如何等待操作完成？

Question

I have C# code which included Python code in which it is run through CMD codes in C#. When the Python code is run the operations are done, a JSON file is created and then it will be opened in C#. In this situation, how the C# code can wait to check if the output of Python ( data.json ) is created or not, and just when the output is created, the rest of C# code is allowed to be run:

Process process = new Process();
process.StartInfo.FileName = "cmd.exe";
process.StartInfo.CreateNoWindow = true;
process.StartInfo.RedirectStandardInput = true;
process.StartInfo.RedirectStandardOutput = true;
process.StartInfo.UseShellExecute = false;
process.Start();
process.StandardInput.WriteLine("F:\\");
process.StandardInput.WriteLine("cd F:\\Path");
process.StandardInput.WriteLine("python Python_Code.py");


process.StandardInput.Flush();
process.StandardInput.Close();
process.WaitForExit();

Then, the generated data with Python will be retrieved:

string Output_Python = File.ReadAllText(@"Data.json");
JavaScriptSerializer Ser = new JavaScriptSerializer();
Predicted Output = Ser.Deserialize<Predicted>(Output_Python);

Answer 1

You don't need to go through cmd.exe. The Python interpreter itself is an executable; in other words, it can be started and executed directly. The arguments for the Python interpreter (like the path+name of the script to be executed) and desired working directory can be set through the appropriate Process.StartInfo properties :

Process process = new Process();
process.StartInfo.FileName = "python.exe";
process.StartInfo.Arguments = "Python_Code.py";
process.StartInfo.WorkingDirectory = @"F:\Path";
process.StartInfo.CreateNoWindow = true;
process.StartInfo.RedirectStandardOutput = true;
process.StartInfo.UseShellExecute = false;
process.Start();

Now you only need to wait for the Python interpreter to exit (which means it finished executing the python script)

process.WaitForExit();

and after the Python process has exited, simply check if the json file exist/has been written:

if (System.IO.File.Exists(pathToJsonFile))
{
    ... do stuff with json file ...
}
else
{
    ... json file does not exist, something went wrong...
}

---

Side note: I kept process.StartInfo.RedirectStandardOutput = true; in my code example here, since i don't know what your program will really do. However, unless your program wants to process the output of the script that normally appears in a console window, setting RedirectStandardOutput to true is not necessary.

Answer 2

You should have a look at the FileSystemWatcher class. Documentation here .

Then you can do something like this:

using (FileSystemWatcher watcher = new FileSystemWatcher())
{
    watcher.Path = YourDirectory;
    // Watch for changes in LastWrite time
    watcher.NotifyFilter = NotifyFilters.LastWrite;

    // Watch for the wanted file
    watcher.Filter = "data.json";

    // Add event handlers.
    watcher.Created += WhateverYouWantToDo;
}

Answer 3

You can check to see if the file data.json is finished being written to its output folder (Code from this answer ):

private bool IsFileLocked(FileInfo file) 
{ 
   FileStream stream = null; 
   try 
  { 
    stream = file.Open(FileMode.Open,    FileAccess.ReadWrite, FileShare.None); 
  } 
  catch (IOException)
  { 
//the file is unavailable because it is: 
//still being written to 
//or being processed by another thread 
//or does not exist (has already been processed) 
    return true; 
  }
  finally 
  { 
    if (stream != null) stream.Close(); 
  } 
//file is not locked return 
return false; 
}