# V3193. Data processing results are potentially used before asynchronous output reading is complete. Consider calling 'WaitForExit' overload with no arguments before using the data.

The analyzer has detected that data processing results can be used before all operations of their creation are complete. In this case, an application uses incorrect or incomplete output data.

Look at the example:

    public void Run()
    {
      var process = new Process();

      process.StartInfo.FileName = GetProcessFile();
      process.StartInfo.UseShellExecute = false;
      process.StartInfo.RedirectStandardOutput = true;

      StringBuilder data = new StringBuilder();

      process.OutputDataReceived +=
        (sender, args) => data.AppendLine(args.Data); // <=

      process.Start();
      process.BeginOutputReadLine();

      WriteData(data.ToString());                     // <=
    }

The code runs the process and saves its result to the 'data' variable. Then the collected results are passed to the 'WriteData' method. The 'data.ToString' method may be called before the entire process output has been processed. For example, if the process outputs several strings, not all of them may be added to the 'data' variable by the time 'ToString' is called.

To solve the issue, make sure that reading of the entire process output has been completed. To do this, call the 'WaitForExit' method with no arguments:

    public void Run()
    {
      var process = new Process();

      process.StartInfo.FileName = GetProcessFile();
      process.StartInfo.UseShellExecute = false;
      process.StartInfo.RedirectStandardOutput = true;

      StringBuilder data = new StringBuilder();

      process.OutputDataReceived +=
        (sender, args) => data.AppendLine(args.Data);

      process.Start();
      process.BeginOutputReadLine();

      process.WaitForExit();

      WriteData(data.ToString());
    }

Calling the 'WaitForExit' method in this way returns control only after the output processing is complete. Please note that the 'WaitForExit(Int32)' overload lacks this feature. That is why the following code may work incorrectly:

    public void Run()
    {
      var process = new Process();

      ....

      StringBuilder data = new StringBuilder();

      process.OutputDataReceived +=
        (sender, args) => data.AppendLine(args.Data);  // <=

      process.Start();
      process.BeginOutputReadLine();

      if (process.WaitForExit(3000))
      {
        WriteData(data.ToString());                    // <=
      }
      else
      {
        .... // throw timeout error
      }
    }

In this example, getting the value from the 'data' variable is done after the process has closed. However, the reading of the process output may not be complete by the time 'ToString' is called. You can learn more about this behavior in the documentation for the 'WaitForExit' method. To ensure that the processing is completed, call the method with no arguments:

    public void Run()
    {
      var process = new Process();

      ....

      StringBuilder data = new StringBuilder();

      process.OutputDataReceived +=
        (sender, args) => data.AppendLine(args.Data);

      process.Start();
      process.BeginOutputReadLine();

      if (process.WaitForExit(3000))
      {
        process.WaitForExit();
        WriteData(data.ToString());
      }
      else
      {
        .... // throw timeout error
      }
    }

This diagnostic is classified as:

CWE-366