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// Copyright (C) 2004, 2006 International Business Machines and others.
// All Rights Reserved.
// This code is published under the Eclipse Public License.
//
// $Id: IpReferenced.hpp 2182 2013-03-30 20:02:18Z stefan $
//
// Authors: Carl Laird, Andreas Waechter IBM 2004-08-13
#ifndef __IPREFERENCED_HPP__
#define __IPREFERENCED_HPP__
#include "IpTypes.hpp"
#include "IpDebug.hpp"
#include <list>
#if COIN_IPOPT_CHECKLEVEL > 3
#define IP_DEBUG_REFERENCED
#endif
namespace Ipopt
{
/** Psydo-class, from which everything has to inherit that wants to
* use be registered as a Referencer for a ReferencedObject.
*/
class Referencer
{}
;
/** 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 "IpReferenced.hpp"
* namespace Ipopt {
*
* class MyClass : public ReferencedObject // must derive from ReferencedObject
* {
* ...
* }
* } // namespace Ipopt
*
*
* In my_usage.cpp...
*
* #include "IpSmartPtr.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
*
* 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.
*
* For every most derived object only one ReferencedObject may exist,
* that is multiple inheritance requires virtual inheritance, see also
* the 2nd point in ticket #162.
*
* 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()
{
DBG_ASSERT(reference_count_ == 0);
}
inline
Index ReferenceCount() const;
inline
void AddRef(const Referencer* referencer) const;
inline
void ReleaseRef(const Referencer* referencer) const;
private:
mutable Index reference_count_;
# ifdef IP_DEBUG_REFERENCED
mutable std::list<const Referencer*> referencers_;
# endif
};
/* inline methods */
inline
Index ReferencedObject::ReferenceCount() const
{
// DBG_START_METH("ReferencedObject::ReferenceCount()", 0);
// DBG_PRINT((1,"Returning reference_count_ = %d\n", reference_count_));
return reference_count_;
}
inline
void ReferencedObject::AddRef(const Referencer* referencer) const
{
// DBG_START_METH("ReferencedObject::AddRef(const Referencer* referencer)", 0);
reference_count_++;
// DBG_PRINT((1, "New reference_count_ = %d\n", reference_count_));
# ifdef IP_DEBUG_REFERENCED
referencers_.push_back(referencer);
# endif
}
inline
void ReferencedObject::ReleaseRef(const Referencer* referencer) const
{
// DBG_START_METH("ReferencedObject::ReleaseRef(const Referencer* referencer)",
// 0);
reference_count_--;
// DBG_PRINT((1, "New reference_count_ = %d\n", reference_count_));
# ifdef IP_DEBUG_REFERENCED
bool found = false;
std::list<const Referencer*>::iterator iter;
for (iter = referencers_.begin(); iter != referencers_.end(); iter++) {
if ((*iter) == referencer) {
found = true;
break;
}
}
// cannot call release on a reference that was never added...
DBG_ASSERT(found);
if (found) {
referencers_.erase(iter);
}
# endif
}
} // namespace Ipopt
#endif
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