dom/canvas/CacheInvalidator.h

   1 /* -*- Mode: C++; tab-width: 13; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=13 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 #ifndef MOZILLA_CACHE_INVALIDATOR_H_
   8 #define MOZILLA_CACHE_INVALIDATOR_H_
   9
  10 #include "mozilla/Maybe.h"
  11 #include "mozilla/UniquePtr.h"
  12 #include <unordered_map>
  13 #include <unordered_set>
  14 #include <vector>
  15
  16 // -
  17
  18 namespace mozilla {
  19
  20 class AbstractCache;
  21
  22 // -
  23
  24 class CacheInvalidator {
  25   friend class AbstractCache;
  26
  27  private:
  28   mutable std::unordered_set<AbstractCache*> mCaches;
  29
  30  public:
  31   virtual ~CacheInvalidator() {
  32     // It's actually generally unsafe to wait until now to invalidate caches,
  33     // because when used as a mixin, this dtor is called after the dtor for the
  34     // derived class. This means that if the derived class holds a cache (or is
  35     // a cache!), OnInvalidate() will be called on a destroyed object.
  36     // MOZ_ASSERT(!mCaches);
  37     InvalidateCaches();
  38   }
  39
  40   void InvalidateCaches() const;
  41 };
  42
  43 // -
  44
  45 class AbstractCache {
  46   using InvalidatorListT = std::vector<const CacheInvalidator*>;
  47
  48  private:
  49   InvalidatorListT mInvalidators;
  50
  51  public:
  52   AbstractCache() = default;
  53
  54   explicit AbstractCache(InvalidatorListT&& invalidators) {
  55     ResetInvalidators(std::move(invalidators));
  56   }
  57
  58   virtual ~AbstractCache() { ResetInvalidators({}); }
  59
  60  public:
  61   virtual void OnInvalidate() = 0;
  62
  63   void ResetInvalidators(InvalidatorListT&&);
  64   void AddInvalidator(const CacheInvalidator&);
  65 };
  66
  67 // -
  68
  69 template <typename T>
  70 class CacheMaybe : public AbstractCache {
  71   Maybe<T> mVal;
  72
  73  public:
  74   template <typename U>
  75   CacheMaybe& operator=(Maybe<U>&& rhs) {
  76     mVal.reset();
  77     if (rhs) {
  78       mVal.emplace(std::move(rhs.ref()));
  79     }
  80     return *this;
  81   }
  82
  83   CacheMaybe& operator=(Nothing) { return *this = Maybe<T>(); }
  84
  85   void OnInvalidate() override {
  86     *this = Nothing();
  87     ResetInvalidators({});
  88   }
  89
  90   explicit operator bool() const { return bool(mVal); }
  91   T* get() const { return mVal.ptrOr(nullptr); }
  92   T* operator->() const { return get(); }
  93 };
  94
  95 // -
  96
  97 template <typename KeyT, typename ValueT>
  98 class CacheWeakMap final {
  99   class Entry final : public AbstractCache {
 100    public:
 101     CacheWeakMap& mParent;
 102     const KeyT mKey;
 103     const ValueT mValue;
 104
 105     Entry(CacheWeakMap& parent, const KeyT& key, ValueT&& value)
 106         : mParent(parent), mKey(key), mValue(std::move(value)) {}
 107
 108     void OnInvalidate() override {
 109       const auto erased = mParent.mMap.erase(&mKey);
 110       MOZ_ALWAYS_TRUE(erased == 1);
 111     }
 112   };
 113
 114   struct DerefHash final {
 115     size_t operator()(const KeyT* const a) const {
 116       return std::hash<KeyT>()(*a);
 117     }
 118   };
 119   struct DerefEqual final {
 120     bool operator()(const KeyT* const a, const KeyT* const b) const {
 121       return *a == *b;
 122     }
 123   };
 124
 125   using MapT =
 126       std::unordered_map<const KeyT*, UniquePtr<Entry>, DerefHash, DerefEqual>;
 127   MapT mMap;
 128
 129  public:
 130   UniquePtr<Entry> MakeEntry(const KeyT& key, ValueT&& value) {
 131     return UniquePtr<Entry>(new Entry(*this, key, std::move(value)));
 132   }
 133   UniquePtr<Entry> MakeEntry(const KeyT& key, const ValueT& value) {
 134     return MakeEntry(key, ValueT(value));
 135   }
 136
 137   const ValueT* Insert(UniquePtr<Entry>&& entry) {
 138     auto insertable = typename MapT::value_type{&entry->mKey, std::move(entry)};
 139
 140     const auto res = mMap.insert(std::move(insertable));
 141     const auto& didInsert = res.second;
 142     MOZ_ALWAYS_TRUE(didInsert);
 143
 144     const auto& itr = res.first;
 145     return &itr->second->mValue;
 146   }
 147
 148   const ValueT* Find(const KeyT& key) const {
 149     const auto itr = mMap.find(&key);
 150     if (itr == mMap.end()) return nullptr;
 151
 152     return &itr->second->mValue;
 153   }
 154
 155   void Clear() const {
 156     while (true) {
 157       const auto itr = mMap.begin();
 158       if (itr == mMap.end()) return;
 159       itr->second->OnInvalidate();
 160     }
 161   }
 162
 163   ~CacheWeakMap() { Clear(); }
 164 };
 165
 166 }  // namespace mozilla
 167
 168 #endif  // MOZILLA_CACHE_INVALIDATOR_H_