{"id":5855,"date":"2022-05-31T19:53:12","date_gmt":"2022-05-31T11:53:12","guid":{"rendered":"https:\/\/damogame.cn:15443\/wordpress\/?p=5855"},"modified":"2022-05-31T19:53:12","modified_gmt":"2022-05-31T11:53:12","slug":"futex%e7%b3%bb%e7%bb%9f%e8%b0%83%e7%94%a8%ef%bc%8cfutex%e6%9c%ba%e5%88%b6%ef%bc%8c%e5%8f%8a%e5%85%b7%e4%bd%93%e6%a1%88%e4%be%8b%e5%88%86%e6%9e%90","status":"publish","type":"post","link":"https:\/\/i007.cc\/wordpress\/archives\/5855","title":{"rendered":"Futex\u7cfb\u7edf\u8c03\u7528\uff0cFutex\u673a\u5236\uff0c\u53ca\u5177\u4f53\u6848\u4f8b\u5206\u6790"},"content":{"rendered":"<p><a href=\"https:\/\/blog.csdn.net\/weixin_44062361\/article\/details\/118357206\">\u539f\u6587\u5730\u5740<\/a><\/p>\n<p>&nbsp;<\/p>\n<p>\u4e0d\u5982\u5403\u4e2a\u836f<\/p>\n<p>\u4e8e 2021-06-30 12:54:34 \u53d1\u5e03<\/p>\n<p>2556<br \/>\n\u6536\u85cf 11<br \/>\n\u5206\u7c7b\u4e13\u680f\uff1a Linux\u5b66\u4e60 \u6587\u7ae0\u6807\u7b7e\uff1a linux \u591a\u7ebf\u7a0b \u540c\u6b65 \u9501<br \/>\n\u7248\u6743<\/p>\n<p>Linux\u5b66\u4e60<br \/>\n\u4e13\u680f\u6536\u5f55\u8be5\u5185\u5bb9<br \/>\n17 \u7bc7\u6587\u7ae00 \u8ba2\u9605<br \/>\n\u8ba2\u9605\u4e13\u680f<br \/>\nFutex<br \/>\n1\u3001\u80cc\u666f<br \/>\n1.1 \u81ea\u5df1\u5b9e\u73b0\u9501<br \/>\n1.1.1 \u81ea\u65cb\u9501<br \/>\n1.1.2 sleep+\u81ea\u65cb<br \/>\n1.1.3 \u5c0f\u7ed3<br \/>\n1.2 futex<br \/>\n1.2.1 \u4ec0\u4e48\u662fFutex<br \/>\n1.2.2 futex\u8bde\u751f\u4e4b\u524d<br \/>\n1.2.3 futex\u8bde\u751f\u4e4b\u540e<br \/>\n2\u3001Futex\u7cfb\u7edf\u8c03\u7528<br \/>\n3\u3001Futex\u673a\u5236<br \/>\n4\u3001\u5177\u4f53\u6848\u4f8b\u5206\u6790<br \/>\n4.1 \u5728Bionic\u4e2d\u7684\u5b9e\u73b0<br \/>\n4.2 C\u8bed\u8a00\u5b9e\u73b0<br \/>\n5\u3001\u53c2\u8003\u53ca\u6269\u5c55\u9605\u8bfb<br \/>\n\u9996\u5148\u8981\u533a\u5206\u4e00\u4e0bfutex\u7cfb\u7edf\u8c03\u7528\u548cfutex\u673a\u5236\u3002futex\u7cfb\u7edf\u8c03\u7528\u662f\u64cd\u4f5c\u7cfb\u7edf\u63d0\u4f9b\u7ed9\u4e0a\u5c42\u7684\u7cfb\u7edf\u8c03\u7528\u63a5\u53e3\u3002\u800cfutex\u673a\u5236\u662f\u4f7f\u7528futex\u63a5\u53e3\u5b9e\u73b0\u7684\u4e00\u79cd\u9501\u3002<\/p>\n<p>1\u3001\u80cc\u666f<br \/>\n\u7ebf\u7a0b\u540c\u6b65\u53ef\u4ee5\u8bf4\u5728\u65e5\u5e38\u5f00\u53d1\u4e2d\u662f\u7528\u7684\u5f88\u591a\uff0c\u4f46\u5bf9\u4e8e\u5176\u5185\u90e8\u5982\u4f55\u5b9e\u73b0\u7684\uff0c\u4e00\u822c\u4eba\u53ef\u80fd\u77e5\u9053\u7684\u5e76\u4e0d\u591a\u3002\u672c\u7bc7\u6587\u7ae0\u5c06\u4ece\u5982\u4f55\u5b9e\u73b0\u7b80\u5355\u7684\u9501\u5f00\u59cb\uff0c\u4ecb\u7ecdlinux\u4e2d\u7684\u9501\u5b9e\u73b0futex\u7684\u4f18\u70b9\u53ca\u539f\u7406\u3002<\/p>\n<p>1.1 \u81ea\u5df1\u5b9e\u73b0\u9501<br \/>\n1.1.1 \u81ea\u65cb\u9501<br \/>\n\u6700\u5bb9\u6613\u60f3\u5230\u53ef\u80fd\u662f\u81ea\u65cb\uff1a<\/p>\n<p>volatile int status=0;<\/p>\n<p>void lock(){<\/p>\n<p>while(!compareAndSet(0,1)){<br \/>\n}<br \/>\n\/\/get lock<\/p>\n<p>}<\/p>\n<p>void unlock(){<br \/>\nstatus=0;<br \/>\n}<\/p>\n<p>boolean compareAndSet(int except,int newValue){<br \/>\n\/\/cas\u64cd\u4f5c,\u4fee\u6539status\u6210\u529f\u5219\u8fd4\u56detrue<br \/>\n}<\/p>\n<p>1<br \/>\n2<br \/>\n3<br \/>\n4<br \/>\n5<br \/>\n6<br \/>\n7<br \/>\n8<br \/>\n9<br \/>\n10<br \/>\n11<br \/>\n12<br \/>\n13<br \/>\n14<br \/>\n15<br \/>\n16<br \/>\n17<br \/>\n18<br \/>\n19<br \/>\n\u4e0a\u9762\u7684\u4ee3\u7801\u901a\u8fc7\u81ea\u65cb\u548ccas\u6765\u5b9e\u73b0\u4e00\u4e2a\u6700\u7b80\u5355\u7684\u9501\u3002<\/p>\n<p>\u8fd9\u6837\u5b9e\u73b0\u7684\u9501\u663e\u7136\u6709\u4e2a\u81f4\u547d\u7684\u7f3a\u70b9\uff1a\u8017\u8d39cpu\u8d44\u6e90\u3002\u6ca1\u6709\u7ade\u4e89\u5230\u9501\u7684\u7ebf\u7a0b\u4f1a\u4e00\u76f4\u5360\u7528cpu\u8d44\u6e90\u8fdb\u884ccas\u64cd\u4f5c\uff0c\u5047\u5982\u4e00\u4e2a\u7ebf\u7a0b\u83b7\u5f97\u9501\u540e\u8981\u82b1\u8d3910s\u5904\u7406\u4e1a\u52a1\u903b\u8f91\uff0c\u90a3\u53e6\u5916\u4e00\u4e2a\u7ebf\u7a0b\u5c31\u4f1a\u767d\u767d\u7684\u82b1\u8d3910s\u7684cpu\u8d44\u6e90\u3002\uff08\u5047\u8bbe\u7cfb\u7edf\u4e2d\u5c31\u53ea\u6709\u8fd9\u4e24\u4e2a\u7ebf\u7a0b\u7684\u60c5\u51b5\uff09\u3002<\/p>\n<p>1.1.2 sleep+\u81ea\u65cb<br \/>\n\u4f60\u53ef\u80fd\u4ece\u4e00\u5f00\u59cb\u5c31\u60f3\u5230\u4e86\uff0c\u5f53\u7ade\u4e89\u9501\u5931\u8d25\u540e\uff0c\u53ef\u4ee5\u5c06\u7528Thread.sleep\u5c06\u7ebf\u7a0b\u4f11\u7720\uff0c\u4ece\u800c\u4e0d\u5360\u7528cpu\u8d44\u6e90\uff1a<\/p>\n<p>volatile int status=0;<\/p>\n<p>void lock(){<\/p>\n<p>while(!compareAndSet(0,1)){<br \/>\nsleep(10);<br \/>\n}<br \/>\n\/\/get lock<\/p>\n<p>}<\/p>\n<p>void unlock(){<br \/>\nstatus=0;<br \/>\n}<\/p>\n<p>1<br \/>\n2<br \/>\n3<br \/>\n4<br \/>\n5<br \/>\n6<br \/>\n7<br \/>\n8<br \/>\n9<br \/>\n10<br \/>\n11<br \/>\n12<br \/>\n13<br \/>\n14<br \/>\n15<br \/>\n16<br \/>\n\u4e0a\u8ff0\u65b9\u5f0f\u6211\u4eec\u53ef\u80fd\u89c1\u7684\u6bd4\u8f83\u591a\uff0c\u901a\u5e38\u7528\u4e8e\u5b9e\u73b0\u4e0a\u5c42\u9501\u3002\u8be5\u65b9\u5f0f\u4e0d\u9002\u5408\u7528\u4e8e\u64cd\u4f5c\u7cfb\u7edf\u7ea7\u522b\u7684\u9501\uff0c\u56e0\u4e3a\u4f5c\u4e3a\u4e00\u4e2a\u5e95\u5c42\u9501\uff0c\u5176sleep\u65f6\u95f4\u5f88\u96be\u8bbe\u7f6e\u3002sleep\u7684\u65f6\u95f4\u53d6\u51b3\u4e8e\u540c\u6b65\u4ee3\u7801\u5757\u7684\u6267\u884c\u65f6\u95f4\uff0csleep\u65f6\u95f4\u5982\u679c\u592a\u77ed\u4e86\uff0c\u4f1a\u5bfc\u81f4\u7ebf\u7a0b\u5207\u6362\u9891\u7e41\uff08\u6781\u7aef\u60c5\u51b5\u548cyield\u65b9\u5f0f\u4e00\u6837\uff09\uff1bsleep\u65f6\u95f4\u5982\u679c\u8bbe\u7f6e\u7684\u8fc7\u957f\uff0c\u4f1a\u5bfc\u81f4\u7ebf\u7a0b\u4e0d\u80fd\u53ca\u65f6\u83b7\u5f97\u9501\u3002\u56e0\u6b64\u6ca1\u6cd5\u8bbe\u7f6e\u4e00\u4e2a\u901a\u7528\u7684sleep\u503c\u3002\u5c31\u7b97sleep\u7684\u503c\u7531\u8c03\u7528\u8005\u6307\u5b9a\u4e5f\u4e0d\u80fd\u5b8c\u5168\u89e3\u51b3\u95ee\u9898\uff1a\u6709\u7684\u65f6\u5019\u8c03\u7528\u9501\u7684\u4eba\u4e5f\u4e0d\u77e5\u9053\u540c\u6b65\u5757\u4ee3\u7801\u4f1a\u6267\u884c\u591a\u4e45\u3002<\/p>\n<p>1.1.3 \u5c0f\u7ed3<br \/>\n\u5bf9\u4e8e\u9501\u51b2\u7a81\u4e0d\u4e25\u91cd\u7684\u60c5\u51b5\uff0c\u7528\u81ea\u65cb\u9501\u4f1a\u66f4\u9002\u5408\uff0c\u8bd5\u60f3\u6bcf\u4e2a\u7ebf\u7a0b\u83b7\u5f97\u9501\u540e\u5f88\u77ed\u7684\u4e00\u6bb5\u65f6\u95f4\u5185\u5c31\u91ca\u653e\u9501\uff0c\u7ade\u4e89\u9501\u7684\u7ebf\u7a0b\u53ea\u8981\u7ecf\u5386\u51e0\u6b21\u81ea\u65cb\u8fd0\u7b97\u540e\u5c31\u80fd\u83b7\u5f97\u9501\uff0c\u90a3\u5c31\u6ca1\u5fc5\u8981\u7b49\u5f85\u8be5\u7ebf\u7a0b\u4e86\uff0c\u56e0\u4e3a\u7b49\u5f85\u7ebf\u7a0b\u610f\u5473\u7740\u9700\u8981\u8fdb\u5165\u5230\u5185\u6838\u6001\u8fdb\u884c\u4e0a\u4e0b\u6587\u5207\u6362\uff0c\u800c\u4e0a\u4e0b\u6587\u5207\u6362\u662f\u6709\u6210\u672c\u7684\u5e76\u4e14\u8fd8\u4e0d\u4f4e\uff0c\u5982\u679c\u9501\u5f88\u5feb\u5c31\u91ca\u653e\u4e86\uff0c\u90a3\u4e0a\u4e0b\u6587\u5207\u6362\u7684\u5f00\u9500\u5c06\u8d85\u8fc7\u81ea\u65cb\u3002<\/p>\n<p>\u76ee\u524d\u64cd\u4f5c\u7cfb\u7edf\u4e2d\uff0c\u4e00\u822c\u662f\u7528\u81ea\u65cb+\u7b49\u5f85\u7ed3\u5408\u7684\u5f62\u5f0f\u5b9e\u73b0\u9501\uff1a\u5728\u8fdb\u5165\u9501\u65f6\u5148\u81ea\u65cb\u4e00\u5b9a\u6b21\u6570\uff0c\u5982\u679c\u8fd8\u6ca1\u83b7\u5f97\u9501\u518d\u8fdb\u884c\u7b49\u5f85\u3002<\/p>\n<p>1.2 futex<br \/>\n1.2.1 \u4ec0\u4e48\u662fFutex<br \/>\nFutex \u662fFast Userspace muTexes\u7684\u7f29\u5199\uff0c\u7531Hubertus Franke, Matthew Kirkwood, Ingo Molnar and Rusty Russell\u5171\u540c\u8bbe\u8ba1\u5b8c\u6210\u3002\u51e0\u4f4d\u90fd\u662flinux\u9886\u57df\u7684\u4e13\u5bb6\uff0c\u5176\u4e2d\u53ef\u80fdIngo Molnar\u5927\u5bb6\u66f4\u719f\u6089\u4e00\u4e9b\uff0c\u6bd5\u7adf\u662fO(1)\u8c03\u5ea6\u5668\u548cCFS\u7684\u5b9e\u73b0\u8005\u3002<\/p>\n<p>Futex\u6309\u82f1\u6587\u7ffb\u8bd1\u8fc7\u6765\u5c31\u662f\u5feb\u901f\u7528\u6237\u7a7a\u95f4\u4e92\u65a5\u4f53\u3002\u5176\u8bbe\u8ba1\u601d\u60f3\u5176\u5b9e \u4e0d\u96be\u7406\u89e3\uff0c\u5728\u4f20\u7edf\u7684Unix\u7cfb\u7edf\u4e2d\uff0cSystem V IPC(inter process communication)\uff0c\u5982 semaphores, msgqueues, sockets\u8fd8\u6709\u6587\u4ef6\u9501\u673a\u5236(flock())\u7b49\u8fdb\u7a0b\u95f4\u540c\u6b65\u673a\u5236\u90fd\u662f\u5bf9\u4e00\u4e2a\u5185\u6838\u5bf9\u8c61\u64cd\u4f5c\u6765\u5b8c\u6210\u7684\uff0c\u8fd9\u4e2a\u5185\u6838\u5bf9\u8c61\u5bf9\u8981\u540c\u6b65\u7684\u8fdb\u7a0b\u90fd\u662f\u53ef\u89c1\u7684\uff0c\u5176\u63d0\u4f9b\u4e86\u5171\u4eab \u7684\u72b6\u6001\u4fe1\u606f\u548c\u539f\u5b50\u64cd\u4f5c\u3002\u5f53\u8fdb\u7a0b\u95f4\u8981\u540c\u6b65\u7684\u65f6\u5019\u5fc5\u987b\u8981\u901a\u8fc7\u7cfb\u7edf\u8c03\u7528(\u5982semop())\u5728\u5185\u6838\u4e2d\u5b8c\u6210\u3002\u53ef\u662f\u7ecf\u7814\u7a76\u53d1\u73b0\uff0c\u5f88\u591a\u540c\u6b65\u662f\u65e0\u7ade\u4e89\u7684\uff0c\u5373\u67d0\u4e2a\u8fdb\u7a0b\u8fdb\u5165 \u4e92\u65a5\u533a\uff0c\u5230\u518d\u4ece\u67d0\u4e2a\u4e92\u65a5\u533a\u51fa\u6765\u8fd9\u6bb5\u65f6\u95f4\uff0c\u5e38\u5e38\u662f\u6ca1\u6709\u8fdb\u7a0b\u4e5f\u8981\u8fdb\u8fd9\u4e2a\u4e92\u65a5\u533a\u6216\u8005\u8bf7\u6c42\u540c\u4e00\u540c\u6b65\u53d8\u91cf\u7684\u3002\u4f46\u662f\u5728\u8fd9\u79cd\u60c5\u51b5\u4e0b\uff0c\u8fd9\u4e2a\u8fdb\u7a0b\u4e5f\u8981\u9677\u5165\u5185\u6838\u53bb\u770b\u770b\u6709\u6ca1\u6709\u4eba \u548c\u5b83\u7ade\u4e89\uff0c\u9000\u51fa\u7684\u65f6\u4faf\u8fd8\u8981\u9677\u5165\u5185\u6838\u53bb\u770b\u770b\u6709\u6ca1\u6709\u8fdb\u7a0b\u7b49\u5f85\u5728\u540c\u4e00\u540c\u6b65\u53d8\u91cf\u4e0a\u3002\u8fd9\u4e9b\u4e0d\u5fc5\u8981\u7684\u7cfb\u7edf\u8c03\u7528(\u6216\u8005\u8bf4\u5185\u6838\u9677\u5165)\u9020\u6210\u4e86\u5927\u91cf\u7684\u6027\u80fd\u5f00\u9500\u3002\u4e3a\u4e86\u89e3\u51b3\u8fd9\u4e2a\u95ee \u9898\uff0cFutex\u5c31\u5e94\u8fd0\u800c\u751f\uff0cFutex\u662f\u4e00\u79cd\u7528\u6237\u6001\u548c\u5185\u6838\u6001\u6df7\u5408\u7684\u540c\u6b65\u673a\u5236\u3002\u9996\u5148\uff0c\u540c\u6b65\u7684\u8fdb\u7a0b\u95f4\u901a\u8fc7mmap\u5171\u4eab\u4e00\u6bb5\u5185\u5b58\uff0cfutex\u53d8\u91cf\u5c31\u4f4d\u4e8e\u8fd9\u6bb5\u5171\u4eab \u7684\u5185\u5b58\u4e2d\u4e14\u64cd\u4f5c\u662f\u539f\u5b50\u7684\uff0c\u5f53\u8fdb\u7a0b\u5c1d\u8bd5\u8fdb\u5165\u4e92\u65a5\u533a\u6216\u8005\u9000\u51fa\u4e92\u65a5\u533a\u7684\u65f6\u5019\uff0c\u5148\u53bb\u67e5\u770b\u5171\u4eab\u5185\u5b58\u4e2d\u7684futex\u53d8\u91cf\uff0c\u5982\u679c\u6ca1\u6709\u7ade\u4e89\u53d1\u751f\uff0c\u5219\u53ea\u4fee\u6539futex,\u800c\u4e0d \u7528\u518d\u6267\u884c\u7cfb\u7edf\u8c03\u7528\u4e86\u3002\u5f53\u901a\u8fc7\u8bbf\u95eefutex\u53d8\u91cf\u544a\u8bc9\u8fdb\u7a0b\u6709\u7ade\u4e89\u53d1\u751f\uff0c\u5219\u8fd8\u662f\u5f97\u6267\u884c\u7cfb\u7edf\u8c03\u7528\u53bb\u5b8c\u6210\u76f8\u5e94\u7684\u5904\u7406(wait \u6216\u8005 wake up)\u3002\u7b80\u5355\u7684\u8bf4\uff0cfutex\u5c31\u662f\u901a\u8fc7\u5728\u7528\u6237\u6001\u7684\u68c0\u67e5\uff0c\uff08motivation\uff09\u5982\u679c\u4e86\u89e3\u5230\u6ca1\u6709\u7ade\u4e89\u5c31\u4e0d\u7528\u9677\u5165\u5185\u6838\u4e86\uff0c\u5927\u5927\u63d0\u9ad8\u4e86low-contention\u65f6\u5019\u7684\u6548\u7387\u3002 Linux\u4ece2.5.7\u5f00\u59cb\u652f\u6301Futex\u3002<\/p>\n<p>linux\u5e95\u5c42\u7528futex\u5b9e\u73b0\u9501\uff0cfutex\u7531\u4e00\u4e2a\u5185\u6838\u5c42\u7684\u961f\u5217\u548c\u4e00\u4e2a\u7528\u6237\u7a7a\u95f4\u5c42\u7684atomic integer\u6784\u6210\u3002\u5f53\u83b7\u5f97\u9501\u65f6\uff0c\u5c1d\u8bd5cas\u66f4\u6539integer\uff0c\u5982\u679cinteger\u539f\u59cb\u503c\u662f0\uff0c\u5219\u4fee\u6539\u6210\u529f\uff0c\u8be5\u7ebf\u7a0b\u83b7\u5f97\u9501\uff0c\u5426\u5219\u5c31\u5c06\u5f53\u671f\u7ebf\u7a0b\u653e\u5165\u5230 wait queue\u4e2d\uff08\u5373\u64cd\u4f5c\u7cfb\u7edf\u7684\u7b49\u5f85\u961f\u5217\uff09\u3002<br \/>\n\u4e0a\u8ff0\u8bf4\u6cd5\u6709\u4e9b\u62bd\u8c61\uff0c\u5982\u679c\u4f60\u6ca1\u770b\u660e\u767d\u4e5f\u6ca1\u5173\u7cfb\u3002\u6211\u4eec\u5148\u770b\u4e00\u4e0b\u6ca1\u6709futex\u4e4b\u524d\uff0clinux\u662f\u600e\u4e48\u5b9e\u73b0\u9501\u7684\u3002<\/p>\n<p>1.2.2 futex\u8bde\u751f\u4e4b\u524d<br \/>\n\u5728futex\u8bde\u751f\u4e4b\u524d\uff0clinux\u4e0b\u7684\u540c\u6b65\u673a\u5236\u53ef\u4ee5\u5f52\u4e3a\u4e24\u7c7b\uff1a\u7528\u6237\u6001\u7684\u540c\u6b65\u673a\u5236 \u548c\u5185\u6838\u540c\u6b65\u673a\u5236\u3002 \u7528\u6237\u6001\u7684\u540c\u6b65\u673a\u5236\u57fa\u672c\u4e0a\u5c31\u662f\u5229\u7528\u539f\u5b50\u6307\u4ee4\u5b9e\u73b0\u7684\u81ea\u65cb\u9501\u3002\u5173\u4e8e\u81ea\u65cb\u9501\u5176\u7f3a\u70b9\u4e5f\u8bf4\u8fc7\u4e86\uff0c\u4e0d\u9002\u7528\u4e8e\u5927\u7684\u4e34\u754c\u533a\uff08\u5373\u9501\u5360\u7528\u65f6\u95f4\u6bd4\u8f83\u957f\u7684\u60c5\u51b5\uff09\u3002<\/p>\n<p>\u5185\u6838\u63d0\u4f9b\u7684\u540c\u6b65\u673a\u5236\uff0c\u5982semaphore\u7b49\uff0c\u4f7f\u7528\u7684\u662f\u4e0a\u6587\u8bf4\u7684\u81ea\u65cb+\u7b49\u5f85\u7684\u5f62\u5f0f\u3002 \u5b83\u5bf9\u4e8e\u5927\u5c0f\u4e34\u754c\u533a\u548c\u90fd\u9002\u7528\u3002\u4f46\u662f\u56e0\u4e3a\u5b83\u662f\u5185\u6838\u5c42\u7684\uff08\u91ca\u653ecpu\u8d44\u6e90\u662f\u5185\u6838\u7ea7\u8c03\u7528\uff09\uff0c\u6240\u4ee5\u6bcf\u6b21lock\u4e0eunlock\u90fd\u662f\u4e00\u6b21\u7cfb\u7edf\u8c03\u7528\uff0c\u5373\u4f7f\u6ca1\u6709\u9501\u51b2\u7a81\uff0c\u4e5f\u5fc5\u987b\u8981\u901a\u8fc7\u7cfb\u7edf\u8c03\u7528\u8fdb\u5165\u5185\u6838\u4e4b\u540e\u624d\u80fd\u8bc6\u522b\u3002<\/p>\n<p>\u7406\u60f3\u7684\u540c\u6b65\u673a\u5236\u5e94\u8be5\u662f\u6ca1\u6709\u9501\u51b2\u7a81\u65f6\u5728\u7528\u6237\u6001\u5229\u7528\u539f\u5b50\u6307\u4ee4\u5c31\u89e3\u51b3\u95ee\u9898\uff0c\u800c\u9700\u8981\u6302\u8d77\u7b49\u5f85\u65f6\u518d\u4f7f\u7528\u5185\u6838\u63d0\u4f9b\u7684\u7cfb\u7edf\u8c03\u7528\u8fdb\u884c\u7761\u7720\u4e0e\u5524\u9192\u3002\u6362\u53e5\u8bdd\u8bf4\uff0c\u5728\u7528\u6237\u6001\u7684\u81ea\u65cb\u5931\u8d25\u65f6\uff0c\u80fd\u4e0d\u80fd\u8ba9\u8fdb\u7a0b\u6302\u8d77\uff0c\u7531\u6301\u6709\u9501\u7684\u7ebf\u7a0b\u91ca\u653e\u9501\u65f6\u5c06\u5176\u5524\u9192\uff1f<br \/>\n\u5982\u679c\u4f60\u6ca1\u6709\u8f83\u6df1\u5165\u5730\u8003\u8651\u8fc7\u8fd9\u4e2a\u95ee\u9898\uff0c\u5f88\u53ef\u80fd\u60f3\u5f53\u7136\u7684\u8ba4\u4e3a\u7c7b\u4f3c\u4e8e\u8fd9\u6837\u5c31\u884c\u4e86\uff08\u4f2a\u4ee3\u7801\uff09\uff1a<\/p>\n<p>void lock(int lockval) {<br \/>\n\/\/trylock\u662f\u7528\u6237\u7ea7\u7684\u81ea\u65cb\u9501<br \/>\nwhile(!trylock(lockval)) {<br \/>\nwait();\/\/\u91ca\u653ecpu\uff0c\u5e76\u5c06\u5f53\u671f\u7ebf\u7a0b\u52a0\u5165\u7b49\u5f85\u961f\u5217\uff0c\u662f\u7cfb\u7edf\u8c03\u7528<br \/>\n}<br \/>\n}<\/p>\n<p>boolean trylock(int lockval){<br \/>\nint i=0;<br \/>\n\/\/localval=1\u4ee3\u8868\u4e0a\u9501\u6210\u529f<br \/>\nwhile(!compareAndSet(lockval,0,1)){<br \/>\nif(++i&gt;10){<br \/>\nreturn false;<br \/>\n}<br \/>\n}<br \/>\nreturn true;<br \/>\n}<\/p>\n<p>void unlock(int lockval) {<br \/>\ncompareAndSet(lockval,1,0);<br \/>\nnotify();<br \/>\n}<br \/>\n1<br \/>\n2<br \/>\n3<br \/>\n4<br \/>\n5<br \/>\n6<br \/>\n7<br \/>\n8<br \/>\n9<br \/>\n10<br \/>\n11<br \/>\n12<br \/>\n13<br \/>\n14<br \/>\n15<br \/>\n16<br \/>\n17<br \/>\n18<br \/>\n19<br \/>\n20<br \/>\n21<br \/>\n22<br \/>\n\u4e0a\u8ff0\u4ee3\u7801\u7684\u95ee\u9898\u662ftrylock\u548cwait\u4e24\u4e2a\u8c03\u7528\u4e4b\u95f4\u5b58\u5728\u4e00\u4e2a\u7a97\u53e3\uff1a\u5982\u679c\u4e00\u4e2a\u7ebf\u7a0btrylock\u5931\u8d25\uff0c\u5728\u8c03\u7528wait\u65f6\u6301\u6709\u9501\u7684\u7ebf\u7a0b\u91ca\u653e\u4e86\u9501\uff0c\u5f53\u524d\u7ebf\u7a0b\u8fd8\u662f\u4f1a\u8c03\u7528wait\u8fdb\u884c\u7b49\u5f85\uff0c\u4f46\u4e4b\u540e\u5c31\u6ca1\u6709\u4eba\u518d\u5c06\u8be5\u7ebf\u7a0b\u5524\u9192\u4e86\u3002<\/p>\n<p>1.2.3 futex\u8bde\u751f\u4e4b\u540e<br \/>\n\/\/uaddr\u6307\u5411\u4e00\u4e2a\u5730\u5740\uff0cval\u4ee3\u8868\u8fd9\u4e2a\u5730\u5740\u671f\u5f85\u7684\u503c\uff0c\u5f53*uaddr==val\u65f6\uff0c\u624d\u4f1a\u8fdb\u884cwait<br \/>\nint futex_wait(int *uaddr, int val);<br \/>\n\/\/\u5524\u9192n\u4e2a\u5728uaddr\u6307\u5411\u7684\u9501\u53d8\u91cf\u4e0a\u6302\u8d77\u7b49\u5f85\u7684\u8fdb\u7a0b<br \/>\nint futex_wake(int *uaddr, int n);<br \/>\n1<br \/>\n2<br \/>\n3<br \/>\n4<br \/>\nfutex_wait\u771f\u6b63\u5c06\u8fdb\u7a0b\u6302\u8d77\u4e4b\u524d\u4f1a\u68c0\u67e5addr\u6307\u5411\u7684\u5730\u5740\u7684\u503c\u662f\u5426\u7b49\u4e8eval\uff0c\u5982\u679c\u4e0d\u76f8\u7b49\u5219\u4f1a\u7acb\u5373\u8fd4\u56de\uff0c\u7531\u7528\u6237\u6001\u7ee7\u7eedtrylock\u3002\u5426\u5219\u5c06\u5f53\u671f\u7ebf\u7a0b\u63d2\u5165\u5230\u4e00\u4e2a\u961f\u5217\u4e2d\u53bb\uff0c\u5e76\u6302\u8d77\u3002<\/p>\n<p>futex\u5185\u90e8\u7ef4\u62a4\u4e86\u4e00\u4e2a\u961f\u5217\uff0c\u5728\u7ebf\u7a0b\u6302\u8d77\u524d\u4f1a\u7ebf\u7a0b\u63d2\u5165\u5230\u5176\u4e2d\uff0c\u540c\u65f6\u5bf9\u4e8e\u961f\u5217\u4e2d\u7684\u6bcf\u4e2a\u8282\u70b9\u90fd\u6709\u4e00\u4e2a\u6807\u8bc6\uff0c\u4ee3\u8868\u8be5\u7ebf\u7a0b\u5173\u8054\u9501\u7684uaddr\u3002\u8fd9\u6837\uff0c\u5f53\u7528\u6237\u6001\u8c03\u7528futex_wake\u65f6\uff0c\u53ea\u9700\u8981\u904d\u5386\u8fd9\u4e2a\u7b49\u5f85\u961f\u5217\uff0c\u628a\u5e26\u6709\u76f8\u540cuaddr\u7684\u8282\u70b9\u6240\u5bf9\u5e94\u7684\u8fdb\u7a0b\u5524\u9192\u5c31\u884c\u4e86\u3002<\/p>\n<p>\u53e6\u5916\uff0cfutex\u662f\u652f\u6301\u591a\u8fdb\u7a0b\u7684\uff0c\u5f53\u4f7f\u7528futex\u5728\u591a\u8fdb\u7a0b\u95f4\u8fdb\u884c\u540c\u6b65\u65f6\uff0c\u9700\u8981\u8003\u8651\u540c\u4e00\u4e2a\u7269\u7406\u5185\u5b58\u5730\u5740\u5728\u4e0d\u540c\u8fdb\u7a0b\u4e2d\u7684\u865a\u62df\u5730\u5740\u662f\u4e0d\u540c\u7684\u3002<\/p>\n<p>2\u3001Futex\u7cfb\u7edf\u8c03\u7528<br \/>\n\u5176\u539f\u578b\u548c\u7cfb\u7edf\u8c03\u7528\u53f7\u4e3a<\/p>\n<p>#include &lt;linux\/futex.h&gt;<br \/>\n#include &lt;sys\/time.h&gt;<br \/>\nint futex (int *uaddr, int op, int val, const struct timespec *timeout,int *uaddr2, int val3);<br \/>\n#define __NR_futex 240<br \/>\n\/*<br \/>\n\u867d\u7136\u53c2\u6570\u6709\u70b9\u957f\uff0c\u5176\u5b9e\u5e38\u7528\u7684\u5c31\u662f\u524d\u9762\u4e09\u4e2a\uff0c\u540e\u9762\u7684timeout\u5927\u5bb6\u90fd\u80fd\u7406\u89e3\uff0c\u5176\u4ed6\u7684\u4e5f\u5e38\u88abignore\u3002<br \/>\nuaddr\u5c31\u662f\u7528\u6237\u6001\u4e0b\u5171\u4eab\u5185\u5b58\u7684\u5730\u5740\uff0c\u91cc\u9762\u5b58\u653e\u7684\u662f\u4e00\u4e2a\u5bf9\u9f50\u7684\u6574\u578b\u8ba1\u6570\u5668\u3002<br \/>\nop\u5b58\u653e\u7740\u64cd\u4f5c\u7c7b\u578b\u3002\u5b9a\u4e49\u7684\u67095\u4e2d\uff0c\u8fd9\u91cc\u6211\u7b80\u5355\u7684\u4ecb\u7ecd\u4e00\u4e0b\u4e24\u79cd\uff0c\u5269\u4e0b\u7684\u611f\u5174\u8da3\u7684\u81ea\u5df1\u53bbman futex<br \/>\nFUTEX_WAIT: \u539f\u5b50\u6027\u7684\u68c0\u67e5uaddr\u4e2d\u8ba1\u6570\u5668\u7684\u503c\u662f\u5426\u4e3aval,\u5982\u679c\u662f\u5219\u8ba9\u8fdb\u7a0b\u4f11\u7720\uff0c\u76f4\u5230FUTEX_WAKE\u6216\u8005\u8d85\u65f6(time-out)\u3002\u4e5f\u5c31\u662f\u628a\u8fdb\u7a0b\u6302\u5230uaddr\u76f8\u5bf9\u5e94\u7684\u7b49\u5f85\u961f\u5217\u4e0a\u53bb\u3002<br \/>\nFUTEX_WAKE: \u6700\u591a\u5524\u9192val\u4e2a\u7b49\u5f85\u5728uaddr\u4e0a\u8fdb\u7a0b\u3002<br \/>\n\/*<br \/>\n1<br \/>\n2<br \/>\n3<br \/>\n4<br \/>\n5<br \/>\n6<br \/>\n7<br \/>\n8<br \/>\n9<br \/>\n10<br \/>\n11<br \/>\n12<br \/>\n3\u3001Futex\u673a\u5236<br \/>\n\u6240\u6709\u7684futex\u540c\u6b65\u64cd\u4f5c\u90fd\u5e94\u8be5\u4ece\u7528\u6237\u7a7a\u95f4\u5f00\u59cb\uff0c\u9996\u5148\u521b\u5efa\u4e00\u4e2afutex\u540c\u6b65\u53d8\u91cf\uff0c\u4e5f\u5c31\u662f\u4f4d\u4e8e\u5171\u4eab\u5185\u5b58\u7684\u4e00\u4e2a\u6574\u578b\u8ba1\u6570\u5668\u3002\u5f53\u8fdb\u7a0b\u5c1d\u8bd5\u6301\u6709\u9501\u6216\u8005\u8981\u8fdb\u5165\u4e92\u65a5\u533a\u7684\u65f6\u5019\uff0c\u5bf9futex\u6267\u884cdown\u64cd\u4f5c\uff0c\u5373\u539f\u5b50\u6027\u7684\u7ed9futex\u540c\u6b65\u53d8\u91cf\u51cf1\u3002\u5982\u679c\u540c\u6b65\u53d8\u91cf\u53d8\u4e3a0\uff0c\u5219\u6ca1\u6709\u7ade\u4e89\u53d1\u751f\uff0c \u8fdb\u7a0b\u7167\u5e38\u6267\u884c\u3002\u5982\u679c\u540c\u6b65\u53d8\u91cf\u662f\u4e2a\u8d1f\u6570\uff0c\u5219\u610f\u5473\u7740\u6709\u7ade\u4e89\u53d1\u751f\uff0c\u9700\u8981\u8c03\u7528futex\u7cfb\u7edf\u8c03\u7528\u7684futex_wait\u64cd\u4f5c\u4f11\u7720\u5f53\u524d\u8fdb\u7a0b\u3002<br \/>\n\u5f53\u8fdb\u7a0b\u91ca\u653e\u9501\u6216 \u8005\u8981\u79bb\u5f00\u4e92\u65a5\u533a\u7684\u65f6\u5019\uff0c\u5bf9futex\u8fdb\u884cup\u64cd\u4f5c\uff0c\u5373\u539f\u5b50\u6027\u7684\u7ed9futex\u540c\u6b65\u53d8\u91cf\u52a01\u3002\u5982\u679c\u540c\u6b65\u53d8\u91cf\u75310\u53d8\u62101\uff0c\u5219\u6ca1\u6709\u7ade\u4e89\u53d1\u751f\uff0c\u8fdb\u7a0b\u7167\u5e38\u6267\u884c\u3002\u5982 \u679c\u52a0\u4e4b\u524d\u540c\u6b65\u53d8\u91cf\u662f\u8d1f\u6570\uff0c\u5219\u610f\u5473\u7740\u6709\u7ade\u4e89\u53d1\u751f\uff0c\u9700\u8981\u8c03\u7528futex\u7cfb\u7edf\u8c03\u7528\u7684futex_wake\u64cd\u4f5c\u5524\u9192\u4e00\u4e2a\u6216\u8005\u591a\u4e2a\u7b49\u5f85\u8fdb\u7a0b\u3002<\/p>\n<p>\u8fd9\u91cc\u7684\u539f\u5b50\u6027\u52a0\u51cf\u901a\u5e38\u662f\u7528CAS(Compare and Swap)\u5b8c\u6210\u7684\uff0c\u4e0e\u5e73\u53f0\u76f8\u5173\u3002CAS\u7684\u57fa\u672c\u5f62\u5f0f\u662f\uff1aCAS(addr,old,new),\u5f53addr\u4e2d\u5b58\u653e\u7684\u503c\u7b49\u4e8eold\u65f6\uff0c\u7528new\u5bf9\u5176\u66ff\u6362\u3002\u5728x86\u5e73\u53f0\u4e0a\u6709\u4e13\u95e8\u7684\u4e00\u6761\u6307\u4ee4\u6765\u5b8c\u6210\u5b83: cmpxchg\u3002<\/p>\n<p>\u53ef\u89c1: futex\u662f\u4ece\u7528\u6237\u6001\u5f00\u59cb\uff0c\u7531\u7528\u6237\u6001\u548c\u6838\u5fc3\u6001\u534f\u8c03\u5b8c\u6210\u7684\u3002<\/p>\n<p>\u8fdb\u7a0b\u6216\u8005\u7ebf\u7a0b\u90fd\u53ef\u4ee5\u5229\u7528futex\u6765\u8fdb\u884c\u540c\u6b65\u3002<br \/>\n\u5bf9\u4e8e\u7ebf\u7a0b\uff0c\u60c5\u51b5\u6bd4\u8f83\u7b80\u5355\uff0c\u56e0\u4e3a\u7ebf\u7a0b\u5171\u4eab\u865a\u62df\u5185\u5b58\u7a7a\u95f4\uff0c\u865a\u62df\u5730\u5740\u5c31\u53ef\u4ee5\u552f\u4e00\u7684\u6807\u8bc6\u51fafutex\u53d8\u91cf\uff0c\u5373\u7ebf\u7a0b\u7528\u540c\u6837\u7684\u865a\u62df\u5730\u5740\u6765\u8bbf\u95eefutex\u53d8\u91cf\u3002<br \/>\n\u5bf9 \u4e8e\u8fdb\u7a0b\uff0c\u60c5\u51b5\u76f8\u5bf9\u590d\u6742\uff0c\u56e0\u4e3a\u8fdb\u7a0b\u6709\u72ec\u7acb\u7684\u865a\u62df\u5185\u5b58\u7a7a\u95f4\uff0c\u53ea\u6709\u901a\u8fc7mmap()\u8ba9\u5b83\u4eec\u5171\u4eab\u4e00\u6bb5\u5730\u5740\u7a7a\u95f4\u6765\u4f7f\u7528futex\u53d8\u91cf\u3002\u6bcf\u4e2a\u8fdb\u7a0b\u7528\u6765\u8bbf\u95eefutex\u7684 \u865a\u62df\u5730\u5740\u53ef\u4ee5\u662f\u4e0d\u4e00\u6837\u7684\uff0c\u53ea\u8981\u7cfb\u7edf\u77e5\u9053\u6240\u6709\u7684\u8fd9\u4e9b\u865a\u62df\u5730\u5740\u90fd\u6620\u5c04\u5230\u540c\u4e00\u4e2a\u7269\u7406\u5185\u5b58\u5730\u5740\uff0c\u5e76\u7528\u7269\u7406\u5185\u5b58\u5730\u5740\u6765\u552f\u4e00\u6807\u8bc6futex\u53d8\u91cf\u3002<\/p>\n<p>4\u3001\u5177\u4f53\u6848\u4f8b\u5206\u6790<br \/>\n4.1 \u5728Bionic\u4e2d\u7684\u5b9e\u73b0<br \/>\n\u6e90\u7801:http:\/\/www.androidos.net.cn\/android\/5.0.1_r1\/xref\/bionic\/libc\/bionic\/pthread_mutex.cpp<\/p>\n<p>&nbsp;<\/p>\n<p>4.2 C\u8bed\u8a00\u5b9e\u73b0<br \/>\nfutex \u7684\u903b\u8f91\u53ef\u4ee5\u7528\u5982\u4e0bC\u8bed\u8a00\u8868\u793a<\/p>\n<p>int val = 0;<br \/>\nvoid lock()<br \/>\n{<br \/>\nint c<br \/>\nif ((c = cmpxchg(val, 0, 1)) != 0) {<br \/>\nif (c != 2)<br \/>\nc = xchg(val, 2);<br \/>\nwhile (c != 0) {<br \/>\nfutex_wait((&amp;val, 2);<br \/>\nc = xchg(val, 2);<br \/>\n}<br \/>\n}<br \/>\n}<\/p>\n<p>void unlock()<br \/>\n{<br \/>\nif (atomic_dec(val) != 1){<br \/>\nval = 0;<br \/>\nfutex_wake(&amp;val, 1);<br \/>\n}<br \/>\n}<br \/>\n\/*<br \/>\nval 0: unlock<br \/>\nval 1: lock, no waiters<br \/>\nval 2: lock , one or more waiters<\/p>\n<p>Linux\u63d0\u4f9b\u4e86\u5f88\u591a\u64cd\u4f5c\u539f\u5b50\u53d8\u91cf\u7684API\u3002\u4ee5arch\/arm\/include\/asm\/atomic.h\u4e3a\u4f8b\u3002<br \/>\n#define atomic_xchg(v, new) (xchg(&amp;((v)-&gt;counter), new))&#8212;&#8212;&#8212;&#8211;\u628anew\u8d4b\u503c\u7ed9\u539f\u5b50\u53d8\u91cfv\uff0c\u8fd4\u56de\u539f\u5b50\u53d8\u91cfv\u7684\u65e7\u503c\u3002<\/p>\n<p>Linux\u5185\u6838\u4e2d\u7684cmpxchg\u51fd\u6570<br \/>\n\u5728Linux\u5185\u6838\u4e2d\uff0c\u63d0\u4f9b\u4e86\u6bd4\u8f83\u5e76\u4ea4\u6362\u7684\u51fd\u6570cmpxchg\uff0c\u4ee3\u7801\u5728include\/asm-i386\/cmpxchg.h\u4e2d\uff0c\u51fd\u6570\u7684\u539f\u578b\u662f\uff1a<br \/>\ncmpxchg(void *ptr, unsigned long old, unsigned long new);<br \/>\n\u51fd\u6570\u5b8c\u6210\u7684\u529f\u80fd\u662f\uff1a\u5c06old\u548cptr\u6307\u5411\u7684\u5185\u5bb9\u6bd4\u8f83\uff0c\u5982\u679c\u76f8\u7b49\uff0c\u5219\u5c06new\u5199\u5165\u5230ptr\u4e2d\uff0c\u8fd4\u56deold\uff0c\u5982\u679c\u4e0d\u76f8\u7b49\uff0c\u5219\u8fd4\u56deptr\u6307\u5411\u7684\u5185\u5bb9\u3002<br \/>\n*\/<br \/>\n1<br \/>\n2<br \/>\n3<br \/>\n4<br \/>\n5<br \/>\n6<br \/>\n7<br \/>\n8<br \/>\n9<br \/>\n10<br \/>\n11<br \/>\n12<br \/>\n13<br \/>\n14<br \/>\n15<br \/>\n16<br \/>\n17<br \/>\n18<br \/>\n19<br \/>\n20<br \/>\n21<br \/>\n22<br \/>\n23<br \/>\n24<br \/>\n25<br \/>\n26<br \/>\n27<br \/>\n28<br \/>\n29<br \/>\n30<br \/>\n31<br \/>\n32<br \/>\n33<br \/>\n34<br \/>\n5\u3001\u53c2\u8003\u53ca\u6269\u5c55\u9605\u8bfb<br \/>\n\uff1ahttps:\/\/github.com\/farmerjohngit\/myblog\/issues\/6<br \/>\n\uff1a\u6df1\u5165\u89e3\u6790Android 5.0\u7cfb\u7edf<\/p>\n<p>\u6587\u7ae0\u77e5\u8bc6\u70b9\u4e0e\u5b98\u65b9\u77e5\u8bc6\u6863\u6848\u5339\u914d\uff0c\u53ef\u8fdb\u4e00\u6b65\u5b66\u4e60\u76f8\u5173\u77e5\u8bc6<br \/>\nCS\u5165\u95e8\u6280\u80fd\u6811Linux\u73af\u5883\u5b89\u88c5\u5b89\u88c5CentOS2534 \u4eba\u6b63\u5728\u7cfb\u7edf\u5b66\u4e60\u4e2d<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u539f\u6587\u5730\u5740 &nbsp; \u4e0d\u5982\u5403\u4e2a\u836f \u4e8e 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