函数原型：
int select(int maxfd,fd_set *readset,fd_set *writeset,fd_set *exceptset,const struct

timeval *timeout);

参数一：当前进程的最大文件描述符个数（这里可以以这样理解）
参数二：读可行性集合（若在该集合中表示可读）
参数三：写可行性集合（若在该集合中表示可写）
参数四：异常集合（若产生异常）------该参数我没有深入理解；自己可以查阅相关手册
参数五：用于设置select为阻塞或是非阻塞

参数五解析：设置阻塞或是非阻塞：当此参数为NULL时表示为阻塞；当为0（timeout指向的内存

中的值）根本不等待立即返回；当为非0（同上一行）设定select检测的等待时间。

阻塞：NULL
当第五个参数设定为NULL时，那我们在检测的描述字，必须要有可读，或可写，或错误异常，才

会返回值
应用：
对于在server中的I/O多路复用，我们用select检测套接字等待某个事件发生，或是新客服连接或

是数据、PIN、RST到达

重点理解：
（这里可能和我们之前理解的accept()来记录连接套接字有区别，但实际上是一样的，我们要肯

定一点：实际上客户端请求server连接时和accept无关，accept()不过是来记录这个连接的套接

字，因而在accept前便可检测客服端是否发送来连接请求信息）

非阻塞：timeout设定

struct timeval time1 = {
 .tv_sec = 0,
 .tv_usec = 0,
};

struct timeval time2 = {
 .tv_sec = 3,
 .tv_usec = 0,
};

用到time1表示select根本不等待就立即返回0，处理下面的数据（比如打印等：）

用到time2 表示select会等待3秒，如果在限定的时间内没有检测到事件的发生（某个事件，或是

新客服端连接，或是数据到达），就返回0；

FD_ZERO(fdset); 将fdset的所有位清零
FD_SET(fd,fdset); 向fdset中添加fd（turn on the bit for fd in fdset  t改变fdset

中的位）
FD_CLR(fd,fdset);       从fdset集合中删除fd，关闭fd在fdset中对应的位
FD_ISSET(fd,fdset); 判断fd是否是在fdset中（这里我要在下面详细说明一下这个用法）

fd_set readfd; 用于可读性检查的集合
应用：套接字的判定
FD_ISSET(s,readfd) ;判断套接字是否可读（这里在该集合中（表示连接请求，或者数据到达）

）） 为非0；否则为0；
这回在我的select阻塞版的server中体现出来，请仔细分析：

效果图：

需要注意的是,本代码只有部署在真机上时才会有效果,当不熟在模拟器时很可能不会有效果

代码实现:
1、traffic_manager_item.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >

    <ImageView
        android:id="@+id/iv_appicon"
        android:layout_width="35dip"
        android:layout_height="35dip"
        android:scaleType="fitXY"
        android:src="/blog_article/@drawable/ic_launcher/index.html" />

    <TextView
        android:id="@+id/tv_appname"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_toRightOf="@id/iv_appicon"
        android:text="我最摇摆"
        android:textColor="@android:color/white"
        android:textSize="20sp" />

    <TextView
        android:id="@+id/tv_apptarffic"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentRight="true"
        android:text="20MB"
        android:textColor="@android:color/white"
        android:textSize="20sp" />

    <LinearLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/tv_appname"
        android:layout_toRightOf="@id/iv_appicon"
        android:orientation="horizontal" >

        <TextView
            android:id="@+id/tv_apptx"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_marginRight="80dp"
            android:text="上传：20MB"
            android:textSize="14sp" />

        <TextView
            android:id="@+id/tv_apprx"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:text="下载:20MB"
            android:textSize="14sp" />
    </LinearLayout>

</RelativeLayout>

2、main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:background="@android:color/background_dark"
    android:orientation="vertical" >

    <TableLayout
        android:layout_width="fill_parent"
        android:layout_height="wrap_content" >

        <TableRow
            android:layout_width="fill_parent"
            android:layout_height="wrap_content" >

            <TextView
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_weight="1"
                android:gravity="center"
                android:text="2g/3g" />

            <TextView
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_weight="1"
                android:gravity="center"
                android:text="wifi" />
        </TableRow>

        <TableRow
            android:layout_width="fill_parent"
            android:layout_height="wrap_content" >

            <TextView
                android:id="@+id/tv_traffic_manager_mobile"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_weight="1"
                android:gravity="center"
                android:text="200Mb" />

            <TextView
                android:id="@+id/tv_traffic_manager_wifi"
                android:layout_width="0dp"
                android:layout_height="wrap_content"
                android:layout_weight="1"
                android:gravity="center"
                android:text="50MB" />
        </TableRow>
    </TableLayout>

    <SlidingDrawer
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        android:content="@+id/lv_traffic_manager_content"
        android:handle="@+id/handle"
        android:orientation="vertical" >

        <ImageView
            android:id="@id/handle"
            android:layout_width="30dp"
            android:layout_height="30dp"
            android:src="/blog_article/@drawable/notification/index.html" />

        <ListView
            android:id="@id/lv_traffic_manager_content"
            android:layout_width="fill_parent"
            android:layout_height="fill_parent" >
        </ListView>
    </SlidingDrawer>

</LinearLayout>

3、TrafficManagerActivity

package com.njupt.testtracfficstate;

import java.util.ArrayList;
import java.util.List;

import android.net.TrafficStats;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.app.Activity;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;

public class MainActivity extends Activity {

	protected static final int SUCCESS_GET_TRAFFICINFO = 0;
	/** Called when the activity is first created. */
	
	private TextView tv_traffic_manager_mobile;
	private TextView tv_traffic_manager_wifi;
	private ListView lv_traffic_manager_content;
	private TrafficManagerService trafficManagerService;
	private List<TrafficInfo> trafficInfos;
	private List<TrafficInfo> realTrafficInfos;
	private TrafficManagerAdapter mAdapter;
	
	private Handler mHandler = new Handler(){
		public void handleMessage(android.os.Message msg) {
			switch (msg.what) {
			case SUCCESS_GET_TRAFFICINFO:
				mAdapter = new TrafficManagerAdapter(getApplicationContext());
				lv_traffic_manager_content.setAdapter(mAdapter);
				break;

			default:
				break;
			}
		};
	};
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
/*        2g3g 接收流量
        TrafficStats.getMobileRxBytes();
        
        //2g/3g 接收的包
        TrafficStats.getMobileRxPackets();
        
        //2g/3g 上传的流量
        TrafficStats.getMobileTxBytes();
        
        //2g/3g 上传的包
        TrafficStats.getMobileTxPackets();
        
        // 手机总共接收的流量
        TrafficStats.getTotalRxBytes(); 
        
        // 手机总共上传的流量
        TrafficStats.getTotalTxBytes();
        
        //得到么个应用程序接收的流量
        TrafficStats.getUidRxBytes(uid);
        TrafficStats.getUidTxBytes(uid);*/
        
        tv_traffic_manager_mobile =  (TextView) findViewById(R.id.tv_traffic_manager_mobile);
        tv_traffic_manager_wifi = (TextView) findViewById(R.id.tv_traffic_manager_wifi);
        lv_traffic_manager_content = (ListView) findViewById(R.id.lv_traffic_manager_content);
        
        tv_traffic_manager_mobile.setText(TextFormat.formatByte(getMobileTotal()));
        tv_traffic_manager_wifi.setText(TextFormat.formatByte(getWifiTotal()));
        
        trafficManagerService = new TrafficManagerService(this);
        new Thread(){
        	public void run() {
        		trafficInfos = trafficManagerService.getLauncherTrafficInfos();
        		realTrafficInfos = new ArrayList<TrafficInfo>();
        		for(TrafficInfo info:trafficInfos){
        			if(TrafficStats.getUidRxBytes(info.getUid()) == -1 && TrafficStats.getUidTxBytes(info.getUid()) == -1){
        				//
        			}else{
        				realTrafficInfos.add(info);
        			}
        		}
        		Message msg = new Message();
        		msg.what = SUCCESS_GET_TRAFFICINFO;
        		mHandler.sendMessage(msg);
        	};
        }.start();
        
    }
    
    /**
     * 2g/3g的总流量
     * @return
     */
    private long getMobileTotal(){
    	long mobile_rx = TrafficStats.getMobileRxBytes();
    	long mobile_tx = TrafficStats.getMobileTxBytes();
    	return mobile_rx + mobile_tx;
    }
    
    /**
     * 得到手机的总流量
     * @return
     */
    private long getTotal(){
    	return TrafficStats.getTotalRxBytes() + TrafficStats.getTotalTxBytes();
    }
    
    /**
     * 得到wifi的总流量
     * @return
     */
    private long getWifiTotal(){
    	return getTotal() - getMobileTotal();
    }
    
    
    static class ViewHolder{
    	ImageView iv_appicon;
    	TextView tv_appname;
    	TextView tv_apptraffic;
    	TextView tv_apptx;
    	TextView tv_apprx;
    }
    
    private final class TrafficManagerAdapter extends BaseAdapter{
    	
    	private LayoutInflater mInflater;
    	public TrafficManagerAdapter(Context context) {
    		mInflater = LayoutInflater.from(context);
		}

		public int getCount() {
			return realTrafficInfos.size();
		}

		public Object getItem(int position) {
			return realTrafficInfos.get(position);
		}

		public long getItemId(int position) {
			return position;
		}

		public View getView(int position, View convertView, ViewGroup parent) {
			View view = null;
			ViewHolder holder = null;
			if(convertView != null){
				view = convertView;
				holder = (ViewHolder) view.getTag();
			}else{
				view = mInflater.inflate(R.layout.traffic_manager_item, null);
				holder = new ViewHolder();
				holder.iv_appicon = (ImageView) view.findViewById(R.id.iv_appicon);
				holder.tv_appname = (TextView) view.findViewById(R.id.tv_appname);
				holder.tv_apptraffic = (TextView) view.findViewById(R.id.tv_apptarffic);
				holder.tv_apptx = (TextView) view.findViewById(R.id.tv_apptx);
				holder.tv_apprx = (TextView) view.findViewById(R.id.tv_apprx);
				view.setTag(holder);
			}
			
			TrafficInfo trafficInfo = realTrafficInfos.get(position);
			
			holder.iv_appicon.setImageDrawable(trafficInfo.getAppicon());
			holder.tv_appname.setText(trafficInfo.getAppname());
			int uid = trafficInfo.getUid();
			long tx = TrafficStats.getUidTxBytes(uid);
			if(tx == -1){
				tx = 0;
			}
			long rx = TrafficStats.getUidRxBytes(uid);
			if(rx == -1){
				rx = 0;
			}
			long total = tx + rx;
			holder.tv_apptraffic.setText(TextFormat.formatByte(total));
			holder.tv_apptx.setText("上传：" + TextFormat.formatByte(tx));
			holder.tv_apprx.setText("下载：" + TextFormat.formatByte(rx));
			
			return view;
		}
    	
    }

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		// Inflate the menu; this adds items to the action bar if it is present.
		getMenuInflater().inflate(R.menu.main, menu);
		return true;
	}

}

4、TrafficManagerService

package com.njupt.testtracfficstate;

import java.util.ArrayList;
import java.util.List;

import android.content.Context;
import android.content.Intent;
import android.content.pm.ApplicationInfo;
import android.content.pm.PackageManager;
import android.content.pm.ResolveInfo;
import android.graphics.drawable.Drawable;

public class TrafficManagerService {
	private Context context;
	private PackageManager pm;
	
	public TrafficManagerService(Context context) {
		this.context = context;
		pm = context.getPackageManager();
	}
	
	/**
	 * 得到所有能启动的应用
	 * @return
	 */
	public List<TrafficInfo> getLauncherTrafficInfos(){
		
		List<TrafficInfo> trafficInfos = new ArrayList<TrafficInfo>();
		//查询能够启动的应用程序  
		Intent intent = new Intent();
		intent.setAction(Intent.ACTION_MAIN);
		intent.addCategory(Intent.CATEGORY_LAUNCHER);
		
		//ResolveInfo  就类似于一个IntentFilter
		List<ResolveInfo> resolveInfos = pm.queryIntentActivities(intent, PackageManager.MATCH_DEFAULT_ONLY);
		for(ResolveInfo info:resolveInfos){
			ApplicationInfo appInfo = info.activityInfo.applicationInfo;
			Drawable appicon = appInfo.loadIcon(pm);
			String appname = appInfo.loadLabel(pm).toString();
			
			String packageName = appInfo.packageName;
			int uid = appInfo.uid;
			
			trafficInfos.add(new TrafficInfo(appicon, appname, packageName, uid));
		}
		return trafficInfos;
	}
}

5、TrafficInfo

package com.njupt.testtracfficstate;

import android.graphics.drawable.Drawable;

public class TrafficInfo {
	private Drawable appicon;
	private String appname;
	private String packageName;
	private int uid;
	
	
	
	public TrafficInfo() {
		super();
	}
	public TrafficInfo(Drawable appicon, String appname, String packageName,
			int uid) {
		super();
		this.appicon = appicon;
		this.appname = appname;
		this.packageName = packageName;
		this.uid = uid;
	}
	public Drawable getAppicon() {
		return appicon;
	}
	public void setAppicon(Drawable appicon) {
		this.appicon = appicon;
	}
	public String getAppname() {
		return appname;
	}
	public void setAppname(String appname) {
		this.appname = appname;
	}
	public String getPackageName() {
		return packageName;
	}
	public void setPackageName(String packageName) {
		this.packageName = packageName;
	}
	public int getUid() {
		return uid;
	}
	public void setUid(int uid) {
		this.uid = uid;
	}
	@Override
	public String toString() {
		return "TrafficInfo [appicon=" + appicon + ", appname=" + appname
				+ ", packageName=" + packageName + ", uid=" + uid + "]";
	}
	
	
}

6、TextFormat

package com.njupt.testtracfficstate;

import java.text.DecimalFormat;

public class TextFormat {
	// 23.87MB 00.87MB/KB byte
	public static String formatByte(long data) {
		DecimalFormat format = new DecimalFormat("##.##");
		if (data < 1024) {
			return data + "bytes";
		} else if (data < 1024 * 1024) {
			return format.format(data / 1024f) + "KB";
		} else if (data < 1024 * 1024 * 1024) {
			return format.format(data / 1024f / 1024f) + "MB";
		} else if (data < 1024 * 1024 * 1024 * 1024) {
			return format.format(data / 1024f / 1024f / 1024f) + "GB";
		} else {
			return "超出统计返回";
		}
	}
}