how to catch command prompt process finish in C# and do something after that?

Question

I am working with voice records. I need to use an .exe file for convert Wav to .mp3 file. Everything is fine I can execute this exe but I need to do something after when process end with my output .mp3 file. I know my output directory but i cant handle MP3 file before its not created yet. I know maybe I need to use Thread.sleep(); or something like that because I cant catch a file before its not exist.

Here is my code:

string mp3GuidName = Guid.NewGuid().ToString();
var mp3FilePath = WavFilePath.Replace("finalWavFile", mp3GuidName).Replace("wav", "mp3");
var extrasFilePath = HttpContext.Current.Server.MapPath("/").Replace("DevApp.Web", "Extras");

string strArguments = "/c start " +  extrasFilePath + "lame.exe --abr 80 -V5 " + WavFilePath + " " + mp3FilePath;

System.Diagnostics.Process process = new System.Diagnostics.Process();
System.Diagnostics.ProcessStartInfo startInfo = new System.Diagnostics.ProcessStartInfo();
startInfo.WindowStyle = ProcessWindowStyle.Hidden;
startInfo.CreateNoWindow = false;
startInfo.UseShellExecute = false;
startInfo.FileName = "cmd.exe";
startInfo.Arguments =  strArguments ;
process.StartInfo = startInfo;
process.Start();
var attactment = new Attachment
    {
        CreatedOn = DateTime.Now,
        UpdatedOn = DateTime.Now,
        Title = mp3GuidName +".mp3",
        Size = _storageProvider.GetFile(mp3FilePath).GetSize(), // here I am trying to get mp3 file but i cant catch it. Because if this wav files size is huge, then convert process is taking time and my mp3 file is not created yet.
        FileExtension = _storageProvider.GetFile(mp3FilePath).GetFileType()
    };
attactment.MimeType = _storageProvider.GetMimeType(attactment.FileExtension);
attactment.FileUrl = mp3GuidName+".mp3";// file.GetName();
attactment.AttachmentFolderId = folder.Id;
_attachmentRepository.Add(attactment);

I was try to use process.WaitForExit(); but I cant solve this problem. I still cant acces to mp3 file.

so how can I catch when the process finish?

Best Regards.

Answer 1

Remove the start command argument from your argument string and you should be able to use process.WaitForExit(); to wait for Lame to finish with encoding:

string strArguments = "/c " +  extrasFilePath + "lame.exe --abr 80 -V5 " + WavFilePath + " " + mp3FilePath;

However, you can simplify your code and avoid this dance with cmd.exe altogether by starting lame.exe directly:

string strArguments = "--abr 80 -V5 " + WavFilePath + " " + mp3FilePath;
...
startInfo.FileName = extrasFilePath + "lame.exe";
startInfo.Arguments = strArguments;
...

---

Below some information about why using the start command argument in your scenario is counterproductive.

Executing console applications such as lame.exe using cmd.exe (or from a console or batch file) normally block cmd.exe (or console/batch file) until the console application exits.

However, using the start command turns this normally blocking execution of a console application into a non-blocking execution. With this argument, the cmd.exe (or console/batch file) will continue execution while the console application is still running. In your particular case it means cmd.exe will exit right after it has started lame.exe (since it has nothing else to execute), effectively sabotaging your attempt to wait for lame.exe to finish.

Answer 2

Edited:

Base on the comments below I have to make it clear that the oroginal solution I recommended does not check if the file is free but it checks only if the file exists ! So I rather recommend the following:

private bool IsBusy(FileInfo file)
{
    FileStream stream = null;

    try
    {
        stream = file.Open(FileMode.Open, FileAccess.Read, FileShare.None);
    }
    catch ()
    {
        return true;
    }
    finally
    {
        if (stream != null)
            stream.Close();
    }
    return false;
}

the usage will be:

while(IsBusy(fileinfo))
{
     //just wait
}

ORIGINAL: You can use a while loop to find out when the file is ready:

while(!File.Exists(mp3FileName))
{
     //just wait
}
// add the attachment here