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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
/* 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/. */
#ifndef mozilla_HoldDropJSObjects_h
#define mozilla_HoldDropJSObjects_h
#include <type_traits>
#include "nsCycleCollectionNoteChild.h"
class nsISupports;
class nsScriptObjectTracer;
class nsCycleCollectionParticipant;
class nsWrapperCache;
namespace JS {
class Zone;
}
// Only HoldJSObjects and DropJSObjects should be called directly.
namespace mozilla {
class JSHolderList;
struct JSHolderListEntry;
// Used to store the position of the holder when it is stored in JSHolderList.
class JSHolderKey {
friend class JSHolderList;
JSHolderListEntry* mEntry = nullptr;
};
// Base class for holders to derive from that includes a JSHolderKey.
class JSHolderBase {
public:
JSHolderKey mJSHolderKey;
};
namespace cyclecollector {
void HoldJSObjectsImpl(void* aHolder, nsScriptObjectTracer* aTracer,
JS::Zone* aZone = nullptr);
void HoldJSObjectsWithKeyImpl(void* aHolder, nsScriptObjectTracer* aTracer,
JSHolderKey* aKey);
void HoldJSObjectsImpl(nsISupports* aHolder);
void HoldJSObjectsWithKeyImpl(nsISupports* aHolder, JSHolderKey* aKey);
void DropJSObjectsImpl(void* aHolder);
void DropJSObjectsWithKeyImpl(void* aHolder, JSHolderKey* aKey);
void DropJSObjectsImpl(nsISupports* aHolder);
void DropJSObjectsWithKeyImpl(nsISupports* aHolder, JSHolderKey* aKey);
} // namespace cyclecollector
template <class T, bool isISupports = std::is_base_of_v<nsISupports, T>,
typename P = typename T::NS_CYCLE_COLLECTION_INNERCLASS>
struct HoldDropJSObjectsHelper {
static void Hold(T* aHolder) {
cyclecollector::HoldJSObjectsImpl(aHolder,
NS_CYCLE_COLLECTION_PARTICIPANT(T));
}
static void Drop(T* aHolder) { cyclecollector::DropJSObjectsImpl(aHolder); }
};
template <class T>
struct HoldDropJSObjectsHelper<T, true> {
static void Hold(T* aHolder) {
cyclecollector::HoldJSObjectsImpl(ToSupports(aHolder));
}
static void Drop(T* aHolder) {
cyclecollector::DropJSObjectsImpl(ToSupports(aHolder));
}
};
template <class T, bool isISupports = std::is_base_of_v<nsISupports, T>,
typename P = typename T::NS_CYCLE_COLLECTION_INNERCLASS>
struct HoldDropJSObjectsWithKeyHelper {
static void Hold(T* aHolder) {
cyclecollector::HoldJSObjectsWithKeyImpl(
aHolder, NS_CYCLE_COLLECTION_PARTICIPANT(T), &aHolder->mJSHolderKey);
}
static void Drop(T* aHolder) {
cyclecollector::DropJSObjectsWithKeyImpl(aHolder, &aHolder->mJSHolderKey);
}
};
template <class T>
struct HoldDropJSObjectsWithKeyHelper<T, true> {
static void Hold(T* aHolder) {
cyclecollector::HoldJSObjectsWithKeyImpl(ToSupports(aHolder),
&aHolder->mJSHolderKey);
}
static void Drop(T* aHolder) {
cyclecollector::DropJSObjectsWithKeyImpl(ToSupports(aHolder),
&aHolder->mJSHolderKey);
}
};
/**
Classes that hold strong references to JS GC things such as `JSObjects` and
`JS::Values` (e.g. `JS::Heap<JSObject*> mFoo;`) must use these, generally by
calling `HoldJSObjects(this)` and `DropJSObjects(this)` in the ctor and dtor
respectively.
For classes that are wrapper cached and hold no other strong references to JS
GC things, there's no need to call these; it will be taken care of
automatically by nsWrapperCache.
The Hold/DropJSObjectsWithKey variants require that the holder derives from
JSHolderBase. These are more efficient as they skip a hash table lookup on add
and remove. However the base class adds a word of storage to the object itself
that so there is a space cost regardless of whether HoldJSObjects has been
called.
**/
template <class T>
void HoldJSObjects(T* aHolder) {
static_assert(!std::is_base_of<nsCycleCollectionParticipant, T>::value,
"Don't call this on the CC participant but on the object that "
"it's for (in an Unlink implementation it's usually stored in "
"a variable named 'tmp').");
static_assert(
!std::is_base_of<JSHolderBase, T>::value,
"Use HoldJSObjectsWithKey for classes derived from JSHolderBase.");
HoldDropJSObjectsHelper<T>::Hold(aHolder);
}
template <class T>
void DropJSObjects(T* aHolder) {
static_assert(!std::is_base_of<nsCycleCollectionParticipant, T>::value,
"Don't call this on the CC participant but on the object that "
"it's for (in an Unlink implementation it's usually stored in "
"a variable named 'tmp').");
static_assert(
!std::is_base_of<JSHolderBase, T>::value,
"Use HoldJSObjectsWithKey for classes derived from JSHolderBase.");
HoldDropJSObjectsHelper<T>::Drop(aHolder);
}
template <class T>
void HoldJSObjectsWithKey(T* aHolder) {
static_assert(!std::is_base_of<nsWrapperCache, T>::value,
"Use HoldJSObjects for classes derived from nsWrapperCache.");
HoldDropJSObjectsWithKeyHelper<T>::Hold(aHolder);
}
template <class T>
void DropJSObjectsWithKey(T* aHolder) {
static_assert(!std::is_base_of<nsWrapperCache, T>::value,
"Use HoldJSObjects for classes derived from nsWrapperCache.");
HoldDropJSObjectsWithKeyHelper<T>::Drop(aHolder);
}
} // namespace mozilla
#endif // mozilla_HoldDropJSObjects_h
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