The Tor Browser: dom/bindings/CallbackObject.h@b8a032363ba2

Incorporate requested changes from Mozilla in review:
https://bugzilla.mozilla.org/show_bug.cgi?id=1123480#c6

     1 /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */

     2 /* vim:set ts=2 sw=2 sts=2 et cindent: */

     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/. */

     7 /**

     8  * A common base class for representing WebIDL callback function and

     9  * callback interface types in C++.

    10  *

    11  * This class implements common functionality like lifetime

    12  * management, initialization with the JS object, and setup of the

    13  * call environment.  Subclasses are responsible for providing methods

    14  * that do the call into JS as needed.

    15  */

    17 #ifndef mozilla_dom_CallbackObject_h

    18 #define mozilla_dom_CallbackObject_h

    20 #include "nsISupports.h"

    21 #include "nsISupportsImpl.h"

    22 #include "nsCycleCollectionParticipant.h"

    23 #include "jswrapper.h"

    24 #include "mozilla/Assertions.h"

    25 #include "mozilla/ErrorResult.h"

    26 #include "mozilla/HoldDropJSObjects.h"

    27 #include "mozilla/MemoryReporting.h"

    28 #include "mozilla/dom/ScriptSettings.h"

    29 #include "nsContentUtils.h"

    30 #include "nsWrapperCache.h"

    31 #include "nsJSEnvironment.h"

    32 #include "xpcpublic.h"

    34 namespace mozilla {

    35 namespace dom {

    37 #define DOM_CALLBACKOBJECT_IID \

    38 { 0xbe74c190, 0x6d76, 0x4991, \

    39  { 0x84, 0xb9, 0x65, 0x06, 0x99, 0xe6, 0x93, 0x2b } }

    41 class CallbackObject : public nsISupports

    42 {

    43 public:

    44   NS_DECLARE_STATIC_IID_ACCESSOR(DOM_CALLBACKOBJECT_IID)

    46   NS_DECL_CYCLE_COLLECTING_ISUPPORTS

    47   NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(CallbackObject)

    49   // The caller may pass a global object which will act as an override for the

    50   // incumbent script settings object when the callback is invoked (overriding

    51   // the entry point computed from aCallback). If no override is required, the

    52   // caller should pass null.

    53   explicit CallbackObject(JS::Handle<JSObject*> aCallback, nsIGlobalObject *aIncumbentGlobal)

    54   {

    55     Init(aCallback, aIncumbentGlobal);

    56   }

    58   virtual ~CallbackObject()

    59   {

    60     DropJSObjects();

    61   }

    63   JS::Handle<JSObject*> Callback() const

    64   {

    65     JS::ExposeObjectToActiveJS(mCallback);

    66     return CallbackPreserveColor();

    67   }

    69   /*

    70    * This getter does not change the color of the JSObject meaning that the

    71    * object returned is not guaranteed to be kept alive past the next CC.

    72    *

    73    * This should only be called if you are certain that the return value won't

    74    * be passed into a JS API function and that it won't be stored without being

    75    * rooted (or otherwise signaling the stored value to the CC).

    76    */

    77   JS::Handle<JSObject*> CallbackPreserveColor() const

    78   {

    79     // Calling fromMarkedLocation() is safe because we trace our mCallback, and

    80     // because the value of mCallback cannot change after if has been set.

    81     return JS::Handle<JSObject*>::fromMarkedLocation(mCallback.address());

    82   }

    84   nsIGlobalObject* IncumbentGlobalOrNull() const

    85   {

    86     return mIncumbentGlobal;

    87   }

    89   enum ExceptionHandling {

    90     // Report any exception and don't throw it to the caller code.

    91     eReportExceptions,

    92     // Throw an exception to the caller code if the thrown exception is a

    93     // binding object for a DOMError from the caller's scope, otherwise report

    94     // it.

    95     eRethrowContentExceptions,

    96     // Throw any exception to the caller code.

    97     eRethrowExceptions

    98   };

   100   size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const

   101   {

   102     return aMallocSizeOf(this);

   103   }

   105 protected:

   106   explicit CallbackObject(CallbackObject* aCallbackObject)

   107   {

   108     Init(aCallbackObject->mCallback, aCallbackObject->mIncumbentGlobal);

   109   }

   111   bool operator==(const CallbackObject& aOther) const

   112   {

   113     JSObject* thisObj =

   114       js::UncheckedUnwrap(CallbackPreserveColor());

   115     JSObject* otherObj =

   116       js::UncheckedUnwrap(aOther.CallbackPreserveColor());

   117     return thisObj == otherObj;

   118   }

   120 private:

   121   inline void Init(JSObject* aCallback, nsIGlobalObject* aIncumbentGlobal)

   122   {

   123     MOZ_ASSERT(aCallback && !mCallback);

   124     // Set script objects before we hold, on the off chance that a GC could

   125     // somehow happen in there... (which would be pretty odd, granted).

   126     mCallback = aCallback;

   127     if (aIncumbentGlobal) {

   128       mIncumbentGlobal = aIncumbentGlobal;

   129       mIncumbentJSGlobal = aIncumbentGlobal->GetGlobalJSObject();

   130     }

   131     mozilla::HoldJSObjects(this);

   132   }

   134   CallbackObject(const CallbackObject&) MOZ_DELETE;

   135   CallbackObject& operator =(const CallbackObject&) MOZ_DELETE;

   137 protected:

   138   void DropJSObjects()

   139   {

   140     MOZ_ASSERT_IF(mIncumbentJSGlobal, mCallback);

   141     if (mCallback) {

   142       mCallback = nullptr;

   143       mIncumbentJSGlobal = nullptr;

   144       mozilla::DropJSObjects(this);

   145     }

   146   }

   148   JS::Heap<JSObject*> mCallback;

   149   // Ideally, we'd just hold a reference to the nsIGlobalObject, since that's

   150   // what we need to pass to AutoIncumbentScript. Unfortunately, that doesn't

   151   // hold the actual JS global alive. So we maintain an additional pointer to

   152   // the JS global itself so that we can trace it.

   153   //

   154   // At some point we should consider trying to make native globals hold their

   155   // scripted global alive, at which point we can get rid of the duplication

   156   // here.

   157   nsCOMPtr<nsIGlobalObject> mIncumbentGlobal;

   158   JS::TenuredHeap<JSObject*> mIncumbentJSGlobal;

   160   class MOZ_STACK_CLASS CallSetup

   161   {

   162     /**

   163      * A class that performs whatever setup we need to safely make a

   164      * call while this class is on the stack, After the constructor

   165      * returns, the call is safe to make if GetContext() returns

   166      * non-null.

   167      */

   168   public:

   169     // If aExceptionHandling == eRethrowContentExceptions then aCompartment

   170     // needs to be set to the compartment in which exceptions will be rethrown.

   171     CallSetup(CallbackObject* aCallback, ErrorResult& aRv,

   172               ExceptionHandling aExceptionHandling,

   173               JSCompartment* aCompartment = nullptr,

   174               bool aIsJSImplementedWebIDL = false);

   175     ~CallSetup();

   177     JSContext* GetContext() const

   178     {

   179       return mCx;

   180     }

   182   private:

   183     // We better not get copy-constructed

   184     CallSetup(const CallSetup&) MOZ_DELETE;

   186     bool ShouldRethrowException(JS::Handle<JS::Value> aException);

   188     // Members which can go away whenever

   189     JSContext* mCx;

   191     // Caller's compartment. This will only have a sensible value if

   192     // mExceptionHandling == eRethrowContentExceptions.

   193     JSCompartment* mCompartment;

   195     // And now members whose construction/destruction order we need to control.

   196     Maybe<AutoEntryScript> mAutoEntryScript;

   197     Maybe<AutoIncumbentScript> mAutoIncumbentScript;

   199     // Constructed the rooter within the scope of mCxPusher above, so that it's

   200     // always within a request during its lifetime.

   201     Maybe<JS::Rooted<JSObject*> > mRootedCallable;

   203     // Can't construct a JSAutoCompartment without a JSContext either.  Also,

   204     // Put mAc after mAutoEntryScript so that we exit the compartment before

   205     // we pop the JSContext. Though in practice we'll often manually order

   206     // those two things.

   207     Maybe<JSAutoCompartment> mAc;

   209     // An ErrorResult to possibly re-throw exceptions on and whether

   210     // we should re-throw them.

   211     ErrorResult& mErrorResult;

   212     const ExceptionHandling mExceptionHandling;

   213     JS::ContextOptions mSavedJSContextOptions;

   214     const bool mIsMainThread;

   215   };

   216 };

   218 template<class WebIDLCallbackT, class XPCOMCallbackT>

   219 class CallbackObjectHolder;

   221 template<class T, class U>

   222 void ImplCycleCollectionUnlink(CallbackObjectHolder<T, U>& aField);

   224 class CallbackObjectHolderBase

   225 {

   226 protected:

   227   // Returns null on all failures

   228   already_AddRefed<nsISupports> ToXPCOMCallback(CallbackObject* aCallback,

   229                                                 const nsIID& aIID) const;

   230 };

   232 template<class WebIDLCallbackT, class XPCOMCallbackT>

   233 class CallbackObjectHolder : CallbackObjectHolderBase

   234 {

   235   /**

   236    * A class which stores either a WebIDLCallbackT* or an XPCOMCallbackT*.  Both

   237    * types must inherit from nsISupports.  The pointer that's stored can be

   238    * null.

   239    *

   240    * When storing a WebIDLCallbackT*, mPtrBits is set to the pointer value.

   241    * When storing an XPCOMCallbackT*, mPtrBits is the pointer value with low bit

   242    * set.

   243    */

   244 public:

   245   explicit CallbackObjectHolder(WebIDLCallbackT* aCallback)

   246     : mPtrBits(reinterpret_cast<uintptr_t>(aCallback))

   247   {

   248     NS_IF_ADDREF(aCallback);

   249   }

   251   explicit CallbackObjectHolder(XPCOMCallbackT* aCallback)

   252     : mPtrBits(reinterpret_cast<uintptr_t>(aCallback) | XPCOMCallbackFlag)

   253   {

   254     NS_IF_ADDREF(aCallback);

   255   }

   257   explicit CallbackObjectHolder(const CallbackObjectHolder& aOther)

   258     : mPtrBits(aOther.mPtrBits)

   259   {

   260     NS_IF_ADDREF(GetISupports());

   261   }

   263   CallbackObjectHolder()

   264     : mPtrBits(0)

   265   {}

   267   ~CallbackObjectHolder()

   268   {

   269     UnlinkSelf();

   270   }

   272   void operator=(WebIDLCallbackT* aCallback)

   273   {

   274     UnlinkSelf();

   275     mPtrBits = reinterpret_cast<uintptr_t>(aCallback);

   276     NS_IF_ADDREF(aCallback);

   277   }

   279   void operator=(XPCOMCallbackT* aCallback)

   280   {

   281     UnlinkSelf();

   282     mPtrBits = reinterpret_cast<uintptr_t>(aCallback) | XPCOMCallbackFlag;

   283     NS_IF_ADDREF(aCallback);

   284   }

   286   void operator=(const CallbackObjectHolder& aOther)

   287   {

   288     UnlinkSelf();

   289     mPtrBits = aOther.mPtrBits;

   290     NS_IF_ADDREF(GetISupports());

   291   }

   293   nsISupports* GetISupports() const

   294   {

   295     return reinterpret_cast<nsISupports*>(mPtrBits & ~XPCOMCallbackFlag);

   296   }

   298   // Boolean conversion operator so people can use this in boolean tests

   299   operator bool() const

   300   {

   301     return GetISupports();

   302   }

   304   // Even if HasWebIDLCallback returns true, GetWebIDLCallback() might still

   305   // return null.

   306   bool HasWebIDLCallback() const

   307   {

   308     return !(mPtrBits & XPCOMCallbackFlag);

   309   }

   311   WebIDLCallbackT* GetWebIDLCallback() const

   312   {

   313     MOZ_ASSERT(HasWebIDLCallback());

   314     return reinterpret_cast<WebIDLCallbackT*>(mPtrBits);

   315   }

   317   XPCOMCallbackT* GetXPCOMCallback() const

   318   {

   319     MOZ_ASSERT(!HasWebIDLCallback());

   320     return reinterpret_cast<XPCOMCallbackT*>(mPtrBits & ~XPCOMCallbackFlag);

   321   }

   323   bool operator==(WebIDLCallbackT* aOtherCallback) const

   324   {

   325     if (!aOtherCallback) {

   326       // If other is null, then we must be null to be equal.

   327       return !GetISupports();

   328     }

   330     if (!HasWebIDLCallback() || !GetWebIDLCallback()) {

   331       // If other is non-null, then we can't be equal if we have a

   332       // non-WebIDL callback or a null callback.

   333       return false;

   334     }

   336     return *GetWebIDLCallback() == *aOtherCallback;

   337   }

   339   bool operator==(XPCOMCallbackT* aOtherCallback) const

   340   {

   341     return (!aOtherCallback && !GetISupports()) ||

   342       (!HasWebIDLCallback() && GetXPCOMCallback() == aOtherCallback);

   343   }

   345   bool operator==(const CallbackObjectHolder& aOtherCallback) const

   346   {

   347     if (aOtherCallback.HasWebIDLCallback()) {

   348       return *this == aOtherCallback.GetWebIDLCallback();

   349     }

   351     return *this == aOtherCallback.GetXPCOMCallback();

   352   }

   354   // Try to return an XPCOMCallbackT version of this object.

   355   already_AddRefed<XPCOMCallbackT> ToXPCOMCallback() const

   356   {

   357     if (!HasWebIDLCallback()) {

   358       nsRefPtr<XPCOMCallbackT> callback = GetXPCOMCallback();

   359       return callback.forget();

   360     }

   362     nsCOMPtr<nsISupports> supp =

   363       CallbackObjectHolderBase::ToXPCOMCallback(GetWebIDLCallback(),

   364                                                 NS_GET_TEMPLATE_IID(XPCOMCallbackT));

   365     // ToXPCOMCallback already did the right QI for us.

   366     return supp.forget().downcast<XPCOMCallbackT>();

   367   }

   369   // Try to return a WebIDLCallbackT version of this object.

   370   already_AddRefed<WebIDLCallbackT> ToWebIDLCallback() const

   371   {

   372     if (HasWebIDLCallback()) {

   373       nsRefPtr<WebIDLCallbackT> callback = GetWebIDLCallback();

   374       return callback.forget();

   375     }

   376     return nullptr;

   377   }

   379 private:

   380   static const uintptr_t XPCOMCallbackFlag = 1u;

   382   friend void

   383   ImplCycleCollectionUnlink<WebIDLCallbackT,

   384                             XPCOMCallbackT>(CallbackObjectHolder& aField);

   386   void UnlinkSelf()

   387   {

   388     // NS_IF_RELEASE because we might have been unlinked before

   389     nsISupports* ptr = GetISupports();

   390     NS_IF_RELEASE(ptr);

   391     mPtrBits = 0;

   392   }

   394   uintptr_t mPtrBits;

   395 };

   397 NS_DEFINE_STATIC_IID_ACCESSOR(CallbackObject, DOM_CALLBACKOBJECT_IID)

   399 template<class T, class U>

   400 inline void

   401 ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback& aCallback,

   402                             CallbackObjectHolder<T, U>& aField,

   403                             const char* aName,

   404                             uint32_t aFlags = 0)

   405 {

   406   CycleCollectionNoteChild(aCallback, aField.GetISupports(), aName, aFlags);

   407 }

   409 template<class T, class U>

   410 void

   411 ImplCycleCollectionUnlink(CallbackObjectHolder<T, U>& aField)

   412 {

   413   aField.UnlinkSelf();

   414 }

   416 } // namespace dom

   417 } // namespace mozilla

   419 #endif // mozilla_dom_CallbackObject_h

The Tor Browser / file revision

dom/bindings/CallbackObject.h@b8a032363ba2

dom/bindings/CallbackObject.h