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Diffstat (limited to 'include/gtest/internal/gtest-linked_ptr.h')
-rw-r--r-- | include/gtest/internal/gtest-linked_ptr.h | 242 |
1 files changed, 242 insertions, 0 deletions
diff --git a/include/gtest/internal/gtest-linked_ptr.h b/include/gtest/internal/gtest-linked_ptr.h new file mode 100644 index 0000000..f98af0b --- /dev/null +++ b/include/gtest/internal/gtest-linked_ptr.h @@ -0,0 +1,242 @@ +// 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. +extern 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_; } + // Release ownership of the pointed object and returns it. + // Sole ownership by this linked_ptr object is required. + T* release() { + bool last = link_.depart(); + assert(last); + T* v = value_; + value_ = NULL; + return v; + } + + 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_ |