CODEWITHSUNDEEP
c#c++pinvokepipenamed-pipes
Shaitan00
Shaitan00

Reputation: 1341

How to unblock ConnectNamedPipe and ReadFile? [C#]

I have a class (NamedPipeManager) which has a thread (PipeThread) that waits for a NamedPipe connection using (ConnectNamedPipe) and then reads (ReadFile) - these are blocking calls (not-overlapped) - however there comes a point when I want to unblock them - for example when the calling class tries to stop the NamedPipeManager...

How can I interupt it? Using Thread.abort? Thread.interrupt? Is there a proper way to handle this? Refer to the code below which illustrates my current situation

main()
{
    NamedPipeManager np = new NamedPipeManager();
        ... do stuff ...
    ... do stuff ...
    np.Stop();      // at this point I want to stop waiting on a connection
}


class NamedPipeManager
{
private Thread PipeThread;

public NamedPipeManager
{
    PipeThread = new Thread(new ThreadStart(ManagePipes));
    PipeThread.IsBackground = true;
    PipeThread.Name = "NamedPipe Manager";
    PipeThread.Start();
}

private void ManagePipes()
{
    handle = CreateNamedPipe(..., PIPE_WAIT, ...);
    ConnectNamedPipe(handle, null);     // this is the BLOCKING call waiting for client connection

    ReadFile(....);             // this is the BLOCKING call to readfile after a connection has been established
    }


public void Stop()
{
    /// This is where I need to do my magic
    /// But somehow I need to stop PipeThread
    PipeThread.abort();     //?? my gut tells me this is bad
}
};

So, in function Stop() - how would I gracefully unblock the call to ConnectNamedPipe(...) or ReadFile(...)?

Any help would be appreciated. Thanks,

Upvotes: 7

Views: 7840

Answers (3)

OGP
OGP

Reputation: 972

Recently I was in a situation, I could not use the Async Overlapped IO. I was stuck on the server side within ConnectNamedPipe. To unlock the thread and free resources, I had to connect to the same pipe as a client for a split second.

  1. Main thread receives the stop signal
  2. Main thread sets the stop event for the listening thread
  3. Main thread connects to the pipe
  4. If succeeded (always) - closes the newly created handle immediately
  1. Listener thread unlocks
  2. Listener thread does whatever required

This worked for me very well.

To unblock ReadFile one needs to connect and write to the pipe. Same effect epected.

Upvotes: 0

Danil
Danil

Reputation: 895

It seems to be working on VC6.0, WinXP if I try to interrupt ConnectNamedPipe by DeleteFile("\\\\.\\pipe\\yourpipehere");

So just specify name, not handle.

Upvotes: 7

Martin v. Löwis
Martin v. Löwis

Reputation: 127467

Starting with Windows Vista, there is a CancelSynchronousIO operation available for threads. I don't think there is a C# wrapper for it, so you would need to use PInvoke to call it.

Before Vista, there isn't really a way to perform such an operation gracefully. I would advise against using thread cancellation (which might work, but doesn't qualify as graceful). Your best approach is to use overlapped IO.

Upvotes: 6

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