线程池的创建

刺骨的言语ヽ痛彻心扉 2024-04-19 08:28 3阅读 0赞

### 线程池的创建 ###

java 通过 Executors提供四种线程池，分别为：

> newCachedThreadPool创建一个可缓存线程池，如果线程池长度超过处理需要，可灵活回收空闲线程，若无可回收，则新建线程。  
> newFixedThreadPool 创建一个定长线程池，可控制线程最大并发数，超出的线程会在队列中等待。  
> newScheduledThreadPool 创建一个定长线程池，支持定时及周期性任务执行。  
> newSingleThreadExecutor 创建一个单线程化的线程池，它只会用唯一的工作线程来执行任务，保证所有任务按照指定顺序(FIFO, LIFO, 优先级)执行。

1.  首先看一下newCachedThreadPool

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

核心线程的长度为0，线程池的大小为 Integer.MAX\_VALUE 等待超时时间1分钟 阻塞队列为SynchronousQueue(SynchronousQueue没有容量，是无缓冲等待队列，是一个不存储元素的阻塞队列，会直接将任务交给消费者，必须等队列中的添加元素被消费后才能继续添加新的元素。)

1.  newFixedThreadPool

public static ExecutorService newFixedThreadPool(int nThreads) { 
        return new ThreadPoolExecutor(nThreads, nThreads,
                                      0L, TimeUnit.MILLISECONDS,
                                      new LinkedBlockingQueue<Runnable>());
    }

public static ExecutorService newFixedThreadPool(int nThreads, ThreadFactory threadFactory) { 
        return new ThreadPoolExecutor(nThreads, nThreads,
                                      0L, TimeUnit.MILLISECONDS,
                                      new LinkedBlockingQueue<Runnable>(),
                                      threadFactory);
    }

1.  ScheduledExecutorService

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

public ScheduledThreadPoolExecutor(int corePoolSize) { 
        super(corePoolSize, Integer.MAX_VALUE, 0, NANOSECONDS,
              new DelayedWorkQueue());
    }

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

1.  newSingleThreadExecutor

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

static class FinalizableDelegatedExecutorService
        extends DelegatedExecutorService { 
        FinalizableDelegatedExecutorService(ExecutorService executor) { 
            super(executor);
        }
        protected void finalize() { 
            super.shutdown();
        }
    }

DelegatedExecutorService(ExecutorService executor) {  e = executor; }