并发编程之定时线程池上课笔记

1、定时任务 ScheduledThreoolExecutor：介绍：之前讲的ThreoolExecutor 是 java 的普通线程池。而 ScheduledThreoolExecutor 是 java 提供的定时任务线程池。使用：常用oolExecutor#schedule 定时任务java.util.concurrent.ScheduledThreoolExecutor#scheduleAtFixedRate 固定速率连续执行java.util.concurrent.ScheduledThreoolExecutor#scheduleWithFixedDelay 非固定速率连续执行java.u

2、til.concurrent.ScheduledThreoolExecutor.DelayedWorkQueue 延迟队列java.util.concurrent.ScheduledThre源码分析：初始化 ScheduledThreoolExecutor调度构造器public ScheduledThre oolExecutor(corePoolSize) super(corePoolSize,eger.MAX_VALUE, 0, NANOSECONDS,new DelayedWorkQueue();scheduleAtFixedRate 方法delayedExecute#ScheduledT

3、hre oolExecutor 方法/总结：add 方法是通过DelayedWorkQueue（初始化时候指定的队列） 延迟队列实现 offer 获取对象的延迟if (isShutdown() &!canRunInCurrentRunS e(task.isPeriodic() & /判断是否已经停止remove(task)if (isShutdown()reject(task);else super.getQueue().add(task);/增加任务 子类实现了public ScheduledFuture scheduleAtFixedRate(Runnabled,long initialD

4、elay,long period,TimeUnit unit) if (d = null | unit = null)throw new NullPo erException();if (period = 0)throw new IllegalArgumentException();ScheduledFutureTask sft =new ScheduledFutureTask(d,null,triggerTime(initialDelay, unit),unit.toNanos(period);/处理时间RunnableScheduledFuture t = decorateTask(d,

5、sft);sft.outerTask = t;delayedExecute(t); return t;Offer#DelayedWorkQueue 二叉树堆排序算法siftUp#DelayedWorkQueue 保证相同的while (k 0) publicoffer(Runnable x) if (x = null)throw new NullPo erException();RunnableScheduledFuture e = (RunnableScheduledFuture)x; /类final ReentrantLock lock = this.lock;lock.lock();tr

6、y i = size;if (i = queue.length)/判断是否扩容grow();size = i + 1;if (i = 0) queue0 = e;/这个队列是setIndex(e, 0); /第一个直接设置索引和下标 0 else siftUp(i, e);/看这儿if (queue0 = e) leader = null;available.signal();/唤醒 finally lock.unlock();return true;task.cancel(false);elseensurePrestart();compareTo#ScheduledFutureTask在回到

7、开始的地方,根据刚才跟代码可以看到执行时间的顺序已经分配好了，那如何确保 work 可以运行了？确保有work 执行ensurePrestart#ThreoolExecutorif (other = this) / compare zero if same objectreturn 0;if (other instanceof ScheduledFutureTask) ScheduledFutureTask x = (ScheduledFutureTask)other;long diff = time - x.time; /判断 timeif (diff 0)return 1;else if

8、(sequenceNumber x.sequenceNumber)return -1;elsereturn 1;long diff = getDelay(NANOSECONDS) - other.getDelay(NANOSECONDS);return (diff 0) ? 1 : 0;parent = (k - 1) 1;RunnableScheduledFuture e = queueparent;if (pareTo(e) = 0)break;queuek = e;setIndex(e, k);k = parent;queuek = key;setIndex(key, k);放到队列 r

9、unwork take 对象take#DelayedWorkQueue/调用startrunrunWorker-getTasktake 方法public RunnableScheduledFuture take() throwserruptedException final ReentrantLock lock = this.lock;lock.lock erruptibly();try for (;) RunnableScheduledFutureif (第一个有没有 没有等着available.await();else long delay =到时间了if (delay = 0)/到时间了

10、return finishPoll();else if (leader != null)available.await();/因为没有执行线程初始化，所以等等什么时候有了自己被他人唤醒else Thread thisThread = Thread.currentThread(); leader = thisThread;try available.awaitNanos(delay);/各种 condition 的 awaitNanos 带时间的 finally if (leader = thisThread) leader = null; finally wc = workerCountOf(ctl.get();if (wc 0) /看这个大于 0 和小于 0 的区别time += p; /假如延迟了这个时间早过了，+当前时候肯