{"id":897,"date":"2014-04-24T22:23:03","date_gmt":"2014-04-24T14:23:03","guid":{"rendered":"http:\/\/coderbee.net\/?p=897"},"modified":"2014-05-03T23:04:15","modified_gmt":"2014-05-03T15:04:15","slug":"juc-exchanger","status":"publish","type":"post","link":"https:\/\/coderbee.net\/index.php\/concurrent\/20140424\/897","title":{"rendered":"JUC Exchanger"},"content":{"rendered":"

\u4e00\u3001\u6982\u8ff0<\/h3>\n

Exchanger<\/code> \u53ef\u4ee5\u5728\u5bf9\u4e2d\u5bf9\u5143\u7d20\u8fdb\u884c\u914d\u5bf9\u548c\u4ea4\u6362\u7684\u7ebf\u7a0b\u7684\u540c\u6b65\u70b9\u3002\u6bcf\u4e2a\u7ebf\u7a0b\u5c06\u6761\u76ee\u4e0a\u7684\u67d0\u4e2a\u65b9\u6cd5\u5448\u73b0\u7ed9 exchange<\/code> \u65b9\u6cd5\uff0c\u4e0e\u4f19\u4f34\u7ebf\u7a0b\u8fdb\u884c\u5339\u914d\uff0c\u5e76\u4e14\u5728\u8fd4\u56de\u65f6\u63a5\u6536\u5176\u4f19\u4f34\u7684\u5bf9\u8c61\u3002Exchanger<\/code> \u53ef\u80fd\u88ab\u89c6\u4e3a SynchronousQueue<\/code> \u7684\u53cc\u5411\u5f62\u5f0f\u3002Exchanger<\/code> \u53ef\u80fd\u5728\u5e94\u7528\u7a0b\u5e8f\uff08\u6bd4\u5982\u9057\u4f20\u7b97\u6cd5\u548c\u7ba1\u9053\u8bbe\u8ba1\uff09\u4e2d\u5f88\u6709\u7528\u3002<\/p>\n

\u4e8c\u3001\u7b97\u6cd5\u63cf\u8ff0<\/h3>\n

\u57fa\u672c\u60f3\u6cd5\u662f\u7ef4\u62a4\u4e00\u4e2a\u69fd\u6307\u5411\u4e00\u4e2a\u7ed3\u70b9\uff0c\u7ed3\u70b9\u5305\u542b\u4e00\u4e2a\u51c6\u5907\u63d0\u4f9b\uff08\u51fa\u53bb\uff09\u7684item\u548c\u4e00\u4e2a\u7b49\u5f85\u586b\u5145\u7684\u6d1e\u3002\u5982\u679c\u4e00\u4e2a\u5230\u6765\u7684\u201coccupying\u201d\u7ebf\u7a0b\u770b\u5230\u69fd\u662f\u7a7a\u7684\uff0cCAS\u7ed3\u70b9\u5230\u90a3\u91cc\u5e76\u7b49\u5f85\u53e6\u4e00\u4e2a\u7ebf\u7a0b\u53d1\u8d77\u4ea4\u6362\u3002\u7b2c\u4e8c\u4e2a\u201cfulfilling\u201d\u7ebf\u7a0b\u770b\u5230\u69fd\u662f\u975e\u7a7a\u7684\uff0c\u628a\u5b83CAS\u56de\u7a7a\uff0c\u4e5f\u901a\u8fc7CAS\u6d1e\u4ea4\u6362item\uff0c\u52a0\u4e0a\u5524\u9192occupying\u7ebf\u7a0b\uff0c\u5982\u679c\u5b83\u662f\u963b\u585e\u7684\u3002\u5728\u6bcf\u79cd\u60c5\u51b5\u4e0bCAS\u53ef\u80fd\u5931\u8d25\uff0c\u56e0\u4e3a\u4e00\u4e2a\u69fd\u4e00\u5f00\u59cb\u770b\u8d77\u6765\u662f\u975e\u7a7a\u7684\uff0c\u4f46\u5728CAS\u65f6\u4e0d\u662f\uff0c\u6216\u8005\u76f8\u53cd\uff0c\u6240\u4ee5\u7ebf\u7a0b\u9700\u8981\u91cd\u8bd5\u8fd9\u4e9b\u52a8\u4f5c\u3002<\/p>\n

\u8fd9\u4e2a\u7b80\u5355\u65b9\u6cd5\u5728\u53ea\u6709\u5c11\u91cf\u7ebf\u7a0b\u4f7f\u7528Exchanger\u65f6\u5de5\u4f5c\u5f97\u5f88\u597d\uff0c\u5f53\u5927\u91cf\u7ebf\u7a0b\u4f7f\u7528\u5355\u4e2aExchanger\u65f6\u6027\u80fd\u5feb\u901f\u6076\u5316\uff0c\u7531\u4e8eCAS\u7ade\u4e89\u3002\u56e0\u6b64\u6211\u4eec\u4f7f\u7528\u4e00\u4e2a\u201carena, \u7ade\u6280\u573a\u201d\uff0c\u57fa\u672c\u4e0a\u662f\u4e00\u4e2a\u54c8\u5e0c\u8868\uff0c\u6709\u52a8\u6001\u53ef\u53d8\u6570\u91cf\u7684\u69fd\uff0c\u6bcf\u4e00\u4e2a\u69fd\u90fd\u53ef\u88ab\u4efb\u610f\u7ebf\u7a0b\u6267\u884c\u4ea4\u6362\u3002\u8fdb\u5165\u7ebf\u7a0b\u57fa\u4e8e\u81ea\u5df1\u7684\u7ebf\u7a0bID\u9009\u62e9\u69fd\uff0c\u5982\u679c\u4e00\u4e2a\u8fdb\u5165\u5728\u5b83\u81ea\u5df1\u9009\u62e9\u7684\u69fd\u4e0aCAS\u5931\u8d25\uff0c\u5b83\u9009\u62e9\u4e00\u4e2a\u4f9b\u66ff\u4ee3\u7684\u69fd\u3002\u5982\u679c\u4e00\u4e2a\u7ebf\u7a0b\u6210\u529fCAS\u5230\u4e00\u4e2a\u69fd\u4f46\u6ca1\u6709\u5176\u4ed6\u7ebf\u7a0b\u5230\u8fbe\uff0c\u5b83\u5c1d\u8bd5\u5176\u4ed6\uff0c\u524d\u5f80 0 \u53f7\u69fd\uff0c\u90a3\u91cc\u603b\u662f\u5b58\u5728\u5982\u679c\u8868\u6536\u7f29\u7684\u8bdd\u3002\u63a7\u5236\u8fd9\u4e2a\u7684\u7279\u6b8a\u673a\u5236\u5982\u4e0b\uff1a<\/p>\n

<\/p>\n

    \n
  • \n

    Waiting<\/strong>\uff1a0 \u53f7\u69fd\u7684\u7279\u6b8a\u4e4b\u5904\u5728\u4e8e\u5f53\u6ca1\u6709\u7ade\u4e89\u65f6\u5b83\u662f\u552f\u4e00\u5b58\u5728\u7684\u69fd\u3002\u4e00\u4e2a\u5360\u636e 0 \u53f7\u69fd\u7684\u7ebf\u7a0b\u5728\u77ed\u6682\u81ea\u65cb\u540e\u5982\u679c\u6ca1\u6709\u7ebf\u7a0b\u6ee1\u8db3\u5b83 \u5c06\u963b\u585e\u3002\u5728\u5176\u4ed6\u60c5\u51b5\u4e0b\uff0c\u5360\u636e\u7ebf\u7a0b\u6700\u7ec8\u653e\u5f03\u5e76\u5c1d\u8bd5\u5176\u4ed6\u69fd\u3002\u7b49\u5f85\u7ebf\u7a0b\u5728\u963b\u585e\uff08\u5982\u679c\u662f0\u53f7\u69fd\uff09\u6216\u653e\u5f03\uff08\u5982\u679c\u662f\u5176\u4ed6\u69fd\uff09\u5e76\u91cd\u65b0\u5f00\u59cb\u4e4b\u524d\u4f1a\u81ea\u65cb\u7b49\u5f85\u4e00\u4f1a\u513f\uff08\u5468\u671f\u5c0f\u4e8e\u5178\u578b\u7684\u4e0a\u4e0b\u6587\u5207\u6362\u65f6\u95f4\uff09\u3002\u6ca1\u6709\u7406\u7531\u8ba9\u7ebf\u7a0b\u963b\u585e\uff0c\u9664\u975e\u4e0d\u5927\u53ef\u80fd\u51fa\u73b0\u5176\u4ed6\u7ebf\u7a0b\u3002\u5360\u636e\u8005\u4e3b\u8981\u907f\u514d\u5185\u5b58\u7ade\u4e89\uff0c\u6240\u4ee5\u5750\u5728\u9759\u9759\u5730\u90a3\u91cc\u77ed\u6682\u5730\u8f6e\u8be2\uff0c\u7136\u540e\u5b83\u4f1a\u963b\u585e\u548c\u89e3\u9664\u963b\u585e\u3002\u975e0\u53f7\u69fd\u7b49\u5f85\u90a3\u6d88\u5931\uff0c\u56e0\u4e3a\u7f3a\u5c11\u5176\u4ed6\u7ebf\u7a0b\uff0c\u5728\u6bcf\u6b21\u5c1d\u8bd5\u4f1a\u6d6a\u8d39\u4e00\u4e2a\u989d\u5916\u7684\u4e0a\u4e0b\u6587\u5207\u6362\uff0c\u5728\u5e73\u5747\u4e0a\u8fd9\u4ecd\u7136\u6bd4\u53ef\u9009\u7684\u65b9\u6cd5\u5feb\u3002<\/p>\n<\/li>\n

  • \n

    Sizing<\/strong>\uff1a\u901a\u5e38\uff0c\u4ec5\u4f7f\u7528\u5c11\u91cf\u7684\u69fd\u8db3\u4ee5\u51cf\u5c11\u7ade\u4e89\u3002\u7279\u522b\u662f\u5c11\u91cf\u7ebf\u7a0b\u65f6\uff0c\u4f7f\u7528\u592a\u591a\u7684\u69fd\u53ef\u80fd\u5bfc\u81f4\u548c\u4f7f\u7528\u592a\u5c11\u7684\u69fd\u4e00\u6837\u7684\u4f4e\u6027\u80fd\uff0c\u4e14\u90a3\u5bf9\u4e8e\u9519\u8bef\u6ca1\u6709\u592a\u591a\u7a7a\u95f4\u3002\u53d8\u91cf\u201cmax\u201d\u7ef4\u6301\u4e86\u5b9e\u9645\u4f7f\u7528\u7684\u69fd\u7684\u6700\u5927\u6570\u91cf\u3002\u5b83\u5728\u5f53\u4e00\u4e2a\u7ebf\u7a0b\u770b\u5230\u5f88\u591aCAS\u5931\u8d25\u65f6\u589e\u52a0\u3002\uff08\u8fd9\u7c7b\u4f3c\u4e8e\u57fa\u4e8e\u76ee\u6807\u7684\u8d1f\u8f7d\u503cresing\u4e00\u4e2a\u5e38\u89c4\u7684\u54c8\u5e0c\u8868\u53ea\u4e0d\u8fc7\u8fd9\u91cc\u7684\u589e\u957f\u6b65\u9aa4\u4ec5\u4ec5\u662f\u4e00\u4e2a\u63a5\u4e00\u4e2a\u800c\u4e0d\u662f\u6309\u6bd4\u4f8b\u7684\u3002\uff09\u589e\u957f\u8981\u6c42\u6bcf\u4e2a\u69fd\u4e0a\u7ade\u4e89\u5931\u8d25\u7684\u6b21\u6570\u8fbe\u52303\u6b21\u3002\u8981\u6c42\u591a\u6b21\u5931\u8d25\u662f\u56e0\u4e3a\u4e00\u4e9bCAS\u5931\u8d25\u4e0d\u662f\u56e0\u4e3a\u7ade\u4e89\uff0c\u800c\u662f\u4e24\u4e2a\u7ebf\u7a0b\u4e4b\u95f4\u7684\u7adf\u6001race\u6216\u51fa\u73b0\u8bfb\u548cCAS\u7684\u7ebf\u7a0b\u4f18\u5148\u7ea7\u3002\u800c\u4e14\uff0c\u7a81\u7136\u7684\u7ade\u4e89\u9ad8\u5cf0\u53ef\u4ee5\u6bd4\u5e73\u5747\u53ef\u63a5\u53d7\u7684\u6c34\u5e73\u9ad8\u5f88\u591a\u3002\u5f53\u4e00\u4e2a\u975e0\u53f7\u69fd\u7684\u7b49\u5f85\u7531\u4e8e\u6ca1\u6709\u7b49\u5230\u6ee1\u8db3\u800c\u6d41\u901delapses\u65f6\uff0c\u5c1d\u8bd5\u51cf\u5c0fmax\u4e0a\u9650\u3002\u7ecf\u5386\u8fc7\u7b49\u5f85\u6d41\u901delapsed\u7684\u7ebf\u7a0b\u79fb\u5f800\u53f7\u69fd\uff0c\u6240\u4ee5\u6700\u7ec8\uff08\u6216\u5c06\uff09\u627e\u5230\u5b58\u5728\u5b58\u5728\u7ebf\u7a0b\uff0c\u5373\u4f7f\u8868\u7531\u4e8e\u4e0d\u6d3b\u8dc3\u800c\u7f29\u51cf\u3002\u7528\u4e8e\u589e\u957f\u548c\u7f29\u51cf\u800c\u9009\u62e9\u7684\u673a\u5236\u548c\u9600\u503c\u90fd\u662f\u56fa\u5b9a\u5730\u4e0e\u4ea4\u6362\u4ee3\u7801\u91cc\u7684\u7d22\u5f15indexing\u548c\u54c8\u5e0chashing\u6df7\u5728\u4e00\u8d77\u7684\uff0c\u4e0d\u80fd\u5f88\u597d\u5730\u62bd\u53d6\u51fa\u6765\u3002<\/p>\n<\/li>\n

  • \n

    Hashing<\/strong>\uff1a\u6bcf\u4e2a\u7ebf\u7a0b\u9009\u62e9\u5b83\u7684\u7684\u521d\u59cb\u69fd\u6765\u4f7f\u7528\uff0c\u4e0e\u4e00\u4e2a\u7b80\u5355\u7684\u54c8\u5e0c\u7801\u4e00\u81f4\u3002\u7ed9\u5b9a\u7684\u4f1a\u4ea4\u4f1a\u7684\u7ebf\u7a0b\u7684\u5e8f\u53f7\u662f\u4e00\u6837\u7684\uff0c\u4f46\u9ad8\u6548\u5730\u968f\u673a\u5206\u5e03\u5728\u7ebf\u7a0b\u95f4\u3002\u4f7f\u7528\u7ade\u6280\u573aarenas\u906d\u9047\u4e86\u6240\u6709\u54c8\u5e0c\u8868\u7684\u5178\u578b\u5f00\u9500 vs \u8d28\u91cf\u4e4b\u95f4\u7684\u5e73\u8861\u3002\u8fd9\u91cc\uff0c\u6211\u4eec\u4f7f\u7528\u4e00\u6b65 FNV-1a \u54c8\u5e0c\u7801\uff0c\u57fa\u4e8e\u5f53\u524d\u7ebf\u7a0b\u7684ID\u548c\u4e00\u4e2a\u5ec9\u4ef7\u7684\u5927\u7ea6\u76f8\u5f53\u4e8e\u53d6\u6a21\u7684\u64cd\u4f5c\uff08\u7528\u4e8e\u9009\u62e9\u4e0b\u6807\uff09\u3002\u7528\u8fd9\u79cd\u65b9\u5f0f\u4f18\u5316\u4e0b\u6807\u9009\u62e9\u7684\u4e00\u4e2a\u8d1f\u9762\u662f\u54c8\u5e0c\u7801\u662f\u56fa\u5b9a\u7684hardwired\uff0c\u4f7f\u7528\u4e86\u8868\u5927\u5c0f\u7684\u6700\u9ad832\u4f4d\u3002\u4f46\u8fd9\u4e2a\u503c\u5bf9\u4e8e\u5df2\u77e5\u7684\u5e73\u53f0\u548c\u5e94\u7528\u7684\u6ee1\u8db3\u7684\u3002<\/p>\n<\/li>\n

  • \n

    Probing<\/strong>\uff1a\u5728\u611f\u89c9\u5230\u9009\u62e9\u7684\u69fd\u4e0a\u7684\u7ade\u4e89\u65f6\uff0c\u6211\u4eec\u987a\u5e8f\u63a2\u6d4b\u8868\uff0c\u5728\u8868\u91cc\u51fa\u73b0\u54c8\u5e0c\u78b0\u649e\u540e\u7c7b\u4f3c\u4e8e\u987a\u5e8f\u63a2\u6d4b\u3002\uff08\u6211\u4eec\u5468\u671f\u6027\u5730\u79fb\u52a8\uff0c\u4ee5\u53cd\u5e8f\u65b9\u5f0f\uff0c\u6765\u543b\u5408\u8868\u7684\u589e\u957f\u548c\u6536\u7f29\u89c4\u5219\u3002\uff09\u6b64\u5916\u4e3a\u4e86\u51cf\u5c11\u865a\u5047\u8b66\u62a5\uff08false-alarms\uff09\u548c\u7f13\u5b58\u98a0\u7c38\uff08cache trashing\uff09\u7684\u5f71\u54cd\uff0c\u6211\u4eec\u5728\u79fb\u52a8\u524d\u4e24\u6b21\u5c1d\u8bd5\u521d\u6b21\u9009\u62e9\u7684\u69fd\u3002<\/p>\n<\/li>\n

  • \n

    Padding<\/strong>\uff1a\u5373\u4f7f\u4e86\u6709\u4e86\u7ade\u4e89\u7ba1\u7406\uff0c\u69fd\u7684\u7ade\u4e89\u4ecd\u7136\u5f88\u4e25\u91cd\uff0c\u6240\u4ee5\u6211\u4eec\u4f7f\u7528 \u7f13\u5b58\u586b\u5145\uff08cache-padding\uff09\u6765\u907f\u514d\u4f4e\u6548\u7684\u5185\u5b58\u6027\u80fd\u3002\u7531\u4e8e\u8fd9\u4e2a\uff0c\u69fd\u53ea\u5728\u4f7f\u7528\u65f6\u5ef6\u8fdf\u5b9e\u4f8b\u5316\uff0c\u6765\u907f\u514d\u4e0d\u5fc5\u8981\u7684\u7a7a\u95f4\u6d6a\u8d39\u3002\u4f4d\u7f6e\u7684\u9694\u79bb\u4e00\u5f00\u59cb\u5728\u4e00\u4e2a\u5e94\u7528\u7a0b\u5e8f\u91cc\u4e0d\u4f1a\u6210\u4e3a\u4e00\u4e2a\u8bae\u9898issue\uff0c\u968f\u7740\u65f6\u95f4\u63a8\u79fb\u548cGC\u5b9e\u884c\u538b\u7f29\uff0c\u69fd\u5f88\u53ef\u80fd\u88ab\u79fb\u5230\u4e34\u8fd1\u7684\uff0c\u8fd9\u53ef\u4ee5\u5bfc\u81f4\u5728\u591a\u6838\u5904\u7406\u5668\u662f\u90a3\u4e2a\u7684\u7f13\u5b58\u884c\u98a0\u7c38\uff0c\u9664\u975e\u4f7f\u7528\u4e86\u586b\u5145\u3002<\/p>\n<\/li>\n<\/ul>\n

    \u8fd9\u662f\u5bf9\u8bba\u6587 \u201cA Scalable Elimination-based Exchange Channel[http:\/\/hdl.handle.net\/1802\/2104]\u201d \u63cf\u8ff0\u7684\u7b97\u6cd5\u7684\u4e00\u4e2a\u6539\u8fdb\u7248\uff0c\u4f5c\u8005\u662f William Scherer, Doug Lea, and Michael Scott \u3002<\/p>\n

    \u4e09\u3001\u7b80\u5355\u7684Exchanger<\/h3>\n

    \u6839\u636e\u7b97\u6cd5\u63cf\u8ff0\u91cc\u7684\u4e00\u90e8\u5206\uff0c\u505a\u4e86\u4e2a\u7b80\u5355\u7684\u5b9e\u73b0\u3002\u672a\u6d4b\u8bd5<\/strong>\u3002<\/p>\n

    public class SimpleExchanger {\n     static class Slot {\n           final Object offer;\n           final Thread waiter;\n           volatile Object other;\n\n           public Slot(Thread waiter, Object offer) {\n               this. offer = offer;\n               this. waiter = waiter;\n          }\n     }\n\n     private volatile AtomicReference<Slot> refer = new AtomicReference<>();\n\n     public Object exchange(Object offer) {\n          Slot me = new Slot(Thread. currentThread(), offer);\n\n          Slot you;\n           for (;;) {\n               if ((you = refer.get()) == null) {\n                    if( refer.compareAndSet( null, me)) {\n                        LockSupport. park();\n                         return me. other;\n                   }\n\n              } else if( refer.compareAndSet(you, null)){\n                   you. other = offer;\n                   LockSupport. unpark(you.waiter);\n                    return you. offer;\n              }\n          }\n     }\n}\n<\/code><\/pre>\n
    \u56db\u3001Exchanger \u6838\u5fc3\u6e90\u7801<\/h3>\n
    \u5185\u90e8\u7c7b\u548c\u5c5e\u6027<\/h4>\n

    \/**\n * arena\uff08\u7ade\u6280\u573a\uff09\u7684\u5bb9\u91cf\u3002\u8bbe\u7f6e\u4e3a\u4e00\u4e2a\u63d0\u4f9b\u4e86\u8db3\u591f\u7a7a\u95f4\u5904\u7406\u7ade\u4e89\u7684\u503c\u3002\u5728\u5c0f\u673a\u5668\u4e0a\uff0c\n * \u5927\u591a\u6570\u69fd\u90fd\u4e0d\u4f1a\u4f7f\u7528\uff0c\u4f46\u5b83\u4ecd\u7136\u4e0d\u662f\u6d6a\u8d39\u7684\uff0c\u56e0\u4e3a\u989d\u5916\u7684\u7a7a\u95f4\u63d0\u4f9b\u4e86\u4e00\u4e9b\u673a\u5668\u5c42\u9762\u7684\u5730\u5740\u586b\u5145\uff0c\n * \u6765\u6700\u5c0f\u5316\u5927\u91cfCAS\u64cd\u4f5c\u7684\u69fd\u7684\u5730\u5740\u7684\u5e72\u6270\u3002\n * \u5728\u6bcf\u4e2a\u5927\u673a\u5668\u4e0a\uff0c\u6027\u80fd\u6700\u7ec8\u53d7\u9650\u4e8e\u5185\u5b58\u7684\u5e26\u5bbd\uff0c\u4e0d\u662f\u7ebf\u7a0b\/CPU\u6570\u91cf\u3002\n *\n * \u8fd9\u4e2a\u5e38\u91cf\u5728\u6ca1\u6709\u4fee\u6539 \u7d22\u5f15(indexing)\u548c\u54c8\u5e0c(hashing)\u7b97\u6cd5\u65f6\u4e0d\u80fd\u4fee\u6539\u3002\n *\/\nprivate static final int CAPACITY = 32;\n\n\/**\n * \u69fd\u6570\u7ec4\u3002\u5143\u7d20\u5728\u9700\u8981\u65f6\u5ef6\u8fdf\u521d\u59cb\u5316\u3002\n * \u58f0\u660e\u4e3avolatile\u662f\u4e3a\u4e86\u786e\u4fdd double -checked\u5ef6\u8fdf\u6784\u5efa\u6709\u6548\u3002\n *\/\nprivate volatile Slot[] arena = new Slot[CAPACITY];\n\n\/**\n * `max` \u7684\u503c\u5c06\u5728\u6ca1\u6709\u7ade\u4e89\u7684\u60c5\u51b5\u4e0b\u6301\u6709\u6240\u6709\u7ebf\u7a0b\u3002\u5f53\u8fd9\u4e2a\u503c\u5c0f\u4e8e CAPACITY \u65f6\uff0c\u80fd\u907f\u514d\u4e00\u4e9b\u81a8\u80c0\u3002\n *\/\nprivate static final int FULL =\n    Math.max(0, Math.min(CAPACITY, NCPU \/ 2) - 1);\n\n\/**\n * \u5728\u963b\u585e\u6216\u653e\u5f03\u7b49\u5f85\u586b\u5145\u4e4b\u524d\u81ea\u65cb\uff08\u4ec0\u4e48\u90fd\u4e0d\u505a\uff0c\u9664\u4e86\u8f6e\u8be2\u5185\u5b58\u4f4d\u7f6e\uff09\u7684\u6b21\u6570\u3002\n * \u5728\u5355\u5904\u7406\u5668\u4e0a\u5e94\u5f53\u662f0\u3002\u5728\u591a\u5904\u7406\u5668\u4e0a\uff0c\u8fd9\u4e2a\u503c\u5e94\u5f53\u8db3\u591f\u5927\u4ee5\u4fbf\u4e24\u4e2a\u7ebf\u7a0b\n * \u5c3d\u53ef\u80fd\u5feb\u5730\u4ea4\u6362\u5143\u7d20\uff0c\u4ec5\u5728\u5176\u4e2d\u4e00\u4e2a\u5931\u901f\uff08stalled\uff0c\u7531\u4e8eGC\u6216\u6216\u88ab\u53d6\u4ee3\uff09\n * \u65f6\u963b\u585e\uff0c\u4f46\u4e5f\u4e0d\u80fd\u592a\u957f\uff0c\u4ee5\u514d\u6d6a\u8d39CPU\u8d44\u6e90\u3002\n * \n * \u8003\u8651\u5404\u79cd\u5dee\u5f02\uff0c\u8fd9\u4e2a\u503c\u6bd4\u5927\u591a\u6570\u7cfb\u7edf\u4e0a\u4e0b\u6587\u5207\u6362\u65f6\u95f4\u7684\u5e73\u5747\u503c\u7684\u4e00\u534a\u5927\u4e00\u70b9\u3002\n *\/\nprivate static final int SPINS = (NCPU == 1) ? 0 : 2000;\n\n\nprivate static final int TIMED_SPINS = SPINS \/ 20;\n\n\nprivate static final Object CANCEL = new Object();\n\n\nprivate static final Object NULL_ITEM = new Object();\n\n\n\/**\n * \u88ab\u4f7f\u7528\u7684\u69fd\u5e8f\u53f7\u7684\u6700\u5927\u503c\u3002\u8fd9\u4e2a\u503c\u5728\u4e00\u4e2a\u7ebf\u7a0b\u7ecf\u5386\u592a\u591aCAS\u7ade\u4e89\u65f6\u589e\u52a0\uff0c\n * \u5728\u81ea\u65cb\u7b49\u5f85 elapses\u65f6\u51cf\u5c11\u3002\u53d8\u5316\u53ea\u80fd\u901a\u8fc7compareAndSet\u6765\u5b9e\u65bd\uff0c\n * \u907f\u514d\u7531\u4e8e\u7ebf\u7a0b\u5728\u8bbe\u7f6e\u524d\u78b0\u5de7\u62d6\u5ef6stall\u800c\u5bfc\u81f4\u81f4\u6570\u636e\u8150\u5316stale\u3002\n *\/\nprivate final AtomicInteger max = new AtomicInteger();\n\n\n\/**\n * Node \u6301\u6709\u4ea4\u6362\u6570\u636e\u7684\u4e00\u90e8\u5206\u3002\u8fd9\u4e2a\u7c7b\u7ee7\u627f\u81eaAtomicReference\u6765\u8868\u793a\u4e00\u4e2a\u6d1e\u3002\n * `get()` \u8fd4\u56de\u6d1e\uff08\u91cc\u7684\u503c\uff09\uff0c`compareAndSet` CAS \u503c\u5230\u6d1e\u91cc\u3002\n *\/\nprivate static final class Node extends AtomicReference<Object> {\n     \/\/ \u6ce8\u610f\u4e24\u4e2a\u5c5e\u6027\u5206\u522b\u7528final\u548cvolatile\u6765\u4fdd\u8bc1\u5185\u5b58\u53ef\u89c6\u6027\n    public final Object item;\n    public volatile Thread waiter;\n\n    public Node(Object item) {\n        this.item = item;\n    }\n}\n\n\/**\n * Slot\u662f\u4e00\u4e2a\u5177\u6709\u7f13\u5b58\u884c\u586b\u5145\u7684AtomicReference\u3002\u7531\u4e8e\u586b\u5145\u663e\u8457\u5730\u589e\u52a0\u4e86\u7a7a\u95f4\uff08\u5f00\u9500\uff09\uff0c\n * \u6240\u6709\u7684\u69fd\u90fd\u662f\u6309\u9700\u521b\u5efa\u7684\uff0c\u8fd9\u6837\uff0c\u5728\u80fd\u591f\u63d0\u5347\u541e\u5410\u91cf\u65f6\u4f1a\u6709\u4e0d\u6b62\u4e00\u4e2a\u69fd\uff0c\u6bd4\u4f7f\u7528\u989d\u5916\u7a7a\u95f4\u66f4\u6709\u4ef7\u503c\u3002\n *\/\nprivate static final class Slot extends AtomicReference<Object> {\n    \/\/ Improve likelihood of isolation on <= 64 byte cache lines\n    long q0, q1, q2, q3, q4, q5, q6, q7, q8, q9, qa, qb, qc, qd, qe;\n}\n<\/code><\/pre>\n
    hashIndex \u65b9\u6cd5<\/h4>\n
    \u6b64\u65b9\u6cd5\u7528\u4e8e\u5b9a\u4f4d\u7ebf\u7a0b\u7684\u9ed8\u8ba4\u69fd\u3002<\/p>\n
    private final int hashIndex() {\n    long id = Thread.currentThread().getId();\n    int hash = ((( int)(id ^ (id >>> 32))) ^ 0x811c9dc5) * 0x01000193;\n\n    int m = max.get();\n    int nbits = (((0xfffffc00  >> m) & 4) | \/\/ Compute ceil(log2(m+1))\n                 ((0x000001f8 >>> m) & 2) | \/\/ The constants hold\n                 ((0xffff00f2 >>> m) & 1)); \/\/ a lookup table\n    int index;\n    while ((index = hash & ((1 << nbits) - 1)) > m)       \/\/ May retry on\n        hash = (hash >>> nbits) | (hash << (33 - nbits)); \/\/ non-power-2 m\n    return index;\n}\n<\/code><\/pre>\n
    spinWait \u65b9\u6cd5<\/h4>\n
    \u6b64\u65b9\u6cd5\u7528\u4e8e\u81ea\u65cb\u7b49\u5f85\uff0c\u4e3b\u8981\u662f\u9ed8\u8ba4\u69fd\u662f\u975e0\u53f7\u69fd\u7684\u7ebf\u7a0b\u5728\u6ca1\u6709\u7ebf\u7a0b\u53ef\u4ea4\u6362\u65f6\u4f7f\u7528\u3002<\/p>\n
    private static Object spinWait(Node node, Slot slot) {\n    int spins = SPINS;\n    for (;;) {\n        Object v = node.get();\n        if (v != null)\n            return v;\n        else if (spins > 0)\n            --spins;\n        else\n            tryCancel(node, slot);\n    }\n}\n\n\/\/ \u6ce8\u610f\uff0ctryCancel\u5e76\u6ca1\u6709\u5904\u7406CAS\u5931\u8d25\u7684\u95ee\u9898\uff0cCAS\u5931\u8d25\u540e\u91cd\u8bd5\u662f\u7531\u8c03\u7528\u8005\u65b9\u6cd5\u8d1f\u8d23\u7684\u3002\nprivate static boolean tryCancel(Node node, Slot slot) {\n    if (!node.compareAndSet( null, CANCEL))\n        return false;\n    if (slot.get() == node) \/\/ \u63d0\u524d\u68c0\u67e5\u4ee5\u51cf\u5c11CAS\u7ade\u4e89\n        slot.compareAndSet(node, null);\n    return true;\n}\n<\/code><\/pre>\n
    \u963b\u585e\u7b49\u5f85<\/h4>\n
    \u5f53\u7ebf\u7a0b\u5728 0 \u53f7\u69fd\u4e5f\u6ca1\u6709\u7ebf\u7a0b\u53ef\u4ea4\u6362\u65f6\u5c31\u4f1a\u5148\u81ea\u65cb\u4e00\u6bb5\u65f6\u95f4\uff0c\u5982\u679c\u4ecd\u7136\u6ca1\u6709\u53ef\u4ea4\u6362\u7ebf\u7a0b\u5219\u8fdb\u5165\u7b49\u5f85\u3002<\/p>\n
    private static Object await(Node node, Slot slot) {\n     Thread w = Thread.currentThread();\n      int spins = SPINS;\n      for (;;) {\n          Object v = node.get();\n           if (v != null)\n               return v;\n           else if (spins > 0) \/\/ \u81ea\u65cb\u7b49\u5f85\u9636\u6bb5\n              --spins;\n           else if (node.waiter == null) \/\/ \u5148\u8bbe\u7f6e\u597d\uff0c\u4e0b\u6b21\u5faa\u73af\u963b\u585e\u3002\n              node.waiter = w;\n           else if (w.isInterrupted()) \/\/ \u4e2d\u65ad\u65f6\u7ec8\u6b62\n              tryCancel(node, slot);\n           else\n               \/\/ Block \u963b\u585e\n              LockSupport.park(node);\n     }\n}\n<\/code><\/pre>\n
    doExchange \u65b9\u6cd5<\/h4>\n
    doExchange \u65b9\u6cd5\u662fExchanger\u7c7b\u7684\u6838\u5fc3\u65b9\u6cd5\uff0c\u6240\u4ee5exchange\u65b9\u6cd5\u6781\u5176\u53d8\u5f62\u6700\u7ec8\u90fd\u662f\u8c03\u7528\u8fd9\u4e2a\u65b9\u6cd5\u3002\u5b83\u7684\u5b9e\u73b0\u5b8c\u5168\u9075\u5faa\u524d\u9762\u7684\u7b97\u6cd5\u63cf\u8ff0\u3002<\/p>\n
    private Object doExchange(Object item, boolean timed, long nanos) {\n    Node me = new Node(item);                 \/\/ \u521b\u5efa\u4e00\u4e2a\u4ee5\u9632\u9700\u8981 occupying\n    int index = hashIndex();                  \/\/ \u5f53\u524d\u69fd\u7684\u5e8f\u53f7\n    int fails = 0;                            \/\/ CAS \u5931\u8d25\u8ba1\u6570\n\n    for (;;) {\n        Object y;                             \/\/ \u5f53\u524d\u69fd\u7684\u5185\u5bb9\n        Slot slot = arena[index];\n        if (slot == null)                     \/\/ \u5ef6\u8fdf\u521d\u59cb\u5316\u69fd\n            createSlot(index);                \/\/ \u7ee7\u7eed\u5faa\u73af\u6765\u91cd\u65b0\u8bfb\u53d6\n\n        else if ((y = slot.get()) != null &&  \/\/ \u5c1d\u8bd5\u6ee1\u8db3\uff0c\u4e5f\u5373\u5df2\u6709\u7ebf\u7a0b\u5728\u7b49\u5f85\u4ea4\u6362\n                 slot.compareAndSet(y, null)) {\n           \/\/ \u5df2\u6709\u7ebf\u7a0b\u5728\u7b49\u5f85\u4ea4\u6362\uff0c\u5c1d\u8bd5\u4ea4\u6362\n            Node you = (Node)y;               \/\/ \u4f20\u8f93\u5143\u7d20\n            if (you.compareAndSet( null, item)) {\n               \/\/ CAS \u8bbe\u7f6e\u5bf9\u8c61\u5230\u7b49\u5f85\u8005\uff0c\u8003\u8651\u4e0e\u5176\u4ed6\u7ebf\u7a0b \u7ade\u4e89\uff0c\u7b49\u5f85\u8005\u53d6AtomicReference.value\n                LockSupport.unpark(you.waiter);  \/\/ \u6210\u529f\u4ea4\u6362\uff0c\u5524\u9192\u5bf9\u65b9\u3002\n                return you.item;   \/\/ \u8fd4\u56de\u5bf9\u65b9\u7684\u5bf9\u8c61\uff0c\u5b8c\u6210\u4ea4\u6362\u8005\u53d6\u7b49\u5f85\u8005Node\u7684item\u3002\n            }\n            \/\/ \u5426\u5219\u53d6\u6d88\uff08\u7531\u4e8e\u4e0e\u5176\u4ed6\u7ebf\u7a0b\u7ade\u4e89\u4ea4\u6362\u5931\u8d25\uff09\uff0c\u7ee7\u7eed\n        }\n\n        else if (y == null &&                 \/\/ \u5c1d\u8bd5\u5360\u4f4f\u69fd\n                 slot.compareAndSet( null, me)) {\n           \/\/ \u6ca1\u6709\u7ebf\u7a0b\u5728\u7b49\u5f85\u4ea4\u6362\uff0c\u5f53\u524d\u7b49\u5f85\u5176\u4ed6\u7ebf\u7a0b\u6765\u4ea4\u6362\u3002\n            if (index == 0)                   \/\/ 0\u53f7\u69fd\u7279\u6b8a\u5904\u7406\uff1a\u963b\u585e\u7b49\u5f85\n                return timed ?\n                    awaitNanos(me, slot, nanos) :\n                    await(me, slot);\n\n            \/\/ \u975e0\u53f7\u69fd\u81ea\u65cb\u7b49\u5f85,\u65b9\u6cd5\u8fd4\u56de\u65f6\u8981\u4e48\u6210\u529f\u4ea4\u6362\uff0c\u8981\u4e48\u88ab\u53d6\u6d88\n            Object v = spinWait(me, slot);\n            if (v != CANCEL) \/\/ \u88abfulfilled\n                return v;\n\n            \/\/ \u53d6\u6d88\u7b49\u5f85\uff0c\u4e5f\u5c31\u662f\u7b49\u5f85\u6d41\u901delapses\u3002\n            me = new Node(item);              \/\/ \u4e22\u5f03\u5df2\u53d6\u6d88\u7684\u7ed3\u70b9\n            int m = max.get();\n            if (m > (index >>>= 1))           \/\/ \u51cf\u5c0f\u5e8f\u53f7\n                max.compareAndSet(m, m - 1);  \/\/ \u53ef\u80fd\u7f29\u51cf\u8868\n        }\n\n        else if (++fails > 1) {               \/\/ \u6bcf\u4e2a\u69fd\u4e0a\u5141\u8bb82\u6b21\u5931\u8d25\u3002\n           \/\/ CAS \u5931\u8d25\u5904\u7406\uff0c\u8fbe\u52303\u6b21\u5219\u589e\u5927 \u8868\uff0c\u4e5f\u5c31\u662f\u589e\u52a0CAS\u7684\u69fd\u3002\n            int m = max.get();\n            if (fails > 3 && m < FULL && max.compareAndSet(m, m + 1))\n                index = m + 1;                \/\/ \u7b2c\u4e09\u6b21\u5931\u8d25\u65f6\u589e\u52a0\u69fd\n\n            else if (--index < 0)\n                index = m;                    \/\/ \u5faa\u73af\u904d\u5386\n        }\n    }\n}\n<\/code><\/pre>\n\n
    \u6b22\u8fce\u5173\u6ce8\u6211\u7684\u5fae\u4fe1\u516c\u4f17\u53f7: coderbee\u7b14\u8bb0<\/strong>\uff0c\u53ef\u4ee5\u66f4\u53ca\u65f6\u56de\u590d\u4f60\u7684\u8ba8\u8bba\u3002<\/p>\n
    <\/p>\n","protected":false},"excerpt":{"rendered":"
    \u4e00\u3001\u6982\u8ff0 Exchanger \u53ef\u4ee5\u5728\u5bf9\u4e2d\u5bf9\u5143\u7d20\u8fdb\u884c\u914d\u5bf9\u548c\u4ea4\u6362\u7684\u7ebf\u7a0b\u7684\u540c\u6b65\u70b9\u3002\u6bcf\u4e2a … \u7ee7\u7eed\u9605\u8bfb →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[121],"tags":[110],"_links":{"self":[{"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/posts\/897"}],"collection":[{"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/comments?post=897"}],"version-history":[{"count":6,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/posts\/897\/revisions"}],"predecessor-version":[{"id":903,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/posts\/897\/revisions\/903"}],"wp:attachment":[{"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/media?parent=897"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/categories?post=897"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/tags?post=897"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}