流程
corePoolSize()是否满，有全局锁
runnableTaskQueue()是否满
ArrayBlockingQueue
LinkedBlockingQueue
SynchronousQueue
PriorityBlockingQueue
maximumPoolSize()是否满，有全局锁
RejectedExecutionHandler接口
AbortPolicy
CallerRunsPolicy
DiscardOldestPolicy
DiscardPolicy
keepAliveTime 无任务后多长时间销毁县城
Executor 接口
ThreadPoolExecutor
FixedThreadPool 线程n
SingleThreadExecutor 线程1
CachedThreadPool 线程 MAX_VALUE
ScheduledThreadPoolExecutor周期性执行
time
sequenceNumber
period
DelayQueue
Future接口
FutureTask 基于aqs
get()
run()
cancel()
