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