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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim: set ts=8 sts=2 et sw=2 tw=80: */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
#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::dom::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 {
auto length = uint32_t(aKey.Length());
entry.OrInsertWith([&]() {
Entry newEntry{mSize, aKey};
mSize += length + 1;
return newEntry;
});
return {entry->mOffset, 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 mozilla::dom::ipc
#endif