线程进入同步块后可以更改锁吗？

Question

I am asking this question is just for curiosity, I know it is stupid to do such thing.

public void doSomething() 
{
      synchronized(object_A){
        count++;
        average = count/total;
      }
}

Now let say I have 2 thread run concurrently (calling function doSomething()), while the first thread already enter the block, let say at the line "count++", the second thread is blocked and waiting the lock.

Now I try to do object_A = new LockObject() (in another thread). Now what happen to thread 1 and thread 2?

Will thread 2 enter the block? Since it already executed statement "synchronized(object_A)", is it too late to change the lock?

Will thread 1 change the lock while in the sync block (assume thread 1 still in the block)?

Answer 1

就像ignis所说，但是线程2完成后，线程2将看到新的引用，因为它必须刷新所有变量。

Answer 2

The only problem would be data integrity. Threads will be synchronizing on different locks and the data protected by the locks will have wrong values. Locks are created in the instance initializer's as private final fields or in the constructor of the class.