如何有效地从儿童Pocress的标准品中读取长行？

Question

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I am launching a child process from a C# class library.

I am using Process.BeginOutputReadLine() to read the output/error in an asynchronous way. I thought it didn't work with very long lines, but the problem seems to be that it's not scalable. In my computer, a 128 kb line is processed instantly, a 512 kb line seems to take around one minute, 1 mb seems to take several minutes, and I've been around two hours waiting for a 10 mb line to be processed, and it was still working when I cancelled it.

It seems easy to fix reading directly from the StandardOutput and StandardError streams, but the data from those streams seems to be buffered. If I get wnough data from stdout to fill the buffer, and then some more data from stderr, I can't find a way to check if there's data pending in one of them, and if I try to read from stderr, it will hang forever. Why is this happening, what am I doing wrong, and what's the right way to do this?

Some code samples to illustrate what I'm trying to achieve.

Program1 :

  // Writes a lot of data to stdout and stderr static void Main(string[] args) { int numChars = 512 * 1024; StringBuilder sb = new StringBuilder(numChars); String s = "1234567890"; for (int i = 0; i < numChars; i++) sb.Append(s[i % 10]); int len = sb.Length; Console.WriteLine(sb.ToString()); Console.Error.WriteLine(sb.ToString()); } 

Program2 :

  // Calls Program1 and tries to read its output. static void Main(string[] args) { StringBuilder sb = new StringBuilder(); StringBuilder sbErr = new StringBuilder(); proc.StartInfo.CreateNoWindow = true; proc.StartInfo.WindowStyle = ProcessWindowStyle.Hidden; proc.StartInfo.UseShellExecute = false; proc.StartInfo.RedirectStandardError = true; proc.StartInfo.RedirectStandardOutput = true; proc.StartInfo.RedirectStandardInput = false; proc.StartInfo.Arguments = ""; proc.StartInfo.FileName = "program1.exe"; proc.ErrorDataReceived += (s, ee) => { if (ee.Data != null) sbErr.AppendLine(ee.Data); }; proc.OutputDataReceived += (s, ee) => { if (ee.Data != null) sb.AppendLine(ee.Data); }; proc.Start(); proc.BeginOutputReadLine(); proc.BeginErrorReadLine(); proc.WaitForExit(); } 

Program1 has a constant that allows to set the size of data to generate, and Program2 launches Program1 and tries to read the data. I should expect the time to grow linearly with size, but it seems much worse than that.

Answer 1

I hope i understand your problem. the application hangs on Process.WaitForExit() because this is what Process.WaitForExit() : it waits for the process to exit .

you might want to call it in a new thread: int your method that create the process:

    Thread trd = new Thread(new ParameterizedThreadStart(Start));
     trd.Start();

and add this method:

  private void Start(object o)
  {
     ((Process)o).WaitForExit();
     // your code after process ended
  }