Android線程池(二)——ThreadPoolExecutor及其拒絕策略RejectedExecutionHandler使用示例

package cc.vv;

import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.ThreadPoolExecutor;
import java.util.concurrent.TimeUnit;

import android.os.Bundle;
import android.app.Activity;

/**
 * Demo描述:
 * 線程池(ThreadPoolExecutor)及其拒絕策略(RejectedExecutionHandler)使用示例
 * 
 * 工作原理:
 * 線程池的工作中主要涉及到:corePoolSize,workQueue,maximumPoolSize,RejectedExecutionHandler
 * 它們的調用原理:
 * 1 當線程池中線程數量小於corePoolSize則創建線程,並處理請求
 * 2 當線程池中線程數量等於corePoolSize則把請求放入workQueue中,線程池中的的空閒線程就從workQueue中取任務並處理
 * 3 當workQueue已滿存放不下新入的任務時則新建線程入池,並處理請求;
 *   如果線程池中線程數大於maximumPoolSize則用RejectedExecutionHandler使用一定的策略來做拒絕處理
 * 
 * 在該機制中還有一個keepAliveTime,文檔描述如下:
 * when the number of threads is greater than the core, 
 * this is the maximum time that excess idle threads will wait for new tasks before terminating.
 * 它是什麼意思呢？
 * 比如線程池中一共有5個線程,其中3個為核心線程(core)其余兩個為非核心線程.
 * 當超過一定時間(keepAliveTime)非核心線程仍然閒置(即沒有執行任務或者說沒有任務可執行)那麼該非核心線程就會被終止.
 * 即線程池中的非核心且空閒線程所能持續的最長時間,超過該時間後該線程被終止.
 * 
 * 
 * RejectedExecutionHandler的四種拒絕策略
 * 
 * hreadPoolExecutor.AbortPolicy:
 * 當線程池中的數量等於最大線程數時拋出java.util.concurrent.RejectedExecutionException異常.
 * 涉及到該異常的任務也不會被執行.
 * 
 * ThreadPoolExecutor.CallerRunsPolicy():
 * 當線程池中的數量等於最大線程數時,重試添加當前的任務;它會自動重復調用execute()方法
 * 
 * ThreadPoolExecutor.DiscardOldestPolicy():
 * 當線程池中的數量等於最大線程數時,拋棄線程池中工作隊列頭部的任務(即等待時間最久Oldest的任務),並執行新傳入的任務
 * 
 * ThreadPoolExecutor.DiscardPolicy():
 * 當線程池中的數量等於最大線程數時,丟棄不能執行的新加任務
 * 
 * 參考資料:
 * http://blog.csdn.net/cutesource/article/details/6061229
 * http://blog.csdn.net/longeremmy/article/details/8231184
 * http://blog.163.com/among_1985/blog/static/275005232012618849266/
 * http://blog.csdn.net/longeremmy/article/details/8231184
 * http://ifeve.com/java-threadpool/
 * http://www.blogjava.net/xylz/archive/2010/07/08/325587.html
 * http://blog.csdn.net/ns_code/article/details/17465497
 * Thank you very much
 * 
 */
public class MainActivity extends Activity {

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
		testRejectedExecutionHandler();
	}

	// 在此分別測試四種策略,替換ThreadPoolExecutor()方法最後一個參數即可.
	private void testRejectedExecutionHandler() {
		int produceTaskMaxNumber = 10;
		// 構造一個線程池
		ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(2, 4, 3,
				TimeUnit.SECONDS, new LinkedBlockingQueue(3),
				new ThreadPoolExecutor.DiscardPolicy());

		for (int i = 1; i <= produceTaskMaxNumber; i++) {
			try {
				String task = "任務" + i;
				System.out.println("將" + task + "放入線程池");
				threadPoolExecutor.execute(new RunnableImpl(task));
			} catch (Exception e) {
				e.printStackTrace();
				System.out.println("AbortPolicy策略拋出異常----> " + e.toString());
			}
		}
	}

	private class RunnableImpl implements Runnable {
		private String taskName;
		private int consumerTaskSleepTime = 2000;

		RunnableImpl(String taskName) {
			this.taskName = taskName;
		}

		public void run() {
			System.out.println("開始 " + taskName);
			try {
				// 模擬耗時任務
				Thread.sleep(consumerTaskSleepTime);
			} catch (Exception e) {
				e.printStackTrace();
			}
			System.out.println("完成 " + taskName);
		}

	}

}

main.xml如下: