Question

It is well known that synchronization is recommended on a final private object (vs. synchronizing on this or even a protected data member).

But what happens when I have multiple classes (modules) in my application that need to synchronize on a common object?

Is there a way to reconcile these two seemingly contradicting requirements?

To better explain, if I have a private data member of class Owner defined as:

private final Object $01pfo = new Object[0]; 

Then any method in Owner could simply use it:

  protected void anyMethod()  {
    synchronized ($01pfo) {
          // do your thing
    }
  }

But if I want to synchronize on $01pfo from a different class (say User), is my only option to make $01pfo protected or public?

protected final Object $01pfo = new Object[0]; 

Is there a better approach? or solution?

Answer 1

synchronized blocks are working well in case if they are not spread among several objects.

in case if you need to synchronize operations using single lock in several classes – it’s better to take a look at Lock implementations.

It will give you much more freedom in granularing access to resources in several threads