dom/base/nsWrapperCacheInlines.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 nsWrapperCacheInline_h___
   8 #define nsWrapperCacheInline_h___
   9
  10 #include "nsWrapperCache.h"
  11 #include "js/RootingAPI.h"
  12 #include "js/TracingAPI.h"
  13
  14 inline JSObject* nsWrapperCache::GetWrapperPreserveColor() const {
  15   JSObject* obj = GetWrapperMaybeDead();
  16   if (obj && js::gc::EdgeNeedsSweepUnbarriered(&obj)) {
  17     // The object has been found to be dead and is in the process of being
  18     // finalized, so don't let the caller see it.
  19     // Don't clear the cache though: this happens when a new wrapper is created
  20     // for this native or when the wrapper is finalized.
  21     return nullptr;
  22   }
  23   MOZ_ASSERT(obj == mWrapper);
  24   return obj;
  25 }
  26
  27 inline JSObject* nsWrapperCache::GetWrapper() const {
  28   JSObject* obj = GetWrapperPreserveColor();
  29   if (obj) {
  30     JS::ExposeObjectToActiveJS(obj);
  31   }
  32   return obj;
  33 }
  34
  35 inline bool nsWrapperCache::HasKnownLiveWrapper() const {
  36   // If we have a wrapper and it's not gray in the GC-marking sense, that means
  37   // that we can't be cycle-collected.  That's because the wrapper is being kept
  38   // alive by the JS engine (and not just due to being traced from some
  39   // cycle-collectable thing), and the wrapper holds us alive, so we know we're
  40   // not collectable.
  41   JSObject* o = GetWrapperPreserveColor();
  42   return o && !JS::ObjectIsMarkedGray(o);
  43 }
  44
  45 static void SearchGray(JS::GCCellPtr aGCThing, const char* aName,
  46                        void* aClosure) {
  47   bool* hasGrayObjects = static_cast<bool*>(aClosure);
  48   if (!*hasGrayObjects && aGCThing && JS::GCThingIsMarkedGray(aGCThing)) {
  49     *hasGrayObjects = true;
  50   }
  51 }
  52
  53 inline bool nsWrapperCache::HasNothingToTrace(nsISupports* aThis) {
  54   nsXPCOMCycleCollectionParticipant* participant = nullptr;
  55   CallQueryInterface(aThis, &participant);
  56   bool hasGrayObjects = false;
  57   participant->Trace(aThis, TraceCallbackFunc(SearchGray), &hasGrayObjects);
  58   return !hasGrayObjects;
  59 }
  60
  61 inline bool nsWrapperCache::HasKnownLiveWrapperAndDoesNotNeedTracing(
  62     nsISupports* aThis) {
  63   return HasKnownLiveWrapper() && HasNothingToTrace(aThis);
  64 }
  65
  66 inline void nsWrapperCache::MarkWrapperLive() {
  67   // Just call GetWrapper and ignore the return value.  It will do the
  68   // gray-unmarking for us.
  69   GetWrapper();
  70 }
  71
  72 template <typename T>
  73 inline void nsWrapperCache::UpdateWrapperForNewGlobal(T* aScriptObjectHolder,
  74                                                       JSObject* aNewWrapper) {
  75   // If the new wrapper is in a different zone we must ensure the
  76   // DropJSObjects/HoldJSObjects are called to move the holder to the new zone.
  77
  78   bool preserving = PreservingWrapper();
  79   bool zoneChanged =
  80       preserving && (JS::GetObjectZone(GetWrapperPreserveColor()) !=
  81                      JS::GetObjectZone(aNewWrapper));
  82
  83   if (zoneChanged) {
  84     ReleaseWrapper(aScriptObjectHolder);
  85   } else if (preserving) {
  86     SetPreservingWrapper(false);
  87   }
  88
  89   SetWrapper(aNewWrapper);
  90
  91   if (zoneChanged) {
  92     PreserveWrapper(aScriptObjectHolder);
  93   } else if (preserving) {
  94     SetPreservingWrapper(true);
  95   }
  96 }
  97
  98 #endif /* nsWrapperCache_h___ */