Add m-esr52 at 52.6.0

1 files changed, 1717 insertions, 0 deletions

diff --git a/xpcom/base/CycleCollectedJSContext.cpp b/xpcom/base/CycleCollectedJSContext.cpp
new file mode 100644
index 000000000..87e123078
--- /dev/null
+++ b/xpcom/base/CycleCollectedJSContext.cpp
@@ -0,0 +1,1717 @@
+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
+/* vim: set ts=8 sts=2 et sw=2 tw=80: */
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+// We're dividing JS objects into 3 categories:
+//
+// 1. "real" roots, held by the JS engine itself or rooted through the root
+//    and lock JS APIs. Roots from this category are considered black in the
+//    cycle collector, any cycle they participate in is uncollectable.
+//
+// 2. certain roots held by C++ objects that are guaranteed to be alive.
+//    Roots from this category are considered black in the cycle collector,
+//    and any cycle they participate in is uncollectable. These roots are
+//    traced from TraceNativeBlackRoots.
+//
+// 3. all other roots held by C++ objects that participate in cycle
+//    collection, held by us (see TraceNativeGrayRoots). Roots from this
+//    category are considered grey in the cycle collector; whether or not
+//    they are collected depends on the objects that hold them.
+//
+// Note that if a root is in multiple categories the fact that it is in
+// category 1 or 2 that takes precedence, so it will be considered black.
+//
+// During garbage collection we switch to an additional mark color (gray)
+// when tracing inside TraceNativeGrayRoots. This allows us to walk those
+// roots later on and add all objects reachable only from them to the
+// cycle collector.
+//
+// Phases:
+//
+// 1. marking of the roots in category 1 by having the JS GC do its marking
+// 2. marking of the roots in category 2 by having the JS GC call us back
+//    (via JS_SetExtraGCRootsTracer) and running TraceNativeBlackRoots
+// 3. marking of the roots in category 3 by TraceNativeGrayRoots using an
+//    additional color (gray).
+// 4. end of GC, GC can sweep its heap
+//
+// At some later point, when the cycle collector runs:
+//
+// 5. walk gray objects and add them to the cycle collector, cycle collect
+//
+// JS objects that are part of cycles the cycle collector breaks will be
+// collected by the next JS GC.
+//
+// If WantAllTraces() is false the cycle collector will not traverse roots
+// from category 1 or any JS objects held by them. Any JS objects they hold
+// will already be marked by the JS GC and will thus be colored black
+// themselves. Any C++ objects they hold will have a missing (untraversed)
+// edge from the JS object to the C++ object and so it will be marked black
+// too. This decreases the number of objects that the cycle collector has to
+// deal with.
+// To improve debugging, if WantAllTraces() is true all JS objects are
+// traversed.
+
+#include "mozilla/CycleCollectedJSContext.h"
+#include <algorithm>
+#include "mozilla/ArrayUtils.h"
+#include "mozilla/AutoRestore.h"
+#include "mozilla/Move.h"
+#include "mozilla/MemoryReporting.h"
+#include "mozilla/Sprintf.h"
+#include "mozilla/Telemetry.h"
+#include "mozilla/TimelineConsumers.h"
+#include "mozilla/TimelineMarker.h"
+#include "mozilla/Unused.h"
+#include "mozilla/DebuggerOnGCRunnable.h"
+#include "mozilla/dom/DOMJSClass.h"
+#include "mozilla/dom/ProfileTimelineMarkerBinding.h"
+#include "mozilla/dom/Promise.h"
+#include "mozilla/dom/PromiseBinding.h"
+#include "mozilla/dom/PromiseDebugging.h"
+#include "mozilla/dom/ScriptSettings.h"
+#include "jsprf.h"
+#include "js/Debug.h"
+#include "nsContentUtils.h"
+#include "nsCycleCollectionNoteRootCallback.h"
+#include "nsCycleCollectionParticipant.h"
+#include "nsCycleCollector.h"
+#include "nsDOMJSUtils.h"
+#include "nsJSUtils.h"
+#include "nsWrapperCache.h"
+
+#ifdef MOZ_CRASHREPORTER
+#include "nsExceptionHandler.h"
+#endif
+
+#include "nsIException.h"
+#include "nsIPlatformInfo.h"
+#include "nsThread.h"
+#include "nsThreadUtils.h"
+#include "xpcpublic.h"
+
+using namespace mozilla;
+using namespace mozilla::dom;
+
+namespace mozilla {
+
+struct DeferredFinalizeFunctionHolder
+{
+  DeferredFinalizeFunction run;
+  void* data;
+};
+
+class IncrementalFinalizeRunnable : public Runnable
+{
+  typedef AutoTArray<DeferredFinalizeFunctionHolder, 16> DeferredFinalizeArray;
+  typedef CycleCollectedJSContext::DeferredFinalizerTable DeferredFinalizerTable;
+
+  CycleCollectedJSContext* mContext;
+  DeferredFinalizeArray mDeferredFinalizeFunctions;
+  uint32_t mFinalizeFunctionToRun;
+  bool mReleasing;
+
+  static const PRTime SliceMillis = 5; /* ms */
+
+public:
+  IncrementalFinalizeRunnable(CycleCollectedJSContext* aCx,
+                              DeferredFinalizerTable& aFinalizerTable);
+  virtual ~IncrementalFinalizeRunnable();
+
+  void ReleaseNow(bool aLimited);
+
+  NS_DECL_NSIRUNNABLE
+};
+
+} // namespace mozilla
+
+struct NoteWeakMapChildrenTracer : public JS::CallbackTracer
+{
+  NoteWeakMapChildrenTracer(JSContext* aCx,
+                            nsCycleCollectionNoteRootCallback& aCb)
+    : JS::CallbackTracer(aCx), mCb(aCb), mTracedAny(false), mMap(nullptr),
+      mKey(nullptr), mKeyDelegate(nullptr)
+  {
+  }
+  void onChild(const JS::GCCellPtr& aThing) override;
+  nsCycleCollectionNoteRootCallback& mCb;
+  bool mTracedAny;
+  JSObject* mMap;
+  JS::GCCellPtr mKey;
+  JSObject* mKeyDelegate;
+};
+
+void
+NoteWeakMapChildrenTracer::onChild(const JS::GCCellPtr& aThing)
+{
+  if (aThing.is<JSString>()) {
+    return;
+  }
+
+  if (!JS::GCThingIsMarkedGray(aThing) && !mCb.WantAllTraces()) {
+    return;
+  }
+
+  if (AddToCCKind(aThing.kind())) {
+    mCb.NoteWeakMapping(mMap, mKey, mKeyDelegate, aThing);
+    mTracedAny = true;
+  } else {
+    JS::TraceChildren(this, aThing);
+  }
+}
+
+struct NoteWeakMapsTracer : public js::WeakMapTracer
+{
+  NoteWeakMapsTracer(JSContext* aCx, nsCycleCollectionNoteRootCallback& aCccb)
+    : js::WeakMapTracer(aCx), mCb(aCccb), mChildTracer(aCx, aCccb)
+  {
+  }
+  void trace(JSObject* aMap, JS::GCCellPtr aKey, JS::GCCellPtr aValue) override;
+  nsCycleCollectionNoteRootCallback& mCb;
+  NoteWeakMapChildrenTracer mChildTracer;
+};
+
+void
+NoteWeakMapsTracer::trace(JSObject* aMap, JS::GCCellPtr aKey,
+                          JS::GCCellPtr aValue)
+{
+  // If nothing that could be held alive by this entry is marked gray, return.
+  if ((!aKey || !JS::GCThingIsMarkedGray(aKey)) &&
+      MOZ_LIKELY(!mCb.WantAllTraces())) {
+    if (!aValue || !JS::GCThingIsMarkedGray(aValue) || aValue.is<JSString>()) {
+      return;
+    }
+  }
+
+  // The cycle collector can only properly reason about weak maps if it can
+  // reason about the liveness of their keys, which in turn requires that
+  // the key can be represented in the cycle collector graph.  All existing
+  // uses of weak maps use either objects or scripts as keys, which are okay.
+  MOZ_ASSERT(AddToCCKind(aKey.kind()));
+
+  // As an emergency fallback for non-debug builds, if the key is not
+  // representable in the cycle collector graph, we treat it as marked.  This
+  // can cause leaks, but is preferable to ignoring the binding, which could
+  // cause the cycle collector to free live objects.
+  if (!AddToCCKind(aKey.kind())) {
+    aKey = nullptr;
+  }
+
+  JSObject* kdelegate = nullptr;
+  if (aKey.is<JSObject>()) {
+    kdelegate = js::GetWeakmapKeyDelegate(&aKey.as<JSObject>());
+  }
+
+  if (AddToCCKind(aValue.kind())) {
+    mCb.NoteWeakMapping(aMap, aKey, kdelegate, aValue);
+  } else {
+    mChildTracer.mTracedAny = false;
+    mChildTracer.mMap = aMap;
+    mChildTracer.mKey = aKey;
+    mChildTracer.mKeyDelegate = kdelegate;
+
+    if (!aValue.is<JSString>()) {
+      JS::TraceChildren(&mChildTracer, aValue);
+    }
+
+    // The delegate could hold alive the key, so report something to the CC
+    // if we haven't already.
+    if (!mChildTracer.mTracedAny &&
+        aKey && JS::GCThingIsMarkedGray(aKey) && kdelegate) {
+      mCb.NoteWeakMapping(aMap, aKey, kdelegate, nullptr);
+    }
+  }
+}
+
+// This is based on the logic in FixWeakMappingGrayBitsTracer::trace.
+struct FixWeakMappingGrayBitsTracer : public js::WeakMapTracer
+{
+  explicit FixWeakMappingGrayBitsTracer(JSContext* aCx)
+    : js::WeakMapTracer(aCx)
+  {
+  }
+
+  void
+  FixAll()
+  {
+    do {
+      mAnyMarked = false;
+      js::TraceWeakMaps(this);
+    } while (mAnyMarked);
+  }
+
+  void trace(JSObject* aMap, JS::GCCellPtr aKey, JS::GCCellPtr aValue) override
+  {
+    // If nothing that could be held alive by this entry is marked gray, return.
+    bool keyMightNeedMarking = aKey && JS::GCThingIsMarkedGray(aKey);
+    bool valueMightNeedMarking = aValue && JS::GCThingIsMarkedGray(aValue) &&
+                                 aValue.kind() != JS::TraceKind::String;
+    if (!keyMightNeedMarking && !valueMightNeedMarking) {
+      return;
+    }
+
+    if (!AddToCCKind(aKey.kind())) {
+      aKey = nullptr;
+    }
+
+    if (keyMightNeedMarking && aKey.is<JSObject>()) {
+      JSObject* kdelegate = js::GetWeakmapKeyDelegate(&aKey.as<JSObject>());
+      if (kdelegate && !JS::ObjectIsMarkedGray(kdelegate) &&
+          (!aMap || !JS::ObjectIsMarkedGray(aMap)))
+      {
+        if (JS::UnmarkGrayGCThingRecursively(aKey)) {
+          mAnyMarked = true;
+        }
+      }
+    }
+
+    if (aValue && JS::GCThingIsMarkedGray(aValue) &&
+        (!aKey || !JS::GCThingIsMarkedGray(aKey)) &&
+        (!aMap || !JS::ObjectIsMarkedGray(aMap)) &&
+        aValue.kind() != JS::TraceKind::Shape) {
+      if (JS::UnmarkGrayGCThingRecursively(aValue)) {
+        mAnyMarked = true;
+      }
+    }
+  }
+
+  MOZ_INIT_OUTSIDE_CTOR bool mAnyMarked;
+};
+
+static void
+CheckParticipatesInCycleCollection(JS::GCCellPtr aThing, const char* aName,
+                                   void* aClosure)
+{
+  bool* cycleCollectionEnabled = static_cast<bool*>(aClosure);
+
+  if (*cycleCollectionEnabled) {
+    return;
+  }
+
+  if (AddToCCKind(aThing.kind()) && JS::GCThingIsMarkedGray(aThing)) {
+    *cycleCollectionEnabled = true;
+  }
+}
+
+NS_IMETHODIMP
+JSGCThingParticipant::Traverse(void* aPtr,
+                               nsCycleCollectionTraversalCallback& aCb)
+{
+  auto runtime = reinterpret_cast<CycleCollectedJSContext*>(
+    reinterpret_cast<char*>(this) - offsetof(CycleCollectedJSContext,
+                                             mGCThingCycleCollectorGlobal));
+
+  JS::GCCellPtr cellPtr(aPtr, JS::GCThingTraceKind(aPtr));
+  runtime->TraverseGCThing(CycleCollectedJSContext::TRAVERSE_FULL, cellPtr, aCb);
+  return NS_OK;
+}
+
+// NB: This is only used to initialize the participant in
+// CycleCollectedJSContext. It should never be used directly.
+static JSGCThingParticipant sGCThingCycleCollectorGlobal;
+
+NS_IMETHODIMP
+JSZoneParticipant::Traverse(void* aPtr, nsCycleCollectionTraversalCallback& aCb)
+{
+  auto runtime = reinterpret_cast<CycleCollectedJSContext*>(
+    reinterpret_cast<char*>(this) - offsetof(CycleCollectedJSContext,
+                                             mJSZoneCycleCollectorGlobal));
+
+  MOZ_ASSERT(!aCb.WantAllTraces());
+  JS::Zone* zone = static_cast<JS::Zone*>(aPtr);
+
+  runtime->TraverseZone(zone, aCb);
+  return NS_OK;
+}
+
+struct TraversalTracer : public JS::CallbackTracer
+{
+  TraversalTracer(JSContext* aCx, nsCycleCollectionTraversalCallback& aCb)
+    : JS::CallbackTracer(aCx, DoNotTraceWeakMaps), mCb(aCb)
+  {
+  }
+  void onChild(const JS::GCCellPtr& aThing) override;
+  nsCycleCollectionTraversalCallback& mCb;
+};
+
+void
+TraversalTracer::onChild(const JS::GCCellPtr& aThing)
+{
+  // Don't traverse non-gray objects, unless we want all traces.
+  if (!JS::GCThingIsMarkedGray(aThing) && !mCb.WantAllTraces()) {
+    return;
+  }
+
+  /*
+   * This function needs to be careful to avoid stack overflow. Normally, when
+   * AddToCCKind is true, the recursion terminates immediately as we just add
+   * |thing| to the CC graph. So overflow is only possible when there are long
+   * or cyclic chains of non-AddToCCKind GC things. Places where this can occur
+   * use special APIs to handle such chains iteratively.
+   */
+  if (AddToCCKind(aThing.kind())) {
+    if (MOZ_UNLIKELY(mCb.WantDebugInfo())) {
+      char buffer[200];
+      getTracingEdgeName(buffer, sizeof(buffer));
+      mCb.NoteNextEdgeName(buffer);
+    }
+    mCb.NoteJSChild(aThing);
+  } else if (aThing.is<js::Shape>()) {
+    // The maximum depth of traversal when tracing a Shape is unbounded, due to
+    // the parent pointers on the shape.
+    JS_TraceShapeCycleCollectorChildren(this, aThing);
+  } else if (aThing.is<js::ObjectGroup>()) {
+    // The maximum depth of traversal when tracing an ObjectGroup is unbounded,
+    // due to information attached to the groups which can lead other groups to
+    // be traced.
+    JS_TraceObjectGroupCycleCollectorChildren(this, aThing);
+  } else if (!aThing.is<JSString>()) {
+    JS::TraceChildren(this, aThing);
+  }
+}
+
+static void
+NoteJSChildGrayWrapperShim(void* aData, JS::GCCellPtr aThing)
+{
+  TraversalTracer* trc = static_cast<TraversalTracer*>(aData);
+  trc->onChild(aThing);
+}
+
+/*
+ * The cycle collection participant for a Zone is intended to produce the same
+ * results as if all of the gray GCthings in a zone were merged into a single node,
+ * except for self-edges. This avoids the overhead of representing all of the GCthings in
+ * the zone in the cycle collector graph, which should be much faster if many of
+ * the GCthings in the zone are gray.
+ *
+ * Zone merging should not always be used, because it is a conservative
+ * approximation of the true cycle collector graph that can incorrectly identify some
+ * garbage objects as being live. For instance, consider two cycles that pass through a
+ * zone, where one is garbage and the other is live. If we merge the entire
+ * zone, the cycle collector will think that both are alive.
+ *
+ * We don't have to worry about losing track of a garbage cycle, because any such garbage
+ * cycle incorrectly identified as live must contain at least one C++ to JS edge, and
+ * XPConnect will always add the C++ object to the CC graph. (This is in contrast to pure
+ * C++ garbage cycles, which must always be properly identified, because we clear the
+ * purple buffer during every CC, which may contain the last reference to a garbage
+ * cycle.)
+ */
+
+// NB: This is only used to initialize the participant in
+// CycleCollectedJSContext. It should never be used directly.
+static const JSZoneParticipant sJSZoneCycleCollectorGlobal;
+
+static
+void JSObjectsTenuredCb(JSContext* aContext, void* aData)
+{
+  static_cast<CycleCollectedJSContext*>(aData)->JSObjectsTenured();
+}
+
+bool
+mozilla::GetBuildId(JS::BuildIdCharVector* aBuildID)
+{
+  nsCOMPtr<nsIPlatformInfo> info = do_GetService("@mozilla.org/xre/app-info;1");
+  if (!info) {
+    return false;
+  }
+
+  nsCString buildID;
+  nsresult rv = info->GetPlatformBuildID(buildID);
+  NS_ENSURE_SUCCESS(rv, false);
+
+  if (!aBuildID->resize(buildID.Length())) {
+    return false;
+  }
+
+  for (size_t i = 0; i < buildID.Length(); i++) {
+    (*aBuildID)[i] = buildID[i];
+  }
+
+  return true;
+}
+
+CycleCollectedJSContext::CycleCollectedJSContext()
+  : mGCThingCycleCollectorGlobal(sGCThingCycleCollectorGlobal)
+  , mJSZoneCycleCollectorGlobal(sJSZoneCycleCollectorGlobal)
+  , mJSContext(nullptr)
+  , mPrevGCSliceCallback(nullptr)
+  , mPrevGCNurseryCollectionCallback(nullptr)
+  , mJSHolders(256)
+  , mDoingStableStates(false)
+  , mDisableMicroTaskCheckpoint(false)
+  , mOutOfMemoryState(OOMState::OK)
+  , mLargeAllocationFailureState(OOMState::OK)
+{
+  nsCOMPtr<nsIThread> thread = do_GetCurrentThread();
+  mOwningThread = thread.forget().downcast<nsThread>().take();
+  MOZ_RELEASE_ASSERT(mOwningThread);
+}
+
+CycleCollectedJSContext::~CycleCollectedJSContext()
+{
+  // If the allocation failed, here we are.
+  if (!mJSContext) {
+    return;
+  }
+
+  MOZ_ASSERT(!mDeferredFinalizerTable.Count());
+
+  // Last chance to process any events.
+  ProcessMetastableStateQueue(mBaseRecursionDepth);
+  MOZ_ASSERT(mMetastableStateEvents.IsEmpty());
+
+  ProcessStableStateQueue();
+  MOZ_ASSERT(mStableStateEvents.IsEmpty());
+
+  // Clear mPendingException first, since it might be cycle collected.
+  mPendingException = nullptr;
+
+  MOZ_ASSERT(mDebuggerPromiseMicroTaskQueue.empty());
+  MOZ_ASSERT(mPromiseMicroTaskQueue.empty());
+
+#ifdef SPIDERMONKEY_PROMISE
+  mUncaughtRejections.reset();
+  mConsumedRejections.reset();
+#endif // SPIDERMONKEY_PROMISE
+
+  JS_DestroyContext(mJSContext);
+  mJSContext = nullptr;
+  nsCycleCollector_forgetJSContext();
+
+  mozilla::dom::DestroyScriptSettings();
+
+  mOwningThread->SetScriptObserver(nullptr);
+  NS_RELEASE(mOwningThread);
+}
+
+static void
+MozCrashWarningReporter(JSContext*, JSErrorReport*)
+{
+  MOZ_CRASH("Why is someone touching JSAPI without an AutoJSAPI?");
+}
+
+nsresult
+CycleCollectedJSContext::Initialize(JSContext* aParentContext,
+                                    uint32_t aMaxBytes,
+                                    uint32_t aMaxNurseryBytes)
+{
+  MOZ_ASSERT(!mJSContext);
+
+  mOwningThread->SetScriptObserver(this);
+  // The main thread has a base recursion depth of 0, workers of 1.
+  mBaseRecursionDepth = RecursionDepth();
+
+  mozilla::dom::InitScriptSettings();
+  mJSContext = JS_NewContext(aMaxBytes, aMaxNurseryBytes, aParentContext);
+  if (!mJSContext) {
+    return NS_ERROR_OUT_OF_MEMORY;
+  }
+
+  NS_GetCurrentThread()->SetCanInvokeJS(true);
+
+  if (!JS_AddExtraGCRootsTracer(mJSContext, TraceBlackJS, this)) {
+    MOZ_CRASH("JS_AddExtraGCRootsTracer failed");
+  }
+  JS_SetGrayGCRootsTracer(mJSContext, TraceGrayJS, this);
+  JS_SetGCCallback(mJSContext, GCCallback, this);
+  mPrevGCSliceCallback = JS::SetGCSliceCallback(mJSContext, GCSliceCallback);
+
+  if (NS_IsMainThread()) {
+    // We would like to support all threads here, but the way timeline consumers
+    // are set up currently, you can either add a marker for one specific
+    // docshell, or for every consumer globally. We would like to add a marker
+    // for every consumer observing anything on this thread, but that is not
+    // currently possible. For now, add global markers only when we are on the
+    // main thread, since the UI for this tracing data only displays data
+    // relevant to the main-thread.
+    mPrevGCNurseryCollectionCallback = JS::SetGCNurseryCollectionCallback(
+      mJSContext, GCNurseryCollectionCallback);
+  }
+
+  JS_SetObjectsTenuredCallback(mJSContext, JSObjectsTenuredCb, this);
+  JS::SetOutOfMemoryCallback(mJSContext, OutOfMemoryCallback, this);
+  JS::SetLargeAllocationFailureCallback(mJSContext,
+                                        LargeAllocationFailureCallback, this);
+  JS_SetDestroyZoneCallback(mJSContext, XPCStringConvert::FreeZoneCache);
+  JS_SetSweepZoneCallback(mJSContext, XPCStringConvert::ClearZoneCache);
+  JS::SetBuildIdOp(mJSContext, GetBuildId);
+  JS::SetWarningReporter(mJSContext, MozCrashWarningReporter);
+#ifdef MOZ_CRASHREPORTER
+    js::AutoEnterOOMUnsafeRegion::setAnnotateOOMAllocationSizeCallback(
+            CrashReporter::AnnotateOOMAllocationSize);
+#endif
+
+  static js::DOMCallbacks DOMcallbacks = {
+    InstanceClassHasProtoAtDepth
+  };
+  SetDOMCallbacks(mJSContext, &DOMcallbacks);
+  js::SetScriptEnvironmentPreparer(mJSContext, &mEnvironmentPreparer);
+
+  JS::SetGetIncumbentGlobalCallback(mJSContext, GetIncumbentGlobalCallback);
+
+#ifdef SPIDERMONKEY_PROMISE
+  JS::SetEnqueuePromiseJobCallback(mJSContext, EnqueuePromiseJobCallback, this);
+  JS::SetPromiseRejectionTrackerCallback(mJSContext, PromiseRejectionTrackerCallback, this);
+  mUncaughtRejections.init(mJSContext, JS::GCVector<JSObject*, 0, js::SystemAllocPolicy>(js::SystemAllocPolicy()));
+  mConsumedRejections.init(mJSContext, JS::GCVector<JSObject*, 0, js::SystemAllocPolicy>(js::SystemAllocPolicy()));
+#endif // SPIDERMONKEY_PROMISE
+
+  JS::dbg::SetDebuggerMallocSizeOf(mJSContext, moz_malloc_size_of);
+
+  nsCycleCollector_registerJSContext(this);
+
+  return NS_OK;
+}
+
+size_t
+CycleCollectedJSContext::SizeOfExcludingThis(MallocSizeOf aMallocSizeOf) const
+{
+  size_t n = 0;
+
+  // We're deliberately not measuring anything hanging off the entries in
+  // mJSHolders.
+  n += mJSHolders.ShallowSizeOfExcludingThis(aMallocSizeOf);
+
+  return n;
+}
+
+void
+CycleCollectedJSContext::UnmarkSkippableJSHolders()
+{
+  for (auto iter = mJSHolders.Iter(); !iter.Done(); iter.Next()) {
+    void* holder = iter.Key();
+    nsScriptObjectTracer*& tracer = iter.Data();
+    tracer->CanSkip(holder, true);
+  }
+}
+
+void
+CycleCollectedJSContext::DescribeGCThing(bool aIsMarked, JS::GCCellPtr aThing,
+                                         nsCycleCollectionTraversalCallback& aCb) const
+{
+  if (!aCb.WantDebugInfo()) {
+    aCb.DescribeGCedNode(aIsMarked, "JS Object");
+    return;
+  }
+
+  char name[72];
+  uint64_t compartmentAddress = 0;
+  if (aThing.is<JSObject>()) {
+    JSObject* obj = &aThing.as<JSObject>();
+    compartmentAddress = (uint64_t)js::GetObjectCompartment(obj);
+    const js::Class* clasp = js::GetObjectClass(obj);
+
+    // Give the subclass a chance to do something
+    if (DescribeCustomObjects(obj, clasp, name)) {
+      // Nothing else to do!
+    } else if (js::IsFunctionObject(obj)) {
+      JSFunction* fun = JS_GetObjectFunction(obj);
+      JSString* str = JS_GetFunctionDisplayId(fun);
+      if (str) {
+        JSFlatString* flat = JS_ASSERT_STRING_IS_FLAT(str);
+        nsAutoString chars;
+        AssignJSFlatString(chars, flat);
+        NS_ConvertUTF16toUTF8 fname(chars);
+        SprintfLiteral(name, "JS Object (Function - %s)", fname.get());
+      } else {
+        SprintfLiteral(name, "JS Object (Function)");
+      }
+    } else {
+      SprintfLiteral(name, "JS Object (%s)", clasp->name);
+    }
+  } else {
+    SprintfLiteral(name, "JS %s", JS::GCTraceKindToAscii(aThing.kind()));
+  }
+
+  // Disable printing global for objects while we figure out ObjShrink fallout.
+  aCb.DescribeGCedNode(aIsMarked, name, compartmentAddress);
+}
+
+void
+CycleCollectedJSContext::NoteGCThingJSChildren(JS::GCCellPtr aThing,
+                                               nsCycleCollectionTraversalCallback& aCb) const
+{
+  MOZ_ASSERT(mJSContext);
+  TraversalTracer trc(mJSContext, aCb);
+  JS::TraceChildren(&trc, aThing);
+}
+
+void
+CycleCollectedJSContext::NoteGCThingXPCOMChildren(const js::Class* aClasp,
+                                                  JSObject* aObj,
+                                                  nsCycleCollectionTraversalCallback& aCb) const
+{
+  MOZ_ASSERT(aClasp);
+  MOZ_ASSERT(aClasp == js::GetObjectClass(aObj));
+
+  if (NoteCustomGCThingXPCOMChildren(aClasp, aObj, aCb)) {
+    // Nothing else to do!
+    return;
+  }
+  // XXX This test does seem fragile, we should probably whitelist classes
+  //     that do hold a strong reference, but that might not be possible.
+  else if (aClasp->flags & JSCLASS_HAS_PRIVATE &&
+           aClasp->flags & JSCLASS_PRIVATE_IS_NSISUPPORTS) {
+    NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(aCb, "js::GetObjectPrivate(obj)");
+    aCb.NoteXPCOMChild(static_cast<nsISupports*>(js::GetObjectPrivate(aObj)));
+  } else {
+    const DOMJSClass* domClass = GetDOMClass(aObj);
+    if (domClass) {
+      NS_CYCLE_COLLECTION_NOTE_EDGE_NAME(aCb, "UnwrapDOMObject(obj)");
+      // It's possible that our object is an unforgeable holder object, in
+      // which case it doesn't actually have a C++ DOM object associated with
+      // it.  Use UnwrapPossiblyNotInitializedDOMObject, which produces null in
+      // that case, since NoteXPCOMChild/NoteNativeChild are null-safe.
+      if (domClass->mDOMObjectIsISupports) {
+        aCb.NoteXPCOMChild(UnwrapPossiblyNotInitializedDOMObject<nsISupports>(aObj));
+      } else if (domClass->mParticipant) {
+        aCb.NoteNativeChild(UnwrapPossiblyNotInitializedDOMObject<void>(aObj),
+                            domClass->mParticipant);
+      }
+    }
+  }
+}
+
+void
+CycleCollectedJSContext::TraverseGCThing(TraverseSelect aTs, JS::GCCellPtr aThing,
+                                         nsCycleCollectionTraversalCallback& aCb)
+{
+  bool isMarkedGray = JS::GCThingIsMarkedGray(aThing);
+
+  if (aTs == TRAVERSE_FULL) {
+    DescribeGCThing(!isMarkedGray, aThing, aCb);
+  }
+
+  // If this object is alive, then all of its children are alive. For JS objects,
+  // the black-gray invariant ensures the children are also marked black. For C++
+  // objects, the ref count from this object will keep them alive. Thus we don't
+  // need to trace our children, unless we are debugging using WantAllTraces.
+  if (!isMarkedGray && !aCb.WantAllTraces()) {
+    return;
+  }
+
+  if (aTs == TRAVERSE_FULL) {
+    NoteGCThingJSChildren(aThing, aCb);
+  }
+
+  if (aThing.is<JSObject>()) {
+    JSObject* obj = &aThing.as<JSObject>();
+    NoteGCThingXPCOMChildren(js::GetObjectClass(obj), obj, aCb);
+  }
+}
+
+struct TraverseObjectShimClosure
+{
+  nsCycleCollectionTraversalCallback& cb;
+  CycleCollectedJSContext* self;
+};
+
+void
+CycleCollectedJSContext::TraverseZone(JS::Zone* aZone,
+                                      nsCycleCollectionTraversalCallback& aCb)
+{
+  MOZ_ASSERT(mJSContext);
+
+  /*
+   * We treat the zone as being gray. We handle non-gray GCthings in the
+   * zone by not reporting their children to the CC. The black-gray invariant
+   * ensures that any JS children will also be non-gray, and thus don't need to be
+   * added to the graph. For C++ children, not representing the edge from the
+   * non-gray JS GCthings to the C++ object will keep the child alive.
+   *
+   * We don't allow zone merging in a WantAllTraces CC, because then these
+   * assumptions don't hold.
+   */
+  aCb.DescribeGCedNode(false, "JS Zone");
+
+  /*
+   * Every JS child of everything in the zone is either in the zone
+   * or is a cross-compartment wrapper. In the former case, we don't need to
+   * represent these edges in the CC graph because JS objects are not ref counted.
+   * In the latter case, the JS engine keeps a map of these wrappers, which we
+   * iterate over. Edges between compartments in the same zone will add
+   * unnecessary loop edges to the graph (bug 842137).
+   */
+  TraversalTracer trc(mJSContext, aCb);
+  js::VisitGrayWrapperTargets(aZone, NoteJSChildGrayWrapperShim, &trc);
+
+  /*
+   * To find C++ children of things in the zone, we scan every JS Object in
+   * the zone. Only JS Objects can have C++ children.
+   */
+  TraverseObjectShimClosure closure = { aCb, this };
+  js::IterateGrayObjects(aZone, TraverseObjectShim, &closure);
+}
+
+/* static */ void
+CycleCollectedJSContext::TraverseObjectShim(void* aData, JS::GCCellPtr aThing)
+{
+  TraverseObjectShimClosure* closure =
+    static_cast<TraverseObjectShimClosure*>(aData);
+
+  MOZ_ASSERT(aThing.is<JSObject>());
+  closure->self->TraverseGCThing(CycleCollectedJSContext::TRAVERSE_CPP,
+                                 aThing, closure->cb);
+}
+
+void
+CycleCollectedJSContext::TraverseNativeRoots(nsCycleCollectionNoteRootCallback& aCb)
+{
+  // NB: This is here just to preserve the existing XPConnect order. I doubt it
+  // would hurt to do this after the JS holders.
+  TraverseAdditionalNativeRoots(aCb);
+
+  for (auto iter = mJSHolders.Iter(); !iter.Done(); iter.Next()) {
+    void* holder = iter.Key();
+    nsScriptObjectTracer*& tracer = iter.Data();
+
+    bool noteRoot = false;
+    if (MOZ_UNLIKELY(aCb.WantAllTraces())) {
+      noteRoot = true;
+    } else {
+      tracer->Trace(holder,
+                    TraceCallbackFunc(CheckParticipatesInCycleCollection),
+                    &noteRoot);
+    }
+
+    if (noteRoot) {
+      aCb.NoteNativeRoot(holder, tracer);
+    }
+  }
+}
+
+/* static */ void
+CycleCollectedJSContext::TraceBlackJS(JSTracer* aTracer, void* aData)
+{
+  CycleCollectedJSContext* self = static_cast<CycleCollectedJSContext*>(aData);
+
+  self->TraceNativeBlackRoots(aTracer);
+}
+
+/* static */ void
+CycleCollectedJSContext::TraceGrayJS(JSTracer* aTracer, void* aData)
+{
+  CycleCollectedJSContext* self = static_cast<CycleCollectedJSContext*>(aData);
+
+  // Mark these roots as gray so the CC can walk them later.
+  self->TraceNativeGrayRoots(aTracer);
+}
+
+/* static */ void
+CycleCollectedJSContext::GCCallback(JSContext* aContext,
+                                    JSGCStatus aStatus,
+                                    void* aData)
+{
+  CycleCollectedJSContext* self = static_cast<CycleCollectedJSContext*>(aData);
+
+  MOZ_ASSERT(aContext == self->Context());
+
+  self->OnGC(aStatus);
+}
+
+/* static */ void
+CycleCollectedJSContext::GCSliceCallback(JSContext* aContext,
+                                         JS::GCProgress aProgress,
+                                         const JS::GCDescription& aDesc)
+{
+  CycleCollectedJSContext* self = CycleCollectedJSContext::Get();
+  MOZ_ASSERT(self->Context() == aContext);
+
+  if (aProgress == JS::GC_CYCLE_END) {
+    JS::gcreason::Reason reason = aDesc.reason_;
+    Unused <<
+      NS_WARN_IF(NS_FAILED(DebuggerOnGCRunnable::Enqueue(aContext, aDesc)) &&
+                 reason != JS::gcreason::SHUTDOWN_CC &&
+                 reason != JS::gcreason::DESTROY_RUNTIME &&
+                 reason != JS::gcreason::XPCONNECT_SHUTDOWN);
+  }
+
+  if (self->mPrevGCSliceCallback) {
+    self->mPrevGCSliceCallback(aContext, aProgress, aDesc);
+  }
+}
+
+class MinorGCMarker : public TimelineMarker
+{
+private:
+  JS::gcreason::Reason mReason;
+
+public:
+  MinorGCMarker(MarkerTracingType aTracingType,
+                JS::gcreason::Reason aReason)
+    : TimelineMarker("MinorGC",
+                     aTracingType,
+                     MarkerStackRequest::NO_STACK)
+    , mReason(aReason)
+    {
+      MOZ_ASSERT(aTracingType == MarkerTracingType::START ||
+                 aTracingType == MarkerTracingType::END);
+    }
+
+  MinorGCMarker(JS::GCNurseryProgress aProgress,
+                JS::gcreason::Reason aReason)
+    : TimelineMarker("MinorGC",
+                     aProgress == JS::GCNurseryProgress::GC_NURSERY_COLLECTION_START
+                       ? MarkerTracingType::START
+                       : MarkerTracingType::END,
+                     MarkerStackRequest::NO_STACK)
+    , mReason(aReason)
+  { }
+
+  virtual void
+  AddDetails(JSContext* aCx,
+             dom::ProfileTimelineMarker& aMarker) override
+  {
+    TimelineMarker::AddDetails(aCx, aMarker);
+
+    if (GetTracingType() == MarkerTracingType::START) {
+      auto reason = JS::gcreason::ExplainReason(mReason);
+      aMarker.mCauseName.Construct(NS_ConvertUTF8toUTF16(reason));
+    }
+  }
+
+  virtual UniquePtr<AbstractTimelineMarker>
+  Clone() override
+  {
+    auto clone = MakeUnique<MinorGCMarker>(GetTracingType(), mReason);
+    clone->SetCustomTime(GetTime());
+    return UniquePtr<AbstractTimelineMarker>(Move(clone));
+  }
+};
+
+/* static */ void
+CycleCollectedJSContext::GCNurseryCollectionCallback(JSContext* aContext,
+                                                     JS::GCNurseryProgress aProgress,
+                                                     JS::gcreason::Reason aReason)
+{
+  CycleCollectedJSContext* self = CycleCollectedJSContext::Get();
+  MOZ_ASSERT(self->Context() == aContext);
+  MOZ_ASSERT(NS_IsMainThread());
+
+  RefPtr<TimelineConsumers> timelines = TimelineConsumers::Get();
+  if (timelines && !timelines->IsEmpty()) {
+    UniquePtr<AbstractTimelineMarker> abstractMarker(
+      MakeUnique<MinorGCMarker>(aProgress, aReason));
+    timelines->AddMarkerForAllObservedDocShells(abstractMarker);
+  }
+
+  if (self->mPrevGCNurseryCollectionCallback) {
+    self->mPrevGCNurseryCollectionCallback(aContext, aProgress, aReason);
+  }
+}
+
+
+/* static */ void
+CycleCollectedJSContext::OutOfMemoryCallback(JSContext* aContext,
+                                             void* aData)
+{
+  CycleCollectedJSContext* self = static_cast<CycleCollectedJSContext*>(aData);
+
+  MOZ_ASSERT(aContext == self->Context());
+
+  self->OnOutOfMemory();
+}
+
+/* static */ void
+CycleCollectedJSContext::LargeAllocationFailureCallback(void* aData)
+{
+  CycleCollectedJSContext* self = static_cast<CycleCollectedJSContext*>(aData);
+
+  self->OnLargeAllocationFailure();
+}
+
+class PromiseJobRunnable final : public Runnable
+{
+public:
+  PromiseJobRunnable(JS::HandleObject aCallback, JS::HandleObject aAllocationSite,
+                     nsIGlobalObject* aIncumbentGlobal)
+    : mCallback(new PromiseJobCallback(aCallback, aAllocationSite, aIncumbentGlobal))
+  {
+  }
+
+  virtual ~PromiseJobRunnable()
+  {
+  }
+
+protected:
+  NS_IMETHOD
+  Run() override
+  {
+    nsIGlobalObject* global = xpc::NativeGlobal(mCallback->CallbackPreserveColor());
+    if (global && !global->IsDying()) {
+      mCallback->Call("promise callback");
+    }
+    return NS_OK;
+  }
+
+private:
+  RefPtr<PromiseJobCallback> mCallback;
+};
+
+/* static */
+JSObject*
+CycleCollectedJSContext::GetIncumbentGlobalCallback(JSContext* aCx)
+{
+  nsIGlobalObject* global = mozilla::dom::GetIncumbentGlobal();
+  if (global) {
+    return global->GetGlobalJSObject();
+  }
+  return nullptr;
+}
+
+/* static */
+bool
+CycleCollectedJSContext::EnqueuePromiseJobCallback(JSContext* aCx,
+                                                   JS::HandleObject aJob,
+                                                   JS::HandleObject aAllocationSite,
+                                                   JS::HandleObject aIncumbentGlobal,
+                                                   void* aData)
+{
+  CycleCollectedJSContext* self = static_cast<CycleCollectedJSContext*>(aData);
+  MOZ_ASSERT(aCx == self->Context());
+  MOZ_ASSERT(Get() == self);
+
+  nsIGlobalObject* global = nullptr;
+  if (aIncumbentGlobal) {
+    global = xpc::NativeGlobal(aIncumbentGlobal);
+  }
+  nsCOMPtr<nsIRunnable> runnable = new PromiseJobRunnable(aJob, aAllocationSite, global);
+  self->DispatchToMicroTask(runnable.forget());
+  return true;
+}
+
+#ifdef SPIDERMONKEY_PROMISE
+/* static */
+void
+CycleCollectedJSContext::PromiseRejectionTrackerCallback(JSContext* aCx,
+                                                         JS::HandleObject aPromise,
+                                                         PromiseRejectionHandlingState state,
+                                                         void* aData)
+{
+#ifdef DEBUG
+  CycleCollectedJSContext* self = static_cast<CycleCollectedJSContext*>(aData);
+#endif // DEBUG
+  MOZ_ASSERT(aCx == self->Context());
+  MOZ_ASSERT(Get() == self);
+
+  if (state == PromiseRejectionHandlingState::Unhandled) {
+    PromiseDebugging::AddUncaughtRejection(aPromise);
+  } else {
+    PromiseDebugging::AddConsumedRejection(aPromise);
+  }
+}
+#endif // SPIDERMONKEY_PROMISE
+
+struct JsGcTracer : public TraceCallbacks
+{
+  virtual void Trace(JS::Heap<JS::Value>* aPtr, const char* aName,
+                     void* aClosure) const override
+  {
+    JS::TraceEdge(static_cast<JSTracer*>(aClosure), aPtr, aName);
+  }
+  virtual void Trace(JS::Heap<jsid>* aPtr, const char* aName,
+                     void* aClosure) const override
+  {
+    JS::TraceEdge(static_cast<JSTracer*>(aClosure), aPtr, aName);
+  }
+  virtual void Trace(JS::Heap<JSObject*>* aPtr, const char* aName,
+                     void* aClosure) const override
+  {
+    JS::TraceEdge(static_cast<JSTracer*>(aClosure), aPtr, aName);
+  }
+  virtual void Trace(JSObject** aPtr, const char* aName,
+                     void* aClosure) const override
+  {
+    js::UnsafeTraceManuallyBarrieredEdge(static_cast<JSTracer*>(aClosure), aPtr, aName);
+  }
+  virtual void Trace(JS::TenuredHeap<JSObject*>* aPtr, const char* aName,
+                     void* aClosure) const override
+  {
+    JS::TraceEdge(static_cast<JSTracer*>(aClosure), aPtr, aName);
+  }
+  virtual void Trace(JS::Heap<JSString*>* aPtr, const char* aName,
+                     void* aClosure) const override
+  {
+    JS::TraceEdge(static_cast<JSTracer*>(aClosure), aPtr, aName);
+  }
+  virtual void Trace(JS::Heap<JSScript*>* aPtr, const char* aName,
+                     void* aClosure) const override
+  {
+    JS::TraceEdge(static_cast<JSTracer*>(aClosure), aPtr, aName);
+  }
+  virtual void Trace(JS::Heap<JSFunction*>* aPtr, const char* aName,
+                     void* aClosure) const override
+  {
+    JS::TraceEdge(static_cast<JSTracer*>(aClosure), aPtr, aName);
+  }
+};
+
+void
+mozilla::TraceScriptHolder(nsISupports* aHolder, JSTracer* aTracer)
+{
+  nsXPCOMCycleCollectionParticipant* participant = nullptr;
+  CallQueryInterface(aHolder, &participant);
+  participant->Trace(aHolder, JsGcTracer(), aTracer);
+}
+
+void
+CycleCollectedJSContext::TraceNativeGrayRoots(JSTracer* aTracer)
+{
+  MOZ_ASSERT(mJSContext);
+
+  // NB: This is here just to preserve the existing XPConnect order. I doubt it
+  // would hurt to do this after the JS holders.
+  TraceAdditionalNativeGrayRoots(aTracer);
+
+  for (auto iter = mJSHolders.Iter(); !iter.Done(); iter.Next()) {
+    void* holder = iter.Key();
+    nsScriptObjectTracer*& tracer = iter.Data();
+    tracer->Trace(holder, JsGcTracer(), aTracer);
+  }
+}
+
+void
+CycleCollectedJSContext::AddJSHolder(void* aHolder, nsScriptObjectTracer* aTracer)
+{
+  MOZ_ASSERT(mJSContext);
+  mJSHolders.Put(aHolder, aTracer);
+}
+
+struct ClearJSHolder : public TraceCallbacks
+{
+  virtual void Trace(JS::Heap<JS::Value>* aPtr, const char*, void*) const override
+  {
+    aPtr->setUndefined();
+  }
+
+  virtual void Trace(JS::Heap<jsid>* aPtr, const char*, void*) const override
+  {
+    *aPtr = JSID_VOID;
+  }
+
+  virtual void Trace(JS::Heap<JSObject*>* aPtr, const char*, void*) const override
+  {
+    *aPtr = nullptr;
+  }
+
+  virtual void Trace(JSObject** aPtr, const char* aName,
+                     void* aClosure) const override
+  {
+    *aPtr = nullptr;
+  }
+
+  virtual void Trace(JS::TenuredHeap<JSObject*>* aPtr, const char*, void*) const override
+  {
+    *aPtr = nullptr;
+  }
+
+  virtual void Trace(JS::Heap<JSString*>* aPtr, const char*, void*) const override
+  {
+    *aPtr = nullptr;
+  }
+
+  virtual void Trace(JS::Heap<JSScript*>* aPtr, const char*, void*) const override
+  {
+    *aPtr = nullptr;
+  }
+
+  virtual void Trace(JS::Heap<JSFunction*>* aPtr, const char*, void*) const override
+  {
+    *aPtr = nullptr;
+  }
+};
+
+void
+CycleCollectedJSContext::RemoveJSHolder(void* aHolder)
+{
+  MOZ_ASSERT(mJSContext);
+
+  nsScriptObjectTracer* tracer = mJSHolders.Get(aHolder);
+  if (!tracer) {
+    return;
+  }
+  tracer->Trace(aHolder, ClearJSHolder(), nullptr);
+  mJSHolders.Remove(aHolder);
+}
+
+#ifdef DEBUG
+bool
+CycleCollectedJSContext::IsJSHolder(void* aHolder)
+{
+  MOZ_ASSERT(mJSContext);
+  return mJSHolders.Get(aHolder, nullptr);
+}
+
+static void
+AssertNoGcThing(JS::GCCellPtr aGCThing, const char* aName, void* aClosure)
+{
+  MOZ_ASSERT(!aGCThing);
+}
+
+void
+CycleCollectedJSContext::AssertNoObjectsToTrace(void* aPossibleJSHolder)
+{
+  MOZ_ASSERT(mJSContext);
+
+  nsScriptObjectTracer* tracer = mJSHolders.Get(aPossibleJSHolder);
+  if (tracer) {
+    tracer->Trace(aPossibleJSHolder, TraceCallbackFunc(AssertNoGcThing), nullptr);
+  }
+}
+#endif
+
+already_AddRefed<nsIException>
+CycleCollectedJSContext::GetPendingException() const
+{
+  MOZ_ASSERT(mJSContext);
+
+  nsCOMPtr<nsIException> out = mPendingException;
+  return out.forget();
+}
+
+void
+CycleCollectedJSContext::SetPendingException(nsIException* aException)
+{
+  MOZ_ASSERT(mJSContext);
+  mPendingException = aException;
+}
+
+std::queue<nsCOMPtr<nsIRunnable>>&
+CycleCollectedJSContext::GetPromiseMicroTaskQueue()
+{
+  MOZ_ASSERT(mJSContext);
+  return mPromiseMicroTaskQueue;
+}
+
+std::queue<nsCOMPtr<nsIRunnable>>&
+CycleCollectedJSContext::GetDebuggerPromiseMicroTaskQueue()
+{
+  MOZ_ASSERT(mJSContext);
+  return mDebuggerPromiseMicroTaskQueue;
+}
+
+nsCycleCollectionParticipant*
+CycleCollectedJSContext::GCThingParticipant()
+{
+  MOZ_ASSERT(mJSContext);
+  return &mGCThingCycleCollectorGlobal;
+}
+
+nsCycleCollectionParticipant*
+CycleCollectedJSContext::ZoneParticipant()
+{
+  MOZ_ASSERT(mJSContext);
+  return &mJSZoneCycleCollectorGlobal;
+}
+
+nsresult
+CycleCollectedJSContext::TraverseRoots(nsCycleCollectionNoteRootCallback& aCb)
+{
+  MOZ_ASSERT(mJSContext);
+
+  TraverseNativeRoots(aCb);
+
+  NoteWeakMapsTracer trc(mJSContext, aCb);
+  js::TraceWeakMaps(&trc);
+
+  return NS_OK;
+}
+
+bool
+CycleCollectedJSContext::UsefulToMergeZones() const
+{
+  return false;
+}
+
+void
+CycleCollectedJSContext::FixWeakMappingGrayBits() const
+{
+  MOZ_ASSERT(mJSContext);
+  MOZ_ASSERT(!JS::IsIncrementalGCInProgress(mJSContext),
+             "Don't call FixWeakMappingGrayBits during a GC.");
+  FixWeakMappingGrayBitsTracer fixer(mJSContext);
+  fixer.FixAll();
+}
+
+bool
+CycleCollectedJSContext::AreGCGrayBitsValid() const
+{
+  MOZ_ASSERT(mJSContext);
+  return js::AreGCGrayBitsValid(mJSContext);
+}
+
+void
+CycleCollectedJSContext::GarbageCollect(uint32_t aReason) const
+{
+  MOZ_ASSERT(mJSContext);
+
+  MOZ_ASSERT(aReason < JS::gcreason::NUM_REASONS);
+  JS::gcreason::Reason gcreason = static_cast<JS::gcreason::Reason>(aReason);
+
+  JS::PrepareForFullGC(mJSContext);
+  JS::GCForReason(mJSContext, GC_NORMAL, gcreason);
+}
+
+void
+CycleCollectedJSContext::JSObjectsTenured()
+{
+  MOZ_ASSERT(mJSContext);
+
+  for (auto iter = mNurseryObjects.Iter(); !iter.Done(); iter.Next()) {
+    nsWrapperCache* cache = iter.Get();
+    JSObject* wrapper = cache->GetWrapperPreserveColor();
+    MOZ_ASSERT(wrapper);
+    if (!JS::ObjectIsTenured(wrapper)) {
+      MOZ_ASSERT(!cache->PreservingWrapper());
+      const JSClass* jsClass = js::GetObjectJSClass(wrapper);
+      jsClass->doFinalize(nullptr, wrapper);
+    }
+  }
+
+#ifdef DEBUG
+for (auto iter = mPreservedNurseryObjects.Iter(); !iter.Done(); iter.Next()) {
+  MOZ_ASSERT(JS::ObjectIsTenured(iter.Get().get()));
+}
+#endif
+
+  mNurseryObjects.Clear();
+  mPreservedNurseryObjects.Clear();
+}
+
+void
+CycleCollectedJSContext::NurseryWrapperAdded(nsWrapperCache* aCache)
+{
+  MOZ_ASSERT(mJSContext);
+  MOZ_ASSERT(aCache);
+  MOZ_ASSERT(aCache->GetWrapperPreserveColor());
+  MOZ_ASSERT(!JS::ObjectIsTenured(aCache->GetWrapperPreserveColor()));
+  mNurseryObjects.InfallibleAppend(aCache);
+}
+
+void
+CycleCollectedJSContext::NurseryWrapperPreserved(JSObject* aWrapper)
+{
+  MOZ_ASSERT(mJSContext);
+
+  mPreservedNurseryObjects.InfallibleAppend(
+    JS::PersistentRooted<JSObject*>(mJSContext, aWrapper));
+}
+
+void
+CycleCollectedJSContext::DeferredFinalize(DeferredFinalizeAppendFunction aAppendFunc,
+                                          DeferredFinalizeFunction aFunc,
+                                          void* aThing)
+{
+  MOZ_ASSERT(mJSContext);
+
+  void* thingArray = nullptr;
+  bool hadThingArray = mDeferredFinalizerTable.Get(aFunc, &thingArray);
+
+  thingArray = aAppendFunc(thingArray, aThing);
+  if (!hadThingArray) {
+    mDeferredFinalizerTable.Put(aFunc, thingArray);
+  }
+}
+
+void
+CycleCollectedJSContext::DeferredFinalize(nsISupports* aSupports)
+{
+  MOZ_ASSERT(mJSContext);
+
+  typedef DeferredFinalizerImpl<nsISupports> Impl;
+  DeferredFinalize(Impl::AppendDeferredFinalizePointer, Impl::DeferredFinalize,
+                   aSupports);
+}
+
+void
+CycleCollectedJSContext::DumpJSHeap(FILE* aFile)
+{
+  js::DumpHeap(Context(), aFile, js::CollectNurseryBeforeDump);
+}
+
+void
+CycleCollectedJSContext::ProcessStableStateQueue()
+{
+  MOZ_ASSERT(mJSContext);
+  MOZ_RELEASE_ASSERT(!mDoingStableStates);
+  mDoingStableStates = true;
+
+  for (uint32_t i = 0; i < mStableStateEvents.Length(); ++i) {
+    nsCOMPtr<nsIRunnable> event = mStableStateEvents[i].forget();
+    event->Run();
+  }
+
+  mStableStateEvents.Clear();
+  mDoingStableStates = false;
+}
+
+void
+CycleCollectedJSContext::ProcessMetastableStateQueue(uint32_t aRecursionDepth)
+{
+  MOZ_ASSERT(mJSContext);
+  MOZ_RELEASE_ASSERT(!mDoingStableStates);
+  mDoingStableStates = true;
+
+  nsTArray<RunInMetastableStateData> localQueue = Move(mMetastableStateEvents);
+
+  for (uint32_t i = 0; i < localQueue.Length(); ++i)
+  {
+    RunInMetastableStateData& data = localQueue[i];
+    if (data.mRecursionDepth != aRecursionDepth) {
+      continue;
+    }
+
+    {
+      nsCOMPtr<nsIRunnable> runnable = data.mRunnable.forget();
+      runnable->Run();
+    }
+
+    localQueue.RemoveElementAt(i--);
+  }
+
+  // If the queue has events in it now, they were added from something we called,
+  // so they belong at the end of the queue.
+  localQueue.AppendElements(mMetastableStateEvents);
+  localQueue.SwapElements(mMetastableStateEvents);
+  mDoingStableStates = false;
+}
+
+void
+CycleCollectedJSContext::AfterProcessTask(uint32_t aRecursionDepth)
+{
+  MOZ_ASSERT(mJSContext);
+
+  // See HTML 6.1.4.2 Processing model
+
+  // Execute any events that were waiting for a microtask to complete.
+  // This is not (yet) in the spec.
+  ProcessMetastableStateQueue(aRecursionDepth);
+
+  // Step 4.1: Execute microtasks.
+  if (!mDisableMicroTaskCheckpoint) {
+    if (NS_IsMainThread()) {
+      nsContentUtils::PerformMainThreadMicroTaskCheckpoint();
+      Promise::PerformMicroTaskCheckpoint();
+    } else {
+      Promise::PerformWorkerMicroTaskCheckpoint();
+    }
+  }
+
+  // Step 4.2 Execute any events that were waiting for a stable state.
+  ProcessStableStateQueue();
+}
+
+void
+CycleCollectedJSContext::AfterProcessMicrotask()
+{
+  MOZ_ASSERT(mJSContext);
+  AfterProcessMicrotask(RecursionDepth());
+}
+
+void
+CycleCollectedJSContext::AfterProcessMicrotask(uint32_t aRecursionDepth)
+{
+  MOZ_ASSERT(mJSContext);
+
+  // Between microtasks, execute any events that were waiting for a microtask
+  // to complete.
+  ProcessMetastableStateQueue(aRecursionDepth);
+}
+
+uint32_t
+CycleCollectedJSContext::RecursionDepth()
+{
+  return mOwningThread->RecursionDepth();
+}
+
+void
+CycleCollectedJSContext::RunInStableState(already_AddRefed<nsIRunnable>&& aRunnable)
+{
+  MOZ_ASSERT(mJSContext);
+  mStableStateEvents.AppendElement(Move(aRunnable));
+}
+
+void
+CycleCollectedJSContext::RunInMetastableState(already_AddRefed<nsIRunnable>&& aRunnable)
+{
+  MOZ_ASSERT(mJSContext);
+
+  RunInMetastableStateData data;
+  data.mRunnable = aRunnable;
+
+  MOZ_ASSERT(mOwningThread);
+  data.mRecursionDepth = RecursionDepth();
+
+  // There must be an event running to get here.
+#ifndef MOZ_WIDGET_COCOA
+  MOZ_ASSERT(data.mRecursionDepth > mBaseRecursionDepth);
+#else
+  // XXX bug 1261143
+  // Recursion depth should be greater than mBaseRecursionDepth,
+  // or the runnable will stay in the queue forever.
+  if (data.mRecursionDepth <= mBaseRecursionDepth) {
+    data.mRecursionDepth = mBaseRecursionDepth + 1;
+  }
+#endif
+
+  mMetastableStateEvents.AppendElement(Move(data));
+}
+
+IncrementalFinalizeRunnable::IncrementalFinalizeRunnable(CycleCollectedJSContext* aCx,
+                                                         DeferredFinalizerTable& aFinalizers)
+  : mContext(aCx)
+  , mFinalizeFunctionToRun(0)
+  , mReleasing(false)
+{
+  for (auto iter = aFinalizers.Iter(); !iter.Done(); iter.Next()) {
+    DeferredFinalizeFunction& function = iter.Key();
+    void*& data = iter.Data();
+
+    DeferredFinalizeFunctionHolder* holder =
+      mDeferredFinalizeFunctions.AppendElement();
+    holder->run = function;
+    holder->data = data;
+
+    iter.Remove();
+  }
+}
+
+IncrementalFinalizeRunnable::~IncrementalFinalizeRunnable()
+{
+  MOZ_ASSERT(this != mContext->mFinalizeRunnable);
+}
+
+void
+IncrementalFinalizeRunnable::ReleaseNow(bool aLimited)
+{
+  if (mReleasing) {
+    NS_WARNING("Re-entering ReleaseNow");
+    return;
+  }
+  {
+    mozilla::AutoRestore<bool> ar(mReleasing);
+    mReleasing = true;
+    MOZ_ASSERT(mDeferredFinalizeFunctions.Length() != 0,
+               "We should have at least ReleaseSliceNow to run");
+    MOZ_ASSERT(mFinalizeFunctionToRun < mDeferredFinalizeFunctions.Length(),
+               "No more finalizers to run?");
+
+    TimeDuration sliceTime = TimeDuration::FromMilliseconds(SliceMillis);
+    TimeStamp started = TimeStamp::Now();
+    bool timeout = false;
+    do {
+      const DeferredFinalizeFunctionHolder& function =
+        mDeferredFinalizeFunctions[mFinalizeFunctionToRun];
+      if (aLimited) {
+        bool done = false;
+        while (!timeout && !done) {
+          /*
+           * We don't want to read the clock too often, so we try to
+           * release slices of 100 items.
+           */
+          done = function.run(100, function.data);
+          timeout = TimeStamp::Now() - started >= sliceTime;
+        }
+        if (done) {
+          ++mFinalizeFunctionToRun;
+        }
+        if (timeout) {
+          break;
+        }
+      } else {
+        while (!function.run(UINT32_MAX, function.data));
+        ++mFinalizeFunctionToRun;
+      }
+    } while (mFinalizeFunctionToRun < mDeferredFinalizeFunctions.Length());
+  }
+
+  if (mFinalizeFunctionToRun == mDeferredFinalizeFunctions.Length()) {
+    MOZ_ASSERT(mContext->mFinalizeRunnable == this);
+    mDeferredFinalizeFunctions.Clear();
+    // NB: This may delete this!
+    mContext->mFinalizeRunnable = nullptr;
+  }
+}
+
+NS_IMETHODIMP
+IncrementalFinalizeRunnable::Run()
+{
+  if (mContext->mFinalizeRunnable != this) {
+    /* These items were already processed synchronously in JSGC_END. */
+    MOZ_ASSERT(!mDeferredFinalizeFunctions.Length());
+    return NS_OK;
+  }
+
+  TimeStamp start = TimeStamp::Now();
+  ReleaseNow(true);
+
+  if (mDeferredFinalizeFunctions.Length()) {
+    nsresult rv = NS_DispatchToCurrentThread(this);
+    if (NS_FAILED(rv)) {
+      ReleaseNow(false);
+    }
+  }
+
+  uint32_t duration = (uint32_t)((TimeStamp::Now() - start).ToMilliseconds());
+  Telemetry::Accumulate(Telemetry::DEFERRED_FINALIZE_ASYNC, duration);
+
+  return NS_OK;
+}
+
+void
+CycleCollectedJSContext::FinalizeDeferredThings(DeferredFinalizeType aType)
+{
+  MOZ_ASSERT(mJSContext);
+
+  /*
+   * If the previous GC created a runnable to finalize objects
+   * incrementally, and if it hasn't finished yet, finish it now. We
+   * don't want these to build up. We also don't want to allow any
+   * existing incremental finalize runnables to run after a
+   * non-incremental GC, since they are often used to detect leaks.
+   */
+  if (mFinalizeRunnable) {
+    mFinalizeRunnable->ReleaseNow(false);
+    if (mFinalizeRunnable) {
+      // If we re-entered ReleaseNow, we couldn't delete mFinalizeRunnable and
+      // we need to just continue processing it.
+      return;
+    }
+  }
+
+  if (mDeferredFinalizerTable.Count() == 0) {
+    return;
+  }
+
+  mFinalizeRunnable = new IncrementalFinalizeRunnable(this,
+                                                      mDeferredFinalizerTable);
+
+  // Everything should be gone now.
+  MOZ_ASSERT(mDeferredFinalizerTable.Count() == 0);
+
+  if (aType == FinalizeIncrementally) {
+    NS_DispatchToCurrentThread(mFinalizeRunnable);
+  } else {
+    mFinalizeRunnable->ReleaseNow(false);
+    MOZ_ASSERT(!mFinalizeRunnable);
+  }
+}
+
+void
+CycleCollectedJSContext::AnnotateAndSetOutOfMemory(OOMState* aStatePtr,
+                                                   OOMState aNewState)
+{
+  MOZ_ASSERT(mJSContext);
+
+  *aStatePtr = aNewState;
+#ifdef MOZ_CRASHREPORTER
+  CrashReporter::AnnotateCrashReport(aStatePtr == &mOutOfMemoryState
+                                     ? NS_LITERAL_CSTRING("JSOutOfMemory")
+                                     : NS_LITERAL_CSTRING("JSLargeAllocationFailure"),
+                                     aNewState == OOMState::Reporting
+                                     ? NS_LITERAL_CSTRING("Reporting")
+                                     : aNewState == OOMState::Reported
+                                     ? NS_LITERAL_CSTRING("Reported")
+                                     : NS_LITERAL_CSTRING("Recovered"));
+#endif
+}
+
+void
+CycleCollectedJSContext::OnGC(JSGCStatus aStatus)
+{
+  MOZ_ASSERT(mJSContext);
+
+  switch (aStatus) {
+    case JSGC_BEGIN:
+      nsCycleCollector_prepareForGarbageCollection();
+      mZonesWaitingForGC.Clear();
+      break;
+    case JSGC_END: {
+#ifdef MOZ_CRASHREPORTER
+      if (mOutOfMemoryState == OOMState::Reported) {
+        AnnotateAndSetOutOfMemory(&mOutOfMemoryState, OOMState::Recovered);
+      }
+      if (mLargeAllocationFailureState == OOMState::Reported) {
+        AnnotateAndSetOutOfMemory(&mLargeAllocationFailureState, OOMState::Recovered);
+      }
+#endif
+
+      // Do any deferred finalization of native objects.
+      FinalizeDeferredThings(JS::WasIncrementalGC(mJSContext) ? FinalizeIncrementally :
+                                                                FinalizeNow);
+      break;
+    }
+    default:
+      MOZ_CRASH();
+  }
+
+  CustomGCCallback(aStatus);
+}
+
+void
+CycleCollectedJSContext::OnOutOfMemory()
+{
+  MOZ_ASSERT(mJSContext);
+
+  AnnotateAndSetOutOfMemory(&mOutOfMemoryState, OOMState::Reporting);
+  CustomOutOfMemoryCallback();
+  AnnotateAndSetOutOfMemory(&mOutOfMemoryState, OOMState::Reported);
+}
+
+void
+CycleCollectedJSContext::OnLargeAllocationFailure()
+{
+  MOZ_ASSERT(mJSContext);
+
+  AnnotateAndSetOutOfMemory(&mLargeAllocationFailureState, OOMState::Reporting);
+  CustomLargeAllocationFailureCallback();
+  AnnotateAndSetOutOfMemory(&mLargeAllocationFailureState, OOMState::Reported);
+}
+
+void
+CycleCollectedJSContext::PrepareWaitingZonesForGC()
+{
+  if (mZonesWaitingForGC.Count() == 0) {
+    JS::PrepareForFullGC(Context());
+  } else {
+    for (auto iter = mZonesWaitingForGC.Iter(); !iter.Done(); iter.Next()) {
+      JS::PrepareZoneForGC(iter.Get()->GetKey());
+    }
+    mZonesWaitingForGC.Clear();
+  }
+}
+
+void
+CycleCollectedJSContext::DispatchToMicroTask(already_AddRefed<nsIRunnable> aRunnable)
+{
+  RefPtr<nsIRunnable> runnable(aRunnable);
+
+  MOZ_ASSERT(NS_IsMainThread());
+  MOZ_ASSERT(runnable);
+
+  mPromiseMicroTaskQueue.push(runnable.forget());
+}
+
+void
+CycleCollectedJSContext::EnvironmentPreparer::invoke(JS::HandleObject scope,
+                                                     js::ScriptEnvironmentPreparer::Closure& closure)
+{
+  nsIGlobalObject* global = xpc::NativeGlobal(scope);
+
+  // Not much we can do if we simply don't have a usable global here...
+  NS_ENSURE_TRUE_VOID(global && global->GetGlobalJSObject());
+
+  AutoEntryScript aes(global, "JS-engine-initiated execution");
+
+  MOZ_ASSERT(!JS_IsExceptionPending(aes.cx()));
+
+  DebugOnly<bool> ok = closure(aes.cx());
+
+  MOZ_ASSERT_IF(ok, !JS_IsExceptionPending(aes.cx()));
+
+  // The AutoEntryScript will check for JS_IsExceptionPending on the
+  // JSContext and report it as needed as it comes off the stack.
+}