I don't understand why this code worked haha

Question about the task

A wise man thinks once before speaking twice

Under discussion

I used a synchronized block in the Solution constructor for all that logic, used a synchronized (this) in the first method and a synchronized (Solution.class) in the second method and the answer validated. What is the point of using both "this" and "Solution.class"?

Comments (2)

Popular
New
Old

You must be signed in to leave a comment

Guadalupe Gagnon

Level 37 , Tampa, United States

30 March 2020, 16:34

The task says that the two methods should simultaneously be accessed from different threads. If you used the same synchronize (this or Solution.class) on both of them, then when a thread accessed one, both would be locked. That would fail the condition. The synch block in the constructor wasn't needed. Just to be sure, the use of synchronize only locks other blocks of synchronize with the same mutex. So if you had a block of synchronize(this), that does not mean that the entire object is locked and can't be used, only what is inside the synch block as well as any other synch blocks that are locked by the same.

void method1(){
   synchronized (this){
      // locked if method 2 is already in use
   }
}

void method2(){
   synchronized (this){
      // locked if method 1 is already in use
   }
}

void method3(){
   // completely unlocked and free to use in all cases
}

John

Level 27 , Washington DC, USA

30 March 2020, 21:30

That was helpful, thanks! I didn't consider the fact that other methods with the same synchronized object ("this" in your case) would be blocked as well, but it makes sense why.