I'm fairly certain I'm either doing something wrong, or understanding something wrong. It's hard to give a piece of code to show my problem, so I'm going to try explaining my scenario, with the outcome.
I'm starting up several instances of a DLL, in the same console application, but in it's own app domain. I then generated a Guid.NewGuid() that I assign to a class in the instance, and set the application's folder to a new folder. This works great so far. I can see everything works great, and my instances are seperated. However... when I started changing my app's folder to the same name as the unique GUID generated for that class I started picking up anomolies.
It works fine, when I instantiate the new instances slowly, but when I hammer new ones in, the application started picking up data in its folder, when it started up. After some investigation, I found that its because that folder already exist, due to that GUID already being instantiated. On further investigation, I can see that the machine takes a bit of a pause, and then continues to generated the new instances, all with the same GUID.
I understand that the GUID generating algorithm uses the MAC as part of it, but I was under the impression that even if the same machine, at the same exact moment generates two GUIDs, it would still be unique.
Am I correct in that statement? Where am I wrong?
Code :
Guid guid = Guid.NewGuid();
string myFolder = Path.Combine(baseFolder, guid.ToString());
AppDomain ad = AppDomain.CurrentDomain;
Console.WriteLine($"{ad.Id} - {guid.ToString()}");
string newHiveDll = Path.Combine(myFolder, "HiveDriveLibrary.dll");
if (!Directory.Exists(myFolder))
{
Directory.CreateDirectory(myFolder);
}
if (!File.Exists(newHiveDll))
{
File.Copy(hiveDll, newHiveDll);
}
Directory.SetCurrentDirectory(myFolder);
var client = ServiceHelper.CreateServiceClient(serviceURL);
ElementConfig config = new ElementConfig();
ElementConfig fromFile = ElementConfigManager.GetElementConfig();
if (fromFile == null)
{
config.ElementGUID = guid;
config.LocalServiceURL = serviceURL;
config.RegisterURL = registerServiceURL;
}
else
{
config = fromFile;
}
Directory.SetCurrentDirectory is a thin wrapper atop the Kernel 32 function SetCurrentDirectory.
Unfortunately, the .NET documentation writers didn't choose to copy the warning from the native function:
Multithreaded applications and shared library code should not use the SetCurrentDirectory function and should avoid using relative path names. The current directory state written by the SetCurrentDirectory function is stored as a global variable in each process, therefore multithreaded applications cannot reliably use this value without possible data corruption from other threads that may also be reading or setting this value
It's your reliance on this function that's creating the appearance that multiple threads have magically selected exactly the same GUID value.