nsWrapperCache.h
/* -*- 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 nsWrapperCache_h___
#define nsWrapperCache_h___
#include "nsCycleCollectionParticipant.h"
#include "mozilla/Assertions.h"
#include "js/HeapAPI.h"
#include "js/TracingAPI.h"
#include "js/TypeDecls.h"
#include "nsISupports.h"
#include "nsISupportsUtils.h"
namespace mozilla {
namespace dom {
class ContentProcessMessageManager;
class InProcessBrowserChildMessageManager;
class BrowserChildMessageManager;
} // namespace dom
} // namespace mozilla
class SandboxPrivate;
class nsWindowRoot;
#define NS_WRAPPERCACHE_IID \
{ \
0x6f3179a1, 0x36f7, 0x4a5c, { \
0x8c, 0xf1, 0xad, 0xc8, 0x7c, 0xde, 0x3e, 0x87 \
} \
}
// There are two sets of flags used by DOM nodes. One comes from reusing the
// remaining bits of the inherited nsWrapperCache flags (mFlags), and another is
// exclusive to nsINode (mBoolFlags).
//
// Both sets of flags are 32 bits. On 64-bit platforms, this can cause two
// wasted 32-bit fields due to alignment requirements. Some compilers are
// smart enough to coalesce the fields if we make mBoolFlags the first member
// of nsINode, but others (such as MSVC) are not.
//
// So we just store mBoolFlags directly on nsWrapperCache on 64-bit platforms.
// This may waste space for some other nsWrapperCache-derived objects that have
// a 32-bit field as their first member, but those objects are unlikely to be as
// numerous or performance-critical as DOM nodes.
#ifdef HAVE_64BIT_BUILD
static_assert(sizeof(void*) == 8, "These architectures should be 64-bit");
# define BOOL_FLAGS_ON_WRAPPER_CACHE
#else
static_assert(sizeof(void*) == 4, "Only support 32-bit and 64-bit");
#endif
/**
* Class to store the wrapper for an object. This can only be used with objects
* that only have one non-security wrapper at a time (for an XPCWrappedNative
* this is usually ensured by setting an explicit parent in the PreCreate hook
* for the class).
*
* An instance of nsWrapperCache can be gotten from an object that implements
* a wrapper cache by calling QueryInterface on it. Note that this breaks XPCOM
* rules a bit (this object doesn't derive from nsISupports).
*
* The cache can store objects other than wrappers. We allow wrappers to use a
* separate JSObject to store their state (mostly expandos). If the wrapper is
* collected and we want to preserve this state we actually store the state
* object in the cache.
*
* The cache can store 3 types of objects: a DOM binding object (regular JS
* object or proxy), an nsOuterWindowProxy or an XPCWrappedNative wrapper.
*
* The finalizer for the wrapper clears the cache.
*
* A compacting GC can move the wrapper object. Pointers to moved objects are
* usually found and updated by tracing the heap, however non-preserved wrappers
* are weak references and are not traced, so another approach is
* necessary. Instead a class hook (objectMovedOp) is provided that is called
* when an object is moved and is responsible for ensuring pointers are
* updated. It does this by calling UpdateWrapper() on the wrapper
* cache. SetWrapper() asserts that the hook is implemented for any wrapper set.
*
* A number of the methods are implemented in nsWrapperCacheInlines.h because we
* have to include some JS headers that don't play nicely with the rest of the
* codebase. Include nsWrapperCacheInlines.h if you need to call those methods.
*/
class JS_HAZ_ROOTED nsWrapperCache {
public:
NS_DECLARE_STATIC_IID_ACCESSOR(NS_WRAPPERCACHE_IID)
nsWrapperCache()
: mWrapper(nullptr),
mFlags(0)
#ifdef BOOL_FLAGS_ON_WRAPPER_CACHE
,
mBoolFlags(0)
#endif
{
}
~nsWrapperCache() {
// Preserved wrappers should never end up getting cleared, but this can
// happen during shutdown when a leaked wrapper object is finalized, causing
// its wrapper to be cleared.
MOZ_ASSERT(!PreservingWrapper() || js::RuntimeIsBeingDestroyed(),
"Destroying cache with a preserved wrapper!");
}
/**
* Get the cached wrapper.
*
* This getter clears the gray bit before handing out the JSObject which means
* that the object is guaranteed to be kept alive past the next CC.
*/
JSObject* GetWrapper() const;
/**
* Get the cached wrapper.
*
* 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 JSAPI function and that it won't be stored without being
* rooted (or otherwise signaling the stored value to the CC).
*/
JSObject* GetWrapperPreserveColor() const;
/**
* Get the cached wrapper.
*
* This getter does not check whether the wrapper is dead and in the process
* of being finalized.
*
* This should only be called if you really need to see the raw contents of
* this cache, for example as part of finalization. Don't store the result
* anywhere or pass it into JSAPI functions that may cause the value to
* escape.
*/
JSObject* GetWrapperMaybeDead() const { return mWrapper; }
#ifdef DEBUG
private:
static bool HasJSObjectMovedOp(JSObject* aWrapper);
static void AssertUpdatedWrapperZone(const JSObject* aNewObject,
const JSObject* aOldObject);
public:
#endif
void SetWrapper(JSObject* aWrapper) {
MOZ_ASSERT(!PreservingWrapper(), "Clearing a preserved wrapper!");
MOZ_ASSERT(aWrapper, "Use ClearWrapper!");
MOZ_ASSERT(HasJSObjectMovedOp(aWrapper),
"Object has not provided the hook to update the wrapper if it "
"is moved");
SetWrapperJSObject(aWrapper);
}
/**
* Clear the cache.
*/
void ClearWrapper() {
// Preserved wrappers should never end up getting cleared, but this can
// happen during shutdown when a leaked wrapper object is finalized, causing
// its wrapper to be cleared.
MOZ_ASSERT(!PreservingWrapper() || js::RuntimeIsBeingDestroyed(),
"Clearing a preserved wrapper!");
SetWrapperJSObject(nullptr);
}
/**
* Clear the cache if it still contains a specific wrapper object. This should
* be called from the finalizer for the wrapper.
*/
void ClearWrapper(JSObject* obj) {
if (obj == mWrapper) {
ClearWrapper();
}
}
/**
* Update the wrapper when the object moves between globals.
*/
template <typename T>
void UpdateWrapperForNewGlobal(T* aScriptObjectHolder, JSObject* aNewWrapper);
/**
* Update the wrapper if the object it contains is moved.
*
* This method must be called from the objectMovedOp class extension hook for
* any wrapper cached object.
*/
void UpdateWrapper(JSObject* aNewObject, const JSObject* aOldObject) {
#ifdef DEBUG
AssertUpdatedWrapperZone(aNewObject, aOldObject);
#endif
if (mWrapper) {
MOZ_ASSERT(mWrapper == aOldObject);
mWrapper = aNewObject;
}
}
bool PreservingWrapper() const {
return HasWrapperFlag(WRAPPER_BIT_PRESERVED);
}
/**
* Wrap the object corresponding to this wrapper cache. If non-null is
* returned, the object has already been stored in the wrapper cache.
*/
virtual JSObject* WrapObject(JSContext* cx,
JS::Handle<JSObject*> aGivenProto) = 0;
/**
* Returns true if the object has a wrapper that is known live from the point
* of view of cycle collection.
*/
bool HasKnownLiveWrapper() const;
/**
* Returns true if the object has a known-live wrapper (from the CC point of
* view) and all the GC things it is keeping alive are already known-live from
* CC's point of view.
*/
bool HasKnownLiveWrapperAndDoesNotNeedTracing(nsISupports* aThis);
bool HasNothingToTrace(nsISupports* aThis);
/**
* Mark our wrapper, if any, as live as far as the CC is concerned.
*/
void MarkWrapperLive();
// Only meant to be called by code that preserves a wrapper.
void SetPreservingWrapper(bool aPreserve) {
if (aPreserve) {
SetWrapperFlags(WRAPPER_BIT_PRESERVED);
} else {
UnsetWrapperFlags(WRAPPER_BIT_PRESERVED);
}
}
void TraceWrapper(const TraceCallbacks& aCallbacks, void* aClosure) {
if (PreservingWrapper() && mWrapper) {
aCallbacks.Trace(this, "Preserved wrapper", aClosure);
}
}
/*
* The following methods for getting and manipulating flags allow the unused
* bits of mFlags to be used by derived classes.
*/
typedef uint32_t FlagsType;
FlagsType GetFlags() const { return mFlags & ~kWrapperFlagsMask; }
bool HasFlag(FlagsType aFlag) const {
MOZ_ASSERT((aFlag & kWrapperFlagsMask) == 0, "Bad flag mask");
return !!(mFlags & aFlag);
}
// Identical to HasFlag, but more explicit about its handling of multiple
// flags.
bool HasAnyOfFlags(FlagsType aFlags) const {
MOZ_ASSERT((aFlags & kWrapperFlagsMask) == 0, "Bad flag mask");
return !!(mFlags & aFlags);
}
bool HasAllFlags(FlagsType aFlags) const {
MOZ_ASSERT((aFlags & kWrapperFlagsMask) == 0, "Bad flag mask");
return (mFlags & aFlags) == aFlags;
}
void SetFlags(FlagsType aFlagsToSet) {
MOZ_ASSERT((aFlagsToSet & kWrapperFlagsMask) == 0, "Bad flag mask");
mFlags |= aFlagsToSet;
}
void UnsetFlags(FlagsType aFlagsToUnset) {
MOZ_ASSERT((aFlagsToUnset & kWrapperFlagsMask) == 0, "Bad flag mask");
mFlags &= ~aFlagsToUnset;
}
void PreserveWrapper(nsISupports* aScriptObjectHolder) {
if (PreservingWrapper()) {
return;
}
nsISupports* ccISupports;
aScriptObjectHolder->QueryInterface(NS_GET_IID(nsCycleCollectionISupports),
reinterpret_cast<void**>(&ccISupports));
MOZ_ASSERT(ccISupports);
nsXPCOMCycleCollectionParticipant* participant;
CallQueryInterface(ccISupports, &participant);
PreserveWrapper(ccISupports, participant);
}
void PreserveWrapper(void* aScriptObjectHolder,
nsScriptObjectTracer* aTracer) {
if (PreservingWrapper()) {
return;
}
JSObject* wrapper = GetWrapper(); // Read barrier for incremental GC.
HoldJSObjects(aScriptObjectHolder, aTracer, JS::GetObjectZone(wrapper));
SetPreservingWrapper(true);
#ifdef DEBUG
// Make sure the cycle collector will be able to traverse to the wrapper.
CheckCCWrapperTraversal(aScriptObjectHolder, aTracer);
#endif
}
void ReleaseWrapper(void* aScriptObjectHolder);
void TraceWrapper(JSTracer* aTrc, const char* name) {
if (mWrapper) {
js::UnsafeTraceManuallyBarrieredEdge(aTrc, &mWrapper, name);
}
}
protected:
void PoisonWrapper() {
if (mWrapper) {
// Set the pointer to a value that will cause a crash if it is
// dereferenced.
mWrapper = reinterpret_cast<JSObject*>(1);
}
}
private:
void SetWrapperJSObject(JSObject* aWrapper);
FlagsType GetWrapperFlags() const { return mFlags & kWrapperFlagsMask; }
bool HasWrapperFlag(FlagsType aFlag) const {
MOZ_ASSERT((aFlag & ~kWrapperFlagsMask) == 0, "Bad wrapper flag bits");
return !!(mFlags & aFlag);
}
void SetWrapperFlags(FlagsType aFlagsToSet) {
MOZ_ASSERT((aFlagsToSet & ~kWrapperFlagsMask) == 0,
"Bad wrapper flag bits");
mFlags |= aFlagsToSet;
}
void UnsetWrapperFlags(FlagsType aFlagsToUnset) {
MOZ_ASSERT((aFlagsToUnset & ~kWrapperFlagsMask) == 0,
"Bad wrapper flag bits");
mFlags &= ~aFlagsToUnset;
}
void HoldJSObjects(void* aScriptObjectHolder, nsScriptObjectTracer* aTracer,
JS::Zone* aZone);
#ifdef DEBUG
public:
void CheckCCWrapperTraversal(void* aScriptObjectHolder,
nsScriptObjectTracer* aTracer);
private:
#endif // DEBUG
/**
* If this bit is set then we're preserving the wrapper, which in effect ties
* the lifetime of the JS object stored in the cache to the lifetime of the
* native object. We rely on the cycle collector to break the cycle that this
* causes between the native object and the JS object, so it is important that
* any native object that supports preserving of its wrapper
* traces/traverses/unlinks the cached JS object (see
* NS_IMPL_CYCLE_COLLECTION_TRACE_PRESERVED_WRAPPER and
* NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER).
*/
enum { WRAPPER_BIT_PRESERVED = 1 << 0 };
enum { kWrapperFlagsMask = WRAPPER_BIT_PRESERVED };
JSObject* mWrapper;
FlagsType mFlags;
protected:
#ifdef BOOL_FLAGS_ON_WRAPPER_CACHE
uint32_t mBoolFlags;
#endif
};
enum { WRAPPER_CACHE_FLAGS_BITS_USED = 1 };
NS_DEFINE_STATIC_IID_ACCESSOR(nsWrapperCache, NS_WRAPPERCACHE_IID)
#define NS_WRAPPERCACHE_INTERFACE_TABLE_ENTRY \
if (aIID.Equals(NS_GET_IID(nsWrapperCache))) { \
*aInstancePtr = static_cast<nsWrapperCache*>(this); \
return NS_OK; \
}
#define NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY \
NS_WRAPPERCACHE_INTERFACE_TABLE_ENTRY \
else
// Cycle collector macros for wrapper caches.
#define NS_IMPL_CYCLE_COLLECTION_TRACE_PRESERVED_WRAPPER \
tmp->TraceWrapper(aCallbacks, aClosure);
#define NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER \
tmp->ReleaseWrapper(p);
#define NS_IMPL_CYCLE_COLLECTION_TRACE_WRAPPERCACHE(_class) \
NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(_class) \
NS_IMPL_CYCLE_COLLECTION_TRACE_PRESERVED_WRAPPER \
NS_IMPL_CYCLE_COLLECTION_TRACE_END
#define NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_0(_class) \
NS_IMPL_CYCLE_COLLECTION_CLASS(_class) \
NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(_class) \
NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER \
NS_IMPL_CYCLE_COLLECTION_UNLINK_END \
NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(_class) \
NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END \
NS_IMPL_CYCLE_COLLECTION_TRACE_WRAPPERCACHE(_class)
#define NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(_class, ...) \
NS_IMPL_CYCLE_COLLECTION_CLASS(_class) \
NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(_class) \
NS_IMPL_CYCLE_COLLECTION_UNLINK(__VA_ARGS__) \
NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER \
NS_IMPL_CYCLE_COLLECTION_UNLINK_END \
NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(_class) \
NS_IMPL_CYCLE_COLLECTION_TRAVERSE(__VA_ARGS__) \
NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END \
NS_IMPL_CYCLE_COLLECTION_TRACE_WRAPPERCACHE(_class)
#define NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_WEAK(_class, ...) \
NS_IMPL_CYCLE_COLLECTION_CLASS(_class) \
NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(_class) \
NS_IMPL_CYCLE_COLLECTION_UNLINK(__VA_ARGS__) \
NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER \
NS_IMPL_CYCLE_COLLECTION_UNLINK_WEAK_REFERENCE \
NS_IMPL_CYCLE_COLLECTION_UNLINK_END \
NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(_class) \
NS_IMPL_CYCLE_COLLECTION_TRAVERSE(__VA_ARGS__) \
NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END \
NS_IMPL_CYCLE_COLLECTION_TRACE_WRAPPERCACHE(_class)
#define NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_WEAK_PTR(_class, ...) \
NS_IMPL_CYCLE_COLLECTION_CLASS(_class) \
NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(_class) \
NS_IMPL_CYCLE_COLLECTION_UNLINK(__VA_ARGS__) \
NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER \
NS_IMPL_CYCLE_COLLECTION_UNLINK_WEAK_PTR \
NS_IMPL_CYCLE_COLLECTION_UNLINK_END \
NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(_class) \
NS_IMPL_CYCLE_COLLECTION_TRAVERSE(__VA_ARGS__) \
NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END \
NS_IMPL_CYCLE_COLLECTION_TRACE_WRAPPERCACHE(_class)
// This is used for wrapper cached classes that inherit from cycle
// collected non-wrapper cached classes.
#define NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_INHERITED(_class, _base, ...) \
NS_IMPL_CYCLE_COLLECTION_CLASS(_class) \
NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN_INHERITED(_class, _base) \
NS_IMPL_CYCLE_COLLECTION_UNLINK(__VA_ARGS__) \
NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER \
NS_IMPL_CYCLE_COLLECTION_UNLINK_END \
NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN_INHERITED(_class, _base) \
NS_IMPL_CYCLE_COLLECTION_TRAVERSE(__VA_ARGS__) \
NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END \
NS_IMPL_CYCLE_COLLECTION_TRACE_WRAPPERCACHE(_class)
#endif /* nsWrapperCache_h___ */
