c# 为什么不用while循环等待标志量，而用重置事件呢？ AutoResetEvent / ManualReset

利用while循环等待标志量实现多线程同步, cpu占用率极高：

bool is_ok = false;
            Task.Run(() =>
            {
                while(!is_ok)
                {
                    Console.WriteLine("thread 1...");
                }
                
            });

            Task.Run(() =>
            {
                while (!is_ok)
                {
                    Console.WriteLine("thread 2...");
                }

            });
            Task.Run(() =>
            {
                while (!is_ok)
                {
                    Console.WriteLine("thread 3...");
                }

            });

            Task.Run(() =>
            {
                Console.WriteLine("thread 4 set before.");
                Thread.Sleep(5000);
                is_ok = true;
                Console.WriteLine("thread 4 set after.");
            });

利用AutoResetEvent：一次唤醒一个线程，cpu占用率低

private static AutoResetEvent event_ = new AutoResetEvent(false);
        static void Main(string[] args)
        {
            Task.Run(() =>
            {
                event_.WaitOne();
                Console.WriteLine("thread 1...");
            });

            Task.Run(() =>
            {
                event_.WaitOne();
                Console.WriteLine("thread 2...");
            });

            Task.Run(() =>
            {
                Console.WriteLine("thread 3 set before.");
                Thread.Sleep(5000);
                Console.WriteLine("thread 3 set after.");
                event_.Set();   // 一次只能唤醒一个线程
            });

利用 ManualReset：一次唤醒所有线程，cpu占用率低

private static ManualResetEvent event_ = new ManualResetEvent(false);

        static void Main(string[] args)
        {
            Task.Run(() =>
            {
                event_.WaitOne();
                Console.WriteLine("thread 1...");
            });

            Task.Run(() =>
            {
                event_.WaitOne();
                Console.WriteLine("thread 2...");
            });
            Task.Run(() =>
            {
                event_.WaitOne();
                Console.WriteLine("thread 3...");
            });

            Task.Run(() =>
            {
                Console.WriteLine("thread 4 set before.");
                Thread.Sleep(5000);
                Console.WriteLine("thread 4 set after.");
                event_.Set();   // 一次只能唤醒一个线程
            });