更新volatile

Author: Java-Edge

concurrency/src/main/java/com/javaedge/concurrency/common/volatiletest/VisibilityDemo.java

@@ -0,0 +1,55 @@
+package com.javaedge.concurrency.common.volatiletest;
+
+/**
+ * @author JavaEdge
+ * @date 2019/10/17
+ */
+import java.util.concurrent.TimeUnit;
+
+// 1、 jre/bin/server  放置hsdis动态链接库
+//  测试代码 将运行模式设置为-server， 变成死循环   。 没加默认就是client模式，就是正常（可见性问题）
+// 2、 通过设置JVM的参数，打印出jit编译的内容 （这里说的编译非class文件），通过可视化工具jitwatch进行查看
+// -server -XX:+UnlockDiagnosticVMOptions -XX:+PrintAssembly -XX:+LogCompilation -XX:LogFile=jit.log
+//  关闭jit优化-Djava.compiler=NONE
+
+public class VisibilityDemo {
+
+    /**
+     * 运行标志
+     */
+    public boolean flag = true;
+
+    /**
+     * JIT just in time
+     * @param args
+     * @throws InterruptedException
+     */
+    public static void main(String[] args) throws InterruptedException {
+        VisibilityDemo demo1 = new VisibilityDemo();
+        System.out.println("代码开始了");
+        Thread thread1 = new Thread(new Runnable() {
+            @Override
+            public void run() {
+                int i = 0;
+//                boolean f = demo1.flag; 不加valo是的jvm优化
+//                if(f) {
+//                    while(true){
+//                        i++;
+//                    }
+//                }
+                while (demo1.flag) {
+                    synchronized (this) {
+                        i++;
+                    }
+                }
+                System.out.println(i);
+            }
+        });
+        thread1.start();
+
+        TimeUnit.SECONDS.sleep(2);
+        // 设置is为false，使上面的线程结束while循环
+        demo1.flag = false;
+        System.out.println("被置为false了.");
+    }
+}

concurrency/src/main/java/com/javaedge/concurrency/common/volatiletest/VisibilityDemo1.java

@@ -0,0 +1,39 @@
+package com.javaedge.concurrency.common.volatiletest;
+
+import java.util.concurrent.TimeUnit;
+
+/**
+ * @author JavaEdge
+ * @date 2019/10/17
+ */
+public class VisibilityDemo1 {
+
+    /**
+     * 状态标识
+     */
+    private static boolean is = true;
+
+    public static void main(String[] args) {
+        new Thread(new Runnable() {
+            @Override
+            public void run() {
+                int i = 0;
+                while (VisibilityDemo1.is) {
+                    synchronized (this) {
+                        i++;
+                    }
+                }
+                System.out.println(i);
+            }
+        }).start();
+
+        try {
+            TimeUnit.SECONDS.sleep(2);
+        } catch (InterruptedException e) {
+            e.printStackTrace();
+        }
+        // 设置is为false，使上面的线程结束while循环
+        VisibilityDemo1.is = false;
+        System.out.println("被置为false了.");
+    }
+}

concurrency/src/main/java/com/javaedge/concurrency/common/volatiletest/VisibilityDemo2.java

@@ -0,0 +1,42 @@
+package com.javaedge.concurrency.common.volatiletest;
+
+import java.util.concurrent.TimeUnit;
+
+/**
+ * @author JavaEdge
+ * @date 2019/10/17
+ */
+public class VisibilityDemo2 {
+
+    /**
+     * 状态标识 (不用缓存)
+     */
+    private volatile boolean flag = true;
+
+    // 源码 -> 字节码class
+
+    /**
+     * JVM 转化为 操作系统能够执行的代码 （JIT Just In Time Compiler 编译器 ）（JVM  --  client   ， --server）
+     *
+     * @param args
+     * @throws InterruptedException
+     */
+    public static void main(String[] args) throws InterruptedException {
+        VisibilityDemo2 demo1 = new VisibilityDemo2();
+        new Thread(new Runnable() {
+            @Override
+            public void run() {
+                int i = 0;
+                while (demo1.flag) {
+                    i++;
+                }
+                System.out.println(i);
+            }
+        }).start();
+
+        TimeUnit.SECONDS.sleep(2);
+        // 设置is为false，使上面的线程结束while循环
+        demo1.flag = false;
+        System.out.println("被置为false了.");
+    }
+}