gecko/dom/bindings/CallbackFunction.h

143 lines
4.0 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 types in C++.
*
* This class implements common functionality like lifetime
* management, initialization with the callable, and setup of the call
* environment. Subclasses corresponding to particular callback
* function types should provide a Call() method that actually does
* the call.
*/
#pragma once
#include "nsISupports.h"
#include "nsISupportsImpl.h"
#include "nsCycleCollectionParticipant.h"
#include "jsapi.h"
#include "jswrapper.h"
#include "mozilla/Assertions.h"
#include "mozilla/Util.h"
#include "nsContentUtils.h"
#include "nsWrapperCache.h"
#include "nsJSEnvironment.h"
#include "xpcpublic.h"
namespace mozilla {
namespace dom {
class CallbackFunction : public nsISupports
{
public:
NS_DECL_CYCLE_COLLECTING_ISUPPORTS
NS_DECL_CYCLE_COLLECTION_SCRIPT_HOLDER_CLASS(CallbackFunction)
/**
* Create a CallbackFunction. aCallable is the callable we're wrapping.
* aOwner is the object that will be receiving this CallbackFunction as a
* method argument, if any. We need this so we can store our callable in the
* same compartment as our owner. If *aInited is set to false, an exception
* has been thrown.
*/
CallbackFunction(JSContext* cx, JSObject* aOwner, JSObject* aCallable,
bool* aInited)
: mCallable(nullptr)
{
MOZ_ASSERT(JS_ObjectIsCallable(cx, aCallable));
// 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, &aCallable)) {
*aInited = false;
return;
}
}
// Set mCallable before we hold, on the off chance that a GC could somehow
// happen in there... (which would be pretty odd, granted).
mCallable = aCallable;
NS_HOLD_JS_OBJECTS(this, CallbackFunction);
*aInited = true;
}
virtual ~CallbackFunction()
{
DropCallback();
}
JSObject* Callable() const
{
xpc_UnmarkGrayObject(mCallable);
return mCallable;
}
protected:
void DropCallback()
{
if (mCallable) {
NS_DROP_JS_OBJECTS(this, CallbackFunction);
mCallable = nullptr;
}
}
JSObject* mCallable;
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);
~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;
};
};
} // namespace dom
} // namespace mozilla