package nachos.threads;

import nachos.machine.*;

/**
 * An implementation of condition variables that disables interrupt()s for
 * synchronization.
 *
 * <p>
 * You must implement this.
 *
 * @see	nachos.threads.Condition
 */
public class Condition2 {
    /**
     * Allocate a new condition variable.
     *
     * @param	conditionLock	the lock associated with this condition
     *				variable. The current thread must hold this
     *				lock whenever it uses <tt>sleep()</tt>,
     *				<tt>wake()</tt>, or <tt>wakeAll()</tt>.
     */
    public Condition2(Lock conditionLock)
	{
		this.conditionLock = conditionLock;
    }

    /**
     * Atomically release the associated lock and go to sleep on this condition
     * variable until another thread wakes it using <tt>wake()</tt>. The
     * current thread must hold the associated lock. The thread will
     * automatically reacquire the lock before <tt>sleep()</tt> returns.
     */
    public void sleep()
	{
		Lib.assertTrue(conditionLock.isHeldByCurrentThread());

		conditionLock.release();
		boolean intStatus=Machine.interrupt().disable();
		waitQueue.waitForAccess(KThread.currentThread());
		KThread.sleep();
		Machine.interrupt().restore(intStatus);
		conditionLock.acquire();
    }

    /**
     * Wake up at most one thread sleeping on this condition variable. The
     * current thread must hold the associated lock.
     */
    public void wake()
	{
		Lib.assertTrue(conditionLock.isHeldByCurrentThread());
		boolean intStatus=Machine.interrupt().disable();
		KThread a=waitQueue.nextThread();
		if(a!=null) a.ready();
		Machine.interrupt().restore(intStatus);
    }

    /**
     * Wake up all threads sleeping on this condition variable. The current
     * thread must hold the associated lock.
     */
    public void wakeAll()
	{
		Lib.assertTrue(conditionLock.isHeldByCurrentThread());
		boolean intStatus=Machine.interrupt().disable();
		while(true)
		{
			KThread a=waitQueue.nextThread();
			if(a!=null) a.ready();
			else break;
		}
		Machine.interrupt().restore(intStatus);
    }

    private Lock conditionLock;
	private ThreadQueue waitQueue=ThreadedKernel.scheduler.newThreadQueue(true);
}