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82bc4d713f
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
128 lines
3.2 KiB
C++
128 lines
3.2 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
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/* vim: set ts=8 sts=4 et sw=4 tw=99: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef dom_ipc_StringTable_h
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#define dom_ipc_StringTable_h
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#include "mozilla/RangedPtr.h"
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#include "nsDataHashtable.h"
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/**
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* This file contains helper classes for creating and accessing compact string
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* tables, which can be used as the building blocks of shared memory databases.
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* Each string table a de-duplicated set of strings which can be referenced
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* using their character offsets within a data block and their lengths. The
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* string tables, once created, cannot be modified, and are primarily useful in
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* read-only shared memory or memory mapped files.
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*/
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namespace mozilla {
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namespace dom {
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namespace ipc {
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/**
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* Contains the character offset and character length of an entry in a string
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* table. This may be used for either 8-bit or 16-bit strings, and is required
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* to retrieve an entry from a string table.
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*/
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struct StringTableEntry
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{
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uint32_t mOffset;
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uint32_t mLength;
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// Ignore mLength. It must be the same for any two strings with the same
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// offset.
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uint32_t Hash() const { return mOffset; }
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bool operator==(const StringTableEntry& aOther) const
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{
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return mOffset == aOther.mOffset;
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}
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};
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template <typename StringType>
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class StringTable
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{
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using ElemType = typename StringType::char_type;
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public:
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MOZ_IMPLICIT StringTable(const RangedPtr<uint8_t>& aBuffer)
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: mBuffer(aBuffer.ReinterpretCast<ElemType>())
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{
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MOZ_ASSERT(uintptr_t(aBuffer.get()) % alignof(ElemType) == 0,
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"Got misalinged buffer");
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}
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StringType Get(const StringTableEntry& aEntry) const
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{
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StringType res;
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res.AssignLiteral(GetBare(aEntry), aEntry.mLength);
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return res;
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}
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const ElemType* GetBare(const StringTableEntry& aEntry) const
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{
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return &mBuffer[aEntry.mOffset];
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}
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private:
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RangedPtr<ElemType> mBuffer;
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};
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template <typename KeyType, typename StringType>
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class StringTableBuilder
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{
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public:
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using ElemType = typename StringType::char_type;
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StringTableEntry Add(const StringType& aKey)
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{
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const auto& entry = mEntries.LookupForAdd(aKey).OrInsert([&] () {
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Entry newEntry { mSize, aKey };
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mSize += aKey.Length() + 1;
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return newEntry;
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});
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return { entry.mOffset, aKey.Length() };
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}
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void Write(const RangedPtr<uint8_t>& aBuffer)
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{
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auto buffer = aBuffer.ReinterpretCast<ElemType>();
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for (auto iter = mEntries.Iter(); !iter.Done(); iter.Next()) {
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auto& entry = iter.Data();
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memcpy(&buffer[entry.mOffset], entry.mValue.BeginReading(),
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sizeof(ElemType) * (entry.mValue.Length() + 1));
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}
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}
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uint32_t Count() const { return mEntries.Count(); }
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uint32_t Size() const { return mSize * sizeof(ElemType); }
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void Clear() { mEntries.Clear(); }
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static constexpr size_t Alignment() { return alignof(ElemType); }
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private:
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struct Entry
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{
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uint32_t mOffset;
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StringType mValue;
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};
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nsDataHashtable<KeyType, Entry> mEntries;
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uint32_t mSize = 0;
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};
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} // namespace ipc
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} // namespace dom
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} // namespace mozilla
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#endif
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