c# - 仅在多线程时抛出 StackOverFlowException

Question

我正在编写一个程序来帮助我为我正在撰写的有关密码安全性的研究报告收集统计数据。当我试图暴力破解 MD5 散列密码以获得明显的性能提升时，我决定让应用程序在多个线程上运行。该应用程序在单个线程上运行良好，但当 2 个线程正在运行时，在 TryPass 函数中“使用 (MD5 md5Hash = MD5.Create())”抛出 StackOverFlowException。

    // Microsoft's GetMd5Hash function.
    static string GetMd5Hash(MD5 md5Hash, string input)
    {
        // Convert the input string to a byte array and compute the hash. 
        byte[] data = md5Hash.ComputeHash(Encoding.UTF8.GetBytes(input));

        // Create a new Stringbuilder to collect the bytes 
        // and create a string.
        StringBuilder sBuilder = new StringBuilder();

        // Loop through each byte of the hashed data  
        // and format each one as a hexadecimal string. 
        for (int i = 0; i < data.Length; i++)
        {
            sBuilder.Append(data[i].ToString("x2"));
        }

        // Return the hexadecimal string. 
        return sBuilder.ToString();
    }

    static bool TryPass(string attempt, string password)
    {
        using (MD5 md5Hash = MD5.Create())
        {
            if (GetMd5Hash(md5Hash, attempt) == password)
                return true;
            else
                return false;
        }
    }



    static bool BruteForce(BruteOptions bruteOptions)
    {
        if (bruteOptions.prefix.Length == 1 && TryPass(bruteOptions.prefix, bruteOptions.password)) // If it's the first in a series, try it.
            return true;

        for (int i = 0; i < bruteOptions.chars.Length; i++)
        {
            if (TryPass(bruteOptions.prefix + bruteOptions.chars[i], bruteOptions.password))
            {
                Console.WriteLine("The password is: " + bruteOptions.prefix + bruteOptions.chars[i]);
                return true;
            }

            if (bruteOptions.prefix.Length + 1 < bruteOptions.maxLength)
                if (BruteForce(bruteOptions))
                    return true;

            //Console.WriteLine(prefix + chars[i]);
        }

        return false;
    }



    public struct BruteOptions
    {
        public string password, prefix;
        public char[] chars;
        public int maxLength;
    }

    static void OptionBruteForce()
    {
        Console.WriteLine("-----------------------");
        Console.WriteLine("----- Brute-Force -----");
        Console.WriteLine("-----------------------");

        BruteOptions bruteOptions = new BruteOptions();
        bruteOptions.password = ReadString("Enter the MD5 password hash to brute-force: ");
        bruteOptions.chars = ReadString("Enter the characters to use: ").ToCharArray();
        bruteOptions.maxLength = ReadIntegerRange("Max length of password: ", 1, 16);
        bruteOptions.prefix = "";

        Stopwatch myStopWatch = Stopwatch.StartNew();

        int NUM_THREADS = bruteOptions.chars.Length;
        Thread[] workers = new Thread[NUM_THREADS]; // Run a thread for each char.
        var countdownEvent = new CountdownEvent(NUM_THREADS);
        bool result = false;

        // Start workers.
        for (int i = 0; i < NUM_THREADS; i++)
        {
            int index = i;
            BruteOptions newBruteOptions = bruteOptions;
            newBruteOptions.prefix = bruteOptions.chars[index].ToString();

            workers[index] = new Thread(delegate()
            {
                // Also check single char.
                if (BruteForce(bruteOptions))
                {
                    result = true;

                    // End all other threads.
                    for (int ii = 0; ii < NUM_THREADS; ii++)
                    {
                        if (workers[ii].ThreadState == System.Threading.ThreadState.Running && index != ii) // Ensures we don't prematurely abort this thread.
                        {
                            workers[ii].Abort();
                            countdownEvent.Signal(); // Signal so we can zero it and continue on the UI thread.
                        }
                    }
                }

                // Signal the CountdownEvent.
                countdownEvent.Signal();
            });

            workers[index].Start();
        }

        // Wait for workers.
        countdownEvent.Wait();

        if (!result)
            Console.WriteLine("No Match.");

        Console.WriteLine("Took " + myStopWatch.ElapsedMilliseconds + " Milliseconds");
    }

这就是所有相关代码。任何关于为什么会发生这种情况的见解将不胜感激!我完全被难住了。我试图在初始化每个线程时指定更大的堆栈大小，但无济于事。

提前致谢!

Answer 1

你的 static bool BruteForce(BruteOptions bruteOptions) 是无限递归的:如果长度允许，它会调用自己，使用相同的参数:

if (bruteOptions.prefix.Length + 1 < bruteOptions.maxLength)
    if (BruteForce(bruteOptions))

bruteOptions 与函数入口处的一样。

作为解决方案，您可以使用此代码:

if (bruteOptions.prefix.Length + 1 < bruteOptions.maxLength)
{
    BruteOptions newOptions = bruteOptions;
    newOptions.prefix += bruteOptions.chars[i];
    if (BruteForce(newOptions))
        return true;
}

另外，您将 bruteOptions 而不是 newBruteOptions 传递给您在 main 函数中使用的委托(delegate)。因此，实际上没有使用您的多线程。您的所有线程都测试相同的密码。将其更改为 newBruteOptions。

此外，不要对线程执行顺序做任何假设。您假设在找到正确密码的那一刻所有工作人员都已满员，这可能是错误的。然后，您将在这一行中得到一个 NullReferenceException:

if (workers[ii].ThreadState == System.Threading.ThreadState.Running && index != ii) // Ensures we don't prematurely abort this thread.