const SharedPrefMap::Pref>
SharedPrefMap::Get(const char* aKey) const
{
Maybe<const Pref> result;
size_t index;
if (Find(aKey, &index)) {
result.emplace(Pref{ this, &Entries()[index] });
}
return result;
}
bool
SharedPrefMap::Find(const char* aKey, size_t* aIndex) const
{
const auto& keys = KeyTable();
return BinarySearchIf(Entries(),
0,
EntryCount(),
[&](const Entry& aEntry) {
return strcmp(aKey, keys.GetBare(aEntry.mKey));
},
aIndex);
}
void
SharedPrefMapBuilder::Add(const char* aKey,
const Flags& aFlags,
bool aDefaultValue,
bool aUserValue)
{
mEntries.AppendElement(Entry{
aKey,
mKeyTable.Add(aKey),
{ aDefaultValue, aUserValue },
uint8_t(PrefType::Bool),
aFlags.mHasDefaultValue,
aFlags.mHasUserValue,
aFlags.mIsSticky,
aFlags.mIsLocked,
});
}
void
SharedPrefMapBuilder::Add(const char* aKey,
const Flags& aFlags,
int32_t aDefaultValue,
int32_t aUserValue)
{
ValueIdx index;
if (aFlags.mHasUserValue) {
index = mIntValueTable.Add(aDefaultValue, aUserValue);
} else {
index = mIntValueTable.Add(aDefaultValue);
}
mEntries.AppendElement(Entry{
aKey,
mKeyTable.Add(aKey),
{ index },
uint8_t(PrefType::Int),
aFlags.mHasDefaultValue,
aFlags.mHasUserValue,
aFlags.mIsSticky,
aFlags.mIsLocked,
});
}
void
SharedPrefMapBuilder::Add(const char* aKey,
const Flags& aFlags,
const nsCString& aDefaultValue,
const nsCString& aUserValue)
{
ValueIdx index;
StringTableEntry defaultVal = mValueStringTable.Add(aDefaultValue);
if (aFlags.mHasUserValue) {
StringTableEntry userVal = mValueStringTable.Add(aUserValue);
index = mStringValueTable.Add(defaultVal, userVal);
} else {
index = mStringValueTable.Add(defaultVal);
}
mEntries.AppendElement(Entry{
aKey,
mKeyTable.Add(aKey),
{ index },
uint8_t(PrefType::String),
aFlags.mHasDefaultValue,
aFlags.mHasUserValue,
aFlags.mIsSticky,
aFlags.mIsLocked,
});
}
Result<Ok, nsresult>
SharedPrefMapBuilder::Finalize(loader::AutoMemMap& aMap)
{
using Header = SharedPrefMap::Header;
// Create an array of entry pointers for the entry array, and sort it by
// preference name prior to serialization, so that entries can be looked up
// using binary search.
nsTArray<Entry*> entries(mEntries.Length());
for (auto& entry : mEntries) {
entries.AppendElement(&entry);
}
entries.Sort([](const Entry* aA, const Entry* aB) {
return strcmp(aA->mKeyString, aB->mKeyString);
});
Header header = { uint32_t(entries.Length()) };
size_t offset = sizeof(header);
offset += GetAlignmentOffset(offset, alignof(Header));
offset += entries.Length() * sizeof(SharedPrefMap::Entry);
header.mKeyStrings.mOffset = offset;
header.mKeyStrings.mSize = mKeyTable.Size();
offset += header.mKeyStrings.mSize;
offset += GetAlignmentOffset(offset, mIntValueTable.Alignment());
header.mUserIntValues.mOffset = offset;
header.mUserIntValues.mSize = mIntValueTable.UserSize();
offset += header.mUserIntValues.mSize;
offset += GetAlignmentOffset(offset, mIntValueTable.Alignment());
header.mDefaultIntValues.mOffset = offset;
header.mDefaultIntValues.mSize = mIntValueTable.DefaultSize();
offset += header.mDefaultIntValues.mSize;
offset += GetAlignmentOffset(offset, mStringValueTable.Alignment());
header.mUserStringValues.mOffset = offset;
header.mUserStringValues.mSize = mStringValueTable.UserSize();
offset += header.mUserStringValues.mSize;
offset += GetAlignmentOffset(offset, mStringValueTable.Alignment());
header.mDefaultStringValues.mOffset = offset;
header.mDefaultStringValues.mSize = mStringValueTable.DefaultSize();
offset += header.mDefaultStringValues.mSize;
header.mValueStrings.mOffset = offset;
header.mValueStrings.mSize = mValueStringTable.Size();
offset += header.mValueStrings.mSize;
MemMapSnapshot mem;
MOZ_TRY(mem.Init(offset));
auto headerPtr = mem.Get<Header>();
headerPtr[0] = header;
auto* entryPtr = reinterpret_cast<SharedPrefMap::Entry*>(&headerPtr[1]);
for (auto* entry : entries) {
*entryPtr = {
entry->mKey, GetValue(*entry),
entry->mType, entry->mHasDefaultValue,
entry->mHasUserValue, entry->mIsSticky,
entry->mIsLocked,
};
entryPtr++;
}
auto ptr = mem.Get<uint8_t>();
mKeyTable.Write(
{ &ptr[header.mKeyStrings.mOffset], header.mKeyStrings.mSize });
mValueStringTable.Write(
{ &ptr[header.mValueStrings.mOffset], header.mValueStrings.mSize });
mIntValueTable.WriteDefaultValues(
{ &ptr[header.mDefaultIntValues.mOffset], header.mDefaultIntValues.mSize });
mIntValueTable.WriteUserValues(
{ &ptr[header.mUserIntValues.mOffset], header.mUserIntValues.mSize });
mStringValueTable.WriteDefaultValues(
{ &ptr[header.mDefaultStringValues.mOffset],
header.mDefaultStringValues.mSize });
mStringValueTable.WriteUserValues(
{ &ptr[header.mUserStringValues.mOffset], header.mUserStringValues.mSize });
mKeyTable.Clear();
mValueStringTable.Clear();
mIntValueTable.Clear();
mStringValueTable.Clear();
mEntries.Clear();
return mem.Finalize(aMap);
}
} // mozilla

854
modules/libpref/SharedPrefMap.h Normal file
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@ -0,0 +1,854 @@
/* -*- 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(); }
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 { this, (Entries() + aIndex).get() };
}
// 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

1
modules/libpref/moz.build
Просмотреть файл

@ -32,6 +32,7 @@ EXPORTS.mozilla += [
UNIFIED_SOURCES += [
'Preferences.cpp',
'SharedPrefMap.cpp',
]
include('/ipc/chromium/chromium-config.mozbuild')