ThreadPool 构造函数以及参数列表

线程池构造函数与参数列表

面试时候问到了关于线程池的构造函数参数列表的问题，下面进行一些总结：

一、线程池种类

• FixedThreadPool
• CachedThreadPool
• ScheduledThreadPool

1. FixedThreadPool

FixedThreadPool， 就是创建有固定线程数量的线程池，来看Executors 静态创建方法：

/**
     * 创建有固定线程数量的线程池
     @param nThreads, 初始化线程大小
     */
    public static ExecutorService newFixedThreadPool(int nThreads) {
        return new ThreadPoolExecutor(nThreads, nThreads,
                                      0L, TimeUnit.MILLISECONDS,
                                      new LinkedBlockingQueue<Runnable>());
    }



/**
   初始化固定大小线程池
   @param nThreads 线程池大小
   @param threadFactory 线程工厂
*/
public static ExecutorService newFixedThreadPool(int nThreads, ThreadFactory threadFactory) {
        return new ThreadPoolExecutor(nThreads, nThreads,
                                      0L, TimeUnit.MILLISECONDS,
                                      new LinkedBlockingQueue<Runnable>(),
                                      threadFactory);
    }

其中参数int nThreads 代表初始化数量，threadFactory是创建工厂， 返回的是ThreadPoolExecutor
代码如下：

// Public constructors and methods

    /**
     * Creates a new {@code ThreadPoolExecutor} with the given initial
     * parameters and default thread factory and rejected execution handler.
     * It may be more convenient to use one of the {@link Executors} factory
     * methods instead of this general purpose constructor.
     *
     * @param corePoolSize 初始化线程池大小
     *        
     * @param maximumPoolSize 允许的最大线程数
     * @param keepAliveTime 最大活跃时间， 当空闲超过这个时间后就会被关闭.
     * @param unit 时间单位
     * @param workQueue 持有等待执行线程的队列
     *       
     * @throws IllegalArgumentException 当发生如下一个情况，就抛出该异常
     *         {@code corePoolSize < 0}
     *         {@code keepAliveTime < 0}
     *         {@code maximumPoolSize <= 0}
     *         {@code maximumPoolSize < corePoolSize}
     * @throws NullPointerException if {@code workQueue} is null
     */
    public ThreadPoolExecutor(int corePoolSize,
                              int maximumPoolSize,
                              long keepAliveTime,
                              TimeUnit unit,
                              BlockingQueue<Runnable> workQueue) {
        this(corePoolSize, maximumPoolSize, keepAliveTime, unit, workQueue,
             Executors.defaultThreadFactory(), defaultHandler);
    }

CachedThreadPool

先看构造函数

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

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

最大线程数是Integer.MAX_VALUE, 一个无参构造，一个有参构造，ThreadFactory

SceduledThradPool

构造函数：

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

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

corePoolSize 参数， 和thredFactory

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