Android线程池简介和基本应用

傷城~ 2021-12-16 08:09 365阅读 0赞

### 一、为什么使用线程池？ ###

1.线程的创建和销毁由线程池维护，节约系统的开销；  
2.执行大量异步任务时，线程池可以提高性能；  
3.控制线程最大并发数，线程的定时任务和单线程的执行任务。

### 二、Android线程池框架结构主要包括3个部分： ###

1.任务：需要实现的接口类：Runnable或Callable  
2.任务的执行器：核心接口类Executor  
3.执行器的创建者：工厂类Executors(包括ThreadPoolExecutor，ScheduledThreadPoolExecutor)

### 三、线程池使用方法和参数解析 ###

1、初始化一个任务执行器。

private static final int CORE_POOL_SIZE = 4;
    private static final int MAX_POOL_SIZE = 8;
    private static final int KEEP_ALIVE_TIME = 10;
    private final Executor mExecutor;
    mExecutor = new ThreadPoolExecutor(
           CORE_POOL_SIZE,MAX_POOL_SIZE,KEEP_ALIVE_TIME,
            TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>(),
            new PriorityThreadFactory("thread-pool", Process.THREAD_PRIORITY_BACKGROUND));

参数解析：  
CORE\_POOL\_SIZE:核心线程，即使它们处在空闲状态，也要保留在池中的线程数  
MAX\_POOL\_SIZE:池中允许的最大线程数  
KEEP\_ALIVE\_TIME:当线程数大于核心线程时，多余线程在终止之前等待新任务的最长时间  
TimeUnit.SECONDS：keepAliveTime的时间单位，这里为秒  
new LinkedBlockingQueue():workQueue,在执行任务之前用于保存任务的队列，这里的LinkedBlockingQueue是一种有界的阻塞队列  
new PriorityThreadFactory(“thread-pool”, Process.THREAD\_PRIORITY\_BACKGROUND):工厂类，执行程序创建的新线程使用的工厂（该参数可不设置）

2.创建一个简单任务

private class Worker implements Runnable{ 
        @Override
        public void run(){ 
            //do something
        }
    }

3.执行任务。

Worker w = new Worker();
    mExecutor.execute(w);

### 四、线程池类封装和应用 ###

使用线程池的好处之一就是在需要大量使用线程的场合，或者当线程里发生了阻塞或者耗时时，由线程池来管理线程的创建和销毁，避免出现大量线程没有销毁的问题。

线程池的类：

/** * Offloads work from other threads by running it in a background thread. */
    public class BackgroundExecutor { 
    
        private static final BackgroundExecutor sInstance = new BackgroundExecutor();
    
    //查看newFixedThreadPool实际上是使用上述new ThreadPoolExecutor创建
        private final ExecutorService mExecutorService = Executors.newFixedThreadPool(2);
    
        /** * @return the static instance of the background executor. */
        public static BackgroundExecutor get() { 
            return sInstance;
        }
    
        /** * Runs the given {@param callable} on one of the background executor threads. */
        public <T> Future<T> submit(Callable<T> callable) { 
            return mExecutorService.submit(callable);
        }
    
        /** * Runs the given {@param runnable} on one of the background executor threads. */
        public Future<?> submit(Runnable runnable) { 
            return mExecutorService.submit(runnable);
        }
    
        /** * Runs the given {@param runnable} on one of the background executor threads. Return * {@param result} when the future is resolved. */
        public <T> Future<T> submit(Runnable runnable, T result) { 
            return mExecutorService.submit(runnable, result);
        }
    }

应用：

private final BackgroundExecutor mBackgroundExecutor;
    
    mBackgroundExecutor = BackgroundExecutor.get();
    
    mBackgroundExecutor.submit(new Runnable() { 
        @Override
        public void run() { 
    		//do something
        }
    });