\u5728\u591a\u7ebf\u7a0b\u7684\u4e16\u754c\u91cc，\u89e3\u51b3\u5e76\u53d1\u5b89\u5168\u95ee\u9898\u901a\u5e38\u6709\u4e24\u4e2a\u6781\u7aef\u601d\u8def：\u4e00\u4e2a\u662f\u201c\u5927\u5bb6\u6392\u961f\u7528\u201d，\u8fd9\u5c31\u662f\u52a0\u9501（Synchronized\/ReentrantLock）；\u53e6\u4e00\u4e2a\u5219\u662f\u201c\u5404\u7528\u5404\u7684\u201d\u6216\u8005\u201c\u8c01\u90fd\u522b\u60f3\u6539\u201d\u3002\u672c\u7bc7\u535a\u5ba2\u6211\u4eec\u5c06\u8df3\u51fa\u4f20\u7edf\u7684\u52a0\u9501\u601d\u7ef4，\u63a2\u8ba8\u5e76\u53d1\u7f16\u7a0b\u4e2d\u6781\u5176\u4f18\u96c5\u7684\u4e24\u79cd\u65e0\u9501\u54f2\u5b66：\u4e0d\u53ef\u53d8\u6027\u8bbe\u8ba1（Final）\u4e0e\u7ebf\u7a0b\u7ea7\u9694\u79bb（ThreadLocal）\u3002<\/p>\n
\u5f88\u591a\u65f6\u5019，\u591a\u7ebf\u7a0b\u7684 BUG \u6765\u6e90\u4e8e\u201c\u5171\u4eab\u4e14\u53ef\u53d8\u201d\u3002\u65e2\u7136\u540c\u65f6\u4fee\u6539\u4e00\u4e2a\u4e1c\u897f\u4f1a\u51fa\u95ee\u9898，\u90a3\u6211\u4eec\u5e72\u8106\u628a\u5b83\u8bbe\u8ba1\u6210\u201c\u4e00\u65e6\u521b\u5efa\u5c31\u4e0d\u53ef\u4fee\u6539\u201d，\u95ee\u9898\u81ea\u7136\u8fce\u5203\u800c\u89e3\u3002<\/p>\n
\u5728\u5e73\u65f6\u7684\u4e1a\u52a1\u4ee3\u7801\u4e2d，\u6211\u4eec\u7ecf\u5e38\u4f1a\u9047\u5230\u8fd9\u6837\u7684\u5751：\u628a SimpleDateFormat \u5b9a\u4e49\u6210\u9759\u6001\u5168\u5c40\u53d8\u91cf，\u591a\u7ebf\u7a0b\u540c\u65f6\u53bb parse() \u6216 format() \u65f6，\u76f4\u63a5\u62a5\u9519\u6216\u8005\u62ff\u5230\u9519\u8bef\u7684\u65f6\u95f4\u3002<\/p>\n
\u6253\u4e2a\u751f\u6d3b\u4e2d\u7684\u6bd4\u65b9：SimpleDateFormat \u5185\u90e8\u7ef4\u62a4\u4e86\u4e00\u4e2a\u5171\u4eab\u7684\u201c\u65e5\u5386\u8349\u7a3f\u672c\u201d（Calendar \u5bf9\u8c61）\u3002\u591a\u7ebf\u7a0b\u5e76\u53d1\u64cd\u4f5c\u65f6，\u76f8\u5f53\u4e8e\u597d\u51e0\u4e2a\u4eba\u540c\u65f6\u5728\u4e00\u9875\u8349\u7a3f\u672c\u4e0a\u64e6\u9664\u3001\u91cd\u5199，\u6700\u540e\u5ff5\u51fa\u6765\u7684\u7ed3\u679c\u80af\u5b9a\u4e71\u5957\u3002<\/p>\n
Java<\/p>\n
\/\/ \u274c \u9519\u8bef\u793a\u8303：\u591a\u7ebf\u7a0b\u5171\u4eab\u4e14\u53ef\u53d8，\u5fc5\u5b9a\u7ebf\u7a0b\u4e0d\u5b89\u5168
\npublic static final SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd");<\/p>\n
\u5982\u4f55\u89e3\u51b3？\u601d\u8def\u8f6c\u5411\u201c\u4e0d\u53ef\u53d8\u7c7b\u201d<\/p>\n
\u50cf String\u3001Integer \u4ee5\u53ca JDK 8 \u5f15\u5165\u7684 DateTimeFormatter，\u5929\u751f\u5c31\u662f\u7ebf\u7a0b\u5b89\u5168\u7684\u3002\u5b83\u4eec\u7684\u8bbe\u8ba1\u601d\u60f3\u975e\u5e38\u4e00\u81f4：<\/p>\n
\u53ea\u77e5\u9053 final \u53d8\u91cf\u4e0d\u80fd\u88ab\u4fee\u6539\u662f\u8fdc\u8fdc\u4e0d\u591f\u7684\u3002\u9762\u8bd5\u5b98\u5f80\u5f80\u4f1a\u5f80\u4e0b\u6316\u4e00\u5c42：\u5728\u5e76\u53d1\u73af\u5883\u4e0b，**final**** \u662f\u600e\u4e48\u4fdd\u8bc1\u5b89\u5168\u7684？**<\/p>\n
\u8fd9\u5c31\u8981\u4ece\u6307\u4ee4\u91cd\u6392\u5e8f\u8bf4\u8d77\u3002\u521b\u5efa\u4e00\u4e2a\u5bf9\u8c61\u901a\u5e38\u9700\u8981\u4e09\u6b65：\u5206\u914d\u5185\u5b58\u7a7a\u95f4\u3001\u521d\u59cb\u5316\u5bf9\u8c61\u3001\u5c06\u5185\u5b58\u5730\u5740\u8d4b\u503c\u7ed9\u5f15\u7528\u3002\u5982\u679c\u53d1\u751f\u6307\u4ee4\u91cd\u6392，\u7ebf\u7a0b B \u53ef\u80fd\u4f1a\u62ff\u5230\u4e00\u4e2a\u5206\u914d\u4e86\u5730\u5740\u4f46\u8fd8\u6ca1\u521d\u59cb\u5316\u5b8c\u6210\u7684\u201c\u534a\u6210\u54c1\u201d\u5bf9\u8c61，\u8bfb\u53d6\u5230\u91cc\u9762\u5c5e\u6027\u7684\u9ed8\u8ba4\u96f6\u503c（\u5982 0 \u6216 null）\u3002<\/p>\n
\u800c final \u5173\u952e\u5b57，\u5c31\u662f JVM \u5c42\u9762\u7ed9\u51fa\u7684\u5f3a\u6709\u529b\u627f\u8bfa\u3002<\/p>\n
\u6838\u5fc3\u63a8\u6f14：<\/p>\n
💡** \u7ed3\u5408\u771f\u5b9e\u4e1a\u52a1\u9632\u5751\u573a\u666f**<\/p>\n
\u9762\u8bd5\u5b98：\u5728\u54b1\u4eec\u5916\u5356\u7cfb\u7edf\u7684\u5546\u54c1\u8be6\u60c5\u9875，\u5982\u679c\u6211\u7528 DCL（\u53cc\u91cd\u68c0\u67e5\u9501）\u5199\u4e86\u4e00\u4e2a\u672c\u5730\u7f13\u5b58\u7684\u5355\u4f8b，\u4f46\u662f\u5fd8\u8bb0\u52a0 volatile \u4fee\u9970\u5b9e\u4f8b\u5f15\u7528\u4e86，\u800c\u5355\u4f8b\u5185\u90e8\u7684\u5c5e\u6027\u5168\u662f final \u7684\u3002\u8bf7\u95ee\u9ad8\u5e76\u53d1\u4e0b\u4f1a\u6709\u5e76\u53d1\u95ee\u9898\u5417？<\/p>\n
\u7834\u5c40\u56de\u7b54：\u4e0d\u4f1a\u51fa\u73b0\u5c5e\u6027\u672a\u521d\u59cb\u5316\u7684\u5e76\u53d1\u95ee\u9898\u3002\u867d\u7136\u5355\u4f8b\u5f15\u7528\u6ca1\u6709\u52a0 volatile，\u53ef\u80fd\u4f1a\u5bfc\u81f4\u5f15\u7528\u672c\u8eab\u7684\u8d4b\u503c\u53d1\u751f\u91cd\u6392\u5e8f，\u4f46\u56e0\u4e3a\u5185\u90e8\u5c5e\u6027\u662f final \u7684，JSR-133（Java \u5185\u5b58\u6a21\u578b\u89c4\u8303）\u589e\u5f3a\u4e86 final \u7684\u8bed\u4e49\u3002final \u7684\u5199\u5c4f\u969c\u4fdd\u8bc1\u4e86\u5728\u6784\u9020\u51fd\u6570\u7ed3\u675f\u524d，final \u5c5e\u6027\u5fc5\u5b9a\u521d\u59cb\u5316\u5b8c\u6bd5\u3002\u6240\u4ee5，\u53ea\u8981\u7ebf\u7a0b\u80fd\u62ff\u5230\u8fd9\u4e2a\u5355\u4f8b\u5bf9\u8c61，\u8bfb\u5230\u7684 final \u5c5e\u6027\u5fc5\u5b9a\u662f\u6b63\u786e\u6784\u5efa\u7684\u3002\u4e0d\u8fc7，\u4e3a\u4e86\u7a0b\u5e8f\u7684\u7edd\u5bf9\u4e25\u8c28，DCL \u5355\u4f8b\u7684\u5f15\u7528\u8fd8\u662f\u5f3a\u70c8\u5efa\u8bae\u52a0\u4e0a volatile\u3002<\/p>\n
\u5728\u6ca1\u6709\u4eab\u5143\u6a21\u5f0f\u4e4b\u524d，\u7cfb\u7edf\u6bcf\u9700\u8981\u64cd\u4f5c\u4e00\u6b21\u6570\u636e\u5e93，\u5c31 new Connection() \u521b\u5efa\u4e00\u4e2a\u8fde\u63a5，\u7528\u5b8c\u5c31\u9500\u6bc1\u3002\u4f46\u521b\u5efa\u8fde\u63a5\u6781\u5176\u8017\u65f6（\u8981\u8fdb\u884c TCP \u4e09\u6b21\u63e1\u624b\u7b49）\u3002<\/p>\n
\u4eab\u5143\u6a21\u5f0f\u7684\u6838\u5fc3\u601d\u60f3\u5c31\u662f：\u5bf9\u8c61\u590d\u7528（\u63d0\u524d\u5efa\u597d，\u501f\u6765\u501f\u53bb）\u3002 \u5bf9\u5e94\u5230\u4ee3\u7801\u91cc：<\/p>\n
\u65e2\u7136\u662f\u5171\u4eab\u5145\u7535\u5b9d，\u5047\u8bbe\u73b0\u5728\u6709\u4e24\u4e2a\u7ebf\u7a0b（\u5f20\u4e09\u548c\u674e\u56db）\u540c\u65f6\u6765\u501f\u5145\u7535\u5b9d\u3002\u5982\u679c\u6211\u4eec\u7528 synchronized \u52a0\u9501，\u90a3\u5c31\u662f\u5f20\u4e09\u5148\u501f，\u674e\u56db\u5728\u540e\u9762\u6392\u961f\u5e72\u7b49（\u963b\u585e）\u3002<\/p>\n
\u600e\u4e48\u505a\u5230\u4e0d\u6392\u961f（\u65e0\u9501）\u5462？\u9760\u7684\u662f **borrow()** \u65b9\u6cd5\u91cc\u7684\u81ea\u65cb + CAS\u3002<\/p>\n
\u6211\u4eec\u6765\u770b\u5f20\u4e09\u501f\u5145\u7535\u5b9d\u7684\u52a8\u4f5c\u62c6\u89e3（\u770b borrow \u65b9\u6cd5）：<\/p>\n
\u4e0b\u9762\u6211\u7ed3\u5408 CAS \u548c\u539f\u5b50\u6570\u7ec4 AtomicIntegerArray，\u624b\u5199\u4e00\u4e2a\u6781\u7b80\u7684\u65e0\u9501\u6570\u636e\u5e93\u8fde\u63a5\u6c60，\u4f53\u4f1a\u4e00\u4e0b\u5982\u4f55\u65e0\u9501\u5316\u5730\u7ba1\u7406\u5171\u4eab\u8d44\u6e90：<\/p>\n
Java<\/p>\n
class MockConnectionPool {
\n private final Connection[] connections;
\n \/\/ \u72b6\u6001\u6570\u7ec4：0\u8868\u793a\u7a7a\u95f2，1\u8868\u793a\u7e41\u5fd9\u3002\u4f7f\u7528\u539f\u5b50\u6570\u7ec4\u4fdd\u8bc1\u5e76\u53d1\u5b89\u5168
\n private final AtomicIntegerArray states; <\/p>\n
public MockConnectionPool(int poolSize) {
\n connections = new Connection[poolSize];
\n states = new AtomicIntegerArray(poolSize); \/\/ \u9ed8\u8ba4\u5168\u4e3a0
\n for (int i = 0; i < poolSize; i++) {
\n connections[i] = new MockConnection(); \/\/ \u63d0\u524d\u521b\u5efa\u597d\u5bf9\u8c61（\u4eab\u5143）
\n }
\n }<\/p>\n
\/\/ \u501f\u51fa\u8fde\u63a5
\n public Connection borrow() {
\n while (true) { \/\/ \u81ea\u65cb\u5c1d\u8bd5
\n for (int i = 0; i < states.length(); i++) {
\n if (states.get(i) == 0) {
\n \/\/ CAS\u5c1d\u8bd5\u5c06\u72b6\u6001\u4ece0\u6539\u4e3a1，\u6210\u529f\u5219\u4ee3\u8868\u62ff\u5230\u4e86\u8fde\u63a5
\n if (states.compareAndSet(i, 0, 1)) {
\n return connections[i];
\n }
\n }
\n }
\n \/\/ \u515c\u5e95：\u5982\u679c\u6ca1\u6709\u7a7a\u95f2\u8fde\u63a5，\u53ef\u4ee5\u9009\u62e9\u4f11\u7720\/\u963b\u585e\u7b49\u5f85…
\n }
\n }<\/p>\n
\/\/ \u5f52\u8fd8\u8fde\u63a5
\n public void free(Connection conn) {
\n for (int i = 0; i < connections.length; i++) {
\n if (connections[i] == conn) {
\n states.set(i, 0); \/\/ \u5f52\u8fd8，\u56e0\u4e3a\u662f\u88ab\u5f53\u524d\u7ebf\u7a0b\u72ec\u5360，\u6240\u4ee5\u76f4\u63a5set\u4e3a0\u5373\u53ef
\n break;
\n }
\n }
\n }
\n}<\/p>\n
\u901a\u8fc7\u8fd9\u79cd\u65b9\u5f0f，\u6211\u4eec\u4e0d\u4ec5\u590d\u7528\u4e86\u5bf9\u8c61，\u8fd8\u901a\u8fc7 CAS \u64cd\u4f5c\u5b8c\u7f8e\u907f\u5f00\u4e86\u91cd\u91cf\u7ea7\u7684\u963b\u585e\u9501，\u5927\u5e45\u63d0\u5347\u4e86\u5e76\u53d1\u6027\u80fd\u3002\u4e4b\u540e\u6211\u4eec\u5c06\u4ecb\u7ecd\u53e6\u4e00\u79cd\u66f4\u52a0\u5f7b\u5e95\u7684\u65e0\u9501\u601d\u8def（ThreadLocal）\u2014\u2014\u65e2\u7136\u5171\u4eab\u8fd9\u4e48\u9ebb\u70e6，\u5e72\u8106\u5c31\u4e0d\u5171\u4eab\u4e86！<\/p>\n
\u5982\u679c\u7528\u4e00\u53e5\u8bdd\u6765\u603b\u7ed3\u5b83\u4eec\u7684\u672c\u8d28\u533a\u522b： Synchronized \u662f\u201c\u4ee5\u65f6\u95f4\u6362\u7a7a\u95f4\u201d（\u5927\u5bb6\u6392\u961f\u53bb\u62ff\u540c\u4e00\u4e2a\u6587\u5177\u76d2\u91cc\u7684\u7b14，\u6162\u4f46\u7701\u7b14），\u800c ThreadLocal \u662f\u201c\u4ee5\u7a7a\u95f4\u6362\u65f6\u95f4\u201d（\u6211\u7ed9\u6bcf\u4e2a\u4eba\u53e3\u888b\u91cc\u90fd\u585e\u4e00\u652f\u4e13\u5c5e\u7684\u7b14，\u4e0d\u7528\u62a2，\u5feb\u4f46\u8d39\u7b14）\u3002<\/p>\n
ThreadLocal \u538b\u6839\u4e0d\u662f\u4e3a\u4e86\u89e3\u51b3\u201c\u591a\u7ebf\u7a0b\u5171\u4eab\u53d8\u91cf\u201d\u7684\u5e76\u53d1\u95ee\u9898，\u800c\u662f\u4e3a\u4e86\u5b9e\u73b0\u7ebf\u7a0b\u7ea7\u7684\u6570\u636e\u9694\u79bb\u3002<\/p>\n
\u5728\u5b9e\u9645\u4e1a\u52a1\u5f00\u53d1\u4e2d，ThreadLocal \u7684 API \u975e\u5e38\u5e72\u51c0\u5229\u843d\u3002\u6211\u4eec\u5c31\u56db\u4e2a\u5e38\u7528\u65b9\u6cd5：set()\u3001get()\u3001remove() \u548c\u91cd\u5199\u521d\u59cb\u503c\u7684 initialValue()\u3002<\/p>\n
\u65e5\u5e38\u5f00\u53d1\u4e2d，\u6211\u4eec\u901a\u5e38\u62ff\u5b83\u5e72\u8fd9\u4e09\u4ef6\u4e8b：<\/p>\n
\u6781\u7b80\u4ee3\u7801\u793a\u8303：<\/p>\n
Java<\/p>\n
public class ThreadLocalDemo {
\n \/\/ \u8fd9\u5c31\u662f\u4e00\u4e2a\u201c\u9b54\u6cd5\u50a8\u7269\u67dc\u201d
\n static ThreadLocal<String> tl = new ThreadLocal<>();<\/p>\n
public static void main(String[] args) {<\/p>\n
\/\/ \u5f20\u4e09\u7ebf\u7a0b
\n new Thread(() -> {
\n tl.set("\u82f9\u679c"); \/\/ \u5f20\u4e09\u5f80\u67dc\u5b50\u91cc\u653e\u4e86\u82f9\u679c
\n try { Thread.sleep(2000); } catch (Exception e) {} \/\/ \u7761\u4e00\u4f1a，\u7b49\u674e\u56db\u653e\u5b8c
\n System.out.println("\u5f20\u4e09\u62ff\u5230\u4e86: " + tl.get()); \/\/ \u6253\u5370：\u5f20\u4e09\u62ff\u5230\u4e86: \u82f9\u679c
\n }, "\u5f20\u4e09").start();<\/p>\n
\/\/ \u674e\u56db\u7ebf\u7a0b
\n new Thread(() -> {
\n tl.set("\u9999\u8549"); \/\/ \u674e\u56db\u5f80\u540c\u4e00\u53f0\u67dc\u5b50\u91cc\u653e\u4e86\u9999\u8549
\n System.out.println("\u674e\u56db\u62ff\u5230\u4e86: " + tl.get()); \/\/ \u6253\u5370：\u674e\u56db\u62ff\u5230\u4e86: \u9999\u8549
\n }, "\u674e\u56db").start();
\n }
\n}<\/p>\n
\u4e3a\u4ec0\u4e48\u8bf4\u5b83\u662f\u5404\u5bb6\u81ea\u626b\u95e8\u524d\u96ea？<\/p>\n
\u56e0\u4e3a _ThreadLocal_ \u5176\u5b9e\u662f\u4e2a\u201c\u76ae\u5305\u516c\u53f8\u201d\u3002\u5f53\u4f60\u8c03\u7528 _tl.set("\u82f9\u679c")_ \u7684\u65f6\u5019，_ThreadLocal__ \u5e76\u6ca1\u6709\u628a\u201c\u82f9\u679c\u201d\u5b58\u5728\u81ea\u5df1\u809a\u5b50\u91cc，\u800c\u662f_\u6084\u6084\u6252\u5f00\u4e86\u5f53\u524d\u7ebf\u7a0b（\u5f20\u4e09）\u7684\u53e3\u888b，\u628a\u201c\u82f9\u679c\u201d\u585e\u8fdb\u4e86\u5f20\u4e09\u81ea\u5df1\u7684\u53e3\u888b\u91cc\u3002<\/p>\n
\u5728 JDK 8 \u524d\u540e，ThreadLocal \u7684\u5e95\u5c42\u6570\u636e\u7ed3\u6784\u53d1\u751f\u4e86\u4e00\u6b21\u6781\u5176\u5173\u952e\u7684\u201c\u4e7e\u5764\u5927\u632a\u79fb\u201d，\u8fd9\u662f\u5927\u5382\u9762\u8bd5\u7684\u8d85\u7ea7\u9ad8\u9891\u8003\u70b9\u3002<\/p>\n
💡****JDK 8 \u4e3a\u4ec0\u4e48\u8981\u53cd\u8f6c ThreadLocalMap \u7684\u8bbe\u8ba1？<\/p>\n
\u9762\u8bd5\u5b98：\u6211\u770b\u4f60\u7b80\u5386\u4e0a\u5199\u4e86\u719f\u6089\u5e76\u53d1\u7f16\u7a0b\u3002\u90a3\u4f60\u8bf4\u8bf4，\u4e3a\u4ec0\u4e48\u73b0\u5728\u7684 Java \u7248\u672c，\u8981\u628a ThreadLocalMap \u6302\u5728 Thread \u8eab\u4e0a，\u800c\u4e0d\u662f\u50cf\u4ee5\u524d\u90a3\u6837\u6302\u5728 ThreadLocal \u8eab\u4e0a？<\/p>\n
\u56de\u7b54： Doug Lea \u5927\u795e\u8fd9\u6837\u6539，\u6838\u5fc3\u662f\u4e3a\u4e86\u89e3\u51b3\u6027\u80fd\u548c\u5185\u5b58\u751f\u547d\u5468\u671f\u4e24\u5927\u75db\u70b9：<\/p>\n
\u65e2\u7136\u524d\u4e00\u7ae0\u8bf4\u4e86，ThreadLocalMap \u662f\u5f53\u524d\u7ebf\u7a0b\u53e3\u888b\u91cc\u7684\u5c0f\u8d26\u672c，\u90a3\u5b83\u662f\u600e\u4e48\u8bb0\u8d26\u7684\u5462？ \u5b83\u5176\u5b9e\u662f\u4e00\u4e2a\u6781\u5176\u7b80\u5355\u7684 Entry[] \u6570\u7ec4\u3002\u6ca1\u6709\u50cf HashMap \u90a3\u6837\u590d\u6742\u7684\u94fe\u8868\u548c\u7ea2\u9ed1\u6811\u3002<\/p>\n
**\u6590\u6ce2\u90a3\u5951\u6563\u5217：\u795e\u5947\u7684\u9b54\u6570 ****0x61c88647** \u6bcf\u6b21\u6211\u4eec\u521b\u5efa\u4e00\u4e2a\u65b0\u7684 ThreadLocal，\u5b83\u5185\u90e8\u5c31\u4f1a\u5206\u914d\u4e00\u4e2a Hash \u503c\u3002\u6e90\u7801\u91cc\u662f\u8fd9\u4e48\u5199\u7684：<\/p>\n
Java<\/p>\n
\/\/ \u6bcf\u6b21\u521b\u5efa\u5bf9\u8c61，\u7d2f\u52a0\u8fd9\u4e2a\u9b54\u6570
\nprivate static final int HASH_INCREMENT = 0x61c88647;
\nprivate static int nextHashCode() {
\n return nextHashCode.getAndAdd(HASH_INCREMENT);
\n}<\/p>\n
\u8fd9\u4e2a\u9b54\u6570 0x61c88647 \u662f\u6590\u6ce2\u90a3\u5951\u6570（\u9ec4\u91d1\u5206\u5272\u6570）\u7684\u4e00\u4e2a\u53d8\u79cd\u3002\u4e00\u53e5\u8bdd\u8bb2\u660e\u767d\u5b83\u7684\u4f5c\u7528：\u65e0\u8bba\u521b\u5efa\u591a\u5c11\u4e2a **ThreadLocal**，\u6bcf\u6b21\u628a\u8fd9\u4e2a Hash \u503c\u548c\u6570\u7ec4\u5927\u5c0f（2\u7684n\u6b21\u5e42）\u505a\u4f4d\u8fd0\u7b97\u540e，\u90fd\u80fd\u6781\u5176\u5747\u5300\u5730\u6563\u5e03\u5728\u6570\u7ec4\u4e2d，\u6781\u5927\u5730\u51cf\u5c11\u4e86 Hash \u51b2\u7a81\u3002<\/p>\n
\u7ebf\u6027\u63a2\u6d4b\u6cd5：\u627e\u5ea7\u4f4d\u7684\u54f2\u5b66 \u867d\u7136\u6563\u5217\u5747\u5300，\u4f46\u51b2\u7a81\u8fd8\u662f\u4e0d\u53ef\u907f\u514d\u7684\u3002HashMap \u9047\u5230\u51b2\u7a81\u662f\u5728\u539f\u4f4d\u7f6e\u6302\u4e2a\u94fe\u8868（\u62c9\u94fe\u6cd5），\u800c ThreadLocalMap \u91c7\u7528\u7684\u662f\u7ebf\u6027\u63a2\u6d4b\u6cd5（\u5f00\u653e\u5bfb\u5740\u6cd5）\u3002<\/p>\n
\u6253\u4e2a\u6bd4\u65b9：\u4f60\u53bb\u7535\u5f71\u9662\u627e\u5ea7\u4f4d（\u7ecf\u8fc7 Hash \u8ba1\u7b97\u4f60\u662f 5 \u53f7\u5ea7）\u3002<\/p>\n
\u8fd9\u5957\u673a\u5236\u7684\u4ee3\u7801\u5f02\u5e38\u7cbe\u7b80：<\/p>\n
Java<\/p>\n
private void set(ThreadLocal<?> key, Object value) {
\n \/\/ 1. \u628a\u5c0f\u8d26\u672c\u62ff\u51fa\u6765
\n Entry[] tab = table; <\/p>\n
\/\/ 2. \u3010\u8ba1\u7b97\u5ea7\u4f4d\u53f7\u3011
\n \/\/ \u7528 ThreadLocal \u7684 hash \u503c\u548c\u6570\u7ec4\u957f\u5ea6\u505a\u4f4d\u8fd0\u7b97（\u76f8\u5f53\u4e8e\u53d6\u6a21）
\n \/\/ \u5047\u8bbe\u7b97\u51fa\u6765 i = 1
\n int i = key.threadLocalHashCode & (tab.length – 1);<\/p>\n
\/\/ 3. \u3010\u627e\u5ea7\u4f4d\u5faa\u73af\u3011
\n \/\/ \u8d70\u5230\u7b2c i \u4e2a\u5ea7\u4f4d（\u6b64\u65f6 i=1），\u770b\u770b\u6709\u6ca1\u6709\u4eba\u5750\u7740\u3002
\n \/\/ \u5982\u679c e != null（\u6709\u4eba\u5750），\u5c31\u8fdb\u5165\u5faa\u73af\u4f53；\u5982\u679c e == null（\u6ca1\u4eba\u5750），\u76f4\u63a5\u8df3\u51fa\u5faa\u73af！
\n \/\/ \u6bcf\u6b21\u5faa\u73af\u7ed3\u675f，i \u5c31\u4f1a\u901a\u8fc7 nextIndex \u5f80\u540e\u632a\u4e00\u4f4d（1\u53d8\u62102，2\u53d8\u62103…）
\n for (Entry e = tab[i]; e != null; e = tab[i = nextIndex(i, len)]) {<\/p>\n
\/\/ — \u5faa\u73af\u4f53\u5185\u90e8 —<\/p>\n
\/\/ \u53d1\u73b0\u5ea7\u4f4d\u4e0a\u6709\u4eba\u3002\u770b\u770b\u8fd9\u4e2a\u4eba\u7684 Key \u662f\u4e0d\u662f\u6211\u81ea\u5df1？
\n if (e.get() == key) {
\n \/\/ \u54ce\u5440，\u539f\u6765\u662f\u6211\u81ea\u5df1\u4e4b\u524d\u5360\u7684\u5ea7！
\n \/\/ \u8bf4\u660e\u6211\u662f\u6765\u66f4\u65b0\u6570\u636e\u7684，\u76f4\u63a5\u628a\u65e7 Value \u66ff\u6362\u6210\u65b0 Value
\n e.value = value;
\n return; \/\/ \u641e\u5b9a，\u4e0b\u73ed！
\n }<\/p>\n
\/\/ \u5982\u679c e.get() != key，\u8bf4\u660e\u5ea7\u4f4d\u4e0a\u5750\u7684\u662f\u522b\u4eba（\u6bd4\u5982 ThreadLocal A）\u3002
\n \/\/ \u8fd9\u5c31\u662f\u53d1\u751f\u4e86\u3010Hash\u51b2\u7a81\u3011！
\n \/\/ \u90a3\u600e\u4e48\u529e？\u5565\u4e5f\u4e0d\u5e72，\u987a\u7740 for \u5faa\u73af\u7684 e = tab[i = nextIndex(i, len)]，
\n \/\/ \u8d70\u5230\u4e0b\u4e00\u4e2a\u5ea7\u4f4d（i=2）\u7ee7\u7eed\u770b！
\n }<\/p>\n
\/\/ 4. \u3010\u843d\u5ea7\u3011
\n \/\/ \u80fd\u8d70\u5230\u8fd9\u91cc，\u8bf4\u660e for \u5faa\u73af\u78b0\u5230\u4e86 e == null \u7684\u60c5\u51b5，\u8df3\u51fa\u4e86\u5faa\u73af\u3002
\n \/\/ \u4e5f\u5c31\u662f\u627e\u5230\u4e86\u4e00\u4e2a\u3010\u7a7a\u5ea7\u4f4d\u3011\u3002
\n \/\/ \u90a3\u5c31\u76f4\u63a5 new \u4e00\u4e2a\u65b0\u7684 Entry，\u4e00\u5c41\u80a1\u5750\u4e0b\u53bb！
\n tab[i] = new Entry(key, value);<\/p>\n
\/\/ … \u68c0\u67e5\u9700\u4e0d\u9700\u8981\u6269\u5bb9（\u6682\u4e0d\u5c55\u5f00）
\n}<\/p>\n
\u4e3a\u4ec0\u4e48\u4e0d\u7528\u94fe\u8868？<\/p>\n
\u4e0d\u7528\u94fe\u8868，\u662f\u56e0\u4e3a ThreadLocal \u6570\u91cf\u5c11\u4e14 Hash \u5206\u5e03\u5747\u5300，\u51b2\u7a81\u6781\u5c11；\u800c\u5728\u51b2\u7a81\u6781\u5c11\u7684\u524d\u63d0\u4e0b，\u8fde\u7eed\u6570\u7ec4\u5e26\u6765\u7684 CPU \u9ad8\u901f\u7f13\u5b58\u547d\u4e2d\u7387 \u548c \u6781\u7b80\u7684\u5783\u573e\u6e05\u7406\u903b\u8f91，\u8ba9\u7ebf\u6027\u63a2\u6d4b\u6cd5\u6210\u4e3a\u4e86\u8fd9\u4e2a\u573a\u666f\u4e0b\u78be\u538b\u94fe\u8868\u7684\u6700\u4f18\u89e3\u3002<\/p>\n
\u8fd9\u662f\u5168\u7bc7\u7684\u6700\u9ad8\u6f6e\u3002\u5982\u679c\u9762\u8bd5\u5b98\u95ee ThreadLocal，\u8fd9\u9053\u9898\u7684\u51fa\u73b0\u6982\u7387\u662f 100%\u3002<\/p>\n
\u5728 ThreadLocalMap \u4e2d，Entry \u7684\u5b9a\u4e49\u662f\u8fd9\u6837\u7684：<\/p>\n
Java<\/p>\n
\/\/ Entry \u7ee7\u627f\u4e86 WeakReference，\u8fd9\u610f\u5473\u7740\u5b83\u7684 Key (ThreadLocal) \u662f\u4e00\u4e2a\u5f31\u5f15\u7528
\nstatic class Entry extends WeakReference<ThreadLocal<?>> {
\n Object value; \/\/ Value \u4f9d\u7136\u662f\u5f3a\u5f15\u7528
\n Entry(ThreadLocal<?> k, Object v) {
\n super(k);
\n value = v;
\n }
\n}<\/p>\n
\u4e3a\u4ec0\u4e48 Key \u8981\u8bbe\u8ba1\u6210\u5f31\u5f15\u7528？\u5f3a\u5f15\u7528\u4e0d\u884c\u5417？ \u5047\u8bbe\u6211\u4eec\u5728\u4e1a\u52a1\u4ee3\u7801\u91cc\u5199\u4e86 ThreadLocal tl = new ThreadLocal()\u3002\u5f53\u4e1a\u52a1\u7ed3\u675f，\u6211\u4eec\u628a tl = null，\u672c\u610f\u662f\u5e0c\u671b\u56de\u6536\u8fd9\u4e2a\u5bf9\u8c61\u3002<\/p>\n
\u81f4\u547d\u7684\u6cc4\u6f0f\u6210\u56e0\u5256\u6790 Key \u53d8\u6210 null \u597d\u50cf\u5f88\u5b8c\u7f8e？\u5927\u9519\u7279\u9519！\u8fd9\u4e5f\u662f\u5927\u5382\u6781\u5176\u5bb9\u6613\u8e29\u5751\u7684\u5730\u65b9\u3002<\/p>\n
\u770b\u770b\u73b0\u5728\u7684\u5f15\u7528\u94fe： CurrentThread -> ThreadLocalMap -> Entry -> Value \u8fd9\u6761\u94fe\u4e0a\u5168\u90e8\u90fd\u662f\u5f3a\u5f15\u7528！<\/p>\n
\u867d\u7136 Key \u88ab\u56de\u6536\u53d8\u6210\u4e86 null（\u8fd9\u79cd Entry \u88ab\u79f0\u4e3a\u810f\u6570\u636e Stale Entry），\u4f46\u662f Value \u4f9d\u7136\u88ab\u5f3a\u5f15\u7528\u7740\u3002\u5728\u73b0\u4ee3\u67b6\u6784\u4e2d，\u6211\u4eec\u57fa\u672c\u90fd\u5728\u4f7f\u7528\u7ebf\u7a0b\u6c60，\u6838\u5fc3\u7ebf\u7a0b\u662f\u4e0d\u4f1a\u88ab\u9500\u6bc1\u7684\u3002 \u8fd9\u5c31\u610f\u5473\u7740，\u53ea\u8981\u7ebf\u7a0b\u5728\u6c60\u5b50\u91cc\u4e0d\u9500\u6bc1，\u8fd9\u4e2a Value \u7684\u5f3a\u5f15\u7528\u94fe\u5c31\u4e00\u76f4\u65ad\u4e0d\u6389，\u6c38\u8fdc\u65e0\u6cd5\u88ab GC \u751a\u81f3\u4f1a\u8d8a\u5806\u8d8a\u591a，\u6700\u7ec8\u5bfc\u81f4 OOM（\u5185\u5b58\u6ea2\u51fa）\u3002<\/p>\n
💡** \u9762\u8bd5\u5b98**：\u65e2\u7136\u8bbe\u8ba1\u6210\u5f31\u5f15\u7528\u8fd8\u662f\u4f1a\u5bfc\u81f4 Value \u6cc4\u6f0f，\u90a3\u515c\u4e86\u4e00\u5927\u5708，Doug Lea \u628a Key \u8bbe\u8ba1\u6210\u5f31\u5f15\u7528\u7684\u610f\u4e49\u5230\u5e95\u662f\u4ec0\u4e48？\u4e24\u8fb9\u4e0d\u90fd\u662f\u5751\u5417？<\/p>\n
\u56de\u7b54：\u8fd9\u662f\u5178\u578b\u7684\u201c\u4e24\u5bb3\u76f8\u6743\u53d6\u5176\u8f7b\u201d\u3002 \u5982\u679c\u7528\u5f3a\u5f15\u7528，\u90a3\u4e48 Key \u548c Value \u4e00\u5b9a\u4f1a\u4e00\u8d77\u6cc4\u6f0f，\u4e14\u5e95\u5c42\u6beb\u65e0\u529e\u6cd5\u3002 \u4f46\u7528\u4e86\u5f31\u5f15\u7528，\u867d\u7136 Value \u4f1a\u6cc4\u6f0f，\u4f46\u81f3\u5c11 Key \u88ab\u56de\u6536\u4e86，\u8fd9\u5c31\u7ed9\u5e95\u5c42\u7559\u4e0b\u4e86\u4e00\u4e2a\u660e\u663e\u7684\u6807\u8bb0（Key \u4e3a null）\u3002Doug Lea \u6b63\u662f\u5229\u7528\u8fd9\u4e2a\u201c\u6807\u8bb0\u201d，\u5728 ThreadLocal \u7684 get()\u3001set() \u64cd\u4f5c\u4e2d，\u57cb\u5165\u4e86\u987a\u624b\u6e05\u7406\u201c\u810f\u6570\u636e\u201d（Key \u4e3a null \u7684 Entry）\u7684\u903b\u8f91\u3002\u5f31\u5f15\u7528\u76f8\u5f53\u4e8e\u4e3a\u5f00\u53d1\u8005\u5fd8\u8bb0\u624b\u52a8 remove() \u63d0\u4f9b\u4e86\u6700\u540e\u4e00\u9053\u9632\u7ebf\u3002<\/p>\n
🚨** \u771f\u5b9e\u4e1a\u52a1\u9632\u5751\u6307\u5357** \u4e0d\u8981\u8fc7\u4e8e\u8ff7\u4fe1\u5e95\u5c42\u7684\u201c\u987a\u624b\u6e05\u7406\u201d，\u56e0\u4e3a\u5982\u679c\u4f60\u540e\u7eed\u4e0d\u518d\u8c03\u7528\u8fd9\u4e2a\u7ebf\u7a0b\u7684 get\/set，\u6e05\u7406\u903b\u8f91\u538b\u6839\u4e0d\u4f1a\u89e6\u53d1\u3002 \u6700\u89c4\u8303\u3001\u552f\u4e00\u5b89\u5168\u7684\u5199\u6cd5：\u5728\u6bcf\u6b21\u4f7f\u7528\u5b8c ThreadLocal \u540e，\u52a1\u5fc5\u5728 finally \u5757\u4e2d\u8c03\u7528 remove()！\u8fd9\u5c31\u597d\u6bd4\u4f60\u501f\u4e86\u516c\u53f8\u7684\u516c\u8f66，\u4e0b\u73ed\u524d\u5fc5\u987b\u62d4\u6389\u8f66\u94a5\u5319\u8fd8\u56de\u8f66\u5e93\u3002<\/p>\n
Java<\/p>\n
\/\/ \u6781\u5176\u91cd\u8981\u7684\u4e1a\u52a1\u89c4\u8303
\ntry {
\n threadLocal.set(user);
\n \/\/ \u6267\u884c\u4e1a\u52a1\u903b\u8f91…
\n} finally {
\n threadLocal.remove(); \/\/ \u5f3a\u5236\u624b\u52a8\u6e05\u7406！
\n}<\/p>\n
\u521a\u624d\u63d0\u5230，\u5e95\u5c42\u7684 set() \u548c get() \u4f1a\u201c\u987a\u624b\u6e05\u7406\u201d\u810f\u6570\u636e\u3002\u5982\u679c\u4f60\u80fd\u7ed9\u9762\u8bd5\u5b98\u8bb2\u6e05\u695a\u8fd9\u4e2a\u673a\u5236，\u606d\u559c\u4f60，\u4f60\u7684 Offer \u5df2\u7ecf\u7a33\u4e86\u3002<\/p>\n
\u6e05\u7406\u4e3b\u8981\u9760\u4e24\u4e2a\u6838\u5fc3\u65b9\u6cd5\u76f8\u4e92\u914d\u5408：\u63a2\u6d4b\u5f0f\u6e05\u7406 (**expungeStaleEntry**) \u548c \u542f\u53d1\u5f0f\u6e05\u7406 (**cleanSomeSlots**)\u3002<\/p>\n
\u63a2\u6d4b\u5f0f\u6e05\u7406（\u6e05\u9053\u592b\u626b\u5927\u8857）： \u5f53\u4f60\u5728\u904d\u5386\u6570\u7ec4\u627e\u5ea7\u4f4d\u65f6，\u5982\u679c\u53d1\u73b0\u4e86\u4e00\u4e2a Key == null \u7684\u810f Entry，\u7cfb\u7edf\u4f1a\u7acb\u523b\u5316\u8eab\u6e05\u9053\u592b\u3002<\/p>\n
\u542f\u53d1\u5f0f\u6e05\u7406（\u968f\u624b\u6254\u5783\u573e）： \u5728 set() \u6210\u529f\u6dfb\u52a0\u4e00\u4e2a\u65b0\u5143\u7d20\u540e，\u7cfb\u7edf\u4e0d\u4f1a\u5168\u76d8\u626b\u63cf（\u592a\u8017\u6027\u80fd），\u800c\u662f\u505a\u4e00\u6b21\u5bf9\u6570\u7ea7\u522b（O(logN)）\u7684\u8f7b\u91cf\u7ea7\u626b\u63cf\u3002\u5982\u679c\u626b\u5230\u4e86\u810f\u6570\u636e，\u5c31\u5524\u9192\u201c\u63a2\u6d4b\u5f0f\u6e05\u7406\u201d\u53bb\u5927\u5e72\u4e00\u573a；\u5982\u679c\u8fde\u7eed\u626b\u4e86\u51e0\u6b21\u90fd\u6ca1\u53d1\u73b0\u810f\u6570\u636e，\u5c31\u8ba4\u4e3a\u5f53\u524d\u73af\u5883\u6bd4\u8f83\u5e72\u51c0，\u76f4\u63a5\u4e0b\u73ed\u3002<\/p>\n
\u8fd9\u79cd**\u201c\u5728\u5e73\u65f6\u8bfb\u5199\u64cd\u4f5c\u4e2d\u5939\u5e26\u79c1\u8d27\u8fdb\u884c\u8f7b\u91cf\u7ea7\u6e05\u7406\u201d**\u7684\u7cbe\u5999\u8bbe\u8ba1，\u5145\u5206\u4f53\u73b0\u4e86\u5e76\u53d1\u5927\u5e08\u5bf9\u4e8e\u6027\u80fd\u548c\u5185\u5b58\u5e73\u8861\u7684\u6781\u81f4\u8ffd\u6c42\u3002<\/p>\n
**\u603b\u7ed3：**ThreadLocal \u7684\u5f31\u5f15\u7528\u662f\u4e3a\u4e86\u5728\u5f00\u53d1\u8005\u5fd8\u8bb0 remove \u65f6，\u901a\u8fc7 GC \u5c06 Key \u7f6e\u4e3a null \u7559\u4e0b\u8bb0\u53f7，\u4f7f\u5f97\u540e\u7eed\u8c03\u7528 get\/set \u65f6\u80fd\u89e6\u53d1\u5e95\u5c42\u88ab\u52a8\u6e05\u7406 Value\u3002\u4f46\u5728\u7ebf\u7a0b\u6c60\u73af\u5883\u4e0b，\u7531\u4e8e\u7ebf\u7a0b\u590d\u7528\u4e14\u4e0d\u4e00\u5b9a\u518d\u6b21\u8c03\u7528 get\/set，\u8fd9\u79cd\u88ab\u52a8\u6e05\u7406\u5e76\u4e0d\u53ef\u9760，\u5fc5\u987b\u5728\u4e1a\u52a1 finally \u5757\u4e2d\u4e3b\u52a8\u8c03\u7528 remove() \u624d\u662f\u9632\u6cc4\u6f0f\u7684\u6839\u672c\u65b9\u6848\u3002<\/p>\n
\u4e3a\u4e86\u89e3\u51b3\u7236\u5b50\u7ebf\u7a0b\u4e4b\u95f4\u7684\u6570\u636e\u4f20\u9012，JDK \u5b98\u65b9\u63d0\u4f9b\u4e86\u4e00\u4e2a ThreadLocal \u7684\u5b50\u7c7b：**InheritableThreadLocal**（\u53ef\u7ee7\u627f\u7684\u672c\u5730\u7ebf\u7a0b\u53d8\u91cf）\u3002<\/p>\n
\u6253\u4e2a\u6bd4\u65b9：\u5f20\u4e09（\u7236\u7ebf\u7a0b）\u81ea\u5df1\u6709\u4e2a\u5c0f\u8d26\u672c，\u4eca\u5929\u4ed6\u62db\u4e86\u4e2a\u52a9\u7406（\u5b50\u7ebf\u7a0b）\u3002\u4e3a\u4e86\u8ba9\u52a9\u7406\u80fd\u63a5\u624b\u5de5\u4f5c，\u5f20\u4e09\u5728**\u529e\u7406\u5165\u804c（\u521b\u5efa\u5b50\u7ebf\u7a0b）**\u7684\u65f6\u5019，\u7279\u610f\u53bb\u590d\u5370\u4e86\u4e00\u4efd\u81ea\u5df1\u7684\u8d26\u672c，\u585e\u8fdb\u4e86\u52a9\u7406\u7684\u53e3\u888b\u91cc\u3002<\/p>\n
\u7528\u6cd5\u6781\u5176\u7b80\u5355，\u53ea\u9700\u8981\u628a ThreadLocal \u66ff\u6362\u6210 InheritableThreadLocal \u5373\u53ef：<\/p>\n
Java<\/p>\n
public class ITLDemo {
\n static InheritableThreadLocal<String> itl = new InheritableThreadLocal<>();<\/p>\n
public static void main(String[] args) {
\n itl.set("\u7236\u7ebf\u7a0b\u7684TraceId-10086");<\/p>\n
\/\/ \u5f00\u542f\u5b50\u7ebf\u7a0b
\n new Thread(() -> {
\n \/\/ \u5b50\u7ebf\u7a0b\u795e\u5947\u5730\u62ff\u5230\u4e86\u7236\u7ebf\u7a0b\u7684\u6570\u636e！
\n System.out.println("\u5b50\u7ebf\u7a0b\u83b7\u53d6: " + itl.get());
\n }).start();
\n }
\n}<\/p>\n
\u5e95\u5c42\u662f\u600e\u4e48\u505a\u5230\u7684？<\/p>\n
\u79d8\u5bc6\u5c31\u85cf\u5728 new Thread() \u7684\u521d\u59cb\u5316\u6e90\u7801\u91cc\u3002\u5728 Thread \u7c7b\u4e2d，\u9664\u4e86\u6211\u4eec\u8bb2\u7684 threadLocals \u5c5e\u6027\u5916，\u8fd8\u6709\u4e00\u4e2a\u4e13\u95e8\u7528\u6765\u505a\u7236\u5b50\u900f\u4f20\u7684\u5c5e\u6027 inheritableThreadLocals\u3002<\/p>\n
\u5f53\u6211\u4eec\u521b\u5efa\u4e00\u4e2a\u65b0\u7ebf\u7a0b\u65f6，\u5e95\u5c42\u5fc5\u7136\u4f1a\u8c03\u7528 Thread#init \u65b9\u6cd5：<\/p>\n
Java<\/p>\n
\/\/ Thread \u7c7b\u521d\u59cb\u5316\u6e90\u7801（\u6781\u7b80\u7248）
\nprivate void init(ThreadGroup g, Runnable target, String name, long stackSize, AccessControlContext acc, boolean inheritThreadLocals) {
\n \/\/ 1. \u83b7\u53d6\u5f53\u524d\u6b63\u5728\u6267\u884c\u7684\u7ebf\u7a0b（\u4e5f\u5c31\u662f\u5373\u5c06\u4f5c\u4e3a\u7236\u7ebf\u7a0b\u7684\u90a3\u4e2a\u7ebf\u7a0b）
\n Thread parent = currentThread();<\/p>\n
\/\/ 2. \u5982\u679c\u7236\u7ebf\u7a0b\u7684 inheritableThreadLocals \u4e0d\u4e3a\u7a7a，\u8bf4\u660e\u6709\u6570\u636e\u9700\u8981\u5411\u4e0b\u4f20
\n if (inheritThreadLocals && parent.inheritableThreadLocals != null) {
\n \/\/ 3. \u6838\u5fc3\u5927\u62db：\u521b\u5efa\u5b50\u7ebf\u7a0b\u7684 Map，\u5e76\u628a\u7236\u7ebf\u7a0b Map \u91cc\u7684 Entry \u9010\u4e2a\u590d\u5236\u8fc7\u6765！
\n this.inheritableThreadLocals = ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);
\n }
\n}<\/p>\n
\u7b80\u5355\u6765\u8bf4，\u5c31\u662f\u5728\u521b\u5efa\u5b50\u7ebf\u7a0b\u7684\u90a3\u4e00\u77ac\u95f4，JVM \u987a\u624b\u628a\u7236\u7ebf\u7a0b InheritableThreadLocal \u91cc\u7684\u6570\u636e\u6d45\u62f7\u8d1d\u4e86\u4e00\u4efd\u7ed9\u5b50\u7ebf\u7a0b\u3002<\/p>\n
InheritableThreadLocal \u770b\u8d77\u6765\u5f88\u7f8e，\u4f46\u5728\u73b0\u4ee3 Java \u5f00\u53d1\u4e2d，\u6211\u4eec\u51e0\u4e4e\u4e0d\u4f1a\u7528\u5b83\u3002\u539f\u56e0\u5f88\u7b80\u5355：\u6211\u4eec\u73b0\u5728\u6839\u672c\u4e0d\u4f1a\u624b\u52a8 **new Thread()**，\u800c\u662f\u5168\u90fd\u7528\u7ebf\u7a0b\u6c60！<\/p>\n
\u8fd9\u91cc\u9762\u6709\u4e00\u4e2a\u81f4\u547d\u7684\u903b\u8f91\u6f0f\u6d1e： \u521a\u624d\u6211\u4eec\u770b\u4e86\u6e90\u7801，\u7236\u5b50\u7ebf\u7a0b\u7684\u6570\u636e\u590d\u5236\u53ea\u53d1\u751f\u5728 **new Thread()** \u521d\u59cb\u5316\u7684\u4e00\u77ac\u95f4\u3002 \u800c\u5728\u7ebf\u7a0b\u6c60（\u5982 Tomcat \u5de5\u4f5c\u7ebf\u7a0b\u6c60\u3001\u4e1a\u52a1\u5f02\u6b65\u7ebf\u7a0b\u6c60）\u4e2d，\u6838\u5fc3\u7ebf\u7a0b\u662f\u88ab\u53cd\u590d\u590d\u7528\u7684\u3002<\/p>\n
\u707e\u96be\u573a\u666f\u6f14\u793a：<\/p>\n
\u5982\u4f55\u7834\u5c40？<\/p>\n
\u4e1a\u754c\u5bf9\u4e8e\u7ebf\u7a0b\u6c60\u4e0a\u4e0b\u6587\u4f20\u9012\u7684\u6807\u51c6\u7b54\u6848\u662f：\u5f15\u5165\u963f\u91cc\u5df4\u5df4\u5f00\u6e90\u7684 **TransmittableThreadLocal** (\u7b80\u79f0 TTL)\u3002 TTL \u7684\u6838\u5fc3\u601d\u60f3\u662f\u5728\u5411\u7ebf\u7a0b\u6c60\u63d0\u4ea4\u4efb\u52a1\u7684\u90a3\u4e00\u523b\u8fdb\u884c\u4e0a\u4e0b\u6587\u7684\u6293\u53d6，\u5e76\u5728\u4efb\u52a1\u6267\u884c\u524d\u8fdb\u884c\u66ff\u6362，\u4efb\u52a1\u6267\u884c\u540e\u8fdb\u884c\u6062\u590d\u3002\u81f3\u4e8e TTL \u5e95\u5c42\u90a3\u4e9b\u7cbe\u5999\u7684\u5305\u88c5\u5668\u6a21\u5f0f（Wrapper）\u548c\u72b6\u6001\u673a\u6d41\u8f6c，\u6211\u4eec\u6709\u673a\u4f1a\u518d\u5c55\u5f00\u3002<\/p>\n
\u5728\u65e5\u5e38\u7684\u4e1a\u52a1\u5f00\u53d1\u4e2d，\u5f88\u591a\u4eba\u4e00\u542c\u5230\u201c\u7ebf\u7a0b\u5b89\u5168\u201d，\u7b2c\u4e00\u53cd\u5e94\u5c31\u662f\u6761\u4ef6\u53cd\u5c04\u822c\u5730\u52a0\u4e0a synchronized \u6216 ReentrantLock\u3002\u4f46\u8bfb\u5b8c\u672c\u6587\u4e4b\u540e\u5e0c\u671b\u4f60\u80fd\u5efa\u7acb\u8d77\u4e00\u79cd\u67b6\u6784\u601d\u7ef4：\u5e76\u53d1\u63a7\u5236\u7684\u6700\u9ad8\u5883\u754c，\u5c31\u662f\u901a\u8fc7\u8bbe\u8ba1\u6765\u6d88\u706d\u5e76\u53d1\u7ade\u4e89\u3002<\/p>\n
\u65e0\u8bba\u662f Final \u5e26\u6765\u7684\u4e0d\u53ef\u53d8\u6027，\u8fd8\u662f ThreadLocal \u5e26\u6765\u7684\u7ebf\u7a0b\u7ea7\u9694\u79bb，\u5b83\u4eec\u672c\u8d28\u4e0a\u90fd\u5728\u5411\u6211\u4eec\u4f20\u8fbe\u4e00\u4e2a\u6838\u5fc3\u6307\u5bfc\u601d\u60f3：\u907f\u514d\u5171\u4eab\u53ef\u53d8\u72b6\u6001\u3002<\/p>\n
\u61c2\u5f97\u4e86\u8fd9\u4e9b，\u4f60\u5c31\u771f\u6b63\u8df3\u51fa\u4e86\u201c\u9762\u5411\u9501\u7f16\u7a0b\u201d\u7684\u4f4e\u7ea7\u9677\u9631，\u80fd\u591f\u5728\u9ad8\u5e76\u53d1\u573a\u666f\u4e0b\u5199\u51fa\u6027\u80fd\u6781\u9ad8\u3001\u7edd\u5bf9\u5b89\u5168\u7684\u4f18\u96c5\u4ee3\u7801\u3002\u5f53\u7136，\u7edd\u6740\u7684\u62a4\u8eab\u7b26\u6c38\u8fdc\u662f\u4e25\u8c28\u7684\u4e1a\u52a1\u89c4\u8303（\u6bd4\u5982 finally \u5757\u4e2d\u7684 remove()）\u3002<\/p>\n
\u4e0b\u4e00\u7bc7\u9884\u544a：\u4e07\u6076\u4e4b\u6e90\u201c\u7ebf\u7a0b\u6c60\u201d\u7684\u5e95\u5c42\u54f2\u5b66<\/p>\n
\u5728\u63a2\u8ba8 ThreadLocal \u5185\u5b58\u6cc4\u6f0f\u5371\u673a\u4ee5\u53ca InheritableThreadLocal \u8de8\u7ebf\u7a0b\u4f20\u503c\u7684\u75db\u70b9\u65f6，\u6211\u4eec\u90fd\u4e0d\u7ea6\u800c\u540c\u5730\u649e\u4e0a\u4e86\u4e00\u5ea7\u5927\u5c71\u2014\u2014\u7ebf\u7a0b\u6c60\u3002<\/p>\n
\u51e0\u4e4e\u6240\u6709\u7684\u9ad8\u7ea7\u5e76\u53d1\u95ee\u9898，\u90fd\u4e0e\u7ebf\u7a0b\u6c60\u7684\u201c\u590d\u7528\u201d\u673a\u5236\u8131\u4e0d\u4e86\u5e72\u7cfb\u3002\u90a3\u4e48，\u5728\u73b0\u4ee3\u540e\u7aef\u67b6\u6784\u4e2d\u5904\u4e8e\u7edd\u5bf9\u6838\u5fc3\u5730\u4f4d\u7684 ThreadPoolExecutor \u5230\u5e95\u662f\u600e\u4e48\u8fd0\u8f6c\u7684？\u963f\u91cc\u300aJava \u5f00\u53d1\u624b\u518c\u300b\u4e3a\u4ec0\u4e48\u4e25\u7981\u4f7f\u7528 Executors \u521b\u5efa\u7ebf\u7a0b\u6c60，\u5b83\u5230\u5e95\u85cf\u7740\u4ec0\u4e48\u5bfc\u81f4 OOM \u7684\u60ca\u5929\u5927\u5751？\u5728\u771f\u5b9e\u7684\u751f\u4ea7\u73af\u5883\u4e2d，\u9762\u5bf9 CPU \u5bc6\u96c6\u578b\u548c I\/O \u5bc6\u96c6\u578b\u4efb\u52a1，\u6838\u5fc3\u7ebf\u7a0b\u6570\u5230\u5e95\u8be5\u600e\u4e48\u914d\u7f6e\u624d\u4e0d\u4f1a\u5bfc\u81f4\u7cfb\u7edf\u96ea\u5d29？
\n\u8fd9\u4e00\u5207，\u5c06\u5728\u4e0b\u4e00\u7bc7 \u300a\u5e76\u53d1\u7f16\u7a0b\u6838\u5fc3：Java \u7ebf\u7a0b\u6c60\u67b6\u6784\u3001\u539f\u7406\u4e0e\u751f\u4ea7\u7ea7\u914d\u7f6e\u300b \u4e2d\u4e3a\u4f60\u5f7b\u5e95\u89e3\u5f00\u3002<\/p>\n","protected":false},"excerpt":{"rendered":"
\u5f15\u8a00
\n\u5728\u591a\u7ebf\u7a0b\u7684\u4e16\u754c\u91cc，\u89e3\u51b3\u5e76\u53d1\u5b89\u5168\u95ee\u9898\u901a\u5e38\u6709\u4e24\u4e2a\u6781\u7aef\u601d\u8def：\u4e00\u4e2a\u662f\u201c\u5927\u5bb6\u6392\u961f\u7528\u201d，\u8fd9\u5c31\u662f\u52a0\u9501（Synchronized\/ReentrantLock）；\u53e6\u4e00\u4e2a\u5219\u662f\u201c\u5404\u7528\u5404\u7684\u201d\u6216\u8005\u201c\u8c01\u90fd\u522b\u60f3\u6539\u201d\u3002\u672c\u7bc7\u535a\u5ba2\u6211\u4eec\u5c06\u8df3\u51fa\u4f20\u7edf\u7684\u52a0\u9501\u601d\u7ef4，\u63a2\u8ba8\u5e76\u53d1\u7f16\u7a0b\u4e2d\u6781\u5176\u4f18\u96c5\u7684\u4e24\u79cd\u65e0\u9501\u54f2\u5b66：\u4e0d\u53ef\u53d8\u6027\u8bbe\u8ba1（Final）\u4e0e\u7ebf\u7a0b\u7ea7\u9694\u79bb（ThreadLocal<\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[99,426,190,188],"topic":[],"class_list":["post-79957","post","type-post","status-publish","format-standard","hentry","category-server","tag-java","tag-jvm","tag-190","tag-188"],"yoast_head":"\n