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