命名管道 - 异步查看

Question

我需要找到一种方式，当以异步模式打开的System.IO.Pipe.NamedPipeServerStream具有更多可读取的数据时 - WaitHandle将是理想的。我不能简单地使用BeginRead（）来获得这样的句柄，因为可能会由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，和NamedPipeServerStream没有一个CancelAsync方法。我也尝试调用BeginRead（），然后在管道上调用win32函数CancelIO，但是我不认为这是一个理想的解决方案，因为如果在数据到达并正在处理的情况下调用CancelIO，它将会被丢弃 - 我仍然希望保留这些数据，但是在写完后稍后再进行处理。我怀疑win32函数PeekNamedPipe可能是有用的，但我想避免不得不连续轮询新数据。

在likley倘上述文字是有点不清楚，这里的大致我想怎么能够做到？

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，所以我只是从我的代码中剔除了这个，希望我删除了所有的应用程序逻辑。这个想法是，你使用ReadFile尝试一个零长度的读取，并等待lpOverlapped.EventHandle（当读取完成时触发）和一个WaitHandle在另一个线程想要写入管道时设置。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

翻翻MSDN，我没有看到任何机制做你想做的事。最快的解决方案是使用互操作来访问PeekNamedPipe。如果您不想使用interop，则可以抽象自定义类中的管道，并在抽象中提供peek功能。抽象将处理所有的信号，并且必须协调读取和写入管道。显然，这不是一项简单的任务。

如果可能的话，另一种选择是使用WCF，它几乎就是抽象。