java并发编程(5)：Executors源码详解

Executors为快速创建线程池的工具类，其可以创建基于ThreadPoolExecutor、ScheduledThreadPoolExecutor、ForkJoinPool及包装的不可配置的线程池。

1、newFixedThreadPool()创建固定数量的普通线程池

有如下实现：

//nThread为线程池中线程的数量
public static ExecutorService newFixedThreadPool(int nThreads) {
    //通过ThreadPoolExecutor实现类，创建核心线程数及最大线程数都为nThreads的线程池
    //空闲超时时间为0，且由于核心线程数和最大线程数一样，核心线程不会空闲超时后被回收
    //LinkedBlockingQueue为任务队列实现
    return new ThreadPoolExecutor(nThreads, nThreads,
                                  0L, TimeUnit.MILLISECONDS,
                                  new LinkedBlockingQueue());
}

//nThread为线程池中线程的数量，线程创建的工厂类实现类为threadFactory 
public static ExecutorService newFixedThreadPool(int nThreads, ThreadFactory threadFactory) {
    return new ThreadPoolExecutor(nThreads, nThreads,
                                  0L, TimeUnit.MILLISECONDS,
                                  new LinkedBlockingQueue(),
                                  threadFactory);
}

2、newWorkStealingPool()创建可任务窃取的线程池

有如下实现：

//parallelism并行任务数
public static ExecutorService newWorkStealingPool(int parallelism) {
    //基于ForkJoinPool创建线程池；
    //使用默认线程创建工厂类
    //执行任务异常处理类为null
    //任务队列模型为FIFO，true为FIFI，false为FILO
    return new ForkJoinPool
        (parallelism,
         ForkJoinPool.defaultForkJoinWorkerThreadFactory,
         null, true);
}

public static ExecutorService newWorkStealingPool() {
    //并行数为处理器的并行数
    return new ForkJoinPool
        (Runtime.getRuntime().availableProcessors(),
         ForkJoinPool.defaultForkJoinWorkerThreadFactory,
         null, true);
}

3、newSingleThreadExecutor()创建单个普通线程池

有如下实现：

//创建单个线程的线程池
public static ExecutorService newSingleThreadExecutor() {
    //用FinalizableDelegatedExecutorService进行封装，其会在
    //finalize()方法中调用线程池的shutdown()方法，对线程池进行关闭
    return new FinalizableDelegatedExecutorService
        (new ThreadPoolExecutor(1, 1,
                                0L, TimeUnit.MILLISECONDS,
                                new LinkedBlockingQueue()));
}


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

4、newCachedThreadPool()创建线程数量不限的普通线程池

有如下实现：

//创建缓存的线程池，即线程池数量不限
public static ExecutorService newCachedThreadPool() {
    //核心线程数量为0，最大线程数量为Integer.MAX_VALUE
    //阻塞队列为SynchronousQueue
    return new ThreadPoolExecutor(0, Integer.MAX_VALUE,
                                  60L, TimeUnit.SECONDS,
                                  new SynchronousQueue());
}

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

5、newSingleThreadScheduledExecutor()创建单个基于时间调度的线程池

有如下实现：

//创建单个可进行时间调度的线程池
public static ScheduledExecutorService newSingleThreadScheduledExecutor() {
    //利用DelegatedScheduledExecutorService对线程池进行包装
    //DelegatedScheduledExecutorService利用门面模式包装了ScheduledExecutorService
    //使得用户无法修改ScheduledExecutorService中的一些参数
    return new DelegatedScheduledExecutorService
        (new ScheduledThreadPoolExecutor(1));
}

public static ScheduledExecutorService newSingleThreadScheduledExecutor(ThreadFactory threadFactory) {
    return new DelegatedScheduledExecutorService
        (new ScheduledThreadPoolExecutor(1, threadFactory));
}

6、newScheduledThreadPool()创建多个基于时间调度的线程池

有如下实现：

//创建固定线程池的可基于时间调度的线程池，corePoolSize为核心线程池测数量
public static ScheduledExecutorService newScheduledThreadPool(int corePoolSize) {
    return new ScheduledThreadPoolExecutor(corePoolSize);
}

public static ScheduledExecutorService newScheduledThreadPool(
        int corePoolSize, ThreadFactory threadFactory) {
    return new ScheduledThreadPoolExecutor(corePoolSize, threadFactory);
}

7、包装配置不可更改的线程池

有如下实现：

//对ExecutorService类型线程池进行包装，使用户无法对一些参数进行修改
public static ExecutorService unconfigurableExecutorService(ExecutorService executor) {
    if (executor == null)
        throw new NullPointerException();
    return new DelegatedExecutorService(executor);
}

//对ScheduledExecutorService类型线程池进行包装，使用户无法对一些参数进行修改
public static ScheduledExecutorService unconfigurableScheduledExecutorService(ScheduledExecutorService executor) {
    if (executor == null)
        throw new NullPointerException();
    return new DelegatedScheduledExecutorService(executor);
}