Java线程池详解

private final HashSet workers = new HashSet();//任务的执行值集合，来消费workQueue里面的任务

private volatile ThreadFactory threadFactory;//线程工厂

private volatile RejectedExecutionHandler handler;//拒绝策略，默认会抛出异异常，还要其他几种拒绝策略如下：

1、CallerRunsPolicy：在调用者线程里面运行该任务
2、DiscardPolicy：丢弃任务
3、DiscardOldestPolicy：丢弃workQueue的头部任务

private volatile int corePoolSize;//最下保活work数量

private volatile int maximumPoolSize;//work上限

step 2:<AbstractExecutorService>
    public Future<?> submit(Runnable task) {
    if (task == null) throw new NullPointerException();
    RunnableFuture<Void> ftask = newTaskFor(task,null);
    execute(ftask);
    return ftask;
}

step 3:<Executor>
void execute(Runnable command);

step 4:<ThreadPoolExecutor>
 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)) { //提交我们的额任务到workQueue
        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)) //使用maximumPoolSize作为边界
        reject(command); //还不行？拒绝提交的任务
}

step 5:<ThreadPoolExecutor>
private boolean addWorker(Runnable firstTask,boolean core) 


step 6:<ThreadPoolExecutor>
w = new Worker(firstTask); //包装任务
final Thread t = w.thread; //获取线程（包含任务）
workers.add(w);   // 任务被放到works中
t.start(); //执行任务</pre>