{"id":10008032,"date":"2023-07-04T12:58:43","date_gmt":"2023-07-04T04:58:43","guid":{"rendered":"https:\/\/ityet.com\/?p=10008032"},"modified":"2023-07-04T12:58:43","modified_gmt":"2023-07-04T04:58:43","slug":"reentrantlock%e6%ba%90%e7%a0%81%e8%a7%a3%e6%9e%90-%e4%ba%ac%e4%b8%9c%e4%ba%91%e6%8a%80%e6%9c%af%e5%9b%a2%e9%98%9f","status":"publish","type":"post","link":"https:\/\/itmax.cn\/?p=10008032","title":{"rendered":"ReentrantLock\u6e90\u7801\u89e3\u6790 | \u4eac\u4e1c\u4e91\u6280\u672f\u56e2\u961f"},"content":{"rendered":"<p>\u5e76\u53d1\u6307\u540c\u4e00\u65f6\u95f4\u5185\u8fdb\u884c\u4e86\u591a\u4e2a\u7ebf\u7a0b\u3002\u5e76\u53d1\u95ee\u9898\u662f\u591a\u4e2a\u7ebf\u7a0b\u5bf9\u540c\u4e00\u8d44\u6e90\u8fdb\u884c\u64cd\u4f5c\u65f6\u4ea7\u751f\u7684\u95ee\u9898\u3002\u901a\u8fc7\u52a0\u9501\u53ef\u4ee5\u89e3\u51b3\u5e76\u53d1\u95ee\u9898\uff0cReentrantLock\u662f\u9501\u7684\u4e00\u79cd\u3002<\/p>\n<h2>1 ReentrantLock<\/h2>\n<h3>1.1 \u5b9a\u4e49<\/h3>\n<p>ReentrantLock\u662fLock\u63a5\u53e3\u7684\u5b9e\u73b0\u7c7b\uff0c\u53ef\u4ee5\u624b\u52a8\u7684\u5bf9\u67d0\u4e00\u6bb5\u8fdb\u884c\u52a0\u9501\u3002ReentrantLock\u53ef\u91cd\u5165\u9501\uff0c\u5177\u6709\u53ef\u91cd\u5165\u6027\uff0c\u5e76\u4e14\u652f\u6301\u53ef\u4e2d\u65ad\u9501\u3002\u5176\u5185\u90e8\u5bf9\u9501\u7684\u63a7\u5236\u6709\u4e24\u79cd\u5b9e\u73b0\uff0c\u4e00\u79cd\u4e3a\u516c\u5e73\u9501\uff0c\u53e6\u4e00\u79cd\u4e3a\u975e\u516c\u5e73\u9501.<\/p>\n<h3>1.2 \u5b9e\u73b0\u539f\u7406<\/h3>\n<p>ReentrantLock\u7684\u5b9e\u73b0\u539f\u7406\u4e3avolatile+CAS\u3002\u60f3\u8981\u8bf4\u660evolatile\u548cCAS\u9996\u5148\u8981\u8bf4\u660eJMM\u3002<\/p>\n<h4>1.2.1 JMM<\/h4>\n<p>JMM(java \u5185\u5b58\u6a21\u578b Java Memory Model \u7b80\u79f0JMM) \u672c\u8eab\u662f\u4e00\u4e2a\u62bd\u8c61\u7684\u6982\u5ff5,\u5e76\u4e0d\u5728\u5185\u5b58\u4e2d\u771f\u5b9e\u5b58\u5728\u7684,\u5b83\u63cf\u8ff0\u7684\u662f\u4e00\u7ec4\u89c4\u8303\u6216\u8005\u89c4\u5219,\u901a\u8fc7\u8fd9\u7ec4\u89c4\u8303\u5b9a\u4e49\u4e86\u7a0b\u5e8f\u4e2d\u5404\u4e2a\u53d8\u91cf\u7684\u8bbf\u95ee\u65b9\u5f0f.  <\/p>\n<p>\u7531\u4e8e JMM \u8fd0\u884c\u7a0b\u5e8f\u7684\u5b9e\u4f53\u662f\u7ebf\u7a0b.\u800c\u6bcf\u4e2a\u7ebf\u7a0b\u521b\u5efa\u65f6JMM\u90fd\u4f1a\u4e3a\u5176\u521b\u5efa\u4e00\u4e2a\u81ea\u5df1\u7684\u5de5\u4f5c\u5185\u5b58(\u6808\u7a7a\u95f4),\u5de5\u4f5c\u5185\u5b58\u662f\u6bcf\u4e2a\u7ebf\u7a0b\u7684\u79c1\u6709 \u6570\u636e\u533a\u57df.\u800cjava\u5185\u5b58\u6a21\u578b\u4e2d\u89c4\u5b9a\u6240\u6709\u7684\u53d8\u91cf\u90fd\u5b58\u50a8\u5728\u4e3b\u5185\u5b58\u4e2d,\u4e3b\u5185\u5b58\u662f\u5171\u4eab\u5185\u5b58\u533a\u57df,\u6240\u6709\u7ebf\u7a0b\u90fd\u53ef\u4ee5\u8bbf\u95ee,\u4f46\u7ebf\u7a0b\u7684\u53d8\u91cf\u7684\u64cd\u4f5c(\u8bfb\u53d6\u8d4b\u503c\u7b49)\u5fc5\u987b\u5728\u81ea\u5df1\u7684\u5de5\u4f5c\u5185\u5b58\u4e2d\u53bb\u8fdb\u884c,\u9996\u5148\u8981 \u5c06\u53d8\u91cf\u4ece\u4e3b\u5b58\u62f7\u8d1d\u5230\u81ea\u5df1\u7684\u5de5\u4f5c\u5185\u5b58\u4e2d,\u7136\u540e\u5bf9\u53d8\u91cf\u8fdb\u884c\u64cd\u4f5c,\u64cd\u4f5c\u5b8c\u6210\u540e\u518d\u5c06\u53d8\u91cf\u64cd\u4f5c\u5b8c\u540e\u7684\u65b0\u503c\u5199\u56de\u4e3b\u5185\u5b58,\u4e0d\u80fd\u76f4\u63a5\u64cd\u4f5c\u4e3b\u5185\u5b58\u7684\u53d8\u91cf,\u5404\u4e2a\u7ebf\u7a0b\u7684\u5de5\u4f5c\u5185\u5b58\u4e2d\u5b58\u50a8\u7740\u4e3b\u5185\u5b58\u7684\u53d8\u91cf\u62f7\u8d1d\u7684\u526f\u672c,\u56e0\u4e0d\u540c\u7684\u7ebf\u7a0b\u95f4\u65e0\u6cd5\u8bbf\u95ee\u5bf9\u65b9\u7684\u5de5\u4f5c\u5185\u5b58,\u7ebf\u7a0b\u95f4\u7684\u901a\u4fe1\u5fc5\u987b\u5728\u4e3b\u5185\u5b58\u6765\u5b8c\u6210\u3002<\/p>\n<p><img decoding=\"async\" referrerpolicy=\"no-referrer\" src=\"https:\/\/segmentfault.com\/img\/remote\/1460000043966721\" alt=\"\" title=\"\" loading=\"lazy\"><\/p>\n<p>\u5982\u56fe\u6240\u793a\uff1a\u7ebf\u7a0bA\u5bf9\u53d8\u91cfA\u7684\u64cd\u4f5c\uff0c\u53ea\u80fd\u662f\u4ece\u4e3b\u5185\u5b58\u4e2d\u62f7\u8d1d\u5230\u7ebf\u7a0b\u4e2d\uff0c\u518d\u5199\u56de\u5230\u4e3b\u5185\u5b58\u4e2d\u3002<\/p>\n<h4>1.2.2 volatile<\/h4>\n<p>volatile \u662fJAVA\u7684\u5173\u952e\u5b57\u7528\u4e8e\u4fee\u9970\u53d8\u91cf\uff0c\u662fjava\u865a\u62df\u673a\u7684\u8f7b\u91cf\u540c\u6b65\u673a\u5236\uff0cvolatile\u4e0d\u80fd\u4fdd\u8bc1\u539f\u5b50\u6027\u3002  <br \/>\u4f5c\u7528\uff1a<\/p>\n<ul>\n<li>\u7ebf\u7a0b\u53ef\u89c1\u6027\uff1a\u4e00\u4e2a\u53d8\u91cf\u5728\u67d0\u4e2a\u7ebf\u7a0b\u91cc\u4fee\u6539\u4e86\u5b83\u7684\u503c\uff0c\u5982\u679c\u4f7f\u7528\u4e86volatile\u5173\u952e\u5b57\uff0c\u90a3\u4e48\u522b\u7684\u7ebf\u7a0b\u53ef\u4ee5\u9a6c\u4e0a\u8bfb\u5230\u4fee\u6539\u540e\u7684\u503c\u3002<\/li>\n<li>\u6307\u4ee4\u91cd\u6392\u5e8f\uff1a\u6ca1\u52a0\u4e4b\u524d\uff0c\u6307\u4ee4\u662f\u5e76\u53d1\u6267\u884c\u7684\uff0c\u7b2c\u4e00\u4e2a\u7ebf\u7a0b\u6267\u884c\u5230\u4e00\u534a\u53e6\u4e00\u4e2a\u7ebf\u7a0b\u53ef\u80fd\u5f00\u59cb\u6267\u884c\u4e86\u3002\u52a0\u4e86volatile\u5173\u952e\u5b57\u540e\uff0c\u4e0d\u540c\u7ebf\u7a0b\u662f\u6309\u7167\u987a\u5e8f\u4e00\u6b65\u4e00\u6b65\u6267\u884c\u7684\u30021.2.3 CASCAS\u662fCompare and Swap\uff0c\u5c31\u662f\u6bd4\u8f83\u548c\u4ea4\u6362\uff0c\u800c\u6bd4\u8f83\u548c\u4ea4\u6362\u662f\u4e00\u4e2a\u539f\u5b50\u64cd\u4f5c\u3002\u7ebf\u7a0b\u57fa\u4e8eCAS\u4fee\u6539\u6570\u636e\u7684\u65b9\u5f0f\uff1a\u5148\u83b7\u53d6\u4e3b\u5185\u5b58\u6570\u636e\uff0c\u5728\u4fee\u6539\u4e4b\u524d\uff0c\u5148\u6bd4\u8f83\u6570\u636e\u662f\u5426\u4e00\u81f4\uff0c\u5982\u679c\u4e00\u81f4\u4fee\u6539\u4e3b\u5185\u5b58\u6570\u636e\uff0c\u5982\u679c\u4e0d\u4e00\u81f4\uff0c\u653e\u5f03\u8fd9\u6b21\u4fee\u6539\u3002<\/li>\n<\/ul>\n<p>\u4f5c\u7528\uff1aCAS\u4f1a\u4f7f\u7528\u73b0\u4ee3\u5904\u7406\u5668\u4e0a\u63d0\u4f9b\u7684\u9ad8\u6548\u673a\u5668\u7ea7\u522b\u539f\u5b50\u6307\u4ee4\uff0c\u8fd9\u4e9b\u539f\u5b50\u6307\u4ee4\u4ee5\u539f\u5b50\u65b9\u5f0f\u5bf9\u5185\u5b58\u6267\u884c\u8bfb-\u6539-\u5199\u64cd\u4f5c\u30021.2.4 AQSAQS\u7684\u5168\u79f0\u662fAbstractQueuedSynchronizer\uff08\u62bd\u8c61\u7684\u961f\u5217\u5f0f\u7684\u540c\u6b65\u5668\uff09\uff0cAQS\u5b9a\u4e49\u4e86\u4e00\u5957\u591a\u7ebf\u7a0b\u8bbf\u95ee\u5171\u4eab\u8d44\u6e90\u7684\u540c\u6b65\u5668\u6846\u67b6\u3002  <\/p>\n<p>AQS\u4e3b\u8981\u5305\u542b\u4e24\u90e8\u5206\u5185\u5bb9\uff1a\u5171\u4eab\u8d44\u6e90\u548c\u7b49\u5f85\u961f\u5217\u3002AQS\u5e95\u5c42\u5df2\u7ecf\u5bf9\u8fd9\u4e24\u90e8\u5206\u5185\u5bb9\u63d0\u4f9b\u4e86\u5f88\u591a\u65b9\u6cd5\u3002<\/p>\n<ul>\n<li>\u5171\u4eab\u8d44\u6e90\uff1a\u5171\u4eab\u8d44\u6e90\u662f\u4e00\u4e2avolatile\u7684int\u7c7b\u578b\u53d8\u91cf\u3002<\/li>\n<li>\u7b49\u5f85\u961f\u5217\uff1a\u7b49\u5f85\u961f\u5217\u662f\u4e00\u4e2a\u7ebf\u7a0b\u5b89\u5168\u7684\u961f\u5217\uff0c\u5f53\u7ebf\u7a0b\u62ff\u4e0d\u5230\u9501\u65f6\uff0c\u4f1a\u88abpark\u5e76\u653e\u5165\u961f\u5217\u3002<\/li>\n<\/ul>\n<h2>2 \u6e90\u7801\u89e3\u6790<\/h2>\n<p>ReentrantLock\u5728\u5305java.util.concurrent.locks\u4e0b\uff0c\u5b9e\u73b0Lock\u63a5\u53e3\u3002<\/p>\n<h3>2.1 lock\u65b9\u6cd5<\/h3>\n<p>lock\u5206\u4e3a\u516c\u5e73\u9501\u548c\u975e\u516c\u5e73\u9501\u3002  <\/p>\n<p>\u516c\u5e73\u9501\uff1a<\/p>\n<pre><code>final void lock() {\n    acquire(1);\n}<\/code><\/pre>\n<p>\u975e\u516c\u5e73\u9501\uff1a\u4e0a\u6765\u5148\u5c1d\u8bd5\u5c06state\u4ece0\u4fee\u6539\u4e3a1\uff0c\u5982\u679c\u6210\u529f\uff0c\u4ee3\u8868\u83b7\u53d6\u9501\u8d44\u6e90\u3002\u5982\u679c\u6ca1\u6709\u6210\u529f\uff0c\u8c03\u7528acquire\u3002state\u662fAQS\u4e2d\u7684\u4e00\u4e2a\u7531volatile\u4fee\u9970\u7684int\u7c7b\u578b\u53d8\u91cf\uff0c\u591a\u4e2a\u7ebf\u7a0b\u4f1a\u901a\u8fc7CAS\u7684\u65b9\u5f0f\u4fee\u6539state\uff0c\u5728\u5e76\u53d1\u60c5\u51b5\u4e0b\uff0c\u53ea\u4f1a\u6709\u4e00\u4e2a\u7ebf\u7a0b\u6210\u529f\u7684\u4fee\u6539state\u3002<\/p>\n<pre><code>final void lock() {\n\/\/\u901a\u8fc7\u539f\u5b50\u65b9\u5f0f\u4fee\u6539\u503c\n    if (compareAndSetState(0, 1))\n        setExclusiveOwnerThread(Thread.currentThread());\n    else\n        acquire(1);\n}\n\n\n \/**\n * \u83b7\u53d6\u9501\u7684\u7ebf\u7a0b.\n *\/\n private transient Thread exclusiveOwnerThread;\n\n\n  \/**\n  * \u8bbe\u7f6e\u62e5\u6709\u9501\u7684\u7ebf\u7a0b\n  *\/\n  protected final void setExclusiveOwnerThread(Thread thread) {\n      exclusiveOwnerThread = thread;<\/code><\/pre>\n<h3>2.2 acquire\u65b9\u6cd5<\/h3>\n<p>acquire\u662f\u4e00\u4e2a\u4e1a\u52a1\u65b9\u6cd5\uff0c\u91cc\u9762\u5e76\u6ca1\u6709\u5b9e\u9645\u7684\u4e1a\u52a1\u5904\u7406\uff0c\u90fd\u662f\u5728\u8c03\u7528\u5176\u4ed6\u65b9\u6cd5\u3002<\/p>\n<pre><code>public final void acquire(int arg) {\n    \/\/\u8c03\u7528tryAcquire\u65b9\u6cd5\uff1a\u5c1d\u8bd5\u83b7\u53d6\u9501\u8d44\u6e90\uff08\u975e\u516c\u5e73\u3001\u516c\u5e73\uff09\uff0c\u62ff\u5230\u9501\u8d44\u6e90\uff0c\u8fd4\u56detrue\uff0c\u76f4\u63a5\u7ed3\u675f\u65b9\u6cd5\n    if (!tryAcquire(arg) &amp;&amp;\n    \/\/\u5f53\u6ca1\u6709\u83b7\u53d6\u9501\u8d44\u6e90\u540e\uff0c\u4f1a\u5148\u8c03\u7528addWaiter\uff1a\u4f1a\u5c06\u6ca1\u6709\u83b7\u53d6\u5230\u9501\u8d44\u6e90\u7684\u7ebf\u7a0b\u5c01\u88c5\u4e3aNode\u5bf9\u8c61\uff0c\n    \/\/\u5e76\u4e14\u63d2\u5165\u5230AQS\u7684\u961f\u5217\u7684\u672b\u5c3e.\n   \/\/\u7ee7\u7eed\u8c03\u7528acquireQueued\u65b9\u6cd5\uff0c\u67e5\u770b\u5f53\u524d\u6392\u961f\u7684Node\u662f\u5426\u5728\u961f\u5217\u7684\u524d\u9762\uff0c\u5982\u679c\u5728\u524d\u9762\uff0c\u5c1d\u8bd5\u83b7\u53d6\u9501\u8d44\u6e90\n    \/\/\u5982\u679c\u6ca1\u5728\u524d\u9762\uff0c\u5c1d\u8bd5\u5c06\u7ebf\u7a0b\u6302\u8d77\uff0c\u963b\u585e\u8d77\u6765\uff01\n     acquireQueued(addWaiter(Node.EXCLUSIVE), arg))\n     selfInterrupt();\n}<\/code><\/pre>\n<h3>2.3 tryAcquire\u65b9\u6cd5<\/h3>\n<p>tryAcquire\u5206\u4e3a\u516c\u5e73\u548c\u975e\u516c\u5e73\u4e24\u79cd\u3002  <\/p>\n<p>\u516c\u5e73\uff1a<\/p>\n<pre><code> protected final boolean tryAcquire(int acquires) {\n   \/\/\u62ff\u5230\u5f53\u524d\u7ebf\u7a0b\n    final Thread current = Thread.currentThread();\n   \/\/\u62ff\u5230AQS\u7684state\n     int c = getState();\n   \/\/ \u5982\u679cstate == 0\uff0c\u8bf4\u660e\u6ca1\u6709\u7ebf\u7a0b\u5360\u7528\u7740\u5f53\u524d\u7684\u9501\u8d44\u6e90\n     if (c == 0) {\n   \/\/\u5982\u679c\u6ca1\u6709\u7ebf\u7a0b\u6392\u961f\uff0c\u76f4\u63a5\u76f4\u63a5CAS\u5c1d\u8bd5\u83b7\u53d6\u9501\u8d44\u6e90\n      if (!hasQueuedPredecessors() &amp;&amp;\n      compareAndSetState(0, acquires)) {\n     \/\/\u5982\u679c\u83b7\u53d6\u8d44\u6e90\u6210\u529f\uff0c\u5c06\u5f53\u524d\u7ebf\u7a0b\u8bbe\u7f6e\u4e3a\u6301\u6709\u9501\u8d44\u6e90\u7684\u7ebf\u7a0b\n       setExclusiveOwnerThread(current);\n        return true;\n          }\n        }\n     \/\/\u5982\u679c\u6709\u7ebf\u7a0b\u6301\u6709\u9501\u8d44\u6e90\uff0c\u5224\u65ad\u6301\u6709\u9501\u8d44\u6e90\u7684\u7ebf\u7a0b\u662f\u5426\u662f\u5f53\u524d\u7ebf\u7a0b\n         else if (current == getExclusiveOwnerThread()) {\n      \/\/\u589e\u52a0AQS\u7684state\u7684\u503c\n            int nextc = c + acquires;\n             if (nextc &lt; 0)\n             throw new Error(&quot;Maximum lock count exceeded&quot;);\n              setState(nextc);\n               return true;\n            }\n          return false;\n        }\n    }<\/code><\/pre>\n<p>\u975e\u516c\u5e73\uff1a<\/p>\n<pre><code>protected final boolean tryAcquire(int acquires) {\n    return nonfairTryAcquire(acquires);\n}\nfinal boolean nonfairTryAcquire(int acquires) {\n   \/\/\u62ff\u5230\u5f53\u524d\u7ebf\u7a0b\n    final Thread current = Thread.currentThread();\n   \/\/\u62ff\u5230AQS\u7684state\n     int c = getState();\n   \/\/ \u5982\u679cstate == 0\uff0c\u8bf4\u660e\u6ca1\u6709\u7ebf\u7a0b\u5360\u7528\u7740\u5f53\u524d\u7684\u9501\u8d44\u6e90\n      if (c == 0) {\n   \/\/\u83b7\u53d6\u9501\u8d44\u6e90\n      if (compareAndSetState(0, acquires)) {\n   \/\/\u5c06\u5f53\u524d\u5360\u7528\u8fd9\u4e2a\u4e92\u65a5\u9501\u7684\u7ebf\u7a0b\u5c5e\u6027\u8bbe\u7f6e\u4e3a\u5f53\u524d\u7ebf\u7a0b\n      setExclusiveOwnerThread(current);\n       return true;\n       }\n       }\n   \/\/\u5982\u679c\u6709\u7ebf\u7a0b\u6301\u6709\u9501\u8d44\u6e90\uff0c\u5224\u65ad\u6301\u6709\u9501\u8d44\u6e90\u7684\u7ebf\u7a0b\u662f\u5426\u662f\u5f53\u524d\u7ebf\u7a0b\n       else if (current == getExclusiveOwnerThread()) {\n          int nextc = c + acquires;\n          if (nextc &lt; 0) \/\/ overflow\n          throw new Error(&quot;Maximum lock count exceeded&quot;);\n           setState(nextc);\n           return true;\n          }\n         return false;\n  }<\/code><\/pre>\n<h3>2.4 addWaiter\u65b9\u6cd5<\/h3>\n<p>\u5728\u83b7\u53d6\u9501\u8d44\u6e90\u5931\u8d25\u540e\uff0c\u9700\u8981\u5c06\u5f53\u524d\u7ebf\u7a0b\u5c01\u88c5\u4e3aNode\u5bf9\u8c61\uff0c\u5e76\u4e14\u63d2\u5165\u5230AQS\u961f\u5217\u7684\u672b\u5c3e\u3002<\/p>\n<pre><code>private Node addWaiter(Node mode) {\n    \/\/ \u5c06\u5f53\u524d\u7ebf\u7a0b\u5c01\u88c5\u4e3aNode\u5bf9\u8c61\uff0cmode\u4e3anull\uff0c\u4ee3\u8868\u4e92\u65a5\u9501\n    Node node = new Node(Thread.currentThread(), mode);\n    \/\/ pred\u662ftail\u8282\u70b9\n    Node pred = tail;\n    \/\/ \u5982\u679cpred\u4e0d\u4e3anull\uff0c\u6709\u7ebf\u7a0b\u6b63\u5728\u6392\u961f\n    if (pred != null) {\n        \/\/ \u5c06\u5f53\u524d\u8282\u70b9\u7684prev\uff0c\u6307\u5b9atail\u5c3e\u8282\u70b9\n        node.prev = pred;\n        \/\/ \u4ee5CAS\u7684\u65b9\u5f0f\uff0c\u5c06\u5f53\u524d\u8282\u70b9\u53d8\u4e3atail\u8282\u70b9\n        if (compareAndSetTail(pred, node)) {\n            \/\/ \u4e4b\u524d\u7684tail\u7684next\u6307\u5411\u5f53\u524d\u8282\u70b9\n            pred.next = node;\n            return node;\n        }\n    }\n    \/\/ \u6dfb\u52a0\u7684\u6d41\u7a0b\u4e3a\uff0c  \u81ea\u5df1prev\u6307\u5411\u3001tail\u6307\u5411\u81ea\u5df1\u3001\u524d\u8282\u70b9next\u6307\u5411\u6211\n    \/\/ \u5982\u679c\u4e0a\u8ff0\u65b9\u5f0f\uff0cCAS\u64cd\u4f5c\u5931\u8d25\uff0c\u5bfc\u81f4\u52a0\u5165\u5230AQS\u672b\u5c3e\u5931\u8d25\uff0c\u5982\u679c\u5931\u8d25\uff0c\u5c31\u57fa\u4e8eenq\u7684\u65b9\u5f0f\u6dfb\u52a0\u5230AQS\u961f\u5217\n    enq(node);\n    return node;\n}\n\/\/ enq\uff0c\u65e0\u8bba\u600e\u6837\u90fd\u6dfb\u52a0\u8fdb\u5165\nprivate Node enq(final Node node) {\n    for (;;) {\n        \/\/ \u62ff\u5230tail\n        Node t = tail;\n        \/\/ \u5982\u679ctail\u4e3anull\uff0c\u8bf4\u660e\u5f53\u524d\u6ca1\u6709Node\u5728\u961f\u5217\u4e2d\n        if (t == null) { \n            \/\/ \u521b\u5efa\u4e00\u4e2a\u65b0\u7684Node\u4f5c\u4e3ahead\uff0c\u5e76\u4e14\u5c06tail\u548chead\u6307\u5411\u4e00\u4e2aNode\n            if (compareAndSetHead(new Node()))\n                tail = head;\n        } else {\n            \/\/ \u548c\u4e0a\u8ff0\u4ee3\u7801\u4e00\u81f4\uff01\n            node.prev = t;\n            if (compareAndSetTail(t, node)) {\n                t.next = node;\n                return t;\n            }\n        }\n    }\n}<\/code><\/pre>\n<h3>2.5 acquireQueued\u65b9\u6cd5<\/h3>\n<pre><code>\/\/ acquireQueued\u65b9\u6cd5\n\/\/ \u67e5\u770b\u5f53\u524d\u6392\u961f\u7684Node\u662f\u5426\u662fhead\u7684next\uff0c\n\/\/ \u5982\u679c\u662f\uff0c\u5c1d\u8bd5\u83b7\u53d6\u9501\u8d44\u6e90\uff0c\n\/\/ \u5982\u679c\u4e0d\u662f\u6216\u8005\u83b7\u53d6\u9501\u8d44\u6e90\u5931\u8d25\u90a3\u4e48\u5c31\u5c1d\u8bd5\u5c06\u5f53\u524dNode\u7684\u7ebf\u7a0b\u6302\u8d77\uff08unsafe.park()\uff09\nfinal boolean acquireQueued(final Node node, int arg) {\n    boolean failed = true;\n    try {\n        for (;;) {\n            \/\/ \u62ff\u5230\u4e0a\u4e00\u4e2a\u8282\u70b9\n            final Node p = node.predecessor();\n            if (p == head &amp;&amp; \/\/ \u8bf4\u660e\u5f53\u524d\u8282\u70b9\u662fhead\u7684next\n                tryAcquire(arg)) { \/\/ \u7ade\u4e89\u9501\u8d44\u6e90\uff0c\u6210\u529f\uff1atrue\uff0c\u5931\u8d25\uff1afalse\n                \/\/ \u8fdb\u6765\u8bf4\u660e\u62ff\u5230\u9501\u8d44\u6e90\u6210\u529f\n                \/\/ \u5c06\u5f53\u524d\u8282\u70b9\u7f6e\u4f4dhead\uff0cthread\u548cprev\u5c5e\u6027\u7f6e\u4f4dnull\n                setHead(node);\n                \/\/ \u5e2e\u52a9\u5feb\u901fGC\n                p.next = null; \n                \/\/ \u8bbe\u7f6e\u83b7\u53d6\u9501\u8d44\u6e90\u6210\u529f\n                failed = false;\n                \/\/ \u4e0d\u7ba1\u7ebf\u7a0b\u4e2d\u65ad\u3002\n                return interrupted;\n            }\n            \/\/ \u5982\u679c\u4e0d\u662f\u6216\u8005\u83b7\u53d6\u9501\u8d44\u6e90\u5931\u8d25,\u5c1d\u8bd5\u5c06\u7ebf\u7a0b\u6302\u8d77\n            \/\/ \u7b2c\u4e00\u4e2a\u4e8b\u60c5\uff0c\u5f53\u524d\u8282\u70b9\u7684\u4e0a\u4e00\u4e2a\u8282\u70b9\u7684\u72b6\u6001\u6b63\u5e38\uff01\n            \/\/ \u7b2c\u4e8c\u4e2a\u4e8b\u60c5\uff0c\u6302\u8d77\u7ebf\u7a0b\n            if (shouldParkAfterFailedAcquire(p, node) &amp;&amp;\n                \/\/ \u901a\u8fc7LockSupport\u5c06\u5f53\u524d\u7ebf\u7a0b\u6302\u8d77\n                parkAndCheckInterrupt())\n        }\n    } finally {\n        if (failed)\n            cancelAcquire(node);\n    }\n}\n\n\n\/\/ \u786e\u4fdd\u4e0a\u4e00\u4e2a\u8282\u70b9\u72b6\u6001\u662f\u6b63\u786e\u7684\nprivate static boolean shouldParkAfterFailedAcquire(Node pred, Node node) {\n    \/\/ \u62ff\u5230\u4e0a\u4e00\u4e2a\u8282\u70b9\u7684\u72b6\u6001\n    int ws = pred.waitStatus;\n    \/\/ \u5982\u679c\u4e0a\u4e00\u4e2a\u8282\u70b9\u4e3a -1\n    if (ws == Node.SIGNAL)\n        \/\/ \u8fd4\u56detrue\uff0c\u6302\u8d77\u7ebf\u7a0b\n        return true;\n    \/\/ \u5982\u679c\u4e0a\u4e00\u4e2a\u8282\u70b9\u662f\u53d6\u6d88\u72b6\u6001\n    if (ws &gt; 0) {\n        \/\/ \u5faa\u73af\u5f80\u524d\u627e\uff0c\u627e\u5230\u4e00\u4e2a\u72b6\u6001\u5c0f\u4e8e\u7b49\u4e8e0\u7684\u8282\u70b9\n        do {\n            node.prev = pred = pred.prev;\n        } while (pred.waitStatus &gt; 0);\n        pred.next = node;\n    } else {\n        \/\/ \u5c06\u5c0f\u4e8e\u7b49\u4e8e0\u7684\u8282\u70b9\u72b6\u6001\u8be5\u4e3a-1\n        compareAndSetWaitStatus(pred, ws, Node.SIGNAL);\n    }\n    return false;\n}<\/code><\/pre>\n<h3>2.6 unlock\u65b9\u6cd5<\/h3>\n<p>\u91ca\u653e\u9501\u8d44\u6e90\uff0c\u5c06state\u51cf1,\u5982\u679cstate\u51cf\u4e3a0\u4e86\uff0c\u5524\u9192\u5728\u961f\u5217\u4e2d\u6392\u961f\u7684Node\u3002<\/p>\n<pre><code>public final boolean release(int arg) {\n    \/\/ \u6838\u5fc3\u7684\u91ca\u653e\u9501\u8d44\u6e90\u65b9\u6cd5\n    if (tryRelease(arg)) {\n        \/\/ \u91ca\u653e\u9501\u8d44\u6e90\u91ca\u653e\u5e72\u51c0\u4e86\u3002  \uff08state == 0\uff09\n        Node h = head;\n        \/\/ \u5982\u679c\u5934\u8282\u70b9\u4e0d\u4e3anull\uff0c\u5e76\u4e14\u5934\u8282\u70b9\u7684\u72b6\u6001\u4e0d\u4e3a0\uff0c\u5524\u9192\u6392\u961f\u7684\u7ebf\u7a0b\n        if (h != null &amp;&amp; h.waitStatus != 0)\n            \/\/ \u5524\u9192\u7ebf\u7a0b\n            unparkSuccessor(h);\n        return true;\n    }\n    \/\/ \u91ca\u653e\u9501\u6210\u529f\uff0c\u4f46\u662fstate != 0\n    return false;\n}\n\/\/ \u6838\u5fc3\u7684\u91ca\u653e\u9501\u8d44\u6e90\u65b9\u6cd5\nprotected final boolean tryRelease(int releases) {\n    \/\/ \u83b7\u53d6state - 1\n    int c = getState() - releases;\n    \/\/ \u5982\u679c\u91ca\u653e\u9501\u7684\u7ebf\u7a0b\u4e0d\u662f\u5360\u7528\u9501\u7684\u7ebf\u7a0b\uff0c\u629b\u5f02\u5e38\n    if (Thread.currentThread() != getExclusiveOwnerThread())\n        throw new IllegalMonitorStateException();\n    \/\/ \u662f\u5426\u6210\u529f\u7684\u5c06\u9501\u8d44\u6e90\u91ca\u653e\u5229\u7d22 \uff08state == 0\uff09\n    boolean free = false;\n    if (c == 0) {\n        \/\/ \u9501\u8d44\u6e90\u91ca\u653e\u5e72\u51c0\u3002\n        free = true;\n        \/\/ \u5c06\u5360\u7528\u9501\u8d44\u6e90\u7684\u5c5e\u6027\u8bbe\u7f6e\u4e3anull\n        setExclusiveOwnerThread(null);\n    }\n    \/\/ \u5c06state\u8d4b\u503c\n    setState(c);\n    \/\/ \u8fd4\u56detrue\uff0c\u4ee3\u8868\u91ca\u653e\u5e72\u51c0\u4e86\n    return free;\n}\n\n\n\/\/ \u5524\u9192\u8282\u70b9\nprivate void unparkSuccessor(Node node) {\n    \/\/ \u62ff\u5230\u5934\u8282\u70b9\u72b6\u6001\n    int ws = node.waitStatus;\n    \/\/ \u5982\u679c\u5934\u8282\u70b9\u72b6\u6001\u5c0f\u4e8e0\uff0c\u6362\u4e3a0\n    if (ws &lt; 0)\n        compareAndSetWaitStatus(node, ws, 0);\n    \/\/ \u62ff\u5230\u5f53\u524d\u8282\u70b9\u7684next\n    Node s = node.next;\n    \/\/ \u5982\u679cs == null \uff0c\u6216\u8005s\u7684\u72b6\u6001\u4e3a1\n    if (s == null || s.waitStatus &gt; 0) {\n        \/\/ next\u8282\u70b9\u4e0d\u9700\u8981\u5524\u9192\uff0c\u9700\u8981\u5524\u9192next\u7684next\n        s = null;\n        \/\/ \u4ece\u5c3e\u90e8\u5f80\u524d\u627e\uff0c\u627e\u5230\u72b6\u6001\u6b63\u5e38\u7684\u8282\u70b9\u3002\uff08\u5c0f\u4e8e\u7b49\u4e8e0\u4ee3\u8868\u6b63\u5e38\u72b6\u6001\uff09\n        for (Node t = tail; t != null &amp;&amp; t != node; t = t.prev)\n            if (t.waitStatus &lt;= 0)\n                s = t;\n    }\n    \/\/ \u7ecf\u8fc7\u5faa\u73af\u7684\u83b7\u53d6\uff0c\u5982\u679c\u62ff\u5230\u72b6\u6001\u6b63\u5e38\u7684\u8282\u70b9\uff0c\u5e76\u4e14\u4e0d\u4e3anull\n    if (s != null)\n        \/\/ \u5524\u9192\u7ebf\u7a0b\n        LockSupport.unpark(s.thread);\n}<\/code><\/pre>\n<h2>3 \u4f7f\u7528\u5b9e\u4f8b<\/h2>\n<h3>3.1 \u516c\u5e73\u9501<\/h3>\n<p>1.\u4ee3\u7801\uff1a<\/p>\n<pre><code>public class ReentrantLockTest {\n\n\n    public static void main(String[] args) {\n        ReentrantLock lock = new ReentrantLock(true);\n        new Thread(()-&gt;test(lock),&quot;\u7ebf\u7a0bA&quot;).start();\n        new Thread(()-&gt;test(lock),&quot;\u7ebf\u7a0bB&quot;).start();\n        new Thread(()-&gt;test(lock),&quot;\u7ebf\u7a0bC&quot;).start();\n    }\n    public static   void test(ReentrantLock lock){\n        for (int i = 0; i &lt; 3;i++){\n            try {\n                lock.lock();\n                System.out.println(Thread.currentThread().getName()+&quot;\u83b7\u53d6\u4e86\u9501\uff01&quot;);\n                Thread.sleep(200);\n            }catch (Exception e){\n                e.printStackTrace();\n            }finally {\n                lock.unlock();\n            }\n        }\n    }\n}<\/code><\/pre>\n<p>2.\u6267\u884c\u7ed3\u679c\uff1a<\/p>\n<p><img decoding=\"async\" referrerpolicy=\"no-referrer\" src=\"https:\/\/segmentfault.com\/img\/remote\/1460000043966722\" alt=\"\" title=\"\" loading=\"lazy\"><\/p>\n<p>3.\u5c0f\u7ed3\uff1a<\/p>\n<p>\u516c\u5e73\u9501\u53ef\u4ee5\u4fdd\u8bc1\u6bcf\u4e2a\u7ebf\u7a0b\u83b7\u53d6\u9501\u7684\u673a\u4f1a\u662f\u76f8\u7b49\u7684\u3002<\/p>\n<h3>3.2 \u975e\u516c\u5e73\u9501<\/h3>\n<p>1.\u4ee3\u7801\uff1a<\/p>\n<pre><code>public class ReentrantLockTest {\n\n\n    public static void main(String[] args) {\n        ReentrantLock lock = new ReentrantLock();\n        new Thread(()-&gt;test(lock),&quot;\u7ebf\u7a0bA&quot;).start();\n        new Thread(()-&gt;test(lock),&quot;\u7ebf\u7a0bB&quot;).start();\n        new Thread(()-&gt;test(lock),&quot;\u7ebf\u7a0bC&quot;).start();\n    }\n    public static   void test(ReentrantLock lock){\n        for (int i = 0; i &lt; 3;i++){\n            try {\n                lock.lock();\n                System.out.println(Thread.currentThread().getName()+&quot;\u83b7\u53d6\u4e86\u9501\uff01&quot;);\n                Thread.sleep(200);\n            }catch (Exception e){\n                e.printStackTrace();\n            }finally {\n                lock.unlock();\n            }\n        }\n    }\n}<\/code><\/pre>\n<p>2.\u6267\u884c\u7ed3\u679c\uff1a<\/p>\n<p><img decoding=\"async\" referrerpolicy=\"no-referrer\" src=\"https:\/\/segmentfault.com\/img\/remote\/1460000043966723\" alt=\"\" title=\"\" loading=\"lazy\"><\/p>\n<p>3.\u5c0f\u7ed3\uff1a<\/p>\n<p>\u975e\u516c\u5e73\u9501\u6bcf\u4e2a\u7ebf\u7a0b\u83b7\u53d6\u9501\u7684\u673a\u4f1a\u662f\u968f\u673a\u7684\u3002<\/p>\n<h3>3.3 \u5ffd\u7565\u91cd\u590d\u64cd\u4f5c<\/h3>\n<p>1.\u4ee3\u7801\uff1a<\/p>\n<pre><code>public class ReentrantLockTest {\n    private ReentrantLock lock = new ReentrantLock();\n\n\n    public void doSomething(){\n        if(lock.tryLock()){\n            try {\n                System.out.println(Thread.currentThread().getName()+&quot;\u83b7\u53d6\u4e86\u9501\uff01&quot;);\n                Thread.sleep(5);\n            }catch (Exception e){\n                e.printStackTrace();\n            }finally {\n                lock.unlock();\n            }\n        }\n    }\n    public static void main(String[] args) throws Exception {\n        ReentrantLockTest test = new ReentrantLockTest();\n        for (int i = 0; i &lt; 10;i++){\n            new Thread(()-&gt;{test.doSomething();},&quot;\u7ebf\u7a0b&quot;+i).start();\n            Thread.sleep(1);\n        }\n    }\n}<\/code><\/pre>\n<p>2.\u6267\u884c\u7ed3\u679c\uff1a<\/p>\n<p><img decoding=\"async\" referrerpolicy=\"no-referrer\" src=\"https:\/\/segmentfault.com\/img\/remote\/1460000043966724\" alt=\"\" title=\"\" loading=\"lazy\"><\/p>\n<p>3.\u5c0f\u7ed3\uff1a<\/p>\n<p>\u5f53\u7ebf\u7a0b\u6301\u6709\u9501\u65f6\uff0c\u4e0d\u4f1a\u91cd\u590d\u6267\u884c\uff0c\u53ef\u4ee5\u7528\u6765\u9632\u6b62\u5b9a\u65f6\u4efb\u52a1\u91cd\u590d\u6267\u884c\u6216\u8005\u9875\u9762\u4e8b\u4ef6\u591a\u6b21\u89e6\u53d1\u65f6\u4e0d\u4f1a\u91cd\u590d\u89e6\u53d1\u3002<\/p>\n<h3>3.4 \u8d85\u65f6\u4e0d\u6267\u884c<\/h3>\n<p>1.\u4ee3\u7801\uff1a<\/p>\n<pre><code>public class ReentrantLockTest {\n\n\n    public static void main(String[] args) {\n        ReentrantLock lock = new ReentrantLock();\n        new Thread(()-&gt;test(lock),&quot;\u7ebf\u7a0bA&quot;).start();\n        new Thread(()-&gt;test(lock),&quot;\u7ebf\u7a0bB&quot;).start();\n    }\n    public static   void test(ReentrantLock lock){\n            try {\n                if(lock.tryLock(2, TimeUnit.SECONDS)){\n                    try {\n                        System.out.println(Thread.currentThread().getName()+&quot;\u83b7\u53d6\u4e86\u9501\uff01&quot;);\n                        Thread.sleep(3000);\n                    }finally {\n                        lock.unlock();\n                    }\n                }\n            }catch (Exception e){\n                e.printStackTrace();\n            }\n\n\n    }<\/code><\/pre>\n<p>2.\u6267\u884c\u7ed3\u679c\uff1a<\/p>\n<p><img decoding=\"async\" referrerpolicy=\"no-referrer\" src=\"https:\/\/segmentfault.com\/img\/remote\/1460000043966725\" alt=\"\" title=\"\" loading=\"lazy\"><\/p>\n<p>3.\u5c0f\u7ed3\uff1a<\/p>\n<p>\u8d85\u65f6\u4e0d\u6267\u884c\u53ef\u4ee5\u9632\u6b62\u7531\u4e8e\u8d44\u6e90\u5904\u7406\u4e0d\u5f53\u957f\u65f6\u95f4\u5360\u7528\u8d44\u6e90\u4ea7\u751f\u7684\u6b7b\u9501\u95ee\u9898\u3002<\/p>\n<h2>4 \u603b\u7ed3<\/h2>\n<p>\u5e76\u53d1\u662f\u73b0\u5728\u8f6f\u4ef6\u7cfb\u7edf\u4e0d\u53ef\u907f\u514d\u7684\u95ee\u9898\uff0cReentrantLock\u662f\u53ef\u91cd\u5165\u7684\u72ec\u5360\u9501\uff0c\u6bd4\u8d77synchronized\u529f\u80fd\u66f4\u52a0\u4e30\u5bcc\uff0c\u652f\u6301\u516c\u5e73\u9501\u5b9e\u73b0\uff0c\u652f\u6301\u4e2d\u65ad\u54cd\u5e94\u4ee5\u53ca\u9650\u65f6\u7b49\u5f85\u7b49\uff0c\u662f\u5904\u7406\u5e76\u53d1\u95ee\u9898\u5f88\u597d\u7684\u89e3\u51b3\u65b9\u6848\u3002<\/p>\n<blockquote>\n<p>\u4f5c\u8005\uff1a\u4eac\u4e1c\u7269\u6d41 \u9648\u660c\u6d69<\/p>\n<p>\u6765\u6e90\uff1a\u4eac\u4e1c\u4e91\u5f00\u53d1\u8005\u793e\u533a<\/p>\n<\/blockquote>\n<p><a href=\"https:\/\/segmentfault.com\/a\/1190000043966719\">https:\/\/segmentfault.com\/a\/1190000043966719<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"<p>\u5e76\u53d1\u6307\u540c\u4e00\u65f6\u95f4\u5185\u8fdb\u884c\u4e86\u591a\u4e2a\u7ebf\u7a0b\u3002\u5e76\u53d1\u95ee\u9898\u662f\u591a\u4e2a\u7ebf\u7a0b\u5bf9\u540c\u4e00\u8d44\u6e90\u8fdb\u884c\u64cd\u4f5c\u65f6\u4ea7\u751f\u7684\u95ee\u9898\u3002\u901a\u8fc7\u52a0\u9501\u53ef\u4ee5\u89e3\u51b3\u5e76\u53d1\u95ee\u9898\uff0cR [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[4],"tags":[],"class_list":["post-10008032","post","type-post","status-publish","format-standard","hentry","category-share"],"jetpack_sharing_enabled":true,"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/itmax.cn\/index.php?rest_route=\/wp\/v2\/posts\/10008032","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/itmax.cn\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/itmax.cn\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/itmax.cn\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/itmax.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=10008032"}],"version-history":[{"count":0,"href":"https:\/\/itmax.cn\/index.php?rest_route=\/wp\/v2\/posts\/10008032\/revisions"}],"wp:attachment":[{"href":"https:\/\/itmax.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=10008032"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/itmax.cn\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=10008032"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/itmax.cn\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=10008032"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}