JDK之延时任务
JDK中延时任务可以使用
ScheduledThreadPoolExecutor.schedule 方法,其实这个方法和普通的线程池ThreadPoolExecutorService没啥区别,唯一的区别就是BlockingQueue
ScheduledThreadPoolExecutor使用的是它的内部类
static class DelayedWorkQueue extends AbstractQueue<Runnable> implements BlockingQueue<Runnable> {
奥秘其实就在这个DelayQueue的take方法里
public RunnableScheduledFuture<?> take() throws InterruptedException { final ReentrantLock lock = this.lock; lock.lockInterruptibly(); try { for (;;) { RunnableScheduledFuture<?> first = queue[0]; if (first == null) available.await(); else { long delay = first.getDelay(NANOSECONDS); if (delay <= 0) return finishPoll(first); first = null; // don't retain ref while waiting if (leader != null) available.await(); else { Thread thisThread = Thread.currentThread(); leader = thisThread; try { available.awaitNanos(delay); } finally { if (leader == thisThread) leader = null; } } } } } finally { if (leader == null && queue[0] != null) available.signal(); lock.unlock(); } }
其中
private final Condition available = lock.newCondition();
之前的文章分析过,DelayQueue里的元素不是普通的元素,而是必须实现了Delay接口的Class,接口方法是getDelay
ScheduledFutureTask(Callable<V> callable, long ns) { super(callable); this.time = ns; this.period = 0; this.sequenceNumber = sequencer.getAndIncrement(); } public long getDelay(TimeUnit unit) { return unit.convert(time - now(), NANOSECONDS); }