synchronize字节码解析

爱被打了一巴掌 2021-12-24 11:25 308阅读 0赞

源java文件：

public class TestSynchronize {
    
        static volatile int b;
        
        public static void main(String[] args) {
    
            String s = new String("xxx");
            int a = 10;
            
            
            synchronized(s){
                a++;
            }
            
            b = 10;
    
        }
    }

字节码文件：

public class com.learn.test.code.bytecode.TestSynchronize {
      static volatile int b;
    
      public com.learn.test.code.bytecode.TestSynchronize();
        Code:
           0: aload_0
           1: invokespecial #1                  // Method java/lang/Object."<init>":()V
           4: return
    
      public static void main(java.lang.String[]);
        Code:
           0: new           #2                  // class java/lang/String
           3: dup
           4: ldc           #3                  // String xxx
           6: invokespecial #4                  // Method java/lang/String."<init>":(Ljava/lang/String;)V
           9: astore_1
          10: bipush        10
          12: istore_2
          13: aload_1
          14: dup
          15: astore_3
          16: monitorenter
          17: iinc          2, 1
          20: aload_3
          21: monitorexit
          22: goto          32
          25: astore        4
          27: aload_3
          28: monitorexit
          29: aload         4
          31: athrow
          32: bipush        10
          34: putstatic     #5                  // Field b:I
          37: return
        Exception table:
           from    to  target type
              17    22    25   any
              25    29    25   any
    }

i++对应的字节码如下：

17: iinc          2, 1
      20: aload_3

他们被moniterenter和moniterexit如下包围起来：

16: monitorenter
      17: iinc          2, 1
      20: aload_3
      21: monitorexit