From cbc20dd21c0c63b3a57a9173596f0b8a786a61ca Mon Sep 17 00:00:00 2001
From: liuyiwei <709224218@qq.com>
Date: Sun, 19 Mar 2023 10:30:07 +0800
Subject: [PATCH] vault backup: 2023-03-19 10:30:07
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Affected files:
inbox/使用 Unsafe 原子性更新对象成员值.md
---
 ...41\346\210\220\345\221\230\345\200\274.md" | 59 +++++++++++++++++++
 1 file changed, 59 insertions(+)
 create mode 100644 "inbox/\344\275\277\347\224\250 Unsafe \345\216\237\345\255\220\346\200\247\346\233\264\346\226\260\345\257\271\350\261\241\346\210\220\345\221\230\345\200\274.md"

diff --git "a/inbox/\344\275\277\347\224\250 Unsafe \345\216\237\345\255\220\346\200\247\346\233\264\346\226\260\345\257\271\350\261\241\346\210\220\345\221\230\345\200\274.md" "b/inbox/\344\275\277\347\224\250 Unsafe \345\216\237\345\255\220\346\200\247\346\233\264\346\226\260\345\257\271\350\261\241\346\210\220\345\221\230\345\200\274.md"
new file mode 100644
index 0000000..935d121
--- /dev/null
+++ "b/inbox/\344\275\277\347\224\250 Unsafe \345\216\237\345\255\220\346\200\247\346\233\264\346\226\260\345\257\271\350\261\241\346\210\220\345\221\230\345\200\274.md"	
@@ -0,0 +1,59 @@
+---
+date created: 2023-03-19, 10:22:08
+date modified: 2023-03-19, 10:22:16
+---
+
+# Meta
+
+- alias:
+- parent ::
+- siblings ::
+- child ::
+- refs:
+    - https://stackoverflow.com/questions/13003871/how-do-i-get-the-instance-of-sun-misc-unsafe
+    - AQS 中的代码
+
+---
+
+```java
+public class ReflectTest {
+    public static void main(String[] args) {
+        Student student = new Student();
+        student.setState(123);
+
+        System.out.println(student.compareAndSetState(123, 99));
+        System.out.println(student.getState()); // 99
+    }
+}
+
+class Student {
+    private int state;
+
+    private static final long stateOffset;
+
+    private static final Unsafe unsafe;
+
+    static {
+        try {
+            Field theUnsafe = Unsafe.class.getDeclaredField("theUnsafe");
+            theUnsafe.setAccessible(true);
+            unsafe = (Unsafe) theUnsafe.get(null);
+            stateOffset = unsafe.objectFieldOffset(Student.class.getDeclaredField("state"));
+        } catch (Exception ex) {
+            throw new Error(ex);
+        }
+    }
+
+    public void setState(int state) {
+        this.state = state;
+    }
+
+    public int getState() {
+        return state;
+    }
+
+    public final boolean compareAndSetState(int expected, int update) {
+        return unsafe.compareAndSwapInt(this, stateOffset, expected, update);
+    }
+}
+```
\ No newline at end of file