关于线程同步的问题，急
private   int   a;
Thread   t   ;
private   void   button1_Click(object   sender,   System.EventArgs   e)
{
start();
MessageBox.Show(a.ToString());
}
private   void   count()
{
for(int   i=0;i <1000;i++)
{
a=i;
}
}
private   void   start()
{
t   =   new   Thread(new   ThreadStart(count));
t.Start();
}


为什么MessageBox.Show(a.ToString());中a的结果是0而不是999呢？如何做才能使a的值为999？

------解决方案--------------------
private void button1_Click(object sender, System.EventArgs e)
{

start();
t.Join();
MessageBox.Show(a.ToString());
}