Question

I have a class which contains a static field that acts like a singleton :

public class A {

    private static MyAPI instance = null;

    protected synchronized static MyAPI getAPI() throws Exception {
        if (instance == null){
            // init API;
        }
        return instance;
    }

    // other methods

}

And I have multiple classes which inherit from the class A and needs to perform actions on the API. I work in a multi-threaded environment and the API can work once at a time, so I have to ensure that all the subclasses don’t work on the API at the same time. To do that, I synchronize the super class when I access the API in subclasses :

public class B extends A {

    public void myMethod(){
        synchronized (A.class) {
            myAPI = getAPI();
            // do stuffs with myAPI
        }
    }
}

With this solution, I lock the entire class instead of just the API instance, so the other methods of my class A are not available when a subclass work on the API and performances can be decreased.

Do you think this is the best solution or do you know a better way ?

Thanks.

Answer 1

If you don’t want to lock on the entire class, you may lock on a static object that you use only in that method:

public class A {

    private static MyAPI instance = null;
    protected static Object lockForMyMethod = new Object(); //have a static lock

    // other methods    
}

public class B extends A {

    public void myMethod(){
        synchronized (A.lockForMyMethod) { //do not lock on A.class
            myAPI = getAPI();
            // do stuffs with myAPI
        }
    }
}