“`” 1\uff09IO\u591a\u8def\u590d\u7528<\/p>\n
IO\u590d\u7528\u6a21\u578b\u5728\u963b\u585eIO\u6a21\u578b\u4e0a\u591a\u4e86\u4e00\u4e2aselect\u51fd\u6570\uff0cselect\u51fd\u6570\u6709\u4e00\u4e2a\u53c2\u6570\u662f\u6587\u4ef6\u63cf\u8ff0\u7b26\u96c6\u5408\uff0c\u610f\u601d\u5c31\u662f\u5bf9\u8fd9\u4e9b\u7684\u6587\u4ef6\u63cf\u8ff0\u7b26\u8fdb\u884c\u5faa\u73af\u76d1\u542c\uff0c\u5f53\u67d0\u4e2a\u6587\u4ef6\u63cf\u8ff0\u7b26\u5c31\u7eea\u7684\u65f6\u5019\uff0c\u5c31\u5bf9\u8fd9\u4e2a\u6587\u4ef6\u63cf\u8ff0\u7b26\u8fdb\u884c\u5904\u7406\u3002<\/p>\n
\u8fd9\u79cdIO\u6a21\u578b\u662f\u5c5e\u4e8e\u963b\u585e\u7684IO\u3002\u4f46\u662f\u7531\u4e8e\u5b83\u53ef\u4ee5\u5bf9\u591a\u4e2a\u6587\u4ef6\u63cf\u8ff0\u7b26\u8fdb\u884c\u963b\u585e\u76d1\u542c\uff0c\u6240\u4ee5\u5b83\u7684\u6548\u7387\u6bd4\u963b\u585eIO\u6a21\u578b\u9ad8\u6548\u3002<\/p>\n
\u00a0<\/p>\n
<img src=""https:\/\/uploadfiles.nowcoder.com\/images\/20190315\/826546_1552638064152_94DD1FAB6C2E289FF496A8013E092EA5"" referrerpolicy=""no-referrer"" alt=""img"" style=""width: 100%;""><\/p>\n
IO\u591a\u8def\u590d\u7528\u5c31\u662f\u6211\u4eec\u8bf4\u7684select\uff0cpoll\uff0cepoll\u3002select\/epoll\u7684\u597d\u5904\u5c31\u5728\u4e8e\u5355\u4e2aprocess\u5c31\u53ef\u4ee5\u540c\u65f6\u5904\u7406\u591a\u4e2a\u7f51\u7edc\u8fde\u63a5\u7684IO\u3002\u5b83\u7684\u57fa\u672c\u539f\u7406\u5c31\u662fselect\uff0cpoll\uff0cepoll\u8fd9\u4e2afunction\u4f1a\u4e0d\u65ad\u7684\u8f6e\u8be2\u6240\u8d1f\u8d23\u7684\u6240\u6709socket\uff0c\u5f53\u67d0\u4e2asocket\u6709\u6570\u636e\u5230\u8fbe\u4e86\uff0c\u5c31\u901a\u77e5\u7528\u6237\u8fdb\u7a0b\u3002<\/p>\n
\u5f53\u7528\u6237\u8fdb\u7a0b\u8c03\u7528\u4e86select\uff0c\u90a3\u4e48\u6574\u4e2a\u8fdb\u7a0b\u4f1a\u88abblock\uff0c\u800c\u540c\u65f6\uff0ckernel\u4f1a\u201c\u76d1\u89c6\u201d\u6240\u6709select\u8d1f\u8d23\u7684socket\uff0c\u5f53\u4efb\u4f55\u4e00\u4e2asocket\u4e2d\u7684\u6570\u636e\u51c6\u5907\u597d\u4e86\uff0cselect\u5c31\u4f1a\u8fd4\u56de\u3002\u8fd9\u4e2a\u65f6\u5019\u7528\u6237\u8fdb\u7a0b\u518d\u8c03\u7528read\u64cd\u4f5c\uff0c\u5c06\u6570\u636e\u4ecekernel\u62f7\u8d1d\u5230\u7528\u6237\u8fdb\u7a0b\u3002<\/p>\n
\u6240\u4ee5\uff0cI\/O \u591a\u8def\u590d\u7528\u7684\u7279\u70b9\u662f\u901a\u8fc7\u4e00\u79cd\u673a\u5236\u4e00\u4e2a\u8fdb\u7a0b\u80fd\u540c\u65f6\u7b49\u5f85\u591a\u4e2a\u6587\u4ef6\u63cf\u8ff0\u7b26\uff0c\u800c\u8fd9\u4e9b\u6587\u4ef6\u63cf\u8ff0\u7b26\uff08\u5957\u63a5\u5b57\u63cf\u8ff0\u7b26\uff09\u5176\u4e2d\u7684\u4efb\u610f\u4e00\u4e2a\u8fdb\u5165\u8bfb\u5c31\u7eea\u72b6\u6001\uff0cselect()\u51fd\u6570\u5c31\u53ef\u4ee5\u8fd4\u56de\u3002<\/p>\n
I\/O\u591a\u8def\u590d\u7528\u548c\u963b\u585eI\/O\u5176\u5b9e\u5e76\u6ca1\u6709\u592a\u5927\u7684\u4e0d\u540c\uff0c\u4e8b\u5b9e\u4e0a\uff0c\u8fd8\u66f4\u5dee\u4e00\u4e9b\u3002\u56e0\u4e3a\u8fd9\u91cc\u9700\u8981\u4f7f\u7528\u4e24\u4e2asystem call (select \u548c recvfrom)\uff0c\u800cblocking IO\u53ea\u8c03\u7528\u4e86\u4e00\u4e2asystem call (recvfrom)\u3002\u4f46\u662f\uff0c\u7528select\u7684\u4f18\u52bf\u5728\u4e8e\u5b83\u53ef\u4ee5\u540c\u65f6\u5904\u7406\u591a\u4e2aconnection\u3002<\/p>\n
\u6240\u4ee5\uff0c\u5982\u679c\u5904\u7406\u7684\u8fde\u63a5\u6570\u4e0d\u662f\u5f88\u9ad8\u7684\u8bdd\uff0c\u4f7f\u7528select\/epoll\u7684web server\u4e0d\u4e00\u5b9a\u6bd4\u4f7f\u7528multi-threading + blocking IO\u7684web server\u6027\u80fd\u66f4\u597d\uff0c\u53ef\u80fd\u5ef6\u8fdf\u8fd8\u66f4\u5927\u3002select\/epoll\u7684\u4f18\u52bf\u5e76\u4e0d\u662f\u5bf9\u4e8e\u5355\u4e2a\u8fde\u63a5\u80fd\u5904\u7406\u5f97\u66f4\u5feb\uff0c\u800c\u662f\u5728\u4e8e\u80fd\u5904\u7406\u66f4\u591a\u7684\u8fde\u63a5\u3002\uff09<\/p>\n
\u5728IO multiplexing Model\u4e2d\uff0c\u5b9e\u9645\u4e2d\uff0c\u5bf9\u4e8e\u6bcf\u4e00\u4e2asocket\uff0c\u4e00\u822c\u90fd\u8bbe\u7f6e\u6210\u4e3anon-blocking\uff0c\u4f46\u662f\uff0c\u5982\u4e0a\u56fe\u6240\u793a\uff0c\u6574\u4e2a\u7528\u6237\u7684process\u5176\u5b9e\u662f\u4e00\u76f4\u88abblock\u7684\u3002\u53ea\u4e0d\u8fc7process\u662f\u88abselect\u8fd9\u4e2a\u51fd\u6570block\uff0c\u800c\u4e0d\u662f\u88absocket IO\u7ed9block\u3002<\/p>\n
2\u3001select<\/p>\n
select\uff1a\u662f\u6700\u521d\u89e3\u51b3IO\u963b\u585e\u95ee\u9898\u7684\u65b9\u6cd5\u3002\u7528\u7ed3\u6784\u4f53fd_set\u6765\u544a\u8bc9\u5185\u6838\u76d1\u542c\u591a\u4e2a\u6587\u4ef6\u63cf\u8ff0\u7b26\uff0c\u8be5\u7ed3\u6784\u4f53\u88ab\u79f0\u4e3a\u63cf\u8ff0\u7b26\u96c6\u3002\u7531\u6570\u7ec4\u6765\u7ef4\u6301\u54ea\u4e9b\u63cf\u8ff0\u7b26\u88ab\u7f6e\u4f4d\u4e86\u3002\u5bf9\u7ed3\u6784\u4f53\u7684\u64cd\u4f5c\u5c01\u88c5\u5728\u4e09\u4e2a\u5b8f\u5b9a\u4e49\u4e2d\u3002\u901a\u8fc7\u8f6e\u5bfb\u6765\u67e5\u627e\u662f\u5426\u6709\u63cf\u8ff0\u7b26\u8981\u88ab\u5904\u7406\u3002<\/p>\n
\u5b58\u5728\u7684\u95ee\u9898\uff1a<\/p>\n
\\1. \u5185\u7f6e\u6570\u7ec4\u7684\u5f62\u5f0f\u4f7f\u5f97select\u7684\u6700\u5927\u6587\u4ef6\u6570\u53d7\u9650\u4e0eFD_SIZE\uff1b<\/p>\n
\\2. \u6bcf\u6b21\u8c03\u7528select\u524d\u90fd\u8981\u91cd\u65b0\u521d\u59cb\u5316\u63cf\u8ff0\u7b26\u96c6\uff0c\u5c06fd\u4ece\u7528\u6237\u6001\u62f7\u8d1d\u5230\u5185\u6838\u6001\uff0c\u6bcf\u6b21\u8c03\u7528select\u540e\uff0c\u90fd\u9700\u8981\u5c06fd\u4ece\u5185\u6838\u6001\u62f7\u8d1d\u5230\u7528\u6237\u6001\uff1b<\/p>\n
\\3. \u8f6e\u5bfb\u6392\u67e5\u5f53\u6587\u4ef6\u63cf\u8ff0\u7b26\u4e2a\u6570\u5f88\u591a\u65f6\uff0c\u6548\u7387\u5f88\u4f4e\uff1b<\/p>\n
3\u3001poll<\/p>\n
poll\uff1a\u901a\u8fc7\u4e00\u4e2a\u53ef\u53d8\u957f\u5ea6\u7684\u6570\u7ec4\u89e3\u51b3\u4e86select\u6587\u4ef6\u63cf\u8ff0\u7b26\u53d7\u9650\u7684\u95ee\u9898\u3002\u6570\u7ec4\u4e2d\u5143\u7d20\u662f\u7ed3\u6784\u4f53\uff0c\u8be5\u7ed3\u6784\u4f53\u4fdd\u5b58\u63cf\u8ff0\u7b26\u7684\u4fe1\u606f\uff0c\u6bcf\u589e\u52a0\u4e00\u4e2a\u6587\u4ef6\u63cf\u8ff0\u7b26\u5c31\u5411\u6570\u7ec4\u4e2d\u52a0\u5165\u4e00\u4e2a\u7ed3\u6784\u4f53\uff0c\u7ed3\u6784\u4f53\u53ea\u9700\u8981\u62f7\u8d1d\u4e00\u6b21\u5230\u5185\u6838\u6001\u3002poll\u89e3\u51b3\u4e86select\u91cd\u590d\u521d\u59cb\u5316\u7684\u95ee\u9898\u3002\u8f6e\u5bfb\u6392\u67e5\u7684\u95ee\u9898\u672a\u89e3\u51b3\u3002<\/p>\n
4\u3001epoll<\/p>\n
epoll\uff1a\u8f6e\u5bfb\u6392\u67e5\u6240\u6709\u6587\u4ef6\u63cf\u8ff0\u7b26\u7684\u6548\u7387\u4e0d\u9ad8\uff0c\u4f7f\u670d\u52a1\u5668\u5e76\u53d1\u80fd\u529b\u53d7\u9650\u3002\u56e0\u6b64\uff0cepoll\u91c7\u7528\u53ea\u8fd4\u56de\u72b6\u6001\u53d1\u751f\u53d8\u5316\u7684\u6587\u4ef6\u63cf\u8ff0\u7b26\uff0c\u4fbf\u89e3\u51b3\u4e86\u8f6e\u5bfb\u7684\u74f6\u9888\u3002<\/p>\n
epoll\u5bf9\u6587\u4ef6\u63cf\u8ff0\u7b26\u7684\u64cd\u4f5c\u6709\u4e24\u79cd\u6a21\u5f0f\uff1aLT\uff08level trigger\uff09\u548cET\uff08edge trigger\uff09\u3002LT\u6a21\u5f0f\u662f\u9ed8\u8ba4\u6a21\u5f0f<\/p>\n
\\1. LT\u6a21\u5f0f<\/p>\n
LT(level triggered)\u662f\u7f3a\u7701\u7684\u5de5\u4f5c\u65b9\u5f0f\uff0c\u5e76\u4e14\u540c\u65f6\u652f\u6301block\u548cno-block socket.\u5728\u8fd9\u79cd\u505a\u6cd5\u4e2d\uff0c\u5185\u6838\u544a\u8bc9\u4f60\u4e00\u4e2a\u6587\u4ef6\u63cf\u8ff0\u7b26\u662f\u5426\u5c31\u7eea\u4e86\uff0c\u7136\u540e\u4f60\u53ef\u4ee5\u5bf9\u8fd9\u4e2a\u5c31\u7eea\u7684fd\u8fdb\u884cIO\u64cd\u4f5c\u3002\u5982\u679c\u4f60\u4e0d\u4f5c\u4efb\u4f55\u64cd\u4f5c\uff0c\u5185\u6838\u8fd8\u662f\u4f1a\u7ee7\u7eed\u901a\u77e5\u4f60\u7684\u3002<\/p>\n
\\2. ET\u6a21\u5f0f<\/p>\n
ET(edge-triggered)\u662f\u9ad8\u901f\u5de5\u4f5c\u65b9\u5f0f\uff0c\u53ea\u652f\u6301no-block socket\u3002\u5728\u8fd9\u79cd\u6a21\u5f0f\u4e0b\uff0c\u5f53\u63cf\u8ff0\u7b26\u4ece\u672a\u5c31\u7eea\u53d8\u4e3a\u5c31\u7eea\u65f6\uff0c\u5185\u6838\u901a\u8fc7epoll\u544a\u8bc9\u4f60\u3002\u7136\u540e\u5b83\u4f1a\u5047\u8bbe\u4f60\u77e5\u9053\u6587\u4ef6\u63cf\u8ff0\u7b26\u5df2\u7ecf\u5c31\u7eea\uff0c\u5e76\u4e14\u4e0d\u4f1a\u518d\u4e3a\u90a3\u4e2a\u6587\u4ef6\u63cf\u8ff0\u7b26\u53d1\u9001\u66f4\u591a\u7684\u5c31\u7eea\u901a\u77e5\uff0c\u76f4\u5230\u4f60\u505a\u4e86\u67d0\u4e9b\u64cd\u4f5c\u5bfc\u81f4\u90a3\u4e2a\u6587\u4ef6\u63cf\u8ff0\u7b26\u4e0d\u518d\u4e3a\u5c31\u7eea\u72b6\u6001\u4e86(\u6bd4\u5982\uff0c\u4f60\u5728\u53d1\u9001\uff0c\u63a5\u6536\u6216\u8005\u63a5\u6536\u8bf7\u6c42\uff0c\u6216\u8005\u53d1\u9001\u63a5\u6536\u7684\u6570\u636e\u5c11\u4e8e\u4e00\u5b9a\u91cf\u65f6\u5bfc\u81f4\u4e86\u4e00\u4e2aEWOULDBLOCK \u9519\u8bef\uff09\u3002\u4f46\u662f\u8bf7\u6ce8\u610f\uff0c\u5982\u679c\u4e00\u76f4\u4e0d\u5bf9\u8fd9\u4e2afd\u4f5cIO\u64cd\u4f5c(\u4ece\u800c\u5bfc\u81f4\u5b83\u518d\u6b21\u53d8\u6210\u672a\u5c31\u7eea)\uff0c\u5185\u6838\u4e0d\u4f1a\u53d1\u9001\u66f4\u591a\u7684\u901a\u77e5(only once)<\/p>\n
\u00a0<\/p>\n
ET\u6a21\u5f0f\u5728\u5f88\u5927\u7a0b\u5ea6\u4e0a\u51cf\u5c11\u4e86epoll\u4e8b\u4ef6\u88ab\u91cd\u590d\u89e6\u53d1\u7684\u6b21\u6570\uff0c\u56e0\u6b64\u6548\u7387\u8981\u6bd4LT\u6a21\u5f0f\u9ad8\u3002epoll\u5de5\u4f5c\u5728ET\u6a21\u5f0f\u7684\u65f6\u5019\uff0c\u5fc5\u987b\u4f7f\u7528\u975e\u963b\u585e\u5957\u63a5\u53e3\uff0c\u4ee5\u907f\u514d\u7531\u4e8e\u4e00\u4e2a\u6587\u4ef6\u53e5\u67c4\u7684\u963b\u585e\u8bfb\/\u963b\u585e\u5199\u64cd\u4f5c\u628a\u5904\u7406\u591a\u4e2a\u6587\u4ef6\u63cf\u8ff0\u7b26\u7684\u4efb\u52a1\u997f\u6b7b\u3002<\/p>\n
3\u3001LT\u6a21\u5f0f\u4e0eET\u6a21\u5f0f\u7684\u533a\u522b\u5982\u4e0b\uff1a<\/p>\n
LT\u6a21\u5f0f\uff1a\u5f53epoll_wait\u68c0\u6d4b\u5230\u63cf\u8ff0\u7b26\u4e8b\u4ef6\u53d1\u751f\u5e76\u5c06\u6b64\u4e8b\u4ef6\u901a\u77e5\u5e94\u7528\u7a0b\u5e8f\uff0c\u5e94\u7528\u7a0b\u5e8f\u53ef\u4ee5\u4e0d\u7acb\u5373\u5904\u7406\u8be5\u4e8b\u4ef6\u3002\u4e0b\u6b21\u8c03\u7528epoll_wait\u65f6\uff0c\u4f1a\u518d\u6b21\u54cd\u5e94\u5e94\u7528\u7a0b\u5e8f\u5e76\u901a\u77e5\u6b64\u4e8b\u4ef6\u3002ET\u6a21\u5f0f\uff1a\u5f53epoll_wait\u68c0\u6d4b\u5230\u63cf\u8ff0\u7b26\u4e8b\u4ef6\u53d1\u751f\u5e76\u5c06\u6b64\u4e8b\u4ef6\u901a\u77e5\u5e94\u7528\u7a0b\u5e8f\uff0c\u5e94\u7528\u7a0b\u5e8f\u5fc5\u987b\u7acb\u5373\u5904\u7406\u8be5\u4e8b\u4ef6\u3002\u5982\u679c\u4e0d\u5904\u7406\uff0c\u4e0b\u6b21\u8c03\u7528epoll_wait\u65f6\uff0c\u4e0d\u4f1a\u518d\u6b21\u54cd\u5e94\u5e94\u7528\u7a0b\u5e8f\u5e76\u901a\u77e5\u6b64\u4e8b\u4ef6\u3002<\/p>\n
<pre><code> "“`
\n<\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"
“`” 1\uff09IO\u591a\u8def\u590d\u7528 IO\u590d\u7528\u6a21\u578b\u5728\u963b\u585eIO\u6a21\u578b\u4e0a\u591a\u4e86\u4e00\u4e2aselect\u51fd\u6570\uff0csel […]<\/p>\n","protected":false},"author":7,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[101],"tags":[],"class_list":["post-40029","post","type-post","status-publish","format-standard","hentry","category-c"],"_links":{"self":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts\/40029","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/users\/7"}],"replies":[{"embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/comments?post=40029"}],"version-history":[{"count":1,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts\/40029\/revisions"}],"predecessor-version":[{"id":40030,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts\/40029\/revisions\/40030"}],"wp:attachment":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/media?parent=40029"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/categories?post=40029"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/tags?post=40029"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}