{"id":118674,"date":"2026-10-27T23:08:47","date_gmt":"2026-10-27T15:08:47","guid":{"rendered":"https:\/\/www.wsisp.com\/helps\/118674.html"},"modified":"2026-10-27T23:08:47","modified_gmt":"2026-10-27T15:08:47","slug":"concurrenthashmap-%e7%9a%84-size-%e4%b8%8e%e6%89%a9%e5%ae%b9%e6%9c%ba%e5%88%b6%ef%bc%9a%e4%bb%8e%e5%88%86%e6%95%a3%e8%ae%a1%e6%95%b0%e5%88%b0%e5%8d%8f%e4%bd%9c%e8%bf%81%e7%a7%bb","status":"publish","type":"post","link":"https:\/\/www.wsisp.com\/helps\/118674.html","title":{"rendered":"ConcurrentHashMap \u7684 size \u4e0e\u6269\u5bb9\u673a\u5236\uff1a\u4ece\u5206\u6563\u8ba1\u6570\u5230\u534f\u4f5c\u8fc1\u79fb"},"content":{"rendered":"

ConcurrentHashMap \u7684 size \u4e0e\u6269\u5bb9\u673a\u5236：\u4ece\u5206\u6563\u8ba1\u6570\u5230\u534f\u4f5c\u8fc1\u79fb<\/h2>\n

\u6587\u7ae0\u6458\u8981<\/h3>\n

ConcurrentHashMap \u65b0\u589e\u4e00\u4e2a\u952e\u4e4b\u540e，\u9700\u8981\u7ef4\u62a4\u5143\u7d20\u6570\u91cf，\u5e76\u5728\u5408\u9002\u7684\u65f6\u673a\u5224\u65ad\u662f\u5426\u6269\u5bb9\u3002\u591a\u4e2a\u7ebf\u7a0b\u540c\u65f6\u589e\u5220\u5143\u7d20\u65f6，\u5b83\u600e\u6837\u907f\u514d\u4e89\u62a2\u540c\u4e00\u4e2a\u8ba1\u6570\u5668？baseCount\u3001CounterCell \u548c size() \u53c8\u600e\u6837\u53c2\u4e0e\u8fd9\u4e2a\u8fc7\u7a0b？\u672c\u6587\u4ee5 JDK 8 \u4e3a\u57fa\u7840，\u5148\u4ecb\u7ecd\u6269\u5bb9\u7684\u6574\u4f53\u8fc7\u7a0b，\u518d\u6cbf\u7740 putVal() \u2192 addCount() \u2192 sumCount() \u2192 transfer() \u89e3\u91ca\u5206\u6563\u8ba1\u6570\u4e0e\u534f\u4f5c\u6269\u5bb9，\u5e76\u8bf4\u660e\u4e3a\u4ec0\u4e48 size() \u9002\u5408\u7edf\u8ba1，\u5374\u4e0d\u80fd\u5355\u72ec\u4fdd\u8bc1\u4e1a\u52a1\u4e0a\u7684\u6570\u91cf\u9650\u5236\u3002<\/p>\n

\u7248\u672c\u8bf4\u660e：\u672c\u6587\u8ba8\u8bba JDK 8，\u6e90\u7801\u6838\u5bf9\u7248\u672c\u4e3a OpenJDK jdk8u402-b06\u3002\u6e90\u7801\u7247\u6bb5\u4e0e\u884c\u53f7\u5747\u4ee5\u6587\u672b\u56fa\u5b9a\u7248\u672c\u94fe\u63a5\u4e3a\u51c6，\u4e0d\u628a JDK 8 \u7684\u5185\u90e8\u5b9e\u73b0\u63a8\u5e7f\u4e3a\u6240\u6709\u7248\u672c\u7684\u89c4\u8303\u3002\u5b8c\u6574\u793a\u4f8b\u4f7f\u7528 JDK 8 \u8bed\u6cd5；\u6807\u6ce8\u4e3a\u201c\u6e90\u7801\u8282\u9009\u201d\u6216\u201c\u903b\u8f91\u793a\u610f\u201d\u7684\u7247\u6bb5\u7528\u4e8e\u9605\u8bfb\u673a\u5236，\u4e0d\u662f\u72ec\u7acb\u7a0b\u5e8f\u3002<\/p>\n

\u8fd0\u884c\u9a8c\u8bc1：\u6587\u4e2d\u7684 CountDemo \u548c CapacityRaceDemo \u5747\u5df2\u5728 Temurin OpenJDK 1.8.0_492 \u4e0a\u7f16\u8bd1\u8fd0\u884c，\u8f93\u51fa\u4e0e\u6b63\u6587\u4e00\u81f4\u3002\u5185\u90e8\u5b9e\u73b0\u7684\u6e90\u7801\u5206\u6790\u4ecd\u4ee5\u4ee5\u4e0a\u56fa\u5b9a\u7248\u672c\u4e3a\u51c6\u3002<\/p>\n

\u4e00\u3001\u5148\u4e86\u89e3 ConcurrentHashMap \u7684\u6269\u5bb9\u673a\u5236<\/h3>\n

ConcurrentHashMap \u7528\u6876\u6570\u7ec4 table \u4fdd\u5b58\u952e\u503c\u5bf9\u3002\u6bcf\u4e2a\u6570\u7ec4\u4f4d\u7f6e\u5bf9\u5e94\u4e00\u4e2a\u6876，\u6876\u5185\u53ef\u4ee5\u7ec4\u7ec7\u4e3a\u94fe\u8868\u6216\u6811\u3002<\/p>\n

\u5143\u7d20\u9010\u6e10\u589e\u591a\u65f6，\u591a\u4e2a\u952e\u843d\u5165\u540c\u4e00\u4e2a\u6876\u7684\u673a\u4f1a\u53ef\u80fd\u589e\u52a0，\u67e5\u8be2\u548c\u66f4\u65b0\u7684\u6210\u672c\u4e5f\u53ef\u80fd\u4e0a\u5347\u3002\u6269\u5bb9\u5c31\u662f\u521b\u5efa\u66f4\u5927\u7684\u6876\u6570\u7ec4，\u628a\u5df2\u6709\u6570\u636e\u8fc1\u79fb\u8fc7\u53bb，\u8ba9\u6570\u636e\u6709\u673a\u4f1a\u5206\u6563\u5230\u66f4\u591a\u6876\u4e2d\u3002<\/p>\n

\u5148\u533a\u5206\u4e24\u4e2a\u6982\u5ff5：<\/p>\n\n\u6982\u5ff5\u8868\u793a\u4ec0\u4e48\u793a\u4f8b<\/tr>\n\n\n\n
\u5143\u7d20\u6570\u91cf<\/td>\n\u5f53\u524d\u6709\u591a\u5c11\u4e2a\u952e\u503c\u5bf9<\/td>\nmap.size() \u8fd4\u56de 10<\/td>\n<\/tr>\n
\u6876\u6570\u7ec4\u5bb9\u91cf<\/td>\ntable \u6570\u7ec4\u7684\u957f\u5ea6<\/td>\ntable.length \u4e3a 16<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

\u6570\u7ec4\u957f\u5ea6\u4e3a 16，\u4e0d\u4ee3\u8868\u6700\u591a\u53ea\u80fd\u653e 16 \u4e2a\u952e\u503c\u5bf9：\u4e00\u4e2a\u6876\u5185\u53ef\u4ee5\u6709\u591a\u4e2a\u5143\u7d20\u3002<\/p>\n

1. \u4ec0\u4e48\u65f6\u5019\u6269\u5bb9<\/h4>\n

\u6876\u6570\u7ec4\u521d\u59cb\u5316\u5b8c\u6210\u3001\u4e14\u6ca1\u6709\u6b63\u5728\u6269\u5bb9\u65f6，sizeCtl \u4fdd\u5b58\u4e0b\u4e00\u6b21\u6269\u5bb9\u7684\u5143\u7d20\u6570\u91cf\u9608\u503c\u3002\u901a\u5e38\u6309\u4e0b\u9762\u7684\u5173\u7cfb\u8bbe\u7f6e：<\/p>\n

\u6269\u5bb9\u9608\u503c = \u6876\u6570\u7ec4\u957f\u5ea6 \u00d7 0.75<\/p>\n

\u6876\u6570\u7ec4\u957f\u5ea6\u4e3a 16 \u2192 \u9608\u503c\u4e3a 12
\n\u6876\u6570\u7ec4\u957f\u5ea6\u4e3a 32 \u2192 \u9608\u503c\u4e3a 24<\/p>\n

\u5143\u7d20\u8ba1\u6570\u8fbe\u5230\u6216\u8d85\u8fc7\u9608\u503c，\u5e76\u8fdb\u5165\u76f8\u5e94\u7684\u6269\u5bb9\u68c0\u67e5\u65f6，\u5c31\u4f1a\u5c1d\u8bd5\u53d1\u8d77\u6269\u5bb9\u3002\u8fbe\u5230\u6700\u5927\u5bb9\u91cf\u7b49\u6761\u4ef6\u4f1a\u9650\u5236\u8fd9\u4e00\u8fc7\u7a0b\u3002<\/p>\n

\u8fd9\u91cc\u5148\u4ecb\u7ecd\u6839\u636e\u5143\u7d20\u8ba1\u6570\u89e6\u53d1\u6269\u5bb9\u7684\u4e3b\u7ebf\u3002\u6876\u5185\u51b2\u7a81\u4e25\u91cd\u3001\u8fdb\u5165\u6811\u5316\u5224\u65ad\u7b49\u573a\u666f，\u4e5f\u53ef\u80fd\u8d70\u5230\u6269\u5bb9\u8def\u5f84，\u540e\u6587\u4f1a\u8865\u5145\u3002<\/p>\n

2. \u600e\u4e48\u6269\u5bb9<\/h4>\n

\u5355\u8f6e\u6876\u6570\u7ec4\u6269\u5bb9\u7684\u4e3b\u8981\u8fc7\u7a0b\u662f：<\/p>\n

\u6ee1\u8db3\u6269\u5bb9\u6761\u4ef6
\n \u2193
\n\u901a\u8fc7 CAS \u4e89\u53d6\u53d1\u8d77\u6269\u5bb9
\n \u2193
\n\u521b\u5efa\u957f\u5ea6\u4e3a\u539f\u6765\u4e24\u500d\u7684\u65b0\u6876\u6570\u7ec4
\n \u2193
\n\u53c2\u4e0e\u7ebf\u7a0b\u9886\u53d6\u4efb\u52a1，\u8fc1\u79fb\u4e0d\u540c\u8303\u56f4\u7684\u6876
\n \u2193
\n\u786e\u8ba4\u8fc1\u79fb\u5b8c\u6210，\u5207\u6362 table \u5e76\u66f4\u65b0\u6269\u5bb9\u9608\u503c<\/p>\n

\u4f8b\u5982，\u4e00\u8f6e\u6269\u5bb9\u53ef\u4ee5\u628a\u6876\u6570\u7ec4\u4ece 16 \u6269\u5230 32\u3002\u8fc1\u79fb\u8fc7\u7a0b\u4e2d，\u5176\u4ed6\u7b26\u5408\u6761\u4ef6\u7684\u66f4\u65b0\u7ebf\u7a0b\u53ef\u4ee5\u534f\u52a9\u5de5\u4f5c，\u4e0d\u5fc5\u59cb\u7ec8\u7531\u4e00\u4e2a\u7ebf\u7a0b\u72ec\u81ea\u5b8c\u6210\u3002[1]<\/p>\n

\u6269\u5bb9\u9700\u8981\u53c2\u8003\u5143\u7d20\u6570\u91cf，\u4f46\u591a\u4e2a\u7ebf\u7a0b\u540c\u65f6\u589e\u5220\u5143\u7d20\u65f6，ConcurrentHashMap \u600e\u6837\u9ad8\u6548\u5730\u7ef4\u62a4\u8fd9\u4e2a\u6570\u91cf？\u5148\u4ece\u201c\u4e3a\u4ec0\u4e48\u4e0d\u80fd\u53ea\u7528\u4e00\u4e2a size \u53d8\u91cf\u201d\u8bf4\u8d77\u3002<\/p>\n

\u4e8c\u3001\u4e3a\u4ec0\u4e48\u4e0d\u80fd\u53ea\u7528\u4e00\u4e2a size \u53d8\u91cf<\/h3>\n

\u6700\u76f4\u63a5\u7684\u60f3\u6cd5\u662f\u4fdd\u5b58\u4e00\u4e2a\u5171\u4eab\u53d8\u91cf，\u65b0\u589e\u5143\u7d20\u65f6\u6267\u884c：<\/p>\n

\/\/ \u9519\u8bef\u7684\u5171\u4eab\u8ba1\u6570\u793a\u610f：\u666e\u901a ++ \u4e0d\u80fd\u4fdd\u8bc1\u5e76\u53d1\u66f4\u65b0\u5b89\u5168\u3002<\/span>
\nsize++<\/span>;<\/span><\/p>\n

++ \u5305\u542b\u8bfb\u53d6\u3001\u52a0\u4e00\u3001\u5199\u56de\u3002\u4e24\u4e2a\u7ebf\u7a0b\u53ef\u80fd\u90fd\u8bfb\u5230 10，\u5206\u522b\u8ba1\u7b97 11，\u518d\u5199\u56de 11，\u5bfc\u81f4\u4e00\u6b21\u589e\u91cf\u88ab\u8986\u76d6\u3002<\/p>\n

\u6539\u7528 CAS \u53ef\u4ee5\u907f\u514d\u8fd9\u79cd\u4e22\u5931\u66f4\u65b0\u7684\u95ee\u9898\u3002CAS \u53ef\u4ee5\u7406\u89e3\u4e3a\u201c\u53ea\u6709\u5f53\u524d\u503c\u4ecd\u4e0e\u9884\u671f\u4e00\u81f4，\u624d\u6267\u884c\u66ff\u6362\u201d，\u5931\u8d25\u65f6\u91cd\u8bd5\u3002<\/p>\n

\u4f46\u5982\u679c\u6240\u6709\u7ebf\u7a0b\u4ecd\u7136\u4fee\u6539\u540c\u4e00\u4e2a\u53d8\u91cf，\u5c31\u4f1a\u7ade\u4e89\u540c\u4e00\u4e2a\u5185\u5b58\u4f4d\u7f6e\u3002\u7ebf\u7a0b\u591a\u3001\u66f4\u65b0\u9891\u7e41\u65f6，CAS \u5931\u8d25\u91cd\u8bd5\u4ee5\u53ca\u7f13\u5b58\u4e00\u81f4\u6027\u5f00\u9500\u90fd\u53ef\u80fd\u589e\u52a0\u3002<\/p>\n

\u56e0\u6b64，JDK 8 ConcurrentHashMap \u91c7\u7528\u4e86\u5206\u6563\u8ba1\u6570\u7684\u601d\u8def：<\/p>\n

\u7ade\u4e89\u8f83\u5c0f\u65f6\u4f7f\u7528\u57fa\u7840\u8ba1\u6570\u5668；\u7ade\u4e89\u51fa\u73b0\u540e，\u628a\u66f4\u65b0\u5206\u6563\u5230\u591a\u4e2a\u8ba1\u6570\u5355\u5143，\u67e5\u8be2\u65f6\u518d\u6c47\u603b\u3002<\/p>\n

\u8fd9\u91cc\u5206\u6563\u7684\u662f\u201c\u6570\u91cf\u53d8\u5316\u201d，\u952e\u503c\u5bf9\u672c\u8eab\u4ecd\u7136\u4fdd\u5b58\u5728\u6876\u6570\u7ec4\u4e2d\u3002<\/p>\n

\u4e09\u3001baseCount \u548c CounterCell \u5206\u522b\u662f\u4ec0\u4e48<\/h3>\n

1. baseCount：\u57fa\u7840\u8ba1\u6570\u5668<\/h4>\n

baseCount \u662f\u4e00\u4e2a volatile long \u5b57\u6bb5，\u66f4\u65b0\u4e3b\u8981\u901a\u8fc7 CAS \u5b8c\u6210\u3002\u6ca1\u6709\u5efa\u7acb\u8ba1\u6570 Cell \u6570\u7ec4\u65f6，\u7ebf\u7a0b\u4f1a\u5148\u5c1d\u8bd5\u66f4\u65b0\u5b83\u3002[1]<\/p>\n

\u4f8b\u5982，\u6ca1\u6709\u5e76\u53d1\u7ade\u4e89\u65f6：<\/p>\n

\u521d\u59cb\u72b6\u6001 baseCount = 0
\n\u65b0\u589e\u952e A baseCount = 1
\n\u65b0\u589e\u952e B baseCount = 2
\n\u7528\u65b0\u503c\u8986\u76d6\u952e A baseCount = 2
\n\u6210\u529f\u5220\u9664\u952e B baseCount = 1<\/p>\n

\u8fd9\u91cc\u7edf\u8ba1\u7684\u662f\u952e\u503c\u5bf9\u6570\u91cf\u3002\u8986\u76d6\u5df2\u6709\u952e\u7684\u503c\u6ca1\u6709\u589e\u52a0\u952e\u503c\u5bf9，\u56e0\u6b64\u4e0d\u4f1a\u628a\u8ba1\u6570\u52a0\u4e00；\u5220\u9664\u4e0d\u5b58\u5728\u7684\u952e\u4e5f\u4e0d\u4f1a\u628a\u8ba1\u6570\u51cf\u4e00\u3002<\/p>\n

2. CounterCell：\u5206\u6563\u4fdd\u5b58\u6570\u91cf\u53d8\u5316<\/h4>\n

\u5f53\u57fa\u7840\u8ba1\u6570\u5668\u7684\u66f4\u65b0\u51fa\u73b0\u7ade\u4e89\u65f6，\u7ebf\u7a0b\u53ef\u80fd\u8fdb\u5165 fullAddCount()，\u5efa\u7acb\u6216\u4f7f\u7528 CounterCell[]\u3002\u5355\u4e2a Cell \u7684\u6838\u5fc3\u5b57\u6bb5\u662f：<\/p>\n

\/\/ JDK 8 \u6e90\u7801\u8282\u9009：\u7701\u7565\u586b\u5145\u6ce8\u89e3\u4e0e\u6784\u9020\u65b9\u6cd5\u3002<\/span>
\nstatic<\/span> final<\/span> class<\/span> CounterCell<\/span> {<\/span>
\n volatile<\/span> long<\/span> value;<\/span>
\n}<\/span><\/p>\n

Cell \u4e0d\u4fdd\u5b58\u952e\u503c\u5bf9，\u4e5f\u4e0d\u4fdd\u5b58\u201c\u8fd9\u4e2a\u7ebf\u7a0b\u4e00\u5171\u6267\u884c\u8fc7\u591a\u5c11\u6b21\u201d\u3002\u5b83\u4fdd\u5b58\u7684\u662f\u5206\u6563\u7d2f\u8ba1\u7684\u6570\u91cf\u53d8\u5316，\u65b0\u589e\u548c\u5220\u9664\u90fd\u53ef\u4ee5\u66f4\u65b0\u5b83\u3002<\/p>\n

\u6bd4\u5982\u5148\u524d\u5df2\u7ecf\u7d2f\u8ba1\u4e86 10 \u4e2a\u5143\u7d20，\u4e4b\u540e\u7684\u53d8\u5316\u5206\u6563\u8bb0\u5f55：<\/p>\n

baseCount = 10<\/p>\n

\u7ebf\u7a0b A \u65b0\u589e\u4e00\u4e2a\u952e \u2192 Cell0 +1
\n\u7ebf\u7a0b B \u65b0\u589e\u4e00\u4e2a\u952e \u2192 Cell1 +1
\n\u7ebf\u7a0b C \u65b0\u589e\u4e00\u4e2a\u952e \u2192 Cell0 +1
\n\u7ebf\u7a0b A \u5220\u9664\u4e00\u4e2a\u952e \u2192 Cell0 -1<\/p>\n

Cell0 = 1，Cell1 = 1
\n\u603b\u8ba1\u6570 = 10 + 1 + 1 = 12<\/p>\n

\u6709\u4e86 Cell \u4e4b\u540e，baseCount \u4e0d\u518d\u5fc5\u7136\u7b49\u4e8e\u603b\u6570\u91cf，\u4f46\u5b83\u4ecd\u7136\u662f\u603b\u8ba1\u6570\u7684\u4e00\u90e8\u5206\u3002 \u5b83\u4e5f\u4e0d\u662f\u8f6c\u6210 Cell \u6a21\u5f0f\u540e\u5c31\u7edd\u5bf9\u4e0d\u518d\u66f4\u65b0，fullAddCount() \u7684\u90e8\u5206\u7ade\u4e89\u8def\u5f84\u4ecd\u4f1a\u5c1d\u8bd5\u56de\u9000\u66f4\u65b0\u5b83\u3002[1]<\/p>\n

3. \u7ebf\u7a0b\u4e0e Cell \u4e0d\u662f\u4e00\u5bf9\u4e00\u5173\u7cfb<\/h4>\n

\u7ebf\u7a0b\u4f1a\u6839\u636e\u81ea\u5df1\u7684\u63a2\u9488\u503c\u9009\u62e9\u4e00\u4e2a Cell，\u9009\u62e9\u65b9\u5f0f\u7c7b\u4f3c：<\/p>\n

\/\/ JDK 8 \u903b\u8f91\u793a\u610f：cells \u8868\u793a\u5f53\u524d CounterCell \u6570\u7ec4\u3002<\/span>
\nint<\/span> index =<\/span> ThreadLocalRandom<\/span>.<\/span>getProbe<\/span>(<\/span>)<\/span> &<\/span> (<\/span>cells.<\/span>length –<\/span> 1<\/span>)<\/span>;<\/span><\/p>\n

getProbe() \u662f JDK \u5185\u90e8\u65b9\u6cd5，\u4e0d\u662f\u4e1a\u52a1\u4ee3\u7801\u53ef\u4ee5\u76f4\u63a5\u4f7f\u7528\u7684\u516c\u5171 API\u3002<\/p>\n

\u591a\u4e2a\u7ebf\u7a0b\u53ef\u80fd\u9009\u4e2d\u540c\u4e00\u4e2a Cell，\u56e0\u6b64\u5bf9 Cell \u7684\u503c\u4e5f\u9700\u8981\u4f7f\u7528 CAS \u66f4\u65b0\u3002\u51b2\u7a81\u65f6\u53ef\u4ee5\u8c03\u6574\u63a2\u9488，\u91cd\u65b0\u9009\u62e9\u4f4d\u7f6e；\u6301\u7eed\u7ade\u4e89\u65f6，\u8fd8\u53ef\u80fd\u6269\u5927 Cell \u6570\u7ec4\u3002<\/p>\n

\u6240\u4ee5\u8981\u8bb0\u4f4f\u4e09\u4e2a\u8fb9\u754c：<\/p>\n

    \n
  • Cell \u4e0d\u5c5e\u4e8e\u67d0\u4e2a\u7ebf\u7a0b\u72ec\u4eab，\u4e5f\u4e0d\u4fdd\u8bc1\u7ebf\u7a0b\u59cb\u7ec8\u66f4\u65b0\u540c\u4e00\u4e2a Cell\u3002<\/li>\n
  • Cell \u4e0e\u54c8\u5e0c\u6876\u6ca1\u6709\u5bf9\u5e94\u5173\u7cfb，\u4e0d\u80fd\u628a\u5b83\u770b\u6210\u67d0\u4e00\u6279\u6876\u7684\u5143\u7d20\u6570\u91cf\u3002<\/li>\n
  • Cell \u7684\u503c\u662f\u589e\u51cf\u7d2f\u8ba1\u7ed3\u679c，\u53ef\u4ee5\u4e3a\u8d1f，\u4e0d\u80fd\u628a\u6bcf\u4e2a Cell \u90fd\u7406\u89e3\u4e3a\u72ec\u7acb\u5bb9\u5668\u7684\u5927\u5c0f\u3002<\/li>\n<\/ul>\n

    \"\u5728\u8fd9\u91cc\u63d2\u5165\u56fe\u7247\u63cf\u8ff0\"<\/p>\n

    \u56fe 1：baseCount \u4e0e\u5404\u4e2a Cell \u4e00\u8d77\u6784\u6210\u603b\u8ba1\u6570\u3002\u7bad\u5934\u8868\u793a\u53ef\u80fd\u7684\u66f4\u65b0\u8def\u5f84，\u4e0d\u8868\u793a\u7ebf\u7a0b\u4e0e Cell \u56fa\u5b9a\u7ed1\u5b9a\u3002<\/p>\n

    \u56db\u3001size() \u600e\u6837\u5f97\u5230\u5143\u7d20\u6570\u91cf<\/h3>\n

    1. \u4ece size() \u8ddf\u5230 sumCount()<\/h4>\n

    JDK 8 \u7684 size() \u8c03\u7528 sumCount()，\u7136\u540e\u5c06\u7ed3\u679c\u5904\u7406\u6210 int：<\/p>\n

    \/\/ JDK 8 \u6e90\u7801\u8282\u9009\u3002<\/span>
    \npublic<\/span> int<\/span> size<\/span>(<\/span>)<\/span> {<\/span>
    \n long<\/span> n =<\/span> sumCount<\/span>(<\/span>)<\/span>;<\/span>
    \n return<\/span> (<\/span>(<\/span>n <<\/span> 0L<\/span>)<\/span> ?<\/span> 0<\/span> :<\/span>
    \n (<\/span>n ><\/span> (<\/span>long<\/span>)<\/span>Integer<\/span>.<\/span>MAX_VALUE<\/span>)<\/span> ?<\/span> Integer<\/span>.<\/span>MAX_VALUE<\/span> :<\/span>
    \n (<\/span>int<\/span>)<\/span>n)<\/span>;<\/span>
    \n}<\/span><\/p>\n

    sumCount() \u7684\u6838\u5fc3\u662f\u628a\u57fa\u7840\u8ba1\u6570\u548c\u6240\u6709\u975e\u7a7a Cell \u76f8\u52a0：<\/p>\n

    \/\/ JDK 8 \u6e90\u7801\u8282\u9009\u3002<\/span>
    \nfinal<\/span> long<\/span> sumCount<\/span>(<\/span>)<\/span> {<\/span>
    \n CounterCell<\/span>[<\/span>]<\/span> as =<\/span> counterCells;<\/span>
    \n CounterCell<\/span> a;<\/span>
    \n long<\/span> sum =<\/span> baseCount;<\/span>
    \n if<\/span> (<\/span>as !=<\/span> null<\/span>)<\/span> {<\/span>
    \n for<\/span> (<\/span>int<\/span> i =<\/span> 0<\/span>;<\/span> i <<\/span> as.<\/span>length;<\/span> ++<\/span>i)<\/span> {<\/span>
    \n if<\/span> (<\/span>(<\/span>a =<\/span> as[<\/span>i]<\/span>)<\/span> !=<\/span> null<\/span>)<\/span> {<\/span>
    \n sum +=<\/span> a.<\/span>value;<\/span>
    \n }<\/span>
    \n }<\/span>
    \n }<\/span>
    \n return<\/span> sum;<\/span>
    \n}<\/span><\/p>\n

    \u4e5f\u5c31\u662f：<\/p>\n

    \u603b\u8ba1\u6570 = baseCount + Cell0.value + Cell1.value + …<\/p>\n

    \u5b83\u4e0d\u9700\u8981\u904d\u5386\u6240\u6709\u952e\u503c\u5bf9，\u4f46\u4e5f\u4e0d\u80fd\u4e00\u6982\u8bf4\u6210\u53ea\u8bfb\u53d6\u4e00\u4e2a\u53d8\u91cf：\u6709 Cell \u6570\u7ec4\u65f6，\u9700\u8981\u904d\u5386\u8be5\u8ba1\u6570\u6570\u7ec4\u3002size() \u8fd4\u56de int，\u8d85\u8fc7 Integer.MAX_VALUE \u65f6\u8fd4\u56de\u8fd9\u4e2a\u4e0a\u9650；mappingCount() \u8fd4\u56de long，\u4f46\u540c\u6837\u4e0d\u4fdd\u8bc1\u5e76\u53d1\u66f4\u65b0\u671f\u95f4\u7684\u539f\u5b50\u5feb\u7167\u3002[1][2]<\/p>\n

    2. \u4e3a\u4ec0\u4e48\u6c47\u603b\u4e0d\u662f\u539f\u5b50\u5feb\u7167<\/h4>\n

    \u6bcf\u4e2a\u5b57\u6bb5\u7684\u8bfb\u53d6\u53ef\u4ee5\u5f97\u5230\u4e00\u4e2a\u503c，\u4f46\u201c\u5148\u8bfb\u53d6\u57fa\u7840\u8ba1\u6570，\u518d\u4f9d\u6b21\u8bfb\u53d6\u591a\u4e2a Cell\u201d\u4e0d\u662f\u4e00\u4e2a\u6574\u4f53\u539f\u5b50\u64cd\u4f5c\u3002\u5176\u4ed6\u7ebf\u7a0b\u53ef\u4ee5\u5728\u8fd9\u4e9b\u8bfb\u53d6\u4e4b\u95f4\u589e\u5220\u5143\u7d20\u3002<\/p>\n

    \u4e3a\u4fbf\u4e8e\u89c2\u5bdf，\u5047\u8bbe baseCount \u4e3a 0，\u53ea\u6709\u4e24\u4e2a Cell：<\/p>\n\n\u65f6\u523b\u5176\u4ed6\u7ebf\u7a0b\u7684\u64cd\u4f5cCell0Cell1\u8ba1\u6570\u5668\u5b9e\u9645\u603b\u548c\u7edf\u8ba1\u7ebf\u7a0b\u7684\u64cd\u4f5c<\/tr>\n\n\n\n\n\n
    \u2460<\/td>\n\u65e0<\/td>\n3<\/td>\n7<\/td>\n10<\/td>\n\u8bfb\u5230 Cell0 = 3<\/td>\n<\/tr>\n
    \u2461<\/td>\n\u5220\u9664\u4e00\u4e2a\u952e，\u5b8c\u6210\u8ba1\u6570\u51cf\u4e00<\/td>\n2<\/td>\n7<\/td>\n9<\/td>\n\u5c1a\u672a\u8bfb\u53d6 Cell1<\/td>\n<\/tr>\n
    \u2462<\/td>\n\u65b0\u589e\u4e00\u4e2a\u952e，\u5b8c\u6210\u8ba1\u6570\u52a0\u4e00<\/td>\n2<\/td>\n8<\/td>\n10<\/td>\n\u5c1a\u672a\u8bfb\u53d6 Cell1<\/td>\n<\/tr>\n
    \u2463<\/td>\n\u65e0<\/td>\n2<\/td>\n8<\/td>\n10<\/td>\n\u8bfb\u5230 Cell1 = 8<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

    \u7edf\u8ba1\u7ebf\u7a0b\u8fd4\u56de 3 + 8 = 11，\u800c\u8fd9\u4e9b\u8ba1\u6570\u5668\u7684\u5b9e\u9645\u603b\u548c\u4f9d\u6b21\u4e3a 10 \u2192 9 \u2192 10，\u6ca1\u6709\u51fa\u73b0\u8fc7 11\u3002<\/p>\n

    \u8fd9\u5c31\u662f\u201c\u6c47\u603b\u4e0d\u662f\u6574\u4f53\u5feb\u7167\u201d：\u8bfb\u5230\u7684\u503c\u53ef\u80fd\u6765\u81ea\u4e0d\u540c\u65f6\u95f4\u3002<\/p>\n

    \u53e6\u5916，\u63d2\u5165\u8282\u70b9\u4e0e\u66f4\u65b0\u8ba1\u6570\u672c\u8eab\u4e5f\u662f\u5148\u540e\u53d1\u751f\u7684\u6b65\u9aa4，\u5e76\u4e0d\u662f\u628a\u6574\u4e2a Map \u548c\u8ba1\u6570\u5668\u540c\u65f6\u539f\u5b50\u5730\u66f4\u65b0\u3002\u5373\u4f7f\u6ca1\u6709 Cell，\u4e5f\u4e0d\u80fd\u636e\u6b64\u628a\u5143\u7d20\u5b58\u50a8\u4e0e\u6570\u91cf\u8bfb\u53d6\u7406\u89e3\u6210\u4e00\u4e2a\u6574\u4f53\u4e8b\u52a1\u3002<\/p>\n

    \u8fd9\u4e0d\u8868\u793a\u8ba1\u6570\u66f4\u65b0\u4f1a\u968f\u610f\u4e22\u5931\u3002 \u5728\u6240\u6709\u76f8\u5173\u589e\u5220\u64cd\u4f5c\u90fd\u5b8c\u6210\u3001\u901a\u8fc7 join() \u7b49\u65b9\u5f0f\u7b49\u5f85\u7ebf\u7a0b\u7ed3\u675f，\u4e14\u6ca1\u6709\u7ee7\u7eed\u5e76\u53d1\u4fee\u6539\u65f6，\u6c47\u603b\u80fd\u5f97\u5230\u51c6\u786e\u6570\u91cf；size() \u8fd8\u9700\u8981\u8003\u8651 int \u7684\u8fd4\u56de\u8303\u56f4\u3002\u5b98\u65b9\u6587\u6863\u4e5f\u660e\u786e\u8bf4\u660e，\u5e76\u53d1\u66f4\u65b0\u671f\u95f4\u7684 size()\u3001isEmpty() \u7b49\u7ed3\u679c\u9002\u5408\u76d1\u63a7\u6216\u4f30\u7b97，\u4e0d\u9002\u5408\u76f4\u63a5\u627f\u62c5\u7a0b\u5e8f\u63a7\u5236\u6761\u4ef6\u3002[2]<\/p>\n

    3. \u4e00\u4e2a\u53ef\u8fd0\u884c\u7684\u8ba1\u6570\u4f8b\u5b50<\/h4>\n

    \u4e0b\u9762\u7684\u7a0b\u5e8f\u5148\u8ba9\u56db\u4e2a\u7ebf\u7a0b\u63d2\u5165\u4e0d\u540c\u7684\u952e，\u518d\u7b49\u5f85\u5b83\u4eec\u7ed3\u675f\u540e\u8bfb\u53d6\u6570\u91cf：<\/p>\n

    \/\/ \u9002\u7528 JDK 8，\u6587\u4ef6\u540d：CountDemo.java\u3002<\/span>
    \nimport<\/span> java.<\/span>util.<\/span>concurrent.<\/span><\/span>ConcurrentHashMap<\/span><\/span>;<\/span><\/p>\n

    public<\/span> class<\/span> CountDemo<\/span> {<\/span>
    \n public<\/span> static<\/span> void<\/span> main<\/span>(<\/span>String<\/span>[<\/span>]<\/span> args)<\/span> throws<\/span> InterruptedException<\/span> {<\/span>
    \n ConcurrentHashMap<\/span><<\/span>Integer<\/span>,<\/span> Integer<\/span>><\/span><\/span> map =<\/span> new<\/span> ConcurrentHashMap<\/span><<\/span>><\/span><\/span>(<\/span>)<\/span>;<\/span>
    \n Thread<\/span>[<\/span>]<\/span> workers =<\/span> new<\/span> Thread<\/span>[<\/span>4<\/span>]<\/span>;<\/span><\/p>\n

    for<\/span> (<\/span>int<\/span> t =<\/span> 0<\/span>;<\/span> t <<\/span> workers.<\/span>length;<\/span> t++<\/span>)<\/span> {<\/span>
    \n final<\/span> int<\/span> start =<\/span> t *<\/span> 1000<\/span>;<\/span>
    \n workers[<\/span>t]<\/span> =<\/span> new<\/span> Thread<\/span>(<\/span>(<\/span>)<\/span> -><\/span> {<\/span>
    \n for<\/span> (<\/span>int<\/span> i =<\/span> 0<\/span>;<\/span> i <<\/span> 1000<\/span>;<\/span> i++<\/span>)<\/span> {<\/span>
    \n map.<\/span>put<\/span>(<\/span>start +<\/span> i,<\/span> i)<\/span>;<\/span>
    \n }<\/span>
    \n }<\/span>)<\/span>;<\/span>
    \n workers[<\/span>t]<\/span>.<\/span>start<\/span>(<\/span>)<\/span>;<\/span>
    \n }<\/span>
    \n for<\/span> (<\/span>Thread<\/span> worker :<\/span> workers)<\/span> {<\/span>
    \n worker.<\/span>join<\/span>(<\/span>)<\/span>;<\/span>
    \n }<\/span><\/p>\n

    System<\/span>.<\/span>out.<\/span>println<\/span>(<\/span>"after inserts = "<\/span> +<\/span> map.<\/span>size<\/span>(<\/span>)<\/span>)<\/span>;<\/span>
    \n map.<\/span>put<\/span>(<\/span>0<\/span>,<\/span> –<\/span>1<\/span>)<\/span>;<\/span>
    \n System<\/span>.<\/span>out.<\/span>println<\/span>(<\/span>"after overwrite = "<\/span> +<\/span> map.<\/span>size<\/span>(<\/span>)<\/span>)<\/span>;<\/span>
    \n map.<\/span>remove<\/span>(<\/span>0<\/span>)<\/span>;<\/span>
    \n System<\/span>.<\/span>out.<\/span>println<\/span>(<\/span>"after remove = "<\/span> +<\/span> map.<\/span>size<\/span>(<\/span>)<\/span>)<\/span>;<\/span>
    \n }<\/span>
    \n}<\/span><\/p>\n

    \u8f93\u51fa\u4e3a：<\/p>\n

    after inserts = 4000
    \nafter overwrite = 4000
    \nafter remove = 3999<\/p>\n

    \u8fd9\u4e2a\u4f8b\u5b50\u9a8c\u8bc1\u7684\u662f\u201c\u589e\u5220\u5b8c\u6210\u540e\u7684\u6570\u91cf\u201d\u4ee5\u53ca\u201c\u8986\u76d6\u5df2\u6709\u952e\u4e0d\u589e\u52a0\u6570\u91cf\u201d\u3002\u5b83\u4e0d\u4fdd\u8bc1\u89e6\u53d1\u67d0\u4e2a Cell \u5206\u914d\u7ed3\u679c，\u4e5f\u4e0d\u7528\u4e8e\u8bc1\u660e\u5e76\u53d1\u8bfb\u53d6\u65f6\u4e00\u5b9a\u51fa\u73b0\u67d0\u4e2a\u4e0d\u51c6\u786e\u7684\u6570\u5b57\u3002<\/p>\n

    \u4e94\u3001\u63d2\u5165\u540e，\u8ba1\u6570\u600e\u6837\u53c2\u4e0e\u6269\u5bb9\u5224\u65ad<\/h3>\n

    1. putVal()：\u5148\u63d2\u5165，\u518d\u66f4\u65b0\u8ba1\u6570<\/h4>\n

    \u666e\u901a put() \u7684\u4e3b\u7ebf\u662f：<\/p>\n

    put(key, value)
    \n \u2193
    \nputVal(key, value, false)
    \n \u2193
    \n\u627e\u5230\u6876，\u63d2\u5165\u65b0\u952e，\u6216\u66f4\u65b0\u5df2\u6709\u952e
    \n \u2193
    \n\u65b0\u589e\u952e\u65f6\u8c03\u7528 addCount(1L, binCount)<\/p>\n

    putVal() \u4e2d，\u5982\u679c\u53ea\u662f\u8986\u76d6\u5df2\u6709\u952e\u7684\u503c，\u4f1a\u8fd4\u56de\u65e7\u503c，\u4e0d\u8d70\u672b\u5c3e\u7684\u65b0\u589e\u8ba1\u6570\u3002\u6210\u529f\u63d2\u5165\u65b0\u952e\u540e，\u624d\u8c03\u7528 addCount(1L, binCount)\u3002[1]<\/p>\n

    2. addCount()：\u5148\u8bb0\u8d26，\u518d\u51b3\u5b9a\u662f\u5426\u68c0\u67e5<\/h4>\n

    addCount(long x, int check) \u7684\u4e24\u4e2a\u53c2\u6570\u627f\u62c5\u4e0d\u540c\u804c\u8d23：<\/p>\n\n\u53c2\u6570\u4f5c\u7528<\/tr>\n\n\n\n
    x<\/td>\n\u672c\u6b21\u6570\u91cf\u589e\u91cf，\u65b0\u589e\u901a\u5e38\u4e3a 1，\u6210\u529f\u5220\u9664\u4e3a -1<\/td>\n<\/tr>\n
    check<\/td>\n\u63a7\u5236\u662f\u5426\u8fdb\u5165\u6269\u5bb9\u68c0\u67e5；\u666e\u901a put \u4f20\u5165\u6876\u904d\u5386\u76f8\u5173\u7684 binCount<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

    \u524d\u534a\u90e8\u5206\u6e90\u7801\u5982\u4e0b，\u7701\u7565\u4e86\u540e\u7eed\u6269\u5bb9\u534f\u8c03\u4ee3\u7801：<\/p>\n

    \/\/ JDK 8 \u6e90\u7801\u8282\u9009：\u5c55\u793a\u8ba1\u6570\u66f4\u65b0\u4e0e\u63d0\u524d\u8fd4\u56de\u7684\u6761\u4ef6\u3002<\/span>
    \nCounterCell<\/span>[<\/span>]<\/span> as;<\/span>
    \nlong<\/span> b,<\/span> s;<\/span>
    \nif<\/span> (<\/span>(<\/span>as =<\/span> counterCells)<\/span> !=<\/span> null<\/span> ||<\/span>
    \n !<\/span>U<\/span>.<\/span>compareAndSwapLong<\/span>(<\/span>this<\/span>,<\/span> BASECOUNT<\/span>,<\/span>
    \n b =<\/span> baseCount,<\/span> s =<\/span> b +<\/span> x)<\/span>)<\/span> {<\/span>
    \n CounterCell<\/span> a;<\/span>
    \n long<\/span> v;<\/span>
    \n int<\/span> m;<\/span>
    \n boolean<\/span> uncontended =<\/span> true<\/span>;<\/span>
    \n if<\/span> (<\/span>as ==<\/span> null<\/span> ||<\/span> (<\/span>m =<\/span> as.<\/span>length –<\/span> 1<\/span>)<\/span> <<\/span> 0<\/span> ||<\/span>
    \n (<\/span>a =<\/span> as[<\/span>ThreadLocalRandom<\/span>.<\/span>getProbe<\/span>(<\/span>)<\/span> &<\/span> m]<\/span>)<\/span> ==<\/span> null<\/span> ||<\/span>
    \n !<\/span>(<\/span>uncontended =<\/span>
    \n U<\/span>.<\/span>compareAndSwapLong<\/span>(<\/span>a,<\/span> CELLVALUE<\/span>,<\/span> v =<\/span> a.<\/span>value,<\/span> v +<\/span> x)<\/span>)<\/span>)<\/span> {<\/span>
    \n fullAddCount<\/span>(<\/span>x,<\/span> uncontended)<\/span>;<\/span>
    \n return<\/span>;<\/span>
    \n }<\/span>
    \n if<\/span> (<\/span>check <=<\/span> 1<\/span>)<\/span> {<\/span>
    \n return<\/span>;<\/span>
    \n }<\/span>
    \n s =<\/span> sumCount<\/span>(<\/span>)<\/span>;<\/span>
    \n}<\/span>
    \n\/\/ \u540e\u7eed：check >= 0 \u65f6\u8fdb\u5165\u6269\u5bb9\u6761\u4ef6\u68c0\u67e5\u3002<\/span><\/p>\n

    \u53ef\u4ee5\u6309\u4e0b\u9762\u51e0\u6761\u8def\u5f84\u9605\u8bfb：<\/p>\n

  • \u6ca1\u6709 Cell \u6570\u7ec4，CAS \u66f4\u65b0 baseCount \u6210\u529f：s \u5df2\u7ecf\u4fdd\u5b58\u66f4\u65b0\u540e\u7684\u57fa\u7840\u8ba1\u6570，\u7ee7\u7eed\u6309 check \u5224\u65ad\u662f\u5426\u68c0\u67e5\u6269\u5bb9，\u4e0d\u5fc5\u518d\u904d\u5386 Cell\u3002<\/li>\n
  • \u8fdb\u5165 Cell \u8def\u5f84，\u4f46\u9700\u8981\u8c03\u7528 fullAddCount()：\u5b8c\u6210\u8ba1\u6570\u66f4\u65b0\u540e，\u672c\u6b21 addCount() \u76f4\u63a5\u8fd4\u56de，\u4e0d\u7ee7\u7eed\u6267\u884c\u540e\u9762\u7684\u6269\u5bb9\u68c0\u67e5\u3002<\/li>\n
  • CAS \u66f4\u65b0 Cell \u6210\u529f，\u4f46 check <= 1：\u540c\u6837\u76f4\u63a5\u8fd4\u56de\u3002<\/li>\n
  • CAS \u66f4\u65b0 Cell \u6210\u529f，\u4e14 check > 1：\u8c03\u7528 sumCount()，\u6c47\u603b\u4e4b\u540e\u7ee7\u7eed\u68c0\u67e5\u3002<\/li>\n

    \u540e\u7eed\u68c0\u67e5\u8fd8\u6709 check >= 0 \u7684\u6761\u4ef6\u3002\u5220\u9664\u901a\u5e38\u4f20\u5165\u8d1f\u6570，\u56e0\u6b64\u4f1a\u66f4\u65b0\u8ba1\u6570，\u4f46\u4e0d\u901a\u8fc7\u8fd9\u6761\u8def\u5f84\u53d1\u8d77\u6269\u5bb9；\u5220\u9664\u4e5f\u4e0d\u4f1a\u81ea\u52a8\u8ba9\u6876\u6570\u7ec4\u7f29\u5bb9\u3002<\/p>\n

    \u56e0\u6b64，\u65b0\u589e\u8ba1\u6570\u4e0d\u7b49\u4e8e\u6bcf\u6b21\u90fd\u626b\u63cf Cell，\u66f4\u4e0d\u7b49\u4e8e\u6bcf\u6b21\u90fd\u5fc5\u987b\u6267\u884c\u6269\u5bb9\u5224\u65ad\u3002 check \u4e5f\u4e0d\u662f\u201c\u7ebf\u7a0b\u7ade\u4e89\u6b21\u6570\u201d，\u800c\u662f\u8c03\u7528\u65b9\u63d0\u4f9b\u7684\u68c0\u67e5\u63a7\u5236\u53c2\u6570\u3002[1]<\/p>\n

    3. sizeCtl：\u6b63\u5e38\u72b6\u6001\u4e0b\u4fdd\u5b58\u6269\u5bb9\u9608\u503c<\/h4>\n

    \u5f53\u6876\u6570\u7ec4\u5df2\u521d\u59cb\u5316\u3001\u6ca1\u6709\u6b63\u5728\u6269\u5bb9\u65f6，\u53ef\u4ee5\u628a\u5143\u7d20\u6570\u91cf\u7684\u68c0\u67e5\u6982\u62ec\u4e3a：<\/p>\n

    \u8ba1\u6570 s >= sizeCtl
    \n\u5e76\u4e14 table \u5b58\u5728\u3001\u957f\u5ea6\u5c0f\u4e8e\u6700\u5927\u5bb9\u91cf
    \n \u2193
    \n\u5c1d\u8bd5\u901a\u8fc7 CAS \u53d1\u8d77\u6269\u5bb9<\/p>\n

    \u4f8b\u5982：<\/p>\n

    table.length = 16
    \nsizeCtl = 12
    \n\u6c47\u603b\u8ba1\u6570 s = 12<\/p>\n

    \u6761\u4ef6\u6ee1\u8db3 \u2192 \u5c1d\u8bd5\u53d1\u8d77\u672c\u8f6e\u6269\u5bb9<\/p>\n

    \u201c\u5c1d\u8bd5\u201d\u5f88\u5173\u952e：\u53e6\u4e00\u4e2a\u7ebf\u7a0b\u53ef\u80fd\u5df2\u7ecf\u5148\u4fee\u6539\u4e86\u63a7\u5236\u72b6\u6001，\u5f53\u524d\u7ebf\u7a0b\u8fd8\u8981\u6839\u636e\u6700\u65b0\u72b6\u6001\u51b3\u5b9a\u4e0b\u4e00\u6b65\u3002<\/p>\n

    sizeCtl \u5728\u4e0d\u540c\u9636\u6bb5\u6709\u4e0d\u540c\u542b\u4e49：<\/p>\n\n\u9636\u6bb5\u542b\u4e49<\/tr>\n\n\n\n\n\n
    \u6876\u6570\u7ec4\u5c1a\u672a\u521d\u59cb\u5316<\/td>\n\u4e3a 0 \u65f6\u91c7\u7528\u9ed8\u8ba4\u521d\u59cb\u5316\u7b56\u7565；\u6b63\u6570\u53ef\u4fdd\u5b58\u5f85\u521d\u59cb\u5316\u7684\u5bb9\u91cf\u4fe1\u606f<\/td>\n<\/tr>\n
    \u6b63\u5728\u521d\u59cb\u5316<\/td>\n\u4e3a -1<\/td>\n<\/tr>\n
    \u5df2\u521d\u59cb\u5316，\u4e14\u6ca1\u6709\u6b63\u5728\u6269\u5bb9<\/td>\n\u6b63\u6570，\u8868\u793a\u4e0b\u4e00\u6b21\u6269\u5bb9\u7684\u5143\u7d20\u6570\u91cf\u9608\u503c<\/td>\n<\/tr>\n
    \u6b63\u5728\u6269\u5bb9<\/td>\n\u8d1f\u6570，\u7f16\u7801\u672c\u8f6e\u6269\u5bb9\u6807\u8bb0\u53ca\u53c2\u4e0e\u7ebf\u7a0b\u7684\u534f\u8c03\u4fe1\u606f<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

    \u4e0d\u8981\u628a\u6269\u5bb9\u671f\u95f4\u7684\u8d1f\u503c\u76f4\u63a5\u89e3\u91ca\u6210\u4e00\u4e2a\u666e\u901a\u9608\u503c，\u4e5f\u4e0d\u8981\u7b80\u5355\u7528\u8d1f\u503c\u7684\u7edd\u5bf9\u503c\u5f53\u4f5c\u5de5\u4f5c\u7ebf\u7a0b\u6570\u3002\u6269\u5bb9\u72b6\u6001\u4f7f\u7528\u4e86\u4f4d\u7f16\u7801，\u9700\u8981\u7ed3\u5408 resizeStamp() \u548c\u79fb\u4f4d\u5e38\u91cf\u7406\u89e3\u3002[1]<\/p>\n

    \u516d\u3001\u8fbe\u5230\u9608\u503c\u540e，\u591a\u4e2a\u7ebf\u7a0b\u600e\u6837\u5b8c\u6210\u6269\u5bb9<\/h3>\n

    1. \u53d1\u8d77\u6269\u5bb9：\u521b\u5efa nextTable<\/h4>\n

    \u5728 addCount() \u7684\u76f8\u5e94\u8def\u5f84\u4e2d，\u7ebf\u7a0b\u901a\u8fc7 CAS \u628a sizeCtl \u6539\u4e3a\u672c\u8f6e\u6269\u5bb9\u72b6\u6001；\u6210\u529f\u7684\u7ebf\u7a0b\u8c03\u7528 transfer(tab, null)\u3002<\/p>\n

    transfer() \u53d1\u73b0\u8fd8\u6ca1\u6709\u65b0\u6570\u7ec4\u65f6，\u521b\u5efa\u957f\u5ea6\u4e3a n << 1 \u7684\u6570\u7ec4，\u4e5f\u5c31\u662f\u539f\u957f\u5ea6\u7684\u4e24\u500d，\u5e76\u4fdd\u5b58\u5230 nextTable\u3002\u968f\u540e\u8bbe\u7f6e transferIndex，\u8ba9\u53c2\u4e0e\u7ebf\u7a0b\u9886\u53d6\u8fc1\u79fb\u4efb\u52a1\u3002[1]<\/p>\n

    \"\u5728\u8fd9\u91cc\u63d2\u5165\u56fe\u7247\u63cf\u8ff0\"<\/p>\n

    \u56fe 2：\u672c\u56fe\u5c55\u793a\u6839\u636e\u5143\u7d20\u8ba1\u6570\u89e6\u53d1\u6876\u6570\u7ec4\u6269\u5bb9\u7684\u4e3b\u7ebf\u3002\u4e0d\u662f\u6bcf\u6b21\u66f4\u65b0\u90fd\u4f1a\u8d70\u5230\u68c0\u67e5，\u4e5f\u4e0d\u662f\u6bcf\u8f6e\u6269\u5bb9\u90fd\u4e00\u5b9a\u6709\u591a\u4e2a\u7ebf\u7a0b\u53c2\u4e0e\u3002<\/p>\n

    2. \u9886\u53d6\u4efb\u52a1：\u8fc1\u79fb\u4e0d\u540c\u8303\u56f4\u7684\u6876<\/h4>\n

    \u53c2\u4e0e\u8fc1\u79fb\u7684\u7ebf\u7a0b\u4f7f\u7528 CAS \u66f4\u65b0 transferIndex，\u9886\u53d6\u4e00\u6bb5\u6876\u4e0b\u6807\u8303\u56f4，\u518d\u9010\u4e2a\u5904\u7406\u3002<\/p>\n

    \u8fd9\u6837，\u591a\u4e2a\u7ebf\u7a0b\u53ef\u4ee5\u5904\u7406\u4e0d\u540c\u7684\u6876，\u51cf\u5c11\u91cd\u590d\u9886\u53d6\u540c\u4e00\u6bb5\u4efb\u52a1\u7684\u60c5\u51b5\u3002\u5bf9\u4e8e\u5f88\u5c0f\u7684\u6570\u7ec4，\u53ef\u9886\u53d6\u7684\u4efb\u52a1\u8303\u56f4\u8f83\u5c11，\u53ef\u80fd\u4ecd\u4e3b\u8981\u7531\u4e00\u4e2a\u7ebf\u7a0b\u5b8c\u6210\u3002<\/p>\n

    \u8fc1\u79fb\u5e76\u4e0d\u662f\u628a\u6574\u4e2a Map \u9501\u4f4f\u518d\u590d\u5236\u3002\u5bf9\u4e8e\u975e\u7a7a\u6876，\u8fc1\u79fb\u4f1a\u7ed3\u5408\u6876\u5934\u540c\u6b65\u4e0e\u72b6\u6001\u590d\u67e5；\u4e0d\u540c\u6876\u7684\u5de5\u4f5c\u53ef\u4ee5\u5e76\u884c\u63a8\u8fdb\u3002<\/p>\n

    3. \u539f\u6876\u4e2d\u7684\u5143\u7d20\u8fc1\u79fb\u5230\u54ea\u91cc<\/h4>\n

    \u6570\u7ec4\u957f\u5ea6\u4ece n \u53d8\u6210 2n \u65f6，\u539f\u6765\u4f4d\u4e8e\u4e0b\u6807 i \u7684\u5143\u7d20，\u6839\u636e\u5df2\u4fdd\u5b58\u7684\u54c8\u5e0c\u503c，\u53ef\u4ee5\u5206\u5230\u4e24\u4e2a\u4f4d\u7f6e：<\/p>\n

    (hash & n) == 0 \u2192 \u4ecd\u4f4d\u4e8e i
    \n(hash & n) != 0 \u2192 \u4f4d\u4e8e i + n<\/p>\n

    \u4f8b\u5982，\u539f\u6570\u7ec4\u957f\u5ea6\u4e3a 16，\u539f\u6876\u4e0b\u6807\u4e3a 3，\u8fc1\u79fb\u540e\u53ef\u80fd\u8fdb\u5165\u65b0\u6570\u7ec4\u7684\u6876 3 \u6216\u6876 19\u3002<\/p>\n

    \u8fd9\u91cc\u4f7f\u7528\u8282\u70b9\u5df2\u7ecf\u4fdd\u5b58\u7684\u54c8\u5e0c\u503c\u8fdb\u884c\u5206\u7ec4，\u4e0d\u9700\u8981\u91cd\u65b0\u8c03\u7528\u6bcf\u4e2a\u952e\u7684 hashCode()\u3002\u94fe\u8868\u6876\u4f1a\u62c6\u5206\u6210\u4e24\u7ec4；\u6811\u6876\u4e5f\u6709\u76f8\u5e94\u7684\u62c6\u5206\u4e0e\u5fc5\u8981\u65f6\u9000\u5316\u4e3a\u94fe\u8868\u7684\u5904\u7406\u3002[1]<\/p>\n

    4. ForwardingNode：\u65e7\u6876\u5df2\u7ecf\u8fc1\u79fb\u7684\u6807\u8bb0<\/h4>\n

    \u67d0\u4e2a\u6876\u8fc1\u79fb\u5b8c\u6210\u540e，\u65e7\u6570\u7ec4\u5bf9\u5e94\u4f4d\u7f6e\u4f1a\u653e\u7f6e ForwardingNode\u3002\u5b83\u7684 hash \u662f\u7279\u6b8a\u503c MOVED，\u5e76\u6301\u6709\u65b0\u6570\u7ec4\u5f15\u7528\u3002<\/p>\n

    \u666e\u901a putVal() \u9047\u5230 MOVED \u65f6，\u4f1a\u8c03\u7528 helpTransfer()：\u5982\u679c\u4ecd\u6709\u53ef\u9886\u53d6\u4efb\u52a1\u4e14\u7b26\u5408\u53c2\u4e0e\u6761\u4ef6，\u5c31\u5c1d\u8bd5\u5e2e\u52a9\u8fc1\u79fb，\u4e4b\u540e\u518d\u57fa\u4e8e\u8fd4\u56de\u7684\u6570\u7ec4\u7ee7\u7eed\u63d2\u5165\u3002<\/p>\n

    \u8bfb\u53d6\u7ebf\u7a0b\u9047\u5230\u8f6c\u53d1\u8282\u70b9\u65f6，\u53ef\u4ee5\u6cbf\u7740\u65b0\u6570\u7ec4\u7ee7\u7eed\u67e5\u627e，\u5e76\u4e0d\u662f\u6240\u6709\u64cd\u4f5c\u90fd\u5fc5\u987b\u52a0\u5165\u8fc1\u79fb\u5de5\u4f5c\u3002<\/p>\n

    5. \u8fc1\u79fb\u5b8c\u6210：\u5207\u6362\u6570\u7ec4\u4e0e\u9608\u503c<\/h4>\n

    \u53c2\u4e0e\u7ebf\u7a0b\u9646\u7eed\u5b8c\u6210\u81ea\u5df1\u7684\u8fc1\u79fb\u5de5\u4f5c\u540e，\u901a\u8fc7\u63a7\u5236\u72b6\u6001\u534f\u8c03\u9000\u51fa\u3002\u6700\u540e\u5b8c\u6210\u6536\u5c3e\u7684\u7ebf\u7a0b\u786e\u8ba4\u65e7\u6876\u5904\u7406\u5b8c\u6210，\u518d\u5207\u6362\u6570\u7ec4\u5e76\u66f4\u65b0\u9608\u503c\u3002\u5173\u952e\u8d4b\u503c\u4e3a：<\/p>\n

    \/\/ JDK 8 \u6e90\u7801\u8282\u9009：n \u662f\u65e7\u6876\u6570\u7ec4\u957f\u5ea6\u3002<\/span>
    \nnextTable =<\/span> null<\/span>;<\/span>
    \ntable =<\/span> nextTab;<\/span>
    \nsizeCtl =<\/span> (<\/span>n <<<\/span> 1<\/span>)<\/span> –<\/span> (<\/span>n >>><\/span> 1<\/span>)<\/span>;<\/span><\/p>\n

    \u65e7\u957f\u5ea6\u4e3a 16 \u65f6，\u65b0\u957f\u5ea6\u4e3a 32，\u9608\u503c\u4e3a 32 – 8 = 24\u3002<\/p>\n

    \u6269\u5bb9\u53ea\u6539\u53d8\u6876\u6570\u7ec4\u5bb9\u91cf\u4e0e\u6570\u636e\u7ec4\u7ec7，\u4e0d\u4f1a\u56e0\u4e3a\u8fc1\u79fb\u540c\u4e00\u4e2a\u952e\u503c\u5bf9\u5c31\u518d\u628a\u5143\u7d20\u6570\u91cf\u52a0\u4e00\u3002\u5982\u679c\u5e76\u53d1\u63d2\u5165\u6301\u7eed\u53d1\u751f，addCount() \u8fd8\u4f1a\u91cd\u65b0\u6c47\u603b\u8ba1\u6570，\u68c0\u67e5\u662f\u5426\u9700\u8981\u7ee7\u7eed\u6269\u5bb9\u3002[1]<\/p>\n

    \u4e03\u3001\u8ba1\u6570\u4e0d\u4e00\u5b9a\u51c6\u786e，\u4e3a\u4ec0\u4e48\u8fd8\u80fd\u5224\u65ad\u6269\u5bb9<\/h3>\n

    1. \u6269\u5bb9\u9608\u503c\u662f\u6027\u80fd\u8c03\u6574\u65f6\u673a<\/h4>\n

    \u6876\u6570\u7ec4\u957f\u5ea6\u4e3a 16\u3001\u9608\u503c\u4e3a 12，\u4e0d\u4ee3\u8868\u7b2c 13 \u4e2a\u5143\u7d20\u5c31\u65e0\u5904\u53ef\u653e\u3002\u6876\u5185\u53ef\u4ee5\u5b58\u653e\u591a\u4e2a\u8282\u70b9，\u6269\u5bb9\u9608\u503c\u7528\u4e8e\u63a7\u5236\u6570\u636e\u5bc6\u5ea6\u548c\u64cd\u4f5c\u6210\u672c\u3002<\/p>\n

    \u56e0\u6b64，\u5e76\u53d1\u8ba1\u6570\u6c47\u603b\u4e0e\u68c0\u67e5\u65f6\u673a\u9020\u6210\u7684\u5c11\u91cf\u63d0\u524d\u6216\u6ede\u540e，\u5e76\u4e0d\u7b49\u4e8e\u952e\u503c\u5bf9\u5b58\u50a8\u51fa\u9519\u3002\u6269\u5bb9\u8fc7\u7a0b\u672c\u8eab\u4ecd\u9700\u8981\u901a\u8fc7 CAS\u3001\u6876\u540c\u6b65\u548c\u8fc1\u79fb\u72b6\u6001\u7b49\u673a\u5236\u4fdd\u8bc1\u6b63\u786e\u6027\u3002<\/p>\n

    \u8fd9\u91cc\u201c\u5141\u8bb8\u8ba1\u6570\u5224\u65ad\u4e0d\u7cbe\u786e\u201d\u548c\u201c\u5141\u8bb8\u8fc1\u79fb\u4e22\u5931\u6570\u636e\u201d\u662f\u4e24\u56de\u4e8b\u3002<\/p>\n

    2. \u4e25\u683c\u4e1a\u52a1\u9650\u5236\u4e0d\u80fd\u53ea\u9760 size()<\/h4>\n

    \u4e0b\u9762\u662f\u9519\u8bef\u7684\u5bb9\u91cf\u9650\u5236\u65b9\u5f0f：<\/p>\n

    \/\/ \u9519\u8bef\u793a\u4f8b：\u4e0d\u80fd\u4fdd\u8bc1\u5e76\u53d1\u60c5\u51b5\u4e0b\u6700\u591a\u53ea\u6709 100 \u4e2a\u952e\u503c\u5bf9\u3002<\/span>
    \nif<\/span> (<\/span>map.<\/span>size<\/span>(<\/span>)<\/span> <<\/span> 100<\/span>)<\/span> {<\/span>
    \n map.<\/span>put<\/span>(<\/span>key,<\/span> value)<\/span>;<\/span>
    \n}<\/span><\/p>\n

    \u5f53\u524d\u6709 99 \u4e2a\u5143\u7d20\u65f6，\u4e24\u4e2a\u7ebf\u7a0b\u90fd\u53ef\u80fd\u8bfb\u5230 99，\u90fd\u901a\u8fc7\u5224\u65ad，\u7136\u540e\u63d2\u5165\u4e24\u4e2a\u4e0d\u540c\u7684\u65b0\u952e，\u6700\u7ec8\u8fbe\u5230 101\u3002<\/p>\n

    \u5373\u4f7f size() \u7684\u8bfb\u53d6\u7ed3\u679c\u5728\u90a3\u4e00\u523b\u5b8c\u5168\u51c6\u786e，\u201c\u68c0\u67e5\u201d\u548c\u201c\u63d2\u5165\u201d\u4ecd\u7136\u662f\u4e24\u4e2a\u6b65\u9aa4，\u7ec4\u5408\u8d77\u6765\u4e0d\u5177\u5907\u539f\u5b50\u6027\u3002<\/p>\n

    \u4e0b\u9762\u7528\u4e24\u4e2a\u7ebf\u7a0b\u548c\u4e00\u4e2a\u95e8\u95e9，\u56fa\u5b9a\u590d\u73b0\u8fd9\u79cd\u4ea4\u9519：<\/p>\n

    \/\/ \u9002\u7528 JDK 8，\u6587\u4ef6\u540d：CapacityRaceDemo.java\u3002<\/span>
    \nimport<\/span> java.<\/span>util.<\/span>concurrent.<\/span><\/span>ConcurrentHashMap<\/span><\/span>;<\/span>
    \nimport<\/span> java.<\/span>util.<\/span>concurrent.<\/span><\/span>CountDownLatch<\/span><\/span>;<\/span><\/p>\n

    public<\/span> class<\/span> CapacityRaceDemo<\/span> {<\/span>
    \n public<\/span> static<\/span> void<\/span> main<\/span>(<\/span>String<\/span>[<\/span>]<\/span> args)<\/span> throws<\/span> InterruptedException<\/span> {<\/span>
    \n ConcurrentHashMap<\/span><<\/span>Integer<\/span>,<\/span> Integer<\/span>><\/span><\/span> map =<\/span> new<\/span> ConcurrentHashMap<\/span><<\/span>><\/span><\/span>(<\/span>)<\/span>;<\/span>
    \n for<\/span> (<\/span>int<\/span> i =<\/span> 0<\/span>;<\/span> i <<\/span> 99<\/span>;<\/span> i++<\/span>)<\/span> {<\/span>
    \n map.<\/span>put<\/span>(<\/span>i,<\/span> i)<\/span>;<\/span>
    \n }<\/span><\/p>\n

    CountDownLatch<\/span> checked =<\/span> new<\/span> CountDownLatch<\/span>(<\/span>2<\/span>)<\/span>;<\/span>
    \n Thread<\/span>[<\/span>]<\/span> workers =<\/span> new<\/span> Thread<\/span>[<\/span>2<\/span>]<\/span>;<\/span>
    \n for<\/span> (<\/span>int<\/span> i =<\/span> 0<\/span>;<\/span> i <<\/span> workers.<\/span>length;<\/span> i++<\/span>)<\/span> {<\/span>
    \n final<\/span> int<\/span> key =<\/span> 99<\/span> +<\/span> i;<\/span>
    \n workers[<\/span>i]<\/span> =<\/span> new<\/span> Thread<\/span>(<\/span>(<\/span>)<\/span> -><\/span> {<\/span>
    \n boolean<\/span> allowed =<\/span> map.<\/span>size<\/span>(<\/span>)<\/span> <<\/span> 100<\/span>;<\/span>
    \n checked.<\/span>countDown<\/span>(<\/span>)<\/span>;<\/span>
    \n try<\/span> {<\/span>
    \n checked.<\/span>await<\/span>(<\/span>)<\/span>;<\/span> \/\/ \u7b49\u4e24\u4e2a\u7ebf\u7a0b\u90fd\u5b8c\u6210\u68c0\u67e5，\u518d\u63d2\u5165\u3002<\/span>
    \n }<\/span> catch<\/span> (<\/span>InterruptedException<\/span> e)<\/span> {<\/span>
    \n Thread<\/span>.<\/span>currentThread<\/span>(<\/span>)<\/span>.<\/span>interrupt<\/span>(<\/span>)<\/span>;<\/span>
    \n return<\/span>;<\/span>
    \n }<\/span>
    \n if<\/span> (<\/span>allowed)<\/span> {<\/span>
    \n map.<\/span>put<\/span>(<\/span>key,<\/span> key)<\/span>;<\/span>
    \n }<\/span>
    \n }<\/span>)<\/span>;<\/span>
    \n workers[<\/span>i]<\/span>.<\/span>start<\/span>(<\/span>)<\/span>;<\/span>
    \n }<\/span>
    \n for<\/span> (<\/span>Thread<\/span> worker :<\/span> workers)<\/span> {<\/span>
    \n worker.<\/span>join<\/span>(<\/span>)<\/span>;<\/span>
    \n }<\/span>
    \n System<\/span>.<\/span>out.<\/span>println<\/span>(<\/span>"final size = "<\/span> +<\/span> map.<\/span>size<\/span>(<\/span>)<\/span>)<\/span>;<\/span>
    \n }<\/span>
    \n}<\/span><\/p>\n

    \u8f93\u51fa：<\/p>\n

    final size = 101<\/p>\n

    \u8fd9\u8bf4\u660e ConcurrentHashMap \u7684\u7ebf\u7a0b\u5b89\u5168，\u5e76\u4e0d\u4f1a\u81ea\u52a8\u8ba9\u591a\u4e2a\u65b9\u6cd5\u7ec4\u6210\u7684\u4e1a\u52a1\u6d41\u7a0b\u4e5f\u5177\u5907\u539f\u5b50\u6027\u3002<\/p>\n

    \u5982\u679c\u91c7\u7528\u9501，\u9700\u8981\u8ba9\u76f8\u5173\u4fee\u6539\u9075\u5b88\u540c\u4e00\u628a\u4e1a\u52a1\u9501\u3002\u4f8b\u5982，\u5728\u6240\u6709\u76f8\u5173\u589e\u5220\u64cd\u4f5c\u90fd\u53d7\u540c\u4e00\u9501\u7ea6\u675f\u7684\u524d\u63d0\u4e0b，\u53ef\u4ee5\u5728\u4e34\u754c\u533a\u5185\u5b8c\u6210\u68c0\u67e5\u548c\u63d2\u5165\u3002\u82e5\u5141\u8bb8\u8986\u76d6\u5df2\u6709\u952e，\u5224\u65ad\u8fd8\u9700\u8981\u533a\u5206\u201c\u66ff\u6362\u503c\u201d\u4e0e\u201c\u65b0\u589e\u952e\u201d，\u4e0d\u80fd\u628a\u8fbe\u5230\u4e0a\u9650\u540e\u7684\u6240\u6709 put \u90fd\u62d2\u7edd\u3002<\/p>\n

    \u4e5f\u53ef\u4ee5\u7528\u4fe1\u53f7\u91cf\u7ba1\u7406\u540d\u989d，\u4f46\u5fc5\u987b\u628a\u91cd\u590d\u952e\u3001\u63d2\u5165\u5931\u8d25\u3001\u5220\u9664\u91ca\u653e\u7b49\u751f\u547d\u5468\u671f\u8bbe\u8ba1\u5b8c\u6574\u3002\u53ea\u5728 put() \u524d\u8c03\u7528\u4e00\u6b21\u8bb8\u53ef\u83b7\u53d6，\u4e0d\u80fd\u81ea\u52a8\u5b8c\u6210\u8fd9\u4e9b\u4e1a\u52a1\u7ea6\u675f\u3002<\/p>\n

    \u516b\u3001\u5bb9\u6613\u6df7\u6dc6\u7684\u51e0\u4e2a\u95ee\u9898<\/h3>\n

    1. Cell \u6570\u7ec4\u6269\u5927，\u662f\u5426\u5c31\u662f Map \u6269\u5bb9<\/h4>\n

    \u4e0d\u662f\u3002\u4e24\u79cd\u6570\u7ec4\u89e3\u51b3\u4e0d\u540c\u95ee\u9898：<\/p>\n\n\u5bf9\u6bd4\u9879CounterCell[] \u6269\u5927\u6876\u6570\u7ec4\u6269\u5bb9<\/tr>\n\n\n\n\n\n
    \u6570\u7ec4\u4e2d\u4fdd\u5b58\u4ec0\u4e48<\/td>\n\u5206\u6563\u7684\u8ba1\u6570\u5355\u5143<\/td>\n\u6876\u4e0e\u952e\u503c\u5bf9\u8282\u70b9<\/td>\n<\/tr>\n
    \u4e3b\u8981\u89e3\u51b3\u4ec0\u4e48\u95ee\u9898<\/td>\n\u591a\u7ebf\u7a0b\u66f4\u65b0\u8ba1\u6570\u5668\u7684\u7ade\u4e89<\/td>\n\u6876\u6570\u7ec4\u7684\u6570\u636e\u5bc6\u5ea6\u4e0e\u51b2\u7a81<\/td>\n<\/tr>\n
    \u4e3b\u8981\u5b9e\u73b0\u4f4d\u7f6e<\/td>\nfullAddCount()<\/td>\ntransfer()，\u4ee5\u53ca\u76f8\u5e94\u89e6\u53d1\u5165\u53e3<\/td>\n<\/tr>\n
    \u662f\u5426\u8fc1\u79fb\u952e\u503c\u5bf9<\/td>\n\u4e0d\u8fc1\u79fb，\u53ea\u4fdd\u7559\u5df2\u6709 Cell \u5f15\u7528\u5e76\u589e\u52a0\u69fd\u4f4d<\/td>\n\u5c06\u65e7\u6876\u6570\u636e\u7ec4\u7ec7\u5230\u65b0\u6570\u7ec4<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

    Cell \u6570\u7ec4\u5e76\u4e0d\u968f Map \u5143\u7d20\u6570\u91cf\u65e0\u9650\u589e\u52a0\u3002\u5176\u6269\u5927\u8fd8\u53d7 CPU \u6570\u91cf\u76f8\u5173\u6761\u4ef6\u9650\u5236；\u7531\u4e8e\u957f\u5ea6\u6309\u4e8c\u6b21\u5e42\u589e\u957f，\u4e0d\u80fd\u7b80\u5355\u8868\u8ff0\u4e3a\u201c\u957f\u5ea6\u4e00\u5b9a\u4e25\u683c\u4e0d\u8d85\u8fc7 CPU \u6570\u91cf\u201d\u3002[1]<\/p>\n

    2. \u8c03\u7528 size() \u4f1a\u89e6\u53d1\u6269\u5bb9\u5417<\/h4>\n

    \u4e0d\u4f1a\u3002size() \u53ea\u6c47\u603b\u8ba1\u6570\u3001\u5904\u7406\u8fd4\u56de\u8303\u56f4，\u4e0d\u8c03\u7528 transfer()\u3002<\/p>\n

    \u662f\u66f4\u65b0\u8def\u5f84\u53ef\u80fd\u89e6\u53d1\u6269\u5bb9\u68c0\u67e5，\u800c\u4e0d\u662f\u201c\u8c03\u7528\u4e00\u6b21 size()，Map \u5c31\u987a\u4fbf\u68c0\u67e5\u4e00\u6b21\u6269\u5bb9\u201d\u3002<\/p>\n

    3. \u8fbe\u5230\u5143\u7d20\u6570\u91cf\u9608\u503c，\u662f\u552f\u4e00\u6269\u5bb9\u5165\u53e3\u5417<\/h4>\n

    \u4e0d\u662f\u3002putVal() \u5728\u6876\u5185\u94fe\u8868\u8fbe\u5230\u76f8\u5e94\u6761\u4ef6\u65f6，\u4f1a\u8c03\u7528 treeifyBin()\u3002\u8fd9\u4e2a\u65b9\u6cd5\u9996\u5148\u770b\u6876\u6570\u7ec4\u662f\u5426\u8db3\u591f\u5927：<\/p>\n

    \/\/ JDK 8 \u6e90\u7801\u8282\u9009：\u7701\u7565\u540e\u7eed\u6811\u5316\u4ee3\u7801\u3002<\/span>
    \nif<\/span> (<\/span>(<\/span>n =<\/span> tab.<\/span>length)<\/span> <<\/span> MIN_TREEIFY_CAPACITY<\/span>)<\/span> {<\/span>
    \n tryPresize<\/span>(<\/span>n <<<\/span> 1<\/span>)<\/span>;<\/span>
    \n}<\/span><\/p>\n

    JDK 8 \u4e2d MIN_TREEIFY_CAPACITY \u4e3a 64\u3002\u5f53\u6570\u7ec4\u957f\u5ea6\u5c0f\u4e8e 64 \u65f6，\u8fd9\u6761\u8def\u5f84\u4f1a\u4f18\u5148\u5c1d\u8bd5\u6269\u5bb9，\u800c\u4e0d\u662f\u76f4\u63a5\u6811\u5316\u3002\u56e0\u6b64\u4e0d\u80fd\u628a\u6240\u6709\u6269\u5bb9\u90fd\u5f52\u7ed3\u4e3a sumCount() >= sizeCtl\u3002[1]<\/p>\n

    \u53e6\u5916，tryPresize() \u63a5\u6536\u7684\u662f\u9884\u5206\u914d\u76f8\u5173\u7684\u5927\u5c0f\u53c2\u6570，\u8fd8\u4f1a\u8fdb\u884c\u5bb9\u91cf\u6362\u7b97\u548c\u5224\u65ad，\u4e0d\u80fd\u628a\u8fd9\u91cc\u7684 n << 1 \u76f4\u63a5\u5f53\u4f5c\u65b0\u6570\u7ec4\u6700\u7ec8\u957f\u5ea6\u3002transfer() \u6bcf\u4e00\u8f6e\u521b\u5efa\u7684\u65b0\u6570\u7ec4，\u624d\u662f\u65e7\u957f\u5ea6\u7684\u4e24\u500d\u3002<\/p>\n

    \u6279\u91cf\u63d2\u5165 putAll() \u4e5f\u6709\u9884\u5148\u8c03\u6574\u5bb9\u91cf\u7684\u5165\u53e3，\u4e0d\u9700\u8981\u7b49\u5230\u6bcf\u6b21\u65b0\u589e\u540e\u7684\u8ba1\u6570\u68c0\u67e5\u624d\u5f00\u59cb\u8003\u8651\u5bb9\u91cf\u3002<\/p>\n

    4. \u4e0e LongAdder \u6709\u4ec0\u4e48\u5173\u7cfb<\/h4>\n

    \u4e24\u8005\u91c7\u7528\u76f8\u4f3c\u7684\u5206\u6563\u8ba1\u6570\u601d\u8def：<\/p>\n

    ConcurrentHashMap：baseCount + CounterCell[]
    \nLongAdder： base + Cell[]<\/p>\n

    JDK 8 \u7684 LongAdder \u7ee7\u627f\u5185\u90e8\u7c7b Striped64，\u7531\u5b83\u63d0\u4f9b\u57fa\u7840\u5b57\u6bb5\u4e0e\u5206\u6563\u66f4\u65b0\u673a\u5236\u3002ConcurrentHashMap \u5219\u5728\u5185\u90e8\u5b9e\u73b0\u4e86\u5bf9\u5e94\u7684\u8ba1\u6570\u7ed3\u6784，\u5e76\u4e0d\u662f\u76f4\u63a5\u4fdd\u5b58\u4e00\u4e2a LongAdder \u5bf9\u8c61\u6765\u7edf\u8ba1\u6570\u91cf\u3002[1][3][4]<\/p>\n

    LongAdder.sum() \u540c\u6837\u4e0d\u4fdd\u8bc1\u5e76\u53d1\u66f4\u65b0\u671f\u95f4\u7684\u539f\u5b50\u5feb\u7167，\u9002\u5408\u9ad8\u5e76\u53d1\u7edf\u8ba1\u3002\u5176\u9ad8\u7ade\u4e89\u4e0b\u7684\u6027\u80fd\u6536\u76ca\u4ee5\u66f4\u591a\u7a7a\u95f4\u548c\u6c47\u603b\u8bfb\u53d6\u6210\u672c\u4e3a\u4ee3\u4ef7，\u4e0d\u80fd\u7531\u6b64\u63a8\u5bfc\u51fa\u201c\u6240\u6709\u573a\u666f\u90fd\u6bd4 AtomicLong \u66f4\u597d\u201d\u3002[5]<\/p>\n

    5. \u53bb\u54ea\u91cc\u7ee7\u7eed\u8bfb\u6e90\u7801<\/h4>\n

    \u4e0b\u9762\u6309\u672c\u6587\u4e3b\u7ebf\u5217\u51fa\u56fa\u5b9a\u7248\u672c\u7684\u9605\u8bfb\u5165\u53e3\u3002\u6e90\u7801\u8def\u5f84\u5747\u76f8\u5bf9\u4e8e OpenJDK jdk8u402-b06 \u4ed3\u5e93：<\/p>\n\n\u7c7b\u6216\u65b9\u6cd5\u6e90\u7801\u4f4d\u7f6e\u9605\u8bfb\u91cd\u70b9<\/tr>\n\n\n\n\n\n\n\n\n\n\n
    \u8ba1\u6570\u4e0e\u63a7\u5236\u5b57\u6bb5<\/td>\nConcurrentHashMap.java:785<\/td>\nbaseCount\u3001sizeCtl\u3001counterCells<\/td>\n<\/tr>\n
    size()<\/td>\nConcurrentHashMap.java:909<\/td>\n\u6c47\u603b\u4e0e\u8fd4\u56de\u8303\u56f4\u5904\u7406<\/td>\n<\/tr>\n
    putVal()<\/td>\nConcurrentHashMap.java:1010<\/td>\n\u65b0\u589e\u952e\u540e\u8c03\u7528 addCount()<\/td>\n<\/tr>\n
    addCount()<\/td>\nConcurrentHashMap.java:2256<\/td>\n\u8ba1\u6570\u66f4\u65b0\u3001\u63d0\u524d\u8fd4\u56de\u3001\u6269\u5bb9\u68c0\u67e5<\/td>\n<\/tr>\n
    helpTransfer()<\/td>\nConcurrentHashMap.java:2295<\/td>\n\u66f4\u65b0\u7ebf\u7a0b\u600e\u6837\u52a0\u5165\u8fc1\u79fb<\/td>\n<\/tr>\n
    transfer()<\/td>\nConcurrentHashMap.java:2365<\/td>\n\u5206\u914d\u4efb\u52a1\u3001\u8fc1\u79fb\u6876\u3001\u5207\u6362\u6570\u7ec4<\/td>\n<\/tr>\n
    sumCount()<\/td>\nConcurrentHashMap.java:2509<\/td>\n\u57fa\u7840\u8ba1\u6570\u4e0e Cell \u7684\u6c42\u548c<\/td>\n<\/tr>\n
    fullAddCount()<\/td>\nConcurrentHashMap.java:2522<\/td>\nCell \u521d\u59cb\u5316\u3001\u51b2\u7a81\u91cd\u8bd5\u4e0e\u6570\u7ec4\u6269\u5927<\/td>\n<\/tr>\n
    treeifyBin()<\/td>\nConcurrentHashMap.java:2609<\/td>\n\u6570\u7ec4\u8f83\u5c0f\u65f6\u4f18\u5148\u5c1d\u8bd5\u6269\u5bb9<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n

    \u53c2\u8003\u8d44\u6599<\/h3>\n
  • OpenJDK jdk8u402-b06：ConcurrentHashMap \u6e90\u7801<\/li>\n
  • Java 8 API：ConcurrentHashMap<\/li>\n
  • OpenJDK jdk8u402-b06：LongAdder \u6e90\u7801<\/li>\n
  • OpenJDK jdk8u402-b06：Striped64 \u6e90\u7801<\/li>\n
  • Java 8 API：LongAdder，\u542b sum() \u7684\u5feb\u7167\u8bed\u4e49\u8bf4\u660e<\/li>\n","protected":false},"excerpt":{"rendered":"

    ConcurrentHashMap \u7684 size \u4e0e\u6269\u5bb9\u673a\u5236：\u4ece\u5206\u6563\u8ba1\u6570\u5230\u534f\u4f5c\u8fc1\u79fb
    \n\u6587\u7ae0\u6458\u8981
    \nConcurrentHashMap \u65b0\u589e\u4e00\u4e2a\u952e\u4e4b\u540e，\u9700\u8981\u7ef4\u62a4\u5143\u7d20\u6570\u91cf，\u5e76\u5728\u5408\u9002\u7684\u65f6\u673a\u5224\u65ad\u662f\u5426\u6269\u5bb9\u3002\u591a\u4e2a\u7ebf\u7a0b\u540c\u65f6\u589e\u5220\u5143\u7d20\u65f6，\u5b83\u600e\u6837\u907f\u514d\u4e89\u62a2\u540c\u4e00\u4e2a\u8ba1\u6570\u5668？baseCount\u3001CounterCell \u548c size() \u53c8\u600e\u6837\u53c2\u4e0e\u8fd9\u4e2a\u8fc7\u7a0b？\u672c\u6587\u4ee5 JDK 8 \u4e3a\u57fa\u7840，\u5148\u4ecb\u7ecd\u6269\u5bb9\u7684\u6574\u4f53\u8fc7\u7a0b&#<\/p>\n","protected":false},"author":2,"featured_media":118672,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[99,305],"topic":[],"class_list":["post-118674","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-server","tag-java","tag-305"],"yoast_head":"\nConcurrentHashMap \u7684 size \u4e0e\u6269\u5bb9\u673a\u5236\uff1a\u4ece\u5206\u6563\u8ba1\u6570\u5230\u534f\u4f5c\u8fc1\u79fb - 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