dom/xbl/nsXBLMaybeCompiled.h

   1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* This Source Code Form is subject to the terms of the Mozilla Public
   3  * License, v. 2.0. If a copy of the MPL was not distributed with this
   4  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   5
   6 #ifndef nsXBLMaybeCompiled_h__
   7 #define nsXBLMaybeCompiled_h__
   8
   9 #include "js/GCAPI.h"
  10
  11 /*
  12  * A union containing either a pointer representing uncompiled source or a
  13  * JSObject* representing the compiled result.  The class is templated on the
  14  * source object type.
  15  *
  16  * The purpose of abstracting this as a separate class is to allow it to be
  17  * wrapped in a JS::Heap<T> to correctly handle post-barriering of the JSObject
  18  * pointer, when present.
  19  *
  20  * No implementation of rootKind() is provided, which prevents
  21  * Root<nsXBLMaybeCompiled<UncompiledT>> from being used.
  22  */
  23 template <class UncompiledT>
  24 class nsXBLMaybeCompiled
  25 {
  26 public:
  27   nsXBLMaybeCompiled() : mUncompiled(BIT_UNCOMPILED) {}
  28
  29   explicit nsXBLMaybeCompiled(UncompiledT* uncompiled)
  30     : mUncompiled(reinterpret_cast<uintptr_t>(uncompiled) | BIT_UNCOMPILED) {}
  31
  32   explicit nsXBLMaybeCompiled(JSObject* compiled) : mCompiled(compiled) {}
  33
  34   bool IsCompiled() const
  35   {
  36     return !(mUncompiled & BIT_UNCOMPILED);
  37   }
  38
  39   UncompiledT* GetUncompiled() const
  40   {
  41     MOZ_ASSERT(!IsCompiled(), "Attempt to get compiled function as uncompiled");
  42     uintptr_t unmasked = mUncompiled & ~BIT_UNCOMPILED;
  43     return reinterpret_cast<UncompiledT*>(unmasked);
  44   }
  45
  46   JSObject* GetJSFunction() const
  47   {
  48     MOZ_ASSERT(IsCompiled(), "Attempt to get uncompiled function as compiled");
  49     if (mCompiled) {
  50       JS::ExposeObjectToActiveJS(mCompiled);
  51     }
  52     return mCompiled;
  53   }
  54
  55   // This is appropriate for use in tracing methods, etc.
  56   JSObject* GetJSFunctionPreserveColor() const
  57   {
  58     MOZ_ASSERT(IsCompiled(), "Attempt to get uncompiled function as compiled");
  59     return mCompiled;
  60   }
  61
  62 private:
  63   JSObject*& UnsafeGetJSFunction()
  64   {
  65     MOZ_ASSERT(IsCompiled(), "Attempt to get uncompiled function as compiled");
  66     return mCompiled;
  67   }
  68
  69   enum { BIT_UNCOMPILED = 1 << 0 };
  70
  71   union
  72   {
  73     // An pointer that represents the function before being compiled, with
  74     // BIT_UNCOMPILED set.
  75     uintptr_t mUncompiled;
  76
  77     // The JS object for the compiled result.
  78     JSObject* mCompiled;
  79   };
  80
  81   friend struct js::GCMethods<nsXBLMaybeCompiled<UncompiledT>>;
  82 };
  83
  84 /* Add support for JS::Heap<nsXBLMaybeCompiled>. */
  85 namespace js {
  86
  87 template <class UncompiledT>
  88 struct GCMethods<nsXBLMaybeCompiled<UncompiledT> >
  89 {
  90   typedef struct GCMethods<JSObject *> Base;
  91
  92   static nsXBLMaybeCompiled<UncompiledT> initial() { return nsXBLMaybeCompiled<UncompiledT>(); }
  93
  94   static bool poisoned(nsXBLMaybeCompiled<UncompiledT> function)
  95   {
  96     return function.IsCompiled() && Base::poisoned(function.GetJSFunction());
  97   }
  98
  99   static bool needsPostBarrier(nsXBLMaybeCompiled<UncompiledT> function)
 100   {
 101     return function.IsCompiled() && Base::needsPostBarrier(function.GetJSFunction());
 102   }
 103
 104   static void postBarrier(nsXBLMaybeCompiled<UncompiledT>* functionp)
 105   {
 106     Base::postBarrier(&functionp->UnsafeGetJSFunction());
 107   }
 108
 109   static void relocate(nsXBLMaybeCompiled<UncompiledT>* functionp)
 110   {
 111     Base::relocate(&functionp->UnsafeGetJSFunction());
 112   }
 113 };
 114
 115 template <class UncompiledT>
 116 class HeapBase<nsXBLMaybeCompiled<UncompiledT> >
 117 {
 118   const JS::Heap<nsXBLMaybeCompiled<UncompiledT> >& wrapper() const {
 119     return *static_cast<const JS::Heap<nsXBLMaybeCompiled<UncompiledT> >*>(this);
 120   }
 121
 122   JS::Heap<nsXBLMaybeCompiled<UncompiledT> >& wrapper() {
 123     return *static_cast<JS::Heap<nsXBLMaybeCompiled<UncompiledT> >*>(this);
 124   }
 125
 126   const nsXBLMaybeCompiled<UncompiledT>* extract() const {
 127     return wrapper().address();
 128   }
 129
 130   nsXBLMaybeCompiled<UncompiledT>* extract() {
 131     return wrapper().unsafeGet();
 132   }
 133
 134 public:
 135   bool IsCompiled() const { return extract()->IsCompiled(); }
 136   UncompiledT* GetUncompiled() const { return extract()->GetUncompiled(); }
 137   JSObject* GetJSFunction() const { return extract()->GetJSFunction(); }
 138   JSObject* GetJSFunctionPreserveColor() const { return extract()->GetJSFunctionPreserveColor(); }
 139
 140   void SetUncompiled(UncompiledT* source) {
 141     wrapper().set(nsXBLMaybeCompiled<UncompiledT>(source));
 142   }
 143
 144   void SetJSFunction(JSObject* function) {
 145     wrapper().set(nsXBLMaybeCompiled<UncompiledT>(function));
 146   }
 147
 148   JS::Heap<JSObject*>& AsHeapObject()
 149   {
 150     MOZ_ASSERT(extract()->IsCompiled());
 151     return *reinterpret_cast<JS::Heap<JSObject*>*>(this);
 152   }
 153 };
 154
 155 } /* namespace js */
 156
 157 #endif // nsXBLMaybeCompiled_h__