.NET 多线程题目汇总

1、交替输出奇数和偶数

internal class Program
{
    private static object _locker = new object();
    private static int _currentNumber = 0;
    private const int MaxNumber = 100;

    static void Main()
    {
        Thread evenThread = new Thread(PrintEven);
        Thread oddThread = new Thread(PrintOdd);

        evenThread.Start();
        oddThread.Start();

        evenThread.Join();
        oddThread.Join();
    }

    // 偶数线程
    static void PrintEven()
    {
        while (_currentNumber <= MaxNumber)
        {
            lock (_locker)
            {
                // 这个线程不行就等着
                while (_currentNumber % 2 != 0)
                {
                    Monitor.Wait(_locker);  
                }

                Console.WriteLine($"Even: {_currentNumber}");
                _currentNumber++;
                Monitor.Pulse(_locker); // 通知奇数线程
            }
        }
    }

    // 奇数线程
    static void PrintOdd()
    {
        while (_currentNumber <= MaxNumber)
        {
            lock (_locker)
            {
                // 如果当前是偶数，则等待偶数线程通知
                while (_currentNumber % 2 == 0)
                {
                    Monitor.Wait(_locker);
                }

                Console.WriteLine($"Odd: {_currentNumber}");
                _currentNumber++;
                Monitor.Pulse(_locker); // 通知偶数线程
            }
        }
    }
}

2、让两个线程A和B将自己的ID轮番写入一个文件中，每个线程重复十次写入后执行一个回调函数，说“I'm OK”

class Program
{
    private static readonly object _locker = new object();
    private static bool _isThreadATurn = true; // 初始由线程A开始
    private static int _writeCountA = 0;
    private static int _writeCountB = 0;
    private const string FilePath = "output.txt";

    static void Main()
    {
        // 清空或创建文件
        File.WriteAllText(FilePath, string.Empty);

        Thread threadA = new Thread(() => RunThread("A", () => Console.WriteLine("A: I'm OK")));
        Thread threadB = new Thread(() => RunThread("B", () => Console.WriteLine("B: I'm OK")));

        threadA.Start();
        threadB.Start();

        threadA.Join();
        threadB.Join();

        Console.WriteLine("File content:");
        Console.WriteLine(File.ReadAllText(FilePath));

        Console.ReadLine();
    }

    static void RunThread(string id, Action callback)
    {
        int writeCount = 0;
        while (writeCount < 10)
        {
            lock (_locker)
            {
                // 检查是否轮到自己
                while ((id == "A" && !_isThreadATurn) || (id == "B" && _isThreadATurn))
                {
                    Monitor.Wait(_locker);
                }

                // 写入文件
                File.AppendAllText(FilePath, id);
                writeCount++;

                // 更新状态并通知对方线程
                _isThreadATurn = !_isThreadATurn;
                Monitor.Pulse(_locker);
            }
        }
        callback(); // 执行回调
    }
}