1 files changed, 168 insertions, 0 deletions
diff --git a/dom/canvas/CacheInvalidator.h b/dom/canvas/CacheInvalidator.h
new file mode 100644
index 0000000000..e63f1e4cc2
--- /dev/null
+++ b/dom/canvas/CacheInvalidator.h
@@ -0,0 +1,168 @@
+/* -*- Mode: C++; tab-width: 13; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=13 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef MOZILLA_CACHE_INVALIDATOR_H_
+#define MOZILLA_CACHE_INVALIDATOR_H_
+
+#include "mozilla/Maybe.h"
+#include "mozilla/UniquePtr.h"
+#include <unordered_map>
+#include <unordered_set>
+#include <vector>
+
+// -
+
+namespace mozilla {
+
+class AbstractCache;
+
+// -
+
+class CacheInvalidator {
+  friend class AbstractCache;
+
+ private:
+  mutable std::unordered_set<AbstractCache*> mCaches;
+
+ public:
+  virtual ~CacheInvalidator() {
+    // It's actually generally unsafe to wait until now to invalidate caches,
+    // because when used as a mixin, this dtor is called after the dtor for the
+    // derived class. This means that if the derived class holds a cache (or is
+    // a cache!), OnInvalidate() will be called on a destroyed object.
+    // MOZ_ASSERT(!mCaches);
+    InvalidateCaches();
+  }
+
+  void InvalidateCaches() const;
+};
+
+// -
+
+class AbstractCache {
+  using InvalidatorListT = std::vector<const CacheInvalidator*>;
+
+ private:
+  InvalidatorListT mInvalidators;
+
+ public:
+  AbstractCache() = default;
+
+  explicit AbstractCache(InvalidatorListT&& invalidators) {
+    ResetInvalidators(std::move(invalidators));
+  }
+
+  virtual ~AbstractCache() { ResetInvalidators({}); }
+
+ public:
+  virtual void OnInvalidate() = 0;
+
+  void ResetInvalidators(InvalidatorListT&&);
+  void AddInvalidator(const CacheInvalidator&);
+};
+
+// -
+
+template <typename T>
+class CacheMaybe : public AbstractCache {
+  Maybe<T> mVal;
+
+ public:
+  template <typename U>
+  CacheMaybe& operator=(Maybe<U>&& rhs) {
+    mVal.reset();
+    if (rhs) {
+      mVal.emplace(std::move(rhs.ref()));
+    }
+    return *this;
+  }
+
+  CacheMaybe& operator=(Nothing) { return *this = Maybe<T>(); }
+
+  void OnInvalidate() override {
+    *this = Nothing();
+    ResetInvalidators({});
+  }
+
+  explicit operator bool() const { return bool(mVal); }
+  T* get() const { return mVal.ptrOr(nullptr); }
+  T* operator->() const { return get(); }
+};
+
+// -
+
+template <typename KeyT, typename ValueT>
+class CacheWeakMap final {
+  class Entry final : public AbstractCache {
+   public:
+    CacheWeakMap& mParent;
+    const KeyT mKey;
+    const ValueT mValue;
+
+    Entry(CacheWeakMap& parent, const KeyT& key, ValueT&& value)
+        : mParent(parent), mKey(key), mValue(std::move(value)) {}
+
+    void OnInvalidate() override {
+      const auto erased = mParent.mMap.erase(&mKey);
+      MOZ_ALWAYS_TRUE(erased == 1);
+    }
+  };
+
+  struct DerefHash final {
+    size_t operator()(const KeyT* const a) const {
+      return std::hash<KeyT>()(*a);
+    }
+  };
+  struct DerefEqual final {
+    bool operator()(const KeyT* const a, const KeyT* const b) const {
+      return *a == *b;
+    }
+  };
+
+  using MapT =
+      std::unordered_map<const KeyT*, UniquePtr<Entry>, DerefHash, DerefEqual>;
+  MapT mMap;
+
+ public:
+  UniquePtr<Entry> MakeEntry(const KeyT& key, ValueT&& value) {
+    return UniquePtr<Entry>(new Entry(*this, key, std::move(value)));
+  }
+  UniquePtr<Entry> MakeEntry(const KeyT& key, const ValueT& value) {
+    return MakeEntry(key, ValueT(value));
+  }
+
+  const ValueT* Insert(UniquePtr<Entry>&& entry) {
+    auto insertable = typename MapT::value_type{&entry->mKey, std::move(entry)};
+
+    const auto res = mMap.insert(std::move(insertable));
+    const auto& didInsert = res.second;
+    MOZ_ALWAYS_TRUE(didInsert);
+
+    const auto& itr = res.first;
+    return &itr->second->mValue;
+  }
+
+  const ValueT* Find(const KeyT& key) const {
+    const auto itr = mMap.find(&key);
+    if (itr == mMap.end()) return nullptr;
+
+    return &itr->second->mValue;
+  }
+
+  void Clear() const {
+    while (true) {
+      const auto itr = mMap.begin();
+      if (itr == mMap.end()) return;
+      itr->second->OnInvalidate();
+    }
+  }
+
+  ~CacheWeakMap() { Clear(); }
+};
+
+}  // namespace mozilla
+
+#endif  // MOZILLA_CACHE_INVALIDATOR_H_