gecko/dom/bindings/CallbackObject.h

383 lines
11 KiB
C++

/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* vim:set ts=2 sw=2 sts=2 et cindent: */
/* 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 "jsapi.h"
#include "jswrapper.h"
#include "mozilla/Assertions.h"
#include "mozilla/ErrorResult.h"
#include "mozilla/Util.h"
#include "nsContentUtils.h" // nsCxPusher
#include "nsWrapperCache.h"
#include "nsJSEnvironment.h"
#include "xpcpublic.h"
#include "nsLayoutStatics.h"
namespace mozilla {
namespace dom {
class CallbackObject : public nsISupports
{
public:
NS_DECL_CYCLE_COLLECTING_ISUPPORTS
NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(CallbackObject)
/**
* Create a CallbackObject. aCallback is the callback object we're wrapping.
* aOwner is the object that will be receiving this CallbackObject as a method
* argument, if any. We need this so we can store our callback object in the
* same compartment as our owner. If *aInited is set to false, an exception
* has been thrown.
*/
CallbackObject(JSContext* cx, JSObject* aOwner, JSObject* aCallback,
bool* aInited)
: mCallback(nullptr)
{
// If aOwner is not null, enter the compartment of aOwner's
// underlying object.
if (aOwner) {
aOwner = js::UnwrapObject(aOwner);
JSAutoCompartment ac(cx, aOwner);
if (!JS_WrapObject(cx, &aCallback)) {
*aInited = false;
return;
}
}
// Set mCallback before we hold, on the off chance that a GC could somehow
// happen in there... (which would be pretty odd, granted).
mCallback = aCallback;
// Make sure we'll be able to drop as needed
nsLayoutStatics::AddRef();
NS_HOLD_JS_OBJECTS(this, CallbackObject);
*aInited = true;
}
virtual ~CallbackObject()
{
DropCallback();
}
JSObject* Callback() const
{
xpc_UnmarkGrayObject(mCallback);
return mCallback;
}
/*
* 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).
*/
JSObject* CallbackPreserveColor() const
{
return mCallback;
}
enum ExceptionHandling {
eReportExceptions,
eRethrowExceptions
};
protected:
explicit CallbackObject(CallbackObject* aCallbackFunction)
: mCallback(aCallbackFunction->mCallback)
{
// Set mCallback before we hold, on the off chance that a GC could somehow
// happen in there... (which would be pretty odd, granted).
// Make sure we'll be able to drop as needed
nsLayoutStatics::AddRef();
NS_HOLD_JS_OBJECTS(this, CallbackObject);
}
void DropCallback()
{
if (mCallback) {
mCallback = nullptr;
NS_DROP_JS_OBJECTS(this, CallbackObject);
nsLayoutStatics::Release();
}
}
JSObject* mCallback;
class NS_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:
CallSetup(JSObject* const aCallable, ErrorResult& aRv,
ExceptionHandling aExceptionHandling);
~CallSetup();
JSContext* GetContext() const
{
return mCx;
}
private:
// We better not get copy-constructed
CallSetup(const CallSetup&) MOZ_DELETE;
// Members which can go away whenever
JSContext* mCx;
nsCOMPtr<nsIScriptContext> mCtx;
// And now members whose construction/destruction order we need to control.
// Put our nsAutoMicrotask first, so it gets destroyed after everything else
// is gone
nsAutoMicroTask mMt;
// Can't construct an XPCAutoRequest until we have a JSContext, so
// this needs to be a Maybe.
Maybe<XPCAutoRequest> mAr;
// Can't construct a TerminationFuncHolder without an nsJSContext. But we
// generally want its destructor to come after the destructor of mCxPusher.
Maybe<nsJSContext::TerminationFuncHolder> mTerminationFuncHolder;
nsCxPusher mCxPusher;
// Can't construct a JSAutoCompartment without a JSContext either. Also,
// Put mAc after mCxPusher 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;
uint32_t mSavedJSContextOptions;
};
};
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);
};
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);
}
explicit CallbackObjectHolder(const CallbackObjectHolder& aOther)
: mPtrBits(aOther.mPtrBits)
{
NS_IF_ADDREF(GetISupports());
}
CallbackObjectHolder()
: mPtrBits(0)
{}
~CallbackObjectHolder()
{
UnlinkSelf();
}
nsISupports* GetISupports() const
{
return reinterpret_cast<nsISupports*>(mPtrBits & ~XPCOMCallbackFlag);
}
// 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;
}
JSObject* thisObj =
js::UnwrapObject(GetWebIDLCallback()->CallbackPreserveColor());
JSObject* otherObj =
js::UnwrapObject(aOtherCallback->CallbackPreserveColor());
return thisObj == otherObj;
}
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()
{
if (!HasWebIDLCallback()) {
nsRefPtr<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 static_cast<XPCOMCallbackT*>(supp.forget().get());
}
// Try to return a WebIDLCallbackT version of this object.
already_AddRefed<WebIDLCallbackT> ToWebIDLCallback()
{
if (HasWebIDLCallback()) {
nsRefPtr<WebIDLCallbackT> callback = GetWebIDLCallback();
return callback.forget();
}
XPCOMCallbackT* callback = GetXPCOMCallback();
if (!callback) {
return nullptr;
}
nsCOMPtr<nsIXPConnectWrappedJS> wrappedJS = do_QueryInterface(callback);
if (!wrappedJS) {
return nullptr;
}
JSObject* obj;
if (NS_FAILED(wrappedJS->GetJSObject(&obj)) || !obj) {
return nullptr;
}
SafeAutoJSContext cx;
JSAutoCompartment ac(cx, obj);
bool inited;
nsRefPtr<WebIDLCallbackT> newCallback =
new WebIDLCallbackT(cx, nullptr, obj, &inited);
if (!inited) {
return nullptr;
}
return newCallback.forget();
}
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;
};
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();
}
} // namespace dom
} // namespace mozilla
#endif // mozilla_dom_CallbackObject_h