android線程池的最佳化

1. 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);           }       }   }  

 輸出：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

 

    從執行個體可以看到for迴圈並沒有被固定的線程池阻塞住，也就是說所有的線程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。這裡有個問題，如果工作清單很大，一定會把記憶體撐爆，如何解決？看下面：

1. 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);           }       }   }  

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

 

    線程池最大值為4（？？這裡我不明白為什麼是設定值+1，即3+1，而不是3），準備執行的任務隊列為3。可以看到for迴圈先處理4個task，然後把3個放到隊列。這樣就實現了自動阻塞隊列的效果。記得要使用ArrayBlockingQueue這個隊列，然後設定容量就OK了。

轉載網址： http://heipark.iteye.com/blog/1393847