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/RootingAPI.h"
  16 #include "js/TracingAPI.h"
  17 #include "js/TypeDecls.h"
  18 #include "nsISupports.h"
  19 #include "nsISupportsUtils.h"
  20 #include <type_traits>
  21
  22 namespace mozilla::dom {
  23 class ContentProcessMessageManager;
  24 class InProcessBrowserChildMessageManager;
  25 class BrowserChildMessageManager;
  26 }  // namespace mozilla::dom
  27 class SandboxPrivate;
  28 class nsWindowRoot;
  29
  30 #define NS_WRAPPERCACHE_IID                          \
  31   {                                                  \
  32     0x6f3179a1, 0x36f7, 0x4a5c, {                    \
  33       0x8c, 0xf1, 0xad, 0xc8, 0x7c, 0xde, 0x3e, 0x87 \
  34     }                                                \
  35   }
  36
  37 // There are two sets of flags used by DOM nodes. One comes from reusing the
  38 // remaining bits of the inherited nsWrapperCache flags (mFlags), and another is
  39 // exclusive to nsINode (mBoolFlags).
  40 //
  41 // Both sets of flags are 32 bits. On 64-bit platforms, this can cause two
  42 // wasted 32-bit fields due to alignment requirements. Some compilers are
  43 // smart enough to coalesce the fields if we make mBoolFlags the first member
  44 // of nsINode, but others (such as MSVC, but that's not officially supported
  45 // by us anymore) are not. Also note that this kind of coalascing tends to
  46 // interact poorly with rust's bindgen, see:
  47 // https://github.com/rust-lang/rust-bindgen/issues/380
  48 //
  49 // So we just store mBoolFlags directly on nsWrapperCache on 64-bit platforms.
  50 // This may waste space for some other nsWrapperCache-derived objects that have
  51 // a 32-bit field as their first member, but those objects are unlikely to be as
  52 // numerous or performance-critical as DOM nodes.
  53 #ifdef HAVE_64BIT_BUILD
  54 static_assert(sizeof(void*) == 8, "These architectures should be 64-bit");
  55 #  define BOOL_FLAGS_ON_WRAPPER_CACHE
  56 #else
  57 static_assert(sizeof(void*) == 4, "Only support 32-bit and 64-bit");
  58 #endif
  59
  60 /**
  61  * Class to store the wrapper for an object. This can only be used with objects
  62  * that only have one non-security wrapper at a time (for an XPCWrappedNative
  63  * this is usually ensured by setting an explicit parent in the PreCreate hook
  64  * for the class).
  65  *
  66  * An instance of nsWrapperCache can be gotten from an object that implements
  67  * a wrapper cache by calling QueryInterface on it. Note that this breaks XPCOM
  68  * rules a bit (this object doesn't derive from nsISupports).
  69  *
  70  * The cache can store objects other than wrappers. We allow wrappers to use a
  71  * separate JSObject to store their state (mostly expandos). If the wrapper is
  72  * collected and we want to preserve this state we actually store the state
  73  * object in the cache.
  74  *
  75  * The cache can store 3 types of objects: a DOM binding object (regular JS
  76  * object or proxy), an nsOuterWindowProxy or an XPCWrappedNative wrapper.
  77  *
  78  * The finalizer for the wrapper clears the cache.
  79  *
  80  * A compacting GC can move the wrapper object. Pointers to moved objects are
  81  * usually found and updated by tracing the heap, however non-preserved wrappers
  82  * are weak references and are not traced, so another approach is
  83  * necessary. Instead a class hook (objectMovedOp) is provided that is called
  84  * when an object is moved and is responsible for ensuring pointers are
  85  * updated. It does this by calling UpdateWrapper() on the wrapper
  86  * cache. SetWrapper() asserts that the hook is implemented for any wrapper set.
  87  *
  88  * A number of the methods are implemented in nsWrapperCacheInlines.h because we
  89  * have to include some JS headers that don't play nicely with the rest of the
  90  * codebase. Include nsWrapperCacheInlines.h if you need to call those methods.
  91  */
  92
  93 class JS_HAZ_ROOTED nsWrapperCache {
  94  public:
  95   NS_DECLARE_STATIC_IID_ACCESSOR(NS_WRAPPERCACHE_IID)
  96
  97   nsWrapperCache() = default;
  98   ~nsWrapperCache() {
  99     // Preserved wrappers should never end up getting cleared, but this can
 100     // happen during shutdown when a leaked wrapper object is finalized, causing
 101     // its wrapper to be cleared.
 102     MOZ_ASSERT(!PreservingWrapper() || js::RuntimeIsBeingDestroyed(),
 103                "Destroying cache with a preserved wrapper!");
 104   }
 105
 106   /**
 107    * Get the cached wrapper.
 108    *
 109    * This getter clears the gray bit before handing out the JSObject which means
 110    * that the object is guaranteed to be kept alive past the next CC.
 111    */
 112   JSObject* GetWrapper() const;
 113
 114   /**
 115    * Get the cached wrapper.
 116    *
 117    * This getter does not change the color of the JSObject meaning that the
 118    * object returned is not guaranteed to be kept alive past the next CC.
 119    *
 120    * This should only be called if you are certain that the return value won't
 121    * be passed into a JSAPI function and that it won't be stored without being
 122    * rooted (or otherwise signaling the stored value to the CC).
 123    */
 124   JSObject* GetWrapperPreserveColor() const;
 125
 126   /**
 127    * Get the cached wrapper.
 128    *
 129    * This getter does not check whether the wrapper is dead and in the process
 130    * of being finalized.
 131    *
 132    * This should only be called if you really need to see the raw contents of
 133    * this cache, for example as part of finalization. Don't store the result
 134    * anywhere or pass it into JSAPI functions that may cause the value to
 135    * escape.
 136    */
 137   JSObject* GetWrapperMaybeDead() const { return mWrapper; }
 138
 139 #ifdef DEBUG
 140  private:
 141   static bool HasJSObjectMovedOp(JSObject* aWrapper);
 142
 143   static void AssertUpdatedWrapperZone(const JSObject* aNewObject,
 144                                        const JSObject* aOldObject);
 145
 146  public:
 147 #endif
 148
 149   void SetWrapper(JSObject* aWrapper) {
 150     MOZ_ASSERT(!PreservingWrapper(), "Clearing a preserved wrapper!");
 151     MOZ_ASSERT(aWrapper, "Use ClearWrapper!");
 152     MOZ_ASSERT(HasJSObjectMovedOp(aWrapper),
 153                "Object has not provided the hook to update the wrapper if it "
 154                "is moved");
 155
 156     SetWrapperJSObject(aWrapper);
 157   }
 158
 159   /**
 160    * Clear the cache.
 161    */
 162   void ClearWrapper() {
 163     // Preserved wrappers should never end up getting cleared, but this can
 164     // happen during shutdown when a leaked wrapper object is finalized, causing
 165     // its wrapper to be cleared.
 166     MOZ_ASSERT(!PreservingWrapper() || js::RuntimeIsBeingDestroyed(),
 167                "Clearing a preserved wrapper!");
 168     SetWrapperJSObject(nullptr);
 169   }
 170
 171   /**
 172    * Clear the cache if it still contains a specific wrapper object. This should
 173    * be called from the finalizer for the wrapper.
 174    */
 175   void ClearWrapper(JSObject* obj) {
 176     if (obj == mWrapper) {
 177       ClearWrapper();
 178     }
 179   }
 180
 181   /**
 182    * Update the wrapper when the object moves between globals.
 183    */
 184   template <typename T>
 185   void UpdateWrapperForNewGlobal(T* aScriptObjectHolder, JSObject* aNewWrapper);
 186
 187   /**
 188    * Update the wrapper if the object it contains is moved.
 189    *
 190    * This method must be called from the objectMovedOp class extension hook for
 191    * any wrapper cached object.
 192    */
 193   void UpdateWrapper(JSObject* aNewObject, const JSObject* aOldObject) {
 194 #ifdef DEBUG
 195     AssertUpdatedWrapperZone(aNewObject, aOldObject);
 196 #endif
 197     if (mWrapper) {
 198       MOZ_ASSERT(mWrapper == aOldObject);
 199       mWrapper = aNewObject;
 200       if (PreservingWrapper() && !JS::ObjectIsTenured(mWrapper)) {
 201         // Can pass prevp as null here since a previous store buffer entry has
 202         // been cleared by the current nursery collection.
 203         JS::HeapObjectPostWriteBarrier(&mWrapper, nullptr, mWrapper);
 204       }
 205     }
 206   }
 207
 208   bool PreservingWrapper() const {
 209     return HasWrapperFlag(WRAPPER_BIT_PRESERVED);
 210   }
 211
 212   /**
 213    * Wrap the object corresponding to this wrapper cache. If non-null is
 214    * returned, the object has already been stored in the wrapper cache.
 215    */
 216   virtual JSObject* WrapObject(JSContext* cx,
 217                                JS::Handle<JSObject*> aGivenProto) = 0;
 218
 219   /**
 220    * Returns true if the object has a wrapper that is known live from the point
 221    * of view of cycle collection.
 222    */
 223   bool HasKnownLiveWrapper() const;
 224
 225   /**
 226    * Returns true if the object has a known-live wrapper (from the CC point of
 227    * view) and all the GC things it is keeping alive are already known-live from
 228    * CC's point of view.
 229    */
 230   bool HasKnownLiveWrapperAndDoesNotNeedTracing(nsISupports* aThis);
 231
 232   bool HasNothingToTrace(nsISupports* aThis);
 233
 234   /**
 235    * Mark our wrapper, if any, as live as far as the CC is concerned.
 236    */
 237   void MarkWrapperLive();
 238
 239   // Only meant to be called by code that preserves a wrapper.
 240   void SetPreservingWrapper(bool aPreserve) {
 241     if (aPreserve) {
 242       SetWrapperFlags(WRAPPER_BIT_PRESERVED);
 243     } else {
 244       UnsetWrapperFlags(WRAPPER_BIT_PRESERVED);
 245     }
 246   }
 247
 248   void TraceWrapper(const TraceCallbacks& aCallbacks, void* aClosure) {
 249     if (PreservingWrapper() && mWrapper) {
 250       aCallbacks.Trace(this, "Preserved wrapper", aClosure);
 251     }
 252   }
 253
 254   /*
 255    * The following methods for getting and manipulating flags allow the unused
 256    * bits of mFlags to be used by derived classes.
 257    */
 258
 259   using FlagsType = uint32_t;
 260
 261   FlagsType GetFlags() const {
 262     MOZ_ASSERT(NS_IsMainThread());
 263     MOZ_ASSERT(!mozilla::IsInServoTraversal());
 264     return mFlags.Get() & ~kWrapperFlagsMask;
 265   }
 266
 267   // This can be called from stylo threads too, so it needs to be atomic, as
 268   // this value may be mutated from multiple threads during servo traversal from
 269   // rust.
 270   bool HasFlag(FlagsType aFlag) const {
 271     MOZ_ASSERT((aFlag & kWrapperFlagsMask) == 0, "Bad flag mask");
 272     return __atomic_load_n(mFlags.AsPtr(), __ATOMIC_RELAXED) & aFlag;
 273   }
 274
 275   // Identical to HasFlag, but more explicit about its handling of multiple
 276   // flags. This can be called from stylo threads too.
 277   bool HasAnyOfFlags(FlagsType aFlags) const { return HasFlag(aFlags); }
 278
 279   // This can also be called from stylo, in the sequential part of the
 280   // traversal, though it's probably not worth differentiating them for the
 281   // purposes of assertions.
 282   bool HasAllFlags(FlagsType aFlags) const {
 283     MOZ_ASSERT((aFlags & kWrapperFlagsMask) == 0, "Bad flag mask");
 284     return (__atomic_load_n(mFlags.AsPtr(), __ATOMIC_RELAXED) & aFlags) ==
 285            aFlags;
 286   }
 287
 288   void SetFlags(FlagsType aFlagsToSet) {
 289     MOZ_ASSERT(NS_IsMainThread());
 290     MOZ_ASSERT((aFlagsToSet & kWrapperFlagsMask) == 0, "Bad flag mask");
 291     mFlags.Set(mFlags.Get() | aFlagsToSet);
 292   }
 293
 294   void UnsetFlags(FlagsType aFlagsToUnset) {
 295     MOZ_ASSERT(NS_IsMainThread());
 296     MOZ_ASSERT((aFlagsToUnset & kWrapperFlagsMask) == 0, "Bad flag mask");
 297     mFlags.Set(mFlags.Get() & ~aFlagsToUnset);
 298   }
 299
 300   void PreserveWrapper(nsISupports* aScriptObjectHolder) {
 301     if (PreservingWrapper()) {
 302       return;
 303     }
 304
 305     nsISupports* ccISupports;
 306     aScriptObjectHolder->QueryInterface(NS_GET_IID(nsCycleCollectionISupports),
 307                                         reinterpret_cast<void**>(&ccISupports));
 308     MOZ_ASSERT(ccISupports);
 309
 310     nsXPCOMCycleCollectionParticipant* participant;
 311     CallQueryInterface(ccISupports, &participant);
 312     PreserveWrapper(ccISupports, participant);
 313   }
 314
 315   void PreserveWrapper(void* aScriptObjectHolder,
 316                        nsScriptObjectTracer* aTracer) {
 317     if (PreservingWrapper()) {
 318       return;
 319     }
 320
 321     JSObject* wrapper = GetWrapper();  // Read barrier for incremental GC.
 322     HoldJSObjects(aScriptObjectHolder, aTracer, JS::GetObjectZone(wrapper));
 323     SetPreservingWrapper(true);
 324 #ifdef DEBUG
 325     // Make sure the cycle collector will be able to traverse to the wrapper.
 326     CheckCCWrapperTraversal(aScriptObjectHolder, aTracer);
 327 #endif
 328   }
 329
 330   void ReleaseWrapper(void* aScriptObjectHolder);
 331
 332   void TraceWrapper(JSTracer* aTrc, const char* name) {
 333     if (mWrapper) {
 334       js::UnsafeTraceManuallyBarrieredEdge(aTrc, &mWrapper, name);
 335     }
 336   }
 337
 338  protected:
 339   void PoisonWrapper() {
 340     if (mWrapper) {
 341       // Set the pointer to a value that will cause a crash if it is
 342       // dereferenced.
 343       mWrapper = reinterpret_cast<JSObject*>(1);
 344     }
 345   }
 346
 347  private:
 348   void SetWrapperJSObject(JSObject* aWrapper);
 349
 350   // We'd like to assert that these aren't used from servo threads, but we don't
 351   // have a great way to do that because:
 352   //  * We can't just assert that they get used on the main thread, because
 353   //    these are used from workers.
 354   //  * We can't just assert that they aren't used when IsInServoTraversal(),
 355   //    because the traversal has a sequential, main-thread-only phase, where we
 356   //    run animations that can fiddle with JS promises.
 357   FlagsType GetWrapperFlags() const { return mFlags.Get() & kWrapperFlagsMask; }
 358
 359   bool HasWrapperFlag(FlagsType aFlag) const {
 360     MOZ_ASSERT((aFlag & ~kWrapperFlagsMask) == 0, "Bad wrapper flag bits");
 361     return !!(mFlags.Get() & aFlag);
 362   }
 363
 364   void SetWrapperFlags(FlagsType aFlagsToSet) {
 365     MOZ_ASSERT((aFlagsToSet & ~kWrapperFlagsMask) == 0,
 366                "Bad wrapper flag bits");
 367     mFlags.Set(mFlags.Get() | aFlagsToSet);
 368   }
 369
 370   void UnsetWrapperFlags(FlagsType aFlagsToUnset) {
 371     MOZ_ASSERT((aFlagsToUnset & ~kWrapperFlagsMask) == 0,
 372                "Bad wrapper flag bits");
 373     mFlags.Set(mFlags.Get() & ~aFlagsToUnset);
 374   }
 375
 376   void HoldJSObjects(void* aScriptObjectHolder, nsScriptObjectTracer* aTracer,
 377                      JS::Zone* aZone);
 378
 379 #ifdef DEBUG
 380  public:
 381   void CheckCCWrapperTraversal(void* aScriptObjectHolder,
 382                                nsScriptObjectTracer* aTracer);
 383
 384  private:
 385 #endif  // DEBUG
 386
 387   /**
 388    * If this bit is set then we're preserving the wrapper, which in effect ties
 389    * the lifetime of the JS object stored in the cache to the lifetime of the
 390    * native object. We rely on the cycle collector to break the cycle that this
 391    * causes between the native object and the JS object, so it is important that
 392    * any native object that supports preserving of its wrapper
 393    * traces/traverses/unlinks the cached JS object (see
 394    * NS_IMPL_CYCLE_COLLECTION_TRACE_PRESERVED_WRAPPER and
 395    * NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER).
 396    */
 397   enum { WRAPPER_BIT_PRESERVED = 1 << 0 };
 398
 399   enum { kWrapperFlagsMask = WRAPPER_BIT_PRESERVED };
 400
 401   JSObject* mWrapper = nullptr;
 402
 403   // Rust code needs to read and write some flags atomically, but we don't want
 404   // to make the wrapper flags atomic whole-sale because main-thread code would
 405   // become more expensive (loads wouldn't change, but flag setting /
 406   // unsetting could become slower enough to be noticeable). Making this an
 407   // Atomic whole-sale needs more measuring.
 408   //
 409   // In order to not mess with aliasing rules the type should not be frozen, so
 410   // we use a RustCell, which contains an UnsafeCell internally. See also the
 411   // handling of ServoData (though that's a bit different).
 412   mozilla::RustCell<FlagsType> mFlags{0};
 413
 414  protected:
 415 #ifdef BOOL_FLAGS_ON_WRAPPER_CACHE
 416   uint32_t mBoolFlags = 0;
 417 #endif
 418 };
 419
 420 enum { WRAPPER_CACHE_FLAGS_BITS_USED = 1 };
 421
 422 NS_DEFINE_STATIC_IID_ACCESSOR(nsWrapperCache, NS_WRAPPERCACHE_IID)
 423
 424 #define NS_WRAPPERCACHE_INTERFACE_TABLE_ENTRY           \
 425   if (aIID.Equals(NS_GET_IID(nsWrapperCache))) {        \
 426     *aInstancePtr = static_cast<nsWrapperCache*>(this); \
 427     return NS_OK;                                       \
 428   }
 429
 430 #define NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY \
 431   NS_WRAPPERCACHE_INTERFACE_TABLE_ENTRY     \
 432   else
 433
 434 // Cycle collector macros for wrapper caches.
 435 //
 436 // The NS_DECL_*WRAPPERCACHE_* macros make it easier to mark classes as holding
 437 // just a single pointer to a JS value. That information is then used for
 438 // certain GC optimizations.
 439
 440 #define NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS_AMBIGUOUS(_class, _base)   \
 441   class NS_CYCLE_COLLECTION_INNERCLASS                                         \
 442       : public nsXPCOMCycleCollectionParticipant {                             \
 443    public:                                                                     \
 444     constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(Flags aFlags = 0)        \
 445         : nsXPCOMCycleCollectionParticipant(aFlags |                           \
 446                                             FlagMaybeSingleZoneJSHolder) {}    \
 447                                                                                \
 448    private:                                                                    \
 449     NS_DECL_CYCLE_COLLECTION_CLASS_BODY(_class, _base)                         \
 450     NS_IMETHOD_(void)                                                          \
 451     Trace(void* p, const TraceCallbacks& cb, void* closure) override;          \
 452     NS_IMETHOD_(void)                                                          \
 453     TraceWrapper(void* aPtr, const TraceCallbacks& aCb, void* aClosure) final; \
 454     NS_IMPL_GET_XPCOM_CYCLE_COLLECTION_PARTICIPANT(_class)                     \
 455   };                                                                           \
 456   NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL(_class)                                  \
 457   static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;         \
 458   NOT_INHERITED_CANT_OVERRIDE
 459
 460 #define NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(_class) \
 461   NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS_AMBIGUOUS(_class, _class)
 462
 463 #define NS_DECL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS_INHERITED(_class,          \
 464                                                               _base_class)     \
 465   class NS_CYCLE_COLLECTION_INNERCLASS                                         \
 466       : public NS_CYCLE_COLLECTION_CLASSNAME(_base_class) {                    \
 467    public:                                                                     \
 468     constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(Flags aFlags)            \
 469         : NS_CYCLE_COLLECTION_CLASSNAME(_base_class)(                          \
 470               aFlags | FlagMaybeSingleZoneJSHolder) {}                         \
 471                                                                                \
 472    private:                                                                    \
 473     NS_DECL_CYCLE_COLLECTION_CLASS_INHERITED_BODY(_class, _base_class)         \
 474     NS_IMETHOD_(void)                                                          \
 475     Trace(void* p, const TraceCallbacks& cb, void* closure) override;          \
 476     NS_IMETHOD_(void)                                                          \
 477     TraceWrapper(void* aPtr, const TraceCallbacks& aCb, void* aClosure) final; \
 478     NS_IMPL_GET_XPCOM_CYCLE_COLLECTION_PARTICIPANT(_class)                     \
 479   };                                                                           \
 480   NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL_INHERITED(_class)                        \
 481   static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;
 482
 483 #define NS_DECL_CYCLE_COLLECTION_SKIPPABLE_WRAPPERCACHE_CLASS_AMBIGUOUS(       \
 484     _class, _base)                                                             \
 485   class NS_CYCLE_COLLECTION_INNERCLASS                                         \
 486       : public nsXPCOMCycleCollectionParticipant {                             \
 487    public:                                                                     \
 488     constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(Flags aFlags)            \
 489         : nsXPCOMCycleCollectionParticipant(aFlags | FlagMightSkip |           \
 490                                             FlagMaybeSingleZoneJSHolder) {}    \
 491                                                                                \
 492    private:                                                                    \
 493     NS_DECL_CYCLE_COLLECTION_CLASS_BODY(_class, _base)                         \
 494     NS_IMETHOD_(void)                                                          \
 495     Trace(void* p, const TraceCallbacks& cb, void* closure) override;          \
 496     NS_IMETHOD_(void)                                                          \
 497     TraceWrapper(void* aPtr, const TraceCallbacks& aCb, void* aClosure) final; \
 498     NS_IMETHOD_(bool) CanSkipReal(void* p, bool aRemovingAllowed) override;    \
 499     NS_IMETHOD_(bool) CanSkipInCCReal(void* p) override;                       \
 500     NS_IMETHOD_(bool) CanSkipThisReal(void* p) override;                       \
 501     NS_IMPL_GET_XPCOM_CYCLE_COLLECTION_PARTICIPANT(_class)                     \
 502   };                                                                           \
 503   NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL(_class)                                  \
 504   static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;         \
 505   NOT_INHERITED_CANT_OVERRIDE
 506
 507 #define NS_DECL_CYCLE_COLLECTION_SKIPPABLE_WRAPPERCACHE_CLASS(_class)     \
 508   NS_DECL_CYCLE_COLLECTION_SKIPPABLE_WRAPPERCACHE_CLASS_AMBIGUOUS(_class, \
 509                                                                   _class)
 510
 511 #define NS_DECL_CYCLE_COLLECTION_SKIPPABLE_WRAPPERCACHE_CLASS_INHERITED(       \
 512     _class, _base_class)                                                       \
 513   class NS_CYCLE_COLLECTION_INNERCLASS                                         \
 514       : public NS_CYCLE_COLLECTION_CLASSNAME(_base_class) {                    \
 515    public:                                                                     \
 516     constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(Flags aFlags = 0)        \
 517         : NS_CYCLE_COLLECTION_CLASSNAME(_base_class)(                          \
 518               aFlags | FlagMightSkip | FlagMaybeSingleZoneJSHolder) {}         \
 519                                                                                \
 520    private:                                                                    \
 521     NS_DECL_CYCLE_COLLECTION_CLASS_BODY(_class, _base_class)                   \
 522     NS_IMETHOD_(void)                                                          \
 523     Trace(void* p, const TraceCallbacks& cb, void* closure) override;          \
 524     NS_IMETHOD_(void)                                                          \
 525     TraceWrapper(void* aPtr, const TraceCallbacks& aCb, void* aClosure) final; \
 526     NS_IMETHOD_(bool) CanSkipReal(void* p, bool aRemovingAllowed) override;    \
 527     NS_IMETHOD_(bool) CanSkipInCCReal(void* p) override;                       \
 528     NS_IMETHOD_(bool) CanSkipThisReal(void* p) override;                       \
 529     NS_IMPL_GET_XPCOM_CYCLE_COLLECTION_PARTICIPANT(_class)                     \
 530   };                                                                           \
 531   NS_CHECK_FOR_RIGHT_PARTICIPANT_IMPL_INHERITED(_class)                        \
 532   static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;
 533
 534 #define NS_DECL_CYCLE_COLLECTION_NATIVE_WRAPPERCACHE_CLASS(_class)             \
 535   void DeleteCycleCollectable(void) { delete this; }                           \
 536   class NS_CYCLE_COLLECTION_INNERCLASS : public nsScriptObjectTracer {         \
 537    public:                                                                     \
 538     constexpr explicit NS_CYCLE_COLLECTION_INNERCLASS(Flags aFlags = 0)        \
 539         : nsScriptObjectTracer(aFlags | FlagMaybeSingleZoneJSHolder) {}        \
 540                                                                                \
 541    private:                                                                    \
 542     NS_DECL_CYCLE_COLLECTION_NATIVE_CLASS_BODY(_class)                         \
 543     NS_IMETHOD_(void)                                                          \
 544     Trace(void* p, const TraceCallbacks& cb, void* closure) override;          \
 545     NS_IMETHOD_(void)                                                          \
 546     TraceWrapper(void* aPtr, const TraceCallbacks& aCb, void* aClosure) final; \
 547     static constexpr nsScriptObjectTracer* GetParticipant() {                  \
 548       return &_class::NS_CYCLE_COLLECTION_INNERNAME;                           \
 549     }                                                                          \
 550   };                                                                           \
 551   static NS_CYCLE_COLLECTION_INNERCLASS NS_CYCLE_COLLECTION_INNERNAME;
 552
 553 #define NS_IMPL_CYCLE_COLLECTION_TRACE_PRESERVED_WRAPPER \
 554   tmp->TraceWrapper(aCallbacks, aClosure);
 555
 556 #define NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER \
 557   tmp->ReleaseWrapper(p);
 558
 559 #define NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(_class)        \
 560   static_assert(std::is_base_of<nsWrapperCache, _class>::value,    \
 561                 "Class should inherit nsWrapperCache");            \
 562   NS_IMPL_CYCLE_COLLECTION_SINGLE_ZONE_SCRIPT_HOLDER_CLASS(_class) \
 563   NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(_class)                     \
 564     TraceWrapper(p, aCallbacks, aClosure);                         \
 565   NS_IMPL_CYCLE_COLLECTION_TRACE_END                               \
 566   void NS_CYCLE_COLLECTION_CLASSNAME(_class)::TraceWrapper(        \
 567       void* p, const TraceCallbacks& aCallbacks, void* aClosure) { \
 568     _class* tmp = DowncastCCParticipant<_class>(p);                \
 569     NS_IMPL_CYCLE_COLLECTION_TRACE_PRESERVED_WRAPPER               \
 570   }
 571
 572 #define NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_0(_class) \
 573   NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(_class)   \
 574   NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(_class)         \
 575     NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER   \
 576   NS_IMPL_CYCLE_COLLECTION_UNLINK_END                   \
 577   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(_class)       \
 578   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 579
 580 #define NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(_class, ...) \
 581   NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(_class)      \
 582   NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(_class)            \
 583     NS_IMPL_CYCLE_COLLECTION_UNLINK(__VA_ARGS__)           \
 584     NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER      \
 585   NS_IMPL_CYCLE_COLLECTION_UNLINK_END                      \
 586   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(_class)          \
 587     NS_IMPL_CYCLE_COLLECTION_TRAVERSE(__VA_ARGS__)         \
 588   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 589
 590 #define NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_WEAK(_class, ...) \
 591   NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(_class)           \
 592   NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(_class)                 \
 593     NS_IMPL_CYCLE_COLLECTION_UNLINK(__VA_ARGS__)                \
 594     NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER           \
 595     NS_IMPL_CYCLE_COLLECTION_UNLINK_WEAK_REFERENCE              \
 596   NS_IMPL_CYCLE_COLLECTION_UNLINK_END                           \
 597   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(_class)               \
 598     NS_IMPL_CYCLE_COLLECTION_TRAVERSE(__VA_ARGS__)              \
 599   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 600
 601 #define NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_WEAK_PTR(_class, ...) \
 602   NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(_class)               \
 603   NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(_class)                     \
 604     NS_IMPL_CYCLE_COLLECTION_UNLINK(__VA_ARGS__)                    \
 605     NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER               \
 606     NS_IMPL_CYCLE_COLLECTION_UNLINK_WEAK_PTR                        \
 607   NS_IMPL_CYCLE_COLLECTION_UNLINK_END                               \
 608   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(_class)                   \
 609     NS_IMPL_CYCLE_COLLECTION_TRAVERSE(__VA_ARGS__)                  \
 610   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 611
 612 // This is used for wrapper cached classes that inherit from cycle
 613 // collected non-wrapper cached classes.
 614 #define NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_INHERITED(_class, _base, ...)   \
 615   static_assert(!std::is_base_of<nsWrapperCache, _base>::value,               \
 616                 "Base class should not inherit nsWrapperCache");              \
 617   NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_CLASS(_class)                         \
 618   NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(_class, _base)              \
 619     NS_IMPL_CYCLE_COLLECTION_UNLINK(__VA_ARGS__)                              \
 620     NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER                         \
 621   NS_IMPL_CYCLE_COLLECTION_UNLINK_END                                         \
 622   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(_class, _base)            \
 623     /* Assert somewhere, in this case in the traverse method, that the */     \
 624     /* parent isn't a single zone holder*/                                    \
 625     MOZ_ASSERT(!_base::NS_CYCLE_COLLECTION_INNERNAME.IsSingleZoneJSHolder()); \
 626     NS_IMPL_CYCLE_COLLECTION_TRAVERSE(__VA_ARGS__)                            \
 627   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END
 628
 629 // if NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_WITH_JS_MEMBERS is used to implement
 630 // a wrappercache class, one needs to use
 631 // NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS and its variants in the class
 632 // declaration.
 633 #define NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_WITH_JS_MEMBERS(              \
 634     class_, native_members_, js_members_)                                   \
 635   static_assert(std::is_base_of<nsWrapperCache, class_>::value,             \
 636                 "Class should inherit nsWrapperCache");                     \
 637   NS_IMPL_CYCLE_COLLECTION_CLASS(class_)                                    \
 638   NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(class_)                             \
 639     using ::ImplCycleCollectionUnlink;                                      \
 640     NS_IMPL_CYCLE_COLLECTION_UNLINK(                                        \
 641         MOZ_FOR_EACH_EXPAND_HELPER native_members_)                         \
 642     NS_IMPL_CYCLE_COLLECTION_UNLINK(MOZ_FOR_EACH_EXPAND_HELPER js_members_) \
 643     NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER                       \
 644   NS_IMPL_CYCLE_COLLECTION_UNLINK_END                                       \
 645   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(class_)                           \
 646     NS_IMPL_CYCLE_COLLECTION_TRAVERSE(                                      \
 647         MOZ_FOR_EACH_EXPAND_HELPER native_members_)                         \
 648   NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END                                     \
 649   NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(class_)                              \
 650     NS_IMPL_CYCLE_COLLECTION_TRACE_JS_MEMBERS(                              \
 651         MOZ_FOR_EACH_EXPAND_HELPER js_members_)                             \
 652     NS_IMPL_CYCLE_COLLECTION_TRACE_PRESERVED_WRAPPER                        \
 653   NS_IMPL_CYCLE_COLLECTION_TRACE_END
 654
 655 #endif /* nsWrapperCache_h___ */