浅谈Java锁

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class {
	
	int a = 0;
	
	public synchronized void writer(){
		sleep(10);
		a++;
	}
	
	public synchronized void reader(){
		int i = a;
	}
	
	public static void main(String[] args) {
	
        Test test = new Test();
        new Thread(() -> {
            test.writer();
        }).start();
        
        sleep(1);
        
        new Thread(() -> {
            test.reader();
        }).start();
    }
}

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class {
	
	static int a = 0;
    public synchronized void writer() {
        System.out.println("writer方法开始调用");
        a++;
        waitNs(20);
        System.out.println("writer方法调用结束");
    }
    public  static synchronized void reader() {
        System.out.println("reader方法开始调用");
        int i = a;
        System.out.println("reader方法调用结束");
    }
    public void writer2() {
        synchronized (this) {
            a--;
        }
    }
}

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...
{
  static int a;
    descriptor: I
    flags: ACC_STATIC
  public com.fonxian.entity.LockDemo();
    descriptor: ()V
    flags: ACC_PUBLIC
    Code:
      stack=1, locals=1, args_size=1
         0: aload_0
         1: invokespecial #1                  // Method java/lang/Object."":()V
         4: return
      LineNumberTable:
        line 6: 0
  
  //同步方法
  public synchronized void writer();
    descriptor: ()V
    flags: ACC_PUBLIC, ACC_SYNCHRONIZED
    Code:
      stack=2, locals=1, args_size=1
         0: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
         3: ldc           #3                  // String writer方法开始调用
         5: invokevirtual #4                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
         8: getstatic     #5                  // Field a:I
        11: iconst_1
        12: iadd
        13: putstatic     #5                  // Field a:I
        16: bipush        20
        18: invokestatic  #6                  // Method waitNs:(I)V
        21: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
        24: ldc           #7                  // String writer方法调用结束
        26: invokevirtual #4                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
        29: return
      LineNumberTable:
        line 11: 0
        line 12: 8
        line 13: 16
        line 14: 21
        line 15: 29
  //静态同步方法
  public static synchronized void reader();
    descriptor: ()V
    flags: ACC_PUBLIC, ACC_STATIC, ACC_SYNCHRONIZED
    Code:
      stack=2, locals=1, args_size=0
         0: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
         3: ldc           #8                  // String reader方法开始调用
         5: invokevirtual #4                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
         8: getstatic     #5                  // Field a:I
        11: istore_0
        12: getstatic     #2                  // Field java/lang/System.out:Ljava/io/PrintStream;
        15: ldc           #9                  // String reader方法调用结束
        17: invokevirtual #4                  // Method java/io/PrintStream.println:(Ljava/lang/String;)V
        20: return
      LineNumberTable:
        line 18: 0
        line 19: 8
        line 20: 12
        line 21: 20
	
  //同步代码块
  public void writer2();
    descriptor: ()V
    flags: ACC_PUBLIC
    Code:
      stack=2, locals=3, args_size=1
         0: aload_0
         1: dup
         2: astore_1
         3: monitorenter
         4: getstatic     #5                  // Field a:I
         7: iconst_1
         8: isub
         9: putstatic     #5                  // Field a:I
        12: aload_1
        13: monitorexit
        14: goto          22
        17: astore_2
        18: aload_1
        19: monitorexit
        20: aload_2
        21: athrow
        22: return
      Exception table:
         from    to  target type
             4    14    17   any
            17    20    17   any
      LineNumberTable:
        line 25: 0
        line 26: 4
        line 27: 12
        line 28: 22
      StackMapTable: number_of_entries = 2
        frame_type = 255 /* full_frame */
          offset_delta = 17
          locals = [ class com/fonxian/entity/LockDemo, class java/lang/Object ]
          stack = [ class java/lang/Throwable ]
        frame_type = 250 /* chop */
          offset_delta = 4
  static {};
    descriptor: ()V
    flags: ACC_STATIC
    Code:
      stack=1, locals=0, args_size=0
         0: iconst_0
         1: putstatic     #5                  // Field a:I
         4: return
      LineNumberTable:
        line 8: 0
}
SourceFile: "LockDemo.java"