layout/style/CachedInheritingStyles.h

   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 #ifndef mozilla_CachedInheritingStyles_h
   8 #define mozilla_CachedInheritingStyles_h
   9
  10 #include "nsAtom.h"
  11 #include "nsCOMPtr.h"
  12 #include "nsTArray.h"
  13
  14 class nsWindowSizes;
  15
  16 namespace mozilla {
  17
  18 enum class PseudoStyleType : uint8_t;
  19 class ComputedStyle;
  20
  21 // Cache of anonymous box and lazy pseudo styles that inherit from a given
  22 // style.
  23 //
  24 // To minimize memory footprint, the cache is word-sized with a tagged pointer
  25 // If there is only one entry, it's stored inline. If there are more, they're
  26 // stored in an out-of-line buffer. See bug 1429126 comment 0 and comment 1 for
  27 // the measurements and rationale that influenced the design.
  28 class CachedInheritingStyles {
  29  public:
  30   void Insert(ComputedStyle* aStyle);
  31   ComputedStyle* Lookup(PseudoStyleType) const;
  32
  33   CachedInheritingStyles() : mBits(0) {}
  34   ~CachedInheritingStyles() {
  35     if (IsIndirect()) {
  36       delete AsIndirect();
  37     } else if (!IsEmpty()) {
  38       RefPtr<ComputedStyle> ref = dont_AddRef(AsDirect());
  39     }
  40   }
  41
  42   void AddSizeOfIncludingThis(nsWindowSizes& aSizes, size_t* aCVsSize) const;
  43
  44  private:
  45   // See bug 1429126 comment 1 for the choice of four here.
  46   typedef AutoTArray<RefPtr<ComputedStyle>, 4> IndirectCache;
  47
  48   bool IsEmpty() const { return !mBits; }
  49   bool IsIndirect() const { return (mBits & 1); }
  50
  51   ComputedStyle* AsDirect() const {
  52     MOZ_ASSERT(!IsIndirect());
  53     return reinterpret_cast<ComputedStyle*>(mBits);
  54   }
  55
  56   IndirectCache* AsIndirect() const {
  57     MOZ_ASSERT(IsIndirect());
  58     return reinterpret_cast<IndirectCache*>(mBits & ~1);
  59   }
  60
  61   uintptr_t mBits;
  62 };
  63
  64 }  // namespace mozilla
  65
  66 #endif  // mozilla_CachedInheritingStyles_h