Explicit Object Lifetime Management in C++
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Memory Safety Without Garbage Collection for Embedded Applications
Memory Safety Without Garbage Collection for Embedded Applications DINAKAR DHURJATI, SUMANT KOWSHIK, VIKRAM ADVE, and CHRIS LATTNER University of Illinois at Urbana-Champaign Traditional approaches to enforcing memory safety of programs rely heavily on run-time checks of memory accesses and on garbage collection, both of which are unattractive for embedded ap- plications. The goal of our work is to develop advanced compiler techniques for enforcing memory safety with minimal run-time overheads. In this paper, we describe a set of compiler techniques that, together with minor semantic restrictions on C programs and no new syntax, ensure memory safety and provide most of the error-detection capabilities of type-safe languages, without using garbage collection, and with no run-time software checks, (on systems with standard hardware support for memory management). The language permits arbitrary pointer-based data structures, explicit deallocation of dynamically allocated memory, and restricted array operations. One of the key results of this paper is a compiler technique that ensures that dereferencing dangling pointers to freed memory does not violate memory safety, without annotations, run-time checks, or garbage collection, and works for arbitrary type-safe C programs. Furthermore, we present a new inter- procedural analysis for static array bounds checking under certain assumptions. For a diverse set of embedded C programs, we show that we are able to ensure memory safety of pointer and dy- namic memory usage in all these programs with no run-time software checks (on systems with standard hardware memory protection), requiring only minor restructuring to conform to simple type restrictions. Static array bounds checking fails for roughly half the programs we study due to complex array references, and these are the only cases where explicit run-time software checks would be needed under our language and system assumptions. -
Memory Leak Or Dangling Pointer
Modern C++ for Computer Vision and Image Processing Igor Bogoslavskyi Outline Using pointers Pointers are polymorphic Pointer “this” Using const with pointers Stack and Heap Memory leaks and dangling pointers Memory leak Dangling pointer RAII 2 Using pointers in real world Using pointers for classes Pointers can point to objects of custom classes: 1 std::vector<int> vector_int; 2 std::vector<int >* vec_ptr = &vector_int; 3 MyClass obj; 4 MyClass* obj_ptr = &obj; Call object functions from pointer with -> 1 MyClass obj; 2 obj.MyFunc(); 3 MyClass* obj_ptr = &obj; 4 obj_ptr->MyFunc(); obj->Func() (*obj).Func() ↔ 4 Pointers are polymorphic Pointers are just like references, but have additional useful properties: Can be reassigned Can point to ‘‘nothing’’ (nullptr) Can be stored in a vector or an array Use pointers for polymorphism 1 Derived derived; 2 Base* ptr = &derived; Example: for implementing strategy store a pointer to the strategy interface and initialize it with nullptr and check if it is set before calling its methods 5 1 #include <iostream > 2 #include <vector > 3 using std::cout; 4 struct AbstractShape { 5 virtual void Print() const = 0; 6 }; 7 struct Square : public AbstractShape { 8 void Print() const override { cout << "Square\n";} 9 }; 10 struct Triangle : public AbstractShape { 11 void Print() const override { cout << "Triangle\n";} 12 }; 13 int main() { 14 std::vector<AbstractShape*> shapes; 15 Square square; 16 Triangle triangle; 17 shapes.push_back(&square); 18 shapes.push_back(&triangle); 19 for (const auto* shape : shapes) { shape->Print(); } 20 return 0; 21 } 6 this pointer Every object of a class or a struct holds a pointer to itself This pointer is called this Allows the objects to: Return a reference to themselves: return *this; Create copies of themselves within a function Explicitly show that a member belongs to the current object: this->x(); 7 Using const with pointers Pointers can point to a const variable: 1 // Cannot change value , can reassign pointer. -
CS 403/503: Programming Languages
BNF for <expression> <expression> → identifier | number | CS 403 -<expression> | (<expression>) | <expression><operator><expression> Organization of Programming Languages <operator> → + | - | * | / Class 3 - August 30, 2001 Topics For Today Parse Tree Review of BNF (Chapter 2.1) Derivations and parse trees (Chapter 2.1) Binding time (Chapter 3.1) Object lifetime and storage slope * x + intercept management (Chapter 3.2) BNF Concept Review Another Parse Tree Terminal symbols: Actual items that are part of the language (0,1,+,-,*,/,etc.) Non-Terminal symbols: <expr>, <op>, etc. Rule/production: A single line of BNF Alternatives: Expressed with | Also: slope * x + intercept *: 0 or more occurrences +:1 or more occurrences 1 Binding Lifetimes • Binding lifetime: The period of time Def: A binding is an association, such between the creation and destruction of a as between an attribute and an entity, name-to-object binding • Object lifetime: The period of time or between an operation and a between the creation and destruction of symbol. an object • These don’t necessarily coincide Def: Binding time is the time at which a • EX. Reference parameters binding takes place. Possible binding times Object Lifetimes… 1. Language design time--e.g., bind operator …correspond to one of three principal symbols to operations 2. Language implementation time--e.g., bind fl. pt. storage allocation mechanisms: type to a representation Static objects: Object lifetime = program 3. Compile time--e.g., bind a variable to a type in C execution. Object bound to one storage or Java location from load time on. 4. Load time--e.g., bind a FORTRAN 77 variable to a memory cell (or a C static variable) Stack objects: Object lifetime = subroutine 5. -
Smart Pointers Raw Pointers (1 of 3)
Data Abstraction & Problem Solving with C++: Walls and Mirrors Seventh Edition C++ Interlude 4 Safe Memory Management Using Smart Pointers Raw Pointers (1 of 3) • Allocate memory in free store by using new operator – Returns reference to newly created object in memory • Store reference to object in a pointer variable – Use pointer variable to access object • Copy reference to another pointer variable – Creates alias to same object Copyright © 2017, 2013, 2007 Pearson Education, Inc. All Rights Reserved Raw Pointers (2 of 3) • Use delete operator to deallocate object’s memory – Must also set to null p t r any pointer variables that referenced the object • Need to keep track number of aliases that reference an object … else results in – Dangling pointers – Memory leaks – Other errors (program crash, wasted memory, …) Copyright © 2017, 2013, 2007 Pearson Education, Inc. All Rights Reserved Raw Pointers (3 of 3) • Languages such as Java and Python disallow direct reference to objects – Use reference counting to track number of aliases that reference an object – Known as the “reference count” • Language can detect when object no longer has references – Can deallocate … known as “garbage collection” Copyright © 2017, 2013, 2007 Pearson Education, Inc. All Rights Reserved Smart Pointers (1 of 2) • C++ now supports “smart” pointers (or managed pointers) – Act like raw pointers – Also provide automatic memory management features • When you declare a smart pointer – Placed on application stack – Smart pointer references an object object is “managed” Copyright © 2017, 2013, 2007 Pearson Education, Inc. All Rights Reserved Smart Pointers (2 of 2) • Smart-pointer templates – shared_p t r – provides shared ownership of object – unique_p t r – no other pointer can reference same object – weak_p t r – reference to an object already managed by a shared pointer … does not have ownership of the object Copyright © 2017, 2013, 2007 Pearson Education, Inc. -
Metaclasses: Generative C++
Metaclasses: Generative C++ Document Number: P0707 R3 Date: 2018-02-11 Reply-to: Herb Sutter ([email protected]) Audience: SG7, EWG Contents 1 Overview .............................................................................................................................................................2 2 Language: Metaclasses .......................................................................................................................................7 3 Library: Example metaclasses .......................................................................................................................... 18 4 Applying metaclasses: Qt moc and C++/WinRT .............................................................................................. 35 5 Alternatives for sourcedefinition transform syntax .................................................................................... 41 6 Alternatives for applying the transform .......................................................................................................... 43 7 FAQs ................................................................................................................................................................. 46 8 Revision history ............................................................................................................................................... 51 Major changes in R3: Switched to function-style declaration syntax per SG7 direction in Albuquerque (old: $class M new: constexpr void M(meta::type target, -
C++/CLI Language Specification
Ecma/TC39-TG5/2004/25 C++/CLI Language Specification Working Draft 1.5, Jun, 2004 Public Review Document Text highlighted like this indicates a placeholder for some future action. It might be a note from the editor to himself, or an indication of the actual or expected direction of some as-yet open issue. Note: In the spirit of the "Working Draft, Standard for Programming Language C++", this is an early draft. It’s known to be incomplet and incorrekt, and it has lots of bad formatting. Publication Time: 6/17/2004 11:44 PM Table of Contents Table of Contents Introduction....................................................................................................................................................xi 1. Scope............................................................................................................................................................. 1 2. Conformance ............................................................................................................................................... 2 3. Normative references .................................................................................................................................. 3 4. Definitions .................................................................................................................................................... 4 5. Notational conventions................................................................................................................................ 7 6. Acronyms and abbreviations -
Transparent Garbage Collection for C++
Document Number: WG21/N1833=05-0093 Date: 2005-06-24 Reply to: Hans-J. Boehm [email protected] 1501 Page Mill Rd., MS 1138 Palo Alto CA 94304 USA Transparent Garbage Collection for C++ Hans Boehm Michael Spertus Abstract A number of possible approaches to automatic memory management in C++ have been considered over the years. Here we propose the re- consideration of an approach that relies on partially conservative garbage collection. Its principal advantage is that objects referenced by ordinary pointers may be garbage-collected. Unlike other approaches, this makes it possible to garbage-collect ob- jects allocated and manipulated by most legacy libraries. This makes it much easier to convert existing code to a garbage-collected environment. It also means that it can be used, for example, to “repair” legacy code with deficient memory management. The approach taken here is similar to that taken by Bjarne Strous- trup’s much earlier proposal (N0932=96-0114). Based on prior discussion on the core reflector, this version does insist that implementations make an attempt at garbage collection if so requested by the application. How- ever, since there is no real notion of space usage in the standard, there is no way to make this a substantive requirement. An implementation that “garbage collects” by deallocating all collectable memory at process exit will remain conforming, though it is likely to be unsatisfactory for some uses. 1 Introduction A number of different mechanisms for adding automatic memory reclamation (garbage collection) to C++ have been considered: 1. Smart-pointer-based approaches which recycle objects no longer ref- erenced via special library-defined replacement pointer types. -
Smart Pointer Demo Goals Time
Outline Smart Pointer Demo Goals Time CPSC 427: Object-Oriented Programming Michael J. Fischer Lecture 13 March 3, 2016 CPSC 427, Lecture 13 1/17 Outline Smart Pointer Demo Goals Time Smart Pointer Demo More on Course Goals Clocks and Time Measurement CPSC 427, Lecture 13 2/17 Outline Smart Pointer Demo Goals Time Smart Pointer Demo CPSC 427, Lecture 13 3/17 Outline Smart Pointer Demo Goals Time Dangling pointers Pointers can be used to permit object sharing from different contexts. One can have a single object of some type T with many pointers in different contexts that all point to that object. CPSC 427, Lecture 13 4/17 Outline Smart Pointer Demo Goals Time Problems with shared objects If the different contexts have different lifetimes, the problem is to know when it is safe to delete the object. It can be difficult to know when an object should be deleted. Failure to delete an object will cause memory leaks. If the object is deleted while there are still points pointing to it, then those pointers become invalid. We call these dangling pointers. Failure to delete or premature deletion of objects are common sources of errors in C++. CPSC 427, Lecture 13 5/17 Outline Smart Pointer Demo Goals Time Avoiding dangling pointers There are several ways to avoid dangling pointers. 1. Have a top-level manager whose lifetime exceeds that of all of the pointers take responsibility for deleting the objects. 2. Use a garbage collection. (This is java's approach.) 3. Use reference counts. That is, keep track somehow of the number of outstanding pointers to an object. -
C++/CLI Tutorial
CC++++//CCLLII TTuuttoorriiaall Author: Adam Sawicki, [email protected], www.asawicki.info Version 1.0, December 2011 Table of Contents Table of Contents .............................................................................................................................................................. 1 Introduction ...................................................................................................................................................................... 2 What is C++/CLI? ............................................................................................................................................................... 2 Why Use C++/CLI? ......................................................................................................................................................... 2 What C++/CLI is Not? .................................................................................................................................................... 2 Hello World Example ........................................................................................................................................................ 3 Project Properties ............................................................................................................................................................. 3 Namespaces ..................................................................................................................................................................... -
An Evolutionary Study of Linux Memory Management for Fun and Profit Jian Huang, Moinuddin K
An Evolutionary Study of Linux Memory Management for Fun and Profit Jian Huang, Moinuddin K. Qureshi, and Karsten Schwan, Georgia Institute of Technology https://www.usenix.org/conference/atc16/technical-sessions/presentation/huang This paper is included in the Proceedings of the 2016 USENIX Annual Technical Conference (USENIX ATC ’16). June 22–24, 2016 • Denver, CO, USA 978-1-931971-30-0 Open access to the Proceedings of the 2016 USENIX Annual Technical Conference (USENIX ATC ’16) is sponsored by USENIX. An Evolutionary Study of inu emory anagement for Fun and rofit Jian Huang, Moinuddin K. ureshi, Karsten Schwan Georgia Institute of Technology Astract the patches committed over the last five years from 2009 to 2015. The study covers 4587 patches across Linux We present a comprehensive and uantitative study on versions from 2.6.32.1 to 4.0-rc4. We manually label the development of the Linux memory manager. The each patch after carefully checking the patch, its descrip- study examines 4587 committed patches over the last tions, and follow-up discussions posted by developers. five years (2009-2015) since Linux version 2.6.32. In- To further understand patch distribution over memory se- sights derived from this study concern the development mantics, we build a tool called MChecker to identify the process of the virtual memory system, including its patch changes to the key functions in mm. MChecker matches distribution and patterns, and techniues for memory op- the patches with the source code to track the hot func- timizations and semantics. Specifically, we find that tions that have been updated intensively. -
C# Programming in Depth Lecture 4: Garbage Collection & Exception
Chair of Software Engineering C# Programming in Depth Prof. Dr. Bertrand Meyer March 2007 – May 2007 Lecture 4: Garbage Collection & Exception Handling Lisa (Ling) Liu Overview Scope and lifetime Garbage collection mechanism Exception handling C# programming lecture 4: Garbage Collection & Exception Handling 2 Scope and lifetime Scope of a variable is portion of program text within which it is declared ¾ Need not be contiguous ¾ In C#, is static: independent of data Lifetime or extent of storage is portion of program execution during which it exists ¾ Always contiguous ¾ Generally dynamic: dependent on data Class of lifetime ¾ Static: entire duration of program ¾ Local or automatic: duration of call or block execution (local variable) ¾ Dynamic: From time of allocation statement (new) to deallocation, if any. C# programming lecture 4: Garbage Collection & Exception Handling 3 Object lifetime in C# Memory allocation for an object should be made using the “new” keyword Objects are allocated onto the managed heap, where they are automatically deallocated by the runtime at “some time in the future” Garbage collection is automated in C# Rule: Allocate an object onto the managed heap using the new keyword and forget about it C# programming lecture 4: Garbage Collection & Exception Handling 4 Object creation When a call to new is made, it creates a CIL “newobj” instruction to the code module public static int Main (string[] args) { Car c = new Car(“Viper”, 200, 100); } IL_000c: newobj instance void CilNew.Car::.ctor (string, int32, -
These Aren't the COM Objects You're Looking For
These Aren't the COM Objects You're Looking For November, 2018 Victor Ciura Technical Lead, Advanced Installer www.advancedinstaller.com Abstract Windows COM is 25 years old. Yet it is relevant today more than ever, because Microsoft has bet its entire modern WinRT API on it (starting with Windows 8/10). But, if you’re familiar with the “old” COM with its idioms and SDK helper classes, you’re in for a treat. With the advent of modern C++ 17, using COM objects and new Windows APIs in your applications feels like a completely new experience. In this session, we’ll explore how using modern C++ features can radically transform the shape of your COM code. By eliminating a lot of boilerplate, your code will be much more readable and maintainable. Classic COM idioms around activation and QueryInterface() can feel totally different with modern C++ helpers. A beautiful example of modern COM usage is C++/WinRT (now part of Windows SDK). This is a standard C++ language projection for the new Windows Runtime API. COM memory management, data marshalling, string handling can all feel quite mechanical in nature and very error prone, so a little help from modern C++ facilities would be more than welcomed. Error handling and debugging can be cumbersome for COM like APIs; we’ll explore some tricks to improve this experience, as well. 2018 Victor Ciura | @ciura_victor !X These Aren't the COM Objects You're Looking For ⚙ Part 1 of N 2018 Victor Ciura | @ciura_victor !2 Why COM ? Why are we talking about this ? Have we really exhausted all the cool C++ template<> topics � ? 2018 Victor Ciura | @ciura_victor !3 Who Am I ? Advanced Installer Clang Power Tools @ciura_victor 2018 Victor Ciura | @ciura_victor !4 How many of you have done any COM programming in the last 20 years ? �$ 2018 Victor Ciura | @ciura_victor !5 How many of you are doing COM programming currently (this year) ? #$ 2018 Victor Ciura | @ciura_victor !6 Let's start using COM..