java八股文_代码007

1线程池中提交 一个 任务得流程是怎样的

    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();
        }
        if (isRunning(c) &amp;&amp; workQueue.offer(command)) {
            int recheck = ctl.get();
            if (! isRunning(recheck) &amp;&amp; remove(command))
                reject(command);
            else if (workerCountOf(recheck) == 0)
                addWorker(null, false);
        }
        else if (!addWorker(command, false))
            reject(command);
    }

2 线程池中有几种 状态？分别是如何变化的？

状态：

1 RUNNING: 会接收新任务并且会处理队列中的任务

2 SHUTDOWN:不会接收新任务并且会处理队列中的任务，任务处理完后会中断所有线程

3 STOP：不会接收新任务并且不会处理队列中的任务，并且会直接中断所有线程

4 TIDYING:所有线程都停止之后，线程池的状态会转为TIDYING，一旦达到此状态，就会调用线程池的terminated()

5 TERMINATED: terminated()执行完之后就会转变为TERMINATED

源码：

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

    // 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;