From 0c17953db4bb3b753603f9f238ce9e0e568d90a2 Mon Sep 17 00:00:00 2001 From: vaughn0223 Date: Wed, 6 Nov 2024 20:14:00 +0800 Subject: [PATCH] update _posts/2024-05-16-shared_ptr_thread_safe.md --- _posts/2024-05-16-shared_ptr_thread_safe.md | 24 ++++++++++++++++++--- 1 file changed, 21 insertions(+), 3 deletions(-) diff --git a/_posts/2024-05-16-shared_ptr_thread_safe.md b/_posts/2024-05-16-shared_ptr_thread_safe.md index 14fe943..997d0b8 100644 --- a/_posts/2024-05-16-shared_ptr_thread_safe.md +++ b/_posts/2024-05-16-shared_ptr_thread_safe.md @@ -1,5 +1,5 @@ --- -title: std::shared_ptr 线程安全 +title: std::shared_ptr 线程安全及性能考量 date: 2024-05-16 +0800 # 2022-01-01 13:14:15 +0800 只写日期也行；不写秒也行；这样也行 2022-03-09T00:55:42+08:00 categories: [cpp] tags: [cpp] # TAG names should always be lowercase @@ -10,6 +10,8 @@ mermaid: true # pin: true --- +## 1. 线程安全 ## + 根据[cppreference](https://en.cppreference.com/w/cpp/memory/shared_ptr)的描述，`std::shared_ptr`线程安全如下（机器翻译）： 1. 如果是每个线程都拥有自己的`std::shared_ptr`对象，则针对线程自己的`std::shared_ptr`对象，其所有成员函数都是线程安全的； @@ -18,6 +20,22 @@ mermaid: true 原文： -```text All member functions (including copy constructor and copy assignment) can be called by multiple threads on different shared_ptr objects without additional synchronization even if these objects are copies and share ownership of the same object. If multiple threads of execution access the same shared_ptr object without synchronization and any of those accesses uses a non-const member function of shared_ptr then a data race will occur; the std::atomic can be used to prevent the data race. -``` + +总结： + +1. 多线程拷贝同一个`std::shared_ptr`对象，是线程安全的(引用计数是线程安全的)。 +2. 多线程访问`std::shared_ptr`指向的同一个内存对象时，访问`const`成员函数是线程安全的。 +3. 其余情况，需要使用同步。 + +## 2. 性能考量 ## + +1. 使用`std::make_shared`，`std::make_shared`将被指向对象的内存分配与`控制块`的内存分配合并为一次分配； +2. `std::make_shared`的性能接近`new`；但`std::shared_ptr(new T)`耗时较明显； +3. 在`x86`平台，`std::shared_ptr`的访问时间应该接近`T*`；但`ARM`平台应该会有明显的性能差异； + +## 3. 更多资料 ## + +* [合集 - C++系列(18) C++: weak_ptr到底有什么用？](https://www.cnblogs.com/qiangz/p/17843039.html) +* [合集 - C++系列(18) C++ 高效使用智能指针的8个建议](https://www.cnblogs.com/qiangz/p/17904768.html) +* [合集 - C++系列(18) C++: 16个基础的C++代码性能优化实例](https://www.cnblogs.com/qiangz/p/18270166) \ No newline at end of file