244 lines
8.2 KiB
C
244 lines
8.2 KiB
C
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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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