Android后台运行的问题

我用socket上传数据到服务器，为了防止上传时间过长，所以将这一部分放在后台处理，但是onPostExecute已经运行了，也就是说doInBackground函数已经运行完毕，但是上传却没有成功，将上传代码放在Activity中操作，文件成功上传，这是为什么呢？

如果像调试后台程序，应该如何进行啊？
后台运行代码如下：

package lmx.graduate;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.io.PrintWriter;
import java.net.Socket;

import android.os.AsyncTask;
import android.os.Environment;
import android.util.Log;
import android.widget.TextView;

public class uploadAsyncTask extends AsyncTask<String, Integer, String>{

public uploadAsyncTask(TextView textView)
{
this.textView = textView;
}
protected String doInBackground(String...param){

int i = 0;
for(i=1;i<=10000;i++)
publishProgress(i);
String path = getSDPath() +"/upload.txt";
try{
FileInputStream fileIS = new FileInputStream(path);
BufferedReader buf = new BufferedReader(new InputStreamReader(fileIS,"utf-8"));
String readString = new String();
int k = 0;
while((readString = buf.readLine())!= null){
k++;
Log.v("error", readString);

//向服务器发送信息
Socket socket = null;
try{
socket = new Socket("192.168.11.17",54321);
//向服务器发送信息
PrintWriter out=new PrintWriter(new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())),true);
out.println(readString);
System.out.println(readString);
//接受服务器的信息
BufferedReader br=new BufferedReader(new InputStreamReader(socket.getInputStream()));
String mstr=br.readLine();
if(mstr!=null)
{
System.out.println(mstr);
}else
{
System.out.println("数据错误");
}
System.out.println("shangchuan");
out.close();
br.close();
socket.close();
}
catch (Exception e) {
// TODO: handle exception
}
}
fileIS.close();
} catch (FileNotFoundException e) {
e.printStackTrace();

} catch (IOException e){
e.printStackTrace();
}


return null;
}
//在doInBackground执行完毕后执行
protected void onPostExecute(String result)
{
textView.setText("本次上传已完成");
}
//在调用异步线程之后第一个执行，在主线程中进行
/**
*
* @param
* @return
* @author Administrator
*/
protected void onPreExecute()
{
textView.setText("开始上传");
}
protected void onProgressUpdate(Integer...values){
//textView.setText("请勿选择继续上传，请勿退出，系统正在上传，"+Integer.toString(values[0]));
textView.setText("请勿选择继续上传，请勿退出，系统正在上传");

}

public String getSDPath(){
File sdDir = null;
boolean sdCardExist = Environment.getExternalStorageState()
.equals(android.os.Environment.MEDIA_MOUNTED); //判断sd卡是否存在
if (sdCardExist)
{
sdDir = Environment.getExternalStorageDirectory();//获取跟目录
}
return sdDir.toString();

}

}