c#中Monitor的使用

首先lock和Minitor有什么區別呢？

其實lock在IL代碼中會被翻譯成Monitor。也就是Monitor.Enter(obj)和Monitor.Exit(obj).
 lock（obj）
 {
 }
 等價為：
 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額外的功能呢？ 

1：Monitor.TryEnter(obj,timespan)----timeout之后，就不執行這段代碼了。lock可是一直會死等的。
 
 2：還有Monitor.Wait()和Monitor.Pulse()。在lock代碼里面如果調用了Monitor.Wait()，會放棄對資源的所有權，讓別的線程lock進來。然后別的線程代碼里Pulse一下（讓原線程進入到等待隊列），然后在Wait一下釋放資源，這樣原線程的就可以繼續執行了（代碼還堵塞在wait那句話呢）。 

也就是說，必須兩個或多個線程共同調用Wait和Pulse，把資源的所有權拋來拋去，才不會死鎖。 

和AutoEvent相似是處理同步關系的，但是AutoEvent是跨進程的，而Monitor是針對線程的。
以下是MSDN的代碼示例，調試起來很容易看出來兩個函數的作用了，因為盡管是多線程程序，但是是同步操作，所以代碼始終是單步執行的。
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());
        }
    }
}