c# – 同时获取多个线程同步锁

我们假设以下代码在我的应用程序中以类似的方式使用：

//-------------------------------------
void UseAllResources ()
{
  bool bSuccess1 = false;
  bool bSuccess2 = false;
  try
  {
    bSuccess1 = Monitor::TryEnter (oResource1,msc_iTimeoutMonitor);
    if (!bSuccess1) return;
    bSuccess2 = Monitor::TryEnter (oResource2,msc_iTimeoutMonitor);
    if (!bSuccess2) return;

    // work on oResource1 and oResource2
  } finally {
    if (bSuccess2)
      Monitor::Exit (oResource2);
    if (bSuccess1)
      Monitor::Exit (oResource1);
  }
}

//-------------------------------------
void UseResource1 ()
{
  bool bSuccess = false;
  try {
    bSuccess = Monitor::TryEnter (oResource1,msc_iTimeoutMonitor);
    if (!bSuccess) return;

    // work on oResource1
  } finally {
    if (bSuccess) Monitor::Exit (oResource1);
  }
}

//-------------------------------------
void UseResource2 ()
{
  same like UseResource1(),but using oResource2
}

这些函数可能随时被不同的线程调用.

可能会发生这种情况
(超时为500毫秒)
@t = 0ms,线程B正在执行UseResource2(),需要400ms,
@t = 100ms,线程Z调用UseAllResources(),对oResource1进行锁定,并且必须等待oResource2上的锁定,
@t = 200ms,线程A正在调用UseResource1()并且必须等待oResource1上的锁定,这是由线程Z占用的,
@t = 400ms,线程B完成,线程Z锁定oResource2并开始工作,
@t = 700ms,线程A超时,虽然它只需要50ms并且可以在线程Z仍在等待时工作.

我宁愿让线程Z失败,如果有的话,因为超时应该是所有锁的整体值.

我可以同时开始获取多个锁吗？

解决方法

解决方案可能是使用readerwriterlockslim类.以下代码在构造函数中包装了一个函数(您要完成的工作).或者,您可以将函数移动到DoWork方法以更改访问资源的方式.

LockedResource implmentation

class LockedResource
{
    public delegate void RefAction();

    readerwriterlockslim resourceLock;

    public LockedResource()
    {
        //Warning: SupportsRecursion is risky,you should remove support for recursive whenever possible
        resourceLock = new readerwriterlockslim(LockRecursionPolicy.SupportsRecursion);
    }

    public bool DoWork(RefAction work,string threadname,int timeout = -1)
    {
        try
        {
            if (resourceLock.TryEnterWriteLock(timeout))
            {
                if (work != null)
                {
                    work();
                }
            }
            else
            {
                Console.WriteLine("Lock time out on thread {0}",threadname);
            }
        }
        finally
        {

            Console.WriteLine("{0} releasing resource",threadname);
            if(resourceLock.IsWriteLockHeld)
            {
                resourceLock.ExitWriteLock();
            }
        }

        return false;
    }
}

样本用法

static void Main(string[] args)
{
        object oResouce1 = "-";
        object oResouce2 = "-";

        LockedResource lock1 = new LockedResource();
        LockedResource lock2 = new LockedResource();

       //the event wait handles is not required,only used to block thread so that resource values can be printed out at the end of the program
        var h1 = new EventWaitHandle(false,EventResetMode.ManualReset);
        var h2 = new EventWaitHandle(false,EventResetMode.ManualReset);
        var h3 = new EventWaitHandle(false,EventResetMode.ManualReset);

        WaitHandle[] waitHandles = { h1,h2,h3 };

        var t1 = new Thread(() =>
        {
            lock1.DoWork(() =>
            {
                oResouce1 = "1";
                Console.WriteLine("Resource 1 set to 1");
            },"T1");

            h1.Set();
        });

        var t2 = new Thread(() =>
        {
            lock2.DoWork(() =>
            {
                oResouce2 = "2";
                Console.WriteLine("Resource 2 set to 2");
                Thread.Sleep(10000);

            },"T2");
            h2.Set();
        });

        var t3 = new Thread(() =>
        {
            lock1.DoWork(() =>
            {
                lock2.DoWork(() =>
                {
                    oResouce1 = "3";
                    Console.WriteLine("Resource 1 set to 3");

                    oResouce2 = "3";
                    Console.WriteLine("Resource 2 set to 3");
                },"T3",1000);
                h3.Set();

            },"T3");

        });
        t1.Start();
        t2.Start();
        t3.Start();


        WaitHandle.WaitAll(waitHandles);
        Console.WriteLine("Resource 1 is {0}",oResouce1);
        Console.WriteLine("Resource 2 is {0}",oResouce2);

        Console.ReadLine();
}

产量

Resource 1 set to 1 Resource 2 set to 2 T1 releasing resource Lock time out on thread T3 T3 releasing resource T3 releasing resource T2 releasing resource Resource 1 is 1 Resource 2 is 2