命名管道 - 异步窥视

Question

当以异步模式打开的 System.IO.Pipe.NamedPipeServerStream 有更多数据可供读取时，我需要找到一种通知方式 - WaitHandle 是理想的选择。我不能简单地使用 BeginRead() 来获取这样的句柄，因为我可能会被另一个想要写入管道的线程发出信号 - 所以我必须释放管道上的锁并等待写入完成，并且 NamedPipeServerStream 没有 CancelAsync 方法。我还尝试调用 BeginRead()，然后在线程收到信号时调用管道上的 win32 函数 CancelIO，但我认为这不是一个理想的解决方案，因为如果在数据到达和处理时调用 CancelIO，它将被删除 - 我仍然希望保留这些数据，但在写入之后稍后处理它。我怀疑 win32 函数 PeekNamedPipe 可能有用，但我想避免使用它不断轮询新数据。

如果上面的文字有点不清楚，这大概是我想做的事情......

NamedPipeServerStream pipe;
ManualResetEvent WriteFlag;
//initialise pipe
lock (pipe)
{
    //I wish this method existed
    WaitHandle NewDataHandle = pipe.GetDataAvailableWaithandle();
    Waithandle[] BreakConditions = new Waithandle[2];
    BreakConditions[0] = NewDataHandle;
    BreakConditions[1] = WriteFlag;
    int breakcode = WaitHandle.WaitAny(BreakConditions);
    switch (breakcode)
    {
        case 0:
            //do a read on the pipe
            break;
        case 1:
            //break so that we release the lock on the pipe
            break;
     }
}

Answer 1

好的，所以我刚刚从我的代码中删除了这个，希望我删除了所有应用程序逻辑的东西。这个想法是您尝试使用 ReadFile 进行零长度读取，并在另一个线程想要写入管道时等待 lpOverlapped.EventHandle（读取完成时触发）和 WaitHandle 集。如果由于写入线程而导致读取中断，请使用CancelIoEx取消零长度读取。

NativeOverlapped lpOverlapped;
ManualResetEvent DataReadyHandle = new ManualResetEvent(false);
lpOverlapped.InternalHigh = IntPtr.Zero;
lpOverlapped.InternalLow = IntPtr.Zero;
lpOverlapped.OffsetHigh = 0;
lpOverlapped.OffsetLow = 0;
lpOverlapped.EventHandle = DataReadyHandle.SafeWaitHandle.DangerousGetHandle();
IntPtr x = Marshal.AllocHGlobal(1); //for some reason, ReadFile doesnt like passing NULL in as a buffer
bool rval = ReadFile(SerialPipe.SafePipeHandle, x, 0, IntPtr.Zero,
   ref lpOverlapped);
int BreakCause;
if (!rval) //operation is completing asynchronously
{
   if (GetLastError() != 997) //ERROR_IO_PENDING, which is in fact good
      throw new IOException();
   //So, we have a list of conditions we are waiting for
   WaitHandle[] BreakConditions = new WaitHandle[3];
   //We might get some input to read from the serial port...
   BreakConditions[0] = DataReadyHandle;
    //we might get told to yield the lock so that CPU can write...
   BreakConditions[1] = WriteRequiredSignal;
   //or we might get told that this thread has become expendable
   BreakConditions[2] = ThreadKillSignal;
   BreakCause = WaitHandle.WaitAny(BreakConditions, timeout);
}
else //operation completed synchronously; there is data available
{
   BreakCause = 0; //jump into the reading code in the switch below
}
switch (BreakCause)
{
   case 0:
      //serial port input
      byte[] Buffer = new byte[AttemptReadSize];
      int BRead = SerialPipe.Read(Buffer, 0, AttemptReadSize);
      //do something with your bytes.
      break;
   case 1:
      //asked to yield
      //first kill that read operation
      CancelIoEx(SerialPipe.SafePipeHandle, ref lpOverlapped);
      //should hand over the pipe mutex and wait to be told to tkae it back
      System.Threading.Monitor.Exit(SerialPipeLock);
      WriteRequiredSignal.Reset();
      WriteCompleteSignal.WaitOne();
      WriteCompleteSignal.Reset();
      System.Threading.Monitor.Enter(SerialPipeLock);
      break;
   case 2:
      //asked to die
      //we are the ones responsible for cleaning up the pipe
      CancelIoEx(SerialPipe.SafePipeHandle, ref lpOverlapped);
      //finally block will clean up the pipe and the mutex
      return; //quit the thread
}
Marshal.FreeHGlobal(x);

Answer 2

查看 MSDN，我没有看到任何机制可以做你想做的事。最快的解决方案可能是使用互操作访问PeekNamedPipe。如果您不想使用interop，您可以在自定义类中抽象管道，并在抽象中提供窥视功能。抽象将处理所有信号，并且必须协调对管道的读取和写入。显然，这不是一项简单的任务。

如果可能的话，另一种选择是研究使用 WCF，这几乎就是抽象。