{"id":1156,"date":"2021-03-11T20:29:50","date_gmt":"2021-03-11T12:29:50","guid":{"rendered":"http:\/\/www.rain1024.com\/?p=1156"},"modified":"2023-08-07T20:57:23","modified_gmt":"2023-08-07T12:57:23","slug":"%e4%bb%8etheadlocalmap%e7%9c%8b%e5%93%88%e5%b8%8c%e7%a2%b0%e6%92%9e%e5%90%8e%e5%bc%80%e6%94%be%e5%af%bb%e5%9d%80%e6%b3%95%e7%9a%84%e5%ae%9e%e7%8e%b0%e8%bf%87%e7%a8%8b","status":"publish","type":"post","link":"http:\/\/rain1024.com\/index.php\/2021\/03\/11\/%e4%bb%8etheadlocalmap%e7%9c%8b%e5%93%88%e5%b8%8c%e7%a2%b0%e6%92%9e%e5%90%8e%e5%bc%80%e6%94%be%e5%af%bb%e5%9d%80%e6%b3%95%e7%9a%84%e5%ae%9e%e7%8e%b0%e8%bf%87%e7%a8%8b\/","title":{"rendered":"\u4eceTheadLocalMap\u770b\u54c8\u5e0c\u78b0\u649e\u540e\u5f00\u653e\u5bfb\u5740\u6cd5\u7684\u5b9e\u73b0\u8fc7\u7a0b"},"content":{"rendered":"<h1>\u4eceTheadLocalMap\u770b\u54c8\u5e0c\u78b0\u649e\u540e\u5f00\u653e\u5bfb\u5740\u6cd5\u7684\u5b9e\u73b0\u8fc7\u7a0b<\/h1>\n<h4>\u672c\u6765\u60f3\u8bf4ThreadLocal\uff0c\u4f46\u770b\u5230\u4e86ThreadLocalMap\u4e2d\u5bf9\u54c8\u5e0c\u78b0\u649e\u662f\u91c7\u7528\u5f00\u653e\u5bfb\u5740\u6cd5\u6765\u5b9e\u73b0\u7684\uff0c\u89c9\u5f97\u5f88\u6709\u610f\u601d\uff0chash\u4f7f\u7528\u7684\u573a\u666f\u5f88\u591a\uff0c\u6563\u5217\u8868\u5c31\u662f\u4e00\u79cd\u9ad8\u6548\u800c\u5e38\u7528\u7684\u6570\u636e\u7ed3\u6784\uff0c\u80fd\u5c06\u67e5\u627e\u7684\u65f6\u95f4\u590d\u6742\u5ea6\u964d\u5230O(1)\uff0c\u5b83\u901a\u8fc7\u54c8\u5e0c\u51fd\u6570\u6765\u751f\u6210\u4e00\u4e2a hashcode \u503c\uff0c\u4ece\u800c\u5bf9\u6570\u636e\u8fdb\u884c\u4e00\u4e00\u5b9a\u4f4d\uff0c\u867d\u7136\u73b0\u5728\u7684\u54c8\u5e0c\u51fd\u6570\u5df2\u7ecf\u80fd\u505a\u5230\u5f88\u597d\u7684\u968f\u673a\uff0c\u4f46\u8fd8\u662f\u4f1a\u6709\u51b2\u7a81\u53d1\u751f\uff0c\u4e5f\u5c31\u662f\u4e0d\u540c\u7684\u5bf9\u8c61\u7ecf\u8fc7\u54c8\u5e0c\u51fd\u6570\u7684\u8ba1\u7b97\uff0c\u751f\u6210\u4e86\u76f8\u540c\u7684 hashcode 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class=\"java\">ThreadLocal.ThreadLocalMap threadLocals = null;\n<\/code><\/pre>\n<p>ThreadLocal\u4e2d\u5305\u542b\u4ee5\u4e0b\u65b9\u6cd5\u548c\u7c7b\u578b<\/p>\n<p><img decoding=\"async\" src=\"http:\/\/uos.rain1024.com\/image\/image-20210311195856512.png\" alt=\"image-20210311195856512\" \/><\/p>\n<p>\u63d0\u4f9b\u4e09\u4e2a\u516c\u5171\u65b9\u6cd5\u6765\u8fdb\u884c\u64cd\u4f5c\uff0c\u5206\u522b\u662fset\uff0cget\uff0cremove\uff0c\u770b\u8d77\u6765\u5f88\u7b80\u5355\u7684\u6837\u5b50\uff0cThreadlocal\u800c\u662f\u4e00\u4e2a\u7ebf\u7a0b\u5185\u90e8\u7684\u5b58\u50a8\u7c7b\uff0c\u53ef\u4ee5\u5728\u6307\u5b9a\u7ebf\u7a0b\u5185\u5b58\u50a8\u6570\u636e\uff0c\u6570\u636e\u5b58\u50a8\u4ee5\u540e\uff0c\u53ea\u6709\u6307\u5b9a\u7ebf\u7a0b\u53ef\u4ee5\u5f97\u5230\u5b58\u50a8\u6570\u636e\u3002<strong>\u5b9e\u9645\u4e0a\u662fThreadLocal\u7684\u9759\u6001\u5185\u90e8\u7c7bThreadLocalMap\u4e3a\u6bcf\u4e2aThread\u90fd\u7ef4\u62a4\u4e86\u4e00\u4e2a\u6570\u7ec4table\uff0cThreadLocal\u901a\u8fc7Thread\u786e\u5b9a\u6570\u7ec4\u4e0b\u6807\uff0c\u800c\u8fd9\u4e2a\u4e0b\u6807\u5c31\u662fvalue\u5b58\u50a8\u7684\u5bf9\u5e94\u4f4d\u7f6e\u3002<\/strong><\/p>\n<p>\u5148\u770b\u521d\u59cb\u5316\u8fc7\u7a0b\uff0cThreadLocal\u662f\u5ef6\u8fdf\u6784\u5efa\u7684\uff0c\u53ea\u6709\u5f53\u6709\u6570\u636e\u8981\u653e\u8fdb\u6765\u7684\u65f6\u5019\u624d\u8fdb\u884c\u521b\u5efa\u3002<\/p>\n<pre><code class=\"java\">ThreadLocalMap(ThreadLocal&lt;?&gt; firstKey, Object firstValue) {\n            table = new Entry[INITIAL_CAPACITY];\n            int i = firstKey.threadLocalHashCode &amp; (INITIAL_CAPACITY - 1);\n            table[i] = new Entry(firstKey, firstValue);\n            size = 1;\n            setThreshold(INITIAL_CAPACITY);\n        }\n<\/code><\/pre>\n<p>set\u65b9\u6cd5\u7684\u5b9e\u73b0\uff0c\u901a\u8fc7 hashCode \u8ba1\u7b97\u7684\u7d22\u5f15\u4f4d\u7f6e i \u5904\u5982\u679c\u5df2\u7ecf\u6709\u503c\u4e86,\u4f1a\u4ece i \u5f00\u59cb,\u901a\u8fc7 +1 \u4e0d\u65ad\u7684\u5f80\u540e\u5bfb\u627e, \u76f4\u5230\u627e\u5230\u7d22\u5f15\u4f4d\u7f6e\u4e3a\u7a7a\u7684\u5730\u65b9,\u628a\u5f53\u524d ThreadLocal \u4f5c\u4e3a key \u653e\u8fdb\u53bb\u3002<\/p>\n<pre><code class=\"java\">private void set(ThreadLocal&lt;?&gt; key, Object value) {\n                        \/\/\u83b7\u53d6\u5f53\u524d\u6570\u7ec4\u548c\u957f\u5ea6\n            Entry[] tab = table;\n            int len = tab.length;\n            \/\/\u901a\u8fc7hash\u8ba1\u7b97\u8981\u5b58\u50a8\u7684\u4e0b\u6807\u4f4d\u7f6e\n            int i = key.threadLocalHashCode &amp; (len-1);\n                        \/\/\u8003\u8651\u5b58\u5728hash\u51b2\u7a81\u7684\u60c5\u51b5\uff0c\u5982\u679c\u5f53\u524d\u5750\u6807\u5df2\u7ecf\u6709\u6570\u636e\u4e86\uff0c\u5c31\u8c03\u7528nextIndex\u83b7\u53d6\u4e0b\u4e00\u4e2a\u4f4d\u7f6e\n            for (Entry e = tab[i];\n                 e != null;\n                 e = tab[i = nextIndex(i, len)]) {\n                ThreadLocal&lt;?&gt; k = e.get();\n\n                if (k == key) {\n                    e.value = value;\n                    return;\n                }\n\n                if (k == null) {\n                    replaceStaleEntry(key, value, i);\n                    return;\n                }\n            }\n                        \/\/\u7ec8\u4e8e\u627e\u5230\u65b0\u7684\u7a7a\u4f4d\u7f6e\n            tab[i] = new Entry(key, value);\n            int sz = ++size;\n            if (!cleanSomeSlots(i, sz) &amp;&amp; sz &gt;= threshold)\n                rehash();\n        }\n\n\n        private static int nextIndex(int i, int len) {\n            \/\/\u5224\u65ad\u4e0b\u4e00\u4e2a\u4f4d\u7f6e\u662f\u5426\u8d85\u8fc7\u6570\u7ec4\u957f\u5ea6\uff0c\u5982\u679c\u8d85\u8fc7\u4e86\uff0c\u5c31\u4ece0\u5f00\u59cb\n            return ((i + 1 &lt; len) ? i + 1 : 0);\n        }\n<\/code><\/pre>\n<p>\u56e0\u4e3aset\u65b9\u6cd5\u7684\u7279\u6b8a\uff0cget\u65b9\u6cd5\u4e5f\u9700\u8981\u6709\u70b9\u6539\u53d8<\/p>\n<pre><code class=\"java\">private Entry getEntry(ThreadLocal&lt;?&gt; key) {\n                        \/\/\u8ba1\u7b97\u5b58\u50a8\u7684\u4e0b\u6807\n            int i = key.threadLocalHashCode &amp; (table.length - 1);\n            Entry e = table[i];\n            \/\/\u5982\u679c\u5f53\u524d\u4e0b\u6807\u4f4d\u7f6e\u7684\u6570\u636e\u7684key\u4e8e\u67e5\u8be2\u7684key\u76f8\u540c\uff0c\u5219\u76f4\u63a5\u8fd4\u56de\n            if (e != null &amp;&amp; e.get() == key)\n                return e;\n            else\n                    \/\/key\u4e0d\u540c\uff0c\u8bf4\u660e\u6709\u51b2\u7a81\uff0c\u9700\u8981\u5f80\u4e0b\u67e5\u627e\n                return getEntryAfterMiss(key, i, e);\n        }\n\nprivate Entry getEntryAfterMiss(ThreadLocal&lt;?&gt; key, int i, Entry e) {\n            Entry[] tab = table;\n            int len = tab.length;\n                        \/\/\u4e00\u76f4\u627e\u5230e\u4e0d\u4e3a\u7a7a\n            while (e != null) {\n                ThreadLocal&lt;?&gt; k = e.get();\n                if (k == key)\n                    return e;\n                if (k == null)\n                        \/\/\u5904\u7406key\u4e3anull\u7684\u8282\u70b9\n                    expungeStaleEntry(i);\n                else\n                        \/\/\u589e\u52a0i\n                    i = nextIndex(i, len);\n                e = tab[i];\n            }\n            return null;\n        }\n\n\n<\/code><\/pre>\n<p>ThreadLocal\u548cSynchronized\u90fd\u662f\u4e3a\u4e86\u89e3\u51b3\u591a\u7ebf\u7a0b\u4e2d\u76f8\u540c\u53d8\u91cf\u7684\u8bbf\u95ee\u51b2\u7a81\u95ee\u9898\uff0c\u4e0d\u540c\u7684\u70b9\u662f<\/p>\n<ul>\n<li>Synchronized\u662f\u901a\u8fc7\u7ebf\u7a0b\u7b49\u5f85\uff0c\u727a\u7272\u65f6\u95f4\u6765\u89e3\u51b3\u8bbf\u95ee\u51b2\u7a81<\/li>\n<li>ThreadLocal\u662f\u901a\u8fc7\u6bcf\u4e2a\u7ebf\u7a0b\u5355\u72ec\u4e00\u4efd\u5b58\u50a8\u7a7a\u95f4\uff0c\u727a\u7272\u7a7a\u95f4\u6765\u89e3\u51b3\u51b2\u7a81\uff0c\u5e76\u4e14\u76f8\u6bd4\u4e8eSynchronized\uff0cThreadLocal\u5177\u6709\u7ebf\u7a0b\u9694\u79bb\u7684\u6548\u679c\uff0c\u53ea\u6709\u5728\u7ebf\u7a0b\u5185\u624d\u80fd\u83b7\u53d6\u5230\u5bf9\u5e94\u7684\u503c\uff0c\u7ebf\u7a0b\u5916\u5219\u4e0d\u80fd\u8bbf\u95ee\u5230\u60f3\u8981\u7684\u503c\u3002<\/li>\n<\/ul>\n<p>\u6b63\u56e0\u4e3aThreadLocal\u7684\u7ebf\u7a0b\u9694\u79bb\u7279\u6027\uff0c\u4f7f\u5b83\u7684\u5e94\u7528\u573a\u666f\u76f8\u5bf9\u6765\u8bf4\u66f4\u4e3a\u7279\u6b8a\u4e00\u4e9b\u3002\u5f53\u67d0\u4e9b\u6570\u636e\u662f\u4ee5\u7ebf\u7a0b\u4e3a\u4f5c\u7528\u57df\u5e76\u4e14\u4e0d\u540c\u7ebf\u7a0b\u5177\u6709\u4e0d\u540c\u7684\u6570\u636e\u526f\u672c\u7684\u65f6\u5019\uff0c\u5c31\u53ef\u4ee5\u8003\u8651\u91c7\u7528ThreadLocal\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u672c\u6765\u60f3\u8bf4ThreadLocal\uff0c\u4f46\u770b\u5230\u4e86ThreadLocalMap\u4e2d\u5bf9\u54c8\u5e0c\u78b0\u649e\u662f\u91c7\u7528\u5f00\u653e\u5bfb\u5740\u6cd5\u6765\u5b9e\u73b0\u7684\uff0c\u89c9\u5f97\u5f88\u6709\u610f\u601d\uff0chash\u4f7f\u7528\u7684\u573a\u666f\u5f88\u591a\uff0c\u6563\u5217\u8868\u5c31\u662f\u4e00\u79cd\u9ad8\u6548\u800c\u5e38\u7528\u7684\u6570\u636e\u7ed3\u6784\uff0c\u80fd\u5c06\u67e5\u627e\u7684\u65f6\u95f4\u590d\u6742\u5ea6\u964d\u5230O(1)\uff0c\u5b83\u901a\u8fc7\u54c8\u5e0c\u51fd\u6570\u6765\u751f\u6210\u4e00\u4e2a hashcode \u503c\uff0c\u4ece\u800c\u5bf9\u6570\u636e\u8fdb\u884c\u4e00\u4e00\u5b9a\u4f4d\uff0c\u867d\u7136\u73b0\u5728\u7684\u54c8\u5e0c\u51fd\u6570\u5df2\u7ecf\u80fd\u505a\u5230\u5f88\u597d\u7684\u968f\u673a\uff0c\u4f46\u8fd8\u662f\u4f1a\u6709\u51b2\u7a81\u53d1\u751f\uff0c\u4e5f\u5c31\u662f\u4e0d\u540c\u7684\u5bf9\u8c61\u7ecf\u8fc7\u54c8\u5e0c\u51fd\u6570\u7684\u8ba1\u7b97\uff0c\u751f\u6210\u4e86\u76f8\u540c\u7684 hashcode 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