feat: add case instruction reordering causes non-final field variab…

…le read error (#64)

README.md

@@ -65,6 +65,10 @@ Examples of concurrency problems you encountered in development are welcome to p
     - [Demo description](#demo-description-7)
     - [Problem statement](#problem-statement-7)
     - [Quickly run](#quickly-run-7)
+- [🍺 Instruction reordering causes non-final field variable read error](#-instruction-reordering-causes-non-final-field-variable-read-error)
+    - [Demo description](#demo-description-8)
+    - [Problem statement](#problem-statement-8)
+    - [Quickly run](#quickly-run-8)
 
 <!-- END doctoc generated TOC please keep comment here to allow auto update -->
 
@@ -233,3 +237,23 @@ this is a livelock.
 ```bash
 ./mvnw compile exec:java -Dexec.mainClass=fucking.concurrency.demo.ReentrantLockLivelockDemo
 ```
+
+## 🍺 Instruction reordering causes non-final field variable read error
+
+Demo class [`FinalInitialDemo`](src/main/java/fucking/concurrency/demo/FinalInitialDemo.java).
+
+### Demo description
+
+The writer thread calls the constructor of the class, and the reader thread obtains the member variables of the non-final domain of the class.
+
+### Problem statement
+
+When calling the constructor, instruction reordering may occur, placing non-final domain variables outside the constructor,
+causing the writer and reader threads to obtain the default initial values of the variables.(Instruction ordering does not necessarily occur
+and requires specific hardware and JVM environments).
+
+### Quickly run
+
+```bash
+./mvnw compile exec:java -Dexec.mainClass=fucking.concurrency.demo.FinalInitialDemo
+```

docs/zh-CN/README.md

@@ -64,6 +64,10 @@
     - [Demo说明](#demo%E8%AF%B4%E6%98%8E-6)
     - [问题说明](#%E9%97%AE%E9%A2%98%E8%AF%B4%E6%98%8E-6)
     - [快速运行](#%E5%BF%AB%E9%80%9F%E8%BF%90%E8%A1%8C-6)
+- [🍺 指令重排序导致非final域变量读取错误](#-指令重排序导致非final域变量读取错误)
+    - [Demo说明](#demo%E8%AF%B4%E6%98%8E-7)
+    - [问题说明](#%E9%97%AE%E9%A2%98%E8%AF%B4%E6%98%8E-7)
+    - [快速运行](#%E5%BF%AB%E9%80%9F%E8%BF%90%E8%A1%8C-7)
 - [一些并发的问题讨论和资料](#%E4%B8%80%E4%BA%9B%E5%B9%B6%E5%8F%91%E7%9A%84%E9%97%AE%E9%A2%98%E8%AE%A8%E8%AE%BA%E5%92%8C%E8%B5%84%E6%96%99)
 
 <!-- END doctoc generated TOC please keep comment here to allow auto update -->
@@ -209,6 +213,25 @@ Demo类[`SymmetricLockDeadlockDemo`](../../src/main/java/fucking/concurrency/dem
 ./mvnw compile exec:java -Dexec.mainClass=fucking.concurrency.demo.SymmetricLockDeadlockDemo
 ```
 
+## 🍺 指令重排序导致非final域变量读取错误
+
+Demo类[`FinalInitialDemo`](../../src/main/java/fucking/concurrency/demo/FinalInitialDemo.java)。
+
+### Demo说明
+
+writer线程调用类的构造函数，reader线程获取类的非final的成员变量。
+
+### 问题说明
+
+调用构造函数时,可能会发生指令重新排序,将非final域变量放置在构造函数之外,导致writer和reader线程获取变量的默认初始值(指令顺序不一定发生,
+并且需要特定的硬件和 JVM 环境)。
+
+### 快速运行
+
+```bash
+./mvnw compile exec:java -Dexec.mainClass=fucking.concurrency.demo.FinalInitialDemo
+```
+
 ## 一些并发的问题讨论和资料
 
 - [ibm developerworks - 多核系统上的`Java`并发缺陷模式（`bug patterns`）](http://www.ibm.com/developerworks/cn/java/j-concurrencybugpatterns/)

src/main/java/fucking/concurrency/demo/FinalInitialDemo.java

@@ -0,0 +1,47 @@
+package fucking.concurrency.demo;
+
+
+/**
+ * @author hyy (hjlbupt at 163 dot com)
+ */
+public class FinalInitialDemo {
+
+    private int a;
+    private boolean flag;
+    private FinalInitialDemo demo;
+
+    public FinalInitialDemo() {
+        a = 1;
+        flag = true;
+    }
+
+    public void writer() {
+        demo = new FinalInitialDemo();
+    }
+
+    public void reader() {
+        if (flag) {
+            int i = a * a;
+            if (i == 0) {
+                // On my dev machine, the variable initial always success.
+                // To solve this problem, add final to the `a` field and `flag` field.
+                System.out.println("Fuck! instruction reordering occurred.");
+            }
+        }
+    }
+
+    @SuppressWarnings("InfiniteLoopStatement")
+    public static void main(String[] args) throws Exception {
+        while (true) {
+            FinalInitialDemo demo = new FinalInitialDemo();
+            Thread threadA = new Thread(demo::writer);
+            Thread threadB = new Thread(demo::reader);
+
+            threadA.start();
+            threadB.start();
+
+            threadA.join();
+            threadB.join();
+        }
+    }
+}