线程同步：System.Core中新的读写锁

读写锁是进程同步中经常使用的锁。

在System.Core中ReaderWriterLockSlim类比较好用，它是基于写优先策略的。它还支持从读锁升级到写锁，称为Upgradable Mode.

简单测试代码如下：

private static void Test()
{
    ReaderWriterLockSlim locker = new ReaderWriterLockSlim();
    ParameterizedThreadStart reader = o =>
    {
        var innerlocker = locker;
        int number = Convert.ToInt32(o);
        while (true)
        {
            locker.EnterReadLock();
            Console.WriteLine("Reading  " + number);
            Thread.Sleep(500);
            locker.ExitReadLock();
        }
    };
    ParameterizedThreadStart writer = o =>
    {
        var innerlocker = locker;
        int number = Convert.ToInt32(o);
        while (true)
        {
            locker.EnterWriteLock();
            Console.WriteLine("Writing  " + number);
            Thread.Sleep(50);
            locker.ExitWriteLock();
        }
    };
    for (int i = 1; i <= 100; i++)
    {
        Thread thread = new Thread(reader);
        thread.Start(i);
    }
    for (int i = 11; i <= 15; i++)
    {
        Thread thread = new Thread(writer);
        thread.Start(i);
    }

    AutoResetEvent waitForever = new AutoResetEvent(false);
    waitForever.WaitOne();
}