{"id":10020925,"date":"2025-07-30T20:50:30","date_gmt":"2025-07-30T12:50:30","guid":{"rendered":"https:\/\/itmax.cn\/?p=10020925"},"modified":"2025-07-30T20:50:30","modified_gmt":"2025-07-30T12:50:30","slug":"java-volatile-%e5%85%b3%e9%94%ae%e5%ad%97%e5%88%b0%e5%ba%95%e6%98%af%e4%bb%80%e4%b9%88%ef%bd%9c%e5%be%97%e7%89%a9%e6%8a%80%e6%9c%af","status":"publish","type":"post","link":"https:\/\/itmax.cn\/?p=10020925","title":{"rendered":"Java volatile \u5173\u952e\u5b57\u5230\u5e95\u662f\u4ec0\u4e48\uff5c\u5f97\u7269\u6280\u672f"},"content":{"rendered":"

\u4e00,\u524d\u8a00<\/strong><\/h2>\n

volatile \u4f5c\u4e3a Java \u7684\u57fa\u7840\u5173\u952e\u5b57\uff0c\u4e00\u76f4\u662f\u4e2a\u719f\u6089\u53c8\u795e\u79d8\u7684\u5b58\u5728\u3002\u6211\u4eec\u5728\u65e5\u5e38\u505a\u5e76\u53d1\u7f16\u7a0b\u7684\u8fc7\u7a0b\u4e2d\u7ecf\u5e38\u7528\u5230\uff0c\u6211\u4eec\u77e5\u9053\u5728\u4ec0\u4e48\u573a\u666f\u4e0b\u9700\u8981\u7528\u5230\uff0c\u4f46\u5374\u59cb\u7ec8\u4e0d\u6e05\u695a\u5e95\u5c42\u7a76\u7adf\u505a\u4e86\u4ec0\u4e48\u3002\u4e92\u8054\u7f51\u4e0a\u641c\u51fa\u6765\u7684\u5927\u591a\u6570\u535a\u5ba2\u90fd\u5728\u89e3\u91ca volatile \u5173\u952e\u5b57\u662f\u4e3a\u4e86\u89e3\u51b3\u6307\u4ee4\u91cd\u6392\u5e8f\u3001\u5185\u5b58\u53ef\u89c1\u6027\u95ee\u9898\uff0c\u6216\u662f\u4ec0\u4e48\u5185\u5b58\u5c4f\u969c\u3001\u7f13\u5b58\u4e00\u81f4\u6027\u534f\u8bae\u4e00\u7c7b\u201c\u5f62\u800c\u4e0a\u7684\u8bcd\u6c47\u201d\u3002\u800c\u7a76\u7adf\u4ec0\u4e48\u662f\u6307\u4ee4\u91cd\u6392\u5e8f\uff0c\u4e3a\u4ec0\u4e48\u8981\u91cd\u65b0\u6392\u5e8f\uff0c\u4ec0\u4e48\u662f\u53ef\u89c1\u6027\u95ee\u9898\uff0c\u5e95\u5c42\u539f\u7406\u662f\u4ec0\u4e48\uff0cvolatile \u53c8\u662f\u5982\u4f55\u89e3\u51b3\u7684\u5374\u9c9c\u6709\u63d0\u53ca\u3002\u5f15\u5f97 Java \u5f00\u53d1\u8005\u4eec\u5982\u96fe\u91cc\u770b\u82b1\uff0c\u7ebf\u4e0a\u7ebf\u4e0b\u5145\u6ee1\u4e86\u7591\u60d1\u7684\u7a7a\u6c14\u3002<\/p>\n

\u672c\u6587\u5c06\u6d45\u6d45\u63a2\u7a76\u4e00\u4e0b\u8fd9\u4e00\u5207\u7684\u5e95\u5c42\u539f\u7406\uff0c\u4e00\u8d77\u6765\u5b66\u4e60\u201c\u6ca1\u6709\u7528\u201d\u7684\u77e5\u8bc6\uff0c\u5404\u4f4d\u770b\u5b98\u770b\u61c2\u4e86\u53ef\u4ee5\u51fa\u53bb\u548c\u9762\u8bd5\u5b98\u5bf9\u7ebf\u3002<\/p>\n

\u4e8c,\u6307\u4ee4\u91cd\u6392\u5e8f<\/strong><\/h2>\n

\u5728\u4e86\u89e3\u6307\u4ee4\u91cd\u6392\u5e8f\u95ee\u9898\u4e4b\u524d\uff0c\u6211\u4eec\u5148\u6765\u770b\u4e00\u4e2a\u7531\u6307\u4ee4\u91cd\u6392\u5e8f\u9020\u6210\u5e76\u53d1\u95ee\u9898\u7684\u4f8b\u5b50\uff1a<\/strong><\/p>\n

static\u00a0int\u00a0x =\u00a00, y =\u00a00;\nstatic\u00a0int\u00a0a =\u00a00, b =\u00a00;\n\npublic\u00a0static\u00a0void\u00a0main(String[] args) throws InterruptedException\u00a0{\u00a0 \n    for\u00a0(int\u00a0i =\u00a00;\u00a0true; i++) {\u00a0\n        x =\u00a00; y =\u00a00; a =\u00a00; b =\u00a00;\n        Thread one =\u00a0new\u00a0Thread(new\u00a0Runnable() {\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0\u00a0\n            public\u00a0void\u00a0run()\u00a0{\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \n                a =\u00a01;\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \n                x = b;\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \n            }\u00a0 \u00a0 \u00a0 \u00a0 \n        });\u00a0 \u00a0 \u00a0 \u00a0 \n        Thread other =\u00a0new\u00a0Thread(new\u00a0Runnable() {\n            public\u00a0void\u00a0run()\u00a0{\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \n                b =\u00a01;\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \n                y = a;\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \n            }\u00a0 \u00a0 \u00a0 \u00a0 \n        });\u00a0 \u00a0 \u00a0 \u00a0 \n        one.start();other.start();\u00a0 \u00a0 \u00a0 \u00a0 \n        one.join();other.join();\u00a0 \u00a0 \u00a0 \u00a0\u00a0\n        if\u00a0(x ==\u00a00\u00a0&& y ==\u00a00) {\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \n            System.err.println("bingo\uff01i: "\u00a0+ i);\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0\u00a0\n            break;\u00a0 \u00a0 \u00a0 \u00a0 \n        }\u00a0 \u00a0 \n   }\n}\n<\/code><\/pre>\n
happens-before \u516b\u6761\u539f\u5219<\/strong><\/p>\n
    \n
  1. \u7a0b\u5e8f\u6b21\u5e8f\u89c4\u5219\uff1a\u5728\u4e00\u4e2a\u7ebf\u7a0b\u5185\uff0c\u6309\u7167\u63a7\u5236\u6d41\u987a\u5e8f\uff0c\u4e66\u5199\u5728\u524d\u9762\u7684\u64cd\u4f5c\u5148\u884c\u53d1\u751f\u4e8e\u4e66\u5199\u5728\u540e\u9762\u7684\u64cd\u4f5c\u3002<\/li>\n
  2. \u7ba1\u7a0b\u9501\u5b9a\u89c4\u5219\uff1a\u4e00\u4e2a unlock \u64cd\u4f5c\u5148\u884c\u53d1\u751f\u4e8e\u540e\u9762\u5bf9\u540c\u4e00\u4e2a\u9501\u7684 lock \u64cd\u4f5c\u3002<\/li>\n
  3. volatile \u53d8\u91cf\u89c4\u5219\uff1a\u5bf9\u4e00\u4e2a volatile \u53d8\u91cf\u7684\u5199\u64cd\u4f5c\u5148\u884c\u53d1\u751f\u4e8e\u540e\u9762\u5bf9\u8fd9\u4e2a\u53d8\u91cf\u7684\u8bfb\u64cd\u4f5c\u3002<\/li>\n
  4. \u7ebf\u7a0b\u542f\u52a8\u89c4\u5219\uff1aThread \u5bf9\u8c61 start()\u65b9\u6cd5\u5148\u884c\u53d1\u751f\u4e8e\u6b64\u7ebf\u7a0b\u7684\u6bcf\u4e00\u4e2a\u52a8\u4f5c\u3002<\/li>\n
  5. \u7ebf\u7a0b\u7ec8\u6b62\u89c4\u5219\uff1a\u7ebf\u7a0bA\u7b49\u5f85\u7ebf\u7a0bB\u5b8c\u6210\uff0c\u5728\u7ebf\u7a0bA\u4e2d\u8c03\u7528\u7ebf\u7a0bB\u7684join()\u65b9\u6cd5\u5b9e\u73b0\uff09\uff0c\u5f53\u7ebf\u7a0bB\u5b8c\u6210\u540e\uff08\u7ebf\u7a0bA\u8c03\u7528\u7ebf\u7a0bB\u7684join()\u65b9\u6cd5\u8fd4\u56de\uff09\uff0c\u5219\u7ebf\u7a0bA\u80fd\u591f\u8bbf\u95ee\u5230\u7ebf\u7a0bB\u5bf9\u5171\u4eab\u53d8\u91cf\u7684\u64cd\u4f5c\u3002<\/li>\n
  6. \u7ebf\u7a0b\u4e2d\u65ad\u89c4\u5219\uff1a\u5bf9\u7ebf\u7a0b interrupt() \u65b9\u6cd5\u7684\u8c03\u7528\u5148\u884c\uff0c\u53d1\u751f\u4e8e\u88ab\u4e2d\u65ad\u7ebf\u7a0b\u7684\u4ee3\u7801\uff0c\u68c0\u6d4b\u5230\u4e2d\u65ad\u4e8b\u4ef6\u7684\u53d1\u751f\uff0c\u53ef\u4ee5\u901a\u8fc7 Thread.interrupted()\u65b9\u6cd5\u68c0\u6d4b\u5230\u662f\u5426\u6709\u4e2d\u65ad\u53d1\u751f\u3002<\/li>\n
  7. \u5bf9\u8c61\u7ec8\u7ed3\u89c4\u5219\uff1a\u4e00\u4e2a\u5bf9\u8c61\u7684\u521d\u59cb\u5316\u5b8c\u6210\uff08\u6784\u9020\u51fd\u6570\u7ed3\u675f\uff09\u5148\u884c\u53d1\u751f\u4e8e\u5b83\u7684 finalize()\u65b9\u6cd5\u7684\u5f00\u59cb\u3002<\/li>\n
  8. \u4f20\u9012\u6027\uff1a\u5982\u679c\u64cd\u4f5c A \u5148\u884c\u53d1\u751f\u4e8e\u64cd\u4f5c B\uff0c\u64cd\u4f5c B \u5148\u884c\u53d1\u751f\u4e8e\u64cd\u4f5c C\uff0c\u90a3\u5c31\u53ef\u4ee5\u5f97\u51fa\u64cd\u4f5c A \u5148\u884c\u53d1\u751f\u4e8e\u64cd\u4f5c C \u7684\u7ed3\u8bba\u3002<\/li>\n<\/ol>\n
    hanpens-beofre \u662f JVM \u5bf9\u5f00\u53d1\u8005\u7684\u4fdd\u8bc1\uff0c\u5373\u4e0d\u7ba1 JVM \u5982\u4f55\u4f18\u5316\uff08JIT \u7f16\u8bd1\uff09\uff0c\u90fd\u4f1a\u4fdd\u8bc1\u4e0a\u8ff0\u539f\u5219\u4e00\u5b9a\u6210\u7acb\u3002\u800c\u5bf9\u4e8e\u5f00\u53d1\u8005\u6765\u8bf4\uff0c\u53ea\u8981\u4e86\u89e3\u4e0a\u8ff0\u539f\u5219\uff0c\u65e0\u9700\u786c\u4ef6\u4ea4\u4e92\u7684\u590d\u6742\u6027\uff0c\u4e5f\u80fd\u591f\u5199\u51fa\u53ef\u9884\u6d4b\u7684\u4ee3\u7801\uff0c\u4ece\u800c\u4fdd\u8bc1\u7ebf\u7a0b\u5b89\u5168\u3002<\/p>\n
    \u4ece hanpens-beofre \u4e2d\u00a0\u7a0b\u5e8f\u6b21\u5e8f\u89c4\u5219\u00a0\u548c\u00a0\u7ebf\u7a0b\u7ec8\u6b62\u89c4\u5219\u00a0\u53ef\u5f97\uff0c\u4e0a\u8ff0\u4ee3\u7801\u6700\u7ec8\u8fd0\u884c\u7ed3\u679c\u7684\u53ef\u80fd\u6027\u4f1a\u6709\u4ee5\u4e0b\u51e0\u79cd\uff1a
    \"image.png\"
    \u53ef\u4ee5\u660e\u663e\u770b\u51fa\uff0c\u7406\u8bba\u4e0a\u4e0d\u4f1a\u5b58\u5728 x =0 && y = 0 \u7684\u8fd0\u884c\u7ed3\u679c\uff0c\u7136\u800c\u5b9e\u9645\u4e0a\u7a0b\u5e8f\u5728\u6267\u884c\u4e86\u4e00\u6bb5\u65f6\u95f4\u540e\uff0c\u6700\u7ec8\u7684\u786e\u4ea7\u751f\u4e86 x = 0 && y = 0 \u7684\u7ed3\u679c\uff01<\/p>\n
    \"image.png\"
    \u8fd9\u5c31\u5f15\u51fa\u4e86 volatile \u89e3\u51b3\u7684\u7b2c\u4e00\u4e2a\u95ee\u9898\uff1a\u907f\u514d\u6307\u4ee4\u91cd\u6392\u5e8f\u3002\u6307\u4ee4\u91cd\u6392\u5e8f\u5728\u7f16\u8bd1\u5668<\/strong>\u548c\u00a0CPU \u5c42\u9762<\/strong>\uff08\u4e71\u5e8f\u6267\u884c\uff09\u90fd\u4f1a\u53d1\u751f\u3002<\/p>\n
    CPU \u7684\u4e71\u5e8f\u6267\u884c<\/strong><\/p>\n
    \u6211\u4eec\u77e5\u9053\uff0cCPU \u8fd0\u7b97\u7684\u672c\u8d28\u5c31\u662f\u4e0d\u65ad\u83b7\u53d6\u4e0b\u4e00\u6761\u6307\u4ee4\u7136\u540e\u6267\u884c\uff0c\u7f16\u8bd1\u5668\u7ed9\u5b83\u4ec0\u4e48\u6307\u4ee4\u5b83\u5c31\u6267\u884c\u4ec0\u4e48\uff0c\u4f55\u6765\u7684\u4e71\u5e8f\u6267\u884c\u5462\uff1f<\/p>\n
    \u8fd9\u8fd8\u8981\u4ece\u8ba1\u7b97\u673a\u7684\u8bde\u751f\u4e4b\u521d\u8bb2\u8d77\u3002<\/p>\n
    \u5185\u5b58\u62d6\u540e\u817f<\/strong><\/p>\n
    \u8ba1\u7b97\u673a\u8bde\u751f\u4e4b\u521d\uff0cCPU \u548c\u5185\u5b58\u4e4b\u95f4\u7684\u901f\u5ea6\u5dee\u5f02\u5e76\u4e0d\u660e\u663e\uff0c\u4e00\u5207\u76f8\u5b89\u65e0\u4e8b\u3002\u968f\u7740\u79d1\u5b66\u7684\u8fdb\u6b65\uff0cCPU \u7684\u8fd0\u7b97\u901f\u5ea6\u8d8a\u6765\u5feb\uff0c\u6839\u636e\u6469\u5c14\u5b9a\u5f8b\u8ba1\u7b97\uff0c\u76f8\u5f53\u4e8e CPU \u7684\u6027\u80fd\u6bcf\u5e74\u589e\u957f 60%\uff0c\u76f8\u6bd4\u4e4b\u4e0b\uff0c\u5185\u5b58\u6027\u80fd\u7684\u589e\u957f\u5374\u76f8\u5bf9\u7f13\u6162\uff0c\u6bcf\u5e74\u7ea6\u4e3a 7%\u3002\u5230\u4eca\u5929\uff0cCPU \u8fd0\u7b97\u548c\u5185\u5b58\u8bbf\u95ee\u7684\u901f\u5ea6\u4ea7\u751f\u4e86\u5de8\u5927\u9e3f\u6c9f\uff0c\u5df2\u7ecf\u8fbe\u5230\u4e86 120 \u500d\u4e4b\u591a\u3002\u8fd9\u65f6\u5982\u679c CPU \u8fd8\u4ee5\u4f20\u7edf\u8ba1\u7b97\u673a\u67b6\u6784\uff0c\u6570\u636e\u4ece\u5185\u5b58\u4e2d\u8bfb\u53d6\u7684\u8bdd\uff0c\u5c06\u4f1a\u4e25\u91cd\u62d6\u6162 CPU \u7684\u8fd0\u884c\u901f\u5ea6<\/strong>\u3002<\/p>\n
    \"image.png\"
    \u203b \u5c40\u90e8\u6027\u539f\u7406<\/strong><\/p>\n
    \u5728\u7a0b\u5e8f\u8fd0\u884c\u8fc7\u7a0b\u4e2d\uff0c\u82af\u7247\u5de5\u7a0b\u5e08\u603b\u7ed3\u4e86\u4e24\u6761\u5b58\u5728\u5c40\u90e8\u6027\u539f\u7406\uff1a\u65f6\u95f4\u5c40\u90e8\u6027<\/strong>\u3001\u7a7a\u95f4\u5c40\u90e8\u6027<\/strong>\u3002<\/p>\n