java八股文-拓冰建站

1线程池中提交一个任务得流程是怎样的

源代码

    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) && workQueue.offer(command)) {int recheck = ctl.get();if (! isRunning(recheck) && 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 bitsprivate 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;