mirror of
https://github.com/mozilla/gecko-dev.git
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363 lines
11 KiB
C++
363 lines
11 KiB
C++
/* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef nsWrapperCache_h___
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#define nsWrapperCache_h___
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#include "nsCycleCollectionParticipant.h"
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#include "mozilla/Assertions.h"
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#include "js/Id.h" // must come before js/RootingAPI.h
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#include "js/Value.h" // must come before js/RootingAPI.h
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#include "js/RootingAPI.h"
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#include "js/TracingAPI.h"
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class XPCWrappedNativeScope;
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#define NS_WRAPPERCACHE_IID \
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{ 0x6f3179a1, 0x36f7, 0x4a5c, \
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{ 0x8c, 0xf1, 0xad, 0xc8, 0x7c, 0xde, 0x3e, 0x87 } }
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/**
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* Class to store the wrapper for an object. This can only be used with objects
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* that only have one non-security wrapper at a time (for an XPCWrappedNative
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* this is usually ensured by setting an explicit parent in the PreCreate hook
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* for the class).
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*
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* An instance of nsWrapperCache can be gotten from an object that implements
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* a wrapper cache by calling QueryInterface on it. Note that this breaks XPCOM
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* rules a bit (this object doesn't derive from nsISupports).
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*
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* The cache can store objects other than wrappers. We allow wrappers to use a
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* separate JSObject to store their state (mostly expandos). If the wrapper is
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* collected and we want to preserve this state we actually store the state
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* object in the cache.
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*
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* The cache can store 2 types of objects:
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*
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* If WRAPPER_IS_DOM_BINDING is not set (IsDOMBinding() returns false):
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* - a slim wrapper or the JSObject of an XPCWrappedNative wrapper
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*
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* If WRAPPER_IS_DOM_BINDING is set (IsDOMBinding() returns true):
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* - a DOM binding object (regular JS object or proxy)
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*
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* The finalizer for the wrapper clears the cache.
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*
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* A number of the methods are implemented in nsWrapperCacheInlines.h because we
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* have to include some JS headers that don't play nicely with the rest of the
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* codebase. Include nsWrapperCacheInlines.h if you need to call those methods.
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*/
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class nsWrapperCache
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{
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public:
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NS_DECLARE_STATIC_IID_ACCESSOR(NS_WRAPPERCACHE_IID)
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nsWrapperCache() : mWrapper(nullptr), mFlags(0)
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{
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}
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~nsWrapperCache()
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{
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MOZ_ASSERT(!PreservingWrapper(),
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"Destroying cache with a preserved wrapper!");
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}
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/**
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* Get the cached wrapper.
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*
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* This getter clears the gray bit before handing out the JSObject which means
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* that the object is guaranteed to be kept alive past the next CC.
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*/
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JSObject* GetWrapper() const;
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/**
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* Get the cached wrapper.
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*
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* This getter does not change the color of the JSObject meaning that the
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* object returned is not guaranteed to be kept alive past the next CC.
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*
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* This should only be called if you are certain that the return value won't
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* be passed into a JS API function and that it won't be stored without being
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* rooted (or otherwise signaling the stored value to the CC).
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*/
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JSObject* GetWrapperPreserveColor() const
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{
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return GetWrapperJSObject();
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}
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void SetWrapper(JSObject* aWrapper)
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{
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MOZ_ASSERT(!PreservingWrapper(), "Clearing a preserved wrapper!");
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MOZ_ASSERT(aWrapper, "Use ClearWrapper!");
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SetWrapperJSObject(aWrapper);
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}
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/**
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* Clear the wrapper. This should be called from the finalizer for the
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* wrapper.
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*/
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void ClearWrapper()
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{
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MOZ_ASSERT(!PreservingWrapper(), "Clearing a preserved wrapper!");
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SetWrapperJSObject(nullptr);
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}
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bool PreservingWrapper()
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{
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return HasWrapperFlag(WRAPPER_BIT_PRESERVED);
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}
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void SetIsDOMBinding()
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{
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MOZ_ASSERT(!mWrapper && !(GetWrapperFlags() & ~WRAPPER_IS_DOM_BINDING),
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"This flag should be set before creating any wrappers.");
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SetWrapperFlags(WRAPPER_IS_DOM_BINDING);
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}
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bool IsDOMBinding() const
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{
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return HasWrapperFlag(WRAPPER_IS_DOM_BINDING);
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}
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/**
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* Wrap the object corresponding to this wrapper cache. If non-null is
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* returned, the object has already been stored in the wrapper cache.
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*/
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virtual JSObject* WrapObject(JSContext* cx)
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{
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MOZ_ASSERT(!IsDOMBinding(), "Someone forgot to override WrapObject");
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return nullptr;
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}
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/**
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* Returns true if the object has a non-gray wrapper.
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*/
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bool IsBlack();
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/**
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* Returns true if the object has a black wrapper,
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* and all the GC things it is keeping alive are black too.
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*/
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bool IsBlackAndDoesNotNeedTracing(nsISupports* aThis);
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bool HasNothingToTrace(nsISupports* aThis);
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// Only meant to be called by code that preserves a wrapper.
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void SetPreservingWrapper(bool aPreserve)
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{
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if(aPreserve) {
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SetWrapperFlags(WRAPPER_BIT_PRESERVED);
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}
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else {
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UnsetWrapperFlags(WRAPPER_BIT_PRESERVED);
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}
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}
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void TraceWrapper(const TraceCallbacks& aCallbacks, void* aClosure)
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{
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if (PreservingWrapper() && mWrapper) {
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aCallbacks.Trace(&mWrapper, "Preserved wrapper", aClosure);
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}
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}
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/*
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* The following methods for getting and manipulating flags allow the unused
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* bits of mFlags to be used by derived classes.
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*/
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typedef uint32_t FlagsType;
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FlagsType GetFlags() const
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{
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return mFlags & ~kWrapperFlagsMask;
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}
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bool HasFlag(FlagsType aFlag) const
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{
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MOZ_ASSERT((aFlag & kWrapperFlagsMask) == 0, "Bad flag mask");
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return !!(mFlags & aFlag);
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}
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void SetFlags(FlagsType aFlagsToSet)
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{
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MOZ_ASSERT((aFlagsToSet & kWrapperFlagsMask) == 0, "Bad flag mask");
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mFlags |= aFlagsToSet;
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}
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void UnsetFlags(FlagsType aFlagsToUnset)
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{
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MOZ_ASSERT((aFlagsToUnset & kWrapperFlagsMask) == 0, "Bad flag mask");
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mFlags &= ~aFlagsToUnset;
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}
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void PreserveWrapper(nsISupports* aScriptObjectHolder)
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{
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if (PreservingWrapper()) {
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return;
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}
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nsISupports* ccISupports;
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aScriptObjectHolder->QueryInterface(NS_GET_IID(nsCycleCollectionISupports),
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reinterpret_cast<void**>(&ccISupports));
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MOZ_ASSERT(ccISupports);
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nsXPCOMCycleCollectionParticipant* participant;
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CallQueryInterface(ccISupports, &participant);
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PreserveWrapper(ccISupports, participant);
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}
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void PreserveWrapper(void* aScriptObjectHolder, nsScriptObjectTracer* aTracer)
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{
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if (PreservingWrapper()) {
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return;
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}
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HoldJSObjects(aScriptObjectHolder, aTracer);
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SetPreservingWrapper(true);
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#ifdef DEBUG
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// Make sure the cycle collector will be able to traverse to the wrapper.
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CheckCCWrapperTraversal(aScriptObjectHolder, aTracer);
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#endif
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}
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void ReleaseWrapper(void* aScriptObjectHolder);
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protected:
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void TraceWrapper(JSTracer* aTrc, const char* name)
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{
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if (mWrapper) {
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JS_CallObjectTracer(aTrc, &mWrapper, name);
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}
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}
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void PoisonWrapper()
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{
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if (mWrapper) {
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mWrapper.setToCrashOnTouch();
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}
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}
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private:
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JSObject *GetWrapperJSObject() const
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{
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return mWrapper;
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}
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void SetWrapperJSObject(JSObject* aWrapper)
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{
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mWrapper = aWrapper;
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UnsetWrapperFlags(kWrapperFlagsMask & ~WRAPPER_IS_DOM_BINDING);
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}
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void TraceWrapperJSObject(JSTracer* aTrc, const char* aName);
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FlagsType GetWrapperFlags() const
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{
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return mFlags & kWrapperFlagsMask;
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}
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bool HasWrapperFlag(FlagsType aFlag) const
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{
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MOZ_ASSERT((aFlag & ~kWrapperFlagsMask) == 0, "Bad wrapper flag bits");
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return !!(mFlags & aFlag);
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}
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void SetWrapperFlags(FlagsType aFlagsToSet)
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{
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MOZ_ASSERT((aFlagsToSet & ~kWrapperFlagsMask) == 0, "Bad wrapper flag bits");
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mFlags |= aFlagsToSet;
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}
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void UnsetWrapperFlags(FlagsType aFlagsToUnset)
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{
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MOZ_ASSERT((aFlagsToUnset & ~kWrapperFlagsMask) == 0, "Bad wrapper flag bits");
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mFlags &= ~aFlagsToUnset;
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}
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static void HoldJSObjects(void* aScriptObjectHolder,
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nsScriptObjectTracer* aTracer);
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#ifdef DEBUG
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void CheckCCWrapperTraversal(void* aScriptObjectHolder,
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nsScriptObjectTracer* aTracer);
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#endif // DEBUG
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/**
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* If this bit is set then we're preserving the wrapper, which in effect ties
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* the lifetime of the JS object stored in the cache to the lifetime of the
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* native object. We rely on the cycle collector to break the cycle that this
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* causes between the native object and the JS object, so it is important that
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* any native object that supports preserving of its wrapper
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* traces/traverses/unlinks the cached JS object (see
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* NS_IMPL_CYCLE_COLLECTION_TRACE_PRESERVED_WRAPPER,
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* NS_IMPL_CYCLE_COLLECTION_TRAVERSE_SCRIPT_OBJECTS and
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* NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER).
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*/
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enum { WRAPPER_BIT_PRESERVED = 1 << 0 };
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/**
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* If this bit is set then the wrapper for the native object is a DOM binding
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* (regular JS object or proxy).
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*/
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enum { WRAPPER_IS_DOM_BINDING = 1 << 1 };
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enum { kWrapperFlagsMask = (WRAPPER_BIT_PRESERVED | WRAPPER_IS_DOM_BINDING) };
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JS::Heap<JSObject*> mWrapper;
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FlagsType mFlags;
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};
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enum { WRAPPER_CACHE_FLAGS_BITS_USED = 2 };
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NS_DEFINE_STATIC_IID_ACCESSOR(nsWrapperCache, NS_WRAPPERCACHE_IID)
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#define NS_WRAPPERCACHE_INTERFACE_TABLE_ENTRY \
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if ( aIID.Equals(NS_GET_IID(nsWrapperCache)) ) { \
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*aInstancePtr = static_cast<nsWrapperCache*>(this); \
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return NS_OK; \
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}
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#define NS_WRAPPERCACHE_INTERFACE_MAP_ENTRY \
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NS_WRAPPERCACHE_INTERFACE_TABLE_ENTRY \
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else
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// Cycle collector macros for wrapper caches.
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#define NS_IMPL_CYCLE_COLLECTION_TRACE_PRESERVED_WRAPPER \
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tmp->TraceWrapper(aCallbacks, aClosure);
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#define NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER \
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tmp->ReleaseWrapper(p);
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#define NS_IMPL_CYCLE_COLLECTION_TRACE_WRAPPERCACHE(_class) \
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NS_IMPL_CYCLE_COLLECTION_TRACE_BEGIN(_class) \
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NS_IMPL_CYCLE_COLLECTION_TRACE_PRESERVED_WRAPPER \
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NS_IMPL_CYCLE_COLLECTION_TRACE_END
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#define NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE_0(_class) \
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NS_IMPL_CYCLE_COLLECTION_CLASS(_class) \
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NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(_class) \
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NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER \
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NS_IMPL_CYCLE_COLLECTION_UNLINK_END \
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NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(_class) \
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NS_IMPL_CYCLE_COLLECTION_TRAVERSE_SCRIPT_OBJECTS \
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NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END \
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NS_IMPL_CYCLE_COLLECTION_TRACE_WRAPPERCACHE(_class)
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#define NS_IMPL_CYCLE_COLLECTION_WRAPPERCACHE(_class, ...) \
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NS_IMPL_CYCLE_COLLECTION_CLASS(_class) \
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NS_IMPL_CYCLE_COLLECTION_UNLINK_BEGIN(_class) \
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NS_IMPL_CYCLE_COLLECTION_UNLINK(__VA_ARGS__) \
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NS_IMPL_CYCLE_COLLECTION_UNLINK_PRESERVED_WRAPPER \
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NS_IMPL_CYCLE_COLLECTION_UNLINK_END \
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NS_IMPL_CYCLE_COLLECTION_TRAVERSE_BEGIN(_class) \
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NS_IMPL_CYCLE_COLLECTION_TRAVERSE(__VA_ARGS__) \
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NS_IMPL_CYCLE_COLLECTION_TRAVERSE_SCRIPT_OBJECTS \
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NS_IMPL_CYCLE_COLLECTION_TRAVERSE_END \
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NS_IMPL_CYCLE_COLLECTION_TRACE_WRAPPERCACHE(_class)
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#endif /* nsWrapperCache_h___ */
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