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Beware of Pointers

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I talk on a variety of Smart Pointers in this lecture as Memory Management idioms in C++.

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October 28, November 4, December 2, 2005 Beware of Pointers! Dr. Partha Pratim Das Interra Systems (India) Pvt. Ltd. Resource Management Series
Resource Management ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Motivation ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Agenda ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Agenda ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Agenda ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Raw Pointers A Raw Deal?
What is a Raw Pointer? ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Pointered Languages : Pascal, Ada, C, C++
What is a Raw Pointer? ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
What is a Raw Pointer? ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Ownership Issue of Pointers ,[object Object],[object Object],// Create ownership MyClass *p = new MyClass; // Lose ownership p = 0;
Ownership Issue of Pointers ,[object Object],[object Object],// Create ownership MyClass *p = new MyClass; // Copy ownership – no Copy Constructor! MyClass *q = p; // Delete Object & Remove ownership delete q; // Delete Object – where is the ownership? delete p;
Ownership Issue of Pointers ,[object Object],[object Object],void MyAction() { // Create ownership MyClass *p = new MyClass; // What if an exception is thrown here? p->Function(); // Delete Object & Remove ownership delete p; }
Ownership Issue of Pointers ,[object Object],void MyAction() { MyClass *p = 0; try { MyClass *p = new MyClass; p->Function(); } catch (…) { delete p; // Repeated code throw; } delete p; }
Ownership Issue of Pointers ,[object Object],void MyDoubleAction() { MyClass *p = 0, *q = 0; try { MyClass *p = new MyClass; p->Function(); MyClass *q = new MyClass; q->Function(); } catch (…) { delete p; // Repeated code delete q; // Repeated code throw; } delete p; delete q; }
Pointer Hazards ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Pointer Hazards: PREfix Simulation Results
A Pointer-free World Reality or Utopia?
How to deal with an Object? ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Pointers vis-à-vis Reference ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Pointers-free Languages ,[object Object],[object Object],[object Object],[object Object]
Pointers-free Languages ,[object Object],[object Object],[object Object],[object Object]
Pointers-free Languages ,[object Object],[object Object],[object Object],“ Most studies agree that pointers are one of the primary features that enable programmers to put bugs into their code. Given that structures are gone, and arrays and strings are objects, the need for pointers to these constructs goes away . ” – The Java Language Environment: A White Paper , Sun 1995. ( http://java.sun.com )
Pointers-free Languages ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Pointers-free Languages ,[object Object],[object Object],[object Object],[object Object],[object Object],“ Programming languages should be designed not by piling feature on top of feature, but by removing the weaknesses and restrictions that make additional features appear necessary. ” – Revised Report on Scheme, 1991
Pointers-free Languages ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],“ A language that doesn't affect the way you think about programming, is not worth knowing. ” – Alan Perlis
Smart Pointers in C++ The Smartness …
What is Smart Pointer? ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
What is Smart Pointer? ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
A Simple Smart Pointer ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
A Smart Pointer mimics a Raw Pointer ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Smart Pointer Member Functions ,[object Object],[object Object],SmartPtr<Printer> spRes = ...; spRes->Acquire(); // acquire the printer ... print a document ... spRes->Release(); // release the printer spRes.Release(); // release the pointer to the printer // GetImpl returns the pointer object stored by SmartPtr template <class T> T* GetImpl(SmartPtr<T>& sp); // GetImplRef returns a reference to the pointer stored by SmartPtr template <class T> T*& GetImplRef(SmartPtr<T>& sp); // Reset resets the underlying pointer to another value, // Releases the previous one template <class T> void Reset(SmartPtr<T>& sp, T* source); // Release releases ownership of the smart pointer template <class T> void Release(SmartPtr<T>& sp, T*& destination);
A Smart Pointer Use-Case ,[object Object],[object Object],[object Object],[object Object],[object Object]
A Smart Pointer Use-Case ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
A Smart Pointer Use-Case ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
A Smart Pointer Use-Case ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
The Smartness … ,[object Object],[object Object],[object Object],[object Object],[object Object]
The Smartness … ,[object Object],[object Object],[object Object],[object Object]
Smart Pointers in C++ Storage Policy
3–Way Storage Policy ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Smart Pointers in C++ Ownership Management Policy
Ownership Management Policy ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Ownership Policy: Destructive Copy ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Ownership Policy: Destructive Copy template <class T> class SmartPtr { public: SmartPtr(SmartPtr& src) { // Src ptr is not const pointee_ = src.pointee_; // Copy src.pointee_ = 0; // Remove ownership for src ptr } SmartPtr& operator=(SmartPtr& src) { // Src ptr is not const if (this != &src) { // Check & skip self-copy delete pointee_; // Release destination object pointee_ = src.pointee_; // Assignment src.pointee_ = 0; // Remove ownership for src ptr } return *this; // Return the assigned Smart Pointer } ... };
Ownership Policy: Destructive Copy – The Maelstrom Effect ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],void Display(SmartPtr<Something> sp); ... SmartPtr<Something> sp(new Something); Display(sp); // sinks sp STL Containers need FCO.
Ownership Policy: Destructive Copy – Advantages ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Ownership Policy: Deep Copy ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Ownership Policy: Deep Copy – Object Slicing ,[object Object],[object Object],[object Object],template <class T> class SmartPtr { public: SmartPtr(const SmartPtr& other): pointee_(new T(*other.pointee_)) { ... } ... };
Ownership Policy: Deep Copy – Transport Polymorphic Objects ,[object Object],[object Object],// Base class provides a prototype for Clone class AbstractBase { ... virtual Base* Clone() = 0; }; // Derived class implements Clone class Concrete : public AbstractBase { ... virtual Base* Clone() { return new Concrete(*this); } };
Ownership Policy: Copy-on-Write (COW) ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Ownership Policy: Reference Counting ,[object Object],[object Object],[object Object],[object Object],[object Object]
Ownership Policy: Reference Counting ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Ownership Policy: Reference Counting: Non-Intrusive Counter ,[object Object],[object Object],[object Object]
Ownership Policy: Reference Counting: Non-Intrusive Counter ,[object Object],[object Object]
Ownership Policy: Reference Counting: Intrusive Counter ,[object Object],[object Object],[object Object]
Ownership Policy: Reference Linking ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Ownership Policy: Reference Linking ,[object Object],[object Object],[object Object],[object Object]
Ownership Policy: Reference Management – Disadvantage ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Ownership Policy: Cyclic Reference – Hack ,[object Object],[object Object],[object Object],[object Object],[object Object],Smart Pointers “own”; Raw Pointers “disowns”?
Ownership Policy: Cyclic Reference – Solution ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Smart Pointers in C++ Implicit Conversion
Implicit Conversion ,[object Object],[object Object],[object Object],// For maximum compatibility this should work void Fun(Something* p); ... SmartPtr<Something> sp(new Something); Fun(sp); // OK or error? template <class T> class SmartPtr { public: operator T*() // user-defined conversion to T* { return pointee_; } ... };
Implicit Conversion: The Pitfall ,[object Object],[object Object],[object Object],[object Object],// A gross semantic error that goes undetected at compile time SmartPtr<Something> sp; ... delete sp; // Compiler passes this by casting to raw pointer template <class T> class SmartPtr { public: operator T*() // User-defined conversion to T* { return pointee_; } operator void*() // Added conversion to void* { return pointee_; } ... }; “ When in doubt, use brute force. ” – Ken Thompson
Smart Pointers in C++ Null Tests
Null Tests ,[object Object],[object Object],[object Object],[object Object],[object Object],SmartPtr<Something> sp1, sp2; Something* p; ... if (sp1) // Test 1: direct test for non-null pointer ... if (!sp1) // Test 2: direct test for null pointer ... if (sp1 == 0) // Test 3: explicit test for null pointer ...
Null Tests ,[object Object],template <class T> class SmartPtr { public: // Returns true iff pointee is NULL bool operator!() { return pointee_ == 0; } }; if (sp1) // Rewrite as if (!!sp1) if (!sp1) // Works fine if (sp1 == 0) // Does not work
Smart Pointers in C++ Checking Policy
Checking Policy ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Checking Policy: Initialization Checking ,[object Object],[object Object],[object Object],[object Object],template <class T> class SmartPtr { public: // Prohibit NULL for initialization SmartPtr(T* p): pointee_(p) { if (!p) throw NullPointerException(); } ... };
Checking Policy: Checking before Dereferencing ,[object Object],[object Object],[object Object],[object Object],template <class T> class SmartPtr { public: T& operator*() const { // Dereferencing if (!pointee_) throw NullPointerException(); else return *pointee_; } T* operator->() const { // Indirection if (!pointee_) throw NullPointerException(); else return pointee_; } ... }; if (p) { /* Dereference & use p */ } else { /* Handle null pointer condition */ }
Checking Policy: Error Reporting ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],template <class T> class SmartPtr { public: T& operator*() { // Dereferencing. No Constant if (!pointee_) pointee_ = new T; return *pointee_; } T* operator->() { // Indirection. No Constant if (!pointee_) pointee_ = new T; return pointee_; } ... };
Smart Pointers in C++ Other Design Issues
What is a Smart Pointer? ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Other Design Issues ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Smart Pointers in C++ Performance Issues
Space Overhead in Smart Pointers 4 pointer_next *n+4 pointer_prev *n Reference Linking 4 counter RC: Intrusive 4 pointer +4 counter RC: Non-Intrusive (1) 4 pointer *n+4 counter RC: Non-Intrusive (n) <= (n-1)*sizeof(<Object>) COW (n-1)*sizeof(<Object>) Deep Copy Nil Destructive Copy Overhead Ownership
Smart Pointer Timing (GCC, MSVC) ,[object Object],[object Object],[object Object]
Smart Pointers in Practice A Few Examples
Smart Pointers in Practice ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],“ Think of the Standard C++ auto_ptr as the Ford Escort of smart pointers: A simple general-purpose smart pointer that doesn't have all the gizmos and luxuries of special-purpose or high-performance smart pointers, but that does many common things well and is perfectly suitable for regular daily use. ” – C/C++ Users Jounral, October 1999.
Smart Pointers in Practice ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Smart Pointers in Practice ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
std::auto_ptr The Smart Pointer in Standard Library
std::auto_ptr ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
std::auto_ptr ,[object Object],“ Think of the Standard C++ auto_ptr as the Ford Escort of smart pointers: A simple general-purpose smart pointer that doesn't have all the gizmos and luxuries of special-purpose or high-performance smart pointers, but that does many common things well and is perfectly suitable for regular daily use. ” – C/C++ Users Jounral, October 1999.
std::auto_ptr ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
std::auto_ptr ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
std::auto_ptr Standard Interface Sample Implementation
std::auto_ptr Interface ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
std::auto_ptr Interface ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
std::auto_ptr Interface ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
std::auto_ptr Interface ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
std::auto_ptr Implementation ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
std::auto_ptr Implementation ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
std::auto_ptr Implementation ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
std::auto_ptr Implementation ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
std::auto_ptr Implementation ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
std::auto_ptr Using Idioms
Using std::auto_ptr – Safety ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Using std::auto_ptr – const-ness ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Guard Maelstrom Effect
Using std::auto_ptr – Common Stuff ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Using std::auto_ptr – reset() ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Using std::auto_ptr – Ownership ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Using std::auto_ptr – Source ,[object Object],[object Object],[object Object],[object Object],[object Object],Resource creator
Using std::auto_ptr – Sink ,[object Object],[object Object],[object Object],[object Object],Resource releaser
std::auto_ptr History
History of auto_ptr ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
History of auto_ptr ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
auto_ptr: Version 1 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
auto_ptr: Version 1 – Shortcomings ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
auto_ptr: Version 2 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
auto_ptr: Version 2 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],These methods matter!
auto_ptr: Version 2 – Shortcomings ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
auto_ptr: Version 3 ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],Colvin-Gibbons Trick
auto_ptr: Version 3 – Advantages ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
auto_ptr: Version 3 – Advantages ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
auto_ptr: Version 3 – Advantages ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
auto_ptr: Version 3 – Advantages ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
auto_ptr: Version 3 – Advantages ,[object Object]
std::auto_ptr Portability
What is your auto_ptr? ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
std::auto_ptr Pitfalls
auto_arrays! ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
auto_arrays! Survival ,[object Object],[object Object]
Coping with COAP ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Coping with COAP: Survival ,[object Object]
Smart Pointers in C++ References & Credits
References: Books ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
References: Papers ,[object Object],[object Object]
References: Online Help ,[object Object],[object Object],[object Object]
References: Codes ,[object Object]
References: Code URLs ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
References: Knowledge URLs ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Credits / Acknowledgements ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Thank You Don’t Beware of Pointers – Just Be Aware of Smart Pointers
std::tr1::shared_ptr std::tr1::weak_ptr Additional Smart Pointers in TR1 Standard Library of C++ ISO/IEC PDTR 19768. Doc No: N1745=05-0005. Date: 2005-01-17
Motivation for a Shared-Ownership Smart Pointer ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Motivation for the shared_ptr (Shared-Ownership) ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Motivation for the shared_ptr (Shared-Ownership) ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Motivation for the weak_ptr (Shared-Ownership-Observer) ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Implementation Difficulty of Shared-Ownership Smart Pointer ,[object Object],[object Object],[object Object]
Implementation Difficulty of Shared-Ownership Smart Pointer ,[object Object],[object Object],[object Object]
Implementation Difficulty of Shared-Ownership Smart Pointer ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Additional Implementation Difficulty of weak_ptr ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Impact on the Standard ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Design Decisions ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Design Decisions: General Principles ,[object Object],[object Object],[object Object],[object Object],[object Object]
As Close to Raw Pointers as Possible’ but no close ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
As Close to Raw Pointers as Possible’ but no Closer ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Just Do the Right Thing ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
No Extra Parameter ,[object Object],[object Object],[object Object],[object Object]
“ Shares Ownership With” is an Equivalence Relation ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
“ Shares Ownership With” is an Equivalence Relation ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
The “Empty Pointer” Concept ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
The “Empty Pointer” Concept ,[object Object],[object Object],[object Object]
The “Empty Pointer” Concept ,[object Object],[object Object],[object Object],[object Object]
The “Empty Pointer” Concept ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
The “Empty Pointer” Concept ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Design Decisions: shared_ptr ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Design Decisions: weak_ptr ,[object Object],[object Object],[object Object]
Design Decisions: enable_shared_from_this
Design Decisions: Size & Performance ,[object Object],[object Object],[object Object]
Design Decisions: Alternatives ,[object Object],[object Object]
Incomplete Type ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Smart Pointer Classes in <memory> ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
class bad_weak_ptr ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
class shared_ptr ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
class shared_ptr ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
class shared_ptr ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
class shared_ptr ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
class shared_ptr ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]
Design Decisions ,[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object],[object Object]

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Beware of Pointers

  • 1. October 28, November 4, December 2, 2005 Beware of Pointers! Dr. Partha Pratim Das Interra Systems (India) Pvt. Ltd. Resource Management Series
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  • 7. Raw Pointers A Raw Deal?
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  • 17. Pointer Hazards: PREfix Simulation Results
  • 18. A Pointer-free World Reality or Utopia?
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  • 27. Smart Pointers in C++ The Smartness …
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  • 39. Smart Pointers in C++ Storage Policy
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  • 41. Smart Pointers in C++ Ownership Management Policy
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  • 44. Ownership Policy: Destructive Copy template <class T> class SmartPtr { public: SmartPtr(SmartPtr& src) { // Src ptr is not const pointee_ = src.pointee_; // Copy src.pointee_ = 0; // Remove ownership for src ptr } SmartPtr& operator=(SmartPtr& src) { // Src ptr is not const if (this != &src) { // Check & skip self-copy delete pointee_; // Release destination object pointee_ = src.pointee_; // Assignment src.pointee_ = 0; // Remove ownership for src ptr } return *this; // Return the assigned Smart Pointer } ... };
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  • 61. Smart Pointers in C++ Implicit Conversion
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  • 64. Smart Pointers in C++ Null Tests
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  • 67. Smart Pointers in C++ Checking Policy
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  • 72. Smart Pointers in C++ Other Design Issues
  • 73.
  • 74.
  • 75. Smart Pointers in C++ Performance Issues
  • 76. Space Overhead in Smart Pointers 4 pointer_next *n+4 pointer_prev *n Reference Linking 4 counter RC: Intrusive 4 pointer +4 counter RC: Non-Intrusive (1) 4 pointer *n+4 counter RC: Non-Intrusive (n) <= (n-1)*sizeof(<Object>) COW (n-1)*sizeof(<Object>) Deep Copy Nil Destructive Copy Overhead Ownership
  • 77.
  • 78. Smart Pointers in Practice A Few Examples
  • 79.
  • 80.
  • 81.
  • 82. std::auto_ptr The Smart Pointer in Standard Library
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  • 87. std::auto_ptr Standard Interface Sample Implementation
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  • 126. Smart Pointers in C++ References & Credits
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  • 134. Thank You Don’t Beware of Pointers – Just Be Aware of Smart Pointers
  • 135. std::tr1::shared_ptr std::tr1::weak_ptr Additional Smart Pointers in TR1 Standard Library of C++ ISO/IEC PDTR 19768. Doc No: N1745=05-0005. Date: 2005-01-17
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  • 160. Design Decisions: enable_shared_from_this
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Hinweis der Redaktion

  1. An object has ValueSemantics when it can be treated as a single value. In C++ this means implementing a copy constructor and an assignment operator in such a way that when a new or existing instance is set equal to some other instance the new instance will be equivalent to the old one without acting as an alias to it. In computing , a first-class object (also -value , -entity , -citizen ), in the context of a particular programming language , is an entity which can be used in programs without restriction (when compared to other kinds of objects in the same language). Depending on the language, this can imply: being expressible as an anonymous literal value being storable in variables being storable in data structures having an intrinsic identity (independent of any given name) being comparable for equality with other entities being passable as a parameter to a procedure/function being returnable as the result of a procedure/function being constructable at runtime For example, in C , it is not possible to create new functions at runtime (however, see discussion ), whereas other kinds of object can be created at runtime. So functions in C are not first-class objects; sometimes they are called &amp;quot; second-class objects &amp;quot;. Similarly, strings are not first class objects in Fortran as it is not possible to assign them to variables, whereas numbers can be so assigned. Retrieved from &amp;quot; http://en.wikipedia.org/wiki/First-class_object &amp;quot;
  2. Source: “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html
  3. Source: “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html
  4. Source: “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html
  5. Source: “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html
  6. Source: “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html
  7. Source: “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html
  8. Source: “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html
  9. Source: “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html
  10. Source: “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html
  11. Source: “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html
  12. Source: “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html
  13. Source: “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html
  14. Source: cv-qualified type : http://www.embedded.com/showArticle.jhtml?articleID=9900322 A cv-qualified type has the form &amp;quot; cv T &amp;quot; where, cv is a sequence of cv-qualifiers ( const and volatile ) and T is a type (without cv-qualifiers). The sequence cv can be empty, just const by itself, just volatile by itself, or const volatile (in either order). For any two sequences of cv-qualifiers cv1 and cv2 , we say that cv1 has the same or greater cv-qualification than cv2 , and write cv1 &gt;= cv2 , if every cv-qualifier in cv2 also appears in cv1 . If cv1 &gt;= cv2 is false, then we say that cv1 has less cv-qualification than cv2 . “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html
  15. Source: “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html
  16. Source: “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html
  17. Source: “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html
  18. Source: “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html
  19. Source: “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html
  20. Source: “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html
  21. Source: “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html
  22. Source: “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html
  23. Source: “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html “ We have since produced a proof of concept implementation that follows the first model and statisfies the requirement without significant size or performance implications. As a result, this version of the proposal requires use_count() == 0 to hold for all empty pointers, and the code sample will reliably print &amp;quot;std::bad_weak_ptr&amp;quot;.” – What does it mean?
  24. Source: “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html
  25. Source: “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html
  26. Source: “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html
  27. Source: “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html
  28. Source: “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html
  29. Source: “ Incomplete Types” (MSDN) http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vccelng/htm/decla_39.asp “ Incomplete Types” (IBM) http://publib.boulder.ibm.com/infocenter/macxhelp/index.jsp?topic=/com.ibm.vacpp6m.doc/language/ref/clrc03incotyp.htm
  30. Source: “ A Proposal to Add General Purpose Smart Pointers to the Library Technical Report ”, 27-Mar-03. http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2003/n1450.html