学习来源：《.net core 底层入门》 第六章第9节：信号量

案例：主线程负责添加数据，子线程负责获取数据

 使用SemaphoreSlim（轻信号量）实现：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace 测试信号量
{
    internal class Program
    {
        private static  SemaphoreSlim _semaphore = new SemaphoreSlim(4);
        public static Queue<int> _queue = new Queue<int>();
        public static object _lock = new object();
        static void Main(string[] args)
        {
            Thread thread = new Thread(work);
            thread.IsBackground = true;
            thread.Start();
            int job = 0;
            while (true) {
                lock (_lock) {
                    _queue.Enqueue(job++);
                }
//释放对象指定次数
                _semaphore.Release(1);
               Thread.Sleep(1000);
            }
        }
        public static void work() {
            while (true) {
//阻止当前线程，直至释放
                _semaphore.Wait();
                lock (_lock)
                {
                    if (_queue.Count > 0)
                    {
                        Console.WriteLine(_queue.Dequeue());
                    }
                }
                Thread.Sleep(1000);
            }
        }
    }
}

使用Monitor实现：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;

namespace 测试信号量
{
    internal class Program
    {
        public static Queue<int> _queue = new Queue<int>();
        public static object _lock = new object();
        static void Main(string[] args)
        {
            Thread thread = new Thread(work);
            thread.IsBackground = true;
            thread.Start();
            int job = 0;
            while (true) {
                lock (_lock) {
                    _queue.Enqueue(job++);
 //通知等待队列中的线程锁对象状态变更
                    Monitor.Pulse(_lock);
                }
               Thread.Sleep(1000);
            }
        }
        public static void work() {
            while (true) {
                lock (_lock)
                {
                    if (_queue.Count > 0)
                    {
                        Console.WriteLine(_queue.Dequeue());
                    }
                    else {
                 //释放对象上的锁并且阻止当前线程，直到他状态变更
                        Monitor.Wait(_lock);
                    }
                }
                Thread.Sleep(1000);
            }
        }
    }
}