Introduction to Smart Pointer

A report on smart pointer, presented in nhpcc in China.

Transcript

1. Smart Pointer Lyd. http://shonenada.com shonenada@gmail.com
2. • More about Smart Pointer • C++0x VS Boost • Performance • Usage • Some advices • Reference Outline • More about Smart Pointer • C++0x VS Boost • Performance • Usage • Some advices • Reference
3. More about Smart Pointer More about Smart Pointer
4. • A decorator (wrapper) of raw pointer. • A template class. • Two Kinds of Smart Pointer: shared and unique More about Smart Pointer • A decorator (wrapper) of raw pointer. • A template class. • Two Kinds of Smart Pointer: shared and unique
5. • A decorator (wrapper) of raw pointer. • A template class. • Two Kinds of Smart Pointer: shared and unique More about Smart Pointer • A decorator (wrapper) of raw pointer. • A template class. • Two Kinds of Smart Pointer: shared and unique
6. C++0x VS Boost C++0x VS Boost
7. • std::shared_ptr is the C++0x form of tr1::shared_ptr, and boost's boost::shared_ptr should behave the same. • According to the Wikipedia C++0x page: The TR1 implementation lacked certain pointer features such as aliasing and pointer arithmetic, but the C++0x version will add these. • Now, C++11 provides std::unique_ptr, as well as improvements to std::shared_ptr and std::weak_ptr from TR1. std::auto_ptr is deprecated. • In generally, there is little different between std and boost on smart pointer operations. C++0x VS Boost • std::shared_ptr is the C++0x form of tr1::shared_ptr, and boost's boost::shared_ptr should behave the same. • According to the Wikipedia C++0x page: The TR1 implementation lacked certain pointer features such as aliasing and pointer arithmetic, but the C++0x version will add these. • Now, C++11 provides std::unique_ptr, as well as improvements to std::shared_ptr and std::weak_ptr from TR1. std::auto_ptr is deprecated. • In generally, there is little different between std and boost on smart pointer operations.
8. Performance Performance
9. • Define a class with a double variable. • Just do one thing: variable num multiply itself 10,000 times. Performance • Define a class with a double variable. • Just do one thing: variable num multiply itself 10,000 times.
10. Performance Raw Pointer Smart Pointer
11. Performance • Simple test for Raw Pointer. • Simple test for Raw Pointer.
12. • Simple test for Smart Pointer. Performance • Simple test for Smart Pointer.
13. Performance
14. Performance How about 10,000 times? How about 50,000 times? How about 50,000 times? How about 100,000 times?
15. Performance • More tests for both raw pointer and smart pointer. • More tests for both raw pointer and smart pointer.
16. Performance • What does the program do? • 1. Allocation. • 2. Multiplying. • 3.Freed. • !Important!: Each multiplying will multipy a double variable for 10,000 times. • What does the program do? • 1. Allocation. • 2. Multiplying. • 3.Freed. • !Important!: Each multiplying will multipy a double variable for 10,000 times.
17. • In this test, the program actually does 10,000 * 10,000 = 100,000,000 times multiplying. Performance • In this test, the program actually does 10,000 * 10,000 = 100,000,000 times multiplying.
18. • In this test, the program actually does 50,000 * 10,000 = 500,000,000 times multiplying. Performance • In this test, the program actually does 50,000 * 10,000 = 500,000,000 times multiplying.
19. • In this test, the program actually does 100,000 * 10,000 = 1,000,000,000 times multiplying. Performance • In this test, the program actually does 100,000 * 10,000 = 1,000,000,000 times multiplying.
20. Performance
21. Performance
22. • Just allocation: Performance
23. • Compared to raw pointer, smart pointer spends more time on allocating. Performance
24. Usage Usage
25. Usage • Create a shared pointer object • weak pointer • Delete • Invoke methods of class • Get the raw pointer • swap • Create a shared pointer object • weak pointer • Delete • Invoke methods of class • Get the raw pointer • swap
26. #include <memory> #include <memory>
27. Usage (Create) • One of constructors: The key word explicit avoids compiler to construct object using implicit conversion. For example: shared_ptr<MyClass> obj = new MyClass(); In the case without using explicit key word: obj will convert to shared_ptr type. More details in 《More Effective C++》
28. • To create a smart pointer object, just: • Or take cGeDBIT as an example: • Vector: Usage (Create) • To create a smart pointer object, just: • Or take cGeDBIT as an example: • Vector: Be carefull!!
29. • In the case like: • It is impossible to freed “Child1” and “Leaf” • So, weak_ptr appears Usage (weak pointer) Root • In the case like: • It is impossible to freed “Child1” and “Leaf” • So, weak_ptr appears Child1 Child2 Child3 Leaf
30. • What is weak_ptr: • weak_ptr is a companion pointer which points to the object owned by shared_ptr without having an increment in the reference counter. Usage (weak pointer) • What is weak_ptr: • weak_ptr is a companion pointer which points to the object owned by shared_ptr without having an increment in the reference counter.
31. • In another case like: • Child1 will be removed when Root is removed Usage (weak pointer) Root • In another case like: • Child1 will be removed when Root is removed Child1 Child2 Child3 Leaf
32. Usage (weak pointer)
33. Usage (delete) • To delete a shared_ptr object,use reset() method: • To delete a shared_ptr object,use reset() method:
34. • Invoking a method looks like raw pointer. Usage (Invoke)
35. • To get the raw pointer, use get() method: Usage (Get raw poiner)
36. • Also take cGeDBIT as an example: Usage(Get raw poiner)
37. Usage(swap)
38. Some advices Some advices
39. Some advices • Type Conversion • Code Writing.
40. Some advices(Type Conversion) • Use C++-style type conversion • Use static_cast<newType*>(expression) instead of using (type*) (expression) • Safe & Readable • Use C++-style type conversion • Use static_cast<newType*>(expression) instead of using (type*) (expression) • Safe & Readable
41. Some advices(more Type Conversion) • More C++-style type conversion • const_cast<type*>(expression) • dynamic_cast<type*>(expression)
42. Some advices(Code Writing) • Codes are written by human. • Codes are read by human!!! • Tidy and readable is so important! • Codes are written by human. • Codes are read by human!!! • Tidy and readable is so important!
43. • Varibale/Function Name • What is “a” Some advices(Code Writing) • Varibale/Function Name • What is “a”
44. • Max length of a line • My hands are on the keyboard, I don’t want to drag the scroll bar..... • https://github.com/facebook/folly/ • https://github.com/chenshuo/muduo-protorpc Some advices(Code Writing) • Max length of a line • My hands are on the keyboard, I don’t want to drag the scroll bar..... • https://github.com/facebook/folly/ • https://github.com/chenshuo/muduo-protorpc
45. • More space and More Enter • Space on both side of operator. Some advices(Code Writing) • More space and More Enter • Space on both side of operator.
46. • More space and More Enter • Space on both side of operator. Some advices(Code Writing) • More space and More Enter • Space on both side of operator.
47. • Suitable brackets Some advices(Code Writing) • Suitable brackets
48. • NO Zombie code, VCS can help you! Some advices(Code Writing) • NO Zombie code, VCS can help you!
49. • http://www.codesynthesis.com/~boris/blog/2010/05/24/smart-pointers-in- boost-tr1-cxx-x0/ • http://pic.dhe.ibm.com/infocenter/aix/v6r1/index.jsp?topic=%2Fcom.ibm.aix. cmds%2Fdoc%2Faixcmds5%2Ftime.htm • http://gcc.gnu.org/onlinedocs/gcc-4.6.0/libstdc++/api/a01033_source.html • http://www.boost.org/doc/libs/1_53_0/libs/smart_ptr/smart_ptr.htm • http://stackoverflow.com/questions/4902313/difference-between- boostshared-ptr-and-stdshared-ptr-from-the-standard-memo • http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3225.pdf • http://en.wikipedia.org/wiki/C%2B%2B0x#General-purpose_smart_pointers • http://en.wikipedia.org/wiki/Smart_pointer#C.2B.2B_smart_pointers • http://en.cppreference.com/w/cpp/memory/shared_ptr • 《More Effective C++》 Reference • http://www.codesynthesis.com/~boris/blog/2010/05/24/smart-pointers-in- boost-tr1-cxx-x0/ • http://pic.dhe.ibm.com/infocenter/aix/v6r1/index.jsp?topic=%2Fcom.ibm.aix. cmds%2Fdoc%2Faixcmds5%2Ftime.htm • http://gcc.gnu.org/onlinedocs/gcc-4.6.0/libstdc++/api/a01033_source.html • http://www.boost.org/doc/libs/1_53_0/libs/smart_ptr/smart_ptr.htm • http://stackoverflow.com/questions/4902313/difference-between- boostshared-ptr-and-stdshared-ptr-from-the-standard-memo • http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2010/n3225.pdf • http://en.wikipedia.org/wiki/C%2B%2B0x#General-purpose_smart_pointers • http://en.wikipedia.org/wiki/Smart_pointer#C.2B.2B_smart_pointers • http://en.cppreference.com/w/cpp/memory/shared_ptr • 《More Effective C++》
50. Thank You! Thank You! Lyd. http://shonenada.com shonenada@gmail.com