[{"data":1,"prerenderedAt":231},["ShallowReactive",2],{"article-how-vector-auto-increased-in-rust":3},{"title":4,"article":5,"hot_article":17,"month_arch":80,"cover":228},"初学rust，数组vector的自增 - 独孤影的博客",{"id":6,"title":7,"uri":8,"author":9,"tags":10,"created_at":14,"view_count":15,"content":16},84,"初学rust，数组vector的自增","how-vector-auto-increased-in-rust","duguying",[11,12,13],"rust","vector","自增","2022-11-25 15:03:29",210,"\u003Cp>在golang中经常会踩一个坑，那就是slice append，golang的动态数组也称为slice，使用append可以对动态数组进行添加元素，但是slice空间不够之后golang会自动重新分配内存空间，每次重新分配的内存空间是原空间的2倍，而且有个更坑的是，golang中slice每次重新分配内存都是重新分配一片 \u003Cspan v-katex:auto>2N\u003C\u002Fspan> 大小的内存，然后把原来的数据拷贝过去，这样一来，性能损耗更大了。\u003C\u002Fp>\n\n\u003Cp>那么rust中的数组是怎么处理动态增长的呢，我们来一段代码测试一下。\u003C\u002Fp>\n\n\u003Cpre style=\"color:#e6edf3;background-color:#0d1117;white-space:pre-wrap;word-break:break-word;\">\u003Ccode>\u003Cspan style=\"display:flex;\">\u003Cspan>\u003Cspan style=\"color:#ff7b72\">fn\u003C\u002Fspan> \u003Cspan style=\"color:#d2a8ff;font-weight:bold\">main\u003C\u002Fspan>()\u003Cspan style=\"color:#6e7681\"> \u003C\u002Fspan>{\u003Cspan style=\"color:#6e7681\">\n\u003C\u002Fspan>\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>\u003Cspan style=\"color:#6e7681\">\u003C\u002Fspan>\u003Cspan style=\"color:#6e7681\">    \u003C\u002Fspan>\u003Cspan style=\"color:#ff7b72\">let\u003C\u002Fspan>\u003Cspan style=\"color:#6e7681\"> \u003C\u002Fspan>\u003Cspan style=\"color:#ff7b72\">mut\u003C\u002Fspan>\u003Cspan style=\"color:#6e7681\"> \u003C\u002Fspan>vec\u003Cspan style=\"color:#6e7681\"> \u003C\u002Fspan>\u003Cspan style=\"color:#ff7b72;font-weight:bold\">=\u003C\u002Fspan>\u003Cspan style=\"color:#6e7681\"> \u003C\u002Fspan>Vec::with_capacity(\u003Cspan style=\"color:#a5d6ff\">100\u003C\u002Fspan>);\u003Cspan style=\"color:#6e7681\">\n\u003C\u002Fspan>\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>\u003Cspan style=\"color:#6e7681\">\u003C\u002Fspan>\u003Cspan style=\"color:#6e7681\">\n\u003C\u002Fspan>\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>\u003Cspan style=\"color:#6e7681\">\u003C\u002Fspan>\u003Cspan style=\"color:#6e7681\">    \u003C\u002Fspan>\u003Cspan style=\"color:#8b949e;font-style:italic\">\u002F\u002F The vector contains no items, even though it has capacity for more\n\u003C\u002Fspan>\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>\u003Cspan style=\"color:#8b949e;font-style:italic\">\u003C\u002Fspan>\u003Cspan style=\"color:#6e7681\">    \u003C\u002Fspan>println!\u003Cspan style=\"color:#6e7681\">\u003C\u002Fspan>(\u003Cspan style=\"color:#6e7681\">\u003C\u002Fspan>\u003Cspan style=\"color:#a5d6ff\">"\u003C\u002Fspan>\u003Cspan style=\"color:#a5d6ff\">vec.len: \u003C\u002Fspan>\u003Cspan style=\"color:#a5d6ff\">{:?}\u003C\u002Fspan>\u003Cspan style=\"color:#a5d6ff\">"\u003C\u002Fspan>,\u003Cspan style=\"color:#6e7681\"> \u003C\u002Fspan>vec.len());\u003Cspan style=\"color:#6e7681\">\n\u003C\u002Fspan>\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>\u003Cspan style=\"color:#6e7681\">\u003C\u002Fspan>\u003Cspan style=\"color:#6e7681\">    \u003C\u002Fspan>println!\u003Cspan style=\"color:#6e7681\">\u003C\u002Fspan>(\u003Cspan style=\"color:#6e7681\">\u003C\u002Fspan>\u003Cspan style=\"color:#a5d6ff\">"\u003C\u002Fspan>\u003Cspan style=\"color:#a5d6ff\">vec.cap: \u003C\u002Fspan>\u003Cspan style=\"color:#a5d6ff\">{:?}\u003C\u002Fspan>\u003Cspan style=\"color:#a5d6ff\">"\u003C\u002Fspan>,\u003Cspan style=\"color:#6e7681\"> \u003C\u002Fspan>vec.capacity());\u003Cspan style=\"color:#6e7681\">\n\u003C\u002Fspan>\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>\u003Cspan style=\"color:#6e7681\">\u003C\u002Fspan>\u003Cspan style=\"color:#6e7681\">\n\u003C\u002Fspan>\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>\u003Cspan style=\"color:#6e7681\">\u003C\u002Fspan>\u003Cspan style=\"color:#6e7681\">    \u003C\u002Fspan>\u003Cspan style=\"color:#8b949e;font-style:italic\">\u002F\u002F These are all done without reallocating...\n\u003C\u002Fspan>\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>\u003Cspan style=\"color:#8b949e;font-style:italic\">\u003C\u002Fspan>\u003Cspan style=\"color:#6e7681\">    \u003C\u002Fspan>\u003Cspan style=\"color:#ff7b72\">for\u003C\u002Fspan>\u003Cspan style=\"color:#6e7681\"> \u003C\u002Fspan>i\u003Cspan style=\"color:#6e7681\"> \u003C\u002Fspan>\u003Cspan style=\"color:#ff7b72\">in\u003C\u002Fspan>\u003Cspan style=\"color:#6e7681\"> \u003C\u002Fspan>\u003Cspan style=\"color:#a5d6ff\">0\u003C\u002Fspan>\u003Cspan style=\"color:#ff7b72;font-weight:bold\">..\u003C\u002Fspan>\u003Cspan style=\"color:#a5d6ff\">100\u003C\u002Fspan>\u003Cspan style=\"color:#6e7681\"> \u003C\u002Fspan>{\u003Cspan style=\"color:#6e7681\">\n\u003C\u002Fspan>\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>\u003Cspan style=\"color:#6e7681\">\u003C\u002Fspan>\u003Cspan style=\"color:#6e7681\">        \u003C\u002Fspan>vec.push(i);\u003Cspan style=\"color:#6e7681\">\n\u003C\u002Fspan>\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>\u003Cspan style=\"color:#6e7681\">\u003C\u002Fspan>\u003Cspan style=\"color:#6e7681\">    \u003C\u002Fspan>}\u003Cspan style=\"color:#6e7681\">\n\u003C\u002Fspan>\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>\u003Cspan style=\"color:#6e7681\">\u003C\u002Fspan>\u003Cspan style=\"color:#6e7681\">    \u003C\u002Fspan>println!\u003Cspan style=\"color:#6e7681\">\u003C\u002Fspan>(\u003Cspan style=\"color:#6e7681\">\u003C\u002Fspan>\u003Cspan style=\"color:#a5d6ff\">"\u003C\u002Fspan>\u003Cspan style=\"color:#a5d6ff\">vec.len: \u003C\u002Fspan>\u003Cspan style=\"color:#a5d6ff\">{:?}\u003C\u002Fspan>\u003Cspan style=\"color:#a5d6ff\">"\u003C\u002Fspan>,\u003Cspan style=\"color:#6e7681\"> \u003C\u002Fspan>vec.len());\u003Cspan style=\"color:#6e7681\">\n\u003C\u002Fspan>\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>\u003Cspan style=\"color:#6e7681\">\u003C\u002Fspan>\u003Cspan style=\"color:#6e7681\">    \u003C\u002Fspan>println!\u003Cspan style=\"color:#6e7681\">\u003C\u002Fspan>(\u003Cspan style=\"color:#6e7681\">\u003C\u002Fspan>\u003Cspan style=\"color:#a5d6ff\">"\u003C\u002Fspan>\u003Cspan style=\"color:#a5d6ff\">vec.cap: \u003C\u002Fspan>\u003Cspan style=\"color:#a5d6ff\">{:?}\u003C\u002Fspan>\u003Cspan style=\"color:#a5d6ff\">"\u003C\u002Fspan>,\u003Cspan style=\"color:#6e7681\"> \u003C\u002Fspan>vec.capacity());\u003Cspan style=\"color:#6e7681\">\n\u003C\u002Fspan>\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>\u003Cspan style=\"color:#6e7681\">\u003C\u002Fspan>\u003Cspan style=\"color:#6e7681\">\n\u003C\u002Fspan>\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>\u003Cspan style=\"color:#6e7681\">\u003C\u002Fspan>\u003Cspan style=\"color:#6e7681\">    \u003C\u002Fspan>\u003Cspan style=\"color:#8b949e;font-style:italic\">\u002F\u002F ...but this may make the vector reallocate\n\u003C\u002Fspan>\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>\u003Cspan style=\"color:#8b949e;font-style:italic\">\u003C\u002Fspan>\u003Cspan style=\"color:#6e7681\">    \u003C\u002Fspan>vec.push(\u003Cspan style=\"color:#a5d6ff\">101\u003C\u002Fspan>);\u003Cspan style=\"color:#6e7681\">\n\u003C\u002Fspan>\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>\u003Cspan style=\"color:#6e7681\">\u003C\u002Fspan>\u003Cspan style=\"color:#6e7681\">    \u003C\u002Fspan>println!\u003Cspan style=\"color:#6e7681\">\u003C\u002Fspan>(\u003Cspan style=\"color:#6e7681\">\u003C\u002Fspan>\u003Cspan style=\"color:#a5d6ff\">"\u003C\u002Fspan>\u003Cspan style=\"color:#a5d6ff\">vec.len: \u003C\u002Fspan>\u003Cspan style=\"color:#a5d6ff\">{:?}\u003C\u002Fspan>\u003Cspan style=\"color:#a5d6ff\">"\u003C\u002Fspan>,\u003Cspan style=\"color:#6e7681\"> \u003C\u002Fspan>vec.len());\u003Cspan style=\"color:#6e7681\">\n\u003C\u002Fspan>\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>\u003Cspan style=\"color:#6e7681\">\u003C\u002Fspan>\u003Cspan style=\"color:#6e7681\">    \u003C\u002Fspan>println!\u003Cspan style=\"color:#6e7681\">\u003C\u002Fspan>(\u003Cspan style=\"color:#6e7681\">\u003C\u002Fspan>\u003Cspan style=\"color:#a5d6ff\">"\u003C\u002Fspan>\u003Cspan style=\"color:#a5d6ff\">vec.cap: \u003C\u002Fspan>\u003Cspan style=\"color:#a5d6ff\">{:?}\u003C\u002Fspan>\u003Cspan style=\"color:#a5d6ff\">"\u003C\u002Fspan>,\u003Cspan style=\"color:#6e7681\"> \u003C\u002Fspan>vec.capacity());\u003Cspan style=\"color:#6e7681\">\n\u003C\u002Fspan>\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>\u003Cspan style=\"color:#6e7681\">\u003C\u002Fspan>}\u003Cspan style=\"color:#6e7681\">\n\u003C\u002Fspan>\u003C\u002Fspan>\u003C\u002Fspan>\u003C\u002Fcode>\u003C\u002Fpre>\n\n\u003Cp>输出如下\u003C\u002Fp>\n\n\u003Cpre style=\"color:#e6edf3;background-color:#0d1117;white-space:pre-wrap;word-break:break-word;\">\u003Ccode>\u003Cspan style=\"display:flex;\">\u003Cspan>vec.len: 0\n\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>vec.cap: 100\n\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>vec.len: 100\n\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>vec.cap: 100\n\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>vec.len: 101\n\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>vec.cap: 200\n\u003C\u002Fspan>\u003C\u002Fspan>\u003C\u002Fcode>\u003C\u002Fpre>\n\n\u003Cp>可以看到，rust中，当vector数组存储满了之后，再往里面添加元素，vector就会重新分配内存，新分配的内存也是原来空间的2倍，但是，他是在原来的内存上扩充的，而不是像golang一样重新分配一片2N的内存空间替换旧的内存。性能损耗上，相比golang少了copy数据和释放旧空间。所以在高性能场景下，这里依然不建议使用vector的自动增长特性，自动增长的内存分配会消耗存储空间，而且 \u003Cspan v-katex:auto>2N\u003C\u002Fspan> 的增长步长会很容易导致内存泄漏，你如果依赖这个自动增长特性，你将会发现你使用的内存可能会发生 \u003Cspan v-katex:auto>2^n\u003C\u002Fspan> 指数级增长。这绝对会在大部分边界条件下导致你的程序迅速的发生OOM。\u003C\u002Fp>\n\n\u003Cp>远离动态数组，远离bug。\u003C\u002Fp>\n",{"title":18,"list":19},"最热文章",[20,26,32,38,44,50,56,62,68,74],{"id":21,"title":22,"uri":23,"author":9,"created_at":24,"view_count":25},28,"docker容器目录与主机目录同步","\u002Farticle\u002Fdocker容器目录与主机目录同步","2014-12-31 12:34:08",15573,{"id":27,"title":28,"uri":29,"author":9,"created_at":30,"view_count":31},21,"beego中使用fis","\u002Farticle\u002Fbeego中使用fis","2014-12-03 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16:54:58",7740,{"id":69,"title":70,"uri":71,"author":9,"created_at":72,"view_count":73},16,"php-fpm网站目录权限配置","\u002Farticle\u002Fphp-fpm网站目录权限配置","2014-10-18 01:36:10",7276,{"id":75,"title":76,"uri":77,"author":9,"created_at":78,"view_count":79},27,"sublime text 2插件开发，外部修改文件无法重新加载","\u002Farticle\u002Fsublime text 2插件开发，外部修改文件无法重新加载","2014-12-26 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