原子整数实现原理解析

.gitignore

@@ -0,0 +1,2 @@
+.idea
+target

.run/Java Concurrency Test (Openjdk-17).run.xml

@@ -0,0 +1,12 @@
+<component name="ProjectRunConfigurationManager">
+  <configuration default="false" name="Java Concurrency Test (Openjdk-17)" type="JarApplication">
+    <option name="JAR_PATH" value="$PROJECT_DIR$/concurrency-test/target/jcstress.jar" />
+    <option name="WORKING_DIRECTORY" value="F:\IdeaProjects\java-concurrent" />
+    <option name="ALTERNATIVE_JRE_PATH_ENABLED" value="true" />
+    <option name="ALTERNATIVE_JRE_PATH" value="openjdk-17" />
+    <module name="concurrency-test" />
+    <method v="2">
+      <option name="Maven.BeforeRunTask" enabled="true" file="$PROJECT_DIR$/pom.xml" goal="package" />
+    </method>
+  </configuration>
+</component>

concurrency-test/pom.xml

@@ -38,8 +38,6 @@ THE POSSIBILITY OF SUCH DAMAGE.
     <packaging>jar</packaging>
     <version>1.0</version>
 
-    <name>JCStress test sample</name>
-
     <dependencies>
         <dependency>
             <groupId>org.openjdk.jcstress</groupId>
@@ -50,17 +48,14 @@ THE POSSIBILITY OF SUCH DAMAGE.
 
     <properties>
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+        <maven.compiler.source>8</maven.compiler.source>
+        <maven.compiler.target>8</maven.compiler.target>
 
         <!--
             jcstress version to use with this project.
           -->
         <jcstress.version>0.15</jcstress.version>
 
-        <!--
-            Java source/target to use for compilation.
-          -->
-        <javac.target>8</javac.target>
-
         <!--
             Name of the test Uber-JAR to generate.
           -->
@@ -74,11 +69,6 @@ THE POSSIBILITY OF SUCH DAMAGE.
                 <groupId>org.apache.maven.plugins</groupId>
                 <artifactId>maven-compiler-plugin</artifactId>
                 <version>3.10.0</version>
-                <configuration>
-                    <compilerVersion>${javac.target}</compilerVersion>
-                    <source>${javac.target}</source>
-                    <target>${javac.target}</target>
-                </configuration>
             </plugin>
 
             <plugin>

pom.xml

@@ -12,7 +12,7 @@
         <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
         <maven.compiler.source>8</maven.compiler.source>
         <maven.compiler.target>8</maven.compiler.target>
-        <logback.version>1.2.10</logback.version>
+        <logback.version>1.2.11</logback.version>
     </properties>
 
     <dependencies>

src/main/java/xyz/xuminghai/atomic/AtomicIntegerAndAtomicLongDemo02.java

@@ -1,21 +1,33 @@
 package xyz.xuminghai.atomic;
 
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
 import sun.misc.Unsafe;
 
-import java.util.concurrent.atomic.AtomicInteger;
+import java.lang.reflect.Field;
+import java.util.function.IntUnaryOperator;
 
 /**
  * 2022/3/7 11:25 星期一<br/>
  * <h1>AtomicInteger和AtomicLong原理分析</h1>
  * AtomicInteger本质使用的是{@link Unsafe}，利用CAS机制，比较期望值和实际值，成功的话则将实际值替换为更新值
+ *
  * @author xuMingHai
  */
+@SuppressWarnings("AlibabaAvoidManuallyCreateThread")
 public class AtomicIntegerAndAtomicLongDemo02 {
 
 
+    /**
+     * 日志记录器
+     */
+    private static final Logger LOGGER = LoggerFactory.getLogger(AtomicIntegerAndAtomicLongDemo02.class);
+
     public static void main(String[] args) {
+
+        // 多个线程共享的资源
         final SimpleAtomicInteger simpleAtomicInteger = new SimpleAtomicInteger();
-        
+
 
 
 
@@ -28,7 +40,7 @@ private static class SimpleAtomicInteger {
         /**
          * 用于执行不安全方法的集合
          */
-        private static final Unsafe UNSAFE = Unsafe.getUnsafe();
+        private static final Unsafe UNSAFE;
 
         /**
          * value字段的偏移量，同一类的不同实例的字段偏移量是相同的
@@ -40,7 +52,12 @@ private static class SimpleAtomicInteger {
          */
         static {
             try {
-                VALUE_OFFSET = UNSAFE.objectFieldOffset(AtomicInteger.class.getDeclaredField("value"));
+                final Field theUnsafe = Unsafe.class.getDeclaredField("theUnsafe");
+                theUnsafe.setAccessible(true);
+                UNSAFE = (Unsafe) theUnsafe.get(null);
+                theUnsafe.setAccessible(false);
+
+                VALUE_OFFSET = UNSAFE.objectFieldOffset(SimpleAtomicInteger.class.getDeclaredField("value"));
             } catch (Exception ex) {
                 throw new Error(ex);
             }
@@ -50,14 +67,24 @@ private static class SimpleAtomicInteger {
 
         /**
          * 获取当前值，因为value是使用volatile修饰的
+         *
          * @return value
          */
         public int get() {
             return value;
         }
 
+        /**
+         * 将当前值设置为新的值
+         * @param newValue 新的值
+         */
+        public void set(int newValue) {
+            value = newValue;
+        }
+
         /**
          * 将预期值和实际值作比较，如果没有线程已经修改了，那么将值改为要更新的值
+         *
          * @param expect 预期值
          * @param update 更新值
          * @return true表示更新成功，false更新失败
@@ -66,6 +93,28 @@ public boolean completeAndSet(int expect, int update) {
             return UNSAFE.compareAndSwapInt(this, VALUE_OFFSET, expect, update);
         }
 
+        /**
+         * 获取并更新原子
+         *
+         * @param intUnaryOperator 返回要更新的值
+         * @return 前一个值
+         */
+        public int getAndUpdate(IntUnaryOperator intUnaryOperator) {
+            // 期望值，要更改的值
+            int prev, next;
+            int i = 1;
+            // 循环修改
+            do {
+                LOGGER.info("第{}次CAS", i++);
+                // 获取最新值
+                prev = get();
+                // 得到要更改的值
+                next = intUnaryOperator.applyAsInt(prev);
+                // CAS设置值
+            } while (!completeAndSet(prev, next));
+
+            return prev;
+        }
 
 
     }