dom/bindings/RootedOwningNonNull.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 file,
   5  * You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 /**
   8  * An implementation of Rooted for OwningNonNull<T>.  This works by assuming
   9  * that T has a Trace() method defined on it which will trace whatever things
  10  * inside the T instance need tracing.
  11  *
  12  * This implementation has one serious drawback: operator= doesn't work right
  13  * because it's declared on Rooted directly and expects the type Rooted is
  14  * templated over.
  15  */
  16
  17 #ifndef mozilla_RootedOwningNonNull_h__
  18 #define mozilla_RootedOwningNonNull_h__
  19
  20 #include "mozilla/OwningNonNull.h"
  21 #include "js/GCPolicyAPI.h"
  22 #include "js/RootingAPI.h"
  23
  24 namespace JS {
  25 template <typename T>
  26 struct GCPolicy<mozilla::OwningNonNull<T>> {
  27   typedef mozilla::OwningNonNull<T> SmartPtrType;
  28
  29   static SmartPtrType initial() { return SmartPtrType(); }
  30
  31   static void trace(JSTracer* trc, SmartPtrType* tp, const char* name) {
  32     // We have to be very careful here.  Normally, OwningNonNull can't be null.
  33     // But binding code can end up in a situation where it sets up a
  34     // Rooted<OwningNonNull> and then before it gets a chance to assign to it
  35     // (e.g. from the constructor of the thing being assigned) a GC happens.  So
  36     // we can land here when *tp stores a null pointer because it's not
  37     // initialized.
  38     //
  39     // So we need to check for that before jumping.
  40     if ((*tp).isInitialized()) {
  41       (*tp)->Trace(trc);
  42     }
  43   }
  44
  45   static bool isValid(const SmartPtrType& v) {
  46     return !v.isInitialized() || GCPolicy<T>::isValid(v);
  47   }
  48 };
  49 }  // namespace JS
  50
  51 namespace js {
  52 template <typename T, typename Wrapper>
  53 struct WrappedPtrOperations<mozilla::OwningNonNull<T>, Wrapper> {
  54   operator T&() const { return static_cast<const Wrapper*>(this)->get(); }
  55 };
  56 }  // namespace js
  57
  58 #endif /* mozilla_RootedOwningNonNull_h__ */