如何理解Java线程池及其使用方法

public ThreadPoolExecutor(int paramInt1, int paramInt2, long paramLong, TimeUnit paramTimeUnit,
        BlockingQueue<Runnable> paramBlockingQueue, ThreadFactory paramThreadFactory,
        RejectedExecutionHandler paramRejectedExecutionHandler) {
    this.ctl = new AtomicInteger(ctlOf(-536870912, 0));
    this.mainLock = new ReentrantLock();
    this.workers = new HashSet();
    this.termination = this.mainLock.newCondition();
    if ((paramInt1 < 0) || (paramInt2 <= 0) || (paramInt2 < paramInt1) || (paramLong < 0L))
        throw new IllegalArgumentException();
    if ((paramBlockingQueue == null) || (paramThreadFactory == null) || (paramRejectedExecutionHandler == null))
        throw new NullPointerException();
    this.corePoolSize = paramInt1;
    this.maximumPoolSize = paramInt2;
    this.workQueue = paramBlockingQueue;
    this.keepAliveTime = paramTimeUnit.toNanos(paramLong);
    this.threadFactory = paramThreadFactory;
    this.handler = paramRejectedExecutionHandler;
}

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.
         * 如果正在运行的线程数小于corePoolSize，那么将调用addWorker 方法来创建一个新的线程，并将该任务作为新线程的第一个任务来执行。　　　　　　 当然，在创建线程之前会做原子性质的检查，如果条件不允许，则不创建线程来执行任务，并返回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.
         * 如果一个任务成功进入阻塞队列，那么我们需要进行一个双重检查来确保是我们已经添加一个线程（因为存在着一些线程在上次检查后他已经死亡）或者　　　　　　 当我们进入该方法时，该线程池已经关闭。所以，我们将重新检查状态，线程池关闭的情况下则回滚入队列，线程池没有线程的情况则创建一个新的线程。
         * 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.　　　　　　 如果任务无法入队列（队列满了），那么我们将尝试新开启一个线程（从corepoolsize到扩充到maximum），如果失败了，那么可以确定原因，要么是　　　　　　 线程池关闭了或者饱和了（达到maximum），所以我们执行拒绝策略。
         */　　　　　　　　// 1.当前线程数量小于corePoolSize，则创建并启动线程。
        int c = ctl.get();
        if (workerCountOf(c) < corePoolSize) {
            if (addWorker(command, true))　　　　　　　　// 成功，则返回
return;
            c = ctl.get();
        }　　　　// 2.步骤1失败，则尝试进入阻塞队列，
        if (isRunning(c) && workQueue.offer(command)) {　　　　　　　// 入队列成功，检查线程池状态，如果状态部署RUNNING而且remove成功，则拒绝任务
            int recheck = ctl.get();
            if (! isRunning(recheck) && remove(command))
                reject(command);　　　　　　　// 如果当前worker数量为0，通过addWorker(null, false)创建一个线程，其任务为null
            else if (workerCountOf(recheck) == 0)
                addWorker(null, false);
        }　　　　// 3. 步骤1和2失败，则尝试将线程池的数量有corePoolSize扩充至maxPoolSize，如果失败，则拒绝任务
        else if (!addWorker(command, false))
            reject(command);
    }

private boolean addWorker(Runnable firstTask, boolean core) {
        retry:　　　　 // 外层循环，用于判断线程池状态
        for (;;) {
            int c = ctl.get();
            int rs = runStateOf(c);

            // Check if queue empty only if necessary.
            if (rs >= SHUTDOWN &&
                ! (rs == SHUTDOWN &&
                   firstTask == null &&
                   ! workQueue.isEmpty()))
                return false;
　　　　　　 // 内层的循环，任务是将worker数量加1
            for (;;) {
                int wc = workerCountOf(c);
                if (wc >= CAPACITY ||
                    wc >= (core ? corePoolSize : maximumPoolSize))
                    return false;
                if (compareAndIncrementWorkerCount(c))
                    break retry;
                c = ctl.get();  // Re-read ctl
                if (runStateOf(c) != rs)
                    continue retry;
                // else CAS failed due to workerCount change; retry inner loop
            }
        }
　　　　// worker加1后，接下来将woker添加到HashSet<Worker>中，并启动worker
        boolean workerStarted = false;
        boolean workerAdded = false;
        Worker w = null;
        try {
            final ReentrantLock mainLock = this.mainLock;
            w = new Worker(firstTask);
            final Thread t = w.thread;
            if (t != null) {
                mainLock.lock();
                try {
                    // Recheck while holding lock.
                    // Back out on ThreadFactory failure or if
                    // shut down before lock acquired.
                    int c = ctl.get();
                    int rs = runStateOf(c);

                    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();
                }　　　　　　　　　// 如果往HashSet<Worker>添加成功，则启动该线程
                if (workerAdded) {
                    t.start();
                    workerStarted = true;
                }
            }
        } finally {
            if (! workerStarted)
                addWorkerFailed(w);
        }
        return workerStarted;
    }

public static ExecutorService newFixedThreadPool(int var0) {
    return new ThreadPoolExecutor(var0, var0, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue());
}
public static ExecutorService newFixedThreadPool(int var0, ThreadFactory var1) {    
    return new ThreadPoolExecutor(var0, var0, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue(), var1);
}

public static ExecutorService newSingleThreadExecutor() {
    return new Executors.FinalizableDelegatedExecutorService(new ThreadPoolExecutor(1, 1, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue()));
}

public static ExecutorService newSingleThreadExecutor(ThreadFactory var0) {
    return new Executors.FinalizableDelegatedExecutorService(new ThreadPoolExecutor(1, 1, 0L, TimeUnit.MILLISECONDS, new LinkedBlockingQueue(), var0));
}

public static ExecutorService newCachedThreadPool() {
    return new ThreadPoolExecutor(0, 2147483647, 60L, TimeUnit.SECONDS, new SynchronousQueue());
}

public static ExecutorService newCachedThreadPool(ThreadFactory var0) {
    return new ThreadPoolExecutor(0, 2147483647, 60L, TimeUnit.SECONDS, new SynchronousQueue(), var0);
}

public static ScheduledExecutorService newScheduledThreadPool(int var0) {
    return new ScheduledThreadPoolExecutor(var0);
}

public static ScheduledExecutorService newScheduledThreadPool(int var0, ThreadFactory var1) {
    return new ScheduledThreadPoolExecutor(var0, var1);
}

public class FixPoolDemo {

    private static Runnable getThread(final int i) {
        return new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep(500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(i);
            }
        };
    }

    public static void main(String args[]) {
        ExecutorService fixPool = Executors.newFixedThreadPool(5);
        for (int i = 0; i < 10; i++) {
            fixPool.execute(getThread(i));
        }
        fixPool.shutdown();
    }
}

public class CachePool {
    private static Runnable getThread(final int i){
        return new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep(1000);
                }catch (Exception e){

                }
                System.out.println(i);
            }
        };
    }

    public static  void main(String args[]){
        ExecutorService cachePool = Executors.newCachedThreadPool();
        for (int i=1;i<=10;i++){
            cachePool.execute(getThread(i));
        }
    }
}

public class SingPoolDemo {
    private static Runnable getThread(final int i){
        return new Runnable() {
            @Override
            public void run() {
                try {

                    Thread.sleep(500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                System.out.println(i);
            }
        };
    }

    public static void main(String args[]) throws InterruptedException {
        ExecutorService singPool = Executors.newSingleThreadExecutor();
        for (int i=0;i<10;i++){
            singPool.execute(getThread(i));
        }
        singPool.shutdown();
    }

public class ScheduledExecutorServiceDemo {
    public static void main(String args[]) {

        ScheduledExecutorService ses = Executors.newScheduledThreadPool(10);
        ses.scheduleAtFixedRate(new Runnable() {
            @Override
            public void run() {
                try {
                    Thread.sleep(4000);
                    System.out.println(Thread.currentThread().getId() + "执行了");
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }, 0, 2, TimeUnit.SECONDS);
    }
}

int ncpus = Runtime.getRuntime().availableProcessors();

public class ThreadFactoryDemo {
    public static class MyTask1 implements Runnable{

        @Override
        public void run() {
            System.out.println(System.currentTimeMillis()+"Thrad ID:"+Thread.currentThread().getId());
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args){
          MyTask1 task = new MyTask1();
        ExecutorService es = new ThreadPoolExecutor(5, 5, 0L, TimeUnit.MICROSECONDS, new SynchronousQueue<Runnable>(), new ThreadFactory() {
            @Override
            public Thread newThread(Runnable r) {
                Thread t = new Thread(r);
                t.setDaemon(true);
                System.out.println("创建线程"+t);
                return  t;
            }
        });
        for (int i = 0;i<=4;i++){
           es.submit(task);
        }
    }
}

public class ThreadFactoryDemo {
    public static class MyTask1 implements Runnable{

        @Override
        public void run() {
            System.out.println(System.currentTimeMillis()+"Thrad ID:"+Thread.currentThread().getId());
            try {
                Thread.sleep(100);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args){
          MyTask1 task = new MyTask1();
        ExecutorService es = new ThreadPoolExecutor(5, 5, 0L, TimeUnit.MICROSECONDS, new SynchronousQueue<Runnable>(), new ThreadFactory() {
            @Override
            public Thread newThread(Runnable r) {
                Thread t = new Thread(r);
                t.setDaemon(true);
                System.out.println("创建线程"+t);
                return  t;
            }
        });
        for (int i = 0;i<=4;i++){
           es.submit(task);
        }
    }
}

private static ExecutorService createDefaultExecutorService(Args args) {
    SynchronousQueue executorQueue = new SynchronousQueue();

    return new ThreadPoolExecutor(args.minWorkerThreads, args.maxWorkerThreads, 60L, TimeUnit.SECONDS,
            executorQueue);
}