// Copyright 2003 Google Inc. // All rights reserved. // // Redistribution and use in source and binary forms, with or without // modification, are permitted provided that the following conditions are // met: // // * Redistributions of source code must retain the above copyright // notice, this list of conditions and the following disclaimer. // * Redistributions in binary form must reproduce the above // copyright notice, this list of conditions and the following disclaimer // in the documentation and/or other materials provided with the // distribution. // * Neither the name of Google Inc. nor the names of its // contributors may be used to endorse or promote products derived from // this software without specific prior written permission. // // THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS // "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT // LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR // A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT // OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, // SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT // LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, // DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY // THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. // // Authors: Dan Egnor (egnor@google.com) // // A "smart" pointer type with reference tracking. Every pointer to a // particular object is kept on a circular linked list. When the last pointer // to an object is destroyed or reassigned, the object is deleted. // // Used properly, this deletes the object when the last reference goes away. // There are several caveats: // - Like all reference counting schemes, cycles lead to leaks. // - Each smart pointer is actually two pointers (8 bytes instead of 4). // - Every time a pointer is assigned, the entire list of pointers to that // object is traversed. This class is therefore NOT SUITABLE when there // will often be more than two or three pointers to a particular object. // - References are only tracked as long as linked_ptr<> objects are copied. // If a linked_ptr<> is converted to a raw pointer and back, BAD THINGS // will happen (double deletion). // // A good use of this class is storing object references in STL containers. // You can safely put linked_ptr<> in a vector<>. // Other uses may not be as good. // // Note: If you use an incomplete type with linked_ptr<>, the class // *containing* linked_ptr<> must have a constructor and destructor (even // if they do nothing!). // // Bill Gibbons suggested we use something like this. // // Thread Safety: // Unlike other linked_ptr implementations, in this implementation // a linked_ptr object is thread-safe in the sense that: // - it's safe to copy linked_ptr objects concurrently, // - it's safe to copy *from* a linked_ptr and read its underlying // raw pointer (e.g. via get()) concurrently, and // - it's safe to write to two linked_ptrs that point to the same // shared object concurrently. // TODO(wan@google.com): rename this to safe_linked_ptr to avoid // confusion with normal linked_ptr. #ifndef GTEST_INCLUDE_GTEST_INTERNAL_GTEST_LINKED_PTR_H_ #define GTEST_INCLUDE_GTEST_INTERNAL_GTEST_LINKED_PTR_H_ #include <stdlib.h> #include <assert.h> #include "gtest/internal/gtest-port.h" namespace testing { namespace internal { // Protects copying of all linked_ptr objects. GTEST_API_ GTEST_DECLARE_STATIC_MUTEX_(g_linked_ptr_mutex); // This is used internally by all instances of linked_ptr<>. It needs to be // a non-template class because different types of linked_ptr<> can refer to // the same object (linked_ptr<Superclass>(obj) vs linked_ptr<Subclass>(obj)). // So, it needs to be possible for different types of linked_ptr to participate // in the same circular linked list, so we need a single class type here. // // DO NOT USE THIS CLASS DIRECTLY YOURSELF. Use linked_ptr<T>. class linked_ptr_internal { public: // Create a new circle that includes only this instance. void join_new() { next_ = this; } // Many linked_ptr operations may change p.link_ for some linked_ptr // variable p in the same circle as this object. Therefore we need // to prevent two such operations from occurring concurrently. // // Note that different types of linked_ptr objects can coexist in a // circle (e.g. linked_ptr<Base>, linked_ptr<Derived1>, and // linked_ptr<Derived2>). Therefore we must use a single mutex to // protect all linked_ptr objects. This can create serious // contention in production code, but is acceptable in a testing // framework. // Join an existing circle. // L < g_linked_ptr_mutex void join(linked_ptr_internal const* ptr) { MutexLock lock(&g_linked_ptr_mutex); linked_ptr_internal const* p = ptr; while (p->next_ != ptr) p = p->next_; p->next_ = this; next_ = ptr; } // Leave whatever circle we're part of. Returns true if we were the // last member of the circle. Once this is done, you can join() another. // L < g_linked_ptr_mutex bool depart() { MutexLock lock(&g_linked_ptr_mutex); if (next_ == this) return true; linked_ptr_internal const* p = next_; while (p->next_ != this) p = p->next_; p->next_ = next_; return false; } private: mutable linked_ptr_internal const* next_; }; template <typename T> class linked_ptr { public: typedef T element_type; // Take over ownership of a raw pointer. This should happen as soon as // possible after the object is created. explicit linked_ptr(T* ptr = NULL) { capture(ptr); } ~linked_ptr() { depart(); } // Copy an existing linked_ptr<>, adding ourselves to the list of references. template <typename U> linked_ptr(linked_ptr<U> const& ptr) { copy(&ptr); } linked_ptr(linked_ptr const& ptr) { // NOLINT assert(&ptr != this); copy(&ptr); } // Assignment releases the old value and acquires the new. template <typename U> linked_ptr& operator=(linked_ptr<U> const& ptr) { depart(); copy(&ptr); return *this; } linked_ptr& operator=(linked_ptr const& ptr) { if (&ptr != this) { depart(); copy(&ptr); } return *this; } // Smart pointer members. void reset(T* ptr = NULL) { depart(); capture(ptr); } T* get() const { return value_; } T* operator->() const { return value_; } T& operator*() const { return *value_; } bool operator==(T* p) const { return value_ == p; } bool operator!=(T* p) const { return value_ != p; } template <typename U> bool operator==(linked_ptr<U> const& ptr) const { return value_ == ptr.get(); } template <typename U> bool operator!=(linked_ptr<U> const& ptr) const { return value_ != ptr.get(); } private: template <typename U> friend class linked_ptr; T* value_; linked_ptr_internal link_; void depart() { if (link_.depart()) delete value_; } void capture(T* ptr) { value_ = ptr; link_.join_new(); } template <typename U> void copy(linked_ptr<U> const* ptr) { value_ = ptr->get(); if (value_) link_.join(&ptr->link_); else link_.join_new(); } }; template<typename T> inline bool operator==(T* ptr, const linked_ptr<T>& x) { return ptr == x.get(); } template<typename T> inline bool operator!=(T* ptr, const linked_ptr<T>& x) { return ptr != x.get(); } // A function to convert T* into linked_ptr<T> // Doing e.g. make_linked_ptr(new FooBarBaz<type>(arg)) is a shorter notation // for linked_ptr<FooBarBaz<type> >(new FooBarBaz<type>(arg)) template <typename T> linked_ptr<T> make_linked_ptr(T* ptr) { return linked_ptr<T>(ptr); } } // namespace internal } // namespace testing #endif // GTEST_INCLUDE_GTEST_INTERNAL_GTEST_LINKED_PTR_H_