Java 线程池分析

    static class DefaultThreadFactory implements ThreadFactory {  //默认线程池工厂方法
        private static final AtomicInteger poolNumber = new AtomicInteger(1);
        private final ThreadGroup group;
        private final AtomicInteger threadNumber = new AtomicInteger(1);
        private final String namePrefix;

        DefaultThreadFactory() {  //设置线程名，group等
            SecurityManager s = System.getSecurityManager();
            group = (s != null) ? s.getThreadGroup() :
                                  Thread.currentThread().getThreadGroup();
            namePrefix = "pool-" +
                          poolNumber.getAndIncrement() +
                         "-thread-";
        }

private static final RejectedExecutionHandler defaultHandler =  //默认饱和策略
        new AbortPolicy();

public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue,
                              ThreadFactory threadFactory, 
                              RejectedExecutionHandler handler) {
        if (corePoolSize < 0 ||
            maximumPoolSize <= 0 ||
            maximumPoolSize < corePoolSize ||
            keepAliveTime < 0)
            throw new IllegalArgumentException();
        if (workQueue == null || threadFactory == null || handler == null)
            throw new NullPointerException();
        this.corePoolSize = corePoolSize;
        this.maximumPoolSize = maximumPoolSize;
        this.workQueue = workQueue;
        this.keepAliveTime = unit.toNanos(keepAliveTime);
        this.threadFactory = threadFactory;
        this.handler = handler;
    }

public class ThreadPoolTest {
    private static Executor executor1= new ThreadPoolExecutor(10,20,0, TimeUnit.MILLISECONDS,new ArrayBlockingQueue<Runnable>(3));

    public static void main(String[] args){

        for(int i=0;i<50;i++){

            executor.execute(new Task());
        }
    }

    static class Task implements Runnable{


        @Override
        public void run() {

            System.out.println(Thread.currentThread().getName());
        }
    }
}

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();  //获取ctl的低29位
        if (workerCountOf(c) < corePoolSize) { //workerCountOf方法根据ctl的低29位，得到线程池的当前线程数，如果当前的线程数小于核心池大小，则直接addWorker
            if (addWorker(command, true))
                return;
            c = ctl.get();
        }
        if (isRunning(c) && workQueue.offer(command)) { //如果当前线程池处于Running状态（即能够接受任务，处理阻塞队列中的任务），且把任务提交给了阻塞队列
            int recheck = ctl.get();
            if (! isRunning(recheck) && remove(command))  //再次检查线程池的状态，如果线程池没有RUNNING（即无法放入队列），并且将任务从队列移除，交给reject处理
                reject(command);
            else if (workerCountOf(recheck) == 0)  //否则，如果线程池数为0，则添加worker，启动一个null任务的线程
                addWorker(null, false);
        }
        else if (!addWorker(command, false))   //否则如果添加addWork失败，则reject。
            reject(command);
    }

boolean workerStarted = false;
        boolean workerAdded = false;
        Worker w = null;
        try {
            w = new Worker(firstTask);
            final Thread t = w.thread;
            if (t != null) {
                final ReentrantLock mainLock = this.mainLock;
                mainLock.lock();
                try {
                    // Recheck while holding lock.
                    // Back out on ThreadFactory failure or if
                    // shut down before lock acquired.
                    int rs = runStateOf(ctl.get());

                    if (rs < SHUTDOWN ||
                        (rs == SHUTDOWN && firstTask == null)) {
                        if (t.isAlive()) // precheck that t is startable
                            throw new IllegalThreadStateException();
                        workers.add(w);
                        int s = workers.size();
                        if (s > largestPoolSize)
                            largestPoolSize = s;
                        workerAdded = true;
                    }
                } finally {
                    mainLock.unlock();
                }
                if (workerAdded) {
                    t.start();
                    workerStarted = true;
                }
            }
        } finally {
            if (! workerStarted)
                addWorkerFailed(w);
        }
        return workerStarted;