dom/ipc/SharedStringMap.cpp

   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
  12 #include "mozilla/BinarySearch.h"
  13 #include "mozilla/ipc/FileDescriptor.h"
  14
  15 using namespace mozilla::loader;
  16
  17 namespace mozilla {
  18
  19 using namespace ipc;
  20
  21 namespace dom::ipc {
  22
  23 static constexpr uint32_t kSharedStringMapMagic = 0x9e3779b9;
  24
  25 static inline size_t GetAlignmentOffset(size_t aOffset, size_t aAlign) {
  26   auto mod = aOffset % aAlign;
  27   return mod ? aAlign - mod : 0;
  28 }
  29
  30 SharedStringMap::SharedStringMap(const FileDescriptor& aMapFile,
  31                                  size_t aMapSize) {
  32   auto result = mMap.initWithHandle(aMapFile, aMapSize);
  33   MOZ_RELEASE_ASSERT(result.isOk());
  34   MOZ_RELEASE_ASSERT(GetHeader().mMagic == kSharedStringMapMagic);
  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   mMap.setPersistent();
  40 }
  41
  42 SharedStringMap::SharedStringMap(SharedStringMapBuilder&& aBuilder) {
  43   auto result = aBuilder.Finalize(mMap);
  44   MOZ_RELEASE_ASSERT(result.isOk());
  45   MOZ_RELEASE_ASSERT(GetHeader().mMagic == kSharedStringMapMagic);
  46   mMap.setPersistent();
  47 }
  48
  49 mozilla::ipc::FileDescriptor SharedStringMap::CloneFileDescriptor() const {
  50   return mMap.cloneHandle();
  51 }
  52
  53 bool SharedStringMap::Has(const nsCString& aKey) {
  54   size_t index;
  55   return Find(aKey, &index);
  56 }
  57
  58 bool SharedStringMap::Get(const nsCString& aKey, nsAString& aValue) {
  59   const auto& entries = Entries();
  60
  61   size_t index;
  62   if (!Find(aKey, &index)) {
  63     return false;
  64   }
  65
  66   aValue.Assign(ValueTable().Get(entries[index].mValue));
  67   return true;
  68 }
  69
  70 bool SharedStringMap::Find(const nsCString& aKey, size_t* aIndex) {
  71   const auto& keys = KeyTable();
  72
  73   return BinarySearchIf(
  74       Entries(), 0, EntryCount(),
  75       [&](const Entry& aEntry) { return Compare(aKey, keys.Get(aEntry.mKey)); },
  76       aIndex);
  77 }
  78
  79 void SharedStringMapBuilder::Add(const nsCString& aKey,
  80                                  const nsString& aValue) {
  81   mEntries.InsertOrUpdate(aKey,
  82                           Entry{mKeyTable.Add(aKey), mValueTable.Add(aValue)});
  83 }
  84
  85 Result<Ok, nsresult> SharedStringMapBuilder::Finalize(
  86     loader::AutoMemMap& aMap) {
  87   using Header = SharedStringMap::Header;
  88
  89   MOZ_ASSERT(mEntries.Count() == mKeyTable.Count());
  90
  91   auto keys = ToTArray<nsTArray<nsCString>>(mEntries.Keys());
  92   keys.Sort();
  93
  94   Header header = {kSharedStringMapMagic, uint32_t(keys.Length())};
  95
  96   size_t offset = sizeof(header);
  97   offset += GetAlignmentOffset(offset, alignof(Header));
  98
  99   offset += keys.Length() * sizeof(SharedStringMap::Entry);
 100
 101   header.mKeyStringsOffset = offset;
 102   header.mKeyStringsSize = mKeyTable.Size();
 103
 104   offset += header.mKeyStringsSize;
 105   offset +=
 106       GetAlignmentOffset(offset, alignof(decltype(mValueTable)::ElemType));
 107
 108   header.mValueStringsOffset = offset;
 109   header.mValueStringsSize = mValueTable.Size();
 110
 111   offset += header.mValueStringsSize;
 112
 113   MemMapSnapshot mem;
 114   MOZ_TRY(mem.Init(offset));
 115
 116   auto headerPtr = mem.Get<Header>();
 117   headerPtr[0] = header;
 118
 119   auto* entry = reinterpret_cast<Entry*>(&headerPtr[1]);
 120   for (auto& key : keys) {
 121     *entry++ = mEntries.Get(key);
 122   }
 123
 124   auto ptr = mem.Get<uint8_t>();
 125
 126   mKeyTable.Write({&ptr[header.mKeyStringsOffset], header.mKeyStringsSize});
 127
 128   mValueTable.Write(
 129       {&ptr[header.mValueStringsOffset], header.mValueStringsSize});
 130
 131   mKeyTable.Clear();
 132   mValueTable.Clear();
 133   mEntries.Clear();
 134
 135   return mem.Finalize(aMap);
 136 }
 137
 138 }  // namespace dom::ipc
 139 }  // namespace mozilla