Java线程池分析

public ThreadPoolExecutor(int corePoolSize,
                          int maximumPoolSize,
                          long keepAliveTime,
                          TimeUnit unit,
                          BlockingQueue<Runnable> workQueue,
                          ThreadFactory threadFactory,
                          RejectedExecutionHandler handler) {
    //先判断参数是否合法
    if (corePoolSize < 0 ||
        maximumPoolSize <= 0 ||
        maximumPoolSize < corePoolSize ||
        keepAliveTime < 0)
        throw new IllegalArgumentException();
    if (workQueue == null || threadFactory == null || handler == null)
        throw new NullPointerException();
    this.acc = System.getSecurityManager() == null ?
        null :
    	AccessController.getContext();
    //核心线程数量
    this.corePoolSize = corePoolSize;
    //最大线程数量
    this.maximumPoolSize = maximumPoolSize;
    //工作队列
    this.workQueue = workQueue;
    //保活时间，unit为时间单位，转换为秒
    this.keepAliveTime = unit.toNanos(keepAliveTime);、
    //线程工厂
    this.threadFactory = threadFactory;
    //拒绝策略
    this.handler = handler;
}

/*
* 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);

// runState is stored in the high-order bits
private static final int RUNNING    = -1 << COUNT_BITS; //接收新的任务并且处理队列中的任务
private static final int SHUTDOWN   =  0 << COUNT_BITS; //不接受新的任务，但是会继续处理队列中的任务
private static final int STOP       =  1 << COUNT_BITS; //不接受新的任务，也不处理队列中的任务，并且打断中正在处理的任务
private static final int TIDYING    =  2 << COUNT_BITS; //所有任务都终止，workerCount为零，线程状态过渡到TIDYING，将会执行terminated()方法
private static final int TERMINATED =  3 << COUNT_BITS; //terminated()函数执行完成

/**
 * A handler for rejected tasks that throws a
 * {@code RejectedExecutionException}.
 */
public static class AbortPolicy implements RejectedExecutionHandler {
    /**
     * Creates an {@code AbortPolicy}.
     */
    public AbortPolicy() { }

    /**
     * Always throws RejectedExecutionException.
     *
     * @param r the runnable task requested to be executed
     * @param e the executor attempting to execute this task
     * @throws RejectedExecutionException always
     */
    public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
        throw new RejectedExecutionException("Task " + r.toString() +
                                             " rejected from " +
                                             e.toString());
    }
}

/**
 * A handler for rejected tasks that runs the rejected task
 * directly in the calling thread of the {@code execute} method,
 * unless the executor has been shut down, in which case the task
 * is discarded.
 */
public static class CallerRunsPolicy implements RejectedExecutionHandler {
    /**
     * Creates a {@code CallerRunsPolicy}.
     */
    public CallerRunsPolicy() { }

    /**
     * Executes task r in the caller's thread, unless the executor
     * has been shut down, in which case the task is discarded.
     *
     * @param r the runnable task requested to be executed
     * @param e the executor attempting to execute this task
     */
    public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
        if (!e.isShutdown()) {
            r.run();
        }
    }
}

/**
 * A handler for rejected tasks that silently discards the
 * rejected task.
 */
public static class DiscardPolicy implements RejectedExecutionHandler {
    /**
     * Creates a {@code DiscardPolicy}.
     */
    public DiscardPolicy() { }

    /**
     * Does nothing, which has the effect of discarding task r.
     *
     * @param r the runnable task requested to be executed
     * @param e the executor attempting to execute this task
     */
    public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
    }
}

/**
 * A handler for rejected tasks that discards the oldest unhandled
 * request and then retries {@code execute}, unless the executor
 * is shut down, in which case the task is discarded.
 */
public static class DiscardOldestPolicy implements RejectedExecutionHandler {
    /**
     * Creates a {@code DiscardOldestPolicy} for the given executor.
     */
    public DiscardOldestPolicy() { }

    /**
     * Obtains and ignores the next task that the executor
     * would otherwise execute, if one is immediately available,
     * and then retries execution of task r, unless the executor
     * is shut down, in which case task r is instead discarded.
     *
     * @param r the runnable task requested to be executed
     * @param e the executor attempting to execute this task
     */
    public void rejectedExecution(Runnable r, ThreadPoolExecutor e) {
        if (!e.isShutdown()) {
            e.getQueue().poll();
            e.execute(r);
        }
    }
}

/**
     * The default thread factory
     */
static class DefaultThreadFactory implements ThreadFactory {
    //记录创建默认线程池的数量，类变量
    private static final AtomicInteger poolNumber = new AtomicInteger(1);
    //线程组
    private final ThreadGroup group;
    //记录创建线程的数量，实例变量
    private final AtomicInteger threadNumber = new AtomicInteger(1);
    //线程名称前缀
    private final String namePrefix;

    DefaultThreadFactory() {、
        //这句话啥意思？
        SecurityManager s = System.getSecurityManager();
        //赋值线程组
        group = (s != null) ? s.getThreadGroup() :
        Thread.currentThread().getThreadGroup();
        namePrefix = "pool-" +
            poolNumber.getAndIncrement() +
            "-thread-";
    }

    public Thread newThread(Runnable r) {
        Thread t = new Thread(group, r,
                              namePrefix + threadNumber.getAndIncrement(),
                              0);
        if (t.isDaemon()) //??为什么这里判断是守护进程，还设置为false？？
            t.setDaemon(false);
        if (t.getPriority() != Thread.NORM_PRIORITY)//设置优先级
            t.setPriority(Thread.NORM_PRIORITY);
        return t;
    }
}