“`”<\/p>\n
\u53cc\u91cd\u68c0\u9a8c\u52a0\u9501\u6a21\u5f0f\uff08double checked locking pattern\uff09\uff0c\u662f\u4e00\u79cd\u4f7f\u7528\u540c\u6b65\u5757\u52a0\u9501\u7684\u65b9\u6cd5\u3002\u7a0b\u5e8f\u5458\u79f0\u5176\u4e3a\u53cc\u91cd\u68c0\u67e5\u9501\uff0c\u56e0\u4e3a\u4f1a\u6709\u4e24\u6b21\u68c0\u67e5 <code>uniqueInstance == null<\/code>\uff0c\u4e00\u6b21\u662f\u5728\u540c\u6b65\u5757\u5916\uff0c\u4e00\u6b21\u662f\u5728\u540c\u6b65\u5757\u5185\u3002\u4e3a\u4ec0\u4e48\u5728\u540c\u6b65\u5757\u5185\u8fd8\u8981\u518d\u68c0\u9a8c\u4e00\u6b21\uff1f\u56e0\u4e3a\u53ef\u80fd\u4f1a\u6709\u591a\u4e2a\u7ebf\u7a0b\u4e00\u8d77\u8fdb\u5165\u540c\u6b65\u5757\u5916\u7684 if\uff0c\u5982\u679c\u5728\u540c\u6b65\u5757\u5185\u4e0d\u8fdb\u884c\u4e8c\u6b21\u68c0\u9a8c\u7684\u8bdd\u5c31\u4f1a\u751f\u6210\u591a\u4e2a\u5b9e\u4f8b\u4e86\u3002<\/p>\n
<pre><code class=""language-java"" lang=""java"">public class Singleton {
\n private static Singleton uniqueInstance;
\n private Singleton (){}<\/p>\n
public static Singleton getSingleton() {
\n if (uniqueInstance == null) { \/\/Single Checked
\n synchronized (Singleton.class) {
\n if (uniqueInstance == null) { \/\/Double Checked
\n uniqueInstance = new Singleton();
\n }
\n }
\n }
\n return uniqueInstance;
\n }
\n}
\n<\/code><\/pre><\/p>\n
\u8fd9\u6bb5\u4ee3\u7801\u770b\u8d77\u6765\u5f88\u5b8c\u7f8e\uff0c\u5f88\u53ef\u60dc\uff0c\u5b83\u662f\u6709\u95ee\u9898\u3002\u4e3b\u8981\u5728\u4e8euniqueInstance = new Singleton()\u8fd9\u53e5\uff0c\u8fd9\u5e76\u975e\u662f\u4e00\u4e2a\u539f\u5b50\u64cd\u4f5c\uff0c\u4e8b\u5b9e\u4e0a\u5728 JVM \u4e2d\u8fd9\u53e5\u8bdd\u5927\u6982\u505a\u4e86\u4e0b\u9762 3 \u4ef6\u4e8b\u60c5\u3002<\/p>\n
<ol start="""">
\n<li>\u7ed9 uniqueInstance \u5206\u914d\u5185\u5b58<\/li>
\n<li>\u8c03\u7528 Singleton \u7684\u6784\u9020\u51fd\u6570\u6765\u521d\u59cb\u5316\u6210\u5458\u53d8\u91cf<\/li>
\n<li>\u5c06uniqueInstance\u5bf9\u8c61\u6307\u5411\u5206\u914d\u7684\u5185\u5b58\u7a7a\u95f4\uff08\u6267\u884c\u5b8c\u8fd9\u6b65 uniqueInstance \u5c31\u4e3a\u975e null \u4e86\uff09<\/li>
\n<\/ol><\/p>\n
\u4f46\u662f\u5728 JVM \u7684\u5373\u65f6\u7f16\u8bd1\u5668\u4e2d\u5b58\u5728\u6307\u4ee4\u91cd\u6392\u5e8f\u7684\u4f18\u5316\u3002\u4e5f\u5c31\u662f\u8bf4\u4e0a\u9762\u7684\u7b2c\u4e8c\u6b65\u548c\u7b2c\u4e09\u6b65\u7684\u987a\u5e8f\u662f\u4e0d\u80fd\u4fdd\u8bc1\u7684\uff0c\u6700\u7ec8\u7684\u6267\u884c\u987a\u5e8f\u53ef\u80fd\u662f 1-2-3 \u4e5f\u53ef\u80fd\u662f 1-3-2\u3002\u5982\u679c\u662f\u540e\u8005\uff0c\u5219\u5728 3 \u6267\u884c\u5b8c\u6bd5\u30012 \u672a\u6267\u884c\u4e4b\u524d\uff0c\u88ab\u7ebf\u7a0b\u4e8c\u62a2\u5360\u4e86\uff0c\u8fd9\u65f6uniqueInstance\u5df2\u7ecf\u662f\u975e null \u4e86\uff08\u4f46\u5374\u6ca1\u6709\u521d\u59cb\u5316\uff09\uff0c\u6240\u4ee5\u7ebf\u7a0b\u4e8c\u4f1a\u76f4\u63a5\u8fd4\u56de uniqueInstance\uff0c\u7136\u540e\u4f7f\u7528\uff0c\u7136\u540e\u987a\u7406\u6210\u7ae0\u5730\u62a5\u9519\u3002<\/p>\n
\u6211\u4eec\u53ea\u9700\u8981\u5c06 uniqueInstance \u53d8\u91cf\u58f0\u660e\u6210 volatile \u5c31\u53ef\u4ee5\u4e86\u3002<\/p>\n
<pre><code class=""language-java"" lang=""java"">public class Singleton {
\n private volatile static Singleton uniqueInstance; \/\/\u58f0\u660e\u6210 volatile
\n private Singleton (){}<\/p>\n
public static Singleton getSingleton() {
\n if (uniqueInstance == null) {
\n synchronized (Singleton.class) {
\n if (uniqueInstance == null) {
\n uniqueInstance = new Singleton();
\n }
\n }
\n }
\n return uniqueInstance;
\n }<\/p>\n
}
\n<\/code><\/pre><\/p>\n
\u6709\u4e9b\u4eba\u8ba4\u4e3a\u4f7f\u7528 volatile \u7684\u539f\u56e0\u662f\u53ef\u89c1\u6027\uff0c\u4e5f\u5c31\u662f\u53ef\u4ee5\u4fdd\u8bc1\u7ebf\u7a0b\u5728\u672c\u5730\u4e0d\u4f1a\u5b58\u6709 uniqueInstance \u7684\u526f\u672c\uff0c\u6bcf\u6b21\u90fd\u662f\u53bb\u4e3b\u5185\u5b58\u4e2d\u8bfb\u53d6\u3002\u4f46\u5176\u5b9e\u662f\u4e0d\u5bf9\u7684\u3002\u4f7f\u7528 volatile \u7684\u4e3b\u8981\u539f\u56e0\u662f\u5176\u53e6\u4e00\u4e2a\u7279\u6027\uff1a\u7981\u6b62\u6307\u4ee4\u91cd\u6392\u5e8f\u4f18\u5316\u3002\u4e5f\u5c31\u662f\u8bf4\uff0c\u5728 volatile \u53d8\u91cf\u7684\u8d4b\u503c\u64cd\u4f5c\u540e\u9762\u4f1a\u6709\u4e00\u4e2a\u5185\u5b58\u5c4f\u969c\uff08\u751f\u6210\u7684\u6c47\u7f16\u4ee3\u7801\u4e0a\uff09\uff0c\u8bfb\u64cd\u4f5c\u4e0d\u4f1a\u88ab\u91cd\u6392\u5e8f\u5230\u5185\u5b58\u5c4f\u969c\u4e4b\u524d\u3002\u6bd4\u5982\u4e0a\u9762\u7684\u4f8b\u5b50\uff0c\u53d6\u64cd\u4f5c\u5fc5\u987b\u5728\u6267\u884c\u5b8c 1-2-3 \u4e4b\u540e\u6216\u8005 1-3-2 \u4e4b\u540e\uff0c\u4e0d\u5b58\u5728\u6267\u884c\u5230 1-3 \u7136\u540e\u53d6\u5230\u503c\u7684\u60c5\u51b5\u3002\u4ece\u300c\u5148\u884c\u53d1\u751f\u539f\u5219\u300d\u7684\u89d2\u5ea6\u7406\u89e3\u7684\u8bdd\uff0c\u5c31\u662f\u5bf9\u4e8e\u4e00\u4e2a volatile \u53d8\u91cf\u7684\u5199\u64cd\u4f5c\u90fd\u5148\u884c\u53d1\u751f\u4e8e\u540e\u9762\u5bf9\u8fd9\u4e2a\u53d8\u91cf\u7684\u8bfb\u64cd\u4f5c\uff08\u8fd9\u91cc\u7684\u201c\u540e\u9762\u201d\u662f\u65f6\u95f4\u4e0a\u7684\u5148\u540e\u987a\u5e8f\uff09\u3002<\/p>\n
\u4f46\u662f\u7279\u522b\u6ce8\u610f\u5728 Java 5 \u4ee5\u524d\u7684\u7248\u672c\u4f7f\u7528\u4e86 volatile \u7684\u53cc\u68c0\u9501\u8fd8\u662f\u6709\u95ee\u9898\u7684\u3002\u5176\u539f\u56e0\u662f Java 5 \u4ee5\u524d\u7684 JMM \uff08Java \u5185\u5b58\u6a21\u578b\uff09\u662f\u5b58\u5728\u7f3a\u9677\u7684\uff0c\u5373\u4f7f\u5c06\u53d8\u91cf\u58f0\u660e\u6210 volatile \u4e5f\u4e0d\u80fd\u5b8c\u5168\u907f\u514d\u91cd\u6392\u5e8f\uff0c\u4e3b\u8981\u662f volatile \u53d8\u91cf\u524d\u540e\u7684\u4ee3\u7801\u4ecd\u7136\u5b58\u5728\u91cd\u6392\u5e8f\u95ee\u9898\u3002\u8fd9\u4e2a volatile \u5c4f\u853d\u91cd\u6392\u5e8f\u7684\u95ee\u9898\u5728 Java 5 \u4e2d\u624d\u5f97\u4ee5\u4fee\u590d\uff0c\u6240\u4ee5\u5728\u8fd9\u4e4b\u540e\u624d\u53ef\u4ee5\u653e\u5fc3\u4f7f\u7528 volatile\u3002<\/p>\n
\u76f8\u4fe1\u4f60\u4e0d\u4f1a\u559c\u6b22\u8fd9\u79cd\u590d\u6742\u53c8\u9690\u542b\u95ee\u9898\u7684\u65b9\u5f0f\uff0c\u5f53\u7136\u6211\u4eec\u6709\u66f4\u597d\u7684\u5b9e\u73b0\u7ebf\u7a0b\u5b89\u5168\u7684\u5355\u4f8b\u6a21\u5f0f\u7684\u529e\u6cd5\u3002<\/p>\n
\u00a0<\/p>\n
<pre><code> "“`
\n<\/code><\/pre>\n","protected":false},"excerpt":{"rendered":"
“`” \u53cc\u91cd\u68c0\u9a8c\u52a0\u9501\u6a21\u5f0f\uff08double checked locking pattern […]<\/p>\n","protected":false},"author":7,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[101],"tags":[],"class_list":["post-39873","post","type-post","status-publish","format-standard","hentry","category-c"],"_links":{"self":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts\/39873","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/users\/7"}],"replies":[{"embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/comments?post=39873"}],"version-history":[{"count":1,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts\/39873\/revisions"}],"predecessor-version":[{"id":39874,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts\/39873\/revisions\/39874"}],"wp:attachment":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/media?parent=39873"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/categories?post=39873"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/tags?post=39873"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}