/usr/include/thunderbird/mozilla/dom/CallbackObject.h is in thunderbird-dev 1:52.8.0-1~deb8u1.
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/* 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/. */
/**
* A common base class for representing WebIDL callback function and
* callback interface types in C++.
*
* This class implements common functionality like lifetime
* management, initialization with the JS object, and setup of the
* call environment. Subclasses are responsible for providing methods
* that do the call into JS as needed.
*/
#ifndef mozilla_dom_CallbackObject_h
#define mozilla_dom_CallbackObject_h
#include "nsISupports.h"
#include "nsISupportsImpl.h"
#include "nsCycleCollectionParticipant.h"
#include "jswrapper.h"
#include "mozilla/Assertions.h"
#include "mozilla/ErrorResult.h"
#include "mozilla/HoldDropJSObjects.h"
#include "mozilla/MemoryReporting.h"
#include "mozilla/OwningNonNull.h"
#include "mozilla/dom/ScriptSettings.h"
#include "nsWrapperCache.h"
#include "nsJSEnvironment.h"
#include "xpcpublic.h"
#include "jsapi.h"
#include "js/TracingAPI.h"
namespace mozilla {
namespace dom {
#define DOM_CALLBACKOBJECT_IID \
{ 0xbe74c190, 0x6d76, 0x4991, \
{ 0x84, 0xb9, 0x65, 0x06, 0x99, 0xe6, 0x93, 0x2b } }
class CallbackObject : public nsISupports
{
public:
NS_DECLARE_STATIC_IID_ACCESSOR(DOM_CALLBACKOBJECT_IID)
NS_DECL_CYCLE_COLLECTING_ISUPPORTS
NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(CallbackObject)
// The caller may pass a global object which will act as an override for the
// incumbent script settings object when the callback is invoked (overriding
// the entry point computed from aCallback). If no override is required, the
// caller should pass null. |aCx| is used to capture the current
// stack, which is later used as an async parent when the callback
// is invoked. aCx can be nullptr, in which case no stack is
// captured.
explicit CallbackObject(JSContext* aCx, JS::Handle<JSObject*> aCallback,
nsIGlobalObject* aIncumbentGlobal)
{
if (aCx && JS::ContextOptionsRef(aCx).asyncStack()) {
JS::RootedObject stack(aCx);
if (!JS::CaptureCurrentStack(aCx, &stack)) {
JS_ClearPendingException(aCx);
}
Init(aCallback, stack, aIncumbentGlobal);
} else {
Init(aCallback, nullptr, aIncumbentGlobal);
}
}
// Instead of capturing the current stack to use as an async parent when the
// callback is invoked, the caller can use this overload to pass in a stack
// for that purpose.
explicit CallbackObject(JS::Handle<JSObject*> aCallback,
JS::Handle<JSObject*> aAsyncStack,
nsIGlobalObject* aIncumbentGlobal)
{
Init(aCallback, aAsyncStack, aIncumbentGlobal);
}
JS::Handle<JSObject*> Callback() const
{
mCallback.exposeToActiveJS();
return CallbackPreserveColor();
}
JSObject* GetCreationStack() const
{
return mCreationStack;
}
void MarkForCC()
{
mCallback.exposeToActiveJS();
mCreationStack.exposeToActiveJS();
}
/*
* This getter does not change the color of the JSObject meaning that the
* object returned is not guaranteed to be kept alive past the next CC.
*
* This should only be called if you are certain that the return value won't
* be passed into a JS API function and that it won't be stored without being
* rooted (or otherwise signaling the stored value to the CC).
*/
JS::Handle<JSObject*> CallbackPreserveColor() const
{
// Calling fromMarkedLocation() is safe because we trace our mCallback, and
// because the value of mCallback cannot change after if has been set.
return JS::Handle<JSObject*>::fromMarkedLocation(mCallback.address());
}
/*
* If the callback is known to be non-gray, then this method can be
* used instead of Callback() to avoid the overhead of
* ExposeObjectToActiveJS().
*/
JS::Handle<JSObject*> CallbackKnownNotGray() const
{
MOZ_ASSERT(!JS::ObjectIsMarkedGray(mCallback));
return CallbackPreserveColor();
}
nsIGlobalObject* IncumbentGlobalOrNull() const
{
return mIncumbentGlobal;
}
enum ExceptionHandling {
// Report any exception and don't throw it to the caller code.
eReportExceptions,
// Throw an exception to the caller code if the thrown exception is a
// binding object for a DOMError or DOMException from the caller's scope,
// otherwise report it.
eRethrowContentExceptions,
// Throw exceptions to the caller code, unless the caller compartment is
// provided, the exception is not a DOMError or DOMException from the
// caller compartment, and the caller compartment does not subsume our
// unwrapped callback.
eRethrowExceptions
};
size_t SizeOfIncludingThis(mozilla::MallocSizeOf aMallocSizeOf) const
{
return aMallocSizeOf(this);
}
protected:
virtual ~CallbackObject()
{
DropJSObjects();
}
explicit CallbackObject(CallbackObject* aCallbackObject)
{
Init(aCallbackObject->mCallback, aCallbackObject->mCreationStack,
aCallbackObject->mIncumbentGlobal);
}
bool operator==(const CallbackObject& aOther) const
{
JSObject* thisObj =
js::UncheckedUnwrap(CallbackPreserveColor());
JSObject* otherObj =
js::UncheckedUnwrap(aOther.CallbackPreserveColor());
return thisObj == otherObj;
}
private:
inline void InitNoHold(JSObject* aCallback, JSObject* aCreationStack,
nsIGlobalObject* aIncumbentGlobal)
{
MOZ_ASSERT(aCallback && !mCallback);
// Set script objects before we hold, on the off chance that a GC could
// somehow happen in there... (which would be pretty odd, granted).
mCallback = aCallback;
mCreationStack = aCreationStack;
if (aIncumbentGlobal) {
mIncumbentGlobal = aIncumbentGlobal;
mIncumbentJSGlobal = aIncumbentGlobal->GetGlobalJSObject();
}
}
inline void Init(JSObject* aCallback, JSObject* aCreationStack,
nsIGlobalObject* aIncumbentGlobal)
{
InitNoHold(aCallback, aCreationStack, aIncumbentGlobal);
mozilla::HoldJSObjects(this);
}
inline void ClearJSReferences()
{
mCallback = nullptr;
mCreationStack = nullptr;
mIncumbentJSGlobal = nullptr;
}
CallbackObject(const CallbackObject&) = delete;
CallbackObject& operator =(const CallbackObject&) = delete;
protected:
void DropJSObjects()
{
MOZ_ASSERT_IF(mIncumbentJSGlobal, mCallback);
if (mCallback) {
ClearJSReferences();
mozilla::DropJSObjects(this);
}
}
// For use from subclasses that want to be usable with Rooted.
void Trace(JSTracer* aTracer);
// For use from subclasses that want to be traced for a bit then possibly
// switch to HoldJSObjects. If we have more than one owner, this will
// HoldJSObjects; otherwise it will just forget all our JS references.
void HoldJSObjectsIfMoreThanOneOwner();
// Struct used as a way to force a CallbackObject constructor to not call
// HoldJSObjects. We're putting it here so that CallbackObject subclasses will
// have access to it, but outside code will not.
//
// Places that use this need to ensure that the callback is traced (e.g. via a
// Rooted) until the HoldJSObjects call happens.
struct FastCallbackConstructor {
};
// Just like the public version without the FastCallbackConstructor argument,
// except for not calling HoldJSObjects. If you use this, you MUST ensure
// that the object is traced until the HoldJSObjects happens!
CallbackObject(JSContext* aCx, JS::Handle<JSObject*> aCallback,
nsIGlobalObject* aIncumbentGlobal,
const FastCallbackConstructor&)
{
if (aCx && JS::ContextOptionsRef(aCx).asyncStack()) {
JS::RootedObject stack(aCx);
if (!JS::CaptureCurrentStack(aCx, &stack)) {
JS_ClearPendingException(aCx);
}
InitNoHold(aCallback, stack, aIncumbentGlobal);
} else {
InitNoHold(aCallback, nullptr, aIncumbentGlobal);
}
}
// mCallback is not unwrapped, so it can be a cross-compartment-wrapper.
// This is done to ensure that, if JS code can't call a callback f(), or get
// its members, directly itself, this code won't call f(), or get its members,
// on the code's behalf.
JS::Heap<JSObject*> mCallback;
JS::Heap<JSObject*> mCreationStack;
// Ideally, we'd just hold a reference to the nsIGlobalObject, since that's
// what we need to pass to AutoIncumbentScript. Unfortunately, that doesn't
// hold the actual JS global alive. So we maintain an additional pointer to
// the JS global itself so that we can trace it.
//
// At some point we should consider trying to make native globals hold their
// scripted global alive, at which point we can get rid of the duplication
// here.
nsCOMPtr<nsIGlobalObject> mIncumbentGlobal;
JS::TenuredHeap<JSObject*> mIncumbentJSGlobal;
class MOZ_STACK_CLASS CallSetup
{
/**
* A class that performs whatever setup we need to safely make a
* call while this class is on the stack, After the constructor
* returns, the call is safe to make if GetContext() returns
* non-null.
*/
public:
// If aExceptionHandling == eRethrowContentExceptions then aCompartment
// needs to be set to the compartment in which exceptions will be rethrown.
//
// If aExceptionHandling == eRethrowExceptions then aCompartment may be set
// to the compartment in which exceptions will be rethrown. In that case
// they will only be rethrown if that compartment's principal subsumes the
// principal of our (unwrapped) callback.
CallSetup(CallbackObject* aCallback, ErrorResult& aRv,
const char* aExecutionReason,
ExceptionHandling aExceptionHandling,
JSCompartment* aCompartment = nullptr,
bool aIsJSImplementedWebIDL = false);
~CallSetup();
JSContext* GetContext() const
{
return mCx;
}
private:
// We better not get copy-constructed
CallSetup(const CallSetup&) = delete;
bool ShouldRethrowException(JS::Handle<JS::Value> aException);
// Members which can go away whenever
JSContext* mCx;
// Caller's compartment. This will only have a sensible value if
// mExceptionHandling == eRethrowContentExceptions or eRethrowExceptions.
JSCompartment* mCompartment;
// And now members whose construction/destruction order we need to control.
Maybe<AutoEntryScript> mAutoEntryScript;
Maybe<AutoIncumbentScript> mAutoIncumbentScript;
Maybe<JS::Rooted<JSObject*> > mRootedCallable;
// Members which are used to set the async stack.
Maybe<JS::Rooted<JSObject*>> mAsyncStack;
Maybe<JS::AutoSetAsyncStackForNewCalls> mAsyncStackSetter;
// Can't construct a JSAutoCompartment without a JSContext either. Also,
// Put mAc after mAutoEntryScript so that we exit the compartment before
// we pop the JSContext. Though in practice we'll often manually order
// those two things.
Maybe<JSAutoCompartment> mAc;
// An ErrorResult to possibly re-throw exceptions on and whether
// we should re-throw them.
ErrorResult& mErrorResult;
const ExceptionHandling mExceptionHandling;
const bool mIsMainThread;
};
};
template<class WebIDLCallbackT, class XPCOMCallbackT>
class CallbackObjectHolder;
template<class T, class U>
void ImplCycleCollectionUnlink(CallbackObjectHolder<T, U>& aField);
class CallbackObjectHolderBase
{
protected:
// Returns null on all failures
already_AddRefed<nsISupports> ToXPCOMCallback(CallbackObject* aCallback,
const nsIID& aIID) const;
};
template<class WebIDLCallbackT, class XPCOMCallbackT>
class CallbackObjectHolder : CallbackObjectHolderBase
{
/**
* A class which stores either a WebIDLCallbackT* or an XPCOMCallbackT*. Both
* types must inherit from nsISupports. The pointer that's stored can be
* null.
*
* When storing a WebIDLCallbackT*, mPtrBits is set to the pointer value.
* When storing an XPCOMCallbackT*, mPtrBits is the pointer value with low bit
* set.
*/
public:
explicit CallbackObjectHolder(WebIDLCallbackT* aCallback)
: mPtrBits(reinterpret_cast<uintptr_t>(aCallback))
{
NS_IF_ADDREF(aCallback);
}
explicit CallbackObjectHolder(XPCOMCallbackT* aCallback)
: mPtrBits(reinterpret_cast<uintptr_t>(aCallback) | XPCOMCallbackFlag)
{
NS_IF_ADDREF(aCallback);
}
CallbackObjectHolder(CallbackObjectHolder&& aOther)
: mPtrBits(aOther.mPtrBits)
{
aOther.mPtrBits = 0;
static_assert(sizeof(CallbackObjectHolder) == sizeof(void*),
"This object is expected to be as small as a pointer, and it "
"is currently passed by value in various places. If it is "
"bloating, we may want to pass it by reference then.");
}
CallbackObjectHolder(const CallbackObjectHolder& aOther) = delete;
CallbackObjectHolder()
: mPtrBits(0)
{}
~CallbackObjectHolder()
{
UnlinkSelf();
}
void operator=(WebIDLCallbackT* aCallback)
{
UnlinkSelf();
mPtrBits = reinterpret_cast<uintptr_t>(aCallback);
NS_IF_ADDREF(aCallback);
}
void operator=(XPCOMCallbackT* aCallback)
{
UnlinkSelf();
mPtrBits = reinterpret_cast<uintptr_t>(aCallback) | XPCOMCallbackFlag;
NS_IF_ADDREF(aCallback);
}
void operator=(CallbackObjectHolder&& aOther)
{
UnlinkSelf();
mPtrBits = aOther.mPtrBits;
aOther.mPtrBits = 0;
}
void operator=(const CallbackObjectHolder& aOther) = delete;
nsISupports* GetISupports() const
{
return reinterpret_cast<nsISupports*>(mPtrBits & ~XPCOMCallbackFlag);
}
// Boolean conversion operator so people can use this in boolean tests
explicit operator bool() const
{
return GetISupports();
}
CallbackObjectHolder Clone() const
{
CallbackObjectHolder result;
result.mPtrBits = mPtrBits;
NS_IF_ADDREF(GetISupports());
return result;
}
// Even if HasWebIDLCallback returns true, GetWebIDLCallback() might still
// return null.
bool HasWebIDLCallback() const
{
return !(mPtrBits & XPCOMCallbackFlag);
}
WebIDLCallbackT* GetWebIDLCallback() const
{
MOZ_ASSERT(HasWebIDLCallback());
return reinterpret_cast<WebIDLCallbackT*>(mPtrBits);
}
XPCOMCallbackT* GetXPCOMCallback() const
{
MOZ_ASSERT(!HasWebIDLCallback());
return reinterpret_cast<XPCOMCallbackT*>(mPtrBits & ~XPCOMCallbackFlag);
}
bool operator==(WebIDLCallbackT* aOtherCallback) const
{
if (!aOtherCallback) {
// If other is null, then we must be null to be equal.
return !GetISupports();
}
if (!HasWebIDLCallback() || !GetWebIDLCallback()) {
// If other is non-null, then we can't be equal if we have a
// non-WebIDL callback or a null callback.
return false;
}
return *GetWebIDLCallback() == *aOtherCallback;
}
bool operator==(XPCOMCallbackT* aOtherCallback) const
{
return (!aOtherCallback && !GetISupports()) ||
(!HasWebIDLCallback() && GetXPCOMCallback() == aOtherCallback);
}
bool operator==(const CallbackObjectHolder& aOtherCallback) const
{
if (aOtherCallback.HasWebIDLCallback()) {
return *this == aOtherCallback.GetWebIDLCallback();
}
return *this == aOtherCallback.GetXPCOMCallback();
}
// Try to return an XPCOMCallbackT version of this object.
already_AddRefed<XPCOMCallbackT> ToXPCOMCallback() const
{
if (!HasWebIDLCallback()) {
RefPtr<XPCOMCallbackT> callback = GetXPCOMCallback();
return callback.forget();
}
nsCOMPtr<nsISupports> supp =
CallbackObjectHolderBase::ToXPCOMCallback(GetWebIDLCallback(),
NS_GET_TEMPLATE_IID(XPCOMCallbackT));
// ToXPCOMCallback already did the right QI for us.
return supp.forget().downcast<XPCOMCallbackT>();
}
// Try to return a WebIDLCallbackT version of this object.
already_AddRefed<WebIDLCallbackT> ToWebIDLCallback() const
{
if (HasWebIDLCallback()) {
RefPtr<WebIDLCallbackT> callback = GetWebIDLCallback();
return callback.forget();
}
return nullptr;
}
private:
static const uintptr_t XPCOMCallbackFlag = 1u;
friend void
ImplCycleCollectionUnlink<WebIDLCallbackT,
XPCOMCallbackT>(CallbackObjectHolder& aField);
void UnlinkSelf()
{
// NS_IF_RELEASE because we might have been unlinked before
nsISupports* ptr = GetISupports();
NS_IF_RELEASE(ptr);
mPtrBits = 0;
}
uintptr_t mPtrBits;
};
NS_DEFINE_STATIC_IID_ACCESSOR(CallbackObject, DOM_CALLBACKOBJECT_IID)
template<class T, class U>
inline void
ImplCycleCollectionTraverse(nsCycleCollectionTraversalCallback& aCallback,
CallbackObjectHolder<T, U>& aField,
const char* aName,
uint32_t aFlags = 0)
{
CycleCollectionNoteChild(aCallback, aField.GetISupports(), aName, aFlags);
}
template<class T, class U>
void
ImplCycleCollectionUnlink(CallbackObjectHolder<T, U>& aField)
{
aField.UnlinkSelf();
}
// T is expected to be a RefPtr or OwningNonNull around a CallbackObject
// subclass. This class is used in bindings to safely handle Fast* callbacks;
// it ensures that the callback is traced, and that if something is holding onto
// the callback when we're done with it HoldJSObjects is called.
template<typename T>
class RootedCallback : public JS::Rooted<T>
{
public:
explicit RootedCallback(JSContext* cx)
: JS::Rooted<T>(cx)
{}
// We need a way to make assignment from pointers (how we're normally used)
// work.
template<typename S>
void operator=(S* arg)
{
this->get().operator=(arg);
}
// But nullptr can't use the above template, because it doesn't know which S
// to select. So we need a special overload for nullptr.
void operator=(decltype(nullptr) arg)
{
this->get().operator=(arg);
}
// Codegen relies on being able to do Callback() on us.
JS::Handle<JSObject*> Callback() const
{
return this->get()->Callback();
}
~RootedCallback()
{
// Ensure that our callback starts holding on to its own JS objects as
// needed. Having to null-check here when T is OwningNonNull is a bit
// silly, but it's simpler than creating two separate RootedCallback
// instantiations for OwningNonNull and RefPtr.
if (IsInitialized(this->get())) {
this->get()->HoldJSObjectsIfMoreThanOneOwner();
}
}
private:
template<typename U>
static bool IsInitialized(U& aArg); // Not implemented
template<typename U>
static bool IsInitialized(RefPtr<U>& aRefPtr)
{
return aRefPtr;
}
template<typename U>
static bool IsInitialized(OwningNonNull<U>& aOwningNonNull)
{
return aOwningNonNull.isInitialized();
}
};
} // namespace dom
} // namespace mozilla
#endif // mozilla_dom_CallbackObject_h
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