漫画：怎么给女朋友讲明白线程池？

/**
?*?The?main?pool?control?state,?ctl,?is?an?atomic?integer?packing
?*?two?conceptual?fields
?*?workerCount,?indicating?the?effective?number?of?threads
?*?runState,?indicating?whether?running,?shutting?down?etc
?*
?*?The?runState?provides?the?main?lifecycle?control,?taking?on?values:看到英文就头晕？没事啦~

@ReachabilitySensitive
private?final?AtomicInteger?ctl?=?new?AtomicInteger(ctlOf(RUNNING,?0));
private?static?final?int?COUNT_BITS?=?Integer.SIZE?-?3;
private?static?final?int?CAPACITY?=?(1?< 1;

//?runState?is?stored?in?the?high-order?bits
private?static?final?int?RUNNING?=?-1?< private?static?final?int?SHUTDOWN?=?0?< private?static?final?int?STOP?=?1?< private?static?final?int?TIDYING?=?2?< private?static?final?int?TERMINATED?=?3?< 

private?final?class?Worker
?????extends?AbstractQueuedSynchronizer
?????implements?Runnable

/**
?*?Creates?with?given?first?task?and?thread?from?ThreadFactory.
?*?@param?firstTask?the?first?task?(null?if?none)
?*/
?Worker(Runnable?firstTask)?{
?????setState(-1);?//?inhibit?interrupts?until?runWorker
?????this.firstTask?=?firstTask;
?????this.thread?=?getThreadFactory().newThread(this);
?}

public?void?execute(Runnable?command)?{
?????if?(command?==?null)
?????????throw?new?NullPointerException();
?/*
?*?Proceed?in?3?steps:
?*
?*?1.?If?fewer?than?corePoolSize?threads?are?running,?try?to
?*?start?a?new?thread?with?the?given?command?as?its?first
?*?task.?The?call?to?addWorker?atomically?checks?runState?and
?*?workerCount,?and?so?prevents?false?alarms?that?would?add
?*?threads?when?it?shouldn't,?by?returning?false.
?*?2.?If?a?task?can?be?successfully?queued,?then?we?still?need
?*?to?double-check?whether?we?should?have?added?a?thread
?*?(because?existing?ones?died?since?last?checking)?or?that
?*?the?pool?shut?down?since?entry?into?this?method.?So?we
?*?recheck?state?and?if?necessary?roll?back?the?enqueuing?if
?*?stopped,?or?start?a?new?thread?if?there?are?none.
?*?3.?If?we?cannot?queue?task,?then?we?try?to?add?a?new
?*?thread.?If?it?fails,?we?know?we?are?shut?down?or?saturated
?*?and?so?reject?the?task.
?*/
?????int?c?=?ctl.get();
?????if?(workerCountOf(c)?< ?corePoolSize)?{
?????????if?(addWorker(command,?true))
?????????????return;
????????c?=?ctl.get();
?????}
?????/**
?????*?2、如果线程池RUNNING状态，且入队列成功
?????*/
?????if?(isRunning(c)?&&?workQueue.offer(command))?{
?????????int?recheck?=?ctl.get();

?????//如果再次校验过程中，线程池不是RUNNING状态，
?????//?并且remove(command)--workQueue.remove()成功，拒绝当前command
?????????if?(!?isRunning(recheck)?&&?remove(command))
?????????????reject(command);

?????????//为什么只检查运行的worker数量是不是0呢？？为什么不和corePoolSize比较呢？？
?????????//?只保证有一个worker线程可以从queue中获取任务执行就行了？？
?????????//?因为只要还有活动的worker线程，就可以消费workerQueue中的任务
?????????else?if?(workerCountOf(recheck)?==?0)
?????????????addWorker(null,?false);
?????????}
?????????/**
?????????*?3、如果线程池不是running状态?或者?无法入队列
?????????*?尝试开启新线程，扩容至maxPoolSize，
?????????*?如果addWork(command,?false)?失败了，拒绝当前command
?????????*/
?????????else?if?(!addWorker(command,?false))
?????????????reject(command);
?????????}}