Can a C# Multithreaded Application use separate WorkingDirectories per thread?

Question

In C# (.NET), can two threads running in the same application have DIFFERENT "WorkingFolders"??

As best I can tell, the answer would be "NO". I think the WORKING DIR is set by the PROCESS in Win32.. Am I wrong here?

According to the following test code, (as well the Win32 SetCurrentDirectory API call), this is NOT possible, but has anyone figured out a way to MAKE it possible?

using System;
using System.Threading;

public class TestClass {

  public  ManualResetEvent _ThreadDone = new ManualResetEvent(false);

  public static void Main() {
    Console.WriteLine(Environment.CurrentDirectory);

    Thread _Thread = new Thread(new ParameterizedThreadStart(Go));
    TestClass test = new TestClass();

    _Thread.Start(test);
    if(test._ThreadDone.WaitOne()) {
      Console.WriteLine("Thread done.  Checking Working Dir...");
      Console.WriteLine(Environment.CurrentDirectory);
    }
  }

  public static void Go(object instance) {
    TestClass m_Test = instance as TestClass;
    Console.WriteLine(Environment.CurrentDirectory);
    System.IO.Directory.SetCurrentDirectory("L:\\Projects\\");
    Console.WriteLine(Environment.CurrentDirectory);
    m_Test._ThreadDone.Set();
  }
}

I know SOMEONE out there has to have ran across this before!

Answer 1

I'm going to guess what you're trying to do is to make code such as File.Open("Foo.txt") behave differently on different threads. Can you do this? The short answer is No - nor should you be trying to do this. On Windows, the current working directory is set at the process level. The .NET framework does not violate that rule.

A better approach would be to create an abstraction on top of Environment.CurrentDirectory that is thread specific. Something like:

public static class ThreadEnvironment
{
   [ThreadStatic]
   static string _currentDir;

   public static string CurrentDirectory
   {
      get
      {
         if (_currentDir == null) // If Current Directory has not been set on this thread yet, set it to the process default
         {
            _currentDir = Environment.CurrentDirectory;
         }

         return _currentDir;
      }

      set
      {
         if (value == null)
            throw new ArgumentException("Cannot set Current Directory to null.");

         _currentDir = value;
      }
   }
}

You can then refer to ThreadEnvironment.CurrentDirectory to get that thread's current directory, which will default to the process directory if it has not been set on that thread. For example:

static void Main(string[] args)
{
   (new Thread(Thread1)).Start();
   (new Thread(Thread2)).Start();
}

static void Thread1()
{
   Console.WriteLine("Thread1 Working Dir is: {0}", ThreadEnvironment.CurrentDirectory);
   ThreadEnvironment.CurrentDirectory = @"C:\";
   Console.WriteLine("Thread1 Working Dir is: {0}", ThreadEnvironment.CurrentDirectory);
}

static void Thread2()
{
   Console.WriteLine("Thread2 Working Dir is: {0}", ThreadEnvironment.CurrentDirectory);
   ThreadEnvironment.CurrentDirectory = @"C:\Windows";
   Console.WriteLine("Thread2 Working Dir is: {0}", ThreadEnvironment.CurrentDirectory);
}

You would, of course, then need to qualify that path whenever dealing with file IO, however this is arguably a safer design anyway.