非阻塞io使用BinaryWriter写入usblp0

Question

I'm doing a program in c# (mono) to print to a fiscal printer (escpos) and it works okay. The problem is that when I print, the program hangs until the buffer I have is cleared. So, as you imagine if I print a couple of images it gets bigger and so it hangs for a while. This is not desirable. I have tested in 2 ways

One way :

BinaryWriter outBuffer;
this.outBuffer = new BinaryWriter(new  FileStream (this.portName,System.IO.FileMode.Open));
.... apend bytes to buffer...
IAsyncResult asyncResult = null; 
asyncResult = outBuffer.BaseStream.BeginWrite(buffer,offset,count,null,null);
asyncResult.AsyncWaitHandle.WaitOne(100);
outBuffer.BaseStream.EndWrite(asyncResult); // Last step to the 'write'.
if (!asyncResult.IsCompleted) // Make sure the write really completed.
{
throw new IOException("Writte to printer failed.");             
}

second Way :

BinaryWriter outBuffer;
this.outBuffer = new BinaryWriter(new  FileStream (this.portName,System.IO.FileMode.Open));
.... apend bytes to buffer...
outBuffer.Write(buffer, 0, buffer.Length);

and neither method is allowing the program to continue the execution. Example: if it starts to print and paper is out it will hang until the printer resumes printing which is not the right way.

Thanks in advance for your time and patience.

Answer 1

The problem is that you're making the program wait for the write to complete. If you want it to happen asynchronously, then you need to provide a callback method that will be called when the write is done. For example:

asyncResult = outBuffer.BaseStream.BeginWrite(buffer,offset,count,WriteCallback,outBuffer);

private void WriteCallback(IAsyncResult ar)
{
    var buff = (BinaryWriter)ar.AsyncState;
    // following will throw an exception if there was an error
    var bytesWritten = buff.BaseStream.EndWrite(ar);

    // do whatever you need to do to notify the program that the write completed.
}

That's one way to do it. You should read up on the Asynchronous Programming Model for other options, and pick the one that best suits your needs.

You can also use the Task Parallel Library , which might be a better fit.