dom/base/nsWrapperCache.cpp

   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 #include "nsWrapperCacheInlines.h"
   8
   9 #include "jsfriendapi.h"
  10 #include "js/Class.h"
  11 #include "js/Proxy.h"
  12 #include "mozilla/CycleCollectedJSRuntime.h"
  13 #include "mozilla/HoldDropJSObjects.h"
  14 #include "nsCycleCollectionTraversalCallback.h"
  15 #include "nsCycleCollector.h"
  16
  17 using namespace mozilla;
  18 using namespace mozilla::dom;
  19
  20 #ifdef DEBUG
  21 /* static */
  22 bool nsWrapperCache::HasJSObjectMovedOp(JSObject* aWrapper) {
  23   return js::HasObjectMovedOp(aWrapper);
  24 }
  25 #endif
  26
  27 void nsWrapperCache::HoldJSObjects(void* aScriptObjectHolder,
  28                                    nsScriptObjectTracer* aTracer,
  29                                    JS::Zone* aWrapperZone) {
  30   cyclecollector::HoldJSObjectsImpl(aScriptObjectHolder, aTracer, aWrapperZone);
  31   if (mWrapper && !JS::ObjectIsTenured(mWrapper)) {
  32     JS::HeapObjectPostWriteBarrier(&mWrapper, nullptr, mWrapper);
  33   }
  34 }
  35
  36 static inline bool IsNurseryWrapper(JSObject* aWrapper) {
  37   return aWrapper && !JS::ObjectIsTenured(aWrapper);
  38 }
  39
  40 void nsWrapperCache::SetWrapperJSObject(JSObject* aNewWrapper) {
  41   JSObject* oldWrapper = mWrapper;
  42   mWrapper = aNewWrapper;
  43   UnsetWrapperFlags(kWrapperFlagsMask);
  44
  45   if (IsNurseryWrapper(aNewWrapper) && !IsNurseryWrapper(oldWrapper)) {
  46     CycleCollectedJSRuntime::Get()->NurseryWrapperAdded(this);
  47   }
  48 }
  49
  50 void nsWrapperCache::ReleaseWrapper(void* aScriptObjectHolder) {
  51   // If the behavior here changes in a substantive way, you may need
  52   // to update css::Rule::UnlinkDeclarationWrapper as well.
  53   if (PreservingWrapper()) {
  54     SetPreservingWrapper(false);
  55     cyclecollector::DropJSObjectsImpl(aScriptObjectHolder);
  56     JS::HeapObjectPostWriteBarrier(&mWrapper, mWrapper, nullptr);
  57   }
  58 }
  59
  60 #ifdef DEBUG
  61
  62 void nsWrapperCache::AssertUpdatedWrapperZone(const JSObject* aNewObject,
  63                                               const JSObject* aOldObject) {
  64   MOZ_ASSERT(js::GetObjectZoneFromAnyThread(aNewObject) ==
  65              js::GetObjectZoneFromAnyThread(aOldObject));
  66 }
  67
  68 class DebugWrapperTraversalCallback
  69     : public nsCycleCollectionTraversalCallback {
  70  public:
  71   explicit DebugWrapperTraversalCallback(JSObject* aWrapper)
  72       : mFound(false), mWrapper(JS::GCCellPtr(aWrapper)) {
  73     mFlags = WANT_ALL_TRACES;
  74   }
  75
  76   NS_IMETHOD_(void)
  77   DescribeRefCountedNode(nsrefcnt aRefCount, const char* aObjName) override {}
  78   NS_IMETHOD_(void)
  79   DescribeGCedNode(bool aIsMarked, const char* aObjName,
  80                    uint64_t aCompartmentAddress) override {}
  81
  82   NS_IMETHOD_(void) NoteJSChild(JS::GCCellPtr aChild) override {
  83     if (aChild == mWrapper) {
  84       mFound = true;
  85     }
  86   }
  87   NS_IMETHOD_(void) NoteXPCOMChild(nsISupports* aChild) override {}
  88   NS_IMETHOD_(void)
  89   NoteNativeChild(void* aChild,
  90                   nsCycleCollectionParticipant* aHelper) override {}
  91
  92   NS_IMETHOD_(void)
  93   NoteWeakMapping(JSObject* aKey, nsISupports* aVal,
  94                   nsCycleCollectionParticipant* aValParticipant) override {}
  95
  96   NS_IMETHOD_(void) NoteNextEdgeName(const char* aName) override {}
  97
  98   bool mFound;
  99
 100  private:
 101   JS::GCCellPtr mWrapper;
 102 };
 103
 104 static void DebugWrapperTraceCallback(JS::GCCellPtr aPtr, const char* aName,
 105                                       void* aClosure) {
 106   DebugWrapperTraversalCallback* callback =
 107       static_cast<DebugWrapperTraversalCallback*>(aClosure);
 108   if (aPtr.is<JSObject>()) {
 109     callback->NoteJSChild(aPtr);
 110   }
 111 }
 112
 113 void nsWrapperCache::CheckCCWrapperTraversal(void* aScriptObjectHolder,
 114                                              nsScriptObjectTracer* aTracer) {
 115   JSObject* wrapper = GetWrapperPreserveColor();
 116   if (!wrapper) {
 117     return;
 118   }
 119
 120   // Temporarily make this a preserving wrapper so that TraceWrapper() traces
 121   // it.
 122   bool wasPreservingWrapper = PreservingWrapper();
 123   SetPreservingWrapper(true);
 124
 125   DebugWrapperTraversalCallback callback(wrapper);
 126
 127   // The CC traversal machinery cannot trigger GC; however, the analysis cannot
 128   // see through the COM layer, so we use a suppression to help it.
 129   JS::AutoSuppressGCAnalysis suppress;
 130
 131   aTracer->TraverseNativeAndJS(aScriptObjectHolder, callback);
 132   MOZ_ASSERT(callback.mFound,
 133              "Cycle collection participant didn't traverse to preserved "
 134              "wrapper! This will probably crash.");
 135
 136   callback.mFound = false;
 137   aTracer->Trace(aScriptObjectHolder,
 138                  TraceCallbackFunc(DebugWrapperTraceCallback), &callback);
 139   MOZ_ASSERT(callback.mFound,
 140              "Cycle collection participant didn't trace preserved wrapper! "
 141              "This will probably crash.");
 142
 143   SetPreservingWrapper(wasPreservingWrapper);
 144 }
 145
 146 #endif  // DEBUG