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// 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. |
void join(linked_ptr_internal const* ptr) |
GTEST_LOCK_EXCLUDED_(g_linked_ptr_mutex) { |
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. |
bool depart() |
GTEST_LOCK_EXCLUDED_(g_linked_ptr_mutex) { |
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 |
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#endif // GTEST_INCLUDE_GTEST_INTERNAL_GTEST_LINKED_PTR_H_ |