FutureTask疑问

1     public V get() throws InterruptedException, ExecutionException {
2         int s = state;
3         if (s <= COMPLETING)
4             s = awaitDone(false, 0L);
5         return report(s);
6     }

 1     private int awaitDone(boolean timed, long nanos)
 2         throws InterruptedException {
 3         final long deadline = timed ? System.nanoTime() + nanos : 0L;
 4         WaitNode q = null;
 5         boolean queued = false;
 6         for (;;) {
 7             if (Thread.interrupted()) {
 8                 removeWaiter(q);
 9                 throw new InterruptedException();
10             }
11 
12             int s = state;
13             if (s > COMPLETING) {
14                 if (q != null)
15                     q.thread = null;
16                 return s;
17             }
18             else if (s == COMPLETING) // cannot time out yet
19                 Thread.yield();
20             else if (q == null)
21                 q = new WaitNode();
22             else if (!queued)
23                 queued = UNSAFE.compareAndSwapObject(this, waitersOffset,
24                                                      q.next = waiters, q);
25             else if (timed) {
26                 nanos = deadline - System.nanoTime();
27                 if (nanos <= 0L) {
28                     removeWaiter(q);
29                     return state;
30                 }
31                 LockSupport.parkNanos(this, nanos);
32             }
33             else
34                 LockSupport.park(this);//全程无锁，只是在入队时使用了CAS
35         }
36     }