Java method synchronization improper usage?

Question

Suppose there is the following code:

class MyClass {
    synchronized void myMethod1() {
        //code 
    }

    synchronized void myMethod2() {
        //code
    }
}

Now suppose myMethod1() and myMethod2() access distinct data; now if there are two threads, thread A calling only myMethod1() and thread B calling only myMethod2().

If thread A is executing myMethod1(), will thread B block waiting on myMethod2() even if they don't access the same data and there is no reason for this? As far as I know, synchronized methods use the monitor of this object for instance methods and that of MyClass.class object for static functions.

Answer 1

Your understanding of the situation is correct.

The typical solution is to have separate dedicated lock objects for the resources in question.

class MyClass {
    private final Lock lock1 = new ReentrantLock();
    private final Lock lock2 = new ReentrantLock();

    void myMethod1() {          
      lock1.lock();

      try {
        //code 
      } finally {
        lock1.unlock();
      }            
    }

    void myMethod2() {
      lock2.lock();

      try {
        //code 
      } finally {
        lock2.unlock();
      }    
    }
}

Answer 2

You are correct in all your suppositions. In the case where no data is in common then there is no reason to synchronize at the method level.