| Les deux révisions précédentesRévision précédenteProchaine révision | Révision précédente |
| helloworld:design_pattern:singleton:cplusplus [2018/03/25 20:43] – Ajout d'un singleton avec constructeur non trivial root | helloworld:design_pattern:singleton:cplusplus [2022/07/04 10:06] (Version actuelle) – [Solution] : lock_guard->scoped_lock root |
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| ====Problème==== | ====Problème==== |
| [[http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html|The "Double-Checked Locking is Broken" Declaration]] {{ :helloworld:design_pattern:singleton:cplusplus:the_double-checked_locking_is_broken_declaration.mhtml |Archive}} | [[http://www.cs.umd.edu/~pugh/java/memoryModel/DoubleCheckedLocking.html|The "Double-Checked Locking is Broken" Declaration]] {{ :helloworld:design_pattern:singleton:cplusplus:the_double-checked_locking_is_broken_declaration_2020-04-28_8_38_20_am_.html |Archive le 28/04/2020}} |
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| [[http://www.aristeia.com/Papers/DDJ_Jul_Aug_2004_revised.pdf|C++ and the Perils of Double-Checked Locking]] {{ :helloworld:design_pattern:singleton:cplusplus:ddj_jul_aug_2004_revised.pdf |Archive}} | [[http://www.aristeia.com/Papers/DDJ_Jul_Aug_2004_revised.pdf|C++ and the Perils of Double-Checked Locking]] {{ :helloworld:design_pattern:singleton:cplusplus:ddj_jul_aug_2004_revised.pdf |Archive}} |
| * Step 3. Make pInstance point to the allocated memory. | * Step 3. Make pInstance point to the allocated memory. |
| Of critical importance is the observation that compilers are not constrained to perform these steps in this order! **In particular, compilers are sometimes allowed to swap Steps 2 and 3**. Why they might want to do that is a question we'll address in a moment. For now, let's focus on what happens if they do. | Of critical importance is the observation that compilers are not constrained to perform these steps in this order! **In particular, compilers are sometimes allowed to swap Steps 2 and 3**. Why they might want to do that is a question we'll address in a moment. For now, let's focus on what happens if they do. |
| <cite>[[http://www.drdobbs.com/cpp/c-and-the-perils-of-double-checked-locki/184405726|C++ and The Perils of Double-Checked Locking: Part I]] {{ :helloworld:design_pattern:singleton:cplusplus:c_and_the_perils_of_double-checked_locking_part_i_dr_dobb_s.mhtml |Archive}}</cite> | <cite>[[http://www.drdobbs.com/cpp/c-and-the-perils-of-double-checked-locki/184405726|C++ and The Perils of Double-Checked Locking: Part I]] {{ :helloworld:design_pattern:singleton:cplusplus:c_and_the_perils_of_double-checked_locking_part_i_dr_dobb_s_2020-04-28_8_41_39_am_.html |Archive du 01/07/2004 le 28/04/2020}}</cite> |
| <cite>[[http://www.drdobbs.com/cpp/c-and-the-perils-of-double-checked-locki/184405772|C++ and The Perils of Double-Checked Locking: Part II]] {{ :helloworld:design_pattern:singleton:cplusplus:c_and_the_perils_of_double-checked_locking_part_ii_dr_dobb_s.mhtml |Archive}}</cite> | <cite>[[http://www.drdobbs.com/cpp/c-and-the-perils-of-double-checked-locki/184405772|C++ and The Perils of Double-Checked Locking: Part II]] {{ :helloworld:design_pattern:singleton:cplusplus:c_and_the_perils_of_double-checked_locking_part_ii_dr_dobb_s_2020-04-28_8_41_46_am_.html |Archive du 01/08/2004 le 28/04/2020}}</cite> |
| </blockquote> | </blockquote> |
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| ====Solution==== | ====Solution==== |
| [[http://preshing.com/20130930/double-checked-locking-is-fixed-in-cpp11/|Double-Checked Locking is Fixed In C++11]], {{ :helloworld:design_pattern:singleton:cplusplus:double-checked_locking_is_fixed_in_c_11.mhtml |Archive}} | [[http://preshing.com/20130930/double-checked-locking-is-fixed-in-cpp11/|Double-Checked Locking is Fixed In C++11]] {{ :helloworld:design_pattern:singleton:cplusplus:double-checked_locking_is_fixed_in_c_11_2020-04-28_8_39_00_am_.html |Archive du 30/09/2013 le 28/04/2020}} |
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| [[http://www.modernescpp.com/index.php/thread-safe-initialization-of-a-singleton|Thread-Safe Initialization of a Singleton]], {{ :helloworld:design_pattern:singleton:cplusplus:thread-safe_initialization_of_a_singleton_-_modernescpp.com.mhtml |Archive}} | [[http://www.modernescpp.com/index.php/thread-safe-initialization-of-a-singleton|Thread-Safe Initialization of a Singleton]] {{ :helloworld:design_pattern:singleton:cplusplus:thread-safe_initialization_of_a_singleton_-_modernescpp.com_2020-04-28_8_40_06_am_.html |Archive du 30/08/2016 le 28/04/2020}} |
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| Si le singleton possède un constructeur trivial : | Si le singleton possède un constructeur trivial : |
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| if (tmp == nullptr) { | if (tmp == nullptr) { |
| std::lock_guard<std::mutex> lock(m_mutex); | std::scoped_lock<std::mutex> lock(m_mutex); |
| tmp = m_instance.load(std::memory_order_relaxed); | tmp = m_instance.load(std::memory_order_relaxed); |
| if (tmp == nullptr) { | if (tmp == nullptr) { |
