ManagedThreadID is not unique?

Question

My program creates some threads for some tasks.

My code is like this:

Dictionary<int, double> threadStates = new Dictionary<int, double>();
for (int i = 0; i < SubNNs.Count(); i++)
{
    Thread tt = new Thread(StartTrainingSubs);
    threadStates.Add(tt.ManagedThreadId, 0);
    tt.Priority = ThreadPriority.Highest;
    tt.Start(i);
}

But sometimes, if SubNNs.Count() becomes large (10-20), The program throws this exception : "An item with the same key has already been added." at line threadStates.Add(tt.ManagedThreadId, 0);

Why I giving this error? Isn't ManagedThreadId unique? If yes, what should I do?

and If no, maybe a thread finishes and another thread starts with same ManagedThreadId? Is it possible? how to prevent this problem?

Or there is another problem?

EDIT : Users said that ManagedThreadId can be reused. So, since in later parts of code, each thread needs to know itself with a unique number, is there any way to add something like a name to thread that every thread can get its unique number?

Thanks for any advise!

Answer 1

If no, maybe a thread finishes and another thread starts with same ManagedThreadId? Is it possible? how to prevent this problem?

Yes. Managed thread IDs can be reused. They are not a good choice for a dictionary state key.

Instead of using the thread ID to track state, you should consider using some other unique value. In your case, "i" is unique per loop - why not use it as your key?