class Lock {
   private:
     int value = FREE;
     SpinLock spinLock;
     Queue waiting;
   public:
     void acquire();
     void release();
}

Lock::acquire() {
    spinLock.acquire(); 
    if (value != FREE) {
        waiting.add(runningThread);
        scheduler.suspend(&spinLock);
       // scheduler releases spinLock
    } else { 
        value = BUSY;
        spinLock.release();
    }
}

void Lock::release() {
    TCB *next;

    spinLock.acquire(); 
    if (waiting.notEmpty()) {
        next = waiting.remove();
        scheduler.makeReady(next);
    } else {
        value = FREE;
    }
    spinLock.release();
}