From 5f8de423f190bbb79a62f804151bc24824fa32d8 Mon Sep 17 00:00:00 2001 From: "Matt A. Tobin" Date: Fri, 2 Feb 2018 04:16:08 -0500 Subject: Add m-esr52 at 52.6.0 --- dom/base/nsWrapperCache.h | 402 ++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 402 insertions(+) create mode 100644 dom/base/nsWrapperCache.h (limited to 'dom/base/nsWrapperCache.h') diff --git a/dom/base/nsWrapperCache.h b/dom/base/nsWrapperCache.h new file mode 100644 index 000000000..3c69a7ec4 --- /dev/null +++ b/dom/base/nsWrapperCache.h @@ -0,0 +1,402 @@ +/* -*- 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/Id.h" // must come before js/RootingAPI.h +#include "js/Value.h" // must come before js/RootingAPI.h +#include "js/RootingAPI.h" +#include "js/TracingAPI.h" + +namespace mozilla { +namespace dom { +class TabChildGlobal; +class ProcessGlobal; +} // namespace dom +} // namespace mozilla +class SandboxPrivate; +class nsInProcessTabChildGlobal; +class nsWindowRoot; + +#define NS_WRAPPERCACHE_IID \ +{ 0x6f3179a1, 0x36f7, 0x4a5c, \ + { 0x8c, 0xf1, 0xad, 0xc8, 0x7c, 0xde, 0x3e, 0x87 } } + +/** + * 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 2 types of objects: + * + * If WRAPPER_IS_NOT_DOM_BINDING is set (IsDOMBinding() returns false): + * - the JSObject of an XPCWrappedNative wrapper + * + * If WRAPPER_IS_NOT_DOM_BINDING is not set (IsDOMBinding() returns true): + * - a DOM binding object (regular JS object or proxy) + * + * 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 nsWrapperCache +{ +public: + NS_DECLARE_STATIC_IID_ACCESSOR(NS_WRAPPERCACHE_IID) + + nsWrapperCache() : mWrapper(nullptr), mFlags(0) + { + } + ~nsWrapperCache() + { + MOZ_ASSERT(!PreservingWrapper(), + "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 JS API function and that it won't be stored without being + * rooted (or otherwise signaling the stored value to the CC). + */ + JSObject* GetWrapperPreserveColor() const + { + return GetWrapperJSObject(); + } + +#ifdef DEBUG +private: + static bool HasJSObjectMovedOp(JSObject* aWrapper); + +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 wrapper. This should be called from the finalizer for the + * wrapper. + */ + void ClearWrapper() + { + MOZ_ASSERT(!PreservingWrapper(), "Clearing a preserved wrapper!"); + + SetWrapperJSObject(nullptr); + } + + /** + * 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) + { + if (mWrapper) { + MOZ_ASSERT(mWrapper == aOldObject); + mWrapper = aNewObject; + } + } + + bool PreservingWrapper() + { + return HasWrapperFlag(WRAPPER_BIT_PRESERVED); + } + + bool IsDOMBinding() const + { + return !HasWrapperFlag(WRAPPER_IS_NOT_DOM_BINDING); + } + + /** + * 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 aGivenProto) = 0; + + /** + * Returns true if the object has a non-gray wrapper. + */ + bool IsBlack(); + + /** + * Returns true if the object has a black wrapper, + * and all the GC things it is keeping alive are black too. + */ + bool IsBlackAndDoesNotNeedTracing(nsISupports* aThis); + + bool HasNothingToTrace(nsISupports* aThis); + + // 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(&mWrapper, "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); + } + + 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(&ccISupports)); + MOZ_ASSERT(ccISupports); + + nsXPCOMCycleCollectionParticipant* participant; + CallQueryInterface(ccISupports, &participant); + PreserveWrapper(ccISupports, participant); + } + + void PreserveWrapper(void* aScriptObjectHolder, nsScriptObjectTracer* aTracer) + { + if (PreservingWrapper()) { + return; + } + + HoldJSObjects(aScriptObjectHolder, aTracer); + 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); + +protected: + void TraceWrapper(JSTracer* aTrc, const char* name) + { + if (mWrapper) { + js::UnsafeTraceManuallyBarrieredEdge(aTrc, &mWrapper, name); + } + } + + void PoisonWrapper() + { + if (mWrapper) { + // Set the pointer to a value that will cause a crash if it is + // dereferenced. + mWrapper = reinterpret_cast(1); + } + } + +private: + friend class mozilla::dom::TabChildGlobal; + friend class mozilla::dom::ProcessGlobal; + friend class SandboxPrivate; + friend class nsInProcessTabChildGlobal; + friend class nsWindowRoot; + void SetIsNotDOMBinding() + { + MOZ_ASSERT(!mWrapper && !(GetWrapperFlags() & ~WRAPPER_IS_NOT_DOM_BINDING), + "This flag should be set before creating any wrappers."); + SetWrapperFlags(WRAPPER_IS_NOT_DOM_BINDING); + } + + JSObject *GetWrapperJSObject() const + { + return mWrapper; + } + + 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); + +#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, + * NS_IMPL_CYCLE_COLLECTION_TRAVERSE_SCRIPT_OBJECTS and + * NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER). + */ + enum { WRAPPER_BIT_PRESERVED = 1 << 0 }; + + /** + * If this bit is set then the wrapper for the native object is not a DOM + * binding. + */ + enum { WRAPPER_IS_NOT_DOM_BINDING = 1 << 1 }; + + enum { kWrapperFlagsMask = (WRAPPER_BIT_PRESERVED | WRAPPER_IS_NOT_DOM_BINDING) }; + + JSObject* mWrapper; + FlagsType mFlags; +}; + +enum { WRAPPER_CACHE_FLAGS_BITS_USED = 2 }; + +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(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_SCRIPT_OBJECTS \ + 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_SCRIPT_OBJECTS \ + NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END \ + NS_IMPL_CYCLE_COLLECTION_TRACE_WRAPPERCACHE(_class) + +#endif /* nsWrapperCache_h___ */ -- cgit v1.2.3