ReentrantLock

The Lock interface in Java offers a choice of unconidtional, polled, timed, and interruptible lock acquisition, and all lock and unlock operations are explicit. ReentrantLock implements Lock, providing the same mutual exclusion and memory-visibility gurantees as synchronized. Acquiring a ReentrantLock has the same memory semantics as entering a synchronized block, and releasing a ReentrantLock has the same memory semantics as exiting a synchronized block.

Design a thread-safe class

The design process for a thread-safe class should include these three basic elements:

1. Identify the variables that form the object’s state.
2. Identify the invariants that constrain the state variables.
3. Establish a policy for managing concurrent access to the object’s state.
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什么是内存模型？我们为什么需要一个内存模型？

我们之前在详解synchronized、volatie和final的文章当中讲过，底层JVM、编译器、处理器执行指令的顺序并不保证和程序员所写的代码的顺序一样。在单线程中，只要遵从as-if-serial语义，就可以进行重排，所以对于程序员来说，底层的实现只是造成了一个程序是按照自己的代码顺序执行的假象。

final的基本语义

final在java中是非常常用的关键字，其语义和C++中的constant有类似之处，都代表不变的意思，其可以用在以下地方：

1. 修饰变量，成员变量或者本地变量均可。
2. 修饰方法的参数。
3. 修饰方法。
4. 修饰类。
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volatile与可见性

我们还是先来看一个例子，这个例子在synchronized这篇文章中用过:

synchronized与原子性

先来看一个大家很熟悉的例子：

Kafka is a distributed messaging system that developed for collecting and delivering high volumes of log data with low latency.

We have introduced one way before to configure blog PV by using the natrually supported LeanCloud counter in NexT theme. But this is somehow broken for my site, so I explored and switched to Valine which supports PV and comments without any backend changes.

ZooKeeper is a service for coordinating processes of distributed applications, which provides wait-free coordination for Internet-scale systems.

我很佩服三浦紫苑，讲好一个故事本身就很不简单，她却偏偏选择依托在编纂辞典《编舟记》或者长跑《强风吹拂》这种让人听上去就觉得枯燥乏味的事物上，然后将一切娓娓道来。相较于其他运动而言，跑步确实听上去不那么让人热血沸腾，不像足篮排那样典型的热血物语，它并不能够给人带来和对手厮杀的压迫感，和赢得比赛、击败对手的畅快感，而更多的时候是一种与自我的搏斗。就像在动画中所说的，箱根驿传的后半段棒次奔跑在路上的时候可能一个人都看不见，所能听见的只有自己的呼吸和心跳。但正是这种习惯在孤独中让自己变得强大的姿态，才是这项运动的迷人之处。