CAS\uff1a\u5373compare and swap \uff08\u6bd4\u8f83\u5e76\u66ff\u6362\uff09\uff0cCAS\u9700\u8981\u89e3\u51b3\u7684\u662f\u591a\u7ebf\u7a0b\u5e76\u53d1\u65f6\u7ebf\u7a0b\u95f4\u5207\u6362\u65f6\u95f4\u7247\u5bfc\u81f4\u7684\u539f\u5b50\u6027\u95ee\u9898\u3002<\/p>\n
\u6211\u4eec\u5148\u770b\u4e00\u6bb5\u4ee3\u7801 *\/ Unsafe<\/p>\n Unsafe\u7c7b\uff0c\u5168\u9650\u5b9a\u540d\u662fsun.misc.Unsafe,\u4ece\u540d\u5b57\u4e2d\u6211\u4eec\u53ef\u4ee5\u770b\u51fa\u6765\u8fd9\u4e2a\u7c7b\u5bf9\u666e\u901a\u7a0b\u5e8f\u5458\u6765\u8bf4 \u662f\u201c\u5371\u9669\u201d\u7684\uff0c\u4e00\u822c\u5e94\u7528\u5f00\u53d1\u8005\u4e0d\u4f1a\u7528\u5230\u8fd9\u4e2a\u7c7b\u3002\u5982\u679c\u6211\u4eec\u5fc5\u987b\u8981\u5b9e\u73b0\u81ea\u5df1\u7684\u57fa\u4e8eUnsafe\u7c7b \u7684\u529f\u80fd\uff0c\u5219\u53ea\u80fd\u901a\u8fc7\u53cd\u5c04\u83b7\u53d6Unsafe\u7c7b\uff0c\u56e0\u4e3aUnsafe\u5728\u521b\u5efa\u65f6\u52a0\u4e86\u9650\u5236\uff0c\u53ea\u6709rt.jar\u5305\u4e0b \u7684\u7c7b\u5177\u6709\u6743\u9650\u8bbf\u95ee,\u4eceUnsafe\u7684getUnsafe\u53ef\u4ee5\u770b\u51fa\u6765 incrementAndGet \u5373\u6700\u7ec8\u4f1a\u628aAtomiclnteger\u4e2d\u7684value+1,\u5e76\u4e14\u8fd4\u56de+1\u540e\u7684\u503c CAS\uff1a\u5373compare and swap \uff08\u6bd4\u8f83\u5e76\u66ff\u6362\uff09\uff0cCAS\u9700\u8981\u89e3\u51b3\u7684\u662f\u591a\u7ebf\u7a0b\u5e76\u53d1\u65f6\u7ebf\u7a0b\u95f4\u5207\u6362\u65f6\u95f4\u7247\u5bfc\u81f4 […]<\/p>\n","protected":false},"author":7,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[118],"tags":[],"class_list":["post-10203","post","type-post","status-publish","format-standard","hentry","category-java"],"_links":{"self":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts\/10203","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=10203"}],"version-history":[{"count":1,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts\/10203\/revisions"}],"predecessor-version":[{"id":10204,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/posts\/10203\/revisions\/10204"}],"wp:attachment":[{"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/media?parent=10203"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/categories?post=10203"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/wx.kaifamiao.info\/index.php\/wp-json\/wp\/v2\/tags?post=10203"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
\npublic class CasDemol {
\nstatic int k = 0;
\npublic static void main(String[] args) {
\nfor(int i = 0;i<10;i++) {
\nThread t = new Thread(() -> {
\n\/\/\u6bcf\u4e2a\u7ebf\u7a0b\u8ba9count\u81ea\u589e100\u6b21
\ntry {
\n\/\/\u7b49\u5f85\u6240\u6709\u7ebf\u7a0b\u90fd\u8d77\u6765
\nThread.sleep (200);
\n} catch (InterruptedException e) {
\ne.printStackTrace();
\n}
\nfor (int j = 0; j < 100; j++) {
\nk++;
\n}
\n});
\nt.start();
\n}
\ntry {
\n\/\/\u963b\u585e2\u79d2\uff0c\u7b49\u5f85\u7ebf\u7a0b\u6267\u884c\u7ed3\u675f
\nThread.sleep(2000);
\n} catch (InterruptedException e) {
\ne.printStackTrace();
\n}
\nSystem.out.println(k);
\n}
\n}
\n\u5341\u4e2a\u7ebf\u7a0b\uff0c\u540c\u65f6\u8ba9k\u7684\u503c+100,\u4f46\u662f\u7ed3\u679c\u8f93\u51fa\u7684\u503c\u662f\u5c0f\u4e8e\u7b49\u4e8e1000\u7684\uff0c\u8fd9\u662f\u4e3a\u4ec0\u4e48\u5462\uff1f
\n\u539f\u56e0\u5728\u4e8ek++\u8fd9\u4e2a\u64cd\u4f5c\u5728CPU\u5c42\u9762\u5e76\u4e0d\u4fdd\u8bc1\u539f\u5b50\u6027\uff0c\u4f1a\u88ab\u62c6\u5206\u4e3a\u591a\u4e2a\u6307\u4ee4
\n1,\u4ece\u5185\u5b58\u52a0\u8f7dk\u7684\u503c\u5230CPU\u5bc4\u5b58\u5668
\n2,\u5728\u5bc4\u5b58\u5668\u628a\u503c+1
\n3,\u628a\u503c\u5199\u5230\u5185\u5b58
\n\u6b64\u65f6\u7531\u4e8e\u7ebf\u7a0b\u95f4\u4f1a\u5b58\u5728\u65f6\u95f4\u7247\u7684\u5207\u6362\uff0c\u5373\u5047\u5982\u7ebf\u7a0bA\u6267\u884c\u5230\u7b2c\u4e00\u6b65\uff0c\u67e5\u8be2k\u7684\u503c=0,\u6b64\u65f6CPU \u8fdb\u884c\u4e86\u5207\u6362\uff0c\u7ebf\u7a0bB\u6210\u529f\u7684\u6267\u884c\u4e86 1\u548c2,\u6b64\u65f6\u5bf9\u4e8e\u7ebf\u7a0bB\u6765\u8bf4K=l,\u6b64\u65f6\u65f6\u95f4\u7247\u5207\u6362\u5230A\u7ebf \u7a0b\uff0cA\u7ebf\u7a0b\u4e2d\u7684k=0,\u6b64\u65f6\u6267\u884c2, k+l=l,\u90a3\u4e48\u5c31\u548c\u6211\u4eec\u7684\u9884\u671f\u4e0d\u540c\u4e86\uff0c\u5e76\u53d1\u95ee\u9898\u5c31\u4ea7\u751f\u4e86
\n\u89e3\u51b3\u65b9\u6848
\n\u4e3a\u4e86\u89e3\u51b3\u4e0a\u8ff0\u95ee\u9898\uff0c\u6211\u4eec\u53ef\u4ee5\u4f7f\u7528\u52a0\u9501\u6765\u907f\u514d\u5e76\u53d1\uff0c\u4f7f\u7528synchronized\u6765\u52a0\u9501\uff0c\u4f46\u662f synchronized\u662f\u4e00\u79cd\u60b2\u89c2\u9501\u7684\u601d\u60f3\uff0c\u6027\u80fd\u4f1a\u6bd4\u8f83\u5dee
\nCAS\u91c7\u7528\u7684\u5c31\u662f\u4e00\u79cd\u4e50\u89c2\u9501\u7684\u601d\u60f3\uff0c\u5373\u6267\u884c\u65f6\u5047\u8bbe\u6ca1\u6709\u5e76\u53d1\u95ee\u9898\uff0c\u5148\u6bd4\u8f83\uff0c\u6bd4\u8f83\u540e\u53d1\u73b0\u6ca1\u6709\u88ab \u6539\u52a8\u5219\u66ff\u6362\uff0c\u88ab\u6539\u52a8\u4e86\u5219\u81ea\u65cb\u91cd\u65b0\u6267\u884c\u4e0a\u8ff01\u548c2\u6b65\u9aa4\u76f4\u5230\u6210\u529f
\njava\u5df2\u7ecf\u63d0\u4f9b\u4e86\u591a\u79cd\u652f\u6301\u5e76\u53d1\u7684cas\u76f8\u5173\u7c7b\uff0c\u4e3b\u8981\u662f\u5728java.util.concurrent.atomic\u5305\u4e0b\uff0c \u5982 Atomiclnteger, AtomicBoolean, AtomicLong \u7b49
\nAtomiclnteger \u6e90\u7801\u5206\u6790
\n\u6211\u4eec\u5c31\u770b\u4e00\u79cdAtomiclnteger\u6e90\u7801\u7684\u5b9e\u73b0
\npublic class Atomiclnteger extends Number implements java.io.Serializable {
\nprivate static final long serialVersionUID = 6214790243416807050L;
\n\/\/ setup to use Unsafe, compareAndSwapInt for updates
\nprivate static final Unsafe unsafe = Unsafe.getUnsafe();
\nprivate static final long valueOffset;
\nstatic {
\ntry {
\nvalueOffset = unsafe.objectFieldOffset
\n(Atomiclnteger.class.getDeclaredField("value"));
\n} catch (Exception ex) { throw new Error(ex) ; }
\n}
\nprivate volatile int value;
\n\/**
\nCreates a new Atomiclnteger with the given initial value.
\n*
\n@param initialValue the initial value
\n\/
\npublic Atomiclnteger(int initialValue) {
\nvalue = initialValue;
\n}
\n\/<\/em>*
\nCreates a new Atomiclnteger with initial value {@code 0}.
\n\/
\npublic Atomiclnteger() {
\n}
\n\/<\/em>*
\nGets the current value.
\n*
\n*@return the current value<\/p>\n
\npublic final int get() {
\nreturn value;
\n}
\npublic final int incrementAndGet() {
\nreturn unsafe.getAndAddlnt(this, valueOffset, 1) + 1;
\npublic final boolean compareAndSet(int expect, int update) {
\nreturn unsafe.compareAndSwapInt(this, valueOffset, expect, update);
\n}<\/p>\n
\nUnsafe\u4e3a\u6211\u4eec\u5728Java\u4e2d\u63d0\u4f9b\u4e86\u76f4\u63a5\u64cd\u4f5c\u5185\u5b58\u7684\u80fd\u529b\u3002
\nvalueOffset
\nvalueOffset =
\nunsafe.objectFieldOffset (Atomiclnteger.class.getDeclaredField( "value\u201d )), \u770b\u81f3Q\u8fd9 \u4e2a\u4ee3\u7801\uff0c\u53ef\u4ee5\u770b\u51fa\u6765valueOffset\u7684\u503c\u662fAtomicInteger\u4e2d\u7684value\u503c\u5728\u5185\u5b58\u4e2d\u7684\u5730\u5740\uff0c\u5373\u504f \u79fb\u91cf
\ncompareAndSwapInt
\nunsafe.compareAndSwapInt(this, valueOffset, expect, update)
\ncas\u7684\u6838\u5fc3\u64cd\u4f5c\uff0c\u5373\u67e5\u8be2\u53c2\u65701\u4e2d\u5185\u5b58\u5730\u5740\u4e3avalueOffset\u7684\u503c\uff0c\u5f53\u7b49\u4e8e\u53c2\u65703\u65f6\u4fee\u6539\u4e3a\u53c2\u6570
\n\u8fd4\u56de\u6210\u529f\uff0c\u5f53\u4e0d\u76f8\u7b49\u65f6\u8fd4\u56defalse
\n\u53c2\u65701:\u64cd\u4f5c\u7684\u5b9e\u4f8b
\n\u53c2\u65702\uff1a\u64cd\u4f5c\u5b9e\u4f8b\u4e2d\u5185\u5b58\u5730\u5740
\n\u53c2\u65703\uff1a\u9884\u671f\u503c
\n\u53c2\u65704\uff1a\u671f\u671b\u4fee\u6539\u6210\u7684\u503c<\/p>\n
\n\u81ea\u589e1\u5e76\u4e14\u8fd4\u56de
\n\u770b getAndAddInt \u65b9\u6cd5
\npublic final int getAndAddlnt(Object varl, long var2, int var4) {
\nint var5;
\ndo {
\n\/\/\u4ece\u5185\u5b58\u4e2d\u8bfb\u53d6\u5f53\u524d\u5bf9\u8c61\u5730\u5740\u4e3avalueOffset\u7684\u503c
\nvar5 = this.getlntVolatile(varl, var2);
\n\/\/\u81ea\u65cb\u76f4\u5230cas\u64cd\u4f5c\u6210\u529f\u4e3a\u6b62\uff0c\u5f53var5\u7684\u503c\u4ecd\u7136\u662fvar5\u65f6\u4fee\u6539\u4e3avar5+var4
\n} while(!this.compareAndSwapInt(varl, var2, var5, var5 + var4));
\nreturn var5;
\n}<\/p>\n
\n\u603b\u7ed3
\n\u770b\u5b8cAtomicInteger\u7684\u6e90\u7801\uff0c\u6211\u4eec\u57fa\u672c\u4e0a\u5df2\u7ecf\u61c2\u4e86 cas\u7684\u5b9e\u73b0\uff0c\u5373\u901a\u8fc7Unsafe\u7c7b\u6765\u76f4\u63a5\u6bd4\u8f83 \u5728\u5185\u5b58\u4e2d\u7684\u503c\uff0c\u5982\u679c\u76f8\u540c\u5219\u66ff\u6362\uff0c\u5931\u8d25\u5219\u81ea\u65cb\u76f4\u5230\u6210\u529f\uff0c\u901a\u8fc7\u76f4\u63a5\u6bd4\u8f83\u5185\u5b58\u4e2d\u7684\u503c\u6765\u89e3\u51b3\u4e0a\u9762 \u65f6\u95f4\u7247\u5207\u6362\u5bfc\u81f4\u7684\u539f\u5b50\u6027\u95ee\u9898<\/p>\n","protected":false},"excerpt":{"rendered":"