dom/base/nsWrapperCache.h

   1 /* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
   2 /* vim: set ts=8 sts=2 et sw=2 tw=80: */
   3 /* This Source Code Form is subject to the terms of the Mozilla Public
   4  * License, v. 2.0. If a copy of the MPL was not distributed with this
   5  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   6
   7 #ifndef nsWrapperCache_h___
   8 #define nsWrapperCache_h___
   9
  10 #include "nsCycleCollectionParticipant.h"
  11 #include "mozilla/Assertions.h"
  12 #include "mozilla/ServoUtils.h"
  13 #include "mozilla/RustCell.h"
  14 #include "js/HeapAPI.h"
  15 #include "js/TracingAPI.h"
  16 #include "js/TypeDecls.h"
  17 #include "nsISupports.h"
  18 #include "nsISupportsUtils.h"
  19 #include <type_traits>
  20
  21 namespace mozilla::dom {
  22 class ContentProcessMessageManager;
  23 class InProcessBrowserChildMessageManager;
  24 class BrowserChildMessageManager;
  25 }  // namespace mozilla::dom
  26 class SandboxPrivate;
  27 class nsWindowRoot;
  28
  29 #define NS_WRAPPERCACHE_IID                          \
  30   {                                                  \
  31     0x6f3179a1, 0x36f7, 0x4a5c, {                    \
  32       0x8c, 0xf1, 0xad, 0xc8, 0x7c, 0xde, 0x3e, 0x87 \
  33     }                                                \
  34   }
  35
  36 // There are two sets of flags used by DOM nodes. One comes from reusing the
  37 // remaining bits of the inherited nsWrapperCache flags (mFlags), and another is
  38 // exclusive to nsINode (mBoolFlags).
  39 //
  40 // Both sets of flags are 32 bits. On 64-bit platforms, this can cause two
  41 // wasted 32-bit fields due to alignment requirements. Some compilers are
  42 // smart enough to coalesce the fields if we make mBoolFlags the first member
  43 // of nsINode, but others (such as MSVC, but that's not officially supported
  44 // by us anymore) are not. Also note that this kind of coalascing tends to
  45 // interact poorly with rust's bindgen, see:
  46 // https://github.com/rust-lang/rust-bindgen/issues/380
  47 //
  48 // So we just store mBoolFlags directly on nsWrapperCache on 64-bit platforms.
  49 // This may waste space for some other nsWrapperCache-derived objects that have
  50 // a 32-bit field as their first member, but those objects are unlikely to be as
  51 // numerous or performance-critical as DOM nodes.
  52 #ifdef HAVE_64BIT_BUILD
  53 static_assert(sizeof(void*) == 8, "These architectures should be 64-bit");
  54 #  define BOOL_FLAGS_ON_WRAPPER_CACHE
  55 #else
  56 static_assert(sizeof(void*) == 4, "Only support 32-bit and 64-bit");
  57 #endif
  58
  59 /**
  60  * Class to store the wrapper for an object. This can only be used with objects
  61  * that only have one non-security wrapper at a time (for an XPCWrappedNative
  62  * this is usually ensured by setting an explicit parent in the PreCreate hook
  63  * for the class).
  64  *
  65  * An instance of nsWrapperCache can be gotten from an object that implements
  66  * a wrapper cache by calling QueryInterface on it. Note that this breaks XPCOM
  67  * rules a bit (this object doesn't derive from nsISupports).
  68  *
  69  * The cache can store objects other than wrappers. We allow wrappers to use a
  70  * separate JSObject to store their state (mostly expandos). If the wrapper is
  71  * collected and we want to preserve this state we actually store the state
  72  * object in the cache.
  73  *
  74  * The cache can store 3 types of objects: a DOM binding object (regular JS
  75  * object or proxy), an nsOuterWindowProxy or an XPCWrappedNative wrapper.
  76  *
  77  * The finalizer for the wrapper clears the cache.
  78  *
  79  * A compacting GC can move the wrapper object. Pointers to moved objects are
  80  * usually found and updated by tracing the heap, however non-preserved wrappers
  81  * are weak references and are not traced, so another approach is
  82  * necessary. Instead a class hook (objectMovedOp) is provided that is called
  83  * when an object is moved and is responsible for ensuring pointers are
  84  * updated. It does this by calling UpdateWrapper() on the wrapper
  85  * cache. SetWrapper() asserts that the hook is implemented for any wrapper set.
  86  *
  87  * A number of the methods are implemented in nsWrapperCacheInlines.h because we
  88  * have to include some JS headers that don't play nicely with the rest of the
  89  * codebase. Include nsWrapperCacheInlines.h if you need to call those methods.
  90  */
  91
  92 class JS_HAZ_ROOTED nsWrapperCache {
  93  public:
  94   NS_DECLARE_STATIC_IID_ACCESSOR(NS_WRAPPERCACHE_IID)
  95
  96   nsWrapperCache() = default;
  97   ~nsWrapperCache() {
  98     // Preserved wrappers should never end up getting cleared, but this can
  99     // happen during shutdown when a leaked wrapper object is finalized, causing
 100     // its wrapper to be cleared.
 101     MOZ_ASSERT(!PreservingWrapper() || js::RuntimeIsBeingDestroyed(),
 102                "Destroying cache with a preserved wrapper!");
 103   }
 104
 105   /**
 106    * Get the cached wrapper.
 107    *
 108    * This getter clears the gray bit before handing out the JSObject which means
 109    * that the object is guaranteed to be kept alive past the next CC.
 110    */
 111   JSObject* GetWrapper() const;
 112
 113   /**
 114    * Get the cached wrapper.
 115    *
 116    * This getter does not change the color of the JSObject meaning that the
 117    * object returned is not guaranteed to be kept alive past the next CC.
 118    *
 119    * This should only be called if you are certain that the return value won't
 120    * be passed into a JSAPI function and that it won't be stored without being
 121    * rooted (or otherwise signaling the stored value to the CC).
 122    */
 123   JSObject* GetWrapperPreserveColor() const;
 124
 125   /**
 126    * Get the cached wrapper.
 127    *
 128    * This getter does not check whether the wrapper is dead and in the process
 129    * of being finalized.
 130    *
 131    * This should only be called if you really need to see the raw contents of
 132    * this cache, for example as part of finalization. Don't store the result
 133    * anywhere or pass it into JSAPI functions that may cause the value to
 134    * escape.
 135    */
 136   JSObject* GetWrapperMaybeDead() const { return mWrapper; }
 137
 138 #ifdef DEBUG
 139  private:
 140   static bool HasJSObjectMovedOp(JSObject* aWrapper);
 141
 142   static void AssertUpdatedWrapperZone(const JSObject* aNewObject,
 143                                        const JSObject* aOldObject);
 144
 145  public:
 146 #endif
 147
 148   void SetWrapper(JSObject* aWrapper) {
 149     MOZ_ASSERT(!PreservingWrapper(), "Clearing a preserved wrapper!");
 150     MOZ_ASSERT(aWrapper, "Use ClearWrapper!");
 151     MOZ_ASSERT(HasJSObjectMovedOp(aWrapper),
 152                "Object has not provided the hook to update the wrapper if it "
 153                "is moved");
 154
 155     SetWrapperJSObject(aWrapper);
 156   }
 157
 158   /**
 159    * Clear the cache.
 160    */
 161   void ClearWrapper() {
 162     // Preserved wrappers should never end up getting cleared, but this can
 163     // happen during shutdown when a leaked wrapper object is finalized, causing
 164     // its wrapper to be cleared.
 165     MOZ_ASSERT(!PreservingWrapper() || js::RuntimeIsBeingDestroyed(),
 166                "Clearing a preserved wrapper!");
 167     SetWrapperJSObject(nullptr);
 168   }
 169
 170   /**
 171    * Clear the cache if it still contains a specific wrapper object. This should
 172    * be called from the finalizer for the wrapper.
 173    */
 174   void ClearWrapper(JSObject* obj) {
 175     if (obj == mWrapper) {
 176       ClearWrapper();
 177     }
 178   }
 179
 180   /**
 181    * Update the wrapper when the object moves between globals.
 182    */
 183   template <typename T>
 184   void UpdateWrapperForNewGlobal(T* aScriptObjectHolder, JSObject* aNewWrapper);
 185
 186   /**
 187    * Update the wrapper if the object it contains is moved.
 188    *
 189    * This method must be called from the objectMovedOp class extension hook for
 190    * any wrapper cached object.
 191    */
 192   void UpdateWrapper(JSObject* aNewObject, const JSObject* aOldObject) {
 193 #ifdef DEBUG
 194     AssertUpdatedWrapperZone(aNewObject, aOldObject);
 195 #endif
 196     if (mWrapper) {
 197       MOZ_ASSERT(mWrapper == aOldObject);
 198       mWrapper = aNewObject;
 199     }
 200   }
 201
 202   bool PreservingWrapper() const {
 203     return HasWrapperFlag(WRAPPER_BIT_PRESERVED);
 204   }
 205
 206   /**
 207    * Wrap the object corresponding to this wrapper cache. If non-null is
 208    * returned, the object has already been stored in the wrapper cache.
 209    */
 210   virtual JSObject* WrapObject(JSContext* cx,
 211                                JS::Handle<JSObject*> aGivenProto) = 0;
 212
 213   /**
 214    * Returns true if the object has a wrapper that is known live from the point
 215    * of view of cycle collection.
 216    */
 217   bool HasKnownLiveWrapper() const;
 218
 219   /**
 220    * Returns true if the object has a known-live wrapper (from the CC point of
 221    * view) and all the GC things it is keeping alive are already known-live from
 222    * CC's point of view.
 223    */
 224   bool HasKnownLiveWrapperAndDoesNotNeedTracing(nsISupports* aThis);
 225
 226   bool HasNothingToTrace(nsISupports* aThis);
 227
 228   /**
 229    * Mark our wrapper, if any, as live as far as the CC is concerned.
 230    */
 231   void MarkWrapperLive();
 232
 233   // Only meant to be called by code that preserves a wrapper.
 234   void SetPreservingWrapper(bool aPreserve) {
 235     if (aPreserve) {
 236       SetWrapperFlags(WRAPPER_BIT_PRESERVED);
 237     } else {
 238       UnsetWrapperFlags(WRAPPER_BIT_PRESERVED);
 239     }
 240   }
 241
 242   void TraceWrapper(const TraceCallbacks& aCallbacks, void* aClosure) {
 243     if (PreservingWrapper() && mWrapper) {
 244       aCallbacks.Trace(this, "Preserved wrapper", aClosure);
 245     }
 246   }
 247
 248   /*
 249    * The following methods for getting and manipulating flags allow the unused
 250    * bits of mFlags to be used by derived classes.
 251    */
 252
 253   using FlagsType = uint32_t;
 254
 255   FlagsType GetFlags() const {
 256     MOZ_ASSERT(NS_IsMainThread());
 257     MOZ_ASSERT(!mozilla::IsInServoTraversal());
 258     return mFlags.Get() & ~kWrapperFlagsMask;
 259   }
 260
 261   // This can be called from stylo threads too, so it needs to be atomic, as
 262   // this value may be mutated from multiple threads during servo traversal from
 263   // rust.
 264   bool HasFlag(FlagsType aFlag) const {
 265     MOZ_ASSERT((aFlag & kWrapperFlagsMask) == 0, "Bad flag mask");
 266     return __atomic_load_n(mFlags.AsPtr(), __ATOMIC_RELAXED) & aFlag;
 267   }
 268
 269   // Identical to HasFlag, but more explicit about its handling of multiple
 270   // flags. This can be called from stylo threads too.
 271   bool HasAnyOfFlags(FlagsType aFlags) const { return HasFlag(aFlags); }
 272
 273   // This can also be called from stylo, in the sequential part of the
 274   // traversal, though it's probably not worth differentiating them for the
 275   // purposes of assertions.
 276   bool HasAllFlags(FlagsType aFlags) const {
 277     MOZ_ASSERT((aFlags & kWrapperFlagsMask) == 0, "Bad flag mask");
 278     return (__atomic_load_n(mFlags.AsPtr(), __ATOMIC_RELAXED) & aFlags) ==
 279            aFlags;
 280   }
 281
 282   void SetFlags(FlagsType aFlagsToSet) {
 283     MOZ_ASSERT(NS_IsMainThread());
 284     MOZ_ASSERT((aFlagsToSet & kWrapperFlagsMask) == 0, "Bad flag mask");
 285     mFlags.Set(mFlags.Get() | aFlagsToSet);
 286   }
 287
 288   void UnsetFlags(FlagsType aFlagsToUnset) {
 289     MOZ_ASSERT(NS_IsMainThread());
 290     MOZ_ASSERT((aFlagsToUnset & kWrapperFlagsMask) == 0, "Bad flag mask");
 291     mFlags.Set(mFlags.Get() & ~aFlagsToUnset);
 292   }
 293
 294   void PreserveWrapper(nsISupports* aScriptObjectHolder) {
 295     if (PreservingWrapper()) {
 296       return;
 297     }
 298
 299     nsISupports* ccISupports;
 300     aScriptObjectHolder->QueryInterface(NS_GET_IID(nsCycleCollectionISupports),
 301                                         reinterpret_cast<void**>(&ccISupports));
 302     MOZ_ASSERT(ccISupports);
 303
 304     nsXPCOMCycleCollectionParticipant* participant;
 305     CallQueryInterface(ccISupports, &participant);
 306     PreserveWrapper(ccISupports, participant);
 307   }
 308
 309   void PreserveWrapper(void* aScriptObjectHolder,
 310                        nsScriptObjectTracer* aTracer) {
 311     if (PreservingWrapper()) {
 312       return;
 313     }
 314
 315     JSObject* wrapper = GetWrapper();  // Read barrier for incremental GC.
 316     HoldJSObjects(aScriptObjectHolder, aTracer, JS::GetObjectZone(wrapper));
 317     SetPreservingWrapper(true);
 318 #ifdef DEBUG
 319     // Make sure the cycle collector will be able to traverse to the wrapper.
 320     CheckCCWrapperTraversal(aScriptObjectHolder, aTracer);
 321 #endif
 322   }
 323
 324   void ReleaseWrapper(void* aScriptObjectHolder);
 325
 326   void TraceWrapper(JSTracer* aTrc, const char* name) {
 327     if (mWrapper) {
 328       js::UnsafeTraceManuallyBarrieredEdge(aTrc, &mWrapper, name);
 329     }
 330   }
 331
 332  protected:
 333   void PoisonWrapper() {
 334     if (mWrapper) {
 335       // Set the pointer to a value that will cause a crash if it is
 336       // dereferenced.
 337       mWrapper = reinterpret_cast<JSObject*>(1);
 338     }
 339   }
 340
 341  private:
 342   void SetWrapperJSObject(JSObject* aWrapper);
 343
 344   // We'd like to assert that these aren't used from servo threads, but we don't
 345   // have a great way to do that because:
 346   //  * We can't just assert that they get used on the main thread, because
 347   //    these are used from workers.
 348   //  * We can't just assert that they aren't used when IsInServoTraversal(),
 349   //    because the traversal has a sequential, main-thread-only phase, where we
 350   //    run animations that can fiddle with JS promises.
 351   FlagsType GetWrapperFlags() const { return mFlags.Get() & kWrapperFlagsMask; }
 352
 353   bool HasWrapperFlag(FlagsType aFlag) const {
 354     MOZ_ASSERT((aFlag & ~kWrapperFlagsMask) == 0, "Bad wrapper flag bits");
 355     return !!(mFlags.Get() & aFlag);
 356   }
 357
 358   void SetWrapperFlags(FlagsType aFlagsToSet) {
 359     MOZ_ASSERT((aFlagsToSet & ~kWrapperFlagsMask) == 0,
 360                "Bad wrapper flag bits");
 361     mFlags.Set(mFlags.Get() | aFlagsToSet);
 362   }
 363
 364   void UnsetWrapperFlags(FlagsType aFlagsToUnset) {
 365     MOZ_ASSERT((aFlagsToUnset & ~kWrapperFlagsMask) == 0,
 366                "Bad wrapper flag bits");
 367     mFlags.Set(mFlags.Get() & ~aFlagsToUnset);
 368   }
 369
 370   void HoldJSObjects(void* aScriptObjectHolder, nsScriptObjectTracer* aTracer,
 371                      JS::Zone* aZone);
 372
 373 #ifdef DEBUG
 374  public:
 375   void CheckCCWrapperTraversal(void* aScriptObjectHolder,
 376                                nsScriptObjectTracer* aTracer);
 377
 378  private:
 379 #endif  // DEBUG
 380
 381   /**
 382    * If this bit is set then we're preserving the wrapper, which in effect ties
 383    * the lifetime of the JS object stored in the cache to the lifetime of the
 384    * native object. We rely on the cycle collector to break the cycle that this
 385    * causes between the native object and the JS object, so it is important that
 386    * any native object that supports preserving of its wrapper
 387    * traces/traverses/unlinks the cached JS object (see
 388    * NS_IMPL_CYCLE_COLLECTION_TRACE_PRESERVED_WRAPPER and
 389    * NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER).
 390    */
 391   enum { WRAPPER_BIT_PRESERVED = 1 << 0 };
 392
 393   enum { kWrapperFlagsMask = WRAPPER_BIT_PRESERVED };
 394
 395   JSObject* mWrapper = nullptr;
 396
 397   // Rust code needs to read and write some flags atomically, but we don't want
 398   // to make the wrapper flags atomic whole-sale because main-thread code would
 399   // become more expensive (loads wouldn't change, but flag setting /
 400   // unsetting could become slower enough to be noticeable). Making this an
 401   // Atomic whole-sale needs more measuring.
 402   //
 403   // In order to not mess with aliasing rules the type should not be frozen, so
 404   // we use a RustCell, which contains an UnsafeCell internally. See also the
 405   // handling of ServoData (though that's a bit different).
 406   mozilla::RustCell<FlagsType> mFlags{0};
 407
 408  protected:
 409 #ifdef BOOL_FLAGS_ON_WRAPPER_CACHE
 410   uint32_t mBoolFlags = 0;
 411 #endif
 412 };
 413
 414 enum { WRAPPER_CACHE_FLAGS_BITS_USED = 1 };
 415
 416 NS_DEFINE_STATIC_IID_ACCESSOR(nsWrapperCache, NS_WRAPPERCACHE_IID)
 417
 418 #define NS_WRAPPERCACHE_INTERFACE_TABLE_ENTRY           \
 419   if (aIID.Equals(NS_GET_IID(nsWrapperCache))) {        \
 420     *aInstancePtr = static_cast<nsWrapperCache*>(this); \
 421     return NS_OK;                                       \
 422   }
 423
 424 #define NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY \
 425   NS_WRAPPERCACHE_INTERFACE_TABLE_ENTRY     \
 426   else
 427
 428 // Cycle collector macros for wrapper caches.
 429 //
 430 // The NS_DECL_*WRAPPERCACHE_* macros make it easier to mark classes as holding
 431 // just a single pointer to a JS value. That information is then used for
 432 // certain GC optimizations.
 433
 434 #define NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS_AMBIGUOUS(_class, _base)   \
 435   class NS_CYCLE_COLLECTION_INNERCLASS                                         \
 436       : public nsXPCOMCycleCollectionParticipant {                             \
 437    public:                                                                     \
 438     constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(Flags aFlags = 0)        \
 439         : nsXPCOMCycleCollectionParticipant(aFlags |                           \
 440                                             FlagMaybeSingleZoneJSHolder) {}    \
 441                                                                                \
 442    private:                                                                    \
 443     NS_DECL_CYCLE_COLLECTION_CLASS_BODY(_class, _base)                         \
 444     NS_IMETHOD_(void)                                                          \
 445     Trace(void* p, const TraceCallbacks& cb, void* closure) override;          \
 446     NS_IMETHOD_(void)                                                          \
 447     TraceWrapper(void* aPtr, const TraceCallbacks& aCb, void* aClosure) final; \
 448     NS_IMPL_GET_XPCOM_CYCLE_COLLECTION_PARTICIPANT(_class)                     \
 449   };                                                                           \
 450   NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL(_class)                                  \
 451   static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;         \
 452   NOT_INHERITED_CANT_OVERRIDE
 453
 454 #define NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(_class) \
 455   NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS_AMBIGUOUS(_class, _class)
 456
 457 #define NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS_INHERITED(_class,          \
 458                                                               _base_class)     \
 459   class NS_CYCLE_COLLECTION_INNERCLASS                                         \
 460       : public NS_CYCLE_COLLECTION_CLASSNAME(_base_class) {                    \
 461    public:                                                                     \
 462     constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(Flags aFlags)            \
 463         : NS_CYCLE_COLLECTION_CLASSNAME(_base_class)(                          \
 464               aFlags | FlagMaybeSingleZoneJSHolder) {}                         \
 465                                                                                \
 466    private:                                                                    \
 467     NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED_BODY(_class, _base_class)         \
 468     NS_IMETHOD_(void)                                                          \
 469     Trace(void* p, const TraceCallbacks& cb, void* closure) override;          \
 470     NS_IMETHOD_(void)                                                          \
 471     TraceWrapper(void* aPtr, const TraceCallbacks& aCb, void* aClosure) final; \
 472     NS_IMPL_GET_XPCOM_CYCLE_COLLECTION_PARTICIPANT(_class)                     \
 473   };                                                                           \
 474   NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL_INHERITED(_class)                        \
 475   static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;
 476
 477 #define NS_DECL_CYCLE_COLLECTION_SKIPPABLE_WRAPPERCACHE_CLASS_AMBIGUOUS(       \
 478     _class, _base)                                                             \
 479   class NS_CYCLE_COLLECTION_INNERCLASS                                         \
 480       : public nsXPCOMCycleCollectionParticipant {                             \
 481    public:                                                                     \
 482     constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(Flags aFlags)            \
 483         : nsXPCOMCycleCollectionParticipant(aFlags | FlagMightSkip |           \
 484                                             FlagMaybeSingleZoneJSHolder) {}    \
 485                                                                                \
 486    private:                                                                    \
 487     NS_DECL_CYCLE_COLLECTION_CLASS_BODY(_class, _base)                         \
 488     NS_IMETHOD_(void)                                                          \
 489     Trace(void* p, const TraceCallbacks& cb, void* closure) override;          \
 490     NS_IMETHOD_(void)                                                          \
 491     TraceWrapper(void* aPtr, const TraceCallbacks& aCb, void* aClosure) final; \
 492     NS_IMETHOD_(bool) CanSkipReal(void* p, bool aRemovingAllowed) override;    \
 493     NS_IMETHOD_(bool) CanSkipInCCReal(void* p) override;                       \
 494     NS_IMETHOD_(bool) CanSkipThisReal(void* p) override;                       \
 495     NS_IMPL_GET_XPCOM_CYCLE_COLLECTION_PARTICIPANT(_class)                     \
 496   };                                                                           \
 497   NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL(_class)                                  \
 498   static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;         \
 499   NOT_INHERITED_CANT_OVERRIDE
 500
 501 #define NS_DECL_CYCLE_COLLECTION_SKIPPABLE_WRAPPERCACHE_CLASS(_class)     \
 502   NS_DECL_CYCLE_COLLECTION_SKIPPABLE_WRAPPERCACHE_CLASS_AMBIGUOUS(_class, \
 503                                                                   _class)
 504
 505 #define NS_DECL_CYCLE_COLLECTION_SKIPPABLE_WRAPPERCACHE_CLASS_INHERITED(       \
 506     _class, _base_class)                                                       \
 507   class NS_CYCLE_COLLECTION_INNERCLASS                                         \
 508       : public NS_CYCLE_COLLECTION_CLASSNAME(_base_class) {                    \
 509    public:                                                                     \
 510     constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(Flags aFlags = 0)        \
 511         : NS_CYCLE_COLLECTION_CLASSNAME(_base_class)(                          \
 512               aFlags | FlagMightSkip | FlagMaybeSingleZoneJSHolder) {}         \
 513                                                                                \
 514    private:                                                                    \
 515     NS_DECL_CYCLE_COLLECTION_CLASS_BODY(_class, _base_class)                   \
 516     NS_IMETHOD_(void)                                                          \
 517     Trace(void* p, const TraceCallbacks& cb, void* closure) override;          \
 518     NS_IMETHOD_(void)                                                          \
 519     TraceWrapper(void* aPtr, const TraceCallbacks& aCb, void* aClosure) final; \
 520     NS_IMETHOD_(bool) CanSkipReal(void* p, bool aRemovingAllowed) override;    \
 521     NS_IMETHOD_(bool) CanSkipInCCReal(void* p) override;                       \
 522     NS_IMETHOD_(bool) CanSkipThisReal(void* p) override;                       \
 523     NS_IMPL_GET_XPCOM_CYCLE_COLLECTION_PARTICIPANT(_class)                     \
 524   };                                                                           \
 525   NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL_INHERITED(_class)                        \
 526   static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;
 527
 528 #define NS_DECL_CYCLE_COLLECTION_NATIVE_WRAPPERCACHE_CLASS(_class)             \
 529   void DeleteCycleCollectable(void) { delete this; }                           \
 530   class NS_CYCLE_COLLECTION_INNERCLASS : public nsScriptObjectTracer {         \
 531    public:                                                                     \
 532     constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(Flags aFlags = 0)        \
 533         : nsScriptObjectTracer(aFlags | FlagMaybeSingleZoneJSHolder) {}        \
 534                                                                                \
 535    private:                                                                    \
 536     NS_DECL_CYCLE_COLLECTION_NATIVE_CLASS_BODY(_class)                         \
 537     NS_IMETHOD_(void)                                                          \
 538     Trace(void* p, const TraceCallbacks& cb, void* closure) override;          \
 539     NS_IMETHOD_(void)                                                          \
 540     TraceWrapper(void* aPtr, const TraceCallbacks& aCb, void* aClosure) final; \
 541     static constexpr nsScriptObjectTracer* GetParticipant() {                  \
 542       return &_class::NS_CYCLE_COLLECTION_INNERNAME;                           \
 543     }                                                                          \
 544   };                                                                           \
 545   static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;
 546
 547 #define NS_IMPL_CYCLE_COLLECTION_TRACE_PRESERVED_WRAPPER \
 548   tmp->TraceWrapper(aCallbacks, aClosure);
 549
 550 #define NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER \
 551   tmp->ReleaseWrapper(p);
 552
 553 #define NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(_class)        \
 554   static_assert(std::is_base_of<nsWrapperCache, _class>::value,    \
 555                 "Class should inherit nsWrapperCache");            \
 556   NS_IMPL_CYCLE_COLLECTION_SINGLE_ZONE_SCRIPT_HOLDER_CLASS(_class) \
 557   NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(_class)                     \
 558     TraceWrapper(p, aCallbacks, aClosure);                         \
 559   NS_IMPL_CYCLE_COLLECTION_TRACE_END                               \
 560   void NS_CYCLE_COLLECTION_CLASSNAME(_class)::TraceWrapper(        \
 561       void* p, const TraceCallbacks& aCallbacks, void* aClosure) { \
 562     _class* tmp = DowncastCCParticipant<_class>(p);                \
 563     NS_IMPL_CYCLE_COLLECTION_TRACE_PRESERVED_WRAPPER               \
 564   }
 565
 566 #define NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_0(_class) \
 567   NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(_class)   \
 568   NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(_class)         \
 569     NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER   \
 570   NS_IMPL_CYCLE_COLLECTION_UNLINK_END                   \
 571   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(_class)       \
 572   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 573
 574 #define NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(_class, ...) \
 575   NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(_class)      \
 576   NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(_class)            \
 577     NS_IMPL_CYCLE_COLLECTION_UNLINK(__VA_ARGS__)           \
 578     NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER      \
 579   NS_IMPL_CYCLE_COLLECTION_UNLINK_END                      \
 580   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(_class)          \
 581     NS_IMPL_CYCLE_COLLECTION_TRAVERSE(__VA_ARGS__)         \
 582   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 583
 584 #define NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_WEAK(_class, ...) \
 585   NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(_class)           \
 586   NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(_class)                 \
 587     NS_IMPL_CYCLE_COLLECTION_UNLINK(__VA_ARGS__)                \
 588     NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER           \
 589     NS_IMPL_CYCLE_COLLECTION_UNLINK_WEAK_REFERENCE              \
 590   NS_IMPL_CYCLE_COLLECTION_UNLINK_END                           \
 591   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(_class)               \
 592     NS_IMPL_CYCLE_COLLECTION_TRAVERSE(__VA_ARGS__)              \
 593   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 594
 595 #define NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_WEAK_PTR(_class, ...) \
 596   NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(_class)               \
 597   NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(_class)                     \
 598     NS_IMPL_CYCLE_COLLECTION_UNLINK(__VA_ARGS__)                    \
 599     NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER               \
 600     NS_IMPL_CYCLE_COLLECTION_UNLINK_WEAK_PTR                        \
 601   NS_IMPL_CYCLE_COLLECTION_UNLINK_END                               \
 602   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(_class)                   \
 603     NS_IMPL_CYCLE_COLLECTION_TRAVERSE(__VA_ARGS__)                  \
 604   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 605
 606 // This is used for wrapper cached classes that inherit from cycle
 607 // collected non-wrapper cached classes.
 608 #define NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_INHERITED(_class, _base, ...)   \
 609   static_assert(!std::is_base_of<nsWrapperCache, _base>::value,               \
 610                 "Base class should not inherit nsWrapperCache");              \
 611   NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(_class)                         \
 612   NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(_class, _base)              \
 613     NS_IMPL_CYCLE_COLLECTION_UNLINK(__VA_ARGS__)                              \
 614     NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER                         \
 615   NS_IMPL_CYCLE_COLLECTION_UNLINK_END                                         \
 616   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(_class, _base)            \
 617     /* Assert somewhere, in this case in the traverse method, that the */     \
 618     /* parent isn't a single zone holder*/                                    \
 619     MOZ_ASSERT(!_base::NS_CYCLE_COLLECTION_INNERNAME.IsSingleZoneJSHolder()); \
 620     NS_IMPL_CYCLE_COLLECTION_TRAVERSE(__VA_ARGS__)                            \
 621   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 622
 623 // if NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_WITH_JS_MEMBERS is used to implement
 624 // a wrappercache class, one needs to use
 625 // NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS and its variants in the class
 626 // declaration.
 627 #define NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_WITH_JS_MEMBERS(              \
 628     class_, native_members_, js_members_)                                   \
 629   static_assert(std::is_base_of<nsWrapperCache, class_>::value,             \
 630                 "Class should inherit nsWrapperCache");                     \
 631   NS_IMPL_CYCLE_COLLECTION_CLASS(class_)                                    \
 632   NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(class_)                             \
 633     using ::ImplCycleCollectionUnlink;                                      \
 634     NS_IMPL_CYCLE_COLLECTION_UNLINK(                                        \
 635         MOZ_FOR_EACH_EXPAND_HELPER native_members_)                         \
 636     NS_IMPL_CYCLE_COLLECTION_UNLINK(MOZ_FOR_EACH_EXPAND_HELPER js_members_) \
 637     NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER                       \
 638   NS_IMPL_CYCLE_COLLECTION_UNLINK_END                                       \
 639   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(class_)                           \
 640     NS_IMPL_CYCLE_COLLECTION_TRAVERSE(                                      \
 641         MOZ_FOR_EACH_EXPAND_HELPER native_members_)                         \
 642   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END                                     \
 643   NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(class_)                              \
 644     NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBERS(                              \
 645         MOZ_FOR_EACH_EXPAND_HELPER js_members_)                             \
 646     NS_IMPL_CYCLE_COLLECTION_TRACE_PRESERVED_WRAPPER                        \
 647   NS_IMPL_CYCLE_COLLECTION_TRACE_END
 648
 649 #endif /* nsWrapperCache_h___ */