CoinSmartPtr.hpp

// Copyright (C) 2004, 2006 International Business Machines and others.
// All Rights Reserved.
// This code is published under the Eclipse Public License.
//
// $Id$
//
// Authors:  Carl Laird, Andreas Waechter     IBM    2004-08-13
// Removed lots of debugging stuff and reformatted: Laszlo Ladanyi, IBM
#ifndef CoinSmartPtr_hpp
#define CoinSmartPtr_hpp

#include <list>
#include <cassert>
#include <cstddef>
#include <cstring>

namespace Coin {

//#########################################################################

/** ReferencedObject class.
     * This is part of the implementation of an intrusive smart pointer 
     * design. This class stores the reference count of all the smart
     * pointers that currently reference it. See the documentation for
     * the SmartPtr class for more details.
     * 
     * A SmartPtr behaves much like a raw pointer, but manages the lifetime 
     * of an object, deleting the object automatically. This class implements
     * a reference-counting, intrusive smart pointer design, where all
     * objects pointed to must inherit off of ReferencedObject, which
     * stores the reference count. Although this is intrusive (native types
     * and externally authored classes require wrappers to be referenced
     * by smart pointers), it is a safer design. A more detailed discussion of
     * these issues follows after the usage information.
     * 
     * Usage Example:
     * Note: to use the SmartPtr, all objects to which you point MUST
     * inherit off of ReferencedObject.
     * 
     * \verbatim
     * 
     * In MyClass.hpp...
     * 
     * #include "CoinSmartPtr.hpp"

     * 
     * class MyClass : public Coin::ReferencedObject // must derive from ReferencedObject
     *    {
     *      ...
     *    }
     * 
     * In my_usage.cpp...
     * 
     * #include "CoinSmartPtr.hpp"
     * #include "MyClass.hpp"
     * 
     * void func(AnyObject& obj)
     *  {
     *    Coin::SmartPtr<MyClass> ptr_to_myclass = new MyClass(...);
     *    // ptr_to_myclass now points to a new MyClass,
     *    // and the reference count is 1
     *    
     *    ...
     * 
     *    obj.SetMyClass(ptr_to_myclass);
     *    // Here, let's assume that AnyObject uses a
     *    // SmartPtr<MyClass> internally here.
     *    // Now, both ptr_to_myclass and the internal
     *    // SmartPtr in obj point to the same MyClass object
     *    // and its reference count is 2.
     * 
     *    ...
     * 
     *    // No need to delete ptr_to_myclass, this
     *    // will be done automatically when the
     *    // reference count drops to zero.
     * 
     *  }   
     *  
     * \endverbatim
     * 
     * Other Notes:
     *  The SmartPtr implements both dereference operators -> & *.
     *  The SmartPtr does NOT implement a conversion operator to
     *    the raw pointer. Use the GetRawPtr() method when this
     *    is necessary. Make sure that the raw pointer is NOT
     *    deleted. 
     *  The SmartPtr implements the comparison operators == & !=
     *    for a variety of types. Use these instead of
     *    \verbatim
     *    if (GetRawPtr(smrt_ptr) == ptr) // Don't use this
     *    \endverbatim
     * SmartPtr's, as currently implemented, do NOT handle circular references.
     *    For example: consider a higher level object using SmartPtrs to point
     *    to A and B, but A and B also point to each other (i.e. A has a
     *    SmartPtr to B and B has a SmartPtr to A). In this scenario, when the
     *    higher level object is finished with A and B, their reference counts
     *    will never drop to zero (since they reference each other) and they
     *    will not be deleted. This can be detected by memory leak tools like
     *    valgrind. If the circular reference is necessary, the problem can be
     *    overcome by a number of techniques:
     *    
     *    1) A and B can have a method that "releases" each other, that is
     *        they set their internal SmartPtrs to NULL.
     *        \verbatim
     *        void AClass::ReleaseCircularReferences()
     *          {
     *          smart_ptr_to_B = NULL;
     *          }
     *        \endverbatim
     *        Then, the higher level class can call these methods before
     *        it is done using A & B.
     * 
     *    2) Raw pointers can be used in A and B to reference each other.
     *        Here, an implicit assumption is made that the lifetime is
     *        controlled by the higher level object and that A and B will
     *        both exist in a controlled manner. Although this seems 
     *        dangerous, in many situations, this type of referencing
     *        is very controlled and this is reasonably safe.
     * 
     *    3) This SmartPtr class could be redesigned with the Weak/Strong
     *        design concept. Here, the SmartPtr is identified as being
     *        Strong (controls lifetime of the object) or Weak (merely
     *        referencing the object). The Strong SmartPtr increments 
     *        (and decrements) the reference count in ReferencedObject
     *        but the Weak SmartPtr does not. In the example above,
     *        the higher level object would have Strong SmartPtrs to
     *        A and B, but A and B would have Weak SmartPtrs to each
     *        other. Then, when the higher level object was done with
     *        A and B, they would be deleted. The Weak SmartPtrs in A
     *        and B would not decrement the reference count and would,
     *        of course, not delete the object. This idea is very similar
     *        to item (2), where it is implied that the sequence of events 
     *        is controlled such that A and B will not call anything using
     *        their pointers following the higher level delete (i.e. in
     *        their destructors!). This is somehow safer, however, because
     *        code can be written (however expensive) to perform run-time 
     *        detection of this situation. For example, the ReferencedObject
     *        could store pointers to all Weak SmartPtrs that are referencing
     *        it and, in its destructor, tell these pointers that it is
     *        dying. They could then set themselves to NULL, or set an
     *        internal flag to detect usage past this point.
     * 
     * Comments on Non-Intrusive Design:
     * In a non-intrusive design, the reference count is stored somewhere other
     * than the object being referenced. This means, unless the reference
     * counting pointer is the first referencer, it must get a pointer to the 
     * referenced object from another smart pointer (so it has access to the 
     * reference count location). In this non-intrusive design, if we are 
     * pointing to an object with a smart pointer (or a number of smart
     * pointers), and we then give another smart pointer the address through
     * a RAW pointer, we will have two independent, AND INCORRECT, reference
     * counts. To avoid this pitfall, we use an intrusive reference counting
     * technique where the reference count is stored in the object being
     * referenced. 
     */
class ReferencedObject {
public:
  ReferencedObject()
    : reference_count_(0)
  {
  }
  virtual ~ReferencedObject() { assert(reference_count_ == 0); }
  inline int ReferenceCount() const { return reference_count_; }
  inline void AddRef() const { ++reference_count_; }
  inline void ReleaseRef() const { --reference_count_; }

private:
  mutable int reference_count_;
};

//#########################################################################

//#define IP_DEBUG_SMARTPTR
#if COIN_IPOPT_CHECKLEVEL > 2
#define IP_DEBUG_SMARTPTR
#endif
#ifdef IP_DEBUG_SMARTPTR
#include "IpDebug.hpp"
#endif

/** Template class for Smart Pointers.
     * A SmartPtr behaves much like a raw pointer, but manages the lifetime 
     * of an object, deleting the object automatically. This class implements
     * a reference-counting, intrusive smart pointer design, where all
     * objects pointed to must inherit off of ReferencedObject, which
     * stores the reference count. Although this is intrusive (native types
     * and externally authored classes require wrappers to be referenced
     * by smart pointers), it is a safer design. A more detailed discussion of
     * these issues follows after the usage information.
     * 
     * Usage Example:
     * Note: to use the SmartPtr, all objects to which you point MUST
     * inherit off of ReferencedObject.
     * 
     * \verbatim
     * 
     * In MyClass.hpp...
     * 
     * #include "CoinSmartPtr.hpp"
     * 
     *  class MyClass : public Coin::ReferencedObject // must derive from ReferencedObject
     *    {
     *      ...
     *    }
     * 
     * In my_usage.cpp...
     * 
     * #include "CoinSmartPtr.hpp"
     * #include "MyClass.hpp"
     * 
     * void func(AnyObject& obj)
     *  {
     *    SmartPtr<MyClass> ptr_to_myclass = new MyClass(...);
     *    // ptr_to_myclass now points to a new MyClass,
     *    // and the reference count is 1
     *    
     *    ...
     * 
     *    obj.SetMyClass(ptr_to_myclass);
     *    // Here, let's assume that AnyObject uses a
     *    // SmartPtr<MyClass> internally here.
     *    // Now, both ptr_to_myclass and the internal
     *    // SmartPtr in obj point to the same MyClass object
     *    // and its reference count is 2.
     * 
     *    ...
     * 
     *    // No need to delete ptr_to_myclass, this
     *    // will be done automatically when the
     *    // reference count drops to zero.
     * 
     *  }   
     *  
     * \endverbatim
     *
     * It is not necessary to use SmartPtr's in all cases where an
     * object is used that has been allocated "into" a SmartPtr.  It is
     * possible to just pass objects by reference or regular pointers,
     * even if lower down in the stack a SmartPtr is to be held on to.
     * Everything should work fine as long as a pointer created by "new"
     * is immediately passed into a SmartPtr, and if SmartPtr's are used
     * to hold on to objects.
     *
     * Other Notes:
     *  The SmartPtr implements both dereference operators -> & *.
     *  The SmartPtr does NOT implement a conversion operator to
     *    the raw pointer. Use the GetRawPtr() method when this
     *    is necessary. Make sure that the raw pointer is NOT
     *    deleted. 
     *  The SmartPtr implements the comparison operators == & !=
     *    for a variety of types. Use these instead of
     *    \verbatim
     *    if (GetRawPtr(smrt_ptr) == ptr) // Don't use this
     *    \endverbatim
     * SmartPtr's, as currently implemented, do NOT handle circular references.
     *    For example: consider a higher level object using SmartPtrs to point to 
     *    A and B, but A and B also point to each other (i.e. A has a SmartPtr 
     *    to B and B has a SmartPtr to A). In this scenario, when the higher
     *    level object is finished with A and B, their reference counts will 
     *    never drop to zero (since they reference each other) and they
     *    will not be deleted. This can be detected by memory leak tools like
     *    valgrind. If the circular reference is necessary, the problem can be
     *    overcome by a number of techniques:
     *    
     *    1) A and B can have a method that "releases" each other, that is
     *        they set their internal SmartPtrs to NULL.
     *        \verbatim
     *        void AClass::ReleaseCircularReferences()
     *          {
     *          smart_ptr_to_B = NULL;
     *          }
     *        \endverbatim
     *        Then, the higher level class can call these methods before
     *        it is done using A & B.
     * 
     *    2) Raw pointers can be used in A and B to reference each other.
     *        Here, an implicit assumption is made that the lifetime is
     *        controlled by the higher level object and that A and B will
     *        both exist in a controlled manner. Although this seems 
     *        dangerous, in many situations, this type of referencing
     *        is very controlled and this is reasonably safe.
     * 
     *    3) This SmartPtr class could be redesigned with the Weak/Strong
     *        design concept. Here, the SmartPtr is identified as being
     *        Strong (controls lifetime of the object) or Weak (merely
     *        referencing the object). The Strong SmartPtr increments 
     *        (and decrements) the reference count in ReferencedObject
     *        but the Weak SmartPtr does not. In the example above,
     *        the higher level object would have Strong SmartPtrs to
     *        A and B, but A and B would have Weak SmartPtrs to each
     *        other. Then, when the higher level object was done with
     *        A and B, they would be deleted. The Weak SmartPtrs in A
     *        and B would not decrement the reference count and would,
     *        of course, not delete the object. This idea is very similar
     *        to item (2), where it is implied that the sequence of events 
     *        is controlled such that A and B will not call anything using
     *        their pointers following the higher level delete (i.e. in
     *        their destructors!). This is somehow safer, however, because
     *        code can be written (however expensive) to perform run-time 
     *        detection of this situation. For example, the ReferencedObject
     *        could store pointers to all Weak SmartPtrs that are referencing
     *        it and, in its destructor, tell these pointers that it is
     *        dying. They could then set themselves to NULL, or set an
     *        internal flag to detect usage past this point.
     * 
     * Comments on Non-Intrusive Design:
     * In a non-intrusive design, the reference count is stored somewhere other
     * than the object being referenced. This means, unless the reference
     * counting pointer is the first referencer, it must get a pointer to the 
     * referenced object from another smart pointer (so it has access to the 
     * reference count location). In this non-intrusive design, if we are 
     * pointing to an object with a smart pointer (or a number of smart
     * pointers), and we then give another smart pointer the address through
     * a RAW pointer, we will have two independent, AND INCORRECT, reference
     * counts. To avoid this pitfall, we use an intrusive reference counting
     * technique where the reference count is stored in the object being
     * referenced. 
     */
template < class T >
class SmartPtr {
public:
  /** Returns the raw pointer contained.  Use to get the value of the
	 * raw ptr (i.e. to pass to other methods/functions, etc.)  Note: This
	 * method does NOT copy, therefore, modifications using this value
	 * modify the underlying object contained by the SmartPtr, NEVER
	 * delete this returned value.
	 */
  T *GetRawPtr() const { return ptr_; }

  /** Returns true if the SmartPtr is NOT NULL.
	 * Use this to check if the SmartPtr is not null
	 * This is preferred to if(GetRawPtr(sp) != NULL)
	 */
  bool IsValid() const { return ptr_ != NULL; }

  /** Returns true if the SmartPtr is NULL.
	 * Use this to check if the SmartPtr IsNull.
	 * This is preferred to if(GetRawPtr(sp) == NULL)
	 */
  bool IsNull() const { return ptr_ == NULL; }

private:
  /**@name Private Data/Methods */
  //@{
  /** Actual raw pointer to the object. */
  T *ptr_;

  /** Release the currently referenced object. */
  void ReleasePointer_()
  {
    if (ptr_) {
      ptr_->ReleaseRef();
      if (ptr_->ReferenceCount() == 0) {
        delete ptr_;
      }
      ptr_ = NULL;
    }
  }

  /** Set the value of the internal raw pointer from another raw
	 * pointer, releasing the previously referenced object if necessary. */
  SmartPtr< T > &SetFromRawPtr_(T *rhs)
  {
    ReleasePointer_(); // Release any old pointer
    if (rhs != NULL) {
      rhs->AddRef();
      ptr_ = rhs;
    }
    return *this;
  }

  /** Set the value of the internal raw pointer from a SmartPtr,
	 * releasing the previously referenced object if necessary. */
  inline SmartPtr< T > &SetFromSmartPtr_(const SmartPtr< T > &rhs)
  {
    SetFromRawPtr_(rhs.GetRawPtr());
    return (*this);
  }

  //@}

public:
#define dbg_smartptr_verbosity 0

  /**@name Constructors/Destructors */
  //@{
  /** Default constructor, initialized to NULL */
  SmartPtr()
    : ptr_(NULL)
  {
  }

  /** Copy constructor, initialized from copy */
  SmartPtr(const SmartPtr< T > &copy)
    : ptr_(NULL)
  {
    (void)SetFromSmartPtr_(copy);
  }

  /** Constructor, initialized from T* ptr */
  SmartPtr(T *ptr)
    : ptr_(NULL)
  {
    (void)SetFromRawPtr_(ptr);
  }

  /** Destructor, automatically decrements the reference count, deletes
	 * the object if necessary.*/
  ~SmartPtr()
  {
    ReleasePointer_();
  }
  //@}

  /**@name Overloaded operators. */
  //@{
  /** Overloaded arrow operator, allows the user to call
	 * methods using the contained pointer. */
  T *operator->() const
  {
#if COIN_COINUTILS_CHECKLEVEL > 0
    assert(ptr_);
#endif
    return ptr_;
  }

  /** Overloaded dereference operator, allows the user
	 * to dereference the contained pointer. */
  T &operator*() const
  {
#if COIN_IPOPT_CHECKLEVEL > 0
    assert(ptr_);
#endif
    return *ptr_;
  }

  /** Overloaded equals operator, allows the user to
	 * set the value of the SmartPtr from a raw pointer */
  SmartPtr< T > &operator=(T *rhs)
  {
    return SetFromRawPtr_(rhs);
  }

  /** Overloaded equals operator, allows the user to
	 * set the value of the SmartPtr from another 
	 * SmartPtr */
  SmartPtr< T > &operator=(const SmartPtr< T > &rhs)
  {
    return SetFromSmartPtr_(rhs);
  }

  /** Overloaded equality comparison operator, allows the
	 * user to compare the value of two SmartPtrs */
  template < class U1, class U2 >
  friend bool operator==(const SmartPtr< U1 > &lhs, const SmartPtr< U2 > &rhs);

  /** Overloaded equality comparison operator, allows the
	 * user to compare the value of a SmartPtr with a raw pointer. */
  template < class U1, class U2 >
  friend bool operator==(const SmartPtr< U1 > &lhs, U2 *raw_rhs);

  /** Overloaded equality comparison operator, allows the
	 * user to compare the value of a raw pointer with a SmartPtr. */
  template < class U1, class U2 >
  friend bool operator==(U1 *lhs, const SmartPtr< U2 > &raw_rhs);

  /** Overloaded in-equality comparison operator, allows the
	 * user to compare the value of two SmartPtrs */
  template < class U1, class U2 >
  friend bool operator!=(const SmartPtr< U1 > &lhs, const SmartPtr< U2 > &rhs);

  /** Overloaded in-equality comparison operator, allows the
	 * user to compare the value of a SmartPtr with a raw pointer. */
  template < class U1, class U2 >
  friend bool operator!=(const SmartPtr< U1 > &lhs, U2 *raw_rhs);

  /** Overloaded in-equality comparison operator, allows the
	 * user to compare the value of a SmartPtr with a raw pointer. */
  template < class U1, class U2 >
  friend bool operator!=(U1 *lhs, const SmartPtr< U2 > &raw_rhs);
  //@}
};

template < class U1, class U2 >
bool ComparePointers(const U1 *lhs, const U2 *rhs)
{
  if (lhs == rhs) {
    return true;
  }
  // If lhs and rhs point to the same object with different interfaces
  // U1 and U2, we cannot guarantee that the value of the pointers will
  // be equivalent. We can guarantee this if we convert to void*.
  return static_cast< const void * >(lhs) == static_cast< const void * >(rhs);
}

} // namespace Coin

//#############################################################################

/**@name SmartPtr friends that are overloaded operators, so they are not in
   the Coin namespace. */
//@{
template < class U1, class U2 >
bool operator==(const Coin::SmartPtr< U1 > &lhs, const Coin::SmartPtr< U2 > &rhs)
{
  return Coin::ComparePointers(lhs.GetRawPtr(), rhs.GetRawPtr());
}

template < class U1, class U2 >
bool operator==(const Coin::SmartPtr< U1 > &lhs, U2 *raw_rhs)
{
  return Coin::ComparePointers(lhs.GetRawPtr(), raw_rhs);
}

template < class U1, class U2 >
bool operator==(U1 *raw_lhs, const Coin::SmartPtr< U2 > &rhs)
{
  return Coin::ComparePointers(raw_lhs, rhs.GetRawPtr());
}

template < class U1, class U2 >
bool operator!=(const Coin::SmartPtr< U1 > &lhs, const Coin::SmartPtr< U2 > &rhs)
{
  return !operator==(lhs, rhs);
}

template < class U1, class U2 >
bool operator!=(const Coin::SmartPtr< U1 > &lhs, U2 *raw_rhs)
{
  return !operator==(lhs, raw_rhs);
}

template < class U1, class U2 >
bool operator!=(U1 *raw_lhs, const Coin::SmartPtr< U2 > &rhs)
{
  return !operator==(raw_lhs, rhs);
}
//@}

#define CoinReferencedObject Coin::ReferencedObject
#define CoinSmartPtr Coin::SmartPtr
#define CoinComparePointers Coin::ComparePointers

#endif

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