今日学习(自律天数：7): 继续深挖线程池+今日在优化简历+力扣

前言

今日让老师给我优化简历，他说我项目很像培训机构出来的。不属于学生时代就能做出来的作品。

学习别人优秀项目，明天去深挖那个项目。

1.深挖线程池源码

昨天挖了他提交任务的源码，任务提交。大概流程如下

当然还有很多操作没有弄，比如他会判断当前线程池状态如果已经结束了也会调用拒绝策略，等细节。

还有一个也是我找源码很久的疑问就是这个工作线程他一直是new好像并没有把他复用啊，到底是哪里复用了。 以下给出哪里复用代码

final void runWorker(Worker w) {
    Thread wt = Thread.currentThread();
    Runnable task = w.firstTask;
    w.firstTask = null;
    w.unlock(); // allow interrupts
    boolean completedAbruptly = true;
    try {
        //线程复用在这里 task = getTask()
        while (task != null || (task = getTask()) != null) {
            w.lock();
            // If pool is stopping, ensure thread is interrupted;
            // if not, ensure thread is not interrupted.  This
            // requires a recheck in second case to deal with
            // shutdownNow race while clearing interrupt
            if ((runStateAtLeast(ctl.get(), STOP) ||
                 (Thread.interrupted() &&
                  runStateAtLeast(ctl.get(), STOP))) &&
                !wt.isInterrupted())
                wt.interrupt();
            try {
                beforeExecute(wt, task);
                Throwable thrown = null;
                try {
                    task.run();
                } catch (RuntimeException x) {
                    thrown = x; throw x;
                } catch (Error x) {
                    thrown = x; throw x;
                } catch (Throwable x) {
                    thrown = x; throw new Error(x);
                } finally {
                    afterExecute(task, thrown);
                }
            } finally {
                task = null;
                w.completedTasks++;
                w.unlock();
            }
        }
        completedAbruptly = false;
    } finally {
        processWorkerExit(w, completedAbruptly);
    }
}

这里哪里进行线程复用了呢

private Runnable getTask() {
    boolean timedOut = false; // Did the last poll() time out?

    for (;;) {
        int c = ctl.get();
        int rs = runStateOf(c);
    
        // Check if queue empty only if necessary.判断状态不看了
        if (rs >= SHUTDOWN && (rs >= STOP || workQueue.isEmpty())) {
            decrementWorkerCount();
            return null;
        }

        int wc = workerCountOf(c);//拿到当前有多少工作线程

        // Are workers subject to culling?
        //看看如果工作线程大于了核心线程
        boolean timed = allowCoreThreadTimeOut || wc > corePoolSize;
        //这里如果当前是否大于了最大线程
        if ((wc > maximumPoolSize || (timed && timedOut))
            && (wc > 1 || workQueue.isEmpty())) {
            //工作线程得少一个
            if (compareAndDecrementWorkerCount(c))
                //这里返回空 外面的while循环就结束了 然后他的finally方法里面会把他remove掉
                return null;
            continue;
        }

        try {
            //大于了核心线程数就只是阻塞对应的时间 因为他需要把那些空闲的线程最大核心干活的给噶了

            Runnable r = timed ?
                workQueue.poll(keepAliveTime, TimeUnit.NANOSECONDS) :
                workQueue.take();//如果没有任务将会一直阻塞在这
            if (r != null)
                return r;
            timedOut = true;
        } catch (InterruptedException retry) {
            timedOut = false;
        }
    }
}

可见线程复用就这这里，被创建出来的工作线程不会停歇一直在等待有任务入队然后换行，这里是通过阻塞队列实习线程阻塞,用的是ReentrantLock的条件队列来实现线程的阻塞和唤醒的。之后有时间给大家