Chris@50: // Copyright (c) 2013-2014 Sandstorm Development Group, Inc. and contributors
Chris@50: // Licensed under the MIT License:
Chris@50: //
Chris@50: // Permission is hereby granted, free of charge, to any person obtaining a copy
Chris@50: // of this software and associated documentation files (the "Software"), to deal
Chris@50: // in the Software without restriction, including without limitation the rights
Chris@50: // to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
Chris@50: // copies of the Software, and to permit persons to whom the Software is
Chris@50: // furnished to do so, subject to the following conditions:
Chris@50: //
Chris@50: // The above copyright notice and this permission notice shall be included in
Chris@50: // all copies or substantial portions of the Software.
Chris@50: //
Chris@50: // THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
Chris@50: // IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
Chris@50: // FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
Chris@50: // AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
Chris@50: // LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
Chris@50: // OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
Chris@50: // THE SOFTWARE.
Chris@50: 
Chris@50: #ifndef KJ_MEMORY_H_
Chris@50: #define KJ_MEMORY_H_
Chris@50: 
Chris@50: #if defined(__GNUC__) && !KJ_HEADER_WARNINGS
Chris@50: #pragma GCC system_header
Chris@50: #endif
Chris@50: 
Chris@50: #include "common.h"
Chris@50: 
Chris@50: namespace kj {
Chris@50: 
Chris@50: // =======================================================================================
Chris@50: // Disposer -- Implementation details.
Chris@50: 
Chris@50: class Disposer {
Chris@50:   // Abstract interface for a thing that "disposes" of objects, where "disposing" usually means
Chris@50:   // calling the destructor followed by freeing the underlying memory.  `Own<T>` encapsulates an
Chris@50:   // object pointer with corresponding Disposer.
Chris@50:   //
Chris@50:   // Few developers will ever touch this interface.  It is primarily useful for those implementing
Chris@50:   // custom memory allocators.
Chris@50: 
Chris@50: protected:
Chris@50:   // Do not declare a destructor, as doing so will force a global initializer for each HeapDisposer
Chris@50:   // instance.  Eww!
Chris@50: 
Chris@50:   virtual void disposeImpl(void* pointer) const = 0;
Chris@50:   // Disposes of the object, given a pointer to the beginning of the object.  If the object is
Chris@50:   // polymorphic, this pointer is determined by dynamic_cast<void*>().  For non-polymorphic types,
Chris@50:   // Own<T> does not allow any casting, so the pointer exactly matches the original one given to
Chris@50:   // Own<T>.
Chris@50: 
Chris@50: public:
Chris@50: 
Chris@50:   template <typename T>
Chris@50:   void dispose(T* object) const;
Chris@50:   // Helper wrapper around disposeImpl().
Chris@50:   //
Chris@50:   // If T is polymorphic, calls `disposeImpl(dynamic_cast<void*>(object))`, otherwise calls
Chris@50:   // `disposeImpl(implicitCast<void*>(object))`.
Chris@50:   //
Chris@50:   // Callers must not call dispose() on the same pointer twice, even if the first call throws
Chris@50:   // an exception.
Chris@50: 
Chris@50: private:
Chris@50:   template <typename T, bool polymorphic = __is_polymorphic(T)>
Chris@50:   struct Dispose_;
Chris@50: };
Chris@50: 
Chris@50: template <typename T>
Chris@50: class DestructorOnlyDisposer: public Disposer {
Chris@50:   // A disposer that merely calls the type's destructor and nothing else.
Chris@50: 
Chris@50: public:
Chris@50:   static const DestructorOnlyDisposer instance;
Chris@50: 
Chris@50:   void disposeImpl(void* pointer) const override {
Chris@50:     reinterpret_cast<T*>(pointer)->~T();
Chris@50:   }
Chris@50: };
Chris@50: 
Chris@50: template <typename T>
Chris@50: const DestructorOnlyDisposer<T> DestructorOnlyDisposer<T>::instance = DestructorOnlyDisposer<T>();
Chris@50: 
Chris@50: class NullDisposer: public Disposer {
Chris@50:   // A disposer that does nothing.
Chris@50: 
Chris@50: public:
Chris@50:   static const NullDisposer instance;
Chris@50: 
Chris@50:   void disposeImpl(void* pointer) const override {}
Chris@50: };
Chris@50: 
Chris@50: // =======================================================================================
Chris@50: // Own<T> -- An owned pointer.
Chris@50: 
Chris@50: template <typename T>
Chris@50: class Own {
Chris@50:   // A transferrable title to a T.  When an Own<T> goes out of scope, the object's Disposer is
Chris@50:   // called to dispose of it.  An Own<T> can be efficiently passed by move, without relocating the
Chris@50:   // underlying object; this transfers ownership.
Chris@50:   //
Chris@50:   // This is much like std::unique_ptr, except:
Chris@50:   // - You cannot release().  An owned object is not necessarily allocated with new (see next
Chris@50:   //   point), so it would be hard to use release() correctly.
Chris@50:   // - The deleter is made polymorphic by virtual call rather than by template.  This is much
Chris@50:   //   more powerful -- it allows the use of custom allocators, freelists, etc.  This could
Chris@50:   //   _almost_ be accomplished with unique_ptr by forcing everyone to use something like
Chris@50:   //   std::unique_ptr<T, kj::Deleter>, except that things get hairy in the presence of multiple
Chris@50:   //   inheritance and upcasting, and anyway if you force everyone to use a custom deleter
Chris@50:   //   then you've lost any benefit to interoperating with the "standard" unique_ptr.
Chris@50: 
Chris@50: public:
Chris@50:   KJ_DISALLOW_COPY(Own);
Chris@50:   inline Own(): disposer(nullptr), ptr(nullptr) {}
Chris@50:   inline Own(Own&& other) noexcept
Chris@50:       : disposer(other.disposer), ptr(other.ptr) { other.ptr = nullptr; }
Chris@50:   inline Own(Own<RemoveConstOrDisable<T>>&& other) noexcept
Chris@50:       : disposer(other.disposer), ptr(other.ptr) { other.ptr = nullptr; }
Chris@50:   template <typename U, typename = EnableIf<canConvert<U*, T*>()>>
Chris@50:   inline Own(Own<U>&& other) noexcept
Chris@50:       : disposer(other.disposer), ptr(other.ptr) {
Chris@50:     static_assert(__is_polymorphic(T),
Chris@50:         "Casting owned pointers requires that the target type is polymorphic.");
Chris@50:     other.ptr = nullptr;
Chris@50:   }
Chris@50:   inline Own(T* ptr, const Disposer& disposer) noexcept: disposer(&disposer), ptr(ptr) {}
Chris@50: 
Chris@50:   ~Own() noexcept(false) { dispose(); }
Chris@50: 
Chris@50:   inline Own& operator=(Own&& other) {
Chris@50:     // Move-assingnment operator.
Chris@50: 
Chris@50:     // Careful, this might own `other`.  Therefore we have to transfer the pointers first, then
Chris@50:     // dispose.
Chris@50:     const Disposer* disposerCopy = disposer;
Chris@50:     T* ptrCopy = ptr;
Chris@50:     disposer = other.disposer;
Chris@50:     ptr = other.ptr;
Chris@50:     other.ptr = nullptr;
Chris@50:     if (ptrCopy != nullptr) {
Chris@50:       disposerCopy->dispose(const_cast<RemoveConst<T>*>(ptrCopy));
Chris@50:     }
Chris@50:     return *this;
Chris@50:   }
Chris@50: 
Chris@50:   inline Own& operator=(decltype(nullptr)) {
Chris@50:     dispose();
Chris@50:     return *this;
Chris@50:   }
Chris@50: 
Chris@50:   template <typename U>
Chris@50:   Own<U> downcast() {
Chris@50:     // Downcast the pointer to Own<U>, destroying the original pointer.  If this pointer does not
Chris@50:     // actually point at an instance of U, the results are undefined (throws an exception in debug
Chris@50:     // mode if RTTI is enabled, otherwise you're on your own).
Chris@50: 
Chris@50:     Own<U> result;
Chris@50:     if (ptr != nullptr) {
Chris@50:       result.ptr = &kj::downcast<U>(*ptr);
Chris@50:       result.disposer = disposer;
Chris@50:       ptr = nullptr;
Chris@50:     }
Chris@50:     return result;
Chris@50:   }
Chris@50: 
Chris@50: #define NULLCHECK KJ_IREQUIRE(ptr != nullptr, "null Own<> dereference")
Chris@50:   inline T* operator->() { NULLCHECK; return ptr; }
Chris@50:   inline const T* operator->() const { NULLCHECK; return ptr; }
Chris@50:   inline T& operator*() { NULLCHECK; return *ptr; }
Chris@50:   inline const T& operator*() const { NULLCHECK; return *ptr; }
Chris@50: #undef NULLCHECK
Chris@50:   inline T* get() { return ptr; }
Chris@50:   inline const T* get() const { return ptr; }
Chris@50:   inline operator T*() { return ptr; }
Chris@50:   inline operator const T*() const { return ptr; }
Chris@50: 
Chris@50: private:
Chris@50:   const Disposer* disposer;  // Only valid if ptr != nullptr.
Chris@50:   T* ptr;
Chris@50: 
Chris@50:   inline explicit Own(decltype(nullptr)): disposer(nullptr), ptr(nullptr) {}
Chris@50: 
Chris@50:   inline bool operator==(decltype(nullptr)) { return ptr == nullptr; }
Chris@50:   inline bool operator!=(decltype(nullptr)) { return ptr != nullptr; }
Chris@50:   // Only called by Maybe<Own<T>>.
Chris@50: 
Chris@50:   inline void dispose() {
Chris@50:     // Make sure that if an exception is thrown, we are left with a null ptr, so we won't possibly
Chris@50:     // dispose again.
Chris@50:     T* ptrCopy = ptr;
Chris@50:     if (ptrCopy != nullptr) {
Chris@50:       ptr = nullptr;
Chris@50:       disposer->dispose(const_cast<RemoveConst<T>*>(ptrCopy));
Chris@50:     }
Chris@50:   }
Chris@50: 
Chris@50:   template <typename U>
Chris@50:   friend class Own;
Chris@50:   friend class Maybe<Own<T>>;
Chris@50: };
Chris@50: 
Chris@50: namespace _ {  // private
Chris@50: 
Chris@50: template <typename T>
Chris@50: class OwnOwn {
Chris@50: public:
Chris@50:   inline OwnOwn(Own<T>&& value) noexcept: value(kj::mv(value)) {}
Chris@50: 
Chris@50:   inline Own<T>& operator*() & { return value; }
Chris@50:   inline const Own<T>& operator*() const & { return value; }
Chris@50:   inline Own<T>&& operator*() && { return kj::mv(value); }
Chris@50:   inline const Own<T>&& operator*() const && { return kj::mv(value); }
Chris@50:   inline Own<T>* operator->() { return &value; }
Chris@50:   inline const Own<T>* operator->() const { return &value; }
Chris@50:   inline operator Own<T>*() { return value ? &value : nullptr; }
Chris@50:   inline operator const Own<T>*() const { return value ? &value : nullptr; }
Chris@50: 
Chris@50: private:
Chris@50:   Own<T> value;
Chris@50: };
Chris@50: 
Chris@50: template <typename T>
Chris@50: OwnOwn<T> readMaybe(Maybe<Own<T>>&& maybe) { return OwnOwn<T>(kj::mv(maybe.ptr)); }
Chris@50: template <typename T>
Chris@50: Own<T>* readMaybe(Maybe<Own<T>>& maybe) { return maybe.ptr ? &maybe.ptr : nullptr; }
Chris@50: template <typename T>
Chris@50: const Own<T>* readMaybe(const Maybe<Own<T>>& maybe) { return maybe.ptr ? &maybe.ptr : nullptr; }
Chris@50: 
Chris@50: }  // namespace _ (private)
Chris@50: 
Chris@50: template <typename T>
Chris@50: class Maybe<Own<T>> {
Chris@50: public:
Chris@50:   inline Maybe(): ptr(nullptr) {}
Chris@50:   inline Maybe(Own<T>&& t) noexcept: ptr(kj::mv(t)) {}
Chris@50:   inline Maybe(Maybe&& other) noexcept: ptr(kj::mv(other.ptr)) {}
Chris@50: 
Chris@50:   template <typename U>
Chris@50:   inline Maybe(Maybe<Own<U>>&& other): ptr(mv(other.ptr)) {}
Chris@50: 
Chris@50:   inline Maybe(decltype(nullptr)) noexcept: ptr(nullptr) {}
Chris@50: 
Chris@50:   inline operator Maybe<T&>() { return ptr.get(); }
Chris@50:   inline operator Maybe<const T&>() const { return ptr.get(); }
Chris@50: 
Chris@50:   inline Maybe& operator=(Maybe&& other) { ptr = kj::mv(other.ptr); return *this; }
Chris@50: 
Chris@50:   inline bool operator==(decltype(nullptr)) const { return ptr == nullptr; }
Chris@50:   inline bool operator!=(decltype(nullptr)) const { return ptr != nullptr; }
Chris@50: 
Chris@50:   Own<T>& orDefault(Own<T>& defaultValue) {
Chris@50:     if (ptr == nullptr) {
Chris@50:       return defaultValue;
Chris@50:     } else {
Chris@50:       return ptr;
Chris@50:     }
Chris@50:   }
Chris@50:   const Own<T>& orDefault(const Own<T>& defaultValue) const {
Chris@50:     if (ptr == nullptr) {
Chris@50:       return defaultValue;
Chris@50:     } else {
Chris@50:       return ptr;
Chris@50:     }
Chris@50:   }
Chris@50: 
Chris@50:   template <typename Func>
Chris@50:   auto map(Func&& f) & -> Maybe<decltype(f(instance<Own<T>&>()))> {
Chris@50:     if (ptr == nullptr) {
Chris@50:       return nullptr;
Chris@50:     } else {
Chris@50:       return f(ptr);
Chris@50:     }
Chris@50:   }
Chris@50: 
Chris@50:   template <typename Func>
Chris@50:   auto map(Func&& f) const & -> Maybe<decltype(f(instance<const Own<T>&>()))> {
Chris@50:     if (ptr == nullptr) {
Chris@50:       return nullptr;
Chris@50:     } else {
Chris@50:       return f(ptr);
Chris@50:     }
Chris@50:   }
Chris@50: 
Chris@50:   template <typename Func>
Chris@50:   auto map(Func&& f) && -> Maybe<decltype(f(instance<Own<T>&&>()))> {
Chris@50:     if (ptr == nullptr) {
Chris@50:       return nullptr;
Chris@50:     } else {
Chris@50:       return f(kj::mv(ptr));
Chris@50:     }
Chris@50:   }
Chris@50: 
Chris@50:   template <typename Func>
Chris@50:   auto map(Func&& f) const && -> Maybe<decltype(f(instance<const Own<T>&&>()))> {
Chris@50:     if (ptr == nullptr) {
Chris@50:       return nullptr;
Chris@50:     } else {
Chris@50:       return f(kj::mv(ptr));
Chris@50:     }
Chris@50:   }
Chris@50: 
Chris@50: private:
Chris@50:   Own<T> ptr;
Chris@50: 
Chris@50:   template <typename U>
Chris@50:   friend class Maybe;
Chris@50:   template <typename U>
Chris@50:   friend _::OwnOwn<U> _::readMaybe(Maybe<Own<U>>&& maybe);
Chris@50:   template <typename U>
Chris@50:   friend Own<U>* _::readMaybe(Maybe<Own<U>>& maybe);
Chris@50:   template <typename U>
Chris@50:   friend const Own<U>* _::readMaybe(const Maybe<Own<U>>& maybe);
Chris@50: };
Chris@50: 
Chris@50: namespace _ {  // private
Chris@50: 
Chris@50: template <typename T>
Chris@50: class HeapDisposer final: public Disposer {
Chris@50: public:
Chris@50:   virtual void disposeImpl(void* pointer) const override { delete reinterpret_cast<T*>(pointer); }
Chris@50: 
Chris@50:   static const HeapDisposer instance;
Chris@50: };
Chris@50: 
Chris@50: template <typename T>
Chris@50: const HeapDisposer<T> HeapDisposer<T>::instance = HeapDisposer<T>();
Chris@50: 
Chris@50: }  // namespace _ (private)
Chris@50: 
Chris@50: template <typename T, typename... Params>
Chris@50: Own<T> heap(Params&&... params) {
Chris@50:   // heap<T>(...) allocates a T on the heap, forwarding the parameters to its constructor.  The
Chris@50:   // exact heap implementation is unspecified -- for now it is operator new, but you should not
Chris@50:   // assume this.  (Since we know the object size at delete time, we could actually implement an
Chris@50:   // allocator that is more efficient than operator new.)
Chris@50: 
Chris@50:   return Own<T>(new T(kj::fwd<Params>(params)...), _::HeapDisposer<T>::instance);
Chris@50: }
Chris@50: 
Chris@50: template <typename T>
Chris@50: Own<Decay<T>> heap(T&& orig) {
Chris@50:   // Allocate a copy (or move) of the argument on the heap.
Chris@50:   //
Chris@50:   // The purpose of this overload is to allow you to omit the template parameter as there is only
Chris@50:   // one argument and the purpose is to copy it.
Chris@50: 
Chris@50:   typedef Decay<T> T2;
Chris@50:   return Own<T2>(new T2(kj::fwd<T>(orig)), _::HeapDisposer<T2>::instance);
Chris@50: }
Chris@50: 
Chris@50: // =======================================================================================
Chris@50: // SpaceFor<T> -- assists in manual allocation
Chris@50: 
Chris@50: template <typename T>
Chris@50: class SpaceFor {
Chris@50:   // A class which has the same size and alignment as T but does not call its constructor or
Chris@50:   // destructor automatically.  Instead, call construct() to construct a T in the space, which
Chris@50:   // returns an Own<T> which will take care of calling T's destructor later.
Chris@50: 
Chris@50: public:
Chris@50:   inline SpaceFor() {}
Chris@50:   inline ~SpaceFor() {}
Chris@50: 
Chris@50:   template <typename... Params>
Chris@50:   Own<T> construct(Params&&... params) {
Chris@50:     ctor(value, kj::fwd<Params>(params)...);
Chris@50:     return Own<T>(&value, DestructorOnlyDisposer<T>::instance);
Chris@50:   }
Chris@50: 
Chris@50: private:
Chris@50:   union {
Chris@50:     T value;
Chris@50:   };
Chris@50: };
Chris@50: 
Chris@50: // =======================================================================================
Chris@50: // Inline implementation details
Chris@50: 
Chris@50: template <typename T>
Chris@50: struct Disposer::Dispose_<T, true> {
Chris@50:   static void dispose(T* object, const Disposer& disposer) {
Chris@50:     // Note that dynamic_cast<void*> does not require RTTI to be enabled, because the offset to
Chris@50:     // the top of the object is in the vtable -- as it obviously needs to be to correctly implement
Chris@50:     // operator delete.
Chris@50:     disposer.disposeImpl(dynamic_cast<void*>(object));
Chris@50:   }
Chris@50: };
Chris@50: template <typename T>
Chris@50: struct Disposer::Dispose_<T, false> {
Chris@50:   static void dispose(T* object, const Disposer& disposer) {
Chris@50:     disposer.disposeImpl(static_cast<void*>(object));
Chris@50:   }
Chris@50: };
Chris@50: 
Chris@50: template <typename T>
Chris@50: void Disposer::dispose(T* object) const {
Chris@50:   Dispose_<T>::dispose(object, *this);
Chris@50: }
Chris@50: 
Chris@50: }  // namespace kj
Chris@50: 
Chris@50: #endif  // KJ_MEMORY_H_