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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
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
}
});