android线程池的优化

import java.io.IOException;   
import java.util.concurrent.ExecutorService;   
import java.util.concurrent.Executors;   
  
public class Test {   
  
    public static void main(String[] args) throws IOException, InterruptedException {   
        ExecutorService service = Executors.newFixedThreadPool(2);   
        for (int i = 0; i < 6; i++) {   
            final int index = i;   
            System.out.println("task: " + (i+1));   
            Runnable run = new Runnable() {   
                @Override  
                public void run() {   
                    System.out.println("thread start" + index);   
                    try {   
                        Thread.sleep(Long.MAX_VALUE);   
                    } catch (InterruptedException e) {   
                        e.printStackTrace();   
                    }   
                    System.out.println("thread end" + index);   
                }   
            };   
            service.execute(run);   
        }   
    }   
}

 输出：

task: 1
task: 2
thread start0
task: 3
task: 4
task: 5
task: 6
task: 7
thread start1
task: 8
task: 9
task: 10
task: 11
task: 12
task: 13
task: 14
task: 15

 

    从实例可以看到for循环并没有被固定的线程池阻塞住，也就是说所有的线程task都被提交到了ExecutorService中，查看 Executors.newFixedThreadPool()如下：

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

    可以看到task被提交都了LinkedBlockingQueue中。这里有个问题，如果任务列表很大，一定会把内存撑爆，如何解决？看下面：

import java.io.IOException;   
import java.util.concurrent.ArrayBlockingQueue;   
import java.util.concurrent.BlockingQueue;   
import java.util.concurrent.ThreadPoolExecutor;   
import java.util.concurrent.TimeUnit;   
  
public class Test {   
  
    public static void main(String[] args) throws IOException, InterruptedException {   
           
        BlockingQueue<Runnable> queue = new ArrayBlockingQueue<Runnable>(3);   
           
        ThreadPoolExecutor executor = new ThreadPoolExecutor(3, 3, 1, TimeUnit.HOURS, queue, new ThreadPoolExecutor.CallerRunsPolicy());   
           
        for (int i = 0; i < 10; i++) {   
            final int index = i;   
            System.out.println("task: " + (index+1));   
            Runnable run = new Runnable() {   
                @Override  
                public void run() {   
                    System.out.println("thread start" + (index+1));   
                    try {   
                        Thread.sleep(Long.MAX_VALUE);   
                    } catch (InterruptedException e) {   
                        e.printStackTrace();   
                    }   
                    System.out.println("thread end" + (index+1));   
                }   
            };   
            executor.execute(run);   
        }   
    }   
}

 输出：

task: 1
task: 2
thread start1
task: 3
task: 4
task: 5
task: 6
task: 7
thread start2
thread start7
thread start6

 

    线程池最大值为4（？？这里我不明白为什么是设置值+1，即3+1，而不是3），准备执行的任务队列为3。可以看到for循环先处理4个task，然后把3个放到队列。这样就实现了自动阻塞队列的效果。记得要使用ArrayBlockingQueue这个队列，然后设置容量就OK了。

转载网址： http://heipark.iteye.com/blog/1393847