Locks between two methods starving one method

Question

In my program i have two methods:

public void methodA() { //gets called very often
   //write something to file
}

public void methodB() {
  //write something to file
}

methodA gets called by the client very often, whereas methodB gets only called from time to time. However, I need to make sure that whenever a client wants to call methodB it can do so (after possible current execution of methodA has finished). I tried to introduce a synchronized block with an locking object within each method however methodB seems to starve, since methodA gets called more often. How can I solve this issue?

Answer 1

Sounds like you are in need of a fair Lock. To make one of these you should pass true as a parameter to the constructor.

Lock lock = new ReentrantLock(true);

public void methodA() {
    lock.lock();
    try {
        // Write something to a file.
    } finally {
        lock.unlock();
    }
}

public void methodB() {
    lock.lock();
    try {
        // Write something to a file.
    } finally {
        lock.unlock();
    }
}