Java线程中synchronized的用法与原理解析

//比如我们可以把当前对象锁起来。
synchronized (this){
    while(number<100){
        System.out.println("本次的号码是："+number++);
    }
}

*****synchronized 可以加在非静态方法上*****
public synchronized void methodName(){
    // code ......
}
*****synchronized 可以加在静态方法上*****
public synchronized static void methodName(){
    // code ......
}

*****synchronized 可以加在某个对象上*****
public void methodName3(){
    synchronized (this){ //这里可以写任意对象，此时是当前对象
        // code ......
    }
}
//也可以是任意对象。但是这个对象必须是final的，因为不同的线程会创建不同的对象，也就会锁住不同的变量，因此这里就会出现不一致问题。
private final Object object =new Object();
public void methodName4(){
    synchronized (object){
        // code ......
    }
}
*****synchronized 可以加在某个类上*****
public void methodName5(){
    synchronized (SynTest.class){
        // code ......
    }
}

//就是再说下面两种修饰方法：
synchronized(this|object) {}  //加在对象上
synchronized 修饰非静态方法

//就是再说下面两种修饰方法：
synchronized(ClassName.class) {} //加在类上
synchronized 修饰静态方法

public class SyncTest {
    public void method(){
        synchronized(this){
            try {
                TimeUnit.MINUTES.sleep(10);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
            System.out.println(Thread.currentThread().getName()+" has started");
        }
    }
    public static void main(String[] args) {
        SyncTest test=new SyncTest();
        for (int i = 0; i <5 ; i++) {
            new Thread(test::method).start();
        }
    }
}

public void method();
    descriptor: ()V
    flags: ACC_PUBLIC
    Code:
      stack=3, locals=4, args_size=1
         0: aload_0
         1: dup
         2: astore_1
         3: monitorenter		***** monitorenter互斥的入口
         4: getstatic     #2                  // Field java/util/concurrent/TimeUnit.MINUTES:Ljava/util/concurrent/TimeUnit;
         7: ldc2_w        #3                  // long 10l
        10: invokevirtual #5                  // Method java/util/concurrent/TimeUnit.sleep:(J)V
        13: goto          21
        16: astore_2
        17: aload_2
        18: invokevirtual #7                  // Method java/lang/InterruptedException.printStackTrace:()V
        21: getstatic     #8                  // Field java/lang/System.out:Ljava/io/PrintStream;
        24: new           #9                  // class java/lang/StringBuilder
        27: dup
        28: invokespecial #10                 // Method java/lang/StringBuilder."<init>":()V
        31: invokestatic  #11                 // Method java/lang/Thread.currentThread:()Ljava/lang/Thread;
        34: invokevirtual #12                 // Method java/lang/Thread.getName:()Ljava/lang/String;
        37: invokevirtual #13                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
        40: ldc           #14                 // String  has started
        42: invokevirtual #13                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
        45: invokevirtual #15                 // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
        48: invokevirtual #16                 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
        51: aload_1
        52: monitorexit		***** 一直到这里退出，可以算作互斥的出口
        53: goto          61
        56: astore_3
        57: aload_1
        58: monitorexit		***** 发现还有一个monitorexit，这个是异常出口，下面有解释
        59: aload_3
        60: athrow
        61: return

public static synchronized void methodName(){
    while(number<100){
        System.out.println("本次的号码是："+number++);
    }
}

 public static synchronized void methodName();
    descriptor: ()V
    flags: ACC_PUBLIC, ACC_STATIC, ACC_SYNCHRONIZED		*方法标记
    Code:
      stack=5, locals=0, args_size=0
         0: getstatic     #15                 // Field number:I
         3: bipush        100
         5: if_icmpge     44
         8: getstatic     #6                  // Field java/lang/System.out:Ljava/io/PrintStream;
        11: new           #7                  // class java/lang/StringBuilder
        14: dup
        15: invokespecial #8                  // Method java/lang/StringBuilder."<init>":()V
        18: ldc           #16                 // String 本次的号码是：
        20: invokevirtual #11                 // Method java/lang/StringBuilder.append:(Ljava/lang/String;)Ljava/lang/StringBuilder;
        23: getstatic     #15                 // Field number:I
        26: dup
        27: iconst_1
        28: iadd
        29: putstatic     #15                 // Field number:I
        32: invokevirtual #17                 // Method java/lang/StringBuilder.append:(I)Ljava/lang/StringBuilder;
        35: invokevirtual #13                 // Method java/lang/StringBuilder.toString:()Ljava/lang/String;
        38: invokevirtual #14                 // Method java/io/PrintStream.println:(Ljava/lang/String;)V
        41: goto          0
        44: return
      LineNumberTable:
        line 19: 0
        line 20: 8
        line 22: 44
      StackMapTable: number_of_entries = 2
        frame_type = 0 /* same */
        frame_type = 43 /* same */