path: root/xpcom/base/nsCycleCollectionParticipant.h

/* -*- 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/. */

#ifndef nsCycleCollectionParticipant_h__
#define nsCycleCollectionParticipant_h__

#include <type_traits>
#include "js/HeapAPI.h"
#include "js/TypeDecls.h"
#include "mozilla/MacroForEach.h"
#include "nsCycleCollectionNoteChild.h"
#include "nsDebug.h"
#include "nsID.h"
#include "nscore.h"

/**
 * Note: the following two IIDs only differ in one bit in the last byte.  This
 * is a hack and is intentional in order to speed up the comparison inside
 * NS_INTERFACE_TABLE_HEAD_CYCLE_COLLECTION_INHERITED.
 */
#define NS_XPCOMCYCLECOLLECTIONPARTICIPANT_IID       \
  {                                                  \
    0xc61eac14, 0x5f7a, 0x4481, {                    \
      0x96, 0x5e, 0x7e, 0xaa, 0x6e, 0xff, 0xa8, 0x5e \
    }                                                \
  }

/**
 * Special IID to get at the base nsISupports for a class. Usually this is the
 * canonical nsISupports pointer, but in the case of tearoffs for example it is
 * the base nsISupports pointer of the tearoff. This allow the cycle collector
 * to have separate nsCycleCollectionParticipant's for tearoffs or aggregated
 * classes.
 */
#define NS_CYCLECOLLECTIONISUPPORTS_IID              \
  {                                                  \
    0xc61eac14, 0x5f7a, 0x4481, {                    \
      0x96, 0x5e, 0x7e, 0xaa, 0x6e, 0xff, 0xa8, 0x5f \
    }                                                \
  }

namespace mozilla {
enum class CCReason : uint8_t {
  NO_REASON,

  // Purple buffer "overflow": enough objects are suspected to be cycle
  // collectable to trigger an immediate CC.
  MANY_SUSPECTED,

  // The previous collection was kCCForced ago, and there are at least
  // kCCForcedPurpleLimit objects suspected of being cycle collectable.
  TIMED,

  // Run a CC after a GC has completed.
  GC_FINISHED,

  // Run a slice of a collection.
  SLICE,

  // Manual reasons are explicitly triggered with a custom listener (as opposed
  // to exceeding some internal threshold.) If a CC is already in progress,
  // continue it. Otherwise, start a new one.
  FIRST_MANUAL_REASON = 128,

  // We want to GC, but must finish any ongoing cycle collection first.
  GC_WAITING = FIRST_MANUAL_REASON,

  // CC requested via an API. Used by tests.
  API,

  // Collecting in order to dump the heap.
  DUMP_HEAP,

  // Low memory situation detected.
  MEM_PRESSURE,

  // IPC message to a content process to trigger a CC. The original reason is
  // not tracked.
  IPC_MESSAGE,

  // Cycle collection on a worker. The triggering reason is not tracked.
  WORKER,

  // Used for finding leaks.
  SHUTDOWN
};

#define FOR_EACH_CCREASON(MACRO) \
  MACRO(NO_REASON)               \
  MACRO(MANY_SUSPECTED)          \
  MACRO(TIMED)                   \
  MACRO(GC_FINISHED)             \
  MACRO(SLICE)                   \
  MACRO(GC_WAITING)              \
  MACRO(API)                     \
  MACRO(DUMP_HEAP)               \
  MACRO(MEM_PRESSURE)            \
  MACRO(IPC_MESSAGE)             \
  MACRO(WORKER)                  \
  MACRO(SHUTDOWN)

static inline bool IsManualCCReason(CCReason reason) {
  return reason >= CCReason::FIRST_MANUAL_REASON;
}

static inline const char* CCReasonToString(CCReason aReason) {
  switch (aReason) {
#define SET_REASON_STR(name) \
  case CCReason::name:       \
    return #name;            \
    break;
    FOR_EACH_CCREASON(SET_REASON_STR)
#undef SET_REASON_STR
    default:
      return "<unknown-reason>";
  }
}

}  // namespace mozilla

/**
 * Just holds the IID so NS_GET_IID works.
 */
class nsCycleCollectionISupports {
 public:
  NS_DECLARE_STATIC_IID_ACCESSOR(NS_CYCLECOLLECTIONISUPPORTS_IID)
};

NS_DEFINE_STATIC_IID_ACCESSOR(nsCycleCollectionISupports,
                              NS_CYCLECOLLECTIONISUPPORTS_IID)

class nsCycleCollectionTraversalCallback;
class nsISupports;
class nsWrapperCache;

namespace JS {
template <class T>
class Heap;
template <typename T>
class TenuredHeap;
} /* namespace JS */

/*
 * A struct defining pure virtual methods which are called when tracing cycle
 * collection paticipants.  The appropriate method is called depending on the
 * type of JS GC thing.
 */
struct TraceCallbacks {
  virtual void Trace(JS::Heap<JS::Value>* aPtr, const char* aName,
                     void* aClosure) const = 0;
  virtual void Trace(JS::Heap<jsid>* aPtr, const char* aName,
                     void* aClosure) const = 0;
  virtual void Trace(JS::Heap<JSObject*>* aPtr, const char* aName,
                     void* aClosure) const = 0;
  virtual void Trace(nsWrapperCache* aPtr, const char* aName,
                     void* aClosure) const = 0;
  virtual void Trace(JS::TenuredHeap<JSObject*>* aPtr, const char* aName,
                     void* aClosure) const = 0;
  virtual void Trace(JS::Heap<JSString*>* aPtr, const char* aName,
                     void* aClosure) const = 0;
  virtual void Trace(JS::Heap<JSScript*>* aPtr, const char* aName,
                     void* aClosure) const = 0;
  virtual void Trace(JS::Heap<JSFunction*>* aPtr, const char* aName,
                     void* aClosure) const = 0;
};

/*
 * An implementation of TraceCallbacks that calls a single function for all JS
 * GC thing types encountered. Implemented in
 * nsCycleCollectorTraceJSHelpers.cpp.
 */
struct TraceCallbackFunc : public TraceCallbacks {
  typedef void (*Func)(JS::GCCellPtr aPtr, const char* aName, void* aClosure);

  explicit TraceCallbackFunc(Func aCb) : mCallback(aCb) {}

  virtual void Trace(JS::Heap<JS::Value>* aPtr, const char* aName,
                     void* aClosure) const override;
  virtual void Trace(JS::Heap<jsid>* aPtr, const char* aName,
                     void* aClosure) const override;
  virtual void Trace(JS::Heap<JSObject*>* aPtr, const char* aName,
                     void* aClosure) const override;
  virtual void Trace(nsWrapperCache* aPtr, const char* aName,
                     void* aClosure) const override;
  virtual void Trace(JS::TenuredHeap<JSObject*>* aPtr, const char* aName,
                     void* aClosure) const override;
  virtual void Trace(JS::Heap<JSString*>* aPtr, const char* aName,
                     void* aClosure) const override;
  virtual void Trace(JS::Heap<JSScript*>* aPtr, const char* aName,
                     void* aClosure) const override;
  virtual void Trace(JS::Heap<JSFunction*>* aPtr, const char* aName,
                     void* aClosure) const override;

 private:
  Func mCallback;
};

/**
 * Participant implementation classes
 */
class NS_NO_VTABLE nsCycleCollectionParticipant {
 public:
  using Flags = uint8_t;
  static constexpr Flags FlagMightSkip = 1u << 0;
  static constexpr Flags FlagTraverseShouldTrace = 1u << 1;
  // The object is a single zone js holder if FlagMaybeSingleZoneJSHolder is set
  // and FlagMultiZoneJSHolder isn't set. This setup is needed so that
  // inheriting classes can unset single zone behavior.
  static constexpr Flags FlagMaybeSingleZoneJSHolder = 1u << 2;
  static constexpr Flags FlagMultiZoneJSHolder = 1u << 3;
  static constexpr Flags AllFlags = FlagMightSkip | FlagTraverseShouldTrace |
                                    FlagMaybeSingleZoneJSHolder |
                                    FlagMultiZoneJSHolder;

  constexpr explicit nsCycleCollectionParticipant(Flags aFlags)
      : mFlags(aFlags) {
    MOZ_ASSERT((aFlags & ~AllFlags) == 0);
  }

  NS_IMETHOD TraverseNative(void* aPtr,
                            nsCycleCollectionTraversalCallback& aCb) = 0;

  nsresult TraverseNativeAndJS(void* aPtr,
                               nsCycleCollectionTraversalCallback& aCb) {
    nsresult rv = TraverseNative(aPtr, aCb);
    if (TraverseShouldTrace()) {
      // Note, we always call Trace, even if Traverse returned
      // NS_SUCCESS_INTERRUPTED_TRAVERSE.
      TraceCallbackFunc noteJsChild(&nsCycleCollectionParticipant::NoteJSChild);
      Trace(aPtr, noteJsChild, &aCb);
    }
    return rv;
  }

  // Implemented in nsCycleCollectorTraceJSHelpers.cpp.
  static void NoteJSChild(JS::GCCellPtr aGCThing, const char* aName,
                          void* aClosure);

  NS_IMETHOD_(void) Root(void* aPtr) = 0;
  NS_IMETHOD_(void) Unlink(void* aPtr) = 0;
  NS_IMETHOD_(void) Unroot(void* aPtr) = 0;
  NS_IMETHOD_(const char*) ClassName() = 0;

  NS_IMETHOD_(void)
  Trace(void* aPtr, const TraceCallbacks& aCb, void* aClosure) {}

  // CanSkip is called during nsCycleCollector_forgetSkippable.  If it returns
  // true, aPtr is removed from the purple buffer and therefore might be left
  // out from the cycle collector graph the next time that's constructed (unless
  // it's reachable in some other way).
  //
  // CanSkip is allowed to expand the set of certainly-alive objects by removing
  // other objects from the purple buffer, marking JS things black (in the GC
  // sense), and so forth.  Furthermore, if aRemovingAllowed is true, this call
  // is allowed to remove aPtr itself from the purple buffer.
  //
  // Things can return true from CanSkip if either they know they have no
  // outgoing edges at all in the cycle collection graph (because then they
  // can't be parts of a cycle) or they know for sure they're alive.
  bool CanSkip(void* aPtr, bool aRemovingAllowed) {
    return MightSkip() ? CanSkipReal(aPtr, aRemovingAllowed) : false;
  }

  // CanSkipInCC is called during construction of the initial set of roots for
  // the cycle collector graph.  If it returns true, aPtr is left out of that
  // set of roots.  Note that the set of roots includes whatever is in the
  // purple buffer (after earlier CanSkip calls) plus various other sources of
  // roots, so an object can end up having CanSkipInCC called on it even if it
  // returned true from CanSkip.  One example of this would be an object that
  // can potentially trace JS things.
  //
  // CanSkipInCC is allowed to remove other objects from the purple buffer but
  // should not remove aPtr and should not mark JS things black.  It should also
  // not modify any reference counts.
  //
  // Things can return true from CanSkipInCC if either they know they have no
  // outgoing edges at all in the cycle collection graph or they know for sure
  // they're alive _and_ none of their outgoing edges are to gray (in the GC
  // sense) gcthings.  See also nsWrapperCache::HasNothingToTrace and
  // nsWrapperCache::HasKnownLiveWrapperAndDoesNotNeedTracing. The restriction
  // on not having outgoing edges to gray gcthings is because if we _do_ have
  // them that means we have a "strong" edge to a JS thing and since we're alive
  // we need to trace through it and mark keep them alive.  Outgoing edges to
  // C++ things don't matter here, because the criteria for when a CC
  // participant is considered alive are slightly different for JS and C++
  // things: JS things are only considered alive when reachable via an edge from
  // a live thing, while C++ things are also considered alive when their
  // refcount exceeds the number of edges via which they are reachable.
  bool CanSkipInCC(void* aPtr) {
    return MightSkip() ? CanSkipInCCReal(aPtr) : false;
  }

  // CanSkipThis is called during construction of the cycle collector graph,
  // when we traverse an edge to aPtr and consider adding it to the graph.  If
  // it returns true, aPtr is not added to the graph.
  //
  // CanSkipThis is not allowed to change the liveness or reference count of any
  // objects.
  //
  // Things can return true from CanSkipThis if either they know they have no
  // outgoing edges at all in the cycle collection graph or they know for sure
  // they're alive.
  //
  // Note that CanSkipThis doesn't have to worry about outgoing edges to gray GC
  // things, because if this object could have those it already got added to the
  // graph during root set construction.  An object should never have
  // CanSkipThis called on it if it has outgoing strong references to JS things.
  bool CanSkipThis(void* aPtr) {
    return MightSkip() ? CanSkipThisReal(aPtr) : false;
  }

  NS_IMETHOD_(void) DeleteCycleCollectable(void* aPtr) = 0;

  bool IsSingleZoneJSHolder() const {
    return (mFlags & FlagMaybeSingleZoneJSHolder) &&
           !(mFlags & FlagMultiZoneJSHolder);
  }

 protected:
  NS_IMETHOD_(bool) CanSkipReal(void* aPtr, bool aRemovingAllowed) {
    NS_ASSERTION(false, "Forgot to implement CanSkipReal?");
    return false;
  }
  NS_IMETHOD_(bool) CanSkipInCCReal(void* aPtr) {
    NS_ASSERTION(false, "Forgot to implement CanSkipInCCReal?");
    return false;
  }
  NS_IMETHOD_(bool) CanSkipThisReal(void* aPtr) {
    NS_ASSERTION(false, "Forgot to implement CanSkipThisReal?");
    return false;
  }

 private:
  bool MightSkip() const { return mFlags & FlagMightSkip; }
  bool TraverseShouldTrace() const { return mFlags & FlagTraverseShouldTrace; }

  const Flags mFlags;
};

class NS_NO_VTABLE nsScriptObjectTracer : public nsCycleCollectionParticipant {
 public:
  constexpr explicit nsScriptObjectTracer(Flags aFlags)
      : nsCycleCollectionParticipant(aFlags | FlagTraverseShouldTrace) {}

  NS_IMETHOD_(void)
  Trace(void* aPtr, const TraceCallbacks& aCb, void* aClosure) override = 0;
};

class NS_NO_VTABLE nsXPCOMCycleCollectionParticipant
    : public nsScriptObjectTracer {
 public:
  constexpr explicit nsXPCOMCycleCollectionParticipant(Flags aFlags)
      : nsScriptObjectTracer(aFlags) {}

  NS_DECLARE_STATIC_IID_ACCESSOR(NS_XPCOMCYCLECOLLECTIONPARTICIPANT_IID)

  NS_IMETHOD_(void) Root(void* aPtr) override;
  NS_IMETHOD_(void) Unroot(void* aPtr) override;

  NS_IMETHOD_(void)
  Trace(void* aPtr, const TraceCallbacks& aCb, void* aClosure) override;

  static bool CheckForRightISupports(nsISupports* aSupports);
};

NS_DEFINE_STATIC_IID_ACCESSOR(nsXPCOMCycleCollectionParticipant,
                              NS_XPCOMCYCLECOLLECTIONPARTICIPANT_IID)

///////////////////////////////////////////////////////////////////////////////
// Helpers for implementing a QI to nsXPCOMCycleCollectionParticipant
///////////////////////////////////////////////////////////////////////////////

#define NS_CYCLE_COLLECTION_CLASSNAME(_class) \
  _class::NS_CYCLE_COLLECTION_INNERCLASS

// The IIDs for nsXPCOMCycleCollectionParticipant and nsCycleCollectionISupports
// are special in that they only differ in their last byte.  This allows for the
// optimization below where we first check the first three words of the IID and
// if we find a match we check the last word to decide which case we have to
// deal with.
#define NS_INTERFACE_MAP_ENTRIES_CYCLE_COLLECTION(_class)                      \
  if (TopThreeWordsEquals(                                                     \
          aIID, NS_GET_IID(nsXPCOMCycleCollectionParticipant),                 \
          NS_GET_IID(                                                          \
              nsCycleCollectionISupports)) && /* The calls to LowWordEquals    \
                                                 here are repeated inside the  \
                                                 if branch. This is due to the \
                                                 fact that we need to maintain \
                                                 the if/else chain for these   \
                                                 macros, so that the control   \
                                                 flow never enters the if      \
                                                 branch unless if we're        \
                                                 certain one of the            \
                                                 LowWordEquals() branches will \
                                                 get executed. */              \
      (LowWordEquals(aIID, NS_GET_IID(nsXPCOMCycleCollectionParticipant)) ||   \
       LowWordEquals(aIID, NS_GET_IID(nsCycleCollectionISupports)))) {         \
    if (LowWordEquals(aIID, NS_GET_IID(nsXPCOMCycleCollectionParticipant))) {  \
      *aInstancePtr = NS_CYCLE_COLLECTION_PARTICIPANT(_class);                 \
      return NS_OK;                                                            \
    }                                                                          \
    if (LowWordEquals(aIID, NS_GET_IID(nsCycleCollectionISupports))) {         \
      *aInstancePtr = NS_CYCLE_COLLECTION_CLASSNAME(_class)::Upcast(this);     \
      return NS_OK;                                                            \
    }                                                                          \
    /* Avoid warnings about foundInterface being left uninitialized. */        \
    foundInterface = nullptr;                                                  \
  } else

#define NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(_class) \
  NS_INTERFACE_MAP_BEGIN(_class)                        \
    NS_INTERFACE_MAP_ENTRIES_CYCLE_COLLECTION(_class)

#define NS_INTERFACE_TABLE_TO_MAP_SEGUE_CYCLE_COLLECTION(_class) \
  if (rv == NS_OK) return rv;                                    \
  nsISupports* foundInterface;                                   \
  NS_INTERFACE_MAP_ENTRIES_CYCLE_COLLECTION(_class)

// The IIDs for nsXPCOMCycleCollectionParticipant and nsCycleCollectionISupports
// are special in that they only differ in their last byte.  This allows for the
// optimization below where we first check the first three words of the IID and
// if we find a match we check the last word to decide which case we have to
// deal with.
#define NS_INTERFACE_TABLE_HEAD_CYCLE_COLLECTION_INHERITED(_class)           \
  NS_IMETHODIMP _class::QueryInterface(REFNSIID aIID, void** aInstancePtr) { \
    MOZ_ASSERT(aInstancePtr, "null out param");                              \
                                                                             \
    if (TopThreeWordsEquals(aIID,                                            \
                            NS_GET_IID(nsXPCOMCycleCollectionParticipant),   \
                            NS_GET_IID(nsCycleCollectionISupports))) {       \
      if (LowWordEquals(aIID,                                                \
                        NS_GET_IID(nsXPCOMCycleCollectionParticipant))) {    \
        *aInstancePtr = NS_CYCLE_COLLECTION_PARTICIPANT(_class);             \
        return NS_OK;                                                        \
      }                                                                      \
      if (LowWordEquals(aIID, NS_GET_IID(nsCycleCollectionISupports))) {     \
        *aInstancePtr = NS_CYCLE_COLLECTION_CLASSNAME(_class)::Upcast(this); \
        return NS_OK;                                                        \
      }                                                                      \
    }                                                                        \
    nsresult rv = NS_ERROR_FAILURE;

#define NS_CYCLE_COLLECTION_UPCAST(obj, clazz) \
  NS_CYCLE_COLLECTION_CLASSNAME(clazz)::Upcast(obj)

#ifdef DEBUG
#  define NS_CHECK_FOR_RIGHT_PARTICIPANT(_ptr) _ptr->CheckForRightParticipant()
#else
#  define NS_CHECK_FOR_RIGHT_PARTICIPANT(_ptr)
#endif

// The default implementation of this class template is empty, because it
// should never be used: see the partial specializations below.
template <typename T, bool IsXPCOM = std::is_base_of<nsISupports, T>::value>
struct DowncastCCParticipantImpl {};

// Specialization for XPCOM CC participants
template <typename T>
struct DowncastCCParticipantImpl<T, true> {
  static T* Run(void* aPtr) {
    nsISupports* s = static_cast<nsISupports*>(aPtr);
    MOZ_ASSERT(NS_CYCLE_COLLECTION_CLASSNAME(T)::CheckForRightISupports(s),
               "not the nsISupports pointer we expect");
    T* rval = NS_CYCLE_COLLECTION_CLASSNAME(T)::Downcast(s);
    NS_CHECK_FOR_RIGHT_PARTICIPANT(rval);
    return rval;
  }
};

// Specialization for native CC participants
template <typename T>
struct DowncastCCParticipantImpl<T, false> {
  static T* Run(void* aPtr) { return static_cast<T*>(aPtr); }
};

template <typename T>
T* DowncastCCParticipant(void* aPtr) {
  return DowncastCCParticipantImpl<T>::Run(aPtr);
}

///////////////////////////////////////////////////////////////////////////////
// Helpers for implementing CanSkip methods
///////////////////////////////////////////////////////////////////////////////

// See documentation for nsCycleCollectionParticipant::CanSkip for documentation
// about this method.
#define NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_BEGIN(_class)                       \
  NS_IMETHODIMP_(bool)                                                        \
  NS_CYCLE_COLLECTION_CLASSNAME(_class)::CanSkipReal(void* p,                 \
                                                     bool aRemovingAllowed) { \
    _class* tmp = DowncastCCParticipant<_class>(p);

#define NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_END \
  (void)tmp;                                  \
  return false;                               \
  }

// See documentation for nsCycleCollectionParticipant::CanSkipInCC for
// documentation about this method.
#define NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_IN_CC_BEGIN(_class)       \
  NS_IMETHODIMP_(bool)                                              \
  NS_CYCLE_COLLECTION_CLASSNAME(_class)::CanSkipInCCReal(void* p) { \
    _class* tmp = DowncastCCParticipant<_class>(p);

#define NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_IN_CC_END \
  (void)tmp;                                        \
  return false;                                     \
  }

// See documentation for nsCycleCollectionParticipant::CanSkipThis for
// documentation about this method.
#define NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_THIS_BEGIN(_class)        \
  NS_IMETHODIMP_(bool)                                              \
  NS_CYCLE_COLLECTION_CLASSNAME(_class)::CanSkipThisReal(void* p) { \
    _class* tmp = DowncastCCParticipant<_class>(p);

#define NS_IMPL_CYCLE_COLLECTION_CAN_SKIP_THIS_END \
  (void)tmp;                                       \
  return false;                                    \
  }

///////////////////////////////////////////////////////////////////////////////
// Helpers for implementing nsCycleCollectionParticipant::Unlink
//
// You need to use NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED if you want
// the base class Unlink version to be called before your own implementation.
// You can use NS_IMPL_CYCLE_COLLECTION_UNLINK_END_INHERITED if you want the
// base class Unlink to get called after your own implementation.  You should
// never use them together.
///////////////////////////////////////////////////////////////////////////////

#define NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(_class)      \
  NS_IMETHODIMP_(void)                                     \
  NS_CYCLE_COLLECTION_CLASSNAME(_class)::Unlink(void* p) { \
    _class* tmp = DowncastCCParticipant<_class>(p);

#define NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(_class, _base_class) \
  NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(_class)                              \
    nsISupports* s = static_cast<nsISupports*>(p);                           \
    NS_CYCLE_COLLECTION_CLASSNAME(_base_class)::Unlink(s);

#define NS_IMPL_CYCLE_COLLECTION_UNLINK_HELPER(_field) \
  ImplCycleCollectionUnlink(tmp->_field);

#define NS_IMPL_CYCLE_COLLECTION_UNLINK(...) \
  MOZ_FOR_EACH(NS_IMPL_CYCLE_COLLECTION_UNLINK_HELPER, (), (__VA_ARGS__))

#define NS_IMPL_CYCLE_COLLECTION_UNLINK_END \
  (void)tmp;                                \
  }

#define NS_IMPL_CYCLE_COLLECTION_UNLINK_END_INHERITED(_base_class) \
  nsISupports* s = static_cast<nsISupports*>(p);                   \
  NS_CYCLE_COLLECTION_CLASSNAME(_base_class)::Unlink(s);           \
  (void)tmp;                                                       \
  }

#define NS_IMPL_CYCLE_COLLECTION_UNLINK_0(_class) \
  NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(_class)   \
  NS_IMPL_CYCLE_COLLECTION_UNLINK_END

///////////////////////////////////////////////////////////////////////////////
// Helpers for implementing nsCycleCollectionParticipant::Traverse
///////////////////////////////////////////////////////////////////////////////

#define NS_IMPL_CYCLE_COLLECTION_DESCRIBE(_class, _refcnt) \
  cb.DescribeRefCountedNode(_refcnt, #_class);

#define NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INTERNAL(_class) \
  NS_IMETHODIMP                                                  \
  NS_CYCLE_COLLECTION_CLASSNAME(_class)::TraverseNative(         \
      void* p, nsCycleCollectionTraversalCallback& cb) {         \
    _class* tmp = DowncastCCParticipant<_class>(p);

#define NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(_class)    \
  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INTERNAL(_class) \
    NS_IMPL_CYCLE_COLLECTION_DESCRIBE(_class, tmp->mRefCnt.get())

// Base class' CC participant should return NS_SUCCESS_INTERRUPTED_TRAVERSE
// from Traverse if it wants derived classes to not traverse anything from
// their CC participant.

#define NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(_class, _base_class) \
  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INTERNAL(_class)                     \
    nsISupports* s = static_cast<nsISupports*>(p);                             \
    if (NS_CYCLE_COLLECTION_CLASSNAME(_base_class)::TraverseNative(s, cb) ==   \
        NS_SUCCESS_INTERRUPTED_TRAVERSE) {                                     \
      return NS_SUCCESS_INTERRUPTED_TRAVERSE;                                  \
    }

#define NS_IMPL_CYCLE_COLLECTION_TRAVERSE_HELPER(_field) \
  ImplCycleCollectionTraverse(cb, tmp->_field, #_field, 0);

#define NS_IMPL_CYCLE_COLLECTION_TRAVERSE(...) \
  MOZ_FOR_EACH(NS_IMPL_CYCLE_COLLECTION_TRAVERSE_HELPER, (), (__VA_ARGS__))

#define NS_IMPL_CYCLE_COLLECTION_TRAVERSE_RAWPTR(_field) \
  CycleCollectionNoteChild(cb, tmp->_field, #_field);

#define NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END \
  (void)tmp;                                  \
  return NS_OK;                               \
  }

///////////////////////////////////////////////////////////////////////////////
// Helpers for implementing nsScriptObjectTracer::Trace
///////////////////////////////////////////////////////////////////////////////

#define NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(_class)               \
  void NS_CYCLE_COLLECTION_CLASSNAME(_class)::Trace(               \
      void* p, const TraceCallbacks& aCallbacks, void* aClosure) { \
    _class* tmp = DowncastCCParticipant<_class>(p);

#define NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN_INHERITED(_class, _base_class) \
  NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(_class)                              \
    nsISupports* s = static_cast<nsISupports*>(p);                          \
    NS_CYCLE_COLLECTION_CLASSNAME(_base_class)::Trace(s, aCallbacks, aClosure);

#define NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK(_field) \
  aCallbacks.Trace(&tmp->_field, #_field, aClosure);

// NB: The (void)tmp; hack in the TRACE_END macro exists to support
// implementations that don't need to do anything in their Trace method.
// Without this hack, some compilers warn about the unused tmp local.
#define NS_IMPL_CYCLE_COLLECTION_TRACE_END \
  (void)tmp;                               \
  }

///////////////////////////////////////////////////////////////////////////////
// Helpers for implementing a concrete nsCycleCollectionParticipant
///////////////////////////////////////////////////////////////////////////////

// If a class defines a participant, then QIing an instance of that class to
// nsXPCOMCycleCollectionParticipant should produce that participant.
#ifdef DEBUG
#  define NS_CHECK_FOR_RIGHT_PARTICIPANT_BASE \
    virtual void CheckForRightParticipant()
#  define NS_CHECK_FOR_RIGHT_PARTICIPANT_DERIVED \
    virtual void CheckForRightParticipant() override
#  define NS_CHECK_FOR_RIGHT_PARTICIPANT_BODY(_class)             \
    {                                                             \
      nsXPCOMCycleCollectionParticipant* p;                       \
      CallQueryInterface(this, &p);                               \
      MOZ_ASSERT(p == &NS_CYCLE_COLLECTION_INNERNAME,             \
                 #_class " should QI to its own CC participant"); \
    }
#  define NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL(_class) \
    NS_CHECK_FOR_RIGHT_PARTICIPANT_BASE               \
    NS_CHECK_FOR_RIGHT_PARTICIPANT_BODY(_class)
#  define NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL_INHERITED(_class) \
    NS_CHECK_FOR_RIGHT_PARTICIPANT_DERIVED                      \
    NS_CHECK_FOR_RIGHT_PARTICIPANT_BODY(_class)
#else
#  define NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL(_class)
#  define NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL_INHERITED(_class)
#endif

#define NS_DECL_CYCLE_COLLECTION_CLASS_NAME_METHOD(_class) \
  NS_IMETHOD_(const char*) ClassName() override { return #_class; };

#define NS_DECL_CYCLE_COLLECTION_CLASS_BODY(_class, _base)                     \
 public:                                                                       \
  NS_IMETHOD TraverseNative(void* p, nsCycleCollectionTraversalCallback& cb)   \
      override;                                                                \
  NS_DECL_CYCLE_COLLECTION_CLASS_NAME_METHOD(_class)                           \
  NS_IMETHOD_(void) DeleteCycleCollectable(void* p) override {                 \
    DowncastCCParticipant<_class>(p)->DeleteCycleCollectable();                \
  }                                                                            \
  static _class* Downcast(nsISupports* s) {                                    \
    return static_cast<_class*>(static_cast<_base*>(s));                       \
  }                                                                            \
  static nsISupports* Upcast(_class* p) {                                      \
    return NS_ISUPPORTS_CAST(_base*, p);                                       \
  }                                                                            \
  template <typename T>                                                        \
  friend nsISupports* ToSupports(T* p, NS_CYCLE_COLLECTION_INNERCLASS* dummy); \
  NS_IMETHOD_(void) Unlink(void* p) override;

#define NS_PARTICIPANT_AS(type, participant) \
  const_cast<type*>(reinterpret_cast<const type*>(participant))

#define NS_IMPL_GET_XPCOM_CYCLE_COLLECTION_PARTICIPANT(_class)           \
  static constexpr nsXPCOMCycleCollectionParticipant* GetParticipant() { \
    return &_class::NS_CYCLE_COLLECTION_INNERNAME;                       \
  }

/**
 * We use this macro to force that classes that inherit from a ccable class and
 * declare their own participant declare themselves as inherited cc classes.
 * To avoid possibly unnecessary vtables we only do this checking in debug
 * builds.
 */
#ifdef DEBUG
#  define NOT_INHERITED_CANT_OVERRIDE \
    virtual void BaseCycleCollectable() final {}
#else
#  define NOT_INHERITED_CANT_OVERRIDE
#endif

#define NS_DECL_CYCLE_COLLECTION_CLASS_AMBIGUOUS(_class, _base)         \
  class NS_CYCLE_COLLECTION_INNERCLASS                                  \
      : public nsXPCOMCycleCollectionParticipant {                      \
   public:                                                              \
    constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(Flags aFlags = 0) \
        : nsXPCOMCycleCollectionParticipant(aFlags) {}                  \
                                                                        \
   private:                                                             \
    NS_DECL_CYCLE_COLLECTION_CLASS_BODY(_class, _base)                  \
    NS_IMPL_GET_XPCOM_CYCLE_COLLECTION_PARTICIPANT(_class)              \
  };                                                                    \
  NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL(_class)                           \
  static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;  \
  NOT_INHERITED_CANT_OVERRIDE

#define NS_DECL_CYCLE_COLLECTION_CLASS(_class) \
  NS_DECL_CYCLE_COLLECTION_CLASS_AMBIGUOUS(_class, _class)

// Cycle collector helper for ambiguous classes that can sometimes be skipped.
#define NS_DECL_CYCLE_COLLECTION_SKIPPABLE_CLASS_AMBIGUOUS(_class, _base)   \
  class NS_CYCLE_COLLECTION_INNERCLASS                                      \
      : public nsXPCOMCycleCollectionParticipant {                          \
   public:                                                                  \
    constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(                      \
        Flags aFlags = FlagMightSkip) /* We always want skippability. */    \
        : nsXPCOMCycleCollectionParticipant(aFlags | FlagMightSkip) {}      \
                                                                            \
   private:                                                                 \
    NS_DECL_CYCLE_COLLECTION_CLASS_BODY(_class, _base)                      \
    NS_IMETHOD_(bool) CanSkipReal(void* p, bool aRemovingAllowed) override; \
    NS_IMETHOD_(bool) CanSkipInCCReal(void* p) override;                    \
    NS_IMETHOD_(bool) CanSkipThisReal(void* p) override;                    \
    NS_IMPL_GET_XPCOM_CYCLE_COLLECTION_PARTICIPANT(_class)                  \
  };                                                                        \
  NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL(_class)                               \
  static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;      \
  NOT_INHERITED_CANT_OVERRIDE

#define NS_DECL_CYCLE_COLLECTION_SKIPPABLE_CLASS(_class) \
  NS_DECL_CYCLE_COLLECTION_SKIPPABLE_CLASS_AMBIGUOUS(_class, _class)

#define NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_AMBIGUOUS(_class, _base) \
  class NS_CYCLE_COLLECTION_INNERCLASS                                        \
      : public nsXPCOMCycleCollectionParticipant {                            \
   public:                                                                    \
    constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(Flags aFlags = 0)       \
        : nsXPCOMCycleCollectionParticipant(aFlags) {}                        \
                                                                              \
   private:                                                                   \
    NS_DECL_CYCLE_COLLECTION_CLASS_BODY(_class, _base)                        \
    NS_IMETHOD_(void)                                                         \
    Trace(void* p, const TraceCallbacks& cb, void* closure) override;         \
    NS_IMPL_GET_XPCOM_CYCLE_COLLECTION_PARTICIPANT(_class)                    \
  };                                                                          \
  NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL(_class)                                 \
  static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;        \
  NOT_INHERITED_CANT_OVERRIDE

#define NS_DECL_CYCLE_COLLECTION_SKIPPABLE_SCRIPT_HOLDER_CLASS_AMBIGUOUS(   \
    _class, _base)                                                          \
  class NS_CYCLE_COLLECTION_INNERCLASS                                      \
      : public nsXPCOMCycleCollectionParticipant {                          \
   public:                                                                  \
    constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(                      \
        Flags aFlags = FlagMightSkip) /* We always want skippability. */    \
        : nsXPCOMCycleCollectionParticipant(aFlags | FlagMightSkip) {}      \
                                                                            \
   private:                                                                 \
    NS_DECL_CYCLE_COLLECTION_CLASS_BODY(_class, _base)                      \
    NS_IMETHOD_(void)                                                       \
    Trace(void* p, const TraceCallbacks& cb, void* closure) override;       \
    NS_IMETHOD_(bool) CanSkipReal(void* p, bool aRemovingAllowed) override; \
    NS_IMETHOD_(bool) CanSkipInCCReal(void* p) override;                    \
    NS_IMETHOD_(bool) CanSkipThisReal(void* p) override;                    \
    NS_IMPL_GET_XPCOM_CYCLE_COLLECTION_PARTICIPANT(_class)                  \
  };                                                                        \
  NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL(_class)                               \
  static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;      \
  NOT_INHERITED_CANT_OVERRIDE

#define NS_DECL_CYCLE_COLLECTION_SKIPPABLE_SCRIPT_HOLDER_CLASS(_class)     \
  NS_DECL_CYCLE_COLLECTION_SKIPPABLE_SCRIPT_HOLDER_CLASS_AMBIGUOUS(_class, \
                                                                   _class)

#define NS_DECL_CYCLE_COLLECTION_SKIPPABLE_SCRIPT_HOLDER_CLASS_INHERITED(      \
    _class, _base_class)                                                       \
  class NS_CYCLE_COLLECTION_INNERCLASS                                         \
      : public NS_CYCLE_COLLECTION_CLASSNAME(_base_class) {                    \
   public:                                                                     \
    constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(                         \
        Flags aFlags = FlagMightSkip | /* We always want skippability. */      \
                       FlagMultiZoneJSHolder)                                  \
        : NS_CYCLE_COLLECTION_CLASSNAME(_base_class)(aFlags | FlagMightSkip) { \
    }                                                                          \
                                                                               \
   private:                                                                    \
    NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED_BODY(_class, _base_class)         \
    NS_IMETHOD_(void)                                                          \
    Trace(void* p, const TraceCallbacks& cb, void* closure) override;          \
    NS_IMETHOD_(bool) CanSkipReal(void* p, bool aRemovingAllowed) override;    \
    NS_IMETHOD_(bool) CanSkipInCCReal(void* p) override;                       \
    NS_IMETHOD_(bool) CanSkipThisReal(void* p) override;                       \
    NS_IMPL_GET_XPCOM_CYCLE_COLLECTION_PARTICIPANT(_class)                     \
  };                                                                           \
  NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL_INHERITED(_class)                        \
  static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;

#define NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(_class) \
  NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_AMBIGUOUS(_class, _class)

#define NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED_BODY(_class, _base_class)   \
 public:                                                                     \
  NS_IMETHOD TraverseNative(void* p, nsCycleCollectionTraversalCallback& cb) \
      override;                                                              \
  NS_DECL_CYCLE_COLLECTION_CLASS_NAME_METHOD(_class)                         \
  static _class* Downcast(nsISupports* s) {                                  \
    return static_cast<_class*>(static_cast<_base_class*>(                   \
        NS_CYCLE_COLLECTION_CLASSNAME(_base_class)::Downcast(s)));           \
  }                                                                          \
  NS_IMETHOD_(void) Unlink(void* p) override;

#define NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED(_class, _base_class)   \
  class NS_CYCLE_COLLECTION_INNERCLASS                                  \
      : public NS_CYCLE_COLLECTION_CLASSNAME(_base_class) {             \
   public:                                                              \
    constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(Flags aFlags = 0) \
        : NS_CYCLE_COLLECTION_CLASSNAME(_base_class)(aFlags) {}         \
                                                                        \
   private:                                                             \
    NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED_BODY(_class, _base_class)  \
    NS_IMPL_GET_XPCOM_CYCLE_COLLECTION_PARTICIPANT(_class)              \
  };                                                                    \
  NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL_INHERITED(_class)                 \
  static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;

#define NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS_INHERITED(_class,         \
                                                               _base_class)    \
  class NS_CYCLE_COLLECTION_INNERCLASS                                         \
      : public NS_CYCLE_COLLECTION_CLASSNAME(_base_class) {                    \
   public:                                                                     \
    constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(Flags aFlags = 0)        \
        : NS_CYCLE_COLLECTION_CLASSNAME(_base_class)(aFlags |                  \
                                                     FlagMultiZoneJSHolder) {} \
                                                                               \
   private:                                                                    \
    NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED_BODY(_class, _base_class)         \
    NS_IMETHOD_(void)                                                          \
    Trace(void* p, const TraceCallbacks& cb, void* closure) override;          \
    NS_IMPL_GET_XPCOM_CYCLE_COLLECTION_PARTICIPANT(_class)                     \
  };                                                                           \
  NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL_INHERITED(_class)                        \
  static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;

// Cycle collector participant declarations.

#define NS_DECL_CYCLE_COLLECTION_NATIVE_CLASS_BODY(_class)                   \
 public:                                                                     \
  NS_IMETHOD_(void) Root(void* p) override {                                 \
    static_cast<_class*>(p)->AddRef();                                       \
  }                                                                          \
  NS_IMETHOD_(void) Unlink(void* n) override;                                \
  NS_IMETHOD_(void) Unroot(void* p) override {                               \
    static_cast<_class*>(p)->Release();                                      \
  }                                                                          \
  NS_IMETHOD TraverseNative(void* n, nsCycleCollectionTraversalCallback& cb) \
      override;                                                              \
  NS_DECL_CYCLE_COLLECTION_CLASS_NAME_METHOD(_class)                         \
  NS_IMETHOD_(void) DeleteCycleCollectable(void* n) override {               \
    DowncastCCParticipant<_class>(n)->DeleteCycleCollectable();              \
  }                                                                          \
  static _class* Downcast(void* s) {                                         \
    return DowncastCCParticipant<_class>(s);                                 \
  }                                                                          \
  static void* Upcast(_class* p) { return static_cast<void*>(p); }

#define NS_DECL_CYCLE_COLLECTION_NATIVE_CLASS(_class)                          \
  void DeleteCycleCollectable(void) { delete this; }                           \
  class NS_CYCLE_COLLECTION_INNERCLASS : public nsCycleCollectionParticipant { \
   public:                                                                     \
    constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(Flags aFlags = 0)        \
        : nsCycleCollectionParticipant(aFlags) {}                              \
                                                                               \
   private:                                                                    \
    NS_DECL_CYCLE_COLLECTION_NATIVE_CLASS_BODY(_class)                         \
    static constexpr nsCycleCollectionParticipant* GetParticipant() {          \
      return &_class::NS_CYCLE_COLLECTION_INNERNAME;                           \
    }                                                                          \
  };                                                                           \
  static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;

#define NS_DECL_CYCLE_COLLECTION_SKIPPABLE_NATIVE_CLASS(_class)                \
  void DeleteCycleCollectable(void) { delete this; }                           \
  class NS_CYCLE_COLLECTION_INNERCLASS : public nsCycleCollectionParticipant { \
   public:                                                                     \
    constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(                         \
        Flags aFlags = FlagMightSkip) /* We always want skippability. */       \
        : nsCycleCollectionParticipant(aFlags | FlagMightSkip) {}              \
                                                                               \
   private:                                                                    \
    NS_DECL_CYCLE_COLLECTION_NATIVE_CLASS_BODY(_class)                         \
    NS_IMETHOD_(bool) CanSkipReal(void* p, bool aRemovingAllowed) override;    \
    NS_IMETHOD_(bool) CanSkipInCCReal(void* p) override;                       \
    NS_IMETHOD_(bool) CanSkipThisReal(void* p) override;                       \
    static nsCycleCollectionParticipant* GetParticipant() {                    \
      return &_class::NS_CYCLE_COLLECTION_INNERNAME;                           \
    }                                                                          \
  };                                                                           \
  static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;

#define NS_DECL_CYCLE_COLLECTION_SKIPPABLE_NATIVE_CLASS_WITH_CUSTOM_DELETE(    \
    _class)                                                                    \
  class NS_CYCLE_COLLECTION_INNERCLASS : public nsCycleCollectionParticipant { \
   public:                                                                     \
    constexpr NS_CYCLE_COLLECTION_INNERCLASS()                                 \
        : nsCycleCollectionParticipant(true) {}                                \
                                                                               \
   private:                                                                    \
    NS_DECL_CYCLE_COLLECTION_NATIVE_CLASS_BODY(_class)                         \
    NS_IMETHOD_(bool) CanSkipReal(void* p, bool aRemovingAllowed) override;    \
    NS_IMETHOD_(bool) CanSkipInCCReal(void* p) override;                       \
    NS_IMETHOD_(bool) CanSkipThisReal(void* p) override;                       \
    static nsCycleCollectionParticipant* GetParticipant() {                    \
      return &_class::NS_CYCLE_COLLECTION_INNERNAME;                           \
    }                                                                          \
  };                                                                           \
  static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;

#define NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_NATIVE_CLASS(_class)     \
  void DeleteCycleCollectable(void) { delete this; }                    \
  class NS_CYCLE_COLLECTION_INNERCLASS : public nsScriptObjectTracer {  \
   public:                                                              \
    constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(Flags aFlags = 0) \
        : nsScriptObjectTracer(aFlags) {}                               \
                                                                        \
   private:                                                             \
    NS_DECL_CYCLE_COLLECTION_NATIVE_CLASS_BODY(_class)                  \
    NS_IMETHOD_(void)                                                   \
    Trace(void* p, const TraceCallbacks& cb, void* closure) override;   \
    static constexpr nsScriptObjectTracer* GetParticipant() {           \
      return &_class::NS_CYCLE_COLLECTION_INNERNAME;                    \
    }                                                                   \
  };                                                                    \
  static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;

#define NS_IMPL_CYCLE_COLLECTION_CLASS(_class) \
  _class::NS_CYCLE_COLLECTION_INNERCLASS _class::NS_CYCLE_COLLECTION_INNERNAME;

// By default JS holders are treated as if they may store pointers to multiple
// zones, but one may optimize GC handling by using single zone holders.
#define NS_IMPL_CYCLE_COLLECTION_SINGLE_ZONE_SCRIPT_HOLDER_CLASS(_class) \
  _class::NS_CYCLE_COLLECTION_INNERCLASS                                 \
      _class::NS_CYCLE_COLLECTION_INNERNAME(                             \
          nsCycleCollectionParticipant::FlagMaybeSingleZoneJSHolder);

// NB: This is not something you usually want to use.  It is here to allow
// adding things to the CC graph to help debugging via CC logs, but it does not
// traverse or unlink anything, so it is useless for anything else.
#define NS_IMPL_CYCLE_COLLECTION_0(_class)        \
  NS_IMPL_CYCLE_COLLECTION_CLASS(_class)          \
  NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(_class)   \
  NS_IMPL_CYCLE_COLLECTION_UNLINK_END             \
  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(_class) \
  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END

#define NS_IMPL_CYCLE_COLLECTION(_class, ...)      \
  NS_IMPL_CYCLE_COLLECTION_CLASS(_class)           \
  NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(_class)    \
    NS_IMPL_CYCLE_COLLECTION_UNLINK(__VA_ARGS__)   \
  NS_IMPL_CYCLE_COLLECTION_UNLINK_END              \
  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(_class)  \
    NS_IMPL_CYCLE_COLLECTION_TRAVERSE(__VA_ARGS__) \
  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END

// If you are looking for NS_IMPL_CYCLE_COLLECTION_INHERITED_0(_class, _base)
// you should instead not declare any cycle collected stuff in _class, so it
// will just inherit the CC declarations from _base.

#define NS_IMPL_CYCLE_COLLECTION_INHERITED(_class, _base, ...)     \
  NS_IMPL_CYCLE_COLLECTION_CLASS(_class)                           \
  NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(_class, _base)   \
    NS_IMPL_CYCLE_COLLECTION_UNLINK(__VA_ARGS__)                   \
  NS_IMPL_CYCLE_COLLECTION_UNLINK_END                              \
  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(_class, _base) \
    NS_IMPL_CYCLE_COLLECTION_TRAVERSE(__VA_ARGS__)                 \
  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END

#define NS_CYCLE_COLLECTION_NOTE_EDGE_NAME CycleCollectionNoteEdgeName

/**
 * Convenience macros for defining nISupports methods in a cycle collected
 * class.
 */

#define NS_IMPL_QUERY_INTERFACE_CYCLE_COLLECTION_INHERITED(aClass, aSuper, \
                                                           ...)            \
  NS_INTERFACE_TABLE_HEAD_CYCLE_COLLECTION_INHERITED(aClass)               \
    NS_INTERFACE_TABLE_INHERITED(aClass, __VA_ARGS__)                      \
  NS_INTERFACE_TABLE_TAIL_INHERITING(aSuper)

#define NS_IMPL_ISUPPORTS_CYCLE_COLLECTION_INHERITED(aClass, aSuper, ...) \
  NS_IMPL_QUERY_INTERFACE_CYCLE_COLLECTION_INHERITED(aClass, aSuper,      \
                                                     __VA_ARGS__)         \
  NS_IMPL_ADDREF_INHERITED(aClass, aSuper)                                \
  NS_IMPL_RELEASE_INHERITED(aClass, aSuper)

#define NS_IMPL_ISUPPORTS_CYCLE_COLLECTION_INHERITED_0(aClass, aSuper) \
  NS_INTERFACE_MAP_BEGIN_CYCLE_COLLECTION(aClass)                      \
  NS_INTERFACE_MAP_END_INHERITING(aSuper)                              \
  NS_IMPL_ADDREF_INHERITED(aClass, aSuper)                             \
  NS_IMPL_RELEASE_INHERITED(aClass, aSuper)

/**
 * Equivalency of the high three words where two IIDs have the same
 * top three words but not the same low word.
 */
inline bool TopThreeWordsEquals(const nsID& aID, const nsID& aOther1,
                                const nsID& aOther2) {
  MOZ_ASSERT((((uint32_t*)&aOther1.m0)[0] == ((uint32_t*)&aOther2.m0)[0]) &&
             (((uint32_t*)&aOther1.m0)[1] == ((uint32_t*)&aOther2.m0)[1]) &&
             (((uint32_t*)&aOther1.m0)[2] == ((uint32_t*)&aOther2.m0)[2]) &&
             (((uint32_t*)&aOther1.m0)[3] != ((uint32_t*)&aOther2.m0)[3]));

  return ((((uint32_t*)&aID.m0)[0] == ((uint32_t*)&aOther1.m0)[0]) &&
          (((uint32_t*)&aID.m0)[1] == ((uint32_t*)&aOther1.m0)[1]) &&
          (((uint32_t*)&aID.m0)[2] == ((uint32_t*)&aOther1.m0)[2]));
}

/**
 * Equivalency of the fourth word where the two IIDs have the same
 * top three words but not the same low word.
 */
inline bool LowWordEquals(const nsID& aID, const nsID& aOther) {
  return (((uint32_t*)&aID.m0)[3] == ((uint32_t*)&aOther.m0)[3]);
}

// Template magic to modify JS::Heap without including relevant headers, to
// prevent excessive header dependency.
template <typename T>
inline void ImplCycleCollectionUnlink(JS::Heap<T>& aField) {
  aField.setNull();
}
template <typename T>
inline void ImplCycleCollectionUnlink(JS::Heap<T*>& aField) {
  aField = nullptr;
}

#define NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBERS(...)                \
  MOZ_ASSERT(!IsSingleZoneJSHolder());                                \
  MOZ_FOR_EACH(NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBER_CALLBACK, (), \
               (__VA_ARGS__))

#define NS_IMPL_CYCLE_COLLECTION_WITH_JS_MEMBERS(class_, native_members_,   \
                                                 js_members_)               \
  NS_IMPL_CYCLE_COLLECTION_CLASS(class_)                                    \
  NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(class_)                             \
    using ::ImplCycleCollectionUnlink;                                      \
    NS_IMPL_CYCLE_COLLECTION_UNLINK(                                        \
        MOZ_FOR_EACH_EXPAND_HELPER native_members_)                         \
    NS_IMPL_CYCLE_COLLECTION_UNLINK(MOZ_FOR_EACH_EXPAND_HELPER js_members_) \
  NS_IMPL_CYCLE_COLLECTION_UNLINK_END                                       \
  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(class_)                           \
    NS_IMPL_CYCLE_COLLECTION_TRAVERSE(                                      \
        MOZ_FOR_EACH_EXPAND_HELPER native_members_)                         \
  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END                                     \
  NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(class_)                              \
    NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBERS(                              \
        MOZ_FOR_EACH_EXPAND_HELPER js_members_)                             \
  NS_IMPL_CYCLE_COLLECTION_TRACE_END

#define NS_IMPL_CYCLE_COLLECTION_INHERITED_WITH_JS_MEMBERS(                 \
    class_, _base, native_members_, js_members_)                            \
  NS_IMPL_CYCLE_COLLECTION_CLASS(class_)                                    \
  NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(class_, _base)            \
    using ::ImplCycleCollectionUnlink;                                      \
    NS_IMPL_CYCLE_COLLECTION_UNLINK(                                        \
        MOZ_FOR_EACH_EXPAND_HELPER native_members_)                         \
    NS_IMPL_CYCLE_COLLECTION_UNLINK(MOZ_FOR_EACH_EXPAND_HELPER js_members_) \
  NS_IMPL_CYCLE_COLLECTION_UNLINK_END                                       \
  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(class_, _base)          \
    NS_IMPL_CYCLE_COLLECTION_TRAVERSE(                                      \
        MOZ_FOR_EACH_EXPAND_HELPER native_members_)                         \
  NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END                                     \
  NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN_INHERITED(class_, _base)             \
    NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBERS(                              \
        MOZ_FOR_EACH_EXPAND_HELPER js_members_)                             \
  NS_IMPL_CYCLE_COLLECTION_TRACE_END

template <typename... Elements>
inline void ImplCycleCollectionUnlink(std::tuple<Elements...>& aField) {
  std::apply([](auto&&... aArgs) { (ImplCycleCollectionUnlink(aArgs), ...); },
             aField);
}
template <typename... Elements>
inline void ImplCycleCollectionTraverse(
    nsCycleCollectionTraversalCallback& aCallback,
    std::tuple<Elements...>& aField, const char* aName, uint32_t aFlags) {
  aFlags |= CycleCollectionEdgeNameArrayFlag;
  std::apply(
      [&](auto&&... aArgs) {
        (ImplCycleCollectionTraverse(aCallback, aArgs, aName, aFlags), ...);
      },
      aField);
}

#endif  // nsCycleCollectionParticipant_h__