[{"data":1,"prerenderedAt":233},["ShallowReactive",2],{"tag-线程安全-1":3},{"title":4,"articles":5,"hot_article":18,"month_arch":81,"total":229,"cover":230},"线程安全 - 独孤影的博客",[6],{"id":7,"title":8,"uri":9,"author":10,"tags":11,"created_at":15,"view_count":16,"content":17},94,"golang程序并发读写全局变量，导致空指针异常","concurrent-reading-and-writing-global-var-caused-nil-pointer-dereference-panic","duguying",[12,13,14],"golang","数据竞争","线程安全","2023-02-28 19:27:48",348,"\u003Cp>最近将一个golang程序由原本的单线程改为双线程处理日志解析，在生产环境节点上运行发现出现了一个空指针异常，异常信息如下：\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>[E] 2023\u002F02\u002F27 11:53:25 panic.go:838: parse error:runtime error: invalid memory address or nil pointer dereference,line:Feb 27 11:53:25 xxxxx.site nginx: [xxxxxxxxxxxxxxxxxxx] [27\u002FFeb\u002F2023:11:53:25 +0800] [https] [120.232.31.196:443] [xxxxx.map.xx.com] [39.144.41.41:37647] [200] [30.171.153.132:10000] [200] [3339597] [POST \u002Ftr?mllc HTTP\u002F1.1] [621] [152] [xxxxxxx.map.xx.com] [Dalvik\u002F2.1.0 (Linux; U; Android 10; HMA-AL00 Build\u002FHUAWEIHMA-AL00)] [-] [0.008] [0.008] [0.004] [0.008] [46795] [311532943564] [1][1:46:0:0:0:0:0] [ECDHE-RSA-AES128-GCM-SHA256] [TLSv1.2] [r][-] [-] [n] [2358837] [-1] [1677470005.398|5|51|126|-1|-1|126|126|130|-1|-1|130|134|134|134|134#200|200|8|152|120.232.31.196|30.171.153.132:10000|0|0] [POST] [\u002Ftr] [mllc] [HTTP\u002F1.1] [39.144.41.41] [-] [-] [-] [-] [-] [-] [-] [-] [-] [-] [169.254.213.29:50937] [0]\n\u003C\u002Fspan>\u003C\u002Fspan>\u003C\u002Fcode>\u003C\u002Fpre>\n\n\u003Cp>修改程序，打印出异常栈\n\u003Cimg src=\"https:\u002F\u002Fimage.duguying.net\u002F2023\u002F02\u002Fx7s4uzea.webp\" alt=\"x7s4uzea\" \u002F>\u003C\u002Fp>\n\n\u003Cp>发现异常发生在代码133行，代码如下\n\u003Cimg src=\"https:\u002F\u002Fimage.duguying.net\u002F2023\u002F02\u002F0zhhoxbp.png\" alt=\"0zhhoxbp\" \u002F>\u003C\u002Fp>\n\n\u003Cp>很明显这里不太可能出现空指针，除非运行到这一行的时候\u003Ccode class=\"inline-code\">sl\u003C\u002Fcode>对象被置为\u003Ccode class=\"inline-code\">nil\u003C\u002Fcode>，但是我很确定这里不存在其他线程共享\u003Ccode class=\"inline-code\">sl\u003C\u002Fcode>的情况，也就是不可能被其他线程置为\u003Ccode class=\"inline-code\">nil\u003C\u002Fcode>，何况，我这里没有任何操作将sl置为\u003Ccode class=\"inline-code\">nil\u003C\u002Fcode>，百思不得其解。最后发现\u003Ccode class=\"inline-code\">key1\u003C\u002Fcode>，\u003Ccode class=\"inline-code\">key2\u003C\u002Fcode>这两个变量是全局变量，全局变量在多线程环境下会存在数据竞争问题。原本定义如下\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>\u003Cspan style=\"color:#ff7b72\">var\u003C\u002Fspan> (\n\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>\turiSep \u003Cspan style=\"color:#ff7b72;font-weight:bold\">*\u003C\u002Fspan>regexp.Regexp = \u003Cspan style=\"color:#79c0ff\">nil\u003C\u002Fspan>\n\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>\n\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>\tkey1 = \u003Cspan style=\"color:#a5d6ff\">""\u003C\u002Fspan>\n\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>\tkey2 = \u003Cspan style=\"color:#a5d6ff\">""\u003C\u002Fspan>\n\u003C\u002Fspan>\u003C\u002Fspan>\u003Cspan style=\"display:flex;\">\u003Cspan>)\n\u003C\u002Fspan>\u003C\u002Fspan>\u003C\u002Fcode>\u003C\u002Fpre>\n\n\u003Cp>可以看到\u003Ccode class=\"inline-code\">key1\u003C\u002Fcode>,\u003Ccode class=\"inline-code\">key2\u003C\u002Fcode>被定义为全局变量，忘记修改了。修改之后，神奇的发现，空指针异常已经不再存在了。\u003C\u002Fp>\n\n\u003Cp>我在发现这个问题之前，在本地开发服务器上尝试重现，但是一直未能重现出来，估计是我本地qps不够高，所以难以复现，生产环境qps是3w到4w左右，这个空指针异常呈现无规律的隔几秒钟出现一次。\u003C\u002Fp>\n\n\u003Cp>golang中，双协程（绑定在双M和双cpu上）中同时读写一个共享变量导致空指针异常，这种情况我还是第一次遇见，以前遇到这种双协程读写一个共享变量的情况都是数据错乱，并没有空指针。据说这种线程安全、数据竞争导致的空指针异常在C++中也是常见的情况。所以，我在想，这里会不会是因为我将2个协程绑核了，所以在双线程绑双核的情况下更容易复现呢。\u003C\u002Fp>\n",{"title":19,"list":20},"最热文章",[21,27,33,39,45,51,57,63,69,75],{"id":22,"title":23,"uri":24,"author":10,"created_at":25,"view_count":26},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":28,"title":29,"uri":30,"author":10,"created_at":31,"view_count":32},21,"beego中使用fis","\u002Farticle\u002Fbeego中使用fis","2014-12-03 10:47:56",9253,{"id":34,"title":35,"uri":36,"author":10,"created_at":37,"view_count":38},20,"用github登录，oauth开发","\u002Farticle\u002F用github登录，oauth开发","2014-11-23 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