说烂了的,单例模式

最新推荐文章于 2025-07-17 23:08:56 发布

原创最新推荐文章于 2025-07-17 23:08:56 发布 · 150 阅读

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本文深入探讨了四种创建线程池的推荐模式：饿汉式、懒汉式、枚举类实现及静态内部类。每种模式均附带代码示例，详细解析其原理与适用场景，为开发者提供全面的线程池设计指南。

几种推荐方式:(例子是获取线程池)

1.饿汉式(一般就用饿汉式就行了,如果非要懒加载那就看下面):

public class ThreadPoolUtil{
     private static BlockingQueue<Runnable> bqueue = new ArrayBlockingQueue<Runnable>(100);
        private static final int SIZE_CORE_POOL = 5;
        private static final int SIZE_MAX_POOL = 100;
        private static final long ALIVE_TIME = 2000;
        private static ThreadPoolExecutor pool = new ThreadPoolExecutor(SIZE_CORE_POOL, SIZE_MAX_POOL, ALIVE_TIME
                , TimeUnit.MILLISECONDS, bqueue, new ThreadPoolExecutor.CallerRunsPolicy());
        
        private ThreadPoolUtil(){ }
        
        static {
            pool.prestartAllCoreThreads();
        }
        
        public static ThreadPoolExecutor getPool() {
            return pool;
        }
}

2.懒汉式(注意双重锁加可见性):

public class ThreadPoolUtil{
        private static BlockingQueue<Runnable> bqueue = new ArrayBlockingQueue<Runnable>(100);
        private static final int SIZE_CORE_POOL = 5;
        private static final int SIZE_MAX_POOL = 100;
        private static final long ALIVE_TIME = 2000;
        private static volatile ThreadPoolExecutor pool;

        private ThreadPoolUtil() {
        }

        public static ThreadPoolExecutor getPool() {
            if (bqueue == null) {
                synchronized (ThreadPoolUtil.class) {
                    if (bqueue == null) {
                        pool = new ThreadPoolExecutor(SIZE_CORE_POOL, SIZE_MAX_POOL, ALIVE_TIME
                                , TimeUnit.MILLISECONDS, bqueue, new ThreadPoolExecutor.CallerRunsPolicy());
                        pool.prestartAllCoreThreads();
                        return pool;
                    }
                }
            }
            return pool;
        }
}

3.枚举类实现(也是比较推荐):

public enum ThreadPoolUtil {
    POOL;

    private ThreadPoolExecutor pool;

    ThreadPoolUtil() {
        BlockingQueue<Runnable> bqueue = new ArrayBlockingQueue<Runnable>(100);
        final int SIZE_CORE_POOL = 5;
        final int SIZE_MAX_POOL = 100;
        final long ALIVE_TIME = 2000;
        pool = new ThreadPoolExecutor(SIZE_CORE_POOL, SIZE_MAX_POOL, ALIVE_TIME
                , TimeUnit.MILLISECONDS, bqueue, new ThreadPoolExecutor.CallerRunsPolicy());
        pool.prestartAllCoreThreads();
    }

    public ThreadPoolExecutor getPool() {
        return pool;
    }
}

4.静态内部类(也很推荐):

public class ThreadPoolUtil {
        private static BlockingQueue<Runnable> bqueue = new ArrayBlockingQueue<Runnable>(100);
        private static final int SIZE_CORE_POOL = 5;
        private static final int SIZE_MAX_POOL = 100;
        private static final long ALIVE_TIME = 2000;
        private static volatile ThreadPoolExecutor pool;

        private ThreadPoolUtil() {
        }

        private static class SingletonHolder{
            private static ThreadPoolExecutor pool =
                    new ThreadPoolExecutor(SIZE_CORE_POOL, SIZE_MAX_POOL, ALIVE_TIME
                            , TimeUnit.MILLISECONDS, bqueue, new ThreadPoolExecutor.CallerRunsPolicy());
            static {
                pool.prestartAllCoreThreads();
            }
        }

        public static ThreadPoolExecutor getPool() {
           return SingletonHolder.pool;
        }
    }