// 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.

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// 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) {

      assert(p->next_ != this &&

             "Trying to join() a linked ring we are already in. "

             "Is GMock thread safety enabled?");

      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) {

      assert(p->next_ != next_ &&

             "Trying to depart() a linked ring we are not in. "

             "Is GMock thread safety enabled?");

      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_