sychronized锁范围

sychronized

• 锁范围

  • 普通同步方法：锁是当前实例对象this，同一个实例中的加锁方法是原子执行的

   /**
    * sychronized范围测试
    */
   @Slf4j(topic = "c.TestLockScope")
   public class TestLockScope {
  
       public static void main(String[] args) throws InterruptedException {
           Resource resource = new Resource();
           //线程1执行5000次加
           Thread t1 = new Thread(() -> {
               for (int i = 0; i < 5000; i++) {
                   resource.add();
               }
           },"t1");
  
           //线程2执行5000次减
           Thread t2 = new Thread(() -> {
               for (int i = 0; i < 5000; i++) {
                   resource.sub();
               }
           },"t2");
           t1.start();
           t2.start();
           t1.join();
           t2.join();
           //锁是当前resource实例对象，同一个对象在不同线程中的同步方法是原子执行的
           //21:32:25 [main] c.TestLockScope - 结果：0
           log.debug("结果：{}",resource.getNum());
       }
   }
  
    class Resource{
       private int num;
  
       public synchronized void add(){
           num++;
       }
  
       public synchronized void sub(){
           num--;
       }
  
       public synchronized int getNum(){
           return num;
       }
   }
  

  • 静态同步方法：锁是当前类的Class对象，使用Class创建的所有实例中的加锁方法是原子执行的

   /**
    * sychronized范围测试
    */
   @Slf4j(topic = "c.TestLockScope")
   public class TestLockScope {
  
       public static void main(String[] args) throws InterruptedException {
   //        Resource resource1 = new Resource();
   //        Resource resource2 = new Resource();
           //线程1执行5000次加
           Thread t1 = new Thread(() -> {
               for (int i = 0; i < 5000; i++) {
   //                resource1.add();
                   Resource.add();
               }
           },"t1");
  
           //线程2执行5000次减
           Thread t2 = new Thread(() -> {
               for (int i = 0; i < 5000; i++) {
   //                resource2.sub();
                   Resource.sub();
               }
           },"t2");
           t1.start();
           t2.start();
           t1.join();
           t2.join();
           //锁是当前Resource类的Class对象，Resource类中的静态同步方法在不同线程是原子执行的
           //21:35:55 [main] c.TestLockScope - 结果：0
           log.debug("结果：{}",Resource.getNum());
       }
   }
  
    class Resource{
       private static int num;
  
       public static synchronized void add(){
           num++;
       }
  
       public static synchronized void sub(){
           num--;
       }
  
       public static synchronized int getNum(){
           return num;
       }
   }
  

  • 同步代码块：锁是()里设置的对象，可以设置当前实例对象，也可以设置类的Class对象

    • 锁是当前实例对象

     /**
      * sychronized范围测试
      */
     @Slf4j(topic = "c.TestLockScope")
     public class TestLockScope {
    
         public static void main(String[] args) throws InterruptedException {
             Resource resource = new Resource();
             //线程1执行5000次加
             Thread t1 = new Thread(() -> {
                 for (int i = 0; i < 5000; i++) {
                     resource.add();
                 }
             }, "t1");
    
             //线程2执行5000次减
             Thread t2 = new Thread(() -> {
                 for (int i = 0; i < 5000; i++) {
                     resource.sub();
                 }
             }, "t2");
             t1.start();
             t2.start();
             t1.join();
             t2.join();
             log.debug("结果：{}", resource.getNum());
         }
     }
    
     class Resource {
         private int num;
    
         public void add() {
             synchronized (this) {
                 num++;
             }
         }
    
         public void sub() {
             synchronized (this) {
                 num--;
             }
         }
    
         public int getNum() {
             synchronized (this) {
                 return num;
             }
         }
     }
    

    • 锁是Class对象

     /**
      * sychronized范围测试
      */
     @Slf4j(topic = "c.TestLockScope")
     public class TestLockScope {
    
         public static void main(String[] args) throws InterruptedException {
             Resource resource1 = new Resource();
             Resource resource2 = new Resource();
             //线程1执行5000次加
             Thread t1 = new Thread(() -> {
                 for (int i = 0; i < 5000; i++) {
                     resource1.add();
                 }
             }, "t1");
    
             //线程2执行5000次减
             Thread t2 = new Thread(() -> {
                 for (int i = 0; i < 5000; i++) {
                     resource2.sub();
                 }
             }, "t2");
             t1.start();
             t2.start();
             t1.join();
             t2.join();
             log.debug("结果：{}", resource2.getNum());
         }
     }
    
     class Resource {
         private static int num;
    
         public void add() {
             synchronized (Resource.class) {
                 num++;
             }
         }
    
         public void sub() {
             synchronized (Resource.class) {
                 num--;
             }
         }
    
         public int getNum() {
             synchronized (Resource.class) {
                 return num;
             }
         }
     }