зеркало из https://github.com/mozilla/gecko-dev.git
120 строки
3.5 KiB
C++
120 строки
3.5 KiB
C++
/* -*- 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_StringTable_h
|
|
#define dom_ipc_StringTable_h
|
|
|
|
#include "mozilla/RangedPtr.h"
|
|
#include "nsTHashMap.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) {
|
|
return mEntries.WithEntryHandle(aKey,
|
|
[&](auto&& entry) -> StringTableEntry {
|
|
entry.OrInsertWith([&]() {
|
|
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 (const auto& entry : mEntries.Values()) {
|
|
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;
|
|
};
|
|
|
|
nsTHashMap<KeyType, Entry> mEntries;
|
|
uint32_t mSize = 0;
|
|
};
|
|
|
|
} // namespace ipc
|
|
} // namespace dom
|
|
} // namespace mozilla
|
|
|
|
#endif
|