{"id":2149,"date":"2021-05-22T16:15:24","date_gmt":"2021-05-22T08:15:24","guid":{"rendered":"https:\/\/coderbee.net\/?p=2149"},"modified":"2021-05-27T21:47:42","modified_gmt":"2021-05-27T13:47:42","slug":"%e5%8f%8c%e9%87%8d%e6%a3%80%e6%9f%a5%e5%8a%a0%e9%94%81-%e4%b8%8e-volatile","status":"publish","type":"post","link":"https:\/\/coderbee.net\/index.php\/concurrent\/20210522\/2149","title":{"rendered":"\u53cc\u91cd\u68c0\u67e5\u52a0\u9501 \u4e0e volatile"},"content":{"rendered":"<p>\u4e00\u4e2a\u95ee\u9898\uff1a\u53cc\u91cd\u68c0\u67e5\u52a0\u9501\u4e3a\u4ec0\u4e48\u7528\u4e86 volatile \u5c31\u53ef\u4ee5\u6b63\u786e\u5de5\u4f5c\uff1f<\/p>\n<p>\u53cd\u8fc7\u6765\u95ee\uff1a\u4e0d\u7528 volatile \u4fee\u9970 <code>resource<\/code> \u5c5e\u6027\u6709\u4ec0\u4e48\u95ee\u9898\uff1f<\/p>\n<p>\u53cc\u91cd\u68c0\u67e5\u52a0\u9501\u7684\u7b80\u5355\u793a\u4f8b\uff1a<\/p>\n<pre><code class=\"java\">public class DoubleCheckedLocking {\n    private static Resource resource;\n\n    public static Resource getInstance() {\n        if (resource == null) {     \/\/ LL01\n            synchronized (DoubleCheckedLocking.class) {\n                if (resource == null) {\n                    resource = new Resource();\n                }\n            }\n        }\n        return resource;\n    }\n}\n<\/code><\/pre>\n<p><!--more--><\/p>\n<p>\u4e0a\u8ff0\u4ee3\u7801\u53cd\u7f16\u8bd1\u540e\u7684\u5b57\u8282\u7801\u6307\u4ee4\u5982\u4e0b\uff1a<\/p>\n<pre><code>$ javap -c DoubleCheckedLocking.class\nCompiled from \"DoubleCheckedLocking.java\"\npublic class net.coderbee.dcl.DoubleCheckedLocking {\n  public net.coderbee.dcl.DoubleCheckedLocking();\n    Code:\n       0: aload_0\n       1: invokespecial #10                 \/\/ Method java\/lang\/Object.\"&lt;init&gt;\":()V\n       4: return\n\n  public static net.coderbee.dcl.Resource getInstance();\n    Code:\n       0: getstatic     #18                 \/\/ Field resource:Lnet\/coderbee\/dcl\/Resource;\n       3: ifnonnull     35\n       6: ldc           #1                  \/\/ class net\/coderbee\/dcl\/DoubleCheckedLocking\n       8: dup\n       9: astore_0\n      10: monitorenter\n      11: getstatic     #18                 \/\/ Field resource:Lnet\/coderbee\/dcl\/Resource;\n      14: ifnonnull     27\n      17: new           #20                 \/\/ class net\/coderbee\/dcl\/Resource\n      20: dup\n      21: invokespecial #22                 \/\/ Method net\/coderbee\/dcl\/Resource.\"&lt;init&gt;\":()V\n      24: putstatic     #18                 \/\/ Field resource:Lnet\/coderbee\/dcl\/Resource;\n      27: aload_0\n      28: monitorexit\n      29: goto          35\n      32: aload_0\n      33: monitorexit\n      34: athrow\n      35: getstatic     #18                 \/\/ Field resource:Lnet\/coderbee\/dcl\/Resource;\n      38: areturn\n    Exception table:\n       from    to  target type\n          11    29    32   any\n          32    34    32   any\n}\n<\/code><\/pre>\n<p>\u6700\u91cd\u8981\u7684\u662f\u4e0b\u9762\u8fd9\u51e0\u884c\uff0cJava \u91cc\u521b\u5efa\u4e00\u4e2a\u5bf9\u8c61\u5305\u542b\u4e09\u4e2a\u6b65\u9aa4\uff1a\u5206\u914d\u5185\u5b58\u3001\u6267\u884c\u521d\u59cb\u5316\u3001\u8d4b\u503c\u7ed9\u5f15\u7528\u3002<\/p>\n<pre><code>17: new           #20                 \/\/ class net\/coderbee\/dcl\/Resource\n20: dup\n21: invokespecial #22                 \/\/ Method net\/coderbee\/dcl\/Resource.\"&lt;init&gt;\":()V\n24: putstatic     #18                 \/\/ Field\n<\/code><\/pre>\n<p>\u7531\u4e8e\u91cd\u6392\u5e8f\u7684\u539f\u56e0\uff0c\u53ef\u80fd\u5728\u521d\u59cb\u5316\u4e4b\u524d\u5c31\u628a\u5bf9\u8c61\u8d4b\u503c\u7ed9\u5f15\u7528\uff0c\u5bfc\u81f4\u8bbf\u95ee\u7684\u7ebf\u7a0b\u770b\u5230\u4e00\u4e2a\u672a\u521d\u59cb\u5316\u5b8c\u6210\u7684\u5bf9\u8c61\u3002\u8fd9\u5c31\u662f\u53cc\u91cd\u68c0\u67e5\u52a0\u9501\u4e0d\u7528 volatile \u7684\u81f4\u547d\u95ee\u9898\u3002<\/p>\n<p>\u300aJava\u5e76\u53d1\u7f16\u7a0b\u5b9e\u8df5\u300b\u91cc\u63d0\u5230\u7684\u4e00\u4e9b\u53ef\u80fd\u91cd\u6392\u5e8f\u7684\u573a\u666f\uff1a<\/p>\n<blockquote>\n<ul>\n<li>\u7f16\u8bd1\u5668\u751f\u6210\u7684\u6307\u4ee4\u987a\u5e8f\u53ef\u4ee5\u4e0e\u6e90\u7801\u4e2d\u7684\u987a\u5e8f\u4e0d\u540c\u3002<\/li>\n<li>\u7f16\u8bd1\u5668\u4f1a\u628a\u53d8\u91cf\u4fdd\u5b58\u5728\u5bc4\u5b58\u5668\u4e2d\uff0c\u800c\u4e0d\u662f\u5185\u5b58\u4e2d\u3002<\/li>\n<li>\u5904\u7406\u5668\u53ef\u4ee5\u91c7\u7528\u4e71\u5e8f\u6216\u5e76\u884c\u7b49\u65b9\u5f0f\u6765\u6267\u884c\u6307\u4ee4\u3002<\/li>\n<li>\u7f13\u5b58\u53ef\u80fd\u4f1a\u6539\u53d8\u5c06\u5199\u5165\u53d8\u91cf\u63d0\u4ea4\u5230\u4e3b\u5185\u5b58\u7684\u987a\u5e8f\u3002<\/li>\n<li>\u4fdd\u5b58\u5728\u5904\u7406\u5668\u672c\u5730\u7f13\u5b58\u4e2d\u7684\u503c\uff0c\u5bf9\u5176\u4ed6\u5904\u7406\u5668\u4e0d\u53ef\u89c1\u3002<\/li>\n<\/ul>\n<\/blockquote>\n<p>\u7ed3\u5408 <code>DoubleCheckedLocking<\/code> \u4ee3\u7801\u6765\u770b\u770b\u4ec0\u4e48\u60c5\u51b5\u4e0b\u5c31\u4f1a\u51fa\u73b0\u4e0a\u8ff0\u95ee\u9898\uff1a<br \/>\n\u52a0\u5165\u7ebf\u7a0bA\u8c03\u7528 <code>getInstance<\/code> \u65b9\u6cd5\uff0c\u53d1\u73b0 resource \u5f15\u7528\u662f\u7a7a\u7684\uff0c\u5c31\u8fdb\u5165\u540c\u6b65\u5757\uff0c\u518d\u6b21\u5224\u65ad\u53d1\u73b0 resource \u8fd8\u662f\u4e3a\u7a7a\uff0c\u5f00\u59cb\u521b\u5efa\u5bf9\u8c61\u7684\u7b2c\u4e00\u6b65 \u5206\u914d\u5185\u5b58\uff0c\u7531\u4e8e\u91cd\u6392\u5e8f\uff0c\u628a\u65b0\u5bf9\u8c61\u7684\u8d4b\u503c\u7ed9\u4e86 resource\uff0c\u5e76\u5237\u65b0\u5230\u4e86\u4e3b\u5b58\uff1b\u6b64\u65f6\u53e6\u4e00\u4e2a\u7ebf\u7a0bB \u4e5f\u8c03\u7528 <code>getInstance<\/code> \u65b9\u6cd5\uff0c\u53d1\u73b0 resource \u5f15\u7528\u975e\u7a7a\uff0c\u76f4\u63a5\u5f00\u59cb\u8bbf\u95ee resouce \u5bf9\u8c61\uff0c\u5b83\u8bbf\u95ee\u7684\u5bf9\u8c61\u53ef\u80fd\u662f\u672a\u521d\u59cb\u5316\u5b8c\u6210\u7684\u3002<\/p>\n<p>\u52a0\u4e0a volatile \u53ef\u80fd\u7981\u6b62\u6307\u4ee4\u91cd\u6392\u5e8f\uff0c\u8981\u6c42\u7ed9\u5f15\u7528\u8d4b\u503c\u5fc5\u987b\u5728\u5bf9\u8c61\u521d\u59cb\u5316\u5b8c\u6210\u4e4b\u540e\u3002<\/p>\n<p>synchronized \u540c\u6b65\u5757\u53ef\u80fd\u4f1a\u7ed9\u4eba\u4e00\u79cd\u5047\u8c61\uff0c\u4ee5\u4e3a\u89e3\u51b3\u4e86\u540c\u6b65\u3001\u53ef\u89c1\u6027\u7684\u95ee\u9898\uff0c\u5b83\u786e\u5b9e\u53ef\u4ee5\u89e3\u51b3\u8fd9\u4e24\u4e2a\u95ee\u9898\uff0c\u524d\u63d0\u662f\u7ebf\u7a0b\u90fd\u7ecf\u8fc7\u540c\u6b65\u5757\u3002<\/p>\n<p>\u800c\u53cc\u91cd\u68c0\u67e5\u52a0\u9501\u5b58\u5728\u4e0d\u7ecf\u8fc7\u540c\u6b65\u5757\u7684\u95ee\u9898\u3002<\/p>\n<p>\u540c\u6b65\u5757\u5185\u7684\u4ee3\u7801\u4ecd\u7136\u662f\u53ef\u4ee5\u91cd\u6392\u5e8f\u7684\u3002<\/p>\n<p>\u5bf9\u4e8e\u5ef6\u8fdf\u521d\u59cb\u5316\uff0c\u63a8\u8350\u7684\u662f\u8d44\u6e90\u5360\u4f4d\u7b26\u7c7b\u6a21\u5f0f\uff0c\u793a\u4f8b\u5982\u4e0b\uff1a<\/p>\n<pre><code class=\"java\">public class ResourceFactory {\n    static class ResourceHolder {\n        static Resource resource = new Resource();\n    }\n\n    public static Resource getInstance() {\n        return ResourceHolder.resource;\n    }\n}\n<\/code><\/pre>\n<hr \/>\n<p>\u6b22\u8fce\u5173\u6ce8\u6211\u7684\u5fae\u4fe1\u516c\u4f17\u53f7: <strong>coderbee\u7b14\u8bb0<\/strong> \u3002<br \/>\n<img loading=\"lazy\" decoding=\"async\" width=\"258\" height=\"258\" src=\"https:\/\/coderbee.net\/wp-content\/uploads\/2019\/01\/coderbee-note.jpg\" class=\"alignnone size-full wp-image-1707\" \/><\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u4e00\u4e2a\u95ee\u9898\uff1a\u53cc\u91cd\u68c0\u67e5\u52a0\u9501\u4e3a\u4ec0\u4e48\u7528\u4e86 volatile \u5c31\u53ef\u4ee5\u6b63\u786e\u5de5\u4f5c\uff1f \u53cd\u8fc7\u6765\u95ee\uff1a &hellip; <a href=\"https:\/\/coderbee.net\/index.php\/concurrent\/20210522\/2149\">\u7ee7\u7eed\u9605\u8bfb <span class=\"meta-nav\">&rarr;<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[121],"tags":[111,354],"_links":{"self":[{"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/posts\/2149"}],"collection":[{"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/comments?post=2149"}],"version-history":[{"count":4,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/posts\/2149\/revisions"}],"predecessor-version":[{"id":2158,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/posts\/2149\/revisions\/2158"}],"wp:attachment":[{"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/media?parent=2149"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/categories?post=2149"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/coderbee.net\/index.php\/wp-json\/wp\/v2\/tags?post=2149"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}