MainActivity如下:
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:
* 线程池(ThreadPoolExecutor)及其拒绝策略(RejectedExecutionHandler)使用示例
*
* 工作原理:
* 线程池的工作中主要涉及到:corePoolSize,workQueue,maximumPoolSize,RejectedExecutionHandler
* 它们的调用原理:
* 1 当线程池中线程数量小于corePoolSize则创建线程,并处理请求
* 2 当线程池中线程数量等于corePoolSize则把请求放入workQueue中,线程池中的的空闲线程就从workQueue中取任务并处理
* 3 当workQueue已满存放不下新入的任务时则新建线程入池,并处理请求;
* 如果线程池中线程数大于maximumPoolSize则用RejectedExecutionHandler使用一定的策略来做拒绝处理
*
* 在该机制中还有一个keepAliveTime,文档描述如下:
* 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.
* 它是什么意思呢？
* 比如线程池中一共有5个线程,其中3个为核心线程(core)其余两个为非核心线程.
* 当超过一定时间(keepAliveTime)非核心线程仍然闲置(即没有执行任务或者说没有任务可执行)那么该非核心线程就会被终止.
* 即线程池中的非核心且空闲线程所能持续的最长时间,超过该时间后该线程被终止.
*
*
* RejectedExecutionHandler的四种拒绝策略
*
* hreadPoolExecutor.AbortPolicy:
* 当线程池中的数量等于最大线程数时抛出java.util.concurrent.RejectedExecutionException异常.
* 涉及到该异常的任务也不会被执行.
*
* ThreadPoolExecutor.CallerRunsPolicy():
* 当线程池中的数量等于最大线程数时,重试添加当前的任务;它会自动重复调用execute()方法
*
* ThreadPoolExecutor.DiscardOldestPolicy():
* 当线程池中的数量等于最大线程数时,抛弃线程池中工作队列头部的任务(即等待时间最久Oldest的任务),并执行新传入的任务
*
* ThreadPoolExecutor.DiscardPolicy():
* 当线程池中的数量等于最大线程数时,丢弃不能执行的新加任务
*
* 参考资料:
* 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();
}
// 在此分别测试四种策略,替换ThreadPoolExecutor()方法最后一个参数即可.
private void testRejectedExecutionHandler() {
int produceTaskMaxNumber = 10;
// 构造一个线程池
ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor(2, 4, 3,
TimeUnit.SECONDS, new LinkedBlockingQueue<Runnable>(3),
new ThreadPoolExecutor.DiscardPolicy());
for (int i = 1; i <= produceTaskMaxNumber; i++) {
try {
String task = "任务" + i;
System.out.println("将" + task + "放入线程池");
threadPoolExecutor.execute(new RunnableImpl(task));
} catch (Exception e) {
e.printStackTrace();
System.out.println("AbortPolicy策略抛出异常----> " + 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("开始 " + taskName);
try {
// 模拟耗时任务
Thread.sleep(consumerTaskSleepTime);
} catch (Exception e) {
e.printStackTrace();
}
System.out.println("完成 " + taskName);
}
}
}
main.xml如下:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/hello_world" />
</RelativeLayout>
