Java同步工具解锁一次即可无限次使用

Question

I want an object that can be

1. locked once by any thread (no ownership!)

2. requested an arbitrary number of times resulting in block (block only if locked)

3. unlocked once by any thread (again, no ownership)

4. all requesting (blocked) threads (including future requests yet to be made!) are no longer blocked

This seems like it would be akin to a semaphore except with infinite permits once unlocked.

Is this possible in Java? How it be accomplished?

Answer 1

Here is the solution I came up with:

public class GateLock {
    private boolean isOpen;
    public GateLock() {
        isOpen = false;
    }

    public synchronized void open(){
        isOpen = true;
        notifyAll();
    }

    public synchronized void close(){
        isOpen = false;
    }

    public synchronized void enter(){
        while(!isOpen) {
            try {
                wait();
            } catch (InterruptedException e) {}
        }
    }
}