/*
 * Written by Doug Lea with assistance from members of JCP JSR-166
 * Expert Group and released to the public domain, as explained at
 * http://creativecommons.org/publicdomain/zero/1.0/
 */

import java.io.ObjectInputStream;
import java.io.IOException;
import java.util.concurrent.*;
import java.util.concurrent.locks.*;

class Mutex implements Lock, java.io.Serializable {

    // Our internal helper class
    private static class Sync extends AbstractQueuedSynchronizer {
        // Report whether in locked state
        protected boolean isHeldExclusively() {
            return getState() == 1;
        }

        // Acquire the lock if state is zero
        public boolean tryAcquire(int acquires) {
            assert acquires == 1; // Otherwise unused
            return compareAndSetState(0, 1);
        }

        // Release the lock by setting state to zero
        protected boolean tryRelease(int releases) {
            assert releases == 1; // Otherwise unused
            if (getState() == 0) throw new IllegalMonitorStateException();
            setState(0);
            return true;
        }

        // Provide a Condition
        Condition newCondition() { return new ConditionObject(); }

        // Deserialize properly
        private void readObject(ObjectInputStream s) throws IOException, ClassNotFoundException {
            s.defaultReadObject();
            setState(0); // reset to unlocked state
        }
    }

    // The sync object does all the hard work. We just forward to it.
    private final Sync sync = new Sync();

    public void lock()                { sync.acquire(1); }
    public boolean tryLock()          { return sync.tryAcquire(1); }
    public void unlock()              { sync.release(1); }
    public Condition newCondition()   { return sync.newCondition(); }
    public boolean isLocked()         { return sync.isHeldExclusively(); }
    public boolean hasQueuedThreads() { return sync.hasQueuedThreads(); }
    public void lockInterruptibly() throws InterruptedException {
        sync.acquireInterruptibly(1);
    }
    public boolean tryLock(long timeout, TimeUnit unit) throws InterruptedException {
        return sync.tryAcquireNanos(1, unit.toNanos(timeout));
    }
}