Day 38 并发线程池底层原理详解与源码分析

任务先放到核心线程池，放不下了再放到阻塞队列，还是放不下就放到最大线程池中.

Screen Shot 2022-04-30 at 9.42.53 PM.png

重点关注，阻塞队列，回收时间实现，拒绝策略，ThreadFactory自定义线程池这些参数.

Screen Shot 2022-04-30 at 9.45.37 PM.png

• 存储线程状态:

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

• 执行任务判断的依据state

 try {
            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);

Screen Shot 2022-04-30 at 9.49.26 PM.png

• 抛出异常 适合业务容错低的场景
• 直接丢失，比如做分析，日志这些场景
• 最老移除
• 谁调用execute谁去执行这个任务

重新认识了阻塞队列后再去看线程池的设计感触就会更多了.

优先级队列用二叉树去排序.

• 循环的从阻塞队列中获取任务.

task不为空 或者阻塞队列中拿到了任务
        while (task != null || (task = getTask()) != null) {
            w.lock();
            // If pool is stopping, ensure thread is interrupted;

• 唤醒线程的几种方式
  notify ,notifyall,unpark,conditional.signal

• DelayQueue实现
  DelayQueue内部封装了一个PriorityQueue，它会根据time的先后时间排序