C# - 无法使用 Invoke() 从后台线程将文本追加到控件

问候，我在 C# 中从工作线程调用 richTextBox 时遇到问题。我正在使用 InvokeRequired/Invoke 方法。请参阅我的代码：

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }
    private void ThreadSafe(MethodInvoker method)
    {
        if (InvokeRequired)
            Invoke(method);
        else
            method();
    }
    private void WorkerThread(object data)
    {
        string msg = "'nhello, i am thread " + data.ToString();
        ThreadSafe(delegate
        {
            richTextBox1.AppendText(msg);
        });
    }
    private void button1_Click(object sender, EventArgs e)
    {
        Thread[] workers = new Thread[3];
        for (int i = 0; i < 3; i++)
        {
            workers[i] = new Thread(WorkerThread);
            workers[i].Start(i);
            string msg = "'nthread " + i.ToString() + "started!";
            richTextBox1.AppendText(msg);
        }
        int j = 3;
        while (j > 0)
        {
            for (int i = 0; i < 3; i++)
            {
                Thread.Sleep(250);
                richTextBox1.AppendText("'nChecking thread");
                if (workers[i].Join(250))
                {
                    string msg = "'nWorker thread " + i.ToString() + " finished.";
                    richTextBox1.AppendText(msg);
                    workers[i] = null;
                    j--;    // decrement the thread watch count
                }
            }
        }
    }
}

它在富文本框中打印以下内容：

thread 0started!
thread 1started!
thread 2started!
Checking thread
Checking thread
Checking thread
Checking thread
....

它一直持续下去，"hello"消息没有打印出来，并且 UI 被冻结。然后我将 Invoke（） 更改为 BeginInvoke（），我知道我不应该这样做，然后结果是这样的：

thread 0started!
thread 1started!
thread 2started!
Checking thread
Worker thread 0 finished.
Checking thread
Worker thread 1 finished.
Checking thread
Worker thread 2 finished.
hello, i am thread 0
hello, i am thread 1
hello, i am thread 2

原因是什么，我该怎么办？

提前谢谢。