{"id":10008412,"date":"2024-02-29T23:53:01","date_gmt":"2024-02-29T15:53:01","guid":{"rendered":"https:\/\/blog.itmax.cn\/?p=10008412"},"modified":"2024-02-29T23:53:01","modified_gmt":"2024-02-29T15:53:01","slug":"%e9%9d%a2%e8%af%95%e5%ae%98%ef%bc%9a%e8%af%b4%e8%af%b4volatile%e5%ba%95%e5%b1%82%e5%ae%9e%e7%8e%b0%e5%8e%9f%e7%90%86%ef%bc%9f","status":"publish","type":"post","link":"https:\/\/itmax.cn\/?p=10008412","title":{"rendered":"\u9762\u8bd5\u5b98\uff1a\u8bf4\u8bf4volatile\u5e95\u5c42\u5b9e\u73b0\u539f\u7406\uff1f"},"content":{"rendered":"

\u5728 Java \u5e76\u53d1\u7f16\u7a0b\u4e2d\uff0c\u6709 3 \u4e2a\u6700\u5e38\u7528\u7684\u5173\u952e\u5b57\uff1asynchronized\u3001ReentrantLock \u548c volatile\u3002<\/p>\n

\u867d\u7136 volatile \u5e76\u4e0d\u50cf\u5176\u4ed6\u4e24\u4e2a\u5173\u952e\u5b57\u4e00\u6837\uff0c\u80fd\u4fdd\u8bc1\u7ebf\u7a0b\u5b89\u5168\uff0c\u4f46 volatile \u4e5f\u662f\u5e76\u53d1\u7f16\u7a0b\u4e2d\u6700\u5e38\u89c1\u7684\u5173\u952e\u5b57\u4e4b\u4e00\u3002\u4f8b\u5982\uff0c\u5355\u4f8b\u6a21\u5f0f\u3001CopyOnWriteArrayList \u548c ConcurrentHashMap \u4e2d\u90fd\u79bb\u4e0d\u5f00 volatile\u3002<\/p>\n

\u90a3\u4e48\uff0c\u95ee\u9898\u6765\u4e86\uff0c\u6211\u4eec\u77e5\u9053 synchronized \u5e95\u5c42\u662f\u901a\u8fc7\u76d1\u89c6\u5668 Monitor \u5b9e\u73b0\u7684\uff0cReentrantLock \u5e95\u5c42\u662f\u901a\u8fc7 AQS \u7684 CAS \u5b9e\u73b0\u7684<\/strong>\uff0c\u90a3 volatile \u7684\u5e95\u5c42\u662f\u5982\u4f55\u5b9e\u73b0\u7684\uff1f<\/p>\n

1.volatile \u4f5c\u7528<\/h2>\n

\u5728\u4e86\u89e3 volatile \u7684\u5e95\u5c42\u5b9e\u73b0\u4e4b\u524d\uff0c\u6211\u4eec\u9700\u8981\u5148\u4e86\u89e3 volatile \u7684\u4f5c\u7528\uff0c\u56e0\u4e3a volatile \u7684\u5e95\u5c42\u5b9e\u73b0\u548c\u5b83\u7684\u4f5c\u7528\u606f\u606f\u76f8\u5173\u3002<\/p>\n

volatile \u4f5c\u7528\u6709\u4e24\u4e2a\uff1a\u4fdd\u8bc1\u5185\u5b58\u53ef\u89c1\u6027\u548c\u6709\u5e8f\u6027\uff08\u7981\u6b62\u6307\u4ee4\u91cd\u6392\u5e8f\uff09<\/strong>\u3002<\/p>\n

1.1 \u5185\u5b58\u53ef\u89c1\u6027<\/h3>\n

\u8bf4\u5230\u5185\u5b58\u53ef\u89c1\u6027\u95ee\u9898\u5c31\u4e0d\u5f97\u4e0d\u63d0 Java \u5185\u5b58\u6a21\u578b\uff0cJava \u5185\u5b58\u6a21\u578b\uff08Java Memory Model\uff09\u7b80\u79f0\u4e3a JMM\uff0c\u4e3b\u8981\u662f\u7528\u6765\u5c4f\u853d\u4e0d\u540c\u786c\u4ef6\u548c\u64cd\u4f5c\u7cfb\u7edf\u7684\u5185\u5b58\u8bbf\u95ee\u5dee\u5f02\u7684\uff0c\u56e0\u4e3a\u5728\u4e0d\u540c\u7684\u786c\u4ef6\u548c\u4e0d\u540c\u7684\u64cd\u4f5c\u7cfb\u7edf\u4e0b\uff0c\u5185\u5b58\u7684\u8bbf\u95ee\u662f\u6709\u4e00\u5b9a\u7684\u5dee\u5f02\u5f97\uff0c\u8fd9\u79cd\u5dee\u5f02\u4f1a\u5bfc\u81f4\u76f8\u540c\u7684\u4ee3\u7801\u5728\u4e0d\u540c\u7684\u786c\u4ef6\u548c\u4e0d\u540c\u7684\u64cd\u4f5c\u7cfb\u7edf\u4e0b\u6709\u7740\u4e0d\u4e00\u6837\u7684\u884c\u4e3a\uff0c\u800c Java \u5185\u5b58\u6a21\u578b\u5c31\u662f\u89e3\u51b3\u8fd9\u4e2a\u5dee\u5f02\uff0c\u7edf\u4e00\u76f8\u540c\u4ee3\u7801\u5728\u4e0d\u540c\u786c\u4ef6\u548c\u4e0d\u540c\u64cd\u4f5c\u7cfb\u7edf\u4e0b\u7684\u5dee\u5f02\u7684\u3002<\/p>\n

Java \u5185\u5b58\u6a21\u578b\u89c4\u5b9a\uff1a\u6240\u6709\u7684\u53d8\u91cf\uff08\u5b9e\u4f8b\u53d8\u91cf\u548c\u9759\u6001\u53d8\u91cf\uff09\u90fd\u5fc5\u987b\u5b58\u50a8\u5728\u4e3b\u5185\u5b58\u4e2d\uff0c\u6bcf\u4e2a\u7ebf\u7a0b\u4e5f\u4f1a\u6709\u81ea\u5df1\u7684\u5de5\u4f5c\u5185\u5b58\uff0c\u7ebf\u7a0b\u7684\u5de5\u4f5c\u5185\u5b58\u4fdd\u5b58\u4e86\u8be5\u7ebf\u7a0b\u7528\u5230\u7684\u53d8\u91cf\u548c\u4e3b\u5185\u5b58\u7684\u526f\u672c\u62f7\u8d1d\uff0c\u7ebf\u7a0b\u5bf9\u53d8\u91cf\u7684\u64cd\u4f5c\u90fd\u5728\u5de5\u4f5c\u5185\u5b58\u4e2d\u8fdb\u884c\u3002\u7ebf\u7a0b\u4e0d\u80fd\u76f4\u63a5\u8bfb\u5199\u4e3b\u5185\u5b58\u4e2d\u7684\u53d8\u91cf\uff0c\u5982\u4e0b\u56fe\u6240\u793a\uff1a
\"image.png\"
\u7136\u800c\uff0cJava \u5185\u5b58\u6a21\u578b\u4f1a\u5e26\u6765\u4e00\u4e2a\u65b0\u7684\u95ee\u9898\uff0c\u90a3\u5c31\u662f\u5185\u5b58\u53ef\u89c1\u6027\u95ee\u9898\uff0c\u4e5f\u5c31\u662f\u5f53\u67d0\u4e2a\u7ebf\u7a0b\u4fee\u6539\u4e86\u4e3b\u5185\u5b58\u4e2d\u5171\u4eab\u53d8\u91cf\u7684\u503c\u4e4b\u540e\uff0c\u5176\u4ed6\u7ebf\u7a0b\u4e0d\u80fd\u611f\u77e5\u5230\u6b64\u503c\u88ab\u4fee\u6539\u4e86\uff0c\u5b83\u4f1a\u4e00\u76f4\u4f7f\u7528\u81ea\u5df1\u5de5\u4f5c\u5185\u5b58\u4e2d\u7684\u201c\u65e7\u503c\u201d\uff0c\u8fd9\u6837\u7a0b\u5e8f\u7684\u6267\u884c\u7ed3\u679c\u5c31\u4e0d\u7b26\u5408\u6211\u4eec\u7684\u9884\u671f\u4e86\uff0c\u8fd9\u5c31\u662f\u5185\u5b58\u53ef\u89c1\u6027\u95ee\u9898\uff0c\u6211\u4eec\u7528\u4ee5\u4e0b\u4ee3\u7801\u6765\u6f14\u793a\u4e00\u4e0b\u8fd9\u4e2a\u95ee\u9898\uff1a<\/p>\n

private static boolean flag = false;\npublic static void main(String[] args) {\n    Thread t1 = new Thread(new Runnable() {\n        @Override\n        public void run() {\n            while (!flag) {\n\n            }\n            System.out.println("\u7ec8\u6b62\u6267\u884c");\n        }\n    });\n    t1.start();\n    Thread t2 = new Thread(new Runnable() {\n        @Override\n        public void run() {\n            try {\n                Thread.sleep(1000);\n            } catch (InterruptedException e) {\n                e.printStackTrace();\n            }\n            System.out.println("\u8bbe\u7f6e flag=true");\n            flag = true;\n        }\n    });\n    t2.start();\n}<\/code><\/pre>\n
\u4ee5\u4e0a\u4ee3\u7801\u6211\u4eec\u9884\u671f\u7684\u7ed3\u679c\u662f\uff0c\u5728\u7ebf\u7a0b 1 \u6267\u884c\u4e86 1s \u4e4b\u540e\uff0c\u7ebf\u7a0b 2 \u5c06 flag \u53d8\u91cf\u4fee\u6539\u4e3a true\uff0c\u4e4b\u540e\u7ebf\u7a0b 1 \u7ec8\u6b62\u6267\u884c\uff0c\u7136\u800c\uff0c\u56e0\u4e3a\u7ebf\u7a0b 1 \u611f\u77e5\u4e0d\u5230 flag \u53d8\u91cf\u53d1\u751f\u4e86\u4fee\u6539\uff0c\u4e5f\u5c31\u662f\u5185\u5b58\u53ef\u89c1\u6027\u95ee\u9898\uff0c\u6240\u4ee5\u4f1a\u5bfc\u81f4\u7ebf\u7a0b 1 \u4f1a\u6c38\u8fdc\u7684\u6267\u884c\u4e0b\u53bb\uff0c\u6700\u7ec8\u6211\u4eec\u770b\u5230\u7684\u7ed3\u679c\u662f\u8fd9\u6837\u7684\uff1a
\"image.png\"
\u5982\u4f55\u89e3\u51b3\u4ee5\u4e0a\u95ee\u9898\u5462\uff1f\u53ea\u9700\u8981\u7ed9\u53d8\u91cf flag \u52a0\u4e0a volatile \u4fee\u9970\u5373\u53ef\uff0c\u5177\u4f53\u7684\u5b9e\u73b0\u4ee3\u7801\u5982\u4e0b\uff1a<\/p>\n
private volatile static boolean flag = false;\npublic static void main(String[] args) {\n    Thread t1 = new Thread(new Runnable() {\n        @Override\n        public void run() {\n            while (!flag) {\n\n            }\n            System.out.println("\u7ec8\u6b62\u6267\u884c");\n        }\n    });\n    t1.start();\n    Thread t2 = new Thread(new Runnable() {\n        @Override\n        public void run() {\n            try {\n                Thread.sleep(1000);\n            } catch (InterruptedException e) {\n                e.printStackTrace();\n            }\n            System.out.println("\u8bbe\u7f6e flag=true");\n            flag = true;\n        }\n    });\n    t2.start();\n}<\/code><\/pre>\n
\u4ee5\u4e0a\u7a0b\u5e8f\u7684\u6267\u884c\u7ed3\u679c\u5982\u4e0b\u56fe\u6240\u793a\uff1a
\"image.png\"<\/p>\n
1.2 \u6709\u5e8f\u6027<\/h3>\n
\u6709\u5e8f\u6027\u4e5f\u53eb\u505a\u7981\u6b62\u6307\u4ee4\u91cd\u6392\u5e8f\u3002<\/p>\n
\u6307\u4ee4\u91cd\u6392\u5e8f\u662f\u6307\u7f16\u8bd1\u5668\u6216 CPU \u4e3a\u4e86\u4f18\u5316\u7a0b\u5e8f\u7684\u6267\u884c\u6027\u80fd\uff0c\u800c\u5bf9\u6307\u4ee4\u8fdb\u884c\u91cd\u65b0\u6392\u5e8f\u7684\u4e00\u79cd\u624b\u6bb5\u3002<\/p>\n
\u6307\u4ee4\u91cd\u6392\u5e8f\u7684\u5b9e\u73b0\u521d\u8877\u662f\u597d\u7684\uff0c\u4f46\u662f\u5728\u591a\u7ebf\u7a0b\u6267\u884c\u4e2d\uff0c\u5982\u679c\u6267\u884c\u4e86\u6307\u4ee4\u91cd\u6392\u5e8f\u53ef\u80fd\u4f1a\u5bfc\u81f4\u7a0b\u5e8f\u6267\u884c\u51fa\u9519\u3002\u6307\u4ee4\u91cd\u6392\u5e8f\u6700\u5178\u578b\u7684\u4e00\u4e2a\u95ee\u9898\u5c31\u53d1\u751f\u5728\u5355\u4f8b\u6a21\u5f0f\u4e2d\uff0c\u6bd4\u5982\u4ee5\u4e0b\u95ee\u9898\u4ee3\u7801\uff1a<\/p>\n
public class Singleton {\n    private Singleton() {}\n    private static Singleton instance = null;\n    public static Singleton getInstance() {\n        if (instance == null) { \/\/ \u2460\n            synchronized (Singleton.class) {\n                if (instance == null) {\n                    instance = new Singleton(); \/\/ \u2461\n                }\n            }\n        }\n        return instance;\n    }\n}<\/code><\/pre>\n
\u4ee5\u4e0a\u95ee\u9898\u53d1\u751f\u5728\u4ee3\u7801 \u2461 \u8fd9\u4e00\u884c\u201cinstance = new Singleton();\u201d\uff0c\u8fd9\u884c\u4ee3\u7801\u770b\u4f3c\u53ea\u662f\u4e00\u4e2a\u521b\u5efa\u5bf9\u8c61\u7684\u8fc7\u7a0b\uff0c\u7136\u800c\u5b83\u7684\u5b9e\u9645\u6267\u884c\u5374\u5206\u4e3a\u4ee5\u4e0b 3 \u6b65\uff1a<\/strong><\/p>\n
    \n
  1. \u521b\u5efa\u5185\u5b58\u7a7a\u95f4\u3002<\/strong><\/li>\n
  2. \u5728\u5185\u5b58\u7a7a\u95f4\u4e2d\u521d\u59cb\u5316\u5bf9\u8c61 Singleton\u3002<\/strong><\/li>\n
  3. \u5c06\u5185\u5b58\u5730\u5740\u8d4b\u503c\u7ed9 instance \u5bf9\u8c61\uff08\u6267\u884c\u4e86\u6b64\u6b65\u9aa4\uff0cinstance \u5c31\u4e0d\u7b49\u4e8e null \u4e86\uff09\u3002<\/strong><\/li>\n<\/ol>\n
    \u5982\u679c\u6b64\u53d8\u91cf\u4e0d\u52a0 volatile\uff0c\u90a3\u4e48\u7ebf\u7a0b 1 \u5728\u6267\u884c\u5230\u4e0a\u8ff0\u4ee3\u7801\u7684\u7b2c \u2461 \u5904\u65f6\u5c31\u53ef\u80fd\u4f1a\u6267\u884c\u6307\u4ee4\u91cd\u6392\u5e8f\uff0c\u5c06\u539f\u672c\u662f 1\u30012\u30013 \u7684\u6267\u884c\u987a\u5e8f\uff0c\u91cd\u6392\u4e3a 1\u30013\u30012\u3002\u4f46\u662f\u7279\u6b8a\u60c5\u51b5\u4e0b\uff0c\u7ebf\u7a0b 1 \u5728\u6267\u884c\u5b8c\u7b2c 3 \u6b65\u4e4b\u540e\uff0c\u5982\u679c\u6765\u4e86\u7ebf\u7a0b 2 \u6267\u884c\u5230\u4e0a\u8ff0\u4ee3\u7801\u7684\u7b2c \u2460 \u5904\uff0c\u5224\u65ad instance \u5bf9\u8c61\u5df2\u7ecf\u4e0d\u4e3a null\uff0c\u4f46\u6b64\u65f6\u7ebf\u7a0b 1 \u8fd8\u672a\u5c06\u5bf9\u8c61\u5b9e\u4f8b\u5316\u5b8c\uff0c\u90a3\u4e48\u7ebf\u7a0b 2 \u5c06\u4f1a\u5f97\u5230\u4e00\u4e2a\u88ab\u5b9e\u4f8b\u5316\u201c\u4e00\u534a\u201d\u7684\u5bf9\u8c61\uff0c\u4ece\u800c\u5bfc\u81f4\u7a0b\u5e8f\u6267\u884c\u51fa\u9519\uff0c\u8fd9\u5c31\u662f\u4e3a\u4ec0\u4e48\u8981\u7ed9\u79c1\u6709\u53d8\u91cf\u6dfb\u52a0 volatile \u7684\u539f\u56e0\u4e86\u3002<\/strong><\/p>\n
    \u8981\u4f7f\u4ee5\u4e0a\u5355\u4f8b\u6a21\u5f0f\u53d8\u4e3a\u7ebf\u7a0b\u5b89\u5168\u7684\u7a0b\u5e8f\uff0c\u9700\u8981\u7ed9 instance \u53d8\u91cf\u6dfb\u52a0 volatile \u4fee\u9970\uff0c\u5b83\u7684\u6700\u7ec8\u5b9e\u73b0\u4ee3\u7801\u5982\u4e0b\uff1a<\/p>\n
    public class Singleton {\n    private Singleton() {}\n    \/\/ \u4f7f\u7528 volatile \u7981\u6b62\u6307\u4ee4\u91cd\u6392\u5e8f\n    private static volatile Singleton instance = null; \/\/ \u3010\u4e3b\u8981\u662f\u6b64\u884c\u4ee3\u7801\u53d1\u751f\u4e86\u53d8\u5316\u3011\n    public static Singleton getInstance() {\n        if (instance == null) { \/\/ \u2460\n            synchronized (Singleton.class) {\n                if (instance == null) {\n                    instance = new Singleton(); \/\/ \u2461\n                }\n            }\n        }\n        return instance;\n    }\n}<\/code><\/pre>\n
    2.volatile \u5b9e\u73b0\u539f\u7406<\/h2>\n
    volatile \u5b9e\u73b0\u539f\u7406\u548c\u5b83\u7684\u4f5c\u7528\u6709\u5173\uff0c\u6211\u4eec\u9996\u5148\u5148\u6765\u770b\u5b83\u7684\u5185\u5b58\u53ef\u89c1\u6027\u3002<\/p>\n
    2.1 \u5185\u5b58\u53ef\u89c1\u6027\u5b9e\u73b0\u539f\u7406<\/h3>\n
    volatile \u5185\u5b58\u53ef\u89c1\u6027\u4e3b\u8981\u901a\u8fc7 lock \u524d\u7f00\u6307\u4ee4\u5b9e\u73b0\u7684\uff0c\u5b83\u4f1a\u9501\u5b9a\u5f53\u524d\u5185\u5b58\u533a\u57df\u7684\u7f13\u5b58\uff08\u7f13\u5b58\u884c\uff09\uff0c\u5e76\u4e14\u7acb\u5373\u5c06\u5f53\u524d\u7f13\u5b58\u884c\u6570\u636e\u5199\u5165\u4e3b\u5185\u5b58\uff08\u8017\u65f6\u975e\u5e38\u77ed\uff09\uff0c\u56de\u5199\u4e3b\u5185\u5b58\u7684\u65f6\u5019\u4f1a\u901a\u8fc7 MESI \u534f\u8bae\u4f7f\u5176\u4ed6\u7ebf\u7a0b\u7f13\u5b58\u4e86\u8be5\u53d8\u91cf\u7684\u5730\u5740\u5931\u6548\uff0c\u4ece\u800c\u5bfc\u81f4\u5176\u4ed6\u7ebf\u7a0b\u9700\u8981\u91cd\u65b0\u53bb\u4e3b\u5185\u5b58\u4e2d\u91cd\u65b0\u8bfb\u53d6\u6570\u636e\u5230\u5176\u5de5\u4f5c\u7ebf\u7a0b\u4e2d\u3002<\/p>\n
    \u4ec0\u4e48 MESI \u534f\u8bae\uff1f<\/h4>\n
    MESI \u534f\u8bae\uff0c\u5168\u79f0\u4e3a Modified, Exclusive, Shared, Invalid\uff0c\u662f\u4e00\u79cd\u9ad8\u901f\u7f13\u5b58\u4e00\u81f4\u6027\u534f\u8bae\u3002\u5b83\u662f\u4e3a\u4e86\u89e3\u51b3\u591a\u5904\u7406\u5668\uff08CPU\uff09\u5728\u5e76\u53d1\u73af\u5883\u4e0b\uff0c\u591a\u4e2a CPU \u7f13\u5b58\u4e0d\u4e00\u81f4\u95ee\u9898\u800c\u63d0\u51fa\u7684\u3002
    MESI \u534f\u8bae\u5b9a\u4e49\u4e86\u9ad8\u901f\u7f13\u5b58\u4e2d\u6570\u636e\u7684\u56db\u79cd\u72b6\u6001\uff1a<\/p>\n
      \n
    1. Modified\uff08M\uff09<\/strong>\uff1a\u8868\u793a\u7f13\u5b58\u884c\u5df2\u7ecf\u88ab\u4fee\u6539\uff0c\u4f46\u8fd8\u6ca1\u6709\u88ab\u5199\u56de\u4e3b\u5b58\u50a8\u5668\u3002\u5728\u8fd9\u79cd\u72b6\u6001\u4e0b\uff0c\u53ea\u6709\u4e00\u4e2a CPU \u80fd\u72ec\u5360\u8fd9\u4e2a\u4fee\u6539\u72b6\u6001\u3002<\/li>\n
    2. Exclusive\uff08E\uff09<\/strong>\uff1a\u8868\u793a\u7f13\u5b58\u884c\u4e0e\u4e3b\u5b58\u50a8\u5668\u76f8\u540c\uff0c\u5e76\u4e14\u662f\u4e3b\u5b58\u50a8\u5668\u7684\u552f\u4e00\u62f7\u8d1d\u3002\u8fd9\u79cd\u72b6\u6001\u4e0b\uff0c\u53ea\u6709\u4e00\u4e2a CPU \u80fd\u72ec\u5360\u8fd9\u4e2a\u72b6\u6001\u3002<\/li>\n
    3. Shared\uff08S\uff09<\/strong>\uff1a\u8868\u793a\u6b64\u9ad8\u901f\u7f13\u5b58\u884c\u53ef\u80fd\u5b58\u50a8\u5728\u8ba1\u7b97\u673a\u7684\u5176\u4ed6\u9ad8\u901f\u7f13\u5b58\u4e2d\uff0c\u5e76\u4e14\u4e0e\u4e3b\u5b58\u50a8\u5668\u5339\u914d\u3002\u5728\u8fd9\u79cd\u72b6\u6001\u4e0b\uff0c\u5404\u4e2a CPU \u53ef\u4ee5\u5e76\u53d1\u7684\u5bf9\u8fd9\u4e2a\u6570\u636e\u8fdb\u884c\u8bfb\u53d6\uff0c\u4f46\u90fd\u4e0d\u80fd\u8fdb\u884c\u5199\u64cd\u4f5c\u3002<\/li>\n
    4. Invalid\uff08I\uff09<\/strong>\uff1a\u8868\u793a\u6b64\u7f13\u5b58\u884c\u65e0\u6548\u6216\u5df2\u8fc7\u671f\uff0c\u4e0d\u80fd\u4f7f\u7528\u3002<\/li>\n<\/ol>\n
      MESI \u534f\u8bae\u7684\u4e3b\u8981\u7528\u9014\u662f\u786e\u4fdd\u5728\u591a\u4e2a CPU \u5171\u4eab\u5185\u5b58\u65f6\uff0c\u5404\u4e2a CPU \u7684\u7f13\u5b58\u6570\u636e\u80fd\u591f\u4fdd\u6301\u4e00\u81f4\u6027\u3002\u5f53\u67d0\u4e2a CPU \u5bf9\u5171\u4eab\u6570\u636e\u8fdb\u884c\u4fee\u6539\u65f6\uff0c\u5b83\u4f1a\u5c06\u8fd9\u4e2a\u6570\u636e\u7684\u72b6\u6001\u4ece S\uff08\u5171\u4eab\uff09\u6216 E\uff08\u72ec\u5360\uff09\u72b6\u6001\u8f6c\u53d8\u4e3a M\uff08\u4fee\u6539\uff09\u72b6\u6001\uff0c\u5e76\u7b49\u5f85\u9002\u5f53\u7684\u65f6\u673a\u5c06\u8fd9\u4e2a\u4fee\u6539\u5199\u56de\u4e3b\u5b58\u50a8\u5668\u3002\u540c\u65f6\uff0c\u5b83\u4f1a\u5411\u5176\u4ed6 CPU \u5e7f\u64ad\u4e00\u4e2a\u201c\u65e0\u6548\u6d88\u606f\u201d\uff0c\u4f7f\u5f97\u5176\u4ed6 CPU \u5c06\u81ea\u5df1\u7f13\u5b58\u4e2d\u5bf9\u5e94\u7684\u6570\u636e\u72b6\u6001\u8f6c\u53d8\u4e3aI\uff08\u65e0\u6548\uff09\u72b6\u6001\uff0c\u4ece\u800c\u5728\u4e0b\u6b21\u8bbf\u95ee\u8fd9\u4e2a\u6570\u636e\u65f6\u80fd\u591f\u4ece\u4e3b\u5b58\u50a8\u5668\u6216\u5176\u4ed6 CPU \u7684\u7f13\u5b58\u4e2d\u91cd\u65b0\u83b7\u53d6\u6b63\u786e\u7684\u6570\u636e\u3002<\/p>\n
      \u8fd9\u79cd\u534f\u8bae\u53ef\u4ee5\u786e\u4fdd\u5728\u591a\u5904\u7406\u5668\u73af\u5883\u4e2d\uff0c\u5404\u4e2a CPU \u7684\u7f13\u5b58\u6570\u636e\u80fd\u591f\u6b63\u786e\u3001\u4e00\u81f4\u5730\u53cd\u6620\u4e3b\u5b58\u50a8\u5668\u4e2d\u7684\u6570\u636e\u72b6\u6001\uff0c\u4ece\u800c\u907f\u514d\u7531\u4e8e\u7f13\u5b58\u4e0d\u4e00\u81f4\u5bfc\u81f4\u7684\u6570\u636e\u9519\u8bef\u6216\u7a0b\u5e8f\u5f02\u5e38\u3002<\/p>\n
      2.2 \u6709\u5e8f\u6027\u5b9e\u73b0\u539f\u7406<\/h3>\n
      volatile \u7684\u6709\u5e8f\u6027\u662f\u901a\u8fc7\u63d2\u5165\u5185\u5b58\u5c4f\u969c\uff08Memory Barrier\uff09\uff0c\u5728\u5185\u5b58\u5c4f\u969c\u524d\u540e\u7981\u6b62\u91cd\u6392\u5e8f\u4f18\u5316\uff0c\u4ee5\u6b64\u5b9e\u73b0\u6709\u5e8f\u6027\u7684\u3002<\/p>\n
      \u4ec0\u4e48\u662f\u5185\u5b58\u5c4f\u969c\uff1f<\/h4>\n
      \u5185\u5b58\u5c4f\u969c\uff08Memory Barrier \u6216 Memory Fence\uff09\u662f\u4e00\u79cd\u786c\u4ef6\u7ea7\u522b\u7684\u540c\u6b65\u64cd\u4f5c\uff0c\u5b83\u5f3a\u5236\u5904\u7406\u5668\u6309\u7167\u7279\u5b9a\u987a\u5e8f\u6267\u884c\u5185\u5b58\u8bbf\u95ee\u64cd\u4f5c\uff0c\u786e\u4fdd\u5185\u5b58\u64cd\u4f5c\u7684\u987a\u5e8f\u6027\uff0c\u963b\u6b62\u7f16\u8bd1\u5668\u548c CPU \u5bf9\u5185\u5b58\u64cd\u4f5c\u8fdb\u884c\u4e0d\u5fc5\u8981\u7684\u91cd\u6392\u5e8f\u3002\u5185\u5b58\u5c4f\u969c\u53ef\u4ee5\u786e\u4fdd\u8de8\u8d8a\u5c4f\u969c\u7684\u8bfb\u5199\u64cd\u4f5c\u4e0d\u4f1a\u4ea4\u53c9\u8fdb\u884c\uff0c\u4ee5\u6b64\u7ef4\u6301\u7a0b\u5e8f\u7684\u5185\u5b58\u4e00\u81f4\u6027\u6a21\u578b\u3002<\/p>\n
      \u5728 Java \u5185\u5b58\u6a21\u578b\uff08JMM\uff09\u4e2d\uff0cvolatile \u5173\u952e\u5b57\u7528\u4e8e\u4fee\u9970\u53d8\u91cf\u65f6\uff0c\u80fd\u591f\u4fdd\u8bc1\u8be5\u53d8\u91cf\u7684\u53ef\u89c1\u6027\u548c\u6709\u5e8f\u6027\u3002\u5173\u4e8e\u6709\u5e8f\u6027\uff0cvolatile \u901a\u8fc7\u5185\u5b58\u5c4f\u969c\u7684\u63d2\u5165\u6765\u5b9e\u73b0\uff1a<\/p>\n