并发编程-线程池

public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue) {
        this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
             Executors.defaultThreadFactory(), defaultHandler);
}

threadPool.execute(new Job());

  private 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

    private final AtomicInteger ctl = new AtomicInteger(ctlOf(RUNNING, 0));

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();//获取当前线程池的状态 
        if (workerCountOf(c) < corePoolSize) {//当前线程数量小于 coreSize 时创建一个新的线程运行
            if (addWorker(command, true))
                return;
            c = ctl.get();
        }
        if (isRunning(c) && workQueue.offer(command)) {//如果当前线程处于运行状态，并且写入阻塞队列成功
            int recheck = ctl.get();
            if (! isRunning(recheck) && remove(command))  //双重检查，再次获取线程状态；如果线程状态变了（非运行状态）就需要从阻塞队列移除任务，并尝试判断线程是否全部执行完毕。同时执行拒绝策略。
                reject(command);
            else if (workerCountOf(recheck) == 0)  //如果当前线程池为空就新创建一个线程并执行。
                addWorker(null, false);
        }
        else if (!addWorker(command, false)) //如果在第三步的判断为非运行状态，尝试新建线程，如果失败则执行拒绝策略
            reject(command);
}

import java.util.Random;
import java.util.concurrent.TimeUnit;

public class TaskDemo implements Runnable{
    @Override
    public void run() {
        System.out.println(Thread.currentThread().getName()+" is running");
        try {
            TimeUnit.SECONDS.sleep(new Random().nextInt(10));
        } catch (InterruptedException e) {
            e.printStackTrace();
        }

    }
}


import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class CachedPool {

    public static void main(String[] args) {
        ExecutorService pool=Executors.newCachedThreadPool();
        for (int i = 0; i < 10; i++) {
                //创建任务
                Runnable task=new TaskDemo();
                //把任务交给pool去执行
                pool.execute(task);
        }

    }
}

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class FixedPoolDemo {

    public static void main(String[] args) {
        //创建固定大小线程池
        ExecutorService pool=Executors.newFixedThreadPool(5);
        //创建10个任务给pool
        for (int i = 0; i < 10; i++) {
            //创建任务
            Runnable task=new TaskDemo();
            //把任务交给pool去执行
            pool.execute(task);
        }
        //关闭
        pool.shutdown();//shutdown
        while (!pool.isTerminated()){
        }
        System.out.println("finished");
    }

}

import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;

public class ScheduledDemo {

    public static void main(String[] args) {
        ScheduledExecutorService pool=Executors.newScheduledThreadPool(5);
        for (int i = 0; i < 10; i++) {
            Runnable task=new TaskDemo();
            //把任务交给pool去执行
            pool.execute(task);
        }
    }
}

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class SingleThreadDemo {
    public static void main(String[] args) {
        ExecutorService pool=Executors.newSingleThreadExecutor();
        for (int i = 0; i < 10; i++) {
            //创建任务
            Runnable task=new TaskDemo();
            //把任务交给pool去执行
            pool.execute(task);
        }
    }
}