Process execution in a multi task enveríroment

Question

I am trying to execute some commands in my program, for that I am using System.Diagnostics.Process. I managed to set it working, when I execute the commands 1 by 1 the returns are correct. I then tried to speed up the process by creating tasks for each process execution, and here is where I am having problems.

Here is the class to execute the commands:

class ProcessExec
{
    public string Start(string command)
    {
        string res = "";

        Process process = new Process();
        process.EnableRaisingEvents = true;
        process.StartInfo.FileName = "powershell.exe";
        process.StartInfo.Arguments = command;
        process.StartInfo.UseShellExecute = false;
        process.StartInfo.RedirectStandardOutput = true;
        process.StartInfo.CreateNoWindow = true;

        process.OutputDataReceived += (object sender, DataReceivedEventArgs e) =>
        {
            res = res + e.Data;
        };

        process.Start();
        process.BeginOutputReadLine();
        process.WaitForExit(10000);

        return res;
    }
}

And this is my Main:

class Program
{
    static void Main(string[] args)
    {
        Console.WriteLine("Start");

        List tasks = new List();

        ProcessExec exec = new ProcessExec();

        Stopwatch sw = new Stopwatch();
        sw.Start();

        string res1 = "";
        tasks.Add(Task.Run(() => { res1 = exec.Start("date"); }));
        string res2 = "";
        tasks.Add(Task.Run(() => { res2 = exec.Start("hostname"); }));
        string res3 = "";
        tasks.Add(Task.Run(() => { res3 = exec.Start("date"); }));
        string res4 = "";
        tasks.Add(Task.Run(() => { res4 = exec.Start("date"); }));
        string res5 = "";
        tasks.Add(Task.Run(() => { res5 = exec.Start("date"); }));
        string res6 = "";
        tasks.Add(Task.Run(() => { res6 = exec.Start("ipconfig"); }));
        string res7 = "";
        tasks.Add(Task.Run(() => { res7 = exec.Start("date"); }));
        string res8 = "";
        tasks.Add(Task.Run(() => { res8 = exec.Start("date"); }));

        Task.WaitAll(tasks.ToArray());

        sw.Stop();

        Console.WriteLine(sw.Elapsed.TotalSeconds);

        Console.WriteLine("1 - " + res1);
        Console.WriteLine("2 - " + res2);
        Console.WriteLine("3 - " + res3);
        Console.WriteLine("4 - " + res4);
        Console.WriteLine("5 - " + res5);
        Console.WriteLine("6 - " + res6);
        Console.WriteLine("7 - " + res7);
        Console.WriteLine("8 - " + res8);

        Console.WriteLine("End");
        Console.ReadKey();
    }
}

This is my output:

Start
7,4867498
1 - 22 de julho de 2017 10:25:46    
2 -    
3 - 22 de julho de 2017 10:25:48
4 - 22 de julho de 2017 10:25:48    
5 -    
6 -    
7 - 22 de julho de 2017 10:25:48
8 - 22 de julho de 2017 10:25:48
End

Now, I think that my problem is related with the OutputDataReceived event being in a diferent thread, but I am not fully sure. Anyone knows what is the problem and how can I solve it?

Process execution in a multi task enveríroment

1 Answers