/** * @file llhandle.h * @brief "Handle" to an object (usually a floater) whose lifetime you don't * control. * * $LicenseInfo:firstyear=2001&license=viewerlgpl$ * Second Life Viewer Source Code * Copyright (C) 2010, Linden Research, Inc. * * This library is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; * version 2.1 of the License only. * * This library is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with this library; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA * * Linden Research, Inc., 945 Battery Street, San Francisco, CA 94111 USA * $/LicenseInfo$ */ #ifndef LLHANDLE_H #define LLHANDLE_H #include "llpointer.h" template <typename T> class LLTombStone : public LLRefCount { public: LLTombStone(T* target = NULL) : mTarget(target) {} void setTarget(T* target) { mTarget = target; } T* getTarget() const { return mTarget; } private: T* mTarget; }; // LLHandles are used to refer to objects whose lifetime you do not control or influence. // Calling get() on a handle will return a pointer to the referenced object or NULL, // if the object no longer exists. Note that during the lifetime of the returned pointer, // you are assuming that the object will not be deleted by any action you perform, // or any other thread, as normal when using pointers, so avoid using that pointer outside of // the local code block. // // https://wiki.lindenlab.com/mediawiki/index.php?title=LLHandle&oldid=79669 template <typename T> class LLHandle { public: LLHandle() : mTombStone(getDefaultTombStone()) {} const LLHandle<T>& operator =(const LLHandle<T>& other) { mTombStone = other.mTombStone; return *this; } template<typename Subclass> LLHandle<T>& operator =(const LLHandle<Subclass>& other) { mTombStone = other.mTombStone; return *this; } bool isDead() const { return mTombStone->getTarget() == NULL; } void markDead() { mTombStone = getDefaultTombStone(); } T* get() const { return mTombStone->getTarget(); } friend bool operator== (const LLHandle<T>& lhs, const LLHandle<T>& rhs) { return lhs.mTombStone == rhs.mTombStone; } friend bool operator!= (const LLHandle<T>& lhs, const LLHandle<T>& rhs) { return !(lhs == rhs); } friend bool operator< (const LLHandle<T>& lhs, const LLHandle<T>& rhs) { return lhs.mTombStone < rhs.mTombStone; } friend bool operator> (const LLHandle<T>& lhs, const LLHandle<T>& rhs) { return lhs.mTombStone > rhs.mTombStone; } protected: protected: LLPointer<LLTombStone<T> > mTombStone; private: static LLPointer<LLTombStone<T> >& getDefaultTombStone() { static LLPointer<LLTombStone<T> > sDefaultTombStone = new LLTombStone<T>; return sDefaultTombStone; } }; template <typename T> class LLRootHandle : public LLHandle<T> { public: LLRootHandle(T* object) { bind(object); } LLRootHandle() {}; ~LLRootHandle() { unbind(); } // this is redundant, since a LLRootHandle *is* an LLHandle LLHandle<T> getHandle() { return LLHandle<T>(*this); } void bind(T* object) { // unbind existing tombstone if (LLHandle<T>::mTombStone.notNull()) { if (LLHandle<T>::mTombStone->getTarget() == object) return; LLHandle<T>::mTombStone->setTarget(NULL); } // tombstone reference counted, so no paired delete LLHandle<T>::mTombStone = new LLTombStone<T>(object); } void unbind() { LLHandle<T>::mTombStone->setTarget(NULL); } //don't allow copying of root handles, since there should only be one private: LLRootHandle(const LLRootHandle& other) {}; }; // Use this as a mixin for simple classes that need handles and when you don't // want handles at multiple points of the inheritance hierarchy template <typename T> class LLHandleProvider { protected: typedef LLHandle<T> handle_type_t; LLHandleProvider() { // provided here to enforce T deriving from LLHandleProvider<T> } LLHandle<T> getHandle() { // perform lazy binding to avoid small tombstone allocations for handle // providers whose handles are never referenced mHandle.bind(static_cast<T*>(this)); return mHandle; } private: LLRootHandle<T> mHandle; }; #endif