LOCK关键字作用理解 实例

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


using System.Threading;
using System.Net.Sockets;
using System.Net;

class Account
{
    private Object thisLock = new Object();
    int balance;

    Random r = new Random();

    public Account(int initial)
    {
        balance = initial;
    }

    int Withdraw(int amount)
    {

        // This condition will never be true unless the lock statement
        // is commented out:
        //if (balance < 0)
        //{
        //    throw new Exception("Negative Balance");
        //}

        // Comment out the next line to see the effect of leaving out
        // the lock keyword:


        /*lock锁定了thisLock，避免了其他线程调用Withdraw时不分先后的操作balance参数，导致混乱*/
        lock (thisLock)
        {
            if (balance >= amount)
            {
                Console.WriteLine("Balance before Withdrawal :  " + balance);
                Console.WriteLine("Amount to Withdraw        : -" + amount);
                balance = balance - amount;
                Console.WriteLine("Balance after Withdrawal  :  " + balance);
                Console.WriteLine(Thread.CurrentThread.Name);
                return amount;
            }
            else
            {
                return 0; // transaction rejected
            }
        }
    }

    public void DoTransactions()
    {
        for (int i = 0; i < 100; i++)
        {
            Withdraw(r.Next(1, 100));
        }
    }
}

class Test
{
    static void Main()
    {
        Thread[] threads = new Thread[10];
        Account acc = new Account(1000);
        for (int i = 0; i < 10; i++)
        {
            Thread t = new Thread(new ThreadStart(acc.DoTransactions));
            t.Name = i.ToString();
            threads[i] = t;
        }
        for (int i = 0; i < 10; i++)
        {
            threads[i].Start();
        }

        Console.Read();
    }
}