package async.up;
import java.util.concurrent.DelayQueue;
import java.util.concurrent.Delayed;
import java.util.concurrent.TimeUnit;

public class DelayRetryUtil {

private static DelayQueue<RetryItem> RETRY_DELAY_QUEUE = null;

static boolean offer(RetryItem e) {

    // 延迟初始化，因为延迟队列是耗费cpu及内存资源的开销，在真正使用时才进行初始化，并执行任务
    // todo 后续可以增加通过其他线程动态监测RETRY_DELAY_QUEUE不再使用时，进行销毁
    if(RETRY_DELAY_QUEUE == null) {
        synchronized (DelayRetryUtil.class) {
            if(RETRY_DELAY_QUEUE == null) {
                initConsumer();
            }
        }
    }
    return RETRY_DELAY_QUEUE.offer(e);
}

private static void initConsumer() {
    RETRY_DELAY_QUEUE  = new DelayQueue<>();
    new Thread(() -> {
        boolean go = true;
        while(go) {
            try {
                RetryItem i = RETRY_DELAY_QUEUE.take();

                if(i != null) {
                    System.out.println("123");
                }
            } catch (InterruptedException e1) {
                go = false;
            }
        }
    }).start();
}


static class RetryItem implements Delayed{

    private long startTime;

    RetryItem(long startTime) {
        this.startTime = startTime;
    }

    @Override
    public long getDelay(TimeUnit unit) {

        return unit.convert(startTime - System.currentTimeMillis(), TimeUnit.MILLISECONDS);
    }

    @Override
    public int compareTo(Delayed o) {
        RetryItem c = (RetryItem) o;
        return this.startTime - c.startTime > 0 ? 1 : (this.startTime - c.startTime < 0 ? -1 : 0);
    }
}

}

上面的程序中,在高并发环境下，return RETRY_DELAY_QUEUE.offer(e); 会不会有NullPointException,以及为什么了？