tor-browser

The Tor Browser
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SharedStringMap.cpp (4193B)

      1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
      2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
      3 /* This Source Code Form is subject to the terms of the Mozilla Public
      4 * License, v. 2.0. If a copy of the MPL was not distributed with this
      5 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
      6 
      7 #include "SharedStringMap.h"
      8 
      9 #include "MemMapSnapshot.h"
     10 #include "ScriptPreloader-inl.h"
     11 #include "mozilla/BinarySearch.h"
     12 #include "mozilla/Try.h"
     13 
     14 using namespace mozilla::loader;
     15 
     16 namespace mozilla {
     17 
     18 using namespace ipc;
     19 
     20 namespace dom::ipc {
     21 
     22 static constexpr uint32_t kSharedStringMapMagic = 0x9e3779b9;
     23 
     24 static inline size_t GetAlignmentOffset(size_t aOffset, size_t aAlign) {
     25  auto mod = aOffset % aAlign;
     26  return mod ? aAlign - mod : 0;
     27 }
     28 
     29 SharedStringMap::SharedStringMap(const ReadOnlySharedMemoryHandle& aMapHandle) {
     30  mHandle = aMapHandle.Clone();
     31  MOZ_RELEASE_ASSERT(mHandle.IsValid());
     32  auto mapping = aMapHandle.Map();
     33  MOZ_RELEASE_ASSERT(mapping.IsValid());
     34 
     35  // We return literal nsStrings and nsCStrings pointing to the mapped data,
     36  // which means that we may still have references to the mapped data even
     37  // after this instance is destroyed. That means that we need to keep the
     38  // mapping alive until process shutdown, in order to be safe.
     39  mMappedMemory = std::move(mapping).Release();
     40 
     41  MOZ_RELEASE_ASSERT(GetHeader().mMagic == kSharedStringMapMagic);
     42 }
     43 
     44 SharedStringMap::SharedStringMap(SharedStringMapBuilder&& aBuilder) {
     45  ReadOnlySharedMemoryMappingWithHandle mappingWithHandle;
     46  auto result = aBuilder.Finalize();
     47  MOZ_RELEASE_ASSERT(result.isOk());
     48  mHandle = result.unwrap();
     49  auto mapping = mHandle.Map();
     50  MOZ_RELEASE_ASSERT(mapping.IsValid());
     51 
     52  mMappedMemory = std::move(mapping).Release();
     53 
     54  MOZ_RELEASE_ASSERT(GetHeader().mMagic == kSharedStringMapMagic);
     55 }
     56 
     57 mozilla::ipc::ReadOnlySharedMemoryHandle SharedStringMap::CloneHandle() const {
     58  return mHandle.Clone();
     59 }
     60 
     61 bool SharedStringMap::Has(const nsCString& aKey) {
     62  size_t index;
     63  return Find(aKey, &index);
     64 }
     65 
     66 bool SharedStringMap::Get(const nsCString& aKey, nsAString& aValue) {
     67  const auto& entries = Entries();
     68 
     69  size_t index;
     70  if (!Find(aKey, &index)) {
     71    return false;
     72  }
     73 
     74  aValue.Assign(ValueTable().Get(entries[index].mValue));
     75  return true;
     76 }
     77 
     78 bool SharedStringMap::Find(const nsCString& aKey, size_t* aIndex) {
     79  const auto& keys = KeyTable();
     80 
     81  return BinarySearchIf(
     82      Entries(), 0, EntryCount(),
     83      [&](const Entry& aEntry) { return Compare(aKey, keys.Get(aEntry.mKey)); },
     84      aIndex);
     85 }
     86 
     87 void SharedStringMapBuilder::Add(const nsCString& aKey,
     88                                 const nsString& aValue) {
     89  mEntries.InsertOrUpdate(aKey,
     90                          Entry{mKeyTable.Add(aKey), mValueTable.Add(aValue)});
     91 }
     92 
     93 Result<ReadOnlySharedMemoryHandle, nsresult>
     94 SharedStringMapBuilder::Finalize() {
     95  using Header = SharedStringMap::Header;
     96 
     97  MOZ_ASSERT(mEntries.Count() == mKeyTable.Count());
     98 
     99  auto keys = ToTArray<nsTArray<nsCString>>(mEntries.Keys());
    100  keys.Sort();
    101 
    102  Header header = {kSharedStringMapMagic, uint32_t(keys.Length())};
    103 
    104  size_t offset = sizeof(header);
    105  offset += GetAlignmentOffset(offset, alignof(Header));
    106 
    107  offset += keys.Length() * sizeof(SharedStringMap::Entry);
    108 
    109  header.mKeyStringsOffset = offset;
    110  header.mKeyStringsSize = mKeyTable.Size();
    111 
    112  offset += header.mKeyStringsSize;
    113  offset +=
    114      GetAlignmentOffset(offset, alignof(decltype(mValueTable)::ElemType));
    115 
    116  header.mValueStringsOffset = offset;
    117  header.mValueStringsSize = mValueTable.Size();
    118 
    119  offset += header.mValueStringsSize;
    120 
    121  MemMapSnapshot mem;
    122  MOZ_TRY(mem.Init(offset));
    123 
    124  auto headerPtr = mem.Get<Header>();
    125  headerPtr[0] = header;
    126 
    127  auto* entry = reinterpret_cast<Entry*>(&headerPtr[1]);
    128  for (auto& key : keys) {
    129    *entry++ = mEntries.Get(key);
    130  }
    131 
    132  auto ptr = mem.Get<uint8_t>();
    133 
    134  mKeyTable.Write({&ptr[header.mKeyStringsOffset], header.mKeyStringsSize});
    135 
    136  mValueTable.Write(
    137      {&ptr[header.mValueStringsOffset], header.mValueStringsSize});
    138 
    139  mKeyTable.Clear();
    140  mValueTable.Clear();
    141  mEntries.Clear();
    142 
    143  return mem.Finalize();
    144 }
    145 
    146 }  // namespace dom::ipc
    147 }  // namespace mozilla