{"id":5045,"date":"2021-02-03T01:14:46","date_gmt":"2021-02-02T17:14:46","guid":{"rendered":"https:\/\/damogame.cn\/wordpress\/?p=5045"},"modified":"2021-02-03T01:14:46","modified_gmt":"2021-02-02T17:14:46","slug":"shared_ptr%e6%98%af%e7%ba%bf%e7%a8%8b%e5%ae%89%e5%85%a8%e7%9a%84%e5%90%97%ef%bc%9f","status":"publish","type":"post","link":"https:\/\/i007.cc\/wordpress\/archives\/5045","title":{"rendered":"shared_ptr\u662f\u7ebf\u7a0b\u5b89\u5168\u7684\u5417\uff1f"},"content":{"rendered":"<div class=\"col-2-article-header\">\n<p class=\"article-title J-articleTitle\"><a href=\"https:\/\/cloud.tencent.com\/developer\/article\/1654442\">\u539f\u6587\u5730\u5740<\/a><\/p>\n<p>&nbsp;<\/p>\n<div class=\"article-infos-wrap\">\n<div class=\"article-infos\"><span class=\"article-info\"><time title=\"2020-07-02 14:41:28\" datetime=\"2020-07-02 14:41:28\">2020-07-02<\/time><\/span><span class=\"article-info\">\u9605\u8bfb\u00a0399<\/span>0<\/div>\n<div class=\"article-infos-extra\"><\/div>\n<\/div>\n<\/div>\n<div class=\"com-markdown-collpase\">\n<div class=\"com-markdown-collpase-main\">\n<div class=\"rno-markdown J-articleContent\">\n<p>\u8bf7\u770b\u4e0b\u9762\u4e00\u6bb5\u4ee3\u7801<\/p>\n<p>&nbsp;<\/p>\n<pre class=\"prism-token token  language-javascript\">#include<span class=\"token operator\">&lt;<\/span>stdio<span class=\"token punctuation\">.<\/span>h<span class=\"token operator\">&gt;<\/span>\r\n#include<span class=\"token operator\">&lt;<\/span>iostream<span class=\"token operator\">&gt;<\/span>\r\n#include <span class=\"token operator\">&lt;<\/span>string<span class=\"token punctuation\">.<\/span>h<span class=\"token operator\">&gt;<\/span>\r\n#include <span class=\"token operator\">&lt;<\/span>memory<span class=\"token operator\">&gt;<\/span>\r\n#include <span class=\"token operator\">&lt;<\/span>mutex<span class=\"token operator\">&gt;<\/span>\r\n#include <span class=\"token operator\">&lt;<\/span>thread<span class=\"token operator\">&gt;<\/span>\r\nusing namespace std<span class=\"token punctuation\">;<\/span>\r\n\r\nshared_ptr<span class=\"token operator\">&lt;<\/span>long<span class=\"token operator\">&gt;<\/span> global_instance <span class=\"token operator\">=<\/span> make_shared<span class=\"token operator\">&lt;<\/span>long<span class=\"token operator\">&gt;<\/span><span class=\"token punctuation\">(<\/span><span class=\"token number\">0<\/span><span class=\"token punctuation\">)<\/span><span class=\"token punctuation\">;<\/span>\r\nstd<span class=\"token punctuation\">:<\/span><span class=\"token punctuation\">:<\/span>mutex g_i_mutex<span class=\"token punctuation\">;<\/span>\r\n\r\n<span class=\"token keyword\">void<\/span> <span class=\"token function\">thread_fcn<\/span><span class=\"token punctuation\">(<\/span><span class=\"token punctuation\">)<\/span>\r\n<span class=\"token punctuation\">{<\/span>\r\n    <span class=\"token comment\">\/\/std::lock_guard&lt;std::mutex&gt; lock(g_i_mutex);<\/span>\r\n     shared_ptr<span class=\"token operator\">&lt;<\/span>long<span class=\"token operator\">&gt;<\/span> local <span class=\"token operator\">=<\/span> global_instance<span class=\"token punctuation\">;<\/span> <span class=\"token comment\">\/\/ thread-safe<\/span>\r\n\r\n    <span class=\"token keyword\">for<\/span><span class=\"token punctuation\">(<\/span>int i <span class=\"token operator\">=<\/span> <span class=\"token number\">0<\/span><span class=\"token punctuation\">;<\/span> i <span class=\"token operator\">&lt;<\/span> <span class=\"token number\">100000000<\/span><span class=\"token punctuation\">;<\/span> i<span class=\"token operator\">++<\/span><span class=\"token punctuation\">)<\/span>\r\n    <span class=\"token punctuation\">{<\/span>\r\n        <span class=\"token operator\">\/<\/span><span class=\"token comment\">\/*global_instance = *global_instance + 1;\r\n        *local = *local + 1;\r\n    }\r\n}\r\n\/\/g++ -std=c++11 thead_01.cpp -lpthread \r\nint main(int argc, char** argv)\r\n{\r\n    thread thread1(thread_fcn);\r\n    thread thread2(thread_fcn);\r\n\r\n    thread1.join();\r\n    thread2.join();\r\n\r\n    cout &lt;&lt; \"*global_instance is \" &lt;&lt; *global_instance &lt;&lt; endl;\r\n\r\n    return 0;\r\n}<\/span><\/pre>\n<p>\u601d\u800310\u79d2<\/p>\n<ul class=\"ul-level-0\">\n<li>\u6267\u884c\u7ed3\u679c\uff1a<\/li>\n<\/ul>\n<figure>\n<div class=\"image-block\"><img decoding=\"async\" class=\"\" src=\"https:\/\/ask.qcloudimg.com\/http-save\/yehe-1640143\/2919b2dx5e.png?imageView2\/2\/w\/1620\" \/><\/div>\n<\/figure>\n<ul class=\"ul-level-0\">\n<li>\u9884\u671f\u7ed3\u679c\uff1a<\/li>\n<\/ul>\n<p>*global_instance is 200000000<\/p>\n<p>\u753b\u5916\u97f3\uff1a<\/p>\n<p>\u6267\u884c\u7ed3\u679c \u4e0d\u662f\u9884\u671f\u7ed3\u679c\uff0c\u80af\u5b9a\u4e0d\u662f\u7ebf\u7a0b\u5b89\u5168\u7684\u3002<\/p>\n<p>\u4e3a\u4ec0\u4e48\u8fd8\u8bf4\u5185\u7f6e\u5b89\u5168\u7684\u3002<\/p>\n<p><code>shared_ptr<\/code> objects offer the same level of thread safety as built-in types<\/p>\n<figure>\n<div class=\"image-block\"><img decoding=\"async\" class=\"\" src=\"https:\/\/ask.qcloudimg.com\/http-save\/yehe-1640143\/15mjjje4jl.png?imageView2\/2\/w\/1620\" \/><\/div>\n<\/figure>\n<p>\u67e5\u770bEffective_Modern_C++.<\/p>\n<p>&nbsp;<\/p>\n<figure>\n<div class=\"image-block\"><img decoding=\"async\" class=\"\" src=\"https:\/\/ask.qcloudimg.com\/http-save\/yehe-1640143\/2zypa35zi6.png?imageView2\/2\/w\/1620\" \/><\/div>\n<\/figure>\n<figure>\n<div class=\"image-block\"><img decoding=\"async\" class=\"\" src=\"https:\/\/ask.qcloudimg.com\/http-save\/yehe-1640143\/jeislv3rs1.png?imageView2\/2\/w\/1620\" \/><\/div>\n<\/figure>\n<figure>\n<div class=\"image-block\"><img decoding=\"async\" class=\"\" src=\"https:\/\/ask.qcloudimg.com\/http-save\/yehe-1640143\/ezn7i2z6mq.png?imageView2\/2\/w\/1620\" \/><\/div>\n<\/figure>\n<p>\u610f\u601d\u662f\u8bf4\uff1a<\/p>\n<ul class=\"ul-level-0\">\n<li>shared_ptr\u7684\u5f15\u7528\u8ba1\u6570\u672c\u8eab\u662f\u5b89\u5168\u4e14\u65e0\u9501\u7684\u3002<\/li>\n<li>\u591a\u7ebf\u7a0b\u73af\u5883\u4e0b\uff0c\u8c03\u7528\u4e0d\u540cshared_ptr\u5b9e\u4f8b\u7684\u6210\u5458\u51fd\u6570\u662f\u4e0d\u9700\u8981\u989d\u5916\u7684\u540c\u6b65\u624b\u6bb5\u7684<\/li>\n<\/ul>\n<figure>\n<div class=\"image-block\"><img decoding=\"async\" class=\"\" src=\"https:\/\/ask.qcloudimg.com\/http-save\/yehe-1640143\/q20647fqmx.png?imageView2\/2\/w\/1620\" \/><\/div>\n<\/figure>\n<p>\u753b\u5916\u97f3<\/p>\n<p>\u667a\u80fd\u6307\u9488\u67092\u4e2a\u6210\u5458\uff0c\u4e00\u4e2a\u662f\u5f15\u7528\u8ba1\u6570\u662f\u539f\u5b50\u7684\uff0c\u53e6\u5916\u4e00\u4e2a\u539f\u59cb\u6307\u9488 \u4e0d\u662f<\/p>\n<p>\u7efc\u5408\u6765\u8bf4 \u5c31\u4e0d\u662f<\/p>\n<p>&nbsp;<\/p>\n<p>\u7ee7\u7eed\u67e5\u770b\u6587\u6863shared_ptr_thread_safety<\/p>\n<p>&nbsp;<\/p>\n<ul class=\"ul-level-0\">\n<li>Examples: \u5f15\u7528\u8ba1\u6570\u6539\u53d8 \u539f\u5b50\u64cd\u4f5c \u5b89\u5168<\/li>\n<\/ul>\n<pre class=\"prism-token token  language-javascript\">shared_ptr<span class=\"token operator\">&lt;<\/span>int<span class=\"token operator\">&gt;<\/span> <span class=\"token function\">p<\/span><span class=\"token punctuation\">(<\/span><span class=\"token keyword\">new<\/span> <span class=\"token class-name\">int<\/span><span class=\"token punctuation\">(<\/span><span class=\"token number\">42<\/span><span class=\"token punctuation\">)<\/span><span class=\"token punctuation\">)<\/span><span class=\"token punctuation\">;<\/span><\/pre>\n<p>Code Example 4. Reading a <code>shared_ptr<\/code> from two threads<\/p>\n<pre class=\"prism-token token  language-javascript\"><span class=\"token comment\">\/\/ thread A<\/span>\r\nshared_ptr<span class=\"token operator\">&lt;<\/span>int<span class=\"token operator\">&gt;<\/span> <span class=\"token function\">p2<\/span><span class=\"token punctuation\">(<\/span>p<span class=\"token punctuation\">)<\/span><span class=\"token punctuation\">;<\/span> <span class=\"token comment\">\/\/ reads p<\/span>\r\n\r\n<span class=\"token comment\">\/\/ thread B<\/span>\r\nshared_ptr<span class=\"token operator\">&lt;<\/span>int<span class=\"token operator\">&gt;<\/span> <span class=\"token function\">p3<\/span><span class=\"token punctuation\">(<\/span>p<span class=\"token punctuation\">)<\/span><span class=\"token punctuation\">;<\/span> <span class=\"token comment\">\/\/ OK, multiple reads are safe<\/span><\/pre>\n<ul class=\"ul-level-0\">\n<li>Code Example 5. Writing different <code>shared_ptr<\/code> instances from two threads \u5f15\u7528\u8ba1\u6570\u6539\u53d8 \u539f\u5b50\u64cd\u4f5c \u5b89\u5168<\/li>\n<\/ul>\n<pre class=\"prism-token token  language-javascript\"><span class=\"token comment\">\/\/ thread A<\/span>\r\np<span class=\"token punctuation\">.<\/span><span class=\"token function\">reset<\/span><span class=\"token punctuation\">(<\/span><span class=\"token keyword\">new<\/span> <span class=\"token class-name\">int<\/span><span class=\"token punctuation\">(<\/span><span class=\"token number\">1912<\/span><span class=\"token punctuation\">)<\/span><span class=\"token punctuation\">)<\/span><span class=\"token punctuation\">;<\/span> <span class=\"token comment\">\/\/ writes p<\/span>\r\n\r\n<span class=\"token comment\">\/\/ thread B<\/span>\r\np2<span class=\"token punctuation\">.<\/span><span class=\"token function\">reset<\/span><span class=\"token punctuation\">(<\/span><span class=\"token punctuation\">)<\/span><span class=\"token punctuation\">;<\/span> <span class=\"token comment\">\/\/ OK, writes p2<\/span><\/pre>\n<ul class=\"ul-level-0\">\n<li>Code Example 6. Reading and writing a <code>shared_ptr<\/code> from two threads<\/li>\n<\/ul>\n<pre class=\"prism-token token  language-javascript\"><span class=\"token comment\">\/\/ thread A<\/span>\r\np <span class=\"token operator\">=<\/span> p3<span class=\"token punctuation\">;<\/span> <span class=\"token comment\">\/\/ reads p3, writes p<\/span>\r\n\r\n<span class=\"token comment\">\/\/ thread B<\/span>\r\np3<span class=\"token punctuation\">.<\/span><span class=\"token function\">reset<\/span><span class=\"token punctuation\">(<\/span><span class=\"token punctuation\">)<\/span><span class=\"token punctuation\">;<\/span> <span class=\"token comment\">\/\/ writes p3; undefined, simultaneous read\/write<\/span><\/pre>\n<ul class=\"ul-level-0\">\n<li>Code Example 7. Reading and destroying a <code>shared_ptr<\/code> from two threads<\/li>\n<\/ul>\n<pre class=\"prism-token token  language-javascript\"><span class=\"token comment\">\/\/ thread A<\/span>\r\np3 <span class=\"token operator\">=<\/span> p2<span class=\"token punctuation\">;<\/span> <span class=\"token comment\">\/\/ reads p2, writes p3<\/span>\r\n\r\n<span class=\"token comment\">\/\/ thread B<\/span>\r\n<span class=\"token comment\">\/\/ p2 goes out of scope: undefined, the destructor is considered a \"write access\"<\/span><\/pre>\n<ul class=\"ul-level-0\">\n<li>Code Example 8. Writing a <code>shared_ptr<\/code> from two threads<\/li>\n<\/ul>\n<pre class=\"prism-token token  language-javascript\"><span class=\"token comment\">\/\/ thread A<\/span>\r\np3<span class=\"token punctuation\">.<\/span><span class=\"token function\">reset<\/span><span class=\"token punctuation\">(<\/span><span class=\"token keyword\">new<\/span> <span class=\"token class-name\">int<\/span><span class=\"token punctuation\">(<\/span><span class=\"token number\">1<\/span><span class=\"token punctuation\">)<\/span><span class=\"token punctuation\">)<\/span><span class=\"token punctuation\">;<\/span>\r\n\r\n<span class=\"token comment\">\/\/ thread B<\/span>\r\np3<span class=\"token punctuation\">.<\/span><span class=\"token function\">reset<\/span><span class=\"token punctuation\">(<\/span><span class=\"token keyword\">new<\/span> <span class=\"token class-name\">int<\/span><span class=\"token punctuation\">(<\/span><span class=\"token number\">2<\/span><span class=\"token punctuation\">)<\/span><span class=\"token punctuation\">)<\/span><span class=\"token punctuation\">;<\/span> <span class=\"token comment\">\/\/ undefined, multiple writes<\/span><\/pre>\n<p>Starting with Boost release 1.33.0, <code>shared_ptr<\/code> uses a lock-free implementation on most common platforms.<\/p>\n<p>\u7ed3\u8bba\uff1a\u591a\u4e2a\u7ebf\u7a0b\u540c\u65f6\u8bfb\u540c\u4e00\u4e2ashared_ptr\u5bf9\u8c61\u662f\u7ebf\u7a0b\u5b89\u5168\u7684\uff0c<\/p>\n<p>\u4f46\u662f\u5982\u679c\u662f\u591a\u4e2a\u7ebf\u7a0b\u5bf9\u540c\u4e00\u4e2ashared_ptr\u5bf9\u8c61\u8fdb\u884c\u8bfb\u548c\u5199\uff0c\u5219\u9700\u8981\u52a0\u9501\u3002<\/p>\n<p>\u8fd9\u91cc\u4e3e\u4e2a\u4f8b\u5b50\uff1a\u600e\u4e48\u591a\u7ebf\u7a0b\u8c03\u5ea6\u6267\u884c\u987a\u5e8f\u7684\u4e0d\u786e\u5b9a\u6027\u3002<\/p>\n<figure>\n<div class=\"image-block\"><img decoding=\"async\" class=\"\" src=\"https:\/\/ask.qcloudimg.com\/http-save\/yehe-1640143\/jlq2vccnkv.png?imageView2\/2\/w\/1620\" \/><\/div>\n<\/figure>\n<p>\u4e3a\u4ec0\u4e48\u591a\u7ebf\u7a0b\u8bfb\u5199 shared_ptr \u8981\u52a0\u9501\uff1f<\/p>\n<p>&nbsp;<\/p>\n<p>\u4ee5\u4e0b\u5185\u5bb9\uff0c\u6458\u81ea\u9648\u7855\u7684 http:\/\/blog.csdn.net\/solstice\/article\/details\/8547547<\/p>\n<figure>\n<div class=\"image-block\"><img decoding=\"async\" class=\"\" src=\"https:\/\/ask.qcloudimg.com\/http-save\/yehe-1640143\/io1uxp3muy.png?imageView2\/2\/w\/1620\" \/><\/div>\n<\/figure>\n<p><strong>1\uff1ashared_ptr \u7684\u6570\u636e\u7ed3\u6784<\/strong><\/p>\n<p>shared_ptr \u662f\u5f15\u7528\u8ba1\u6570\u578b\uff08reference counting\uff09\u667a\u80fd\u6307\u9488\uff0c\u51e0\u4e4e\u6240\u6709\u7684\u5b9e\u73b0\u90fd\u91c7\u7528\u5728\u5806\uff08heap\uff09\u4e0a\u653e\u4e2a\u8ba1\u6570\u503c\uff08count\uff09\u7684\u529e\u6cd5\uff08\u9664\u6b64\u4e4b\u5916\u7406\u8bba\u4e0a\u8fd8\u6709\u7528\u5faa\u73af\u94fe\u8868\u7684\u529e\u6cd5\uff0c\u4e0d\u8fc7\u6ca1\u6709\u5b9e\u4f8b\uff09\u3002<\/p>\n<p>\u5177\u4f53\u6765\u8bf4\uff0cshared_ptr&lt;Foo&gt; \u5305\u542b\u4e24\u4e2a\u6210\u5458\uff0c\u4e00\u4e2a\u662f\u6307\u5411 Foo \u7684\u6307\u9488 ptr\uff0c\u53e6\u4e00\u4e2a\u662f ref_count \u6307\u9488\uff08\u5176\u7c7b\u578b\u4e0d\u4e00\u5b9a\u662f\u539f\u59cb\u6307\u9488\uff0c\u6709\u53ef\u80fd\u662f class \u7c7b\u578b\uff0c\u4f46\u4e0d\u5f71\u54cd\u8fd9\u91cc\u7684\u8ba8\u8bba\uff09\uff0c\u6307\u5411\u5806\u4e0a\u7684 ref_count \u5bf9\u8c61\u3002ref_count \u5bf9\u8c61\u6709\u591a\u4e2a\u6210\u5458\uff0c\u5177\u4f53\u7684\u6570\u636e\u7ed3\u6784\u5982\u56fe 1 \u6240\u793a\uff0c\u5176\u4e2d deleter \u548c allocator \u662f\u53ef\u9009\u7684\u3002<\/p>\n<figure>\n<div class=\"image-block\"><img decoding=\"async\" class=\"\" src=\"https:\/\/ask.qcloudimg.com\/http-save\/yehe-1640143\/kqa1jq44li.png?imageView2\/2\/w\/1620\" \/><\/div>\n<\/figure>\n<p>\u56fe 1\uff1ashared_ptr \u7684\u6570\u636e\u7ed3\u6784\u3002<\/p>\n<p>\u4e3a\u4e86\u7b80\u5316\u5e76\u7a81\u51fa\u91cd\u70b9\uff0c\u540e\u6587\u53ea\u753b\u51fa use_count \u7684\u503c\uff1a<\/p>\n<figure>\n<div class=\"image-block\"><img decoding=\"async\" class=\"\" src=\"https:\/\/ask.qcloudimg.com\/http-save\/yehe-1640143\/0x26cv9eah.png?imageView2\/2\/w\/1620\" \/><\/div>\n<\/figure>\n<p>\u4ee5\u4e0a\u662f shared_ptr&lt;Foo&gt; x(new Foo); \u5bf9\u5e94\u7684\u5185\u5b58\u6570\u636e\u7ed3\u6784\u3002<\/p>\n<p>\u5982\u679c\u518d\u6267\u884c shared_ptr&lt;Foo&gt; y = x; \u90a3\u4e48\u5bf9\u5e94\u7684\u6570\u636e\u7ed3\u6784\u5982\u4e0b\u3002<\/p>\n<figure>\n<div class=\"image-block\"><img decoding=\"async\" class=\"\" src=\"https:\/\/ask.qcloudimg.com\/http-save\/yehe-1640143\/aw4dbqjma9.png?imageView2\/2\/w\/1620\" \/><\/div>\n<\/figure>\n<figure>\n<hr \/>\n<\/figure>\n<p>\u4f46\u662f y=x \u6d89\u53ca\u4e24\u4e2a\u6210\u5458\u7684\u590d\u5236\uff0c\u8fd9\u4e24\u6b65\u62f7\u8d1d\u4e0d\u4f1a\u540c\u65f6\uff08\u539f\u5b50\uff09\u53d1\u751f\u3002<\/p>\n<ul class=\"ul-level-0\">\n<li>\u4e2d\u95f4\u6b65\u9aa4 1\uff0c\u590d\u5236 ptr \u6307\u9488\uff1a<\/li>\n<\/ul>\n<figure>\n<div class=\"image-block\"><img decoding=\"async\" class=\"\" src=\"https:\/\/ask.qcloudimg.com\/http-save\/yehe-1640143\/cykekcnk5l.png?imageView2\/2\/w\/1620\" \/><\/div>\n<\/figure>\n<ul class=\"ul-level-0\">\n<li>\u4e2d\u95f4\u6b65\u9aa4 2\uff0c\u590d\u5236 ref_count \u6307\u9488\uff0c\u5bfc\u81f4\u5f15\u7528\u8ba1\u6570\u52a0 1\uff1a<\/li>\n<\/ul>\n<figure>\n<div class=\"image-block\"><img decoding=\"async\" class=\"\" src=\"https:\/\/ask.qcloudimg.com\/http-save\/yehe-1640143\/sawlj31a15.png?imageView2\/2\/w\/1620\" \/><\/div>\n<\/figure>\n<p>\u6b65\u9aa41\u548c\u6b65\u9aa42\u7684\u5148\u540e\u987a\u5e8f\u8ddf\u5b9e\u73b0\u76f8\u5173\uff08\u56e0\u6b64\u6b65\u9aa4 2 \u91cc\u6ca1\u6709\u753b\u51fa y.ptr \u7684\u6307\u5411\uff09\uff0c<\/p>\n<p>\u6211\u89c1\u8fc7\u7684\u90fd\u662f\u51481\u540e2\u3002<\/p>\n<p>\u65e2\u7136 y=x \u6709\u4e24\u4e2a\u6b65\u9aa4\uff0c\u5982\u679c\u6ca1\u6709 mutex \u4fdd\u62a4\uff0c\u90a3\u4e48\u5728\u591a\u7ebf\u7a0b\u91cc\u5c31\u6709 race condition\u3002<\/p>\n<p><strong>2\uff1a\u591a\u7ebf\u7a0b\u65e0\u4fdd\u62a4\u8bfb\u5199 shared_ptr \u53ef\u80fd\u51fa\u73b0\u7684 race condition<\/strong><\/p>\n<p>\u8003\u8651\u4e00\u4e2a\u7b80\u5355\u7684\u573a\u666f\uff0c\u6709 3 \u4e2a shared_ptr&lt;Foo&gt; \u5bf9\u8c61 x\u3001g\u3001n\uff1a<\/p>\n<pre class=\"prism-token token  language-javascript\">shared_ptr<span class=\"token operator\">&lt;<\/span>Foo<span class=\"token operator\">&gt;<\/span> <span class=\"token function\">g<\/span><span class=\"token punctuation\">(<\/span><span class=\"token keyword\">new<\/span> <span class=\"token class-name\">Foo1<\/span><span class=\"token punctuation\">)<\/span><span class=\"token punctuation\">;<\/span> <span class=\"token comment\">\/\/ \u7ebf\u7a0b\u4e4b\u95f4\u5171\u4eab\u7684 shared_ptr<\/span>\r\nshared_ptr<span class=\"token operator\">&lt;<\/span>Foo<span class=\"token operator\">&gt;<\/span> x<span class=\"token punctuation\">;<\/span> <span class=\"token comment\">\/\/ \u7ebf\u7a0b A \u7684\u5c40\u90e8\u53d8\u91cf<\/span>\r\nshared_ptr<span class=\"token operator\">&lt;<\/span>Foo<span class=\"token operator\">&gt;<\/span> <span class=\"token function\">n<\/span><span class=\"token punctuation\">(<\/span><span class=\"token keyword\">new<\/span> <span class=\"token class-name\">Foo2<\/span><span class=\"token punctuation\">)<\/span><span class=\"token punctuation\">;<\/span> <span class=\"token comment\">\/\/ \u7ebf\u7a0b B \u7684\u5c40\u90e8\u53d8\u91cf<\/span>\r\n<span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">-<\/span>\r\n\u7ebf\u7a0b A\r\nx <span class=\"token operator\">=<\/span> g<span class=\"token punctuation\">;<\/span> \uff08\u5373 read g\uff09 <span class=\"token comment\">\/\/\u4ee3\u78011 :\u8d4b\u503c\u6307\u9488,\u8d4b\u503c \u5f15\u7528\u8ba1\u6570<\/span>\r\n<span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">--<\/span><span class=\"token operator\">-<\/span>\r\n\u7ebf\u7a0b B\r\ng <span class=\"token operator\">=<\/span> n<span class=\"token punctuation\">;<\/span><span class=\"token comment\">\/\/\u4ee3\u78012 :\u52a8\u4f5cA \u6e05\u7a7a\u539f\u6765G\u6307\u5411Foo1, \u52a8\u4f5cB \u7136\u540e\u91cd\u65b0\u8d4b\u503c Foo2<\/span>\r\n\r\n\u6d4b\u8bd5\u573a\u666f\uff1a\r\n\r\n\u7ebf\u7a0bA \r\n  \u667a\u80fd\u6307\u9488x \u8bfb\u53d6Foo1<span class=\"token punctuation\">,<\/span>\u7136\u540e\u8fd8\u91cd\u7f6eFoo1\u8ba1\u6570\u3002\r\n\r\n\u7ebf\u7a0b B<span class=\"token punctuation\">:<\/span>\r\n \u9500\u6bc1\u4e86Foo1\r\n\u7ebf\u7a0bA\r\n\u91cd\u7f6e\u8ba1\u6570\u662f\uff0cfoo1\u5df2\u7ecf\u88ab\u9500\u6bc1\u3002<\/pre>\n<p>\u4e00\u5f00\u59cb\uff0c\u5404\u5b89\u5176\u4e8b\uff1a<\/p>\n<figure>\n<div class=\"image-block\"><img decoding=\"async\" class=\"\" src=\"https:\/\/ask.qcloudimg.com\/http-save\/yehe-1640143\/dl4zpn5u1e.png?imageView2\/2\/w\/1620\" \/><\/div>\n<\/figure>\n<ul class=\"ul-level-0\">\n<li>\u53d8\u91cf x \u6ca1\u6709\u6307\u5411\u4efb\u4f55\u5bf9\u8c61<\/li>\n<\/ul>\n<p>\u7ebf\u7a0b A \u6267\u884c x = g; \uff08\u5373 read g\uff09\uff0c\u4ee5\u4e0b\u5b8c\u6210\u4e86\u6b65\u9aa4 1\uff0c\u8fd8\u6ca1\u6765\u53ca\u6267\u884c\u6b65\u9aa4 2\u3002\u8fd9\u65f6\u5207\u6362\u5230\u4e86 B \u7ebf\u7a0b\u3002<\/p>\n<figure>\n<div class=\"image-block\"><img decoding=\"async\" class=\"\" src=\"https:\/\/ask.qcloudimg.com\/http-save\/yehe-1640143\/9lhurto95x.png?imageView2\/2\/w\/1620\" \/><\/div>\n<\/figure>\n<ul class=\"ul-level-0\">\n<li>x \u5f00\u59cb\u8d4b\u503c\uff0c\u5176\u4e2d2\u4e2a\u6210\u5458 \uff0c\u7b2c\u4e00\u662f\u539f\u59cb\u6307\u9488 FOO1\uff0c\u7b2c\u4e8c\u4e2a\u5e94\u7528\u8ba1\u6570\u6ca1\u6765\u5f97\u53ca\u5b8c\u6210\u3002<\/li>\n<\/ul>\n<p>\u540c\u65f6\u7f16\u7a0b B \u6267\u884c g = n; \uff08\u5373 write g\uff09\uff0c\u4e24\u4e2a\u6b65\u9aa4\u4e00\u8d77\u5b8c\u6210\u4e86\u3002<\/p>\n<p>\u5148\u662f\u6b65\u9aa4 1\uff1a<\/p>\n<figure>\n<div class=\"image-block\"><img decoding=\"async\" class=\"\" src=\"https:\/\/ask.qcloudimg.com\/http-save\/yehe-1640143\/g21rpt5oax.png?imageView2\/2\/w\/1620\" \/><\/div>\n<\/figure>\n<ul class=\"ul-level-0\">\n<li>\u518d\u662f\u6b65\u9aa4 2\uff1a<\/li>\n<\/ul>\n<figure>\n<div class=\"image-block\"><img decoding=\"async\" class=\"\" src=\"https:\/\/ask.qcloudimg.com\/http-save\/yehe-1640143\/z94sp2z3ry.png?imageView2\/2\/w\/1620\" \/><\/div>\n<\/figure>\n<p>\u8fd9\u65f6 Foo1 \u5bf9\u8c61\u5df2\u7ecf\u9500\u6bc1\uff0cx.ptr \u6210\u4e86\u7a7a\u60ac\u6307\u9488\uff01<\/p>\n<ul class=\"ul-level-0\">\n<li>FOO1 \u56e0\u4e3a \u5168\u5c40\u5bf9\u8c61g\u91cd\u7f6e\uff0c\u5f00\u59cb\u9500\u6bc1<\/li>\n<\/ul>\n<p>\u6700\u540e\u56de\u5230\u7ebf\u7a0b A\uff0c\u5b8c\u6210\u6b65\u9aa4 2\uff1a<\/p>\n<figure>\n<div class=\"image-block\"><img decoding=\"async\" class=\"\" src=\"https:\/\/ask.qcloudimg.com\/http-save\/yehe-1640143\/gowqm58qek.png?imageView2\/2\/w\/1620\" \/><\/div>\n<\/figure>\n<p>\u591a\u7ebf\u7a0b\u65e0\u4fdd\u62a4\u5730\u8bfb\u5199 g\uff0c\u9020\u6210\u4e86\u201cx \u662f\u7a7a\u60ac\u6307\u9488\u201d\u7684\u540e\u679c\u3002<\/p>\n<figure>\n<div class=\"image-block\"><img decoding=\"async\" class=\"\" src=\"https:\/\/ask.qcloudimg.com\/http-save\/yehe-1640143\/an2807efms.png?imageView2\/2\/w\/1620\" \/><\/div>\n<\/figure>\n<ul class=\"ul-level-0\">\n<li>\u6700\u540e\u7ebf\u7a0bA \u5f00\u59cb\u4f7f\u7528 foo1 \u6765 \u6267\u884c\u5176\u4ed6\u64cd\u4f5c\u3002\u5176\u5b9e\u5df2\u7ecf\u88ab\u9500\u6bc1\u4e86\u3002\u4e0d\u5b58\u5728<\/li>\n<\/ul>\n<p>\u8fd9\u6b63\u662f\u591a\u7ebf\u7a0b\u8bfb\u5199\u540c\u4e00\u4e2a shared_ptr \u5fc5\u987b\u52a0\u9501\u7684\u539f\u56e0<\/p>\n<figure>\n<div class=\"image-block\"><img decoding=\"async\" class=\"\" src=\"https:\/\/ask.qcloudimg.com\/http-save\/yehe-1640143\/8bir0syhls.png?imageView2\/2\/w\/1620\" \/><\/div>\n<\/figure>\n<p>\u67e5\u770b\u4ee3\u7801<\/p>\n<p>&nbsp;<\/p>\n<pre class=\"prism-token token  language-javascript\">https<span class=\"token punctuation\">:<\/span><span class=\"token operator\">\/<\/span><span class=\"token operator\">\/<\/span>www<span class=\"token punctuation\">.<\/span>boost<span class=\"token punctuation\">.<\/span>org<span class=\"token operator\">\/<\/span>doc<span class=\"token operator\">\/<\/span>libs<span class=\"token operator\">\/<\/span>1_32_0<span class=\"token operator\">\/<\/span>boost<span class=\"token operator\">\/<\/span>detail<span class=\"token operator\">\/<\/span>shared_count<span class=\"token punctuation\">.<\/span>hpp\r\n\r\ntemplate<span class=\"token operator\">&lt;<\/span><span class=\"token keyword\">class<\/span> <span class=\"token class-name\">T<\/span><span class=\"token operator\">&gt;<\/span> \r\n<span class=\"token keyword\">class<\/span> <span class=\"token class-name\">shared_ptr<\/span>\r\n<span class=\"token punctuation\">{<\/span>\r\n  T <span class=\"token operator\">*<\/span> px<span class=\"token punctuation\">;<\/span>                     <span class=\"token comment\">\/\/ contained pointer<\/span>\r\n  boost<span class=\"token punctuation\">:<\/span><span class=\"token punctuation\">:<\/span>detail<span class=\"token punctuation\">:<\/span><span class=\"token punctuation\">:<\/span>shared_count pn<span class=\"token punctuation\">;<\/span> <span class=\"token comment\">\/\/ reference counter ,<\/span>\r\n\r\n<span class=\"token punctuation\">}<\/span>\r\n<span class=\"token keyword\">class<\/span> <span class=\"token class-name\">shared_count<\/span>\r\n<span class=\"token punctuation\">{<\/span>\r\n<span class=\"token keyword\">private<\/span><span class=\"token punctuation\">:<\/span>\r\n\r\n    sp_counted_base <span class=\"token operator\">*<\/span> pi_<span class=\"token punctuation\">;<\/span>\r\n<span class=\"token punctuation\">}<\/span><\/pre>\n<p>\u601d\u8003\u4e0e\u884c\u52a8\uff1a<\/p>\n<p>1\u3002\u4e3a\u4ec0\u4e48\u7528\u4e00\u4e2a\u7c7b\u6765\u7ba1\u7406\u53e6\u5916\u4e00\u4e2a\u6307\u9488\u5462<\/p>\n<p>\u63d0\u793a\uff1a<\/p>\n<p>\u805a\u5408\u5173\u7cfb\u56fe\uff1a<\/p>\n<figure>\n<div class=\"image-block\"><img decoding=\"async\" class=\"\" src=\"https:\/\/ask.qcloudimg.com\/http-save\/yehe-1640143\/ukik1u9qgk.jpeg?imageView2\/2\/w\/1620\" \/><\/div>\n<\/figure>\n<p>\u7ec4\u5408\u5173\u7cfb\u56fe\uff1a<\/p>\n<figure>\n<div class=\"image-block\"><img decoding=\"async\" class=\"\" src=\"https:\/\/ask.qcloudimg.com\/http-save\/yehe-1640143\/wvtdwhjujn.jpeg?imageView2\/2\/w\/1620\" \/><\/div>\n<\/figure>\n<p>2. \u5171\u4eab\u6307\u9488\u7f3a\u70b9<\/p>\n<p>\u63d0\u793a\uff1a<\/p>\n<figure>\n<div class=\"image-block\"><img decoding=\"async\" class=\"\" src=\"https:\/\/ask.qcloudimg.com\/http-save\/yehe-1640143\/5e2djzgrxu.png?imageView2\/2\/w\/1620\" \/><\/div>\n<\/figure>\n<figure>\n<div class=\"image-block\"><img decoding=\"async\" class=\"\" src=\"https:\/\/ask.qcloudimg.com\/http-save\/yehe-1640143\/hdbc7ho9sd.png?imageView2\/2\/w\/1620\" \/><\/div>\n<\/figure>\n<\/div>\n<div class=\"col-2-article-source\">\n<p>\u672c\u6587\u5206\u4eab\u81ea\u5fae\u4fe1\u516c\u4f17\u53f7 &#8211;\u00a0\u67b6\u6784\u8bf4\uff08JiaGouS\uff09\uff0c\u4f5c\u8005\uff1a\u738b\u4f20\u4e49<\/p>\n<p>\u539f\u6587\u51fa\u5904\u53ca\u8f6c\u8f7d\u4fe1\u606f\u89c1\u6587\u5185\u8be6\u7ec6\u8bf4\u660e\uff0c\u5982\u6709\u4fb5\u6743\uff0c\u8bf7\u8054\u7cfb\u00a0yunjia_community@tencent.com\u00a0\u5220\u9664\u3002<\/p>\n<p>\u539f\u59cb\u53d1\u8868\u65f6\u95f4\uff1a2020-06-25<\/p>\n<p>\u672c\u6587\u53c2\u4e0e<a class=\"com-link\" href=\"https:\/\/cloud.tencent.com\/developer\/support-plan\">\u817e\u8baf\u4e91\u81ea\u5a92\u4f53\u5206\u4eab\u8ba1\u5212<\/a>\uff0c\u6b22\u8fce\u6b63\u5728\u9605\u8bfb\u7684\u4f60\u4e5f\u52a0\u5165\uff0c\u4e00\u8d77\u5206\u4eab\u3002<\/p>\n<\/div>\n<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>\u539f\u6587\u5730\u5740 &nbsp; 2020-07-<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"colormag_page_container_layout":"default_layout","colormag_page_sidebar_layout":"default_layout","footnotes":""},"categories":[],"tags":[119],"class_list":["post-5045","post","type-post","status-publish","format-standard","hentry","tag-03-"],"_links":{"self":[{"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/posts\/5045","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/comments?post=5045"}],"version-history":[{"count":0,"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/posts\/5045\/revisions"}],"wp:attachment":[{"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/media?parent=5045"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/categories?post=5045"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/i007.cc\/wordpress\/wp-json\/wp\/v2\/tags?post=5045"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}