前言
在学习JAVA并发工具时，分析JUC下的源码，发现有三个利器：状态、队列、CAS。
状态
一般是state属性，如AQS源码中的状态，是整个工具的核心，一般操作的执行都要看当前状态是什么，由于状态是多线程共享的，所以都是volatile修饰，保证线程直接内存可见。
/*** AbstractQueuedSynchronizer中的状态*/private volatile int state;/*** Status field, taking on only the values:* SIGNAL: The successor of this node is (or will soon be)* blocked (via park), so the current node must* unpark its successor when it releases or* cancels. To avoid races, acquire methods must* first indicate they need a signal,* then retry the atomic acquire, and then,* on failure, block.* CANCELLED: This node is cancelled due to timeout or interrupt.* Nodes never leave this state. In particular,* a thread with cancelled node never again blocks.* CONDITION: This node is currently on a condition queue.* It will not be used as a sync queue node* until transferred, at which time the status* will be set to 0. (Use of this value here has* nothing to do with the other uses of the* field, but simplifies mechanics.)* PROPAGATE: A releaseShared should be propagated to other* nodes. This is set (for head node only) in* doReleaseShared to ensure propagation* continues, even if other operations have* since intervened.* 0: None of the above** The values are arranged numerically to simplify use.* Non-negative values mean that a node doesn't need to* signal. So, most code doesn't need to check for particular* values, just for sign.** The field is initialized to 0 for normal sync nodes, and* CONDITION for condition nodes. It is modified using CAS* (or when possible, unconditional volatile writes).*/volatile int waitStatus;
队列
队列一般由链表实现（单向链表，双向链表），在线程获取不到想要的资源或者状态时，将线程封装成特定节点，扔到等待队列中，等待时机成熟，再从队列中取出，是悲观锁思想。如AQS中的Node节点，代码太长就不贴了。
CAS
CAS操作是乐观锁思想，是轻量级的并发处理。一般用于对上述状态的修改，而且能保证有且只有一个线程能修改这个状态。一般由Unsafe类中的compareAndSwap之类的方法实现。使用CAS,往往伴随自旋，如果修改状态失败，则不断地重试，直到修改状态成功。
以上就是java并发编程中的套路，抓住这个思路，想必能在学习中有所帮助。
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本文标题: 了解JAVA并发工具常用设计套路
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