Multiple Threads calling static helper method

Question

I have a web application running on Tomcat.

There are several calculations that need to be done on multiple places in the web application. Can I make those calculations static helper functions? If the server has enough processor cores, can multiple calls to that static function (resulting from multiple requests to different servlets) run parallel? Or does one request have to wait until the other request finished the call?

public class Helper {
    public static void doSomething(int arg1, int arg2) {
        // do something with the args
        return val;
    }
}

if the calls run parallel: I have another helper class with static functions, but this class contains a private static member which is used in the static functions. How can I make sure that the functions are thread-safe?

public class Helper {

    private static SomeObject obj;

    public static void changeMember() {
        Helper.obj.changeValue();
    }

    public static String readMember() {
        Helper.obj.readValue();
    }

}

changeValue() and readValue() read/change the same member variable of Helper.obj. Do I have to make the whole static functions synchronized, or just the block where Helper.obj is used? If I should use a block, what object should I use to lock it?

Answer 1

For the first part: Yes, these calls are independent and run in parallel when called by different threads.

For the last part: Use synchronize blocks on the concurrent object, a dummy object or class object. Be aware of cascaded synchronize blocks. They can lead into dead locks when acquired in different order.