c#中Monitor的使用

首先lock和Minitor有什么区别呢？

其实lock在IL代码中会被翻译成Monitor。也就是Monitor.Enter(obj)和Monitor.Exit(obj).

lock（obj）

{

}

等价为：

try

{    

      Monitor.Enter(obj)


}

catch（）

{}

finally

{

      Monitor.Exit(obj)


}
所以lock能做的，Monitor肯定能做，Monitor能做的，lock不一定能做。那么Monitor额外的功能呢？

1：Monitor.TryEnter(obj,timespan)----timeout之后，就不执行这段代码了。lock可是一直会死等的。



2：还有Monitor.Wait()和Monitor.Pulse()。在lock代码里面如果调用了Monitor.Wait()，会放弃对资源的所有权，让别的线程lock进来。然后别的线程代码里Pulse一下（让原线程进入到等待队列），然后在Wait一下释放资源，这样原线程的就可以继续执行了（代码还堵塞在wait那句话呢）。

也就是说，必须两个或多个线程共同调用Wait和Pulse，把资源的所有权抛来抛去，才不会死锁。

和AutoEvent相似是处理同步关系的，但是AutoEvent是跨进程的，而Monitor是针对线程的。
以下是MSDN的代码示例，调试起来很容易看出来两个函数的作用了，因为尽管是多线程程序，但是是同步操作，所以代码始终是单步执行的。
using System;
using System.Threading;
using System.Collections;

namespace MonitorCS1
{
    class MonitorSample
    {
        const int MAX_LOOP_TIME = 100;
        Queue m_smplQueue;

        public MonitorSample()
        {
            m_smplQueue = new Queue();
        }
        public void FirstThread()
        {
            int counter = 0;
            lock (m_smplQueue)
            {
                while (counter < MAX_LOOP_TIME)
                {
                    //Wait, if the queue is busy.
                    Monitor.Wait(m_smplQueue);
                    //Push one element.
                    m_smplQueue.Enqueue(counter);
                    //Release the waiting thread.
                    Monitor.Pulse(m_smplQueue);

                    counter++;
                }
                int i = 0;
            }
        }
        public void SecondThread()
        {
            lock (m_smplQueue)
            {
                //Release the waiting thread.
                Monitor.Pulse(m_smplQueue);
                //Wait in the loop, while the queue is busy.
                //Exit on the time-out when the first thread stops.
                while (Monitor.Wait(m_smplQueue, 50000))
                {
                    //Pop the first element.
                    int counter = (int)m_smplQueue.Dequeue();
                    //Print the first element.
                    Console.WriteLine(counter.ToString());
                    //Release the waiting thread.
                    Monitor.Pulse(m_smplQueue);
                }
            }
        }
        //Return the number of queue elements.
        public int GetQueueCount()
        {
            return m_smplQueue.Count;
        }

        static void Main(string[] args)
        {
            //Create the MonitorSample object.
            MonitorSample test = new MonitorSample();
            //Create the first thread.
            Thread tFirst = new Thread(new ThreadStart(test.FirstThread));
            //Create the second thread.
            Thread tSecond = new Thread(new ThreadStart(test.SecondThread));
            //Start threads.
            tFirst.Start();
            tSecond.Start();
            //wait to the end of the two threads
            tFirst.Join();
            tSecond.Join();
            //Print the number of queue elements.
            Console.WriteLine("Queue Count = " + test.GetQueueCount().ToString());
        }
    }
}