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/Try.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 SharedMemoryHandle& aMapHandle,
  31                                  size_t aMapSize) {
  32   auto map = MakeRefPtr<SharedMemory>();
  33   {
  34     auto result = map->SetHandle(SharedMemory::CloneHandle(aMapHandle),
  35                                  SharedMemory::OpenRights::RightsReadOnly);
  36     MOZ_RELEASE_ASSERT(result);
  37   }
  38   {
  39     auto result = map->Map(aMapSize);
  40     MOZ_RELEASE_ASSERT(result);
  41   }
  42
  43   // We return literal nsStrings and nsCStrings pointing to the mapped data,
  44   // which means that we may still have references to the mapped data even
  45   // after this instance is destroyed. That means that we need to keep the
  46   // mapping alive until process shutdown, in order to be safe.
  47   mMappedMemory = map->TakeMapping();
  48   mHandle = map->TakeHandle();
  49
  50   MOZ_RELEASE_ASSERT(GetHeader().mMagic == kSharedStringMapMagic);
  51 }
  52
  53 SharedStringMap::SharedStringMap(SharedStringMapBuilder&& aBuilder) {
  54   RefPtr<SharedMemory> map;
  55   auto result = aBuilder.Finalize(map);
  56   MOZ_RELEASE_ASSERT(result.isOk() && map);
  57
  58   mMappedMemory = map->TakeMapping();
  59   mHandle = map->TakeHandle();
  60
  61   MOZ_RELEASE_ASSERT(GetHeader().mMagic == kSharedStringMapMagic);
  62 }
  63
  64 mozilla::ipc::SharedMemoryHandle SharedStringMap::CloneHandle() const {
  65   return SharedMemory::CloneHandle(mHandle);
  66 }
  67
  68 bool SharedStringMap::Has(const nsCString& aKey) {
  69   size_t index;
  70   return Find(aKey, &index);
  71 }
  72
  73 bool SharedStringMap::Get(const nsCString& aKey, nsAString& aValue) {
  74   const auto& entries = Entries();
  75
  76   size_t index;
  77   if (!Find(aKey, &index)) {
  78     return false;
  79   }
  80
  81   aValue.Assign(ValueTable().Get(entries[index].mValue));
  82   return true;
  83 }
  84
  85 bool SharedStringMap::Find(const nsCString& aKey, size_t* aIndex) {
  86   const auto& keys = KeyTable();
  87
  88   return BinarySearchIf(
  89       Entries(), 0, EntryCount(),
  90       [&](const Entry& aEntry) { return Compare(aKey, keys.Get(aEntry.mKey)); },
  91       aIndex);
  92 }
  93
  94 void SharedStringMapBuilder::Add(const nsCString& aKey,
  95                                  const nsString& aValue) {
  96   mEntries.InsertOrUpdate(aKey,
  97                           Entry{mKeyTable.Add(aKey), mValueTable.Add(aValue)});
  98 }
  99
 100 Result<Ok, nsresult> SharedStringMapBuilder::Finalize(
 101     RefPtr<SharedMemory>& aMap) {
 102   using Header = SharedStringMap::Header;
 103
 104   MOZ_ASSERT(mEntries.Count() == mKeyTable.Count());
 105
 106   auto keys = ToTArray<nsTArray<nsCString>>(mEntries.Keys());
 107   keys.Sort();
 108
 109   Header header = {kSharedStringMapMagic, uint32_t(keys.Length())};
 110
 111   size_t offset = sizeof(header);
 112   offset += GetAlignmentOffset(offset, alignof(Header));
 113
 114   offset += keys.Length() * sizeof(SharedStringMap::Entry);
 115
 116   header.mKeyStringsOffset = offset;
 117   header.mKeyStringsSize = mKeyTable.Size();
 118
 119   offset += header.mKeyStringsSize;
 120   offset +=
 121       GetAlignmentOffset(offset, alignof(decltype(mValueTable)::ElemType));
 122
 123   header.mValueStringsOffset = offset;
 124   header.mValueStringsSize = mValueTable.Size();
 125
 126   offset += header.mValueStringsSize;
 127
 128   MemMapSnapshot mem;
 129   MOZ_TRY(mem.Init(offset));
 130
 131   auto headerPtr = mem.Get<Header>();
 132   headerPtr[0] = header;
 133
 134   auto* entry = reinterpret_cast<Entry*>(&headerPtr[1]);
 135   for (auto& key : keys) {
 136     *entry++ = mEntries.Get(key);
 137   }
 138
 139   auto ptr = mem.Get<uint8_t>();
 140
 141   mKeyTable.Write({&ptr[header.mKeyStringsOffset], header.mKeyStringsSize});
 142
 143   mValueTable.Write(
 144       {&ptr[header.mValueStringsOffset], header.mValueStringsSize});
 145
 146   mKeyTable.Clear();
 147   mValueTable.Clear();
 148   mEntries.Clear();
 149
 150   return mem.Finalize(aMap);
 151 }
 152
 153 }  // namespace dom::ipc
 154 }  // namespace mozilla