Synchronizing overlapping sets of methods

Question

Imagine a Java class with three methods:

1. master()
2. foo()
3. bar()

I want to synchronize master() and foo() and also master() and bar(), without synchronizing foo() and bar(). It can be done will a separate lock for every pair of synchronized methods, but my actual code has many more than three methods so I was hoping there's a way to do it without so many lock objects.

Answer 1

You are essentially describing a ReadWriteLock. Every two methods are allowed to run simultaneously (a "read lock"), except for master(), which excludes all others (a "write lock"):

public class MyClass {
    private final ReadWriteLock rwLock = new ReentrantReadWriteLock();
    private final Lock r = rwLock.readLock();
    private final Lock w = rwLock.writeLock();

    public void master() {
        w.lock();
        // do stuff
        w.unlock();
    }

    public void foo() {
        r.lock();
        // do stuff
        r.unlock();
    }

    public void bar() {
        r.lock();
        // do stuff
        r.unlock();
    }
}