C#使用task時候假面卡死

下面的代碼是測試使用3個task去執行count_wast_time()這個函數；然後再畫面上面顯示“count_wast_time 開始”；但是一旦添加 Task.WaitAll界面就卡死了，為什麼？？
求告知錯誤的原因，還有如何合理的修改


```
private void button3_Click(object sender, EventArgs e)
{
var tasks = new Task[3];
int i = 0;
int j = 0;
int k = 0;

a2 = 0;
string s1 = "";

tasks[0] = Task.Factory.StartNew(() =>
{
count_wast_time();
}
);

tasks[1] = Task.Factory.StartNew(() =>
{
count_wast_time();
}
);

tasks[2] = Task.Factory.StartNew(() =>
{
count_wast_time();
}
);
Task.WaitAll(tasks[0], tasks[1], tasks[2]); //？？？出問題

label3.Text = label3.Text + "全部執行完畢";
}

```


```
private void count_wast_time()
{
this.label3.Invoke(new Action(() =>
{
label3.Text = "count_wast_time 開始\n";
}));


for (int i2 = 0; i2 < 600; i2++)
{

for (int j2 = 0; j2 < 200; j2++)
{
for (int k3 = 0; k3< 100; k3++)
{
}
}
}
}
```